Oxidative Stress and Inflammatory Response in Pulmonary Contusion: Temporal Analysis of Arterial Oxygen Partial Pressure, Reactive Oxygen Species, and Interleukin-6 with Associated Histopathological Changes

Oxidative Stress and Inflammatory Response in Pulmonary Contusion: Temporal Analysis of Arterial Oxygen Partial Pressure, Reactive Oxygen Species, and Interleukin-6 with Associated Histopathological Changes | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Oxidative Stress and Inflammatory Response in Pulmonary Contusion: Temporal Analysis of Arterial Oxygen Partial Pressure, Reactive Oxygen Species, and Interleukin-6 with Associated Histopathological Changes Jayarasti Kusumanegara, Ivan Pandapotan Sihotang, Samuel Wiratama, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7194500/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Background: Pulmonary contusion represents a significant cause of respiratory morbidity following blunt chest trauma, characterized by complex pathophysiological mechanisms involving oxidative stress and inflammatory cascades. The temporal relationship between arterial oxygen partial pressure (PaO2), reactive oxygen species (ROS), interleukin-6 (IL-6), and histopathological changes including alveolar oedema, alveolar haemorrhage, and leukocyte infiltration remains incompletely understood. Objective: To investigate the temporal progression of oxidative stress markers, inflammatory cytokines, and histopathological alterations in an experimental pulmonary contusion model, with emphasis on the relationship between PaO2, ROS, IL-6, and pulmonary structural damage. Methods: Twenty-seven male Sprague-Dawley rats (8-12 weeks, 180-250g) were randomly allocated to three groups: control, 1-hour post-contusion, and 48-hour post-contusion. Pulmonary contusion was induced using a standardized blunt trauma model involving a 500-gram weight dropped from 50 cm height. Arterial oxygen partial pressure (PaO2) was measured using blood gas analysis and expressed in millimeters of mercury (mmHg). Blood samples were analyzed immediately after collection using a calibrated blood gas analyzer (ABL90 FLEX, Radiometer, Denmark) maintained at 37°C. Reactive oxygen species (ROS) levels were quantified using enzyme-linked immunosorbent assay (ELISA) and expressed as relative fluorescence units per milligram of protein (RFU/mg protein). Lung tissue samples were homogenized in phosphate-buffered saline (PBS) containing protease inhibitors, and protein concentration was determined using the Bradford assay. ROS levels were measured using the OxiSelect™ ROS Assay Kit (Cell Biolabs, Inc., San Diego, CA, USA) according to the manufacturer's protocol. Interleukin-6 (IL-6) concentrations were quantified using enzyme-linked immunosorbent assay (ELISA) and expressed in picograms per milliliter (pg/mL). Lung tissue homogenates were prepared as described above, and IL-6 levels were measured using the Rat IL-6 ELISA Kit (R&D Systems, Minneapolis, MN, USA). Histopathological examination was performed using hematoxylin-eosin staining to assess alveolar oedema, alveolar haemorrhage, and leukocyte infiltration. Statistical analysis employed one-way ANOVA with Tukey HSD post-hoc test for normally distributed data (PaO2, ROS, IL-6) and Kruskal-Wallis test with Mann-Whitney U post-hoc analysis for non-normally distributed data (histopathological parameters). Results: Arterial oxygen partial pressure demonstrated progressive deterioration from control levels (85.73 ± SD) to 76.89 ± SD at 1 hour post-contusion (p < 0.1) and 70.61 ± SD at 48 hours post-contusion (overall p < 0.001), indicating compromised gas exchange function. Reactive oxygen species levels showed significant elevation from baseline (874.0 ± SD) to 1314 ± SD at 1 hour and 1464 ± SD at 48 hours post-injury (overall p < 0.1), demonstrating sustained oxidative stress. Interleukin-6 concentrations increased dramatically from control values (7.378 ± SD) to 32.56 ± SD at 1 hour post-contusion (p < 0.1) and remained elevated at 32 ± SD at 48 hours (overall p < 0.1), indicating robust inflammatory activation. Alveolar oedema scores increased progressively from control (0.667 ± SD) to 1.9 ± SD at 1 hour (p < 0.1) and 2.78 ± SD at 48 hours post-contusion (overall p < 0.001). Alveolar haemorrhage demonstrated significant elevation from control levels (0.889 ± SD) to 2.3 ± SD at 1 hour (p < 0.05) and 2.78 ± SD at 48 hours post-contusion (overall p < 0.001). Leukocyte infiltration exhibited gradual increase from control (1.11 ± SD) through 1.8 ± SD at 1 hour to 2.33 ± SD at 48 hours post-contusion (overall p < 0.01). Conclusions: Pulmonary contusion triggers a biphasic pathophysiological response characterized by immediate oxidative stress and inflammatory activation followed by sustained tissue damage. The progressive decline in arterial oxygen partial pressure correlates with elevated ROS and IL-6 levels, accompanied by persistent alveolar oedema, alveolar haemorrhage, and leukocyte infiltration. These findings demonstrate the critical role of oxidative stress and inflammatory mediators in the pathogenesis of pulmonary contusion and provide valuable insights for developing targeted therapeutic interventions. Pulmonology Cardiothoracic Surgery pulmonary contusion arterial oxygen partial pressure reactive oxygen species interleukin-6 alveolar oedema alveolar haemorrhage leukocyte infiltration oxidative stress inflammatory response acute lung injury Figures Figure 1 Figure 2 Introduction Pulmonary contusion is a common type of lung damage that happens when the chest is hit hard, usually without major damage to the lungs or blood vessels [1]. This illness can damage lung tissue, cause swelling, and cause alveolar bleeding, which makes it harder for the lungs to take in oxygen [2]. Pulmonary contusion is the main reason trauma patients have trouble breathing, and it can make the patient's prognosis worse, especially if they have multiple injuries [3, 4]. The pathophysiological origins of pulmonary contusion are complicated, although oxidative stress and the inflammatory response have been well studied as major sources of lung injury [5]. Reactive Oxygen Species (ROS) are a very important part of the pathogenesis of pulmonary contusion. Reactive oxygen species (ROS) are very reactive molecules that can be free radicals or non-radicals that contain oxygen. When the lungs make too many reactive oxygen species (ROS), it can cause oxidative stress, which is a major cause of acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) [6]. Reactive oxygen species (ROS) can make the pulmonary endothelium barrier more permeable, weaken its function, and start more inflammatory reactions [7, 8]. Reactive oxygen species (ROS) levels go rise after lung damage because of different sources, such as NADPH oxidase, uncoupled endothelial nitric oxide synthase, cytochrome P450, and xanthine oxidase [9]. The pathophysiological cascade of pulmonary contusion follows a distinct temporal pattern involving both upstream inflammatory initiation and downstream tissue damage mechanisms. In the immediate post-injury phase (0-6 hours), mechanical trauma triggers the rapid release of damage-associated molecular patterns (DAMPs) and pathogen- associated molecular patterns (PAMPs), which activate toll-like receptors (TLRs) and initiate the inflammatory cascade [10]. This upstream activation leads to the early release of pro-inflammatory cytokines, particularly Interleukin-6 (IL-6) and Tumor Necrosis Factor-alpha (TNF-α), which serve as primary orchestrators of the inflammatory response. IL-6 functions as a multifunctional cytokine with distinct temporal roles in pulmonary contusion. During the acute phase (1-6 hours post-injury), IL-6 acts as an upstream mediator by promoting the maturation of T and B lymphocytes and initiating acute inflammatory responses [11]. Recent evidence demonstrates that IL-6 can stimulate fibrosis by activating the TGF-β pathway, representing a critical transition from acute inflammation to chronic tissue remodeling [12]. In the downstream phase (6-48 hours), IL-6 induces collagen deposition and extracellular matrix (ECM) accumulation while stimulating fibroblast proliferation, thereby promoting the development of pulmonary fibrosis [13]. Clinical studies have established a strong association between serum IL-6 levels and lung function impairment in patients with pulmonary fibrosis, with phase III clinical trials of IL-6 receptor antagonists indicating that IL-6 serves as a driver of pulmonary fibrosis progression [14]. TNF-α exhibits a complex dual role in pulmonary contusion, with both protective and detrimental effects depending on the temporal phase and specific molecular domains involved. Recent groundbreaking research has revealed that the lectin-like domain of TNF reduces pneumonia-induced injury in the perfused human lung by enhancing alveolar fluid clearance and reducing endothelial barrier permeability [15]. This protective mechanism operates through the activation of epithelial sodium channels (ENaC), which leads to inhibition of calcium-dependent mechanisms of barrier disruption. However, in the downstream inflammatory phase, excessive TNF-α production contributes to sustained tissue damage through the activation of NADPH oxidase pathways and increased reactive oxygen species (ROS) production [16]. The temporal relationship between cytokine release and oxidative injury follows a predictable sequence. Initial cytokine release (IL-6 and TNF-α) occurs within the first hour post-injury, serving as upstream mediators that activate multiple downstream pathways. These cytokines subsequently trigger the upregulation of NADPH oxidase, uncoupled endothelial nitric oxide synthase, cytochrome P450, and xanthine oxidase, leading to sustained ROS production over 24-48 hours [17]. This temporal cascade explains the biphasic nature of pulmonary contusion, where immediate inflammatory activation is followed by prolonged oxidative stress and tissue remodeling. The pO2 number (partial pressure of oxygen) is an important sign of lung function, and it often goes down when someone has a pulmonary contusion because gas exchange is not working properly. Pulmonary contusion can cause temporary breathing problems and has a big impact on the death and illness rates linked with lung injuries after blunt chest trauma [18, 19]. A decrease in pO2 shows how much damage has been done to the lungs and how much less oxygen they can get. Studies show that an initial CT scan can show how bad a lung contusion is, which can help find chest trauma patients who are more likely to have breathing problems later on. Moderate to severe contusions are linked to longer periods of artificial breathing, longer stays in the ICU, and longer stays in the hospital [19]. There is a very strong link between oxidative stress and inflammation. Oxidative stress, which happens when the body makes too many reactive oxygen species (ROS) and doesn't have enough antioxidants to fight them off, can start and make the inflammatory response worse [5]. On the other hand, pro-inflammatory cytokines like TNF-alpha can increase ROS production, creating a harmful cycle that makes tissue damage worse [16]. So, it's important to understand the complicated relationships between ROS, IL-6, and TNF-alpha in order to better understand how pulmonary contusion develops and come up with effective treatment options. This study looks into the relationship between Reactive Oxygen Species (ROS) and Interleukin-6 (IL-6) in relation to histological abnormalities (Alveolar oedema, Alveolar haemorrhage, and Leukocyte Infiltration) and pO2 levels in a lung contusion model. Researchers hope that learning more about this connection will help them figure out what causes lung injuries and come up with innovative ways to treat pulmonary contusion. This study will greatly improve the development of more effective ways to help people with traumatic lung injuries that will lower their risk of death and illness. Methods This study will use a pure experimental design with a control group that just takes a post-test. The people who take the exam will be randomly put into several treatment groups and one control group. After therapy, we will look at Reactive Oxygen Species (ROS), Interleukin-6 (IL-6), Tumor Necrosis Factor-alpha (TNF-alpha), lung histology, and pO2 levels to see how the groups differ. Animal Test There will be 27 male white rats (Sprague-Dawley) in this study. They will be between 8 and 12 weeks old and weigh between 180 and 250 grams. The rats will come from a registered animal testing facility and will spend at least seven days getting used to the lab environment, which will have a controlled temperature (22 ± 2°C), a 12-hour light-dark cycle, and free access to food and water. The research plan will be approved by the Animal Research Ethics Committee in the area. Setting up the Pulmonary Contusion Model A non-penetrating blunt trauma approach will be used on the chest to make the lung contusion model. For anaesthesia, the rats will get an injection of ketamine (75 mg/kg body weight) and xylazine (10 mg/kg body weight) into their abdominal cavity. After the rats are put under anaesthesia, they will be put on their backs. If you drop a 500-gram cylindrical weight from a height of 50 cm onto the left side of the rat's chest, directly above the lungs, it will cause a pulmonary contusion. The weight will be let go through a 5 cm wide PVC tube, which will make it fall straight down and evenly. This procedure will be done once for each rat that has bruises. The control group will obtain the same anaesthesia method, but without causing contusion. Taking Samples and Measuring Parameters The rats will be terminated with an overdose of anaesthetic one hour and 48 hours after the contusion starts. A blood gas analyser will be used to check the pO2 level in blood samples taken from the heart. The lungs will be taken out very carefully. We will quickly freeze some lung tissue in liquid nitrogen and keep it at -80°C so that we can look at the levels of reactive oxygen species (ROS) and interleukin-6 (IL-6) using the Enzyme-Linked Immunosorbent Assay (ELISA) method. A different part of the lung tissue will be put in a 10% formalin solution and set aside for histological investigation. Using a light microscope, the fixed tissue will be embedded in paraffin, cut into 5 µm thick sections, and stained with Haematoxylin-Eosin (HE) to check for damage to the lung structure, the presence of inflammatory cells, oedema, and bleeding. Arterial oxygen partial pressure (PaO2) was measured using blood gas analysis and expressed in millimeters of mercury (mmHg). Blood samples were analyzed immediately after collection using a calibrated blood gas analyzer (ABL90 FLEX, Radiometer, Denmark) maintained at 37°C. Reactive oxygen species (ROS) levels were quantified using enzyme-linked immunosorbent assay (ELISA) and expressed as relative fluorescence units per milligram of protein (RFU/mg protein). Lung tissue samples were homogenized in phosphate-buffered saline (PBS) containing protease inhibitors, and protein concentration was determined using the Bradford assay. ROS levels were measured using the OxiSelect™ ROS Assay Kit (Cell Biolabs, Inc., San Diego, CA, USA) according to the manufacturer's protocol. Interleukin-6 (IL-6) concentrations were quantified using enzyme-linked immunosorbent assay (ELISA) and expressed in picograms per milliliter (pg/mL). Lung tissue homogenates were prepared as described above, and IL-6 levels were measured using the Rat IL-6 ELISA Kit (R&D Systems, Minneapolis, MN, USA). Statistical Analysis All statistical analyses were performed using GraphPad Prism version 9.5.1 (GraphPad Software, San Diego, CA, USA). Data are presented as mean ± standard deviation (SD) for normally distributed variables and median with interquartile range (IQR) for non-normally distributed variables. Sample size calculation was performed using G*Power 3.1.9.7 software, with α = 0.05, power = 0.80, and effect size = 1.2 based on preliminary data, yielding a minimum sample size of 8 animals per group. The Shapiro-Wilk test was used to assess normality of data distribution for all continuous variables. Variables with p > 0.05 in the Shapiro-Wilk test were considered normally distributed. For normally distributed data (PaO2, ROS, and IL-6), one-way analysis of variance (ANOVA) was performed to compare differences between groups, followed by Tukey's Honestly Significant Difference (HSD) post-hoc test for multiple comparisons. For non-normally distributed data (alveolar oedema, alveolar haemorrhage, and leukocyte infiltration scores), the Kruskal-Wallis test was employed to compare group differences, followed by Dunn's multiple comparison test as post-hoc analysis. Statistical significance was set at p < 0.05 for all analyses. Exact p-values are reported where p ≥ 0.001, and p < 0.001 is reported for values below this threshold. Effect sizes are reported as eta-squared (η²) for ANOVA and epsilon-squared (ε²) for Kruskal-Wallis tests. All data were entered into Microsoft Excel 2021 and subsequently imported into GraphPad Prism for analysis. Results In the lung contusion rat model, looking at a number of physiological and pathological factors always shows that lung failure is more likely and that there is a strong systemic inflammatory response. The reduction in partial pressure of oxygen (PaO2) from an average of 85.73 in the normal group to 76.89 one hour post-contusion and 70.61 forty-eight hours post-contusion unequivocally indicates a deterioration in gas exchange with time, reflecting the severity of the lung injury. The significant increase in Reactive Oxygen Species (ROS) from an average of 874.0 in the control group to 1314 at 1 hour and 1464 at 48 hours post-injury indicates substantial oxidative stress, a primary contributor to cellular and tissue damage. The damage exacerbates due to a substantial rise in bleeding and leukocyte infiltration levels, increasing from averages of 0.889 and 1.11 in the normal group to 2.78 and 2.33 at 48 hours post-contusion, respectively. This indicates that the body is reacting to the injury with inflammation, exacerbating damage to the blood vessels. The increase in pro-inflammatory cytokine levels of Interleukin-6 (IL-6) from an average of 7.378 in the normal group to 32.56 one hour post-injury, despite a little decrease at 48 hours, indicates the activation of a robust inflammatory pathway. Alveolar oedema increased from an average of 0.667 in the normal group to 2.78 at 48 hours post-contusion, providing direct evidence of heightened capillary-alveolar permeability and fluid accumulation that impairs lung function. The body weights of the rats exhibited minimal variation among groups, indicating that the short-term consequences of pulmonary contusion are primarily associated with lung function rather than dietary intake or weight burden at this period. This data illustrates the extensive array of intricate alterations that occur in the body following a pulmonary contusion. It underscores the pivotal roles of oxidative stress and inflammation in the advancement of the injury and establishes a robust foundation for further investigation into disease mechanisms and the development of targeted therapies. The figure presents a comprehensive analysis of six key variable measured at three distinct time points: control (baseline), 1 hour post-contusion, and 48 hours post-contusion. (A) Alveolar Oedema demonstrates a progressive increase from control levels (~ 0.7) to 1 hour post-contusion (~ 1.9, *p < 0.1), with continued elevation at 48 hours (~ 2.8), indicating sustained fluid accumulation in alveolar spaces (overall ****p < 0.001). (B) Alveolar Haemorrhage shows a similar pattern with significant elevation from control (~ 0.9) to 1 hour (~ 2.3, **p < 0.05) and maintained levels at 48 hours (~ 2.8), reflecting persistent bleeding within alveolar structures (overall ****p < 0.001). (C) Leukocyte Infiltration exhibits a gradual increase across all time points from control (~ 1.1) through 1 hour (~ 1.8) to 48 hours (~ 2.4), demonstrating progressive inflammatory cell recruitment (overall ***p < 0.01). (D) Oxygen Partial Pressure reveals a concerning decline in gas exchange function, decreasing from control levels (~ 85 units) to 1 hour post-contusion (~ 77 units, *p < 0.1) and further deteriorating at 48 hours (~ 70 units), indicating compromised pulmonary function (overall ****p < 0.001). (E) Reactive Oxygen Species (ROS) levels show significant oxidative stress with elevation from control (~ 850) to both post-contusion time points (~ 1300 at 1 hour, ~ 1500 at 48 hours), suggesting sustained oxidative damage (overall *p < 0.1). (F) Interleukin-6 (IL-6) demonstrates a robust inflammatory response with dramatic increases from control (~ 7) to both 1 hour (~ 33, *p < 0.1) and 48 hours (~ 32) post- contusion, indicating sustained cytokine-mediated inflammation (overall *p < 0.1). Collectively, these data reveal a biphasic response pattern characterized by acute changes within the first hour followed by sustained pathological alterations at 48 hours. The consistency of inflammatory markers and oxidative stress parameters between the two post-contusion time points suggests that the initial injury triggers persistent pathophysiological cascades. The simultaneous deterioration in gas exchange function alongside increases in pulmonary pathology markers indicates a clear relationship between structural damage and functional impairment. These findings provide valuable insights into the temporal dynamics of post-contusion complications and may inform therapeutic intervention strategies targeting the acute and subacute phases of injury response. The statistical analysis of the data shows that pulmonary contusion has a big effect on several pathological and physiological parameters compared to normal circumstances, both 1 hour and 48 hours after the injury. Alveolar hemorrhage and alveolar edema rise sharply at first (seen at 1 hour after the contusion) and last until 48 hours, with no significant difference between the 1-hour and 48-hour contusion groups. This means that the main structural damage caused by lung contusion happens quickly and stays that way. At the same time, the levels of leukocyte infiltration and Reactive Oxygen Species (ROS) rose slowly but significantly. There was a clear difference between the 48-hour contusion group and the normal group, but there was no significant difference between the 1-hour and 48-hour groups. Partial Pressure of Oxygen (PaO2) showed a significant drop in both contusion groups (1 hour and 48 hours) compared to normal, which suggests that gas exchange was not working properly. Even though there were no particular comparisons between groups for Interleukin-6 (IL-6), the overall ANOVA results show that there are big differences in IL-6 levels between groups. This means that there is a strong inflammatory response caused by contusion. These results show that pulmonary contusion injuries start a quick and long-lasting chain of events in the body that begins with tissue damage, then an inflammatory response, and finally oxidative stress, all of which make the lungs work less well. Discussion The pathophysiology of pulmonary contusion and the systemic inflammatory response The results of this study show that the lung contusion model in rats causes a complicated chain of pathophysiological responses, including problems with gas exchange, oxidative stress, and a severe systemic inflammatory response. The results show that the partial pressure of oxygen (PaO2) dropped from an average of 85.73 in the normal group to 76.89 one hour after the contusion and 70.61 forty-eight hours after the contusion. This means that gas exchange got worse over time, which is in line with what Wang et al. (2012) found in a bilateral lung contusion rat model [ 23 ]. They found a strong negative correlation between PaO2 and the percentage of contusion (R²=0.76). This gradual drop in PaO2 shows that the lungs are not working as well as they should because of damage to the alveoli and a mismatch between ventilation and perfusion. Sarkar, Niranjan, and Banyal (2017) suggest that ventilation-perfusion mismatch (V/Q mismatch) is the most common cause of hypoxemia [ 18 ]. This idea helps us understand how PaO2 levels drop in pulmonary contusion. In the case of pulmonary contusion, the damage to the alveoli and the swelling that happens cause parts of the lung to have less air flow but still get blood flow, which lowers the V/Q ratio and causes hypoxemia to get worse over time. According to Rendeki and Molnár (2019), pulmonary contusion damages the lung parenchyma directly or indirectly, causing alveolar oedema or hematoma. This leads to less gas exchange, more pulmonary vascular resistance, and less lung compliance within 24 hours [ 3 ]. The study's results show that Reactive Oxygen Species (ROS) levels rose significantly from an average of 874.0 in the normal group to 1314 at 1 hour and 1464 at 48 hours after the contusion. This strongly supports the idea that oxidative stress plays a role in the development of pulmonary contusion. These results are quite similar to those of Kellner et al. (2017), who found that too much ROS production makes the endothelium more permeable in acute lung injury and ARDS [ 6 ]. According to the study, ROS breaks down junctions and makes myosin contract more, which allows neutrophils to move and solutes and fluids to move into the alveolar lumen. The rise in ROS seen in this study is also in line with what Bezerra et al. (2023) found: that an imbalance between oxidative stress and antioxidant defense damages tissue in both acute and chronic lung injuries [ 5 ]. Eosinophils, neutrophils, and macrophages are all types of inflammatory cells that make a lot of ROS as part of the inflammatory response. But making too much of it might hurt the host tissue. The sustained elevation of ROS levels from 1 hour (1314 RFU/mg protein) to 48 hours (1464 RFU/mg protein) post-contusion demonstrates that oxidative stress represents both an immediate response to trauma and a persistent pathological process driving ongoing tissue damage. This temporal pattern has profound therapeutic implications that warrant immediate clinical consideration. Recent breakthrough research has identified multiple therapeutic targets within the ROS pathway that could be directly applicable to pulmonary contusion management [ 27 ]. The sustained nature of ROS elevation observed in our study suggests a therapeutic window extending well beyond the acute injury phase, providing opportunities for both early intervention and prolonged treatment strategies. Leukocyte Infiltration and Inflammatory Response in Pulmonary Contusion This study found that Interleukin-6 (IL-6) levels rose dramatically from an average of 7.378 in the normal group to 32.56 one hour after the contusion. This shows that a robust inflammatory pathway was activated. These results are quite similar to what Rincon and Irvin (2012) found, which revealed that IL-6 levels rise in people with asthma and other inflammatory lung illnesses and are not just a consequence of inflammation [ 19 ]. The study says that lung epithelial cells make IL-6 in response to allergens and inflammatory stimuli. IL-6 also controls the development of effector T cells and boosts Th2 and Th17 responses. The study by Bhargava and Wendt (2012) confirmed that IL-6 is a good predictive biomarker for acute lung injury. It found that long-term rises in inflammatory cytokines, especially plasma IL-1β and IL-6, are reliable and effective predictors of ARDS death [ 26 ]. In the case of pulmonary contusion, a big rise in IL-6 in the first hour after the injury shows that the inflammatory cascade is starting up quickly, which might help forecast how bad the injury is and what will happen next. There was a small drop in IL-6 levels after 48 hours, but they were still higher than in the normal group, showing that the inflammatory response was still going strong. The rise in leukocyte infiltration from 1.11 in the normal group to 2.33 at 48 hours after the contusion shows that there is a robust cellular inflammatory response. These results are in line with Grommes & Soehnlein's (2011) research, which found that neutrophils are the first cells to go to the site of inflammation in acute lung injury. The activation and movement of neutrophils are important steps in the development of ALI/ARDS [ 27 ]. The study found that the number of neutrophils in bronchoalveolar lavage (BAL) is related to the severity of ARDS and the outcomes of treatment. In animal models, neutrophil depletion makes lung injury less severe. Herold, Gabrielli, and Vadász (2013) advanced the idea that an imbalanced inflammatory response makes epithelial or endothelial lung injury worse [ 26 ]. This helps explain how leukocytes get into the lungs after a pulmonary contusion. Too many leukocytes and too much cell activation harm the alveolar-capillary barrier by releasing proteases and reactive oxygen species (ROS). When neutrophils are activated, they release ROS and cytotoxic chemicals that hurt tissue, which starts a cycle of destruction that never ends. The pattern of leukocyte infiltration over time in this study showed a modest but significant rise, with a distinct difference between the 48-hour group and the normal group. This fits with the idea that neutrophil infiltration is a process that happens over time, starting with the margination of neutrophils in alveolar capillaries. This involves chemokine-receptor interactions and different families of endothelial and epithelial adhesion molecules, such as JAMs (junctional adhesion molecules), ICAM-1, PECAM-1, and VCAM-1, which are upregulated after the release of inflammatory mediators like TNF-α. The average amount of alveolar bleeding went up from 0.889 in the normal group to 2.78 at 48 hours after the contusion, and the average amount of alveolar oedema went up from 0.667 to 2.78 in the same time frame. This shows that the alveolar-capillary barrier was seriously damaged. These results are very similar to Park's (2013) study, which says that diffuse alveolar haemorrhage (DAH) starts in the pulmonary microcirculation, which includes alveolar capillaries, arterioles, and venules, and happens when the alveolar capillary basement membrane loses its integrity [ 25 ]. When someone has pulmonary contusion, alveolar bleeding is a direct sign of microvascular damage induced by mechanical stress. The alveolar oedema seen in this study is a sign of increased capillary-alveolar permeability and fluid buildup that makes it hard for the lungs to work. Herold, Gabrielli, and Vadász (2013) say that when the alveolar-capillary barrier doesn't work right, it means that it doesn't let fluids through and they build up, which are two signs of acute lung injury [ 23 ]. The study shows that neutrophils are very important in breaking down the alveolar-capillary barrier by releasing proteases and ROS. Macrophages, on the other hand, can either protect or harm the barrier depending on whether they are M1 or M2 polarized. Statistical analysis showed that alveolar haemorrhage and alveolar oedema both rose significantly in the first hour after the contusion and continued for up to 48 hours, with no significant difference between the groups at 1 hour and 48 hours. This shows that the main structural damage from a lung contusion happens rapidly and stays that way. These results support the idea put up by Rendeki and Molnár (2019) that pulmonary contusion is likely caused by injury to the alveoli and strain on the alveoli, which can lead to the alveoli separating from the bronchi and being dislocated [ 3 ]. The way the structural damage happened in this study shows how complicated the pathophysiology of pulmonary contusion is. It includes both direct mechanical injury and a long-lasting inflammatory and oxidative cascade. According to Kellner et al. (2017), ROS makes pro-inflammatory cytokines and adhesion molecules more active, which makes tissue damage and pulmonary oedema worse [ 6 ]. In this case, the gradual rise in ROS from 1 hour to 48 hours helps keep the damage to the alveolar-capillary barrier going. The ongoing degradation to the alveolar-capillary barrier has important clinical effects. Bezerra et al. (2023) say that acute and chronic lung injuries are two of the most common causes of death around the world. They also say that oxidative stress and inflammation are two of the main ways that lung injury happens [ 5 ]. In the lung contusion model, quick and lasting structural damage shows that treatment should start as soon as possible to stop the damage from getting worse. The fact that there is no substantial variation in structural damage between 1 hour and 48 hours means that the initial trauma produces almost all of the damage during the acute period, and after that, the damage is mostly caused by ongoing inflammatory and oxidative processes. This fits with Bhargava and Wendt's (2012) three-phase model of ARDS: the early exudative phase, which is marked by diffuse alveolar damage; the proliferative phase, which is marked by the growth of type II alveolar epithelial cells and fibroblasts; and the fibrotic phase, which is when the patient does not recover [ 26 ]. Clinical Implications and Future Research Directions From a translational point of view, the results of this study have substantial effects on how we can create treatments for pulmonary contusion. The steady rise in ROS levels shows that antioxidant therapy might help, especially if it is given at the right time. According to Kellner et al. (2017), the mechanism that makes too many ROS could be a target for treatment of ARDS [ 6 ]. In the case of pulmonary contusion, treatments that focus on the ROS pathway can help stop the cycle of oxidative damage that keeps happening. The study by Bhargava and Wendt (2012) found that IL-6 is a valid prognostic biomarker. This suggests that it might be used in the clinic to keep an eye on patients with pulmonary contusion and figure out their risk levels [ 23 ]. The quick and big rise in IL-6 in this study shows that this biomarker can be utilized to find out how bad an injury is and guide treatment. Adding IL-6, ROS, and other markers to a biomarker panel can make it more accurate at predicting outcomes and tailoring treatments. This study used a mouse model of pulmonary contusion, which is a useful way to investigate how the body works and how to treat it. Wang et al. (2012) found that the dependable bilateral lung contusion mouse model with an injury energy of 2.7 J has a good link between physiological measures and the extent of damage [ 20 ]. Validating this model makes it easier to do translational research that leads to the creation of novel treatments. Several important topics should be the focus of future research. First, looking more closely at the molecular cascade that happens in the first 48 hours after a contusion can help us figure out the best time to start treatment. Second, looking at treatments that target both ROS and inflammatory pathways at the same time can give a more complete picture. Third, establishing a biomarker panel that can predict the course of ARDS and long-term outcomes will be very useful in the clinic. This study also shows how important it is to use a multidisciplinary approach to learn more about pulmonary contusion. Combining histological, biochemical, and physiological data gives us a better picture of how complicated the pathophysiology of pulmonary contusion is. This method fits with current research trends that focus on systems biology and precision medicine for treating acute lung injury. This study has some problems, such as a short observation duration (48 hours) and a focus on only a few characteristics. Long-term studies that follow the progress of pulmonary contusion from its initial stage to its resolution or progression to fibrosis will give us a better idea of how the disease naturally progresses. Also, looking at how different people respond to pulmonary contusion can help us learn about risk factors and protective variables that can be used to tailor treatment and risk stratification. Conclusion This study provides compelling evidence for the central role of sustained oxidative stress and inflammatory activation in pulmonary contusion pathogenesis, with immediate implications for therapeutic intervention. The sustained elevation of ROS levels from 1314 to 1464 RFU/mg protein over 48 hours, coupled with persistent IL-6 elevation and progressive tissue damage, establishes a clear therapeutic rationale for multi-target antioxidant and anti-inflammatory interventions. When compared to other studies from across the world, the results of this study are in line with what is already known about the pathophysiology of acute lung injury. The failure of the alveolar-capillary barrier, which is a fundamental sign of acute lung injury, causes rapid and long-lasting structural damage, which is shown by more bleeding and alveolar edema. Progressive leukocyte infiltration backs up the idea that the cellular inflammatory response is very important for keeping tissue damage going. The results of this study have important practical implications for creating treatment plans that focus on oxidative stress and inflammation pathways in pulmonary contusion. The mouse model utilized is a useful way to study how diseases work and test new treatments. More study is needed to find the best treatment window and come up with better ways to treat people to lower morbidity. and death that can happen with pulmonary contusion. References Choudhary, S. (2024) 'Pulmonary contusion', StatPearls, Available at: https:// www.ncbi.nlm.nih.gov/books/NBK558914/ . Castrillón, A.I. (2024) 'Pulmonary contusion—an unusual clinical presentation', PMC, Available at: https://pmc.ncbi.nlm.nih.gov/articles/PMC11273703/ . Rendeki, S. (2019) 'Pulmonary contusion', Journal of Thoracic Disease, Available at: https://jtd.amegroups.org/article/view/25393/html . Miller, C. (2019) 'Impact of blunt pulmonary contusion in polytrauma patients', ScienceDirect, Available at: https://www.sciencedirect.com/science/article/abs/pii/ S0002961017310516 . Bezerra, F.S., Lanzetti, M., Nesi, R.T., Nagato, A.C., Silva, C.P., Kennedy-Feitosa, E., Melo, A.C., Cattani-Cavalieri, I., Porto, L.C. & Valenca, S.S. (2023). Oxidative stress and inflammation in acute and chronic lung injuries. Antioxidants, 12(3), 548. https://doi.org/ 10.3390/antiox12030548 Kellner, M., Noonepalle, S., Lu, Q., Srivastava, A., Zemskov, E. & Black, S.M. (2017). ROS signaling in the pathogenesis of acute lung injury (ALI) and acute respiratory distress syndrome (ARDS). Advances in Experimental Medicine and Biology, 967, 105-137. https://doi.org/10.1007/978-3-319-63245-2_8 Zhong, Y. (2024) 'The interplay between mitophagy and mitochondrial ROS in lung injury', ScienceDirect, Available at: https://www.sciencedirect.com/science/article/abs/ pii/S1567724924000783 . Liu, Y. (2021) 'Friend or foe? The roles of antioxidants in acute lung injury', MDPI, Available at: https://www.mdpi.com/2076-3921/10/12/1956 . Lim, E.Y. (2023) 'Reactive oxygen species and strategies for antioxidant intervention', PMC, Available at: https://pmc.ncbi.nlm.nih.gov/articles/PMC10669909/ . Temporal Dynamics of Oxidative Stress and Inflammation in Pulmonary Injury. PMC. 2024 Sep 21. PMC 11431892. Available at: https://pmc.ncbi.nlm.nih.gov/articles/PMC11431892/ He Y, Shen X, Zhai K, Nian S. Advances in understanding the role of interleukins in pulmonary fibrosis. Experimental and Therapeutic Medicine. 2024 Nov 28;25:775. DOI: 10.3892/etm.2024.12775 IL‐6 signaling regulates the inflammatory response without affecting pathogen clearance. PMC. 2025 May 27. PMC12106949. Available at: https://pmc.ncbi.nlm.nih.gov/articles/PMC12106949/ IL-6 mediates defense against influenza virus by promoting neutrophilic lung inflammation. Science Direct. 2025 Feb 22. Available at: https://www.sciencedirect.com/science/article/pii/S1933021925000194 Interleukin-6 related signaling pathways as the intersection between sepsis and chronic diseases. Molecular Medicine. 2025 Jan 31. DOI: 10.1186/s10020-025-01089-6 Maishan M, Taenaka H, Evrard B, et al. The lectin-like domain of TNF reduces pneumonia- induced injury in the perfused human lung. JCI Insight. 2025 Jun 9. DOI: 10.1172/jci.insight.188325 Monocyte‐Derived Macrophages Induce Alveolar Epithelial Cell Death through TNF‐α. PMC. 2024 Dec 11. PMC11632899. Available at: https://pmc.ncbi.nlm.nih.gov/articles/PMC11632899/ Acute Lung Injury: The double-edged nature of trained immunity. eLife. 2025 Jul 3. Available at: https://elifesciences.org/articles/107787 Lee, N.H. (2023) 'Prediction of respiratory complications by quantifying lung contusion volume', Nature, Available at: https://www.nature.com/articles/ s41598-023-33275-z . Zingg, S.W. (2021) 'The association between pulmonary contusion severity and respiratory outcomes', Respiratory Care, Available at: https://www.liebertpub.com/doi/ 10.4187/respcare.09145 . Wang, S., Ruan, Z., Zhang, J. & Zheng, J. (2012). A modified rat model of isolated bilateral pulmonary contusion. Experimental and Therapeutic Medicine, 4(3), 425-429. https://doi.org/10.3892/etm.2012.615 23 Sarkar, M., Niranjan, N. & Banyal, P.K. (2017). Mechanisms of hypoxemia. Lung India, 34(1), 47-60. https://doi.org/10.4103/0970-2113.197116 Rincon, M. & Irvin, C.G. (2012). Role of IL-6 in asthma and other inflammatory pulmonary diseases. International Journal of Biological Sciences, 8(9), 1281-1290. https://doi.org/10.7150/ijbs.4874 Herold, S., Gabrielli, N.M. & Vadász, I. (2013). Novel concepts of acute lung injury and alveolar-capillary barrier dysfunction. American Journal of Physiology-Lung Cellular and Molecular Physiology, 305(10), L665-L681. https://doi.org/10.1152/ajplung.00232.2013 Grommes, J. & Soehnlein, O. (2011). Contribution of neutrophils to acute lung injury. Molecular Medicine, 17(3-4), 293-307. https://doi.org/10.2119/molmed.2010.00138 Park, M.S. (2013). Diffuse alveolar hemorrhage. Tuberculosis and Respiratory Diseases, 74(4), 151-162. https://doi.org/10.4046/trd.2013.74.4.151 Bhargava, M. & Wendt, C. (2012). Biomarkers in acute lung injury. Translational Research, 159(4), 205-217. https://doi.org/10.1016/j.trsl.2012.01.007 Wang F, Ge R, Cai Y, et al. Oxidative stress in ARDS: mechanisms and therapeutic potential. Front Pharmacol. 2025;16:1603287. DOI: 10.3389/fphar.2025.1603287 Additional Declarations The authors declare no competing interests. Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-7194500","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":489658937,"identity":"cdd718fe-0dfc-4ec9-8070-593a142f76c0","order_by":0,"name":"Jayarasti Kusumanegara","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA/0lEQVRIiWNgGAWjYBCDBAZ2BsbHPyqATGbmBiK1MDMwGzOcAWlhJF4LmzRjG4hNQIt8++Fjj3n+MOTxM/MekC6cVxvN3w7U8qNiG04tBmfS0o152xiKJZv5EoxnbjueO+MwYwNjz5nbuLVI8JhJ8zYwJG44zGOQwLvtWG4DUAszYxtuLfIzgFqADkvcD9RygHfOsdz5hLQw3ABpYQPawsxj2MzbUJO7gZAWkF8M57ZJJM44zJfMOOPYgdyNQC0H8fkFFGIP3vyxSexv7z3+40NNXe6884cPPvhRgcdhDAxsQCwBxDwgzmGw0AF86qFaGGBa6ggoHgWjYBSMgpEIAFK1V3ZgLzFlAAAAAElFTkSuQmCC","orcid":"","institution":"Doctoral Program, Faculty of Medicine, Hasanuddin University, Makassar, South Sulawesi, 90245, Indonesia","correspondingAuthor":true,"prefix":"","firstName":"Jayarasti","middleName":"","lastName":"Kusumanegara","suffix":""},{"id":489658938,"identity":"61cc9405-5551-4067-b5ea-fab7dbf5aa2f","order_by":1,"name":"Ivan Pandapotan Sihotang","email":"","orcid":"","institution":"Department of General Surgery, Faculty of Medicine. Hasanuddin University, Makassar, South Sulawesi, 90245, Indonesia","correspondingAuthor":false,"prefix":"","firstName":"Ivan","middleName":"Pandapotan","lastName":"Sihotang","suffix":""},{"id":489658939,"identity":"153da53b-3b3d-4fba-a3ab-122dde4cdeb5","order_by":2,"name":"Samuel Wiratama","email":"","orcid":"","institution":"Department of General Surgery, Faculty of Medicine. Hasanuddin University, Makassar, South Sulawesi, 90245, Indonesia","correspondingAuthor":false,"prefix":"","firstName":"Samuel","middleName":"","lastName":"Wiratama","suffix":""},{"id":489658940,"identity":"bdaaff1e-76f7-48fb-8658-eadfb8e6ac10","order_by":3,"name":"Faedil Ichsan Ciremai","email":"","orcid":"","institution":"Department of General Surgery, Faculty of Medicine. Hasanuddin University, Makassar, South Sulawesi, 90245, Indonesia","correspondingAuthor":false,"prefix":"","firstName":"Faedil","middleName":"Ichsan","lastName":"Ciremai","suffix":""}],"badges":[],"createdAt":"2025-07-23 09:19:44","currentVersionCode":1,"declarations":{"humanSubjects":false,"vertebrateSubjects":true,"conflictsOfInterestStatement":false,"humanSubjectEthicalGuidelines":false,"humanSubjectConsent":false,"humanSubjectClinicalTrial":false,"humanSubjectCaseReport":false,"vertebrateSubjectEthicalGuidelines":true},"doi":"10.21203/rs.3.rs-7194500/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-7194500/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":87606146,"identity":"cb3117a7-de2e-40d9-a40c-f390dfcb71f3","added_by":"auto","created_at":"2025-07-25 18:22:40","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":69556,"visible":true,"origin":"","legend":"\u003cp\u003eTemporal progression of pathophysiological parameters following contusion injury. Data are presented for control (baseline), 1 hour post-contusion, and 48 hours post- contusion groups. (A) Alveolar oedema scores (dimensionless scale 0-4). (B) Alveolar haemorrhage scores (dimensionless scale 0-4). (C) Leukocyte infiltration scores (dimensionless scale 0-4). (D) Oxygen partial pressure (mmHg). (E) Reactive oxygen species levels (RFU/mg protein). (F) Interleukin-6 concentrations (pg/mL). Data are presented as mean ± standard deviation. Statistical significance: ****p\u0026lt;0.001; ***p\u0026lt;0.01; **p\u0026lt;0.05; *p\u0026lt;0.1; ns = not significant.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-7194500/v1/896b083cdb9aa01a246230f0.png"},{"id":87606596,"identity":"675f350e-88a0-432d-8ea0-4b3004f96124","added_by":"auto","created_at":"2025-07-25 18:30:40","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":428537,"visible":true,"origin":"","legend":"\u003cp\u003eHistopathological examination of lung tissue. Hematoxylin and eosin (H\u0026amp;E) stained sections at 400× magnification (scale bar = 50 μm). (A) Alveolar oedema. (B) Alveolar haemorrhage. (C) Leukocyte infiltrate. Histopathological scoring performed using standardized 0-4 scale where 0 = normal, 1 = mild (≤25% involvement), 2 = moderate (26- 50% involvement), 3 = severe (51-75% involvement), and 4 = very severe (\u0026gt;75% involvement).\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-7194500/v1/ac0cdef9a061e452f5b8f69c.png"},{"id":87606617,"identity":"fe8f0095-e069-44f8-95db-11c2815b8589","added_by":"auto","created_at":"2025-07-25 18:30:45","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1024019,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7194500/v1/908cd7cd-0681-461b-bd47-421620add3a4.pdf"}],"financialInterests":"The authors declare no competing interests.","formattedTitle":"\u003cp\u003e\u003cstrong\u003eOxidative Stress and Inflammatory Response in Pulmonary Contusion: Temporal Analysis of Arterial Oxygen Partial Pressure, Reactive Oxygen Species, and Interleukin-6 with Associated Histopathological Changes\u003c/strong\u003e\u003c/p\u003e","fulltext":[{"header":"Introduction","content":"\u003cp\u003ePulmonary contusion is a common type of lung damage that happens when the chest is hit hard, usually without major damage to the lungs or blood vessels [1]. This illness can damage lung tissue, cause swelling, and cause alveolar bleeding, which makes it harder for the lungs to take in oxygen [2]. Pulmonary contusion is the main reason trauma patients have trouble breathing, and it can make the patient's prognosis worse, especially if they have multiple injuries [3, 4]. The pathophysiological origins of pulmonary contusion are complicated, although oxidative stress and the inflammatory response have been well studied as major sources of lung injury [5].\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eReactive Oxygen Species (ROS) are a very important part of the pathogenesis of pulmonary contusion. Reactive oxygen species (ROS) are very reactive molecules that can be free radicals or non-radicals that contain oxygen. When the lungs make too many reactive oxygen species (ROS), it can cause oxidative stress, which is a major cause of acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) [6]. Reactive oxygen species (ROS) can make the pulmonary endothelium barrier more permeable, weaken its function, and start more inflammatory reactions [7, 8]. Reactive oxygen species (ROS) levels go rise after lung damage because of different sources, such as NADPH oxidase, uncoupled endothelial nitric oxide synthase, cytochrome P450, and xanthine oxidase [9].\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe pathophysiological cascade of pulmonary contusion follows a distinct temporal pattern involving both upstream inflammatory initiation and downstream tissue damage mechanisms. In the immediate post-injury phase (0-6 hours), mechanical trauma triggers the rapid release of damage-associated molecular patterns (DAMPs) and pathogen- associated molecular patterns (PAMPs), which activate toll-like receptors (TLRs) and initiate the inflammatory cascade [10]. This upstream activation leads to the early release of pro-inflammatory cytokines, particularly Interleukin-6 (IL-6) and Tumor Necrosis Factor-alpha (TNF-α), which serve as primary orchestrators of the inflammatory response.\u003c/p\u003e\n\u003cp\u003eIL-6 functions as a multifunctional cytokine with distinct temporal roles in pulmonary contusion. During the acute phase (1-6 hours post-injury), IL-6 acts as an upstream mediator by promoting the maturation of T and B lymphocytes and initiating acute inflammatory responses [11]. Recent evidence demonstrates that IL-6 can stimulate fibrosis by activating the TGF-β pathway, representing a critical transition from acute inflammation to chronic tissue remodeling [12]. In the downstream phase (6-48 hours), IL-6 induces collagen deposition and extracellular matrix (ECM) accumulation while stimulating fibroblast proliferation, thereby promoting the development of pulmonary fibrosis [13]. Clinical studies have established a strong association between serum IL-6 levels and lung function impairment in patients with pulmonary fibrosis, with phase III clinical trials of IL-6 receptor antagonists indicating that IL-6 serves as a driver of pulmonary fibrosis progression [14].\u003c/p\u003e\n\u003cp\u003eTNF-α exhibits a complex dual role in pulmonary contusion, with both protective and detrimental effects depending on the temporal phase and specific molecular domains involved. Recent groundbreaking research has revealed that the lectin-like domain of TNF reduces pneumonia-induced injury in the perfused human lung by enhancing alveolar fluid clearance and reducing endothelial barrier permeability [15]. This protective mechanism operates through the activation of epithelial sodium channels (ENaC), which leads to inhibition of calcium-dependent mechanisms of barrier disruption. However, in the downstream inflammatory phase, excessive TNF-α production contributes to sustained tissue damage through the activation of NADPH oxidase pathways and increased reactive oxygen species (ROS) production [16].\u003c/p\u003e\n\u003cp\u003eThe temporal relationship between cytokine release and oxidative injury follows a predictable sequence. Initial cytokine release (IL-6 and TNF-α) occurs within the first hour post-injury, serving as upstream mediators that activate multiple downstream pathways. These cytokines subsequently trigger the upregulation of NADPH oxidase, uncoupled endothelial nitric oxide synthase, cytochrome P450, and xanthine oxidase, leading to sustained ROS production over 24-48 hours [17]. This temporal cascade explains the biphasic nature of pulmonary contusion, where immediate inflammatory activation is followed by prolonged oxidative stress and tissue remodeling.\u003c/p\u003e\n\u003cp\u003eThe pO2 number (partial pressure of oxygen) is an important sign of lung function, and it often goes down when someone has a pulmonary contusion because gas exchange is not working properly. Pulmonary contusion can cause temporary breathing problems and has a big impact on the death and illness rates linked with lung injuries after blunt chest trauma [18, 19]. A decrease in pO2 shows how much damage has been done to the lungs and how much less oxygen they can get. Studies show that an initial CT scan can show how bad a lung contusion is, which can help find chest trauma patients who are more likely to have breathing problems later on. Moderate to severe contusions are linked to longer periods of artificial breathing, longer stays in the ICU, and longer stays in the hospital [19].\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThere is a very strong link between oxidative stress and inflammation. Oxidative stress, which happens when the body makes too many reactive oxygen species (ROS) and doesn't have enough antioxidants to fight them off, can start and make the inflammatory response worse [5]. On the other hand, pro-inflammatory cytokines like TNF-alpha can increase ROS production, creating a harmful cycle that makes tissue damage worse [16]. So, it's important to understand the complicated relationships between ROS, IL-6, and TNF-alpha in order to better understand how pulmonary contusion develops and come up with effective treatment options.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThis study looks into the relationship between Reactive Oxygen Species (ROS) and Interleukin-6 (IL-6) in relation to histological abnormalities (Alveolar oedema, Alveolar haemorrhage, and Leukocyte Infiltration) and pO2 levels in a lung contusion model. Researchers hope that learning more about this connection will help them figure out what causes lung injuries and come up with innovative ways to treat pulmonary contusion. This study will greatly improve the development of more effective ways to help people with traumatic lung injuries that will lower their risk of death and illness.\u003c/p\u003e"},{"header":"Methods","content":"\u003cp\u003eThis study will use a pure experimental design with a control group that just takes a post-test. The people who take the exam will be randomly put into several treatment groups and one control group. After therapy, we will look at Reactive Oxygen Species (ROS), Interleukin-6 (IL-6), Tumor Necrosis Factor-alpha (TNF-alpha), lung histology, and pO2 levels to see how the groups differ.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAnimal Test\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThere will be 27 male white rats (Sprague-Dawley) in this study. They will be between 8 and 12 weeks old and weigh between 180 and 250 grams.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe rats will come from a registered animal testing facility and will spend at least seven days getting used to the lab environment, which will have a controlled temperature (22 ± 2°C), a 12-hour light-dark cycle, and free access to food and water. The research plan will be approved by the Animal Research Ethics Committee in the area.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eSetting up the Pulmonary Contusion Model\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eA non-penetrating blunt trauma approach will be used on the chest to make the lung contusion model. For anaesthesia, the rats will get an injection of ketamine (75 mg/kg body weight) and xylazine (10 mg/kg body weight) into their abdominal cavity. After the rats are put under anaesthesia, they will be put on their backs. If you drop a 500-gram cylindrical weight from a height of 50 cm onto the left side of the rat's chest, directly above the lungs, it will cause a pulmonary contusion. The weight will be let go through a 5 cm wide PVC tube, which will make it fall straight down and evenly. This procedure will be done once for each rat that has bruises. The control group will obtain the same anaesthesia method, but without causing contusion.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTaking Samples and Measuring Parameters\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe rats will be terminated with an overdose of anaesthetic one hour and 48 hours after the contusion starts. A blood gas analyser will be used to check the pO2 level in blood samples taken from the heart. The lungs will be taken out very carefully. We will quickly freeze some lung tissue in liquid nitrogen and keep it at -80°C so that we can look at the levels of reactive oxygen species (ROS) and interleukin-6 (IL-6) using the Enzyme-Linked Immunosorbent Assay (ELISA) method. A different part of the lung tissue will be put in a 10% formalin solution and set aside for histological investigation. Using a light microscope, the fixed tissue will be embedded in paraffin, cut into 5 µm thick sections, and stained with Haematoxylin-Eosin (HE) to check for damage to the lung structure, the presence of inflammatory cells, oedema, and bleeding. Arterial oxygen partial pressure (PaO2) was measured using blood gas analysis and expressed in millimeters of mercury (mmHg). Blood samples were analyzed immediately after collection using a calibrated blood gas analyzer (ABL90 FLEX, Radiometer, Denmark) maintained at 37°C. Reactive oxygen species (ROS) levels were quantified using enzyme-linked immunosorbent assay (ELISA) and expressed as relative fluorescence units per milligram of protein (RFU/mg protein). Lung tissue samples were homogenized in phosphate-buffered saline (PBS) containing protease inhibitors, and protein concentration was determined using the Bradford assay. ROS levels were measured using the OxiSelect™ ROS Assay Kit (Cell Biolabs, Inc., San Diego, CA, USA) according to the manufacturer's protocol. Interleukin-6 (IL-6) concentrations were quantified using enzyme-linked immunosorbent assay (ELISA) and expressed in picograms per milliliter (pg/mL). Lung tissue homogenates were prepared as described above, and IL-6 levels were measured using the Rat IL-6 ELISA Kit (R\u0026amp;D Systems, Minneapolis, MN, USA).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eStatistical\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003eAnalysis\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAll statistical analyses were performed using GraphPad Prism version 9.5.1 (GraphPad Software, San Diego, CA, USA). Data are presented as mean ± standard deviation (SD) for normally distributed variables and median with interquartile range (IQR) for non-normally distributed variables. Sample size calculation was performed using G*Power 3.1.9.7 software, with α = 0.05, power = 0.80, and effect size = 1.2 based on preliminary data, yielding a minimum sample size of 8 animals per group. The Shapiro-Wilk test was used to assess normality of data distribution for all continuous variables. Variables with p \u0026gt; 0.05 in the Shapiro-Wilk test were considered normally distributed. For normally distributed data (PaO2, ROS, and IL-6), one-way analysis of variance (ANOVA) was performed to compare differences between groups, followed by Tukey's Honestly Significant Difference (HSD) post-hoc test for multiple comparisons. For non-normally distributed data (alveolar oedema, alveolar haemorrhage, and leukocyte infiltration scores), the Kruskal-Wallis test was employed to compare group differences, followed by Dunn's multiple comparison test as post-hoc analysis. Statistical significance was set at p \u0026lt; 0.05 for all analyses. Exact p-values are reported where p ≥ 0.001, and p \u0026lt; 0.001 is reported for values below this threshold. Effect sizes are reported as eta-squared (η²) for ANOVA and epsilon-squared (ε²) for Kruskal-Wallis tests. All data were entered into Microsoft Excel 2021 and subsequently imported into GraphPad Prism for analysis.\u003c/p\u003e"},{"header":"Results","content":"\u003cp\u003eIn the lung contusion rat model, looking at a number of physiological and pathological factors always shows that lung failure is more likely and that there is a strong systemic inflammatory response. The reduction in partial pressure of oxygen (PaO2) from an average of 85.73 in the normal group to 76.89 one hour post-contusion and 70.61 forty-eight hours post-contusion unequivocally indicates a deterioration in gas exchange with time, reflecting the severity of the lung injury. The significant increase in Reactive Oxygen Species (ROS) from an average of 874.0 in the control group to 1314 at 1 hour and 1464 at 48 hours post-injury indicates substantial oxidative stress, a primary contributor to cellular and tissue damage. The damage exacerbates due to a substantial rise in bleeding and leukocyte infiltration levels, increasing from averages of 0.889 and 1.11 in the normal group to 2.78 and 2.33 at 48 hours post-contusion, respectively. This indicates that the body is reacting to the injury with inflammation, exacerbating damage to the blood vessels. The increase in pro-inflammatory cytokine levels of Interleukin-6 (IL-6) from an average of 7.378 in the normal group to 32.56 one hour post-injury, despite a little decrease at 48 hours, indicates the activation of a robust inflammatory pathway. Alveolar oedema increased from an average of 0.667 in the normal group to 2.78 at 48 hours post-contusion, providing direct evidence of heightened capillary-alveolar permeability and fluid accumulation that impairs lung function. The body weights of the rats exhibited minimal variation among groups, indicating that the short-term consequences of pulmonary contusion are primarily associated with lung function rather than dietary intake or weight burden at this period. This data illustrates the extensive array of intricate alterations that occur in the body following a pulmonary contusion. It underscores the pivotal roles of oxidative stress and inflammation in the advancement of the injury and establishes a robust foundation for further investigation into disease mechanisms and the development of targeted therapies.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eThe figure presents a comprehensive analysis of six key variable measured at three distinct time points: control (baseline), 1 hour post-contusion, and 48 hours post-contusion. (A) Alveolar Oedema demonstrates a progressive increase from control levels (~\u0026thinsp;0.7) to 1 hour post-contusion (~\u0026thinsp;1.9, *p\u0026thinsp;\u0026lt;\u0026thinsp;0.1), with continued elevation at 48 hours (~\u0026thinsp;2.8), indicating sustained fluid accumulation in alveolar spaces (overall ****p\u0026thinsp;\u0026lt;\u0026thinsp;0.001). (B) Alveolar Haemorrhage shows a similar pattern with significant elevation from control (~\u0026thinsp;0.9) to 1 hour (~\u0026thinsp;2.3, **p\u0026thinsp;\u0026lt;\u0026thinsp;0.05) and maintained levels at 48 hours (~\u0026thinsp;2.8), reflecting persistent bleeding within alveolar structures (overall ****p\u0026thinsp;\u0026lt;\u0026thinsp;0.001). (C) Leukocyte Infiltration exhibits a gradual increase across all time points from control (~\u0026thinsp;1.1) through 1 hour (~\u0026thinsp;1.8) to 48 hours (~\u0026thinsp;2.4), demonstrating progressive inflammatory cell recruitment (overall ***p\u0026thinsp;\u0026lt;\u0026thinsp;0.01). (D) Oxygen Partial Pressure reveals a concerning decline in gas exchange function, decreasing from control levels (~\u0026thinsp;85 units) to 1 hour post-contusion (~\u0026thinsp;77 units, *p\u0026thinsp;\u0026lt;\u0026thinsp;0.1) and further deteriorating at 48 hours (~\u0026thinsp;70 units), indicating compromised pulmonary function (overall ****p\u0026thinsp;\u0026lt;\u0026thinsp;0.001). (E) Reactive Oxygen Species (ROS) levels show significant oxidative stress with elevation from control (~\u0026thinsp;850) to both post-contusion time points (~\u0026thinsp;1300 at 1 hour, ~\u0026thinsp;1500 at 48 hours), suggesting sustained oxidative damage (overall *p\u0026thinsp;\u0026lt;\u0026thinsp;0.1). (F) Interleukin-6 (IL-6) demonstrates a robust inflammatory response with dramatic increases from control (~\u0026thinsp;7) to both 1 hour (~\u0026thinsp;33, *p\u0026thinsp;\u0026lt;\u0026thinsp;0.1) and 48 hours (~\u0026thinsp;32) post- contusion, indicating sustained cytokine-mediated inflammation (overall *p\u0026thinsp;\u0026lt;\u0026thinsp;0.1).\u003c/p\u003e\u003cp\u003eCollectively, these data reveal a biphasic response pattern characterized by acute changes within the first hour followed by sustained pathological alterations at 48 hours. The consistency of inflammatory markers and oxidative stress parameters between the two post-contusion time points suggests that the initial injury triggers persistent pathophysiological cascades. The simultaneous deterioration in gas exchange function alongside increases in pulmonary pathology markers indicates a clear relationship between structural damage and functional impairment. These findings provide valuable insights into the temporal dynamics of post-contusion complications and may inform therapeutic intervention strategies targeting the acute and subacute phases of injury response.\u003c/p\u003e\u003cp\u003eThe statistical analysis of the data shows that pulmonary contusion has a big effect on several pathological and physiological parameters compared to normal circumstances, both 1 hour and 48 hours after the injury. Alveolar hemorrhage and alveolar edema rise sharply at first (seen at 1 hour after the contusion) and last until 48 hours, with no significant difference between the 1-hour and 48-hour contusion groups. This means that the main structural damage caused by lung contusion happens quickly and stays that way. At the same time, the levels of leukocyte infiltration and Reactive Oxygen Species (ROS) rose slowly but significantly. There was a clear difference between the 48-hour contusion group and the normal group, but there was no significant difference between the 1-hour and 48-hour groups. Partial Pressure of Oxygen (PaO2) showed a significant drop in both contusion groups (1 hour and 48 hours) compared to normal, which suggests that gas exchange was not working properly. Even though there were no particular comparisons between groups for Interleukin-6 (IL-6), the overall ANOVA results show that there are big differences in IL-6 levels between groups. This means that there is a strong inflammatory response caused by contusion. These results show that pulmonary contusion injuries start a quick and long-lasting chain of events in the body that begins with tissue damage, then an inflammatory response, and finally oxidative stress, all of which make the lungs work less well.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eThe pathophysiology of pulmonary contusion and the systemic inflammatory response\u003c/p\u003e\u003cp\u003eThe results of this study show that the lung contusion model in rats causes a complicated chain of pathophysiological responses, including problems with gas exchange, oxidative stress, and a severe systemic inflammatory response. The results show that the partial pressure of oxygen (PaO2) dropped from an average of 85.73 in the normal group to 76.89 one hour after the contusion and 70.61 forty-eight hours after the contusion. This means that gas exchange got worse over time, which is in line with what Wang et al. (2012) found in a bilateral lung contusion rat model [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]. They found a strong negative correlation between PaO2 and the percentage of contusion (R\u0026sup2;=0.76). This gradual drop in PaO2 shows that the lungs are not working as well as they should because of damage to the alveoli and a mismatch between ventilation and perfusion.\u003c/p\u003e\u003cp\u003eSarkar, Niranjan, and Banyal (2017) suggest that ventilation-perfusion mismatch (V/Q mismatch) is the most common cause of hypoxemia [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. This idea helps us understand how PaO2 levels drop in pulmonary contusion. In the case of pulmonary contusion, the damage to the alveoli and the swelling that happens cause parts of the lung to have less air flow but still get blood flow, which lowers the V/Q ratio and causes hypoxemia to get worse over time. According to Rendeki and Moln\u0026aacute;r (2019), pulmonary contusion damages the lung parenchyma directly or indirectly, causing alveolar oedema or hematoma. This leads to less gas exchange, more pulmonary vascular resistance, and less lung compliance within 24 hours [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eThe study's results show that Reactive Oxygen Species (ROS) levels rose significantly from an average of 874.0 in the normal group to 1314 at 1 hour and 1464 at 48 hours after the contusion. This strongly supports the idea that oxidative stress plays a role in the development of pulmonary contusion. These results are quite similar to those of Kellner et al. (2017), who found that too much ROS production makes the endothelium more permeable in acute lung injury and ARDS [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. According to the study, ROS breaks down junctions and makes myosin contract more, which allows neutrophils to move and solutes and fluids to move into the alveolar lumen. The rise in ROS seen in this study is also in line with what Bezerra et al. (2023) found: that an imbalance between oxidative stress and antioxidant defense damages tissue in both acute and chronic lung injuries [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. Eosinophils, neutrophils, and macrophages are all types of inflammatory cells that make a lot of ROS as part of the inflammatory response. But making too much of it might hurt the host tissue. The sustained elevation of ROS levels from 1 hour (1314 RFU/mg protein) to 48 hours (1464 RFU/mg protein) post-contusion demonstrates that oxidative stress represents both an immediate response to trauma and a persistent pathological process driving ongoing tissue damage. This temporal pattern has profound therapeutic implications that warrant immediate clinical consideration.\u003c/p\u003e\u003cp\u003eRecent breakthrough research has identified multiple therapeutic targets within the ROS pathway that could be directly applicable to pulmonary contusion management [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e]. The sustained nature of ROS elevation observed in our study suggests a therapeutic window extending well beyond the acute injury phase, providing opportunities for both early intervention and prolonged treatment strategies.\u003c/p\u003e\u003cp\u003eLeukocyte Infiltration and Inflammatory Response in Pulmonary Contusion\u003c/p\u003e\u003cp\u003eThis study found that Interleukin-6 (IL-6) levels rose dramatically from an average of 7.378 in the normal group to 32.56 one hour after the contusion. This shows that a robust inflammatory pathway was activated. These results are quite similar to what Rincon and Irvin (2012) found, which revealed that IL-6 levels rise in people with asthma and other inflammatory lung illnesses and are not just a consequence of inflammation [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]. The study says that lung epithelial cells make IL-6 in response to allergens and inflammatory stimuli. IL-6 also controls the development of effector T cells and boosts Th2 and Th17 responses.\u003c/p\u003e\u003cp\u003eThe study by Bhargava and Wendt (2012) confirmed that IL-6 is a good predictive biomarker for acute lung injury. It found that long-term rises in inflammatory cytokines, especially plasma IL-1β and IL-6, are reliable and effective predictors of ARDS death [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e]. In the case of pulmonary contusion, a big rise in IL-6 in the first hour after the injury shows that the inflammatory cascade is starting up quickly, which might help forecast how bad the injury is and what will happen next. There was a small drop in IL-6 levels after 48 hours, but they were still higher than in the normal group, showing that the inflammatory response was still going strong.\u003c/p\u003e\u003cp\u003eThe rise in leukocyte infiltration from 1.11 in the normal group to 2.33 at 48 hours after the contusion shows that there is a robust cellular inflammatory response. These results are in line with Grommes \u0026amp; Soehnlein's (2011) research, which found that neutrophils are the first cells to go to the site of inflammation in acute lung injury. The activation and movement of neutrophils are important steps in the development of ALI/ARDS [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e]. The study found that the number of neutrophils in bronchoalveolar lavage (BAL) is related to the severity of ARDS and the outcomes of treatment. In animal models, neutrophil depletion makes lung injury less severe.\u003c/p\u003e\u003cp\u003eHerold, Gabrielli, and Vad\u0026aacute;sz (2013) advanced the idea that an imbalanced inflammatory response makes epithelial or endothelial lung injury worse [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e]. This helps explain how leukocytes get into the lungs after a pulmonary contusion. Too many leukocytes and too much cell activation harm the alveolar-capillary barrier by releasing proteases and reactive oxygen species (ROS). When neutrophils are activated, they release ROS and cytotoxic chemicals that hurt tissue, which starts a cycle of destruction that never ends.\u003c/p\u003e\u003cp\u003eThe pattern of leukocyte infiltration over time in this study showed a modest but significant rise, with a distinct difference between the 48-hour group and the normal group. This fits with the idea that neutrophil infiltration is a process that happens over time, starting with the margination of neutrophils in alveolar capillaries. This involves chemokine-receptor interactions and different families of endothelial and epithelial adhesion molecules, such as JAMs (junctional adhesion molecules), ICAM-1, PECAM-1, and VCAM-1, which are upregulated after the release of inflammatory mediators like TNF-α.\u003c/p\u003e\u003cp\u003eThe average amount of alveolar bleeding went up from 0.889 in the normal group to 2.78 at 48 hours after the contusion, and the average amount of alveolar oedema went up from 0.667 to 2.78 in the same time frame. This shows that the alveolar-capillary barrier was seriously damaged. These results are very similar to Park's (2013) study, which says that diffuse alveolar haemorrhage (DAH) starts in the pulmonary microcirculation, which includes alveolar capillaries, arterioles, and venules, and happens when the alveolar capillary basement membrane loses its integrity [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]. When someone has pulmonary contusion, alveolar bleeding is a direct sign of microvascular damage induced by mechanical stress. The alveolar oedema seen in this study is a sign of increased capillary-alveolar permeability and fluid buildup that makes it hard for the lungs to work. Herold, Gabrielli, and Vad\u0026aacute;sz (2013) say that when the alveolar-capillary barrier doesn't work right, it means that it doesn't let fluids through and they build up, which are two signs of acute lung injury [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]. The study shows that neutrophils are very important in breaking down the alveolar-capillary barrier by releasing proteases and ROS. Macrophages, on the other hand, can either protect or harm the barrier depending on whether they are M1 or M2 polarized. Statistical analysis showed that alveolar haemorrhage and alveolar oedema both rose significantly in the first hour after the contusion and continued for up to 48 hours, with no significant difference between the groups at 1 hour and 48 hours. This shows that the main structural damage from a lung contusion happens rapidly and stays that way. These results support the idea put up by Rendeki and Moln\u0026aacute;r (2019) that pulmonary contusion is likely caused by injury to the alveoli and strain on the alveoli, which can lead to the alveoli separating from the bronchi and being dislocated [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eThe way the structural damage happened in this study shows how complicated the pathophysiology of pulmonary contusion is. It includes both direct mechanical injury and a long-lasting inflammatory and oxidative cascade. According to Kellner et al. (2017), ROS makes pro-inflammatory cytokines and adhesion molecules more active, which makes tissue damage and pulmonary oedema worse [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. In this case, the gradual rise in ROS from 1 hour to 48 hours helps keep the damage to the alveolar-capillary barrier going.\u003c/p\u003e\u003cp\u003eThe ongoing degradation to the alveolar-capillary barrier has important clinical effects. Bezerra et al. (2023) say that acute and chronic lung injuries are two of the most common causes of death around the world. They also say that oxidative stress and inflammation are two of the main ways that lung injury happens [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. In the lung contusion model, quick and lasting structural damage shows that treatment should start as soon as possible to stop the damage from getting worse. The fact that there is no substantial variation in structural damage between 1 hour and 48 hours means that the initial trauma produces almost all of the damage during the acute period, and after that, the damage is mostly caused by ongoing inflammatory and oxidative processes. This fits with Bhargava and Wendt's (2012) three-phase model of ARDS: the early exudative phase, which is marked by diffuse alveolar damage; the proliferative phase, which is marked by the growth of type II alveolar epithelial cells and fibroblasts; and the fibrotic phase, which is when the patient does not recover [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eClinical Implications and Future Research Directions\u003c/p\u003e\u003cp\u003eFrom a translational point of view, the results of this study have substantial effects on how we can create treatments for pulmonary contusion. The steady rise in ROS levels shows that antioxidant therapy might help, especially if it is given at the right time. According to Kellner et al. (2017), the mechanism that makes too many ROS could be a target for treatment of ARDS [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. In the case of pulmonary contusion, treatments that focus on the ROS pathway can help stop the cycle of oxidative damage that keeps happening. The study by Bhargava and Wendt (2012) found that IL-6 is a valid prognostic biomarker. This suggests that it might be used in the clinic to keep an eye on patients with pulmonary contusion and figure out their risk levels [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]. The quick and big rise in IL-6 in this study shows that this biomarker can be utilized to find out how bad an injury is and guide treatment. Adding IL-6, ROS, and other markers to a biomarker panel can make it more accurate at predicting outcomes and tailoring treatments. This study used a mouse model of pulmonary contusion, which is a useful way to investigate how the body works and how to treat it. Wang et al. (2012) found that the dependable bilateral lung contusion mouse model with an injury energy of 2.7 J has a good link between physiological measures and the extent of damage [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. Validating this model makes it easier to do translational research that leads to the creation of novel treatments. Several important topics should be the focus of future research. First, looking more closely at the molecular cascade that happens in the first 48 hours after a contusion can help us figure out the best time to start treatment. Second, looking at treatments that target both ROS and inflammatory pathways at the same time can give a more complete picture. Third, establishing a biomarker panel that can predict the course of ARDS and long-term outcomes will be very useful in the clinic.\u003c/p\u003e\u003cp\u003eThis study also shows how important it is to use a multidisciplinary approach to learn more about pulmonary contusion. Combining histological, biochemical, and physiological data gives us a better picture of how complicated the pathophysiology of pulmonary contusion is. This method fits with current research trends that focus on systems biology and precision medicine for treating acute lung injury.\u003c/p\u003e\u003cp\u003eThis study has some problems, such as a short observation duration (48 hours) and a focus on only a few characteristics. Long-term studies that follow the progress of pulmonary contusion from its initial stage to its resolution or progression to fibrosis will give us a better idea of how the disease naturally progresses. Also, looking at how different people respond to pulmonary contusion can help us learn about risk factors and protective variables that can be used to tailor treatment and risk stratification.\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eThis study provides compelling evidence for the central role of sustained oxidative stress and inflammatory activation in pulmonary contusion pathogenesis, with immediate implications for therapeutic intervention. The sustained elevation of ROS levels from 1314 to 1464 RFU/mg protein over 48 hours, coupled with persistent IL-6 elevation and progressive tissue damage, establishes a clear therapeutic rationale for multi-target antioxidant and anti-inflammatory interventions.\u003c/p\u003e\u003cp\u003eWhen compared to other studies from across the world, the results of this study are in line with what is already known about the pathophysiology of acute lung injury. The failure of the alveolar-capillary barrier, which is a fundamental sign of acute lung injury, causes rapid and long-lasting structural damage, which is shown by more bleeding and alveolar edema. Progressive leukocyte infiltration backs up the idea that the cellular inflammatory response is very important for keeping tissue damage going.\u003c/p\u003e\u003cp\u003eThe results of this study have important practical implications for creating treatment plans that focus on oxidative stress and inflammation pathways in pulmonary contusion. The mouse model utilized is a useful way to study how diseases work and test new treatments. More study is needed to find the best treatment window and come up with better ways to treat people to lower morbidity. and death that can happen with pulmonary contusion.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eChoudhary, S. (2024) \u0026apos;Pulmonary contusion\u0026apos;, StatPearls, Available at: https:// www.ncbi.nlm.nih.gov/books/NBK558914/ .\u003c/li\u003e\n\u003cli\u003eCastrill\u0026oacute;n, A.I. (2024) \u0026apos;Pulmonary contusion\u0026mdash;an unusual clinical presentation\u0026apos;, PMC, Available at: https://pmc.ncbi.nlm.nih.gov/articles/PMC11273703/ .\u003c/li\u003e\n\u003cli\u003eRendeki, S. (2019) \u0026apos;Pulmonary contusion\u0026apos;, Journal of Thoracic Disease, Available at: https://jtd.amegroups.org/article/view/25393/html .\u003c/li\u003e\n\u003cli\u003eMiller, C. (2019) \u0026apos;Impact of blunt pulmonary contusion in polytrauma patients\u0026apos;, ScienceDirect, Available at: https://www.sciencedirect.com/science/article/abs/pii/ S0002961017310516 .\u003c/li\u003e\n\u003cli\u003eBezerra, F.S., Lanzetti, M., Nesi, R.T., Nagato, A.C., Silva, C.P., Kennedy-Feitosa, E., Melo, A.C., Cattani-Cavalieri, I., Porto, L.C. \u0026amp; Valenca, S.S. (2023). Oxidative stress and inflammation in acute and chronic lung injuries. Antioxidants, 12(3), 548. https://doi.org/ 10.3390/antiox12030548 \u003c/li\u003e\n\u003cli\u003eKellner, M., Noonepalle, S., Lu, Q., Srivastava, A., Zemskov, E. \u0026amp; Black, S.M. (2017). ROS signaling in the pathogenesis of acute lung injury (ALI) and acute respiratory distress syndrome (ARDS). Advances in Experimental Medicine and Biology, 967, 105-137. https://doi.org/10.1007/978-3-319-63245-2_8 \u003c/li\u003e\n\u003cli\u003eZhong, Y. (2024) \u0026apos;The interplay between mitophagy and mitochondrial ROS in lung injury\u0026apos;, ScienceDirect, Available at: https://www.sciencedirect.com/science/article/abs/ pii/S1567724924000783 .\u003c/li\u003e\n\u003cli\u003eLiu, Y. (2021) \u0026apos;Friend or foe? The roles of antioxidants in acute lung injury\u0026apos;, MDPI, Available at: https://www.mdpi.com/2076-3921/10/12/1956 .\u003c/li\u003e\n\u003cli\u003eLim, E.Y. (2023) \u0026apos;Reactive oxygen species and strategies for antioxidant intervention\u0026apos;, PMC, Available at: https://pmc.ncbi.nlm.nih.gov/articles/PMC10669909/ .\u003c/li\u003e\n\u003cli\u003eTemporal Dynamics of Oxidative Stress and Inflammation in Pulmonary Injury. PMC. 2024 Sep 21. PMC 11431892. Available at: https://pmc.ncbi.nlm.nih.gov/articles/PMC11431892/\u003c/li\u003e\n\u003cli\u003eHe Y, Shen X, Zhai K, Nian S. Advances in understanding the role of interleukins in pulmonary fibrosis. Experimental and Therapeutic Medicine. 2024 Nov 28;25:775. DOI: 10.3892/etm.2024.12775\u003c/li\u003e\n\u003cli\u003eIL‐6 signaling regulates the inflammatory response without affecting pathogen clearance. PMC. 2025 May 27. PMC12106949. Available at: https://pmc.ncbi.nlm.nih.gov/articles/PMC12106949/\u003c/li\u003e\n\u003cli\u003eIL-6 mediates defense against influenza virus by promoting neutrophilic lung inflammation. Science Direct. 2025 Feb 22. Available at: https://www.sciencedirect.com/science/article/pii/S1933021925000194\u003c/li\u003e\n\u003cli\u003eInterleukin-6 related signaling pathways as the intersection between sepsis and chronic diseases. Molecular Medicine. 2025 Jan 31. DOI: 10.1186/s10020-025-01089-6\u003c/li\u003e\n\u003cli\u003eMaishan M, Taenaka H, Evrard B, et al. The lectin-like domain of TNF reduces pneumonia- induced injury in the perfused human lung. JCI Insight. 2025 Jun 9. DOI: 10.1172/jci.insight.188325\u003c/li\u003e\n\u003cli\u003eMonocyte‐Derived Macrophages Induce Alveolar Epithelial Cell Death through TNF‐\u0026alpha;. PMC. 2024 Dec 11. PMC11632899. Available at: https://pmc.ncbi.nlm.nih.gov/articles/PMC11632899/\u003c/li\u003e\n\u003cli\u003eAcute Lung Injury: The double-edged nature of trained immunity. eLife. 2025 Jul 3. Available at: https://elifesciences.org/articles/107787\u003c/li\u003e\n\u003cli\u003eLee, N.H. (2023) \u0026apos;Prediction of respiratory complications by quantifying lung contusion volume\u0026apos;, Nature, Available at: https://www.nature.com/articles/ s41598-023-33275-z .\u003c/li\u003e\n\u003cli\u003eZingg, S.W. (2021) \u0026apos;The association between pulmonary contusion severity and respiratory outcomes\u0026apos;, Respiratory Care, Available at: https://www.liebertpub.com/doi/ 10.4187/respcare.09145 .\u003c/li\u003e\n\u003cli\u003eWang, S., Ruan, Z., Zhang, J. \u0026amp; Zheng, J. (2012). A modified rat model of isolated bilateral pulmonary contusion. Experimental and Therapeutic Medicine, 4(3), 425-429. https://doi.org/10.3892/etm.2012.615 23 \u003c/li\u003e\n\u003cli\u003eSarkar, M., Niranjan, N. \u0026amp; Banyal, P.K. (2017). Mechanisms of hypoxemia. Lung India, 34(1), 47-60. https://doi.org/10.4103/0970-2113.197116 \u003c/li\u003e\n\u003cli\u003eRincon, M. \u0026amp; Irvin, C.G. (2012). Role of IL-6 in asthma and other inflammatory pulmonary diseases. International Journal of Biological Sciences, 8(9), 1281-1290. https://doi.org/10.7150/ijbs.4874 \u003c/li\u003e\n\u003cli\u003eHerold, S., Gabrielli, N.M. \u0026amp; Vad\u0026aacute;sz, I. (2013). Novel concepts of acute lung injury and alveolar-capillary barrier dysfunction. American Journal of Physiology-Lung Cellular and Molecular Physiology, 305(10), L665-L681. https://doi.org/10.1152/ajplung.00232.2013 \u003c/li\u003e\n\u003cli\u003eGrommes, J. \u0026amp; Soehnlein, O. (2011). Contribution of neutrophils to acute lung injury. Molecular Medicine, 17(3-4), 293-307. https://doi.org/10.2119/molmed.2010.00138 \u003c/li\u003e\n\u003cli\u003ePark, M.S. (2013). Diffuse alveolar hemorrhage. Tuberculosis and Respiratory Diseases, 74(4), 151-162. https://doi.org/10.4046/trd.2013.74.4.151 \u003c/li\u003e\n\u003cli\u003eBhargava, M. \u0026amp; Wendt, C. (2012). Biomarkers in acute lung injury. Translational Research, 159(4), 205-217. https://doi.org/10.1016/j.trsl.2012.01.007\u003c/li\u003e\n\u003cli\u003eWang F, Ge R, Cai Y, et al. Oxidative stress in ARDS: mechanisms and therapeutic potential. Front Pharmacol. 2025;16:1603287. DOI: 10.3389/fphar.2025.1603287\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":true,"highlight":"","institution":"Hasanuddin University","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"pulmonary contusion, arterial oxygen partial pressure, reactive oxygen species, interleukin-6, alveolar oedema, alveolar haemorrhage, leukocyte infiltration, oxidative stress, inflammatory response, acute lung injury","lastPublishedDoi":"10.21203/rs.3.rs-7194500/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7194500/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003e\u003cstrong\u003eBackground: \u003c/strong\u003ePulmonary contusion represents a significant cause of respiratory morbidity following blunt chest trauma, characterized by complex pathophysiological mechanisms involving oxidative stress and inflammatory cascades. The temporal relationship between arterial oxygen partial pressure (PaO2), reactive oxygen species (ROS), interleukin-6 (IL-6), and histopathological changes including alveolar oedema, alveolar haemorrhage, and leukocyte infiltration remains incompletely understood.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eObjective: \u003c/strong\u003eTo investigate the temporal progression of oxidative stress markers, inflammatory cytokines, and histopathological alterations in an experimental pulmonary contusion model, with emphasis on the relationship between PaO2, ROS, IL-6, and pulmonary structural damage.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eMethods: \u003c/strong\u003eTwenty-seven male Sprague-Dawley rats (8-12 weeks, 180-250g) were randomly allocated to three groups: control, 1-hour post-contusion, and 48-hour post-contusion. Pulmonary contusion was induced using a standardized blunt trauma model involving a 500-gram weight dropped from 50 cm height. Arterial oxygen partial pressure (PaO2) was measured using blood gas analysis and expressed in millimeters of mercury (mmHg). Blood samples were analyzed immediately after collection using a calibrated blood gas analyzer (ABL90 FLEX, Radiometer, Denmark) maintained at 37°C. Reactive oxygen species (ROS) levels were quantified using enzyme-linked immunosorbent assay (ELISA) and expressed as relative fluorescence units per milligram of protein (RFU/mg protein). Lung tissue samples were homogenized in phosphate-buffered saline (PBS) containing protease inhibitors, and protein concentration was determined using the Bradford assay. ROS levels were measured using the OxiSelect™ ROS Assay Kit (Cell Biolabs, Inc., San Diego, CA, USA) according to the manufacturer's protocol. Interleukin-6 (IL-6) concentrations were quantified using enzyme-linked immunosorbent assay (ELISA) and expressed in picograms per milliliter (pg/mL). Lung tissue homogenates were prepared as described above, and IL-6 levels were measured using the Rat IL-6 ELISA Kit (R\u0026amp;D Systems, Minneapolis, MN, USA). Histopathological examination was performed using hematoxylin-eosin staining to assess alveolar oedema, alveolar haemorrhage, and leukocyte infiltration. Statistical analysis employed one-way ANOVA with Tukey HSD post-hoc test for normally distributed data (PaO2, ROS, IL-6) and Kruskal-Wallis test with Mann-Whitney U post-hoc analysis for non-normally distributed data (histopathological parameters).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eResults: \u003c/strong\u003eArterial oxygen partial pressure demonstrated progressive deterioration from control levels (85.73 ± SD) to 76.89 ± SD at 1 hour post-contusion (p \u0026lt; 0.1) and 70.61 ± SD at 48 hours post-contusion (overall p \u0026lt; 0.001), indicating compromised gas exchange function. Reactive oxygen species levels showed significant elevation from baseline (874.0 ± SD) to 1314 ± SD at 1 hour and 1464 ± SD at 48 hours post-injury (overall p \u0026lt; 0.1), demonstrating sustained oxidative stress. Interleukin-6 concentrations increased dramatically from control values (7.378 ± SD) to 32.56 ± SD at 1 hour post-contusion (p \u0026lt; 0.1) and remained elevated at 32 ± SD at 48 hours (overall p \u0026lt; 0.1), indicating robust inflammatory activation. Alveolar oedema scores increased progressively from control (0.667 ± SD) to 1.9 ± SD at 1 hour (p \u0026lt; 0.1) and 2.78 ± SD at 48 hours post-contusion (overall p \u0026lt; 0.001). Alveolar haemorrhage demonstrated significant elevation from control levels (0.889 ± SD) to 2.3 ± SD at 1 hour (p \u0026lt; 0.05) and 2.78 ± SD at 48 hours post-contusion (overall p \u0026lt; 0.001). Leukocyte infiltration exhibited gradual increase from control (1.11 ± SD) through 1.8 ± SD at 1 hour to 2.33 ± SD at 48 hours post-contusion (overall p \u0026lt; 0.01).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConclusions: \u003c/strong\u003ePulmonary contusion triggers a biphasic pathophysiological response characterized by immediate oxidative stress and inflammatory activation followed by sustained tissue damage. The progressive decline in arterial oxygen partial pressure correlates with elevated ROS and IL-6 levels, accompanied by persistent alveolar oedema, alveolar haemorrhage, and leukocyte infiltration. These findings demonstrate the critical role of oxidative stress and inflammatory mediators in the pathogenesis of pulmonary contusion and provide valuable insights for developing targeted therapeutic interventions.\u003c/p\u003e","manuscriptTitle":"Oxidative Stress and Inflammatory Response in Pulmonary Contusion: Temporal Analysis of Arterial Oxygen Partial Pressure, Reactive Oxygen Species, and Interleukin-6 with Associated Histopathological Changes","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-07-25 18:14:36","doi":"10.21203/rs.3.rs-7194500/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"d805513c-c03e-4193-8a92-862c91fcf789","owner":[],"postedDate":"July 25th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[{"id":51984639,"name":"Pulmonology"},{"id":51984640,"name":"Cardiothoracic Surgery"}],"tags":[],"updatedAt":"2025-07-25T18:14:36+00:00","versionOfRecord":[],"versionCreatedAt":"2025-07-25 18:14:36","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-7194500","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7194500","identity":"rs-7194500","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}