Plasmodium Infection Is Associated with Impaired Hepatic Dimethylarginine Dimethylaminohydrolase Activity and Disruption of Nitric Oxide Synthase Inhibitor/Substrate Homeostasis

Oxidative Stress in Malaria: Potential Benefits of Antioxidant Therapy

Malaria is an infectious disease and a serious public health problem in the world, with 3.3 billion people in endemic areas in 100 countries and about 200 million new cases each year, resulting in almost 1 million deaths in 2018. Although studies look for strategies to eradicate malaria, it is necessary to know more about its pathophysiology to understand the underlying mechanisms involved, particularly the redox balance, to guarantee success in combating this disease. In this review, we addressed the involvement of oxidative stress in malaria and the potential benefits of antioxidant supplementation as an adjuvant antimalarial therapy.

Decreased parasite burden and altered host response in children with sickle cell anemia and severe anemia with malaria

Plasmodium falciparum malaria causes morbidity and mortality in African children with sickle cell anemia (SCA), but comparisons of host responses to P falciparum between children with SCA (homozygous sickle cell disease/hemoglobin SS [HbSS]) and normal hemoglobin genotype/hemoglobin AA (HbAA) are limited. We assessed parasite biomass and plasma markers of inflammation and endothelial activation in children with HbAA (n = 208) or HbSS (n = 22) who presented with severe anemia and P falciparum parasitemia to Mulago Hospital in Kampala, Uganda. Genotyping was performed at study completion. No child had known SCA at enrollment. Children with HbSS did not differ from children with HbAA in peripheral parasite density, but had significantly lower sequestered parasite biomass. Children with HbSS had greater leukocytosis but significantly lower concentrations of several plasma inflammatory cytokines, including tumor necrosis factor α (TNF-α). In contrast, children with HbSS had threefold greater concentrations of angiopoietin-2 (Angpt-2), a marker of endothelial dysregulation associated with mortality in severe malaria. Lower TNF-α concentrations were associated with increased risk of postdischarge mortality or readmission, whereas higher Angpt-2 concentrations were associated with increased risk of recurrent clinical malaria. Children with SCA have decreased parasite sequestration and inflammation but increased endothelial dysregulation during severe anemia with P falciparum parasitemia, which may ameliorate acute infectious complications but predispose to harmful long-term sequelae.

DDAH-1, via regulation of ADMA levels, protects against ischemia-induced blood-brain barrier leakage

Dimethylarginine dimethylamino hydrolase-1 (DDAH-1) is an important regulator of nitric oxide (NO) metabolism that has been implicated in the pathogenesis of cardiovascular diseases. Nevertheless, its role in cerebral ischemia still needs to be elucidated. Herein, we examined the expression of DDAH-1 in the brain of rat by double-label immunofluorescence staining. DDAH-1 knock-out (DDAH-1-/-) and wild-type rats underwent middle cerebral artery occlusion/reperfusion (MCAO/R). After 24 h, neurological scores, TTC staining and TUNEL assay were used to evaluate neurological damages. 3 and 7-days infarct outcomes were also shown. Blood-brain-barrier (BBB) permeability was examined via Evans blue extravasation and tight junction (TJ) proteins expression and mRNA levels by western blot and RT-qPCR. The levels of plasma asymmetric dimethylarginine (ADMA), NO and ADMA in brain tissue were also assessed. In addition, supplementation of L-arginine to DDAH-1-/- rats was used to explore its role in regulating NO. DDAH-1 was abundantly distributed in cerebral cortex and basal nuclei, and mainly expressed in neurons and endothelial cells. DDAH-1-/- rats showed aggravated neurological damage and BBB disruption, including decrease of TJ proteins expression but indistinguishable mRNA levels after MCAO/R. DDAH-1 depletion and neurological damages were accompanied with increased ADMA levels and decreased NO concentrations. The supplementation with L-arginine partly restored the neurological damages and BBB disruption. To sum up, DDAH-1 revealed to have a protective role in ischemia stroke (IS) and IS-induced leakage of BBB via decreasing ADMA level and possibly via preventing TJ proteins degradation.

Serum Angiopoietin-1 and -2 and VEGF are associated with severe disease in vivax malaria

BACKGROUND & OBJECTIVES

Malaria continues to be a significant public health problem in tropical countries including India; however, there are limited tools to predict occurrence of severe disease due to malaria. This study was designed to evaluate the role of Angiopoietin-1 (Ang-1), Angiopoietin-2 (Ang-2), Vascular endothelial growth factor (VEGF) and Asymmetric Dimethylarginine (ADMA)as disease biomarkers in uncomplicated malaria (UM) and severe malaria (SM).

METHODS

This is a prospective observational study carried out at All India Institute of Medical Sciences (AIIMS), tertiary referral hospital in New Delhi, India. The study population included patients diagnosed with malaria (Plasmodium falciparum or Plasmodium vivax) either by rapid diagnostic kit test or positive peripheral smear and age more than 12 years. Forty-nine patients (25 with SM, 24 with UM) and 22 controls were recruited. In addition to routine investigations, serum concentrations of Ang-1, Ang-2, VEGF and ADMA were measured using ELISA technique.

RESULTS

We observed Ang-1 serum levels to be significantly lower in patients with severe malaria (7775 pg/ml) compared to uncomplicated malaria (17629 pg/ml) and healthy controls (43472 pg/ml) [p <0.001]. Ang-2 levels were significantly higher in severe malaria (11100 pg/ml) compared to uncomplicated malaria (7315 pg/ml) and healthy controls (3679 pg/ml) (p <0.001). The ratio of Ang-2/Ang-1 was significantly higher in patients with severe malaria. VEGF serum levels was significantly lower in severe malaria (130.36 pg/ml) compared to uncomplicated malaria (317.3 pg/ml). The Ang-1, Ang-2 and VEGF levels were able to differentiate severe malaria from uncomplicated malaria caused by P. vivax but not with P. falciparum.

INTERPRETATION & CONCLUSION

We conclude that Ang-1, Ang-2 and VEGF are markers of disease severity in vivax malaria.

Malaria in Pregnancy and Adverse Birth Outcomes: New Mechanisms and Therapeutic Opportunities

Malaria infection during pregnancy is associated with adverse birth outcomes but underlying mechanisms are poorly understood. Here, we discuss the impact of malaria in pregnancy on three pathways that are important regulators of healthy pregnancy outcomes: L-arginine-nitric oxide biogenesis, complement activation, and the heme axis. These pathways are not mutually exclusive, and they collectively create a proinflammatory, antiangiogenic milieu at the maternal-fetal interface that interferes with placental function and development. We hypothesize that targeting these host-response pathways would mitigate the burden of adverse birth outcomes attributable to malaria in pregnancy.

Malaria in pregnancy alters l-arginine bioavailability and placental vascular development

Reducing adverse birth outcomes due to malaria in pregnancy (MIP) is a global health priority. However, there are few safe and effective interventions. L-arginine is an essential amino acid in pregnancy and an immediate precursor in the biosynthesis of nitric oxide (NO), but there are limited data on the impact of MIP on NO biogenesis. We hypothesized that hypoarginemia contributes to the pathophysiology of MIP and that L-arginine supplementation would improve birth outcomes. In a prospective study of pregnant Malawian women, we show that MIP was associated with lower concentrations of L- arginine and higher concentrations of endogenous inhibitors of NO biosynthesis, asymmetric and symmetric dimethylarginine, which were associated with adverse birth outcomes. In a model of experimental MIP, L-arginine supplementation in dams improved birth outcomes (decreased stillbirth and increased birth weight) compared with controls. The mechanism of action was via normalized angiogenic pathways and enhanced placental vascular development, as visualized by placental microcomputerized tomography imaging. These data define a role for dysregulation of NO biosynthetic pathways in the pathogenesis of MIP and support the evaluation of interventions to enhance L-arginine bioavailability as strategies to improve birth outcomes.

L-arginine supplementation and thromboxane synthase inhibition increases cerebral blood flow in experimental cerebral malaria

Cerebral malaria pathogenesis involves vascular dysfunction with low nitric oxide (NO) bioavailability, vasoconstriction and impaired vasodilation, leading to ischemia, tissue hypoxia and ultimately death. Cerebral blood flow (CBF) involves NO and other pathways, including arachidonic acid (AA)-derived metabolites. Here we show that mice with experimental cerebral malaria (ECM) by P. berghei ANKA showed marked decreases in CBF (as assessed by laser speckle contrast imaging - LSCI) and that administration of L-arginine supplementation (50 mg/kg) and/or of the thromboxane synthase inhibitor Ozagrel (100 mg/kg) induced immediate increases in CBF. L-arginine in combination with artesunate (32 mg/kg) induced immediate reversal of brain ischemia in the short-term (1 hour), but the effect subsided after 3 and 6 hours. Neither L-arginine nor Ozagrel reversed blood brain barrier breakdown. Mice with ECM showed brain levels of selected AA-derived metabolites with a vasoconstrictor profile, with increased levels of 8-isoprostanes, 20-HETE and 14,15-DHET, whereas mice infected with a non-ECM-inducing strain of P. berghei (NK65) showed a vasodilator profile, with normal levels of 20-HETE and 14,15-DHET and increased levels of PGE2. L-arginine is capable of partially reversing cerebral ischemia and AA metabolites may play a role in the cerebrovascular dysfunction in ECM.

Perspective: L-arginine and L-citrulline Supplementation in Pregnancy: A Potential Strategy to Improve Birth Outcomes in Low-Resource Settings

The available data support the hypothesis that L-arginine or L-citrulline supplementation would be suitable for implementation in resource-constrained settings and will enhance placental vascular development and improve birth outcomes. In resource-constrained settings, the rates of adverse birth outcomes, including fetal growth restriction, preterm birth, and low birth weight, are disproportionately high. Complications resulting from preterm birth are now the leading cause of mortality in children <5 y of age worldwide. Despite the global health burden of adverse birth outcomes, few effective interventions are currently available and new strategies are urgently needed, especially for low-resource settings. L-arginine is a nutritionally essential amino acid in pregnancy and an immediate precursor of nitric oxide. During pregnancy, placental and embryonic growth increases the demand for L-arginine, which can exceed endogenous synthesis of L-arginine from L-citrulline, necessitating increased dietary intake. In many low-resource settings, dietary intake of L-arginine in pregnancy is inadequate owing to widespread protein malnutrition and depletion of endogenous L-arginine due to maternal infections, in particular malaria. Here we examine the role of the L-arginine-nitric oxide biosynthetic pathway in pregnancy including placental vascular development and fetal growth. We review the evidence for the relations between altered L-arginine bioavailability and pregnancy outcomes, and strategies for arginine supplementation in pregnancy. Existing studies of L-arginine supplementation in pregnancy in high-resource settings have shown improved maternal and fetal hemodynamics, prevention of pre-eclampsia, and improved birth outcomes including higher birth weight and longer gestation. Arginine supplementation studies now need to be extended to pregnant women in low-resource settings, especially those at risk of malaria.

Kinetic and Cross-Sectional Studies on the Genesis of Hypoargininemia in Severe Pediatric Plasmodium falciparum Malaria

The low bioavailability of nitric oxide (NO) and its precursor, arginine, contributes to the microvascular pathophysiology of severe falciparum malaria. To better characterize the mechanisms underlying hypoargininemia in severe malaria, we measured the plasma concentrations of amino acids involved in de novo arginine synthesis in children with uncomplicated falciparum malaria (UM; n = 61), children with cerebral falciparum malaria (CM; n = 45), and healthy children (HC; n = 109). We also administered primed infusions of l-arginine uniformly labeled with ¹³C₆ and ¹⁵N₄ to 8 children with severe falciparum malaria (SM; age range, 4 to 9 years) and 7 healthy children (HC; age range, 4 to 8 years) to measure the metabolic flux of arginine, hypothesizing that arginine flux is increased in SM. Using two different tandem mass spectrometric methods, we measured the isotopic enrichment of arginine in plasma obtained at 0, 60, 90, 120, 150, and 180 min during the infusion. The plasma concentrations of glutamine, glutamate, proline, ornithine, citrulline, and arginine were significantly lower in UM and CM than in HC (P ≤ 0.04 for all pairwise comparisons). Of these, glutamine concentrations were the most markedly decreased: median, 457 μM (interquartile range [IQR], 400 to 508 μM) in HC, 300 μM (IQR, 256 to 365 μM) in UM, and 257 μM (IQR, 195 to 320 μM) in CM. Arginine flux during steady state was not significantly different in SM than in HC by the respective mass spectrometric methods: 93.2 μmol/h/kg of body weight (IQR, 84.4 to 129.3 μmol/h/kg) versus 88.0 μmol/h/kg (IQR, 73.0 to 102.2 μmol/h/kg) (P = 0.247) by the two mass spectrometric methods in SM and 93.7 μmol/h/kg (IQR, 79.1 to 117.8 μmol/h/kg) versus 81.0 μmol/h/kg (IQR, 75.9 to 88.6 μmol/h/kg) (P = 0.165) by the two mass spectrometric methods in HC. A limited supply of amino acid precursors for arginine synthesis likely contributes to the hypoargininemia and NO insufficiency in falciparum malaria in children.

Importance of endothelial dysfunction biomarkers in patients with Crimean-Congo hemorrhagic fever

The pathogenesis of the Crimean-Congo hemorrhagic fever (CCHF) and the cause of the hemorrhage are not yet fully understood. However, the endothelium plays a key role in the pathogenesis. The purpose of this study was to investigate endothelial dysfunction markers (asymmetrical dimethyl arginine [ADMA], endothelin 1[ET-1], thrombomodulin [TM], von Willebrand factor [vWf], and intercellular adhesion molecule [ICAM-1]) in serum in patients with CCHF and their associations with hemorrhage. Seventy-three patients with CCHF were included in the study. All patients' endothelial dysfunction markers were studied using routine biochemical and hematological tests. The data obtained were then subjected to statistical analysis. Statistically significant differences were determined between the patients and healthy control groups at time of presentation to hospital in terms of ADMA (P < 0.001), ET-1 (P < 0.001), TM (P = 0.039), vWf (P < 0.001), and ICAM-1 (P < 0.001) levels. Only the differences in TM and vWf were significant between the hemorrhagic and non-hemorrhagic groups (P < 0.05). Both serum ADMA and TM levels were significantly higher in the hemorrhage and non-hemorrhage CCHF groups on the 5th day compared to the 1st day (P < 0.05). Levels of endothelial dysfunction markers in CCHF vary in proportion to the damage occurring in the endothelium. ADMA and TM levels were lower in periods with mild endothelial injury. They were increased in line with severity endothelial injury. They may be an early marker in showing hemorrhage. Elevation in ADMA levels and low nitric oxide levels lead to endothelial injury and hemorrhage. Soluble TM that entered the circulation in line with the increased endothelial injury in hemorrhagic patients has been compromised the coagulation cascade.

Decreased Rate of Plasma Arginine Appearance in Murine Malaria May Explain Hypoargininemia in Children With Cerebral Malaria

BACKGROUND

 Plasmodium infection depletes arginine, the substrate for nitric oxide synthesis, and impairs endothelium-dependent vasodilation. Increased conversion of arginine to ornithine by parasites or host arginase is a proposed mechanism of arginine depletion.

METHODS

 We used high-performance liquid chromatography to measure plasma arginine, ornithine, and citrulline levels in Malawian children with cerebral malaria and in mice infected with Plasmodium berghei ANKA with or without the arginase gene. Heavy isotope-labeled tracers measured by quadrupole time-of-flight liquid chromatography-mass spectrometry were used to quantify the in vivo rate of appearance and interconversion of plasma arginine, ornithine, and citrulline in infected mice.

RESULTS

 Children with cerebral malaria and P. berghei-infected mice demonstrated depletion of plasma arginine, ornithine, and citrulline. Knock out of Plasmodium arginase did not alter arginine depletion in infected mice. Metabolic tracer analysis demonstrated that plasma arginase flux was unchanged by P. berghei infection. Instead, infected mice exhibited decreased rates of plasma arginine, ornithine, and citrulline appearance and decreased conversion of plasma citrulline to arginine. Notably, plasma arginine use by nitric oxide synthase was decreased in infected mice.

CONCLUSIONS

 Simultaneous arginine and ornithine depletion in malaria parasite-infected children cannot be fully explained by plasma arginase activity. Our mouse model studies suggest that plasma arginine depletion is driven primarily by a decreased rate of appearance.

Relationship between asymmetric dimethylarginine in umbilical cord plasma and birth weight follows a U-shaped curve

Asymmetric dimethylarginine (ADMA) is a nonselective nitric oxide (NO) synthase inhibitor associated with cardiovascular and metabolic disorders. NO regulates placental blood flow, which plays an important role in fetal growth. Many epidemiological studies have disclosed that restricted fetal growth is associated with an increased risk of insulin resistance in adult life. We studied the relationship between ADMA in cord blood and birth size. Nine small for gestational age (SGA) and 32 appropriate for gestational age (AGA) infants were studied. Their cord plasma ADMA, insulin, insulin-like growth factor-1 (IGF-1), and adipocytokine levels were determined using enzyme-linked immunosorbent assays. The relationship between birth weight and ADMA levels followed a U-shaped curve rather than inverse linear associations expected over a full range of birth weight distribution. ADMA positively correlated with birth weight in the AGA group (p<0.001, R=0.590), and inversely correlated with birth weight in the SGA group (p<0.05, R=-0.741). ADMA inversely correlated with adiponectin (p<0.05, R=-0.289) and quantitative insulin sensitivity check index (QUICKI) (p<0.05, R=-0.294) in all subjects, and did not correlate with nitrogen oxides (NO_X). Insulin, IGF-1, leptin, adiponectin and QUICKI were lower in the SGA than the AGA group. Plasma ADMA levels in cord blood may be a marker of fetal growth and insulin resistance.

Tetrahydrobiopterin Supplementation Improves Phenylalanine Metabolism in a Murine Model of Severe Malaria

Tetrahydrobiopterin (BH4) is an essential cofactor for both phenylalanine hydroxylase and nitric oxide synthase. Patients with severe malaria have low urinary BH4, elevated plasma phenylalanine, and impaired endothelium-dependent vasodilation, suggesting that BH4 depletion may limit phenylalanine metabolism and nitric oxide synthesis. We infected C57BL/6 mice with Plasmodium berghei ANKA to characterize BH4 availability and to investigate the effects of BH4 supplementation. P. berghei ANKA infection lowered BH4 in plasma, erythrocytes, and brain tissue but raised it in aorta and liver tissue. The ratio of BH4 to 7,8-BH2 (the major product of BH4 oxidation) was decreased in plasma, erythrocytes, and brain tissue, suggesting that oxidation contributes to BH4 depletion. The continuous infusion of sepiapterin (a BH4 precursor) and citrulline (an arginine precursor) raised the concentrations of BH4 and arginine in both blood and tissue compartments. The restoration of systemic BH4 and arginine availability in infected mice produced only a minor improvement in whole blood nitrite concentrations, a biomarker of NO synthesis, and failed to prevent the onset of severe disease symptoms. However, sepiapterin and citrulline infusion reduced the ratio of phenylalanine to tyrosine in plasma, aortic tissue, and brain tissue. In summary, BH4 depletion in P. berghei infection may compromise both nitric oxide synthesis and phenylalanine metabolism; however, these findings require further investigation in human patients with severe malaria.

Exported Epoxide Hydrolases Modulate Erythrocyte Vasoactive Lipids during Plasmodium falciparum Infection

Erythrocytes are reservoirs of important epoxide-containing lipid signaling molecules, including epoxyeicosatrienoic acids (EETs). EETs function as vasodilators and anti-inflammatory modulators in the bloodstream. Bioactive EETs are hydrolyzed to less active diols (dihydroxyeicosatrienoic acids) by epoxide hydrolases (EHs). The malaria parasite Plasmodium falciparum infects host red blood cells (RBCs) and exports hundreds of proteins into the RBC compartment. In this study, we show that two parasite epoxide hydrolases, P. falciparum epoxide hydrolases 1 (PfEH1) and 2 (PfEH2), both with noncanonical serine nucleophiles, are exported to the periphery of infected RBCs. PfEH1 and PfEH2 were successfully expressed in Escherichia coli, and they hydrolyzed physiologically relevant erythrocyte EETs. Mutations in active site residues of PfEH1 ablated the ability of the enzyme to hydrolyze an epoxide substrate. Overexpression of PfEH1 or PfEH2 in parasite-infected RBCs resulted in a significant alteration in the epoxide fatty acids stored in RBC phospholipids. We hypothesize that the parasite disruption of epoxide-containing signaling lipids leads to perturbed vascular function, creating favorable conditions for binding and sequestration of infected RBCs to the microvascular endothelium.

The malaria parasite exports hundreds of proteins into the erythrocyte compartment. However, for most of these proteins, their physiological function is unknown. In this study, we investigate two “hypothetical” proteins of the α/β-hydrolase fold family that share sequence similarity with epoxide hydrolases (EHs)—enzymes that destroy bioactive epoxides. Altering EH expression in parasite-infected erythrocytes resulted in a significant change in the epoxide fatty acids stored in the host cell. We propose that these EH enzymes may help the parasite to manipulate host blood vessel opening and inflame the vessel walls as they pass through the circulation system. Understanding how the malaria parasite interacts with its host RBCs will aid in our ability to combat this deadly disease.

Nitric Oxide-Dependent Endothelial Dysfunction and Reduced Arginine Bioavailability in Plasmodium vivax Malaria but No Greater Increase in Intravascular Hemolysis in Severe Disease

BACKGROUND

Pathogenesis of severe Plasmodium vivax malaria is poorly understood. Endothelial dysfunction and reduced nitric oxide (NO) bioavailability characterize severe falciparum malaria, but have not been assessed in severe vivax malaria.

METHODS

In patients with severe vivax malaria (n = 9), patients with nonsevere vivax malaria (n = 58), and healthy controls (n = 79), we measured NO-dependent endothelial function by using reactive hyperemia-peripheral arterial tonometry (RH-PAT) and assessed associations with arginine, asymmetric dimethylarginine (ADMA), and hemolysis.

RESULTS

The L-arginine level and the L-arginine to ADMA ratio (a measure of L-arginine bioavailability) were reduced in patients with severe vivax malaria and those with nonsevere vivax malaria, compared with healthy controls (median L-arginine level, 65, 66, and 98 µmol/mL, respectively [P = .0001]; median L-arginine to ADMA ratio, 115, 125, and 187, respectively [P = .0001]). Endothelial function was impaired in proportion to disease severity (median RH-PAT index, 1.49, 1.73, and 1.97 in patients with severe vivax malaria, those with nonsevere vivax malaria, and healthy controls, respectively; P = .018) and was associated with the L-arginine to ADMA ratio. While the posttreatment fall in hemoglobin level was greater in severe vivax malaria as compared to nonsevere vivax malaria (2.5 vs 1 g/dL; P = .0001), markers of intravascular hemolysis were not higher in severe disease.

CONCLUSIONS

Endothelial function is impaired in nonsevere and severe vivax malaria, is associated with reduced L-arginine bioavailability, and may contribute to microvascular pathogenesis. Severe disease appears to be more associated with extravascular hemolysis than with intravascular hemolysis.

Pathophysiological Mechanisms in Gaseous Therapies for Severe Malaria

Over 200 million people worldwide suffer from malaria every year, a disease that causes 584,000 deaths annually. In recent years, significant improvements have been achieved on the treatment of severe malaria, with intravenous artesunate proving superior to quinine. However, mortality remains high, at 8% in children and 15% in adults in clinical trials, and even worse in the case of cerebral malaria (18% and 30%, respectively). Moreover, some individuals who do not succumb to severe malaria present long-term cognitive deficits. These observations indicate that strategies focused only on parasite killing fail to prevent neurological complications and deaths associated with severe malaria, possibly because clinical complications are associated in part with a cerebrovascular dysfunction. Consequently, different adjunctive therapies aimed at modulating malaria pathophysiological processes are currently being tested. However, none of these therapies has shown unequivocal evidence in improving patient clinical status. Recently, key studies have shown that gaseous therapies based mainly on nitric oxide (NO), carbon monoxide (CO), and hyperbaric (pressurized) oxygen (HBO) alter vascular endothelium dysfunction and modulate the host immune response to infection. Considering gaseous administration as a promising adjunctive treatment against severe malaria cases, we review here the pathophysiological mechanisms and the immunological aspects of such therapies.

Asymmetric Dimethylarginine in Adult Falciparum Malaria: Relationships With Disease Severity, Antimalarial Treatment, Hemolysis, and Inflammation

Asymmetric Dimethylarginine (ADMA) and arginine bioavailability are reduced acutely in adult falciparum malaria. ADMA increases following commencement of antimalarial therapy, is associated with arginine and haemolysis, and likely contributes to reduced nitric oxide bioavailability in severe falciparum malaria.

Background. Endothelial nitric oxide (NO) bioavailability is impaired in severe falciparum malaria (SM). Asymmetric dimethylarginine (ADMA), an endogenous inhibitor of NO synthase (NOS), contributes to endothelial dysfunction and is associated with mortality in adults with falciparum malaria. However, factors associated with ADMA in malaria, including the NOS-substrate l-arginine, hemolysis, and antimalarial treatment, are not well understood.

Methods. In a prospective observational study of Malaysian adults with SM (N = 22) and non-SM (NSM; N = 124) and healthy controls (HCs), we investigated factors associated with plasma ADMA including the effects of antimalarial treatment.

Results. Compared with HCs, ADMA levels were lower in NSM (0.488 µM vs 0.540 µM, P = .001) and in the subset of SM patients enrolled before commencing treatment (0.453 µM [N = 5], P = .068), but levels were higher in SM patients enrolled after commencing antimalarial treatment (0.610 µM [N = 17], P = .026). In SM and NSM, ADMA levels increased significantly to above-baseline levels by day 3. Baseline ADMA was correlated with arginine and cell-free hemoglobin in SM and NSM and inversely correlated with interleukin-10 in NSM. Arginine and the arginine/ADMA ratio (reflective of arginine bioavailability) were lower in SM and NSM compared with HCs, and the arginine/ADMA ratio was lower in SM compared with NSM.

Conclusions. Pretreatment ADMA concentrations and l-arginine bioavailability are reduced in SM and NSM. Asymmetric dimethylarginine increases to above-baseline levels after commencement of antimalarial treatment. Arginine, hemolysis, and posttreatment inflammation all likely contribute to ADMA regulation, with ADMA likely contributing to the reduced NO bioavailability in SM.