Inhibition of copper-mediated aggregation of human γD-crystallin by Schiff bases

Protein aggregation, due to the imbalance in the concentration of Cu2+ and Zn2+ ions is found to be allied with various physiological disorders. Copper is known to promote the oxidative damage of beta/gamma-crystallins in aged eye lens and causes their aggregation leading to cataract. Therefore, synthesis of a small-molecule 'chelator' for Cu2+ with complementary antioxidant effect will find potential applications against aggregation of beta/gamma-crystallins. In this paper, we have reported the synthesis of different Schiff bases and studied their Cu2+ complexation ability (using UV-Vis, FT-IR and ESI-MS) and antioxidant activity. Further based on their copper complexation efficiency, Schiff bases were used to inhibit Cu2+-mediated aggregation of recombinant human gamma D-crystallin (HGD) and beta/gamma-crystallins (isolated from cataractous human eye lens). Among these synthesized molecules, compound 8 at a concentration of 100 mu M had shown 95% inhibition of copper (100 mu M)-induced aggregation. Compound 8 also showed a positive cooperative effect at a concentration of 5-15 mu M on the inhibitory activity of human alpha A-crystallin (HAA) during Cu2+-induced aggregation of HGD. It eventually inhibited the aggregation process by additional 20%. However, 50% inhibition of copper-mediated aggregation of beta/gamma-crystallins (isolated from cataractous human eye lens) was recorded by compound 8 (100 mu M). Although the reductive aminated products of the imines showed better antioxidant activity due to their lower copper complexing ability, they were found to be non-effective against Cu2+-mediated aggregation of HGD.