A sulfated polysaccharide ascophyllan inhibited α-glucosidase in a concentration dependent manner, and >90% activity was inhibited at 1.0 mg/mL. The inhibitory activity was much higher than that of acarbose. No significant inhibitory effect of ascophyllan on α-amylase was observed up to 10.0 mg/mL. Ascophyllan HS, a commercially available ascophyllan preparation showed even higher inhibitory effect on α-glucosidase than ascophyllan. Interestingly, ascophyllan and ascophyllan HS induced the secretion of glucagon-like peptide-1 (GLP-1) from human intestinal NCI-H716 cell line in a concentration dependent manner (10-100 ng/mL). The oral glucose tolerance tests revealed that after continuous 8-week ingestion of ascophyllan HS at 100 mg/day, the glucose area under the curve values of the ascophyllan HS ingested group were significantly lower than placebo ingested group. Serum glycosylated hemoglobin (HbA1c) level in ascophyllan HS ingested group tended to decrease after 8-week ingestion, whereas no significant change was observed in placebo ingested group. This is the first report indicating that ascophyllan can induce the secretion of GLP-1 from human intestinal cell line (NCI-H716), besides the potent inhibitory effect on α-glucosidase. Furthermore, clinical trial suggested that ascophyllan HS may be a practically applicable blood glucose controlling agent in humans.
Keywords: Anti-diabetic effect; Ascophyllan; Ascophyllan ΗS; Ascophyllum nodosum; HbA1c; Secretagogue of GLP-1; α-glucosidase inhibitor.
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