Inhibition of eryptosis and intraerythrocytic growth of Plasmodium falciparum by flufenamic acid

Non-selective (NSC) cation channels participate in the Ca2+ leak of human erythrocytes. Sustained activity of these channels triggers suicidal erythrocyte death (eryptosis), which is characterized by Ca2+ stimulated cell shrinkage and phosphatidylserine (PS) exposure. PS-exposing erythrocytes are rapidly cleared from circulating blood. PGE(2) activates the NSC channels, and erythrocyte PGE(2) formation is stimulated by a decrease in intra- or extracellular Cl- concentration. In addition, the intraerythrocytic malaria parasite Plasmodium falciparum activates the NSC channels, most probably to accomplish Na+ and Ca2+ entry into the erythrocyte cytosol required for parasite development. By Ca2+ uptake the parasite maintains a low Ca2+ concentration in the erythrocyte cytosol and thus delays the suicidal death of the host erythrocyte. Flufenamic acid has previously been shown to inhibit NSC channels. The present study thus explored the effect of flufenamic acid on erythrocyte Ca2+ entry, on suicidal erythrocyte death and on intraerythrocytic growth of P falciparum. Within 48 h, replacement of extracellular Cl- with gluconate or application of PGE(2) (50 mu M) increased Fluo3 fluorescence reflecting cytosolic Ca2+ activity, decreased forward scatter reflecting cell volume and increased annexin V binding reflecting PS exposure in FACS analysis. All those effects were significantly blunted in the presence of flufenamic acid (10 mu M). Flufenamic acid (25 mu M) further significantly delayed the intraerythrocytic growth of P.falciparum and the PS exposure of the infected erythrocytes. The present observations disclose a novel effect of flufenamic acid, which may allow the pharmacological manipulation of erythrocyte survival and the course of malaria.