Polymorphisms of the pfmdr1 but not the pfnhe-1 gene is associated with in vitro quinine sensitivity in Thai isolates of Plasmodium falciparum.
BACKGROUND
The emergence of Plasmodium falciparum resistance to most currently used anti-malarial drugs is a major problem in malaria control along the Thai-Myanmar and Thai-Cambodia borders. Quinine (QN) with tetracycline/doxycycline has been used as the second-line treatment for uncomplicated falciparum malaria. In addition, QN monotherapy has been the first-line treatment for falciparum malaria in pregnant women. However, reduced in vitro and in vivo responses to QN have been reported. To date, a few genetic markers for QN resistance have been proposed including Plasmodium falciparum chloroquine resistance transporter (pfcrt), P. falciparum multidrug resistance 1 (pfmdr1), and P. falciparum Na+/H+ exchanger (pfnhe-1). This study was to investigate the role of the pfmdr1 and pfnhe-1 gene on in vitro QN sensitivity in Thai isolates of P. falciparum.


METHODS
Eighty-five Thai isolates of P. falciparum from the Thai-Myanmar and Thai-Cambodia borders from 2003-2008 were determined for in vitro QN sensitivity using radioisotopic assay. Polymorphisms of the pfmdr1 and pfnhe-1 gene were determined by PCR-RFLP and sequence analysis. Associations between the in vitro QN sensitivity and the polymorphisms of the pfmdr1 and pfnhe-1 gene were evaluated.


RESULTS
The mean QN IC50 was 202.8 nM (range 25.7-654.4 nM). Only four isolates were QN resistant when the IC50 of >500 nM was used as the cut-off point. Significant associations were found between the pfmdr1 mutations at codons N86Y and N1042D and in vitro QN sensitivity. However, no associations with the number of DNNND, DDNNNDNHNDD, and NHNDNHNNDDD repeats in the microsatellite ms4760 of the pfnhe-1 gene were identified.


CONCLUSIONS
Data from the present study put doubt regarding the pfnhe-1 gene as to whether it could be used as the suitable marker for QN resistance in Thailand. In contrast, it confirms the influence of the pfmdr1 gene on in vitro QN sensitivity.
Department of Parasitology, Phramongkutklao College of Medicine, 315 Ratchawithi Rd., Ratchathewi, Bangkok, Thailand.
Teera
T
Poyomtip
Nantana
N
Suwandittakul
Narumon
N
Sitthichot
Rommanee
R
Khositnithikul
Peerapan
P
Tan-ariya
Mathirut
M
Mungthin
D000962:Antimalarials / Q000494:pharmacology*; D002160:Cambodia; D016054:DNA, Protozoan / Q000235:genetics; D005260:Female; D006801:Humans; D020128:Inhibitory Concentration 50; D016778:Malaria, Falciparum / Q000469:parasitology*; D027425:ATP-Binding Cassette, Sub-Family C Proteins / Q000235:genetics*; D002052:Myanmar; D021261:Parasitic Sensitivity Tests / Q000379:methods; D010963:Plasmodium falciparum / Q000187:drug effects* / Q000235:genetics / Q000302:isolation & purification; D016133:Polymerase Chain Reaction; D012150:Polymorphism, Restriction Fragment Length; D020641:Polymorphism, Single Nucleotide; D011247:Pregnancy; D011803:Quinine / Q000494:pharmacology*; D017923:Sodium-Hydrogen Exchangers / Q000235:genetics*; D013785:Thailand
D000962:Antimalarials; D016054:DNA, Protozoan; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D011803:Quinine; D017923:Sodium-Hydrogen Exchangers; C513498:Mdr1 protein, Plasmodium falciparum; C069139:growth factor-activatable Na-H exchanger NHE-1