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.