Aflatoxin M1: in vitro preparation and comparative in vitro metabolism versus aflatoxin B1 in the rat and mouse.

A rapid, simple and relatively inexpensive biotransformation method using microsomes from 3-methylcholanthrene (3MCA) pretreated rats is described for the production of aflatoxin M1 (AFM1) is sufficient quantities for metabolism studies. A comparison is made of the metabolism of AFM1 and AFB1 by the postmitochondrial (S-10) fraction from mouse and rat hepatocytes. AFM1, in both species, is metabolized more slowly than AFB1, with its major metabolites being found in the aqueous fraction and very little associated with S-10 protein. In contrast, AFB1 is metabolized to numerous chloroform-extractable, protein bound and water-soluble metabolites. The toxicological implications of reduced protein binding and slower metabolism for AFM1 are discussed.