GENOTOXICITY OF ACYL GLUCURONIDE METABOLITES FORMED FROM CLOFIBRIC ACID AND GEMFIBROZIL - A NOVEL ROLE FOR PHASE-II-MEDIATED BIOACTIVATION IN THE HEPATOCARCINOGENICITY OF THE PARENT AGLYCONES

Glucuronides formed from carboxylate-containing xenobiotics are more c hemically reactive than most Phase II conjugates. However, while they have been shown to form protein adducts, their reactions with DNA have received little attention. We thus used the M13 forward mutational as say to assess the genotoxicity of acyl glucuronides formed from two wi dely used fibrate hypolipidemics, clofibric acid and gemfibrozil. Sing le-stranded M13mp19 bacteriophage DNA was incubated in pH 7.4 buffer f or 16 h in the presence of 0, 1, 2.5, and 5 mM concentrations of each glucuronide as well as the respective aglycones. The modified DNA was then transfected into SOS-induced competent Escherichia coli JM105 cel ls and the transfection efficiency was determined after phage growth o vernight at 37 degrees C. Significantly, both acyl glucuronides, but n ot the aglycones, caused a concentration-dependent decrease in the tra nsfection efficiency of the DNA, with a greater than 80% decrease in p hage survival produced by the 5 mM concentrations of the glucuronides. No increase in IacZ(a) mutations accompanied the loss of phage surviv al. We propose that these genotoxic effects involve reactions with nuc leophilic centers in DNA via a Schiff base mechanism that is analogous to the glycosylation of DNA by endogenous sugars. Since strand nickin g is known to accompany such damage, we also analyzed glucuronide-trea ted pSP189 plasmids for strand breakages via agarose gel electrophores is. Both clofibric acid and gemfibrozil glucuronides produced signific ant concentration-related strand nicking and exhibited over 10-fold gr eater reactivity than the endogenous glycosylating agent, glucose 6-ph osphate. On the basis of these findings, the possibility that this nov el bioactivation route participates in the carcinogenicity of the fibr ate hypolipidemics deserves investigation. (C) 1997 Academic Press.