Heme processing in the malaria parasite, Plasmodium falciparum: a time-dependent basal-level analysis

Malaria is a deadly disease for which therapeutic options are threatened by the rise of antimalarial resistance. Inhibiting the formation of hemozoin (the product of heme detoxification) in the digestive vacuole (DV) is the mechanism of action of numerous antimalarial drugs, including those in development as new therapies. This drug target remains attractive as hemozoin is an abiotic and non-mutable molecule, unique to the parasite. The underlying parasite biology of the heme detoxification pathway is complex and requires a deeper understanding. This study focuses on the DV of Plasmodium falciparum, utilizing confocal microscopy, immunofluorescence, immunoblotting and cellular fractionation techniques to study its native state over time. Using parameters such as the uptake into and growth of the DV, relative abundance of plasmepsins (PMs) I and IV as well as basal levels of hemoglobin, heme and hemozoin, it was found that DV physiology in chloroquine (CQ)-sensitive NF54 follows three distinct developmental phases: the lag-type growth (20 to 28 h), rapid growth phase (28 to 40 h) and the plateau (40 to 48 h). These phases hold specific characteristics with respect to the investigated parameters. In addition, key differences between CQ-sensitive NF54 and CQ-resistant Dd2 parasites were observed.