Antioxidant and Antiglycation Activities of Some Edible and Medicinal Plants

Protein glycation and oxidative stress caused by chronic hyperglycemia are the major factors in diabetic complications. In the attempt to search for natural remedies, ethyl acetate and ethanol extracts from twenty Thai edible and medicinal plants were assessed in terms of their phenolic and flavonoid contents as well as their antioxidant and antiglycation activities. The highest amounts of phenolic and flavonoid compounds were found in the ethanolic extract of the young leaves of Punica granatum followed by those of Dimorcarpus longan and Mangifera indica, respectively. These three plant extracts also exhibited the highest antioxidant activity. A high correlation between the antiglycation activity and the phenolic and flavonoid contents was observed in all extracts. In addition, five ethanolic extracts-from Tamarindus indica, Psidium guajava, Mangifera indica, Dimocarpus longan and Punica granatum young leaves-were determined for their concentrations required to inhibit 50% (IC 50) of either glucose or methyl glyoxal-derived glycation. P. granatum, M. indica and P. guajava extracts showed high antiglycation activity in the BSA-glucose model, with IC 50 values of 110.4, 214.4 mu g/ mL and 243.3 mu g/ mL, respectively. The IC 50 values of antiglycation activity in the BSA-methylglyoxal model of M. indica (54.1 mu g/ mL), P. granatum (69.1 mu g/ mL) and D. longan (74.2 mu g/ mL) were higher than that of the standard AGE inhibitor, aminoguanidine (91.2 mu g/ mL). These results indicated that some Thai edible and medicinal plants possessed high contents of phenolic and flavonoid and have potential applications towards the prevention of glycation-associated diabetic complications.