In Vitro Screening of α-Amylase Inhibition by Selected Terpenes from Essential Oils

Purpose: To assess some terpenes from herbal products for possible inhibitory effects on serum α- amylase in order to ascertain their potential usefulness in the prevention and/or treatment of diabetes Type 2.
Methods: Solutions of terpenes (citral, eukalyptol, β-pinene, myrcene, eugenol and terpineol) in deonized water were prepared by ultrasonic and manual mixing in four different concentrations ranging from 0.39 – 5.50 μmol cm^-3. Commercial sera (with normal-N and high-H enzyme activity) were used as a source of α-amylase. α-Amylase activity was determined by standard methods using an automated analyzer.
Results: All the selected terpenes at their maximal concentrations inhibited α-amylase in N-sera in the range 9.68 – 38.70 and 10.71 - 25.00 % for ultrasonic and manual mixing, respectively, while in H-sera, inhibition was in the range 17.10 - 21.05 and 13.58 – 25.92 % for ultrasonic and manual mixing, respectively. Regardless of the concentration of the inhibitor or the method of mixing, citral was the strongest inhibitor of α-amylase.
Conclusion: The selected terpenes, in their appropriate concentrations, influence α-amylase activity to varying degrees. Principal component and agglomerative hierarchical analysis reveal that the most significant factor in α-amylase inhibition is the mode of mixing the samples, rather than their concentrations.

Keywords
α-Amylase; β-Pinene; Citral; Diabetes; Essential oil; Eugenol; Eukalyptol; Myrcene; Terpenes; Terpineol