Uptake and efflux of chloroquine by chloroquine-resistant Plasmodium falciparum clones recently isolated in Africa (original) (raw)
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Biochemical Pharmacology, 1986
Chloroquine accumulation by human erythrocytes infected with nine different strains of the malarial parasite Plasmodium falciparum, which varied by greater than or equal to 20-fold sensitivity to the drug, was measured as a function of time and drug concentration. Although the kinetics of uptake were clearly quite complex in this system, at least two general phases were observed, an extremely rapid short phase (less than 30 sec), followed by a slower phase leading to steady state within 60 min. The concentration of chloroquine in the parasite food vacuole quickly exceeded 1 mM at 10(-6) M external drug concentration. Minor alkalinization of this organelle was observed during the first 30 sec; this pH was reduced progressively over time in a concentration-dependent manner. The rate of pH reduction was highest in the drug-sensitive strains. Neither the rate of chloroquine accumulation nor intracellular chloroquine concentrations at steady state could adequately differentiate sensitive from resistant strains. Higher intracellular drug concentrations were required to kill resistant versus sensitive strains, suggesting that a change in sensitivity to chloroquine of an intracellular effector is the mechanism of resistance. The rapid rate and extensive accumulation of chloroquine, and the lack of significant alkalinization, indicate that a new theory of the mechanism of antimalarial action of the drug is required.
Bulletin of the World Health Organization, 1991
The in vitro sensitivity to chloroquine and pyrimethamine of 19 culture-adapted southern African reference isolates of Plasmodium falciparum was determined using a 48-hour assay. Four isolates collected in KwaZulu, Natal, were sensitive to chloroquine, and one of these was sensitive to the drug in vivo. Eight isolates from KwaZulu or Mozambique were resistant to chloroquine in vitro. Six of these isolates were chloroquine-resistant in varying degrees in vivo. Four of five isolates from north-eastern Transvaal and two clinically chloroquine-resistant Malawian isolates were resistant to chloroquine in vitro. A wide range of pyrimethamine susceptibilities was detected (0.01 mumol/l to greater than 3.0 mumol/l), although most isolates were inhibited at 0.1 mumol/l, indicating a low level of resistance. These results confirm the presence of both chloroquine and pyrimethamine resistance in the endemic areas of South Africa. This has serious implications for the prophylaxis and treatment o...
Scientific Reports, 2018
Chloroquine (CQ) treatment failure in Plasmodium falciparum parasites has been documented for decades, but the pharmacological explanation of this phenotype is not fully understood. Current concepts attribute CQ resistance to reduced accumulation of the drug at a given external CQ concentration ([CQ]ex) in resistant compared to sensitive parasites. The implication of this explanation is that the mechanisms of CQ-induced toxicity in resistant and sensitive strains are similar once lethal internal concentrations have been reached. To test this hypothesis, we investigated the mechanism of CQ-induced toxicity in CQ-sensitive (CQS) versus CQ-resistant (CQR) parasites by analyzing the time-course of cellular responses in these strains after exposure to varying [CQ]ex as determined in 72 h toxicity assays. Parasite killing was delayed in CQR parasites for up to 10 h compared to CQS parasites when exposed to equipotent [CQ]ex. In striking contrast, brief exposure (1 h) to lethal [CQ]ex in C...
Biochemistry, 2005
Resistance to the antimalarial drug chloroquine has been linked with polymorphisms within a gene termed pfcrt in the human malarial parasite Plasmodium falciparum, yet the mechanism by which this gene confers the reduced drug accumulation phenotype associated with resistance is largely unknown. To investigate the role of pfcrt in mediating chloroquine resistance, we challenged P. falciparum clones differing only in their pfcrt allelic form with the "varying-trans" procedure. In this procedure, movement of labeled substrate across a membrane is measured when unlabeled substrate is present on the trans side of the membrane. If a transporter is mediating the substrate flow, a stimulation of cis-to-trans movement may be observed with increasing concentrations of trans substrate. We present evidence for an association of those pfcrt alleles found in chloroquine-resistant P. falciparum strains with the phenomenon of stimulated chloroquine accumulation under varying-trans conditions. Such an association is not seen with polymorphisms within pfmdr1, which encodes a homologue of the human multidrug resistance efflux pump. Our data are interpreted in terms of a model in which pfcrt is directly or indirectly involved in carrier-mediated chloroquine efflux from resistant cells.
Comparative assessment of Plasmodium falciparum sensitivity to chloroquine and amodiaquine in vitro
African Journal of …, 2011
The in vitro sensitivity of Plasmodium falciparum isolates to chloroquine and amodiaquine were assessed in children with symptomatic uncomplicated malaria in Ibadan, Nigeria. The WHO standard in vitro micro-test method was employed for the study. A total of one hundred and two children were admitted into the study. Inhibition of schizont maturation at varying concentration of the study drugs was used as an index for drug activity. Effective concentrations by probit analysis of log dose/response for 50, 90 and 99% (EC 50 , EC 90 and EC 99 ) inhibition were 0.37, 2.38 and 5.76 mol/l, respectively, for chloroquine and 0.06, 0.26 and 0.59 mol/l, respectively, for amodiaquine. Forty isolates of P. falciparum were tested for chloroquine sensitivity. Eighty percent (32/40) showed schizont maturation at 1.6 mol/l and were classified as resistant, while 39% (14/36) of isolates tested for amodiaquine matured at 0.4 mol/l and were also classified as resistant. This shows that amodiaquine is significantly more effective than chloroquine. While this data provides no absolute demonstration of chloroquine resistance, it underlies the need for continuous monitoring of the susceptibility of P. falciparum to chloroquine in southwest Nigeria.
Detection of in Vivo Chloroquine Resistance in Plasmodium Falciparum in Chennai, India
The American journal of tropical medicine and hygiene
Resistance to chloroquine (CQ) in Plasmodium falciparum is one of the main causes of the widespread resurgence of malaria in India and a challenge to the effective control of the disease. In the pilgrim centre of Rameswaram Island, malaria has persisted despite the various control measures undertaken over the years. When CQ resistance in Rameswaram was investigated in vivo, recrudescent parasitaemias were observed in 25 (58%) of the 43 study subjects who were given CQ and completed follow-up, all occurring between days 10 and 28 (late treatment failures). The results of the msp 1 , msp 2 and glurp genotyping of paired samples of P. falciparum, collected on day 0 and the day of recrudescence from 23 of the apparent treatment failures, indicated that 21 (91%) of the 23 were probably true treatment failures. All of the paired samples harboured parasites with the K76T mutation in their pfcrt genes, and subsequent sequencing of nine day-0 samples revealed the SVMNT haplotype in all nine. This is the first report of in-vivo drug resistance in P. falciparum from Rameswaram Island. Such resistance, which is probably the result of the indiscriminate use of CQ and/or the import of malaria from mainland India, warrants a change in the drug regimen used locally for the first-line treatment of uncomplicated, P. falciparum malaria, to make treatment more effective and slow the development and spread of more foci of CQ resistance.
Molecular Microbiology, 2007
The mechanism underpinning chloroquine drug resistance in the human malarial parasite Plasmodium falciparum has remained controversial. Currently discussed models include a carrier or a channel for chloroquine, the former actively expelling the drug, the latter facilitating its passive diffusion, out of the parasite's food vacuole, where chloroquine accumulates and inhibits haem detoxification. Here we have challenged both models using an established trans-stimulation efflux protocol. While carriers may demonstrate trans-stimulation, channels do not. Our data reveal that extracellular chloroquine stimulates chloroquine efflux in the presence and absence of metabolic energy in both chloroquine-sensitive and -resistant parasites, resulting in a hyperbolic increase in the apparent initial efflux rates as the concentration of external chloroquine increases. In the absence of metabolic energy, the apparent initial efflux rates were comparable in both parasites. Significant differences were only observed in the presence of metabolic energy, where consistently higher apparent initial efflux rates were found in chloroquine-resistant parasites. As trans-stimulation is characteristic of a carrier, and not a channel, we interpret our data in favour of a carrier for chloroquine being present in both chloroquine-sensitive and -resistant parasites, however, with different transport modalities.