ToxSci Advance Access originally published online on January 17, 2008
Toxicological Sciences 2008 102(2):337-344; doi:10.1093/toxsci/kfn007
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Persistent Induction of Hepatic and Pulmonary Phase II Enzymes by 3-Methylcholanthrene in Rats
* Department of Pediatrics, Baylor College of Medicine, Houston, Texas 77030
Department of Pharmacology, The University of Maryland School of Medicine, Baltimore, Maryland 21201
1 To whom correspondence should be addressed at Baylor College of Medicine, 6621 Fannin, FC 530.01, Houston, TX 77030. Fax: (832) 825-3204. E-mail: bmoorthy{at}bcm.tmc.edu.
Received October 28, 2007; accepted January 7, 2008
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Abstract |
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We reported earlier that exposure of rats to 3-methylcholanthrene (MC) causes sustained induction of hepatic cytochrome P450 (CYP)1A expression for up to 45 days by mechanisms other than persistence of the parent MC (Moorthy, J. 2000. Pharmacology. Exp. Ther. 294, 313–322). The CYP1A genes are members of the Ah gene battery that also encode CYP1B1 and phase II enzymes such as glutathione S-transferase (GST-
), UDP glucuronyl transferase (UGT)1A, NAD(P)H (nicotinamide adenine dinucleotide phosphate, reduced):quinone oxidoreductase I (NQO1), aldehyde dehydrogenase (ALDH), etc. Therefore, in this investigation, we tested the hypothesis that MC elicits persistent induction of CYP1B1 and phase II genes, which are in part regulated by the Ah receptor (AHR). Female Sprague–Dawley rats were treated with MC (100 µmol/kg), ip, once daily for 4 days, and expression of CYP1B1 and several phase II (e.g., GST-, NQO1) genes and their corresponding proteins were determined in lung and liver. The major finding was that MC persistently induced (3- to 10-fold) the expression of several phase II enzymes, including GST-, NQO1, UGT1A1, ALDH, and epoxide hydrolase in both tissues for up to 28 days. However, MC did not elicit sustained induction of CYP1B1. Our results thus support the hypothesis that MC elicits coordinated and sustained induction of phase II genes presumably via persistent activation of the AHR, a phenomenon that may have implications for chemical-induced carcinogenesis and chemopreventive strategies in humans.
Key Words: 3-methylcholanthrene; phase II enzymes; CYP1A1; gene expression; carcinogenesis; CYP1B1; Ah receptor; NAD(P)H:quinone oxidoreductase; rat; in vivo.