ToxSci Advance Access published online on May 24, 2007
Toxicological Sciences, doi:10.1093/toxsci/kfm133
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Protective efficacy of hGSTM1-1 against B[a]P and (+)- or (–)-B[a]P-7,8-dihydrodiol cytotoxicity, mutagenicity, and macromolecular adducts in V79 cells co-expressing hCYP1A1
* Department of Cancer Biology
Department of Biochemistry and Comprehensive Cancer Center, Wake Forest University, Winston-Salem NC, USA 27157
Gen Pharm Tox, Munich, Germany
Corresponding Author: Alan J. Townsend, Ph.D., Biochemistry Department, Wake Forest University School of Medicine, Medical Center Blvd., Winston-Salem N.C. 27157, Phone (336)-713-7215; FAX (336)-716-7671, E-mail: atown{at}wfubmc.edu
Received April 9, 2007; revision received May 17, 2007; accepted May 18, 2007
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Abstract |
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Transgenic cell lines were constructed to study the dynamics of competition between activation versus detoxification of benzo[a]pyrene (B[a]P) or B[a]P-7,8-dihydrodiol metabolites. Stably transfected V79MZ cells expressing human cytochrome P4501A1 (hCYP1A1) alone or in combination with human glutathione S-transferase M1 (hGSTM1) were used to determine how effectively this GST isozyme protects against cytotoxic, genotoxic, and mutagenic effects of B[a]P or the enantiomeric dihydrodiol metabolites (+)-benzo[a]pyrene-7,8-dihydrodiol ((+)B[a]P-7,8-diol) and (–)-benzo[a]pyrene-7,8-dihydrodiol ((–)-B[a]P-7,8-diol). Expression of hGSTM1 in the presence of hCYP1A1 conferred significant 8.5-fold protection against B[a]P-induced cytotoxicity, but protection against cytotoxicity of either B[a]P-7,8-diol enantiomer was not significant. Mutagenicity of B[a]P at the hprt locus was dose- and time-dependent in cells that expressed hCYP1A1. Mutagenicity of B[a]P was reduced by 21% to 32% and mutagenicity induced by the B[a]P-7,8-diols was reduced 20% - 58% in cells further modified to co-express hGSTM1-1 compared to cells expressing hCYP1A1 alone. Expression of hGSTM1-1 reduced adducts in total cellular macromolecules by 2-fold, in good correlation with the reduction in B[a]P mutagenicity. These results indicate that while hGSTM1-1 effectively protects against hCYP1A1-mediated cytotoxicity of B[a]P, a significant fraction of the mutagenicity that results from activation of B[a]P and its 7,8-dihydrodiol metabolites by hCYP1A1 is derived from B[a]P metabolites that are not detoxified by hGSTM1.