Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0024530 (malaria)
 44,886 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The mutant genotype at codon 76 of the pfcrt gene (T76) has been proposed as a molecular marker for surveillance of chloroquine (CQ)-resistant Plasmodium falciparum malaria but this proposal has not been validated by population-based surveys. In 1998-99, in 6 Ugandan sentinel sites, the prevalence of P. falciparum infections with the T76 genotype and the level of CQ use were measured by community surveys, and CQ resistance was determined by in-vivo tests on 6-59-month-old children with clinical malaria. The prevalence of T76 was not related to the overall clinical (early and late treatment failure: ETF + LTF; r = 0.14, P = 0.78) or parasitological (RI + RII + RIII; r = 0.17, P = 0.73) CQ resistance. However, the percentage of individuals carrying only infections with the T76 genotype (T76 alone) increased with increasing ETF (r = 0.76, P = 0.07) and type RIII parasitological failure (r = 0.69, P = 0.12). Similarly, the ratio between T76 and K76 (the wild type) prevalences (T76/K76) was strongly and positively correlated with ETF (r = 0.85, P = 0.03) and RIII (r = 0.82, P = 0.04). Moreover, T76 alone (r = 0.90, P = 0.01) as well as T76/K76 (r = 0.90, P = 0.01) significantly increased with increasing community CQ use. T76 alone and T76/K76 can be useful markers to estimate the ETF and RIII prevalence as well as the amount of CQ use in the community.
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PMID:Role of the pfcrt codon 76 mutation as a molecular marker for population-based surveillance of chloroquine (CQ)-resistant Plasmodium falciparum malaria in Ugandan sentinel sites with high CQ resistance. 1247 88

Analysis of imported malaria in travelers may represent a novel surveillance system for drug-resistant malaria. We analyzed consecutive falciparum malaria isolates from Canadian travelers from 1994 to 2000, for polymorphisms in pfcrt, dhfr, and dhps linked to chloroquine and pyrimethamine/sulfadoxine resistance. Forty percent of isolates possessed the K76 pfcrt allele, suggesting that many imported falciparum infections are still responsive to chloroquine. Travelers who had recently taken chloroquine had a significantly increased risk of harboring isolates with pfcrt resistance alleles (odds ratio = 4.47; p=0.03). The presence of two or more mutations in dhfr or dhps was found in 64.8% (95% confidence interval [CI] 54.6 to 73.9) and in 30.4% (95% CI 21.7 to 40.3) of isolates, respectively, and increased significantly over the course of the study. These molecular markers indicate that pyrimethamine/sulfadoxine resistance is increasing and is now too high to rely on this drug as a routine therapeutic agent to treat malaria in travelers.
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PMID:A molecular surveillance system for global patterns of drug resistance in imported malaria. 1253 79

The relationship between Pfcrt T76 and Pfmdr-1 Y86 mutations in Plasmodium falciparum was explored in samples from patients with uncomplicated malaria and tested in vitro and in vivo with chloroquine (CQ) in Burkina Faso. The two mutations were strongly related. The Pfcrt T76 mutation was found in 82% of the samples having the Pfmdr-1 Y86 mutation too (odds ratio (OR)=4.8 [95% CI: 1.7-13.3]; P=0.002). However, only half (16/34) of samples with Pfcrt T76 mutation had also the Pfmdr-1 Y86 mutation. The latter was apparently associated with in vitro resistance (OR=4.8 [95% CI: 1.4-16.5]; P=0.01) but such association disappeared (P=0.77) after adjusting for the presence of the Pfcrt T76 mutation. This suggests that the occurrence of the Pfmdr-1 Y86 mutation is dependent on that of Pfcrt T76 mutation and could explain previous reports linking the Pfmdr-1 Y86 mutation with CQ resistance (CQR). The isolates carrying both the Pfcrt K76 and Pfmdr-1 N86 alleles (wild/wild (WW)) and the single mutant Pfmdr-1 Y86 (WM) had the lowest IC50 geometric mean (GMIC50) values, while those carrying both Pfcrt T76/Pfmdr-1 Y86 alleles (mutant/mutant (MM)), and the single mutant Pfcrt T76 (MW) had the highest. Among pre-treatment samples there was a strong linkage disequilibrium with an excess of MM and WW and a deficit of single mutants (MW and WM), suggesting that parasite fitness is higher for the former and lower for the latter.
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PMID:Relationship between the Pfcrt T76 and the Pfmdr-1 Y86 mutations in Plasmodium falciparum and in vitro/in vivo chloroquine resistance in Burkina Faso, West Africa. 1463 90

Over 3 years (1999-2002), 305 cases of falciparum malaria were diagnosed in Toulouse, France. After retrospective analysis, only 131 patients entered the study. The diagnosis of malaria was ensured by optical methods (QBC then thin smear examination), the results of which were checked from 1999 to mid-2001 by a conventional PCR method, replaced at that time by a real-time PCR using LightCycler. To detect Pfcrt K(lysine)76T(threonine) mutation, a real-time PCR assay was developed, the sensitivity of which was one mutated parasite per microliter, or 2% mutant asexual forms in a mixed population. Eighty-one patients harbored only mutant parasites, and 11 had a K76K/T76-mixed infection. The distribution of K76T mutation was significantly affected by the use of a chloroquine + proguanil (CQ + P) prophylaxis (P = 0.00037). Among 96 subjects who had no exposure to chloroquine or any history of CQ + P prophylaxis, the mean parasitemia was higher in K76-infected patients (P = 0.038), which suggested a lack of virulence in the falciparum mutant population.
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PMID:Pfcrt K76T mutation and its associations in imported Plasmodium falciparum malaria cases. 1537 34

Malaria is one of the major parasitic diseases. Current treatment of malaria is seriously hampered by the emergence of drug resistant cases. A once-effective drug chloroquine (CQ) has been rendered almost useless. The mechanism of CQ resistance is complicated and largely unknown. Recently, a novel transmembrane protein, Plasmodium falciparum chloroquine resistance transporter (PfCRT), has fulfilled all the requirements of being the CQ resistance gene. In order to elucidate the mechanism how PfCRT mediates CQ resistance, we have cloned the cDNA from a CQ sensitive parasite (3D7) and tried to express it in Pichia pastoris (P. pastoris) but with unsuccessful results due to AT-rich sequences in the malaria genome. We have therefore, based on the codon usage in P. pastoris, chemically synthesized a codon-modified pfcrt with an overall 55% AT content. This codon-modified pfcrt has now been successfully expressed in P. pastoris. The expressed PfCRT has been purified with immuno metal affinity chromatography (IMAC) and then reconstituted into proteoliposome. It was found that proteoliposomes have a saturable, concentration and time-dependent CQ transport activity. In addition, we found that proteoliposomes with resistant PfCRT(r) (K76T or K76I) showed an increased CQ transport activity compared to liposomes with lipid alone, or proteoliposomes reconstituted with sensitive PfCRT(s) (K76) protein. This activity could be inhibited by nigericin and decreased with the removal of Cl(-). This work suggests that PfCRT is mediating CQR in P. falciparum by virtue of its changes in CQ transport activity depending on pH gradient and chloride ion in the food vacuole.
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PMID:Functional reconstitution of purified chloroquine resistance membrane transporter expressed in yeast. 1688 78

The Plasmodium falciparum chloroquine resistance transporter (Pfcrt) K76T mutation and haplotype (amino acids 72-76) were analyzed as markers of chloroquine (CQ) resistance in the blood samples of patients from two sites of different intensities of malaria transmission (high, n=70; low, n=68) in Sundergarh district of Orissa, India and correlated with the in-vivo response. Early treatment failure (ETF) was significantly more frequent in the high endemic area (32.9 vs. 7.4%, P<0.001), with children below 5 years suffering more. A high frequency of pfcrt K76T mutation was observed in both the areas (87.1 vs. 79.4%, P=0.22). Patients carrying pfcrt 76T were the most likely to develop ETF (odds ratio 36; 95% CI 3.35-1653.3; P<0.001). The ratio of 76T:K76 was 22:9 and 11:14, respectively, in high and low endemic areas (odds ratio 3.1; 95% CI 0.9-11.03; P=0.04), which may be used as a measure of drug pressure. Sequences of pfcrt codons 72-76 showed 16 of the CQ-resistant haplotypes to be SVMNT, 5 CVMNT and 12 CVIET. The CQ-sensitive haplotypes were mostly CVMNK in 10 samples; CVIEK in 2 samples. Both Southeast Asian and South American haplotypes were present, with the latter predominating.
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PMID:Pfcrt haplotypes and in-vivo chloroquine response in Sundergarh district, Orissa, India. 1742 14

The development of chloroquine as an antimalarial drug and the subsequent evolution of drug resistant Plasmodium strains had major impacts on global public health in the 20th century. In P. falciparum, the cause of the most lethal human malaria, chloroquine resistance is linked to multiple mutations in PfCRT, a protein that likely functions as a transporter in the parasite's digestive vacuole membrane. Rapid diagnostic assays for PfCRT mutations are already employed as surveillance tools for drug resistance. However, several reports have been published demonstrating cases with CO resistance. Sporadic cases have been reported as well as one large scale study demonstrated 12.4% resistance. However, all these reports were based on treatment failure (in vivo). rather than in vitro or molecular bases. Evidence suggests a crucial role for a point mutation in the P. falciparum chloroquine resistance transporter (pfcrt) gene on chromosome 7 in conferring CQ resistance. The mutation in the K76 codon in 3 cases out of 60 (5%) using ApoI restriction enzyme was detected. Although the percentage of drug resistance was not quite disturbing, but represented the possible establishment of chloroquine-resistant P. falciparum in Saudi Arabia, or the beginning of resistant strains by labors coming from abroad. Cross-border importation of resistant strains from neighboring countries must be considered. In vivo tests must be conducted parallel with the molecular markers to estimate more precisely the actual prevalence of resistance. Validation of molecular markers is urgently required and needs strong collaborative partnerships between subregional and regional networks.
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PMID:Molecular surveillance of Plasmodium falciparum chloroquine resistance transporter variant T76 in Jazan area, Kingdom of Saudi Arabia. 1979 57

Ferroquine (FQ), a chloroquine (CQ) analog, is being developed to treat persons with Plasmodium falciparum malaria. In 146 P. falciparum field isolates from western Kenya, we measured 50% inhibitory concentrations (IC(50); nM) of CQ and FQ by a SYBR Green I in vitro assay. Reference clones included W2 (CQ resistant) and D6 (CQ sensitive). Mutation analysis was done for P. falciparum CQ-resistance transporter gene (Pfcrt K76T). Median IC(50) values for FQ were lower than CQ for field isolates and the W2 clone (both P < 0.05). The Pfcrt mutation (76T), which was detected in > 80% of isolates, conferred higher CQ IC(50) values (P < 0.05) and modestly lower FQ IC(50) values (P < 0.05), versus Pfcrt wild type (K76). FQ is more potent than CQ against CQ-resistant P. falciparum field isolates and the W2 clone, and is less affected by Pfcrt 76T. These findings support the notion that FQ could be useful in treating persons with P. falciparum malaria.
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PMID:Inhibitory activity of ferroquine, versus chloroquine, against western Kenya Plasmodium falciparum field isolates determined by a SYBR Green I in vitro assay. 2214 31

Chloroquine (CQ) remains the first line drug for the prevention and treatment of malaria in Malaysia in spite of the fact that resistance to CQ has been observed in Malaysia since the 1960s. CQ-resistance is associated with various mutations in pfcrt, which encodes a putative transporter located in the digestive vacuolar membrane of P. falciparum. Substitution of lysine (K) to threonine (T) at amino acid 76 (K76T) in pfcrt is the primary genetic marker conferring resistance to CQ. To determine the presence of T76 mutation in pfcrt from selected areas of Kalabakan, Malaysia 619 blood samples were screened for P. falciparum, out of which 31 were positive. Blood samples were collected on 3 MM Whatman filter papers and DNA was extracted using QIAmp DNA mini kit. RFLP-PCR for the detection of the CQ-resistant T76 and sensitive K76 genotype was carried out. Twenty-five samples were shown to have the point mutation in pfcrt whereas the remaining samples were classified as CQ-sensitive (wild-type). In view of the fact that CQ is the first line anti-malarial drug in Malaysia, this finding could be an important indication that treatment with CQ may no longer be effective in the future.
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PMID:High prevalence of pfcrt K76t mutants among Plasmodium falciparum isolates from Sabah, Malaysia. 2229 99

The Cinchona alkaloids are quinoline aminoalcohols that occur as diastereomer pairs, typified by (-)-quinine and (+)-quinidine. The potency of (+)-isomers is greater than the (-)-isomers in vitro and in vivo against Plasmodium falciparum malaria parasites. They may act by the inhibition of heme crystallization within the parasite digestive vacuole in a manner similar to chloroquine. Earlier studies showed that a K76I mutation in the digestive vacuole-associated protein, PfCRT (P. falciparum chloroquine resistance transporter), reversed the normal potency order of quinine and quinidine toward P. falciparum. To further explore PfCRT-alkaloid interactions in the malaria parasite, we measured the in vitro susceptibility of eight clonal lines of P. falciparum derived from the 106/1 strain, each containing a unique pfcrt allele, to four Cinchona stereoisomer pairs: quinine and quinidine; cinchonidine and cinchonine; hydroquinine and hydroquinidine; 9-epiquinine and 9-epiquinidine. Stereospecific potency of the Cinchona alkaloids was associated with changes in charge and hydrophobicity of mutable PfCRT amino acids. In isogenic chloroquine-resistant lines, the IC(50) ratio of (-)/(+) CA pairs correlated with side chain hydrophobicity of the position 76 residue. Second-site PfCRT mutations negated the K76I stereospecific effects: charge-change mutations C72R or Q352K/R restored potency patterns similar to the parent K76 line, while V369F increased susceptibility to the alkaloids and nullified stereospecific differences between alkaloid pairs. Interactions between key residues of the PfCRT channel/transporter with (-) and (+) alkaloids are stereospecifically determined, suggesting that PfCRT binding plays an important role in the antimalarial activity of quinine and other Cinchona alkaloids.
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PMID:Mutation in the Plasmodium falciparum CRT protein determines the stereospecific activity of antimalarial cinchona alkaloids. 2286 67


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