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DOI: 10.1055/s-0035-1565726
Investigation of α-amylase inhibitory activities of herbal extracts with a HPLC-based assay
Inhibition of α-amylase, an enzyme that plays a key role in digestion of starch, is considered as a strategy in the treatment of type-II diabetes. Several herbal extracts and natural products with remarkable amylase-inhibiting activity have been identified so far. Although in the human medicine α-glucosidase inhibitors have greater importance, inhibition of pancreatic amylase is a potential target for antidiabetic drugs. Moreover, the widely applied α-glucosidase inhibitor acarbose exerts inhibitory activity on both enzymes, therefore the identification of α-amylase inhibitors may contribute the development of acarbose-type drugs as well.
Screening of plant extracts for α-amylase inhibitory activity is usually based on the application of spectrophotometric methods. The aim of our work was the development of a HPLC-based method which provides quick, specific and reliable determination of enzyme activity. For this purpose, a 2-chloro-4-nitrophenyl β-glycoside was synthesized and introduced as an α-amylase substrate [1]. After incubating with the enzyme, the reaction mixture was analyzed by HPLC. Assessment of enzyme inhibitory activity was carried out based on the kinetic of formation of the major chromophor containing degradation product. HPLC analysis was done on a C18 column, using MeCN-H2O as eluent and UV detection at 300nm with a running time of 20 min.
This method was tested by the analysis of 10 plant extracts, some of which have reported to have α-amylase inhibitory activities. Water extracts of 5 plants (bay leaves, cranberry, cinnamon, cloves, green tea) exhibited remarkable activities, with IC50 values in the range of 0.92 – 35.17 µg/mL. Results reassured that our HPLC-based method is an appropriate tool for the quick assessment of specific α-amylase inhibitory activity of herbal extracts.
References:
[1] Farkas E, Janossy L, Harangi J, Kandra L, Liptak A. Synthesis of chromogenic substrates of alpha-amylases on a cyclodextrin basis. Carbohydr Res 1997; 303: 407 – 415