Endometriosis and infertility: raised iron concentration in the peritoneal fluid and its effect on the acrosome reaction

Pyroptotic T cell-derived active IL-16 has a driving function in ovarian endometriosis development

Endometriosis, affecting 6%-10% of women, often leads to pain and infertility and its underlying inflammatory mechanisms are poorly understood. We established endometriosis models in wild-type and IL16KO mice, revealing the driver function of IL-16 in initiating endometriosis-related inflammation. Using an in vitro system, we confirmed iron overload-induced GSDME-mediated pyroptosis as a key trigger for IL-16 activation and release. In addition, our research led to the development of Z30702029, a compound inhibiting GSDME-NTD-mediated pyroptosis, which shows promise as a therapeutic intervention for endometriosis. Importantly, our findings extend beyond endometriosis, highlighting GSDME-mediated pyroptosis as a broader pathway for IL-16 release and offering insights into potential treatments for various inflammatory conditions.

Epidemiology of infertility in women with endometriosis

Endometriosis is a benign, chronic, inflammatory condition affecting up to 10 % of women and characterised by the presence of glands and stroma tissue outside the uterus. Epidemiological and clinical studies demonstrate a consistent association between endometriosis and infertility. However, this relationship is far to be clearly understood and several mechanisms are involved. Available data show that patients with endometriosis have an increased estimated risk of infertility between two and four times compared with the general population. On the other hand, the probability of patients with infertility to have endometriosis is reported up to about 50 % of the cases. Future studies should aim to better elucidate the mechanisms behind endometriosis-associated infertility in order to offer the more appropriate and tailored management for the patients.

The Pathological Role of miRNAs in Endometriosis

Association studies investigating miRNA in relation to diseases have consistently shown significant alterations in miRNA expression, particularly within inflammatory pathways, where they regulate inflammatory cytokines, transcription factors (such as NF-κB, STAT3, HIF1α), and inflammatory proteins (including COX-2 and iNOS). Given that endometriosis (EMS) is characterized as an inflammatory disease, albeit one influenced by estrogen levels, it is natural to speculate about the connection between EMS and miRNA. Recent research has indeed confirmed alterations in the expression levels of numerous microRNAs (miRNAs) in both endometriotic lesions and the eutopic endometrium of women with EMS, when compared to healthy controls. The undeniable association of miRNAs with EMS hints at the emergence of a new era in the study of miRNA in the context of EMS. This article reviews the advancements made in understanding the pathological role of miRNA in EMS and its association with EMS-associated infertility. These findings contribute to the ongoing pursuit of developing miRNA-based therapeutics and diagnostic markers for EMS.

The role of iron in the pathogenesis of endometriosis: a systematic review

STUDY QUESTION

What is the role of iron in the pathophysiology of endometriosis?

SUMMARY ANSWER

Iron excess is demonstrated wherever endometriotic tissues are found and is associated with oxidative stress, an inflammatory micro-environment, and cell damage; the iron-mediated oxidative stress is independently linked to subfertility, symptom severity, and malignant transformation.

WHAT IS KNOWN ALREADY

Iron is found in excess in endometriotic tissues, and multiple mechanisms have been studied and posited to explain this. It is clear that iron excess plays a vital role in promoting oxidative stress and cell damage. The evidence base is large, but no comprehensive reviews exist to summarize our understanding and highlight the overarching themes to further our understanding and suggest future directions of study for the field.

STUDY DESIGN SIZE DURATION

This systematic review with a thematic analysis retrieved studies from the PubMed, Embase, Web of Science, and Cochrane Library databases and searches were conducted from inception through to August 2022. Human and animal studies published in the English language were included and identified using a combination of exploded MeSH terms ('Iron' and 'Endometriosis') and free-text search terms ('Iron', 'Ferric', 'Ferrous', 'Endometriosis', 'Endometrioma').

PARTICIPANTS/MATERIALS SETTING METHODS

This review was reported in accordance with the PRISMA guidelines. All studies reporting original data concerning the role of iron or iron complexes in the pathophysiology of endometriosis were included. Studies that did not report original data or provided a review of the field were excluded. Bias analysis was completed for each included study by using the Newcastle-Ottawa scoring system.

MAIN RESULTS AND THE ROLE OF CHANCE

There were 776 records identified and these were screened down to 53 studies which met the eligibility criteria, including 6 animal and 47 human studies, with 3556 individual participants. Iron excess is demonstrated in various tissues and fluids, including ovarian endometriomas, ovarian follicles, ectopic endometriotic lesions, and peritoneal fluid. Markers of oxidative stress are strongly associated with high iron levels, and aberrant expression of iron-transport proteins has been demonstrated. Abnormal resistance to ferroptosis is likely. Iron-mediated oxidative stress is responsible for a pro-inflammatory micro-environment and is linked to subfertility, symptom severity, and, possibly, malignant transformation.

LIMITATIONS REASONS FOR CAUTION

A minority of the included studies were of objectively low quality with a high risk of bias and may lead to misleading conclusions. Additionally, multiple studies failed to appropriately characterize the included patients by known confounding variables, such as menstrual cycle phase, which may introduce bias to the findings.

WIDER IMPLICATIONS OF THE FINDINGS

Current literature depicts a central role of aberrant iron mechanics and subsequent oxidative stress in endometriosis. It is likely that iron excess is at least partly responsible for the persistence and proliferation of ectopic endometriotic lesions. As such, iron mechanics represent an attractive target for novel therapeutics, including iron chelators or effectors of the iron-oxidative stress pathway. There are significant gaps in our current understanding, and this review highlights and recommends several topics for further research. These include the role of iron chelation, resistance to ferroptosis, the relationship between iron excess and localized hypoxia, systemic iron pathophysiology in endometriosis, and the role of oxidative stress in malignant transformation.

STUDY FUNDING/COMPETING INTERESTS

J.W. and S.G.P. are supported by clinical fellowships at Liverpool University Hospital NHS Foundation trust. No additional funding was requested or required for the completion of this work. C.J.H. is supported by a Wellbeing of Women project grant (RG2137). D.K.H. is supported by a Wellbeing of Women project grant (RG2137) and an MRC clinical research training fellowship (MR/V007238/1). The authors have no conflicts of interest to declare.

REGISTRATION NUMBER

A protocol was prospectively registered with the PROSPERO database in August 2021 (CRD42021272818).

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.

Iron overload in endometriosis peritoneal fluid induces early embryo ferroptosis mediated by HMOX1

Endometriosis is one of the most common disorders that causes infertility in women. Iron is overloaded in endometriosis peritoneal fluid (PF), with harmful effects on early embryo development. However, the mechanism by which endometriosis peritoneal fluid affects embryonic development remains unclear. Hence, this study investigated the effect of iron overload on mouse embryos and elucidated the molecular mechanism. Iron overload in endometriosis PF disrupted blastocyst formation, decreased GPX4 expression and induced lipid peroxidation, suggesting that iron overload causes embryotoxicity and induces ferroptosis. Moreover, mitochondrial damage occurs in iron overload-treated embryos, presenting as decreased ATP levels, increased ROS levels and MMP hyperpolarization. The cytotoxicity of iron overload is attenuated by the ferroptosis inhibitor Fer-1. Furthermore, Smart-seq analysis revealed that HMOX1 is upregulated in embryo ferroptosis and that HMOX1 suppresses ferroptosis by maintaining mitochondrial function. This study provides new insight into the mechanism of endometriosis infertility and a potential target for future endometriosis infertility treatment efforts.

Iron overload compromises preimplantation mouse embryo development

We and others have previously shown that abnormal pelvic environment plays an important role in the unexplained infertility of endometriosis. However, whether iron overload caused by ectopic periodic bleeding found in patients with endometriosis participates in endometriosis-associated reproductive failure is unknown. This study aimed to investigate effects of iron at level relevant to pelvic iron overload on the development of preimplantation mouse embryo. Two-cell embryos were collected, and cultured to blastocysts in G1/G2 medium supplemented with iron alone or in combination with iron chelator. The development rates, ATP level, mitochondrial membrane potential (MMP), reactive oxygen species level (ROS), and apoptotic and ferroptotic indices were compared between control and iron treatments across each specific developmental stage. Prolonged exposure to iron remarkably impaired early embryo development in vitro by hampering blastocyst formation (P < 0.001), which could be partly restored by iron chelator (P < 0.001). The arrest of embryo development was linked with iron-initiated mitochondrial dysfunction with reduction of ATP generation and MMP (P < 0.05 and P < 0.001, respectively). Impaired mitochondria altered ROS accumulation post-iron exposure at morula stage and blastocyst stage (P < 0.05). Moreover, Iron-exposed blastocyst stage embryos showed higher apoptotic and ferroptotic rates (P < 0.001 and P < 0.05, respectively). Our results highlight that pathologically relevant level of iron compromises preimplantation mouse embryo development by disrupting mitochondrial function and triggering both apoptosis and ferroptosis, which implicates that excess iron found in peritoneal fluid of women with endometriosis likely participates in endometriosis-associated reproductive failure.

Mast Cells in Peritoneal Fluid From Women With Endometriosis and Their Possible Role in Modulating Sperm Function

Endometriosis is a local pelvic inflammatory process, frequently associated with infertility, with altered function of immune-related cells in the peritoneal environment. Mast cells are known to be key players of the immune system and have been recently involved in endometriosis and in infertility, with their mediators directly suppressing sperm motility. In this study, we evaluated the mast cell population and their mediators in the peritoneal fluid of infertile patients with endometriosis and their impact on human sperm motility. Peritoneal fluids, collected by laparoscopy from 11 infertile patients with endometriosis and 9 fertile controls were evaluated for the presence of mast cells, tryptase levels and their effect on sperm motility. Furthermore, an in vitro model of mast cells-sperm interaction in peritoneal fluid was set up, using LAD2 cell line as a mast cell model, and analyzed from a functional as well as a morphological point of view. Mast cell peritoneal fluid population and its main mediator, tryptase, is more represented in endometriosis confirming an involvement of these cells in this disease. Anyway it appears unlikely that tryptase enriched peritoneal fluid, which fails to inhibit sperm motility, could contribute to endometriosis associated infertility. Despite of this, sperm interaction with the mast cell surface (LAD2) induced a significantly mast cell-degranulation response in the peritoneal fluid from endometriosis which could directly modulate sperm function other than motility. This evidence lead us to suppose that there is, between these elements, an interrelationship which deserves further studies.

Peritoneal fluid from women with endometriosis impairs human spermatozoa functionality

The success of mammalian fertilization depends largely on spermatozoa physiological events. However, the manner in which endometriosis influence morpho-functional spermatozoa biomarkers is poorly defined. Here, we studied in vitro the effect of peritoneal fluid (PF) from women with endometriosis (PFE) and non-endometriosis (PFNE) on spermatozoa parameters. This research was prospective and double-blind. A total of 45 PF samples were collected from women with (n = 25) and without endometriosis (n = 20). Semen samples were obtained from normozoospermic donors (n = 15) and cultured with 20 % (v/v) of PF or commercial culture medium (controls) during 0, 24, and 48 h. The outcome measures were spermatozoa/viability, motility, tyrosine phosphorylation (TP) and spontaneous acrosomal reaction. In addition, plasma membrane sugars were characterized by lectins [Aleuria aurantia agglutinin (AAA), Concanavalin A (ConA), Peanut agglutinin (PNA), and Wheat germ agglutinin (WGA)]. After a 24 -h culture, results reported a significant decrease in motility in cells cultured with PFE compared to the control, together with differences in the AAA and WGA-binding sites. Moreover, spermatozoa in contact with PFNE presented a significantly lower level of acrosome spontaneous reaction. At 48 h, no differences were observed in the biomarkers studied between the PFNE and the control, excluding ConA-binding sites. On the other hand, cells cultured with PFE exhibited significantly less motility, TP, and differences in the relocation of spermatozoa surface sugars. Viability was not affected in any culture condition. Overall, the effects of PFE could negatively affect spermatozoa quality, contributing to explain and diagnose the infertility associated to male partners of women with endometriosis.

Ethiopathogenic mechanisms of endometriosis-related infertility

Endometriosis is a highly prevalent disease among women of reproductive age and is frequently associated to infertility. However, the mechanisms underlying endometriosis-related infertility are still not completely known. Several studies have been conducted in order to elucidate this question. Besides anatomical changes that may impair gametes and embryo transport along the tubes; a smaller ovarian reserve due to advanced endometriosis and endometriomas; and a dysregulated hypothalamic-pituitary-ovarian axis, there are pieces of evidence suggesting that the peritoneal ectopic endometrial foci may induce a local inflammatory response, with the recruitment of macrophages, cytokine release, and reactive oxygen species generation, leading to a pro-oxidant peritoneal microenvironment. These alterations may be systemically reflected and also affect the follicular microenvironment. A harmful follicular fluid may disrupt cumulus cells functions and, consequently, compromise oocyte competence. There is also evidence suggesting that the peritoneal fluid of women with endometriosis may alter sperm function. Reduced endometrial receptivity is also pointed as a possible mechanism involved in endometriosis-related infertility, which needs further investigation.

The association between iron, calcium, and oxidative stress in seminal plasma and sperm quality

The present study aimed to determine the level of iron and calcium in the seminal plasma of men with different fertility potentials and to examine its relationship with oxidative stress. Seventy-nine sub-fertile patients with asthenoteratozoospermia (AT), n 27; teratoleucozoospermia (TL), n 20; teratozoospermia (Terato), n 32; and 29 healthy donors were included. The ability of spermatozoa to produce reactive oxygen species (ROS) was evaluated by using nitroblue tetrazolium (NBT) staining. The lipid peroxidation end product, malondialdehyde (MDA), and the trace element levels (iron and calcium) were measured spectrophotometrically. Iron and calcium concentrations in seminal plasma of the patient groups were significantly more elevated than the normal group. Nevertheless, both calcium and iron showed strong negative correlations with the total sperm motility and normal sperm morphology, but only iron was positively and significantly associated with multiple anomalies index and seminal leucocyte concentration. On the other hand, the rates of MDA and ROS production in semen were significantly higher in the three abnormal groups than in controls. These two oxidative stress biomarkers were significantly associated with the percentage of atypical forms in semen. However, only semen ROS level was significantly associated with the decreased sperm motility and the sperm leucocytes concentration. Meanwhile, there are positive correlations between seminal iron and calcium content and the studied oxidative stress biomarkers. Oxidative stress and trace element excess are implicated in low sperm quality. Iron and calcium might be the mediators of the effects of oxidative damage and induces lipid peroxidation.

Involvement of Iron, Nuclear Factor-Kappa B (NF-κB) and Prostaglandins in the Pathogenesis of Peritoneal Endometriosis-Associated Inflammation: A Review

Peritoneal endometriosis is a chronic pelvic inflammatory disease, characterized by increased numbers of peritoneal macrophages and their secreted products such as cytokines, growth and angiogenic factors in peritoneal fluid. Inflammation plays a major role in pain and infertility associated with endometriosis, but is also extensively involved in the molecular and cellular processes that lead to peritoneal endometriotic lesion development. Several inflammatory mediators have therefore been studied in the context of endometriosis over the last few years.

The aim of this review is to focus on three that have been clearly implicated in the pathogenesis of endometriosis and may be linked: peritoneal iron metabolism, nuclear factor-kappa B (NF-κB) activation, and prostaglandin biosynthesis.

Peritoneal iron overload has been conclusively demonstrated in endometriosis patients and may induce oxidative stress in the peritoneal cavity. Oxidative stress and proinflammatory cytokines are well known to be potent activators of the NF-κB pathway, which has recently been implicated in peritoneal endometriosis. Induced NF-κB activation leads to expression of numerous proinflammatory genes such as cytokines, which may provide positive feedback to the pathway, self-perpetuating the inflammatory response. Other important NF-κB-regulated molecules are prostaglandin biosynthesis enzymes, and cyclooxygenase-2 (COX-2) in particular. Increased concentrations of prostaglandins have been evidenced in the peritoneal fluid of endometriosis patients and COX-2 inhibitors have proved to be effective in ‘in vitro’ and ‘in vivo’ experimental models.

In the light of available data collected from patient biopsies, as well as ‘in vitro’ and ‘in vivo’ studies, the respective implication and potential molecular association of iron, NF-κB and prostaglandins in the pathogenesis of endometriosis are discussed. The key role of peritoneal macrophages is emphasized and potential therapeutic targets are examined.

Clinical management of endometriosis-associated infertility

Endometriosis is a common chronic benign disease that affects reproductive age women and causes chronic pelvic pain and infertility. Despite its prevalence, the exact mechanisms of the pathogenesis of endometriosis-associated infertility are unknown, and precise standards of management have not yet been established. Medical and surgical treatments for endometriosis have different effects on the chance of conception, either spontaneously or via assisted reproductive technologies (ART). In this manuscript, we review the literature from years 1979 to 2015 to report on the proposed mechanism of endometriosis-associated infertility, the staging system of endometriosis for pregnancy outcomes and the current management of patients with endometriosis-associated infertility.

Dating Endometriotic Ovarian Cysts Based on the Content of Cyst Fluid and its Potential Clinical Implications

This study was undertaken to test the hypotheses that, due to gradual accumulation of dead erythrocytes and their ingested products resulting from repeated hemorrhage, older endometriomas (whitish in color) contain chocolate fluid with higher iron content than younger (brownish/blackish in color) ones with concomitant higher collagen content and more adhesions. We recruited 30 premenopausal women with histologically confirmed ovarian endometriomas and collected samples of their endometriotic lesions and chocolate fluid and measured the viscosity, density, and the concentration of total bilirubin, ferritin, and free iron of the chocolate fluid. We also evaluated the lesion color and adhesion scores. In addition, we performed Masson trichrome and Picro-Sirius red staining on all endometriotic cysts and evaluated the extent of fibrosis in the lesions. We found that fluids taken from white-colored endometriomas had significantly higher concentration of total bilirubin, ferritin, and free iron, respectively, than black/brown-colored ones. In addition, older cysts had fluids that had significantly higher density and viscosity. Fluid density correlated positively with the concentrations of total bilirubin, ferritin, and free iron. Older lesions had significantly more collagen content and higher adhesion scores. Taken together, these data supports the notion that older cysts, having experienced more bleeding episodes, contain chocolate fluid that is higher in viscosity, density, and iron content and higher fibrotic content than younger ones. This provides another piece of evidence that endometriotic lesions are wounds that undergo repeated injury and repair, resulting ultimately fibrotic lesions that are resistant to hormonal treatment.

Effect of endometriosis on implantation rates when compared to tubal factor in fresh non donor in vitro fertilization cycles

OBJECTIVE:

The objective of the following study is to compare the outcome of in vitro fertilization and embryo transfer (IVF-ET) in women with endometriosis and tubal-factor infertility.

DESIGN:

Retrospective study.

SETTING:

Tertiary referral hospital, assisted reproductive technologies unit.

MATERIALS AND METHOD:

The study group consisted of 78 women diagnosed with advanced stage endometriosis. The control group included 100 women with tubal-factor infertility. These groups were retrospectively analyzed regarding stimulation, fertilization, embryo development, implantation and pregnancy outcome.

INTERVENTION (S):

Controlled ovarian hyperstimulation and IVF-ET.

RESULTS:

Lower oocyte yield with lower fertilization rate were found in women with endometriosis compared with tubal-factor control subjects. However, no differences were found in cleavage, implantation and clinical pregnancy rates between the endometriosis and tubal-factor groups.

CONCLUSIONS:

Our results showed that women with endometriosis have a lower oocyte yield and lower fertilization rate compared with women with tubal-factor infertility. However, once the oocyte is fertilized, it seems that the embryo has a normal chance of implantation, leading to similar pregnancy rates and adequately treated women with endometriosis have equal chances of conception as seen with tubal-factor infertility.

Nuclear factor-kappaB: a main regulator of inflammation and cell survival in endometriosis pathophysiology

OBJECTIVE

To update, analyze, and summarize the literature concerning nuclear factor-kappaB (NF-κB) participation in endometriosis pathophysiology.

DESIGN

Review.

RESULT(S)

Nuclear factor-kappaB is physiologically activated in the human endometrium, showing variable activity. A cyclic p65-DNA binding pattern was shown in the endometrium of healthy women. This cyclic pattern was altered in the endometrium of patients with endometriosis. Nuclear factor-kappaB is basally activated in peritoneal endometriotic lesions, showing higher p65 activity in red endometriotic lesions than in black lesions. In vivo and in vitro studies show up-regulation of inflammation and cell proliferation and down-regulation of apoptosis by NF-κB activity. Iron overload has been shown in the pelvic cavity of endometriosis patients, and iron overload and oxidative stress activate NF-κB in macrophages, which have been shown to participate in the endometriosis-associated inflammatory reaction.

CONCLUSION(S)

Nuclear factor-kappaB activation dysregulation in the endometrium of endometriosis patients may explain some endometrial biological alterations associated with endometriosis. The scientific evidence strongly suggests that NF-κB activity in endometriotic cells stimulates inflammation and cell proliferation and inhibits apoptosis, favoring the development and maintenance of endometriosis. Iron overload in the pelvic cavity of endometriosis patients could be a main factor enhancing oxidative stress and activating NF-κB in a chronic manner, contributing to endometriosis establishment and growth.

Iron storage is significantly increased in peritoneal macrophages of endometriosis patients and correlates with iron overload in peritoneal fluid

OBJECTIVE

To further investigate peritoneal iron disruption in endometriosis by studying iron storage in peritoneal macrophages of patients with endometriosis compared with controls.

DESIGN

Cross-sectional study.

SETTING

Academic gynecology research unit in a university hospital.

PATIENT(S)

Fifty patients undergoing laparoscopy.

INTERVENTION(S)

Collection of peritoneal fluid samples (N = 50) from patients with (n = 27) and without (n = 23) endometriosis undergoing laparoscopy.

MAIN OUTCOME MEASURE(S)

Quantification of peritoneal macrophage ferritin by immunocytochemical staining and immunodensitometry and measurement of peritoneal iron, transferrin, ferritin, and prohepcidin concentrations.

RESULT(S)

The optical density of peritoneal macrophage ferritin staining was statistically significantly higher in endometriosis patients than in controls. Higher iron concentrations, transferrin saturations, and ferritin concentrations were also detected in case of endometriosis. A statistically significant positive correlation was found between the optical density of macrophage ferritin staining and peritoneal iron concentrations in endometriosis and control patients.

CONCLUSION(S)

Iron storage is statistically significantly increased in peritoneal macrophages of patients with endometriosis and correlates with iron overload in peritoneal fluid. The potential implications of iron accumulation in peritoneal macrophages in case of endometriosis are discussed.

Paracrine regulation of endometriotic tissue

Endometriosis is a chronic estrogen-dependent gynecological disease, characterized by pelvic pain and infertility, defined as the presence of endometrial glands and stroma within the pelvic peritoneum and other extrauterine sites. In the peritoneal cavity endometrial cells adhere, proliferate and induce an inflammatory response. Despite a long history of clinical and experimental research, the pathogenesis of endometriosis is still controversial. Abnormal immunological activation, the endocrine milieu and the peritoneal environment all dramatically affect endometriotic tissue function. Recent studies suggest that the peritoneal fluid of women with endometriosis contains an increased number of activated macrophages and other immune cells that secrete various local products, such as growth factors and cytokines, which exert a paracrine action on endometriotic cells. Since the peculiar biological characteristics of eutopic endometrium from women with endometriosis differ from endometrium of normal subjects, an important role in the pathogenesis of this complex disease has been suggested. All of these factors contribute to enhanced proliferative and angiogenic activity and a number of functional and structural changes, resulting in the particular behavior of this tissue.

Iron overload enhances epithelial cell proliferation in endometriotic lesions induced in a murine model

BACKGROUND

Iron deposits are characteristic of endometriotic lesions, and pelvic iron concentrations are higher in endometriosis patients than in women without endometriosis. In this study, the effect of iron overload and iron chelation on the development of endometriosis in a murine model was investigated.

METHODS

Human menstrual endometrium was injected i.p. into nude mice, either alone (controls) or supplemented with erythrocytes or desferrioxamine (DFO), an iron chelator. After 5 days, the iron load of endometriosis-like lesions and peritoneal macrophages and fluid was evaluated. Lesions were quantified by immunohistochemical morphometry, and their proliferative activity was assessed.

RESULTS

Injection of erythrocytes into the pelvic cavity caused iron overload in lesions (P < 0.025) and peritoneal macrophages (P < 0.01) and fluid (P < 0.05), whereas DFO effectively reduced iron status in lesions (P < 0.05) and macrophages (P < 0.01) compared with controls. No difference was observed in the number or surface area of lesions between the three groups. Erythrocytes increased (P < 0.05) and DFO significantly decreased (P < 0.01) the proliferative activity of lesions.

CONCLUSIONS

Iron overload does not appear to affect lesion establishment but may contribute to the further growth of endometriosis by promoting cell proliferation of lesions. Iron chelator treatment could therefore be beneficial in endometriosis to prevent iron overload in the pelvic cavity and decrease cellular proliferation of lesions.

Reduction of estrogen production by interleukin-6 in a human granulosa tumor cell line may have implications for endometriosis-associated infertility

OBJECTIVE

To examine the effect of interleukin-6 (IL-6) on estrogen production and aromatase activity using a human granulosa tumor cell line (KGN cells). The involvement of the mitogen-activated protein kinase (MAPK) cascade in the inhibitory effects of IL-6 on estrogen production was also evaluated.

DESIGN

Molecular and biological studies of KGN cells.

SETTING

Department of Obstetrics and Gynecology, Tottori University Hospital, Yonago, Japan.

MAIN OUTCOME MEASURE(S)

Gene expression of IL-6 and the IL-6 receptor was analyzed by reverse transcription-polymerase chain reaction and Southern blot analysis. KGN cells were cultured for 48 hours with IL-6 (0.1-10 ng/mL) or IL-6 (10 ng/mL) plus a mitogen activated protein kinase-extracellular signal regulated kinase kinase 1/2 (MEK1/2) inhibitor U0126 (10 microM). Estradiol concentration in the culture supernatants was measured by means of enzyme immunoassay, [1beta-(3)H] androstenedione was added to the cell lysate supernatant, and aromatase activity was determined by measuring the amount of [(3)H] H(2)O released upon the conversion of [1beta-(3)H] androstenedione to estrone. To examine the activation of intracellular signal transduction molecules induced by IL-6, the phosphorylation of Stat3, p38 MAPK, and extracellular signal-regulated kinase 1/2 (ERK1/2) was examined by Western blotting.

RESULT(S)

Gene expression of IL-6 and its receptor was detected in KGN cells. Estradiol secretion was significantly inhibited by adding IL-6, which also suppressed aromatase activity to 50% of the control. In addition, pretreatment with U0126 restored the IL-6-induced suppression of aromatase activity. IL-6 markedly enhanced the phosphorylation of ERK1/2, but not Stat3 and p38 MAPK. U0126 markedly reduced the level of the IL-6-induced phosphorylation of ERK1/2.

CONCLUSION(S)

These findings demonstrate that IL-6 may reduce estrogen production via the MAPK signal pathway in human granulosa cells. The results may support the notion that IL-6 is related to impaired estrogen biosynthesis in patients with endometriosis.

Endometriosis and Inflammation in Infertility

A wealth of publications proposes that endometriosis and inflammation may have an unfavorable influence on fertility. A recent meta-analysis of assisted reproductive technologies demonstrated that, once confounding factors are controlled for, the pregnancy rate in women with endometriosis is approximately 50% of the rate of women with tubal factor infertility. Peritoneal fluid of women with endometriosis contains elevated amounts of macrophages and their secreted products, such as growth factors, cytokines, and angiogenic factors. Because reproductive organs are bathed in and thus will be influenced by peritoneal fluid, these proinflammatory mediators would affect various aspects of reproduction in women with endometriosis. Advanced stages of endometriosis may have easily understandable factors, such as distortion of the anatomy, causing infertility. On the other hand, in minimal or mild endometriosis mechanisms underlying reproductive failure are subtle and remain controversial. Recent reports suggest that inflammatory factors play a role in this endometriosis-associated reproductive failure. This review provides an overview of recent data on the effects of endometriosis-associated inflammation on fertility.

Typical and subtle atypical presentations of endometriosis

PURPOSE OF REVIEW

To review the concept of typical, subtle and invisible endometriosis and analyze the evolution and progression of the disease, as well as some factors possibly involved in the pathogenesis.

RECENT FINDINGS

Although rejected by Redwine, the concept of non-visible endometriosis has been proven to exist. Some new ideas on the implication of reactive oxygen species in the development of endometriosis and its early stages are described here.

SUMMARY

The increased diagnosis of endometriosis can be explained not only by the increased experience and ability of the surgeon to detect typical and non-typical endometriotic lesions, but also by a better understanding of the pathogenesis.

Iron overload in the peritoneal cavity of women with pelvic endometriosis

OBJECTIVE

To examine the possible involvement of iron in the physiopathology of endometriosis.

DESIGN

Prospective study.

SETTING

Department of gynecology in a university hospital.

PATIENT(S)

Seventy patients undergoing laparoscopy.

INTERVENTION(S)

Collection of peritoneal fluid (n = 57), blood samples, and biopsy samples from endometrium (n = 62) and from endometriotic (n = 33) and normal-appearing peritoneum (n = 53).

MAIN OUTCOME MEASURE(S)

Measurement of iron and ferritin in serum and peritoneal fluid and staining of iron deposits with Prussian blue in tissues.

RESULT(S)

Iron and ferritin concentrations were significantly higher in the peritoneal fluid of patients with endometriosis compared with controls during the secretory phase. Higher rates of ferritin and hemosiderin deposits were observed in the peritoneum adjacent to red (100%), black (57%), and white (62%) lesions compared with normal-appearing peritoneum (25%). Deposits were more frequent during the secretory phase than the proliferative phase in healthy peritoneum from controls, whereas they were found throughout the cycle in the vicinity of lesions in patients with endometriosis. Similar rates of iron deposition were observed in the stroma of black and white lesions and in eutopic endometrium from patients with endometriosis.

CONCLUSION(S)

Iron overload was observed in the cellular and peritoneal fluid compartments of the peritoneal cavity of women with endometriosis. Iron deposits seem to be related to the presence of lesions, suggesting that iron may be involved in the pathogenesis of endometriosis.

Oxidative stress and peritoneal endometriosis

OBJECTIVE

To review the literature associating pelvic endometriosis with oxidative stress and to discuss the potential causes and consequences of a pro-oxidant environment in the peritoneal cavity.

DESIGN

Literature survey.

RESULT(S)

Several studies suggest that oxidative stress is a component of the inflammatory reaction associated with endometriosis. Evidence includes the prevention of endometriosis induction in rabbits by the addition of antioxidants, an increase in reactive oxygen species release by macrophages, increased peritoneal levels of oxidized low-density lipoproteins and their by-products, altered expression of endometrial pro-oxidant and antioxidant enzymes, and consumption of peritoneal fluid vitamin E. Retrograde menstruation is likely to carry highly pro-oxidant factors, such as heme and iron, into the peritoneal cavity, as well as apoptotic endometrial cells, which are well-known inducers of oxidative stress. Reactive oxygen species may be involved in endometriosis-associated infertility and may play a role in the regulation of the expression of genes encoding immunoregulators, cytokines and cell adhesion molecules implicated in the pathogenesis of endometriosis.

CONCLUSION(S)

Better understanding of the mechanisms of reactive oxygen species production and detoxification and further investigation of their effect on the peritoneal environment are essential to obtain new insight into this disease and eventually develop new diagnostic and therapeutic strategies.

Macrophages, oxidation, and endometriosis

Retrograde menstruation has been suggested to be the cause for the presence of endometrial cells in the peritoneal cavity. However, little is known about the events that lead to the adhesion and growth of these cells that ultimately result in endometriosis, considering the fact that the disease occurs only in certain women despite the common occurrence of retrograde menstruation in most women. We postulate that, in normal women, the endometrial cells and tissue that arrive in the peritoneal cavity during menstruation are effectively removed by macrophages that are chemoattracted and become resident tissue macrophages in the peritoneal cavity. In contrast, the peritoneal macrophages in women with endometriosis are nonadherent and ineffectively scavenged, resulting in the sustained presence and growth of the endometrial cells. We also postulate that the peritoneal fluid is not a passive reservoir of the factors secreted by cells of the peritoneum, but actively promotes endometriosis. The peritoneal fluid is rich in lipoproteins, particularly low-density lipoprotein, which generates oxidized lipid components in a macrophage-rich inflammatory milieu. The oxidants exacerbate the growth of endometriosis by inducing chemoattractants such as MCP-1 and endometrial cell growth-promoting activity. We provide evidence for the presence of oxidative milieu in the peritoneal cavity of women with endometriosis, the nonscavenging properties of macrophages that are nonadherent, and the synergistic interaction between macrophages, oxidative stress, and the endometrial cells. For example, the peritoneal fluid lipoproteins of subjects with endometriosis have increased the propensity to undergo oxidation as compared with plasma lipoproteins, and the subjects also have increased titer of autoantibodies to oxidatively modified proteins. If the oxidative proinflammatory nature of the peritoneal fluid is an important mediator of endometriosis growth, anti-inflammatory agents and antioxidants might afford protection against endometriosis.

Role of cytokines in endometriosis

OBJECTIVE

To review the literature on the role of cytokines in the pathogenesis of endometriosis and endometriosis-associated infertility.

DESIGN

Pertinent studies were identified by a computer search of MEDLINE. References of selected articles were hand-searched for additional citations.

RESULT(S)

Recent studies suggest that the peritoneal fluid of women with endometriosis contains an increased number of activated macrophages that secrete various local products, such as growth factors and cytokines. Levels of several cytokines were reported to be elevated in the peritoneal fluid of women with endometriosis. Because the peritoneal environment may be controlled by locally regulated factors, cytokines are believed to play a role in the development and progression of endometriosis and endometriosis-associated infertility. A possible pathogenic mechanism links cytokines with endometriosis.

CONCLUSION(S)

Cytokines, which are produced by many cell types including endometriotic tissues, play diverse roles in the pathogenesis of endometriosis and endometriosis-associated infertility. More studies about the specific role of these cells and soluble factors are needed to improve understanding of endometriosis and to develop novel therapies.

Effects of human hydrosalpinx fluid on in-vitro murine fertilization

Patients with hydrosalpinges show a decrease of both fertility and clinical outcome of IVF and embryo transfer treatment. Several reports have demonstrated the negative effects of hydrosalpinx fluid (HSF) on embryo development and implantation. The aim of this study was to determine whether human HSF, collected from infertile patients, might exhibit a deleterious effect on gametes and fertilization using a murine IVF system. Murine gametes were co-incubated during IVF until first cleavage with human HSF diluted to 50% from four patients (HSF1-4). It was demonstrated that HSF affected fertilization, as determined by the count of the 2-cell embryos. Pre-incubation of spermatozoa with HSF during capacitation significantly lowered the percentage of 2-cell embryos (P < 0.05). While HSF1-3 had no significant effect on motility and viability of spermatozoa, HSF4 almost completely affected their survival. In contrast, pre-incubation of ovulated oocytes surrounded by their cumulus cells with HSF before IVF did not impede first cleavage. Taken together, these results suggest that HSF has a cytotoxic effect on spermatozoa and/or impairs the fertilization process, probably by altering capacitation/acrosome reaction and/or ligand(s)-receptor(s) interactions. Hydrosalpinges may be partly associated with sterility through HSF inhibitory effects on fertilization.

Peritoneal fluid modulates the sperm acrosomal exocytosis induced by N-acetylglucosaminyl neoglycoprotein

The effect of peritoneal fluid (PF) on the human sperm acrosome reaction (AR) was tested. Sperm was pre-incubated with PF and the AR was induced by calcium ionophore A23187 and a neoglycoprotein bearing N-acetylglycosamine residues (NGP). The AR induced by calcium ionophore was inhibited 40% by PF from controls (PFc) and 50% by PF from the endometriosis (PFe) group, but not by PF from infertile patients without endometriosis (PFi). No significant differences were found in the spontaneous AR. When the AR was induced by NGP, pre-incubation with PFc reduced (60%) the percentage of AR, while PFe and PFi caused no significant differences. The average rates of acrosome reactions obtained in control. NGP- and ionophore-treated sperm showed that NGP-induced exocytosis differed significantly between the PFc (11%) and PFe/PFi groups (17%), and the ionophore-induced AR was higher for PFi (33%) than PFc/PFe (25%). The incidence of the NGP-induced AR was reduced in the first hour of pre-incubation with PFc and remained nearly constant throughout 4 h of incubation. The present data indicate that PF possesses a protective factor which prevents premature AR.

Outcome of IVF in patients with endometriosis in comparison with tubal-factor infertility

PURPOSE

The aim of this retrospective study was to compare the outcome of in vitro fertilization and embryo transfer in women with endometriosis and a control group with tubal-factor infertility.

METHODS

Forty-eight patients with endometriosis underwent 65 cycles of in vitro fertilization and embryo transfer at Huddinge University Hospital. The matched control group with tubal-factor infertility consisted of 98 cycles in 98 patients. These groups were retrospectively analyzed regarding stimulation, fertilization, embryo development, implantation, and pregnancy outcome.

RESULTS

The fertilization rate was significantly lower in women with endometriosis, but the cleavage, implantation, and pregnancy rates did not differ.

CONCLUSIONS

Our results show that women with endometriosis have a lower fertilization rate compared with women with tubal-factor infertility. However, once the oocyte is fertilized, it seems that the preembryo has a normal chance of implantation, leading to similar pregnancy rates.

Effects of antibodies to transferrin and alpha 2-HS glycoprotein on in vitro sperm motion: implications in infertility associated with endometriosis

PROBLEM

Women with endometriosis have antibodies to endometrial transferrin and alpha 2-HS glycoprotein in their serum and peritoneal fluid. The objective of this study was to determine whether antibodies to transferrin and alpha 2-HS glycoprotein adversely affect sperm motility and survival.

METHOD OF STUDY

Spermatozoa obtained from normal fertile donors and washed free of seminal plasma were incubated with the medium (control), 1:2 and 1:100 dilutions of antitransferrin, 1:4, 1:8 and 1:100 dilutions of anti-alpha 2-HS glycoprotein, and a 1:2 dilution of antialbumin antiserum (negative control). Sperm motion characteristics in 10 microliters aliquots were evaluated at 30 min, 1 hr, 2 hr, 4 hr, and 24 hr using computerized sperm motion analysis. A paired t-test was done to analyze the effects of the various antibodies on sperm motion characteristics.

RESULTS

Antibodies to albumin failed to adversely affect sperm motility in general or the several sperm motion characteristics in particular. In contrast, antibodies to transferrin at the dilution of 1:2 adversely affected the percentage of motile and rapid spermatozoa, progressive and path velocities, straightness, linearity, track speed, and anterior-lateral head displacement (P < 0.001) at all the time intervals, whereas a 1:100 dilution of this antiserum adversely affected these parameters only at 24 hr. Elongation and beat cross-frequency were significantly affected at 4 and 24 hr by a 1:2 dilution of antitransferrin antiserum. The effects of anti-alpha 2-HS glycoprotein were more pronounced than those of antitransferrin, but they were similar. Dilutions of 1:4 and 1:8 were effective at all time intervals, whereas a 1:100 dilution was effective in reducing the track speed and the percentage of rapid cells at 24 hr (P < 0.001).

CONCLUSION

Antibodies to endometrial transferrin and alpha 2-HS glycoprotein present in the peritoneal fluid, and possibly in the oviductal fluid, of patients with endometriosis may adversely affect postcoital sperm motility and sperm survival.

Peritoneal fluid from women with moderate or severe endometriosis inhibits sperm motility: the role of seminal fluid components

OBJECTIVE

To examine the mechanism of sperm motility inhibition by peritoneal fluid (PF) from women with endometriosis.

DESIGN

Prospective, randomized study.

SETTING

University-based andrology laboratory.

PATIENTS

Women with and without endometriosis.

INTERVENTIONS

Fresh semen or Percoll-purified sperm fractions were combined with PF from women with endometriosis (n = 20), from fertile women without endometriosis (n = 10), or with physiological saline.

MAIN OUTCOME MEASURE

Sperm motility parameters were determined with computer assisted semen analysis. Data were evaluated by the analysis of variance and the Student's t-test.

RESULTS

Peritoneal fluid from women with minimal or mild endometriosis did not inhibit sperm motility in semen. Peritoneal fluid from women with moderate or severe endometriosis caused approximately 40%, 50%, and 80% declines in sperm motility and in percent progressive motile sperm after 4,7, and 24 hours, respectively. Sperm velocity was inhibited by approximately 30% and 60% after 7 and 24 hours, respectively. However, in the Percoll-purified sperm fractions the same PF did not inhibit sperm motility within the 4- to 7-hour time frame, and only a 17% to 42% inhibition occurred after the overnight incubation. Sperm velocity was not affected.

CONCLUSION

Cellular components of seminal fluid appear to mediate the inhibitory action of PF. Assuming that the leukocyte components of semen and PF are common, the cell-mediated inhibition of sperm motility is a likely contributor to endometriosis related infertility.