α-glucosidase inhibition activity of the extracts of katsura tree (Cercidiphyllum japonicum Sieb. Et Zucc) leaves

초록

Katsura tree (Cercidiphyllum japonicum Sieb. Et Zucc) leaves were collected, air-dried and extracted with 70% aqueous acetone, then concentrated and sequentially fractionated using n-hexane, CH<inf>2</inf>Cl<inf>2</inf>, EtOAc, and H<inf>2</inf>O to be freeze dried for antioxidant and α-glucosidase inhibition activity tests. The antioxidant activity of the extracts was evaluated using DPPH (1,1-diphenyl 2-picrylhydrazyl) free radical scavenging assay. The test concentrations were adjusted to 500, 250, 125, 62.5, 31.25, 15.62, 7.81, 3.9, 1.95 and 0.97 ppm. The H<inf>2</inf>O and EtOAc fractions showed higher activities compared with the control, α-tocopherol, at all concentrations. The crude fraction also gave better activity at the concentrations lower than 62.5 ppm. However, the nonpolar n-hexane and CH<inf>2</inf>Cl<inf>2</inf> fractions gave prominently lower activities compared with the control at all concentrations. The IC<inf>50</inf> values of the crude, EtOAc, and H<inf>2</inf>O fractions exhibited 11.78, 4.29 and 9.80 μg/mℓ, respectively, compared with 12.08 μg/mℓ of the control. But the n-hexane and CH<inf>2</inf>Cl<inf>2</inf> fractions indicated 300 and 91.85 μg/mℓ of IC<inf>50</inf>, respectively. α-Glucosidase inhibition activity was evaluated at the concentrations of 50, 25, 12.5, 6.3, 3.1, 1.6 and 0.8 ppm. The inhibition activities were increased according to as the increase of sample concentrations. However, the nonpolar n-hexane and CH<inf>2</inf>Cl<inf>2</inf> fractions indicated very low inhibition activities compared with acarbose, a positive control. The EtOAc fraction showed very good capability as almost 100% compared with the control at the higher concentrations than 12.5 ppm and the crude fraction also indicated good potential as 95% and 100% at 25 and 50 ppm, respectively. The H<inf>2</inf>O fraction gave good inhibition value as 90% at 50 ppm although the value was lower than the control. These results showed that the polar fractions had better α-glucosidase inhibition activities. The IC<inf>50</inf> values of the nonpolar fractions, n-hexane and CH<inf>2</inf>Cl<inf>2</inf>, showed very lower values as 468 and 103.6 μg/mℓ, respectively, than the control. However, the polar fractions, crude, EtOAc and H<inf>2</inf>O, showed 7.1, 3.7 and 13 μg/mℓ, respectively, indicating that these fractions can be used as natural bioresources for treating diabetes mellitus. Also α-glucosidase inhibition activity had a positive correlation with antioxidant activity of the extracts.

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