Rat hepatic CYP2E1 is induced by very low nicotine doses: an investigation of induction, time course, dose response, and mechanism.
ABSTRACT CYP2E1 is an ethanol- and drug-metabolizing enzyme that can also activate procarcinogens and hepatotoxicants and generate reactive oxygen species; it has been implicated in the pathogenesis of liver diseases and cancer. Cigarette smoke increases CYP2E1 activity in rodents and in humans and we have shown that nicotine (0.1-1.0 mg/kg s.c. x 7 days) increases CYP2E1 protein and activity in the rat liver. In the current study, we have shown that the induction peaks at 4 h postnicotine (1 mg/kg s.c. x 7 days) treatment and recovers within 24 h. No induction was observed after a single injection, and 18 days of treatment did not increase the levels beyond that found at 7 days. We found that CYP2E1 is induced by very low doses of chronic (x 7 days) nicotine with an ED50 value of 0.01 mg/kg s.c.; 0.01 mg/kg in a rat model results in peak cotinine levels (nicotine metabolite) similar to those found in people exposed to environmental tobacco smoke (passive smokers; 2-7 ng/ml). Previously, we have shown no change in CYP2E1 mRNA, and our current mechanistic study indicates that nicotine does not regulate CYP2E1 expression by protein stabilization. We postulated that a nicotine metabolite could be causing the induction but found that cotinine (1 mg/kg x 7 days) did not increase CYP2E1. Our findings indicate that nicotine increases CYP2E1 at very low doses and may enhance CYP2E1-related toxicity in smokers, passive smokers, and people treated with nicotine (e.g., smokers, patients with Alzheimer's disease, ulcerative colitis or Parkinson's disease).
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ABSTRACT: The effects of six Thai fruits, namely banana, guava, mangosteen, pineapple, ripe mango and ripe papaya, on cytochrome P450 (P450) activities were investigated. The median inhibitory concentrations (IC(50) ) of each of the fruit juices on CYP1A1, CYP1A2, CYP2E1 and CYP3A11 activities were determined. Pineapple juice showed the strongest inhibitory effect against all the evaluated P450 isozyme activities in mouse hepatic microsomes, followed by mangosteen, guava, ripe mango, ripe papaya and banana. The study was further performed in male ICR mice given pineapple juice intragastrically at doses of 10, 20 and 40 mg kg(-1) per day for 7 or 28 days. In a concentration-dependent fashion, the pineapple juice raised ethoxyresorufin O-deethylase, aniline hydroxylase and erythromycin N-demethylase activities, which are marker enzymatic reactions responsible for CYP1A1, CYP2E1 and CYP3A11, respectively. The effect of pineapple juice on the expression of CYP1A1, CYP2E1 and CYP3A11 mRNAs corresponded to their enzymatic activities. However, the pineapple juice significantly decreased methoxyresorufin O-demethylase activity. These observations supported that the six Thai fruits were a feasible cause of food-drug interaction or adverse drug effects owing to their potential to modify several essential P450 activities. Individuals consuming large quantities of pineapple for long periods of time should be cautioned of these potential adverse effects. Copyright © 2012 John Wiley & Sons, Ltd.Journal of Applied Toxicology 04/2012; 32(12):994-1001. · 2.60 Impact Factor
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ABSTRACT: Drug-drug interactions (DDIs) caused by direct chemical inhibition of key drug-metabolizing cytochrome P450 enzymes by a co-administered drug have been well documented and well understood. However, many other well-documented DDIs cannot be so readily explained. Recent investigations into drug and other xenobiotic-mediated expression changes of P450 genes have broadened our understanding of drug metabolism and DDI. In order to gain additional information on DDI, we have integrated existing information on drugs that are substrates, inhibitors, or inducers of important drug-metabolizing P450s with new data on drug-mediated expression changes of the same set of cytochrome P450s from a large-scale microarray gene expression database of drug-treated rat tissues. Existing information on substrates and inhibitors has been updated and reorganized into drug-cytochrome P450 matrices in order to facilitate comparative analysis of new information on inducers and suppressors. When examined at the gene expression level, a total of 119 currently marketed drugs from 265 examined were found to be cytochrome P450 inducers, and 83 were found to be suppressors. The value of this new information is illustrated with a more detailed examination of the DDI between PPARalpha agonists and HMG-CoA reductase inhibitors. This paper proposes that the well-documented, but poorly understood, increase in incidence of rhabdomyolysis when a PPARalpha agonist is co-administered with a HMG-CoA reductase inhibitor is at least in part the result of PPARalpha-induced general suppression of drug metabolism enzymes in liver. The authors believe this type of information will provide insights to other poorly understood DDI questions and stimulate further laboratory and clinical investigations on xenobiotic-mediated induction and suppression of drug metabolism.Xenobiotica 01/2006; 36(10-11):1013-80. · 1.98 Impact Factor
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ABSTRACT: The purpose of this report is to summarize the roles of alcohol and tobacco exposure in the development of hepatocellular carcinoma (HCC). Chronic heavy alcohol exposure is a major risk factor for HCC, which is the most frequent type of liver cancer. Alcohol ingestion may initiate and or promote the development of HCC by: 1) acetaldehyde-DNA adduct formation; 2) cytochrome P4502E1-associated reactive oxygen species (ROS) generation , lipid peroxidation, p53 mutation, and conversion of pro-carcinogens to carcinogens; 3) iron accumulation that leads to ROS generation, lipid peroxidation, p53 mutation, and initiation of inflammatory cascade via nuclear factor-KappaB (NF-kB) activation; 4) glutathione depletion leading to oxidative stress; 5) s-adenosylmethionine (SAM) depletion and associated DNA hypomethylation of oncogenes ; 6) retinoic acid depletion and resultant hepatocyte proliferation via up-regulation of activator protein-1 (AP-1); 7) initiating an inflammatory cascade through increased transfer of endotoxin from intestine to liver, Kupffer cell activation via CD14/toll-like receptor-4 (TLR-4), oxidative stress, NF-kB or early growth response-1(Egr-1) activation, and generation of inflammatory cytokines and chemokines; 8) induction of liver fibrosis; and 9) decreasing the number and/or function of Natural Killer cells. Tobacco exposure is also a risk factor for HCC. It may contribute to the initiation and promotion of HCC due the presence of mutagenic and carcinogenic compounds as well as by causing oxidative stress due to generation of ROS and depletion of endogenous antioxidants. Simultaneous exposure to alcohol and tobacco is expected to promote the development of HCC in an additive and/or synergistic manner.Life sciences 10/2012; · 2.56 Impact Factor