Jian Hua Gu

Rotational Rheology of Bovine Serum Albumin Solutions: Confounding Effects of Impurities, Mechanistic Considerations and Potential Implications on Protein Formulation Development

PurposeTo show and rationalize the confounding effects on the rotational/oscillatory rheology of surface active impurities in commercial protein formulations such as bovine serum albumin, BSA.MethodsBulk and interfacial rotational/oscillatory rheology were used to study the viscosity, complex viscosity, storage/elastic modulus, G’ and loss/viscous modulus, G”, as a function of time of aqueous formulations of BSA and their purified components.ResultsViscosity/time profiles at steady shear for different commercial BSA products and lots showed viscosity increase, decrease and time-independent profiles at low shear rates. All lots showed shear thinning. BSA monomer and dimers/aggregates, in general, showed similar profiles. Addition of low levels of surfactant or high shear rates rendered all solutions to be Newtonian-like. Interfacial viscosity studies paralleled those on the rotational rheometer. G’ > G” with viscosity increase and G’ < G” with viscosity decrease over time.ConclusionsWe provide a rational explanation for the time-dependent and source-dependent rheological behavior of aqueous formulations of commercially available BSA proteins based on the migration of protein and surface active impurities to the air/water interface within the rheometer plates leading to the formation and breakdown of protein networks. Highly purified proteins is warranted in rheological studies of protein drug product candidates.

Practical Considerations for High Concentration Protein Formulations

Practical issues that arise for high concentration protein formulations can complicate manufacturing and affect injectability/device compatibility. High concentration protein formulations have an increased tendency for high solution viscosity, physical stability sensitivities (aggregation/particulation), and non-Newtonian solution behavior (shear thinning) due to high shear rates. Process unit operations can be negatively impacted by these factors, and it is critical to understand how they influence process performance. Device compatibility can be affected by changes in protein concentration and temperature that will impact product viscosity and injectability. Complete characterization of the solution physical properties (viscosity and shear thinning profile) as well as the stability profile must be understood to ensure efficient processing, delivery, and efficacy of the therapeutic product. If potential candidates with impeding viscosity values are not identified early in development, subsequent mitigation efforts to reduce viscosity likely pivot from a protein engineering approach to changes in formulation.