The effects of different levels of all-rac- and RRR-α-tocopheryl acetate (vitamin E) on visual function in rats

Objective: A rat model of vitamin E (α-tocopherol) deficiency with similar ‘clinical’, electrophysiological and neuropathological abnormalities to that seen in man was used to investigate the effects of various dietary intakes of synthetic (all-rac-) and natural (RRR-) α-tocopheryl acetate (αTA) on visual function. Methods: Longitudinal measurements of the electroretinogram (ERG) and visual evoked potentials (VEPs) were made monthly for 14 months in 9 groups of rats (n=12/group) receiving different amounts and types of αTA. The animals were then killed for biochemical analyses. Results: (1) The first significant abnormalities of both the ERG and VEP were found after 8 months of deficiency. (2) A diet containing 1.25 mg/kg of αTA provided marginal protection. (3) The biological activity of all-rac- was approximately 75% of RRR-αTA. (4) The concentration of free malondialdehyde (a measure of lipid peroxidation) was significantly increased in all tissues, including the eye, from deficient compared to control rats. Conclusions: These results are consistent with α-tocopherol deficiency causing increased lipid peroxidation leading to abnormal visual function but could also be explained by more specific but undefined function(s) of α-tocopherol in the eye.