IRON METABOLISM IN PLASMODIUM

Johns Hopkins University, Baltimore MD

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Abstract

An increase in antimalarial drug resistance is an important contributing component to the current escalating mortality due to Plasmodium falciparum malaria. Two major classes of currently used antimalarials, the quinolines like chloroquine and the endoperoxides like artmesinin, interfere with iron metabolism to kill the parasite. Iron chelators, while cytostatic for bacterial and mammalian cells, actually kill Plasmodium despite the availability of millimolar heme iron in the parasitized erythrocyte. This indicates that the amount of bioavailable iron is limited and crucial for parasite survival. Therefore, interference with iron metabolism is an important and promising chemotherapeutic target for Plasmodium. The long term objectives of this proposal are to improve targeted antimalarial chemotherapy by further definition of the vital sources of parasitic iron and by characterization of iron transport to essential compartments. Preliminary data implicate erythrocytic ferritin as a source of iron. Recent cloning of the P. falciparum homologue to the mammalian iron transporter Natural Resistance Associated Macrophage Protein (NRAMP) will enable characterization of parasite iron transport. The specific aims are to test erythrocytic iron as an iron source, to localize the compartments in which PfNRAMP resides, to assess the specificity of divalent metal cations transported by PfNRAMP, to evaluate the kinetics and inhibition of this proton/cation symporter and to analyze its level of expression amongst quinoline-sensitive and -resistant parasites. The techniques of Plasmodium culture in resealed erythrocytes, recombinant gene expression, immunolocalization, cell transfection, and site-directed mutagenesis will be used to achieve these aims. The significant impact of this research is to improve the understanding of Plasmodium iron metabolism that is perturbed by antimalarial drugs. To improve the present antimalarial armamentarium for the US military and travelers as well as endemic populations is an essential component of malarial control.