Extensive Genetic Diversity in the Plasmodium falciparum Na ⁺ /H ⁺ Exchanger 1 Transporter Protein Implicated in Quinine Resistance

Abstract

The Plasmodium falciparum Na ؉ /H ؉ exchanger (Pfnhe-1) locus at chromosome 13 and another locus at chromosome 9 have recently been proposed to influence quinine resistance. Here, we sequenced the ms4760 locus of the Pfnhe-1 gene from 244 P. falciparum isolates collected from five different regions of India. A total of 16 different ms4760 alleles (with one to five DNNND repeats) were observed among these isolates. Interestingly, areas with a high prevalence of chloroquine and sulfadoxine-pyrimethamine resistance showed more Pfnhe-1 DNNND repeats compared to low drug resistance areas. The extent of genetic diversity at the ms4760 locus also varied from one region to another, with expected heterozygosity values ranging from 0.47 to 0.88.

Plasmodium falciparum Na+/H+ Exchanger (pfnhe-1) Genetic Polymorphism in Indian Ocean Malaria-Endemic Areas

“…19,22 This situation is likely reflecting the level of malaria transmission, but it also could be related to the prevalence of resistant parasites to quinoline antimalarial drugs. This latter hypothesis is strengthened by our data, which show that isolates from the Comoros (an area with a high prevalence of antimalarial drugs resistance, although specific data about QN resistance are lacking) had significantly more repeats in block II (DNNND) than those isolates from Madagascar (a low drug-resistance area); these findings are consistent with some previous findings observed in culture-adapted parasites from Asia, 13,18,19,21,22 India, 23 and East Africa. 20 In conclusion, current observations from molecular surveys that aimed to define an association between potential contributors to QN resistance, such as ms4760 allele polymorphism, have generated conflicting data and do not allow for proposing a simple molecular typing methodology of global application based on this molecular marker.…”

“…14,15,[17][18][19][20][21][22] However, significant differences in the distribution and prevalence of allele were observed both between countries and within sites in the Comoros ( Table 1). The genetic diversity of the ms4760 allele observed in our study was similar between both countries (0.84 and 0.85), and it was comparable with the genetic diversity previously described in African (Congo = 0.76, Uganda = 0.79, and Kenya = 0.66) 15,17,20 and Indian isolates (0.68) 23 and significantly higher than the diversity found in Asian isolates (China/Myanmar = 0.68, P = 0.04; Vietnam = 0.49, P 0.0001). 19,22 This situation is likely reflecting the level of malaria transmission, but it also could be related to the prevalence of resistant parasites to quinoline antimalarial drugs.…”

“…Among the 595 studied sequences, we have observed 29 different alleles, including 8 new alleles (27%). By compiling our data with previous published sequences available in GenBank, [14][15][16][17][18][19][20][21][22][23][24] we estimate that 101 different ms4760 alleles have been described to date. However, in most publications, the numbering of the ms4760 alleles did not always taking into account the previously described alleles, making data comparison difficult.…”

“…The mechanism underlying QN resistance is not well-understood, and it is probably complex and multigenic. Since the seminal work by Ferdig and others 13 in 2004, 11 studies have been conducted in different countries to evaluate implication of ms4760 polymorphisms in QN resistance, [14][15][16][17][18][19][20][21][22][23][24] and conflicting data have been reported, likely because of the different geographical origin of parasites (implying different genetic backgrounds), the type of parasites used (fresh isolates, culture-adapted strains, and reference lines), and the method used to assess in vitro QN susceptibility. 21,25 In this context and to extend our previous work regarding ms4760 polymorphisms in Plasmodium falciparum parasites circulating in malaria-endemic areas in the Indian Ocean, 14 we have analyzed ms4760 sequences from 595 isolates (Madagascar, N = 345; Comoros, N = 250).…”

In Vitro Activities of Quinine and Other Antimalarials and pfnhe Polymorphisms in Plasmodium Isolates from Kenya

“…A seminal study on the association of polymorphisms in pfnhe, a sodium hydrogen exchanger gene, and the in vitro activity of QN indicated that an increase in the number of DNNND repeats (1)(2)(3)(4)(5) in an ms4760 microsatellite was associated with reduced susceptibility to QN (10), and this finding was confirmed recently (13). Variations in the copy number of this repeat in isolates from areas where QN efficacy is known to be reduced in vivo have also been reported (41).…”