Oleanolic acid (pentacyclic triterpenes) as a potential candidate for α-glycosidase inhibition activity

Background: Diabetes mellitus is a common health dilemma worldwide and is characterized by hyperglycemia. Inhibition in the activity of one of the digestive tract enzymes α-glucosidase is one of the therapeutic approaches to hydrolyze carbohydrates into glucose using natural agents. Many natural compounds with α-glucosidase inhibitory activity have transpired to be secondary metabolites. Monotheca buxifolia, native to Pakistan is a major medicinal tree, which has been known for its extensive pharmacological activities.Methods: α-glucosidase activity of ten isolated compounds (lupeol, lupeol acetate, betulin, β-sitosterol, β-amyrin, oleanolic acid, vanillic acid, protocatechuic acid, kaempferol and quercetin) from lipophilic hexane fraction of M. buxifolia (stem and leaves) was assessed against α-glucosidase enzyme using acarbose as a control.Results: All ten compounds hold α-glucosidase inhibition potential (91-99%). However, IC50 (half-maximal inhibitory concentration) values of oleanolic acid (5 µM) were 8-fold lower than that of acarbose. Moreover, inhibition potencies of lupeol (15.87 µM), β-amyrin (18.14 µM) betulin (21.49 µM), quercetin (23.47 µM), and lupeol acetate (29.45 µM) were much stronger than the inhibitory effect obtained from acarbose (38.25 µM).Conclusion: Oleanolic acid of M. buxifolia exhibited a potent inhibitory effect against α-glucosidase, therefore, oleanolic acid may be utilized in medicinal formulations against diabetic disorders.