Effects of pure oxygen atmosphere in vivo on plasma lecithin-cholesterol acyltransferase reaction

Abstract

Exposure to pure oxygen atmospheres for more than three days resulted in loss of red blood cell mass in astronauts in some flights. Oxidation of lipid or protein membrane components may account for this phenomenon, since tocopherol deficient red blood cells have been shown to hemolyze on exposure to elevated oxygen pressures in vitro and in vivo. An additional contributing cause to the induced red cell loss may be the inhibition of the plasma lecithin-cholesterol acyltransferase reaction by oxygen, since congenital absence of the enzyme is associated with anemia. This possibility was explored in eight human subjects who lived in a sealed environmental chamber and breathed 100% oxygen at 258 mm Hg pressure for 30 days. In their plasma a 40% decrease in the conversion of free cholesterol to ester was demonstrated in vitro after four weeks’ exposure to 100% oxygen. Plasma cholesteryl ester concentration was also decreased. Red blood cell mass was reduced and erythropoiesis was depressed. These findings support the hypothesis that the anemia induced by exposure to 100% oxygen was caused in part by decreased synthesis of cholesteryl esters secondary to an inhibition of the plasma lecithin-cholesterol acyltransferase reaction.