Effect of prenatal exposure to TCDD on the promotion of endometriotic lesion growth by TCDD in adult female rats and mice

Potential Mechanisms of Guizhi Fuling Wan in Treating Endometriosis: An Analysis Based on TCMSP and DisGeNET Databases

ETHNOPHARMACOLOGICAL RELEVANCE

Guizhi Fuling Wan (GFW), is a traditional Chinese herbal formula that consists of Cinnamomi Ramulus (Guizhi), Poria Cocos(Schw.) Wolf. (Fuling), Persicae Semen (Taoren), Radix Paeoniae Rubra (Chishao), and Cortex Moutan (Mudanpi). This formula has been used in traditional Chinese medicine for more than 1800 years to treat disorders caused by stagnation of circulation and qi (air).

AIM OF THE STUDY

Based on pre-clinical and clinical studies, this review aimed to reveal the potential mechanisms of GFW in inhibiting endometriosis. The enhancement of therapeutic effects of western medications on endometriosis by GFW was also shown.

MATERIALS AND METHODS

A bibliographic assessment of publications on "Guizhi Fuling Wan" and "endometriosis" indexed in PubMed, Science Direct, and China National Knowledge Infrastructure (CNKI) was conducted. Five pre-clinical studies and 13 clinical studies were selected for this review. Moreover, the targeted molecules of each herb were first extracted from the Traditional Chinese Medicine Systems Pharmacology (TCMSP) Database and Analysis Platform followed by obtaining the endometriosis-related genes from DisGeNET. Subsequently, pathway and gene ontology analyses using David Bioinformatics Resources explored the potential mechanisms of therapeutic effects of GFW in treating endometriosis.

RESULTS

Pre-clinical and clinical studies showed that GFW might inhibit the growth of endometriotic lesion through the modulation of immunity, apoptosis-regulating molecules, and angiogenesis-associated factors, while enhancing the therapeutic effects of western medications in treating endometriosis. Furthermore, pathway and gene ontology analyses demonstrated that GFW might attenuate the disease primarily by affecting AGE-RAGE signaling pathway in diabetic complications (hsa04933) as well as pathways involved in Kaposi sarcoma-associated herpesvirus infection (hsa05167), human cytomegalovirus infection (has05163), and fluid shear stress and atherosclerosis (hsa05418). These pathways were all involved in the regulation of inflammation, angiogenesis, and apoptosis and commonly affected by all herbs.

CONCLUSIONS

The current review revealed that endometriosis is highly associated with aberrant inflammatory, angiogenic, and apoptotic activities. The therapeutic effects of GFW on endometriosis are likely to act through regulating these activities.

Endometriosis: Update of Pathophysiology, (Epi) Genetic and Environmental Involvement

Endometriosis is a chronic disease caused by ectopic endometrial tissue. Endometriotic implants induce inflammation, leading to chronic pain and impaired fertility. Characterized by their dependence on estradiol (via estrogen receptor β (ESRβ)) and their resistance to progesterone, endometriotic implants produce their own source of estradiol through active aromatase. Steroidogenic factor-1 (SF1) is a key transcription factor that promotes aromatase synthesis. The expression of SF1 and ESRβ is enhanced by the demethylation of their promoter in progenitor cells of the female reproductive system. High local concentrations of estrogen are involved in the chronic inflammatory environment favoring the implantation and development of endometriotic implants. Similar local conditions can promote, directly and indirectly, the appearance and development of genital cancer. Recently, certain components of the microbiota have been identified as potentially promoting a high level of estrogen in the blood. Many environmental factors are also suspected of increasing the estrogen concentration, especially prenatal exposure to estrogen-like endocrine disruptors such as DES and bisphenol A. Phthalates are also suspected of promoting endometriosis but throughmeans other than binding to estradiol receptors. The impact of dioxin or tobacco seems to be more controversial.

The Gut Microbiota: A Double Edge Sword in Endometriosis

Endometriosis that afflicts 1 in 10 women of reproductive age is characterized by growth of endometrial tissue in the extra-uterine sites and encompasses metabolic-, immunologic- and endocrine-disruption. Importantly, several comorbidities are associated with endometriosis, especially autoimmune disorders such as inflammatory bowel disease. Primarily thought of as a condition arising from retrograde menstruation, emerging evidence uncovered a functional link between the gut microbiota and endometriosis. Specifically, recent findings revealed altered gut microbiota profiles in endometriosis and in turn this altered microbiota appears to be causal in the disease progression, implying a bi-directional crosstalk. In this review, we discuss the complex etiology and pathogenesis of endometriosis emphasizing on this recently recognized role of gut microbiome. We review the gut microbiome structure and functions and its complex network of interactions with the host for maintenance of homeostasis that is crucial for disease prevention. We highlight the underlying mechanisms on how some bacteria promotes disease progression and others protects against endometriosis. Further, we highlight the areas that require future emphases in the gut microbiome-endometriosis nexus and the potential microbiome-based therapies for amelioration of endometriosis.

2, 3, 7, 8-Tetrachlorodibenzo-p-dioxin potential impacts on peripheral blood mononuclear cells of endometriosis women

Endometriosis happens following the implantation of endometrial-derived tissues outside the uterine cavity. It has been suggested that 2, 3, 7, 8-Tetrachlorodibenzo-p-dioxin (TCDD) is involved in endometriosis development. Furthermore, aryl hydrocarbon receptor (AHR), as a TCDD receptor, has been demonstrated to regulate immune responses. Nonetheless, data regarding the mechanisms, through which TCDD influences the immune system in endometriosis, are still inconclusive. Therefore, frequency of regulatory T cells (Tregs) and the expression of FOXP3, AHR and indoleamine 2, 3-dioxygenase 1 (IDO1) from endometriosis and non-endometriosis individuals were investigated in the absence and presence of TCDD; also, the concentration of IL-6 and kynurenine in the supernatant of cultures was assessed. The impact of TCDD-treated PBMCs on the migration capacity of menstrual blood-derived stromal stem cells (MenSCs) and monocyte chemoattractant protein-1 (MCP-1) and IL-6 production was determined. Here, we found that AHR and IDO1 expression levels were lower in endometriosis PBMCs; however, TCDD treatment increased AHR, FOXP3, IDO1, IL-6, and Treg levels in the endometriosis group (P ≤ 0.05-0.0001). TCDD-treated PBMCs increased the migration capacity of MenSCs and up-regulated MCP-1 and IL-6 levels in the PBMCs/MenSCs co-culture (P ≤ 0.01-0.0001). In conclusion, these results shed light on the probable mechanisms, through which AHR activation by chemical toxicants can impact inflammatory immune mediators involved in the development of endometriosis; also, these data support the idea that TCDD could promote endometriosis progression.

Environmental Factors and Endometriosis

Endometriosis is a common disease, affecting up to 60-80% of women, with pelvic pain or/and infertility. Despite years of studies, its pathogenesis still remains enigmatic. Genetic, hormonal, environmental, and lifestyle-related factors may be involved in its pathogenesis. Thus, the design of the review was to discuss the possible role of environmental factors in the development of endometriosis. The results of individual studies greatly differ, making it very difficult to draw any definite conclusions. There is no reasonable consistency in the role of environmental factors in endometriosis etiopathogenesis.

Associations between Exposure to Organochlorine Chemicals and Endometriosis: A Systematic Review of Experimental Studies and Integration of Epidemiological Evidence

BACKGROUND

Growing epidemiological evidence suggests that organochlorine chemicals (OCCs), including 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), may play a role in the pathogenesis of endometriosis.

OBJECTIVES

We aimed to systematically review the experimental evidence (in vivo and in vitro) on the associations between exposure to OCCs and endometriosis-related end points.

METHODS

A systematic review protocol was developed following the National Toxicology Program /Office of Health Assessment and Translation (NTP/OHAT) framework and managed within a web-based interface. In vivo studies designed to evaluate the impact of OCCs on the onset or progression of endometriosis and proliferation of induced endometriotic lesions were eligible. Eligible in vitro studies included single-cell and co-culture models to evaluate the proliferation, migration, and/or invasion of endometrial cells. We applied the search strings to PubMed, Web of Science, and Scopus®. A final search was performed on 24 June 2020. Assessment of risk of bias and the level of evidence and integration of preevaluated epidemiological evidence was conducted using NTP/OHAT framework Results: Out of 812 total studies, 39 met the predetermined eligibility criteria (15 in vivo, 23 in vitro, and 1 both). Most studies (n=27) tested TCDD and other dioxin-like chemicals. In vivo evidence supported TCDD's promotion of endometriosis onset and lesion growth. In vitro evidence supported TCDD's promotion of cell migration and invasion, but there was insufficient evidence for cell proliferation. In vitro evidence further supported the roles of the aryl hydrocarbon receptor and matrix metalloproteinases in mediating steroidogenic disruption and inflammatory responses. Estrogen interactions were found across studies and end points.

CONCLUSION

Based on the integration of a high level of animal evidence with a moderate level of epidemiological evidence, we concluded that TCDD was a known hazard for endometriosis in humans and the conclusion is supported by mechanistic in vitro evidence. Nonetheless, there is need for further research to fill in our gaps in understanding of the relationship between OCCs and their mixtures and endometriosis, beyond the prototypical TCDD. https://doi.org/10.1289/EHP8421.

Environmental Endocrine Disruptors and Endometriosis

As a consequence of industrialization, thousands of man-made chemicals have been developed with few undergoing rigorous safety assessment prior to commercial use. Ubiquitous exposure to these compounds, many of which act as endocrine-disrupting chemicals (EDCs), has been suggested to be one factor in the increasing incidence of numerous diseases, including endometriosis. Endometriosis, the presence of endometrial glands and stroma outside the uterus, is a common disorder of reproductive-age women. Although a number of population-based studies have suggested that exposure to environmental EDCs may affect a woman's risk of developing this disease, results of epidemiology assessments are often equivocal. The development of endometriosis is, however, a process occurring over time; thus, a single assessment of toxicant body burden cannot definitively be linked to causation of disease. For this reason, numerous investigators have utilized a variety of rodent models to examine the impact of specific EDCs on the development of experimental endometriosis. These studies identified multiple chemicals capable of influencing physiologic processes necessary for the establishment and/or survival of ectopic tissues in rodents, suggesting that these compounds may also be of concern for women. Importantly, these models serve as useful tools to explore strategies that may prevent adverse outcomes following EDC exposure.

Proposed Key Characteristics of Female Reproductive Toxicants as an Approach for Organizing and Evaluating Mechanistic Data in Hazard Assessment

BACKGROUND

Identification of female reproductive toxicants is currently based largely on integrated epidemiological and in vivo toxicology data and, to a lesser degree, on mechanistic data. A uniform approach to systematically search, organize, integrate, and evaluate mechanistic evidence of female reproductive toxicity from various data types is lacking.

OBJECTIVE

We sought to apply a key characteristics approach similar to that pioneered for carcinogen hazard identification to female reproductive toxicant hazard identification.

METHODS

A working group of international experts was convened to discuss mechanisms associated with chemical-induced female reproductive toxicity and identified 10 key characteristics of chemicals that cause female reproductive toxicity: 1) alters hormone receptor signaling; alters reproductive hormone production, secretion, or metabolism; 2) chemical or metabolite is genotoxic; 3) induces epigenetic alterations; 4) causes mitochondrial dysfunction; 5) induces oxidative stress; 6) alters immune function; 7) alters cell signal transduction; 8) alters direct cell–cell interactions; 9) alters survival, proliferation, cell death, or metabolic pathways; and 10) alters microtubules and associated structures. As proof of principle, cyclophosphamide and diethylstilbestrol (DES), for which both human and animal studies have demonstrated female reproductive toxicity, display at least 5 and 3 key characteristics, respectively. 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD), for which the epidemiological evidence is mixed, exhibits 5 key characteristics.

DISCUSSION

Future efforts should focus on evaluating the proposed key characteristics against additional known and suspected female reproductive toxicants. Chemicals that exhibit one or more of the key characteristics could be prioritized for additional evaluation and testing. A key characteristics approach has the potential to integrate with pathway-based toxicity testing to improve prediction of female reproductive toxicity in chemicals and potentially prevent some toxicants from entering common use. https://doi.org/10.1289/EHP4971.

Human epidemiological evidence about the associations between exposure to organochlorine chemicals and endometriosis: Systematic review and meta-analysis

BACKGROUND

Endometriosis is a gynaecological disease characterized by the presence of ectopic endometrial tissue that affects women during their reproductive years, having a strong impact on their lives, fertility and healthcare costs. The aetiology remains largely unknown, but current evidence suggests that it is multi-causal and oestrogen-dependent. Many epidemiologic studies have explored associations between organochlorine chemicals (OCCs) and endometriosis, but the findings are inconsistent.

OBJECTIVES

A systematic review (SR) and meta-analysis were conducted to gather and synthesize all the available evidence from human epidemiological studies about the associations between OCCs and endometriosis.

DATA SOURCES

The searches were conducted in PubMed and Web of Science in June 2016 with a final follow-up in August 2018.

STUDY ELIGIBILITY CRITERIA

Only human epidemiological studies were considered, independent of participant age, body mass index or life-stage. Studies reporting individual measures of exposure to OCCs were included, considering but not limited to polychlorinated dibenzodioxins and dibenzofurans (PCDD/Fs), polychlorinated biphenyls (PCBs), or organochlorine pesticides (OCPs). The primary health outcome was presence of endometriosis, including all sub-types. Eligibility criteria excluded articles not written in English, conference papers, reviews and studies with overlapping information.

STUDY APPRAISAL AND SYNTHESIS METHODS

A SR protocol pre-registered at PROSPERO was applied in duplicate to gather and extract all eligible original papers from PUBMED and Web of Science databases. Odds ratios were pooled using the inverse variance method for random effects meta-analysis for each group of OCCs. Risk of bias was assessed using the National Toxicology Program/Office of Health Assessment and Translation (NTP/OHAT) Risk of Bias Rating Tool for Human and Animal Studies adapted to the review question. The confidence in the body of evidence and related level of evidence was measured by using the Grading of Recommendations Assessment, Development and Evaluation (GRADE) based NTP/OHAT framework. The results were structured and presented in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines.

RESULTS

Of the 51 studies retained for the full-text screening, 17 provided effect sizes and metrics sufficient for pooling estimates through meta-analysis. The overall odds ratios and 95% confidence intervals were 1.65 (1.14; 2.39) for dioxins (n = 10), 1.70 (1.20; 2.39) for PCBs (n = 9), and 1.23 (1.13; 1.36) for OCPs (n = 5). Despite being statistically significant, these estimates should be considered with caution given the notable heterogeneity and small estimated effect size. Misclassification of exposure, due to varying laboratory detection rate capabilities, and disease status, due to varying definitions of endometriosis, were identified as major sources of uncertainty.

LIMITATIONS, CONCLUSIONS, AND IMPLICATIONS OF KEY FINDINGS

The level of evidence was considered to be "moderate" with "serious" risk of bias according the NTP/OHAT criteria, supporting the need for further well-designed epidemiological research to fill lingering data gaps. Given the complexity of endometriosis and lack of known biomarkers suitable for population-based research, carefully designed observational studies play an important role in better understanding the aetiology of endometriosis, as will evolving mixture modeling approaches capable of handling various environmental chemical exposures. Attention to critical windows of exposure will shed further light on the possible developmental origin of endometriosis. Considering the high economic and societal cost associated with endometriosis, further research on this field is urged.

SYSTEMATIC REVIEW REGISTRATION NUMBER

CRD42018080956.

Exposure to environmental concentrations of hexachlorobenzene induces alterations associated with endometriosis progression in a rat model

Hexachlorobenzene (HCB) is a dioxin-like compound widely distributed and is a weak ligand of the aryl hydrocarbon receptor (AhR). Endometriosis is a disease characterized by growth of endometrial tissue in ectopic sites. Our aim was to investigate the impact of HCB on the endocrine, invasion and inflammatory parameters in a rat endometriosis model surgically induced. Female rats were exposed to HCB (1, 10 and 100 mg/kg b.w.) during 30 days. Results showed that HCB increases endometriotic like-lesions (L) volume in a dose-dependent manner. In L, HCB10 increases microvessel density (immunohistochemistry) and the vascular endothelial growth factor (VEGF), cyclooxygenase-2 (COX-2) and AhR levels (Western Blot), while HCB1 enhances aromatase expression (Western Blot). In addition, in eutopic endometrium (EU), HCB10/HCB100 augments microvessel density, VEGF and MMP-9 expression, while HCB1/HCB10 increases tumor necrosis factor-α (TNF-α) content in peritoneal fluid (ELISA). Interestingly, both L and EU from HCB-treated rats exhibited higher estrogen receptor α (ERα) (immunohistochemistry) and metalloproteases (MMP)-2 and -9 levels (Western Blot), as well as lower progesterone receptor (PR) expression (immunohistochemistry) than in control rats. Environmentally relevant concentrations of HCB could contribute to abnormal changes associated with endometriosis progression and development.

Rodent Models of Experimental Endometriosis: Identifying Mechanisms of Disease and Therapeutic Targets

BACKGROUND

Although it has been more than a century since endometriosis was initially described in the literature, understanding the etiology and natural history of the disease has been challenging. However, the broad utility of murine and rat models of experimental endometriosis has enabled the elucidation of a number of potentially targetable processes which may otherwise promote this disease.

OBJECTIVE

To review a variety of studies utilizing rodent models of endometriosis to illustrate their utility in examining mechanisms associated with development and progression of this disease.

RESULTS

Use of rodent models of endometriosis has provided a much broader understanding of the risk factors for the initial development of endometriosis, the cellular pathology of the disease and the identification of potential therapeutic targets.

CONCLUSION

Although there are limitations with any animal model, the variety of experimental endometriosis models that have been developed has enabled investigation into numerous aspects of this disease. Thanks to these models, our under-standing of the early processes of disease development, the role of steroid responsiveness, inflammatory processes and the peritoneal environment has been advanced. More recent models have begun to shed light on how epigenetic alterations con-tribute to the molecular basis of this disease as well as the multiple comorbidities which plague many patients. Continued de-velopments of animal models which aid in unraveling the mechanisms of endometriosis development provide the best oppor-tunity to identify therapeutic strategies to prevent or regress this enigmatic disease.

Melatonin preserves ovarian tissues of rats exposed to chronic TCDD: An electron microscopic approach to effects of TCDD on ovarian cells

2,3,7,8-Tetrachlorodibenzo- p-dioxin (TCDD) is a toxic agent and has disruptive effects on reproductive tissues in females. TCDD disrupts the hormonal regulation of the body and decreases the production of melatonin. In this study, we investigated the protective effects of melatonin supplements against the toxic effects of TCDD on ovaries of female rats. TCDD caused a significant decrease in the average number of corpora lutea and follicles per tissue section (2.1 ± 0.7; 2.3 ± 0.8, respectively), whereas these numbers were maintained in the melatonin supplemented group (5.0 ± 0.8; 5.1 ± 0.8, respectively) and were similar to the control group (5.3 ± 1.0; 5.9 ± 0.9, respectively). Electron microscopic analysis showed that the disruption of ultrastructure components such as cell membrane and organelles due to TCDD exposure was inhibited by melatonin supplements. This study suggested that melatonin has a protective and a possible ameliorative effect over histopathological damage of rat ovaries exposed to TCDD.

Associations between internal exposure levels of persistent organic pollutants in adipose tissue and deep infiltrating endometriosis with or without concurrent ovarian endometrioma

Endometriosis is a gynaecological disease characterized by the presence of ectopic endometrial tissue. Histologically, it appears as different sub-types, being peritoneal endometriosis, ovarian endometrioma (OvE) and deep infiltrating endometriosis (DIE), which are of major relevance due to their varying clinical presentations. A number of persistent organic pollutants (POPs) have been associated with the onset of endometriosis, yet the overall set of existing studies remains fairly divergent. In this preliminary case-control study we aimed to assess the potential associations between the internal exposure to POPs and the presence of DIE with or without concurrent OvE. Adipose tissue and serum samples were collected from surgically confirmed cases (n=55) and controls (n=44) enrolled during 2013 and 2015 in Pays de la Loire, France. Targeted pollutants (76 historical or more emerging POPs including dioxins, polychlorobiphenyls (PCB), polybrominated diphenyl ethers (PBDEs), polybrominated biphenyls (PBBs), hexabromocyclododecanes (HBCDs) and organochlorine pesticides (OCPs) were quantified by chromatography coupled to mass spectrometry. Odds ratios (ORs) and 95% confidence intervals (CI) were estimated from unconditional logistic regression adjusted for known confounding variables. The results showed significant associations between DIE and adipose tissue levels of 1.2.3.7.8 - PeCDD, OCDF, PCB 105, 114, 118 and 123, PBDE 183, PBB 153, and several OCPs including trans‑nonachlor, cis‑heptachlor epoxide, dieldrin, β-hexachlorocyclohexane and hexachlorobenzene. The largest associations were observed for OCDF followed by cis‑heptachlor epoxide, exhibiting adjusted ORs (95% CI) of 5.42 (2.73-12.85) and 5.36 (2.44-14.84) per 1-SD increase, respectively. The stratified analysis comparing both disease sub-types suggested that adipose tissue exposure markers may be more associated with DIE concurrent with OvE, however these results need to be confirmed in a larger population.

My Winding Road: From Microbiology to Toxicology and Environmental Health

I would certainly never have predicted that I would become the director of the National Institute of Environmental Health Sciences (NIEHS) and the National Toxicology Program (NTP) when I was a Jewish girl growing up in Teaneck, New Jersey. My family stressed the importance of education. Yet for a girl there were many not-so-subtle suggestions that the appropriate careers were in teaching or nursing, and the most important thing was to be a wife and mother. Well, I can't disagree with the latter, although I would have to add grandmother to that list of achievements. My parents were both college graduates, but my mom only taught high school English for one year before leaving the field to start our family. My dad returned from World War II and joined his brother in accounting. After my first sister was born, my father joined my mother's family jewelry business and helped to open a second retail store. My mother helped my dad out during the busy times—Christmas and wedding season—but otherwise focused on our growing family of three girls and one boy. This became increasingly challenging when it became clear that my little brother was severely retarded and would require extra care.

Effects of diethylstilbestrol exposure during gestation on both maternal and offspring behavior

Endocrine disruption during gestation impairs the physical and behavioral development of offspring. However, it is unclear whether endocrine disruption also impairs maternal behavior and in turn further contributes to the developmental and behavioral dysfunction of offspring. We orally administered the synthetic non-steroidal estrogen diethylstilbestrol (DES) to pregnant female C57BL/6J mice from gestation day 11-17 and then investigated the maternal behavior of mothers. In addition, we examined the direct effects of in utero DES exposure and the indirect effects of aberrant maternal behavior on offspring using the cross-fostering method. In mothers, endocrine disruption during gestation decreased maternal behavior. In addition, endocrine disruption of foster mother influenced anxiety-related behavior and passive avoidance learning of pups regardless of their exposure in utero. The influence of DES exposure in utero, irrespective of exposure to the foster mother, was also shown in female offspring. These results demonstrate the risks of endocrine disruptors on both mother as well as offspring and suggest that developmental deficits may stem from both in utero toxicity and aberrant maternal care.

Molecular aspects of development and regulation of endometriosis

Endometriosis is a common and painful condition affecting women of reproductive age. While the underlying pathophysiology is still largely unknown, much advancement has been made in understanding the progression of the disease. In recent years, a great deal of research has focused on non-invasive diagnostic tools, such as biomarkers, as well as identification of potential therapeutic targets. In this article, we will review the etiology and cellular mechanisms associated with endometriosis as well as the current diagnostic tools and therapies. We will then discuss the more recent genomic and proteomic studies and how these data may guide development of novel diagnostics and therapeutics. The current diagnostic tools are invasive and current therapies primarily treat the symptoms of endometriosis. Optimally, the advancement of "-omic" data will facilitate the development of non-invasive diagnostic biomarkers as well as therapeutics that target the pathophysiology of the disease and halt, or even reverse, progression. However, the amount of data generated by these types of studies is vast and bioinformatics analysis, such as we present here, will be critical to identification of appropriate targets for further study.

A single gestational exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin disrupts the adult uterine response to estradiol in mice

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) given as a cotreatment with estrogen exhibits antiestrogenic properties on the rodent adult uterus, but less is understood regarding hormonal responsiveness of the adult uterus from animals having been exposed to TCDD during critical periods of development. We characterized the inhibitory effects of TCDD (T) exposure at gestational day 15 (GD15), 4 weeks, and 9 weeks of age (TTT) on the adult uterus following hormone treatment. TTT-exposed mice in response to hormone treatment exhibited a blunted weight increase, had fewer uterine glands, displayed morphological anomalies, and had marked decreases in the hormonal regulation of genes involved in fluid transport (Aqp3 and Aqp5), cytoarchitectural (Dsc2 and Sprr2A), and immune (Lcn2 and Ltf) regulation. To determine if the 9-week exposure was responsible for the blunted uterine response, due to the 7- to 11-day half-life of TCDD in mice, a second set of experiments was performed to examine exposure to TCDD given at GD15, GD15 only (cross-fostered at birth), only during lactation (cross-fostered at birth), or at GD15 and 4 weeks of age. Our studies demonstrate that a single developmental TCDD exposure at GD15 is sufficient to elicit a blunted adult uterine response to estradiol and is due in part to fewer gland numbers and the reduced expression of forkhead box A2 (FoxA2), a gene involved in gland development. Together, these results provide insight regarding the critical nature of in utero exposure and the potential impact on ensuing uterine biology and reproductive health later in life.

Mouse model of surgically-induced endometriosis by auto-transplantation of uterine tissue

Endometriosis is a chronic, painful disease whose etiology remains unknown. Furthermore, treatment of endometriosis can require laparoscopic removal of lesions, and/or chronic pharmaceutical management of pain and infertility symptoms. The cost associated with endometriosis has been estimated at 22 billion dollars per year in the United States. To further our understanding of mechanisms underlying this enigmatic disease, animal models have been employed. Primates spontaneously develop endometriosis and therefore primate models most closely resemble the disease in women. Rodent models, however, are more cost effective and readily available. The model that we describe here involves an autologous transfer of uterine tissue to the intestinal mesentery (Figure 1) and was first developed in the rat and later transferred to the mouse. The goal of the autologous rodent model of surgically-induced endometriosis is to mimic the disease in women. We and others have previously shown that the altered gene expression pattern observed in endometriotic lesions from mice or rats mirrors that observed in women with the disease. One advantage of performing the surgery in the mouse is that the abundance of transgenic mouse strains available can aid researchers in determining the role of specific components important in the establishment and growth of endometriosis. An alternative model in which excised human endometrial fragments are introduced to the peritoneum of immunocompromised mice is also widely used but is limited by the lack of a normal immune system which is thought to be important in endometriosis. Importantly, the mouse model of surgically induced endometriosis is a versatile model that has been used to study how the immune system, hormones and environmental factors affect endometriosis as well as the effects of endometriosis on fertility and pain.

Reproductive medicine and inheritance of infertility by offspring: the role of fetal programming

OBJECTIVE

To summarize the molecular processes involved in fetal programming, to describe how assisted reproduction technologies (ART) may affect the epigenetic pattern of the embryo, and to highlight the current knowledge of the role of perinatal events in the subsequent development of reproductive pathology affecting infertile patients.

DESIGN

A literature review of fetal programming of adulthood gynecologic diseases and ART. A Medline search was performed with the following keywords: (fetal programming OR epigenetics OR methylation OR acetylation) AND (IVF OR ART) AND (gynecology). Articles up to October 2010 were selected. Articles and recent reviews were classified by human and animals studies and also according to their experimental or observational design.

SETTING

University hospital research center.

PATIENT(S)

None.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

None.

RESULT(S)

Data from experimental animal models and case-control studies support the potential effect of ART in changing methylation patterns in gametes and embryos. However, these findings are not supported by population studies or experimental studies performed in human gametes/embryos. Experimental and epidemiologic studies support the hypothesis that some adult gynecologic diseases causing infertility may have a fetal origin.

CONCLUSION(S)

Although it seems clear that some adult gynecologic diseases causing infertility may have a fetal origin, there is insufficient evidence to confirm that ART is the origin of later onset, adulthood diseases. Further research in this field must be conducted.

Dioxin and endometrial progesterone resistance

Development of endometriosis likely requires multiple, interactive mechanisms involving both the endocrine and immune systems. Environmental toxicants, such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), are of particular interest as potential contributory agents in the development of this disease because they can disrupt both systems. Nevertheless, defining the potential role that environmental exposure to TCDD plays in the development of endometriosis requires a better understanding of how this toxicant affects the biological processes that promote the disease. Although the disease mechanism(s) responsible for progesterone resistance in the endometrium of endometriosis patients remains speculative, our studies indicate that developmental exposure of mice to TCDD leads to a progesterone-resistant phenotype in adult animals that can persist for several generations. These studies and others underscore the importance of developing a greater understanding of the mechanisms of TCDD action that relate to reproductive disorders such as endometriosis.

Priorities for endometriosis research: recommendations from an international consensus workshop

Endometriosis is an estrogen-dependent disorder where endometrial tissue forms lesions outside the uterus. Endometriosis affects an estimated 10% of women in the reproductive-age group, rising to 30% to 50% in patients with infertility and/or pain, with significant impact on their physical, mental, and social well-being. There is no known cure, and most current medical treatments are not suitable long term due to their side-effect profiles. Endometriosis has an estimated annual cost in the United States of $18.8 to $22 billion (2002 figures). Although endometriosis was first described more than 100 years ago, current knowledge of its pathogenesis, spontaneous evolution, and the pathophysiology of the related infertility and pelvic pain, remain unclear. A consensus workshop was convened following the 10th World Congress on Endometriosis to establish recommendations for priorities in endometriosis research. One major issue identified as impacting on the capacity to undertake endometriosis research is the need for multidisciplinary expertise. A total of 25 recommendations for research have been developed, grouped under 5 subheadings: (1) diagnosis, (2) classification and prognosis, (3) treatment and outcome, (4) epidemiology, and (5) pathophysiology. Endometriosis research is underfunded relative to other diseases with high health care burdens. This may be due to the practical difficulties of developing competitive research proposals on a complex and poorly understood disease, which affects only women. By producing this consensus international research priorities statement it is the hope of the workshop participants that researchers will be encouraged to develop new interdisciplinary research proposals that will attract increased funding support for work on endometriosis.

Serum dioxins, polychlorinated biphenyls, and endometriosis: a case-control study in Atlanta

Endometriosis among women of reproductive age can result in pain and infertility. The objectives of this study were to test if there is a relation between endometriosis and serum dioxin concentrations as expressed by total toxic equivalence and serum total polychlorinated biphenyl concentrations among women patients at one Atlanta reproductive medicine clinic during 1998-1999; a secondary objective was to provide exposure data for individual congeners of these chemicals and 1,1-dichloro-2,2-bis(4-chlorophenyl)ethane (p,p'-DDE) in women in Atlanta. Laparoscopy including biopsy and visualization of the peritoneal cavity, ovaries, outside of the fallopian tubes and uterus confirmed all endometriosis cases (n=60) and confirmed 30 controls without endometriosis. Other controls had an infertile partner (n=27) or ovulation problems (n=7) with no signs or symptoms of endometriosis. All serum samples were analyzed at the U.S. Centers for Disease Control and Prevention in 2003. Statistical analyses included Fisher's exact chi-square tests and logistic regression. Models were presented for the full study sample and for the subset that included all cases (n=60) and only controls (n=30) with surgical confirmation of disease-free status. Serum concentrations (lipid-adjusted and non lipid-adjusted) of analyzed exposure measures were low and similar for cases and controls and did not explain endometriosis in the study population.

Proteomic analysis of the rat ovary following chronic low-dose exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is a ubiquitously distributed endocrine-disrupting chemical and reproductive toxicant. In order to elucidate low-dose TCDD-mediated effects on reproductive or endocrine functions, female Sprague-Dawley rats were orally administered various concentrations (20, 50, or 125 ng/kg once weekly) TCDD for 29 wk. A proteomic analysis of the ovaries by two-dimensional gel electrophoresis and matrix-assisted laser desorption/ionization (MALDI) tandem mass spectrometry showed distinct changes in the levels of several proteins that are relevant markers of TCDD toxicity. Serum estradiol (E2) levels of TCDD-treated animals were markedly lower than control. There were no significant differences in bone mineral density (BMD) of femurs. The body weight of the 125-ng/kg TCDD group was significantly decreased relative to control and there was also a significant reduction in absolute and relative ovarian weights. Expressions of selenium binding protein 2, glutathione S-transferase mu type 3, Lrpap1 protein, NADPH, and peptidylprolyl isomerase D were upregulated, while prohibitin and N-ethylmaleimide-sensitive factor expression levels were downregulated. Data provide further insight into the mechanisms by which TCDD disrupts ovarian function by indicating which differential protein expressions following low-dose TCDD exposure.

Female reproductive disorders: the roles of endocrine-disrupting compounds and developmental timing

OBJECTIVE

To evaluate the possible role of endocrine-disrupting compounds (EDCs) on female reproductive disorders emphasizing developmental plasticity and the complexity of endocrine-dependent ontogeny of reproductive organs. Declining conception rates and the high incidence of female reproductive disruptions warrant evaluation of the impact of EDCs on female reproductive health.

DESIGN

Publications related to the contribution of EDCs to disorders of the ovary (aneuploidy, polycystic ovary syndrome, and altered cyclicity), uterus (endometriosis, uterine fibroids, fetal growth restriction, and pregnancy loss), breast (breast cancer, reduced duration of lactation), and pubertal timing were identified, reviewed, and summarized at a workshop.

CONCLUSION(S)

The data reviewed illustrate that EDCs contribute to numerous human female reproductive disorders and emphasize the sensitivity of early life-stage exposures. Many research gaps are identified that limit full understanding of the contribution of EDCs to female reproductive problems. Moreover, there is an urgent need to reduce the incidence of these reproductive disorders, which can be addressed by correlative studies on early life exposure and adult reproductive dysfunction together with tools to assess the specific exposures and methods to block their effects. This review of the EDC literature as it relates to female health provides an important platform on which women's health can be improved.

AhR acts as an E3 ubiquitin ligase to modulate steroid receptor functions

The arylhydrocarbon receptor (AhR) mediates the adverse effects of dioxins, including modulation of sex steroid hormone signaling. The role of AhR as a transcription factor is well described. AhR regulates the expression of target genes such as CYP1A1; however, the mechanisms of AhR function through other target-selective systems remain elusive. Accumulating evidence suggests that AhR modulates the functions of other transcription factors. The ligand-activated AhR directly associates with estrogen or androgen receptors (ERalpha or AR) and modulates their function both positively and negatively. This may, in part explain the sex steroid hormone-related adverse effects of dioxins. AhR has recently been shown to promote the proteolysis of ERalpha/AR through assembling a ubiquitin ligase complex, CUL4B(AhR). In the CUL4B(AhR) complex, AhR acts as a substrate-recognition subunit to recruit ERalpha/AR. This action defines a novel role for AhR as a ligand-dependent E3 ubiquitin ligase. We propose that target-specific regulation of protein destruction, as well as gene expression, is modulated by environmental toxins through the E3 ubiquitin ligase activity of AhR.

Endocrine toxicants including 2,3,7,8-terachlorodibenzo-p-dioxin (TCDD) and dioxin-like chemicals and endometriosis: is there a link?

Endometriosis is a common gynecologic disease of unknown etiology affecting approximately 10-15% of women of reproductive age and 50% of infertile women. Estrogen dependence and immune modulation are established features of endometriosis but do not adequately explain the cause of this disorder. In recent years evidence indicated that exposure to environmental toxicants possessing estrogenic activity resulted in endometriosis. However, scant hospital-based case-control studies yielded inconsistent findings and thus did not provide a compelling argument for or against an association between environmental toxicant exposure and endometriosis. Results of animal studies and cell culture experiments, however, suggested that it is biologically plausible for environmental toxicants to affect the pathobiology of endometriosis. In this article, the literature linking environmental toxicants with endometriosis was reviewed and the link with endocrine toxicants discussed.

A critical comparison of murine pathology and epidemiological data of TCDD, PCB126, and PeCDF

2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD, or dioxin) and dioxin-like compounds (DLCs) induce numerous toxicities, including developmental, endocrine, immunological, and multi-organ carcinogenic, in animals and/or humans. Multiple studies completed by the National Toxicology Program (NTP) focused on the effects caused in Harlan Sprague-Dawley rats by specific DLCs, among them the prototypical dioxin, TCDD. Because humans are exposed daily to a combination of DLCs, primarily via ingestion of food, the Toxic Equivalency Factor (TEF) was developed in order to evaluate health hazards caused by these mixtures. Herein we review the pathological effects reported in humans exposed to TCDD; 3,3',4,4',5-pentachlorobiphenyl (PCB 126); and 2,3,4,7,8,-pentachlorodibenzofuran (PeCDF) and compare them to similar changes seen in NTP murine studies performed with the same compounds. While there were differences in specific pathologies observed, clear consistency in the target organs affected (liver, oral cavity, cardiovascular system, immune system, thyroid, pancreas, and lung) could be seen in both human studies and rodent toxicity and carcinogenicity investigations.

Environmental PCB exposure and risk of endometriosis

BACKGROUND

Hormonally active environmental agents have recently been associated with the development of endometriosis.

METHODS

We undertook a study to assess the relationship between endometriosis, an estrogen-dependent gynaecological disease, and 62 individual polychlorinated biphenyl (PCBs) congeners. We enrolled 84 eligible women aged 18-40 years undergoing laparoscopy for study, which included an interview and blood specimen (n=79; 94%). Thirty-two women had visually confirmed endometriosis at laparoscopy while 52 did not. Blood specimens were run in batches of 14 including four quality control samples for toxicological analysis. Each PCB congener was adjusted for recovery; batch-specific reagent blanks were subtracted. All PCB concentrations were log transformed and expressed in ng/g serum first as a sum and then as tertiles by purported estrogenic or anti-estrogenic activity of PCB congeners.

RESULTS

Using unconditional logistic regression analysis, a significantly elevated odds ratio (OR) was observed for women in the third tertile of anti-estrogenic PCBs [OR 3.77; 95% confidence interval (CI) 1.12-12.68]. Risk remained elevated after controlling for gravidity, current cigarette smoking and serum lipids (OR 3.30; 95% CI 0.87-12.46).

CONCLUSIONS

These data suggest that anti-estrogenic PCBs may be associated with the development of endometriosis.

Basis for a proposed reference dose (RfD) for dioxin of 1-10 pg/kg-day: a weight of evidence evaluation of the human and animal studies

The dioxins have been perhaps the most studied of all chemicals to which humans are routinely exposed. It has been reported that more than 5,000 scientific papers have been published that have evaluated the toxicology of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Although the cancer hazard posed by this chemical has probably received the bulk of attention over the past 20 years, the U.S. Environmental Protection Agency (EPA) and the recent U.S. EPA Science Advisory Board (SAB) that reviewed the "Reassessment" have suggested that the noncancer hazard may well be more important than the cancer hazard at current background doses to the general public. The World Health Organization (WHO) and U.K. Food Standards Agency (FAO) committee (JECFA) on dioxins has reached similar conclusions. This article reviews the published studies involving laboratory animals and humans that address the noncancer effects. Based on our review, developmental toxicity is the most sensitive effect of TCDD consistently seen in mice and rats. Specifically, of the various studies, a no-observed-adverse-effects level (NOAEL) of 13 ng/kg (maternal body burden) was identified as the most pertinent for deriving a reference dose (RfD) for humans. Although more than a dozen different adverse effects have been reported in various studies of humans over the past 25 years, the most consistent clinically important adverse effect of human exposure appears to be chloracne. Following a review of all published studies, we concluded that the best estimate of a LOAEL for production of chloracne is approximately 160 ng/kg (body burden). Based on our analysis, an RfD of between 1 and 10 pg/kg-d (TCDD TEQ) is consistent with the objectives of this risk criterion. Maintaining a lifetime average daily dose below this concentration, based on what is known today, should prevent noncancer effects in virtually all persons. This value is consistent with the JECFA recommendation of 70 pg/kg-mo.

The potential role of exposure to environmental toxicants in the pathophysiology of endometriosis

Humans and animals are exposed daily to a complex mixture of polyhalogenated aromatic hydrocarbons (PHAHs). Previous work has shown that exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is associated with a dose-dependent increase in the incidence and severity of endometriosis in the rhesus monkey. Dioxin-like chemicals can also exert effects in combination with TCDD via the aryl hydrocarbon receptor. Using a rhesus model of chronic TCDD exposure and endometriosis, serum concentrations of TCDD and 19 dioxin-like PHAHs were quantified 13 years after termination of exposure to TCDD. In additional studies, the immune status of TCDD-exposed monkeys was evaluated. For TCDD-exposed and unexposed animals, TCDD exposure correlated with an increased serum TCDD concentration. Furthermore, TCDD exposure and an elevated serum TCDD concentration were associated with increased serum levels of triglycerides, 1,2,3,6,7,8-hexachlorodibenzofuran (HxCDF), PCB77, and PCB126. Importantly, the animals with elevated serum levels of PCB77 and PCB126 and increased total serum TCDD equivalents (TEQs) had a high prevalence of endometriosis, and the severity of disease correlated with the serum concentration of PCB77. In immune studies, TCDD exposure correlated with increased tumor necrosis factor alpha (TNFalpha) production by peripheral blood mononuclear cells (PBMC) in response to stimulation by T cell mitogen and decreased NK cytolytic activity. Elevated serum concentrations of TCDD, 1,2,3,6,7,8-HxCDF, and PCB126 correlated with increased numbers of CD3+/CD25- and CD3-/CD25+ leukocytes and enhanced secretion of TNFalpha by mitogen-stimulated PBMC. This evidence suggests that TCDD exposure and endometriosis in the rhesus monkey may be associated with increased serum concentrations of specific coplanar PCB compounds and long-term alterations in systemic immunity. Furthermore, the data suggest a potential involvement of an increased body burden of PCB compounds in the etiology of endometriosis in the rhesus. Recent advances in the detection and assay of individual PHAH congeners in biological samples have made it possible to assess total PHAH body burden in humans and animals. Future studies are expected to exploit this advance to assess the health impact of PHAH body burdens in both exposed individuals and the general population. Serum PHAH concentrations and TEQs in TCDD-exposed monkeys with endometriosis are similar to or lower than blood levels in the general human population; thus, it is important to consider the implications of these findings for human health and the prevalence of endometriosis in humans. Additional studies are warranted, particularly in human subjects, to explore the potential implications of these data.

Tampons, dioxins, and endometriosis

Concern has been expressed that rayon tampons contain dioxins as a result of chlorine bleaching and, further, that the dioxins in tampons may increase the risk of endometriosis. Rayon tampons do not contain 2,3,7,8-tetrachlorodibenzo-p-dioxin, the chemical commonly meant when the generic term "dioxin" is used. In addition, rayon tampons contain only trivial amounts of dioxin-like environmental contaminants, similar to the amounts contained in unbleached cotton tampons. The amount of dioxin-like material that is theoretically available from tampons is at least six orders of magnitude lower than estimated daily food exposure levels to these contaminants. The evidence for a causal relationship between environmental exposure to dioxins and endometriosis is inconsistent. Prediction of the effective dioxin dose based on the most suggestive of the primate studies on endometriosis does not raise concerns about typical human food exposures to these compounds, let alone the considerably lower levels that could be present in tampons.