Insulin adsorption

The ability of some macromolecules to adsorb at interfaces is made use of in suspension and emulsion stabilisation (see Chapter 7). Gelatin, acacia, poly(vinyl alcohol) and proteins adsorb at interfaces. Sometimes such adsorption is unwanted, as in the case of insulin adsorption onto glass infusion bottles and poly(vinyl chloride) infusion containers and tubing used in giving sets. Adsorption of insulin to glass bottles and plastic i.v. tubing at slow rates of infusion is well documented. It... 

Wright, J.E.L, Cosman, N.P., Fatih, K., Omanovic, S., and Roscoe, S.G. (2004) Electrochemical impedance spectroscopy and quartz crystal nanobalance (EQCN) studies of insulin adsorption on Pt. Journal of Eiectroanaiytical Chemistry,... 

Henry, M., Dupont-Gillain, C., Bertrand, P. (2008) Characterization of insulin adsorption in the presence of albumin by time-of-fiight secondary ion mass spectrometry and X-ray photoelectron spectroscopy. Langmuir, 24,458-464. 

Hirsch, J. 1., Wood, J. H., and Thomas, R. B., 1981, Insulin adsorption to polyolefin infusion bottles and pol5rvinyl chloride administration sets, Am. J. Hasp. Pharm. 38 995-997. 

Razumas et al studied adsorption of insulin on platinum from a physiological saline solution of pH 7.4 at 298 K using both cyclic voltammetry and ellipsometry. They compared the surface adsorption of insulin for different potentials using ellipsometric measurements and found at a potential of 0.4 V (vs. SCE), the surface concentration / = 1.27 mg m for insulin. Adsorption was found to increase when zinc ions were added to the protein solutions. 

Human serum albumin (HSA) may be used as a protectant against adsorptive loss of proteins present at low concentrations. HSA is present at higher concentration than the active substance and is preferentially adsorbed, coating the surface of interest and preventing adsorption of the drug. For example, insulin is subject to adsorptive loss to hydrophobic materials. Addition of 0.1-1.0% HSA has been reported to prevent this adsorptive loss [9],... 

This flattened erythrocyte preparation has been used to study reversible nonspecific adsorption kinetics and surface diffusion of insulin on the external surface of erythrocytes.(123) The nonspecific adsorption of insulin to the polylysine-coated substrate is very large compared to the adsorption to the flattened membrane adhered to the substrate. Fortunately, this nonspecific background fluorescence can be very successfully quenched simply by preparing the polylysine coating on an aluminum-film-coated glass surface, rather than on bare glass. As discussed in Section 7.3, the aluminum abolishes the fluorescence of fluorophores adsorbed directly onto the polylysine substrate, but the fluorophores adsorbed to the erythrocyte surface are not substantially quenched, because they are spaced at least two membrane thicknesses away. 

R. M. Fulbright, Adsorption kinetics of insulin at erythrocyte membranes, Ph.D. thesis, University of Michigan (1991), manuscript submitted. 

FIGURE 10.13 Experimental adsorption data (symbols) and the best Toth isotherm (solid line) for porcine insulin, human insulin Lispro. (Reproduced from Liu, X. et al., Biotechnol. Prog., 18, 796, 2002. With permission from John Wiley Sons.)... 

Depending on the fit, the number and strength of contacts, and other factors, a monomer-oligomer equilibrium will exist. For example, in the case of Concanavalin A the tetramer is in equilibrium with dimer and monomer under normal conditions. In the case of insulin the monomer, dimer, and hexamer are all in equilibrium. In hemoglobin the dimer and tetramer are in equilibrium. In the case of the adsorption of such proteins, one must not only know what is the aggregation state of the protein in solution, but must be able to deduce the adsorbed state. Do the molecules adsorb as dimers 21) Do they adsorb as dimers and then associate as tetramers or hexamers on the surface, etc. ... 

Hashimoto, T., et al. Improvement of intestinal absorption of peptides Adsorption of Bl-Phe monoglucosylated insulin to rat intestinal brush-border membrane vesicles. Eur J Pharm Biopharm 50 197. 

These polymer-coated liposomes showed high potency in oral delivery of peptide drugs such as insulin and calcitonin, mainly because of the mucoadhe-sion of the chitosan-coated liposomes to the intestinal tract (Takeuchi et al. 1996, 2001,2003,2005a). Similar trials have been reported by Guo et al. (2003), who investigated the effect of chitosan concentration and lipid type on the characteristics of chitosan-coated liposomes and their interactions with leupro-lide. They found that a thicker adsorptive layer could be realized by using low... 

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