Conformational stability as a quality attribute for the cell therapy raw material human serum albumin

Although human serum albumin (HSA) has been used for many decades, there is still a lack of suitable quality control (QC) attributes. Its current use as a raw material in gene-, cell- and tissue-therapies requires more appropriate functionally-relevant quality attributes and methods. This study investigated the conformational stability of serum albumin using circular dichroism (CD) spectroscopy and dynamic light scattering (DLS) for evaluating the thermal sensitivity, and quartz crystal microbalance-dissipation (QCM-D) and localized surface plasmon resonance (LSPR) for assessing the adsorption behavior. Different serum albumin samples were used, encompassing plasma-derived HSA (pHSA), recombinant octanoate-stabilized HSA (rHSA) and bovine serum albumin (BSA). The melting temperature (Tm) as well as the onset temperature (Tonset) were obtained from the derivative curves of the temperature gradient CD data at 222 nm. The results from DLS, as well as from real-time QCM-D and LSPR silica-adsorption kinetic profiles confirmed the relatively higher conformational stability of the octanoate (fatty acid) containing rHSA, while the additional negative charge resulted in a lower amount adsorbed to the silica surface compared to the non-stabilized HSA and BSA. Adsorption studies further revealed that BSA has a lower conformational stability and undergoes more extensive adsorption-induced spreading compared to the non-stabilized HSA. Collectively, the temperature-based (CD and DLS) as well as adsorption-based biosensor (QCM-D and LSPR) approaches gave congruent and discriminatory information about the conformational stability of different serum albumins, indicating that these techniques provide information on valuable QC attributes.