Severe falciparum malaria (SM) is associated with tissue ischemia related to cytoadherence of parasitized erythrocytes to microvascular endothelium and reduced levels of NO and its precursor, l-arginine. Endothelial function has not been characterized in SM but can be improved by l-arginine in cardiovascular disease. In an observational study in Indonesia, we measured endothelial function using reactive hyperemia–peripheral arterial tonometry (RH-PAT) in 51 adults with SM, 48 patients with moderately severe falciparum malaria (MSM), and 48 controls. The mean RH-PAT index was lower in SM (1.41; 95% confidence interval [CI] = 1.33–1.47) than in MSM (1.82; 95% CI = 1.7–2.02) and controls (1.93; 95% CI = 1.8–2.06; P < 0.0001). Endothelial dysfunction was associated with elevated blood lactate and measures of hemolysis. Exhaled NO was also lower in SM relative to MSM and controls. In an ascending dose study of intravenous l-arginine in 30 more patients with MSM, l-arginine increased the RH-PAT index by 19% (95% CI = 6–34; P = 0.006) and exhaled NO by 55% (95% CI = 32–73; P < 0.0001) without important side effects. Hypoargininemia and hemolysis likely reduce NO bioavailability. Endothelial dysfunction in malaria is nearly universal in severe disease, is reversible with l-arginine, and likely contributes to its pathogenesis. Clinical trials in SM of adjunctive agents to improve endothelial NO bioavailability, including l-arginine, are warranted.

SummaryNitric oxide (NO)-related activity has been shown to be protective against Plasmodium fakiparum in vitro. It has been hypothesized, however, that excess NO production contributes to the pathogenesis of cerebral malaria. The purpose of this study was to compare markers of NO production [urinary and plasma nitrate + nitrite (NO~)], leukocyte-inducible nitric oxide synthase type 2 (NOS2), and plasma TNF-c~ and IL-10 levels with disease severity in 191 Tanzanian children with and without malaria. Urine NO• excretion and plasma NOx levels (corrected for renal impairment) were inversely related to disease severity, with levels highest in subclinical infection and lowest in fatal cerebral malaria. Results could not be explained by differences in dietary nitrate ingestion among the groups. Plasma levels of IL-10, a cytokine known to suppress NO synthesis, increased with disease severity. Leukocyte NOS2 antigen was detectable in all control children tested and in all those with subclinical infection, but was undetectable in all but one subject with cerebral malaria. This suppression of NO synthesis in cerebral malaria may contribute to pathogenesis. In contrast, high fasting NO x levels and leukocyte NOS2 in healthy controls and asymptomatic infection suggest that increased NO synthesis might protect against clinical disease. NO appears to have a protective rather than pathological role in African children with malaria.

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Cryptococcus neoformans is variably encapsulated in vitro, whereas in tissues it develops a large capsule. We observed that cells of a strain with thin capsules, when growing in a standard fungal culture medium, became heavily encapsulated when incubated in serum-free cell culture medium (Dulbecco's modified Eagle's medium IDMEI). Capsule size was quantitated physically by measuring cell volume, and chemically by determining the content of a capsular monosaccharide, glucuronate. The C02/HCO3 couple stimulated capsule development, resulting in visible enlargement by 3 h after exposure to high C02/HCO3. The amount of capsule per cell was directly proportional to the total millimolar C02/HCO3 concentration between 24 and 2.4 mM at pH 7.35, but at constant Pco2 (40 torr) and varying [HCO3J the cells were heavily encapsulated down to pH 6.8. Concentration of C02/HCO3 in the physiologic range increased elaboration of polysaccharide into the medium and slowed the cell generation time from 2 to 6 h. Four other first-passage clinical isolates were all heavily encapsulated in DME with C02/HCO3, but variably encapsulated in DME without C02/HCO3. Exposure of yeast to increased C02/HCO3 caused a marked reduction in complement-mediated phagocytosis by mouse macrophages. A stable clone was isolated which contained capsular polysaccharide, but lacked the C02-inducible phenotype. This clone was avirulent for steroid-treated rabbits. Thus, the prevailing CO2 concentration in mammalian tissues may be one stimulus for capsular polysaccharide synthesis. This could serve as an adaptive mechanism favoring parasite survival in the host.

Summary MRL-I/r/I/rHowever, the chromosomal location of the NOS gene was consistent with an insulin-dependent diabetes locus identified in an analysis of nonobese diabetic (NOD) mice. These results suggest that elevated nitric oxide production could be important in the pathogenesis of autoimmunity, and that treatments to block the production of nitric oxide or block its effects might be valuable therapeutically.

L-arginine is required for the fungistatic action of murine macrophages in vitro. To

The microbiostatic action of macrophages was studied in vitro employing peritoneal cytotoxic macrophages (CM) from mice acting against Cryptococcus neoformans cultured in Dulbecco's medium with 10% dialyzed fetal bovine serum. Fungistasis was measured using electronic particle counting after lysis of macrophages with detergent.Macrophage fungistasis failed in medium lacking only Larginine. Complete fungistasis was restored by L-arginine; restoration was concentration dependent, maximal at 200 MuM. Deletion of all other essential amino acids did not abrogate fungistasis provided that L-arginine was present. Of twenty guanido compounds, including D-arginine, only three (L-arginine, L-homoarginine, and L-arginine methylester) supported fungistasis. Known activators or mediators of macrophage cytotoxicity (endotoxin, interferon gamma, tumor necrosis factor) did not replace L-arginine for CM-mediated fungistasis. The guanido analogue NG-monomethyl-L-arginine was a potent competitive inhibitor of CM-mediated fungistasis giving 50% inhibition at an inhibitor/L-arginine ratio of 1:27. Although CM completely blocked fungal reproduction via an Larginine-dependent mechanism, the majority of the dormant fungi remained viable. Thus, this mechanism is viewed as a microbiostatic process similar or identical to the tumoristatic effect of macrophages. This suggests the production of a broad spectrum biostatic metabolite(s) upon consumption of L-arginine by cytotoxic macrophages.