Comparison of inhibitory activities of 50 Salvia species against α-Glucosidase

Objectives Type 2 diabetes is a common metabolic disease affecting millions of people worldwide. alpha-Glucosidase inhibitors can be used as one of the therapeutic approaches to decrease the postprandial glucose levels through the inhibition of carbohydrate hydrolysis. Medicinal plants are one of the main sources of alpha-glucosidase's natural inhibitors. In this study, we report the inhibitory effects of 50 different accessions of 32 Salvia species against a-glucosidase. Methods To estimate the relative potency of the crude extracts, the inhibitory activities of the 80% methanol of the plants extracts were determined in three different concentrations (1000, 500 and 250 mu g/ml) and compared to that of acarbose as the positive control. Results S. multicaulis, S. santolinifolia, S. dracocephaloides, and S. eremophila were stronger inhibitors than acarbose (p < 0.05) with IC50 values in the range of 26.23- 92.35 mu g/mL. According to the LC-PDA-ESIMS and NMR analysis of crude extracts of the studied Salvia species, 8 phytochemicals including luteolin-7-O-glucoside (1) luteolin-7-O-glucuronide (2), apigenin-7-O-glucoside (3), apigenin-7-O-glucuronide ( 4), Hispidulin-7-O-glucuronide (5), hispidulin-7-O-glucoside (6), rosmarinic acid (7), carnosol (8) and carnosic acid (9) were identified as the most common a- glucosidase inhibitors. The above compounds constituted the major compounds in the active Salvia species in the range of 1.5-95.0%. Among them rosmarinic acid (39-95%) was detected in almost all potent a -glucosidase inhibitor species. Therefore, it can be considered as a biochemical marker in the antidiabetic Salvia species in addition to the other minor compounds. Conclusions Considering the high a-glucosidase inhibitory potential of the four- out of fifty Salvia species, they are suggested for further in vivo antidiabetic tests as potential medicinal plants.