Effects of Brain Amyloid Deposition and Reduced Glucose Metabolism on the Default Mode of Brain Function in Normal Aging
ABSTRACT Brain β-amyloid (Aβ) deposition during normal aging is highlighted as an initial pathogenetic event in the development of Alzheimer's disease. Many recent brain imaging studies have focused on areas deactivated during cognitive tasks [the default mode network (DMN), i.e., medial frontal gyrus/anterior cingulate cortex and precuneus/posterior cingulate cortex], where the strength of functional coordination was more or less affected by cerebral Aβ deposits. In the present positron emission tomography study, to investigate whether regional glucose metabolic alterations and Aβ deposits seen in nondemented elderly human subjects (n = 22) are of pathophysiological importance in changes of brain hemodynamic coordination in DMN during normal aging, we measured cerebral glucose metabolism with [(18)F]FDG, Aβ deposits with [(11)C]PIB, and regional cerebral blood flow during control and working memory tasks by H(2)(15)O on the same day. Data were analyzed using both region of interest and statistical parametric mapping. Our results indicated that the amount of Aβ deposits was negatively correlated with hemodynamic similarity between medial frontal and medial posterior regions, and the lower similarity was associated with poorer working memory performance. In contrast, brain glucose metabolism was not related to this medial hemodynamic similarity. These findings suggest that traceable Aβ deposition, but not glucose hypometabolism, in the brain plays an important role in occurrence of neuronal discoordination in DMN along with poor working memory in healthy elderly people.
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ABSTRACT: Nicotinic acetylcholine receptor subtype α4β2 is considered important in the regulation of attention and memory, and cholinergic degeneration is known as one pathophysiology of Alzheimer's disease. Brain amyloid-β protein deposition is also a key pathological marker of Alzheimer's disease. Recent amyloid-β imaging has shown many cognitively normal subjects with amyloid-β deposits, indicating a missing link between amyloid-β deposition and cognitive decline. To date, the relationship between the α4β2 nicotinic acetylcholine receptor and amyloid-β burden has not been elucidated in vivo. In this study we investigated the relation between α4β2 nicotinic acetylcholine receptor availability in the brain, cognitive functions and amyloid-β burden in 20 non-smoking patients with Alzheimer's disease at an early stage and 25 age-matched non-smoking healthy elderly adults by measuring levels of α4β2 nicotinic acetylcholine receptor binding estimated from a simplified ratio method (BPRI) and Logan plot-based amyloid-β accumulation (BPND) using positron emission tomography with α4β2 nicotinic acetylcholine receptor tracer (18)F-2FA-85380 and (11)C-Pittsburgh compound B. The levels of tracer binding were compared with clinical measures for various brain functions (general cognition, episodic and spatial memory, execution, judgement, emotion) using regions of interest and statistical parametric mapping analyses. Between-group statistical parametric mapping analysis showed a significant reduction in (18)F-2FA-85380 BPRI in the cholinergic projection region in patients with Alzheimer's disease with a variety of (11)C-Pittsburgh compound B accumulation. Spearman rank correlation analyses showed positive correlations of (18)F-2FA-85380 BPRI values in the medial frontal cortex and nucleus basalis magnocellularis region with scores of the Frontal Assessment Battery (a test battery for executive functions and judgement) in the Alzheimer's disease group (P < 0.05 corrected for multiple comparison), and also positive correlations of the prefrontal and superior parietal (18)F-2FA-85380 BPRI values with the Frontal Assessment Battery score in the normal group (P < 0.05 corrected for multiple comparison). These positive correlations indicated an in vivo α4β2 nicotinic acetylcholine receptor role in those specific functions that may be different from memory. Both region of interest-based and voxelwise regression analyses showed a negative correlation between frontal (11)C-Pittsburgh compound B BPND and (18)F-2FA-85380 BPRI values in the medial frontal cortex and nucleus basalis magnocellularis region in patients with Alzheimer's disease (P < 0.05 corrected for multiple comparison). These findings suggest that an impairment of the cholinergic α4β2 nicotinic acetylcholine receptor system with the greater amount of amyloid deposition in the system plays an important role in the pathophysiology of Alzheimer's disease.Brain 08/2013; DOI:10.1093/brain/awt195 · 10.23 Impact Factor
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ABSTRACT: The aim of this study is to evaluate the protective effects of 2,3,5,4'-tetrahydroxystilbene-2-O-β-D-glucoside (TSG) on learning and (or) memory deficit in aged rats, as well as to explore the possible connection between TSG and the β-amyloid precursor protein (APP) pathway. Sprague-Dawley rats were randomly divided into a young control group (age, 4 months), an aged control group (age, 22 months), and a TSG-treated group (age, 22 months). TSG at doses of 50 mg·kg(-1)·day(-1) was intragastrically administered to 22-month-old rats for 4 weeks. The learning and (or) memory ability was measured using the Morris water maze (MWM) test, and the mRNA and protein expression of APP pathway proteins was measured by real-time polymerase chain reaction (RT-PCR) and Western blot, respectively. The aged rats exhibited obvious learning and (or) memory deficit when compared with the young rats, but TSG treatment significantly improved the learning and (or) memory ability in the aged rats, as noted from the MWM test. RT-PCR and Western blot analysis showed an increase in the expression of beta-site APP cleaving enzyme 1 (BACE1) and A Disintegrin And Metalloproteinase 17 (ADAM17) in aged rats, and a decrease in ADAM10; however, TSG treatment significantly increased the mRNA and protein expression of ADAM10 (p < 0.01, compared with aged control rats). These results provide solid evidence for the therapeutic effect of TSG on age-related cognitive impairment, especially spatial learning and memory deficit. TSG might exert this effect through the APP pathway, although further studies on the topic are required.Canadian Journal of Physiology and Pharmacology 11/2011; 89(11):801-9. DOI:10.1139/y11-081 · 1.55 Impact Factor
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ABSTRACT: Amyloid-β (Aβ) deposition in the brain is one of the key pathological features of Alzheimer's disease (AD). Neither traditional clinical-pathological studies nor modern in vivo biomarker investigations of brain amyloid load, however, could reveal a convincing relationship between brain Aβ load and cognitive deficits and decline in patients with AD. Evidence suggests that pathophysiological Aβ dysregulation and accumulation are very early events that precede the onset of cognitive impairment reaching a plateau at the clinical stage of the beginning dementia syndrome. Therefore, research efforts have focused on the role of Aβ in asymptomatic older adults: the results of combined amyloid-PET and neuropsychological studies show a modest but significant correlation between brain fibrillar amyloid load and various subtle cognitive deficits, most notably in challenging episodic associative memory tasks. In order to elucidate the pathophysiological link between cognition and Aβ, a number of combined functional neuroimaging studies have been performed, resulting in early and complex functional alterations in cognitively relevant neural networks such as the default mode network and the largely overlapping episodic memory networks. Multimodal studies using amyloid-tracing imaging methods and neurodegeneration biomarkers strongly suggest that neural network discoordination is specifically related to Aβ-mediated functional and potentially reversible disruption of synaptic plasticity rather than a direct consequence to neurodegenerative pathological processes. These pathophysiological processes and mechanisms may dynamically and non-linearly evolve through fully reversible adaptive compensatory stages and through reactive decompensatory stages into fully irreversible neurodegenerative stages of AD.Journal of Alzheimer's disease: JAD 04/2012; 33. DOI:10.3233/JAD-2012-129003 · 3.61 Impact Factor