Anti-diabetic activity of rosmarinic acid rich fractions from orthosiphon stamineus

Background: There has been a great interest in the discovery of alternative medicines from medicinal herbs for type 2 diabetes, specifically screening for phytochemicals which are able to inhibit or delay glucose absorption. Introduction: The aim of this study was to evaluate the inhibition of crude extract and rosmarinic acid rich fractions from Orthosiphon stamineus on α-amylase and α-glucosidase activities. Methods: The plant crude extract was prepared by a reflux method using 70 %v/v ethanol, followed by fractionation using column chromatography to obtain rosmarinc acid rich fractions. Results: The crude extract and its rosmarinic acid rich fractions showed a dose dependent manner to inhibit the saccharide hydrolysing enzymes. Fr. A (100 % rosmarinic acid) was found to have comparable performance with standard rosmarinic acid as an inhibitor for both enzymes. Approximately, 62.50 mg/mL and 5 mg/mL of Fr. A were sufficient to achieve almost 100 % inhibition against α- amylase and α-glucosidase, respectively. Rosmarinic acid in Fr. A (IC50 0.34 mg/mL) was found to be 5 times more active than the anti-diabetic drug acarbose (IC50 1.66 mg/mL) in the inhibition of α- glucosidase. Fr. B with 50 % rosmarinic acid (IC50 1.48 mg/mL) had an inhibitory power comparable to that of acarbose. Kinetic studies revealed that Fr. A inhibited α-amylase competitively, but displayed non-competitive inhibition towards α-glucosidase. Rosmarinic acid had higher affinity towards α-glucosidase with lower Michaelis-Menten constant (Km), 1.42 mM. Conclusion: The findings suggest that rosmarinic acid rich fractions of O. stamineus could be a potential drug to regulate and manage type 2 diabetes mellitus