Antioxidant activity and antidiabetic activities of Northern Thai indigenous edible plant extracts and their phytochemical constituents

Diabetes mellitus is the most common non-infective disease characterized by hyperglycemia (high level of blood glucose). Formation of advanced glycation end products (AGEs) in long termed-hyperglycemia and oxidative stress are the key factors to accelerate diabetic complications. To screen potential candidates for treating diabetes, total phenolic content, total flavonoid content, antioxidant activity from crude extracts of some Thai edible plants were primarily assessed, and the inhibiting potential of diabetes and its complications provided from some of these plants were evaluated in terms of their inhibitory activities of alpha-amylase, alpha-glycosidase, and AGEs formation. The highest amounts of phenolic and flavonoid compounds were found in the ethanolic extract of Caesalpinia mimosoides (S20, 12.63 +/- 1.70 mg GAE/g DW) and Glochidion hirsutum (S8, 3.02 +/- 0.25 mg CE/g DW), respectively. The highest antioxidant activity was found in Schinus terebinthifolius Raddi (S26, 217.94 +/- 32.30 mu g AAE/g DW) whereas the highest inhibitory activities of alpha-amylase and alpha-glycosidase were obtained from Basella alba L. (S11, IC50 = 0.21 +/- 0.01 mg/ml) and S. terebinthifolius (S26, IC50 = 0.05 +/- 0.02 mg/ml) respectively. The inhibitory effects of AGEs formation were studied in vitro using two model systems: BSA-glucose and BSA-methylglycoxal (MGO). The extracts of Glochidion hirsutum (Roxb.) Voigt (S8, IC50 = 0.20 +/- 0.01 mg/ml) and Polygonum odoratum Lour. (S13, IC50 = 0.03 +/- 0.01 mg/ml) exhibited the inhibitory activity of AGEs formation derived from glucose (BSA-glucose system) stronger than aminoguanidine (AG) (0.26 +/- 0.00 mg/ml), which is a common AGEs formation inhibitory drug. By BSA-MGO assay, the inhibition of some selected extracts in this study (G. hirsutum, G. sphaerogynum, and S. terebinthifolius with IC50 = 0.11 +/- 0.01, 0.11 +/- 0.01, and 0.10 +/- 0.00 mg/ml, respectively) were slightly less efficient than AG (the IC50 = 0.06 +/- 0.00 mg/ml). These results indicated that some selected Thai edible plants in this present study provided potential applications towards the prevention of diabetes and their complications via the inhibitory of alpha-amylase, alpha-glycosidase, AGEs formation, and oxidative stress. This fundamental information would be important for alternative drug discovery and nutritional recommendations for diabetic patients.

Automated summary

This study evaluated the potential of some Thai edible plants in terms of their antioxidant activity and inhibitory effects on diabetic complications. The results showed that Caesalpinia mimosoides and Glochidion hirsutum had the highest phenolic and flavonoid content, respectively, while Schinus terebinthifolius had the highest antioxidant activity. Basella alba and S. terebinthifolius exhibited the strongest inhibitory activities against alpha-amylase and alpha-glycosidase, respectively. The extracts of Glochidion hirsutum and Polygonum odoratum showed stronger inhibitory effects on AGEs formation from glucose compared to the common drug aminoguanidine. The selected extracts in this study demonstrated their potential applications for the prevention of diabetes and its complications through the inhibitory effects on alpha-amylase, alpha-glycosidase, AGEs formation, and oxidative stress.