Ocular light injury is caused by several mechanisms, in particular, by short wavelength ultraviolet light. Ultraviolet light is divided into three categories: UVC (200-290 nm), UVB (290-320 nm) and UVA (320-400 nm).
1 The ultraviolet light between 200 nm and 300 nm is absorbed into the cornea, but ultraviolet light between 300 nm and 400 nm penetrates the cornea and is absorbed into the lens.
2,
3 The mechanistic cause of cataracts is complicated, but they can arise as a result of systemic diseases like diabetic mellitus, ultraviolet light, heat, hormone abnormalities, and smoking.
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6 Epidemiological reports and experiments indicate that ultraviolet light may be a primary cause of cataracts.
4-
6 The exact mechanism of UV-induced cataract formation is not fully understood. Cataract formation results from the accumulation of UV-induced DNA damage, changes in membrane transport and permeability, and changes in the biochemistry and physiology of the lens by reactive oxygen species such as hydrogen peroxide (H
2O
2), superoxide anion (O
2-), singlet oxygen (
1O
2), and hydroxyl radical (HO
-).
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8 Flavonoids are a class of natural biological products that have evolved to protect plants from oxidative damage induced by chronic exposure to ultraviolet light.
9 Flavonoids have many physiological health benefits, including protection from cardiovascular disease and cancer, and most of these beneficial effects are thought to stem from their potent antioxidant and free radical-scavenging properties, as well as their abilities to modulate many cellular enzyme functions.
9 The toxicities of most effective flavonoids are low. These include the dietary flavonoids such as fisetin, luteolin, quercetin, eriodictyol, baicalein, galangin, and EGCG, as well as synthetic flavonoids such as 3, 6-dihydroxy flavonol, and 3, 7-dihydroxy flavonol. (-)-epigallocatechin-3-gallate (EGCG) is the major polyphenolic constituent found in green tea.
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11 Several other polyphenolic compounds, known as catechins, are also found in green tea, though to a lesser degree. In addition to EGCG, the catechins include (-)-epicatechin-3-gallate (ECG), (-)-epigallocatechin (EGC), (-)-epicatechin (EC), and (+)-catechin. More than 50% of the tea catechin mass is composed of EGCG, and a vast body of scientific research suggests that EGCG (and the other catechins) are responsible for the majority of the potential health benefits attributed to green tea consumption.
12 However, few studies have assessed the protective effects of EGCG after UV irradiation ofhuman lens epithelial cells.
To evaluate the protective effects of EGCG against UV irradiation of cultured human lens epithelial cells we treated the cells with different concentration of EGCG. Five minutes and 1 hour after irradiation, we measured the effects on cell survival and viability. We choose these time points with future in vivo experiments in mind, in particular those that would evaluate green tea absorption and the protective effects of EGCG on the lens epithelium. Specifically, most people drink green tea indoors from 5 minutes to 1 hour after outdoor UV exposure. After another 24-hour incubation, the total cell count was measured and cell activity was evaluated using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay. The aim of this study was to determine whether EGCG can protect human lens epithelial cells from UV-induced damage, and to develop a new in vivo model of UV protection for human lenses using epigallocatechin gallate (EGCG).