Hemozoin formation, disposition and detection in Plasmodium species.

摘要

Malaria remains a major public health problem throughout much of the world. The intraerythrocytic stage Plasmodium parasite is responsible for malaria pathology. Erythrocyte hemoglobin is catabolized in the parasite's digestive vacuole which releases soluble and toxic free heme. The Plasmodium parasite biomineralizes heme into an insoluble and relatively inert heme crystal called hemozoin. The in vivo mechanism of hemozoin formation, the process targeted by the medically important quinolines, has not been established. This research identifies neutral lipid nanospheres (NLNs) in the parasite digestive vacuole as the in vivo site of hemozoin formation and shifts the long held conception that heme crystallization occurs in an aqueous, polar environment to a non-polar, hydrophobic microenvironment. Quinoline drug resistance in malaria parasites is increasing and the identification of new drugs that selectively target hemozoin formation, yet are not subject to quinoline cross-resistance, is a priority. From over one thousand safe, FDA approved compounds five promising drugs were identified using an in vitro NLN-based method. These drugs also showed direct activity against parasites in culture. Accurate diagnosis is needed for effective malaria treatment. Laser desorption mass spectrometry (LDMS) was found to be a sensitive diagnostic technique for identification of malaria hemozoin in human blood. As confirmed by PCR, LDMS successfully detected Plasmodium hemozoin in the blood of pregnant Zambian women negative by optical microscopy alone. LDMS successfully identified all four species responsible for human malaria in human clinical blood samples. Potential protein evidence of P. falciparum was identified in 800 year old human remains. Hemozoin is formed in NLNs in Plasmodium and is a useful biomarker of blood stage malaria infection by LDMS.