Inhibition of human starch digesting enzymes and intestinal glucose transport by walnut polyphenols

Author:Farazi M, Houghton MJ, Nicolotti L, Murray M, Cardoso BR, Williamson G.

Journal:

Food Res Int. 2024 Aug;189:114572.

Abstract:One approach to controlling type 2 diabetes (T2D) is to lower postprandialglucose spikesby slowing down the digestion of carbohydrates and the absorption of glucose in the small intestine. The consumption of walnuts is associated with a reduced risk of chronic diseases such as T2D, suggested to be partly due to the high content of (poly)phenols. This study evaluated, for the first time, the inhibitory effect of a (poly)phenol-rich walnut extract on human carbohydrate digesting enzymes (salivary and pancreatic 伪-amylases, brush border sucrase-isomaltase) and on glucose transport across fully differentiated human intestinal Caco-2/TC7 monolayers. The walnut extract was rich in multiple (poly)phenols (70 % w/w) as analysed by Folin-Ciocalteau and by LCMS. It exhibited potent inhibition of both human salivary (IC50: 32.2 卤 2.5 碌g walnut (poly)phenols (WP)/mL) and pancreatic (IC50: 56.7 卤 1.7 碌g WP/mL) 伪-amylases, with weaker effects on human sucrase (IC50: 990 卤 20 碌g WP/mL), maltase (IC50: 1300 卤 80 碌g WP/mL), and isomaltase (IC25: 830 卤 60 碌g WP/mL) activities. Selected individual walnut (poly)phenols inhibited human salivary 伪-amylase in the order: 1,3,4,6-tetragalloylglucose > ellagic acid pentoside > 1,2,6-tri-O-galloyl-尾-D-glucopyranose, with no inhibition by ellagic acid, gallic acid and 4-O-methylgallic acid. The (poly)phenol-rich walnut extract also attenuated (up to 59 %) the transfer of 2-deoxy-D-glucose across differentiated Caco-2/TC7 cell monolayers. This is the first report on the effect of (poly)phenol-rich extracts from any commonly-consumed nut kernel on any human starch-digesting enzyme, and suggests a mechanism through which walnut consumption may lower postprandial glucose spikes and contribute to their proposed health benefits.