The
aflatoxin B 1 aldehyde reductases (AFARs), inducible members of the
aldo-keto reductase superfamily, convert
aflatoxin B 1 dialdehyde derived from the exo- and endo-8,9-epoxides into a number of reduced alcohol products that might be less capable of forming covalent adducts with
proteins. An
isotope dilution tandem mass spectrometry method for quantification of the metabolites, C-8 monoalcohol, dialcohol, and C-6a monoalcohol, was developed to ascertain their possible role as urinary
biomarkers for application to
chemoprevention investigations. This method uses a novel (13)C 17-aflatoxin B 1 dialcohol internal standard, synthesized from (13)C 17-aflatoxin B 1 biologically produced by Aspergillus flavus. Chromatographic standards of the
alcohols were generated through
sodium borohydride reduction of the
aflatoxin B 1 dialdehyde. This method was then explored for sensitivity and specificity in urine samples of
aflatoxin B 1-dosed rats that were pretreated with 3 H-1,2-dithiole-3-thione to induce the expression of
AKR7A1, a rat
isoform of AFAR. One of the two known monoalcohols and the dialcohol metabolite were detected in all urine samples. The concentrations were 203.5 +/- 39.0 ng of monoalcohol C-6a/mg of urinary
creatinine and 10.0 +/- 1.0 ng of dialcohol/mg of
creatinine (mean +/- standard error). These levels represented about 8.0 and 0.4% of the administered
aflatoxin B 1 dose that was found in the urine at 24 h, respectively. Thus, this highly sensitive and specific
isotope dilution method is applicable to in vivo quantification of urinary alcohol products produced by AFAR. Heretofore, the metabolic fate of the 8,9-epoxides that are critical for
aflatoxin toxicities has been measured by
biomarkers of
lysine-
albumin adducts, hepatic and urinary
DNA adducts, and urinary mercapturic
acids. This urinary detection of the alcohol products directly contributes to the goal of mass balancing the fate of the bioreactive 8,9-epoxides of AFB 1 in vivo.