Glutathione reductase in human lens epithelium: FAD-induced in vitro activation

Glutathione reductase (GR) activity was measured with and without the addition of flavin adenine dinucleotide (FAD) in freshly excised human lens epithelium following cataract surgery, and in control eye bank lens epithelium. Large individual variations in activity were found in both groups. Out of 32 epithelia obtained from cataractous lenses, 14 showed no measurable GR activity. Activity in eight of these 14 epithelia was restored after FAD was added, implying that the apo-enzyme in these 8 epithelia was functional but FAD was not available. Another group of 8 active epithelia showed a significant increase in GR activity upon the addition of FAD, suggesting a mixed population of active enzyme and available fraction of apo-enzyme which was reactivated by the addition of FAD. Unusually high GR activities were observed in epithelia of several patients. This correlated principally with daily intake of thyroxine which is known to have a direct effect on the metabolism of riboflavin. The fact that in a significant number of cataract patients epithelial GR was not active, and the observation that activity could be restored by adding in vitro FAD, demands that more attention should be given to riboflavin nutritional status and FAD synthesis in the eye.