Context
Blood-based analytes as indicators of pathological processes in Alzheimer's disease (AD).
Objective
Combined proteomic and neuroimaging approach to identify plasma proteins associated with AD pathology.
Design
Discovery-phase proteomic experiments to identify plasma proteins associated with correlates of AD pathology including evidence of atrophy using neuroimaging and more rapid clinical progression, followed by replication using quantitative immunoassay. Extension studies in older non-demented humans using 11C-PiB amyloid imaging and transgenic mice with amyloid pathology.
Setting
Multi-center European study, AddNeuroMed, and the Baltimore Longitudinal Study of Aging (BLSA) in United States.
Participants
AD patients, mild cognitive impairment (MCI) subjects and healthy controls with standardized clinical assessments and structural neuroimaging. Plasma samples from non-demented older BLSA participants with brain amyloid imaging by PET.
Main outcome measures
Association of plasma proteins with brain atrophy, disease severity and rate of clinical progression. Extension studies in man and transgenic mice tested association between plasma proteins and brain amyloid.
Results
Clusterin/apolipoprotein-J was associated with atrophy of the entorhinal cortex, baseline disease severity and rapid clinical progression in AD. Increased plasma concentration of clusterin was predictive of greater beta amyloid (Aβ) burden in the medial temporal lobe. Subjects with AD had increased clusterin mRNA in blood but there was no effect of SNPs in the gene encoding clusterin (CLU) with gene or protein expression. Finally, APP/PS1 transgenic mice showed increased plasma clusterin, age-dependent increase in brain clusterin and amyloid and clusterin co-localisation in plaques.
Conclusions
Clusterin/apolipoprotein-J is a known amyloid chaperone associated with Alzheimer's disease severity, pathology and progression. Increased plasma concentration of clusterin is also associated with greater burden of fibrillar Aβ in the brain. These results demonstrate an important role of clusterin in the pathogenesis of AD and suggest that alterations in amyloid chaperone proteins may be a biologically relevant peripheral signature of Alzheimer's disease.
Dementia with Lewy bodies (DLB) and Parkinson's disease dementia (PDD) are characterized by the presence of α-synuclein-containing Lewy bodies and Lewy neurites. However, both dementias also show variable degrees of Alzheimer's disease (AD) pathology (senile plaques and neurofibrillary tangles), particularly in areas of the cortex associated with higher cognitive functions. This study investigates the contribution of the individual and combined pathologies in determining the rate of cognitive decline. Cortical α-synuclein, phosphorylated tau (phosphotau) and Aβ plaque pathology in 34 PDD and 55 DLB patients was assessed semi-quantitatively in four regions of the neocortex. The decline in cognition, assessed by Mini Mental State Examination, correlated positively with the cortical α-synuclein load. Patients also had varying degrees of senile Aβ plaque and phosphotau pathology. Regression analyses pointed to a combined pathology (Aβ plaque plus phosphotau plus α-synuclein-positive features), particularly in the prefrontal cortex (BA9) and temporal lobe neocortex with the superior and middle temporal gyrus (BA21, 22), being a major determining factor in the development of dementia. Thus, cognitive decline in Lewy body dementias is not a consequence of α-synuclein-induced neurodegeneration alone but senile plaque and phosphorylated tau pathology also contribute to the overall deficits.
A series of benzofuran derivatives have been identified as inhibitors of fibril formation in the beta-amyloid peptide. The activity of these compounds has been assessed by a novel fibril-formation-specific immunoassay and for their effects on the production of a biologically active fibril product. The inhibition afforded by the compounds seems to be associated with their binding to beta-amyloid, as identified by scintillation proximity binding assay. Binding assays and NMR studies also indicate that the inhibition is associated with self-aggregation of the compounds. There is a close correlation between the activity of the benzofurans as inhibitors of fibril formation and their ability to bind to beta-amyloid. Non-benzofuran inhibitors of the fibril formation process do not seem to bind to the same site on the beta-amyloid molecule as the benzofurans. Thus a specific recognition site might exist for benzofurans on beta-amyloid, binding to which seems to interfere with the ability of the peptide to form fibrils.
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