Alpha-amylase and alpha-glucosidase inhibition is differentially modulated by fucoidan obtained from Fucus vesiculosus and Ascophyllum nodosum

Fucoidan is a water-soluble, negatively charged, biologically active polysaccharide found in great abundance in brown marine algae. However, the inhibition of alpha-amylase and alpha-glucosidase by fucoidan derived from two algal species (Ascophyllum nodosum and Focus vesiculosus) harvested at different periods (accounting for seasonal and yearly variations) has never been investigated. It was found that fucoidans inhibited alpha-glucosidase differently, depending on the algal species from which it was extracted and the algae's season of harvest. Fucoidan extracted from A. nodosum was a more potent inhibitor of alpha-glucosidase, with an IC50 ranging from 0.013 to 0.047 mg/mL, than the inhibition by fucoidan extracted from F. vesiculosus (IC50 = 0.049 mg/mL). In contrast, fucoidan extracted from F. vesiculosus did not inhibit alpha-amylase activity, while fucoidan from A. nodosum decreased alpha-amylase activity by 7-100% at 5 mg/mL depending upon the algae harvest period. An IC50 of 0.12-4.64 mg/mL for fucoidan from A. nodosum was found for the alpha-amylase inhibition. The ability of fucoidan to inhibit alpha-amylase and alpha-glucosidase thus varies according to the algae species and harvest period. A. nodosum is more suitable than F. vesiculosus as a source of fucoidan to inhibit alpha-amylase and alpha-glucosidase activities. Their potential benefits towards Type 2 diabetes management should be further investigated. (C) 2013 Elsevier Ltd. All rights reserved.