l-Arabinose selectively inhibits intestinal sucrase in an uncompetitive manner and suppresses glycemic response after sucrose ingestion in animals

The objective of this study was to investigate the effects of l-arabinose on intestinal α-glucosidase activities in vitro and to evaluate its effects on postprandial glycemic responses in vivo. L-Arabinose inhibited the sucrase activity of intestinal mucosa in an uncompetitive manner (Ki, 2 mmol/L). Neither the optical isomer d-arabinose nor the disaccharide l-arabinobiose inhibited sucrase activity, whereas d-xylose was as potent as l-arabinose in inhibiting this activity. l-Arabinose and d-xylose showed no inhibitory effect on the activities of intestinal maltase, isomaltase, trehalase, lactase, and glucoamylase, or pancreatic amylase. In contrast, a known α-glucosidase inhibitor, acarbose, competitively inhibited (ki, 1.1 μmol/L) sucrase activity and also inhibited intestinal maltase, glucoamylase, and pancreatic amylase. l-Arabinose suppressed the increase of blood glucose after sucrose loading dose-dependently in mice (ED50, 35 mg/kg), but showed no effect after starch loading. The suppressive effect of d-xylose on the increase of blood glucose after sucrose loading was 2.4 times less than that of l-arabinose, probably due to intestinal absorption of the former. Acarbose strongly suppressed glycemic responses in both sucrose loading (ED50, 1.1 mg/kg) and starch loading (ED50, 1.7 mg/kg) in mice. l-Arabinose suppressed the increase of plasma glucose and insulin in rats after sucrose loading, the suppression of the former being uninterruptedly observed in mice for 3 weeks. Thus, the results demonstrated that l-arabinose selectively inhibits intestinal sucrase activity in an uncompetitive manner and suppresses the glycemic response after sucrose ingestion by inhibition of sucrase activity.