Induction of endometriosis in mice: a new model sensitive to estrogen

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.

Experimental murine endometriosis induces DNA methylation and altered gene expression in eutopic endometrium

The eutopic endometrium in women with endometriosis demonstrates diminished endometrial receptivity and altered gene expression. It is unknown if the endometrium being defective gives rise to a predisposition toward endometriosis and infertility or, alternatively, if endometriosis causes the altered endometrial receptivity. Here we created experimental endometriosis in mice and examined the expression of several markers of endometrial receptivity in the eutopic endometrium. Methylation of Hoxa10 was also evaluated as a potential mechanism responsible for altered gene expression. Expression of each gene was measured using quantitative real-time RT-PCR at 14 wk after induction of endometriosis. Expression of Hoxa10 and Hoxa11, which are necessary for endometrial receptivity, were decreased in the endometriosis group. Insulin-like growth factor binding protein-1 (Igfbp1) mRNA was decreased in the endometriosis group. However, there was no change in Integrin beta3 (Itgb3) mRNA expression. Total progesterone receptor (Pgr-AB) was increased in the endometriosis group and the ratio of Pgr-B to Pgr-AB was increased, indicating a shift from Pgr-A to Pgr-B expression. Basic transcription element-binding protein-1 (Bteb1), official symbol and name Klf9, Kruppel-like factor 9, which functionally interacts with Pgr in endometrium, was also decreased in the endometriosis group. In addition, hypermethylation of Hoxa10 in the endometriosis group was shown by methylation-specific PCR and confirmed by bisulfite sequencing. These findings demonstrate that normal endometrium, when placed in an ectopic location to create experimental endometriosis, led to characteristic changes in gene expression in eutopic endometrium. These data suggest the existence of a signal conduction pathway from endometriosis that alters endometrial gene expression through altered Pgr signaling and epigenetic programming.

Does gestrinone antagonize the effects of estrogen on endometrial implants upon the peritoneum of rats?

OBJECTIVE

To evaluate the effects of estrogen treatment in combination with gestrinone on an experimental rat model of endometriosis.

METHODS

Uterine transplants were attached to the peritoneum of female Wistar rats via a surgical autotransplantation technique. The implanted area was measured during the proestrus phase and after hormonal treatment. We performed morphometric analysis and examined the macroscopic and morphometric alterations of endometrial implants after hormonal treatment in ovariectomized rats.

RESULTS

The high dose of estrogen caused macroscopic increases in the endometrial implant group compared with other groups, which were similar to increases in the proestrus phase. The low dose showed morphometric development of implants, such as an increase in number of endometrial glands, leukocyte infiltration and mitosis. Gestrinone antagonized both doses of estrogen.

CONCLUSION

Our findings suggest that gestrinone antagonizes estrogen's effects on rat peritoneal endometrial implants.

Intraperitoneal inflammation decreases endometriosis in a mouse model

BACKGROUND

The role of the immune system in the pathogenesis of endometriosis remains elusive. It has been shown that patients have an altered peritoneal environment with increased levels of inflammatory cytokines, activated macrophages and reduced clearance of retrogradely transported endometrial fragments. However, it is not known if this unique inflammatory situation is cause or consequence of endometriosis. This study investigates the impact of a pre-existing peritoneal inflammation on endometriosis establishment in a mouse model.

METHODS

Endometriosis was induced by intraperitoneal injection of enhanced green fluorescent protein (EGFP)-expressing endometrium in mice. In parallel, a peritonitis model was established via intraperitoneal injection of thioglycolate medium (TM). Finally, endometriosis was induced in the inflamed peritoneal cavity and lesion establishment as well as morphological and histological characteristics were analysed.

RESULTS

Induction of endometriosis in an inflamed peritoneal cavity resulted in fewer lesions and significantly lower sum of lesion surface area per mouse in the TM-treated group. Additionally, a higher amount of non-attached debris could be detected in the peritoneal cavity of TM-treated mice.

CONCLUSIONS

An intraperitoneal inflammation decreases endometriosis establishment in this mouse model. Thus, a pre-existing peritoneal inflammation might not be a factor favouring the development of endometriosis.

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.

2-methoxyestradiol inhibits hypoxia-inducible factor-1{alpha} and suppresses growth of lesions in a mouse model of endometriosis

Endometriosis, the presence of ectopic endometrial tissue outside the uterine cavity, is a common disease affecting women during their reproductive years. Current therapeutic success is often unsatisfactory because of limited insight into disease mechanisms. Nevertheless, angiogenesis plays an essential role in the pathogenesis of the disease, making it a potential novel target for therapy. In the current study, we demonstrate in an established mouse model of endometriosis that transient hypoxia in transplanted endometriosis-like lesions results in the up-regulation of hypoxia-inducible factor-1alpha (HIF-1alpha), leading to the expression of vascular endothelial growth factor (VEGF), a key player in endometriosis-associated angiogenesis. Systemic treatment with the angiogenesis inhibitor 2-methoxyestradiol suppressed HIF-1alpha expression in vivo, resulting in a decreased downstream expression of HIF-1alpha target genes, such as for VEGF, phosphoglycerate kinase, and glucose transporter-1. 2-Methoxyestradiol also suppressed VEGF-induced vascular permeability, as demonstrated in a modified Miles assay. Finally, systemic treatment with 2-methoxyestradiol significantly inhibited the growth of endometriosis-like lesions in a dose-dependent manner. In conclusion, hypoxia appears to play an important role in the pathogenesis of endometriosis and endometriosis-associated angiogenesis, and the angiogenesis inhibitor 2-methoxyestradiol may be a potential candidate for systemic treatment in the future.

Targeting mast cells in endometriosis with janus kinase 3 inhibitor, JANEX-1

Endometriosis (EMS) is a chronic inflammatory disease of multifactorial etiology characterized by implantation and growth of endometrial glands and stroma outside the uterine cavity. EMS is a significant public health issue as it affects 15-20% of women in their reproductive age. Clinical symptoms may include pelvic pain, dysmenorrhea, dyspareunia, pelvic/abdominal masses, and infertility. Symptomatic treatments such as surgical resection and/or hormonal suppression of ovarian function and analgesics are not as effective as desired. Consequently, there is an enormous unmet need to develop effective medical therapy capable of preventing the occurrence and recurrence of EMS without undesirable side-effects. EMS-associated intra-abdominal bleeding episodes, local inflammation, adhesions, and i.p. immunologic dysfunction leads to pelvic nociception and pelvic pain. Increasing evidence supports the involvement of allergic-type inflammation in EMS. Invasion of mast cells, degranulation, and proliferation of interstitial component are observed in endometriotic lesions. Presence of activated and degranulating mast cells within the nerve structures can contribute to the development of pain and hyperalgesia by direct effects on primary nociceptive neurons. Therefore, treatments targeting endometrial mast cells may prove effective in preventing or alleviating EMS-associated symptoms. The Janus kinase 3 (JAK3) is abundantly expressed in mast cells and is required for the full expression of high-affinity IgE receptor-mediated mast cell inflammatory sequelae. JANEX-1/WHI-P131 is a rationally designed novel JAK3 inhibitor with potent anti-inflammatory activity in several cellular and in vivo animal models of inflammation, including mouse models of peritonitis, colitis, cellulitis, sunburn, and airway inflammation with favorable toxicity and pharmacokinetic profile. We hypothesize that JAK3 inhibitors, especially JANEX-1, may prove useful to prevent or alleviate the symptoms of EMS.

Animal models in endometriosis research

Endometriosis is a common gynaecological disease, defined as the presence of endometrial tissue outside the uterus, causing pelvic pain and subfertility in approximately 10% of women of reproductive age. Current therapies lead to pain relief, however, do not address the causes and entail severe side effects. Still little is known about the pathogenic processes leading to the development and maintenance of endometriosis. Because endometriosis occurs spontaneously only in humans and some non-human primates, animal models of induced endometriosis have been developed and are of high value for the evaluation of pathophysiological mechanisms underlying the development of this disease. These experimental models include the autotransplantation of uterine fragments into the peritoneal cavity of rodents and non-human primates or the heterotransplantation of human endometrial or endometriotic tissue to immunodeficient mice or onto the chicken chorioallantoic membrane (CAM). This review describes the animal models for endometriosis and assesses their different potentials and limitations in regard to endometriosis research, with the aim of developing novel non-invasive diagnostic tools and improved strategies for the treatment of endometriosis in women.

A novel noninvasive model of endometriosis for monitoring the efficacy of antiangiogenic therapy

Endometriosis, the presence of ectopic endometrial tissue, is a common disease associated with high morbidity and socioeconomic problems. Angiogenesis, the formation of new blood vessels, plays an important role in the formation and growth of endometriotic lesions. We have created a novel, noninvasive model to monitor the growth of these lesions and the associated angiogenesis in vivo. First, we generated luciferase-expressing transgenic mice by inserting the human ubiquitin C promoter coupled to the firefly luciferase reporter. Injection of luciferin in these mice causes full-body bioluminescence, which can be detected using a low-light CCD camera. Endometrial tissue from these transgenic mice was surgically implanted into nonluminescent recipients. Bioluminescence of lesions was noninvasively imaged after intravenous or intraperitoneal injection of luciferin. Transabdominal luminescence compared well with the location of the transgenic endometriotic lesions, and lesion size correlated with the intensity of luminescence. Systemic treatment with the angiogenesis inhibitors caplostatin and endostatin peptide mP-1 delayed and suppressed the onset and intensity of the luminescent signal. Caplostatin suppressed the growth of endometriotic lesions by 59% compared with controls. This novel, noninvasive model of endometriosis provides a means to study early angiogenesis in vivo and to monitor endometriotic growth and the efficacy of systemic antiangiogenic therapy.

Neutrophils and macrophages promote angiogenesis in the early stage of endometriosis in a mouse model

Substantial evidence suggests that inflammatory cytokines, immune cells, and angiogenesis are important for endometriosis. In this study, we investigated the role of the sequential events in the development of endometriosis in a mouse model. Uterine tissue was transplanted into the peritoneum of ovariectomized mice and then supplemented with estrogen or vehicle. On different days after transplantation, cell proliferation, angiogenesis, and infiltrated immune cells in ectopic tissue were examined using immunochemical staining. Many disintegrated blood vessels but no bromodeoxyuridine-positive cells in ectopic tissue were observed in the estrogen-treated group on posttransplantation d 1 and 2. On d 4-7, bromodeoxyuridine-positive cells were detected in the blood vessels of ectopic tissue, indicating that angiogenesis was initiated in this stage. Angiogenesis also occurred in ectopic tissue in the vehicle-treated group. Profound infiltration of neutrophils in ectopic tissue occurred on d 1-4, when the number of neutrophils and levels of macrophage inflammatory protein (MIP)-1alpha and MIP-2 chemokines in peritoneal fluids also reached their peak. Peritoneal macrophage numbers did not change, but secretions of TNFalpha, IL-6, MIP-1alpha, and MIP-2 from macrophages isolated on d 2 were higher than on d 0. In vitro studies showed that peritoneal neutrophils and macrophages secreted vascular endothelial growth factor, which was up-regulated by TNFalpha and IL-6. Our results suggest that neutrophils and macrophages may promote angiogenesis in the early stage of endometriosis and that chemokines and cytokines amplify the angiogenic signal for the growth of endometriotic tissue.

Endostatin inhibits the growth of endometriotic lesions but does not affect fertility

OBJECTIVE

To determine whether endometriosis can be treated with the angiogenesis inhibitor endostatin and the effect of this treatment on fertility and reproduction.

DESIGN

Pharmacologic intervention in a surgically induced model of endometriosis and in female mice undergoing mating.

SETTING

Animal research facility.

ANIMAL(S)

Eight-week-old, female C57BL/6 and SCID mice.

INTERVENTION(S)

After implantation of autologous endometrium, mice received endostatin or the vehicle-matched control for 4 weeks. For the reproductive function study, mice receiving endostatin or vehicle were mated and reproductive functions were observed.

MAIN OUTCOME MEASURE(S)

Growth of endometriotic lesions after 4 weeks of treatment; estrous cycling, corpus luteum formation, serum hormone levels, and mating time as fertility measures; and pregnancy rates, length of pregnancy, fetal vitality, number, and outcome of litter as reproductive measures.

RESULT(S)

Endostatin suppressed the growth of endometriotic lesions by 47% compared with controls. Estrous cycling and corpus luteum formation were normal in both groups. Female mice receiving endostatin were as fertile as mice receiving vehicle, had normal pregnancies, and delivered the same number of pups. The offspring were healthy without teratogenic stigmata and reproduced normally themselves.

CONCLUSION(S)

Antiangiogenic therapy with endostatin may present a promising novel, nontoxic therapeutic option for patients with endometriosis.

Short synthetic endostatin peptides inhibit endothelial migration in vitro and endometriosis in a mouse model

OBJECTIVE

To determine the active peptide regions inside the angiogenesis inhibitor endostatin that can inhibit endothelial migration in vitro and also inhibit endometriosis in a mouse model.

DESIGN

Pharmacologic intervention in a surgically induced mouse model of endometriosis and endothelial migration assay.

SETTING

Animal research and laboratory facility.

SUBJECT(S)

Eight-week-old, female C57BL/6 mice and human microvascular endothelial cells.

INTERVENTION(S)

Eight overlapping synthetic peptides were tested for inhibitory potential on endothelial migration in vitro. The peptides with significant activity then were given for 4 weeks to mice after implantation of autologous endometrium.

MAIN OUTCOME MEASURE(S)

Inhibition of vascular endothelial growth factor-induced endothelial migration for in vitro studies. In vivo studies examined the growth rate of endometriotic lesions after 4 weeks of treatment, as well as the effect on estrous cycling and ovulation as assessed by corpus luteum formation.

RESULT(S)

The N-terminal mP-1 peptide and the internal mP-6 peptide inhibited endothelial migration in a dose-dependent manner. Additionally, both synthetic peptides suppressed growth of endometriotic lesions significantly in vivo. However, estrous cycling and corpus luteum formation were normal in both groups.

CONCLUSION(S)

Short endostatin fragments may be promising as a new, nontoxic therapeutic strategy for the treatment of endometriosis without inhibition of normal estrous cycles.

Quantification of endometriotic lesions in a murine model by fluorimetric and morphometric analyses

BACKGROUND

In animal models of endometriosis, the identification and quantification of lesions originating from human endometrium is often hampered by the small size of the implants and their embedding in murine tissue. The purpose of the present study was to develop two new methods of quantifying endometriosis-like lesions in a nude mouse model: fluorimetry and morphometry.

METHODS

Human menstrual endometrium was labelled using a fluorescent tracker, carboxyfluorescein diacetate, succinimidyl ester (CFDA-SE), and transplanted into the pelvic cavity of mice by injection through the peritoneum after performing a cutaneous incision. After 5 days, lesions were recovered by laparotomy. The fluorescence of the recovered endometriotic lesions was measured. Endometrial stroma and glands were immunostained in lesion sections with anti-CD10 and anti-CK22 antibodies, and their surface area was evaluated by morphometric analysis.

RESULTS

Fluorescent labelling allows identification of lesions not visible macroscopically. A good correlation was observed between fluorimetry and morphometry (r=0.88) applied for lesion quantification.

CONCLUSIONS

Fluorimetric evaluation combined with morphometric analysis of endometriosis-like lesions allows objective and reliable recording of endometriosis development in a nude mouse model. This quantification method could therefore be useful for future pharmacological and toxicological studies.

Nonsteroidal antiinflammatory drugs differentially suppress endometriosis in a murine model

OBJECTIVE

To determine whether nonsteroidal antiinflammatory drugs (NSAIDs) affect the establishment and progression of endometriotic lesions in a murine model.

DESIGN

Pharmacologic intervention in a surgically induced murine model of abdominal/peritoneal endometriosis.

SETTING

Animal research facility.

PATIENT(S)

Eight-week-old, female C57BL/6 mice.

INTERVENTION(S)

After implantation of autologous endometrium, mice were randomized into groups and treated with one of several NSAIDs or the vehicle-matched control for 4 weeks.

MAIN OUTCOME MEASURE(S)

Establishment, growth, and total burden of endometriotic lesions.

RESULT(S)

The NSAIDs differentially inhibited lesion establishment and growth, resulting in significantly reduced disease burden. Compared with controls (5.7 +/- 2.3 mm(2)), lesion burden was reduced by celecoxib (1.3 +/- 1.2 mm(2)), indomethacin (1.4 +/- 1.4 mm(2)), naproxen (2.7 +/- 1.2 mm(2)), sulindac (3.1 +/- 1.5 mm(2)), rofecoxib (3.4 +/- 3.0 mm(2)), and ibuprofen (4.1 +/- 1.4 mm(2)). In contrast, aspirin (5.9 +/- 1.2 mm(2)) had no statistically significant effect. Uninterrupted estrus cycling was confirmed by vaginal exams and smears in celecoxib-treated mice.

CONCLUSION(S)

Chronic administration of certain NSAIDs limits the progression of endometriosis in this murine model. The data suggest that NSAID selection in the treatment of endometriosis should be extended beyond pain management to maximize the inhibitory effect on disease burden.

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

OBJECTIVE

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

DESIGN

Animal study.

SETTING

Academic medical center.

ANIMAL(S)

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

INTERVENTION(S)

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

MAIN OUTCOME MEASURE(S)

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

RESULTS

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

CONCLUSION(S)

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

Histomorphometric alteration and cell-type specific modulation of arylhydrocarbon receptor and estrogen receptor expression by 2,3,7,8-tetrachlorodibenzo-p-dioxin and 17β-estradiol in mouse experimental model of endometriosis

Our purpose was to examine the effect of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), either singly (10 microg/kg) or with 17beta-estradiol (E2, 100 microg/kg), on the growth of endometriosis in a mouse endometriosis model by employing histo-morphometrical analysis as well as expression of arylhydrocarbon receptor (AhR) and estrogen receptor (ER). Epithelial height, stromal thickness, and proliferative activity of the endometriotic lesions were significantly increased by E2 in ovariectomized mice, whereas co-administered TCDD significantly reduced these effects. TCDD alone did not affect the proliferative activity but rather reduced the epithelial height and stromal thickness. ER expression in the luminal epithelium was decreased by E2 compared with ovariectomy alone, while TCDD significantly increased it. On the other hand, stromal ER expression was significantly increased by ovariectomy and decreased by E2, though TCDD did not further enhance this expression. These results indicate that a short-term exposure to TCDD failed to increase the growth of endometriotic lesion and the direct effect of TCDD probably depends on a cell-specific interaction with ovarian steroids mediated by their own receptors. These initial findings in intact tissue of mouse endometriosis may suggest critical roles of steroid hormones in the pathogenesis of endometriosis in relation to endocrine disruptors.

CYP1A1, CYP19, and GSTM1 polymorphisms increase the risk of endometriosis

OBJECTIVE

To investigate the possibility of genetic contribution of CYP1A1, CYP19, GSTM1, and GSTT1 polymorphisms to endometriosis.

DESIGN

Genetic polymorphism analysis.

SETTING

Case-control study.

PATIENT(S)

A group of 275 women with sporadic endometriosis was compared with a group of 346 fertile, endometriosis-free women.

INTERVENTION(S)

Surgical, laparoscopic, and histological examination.

MAIN OUTCOME MEASURE(S)

Blood specimens were obtained from endometriosis cases and controls. Polymerase chain reaction-based assays were performed for the determination of individual's genotype.

RESULT(S)

The CYP19 VNTR, located in intron 4 (TTTA)(10) allele increases the risk for endometriosis development (odds ratio [OR], 4.99; 95% confidence interval [95% CI], 1.351 to 18.436). The combined genotype CYP1A1 wt/m1 or m1/m1 and GSTM1 null deletion adds to this risk (OR, 1.95; 95% CI, 1.266 to 2.995 and OR, 2.23; 95% CI, 0.631 to 7.906, respectively). In contrast, the CYP1A1 wt/wt genotype exhibits a protective effect, with a 38% reduction in the odds for endometriosis development (OR, 0.62; 95% CI, 0.440 to 0.883).

CONCLUSION(S)

Our data suggest that CYP19 VNTR (TTTA)(10) allele as well as the combined genotype CYP1A1 m1 polymorphism and GSTM1 null deletion associate with the endometriosis phenotype, whereas the GSTT1 null deletion does not.

Do environmental contaminants adversely affect human reproductive physiology?

There is increasing concern among Canadian women that unwitting and unwanted exposures to environmental contaminants are adversely affecting their health, particularly their ability to become pregnant and have a healthy baby. Evidence of adverse reproductive outcomes among populations exposed to environmental contaminants in the workplace via accidental poisoning, together with detection of environmental contaminant residues in serum and ovarian follicular fluid, has led to the hypothesis that chemical contaminants may be contributing to adverse reproductive outcomes such as infertility, endometriosis, polycystic ovary syndrome, spontaneous abortion, preterm labour, intrauterine growth restriction, and pregnancy-induced hypertension in the general population. The lack of clear evidence concerning the association between exposure to environmental contaminants and adverse reproductive outcomes hampers the clinician's ability to counsel women who are trying to conceive or who have concerns about their pregnancy. This review summarizes the evidence linking environmental contaminant exposure to selected adverse health outcomes by examining the changes in health-outcome trends, the consistency of the epidemiological evidence of an association between the health outcome of concern and exposure to environmental contaminants, and the biological plausibility for environmental contaminant mediated effects on human reproductive health. At best, only a moderate association can be found linking exposure to environmental contaminants with evidence of deleterious reproductive effects in women. Lack of disease trend data, weak exposure assessments, and limited mechanistic data supporting the biological plausibility of potential effects are the primary limitations to the hypothesis that exposure to environmental contaminants adversely affects human reproductive physiology.

Genetic or enzymatic disruption of aromatase inhibits the growth of ectopic uterine tissue

Aromatase P450 (P450arom) is the key enzyme for the biosynthesis of estrogen that is essential for the growth of human endometriosis, a pathology characterized by endometrium-like tissue on the peritoneal surfaces of abdominal organs manifest by pelvic pain and infertility. Surgically transplanted autologous uterine tissue to ectopic sites on the peritoneum in mice has been used as an animal model to study endometriosis. Using this mouse model, we evaluated the roles of the P450arom gene and aromatase enzyme activity in the growth of endometriosis represented by ectopic uterine tissues in mice. Endometriosis was induced surgically in the following groups of mice: 1) untreated transgenic mice with disrupted P450arom gene (ArKO); 2) ArKO mice treated with systemic estrogen; 3) untreated wild-type (WT) mice; 4) WT mice treated with estrogen; 5) WT mice treated with the aromatase inhibitor, letrozole; and 6) WT mice treated with letrozole and estrogen. Each group contained eight mice; +/+ littermates of ArKO mice were used as WT controls. Treatment with estrogen increased the size of ectopic uterine tissues in ArKO and WT mice significantly. The ectopic uterine lesions in untreated and estrogen-treated ArKO mice were strikingly smaller than those in untreated and estrogen-treated WT controls, respectively. Systemic treatment of WT mice with letrozole significantly decreased the lesion size in a dose-dependent manner. The addition of estrogen to letrozole treatment increased the ectopic lesion size, although these lesions were significantly smaller than those in mice treated with estrogen only. As tissue controls, the effects of these conditions on normally located (eutopic) uterine tissue were evaluated. The effects of disruption of the P450arom gene and treatments with letrozole and estrogen seemed to be more profound on ectopic tissues, suggesting that ectopic tissues might be more sensitive to estrogen for growth. We conclude that both an intact P450arom gene and the presence of aromatase enzyme activity are essential for the growth of ectopic uterine tissue in a mouse model of endometriosis.

Environmental contaminants and dietary factors in endometriosis

Endometriosis is an estrogen-dependent disease characterized by the presence of endometrial glands and stroma outside the uterine cavity. The etiology of this disease remains elusive, but is clearly influenced by genetic, immune, and endocrine factors. Exposure to environmental contaminants has recently been added to the list of potential factors that contribute to the pathogenesis of endometriosis. The objective of this paper is to review the weight of the evidence from hospital-based case-control studies and animal experiments for an association between exposure to environmental contaminants and endometriosis.

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.

Expression of dioxin-related transactivating factors and target genes in human eutopic endometrial and endometriotic tissues

OBJECTIVE

Although an association between dioxin exposure and endometriosis has been proposed, the effects of this environmental toxin on human endometriosis are not known. To understand the potential underlying molecular mechanisms we studied the expressions of cytochrome P-450 genes (CYP1A1, CYP1A2, and CYP1B1 ), which are induced by dioxin, and the expressions of cytosolic receptor for dioxin, aryl hydrocarbon receptor, and its nuclear translocator, aryl hydrocarbon receptor nuclear translocator protein, in endometriotic and eutopic endometrial tissues.

STUDY DESIGN

Levels of transcripts of CYP1A1, CYP1A2, CYP1B1, aryl hydrocarbon receptor, and aryl hydrocarbon receptor nuclear translocator protein were determined by a quantitative reverse transcriptase-polymerase chain reaction and Southern blot assay in total ribonucleic acid samples from endometriotic and eutopic endometrial tissues. Eutopic endometrial tissue samples (n = 33) and endometriotic tissue samples (n = 10) were obtained at the time of uterine curettage and laparoscopy from disease-free women and from patients with endometriosis. Portions of these eutopic endometrial and endometriotic tissues were obtained simultaneously from the same patients (n = 8 pairs of samples). Levels of transcripts of CYP1A1, CYP1A2, CYP1B1, aryl hydrocarbon receptor, and aryl hydrocarbon receptor nuclear translocator protein were determined in endometrial and endometriotic tissues during follicular and luteal phases of the cycle and in cultured endometriotic stromal cells treated with forskolin, phorbol diacetate, medroxyprogesterone acetate,and serum.

RESULTS

Transcripts of dioxin receptor, its nuclear translocator, and two dioxin-induced target genes (CYP1A2 and CYP1B1) were demonstrated during follicular and luteal phases of the cycle in both eutopic endometrial tissues and tissues affected by pelvic endometriosis, with no readily detectable differences between these tissues. On the other hand, levels of transcripts of another dioxin-induced gene, CYP1A1, were found to be strikingly higher in endometriotic tissues than in the eutopic endometrium. Mean levels in endometriotic tissues were 8.7 times those found in eutopic endometrium. Various hormonal treatments of endometriotic stromal cells did not significantly alter these levels.

CONCLUSION

We demonstrated for the first time the expression of dioxin-related transcription factors aryl hydrocarbon receptor and aryl hydrocarbon receptor nuclear translocator protein and target genes CYP1A1, CYP1A2, and CYP1B1 in endometriotic tissues and stromal cells. Strikingly elevated CYP1A1 transcripts in endometriosis may give rise to significantly increased P-4501A1 enzyme activity and thus promote the development and growth of endometriosis by either activating procarcinogens or inducing the formation of catechol estrogens or both. In fact, the proposed link between dioxin exposure and endometriosis may be explained in part by the up-regulation of the CYP1A1 gene expression in endometriotic tissues.

Non-carcinogenic effects of TCDD in animals

Exposure to TCDD and related chemicals leads to a plethora of effects in multiple species, tissues, and stages of development. Responses range from relatively simple biochemical alterations through overtly toxic responses, including lethality. The spectrum of effects shows some species variability, but many effects are seen in multiple wildlife, domestic, and laboratory species, ranging from fish through birds and mammals. The same responses can be generated regardless of the route of exposure, although the administered dose may vary. The body burden appears to be the most appropriate dosimetric. Many of the effects often attributed to TCDD are associated with relatively high doses: lethality, wasting, lymphoid and gonadal atrophy, chloracne, hepatotoxicity, adult neurotoxicity, and cardiotoxicity. Changes in multiple endocrine and growth factor systems have been reported in a manner which is tissue, sex, and age-dependent. The most sensitive adverse effects observed in multiple species appear to be developmental, including effects on the developing immune, nervous, and reproductive systems. Such effects have been observed at maternal body burdens in the range of 30-80 ng/kg in both non-human primates and rodents. Biochemical effects on cytokine expression and metabolizing enzymes occur at body burdens which are within a factor of ten of the clearly adverse developmental responses. Thus, effects on the immune system, learning, and the developing reproductive system of multiple animals occur at body burdens which are close to those present in the background human population.

Reduced fertility among female wood workers exposed to formaldehyde

BACKGROUND

The aim of the study was to investigate whether exposure to formaldehyde, organic solvents or other chemicals in the wood-processing industry affects the fertility of women.

METHODS

For this purpose, a retrospective study on time to pregnancy was conducted among female wood workers who had given birth during 1985-1995. Data on pregnancy history, time to pregnancy, occupational exposures, and potential confounders were collected by a questionnaire; 64% (699/1,094) participated. The exposure assessment was conducted by an occupational hygienist. The data on time to pregnancy were analyzed with the discrete proportional hazards regression.

RESULTS

Exposure to formaldehyde was significantly associated with delayed conception: adjusted fecundability density ratio, FDR, was 0.64 (95% CI 0.43-0.92). At high exposure if no gloves were used, the FDR was 0.51 (% CI 0.28-0.92). Exposure to phenols, dusts, wood dusts, or organic solvents was not related to the time to pregnancy. Additionally, an association was observed between exposure to formaldehyde and an increased risk of spontaneous abortion (concerning previous spontaneous abortions, reported by the women). Associations between exposure to formaldehyde or to organic solvents and endometriosis, and between exposure to organic solvents or to dusts and salpingo-oophoritis were also suggested.

CONCLUSIONS

The study suggests that a woman's occupational exposure to formaldehyde has an adverse effect on fertility.

Environmental toxins and endometriosis

The effect of natural, environmental, or manufactured substances on endocrine organs is a current topic of discussion. Recently, some toxicants have been suggested to promote endometriosis; therefore, attention has turned to the role of environmental factors as a stimulant for endometriosis growth and maintenance. This article reviews the influence of various toxicants on endometriosis.

Continuous exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin inhibits the growth of surgically induced endometriosis in the ovariectomized mouse treated with high dose estradiol

The objectives of this study were to evaluate the effects of repeated injection of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on the growth of endometriosis and the formation of adhesions in the mouse. Sexually mature female B6C3F1 mice (n = 19) were ovariectomized and subcutaneously implanted with a silastic capsule containing estradiol (E2). Uterine tissues in full thickness (I x I mm2, 5 pieces) from the left uterine horn were surgically autotransplanted to 5 different locations in the peritoneal cavity. One week later the animals were randomly assigned to four groups and treated with: vehicle alone (corn oil). 10.50 or 100 ng/kg/day TCDD for 28 days. Two days after last dose a necropsy was performed to measure the diameter of endometrial implants and to score the adhesions. Endometrial implants were harvested for histology and blood was collected for assessment of E2 levels. The diameter of endometrial implants was significantly smaller in the TCDD treated groups compared to the controls (p < 0.05). Survival of endometrial implants, the formation and scores of adhesions, and serum E2 levels were not significantly different among the dosing groups. Histology of implants showed a significant regression of endometrial tissues in the animals receiving 50 and 100 ng/kg/day TCDD compared to the controls. We conclude that continuous exposure to TCDD resulted in regression of the endometriotic implants in the ovariectomized mice treated with a high dose exogenous F2.

Selected lesions of dioxin in laboratory rodents

Dioxin (2,3,7,8-tetrachlorodibenzo-p-dioxin) has been the subject of intensive investigations in laboratory animals during the last 2 decades. Toxicity studies have been conducted in several species of rodents and include several carcinogenicity studies as well as numerous mechanistic studies initiated to elucidate dioxin's mode of action, as both a carcinogen and a toxicant. Hepatotoxicity is a primary effect of dioxin. There has been an increase in hepatocellular tumors reported in both rats and mice exposed to dioxin. In addition to neoplastic changes, dioxin causes a spectrum of toxic changes in the liver. Additional neoplastic changes include subcutaneous fibrosarcomas and thyroid follicular cell tumors in both rats and mice and histiocytic sarcomas in mice. Dioxin causes developmental effects in the palate and kidney of mice. Changes in the female reproductive tract include ovarian atrophy, sertoliform hyperplasia, and Sertoli cell tumors. Dosing in utero results in gross malformations of the external genetalia. The effects of dioxin on the rodent model of endometriosis are described. In males, there are lowered sperm counts in the epididymis and minor testicular effects following gestational administration of dioxin. Both estrogenic and antiestrogenic-like effects have been ascribed to dioxin in laboratory animals; these activities are the result of dioxin-specific pathways resulting in the same end points as classic reproductive toxicants.