Abstract
BACKGROUND: The most widely used anti-malarial drug artemisinin (ART) is metabolized extensively, but the therapeutic capacity of its major metabolite remains unknown. Whether the major metabolite of ART (ART-M) contributes to its antiplasmodial potency was investigated in this study. METHODS: The metabolite identification and enzyme phenotyping of ART were performed using human liver microsomes (HLMs). The stereostructure of the major metabolite ART-M was elucidated by spectroscopic and X-ray crystallographic analysis. The anti-malarial activity of ART-M against two reference Plasmodium strains (Pf3D7 and PfDd2) was evaluated. The pharmacokinetic profiles of ART and its metabolite ART-M were investigated in healthy Chinese subjects after a recommended two-day oral dose of ART plus piperaquine. Pharmacodynamic parameters based on minimum inhibitory concentration (MIC(50)) and free plasma concentration were employed to evaluate the therapeutic potency of ART-M, including fAUC(0-t)/MIC(50), fC(max)/MIC(50) and T > MIC(50). RESULTS: A major metabolite 10β-hydroxyartemisinin (ART-M) was found for ART in human, and CYP3A4/3A5 was the major enzymes responsible for ART 10β-hydroxylation. Compared with ART (MIC(50), 10.1 nM against Pf3D7), weaker antiplasmodial activity was found for ART-M (MIC(50), 61.4 nM against Pf3D7). However, a 3.5-fold higher maximal free plasma concentration was achieved for ART-M (fC(max), 180.0 nM vs. 51.8 nM for ART). ART-M displayed comparable antiplasmodial potency to ART, in terms of fAUC(0-t)/MIC(50) (12.5 h), fC(max)/MIC(50) (2.8) and T > MIC(50) (5 h). CONCLUSIONS: The major metabolite 10β-hydroxyartemisinin contributes to the antiplasmodial efficacy of ART, which should be considered when evaluation of ART dosing regimens and/or clinical outcomes.