A Critical Evaluation of Screening versus Sample-by-Sample Analysis of Protein Aggregation using a Variety of Chromatographic and Spectroscopic Techniques

While protein aggregation has been widely studied, it is still poorly understood. Protein aggregation is a complex process, resulting in heterogeneous populations of particles from a variety of mechanisms, which provides both intellectual and technical challenges. This thesis probes the mechanisms leading to protein aggregation by characterising the aggregation of two model proteins, lysozyme and bovine serum albumin, using a variety of chemical and biophysical techniques. High-throughput assays are commonly utilised for screening protein formulations. Two high-throughput assays were critically examined to assess the effectiveness and robustness of this approach for detecting protein aggregation after forced degradation (or accelerated aggregation testing). While these high-throughput assays do play a role in formulation and screening, careful consideration must be given to the interpretation of the analysis and the results must be viewed in context and as part of a wider characterization process. Chemical modification of protein structure via oxidation was also examined as a mechanism leading to aggregation. Oxidation of lysozyme and bovine serum albumin was induced with hydrogen peroxide. The secondary structure of both proteins were vulnerable to oxidative attack, resulting in a loss of native structure and the formation of both protein aggregates and protein fragments, the extent of which depended on both the specific protein chemistry and solution conditions. The mechanism of chemical unfolding was probed for both lysozyme and BSA with the addition of two denaturants; urea and guanidine hydrochloride. The mechanism by which each denaturant unfolds both proteins has been thoroughly studied in the past. Lysozyme is known to follow a two-state model, while BSA conforms to a two-step unfolding process via three transition states. We have demonstrated the sensitivity and reliability of second derivative UV analysis to characterise the unfolding states of both proteins. Finally, a monoclonal antibody, IgG1, was purified and characterised. Initial studies where carried out to assess the stability of this protein. Glyco-analysis was carried out to determine the glycan profile of the IgG1 protein and to ensure for consistency in product glycosylation. The stability of the glycoform was also examined in terms of length of storage under, different storage conditions.