Cranberry phytochemicals inhibit glycation of human hemoglobin and serum albumin by scavenging reactive carbonyls

Protein glycation caused by sugars and reactive carbonyls is a contributing factor to diabetic complications, aging, and other chronic diseases. The objective of this study was to investigate the inhibitory effects of cranberry phytochemicals on protein glycation. Cranberries, purified to yield sugar-free phytochemical powder, were fractionated into ethyl acetate and water fractions. Water fraction was further separated into water fraction I, II, and III on a Sephadex LH-20 column. Cranberry phytochemical powder and its fractions significantly inhibited the formation of glycated hemoglobin. The concentrations of cranberry phytochemicals required to inhibit 50% of albumin glycation (EC50) in albumin-glucose assay were lower than that of aminoguanidine except for water fraction I. Cranberry phytochemicals inhibited glycation of human serum albumin mediated by methylglyoxal, but the EC50 were higher than that of aminoguanidine. Carbonyl scavenging assay showed that water fraction II scavenged 89.3% of methylglyoxal at 6 h of reaction. Fractions enriched with procyanidins showed higher antiglycation activities, suggesting procyanidins were the major active components. The hypothesis whether cranberry procyanidins scavenged reactive carbonyls by forming adducts was tested. Epicatechin was used as a model compound to react with methylglyoxal and glyoxal at pH 7.4. Five adducts were detected and their structures were tentatively identified using HPLC-ESI-MS/MS.