| Environmental endocrine disruptors (EEDs) or endocrine disrupting chemicals (EDCs) are a class of naturally occurring or synthetic compounds that can synthesis, release, transport animal hormone and interfere animal endocrine system. EDCs could also bind hormone receptors and interfer series of biological processes. Pentachlorophenol (PCP) belongs one of endocrine-disrupting chemical (EDC) for priority testing chemicals, which was used as cheap and efficient pesticide, wood preservations for a long time in China. As reported, PCP has a strong carcinogenic, teratogenic, mutagenic effect and has significant damage on reproductive system. This chemical poses significant toxicological risks and may cause hormonal alterations in resident organisms. Many waters are contaminated with low concentrations of PCP and its bio-accumulate has potentially adverse effects on aquatic organisms. PCP and its salts not only cause acute toxicity in many organisms but also act as endocrine disruptors and are suspected to be human carcinogens. Some studies have shown that PCP has estrogenic effects, while in contrast, PCP was anti-estrogenic when juvenile goldfish primary hepatocytcs were exposed to PCP. There are extensive studies on the mechanisms of PCP toxicity, but limited work had been conducted on the endocrine effects of PCP in fish. So the mechanisms by which PCP exerts its endocrine-disrupting (ED) effects are not well understood.The objectives of the present study were (1) to determine whether PCP has an estrogenic effect; and (2) to provide preliminary evidence for the estrogenic effect of PCP caused by both receptor and non-receptor pathways and (3) to determine whether these pathways involve the HPG axis. So far, this is the most comprehensive study on mechanisms of the estrogenic effects of PCP. To evaluate the estrogenic effect of PCP in Gobiocypris rarus, the qPCR method was applied to analyze the endocrine-disrupting effects of PCP on the expression of a panel of genes associated with the hypothalamic-pituitary-gonadal (HPG) axis. The influence of PCP on the transcript abundance of the Vitellogenin (VTG) group (VTG1, VTG2), exposure to8,16,80, or160μg/L PCP or to50ng/L EE2for21days resulted in non-significant decreases in VTG1and VTG2gene expression in the brain, liver and gonads at low concentrations of PCP compared to the control group. In contrast, high concentrations of PCP increased the expression of these genes in the same tissues. The expression of VTG1and VTG2in the liver tissue was increased more significantly than in the brain and gonads in response to exposure to160μg/L PCP and the positive control EE2. Which indicate that PCP has estrogenic effect as EE2rather than anti-estrogenic effectExposure to8,16,80or160μg/L PCP or50ng/L EE2for21days resulted in non-significant decreases in ERβ2expression in liver tissue but increases in the brain and gonads. All of the other steroid receptor genes demonstrated increasing trends as a function of exposure to the four concentrations of PCP and the positive control EE2compared to the control group. Although ERβ2expression in the liver tissue did not increase, AR, ERa and ERβ1increased significantly in this tissue. Low concentrations of PCP had a greater impact on the four steroid receptor genes in the gonads. Specifically, in the gonad tissue, AR, ERa, ERβ1and ERβ2were more significantly increased following exposure to8or16μg/L PCP than for the other concentrations. This phenomenon indicated that PCP estrogenic effect trough binding steroid receptors. The key enzymes cytochrome P450aromatase (CYP3A, CYP17, CYP19a, CYP19b) and HMGR were investigated in the brain, liver and gonads of male rare minnows. After exposure of male rare minnows to8,16,80or160μg/L PCP or50ng/L EE2for21days caused a clear downward trend for the expression of CYP3A in the brain and gonads, but there was no obvious upward trend in the liver. The expression of CYP17was significantly inhibited in the brain and liver. CYP19a in the liver at80μg/L PCP and in the gonads at16μg/L PCP appeared to represent a rebound phenomenon because the rest of the exposure concentrations demonstrated a significant downward trend. In contrast to the effects on CYP19a, CYP19b was up-regulated, particularly in the liver at the80μg/L PCP exposure level and in the brain and gonads at the160μg/L PCP exposure level. HMGR in all three tissues demonstrated downward trends within the low concentration ranges of PCP, with the exception of the effect of80μg/L PCP in the liver. Overall, in these three tissues of the HPG axis, the expression of CYP3A, CYP17, CYPl9a and HMGR demonstrated downward trends within the low concentration range of PCP but were up-regulated at the higher concentrations. However, CYP19was increased in the brain and liver and at the160μg/L PCP exposure level in gonads。 Exposure to8,16,80, or160μg/L PCP or to50nM EE2for21days caused significant up-regulation of the expression of VTG and steroid receptor genes. The steroid receptor genes in liver tissue were sensitive to high concentrations of PCP, in contrast to the effects in gonadal tissue. However, the key enzyme genes were down-regulated. The expression of CYP19a, CYP19b and HMGR increased in the liver after exposure to80μg/L PCP and in the gonads after exposure to160μg/L PCP. Which indicate non-receptor pathway of PCP estrogenic effect and a mechanism of endogenous regulation. |
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