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We have incubated control and Plasmodium falciparum parasitized human erythrocytes with lipid vesicles containing radiolabeled long-chain phosphatidylcholine and sphingomyelin, in the presence of a nonspecific lipid transfer protein. Most of the radiolabeled phospholipids were, immediately thereafter, available for extracellular phospholipases, suggesting that uptake of vesicles as such did not occur. In time, the amount of phosphatidylcholine inserted in the outer leaflet of the host cell membrane of parasitized erythrocytes decreased, indicating that phosphatidylcholine was being internalized in parasitized erythrocytes. The exclusion of sphingomyelin from the internalization process suggests that the removal of phosphatidylcholine from the outer leaflet of the erythrocyte membrane is caused by transbilayer migration, rather than by endocytosis. The extent of phosphatidylcholine internalization indicates that part of it does not remain in the inner leaflet of the host cell membrane, but is taken up by the intraerythrocytic parasite. Individual phosphatidylcholine species, containing 16:0/18:1-, 16:0/18:2- and 16:0/20:4-fatty acids, showed similar extents of internalization, after being incorporated in parasitized erythrocytes by a phosphatidylcholine specific transfer protein.

Pig pancreatic phospholipase A2 does not act on normal erythrocytes, but the membrane penetrating capacity is enhanced by the covalent attachment of one fatty acyl chain to Lys-116 of the enzyme. Taking advantage of the impaired packing of phospholipids in the membrane of Plasmodium infected erythrocytes it was demonstrated that a lauric acid derivative of phospholipase A2 is capable of exclusively attaching the infected erythrocytes in vitro, leaving the uninfected cells undisturbed. The chemically modified phospholipase A2 appeared to cause death of the parasite in cell cultures of infected erythrocytes.

International audience; Using high performance liquid chromatograpy and gas-liquid chromatography, we have characterized the phosphatidylcholine and phosphatidylethanolamine molecular species composition of trophozoite and schizont forms of Plasmodium knowlesi parasitized erythrocytes. Similarly, we determined these parameters in the erythrocyte membranes of trophozoite parasitized cells, unparasitized erythrocytes from infected monkeys before and after a chloroquine treatment and erythrocytes from monkeys that had never been infected. Plasma phosphatidylcholine molecular species composition was also studied. P. knowlesi parasitized erythrocytes presented higher amounts of 16:0/18:2-phosphatidylcholine than the various control cells, which appeared to be compensated for by a decrease in 18:0/20:4-, 16:0/20:3-, 16:0/18:1-, 18:0/18:2-, 18:0/20:3-, 16:0/16:0- and 16:0/18:0-phosphatidylcholines. In the case of phosphatidylethanolamine, the alterations were quantitatively of greater importance and consisted of an increase in, again, 16:0/18:2-phosphatidylethanolamine and a decrease in several species containing 20:4, namely 16:0/20:4-, 18:0/20:4- and 18:1/20:4-phosphatidylethanolamine; also the levels of alkoxy-phosphatidylethanolamines were markedly decreased. P. knowlesi development within monkey erythrocytes therefore appears to be associated with changes in phosphatidylcholine and phosphatidylethanolamine molecular species in the whole parasitized cell. These alterations are also exhibited by the host cell membrane, which provides the first experimental evidence that the parasite is able to manipulate the erythrocyte membrane lipid species composition. The consequences of these alterations on membrane physiology are discussed, as well as the implications that these data may have on the trafficking of phosphatidylcholine and phosphatidylethanolamine in the erythrocytes of P. knowlesi infected monkeys.

The erythrocyte plays an essential role in a particular part of the complex life cycle of Plasmodium, the malaria causing parasite, when it serves as a host cell in which the parasite feeds, grows and multiplies asexually. This part of the cycle is generally seen to offer potentially interesting possibilities of destroying the parasite, thereby breaking the fatal cycle. Many studies therefore aim to unravel the parasite-induced changes in the structural and functional characteristics of the membrane of the infected erythrocyte. Understandably, membrane proteins, many of which newly inserted as they have been produced by the parasite, have drawn a great deal of attention (Howard 1988, Hommel and Semoff, 1988), membrane permeability is increased (Tanabe et al., 1982; Sherman, 1979, 1988) pores are formed (Ginsburg et al., 1986), and the ultrastructural appearance of the cell can be modified by the development of knobs on the membrane surface (Howard, 1988). Recently, a series of studies was undertaken to investigate the fate of the phospholipid complement of the host cell membrane and to establish possible, parasite-induced, modifications in the composition as well as the organization of these basic membrane constituents.

The transbilayer distribution of glycerophospholipids in the plasma membrane of Plasmodium knowlesi infected erythrocytes was studied by using lysine-116-ε-N-palmitoyl amidinated pancreatic phospholipase A2. As a consequence of its superior membrane penetrating capacities, this modified enzyme rapidly degrades its substrates in the outer membrane leaflet of intact erythrocytes, a property that makes the enzyme an excellent tool to study the malaria parasitized red cell. The modified phospholipase A2 caused a nonlytic hydrolysis of up to 12–15% of the phosphatidylethanolamine and none of the phosphatidylserine in the red cell membrane, irrespective of whether the cells harboured trophozoite and schizont stages of parasites or no parasites at all. The absence of phosphatidylserine at the exterior surface of Plasmodium infected erythrocytes was confirmed by applying the prothrombinase assay on Plasmodium falciparum infected human erythrocytes. Consequently, the results from these and previous studies indicate that the plasma membrane of Plasmodium infected erythrocytes exhibit a normal transbilayer phospholipid asymmetry.Key words: malaria, plasma membrane, phospholipid asymmetry, erythrocyte, prothrombinase assay.

The uptake of phosphatidylcholine (PC), phosphatidylethanolamine (PE) and phosphatidylserine (PS) in Plasmodium knowlesi infected erythrocytes has been studied. Whereas uptake of phospholipids, in the absence of phospholipid transfer proteins, is negligible in control cells, the infected cells can incorporate considerable amounts of added phospholipids. The uptake is enhanced by the presence of lipid transfer proteins. Doubly labeled [3H]oleate, [14C]choline) PC does not undergo any appreciable remodelling following uptake, which strongly suggests that plasma PC is used as such for the biogenesis of the parasite membranes. Transport of extracellularly offered PS and PE towards the intraerythrocytic parasite and utilization of these lipids by the parasite are confirmed by the observation that these lipids are converted into respectively PE and PC. The extent and rate of these conversions depend on the way the phospholipids are introduced into the infected cells.