In Vitro Metabolism of the Mycotoxin Enniatin B in Different Species and Cytochrome P450 Enzyme Phenotyping by Chemical Inhibitors

Enniatins are cyclic hexapeptidic mycotoxins produced by fungi growing on field grains, especially in wet climates. They show considerable resistance to food and feed processing technologies and might cause intoxication of humans and animals. Enniatins are also under exploration as anticancer drugs. The observed difference of in vitro and in vivo toxicities suggests low absorption or fast elimination of the enniatins after oral uptake. In the study presented here, in vitro metabolism studies of enniatin B were performed using rat, dog, and human liver microsomes under conditions of linear kinetics to estimate the respective elimination rates. Furthermore, cytochrome P450 reaction phenotyping with chemical inhibitors selective for human enzymes was carried out. Twelve metabolites were separated and characterized by multiple high-performance liquid chromatographic/mass spectrometric analyses as products of oxidation and demethylation reactions. Biotransformation rates and metabolite patterns varied considerably in the three species. The intrinsic clearances determined in assays with rat, dog, and human liver microsomes were 1.16, 8.23, and 1.13 l/(h . kg), respectively. The predicted enniatin B in vivo blood clearances were 1.57 l/(h . kg) in rats, 1.67 l/(h . kg) in dogs, and 0.63 l/(h . kg) in humans. CYP3A4 was important for enniatin B metabolism in human microsomes as shown by 80% inhibition and impaired metabolite formation in the presence of troleandomycin. CYP1A2 and CYP2C19 were additionally involved. Preliminary results showed that CYP3A and CYP1A might also be relevant in rats and dogs. The extensive hepatic metabolism could explain the reduced in vivo potential of enniatin B.