Antioxidant activity of retinol, glutathione, and taurine in bovine photoreceptor cell membranes.

The antioxidant activities of compounds endogenous to mammalian rod outer segments (ROS) were investigated in vitro by measuring the oxidative loss of polyunsaturated fatty acids (PUFA's) from the membranes of intact ROS and from liposomes made from ROS phospholipids (PL) to which lipid soluble compounds had been added. The membranes were exposed to the water-soluble oxidant 2, 2'-azobis(2-amidinopropane) dihydrochloride (AAPH). Retinol protected PUFA's in ROS liposome PL's, whereas retinaldehyde promoted lipid peroxidation. When isolated ROS were stimulated to produce endogenous retinol, PUFA loss was inhibited by up to 17%. These findings suggest an antioxidant function for the enzymatic reduction of retinaldehyde to retinol during the visual cycle. Water-soluble antioxidants, taurine and reduced glutathione (GSH), were investigated individually and in combination with retinol in ROS PL liposomes. GSH protected PUFA's in ROS PL liposomes. Taurine alone showed little antioxidant activity, but in combination with retinol it protected lipids twice as much as retinol alone. These results support previous findings that taurine protects ROS lipids during exposure to cyclic light.