β-cyclodextrin encapsulated polyphenols as effective antioxidants.

Formation of dityrosine (DT) cross-linkages in proteins is one of the most widely used markers of oxidative stress. Ribonuclease A (RNase A) has 6 Tyr residues and shows a characteristic DT fluorescence peak upon oxidation in addition to major changes in its secondary structure. DT formation can be prevented by using polyphenols (GA, ECG, and EGCG) which are known to have strong antioxidant activity. However, it has been observed that ECG and EGCG initiate protein oligomerization due to protein-polyphenol cross-linkages. To prevent the formation of such cross-linkages we have used β-cyclodextrin (β-CD) to encapsulate the polyphenols and studied its antioxidant properties along with that of free polyphenols. The polyphenol/β-cyclodextrin (β-CD) inclusion complexes not only prevent DT formation but also reduce protein oligomerization. This may be attributed to the fact that the quinone forming rings of ECG and EGCG become encapsulated in the cavity of β-CD and are no longer available for protein cross-linking.