Blockage of Spontaneous Ca2+ Oscillation Causes Cell Death in Intraerythrocitic Plasmodium falciparum

Abstract

Malaria remains one of the world’s most important infectious diseases and is responsible for enormous mortality and morbidity. Resistance to antimalarial drugs is a challenging problem in malaria control. Clinical malaria is associated with the proliferation and development of Plasmodium parasites in human erythrocytes. Especially, the development into the mature forms (trophozoite and schizont) of Plasmodium falciparum (P. falciparum) causes severe malaria symptoms due to a distinctive property, sequestration which is not shared by any other human malaria. Ca2+ is well known to be a highly versatile intracellular messenger that regulates many different cellular processes. Cytosolic Ca2+ increases evoked by extracellular stimuli are often observed in the form of oscillating Ca2+ spikes (Ca2+ oscillation) in eukaryotic cells. However, in lower eukaryotic and plant cells the physiological roles and the molecular mechanisms of Ca2+ oscillation are poorly understood. Here, we showed the observation of the inositol 1,4,5-trisphospate (IP3)-dependent spontaneous Ca2+ oscillation in P. falciparum without any exogenous extracellular stimulation by using live cell fluorescence Ca2+ imaging. Intraerythrocytic P. falciparum exhibited stage-specific Ca2+ oscillations in ring form and trophozoite stages which were blocked by IP3 receptor inhibitor, 2-aminoethyl diphenylborinate (2-APB). Analyses of parasitaemia and parasite size and electron micrograph of 2-APB-treated P. falciparum revealed that 2-APB severely obstructed the intraerythrocytic maturation, resulting in cell death of the parasites. Furthermore, we confirmed the similar lethal effect of 2-APB on the chloroquine-resistant strain of P. falciparum. To our best knowledge, we for the first time showed the existence of the spontaneous Ca2+ oscillation in Plasmodium species and clearly demonstrated that IP3-dependent spontaneous Ca2+ oscillation in P. falciparum is critical for the development of the blood stage of the parasites. Our results provide a novel concept that IP3/Ca2+ signaling pathway in the intraerythrocytic malaria parasites is a promising target for antimalarial drug development.

Acidocalcisomes of Trypanosoma brucei have an inositol 1,4,5-trisphosphate receptor that is required for growth and infectivity

“…6C shows an example of a spontaneous Ca 2+ response occurring before the IP 3 -dependent Ca 2+ release elicited by IP 3 uncaging. Spontaneous Ca 2+ transients have also been reported in other protists (18,32,33). Because spontaneous Ca 2+ transients were observed at similar rates in both uninduced and TbIP 3 R RNAi-induced cells (Fig.…”

A High-Content Phenotypic Screen Reveals the Disruptive Potency of Quinacrine and 3′,4′-Dichlorobenzamil on the Digestive Vacuole of Plasmodium falciparum

“…This could confound our objective of identifying compounds that disrupt the DV. Nevertheless, Ca 2ϩ dysfunction would still be detrimental to parasite development, as blocking of Ca 2ϩ oscillations has been shown to be lethal to the parasite (29,30). Despite this, we believe that DCB does indeed destabilize the DV membrane, as postscreening validation showed that DCB induces phenotypes reminiscent of PCD ( Fig.…”

Simultaneous Administration of 2-Aminoethyl Diphenylborinate and Chloroquine Reverses Chloroquine Resistance in Malaria Parasites

“…We recently, for the first time, demonstrated spontaneous Ca 2ϩ oscillation in Plasmodium falciparum. Furthermore, we showed that the blockage of this oscillation in the trophozoite stage by 2-aminoethyl diphenylborinate (2-APB) inhibited 1,4,5-trisphosphate (IP 3 )-induced Ca 2ϩ release (10)(11)(12), resulting in the death of the parasite (13). Chloroquine (CQ) is thought to exert its toxic effect in the intraerythrocytic parasite at the digestive vacuole (14).…”