Preventive role of lens antioxidant defense mechanism against riboflavin-mediated sunlight damaging of lens crystallins

Abstract

The main components of sunlight reaching the eye lens are UVA and visible light exerting their photo-damaging effects indirectly by the aid of endogenous photosensitizer molecules such as riboflavin (RF). In this study, lens proteins solutions were incubated with RF and exposed to the sunlight. Then, gel mobility shift analysis and different spectroscopic assessments were applied to examine the structural damaging effects of solar radiation on these proteins. Exposure of lens proteins to direct sunlight, in the presence of RF, leads to marked structural crosslinking, oligomerization and proteolytic instability. These structural damages were also accompanied with reduction in the emission fluorescence of Trp and Tyr and appearance of a new absorption peak between 300 and 400nm which can be related to formation of new chromophores. Also, photo-oxidation of lens crystallins increases their oligomeric size distribution as examined by dynamic light scattering analysis. The above mentioned structural insults, as potential sources of sunlight-induced senile cataract and blindness, were significantly attenuated in the presence of ascorbic acid and glutathione which are two important components of lens antioxidant defense system. Therefore, the powerful antioxidant defense mechanism of eye lens is an important barrier against molecular photo-damaging effects of solar radiations during the life span.

S-Allylmercapro-N-Acetylcysteine Attenuates the Oxidation-Induced Lens Opacification and Retinal Pigment Epithelial Cell Death In Vitro

“…Both NAC and NACA are supplying cells with cysteine, the rate limiting substrate in glutathione biosynthesis, thereby increasing glutathione cellular content that protects them from oxidative stress. Also, the natural antioxidant defense mechanism was shown to prevent molecular photo-damaging effects of solar radiation in lens crystallins in vitro [12]. Several antioxidant compounds were shown to attenuate cataract progression: (i) Curcumin, the bioavailability of which is limited [13]; (ii) acetyl- l -carnitine [14]; (iii) NAC in combination with the allicin derivative diallyl disulfide [15]; (iv) Negerloxin [16]; (v) Quercetin and its derivative Rutin [17,18].…”

Effects of Folic Acid and Caffeic Acid on Indirect Photo-oxidation of Proteins and Their Costabilization under Irradiation

“…14 Ascorbic acid and glutathione, two important antioxidants of eye lens, were shown to significantly protect sulfhydryls of lens proteins against photo-oxidation under sunlight. 42 Vanillin at 2.5 mM reduced the formation of carbonyls of protein in hepatic mitochondria at 0.5 g/L induced by photosensitization with methylene blue, which was comparable to ascorbic acid. 58 However, these reports only focused on the changes in protein itself without clarifying the changes of antioxidants and photosensitizers.…”

“…For example, CA at 250 μM was needed to inhibit the loss of tryptophan of 23 μM lysozyme photoinduced by 100 μM riboflavin . Ascorbic acid and glutathione, two important antioxidants of eye lens, were shown to significantly protect sulfhydryls of lens proteins against photo-oxidation under sunlight . Vanillin at 2.5 mM reduced the formation of carbonyls of protein in hepatic mitochondria at 0.5 g/L induced by photosensitization with methylene blue, which was comparable to ascorbic acid .…”

“…Similar results have been reported for BSA, whey protein isolate, and lens proteins photosensitized by pterins and riboflavin. 8,41,42 To quantify the concentration of proteins, the gels were submitted to densitometric analysis (Figures 4E and S3E). In the presence of FA, the concentrations of β-LG, α-LA, BSA, and βcasein decreased to 6.1, 7.2, 7.5, and 6.6 μM, respectively, after UVA irradiation for 240 min (Figure 4E).…”

Current Trends in the Pharmacotherapy of Cataracts

“…Indeed, GSH mitigated lipid peroxidation and enhanced the activity of SOD, CAT, and GSH-Px enzymes in H 2 O 2 (10 mM)-induced cataract formation in cultured goat lenses, ex vivo [87]. There is evidence that endogenous antioxidants, vitamin C, and GSH attenuated structural crosslinking, oligomerization, and proteolytic instability of lens crystallins in a lens protein solution exposed to sunlight in the presence of a photosensitizer, riboflavin [88]. Taken together, these studies affirm the protective role of GSH in the pathophysiology of the lens.…”