BackgroundIn Honduras, chloroquine and primaquine are recommended and still appear to be effective for treatment of Plasmodium falciparum and Plasmodium vivax malaria. The aim of this study was to determine the proportion of resistance associated genetic polymorphisms in P. falciparum and P. vivax collected in Honduras.MethodsBlood samples were collected from patients seeking medical attention at the Hospital Escuela in Tegucigalpa from 2004 to 2006 as well as three regional hospitals, two health centres and one regional laboratory during 2009. Single nucleotide polymorphisms in P. falciparum chloroquine resistance transporter (pfcrt), multidrug resistance 1 (pfmdr1), dihydrofolate reductase (pfdhfr) and dihydropteroate synthase (pfdhps) genes and in P. vivax multidrug resistance 1 (pvmdr1) and dihydrofolate reductase (pvdhfr) genes were detected using PCR based methods.ResultsThirty seven P. falciparum and 64 P. vivax samples were collected. All P. falciparum infections acquired in Honduras carried pfcrt, pfmdr1, pfdhps and pfdhfr alleles associated with chloroquine, amodiaquine and sulphadoxine-pyrimethamine sensitivity only. One patient with parasites acquired on a Pacific Island had pfcrt 76 T and pfmdr1 86Y alleles. That patient and a patient infected in West Africa had pfdhfr 51I, 59 R and 108 N alleles. Pvmdr1 976 F was found in 7/37 and two copies of pvmdr1 were found in 1/37 samples. Pvdhfr 57 L + 58 R was observed in 2/57 samples.ConclusionThe results indicate that P. falciparum from Honduras remain sensitive to chloroquine and sulphadoxine-pyrimethamine. This suggests that chloroquine and sulphadoxine-pyrimethamine should be efficacious for treatment of uncomplicated P. falciparum malaria, supporting current national treatment guidelines. However, genetic polymorphisms associated with chloroquine and sulphadoxine-pyrimethamine tolerance were detected in local P. vivax and imported P. falciparum infections. Continuous monitoring of the prevalence of drug resistant/tolerant P. falciparum and P. vivax is therefore essential also in Honduras.

BACKGROUND AND PURPOSEWidespread resistance to antimalarial drugs requires combination therapies with increasing risk of pharmacokinetic drug-drug interactions. Here, we explore the capacity of antimalarial drugs to induce drug metabolism via activation of constitutive androstane receptors (CAR) by ligand binding. EXPERIMENTAL APPROACHA total of 21 selected antimalarials and 11 major metabolites were screened for binding to CAR isoforms using cellular and in vitro CAR-coactivator interaction assays, combined with in silico molecular docking. Identified ligands were further characterized by cell-based assays and primary human hepatocytes were used to elucidate induction of gene expression. KEY RESULTSOnly two artemisinin derivatives arteether and artemether, the metabolite deoxyartemisinin and artemisinin itself demonstrated agonist binding to the major isoforms CAR1 and CAR3, while arteether and artemether were also inverse agonists of CAR2. Dihydroartemisinin and artesunate acted as weak inverse agonists of CAR1. While arteether showed the highest activities in vitro, it was less active than artemisinin in inducing hepatic CYP3A4 gene expression in hepatocytes. CONCLUSIONS AND IMPLICATIONSArtemisinin derivatives and metabolites differentially affect the activities of CAR isoforms and of the pregnane X receptor (PXR). This negates a common effect of these drugs on CAR/PXR-dependent induction of drug metabolism and further provides an explanation for artemisinin consistently inducing cytochrome P450 genes in vivo, whereas arteether and artemether do not. All these drugs are metabolized very rapidly, but only artemisinin is converted to an enzyme-inducing metabolite. For better understanding of pharmacokinetic drug-drug interaction possibilities, the inducing properties of artemisinin metabolites should be considered.

Translation in this moment is not operationally possible at an individual level, but large population studies are achievable for: i) the development of robust pharmacogenetics markers; and ii) the parallel development of a pharmacogenetic cartography of malaria settings. Advances in the understanding of antimalarial pharmacogenetics are urgent in order to protect the exposed populations, enhance the effectiveness of ACT and, consequently, contributing for the long aimed elimination of the disease.

This is the first study showing the influence of CYP2C8 genotypes on diclofenac metabolism in vivo. The linkage disequilibrium between CYP2C8*3 and CYP2C9*2 alleles was confirmed in this Spanish population.

Cytochrome P450 2C8 (CYP2C8) is a polymorphic phase I drug-metabolising enzyme involved in the metabolism of a wide variety of xenobiotics, as well as a proposed player in the regulation of vascular tone. Polymorphisms in this gene may have an impact on the metabolism of therapeutic drugs such as paclitaxel and verapamil. In this report we have determined the frequencies of the main non-synonymous CYP2C8 alleles, 805A>T (CYP2C8*2), 416G>A/1196A>G (CYP2C8*3) and 792C>G (CYP2C8*4) in a sample representative of Portuguese Caucasians. The allelic frequencies determined were 1.2%, 19.8%, and 6.4% for CYP2C8*2, CYP2C8*3, and CYP2C*4, respectively. The observed CYP2C8*3 prevalence is significantly different from the frequencies previously reported in North European populations.

LUM body disposition may be influenced by MRP2/ABCC2 genotype.

f Malaria patients are frequently coinfected with HIV and mycobacteria causing tuberculosis, which increases the use of coadministered drugs and thereby enhances the risk of pharmacokinetic drug-drug interactions. Activation of the pregnane X receptor (PXR) by xenobiotics, which include many drugs, induces drug metabolism and transport, thereby resulting in possible attenuation or loss of the therapeutic responses to the drugs being coadministered. While several artemisinin-type antimalarial drugs have been shown to activate PXR, data on nonartemisinin-type antimalarials are still missing. Therefore, this study aimed to elucidate the potential of nonartemisinin antimalarial drugs and drug metabolites to activate PXR. We screened 16 clinically used antimalarial drugs and six major drug metabolites for binding to PXR using the two-hybrid PXR ligand binding domain assembly assay; this identified carboxymefloquine, the major and pharmacologically inactive metabolite of the antimalarial drug mefloquine, as a potential PXR ligand. Two-hybrid PXR-coactivator and -corepressor interaction assays and PXR-dependent promoter reporter gene assays confirmed carboxymefloquine to be a novel PXR agonist which specifically activated the human receptor. In the PXR-expressing intestinal LS174T cells and in primary human hepatocytes, carboxymefloquine induced the expression of drug-metabolizing enzymes and transporters on the mRNA and protein levels. The crucial role of PXR for the carboxymefloquine-dependent induction of gene expression was confirmed by small interfering RNA (siRNA)-mediated knockdown of the receptor. Thus, the clinical use of mefloquine may result in pharmacokinetic drug-drug interactions by means of its metabolite carboxymefloquine. Whether these in vitro findings are of in vivo relevance has to be addressed in future clinical drug-drug interaction studies. M alaria, which is caused by infection with parasitic protozoans of the genus Plasmodium, is still a major global health burden, with an estimated 207 million cases and 627,000 deaths worldwide in 2012 (1). The emerging resistance of the parasite to artemisinins (2) and the need to treat malaria patients coinfected with HIV and/or mycobacteria causing tuberculosis (3) increasingly necessitates the use of combination drug therapies and coadministration of drugs, respectively, which also may be accompanied by a higher risk for drug-drug interactions. Mechanistically, these may arise from the inhibition or induction of metabolism and/or transport of coadministered drugs. Competitive or noncompetitive enzyme inhibition may result in adverse toxic effects due to higher-than-expected drug concentrations, whereas clinically relevant induction may result in therapeutic failure due to insufficient drug levels. The interaction potential of antimalarial drugs due to the inhibition of cytochrome P450 (CYP) drugmetabolizing enzymes has been analyzed quite extensively in vitro, and it has been shown to result in some clinically relevant drugdrug interactions, as exemplified...

f Artemisinins induce drug metabolism through the activation of the pregnane X receptor (PXR) in vitro. Here, we report the resequencing and genotyping of PXR variants in 75 Vietnamese individuals previously characterized for CYP3A enzyme activity after artemisinin exposure. We identified a total of 31 PXR variants, including 5 novel single nucleotide polymorphisms (SNPs), and we identified significantly different allele frequencies relative to other ethnic groups. A trend of significance was observed between the level of CYP3A4 induction by artemisinin and two PXR variants, the 8118C¡T (Y328Y) and 10719A¡G variants.A rtemisinin combination therapy (ACT) is an integral part of the global management of malaria (7). In this treatment strategy, an artemisinin-related compound with a short half-life (t 1/2 ; ϳ0.25 to 4 h) is combined with a more slowly eliminated antimalarial to reduce recrudescence and to slow the development of resistance (24). Currently, several ACT formulations, including artesunate-mefloquine, artemether-lumefantrine, and artesunate-amodiaquine, are used (27), and a second generation of ACTs is being scheduled for global launch. These ACTs include dihydroartemisinin-piperaquine (5) and artesunate-pyronaridine (30).In vitro studies indicate that artemisinin, arteether, and artemether are effective ligands of the pregnane X receptor (PXR) (4), a nuclear receptor and a key player in the regulation of the expression of proteins involved in drug metabolism (e.g., cytochrome P450s [CYP450s]) and transport (e.g., ABC transporters) (6). Variability in the expression and function of these proteins may lead to alterations in the pharmacokinetics of artemisinin derivatives, possibly resulting in pharmacodynamic changes and subsequent clinical consequences such as side effects (14).A previously performed in vivo study including 75 Vietnamese subjects showed a significant interindividual variation in the degree of artemisinin-driven induction of several CYP450 enzymes, including CYP3As, the genes which are canonical targets of PXR (1). In the present work, we built upon this study by hypothesizing that specific single nucleotide polymorphisms (SNPs) in PXR might explain the observed interindividual variability in the level of CYP3A induction. For this purpose, the PXR gene was fully resequenced in all individuals who participated in the study mentioned above, with a focus on the open reading frame (ORF) (mutations in which could lead to proteins with altered activities), intron-exon boundaries (mutations in which could lead to disturbances in the well-documented alternative splicing of PXR), and the proximal promoter (mutations in which could modulate basal expression). Additionally, known variants with putative functional consequences located in introns and other regions (e.g., the 3= region) were genotyped by using matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) technology. Primers and amplification conditions are listed in Table S1 in the supplemental material....