Beta-cyclodextrin solubilized and refolds CTAB-induced insulin amyloid fibrils by surfactant sequestration

Amyloid fibrils are associated with more than fifty human disorders, yet no effective treatments are currently available. This study investigated the potential of beta-cyclodextrin (β-CD) to disaggregate and refold insulin amyloid fibrils induced by the cetyltrimethylammonium bromide (CTAB) under physiological pH. To measure this, several biophysical techniques were used, including turbidity, light scattering, ThT fluorescence, far-UV circular dichroism (CD), and transmission electron microscopy measurements. Spectroscopic analyses confirmed that insulin exposed to 100 μM CTAB formed amyloid-like aggregates at pH 7.4 and β-CD disrupted these fibrils in a concentration-dependent manner. Concentrations below 100 μM of β-CD produced negligible effects, whereas higher concentrations resulted in complete solubilization of the fibrillar structures at the same pH. Far-UV CD spectra further revealed that 300 μM of β-CD was enough to regain secondary structure, signifying successful refolding of insulin. The proposed mechanism suggests that β-CD functions as a chemical chaperone by preferentially binding to CTAB with a higher affinity than insulin, thereby removing the surfactant and solubilizing the amyloid fibril. These findings emphasize the solubilizing action of β-CD and suggest its potential as a foundation for therapeutic approaches to mitigate amyloid-related diseases.