Amyloid β-associated cognitive decline in the absence of clinical disease progression and systemic illness

Introduction

High levels of amyloid β (Aβ) are associated with cognitive decline in cognitively normal (CN) older adults. This study investigated the nature of cognitive decline in healthy individuals who did not progress to mild cognitive impairment or dementia.

Method

Cognition was measured over 72 months and compared between low (Aβ−) and high (Aβ+) CN older adults (n = 335) who did not progress to mild cognitive impairment or dementia and who remained free of severe or uncontrolled systemic illness.

Results

Compared to the Aβ− group, the Aβ+ group showed no cognitive impairment at baseline but showed substantial decline in verbal learning, episodic memory, and attention over 72 months.

Discussion

Moderate cognitive decline, particularly for learning and memory, was associated with Aβ+ in CN older adults in the absence of clinical disease progression and uncontrolled or serious comorbid illness.

Amyloid burden and incident depressive symptoms in cognitively normal older adults

OBJECTIVE

Several studies have reported that non-demented older adults with clinical depression show changes in amyloid-β (Aβ) levels in blood, cerebrospinal fluid and on neuroimaging that are consistent with those observed in patients with Alzheimer's disease. These findings suggest that Aβ may be one of the mechanisms underlying the relation between the two conditions. We sought to determine the relation between elevated cerebral Aβ and the presence of depression across a 54-month prospective observation period.

METHODS

Cognitively normal older adults from the Australian Imaging Biomarkers and Lifestyle study who were not depressed and had undergone a positron emission tomography scan to classify them as either high Aβ (n = 81) or low Aβ (n = 278) participated. Depressive symptoms were assessed using the Geriatric Depression Scale - Short Form at 18-month intervals over 54 months.

RESULTS

Whilst there was no difference in probable depression between groups at baseline, incidence was 4.5 (95% confidence interval [CI] 1.3-16.4) times greater within the high Aβ group (9%) than the low Aβ group (2%) by the 54-month assessment.

CONCLUSIONS

Results of this study suggest that elevated Aβ levels are associated with a 4.5-fold increased likelihood of developing clinically significant depressive symptoms on follow-up in preclinical Alzheimer's disease. This underscores the importance of assessing, monitoring and treating depressive symptoms in older adults with elevated Aβ. Copyright © 2016 John Wiley & Sons, Ltd.

β-Amyloid, APOE and BDNF Genotype, and Depressive and Anxiety Symptoms in Cognitively Normal Older Women and Men

OBJECTIVE

To examine how β-amyloid (Aβ), APOE and BDNF genotypes, and cortisol relate to depressive and anxiety symptoms in cognitively normal older women and men.

METHODS

Cross-sectional data were analyzed from 423 older adults from the Australian Imaging Biomarkers and Lifestyle study. Analyses of covariance evaluated associations between Aβ, APOE and BDNF genotype, and cortisol in relation to severity of depressive and anxiety symptoms.

RESULTS

Among Aβ+ older adults, APOE ε4 carriage was associated with greater severity of anxiety symptoms (d = 0.55); and in the full sample, APOE ε4 carriage was linked to greater severity of depressive (d = 0.26) and anxiety (d = 0.21) symptoms. Among Aβ+ women, ε4 carriers reported greater anxiety symptoms than non-ε4 carriers (d = 0.83), and female BDNF rs6265 Val66 Met allele carriers reported greater depressive symptoms (d = 0.29).

CONCLUSION

Sex moderated the relationship between Aβ, APOE genotype, and BDNF genotype in predicting severity of anxiety and depressive symptoms in cognitively normal older adults.

Subjective Memory Complaints in APOEɛ4 Carriers are Associated with High Amyloid-β Burden

BACKGROUND

APOEɛ4 genotype and aging have been identified as risk factors for Alzheimer's disease (AD). In addition, subjective memory complaints (SMC) might be a first clinical expression of the effect of AD pathology on cognitive functioning.

OBJECTIVE

To assess whether APOEɛ4 genotype, age, SMC, and episodic memory are risk factors for high amyloid-β (Aβ) burden in cognitively normal elderly.

METHODS

307 cognitively normal participants (72.7 ± 6.8 years, 53% female, 55% SMC) from the Australian Imaging, Biomarkers and Lifestyle (AIBL) study underwent amyloid PET and APOE genotyping. Logistic regression analyses were performed to determine the association of APOEɛ4 genotype, age, SMC, and episodic memory with Aβ pathology.

RESULTS

Odds of high Aβ burden were greater at an older age (OR = 3.21; 95% CI = 1.68-6.14), when SMC were present (OR = 1.90; 95% CI = 1.03-3.48), and for APOEɛ4 carriers (OR = 7.49; 95% CI = 3.96-14.15), while episodic memory was not associated with odds of high Aβ burden. Stratified analyses showed that odds of SMC for high Aβ burden were increased in specifically APOEɛ4 carriers (OR = 4.58, 95% CI = 1.83-11.49) and younger participants (OR = 3.73, 95% CI = 1.39-10.01).

CONCLUSION

Aging, APOEɛ4 genotype, and SMC were associated with high Aβ burden. SMC were especially indicative of high Aβ burden in younger participants and in APOEɛ4 carriers. These findings suggest that selection based on the presence of SMC, APOEɛ4 genotype and age may help identify healthy elderly participants with high Aβ burden eligible for secondary prevention trials.

Automated visibility map of the internal colon surface from colonoscopy video

PURPOSE

Optical colonoscopy is a prominent procedure by which clinicians examine the surface of the colon for cancerous polyps using a flexible colonoscope. One of the main concerns regarding the quality of the colonoscopy is to ensure that the whole colonic surface has been inspected for abnormalities. In this paper, we aim at estimating areas that have not been covered thoroughly by providing a map from the internal colon surface.

METHODS

Camera parameters were estimated using optical flow between consecutive colonoscopy frames. A cylinder model was fitted to the colon structure using 3D pseudo stereo vision and projected into each frame. A circumferential band from the cylinder was extracted to unroll the internal colon surface (band image). By registering these band images, drift in estimating camera motion could be reduced, and a visibility map of the colon surface could be generated, revealing uncovered areas by the colonoscope. Hidden areas behind haustral folds were ignored in this study. The method was validated on simulated and actual colonoscopy videos. The realistic simulated videos were generated using a colonoscopy simulator with known ground truth, and the actual colonoscopy videos were manually assessed by a clinical expert.

RESULTS

The proposed method obtained a sensitivity and precision of 98 and 96 % for detecting the number of uncovered areas on simulated data, whereas validation on real videos showed a sensitivity and precision of 96 and 78 %, respectively. Error in camera motion drift could be reduced by almost 50 % using results from band image registration.

CONCLUSION

Using a simple cylindrical model for the colon and reducing drift by registering band images allows for the generation of visibility maps. The current results also suggest that the provided feedback through the visibility map could enhance clinicians' awareness of uncovered areas, which in return could reduce the probability of missing polyps.

Clinical and cognitive trajectories in cognitively healthy elderly individuals with suspected non-Alzheimer's disease pathophysiology (SNAP) or Alzheimer's disease pathology: a longitudinal study

BACKGROUND

Brain amyloid β (Aβ) deposition and neurodegeneration have been documented in about 50-60% of cognitively healthy elderly individuals (aged 60 years or older). The long-term cognitive consequences of the presence of Alzheimer's disease pathology and neurodegeneration, and whether they have an independent or synergistic effect on cognition, are unclear. We aimed to characterise the long-term clinical and cognitive trajectories of healthy elderly individuals using a two-marker (Alzheimer's disease pathology and neurodegeneration) imaging construct.

METHODS

Between Nov 3, 2006, and Nov 25, 2014, 573 cognitively healthy individuals in Melbourne and Perth, Australia, (mean age 73·1 years [SD 6·2]; 58% women) were enrolled in the Australian Imaging, Biomarker and Lifestyle (AIBL) study. Alzheimer's disease pathology (A) was determined by measuring Aβ deposition by PET, and neurodegeneration (N) was established by measuring hippocampal volume using MRI. Individuals were categorised as A(-)N(-), A(+)N(-), A(+)N(+), or suspected non-Alzheimer's disease pathophysiology (A(-)N(+), SNAP). Clinical progression, hippocampal volume, standard neuropsychological tests, and domain-specific and global cognitive composite scores were assessed over 6 years of follow-up. Linear mixed effect models and a Cox proportional hazards model of survival were used to evaluate, compare, and contrast the clinical, cognitive, and volumetric trajectories of patients in the four AN categories.

FINDINGS

50 (9%) healthy individuals were classified as A(+)N(+), 87 (15%) as A(+)N(-), 310 (54%) as A(-)N(-), and 126 (22%) as SNAP. APOE ε4 was more frequent in participants in the A(+)N(+) (27; 54%) and A(+)N(-) (42; 48%) groups than in the A(-)N(-) (66; 21%) and SNAP groups (23; 18%). The A(+)N(-) and A(+)N(+) groups had significantly faster cognitive decline than the A(-)N(-) group (0·08 SD per year for AIBL-Preclinical AD Cognitive Composite [PACC]; p<0·0001; and 0·25; p<0·0001; respectively). The A (+)N(+) group also had faster hippocampal atrophy than the A(-)N(-) group (0·04 cm(3) per year; p=0·02). The SNAP group generally did not show significant decline over time compared with the A(-)N(-) group (0·03 SD per year [p=0·19] for AIBL-PACC and a 0·02 cm(3) per year increase [p=0·16] for hippocampal volume), although SNAP was sometimes associated with lower baseline cognitive scores (0·20 SD less than A(-)N(-) for AIBL-PACC). Within the follow-up, 24% (n=12) of individuals in the A(+)N(+) group and 16% (n=14) in the A(+)N(-) group progressed to amnestic mild cognitive impairment or Alzheimer's disease, compared with 9% (n=11) in the SNAP group.

INTERPRETATION

Brain amyloidosis, a surrogate marker of Alzheimer's disease pathology, is a risk factor for cognitive decline and for progression from preclinical stages to symptomatic stages of the disease, with neurodegeneration acting as a compounding factor. However, neurodegeneration alone does not confer a significantly different risk of cognitive decline from that in the group with neither brain amyloidosis or neurodegeneration.

FUNDING

CSIRO Flagship Collaboration Fund and the Science and Industry Endowment Fund (SIEF), National Health and Medical Research Council, the Dementia Collaborative Research Centres programme, McCusker Alzheimer's Research Foundation, and Operational Infrastructure Support from the Government of Victoria.