Levels of alpha- and gamma-tocopherol in human eyes: evaluation of the possible role of IRBP in intraocular alpha-tocopherol transport.

Alpha-tocopherol was distributed almost equally between the retina and its underlying pigmented layers (pigment epithelium and choroid). Only 8.4% of the total alpha-tocopherol occurred in the iris and ciliary body. Alpha-tocopherol content was expressed as amount per eye, per cm2, and per 100 g wet weight. The combined retina and pigment epithelium-choroid contained 2.9 +/- 1.0 mg/100 g wet weight (means +/- SD, n = 30 donors). Gamma-tocopherol represented 20.9 +/- 12.2 mol % of the alpha-tocopherol. The anterior tissues contained 0.4 +/- 0.2 mg/100 g (n = 19 donors). No significant correlation with age was found. Purified bovine interstitial retinol-binding protein (IRBP) bound exogenous 3H-alpha-tocopherol, which could be displaced by unlabeled all-trans retinol (KD = 10(-6) M). Much higher concentrations of unlabeled alpha-tocopherol were required to achieve a partial displacement of bound 3H-all-trans retinol. No endogenous alpha-tocopherol could be detected in bovine interphotoreceptor matrix.