Protective effect of α-lipoic acid as an antioxidant compound against riboflavin-mediated photo-oxidation of TSPs (Total Soluble lens Proteins)

Among different solar ultraviolet radiations only UV-A completely passes through the atmosphere and reaches the ground. UV-A and visible spectrum of sunlight can induce photo damaging of lens proteins through endogenous photosensitizer molecules such as riboflavin (RF). In the current study, total soluble lens proteins (TSP) was incubated under direct sunlight in the presence of riboflavin as a light-sensitive molecule that naturally is present in the lens. Photo damaging effects of RF were evaluated by gel electrophoresis and various spectroscopic analyses. SDS-PAGE analysis indicated that exposure of lens-soluble proteins under direct sunlight in the presence of riboflavin leads to extensive protein crosslinking and also three-dimensional structural alteration of these proteins which confirmed by fluorescence spectroscopy assessments. The structural alteration of protein samples was accompanied with appearance of a new absorption peak between ۳۰۰ and ۴۰۰ nm which may be related to formation of new chromophores. Moreover, protein samples were incubated with α-lipoic acid antioxidant as a preventive and therapeutic agent that naturally is present in the lens, to evaluate its protective role against photo damaging effects of RF. Our results indicate that α-lipoic acid can protect lens proteins against photo oxidative impairment induced by RF in a dose dependent manner. Finally, the results of this study indicate that the antioxidant defense mechanism of the lens significantly contributes to protecting the lens from damaging effects of sunlight during life span.