Identification of the human cytochrome P450 enzymes involved in the in vitro metabolism of artemisinin

Abstract

AimsThe study aimed to identify the specific human cytochrome P450 (CYP450) enzymes involved in the metabolism of artemisinin. Methods Microsomes from human B-lymphoblastoid cell lines transformed with individual CYP450 cDNAs were investigated for their capacity to metabolize artemisinin. The effect on artemisinin metabolism in human liver microsomes by chemical inhibitors selective for individual forms of CYP450 was investigated. The relative contribution of individual CYP450 isoenzymes to artemisinin metabolism in human liver microsomes was evaluated with a tree-based regression model of artemisinin disappearance rate and specific CYP450 activities. Results The involvement of CYP2B6 in artemisinin metabolism was demonstrated by metabolism of artemisinin by recombinant CYP2B6, inhibition of artemisinin disappearance in human liver microsomes by orphenadrine (76%) and primary inclusion of CYP2B6 in the tree-based regression model. Recombinant CYP3A4 was catalytically competent in metabolizing artemisinin, although the rate was 10% of that for recombinant CYP2B6. The tree-based regression model suggested CYP3A4 to be of importance in individuals with low CYP2B6 expression. Even though ketoconazole inhibited artemisinin metabolism in human liver microsomes by 46%, incubation with ketoconazole together with orphenadrine did not increase the inhibition of artemisinin metabolism compared to orphenadrine alone. Troleandomycin failed to inhibit artemisinin metabolism. The rate of artemisinin metabolism in recombinant CYP2A6 was 15% of that for recombinant CYP2B6. The inhibition of artemisinin metabolism in human liver microsomes by 8-methoxypsoralen (a CYP2A6 inhibitor) was 82% but CYP2A6 activity was not included in the regression tree. Conclusions Artemisinin metabolism in human liver microsomes is mediated primarily by CYP2B6 with probable secondary contribution of CYP3A4 in individuals with low CYP2B6 expression. The contribution of CYP2A6 to artemisinin metabolism is likely of minor importance.Keywords: artemisinin, CYP2B6, CYP3A4, cytochrome P450, metabolism species. The fraction excreted unchanged in urine in Introduction humans is less than 1% of an oral administration [2]. In rats, the liver is the major organ of elimination [3]. Four Artemisinin is the parent compound of an emerging class of antimalarial drugs of importance in the treatment of metabolites, deoxy-artemisinin, deoxy-dihydroartemisinin, dihydroxyartemisinin and the so-called 'crystal-7' malaria in areas with multidrug resistant Plasmodium falciparum. Artemisinin is a sesquiterpene lactone with an were identified in urine following oral administration of artemisinin to humans, but plasma metabolites remain internal peroxide bridge (Figure 1) necessary for its antiparasitic effect [1]. Limited data are available on unknown [4]. Artemisinin is commonly used together with other artemisinin metabolism in both humans and animal antimalarial drugs and information on its enzymatic

Dried whole-plant Artemisia annua slows evolution of malaria drug resistance and overcomes resistance to artemisinin

“…The improved antimalarial activity of WP over pure AN may possibly be explained by enhanced bioavailability of artemisinin due to inhibitory effects of some A. annua flavonoids on the hepatic and intestinal cytochrome P450 enzymes that metabolize artemisinin (53,54). Plant material enhanced by >40-fold the amount of artemisinin that entered the blood stream (55).…”

Treatment with Coartem (Artemether-Lumefantrine) in Papua New Guinea

“…Sixty-four (64) different individuals representing persistent or new infections were genotyped for the cytochrome P450 3A4 392A>G and 2B6 516G>T and for the UDP-glucuronosyltransferase UGT2B7 802C>T, which are all involved in the metabolism of artemisinin drugs and/or lumefantrine. [15][16][17][18] Sequencing of cytochrome P450 3A4 was successfully performed for 56/64 participants. Results from sequencing of cytochrome P450 3A4 showed homozygote wild-type carriers at position 392, i.e., adenosine, for all 56 individuals.…”

“…Artemisinin derivatives are mainly metabolized by the human cytochrome P450 3A4 16 and 2B6 18 and also by the metabolic enzyme UDP-glucuronosyltransferase UGT2B7 . 17 The lumefantrine component of Coartem is also metabolized by CYP3A4 .…”

Assessment of the antimalarial potential of tetraoxane WR 148999.

“…Thus, we suspect that the oral bioavailability of WR 148999 is more a function of metabolism than solubility-limited dissolution, especially since various tetraoxane formulation strategies (Vennerstrom JL and others, unpublished data) and incorporation of polar functional groups in a series of WR 148999 analogs 29 both failed to enhance tetraoxane oral antimalarial activity. However, further studies determining the oral pharmacokinetic properties of WR 148999 are necessary to place the CYP1A2 inhibition data into perspective.…”

“…Interestingly, artemisinin induces its own metabolism 9 and is metabolized principally by CYP2B6, and to a lesser extent, CYP3A4. 29 In contrast, WR 148999 is most likely metabolized by CYP1A2. Since each compound was dissolved in peanut oil in this sc experiment, it is also possible that a depot was formed from which WR 148999 was released more slowly than artemisinin.…”