PXR Variants and Artemisinin Use in Vietnamese Subjects: Frequency Distribution and Impact on the Interindividual Variability of CYP3A Induction by Artemisinin

Abstract

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....

Pharmacogenomics of Cytochrome P450 3A4: Recent Progress Toward the “Missing Heritability” Problem

“…Moreover, the PXR*1B haplotype, which is tagged by the SNPs 2654T > C and IVS6-17C > T, was related to doxorubicin clearance in Asian breast cancer patients (Sandanaraj et al, 2008). Further studies analyzing patient cohorts under fosamprenavir/lopinavir or artemisinin treatment gave additional hints to some PXR variants that may affect inducibility of CYP3A4 phenotype expression (Svärd et al, 2010; Piedade et al, 2012). The occurrence of two SNPs in the 3′UTR region of PXR , rs3732359 and rs3732360, has been shown to be associated with altered midazolam 1′-hydroxylation in a liver bank and with more pronounced effect in midazolam clearance of healthy volunteers of African American descent (Oleson et al, 2010).…”

PXR and CAR single nucleotide polymorphisms influence plasma efavirenz levels in South African HIV/AIDS patients

“…PXR and CAR are transcriptional regulators of a wide range of genes whose products metabolise a wide range of drugs [2,3]. …”

Influences of an NR1I2 polymorphism on heterogeneous antiplatelet reactivity responses to clopidogrel and clinical outcomes in acute ischemic stroke patients

“…In our previous studies, NR1I2 (rs13059232) was found to affect the occurrence of CR in IS patients treated with clopidogrel [28]. Studies have shown that the expression levels of NR1I2 could be affected by gene polymorphisms of NR1I2, which could further influence the activities of downstream metabolic enzymes and transporters [20,21]. For example, it was reported that NR1I2 (rs13059232) influences the phenotypes of CYP3A4 [29], an important enzyme that metabolizes clopidogrel.…”

“…NR1I2 genetic polymorphisms have a significant impact; specifically, they affect the uptake, transport, and metabolism of various endogenous and exogenous substances. Therefore, NR1I2 genetic polymorphisms are of great significance in studying the metabolic processing of clinical drugs [20,21]. Nevertheless, research on the relationship between the genetic polymorphisms of NR1I2 and individual differences in the therapeutic effects of clopidogrel is currently limited.…”