Inhibitory effects of guava (Psidium guajava L.) leaf extracts and its active compounds on the glycation process of protein

Hyperglycaemia causes increased protein glycation and the formation of early glycation products and advanced glycation end products (AGEs) which are major factors responsible for the complications of diabetes. This study investigated the ability of guava leaf and compounds to inhibit glycation process in an albumin/glucose model system and compared the potency of these extracts with Polyphenon 60 which is a commercial polyphenol product extracted from green tea and with the standard antiglycation agent, aminoguanidine. The results showed that the inhibitory effects of guava leaf extracts on the formation of α-dicarbonyl compounds were over 95% at 50 μg/ml. Phenolic compounds present, namely gallic acid, catechin and quercetin exhibited over 80% inhibitory effects, but ferulic acid showed no activity. The guava leaf extracts also showed strong inhibitory effects on the production of Amadori products and AGEs from albumin in the presence of glucose. The phenolic compounds also showed strong inhibitory effects on the glycation of albumin, especially quercetin exhibited over 95% inhibitory effects at 100 μg/ml. According to the results obtained, guava leaf extracts are potent antiglycation agents, which can be of great value in the preventive glycation-associated complications in diabetes.