Anti-proliferative and potential anti-diabetic effects of phenolic-rich extracts from edible marine algae

Phenolic-rich extracts from four edible marine macroalgae commonly found in UK waters were tested for their potential biological effects towards cultured colon cancer cells and for their ability to inhibit digestive enzymes to achieve potential anti-diabetic effects. Extracts from Palmaria, Ascophyllum and Alaria, but not Ulva, gave reasonable recoveries of phenolics and inhibited the proliferation of colon cancer cells in a dose-responsive manner. Alaria extracts were more effective than Palmaria or Ascophyllum extracts, but Palmaria and Ascophyllum would provide greater amounts of phenolics per gram intake. ts from Palmaria, Ascophyllum and Alaria all inhibited α-amylase activity to some extent, but Ascophyllum extracts were very effective with an IC50 of ∼0.1 μg/ml GAE. The Ascophyllum extracts also inhibited α-glucosidase, the other key enzyme involved in starch digestion and blood glucose regulation, at low levels (e.g. IC50 ∼20 μg/ml GAE). fractionation on Sephadex LH-20, the inhibitory activity from Ascophyllum was concentrated in the fraction which, from mass spectrometric evidence, was enriched in phlorotannins. These components have the capacity to inhibit α-amylase and α-glucosidase activities at μM levels, which are easily achievable in the gut. This may explain the anti-diabetic properties associated with algal extracts and algal phenolics in various in vivo studies.