Molecular detection of intrauterine microbial colonization in women with endometriosis

Intrauterine Shaping of Fetal Microbiota

Mechanisms resulting from the physiological immaturity of the digestive system in children delivered before 32 weeks of gestation and, in particular, different interactions between the microbiome and the body have not been fully elucidated yet. Next-generation sequencing methods demonstrated the presence of bacterial DNA in the placenta and amniotic fluid, which may reflect bacterial populations that initiate intestinal colonization in utero. Numerous studies confirmed the hypothesis stating that intestinal bacteria played an important role in the pathogenesis of necrotizing enterocolitis (NEC) early- and late-onset neonatal sepsis (EONS and LONS). The model and scale of disorders within the intestinal microbiome are the subject of active research in premature infants. Neonatal meconium was primarily used as an indicator defining the environment in utero, as it is formed before birth. Metagenomic results and previous data from microbiological bacterial cultures showed a correlation between the time from birth to sample collection and the detection of bacteria in the neonatal meconium. Therefore, it may be determined that the colonization of the newborn's intestines is influenced by numerous factors, which may be divided into prenatal, perinatal, and postnatal, with particular emphasis put on the mode of delivery and contact with the parent immediately after birth. Background: The aim of this review was to collect available data on the intrauterine shaping of the fetal microbiota. Methods: On 13 March 2024, the available literature in the PubMed National Library of Medicine search engine was reviewed using the following selected keywords: "placental microbiome", "intestinal bacteria in newborns and premature infants", and "intrauterine microbiota". Results: After reviewing the available articles and abstracts and an in-depth analysis of their content, over 100 articles were selected for detailed elaboration. We focused on the origin of microorganisms shaping the microbiota of newborns. We also described the types of bacteria that made up the intrauterine microbiota and the intestinal microbiota of newborns. Conclusions: The data presented in the review on the microbiome of both term newborns and those with a body weight below 1200 g indicate a possible intrauterine colonization of the fetus depending on the duration of pregnancy. The colonization occurs both via the vaginal and intestinal route (hematogenous route). However, there are differences in the demonstrated representatives of various types of bacteria, phyla Firmicutes and Actinobacteria in particular, taking account of the distribution in their abundance in the individual groups of pregnancy duration. Simultaneously, the distribution of the phyla Actinobacteria and Proteobacteria is consistent. Considering the duration of pregnancy, it may also be concluded that the bacterial flora of vaginal origin dominates in preterm newborns, while the flora of intestinal origin dominates in term newborns. This might explain the role of bacterial and infectious factors in inducing premature birth with the rupture of fetal membranes.

Uterine Endometrium Microbiome in Women with Repeated Implantation Failure Complicated by Endometriosis

Objectives: This prospective study evaluated whether endometriosis is associated with chronic endometritis (CE) and affects the uterine endometrium microbiome (UEM) in women with repeated implantation failure (RIF). Methods: Forty-three women with RIF were divided into 12 with endometriosis (EM) and 31 without endometriosis (non-EM). The UEM was examined by 16S ribosomal RNA (rRNA) sequencing, and CE was determined by CD 138 staining (plasma cells > 5.15/10 mm2) simultaneously. Results: The EM group had a higher bacterial number (EM vs. non-EM; median [range], 6.5 vs. 3 [3-11, 1-16], p = 0.009), while the frequency of Lactobacillus species did not change. The rates of presence of Dialister (41.7% [5/12] vs. 3.3% [1/31], p = 0.004) and Streptococcus species (58.3% [7/12] vs. 16.1% [5/31], p = 0.017) were higher in the EM group. The prevalence of CE did not differ between the two groups. Multivariable logistic regression analysis revealed that the presence of Dialister species (odds ratio, 10.97, 95% confidence interval, 1.17-249.37, p = 0.036) was associated with endometriosis. In the EM group, five women with Dialister species had a higher number of bacterial species (10 vs. 5 [6-11, 3-7], p = 0.021) and higher Shannon diversity index (0.50 vs. 0.20 [0.19-1.39, 0.03-0.46], p = 0.026) than seven without Dialister species. Conclusions: Dialister and Streptococcus species, and the increased number of bacterial species in UEM may be related to the pathogenesis of RIF complicated by endometriosis.

The impact of metronidazole on pain persistence after fertility-sparing endometriosis surgery: METROFERT randomized study

BACKGROUND

Recent studies have shown that a disrupted microbiome is associated with endometriosis. Despite endometriosis affecting 1 in 10 reproductive-aged women, there is a lack of innovative and nonhormonal long-term effective treatments. Studies have reported an approximately 20% to 37.5% persistence of pain after fertility-sparing endometriosis surgery. Metronidazole has been shown to decrease inflammatory markers and the size of endometriosis lesions in animal studies.

OBJECTIVE

To determine if modulating the microbiome with oral metronidazole for 14 days after fertility-sparing endometriosis surgery decreases pain persistence postoperatively.

STUDY DESIGN

This was a randomized, multicenter, placebo-controlled, double-blind trial. Individuals 18 to 50 years old were prospectively randomized to placebo vs oral metronidazole for 14 days immediately after endometriosis fertility-sparing excision surgery. The primary outcome was binary, subjective pain persistence at 6 weeks postoperatively. Secondary outcomes included quality of life, sexual function, and endometriosis-associated pain scores according to the Endometriosis Health Profile-5, Female Sexual Function Index, and a visual analog scale.

RESULTS

One hundred fifty-two participants were approached from October 2020 to October 2023 to enroll in the study. Sixty-four participants were excluded either because they did not meet inclusion or exclusion criteria or because they declined to participate. Eighty-eight participants were randomized in a 1:1 ratio to receive either the oral placebo or metronidazole after endometriosis excision surgery; 18.2% of participants were lost to follow-up or discontinued treatment and this was not significantly different between the 2 arms, yielding a final cohort of 72 participants. Baseline demographics of the 2 study groups were similar. There was no statistically significant improvement in the primary outcome of binary subjective pain persistence between the metronidazole group compared to placebo (84% vs 88%, P=.74) at 6 weeks postoperatively. Further, no significant differences between treatments were detected in the secondary outcomes.

CONCLUSION

A postoperative 14-day regimen of oral metronidazole immediately after fertility-sparing endometriosis surgery was not associated with any significant differences between treatment groups in the persistence of endometriosis-related pain symptoms compared to placebo at 6 weeks.

Microbial signatures and continuum in endometrial cancer and benign patients

BACKGROUND

Endometrial cancer is a multifactorial disease with inflammatory, metabolic and potentially microbial cues involved in disease pathogenesis. The endometrial cancer microbiome has been poorly characterised so far and studies have often overestimated bacterial biomass due to lack of integration of appropriate contamination controls. There is also a scarcity of evidence on the functionality of microbial microenvironments in endometrial cancer. This work addresses that knowledge gap by interrogating the genuine, contamination-free microbial signatures in the female genital tract and rectum of women with endometrial cancer and the mechanistic role of microbiome on carcinogenic processes.

RESULTS

Here we sampled different regions of the reproductive tract (vagina, cervix, endometrium, fallopian tubes and ovaries) and rectum of 61 patients (37 endometrial cancer; 24 benign controls). We performed 16S rRNA gene sequencing of the V1-V2 hypervariable regions and qPCR of the 16S rRNA gene to qualitatively and quantitatively assess microbial communities and used 3D benign and endometrial cancer organoids to evaluate the effect of microbial products of L. crispatus, which was found depleted in endometrial cancer patients following primary analysis, on endometrial cell proliferation and inflammation. We found that the upper genital tract of a subset of women with and without endometrial cancer harbour microbiota quantitatively and compositionally distinguishable from background contaminants. Endometrial cancer was associated with reduced cervicovaginal and rectal bacterial load together with depletion of Lactobacillus species relative abundance, including L. crispatus, increased bacterial diversity and enrichment of Porphyromonas, Prevotella, Peptoniphilus and Anaerococcus in the lower genital tract and endometrium. Treatment of benign and malignant endometrial organoids with L. crispatus conditioned media exerted an anti-proliferative effect at high concentrations but had minimal impact on cytokine and chemokine profiles.

CONCLUSIONS

Our findings provide evidence that the upper female reproductive tract of some women contains detectable levels of bacteria, the composition of which is associated with endometrial cancer. Whether this is a cause or consequence of cancer pathophysiology and what is the functional significance of this finding remain to be elucidated to guide future screening tools and microbiome-based therapeutics. Video Abstract.

Endometriosis, Pain, and Related Psychological Disorders: Unveiling the Interplay among the Microbiome, Inflammation, and Oxidative Stress as a Common Thread

Endometriosis (EM), a chronic condition in endometrial tissue outside the uterus, affects around 10% of reproductive-age women, significantly affecting fertility. Its prevalence remains elusive due to the surgical confirmation needed for diagnosis. Manifesting with a range of symptoms, including dysmenorrhea, dyschezia, dysuria, dyspareunia, fatigue, and gastrointestinal discomfort, EM significantly impairs quality of life due to severe chronic pelvic pain (CPP). Psychological manifestations, notably depression and anxiety, frequently accompany the physical symptoms, with CPP serving as a key mediator. Pain stems from endometrial lesions, involving oxidative stress, neuroinflammation, angiogenesis, and sensitization processes. Microbial dysbiosis appears to be crucial in the inflammatory mechanisms underlying EM and associated CPP, as well as psychological symptoms. In this scenario, dietary interventions and nutritional supplements could help manage EM symptoms by targeting inflammation, oxidative stress, and the microbiome. Our manuscript starts by delving into the complex relationship between EM pain and psychological comorbidities. It subsequently addresses the emerging roles of the microbiome, inflammation, and oxidative stress as common links among these abovementioned conditions. Furthermore, the review explores how dietary and nutritional interventions may influence the composition and function of the microbiome, reduce inflammation and oxidative stress, alleviate pain, and potentially affect EM-associated psychological disorders.

The role of innate and adaptive immunity in endometriosis

The innate and adaptive immune systems are the two key branches that determine host protection at all mucosal surfaces in human body, including the female reproductive tract. The pattern recognition receptors within the host that recognize pathogen-associated molecular patterns are expressed on the cells of the innate immune system. Rapidly reactive, theinnate immune system, responds immediately to the presence of infectious or other non-self agents, thereby launching an inflammatory response to protect the host until the activation of slower adaptive immune system. Macrophages, dendritic cells, and toll-like receptors are integral components of the innate immune system. In contrast, T-helper (Th1/Th2/Th17) cells and regulatory T (Treg) cells are the primary components of adaptive immune system. Studies showed that the growth and progression of endometriosis continue even in unilateral ovariectomized animal suggesting that besides ovarian steroid hormones, the growth of endometriosis could be regulated by innate/adaptive immune systems in pelvic environment. Recent reports demonstrated a potential role of Th1/Th2/Th17/Treg cells either individually or collectively in the initiation, maintenance, and progression of endometriosis. Herewe review the fundamental knowledge of innate and adaptive immunity and elaborate the role of innate and adaptive immunity in endometriosis based on both human and experimental data.

Horizons in Endometriosis: Proceedings of the Montreux Reproductive Summit, 14-15 July 2023

Endometriosis is a complex and chronic gynaecological disorder that affects millions of women worldwide, leading to significant morbidity and impacting reproductive health. This condition affects up to 10% of women of reproductive age and is characterised by the presence of endometrial-like tissue outside the uterus, potentially leading to symptoms such as chronic pelvic pain, dysmenorrhoea, dyspareunia, and infertility. The Montreux summit brought a number of experts in this field together to provide a platform for discussion and exchange of ideas. These proceedings summarise the six main topics that were discussed at this summit to shed light on future directions of endometriosis classification, diagnosis, and therapeutical management. The first question addressed the possibility of preventing endometriosis in the future by identifying risk factors, genetic predispositions, and further understanding of the pathophysiology of the condition to develop targeted interventions. The clinical presentation of endometriosis is varied, and the correlation between symptoms severity and disease extent is unclear. While there is currently no universally accepted optimal classification system for endometriosis, several attempts striving towards its optimisation - each with its own advantages and limitations - were discussed. The ideal classification should be able to reconcile disease status based on the various diagnostic tools, and prognosis to guide proper patient tailored management. Regarding diagnosis, we focused on future tools and critically discussed emerging approaches aimed at reducing diagnostic delay. Preserving fertility in endometriosis patients was another debatable aspect of management that was reviewed. Moreover, besides current treatment modalities, potential novel medical therapies that can target underlying mechanisms, provide effective symptom relief, and minimise side effects in endometriotic patients were considered, including hormonal therapies, immunomodulation, and regenerative medicine. Finally, the question of hormonal substitution therapy after radical treatment for endometriosis was debated, weighing the benefits of hormone replacement.

Bacterial infection in endometriosis: a silver-lining for the development of new non-hormonal therapy?

The pathogenesis of endometriosis is a hotly debated topic, yet still cloaked in multiple layers of hypothetical theories. A recent report raises the possibility that bacterial infection, especially those of the genus Fusobacterium, may be the cause of endometriosis, at least in certain women. More importantly, the demonstration that treatment with broad-spectrum antibiotics significantly reduced the size of lesions in a mouse endometriosis model rekindles the hope for new non-hormonal treatments. The development of new therapies has been plagued by strings of unsuccessful clinical trials over the last two decades. Is this antibiotic therapy, a silver lining for the research and development of non-hormonal drugs for endometriosis?

Emerging bacterial factors for understanding pathogenesis of endometriosis

The pathogenesis of endometriosis is a complex process, and recent research has introduced novel hypotheses in this field. This review summarizes recent studies on the pathogenesis of endometriosis. We focused on several classical hypotheses, as well as their interactions with the microenvironment of hormonal dependence and immunosuppression. Furthermore, we highlighted the emergence of bacterial factors associated with endometriosis. Recent advances in next-generation sequencing (NGS) have revealed the presence and detailed distribution of these bacteria as well as the involvement of specific bacteria in pathogenesis. These factors alter the microenvironment in the early stages of endometriosis development, leading to lesion formation. Understanding the mechanisms underlying the early development of endometriosis from a new perspective would be helpful for the development of novel therapeutic agents for endometriosis.

A Landscape View of the Female Genital Tract Microbiome in Healthy Controls and Women With Reproductive Health Conditions Associated With Ectopic Pregnancy

Disruption of the female genital microbiome is associated with several pregnancy complications, including miscarriage, preterm onset of labour, and tubal pregnancy. Ectopic pregnancy is a known cause of maternal morbidity and mortality, but early diagnosis and treatment of ectopic pregnancy remain a challenge. Despite growing established associations between genital microbiome and female reproductive health, few studies have specifically focused on its link with ectopic pregnancy. Therefore, the current review aims to provide a comprehensive account of the female genital microbiome in healthy and fertile women compared to those in ectopic pregnancy and its associated risk factors. The microbial diversity from various sites of the female genital tract was explored for a reliable proxy of female reproductive health in sequencing-based ectopic pregnancy research. Our report confirmed the predominance of Lactobacillus in the vagina and the cervix among healthy women. The relative abundance decreased in the vaginal and cervical microbiome in the disease state. In contrast, there were inconsistent findings on the uterine microbiome across studies. Additionally, we explore a spectrum of opportunities to enhance our understanding of the female genital tract microbiome and reproductive conditions. In conclusion, this study identifies gaps within the field and emphasises the need for visionary solutions in metagenomic tools for the early detection of ectopic pregnancy and other gynaecological diseases.

Association Between Pelvic Inflammatory Disease and Risk of Endometriosis: A Systematic Review and Meta-Analysis

Background: Endometriosis is a common chronic disorder, which leads to dysmenorrhea, dyspareunia, pelvic chronic pain, and infertility. It affects ∼6% to 10% of the general female population. However, the etiology of endometriosis remained unclear. We aimed to systematically assess the association between pelvic inflammatory disease (PID) and the risk of endometriosis. Materials and Methods: Eligible studies published until May 21, 2022, were retrieved from the PubMed, EMBASE, and Web of Science databases. The studies were included based on the following criteria: (1) original articles on the association between PID and risk of endometriosis; (2) randomized controlled trials and cross-sectional, case-control, and cohort studies; and (3) studies involving humans. The Newcastle-Ottawa Quality Assessment Scale was used to assess the quality of the studies included in this systematic review. The association between PID and risk of endometriosis was evaluated using the overall odds ratio (OR) and correlative 95% confidence interval (CI). Results: The meta-analysis included 14 studies with 747,733 patients. The mean prevalence of PID in women with endometriosis was 33.80%. Our quantitative synthesis revealed that endometritis was associated with a significantly increased risk of endometriosis (OR: 1.63, 95% CI: 1.53-1.74, I2 = 59%). Conclusion: We study a statistically significant association between PID and the risk of endometriosis. In particular, endometritis might play an important role in endometriosis, based on the lower heterogeneity of the subgroup analysis. This finding suggests that reducing the incidence of endometritis might aid in the prevention and treatment of endometriosis.

Gut Microbiota and Endometriosis: Exploring the Relationship and Therapeutic Implications

Endometriosis is a common inflammatory disease affecting women of reproductive age, characterized by the growth of endometrial tissue beyond the uterus. In addition to gynecological manifestations, many endometriosis patients experience gastrointestinal symptoms, indicating a potential association between gut health and the disease. Recent studies have revealed alterations in the gut microbiota of individuals with endometriosis, including reduced diversity, microbial composition imbalances, and pathogenic bacteria. These changes can disrupt immune function, increase inflammation, and contribute to the chronic inflammatory state observed in endometriosis. Moreover, dysregulation of intestinal permeability may further exacerbate gastrointestinal symptoms in affected individuals. Understanding the role of the gut microbiota and intestinal permeability in endometriosis can provide valuable insights into disease pathogenesis, aid in non-invasive diagnostic approaches, and open new avenues for therapeutic interventions. Probiotics, in particular, have shown promise in improving endometriosis-associated pain symptoms and reducing endometriotic lesions in animal models. This review suggests that additional research and well-designed clinical trials are necessary to validate the potential diagnostic and therapeutic benefits of manipulating the gut microbiota in managing endometriosis and its gastrointestinal symptoms, thereby improving the quality of life for those affected.

Cannabis and Endometriosis: The Roles of the Gut Microbiota and the Endocannabinoid System

Endometriosis, a chronic condition affecting around 10-14% of women, is challenging to manage, due to its complex pathogenesis and limited treatment options. Research has suggested a potential role of the gut microbiota and the endocannabinoid system in the development and progression of endometriosis. This narrative review aims to explore the role of, and any potential interactions between, the endocannabinoid system (ECS) and the gut microbiota in endometriosis. This review found that both the ECS and microbiota influence endometriosis, with the former regulating inflammation and pain perception and the latter influencing immune responses and hormonal balance. There is evidence that a dysregulation of the endocannabinoid system and the gut microbiota influence endometriosis symptoms and progression via changes in CB1 receptor expression and increased circulating levels of endocannabinoids. Microbial imbalances in the gut, such as increases in Prevotella, have been directly correlated to increased bloating, a common endometriosis symptom, while increases in E. coli have supported the bacterial contamination hypothesis as a potential pathway for endometriosis pathogenesis. These microbial imbalances have been correlated with increases in inflammatory markers such as TNF-α and IL-6, both often raised in those with endometriosis. Protective effects of the ECS on the gut were observed by increases in endocannabinoids, including 2-AG, resulting in decreased inflammation and improved gut permeability. Given these findings, both the ECS and the gut microbiota may be targets for therapeutic interventions for endometriosis; however, clinical studies are required to determine effectiveness.

The interplay of obesity, microbiome dynamics, and innovative anti-obesity strategies in the context of endometrial cancer progression and therapeutic approaches

Endometrial cancer (EC) is the most common gynecologic malignancy in the United States, and its incidence and mortality are rising. Obesity is more tightly associated with EC than any other cancer. Thus, the rising prevalence of obesity and associated risk factors, including diabetes and insulin resistance, cause alarm. The metabolic derangements of obesity increase the bioavailability of estrogen, hyperinsulinemia, and inflammation in a complex system with direct and indirect effects on the endometrium, resulting in proliferation and, ultimately, carcinogenesis. In addition, the gut dysbiosis associated with obesity helps contribute to these metabolic derangements, priming an individual for developing EC and perhaps affecting treatment efficacy. More recent studies are beginning to explore obesity's effect on the local tumor microbiome of EC and its role in carcinogenesis. Significant and sustained weight loss in individuals can considerably decrease the risk of EC, likely through reversal of the altered metabolism and dysbiosis resulting obesity. Bariatric surgery is the gold standard for successful weight loss and highlights how reversing of the systemic effects of obesity can reduce EC risk. However, the current limited availability, knowledge, and imposed stigma of bariatric surgery prohibits population-level reductions in EC. Therefore, effective and maintainable non-surgical dietary and pharmacologic interventions are needed.

Uterine Microbiome: Does the Sampling Technique Matter?

Studies have proven the significance of microbial communities in various parts of the human body for health. In recent years it has been discovered that the uterine cavity is not sterile, and endometrium has its own microbiome which appears to have an impact on female fertility and gynecological pathologies. Lactobacillus has shown to dominate the microbial profile in the uterus and is considered an indicator of a healthy uterine environment. Yet, many argue that the Lactobacillus dominance is due to vaginal contamination during the sampling process. To date there is no clearly defined healthy endometrial microbial profile, which is largely due to the fact that determining the microbial community from the endometrium is complicated, and there is currently no consensus on sampling methods for the endometrial microbiome. As a result, this restricts ability to replicate discoveries made in other cohorts. Here we aim to give an overview of the sampling methods used and discuss what impedes the endometrial microbiome studies as well as how to reach a consensus on the study design. This knowledge could be incorporated into the future research and the knowledge on endometrial microbiome could be included into the diagnostics and treatment of female reproductive health.

Gut and reproductive tract microbiota: Insights into the pathogenesis of endometriosis (Review)

Endometriosis is characterized by the presence of endometrial-like tissue outside the uterus and is associated with an inflammatory immune response. The gut and reproductive tract microbiota constitute a protective barrier against infection by pathogens and regulate inflammatory and immune functions. This review summarizes microbiota imbalance (i.e., dysbiosis) in endometriosis and discusses how dysbiosis influences disease development. The literature was searched for studies published from inception to March 2022 in the PubMed and Google Scholar databases using a combination of specific terms. An altered gut and reproductive tract microbiome has been reported in numerous conditions, such as inflammatory bowel disease, allergies, autoimmunity, cancer and reproductive disorders (e.g., endometriosis). Furthermore, microbial dysbiosis is a hallmark of endometriosis and is characterized by a decrease in beneficial probiotics and an increase in pathogenic microbes, which leads to a series of estrobolomic and metabolomic changes. Gut or reproductive tract microbiome dysbiosis was reported in mice, nonhuman primates, and females with endometriosis. Animal models of endometriosis demonstrated the effects of the gut microbiome on lesion growth and vice versa. The immune system mediated by the microbiota-gut-reproductive tract axis triggers an inflammatory response that damages reproductive tract tissue, which possibly leads to endometriosis. However, whether the alteration of eubiosis (a balanced microbiota) to dysbiosis is a cause or a result of endometriosis is unclear. In conclusion, this review provides an overview of the relationship between the gut and reproductive tract microbiome and endometriosis, focusing on the mechanisms by which dysbiosis may increase the risk of disease.

An Overview of the Microbiota of the Human Urinary Tract in Health and Disease: Current Issues and Perspectives

This article is intended to deepen our knowledge to date regarding the functions of the resident microbiota/microbiome in the urinary system for human health and disease. First, we sought to report the general characteristics (composition and stability) of the normal urinary system microbiota in the different anatomical sites in relation to some factors such as the effect of age, gender and diet, analyzing in detail the functions and the composition of the microbiota in the light of current knowledge. Several pieces of evidence suggest the importance of preserving the micro-ecosystem of the urinary system, and in some cases their relationship with diseases is important for maintaining human health is well understood. The female and male reproductive microbiota have mainly been studied over the past decade. In the past, the arrest was thought to have taken place in a sterile environment. Microorganisms of the microbiota form biofilms, three-dimensional structures, that differ in the reproductive organs and interact with both gametes and the embryo as well as with maternal tissues. These biofilms from the reproductive system also interact with others, such as that of the gastrointestinal tract. Reduction in its diversity intestinal microbiota can disrupt estrogen metabolism and affect the reproductive microbiota. It is therefore understood that its quantitative and qualitative identification is important for microbiota, but also the study of the structures formed by the microorganisms. A dysbiosis with local or systemic causes can lead to serious diseases. The role of probiotics in maintaining microbial population harmony (eubiosis) and preventing certain pathologies of the urinary and reproductive system was also investigated. A negative variation in the qualitative and quantitative composition of certain strains of microorganisms (dysbiosis) due to local or systemic causes can even lead to serious diseases. The role of probiotics in maintaining the healthy balance of microorganism populations (eubiosis), and thus in the prevention of certain pathologies of the urinary and reproductive system, has also been studied.

Fusobacterium infection facilitates the development of endometriosis through the phenotypic transition of endometrial fibroblasts

Retrograde menstruation is a widely accepted cause of endometriosis. However, not all women who experience retrograde menstruation develop endometriosis, and the mechanisms underlying these observations are not yet understood. Here, we demonstrated a pathogenic role of Fusobacterium in the formation of ovarian endometriosis. In a cohort of women, 64% of patients with endometriosis but <10% of controls were found to have Fusobacterium infiltration in the endometrium. Immunohistochemical and biochemical analyses revealed that activated transforming growth factor-β (TGF-β) signaling resulting from Fusobacterium infection of endometrial cells led to the transition from quiescent fibroblasts to transgelin (TAGLN)-positive myofibroblasts, which gained the ability to proliferate, adhere, and migrate in vitro. Fusobacterium inoculation in a syngeneic mouse model of endometriosis resulted in a marked increase in TAGLN-positive myofibroblasts and increased number and weight of endometriotic lesions. Furthermore, antibiotic treatment largely prevented establishment of endometriosis and reduced the number and weight of established endometriotic lesions in the mouse model. Our data support a mechanism for the pathogenesis of endometriosis via Fusobacterium infection and suggest that eradication of this bacterium could be an approach to treat endometriosis.

Gut and Vaginal Microbiota in the Endometriosis: Systematic Review and Meta-Analysis

Background

Endometriosis is a clinical condition associated with genetic, endocrine, and immunological factors, present in 6 to 10% of women of reproductive age. Currently, the human microbiota has been studied and associated with the evolution of diseases due to its influence on pathogenesis, indicating that changes in the colonization of microorganisms in the genitourinary and gastrointestinal systems can promote physiological changes that can trigger inflammatory and immunological processes and hormonal dysregulation, which can be linked to endometriosis. Thus, this systematic review and meta-analysis evaluated microbiota changes in women with endometriosis.

Methods

The following electronic databases were searched up to April 2022: Medline, Embase, Web of Science, Cochrane Library, and gray literature (Google Scholar), using the keywords "dysbiosis", "microbiome" and "endometriosis", combined with their synonyms. The observational studies conducted with women diagnosed with endometriosis and women without endometriosis as controls were included. For the analyses, a standard mean difference with a 95% confidence interval was used using RevMan software (version 5.4), and for methodological quality assessment, the Newcastle-Ottawa scale was used.

Results

A total of 16 studies were found in the literature assessing the composition of the microbiota in women with endometriosis, and no significant difference were found for changes in alpha diversity analysis in gut microbiota (SMD = -0.28; 95% CI = -0.70 to 0.14; P = 0.19; I2 = 52%; four studies, 357 participants) or vaginal microbiota (SMD = -0.68; 95% CI = -1.72 to 0.35; P = 0.19; I2 = 66%; two studies, 49 participants).

Conclusion

In intestinal and vaginal samples from women with endometriosis, alpha-diversity did not present a significant difference when compared to the control population. However, each study individually showed a possible relationship between the female microbiota and endometriosis. This trial is registered with CRD42021260972.

The role of microbiota in the pathophysiology of uterine fibroids - a systematic review

For a long time, the uterus had been considered a sterile organ, meaning that under physiological conditions the uterus would not be colonized by bacteria. Based on available data, it may be concluded that the gut and uterine microbiome are related, and that the role of this microbiome is greater than expected. Despite being the most common pelvic neoplasms in women of reproductive age, uterine fibroids (UFs) are still poorly understood tumors whose etiology has not been fully determined. This systematic review presents the relationship between intestinal and uterine dysbiosis and uterine fibroids. A systematic review of three medical databases was carried out: the MEDLINE/PubMed, Scopus and Cochrane. In this study, 195 titles and abstracts were reviewed, including only original articles and clinical trials of uterine microbiome criteria. Finally, 16 studies were included to the analysis. In recent years, researchers dealing with reproduction in a broad sense have focused on the microbiome in various locations to study its role in the pathogenesis and, consequently, the prevention and treatment of diseases of the genital organ. Conventional microbial detection methods are not suitable for identifying bacteria, which are difficult to culture. Next-generation sequencing (NGS) provides an easier and faster and more informative analysis of bacterial populations. It seems that gut microbiota dysbiosis has the potential to be a risk factor for uterine fibroids or affect the disease process. Some changes were shown in many types of bacteria, such as Firmicutes, Proteobacteria, Actinobacteria and Verrucomicrobia detected in fecal samples in patients with uterine fibroids. In view of the few results on the link between the microbiome and uterine fibroids, further intensive studies in humans and animal models are necessary, including the possible use of different microbiome modulations in the prevention or treatment of uterine fibroids.

New concepts on the etiology of endometriosis

Endometriosis is a serious, chronic disorder where endometrial tissue grows outside the uterus, causing severe pelvic pain and infertility. It affects 11% of women. Endometriosis is a multifactorial disorder of unclear etiology, although retrograde menstruation plays a major role. It has a genetic component with over 40 genetic risk factors mapped, although their mechanism of action is still emerging. New evidence suggests a role for retrograde menstruation of endometrial stem/progenitor cells, now that identifying markers of these cells are available. Recent lineage tracing and tissue clearing microscopy and 3D reconstruction has provided new understanding of endometrial glandular structure, particularly the horizontal orientation and interconnection of basalis glands. New sequencing technologies, particularly whole genome DNA sequencing are revealing somatic mutations, including in cancer driver genes, in normal and eutopic endometrium of patients with endometriosis, as well as ectopic endometriotic lesions. Methylome sequencing is offering insight into the regulation of genes and the role of the environmental factors. Single cell RNA sequencing reveals the transcriptome of individual endometrial cells, shedding new light on the diversity and range of cellular subpopulations of the major cell types present in the endometrium and in endometriotic lesions. New endometrial epithelial organoid cultures replicating glandular epithelium are providing tractable models for studying endometriosis. Organoids derived from menstrual fluid offer a non-invasive source of endometrial tissue and a new avenue for testing drugs and developing personalized medicine for treating endometriosis. These new approaches are rapidly advancing our understanding of endometriosis etiology.

Current Updates on the Role of Microbiome in Endometriosis: A Narrative Review

Endometriosis affects approximately 6 to 10% of reproductive-age women globally. Despite much effort invested, the pathogenesis that promotes the development, as well as the progression of this chronic inflammatory disease, is poorly understood. The imbalance in the microbiome or dysbiosis has been implicated in a variety of human diseases, especially the gut microbiome. In the case of endometriosis, emerging evidence suggests that there may be urogenital-gastrointestinal crosstalk that leads to the development of endometriosis. Researchers may now exploit important information from microbiome studies to design endometriosis treatment strategies and disease biomarkers with the use of advanced molecular technologies and increased computational capacity. Future studies into the functional profile of the microbiome would greatly assist in the development of microbiome-based therapies to alleviate endometriosis symptoms and improve the quality of life of women suffering from endometriosis.

Endometriosis and dysbiosis: State of art

Endometriosis is a complex and heterogeneous disease affecting approximately 10% of reproductive age women. The hypothesis that alterations in the microbiota are involved in the pathogenesis of endometriosis has been postulated. Possible explanations for the implications of dysbiosis in endometriosis include the Bacterial Contamination hypothesis and immune activation, cytokine-impaired gut function, altered estrogen metabolism and signaling. Thus, dysbiosis, disrupt normal immune function, leading to the elevation of proinflammatory cytokines, compromised immunosurveillance and altered immune cell profiles, all of which may contribute to the pathogenesis of endometriosis. The aim of this review is to summarize the available literature data about the relationship between microbiota and endometriosis.

The bidirectional relationship between endometriosis and microbiome

Endometriosis has been described by many different theories of pathogenesis over the years. It is now also appreciated to be a state of chronic inflammation, and the role of immune dysfunction in its development has been proven. There is increasing evidence to support the role of the microbiome in the formation and progression of endometriosis via inflammatory pathways. The dysbiosis seen in endometriosis is thought to be both causative and a consequence of the pathogenesis. Gut, peritoneal fluid and female reproductive tract microbiota has been studied to understand if there are any microbiome signatures specific to endometriosis. New research on how to manipulate the microbiome for better detection and treatment of endometriosis is emerging.

Characterization of cervical canal and vaginal bacteria in pregnant women with cervical incompetence

Vaginal and cervical canal bacteria are associated with women’s health and pregnancy outcomes. Here, we compared their composition and characteristics in 37 reproductive-aged Chinese women including 24 pregnant women with cervical incompetence (vaginal and cervical canal bacteria formed Groups A and B, respectively) and 13 healthy pregnant women (vaginal and cervical canal bacteria formed Groups C and D, respectively) using high-throughput sequencing of the V4 region of 16S rRNA gene. The results of alpha and beta diversity analysis, respectively, indicated no statistical differences between Groups A and B (p = 0.32, 0.06), nor Groups B and D (p = 0.69, 0.74); however, differences were found between Groups C and D (p = 0.02, 0.01) and between Groups A and C (p = 0.04, 0.02). PLS-DA analysis showed that the individuals from each group were irregularly distributed according to their clade. Lactobacillus, Bifidobacterium and Ureaplasma were the dominant genera in all groups. Phylogenetic Investigation of Communities by Reconstruction of Unobserved States (PICRUSts) analysis identified 31 Kyoto Encyclopedia of Genes and Genomes (KEGG) orthologs associated with the bacterial communities from the four groups, including membrane transport, folding, sorting and degradation, xenobiotics biodegradation and metabolism, and nucleotide metabolism. We further determined relationships between pregnancy outcomes (Apgar scores) and certain bacterial species. A significant positive correlation was found between Apgar scores and Actinomyces neuii and Anoxybacillus flavithermus in the vagina and cervical canal of pregnant women with cervical incompetence while Bacteroides plebeius, Bifidobacterium pseudopodium and Staphylococcus petrasii in the cervical canal displayed negative correlations with Apgar scores. Moreover, Clostridium fimetarium, Methanobacterium congolense, Pseudomonas chlororaphis, and Psychrobacter nivimaris in the vagina were negatively correlated with Apgar scores. These bacteria may serve as potential biomarkers, however, additional research is warranted to verify their role in clinical outcomes.

“Iron triangle” of regulating the uterine microecology: Endometrial microbiota, immunity and endometrium

The uterus is the core place for breeding new life. The balance and imbalance of uterine microecology can directly affect or even dominate the female reproductive health. Emerging data demonstrate that endometrial microbiota, endometrium and immunity play an irreplaceable role in regulating uterine microecology, forming a dynamic iron triangle relationship. Up to nowadays, it remains unclear how the three factors affect and interact with each other, which is also a frontier topic in the emerging field of reproductive tract microecology. From this new perspective, we aim to clarify the relationship and mechanism of the interaction of these three factors, especially their pairwise interactions. Finally, the limitations and future perspectives of the current studies are summarized. In general, these three factors have a dynamic relationship of mutual dependence, promotion and restriction under the physiological or pathological conditions of uterus, among which the regulatory mechanism of microbiota and immunity plays a role of bridge. These findings can provide new insights and measures for the regulation of uterine microecology, the prevention and treatment of endometrial diseases, and the further multi-disciplinary integration between microbiology, immunology and reproductive medicine.

The microbiome and endometriosis

The objective of this study was to systematically review the literature on the human microbiome in association with endometriosis. PubMed/Medline, Cochrane, and Embase databases were searched for literature published from 1986 to August 2021. All human studies that assessed the microbiome using 16S rRNA sequencing or shotgun sequencing in women with endometriosis were included. Two reviewers independently abstracted data from the selected articles into tables. To assess the quality of included studies, the National Institutes of Health Study Quality Assessment Tools were utilized. This review included 12 case–control studies. Included studies compared the microbiome from various anatomical sources (fecal, vaginal, cervical, peritoneal, endometrial, and intra-lesional) between patients with endometriosis and a heterogeneous set of control patients. Study quality ranged from poor to good, with 8 of 12 studies rated fair. Multiple studies reported a different distribution of bacteria among women with endometriosis across anatomical sites, but the results were highly heterogeneous. Pseudomonas was overrepresented in peritoneal fluid among women with endometriosis across multiple studies but was also observed to be increased in vaginal, endometrial, and intra-lesional samples. Among bacteria noted across different anatomical samples, Gardnerella was found to be increased in cervical but decreased in endometrial, fecal, and vaginal samples of patients with endometriosis, while Atopium was found to be decreased in vaginal and cervical samples from patients with endometriosis. Sphingobium was found to be increased in vagina, endometrium, and peritoneal fluid from patients with endometriosis. Streptococcus was found to be increased in peritoneal, endometrial, and cervical samples from women with endometriosis. Microbiomal comparisons stratified by endometriosis stage or site of endometriosis involvement were limited and highly heterogeneous.

Lay summary

The microbiome, a group of bacteria found in a particular place in the body, has been shown to vary when patients have some diseases, such as cancer or inflammatory bowel disease. Less is known about the microbiome in patients with endometriosis. This review looked at existing studies comparing the bacteria found in patients with endometriosis and others without. Twelve studies were found that assessed the bacteria from swabs collected from different places, including the vagina, cervix, endometrium, peritoneum, feces, and endometriosis lesions themselves. Most of the studies found higher or lower levels of specific bacteria at each of these places, but the findings were often inconsistent. The findings were probably limited by the small numbers of patients involved and variations in the groups studied. More research is needed to find out which bacteria are over- and underrepresented in patients with endometriosis and where they are found.

The colonized microbiota composition in the peritoneal fluid in women with endometriosis

PURPOSE

The imbalance of microbiome in vivo is believed to be involved in the pathogenicity of endometriosis. This study aimed to investigate and analyze the composition of bacterial communities in the peritoneal fluid of women with endometriosis.

METHODS

To collect peritoneal fluid samples from women with (N = 36) and without (N = 25) endometriosis in a generalized hospital in Hunan, China during January to December of 2019. Genomic DNA was extracted from peritoneal fluid samples, and targeted amplified for the V4 region of 16S ribosomal RNA gene followed by amplicon sequencing. Non-parametric Wilcoxon rank-sum test and chi-squared test were used to compare and analysis the difference between groups.

RESULTS

Analysis showed that microbiota diversity was similar in the peritoneal fluid of women with or without endometriosis. Ralstonia mainly dominated in the peritoneal fluid of patients in both groups, with an overall relative abundance of 11.15% (95% CI: 10.51-11.80%) in endometriosis patients, followed by Acinetobacter, Pseudomonas, Asticcacaulis, and Methyloversatilis, with no significant difference between endometriosis patients and the control group. Nevertheless, there were microbes with different abundance in peritoneal fluid of the two groups, and the relative abundance was less than 0.5%. Acidovorax (P = 0.01), Devosia (P = 0.03), Methylobacterium (P = 0.03), Phascolarctobacterium (P = 0.03), and Streptococcus (P = 0.04) were more abundant in the peritoneal fluid of endometriosis patients than the controls, while Brevundimonas (P = 0.01) and Stenotrophomonas (P = 0.04) were less abundant.

CONCLUSION

The composition of minority microbiota including Acidovorax, Devosia, Methylobacterium, Phascolarctobacterium, and Streptococcus in peritoneal fluid were found to change among women with endometriosis. Further research is needed to explore the mechanisms of these microorganisms in the pathophysiology of endometriosis.

Metformin as a Potential Treatment Option for Endometriosis

Endometriosis is a common disease in women of reproductive age, and its pathogenesis seems to be largely affected by hormone imbalance, inflammation, oxidative stress, and autophagy dysregulation. These pathophysiological disturbances interact with one another through mechanisms that are still awaiting elucidation. The aim of this article is to present current knowledge regarding the possibilities of using metformin in the pharmacological treatment of endometriosis. Metformin is an insulin sensitizer widely used for the treatment of type 2 diabetes mellitus. The pleiotropic effects of metformin are mainly exerted through the activation of AMP-activated protein kinase, which is the key cellular energy homeostasis regulator that inhibits mTOR, a major autophagy suppressor. Metformin regresses endometriotic implants by increasing the activity of superoxide dismutase. It is also an inhibitor of metalloproteinase-2, decreasing the levels of the vascular endothelial growth factor and matrix metalloproteinase-9 in animal studies. In endometriosis, metformin might modify the stroma-epithelium communication via Wnt2/β-catenin. With its unique therapeutic mechanisms and no serious side effects, metformin seems to be a helpful anti-inflammatory and anti-proliferative agent in the treatment of endometriosis. It could be a missing link for the successful treatment of this chronic disease.

Association Between Vaginal Gardnerella and Tubal Pregnancy in Women With Symptomatic Early Pregnancies in China: A Nested Case-Control Study

The early diagnosis and treatment of ectopic pregnancy (EP) remains a major challenge. Despite a known link between vaginal microbiota and female reproductive health, few studies have focused on the association between vaginal microbiota and pregnancy location. This nested case-control study aimed to characterize the vaginal microbiota in tubal pregnancy (TP) among symptomatic women in early pregnancy. Women with symptomatic early pregnancy of unknown location (PUL) were included in this study. 16S rDNA gene sequencing was performed to assess vaginal microbial diversity and relative abundance. Machine learning and multivariate logistic regression were also used to evaluate the association between Gardnerella and TP. The results indicate that the vaginal microbiome in TP was more diverse (Shannon, p < 0.05) and was different in composition to that of women with intrauterine pregnancy (IUP) (weighted Unifrac, R = 0.08, p = 0.01). The genus Gardnerella was significantly enriched in TP. The XGBoost analysis was able to classify Gardnerella-induced TP more reliably (AUC = 0.621). Moreover, after adjusting potential confounders, our results indicate a robust association between Gardnerella and TP (as a continuous variable, adjusted OR: 12.0, 95% CI: 2.1–67.4, p < 0.01; as a categorical variable (≥0.85%), and adjusted OR: 4.2, 95% CI: 2.0–8.8, p < 0.01). In conclusion, we found that higher virginal Gardnerella levels were associated with TP in women with symptomatic early pregnancy.

A More Diverse Cervical Microbiome Associates with Better Clinical Outcomes in Patients with Endometriosis: A Pilot Study

Infection-induced chronic inflammation is common in patients with endometriosis. Although microbial communities in the reproductive tracts of patients have been reported, little was known about their dynamic profiles during disease progression and complication development. Microbial communities in cervical mucus were collected by cervical swabs from 10 healthy women and 23 patients, and analyzed by 16S rRNA amplicon sequencing. The abundance, ecological relationships and functional networks of microbiota were characterized according to their prevalence, clinical stages, and clinical features including deeply infiltrating endometriosis (DIE), CA125, pain score and infertility. Cervical microbiome can be altered during endometriosis development and progression with a tendency of increased Firmicutes and decreased Actinobacteria and Bacteroidetes. Distinct from vaginal microbiome, upregulation of Lactobacillus, in combination with increased Streptococcus and decreased Dialister, was frequently associated with advanced endometriosis stages, DIE, higher CA125 levels, severe pain, and infertility. Significantly, reduced richness and diversity of cervical microbiome were detected in patients with more severe clinical symptoms. Clinical treatments against infertility can partially reverse the ecological balance of microbes through remodeling nutrition metabolism and transport and cell-cell/cell-matrix interaction. This study provides a new understanding on endometriosis development and a more diverse cervical microbiome may be beneficial for patients to have better clinical outcomes.

Microbiome analysis in women with endometriosis: Does a microbiome exist in peritoneal fluid and ovarian cystic fluid?

Purpose

To investigate the relationship between the microbiome of the female genital tract and endometriosis.

Methods

This prospective cohort study included 36 women who underwent laparoscopic surgery for ovarian tumor from July 2019 to April 2020. Of them, 18 had endometriosis, and 18 did not have endometriosis. Vaginal secretions, endometrial fluid, peritoneal fluid, and ovarian cystic fluid were collected during surgery. Next-generation sequencing of bacterial 16S rRNA was performed to characterize the microbiome.

Results

Specific microbiomes were not detected in either peritoneal fluid or ovarian cystic fluid regardless of the presence or absence of endometriosis and the type of cyst. When the cutoff value of infectious bacterial abundance in the vagina was set as 64.3%, there were many cases more than a cutoff value in the endometriosis group significantly (p = 0.01). When the cutoff value of infectious bacterial abundance in the endometrium was set as 18.6%, there were many cases more than a cutoff level in the endometriosis cases significantly (p = 0.02).

Conclusion

Peritoneal fluid and ovarian cystic fluid are almost sterile, although dysbiosis may occur in the vaginal and endometrial microbiome in women with endometriosis.

The Endometrial Microbiome and Its Impact on Human Conception

Changes in the female genital tract microbiome are consistently correlated to gynecological and obstetrical pathologies, and tract dysbiosis can impact reproductive outcomes during fertility treatment. Nonetheless, a consensus regarding the physiological microbiome core inside the uterine cavity has not been reached due to a myriad of study limitations, such as sample size and experimental design variations, and the influence of endometrial bacterial communities on human reproduction remains debated. Understanding the healthy endometrial microbiota and how changes in its composition affect fertility would potentially allow personalized treatment through microbiome management during assisted reproductive therapies, ultimately leading to improvement of clinical outcomes. Here, we review current knowledge regarding the uterine microbiota and how it relates to human conception.

The role of gut and genital microbiota and the estrobolome in endometriosis, infertility and chronic pelvic pain

BACKGROUND

Endometriosis is a chronic, burdensome condition that is historically understudied. Consequently, there is a lack of understanding of the etiology of the disease and its associated symptoms, including infertility and chronic pelvic pain (CPP). Endometriosis development is influenced by estrogen metabolism and inflammation, which are modulated by several factors including the microbiome and the estrobolome (the collection of genes encoding estrogen-metabolizing enzymes in the gut microbiome). Therefore, there is increasing interest in understanding the role of microbiota in endometriosis etiology.

OBJECTIVE AND RATIONALE

To date, there is no cure for endometriosis and treatment options often are ineffective. This manuscript will review the potential relationship between the microbiome and endometriosis, infertility and CPP and highlight the available data on the microbiome in relation to endometriosis and its related symptoms. The overarching goal of this manuscript is to inform future microbiome research that will lead to a deeper understanding of the etiology of the disease and possible diagnostic modalities and treatments. The potential impact of the microbiome on estrogen regulation modulated by the estrobolome, as well as inflammation and other endometriosis-promoting mechanisms within the genital tract, will be reviewed. The methodological limitations of microbiome-related studies will be critically assessed to provide improved guidelines for future microbiome and clinical studies.

SEARCH METHODS

PubMed databases were searched using the following keywords: endometriosis AND microbiome, infertility AND microbiome, pelvic pain AND microbiome, IVF (in-vitro fertilization) AND microbiome, endometriosis AND infertility. Clinical and preclinical animal trials that were eligible for review, and related to microbiome and endometriosis, infertility or CPP were included. All available manuscripts were published in 2002-2021.

OUTCOMES

In total, 28 clinical and 6 animal studies were included in the review. In both human and animal studies, bacteria were enriched in endometriosis groups, although there was no clear consensus on specific microbiota compositions that were associated with endometriosis, and no studies included infertility or CPP with endometriosis. However, bacterial vaginosis-associated bacteria and Lactobacillus depletion in the cervicovaginal microbiome were associated with endometriosis and infertility in the majority (23/28) of studies. Interpretation of endometrial studies is limited owing to a variety of methodological factors, discussed in this review. In addition, metadata outlining antibiotic usage, age, race/ethnicity, menopausal status and timing of sample collection in relation to diagnosis of endometriosis was not consistently reported. Animal studies (6/6) support a bidirectional relationship between the gut microbiota and endometriosis onset and progression.

WIDER IMPLICATIONS

There is evidence that a dysbiotic gut or genital microbiota is associated with multiple gynecologic conditions, with mounting data supporting an association between the microbiome and endometriosis and infertility. These microbiomes likely play a role in the gut-brain axis, which further supports a putative association with the spectrum of symptoms associated with endometriosis, including infertility and CPP. Collectively, this review highlights the demand for more rigorous and transparent methodology and controls, consistency across the field, and inclusion of key demographic and clinical characteristics of disease and comparison participants. Rigorous study designs will allow for a better understanding of the potential role of the microbiome in endometriosis etiology and the relationship to other disorders of the female reproductive tract.

Novel diagnostic options for endometriosis - Based on the glycome and microbiome

Background

Endometriosis is a chronic gynaecological disease whose aetiology is still unknown. Despite its prevalence among women of reproductive age, the pathology of the disease has not yet been elucidated and only symptomatic treatment is available. Endometriosis has high latency and diagnostic methods are both limited and invasive.

Aim of review

The aim of this review is to summarise minimally invasive or non-invasive diagnostic methods for endometriosis and their diagnostic efficiencies. Furthermore, we discuss the identification and diagnostic potential of novel disease biomarkers of microbial or glycan origin.

Key scientific concepts of review

Great efforts have been made to develop minimally invasive or non-invasive diagnostic methods in endometriosis. The problem with most potential biomarker candidates is that they have high accuracy only in cases of severe disease. Therefore, it is necessary to examine other potential biomarkers more closely. Associations between gastrointestinal and genital tract microbial health and endometriosis have been identified. For instance, irritable bowel syndrome is more common in women with endometriosis, and hormonal imbalance has a negative impact on the microbiome of both the genital tract and the gastrointestinal system. Further interrogation of these associations may have potential diagnostic significance and may identify novel therapeutic avenues. Glycomics may also be a potent source of biomarkers of endometriosis, with a number of glyco-biomarkers already approved by the FDA. Endometriosis-associated microbial and glycomic profiles may represent viable targets for development of innovative diagnostics in this debilitating disease.

The impact of the female genital tract microbiome in women health and reproduction: a review

PURPOSE

The aim of this review is to gather the available research focusing on female genital tract (FGT) microbiome. Research question focuses in decipher which is the role of FGT microbiota in eubiosis, assisted reproduction techniques (ARTs), and gynaecological disorders, and how microbiome could be utilised to improve reproduction outcomes and to treat fertility issues.

METHODS

PubMed was searched for articles in English from January 2004 to April 2021 for "genital tract microbiota and reproduction", "endometrial microbiome", "microbiome and reproduction" and "microbiota and infertility". Manual search of the references within the resulting articles was performed.

RESULTS

Current knowledge confirms predominance of Lactobacillus species, both in vagina and endometrium, whereas higher variability of species is both found in fallopian tubes and ovaries. Microbial signature linked to different disorders such endometriosis, bacterial vaginosis, and gynaecological cancers are described. Broadly, low variability of species and Lactobacillus abundance within the FGT is associated with better reproductive and ART outcomes.

CONCLUSION

Further research regarding FGT microbiome configuration needs to be done in order to establish a more precise link between microbiota and eubiosis or dysbiosis. Detection of bacterial species related with poor reproductive outcomes, infertility or gynaecological diseases could shape new tools for their diagnosis and treatment, as well as resources to assess the pregnancy prognosis based on endometrial microbiota. Data available suggest future research protocols should be standardised, and it needs to include the interplay among microbiome, virome and mycobiome, and the effect of antibiotics or probiotics on the microbiome shifts.

Endometrial microbiota is more diverse in people with endometriosis than symptomatic controls

Endometriosis is a chronic, estrogen-dependent gynecological condition affecting approximately 10% of reproductive age women. The most widely accepted theory of its etiology includes retrograde menstruation. Recent reports suggest the uterus is not sterile. Thus, the refluxed menstrual effluent may carry bacteria, and contribute to inflammation, the establishment and growth of endometriotic lesions. Here, we compared and contrasted uterine bacteria (endometrial microbiota) in people with surgically confirmed presence (N = 12) or absence of endometriosis (N = 9) using next-generation 16S rRNA gene sequencing. We obtained an average of > 9000 sequence reads per endometrial biopsy, and found the endometrial microbiota of people with endometriosis was more diverse (greater Shannon Diversity Index and proportion of 'Other' taxa) than symptomatic controls (with pelvic pain, surgically confirmed absence of endometriosis; diagnosed with other benign gynecological conditions). The relative abundance of bacterial taxa enriched in the endometrial microbiota of people with endometriosis belonged to the Actinobacteria phylum (Gram-positive), Oxalobacteraceae (Gram-negative) and Streptococcaceae (Gram-positive) families, and Tepidimonas (Gram-negative) genus, while those enriched in the symptomatic controls belonged to the Burkholderiaceae (Gram-negative) family, and Ralstonia (Gram-negative) genus. Taken together, results suggest the endometrial microbiota is perturbed in people with endometriosis.

Microbes in gynecologic cancers: Causes or consequences and therapeutic potential

Gynecologic cancers, starting in the reproductive organs of females, include cancer of cervix, endometrium, ovary commonly and vagina and vulva rarely. The changes in the composition of microbiome in gut and vagina affect immune and metabolic signaling of the host cells resulting in chronic inflammation, angiogenesis, cellular proliferation, genome instability, epithelial barrier breach and metabolic dysregulation that may lead to the onset or aggravated progression of gynecologic cancers. While microbiome in gynecologic cancers is just at horizon, certain significant microbiome signature associations have been found. Cervical cancer is accompanied with high loads of human papillomavirus, Fusobacteria and Sneathia species; endometrial cancer is reported to have presence of Atopobium vaginae and Porphyromonas species and significantly elevated levels of Proteobacteria and Firmicutes phylum bacteria, with Chlamydia trachomatis, Lactobacillus and Mycobacterium reported in ovarian cancer. Balancing microbiome composition in gynecologic cancers has the potential to be used as a therapeutic target. For example, the Lactobacillus species may play an important role in blocking adhesions of incursive pathogens to vaginal epithelium by lowering the pH, producing bacteriocins and employing competitive exclusions. The optimum or personalized balance of the microbiota can be maintained using pre- and probiotics, and fecal microbiota transplantations loaded with specific bacteria. Current evidence strongly suggest that a healthy microbiome can train and trigger the body's immune response to attack various gynecologic cancers. Furthermore, microbiome modulations can potentially contribute to improvements in immuno-oncology therapies.

Levofloxacin or gonadotropin releasing hormone agonist treatment decreases intrauterine microbial colonization in human endometriosis

OBJECTIVE

We examined the hypothesis that antibiotic treatment with or without gonadotropin releasing hormone agonist (GnRHa) may decrease intrauterine infection with consequent decrease in tissue inflammation, cell proliferation and angiogenesis in human endometriosis.

STUDY DESIGN

This is a prospective non-randomized observational study. Endometrial/endometriotic samples were collected during surgery from 53 women with endometriosis and 47 control women who were treated with levofloxacin (LVFX, 500 mg, once per os) or GnRHa (1.88 mg/IM for 3 months) before surgery. Endometrial samples were analyzed by broad-range polymerase-chain reaction (PCR) amplification of bacteria targeting V5-V6 region of 16S rRNA gene. Immunohistochemical analysis was performed using antibodies against CD138 (Syndecan-1, a marker of plasma cells), CD68 (marker of macrophages), Ki-67 (cell proliferation marker), and CD31 (vascular cells marker).

RESULTS

16S rDNA metagenome assay indicated that treatment with either of LVFX or GnRHa + LVFX significantly decreased some components of major bacterial genera comparing to untreated group. In women with endometriosis, treatment with either of LVFX or GnRHa + LVFX significantly decreased Gardnerella, Prevotella, Acidibactor, Atopobium, Megasphaera, and Bradyrhizobium (p < 0.05 for each) comparing to untreated group. Cochran-Mantel-Haenszel test indicated that occurrence rate of chronic endometritis was significantly decreased after GnRHa + LVFX treatment comparing to GnRHa treatment group (p = 0.041). These findings were coincided with significantly decreased CD68-stained macrophage infiltration, Ki-67- stained cell proliferation and CD31-stained micro-vessel density in endometria and endometriotic lesions with histology proven improvement in the morphological appearance of ovarian endometrioma.

CONCLUSIONS

These findings suggest that clinical administration of a broad-spectrum antibiotic with or without GnRHa may be effective in improving uterine infection with decrease of tissue inflammation, cell proliferation, and angiogenesis in human endometriosis.

Antibacterial and Antifungal Activity of the Human Endometrial Fluid during the Natural Cycle

Purpose

Some microbiota patterns have been associated with favorable IVF prognosis and others with pathological conditions. The endometrial fluid aspirate (EFA) contains antibacterial proteins that are enriched in implantative IVF cycles, but the antimicrobial effect of EFA has not been addressed. We aimed to evaluate the antimicrobial activity of the human endometrial fluid during the natural cycle.

Methods

EFA was obtained through an embryo transfer catheter in 38 women, aged 18-40 years, with regular cycles attending to a fertility clinic. The antimicrobial activity of EFAs was tested against two strains of Staphylococcus aureus; one strain each of Streptococcus agalactiae, Enterococcus faecalis, Escherichia coli, and Klebsiella pneumoniae; and three yeasts (Candida albicans, Candida glabrata, and Candida krusei).

Results

All samples exhibited antibacterial activity against S. aureus. In addition, 32.4% of EFAs were active against one of the other microorganisms assayed, 16.2% against two, and 5.4% against four of them. In contrast, none exhibited antibacterial activity against E. coli or K. pneumoniae. The antimicrobial activity differs considerably between EFA samples, and we failed to observe a cycle-related pattern.

Conclusions

EFA presented two antimicrobial activity patterns: (a) one common to all the samples, exhibiting activity against S. aureus and lack of activity against E. coli and K. pneumoniae, and (b) an individualized pattern, showing activity against some of the other microorganisms tested. The intensity of antibacterial activity differs between EFA samples. Our data suggest that the uterine microbiota is controlled by means of endometrial fluid components.

The Female Reproductive Tract Microbiome-Implications for Gynecologic Cancers and Personalized Medicine

The microbial colonization of the lower female reproductive tract has been extensively studied over the past few decades. In contrast, the upper female reproductive tract including the uterine cavity and peritoneum where the ovaries and fallopian tubes reside were traditionally assumed to be sterile under non-pathologic conditions. However, recent studies applying next-generation sequencing of the bacterial 16S ribosomal RNA gene have provided convincing evidence for the existence of an upper female reproductive tract microbiome. While the vaginal microbiome and its importance for reproductive health outcomes has been extensively studied, the microbiome of the upper female reproductive tract and its relevance for gynecologic cancers has been less studied and will be the focus of this article. This targeted review summarizes the pertinent literature on the female reproductive tract microbiome in gynecologic malignancies and its anticipated role in future research and clinical applications in personalized medicine.

Mapping the entire functionally active endometrial microbiota

STUDY QUESTION

Does endometrium harbour functionally active microorganisms and whether the microbial composition differs between proliferative and mid-secretory phases?

SUMMARY ANSWER

Endometrium harbours functionally alive microorganisms including bacteria, viruses, archaea and fungi whose composition and metabolic functions change along the menstrual cycle.

WHAT IS KNOWN ALREADY

Resident microbes in the endometrium have been detected, where microbial dysfunction has been associated with reproductive health and disease. Nevertheless, the core microorganismal composition in healthy endometrium is not determined and whether the identified bacterial DNA sequences refer to alive/functionally active microbes is not clear. Furthermore, whether there are cyclical changes in the microbial composition remains an open issue.

STUDY DESIGN, SIZE, DURATION

RNA sequencing (RNAseq) data from 14 endometrial paired samples from healthy women, 7 samples from the mid-secretory phase and 7 samples from the consecutive proliferative phase were analysed for the microbial RNA sequences.

PARTICIPANTS/MATERIALS, SETTING, METHODS

The raw RNAseq data were converted into FASTQ format using SRA Toolkit. The unmapped reads to human sequences were aligned to the reference database Kraken2 and visualised with Krona software. Menstrual phase taxonomic differences were performed by R package metagenomeSeq. The functional analysis of endometrial microbiota was obtained with HUMANn2 and the comparison between menstrual phases was conducted by one-way ANOVA. Human RNAseq analysis was performed using miARma-Seq and the functional enrichment analysis was carried out using gene set enrichment analysis (GSEA; HumanCyc). The integration of metabolic pathways between host and microbes was investigated. The developed method of active microbiota mapping was validated in independent sample set.

MAIN RESULTS AND THE ROLE OF CHANCE

With the novel metatranscriptomic approach, we mapped the entire alive microbiota composing of >5300 microorganisms within the endometrium of healthy women. Microbes such as bacteria, fungi, viruses and archaea were identified. The validation of three independent endometrial samples from different ethnicity confirmed the findings. Significant differences in the microbial abundances in the mid-secretory vs. proliferative phases were detected with possible metabolic activity in the host-microbiota crosstalk in receptive phase endometrium, specifically in the prostanoid biosynthesis pathway and L-tryptophan metabolism.

LARGE SCALE DATA

The raw RNAseq data used in the current study are available at GEO GSE86491 and at BioProject PRJNA379542.

LIMITATIONS, REASONS FOR CAUTION

These pioneering results should be confirmed in a bigger sample size.

WIDER IMPLICATIONS OF THE FINDINGS

Our study confirms the presence of active microbes, bacteria, fungi, viruses and archaea in the healthy human endometrium with implications in receptive phase endometrial functions, meaning that microbial dysfunction could impair the metabolic pathways important for endometrial receptivity. The results of this study contribute to the better understanding of endometrial microbiota composition in healthy women and its possible role in endometrial functions. In addition, our novel methodological pipeline for analysing alive microbes with transcriptional and metabolic activities could serve to inspire new analysis approaches in reproductive medicine.

STUDY FUNDING/COMPETING INTERESTS

This work is supported by the Spanish Ministry of Economy, Industry and Competitiveness (MINECO) and European Regional Development Fund (FEDER): grants RYC-2016-21199 and ENDORE SAF2017-87526-R; FEDER/Junta de Andalucía-Consejería de Economía y Conocimiento: MENDO (B-CTS-500-UGR18) and by the University of Granada Plan Propio de Investigación 2016 - Excellence actions: Unit of Excellence on Exercise and Health (UCEES) (SOMM17/6107/UGR). A.S.-L. and N.M.M. are funded by the Spanish Ministry of Science, Innovation and Universities (PRE2018-0854409 and FPU19/01638). S.A. has received honoraria for lectures from Merck. The funder had no role in this study.

Intricate Connections between the Microbiota and Endometriosis

Imbalances in gut and reproductive tract microbiota composition, known as dysbiosis, disrupt normal immune function, leading to the elevation of proinflammatory cytokines, compromised immunosurveillance and altered immune cell profiles, all of which may contribute to the pathogenesis of endometriosis. Over time, this immune dysregulation can progress into a chronic state of inflammation, creating an environment conducive to increased adhesion and angiogenesis, which may drive the vicious cycle of endometriosis onset and progression. Recent studies have demonstrated both the ability of endometriosis to induce microbiota changes, and the ability of antibiotics to treat endometriosis. Endometriotic microbiotas have been consistently associated with diminished Lactobacillus dominance, as well as the elevated abundance of bacterial vaginosis-related bacteria and other opportunistic pathogens. Possible explanations for the implications of dysbiosis in endometriosis include the Bacterial Contamination Theory and immune activation, cytokine-impaired gut function, altered estrogen metabolism and signaling, and aberrant progenitor and stem-cell homeostasis. Although preliminary, antibiotic and probiotic treatments have demonstrated efficacy in treating endometriosis, and female reproductive tract (FRT) microbiota sampling has successfully predicted disease risk and stage. Future research should aim to characterize the "core" upper FRT microbiota and elucidate mechanisms behind the relationship between the microbiota and endometriosis.

A systematic review of toll-like receptors in endometriosis

INTRODUCTION

The pathogen-associated molecular patterns and the danger-associated molecular patterns are possibly responsible for the activation of the inflammatory process in endometriosis through the activation of toll-like receptors (TLRs).

OBJECTIVE

The aim of this systematic review was to critically analyze the findings of published articles on TLRs in endometriosis.

METHODS

The keywords used were "endometriosis" and "toll-like" and the search was performed in Pubmed, Scielo and Lilacs databases. This study followed the PRISMA guidelines and the risk of bias of articles was conducted by Newcastle-Ottawa scale (NOS).

RESULTS

Overall, the studies analyzed in this review point toward an increased expression of TLRs two, four and nine in women with endometriosis. Among all TLRs, TLR4 was the most cited receptor.

CONCLUSION

Despite the evidence demonstrating elevated TLR levels in endometriosis, the relationship with the disease is still unclear and needs to be clarified in further studies about innate immune response.

Altered Composition of Microbiota in Women with Ovarian Endometrioma: Microbiome Analyses of Extracellular Vesicles in the Peritoneal Fluid

Human microbiota refers to living microorganisms which colonize our body and crucially contribute to the metabolism of nutrients and various physiologic functions. According to recently accumulated evidence, human microbiota dysbiosis in the genital tract or pelvic cavity could be involved in the pathogenesis and/or pathophysiology of endometriosis. We aimed to investigate whether the composition of microbiome is altered in the peritoneal fluid in women with endometriosis. We recruited 45 women with histological evidence of ovarian endometrioma and 45 surgical controls without endometriosis. Following the isolation of extracellular vesicles from peritoneal fluid samples from women with and without endometriosis, bacterial genomic DNA was sequenced using next-generation sequencing of the 16S rDNA V3–V4 regions. Diversity analysis showed significant differences in the microbial community at phylum, class, order, family, and genus levels between the two groups. The abundance of Acinetobacter, Pseudomonas, Streptococcus, and Enhydrobacter significantly increased while the abundance of Propionibacterium, Actinomyces, and Rothia significantly decreased in the endometriosis group compared with those in the control group (p < 0.05). These findings strongly suggest that microbiome composition is altered in the peritoneal environment in women with endometriosis. Further studies are necessary to verify whether dysbiosis itself can cause establishment and/or progression of endometriosis.

Is Chronic Endometritis Associated with Tubal Infertility? A Prospective Cohort Study

STUDY OBJECTIVE

Chronic endometritis (CE), which often presents asymptomatically, is associated with recurrent pregnancy loss, recurrent implantation failure after in vitro fertilization, and endometriosis. Data connecting CE with fallopian tubal occlusion are limited. The aim was to assess a potential association of CE, defined by the presence of syndecan-1 (CD138)-positive plasma cells in endometrial tissue samples, with fallopian tube patency and other factors for infertility, including endometriosis, adenomyosis, and hydrosalpinges.

DESIGN

Prospective, monocentral pilot study.

SETTING

Tertiary care center.

PATIENTS

A cohort of 100 women who were infertile was enrolled from July 2019 to December 2020.

INTERVENTIONS

Hysteroscopy with endometrial biopsy and laparoscopy with chromopertubation.

MEASUREMENTS AND MAIN RESULTS

CE was found in 13 women (13.0%) and was associated with endometriosis (p = .034) and unilateral/bilateral fallopian tube blockage (p = .013). In women with endometriosis, the mean number of CD138-positive cells was positively correlated with the revised American Society for Reproductive Medicine score (r = .302, p = .028). In a binary regression model, the presence of a hydrosalpinx on one or both sides (odds ratio 15.308; 95% confidence interval, 1.637-143.189; p = .017) and the finding of CE in the endometrial tissue sample (odds ratio 5.273; 95% confidence interval, 1.257-22.116; p = .023) were significantly associated with fallopian tubal occlusion.

CONCLUSION

CE was significantly associated with blockage of the fallopian tubes and endometriosis. Endometriosis stage was associated with the number of CD138-positive cells in endometrial biopsies.

Possible role of microbiome in the pathogenesis of endometriosis

INTRODUCTION

There is an urgent necessity to explore the complex pathophysiological nature of endometriosis, which may enable the rationale for new diagnostic and therapeutic strategies to be discovered. This systematic review aimed to clarify the bidirectional relationship between endometriosis and the microbiome and evaluate if the microbiome may be involved in endometriosis's pathogenesis, establishing a potential connection between the different studies.

EVIDENCE ACQUISITION

Studies were identified through a systematic literature search of papers that evaluated the microbiomes of human or other animal species with endometriosis and of those without in the electronic database PubMed/Medline, and Embase without a date restriction. We included all cohort studies focusing on the interaction between endometriosis and the microbiomes of humans or other mammals, evaluating if the microbiome may be involved in endometriosis's pathogenesis.

EVIDENCE SYNTHESIS

Endometriosis appears to be associated with elevated levels of different microorganisms across various microbiome sites. An ineffective immune response seems to play a key role in endometriosis pathogenesis, and there is some scientific proof to state that the immune response may be modulated by the microbiome. Interestingly, nine studies of our review detected species belonging to the phyla Proteobacteria, Bacteroidetes, and Negativicutes characterized by Gram-negative staining, that were significantly increased in endometriosis cohorts.

CONCLUSIONS

Laboratory and clinical investigations indicate that hosts' microbiome profiles with and without endometriosis can be significantly different. To further our understanding of the relationships between endometriosis and the host microbiome, more studies are necessary.

Eutopic endometrium from women with endometriosis and chlamydial endometritis share immunological cell types and DNA repair imbalance: A transcriptome meta-analytical perspective

The aim of this study was to identify the key similarities between the eutopic endometrium of women with endometriosis and chlamydia-induced endometritis taking into account tissue microenvironment heterogeneity, transcript gene profile, and enriched pathways. A meta-analysis of whole transcriptome microarrays was performed using publicly available data, including samples containing both glandular and stromal endometrial components. Control samples were obtained from women without any reported pathological condition. Only samples obtained during the proliferative menstrual phase were included. Cellular tissue heterogeneity was predicted using a method that integrates gene set enrichment and deconvolution approaches. The batch effect was estimated by principal variant component analysis and removed using an empirical Bayes method. Differentially expressed genes were identified using an adjusted p-value < 0.05 and fold change = 1.5. The protein-protein interaction network was built using the STRING database and interaction score over 400. The Molecular Signatures Database was used to analyse the functional enrichment analysis. Both conditions showed similarities in cell types in the microenvironment, particularly CD4⁺ and CD8⁺ Tem cells, NKT cells, Th2 cells, basophils, and eosinophils. With regards to the regulation of cellular senescence and DNA integrity/damage checkpoint, which are commonly enriched pathways, 21 genes were down-regulated and directly related to DNA repair. Compared to the endometriosis samples, some chlamydial endometritis samples presented a lack of enriched immune pathways. Our results suggest that both conditions show similar distributions of microenvironment cell types, the downregulation of genes involved in DNA repair and cell cycle control, and pathways involved in immune response evasion.

Analysing endometrial microbiome: methodological considerations and recommendations for good practice

There is growing evidence that the upper female genital tract is not sterile, harbouring its own microbial communities. However, the significance and the potential effect of endometrial microorganisms on reproductive functions remain to be fully elucidated. Analysing the endometrial microbiome, the microbes and their genetic material present in the endometrium, is an emerging area of study. The initial studies suggest it is associated with poor reproductive outcomes and with different gynaecological pathologies. Nevertheless, studying a low-biomass microbial niche as is endometrium, the challenge is to conduct well-designed and well-controlled experiments in order to avoid and adjust for the risk of contamination, especially from the lower genital tract. Herein, we aim to highlight methodological considerations and propose good practice recommendations for future endometrial microbiome studies.