| 20153624 |
Feng Z, Liu Z, Li X, Jia H, Sun L, Tian C, Jia L, Liu J: alpha-Tocopherol is an effective Phase II enzyme inducer: protective effects on acrolein-induced oxidative stress and mitochondrial dysfunction in human retinal pigment epithelial cells. J Nutr Biochem. 2010 Feb 12.
Vitamin E has long been identified as a major lipid-soluble chain-breaking antioxidant in mammals. alpha-Tocopherol is a vitamin E component and the major form in the human body. We propose that, besides its direct chain-breaking antioxidant activity, alpha-tocopherol may exert an indirect antioxidant activity by enhancing the cell's antioxidant system as a Phase II enzyme inducer. We investigated alpha-tocopherol's inducing effect on Phase II enzymes and its protective effect on acrolein-induced toxicity in a human retinal pigment epithelial (RPE) cell line, ARPE-19. Acrolein, a major component of cigarette smoke and also a product of lipid peroxidation, at 75 mumol/L over 24 h, caused significant loss of ARPE-19 cell viability, increased oxidative damage, decreased antioxidant defense, inactivation of the Keap1/Nrf2 pathway, and mitochondrial dysfunction. ARPE-19 cells have been used as a model of smoking- and age-related macular degeneration. Pretreatment with alpha-tocopherol activated the Keap1/Nrf2 pathway by increasing Nrf2 expression and inducing its translocation to the nucleus. Consequently, the expression and/or activity of the following Phase II enzymes increased: glutamate cysteine ligase, NAD (P) H:quinone oxidoreductase 1, heme-oxygenase 1, glutathione S-transferase and superoxide dismutase; total antioxidant capacity and glutathione also increased. This antioxidant defense enhancement protected ARPE-19 cells from an acrolein-induced decrease in cell viability, lowered reactive oxygen species and protein oxidation levels, and improved mitochondrial function. These results suggest that alpha-tocopherol protects ARPE-19 cells from acrolein-induced cellular toxicity, not only as a chain-breaking antioxidant, but also as a Phase II enzyme inducer. |
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