Stabilisation of dissolved proteins against denaturation at hydrophobie interfaces

Abstract

Studies with insulin delivery devices have shown that denaturation of dissolved proteins at hydrophobic interfaces is a basic obstacle to long-term insulin stability in pumps. This study shows that polypropylene glycol/polyethylene glycol block polymers prevent both the adsorption of dissolved proteins to hydrophobic interfaces and the resultant aggregation. At a concentration of 0.001% (w/v), the block polymer Genapol PF-IO stabilises insulin solutions over a wide range of concentrations. Insulin solutions thus stabilised are at present being clinically tested. The effectiveness of molecular variants of Genapol PF-10 to stabilise other proteins (human ?'-globulin, myoglobin and serum albumin) is presented also.

Aggregation of Insulin at the Interface

“…41,45,57 The driving force is mainly hydrophobic interaction between the unfolded monomer and the hydrophobic interface. 44 Subsequently, the dissolved insulin molecules associate over the exposed hydrophobic regions, eventually forming aggregates. Compared to hydrophobic solid or oil surfaces, the hydrophilic surface induces less conformational change of insulin.…”

“…In this article, the recent progress of insulin aggregation is briefly summarized at the aqueous–solid, water–oil, and air–water interfaces. The aggregation of insulin initiates with diffusion and adsorption of insulin at the hydrophobic solid or oil interfaces, resulting in conformational changes of the monomeric insulin to expose the hydrophobic residues. ,, The driving force is mainly hydrophobic interaction between the unfolded monomer and the hydrophobic interface . Subsequently, the dissolved insulin molecules associate over the exposed hydrophobic regions, eventually forming aggregates.…”

“…It is widely accepted that the adsorbed protein changes its conformation upon adsorption, and thus, some hydrophobic regions are exposed to contact with the hydrophobic interface. 44 Subsequently, the protein molecules in the boundary layer associate over these exposed hydrophobic regions, forming aggregates. The aggregates eventually desorb from the surface to aqueous solution and may serve as nuclei for further fibrillation.…”

“…It has long been suggested that aggregation of dissolved proteins can occur at hydrophobic interfaces in a general process. ,, This process is initiated by diffusion and adsorption of protein molecules to the interface. It is widely accepted that the adsorbed protein changes its conformation upon adsorption, and thus, some hydrophobic regions are exposed to contact with the hydrophobic interface . Subsequently, the protein molecules in the boundary layer associate over these exposed hydrophobic regions, forming aggregates.…”

“…Interfaces and surfaces are ubiquitous environments and play important roles in a multitude of physical and chemical processes, including biomedical engineering, catalysis, chemical sensors, and drug delivery. , As a large number of important physicochemical processes occur at the place of interfaces in biological systems, much attention has been drawn to the properties of biomolecules at interfaces, such as liquid–solid interface, , liquid–liquid interface, − and gas–liquid interface. , Adsorption of proteins at the interface often results in conformational changes, reducing the biological activity and physical/chemical stability of proteins. , This process has been shown to be very complex and can be influenced by many factors, such as electrostatic interactions, surface roughness and curvature, and hydrophilicity/hydrophobicity, to name a few. − In the case of insulin, the great interest for studies at various interfaces started from the early observation that insulin was vulnerable to change conformation and develop aggregates in storage vials, infusion pumps, controlled release devices, etc. − Since then, studies of adsorption, aggregation, and fibril formation of insulin have been performed at various interfaces, such as the aqueous–solid interface, ,− water–oil interface, ,,, and air–water interface. − Although much progress has been achieved in the past few years, a molecule-level understanding of the detailed structure and property of insulin at the interfaces remains a great challenge.…”