Plasmodium falciparum clearance with artemisinin-based combination therapy (ACT) in patients with glucose-6-phosphate dehydrogenase deficiency in Mali

URL : http://www.malariajournal.com/content/9/1/332Background: Artemisinin-based combination therapy (ACT) is currently the most effective medicine for the treatment of uncomplicated malaria. Artemisinin has previously been shown to increase the clearance of Plasmodium falciparum in malaria patients with haemoglobin E trait, but it did not increase parasite inhibition in an in vitro study using haemoglobin AS erythrocytes. The current study describes the efficacy of artemisinin derivatives on P. falciparum clearance in patients with glucose-6-phosphate dehydrogenase deficiency (G6PD), a haemoglobin enzyme deficiency, not yet studied in the same context, but nonetheless is a common in malaria endemic areas, associated with host protection against uncomplicated and severe malaria. The impact of G6PD deficiency on parasite clearance with ACT treatment was compared between G6PD-deficient patients and G6PD-normal group. Methods: Blood samples from children and adults participants (1 to 70 years old) with uncomplicated P. falciparum malaria residing in Kambila, Mali were analysed. Study participants were randomly assigned to receive either artemether-lumefantrine (Coartem®) or artesunate plus mefloquine (Artequin™). A restriction-fragment length polymorphism analysis of PCR-amplified DNA samples was used to identify the (A-) allele of the gene mutation responsible for G6PD deficiency (G6PD*A-). 470 blood samples were thus analysed and of these, DNA was extracted from 315 samples using the QIAamp kit for PCR to identify the G6PD*A- gene. Results

α-Thalassemia Impairs the Cytoadherence of Plasmodium falciparum-Infected Erythrocytes

α-Thalassemia results from decreased production of α-globin chains that make up part of hemoglobin tetramers (Hb; α(2)β(2)) and affects up to 50% of individuals in some regions of sub-Saharan Africa. Heterozygous (-α/αα) and homozygous (-α/-α) genotypes are associated with reduced risk of severe Plasmodium falciparum malaria, but the mechanism of this protection remains obscure. We hypothesized that α-thalassemia impairs the adherence of parasitized red blood cells (RBCs) to microvascular endothelial cells (MVECs) and monocytes--two interactions that are centrally involved in the pathogenesis of severe disease.We obtained P. falciparum isolates directly from Malian children with malaria and used them to infect αα/αα (normal), -α/αα and -α/-α RBCs. We also used laboratory-adapted P. falciparum clones to infect -/-α RBCs obtained from patients with HbH disease. Following a single cycle of parasite invasion and maturation to the trophozoite stage, we tested the ability of parasitized RBCs to bind MVECs and monocytes. Compared to parasitized αα/αα RBCs, we found that parasitized -α/αα, -α/-α and -/-α RBCs showed, respectively, 22%, 43% and 63% reductions in binding to MVECs and 13%, 33% and 63% reductions in binding to monocytes. α-Thalassemia was associated with abnormal display of P. falciparum erythrocyte membrane protein 1 (PfEMP1), the parasite's main cytoadherence ligand and virulence factor, on the surface of parasitized RBCs.Parasitized α-thalassemic RBCs show PfEMP1 display abnormalities that are reminiscent of those on the surface of parasitized sickle HbS and HbC RBCs. Our data suggest a model of malaria protection in which α-thalassemia ameliorates the pro-inflammatory effects of cytoadherence. Our findings also raise the possibility that other unstable hemoglobins such as HbE and unpaired α-globin chains (in the case of β-thalassemia) protect against life-threatening malaria by a similar mechanism

Schematic representation of the cytoadherence assay.

<p>Ring-stage parasites from HbAA and HbAS (or HbAC) children were cultured to trophozoites (a), and then purified by magnetic column and inoculated into wildtype donor RBCs (b). After invasion and maturation to trophozoites expressing PfEMP1 (c), parasites from HbAS or HbAC children were compared for binding to MVECs in parallel with those from HbAA children (d).</p

Schematic representation of the cytoadherence assay.

<p>Ring-stage parasites from HbAA and HbAS (or HbAC) children were cultured to trophozoites (a), and then purified by magnetic column and inoculated into wildtype donor RBCs (b). After invasion and maturation to trophozoites expressing PfEMP1 (c), parasites from HbAS or HbAC children were compared for binding to MVECs in parallel with those from HbAA children (d).</p

Characteristics of Malian HbAA, HbAS, and HbAC children from which parasite isolates were obtained.

<p>The number of samples (n), proportion of samples with α-thalassemia (wildtype, WT; heterozygous, HET; not determined, ND) and <i>G6PD*</i>A- (G202A) (absent, ABS; heterozygous, HET; hemizygous, HEM) genotypes, mean age (years), median parasite density (/μl), and proportion of severe malaria cases are shown for <i>all</i> HbAA, HbAS, and HbAC samples used in comparisons, and <i>unique</i> HbAA, HbAS, and HbAC samples used in comparisons. <i>All</i> samples (n = 62) include 10 parasite strains that were used in multiple comparisons, while <i>unique</i> samples include 52 parasite strains that were used in single comparisons. Three <i>unique</i> samples (2 HbAS and 1 HbAC) were classified as severe since they met one or more of these criteria: cessation of eating/drinking, repetitive vomiting, or prostration.</p

Relative cytoadherence of parasitized HbAA, HbAS, and HbAC RBCs to MVECs.

<p>Over three transmission seasons (2008, 2009, and 2010), a total of 31 cytoadherence comparisons were performed between parasites from HbAA and HbAS (or HbAC) children by inoculating them into wild-type donor RBCs and assaying their binding to MVECs in parallel. The ratio of parasitized RBCs (pRBC) bound per MVEC (pRBC/MVEC) was calculated for each sample tested. The pRBC/MVEC ratio from the HbAS- or HbAC-derived parasite in each comparison was then normalized to that of the HbAA-derived parasite from the same comparison to give a measure of the relative cytoadherence. Two comparisons (AS13 <i>vs.</i> AA12 and AC10 <i>vs.</i> AA22) were performed over multiple slides, as shown. Also, several samples (indicated in bold) were used in multiple comparisons.</p

Relationship between cytoadherence, Hb type, and host age.

<p>A Poisson regression model was constructed to examine the effect of Hb type and host age on the cytoadherence of parasitized RBCs to MVECs. Fold-changes and 95% CIs of the relative binding compared to parasites from HbAA (for HbAS and HbAC) children and parasites from >5-year-old (for ≤5-year-old) children are indicated.</p

Distribution and morphology of knobs on the surface of parasitized RBCs.

<p>Atomic force micrographs (AFMs) of parasitized −α/αα (HE) (<b>a,d</b>) and −α/−α (HO) (<b>b,e</b>) RBCs obtained from naturally-parasitized Malian children with malaria and −/−α (HH) (<b>c,f</b>) RBCs infected with a laboratory-adapted <i>P. falciparum</i> clone showing normal (<b>a,b</b>) or abnormal (<b>c–f</b>) knob distributions and morphologies. AFM images are representative of 32, 10 and 18 images of parasites in −α/αα, −/−αα and −/−α RBCs. Inlays show YOYO-1-stained parasites that correspond to those imaged by AFM. Comparison AFMs of parasitized HbA, HbC and HbS RBCs have been reported previously <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0037214#pone.0037214-Arie1" target="_blank">[22]</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0037214#pone.0037214-Cholera1" target="_blank">[37]</a>.</p

Relative cytoadherence and surface PfEMP1 levels of parasitized RBCs. a,

<p>Adherence of parasitized RBCs to MVECs. The numbers of parasitized −α/αα (HE), −α/−α (HO) and −/−α (HH) RBCs adhering to MVECs were normalized to those of parasitized αα/αα RBCs tested in parallel. The mean (± SEM) number of parasitized αα/αα RBCs per 100 MVECs was 260±40, <i>N</i> = 19. Results were obtained from 19 naturally-circulating parasite isolates and 2 laboratory-adapted parasite clones (A4tres and FCR-3), multiple blood donors (5 αα/αα, 2−α/αα, 2 −α/−α and 2−/−α), and 4 MVEC donors (not all combinations tested). This resulted in −α/αα, −α/−α and −/−α samples being compared to αα/αα samples 12, 5 and 4 times. <b>b,</b> Adherence of parasitized RBCs to monocytes. The numbers of parasitized −α/αα, −α/−α and −/−α RBCs adhering to monocytes were normalized to those of αα/αα RBCs tested in parallel. The mean (± SEM) number of parasitized αα/αα RBCs per 100 monocytes was 136±10, <i>N</i> = 12. Results were obtained from 3 naturally-circulating parasite isolates and 3 laboratory-adapted parasite clones (3D7, A4tres and FCR-3), multiple blood donors (5 αα/αα, 3 −α/αα, 2 −α/−α and 2−/−α) and 4 monocyte donors (not all combinations tested). This resulted in −α/αα, −α/−α and −/−α samples being compared to αα/αα samples 20, 3 and 4 times. The αα/αα and −α/αα RBCs were different from those used in endothelial cell adherence assays. <b>c,</b> PfEMP1 expression levels (median fluorescence intensities, MFI) on the surface of parasitized RBCs. The mean (± SEM) MFI of parasitized αα/αα RBCs was 556±153, <i>N</i> = 6. Results were obtained from 2 laboratory-adapted parasite clones (A4tres, FVO and FCR3^CSA), multiple blood donors (4 αα/αα, 6 −α/αα and 2−/−α), and various concentrations of 2 antisera (not all combinations tested). This resulted in −α/αα, and −/−α samples being compared to αα/αα samples 10 and 6 times. The αα/αα and −α/αα RBCs were different from those used in endothelial cell and monocyte adherence assays.</p

Filariasis attenuates anemia and proinflammatory responses associated with clinical malaria: a matched prospective study in children and young adults.

Wuchereria bancrofti (Wb) and Mansonella perstans (Mp) are blood-borne filarial parasites that are endemic in many countries of Africa, including Mali. The geographic distribution of Wb and Mp overlaps considerably with that of malaria, and coinfection is common. Although chronic filarial infection has been shown to alter immune responses to malaria parasites, its effect on clinical and immunologic responses in acute malaria is unknown.To address this question, 31 filaria-positive (FIL+) and 31 filaria-negative (FIL-) children and young adults, matched for age, gender and hemoglobin type, were followed prospectively through a malaria transmission season. Filarial infection was defined by the presence of Wb or Mp microfilariae on calibrated thick smears performed between 10 pm and 2 am and/or by the presence of circulating filarial antigen in serum. Clinical malaria was defined as axillary temperature ≥37.5°C or another symptom or sign compatible with malaria infection plus the presence of asexual malaria parasites on a thick blood smear. Although the incidence of clinical malaria, time to first episode, clinical signs and symptoms, and malaria parasitemia were comparable between the two groups, geometric mean hemoglobin levels were significantly decreased in FIL- subjects at the height of the transmission season compared to FIL+ subjects (11.4 g/dL vs. 12.5 g/dL, p<0.01). Plasma levels of IL-1ra, IP-10 and IL-8 were significantly decreased in FIL+ subjects at the time of presentation with clinical malaria (99, 2145 and 49 pg/ml, respectively as compared to 474, 5522 and 247 pg/ml in FIL- subjects).These data suggest that pre-existent filarial infection attenuates immune responses associated with severe malaria and protects against anemia, but has little effect on susceptibility to or severity of acute malaria infection. The apparent protective effect of filarial infection against anemia is intriguing and warrants further study in a larger cohort