Blueberry Polyphenols Ameliorate Visible Light and Lipid-Induced Injury of Retinal Pigment Epithelial Cells.

Although dietary polyphenols are known to be beneficial to vision, the protective distinctions among different types of polyphenols are unclear. In this work, the visual benefits of various blueberry polyphenols were evaluated using an in vitro model of visible light-lipid-induced injury of retinal pigment epithelial cells. Results showed that, at 10.0 µg/mL, the phenolic acid-rich fraction was superior in inhibiting cell death (93.6% ± 2.8% of cell viability). Anthocyanin- and flavonoid-rich fractions shared similar advantages in preventing the expression of senescence-associated ß-galactosidase (34.8% ± 11.1% and 32.2% ± 9.7% of aged cells, respectively) and overexpression of vascular endothelial growth factor (51.8 ± 3.5 and 54.1 ± 6.5 pg/mL, respectively). The flavonoid-rich fraction also showed high activity in ameliorating phagocytosis (70.3% ± 12.6%) and cellular oxidative stress. These results were further confirmed by using the corresponding polyphenol standards. Improved inhibitory effects of polyphenol mixture on cell death and senescence-associated ß-galactosidase expression were also observed. Therefore, various polyphenols play diverse roles and exert synergistic effects in nourishing the retina.

Potential Retinal Benefits of Dietary Polyphenols Based on Their Permeability across the Blood-Retinal Barrier.

Whether all dietary polyphenols nourish the eyes via oral supplementation is controversial. Given that passage of dietary polyphenols across the blood-retina barrier (BRB) is the precondition for polyphenols to exhibit ocular benefits, the BRB permeability of polyphenols was assessed in this study. Being common dietary polyphenols in fruits and vegetables, nonanthocyanin flavonoids, anthocyanins, and phenolic acids were investigated. BRB was simulated in vitro by using a differentiated retinal pigment epithelial cell monolayer cultivated on a Transwell culture system. Penetration rate was calculated by quantitatively analyzing the polyphenols in basolateral media. The BRB permeability of different polyphenols obviously (p < 0.05) differed, as follows: phenolic acids > nonanthocyanin flavonoids > anthocyanins. Glycosylation and methylation improved the BRB permeability of nonanthocyanin flavonoids and anthocyanins. However, instability and carbonylation at the C-4 position severely suppressed the BRB permeability of anthocyanins and nonanthocyanin flavonoids. Moreover, a new metabolite was discovered during penetration of anthocyanins into the BRB. However, hydrophilic phenolic acids exhibited better BRB permeability than hydrophobic ones. Data demonstrate that BRB permeability of polyphenols was determined based on structural characteristics, hydrophilicity, stability, and metabolic changes.

Protective Effect of Fucoxanthin Isolated from Laminaria japonica against Visible Light-Induced Retinal Damage Both in Vitro and in Vivo.

With increasingly serious eye exposure to light stresses, such as light-emitting diodes, computers, and widescreen mobile phones, efficient natural compounds for preventing visible light-induced retinal damages are becoming compelling needs in the modern society. Fucoxanthin, as the main light absorption system in marine algae, may possess an outstanding bioactivity in vision protection because of its filtration of blue light and excellent antioxidative activity. In this work, both in vitro and in vivo simulated visible light-induced retinal damage models were employed. The in vitro results revealed that fucoxanthin exhibited better bioactivities than lutein, zeaxanthin, and blueberry anthocyanins in inhibiting overexpression of vascular endothelial growth factor, resisting senescence, improving phagocytic function, and clearing intracellular reactive oxygen species in retinal pigment epithelium cells. The in vivo experiment also confirmed the superiority of fucoxanthin than lutein in protecting retina against photoinduced damage. This excellent bioactivity may be attributed to its unique structural features, including allenic, epoxide, and acetyl groups. Fucoxanthin is expected to be an important ocular nutrient in the future.

Visible Light-Induced Lipid Peroxidation of Unsaturated Fatty Acids in the Retina and the Inhibitory Effects of Blueberry Polyphenols.

The lipid peroxidation of unsaturated fatty acids (UFAs) in the retina not only threatens visual cells but also affects the physiological health of the retina. In this work, the potential damages caused by daily visible light exposure on retinal UFAs were evaluated via a simulated in vitro model. At the same time, the benefits of dietary supplementation of blueberries to the eyes were also assessed. After prolonged light exposure, lipid peroxidation occurred for both docosahexaenoic and arachidonic acids (DHA and AA, respectively). The oxidized UFAs presented obvious cytotoxicity and significantly inhibited cell growth in retinal pigment epithelium cells. Among the different blueberry polyphenol fractions, the flavonoid-rich fraction, in which quercetin was discovered as the main component, was considerably better in preventing visible light-induced DHA lipid peroxidation than the anthocyanin- and phenolic acid-rich fractions. Then the retinal protective activity of blueberry polyphenols against light-induced retinal injury was confirmed in vivo. On the basis of the above results, inhibiting lipid peroxidation of UFAs in the retina is proposed to be another important function mechanism for antioxidants to nourish eyes.