Facially Amphiphilic Cholate-Conjugated Polymers for Regulating Insulin Fibrillation

To understand the influence of facially amphiphilic polymers (FAPs) on insulin fibril (IF) inhibition, three different cholate-based FAPs [cationic (PFCAQA), anionic (PFCASF), and zwitterionic (PFCASB)] have been synthesized. Besides, two control polymers [cholate and sulfobetaine-pendant random copolymer PRCASB (without facial amphiphilicity) and sulfobetaine-tethered homopolymer PSBMA (without cholate pendants)] are also prepared. Several biophysical experiments such as spectroscopic techniques [thioflavin T (ThT), Nile red (NR), tyrosine (Tyr) fluorescence assay], turbidity assay by ultraviolet-visible (UV-vis) spectroscopy, dynamic light scattering (DLS), circular dichroism (CD) study, and microscopic investigation are performed to investigate the role of polymers as antiamyloidogenic agents during insulin fibrillation. Interestingly, the PFCASB zwitterionic polymer behaves as the most efficacious antiamyloidogenic agent. To clarify the interaction of PFCASB and native insulin (NI), an isothermal titration calorimetry (ITC) experiment is carried out. Tyr and the NR fluorescence investigation suggest the important role of hydrophobic interactions, whereas the ITC experiment confirms the significance of hydrophobic and electrostatic interactions in the IF inhibitory process. A hemolytic test is conducted to investigate the toxicity caused by IF and the efficacy of PFCASB in prohibiting erythrocyte disruption caused by IF. Overall, the present work reveals the impact of the facially amphiphilic cholic acid (CA)-based zwitterionic polymer in modulating the insulin aggregation process and gives a new perspective for investigations on different protein aggregations.