Thalassaemia trait, red blood cell age and oxidant stress: effects on Plasmodium falciparum growth and sensitivity to artemisinin

Micromolar Dihydroartemisinin Concentrations Elicit Lipoperoxidation in Plasmodium falciparum-Infected Erythrocytes

Malaria is still the most important parasitic infectious disease. Numerous substances are known to have antimalarial activity; among them, artemisinin is the most widely used one, and artemisinin-based combination therapy (ACT) is recommended for the treatment of Plasmodium falciparum (P.f.) malaria. Antitumor, immunomodulatory, and other therapeutic applications of artemisinin are under extensive study. Several different mechanisms of action were proposed for dihydroartemisinin (DHA), the active metabolite of artemisinin, such as eliciting oxidative stress in target cells. The goal of this study is to monitor the generation of reactive oxygen species (ROS) and lipid peroxidation product 4-hydroxynonenal (4-HNE) by DHA in P.f.-infected human erythrocytes. Checking ROS and 4-HNE-protein adducts kinetics along the maturation of the parasite, we detected the highest level of 4-HNE in ring forms of P.f. due to DHA treatment. Low micromolar concentrations of DHA quickly induced levels of 4-HNE-adducts which are supposed to be damaging. Mass spectrometry identified the P.f. protein cysteine proteinase falcipain-1 as being heavily modified by 4-HNE, and plausibly, 4-HNE conjugation with vital P.f. proteins might contribute to DHA-elicited parasite death. In conclusion, significant 4-HNE accumulation was detectable after DHA treatment, though, at concentrations well above pharmacologically effective ranges in malaria treatment, but at concentrations described for antitumor activity. Thus, lipid peroxidation with consequent 4-HNE conjugation of functionally relevant proteins might be considered as a uniform mechanism for how DHA potentiates antimalarials' action in ACT and controls the progression of tumors.

Sickle Cell Anemia and Babesia Infection

Babesia is an intraerythrocytic, obligate Apicomplexan parasite that has, in the last century, been implicated in human infections via zoonosis and is now widespread, especially in parts of the USA and Europe. It is naturally transmitted by the bite of a tick, but transfused blood from infected donors has also proven to be a major source of transmission. When infected, most humans are clinically asymptomatic, but the parasite can prove to be lethal when it infects immunocompromised individuals. Hemolysis and anemia are two common symptoms that accompany many infectious diseases, and this is particularly true of parasitic diseases that target red cells. Clinically, this becomes an acute problem for subjects who are prone to hemolysis and depend on frequent transfusions, like patients with sickle cell anemia or thalassemia. Little is known about Babesia's pathogenesis in these hemoglobinopathies, and most parallels are drawn from its evolutionarily related Plasmodium parasite which shares the same environmental niche, the RBCs, in the human host. In vitro as well as in vivo Babesia-infected mouse sickle cell disease (SCD) models support the inhibition of intra-erythrocytic parasite proliferation, but mechanisms driving the protection of such hemoglobinopathies against infection are not fully studied. This review provides an overview of our current knowledge of Babesia infection and hemoglobinopathies, focusing on possible mechanisms behind this parasite resistance and the clinical repercussions faced by Babesia-infected human hosts harboring mutations in their globin gene.

Artemisinin Therapy for Malaria in Hemoglobinopathies: A Systematic Review

Artemisinin derivatives are widely used antimalarial drugs. There is some evidence from in vitro, animal and clinical studies that hemoglobinopathies may alter their disposition and antimalarial activity. This review assesses relevant data in α-thalassemia, sickle cell disease (SCD), β-thalassemia and hemoglobin E. There is no convincing evidence that the disposition of artemisinin drugs is affected by hemoglobinopathies. Although in vitro studies indicate that Plasmodium falciparum cultured in thalassemic erythrocytes is relatively resistant to the artemisinin derivatives, mean 50% inhibitory concentrations (IC50s) are much lower than in vivo plasma concentrations after recommended treatment doses. Since IC50s are not increased in P. falciparum cultures using SCD erythrocytes, delayed post-treatment parasite clearance in SCD may reflect hyposplenism. As there have been no clinical studies suggesting that hemoglobinopathies significantly attenuate the efficacy of artemisinin combination therapy (ACT) in uncomplicated malaria, recommended artemisinin doses as part of ACT remain appropriate in this patient group.

Therapeutic strategies in Sickle Cell Anemia: The past present and future

Sickle Cell Anemia (SCA) was one of the first hemoglobinopathies to be discovered. It is distinguished by the mutation-induced expression of a sickle cell variant of hemoglobin (HbS) that triggers erythrocytes to take a characteristic sickled conformation. The complex physiopathology of the disease and its associated clinical complications has initiated multi-disciplinary research within its field. This review attempts to lay emphasis on the evolution, current standpoint and future scope of therapeutic strategies in SCA.

Artesunate-amodiaquine versus artemether-lumefantrine for the treatment of acute uncomplicated malaria in Congolese children under 10 years old living in a suburban area: a randomized study

BACKGROUND

The Republic of Congo adopted a new anti-malarial treatment policy in 2006, with artesunate-amodiaquine (ASAQ) and artemether-lumefantrine (AL) as the first- and second-line anti-malarial drugs, respectively. Only three clinical studies had been conducted before the policy change. A randomized study on these two artemisinin-based combinations was conducted, and the effect that sickle cell trait may have on treatment outcomes was evaluated in children under 10 years old followed during 12 months in Brazzaville in 2010-2011.

METHODS

A cohort of 330 children under 10 years of age living in a suburban area in the south of Brazzaville were passively followed for registration of malaria episodes. Uncomplicated Plasmodium falciparum episodes were randomly treated with co-formulated ASAQ (Coarsucam(®)) or AL (Coartem(®)). Patients were followed according to the 2009 World Health Organization protocol for the evaluation of anti-malarial drug efficacy. Plasmodium falciparum recrudescent isolates were compared to pre-treatment isolates by polymerase chain reaction (PCR) to distinguish between re-infection and recrudescence. PCR-uncorrected and PCR-corrected responses to treatment were determined using per protocol analysis. Haemoglobin type (AA, AS, SS) was determined by PCR.

RESULTS

Of 282 clinical malaria episodes registered during 1-year follow-up period, 262 children with uncomplicated malaria were treated with ASAQ (129 patients) or AL (133 patients). The PCR-corrected efficacy, expressed as the percentage of adequate clinical and parasitological response, was 97.0 % for ASAQ and 96.4 % for AL. Among ASAQ-treated patients, 112 (86.8 %) carried AA genotype and 17 (13.2 %) were AS carriers. The PCR-corrected efficacy was 96.4 % for AA-carriers and 100 % for AS-carriers treated with ASAQ [relative risk (RR) = 0.96; 95 % confidence interval, 0.93-1.00, p = 0.5]. Among 133 AL-treated children, 109 (82 %) carried AA, and 24 (18 %) AS genotypes. The PCR-corrected efficacy was 96.7 % among AA-carriers and 95.2 % among AS-carriers [RR = 1.01 (0.92-1.12), p = 0.6]. Nausea, jaundice, headache, dizziness, vomiting, pruritus, abdominal pain, and diarrhoea were registered as adverse events in both groups. ASAQ was associated with significantly more frequent adverse events (P < 0.05).

CONCLUSION

This first randomized study in Brazzaville confirmed the excellent efficacy of these co-formulated anti-malarial drugs in children. Sickle cell genotype did not influence the treatment efficacy of artemisinin-based combination therapy.

The Haldane malaria hypothesis: facts, artifacts, and a prophecy

Heterozygous thalassemia and sickle cell disease produce mild hematological symptoms but provide protection against malaria mortality and severe malaria symptoms. Two explanations for resistance are considered in the literature - impaired growth of the parasite or enhanced removal by the host immune cells. A critical overview of studies that connect malaria resistance with impaired intra-erythrocytic growth is presented. All studies are fraught with two kinds of bias. The first one resides in the impossibility of reproducing the in vivo situation in the simplified model in vitro. The second stems from the generalized use of RPMI 1640 culture medium. RPMI 1640 has critically low levels of several amino acids; is devoid of hypoxanthine (essential for parasite growth) and adenine; and is low in reduced glutathione. Analysis of representative studies indicates that impaired parasite growth in heterozygous red blood cells (RBCs) may derive from nutrient limitations and, therefore, possibly be of artefactual origin. This conclusion seems plausible because studies were performed with RPMI 1640 medium at relatively high hematocrit and for prolonged periods of time. Mutations considered are particularly sensitive to nutrient deprivation because they have higher metabolic demands due to permanent oxidant stress related to unpaired globin chains, sickle hemoglobin and high levels of membrane-free iron. In addition, non-parasitized AS- and thalassemic-RBCs are dehydrated and microcytic. Thus, the number of metabolically active elements per unit of blood volume is remarkably larger in mutant RBCs compared to normocytes. The latter point may represent a confirmation of Haldane's prophetic statement: 'The corpuscles of the anaemic heterozygotes are smaller than normal, and more resistant to hypotonic solutions. It is at least conceivable that they are also more resistant to attacks by the sporozoa which cause malaria.'

Out-of-Africa, the peopling of continents and islands: tracing uniparental gene trees across the map

Genetic relationships between human groups were first studied by comparisons of relative allele frequency at multiple loci. Geographical study of detailed, highly resolved trees of single, non-recombining uniparental loci (mitochondrial DNA: mtDNA and Y chromosome/non-recombining Y: NRY), following specific lineages rather than populations, then revolutionized knowledge of the peopling of the world, although, curiously, the use of geographically highly specific mutations that protect against malaria, found on individual autosomal globin genes, were first in single-locus phylogeography. mtDNA, with its high single nucleotide polymorphism (SNP) mutation rates and relative ease of dating, led the way and gave stronger proof of the recent near replacement of all human species by anatomically modern humans (AMH). AMH left Africa via a single southern exit about 70 000 years ago and rapidly spread around the Indian Ocean towards the Antipodes, long before a small branch left a South Asian colony, earlier on the trail, to populate Europe. The worldwide skeleton phylogeny of mtDNA is fully resolved, but a regional analysis will continue to illuminate subsequent migrations. NRY with a lower SNP mutation rate still has a dating problem relating to use the of single tandem repeats (STRs), but has validated mtDNA results and with more geographical specificity and genomic size, as with the autosomal human genome, has much more detail to offer for the future.

Artesunate and artelinic acid: association of embryotoxicity, reticulocytopenia, and delayed stimulation of hematopoiesis in pregnant rats

The artemisinin antimalarials cause embryo death and malformations in animals by killing embryonic erythroblasts. Groups of pregnant rats (N = 4) were administered 35 and 48 µmol/kg artesunate and 17.2, 28.7, 48, 96, and 191 µmol/kg artelinic acid as a single oral dose on gestational day (GD) 12. Litters were examined on GD21. The ED(50) for embryo death with artelinic acid (23.4 µmol/kg) was just slightly lower than that for decreased reticulocyte count at 24 hr postdose (33.5 µmol/kg) and both had similarly steep dose responses (maximal effects of total litter loss and ∼60% decreases in reticulocyte count at 48 µmol/kg). Results with artesunate were similar. The correlation coefficient between embryo death and decreased reticulocyte count was 0.82 (p<0.01). The close relationship between embryotoxicity and reticulocytopenia is suggestive of a common mechanism-artemisinin-induced mitochondrial damage leading to cell death. At 9 days postdose, treatment with artesunate and artelinic acid also caused increases in counts of reticulocytes, lymphocytes, basophils, and monocytes (up to 3.7 ×, 1.7 ×, 4.7 ×, and 1.7 × control, respectively). This stimulation of hematopoiesis may have been mediated by the direct oxidative conversion of artesunate or artelinic acid to the artemisininyl hydroperoxide within the bone marrow cells or by an indirect increase in reactive oxygen species. The high correlation between embryotoxicity and reticulocytopenia further supports the assertion that therapeutic dosage regimens of artemisinins that cause decreases in reticulocyte count in pregnant women during the putative critical period (approximately postconception wk 3 to 9) are at risk of also causing adverse effects on the embryo.

Plasmodium falciparum: Activity of artemisinin against Plasmodium falciparum cultured in sickle trait hemoglobin AS and normal hemoglobin AA red blood cells

The presence of sickle hemoglobin causes accumulation of hemoglobin degradative products that favor oxidative reaction in erythrocytes. Artemisinin derivatives exert antiparasite effects through oxidative reactions within infected erythrocytes. Using [(3)H]-hypoxanthine incorporation, we therefore did an in vitro comparison of IC(50) values for artemisinin in Plasmodium falciparum-infected erythrocytes from sickle cell trait (AS) and normal (AA) individuals. IC(50) values for chloroquine served as control. Without drugs, parasite growth was similar in AA and AS erythrocytes. Gender, age and blood group of donors had no significant effects on parasite growth. IC(50) value for artemisinin was 27+/-14nM in AS (N=22) compared to 24+/-9nM (N=27) in AA erythrocytes (P=0.4). IC(50) values for chloroquine were also similar in AA (22+/-8nM) and AS (20+/-11nM) erythrocytes. These results show no evidence of elevated artemisinin activity on P. falciparum in AS erythrocytes in vitro.

Ultrastructural assessment of Plasmodium falciparum in age-fractionated thalassaemic erythrocytes

Culture of Plasmodium falciparum in age-fractionated thalassaemic red blood cells (RBC) has shown evidence of parasite damage on light microscopy in older cells during the third culture cycle (96-144 h). In this report, parasites growing in thalassaemic trait and normal RBC were examined ultrastructurally from 96 to 144 h. All parasite stages in old thalassaemic RBC showed evidence of damage worsening with culture duration. There were cytoplasmic alterations with ribosomal damage, and parasite cytoplasm became increasingly loose and grainy, with multiple fissures. Discontinuity of the nuclear membrane with an abnormal nucleolus was seen at l20 h. Cytosomes remained normal, but damage to the food vacuole and shrunken disintegrating parasites were observed at 144 h. These changes are compatible with cellular degeneration and developmental retardation and would account for the schizont maturation arrest and reduced reinvasion rates previously reported. Increased free radicals associated with thalassaemic erythrocytes would explain these changes, further supporting the role for oxidant stress in the protective mechanism.

The hydration state of human red blood cells and their susceptibility to invasion by Plasmodium falciparum

In most inherited red blood cell (RBC) disorders with high gene frequencies in malaria-endemic regions, the distribution of RBC hydration states is much wider than normal. The relationship between the hydration state of circulating RBCs and protection against severe falciparum malaria remains unexplored. The present investigation was prompted by a casual observation suggesting that falciparum merozoites were unable to invade isotonically dehydrated normal RBCs. We designed an experimental model to induce uniform and stable isotonic volume changes in RBC populations from healthy donors by increasing or decreasing their KCl contents through a reversible K(+) permeabilization pulse. Swollen and mildly dehydrated RBCs were able to sustain Plasmodium falciparum cultures with similar efficiency to untreated RBCs. However, parasite invasion and growth were progressively reduced in dehydrated RBCs. In a parallel study, P falciparum invasion was investigated in density-fractionated RBCs from healthy subjects and from individuals with inherited RBC abnormalities affecting primarily hemoglobin (Hb) or the RBC membrane (thalassemias, hereditary ovalocytosis, xerocytosis, Hb CC, and Hb CS). Invasion was invariably reduced in the dense cell fractions in all conditions. These results suggest that the presence of dense RBCs is a protective factor, additional to any other protection mechanism prevailing in each of the different pathologies.

Artemisinins: activities and actions

Multidrug-resistant malaria caused by Plasmodium falciparum has severely limited treatment options over recent years. Artemisinins are still effective for treating uncomplicated as well as severe malaria, because resistance is not yet clinically apparent. This article reviews some clinically useful properties of artemisinins and how they might work.

Disposition of artesunate and dihydroartemisinin after administration of artesunate suppositories in children from Papua New Guinea with uncomplicated malaria

A detailed pharmacokinetic analysis was performed with 47 children from Papua New Guinea with uncomplicated falciparum or vivax malaria treated with artesunate (ARTS) suppositories (Rectocaps) given in two doses of approximately 13 mg/kg of body weight 12 h apart. Following an intensive sampling protocol, samples were assayed for ARTS and its primary active metabolite, dihydroartemisinin (DHA), by liquid chromatography-mass spectrometry. A population pharmacokinetic model was developed to describe the data. Following administration of the first dose, the mean maximal concentrations of ARTS and DHA were 1,085 nmol/liter at 0.9 h and 2,525 nmol/liter at 2.3 h, respectively. The absorption half-life for ARTS was 2.3 h, and the conversion half-life (ARTS to DHA) was 0.27 h, while the elimination half-life of DHA was 0.71 h. The mean common volumes of distribution for ARTS and DHA relative to bioavailability were 42.8 and 2.04 liters/kg, respectively, and the mean clearance values relative to bioavailability were 6 and 2.2 liters/h/kg for ARTS and DHA, respectively. Substantial interpatient variability was observed, and the bioavailability of the second dose relative to that of the first was estimated to be 0.72. The covariates age, sex, and alpha-thalassemia genotype were not influential in the pharmacokinetic model development; but the inclusion of weight as a covariate significantly improved the performance of the model. An ARTS suppositories dose of 10 of 20 mg/kg is appropriate for use in children with uncomplicated malaria.

Oxidative stress in malaria parasite-infected erythrocytes: host–parasite interactions

Experimenta naturae, like the glucose-6-phosphate dehydrogenase deficiency, indicate that malaria parasites are highly susceptible to alterations in the redox equilibrium. This offers a great potential for the development of urgently required novel chemotherapeutic strategies. However, the relationship between the redox status of malarial parasites and that of their host is complex. In this review article we summarise the presently available knowledge on sources and detoxification pathways of reactive oxygen species in malaria parasite-infected red cells, on clinical aspects of redox metabolism and redox-related mechanisms of drug action as well as future prospects for drug development. As delineated below, alterations in redox status contribute to disease manifestation including sequestration, cerebral pathology, anaemia, respiratory distress, and placental malaria. Studying haemoglobinopathies, like thalassemias and sickle cell disease, and other red cell defects that provide protection against malaria allows insights into this fine balance of redox interactions. The host immune response to malaria involves phagocytosis as well as the production of nitric oxide and oxygen radicals that form part of the host defence system and also contribute to the pathology of the disease. Haemoglobin degradation by the malarial parasite produces the redox active by-products, free haem and H(2)O(2), conferring oxidative insult on the host cell. However, the parasite also supplies antioxidant moieties to the host and possesses an efficient enzymatic antioxidant defence system including glutathione- and thioredoxin-dependent proteins. Mechanistic and structural work on these enzymes might provide a basis for targeting the parasite. Indeed, a number of currently used drugs, especially the endoperoxide antimalarials, appear to act by increasing oxidant stress, and novel drugs such as peroxidic compounds and anthroquinones are being developed.

Oxidative stress in patients with non-complicated malaria

AIM

To compare oxidative stress in adults with non-complicated malaria and healthy controls.

METHODOLOGY

We measured malondialdehyde (MDA), total antioxidant status (TAS), catalase, superoxide dismutase (SOD) and glutathione peroxidase (GSH-PX). Oxidative stress was calculated based on MDA/TAS, MDA/GSH-PX and SOD/catalase indexes.

RESULTS

Mean MDA in patients was 3.9 micromol/L (controls = 1.3 micromol/L). Mean TAS was 0.9 mmol/L in patients and controls. Malaria patients had less catalase activity when compared to controls (209.4 vs. 320.4 k/gr), while SOD and GSH-PX activity was higher (79.4 U/mL, 11,884.2U/L vs. 54.3 U/mL, 9,672.6 U/L). MDA/TAS index was 3.5 fold more in patients than in controls, MDA/GSH-PX and SOD/catalase indexes were increased by 6 and 2.8 fold. MDA levels and MDA/TAS index showed no differences according to malarial history, parasitaemia, Plasmodium species, parasite's stage, place of residence and drinking or smoking habits.

CONCLUSIONS

During acute non-complicated P. falciparum or P. vivax malaria, we observed high oxidative stress. This resulted from lipid peroxidation rather than from a reduced TAS. We propose MDA/TAS index as a useful marker of oxidative stress during malaria infection.

Artemisinin: mechanisms of action, resistance and toxicity

Artemisinin and its derivatives are widely used throughout the world. The mechanism of action of these compounds appears to involve the heme-mediated decomposition of the endoperoxide bridge to produce carbon-centred free radicals. The involvement of heme explains why the drugs are selectively toxic to malaria parasites. The resulting carbon-centred free radicals are alkylate heme and proteins, one of which is the translationally controlled tumour protein. Clinically relevant artemisinin resistance has not been demonstrated, but it is likely to occur since artemisinin resistance has been obtained in laboratory models. At high doses, artemisinin can be neurotoxic but toxicity has not been found in clinical studies. The mechanism of neurotoxicity may be similar to the mechanism of action.

Hemoglobin E: a balanced polymorphism protective against high parasitemias and thus severe P falciparum malaria

Hemoglobin E is very common in parts of Southeast Asia. The possible malaria protective effects of this and other inherited hemoglobin abnormalities prevalent in Thailand were assessed in a mixed erythrocyte invasion assay. In vitro, starting at 1% parasitemia,Plasmodium falciparum preferentially invaded normal (HbAA) compared to abnormal hemoglobin (HbH, AE, EE, HCS, β-thalassemia E) red cells (HRBCs). The median (range) ratio of parasitization of HRBCs (n = 109) compared to the controls of different major blood groups was 0.40 (0.08, 0.98), less than half that of the normal red cells (NRBCs) compared to their controls 0.88 (0.53, 1.4;P = .001). The median (range) parasitemia in the HRBCs was 2% (0.1%-9%) compared to 5.2% (1.2%-16.3%) in the NRBCs (P = .001). The proportion of the RBC population that is susceptible to malaria parasite invasion can be described by a selectivity index (SI; observed number of multiply invaded RBCs/number predicted). The heterozygote AE cells differed markedly from all the other cells tested with invasion restricted to approximately 25% of the RBCs; the median (range) SI was 3.8 (1-15) compared with 0.75 (0.1-0.9) for EE RBCs (P &lt; .01). Despite their microcytosis, AE cells are functionally relatively normal in contrast to the RBCs from the other hemoglobinopathies studied. These findings suggest that HbAE erythrocytes have an unidentified membrane abnormality that renders the majority of the RBC population relatively resistant to invasion by P falciparum. This would not protect from uncomplicated malaria infections but would prevent the development of heavy parasite burdens and is consistent with the “Haldane” hypothesis of heterozygote protection against severe malaria for hemoglobin E.