Bovine Insulin–Phosphatidylcholine Mixed Langmuir Monolayers: Behavior at the Air–Water Interface

Abstract

The behavior of the binary mixed Langmuir monolayers of bovine insulin (INS) and phosphatidylcholine (PC) spread at the air-water interface was investigated under various subphase conditions. Pure and mixed monolayers were spread on water, on NaOH and phosphate-buffered solutions of pH 7.4, and on Zn(2+)-containing solutions. Miscibility and interactions between the components were studied on the basis of the analysis of the surface pressure (π)-mean molecular area (A) isotherms, surface compression modulus (C(s)(-1))-π curves, and plots of A versus mole fraction of INS (X(INS)). Our results indicate that intermolecular interactions between INS and PC depend on both the monolayer state and the structural characteristics of INS at the interface, which are strongly influenced by the subphase pH and salt content. Brewster angle microscopy (BAM) was applied to investigate the peptide aggregation pattern at the air-water interface in the presence of the studied lipid under any experimental condition investigated. The influence of the lipid on the INS behavior at the interface strongly depends on the subphase conditions.

Surface interactions, thermodynamics and topography of binary monolayers of Insulin with dipalmitoylphosphatidylcholine and 1-palmitoyl-2-oleoylphosphatidylcholine at the air/water interface

“…The Insulin monomer is unstable and tends to macroscopically aggregate in aqueous solutions during storage [16,13,6]. This is a consequence of solid fibers formed by aggregation of monomers and dimers under low pH conditions [32,30]; and causes loss of hormone biological activity which is a major obstacle for developing long-term delivery formulations. Though the mechanism of aggregation of Insulin still remains unclear, some studies suggested that the presence of different hydrophobic environments (i.e.…”

“…Insulin Langmuir monolayers at the air/water interface were previously described under different experimental conditions such as pH, temperature and ion concentration [29,32,24]. Also, it has been recently shown that the presence of Zn 2+ has a profound effect on the surface behavior of Insulin monolayers [32,24,20].…”

“…Also, it has been recently shown that the presence of Zn 2+ has a profound effect on the surface behavior of Insulin monolayers [32,24,20]. We recently described the rheological properties of regular Insulin and aspart Insulin in presence on Zn 2+ .…”

“…The works by Pérez-López et al using natural phospholipid mixtures represents a pioneering step in that regard [31,32]. These authors have described the behavior of binary monolayers of Insulin-sphingomyelin and Insulin-egg phosphatidylcholine (PC) at the air/water interface on pure water, NaOH and phosphatebuffered solutions of pH 7.4, and on Zn 2+ -containing solutions [32,31].…”

“…The works by Pérez-López et al using natural phospholipid mixtures represents a pioneering step in that regard [31,32]. These authors have described the behavior of binary monolayers of Insulin-sphingomyelin and Insulin-egg phosphatidylcholine (PC) at the air/water interface on pure water, NaOH and phosphatebuffered solutions of pH 7.4, and on Zn 2+ -containing solutions [32,31]. Their results indicated that intermolecular interactions between Insulin, sphingomyelin and egg-PC depend on both the monolayer state and the structural characteristics of Insulin at the interface, which are strongly influenced by the subphase pH and salt content.…”