Prevention of the rise in plasma cholesterol and glucose levels by kaki-tannin and characterization of its bile acid-binding capacity

Background: Bile acid-binding agents, such as cholestyramine and colesevelam, improve both cholesterol and glucose metabolism. Kaki-tannin, a polymerized condensed tannin derived from persimmon (Diospyros kaki), has been shown to have bile acid-binding capacity and a hypocholesterolemic effect. However, its effects on glucose metabolism have not been well studied, and the binding selectivity of kaki-tannin to bile acid molecules has not been reported.

Results: In vivo experiments using mice with high-fat diet-induced obesity showed that kaki-tannin intake (20 g kg^-1 of the diet) increased fecal bile acid excretion by 2.3-fold and prevented the rise in plasma cholesterol levels and fasting plasma glucose levels. Kaki-tannin also suppressed the development of impaired glucose tolerance. To characterize the bile acid-binding capacity of kaki-tannin, we investigated its binding capacity to eight types of bile acid and cholesterol in vitro. Kaki-tannin showed strong binding capacity (85.5%) to lithocholic acid, which has one hydroxy group. Furthermore, it showed moderate binding capacity to bile acids with two hydroxy groups (53.3%), followed by those with three hydroxy groups (39.0%), but kaki-tannin did not show binding capacity to cholesterol. These results suggest that the binding capacity of kaki-tannin to bile acids tends to decrease as the number of hydroxy groups increases. Interestingly, the binding capacity of kaki-tannin correlated with that of cholestyramine (correlation coefficient: r = 0.900).

Conclusion: Our findings indicate that kaki-tannin binds preferentially to bile acids with fewer hydroxy groups and has beneficial effects on glucose metabolism as well as cholesterol metabolism. This article is protected by copyright. All rights reserved.

Keywords: Diospyros kaki; animal experiment; bile acid-binding capacity; condensed tannin.