AN INSIGHT INTO ENDOMETRIOSIS: ROLE AND INFLUENCE OF THE PROCESS OF ANGIOGENESISS

Introduction: Endometriosis is one of the most com- mon gynaecological disorders present in females. Accord- ing to the implantation of ectopic endometrial tissue out- side of the uterine cavity, angiogenesis is an essential pre- requisite for the progression of the disease. The purpose is to provide insight and a better un- derstanding of the role that angiogenetic factors play within endometriosis and how this can translate into more effective diagnostic and therapeutic approaches taken by medical specialists when treating this disease.

We conducted a review of the available scientific literature on PubMed, Google Scholar and Science Direct, which included randomized controlled trials, observational studies, prospective control- led studies and case reports.

and Discussion: Our review of the scientific literature showed that the role of angiogenesis upon the development of endometrial ectopic tissue is very signifi- cant, and a positive relationship is established with an in- crease in neo-angiogenesis and a quicker rate of develop- ment of ectopic endometrial tissue. We also found data in- dicating that there are a multitude of angiogenetic and anti- angiogenetic factors functioning in a homeostatic manner to provide an optimal environment for the endometrial tis- sue to proliferate and for translocation for the implanta- tion of the ectopic tissue within different locations both within the uterine cavity and distant anatomical locations and regions located outside of the uterine cavity.

Recently, the research surrounding the process of angiogenesis is positive and positive correla- tions have been established between the role of angiogen- esis and the extent to which the ectopic endometrial tissue proliferates.

endometriosis, infertility, polymorphism, incidence, morphogenesis,

Endometriosis is an oestrogen-dependent inflamma- tory disease that is characterized by the presence of endome- trial glands and stroma outside the realms of the uterus. It can lead to chronic inflammatory reactions that may result in the formation of scar tissue, such as adhesions and/or fibrosis, confined within the pelvis. [1] Clinically, there are types characterized by way of lesion type, and these in- clude; Superficial endometriosis, which is found mainly in the pelvic peritoneum; cystic ovarian endometriosis, which is found in the ovaries, deep endometriosis, which is found in the recto-vaginal septum, bladder, bowel and in some rare cases it can also be found outside of the pelvis. En- dometriosis lesions are primarily located on the pelvic peri- toneum and ovaries but can slowly disseminate via hematogenic and lymphatic routes to the pericardium, pleura of the lung, lung parenchyma and in some cases, it can manifest within the meninges of the brain . The aetio- logical factors influencing the onset of endometriosis are retrograde menstruation, coelemic metaplasia, haematogenic and lymphatic spread, remnants of the Mul- lerian ducts and various interleukins and growth factors produced within the endometrial stromal or progenitor cells. The prevalence of the disease is varied due to the heterogeneous clinical manifestations, which include dysmenorrhea, dyspareunia, dysuria and chronic or severe long-lasting abdominal pain, and in some cases infertility leading to a severe limitation in the quality of life. [2, 3] The development of endometriosis is proposed as retro- grade menstruation, which is, in fact, where the menstrual blood and uterine tissues enter the peritoneal cavity by way of the fallopian tubes . [4] However, in more than 90% of women participating in investigations such as laparoscopy, it has been revealed that, in fact, the theory of retrograde menstruation facilitated the transport of endometrial tissue to the peritoneal cavity; however, an external factor is re- sponsible for increasing the susceptibility of certain women to experience this implantation and growth of this ectopic endometrium. [5] Within this, other theories have been suggested, such as an altered peritoneal environment, im- munological susceptibility and a greater amount of retro- grade menstruation and not to mention the influence of ge- netic predisposition, which can increase the likelihood of this atypical process of endometriosis to occur. In addition https://doi.org/10.5272/jimab.2024301.5323 5324 https://www.journal-imab-bg.org J of IMAB. 2024 Jan-Mar;30(1) to this, it can be proposed that the undergoing of prolif- eration, secretion, regression and regeneration of the en- dometrial lining of the uterus during the period of the men- strual cycle can influence the pathological atypicality of the endometrium in subtle alterations in the events that take place during the menstrual phase. One of the main theories includes the ability of the endometrium to divide and, hence, the resulting implantation and growth within the peritoneal cavity. Furthermore, within the complex se- ries of events that arise within the menstrual cycle, the role of blood vessel proliferation and stimulation of endome- trial gland development is important, and three different separate episodes of angiogenesis of blood vessels have been proposed and comprise of post-menstrual repair dur- ing the early proliferative phase, mid-proliferative phase growth under the direct influence of oestrogen and growth of the coiling of the spiral arteries and arterioles situated in the stratum functionalis of the endometrium which is in- fluences by the presence and production of progesterone via the corpus luteum in the secretory or luteal phase of the menstrual cycle. [6] The presence of angiogenesis within the endometrium can be denoted via laparoscopy, and findings include dense vascularization. In early le- sions, blood vessels appear pink-red with a high blood ves- sel density, dilated vascular structures and an increased number of immature vessels when compared with black le- sions and a general increase in vascularization surround- ing the area of abnormal vessel geography. Researchers and specialists within this field have been investigating the angiogenetic processes within the endometrium in order to develop anti-angiogenetic treatment strategies, which may reduce the side effects and recurrences seen in women un- dergoing conventional conservative therapies or main- stream surgical treatment. This review article will look at the angiogenetic factors and pathophysiological processes that occur within the endometrium and whether this infor- mation is sufficient in the diagnosis and treatment of en- dometriosis. [7, 8]

We conducted a review of the available scientific lit- erature at Pub Med, Google, Science Direct, which included randomized trials, prospective controlled trials, research reports and guidelines in the approach taken in the research of angiogenetic factors influencing endometriosis in terms of development and clinical application of treatment strat- egies involving angiogenetic factors. In the Scientific lit- erature, we searched for outcomes that included Endome- triosis, Pathophysiology of Endometriosis, therapy of en- dometriosis, angiogenetic factors, angiogenetic theories proposed in the process of endometriosis. We have also in- cluded research and analysis of conventional treatment

utilized in the treatment of endometriosis that may have an impact on the development of angiogenetic factor treatment therapies, which can be used in treating endome- triosis.

Our review of the scientific literature indicated evi- dence of the importance of angiogenetic processes within the pathophysiological development of endometriosis and whether new mainstream forms of treatment can be devel- oped based on the proposed theories to revolutionize the way obstetricians and gynaecologists treat women suffer- ing from this disease. Obstetrics and gynaecology is a medical speciality which is widely needed as it is a dual-speciality both work- ing to keep pregnancies healthy whilst being responsible for the delivery of viable foetuses, and it also focuses on the broader spectrum of issues relevant to a woman, spe- cifically the health and disease manifestation of the female reproductive system. A normal endometrial lining of the uterus, the proposed mechanism of angiogenesis occurs in the form of vessel elongation rather than a branch spout- ing of the spiral arteries, and it is the primary mechanism for development and growth of the endometrium during the first 14 days of the menstrual cycle namely known as the proliferative phase. However, it seems that there is a recruit- ment of new capillaries from existing adjacent peritoneal microvessels in conjunction with this, it is also essential to mention the importance of the newly synthesized blood vessels derived from the circulation endothelial progeni- tor cells in a process called vasculogenesis, which is also involved in the pathogenesis of endometriosis. The en- dometrium is a dynamic tissue which displays various prop- erties, such as populations of clonogenic epithelial and stro- mal stem cells that require indefinitely active cyclical an- giogenesis. [9, 10] Endometriosis can produce various chemotactic fac- tors, such as cytokines and growth factors, that regulate their proliferation and vascularization. Interleukin-1 Beta is an important interleukin-1 secreted by the peritoneal macrophages, and it plays a pivotal part in the neovascularization of the endometriotic like lesions. In ad- dition to this, IL-6 is a multi-subunit and multifunctional protein which promotes endometrial cellular proliferation and angiogenesis, and its production is elevated in en- dometriosis and the concentrations of IL-6 can be found in high quantities in the peritoneal fluid of such individu- als. IL-8 is worth mentioning as it is a pro-inflammatory cytokine that induces the chemotaxis of neutrophils and has a potent stimulatory effect on the angiogenetic mecha- nism. The presence of IL-1B influences and increases the angiogenetic factors in neutrophils to stimulate endome- triosis-associated angiogenesis. On the other hand, in the presence of specific transcription factors, hypoxic-induc- ible factors enhance the expression of pro-angiogenetic fac- tors like VEGF to induce hypoxia-induced angiogenesis. In the presence of transcriptional factor HIF-1 alpha, VEGF m-rna expression levels increase in response to hypoxia; moreover, the HIF-1 alpha factor is responsible for regulat- ing the expression of transcriptional genes encoded in the transcriptional synthesis of VEGF to induce hypoxemic-in- duced angiogenesis. [11] J of IMAB. 2024 Jan-Mar;30(1) https://www.journal-imab-bg.org 5325 Activin A is a growth factor member of TGF-beta with subsequent effects on inflammation and angiogenesis. The human endometrium is both a source and target of Activin A, and it can both up and down-regulate the ex- pression and secretion of IL-8 and vascular endothelial growth factor, which are produced from the endothelial stro- mal cells. Consequently, the vascular growth factor is the most potent and specific angiogenetic factor responsible for a variety of effects such as endothelial cell prolifera- tion and migration, organization of endothelial cells into tubular like structures, and incr ease in permeability, all of which participate in the endometrial angiogenetic cascade. The basis of the so-called vascular endothelial growth fac- tor is influenced by the presence and levels of oestrogen, which in the late proliferative phase of the menstrual cy- cle increases in quantity VEGF to promote the prolifera- tion and neovascularization of the endometrium in order to prepare the endometrial lining of the uterus for concep- tion and implantation of the blastocyst which is being brought in via the fallopian tubes from the ovaries, how- ever, it is important to note that the concentration of VEGF is at its peak in the secretory phase and phase of menses . Angiogenesis can occur throughout fetal growth and development, but in adults, it is concentrated in the men- strual cycle, the ovaries in the liberation of the mature graafian follicle and formation of corpus luteum and in vari- ous pathological conditions such as wound healing, dia- betic retinopathy, tumour growth and not to mention en- dometriosis. Specifically within the menstrual cycle, the process of angiogenesis plays a crucial role in the follicular maturation development of a functional corpus luteum. The importance of angiogenesis within endometriosis is such that the nova vasculogenesis that takes place from pre-ex- isting blood vessels is necessary for the survival and pro- gression of ectopic endometrial tissue situated outside of the uterine cavity. Oestrogen is an important hormone within the menstrual cycle and plays an important role in the development of blood vessels for endometriotic im- plants. The 17-Beta estradiol up-regulates the VEGF expres- sion in the endometrial human stromal cells by activating the Wnt/B-catenin axis through estrogenic receptors and thus enhances their ability to establish a new blood sup- ply to the endometrium. Furthermore, estrogenic receptors of the beta sub-type directly regulate the expression of genes involved in hypoxia-induced angiogenesis, such as HIF-1 alpha, VEGF, angiotensin 1 receptors in ectopic le- sions of the endometrium to support the progression of en- dometriosis. In addition to this, there are various other fac- tors which interact with one another to up-regulate or in- hibit the activation of VEGF within the endometrial tissue. For example, peptide hormones regulate angiogenesis by stimulation or inhibition to promote or prevent the growth of the ectopic tissue and through the process of proteoly- sis, we have a conversion of the original hormone into ei- ther a pro-angiogenetic peptide, which is a stimulating fac- tor in the progression of ectopic endometrial tissue, or it can lead to anti-angiogenic peptide formation which acts in an inhibitory form preventing the progression of ectopic endometrial tissue . Furthermore, if we look at the findings, it demon- strates that angiogenesis within endometriosis is influenced by an interaction of various intra and extracellular signal- ling molecules, which interact with one another and are in- fluenced by local hypoxic and inflammatory stimuli within the specific microenvironment of the peritoneal cavity. The ability to determine the type of transcriptional factors and hormonal elements and the extent of influence of endome- triosis is very difficult because different endometrial phe- notypes markedly have different levels of genetic expres- sion levels of genes associated with hypoxia and angio- genesis. With regards to endometriosis and the influence of angiogenesis on a clinical basis, we can say that within the role of angiogenesis and influence over the progres- sion of endometriosis is reflected in the fact that the peri- toneal fluid from endometriosis patients significantly in- creases the proliferation of endothelial cells and induces a strong vascular reaction leading to new blood vessel for- mation within the ectopic tissue of endometrium type. This is due to the fact that peritoneal fluid contains elevated concentrations of different angiogenetic promoting factors such as VEGF, insulin growth factor 1, angiotensin-2, eryth- ropoietin, hepatocyte growth factor and on the other hand the peritoneal fluid also contains lower concentrations of anti-angiogenetic factors namely adiponectin, interferon- gamma induced protein-10. These findings are interesting as they serve as a basis that when diagnosing endometrio- sis, we may be able to use the interaction of these pro and anti-angiogenetic factors as biomarkers for determining a working diagnosis of endometriosis as well as for assess- ing the efficacy of therapeutic approaches taken to treat endometriosis. However, although promising studies have indicated a positive indication of these factors as biomarkers in endometriosis, as of yet, they are of insuffi- cient diagnostic sensitivity and specificity. This can be ex- plained by the low study sample or the heterogeneous dis- eases stages of the subjects within the study sample. To fur- ther this, it is important to use a combination of biomarkers to diagnosis endometriosis. Currently, such proposals for utilizing these tools can only be used to assess the risk of developing endometriosis or adenomyosis. [12, 13] In line with the proposal to use medicinal compounds containing anti-angiogenetic constituents, it has shown to be a prom- ising target for gene therapy or pharmacological-based treatment of endometriosis. These include growth factor in- hibitors, endogenous angiogenesis inhibitors, fumagillin analogues and statins, immunomodulators in which these medicaments have been proven to reduce the micro vessel density of endometriotic lesions in animal models with a resulting effect of engrafted lesions or a suppressed lesion growth. In studies carried out on mice, the concept of treat- ment containing angiogenetic compounds, the blood ves- sels invading the endometrium are accompanied by nerve fibres. These nerve fibres stimulate the dorsal root neurons within the central nervous system, which increases the pain perception in endometriosis patients. Due to this finding, the treatment of endometriosis with anti-angiogenetic com- pounds not only leads to a reduction of blood vessel for- mation but also nerve fibre growth in the ectopic tissue. 5326 https://www.journal-imab-bg.org J of IMAB. 2024 Jan-Mar;30(1) Despite the promising results, anti-angiogenic therapy has not been implemented for clinical use because of several reasons. The first is because endometriosis is a heteroge- neous disease with diverse types of lesions in different lo- cations, and so each location containing ectopic endome- trial tissue will have a varying degree of vascularization and composition. Anti-angiogenic compounds target the early red lesions with a high level of angiogenic activity and immature micro vessels, so the older, black and white lesions may be resistant to this form of treatment. Thus, the administration of anti-angiogenic compounds may not be suitable as a monotherapeutic drug focusing on pharma- cological-based eradication as well as eradication of well- established endometriotic lesions in the peritoneal cavity. However, the anti-angiogenic compounds may serve as an importance in the prevention of new lesion formation after surgical removal and, therefore, can help to reduce high recurrence rates of surgical based endometriosis therapies. In addition to this, the resistance to anti-angiogenic drugs poses an issue with the usage of anti-angiogenic com- pounds, but this can be overcome by simultaneously sup- pressing different angiogenic compounds or by means of combination therapy. Finally, the women who suffer from endometriosis are of reproductive age and may wish to pre- serve their fertility; this poses as a problem as the fertility and uterus are heavily dependent upon the physiological angiogenesis in the ovary, uterus and placenta and, there- fore, the long-term administration of anti-angiogenic agents is contraindicated due to the unknown effects on the fe- male reproductive organs which may compromise the ability of the women to conceive and bear a child should the fe- male have the desire or wish to have children. In order to overcome this, trials are currently being carried out utiliz- ing anti-angiogenic agents with a more acceptable and safe profile to see whether the same adverse effects are produced or if milder side effects are present, which can be contained with combined therapy. [14] Anti-angiogenic agents are agents which block the action of VEGF and inhibit the ability of VEGF to initiate arteriole proliferation and neogenesis. Bevacizumab is a recombinant human monoclonal antibody that inhibits VEGF, inhibiting the development and proliferation of endometriotic lesions with a reduction in the vascular den- sity and increased apoptosis with a reduction of VEGF lev- els in the peritoneal fluid. Sorafenib is another anti-ang- iogenic agent, which in its form is an orally active multikinase inhibitor that interferes with the activity of the VEGF receptor and tyrosine kinase receptors, and in the mice model, it reduces the micro vessel density and lesion volume in patients suffering from endometriosis. Lipoxin A4 is an endogenous eicosanoid whose role is to regulate inflammation. This lipid-based medicament blocks the mi- gration of endothelial cells and VEGF-stimulated angiogen- esis. The Lipoxin A4 r educes the endometrial lesion size and down regulates the inflammation-associated proteins such as IL-6, VEGF and matrix metalloproteinase 9. Parecoxib, a selective cyclooxygenase-2 inhibitor, reduces the lesion size, micro vessel density, the number of macrophages and the expression of VEGF, which leads to atrophy and regression of endometrial ectopic tissues when carried out on mice. Statins are inhibitors of HmG-COA with an intrinsic antioxidant, anti-inflammatory and anti- angiogenic properties, f or example, Atorvastatin inhibited the inflammatory and angiogenetic genes COX-2 and VEGF in endometrial stromal cells. Another important anti- angiogenic agent is the dopamine agonist cabergoline, which exerts its effect thr ough VEGFR-2 inactivation, in- hibiting the growth of established endometrial lesions. Fi- nally, progestogens reduce the proliferation of endometrial stromal cells and suppress the transcription of VEGF-A and the microvessel density in human ectopic endometrial le- sions. [15, 16]

Within the last decade, it has become evident that the process of angiogenesis plays a central role in the pathogenesis of endometriosis. Many angiogenetic induc- ing factors can be determined, such as VEGF, which is present in peritoneal fluid and ectopic endometrial tissue from endometriotic patients. However, despite all of this, there is still limited evidence in the knowledge of under- standing the mechanisms behind blood vessel angiogen- esis and the complex and dynamic interactions between various factors and pathophysiological processes which work together to regulate angiogenesis specifically within the endometrium. To conclude, more research is needed on the mechanisms of angiogenesis and the general physiologi- cal process of developing new blood vessels within the en- dometrial ectopic tissue to ascertain a broader and more complete understanding of endometriosis. J of IMAB. 2024 Jan-Mar;30(1) https://www.journal-imab-bg.org 5327 1. Rocha AL, Reis FM, Taylor RN. Angiogenesis and endometriosis. Obstet Gynecol Int. 2013;2013: 859619. [ PubMed ] 2. Krikun G. Endometriosis, ang- iogenesis and tissue factor. Scientifica (Cairo). 2012;2012: 306830. [ PubMed ] 3. Qiu JJ, Lin XJ, Zheng TT, Tang XY , Zhang Y , Hua KQ. The Exosomal Long Noncoding RNA aHIF is Upregulated in Serum From Patients With Endometriosis and Promotes An- giogenesis in Endometriosis. Reprod Sci . 2019 Dec;26(12):1590-1602. [ PubMed ] 4. Vinatier D, Orazi G, Cosson M, Dufour P. Theories of endometriosis. Eur J Obstet Gynecol Reprod Biol. 2001 May;96(1):21-34. [ PubMed ] 5. Kapoor R, Stratopoulou CA, Dolmans MM. Pathogenesis of En- dometriosis: New Insights into Pro- spective Therapies. Int J Mol Sci. 2021 Oct 28;22(21):11700. [ PubMed ] 6. Becker CM, D’Amato RJ. Ang-

iogenesis and antiangiogenic therapy in endometriosis. Microvasc Res. 2007 Sep-Nov;74(2-3):121-30. [ PubMed] 7. Tsaltas J, Rogers PAW, Gargett C, Healy DL. Excessive angiogenesis: a new theory for endometriosis . Curr Obstet Gynaecol. 1998 Dec:8(4)186- 190. [ Crossref] 8. McLaren J. Vascular endothelial growth factor and endometriotic ang- iogenesis. Hum Reprod Update. 2000 Jan-Feb;6(1):45-55. [ PubMed ] 9. Ke J, Ye J, Li M, Zhu Z. The Role of Matrix Metalloproteinases in Endometriosis: A Potential Target. Biomolecules. 2021 Nov 22;11(11): 1739. [ PubMed ] 10. Healy DL, Rogers PA, Hii L, Wingfield M. Angiogenesis: a new theory for endometriosis. Hum Reprod Update. 1998 Sep-Oct;4(5):736-40. [ PubMed] 11. Laschke MW, Menger MD. Basic mechanisms of vascularization in endometriosis and their clinical implications. Hum Reprod Update. 2018 Mar 1;24(2):207-224. [ PubMed] 12. Harada T, Iwabe T, Terakawa N. Role of cytokines in endometriosis. Fertility and Sterility. 2001 Jul;76(1):1-10. [ Crossref ] 13. Djokovic D, Calhaz-Jorge C. Angiogenesis as a therapeutic target in endometriosis. Acta Med Port. 2014 Jul-Aug;27(4):489-97. [ PubMed ] 14. Chung MS, Han SJ. Endome- triosis-Associated Angiogenesis and Anti-angiogenic Therapy for En- dometriosis. Front Glob Womens Health. 2022 Apr 5;3:856316. [ PubMed] 15. Smith SK. Regulation of ang- iogenesis in the endometrium. Trends Endocrinol Metab. 2001 May- Jun;12(4):147-51. [ PubMed ] 16. Laschke MW, Menger MD. In vitro and in vivo approaches to study angiogenesis in the pathophysiology and therapy of endometriosis. Hum Reprod Update. 2007 Jul-Aug; 13(4):331-42. [ PubMed ] Address for correspondence: Nikolay Lazarov Department of Obstetrics and Gynaecology, Medical Faculty, Trakia Univer- sity, Stara Zagora; 11, Armejska Street, Stara Zagora, Bulgaria. E-mail: [email protected] Please cite this ar ticle as: Lazarov N, Saghir F. An Insight into Endometriosis: Role and Influence of the Process of Angiogenesis. J of IMAB. 2024 Jan-Mar;30(1):5323-5327. [Crossref - https://doi.org/10.5272/jimab.2024301.5323 ] Received: 15/06/2023; Published online: 23/01/2024