Phase 2 metabolites of H-hydroxylated amidines (amidoximes): Synthesis, in vitro formation by pig hepatocytes, and mutagenicity testing

A pig hepatocyte culture system was used for phase 2 biotransformation studies in vitro. The viability of the cultured hepatocytes was characterized daily during cultivation by lactate dehydrogenase release into the supernatant and albumin synthesis of the cells. The metabolic activity of the hepatocyte cultures was measured by 7-ethoxycoumarin (ECOD) and 7-ethoxyresorufin O-deethylation (EROD). The viability and metabolic activity of these pig hepatocytes were preserved for several days by culturing the cells in a monolayer culture system. Besides the known reduction of N-hydroxylated benzamidine (benzamidoxime) (2) to benzamidine (1), glucuronidation and, to a much smaller extent, sulfation of 2 to benzamidoxime O-glucuronide (3) and benzamidoxime O-sulfate (4) by cultured pig hepatocytes were found. The analyses were performed using HPLC and LC/MS studies. For unequivocal assignment, the hitherto unknown metabolites 3 and 4 were synthesized and characterized by spectroscopic techniques. Examination of benzamidoxime O-glucuronide and benzamidoxime O-sulfate for mutagenicity by means of the Ames test revealed that both phase 2 conjugates have no mutagenic effects in the TA98 and TA100 strains. So the phase 2 conjugation of benzamidoxime is significant in terms of detoxification.