Effect of pelvic endometrial implants on overall reproductive functions of female rats

Diminished Ovarian Reserve in Endometriosis: Insights from In Vitro, In Vivo, and Human Studies-A Systematic Review

Endometriosis, a prevalent disorder in women of reproductive age, is often associated with undesired infertility. Ovarian reserve, an essential measure of ovarian function that is crucial for maintaining fecundity, is frequently diminished in women with endometriosis. Though the causative relationship between endometriosis and reduced ovarian reserve is not fully understood due to the lack of standardized and precise measurements of ovarian reserve, there is ongoing discussion regarding the impact of interventions for endometriosis on ovarian reserve. Therefore, in this review, we investigate articles that have related keywords and which were also published in recent years. Thereafter, we provide a comprehensive summary of evidence from in vitro, in vivo, and human studies, thereby shedding light on the decreased ovarian reserve in endometriosis. This research consolidates evidence from in vitro, in vivo, and human studies on the diminished ovarian reserve associated with endometriosis, as well as enhances our understanding of whether and how endometriosis, as well as its interventions, contribute to reductions in ovarian reserve. Furthermore, we explore potential strategies to modify existing therapy options that could help prevent diminished ovarian reserve in patients with endometriosis.

Endometriosis-associated infertility: From pathophysiology to tailored treatment

Despite the clinically recognized association between endometriosis and infertility, the mechanisms implicated in endometriosis-associated infertility are not fully understood. Endometriosis is a multifactorial and systemic disease that has pleiotropic direct and indirect effects on reproduction. A complex interaction between endometriosis subtype, pain, inflammation, altered pelvic anatomy, adhesions, disrupted ovarian reserve/function, and compromised endometrial receptivity as well as systemic effects of the disease define endometriosis-associated infertility. The population of infertile women with endometriosis is heterogeneous, and diverse patients' phenotypes can be observed in the clinical setting, thus making difficult to establish a precise diagnosis and a single mechanism of endometriosis related infertility. Moreover, clinical management of infertility associated with endometriosis can be challenging due to this heterogeneity. Innovative non-invasive diagnostic tools are on the horizon that may allow us to target the specific dysfunctional alteration in the reproduction process. Currently the treatment should be individualized according to the clinical situation and to the suspected level of impairment. Here we review the etiology of endometriosis related infertility as well as current treatment options, including the roles of surgery and assisted reproductive technologies.

What We Have Learned from Animal Models to Understand the Etiology and Pathology of Endometrioma-Related Infertility

Endometrioma (OMA) is the most common subtype of endometriosis, in which the endometriotic lesions are implanted in the ovary. Women with OMA are usually associated with infertility, presenting with reduced ovarian reserve, low oocyte quantity and quality, and poor fertility outcomes. However, the underlying pathological mechanisms in OMA-related infertility are still unclear. Due to the limitations and ethical issues of human studies in reproduction, animal models that recapitulate OMA characteristics and its related infertility are critical for mechanistic studies and subsequent drug development, preclinical testing, and clinical trials. This review summarized the investigations of OMA-related infertility based on previous and latest endometrioma models, providing the possible pathogenesis and potential therapeutic targets for further studies.

Novel therapeutic targets to improve IVF outcomes in endometriosis patients: a review and future prospects

BACKGROUND

Patients with endometriosis often experience infertility and have poor IVF outcomes, with low fertilization and pregnancy rates. Although many theories have tried to explain the mechanisms underlying infertility in these patients, none of them is conclusive.

OBJECTIVE AND RATIONALE

In this review, we discuss the pathologic mechanisms through which endometriosis likely leads to infertility along with the therapeutic options used to date to treat endometriosis-related infertility and, thereby, to improve IVF outcomes in patients with endometriosis.

SEARCH METHODS

We performed a comprehensive literature search of clinical outcomes in endometriosis and the molecular mechanisms contributing to oocyte quality using the PubMed database to identify human and animal studies published from 1992 until September 2020. In total, 123 manuscripts were included.

OUTCOMES

While some theories propose that endometriosis patients may have fertility problems as a result of decreased endometrial receptivity, others reinforce the idea that infertility could be associated with oocyte alterations and lower implantation rates. Single-cell RNA sequencing of oocytes from patients with endometriosis has identified dysregulated mechanisms involved in steroid metabolism and biosynthesis, response to oxidative stress and cell cycle regulation. Dysregulation of these mechanisms could result in the poor IVF outcomes observed in patients with endometriosis. Further, impaired steroidogenesis may directly affect oocyte and embryo quality. Increased oxidative stress in patients with endometriosis also has a detrimental effect on the follicular microenvironment, inducing cell cycle dysregulation in oocytes, poor oocyte quality, and infertility. Moreover, granulosa cells in the context of endometriosis undergo increased apoptosis and have an altered cell cycle that could adversely affect folliculogenesis, oocyte and embryo quality, and IVF outcomes. Endometriosis is also associated with inflammatory damage and impaired angiogenesis, which could be directly correlated with poor IVF outcomes. While therapeutic options using GnRH analogues, progestins and aromatase inhibitors do not improve endometriosis-related infertility, anti-inflammatory agents and antioxidant supplementation could improve oocyte quality as well as implantation and clinical pregnancy rates in patients with endometriosis.

WIDER IMPLICATIONS

Endometriosis is a heterogeneous disease whose pathogenesis is complex and could affect fertility by altering a collection of molecular mechanisms in oocytes. Thus, a single model is not sufficient to describe endometriosis-related infertility. Dysregulation of steroidogenesis, oxidative stress, cell cycle progression, inflammation and angiogenesis in the follicular environment and oocytes in individuals with endometriosis are all possible contributors to endometriosis-related infertility. Therefore, treatments targeting these mechanisms could be therapeutic alternatives to improve IVF outcomes for these patients.

Identifying Mechanisms of Endometriosis-Associated Reduced Fecundity in a Rat Model: Novel Insights toward Understanding Human Infertility

The existence of endometriosis has been known since at least the nineteenth century, yet the lack of understanding of causes of infertility and therefore inadequate treatment approaches in endometriosis creates a significant challenge in reproductive medicine. Women worldwide suffer not only pain and infertility but also economical, societal, and physiological burdens. Studies of reproductive events in women are difficult to conduct due to a host of confounding personal and environmental factors and ethically limited due to the very nature of working with reproductive tissues and cells, especially embryos. Animal models are a viable adjunct to study mechanisms causing human reproductive anomalies and infertility in endometriosis. This chapter discusses reproductive anomalies causing infertility in endometriosis and well-established animal models which help decipher the problems and lead to heretofore unknown nonsurgical, nonhormonal methods to manage endometriosis in women. In addition, studies of effects of developmental exposure to endometriosis are revealing for the first time, in both female and male offspring, transgenerational subfertility in a rat model providing insights into the familial nature of endometriosis and possible epigenetic involvement.

Dose-Dependent Decreased Fertility in Response to the Burden of Endometriosis in a Murine Model

Endometriosis is a gynecological disease caused by the growth of endometrial cells outside the uterus leading to inflammation, pelvic pain, and infertility. The relationship between the amount of ectopic uterine tissue growth and the severity of symptoms is still unclear. The presence or degree of pain and infertility does not correlate with the stage of disease as currently defined. Here, we report a clear dose-response relationship between the amount of ectopic tissue transplanted and the reproductive outcomes in a murine model of endometriosis. Endometriosis was induced in mice using various amounts of transplanted uterine tissue. Four groups of mice consisted of a sham surgery control or those transplanted with 1, 2, or 4 endometrial segments of 5 mm each. Pregnancy rates were significantly lower in those transplanted with 2 or 4 segments compared to sham or the 1 segment groups. We demonstrate that infertility does correlate with the extent of active disease. Current clinical staging systems do not account for disease activity and may inappropriately weight sequela of disease. Early recognition and treatment in women may help to minimize the effect of endometriosis on fertility. Here, we describe a mouse model of endometriosis and infertility that may be useful to elucidate the mechanisms of infertility in endometriosis.

Effect of induced peritoneal endometriosis on oocyte and embryo quality in a mouse model

PURPOSE

To assess the impact of peritoneal endometriosis on oocyte and embryo quality in a mouse model.

METHODS

Peritoneal endometriosis was surgically induced in 33 B6CBA/F1 female mice (endometriosis group, N = 17) and sham-operated were used as control (sham group, N = 16). Mice were superovulated 4 weeks after surgery and mated or not, to collect E0.5-embryos or MII-oocytes. Evaluation of oocyte and zygote quality was done by immunofluorescence under spinning disk confocal microscopy.

RESULTS

Endometriosis-like lesions were observed in all mice of endometriosis group. In both groups, a similar mean number of MII oocytes per mouse was observed in non-mated mice (30.2 vs 32.6), with a lower proportion of normal oocytes in the endometriosis group (61 vs 83 %, p < 0.0001). Abnormalities were incomplete extrusion or division of the first polar body and spindle abnormalities. The mean number of zygotes per mouse was lower in the endometriosis group (21 vs 35.5, p = 0.02) without difference in embryo quality.

CONCLUSIONS

Our results support that induced peritoneal endometriosis in a mouse model is associated with a decrease in oocyte quality and embryo number. This experimental model allows further studies to understand mechanisms of endometriosis-associated infertility.

Cellular and molecular basis for endometriosis-associated infertility

Endometriosis is a gynecological disease characterized by the presence of endometrial glandular epithelial and stromal cells growing in the extra-uterine environment. The disease afflicts 10%–15% of menstruating women causing debilitating pain and infertility. Endometriosis appears to affect every part of a woman’s reproductive system including ovarian function, oocyte quality, embryo development and implantation, uterine function and the endocrine system choreographing the reproductive process and results in infertility or spontaneous pregnancy loss. Current treatments are laden with menopausal-like side effects and many cause cessation or chemical alteration of the reproductive cycle, neither of which is conducive to achieving a pregnancy. However, despite the prevalence, physical and psychological tolls and health care costs, a cure for endometriosis has not yet been found. We hypothesize that endometriosis causes infertility via multifaceted mechanisms that are intricately interwoven thereby contributing to our lack of understanding of this disease process. Identifying and understanding the cellular and molecular mechanisms responsible for endometriosis-associated infertility might help unravel the confounding multiplicities of infertility and provide insights into novel therapeutic approaches and potentially curative treatments for endometriosis.

The display of paced mating behavior in a rat model of endometriosis

Endometriosis is a disorder associated with chronic pelvic pain and ill effects on women's sexual health. The present study examined the effects of pelvic endometriotic implants on the display of paced mating behavior in female rats. Approximately 2 months after the surgical induction of endometriosis, rats were tested for paced mating behavior during proestrus (Experiment 1) or after bilateral ovariectomy and hormone replacement (Experiment 2). Although endometriotic implants were confirmed at autopsy, rats with surgical endometriosis in both experiments exhibited normal patterns of paced mating behavior. The positive relationship between implant material and contact-return latency following ejaculation in Experiment 2 suggests that the sensitivity to vigorous mating stimulation may be influenced by endometriosis.

Neutralizing TIMP1 restores fecundity in a rat model of endometriosis and treating control rats with TIMP1 causes anomalies in ovarian function and embryo development

Human and rat endometriotic lesions synthesize and secrete tissue inhibitor of metalloproteinase 1 (TIMP1). More TIMP1 localizes in the ovarian theca in an established rat model for endometriosis (Endo) when compared to surgical controls (Sham). We hypothesized that endometriotic TIMP1 secreted into peritoneal fluid (PF) negatively affects ovarian function and embryogenesis by altering the balance of matrix metalloproteinases (MMPs) and TIMPs. Three experiments were performed modulating TIMP1 in vitro and in vivo to investigate ovarian and embryonic anomalies. The first experiment demonstrated control embryos treated in vitro with endometriotic PF concentrations of TIMP1 developed abnormally. In the second experiment where TIMP1 was modulated in vivo, TIMP1-treated Sham rats had fewer zygotes, ovarian follicles, and corpora lutea (CLs) and poorer embryo quality and development, which is analogous to the findings in Endo rats. Importantly, Endo rats treated with a TIMP1 function-blocking antibody had zygote, follicle, and CL numbers and embryo quality similar to Sham rats. In addition, more TIMP1 inhibitory activity was found in ovaries from Endo and TIMP1-treated Sham rats than in ovaries from Sham or TIMP1 antibody-treated Endo rats. In experiment three, control rats (no surgery) treated with Endo PF had fewer follicles and CLs and increased TIMP1 localization in the ovarian theca whereas treatment with Endo PF stripped of TIMP1 or with Sham PF had no effect, providing further evidence that endometriotic TIMP1 sequesters in the ovary and inhibits MMPs necessary for ovulation. Collectively, these results showed that excessive TIMP1 was deleterious to ovulation and embryo development. Thus, novel TIMP1-modulating therapies may be developed to alleviate infertility in women with endometriosis.

Fertility inducing effect of aerial parts of Coccinia cordifolia L. in female rats

ETHNOPHARMACOLOGICAL RELEVANCE

The aerial parts of Coccinia cordifolia L. are used to treat female infertility in West Bengal state of India.

AIM OF THE STUDY

The present study was undertaken to evaluate the fertility inducing effect of aerial parts of Coccinia cordifolia L. in female rats.

MATERIALS AND METHODS

The effect of aqueous extract of Coccinia cordifolia L. on hyperprolactinemia induced infertility, endometriosis induced infertility and androgen-induced infertility was studied. The effect on serum estrogen level, serum progesterone level and reproductive tract was also evaluated in normal healthy female rats. The extract was administered orally at two different doses of 500 mg/kg and 1000 mg/kg.

RESULTS

In hyperprolactinemia induced infertility model, the numbers of uterine implants were almost 10 times more in the extract treated groups as compared to control. The high dose of extract also produced a significant increase in serum estrogen levels (p<0.01) and number of corpus luteum (p<0.05) in healthy female rats. The extract at both doses was effective in reducing the weight of endometrial implants by 70-80%, but failed to induce fertility in rats with endometriosis. The extract was ineffective in inducing fertility in androgen-induced infertility model.

CONCLUSIONS

The aqueous extract of Coccinia cordifolia L. induces fertility in hyperprolactinemia induced infertility model in female rats.

Reduced fecundity in female rats with surgically induced endometriosis and in their daughters: a potential role for tissue inhibitors of metalloproteinase 1

The cause of reduced fecundity in women with endometriosis is unknown. Expression of matrix metalloproteinases (MMPs) and tissue inhibitors of metalloproteinases (TIMPs) by both ectopic and eutopic endometrium reportedly has a role in the pathogenesis of endometriosis. We hypothesize that anomalous endometriotic TIMP protein synthesis, secretion, and localization also cause reproductive pathologies resulting in reduced fecundity. An established rat model for endometriosis (Endo) compared with nonendometriotic controls (Shams) was used to investigate reduced fecundity in endometriosis. Comparing Endo and Sham rats, Endo rats had altered ovarian dynamics, including fewer ovarian follicles and corpora lutea with luteinized unruptured follicles. Furthermore, in vivo anomalies in postovulatory oocyte structure and preimplantation embryo development, including misaligned chromosomes, nuclear and cytoplasmic fragmentation, and delayed or arrested cleavage, as well as spontaneous abortions, were found only in Endo rats. A causative role for TIMP1 in these phenomena is supported by our findings that Endo rats have more TIMP1 in their peritoneal fluid as detected by ELISA and more TIMP1 immunolocalization in the theca of antral follicles as measured by computer-assisted morphometric analysis. These data suggest that in endometriosis the accumulation of TIMP1 disrupts the normal MMP/TIMP enzymatic milieu in the peritoneal cavity and negatively affects ovarian dynamics, oocyte quality, and preimplantation embryo development, thereby decreasing fecundity. Most intriguingly, daughters of Endo rats that had no experimental interventions exhibited these same reproductive abnormalities. We predict that developmental exposure to endometriosis leads to permanent epigenetic changes in subsequent generations.