STUDIES ON THE DENATURATION OF ANTIBODY

Transparent, Hydrophobic Fluorinated Ethylene Propylene Offers Rapid, Robust, and Irreversible Passive Adsorption of Diagnostic Antibodies for Sensitive Optical Biosensing

Current literature data is scarce and somehow contradictory in respect to the suitability of "nonstick" fluoropolymer surfaces for immobilization of biomolecules. We have previously shown empirically that transparent Teflon fluorinated ethylene propylene (FEP) offers rapid and sensitive optical biosensing of clinically relevant biomarkers. This study shows for the first time a comprehensive experimental analysis of passive adsorption of diagnostic IgG antibodies on actual Teflon FEP microfluidic strips. Full equilibrium isotherms and kinetics for passive adsorption were studied and modeled employing a protein titration method using hundreds of multibore microfluidic strips for a range of temperatures, pH, ionic strengths, and inner diameters, using both polyclonal and monoclonal antibody systems. Results were benchmarked against other plastic hydrophobic and glass hydrophilic capillary surfaces. For the first time, it was shown quantitatively that the hydrophobicity of fluoropolymer surfaces encourages the passive adsorption of diagnostic antibodies for biosensing and is insensitive to the temperature of incubation and to ionic buffer strength. The mass of captured antigen increased with increasing antibody surface coverage up to ∼400 ng/cm², with an optimal adsorbed antibody activity for 45-69% of full monolayer coverage, matching results of other biosensing surfaces. The equilibrium was reached fast, within 5-10 min, and surprisingly both the kinetics and equilibrium of antibody adsorption were dependent on the inner diameter of microcapillaries. This is a novel and relevant result that will generally impact on the design of miniaturized microfluidic biosensing devices. The antibody surface densities obtained with hydrophobic plastic surfaces were 2- to 4-fold lower than for a hydrophilic, glass surface, however the former presented a monolayered adsorption with a higher level of irreversibility, as shown by the adsorption and desorption rates around 1 order of magnitude smaller than for glass, which is highly desirable for biosensing with surface-coated biomolecules.

Viscosity of concentrated therapeutic protein compositions

The use of monoclonal antibodies as therapeutic agents has been increasing steadily over the last decade for the treatment of various conditions. There is often a need to deliver a large dose of the protein, so there is a trend toward developing commercially viable liquid formulations of highly concentrated antibodies. Such concentrated solutions are associated with a number of challenges, including optimization of production processes, plus chemical and physical stability of the final product where solution viscosity becomes a critical quality attribute. Assessment of the rheological characteristics of concentrated compositions is essential as are development strategies to reduce the viscosity. This review covers the state-of-the-art rheology measurement techniques, focusing particularly on concentrated protein solutions. Current understanding of the mechanisms leading to high viscosity and control by formulation parameters is discussed.

Analysis of solvent-mediated conformational changes of insulin by radioimmunoassay (RIA) techniques

Stationary phase radioimmunoassay (RIA) (i.e. antibodies bound to polystyrene test tubes) techniques are used as an analytical probe of secondary and tertiary structural changes of radiolabelled (125)I porcine insulin. The effects of temperature, buffer composition, pH and ionic strength and solvents on insulin binding are studied. Optimum insulin-antibody binding occurred at 22 degrees C, pH 6 and a buffer strength of 0.1 M or less. Results of experiments with three pH 6 buffers (0.005 M phosphate, 0.1 M acetate and 0.1 M Tris) showed no statistical difference in binding properties. For all solvents tested, increasing the solvent concentration decreased the amount of insulin binding. Comparison of the various solvents tested indicated that ethylene glycol and methanol are the least denaturant whilst 1-propanol and acetonitrile are among the most denaturant.