Inhibition of non-enzymatic protein glycation by pomegranate (Punica granatum) polyphenolics
Dorsey, Pamela Garner
MetadataShow full item record
Protein glycation is the non-enzymatic reaction of a reducing sugar or sugar derivative with amino acids, peptides, or proteins resulting in advanced glycation endproducts (AGEs) and crosslinking of proteins. This process is accelerated in diabetes mellitus, and detrimental for proteins that are not readily recycled, such as collagen and lens crystallins. The current study investigates the effect of commercially available pomegranate juice, major phytochemicals found in pomegranate juice (ellagic acid, punicalagin), whole pomegranate fruit and various fractions of pomegranate fruit (peel, membrane, aril) on the in vitro fructose mediated glycation of bovine serum albumin (BSA). Total phenolic content and antioxidant capacity for all juices and pomegranate extracts were determined by the Folin-Ciocalteu method and the FRAP (ferric reducing antioxidant potential) assay, respectively. AGE formation was detected by a fluorescence spectroscopy assay. The effect of pomegranate juice on the inhibition of glycation for other proteins (gelatin, IgG, ribonuclease, lysozyme) was also investigated to determine whether pomegranate polyphenolics are generalized inhibitors of this process. Pomegranate juice produced the greatest inhibition of BSA glycation on the basis of volume, phenolic content, and antioxidant capacity when compared to other juices. Punicalagin and ellagic acid produced similar results to that of pomegranate juice. Whole pomegranate had a much greater inhibitory activity than whole apple and the membrane extract of pomegranate fruit was the most potent inhibitor of BSA glycation compared to the aril and peel pomegranate extracts. Pomegranate juice, incubated with gelatin, IgG, ribonuclease A (RNase), and lysozyme inhibited the glycation of these proteins in the presence of fructose, similar to that observed with BSA. SDS PAGE analysis of BSA and RNase revealed that pomegranate juice prevented chemical modifications to the native protein structure associated with glycation. This work suggests that the pomegranate is a robust inhibitor of protein glycation in various model proteins, owing the majority of its inhibitory activity to the antioxidant capacity of phytochemicals found within the membrane of the fruit.