Received for publication December 13, 2006.
Revised February 28, 2007.
Accepted for publication March 6, 2007.

Investigation of the metabolism and reductive activation of carcinogenic aristolochic acids in rats

Abstract

The metabolic activation of aristolochic acids (AAs) that have been demonstrated to be mutagenic and carcinogenic was investigated. In vitro metabolism study indicated that AAs were metabolized to N-hydroxyaristolactam which could be either reduced to aristolactams or rearranged to 7-hydroxyaristolactams via Bamberger rearrangement. In vivo metabolism study is important because the intermediates (aristolactam-nitriumion) of the nitroreduction process are thought to be responsible for the carcinogenicity of AAs. LC-MS and LC-MS-MS were applied to the analyses of a series of positional isomers of hydroxyaristolactams in rat urine samples after the in vivo study of AAs. Three hydroxylated metabolites of aristolactam II and two hydroxylated metabolites of aristolactam I were identified. The structures of the positional isomers were elucidated from the interpretation of MS-MS spectra and the theoretical calculations of molecular augmentation. In addition, several new metabolites were detected in the rat urine by HR-MS and MS-MS, including those from the decarboxylation of AAs and the conjugations of acetylation, glucuronidation and sulfation of aristolochic acid Ia (AAIa).

Key words: analytical pharmacology/toxicology, carcinogen metabolism, chemical carcinogenesis, drug toxicity, mass spectrometry, metabolite identification, renal toxicity, structure elucidation