Amyloid fibril formation of human recombinant insulin due to the interfacial hydrophobicity of fluorocarbon polymer membranes

Aim: Although polytetrafluoroethylene (PTFE) is more hydrophobic than polyvinylidene fluoride (PVDF) in fluorocarbon polymer (FCP) membrane filters, it has been reported that the rate of amyloid fibril formation is faster on PVDF than on PTFE. To clarify whether the effect is due to the membrane’s chemical structure or its hydrophobicity at the membrane interface, studies on amyloid fibril formation were conducted using both hydrophobic and hydrophilic PVDF and PTFE membranes. Methods: Heat-treated insulin (INS) was adsorbed onto the FCP membrane filters. Gaussian integrals were employed to determine the amounts of β-sheet and their abundance ratios by curve fitting of attenuated total reflection Fourier transform infrared spectra. Results: Adsorbed heat-treated INS onto the FCP membrane filters showed a β-sheet form, with a similar or higher affinity in comparison with that of the β-rich concanavalin A. The adsorption followed a sigmoidal curve with a 2-hour lag time, reaching a plateau after 4–5 hours. The spectral patterns of the adsorbed INS indicated the β-sheet form, demonstrating that INS transformed into β-sheet and then, or simultaneously, adsorbed onto the FCP membrane filters. Conclusions: The results regarding the rate and strength of amyloid fibril formation for each FCP membrane filter suggest that, beyond the membrane’s surface hydrophobicity or hydrophilicity, other factors, such as the electron affinity of hydrogen in the PVDF membrane, also influence nucleation. This study provides insight into the role of INS in amyloid fibril formation within FCP membrane filters.