Fenofibrate reduces pain hypersensitivity and associated depression-like behavior in mice with oxaliplatin- induced neuropathy

Fenofibrate reduces pain hypersensitivity and associated depression-like behavior in mice with oxaliplatin- induced neuropathy | 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 Article Fenofibrate reduces pain hypersensitivity and associated depression-like behavior in mice with oxaliplatin- induced neuropathy Liang Yue, Yimin Yuan, Dai Li, Li Sun, Yijia Shen, Yu Ma, Li Cao, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4339586/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 The population of patients with chemotherapy-induced neuropathy is increasing in parallel with the growing number of cancer survivors, creating an urgent need for effective treatments that address both the neuropathic symptoms and the accompanying depression. In this study, we established a mouse model of chronic oxaliplatin-induced neuropathy (OIPN) that closely mimics significant cold and mechanical allodynia, along with depression-like behaviors observed in patients, over a clinically relevant timeframe. We investigated the effects of fenofibrate on pain hypersensitivity and depression-like behaviors in the OIPN mouse model. Administration of fenofibrate significantly reduced mechanical allodynia in the Von Frey test and cold allodynia in the cold plate test among OIPN mice. Moreover, fenofibrate reduced depression-like behaviors in OIPN mice, as demonstrated by improved performance in the forced swimming test, sucrose preference test and tail suspension test. The analgesic and antidepressant-like effects observed with fenofibrate may be linked to its protective actions on oligodendrocyte progenitor cells (OPCs) in the medial prefrontal cortex (mPFC) of oxaliplatin-treated mice. These findings suggest that fenofibrate holds promise as a potential therapeutic agent for the prevention and treatment of OIPN, offering relief from both pain and comorbid depressive symptoms. Further clinical testing is warranted to confirm its efficacy and safety in this context. Fenofibrate Oxaliplatin-induced neuropathy Depression-like behavior Medial prefrontal cortex Oligodendrocyte progenitor cells Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Introduction Oxaliplatin (OXA), a third-generation platinum-based antitumor agent, finds widespread application in the treatment of various solid tumors 1,2 . Nevertheless, its therapeutic benefits often come hand in hand with considerable adverse effects, notably chemotherapy-induced peripheral neuropathy (CIPN) 3,4 . Specifically, over 90% of patients report acute pain symptoms exacerbated by cold following oxaliplatin administration, while 30–50% endure chronic oxaliplatin-induced peripheral neuropathy (OIPN) 5–7 . This condition frequently manifests as neuropathic pain, which significantly impairs patients' quality of life by causing comorbidities such as distress, depression, and anxiety, often leading to modifications or discontinuation of standard treatment regimens 8,9 . The coexistence of chronic pain and depression is well-documented, albeit the underlying mechanisms remain elusive and incompletely understood 10,11 . Comorbid depression can exacerbate pain perception and diminish the efficacy of pain management, underscoring the importance of concurrently addressing both conditions 10 . In this context, dual-acting agents emerge as promising therapeutic options. Presently, duloxetine, an antidepressant acting as a 5-HT/NA reuptake inhibitor, stands as the sole recommended agent for alleviating sensory symptoms of established CIPN, while no definitive recommendations exist for CIPN prevention due to insufficient evidence 12–14 . Fenofibrate, a fibric acid derivative, serves as a mainstay treatment for primary hypercholesterolemia, mixed dyslipidemia and hypertriglyceridemia in adults 15 . It functions as a prodrug, undergoing de-esterification in the liver to yield fenofibric acid, the pharmacologically active metabolite, which subsequently enters the plasma and distributes to various tissues 16 . Lately, fenofibrate has garnered attention for its expanding pharmacological effects on the central nervous system (CNS), including its potential in preventing paclitaxel-induced peripheral neuropathy (PIPN) development 17 and exhibiting antidepressant-like effects in rodent models of chronic social defeat and unavoidable stress 18,19 . In our current study, we aim to investigate the potential of fenofibrate in mitigating chronic pain and comorbid depression induced by the chemotherapy drug oxaliplatin. Additionally, we seek to explore whether these effects are mediated through oligodendrocyte progenitor cells (OPCs) in the medial prefrontal cortex (mPFC). Materials and Methods Animals All animal experiments were granted approval by the Animal Care and Use Committee of the Naval Medical University and were conducted in strict adherence to the Chinese Academy of Sciences Animal Experiment Guide. The experiments were reported in accordance with the ARRIVE guidelines. The studies were carried out on male C57BL/6 mice (weighing 20–30 g), obtained from the Experimental Animal Center of the Naval Medical University. The animals were housed under standard laboratory conditions: a temperature maintained at 22 ± 1°C, relative humidity of 55 ± 5%, and a 12-hour light/dark cycle. Mice had unrestricted access to regular food or fenofibrate diet and water (with the exception of during the experimental procedures). To minimize the influence of diurnal variations on behavioral tests, the experiments were conducted in a blinded manner between 8:00 and 16:00. The mice were euthanized humanely at the end of the research by administering intravenous barbiturates. Primary oligodendrocyte progenitor cell culture OPCs were cultured and purified according to previously described methods 20,21 . In brief, mixed glial cells were harvested from the cortex of P1 Sprague Dawley rats (SD rats) and cultured in Dulbecco's modified Eagle's medium supplemented with 10% fetal bovine serum for 10 days at 37°C in a 5% CO 2 incubator. The medium was replaced every 3 days. For purification, the flasks were initially shaken rpm for 1 hour (180 rpm, 37°C) to eliminate microglia, followed by shaking for 16 hours (200 rpm, 37°C) with fresh medium at 37°C to collect OPCs. The harvested cells were allowed to adhere to uncoated plates for 30 minutes, twice in total, to remove contaminating cells. Subsequently, the purified OPCs were gently detached and seeded at a density ranging from 5,000 cells/cm 2 to 50,000 cells/cm 2 onto coverslips that had been pre-coated with poly-D-lysine. To promote the expansion of OPCs while maintaining their undifferentiated state, the culture medium was supplemented with 10 ng/mL basic fibroblast growth factor (b-FGF, Sigma-Aldrich) and 10 ng/mL PDGF-AA (R&D Systems). Drugs administration and experimental design The fenofibrate diet, consisting of 0.2% fenofibrate (F6020, Sigma-Aldrich), was prepared by thoroughly blending it with regular food 22 . The administration of this fenofibrate-enriched diet began 3 days prior to oxaliplatin treatment and continued for 25 days. The dosages of fenofibrate were determined in accordance with previous literature 22 . For chronic administration, fenofibrate was administered through dietary intake rather than via gavage or injection, in order to minimize the stress associated with repeated gavages or daily injections. Oxaliplatin (S1224, Selleck) was dissolved in 5% Glucose and the volume was adjusted to achieve a concentration of 1 mg/mL. Oxaliplatin was administered intraperitoneally at a dose of 6 mg/kg every other day, with a total of four administrations per regimen. The vehicle-treated animals received an equivalent volume of 5% Glucose administered intraperitoneally, following the identical injection regimen (Fig. 1 A). Basal behavioral parameters (paw withdrawal threshold in the Von Frey test, latency time to pain reaction in the cold plate test) were assessed before the administration of oxaliplatin/vehicle. To examine the development of mechanical and cold allodynia, as well as the anti-allodynic effect of fenofibrate, the Von Frey and cold plate tests were performed on the 7th, 14th, and 21st days following the initial injection of oxaliplatin. At each time point, the Von Frey test was administered prior to the cold plate test in the same group of animals. To assess depressive-like behavior in mice treated with oxaliplatin and the antidepressive-like effects of fenofibrate, the sucrose preference test (SPT), tail suspension test (TST), and forced swimming test (FST) were performed on the 14th day following the initial injection of oxaliplatin. These tests (SPT, TST, and FST) were conducted on animals that had previously undergone allodynia testing. For in vitro studies, fenofibric acid (HY-B0760, MedChemExpress, China) was dissolved in dimethyl sulfoxide (DMSO, Sigma-Aldrich) and added to the medium to achieve the desired concentration. After a 6-hour treatment with fenofibric acid, oxaliplatin (S1224, Selleck) was dissolved in DMSO, subsequently diluted with sterile PBS, and finally added to the medium to achieve the desired concentration. The cells were then treated for 3 hours before being fixed. Cells were not exposed to more than 0.1% DMSO during the experiments. All studies involving light-sensitive drugs were conducted in the dark. Behavioral evaluations Von Frey test Mechanical allodynia was assessed using an Electronic Von Frey Anesthesiometer (IITC Life Science, Woodland Hills, CA) 23 . Adult mice were placed on a metallic mesh floor inside plexiglass boxes for 30 min. A mechanical stimulus was applied by means of a rigid tip connected to a force transducer, which was pressed through the metallic mesh floor at a 90° angle against the plantar region of either hind paw. The pressure was gradually increased over approximately 5 s, and the paw withdrawal threshold (PWT; in grams) was automatically recorded on the readout unit when the hind paw was withdrawn. For each animal, the final PWT at each time point was calculated as the average of a total of 8 readings (4 readings from each paw). Cold plate test The cold plate test is one of the simplest assays for determining behavioral responses to both noxious and innocuous cold temperatures in mice 24 . It provides an insight into how sensitive an animal is to cold temperatures and thus provides an indirect measure of cold-induced hyperalgesia and allodynia. The cold plate test was performed using the hot/cold plate analgesia meter (IITC Life Science, Woodland Hills, CA) set at 4°C ± 1°C. Pain-related behaviors (i.e., lifting and licking of the hind paw) were observed, and the time (s) of the first sign was recorded. In this assay, a cut-off time of 60 s was established to avoid potential paw tissue damage, and animals not responding within 60 s were removed from the apparatus and assigned a score of 60 s. Forced swimming test Depressive-like behavior was assessed by forced swimming test 25 . In this test, the immobility time of mice was used as a measure of behavioral despair, a common feature of depression (i.e. the animal loses hope to escape the stressful environment). During the test, mice were placed in transparent cylindrical tanks (30 cm height × 20 cm diameter) filled with tap water set at room temperature (24 ± 1°C). The water level was 15 cm from the bottom, so the mice could not touch the bottom nor escape from the tank. The test lasted 6 minutes, but only the last 4 minutes were analyzed due to increased activity during the initial 2 minutes. The immobility time, i.e. the time spent performing the movements necessary only to balance the body and keep the head above the water, was used to assess the development of depressive-like behavior and antidepressant-like effects of the drugs. As it was easier to detect and measure active movements than the lack of such movements, we measured the time that each mouse spent mobile and subtracted the amount of mobility time from total test time (240 s) to obtain the immobility time. Sucrose preference test Anhedonia is a core symptom of human depression and can be measured through the sucrose preference test 26 . The test mice were housed individually and allowed to drink 1% sucrose solution and pure water freely. Before the test, a 2 days sucrose preference training process was performed. Each test mouse was given one bottle of pure water and one bottle of 1% sucrose solution. During this period, the positions of the two bottles were exchanged every 6 hours to avoid side preference. On the 3rd day, the test mice were deprived of food and water for 18 hours. On the 4th day, each mouse was provided with two pre-weighed bottles for 6 hours. Afterward, the two bottles were weighed again. The sucrose preference index was calculated as the percentage of the consumed sucrose solution relative to the total amount of liquid intake. Tail suspension test The tail suspension test is one of the most widely used models for assessing antidepressant-like activity in mice 27 . The tail tip of each mouse was individually affixed to a rail positioned 60 cm above the floor, and suspended for a duration of 6 minutes. Throughout this timeframe, the period of immobility (completely motionless) was meticulously documented for every mouse. This test was conducted with the observer blinded to the experimental grouping. Tissue preparation and immunohistofluorescence For immunohistofluorescence, animals were anaesthetized and transcardially perfused with PBS followed by 4% paraformaldehyde (PFA in PBS). Brains were post-fixed with 4% PFA overnight at 4°C, cryopreserved in 30% sucrose in PBS for 48–72 h, and sectioned coronally at 10 µm using a cryostat (Leica). Cryosections were then washed with PBS, blocked for 1 h at room temperature (3% bovine serum albumin, BSA) and 0.3% Triton X-100 diluted in PBS), and incubated overnight at 4°C with primary antibodies in blocking solution. Primary antibodies used were: anti-Sox10 (rabbit, 1:100; 78330S, Cell Signaling), anti-PDGFRα (goat, 1:75; AF1062, R&D Systems) and anti-BrdU (rat, 1:100; ab6326, Abcam). Cryosections were then washed with PBS and incubated with secondary antibodies for either 1 h at room temperature (cryosections). Alexa Fluor secondary antibodies (Jackson ImmunoResearch) diluted in blocking solution at 1:200 were used. Following washes with PBS, nuclei were visualized with Hoechst 33342 (Hst). Images were captured with a confocal microscope (Dragonfly 200, ANDOR, England). The subsequent processing of images was performed by Imaris (ANDOR, England) and Image-Pro Plus (Media Cybernetics). Immunocytofluorescence Cultured OPCs were fixed with 4% PFA for 15 minutes at room temperature. After permeabilization with 0.6% Triton X in PBS for 15 minutes and blocking with 3% BSA in PBS for 1 hour at room temperature, the cells were incubated with the primary antibodies diluted in blocking solution for 24–48 hours at 4°C. Primary antibodies used were: anti-BrdU (rat, 1:200; ab6326, Abcam), anti-Ki67 (rabbit, 1:400; #9129, Cell Signaling) and anti-Sox10 (goat, 1:150; AF2864, R&D Systems). The appropriate Alexa Fluor secondary antibodies (Jackson ImmunoResearch) were used for indirect fluorescence. Immunofluorescence staining images were captured using a confocal microscope (Dragonfly 200, ANDOR, England) and were subsequently quantified with both Imaris (ANDOR, England) and Image-Pro Plus (Media Cybernetics). BrdU labeling and staining Dilute 5-bromo-2-deoxyuridine (BrdU, B5002, Sigma-Aldrich) in PBS to make a sterile solution of 10 mg/mL. We injected BrdU into mice two times a day for eight consecutive days (100 mg/kg per injection) to label all the proliferating cells. The labeled mice were sacrificed 12 hours after the last BrdU injection to identify proliferating cells. (Fig. 4 C) In vitro, 10 µM BrdU was added to the cultured OPCs. For BrdU staining, the cultures were washed with PBS and fixed with 4% PFA for 20 min. Then, 2 N HCl was added to the cultures, followed by incubation for 30 min at 37°C. After washing off the hydrochloric acid, the cells were incubated twice with 0.1 mol/L sodium tetraborate for 5 min each time. Finally, BrdU incorporation was detected in the cells by immunostaining with BrdU antibody. Statistical Analyses Data are presented as mean ± SEM, unless otherwise indicated. Results from representative experiments were reproduced with comparable outcomes in at least three independent biological replicates, unless otherwise stated. Sample sizes were determined empirically based on previous studies. Data obtained from the Von Frey test and cold plate test were analyzed using two-way repeated measures analysis of variance (RM ANOVA), followed by the Tukey’s multiple comparisons test. Data from other tests were analyzed using one-way ANOVA, also followed by the Tukey’s multiple comparisons test. p < 0.05 was considered statistically significant. Results Oxaliplatin-chemotherapy induces mechanically and cold hypersensitivity that is prevented by fenofibrate The development of mechanical and cold hypersensitivity phenotypes was carefully evaluated on days 7, 14, and 21 (Fig. 1 A) using two established tests: the Von Frey test (VFT) for mechanical sensitivity and the cold plate test (CPT) for cold sensitivity. Mice administered with oxaliplatin injections exhibited pronounced mechanical and cold allodynia on these designated assessment days. Specifically, a marked reduction in the paw withdrawal threshold was observed during the Von Frey test in comparison to mice injected with the vehicle alone. Notably, prophylactic administration of fenofibrate demonstrated a significant analgesic effect in these mice, as indicated by an increased paw withdrawal threshold (Fig. 1 B). Moreover, mice treated with oxaliplatin showed a considerable decrease in the latency period of pain-related behaviors during the cold plate test on days 7, 14, and 21, in contrast to the vehicle-injected controls. The prophylactic use of fenofibrate in these mice proved highly effective in attenuating cold-induced hyperalgesia and allodynia, as evidenced by the prolonged latency of pain-related responses during the cold plate test (Fig. 1 C). Collectively, these findings highlight the potential therapeutic utility of fenofibrate in managing oxaliplatin-induced neuropathic pain. Oxaliplatin-chemotherapy induces depression-like symptoms that are prevented by fenofibrate The depression-like phenotype was carefully evaluated on day 21 (Fig. 2 A) using three standard behavioral tests: the forced swimming test (FST), sucrose preference test (SPT), and tail suspension test (TST). Mice treated with oxaliplatin exhibited a depression-like phenotype on day 21, as indicated by increased immobilization time during the FST, decreased sucrose preference in the SPT, and extended immobilization time in the TST (Fig. 2 B, C, D). To assess despair behavior, we measured the immobilization time of mice during the FST and TST over a defined duration. Mice in the model group displayed notably longer immobilization times than those in the vehicle group. As anticipated, fenofibrate administration led to a reduction in immobilization time in both the FST and TST compared to the model group (Fig. 2 B, D). Additionally, mice in the OXA group exhibited a substantial decrease in sucrose preference during the SPT compared to the vehicle group, suggesting deficits in hedonic behavior and impairments in brain reward mechanisms. Importantly, fenofibrate administration significantly alleviated this reduction in sucrose preference in the model mice (Fig. 2 C). Oxaliplatin-chemotherapy reduces OPCs in the mPFC that are prevented by fenofibrate Recent studies have demonstrated that the depletion of OPCs in the mPFC resulting from chronic psychosocial stress is sufficient to hinder astrocytic activity, ultimately leading to neuronal dysfunction and depressive-like behaviors 28 . Platinum accumulates in the brain following chronic oxaliplatin treatment 29 . To investigate the influence of oxaliplatin chemotherapy on both the density and proportion of OPCs in the mPFC, mice were euthanized on day 21 (Fig. 2 A) for immunohistochemical analysis (Fig. 3 A). Immunohistochemical analysis demonstrated a significant reduction in both the density and proportion of OPCs (Sox10 + /PDGFRα + ) within the mPFC in the OXA group as compared to the Vehicle group. Importantly, prophylactic administration of fenofibrate mitigated this reduction in the density and proportion of OPCs (Sox10 + /PDGFRα + ) in the mPFC (Fig. 3 C, D). These findings suggest that oxaliplatin chemotherapy is a significant factor in the reduction of OPC density in the mPFC, while prophylactic fenofibrate administration exerts a protective effect on OPCs. Oxaliplatin-chemotherapy reduces the proliferation of OPCs in the mPFC, which is prevented by fenofibrate To investigate the effects of oxaliplatin chemotherapy on OPC proliferation in the mPFC, BrdU was administered. Mice were euthanized on day 8 following oxaliplatin treatment for immunohistochemical analysis (Fig. 4 B). Cryosections from the brains of various mice were consistently obtained at the same anatomical level (Fig. 3 B). Immunohistochemical analysis of the mPFC revealed a significant reduction in the proportion of BrdU + OPCs (Sox10 + /PDGFRα + ) in the OXA group compared to the Vehicle group (Fig. 4 C). Moreover, a significant increase in the proportion of BrdU label-retaining OPCs (Sox10 + /PDGFRα + ) was observed in the OXA + Feno group compared to the OXA group (Fig. 4 C). On day 8, there was no significant difference observed in the density of OPCs (Sox10 + /PDGFRα + ) between the OXA group and the OXA + Feno group, as both demonstrated a notable decrease when compared to the Vehicle group (Fig. 4 D). However, interestingly, on day 21, continuous fenofibrate treatment effectively reversed the oxaliplatin-induced reduction in OPC density (Fig. 3 C). Oxaliplatin chemotherapy reduces the proliferation of OPCs in vitro, which is prevented by fenofibric acid In vitro experiments were conducted to expose OPCs to oxaliplatin, fenofibric acid, or a combination thereof. Compared to the Vehicle group, oxaliplatin notably decreased the proportion of BrdU + OPCs (Sox10 + ) and Ki67 + OPCs (Sox10 + ) (Fig. 5 A, B, C). Moreover, a noteworthy surge in the proportion of BrdU label-retaining OPCs (Sox10 + ) and Ki67 + OPCs (Sox10 + ) was documented in the OXA + Feno group when compared to the OXA group. The introduction of fenofibric acid proved beneficial as it mitigated the oxaliplatin-induced mortality of OPCs. Discussion This study uniquely demonstrates that fenofibrate treatment can potentially prevent oxaliplatin-induced neuropathy symptoms and depression-like behavior in animals. Furthermore, it is the inaugural research to highlight alterations in the density of OPCs in the mPFC resulting from oxaliplatin administration, an impact mitigated by concurrent fenofibrate therapy. In our investigation, a chronic oxaliplatin model induced prominent cold and mechanical allodynia, alongside depression-like behavior, echoing previous observations 30–32 . The onset and nature of sensory disturbances and depressive symptoms closely parallel the effects of oxaliplatin in humans 33 . Oxaliplatin, a predominant neurotoxic chemotherapy agent, disrupts tumor cell proliferation by forming DNA-platinum adducts, leading to cancer cell destruction 3 . However, chronic neurotoxicity, exacerbated by cumulative oxaliplatin dosing, is often irreversible and associated with significant morbidity and diminished quality of life long after treatment completion. Therefore, we developed a model mimicking sustained neuropathic pain symptoms and delayed depression-like symptoms observed in patients treated with this anticancer agent, induced by repeated oxaliplatin injections. Due to fenofibrate's low oral bioavailability, a prophylactic dietary fenofibrate regimen was employed to maintain stable blood drug concentrations 17 . Peroxisome proliferator-activated receptor-α (PPARα), a nuclear receptor, undergoes conformational changes, heterodimerizes with RXR, recruits coactivators, and regulates reactive gene transcription upon ligand binding, among other functions 34 . Fenofibrate, FDA-approved for hyperlipidemia, mixed dyslipidemia, and hypertriglyceridemia, and for increasing HDL-cholesterol, exerts its effects through the activation of PPARα receptors, regulating genes involved in lipoprotein metabolism 16,35 . Numerous studies indicate that activating PPARα can alleviate neuropathic pain signs in various models 17,36–38 . Research 39 implicates several mechanisms by which chemotherapy induces peripheral nerve damage, dysfunction, and death, including altered ion channel and receptor expression, innate immune response and inflammation, mitochondrial dysfunction, and changes in cell-signaling pathways like G-protein-coupled receptors (GPCRs) and mitogen-activated protein kinases (MAPKs). Concurrently with mechanical hyperalgesia, oxaliplatin-treated animals exhibit decreased intraepidermal nerve fibers 40 . In a mouse model of PIPN, fenofibrate treatment prevents paclitaxel-induced intra-epidermal nerve fiber loss and mitigates mitochondrial damage 22 . Fenofibrate's neuroprotective effects at the mitochondrial level may also safeguard nerve fibers from degeneration 38 . In our study, prophylactic fenofibrate administration significantly attenuated mechanical and cold allodynia in oxaliplatin-treated mice. Previous research on the pathophysiology of CIPN has primarily focused on peripheral nerves, as CIPN symptoms predominantly manifest in the hands and feet 41 . The notion that chemotherapy accumulates in the human brain has been subject to debate, and its validity likely hinges on the specific chemotherapy type, dose density, and other variables that could potentially compromise the blood-brain barrier 42 . However, recent studies have presented contrasting viewpoints, with evidence suggesting that platinum accumulates in the brains of rats following chronic oxaliplatin treatment 29 . Our study reveals that oxaliplatin chemotherapy significantly impairs the proliferation of OPCs in the mPFC, subsequently reducing their density. Furthermore, our in vitro experiments corroborate these findings, demonstrating a substantial decrease in OPC proliferation induced by oxaliplatin treatment. The dorsolateral prefrontal cortex (dlPFC) in humans plays a crucial role in the cognitive and affective modulation of pain perception 43–45 . The mPFC in rodents is considered to be homologous to the dlPFC in primates 46 . The prefrontal cortex (PFC), renowned for its crucial role in executive functions, also plays a pivotal part in pain processing. This latter function is facilitated by its extensive connections with other regions of the cerebral neocortex, hippocampus, periaqueductal gray (PAG), thalamus, amygdala, and basal nuclei 47–51 . During acute and chronic pain states, the PFC undergoes alterations in neurotransmitters, gene expression, glial cells, and neuroinflammation, ultimately leading to changes in its structure, activity, and connectivity 52 . The mPFC is a region implicated in both acute and chronic pain conditions in humans, wherein the corticolimbic connection between the mPFC and the nucleus accumbens (NAc) serves as a reliable indicator of the transition from subacute to chronic pain 50 . The mechanism by which persistent inflammation in the mPFC could lead to the development of chronic pain involves the continual activation of the mPFC, resulting in enhanced connectivity between the mPFC and the nucleus accumbens 53,54 . This heightened connectivity has been observed to correlate with the progression of pain towards a chronic state. A three-year longitudinal study of patients with subacute back pain suggests that stronger functional connectivity within the dorsal mPFC-amygdala-nucleus accumbens circuit is associated with an increased risk of developing chronic pain 51 . Numerous studies have reported a loss of grey matter in the PFC associated with chronic pain conditions. For instance, patients with chronic back pain exhibit regional grey matter reductions in the bilateral mPFC, extending to the anterior cingulate cortex (ACC) and the right mPFC, which extends to the orbitofrontal cortex 55 . Additionally, atrophy of the ventromedial PFC grey matter, combined with reduced white matter integrity and connectivity to the basal ganglia, has been observed in individuals with chronic complex regional pain syndrome 56 . The presence of a depressive mood may exacerbate pain sensation, as clinical studies and animal models have demonstrated that this interaction likely involves implicates the PFC. Depression scores among chronic pain patients have been found to correlate with alterations in the thalamus, as well as in the cingulate, dlPFC, and hippocampal cortices 57 . Furthermore, RNA sequencing and pathway analysis have revealed a considerable number of signaling pathway-associated genes exhibiting comparable expression changes in mice with spared nerve injury (SNI) and those exposed to chronic unpredictable stress. This finding implicates shared molecular pathways within the PFC that underlie the interplay between pain and depression 58,59 . OPCs have been extensively studied for their proliferative and differentiation capabilities. However, recent research has uncovered a plethora of additional functions performed by OPCs that significantly impact brain function in both healthy and diseased states. Notably, OPCs not only receive synaptic input from neurons but also release neuromodulators that effectively modulate neuronal density, activity, local neural circuits, and synaptic plasticity 60 . While OPCs are known to generate myelinating oligodendrocytes throughout life, their functions extend beyond oligodendrogenesis; they also regulate synaptic connectivity in the brain 61 . A recent study has implicated oligodendrocyte apoptosis in the mPFC as a critical factor in fentanyl-induced hyperalgesia 62 . Postmortem studies consistently reveal a notable decrease in both the density and number of glial cells, along with a reduction in the size of neuronal cell bodies, particularly in cortical regions such as the prefrontal and cingulate areas, among depressed patients 63 . Utilizing the repeated social defeat (RSDS) mouse model, a study illustrates that chronic psychosocial stress triggers enduring losses of OPCs, leading their aberrant differentiation into oligodendrocytes and marked hypomyelination within the prefrontal cortex 64 . Birey et al. have reported that the ablation of OPCs in the PFC of the brain results in deficits of excitatory glutamatergic neurotransmission and astrocytic extracellular glutamate uptake, ultimately leading to depressive-like behaviors in mice. Additionally, they discovered that the density of OPCs in the frontal cortices of human subjects with major depressive disorder (MDD) was significantly lower compared to age-matched controls 28 . Another study posits that the beneficial impacts of running exercise on the mPFC volume and oligodendrocytes within the mPFC could constitute a crucial structural foundation for its antidepressant effects 65 . Recent research underscores that in major depressive disorder, OPCs not only serve as precursor cells for oligodendrocytes but also function as an independent cell type 66 . Our investigation reveals that the prophylactic administration of fenofibrate significantly mitigates depressive-like behaviors in mice receiving oxaliplatin treatment. On day 8 post-injection of oxaliplatin, there was no significant difference observed in the density of OPCs between the OXA group and the OXA + Feno group, as both demonstrated a notable decrease when compared to the Vehicle group. However, a significantly increased proportion of BrdU-labeled retained OPCs was observed in the OXA + Feno group compared to the OXA group. Interestingly, on day 21, continuous fenofibrate treatment effectively reversed the oxaliplatin-induced reduction in OPC density. This antidepressant efficacy of fenofibrate might be attributed to its protective influence on the proliferation of OPCs within the mPFC. In summary, our study demonstrates that fenofibrate significantly reduces mechanical and cold allodynia, as well as depressive-like behaviors, in mice with oxaliplatin-induced neuropathy. The anti-allodynic and antidepressant effects of fenofibrate are potentially associated with its beneficial impact on OPCs in the mPFC of these mice. Nonetheless, the exact mechanisms through which fenofibrate shields OPCs from oxaliplatin-induced harm are not fully comprehended. The pathogenesis of oxaliplatin chemotherapy-induced pain and depression is complex, with impaired OPC proliferation emerging as a potential contributor. Fenofibrate, which is widely used clinically for the treatment of dyslipidemia with well-established safety, could emerge as a potential therapeutic agent for alleviating oxaliplatin chemotherapy-induced pain and depression. Future clinical trials are warranted to evaluate the efficacy of fenofibrate in chemotherapy patients experiencing neuropathy and depressive symptoms. Declarations Acknowledgement This work was supported by the National Natural Science Foundation of China (81971048), Natural Science Foundation of Shanghai (17ZR1438200) and "Deep Blue 123" Military Medical Research Special Key Research Project (2019YSL008), Key Research and Development Program of Hainan Province of China (ZDYF2023SHFZ127), Key Projects of Military Theory of the PLA (JJ2023A05-B). Contributors Liang Yue, Yimin Yuan, Yu Ma, Li Cao and Yuanchang Xiong designed the study, analyzed the data and co-authored the manuscript. Liang Yue, Yimin Yuan, Dai Li, Li Sun and Yijia Shen conducted the experiments and analyzed the data. All authors contributed to the drafting of the manuscript and approved the final version. Conflict of Interest The authors have no relevant financial or non-financial interests to disclose. 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Single-nucleus transcriptomics of the prefrontal cortex in major depressive disorder implicates oligodendrocyte precursor cells and excitatory neurons. Nat Neurosci 23 , 771-781, doi:10.1038/s41593-020-0621-y (2020). Additional Declarations No competing interests reported. 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-4339586","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":299834545,"identity":"ffe9a9d8-d856-405d-84d5-530779c8dd5b","order_by":0,"name":"Liang Yue","email":"","orcid":"","institution":"Changhai Hospital, Naval Medical University","correspondingAuthor":false,"prefix":"","firstName":"Liang","middleName":"","lastName":"Yue","suffix":""},{"id":299834546,"identity":"d4ca3409-746a-4e37-bb27-43f0961349ab","order_by":1,"name":"Yimin Yuan","email":"","orcid":"","institution":"Naval Medical University","correspondingAuthor":false,"prefix":"","firstName":"Yimin","middleName":"","lastName":"Yuan","suffix":""},{"id":299834547,"identity":"afef57fc-03c0-487f-82ad-d0f9dc315935","order_by":2,"name":"Dai Li","email":"","orcid":"","institution":"Changhai Hospital, Naval Medical University","correspondingAuthor":false,"prefix":"","firstName":"Dai","middleName":"","lastName":"Li","suffix":""},{"id":299834548,"identity":"9885503e-cabb-4649-b904-508670d34139","order_by":3,"name":"Li Sun","email":"","orcid":"","institution":"Changhai Hospital, Naval Medical University","correspondingAuthor":false,"prefix":"","firstName":"Li","middleName":"","lastName":"Sun","suffix":""},{"id":299834550,"identity":"3d0a7589-fc43-4c86-aeb7-817b14ce844e","order_by":4,"name":"Yijia Shen","email":"","orcid":"","institution":"Changhai Hospital, Naval Medical University","correspondingAuthor":false,"prefix":"","firstName":"Yijia","middleName":"","lastName":"Shen","suffix":""},{"id":299834552,"identity":"39af5380-7159-4f20-a34f-360720aa4bae","order_by":5,"name":"Yu Ma","email":"","orcid":"","institution":"Changhai Hospital, Naval Medical University","correspondingAuthor":false,"prefix":"","firstName":"Yu","middleName":"","lastName":"Ma","suffix":""},{"id":299834553,"identity":"e69f7274-2afb-43bf-806b-760022dec127","order_by":6,"name":"Li Cao","email":"","orcid":"","institution":"Naval Medical University","correspondingAuthor":false,"prefix":"","firstName":"Li","middleName":"","lastName":"Cao","suffix":""},{"id":299834554,"identity":"d78f719f-9225-4998-a9bc-f683fb480b90","order_by":7,"name":"Yuanchang Xiong","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA0klEQVRIiWNgGAWjYLACxgYGHhD1IKGihjQtzAYPzhwjXgsIsEk+bGEmrNpc+vAxiZ87DsvwS7dfq0hsYGPgb+9OwKvFsi8tTbL3TBqP5JwzZTcSd8gwSJw5uwGvFoMzPGbSjG02PAY3ctJuJJ5hYzCQyCVKiwRYS0FiGzPRWkC2pB9jIEqLZQ9bsmVvG9AvM3KYJRLOHOMh6BdzHuaDN362Hbbnl0h/+PFHRY0cf3svAYcxMLBIQJg8BmASr3KoFuYPECb7A4KqR8EoGAWjYGQCAHDPRTxchn1KAAAAAElFTkSuQmCC","orcid":"","institution":"Changhai Hospital, Naval Medical University","correspondingAuthor":true,"prefix":"","firstName":"Yuanchang","middleName":"","lastName":"Xiong","suffix":""}],"badges":[],"createdAt":"2024-04-29 01:21:33","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4339586/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4339586/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":56405386,"identity":"8ffb1cbf-02a9-4cad-9dbd-4b3546abea20","added_by":"auto","created_at":"2024-05-13 18:11:53","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":208339,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eOxaliplatin-chemotherapy induces mechanically and cold hypersensitivity that is prevented by fenofibrate.\u003c/strong\u003e \u003cstrong\u003eA\u003c/strong\u003e Prevention of oxaliplatin-induced peripheral neuropathy (OIPN) signs by fenofibrate diet treatment: Mice were treated with 0.2% fenofibrate diets for 25 days (before, during and after oxaliplatin treatment). \u003cstrong\u003eB\u003c/strong\u003e Mechanical hypersensitivity was tested at baseline (BL), day 7, day 14, day 21 with the Von Frey test. Two-way RM ANOVA, Tukey’s multiple comparisons test, N = 10, treatment: F (3, 36) = 283.8, P \u0026lt; 0.0001; time: F (2.435, 87.68) = 169.8, P \u0026lt; 0.0001; interaction: F (9, 108) = 77.81, P \u0026lt; 0.0001. \u003cstrong\u003eC\u003c/strong\u003e Cold hypersensitivity was tested at BL, day 7, day 14, day 21 with the cold plate test. Two-way RM ANOVA, Tukey’s multiple comparisons test, N = 10, treatment: F (3, 36) = 362.4, P \u0026lt; 0.0001; time: F (2.658, 95.68) = 99.81, P \u0026lt; 0.0001; interaction: F (9, 108) = 56.98, P \u0026lt; 0.0001. Data presented as mean ± SEM. *: p \u0026lt; 0.05, **: p \u0026lt; 0.01, ***: p \u0026lt; 0.001 vs. Vehicle; #: p \u0026lt; 0.05, ##: p \u0026lt; 0.01, ###: p \u0026lt; 0.001 vs. OXA. BL = Baseline; Feno = Fenofibrate; OXA = Oxaliplatin; VFT = Von Frey test; CPT = Cold plate test.\u003c/p\u003e","description":"","filename":"Fig1.png","url":"https://assets-eu.researchsquare.com/files/rs-4339586/v1/0e7fc3243fc458454b80e75d.png"},{"id":56405388,"identity":"632af103-84c0-476e-bd9b-69ee2d533765","added_by":"auto","created_at":"2024-05-13 18:11:53","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":347711,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eOxaliplatin-chemotherapy induces depression-like symptoms that are prevented by fenofibrate.\u003c/strong\u003e \u003cstrong\u003eA\u003c/strong\u003e Prevention of oxaliplatin-induced depression-like behavior signs via fenofibrate diet treatment: Mice were administered a 0.2% fenofibrate diet for 25 days (before, during and after oxaliplatin treatment). \u003cstrong\u003eB-D\u003c/strong\u003e Antidepressant-like effects were assessed on day 21 with forced swimming test (\u003cstrong\u003eB\u003c/strong\u003e), sucrose preference test (\u003cstrong\u003eC\u003c/strong\u003e) and tail suspension test (\u003cstrong\u003eD\u003c/strong\u003e). For panels (\u003cstrong\u003eB-D\u003c/strong\u003e): One-way ANOVA, Tukey’s multiple comparisons test, N = 10. (\u003cstrong\u003eB\u003c/strong\u003e F (3, 36) = 53.43, P \u0026lt; 0.0001. \u003cstrong\u003eC\u003c/strong\u003e F (3, 36) = 43.04, P \u0026lt; 0.0001. \u003cstrong\u003eD\u003c/strong\u003e F (3, 36) = 24.47, P \u0026lt; 0.0001.) Data presented as mean ± SEM. *: p \u0026lt; 0.05, **: p \u0026lt; 0.01, ***: p \u0026lt; 0.001; ns: not significant. FST = forced swimming test; SPT = sucrose preference test; TST = tail suspension test.\u003c/p\u003e","description":"","filename":"Fig2.png","url":"https://assets-eu.researchsquare.com/files/rs-4339586/v1/bbb5688982172f127c61b876.png"},{"id":56405382,"identity":"5e19265c-02a5-4e42-a3bd-dec9bc5b7368","added_by":"auto","created_at":"2024-05-13 18:11:51","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":1822228,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eOxaliplatin-chemotherapy reduces OPCs in the mPFC that are prevented by fenofibrate. A\u003c/strong\u003e Representative images of OPCs (Sox10\u003csup\u003e+\u003c/sup\u003e in green and PDGFRα\u003csup\u003e+\u003c/sup\u003e in purple) and nuclei (Hoechst\u003csup\u003e+\u003c/sup\u003e in blue) in mPFC on day 21; Scale bar = 100 µm. \u003cstrong\u003eB\u003c/strong\u003e Schematic of the sampled area within the mPFC: the green area depicts the regions examined, and cryosections were consistently obtained from distinct mice brains at the same anatomical level. \u003cstrong\u003eC\u003c/strong\u003e The density of OPCs (Sox10\u003csup\u003e+\u003c/sup\u003e/PDGFRα\u003csup\u003e+\u003c/sup\u003e) in mPFC on day 21. One-way ANOVA, Tukey’s multiple comparisons test, N = 4, F (3, 12) = 18.32, P \u0026lt; 0.0001. \u003cstrong\u003eD\u003c/strong\u003e The proportion of OPCs (Sox10\u003csup\u003e+\u003c/sup\u003e/PDGFRα\u003csup\u003e+\u003c/sup\u003e) in mPFC on day 21. One-way ANOVA, Tukey’s multiple comparisons test, N = 4, F (3, 12) = 10.16, P = 0.0013. Data presented as mean ± SEM. *: p \u0026lt; 0.05, **: p \u0026lt; 0.01, ***: p \u0026lt; 0.001; ns: not significant. mPFC = medial prefrontal cortex.\u003c/p\u003e","description":"","filename":"Fig3.png","url":"https://assets-eu.researchsquare.com/files/rs-4339586/v1/daec007dc0a47caebbd9d2cb.png"},{"id":56405410,"identity":"53a92516-8e9b-4993-885c-2a9d01f3ad3a","added_by":"auto","created_at":"2024-05-13 18:11:58","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":1578690,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eOxaliplatin-chemotherapy reduces the proliferation of OPCs in the mPFC, which is prevented by fenofibrate.\u003c/strong\u003e \u003cstrong\u003eA\u003c/strong\u003e Representative images of BrdU\u003csup\u003e+\u003c/sup\u003e (green) label retaining OPCs (Sox10\u003csup\u003e+\u003c/sup\u003e in red and PDGFRα\u003csup\u003e+\u003c/sup\u003e in purple) in mPFC on day 8; Scale bar = 100 µm. \u003cstrong\u003eB\u003c/strong\u003e Detailed protocols outline the administration of oxaliplatin and fenofibrate, along with the implemented BrdU labeling scheme. \u003cstrong\u003eC\u003c/strong\u003e The proportion of OPCs (Sox10\u003csup\u003e+\u003c/sup\u003e/PDGFRα\u003csup\u003e+\u003c/sup\u003e) that were BrdU\u003csup\u003e+\u003c/sup\u003e in mPFC on day 8. One-way ANOVA, Tukey’s multiple comparisons test, N = 3, F (3, 8) = 56.05, P \u0026lt; 0.0001. \u003cstrong\u003eD\u003c/strong\u003e The density of OPCs (Sox10\u003csup\u003e+\u003c/sup\u003e/PDGFRα\u003csup\u003e+\u003c/sup\u003e) in mPFC on day 8. One-way ANOVA, Tukey’s multiple comparisons test, N = 3, F (3, 8) = 12.90, P = 0.0020. Data presented as mean ± SEM. *: p \u0026lt; 0.05, **: p \u0026lt; 0.01, ***: p \u0026lt; 0.001; ns: not significant. mPFC = medial prefrontal cortex, IHF = Immunohistofluorescence.\u003c/p\u003e","description":"","filename":"Fig4.png","url":"https://assets-eu.researchsquare.com/files/rs-4339586/v1/f58791c23f7f06e6d22bc51d.png"},{"id":56405411,"identity":"02b0b717-80d8-4f0b-b719-b2bf766f0803","added_by":"auto","created_at":"2024-05-13 18:11:59","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":2942928,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eOxaliplatin chemotherapy reduces the proliferation of OPCs in vitro, which is prevented by fenofibric acid. A \u003c/strong\u003eRepresentative images of BrdU\u003csup\u003e+\u003c/sup\u003e (green) label retaining OPCs (Sox10\u003csup\u003e+\u003c/sup\u003e in purple) and current proliferation capacity Ki67\u003csup\u003e+\u003c/sup\u003e (red) OPCs; Scale bar = 100 µm. \u003cstrong\u003eB\u003c/strong\u003e The proportion of OPCs (Sox10\u003csup\u003e+\u003c/sup\u003e) that were BrdU\u003csup\u003e+\u003c/sup\u003e. One-way ANOVA, Tukey’s multiple comparisons test, N = 4, F (3, 12) = 14.51, P = 0.0003.\u003cstrong\u003e C\u003c/strong\u003e The proportion of OPCs (Sox10\u003csup\u003e+\u003c/sup\u003e) that were Ki67\u003csup\u003e+\u003c/sup\u003e. One-way ANOVA, Tukey’s multiple comparisons test, N = 4, F (3, 12) = 59.24, P \u0026lt; 0.0001. Data presented as mean ± SEM. *: p \u0026lt; 0.05, **: p \u0026lt; 0.01, ***: p \u0026lt; 0.001; ns: not significant.\u003c/p\u003e","description":"","filename":"Fig5.png","url":"https://assets-eu.researchsquare.com/files/rs-4339586/v1/ed383d8f797b9842e9e855a9.png"},{"id":64906959,"identity":"a0e1cf5d-0dcb-4d95-a8a2-affae9ba5b46","added_by":"auto","created_at":"2024-09-20 09:00:49","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":7415825,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4339586/v1/7fdf0db9-6619-4393-b4bc-f405fad9f323.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Fenofibrate reduces pain hypersensitivity and associated depression-like behavior in mice with oxaliplatin- induced neuropathy","fulltext":[{"header":"Introduction","content":"\u003cp\u003eOxaliplatin (OXA), a third-generation platinum-based antitumor agent, finds widespread application in the treatment of various solid tumors\u003csup\u003e1,2\u003c/sup\u003e. Nevertheless, its therapeutic benefits often come hand in hand with considerable adverse effects, notably chemotherapy-induced peripheral neuropathy (CIPN)\u003csup\u003e3,4\u003c/sup\u003e. Specifically, over 90% of patients report acute pain symptoms exacerbated by cold following oxaliplatin administration, while 30\u0026ndash;50% endure chronic oxaliplatin-induced peripheral neuropathy (OIPN)\u003csup\u003e5\u0026ndash;7\u003c/sup\u003e. This condition frequently manifests as neuropathic pain, which significantly impairs patients' quality of life by causing comorbidities such as distress, depression, and anxiety, often leading to modifications or discontinuation of standard treatment regimens\u003csup\u003e8,9\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eThe coexistence of chronic pain and depression is well-documented, albeit the underlying mechanisms remain elusive and incompletely understood\u003csup\u003e10,11\u003c/sup\u003e. Comorbid depression can exacerbate pain perception and diminish the efficacy of pain management, underscoring the importance of concurrently addressing both conditions\u003csup\u003e10\u003c/sup\u003e. In this context, dual-acting agents emerge as promising therapeutic options. Presently, duloxetine, an antidepressant acting as a 5-HT/NA reuptake inhibitor, stands as the sole recommended agent for alleviating sensory symptoms of established CIPN, while no definitive recommendations exist for CIPN prevention due to insufficient evidence\u003csup\u003e12\u0026ndash;14\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eFenofibrate, a fibric acid derivative, serves as a mainstay treatment for primary hypercholesterolemia, mixed dyslipidemia and hypertriglyceridemia in adults\u003csup\u003e15\u003c/sup\u003e. It functions as a prodrug, undergoing de-esterification in the liver to yield fenofibric acid, the pharmacologically active metabolite, which subsequently enters the plasma and distributes to various tissues\u003csup\u003e16\u003c/sup\u003e. Lately, fenofibrate has garnered attention for its expanding pharmacological effects on the central nervous system (CNS), including its potential in preventing paclitaxel-induced peripheral neuropathy (PIPN) development\u003csup\u003e17\u003c/sup\u003e and exhibiting antidepressant-like effects in rodent models of chronic social defeat and unavoidable stress\u003csup\u003e18,19\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eIn our current study, we aim to investigate the potential of fenofibrate in mitigating chronic pain and comorbid depression induced by the chemotherapy drug oxaliplatin. Additionally, we seek to explore whether these effects are mediated through oligodendrocyte progenitor cells (OPCs) in the medial prefrontal cortex (mPFC).\u003c/p\u003e"},{"header":"Materials and Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eAnimals\u003c/h2\u003e \u003cp\u003e All animal experiments were granted approval by the Animal Care and Use Committee of the Naval Medical University and were conducted in strict adherence to the Chinese Academy of Sciences Animal Experiment Guide. The experiments were reported in accordance with the ARRIVE guidelines. The studies were carried out on male C57BL/6 mice (weighing 20\u0026ndash;30 g), obtained from the Experimental Animal Center of the Naval Medical University. The animals were housed under standard laboratory conditions: a temperature maintained at 22\u0026thinsp;\u0026plusmn;\u0026thinsp;1\u0026deg;C, relative humidity of 55\u0026thinsp;\u0026plusmn;\u0026thinsp;5%, and a 12-hour light/dark cycle. Mice had unrestricted access to regular food or fenofibrate diet and water (with the exception of during the experimental procedures). To minimize the influence of diurnal variations on behavioral tests, the experiments were conducted in a blinded manner between 8:00 and 16:00. The mice were euthanized humanely at the end of the research by administering intravenous barbiturates.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003ePrimary oligodendrocyte progenitor cell culture\u003c/h2\u003e \u003cp\u003eOPCs were cultured and purified according to previously described methods\u003csup\u003e20,21\u003c/sup\u003e. In brief, mixed glial cells were harvested from the cortex of P1 Sprague Dawley rats (SD rats) and cultured in Dulbecco's modified Eagle's medium supplemented with 10% fetal bovine serum for 10 days at 37\u0026deg;C in a 5% CO\u003csub\u003e2\u003c/sub\u003e incubator. The medium was replaced every 3 days. For purification, the flasks were initially shaken rpm for 1 hour (180 rpm, 37\u0026deg;C) to eliminate microglia, followed by shaking for 16 hours (200 rpm, 37\u0026deg;C) with fresh medium at 37\u0026deg;C to collect OPCs. The harvested cells were allowed to adhere to uncoated plates for 30 minutes, twice in total, to remove contaminating cells. Subsequently, the purified OPCs were gently detached and seeded at a density ranging from 5,000 cells/cm\u003csup\u003e2\u003c/sup\u003e to 50,000 cells/cm\u003csup\u003e2\u003c/sup\u003e onto coverslips that had been pre-coated with poly-D-lysine. To promote the expansion of OPCs while maintaining their undifferentiated state, the culture medium was supplemented with 10 ng/mL basic fibroblast growth factor (b-FGF, Sigma-Aldrich) and 10 ng/mL PDGF-AA (R\u0026amp;D Systems).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003eDrugs administration and experimental design\u003c/h2\u003e \u003cp\u003eThe fenofibrate diet, consisting of 0.2% fenofibrate (F6020, Sigma-Aldrich), was prepared by thoroughly blending it with regular food\u003csup\u003e22\u003c/sup\u003e. The administration of this fenofibrate-enriched diet began 3 days prior to oxaliplatin treatment and continued for 25 days. The dosages of fenofibrate were determined in accordance with previous literature\u003csup\u003e22\u003c/sup\u003e. For chronic administration, fenofibrate was administered through dietary intake rather than via gavage or injection, in order to minimize the stress associated with repeated gavages or daily injections.\u003c/p\u003e \u003cp\u003eOxaliplatin (S1224, Selleck) was dissolved in 5% Glucose and the volume was adjusted to achieve a concentration of 1 mg/mL. Oxaliplatin was administered intraperitoneally at a dose of 6 mg/kg every other day, with a total of four administrations per regimen. The vehicle-treated animals received an equivalent volume of 5% Glucose administered intraperitoneally, following the identical injection regimen (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eA).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eBasal behavioral parameters (paw withdrawal threshold in the Von Frey test, latency time to pain reaction in the cold plate test) were assessed before the administration of oxaliplatin/vehicle. To examine the development of mechanical and cold allodynia, as well as the anti-allodynic effect of fenofibrate, the Von Frey and cold plate tests were performed on the 7th, 14th, and 21st days following the initial injection of oxaliplatin. At each time point, the Von Frey test was administered prior to the cold plate test in the same group of animals. To assess depressive-like behavior in mice treated with oxaliplatin and the antidepressive-like effects of fenofibrate, the sucrose preference test (SPT), tail suspension test (TST), and forced swimming test (FST) were performed on the 14th day following the initial injection of oxaliplatin. These tests (SPT, TST, and FST) were conducted on animals that had previously undergone allodynia testing.\u003c/p\u003e \u003cp\u003eFor in vitro studies, fenofibric acid (HY-B0760, MedChemExpress, China) was dissolved in dimethyl sulfoxide (DMSO, Sigma-Aldrich) and added to the medium to achieve the desired concentration. After a 6-hour treatment with fenofibric acid, oxaliplatin (S1224, Selleck) was dissolved in DMSO, subsequently diluted with sterile PBS, and finally added to the medium to achieve the desired concentration. The cells were then treated for 3 hours before being fixed. Cells were not exposed to more than 0.1% DMSO during the experiments. All studies involving light-sensitive drugs were conducted in the dark.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003eBehavioral evaluations\u003c/h2\u003e \u003cdiv id=\"Sec7\" class=\"Section3\"\u003e \u003ch2\u003eVon Frey test\u003c/h2\u003e \u003cp\u003eMechanical allodynia was assessed using an Electronic Von Frey Anesthesiometer (IITC Life Science, Woodland Hills, CA)\u003csup\u003e23\u003c/sup\u003e. Adult mice were placed on a metallic mesh floor inside plexiglass boxes for 30 min. A mechanical stimulus was applied by means of a rigid tip connected to a force transducer, which was pressed through the metallic mesh floor at a 90\u0026deg; angle against the plantar region of either hind paw. The pressure was gradually increased over approximately 5 s, and the paw withdrawal threshold (PWT; in grams) was automatically recorded on the readout unit when the hind paw was withdrawn. For each animal, the final PWT at each time point was calculated as the average of a total of 8 readings (4 readings from each paw).\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003eCold plate test\u003c/h2\u003e \u003cp\u003eThe cold plate test is one of the simplest assays for determining behavioral responses to both noxious and innocuous cold temperatures in mice\u003csup\u003e24\u003c/sup\u003e. It provides an insight into how sensitive an animal is to cold temperatures and thus provides an indirect measure of cold-induced hyperalgesia and allodynia. The cold plate test was performed using the hot/cold plate analgesia meter (IITC Life Science, Woodland Hills, CA) set at 4\u0026deg;C\u0026thinsp;\u0026plusmn;\u0026thinsp;1\u0026deg;C. Pain-related behaviors (i.e., lifting and licking of the hind paw) were observed, and the time (s) of the first sign was recorded. In this assay, a cut-off time of 60 s was established to avoid potential paw tissue damage, and animals not responding within 60 s were removed from the apparatus and assigned a score of 60 s.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003eForced swimming test\u003c/h2\u003e \u003cp\u003eDepressive-like behavior was assessed by forced swimming test\u003csup\u003e25\u003c/sup\u003e. In this test, the immobility time of mice was used as a measure of behavioral despair, a common feature of depression (i.e. the animal loses hope to escape the stressful environment). During the test, mice were placed in transparent cylindrical tanks (30 cm height \u0026times; 20 cm diameter) filled with tap water set at room temperature (24\u0026thinsp;\u0026plusmn;\u0026thinsp;1\u0026deg;C). The water level was 15 cm from the bottom, so the mice could not touch the bottom nor escape from the tank. The test lasted 6 minutes, but only the last 4 minutes were analyzed due to increased activity during the initial 2 minutes. The immobility time, i.e. the time spent performing the movements necessary only to balance the body and keep the head above the water, was used to assess the development of depressive-like behavior and antidepressant-like effects of the drugs. As it was easier to detect and measure active movements than the lack of such movements, we measured the time that each mouse spent mobile and subtracted the amount of mobility time from total test time (240 s) to obtain the immobility time.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003eSucrose preference test\u003c/h2\u003e \u003cp\u003eAnhedonia is a core symptom of human depression and can be measured through the sucrose preference test\u003csup\u003e26\u003c/sup\u003e. The test mice were housed individually and allowed to drink 1% sucrose solution and pure water freely. Before the test, a 2 days sucrose preference training process was performed. Each test mouse was given one bottle of pure water and one bottle of 1% sucrose solution. During this period, the positions of the two bottles were exchanged every 6 hours to avoid side preference. On the 3rd day, the test mice were deprived of food and water for 18 hours. On the 4th day, each mouse was provided with two pre-weighed bottles for 6 hours. Afterward, the two bottles were weighed again. The sucrose preference index was calculated as the percentage of the consumed sucrose solution relative to the total amount of liquid intake.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003eTail suspension test\u003c/h2\u003e \u003cp\u003eThe tail suspension test is one of the most widely used models for assessing antidepressant-like activity in mice\u003csup\u003e27\u003c/sup\u003e. The tail tip of each mouse was individually affixed to a rail positioned 60 cm above the floor, and suspended for a duration of 6 minutes. Throughout this timeframe, the period of immobility (completely motionless) was meticulously documented for every mouse. This test was conducted with the observer blinded to the experimental grouping.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003eTissue preparation and immunohistofluorescence\u003c/h2\u003e \u003cp\u003e For immunohistofluorescence, animals were anaesthetized and transcardially perfused with PBS followed by 4% paraformaldehyde (PFA in PBS). Brains were post-fixed with 4% PFA overnight at 4\u0026deg;C, cryopreserved in 30% sucrose in PBS for 48\u0026ndash;72 h, and sectioned coronally at 10 \u0026micro;m using a cryostat (Leica). Cryosections were then washed with PBS, blocked for 1 h at room temperature (3% bovine serum albumin, BSA) and 0.3% Triton X-100 diluted in PBS), and incubated overnight at 4\u0026deg;C with primary antibodies in blocking solution. Primary antibodies used were: anti-Sox10 (rabbit, 1:100; 78330S, Cell Signaling), anti-PDGFRα (goat, 1:75; AF1062, R\u0026amp;D Systems) and anti-BrdU (rat, 1:100; ab6326, Abcam). Cryosections were then washed with PBS and incubated with secondary antibodies for either 1 h at room temperature (cryosections). Alexa Fluor secondary antibodies (Jackson ImmunoResearch) diluted in blocking solution at 1:200 were used. Following washes with PBS, nuclei were visualized with Hoechst 33342 (Hst). Images were captured with a confocal microscope (Dragonfly 200, ANDOR, England). The subsequent processing of images was performed by Imaris (ANDOR, England) and Image-Pro Plus (Media Cybernetics).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003eImmunocytofluorescence\u003c/h2\u003e \u003cp\u003eCultured OPCs were fixed with 4% PFA for 15 minutes at room temperature. After permeabilization with 0.6% Triton X in PBS for 15 minutes and blocking with 3% BSA in PBS for 1 hour at room temperature, the cells were incubated with the primary antibodies diluted in blocking solution for 24\u0026ndash;48 hours at 4\u0026deg;C. Primary antibodies used were: anti-BrdU (rat, 1:200; ab6326, Abcam), anti-Ki67 (rabbit, 1:400; #9129, Cell Signaling) and anti-Sox10 (goat, 1:150; AF2864, R\u0026amp;D Systems). The appropriate Alexa Fluor secondary antibodies (Jackson ImmunoResearch) were used for indirect fluorescence. Immunofluorescence staining images were captured using a confocal microscope (Dragonfly 200, ANDOR, England) and were subsequently quantified with both Imaris (ANDOR, England) and Image-Pro Plus (Media Cybernetics).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003eBrdU labeling and staining\u003c/h2\u003e \u003cp\u003eDilute 5-bromo-2-deoxyuridine (BrdU, B5002, Sigma-Aldrich) in PBS to make a sterile solution of 10 mg/mL. We injected BrdU into mice two times a day for eight consecutive days (100 mg/kg per injection) to label all the proliferating cells. The labeled mice were sacrificed 12 hours after the last BrdU injection to identify proliferating cells. (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e4\u003c/span\u003eC)\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIn vitro, 10 \u0026micro;M BrdU was added to the cultured OPCs. For BrdU staining, the cultures were washed with PBS and fixed with 4% PFA for 20 min. Then, 2 N HCl was added to the cultures, followed by incubation for 30 min at 37\u0026deg;C. After washing off the hydrochloric acid, the cells were incubated twice with 0.1 mol/L sodium tetraborate for 5 min each time. Finally, BrdU incorporation was detected in the cells by immunostaining with BrdU antibody.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec15\" class=\"Section2\"\u003e \u003ch2\u003eStatistical Analyses\u003c/h2\u003e \u003cp\u003eData are presented as mean\u0026thinsp;\u0026plusmn;\u0026thinsp;SEM, unless otherwise indicated. Results from representative experiments were reproduced with comparable outcomes in at least three independent biological replicates, unless otherwise stated. Sample sizes were determined empirically based on previous studies. Data obtained from the Von Frey test and cold plate test were analyzed using two-way repeated measures analysis of variance (RM ANOVA), followed by the Tukey\u0026rsquo;s multiple comparisons test. Data from other tests were analyzed using one-way ANOVA, also followed by the Tukey\u0026rsquo;s multiple comparisons test. p\u0026thinsp;\u0026lt;\u0026thinsp;0.05 was considered statistically significant.\u003c/p\u003e \u003c/div\u003e"},{"header":"Results","content":"\u003cdiv id=\"Sec17\" class=\"Section2\"\u003e \u003ch2\u003eOxaliplatin-chemotherapy induces mechanically and cold hypersensitivity that is prevented by fenofibrate\u003c/h2\u003e \u003cp\u003eThe development of mechanical and cold hypersensitivity phenotypes was carefully evaluated on days 7, 14, and 21 (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eA) using two established tests: the Von Frey test (VFT) for mechanical sensitivity and the cold plate test (CPT) for cold sensitivity. Mice administered with oxaliplatin injections exhibited pronounced mechanical and cold allodynia on these designated assessment days. Specifically, a marked reduction in the paw withdrawal threshold was observed during the Von Frey test in comparison to mice injected with the vehicle alone. Notably, prophylactic administration of fenofibrate demonstrated a significant analgesic effect in these mice, as indicated by an increased paw withdrawal threshold (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eB).\u003c/p\u003e \u003cp\u003eMoreover, mice treated with oxaliplatin showed a considerable decrease in the latency period of pain-related behaviors during the cold plate test on days 7, 14, and 21, in contrast to the vehicle-injected controls. The prophylactic use of fenofibrate in these mice proved highly effective in attenuating cold-induced hyperalgesia and allodynia, as evidenced by the prolonged latency of pain-related responses during the cold plate test (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eC). Collectively, these findings highlight the potential therapeutic utility of fenofibrate in managing oxaliplatin-induced neuropathic pain.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec18\" class=\"Section2\"\u003e \u003ch2\u003eOxaliplatin-chemotherapy induces depression-like symptoms that are prevented by fenofibrate\u003c/h2\u003e \u003cp\u003eThe depression-like phenotype was carefully evaluated on day 21 (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e2\u003c/span\u003eA) using three standard behavioral tests: the forced swimming test (FST), sucrose preference test (SPT), and tail suspension test (TST). Mice treated with oxaliplatin exhibited a depression-like phenotype on day 21, as indicated by increased immobilization time during the FST, decreased sucrose preference in the SPT, and extended immobilization time in the TST (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e2\u003c/span\u003eB, C, D). To assess despair behavior, we measured the immobilization time of mice during the FST and TST over a defined duration. Mice in the model group displayed notably longer immobilization times than those in the vehicle group. As anticipated, fenofibrate administration led to a reduction in immobilization time in both the FST and TST compared to the model group (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e2\u003c/span\u003eB, D). Additionally, mice in the OXA group exhibited a substantial decrease in sucrose preference during the SPT compared to the vehicle group, suggesting deficits in hedonic behavior and impairments in brain reward mechanisms. Importantly, fenofibrate administration significantly alleviated this reduction in sucrose preference in the model mice (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e2\u003c/span\u003eC).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec19\" class=\"Section2\"\u003e \u003ch2\u003eOxaliplatin-chemotherapy reduces OPCs in the mPFC that are prevented by fenofibrate\u003c/h2\u003e \u003cp\u003eRecent studies have demonstrated that the depletion of OPCs in the mPFC resulting from chronic psychosocial stress is sufficient to hinder astrocytic activity, ultimately leading to neuronal dysfunction and depressive-like behaviors\u003csup\u003e28\u003c/sup\u003e. Platinum accumulates in the brain following chronic oxaliplatin treatment\u003csup\u003e29\u003c/sup\u003e. To investigate the influence of oxaliplatin chemotherapy on both the density and proportion of OPCs in the mPFC, mice were euthanized on day 21 (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e2\u003c/span\u003eA) for immunohistochemical analysis (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e3\u003c/span\u003eA). Immunohistochemical analysis demonstrated a significant reduction in both the density and proportion of OPCs (Sox10\u003csup\u003e+\u003c/sup\u003e/PDGFRα\u003csup\u003e+\u003c/sup\u003e) within the mPFC in the OXA group as compared to the Vehicle group. Importantly, prophylactic administration of fenofibrate mitigated this reduction in the density and proportion of OPCs (Sox10\u003csup\u003e+\u003c/sup\u003e/PDGFRα\u003csup\u003e+\u003c/sup\u003e) in the mPFC (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e3\u003c/span\u003eC, D). These findings suggest that oxaliplatin chemotherapy is a significant factor in the reduction of OPC density in the mPFC, while prophylactic fenofibrate administration exerts a protective effect on OPCs.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec20\" class=\"Section2\"\u003e \u003ch2\u003eOxaliplatin-chemotherapy reduces the proliferation of OPCs in the mPFC, which is prevented by fenofibrate\u003c/h2\u003e \u003cp\u003eTo investigate the effects of oxaliplatin chemotherapy on OPC proliferation in the mPFC, BrdU was administered. Mice were euthanized on day 8 following oxaliplatin treatment for immunohistochemical analysis (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e4\u003c/span\u003eB). Cryosections from the brains of various mice were consistently obtained at the same anatomical level (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e3\u003c/span\u003eB). Immunohistochemical analysis of the mPFC revealed a significant reduction in the proportion of BrdU\u003csup\u003e+\u003c/sup\u003e OPCs (Sox10\u003csup\u003e+\u003c/sup\u003e/PDGFRα\u003csup\u003e+\u003c/sup\u003e) in the OXA group compared to the Vehicle group (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e4\u003c/span\u003eC). Moreover, a significant increase in the proportion of BrdU label-retaining OPCs (Sox10\u003csup\u003e+\u003c/sup\u003e/PDGFRα\u003csup\u003e+\u003c/sup\u003e) was observed in the OXA\u0026thinsp;+\u0026thinsp;Feno group compared to the OXA group (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e4\u003c/span\u003eC). On day 8, there was no significant difference observed in the density of OPCs (Sox10\u003csup\u003e+\u003c/sup\u003e/PDGFRα\u003csup\u003e+\u003c/sup\u003e) between the OXA group and the OXA\u0026thinsp;+\u0026thinsp;Feno group, as both demonstrated a notable decrease when compared to the Vehicle group (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e4\u003c/span\u003eD). However, interestingly, on day 21, continuous fenofibrate treatment effectively reversed the oxaliplatin-induced reduction in OPC density (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e3\u003c/span\u003eC).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec21\" class=\"Section2\"\u003e \u003ch2\u003eOxaliplatin chemotherapy reduces the proliferation of OPCs in vitro, which is prevented by fenofibric acid\u003c/h2\u003e \u003cp\u003eIn vitro experiments were conducted to expose OPCs to oxaliplatin, fenofibric acid, or a combination thereof. Compared to the Vehicle group, oxaliplatin notably decreased the proportion of BrdU\u003csup\u003e+\u003c/sup\u003e OPCs (Sox10\u003csup\u003e+\u003c/sup\u003e) and Ki67\u003csup\u003e+\u003c/sup\u003e OPCs (Sox10\u003csup\u003e+\u003c/sup\u003e) (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eA, B, C). Moreover, a noteworthy surge in the proportion of BrdU label-retaining OPCs (Sox10\u003csup\u003e+\u003c/sup\u003e) and Ki67\u003csup\u003e+\u003c/sup\u003e OPCs (Sox10\u003csup\u003e+\u003c/sup\u003e) was documented in the OXA\u0026thinsp;+\u0026thinsp;Feno group when compared to the OXA group. The introduction of fenofibric acid proved beneficial as it mitigated the oxaliplatin-induced mortality of OPCs.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"Discussion","content":"\u003cp\u003eThis study uniquely demonstrates that fenofibrate treatment can potentially prevent oxaliplatin-induced neuropathy symptoms and depression-like behavior in animals. Furthermore, it is the inaugural research to highlight alterations in the density of OPCs in the mPFC resulting from oxaliplatin administration, an impact mitigated by concurrent fenofibrate therapy.\u003c/p\u003e \u003cp\u003eIn our investigation, a chronic oxaliplatin model induced prominent cold and mechanical allodynia, alongside depression-like behavior, echoing previous observations\u003csup\u003e30\u0026ndash;32\u003c/sup\u003e. The onset and nature of sensory disturbances and depressive symptoms closely parallel the effects of oxaliplatin in humans\u003csup\u003e33\u003c/sup\u003e. Oxaliplatin, a predominant neurotoxic chemotherapy agent, disrupts tumor cell proliferation by forming DNA-platinum adducts, leading to cancer cell destruction\u003csup\u003e3\u003c/sup\u003e. However, chronic neurotoxicity, exacerbated by cumulative oxaliplatin dosing, is often irreversible and associated with significant morbidity and diminished quality of life long after treatment completion. Therefore, we developed a model mimicking sustained neuropathic pain symptoms and delayed depression-like symptoms observed in patients treated with this anticancer agent, induced by repeated oxaliplatin injections. Due to fenofibrate's low oral bioavailability, a prophylactic dietary fenofibrate regimen was employed to maintain stable blood drug concentrations\u003csup\u003e17\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003ePeroxisome proliferator-activated receptor-α (PPARα), a nuclear receptor, undergoes conformational changes, heterodimerizes with RXR, recruits coactivators, and regulates reactive gene transcription upon ligand binding, among other functions\u003csup\u003e34\u003c/sup\u003e. Fenofibrate, FDA-approved for hyperlipidemia, mixed dyslipidemia, and hypertriglyceridemia, and for increasing HDL-cholesterol, exerts its effects through the activation of PPARα receptors, regulating genes involved in lipoprotein metabolism\u003csup\u003e16,35\u003c/sup\u003e. Numerous studies indicate that activating PPARα can alleviate neuropathic pain signs in various models\u003csup\u003e17,36\u0026ndash;38\u003c/sup\u003e. Research\u003csup\u003e39\u003c/sup\u003e implicates several mechanisms by which chemotherapy induces peripheral nerve damage, dysfunction, and death, including altered ion channel and receptor expression, innate immune response and inflammation, mitochondrial dysfunction, and changes in cell-signaling pathways like G-protein-coupled receptors (GPCRs) and mitogen-activated protein kinases (MAPKs). Concurrently with mechanical hyperalgesia, oxaliplatin-treated animals exhibit decreased intraepidermal nerve fibers\u003csup\u003e40\u003c/sup\u003e. In a mouse model of PIPN, fenofibrate treatment prevents paclitaxel-induced intra-epidermal nerve fiber loss and mitigates mitochondrial damage\u003csup\u003e22\u003c/sup\u003e. Fenofibrate's neuroprotective effects at the mitochondrial level may also safeguard nerve fibers from degeneration\u003csup\u003e38\u003c/sup\u003e. In our study, prophylactic fenofibrate administration significantly attenuated mechanical and cold allodynia in oxaliplatin-treated mice.\u003c/p\u003e \u003cp\u003ePrevious research on the pathophysiology of CIPN has primarily focused on peripheral nerves, as CIPN symptoms predominantly manifest in the hands and feet\u003csup\u003e41\u003c/sup\u003e. The notion that chemotherapy accumulates in the human brain has been subject to debate, and its validity likely hinges on the specific chemotherapy type, dose density, and other variables that could potentially compromise the blood-brain barrier\u003csup\u003e42\u003c/sup\u003e. However, recent studies have presented contrasting viewpoints, with evidence suggesting that platinum accumulates in the brains of rats following chronic oxaliplatin treatment\u003csup\u003e29\u003c/sup\u003e. Our study reveals that oxaliplatin chemotherapy significantly impairs the proliferation of OPCs in the mPFC, subsequently reducing their density. Furthermore, our in vitro experiments corroborate these findings, demonstrating a substantial decrease in OPC proliferation induced by oxaliplatin treatment.\u003c/p\u003e \u003cp\u003eThe dorsolateral prefrontal cortex (dlPFC) in humans plays a crucial role in the cognitive and affective modulation of pain perception\u003csup\u003e43\u0026ndash;45\u003c/sup\u003e. The mPFC in rodents is considered to be homologous to the dlPFC in primates\u003csup\u003e46\u003c/sup\u003e. The prefrontal cortex (PFC), renowned for its crucial role in executive functions, also plays a pivotal part in pain processing. This latter function is facilitated by its extensive connections with other regions of the cerebral neocortex, hippocampus, periaqueductal gray (PAG), thalamus, amygdala, and basal nuclei\u003csup\u003e47\u0026ndash;51\u003c/sup\u003e. During acute and chronic pain states, the PFC undergoes alterations in neurotransmitters, gene expression, glial cells, and neuroinflammation, ultimately leading to changes in its structure, activity, and connectivity\u003csup\u003e52\u003c/sup\u003e. The mPFC is a region implicated in both acute and chronic pain conditions in humans, wherein the corticolimbic connection between the mPFC and the nucleus accumbens (NAc) serves as a reliable indicator of the transition from subacute to chronic pain\u003csup\u003e50\u003c/sup\u003e. The mechanism by which persistent inflammation in the mPFC could lead to the development of chronic pain involves the continual activation of the mPFC, resulting in enhanced connectivity between the mPFC and the nucleus accumbens\u003csup\u003e53,54\u003c/sup\u003e. This heightened connectivity has been observed to correlate with the progression of pain towards a chronic state. A three-year longitudinal study of patients with subacute back pain suggests that stronger functional connectivity within the dorsal mPFC-amygdala-nucleus accumbens circuit is associated with an increased risk of developing chronic pain\u003csup\u003e51\u003c/sup\u003e. Numerous studies have reported a loss of grey matter in the PFC associated with chronic pain conditions. For instance, patients with chronic back pain exhibit regional grey matter reductions in the bilateral mPFC, extending to the anterior cingulate cortex (ACC) and the right mPFC, which extends to the orbitofrontal cortex\u003csup\u003e55\u003c/sup\u003e. Additionally, atrophy of the ventromedial PFC grey matter, combined with reduced white matter integrity and connectivity to the basal ganglia, has been observed in individuals with chronic complex regional pain syndrome\u003csup\u003e56\u003c/sup\u003e. The presence of a depressive mood may exacerbate pain sensation, as clinical studies and animal models have demonstrated that this interaction likely involves implicates the PFC. Depression scores among chronic pain patients have been found to correlate with alterations in the thalamus, as well as in the cingulate, dlPFC, and hippocampal cortices\u003csup\u003e57\u003c/sup\u003e. Furthermore, RNA sequencing and pathway analysis have revealed a considerable number of signaling pathway-associated genes exhibiting comparable expression changes in mice with spared nerve injury (SNI) and those exposed to chronic unpredictable stress. This finding implicates shared molecular pathways within the PFC that underlie the interplay between pain and depression\u003csup\u003e58,59\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eOPCs have been extensively studied for their proliferative and differentiation capabilities. However, recent research has uncovered a plethora of additional functions performed by OPCs that significantly impact brain function in both healthy and diseased states. Notably, OPCs not only receive synaptic input from neurons but also release neuromodulators that effectively modulate neuronal density, activity, local neural circuits, and synaptic plasticity\u003csup\u003e60\u003c/sup\u003e. While OPCs are known to generate myelinating oligodendrocytes throughout life, their functions extend beyond oligodendrogenesis; they also regulate synaptic connectivity in the brain\u003csup\u003e61\u003c/sup\u003e. A recent study has implicated oligodendrocyte apoptosis in the mPFC as a critical factor in fentanyl-induced hyperalgesia\u003csup\u003e62\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003ePostmortem studies consistently reveal a notable decrease in both the density and number of glial cells, along with a reduction in the size of neuronal cell bodies, particularly in cortical regions such as the prefrontal and cingulate areas, among depressed patients\u003csup\u003e63\u003c/sup\u003e. Utilizing the repeated social defeat (RSDS) mouse model, a study illustrates that chronic psychosocial stress triggers enduring losses of OPCs, leading their aberrant differentiation into oligodendrocytes and marked hypomyelination within the prefrontal cortex\u003csup\u003e64\u003c/sup\u003e. Birey et al. have reported that the ablation of OPCs in the PFC of the brain results in deficits of excitatory glutamatergic neurotransmission and astrocytic extracellular glutamate uptake, ultimately leading to depressive-like behaviors in mice. Additionally, they discovered that the density of OPCs in the frontal cortices of human subjects with major depressive disorder (MDD) was significantly lower compared to age-matched controls\u003csup\u003e28\u003c/sup\u003e. Another study posits that the beneficial impacts of running exercise on the mPFC volume and oligodendrocytes within the mPFC could constitute a crucial structural foundation for its antidepressant effects\u003csup\u003e65\u003c/sup\u003e. Recent research underscores that in major depressive disorder, OPCs not only serve as precursor cells for oligodendrocytes but also function as an independent cell type\u003csup\u003e66\u003c/sup\u003e. Our investigation reveals that the prophylactic administration of fenofibrate significantly mitigates depressive-like behaviors in mice receiving oxaliplatin treatment. On day 8 post-injection of oxaliplatin, there was no significant difference observed in the density of OPCs between the OXA group and the OXA\u0026thinsp;+\u0026thinsp;Feno group, as both demonstrated a notable decrease when compared to the Vehicle group. However, a significantly increased proportion of BrdU-labeled retained OPCs was observed in the OXA\u0026thinsp;+\u0026thinsp;Feno group compared to the OXA group. Interestingly, on day 21, continuous fenofibrate treatment effectively reversed the oxaliplatin-induced reduction in OPC density. This antidepressant efficacy of fenofibrate might be attributed to its protective influence on the proliferation of OPCs within the mPFC.\u003c/p\u003e \u003cp\u003eIn summary, our study demonstrates that fenofibrate significantly reduces mechanical and cold allodynia, as well as depressive-like behaviors, in mice with oxaliplatin-induced neuropathy. The anti-allodynic and antidepressant effects of fenofibrate are potentially associated with its beneficial impact on OPCs in the mPFC of these mice. Nonetheless, the exact mechanisms through which fenofibrate shields OPCs from oxaliplatin-induced harm are not fully comprehended. The pathogenesis of oxaliplatin chemotherapy-induced pain and depression is complex, with impaired OPC proliferation emerging as a potential contributor. Fenofibrate, which is widely used clinically for the treatment of dyslipidemia with well-established safety, could emerge as a potential therapeutic agent for alleviating oxaliplatin chemotherapy-induced pain and depression. Future clinical trials are warranted to evaluate the efficacy of fenofibrate in chemotherapy patients experiencing neuropathy and depressive symptoms.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgement\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis work was supported by the National Natural Science Foundation of China (81971048), Natural Science Foundation of Shanghai (17ZR1438200) and \u0026quot;Deep Blue 123\u0026quot; Military Medical Research Special Key Research Project (2019YSL008), Key Research and Development Program of Hainan Province of China (ZDYF2023SHFZ127), Key Projects of Military Theory of the PLA (JJ2023A05-B).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eContributors\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eLiang Yue, Yimin Yuan, Yu Ma, Li Cao and Yuanchang Xiong designed the study, analyzed the data and co-authored the manuscript. Liang Yue, Yimin Yuan, Dai Li, Li Sun and Yijia Shen conducted the experiments and analyzed the data. All authors contributed to the drafting of the manuscript and approved the final version.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConflict of Interest\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors have no relevant financial or non-financial interests to disclose.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData availability\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe datasets generated and analyzed during the current study are not publicly available due to privacy concerns and ongoing research, but they are available from the corresponding author on reasonable request.\u0026nbsp;\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eNordlinger, B.\u003cem\u003e et al.\u003c/em\u003e Perioperative FOLFOX4 chemotherapy and surgery versus surgery alone for resectable liver metastases from colorectal cancer (EORTC 40983): long-term results of a randomised, controlled, phase 3 trial. \u003cem\u003eLancet Oncol\u003c/em\u003e \u003cstrong\u003e14\u003c/strong\u003e, 1208-1215, doi:10.1016/s1470-2045(13)70447-9 (2013).\u003c/li\u003e\n\u003cli\u003eHershman, D. 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In this study, we established a mouse model of chronic oxaliplatin-induced neuropathy (OIPN) that closely mimics significant cold and mechanical allodynia, along with depression-like behaviors observed in patients, over a clinically relevant timeframe. We investigated the effects of fenofibrate on pain hypersensitivity and depression-like behaviors in the OIPN mouse model. Administration of fenofibrate significantly reduced mechanical allodynia in the Von Frey test and cold allodynia in the cold plate test among OIPN mice. Moreover, fenofibrate reduced depression-like behaviors in OIPN mice, as demonstrated by improved performance in the forced swimming test, sucrose preference test and tail suspension test. The analgesic and antidepressant-like effects observed with fenofibrate may be linked to its protective actions on oligodendrocyte progenitor cells (OPCs) in the medial prefrontal cortex (mPFC) of oxaliplatin-treated mice. These findings suggest that fenofibrate holds promise as a potential therapeutic agent for the prevention and treatment of OIPN, offering relief from both pain and comorbid depressive symptoms. Further clinical testing is warranted to confirm its efficacy and safety in this context.\u003c/p\u003e","manuscriptTitle":"Fenofibrate reduces pain hypersensitivity and associated depression-like behavior in mice with oxaliplatin- induced neuropathy","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-05-13 18:10:19","doi":"10.21203/rs.3.rs-4339586/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":"9912f91f-e3a8-46ee-9ada-81f32a573b31","owner":[],"postedDate":"May 13th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2024-09-20T08:52:36+00:00","versionOfRecord":[],"versionCreatedAt":"2024-05-13 18:10:19","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-4339586","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4339586","identity":"rs-4339586","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}