Influence of amitriptyline on eryptosis, parasitemia and survival of Plasmodium berghei-infected mice

Plasmodia express a sphingomyelinase, which is apparently required for their development. On the other hand, the sphingomyelinase product ceramide has previously been shown to delay parasite development. Moreover, ceramide triggers suicidal erythrocyte death or eryptosis, characterized by exposure of phosphatidylserine at the erythrocyte surface and cell shrinkage. Accelerated eryptosis of infected erythrocytes is considered to clear infected erythrocytes from circulating blood and, thus, to favourably influence the clinical course of malaria. The present experiments explored whether the sphingomyelinase inhibitor amitriptyline or genetic knockout of host acid sphingomyelinase influence in vitro parasite growth, eryptosis of Plasmodium falciparum-infected human erythrocytes, in vivo parasitemia and survival of P. berghei-infected mice. Phosphatidylserine exposure was determined by annexin V-binding and cell volume by forward scatter in FACS analysis. In vitro infection of human erythrocytes increased annexin- binding, an effect blunted in the presence of amitriptyline (>or=50 microM). Amitriptyline did not significantly alter intraerythrocytic parasite development but significantly (>or= 1 microM) delayed the increase in parasitemia in vitro. Most importantly, amitriptyline treatment (1 mM in drinking water) resulted in a significant delay of parasitemia and death of infected mice. However, upon infection, ceramide formation was stimulated in both, acid sphingomyelinase knockout mice (Smpd1(-/-)) and their wild type littermates (Smpd1(+/+)). Parasitemia following P. berghei infection was significantly lower in Smpd1(-/-) than in Smpd1(+/+) mice but did not significantly extend the life span of infected animals. In conclusion, mammalian and parasite sphingomyelinase contribute to ceramide formation during malaria, whereby the parasite sphingomyelinase ultimately determines the course of the infection. Amitriptyline presumably blocks both sphingomyelinases and, thus, its use might be a novel strategy to treat malaria.