Levels of α- and γ-tocopherol in human eyes: Evaluation of the possible role of IRBP in intraocular α-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 α-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 (χ̄ ± SD, n = 30 donors). Gamma-tocopherol represented 20.9 ± 12.2 mol % of the α-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-α-tocopherol, which could be displaced by unlabeled all-trans retinol (K(D) = 10^-6M). Much higher concentrations of unlabeled α-tocopherol were required to achieve a partial displacement of bound ³H-all-trans retinol. No endogenous α-tocopherol could be detected in bovine interphotoreceptor matrix.