Molecular basis for treating endometriosis with aromatase inhibitors

Endometriosis: New Genetic Approaches and Therapy

Endometriosis is a relatively common condition in women of reproductive age and is associated with considerable morbidity. Despite an extensive literature describing its multiple clinical manifestations, their management, and many aspects of the biology of endometriotic lesions, the pathophysiological mechanisms involved remain poorly understood. A genetic component in endometriosis is now recognized, and several groups have taken up the challenge of using genetic techniques to identify the aberrant molecular and cellular mechanisms in endometriosis with the intention of providing much-needed insights that might, in turn, lead to new therapies. The techniques that have been applied include expression profiling, tumor genetic studies, functional candidate gene studies, and linkage studies that can adopt a hypothesis-free approach. This review describes the current status of these studies and explores the prospects for new therapies.

Lack of association between endometriosis and the CYP17 MspA1 polymorphism in UK and Japanese populations

Endometriosis is a complex trait, which means that multiple susceptibility genes interact with one another and the environment to produce the phenotype. One of the genes previously implicated in the disease is CYP17; this encodes the enzyme P450c17alpha, which plays a vital role in steroid biosynthesis in the ovary. The presence of a single nucleotide polymorphism (T-->C) in the 5'-promoter region of the gene creates a new recognition site for the restriction enzyme MspA1 producing a mutant allele (A2), which affects circulating estrogen levels. In this study, we compared the frequency of the CYP17 MspA1 polymorphism in two different ethnic populations. DNA was obtained from (1) 94 women with revised American Fertility Society (rAFS) stage III-IV endometriosis and 97 male blood donors in the UK, and (2) 130 women with rAFS stage III-IV endometriosis and 179 female newborn infants in Japan. No significant differences in allele or genotype frequencies were seen in either population. The genotype distribution in the UK population was 33/94 [35.1%] (cases) and 39/97 [40.2%] (controls) for A1A1 (homozygous wild-type); 43/94 [45.7%] (cases) and 44/97 [45.4%] (controls) for A1A2; and 18/94 [19.1%] (cases) and 14/97 [14.4%] (controls) for A2A2. The genotype distribution in the Japanese population was 31/130 [23.9%] (cases) and 57/179 [31.8%] (controls) for A1A1; 73/130 [56.2%] (cases) and 89/179 [49.7%] (controls) for A1A2; and 26/130 [20.0%] (cases) and 33/179 [18.4%] (controls) for A2A2. The CYP17 MspA1 polymorphism is probably not associated with endometriosis in either the UK or the Japanese population.

Endometriosis

Endometriosis is an oestrogen-dependent disorder that can result in substantial morbidity, including pelvic pain, multiple operations, and infertility. New findings on the genetics, the possible roles of the environment and the immune system, and intrinsic abnormalities in the endometrium of affected women and secreted products of endometriotic lesions have given insight into the pathogenesis of this disorder and serve as the background for new treatments for disease-associated pain and infertility. Affected women are at higher risk than the general female population of developing ovarian cancer, and they also may be at increased risk of breast and other cancers as well as autoimmune and atopic disorders. Clinicians should assess and follow up affected women for these and other associated disorders. There will probably be a new repertoire of approaches for treatment and perhaps cure of this enigmatic disorder in the near future.

Prevention by 17β-estradiol and progesterone of calcitonin gene-related peptide-induced elevation of skin temperature in castrated male rats

OBJECTIVES

To clarify the relationship between calcitonin gene-related peptide (CGRP) and ovarian hormones (17beta-estradiol and progesterone) in hot flashes in men who undergo androgen deprivation therapy for prostate cancer, we studied the effects of ovarian hormones on CGRP-induced elevation of skin temperature in castrated male rats. The results were compared with those from rats treated with testosterone replacement.

METHODS

Adult male rats were castrated by either a single injection of gonadotropin-releasing hormone analogue (Leuplin, 1.0 mg/kg, subcutaneously) or bilateral orchiectomy. The castrated animals were subcutaneously injected daily for 14 days with ovarian hormones, testosterone, or olive oil as the vehicle. On the day after the final administration of the drug, the changes in skin temperature induced by exogenous CGRP (10 mug/kg intravenously), serum testosterone concentration, and prostate weight were measured.

RESULTS

The CGRP-induced elevation of skin temperature was significantly greater in the castrated rats than in the sham-treated rats. This potentiation was significantly inhibited by treatment with ovarian hormones, as well as by testosterone replacement. The testosterone replacement restored decreases in both the serum testosterone level and the prostate weight due to castration; the treatment with ovarian hormones did not affect them.

CONCLUSIONS

17beta-Estradiol and progesterone, which do not confer testosterone activity on serum, may be useful for the treatment of hot flashes in patients for whom testosterone replacement therapy is contraindicated, such as those with prostate carcinoma. In addition, we suggest that CGRP is closely involved in the amelioration of hot flashes by ovarian hormones in men who undergo androgen deprivation therapy.

Regression of endometrial explants in rats treated with the cyclooxygenase-2 inhibitor rofecoxib

OBJECTIVE

To investigate the effects of cyclooxygenase-2 (COX-2) inhibitor rofecoxib on endometrial explants and on peritoneal vascular endothelial growth factor (VEGF) levels in the rat endometriosis model.

DESIGN

Prospective, placebo-controlled study.

SETTING

Laboratory at Dokuz Eylül University.

ANIMAL(S)

Twenty-six rats with experimentally induced endometriosis.

INTERVENTION(S)

Rats were treated for 3 weeks with oral rofecoxib (3 mg/kg per day; n = 9); single subcutaneous injection of depot leuprolide acetate (1 mg/kg; n = 9); or vehicle (control; n = 8).

MAIN OUTCOME MEASURE(S)

Change in explant area and histologic examination by semiquantitative analysis of endometriotic explants and measurement of peritoneal VEGF levels.

RESULT(S)

Three weeks of treatment with rofecoxib statistically significantly decreased the implant size (62.4%) compared with control (16.6%), and this effect was comparable with the decrease in leuprolide (64.3%). Histologic examination of the explants indicated mostly atrophy and regression in treatment groups, and semiquantitative analysis showed statistically significantly lower scores in rats treated with rofecoxib and leuprolide compared with controls. Both rofecoxib and leuprolide statistically significantly decreased VEGF levels compared with controls.

CONCLUSION(S)

Rofecoxib causes regression and atrophy of the endometriotic lesions and is as effective as a GnRH agonist with an accompanying decrease in the VEGF levels.

Cyclooxygenase enzymes and prostaglandins in reproductive tract physiology and pathology

Prostaglandins, thromboxanes (TX) and leukotrienes, collectively referred to as eicosanoids, are cyclooxygenase (COX) metabolites of arachidonic acid (AA). Prostaglandins, have been recognised for many years as key molecules in regulating reproductive tract physiology and pathology. Numerous recent studies in in vitro model systems and knockout mouse models have demonstrated specific functional roles for the respective cyclooxygenase enzymes, prostaglandins and prostanoid receptors. Here we review the findings obtained in several of these studies with emphasis on the roles played by cyclooxygenase enzymes and prostaglandins, specifically prostaglandin E2 (PGE2) and F2alpha in reproductive tract physiology and pathology.

New medical treatments for endometriosis

The medical treatment of endometriosis has long centered upon producing a hypoestrogenic environment by producing pituitary suppression or a progestin-dominant environment. However, as more is uncovered regarding the pathogenesis and pathophysiology of this disease, more targeted therapies can be developed. Current research has focused upon medications designed to attack specific aspects of the development and maintenance of endometriosis. These include progesterone receptor modulators, gonadotropin releasing hormone (GnRH) antagonists, aromatase inhibitors, tumor necrosis factor alpha (TNF-alpha) inhibitors, angiogenesis inhibitors, matrix metalloproteinase inhibitors, pentoxifylline (and other general immune modulators), and estrogen receptor beta agonists. It is hoped that this new wave of medications will improve the response to medical therapy for this disorder.

Endometriosis from thelarche to midteens: pathogenesis and prognosis, prevention and pedagogy

John Huffman, a founder of the subspecialty of pediatric and adolescent gynecology in North America, first related the diagnosis of endometriosis to thelarche. Subsequently, endometriosis was diagnosed in early puberty between thelarche and menarche. Based on solid evidence, we suggest that the theory of embryonic mullerian rests be added to currently accepted theories of pathogenesis of endometriosis. This article argues for recognition of embryonic mullerian rests as the pathogenesis of some cases of endometriosis not explained by accepted theories. Along with Huffman, we propose that thelarche be recognized as a developmental benchmark, after which endometriosis is included in the differential diagnosis of chronic pelvic pain. Thus, in an effort to refocus research and patient care to early adolescence, this review is limited to endometriosis occurring in young women from thelarche to their sixteenth birthday. Relating endometriosis to thelarche has fundamental implications for pathogenesis, early diagnosis, prognosis, treatment, education, and long-term care of adolescents.

Cyclooxygenase enzymes and prostaglandins in pathology of the endometrium

Prostaglandins are bioactive lipids produced from arachidonic acid by cyclooxygenase (COX) enzymes and specific terminal prostanoid synthase enzymes. After biosynthesis, prostaglandins exert an autocrine-paracrine function by coupling to specific prostanoid G protein-coupled receptors to activate intracellular signalling and gene transcription. For many years, prostaglandins have been recognized as key molecules in reproductive biology by regulating ovulation, endometrial physiology and proliferation of endometrial glands and menstruation. More recently, a role for COX enzymes and prostaglandins has been ascertained in reproductive tract pathology, including carcinomas, menorrhagia, dysmenorrhoea and endometriosis. Although the mechanism by which prostaglandins modulate these pathologies is still unclear, a large body of evidence supports a role for COX enzymes, prostaglandins and prostaglandin receptor signalling pathways in angiogenesis, apoptosis and proliferation, tissue invasion and metastases and immunosuppression. Here, an overview is provided of some of the findings from these studies with specific emphasis on the role of COX enzymes, prostaglandin E(2) and F(2alpha) in disorders of endometrial proliferation and menstruation in non-pregnant women.

Medical management of endometriosis-associated pain

In the coming years, basic science research into the mechanisms of endometriosis development and persistence almost certainly will open new avenues for treatment. A wide armamentarium of medical therapies already exists, however. The efficacy of most of these methods in reducing endometriosis-associated pain is well established. The choice of which to use depends largely on patient preference after an appropriate discussion of risks, side effects, and cost. Typically, oral contraceptives and NSAIDs are first-line therapy because of their low cost and mild side effects (Box 6). Because of its greater potential for suppressing endometrial development, consideration should be given to prescribing a low-dose monophasic oral contraceptive continuously. If adequate relief is not obtained or if side effects prove intolerable, consideration should be given to the use of progestins (oral, intramuscular, or IUD) or a GnRH agonist with immediate add-back therapy. Progestins are less expensive, but GnRH agonists with add-back may be better tolerated. If none of these medications proves beneficial or if side effects are too pronounced, then repeat surgery is warranted. The surgery may have analgesic value and serves to reconfirm the diagnosis. Finally, if endometriosis is identified at the time of surgery, then consideration should be given to prescribing medical therapy postoperatively.

Adolescent endometriosis

PURPOSE OF REVIEW

Endometriosis can exist in the adolescent female. It can be a very disruptive disease and cause significant dysfunction at a time in life when self-esteem, school attendance, and school performance are critical to achievement of life goals. Approaches to diagnosis and management in the recent literature are reviewed, focusing on those that apply directly to the adolescent or indirectly, by extrapolation from work done in the adult population. Practical strategies for adolescent patient care are presented.

RECENT FINDINGS

Recent research has focused on the efficacy of current treatment modalities and management of potential adverse side effects. Possible etiologies of endometriosis have been proposed, and therapies directed at those causes are being explored. Methods of diagnosis, both invasive and noninvasive, have been studied in order to determine the most effective way of diagnosing the disease.

SUMMARY

A better understanding of the etiology of endometriosis would probably assist in determining the most suitable treatment strategies. Future work in adolescent endometriosis should focus on developing safe, minimally invasive, yet definitive options for diagnosis and treatment.

Identification of Indian hedgehog as a progesterone-responsive gene in the murine uterus

Progesterone (P4) plays a central role in normal uterine function, from embryo implantation in endometrium to establishment and maintenance of uterine quiescence during pregnancy in the myometrium. Considering its diverse physiological effects on female reproductive function, rather little is known about downstream events of P4 action. Recent progress in differential screening technologies facilitated identification of such inducible genes. We used uteri of wild-type and progesterone receptor null mutant mice as a starting material and screened for differentially expressed genes by medium-density cDNA expression array. Here, we report that the expression of the morphogen, Indian hedgehog (Ihh), is rapidly stimulated by P4 in the mouse uterus. The level of Ihh mRNA is induced within 3 h, after a single administration of P4 to ovariectomized mice. The induced Ihh mRNA and protein were localized to the luminal and glandular epithelial compartment of the endometrium. During pseudopregnancy, the Ihh mRNA level was transiently increased in the preimplantation period and d 3 and d 4 post coitum and then decreased rapidly at d 5 post coitum. Furthermore, the expression profile of patched-1, hedgehog interacting protein-1, and chicken ovalbumin upstream promoter-transcription factor II, genes known to be in the hedgehog signaling pathway in other tissues, followed the expression pattern of Ihh during the periimplantation period. Our results suggested that Ihh is regulated by P4, and the Ihh signaling axis may play a role in the preparation of the uterus for implantation during the periimplantation period.

Endometriosis: novel etiopathogenetic concepts and clinical perspectives

OBJECTIVE

To discuss current ideas about therapy for endometriosis derived from new observations generated by using molecular biology techniques and in vivo animal models of disease.

METHOD(S)

The MEDLINE database was reviewed for English-language articles on new drugs that affect the endocrine or immunologic system, the possibility that endometriosis has multiple forms, and the association of endometriosis with cancer. Specific attention was given to in vivo studies in animals or humans.

CONCLUSION(S)

Among the novel potential candidate drugs, aromatase inhibitors and raloxifene should be considered for treatment of postmenopausal women with endometriosis. Notable observations have emerged from studies of immunomodulators and antiinflammatory agents in animal models of disease. These findings must be confirmed in women. The histogenesis of ovarian endometriomas is still unclear, thus limiting new experimental approaches to this form of disease. Given the low but established risk for malignant transformation of endometriosis, efforts should be directed toward identification of susceptibility loci for the disease and its potential transformation into cancer.

Structural determinants of aromatase cytochrome p450 inhibition in substrate recognition site-1

The porcine gonadal form of aromatase cytochrome P450 (P450arom) exhibits higher sensitivity to inhibition by the imidazole, etomidate, than the placental isozyme. The residue(s) responsible for this functional difference was mapped using chimeragenesis and point mutation analysis of the placental isozyme, and the kinetic analysis was conducted on native and mutant enzymes after overexpression in insect cells. The etomidate sensitivity of the placental isozyme was markedly increased by substitution of the predicted substrate recognition site-1 (SRS-1) and essentially reproduced that of the gonadal isozyme by substitution of SRS-1 and the predicted B helix. A single isoleucine (I) to methionine (M) substitution at position 133 of the placental isozyme (I(133)M) was proven to be the critical residue within SRS-1. Residue 133 is located in the B'-C loop and has been shown to be equally important in other steroid-metabolizing P450s. Single point mutations (including residues 110, 114, 120, 128, 137, and combinations thereof among others) and mutation of the entire B and C helixes were without marked effect on etomidate inhibitory sensitivity. The same mutation (I(133)M) introduced into human P450arom also markedly increased etomidate sensitivity. Mutation of Ile(133) to either alanine (I(133)A) or tyrosine (I(133)Y) decreased apparent enzyme activity, but the I(133)A mutant was sensitive to etomidate inhibition, suggesting that it is Ile(133) that decreases etomidate binding rather than Met(133) increasing enzyme sensitivity. Androstenedione turnover and affinity were similar for the I(133)M mutant and the native placental isozyme. These data suggest that Ile(133) is a contact residue in SRS-1 of P450arom, emphasize the functional conservation that exists in SRS-1 of a number of steroid-hydroxylating P450 enzymes, and suggest that substrate and inhibitor binding are dependent on different contact points to varying degrees.

The molecular basis for implantation failure in endometriosis: on the road to discovery

Endometriosis is a benign gynecologic disorder associated with pelvic pain and infertility, with the latter being due, in part, to failure of embryonic implantation in the maternal endometrium. Adequacy of the endometrium for fertility has been classically investigated by histologic evaluation of a mid-late luteal phase biopsy and, historically, normal histology has been reassuring. However, recent studies demonstrate histologically normal, but biochemically abnormal, endometrium during the window of implantation in some women with endometriosis. In the pregenomic era, a "one-by-one" approach has been adopted to investigate proteins and genes expressed in the window of implantation, and several genes or gene products have been found to be aberrantly expressed in endometrium of women with endometriosis either during the implantation window or at other times of the cycle. Some of these are related to failure of implantation, while others likely contribute to the establishment and growth of endometriotic lesions. The time has come for a genome-wide approach to evaluate uterine endometrium for embryonic implantation. Knowing the biochemical mechanisms underlying normal implantation and the abnormalities in endometriosis will facilitate development of new diagnostic criteria beyond histologic evaluation and will permit identification and validation of molecular targets for future drug discovery. This monograph reviews (a) some of the evidence of compromised fertility in women with endometriosis and treatments targeted to improve their fertility; (b) the concept of the window of implantation; (c) genes/gene products aberrantly expressed in endometrium during the window of implantation or other times of the cycle in women with endometriosis; and (d) the use of microarray technology to investigate endometrial gene expression in human endometrial stromal cells and preliminary data resulting from a collaborative consortium effort of a genome-wide investigation of gene expression in the window of implantation of women with versus without endometriosis.

Selective progesterone receptor modulators (SPRMs): a novel therapeutic concept in endometriosis

Endometriosis, the presence of endometrial tissue outside the uterus, is a progressive, estrogen-dependent disease and occurs nearly exclusively in menstruating women of reproductive age. Pain syndrome, however, represents the major clinical problem of this disease, manifested as dysmenorrhea, pelvic pain, lower abdominal pain, and dyspareunia. The manifestation of the disease, that is, the pain syndrome, rather than the disease itself currently represents the major indication for both the medical and surgical therapies of endometriosis. The major drawbacks of current medical therapies of endometriosis are sometimes severe side effects. In this review, selective progesterone receptor modulators (SPRMs, mesoprogestins) as a potential therapeutic concept in endometriosis are discussed. Due to endometrial selectivity and favorable pharmacological profile, SPRMs may have advantages over the current medical treatments of this disease. Other emerging therapeutic approaches for this disease are also mentioned.

New considerations for the pathogenesis of endometriosis

OBJECTIVES

To review the available evidence regarding the immunological, epidemiological and other factors involved in the pathogenesis of endometriosis.

METHODS

Literature review.

RESULTS

Endometriosis remains a poorly-understood disease of unknown etiology and pathogenesis.

CONCLUSIONS

There is evidence to suggest that alterations in the immune response, whether genetically transmitted or environmentally induced, predispose women to the ectopic implantation of endometrial cells transported into the peritoneal cavity by way of retrograde menstruation. This predisposition may exist because of an impaired peritoneal clearing of endometrial cells and fragments or because of pathological angiogenesis.