Hemolysis Lecithin

T6. The Action of Phospholipases The venom of the Eastern diamondback rattler and the Indian cobra contains phospholipase A2, which catalyzes the hydrolysis of fatty acids at the C-2 position of glycerophospholipids. The phospholipid breakdown product of this reaction is lysolecithin (lecithin is phosphatidylcholine). At high concentrations, this and other lysophospholipids act as detergents, dissolving the membranes of erythrocytes and lysing the cells. Extensive hemolysis may be life-threatening. 

These experiments are characterized by that extreme selectivity usually associated only with biological processes. This led Hughes to trace a parallelism with hemolysis caused by the venoms. He found that blacksnake venom reacted with the lecithin film at a rate which was indeed related to the speed of hemolysis of washed guinea-pig cells. Further experiments, however, showed that the ability of a venom to react with a lecithin monolayer did not necessarily imply hemolytic activity towards the red cells of any given species. Black tiger venom, for example, was only very slightly reactive towards red cells, even after sixteen hours, while the venoms of copperhead and cobra as well as of blacksnake were strongly hemolytic within two hours in concentrations as low as 0.2 mg. ml. . ... 

Erythrocytes contain 32 to 55% hemoglobin, about 60% water, and the rest as siroma. Stroma can be obtained, after hemolysis of the corpuscles by dilution, through the process of centrifuging and consists of lecithin, cholesterol, inorganic salts, and a protein, siromalin. Hemoly.sis of the corpuscles. or "laking" as i( is sometimes culled, may be brought about by hypotonic solution, by fat solvents, by bile... 

Schubert and Miiller-Goymann studied the hemolytic activity of hard fat SLN with high amounts of lecithin and further stabilized with Solutol HS 15 on red blood cells obtained from human blood. The aqueous phase used for the preparation of the SLN caused a hemolysis of 0.4%. The hemolytic activity of the SLN was higher (1-2%) but still below the critical level of 5%. A low hemolytic activity was also found for SLN of emulsifying wax stabilized with Brij 78. In this study also the effect of the free surfactant was investigated and a time and concentration dependent cell lysis was observed. Comparing the SLN formulation with the free surfactant solution with the same surfactant concentration, hemolysis was less in the nanoparticle formulation. The authors concluded that the free surfactant molecules in the SLN formulation are possibly responsible for the observed hemolysis after incubation with the SLN formulation. ... 

Simple esters are split by extracts of all tissues. The number of different esterases is not known. The digestive esterases produced by the pancreas are called lipases because they hydrolyze the triglycerides that are the most prominent lipids. They also hydrolyze simple esters. A special group of enzymes hydrolyze phospholipids. So-called lecithinase A removes one acyl group from lecithin to form lysolecithin, which causes hemolysis of erythrocytes. This enzyme has been crystallized from snake venom. Other animal toxins and bacteria also form lysolecithin by hydrolysis of lecithin. The removal of the second acyl group is catalyzed by phospholipase B, which has been studied in plant and animal extracts and also occurs in bacteria. Other enzymes, phospholipase C and D, specifically remove phosphorylcholine and choline, respectively, from lecithin. 

Correlation of lytic activity to surface activity, analogous to that observed for bactericidal efficacy has been suggested (57), but it appears that the mechanism of hemolysis may be similar to that already proposed for antibacterial action. Indeed, Ponder (111) has found that both the lipide and protein components of plasma inhibit hemolyms by detergents and from this has inferred that the alkyl sulfates can combine with lecithin and cholesterol, as well as with proteins, and that hemolysis by detergents may be initiated by combination with the lipide, lipoprotein, and protein components of the red cell ultrastructure. 

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