Polyphenols protect against protein glycoxidation

Abstract

Glycoxidation belongs to posttranslational protein modifications which underlie pathological sequelae of diabetes and other diseases, and contribute to aging. Search for efficient inhibitors of glycoxidation is therefore of considerable importance. We studied the effect of various polyphenols on the glycoxidation of bovine serum albumin (90 uM) incubated in vitro with glucose, fructose or ribose (100mM) for 6 days in 0.1M phosphate buffer, pH 7.4. Polyphenols have multiple biological actions including antioxidant activity and chelation of transition metal ions. The extent of glycoxidation was evaluated using fluorimetic parameters reflecting formation of Advanced Glycoxidation End Products (AGEs: 325/440nm), dityrosine (330/415nm), formylkynurenine (325/434nm) and kynurenine (365/480nm) and confirmed by estimation of AGEs using an ELISA kit. The results confirmed reliability of easily measurable fluorimetric parameters such as AGEs, dityrosine and formylkynurenine level for estimation of the extent of glycoxidation.All the polyphenols used (caffeic acid, ferulic acid, gallic acid, genistein, naringin, propyl gallate, quercitrin and rutin) decreased the extent of albumin glycoxidation. The extent of protection varied for different sugars (e. g. 1mM genistein: 24.4±1.7 for glucose, 44.5±0.2 for fructose 51.4±0.3 for ribose) The sequence of protective effect was: ferulic acid>caffeic acid>propyl gallate>naringin>quercitrin>genistein for glucose, caffeic acid>ferulic acid>propyl gallate>genistein>quercitrin>rutin>naringin for fructose and genistein>ferulic acid>caffeic acid>rutin>propyl gallate>naringin>quercitrin>gallic acid. These results confirm that polyphenols, natural components of human diet, protect against protein glycation in a model in vitro system. This study was performed within the framework of COSTCM1001 action and was sponsored by Grant 2011/01/M/N23-02065 of the National Science Center of Poland.