Biotransformation And Time-dependent Pharmacokinetic Studies Of Artemisinin Antimalarials

Artemisinin drugs have become the first-line antimalarials in areas of multi-drug resistance. However, monotherapy with artemisinin drugs can result in comparatively high recrudescence rates. Autoinduction of CYP-mediated metabolism, resulting in reduced exposure, has been supposed to be the underlying mechanism. To better understand the autoinduction of artemisinin drugs, the biotransformation of four typical artemisinin drugs(artemisinin, dihydroartemisinin, artemether and artesunate) both in vitro and in vivo. The time-dependent pharmacokinetics of artemisinin was also investigated in rats.1. The biotransformation of artemisinin (QHS), dihydroartemisinin (DHA), artemether (ARM) and artesunate (ARS) in vitro and in vivo were studied, by using an LTQ-Orbitrap spectrometer in conjunction with online hydrogen (H)/deuterium (D) exchange LC-HRMS for rapid structural characterization. The LC separation was improved allowing the separation of these parent drugs and their metabolites from their diastereomers. The product ions in the stage of HR-MS2and HR-MS3were compared with those of their parent drugs to elucidate the most probable metabolites structures.Twenty-three phase I metabolites were detected in liver microsomal incubates, rat plasma, urine and bile, while eleven phase Ⅱ metabolites were detected in rat plasma, urine and bile. Twenty seven, eighty and thirty nine phase I metabolites of DHA, ARM, ARS were detected. In addition, nine, eleven and six phase II metabolites were found for DHA, ARM and ARS. These antimalarials undergo similar phase I metabolic pathways including hydroxylation, loss of oxygen, desaturation. These phase I metabolic products will undergo subsequent phase II glucuronidation process. Most metabolites were reported for the first time.2. The time-dependent pharmacokinetics profile of artemisinin in rats was studied by comparison of the plasma concentration of QHS and its main metabolite deoxyartemisinin after one single oral dose and a5-day multiple dose oral administrations. A selective and sensitive liquid chromatography high resolution mass spectrometry (LC-HRMS) were established for the determination of QHS and deoxyartemisinin in rat plasma. Artemisinin, deoxyartemisinin and internal standard (IS, ARM) in rat plasma were detected by HRMS in full-scan mode. The validation results showed satisfactory accuracy (<6%) and precision (<15%) at linear dynamic range (5.0-200.0ng·mL-1).The pharmacokinetic study was designed to get the direct evidence of the auto-induction metabolism for QHS. The gender effect on the pharmacokinetic profile of QHS and its main metabolite deoxyartemisinin was also studied.The AUCo-t of the parent drug QHS and its metabolite deoxyartemisinin decreased significantly (P<0.05) with increased oral clearance (CL/F)(P<0.05) after a5-day oral administration of QHS to rats. Gender difference was also observed for QHS and deoxyartemisinin, QHS and deoxyartemisinin exposure level is much higher in female rats compared with male rats (P<0.05).