In vitro susceptibility to quinine and microsatellite variations of the Plasmodium falciparum Na+/H+ exchanger transporter (Pfnhe-1) gene in 393 isolates from Dakar, Senegal

Abstract

BackgroundAlthough the World Health Organization recommends replacing quinine (QN) by artesunate due to its increased efficacy and the higher tolerance to the drug in both adults and children, QN remains a first-line treatment for severe malaria, especially in Africa. Investigations of microsatellite Pfnhe-1 ms4760 polymorphisms in culture-adapted isolates from around the world have revealed that an increase in the number of DNNND amino acid motifs was associated with decreased QN susceptibility, whereas an increase in the number of DDNHNDNHNND motifs was associated with increased QN susceptibility.MethodsIn this context, to further analyse associations between Pfnhe-1 ms4760 polymorphisms and QN susceptibility, 393 isolates freshly collected between October 2009 and January 2010 and July 2010 and February 2011, respectively, at the Hôpital Principal de Dakar, Senegal were assessed ex vivo for QN susceptibility, and their genes were amplified and sequenced.ResultsOf the 393 Plasmodium falciparum clinical isolates collected, 145 were successfully cultured. The 145 QN IC50s ranged from 2.1 to 1291 nM, and 17 isolates (11.7%) exceed the QN reduced susceptibility threshold of 611 nM. Among the 393 P. falciparum clinical isolates, 47 different alleles were observed. The three most prevalent profiles were ms4760-1 (no = 72; 18.3%), ms4760-3 (no = 65; 16.5%) and ms4760-7 (no = 40; 10.2%). There were no significant associations observed between QN IC50 values and i) the number of repeats of DNNND in block II (p = 0.0955, Kruskal-Wallis test); ii) the number of repeats of DDNHNDNHNND in block V (p = 0.1455, Kruskal-Wallis test); or iii) ms4760 profiles (p = 0.1809, Kruskal-Wallis test).ConclusionsPfnhe-1 ms4760 was highly diverse in parasite isolates from Dakar (47 different profiles). Three profiles (ms4760-1, ms4760-3 and ms4760-7) were predominant. The number of repeats for block II (DNNND) or block V (DDNHNDNHNND) was not significantly associated with QN susceptibility. New studies, and especially in vivo studies, are necessary to confirm the role of Pfnhe-1 ms4760 as a marker of QN resistance.

Single nucleotide polymorphisms in Plasmodium falciparum V type H+ pyrophosphatase gene (pfvp2) and their associations with pfcrt and pfmdr1 polymorphisms

“…Though QN was not used in the Yekepa area at the time of this study the frequency of pfnhe1 ms4760-1 (26%) was similar to the frequency found at day 0 in a recent study in Mali where ms4760-1 was associated with QN resistance [97]. Furthermore, the number and frequencies of DDNHNDNHNND repeats in this study were similar to data found in 393 clinical isolates recently reported from Senegal [286]. Despite the geographic separation, the similarity to that found in Liberia in 1978 , prior to a drug selective pressure, suggests that ms4760-1 did not play a significant role in the emergence of resistance in West Africa over subsequent years.…”

“…Eight of the 114 previously described pfnhe1 variants [97,249] [75,97,249,286]. Though QN was not used in the Yekepa area at the time of this study the frequency of pfnhe1 ms4760-1 (26%) was similar to the frequency found at day 0 in a recent study in Mali where ms4760-1 was associated with QN resistance [97].…”

Ex vivo anti-malarial drug susceptibility of Plasmodium falciparum isolates from pregnant women in an area of highly seasonal transmission in Burkina Faso

“…LUM, MQ and PiP are partner drugs in ACT and all of them had a relatively low mean IC 50 , the first two around 1 nM and the latter at 5.0 nM. In addition, DHA’s mean IC 50 was also low, confirming earlier reports from other parts of Burkina Faso as well as other sub-Saharan African countries [ 17 , 33 – 35 ]. This suggests that the efficacy of both AL and AS–AQ should be good as most parasite isolates were sensitive to both components of the two ACT.…”

Association between Polymorphisms in the Pf mdr6 Gene and Ex Vivo Susceptibility to Quinine in Plasmodium falciparum Parasites from Dakar, Senegal

“…QN susceptibility was previously associated with microsatellite repeats in P. falciparum Na ϩ /H ϩ exchanger 1 (Pfnhe-1) (14,15). However, this association was location specific and differed between African and Asian P. falciparum isolates (15)(16)(17). The low number of P. falciparum isolates and the modest association limited the interpretation of the present results.…”