Species differences in zearalenone-reductase activity.

Thin-layer and high-pressure liquid chromatography (HPLC) were used to investigate in several animal species the hepatic metabolites of zearalenone (ZEN), a non-steroidal oestrogenic fungal toxin produced by species of Fusarium. ZEN was reduced to zearalenol (ZEL) by the S-9 fraction of rat-liver homogenates in the presence of NADH or NADPH. In this species ZEN reductase showed two peaks of activity at pH 4.5 and 7.4. Of the species tested, cows showed the highest activity of NADH-dependent ZEN reductase in the hepatic S-9 fraction, followed in decreasing order by mice, pigs, rats, rabbits and guinea-pigs. The S-9 fraction of hamster liver showed optimal activity at pH 5.5 and 8.0 with NADH and at pH 6.0 and 8.5 with NADPH; NADPH was more efficient than NADH only in this species. HPLC showed that alpha-ZEL was a major hepatic metabolite in the rat, mouse, pig, cow and rabbit in incubations at pH 4.5 with either NADH or NADPH and at pH 7.4 with NADH, although at pH 7.4 with NADPH, beta-ZEL was the predominant metabolite. In guinea-pigs, both alpha- and beta-ZELs were produced in roughly similar amounts irrespective of the pH and cofactor, while in hamsters beta-ZEL was the major metabolite. These findings indicate that there are two types of ZEN reductase differing in optimum pH and that the stereospecific reduction of ZEN depends on the source of S-9 and cofactors. Since the oestrogenic activity of alpha-ZEL is about ten times greater than that of ZEN, the possible presence of ZEN metabolites in edible tissues of livestock fed on ZEN-contaminated feeds is an important mycotoxicological problem.