Bisphenol A induces Nrf2-dependent drug-metabolizing enzymes through nitrosylation of Keap1.

Bisphenol A (BPA) is an endocrine-disrupting chemical, and activates the aryl hydrocarbon receptor (AhR) and the estrogen receptor, leading to the induction of drug metabolizing enzymes. In this study, we found that BPA increased nitric oxide (NO) levels but not reactive oxygen species (ROS) levels in the human hepatoma cell line, Hep3B, and induced drug-metabolizing enzymes such as UDP-glucuronosyltransferase (UGT). Nuclear factor erythroid 2-related factor 2 (Nrf2) has been reported to be activated by ROS through inactivation of its regulating protein, Kelch-like ECH-associated protein (Keap1), and to be the key mediator of phase I and phase II drug metabolizing enzymes, and phase III drug transporters. Treatment of Hep3B with BPA increased the levels of nitrous oxide, a metabolite of nitric oxide and activated Nrf2 by nitrosylation of Keap1, leading to the induction of heme oxygenase-1 (HO-1) and UGT2B1 mRNAs. A nitric oxide donor, 1-Hydroxy-2-oxo-3-(N-methyl-3-aminopropyl)-3-methyl-1-triazene (NOC7), also activated Nrf2 and a NOS inhibitor, N-Monomethyl-l-arginine, monoacetate salt (L-NMMA), inhibited activation of Nrf2 by BPA. Furthermore, calcium efflux by BPA was observed. These results suggested the new idea that BPA increases NO levels and activates Nrf2 via Keap1 inactivation, leading to induction of Nrf2-dependent drug-metabolizing enzymes.