ABSTRACT
Severe Plasmodium falciparum malaria is associated with hypoargininemia, which contributes to impaired systemic and pulmonary nitric oxide (NO) production and endothelial dysfunction. Since intravascular hemolysis is an intrinsic feature of severe malaria, we investigated whether and by which mechanisms free heme [Fe(III)-protoporphyrin IX (FP)] might contribute to the dysregulation of L-arginine (L-Arg) metabolism and bioavailability. Carrier systems "y+" [or cationic amino acid transporter (CAT)] and "y+L" transport L-Arg into red blood cells (RBC), where it is hydrolyzed to ornithine and urea by arginase (isoform I) or converted to NO* and citrulline by endothelial nitric oxide synthase (eNOS). Our results show a significant and dose-dependent impairment of L-Arg transport into RBC pretreated with FP, with a strong inhibition of the system carrier y+L. Despite the impaired L-Arg influx, higher amounts of L-Arg-derived urea are produced by RBC preexposed to FP caused by activation of RBC arginase I. This activation appeared not to be mediated by oxidative modifications of the enzyme. We conclude that L-Arg transport across RBC membrane is impaired and arginase-mediated L-Arg consumption enhanced by free heme. This could contribute to reduced NO production in severe malaria.
Subject(s)
Arginine/blood , Endothelial Cells/metabolism , Erythrocytes/metabolism , Hemin/metabolism , Malaria, Falciparum/blood , Microvessels/metabolism , Amino Acid Transport System y+/blood , Amino Acid Transport System y+L/blood , Arginase/blood , Biological Availability , Biological Transport , Cells, Cultured , Citrulline/metabolism , Enzyme Activation , Humans , Hydrolysis , Kinetics , Microvessels/cytology , Nitric Oxide/metabolism , Nitric Oxide Synthase Type III/metabolism , Ornithine/blood , Urea/bloodABSTRACT
Clinical treatment-failures to affordable drugs encouraged new investigation for discovery and development of new prophylactic and therapeutic interventions against malaria. The Drug Discovery Cluster (DDcl) of the Italian Malaria Network gathers several highly integrated and complementary laboratories from different Italian Institutions to identify, synthesise, screen in vitro and in vivo new antimalarial molecules directed against the intraerythrocytic stage of P. falciparum parasites and/or with transmission blocking activity to select lead compounds for further development. Complementary research activities, both in vitro and in the clinics, aim at investigating the pathogenetic mechanisms of severe malaria anaemia and the different manifestations of the disease in malaria-HIV co-infected patients to identify new therapies and improve survival.
