EFFECT OF CYP2E1 INDUCTION BY ETHANOL ON THE IMMUNOTOXICITY AND GENOTOXICITY OF EXTENDED LOW-LEVEL BENZENE EXPOSURE

Abstract

Potential additive effects of ethanol consumption, a common life-style factor, and lowlevel benzene exposure, a ubiquitous environmental pollutant, were investigated. Ethanol is a potent inducer of the cytochrome P-450 2E1 (CYP2E1) enzyme, which bioactivates benzene to metabolites with known genotoxicity and immunotoxicity. A liquid diet containing 4.1% ethanol was used to induce hepatic CYP2E1 activity by 4-fold in female CD-1 mice. Groups of ethanol-treated or pair-fed control mice were exposed to benzene or filtered air in inhalation chambers for 7 h/d, 5 d/wk for 6 or 11 wk. The initial experiment focused on immunotoxicity endpoints based on literature reports that ethanol enhances high-dose benzene effects on spleen, thymus, and bone marrow cellularity and on peripheral red blood cell (RBC) and white blood cell (WBC) counts. No statistically significant alterations were found in spleen lymphocyte cellularity, subtype profile, or function (mitogen-induced proliferation, cytokine production, or natural killer cell lytic activity) after 6 wk of ethanol diet, 0.44 ppm benzene exposure, or both. This observed absence of immunomodulation by ethanol alone, a potential confounding factor, further validates our previously established murine model of sustained CYP2E1 induction by dietary ethanol. Subsequent experiments involved a 10-fold higher benzene level for a longer time of 11 wk and focused on genotoxic endpoints in known target tissues. Bone marrow and spleen cells were evaluated for DNA-protein cross-links, a sensitive transient index of genetic damage, and spleen lymphocytes were monitored for hprt -mutant frequency, a biomarker of cumulative genetic insult. No treatment-associated changes in either genotoxic endpoint were detected in animals exposed to 4.4 ppm benzene for 6 or 11 wk with or without coexposure to ethanol. Thus, our observations suggest an absence of genetic toxicity in CD-1 mice exposed to environmentally relevant levels of benzene with or without CYP2E1 induction.