Effect of colon-derived polyphenol metabolites on in vitro protein glycation

Polyphenols are thought to be beneficial in the control of diabetic complications because of their ability to inhibit oxidative stress and protein glycation. Polyphenols undergo extensive metabolism during their absorption though the first-intestinal tract. Polyphenol catabolites produced by microbia of colon enter the circulatory system. The aim was to investigate the inhibitory activity of colonic-derived catabolites against protein glycation. Protein glycation was measured, after a two weeks incubation under physiological condition (pH 7.4; 37°C) of bovine serum albumin (40 mg/mL) and glucose (30 mmol/L) in presence or absence of polyphenol catabolites, with fluorescence at the excitation and emission maxima of 355 and 405 nm, respectively. A dose dependent inhibition of glycation was observed with urolithin A and B (catabolites of pomegranates and raspberries) and dihydroferulic acid (from coffee.) The IC50 of urolithin A is 12mM. Urolithin B and dihydroferulic acid are less effective. The catabolites were also tested in association, based on the dietary sources. The pomegranate-derived catabolites urolithin A, B and pyrogallol, inhibit glycation by 37 and 44% at 1 and 2µmol/L respectively, suggesting a synergic action between catabolites. The red wine-derived catabolites in association show a lower antiglycative activity (15% inhibition at 2µmol/L) while coffee catabolites are inactive. Polyphenol colon-catabolites inhibit protein glycation at concentrations observed in blood after consumption of a portion of pomegranate or raspberry. These observations suggest that some polyphenols may contribute to reduce the hyperglycemia-correlated pathologies.