Cortical florbetapir-PET amyloid load in prodromal Alzheimer's disease patients

X chromosome-wide association study of quantitative biomarkers from the Alzheimer's Disease Neuroimaging Initiative study

Introduction

Alzheimer's disease (AD) is a complex neurodegenerative disease with high heritability. Compared to autosomes, a higher proportion of disorder-associated genes on X chromosome are expressed in the brain. However, only a few studies focused on the identification of the susceptibility loci for AD on X chromosome.

Methods

Using the data from the Alzheimer's Disease Neuroimaging Initiative Study, we conducted an X chromosome-wide association study between 16 AD quantitative biomarkers and 19,692 single nucleotide polymorphisms (SNPs) based on both the cross-sectional and longitudinal studies.

Results

We identified 15 SNPs statistically significantly associated with different quantitative biomarkers of the AD. For the cross-sectional study, six SNPs (rs5927116, rs4596772, rs5929538, rs2213488, rs5920524, and rs5945306) are located in or near to six genes DMD, TBX22, LOC101928437, TENM1, SPANXN1, and ZFP92, which have been reported to be associated with schizophrenia or neuropsychiatric diseases in literature. For the longitudinal study, four SNPs (rs4829868, rs5931111, rs6540385, and rs763320) are included in or near to two genes RAC1P4 and AFF2, which have been demonstrated to be associated with brain development or intellectual disability in literature, while the functional annotations of other five novel SNPs (rs12157031, rs428303, rs5953487, rs10284107, and rs5955016) have not been found.

Discussion

15 SNPs were found statistically significantly associated with the quantitative biomarkers of the AD. Follow-up study in molecular genetics is needed to verify whether they are indeed related to AD. The findings in this article expand our understanding of the role of the X chromosome in exploring disease susceptibility, introduce new insights into the molecular genetics behind the AD, and may provide a mechanistic clue to further AD-related studies.

MRAβ: A multimodal MRI-derived amyloid-β biomarker for Alzheimer's disease

Florbetapir 18 F (AV45), a highly sensitive and specific positron emission tomographic (PET) molecular biomarker binding to the amyloid-β of Alzheimer's disease (AD), is constrained by radiation and cost. We sought to combat it by combining multimodal magnetic resonance imaging (MRI) images and a collaborative generative adversarial networks model (CollaGAN) to develop a multimodal MRI-derived Amyloid-β (MRAβ) biomarker. We collected multimodal MRI and PET AV45 data of 380 qualified participants from the ADNI dataset and 64 subjects from OASIS3 dataset. A five-fold cross-validation CollaGAN were applied to generate MRAβ. In the ADNI dataset, we found MRAβ could characterize the subject-level AV45 spatial variations in both AD and mild cognitive impairment (MCI). Voxel-wise two-sample t-tests demonstrated amyloid-β depositions identified by MRAβ in AD and MCI were significantly higher than healthy controls (HCs) in widespread cortices (p < .05, corrected) and were much similar to those by AV45 (r > .92, p < .001). Moreover, a 3D ResNet classifier demonstrated that MRAβ was comparable to AV45 in discriminating AD from HC in both the ADNI and OASIS3 datasets, and in discriminate MCI from HC in ADNI. Finally, we found MRAβ could mimic cortical hyper-AV45 in HCs who later converted to MCI (r = .79, p < .001) and was comparable to AV45 in discriminating them from stable HC (p > .05). In summary, our work illustrates that MRAβ synthesized by multimodal MRI could mimic the cerebral amyloid-β depositions like AV45 and lends credence to the feasibility of advancing MRI toward molecular-explainable biomarkers.

miRNAs and Stem Cells as Promising Diagnostic and Therapeutic Targets for Alzheimer's Disease

Alzheimer's disease (AD) is a cumulative progressive neurodegenerative disease characterized mainly by impairment in cognitive functions accompanied by memory loss, disturbance in behavior and personality, and difficulties in learning. Although the main causes of AD pathogenesis are not fully understood yet, amyloid-β peptides and tau proteins are supposed to be responsible for AD onset and pathogenesis. Various demographic, genetic, and environmental risk factors are involved in AD onset and pathogenesis such as age, gender, several genes, lipids, malnutrition, and poor diet. Significant changes were observed in microRNA (miRNA) levels between normal and AD cases giving hope for a diagnostic procedure for AD through a simple blood test. As yet, only two classes of AD therapeutic drugs are approved by FDA. They are classified as acetylcholinesterase inhibitors and N-methyl-D-aspartate antagonists (NMDA). Unfortunately, they can only treat the symptoms but cannot cure AD or stop its progression. New therapeutic approaches were developed for AD treatment including acitretin due to its ability to cross blood-brain barrier in the brain of rats and mice and induce the expression of ADAM 10 gene, the α-secretase of human amyloid-β protein precursor, stimulating the non-amyloidogenic pathway for amyloid-β protein precursor processing resulting in amyloid-β reduction. Also stem cells may have a crucial role in AD treatment as they can improve cognitive functions and memory in AD rats through regeneration of damaged neurons. This review spotlights on promising diagnostic techniques such as miRNAs and therapeutic approaches such as acitretin and/or stem cells keeping in consideration AD pathogenesis, stages, symptoms, and risk factors.

Spatial normalization and quantification approaches of PET imaging for neurological disorders

Quantification approaches of positron emission tomography (PET) imaging provide user-independent evaluation of pathophysiological processes in living brains, which have been strongly recommended in clinical diagnosis of neurological disorders. Most PET quantification approaches depend on spatial normalization of PET images to brain template; however, the spatial normalization and quantification approaches have not been comprehensively reviewed. In this review, we introduced and compared PET template-based and magnetic resonance imaging (MRI)-aided spatial normalization approaches. Tracer-specific and age-specific PET brain templates were surveyed between 1999 and 2021 for ¹⁸F-FDG, ¹¹C-PIB, ¹⁸F-Florbetapir, ¹⁸F-THK5317, and etc., as well as adaptive PET template methods. Spatial normalization-based PET quantification approaches were reviewed, including region-of-interest (ROI)-based and voxel-wise quantitative methods. Spatial normalization-based ROI segmentation approaches were introduced, including manual delineation on template, atlas-based segmentation, and multi-atlas approach. Voxel-wise quantification approaches were reviewed, including voxel-wise statistics and principal component analysis. Certain concerns and representative examples of clinical applications were provided for both ROI-based and voxel-wise quantification approaches. At last, a recipe for PET spatial normalization and quantification approaches was concluded to improve diagnosis accuracy of neurological disorders in clinical practice.

Resting-state functional MRI signal fluctuation amplitudes are correlated with brain amyloid- deposition in patients with mild cognitive impairment

Mounting evidence suggests that amyloid-β (Aβ) and vascular etiologies are intertwined in the pathogenesis of Alzheimer's disease (AD). Blood-oxygen-level-dependent (BOLD) signals, measured by resting-state functional MRI (rs-fMRI), are associated with neuronal activity and cerebrovascular hemodynamics. Nevertheless, it is unclear if BOLD fluctuations are associated with Aβ deposition in individuals at high risk of AD. Thirty-three patients with amnestic mild cognitive impairment underwent rs-fMRI and AV45 PET. The AV45 standardized uptake value ratio (AV45-SUVR) was calculated using cerebral white matter as reference, to assess Aβ deposition. The whole-brain normalized amplitudes of low-frequency fluctuations (sALFF) of local BOLD signals were calculated in the frequency band of 0.01-0.08 Hz. Stepwise increasing physiological/vascular signal regressions on the rs-fMRI data examined whether sALFF-AV45 correlations were driven by vascular hemodynamics, neuronal activities, or both. We found that sALFF and AV45-SUVR were negatively correlated in regions of default-mode and visual networks (precuneus, angular, lingual and fusiform gyri). Regions with higher sALFF had less Aβ accumulation. Correlated cluster sizes in MNI space (r ≈ -0.47) were reduced from 3018 mm³ to 1072 mm³ with stronger cardiovascular regression. These preliminary findings imply that local brain blood fluctuations due to vascular hemodynamics or neuronal activity can affect Aβ homeostasis.

Clinical application of serological Alzheimer's disease diagnosis using a highly sensitive biosensor with hydrogel-enhanced dielectrophoretic force

Analysis of a ratio between amyloid beta 1-40 and 1-42 (Aβ_1-40 and Aβ_1-42) presented in plasm enables a highly accurate diagnosis of Alzheimer's disease (AD). However, the analysis of plasma Aβs is not routinely conducted because of the lack of Aβ detection techniques sensitive enough to specifically detect Aβ from thousands of biomaterials present in the plasma. We developed a hydrogel-patterned spiral microelectrode sensor combined with a hopping dielectrophoretic (DEP) force, combining the negative DEP and positive DEP forces, for Aβ detection. The hydrogel effectively increased the number of immobilized fragmented antibodies in the reaction region of the sensor and enabled size-exclusive passive filtration of non-specific plasma proteins from that region. The hopping DEP force further concentrated the Aβs and removed the non-specific plasma proteins. Consequently, our sensor achieved a limit of detection (LOD) of approximately ∼ 0.15 pg/mL for both Aβ_1-40 and Aβ_1-42 in the standard plasma. Finally, comparing the ratio between Aβ_1-40 and Aβ_1-42 signals, we distinguished AD patients from cognitively normal subjects with 95.83% accuracy and 92.31% precision (n = 24, p < 0.0001, One-way ANOVA).

Unique regional patterns of amyloid burden predict progression to prodromal and clinical stages of Alzheimer's disease

Although beta-amyloid (Aβ) positivity has shown to be associated with higher risk of progression to Alzheimer's disease (AD) in mild cognitive impairment (MCI), information on the time to conversion to manifest dementia cannot be readily deduced from this binary classification. Here, we assessed if regional patterns of Aβ deposition measured with 18F-florbetapir may serve as biomarker for progression risk in Aβ-positive cognitively normal (CN) and MCI patients, including clinical follow-up data and cerebrospinal fluid (CSF) biomarkers. Voxel-wise group comparisons between age and sex-matched Aβ-positive groups (i.e., CN-stables [n = 38] vs. CN-to-MCI/AD progressors [n = 38], MCI-stables [n = 104] versus MCI-to-AD progressors [n = 104]) revealed higher Aβ burden in precuneus, subcortical, and parietal regions in CN-to-MCI/AD progressors and cingulate, temporal, and frontal regions in MCI-to-AD progressors. Importantly, these regional patterns predicted progression to advanced stages on the AD spectrum in the short and the long-term beyond global Aβ burden and CSF biomarkers. These results suggest that distinct regional patterns of Aβ burden are a valuable biomarker for risk of disease progression in CN and MCI.

Florbetapir Regional Distribution in Cerebral Amyloid Angiopathy and Alzheimer's Disease: A PET Study

Background:

Sporadic cerebral amyloid angiopathy shows progressive amyloid-β deposition in the wall of small arterioles and capillaries of the leptomeninges and cerebral cortex.

Objective:

To investigate whether amyloid load and distribution, assessed by florbetapir positron emission tomography (PET), differs between patients with probable CAA-related intracerebral hemorrhage (CAA-ICH) and mild cognitive impairment due to Alzheimer’s disease (MCI-AD).

Methods:

We assessed [¹⁸F]florbetapir uptake in 15 patients with probable CAA-ICH and 20 patients with MCI-AD patients. Global and regional florbetapir retention were assessed using standard uptake values ratio (SUVr) in region-based and voxel-wise approaches. Visual reading of florbetapir scans was performed for all participants. Group comparisons were performed using univariate and multivariate analysis.

Results:

Global florbetapir retention was lower in patients with CAA-ICH than MCI-AD (median SUVr, 1.33 [1.21–1.41] versus 1.44 [1.35–1.66]; p = 0.032). In the region-based analysis, regional florbetapir distribution was similar between the two groups. There was a trend for an increased occipital/global ratio in CAA-ICH patients compared to MCI-AD (p = 0.060). In the voxel-wise approach, two clusters, one in parietal regions and the other in temporal regions, had higher uptake in MCI-AD relative to CAA patients.

Conclusions:

Patients with CAA-ICH had a lower global florbetapir PET burden than patients with MCI-AD. Relative florbetapir retention in the posterior regions tended to be higher in CAA patients in region-based analysis but was not statistically different between groups. Investigation on differences in amyloid deposits distribution between groups required a fine-grained voxel-wise analysis. In future studies, selective amyloid tracers are needed to differentiate vascular from parenchymal amyloid.

Optical Coherence Tomography in Patients with Alzheimer's Disease: What Can It Tell Us?

PURPOSE

Although Alzheimer's disease (AD) is a leading cause of dementia worldwide, its clinical diagnosis remains a challenge. Optical coherence tomography (OCT) and OCT with angiography (OCTA) are non-invasive ophthalmic imaging tools with the potential to detect retinal structural and microvascular changes in patients with AD, which may serve as biomarkers for the disease. In this systematic review, we evaluate whether certain OCT and OCTA parameters are significantly associated with AD and mild cognitive impairment (MCI).

METHODS

PubMed database was searched using a combination of MeSH terms to identify studies for review. Studies were organized by participant diagnostic groups, type of imaging modality, and OCT/OCTA parameters of interest. Participant demographic data was also collected and baseline descriptive statistics were calculated for the included studies.

RESULTS

Seventy-one studies were included for review, representing a total of 6757 patients (2350 AD, 793 MCI, 2902 healthy controls (HC), and 841 others with a range of other neurodegenerative diagnoses). The mean baseline ages were 72.78±3.69, 71.52±2.88, 70.55±3.85 years for AD, MCI and HC groups, respectively. The majority of studies noted significant structural and functional decline in AD patients when compared to HC. Although analysis of MCI groups yielded more mixed results, a similar pattern of decline was often noted amongst patients with MCI relative to HC. OCT and OCTA measurements were also shown to correlate with established measures of AD such as neuropsychological testing or neuroimaging.

CONCLUSION

OCT and OCTA show great potential as non-invasive technologies for the diagnosis of AD. However, further research is needed to determine whether there are AD-specific patterns of structural or microvascular change in the retina and optic nerve that distinguish AD from other neurodegenerative diseases. Development of sensitive and specific OCT/OCTA parameters will be necessary before they can be used to detect AD in clinical settings.

Interhemispheric distribution of amyloid and small vessel disease burden in cerebral amyloid angiopathy-related intracerebral hemorrhage

BACKGROUND AND PURPOSE

Intracerebral hemorrhage (ICH) is a devastating presentation of cerebral amyloid angiopathy (CAA), but the mechanisms leading from vascular amyloid deposition to ICH are not well known. Whether amyloid burden and magnetic resonance imaging (MRI) markers of small vessel disease (SVD) are increased in the ICH-affected hemisphere compared to the ICH-free hemisphere in patients with a symptomatic CAA-related ICH was investigated.

METHODS

Eighteen patients with CAA-related ICH and 18 controls with deep ICH who underwent brain MRI and amyloid positron emission tomography using ¹⁸ F-florbetapir were prospectively enrolled. In each hemisphere amyloid uptake using the standardized uptake value ratio and the burden of MRI markers of SVD including cerebral microbleeds, chronic ICH, cortical superficial siderosis, white matter hyperintensities and lacunes were evaluated. Interhemispheric comparisons were assessed by non-parametric matched-pair tests within each patient group.

RESULTS

Amyloid burden was similarly distributed across the brain hemispheres in patients with CAA-related ICH (standardized uptake value ratio 1.11 vs. 1.12; P = 0.74). Cortical superficial siderosis tended to be more common in the ICH-affected hemisphere compared to the ICH-free hemisphere (61% vs. 33%; P = 0.063). Other MRI markers of SVD did not differ across brain hemispheres. In controls with deep ICH, no interhemispheric difference was observed either for amyloid burden or for MRI markers of SVD.

CONCLUSIONS

Brain hemorrhage does not appear to be directly linked to amyloid burden in patients with CAA-related ICH. These findings provide new insights into the mechanisms leading to hemorrhage in CAA.

Disruption of cholinergic neurotransmission, within a cognitive challenge paradigm, is indicative of Aβ-related cognitive impairment in preclinical Alzheimer's disease after a 27-month delay interval

BACKGROUND

Abnormal beta-amyloid (Aβ) is associated with deleterious changes in central cholinergic tone in the very early stages of Alzheimer's disease (AD), which may be unmasked by a cholinergic antagonist (J Prev Alzheimers Dis 1:1-4, 2017). Previously, we established the scopolamine challenge test (SCT) as a "cognitive stress test" screening measure to identify individuals at risk for AD (Alzheimer's & Dementia 10(2):262-7, 2014) (Neurobiol. Aging 36(10):2709-15, 2015). Here we aim to demonstrate the potential of the SCT as an indicator of cognitive change and neocortical amyloid aggregation after a 27-month follow-up interval.

METHODS

Older adults (N = 63, aged 55-75 years) with self-reported memory difficulties and first-degree family history of AD completed the SCT and PET amyloid imaging at baseline and were then seen for cognitive testing at 9, 18, and 27 months post-baseline. Repeat PET amyloid imaging was completed at the time of the 27-month exam.

RESULTS

Significant differences in both cognitive performance and in Aβ neocortical burden were observed between participants who either failed vs. passed the SCT at baseline, after a 27-month follow-up period.

CONCLUSIONS

Cognitive response to the SCT (Alzheimer's & Dementia 10(2):262-7, 2014) at baseline is related to cognitive change and PET amyloid imaging results, over the course of 27 months, in preclinical AD. The SCT may be a clinically useful screening tool to identify individuals who are more likely to both have positive evidence of amyloidosis on PET imaging and to show measurable cognitive decline over several years.

Amyloid and FDG PET of Successful Cognitive Aging: Global and Cingulate-Specific Differences

BACKGROUND

Some individuals, called Supernormals (SN), maintain excellent memory in old age. While brain structural and functional integrity in SN seem to be aging-resistant, their amyloidosis and neural injury status has not been well studied.

OBJECTIVE

The goal of this study was to compare cortical amyloid deposition and glucose metabolism between SN and older adults with normal cognition (NC), amnestic mild cognitive impairment (MCI), and Alzheimer's disease (AD).

METHODS

Subjects from the ADNI database were included if they received T1-weighted MRI, amyloid PET, FDG-PET, and cognitive testing within a 6-month period, yielding 27 AD, 69 MCI, 172 NC, and 122 SN. PET standardized uptake value ratios (SUVrs) were calculated for the whole cortex and 68 regions of interest, with whole cerebellum serving as reference.

RESULTS

SN had lower whole cortex amyloid than MCI, and higher glucose metabolism than all others. Regional analysis revealed that amyloid burden and glucose metabolism in the right isthmus cingulate cortex differed in SN compared to others, while SN glucose metabolism also differed from others in several frontal and temporal regions.

CONCLUSION

Preserved cortical glucose metabolism, and lower levels of amyloidosis and glucose hypometabolism in the right isthmus cingulate cortex, contributes to the Supernormal phenomenon. These findings may be informative for development of early screening biomarkers and therapeutic targets for modification of cognitive trajectories.

Current understanding of Alzheimer's disease diagnosis and treatment

Alzheimer’s disease is the most common cause of dementia worldwide, with the prevalence continuing to grow in part because of the aging world population. This neurodegenerative disease process is characterized classically by two hallmark pathologies: β-amyloid plaque deposition and neurofibrillary tangles of hyperphosphorylated tau. Diagnosis is based upon clinical presentation fulfilling several criteria as well as fluid and imaging biomarkers. Treatment is currently targeted toward symptomatic therapy, although trials are underway that aim to reduce the production and overall burden of pathology within the brain. Here, we discuss recent advances in our understanding of the clinical evaluation and treatment of Alzheimer’s disease, with updates regarding clinical trials still in progress.

Amyloid pathology fingerprint differentiates post-traumatic stress disorder and traumatic brain injury

Introduction

Traumatic brain injury (TBI) and post-traumatic stress disorder (PTSD) are risk factors for early onset of Alzheimer's disease (AD) and may accelerate the progression rate of AD pathology. As amyloid-beta (Aβ) plaques are a hallmark of AD pathology, we hypothesized that TBI and PTSD might increase Aβ accumulation in the brain.

Methods

We examined PET and neuropsychological data from Vietnam War veterans compiled by the US Department of Defense Alzheimer's Disease Neuroimaging Initiative, to examine the spatial distribution of Aβ in male veterans' who had experienced a TBI and/or developed PTSD. Subjects were classified into controls, TBI only, PTSD only, and TBI with PTSD (TBI_PTSD) groups and data were analyzed using both voxel-based and ROI-based approaches.

Results

Compared to controls, all three clinical groups showed a pattern of mainly increased referenced standard uptake values (SUVR) for the amyloid tracer [18F]-AV45 PET, with rank order PTSD > TBI_PTSD > TBI > Control, and same rank order was seen in the deficits of cognitive functions. SUVR increase was observed in widespread cortical regions of the PTSD group; in white matter of the TBI_PTSD group; and cerebellum and precuneus area of the TBI group, in contrast with controls. The [18F]-AV45 SUVR correlated negatively with cerebrospinal fluid (CSF) amyloid levels and positively with the CSF tau concentrations.

Conclusion

These results suggest that both TBI and PTSD are substantial risk factors for cognition decline and increased Aβ deposition resembling that in AD. In addition, both PTSD and TBI_PTSD have a different pathways of Aβ accumulation.

Classification of Alzheimer's and MCI Patients from Semantically Parcelled PET Images: A Comparison between AV45 and FDG-PET

Early identification of dementia in the early or late stages of mild cognitive impairment (MCI) is crucial for a timely diagnosis and slowing down the progression of Alzheimer's disease (AD). Positron emission tomography (PET) is considered a highly powerful diagnostic biomarker, but few approaches investigated the efficacy of focusing on localized PET-active areas for classification purposes. In this work, we propose a pipeline using learned features from semantically labelled PET images to perform group classification. A deformable multimodal PET-MRI registration method is employed to fuse an annotated MNI template to each patient-specific PET scan, generating a fully labelled volume from which 10 common regions of interest used for AD diagnosis are extracted. The method was evaluated on 660 subjects from the ADNI database, yielding a classification accuracy of 91.2% for AD versus NC when using random forests combining features from cross-sectional and follow-up exams. A considerable improvement in the early versus late MCI classification accuracy was achieved using FDG-PET compared to the AV-45 compound, yielding a 72.5% rate. The pipeline demonstrates the potential of exploiting longitudinal multiregion PET features to improve cognitive assessment.

Classification of Alzheimer's Disease, Mild Cognitive Impairment, and Cognitively Unimpaired Individuals Using Multi-feature Kernel Discriminant Dictionary Learning

Accurate classification of either patients with Alzheimer's disease (AD) or patients with mild cognitive impairment (MCI), the prodromal stage of AD, from cognitively unimpaired (CU) individuals is important for clinical diagnosis and adequate intervention. The current study focused on distinguishing AD or MCI from CU based on the multi-feature kernel supervised within-Class-similar discriminative dictionary learning algorithm (MKSCDDL), which we introduced in a previous study, demonstrating that MKSCDDL had superior performance in face recognition. Structural magnetic resonance imaging (sMRI), fluorodeoxyglucose (FDG) positron emission tomography (PET), and florbetapir-PET data from the Alzheimer's Disease Neuroimaging Initiative (ADNI) database were all included for classification of AD vs. CU, MCI vs. CU, as well as AD vs. MCI (113 AD patients, 110 MCI patients, and 117 CU subjects). By adopting MKSCDDL, we achieved a classification accuracy of 98.18% for AD vs. CU, 78.50% for MCI vs. CU, and 74.47% for AD vs. MCI, which in each instance was superior to results obtained using several other state-of-the-art approaches (MKL, JRC, mSRC, and mSCDDL). In addition, testing time results outperformed other high quality methods. Therefore, the results suggested that the MKSCDDL procedure is a promising tool for assisting early diagnosis of diseases using neuroimaging data.

Applications of Resting State Functional MR Imaging to Neuropsychiatric Diseases

Resting state studies in neuropsychiatric disorders have already provided much useful information, but the field is regarded as being at a relatively preliminary stage and subject to several design issues that set limits on the overall utility.

Multi-modal discriminative dictionary learning for Alzheimer's disease and mild cognitive impairment

BACKGROUND AND OBJECTIVE

The differentiation of mild cognitive impairment (MCI), which is the prodromal stage of Alzheimer's disease (AD), from normal control (NC) is important as the recent research emphasis on early pre-clinical stage for possible disease abnormality identification, intervention and even possible prevention.

METHODS

The current study puts forward a multi-modal supervised within-class-similarity discriminative dictionary learning algorithm (SCDDL) we introduced previously for distinguishing MCI from NC. The proposed new algorithm was based on weighted combination and named as multi-modality SCDDL (mSCDDL). Structural magnetic resonance imaging (sMRI), fluorodeoxyglucose (FDG) positron emission tomography (PET) and florbetapir PET data of 113 AD patients, 110 MCI patients and 117 NC subjects from the Alzheimer's disease Neuroimaging Initiative database were adopted for classification between MCI and NC, as well as between AD and NC.

RESULTS

Adopting mSCDDL, the classification accuracy achieved 98.5% for AD vs. NC and 82.8% for MCI vs. NC, which were superior to or comparable with the results of some other state-of-the-art approaches as reported in recent multi-modality publications.

CONCLUSIONS

The mSCDDL procedure was a promising tool in assisting early diseases diagnosis using neuroimaging data.

Florbetapir imaging in cerebral amyloid angiopathy-related hemorrhages

OBJECTIVE

To assess whether ¹⁸F-florbetapir, a PET amyloid tracer, could bind vascular amyloid in cerebral amyloid angiopathy (CAA) by comparing cortical florbetapir retention during the acute phase between patients with CAA-related lobar intracerebral hemorrhage (ICH) and patients with hypertension-related deep ICH.

METHODS

Patients with acute CAA-related lobar ICH were prospectively enrolled and compared with patients with deep ICH. ¹⁸F-florbetapir PET, brain MRI, and APOE genotype were obtained for all participants. Cortical florbetapir standard uptake value ratio (SUVr) was calculated with the whole cerebellum used as a reference. Patients with CAA and those with deep ICH were compared for mean cortical florbetapir SUVr values.

RESULTS

Fifteen patients with acute lobar ICH fulfilling the modified Boston criteria for probable CAA (mean age = 67 ± 12 years) and 18 patients with acute deep ICH (mean age = 63 ± 11 years) were enrolled. Mean global cortical florbetapir SUVr was significantly higher among patients with CAA-related ICH than among patients with deep ICH (1.27 ± 0.12 vs 1.12 ± 0.12, p = 0.001). Cortical florbetapir SUVr differentiated patients with CAA-ICH from those with deep ICH (area under the curve = 0.811; 95% confidence interval [CI] 0.642-0.980) with a sensitivity of 0.733 (95% CI 0.475-0.893) and a specificity of 0.833 (95% CI 0.598-0.948).

CONCLUSIONS

Cortical florbetapir uptake is increased in patients with CAA-related ICH relative to those with deep ICH. Although ¹⁸F-florbetapir PET can label vascular β-amyloid and might serve as an outcome marker in future clinical trials, its diagnostic value in acute CAA-related ICH seems limited in clinical practice.

High prevalence of cognitive impairment after intracerebral hemorrhage

Background

Cognitive impairment seems to be frequent in intracerebral hemorrhage (ICH) survivors, but remains widely understudied. In this study, we investigated the frequency and patterns of vascular cognitive disorders (VCDs) in patients with cerebral amyloid angiopathy (CAA)-related and deep ICH compared to patients with mild cognitive impairment due to Alzheimer’s disease (MCI-AD) and healthy controls.

Methods

We prospectively recruited 20 patients with CAA-related lobar ICH, 20 with deep ICH, 20 with MCI-AD and 17 healthy controls. Patients with cognitive decline pre-ICH were excluded from the analysis. Each participant underwent a comprehensive neuropsychological assessment and a structural brain MRI. Cognitive assessment was performed at a median delay of 4 months after the acute phase in ICH patients, and more than 6 months after the first complaint in MCI-AD patients. Cognitive profiles were compared between groups. The prevalence of VCDs in the ICH groups was estimated using the recent VASCOG criteria.

Results

“Mild” and “major VCDs” were respectively observed in 87.5% and 2.5% of all ICH patients. Every patient in the CAA group had mild VCDs. No significant difference was observed in cognitive functioning between CAA-related and deep ICH patients. The most impaired process in the CAA group was naming, with a mean (±standard deviation) z-score of -5.2 ±5.5, followed by processing speed (-4.1±3.3), executive functioning (-2.6 ±2.5), memory (-2.4 ±3.5) and attention (-0.9 ±1.3). This cognitive pattern was different from the MCI-AD patients, but the groups were only different in gestural praxis, and by construction, in memory processes.

Conclusions

VCDs are frequent after ICH. Cognitive patterns of patients with deep or CAA-related ICH did not differ, but there was impaired performance in specific domains distinct from the effects of Alzheimer’s disease.

Clinical trial registration

URL: http://www.clinicaltrials.gov. Unique identifier: NCT01619709.

Multimodal Magnetic Resonance Imaging in Alzheimer's Disease Patients at Prodromal Stage

One objective of modern neuroimaging is to identify markers that can aid in diagnosis, monitor disease progression, and impact long-term drug analysis. In this study, physiopathological modifications in seven subcortical structures of patients with mild cognitive impairment (MCI) due to Alzheimer’s disease (AD) were characterized by simultaneously measuring quantitative magnetic resonance parameters that are sensitive to complementary tissue characteristics (e.g., volume atrophy, shape changes, microstructural damage, and iron deposition). Fourteen MCI patients and fourteen matched, healthy subjects underwent 3T-magnetic resonance imaging with whole-brain, T1-weighted, T2^*-weighted, and diffusion-tensor imaging scans. Volume, shape, mean R2^*, mean diffusivity (MD), and mean fractional anisotropy (FA) in the thalamus, hippocampus, putamen, amygdala, caudate nucleus, pallidum, and accumbens were compared between MCI patients and healthy subjects. Comparisons were then performed using voxel-based analyses of R2^*, MD, FA maps, and voxel-based morphometry to determine which subregions showed the greatest difference for each parameter. With respect to the micro- and macro-structural patterns of damage, our results suggest that different and distinct physiopathological processes are present in the prodromal phase of AD. MCI patients had significant atrophy and microstructural changes within their hippocampi and amygdalae, which are known to be affected in the prodromal stage of AD. This suggests that the amygdala is affected in the same, direct physiopathological process as the hippocampus. Conversely, atrophy alone was observed within the thalamus and putamen, which are not directly involved in AD pathogenesis. This latter result may reflect another mechanism, whereby atrophy is linked to indirect physiopathological processes.

Multi-modality sparse representation-based classification for Alzheimer's disease and mild cognitive impairment

BACKGROUND AND OBJECTIVE

The discrimination of Alzheimer's disease (AD) and its prodromal stage known as mild cognitive impairment (MCI) from normal control (NC) is important for patients' timely treatment. The simultaneous use of multi-modality data has been demonstrated to be helpful for more accurate identification. The current study focused on extending a multi-modality algorithm and evaluating the method by identifying AD/MCI.

METHODS

In this study, sparse representation-based classification (SRC), a well-developed method in pattern recognition and machine learning, was extended to a multi-modality classification framework named as weighted multi-modality SRC (wmSRC). Data including three modalities of volumetric magnetic resonance imaging (MRI), fluorodeoxyglucose (FDG) positron emission tomography (PET) and florbetapir PET from the Alzheimer's disease Neuroimaging Initiative database were adopted for AD/MCI classification (113 AD patients, 110 MCI patients and 117 NC subjects).

RESULTS

Adopting wmSRC, the classification accuracy achieved 94.8% for AD vs. NC, 74.5% for MCI vs. NC, and 77.8% for progressive MCI vs. stable MCI, superior to or comparable with the results of some other state-of-the-art models in recent multi-modality researches.

CONCLUSIONS

The wmSRC method is a promising tool for classification with multi-modality data. It could be effective for identifying diseases from NC with neuroimaging data, which could be helpful for the timely diagnosis and treatment of diseases.

Brain Amyloid Deposition Is Associated With Lower Instrumental Activities of Daily Living Abilities in Older Adults. Results From the MAPT Study

BACKGROUND

Brain amyloid deposition is one of the key pathological hallmarks underlying the cognitive changes associated with Alzheimer's disease. Growing interest has been given to the earliest clinical manifestations of amyloid plaques. However, the relationship between amyloid status and activities of everyday function remains largely unknown. In the present study, we examined the relationship between instrumental activities of daily living performance (using the ADL-PI score) and amyloid status in older adults.

METHODS

Cross-sectional analyses of data from the Multidomain Alzheimer Preventive Trial (MAPT) were performed. Volunteers underwent a brain 18F-AV45 positron emission tomography examination. Bivariate analysis and regression models were conducted to study the relationships between brain amyloid deposition and the total ADL-PI score.

RESULTS

We included 271 participants (women = 60%; age = 76±4 years). Amyloid positron emission tomography was positive (standard uptake value ≥1.17) for 103 participants (38%). The ADL-PI score was lower in amyloid positive participants than in their amyloid negative counterparts (38.8 vs 40.3, p = .007). This association was also confirmed in regression models adjusted for age, gender, and familial history of Alzheimer's disease (odds ratio = 0.94; 95% confidence interval 0.89-0.99; p = .02). This finding was consistent in cognitively normal individuals and in those with mild cognitive impairment, using the clinical dementia rating scale.

CONCLUSIONS

This study highlighted an association between early functional limitations and brain amyloid deposition in elderly subjects. These symptoms could be the clinical manifestations of amyloid plaques even in the absence of overt dementia. Further prospective studies are warranted for examining the evolution of ADL-PI score over the course of Alzheimer's disease.

18F-FDG and 18F-florbetapir PET in clinical practice: regional analysis in mild cognitive impairment and Alzheimer disease

OBJECTIVE

The aim of this study is to compare regional cerebral metabolic rate of glucose metabolism and amyloid-β density in patients with Alzheimer disease (AD), mild cognitive impairment (MCI), and healthy elderly subjects.

METHODS

Eighteen patients (including 6 AD, 5 amnestic MCI, and 7 controls) were enrolled at the University Hospital of Tours, France, and submitted to clinical, neuropsychological, and MRI examinations. PET images using F-florbetapir (266 MBq) and F-FDG (185 MBq) were acquired. SUV ratios in specific regions were defined using PMOD3.2 software.

RESULTS

The mean values of F-FDG SUV ratio were significantly lower in frontal, anterior cingulate, and temporal regions in MCI patients than in normal elderly (-15%, -22%, and -11%, respectively). Alzheimer disease patients showed global cerebral metabolic rate of glucose metabolism decrease, especially in parietal and precuneus regions (-15% and -13% compared with healthy control subjects). Only precuneus cortex showed an increased F-florbetapir uptake in AD. There was no other significant regional difference in the amyloid-β density.

CONCLUSIONS

In this study, we observed regional brain metabolic changes between MCI, AD, and controls, whereas only precuneus showed an increased amyloid-β density in AD. F-florbetapir PET analysis needs to be visual and global, whereas F-FDG analysis can be regional.

White matter disruption at the prodromal stage of Alzheimer's disease: relationships with hippocampal atrophy and episodic memory performance

White matter tract alterations have been consistently described in Alzheimer's disease (AD). In particular, limbic fronto-temporal connections, which are critical to episodic memory function, may degenerate early in the course of the disease. However the relation between white matter tract degeneration, hippocampal atrophy and episodic memory impairment at the earliest stages of AD is still unclear. In this magnetic resonance imaging study, white matter integrity and hippocampal volumes were evaluated in patients with amnestic mild cognitive impairment due to AD (Albert et al., 2011) (n = 22) and healthy controls (n = 15). Performance in various episodic memory tasks was also evaluated in each participant. Relative to controls, patients showed a significant reduction of white matter fractional anisotropy (FA) and increase of radial diffusivity (RD) in the bilateral uncinate fasciculus, parahippocampal cingulum and fornix. Within the patient group, significant intra-hemispheric correlations were notably found between hippocampal grey matter volume and FA in the uncinate fasciculus, suggesting a relationship between atrophy and disconnection of the hippocampus. Moreover, episodic recognition scores were related with uncinate fasciculus FA across patients. These results indicate that fronto-hippocampal connectivity is reduced from the earliest pre-demential stages of AD. Disruption of fronto-hippocampal connections may occur progressively, in parallel with hippocampal atrophy, and may specifically contribute to early initial impairment in episodic memory.

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Limbic fronto-temporal connections (cingulum, uncinate fasciculus and fornix) are altered from the prodromal stage of AD.

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In prodromal AD patients, intra-hemispheric correlations were found between uncinate fasciculus FA and hippocampal atrophy.

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In prodromal AD patients, uncinate fasciculus FA was correlated with scores on episodic recognition.

Harnessing the immune system for treatment and detection of tau pathology

The tau protein is an attractive target for therapy and diagnosis. We started a tau immunotherapy program about 13 years ago and have since demonstrated that active and passive immunotherapies diminish tau pathology and improve function, including cognition, in different mouse models. These findings have been confirmed and extended by several groups. We routinely detect neuronal, and to a lesser extent microglial, antibody uptake correlating with tau pathology. Antibodies bind tau aggregates in the endosomal/lysosomal system, enhancing clearance presumably by promoting their disassembly. Extracellular clearance has recently been shown by others, using antibodies that apparently are not internalized. As most pathological tau is neuronal, intracellular targeting may be more efficacious. However, extracellular tau may be more accessible to antibodies, with tau-antibody complexes a target for microglial phagocytosis. The extent of involvement of each pathway may depend on numerous factors including antibody properties, degree of pathology, and experimental model. On the imaging front, multiple tau ligands derived from β-sheet dyes have been developed by several groups, some with promising results in clinical PET tests. Postmortem analysis should clarify their tau specificity, as in theory and based on histological staining, those are likely to have some affinity for various amyloids. We are developing antibody-derived tau probes that should be more specific, and have in mouse models shown in vivo detection and binding to pathological tau after peripheral injection. These are exciting times for research on tau therapies and diagnostic agents that hopefully can be applied to humans in the near future.

Comparison between PET template-based method and MRI-based method for cortical quantification of florbetapir (AV-45) uptake in vivo

PURPOSE

Florbetapir (AV-45) has been shown to be a reliable tool for assessing in vivo amyloid load in patients with Alzheimer's disease from the early stages. However, nonspecific white matter binding has been reported in healthy subjects as well as in patients with Alzheimer's disease. To avoid this issue, cortical quantification might increase the reliability of AV-45 PET analyses. In this study, we compared two quantification methods for AV-45 binding, a classical method relying on PET template registration (route 1), and a MRI-based method (route 2) for cortical quantification.

METHODS

We recruited 22 patients at the prodromal stage of Alzheimer's disease and 17 matched controls. AV-45 binding was assessed using both methods, and target-to-cerebellum mean global standard uptake values (SUVr) were obtained for each of them, together with SUVr in specific regions of interest. Quantification using the two routes was compared between the clinical groups (intragroup comparison), and between groups for each route (intergroup comparison). Discriminant analysis was performed.

RESULTS

In the intragroup comparison, differences in uptake values were observed between route 1 and route 2 in both groups. In the intergroup comparison, AV-45 uptake was higher in patients than controls in all regions of interest using both methods, but the effect size of this difference was larger using route 2. In the discriminant analysis, route 2 showed a higher specificity (94.1 % versus 70.6 %), despite a lower sensitivity (77.3 % versus 86.4 %), and D-prime values were higher for route 2.

CONCLUSION

These findings suggest that, although both quantification methods enabled patients at early stages of Alzheimer's disease to be well discriminated from controls, PET template-based quantification seems adequate for clinical use, while the MRI-based cortical quantification method led to greater intergroup differences and may be more suitable for use in current clinical research.

The Janus face of the heme oxygenase/biliverdin reductase system in Alzheimer disease: it's time for reconciliation

Alzheimer disease (AD) is the most common form of dementia among the elderly and is characterized by progressive loss of memory and cognition. These clinical features are due in part to the increase of reactive oxygen and nitrogen species that mediate neurotoxic effects. The up-regulation of the heme oxygenase-1/biliverdin reductase-A (HO-1/BVR-A) system is one of the earlier events in the adaptive response to stress. HO-1/BVR-A reduces the intracellular levels of pro-oxidant heme and generates equimolar amounts of the free radical scavengers biliverdin-IX alpha (BV)/bilirubin-IX alpha (BR) as well as the pleiotropic gaseous neuromodulator carbon monoxide (CO) and ferrous iron. Two main and opposite hypotheses for a role of the HO-1/BVR-A system in AD propose that this system mediates neurotoxic and neuroprotective effects, respectively. This apparent controversy was mainly due to the fact that for over about 20years HO-1 was the only player on which all the analyses were focused, excluding the other important and essential component of the entire system, BVR. Following studies from the Butterfield laboratory that reported alterations in BVR activity along with decreased phosphorylation and increased oxidative/nitrosative post-translational modifications in the brain of subjects with AD and amnestic mild cognitive impairment (MCI) subjects, a debate was opened on the real pathophysiological and clinical significance of BVR-A. In this paper we provide a review of the main discoveries about the HO/BVR system in AD and MCI, and propose a mechanism that reconciles these two hypotheses noted above of neurotoxic and the neuroprotective aspects of this important stress responsive system.