Modulating Insulin Aggregation with Charge Variable Cholic Acid-Derived Polymers

To understand the effect of cholic acid (CA)-based charge variable polymeric architectures on modulating the insulin aggregation process, herein, we have designed side-chain cholate-containing charge variable polymers. Three different types of copolymers from 2-(methacryloyloxy)ethyl cholate with anionic or cationic or neutral units have been synthesized by reversible addition-fragmentation chain transfer polymerization. The effects of these copolymers on the insulin fibrillation process was studied by multiple biophysical approaches including different types of spectroscopic and microscopic analyses. Interestingly, the CA-based cationic polymer (CP-10) was observed to inhibit the insulin fibrillation process in a dose-dependent manner and to act as an effective anti-amyloidogenic agent. Corresponding anionic (AP-10) and neutral (NP-10) copolymers with cholate pendants remained insignificant in controlling the aggregation process. Tyrosine fluorescence assays and Nile red fluorescence measurements demonstrate the role of hydrophobic interaction to explain the inhibitory potencies of CP-10. Furthermore, circular dichroism spectroscopic measurements were carried out to explore the secondary structural changes of insulin fibrils in the presence of cationic polymers with and without cholate moieties. Isothermal titration calorimetry measurements revealed the involvement of electrostatic polar interaction between the CA-based cationic polymer and insulin at different stages of fibrillation. Overall, this work demonstrates the efficacy of the CA-based cationic polymer in controlling the insulin aggregation process and provides a novel dimension to the studies on protein aggregation.