Oxidative metabolic pathway of diquat mediated by aldehyde oxidase and its detoxification effect in vitro

Abstract Diquat (DQ) is a fast-acting herbicide that kills both weeds and grasses and is widely used in the agricultural industry. The reported DQ poisoning cases have significantly increased in recent years. However, there is no effective antidote for the treatment of DQ poisoning. In this study, aldehyde oxidase (AOX) has been validated as the vital enzyme involved in the DQ oxidative metabolism. The metabolism of DQ to diquat monopyridone (DQ M) was significantly inhibited by AOX inhibiters including raloxifene and hydralazine. The source of oxygen atom incorporated into DQ M was proved to be from water with H218O incubation experiment which further corroborated DQ M formation via AOX metabolism. The tissue distribution of DQ M in vivo and generation of DQ M in vitro by tissue co-incubation were consistent with AOX mRNA expression in tissues. The molecular docking analysis results also showed that DQ could bind to AOX. These results collectively demonstrated that AOX played a crucial in the metabolism of DQ to DQ M. Furthermore, the cytotoxicity of DQ was higher than DQ M at the same concentrations in HCCLM3, Huh7, A549, 16HBE, HEK293T and GMC cells. This study is the first to reveal the oxidative metabolic enzyme of DQ and the toxicity of DQ and its metabolite providing an important reference for clinical management of DQ poisoning.