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Title: Analysis of drug delivery for the treatment of Alzheimer's disease using an in vitro blood-brain barrier
Author: Al-Edresi, Sarmad
ISNI:       0000 0005 0288 9226
Awarding Body: University of Manchester
Current Institution: University of Manchester
Date of Award: 2017
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Alzheimer's disease (AD) is a chronic neurodegenerative disease. Aggregation of amyloid β₁₋₄₂ (Aβ₁₋₄₂) peptide within the brain is considered the main cause of the neuropathological changes associated with AD, and development of compounds that target Aβ₁₋₄₂ peptide aggregation is a highly active research area. The blood brain barrier (BBB) can prevent efficient delivery of compounds to the brain, which limits treatment options for diseases of the central nervous system (CNS). Transferrin-functionalised liposomes are considered promising vectors for delivery to the brain since they overcome the barrier function of the BBB by binding to transferrin receptors expressed on the surface of the BBB endothelium. Resveratrol, melatonin, carnosine, tramiprosate and scyllo-inositol have previously been reported to reduce Aβ₁₋₄₂ peptide aggregation, attenuating Aβ₁₋₄₂ peptide-induced toxicity. In this thesis, the inhibitory effects of the selected compounds were reproduced using the thioflavin T (ThT) assay. In addition, more in-depth studies employing atomic force microscopy (AFM), matrix assisted laser desorption/ionization-time of flight (MALDI-TOF) and high performance liquid chromatography (HPLC) confirmed that resveratrol has antiaggregation properties. Resveratrol was also confirmed to have a significant inhibitory effect on the aggregation of Aβ₁₋₄₂ peptide under oxidative stress and fibril elongation conditions over ten days. This is the first study to demonstrate the anti-aggregation mechanism of resveratrol involves cleavage of Aβ₁₋₄₂ peptide into smaller fragments. The Plackett-Burman experimental approach was used to optimally design transferrinfunctionalised liposomes. The latter, composed of 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC) and cholesterol, were prepared by the thin lipid film rehydration method. Liposomes were characterised using dynamic light scattering (DLS), diffraction scanning calorimetry (DSC), transmission electron microscopy (TEM), Stewart assay, Bradford assay and small angle X-ray diffraction (SAXS). Liposomes were spherical and homogeneous with particle size of 80-100 nm and polydispersity index (PDI) of < 0.2, and were stable over 60 days. Liposomes were also confirmed to possess a single bilayer membrane, and the release profile of resveratrol was biphasic. Liposomes were successfully functionalised with transferrin and the entrapment efficacy percentage (EE%) of resveratrol was dramatically increased from 2.6 % (in passive loading) to 64.9 % (in active loading). In order to study delivery of resveratrol across BBB endothelial cells, an in vitro BBB model was generated on Transwell® inserts. The model possessed high transendothelial electrical resistance (TEER), 400 ± 150 Ω.cm², and highly restrictive, with an apparent permeability of Lucifer Yellow of 10.6 ± 7 x 10⁻⁷ cm.s⁻¹. Significantly more resveratrol (14-fold) was delivered across the BBB model using transferrin-functionalised liposomes than was delivered using non-functionalised liposomes (p ≤ 0.001) and free resveratrol (p ≤ 0.001). Transferrin-functionalised liposomes may therefore hold great potential for delivery of compounds, including therapeutic drugs, across the BBB.
Supervisor: Aojula, Harmesh Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available