Analysis of gene expression profiles in the offspring of rats following maternal exposure to xenoestrogens

Depletion of follicles accelerated by combined exposure to phthalates and 4-vinylcyclohexene diepoxide, leading to premature ovarian failure in rats

Humans are at daily risk by simultaneous exposures to a broad spectrum of man-made chemicals in the commercial products. Several classes of chemicals have been shown to alter follicle development and reduce fertility, leading to premature ovarian failure (POF) in mammals. We investigate the synergistic effects of 4-vinylcyclohexene diepoxide (VCD) and phthalate, including di(2-ethylhexyl) phthalate (DEHP), butyl benzyl phthalate (BBP) and di-n-butyl phthalate (DBP) on POF. Combination exposure with VCD and phthalate significantly reduced the numbers of primary follicles. The expressions of Amh and Sohlh2 were significantly decreased in the combination groups. Serum Amh levels were significantly lower in the combination groups. Additionally, serum levels of follicle-stimulating hormone were significantly increased in combination groups. Taken together, exposure to phthalates promotes the depletion of follicular follicles and consequently increases the risk of premature menopause, and combined exposure of phthalates and VCD to early menopausal women is likely to aggravate the POF syndrome.

Altered gene expression patterns during the initiation and promotion stages of neonatally diethylstilbestrol-induced hyperplasia/dysplasia/neoplasia in the hamster uterus

Neonatal treatment of hamsters with diethylstilbestrol (DES) induces uterine hyperplasia/dysplasia/neoplasia (endometrial adenocarcinoma) in adult animals. We subsequently determined that the neonatal DES exposure event directly and permanently disrupts the developing hamster uterus (initiation stage) so that it responds abnormally when it is stimulated with estrogen in adulthood (promotion stage). To identify candidate molecular elements involved in progression of the disruption/neoplastic process, we performed: (1) immunoblot analyses and (2) microarray profiling (Affymetrix Gene Chip System) on sets of uterine protein and RNA extracts, respectively, and (3) immunohistochemical analysis on uterine sections; all from both initiation stage and promotion stage groups of animals. Here we report that: (1) progression of the neonatal DES-induced hyperplasia/dysplasia/neoplasia phenomenon in the hamster uterus involves a wide spectrum of specific gene expression alterations and (2) the gene products involved and their manner of altered expression differ dramatically during the initiation vs. promotion stages of the phenomenon.

Toxicological mechanism of endocrine disrupting chemicals:is estrogen receptor involved?

Endocrine disrupting chemicals (EDCs) have been shown to interfere with physiological systems, i.e., adversely affecting hormone balance (endocrine system) , or disrupting normal function, in the female and male reproductive organs. Although endocrine disruption is a global concern for human health, its impact and significance and the screening strategy for detecting these synthetic or man-made chemicals are not clearly understood in female and male reproductive functions. Thus, in this review, we summarize the interference of environmental EDCs on reproductive development and function, and toxicological mechanism (s) of EDCs in in vitro and in vivo models of male and female reproductive system. In addition, this review highlights the effect of exposure to multiple EDCs on reproductive functions, and brings attention to their toxicological mechanism (s) through estrogen receptors.

Molecular mechanism(s) of endocrine-disrupting chemicals and their potent oestrogenicity in diverse cells and tissues that express oestrogen receptors

Endocrine-disrupting chemicals (EDCs) are natural or synthetic compounds present in the environment which can interfere with hormone synthesis and normal physiological functions of male and female reproductive organs. Most EDCs tend to bind to steroid hormone receptors including the oestrogen receptor (ER), progesterone receptor (PR) and androgen receptor (AR). As EDCs disrupt the actions of endogenous hormones, they may induce abnormal reproduction, stimulation of cancer growth, dysfunction of neuronal and immune system. Although EDCs represent a significant public health concern, there are no standard methods to determine effect of EDCs on human beings. The mechanisms underlying adverse actions of EDC exposure are not clearly understood. In this review, we highlighted the toxicology of EDCs and its effect on human health, including reproductive development in males and females as shown in in vitro and in vivo models. In addition, this review brings attention to the toxicity of EDCs via interaction of genomic and non-genomic signalling pathways through hormone receptors.

Biomarker genes for detecting estrogenic activity of endocrine disruptors via estrogen receptors

Endocrine disruptors (EDs) are compounds used in various industrial products, drugs, and cosmetics. They can be found in the environment and disturb the endocrine and reproductive systems, resulting in adverse effects to humans and wildlife such as birth defects and developmental disorders. Since several EDs have a structure similar to that of endogenous steroid hormones such as estrogens, they intend to have an affinity for steroid hormone receptors and alter hormone-mediated metabolism by binding to these receptors. EDs are therefore a global concern and assays should be developed to efficiently determine whether these compounds are detrimental to biological systems. Diverse experimental methods may help determine the endocrine disrupting potential of EDs and evaluate the adverse effects of a single and/or combination of these reagents. Currently, biomarkers have been employed to objectively measure EDs potency and understand the underlying mechanisms. Further studies are required to develop ideal screening methods and biomarkers to determine EDs potency at environmentally relevant concentrations. In this review, we describe the biomarkers for estrogenicity of EDs identified both in vitro and in vivo, and introduce a biomarker, cabindin-D_9k (CaBP-9k), that may be used to assess estrogenic activity of EDs.

Oral p-tert-octylphenol exposures induce minimal toxic or estrogenic effects in adult female Sprague-Dawley rats

Contamination of the environment with endocrine-disrupting chemicals (EDC) has raised concerns about potential health hazards for humans and wildlife. Human and wildlife exposure to one such ubiquitous chemical, p-tert-octylphenol (OP), are likely, due to its persistence in the environment and its presence in food, water, and items of daily use. OP is reported to bind to the estrogen receptor (ER) and alter expression of estrogen-responsive genes. Detrimental effects of OP exposures on the reproductive system have been observed in most, but not all, in vivo experiments. This study examined estrogenic effects of oral exposures of adult female rats to OP. In vitro, OP bound weakly to human ER and a co-activator protein, and accelerated proliferation of MCF-7 cells. Adult Sprague-Dawley rats were given OP by gavage daily for 35 d (25, 50, or 125 mg/kg/d). Body and organ weights and ovarian follicle populations were not significantly altered in OP-exposed adult rats, despite detectable levels of OP in reproductive organs. The estrous cycle of rats was slightly altered, but there were no significant estrogen-like changes in histomorphology or gene expression of the uterus. Prepubertal rats given 125 or 250 mg/kg OP by gavage for 3 d had reduced body weight compared to vehicle-exposed rats but failed to show any uterotrophic response, although 17alpha-ethinyl estradiol (EE, 10 microg/kg/d, ip) induced a threefold increase in uterine weight. Overall, results suggest that toxicity will occur before estrogenic effects with oral exposures to OP. Relevant environmental exposures likely pose little risk for estrogenic effects.

In vitro exposure to xenoestrogens induces growth hormone transcription and release via estrogen receptor-dependent pathways in rat pituitary GH3 cells

In this study, we employed an in vitro model to examine the effects of endocrine disruptors (EDs) in the regulation of growth hormone (GH) gene, an important hormone in growth, development and body composition. The rat pituitary cells, GH3, were treated with alkyl-phenols (APs), i.e., 4-tert-octyl-phenol (OP), p-nonyl-phenol (NP) or bisphenol A (BPA) for 24h in a dose-dependent manner (10(-5), 10(-6) and 10(-7)M) and in a time-dependent fashion (1, 3, 6, 12 and 24h) at a high concentration (10(-5)M). An anti-estrogen, ICI 182,780, was used to examine the potential involvement of estrogen receptor (ER) in the induction of GH by EDs through an ER-mediated pathway. Treatment with OP, NP and BPA induced a significant increase in GH gene expression at high and medium doses at 24h. ED-exposure induced a marked increase in GH gene transcription as early as 6h and peaked at 12h. Co-treatment with ICI 182,780 significantly attenuated ED-induced GH expression in GH3 cells. Interestingly, the level of in vitro GH release was significantly increased at 24h in response to OP, NP or BPA, whereas co-treatment with ICI 182,780 significantly reversed ED-induced GH secretion, indicating that ER may take part in both GH gene transcription and its release in these cells. In addition, the activation of extracellular signal-regulated kinases (ERKs), protein kinases B (Akt) or G protein in response to OP, NP or BPA at 24h was observed in this study. Exposure to these APs resulted in a rapid and significant activation of ERK phosphorylation, reflecting that EDs-induced response may involve both genomic and non-genomic pathways in these cells. Taken together, these results may provide new insight into the mode of ED-induced action in GH gene regulation as well as the biological pathway underlying these molecular events.

Toxicogenomics: transcription profiling for toxicology assessment

Toxicogenomics, the application of transcription profiling to toxicology, has been widely used for elucidating the molecular and cellular actions of chemicals and other environmental stressors on biological systems, predicting toxicity before any functional damages, and classification of known or new toxicants based on signatures of gene expression. The success of a toxicogenomics study depends upon close collaboration among experts in different fields, including a toxicologist or biologist, a bioinformatician, statistician, physician and, sometimes, mathematician. This review is focused on toxicogenomics studies, including transcription profiling technology, experimental design, significant gene extraction, toxicological results interpretation, potential pathway identification, database input and the applications of toxicogenomics in various fields of toxicological study.

Effects of bisphenol-A and other endocrine disruptors compared with abnormalities of schizophrenia: an endocrine-disruption theory of schizophrenia

In recent years, numerous substances have been identified as so-called "endocrine disruptors" because exposure to them results in disruption of normal endocrine function with possible adverse health outcomes. The pathologic and behavioral abnormalities attributed to exposure to endocrine disruptors like bisphenol-A (BPA) have been studied in animals. Mental conditions ranging from cognitive impairment to autism have been linked to BPA exposure by more than one investigation. Concurrent with these developments in BPA research, schizophrenia research has continued to find evidence of possible endocrine or neuroendocrine involvement in the disease. Sufficient information now exists for a comparison of the neurotoxicological and behavioral pathology associated with exposure to BPA and other endocrine disruptors to the abnormalities observed in schizophrenia. This review summarizes these findings and proposes a theory of endocrine disruption, like that observed from BPA exposure, as a pathway of schizophrenia pathogenesis. The review shows similarities exist between the effects of exposure to BPA and other related chemicals with schizophrenia. These similarities can be observed in 11 broad categories of abnormality: physical development, brain anatomy, cellular anatomy, hormone function, neurotransmitters and receptors, proteins and factors, processes and substances, immunology, sexual development, social behaviors or physiological responses, and other behaviors. Some of these similarities are sexually dimorphic and support theories that sexual dimorphisms may be important to schizophrenia pathogenesis. Research recommendations for further elaboration of the theory are proposed.

Effects of chronic exposure to octylphenol on the male rat reproductive system

p-tert-Octylphenol (OP) is a degradation product of alkylphenol ethoxylates. OP is an endocrine disruptor known to bind to the estrogen receptor; however, effects on males are controversial. The objective of this study was to evaluate the effects of chronic exposure to OP on male reproduction. Adult Sprague-Dawley rats were administered OP for 60 d, representing 1.5 cycles of spermatogenesis. Experimental groups included a vehicle control, and three doses of OP (25, 50, or 125 mg/kg body weight [bw]) administered daily by gavage. There was a significant decrease in body weight in the 125-mg/kg group after 60 d of treatment. Both testicular and epididymal weights and histology were not altered by treatment with OP at any of the doses administered. There were no marked differences in cauda epididymal sperm counts at any doses; however, total percent sperm motility was significantly lower in rats exposed to the intermediate dose (50 mg/kg bw). There was an increase in percent static sperm cells in all OP-treated groups, with the intermediate dose (50 mg/kg) displaying a significantly higher proportion of static cells relative to untreated controls. Caput epididymal sperm motility was unaltered by OP treatment. Gene expression profiles of testes from control and high-dose-exposed rats indicate that 14 genes were modulated by at least twofold, although these changes were not statistically significant. Taken together, results from this study indicate that OP treatment of adult rats does not appear to exert major effects on male reproductive endpoints at relevant environmental exposure doses.