UC San Diego

Environmental toxicants such as heavy metals from contaminated water or soil and isothiocyanates (ITC) from dietary sources act as pro-oxidants by directly generating reactive oxygen species (ROS) or through depleting cellular antioxidants such as glutathione. Toxicants can alter drug metabolism, and it was reported that CYP2B10 and UGT1A1 are induced by phenethyl isothiocyanate (PEITC) through the constitutive androstane receptor (CAR). The possibility that nuclear factor erythroid 2-related factor 2 (NRF2), the master regulator of the antioxidant response, could coactivate CAR was investigated in neonatal hUGT1/Nrf2 ^-/- mice. Neonatal mice were treated with PEITC or cadmium (Cd²⁺) by oral gavage for 2 days. Both PEITC and Cd²⁺ induced UGT1A1 RNA and protein in intestinal tissues in both hUGT1/Nrf2 ^+/- and hUGT1/Nrf2 ^-/- neonates, indicating NRF2-independent regulation of UGT1A1. Increases in CYP2B10 RNA in intestinal tissues were observed following PEITC or Cd²⁺ exposure. Activation of intestinal CAR by Cd²⁺ exposure was directly assessed by nuclear fractionation and Western blot analyses at 0.5, 1, 2, and 4 hours after treatment in hUGT1 neonates and after 48 hours in hUGT1/Nrf2 ^+/- and hUGT1/Nrf2 ^-/- neonates. CAR localized to the nucleus independently of NRF2 48 hours after exposure. Substantial CAR localization to the nucleus occurred at the 2- and 4-hour time points, coinciding with a decrease in phosphorylation of cytoplasmic extracellular signal-regulated kinases 1 and 2 and a nuclear increase in P38/p-P38 content. This suggests that a novel oxidative stress-MAPK-CAR axis exists with phenotypic consequences. SIGNIFICANCE STATEMENT: Pro-oxidant toxicants can alter drug metabolism through activation of CAR, independent of the NRF2-KEAP1 signaling pathway. Changes in proteins associated with drug metabolism and linked to increases in intestinal maturation are mediated through an oxidative stress-MAPK-CAR axis.