Identification of ochratoxin A metabolites and species metabolism differences based on microsomal model

This study aimed to elucidate the metabolic pathways, interspecies differences and ochratoxin A (OTA) metabolism. The metabolism of OTA was investigated in liver microsomes derived from rat, human, mouse, beagle dog, chicken and pig, and in rat intestinal microsomes, using ultra–high–performance liquid chromatography–quadrupole/time–of–flight method. Additionally, the mechanism of action of OTA and the involvement of key metabolic enzymes were examined in vitro to clarify the pharmacological and toxicological mechanisms, thereby facilitating a better risk assessment of OTA in humans and animals. Seven metabolites were identified, comprising four phase Ⅰ hydroxylated metabolites and three phase Ⅱ glucosylated metabolites. All liver microsomes exhibited the presence of these seven metabolites, with 10-OH-OTA being identified for the first time in species other than rabbit liver microsomes. Interspecies metabolic variations were noted; the major metabolite in rat, mouse, and human liver microsomes was 4(R)-OH-OTA, whereas the beagle dog liver microsomes showed the highest ability for OTA metabolism. The ability of rat intestine microsomes to metabolize OTA was found to be limited. Furthermore, enzyme kinetic analysis indicated that CYP3A4 serves as the key metabolic enzyme for OTA, with evidence suggesting that OTA acts as a non-competitive inhibitor of CYP3A4.