Cytochrome P450-based toxicity research of Pyrrolizidine alkaloids

Pyrrolizidine alkaloids were considered as the essential components in the toxicity of some composite plants. The previous study suggested that cytochrome P450 (CYPs)–mediated bioactivation and succedent formation of DNA adducts triggered toxicity of pyrrolizidine alkaloids including Clivorine and Riddline, such as genotoxicity and mutagenesis. However, there is little knowledge about the metabolism properties of Adonifoline, another pyrrolizidine alkaloid in the plant of Seneciea scandens, and there is little knowledge about the influence to CYPs activity directly or indirectly by pyrrolizidine alkaloids used in previous study. The purpose was to study the metabolism properties of several pyrrolizidine alkaloids including Adonifoline, Monocrotaline, Isoline, Clivorine and Senecionine, as well as their potential of CYPs-mediated bioactivation. METHODS A classical in vitro human microsomes incubation system was used in this study, and experiments included: 1) Assay of metabolism of Adonifoline, the major pyrrolizidine alkaloid in the plant of Seneciea scandens; 2) Assay of inhibitory effects against CYPs acticities by Adonifoline, Monocrotaline, Isoline, Clivorine and Senecionine; 3) Assay of time-dependent and NADPH-dependent inhibition of CYPs activities by Adonfioline, Monocrotaline, Isoline, Clivorine and Senecionine. RESULTS One metabolite, that is Adonifoline N-oxide, of Adonifoline was identified by LC-MS. Adonifoline, Monocrotaline, Isoline, Clivorine and Senecionine showed no inhibitory effects against tested CYPs activities including CYP3A4, CYP1A2, CYP2A6, CYP2D6, CYP2E1, CYP2C8 and CYP2C9 at a high concentration of 100 μM; and there were also no time-dependent and NADPH-dependent inhibition against CYPs described above found. CONCLUSION A N-oxide metabolite of Adonifoline was identified. In addition, the tested pyrrolizidine alkaloids have no inhibitory effects against tested CYPs activities, and also no CYPs-mediated bioactivation found. Key words: pyrrolizidine alkaloids; cytochrome P450;bioactivation; inhibitio