{"paper_id":"b97e8345-c401-4ab1-8454-bebd6aa59b97","body_text":"REPRODUCTIVE HEALTH  •  August 2017  •  Creative Commons Attribution-Non Commercial 4.0 EMJ  EUROPEAN MEDICAL JOURNAL  REPRODUCTIVE HEALTH  •  August 2017  •  Creative Commons Attribution-Non Commercial 4.0 EMJ  EUROPEAN MEDICAL JOURNAL 76 77\nTARGETING MAST CELLS AS A VIABLE  \nTHERAPEUTIC OPTION IN ENDOMETRIOSIS\n*David A. Hart\nDepartment of Surgery, McCaig Institute, University of Calgary, Calgary, Alberta, Canada.\n*Correspondence to hartd@ucalgary.ca\nDisclosure: The author has declared no conflicts of interest.\nAcknowledgements: The author thanks the Institute for Gender and Health of the Canadian Institutes for \nHealth Research for past funding, Alberta Health Services for current support, and Dr Kevin A. Hildebrand \nfor his critical review of the manuscript.\nReceived: 03.03.17  Accepted: 05.07.17\nCitation: EMJ Repro Health. 2017;3[1]:76-83.\nABSTRACT\nEndometriosis is a chronic condition that affects ˜10% of young women worldwide. Pain and infertility \nare the two most common features of the disease. The condition appears to be sex hormone-dependent, \nalthough a subset of females with the condition still experience symptoms post-menopause. The aetiology \nof endometriosis induction still remains elusive, and surgery to remove the lesions often fails to cure the  \ncondition, as the lesions often reappear. The lesions contain stromal cells, blood vessels, nerves, and \nnumerous mast cells. In some respects, endometrial lesions resemble a chronic fibrotic scar-like tissue \nthat does not resolve. Studies in other fibrotic abnormal healing conditions have revealed that targeting \nmast cells, as a central component of what is called a ‘neural–mast cell–fibroblast’ axis, by repurposing \nasthma drugs can prevent induction of the abnormal healing phenotype. Given the similarities between \nconditions with abnormal healing phenotypes and endometrial lesions, it is postulated that taking a similar \napproach to target endometrial lesion mast cells could exert a benefit for patients with endometriosis.  \nThis review also outlines approaches to assess the likelihood that targeting mast cells could lead to clinical  \ntrials using such ‘repurposed’ mast cell targeted drugs.\nKeywords: Mast cells, mast cell stabilisers, endometriosis, cell biology of endometriosis, neuroinflammatory \npathways, biochemistry of endometriosis.\nPREAMBLE \nThis review is intended to focus on the rationale and \nfeasibility of targeting mast cells in endometriosis, \nand discussing selected findings in the literature \nrelated to this focus. Due to space limitations,  \nit is not intended to be an exhaustive review of \nall aspects of endometriosis. Thus, the reader is \nencouraged to read the large number of recent \nreviews in the literature which address other \naspects of this complex disease to complement  \nthe discussion below. \nTHE CLINICAL PROBLEM\nEndometriosis is an inflammatory condition that  \naffects ~10% of young women of reproductive age. 1  \nThe disease appears to be sex hormone-dependent  \nas symptoms can vary across the menstrual cycle, \nwith pain as a prominent symptom. The condition \nis also frequently accompanied by dysmenorrhoea \nand infertility, with the presence of pelvic  \nabdominal lesions. Conservative treatment with  \nanti-inflammatory drugs is often ineffective,  \nand surgical removal of the lesions becomes a viable \nalternative.2 However, after surgery, the condition \ncan reappear with pain and associated lesions.  \nAs the condition is chronic, it can be accompanied \nby epigenetic changes that may complicate the \neffectiveness of treatment.3,4  \nThe disease is characterised by the growth of \nendometrial elements outside of the uterine cavity.  \nWhy this occurs is currently unknown, and what \nfactors predispose or contribute to this very \ncommon condition in a subpopulation of younger \nfemales is not yet evident. It may result from \nretrograde menstruation, 5,6 with attachment and \n\n REPRODUCTIVE HEALTH  •  August 2017  •  Creative Commons Attribution-Non Commercial 4.0 EMJ  EUROPEAN MEDICAL JOURNAL  REPRODUCTIVE HEALTH  •  August 2017  •  Creative Commons Attribution-Non Commercial 4.0 EMJ  EUROPEAN MEDICAL JOURNAL 76 77\ngrowth of endometrial tissue in this environment. \nThe tissue associated with endometriosis contains \nblood vessels, nerves, mast cells, myofibroblasts,  \nand macrophages, 7-10 and, thus, appears to be a \nfibrotic lesion that in some respects resembles \na progressive scar. As endometriosis tissue can \nbe influenced by sex hormones, 11-13 and possibly \nneuroinflammatory elements, 14 it may resemble \nabnormal scarring such as occurs following a burn \ninjury (hypertrophic scar), or following a traumatic \nelbow injury leading to a joint contracture. 15,16  \nThus, the initiating events may differ but the cellular \nand molecular interactions leading to fibrotic \nprogression may share a number of commonalities. \nInterestingly, endometriosis has also been linked  \nwith risk for other chronic diseases such as  \nasthma,17,18 in which mast cells also play a central role.\nPRECLINICAL MODELS\nEndometriosis can occur naturally in horses 19 and  \nnon-human primates,20 and can be induced in rats \nby auto-transplantation of uterine tissue to the \nabdomen, or in nude mice by transplantation of \nhuman endometrial tissue. 21,22 Such models can \nprovide some insights into aspects of endometriosis \ndevelopment and progression, as well as insights  \ninto potential interventions, but, thus far,  \nthe aetiology of endometriosis in humans and in  \nnon-human primates remains undefined.\nROLE OF SEX HORMONES \nIN ENDOMETRIOSIS\nAs discussed above, endometriosis is a sex   \nhormone-mediated inflammatory disease. With \nregard to endometriosis, oestrogen has been \nimplicated in the activity of macrophages, 10 \nfibroblasts and myofibroblasts, 13 nerves, 10,12 and \nmast cells. 7,23 It is also clear that oestrogen is a \nregulator of inflammatory processes, and activation \nof inflammatory cells can contribute to nerve  \nfibre-mediated pain. 14 In addition, sex hormones, \nsuch as oestrogen, are known to contribute to  \nwound healing in response to injury. 24,25 Both  \noestrogen and progesterone have been implicated \nin mast cell degranulation.26\nAfter menopause, inflammatory processes decline, \nwound healing is compromised, and endometriosis \nin most patients becomes latent. 5,27 However, 2–4% \nof women still continue to experience endometriosis \nafter menopause. 5 Therefore, either alternative \nmechanisms could potentially allow the disease \nto continue in this subpopulation (e.g. due to \nepigenetic modifications 4,28) or local production of  \noestrogen could continue to contribute to disease  \nactivity in the post-menopausal state.\nWhile endometriosis is considered oestrogen-\ndependent, in part based on menstrual cycle \ndependency, a role for progesterone is also likely. 29 \nFurthermore, the impact of sex hormones could \nbe a secondary sequela of hormone level changes  \n(e.g. water retention with increased turgor of \nendometrial lesions contributing to pain).\nREGULATION OF PROTEINASE \nEXPRESSION IN ENDOMETRIOSIS\nRole of Sex Hormones and Their Receptors\nProteinases such as tissue factor, 30 elements of the \nfibrinolytic system,31 cathepsins,32 mast cell tryptase \nand chymase, 33 and matrix metalloproteinases \n(MMP)34 have all been implicated in endometriosis. \nAs these enzymes can facilitate extracellular \nmatrix turnover, activate pro-enzymes and other  \nmolecules, and serve other functions related to \ninflammation, coagulation, collagen deposition, \nand angiogenesis, they are likely central to  \nendometriosis progression. In this regard, their \nrole is likely not different from their roles in other \nfibrogenic processes and wound healing.\nMuch research has focussed on the MMP, their \nexpression in endometriosis, and their regulation \nby progesterone35,36 and oestrogen. 34 Progesterone \nappears to limit MMP expression,35,36 while oestrogen \nis reported to enhance MMP-9 expression, 37 and \nMMP-9 levels are enhanced in endometriosis. 38  \nAs oestrogen functions primarily via estrogen \nreceptor (ER)-alpha and ER-beta in cells, receptors \nknown to be expressed in endometrial tissue, 39,40  \nthis response is potentially contributing to the \nsymptoms of endometriosis and its progression. \nHowever, the role of oestrogen receptors in \nendometriosis is somewhat controversial, 39,40 with \nER-beta a more prominent variant in endometriosis \nthan normal tissue.39\nInterestingly, oestrogen receptors in the absence \nof oestrogen can also regulate expression of some \nMMP41-43 and these include MMP-1 and MMP-13.  \nThe addition of oestrogen actually depressed \nexpression rather than enhancing expression.  \nER-beta was more effective than ER-alpha in many \nof these responses, and, interestingly, genetic \nvariants of the MMP-1 promoter region were also \n\n REPRODUCTIVE HEALTH  •  August 2017  •  Creative Commons Attribution-Non Commercial 4.0 EMJ  EUROPEAN MEDICAL JOURNAL  REPRODUCTIVE HEALTH  •  August 2017  •  Creative Commons Attribution-Non Commercial 4.0 EMJ  EUROPEAN MEDICAL JOURNAL 78 79\ndifferentially regulated. Some of these same  \nvariants, as well as those for MMP-2, 7, and 9 were \nfound to be associated with risk of endometriosis. 44 \nIntriguingly, splice variants of ER-beta that do not \nbind oestrogen were also effective in upregulating \nexpression of MMP-1,45 and splice variants have  \nalso been detected in endometriosis tissues.46 \nMAST CELLS IN ENDOMETRIOSIS \nMast cells, often thought of in the context of  \nallergies or asthma, are present in most tissues  \nthroughout the body, including connective tissues  \nand many organs. 7,15,16 Mast cells are also very \nprevalent in normal and abnormal healing \nenvironments, with elevated numbers, in abnormal \nhealing conditions.7,15,16 Mast cells are very prevalent \nin endometriosis tissue, and many of them appear \nto be activated and degranulated. 47-49 In addition, \nmany of the mast cells were localised very close to \nneural elements,49 and, as such, could play an active \nrole in neuroinflammatory processes. 7,15,16 We have \npreviously seen neural elements ending in normal \ndense connective tissues very close to a mast cell,  \nimplying that nerve-mast cell co-localisation may  \nalso play a role in normal tissue functioning  \nas well.7,15,16\nMast cells and their products could contribute \nto several features of endometriosis. Mast cell \ntryptase can activate protease activated receptors \n(PAR), particularly PAR-2. 50 PAR are known to be \nexpressed in endometrium and endometriosis. 51 \nActivation of PAR-2 on cells may participate in pain \nprocessing52 and angiogenesis. 53 Mast cell tryptase \ncan also activate myofibroblasts and contribute to \nfibrosis.15,16 Histamine released from mast cells has \nbeen studied for decades and has multiple activities,  \nincluding enhancing tissue oedema and many other \neffects. Activated mast cells can also release a \nnumber of pro-inflammatory cytokines, mediators, \nand growth factors, and thus, can have a very potent \nand varied impact on a target tissue, particularly \none that appears to be abnormally regulated, \nas in endometriosis. The enhanced presence of \nmast cells, many of which appear to be activated, \nin endometriosis tissue has led to the proposal \nthat mast cells should be targeted with drug  \ninterventions to assist in controlling endometriosis \nprogression and symptoms. 7,23,54,55 Based on the \nfindings that activated mast cells are present in \nendometrial tissues, oestrogen/progesterone can \ninfluence mast cells, mast cells can release many \nbiologically active molecules, and mast cell numbers \nare increased in endometrial tissues, this cell may  \nbe an excellent cell to target in endometriosis,  \nalone or in combination with other targets.\nMAST CELL STABILISERS\nMast cell stabilisers are drugs which inhibit or  \nprevent mast cell degranulation. These include \ntwo drugs, ketotifen and sodium cromoglycate, \nthat have a long history of use in the treatment \nof asthma. While ketotifen is now off patent  \nprotection, it has been used safely for >40 years \nin adult and paediatric populations. It is not  \ntotally targeted specifically for mast cells, and \nis also reported to inhibit degranulation of \npolymorphonuclear leukocytes. 17,18 Thus, with  \nthe development of new potential indications  \n(e.g. endometriosis), there may be an impetus \nfor industry to develop newer versions that may \nbe more specific for mast cells, or more active in  \nspecific diseases or conditions.\nUSE OF MAST CELL \nSTABILISERS IN ABNORMAL \nFIBROPROLIFERATIVE CONDITIONS\nAbnormal healing follows induction of skin injuries \nin the red Duroc pig 56,57 and following trauma \nand immobilisation of a knee injury in a rabbit \nmodel.58 The former exhibits characteristics of  \nhypertrophic scarring and also fibrogenic scarring.59 \nIn the red Duroc pig, this abnormal scarring  \nresponse appears to have a genetic component. 60 \nThe rabbit model exhibits cellular and molecular \ncharacteristics of joint contractures that occur \nin a subset of humans who experience an  \nelbow injury.15,16 \nIn these two models, elevated numbers of mast cells, \nnerves, and myofibroblasts have been observed \nleading to the conclusion that the cells contribute \nto fibroproliferative dysfunction. These cells have \nbeen postulated to form a cellular ‘axis’ ( Figure 1) \nin which the mast cell plays a central role.7,15,16 In this \nproposed axis, the fibroblasts and myofibroblasts  \nare the effector cells which release fibrotic  \nmolecules, such as collagens, and contract the  \nfibrotic matrix. Neuropeptides from nerves or,  \nin the case of endometriosis, possibly sex hormones,  \nimpact mast cells, which then release molecules \nthat enhance the activity of fibroblasts and \nmyofibroblasts. Thus, the mast cells function \nas accelerators or amplifiers of the fibrotic  \nenvironment. This axis is postulated to be \n\n REPRODUCTIVE HEALTH  •  August 2017  •  Creative Commons Attribution-Non Commercial 4.0 EMJ  EUROPEAN MEDICAL JOURNAL  REPRODUCTIVE HEALTH  •  August 2017  •  Creative Commons Attribution-Non Commercial 4.0 EMJ  EUROPEAN MEDICAL JOURNAL 78 79\ndysfunctional in the two models, but whether the \ninitiator of the dysfunction is only due to the nerves \n(e.g. neuroinflammation), or some other cell type \nor stimulus, remains to be determined. Treatment \nof skin wounds on red Duroc pigs with the asthma \ndrug ketotifen from the time of injury prevented \ndevelopment of the abnormal fibrogenic response \nto injury and led to a more typical healing response.57\nIf treatment was delayed until 28 days post-injury, \nthe drug was without effect. Stopping the drug \ntreatment after epithelisation of the wounds \ndid not lead to a reactivation of the abnormal \nfibrogenic response. Thus, this mast cell stabiliser \nappeared to exert its influence early in the response \nto injury. Interestingly, treatment with ketotifen \nled to a decline in detectable nerves, mast cells,  \nand myofibroblasts in the skin scar tissue, which \nlikely also indicated that the postulated axis \nwas not unidirectional and interfering with mast \ncell degranulation impacted other elements of \nthis axis. Finally, treatment of skin wounds with \nketotifen in Yorkshire pigs that healed normally \nwas without effect and did not influence the \nnumber of cells in the axis that could be detected.  \nThus, the drug did not appear to influence normal \nhealing of skin wounds.\nLocal mast cell secretagogues\nHistamine\nCTGF, TNF-α\nTGF-β, bFGF, PDGF\nTryptase\nAcute and chronic \ninflammation\nMast cells Fibroblasts Myofibroblasts\nSCF SCF\nTGF-β \nSubstance P \nCGRP\nComplement C3a\nVIP\nOpiates\nHistamine\nInterleukins\nSCF\nNGF\nTGF-β\nTNF-α\nlgE\nFigure 1: Mast cells mediated inflammation and fibrosis.\nMast cells circulate as CD34-positive precursor cells and terminally differentiate in connective tissues. Both \nIgE-dependent and independent mechanisms can activate mast cells causing the release of preformed and \nnewly synthesised pro-inflammatory mediators. Many of these mediators increase vascular permeability \nand promote the recruitment of other inflammatory cells and additional mast cell precursors. SCF is also \nsecreted by activated fibroblasts and myofibroblasts, further potentiating mast cell recruitment and \nproliferation. TGF-β is a potent fibroblast mitogen and stimulator of myofibroblast differentiation. It also \nimpedes myofibroblast apoptosis. \nbFGF: basic fibroblast growth factor; CGRP: calcitonin gene-related peptide; CTGF: connective tissue \ngrowth factor; IgE: immunoglobulin E; NGF: nerve growth factor; PDGF: platelet-derived growth factor; \nSCF: stem cell factor; TGF-β: transforming growth factor beta; TNF-a: tumor necrosis factor alpha; VIP: \nvasoactive intestinal peptide.\nAdapted from Monument et al.16\nGrowth arrest \nApoptosis\nProliferation \nDifferentiation\nCollagen synthesis\n\n REPRODUCTIVE HEALTH  •  August 2017  •  Creative Commons Attribution-Non Commercial 4.0 EMJ  EUROPEAN MEDICAL JOURNAL  REPRODUCTIVE HEALTH  •  August 2017  •  Creative Commons Attribution-Non Commercial 4.0 EMJ  EUROPEAN MEDICAL JOURNAL 80 81\nSimilar studies in the rabbit model of post-traumatic \njoint contractures using ketotifen treatment  \nalso led to improvement in the healing process \nand significant declines in the extent of the joint \ncontractures (˜50%), as well as cells of the nerve–\nmast cell–myofibroblast axis.61,62 The suggestion that \nketotifen was likely inhibiting mast cell degranulation, \narose from recent studies demonstrating that \nserum levels of mast cell tryptase were significantly \ndepressed in the treated rabbits.63\nThe mast cell stabiliser sodium cromoglycate \nhas also shown effectiveness in a rat model of  \nexperimental endometriosis. 55 In this model, \ntransplantation of endometrial tissue to the \nabdominal wall followed by a 2-week treatment \nregimen with sodium cromoglycate led to significant \ndeclines in activated mast cells, as well as tissue \nlevels of mast cell tryptase and serum levels of  \ntumour necrosis factor alpha. However, the size \nof the lesions was not apparently influenced by \nthe treatment. As myofibroblasts have also been \nidentified in endometriosis lesions, 9 as well as  \nnerves,49 it would be of interest to assess the  \ninfluence of mast cell stabiliser treatment of the \ntransplanted tissues on levels of these two cells \nas well, particularly since mast cells and nerve \nelements have been detected in close proximity \nin human endometriosis tissues. 49  Interestingly,  \nclose proximity of nerves and mast cells have been \nnoted in unrelated tissues, and it appeared that \nneuropeptides released from nerves could impact \nthe mast cells ( Figure 1 ), leading to an amplified \nimpact on the target tissue.\nFrom our studies using ketotifen, 57,61,62 and those of \nZhu et al. 55 with sodium cromoglycate, inhibition of \nmast cell degranulation may be a viable direction to \nexplore. In contrast, D’Cruz and Uckun 54 proposed \nusing a janus kinase (JNK) 3 inhibitor, JANEX-1, \nand recently a JNK inhibitor has been reported \nto cause regression of endometriotic lesions in \nTable 1: Potential clinical pathway to confirming mast cells as a therapeutic target in endometriosis.\nELISA: enzyme-linked immunosorbent assay; RCT: randomised controlled trial; RT-qPCR: quantitative \nreverse transcription polymerase chain reaction.\nPhase 1: Amass evidence for mast cell activation in patients with endometriosis\nAssess mast cell tryptase in serum of age matched individuals with and without established endometriosis at three \ndefined points during their menstrual cycle using a validated ELISA.63 If indeed mast cell degranulation is involved in \nendometriosis activity and symptoms across the menstrual cycle, the ELISA results should parallel symptoms.\nAs surgery is recommended for many patients with endometriosis, one could assess serum mast cell tryptase levels \nbefore and post-surgery during specific points in the menstrual cycle to address the question of whether serum \ntryptase levels can be used as a biomarker for a return of the endometriosis.\nHistologic assessment of the nerve–mast cell–myofibroblast axis (Figure 1) in tissue obtained at the time of surgery, \nusing immunolocalisation protocols developed for assessing human joint contracture tissues.58 \nIn vitro explant studies using tissue obtained at the time of surgery. Such tissues could be incubated plus or minus \nketotifen and supernatant levels of tryptase assessed using an ELISA.63 A search of the literature did not reveal \nwhether such surgery is preferentially performed at specific times in the menstrual cycle of patients, but certainly  \nthis may impact the results of the studies outlined.\nPhase 2: Short-term ketotifen trial in endometriosis patients scheduled for surgery\nPatients would be randomly assigned to a ketotifen arm or a sham solution arm of the protocol (oral dosing of \nketotifen or sham solution) in a blinded fashion. Daily diaries for symptoms would be maintained for the 3 months \nprior to surgery, as well as serum levels for mast cell tryptase (blood draws once per month at the optimal timing). \nTissue obtained at the time of subsequent surgery could be assessed for nerves, mast cells, myofibroblasts, and \nmacrophage subsets, by immunolocalisation techniques, as well as RNA isolated from the tissue by RT-qPCR, and \nincubation of culture supernatants for detection of relevant proteins by established array technologies.\nPhase 3: Large scale clinical trials of ketotifen (single-centre and multicentre)\nThese trials could take many designs, optimal designs determined by clinical experts to yield the most information \nand maintain patient safety.\nKetotifen pilot trial in patients: pain assessments (diary) for 3 months prior to drug or sham initiation and then daily \nfor 3 months. Washout for 3 months and then cross over for 3 months. \nKetotifen implementation trial: Cohort of patients to receive ketotifen or sham for 12 months and then stop and follow \nfor a defined period of time to determine whether any improvements revert following cessation of treatment.\nLarge-scale RCTs: Double-blind multicentre trials\n\n REPRODUCTIVE HEALTH  •  August 2017  •  Creative Commons Attribution-Non Commercial 4.0 EMJ  EUROPEAN MEDICAL JOURNAL  REPRODUCTIVE HEALTH  •  August 2017  •  Creative Commons Attribution-Non Commercial 4.0 EMJ  EUROPEAN MEDICAL JOURNAL 80 81\nrodent models. 64 While targeting mast cells using \nthese approaches has not yet led to clinical trials in \nendometriosis, a clinical trial is currently underway \nusing ketotifen to prevent joint contracture \ndevelopment following traumatic elbow injuries.65 \nAre There Commonalities in  \nDysregulated Fibrogenic Responses  \nto Inflammation and Injuries?\nJoint contracture development following a trauma \nto the elbow occurs in 10–15% of those injured. 15,16 \nDevelopment of a contracture is accompanied by \na fibrotic response in which the healing process is \ndysregulated and does not proceed through to \nmaturation and remodelling of the scar. In many \ncases, the patients undergo surgery to release the \ncontracture, but often with only partial recovery.15,16 \nSimilarly, development of a hypertrophic scar after \na severe burn injury is also a fibrotic response \nto the injury, with excessive matrix deposition, \nmyofibroblasts, and mast cells.  For many patients, \nthe hypertrophic scars have to be surgically \nremoved. Interestingly, female sex is also a risk  \nfactor for hypertrophic scar development. 66  \nThe abnormal fibrogenic skin wound healing,  \nin the previously discussed porcine models, also  \nexhibits some similarities with hypertrophic scarring.\nGiven these similarities, perhaps much of the \nuniqueness of endometriosis is associated with \nwhere the abnormal fibrotic tissue is located,  \nits sex hormone dependency, and the sequelae of \nthe fibrosis, rather than any intrinsic uniqueness in \nthe cellular aspects of the dysregulated processes \ncontributing to progression and chronicity.  \nThus, some of what has been learned from these \nother diseases or conditions, as well as from the  \npreclinical models discussed, could provide insights \ninto focussing research directions forward with  \nmast cells as a target.\nFuture Directions for Assessment of Efficacy \nand Implementation of Mast Cell Stabilisers  \nin Patients with Endometriosis\nTo undertake a clinical trial of mast cell stabilisers, \nsuch as ketotifen or sodium cromoglycate, in \npopulations of young females with endometriosis, \ninvestigators must proceed with caution as many of \nthese individuals are of reproductive age, and mast  \ncells have been implicated in normal ovulation \nevents and others related to reproduction in some \nspecies.67 However, the complexity of endometriosis \nin patient populations could be approached in  \nphases to strengthen the link between mast cell \nactivity and symptoms and then identify those  \nbest suited to participate in pilot trials using the  \nmast cell stabilisers (Table 1). \nOne of the current gaps in endometriosis research \nis a lack of good biomarkers, such as serum \ncomponents, that can be used to monitor disease \nactivity, assess the impact of interventions,  \nor assess the return of disease activity following  \nsurgery prior to overt symptoms being evident.  \nSerum mast cell tryptase levels, as assessed by \nan enzyme-linked immunosorbent assay 63 could \ncontribute to filling this gap.\nFinally, it is clear that epigenetic changes occur \nduring progression of endometriosis. 3,4,28 These \nchanges (DNA methylation, histone modifications, \nand alterations to miRNA profiles) can lead to \nalterations in cell responsiveness to interventions. \nIn some chronic diseases (e.g. rheumatoid \narthritis), these changes can occur in fibroblasts \nand other cells. Thus, endometrial lesions early in \nthe disease may respond differently to targeting \nmast cells than those with more advanced disease. \nSuch factors may need to be considered when  \nassessing effectiveness.\nCONCLUSIONS\nBased on the above discussion, there is considerable \ncircumstantial evidence to support the use of mast \ncell targeted drug interventions in the treatment \nof endometriosis. There is an advantage for \nusing known drugs such as ketotifen and sodium \ncromoglycate, both with long track records of \nuse for the treatment of asthma in a variety of  \npopulations. Thus, their safety and efficacy is well  \ndocumented. However, repurposing these drugs \nis a viable approach, but one that will require a  \nsystematic analysis in patient populations ( Table 1). \nGiven the large population of females with  \nendometriosis (5–15% of females worldwide),  \nand the impact of the condition on these young \nwomen, new approaches that could impact their  \nquality of life should be entertained. However, this  \napproach using mast cell targeted drugs may  \naddress the how of the disease, but not why the  \ndisease occurs, so it would only be a stop-gap  \napproach until new information arises as to why it  \ndevelops, and what is unique about the subset of \nwomen who experience the disease (e.g. genetics, \nepigenetics, exposure to environmental stimuli,  \nand stochastic events).\n \n\n REPRODUCTIVE HEALTH  •  August 2017  •  Creative Commons Attribution-Non Commercial 4.0 EMJ  EUROPEAN MEDICAL JOURNAL  REPRODUCTIVE HEALTH  •  August 2017  •  Creative Commons Attribution-Non Commercial 4.0 EMJ  EUROPEAN MEDICAL JOURNAL 82 83\n1. Greene AD et al. Endometriosis: \nwhere are we and where are we going? \nReproduction. 2016;152(3):R63-78.\n2. Bedaiwy MA et al. New developments in \nthe medical treatment of endometriosis. \nFertil Steril. 2017;107(3):555-65.\n3. Borghese B et al. Recent insights \non the genetics and epigenetics of \nendometriosis. Clin Genet. 2017;91(2):  \n254-64.\n4. Koukoura O et al. DNA methylation in \nendometriosis (Review). Mol Med Res.  \n2016;13(4):2939-48.\n5. Bendon CL, Becker CM. Potential \nmechanisms of postmenopausal \nendometriosis. Maturitas. 2012;72(3):  \n214-9.\n6 Vercellini P et al. Endometriosis: \npathogenesis and treatment. Nat Rev \nEndocrinol. 2014;10(4):261-75.\n7. Hart DA. Curbing inflammation in \nmultiple sclerosis and endometriosis: \nshould mast cells be targeted? Int J \nInflam. 2015;2015:452095.\n8. McKinnon B et al. Endometriosis-\nassociated nerve fibers, peritoneal fluid \ncytokine concentrations, and pain in \nendometriotic lesions from different \nlocations. Fertil Steril.   2012;97(2):373-80.\n9. Ibrahim MG et al. Abdominal wall \nendometriosis: myofibroblasts as a \npossible evidence of metaplasia: a case \nreport. Gynecol Obstet Invest. 2017;82(1): \n90-101.\n10. Greaves E et al. Estradiol is a critical \nmediator of macrophage-nerve cross talk \nin peritoneal endometriosis. Am J Pathol. \n2015;185(8):2286-97.\n11. Bedaiwy MA et al. Medical  \nManagement of endometriosis in patients \nwith chronic pelvic pain. Semin Reprod \nMed. 2017;35(1):38-53.\n12. Liang Y, Yao S. Potential role of \nestrogen in maintaining the imbalanced \nsympathetic and senory innervation in \nendometriosis. Mol Cell Endocrinol. 2016;  \n424:42-9.\n13. Da Costa e Silva Rde C et al. \nEstrogen signaling in the proliferative  \nendometrium: implications in \nendometriosis. Rev Assoc Med Bras. 2016; \n62(1):72-7.\n14. McKinnon BD et al. Inflammation and \nnerve fiber interaction in endometriotic \npain. Trends Endocrinol Metab. 2015;  \n26(1):1-10.\n15. Monument MJ et al. Posttraumatic \nelbow contractures: targeting \nneuroinflammatory fibrogenic \nmechanisms. J Orthop Sci. 2013;18(6):  \n869-77.\n16. Monument MJ et al. Neuroinflammatory \nmechanisms of connective tissue fibrosis: \ntargeting neurogenic and mast cell \ncontributions. Adv Wound Care. 2015;  \n4(3):137-51.\n17. Kvaskoff M et al. Endometriosis: a \nhigh-risk population for major chronic  \ndiseases? Hum Reprod Update. 2015:  \n21(4):500-16.\n18. Fourquet J et al. Characteristics of \nwomen with endometriosis from the  \nUSA and Puerto Rico. J Endometr Pelvic \nPain Disord. 2015:7(4):129-35.\n19. Rebordao MR et al. Physiopathologic \nmechanisms involved in mare \nendometriosis. Reprod Domest Anim. \n2014;49(suppl 4):82-7.\n20. Yamanaka A et al. Primate model \nresearch for endometriosis. Tohoku J Exp \nMed. 2012;226(2):95-9.\n21. Grummer R. Animal models in \nendometriosis research. Hum Reprod \nUpdate. 2006;12(5):641-9.\n22. Tirado-Gonzalez I et al. Endometriosis \nresearch: animal models for the study of \na complex disease. J Reprod Immunol. \n2010;86(2):141-7.\n23. Binda MM et al. Targeting mast cells: \na new way to treat endometriosis. Expert \nOpin Ther Targets. 2017;21(1):67-75.\n24. Ashcroft GS, Ashworth JJ. Potential \nrole of estrogens in wound healing. Am J \nClin Dermatol. 2003;4(11):737-43.\n25. Gilliver SC, Ashcroft GS. Sex steroids \nand cutaneous wound healing: the \ncontrasting influences of estrogens and \nandrogens. Climacteric. 2007;10(4):  \n276-88.\n26. Zierau O et al. Role of female sex \nhormones, estradiol and progesterone, in \nmast cell behavior. Front Immunol. 2012:  \n3:169. \n27. Inceboz U. Endometriosis after \nmenopause. Women’s Health. 2015;11(5):  \n711-5.\n28. Koike N et al. Epigenetic dysregulation \nof endometriosis susceptibility genes \n(Review). Mol Med Rep. 2015;12(2):1611-6.\n29. Patel BG et al. Progesterone  \nresistance in endometriosis: origins, \nconsequences and interventions. Acta \nObstet Gynecol Scand. 2017:96(6):  \n623-32.\n30. Krikun G et al. Endometriosis and \ntissue factor. Ann N Y Acad Sci. 2008;  \n127(1):101-5.\n31. Zorio E et al. Fibrinolysis: the key to \nnew pathogenetic mechanisms. Curr Med \nChem. 2008;15(9):923-9.\n32. Porter KM et al. Cathepsin Protease \ninhibition reduces endometriosis \nlesion establishment. Reprod Sci. 2016;  \n23(5):623-9.\n33. Paula R Jr et al. The intricate role \nof mast cell proteases and the annexin \nA1-FPR1 system in abdominal wall \nendometriosis. J Mol Histol. 2015;46(1):  \n33-43.\n34. Pitsos M, Kanakas N. The role \nof matrix metalloproteinase in the \npathogenesis of endometriosis. Reprod \nSci. 2009;16(8):717-26.\n35. Osteen KG et al. Progesterone-\nmediated endometrial maturation \nlimits matrix metalloproteinase (MMP) \nexpression in an inflammatory-like \nenvironment: a regulatory system altered \nin endometriosis. Ann N Y Acad Sci. 2002: \n955:37-47.\n36. Monckedieck V et al. Progestins inhibit \nexpression of MMPs and of angiogenic \nfactors in human ectopic endometrial \nlesions in a mouse model. Mol Hum \nReprod. 2009;15(10):633-43.\n37. Zhang L et al. Intracellular Wnt/\nbeta-catenin signaling underlying \n17beta-estradiol-induced matrix \nmetalloproteinase 9 expression in \nhuman endometriosis. Biol Reprod. 2016;  \n94(3):70.\n38. Liu H et al. Correlation between  \nmatrix metalloproteinase-9 and  \nendometriosis. Int J Clin Exp Pathol.  \n2015;8(10):13399-404.\n39. Bulun SE et al. Role of estrogen \nreceptor-β in endometriosis. Semin \nReprod Med. 2012;30(1):39-45.\n40. Shao R et al. The elusive and \ncontroversial roles of estrogen and \nprogesterone receptors in human \nendometriosis. Am J Transl Res. 2014;  \n6(2):104-13.\n41. Achari Y et al. Polymorphisms in the \npromoter regions for human MMP-1 and \nMMP-13 lead to differential responses \nto alpha and beta isoforms of estrogen \nreceptors and their ligand in vitro.  \nBiochim Biophys Acta. 2008;1782(6):  \n391-400.\n42. Achari Y et al. Distinct roles for \nAF-1 and -2 of ER-alpha in regulation  \nof MMP-13 promoter activity. Biochim \nBiophys Acta. 2009;1792(3):211-20.\n43. Lu et al. Evidence that estrogen \nreceptor beta enhances MMP-13  \npromoter activity in HIG-82 cells and that \nthis enhancement can be influenced by \nligands and involves specific promoter \nsites. Biochem Cell Biol. 2007;85(3):  \n326-36.\n44. Yang H et al. Associations \nbetween various possible promoter  \npolymorphisms of MMPs genes and \nendometriosis risk: a meta-analysis. Eur \nJ Obstet Gynecol Reprod Biol. 2016;  \n205:174-88.\nREFERENCES\n\n REPRODUCTIVE HEALTH  •  August 2017  •  Creative Commons Attribution-Non Commercial 4.0 EMJ  EUROPEAN MEDICAL JOURNAL  REPRODUCTIVE HEALTH  •  August 2017  •  Creative Commons Attribution-Non Commercial 4.0 EMJ  EUROPEAN MEDICAL JOURNAL 82 83\n45. Thaler JD et al. Estrogen receptor \nbeta and truncated variants enhance the \nexpression of transfects MMP-1 promoter \nconstructs in response to specific \nmechanical loading. Biol Sex Differ. 2014;  \n5(1):14.\n46. Juhasz-Böss I et al. Endometrial \nexpression of estrogen receptor beta \nand its splice variants in patients with \nand without endometriosis. Arch Gynecol \nObstet. 2011;284(4): 885-91.\n47. Kempuraj D et al. Increased numbers \nof activated mast cells in endometriosis \nlesions positive for corticotropin-\nreleasing hormone and urocortin. Am J \nReprod Immunol. 2004;52(4):267-75.\n48. Sugamata M et al. Increase of  \nactivated mast cells in human \nendometriosis. Am J Reprod Immunol. \n2005;53(3):120-5.\n49. Anaf V et al. Pain, mast cells, and \nnerves in peritoneal, ovarian, and deep \ninfiltrating endometriosis. Fertil Steril. \n2006;86(5):1336-43.\n50. Cottrell GS et al. Protease-activated \nreceptors: the role of cell-surface \nproteolysis in signalling. Essays Biochem. \n2002;38:169-83.\n51. Osuga Y et al. Proteinase-activated \nreceptors in the endometrium and \nendometriosis. Front Biosci. 2012;4:  \n1201-12.\n52. Bao Y et al. Protease-activated \nreceptor 2 signalling pathways: a role \nin pain processing. Expert Opin Ther \nTargets. 2014;18(1):15-27.\n53. Ammendola M et al. Targeting mast \ncells tryptase in tumor microenvironment: \na potential antiangiogenic strategy. \nBiomed Res Int. 2014;2014:154702.\n54. D’Cruz OJ, Uckun FM. Targeting \nmast cells in endometriosis with janus \nkinase 3 inhibitor, JANEX-1. Am J Reprod  \nImmunol. 2007;58(2):75-97.\n55. Zhu LB et al. Sodium cromoglycate \nattenuates experimental endometriosis \nin rats by regulating mast cells. Zhejiang \nDa Xue Xue Bao Yi Xue Ban. 2015;44(3):  \n278-84. (In Chinese).\n56. Gallant CL et al. Molecular, histologic, \nand gross phenotype of skin wound  \nhealing in red Duroc pigs reveals \nan abnormal healing phenotype of \nhypercontracted, hyperpigmented \nscarring. Wound Repair Regen. 2004;  \n12(3):305-19.\n57. Gallant-Behm CL et al. The mast cell \nstabilizer ketotifen prevents development \nof excessive skin wound contraction  \nand fibrosis in red Duroc pigs. Wound \nRepair Regen. 2008;16(2):226-33.\n58. Hildebrand KA et al. Joint capsule \nturnover in a rabbit model of chronic \njoint contracture: correlation with human \ncontractures. J Orthop Res. 2006;24(5):  \n1036-43.\n59. Engrav LH et al. Hypertrophic \nscar, wound contraction and hyper-\nhypopigmentation. J Burn Care Res. 2007; \n28(4):593-7.\n60. Gallant-Behm CL et al. Skin wound \nhealing in the first generation (F1) \noffspring of Yorskshire and red Duroc  \npigs: evidence for genetic inheritance of \nwound phenotype. Burns. 2006;32(2):  \n180-93.\n61. Monument M et al. The mast cell \nstabilizer, ketotifen fumarate, lessens \ncontracture severity and myofibroblast \nhyperplasia in a rabbit model of \nposttraumatic joint contractures. J Bone \nJoint Surg. 2010;92(6):1468-77.\n62. Monument et al. The mast cell \nstabilizer ketotifen reduces joint capsule \nfibrosis in a rabbit model of post-\ntraumatic joint contractures. Inflamm  \nRes. 2012;61(4):285-92.\n63. Kopka M et al. Serum mast cell \ntryptase as a marker of posttraumatic \njoint contracture in a rabbit model. J \nOrthop Trauma. 2016;31(3)e86-9.\n64. Palmer SS et al. Bentamapimod (JNK \nInhibitor AS602801) induces regression \nof endometriotic lesions in animal  \nmodels. Reprod Sci. 2016:23(1):11-23.\n65. University of Calgary. Investigations \nof mechanisms and treatment in post-\ntraumatic joint contractures (Ketotifen). \nNCT01902017. Available at: https:/ /\nclinicaltrials.gov/ct2/show/NCT01902017. \n66. Thompson CM et al. Genetic \nrisk factors for hypertrophic scar  \ndevelopment. J Burn Care Res. 2013;  \n34(5):477-82.\n67. Jensen F et al. Estradiol and \nprogesterone regulate the migration \nof mast cells from the periphery to the \nuterus and induce their maturation \nand degranulation. PLoS One. 2010;  \n5(12):e14409.","source_license":"CC0","license_restricted":false}