We propose that low nitric oxide (NO) bioavailability mediates the microcirculatory complications of severe malaria;NO quenching by cell-free hemoglobin (Hb) released as an unavoidable consequence of parasite replication and low NO production due to hypoargininemia lead to low NO bioavailability. Vascular leak, petechial hemorrhaging, and hypotension are well recognized complications of experimental cerebral malaria (ECM), and the proposed studies will determine whether poor tissue oxygenation also functions in malaria pathogenesis by altering blood flow or functional capillary density. Our observations that (i) free hemoglobin (Hb) is markedly elevated during ECM, (ii) free Hb scavenges nitric oxide (NO) and (iii) marked hypoargininemia occurs during ECM indicate that, in contrast to sepsis, malaria shock is caused by low NO bioavailability. A major controversy in microcirculation research is the role of NO in mediating vascular leak and pathogenesis, and our proposed studies will define its role in vascular leak during ECM. A key prediction of our hypothesis is that exogenous NO should protect against ECM pathogenesis;indeed, NO donor administration significantly (P=0.003) protects animals from the development of disease. The markedly protected NO donor-treated mice abrogated the vascular leak, petechial hemorrhage, hypotension, and impaired NO mediated signaling (cGMP levels) that were detected in saline-injected controls with ECM. These studies will be extended to define whether NO donor administration protects against other microcirculatory dysfunction during ECM, such as low tissue perfusion and oxygenation (aim 1). Adhesion of parasitized erythrocytes (pRBCs), platelets, and leukocytes occur during ECM and deficiency of selected cell adhesion molecules protects against malaria pathogenesis. We will interrelate the results of the microcirculatory complications of ECM to cell adhesion and eCAM expression to define the cellular and molecular mechanisms whereby cell adhesion contributes to disruption of the blood brain barrier and pathogenesis and identify whether and how exogenous NO protects against ECM cell adhesion (aim 2).
The final aim will assess by bioassay (arteriolar dilation, and venular leak) and actual measurement (NO electrode) whether NO bioavailability is impaired during ECM and restored by the protective NO donor. The response of eNOS to ECM and NO donor treatment will also be elucidated;a detailed understanding of in vivo eNOS responses to free Hb or to low NO bioavailability that occurs during other diseases (sickle cell anemia) is currently lacking. Besides providing new information about the microcirculation, the proposed studies may lead to adjunct therapy for malaria that rescues millions of children from death or impaired cognition. These studies will also address long standing controversies about malaria pathogenesis, such as whether pRBC adhesion leads to hypoxia and multi-organ failure (sequestration hypothesis).

Agency
National Institute of Health (NIH)
Institute
National Heart, Lung, and Blood Institute (NHLBI)
Type
Research Project (R01)
Project #
5R01HL087290-04
Application #
7845632
Study Section
Hypertension and Microcirculation Study Section (HM)
Program Officer
Qasba, Pankaj
Project Start
2007-04-01
Project End
2012-03-31
Budget Start
2010-04-01
Budget End
2012-03-31
Support Year
4
Fiscal Year
2010
Total Cost
$426,150
Indirect Cost
Name
La Jolla Institute
Department
Type
DUNS #
114215473
City
San Diego
State
CA
Country
United States
Zip Code
92121
Ong, Peng Kai; Moreira, Aline S; Daniel-Ribeiro, Cláudio T et al. (2018) Reversal of cerebrovascular constriction in experimental cerebral malaria by L-arginine. Sci Rep 8:15957
Martins, Yuri C; Clemmer, Leah; Orjuela-Sanchez, Pamela et al. (2013) Slow and continuous delivery of a low dose of nimodipine improves survival and electrocardiogram parameters in rescue therapy of mice with experimental cerebral malaria. Malar J 12:138
Ong, Peng Kai; Meays, Diana; Frangos, John A et al. (2013) A chronic scheme of cranial window preparation to study pial vascular reactivity in murine cerebral malaria. Microcirculation 20:394-404
Ong, Peng Kai; Melchior, Benoît; Martins, Yuri C et al. (2013) Nitric oxide synthase dysfunction contributes to impaired cerebroarteriolar reactivity in experimental cerebral malaria. PLoS Pathog 9:e1003444
Orjuela-Sanchez, Pamela; Duggan, Erika; Nolan, John et al. (2012) A lactate dehydrogenase ELISA-based assay for the in vitro determination of Plasmodium berghei sensitivity to anti-malarial drugs. Malar J 11:366
Martins, Yuri C; Zanini, Graziela M; Frangos, John A et al. (2012) Efficacy of different nitric oxide-based strategies in preventing experimental cerebral malaria by Plasmodium berghei ANKA. PLoS One 7:e32048
Zanini, Graziela M; Martins, Yuri C; Cabrales, Pedro et al. (2012) S-nitrosoglutathione prevents experimental cerebral malaria. J Neuroimmune Pharmacol 7:477-87
Cabrales, Pedro; Zanini, Graziela M; Meays, Diana et al. (2011) Nitric oxide protection against murine cerebral malaria is associated with improved cerebral microcirculatory physiology. J Infect Dis 203:1454-63
Clemmer, L; Martins, Y C; Zanini, G M et al. (2011) Artemether and artesunate show the highest efficacies in rescuing mice with late-stage cerebral malaria and rapidly decrease leukocyte accumulation in the brain. Antimicrob Agents Chemother 55:1383-90
Bertinaria, Massimo; Guglielmo, Stefano; Rolando, Barbara et al. (2011) Amodiaquine analogues containing NO-donor substructures: synthesis and their preliminary evaluation as potential tools in the treatment of cerebral malaria. Eur J Med Chem 46:1757-67

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