Chloroquine-resistant Malaria Research Articles

In vitro antimalarial activity of chalcones and their derivatives.

A series of chalcones and their derivatives have been synthesized and identified as novel potential antimalarials using both molecular modeling and in vitro testing against the intact parasite. A large number of chalcones and their derivatives were prepared using one-step Claisen-Schmidt condensations of aldehydes with methyl ketones. These condensates were screened in vitro against both chloroquine-sensitive and chloroquine-resistant strains of Plasmodium falciparum and shown to be active at concentrations in the nanomolar range. The most active chalcone derivative, 1-(2,5-dichlorophenyl)-3-(4-quinolinyl)-2-propen-1-one (7), had an IC50 value of 200 nM against both a chloroquine-resistant strain (W2) and a chloroquine-sensitive strain (D6). The resistance indexes for all compounds were substantially lower than for chloroquine, suggesting that this series will be active against chloroquine-resistant malaria. Structure-activity relationships (SAR) of the chalcones in the context of a homology-based model structure of the malaria trophozoite cysteine protease, the most likely target enzyme, are presented.

A mutation-specific PCR system to detect sequence variation in the dihydropteroate synthetase gene of Plasmodium falciparum

Sulphur-based antimalarial drugs targeted at dihydropteroate synthetase (DHPS) are frequently used in synergistic combination with inhibitors of dihydrofolate reductase (DHFR) to combat chloroquine-resistant malaria. We have previously shown that lines of Plasmodium falciparum resistant to the most commonly used sulpha drug, sulphadoxine, carry point mutations in the DHPS coding region, relative to the sequence of sensitive strains (Brooks et al., Eur. J. Biochem. 224 (1994) 397–405). We have now developed PCR diagnostic assays based on allele-specific amplification that are able to detect such mutations. The four tests described can reliably discriminate all of the mutations observed to alter codons 436, 581 and 613, yielding allele-specific amplification products of different sizes in each case. Moreover, by careful adjustment of primer length and the degree of mismatch to target and non-target alleles, we were able to standardise all four tests to a single set of PCR conditions, allowing all possible mutations to be monitored simultaneously on one thermocycler. These assays should prove invaluable in further assessing the contribution of specific base changes in the DHPS gene of the parasite to the sulphadoxine resistance phenotype and to the clinical failure of the sulphadoxine/pyrimethamine combination Fansidar.

Child health in Malaysia.

In Malaysia the Ministry of Healths (MOH) general hospitals in each state and some larger district hospitals provide pediatric specialty services. The countrys only childrens hospital provides pediatric subspecialty services and is the ultimate referral center for Malaysia. MOH operates maternal and child health clinics. Common child health problems are communicable diseases and malnutrition. Emerging problems are HIV infection chloroquine resistant malaria severe dengue (encephalopathy renal failure fulminant hepatopathy) gonococcal ophthalmia neonatorum and asthma. Child morbidity and other problems related to social changes include child physical and sexual abuse accidents runaways and drug abuse. MOH child-centered prevention activities are primary immunization vitamin K prophylaxis against hemorrhagic disease of the newborn and glucose-6-phosphate dehydrogenase screening in newborns to prevent favism. Malaysia will soon expand the child health card system nationwide. This system allows the parents to record and monitor their childs growth development and immunization status. Malaysia promotes the baby-friendly hospital concept to encourage breast feeding. New technologies are bone transplant and kidney transplant capabilities availability of new drugs (e.g. interferon) magnetic resonance imaging at a MOH hospital and neonatal intensive care units. MOH operates a quality assurance program. The Malaysian Paediatric Association oversees and advises on the quality of pediatric care in the country. The larger cities have the best health facilities. Families only take children to the hospital after treatment by traditional healers has failed. Pediatric research is commonplace. In 1992 MOH hospitals only had 48 pediatricians compared to around 100 in private practice and teaching hospitals. There is also a shortage of nurses. Some private hospitals have begun training their own nurses. In the past only MOH and university hospitals trained them.

Anti-malarial drug development using models of enzyme structure

Background: The trophozoite stage of the malaria parasite infects red blood cells. During this phase of their lifecycle, the parasites use hemoglobin as their principal source of amino acids, using a cysteine protease to degrade it. We have previously reported a three-dimensional model of this cysteine protease, based on the structures of homologous proteases, and the use of the program DOCK to identify a ligand for the malaria protease. Results: Here we describe the design of improved ligands starting from this lead. Ligand design was based on the predicted configuration of the lead compound docked to the model three-dimensional structure of the protease. The lead compound has an IC 50 of 6 μM, and our design/synthesis strategy has resulted in increasingly potent derivatives that block the ability of the parasites to infect and/or mature in red blood cells. The two best derivatives to date have IC 50s of 450 nM and 150 nM. Conclusions: A new class of anti-malarial chemotherapeutics has resulted from a computational search that was based on a model of the target protease. Despite the lack of a detailed experimental structure of the target enzyme or the enzyme-inhibitor complex, we have been able to identify compounds with increased potency. These compounds approach the activity of chloroquine (IC 50 = 20 nM), but have a distinct mechanism of action. This series of compounds could thus lead to new therapies for chloroquine-resistant malaria.

Comparison of Micronized Halofantrine with Chloroquine-Antibiotic Combinations for Treating Plasmodium falciparum Malaria in Adults from Gabon

Multidrug resistance of Plasmodium falciparum is spreading throughout Africa. In Lambarene, Gabon where chloroquine-resistant malaria is prevalent, a randomized comparative trial with three regimens for treating P. falciparum malaria in adults was performed. One hundred two patients evaluated received either a new micronized formulation of halofantrine (8 mg/kg every 6 hr in three doses) (group H) or chloroquine (25 mg/kg for a 48-hr period) plus clindamycin (5 mg/kg every 12 hr in six doses) (group CC1), or chloroquine (as above) plus doxycycline (2 mg/kg every 12 hr in six doses) (group CD). All treatment regimens were well-tolerated. In group H, 100% of the patients were cured, and in group CC1, 97% of the patients were cured by day 28 of follow-up. In group CD, a significantly lower cure rate of 75% (P < 0.01) and a slower parasite clearance was observed, but only low grade (RI) resistance occurred.

Mefloquine pharmacokinetics in pregnant women with acute falciparum malaria

Mefloquine has an established place in the treatment of chloroquine-resistant falciparum malaria. To investigate mefloquine pharmocokinetics in pregnancy, 9 untreated pregnant women aged 16–33 years and 8 non-pregnant females aged 16–38 years received an average of 15 (range 13–19) mg mefloquine/kg body-weight as single-dose treatment for uncomplicated falciparum malaria. Regular blood samples were taken during the subsequent 48 h and then intermittently for 3–26 d after treatment. Whole blood mefloquine concentrations were analysed by high-performance liquid chromatography and a one-compartment open pharmacokinetic model was fitted to the data. Peak mefloquine concentrations were significantly lower in the pregnant patients (median [range]; 1257 [650–1584] vs. 1617 [1051–3111] ng/mL) and the total apparent volume of distribution ( V d f ) was larger (10·8 [8·3–26·1] vs. 10·0 [4·8–13·9] L/kg; P < 0·05 in each case), consistent with an expanded circulating blood volume and increased tissue binding in pregnancy. There was no significant difference between the 2 groups in half-times of absorption or elimination ( P > 0·1), and systemic clearance rates were also similar. These results suggest that pregnant patients need larger doses of mefloquine than non-pregnant women to achieve comparable blood levels, an important consideration in areas where multi-drug resistant falciparum malaria is emerging.

1993 Sir Henry Wellcome Medal and Prize Recipient

Mefloquine is an antimalarial drug developed by the U.S. Army Antimalarial Drug Program in conjunction with the World Health Organization and Hoffmann-La Roche to address the problem of chloroquine-resistant falciparum malaria encountered during the Vietnam War. Despite the expenditure of millions of dollars over a 20-year period, it is unlikely that mefloquine will ever be used for U.S. soldiers deployed to South East Asia. Although mefloquine met the specifications set by its developers, its usefulness is now limited by the rapid evolution of drug resistance following its release to the civilian population. Drug development for particular military needs was compromised by a rapid biological response from the parasite and commercial concerns. In an era of shrinking military budgets, military drug development programs will by necessity be more resource constrained, thus yielding fewer new drugs per decade. In the short-term, emphasis should be directed toward adapting available antimicrobial drugs for antimalarial purposes.

Treatment of chloroquine-resistant Plasmodium falciparum infections with clindamycin hydrochloride in Dili, East Timor, Indonesia

The objectives of this study were to determine the efficacy and safety of clindamycin hydrochloride, 300 mg twice daily for 5 days, in the treatment of patients with chloroquine-resistant falciparum malaria in Dili, East Timor, Indonesia. The patients were hospitalized for 28 days and instructed to remain in the screened wards, especially in the late afternoon and night. Thirty-four patients in the clindamycin group and five patients in the sulfadoxine-pyrimethamine group completed the 28-day observation period. Plasmodium vivax was found during the observation period in four patients in the clindamycin group, however. Therefore, 30 patients in the clindamycin group and five patients in the sulfadoxine-pyrimethamine group remained parasite-free until discharge. In the clindamycin group, parasite clearance was obtained between days 3 and 6, with 43.3% cleared by day 4 and a cumulative total of 66.6% by day 5. In the sulfadoxin-pyrimethamine group, parasite clearance was obtained by day 3. After discharge, 4 patients in the clindamycin group returned with malaria: 1 returned on day 37 with P vivax and P falciparum infection; 1 returned on day 50 with a mixed infection of P vivax and Plasmodium falciparum; 1 returned on day 58 with a P falciparum infection; and 1 returned on day 77 with a P vivax infection. Although reinfections were considered in these patients, late relapses could not be entirely eliminated. In the clindamycin group, a temporary increase of parasite densities from day 0 levels was seen in 11 patients but all decreased to 0 levels between days 3 and 6. The results of this study indicate that clindamycin can be used as an alternative drug in the treatment of chloroquine-resistant P falciparum infections.

Antimalarial 4-aminoquinolines: mode of action and pharmacokinetics.

In the last ten years, the widespread increase in Plasmodium falciparum resistance to chloroquine has prompted research into antimalarial 4-aminoquinolines, empirically used up to now. The mechanism of action of 4-aminoquinolines is characterized by the concentration of the drug in the digestive vacuole of the intraerythrocytic parasite. Various hypotheses have been advanced to explain the specificity of action on the parasite; the most recent one is the inhibition of the haem polymerase of the parasite, leading to the accumulation of soluble haem toxic for the parasite. Chloroquine-resistant parasites accumulate the drug to a lesser extent than do sensitive parasites. Recent findings have shown that chloroquine resistance can be reversed by various tricyclic drugs, which are able to restore the effective concentrations of chloroquine in the infected erythrocyte, but intrinsic mechanisms of action of these reversing agents are unknown. Four-aminoquinolines are extensively distributed in tissues and characterized by a long elimination half-life. Despite similarities in their chemical structures, these drugs show differences in their biotransformation and routes of elimination: chloroquine is partly metabolized into a monodesethylderivative and eliminated mainly by the kidney. In contrast, amodiaquine is a prodrug and amopyroquine is poorly metabolized; both drugs are excreted mainly in the bile. The understanding of the pharmacokinetics of 4-aminoquinolines has led to an improvement in empirically defined therapeutic regimens. Finally, the emergence of severe adverse-effects after prolonged prophylaxis with amodiaquine and the lack of cross resistance of Plasmodium falciparum between chloroquine and amopyroquine, have led to a proposal for the use of intramuscular amopyroquine as an alternative for the treatment of chloroquine-resistant malaria.

Effect of Nifedipine on Oxidative Damage of Erythrocytes in Plasmodium berghei-Infected Mice

It is known that the calcium channel blocker (CCB), nifedipine, can inhibit phagocyte oxidative burst in Plasmodium berghei-infected mice. The extent of immunopathological changes as seen by the course of infection and membrane lipid peroxidation in nifedipine-treated mice was examined in comparison with untreated mice at different parasite loads. The glutathione antioxidant system was also studied in these animals to assess its capacity to neutralize reactive oxygen species (ROS) in infected erythrocytes. The survival period of nifedipine-treated, infected mice decreased significantly. It was observed that the accumulation of reduced glutathione was greater and the decrease in glutathione peroxidase activity was less marked in drug-treated animals, suggesting better protection of the parasites against oxidative injury. The accumulation of the lipid peroxidation product, malonyldialdehyde was significantly lower in nifedipine-treated animals at all parasitemia levels studied, indicating decreased ROS generation and parasite damage. These observations reveal the shortcomings of using CCB to reverse the chloroquine resistance in malaria as this would minimize oxidative damage of parasitized red cells and phagocyte-mediated parasite killing.

Curing of Chloroquine-Resistant Malaria with Clindamycin

A randomized comparative trial for treating adult patients with Plasmodium falciparum malaria was performed in Lambarene, Gabon. Forty-two patients received chloroquine (25 mg/kg for 48 hr) and 38 patients received clindamycin (5 mg/kg twice a day, for five days). Chloroquine treatment cured 15 patients (36%). Twenty patients (48%) showed recrudescent malaria by day 28 of follow-up (RI resistance) and seven patients (17%) showed persistent parasitemia after chloroquine treatment (RII/III resistance). In contrast, clindamycin treatment cured 37 of 38 patients (97%) and only one (3%) showed a recrudescence by day 28 (P < 0.001). Although the parasite clearance time was significantly longer after clindamycin treatment (median five days, range 3-6) than after chloroquine treatment (median four days, range 2-8) (P < 0.01), no differences were seen in the duration of symptoms after chemotherapy. In both treatment groups, no severe side effects occurred. Clindamycin can be used as a safe alternative to achieve radical cure in semi-immune adult patients with chloroquine-resistant P. falciparum malaria in Central Africa.

The Diagnostic Histopathologic Features of Ocular Malaria

The ocular complications in patients with malaria have been studied clinically by many investigators, but the histopathologic changes were rarely described and generally regarded as nonspecific. The eye of a 53-year-old man who died of chloroquine-resistant Plasmodium falciparum malaria was studied by brightfield and polarized light microscopy. An epibulbar hemorrhage that involved the conjunctiva, episclera, and tendinous insertion of the medial rectus muscle was present. Cytoadherence and rosetting of the parasitized erythrocytes were observed within the partially occluded lumens of small retinal and uveal blood vessels. The birefringence of hemozoin (malarial pigment) within the lumens of small ocular blood vessels and in the hemorrhagic epibulbar area was demonstrated by polarized light. Birefringent hemozoinemia in vascular lumens of ocular tissues indicates systemic malarial infestation by any of the four species of malaria. Cytoadherence and rosetting of the parasitized erythrocytes inside ocular capillaries and venules is diagnostic of P. falciparum and is an important cause of ocular hemorrhage.

Intramuscular sulfadoxine-pyrimethamine in uncomplicated chloroquine-resistant falciparum malaria during pregnancy

Journal Article Intramuscular sulfadoxine-pyrimethamine in uncomplicated chloroquine-resistant falciparum malaria during pregnancy Get access A. Sowunmi, A. Sowunmi 1Department of Pharmacology and Therapeutics, University of Ibadan, Ibadan, Nigeria Address for correspondence: Dr A. Sowunmi, Clinical Pharmacology Unit, University College Hospital, Ibadan, Nigeria. Search for other works by this author on: Oxford Academic PubMed Google Scholar J.A. Akindele, J.A. Akindele 2Department of Paediatrics, University of Ibadan, Ibadan, Nigeria Search for other works by this author on: Oxford Academic PubMed Google Scholar G.O. Omitowoju, G.O. Omitowoju 1Department of Pharmacology and Therapeutics, University of Ibadan, Ibadan, Nigeria Search for other works by this author on: Oxford Academic PubMed Google Scholar A.O. Omigbodun, A.O. Omigbodun 3Department of Obstetrics and Gynaecology, University of Ibadan, Ibadan, Nigeria Search for other works by this author on: Oxford Academic PubMed Google Scholar A.M.J. Oduola, A.M.J. Oduola 1Department of Pharmacology and Therapeutics, University of Ibadan, Ibadan, Nigeria Search for other works by this author on: Oxford Academic PubMed Google Scholar L.A. Salako L.A. Salako 1Department of Pharmacology and Therapeutics, University of Ibadan, Ibadan, Nigeria Search for other works by this author on: Oxford Academic PubMed Google Scholar Transactions of The Royal Society of Tropical Medicine and Hygiene, Volume 87, Issue 4, July-August 1993, Page 472, https://doi.org/10.1016/0035-9203(93)90043-P Published: 01 July 1993 Article history Received: 04 February 1992 Revision received: 05 October 1992 Accepted: 07 October 1992 Published: 01 July 1993

Altered course ofPlasmodium bergheiinfection by nifedipine treatment

The effect of nifedipine (a calcium channel blocker) on the course of P. berghei infection was examined. It was observed that mice receiving a daily dose of 0.015 mg/kg of nifedipine had significantly shorter prepatent, patent and survival periods as compared to untreated P. berghei-infected animals (p < 0.001). This shows that the calcium channel blockers, in addition to possessing the property of reversing drug resistance during combined therapy with chloroquine, may also alter the pathophysiology of malaria infection. The decreased resistance of the host to the invading parasite suggests that the effect of CCB on the host-parasite interaction in human malaria needs to be investigated further before CCB can be used in combination with chloroquine for the treatment of chloroquine-resistant malaria or for chemoprophylaxis.

Long-term malaria prophylaxis with weekly mefloquine

The spread of chloroquine-resistant Plasmodium falpicarum malaria has led to increased use of mefloquine prophylaxis by US Peace Corps volunteers in sub-Saharan Africa. We compared long-term mefloquine with other drug regimens for effectiveness and tolerance.The incidence of Plasmodium falciparuminfections and of adverse reactions was compared in Peace Corps volunteers who took chloroquine weekly, mefloquine weekly, mefloquine every other week, or weekly chloroquine plus daily proguanil. Weekly mefloquine was 94% more effective than chloroquine (95% Cl 86% to 97%), 86% more effective than chloroquine plus proguanil (95% Cl 67% to 94%), and 82% more effective than prophylaxis with mefloquine when taken every other week (95% Cl 68% to 90%). No serious adverse reactions were observed. Mild adverse events were equally frequent in mefloquine users and chloroquine users, and the frequency of these events declined with increasing duration of prophylaxis.Mefloquine is an effective and well-tolerated drug for prophylaxis of malaria by short-term and long-term travellers.

Plasmodium Falciparum-Associated Anemia in Children at a Large Urban Hospital in Zaire

Chloroquine-resistant Plasmodium falciparum malaria and human virus (HIV) infection through blood transfusions used to treat malaria-associated anemia are causes of increasing morbidity and mortality among children in Africa. To evaluate the role of malaria and other risk factors for pediatric anemia, we conducted a study of children brought to the emergency ward of a large urban hospital in Kinshasa, Zaire. A total of 748 children ages six through 59 months were enrolled; 318 (43%) children were anemic (hematocrit < 33%), including 74 (10%) who were severely anemic (hematocrit < 20%). Plasmodium falciparum parasites were detected in 166 children (22%); hematocrits for these children (mean 25.8%) were significantly lower than for aparasitemic children (mean 33.7%; P < 10(-6)). Fever with splenomegaly (odds ratio [OR] = 6.5, P = 0.02), parasitemia (OR = 3.5, P < 0.001), lower socioeconomic status (OR = 2.0, P = 0.004), and malnutrition (OR = 1.8, P = 0.06) were independently associated with anemia in a multivariate model. Recent antimalarial therapy was also associated with a lower hematocrit, suggesting that chloroquine may have aggravated the anemia. A reassessment of the effectiveness of strategies to diagnose and treat malaria and malnutrition is necessary to decrease the high prevalence of anemia and the resultant high rate of blood transfusions in areas endemic for malaria and HIV.

Four Imported Cases of Falciparum Malaria Successfully Treated with Halofantrine.

Halofantrine, a phenanthrene derivative, has been used for the treatment of human malaria since 1984, and reported to be effective against all parasite species without any major side effects. The chemical structure of the drug is unique and not closely related to any other antimalarials, therefore, it is particularly effective for the treatment of the wide-spread drug resistant malaria. Four cases of imported falciparum malaria, including chloroquine and pyrimethamine resistant malaria, were treated with halofantrine and reported in this paper. Halofantrine cleared parasites and fever of all the cases rapidly and produced salutary symptomatic improvement of the patients. No adverse reactions were recognized after the administration of the drug, nor was there recrudescence. Fansidar is the only antimalarial drug commercially available in Japan, and imported drug resistant malaria not only against chloroquine but also Fansidar has been on the increase. The general use of halofantrine is thus expected in Japan.

Chloroquine: Mechanism of drug action and resistance in plasmodium falciparum

Quinoline-containing drugs such as chloroquine and quinine have had a long and successful history in antimalarial chemotherapy. Although these drugs are known to accumulate by a weak base mechanism in the acidic food vacuoles of intraerythrocytic trophozoites and thereby prevent hemoglobin degradation from occuring in that organelle, the mechanism by which their selective toxicity for lysosomes of malaria trophozoites is achieved has been subject to much discussion and argument. In this review the recent discovery that chloroquine and related quinolines inhibit the novel heme polymerase enzyme that is also present in the trophozoite food vacuole is introduced. The proposal that this inhibition of heme polymerase can explain the specific toxicity of these drugs for the intraerythrocytic malaria parasite is then developed by showing that it is consistent with much of the disparate information currently available. The clinical usefulness of chloroquine, and in some recent cases of quinine as well, has been much reduced by the evolution and spread of chloroquine resistant malaria parasites. The mechanism of resistance involves a reduced accumulation of the drug, although again the mechanism involved is controversial. Possible explanations include an energy-dependent efflux of preaccumulated drug via an unidentified transmembrane protein pump, or an increase in vacuolar pH such that the proton gradient responsible for drug concentration is reduced. New data are also presented which show that heme polymerase isolated from chloroquine resistant trophozoites retains full sensitivity to drug inhibition, consistent with the observation that resistance involves a reduced accumulation of the drug at the (still vulnerable) target site. The significance of this result is discussed in relation to developing new strategies to overcome the problem presented by chloroquine resistant malaria parasites.

Seasonal variation of paediatric diseases in The Gambia, west Africa.

In a 3-year prospective study of 9584 consecutive paediatric admissions to the Royal Victoria Hospital in Banjul, The Gambia, we examined the impact of seasonal variations in childhood diseases. The four principal diseases (falciparum malaria, pneumonia, gastro-enteritis and malnutrition) all peaked in September to October following the rainy season. The mortality rate was also higher in the rainy season than in the dry season. Of the 1525 children with cerebral malaria, 83% were admitted during the extended rainy season from July to December. With the emergence of chloroquine-resistant malaria over the 3 years, there was a 27% annual increase in severe anaemia owing to malaria. The median age of malarial anaemia (23 months) was significantly younger than that of cerebral malaria (42 months). Malnutrition peaked immediately following the annual rainy season epidemics of bacterial gastro-enteritis but was not associated with the cool dry season rotavirus outbreaks. Rainy season diarrhoea was also associated with more persistent diarrhoea, an older mean age and a higher mortality. Meningitis was caused by either pneumococcus or Haemophilus influenzae in 64% of cases, of whom 19% were 0-2 months of age. Causes of death in hospital showed good agreement with Gambian community studies. We conclude that analysis of hospital data in a developing country can give accurate information on childhood morbidity and mortality patterns which can be used to set priorities for health care interventions. Seasonal variation is a cardinal feature of paediatric diseases in this part of Africa, and accentuates the vulnerability of children in poor families.

The chemotherapy of rodent malaria. XLIX. The activities of some synthetic 1,2,4-trioxanes against chloroquine-sensitive and chloroquine-resistant parasites. Part 2: Structure-activity studies on cis-fused cyclopenteno-1,2,4-trioxanes (fenozans) against drug-sensitive and drug-resistant lines of Plasmodium berghei and P. yoelii ssp. NS in vivo.

The activity of 51 synthetic cis-fused cyclopenteno-1,2,4-trioxanes has been examined against drug-sensitive and chloroquine-resistant malaria parasites in vivo. Some of them display high levels of blood schizontocidal activity when administered orally or subcutaneously. They retain their activity against lines of parasites that are resistant to widely differing antimalarials such as 4-aminoquinolines, aminoalcohols, dihydrofolate reductase inhibitors and artemisinin. The most potent compound of the present series is cis-(+/-)-4a,7a-dihydro-6,7a-di(p-fluorophenyl)spiro [cyclopentane-3,3'-7H-cyclopenta-1,2,4-trioxin], otherwise known as Fenozan-50F.