Phenolic-rich extracts from the edible seaweed, ascophyllum nodosum, inhibit α-amylase and α-glucosidase: Potential anti-hyperglycemic effects

Different extracts of the edible seaweed, Ascophyllum nodosum, were compared for their ability to inhibit α-amylase and effectiveness was linked to phenol and apparent phlorotannin contents. After solid phase extraction, phenolic-enriched extracts retained potent α-amylase inhibition [IC50 ~ 0.05 µg GAE/mL], whereas phlorotannin-rich sub-fractions were threefold less potent. Potency could be restored by re-addition of the wash fraction suggesting synergy between tannin and non-tannin components. The phenolic-rich extract and the phlorotannin-rich fraction inhibited α-glucosidase equally effectively (IC50 ~ 10 µg GAE/mL). Co-incubation of the tannin-rich fraction with acarbose reduced the concentration of acarbose required for effective inhibition of both amylase and glucosidase. That pre-incubation of amylase with the tannin-rich fraction markedly improved but the addition of BSA reduced inhibitory effectiveness suggested that phlorotannins inhibit amylase, but not glucosidase, through a protein-binding mechanism. The use of phlorotannins in combination with acarbose for postprandial glycemic control in type-2 diabetics is discussed.