Microsatellites Polymorphism Within Pfnhe-L And Pfmdr-6 Genes in Association with ant malarial Drug Susceptibility in Kenyan Plasmodium Falciparum Isolates Circulating In 2010-2011

Abstract

Drug resistance continues to undermine malaria control, threatening malaria elimination efforts. Resistance to artemisinin has now been confirmed in Southeast Asia and quinine monotherapy clinical failure, although rare, has been reported as well. Studies in Kenyan coast have reported parasite reduced sensitivity to quinine and artemisinin, indicating an urgent: need for surveillance of the first-line drugs in Kenya. Quinine and Artemether-lumefantrine are the first-line treatment for complicated and uncomplicated falciparum malaria respectively in Kenya. The present study established the association between in vitro quinine and dihydroartemisinin (the active metabolite of artemisinin) sensitivity and micro satellite polymorphism within P. falciparum sodium/hydrogen exchanger-l (Pfnhe-l) and multidrug resistance-6 (Pfmdr-6) genes in samples collected from western, highlands and coastal regions of Kenya. In vitro activity was assessed as the drug concentration that inhibits 50% of parasite growth (IC50) and parasite genetic polymorphisms were determined by DNA sequencing. Associations between the in vitro quinine and dihydroartemisinin sensitivity [phenotypic] with the polymorphisms of the Pfnhe-I and Pfmdr-6 genes [genotypic] were established using regression method. The median (Interquartile range) IC50svalues in nM for quinine and dihydroartemisinin were 65.56 (18.19-337.7) and 8.18 (3.39-13.48), respectively. Data revealed significant association between 1 and 2 DNNND repeat and parasite susceptibility to quinine (p=0.014 and p=0.043, respectively). In addition, significant association .was seen between DNNND single repeat and parasite response to dihydroartemisinin (p=0.04).While No significant different between quinine and dihydroartemisinin IC50with DDNHNDNHNND and DDNNNDNHNDD repeats (p=0.199 and p=O.S7).On the other hand, due to variation in Nand NIN microsatellite repeat of Pfmdr-6 ten haplotypes was established, there was significant association between 8, 9 and 13 Pfmdr-6 R1repeat and parasite susceptibility to quinine (p=0.02, p=0.012 and p=0.041). Out of 87 and 34 isolates tested against quinine and dihydroartemisinin 29% and 44% contained high IC50s, which are considered quinine and dihydroartemisinin resistance based on World Health Organization cut-off points (quinine IC50 > 31SnM and dihydroartemisinin IC50 > lOnM), respectively. This indicates quinine and dihydroartemisinin resistance may be emerging in Kenya. Clinical efficacy studies are required to confirm the validity of these markers and the importance of parasite genetic background given the importance of these drugs in the management of malaria. To further validate our observation and conclusions, it will be important isolates from different malaria ecological zones and malaria endemicity regions of Kenya are analyzed.