Nutritional zinc deficiency, immune capacity and malaria : a study on mediators of immunity to malaria caused by Plasmodium falciparum in African children
1
Citation
0
Reference
10
Related Paper
Citation Trend
Abstract:
This thesis aimed at investigating the role of genetic and nutritional factors that affect the immune response to malaria in Tanzanian children. The introductory chapter (Chapter 1) reviews the importance of nutritional deficiencies, particularly of zinc, and presents the hypothesis that such deficiencies lead to impaired immunity and contribute to the burden of malaria. The chapter also describes current efforts to prevent malaria through intermittent preventive treatment, both in infants (IPTi) and pregnant women (IPTp). Sulfadoxinepyrimethamine is still used for first-line treatment of uncomplicated malaria, or, in many countries, to prevent malaria and anaemia in pregnancy. In malaria endemic areas, development of resistance to previously valuable antimalarial drugs has been continuously reported for decades. Thus our initial longitudinal study aimed at measuring the prevalence of resistance-associated mutations on dihydrofolate reductase (DHFR) and dihydropteroate synthase (DHPS) genes (dhfr and dhps) that confer parasite resistance to sulphadoxinepyrimethamine (SP) that was used as an interim antimalarial drug after chloroquine resistance. Although SP resistance-associated point mutations were highly prevalent, we observed an adequate parasite response to SP (Chapter 2). We speculated that the impact of the dhfr and dhps mutations on SP resistance may be dependent at least in part on the protective immunity that has developed in response to frequent exposure to infection and may be weighed down by host immunity in endemic areas and thus impacts in the continued use of the drug for treatment of malaria. The impact of other drugs with similar mechanisms of action used as antibiotics in selecting mutations responsible for SP resistance needs therefore to be studied for their modulating activity of the immune response. These findings underscore the relevance to further study the crucial involvement of the immune system in the development of protection against malaria but also affecting the efficacy of treatment modalities of malaria in various African conditions. In the subsequent cross-sectional studies, we assessed the effect of deficiencies of zinc and magnesium as well as iron deficiency anaemia on malaria-specific cytokine responses indicative of innate immunity to Plasmodium falciparum (Chapter 3). In this study, we used Plasmodium falciparum-parasitised red blood cells (pRBCs) as antigens for in vitro stimulation of peripheral blood mononuclear cells (PBMCs). Cytokines were measured in the supernatant of cultured PBMCs after 24 hours of stimulation. Zinc deficiency was associated with a marked increase in monocyte-derived TNF-α concentration in children with malarial infection but not in their uninfected peers. In children with malarial infection, iron deficiency anaemia was associated with elevated concentrations of TNF-α, whereas magnesium deficiency in children without malaria seemed to be associated with increased concentrations of IL-10. Our findings reflected plasticity in cytokine profiles of monocytes reacting to malaria infection under conditions of different nutrient deficiencies. Following the observation of the variable impact of micronutrients on innate cytokines, we evaluated the profile of both type I and type II cytokines and whether they were influenced by nutritional and malaria status (Chapter 4). The cytokine measurements were performed at day 7 of stimulation anticipating that this timing was optimal for measuring effects on these cytokines mainly derived from activated T-cells. The results indicated a variable influence of nutrient deficiencies on increased cytokine response with zinc deficiency and iron deficiency anemia having greater impact on type I and magnesium deficiency on type II cytokines. The subsequent study evaluated the plasma levels of naturally acquired antimalarial antibodies of variousIgG subclasses plus the total IgG and IgM levels and whether they were associated with zinc deficiency based on preceding chapters (Chapter 5). The results indicated a high variability in antibody levels with zinc deficiency, varying with age of the affected child. IgG3 appeared to be predominant across all age subgroups within < 5 yrs aged children providing clues that IgG3 might confer immune protection to malaria under conditions of zinc deficiency. Chapter 6 explored the association between CD36 deficiency, P. falciparum in vitro adherence on purified CD36 and anemia in children. CD36 is a receptor that occurs on the surface of activated immune cells and vascular endothelial cells and participates in phagocytosis and lipid metabolism. We hypothesized that it could play a fundamental role in cytoadherence of erythrocytes that are parasitized by Plasmodium. Our results showed that CD36 deficiency was associated with protection against the development of malarial anemia in children and that it may be mediated through reduced cytoadherence of infected red blood cells to vascular endothelium. These studies demonstrate that despite antimalarial drug resistance, there is a potential for optimizing the immunological protective capacity in the population to confer parasite clearance that can be variably influenced by micronutrient status. Improving nutritional status in this population could be rewarding not only to increase protection to malaria but possibly also to other infections.Keywords:
DHPS
Sulfadoxine
Dihydropteroate synthase
Topics:
Cite
Antifolate antimalarials like sulfadoxine-pyrimethamine are used as second-line treatment for Plasmodium falciparum malaria patients who fail to respond to chloroquine. The efficacy of the sulfa-pyrimethamine combination in the treatment is also compromised by the development of resistance in the parasite. Resistance to these drugs has been shown to encode with point mutations in dihydrofolate reductase and dihydropteroate synthetase genes.An experimental study.Forty clinical isolates collected from different geographical locations in India were used to assess the relationships between resistance to sulfadoxine-pyrimethamine (SP) and mutations in P. falciparum dihydrofolate reductase (DHFR) and dihydropteroate synthetase (DHPS). In vitro drug susceptibility and mutation-specific polymerase chain reaction (PCR) assays were also done.It was observed that a number of isolates possessed mutant genotypes and showed low sensitivity to SP in vitro. Of the 40 clinical isolates studied, 87.5% had DHFR and 15% had DHPS gene mutations. As observed from PCR results, 55( (22/40) presented double mutation of DHFR Arg-59 and Asn-108 and 32.5 % (13/40) had single mutant type allele of Asn-108. Of the 40 isolates, 10 % (4/40) presented doubly mutated forms of DHPS Phe-436 and Thr-613 and single mutant type allele Gly-581 was detected in 5 % (2/40) isolates. Parasites carrying double or single mutant forms of DHFR/DHPS showed elevated minimum inhibitory concentration (MIC) values of both pyrimethamine (760-6754 nM; r=0.69) and sulfadoxine (108 - 540 micro M; r=0.87) when compared to sensitive and resistant strains.Though there was a correlation between molecular techniques and in vitro drug sensitivity profiles, the relevance of these findings to the clinical efficacy of SP combination drugs needs to be established by controlled clinical trials.
Dihydropteroate synthase
DHPS
Dihydrofolate reductase
Sulfadoxine
Antifolate
Sulfadoxine/pyrimethamine
Cite
Citations (14)
Over a 2-year study period, three methods [a test of therapeutic efficacy, an in-vitro assay, and sequencing of the parasites' dihydrofolate-reductase (dhfr) and dihydropteroate-synthase (dhps) genes] were used to monitor sulfadoxine-pyrimethamine (SP) resistance in the Plasmodium falciparum strains infecting young children near Abidjan, the largest city in Côte d'Ivoire. Overall, 118 children aged<5 years and infected with P. falciparum were treated with SP. Twenty-one (23.5%) of the 89 children who completed the 14 days of follow-up were categorized as therapeutic failures. When P. falciparum isolates from the 61 children with adequate parasitaemias were investigated in the in-vitro assay, 24 (39.5%) were found to be highly resistant to pyrimethamine, each having a median inhibitory concentration (IC50) of at least 2000 nM. Polymorphism analysis of gene fragments of 118 P. falciparum isolates (one from each child enrolled in the study) revealed that 46 (39%) of the isolates had mutant dhfr and 111 (94%) had mutant dhps. The mutations mainly affected DHFR codon 108 (39% of the isolates) and DHPS codons 436 (65%), 437 (52%) and 613 (27%). Of the 37 DHFR mutant isolates from children who completed follow-up, 21 were from children with therapeutic failure, indicating that mutant DHFR was associated with resistance to pyrimethamine in vivo (kappa=0.61). A mutant dhfr genotype was also found to be strongly associated with resistance to pyrimethamine in vitro (kappa=0.79). There was, however, little evidence of an association between SP efficacy and dhps genotype (kappa=0.04). Resistance to SP appears to be an increasing problem in southern Côte d'Ivoire and one which may now justify a change away from this drug combination as the first- or second-line treatment for P. falciparum malaria in this area.
Dihydropteroate synthase
DHPS
Dihydrofolate reductase
Sulfadoxine/pyrimethamine
Sulfadoxine
Cite
Citations (15)
Dihydropteroate synthase
DHPS
Dihydrofolate reductase
Sulfadoxine
Trimethoprim
Antifolate
Cite
Citations (5)
To assess the relationship between the presence of DHFR and DHPS mutations in Plasmodium falciparum, parasite in vitro resistance, and in vivo efficacy of sulfadoxine-pyrimethamine (SP) treatment.Measurement of SP treatment efficacy in malaria-infected children in Gabon was combined with in vitro tests of susceptibility to pyrimethamine and cycloguanil, and molecular genotyping at several DHFR and DHPS loci of parasites isolated before treatment. DHFR was studied at codons 108, 51, and 59, whereas DHPS gene was typed at positions 436, 437, 540 and 581.SP treatment was effective in 86% of children by day 28. Seventy-five percent of isolates were in vitro resistant to pyrimethamine and 65.5% to cycloguanil. No mutation was detected at codons 540 and 581 of the DHPS gene. Most isolates (71.8%) presented with the triple mutant DHFR genotype, whereas 64.3% combined at least three DHFR and one DHPS mutations. The increase in the number of DHFR mutations was associated with an increase in in vitro resistance to pyrimethamine and cycloguanil; three DHFR mutations conferred pyrimethamine and to a lesser extent cycloguanil resistance. Treatment failures only occurred with isolates presenting at least two DHFR mutations (S108N and C59R) and one DHPS mutation (S436A or A437G), but SP treatment of infections with such parasites gave treatment success in 82.0% of children.DHFR mutations that lead to high-level in vitro resistance to pyrimethamine plus 1-2 DHPS mutations are not sufficient to induce in vivo failure of SP treatment in young children from Gabon.
DHPS
Sulfadoxine
Dihydrofolate reductase
Dihydropteroate synthase
Cite
Citations (60)
DHPS
Dihydrofolate reductase
Dihydropteroate synthase
Sulfadoxine
Trimethoprim
Cite
Citations (0)
Background. The A581G mutation in the gene encoding Plasmodium falciparum dihydropteroate synthase (dhps), in combination with the quintuple mutant involving mutations in both dhps and the gene encoding dihydrofolate reductase (dhfr), the so-called sextuple mutant, has been associated with increased placental inflammation and decreased infant birth weight among women receiving intermittent preventive treatment with sulfadoxine-pyrimethamine (IPTp-SP) during pregnancy.
DHPS
Dihydropteroate synthase
Sulfadoxine
Sulfadoxine/pyrimethamine
Dihydrofolate reductase
Cite
Citations (93)
Sulfadoxine-pyrimethamine is one of the alternative antimalarial drugs used to treat chloroquine-resistant Plasmodium falciparum malaria. The molecular target of sulfadoxine, an analog of p-aminobenzoic acid that inhibits the folate biosynthetic pathway, is dihydropteroate synthase (DHPS). The nucleotide sequence of the DHPS gene was determined in 32 clinical isolates obtained in Yaounde, Cameroon, and compared with the sequence of reference clones and Cambodian strains of P. falciparum. Of the 32 Cameroonian isolates, 31 displayed one of the sulfadoxine-sensitive mutation patterns: Ala-436/Ala-437/Ala-581/Ala-613 (n = 20), Ser-436/Gly-437/Ala-581/Ala-613 (n = 6), Ser-436/Ala-437/Ala-581/Ala-613 (n = 4), and Ala-436/Gly-437/Ala-581/Ala-613 (n = 1). One isolate had a sulfadoxine-resistant profile characterized by a double mutation: Phe-436/Ala-437/Ala-581/Ser-613. Although the majority of the isolates had a sulfadoxine-sensitive genetic profile, further studies are needed to correlate the mutation patterns and in vitro and in vivo sulfadoxine sensitivity.
Dihydropteroate synthase
DHPS
Sulfadoxine
Sulfadoxine/pyrimethamine
Cite
Citations (26)
ABSTRACT In vitro sulfadoxine and pyrimethamine resistance has been associated with point mutations in the dihydropteroate synthase and dihydrofolate reductase domains, respectively, but the in vivo relevance of these point mutations has not been well established. To analyze the correlation between genotype and phenotype, 10 Cameroonian adult patients were treated with sulfadoxine-pyrimethamine and followed up for 28 days. After losses to follow-up ( n = 1) or elimination of DNA samples due to mixed parasite populations with pyrimethamine-sensitive and pyrimethamine-resistant profiles ( n = 3), parasite genomic DNA from day 0 blood samples of six patients were analyzed by DNA sequencing. Three patients who were cured had isolates characterized by a wild-type or mutant dihydrofolate reductase gene (with one or two mutations) and a wild-type dihydropteroate synthase gene. Three other patients who failed to respond to sulfadoxine-pyrimethamine treatment carried isolates with triple dihydrofolate reductase gene mutations and either a wild-type or a mutant dihydropteroate synthase gene. Three dihydrofolate reductase gene codons (51, 59, and 108) may be reliable genetic markers that can accurately predict the clinical outcome of sulfadoxine-pyrimethamine treatment in Africa.
Dihydropteroate synthase
Dihydrofolate reductase
Sulfadoxine/pyrimethamine
DHPS
Sulfadoxine
Antifolate
Cite
Citations (83)
Antimalarial resistance to sulfadoxine-pyrimethamine (SP) is mediated by mutations in the dihydrofolate reductase (dhfr) and dihydropteroate synthase (dhps) genes. However, the relative importance of different mutations is incompletely understood and has not been studied with combination therapy. Samples from 812 patients treated for uncomplicated malaria in Kampala, Uganda were tested for the presence of mutations commonly found in Africa. The dhps Glu-540 mutation was the strongest independent predictor of treatment failure. The dhfr Arg-59 mutation was only predictive of treatment failure in the presence of the dhps Glu-540 mutation. Comparing combination regimens with SP monotherapy, the addition of chloroquine to SP did not improve efficacy, the addition of artesunate lowered the risk of treatment failure only for infections with both the dhfr Arg-59 and dhps Glu-540 mutations, and the addition of amodiaquine lowered this risk for all dhfr/dhps mutation patterns. The dhps Glu-540 mutation played a principal role and the dhfr Arg-59 mutation a secondary role in mediating resistance to SP alone and in combination.
DHPS
Dihydropteroate synthase
Dihydrofolate reductase
Sulfadoxine
Sulfadoxine/pyrimethamine
Artesunate
Cite
Citations (53)
To assess the relationship between mutations in Plasmodium falciparum dihydrofolate reductase (DHFR) and dihydropteroate synthase (DHPS) and clinical pyrimethamine-sulfadoxine resistance, polymerase chain reaction surveys and analyses for new mutations were conducted in four countries with increasing levels of pyrimethamine-sulfadoxine resistance: Mali, Kenya, Malawi, and Bolivia. Prevalence of mutations at DHFR codon 108 and a new mutation at DHPS 540 correlated with increased pyrimethamine-sulfadoxine resistance (P < .05). Mutations at DHFR 51, DHFR 59, and DHPS 437 correlated with resistance without achieving statistical significance. Mutations at DHFR 164 and DHPS 581 were common in Bolivia, where pyrimethamine-sulfadoxine resistance is widespread, but absent in African sites. Two new DHFR mutations, a point mutation at codon 50 and an insert at codon 30, were found only in Bolivia. DHFR and DHPS mutations occur in a progressive, stepwise fashion. Identification of specific sets of mutations causing in vivo drug failure may lead to the development of molecular surveillance methods for pyrimethamine-sulfadoxine resistance.
DHPS
Dihydropteroate synthase
Dihydrofolate reductase
Sulfadoxine/pyrimethamine
Sulfadoxine
Cite
Citations (415)