Inhibition of α-Glucosidase Activity by 3,5-Dicaffeoylquinic Acid from Lonicera japonica Thunb Flower Buds
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Abstract:
Inhibitory effect of 3,5-dicaffeoylquinic acid (3,5-DCQA) from flower buds of Lonicera japonica Thunb on α-glucosidase was investigated. The 3,5-DCQA was isolated from a 50%-methanol extract of L. japonica flower buds using chromatography and its structure was identified by mass spectrometry (MS) and nuclear magnetic resonance (NMR) spectroscopy. The selectivity of 3,5-DCQA in its inhibition of ?-glucosidase was evaluated using ?-glucosidase I from rat small intestine and ?-glucosidase II from Saccharomyces cerevisiae, baker’s yeast, and Bacillus stearothermophilus. The result indicated that the degree of ?-glucosidase inhibition by 3,5-DCQA was related to the origin of the enzyme. In addition, 3,5-DCQA selectively inhibited maltose hydrolysis activity of rat intestinal ?-glucosidase I. Kinetic study revealed that 3,5-DCQA was a noncompetitive inhibitor of rat intestinal maltase with a Ki value of 0.22 mM. Furthermore, the structure-activity relationship (SAR) study suggested that the two caffeoyl groups in 3,5-DCQA play an essential role in ?-glucosidase inhibitory activity and that the number of caffeoyl groups in 3,5-DCQ are related to its activity. Therefore, 3,5-DCQA obtained from the flower buds of Lonicera japonica Thunb can be used in development and application of functional foods for the management of postprandial hyperglycemia.
