INDUCTION OF PHASE-I AND PHASE-II DRUG-METABOLIZING ENZYME MESSENGER-RNA, PROTEIN, AND ACTIVITY BY BHA, ETHOXYQUIN, AND OLTIPRAZ

Various natural and synthetic compounds are known to protect against c ancer by elevating phase II detoxification enzymes. Generally classifi ed as nonfunctioning, these inducers are believed to trigger cellular signal(s) that activate gene transcription through an antioxidant or e lectrophile response element (ARE/EpRE) in responsive genes. In contra st, the phase I enzymes of drug metabolism (cytochrome P450s) are not believed to be induced by monofunctional inducers and P450 genes have not been found to contain functional ARE/EpREs. In this study, rats we re treated with the monofunctional inducers tert-butylated hydroxyanis ole, ethoxyquin, and oltipraz to study the inducibility of individual glutathione S-transferase isozymes, NADP(H):quinone oxidoreductase, ga mma-glutamylcysteine synthetase, UDP-glucuronosyl transferase, and cyt ochrome P450 enzymes. Hepatic mRNAs were analyzed on Northern blots us ing gene-specific oligonucleotide probes for GST Ya1, Ya2, Yc1, Yc2, Y b1, Yb2, and Yf, for UGT 106, and for P450 1A1, 1A2, 2B1, 2C11, 3A2, and 4A1. NADP(H):quinone oxidoreductase and gamma-glutamylcysteine syn thetase mRNAs were detected using cDNA probes. All the phase II detoxi fication enzymes analyzed, except GST Yf, were induced by the three mo nofunctional inducers, suggesting that these genes may be regulated by a mechanism involving an ARE/EpRE element in their promoter region. I nterestingly, it was found that ethoxyquin was a particularly good ind ucer for both members of the P450 2B family, 2B1 and 2B2, and both eth oxyquin and oltipraz were also capable of modestly inducing P450 1A2 a nd 3A2. Oltipraz was found to slightly induce P450 2B2, but not 2B1, a t the dose and time analyzed. Induction of mRNA generally correlated w ell with induction of protein levels determined by Western blot and/or enzyme activity measurements for selected enzymes. The results of thi s study suggest that many phase II enzymes may contain ARE/EpRE elemen ts in addition to those confirmed to be regulated by a mechanism invol ving ARE/EpRE elements. In addition, it was found that several P450 en zymes were induced by monofunctional inducers, suggesting a possibilit y that some phase I enzymes may also be regulated by a mechanism invol ving ARE/EpRE elements. (C) 1995 Academic Press, Inc.