Nanomaterials As Drug And Drug Carriers In Inhibiting Aβ Aggregation Associated With Alzheimer’s Disease

Alzheimer’s disease(AD) is a progressive neurodegenerative disorder and the most common form of age-related senile dementia. The pathological hallmark of AD is the deposition of cerebral extracellular amyloid plaques and intracellular neurofibrillary tangles. These plaques are composed primarily of 42 and 40 amino acids long amyloid-β peptides(Aβ) that are generated from the amyloid precursor protein(APP) after the enzymatic cleavage by β-and γ-secretases. Although the molecular mechanisms of AD pathogenesis are not clearly understood, Aβ aggregation is believed to be the central process leading to the progressive neurodegeneration in AD. Metal ions play an important role in amyloid aggregation and neurotoxicity in the AD pathogenesis. Aβ aggregates and the over-dose metal ions are considered as possible targets for therapy of AD.Based on the above research, four kinds of nanoparticles have been designed, synthesized and studied for their biological activities as inhibitor or drug carrier in inhibited Aβ aggregation and its neurotoxicity. The mechanism of nanoparticles as inhibitors of Aβ aggregation was also discussed.This thesis consists of five chapters:In chapter 1, we briefly introduced AD symptoms, the pathological characteristics of AD, the pathogenic mechanism of AD-amyloid cascade hypothesis, the mechanism of Aβ aggregation and the neurotoxicity of Aβ aggregate, finally summarized the progress of nanoparticles inhibited the Aβ aggregation.In chapter 2, L-Cys-modified Selenium nanoparticles(Se NPs), Ruthenium nanoparticles(Ru NPs) and Selenium/Ruthenium nanoparticles(Se/Ru NPs) have been designed as Aβ-binding unit to inhibit metal-induced Aβ aggregation. We found that Ru NPs and Se/Ru NPs have a strong affinity toward Aβ species and efficiently suppress extracellular Aβ40 self-assembly and Zn2+-induced fibrillization. Also, Se/Ru NPs can suppress the Zn2+-Aβ40 mediated generation of reactive oxygen species(ROS) and their corresponding neurotoxicity in PC12 cells. In addition, Se/Ru NPs also decrease intracellular Aβ40 fibrillization, but this process does not involve the lysosomal pathway. Intriguingly, Se NPs did not have the same ability as Se/Ru NPs. These results suggest that ruthenium significantly enhances the activity of Se/Ru NPs binding to Aβ40. This interaction would block the Zn2+ binding to Aβ40 peptides and lower the concentration of the free monomer, thus decreasing fibrillization.In chapter 3, two peptides(LPFFD target for bind to Aβ and TGN target for cross blood brain barrier) were conjugated to Se NPs to form dual-functional Se NPs. The optimal molar ratio for LPFFD and TGN in dual-functional Se NPs was 1:1, respectively. We investigated the mechanism of how these dual-functional Se NPs inhibited Aβ aggregation. We found that electrostatic interaction is important for Se NPs bound to Aβ40 and that the conjugation of LPFFD to Se NPs can enhance the hydrophobic interaction between Se NPs and Aβ40. Therefore, dual-functional Se NPs inhibited the aggregation of Aβ40 by disrupting hydrophobic and electrostatic interactions that are important for Aβ40 nucleation,finally protect PC12 cell from the neurotoxicity of Aβ fibers. TGN peptide could significantly enhance ability of dual-functional Se NPs to cross the blood-brain barrier(BBB). The ability of dual-functional Se NPs to cross the BBB even higher than TGN peptide itself. Overall, these targeting peptides and Se NPs exert a synergistic effect on the inhibition of Aβ aggregation and cross BBB efficiently.In chapter 4, metal ions have been demonstrated to participate in the pathology of AD: Aβ aggregation and formation of neurotoxic reactive oxygen species(ROS), such as H2O2. Although metal chelators can block these effects, their therapeutic potential is marred by their inability to cross the BBB and by their non-specific interactions with metal ions necessary for normal cellular processes, which could result in adverse side effects.Thus, a novel gold nanoparticles-capped mesoporous silica(MSN-Au NPs)-based H2O2-responsive controlled release system to target delivery of metal chelator CQ was synthesized. The CQ and Au NPs in this system only be released by the increased levels of H2O2 in Aβ plaque. The Au NPs help in decrease the Aβ self-assembly, due to this, MSN-CQ-Au NPs is more efficient than MSN-CQ in inhibit Cu2+-induced Aβ40 aggregation and prevent PC12 cells from Aβ40-Cu2+ complexes-induced cell membrane disruption, microtubular defects and ROS-mediated apoptosis. MSN can traverse the BBB and the conjugation of Au NPs on the surface of MSN did not affect the controlled release system(MSN-Au NPs) to cross the BBB. Thus, MSN-CQ-Au NPs has the high BBB permeability and precise release of CQ in biological system.In chapter 5, to enhance the biocompatibility and positive surface charge of metal organic framework MIL-101, the PEG-NH2 coated MIL-101(PEG@MIL-101) was synthesized. We found PEG@MIL-101 can interfere Aβ40 aggregation in the lag period. However, due to the weak binding ability between PEG@MIL-101 and Aβ40 fiber, the ability of PEG@MIL-101 in destroying of Aβ40 fiber structure was also hindered. Therefore, the negative charged Au NPs was linked to PEG@MIL-101 via electrostatic interaction to format Au NPs@PEG@MIL-101. The Au NPs promoted PEG@MIL-101 to bind to fibrils and results in the destroy of Aβ40 fiber. In that case, PEG@MIL-101 and Au NPs@PEG@MIL-101 can prevent PC12 cells from Aβ40 aggregates-induced ROS formation, apoptosis, cell membrane disruption, microtubular defects and reduced uptake of Aβ40 peptide in PC12 cells, finally decreased the neurotoxicity of Aβ40 aggregates. Au NPs@PEG@MIL-101 can also protect PC12 cells through the destruction of Aβ40 fiber.