Department of Environmental and Molecular Toxicology, Box 7633, North Carolina State University, Raleigh, NC 27695, USA.
Toxicol Appl Pharmacol. 2010 Jun 15;245(3):335-43. doi: 10.1016/j.taap.2010.03.017. Epub 2010 Mar 31.
Endosulfan is an organochlorine pesticide commonly used in agriculture. Endosulfan has affects on vertebrate xenobiotic metabolism pathways that may be mediated, in part, by its ability to activate the pregnane X receptor (PXR) and/or the constitutive androstane receptor (CAR) which can elevate expression of cytochrome P450 (CYP) enzymes. This study examined the dose-dependency and receptor specificity of CYP induction in vitro and in vivo. The HepG2 cell line was transiently transfected with CYP2B6- and CYP3A4-luciferase promoter reporter plasmids along with human PXR (hPXR) or hCAR expression vectors. In the presence of hPXR, endosulfan-alpha exposure caused significant induction of CYP2B6 (16-fold) and CYP3A4 (11-fold) promoter activities over control at 10 microM. The metabolite endosulfan sulfate also induced CYP2B6 (12-fold) and CYP3A4 (6-fold) promoter activities over control at 10 microM. In the presence of hCAR-3, endosulfan-alpha induced CYP2B6 (2-fold) promoter activity at 10 microM, but not at lower concentrations. These data indicate that endosulfan-alpha significantly activates hPXR strongly and hCAR weakly. Using western blot analysis of human hepatocytes, the lowest concentrations at which CYP2B6 and CYP3A4 protein levels were found to be significantly elevated by endosulfan-alpha were 1.0 microM and 10 microM, respectively. In mPXR-null/hPXR-transgenic mice, endosulfan-alpha exposure (2.5mg/kg/day) caused a significant reduction of tribromoethanol-induced sleep times by approximately 50%, whereas no significant change in sleep times was observed in PXR-null mice. These data support the role of endosulfan-alpha as a strong activator of PXR and inducer of CYP2B6 and CYP3A4, which may impact metabolism of CYP2B6 or CYP3A4 substrates.
硫丹是一种常用的农业有机氯农药。硫丹会影响脊椎动物异生物质代谢途径，部分原因可能是其激活孕烷 X 受体 (PXR) 和/或组成型雄烷受体 (CAR) 的能力，这可以提高细胞色素 P450 (CYP) 酶的表达。本研究在体外和体内检查了 CYP 诱导的剂量依赖性和受体特异性。将 HepG2 细胞系瞬时转染 CYP2B6-和 CYP3A4-荧光素酶启动子报告质粒，以及人 PXR (hPXR) 或 hCAR 表达载体。在 hPXR 的存在下，10 μM 时，硫丹-α暴露导致 CYP2B6（16 倍）和 CYP3A4（11 倍）启动子活性相对于对照显著诱导。代谢物硫丹硫酸盐也在 10 μM 时诱导 CYP2B6（12 倍）和 CYP3A4（6 倍）启动子活性相对于对照。在 hCAR-3 的存在下，硫丹-α在 10 μM 时诱导 CYP2B6 启动子活性（2 倍），但在较低浓度时则不然。这些数据表明，硫丹-α显著激活 hPXR 强烈且激活 hCAR 较弱。使用人肝细胞的 Western blot 分析，发现硫丹-α使 CYP2B6 和 CYP3A4 蛋白水平显著升高的最低浓度分别为 1.0 μM 和 10 μM。在 mPXR-null/hPXR-transgenic 小鼠中，硫丹-α暴露（2.5mg/kg/天）导致三溴乙醇诱导的睡眠时间显著减少约 50%，而在 PXR-null 小鼠中观察到睡眠时间没有明显变化。这些数据支持硫丹-α作为 PXR 的强激活剂和 CYP2B6 和 CYP3A4 的诱导剂的作用，这可能会影响 CYP2B6 或 CYP3A4 底物的代谢。
