Plasma Plasmodium falciparum histidine-rich protein-2 (PfHRP-2) concentrations, a measure of parasite biomass, have been correlated with malaria severity in adults, but not yet in children. We measured plasma PfHRP-2 in Tanzanian children with uncomplicated (n = 61) and cerebral malaria (n = 45; 7 deaths). Median plasma PfHRP-2 concentrations were higher in cerebral malaria (1008 [IQR 342–2572] ng/mL) than in uncomplicated malaria (465 [IQR 36–1426] ng/mL; p = 0.017). In cerebral malaria, natural log plasma PfHRP-2 was associated with coma depth (r = −0.42; p = 0.006) and mortality (OR: 3.0 [95% CI 1.03–8.76]; p = 0.04). In this relatively small cohort study in a mesoendemic transmission area of Africa, plasma PfHRP-2 was associated with pediatric malaria severity and mortality. Further studies among children in areas of Africa with higher malaria transmission and among children with different clinical manifestations of severe malaria will help determine the wider utility of quantitative PfHRP-2 as a measure of parasite biomass and prognosis in sub-Saharan Africa.

We earlier established that nitric oxide (NO) is protective against severe malaria and that arginine and NO levels are reduced in malaria patients. We now show that an M2-like blood monocyte phenotype is significantly associated with hypoargininemia, NO insufficiency, and disease severity in Tanzanian children with falciparum malaria. Compared to control children (n = 106), children with moderately severe (n = 77) and severe falciparum malaria (n = 129) had significantly higher mononuclear cell arginase 1 mRNA, protein, and enzyme activity; lower NOS2 mRNA; lower plasma arginine; and higher plasma IL-10, IL-13, and IL-4. In addition, monocyte CD206 and CD163 and plasma soluble CD163 were elevated. Multivariate logistic regression analysis revealed a significant correlation of risk of severe malaria with both plasma IL-10 and soluble CD163 levels. Monocyte M2 skewing likely contributes to NO bioinsufficiency in falciparum malaria in children. Treatments that reverse the M2 polarization may have potential as adjunctive treatment for malaria.

In contrast to adults, plasma ADMA is reduced in SM in children, but hypoargininemia is more severe. Arginine bioavailability (reflected by low arginine:ADMA ratios) is therefore comparably low in SM in children as in adults. Therapies to increase NO bioavailability in malaria may be useful as adjunctive treatment of severe malaria in children.

Decreased bioavailability of nitric oxide (NO) is a major contributor to the pathophysiology of severe falciparum malaria. Tetrahydrobiopterin (BH4) is an enzyme cofactor required for NO synthesis from L-arginine. We hypothesized that systemic levels of BH4 would be decreased in children with cerebral malaria, contributing to low NO bioavailability. In an observational study in Tanzania, we measured urine levels of biopterin in its various redox states (fully reduced [BH4] and the oxidized metabolites, dihydrobiopterin [BH2] and biopterin [B0]) in children with uncomplicated malaria (UM, n = 55), cerebral malaria (CM, n = 45), non-malaria central nervous system conditions (NMC, n = 48), and in 111 healthy controls (HC). Median urine BH4 concentration in CM (1.10 [IQR:0.55–2.18] μmol/mmol creatinine) was significantly lower compared to each of the other three groups — UM (2.10 [IQR:1.32–3.14];p<0.001), NMC (1.52 [IQR:1.01–2.71];p = 0.002), and HC (1.60 [IQR:1.15–2.23];p = 0.005). Oxidized biopterins were increased, and the BH4:BH2 ratio markedly decreased in CM. In a multivariate logistic regression model, each Log10-unit decrease in urine BH4 was independently associated with a 3.85-fold (95% CI:1.89–7.61) increase in odds of CM (p<0.001). Low systemic BH4 levels and increased oxidized biopterins contribute to the low NO bioavailability observed in CM. Adjunctive therapy to regenerate BH4 may have a role in improving NO bioavailability and microvascular perfusion in severe 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 ϭ 61), children with cerebral falciparum malaria (CM; n ϭ 45), and healthy children (HC; n ϭ 109). We also administered primed infusions of L-arginine uniformly labeled with 13 C 6 and 15 N 4 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 Յ 0.04 for all pairwise comparisons). Of these, glutamine concentrations were the most markedly decreased: median, 457 M (interquartile range [IQR], 400 to 508 M) in HC, 300 M (IQR, 256 to 365 M) in UM, and 257 M (IQR, 195 to 320 M) in CM. Arginine flux during steady state was not significantly different in SM than in HC by the respective mass spectrometric methods: 93.2 mol/h/kg of body weight (IQR, 84.4 to 129.3 mol/h/ kg) versus 88.0 mol/h/kg (IQR, 73.0 to 102.2 mol/h/kg) (P ϭ 0.247) by the two mass spectrometric methods in SM and 93.7 mol/h/kg (IQR, 79.1 to 117.8 mol/h/ kg) versus 81.0 mol/h/kg (IQR, 75.9 to 88.6 mol/h/kg) (P ϭ 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. Granger DL. 2019. Kinetic and cross-sectional studies on the genesis of hypoargininemia in severe pediatric Plasmodium falciparum malaria. Infect Immun 87:e00655-18. https:// RESULTSArginine amino acid precursor observational study. We enrolled 116 HC, 66 UM, and 52 children with cerebral falciparum malaria (CM). A total of 109 HC, 61 UM, and 45 CM had sufficient plasma for amino acid analysis. The baseline characteristics of the three groups are shown in Table 1. Among the CM, seven died. CM were significantly older than the children in the other two groups, and the time since the last meal was longer in both UM and CM than in HC.Glutamine levels were significantly lower in UM and CM than in HC (Fig. 2) (P Յ 0.025 for all pairwise comparisons). In addition, glutamate levels were lower in children with malaria than in HC (Fig. 2) (P Յ 0.036 for all pairwise comparisons). Rubach et al. Infection and Immunity April 2019 Volume 87 Issue 4 e00655-18 iai.asm.org 2 on July 4, 2020 by guest http://iai.asm.org/ Downloaded fromCitrulline, arginine, proline, and ornithine level...