A Novel Nanocomposite For Tau-targeted Theranostics Of Alzheimer’s Disease

Alzheimer’s disease(AD)is one of the most common neurodegenerative diseases that mainly occurs in elderly individuals,usually of a chronic or progressive nature,characterized by disturbance in memory and learning capability,accompanied by deterioration in social behavior.According to the World Alzheimer Report 2018,approximately 50 million people worldwide are living with AD and the amount is expected to reach 152 million by the year 2050,which brings tremendous pressure for the families and the society.Neuropathological hallmarks of AD include extracellular senile plaques composed of Amyloid β(Aβ)deposits and intracellular neurofibrillary tangles(NFTs)formed by filaments of hyperphosphorylated Tau protein.Intervention strategies targeting Aβ have showed no evidence of beneficial effects on clinically significant improvements in cognition,indicating that removal of Aβ plaques was insufficient to induce cognitive improvements.Alternatively,the microtubule-associated protein Tau and its hyperphosphorylated version correlate better with cognitive impairments than do A(3 plaques.Herein,targeting Tau pathology holds great potential for AD treatment.As a non-invasive,dynamic and sensitive imaging method,18F-AV-1451 positron emission computed tomography(PET)molecular imaging offers unique advantages on visualization of pathological Tau,and on spatiotemporal monitoring of disease progression,thus it provides evidence for therapeutic evaluation of Tau-targeted strategies.Inorganic nanomaterials have recently emerged as promising candidates for diagnosis and treatment of various disease models,particularly neurodegenerative diseases,owing to their high stability,intrinsic imaging,antioxidative and drug-delivery properties.However,the applications of inorganic nanomaterials for simultaneous diagnosis and targeted therapy of AD have rarely been reported.Therefore,we proposed a novel approach by combining inorganic nanomaterials with anti-paired helical filament-tau(PHF-tau)monoclonal antibody to obtain Tau-targeted nanocomposites,which were capable of improving cognitive function and preventing AD progression.18F-AV-1451 PET molecular imaging should be feasible for precise diagnosis of AD and therapeutic response evaluation of the Tau-targeted nanocomposites.In this study,we developed a novel Tau-targeted nanocomposite(TNC-AT8)by assembling of cerium oxide nanoparticles(CeONP)onto the surface of magnetic mesoporous silica nanoparticles(MMSN),followed by ’conjugating with an anti-PHF-tau monoclonal antibody AT8.Transmission electron microscope(TEM)images showed the nanocomposites were spherical,small-sized,and uniformly distributed.X-ray energy-dispersive spectroscopy(EDS)confirmed immobilization of MMSN and CeONP.The successful coating of AT8 antibody onto the surface of the nanocomposite was determined by SDS-PAGE electrophoresis.T2 phantom images of TNC-AT8 revealed its high potential as a contrast agent for magnetic resonance imaging(MRI).TNC-AT8 showed minimal cytotoxicity to SH-SY5Y neuronal-like cells.The therapeutic effects of TNC-AT8 were first investigated in an okadaic acid(OA)-induced AD cell model.In vitro immunofluorescence and western blotting indicated that after incubation with TNC-AT8,the intracellular phosphorylated tau(p-tau)and the lysosomal substrate p62(also known as SQSTM1)were significantly reduced,which might be degradated by induction of autophagy,since the microtubule-associated light chain protein 3B(LC3B)and lysosome-associated membrane glycoprotein 1(LAMP 1)were upregulated in SH-SY5Y cells.The autophagic ultrastructures induced by TNC-AT8 were confirmed by TEM.Living cell fluorescence imaging showed that TNC-AT8 could relieve oxidative stress through scavenging mitochondrial reactive oxygen species(ROS).Then TNC-AT8 was further employed for theranostic applications in an OA-induced AD rat model.In vivo 18F-AV-1451 microPET/CT imaging verified that after intracerebroventricular injection of TNC-AT8,PHF-tau within the hippocampal foci of AD rats could be selectively targeted and effectively removed.Behavioral testing by Morris water maze demonstrated spatial learning and memory improvement of AD rats after TNC-AT8 treatment.Immunohistochemical results revealed that TNC-AT8 could substantially inhibit inflammatory gliosis and protect hippocampal neurons.In vivo MRI and ex vivo inductively coupled plasma mass spectrometry(ICP-MS)results suggested that TNC-AT8 could be targeted and retained within the hippocampal foci as a T2 contrast agent for diagnosis of AD rats.In conclusion,we developed a novel Tau-targeted nanocomposite(TNC-AT8)with good biocompatibility.TNC-AT8 was able to effectively reduce intracellular neurotoxic PHF-tau by induction of autophagy.18F-AV-1451 PET molecular imaging could be a spatiotemporal and dynamic approach to evaluate TNC-AT8 in the brain of AD rats for diagnostics of AD.