Glucuronidation of the mycotoxins alternariol and alternariol-9-methyl ether in vitro: chemical structures of glucuronides and activities of human UDP-glucuronosyltransferase isoforms.

Alternariol (AOH) and alternariol-9-methyl ether (AME) are major toxins produced by fungi of the genus Alternaria and are frequently found in various food items. Because AOH has three hydroxyl groups and AME two, the formation of various glucuronides must be expected. When AOH was incubated with hepatic and intestinal microsomes from rats, pigs and humans in the presence of uridine diphosphate glucuronic acid, two glucuronides were detected and tentatively identified as AOH-3-O-glucuronide and AOH-9-O-glucuronide. Under the same conditions, AME yielded predominantly AME-3-O-glucuronide and only small amounts of AME-7-O-glucuronide. The activities of all microsomes for the glucuronidation of AOH and AME were in the same range. Nine out of ten recombinant human UDP-glucuronosyltransferases (UGTs) were able to glucuronidate AOH, and eight out of ten UGTs had activity for AME. These data suggest that AOH and AME are readily glucuronidated in hepatic and extrahepatic tissues, implying that glucuronidation constitutes a major metabolic pathway in the disposition of these mycotoxins.