Oxidative in vitro metabolism of the Alternaria toxins altenuene and isoaltenuene.

The mycotoxins altenuene (ALT) and isoaltenuene (iALT) frequently occur in food and feed items infested by fungi of the genus Alternaria, but nothing is known about their oxidative metabolism in mammals. We have therefore incubated ALT and iALT with microsomes from rat liver in the presence of a nicotinamide adenine dinucleotide phosphate (NADPH)-generating system and analyzed the extracted metabolites with HPLC and GC-MS after trimethylsilylation. Both toxins formed a major metabolite, which was tentatively identified as the 8-hydroxylation product by GC-MS analysis and by its methylation by the enzyme catechol-O-methyltransferase. Three minor metabolites were tentatively identified as 10-hydroxy- and two stereoisomers of 4-hydroxy-ALT and -iALT. The same metabolic pattern was observed in microsomes from different rat strains and from pigs and humans. Moreover, incubation of ALT with rat liver slices provided evidence that the same oxidative metabolites were formed under in vivo-like conditions. Thus, ALT and iALT exhibit a considerable propensity for undergoing metabolic hydroxylation reactions, and the toxicological properties of the oxidative metabolites should now be studied.