Bisphenol A-induced apoptosis of cultured rat Sertoli cells

Maternal and fetal exposure to bisphenol A in Korea

Bisphenol A (BPA) is a well-known endocrine disrupter used widely. Despite the potential risk of human exposure to BPA, little information exists concerning maternal and fetal exposure to BPA during pregnancy in Korea. This study purposed to evaluate the correlation between maternal and fetal exposure, and to determine exposure levels to BPA in Korean pregnant women and their fetuses. Maternal blood and umbilical cord blood were collected from 300 subjects, and total BPA levels were measured. Blood BPA concentrations ranged from non-detectable to 66.48 microg/L in pregnant women and from non-detectable to 8.86 microg/L in umbilical cords. Serum BPA levels in most pregnant women were higher than in corresponding fetal umbilical cords and a positive correlation was found between in maternal and fetal BPA concentrations (p<0.05).

Induction of apoptosis by UV-irradiated chlorinated bisphenol A in Jurkat cells

Chlorinated derivatives of bisphenol A (ClBPAs) have been detected in wastewater from waste paper recycling plants. We previously reported that bisphenol A (BPA) and ClBPAs [3-chlorobisphenol A, 3,3'-dichlorobisphenol A, and 3,3',5-trichlorobisphenol A] irradiated with ultraviolet (UV) B or UVC (not with UVA) induced inhibition of cell growth, and that 3-hydroxybisphenol A (3-OHBPA) was detected in the photoproducts [Mutou, Y., Ibuki, Y., Terao, Y., Kojima, S., Goto, R., 2006b. Chemical change of chlorinated bisphenol A by ultraviolet irradiation and cytotoxicity of their products on Jurkat cells. Environmental Toxicology and Pharmacology, 21, 283-289]. The formation of hydroxylated BPAs by UV irradiation might contribute to the inhibition of cell growth, but the mechanism of the growth inhibition is not clarified. In this study, we investigated whether BPA and ClBPAs exposed to UVA, UVB, or UVC, and 3-OHBPA could induce the death of Jurkat cells and whether the pattern of cell death was apoptosis. ClBPAs exposed to UVB and UVC induced significant cell death, but those exposed to UVA and BPA did not. The cell death was apoptosis because chromatin condensation and DNA fragmentation were detected. Activation of caspase-3, -8, and -9 and cytochrome c release indicated that ClBPAs exposed to UVB or UVC induced apoptosis via typical apoptotic pathways. In addition, 3-OHBPA induced apoptosis similar to UVB- or UVC-irradiated ClBPA. These results suggested that the photoproducts of ClBPAs generated by UV irradiation, containing 3-OHBPA, contributed to the induction of apoptosis.

Estrogen receptor independent neurotoxic mechanism of bisphenol A, an environmental estrogen

Bisphenol A (BPA), a ubiquitous environmental contaminant, has been shown to cause developmental toxicity and carcinogenic effects. BPA may have physiological activity through estrogen receptor (ER) -α and -β, which are expressed in the central nervous system. We previously found that exposure of BPA to immature mice resulted in behavioral alternation, suggesting that overexposure of BPA could be neurotoxic. In this study, we further investigated the molecular neurotoxic mechanisms of BPA. BPA increased vulnerability (decrease of cell viability and differentiation, and increase of apoptotic cell death) of undifferentiated PC12 cells and cortical neuronal cells isolated from gestation 18 day rat embryos in a concentration-dependent manner (more than 50 µM). The ER antagonists, ICI 182,780, and tamoxifen, did not block these effects. The cell vulnerability against BPA was not significantly different in the PC12 cells overexpressing ER-α and ER-β compared with PC12 cells expressing vector alone. In addition, there was no difference observed between BPA and 17-β estradiol, a well-known agonist of ER receptor in the induction of neurotoxic responses. Further study of the mechanism showed that BPA significantly activated extracellular signal-regulated kinase (ERK) but inhibited anti-apoptotic nuclear factor kappa B (NF-κB) activation. In addition, ERK-specific inhibitor, PD 98,059, reversed BPA-induced cell death and restored NF-κB activity. This study demonstrated that exposure to BPA can cause neuronal cell death which may eventually be related with behavioral alternation in vivo. However, this neurotoxic effect may not be directly mediated through an ER receptor, as an ERK/NF-κB pathway may be more closely involved in BPA-induced neuronal toxicity.

In vitro molecular mechanisms of bisphenol A action

Bisphenol A (BPA, 2,2-bis (4-hydroxyphenyl) propane; CAS# 80-05-7) is a chemical used primarily in the manufacture of polycarbonate plastic, epoxy resins and as a non-polymer additive to other plastics. Recent evidence has demonstrated that human and wildlife populations are exposed to levels of BPA which cause adverse reproductive and developmental effects in a number of different wildlife species and laboratory animal models. However, there are major uncertainties surrounding the spectrum of BPA's mechanisms of action, the tissue-specific impacts of exposures, and the critical windows of susceptibility during which target tissues are sensitive to BPA exposures. As a foundation to address some of those uncertainties, this review was prepared by the "In vitro" expert sub-panel assembled during the "Bisphenol A: An Examination of the Relevance of Ecological, In vitro and Laboratory Animal Studies for Assessing Risks to Human Health" workshop held in Chapel Hill, NC, Nov 28-29, 2006. The specific charge of this expert panel was to review and assess the strength of the published literature pertaining to the mechanisms of BPA action. The resulting document is a detailed review of published studies that have focused on the mechanistic basis of BPA action in diverse experimental models and an assessment of the strength of the evidence regarding the published BPA research.

In vivo effects of BISGMA-a component of dental composite-on male mouse reproduction and fertility

The aim of this study is to investigate the effects of the resin monomer bisphenol A glycerolate dimethacrylate (BISGMA) on adult male mouse fertility. Male Swiss mice were administered various concentrations of BISGMA (0, 25, and 100 microg/kg) for a period of 28 days, and the effects on fertility was assessed by breeding these males with untreated female mice after the exposure periods. The results showed that fertility was significantly reduced when male mice were exposed to BISGMA, in comparison with their control counterparts. In females mated with males exposed to BISGMA, there was a significant reduction in the pregnancy rates as well as the number of viable fetuses. The number of resorptions out of the total number of implantations was significantly increased in females mated with males that had been exposed to BISGMA. Furthermore, the number of females with resorptions was also significantly increased. Significant reductions in bodyweight and weights of the testis and preputial glands were also observed. The weights of the seminal vesicles were significantly increased in males exposed to BISGMA in comparison with their control counterparts. There were significant reductions in testicular sperm counts, epididymal sperm counts and in the efficiency of sperm production. In conclusion, exposure of male mice to BISGMA results in an impairment of the reproductive system and fertility.

Octylphenol induces apoptosis in cultured rat Sertoli cells

In this study, the effects of 4-tert-octylphenol (OP) were examined on the viability of rat cultured Sertoli cells using the MTT assay and OP-induced apoptosis was detected by transmission electron microscope (TEM), flow cytometric analysis and Hoechst staining. In addition, RT-PCR was used to analyze the levels of Bcl-2 and Bax mRNA. Bcl-2, Bax and caspase-3 protein expressions were determined by Western blot analysis. Sertoli cells were treated with OP from 30 to 60microM for 6-24h. Decreased viability of Sertoli cells and increased apoptosis occurred in a concentration- and a time-dependent manner. The expression of Bcl-2 was down-regulated, while the expression of Bax up-regulated. OP also down-regulated the expression of 32kDa procaspase-3, which was cleaved to generate active subunit (17kDa). These results suggest that OP may induce Sertoli cell apoptosis by regulation of Bcl-2/Bax and caspase-3 activation.

Chemical change of chlorinated bisphenol A by ultraviolet irradiation and cytotoxicity of their products on Jurkat cells

Chlorinated derivatives of bisphenol A (ClBPAs) have been detected in wastewater from waste paper recycling plants. BPA and ClBPAs are always exposed to ultraviolet (UV) radiation in the environment and consequently various photoproducts might be produced. Acute cytotoxicity of photoproducts of BPA and ClBPAs are not known. In this study, we investigated the cytotoxicity and chemical structure of photoproducts of BPA and ClBPAs (3-chlorobisphenol A (3-ClBPA), 3,3'-dichlorobisphenol A (3,3'-diClBPA) and 3,3',5-trichlorobisphenol A (3,3',5-triClBPA)) after UV irradiation (UVA, UVB and UVC). The toxicities of photoproducts on Jurkat cells were determined by Alamar Blue assay, and the chemical structures of the photoproducts were identified using GC/MS. The cytotoxicities of 3-ClBPA and 3,3'-diClBPA were higher than that of BPA and 3,3',5-triClBPA. In addition, the toxicities of ClBPAs were increased by the irradiation of UVB and UVC at 100J/cm(2) and decreased at 1000J/cm(2) in comparison with those at 100J/cm(2), indicating that their structures had changed. 3-Hydroxybisphenol A (3-OHBPA) was detected in the photoproducts of 3-ClBPA irradiated with UVB and UVC at 100J/cm(2), and 3-OHBPA and 3-chloro-3'-hydroxybisphenol A (3-Cl-3'-OHBPA) were detected in those of 3,3'-diClBPA. However, these hydroxylated BPAs were not detected in the photoproducts exposed to 1000J/cm(2). The cytotoxicity of 3-OHBPA was the almost same as ClBPAs after UVB and UVC irradiation. These results indicate that the formation of hydroxylated BPAs might contribute to the increase in toxicity caused by UV irradiation.

Effect of environmental contaminants on male reproduction

A substantial body of evidence has accumulated in recent years that consistently indicate various adverse effects of environmental contaminants on human health. Decreasing trend of male fertility in terms of sperm counts and sperm quality, along with other changes in male reproductive health, including congenital malformations and testicular cancer in humans, and similar problems in wildlife has been correlated to the exposure to environmental contaminants. Many environmental chemicals have been reported to cause these reproductive abnormalities by eliciting changes in endocrine control of reproduction; however the specific underlying mechanisms are poorly understood. The present review summarizes recent studies on environmental contaminants and associated possible mechanism leading to adverse effects on male reproduction. Numerous studies demonstrate the interaction of environmental toxicants with steroid receptors and thereby causing interference with developmental and functional aspects of testis, epididymis and accessory sex organs. Induction of reactive oxygen species (ROS) by environmental contaminants and associated oxidative stress also have role in defective sperm function and male infertility.

Nonylphenol-induced thymocyte apoptosis is related to Fas/FasL pathway

Nonylphenol (NP) is the final biodegradation product of nonylphenol polyethoxylates, which are widely used as surfactants in domestic and industrial products. NP has been reported to have estrogenic activity and shown to have potential reproductive toxicity. However, its influence on immune system function remains unclear. In this study, to determine the immunological effects of NP, the effects of NP on apoptosis and Fas/FasL gene expression in rat thymocyte in vitro were investigated. Thymocytes were treated with NP 0.1, 1, and 10 ppm, respectively. Viable cell numbers were determined by MTT assay. Apoptotic cells were identified by DNA fragment analysis. A semi-quantitative reverse transcriptase-polymerase chain reaction method was used to analyze Fas and FasL mRNA levels. Fas and FasL protein expression was evaluated by flow cytometry. The results showed that NP decreased the cellularity; induced apoptotic death and enhanced the expression of Fas and FasL mRNA as well as proteins in thymocytes. These findings suggest that NP may induce apoptosis by altering the expression of Fas and FasL in thymocytes so as to affect the immune system function.

Identification of rab12 as a vesicle-associated small GTPase highly expressed in Sertoli cells of rat testis

We examined the expression and the localization of a small GTPase, rab12, in rat testis. Northern blot analysis showed that 2.3 kb transcript of rab12 was expressed in rat testis. RT-PCR analysis indicated constant expression of rab12 throughout testis development. Immunohistochemical studies revealed that rab12 protein was highly expressed in Sertoli cells in the seminiferous tubules, while both spermatogenic germ cells and interstitial cells exhibited faint or no immunosignal for rab12. The expression pattern of rab12 in Sertoli cells varied between the tubules: its immunostaining appeared as a wheel-like pattern at stage I approximately III and as a luminal staining pattern at stage IV approximately VI, whereas the immunostaining signals were only rudimentary detected at stage VIII and thereafter (approximately stage XIV). The diversified staining pattern of rab12 in the tubules seemed to reflect either the different shape of Sertoli cells during the cycle of the seminiferous epithelium or the variant expression levels of rab12 in Sertoli cells at each stage of the tubules. In cultured rat Sertoli cells and normal rat kidney (NRK) cells, rab12 was found to be associated with small vesicles distributed throughout the cytoplasm, but not with the Golgi apparatus. When overexpressed in NRK cells, rab12-associated small vesicles were not only distributed throughout the cytoplasm but also accumulated in the perinuclear cytoplasm around centrosome. We interrupt these data as a potential role of rab12 in acceleration of vesicular transport from the cell periphery to the perinuclear centrosome region.

Estrogen-induced spermatogenic cell apoptosis occurs via the mitochondrial pathway: role of superoxide and nitric oxide

The detrimental effects of estrogen on testicular function provide a conceptual basis to examine the speculative link between increased exposure to estrogens and spermatogenic cell death. Using an in vitro model, we provide an understanding of the events leading to estrogen-induced apoptosis in cells of spermatogenic lineage. Early events associated with estrogen exposure were up-regulation of FasL and increased generation of H(2)O(2), superoxide, and nitric oxide. The ability of anti-FasL antibodies to prevent several downstream biochemical changes and cell death induced by 17beta-estradiol substantiates the involvement of the cell death receptor pathway. Evidence for the amplification of the death-inducing signals through mitochondria was obtained from the transient mitochondrial hyperpolarization observed after estradiol exposure resulting in cytochrome c release. A combination of nitric oxide and superoxide but not H(2)O(2) was responsible for the mitochondrial hyperpolarization. Mn(III) tetrakis(4-benzoic acid)porphyrin chloride, an intracellular peroxynitrite scavenger, was able to reduce mitochondrial hyperpolarization and cell death. Although nitric oxide augmentation occurred through an increase in the expression of inducible nitric-oxide synthase, superoxide up-regulation was a product of estradiol metabolism. All of the above changes were mediated through an estrogen receptor-based mechanism because tamoxifen, the estrogen receptor modulator, was able to rescue the cells from estrogen-induced alterations. This study establishes the importance of the independent capability of cells of the spermatogenic lineage to respond to estrogens and most importantly suggests that low dose estrogens can potentially cause severe spermatogenic cellular dysfunction leading to impaired fertility even without interference of the hypothalamo-hypophyseal axis.