Comparison of edible brown algae extracts for the inhibition of intestinal carbohydrate digestive enzymes involved in glucose release from the diet

Abstract

Type II diabetes is considered the most common metabolic disorder in the developed world and currently affects about one in ten globally. A therapeutic target for the management of type II diabetes is the inhibition of α- glucosidase, an essential enzyme located at the brush border of the small intestinal epithelium. The inhibition of α-glucosidase results in reduced digestion of carbohydrates and a decrease in postprandial blood glucose. Although pharmaceutical synthetic inhibitors are available, these are usually associated with significant gastrointestinal side effects. In the present study, the impact of inhibitors derived from edible brown algae is being investigated and compared for their effect on glycaemic control. Carbohydrate- and polyphenolic-enriched extracts derived from Ascophyllum nodosum, Fucus vesiculosus and Undaria pinnatifida were characterised and screened for their inhibitory effects on maltase and sucrase enzymes. Furthermore, enzyme kinetics and the mechanism of inhibition of maltase and sucrase were determined using linear and nonlinear regression methods. All tested extracts showed a dose-dependent inhibitory effect of α-glucosidase with IC₅₀ values ranging from 0⋅26 to 0⋅47 mg/ml for maltase; however, the only extract that was able to inhibit sucrase activity was A. nodosum, with an IC₅₀ value of 0⋅83 mg/ml. The present study demonstrates the mechanisms in which different brown seaweed extracts with varying composition and molecular weight distribution differentially inhibit α-glucosidase activities. The data highlight that all brown seaweed extracts are not equal in the inhibition of carbohydrate digestive enzymes involved in postprandial glycaemia.

Keywords: AFCE, combination of polyphenols from Aschophyllum nodosum and Fucus vesiculosus and chromium; AFE, polyphenol-rich extract from Aschophyllum nodosum and Fucus vesiculosus; Ascophyllum nodosum; Fucus vesiculosis; HPAEC-PAD, high-performance anion exchange chromatography with pulsed amperometric detection; MANE, pure seaweed extract from Ascophyllum nodosum; PCA, principal component analysis; Seaweed; Type II diabetes; UPE, fucoidan-rich extract from Undaria pinnatifida; Undaria pinnatifida; pNPG, 4-nitrophenyl-β-d-glucopyranoside; α-Glucosidase.