Regulation of Uridine Diphosphate Glucuronosyltransferase Expression by Phenolic Antioxidants

Dietary antioxidants protect laboratory animals against the induction of tumors by a variety of chemical carcinogens. Among possible mechanisms, protection against chemical carcinogenesis could be mediated via antioxidant- dependent induction of detoxifying enzymes. Therefore, we investigated the effects of two commonly used food preservatives, butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT), on the expression of UDP- glucuronosyltransferase isoforms in rat liver. Male Wistar rats were fed a control diet or diets containing BHA (0.75%) or BHT (0.5%) for 2 weeks. BHT and BHA increased UDP-glucuronosyltransferase activities in liver microsomes for p-nitrophenol (236 and 218%, respectively), 3-hydroxybenzo(a)pyrene (246 and 175%, respectively), and androsterone (269 and 152%, respectively). Immunoblots showed changes in the amounts of UDP-glucuronosyltransferase isoforms corresponding to the changes in enzyme activities. Northern blot analysis showed that the concentration of UDP-glucuronosyltransferase mRNA paralleled the concentration of enzyme proteins and their respective levels of enzyme activity. BHT, for example, caused about a 250% increase in mRNA using a probe that recognizes the common 3'-domain of bilirubin/phenol UDP- glucuronosyltransferase mRNAs. In addition to inducing hepatic enzyme activities, BHT and BHA increased the activity of UDP-glucuronosyltransferase in the small intestine and kidney.