Oxidation and denaturation of hemoglobin encapsulated in liposomes.

A study was made of the in vitro stability of hemoglobin-containing liposomes ('hemosomes') prepared from phosphatidylcholines, equimolar cholesterol and red cell lysate by the hand-shaking and ether-injection methods. Absorption spectra indicated hemichrome formation in 'hemosomes' prepared by the ether-injection technique, and increased oxidation of hemoglobin in hand-shaken 'hemosomes'. The denaturation of hemoglobin in ether-injection 'hemoglobin' was increased if the initial methemoglobin content of the hemolysate, or the temperature of preparation was elevated. It was slower if liposomes were prepared under either N2 or CO, or if the radical scavenger 1,3-diphenylisobenzofuran was added with the ether. Egg phosphatidylcholine and synthetic saturated phospholipids gave the same results. With hand-shaken 'hemosomes' the oxidized product was primarily methemoglobin, and oxidation could be inhibited by using saturated phosphatidylcholines instead of egg phosphatidylcholine. Lysophosphatidylcholine levels were higher and arachidonic acid levels lower in egg phosphatidylcholine 'hemosomes' than in equivalent liposomes containing no hemolysate. The 'hemosome' seems to be a suitable model for the study of hemoglobin-lipid membrane interactions and the resulting hemoglobin denaturation process.

Platelet phospholipids in thrombocytosis due to myeloproliferative disorders.

Platelet phospholipids were analyzed in patients with thrombocytosis due to myeloproliferative disorders and secondary thrombocytosis. A significant increase of phosphatidylcholine together with a decrease of sphingomyelin was observed in each of the 8 patients with primary thrombocythaemia and in each of the 5 patients with excessive thrombocytosis due to primary polycythaemia. The phospholipid pattern of the 3 patients with secondary thrombocytosis did not differ from that of the normal controls. This marked difference in the platelet phospholipids may be helpful in distinguishing secondary thrombocytosis persisting for a prolonged period of time after splenectomy from previously unrecognized primary thrombocythaemia unmasked by splenectomy. The decreased sphingomyelin/lecithin ratio of platelets in primary thrombocythaemia may interfere with platelet function by increasing the fluidity of their membrane.

Interactions of haemoglobin with erythrocyte membrane phospholipids in monomolecular lipid layers.

The role of red cell membrane lipids in the membrane-haemoglobin interaction was studied by measuring the surface potential and surface pressure of monomolecular lipid layers interacting with haemoglobin. Lipids of the outer and inner half of the red cell membrane were compared in respect to their haemoglobin-binding capacity. It was shown, that haemoglobin molecules interacted readily with the inner layer lipid film in acidic pH regions. This interaction is reduced as pH is increasing but still exists in the physiological pH range. It is in contrast with the increasing but still exists in the physiological pH range. It is in contrast with the findings for the outer layer lipid film, where only a partial interaction could be shown at pH 4, which was reduced to zero reaching the physiological pH range. It can be concluded from titration experiments that the process of haemoglobin binding as reflected in the measured parameters is irreversible. The result of this model experiments support the hypothesis on phosphatidylserine binding sites for haemoglobin in the inner side of red cell membrane.