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Association of hypometabolism and amyloid levels in aging, normal subjects.

ABSTRACT: We evaluated the relationship of amyloid, seen on Pittsburgh compound B (PiB)-PET, and metabolism, seen on [(18)F]-fluorodeoxyglucose (FDG)-PET, in normal subjects to better understand pathogenesis and biomarker selection in presymptomatic subjects.Normal participants (aged 70-95 years; 600 with PiB-PET, FDG-PET, and MRI) were included. We performed a cross-sectional evaluation and subcategorized participants into amyloid-negative (<1.4), high-normal (1.4-1.5), positive (1.5-2.0), and markedly positive (>2.0) PiB standardized uptake value ratio groups representing different levels of amyloid brain load. Associations with metabolism were assessed in each group. Relationships with APOE ?4 carriage were evaluated.Hypometabolism in "Alzheimer disease (AD)-signature" regions was strongly associated with PiB load. Hypometabolism was greater with more positive PiB levels. Additional, more-diffuse cortical hypometabolism was also found to be associated with PiB, although less so. No hypermetabolism was seen in any subset. No significant incremental hypometabolism was seen in APOE-positive vs -negative subjects.Hypometabolism in PiB-positive, cognitively normal subjects in a population-based cohort occurs in AD-signature cortical regions and to a lesser extent in other cortical regions. It is more pronounced with higher amyloid load and supports a dose-dependent association. The effect of APOE ?4 carriage in this group of subjects does not appear to modify their hypometabolic "AD-like" neurodegeneration. Consideration of hypometabolism associated with amyloid load may aid trials of AD drug therapy.

SUBMITTER: Lowe VJ

PROVIDER: S-EPMC4105262 | biostudies-other | 2014 Jun

REPOSITORIES: biostudies-other

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Association of hypometabolism and amyloid levels in aging, normal subjects.

Lowe Val J VJ Weigand Stephen D SD Senjem Matthew L ML Vemuri Prashanthi P Jordan Lennon L Kantarci Kejal K Boeve Bradley B Jack Clifford R CR Knopman David D Petersen Ronald C RC

Neurology 20140502 22

<h4>Objective</h4>We evaluated the relationship of amyloid, seen on Pittsburgh compound B (PiB)-PET, and metabolism, seen on [(18)F]-fluorodeoxyglucose (FDG)-PET, in normal subjects to better understand pathogenesis and biomarker selection in presymptomatic subjects.<h4>Methods</h4>Normal participants (aged 70-95 years; 600 with PiB-PET, FDG-PET, and MRI) were included. We performed a cross-sectional evaluation and subcategorized participants into amyloid-negative (<1.4), high-normal (1.4-1.5), ...[more]

PMID: 24793183

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Project description:Dysfunctional insulin signaling may affect brain metabolism or amyloid deposition. We investigated the associations of type 2 diabetes with amyloid accumulation measured using (11)C-Pittsburgh compound B ((11)C-PiB) and brain hypometabolism measured using (18)F-FDG PET.We studied a sample of nondemented participants from the population-based Mayo Clinic Study of Aging. All subjects underwent MR imaging, amyloid PET, and (18)F-FDG PET. Alzheimer disease (AD) signature and region-of-interest (ROI) measures for (11)C-PiB retention ratio and (18)F-FDG ratio were measured. Diabetes was assessed from the Rochester Epidemiology Project medical records linkage system.Among 749 participants (median age, 79.0 y; 56.5% men, 81.0% cognitively normal; 20.6% diabetic individuals), (18)F-FDG hypometabolism ((18)F-FDG ratio < 1.31) in the AD signature meta-ROI was more common in diabetic individuals (48.1%) than in nondiabetic individuals (28.9%; P < 0.001). The median (18)F-FDG ratio was lower in diabetic individuals than in nondiabetic individuals in the AD signature meta-ROI (1.32 vs. 1.40, P < 0.001) and in the angular (1.40 vs. 1.48, P < 0.001) and posterior cingulate gyri ROIs (1.63 vs. 1.72, P < 0.001). The odds ratio (OR) for abnormal AD signature (18)F-FDG hypometabolism was elevated (2.28; 95% confidence interval [CI], 1.56-3.33) in diabetic individuals versus nondiabetic individuals after adjustment for age, sex, and education and after additional adjustment for apolipoprotein ?4 allele, glycemic level, and cognitive status (OR, 1.69; 95% CI, 1.10-2.60). However, the AD signature (11)C-PiB retention ratio was similar in diabetic individuals versus nondiabetic individuals (OR, 1.03; 95% CI, 0.71-1.51; P = 0.87). In post hoc analyses in nondiabetic individuals, a 1% increase in hemoglobin A1c was associated with greater AD signature hypometabolism in cognitively normal subjects (OR, 1.93; 95% CI, 1.03-3.62; P = 0.04) and in the total cohort (OR 1.59; 95% CI, 0.92-2.75; P = 0.10).Diabetes and poor glycemic control in nondiabetic individuals may enhance glucose hypometabolism in AD signature regions. These factors should be investigated in longitudinal studies for their role in detecting onset of symptoms in AD.

Project description:ImportanceThe role of amyloid in the progression of Alzheimer disease (AD) pathophysiology is of central interest to the design of randomized clinical trials. The presence of amyloid has become a prerequisite for enrollment in several secondary prevention trials for AD, yet the precise effect of elevated amyloid levels on subsequent clinical and biomarker events is less certain.ObjectiveTo explore the effect of elevated amyloid levels on subsequent changes in cognition and biomarkers.Design, setting, and participantsA total of 564 cognitively normal individuals (median age, 78 years) from the Mayo Clinic Study of Aging, a population-based longitudinal study in Olmsted County, Minnesota, with serial cognitive data were selected for this study. The data used in this study were collected from January 12, 2006, to January 9, 2014. Individuals included in this study had undergone magnetic resonance imaging, fluorodeoxyglucose positron emission tomography (FDG-PET), and Pittsburgh Compound B (PiB) PET at baseline were not cognitively impaired at baseline and had at least 1 clinical follow-up. A subset of 286 individuals also underwent serial imaging. Elevated amyloid level was defined as a standardized uptake value ratio of greater than 1.5 on PiB PET. Associations with baseline amyloid status and baseline and longitudinal change in clinical and imaging measures were evaluated after adjusting for age and hippocampal volume. APOE4 effects were also evaluated.Main outcomes and measuresCognitive measures of memory, language, attention/executive function, visuospatial skills, PiB levels, hippocampal and ventricular volumes, and FDG-PET measures.ResultsAt baseline, 179 (31.7%) individuals with elevated amyloid levels had poorer cognition in all domains measured, reduced hippocampal volume, and greater FDG-PET hypometabolism. Elevated amyloid levels at baseline were associated with a greater rate of cognitive decline in all domains (0.04 to 0.09 z score units per year) except language and a greater rate of amyloid accumulation (1.6% per year), hippocampal atrophy (30 mm3 per year), and ventricular enlargement (565 mm3 per year). Elevated amyloid levels were also associated with an increased risk of mild cognitive impairment (hazard ratio, 2.9; 95% CI, 1.7-5.0, and hazard ratio, 1.6; 95% CI, 0.9-2.8, for PiB+ APOE4 carriers and PiB+ noncarriers, respectively, compared with PiB- noncarriers). These associations were largely independent of APOE4.Conclusions and relevanceIn persons selected from a population-based study, elevated amyloid levels at baseline were associated with worse cognition and imaging biomarkers at baseline and with greater clinical decline and neurodegeneration. These results have implications for the design of randomized clinical trials for AD.

Project description:In its original form, the amyloid cascade hypothesis of Alzheimer's disease holds that fibrillar deposits of amyloid are an early, driving force in pathological events leading ultimately to neuronal death. Early clinicopathological investigations highlighted a number of inconsistencies leading to an updated hypothesis in which amyloid plaques give way to amyloid oligomers as the driving force in pathogenesis. Rather than focusing on the inconsistencies, amyloid imaging studies have tended to highlight the overlap between regions that show early amyloid plaque signal on positron emission tomography and that also happen to be affected early in Alzheimer's disease. Recent imaging studies investigating the regional dependency between metabolism and amyloid plaque deposition have arrived at conflicting results, with some showing regional associations and other not. We extracted multimodal neuroimaging data from the Alzheimer's disease neuroimaging database for 227 healthy controls and 434 subjects with mild cognitive impairment. We analysed regional patterns of amyloid deposition, regional glucose metabolism and regional atrophy using florbetapir ((18)F) positron emission tomography, (18)F-fluordeoxyglucose positron emission tomography and T1-weighted magnetic resonance imaging, respectively. Specifically, we derived grey matter density and standardized uptake value ratios for both positron emission tomography tracers in 404 functionally defined regions of interest. We examined the relation between regional glucose metabolism and amyloid plaques using linear models. For each region of interest, correcting for regional grey matter density, age, education and disease status, we tested the association of regional glucose metabolism with (i) cortex-wide florbetapir uptake; (ii) regional (i.e. in the same region of interest) florbetapir uptake; and (iii) regional florbetapir uptake while correcting in addition for cortex-wide florbetapir uptake. P-values for each setting were Bonferroni corrected for 404 tests. Regions showing significant hypometabolism with increasing cortex-wide amyloid burden were classic Alzheimer's disease-related regions: the medial and lateral parietal cortices. The associations between regional amyloid burden and regional metabolism were more heterogeneous: there were significant hypometabolic effects in posterior cingulate, precuneus, and parietal regions but also significant positive associations in bilateral hippocampus and entorhinal cortex. However, after correcting for global amyloid burden, few of the negative associations remained and the number of positive associations increased. Given the wide-spread distribution of amyloid plaques, if the canonical cascade hypothesis were true, we would expect wide-spread, cortical hypometabolism. Instead, cortical hypometabolism appears to be linked to global amyloid burden. Thus we conclude that regional fibrillar amyloid deposition has little to no association with regional hypometabolism.

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Association of hypometabolism and amyloid levels in aging, normal subjects.

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Association of hypometabolism and amyloid levels in aging, normal subjects.

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