Effects of genetic variation at the CYP2C19/CYP2C9 locus on pharmacokinetics of chlorcycloguanil in adult Gambians

Abstract

Aims: Antimalarial biguanides are metabolized by CYP2C19, thus genetic variation at the CYP2C locus might affect pharmacokinetics and so treatment outcome for malaria.

Materials & methods: Polymorphisms in CYP2C19 and CYP2C9 in 43 adult Gambians treated with chlorproguanil/dapsone for uncomplicated malaria were assessed. Chlorcycloguanil pharmacokinetics were measured and associations with CYP2C19 and CYP2C9 alleles and CYP2C19 metabolizer groups investigated.

Results: All CYP2C19/CYP2C9 alleles obeyed Hardy-Weinberg equilibrium. There were 15 CYP2C19/2C9 haplotypes with a common haplotype frequency of 0.23. Participants with the CYP2C19*17 allele had higher chlorcycloguanil area under the concentration versus curve at 24 h (AUC(0-24)) than those without (geometric means: 317 vs 216 ng.h/ml; ratio of geometric means: 1.46; 95% CI: 1.03 to 2.09; p = 0.0363) and higher C(max) (geometric mean ratio: 1.52; 95% CI: 1.13 to 2.05; p = 0.0071).

Conclusion: CYP2C19*17 determines antimalarial biguanide metabolic profile at the CYP2C19/CYP2C9 locus.

Figure 1. Allele frequencies and haplotypes in 43 Gambian adults following genotyping of polymorphic CYP2C19 and CYP2C9 alleles by PCR-sequence specific primers and Taqman^® real-time PCR

CYP2C19 minor allele frequency is compared with allele frequencies of West-African Yorubas from the HapMap project. Haplotypes were determined by PHASE version 2.1. The SNPs are arranged according to contig positions as given by the NCBI reference assembly. The positions of the SNPs in promoter, intron and exons of the genes are indicated. *Minor allele frequencies for African–Americans from Applied Biosystems (CA, USA) [105] were used where allele frequencies for HapMap Yoruba were not available.

Figure 2. Haplotype block diagram of CYP2C19 and CYP2C9

The diagram was generated using the Haploview program [106]. The NCBI rs ID numbers of the polymorphisms in CYP2C19 and CYP2C9 that were investigated are indicated. Three main haplotype blocks were identified with strong LD generally between the two genes (D′ values > 0.9). Block 1 contained the CYP2C19*17 marker, which was in strong LD with the nearby promoter SNP rs7067866. Block 2 contained the CYP2C19*2 allele. Block 3 comprised two SNPs in CYP2C9. The diagram also shows each haplotype in a block with its population frequency and connections from one block to the next. In the crossing areas, a value of multiallelic D′ is indicated, which represents the level of recombination between the two blocks. Interestingly the decreased function CYP2C9*8 allele is in complete LD with both the gain-of-function CYP2C19*17 allele (D′ = 1) and the reduced function CYP2C19*2 allele (D′= 1). LD: Linkage disequilibrium; LOD: Log of the likelihood odds ratio.