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

Abstract

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...

Insights into malaria pathogenesis gained from host metabolomics

“…A significant depletion of amino acids occurs in the bloodstream of Plasmodium-infected hosts, and a number of studies have characterized these perturbations [9][10][11][12][13][14][15][16][17][18][19][20][21][22]. Of these, arginine, glutamine, and tryptophan have received the most attention in recent studies due to the direct clinical consequences when either are decreased.…”

“…https://doi.org/10.1371/journal.ppat.1008930.g001 glutamine levels are depleted in the human host in both falciparum and vivax malaria [9,21,22,28]. In addition to impacting arginine biosynthesis ( Fig 1A), low plasma glutamine has been associated with severe malarial anemia in children with P. falciparum [29] and with impaired humoral immunity in a murine model of severe malaria [27].…”

“…Low levels of arginine in the bloodstream during malaria may underlie downstream consequences of impaired vasodilation, endothelial disruption, and reduced nitric oxide production [ 16 ]. While depletion of host arginine could derive in part from parasite-specific processes (e.g., elevated Plasmodium arginase activity [ 19 ]), experiments using murine and nonhuman primate models paired with analyses of human samples have demonstrated simultaneously diminished levels of arginine and its biosynthetic pathway metabolites (e.g., ornithine and citrulline) in the blood of malaria-infected hosts [ 9 , 18 , 21 ] ( Fig 1A ). This work suggests that arginine depletion results, at least in part, from a block in host production, in addition to parasite arginase activity.…”

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

“…Patients with severe malaria show low nitric oxide (NO) bioavailability resulting in impaired microvascular function 6,7 . Low levels of the NO synthase (NOS) substrate L-arginine and of the NOS cofactor tetrahydrobiopterin are also observed 8–10 , as well as disruption of NOS substrate/inhibitor homeostasis, all these factors limiting NO production 11,12 . These findings prompted the proposal of L-arginine supplementation as a tool to improve vascular function in severe malaria and a number of safety and efficacy studies have been conducted in recent years 13–15 .…”

Signatures of divergent anti-malarial treatment responses in peripheral blood from adults and young children in Malawi

“…Studies over the last several decades have shown that nitric oxide (NO) levels are associated with protection from malarial disease [51–55], and prior work has reported age-associated effects on NO metabolites during malaria infection [56]. The results presented here suggest that NO metabolite levels are upregulated in young children compared with adults, however, it is important to note that these measures did not change between V1 and V2, and they did not correlate with parasitaemia as other studies have found [57].…”