Variation in Human Cytochrome P-450 Drug-Metabolism Genes: A Gateway to the Understanding of Plasmodium vivax Relapses

Abstract

Although Plasmodium vivax relapses are classically associated with hypnozoite activation, it has been proposed that a proportion of these cases are due to primaquine (PQ) treatment failure caused by polymorphisms in cytochrome P-450 2D6 (CYP2D6). Here, we present evidence that CYP2D6 polymorphisms are implicated in PQ failure, which was reinforced by findings in genetically similar parasites, and may explain a number of vivax relapses. Using a computational approach, these polymorphisms were predicted to affect the activity of CYP2D6 through changes in the structural stability that could lead to disruption of the PQ-enzyme interactions. Furthermore, because PQ is co-administered with chloroquine (CQ), we investigated whether CQ-impaired metabolism by cytochrome P-450 2C8 (CYP2C8) could also contribute to vivax recurrences. Our results show that CYP2C8-mutated patients frequently relapsed early (<42 days) and had a higher proportion of genetically similar parasites, suggesting the possibility of recrudescence due to CQ therapeutic failure. These results highlight the importance of pharmacogenetic studies as a tool to monitor the efficacy of antimalarial therapy.

Fig 1. Frequency of CYP2D6 polymorphisms and parasite haplotype among P. vivax-infected patients who had single (n = 28) or multiple (n = 18) episodes of relapse.

(A) The number of CYP2D6 polymorphisms is represented by the different intensity of color as specified in the legend. A simple logistic regression model shows a significant relationship between the mutant status for CYP2D6 and the increased number of relapses (OR, 12.4; 95% CI, 2.80–88.57; P = .003). (B) Frequency of parasite haplotype in patients without or with CYP2D6 mutation. Parasites were classified according to the number of markers containing identical alleles: identical in black (parasites showing all 10 identical markers); related in gray (8 to 9 identical markers); and heterologous in light gray (less than 8 identical markers).

Fig 2. Analysis of the molecular interactions of polymorphic residues of CYP2D6 and their effects on the metabolism of primaquine.

(A) The residue P34 has a buried side chain that is inserted into a predominantly hydrophobic environment (the hydrophobic interactions are depicted as gray dots) and is performing a main-chain to side-chain polar interaction with a neighboring beta strand (red dashes). The mutation P34S is predicted to destabilize the protein because it disrupts the local hydrophobic interaction network and affects the backbone rigidity. (B) The interactions for docked PQ (dark gray) and residue T107 (green). Threonine 107 is located in the vicinity of the PQ binding pocket (6.1 Å from PQ) and also nearby important catalytic residues (depicted in blue). (C) The mutation T107I results in the formation of increased local interactions, reducing CYP2D6 flexibility. Residues are colored based on their predicted effect on flexibility, ranging from more flexible (red) to less flexible (blue).

Fig 3. Analysis of the parasite haplotype and time to relapse in days for carriers of CYP2C8 polymorphisms.

Frequency of parasite haplotype between patients without or with CYP2C8 mutation. Parasites were classified according to the number of identical markers: identical in black (10 identical markers); related in gray (8 to 9 identical markers); and heterologous in light gray (less than 8 identical markers).