Toxic factors in the red blood cell membrane

The toxic effects of hemolysed RBCs have been studied for more than 100 years, but the specific factors involved have not been identified. This study focused on phosphatidylethanolamine (PE) and phosphatidylserine (PS), two aminophospholipids that normally reside on the cytoplasmic side of the red cell membrane. An in vitro experiment with murine peritoneal exudate macrophages showed that PE and PS: a) stimulated the production of H2O2, complement factor C3a, prostacyclin, and thromboxane at a dose of 5 micrograms/ml; b) produced cell injury, evidenced by release of lipid peroxides, LDH, and by morphologic changes on phase-contrast and electron microscopy at a dose of 50 micrograms/ml; and c) caused cell death in 50-66% of cells at a dose of 100 micrograms/ml. An in vivo experiment showed that PE and PS injected intravenously into various groups of rabbits: a) caused only transient hypotension at a dose of 0.05 mg/kg body weight; b) caused significant hypotension, cardiac arrhythmias, bronchospasm, activation of intravascular coagulation, complement, platelets, and leukocytes with release of histamine, serotonin, and thromboxane at a dose of 0.10 mg/kg; and c) caused cardiac arrest and death at a dose of 0.30 mg/kg. In contrast, the phospholipids of the outer cell membrane (phosphatidylcholine and phosphatidylinositol) caused minimal toxicity in vitro and none in vivo.