DETECTION AND IDENTIFICATION OF METABOLITES OF MICROCYSTINS FORMED IN-VIVO IN MOUSE AND RAT LIVERS

The hepatic metabolism of microcystins (MCs), potent cyclic peptide he patotoxins produced by cyanobacteria, was studied by ip injection in m ice and rats. An immunoaffinity purification method using an anti-MC-L R monoclonal antibody showed a remarkable effect on the removal of con taminants in the hepatic cytosol and enabled us to analyze MCs and the ir metabolites by HPLC and Frit-FAB LC/MS. At 3, 6, and 24 h post-inje ction of MC-RR, a small percent of the applied dose was detected in al l of the mouse livers together with several metabolites. Among them, G SH and Cys conjugates of MC-RR were identified at 3 and 24 h, respecti vely, by comparison with the chemically prepared standards, indicating that the thiols of GSH and Cys nucleophilically bound to the Mdha moi ety of MCs. Another metabolite was presumed to be formed by both epoxi dation followed by hydrolysis and sulfate conjugation in the Adda moie ty and GSH conjugation in the Mdha moiety. In rat livers, MC-LR showed almost the same behavior as that of MC-RR in mouse livers. These resu lts suggest that the conjugation of GSH with MCs may play a role in th e metabolic pathway leading to detoxification of MCs.