Prevention of non-enzymic glycation of proteins by dietary agents: prospects for alleviating diabetic complications

The accumulation of advanced glycation endproducts (AGE) due to non-enzymic glycation of proteins has been implicated in several pathophysiologies associated with ageing and diabetes. The formation of AGE is accelerated in hyperglycaemic conditions, which alter the structure and function of long-lived proteins. Thus inhibition of the formation of AGE is believed to play a role in the prevention of diabetic complications. In the present study we evaluated the antiglycating effect of aqueous extracts of various plant-based foods. The effect of aqueous extracts of these agents in terms of their ability to prevent the accumulation of AGE due to fructose-mediated in vitro glycation of eye lens soluble proteins was investigated. The degree of protein glycation in the absence and presence of dietary extracts was assessed by different complementary methods, i.e. non-tryptophan AGE fluorescence, AGE-induced cross-linking by SDS-PAGE and glyco-oxidative damage by carbonyl assay. Five out of the seventeen agents tested showed significant inhibitory potential against in vitro protein glycation in a dose-dependent manner. Prominent among them were ginger, cumin, cinnamon, black pepper and green tea, which inhibited in vitro AGE formation to lens proteins 40-90 % at 1.0 mg/ml concentration. Assessing their potential to reduce the amount of glycated protein using boronate affinity chromatography and also their ability to prevent the formation of specific antigenic-AGE structures by immunodetection further substantiated the importance of ginger, cumin and cinnamon in reducing AGE burden. These findings indicate the potential of some dietary components to prevent and/or inhibit protein glycation. Thus these dietary agents may be able to be exploited for controlling AGE-mediated diabetic pathological conditions in vivo.