Relaxometric studies of erythrocyte suspensions infected by Plasmodium falciparum: a tool for staging infection and testing anti-malarial drugs. 2020

Enza Di Gregorio, and Giuseppe Ferrauto, and Evelin Schwarzer, and Eliana Gianolio, and Elena Valente, and Daniela Ulliers, and Silvio Aime, and Oleksii Skorokhod
Molecular Imaging Center, Department of Molecular Biotechnologies and Health Sciences, University of Torino, Torino, Italy.

Malaria is a global health problem with the most malignant form caused by Plasmodium falciparum (P. falciparum). Parasite maturation in red blood cells (RBCs) is accompanied by changes including the formation of paramagnetic hemozoin (HZ) nanocrystals, and increased metabolism and variation in membrane lipid composition. Herein, MR relaxometry (MRR) was applied to investigate water exchange across RBCs' membrane and HZ formation in parasitized RBCs. Transverse water protons relaxation rate constants (R2 = 1/T2 ) were measured for assessing HZ formation in P. falciparum-parasitized human RBCs. Moreover, water exchange lifetimes across the RBC membrane (τi ) were assessed by measuring longitudinal relaxation rate constants (R1 = 1/T1 ) at 21.5 MHz in the presence of a gadolinium complex dissolved in the suspension medium. τi increased after invasion of parasites (ring stage, mean τi / = 1.234 ± 0.022) and decreased during maturation to late trophozoite (mean τi / = 0.960 ± 0.075) and schizont stages (mean τi / = 1.019 ± 0.065). The HZ accumulation in advanced stages was revealed by T2 -shortening. The curves reporting R2 (1/T2 ) vs. magnetic field showed different slopes for non-parasitized RBCs (npRBCs) and parasitized RBCs (pRBCs), namely 0.003 ± 0.001 for npRBCs, 0.009 ± 0.002, 0.028 ± 0.004 and 0.055 ± 0.002 for pRBCs at ring-, early trophozoite-, and late trophozoite stage, respectively. Antimalarial molecules dihydroartemisinin and chloroquine elicited measurable changes in parasitized RBCs, namely dihydroartemisinin modified τi , whereas the interference of chloroquine with HZ formation was detectable by a significant T2 increase. MRR can be considered a useful tool for reporting on P. falciparum blood stages and for screening potential antimalarial molecules.

UI MeSH Term Description Entries
D010963 Plasmodium falciparum A species of protozoa that is the causal agent of falciparum malaria (MALARIA, FALCIPARUM). It is most prevalent in the tropics and subtropics. Plasmodium falciparums,falciparums, Plasmodium
D004912 Erythrocytes Red blood cells. Mature erythrocytes are non-nucleated, biconcave disks containing HEMOGLOBIN whose function is to transport OXYGEN. Blood Cells, Red,Blood Corpuscles, Red,Red Blood Cells,Red Blood Corpuscles,Blood Cell, Red,Blood Corpuscle, Red,Erythrocyte,Red Blood Cell,Red Blood Corpuscle
D006801 Humans Members of the species Homo sapiens. Homo sapiens,Man (Taxonomy),Human,Man, Modern,Modern Man
D000962 Antimalarials Agents used in the treatment of malaria. They are usually classified on the basis of their action against plasmodia at different stages in their life cycle in the human. (From AMA, Drug Evaluations Annual, 1992, p1585) Anti-Malarial,Antimalarial,Antimalarial Agent,Antimalarial Drug,Anti-Malarials,Antimalarial Agents,Antimalarial Drugs,Agent, Antimalarial,Agents, Antimalarial,Anti Malarial,Anti Malarials,Drug, Antimalarial,Drugs, Antimalarial
D013535 Suspensions Colloids with liquid continuous phase and solid dispersed phase; the term is used loosely also for solid-in-gas (AEROSOLS) and other colloidal systems; water-insoluble drugs may be given as suspensions. Suspension
D016778 Malaria, Falciparum Malaria caused by PLASMODIUM FALCIPARUM. This is the severest form of malaria and is associated with the highest levels of parasites in the blood. This disease is characterized by irregularly recurring febrile paroxysms that in extreme cases occur with acute cerebral, renal, or gastrointestinal manifestations. Plasmodium falciparum Malaria,Malaria, Plasmodium falciparum

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