Master's Program in Environmental Sciences, University of Tsukuba, Ibaraki, Japan.
J Toxicol Sci. 2009 Dec;34(6):627-35. doi: 10.2131/jts.34.627.
The catechol metabolites (2-OHE and 4-OHE) of estrogen enter a redox cycle, thereby generating not only reactive oxygen species (ROS) but also electrophilic quinones. It is well recognized that chemicals causing oxidative stress or electrophiles activate a transcription factor Nrf2 that is negatively regulated by Keap1, leading to up-regulation of downstream proteins responsible for detoxification of electrophiles in cells. The purpose of the present study is to explore the roles of oxidative and electrophilic stress in Nrf2 activation caused by redox-active catechol estrogens. Exposure of RAW264.7 cells to 2- and 4-OHE activated Nrf2, resulting in induction of heme oxygenase-1 (HO-1) and glutamate cysteine ligase catalytic subunit (GCLC). Under these conditions, intracellular oxidants were generated; however, subsequent examinations revealed that quinoid metabolites derived from 2- and 4-OHE mainly participate in the Nrf2 activation. Matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) analysis revealed Keap1 undergoes modification by such quinoid species through multiple reactive thiol groups. These results suggest that Nrf2 activation during redox cycling of catechol estrogens is dominantly attributable to formation of their ortho-quinones that covalently bind to Keap1.
儿茶酚代谢物（2-OHE 和 4-OHE）雌激素进入氧化还原循环，从而产生不仅活性氧物种（ROS），而且亲电醌。这是公认的化学物质引起氧化应激或亲电试剂激活转录因子 Nrf2，这是由 Keap1 负调节，导致细胞中负责解毒亲电试剂的下游蛋白上调。本研究的目的是探讨氧化和亲电应激在儿茶酚雌激素引起的 Nrf2 激活中的作用。暴露于 RAW264.7 细胞 2-OHE 和 4-OHE 激活 Nrf2，导致血红素加氧酶-1（HO-1）和谷胱甘肽半胱氨酸连接酶催化亚基（GCLC）的诱导。在这些条件下，细胞内氧化剂生成；然而，随后的检查表明，来自 2-OHE 和 4-OHE 的醌类代谢物主要参与 Nrf2 的激活。基质辅助激光解吸电离飞行时间质谱（MALDI-TOF MS）分析表明，Keap1 通过多个反应性巯基基团被这种醌类物质修饰。这些结果表明，儿茶酚雌激素氧化还原循环过程中的 Nrf2 激活主要归因于其邻醌的形成，邻醌与 Keap1 发生共价结合。
