RESUMO
Plasmodium falciparum with reduced sensitivity to artemisinin derivatives has been observed in endemic areas, but the molecular mechanisms for this reduced sensitivity remain unclear. We evaluated the association between in vitro susceptibility of P. falciparum isolates obtained from southwest Nigeria and polymorphisms in selected putative transporter genes (PFE0775C, PF13_0271, pfmrp1, pfcrt, and pfmdr1). Modified schizont inhibition assay was used to determine the in vitro parasite susceptibility to artemether (ATH). Polymorphisms in selected genes were detected by polymerase chain reaction followed by direct DNA sequencing. The half-maximal inhibitory concentration (IC(50)) geometric mean (GM) for all P. falciparum isolates was 1.78 nM (range, 0.03-10.43 nM). Polymorphisms at codons 241, 86, and 76 of PFE0775C, pfmdr1, and pfcrt genes, respectively, were associated with reduced susceptibility to ATH. A new S263P single-nucleotide polymorphism on the PFE0775C gene was also detected in 27% of the isolates. Patient isolates harboring V241L or S263P polymorphisms on the PFE0775C gene showed increased IC(50) (GM: 3.08 nM and 1.79 nM, respectively). Plasmodium falciparum isolates harboring mutant Y86 pfmdr1 and P263 PFE0775C alleles showed a 2.5-5.5-fold increase in ATH IC(50.) This study shows that polymorphisms on the PFE0775C and pfmdr1 genes are associated with reduced sensitivity to ATH in fresh isolates of P. falciparum from Nigeria.
Assuntos
Antimaláricos/farmacologia , Artemisininas/farmacologia , Proteínas de Transporte/genética , Resistência a Medicamentos/genética , Plasmodium falciparum/efeitos dos fármacos , Polimorfismo Genético , Artemeter , Proteínas de Transporte/metabolismo , Criança , DNA de Protozoário/genética , DNA de Protozoário/isolamento & purificação , Regulação da Expressão Gênica , Humanos , Concentração Inibidora 50 , Testes de Sensibilidade Parasitária/métodos , Reação em Cadeia da Polimerase/métodos , Proteínas de Protozoários/genética , Proteínas de Protozoários/metabolismoRESUMO
The effect of antimalarial drug selection on pfcrt and pfmdr1 polymorphisms in Plasmodium falciparum isolates from two distinct geographical locations was determined in 70 and 18 P. falciparum isolates from Nigeria and Brazil, respectively, using nested polymerase chain reaction and direct DNA sequencing approaches. All isolates from Brazil and 72% from Nigeria harbored the mutant SVMNT and CVIET pfcrt haplotype, respectively. The pfcrt CVMNT haplotype was also observed in (7%) of the Nigerian samples. One hundred percent (100%) and 54% of the parasites from Brazil and Nigeria, respectively, harbored wild-type pfmdr1Asn86. We provide first evidence of emergence of the CVMNT haplotype in West Africa. The high prevalence of pfcrt CVIET and SVMNT haplotypes in Nigeria and Brazil, respectively, is indicative of different selective pressure by chloroquine and amodiaquine. Continuous monitoring of pfcrt SVMNT haplotype is required in endemic areas of Africa, where artesunate-amodiaquine combination is used for treatment of acute uncomplicated malaria.
Assuntos
Antimaláricos/uso terapêutico , Proteínas de Membrana Transportadoras/genética , Proteínas Associadas à Resistência a Múltiplos Medicamentos/genética , Plasmodium falciparum/efeitos dos fármacos , Polimorfismo de Nucleotídeo Único , Proteínas de Protozoários/genética , Alelos , Amodiaquina/uso terapêutico , Artemisininas/uso terapêutico , Brasil/epidemiologia , Variações do Número de Cópias de DNA , Combinação de Medicamentos , Genótipo , Haplótipos , Humanos , Malária Falciparum/tratamento farmacológico , Malária Falciparum/epidemiologia , Proteínas de Membrana Transportadoras/metabolismo , Proteínas Associadas à Resistência a Múltiplos Medicamentos/metabolismo , Família Multigênica , Mutação , Nigéria/epidemiologia , Plasmodium falciparum/genética , Plasmodium falciparum/isolamento & purificação , Reação em Cadeia da Polimerase , Proteínas de Protozoários/metabolismo , Análise de Sequência de DNARESUMO
Resistance in Plasmodium falciparum to amodiaquine (AQ) can be reversed in vitro with with antihistaminic and tricyclic antidepressant compounds, but its significance in vivo is unclear. The present report presents the enhancement of the antimalarial efficacy of AQ by chlorpheniramine, an H1 receptor antagonist that reverses chloroquine (CQ) resistance in vitro and enhances its efficacy in vivo, in five children who failed CQ and/or AQ treatment, and who were subsequently retreated and cured with a combination of AQ plus CP, despite the fact that parasites infecting the children harboured mutant pfcrtT76 and pfmdr1Y86 alleles associated with AQ resistance. This suggests a potential clinical application of the reversal phenomenon.
Assuntos
Amodiaquina/administração & dosagem , Antimaláricos/administração & dosagem , Cloroquina/administração & dosagem , Clorfeniramina/administração & dosagem , Antagonistas dos Receptores Histamínicos H1/administração & dosagem , Malária Falciparum/tratamento farmacológico , Adolescente , Animais , Criança , Pré-Escolar , Sinergismo Farmacológico , Quimioterapia Combinada , Humanos , Lactente , Malária Falciparum/parasitologia , Proteínas de Membrana Transportadoras/genética , Plasmodium falciparum/efeitos dos fármacos , Plasmodium falciparum/genética , Proteínas de Protozoários/genéticaRESUMO
Resistance in Plasmodium falciparum to amodiaquine (AQ) can be reversed in vitro with with antihistaminic and tricyclic antidepressant compounds, but its significance in vivo is unclear. The present report presents the enhancement of the antimalarial efficacy of AQ by chlorpheniramine, an H1 receptor antagonist that reverses chloroquine (CQ) resistance in vitro and enhances its efficacy in vivo, in five children who failed CQ and/or AQ treatment, and who were subsequently retreated and cured with a combination of AQ plus CP, despite the fact that parasites infecting the children harboured mutant pfcrtT76 and pfmdr1Y86 alleles associated with AQ resistance. This suggests a potential clinical appliation of the reversal phenomenon.