CORTICOSTEROID (METHYLPREDNISOLONE) MODULATION OF PHOTOPEROXIDATION BY ULTRAVIOLET-LIGHT IN LIPOSOMES

Abstract— UV irradiation of ovolecithin liposomes produced a dose dependent wave of peroxidation which reached a peak and then fell again coincident with substrate exhaustion. This correlated well with subsequent increases in membrane permeability. There was a progressive loss of unsaturated fatty acids, and when cholesterol was incorporated into liposomes, the UV produced a progressive loss of this steroid. Methylprednisolone sodium succinate, a synthetic corticosteroid, was found to inhibit this peroxidation in a dose dependent manner, also ameliorating membrane permeability increases when present during irradiation, but not able to compensate for pre‐existing damage. When cholesterol was present in the liposomes, methylprednisolone sodium succinate was also able to protect this steroid from UV peroxidative damage. The rates of reaction in this system suggested that polyunsaturated fatty acids, even when present in extremely small concentrations, underwent an initial rapid wave of peroxidation, which served to initiate the slower rate of lipoperoxidation within the bulk of mono‐ and di‐“unsaturates”. At low concentrations, the corticosteroid preferentially blocked damage to mono‐ and di‐unsaturated fatty acids, affecting the polyunsaturated fatty acids as well, at higher concentrations. This study suggests that the corticosteroid, methylprednisolone sodium succinate, possesses antioxidant properties in lipid systems subjected to free radical peroxidation. Copyright © 1979, Wiley Blackwell. All rights reserved