Vitamin E, membrane order, and antioxidant behavior in lung microsomes and reconstituted lipid vesicles

Vitamin E, a dietary antioxidant, is known to inhibit peroxidation of membrane lipids and to protect the lungs of vitamin E-deficient animals and to a lesser extent vitamin E-sufficient animals from oxidant injury. Since the protective interaction between vitamin E and biological membranes may be related to alterations in composition and physical state of membrane lipids, we evaluated the effect of vitamin E deficiency on lung microsomal lipids and membrane fluidity. Both intact microsomes and lipid vesicles prepared from the total lipid extracts of these microsomes were used. The percentage incorporation of vitamin E and cholesterol, membrane fluidity, and lipid peroxidation were measured in microsomes as well as their lipid vesicles. Fluidity was measured by monitoring changes in fluorescence anisotropy for 1,6-diphenyl-1,3,5-hexatriene (DPH). Lipid peroxidation was measured by thiobarbituric acid reaction. There were significant increases in the phospholipid (p less than 0.01), the total cholesterol (p less than 0.05), and the total saturated fatty acids (p less than 0.05) and decreases in total polyunsaturated fatty acid (p less than 0.01) content of vitamin E-deficient microsomes. There were no detectable peroxidative products in freshly isolated microsomes from either vitamin E-sufficient or -deficient lungs. However, lipids from vitamin E-deficient microsomal membranes were more susceptible to free radical initiated peroxidation than lipids from vitamin E-sufficient microsomes. Fluidity in vitamin E-deficient microsomes or in their lipid vesicles was significantly (p less than 0.05) decreased compared to the respective controls. In vitamin E-deficient microsomes or their lipid vesicles, the incorporation rate of vitamin E was two- to three-fold greater than in vesicles of vitamin E-sufficient microsomes or their lipid vesicles. However, the percentage incorporation of cholesterol was identical in both vitamin E-deficient and vitamin E-sufficient microsomes or in their respective lipid vesicles. As a result of vitamin E incorporation, fluidity was significantly decreased (p less than 0.05) in vitamin E-sufficient vesicles and was further decreased (p less than 0.001) in vitamin E-deficient vesicles. Incorporation of cholesterol also decreased fluidity in both vitamin E-deficient and vitamin E-sufficient vesicles but to the same extent (p less than 0.001). Lipid peroxide formation was two-fold greater in the vitamin E-deficient than in the vitamin E-sufficient vesicles.(ABSTRACT TRUNCATED AT 400 WORDS)