Logo: to the web site of Uppsala University

Peptides as therapeutic agents have gained significant interest during the last few decades due to their specificity, potency, and efficacy compared with small-molecular drugs. However, peptide aggregation remains a considerable concern during production, formulation, and storage of therapeutic peptides. Peptide aggregation can result in loss of therapeutic effect or, in worst case, immunogenic response and side effects. However, in some cases, peptide aggregation can be utilised to achieve extended-release formulations. In both scenarios, the aggregation mechanisms are essential to understand in order to predict and prevent aggregation, or know when aggregation can be utilised. Excipients in peptide formulations and biological components can also affect the aggregation behaviour of therapeutic peptides, highlighting the need to investigate the effect of additional components on peptide self-assembly. 

The structure of self-assembled peptide aggregates can offer insights into the aggregation mechanisms of therapeutic peptides. The size and structure of peptide self-assemblies can be investigated with scattering techniques, such as small-angle X-ray and neutron scattering and dynamic and static light scattering. 

The aggregation behaviour of three different peptides were investigated based on structural determination of peptide aggregates with scattering techniques. The peptides were dissolved in aqueous solutions and additional components were added gradually to investigate the specific effects of added salt, varying pH, different buffers, and amphiphilic compounds on peptide aggregate structure. Small-angle scattering data were analysed by model fitting to determine the size and structure of self-assembled aggregates. 

The different peptides investigated in this thesis displayed different aggregation behaviour in solution and different interaction behaviour with added components, highlighting the wide variety of possible aggregate structures peptides can form in solution. The supramolecular network formed by an amyloid-forming peptide, the type of interaction behaviour of a small cyclical peptide with a surfactant, and the ability of a lipidated peptide to dissolve phospholipids could be studied through combining different scattering techniques. Using systems with few components, the work in this thesis provides strategies to explore the fundamentals of therapeutic peptide aggregation which can be useful during design and formulation of therapeutic peptides, as well as understanding the behaviour of a peptide drug after administration.