Neurodegenerative diseases are now one of the leading causes of death in the United Kingdom with cases rising. There is a heightened need for new drug therapeutics to limit or halt neurodegenerative disease progression and/or ameliorate the disease pathologies altogether. A major challenge in neurology is the lack of small brain penetrable neuroprotectants that target multiple disease mechanisms and also the Blood Brain Barrier (BBB) which severely restricts entry of neuroprotectants into the central nervous systems (CNS). There is an urgent need to develop new strategies that can target the BBB and effectively deliver drugs into the CNS. Due to their size, ease of functionalisation for maximum surface area of drug loading and ability to pass through the BBB, nanoparticles are a potential solution to deliver neurotherapeutic drugs directly to damaged neurons inside the brain to increase the efficacy of neuroprotectants.
The small peptides (H3/H6) that encompass the active motifs of the neurotrophic protein S100A4 have been shown to reduce oxidative stress and excitotoxicity via multiple pathways and protect neurons in animal models of neurological disorders. However, these peptides have limited brain penetration and circulation half-life. Therefore a delivery system that can improve the half – life of the peptides, shuttle the drugs across the BBB and interact directly with neurons is required. Plasmonic gold nanostars are promising candidates for delivery of standard-of-care drugs inside the brain and fluorescence-based deep tissue imaging but have not previously been trialled as carriers for neuroprotectants.
The objective of this thesis was to design, synthesise and fully characterise a new gold nanostar delivery vehicles to shuttle the H3/H6 peptides across the BBB to impaired neurons and evaluate their potential as a future treatment of Parkinson’s disease. Star and spherical nanostructures were synthesised and compared, and a new protocol was devised to conjugate H3/H6 peptides onto their surface. These nanostructures were subsequently tested on in vitro models of neurological disorders to investigate the effects of the nanostructure geometry on biological responses, including their potential as neuroprotectants and their interaction with neurons. Transmission electron microscopy was used to compare the interaction of the star and spherical nanostructures with cell membranes to understand the mechanisms by which the spikes of the nanostars increase their cell binding properties.
The H3/H6-nanostructures induced neuritogenesis in neurons and the star shaped nanostructures proved higher potency/efficacy than spherical AuNPs. The H3-Au nanostructures (stars and spheres) protected neurons against oxidative stress with the H3 – nanostars being more potent. Conjugation of these peptides to the surface of the nano structures did not inhibit the neurotrophic capabilities previously seen from the isolated peptides alone. ICP analysis confirmed the affinity and interaction of the nano therapeutics to the neurons, while electron microscopy demonstrated that the spikes of the nanostars were able to embed into the plasma membrane of neurons more effectively than the nanospheres, thus enhancing the internalisation rate of the nanostars, whereas the nanospheres were rarely internalised. Finally a synthesis route was devised to further functionalise these nano compounds with the small molecular L - dopa to, in future, deliver them across the BBB. This thesis shows that conjugation of custom-made dendrimers to the surface of gold nanostars may be used to activate multiple neuroprotective pathways and increase the drug potency to treat a broad spectrum of neurodegenerative disorders.