Characteristics of proanthocyanidins in leaves of Chamaecyparis obtusa var. formosana as strong α-glucosidase inhibitors.

BACKGROUND: In recent decades, there has been a growing demand for natural products with a view to using them as α-glucosidase inhibitors for reducing postprandial hyperglycemia. In this study, the hot water extract (HWE) from Chamaecyparis obtusa var. formosana (Hayata) Rehder (Cupressaceae) leaves and its soluble fractions were screened for α-glucosidase inhibition properties. The n-butanol-soluble fraction of HWE was further fractionated into 14 subfractions (B1-B14) using a Sephadex LH-20 column. The α-glucosidase-inhibitory activities and proanthocyanidin contents of all subfractions were determined. The structural characteristics of proanthocyanidins in proanthocyanidin-rich fractions were also elucidated.
RESULTS: HWE produced a dose-dependent inhibition of α-glucosidase at low dose. Its IC50 value was 1.4 µg mL-1 , showing high inhibitory activity. Subfractions B7-B14 displayed powerful α-glucosidase-inhibitory activities with IC50 values ranging between 1 and 0.015 µg mL-1 and contained abundant proanthocyanidins exceeding 300 mg g-1 . The proanthocyanidins with higher mean degree of polymerization (mDP), higher proportions of procyanidin dimer (A1 or A2) and (epi)afzelechin of extension units and a lower proportion of epicatechin of terminal units displayed high α-glucosidase-inhibitory activities.
CONCLUSION: Proanthocyanidins in HWE were viewed as potential natural α-glucosidase inhibitors for decreasing postprandial hyperglycemia. The results indicated that specific structural characteristics of proanthocyanidins would be required for α-glucosidase-inhibitory activity.