In Vivo Metabolism of Aristolochic Acid I and II in Rats Is Influenced by Their Coexposure

Abstract

The plant extract aristolochic acid (AA), containing aristolochic acid I (AAI) and II (AAII) as major components, causes aristolochic acid nephropathy and Balkan endemic nephropathy, unique renal diseases associated with upper urothelial cancer. Differences in the metabolic activation and detoxification of AAI and AAII and their effects on the metabolism of AAI/AAII mixture in the plant extract might be of great importance for an individual's susceptibility in the development of AA-mediated nephropathies and malignancies. Here, we investigated in vivo metabolism of AAI and AAII after ip administration to Wistar rats as individual compounds and as AAI/AAII mixture using high performance liquid chromatography/electrospray ionization mass spectrometry. Experimental findings were supported by theoretical calculations using density functional theory. We found that exposure to AAI/AAII mixture affected the generation of their oxidative and reductive metabolites formed during Phase I biotransformation and excreted in rat urine. Several Phase II metabolites of AAI and AAII found in the urine of exposed rats were also analyzed. Our results indicate that AAI is more efficiently metabolized in rats in vivo than AAII. Whereas AAI is predominantly oxidized during in vivo metabolism, its reduction is the minor metabolic pathway. In contrast, AAII is mainly metabolized by reduction. The oxidative reaction only occurs if aristolactam II, the major reductive metabolite of AAII, is enzymatically hydroxylated, forming aristolactam Ia. In AAI/AAII mixture, the metabolism of AAI and AAII is influenced by the presence of both AAs. For instance, the reductive metabolism of AAI is increased in the presence of AAII while the presence of AAI decreased the reductive metabolism of AAII. These results suggest that increased bioactivation of AAI in the presence of AAII also leads to increased AAI genotoxicity, which may critically impact AAI-mediated carcinogenesis. Future studies are needed to explain the underlying mechanism(s) for this phenomenon.

Co-Exposure to Aristolochic Acids I and II Increases DNA Adduct Formation Responsible for Aristolochic Acid I-Mediated Carcinogenicity in Rats

“…Preliminary findings examining the hydroxylation of AAII to AAIa by hepatic and renal microsomes in vitro indicated that no hydroxylated (detoxification) product is formed (Stiborova et al, unpublished data). These findings are in agreement with previous studies [ 49 ] and our recent data showing that no AAIa was detectable in the urine of AAII-treated rats [ 48 ]. This indicates that AAII is metabolised specifically via the reduction pathway, ultimately leading to DNA adduct formation.…”

“…One key question of this study was how enzymes participating in AAI biotransformation are affected by co-exposure to AAII in vivo . Although previous studies showed AA-DNA adduct formation 24 h after administration, in the present study rats were sacrificed and analysed after 48 h in order to simultaneously measure and identify AA metabolites in urine [ 48 ].…”

“…The oxidative metabolism of AAII has not been studied in detail, although this compound is present in high concentrations in some Aristolochia species and may even exceed the concentration of AAI [ 1 , 46 , 47 ]. Some studies assumed higher genotoxicity of AAII than AAI [ 63 ] and indicated that AAII induces more severe kidney and liver dysfunction [ 78 ]; however, other studies have demonstrated that AAII is not metabolised to AAIa in vitro , unlike AAI [ 49 ], and using the same rat model we previously showed that the major detoxification metabolites found in the urine were N -hydroxyaristolactam II and 7-hydroxyaristolactam II [ 48 ]. These findings indicate that AAII metabolism via activation is preferred to the oxidation pathway.…”

“…In this experimental model, rats were previously exposed to AAI, AAII and an AAI/AAII mixture [ 48 ]. As part of a complex investigation, the first results showed that the in vivo metabolism of AAI and AAII in rats is influenced by the presence of both AAs.…”

“…As part of a complex investigation, the first results showed that the in vivo metabolism of AAI and AAII in rats is influenced by the presence of both AAs. Exposure to the AAI/AAII mixture affected the generation of their urinary metabolites formed by oxidation, reduction and conjugation reactions [ 48 ]. For instance, the reductive (activation) metabolism of AAI was increased in the presence of AAII, while in the presence of AAI the reductive metabolism of AAII decreased.…”