Identifying Cysteine, N-Acetylcysteine, and Glutathione Conjugates as Novel Metabolites of Aristolochic Acid I: Emergence of a New Detoxification Pathway

There is accumulating evidence that Balkan endemic nephropathy (BEN) is an environmental disease caused by aristolochic acids (AAs) released from the decomposition of Aristolochia clematitis L., an AA-containing weed that grows abundantly in the Balkan Peninsula. AA exposure has also been associated with carcinoma development in the upper urinary tract of some patients suffering from BEN. It is believed that an aristolactam-nitrenium ion intermediate with a delocalized positive charge produced in the hepatic metabolism of AAs binds to DNA and the resulting DNA adduct is responsible for initiating the carcinoma development process. In this study, we demonstrated for the first time that the aristolactam-nitrenium ion intermediate will also react with endogenous aminothiols, for example, cysteine, N-acetylcysteine, and glutathione in vitro, and in rats, producing phase II-conjugated metabolites in a dosage-dependent manner. It is highly possible that this conjugation process consumes and ultimately deactivates this carcinogenic intermediate and acts as an important, but previously unreported, detoxification mechanism of AAs. Results also showed AAs, phase I metabolites, and the aminothiol-conjugated metabolites are rapidly eliminated from AA-exposed rats. Furthermore, we found evidence that AA exposure induced oxidative stress in rats, as indicated by the glutathione depletion in rat serum samples.