Inhibitory effects of the water yam (Dioscorea alata L.) on glucose-induced protein glycation

Diabetes is one of the five leading causes of death in Taiwan. Diabetic hyperglycemia leads to protein glycation and oxidative stress in cells and tissues, and these have been implicated in the pathogenesis of diabetic complications. Therefore, exploring natural compounds that possess both antioxidant and antiglycation activities might have great therapeutic potential for treating diabetic complications. The object of this study was to evaluate the antiglycating and antioxidant properties of extracts from edible Shan-Yao (water yam; Dioscorea alata L.) tubers and several other traditional Chinese herbs used to treat diabetes, including Fu-Ling, Tian-Hua-Fen, Huang-Chi, and Ze-Xie by thermal glycation of bovine serum albumin (BSA) and an in vitro free radical-scavenging assay. The results showed that the water extracts of Shan-Yao, Tian-Hua-Fen, Huang-Chi, and Ze-Xie caused a significant decrease in the thermal glycation of BSA by glucose, with the extract from Tian-Hua-Fen being the most effective. The extract of Fu-Ling markedly enhanced the level of thermal glycation of BSA by glucose. The total phenolic concentration was strongly correlated with the antiglycation activity (r = 0.93 p < 0.05) and with the free radical-scavenging activity (r = 0.98 p < 0.01 ). The antiglycation activities of Shan-Yao, Tian-Hua-Fen, Huang-Chi, and Ze-Xie were consistent with their phenolic contents and free radical-scavenging activities. Again the lowest content of phenolics and free radical-scavenging activity were found in the extract of Fu-Ling. Our study results suggest that water extracts from Shan-Yao, Tian-Hua-Fen, Huang-Chi, and Ze-Xie, especially Tian-Hua-Fen, may offer therapeutic potential in protection against diabetic complications due to their combined antiglycation and antioxidant properties.