Differential accumulation levels in the brain of rats exposed to the endocrine disruptor 4-tert-octylphenol (OP)

Human risk assessment through development and application of a physiologically based toxicokinetic model for 4-tert-octylphenol

4-tert-octylphenol (4-tert-OP) is an ecologically hazardous substance, and exposure to it in the environment has been consistently reported in the past. Despite the hazards and widespread exposure to 4-tert-OP, tools for scientific assessment of 4-tert-OP exposure risk level in humans are lacking. The main purpose of this study was to develop a physiologically-based-toxicokinetic (PBTK) model for 4-tert-OP and to perform quantitative risk assessment of 4-tert-OP in various population groups using the established model. Based on the results of toxicokinetic experiments on male rats, the PBTK model for 4-tert-OP was established and verified, and this was converted to a model for humans through interspecies extrapolation. Based on the previously reported no-observed-adverse-effect-levels for rats, it was possible to estimate the 4-tert-OP reference dose in humans through reverse dosimetry using the model. Biomonitoring data derived from various population groups were applied to the human PBTK model to calculate external exposures and margin of safety for 4-tert-OP for each population group. The PBTK model established in this study adequately explained the toxicokinetic experimental values at acceptable levels and was able to quantitatively predict the 4-tert-OP exposure level in the testes related to male reproductive toxicity. In addition, the degree of external exposure to 4-tert-OP could be scientifically estimated based on biomonitoring values derived from various biological matrices. The reference doses for systemic and reproductive toxicity caused by 4-tert-OP in male humans were calculated to be 0.16 and 1.12 mg/kg/day, respectively. The mean external exposure to 4-tert-OP in each population group estimated based on plasma and urine biomonitoring data was 0.04-66.24 mg/kg/day, showing very large exposure diversity between groups. Exposure risks to 4-tert-OP in populations ranged from safe to risky, suggesting the need for continued monitoring and risk management of 4-tert-OP worldwide. This study provides valuable scientific insight regarding the 4-tert-OP human risk assessment.

Endocrine disruptors also function as nervous disruptors and can be renamed endocrine and nervous disruptors (ENDs)

Endocrine disruption (ED) and endocrine disruptors (EDs) emerged as scientific concepts in 1995, after numerous chemical pollutants were found to be responsible for reproductive dysfunction. The World Health Organization established in the United Nations Environment Programme a list of materials, plasticizers, pesticides, and various pollutants synthesized from petrochemistry that impact not only reproduction, but also hormonal functions, directly or indirectly. Cells communicate via either chemical or electrical signals transmitted within the endocrine or nervous systems. To investigate whether hormone disruptors may also interfere directly or indirectly with the development or functioning of the nervous system through either a neuroendocrine or a more general mechanism, we examined the scientific literature to ascertain the effects of EDs on the nervous system, specifically in the categories of neurotoxicity, cognition, and behaviour. To date, we demonstrated that all of the 177 EDs identified internationally by WHO are known to have an impact on the nervous system. Furthermore, the precise mechanisms underlying this neurodisruption have also been established. It was previously believed that EDs primarily function via the thyroid. However, this study presents substantial evidence that approximately 80 % of EDs operate via other mechanisms. It thus outlines a novel concept: EDs are also neurodisruptors (NDs) and can be collectively termed endocrine and nervous disruptors (ENDs). Most of ENDs are derived from petroleum residues, and their various mechanisms of action are similar to those of "spam" in electronic communications technologies. Therefore, ENDs can be considered as an instance of spam in a biological context.

4-Nonylphenol and 4-tert-octylphenol induce anxiety-related behaviors through alternation of 5-HT receptors and transporters in the prefrontal cortex

Environmental endocrine disruptors 4-nonylphenol (NP) and 4-tert-octylphenol (OP) may cast huge harm to human health. We used a rat model to observe the influence of NP or/and OP exposure on anxiety-related behaviors and the underlying mechanisms. Eighty male Sprague-Dawley (SD) rats were randomly divided into 10 groups: control group (corn oil), NP groups [30, 90, 270 mg/kg], OP groups [40, 120, 360 mg/kg] and NO groups [(mixed with the corresponding NP, OP alone exposed low, medium and high dose according to the natural environment exists NP:OP = 4:1]. The rats were orally administered every other day for 30 days. The neurobehaviors of rats were evaluated by open-field test (OFT) and elevated plus-maze test (EPM), and the concentrations of 5-HT, monoamine oxidase (MAOA), serotonin transporter (SERT), vesicular monoamine transporter 2 (VAMT2), 5-hydroxytryptamine 1A (5-HT_1A), 5-hydroxytryptamine 2A (5-HT_2A)，and 5-hydroxytryptamine 2C (5-HT_2C) in the rat prefrontal cortex were analyzed by ELISA. OFT and EPM tests showed that NP or/and OP exposure induced anxiety-related behaviors in rats. 5-HT levels were significantly increased compared with the control group. The levels of MAOA, SERT, VAMT2, 5-HT_1A, 5-HT_2A, and 5-HT_2C in the prefrontal cortex reduced in different degrees by high-doses NP or/and OP exposure. In summary, NP or/and OP exposure might cause anxiety-related behaviors in rats through regulating neurotransmitter 5-HT levels by altering the expression of 5-HT decomposition enzyme MAOA, transporters SERT and VMAT2, and 5-HT receptors 5-HT_1A, 5-HT_2A, and 5-HT_2C.

Environmental Water Pollution, Endocrine Interference and Ecotoxicity of 4-tert-Octylphenol: A Review

4-tert-Octylphenol is a degradation product of non-ionic surfactants alkylphenol polyethoxylates as well as raw material for a number of industrial applications. It is a multimedia compound having been detected in all environmental compartments such as indoor air and surface waters. The pollutant is biodegradable, but certain degradation products are more toxic than the parent compound. Newer removal techniques from environmental waters have been presented, but they still require development for large-scale applications. Wastewater treatment by plant enzymes such as peroxidases offers promise in total removal of 4-tert-octylphenol leaving less toxic degradation products. The pollutant's endocrine interference has been well reported but more in oestrogens than in any other signalling pathways through which it is believed to exert toxicity on human and wildlife. In this paper we carried out a review of the activities of this pollutant in environmental waters, endocrine interference and relevance to its toxicities and concluded that inadequate knowledge of its endocrine activities impedes understanding of its toxicity which may frustrate current efforts at ridding the compound from the environment.

Effects of octylphenol on the expression of StAR, CYP17 and CYP19 in testis of Rana chensinensis

It has been proposed that a decline in sperm quality is associated with exposure to environmental chemicals with estrogenic activity. Seeking possible explanations for this effect, this study investigated the effects of octylphenol (OP) on the synthesis of steroid hormones in amphibian. Rana chensinensis were exposed to 10^-8, 10^-7 and 10^-6mol/L OP after 10, 20, 30 and 40 days. The cDNA fragments of StAR (274bp), CYP17 (303bp) and CYP19 (322bp) were cloned. In situ hybridization and immunohistochemistry revealed that positive signals of StAR, CYP17, CYP19 mRNA and proteins mainly in the Leydig cells of testes. Real-time PCR showed that up-regulation of StAR and CYP19, and down-regulation of CYP17 after exposure to 10^-8, 10^-7 and 10^-6mol/L OP. The results suggest that OP can alter transcriptions of StAR, CYP17 and CYP19, thus disturb the expressions of StAR, P450c17 and P450arom, thereby adversely affect steroid synthesis.

Photoperiod-Dependent Effects of 4-tert-Octylphenol on Adherens and Gap Junction Proteins in Bank Vole Seminiferous Tubules

In the present study we evaluated in vivo and in vitro effects of 4-tert-octylphenol (OP) on the expression and distribution of adherens and gap junction proteins, N-cadherin, β -catenin, and connexin 43 (Cx43), in testes of seasonally breeding rodents, bank voles. We found that in bank vole testes expression and distribution of N-cadherin, β -catenin, and Cx43 were photoperiod dependent. Long-term treatment with OP (200 mg/kg b.w.) resulted in the reduction of junction proteins expressions (P < 0.05, P < 0.01) and their delocalization in the testes of males kept in long photoperiod, whereas in short-day animals slight increase of Cx43 (P < 0.05), N-cadherin, and β -catenin (statistically nonsignificant) levels was observed. Effects of OP appeared to be independent of FSH and were maintained during in vitro organ culture, indicating that OP acts directly on adherens and gap junction proteins in the testes. An experiment performed using an antiestrogen ICI 182,780 demonstrated that the biological effects of OP on β -catenin and Cx43 involve an estrogen receptor-mediated response. Taken together, in bank vole organization of adherens and gap junctions and their susceptibility to OP are related to the length of photoperiod. Alterations in cadherin/catenin and Cx43-based junction may partially result from activation of estrogen receptor α and/or β signaling pathway.

Assessment of source water contamination by estrogenic disrupting compounds in China

Detection of estrogenic disrupting compounds (EDCs) in drinking waters around China has led to rising concerns about health risks associated with these compounds. There is, however, a paucity of studies on the occurrence and identification of the main compounds responsible for this pollution in the source waters. To fill this void, we screened estrogenic activities of 23 source water samples from six main river systems in China, using a recombinant two-hybrid yeast assay. All sample extracts induced significant estrogenic activity, with E2 equivalents (EEQ) of raw water ranging from 0.08 to 2.40 ng/L. Additionally, 16 samples were selected for chemical analysis by gas chromatography-mass spectrometry. The EDCs of most concern, including estrone (E1), 17beta-estradiol (E2), 17alpha-ethinylestradiol (EE2), estriol (E3), diethylstilbestrol (DES), estradiol valerate (EV), 4-t-octylphenol (4-t-OP), 4-nonylphenols (4-NP) and bisphenol A (BPA), were determined at concentrations of up to 2.98, 1.07, 2.67, 4.37, 2.52, 1.96, 89.52, 280.19 and 710.65 ng/L, respectively. Causality analysis, involving comparison of EEQ values from yeast assay and chemical analysis identified E2, EE2 and 4-NP as the main responsible compounds, accounting for the whole estrogenic activities (39.74% to 96.68%). The proposed approach using both chemical analysis and yeast assay could be used for the identification and evaluation of EDCs in source waters of China.

Differential accumulation of BPA in some tissues of offspring of Balb-C mice exposed to different BPA doses

Pregnant adult Balb-C mice were exposed daily to two different doses of Bisphenol A (BPA) by subcutaneous injection beginning on gestational day 1 through the seventh day after delivery. The mothers were sacrificed on postpartum day 21, and the offspring were sacrificed at 3 months of age. Control mice were subjected to the same experimental protocol but received saline injections. The liver, muscles, hindbrain and forebrain of the offspring were dissected and processed using HPLC to assess the level of BPA in the tissues and to determine its dependence on the exposure dose and gender. For comparison, the same tissues were dissected from the mothers and analysed. We report the following results: (1) the level of BPA that accumulated in a given tissue was dependent on the exposure dose; (2) the rank order of BPA accumulation in the various tissues was dependent on the gender of the offspring; (3) the average BPA concentrations in the liver and muscle of the female offspring were higher than in the males; and (4) the average BPA concentration in the central nervous system (i.e., the hindbrain and forebrain) of the male offspring was higher than in the females.