Dual effects of phloretin and phloridzin on the glycation induced by methylglyoxal in model systems

Abstract

In the present study, the dual effects of phloretin and phloridzin on methylglyoxal (MGO)-induced glycation were investigated in three N α-acetyl amino acid (arginine, cysteine, and lysine) models and three N-terminal polypeptide (PP01, PP02, and PP03 containing arginine, cysteine, and lysine, respectively) models. In both N α-acetyl amino acids and N-terminal polypeptides models, the arginine residue was confirmed as the major target for modification induced by MGO. Meanwhile, MGO modification was significantly inhibited by the addition of phloretin or phloridzin via their MGO-trapping abilities, with phloretin being more effective. Interestingly, the cysteine residue was intact when solely incubated with MGO, whereas the consumption of N α-acetylcysteine and PP02 was promoted by the addition of phloretin. Additional adducts, [N α-acetylcysteine + 2MGO + phloretin-H 2O] and [2N α-acetylcysteine + 2MGO + phloretin-2H 2O] were formed in the model composed of N α-acetylcysteine, MGO, and phloretin. Another adduct, [PP02 + 2MGO + phloretin-H 2O] was observed in the model composed of PP02, MGO, and phloretin. The generation of adducts indicates that phloretin could directly participate in the modification of the cysteine residue in the presence of MGO. When creatine kinase (model protein) was exposed to MGO, the addition of phloridzin did not show a significant effect on retaining the activity of creatine kinase impaired by MGO, whereas the addition of phloretin completely inactivated creatine kinase. Results of the mass spectrometric analysis of intact creatine kinase in different models demonstrated that phloretin could directly participate in the reaction between creatine kinase and MGO, which would lead to the inactivation of creatine kinase. Furthermore, the addition of N α-acetylcysteine was found to maintain the activity of creatine kinase incubated with phloretin and MGO. These results showed that phloretin and phloridzin could inhibit the modification of the arginine residue by MGO and that phloretin could directly participate in the reaction between the thiol group and MGO. © 2011 American Chemical Society.