Self-assembling behaviour of the peptide hormone PYY3-36 and its lipidated conjugates for future applications in controlling satiety levels

Obesity is a global healthissue with nations struggling to deal with itstreatmentand economic impacts. Modified peptide hormones have already been shown to be effective at improving the treatment of other chronic conditions such as lymphoma or anaemia. However, peptide hormones, especially those targeted in treating obesity, are known to suffer from short drug lifetimes and thus requiring frequent administration. For the drug to take effect over a longer period requires a gel matrix-based drug carrier or a modification to the peptide itself. This thesis looks at how to use peptide modifications to potentially improve the delivery methods and efficacy of drugs used to control satiety levels. Anovel lipopeptide, based on Peptide Tyrosine-Tyrosine (PYY3-36), was characterised by using circular dichroism spectroscopy (CD), small angle X-ray scattering, critical aggregation concentration experiments, and cryo-TEM. Studies were completed to investigate the secondary structures and the self-assembly processes over a range of physiological pHs and temperatures. While native PYY3-36failedto form gels, PYY lipopeptides formed into gels with elongated fibre-like structures with a secondary structural change from α-helical to β-sheet. Gels formed from natural peptides and water offer the potential for a highly biocompatible gel with a slow release profile. Using the same analytical techniques, the thesis goes on to investigate co-aggregation of PYY3-36with β-cyclodextrin to establish if this common low-cost drug carrier can be used as an alternative delivery method. The results showed that β-cyclodextrin did show aggregation around the twisted sheet structure of the self-assembled PYY3-36butdidnot show co-assembly or encapsulation, rendering it ineffective as a delivery mechanism. Lipidated PYY3-36was mixed with lipopolysaccharide (LPS), providing some insight into how lipidated PYY3-36 could interact with amphiphilic molecules such as bacteria endotoxins. The results show that LPS do co-assemble with lipidated PYY3-36,however, unexpectedly the lipidated PYY3-36 elongated fibre structure remains largely unchanged following the co-assembly. The implications of this observation warrant further analysis. Ultimately, the findings of this thesis could be applied to the development of drug formulations for other conditions, such as lymphoma or anaemia, which would benefit from the lipidation of large peptides that enable slow release mechanisms. Additionally, the results within this thesis add knowledge to the fundamental research of self-assembly and clarifies the effects of lipidation on larger peptides that allow gelation to occur