Fructose induced deactivation of antioxidant enzymes: Preventive effect ofpyruvate

Glycation initiated changes in tissue proteins, which are triggered by the Schiff base formation between the sugar carbonyl and the protein -NH2, have been suggested to play an important role in the development of diabetes-re lated pathological changes such as the formation of cataracts. While the in itial reaction takes place by the interaction of >C=O of the parent sugars with the -NH2 of proteins, reactive oxygen species (ROS) dependent generati on of more reactive dicarbonyl derivatives from the oxidation of sugars als o plays a significant role in these changes, altering the structural as wel l as functional properties of proteins. The purpose of this study was to ex amine whether the activities of glyceraldehyde-3-phosphate dehydrogenase (G APDH), catalase and superoxide dismutase (SOD) could be affected by the hig h levels of fructose prevalent in diabetic lenses. Incubation of the enzyme s with this sugar led to a significant loss of their activities. GAPDH was inactivated within a day. This was followed by the inactivation of catalase (3-4 days) and SOD (6 days). The loss of the activities was prevented sign ificantly by incorporation of pyruvate in the incubation mixture. The prote ctive effect is ascribable to its ability to competitively inhibit glycatio n as well as to its ROS scavenging activity. Hence, it could play a signifi cant role in the maintenance of lens physiology and cataract prevention.