Polybrominated diphenylethers (PBDEs) act as apoptotic factors in the corpus luteum in addition to having a short-term stimulatory effect on progesterone secretion by luteal cells

Toxic Effects and Mechanisms of Polybrominated Diphenyl Ethers

Polybrominated diphenyl ethers (PBDEs) are a group of flame retardants used in plastics, textiles, polyurethane foam, and other materials. They contain two halogenated aromatic rings bonded by an ester bond and are classified according to the number and position of bromine atoms. Due to their widespread use, PBDEs have been detected in soil, air, water, dust, and animal tissues. Besides, PBDEs have been found in various tissues, including liver, kidney, adipose, brain, breast milk and plasma. The continued accumulation of PBDEs has raised concerns about their potential toxicity, including hepatotoxicity, kidney toxicity, gut toxicity, thyroid toxicity, embryotoxicity, reproductive toxicity, neurotoxicity, and immunotoxicity. Previous studies have suggested that there may be various mechanisms contributing to PBDEs toxicity. The present study aimed to outline PBDEs' toxic effects and mechanisms on different organ systems. Given PBDEs' bioaccumulation and adverse impacts on human health and other living organisms, we summarize PBDEs' effects and potential toxicity mechanisms and tend to broaden the horizons to facilitate the design of new prevention strategies for PBDEs-induced toxicity.

Effects of bisphenol A, diethylhexyl phthalate and pentabrominated diphenyl ether 99 on steroid synthesis in cultured bovine luteal cells

Bisphenol A (BPA), diethylhexyl phthalate (DEHP) and pentabrominated diphenyl ether 99 (PBDE 99) are environmental toxicants belonging to the endocrine disrupting compounds (EDCs). They exert adverse effects on the various physiological systems, especially the reproductive system of humans and animals. The aim of this study was to investigate the effects of BPA, DEHP and PBDE 99 on progesterone (P4) synthesis in cultured bovine luteal cells. The bovine luteal cells isolated from the mid-luteal corpora lutea were exposed to different concentrations of BPA (1, 3, 10 and 30 µM), DEHP (1, 3, 10 and 30 µM) and PBDE 99 (0.1, 0.3, 1 and 3 µM) in a serum-free culture media for 48 and 96 hr. At 48 hr, the P4 level in the luteal cells decreased after treatment with all concentrations of BPA; 3, 10 and 30 µM of DEHP; and 3 µM of PBDE 99 compared to the control (p < .05). Treatment of cells with 3-30 µM of BPA, 1-30 µM of DEHP and 1-3 µM of PBDE 99 for 96 hr resulted in reduction in P4 synthesis (p < .05). However, lower concentrations of PBDE 99 (0.1 and 0.3 µM) increased P4 levels at 48 and 96 hr. Synthesis of P4 was lower at 96 hr compared to the 48 hr in the groups treated with BPA (30 µM), DEHP (1-30 µM), PBDE 99 (0.3-3 µM) and control group. Our results showed that BPA, DEHP and PBDE 99 are able to alter luteal steroidogenesis in bovine cells and can disrupt hormonal balance in the ovary. However, it is necessary to evaluate the exact mechanism underlying these effects in future studies.

BDE-47 Decreases Progesterone Levels in BeWo Cells by Interfering with Mitochondrial Functions and Genes Related to Cholesterol Transport

Polybrominated diphenyl ethers (PBDEs) have been reported to exert reproductive endocrine toxicity, but the mechanisms for this process remain unclear. Currently available studies have concentrated on the enzymatic reactions during steroidogenesis, but the results are not consistent. In this study, we explored the effects of 2,2',4,4'-tertrabromodiphenyl ether (BDE-47) on progesterone biosynthesis and the potential mechanisms in human placental choriocarcinoma cells. The results showed that BDE-47 decreased progesterone production in a dose-dependent manner but had no effect on key enzymes (Cyp11a1 and 3β-HSD). BDE-47 exposure depolarized the mitochondrial membrane potential and downregulated adenosine triphosphate levels. The gene expression levels of Mfn2, Tspo, Atad3, Vdac1, Fis1, and Drp1, which are involved in mitochondrial dynamics and cholesterol transport, were disturbed. The demethylation of some CpG loci of mitochondrial biomarkers (Drp1, Opa1, Vdac2, and Atad3) was induced in the 1 μM BDE-47 exposure group, but no methylation change was observed with 50 μM treatment. Our findings unveiled that the reduction of progesterone synthesis induced by BDE-47 might be associated with cholesterol transportation, mitochondrial dynamics, and mitochondrial functions. These findings provide substantial data on the reproductive endocrine toxicity of PBDEs.

Environmental immune disruptors, inflammation and cancer risk

An emerging area in environmental toxicology is the role that chemicals and chemical mixtures have on the cells of the human immune system. This is an important area of research that has been most widely pursued in relation to autoimmune diseases and allergy/asthma as opposed to cancer causation. This is despite the well-recognized role that innate and adaptive immunity play as essential factors in tumorigenesis. Here, we review the role that the innate immune cells of inflammatory responses play in tumorigenesis. Focus is placed on the molecules and pathways that have been mechanistically linked with tumor-associated inflammation. Within the context of chemically induced disturbances in immune function as co-factors in carcinogenesis, the evidence linking environmental toxicant exposures with perturbation in the balance between pro- and anti-inflammatory responses is reviewed. Reported effects of bisphenol A, atrazine, phthalates and other common toxicants on molecular and cellular targets involved in tumor-associated inflammation (e.g. cyclooxygenase/prostaglandin E2, nuclear factor kappa B, nitric oxide synthesis, cytokines and chemokines) are presented as example chemically mediated target molecule perturbations relevant to cancer. Commentary on areas of additional research including the need for innovation and integration of systems biology approaches to the study of environmental exposures and cancer causation are presented.

Effects of 2,2',4,4'-tetrabromodiphenyl ether (BDE47) on the enzymes of phase I (CYP2B1/2) and phase II (SULT1A and COMT) metabolism, and differences in the action of parent BDE-47 and its hydroxylated metabolites, 5-OH-BDE-47 and 6-OH-BDE47, on steroid secretion by luteal cells

In this study we determined the effects of BDE-47 on the expression and activity of phase I (CYP2B1/2) and phase II (SULT1A and COMT) enzymes, and assessed the actions of BDE-47 and its metabolites on luteal steroidogenesis. Luteal cells collected during early (ELP), middle (MLP) and late (LLP) luteal phase were exposed to BDE-47 (0.5, 25, and 50ng/ml) or metabolites (2.5, 5 and 25ng/ml). BDE-47 decreased CYP2B1/2 activity and expression but had no effect on SULT1A or COMT. BDE-47 exerted a stimulatory action on estrogen secretion in MLP and an inhibitory in LLP, but had no effect on progesterone secretion. 5-OH-BDE-47 and 6-OH-BDE-47 decreased progesterone, but had no effect on estrogen secretion.

CONCLUSIONS

The inhibitory effect of BDE-47 on CYP2B1/2 suggests the possibility of BDE-47 accumulation in the corpus luteum; by affecting steroid secretion and steroidogenesis enzymes, BDE-47 and its metabolites can be responsible for shortening luteal phase.

Developmental effects of perinatal exposure to PBDE and PCB on gene expression in sexually dimorphic rat brain regions and female sexual behavior

The developing nervous system is a potential target of environmental contaminants such as polybrominated diphenylethers (PBDE), which accumulate in the biosphere. We compared effects of 2,2',4,4',5-pentabromo-BDE (PBDE99), a PBDE congener present in environmental samples, and PCB on brain development. Time-pregnant rats were subcutaneously injected with PBDE99 (1 or 10mg/kg), the PCB mixture Aroclor 1254 (10mg/kg), or vehicle from gestational day 10-18. mRNA levels of genes involved in central control of reproductive functions and sexual behavior were analyzed by real time RT PCR in two sexually dimorphic brain regions, medial preoptic area (MPO) and ventromedial hypothalamus (VMH) of adult offspring of both sexes. Exposure to PBDE99 or the PCB mixture during pre- and postnatal development affected mRNA expression levels in a treatment-, region- and sex-specific manner, and changed the sensitivity of target genes to estradiol. The sex difference in progesterone receptor mRNA levels of VMH normally seen in untreated controls was abolished by both, PBDE99 and PCB. Estrous cycles were significantly affected, and preliminary experiments suggest an impairment of female sexual behavior. Our data indicate that developmental exposure to PBDE99 at doses below signs of general toxicity affects the regulation of estrogen target genes in rat brain. Since PBDE99 was detected in blood and adipose tissue of adult offspring, these effects may result from interactions with developmental processes, with adult functions, or a combination of both.