Characterization of in vitro metabolites of evocarpine in rat liver microsomes and their influence on antibacterial activity

After incubation of evocarpine, the major bioactive compound of the n-hexane extract of the fruits of Evodiae fructus, with rat liver microsomes (S9 mix) nine metabolites were identified by their characteristic product ions using LC-PDA-ESI-MS analysis. The main biotransformation reactions observed were hydroxylation, hydration, dehydrogenation and N-demethylation. Comparison of incubation times between 1 and 72 hours showed no qualitative difference in biotransformation. In order to assess the influence of metabolism on the antibacterial activity of evocarpine and the crude extract, the test solutions were pre-incubated with the S9 mix prior the determination of the minimum inhibitory concentration (MIC), which revealed a four-fold increase of the MIC against Mycobacterium smegmatis ATCC 14468 for pre-incubation times of 1, 24 and 72 hours for the crude extract and a sixteen-fold increase for evocarpine for a pre-incubation time of 1 hour.