Comparative activities of glutathione-S-transferase and dialdehyde reductase toward aflatoxin B1 in livers of experimental and farm animals.

In order to gain a better understanding of the relative activities of glutathione-S-transferase (GST) and aldehyde reductase toward aflatoxin B1 (AFB1) in relation to the variation of species susceptibilities, we studied the in vitro cytosolic GST and reductase activities in liver tissues from male Fischer rats, ICR mice and golden hamsters, adult male rainbow trouts and female piglets. The GST activity was determined by incubating the liver cytosol with glutathione (GSH) and AFB1 in the presence of the hamster liver microsomes to metabolize AFB1 to AFB1-8, 9-epoxide. The reaction product, AFB1 and GSH conjugate (AFB1-GSH), was quantified with HPLC. The reductase activity was determined by incubating liver cytosol with AFB1-dialdehyde, followed by the quantification of the metabolic product, AFB1-dialcohol, with HPLC. All the animal species possessed the GST activities, and AFB1-GSH formed increasingly with the increase of the AFB1 concentration according to the model of first-order enzyme reaction kinetics. The V(max) and K(m) values of the GST activities in rodent species were higher and lower, respectively, than those in the trout and pig, being consistent with the relative susceptibilities to AFB1 of these animal species. However, no relationship was noted between the reductase activity and species susceptibility. Thus, the result of this study shows that GST toward AFB1, but not aldehyde reductase, is a determinant of the variation of species susceptibilities.