Quantification of urinary aflatoxin B1 dialdehyde metabolites formed by aflatoxin aldehyde reductase using isotope dilution tandem mass spectrometry


The aflatoxin B1 aldehyde reductases (AFARs), inducible members of the aldo-keto reductase superfamily, convert aflatoxin B1 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 13C 17-aflatoxin B1 dialcohol internal standard, synthesized from 13C17-aflatoxin B1 biologically produced by Aspergillus flavus. Chromatographic standards of the alcohols were generated through sodium borohydride reduction of the aflatoxin B1 dialdehyde. This method was then explored for sensitivity and specificity in urine samples of aflatoxin B1-dosed rats that were pretreated with 3H-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 B1 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 AFB1 in vivo. © 2008 American Chemical Society.

Publication Title

Chemical Research in Toxicology