Experimentally induced endometriosis in rats: effect on fertility and the effects of pregnancy and lactation on the ectopic endometrial tissue

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.

Impact of Chronic Exposure to Endometriosis on Perinatal Outcomes: Establishment of a Mouse Model

The purpose of this study was to establish a new mouse model of endometriosis that mimics real-world women’s health problems, in which women continue to be affected by endometriosis long before they wish to become pregnant, and to evaluate the impact of “chronic exposure to endometriosis” on perinatal outcome. Endometriosis was established by the intraperitoneal injection of homologous minced mouse uteri. Vehicle was injected for the control. Mating was initiated either 1 or 43 days after disease establishment (Young or Aged studies, respectively). Mice were sacrificed on 18 dpc. The number pups and resorptions were counted and pups’ body weights (BW) were measured, and the endometriosis lesion was identified and weighted. In the Young study, the number of resorptions and BW were comparable between the groups. In the Aged study, the number of resorptions was significantly higher and BW was significantly lower in endometriosis than that in control. The total weight of endometriosis lesion per dam was significantly lower in the Aged compared to the Young endometriosis group; however, not a single mouse was found to have any lesions at all. These results suggest that in addition to the presence of endometriosis per se, “chronic exposure to endometriosis” prior to pregnancy affect perinatal outcomes.

The interplay between endometriosis and fertility in rats: a systematic review

For the last decades, endometriosis has been a major gynecological problem and a significant cause of infertility for women worldwide. It is estimated that the disease affects about 10-15% of all women of reproductive age and 70% of women suffering from chronic pelvic pain. At the same time, the incidence is about 40-60% in women with dysmenorrhea and 20-30% in women with subfertility. Despite the high percentage of affected women, endometriosis is still characterized by insufficient knowledge of the pathogenic processes, leading to the development and continuity of the disease. For this reason, there is a significant need for insight and understanding of the pathogenesis of endometriosis. This systematic review aims to present the latest data on the use of rats in endometriosis research and to explore how fertility is affected in rats with endometriosis. The methodology included a review of the available publications retrieved by a search in various scientific databases, such as PubMed, Scopus, Medline, and Google Scholar. The initial search generated 30 titles, with 10 articles fulfilling the inclusion criteria. In conclusion, several surgical techniques have been proposed to induce endometriosis, mainly using rats as the appropriate animal model. Studies in rats showed that endometriosis causes infertility and that pregnancy rates are lower for rats with endometriosis than those without endometriosis. In addition, rats with endometriosis have significant abnormalities in the structure of their oocytes as well as in the development of their embryos (genetic abnormalities).

Environmental Risk Factors for Endometriosis: An Umbrella Review of a Meta-Analysis of 354 Observational Studies With Over 5 Million Populations

Background: The association between a diverse array of environmental risk factors and the risk of endometriosis is contradictory. Objective: To summarize the evidence of associations between environmental risk factors and the risk of endometriosis. Methods: Databases such as PubMed, EMBASE, Web of Science, and ClinicalTrial.gov were systematically searched in June 2020. Meta-analyses of observational studies investigated any environmental exposure (non-genetic) and endometriosis risk. For each article, we estimated the summary effect size, 95% CIs, and the 95% prediction interval (PI). We also estimated the between-study heterogeneity expressed by I ², evidence for small-study effects, and evidence of excess significance bias. Results: About 12 eligible articles (featuring 143,422 cases and 5,112,967 participants) yielded data on 40 unique environmental risk factors, including life styles (n = 16), reproductive factors (n = 3), early life factors (n = 4), and a range of other risk factors [e.g., phthalate metabolites, endocrine-disrupting chemicals, and body mass index (BMI)]. About 25 of these 40 associations (62.5%) were statistically significant (p < 0.05) under random-effects models. Evidence for an association was indicated for alcohol intake [relative risk (RR): 1.25; 95% CI: 1.11-1.41] and the exposure to endocrine disruptor chemicals (EDCs) (RR: 1.41; 95% CI: 1.23-1.60) while 15 associations presented only weak evidence. Conclusions: Our analyses showed that alcohol intake and exposure to endocrine-disrupting chemicals may be potential risk factors for endometriosis and supported by suggestive epidemiological evidence. However, it was evident that there was substantial heterogeneity and/or bias between the different studies featured in various meta-analyses included in this review; therefore, the outcomes of our analysis should be interpreted cautiously.

Interplay between Endometriosis and Pregnancy in a Mouse Model

Objectives

To evaluate the effect of endometriosis on fertility and the levels of the IL-2 and IFN-γ in the peritoneal fluid in a mouse model; to evaluate the effect of pregnancy on endometriotic lesion growth, apoptosis and cell proliferation.

Study Design

Two month old C57BL/6 female mice underwent either a surgical procedure to induce endometriosis or a sham surgery. Four weeks after surgery mice were mated and sacrificed at day 18 of pregnancy. Number of implantation sites, fetuses and fetal weight were recorded. Endometriotic lesions were counted, measured, excised and fixed. Apoptosis and cell proliferation were evaluated in lesions by TUNEL and immunohistochemistry for PCNA respectively. Levels of IL-2 and IFN-γ were assessed by ELISA in the peritoneal fluid.

Results

Pregnancy rate (i.e. pregnant mice/N) decreased in mice with endometriosis. However there were no significant differences in resorption rate, litter size and pup weight between groups. IFN-γ augmented in endometriosis mice independently of pregnancy outcome. Additionally IFN-γ increased in pregnant endometriosis mice compared to pregnant sham animals. While IFN-γ increased in non pregnant versus pregnant mice in the sham group, IL-2 was increased in non pregnant mice in the endometriosis group. The size of endometriotic lesions increased in pregnant mice while apoptosis increased in the stroma and cell proliferation decreased in the epithelium of these lesions. Additionally, leukocyte infiltration, necrosis and decidualization were increased in the same lesions.

Conclusions

Pregnancy rate is reduced in this mouse model of endometriosis. Levels of IL-2 are increased in the peritoneal fluid of mice with endometriosis suggesting a role of this cytokine in infertility related to this disease. The size of endometriotic lesions is increased in pregnant mice; however pregnancy has a beneficial effect on lesions by decreasing cell proliferation and by increasing apoptosis, decidualization and necrosis.

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.

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.

Intraperitoneal recombinant interleukin-2 activates leukocytes in rat endometriosis

The aim of this double-blinded study was to determine changes in leukocyte populations in blood, peritoneal lavage fluid, eutopic and ectopic endometrium after treatment with recombinant rat interleukin-2 (IL-2) using an in vivo experimental model of rat endometriosis. The in vivo model involved transplanting four square fragments of autologous endometrium onto the inner surface of the abdominal wall in 20 Wistar rats. The control group was constituted by 20 sham-operated rats. Both groups were randomly treated (1-month interval treatment) with 2 intraperitoneal doses of glucose solution (5%) that did or did not contain recombinant IL-2, and animals were sacrificed 4 weeks after the last dose of treatment. Blood and peritoneal lavage were obtained during the initial and final laparotomy, whereas eutopic and ectopic endometrium were collected at the end of the experiment. Endometriotic implants were measured in each laparotomy to determine any change in size. Leukocyte populations were analyzed by flow cytometry and immunofluorescence microscopy. Cytometric results were similar in blood and peritoneal lavage. CD25+ and natural killer (NK) cell levels in peripheral blood were lower in rats with endometriosis treated with IL-2, whereas NK cells increased in lavage compared to placebo group. The percentage of macrophages and dendritic cells in blood were higher in all rats treated with IL-2, as well as peritoneal dendritic cells. Implant size of these rats decreased significantly, showing a greater number of activated lymphocytes, macrophages, NK and dendritic cells inside them. In conclusion, recombinant IL-2 induced recruitment of activated leukocytes into endometriotic-like foci, and this was related to a reduction of the implant size, suggesting potential effectiveness of IL-2 as an immunomodulatory agent in this pathology.

Analysis of the AhR, ARNT, and AhRR gene polymorphisms: genetic contribution to endometriosis susceptibility and severity

OBJECTIVE

To explore whether polymorphisms in AhR, ARNT, and AhRR contribute to endometriosis susceptibility and severity.

DESIGN

Case control study.

SETTING

Hospital.

PATIENT(S)

One hundred thirty-eight Japanese women with or without endometriosis, diagnosed endoscopically.

INTERVENTION(S)

Endoscopic laparoscopy, with blood samples for genotyping obtained before the laparoscopic examination for genomic DNA extraction from peripheral leukocytes.

MAIN OUTCOME MEASURE(S)

AhR, ARNT, and AhRR polymorphisms were genotyped using real-time polymerase chain reaction (PCR) analysis. Odds ratios and 95% confidence intervals were calculated for AhR, ARNT, and AhRR genotypes to evaluate the risk of endometriosis. Associations between these polymorphisms and stage of endometriosis were also examined.

RESULT(S)

The C/G + G/G genotypes at codon 185 of AhRR showed a statistically significant association with risk of endometriosis (adjusted odds ratio, 2.53; 95% confidence interval, 1.16-5.55). Furthermore, a statistically significant trend associated the C/G + G/G genotypes with the clinical stage of endometriosis. No statistically significant association was observed between AhR codon 554 or ARNT codon 189 polymorphisms and endometriosis.

CONCLUSION(S)

AhRR codon 185 polymorphism was associated with susceptibility to and severity of endometriosis in Japanese women.

Reproductive history and endometriosis among premenopausal women

OBJECTIVE

To clarify the temporal complexities of the relation between reproductive factors and endometriosis.

METHODS

We analyzed 10 years of prospective data from the Nurses' Health Study II cohort. Information was obtained through questionnaires sent every 2 years to 116,678 women aged 25-42 years when enrolled in 1989. Cox proportional hazards models were used to adjust for age, calendar time, and confounding variables.

RESULTS

During 726,205 woman-years of follow-up, 1,721 cases of laparoscopically confirmed endometriosis were reported among women with no past infertility. Greater incidence was observed among women with an earlier age at menarche (rate ratio of 1.3 comparing menarche at age < 10 to age 12 years; 95% confidence interval [CI] 1.0-1.8; P value, test for trend < .001) and shorter cycle length during late adolescence (rate ratio of 1.3 comparing < 26 days to 26-31 days; 95% CI 1.1-1.5). Time to cycle regularity was not associated with risk. Among parous women, a linear decrease in risk was observed with number of liveborn children (rate ratio of 0.5 comparing > 3 with 2 children; 95% CI 0.4-0.7; P value, test for trend < .001) and lifetime duration of lactation if time since last birth was less than 5 years (rate ratio of 0.2 comparing > 23 months with never; 95% CI 0.1-0.4; P value, test for trend < .001).

CONCLUSION

Hormonal and anatomical changes associated with menstruation and pregnancy may affect the rate of laparoscopically confirmed endometriosis. Within this cohort, risk was greatest among nulliparous women with earlier age at menarche and shorter menstrual cycles. Among parous women, parity and lifetime duration of lactation were associated with decreased risk.

Intact progesterone receptors are essential to counteract the proliferative effect of estradiol in a genetically engineered mouse model of endometriosis

OBJECTIVE

To determine the role of P and its nuclear receptor PR in the growth of ectopic uterine tissue of mice with or without a disrupted PR gene.

DESIGN

Animal study.

SETTING

Academic medical center.

ANIMAL(S)

Female wild-type (WT) and transgenic knockout mice for P receptor (PRKO).

INTERVENTION(S)

Endometriosis was induced in the following groups of ovariectomized adult mice: [1] untreated WT, [2] estradiol (E(2))-treated WT, [3] P-treated WT, [4] E(2) + P-treated WT, [5] untreated PRKO, [6] E(2)-treated PRKO, and [7] E(2) + P-treated PRKO (n = 5 in each group).

MAIN OUTCOME MEASURE(S)

The size of ectopic uterine tissue in WT and PRKO mice were compared between the groups subjected to treatments with P or E(2). Tissue proliferating cell nuclear antigen (PCNA) levels were compared among these groups.

RESULTS

Treatment with P only significantly decreased the size of WT ectopic uterine tissue. The untreated PRKO ectopic uterine tissue was significantly larger than WT tissue. Estradiol increased the size of ectopic uterine tissues, and this E(2)-dependent growth could be suppressed by P in WT tissues but not in PRKO tissues. Finally, the hormone-dependent changes in ectopic uterine tissue size were accompanied by comparable alterations in PCNA levels.

CONCLUSION(S)

Intact PR in ectopic uterine tissue is essential to abolish E(2)-dependent or -independent proliferation. We also suggest that ectopic uterine tissue is associated with significantly increased resistance to P action and increased predisposition to E(2)-dependent proliferation in the absence of PR. Overall, these findings support the hypothesis that P resistance in human endometriosis may be due to the absence of sufficient levels of functional PR in this tissue.

Was Sampson wrong?

OBJECTIVE

Sampson's theory of reflux menstruation suggests that endometriosis is one form of a condition known as an autotransplant. This study seeks to characterize autotransplants as they are described in the literature and to determine whether endometriosis resembles an autotransplant.

DESIGN

Literature review of published studies containing the following types of information: [1] characterization of the histologic features, immunohistochemistry, or structural function of autotransplants; and [2] comparisons of endometriosis with endometrium.

MAIN OUTCOME MEASURE(S)

Characteristics of multiple types of autotransplants were noted. Similarity or dissimilarity of endometriosis and endometrium was tabulated to judge qualitatively whether the bulk of the evidence supports the notion that endometriosis is an autotransplant.

RESULT(S)

Autotransplants remain very similar or identical to eutopic tissues of origin, regardless of the length of time following autotransplantation. Endometriosis differs in many profound and fundamental ways from eutopic endometrium, including clonality of origin, enzymatic activity, protein expression, and histologic and morphologic characteristics. A minority of studies has found similarities between endometriosis and eutopic endometrium.

CONCLUSION(S)

Endometriosis is dissimilar to eutopic endometrium and therefore lacks characteristics of an autotransplant. Sampson's theory of origin of endometriosis is not supported by the results of this study. Studies of experimental endometriosis that have not used menstrual endometrium may be misleading.

Effect of peritoneal fluid from women with endometriosis on implantation in the mouse model

OBJECTIVE

To investigate the potential role of peritoneal fluid (PF) from women with or without endometriosis in implantation in mice with use of the delayed implantation model.

DESIGN

A murine experimental model with markers of uterine receptivity and prospective comparison of the effects of human PF on implantation.

SETTING

Academic university and hospital program.

INTERVENTION(S)

PF collected from women with and without endometriosis was injected intraperitoneally into recently mated mice.

MAIN OUTCOME MEASURE(S)

Implantation sites were counted in treated and untreated animals, and the alphavbeta3 integrin was measured in the pregnant mouse uterus by immunohistochemistry with in situ hybridization. Leukemia inhibitory factor and the beta3 subunit of alphavbeta3 were measured by Northern blot during early pregnancy and after injections of PF.

RESULT(S)

Animals receiving PF from infertile women with endometriosis had a reduction in the number of implantation sites compared with animals that received PF from fertile women or from patients with recently treated endometriosis. In the mouse, expression of alphavbeta3 and leukemia inhibitory factor peaked at the time of implantation and was reduced by injections of human PF from infertile patients with endometriosis.

CONCLUSION(S)

Leukemia inhibitory factor and alphavbeta3 are coexpressed at the time of implantation in the mouse. PF from women with endometriosis has a detrimental effect on embryo implantation, perhaps by adversely affecting uterine receptivity.

Medical management of endometriosis and infertility

OBJECTIVE

To review the literature on the use of medical management of endometriosis and infertility.

DESIGN

Literature review.

RESULT(S)

Endometriosis is a common finding in women with infertility, but the mechanism by which it renders a woman infertile remains unclear. Despite many years of controversy and debate, there remains a strong bias against medical treatment for endometriosis-associated infertility. A review of the current literature suggests that medical management of endometriosis may be effective in selected patients and in certain settings, including patients undergoing IVF.

CONCLUSION(S)

A closer look at the question of medical management of endometriosis reveals that much remains to be learned before a final decision can be made about the use of medical therapies, such as GnRH agonists, for endometriosis and associated infertility.

Intraperitoneal and subcutaneous treatment of experimental endometriosis with recombinant human interferon-alpha-2b in a murine model

OBJECTIVE

To determine the effect of human interferon (IFN)-alpha-2b on experimental endometriosis in rats.

DESIGN

Experimental, controlled, double-blind randomized study.

SETTING

Experimental surgery laboratory in a university department.

ANIMAL(S)

Ninety-six Wistar rats with endometriosis, induced by transplanting four endometrial fragments into the peritoneal cavity.

INTERVENTION(S)

One third of the animals served as controls (group A). The others were randomly divided into two groups and were given IFN-alpha-2b either as a single intraperitoneal dose (group B) or as three SC doses (on alternate days) (group C).

MAIN OUTCOME MEASURE(S)

Laparotomy was performed to measure the size of each implant at various times (days 0, 6, 12, 20, and 120 after treatment).

RESULT(S)

There were no differences among the groups in the size of the average implants before IFN was administered (17.3+/-6.7, 19.7+/-7.8, and 18.1+/-9.2 mm for groups A, B, and C, respectively). These values were significantly smaller after treatment in group B (14.9+/-8.0 mm) and group C (14.0+/-9.5 mm) than in the control group (17.6+/-7.5 mm) (P<.05). Intraperitoneal IFN produced an initial maximum decrease in the size of the implants (40% reduction on day 6), which diminished until day 20 (20%) and then was maintained on a plateau until day 120 (25%). By contrast, group C showed an initial minimal reduction (13% at day 6), which increased up to day 20 (19%), after which a plateau was reached (23% at day 120). Thus, the effects in both treatment groups were similar in the long term.

CONCLUSION(S)

Two short regimens of human IFN-alpha-2b reduced the size of experimental endometriosis in rats.

Individual and combined effects of triptoreline and gestrinone on experimental endometriosis in rats

OBJECTIVES

To evaluate the effects of triptoreline, gestrinone, and both, on experimental endometriosis in rats.

STUDY DESIGN

Experimental endometriosis was surgically induced in 225 Wistar rats. Of these, 202 rats showed at least one grown implant, 22 of which composed the control group, while 180 were treated with triptoreline, gestrinone, or both, for 28 days. The implants were evaluated again after 25 days.

RESULTS

There were no changes in size in the control group. About 73% of the implants treated with triptoreline showed a high reduction (> 50%), vs. 51% with gestrinone (P < 0.0005) and 65% with both (P < 0.005). Triptoreline caused macroscopic resolution in 40% of the implants vs. 31% for gestrinone (not significant) and 26% for both substances (P < 0.05). In the triptoreline group, the mean size of the implants decreased by 65% between the 25th and 28th days, 58% between the 29th and the 35th, and 39% after the 36th day. This reduction was 51%, 36%, and 33%, respectively, in gestrinone group.

CONCLUSIONS

Triptoreline was more effective than gestrinone, but perhaps not in the long run. Their association did not improve the results.