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

Implantation defects in infertile women with endometriosis

The endometrium undergoes characteristic histologic changes during the menstrual cycle as it prepares for embryo implantation. Historic and current data suggest the presence of a defined period of maximal uterine receptivity during the mid-secretory phase occurring between days 7 and 10 postovulation. In recent years, we and others have sought to define biochemical markers of receptivity that might be used to better understand this time of endometrial differentiation. Based on the work with cell adhesion molecules, we have discovered three different integrins that are only coexpressed during this time in the cycle when embryos will successfully implant. By studying the regulation of one of these, the alpha(v)beta3 integrin, and its extracellular matrix ligand, osteopontin (OPN), we have defined two separate regulatory pathways that may regulate endometrial receptivity. While alpha(v)beta3 expression appears to be stimulated by EGF or heparin-binding EGF, osteopontin is stimulated by progesterone. We now believe the former pathway is a paracrine-mediated signal, while the latter is a direct effect of progesterone on the estrogen-primed endometrial epithelium. In women with endometriosis, it appears that alpha(v)beta3 expression is reduced, while OPN expression is unaffected. Interestingly, binding of OPN to the surface epithelium appears quite limited when alpha(v)beta3 expression is lacking. Such evidence continues to reinforce the notion that endometrium from some women with endometriosis is dysfunctional and may account for the reduction in cycle fecundity noted in this group of patients.

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.

Embryotoxicity of peritoneal fluid in women with endometriosis. Its relation with cytokines and lymphocyte populations

BACKGROUND

The goals of the present work were to study the embryotoxic effects of peritoneal fluid (PF) in women with or without endometriosis, and to relate any embryotoxicity to the severity of endometriosis, infertility or achievement of pregnancy, cytokine concentrations and lymphocyte populations.

METHODS

Sixty-six consecutive women of reproductive age, 54 with endometriosis (21 infertile) and 12 infertile without endometriosis, and another 12 fertile women as control group, were included in this study. They all underwent laparoscopy or laparotomy in the second half of the cycle, and PF was collected from the pouch of Douglas. The embryotoxicity of the PF was assessed by means of a mouse embryo assay, and expressed as the number of embryos that did not reach blastocyst stage. Cytokines and lymphocyte populations present in PF were also studied and correlated with embryotoxicity.

RESULTS

PF embryotoxicity was increased in women with endometriosis, but there was little correlation with the severity of the disease. However, although a clear relationship to the presence of infertility was not found, embryotoxicity appeared to be lower in those infertile patients with endometriosis who later became pregnant. We found a significant increase in embryotoxicity in the presence of high cytokine concentrations, especially with interleukin-6, and less so with interleukin-8 (P < 0.05). No good correlation was observed with lymphocyte populations, but CD56 (NK) cells were significantly increased in the PF of women with endometriosis. In general, the correlations for embryotoxicity were better when PF was diluted at 20% (91.4 +/- 17 versus 68.1 +/- 31, P < 0.01).

CONCLUSIONS

These results suggest that alteration in the production of cytokines in the PF, especially IL-6, besides contributing to the endometriosis and its evolution, probably increases embryotoxicity. However, no correlation was found between the latter and associated infertility.

Endometriosis and infertility: the debate continues

A causal relationship between minor endometriosis and infertility or subfertility has not yet been demonstrated, although a significant association is shown by prevalence studies. This article critically reviews the evidence for pituitary-ovarian dysfunction as a cause for subfertility in women with minor endometriosis. The lack of fertile controls with endometriosis presents a methodological problem. Group comparison in studies using tubal infertility cases as controls has demonstrated impaired follicular growth, reduced circulating oestradiol concentrations during the preovulatory phase and oestradiol and progesterone during the early luteal phase, and disturbed luteinizing hormone (LH) surge patterns. LH concentration in preovulatory follicular fluid is also reduced, and granulosa cells collected at the same time have impaired steroidogenic capacity in vitro. However, these findings are not consistent in published studies. Significantly lower oocyte fertilization rates (49%) are found compared with controls (69%), even after maximum stimulation with exogenous follicle-stimulating hormone and human chorionic gonadotrophin (52% versus 69%). The implantation rate is also lower (11% versus 13%). An inherent disorder of follicular function seems likely, and LH surge impairment is probably a secondary effect. Impairment of oocyte fertilization would thus contribute substantially to the natural subfertility associated with endometriosis, but in vitro fertilization is still successful as excess numbers of oocytes are available.

Endometriosis and assisted reproductive technologies: are outcomes affected?

The preponderance of recent data suggests that endometriosis does not adversely affect in-vitro fertilization pregnancy rates. However, many studies demonstrate impaired oocyte quality, decreased fertilization, and compromised implantation rates. Such findings give insight into the mechanisms by which endometriosis may impact on fertility, and provide clues as how to focus assisted reproductive technologies in order to overcome these deficiencies. Specifically, extended downregulation protocols, ample use of gonadotropins for ovarian stimulation, and conservative management of endometriomas have all been suggested as means to optimize in-vitro fertilization outcomes for women with endometriosis.

Molecular markers of implantation: clinical implications

The endometrium has been conventionally studied using histologic criteria. Our understanding of endometrial physiology has been advanced tremendously by research into the molecules that mediate its development and function. These molecules demonstrate a dynamic expression pattern through the menstrual cycle and have been implicated in endometrial growth, differentiation, and receptivity. These molecules include secreted proteins (endometrial bleeding-associated factor, glycodelin-A, insulin-like growth factor binding protein-1), cell-surface receptors (integrins), and nuclear transcription factors (HOXA10 and HOXA11). The homeobox genes Hoxa10 and Hoxa11 are necessary for implantation because mice with mutations in these genes exhibit a failure of implantation. HOXA10 and HOXA11 have been shown to be important for implantation in humans as well. Knowledge of endometrial molecular dynamics may now be used to enhance our ability to diagnose implantation defects. It may soon be possible to treat individual molecular defects by protein supplementation or gene therapy.

Endometrial receptivity and the window of implantation

Implantation is a highly co-ordinated event that involves both embryonic and endometrial participation. The endometrium expresses a sophisticated repertoire of proteins during the menstrual cycle many of which help to define a period of receptivity collectively known as the 'window of implantation'. Many of these factors, which are temporally aligned with this window, are now seen as chemical messengers that are recognized by the embryo and facilitate embryonic growth and differentiation. The use of such proteins as biomarkers has also advanced our understanding of the implantation process and may identify women with implantation failure and infertility. While the study of endometrial receptivity is still evolving, the field is growing rapidly and will probably enhance our ability to diagnose and treat couples with infertility, especially in the arena of assisted reproductive technologies (ART).

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.