Endometriosis,Pathophysiology, Inflammatory Mediators and Pre sacral Neurectomy.Dr.M.Sirisha
  • Endometriosis is a clinical and pathologic entity initially described by von Rockitansky in 1860 that is characterised by the presence of tissue resembling functioning endometrial glands and stroma outside the uterine cavity. Endometriosis is one of the most mysterious and fascinating gynecological disorders.
  • Endometriosis is a disease of contrast. It is benign but it is locally invasive, disseminates widely.
  • This ectopic endometrial tissue has capability to respond to cyclical harmonal stimulation.

 

  • Endometriosis is found predominantly in woman of reproductive age group (25-40 yr) but is reproted in adoloscent  girls and post menopausal women receiving  harmonal replacement.
  • It is found in women of all ethnic and social group
  • The estimated prevalance of endometriosis among population group varies depending on the presenting symptoms,

 

  • Theories

 

 

  • Sampson’s Theory
  • It proposes that endometrial tissue is disseminated into the peritoneal cavity via the fallopian tubes during menstruation and subsequently implants onto peritoneal tissues.
  • Substantial clinical and experimental data supports this theory.
  • The presence of endometrial cells in dialysate of women undergoing peritoneal dialysis during menses, higher incidence of endometriosis in women having obstruction of outflow of menstrual blood favouring retrograde menstruation, high risk of endometriosis in women who have longer duration of menses and shorter intervals between menstruation, 50% incidence of endometriosis in rhesus monkeys after surgical transposition of the cervix to allow intra-abdominal menstruation supports this theory.
  • Although only 1-10% of women are diagnosed with endometriosis, it has been found that 76-90% of healthy women undergo retrograde menstruation.
  • While it may predispose women into developing endometriosis, it is likely that women with disease suffer from fundamental differences in genetic, immunological, or biochemical factors.
  • Despite multiple lines of evidences favoring this theory, cases of endometriosis in premenarchal girls, newborns, and males all demand secondary explanation.
  • Coelomic Metaplasia Theory
  • This theory was proposed was MEYER and IVANOFF.It postulates that endometriosis arises from the metaplasia of cells lining the visceral and abdominal peritoneum following various hormonal, environmental, or infectious stimuli.
  • It is based on the embryological studies that reveal that the germinal epithelium, endometrium, and petritoneum all originate from the same totipotent coelomic epithelium.
  • This theory explains the development of endometriotic lesions in unusual locations and in the odd cases of male patients in whom endometriosis develops after prostatectomy, orchiectomy, or prolonged treatment with oestrogen.

 

 

Induction Theory

This theory is extension of coelomic metaplasia theory.

  • It proposes that some undefined endogenous biochemical factor can induce undifferentiated peritoneal cells to develop into endometrial tissue

 

 

Pathophysiology

A unifying theory regarding the origin of endometriosis has remained mystifyingly elusive. Instead, several theories have arisen to account for the disparate observations regarding pathogenesis, and these can generally be categorized as those proposing that implants originate from uterine endometrium and those proposing that implants arise from tissues other than the uterus. Intrinsic to these theories are inciting factors and genetic susceptibilities whose roles are beginning to be delineated, though insufficiently established to confirm cause and effect and subsequent development of endometriosis. For example, reports linking endocrine disrupting chemicals (EDCs) with endometriosis  suggest these, and endogenous/exogenous estrogens, as potential transforming/inductive/ stimulant candidates in theories of endometriosis pathogenesis. The developmental timing of action of such agents and their roles in influencing other systems that predispose to endometriosis (endocrine, immune, stem/progenitor cells, epigenetic modifications) must be considered in the context of genetic background as well as stimulus-driven reprogramming of the female reproductive tract .

 

Figure 1

Theories regarding endometriosis pathogenesis. E2=estradiol

Among theories proposing a non-uterine origin of disease, coelomic metaplasia involves the transformation of normal peritoneal tissue to ectopic endometrial tissue . Agents responsible for such transformation remain poorly defined, although EDCs may be candidates. The closely related induction theory holds that an endogenous inductive stimulus, such as a hormonal or immunologic factor, promotes the differentiation of cells in the peritoneal lining to endometrial cells . Finally, the theory of embryonic Mullerian rests, or mullerianosis, purports cells residual from embryologic Mullerian duct migration maintain the capacity to develop into endometriotic lesions under the influence of estrogen beginning at puberty  or perhaps in response to estrogen mimetics. These theories find support in epidemiologic studies reporting a twofold increased risk of endometriosis in women exposed to diethylstilbestrol in utero.

A more recent proposal suggests extra-uterine stem/progenitor cells originating from bone marrow may differentiate into endometriotic tissue . Candidate cell lineages include bone marrow mesenchymal stem progenitors and endothelial progenitors, and this represents an active area of investigation. Support for theories advocating a non-endometrial origin for endometriosis is derived from clinical accounts of histologically confirmed endometriotic tissue in patients without menstrual endometrium, such as individuals with Rokitansky-Kuster-Hauser syndrome and men with prostate cancer undergoing high dose estrogen treatment .

The theory of benign metastasis holds that ectopic endometrial implants are the result of lymphatic or hematogenous dissemination of endometrial cell. Microvascular studies demonstrated flow of lymph from the uterine body into the ovary, rendering possible a role for the lymphatic system in the etiology of ovarian endometriosis. Endometriosis within lymph nodes has been documented in a baboon model of induced endometriosis , and in 6-7% of women at lymphadenectomy . The strongest evidence for the theory of benign metastasis is derived from reports of histologically proven endometriotic lesions occurring in sites distant from the uterus to include bone, lung and brain .

Initially proposed by Sampson in the 1920s, the theory of retrograde menstruation is both intuitively attractive and supported by multiple lines of scientific evidence . According to this theory, eutopic endometrium is sloughed via patent fallopian tubes into the peritoneal cavity during menstruation. Indeed, the universality of this phenomenon is supported by the finding of menstrual blood in the peritoneal fluid of up to 90% of healthy women with patent fallopian tubes undergoing laparoscopy during the peri-menstrual time of the cycle.

Further support for this etiology is derived from studies of obstructed or compromised outflow tracts. In adolescent girls with congenital outflow obstruction, the prevalence of endometriosis is high . Likewise, iatrogenic obstruction of the outflow tract in a non-human primate model results in endometriotic lesions within the peritoneal cavity . Even subtle compromise of antegrade menstruation may predispose to endometriosis, as evidenced by the higher prevalence of endometriosis in women with a uterine septum  and cervical stenosis . The anatomic distribution of endometriotic lesions also favors the retrograde menstruation theory. Superficial implants are more often located in the posterior compartment of the pelvis and in the left hemipelvis . The propensity for lesions to implant in the posterior cul de sac is explained by the accumulation of regurgitated menstrual effluent in this most dependent portion of the peritoneal cavity under the influence of gravity. In allowing flow from the anterior to posterior compartment in the upright or supine position, a retroverted uterine position is correlated with the finding of endometriosis. By acting as an obstacle to the diffusion of menstrual effluent from the left fallopian tube, the sigmoid colon promotes stasis of this effluent, thereby extending the interval for refluxed endometrial fragments to implant in the left hemipelvis.

A murine model of endometriosis has provided insight into the pathogenesis of peritoneal endometriosis . The conditional activation of the K-ras oncogene in endometrial cells deposited into the peritoneum resulted in histologically confirmed peritoneal endometriotic implants in nearly 50% of mice within 8 months. On the other hand, similar activation of the K-ras oncogene in peritoneal cells showed no progression to endometriosis. These preclinical observations favor an endometrial origin to the development of peritoneal lesions.

Though retrograde menstruation explains the physical displacement of endometrial fragments into the peritoneal cavity, additional steps are necessary for the development of endometriotic implants. Escape from immune clearance, attachment to peritoneal epithelium, invasion of the epithelium, establishment of local neurovascularity and continued growth and survival are necessary if endometriosis is to develop from retrograde passage of endometrium. Collectively, investigations involving the pathophysiology of endometriosis have revealed several well supported molecular hallmarks of this disease:

  1. Genetic predisposition
  2. Estrogen dependence
  3. Progesterone resistance
  4. Inflammation

It is the propensity for implantation that best accounts for the discrepancy between the 90% prevalence of retrograde menstruation and the nearly 10% prevalence of the disease. Hereditary or acquired properties of the endometrium, hereditary or acquired defects of the peritoneal epithelium, and/or defective immune clearance of sloughed endometrium are areas of active investigation in the search for the factor or factors that influence predisposition toward implantation of the displaced endometrial cells – a necessary correlate to theories proposing an endometrial origin to disease pathogenesis.

Endometrial cell survival

The evidence for an innate or acquired condition of the endometrial cells as the predisposing factor toward implantation is compelling. The eutopic endometrium from women with endometriosis shares certain alterations with ectopic lesions that are not observed in the endometrium from healthy women. Up-regulation of the anti-apoptotic gene BCL-2 has been shown in both eutopic and ectopic endometrium from affected women . In addition to decreased apoptosis, enhanced proliferation may confer a selective survival advantage to endometrium of women predisposed to endometriosis .

A genetic alteration of the endometrial cells influencing their tendency to implant may be hereditary, as a heritable component to the disease has been established. The risk for first degree relatives of women with severe endometriosis is six times higher than that for relatives of unaffected women . Studies of monozygotic twins demonstrate high concordance rates for histologically confirmed endometriosis . Linkage analysis has elucidated candidate genes with biological plausibility. The largest of these involved over 1100 families with two or more affected sib-pairs, and established significance for a susceptibility loci in the regions of chromosome 10q26 and 7p15 .

Acquired genomic alterations represent a potential source for a conferred survival advantage to sloughed endometrial cells in the establishment of endometriotic implants. The endometrium is a setting of extraordinary cell turnover and consequently, vulnerable to errors of genetic recombination. The occurrence of genomic alteration in eutopic endometrium is well documented, and may be consequent to epigenetic factors or oxidative stress . Loss of heterozygosity and somatic mutation of the tumor suppressor gene, PTEN, has been documented in 56% and 21% of solitary endometrial cysts of the ovary, respectively . Genomic alterations within endometriotic implants have been described using comparative genomic hybridization (CGH) microarrays . Interestingly, the CGH profiles (chromosome loss or gain) clustered by anatomic location of the implant as peritoneal or ovarian.

Finally, increasing evidence supports epigenetic regulation of steroid hormone action in the endometrium  and dysregulation in women with endometriosis. In particular, aberrant DNA methylation of promoters of genes whose products are critical for normal endometrial progesterone response have been reported in endometriosis and animal models of the disease, with resulting progesterone resistance . MicroRNAs (miRNAs) are short non-coding RNAs which generally repress gene expression through mRNA degradation. Differential and ovarian steroid dependent expression of miRNAs in eutopic endometrium from women with and without endometriosis has been demonstrated .

The search for an innate or acquired survival advantage of eutopic endometrium toward ectopic implantation has fueled a number of studies comparing eutopic endometrium from women with and without endometriosis. Collectively, these studies reveal striking differences in gene and protein expression that may predispose to disease development, and these have been nicely synopsized recently. Validation of these genes/proteins requires temporally controlled experiments that can only be conducted using preclinical models such as the non-human primate, the only other species documented to spontaneously develop endometriosis .

 

Table 1

Candidate factors implicated in the pathophysiology of endometriosis

Gene

Function

17βHSD-2

Hydroxysteroid dehydrogenase

BCL-2

Anti-apoptosis

CYP19

Aromatase enzyme

HOXA10

Transcription factor

IL-6

Cytokine

KRAS

Oncogene

MMP 3,7

Matrix metalloproteinases

NF-KB

Transcription factor

PGE2

Prostaglandin

PTEN

Tumor suppressor gene

TGF-B

Cytokine

TNF-α

Cytokine

Altered hormonal milieu: estrogen dependence and progesterone resistance

Hormonal alterations may influence the ability of endometrial cells to proliferate, attach to the mesothelium and/or evade immune mediated clearance. Long appreciated clinically, the concept of endometriosis as an estrogen dependent disorder is well supported by molecular evidence . A striking finding in endometriotic tissue relative to eutopic endometrium is the increased expression of the aromatase enzyme and decreased expression of 17β-hydroxysteroid dehydrogenase (17β-HSD) type 2 . The sum consequence of this differential expression profile is a marked increase in the locally bioavailable estradiol concentration. Estradiol stimulates the production of prostaglandin E2 which further stimulates aromatase activity . These findings support the capacity of endometriotic lesions for estradiol biosynthesis, and substantiate treatments aimed at promoting a hypoestrogenic peritoneal microenvironment.

In addition to estrogen dependence, there is increasing evidence to support a profile of progesterone resistance in the pathophysiology of endometriosis . Endometriotic lesions exhibit an overall reduction in progesterone receptor expression relative to eutopic endometrium, and an absence of progesterone receptor-B . Additionally, endometrial expression profiling has documented dysregulation of progesterone responsive genes in the luteal phase . An incomplete transition of endometrium from the proliferative to secretory phase has significant molecular implications toward enhancing the survival and implantation of refluxed endometrium.

Evasion from immune clearance

Normally, refluxed endometrial tissue is cleared from the peritoneum by the immune system, and the dysregulation of this clearance mechanism has been implicated in the predisposition to implantation and growth of endometrial cells. Interestingly, larger tissue fragments as opposed to individual cells demonstrate an increased capacity to implant, presumably due to the protection from immune clearance afforded the cells residing on the inner aspects of such fragments . Additionally, the eutopic endometrium from women with endometriosis was found to be more resistant to lysis by natural killer (NK) cells than the eutopic endometrium from women without disease . Subsequent studies identified the constitutive shedding of intercellular adhesion molecule-1 (ICAM-1) by endometrial stromal cells from women with endometriosis as the potential mechanism by which these cells escape NK cell mediated clearance . Impaired NK cell function may confer an immune-priveleged status to the refluxed endometrial cells, thereby predisposing to disease. Compromised macrophage function in women with endometriosis (below) may further contribute to decreased clearance of lesions by this cell type.

Further support for a fundamentally altered immune system in the predisposition to endometriosis is derived from studies demonstrating a high concordance of autoimmune (systemic lupus erythematosus, rheumatoid arthritis, Sjogren’s syndrome, autoimmune thyroid disease) and atopic disease (allergies, asthma and eczema) in affected women . A number of non-organ specific antibodies have been found in association with endometriosis . Several studies have demonstrated clustering of autoimmune thyroid disease with endometriosis associated infertility, as evidenced by a high prevalence of positive anti-TPO titer in this cohort of women .

Endometrial cell attachment and invasion

Though endometriosis is a benign disorder, the process by which endometrial cells attach and invade surfaces shares features of malignancy. The endometrial stromal cell (ESC) fraction is primarily involved in the interaction of endometrial tissue with the mesothelial cell lining of the peritoneum. A study using ESCs and peritoneal mesothelial cells (PMCs) from a variety of sources in an in vitro binding assay demonstrated that the source of the endometrial stromal cells rather than the source of the peritoneal cells had the greatest impact on the rate of implantation .

A heritable or acquired condition of the peritoneum may predispose to the attachment and trans-mesothelial invasion by refluxed endometrial cells. An intact mesothelium is likely to act as a protective barrier against the implantation of regurgitated endometrial tissue. Indeed, in vitro studies showed that endometrial fragments adhered to the peritoneum only at locations where the basement membrane or extracellular matrix was exposed due to mesothelial layer damage . Menstrual effluent has a harmful effect on the mesothelium, and may autologously induce the local injury that promotes the implantation of endometrial cells . However, the exact factors involved in mediating mesothelial damage are unknown. Gene expression profiling of the peritoneum from subjects with and without endometriosis demonstrated upregulation of MMP-3 during the luteal phase and upregulation of ICAM-1, transforming growth factor-beta (TGF-β) and IL-6 during the menstrual phase . The differential expression of these cytokines and growth factors may create a microenvironment that encourages implantation of endometrial cells or protects them from immune mediated clearance. Among the cytokines that are elevated in the peritoneal fluid of women with endometriosis , TGF-β was observed to induce endometrial cell invasion in an in vitro model of the peritoneum .

Matrix metalloproteinases (MMPs) and their inhibitors (tissue inhibitors of metalloproteinases, TIMPs) are involved in extracellular matrix remodeling and have been implicated in cyclic endometrial turnover and menstruation . Menstrual cycle phase specific expression of MMPs suggests ovarian steroid regulation. The balance between MMPs and TIMPs is critical in maintaining the appropriate level of MMP activity, and failure to maintain this balance may contribute to matrix breakdown and cellular invasion. Endometrial MMP-7 expression is normally suppressed by progesterone during the secretory phase, yet endometriotic lesions exhibit persistent expression of MMP-7 during this phase . In a compelling illustration of intrinsic progesterone resistance in the pathophysiology of endometriosis, the in vitro treatment of eutopic endometrium acquired from affected women with progesterone failed to fully suppress pro-MMP-7 secretion and failed to prevent the ability of the transplanted endometrium to establish experimental disease in mice .

Lesional neuroangiogenesis and growth

A rich vascular supply is necessary for the development and sustenance of endometriotic lesions, particularly in the peritoneal microenvironment which is relatively avascular compared to the eutopic endometrium. Neoangiogenesis and capillary recruitment are visibly associated with endometriotic lesions at laparoscopy, most notably in the context of the red vesicular phenotype . In addition, nerves frequently accompany angiogenesis (neuroangiogensis), likely contributing to pain associated with this disorder . Gene expression profiling of menstrual phase endometrium in women with endometriosis demonstrated upregulation of tumor necrosis factor-α (TNF-α), interleukin-8 (IL-8) and MMP-3 . As IL-8 and TNF-α promote proliferation and adhesion of endometrial cells and angiogenesis, an overabundance of these cytokines may facilitate growth and local neovascularization. Vascular endothelial growth factor (VEGF) has been consistently detected in high concentration in peritoneal fluid from women with endometriosis, and the level appears to correlate with stage of disease . VEGF is abundantly expressed in the glandular compartment of peritoneal implants, in endometriomas, and is secreted by activated peritoneal macrophages . The expression of VEGF exhibits a cycle phase dependence consistent with ovarian steroid regulation. Evidence for VEGF as the prominent angiogenic factor is compelling. Other angiogenic factors implicated in disease pathophysiology include angiogenin , platelet-derived endothelial growth factor , and macrophage migration inhibitory factor .

 

Red vesicular lesions with focal hemorrhage observed on the posterior aspect of the broad ligament. Note prominent focal vascularity in immediate vicinity of lesions.

Growth factors may play a fundamental role in stimulating ectopic endometrial growth and differentiation. Hepatocyte growth factor is a mitogen and morphogen for endometrial epithelial cells when co-cultured with stromal cells and may play a role in the regeneration of endometrial glands in ectopic locations . Epidermal growth factor (EGF) , insulin-like growth factors (IGF) , platelet derived growth factor , and basic fibroblast growth factor  are potent mitogens for endometrial stromal cells in vitro. IGF-1 is an anti-apoptotic growth factor and may enhance cell survival. EGF and IGF mediate estrogen actions in many tissues and, thus, are potential participants in the pathophysiology of endometriosis.

Inflammation

Increasing evidence supports conceptualization of endometriosis as a pelvic inflammatory condition. In women with endometriosis, the peritoneal fluid is remarkable for an increased number of activated macrophages and important differences in the cytokine/chemokine profile. A proteomics approach identified a unique protein structurally similar to haptoglobin in the peritoneal fluid of patients with endometriosis. This protein was subsequently found to bind to macrophages, reduce their phagocytic capacity and increase their production of interleukin 6. Other cytokines or chemokines found to be increased in the peritoneal fluid of patients with endometriosis include macrophage migration inhibitory factor, TNF-α , IL-1β, IL-6, IL-8, regulated on activation, normal T expressed and secreted (RANTES), and monocyte chemoattractant protein-1 (MCP-1) . The latter three are chemoattractants, which facilitate the recruitment of macrophages. Whether observed cytokine profiles are a cause or a consequence of endometriosis remains to be definitively determined. The non-human primate model of endometriosis may allow the dissection of the temporal relationship between lesional development and cytokine profiles.

The peritoneal microenvironment in the setting of endometriosis is notably rich in prostaglandins, and these mediators likely play a central role in disease pathophysiology as well as clinical sequelae of pain and infertility. Peritoneal macrophages from women with endometriosis express higher levels of cyclo-oxygenase-2 (COX-2) and release significantly higher amounts of prostaglandins than macrophages from healthy women. At the lesional level, TNF-α promotes endometrial cell production of prostaglandin Fand prostaglandin E2 .IL-1β activation of COX-2 increases production of PGE2 which activates steroidogenic acute regulatory (StAR) and aromatase. By upregulating PGE2 synthesis, estrogen completes a positive feedback loop that promotes the increased local bioavailability of estradiol.This pathway highlights the interplay of estrogen dependence and inflammation in endometriosis.

Inflammation is not only present in the peritoneal microenvironment, but also in the eutopic endometrium of women with endometriosis. As progesterone has well described anti-inflammatory properties, these changes may reflect attenuated progesterone action at the level of the endometrium. An increase in macrophage numbers is present in women with endometriosis throughout the menstrual cycle. Compared to disease-free controls, eutopic endometrium from women with endometriosis showed an increased basal production of interleukin-6. IL-6 plays a prominent role in many chronic inflammatory conditions and is secreted by macrophages as well as epithelial endometrial cells. Interestingly, IL-6 was shown to significantly stimulate aromatase expression in cultured endometriotic stromal cells.

The inflammatory environment within the pelvis may contribute to the pathophysiology of pain perception in symptomatic women with endometriosis. It is believed that nerve fibers in endometriosis implants influence dorsal root neurons within the central nervous system, increasing pain perception in patients. The pathophysiology of pain has recently been extensively reviewed .

 

 

 

Figure 3

Local estradiol production in endometriotic lesions and eutopic endometrium, inflammation, and pain. 17βHSD = 17β hydroxysteroid dehydrogenase; E1=estrone; E2=estradiol; PGE2=prostaglandin E2; PGF2α=prostaglandin F; NGF= nerve growth factor.

Lesional progression and sequelae

Clinical and molecular lines of evidence converge to support a stagewise phenotypic progression associated with peritoneal endometriotic lesions. These stages include red vesicular, black powder-burn, and fibrotic lesional phenotypes. Longituginal placebo-controlled trials with second look laparoscopy have demonstrated that 71-83% of untreated lesions will progress or remain stable over a 12-month period . The earliest lesion is the red vesicular subtype. Red vesicular lesions have been cytoarchitecturally defined as a cluster of communicating glands , are more biochemically active than black powder-burn lesions , and may be more responsive to cyclic sex hormones than other lesion subtypes . Laparoscopy timed to menstruation has observed these lesions to be focally hemorrhagic in response to progesterone withdrawal . MMP-1 is expressed focally in red peritoneal lesions regardless of the menstrual phase, but not in black peritoneal lesions . Foci of MMP-1 expression closely correlate with matrix breakdown and with the absence of progesterone receptors in adjacent epithelial cells, suggesting MMP-1 expression may be involved in tissue remodeling and bleeding of these early endometriotic lesions. Lesional bleeding could be the precursor to development of fibrin mediated adhesions . Most lesions evolve toward cicatrisation. A temporal progression of peritoneal lesions from red vesicular to fibrotic stages is supported by a large prospective surgical study finding red vesicular lesions predominantly in younger (20-25 year old) women and white plaques predominantly in older (41-45 year old) women . The cyclic inflammatory reaction to the peritoneal endometriotic lesion may result in a peritoneal defect referred to as an Allen-Masters window, a finding more frequently encountered in women with endometriosis

 

 

 

Tumor necrosis factor and endometriosis

TNF-α, a pro-inflammatory cytokine, was one of the early non-hormonal targets for potential endometriosis therapy It was first demonstrated to be elevated in the peritoneal fluid and serum  of women with endometriosis but is now known to be produced by several cell types, including cells of the endometriotic lesion. In vitro studies demonstrated that this cytokine stimulated cellular events conducive to the establishment and progression of endometriosis, such as adhesion and induction of protease and inflammatory mediators.

Based upon these observations, initial studies evaluated the efficacy of targeting TNF-α as a potential treatment for endometriosis. The first studies tested a recombinant human TNF-α-binding protein (rhTBP-1) in a rat model of endometriosis; these were followed by a series of studies using rhTBP-1 in a baboon model of endometriosis. Unfortunately, studies showing a reduction in disease burden in experimental models have not paralleled studies on efficacy of anti-TNF-α therapy for endometriosis symptomology, as summarized by Lu and colleagues in a recent Cochrane Database review . Thus, studies on the use of anti-TNF-α have stalled and no new data have emerged to support the use of such compounds for the treatment of symptomatic endometriosis.

The discrepancy between the encouraging results reported in experimental animal model studies and the lack of an effect detected in clinical trials likely stems from the differences in endpoint analysis. Experimental animal model studies focused primarily on reduced disease burden/lesion size, whereas the clinical trials have focused on the alleviation of pain. Unfortunately, it is unclear whether anti-TNF-α therapy reduced disease burden (stage of endometriosis) in women who received these compounds. We do know from these trials that anti-TNF-α therapy does not reduce pain, which is a chief complaint associated with the disease. The fact that pain is a symptom that is strongly associated with disease presence, but not with disease burden, does not allow conclusions to be drawn with respect to potential impact (or lack of impact) on disease stage in these patients. In animal models, although we do know there is a reduction in disease burden, we do not know whether there is a reduction in pain in those animals treated with anti-TNF-α therapies. Induction of experimental endometriosis in animal models has been demonstrated to elicit pain, initially described in rats by independent groups and more recently in a mouse model 26. Unfortunately, these early studies on anti-TNF-α therapy were conducted prior to the validation of rodent models of pain assessment in animals with experimentally induced endometriosis. One lesson from these studies is that a focus on multiple clinically relevant endpoints in the animal models would be of benefit. Another lesson is that we lack non-surgical clinical biomarkers of disease burden that would be of great use in human studies.

Despite this uncertainty on the role and potential therapeutic benefits of targeting inflammatory mediators such as TNF-α, there is still considerable interest in studying the role of pro-inflammatory mediators in the pathogenesis of endometriosis and the potential benefit of targeting these molecules. Although the initial excitement of anti-TNF-α therapy has waned, additional research on other mediators of inflammation has intensified. Targets getting increased attention are MIF and PGE2.

Macrophage migration inhibitory factor and endometriosis

Like TNF-α, MIF is elevated in the peritoneal fluid circulation , and peritoneal macrophages from women with endometriosis. MIF is also expressed in active and early/stage I endometriotic lesions , as well as overexpressed in eutopic endometrium in women with the disease . Within endometriotic lesion cells, MIF is induced by estrogen, and we have recently demonstrated that MIF expression is associated with endometriotic lesion survival status in women with the disease.

MIF was originally identified as a potent mitogenic factor for human endothelial cells in vitro and tumor angiogenesis in vivo. Yang and colleagues demonstrated that, in patients with endometriosis, MIF could stimulate endothelial cell proliferation. Further supporting a role of MIF in endometriotic lesion survival, MIF has been shown to stimulate PGE2, COX-2, vascular endothelial growth factor (VEGF), interleukin-8 (IL-8), and monocyte chemotactic protein-1 (MCP-1) expression, as well as the induction of aromatase expression in a feed-forward mechanism . Interestingly, MIF also stimulates TNF-α secretion , whereas TNF-α is also capable of inducing MIF production  in endometrial cells. Thus, it is tempting to speculate that a feed-forward amplification of these cytokines and their downstream pathways exists in endometriosis. Also of relevance to the pathophysiology of endometriosis is the demonstration that many of these MIF-induced factors are associated with a proliferative and angiogenic phenotype conducive to endometriotic establishment or growth (or both). As such, there is ample evidence to suggest a strong association between elevated MIF expression/levels and endometriosis in vivo, as well as in vitro evidence which indicates that MIF can induce factors which are believed to be essential for endometriosis development and survival.

Building upon these initial observations, several studies have evaluated the efficacy of targeting MIF as a potential endometriosis treatment. In 2011, we first reported the utility of targeting MIF as a potential therapy for endometriosis . In that study, we used an experimental mouse model of endometriosis in which the females were immune-competent and reproductively intact (non-ovariectomized and non-estrogen-supplemented) and harbored endometriotic lesions derived from donor wild-type mice. We demonstrated that the MIF antagonist, ISO-1, could induce a significant reduction in lesion size. Of potential clinical significance was the finding that ISO-1 reduced lesion burden without affecting reproductive cyclicity or presumed estrogen action Using a mouse model for endometriosis in which immune-compromised mice harbored endometriotic lesions derived from human tissue, Khoufache and colleagues demonstrated a similar ability of ISO-1 to decrease the number, size, and dissemination of endometriotic lesions. Furthermore, they demonstrated that inhibition of MIF by ISO-1 impedes lesion dynamics by inhibiting cell adhesion, tissue remodeling, angiogenesis, and inflammation, in addition to altering the balance of pro- and anti-apoptotic factors. More recently, this group provided additional proof of principal by using an ovariectomized, estrogen-supplemented mouse model for endometriosis incorporating Mif-deficient mice as both tissue recipient and tissue donors . Consistent with previous studies in mouse models, both pharmacologic inhibition of MIF (with ISO-1) and genetic ablation ofMif ( Mif-deficient mice) induced a reduction in lesion burden. Of notable interest was the demonstration that Mif-deficient hosts that harbored either normal (expressing Mif) or Mif-deficient lesions had impaired lesion growth, strongly suggesting the critical importance of Mif in the pathogenesis of endometriosis.

Initial studies evaluating ISO-1 as a therapeutic agent for endometriosis treatment are encouraging as the MIF antagonist reduces lesion burden in mouse models which harbor both mouse and human tissue, demonstrating efficacy. Furthermore, this inhibitory effect of MIF antagonism occurs independently of reproductive cyclicity/estrogen levels and action, and may permit continuation of reproductive cycles while relieving disease burden. Clearly, studies are warranted to evaluate whether these beneficial effects of ISO-1 can be extended to alleviating the pain associated with endometriosis in animal models with the extension of MIF antagonist into clinical trials.

 

In addition to regulating cytokine production, MIF has been shown to stimulate PGE 2 production . PGE2 has been proposed as a master regulator of endometriosis  on the basis of its pro-inflammatory actions. PGE 2 and the biosynthesis enzymes responsible for its liberation are elevated in human endometriotic lesion tissue as well as peritoneal macrophages  and peritoneal fluid from women with endometriosis. In vitro studies support a role for PGE 2 in the mechanisms conducive to endometriosis establishment and survival. For example, selective inhibition of the PGE 2 receptors, prostanoid receptor-2 and (EP2) and EP4, inhibits cellular adhesion, invasion, growth, and survival of human endometriotic epithelial and stromal cells in vitro.

Inhibition of PGE 2 action has also been associated with favorable outcome in experimental animal models of endometriosis. Using a hamster model of endometriosis, Laschke and colleagues  demonstrated that administration of the selective COX-2 inhibitor, NS398, induced a marked regression of ectopic lesions by inhibiting angiogenesis and suppressing cellular proliferation and inducing apoptosis. More recently, Arosh and colleagues incorporated mouse models of endometriosis and demonstrated that selective inhibition of the PGE 2 receptors EP2/EP4 decreased growth and survival, as well as angiogenesis and innervation of ectopic lesions. Furthermore, inhibition of PGE 2 signaling was associated with suppression of the pro-inflammatory state of dorsal root ganglia neurons and decreased pelvic pain as well as a decrease in the pro-inflammatory, estrogen-dominant, and progesterone-resistant molecular environment of the eutopic endometrium and ectopic lesions. There are also clinical data which demonstrate that use of rofecoxib, a COX-2 inhibitor (at 25 mg per day for 6 months), resulted in a significant improvement in pelvic pain and dyspareunia after the course of treatment in women with disease, both by comparison with pre- and post-treatment as well as compared with pain assessment in subjects receiving placebo only . Given that PGE2 is induced by both MIF and TNF-α, it is tempting to speculate that inhibition of these cytokines and the reduction in lesion burden may have been due at least in part to reduction in PGE2 levels or action (or both).

Estrogen receptor-beta and endometriosis

As mentioned earlier in this review, it is well established that endometriosis is an estrogen-dependent disease and that there is a strong connection between estrogen and the inflammatory environment associated with the disease. However, the complex downstream mediators which impart the pathophysiology of the disease are only partially understood. ER-β is one of the two nuclear receptors that mediate estrogen action. Within the context of endometriosis, ER-β is significantly higher (over 100-fold) in endometriotic lesion tissue compared with eutopic endometrium, and this may be due to altered methylation in the gene promoter. This overexpression of ER-β leads to a decrease in ER-α expression, resulting in an abnormally high ER-β-to-ER-α ratio which is associated with elevated endometriotic lesion COX-2 levels. Activation of ER-β has also been demonstrated to induce MIF expression by endometriotic lesion cells. Thus, estrogen acting through ER-β-stimulated pathways may play a role in the pathophysiology of endometriosis. Given that endometriosis is an estrogen-dependent disease, inhibition of this pathway might be anticipated to suppress lesion survival and symptoms of endometriosis. If so, one would anticipate that inhibition of ER-β-mediated signaling, though effective in reducing endometriotic lesion burden, may also be associated with an induction of a hypo-estrogenic state, with resultant adverse effects, including menopausal signs and symptoms and loss of reproductive cyclicity.

Three studies to date have evaluated the use of ER-β ligands in the potential treatment of endometriosis using experimental animal models. An early study by Harris and colleagues used an ER-β-specific agonist (ERB-041) in an experimental mouse model of endometriosis and reported a regression of ectopic lesion growth. Assessment of lesion tissue (derived from human endometrium) revealed a lack of ER-β expression, leading the authors to conclude that ERB-041 exerted its effects on the host immune system, rather than on the implanted tissue, possibly by induction of apoptosis. Unfortunately, the investigators did not elaborate on the mechanism by which this occurred. As activation of ER-β decreases ER-α expression, it may be possible that downregulation of ER-α contributed to these observations.

More recently, Zhao and colleagues elegantly dissected the role of both ER-α and ER-β signaling by using an experimental mouse model of endometriosis incorporating the novel ER ligands chloroindazole (CLI) (exhibits ER-β-dependent activity) and oxabicycloheptene sulfonate (OBHS) (greater ER-α-preferential binding selectivity) which exhibit both anti-estrogenic and anti-inflammatory activity. Most importantly, both CLI and OBHS induced lesion regression and suppression of inflammatory events associated with endometriosis without disrupting normal reproductive cyclicity and fertility. Thus, the anti-estrogenic/antagonistic effect of these ligands suggests that the ER-β (and ER-α) pathway is involved in the pathogenesis of endometriosis, and that the effects of estrogen antagonism can be separated between those that impact inflammation and lesion regression and those that regulate reproductive cyclicity and fertility.

This postulate is further supported by the work of Han and colleagues, who demonstrated that activation of the ER-β pathway may contribute to the pathogenesis of endometriosis. Using experimental mouse models of endometriosis which incorporate genetically modified mice in which ER-α and ER-β are conditionally deleted, these investigators demonstrated that use of the ER-β antagonist, PHTPP, was associated with a regression of ectopic lesions. These investigators went on to dissect the mechanism by using experimental endometriosis models that incorporated genetically modified mice which either overexpressed ER-β, or had ER-α or ER-β (or both) deleted from uterine/endometriotic tissue. This study demonstrated that ER-β is responsible for inhibiting endometriotic cell apoptosis and increases cytokine production to enhance cellular adhesion and proliferation as well as enhance epithelial-mesenchymal transition signaling to increase cell invasion. As suggested by Han and colleagues, and supported by the study by Zhoa and colleagues, targeting ER-β may have beneficial effects on lesion growth/survival as well as the potential to improve infertility at the level of the eutopic endometrium, or at least spare reproductive competency while reducing lesion burden. The potential efficacy of targeting ER-β/ER-α with these novel ligands to reduce pain associated with endometriosis remains to be determined, as does the assessment of the potential impact on bone density.

Laparoscopic Presacral Neurectomy

 

Presacral Neurectomy is the surgical removal of the presacral plexus, the group of nerves that conducts the pain signal from the uterus to the brain. Indicated for the treatment of central pelvic pain including severe dysmenorrhea, it was modified by Dr. Cotte to its current format.

Laparoscopic Presacral Neurectomy (LPSN) is the same procedure done by a minimally invasive method. It is a surgical approach in patients with central dysmenorrheal (painful periods), adenomyosis, and endometriosis.

Done through a small umbilical and bikini line incisions, LPSN is carried out by removing the nerve fibers that innervate the uterus, thus blocking the pathways for pain impulses to the brain. LPSN does not cure the pelvic pain that is lateral, which is related to the ovarian or other pelvic sidewall structures.

When performed correctly and in the appropriately chosen patient, the complications PSN are minimal and sometimes include constipation, urinary symptoms, or painless labor.

Central Pelvic Pain

Central pelvic pain (CPP) is reported in about 20 percent of menstruating females. Chronic pelvic pain refers to menstrual or non-menstrual pain of at least six months’ duration.

Dysmenorrhea

Dysmenorrhea, one of the most frequently reported gynecological problems, is characterized by sharp, intermittent spasms. Symptoms of headache, nausea, vomiting, diarrhea and fatigue are also present. Pain typically begins before or at the onset of menses.

The prevalence of the disorder is highest in adolescents with estimates ranging from 20-90 percent.

 

Risk Factors

Risk factors for the disorder include nulliparity, heavy menstrual flow, smoking, and depression.

Treatment

Medical therapy for dysmenorrhea includes NSAIDs (such as Motrin) and/or oral contraceptives. Approximately 10-25 percent of women with dysmenorrhea do not respond to medical management and may require surgical intervention, such as presacral neurectomy.

Strict selection of patients and adherence to the established protocol are the requirements for the successful presacral neurectomy (PSN), leading to the reported cure rates between 65 and 80 percent.

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