Reciprocal protective effects of all-trans retinol and alpha-tocopherol during lipid peroxidation in retinal membranes.

Interactions between vitamin A and vitamin E in suppressing lipid peroxidation were observed in bovine retinal membrane preparations submitted to peroxidative injury by the water soluble azo initiator 2,2'-azobis(2-amidino-propane) hydrochloride (AAPH). Incorporation of 0.75 nmol mg prot(-1) all-trans retinol, an amount comparable with that of the endogenous alpha-tocopherol, significantly elongated the induction time preceding the release of TBA-reactive lipid peroxidation products, and reduced the consumption rate of the endogenous alpha-tocopherol. On the other hand, all-trans retinol was not able to induce any delay to the onset of lipid peroxidation when incorporated in membranes deprived of endogenous alpha-tocopherol by exposure to UV light, although TBARS produced within 60 min decreased slightly. Consumption of all-trans retinol during peroxidation was more rapid when all-trans retinol was incorporated in membranes deprived of alpha-tocopherol than in native membranes. These data suggest that reciprocal protective effects between vitamin A and vitamin E may strongly contribute to the defence of membranes against oxidative stress.