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About 20 million Americans have vision-obstructing cataracts, with 500,000 new cases diagnosed annually. The estimated current cost of $3.4 billion annually to surgically extract cataracts is expected to increase along with the growing number of people over the age of 65. Among the risk factors associated with age-related cataracts, UV exposure and oxidative stress appear to be the most relevant. The lens is equipped with antioxidant mechanisms - such as glutathione peroxidase, vitamins C and E and carotenoids - to defend against the harmful effects of UV radiation and reactive oxygen species (ROS). Indeed, some epidemiologic studies suggest a reduced risk of developing various types of cataract with higher intake of vitamin C, E or lutein and zeaxanthin, the only carotenoids present in the lens and macula.
Although considerable efforts are being made to define the potential role of the xanthophylls lutein and zeaxanthin in the macula, information about their uptake and function in the lens is extremely limited. Epithelial cells, the outermost cellular layer of the lens, are exposed to UV irradiation not filtered by the cornea. UV-induced damage is mediated via production of ROS, and characterized by alterations in cell growth, morphology, changes in membrane potential, and oxidation of lipids, proteins and DNA. The present study examined the ability of xanthophylls to protect cultures of immortalized human lens epithelial cells (HLE) against UVB insult.
Cultured HLE cells accumulated xanthophylls and alpha tocopherol in a dose and time-dependent manner, with uptake of lutein exceeding that of zeaxanthin. Cultures were pretreated with either xanthophylls (2 µmol/L) or alpha tocopherol (10 µmol/L) for 4 hours, then exposed to 300 J/m2 UVB radiation - a dose roughly equivalent to that a person receives when they get a mild tan. Lipid peroxidation was observed to decrease by 47-57% compared with UVB-treated control cells.
The ability of xanthophylls and vitamin E to inhibit UVB-induced stress signaling was also assessed. Pretreatment with xanthophylls and alpha tocopherol inhibited UVB-induced activation of c-JUN NH2 terminal kinase and p38 activation by 50-60% and 25-32%, respectively. The concentration of Vitamin E required to significantly inhibit these stress signaling markers was roughly 10-fold higher than that of the xanthophylls, suggesting that xanthophylls are more potent for protecting HLE cells against UVB insult in this model.
According to the researchers from Ohio State University, their results are the first to provide physical evidence suggesting that lutein and zeaxanthin decrease damage caused by UV radiation. "In addition to protective enzymes and compounds like vitamins C and E, we think that low concentrations of lutein and zeaxanthin in the eye's lens help shield the eye from the harmful effects of UVB radiation", they stated in a post-publication interview.
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