IRON METABOLISM IN PLASMODIUM

抗疟药耐药性的增加是目前恶性疟原虫疟疾死亡率不断上升的一个重要因素。目前使用的两大类抗疟药物，如氯喹等喹啉类药物和青蒿素等内过氧化物，会干扰铁代谢以杀死寄生虫。铁螯合剂虽然对细菌和哺乳动物细胞具有细胞抑制作用，但实际上可以杀死疟原虫，尽管寄生红细胞中存在毫摩尔血红素铁。这表明生物可利用铁的数量是有限的，对寄生虫的生存至关重要。因此，干扰铁代谢是疟原虫重要且有前景的化疗靶点。本建议的长期目标是通过进一步确定寄生铁的重要来源和铁向基本腔室运输的特征来改进靶向抗疟疾化疗。初步数据表明红细胞铁蛋白是铁的来源之一。最近克隆的恶性疟原虫与哺乳动物铁转运蛋白天然耐药相关巨噬细胞蛋白（NRAMP）的同源物将使寄生虫铁转运的表征成为可能。具体目的是检测红细胞铁作为铁源，定位PfNRAMP所在的区室，评估PfNRAMP运输的二价金属阳离子的特异性，评估这种质子/阳离子同向转运体的动力学和抑制作用，并分析其在喹啉敏感和耐药寄生虫中的表达水平。这些目标的实现将采用重新密封红细胞培养、重组基因表达、免疫定位、细胞转染和定点诱变等技术。本研究的重大影响是提高对抗疟药物干扰疟原虫铁代谢的认识。改善目前美国军队和旅行者以及流行人群的抗疟疾装备是疟疾控制的重要组成部分。

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.