Amyloid-plaque imaging in early and differential diagnosis of dementia

Neuropsychological and Neuroanatomical Features of Patients with Behavioral/Dysexecutive Variant Alzheimer’s disease (AD): A Comparison to Behavioral Variant Frontotemporal Dementia and Amnestic AD Groups

Background: An understudied variant of Alzheimer’s disease (AD), the behavioral/dysexecutive variant of AD (bvAD), is associated with progressive personality, behavior, and/or executive dysfunction and frontal atrophy. Objective: This study characterizes the neuropsychological and neuroanatomical features associated with bvAD by comparing it to behavioral variant frontotemporal dementia (bvFTD), amnestic AD (aAD), and subjects with normal cognition. Methods: Subjects included 16 bvAD, 67 bvFTD, and 18 aAD patients, and 26 healthy controls. Neuropsychological assessment and MRI data were compared between these groups. Results: Compared to bvFTD, bvAD showed more significant visuospatial impairments (Rey Figure copy and recall), more irritability (Neuropsychological Inventory), and equivalent verbal memory (Philadelphia Verbal Learning Test). Compared to aAD, bvAD indicated more executive dysfunction (F-letter fluency) and better visuospatial performance. Neuroimaging analysis found that bvAD showed cortical thinning relative to bvFTD posteriorly in left temporal-occipital regions; bvFTD had cortical thinning relative to bvAD in left inferior frontal cortex. bvAD had cortical thinning relative to aAD in prefrontal and anterior temporal regions. All patient groups had lower volumes than controls in both anterior and posterior hippocampus. However, bvAD patients had higher average volume than aAD patients in posterior hippocampus and higher volume than bvFTD patients in anterior hippocampus after adjustment for age and intracranial volume. Conclusion: Findings demonstrated that underlying pathology mediates disease presentation in bvAD and bvFTD.

Prognosis of Alzheimer's Disease Using Quantitative Mass Spectrometry of Human Blood Plasma Proteins and Machine Learning

Early recognition of the risk of Alzheimer's disease (AD) onset is a global challenge that requires the development of reliable and affordable screening methods for wide-scale application. Proteomic studies of blood plasma are of particular relevance; however, the currently proposed differentiating markers are poorly consistent. The targeted quantitative multiple reaction monitoring (MRM) assay of the reported candidate biomarkers (CBs) can contribute to the creation of a consistent marker panel. An MRM-MS analysis of 149 nondepleted EDTA-plasma samples (MHRC, Russia) of patients with AD (n = 47), mild cognitive impairment (MCI, n = 36), vascular dementia (n = 8), frontotemporal dementia (n = 15), and an elderly control group (n = 43) was performed using the BAK 125 kit (MRM Proteomics Inc., Canada). Statistical analysis revealed a significant decrease in the levels of afamin, apolipoprotein E, biotinidase, and serum paraoxonase/arylesterase 1 associated with AD. Different training algorithms for machine learning were performed to identify the protein panels and build corresponding classifiers for the AD prognosis. Machine learning revealed 31 proteins that are important for AD differentiation and mostly include reported earlier CBs. The best-performing classifiers reached 80% accuracy, 79.4% sensitivity and 83.6% specificity and were able to assess the risk of developing AD over the next 3 years for patients with MCI. Overall, this study demonstrates the high potential of the MRM approach combined with machine learning to confirm the significance of previously identified CBs and to propose consistent protein marker panels.

Mars Shot for Nuclear Medicine, Molecular Imaging, and Molecularly Targeted Radiopharmaceutical Therapy

The Society of Nuclear Medicine and Molecular Imaging created the Value Initiative in 2017 as a major component of its strategic plan to further demonstrate the value of molecular imaging and molecularly targeted radiopharmaceutical therapy to patients, physicians, payers, and funding agencies. The research and discovery domain, 1 of 5 under the Value Initiative, has a goal of advancing the research and development of diagnostic and therapeutic nuclear medicine. Research and discovery efforts and achievements are essential to ensure a bright future for NM and to translate science to practice. Given the remarkable progress in the field, leaders from the research and discovery domain and society councils identified 5 broad areas of opportunity with potential for substantive growth and clinical impact. This article discusses these 5 growth areas, identifying specific areas of particularly high importance for future study and development. As there was an understanding that goals should be both visionary yet achievable, this effort was called the Mars shot for nuclear medicine.

In vivo Imaging With 18F-FDG- and 18F-Florbetaben-PET/MRI Detects Pathological Changes in the Brain of the Commonly Used 5XFAD Mouse Model of Alzheimer's Disease

Imaging biomarkers of Alzheimer's disease (AD) that are able to detect molecular changes in vivo and transgenic animal models mimicking AD pathologies are essential for the evaluation of new therapeutic strategies. Positron-emission tomography (PET) using either ¹⁸F-Fluorodeoxyglucose (¹⁸F-FDG) or amyloid-tracers is a well-established, non-invasive tool in the clinical diagnostics of AD assessing two major pathological hallmarks. ¹⁸F-FDG-PET is able to detect early changes in cerebral glucose metabolism and amyloid-PET shows cerebral amyloid load. However, the suitability of ¹⁸F-FDG- and amyloid-PET in the widely used 5XFAD mouse model of AD is unclear as only a few studies on the use of PET biomarkers are available showing some conflicting results. The aim of this study was the evaluation of ¹⁸F-FDG-PET and amyloid-PET in 5XFAD mice in comparison to neurological deficits and neuropathological changes. Seven- and 12-month-old male 5XFAD mice showed a significant reduction in brain glucose metabolism in ¹⁸F-FDG-PET and amyloid-PET with ¹⁸F-Florbetaben demonstrated an increased cerebral amyloid deposition (n = 4-6 per group). Deficits in spatial reference memory were detected in 12-month-old 5XFAD mice in the Morris Water Maze (n = 10-12 per group). Furthermore, an increased plaque load and gliosis could be proven immunohistochemically in 5XFAD mice (n = 4-6 per group). PET biomarkers ¹⁸F-FDG and ¹⁸F-Florbetaben detected cerebral hypometabolism and increased plaque load even before the onset of severe memory deficits. Therefore, the 5XFAD mouse model of AD is well-suited for in vivo monitoring of AD pathologies and longitudinal testing of new therapeutic approaches.

Nuclear medical imaging as part of dementia diagnostics in psychiatric day-care clinics and inpatient care settings

BACKGROUND

Current guidelines support the use of nuclear medical imaging (NMI) techniques for differential diagnostics of certain cases of dementia.

AIMS

We aimed at studying the association between using NMI and the accuracy of dementia diagnoses. Additionally, we evaluated the effect of conducting NMI on the duration of hospital treatment.

METHODS

This study was based on data collected according to §21 of the German hospital remuneration law, including relevant diagnostic and procedural codes for NMI in dementia patients. In total, more than 7.2 million cases treated in German psychiatric and somatic hospitals between 2015 and 2017 were included. Associations between the frequency of NMI and the accuracy of dementia diagnoses in terms of specific vs. unspecific diagnostic codes were analyzed using Fischer's exact test.

RESULTS

In total, 351,106 cases with a dementia diagnosis were encoded during the study period. NMI was performed in 1.03% or 0.15% of all patients with dementia in psychiatric or somatic clinics, respectively. In psychiatric clinics, the proportion of unspecific dementia diagnoses decreased from 20.86% in 2015 to 17.73% in 2017. NMI was mainly performed within psychiatric day-care settings. Interestingly, patients receiving NMI stayed shorter within day-care settings (8.1 ± 16.0 days) compared to inpatient settings (38.3 ± 44.7 days).

CONCLUSIONS

Nuclear medical imaging is often performed in psychiatric day-care settings. Further studies are warranted to understand the predictive diagnostic value of NMI in dementia diagnosis compared with clinical, CSF and structural imaging in different healthcare settings.

Current radiotracers to image neurodegenerative diseases

The term of neurodegenerative diseases covers a heterogeneous group of disorders that are distinguished by progressive degeneration of the structure and function of the nervous system such as dementias, movement disorders, motor neuron disorders, as well as some prion disorders. In recent years, a paradigm shift started for the diagnosis of neurodegenerative diseases, for which successively clinical testing is supplemented by biomarker information. In research scenarios, it was even proposed recently to substitute the current syndromic by a biological definition of Alzheimer's diseases. PET examinations with various radiotracers play an important role in providing non-invasive biomarkers and co-morbidity information in neurodegeneration. Information on co-morbidity, e.g. Aβ plaques and Lewy-bodies or Aβ plaques in patients with aphasia or the absence of Aβ plaques in clinical AD patients are of interest to expand our knowledge about the pathogenesis of different phenotypically defined neurodegenerative diseases. Moreover, this information is also important in therapeutic trials targeting histopathological abnormalities.The aim of this review is to present an overview of the currently available radiotracers for imaging neurodegenerative diseases in research and in routine clinical settings. In this context, we also provide a short summary of the most frequent neurodegenerative diseases from a nuclear medicine point of view, their clinical and pathophysiological as well as nuclear imaging characteristics, and the resulting need for new radiotracers.

[The importance of molecular imaging (PET) in the diagnostics of dementia]

Due to the expanding older population and increasing prevalence of dementia and currently lacking curative therapy but potentially conceivable availability of molecular-specific treatment to delay the progression of cognitive decline, the early diagnosis of cognitive deficits and their etiological differential diagnosis becomes increasingly more important. The advances in nuclear medicine diagnostics in the field of neurodegenerative diseases within the last few years have been substantial. In this article the relevance of these technologies in the diagnostic process of dementia is described.

Biomarkers study in atypical dementia: proof of a diagnostic work-up

BACKGROUND

An early differentiation between Alzheimer's Disease (AD) and other dementias is crucial for an adequate patients' management, albeit it may result difficult for the occurrence of "atypical presentations." Current diagnostic criteria recognize the importance of biomarkers for AD diagnosis, but still an optimal diagnostic work-up isn't available.

OBJECTIVE

Evaluate the utility and reproducibility of biomarkers and propose an "optimal" diagnostic work-up in atypical dementia.

METHODS

(1) a retrospective selection of "atypical dementia cases"; (2) a repetition of diagnostic assessment by two neurologists following two different diagnostic work-ups, each consisting of multiple steps; (3) a comparison between diagnostic accuracy and confidence reached at each step by both neurologists and evaluation of the inter-rater agreement.

RESULTS

In AD, regardless of the undertaken diagnostic work-up, a significant gain in accuracy was reached by both neurologists after the second step, whereas in frontotemporal dementia (FTD), adding subsequent steps was not always sufficient to increase significantly the baseline accuracy. A relevant increment in diagnostic confidence was detectable after studying pathophysiological markers in AD, and after assessing brain metabolism in FTD. The inter-rater agreement was higher at the second step for the AD group when the pathophysiological markers were available and for the FTD group when the results of FDG-PET were accessible.

CONCLUSIONS

In atypical cases of dementia, biomarkers significantly raise diagnostic accuracy, confidence, and agreement. This study introduces a proof of diagnostic work-up that combines imaging and CSF biomarkers and suggests distinct ways to proceed on the basis of a greater diagnostic likelihood.

[German Society of Nuclear Medicine procedure guideline on beta-amyloid brain PET imaging]

Recently, a number of positron emission tomography (PET) radiotracers have been approved for clinical use. These tracers target cerebral beta-amyloid (Aβ) plaques, a hallmark of Alzheimer's disease. Increasing use of this method implies the need for respective standards. This German Society of Nuclear Medicine guideline describes adequate procedures for Aβ plaque PET imaging. It not only discusses the tracers used for that purpose, but also lists measures for correct patient preparation, image data generation, processing, analysis and interpretation. With that, this "S1" category (according to the German Association of the Scientific Medical Societies standard) guideline aims at contributing to quality assurance of nuclear imaging in Germany.

A survey of FDG- and amyloid-PET imaging in dementia and GRADE analysis

PET based tools can improve the early diagnosis of Alzheimer's disease (AD) and differential diagnosis of dementia. The importance of identifying individuals at risk of developing dementia among people with subjective cognitive complaints or mild cognitive impairment has clinical, social, and therapeutic implications. Within the two major classes of AD biomarkers currently identified, that is, markers of pathology and neurodegeneration, amyloid- and FDG-PET imaging represent decisive tools for their measurement. As a consequence, the PET tools have been recognized to be of crucial value in the recent guidelines for the early diagnosis of AD and other dementia conditions. The references based recommendations, however, include large PET imaging literature based on visual methods that greatly reduces sensitivity and specificity and lacks a clear cut-off between normal and pathological findings. PET imaging can be assessed using parametric or voxel-wise analyses by comparing the subject's scan with a normative data set, significantly increasing the diagnostic accuracy. This paper is a survey of the relevant literature on FDG and amyloid-PET imaging aimed at providing the value of quantification for the early and differential diagnosis of AD. This allowed a meta-analysis and GRADE analysis revealing high values for PET imaging that might be useful in considering recommendations.

Biomarker modeling of Alzheimer's disease

Alzheimer's disease (AD) is a slowly progressing disorder in which pathophysiological abnormalities, detectable in vivo by biomarkers, precede overt clinical symptoms by many years to decades. Five AD biomarkers are sufficiently validated to have been incorporated into clinical diagnostic criteria and commonly used in therapeutic trials. Current AD biomarkers fall into two categories: biomarkers of amyloid-β plaques and of tau-related neurodegeneration. Three of the five are imaging measures and two are cerebrospinal fluid analytes. AD biomarkers do not evolve in an identical manner but rather in a sequential but temporally overlapping manner. Models of the temporal evolution of AD biomarkers can take the form of plots of biomarker severity (degree of abnormality) versus time. In this Review, we discuss several time-dependent models of AD that take into consideration varying age of onset (early versus late) and the influence of aging and co-occurring brain pathologies that commonly arise in the elderly.

Structural and Functional Magnetic Resonance Imaging: Mild Cognitive Impairment and Alzheimer Disease

Magnetic resonance (MR) imaging is playing an increasingly pivotal role in the clinical management of dementia, including Alzheimer disease (AD). In addition to established MR imaging procedures, the introduction of advanced instrumentation such as 7-T MR imaging, as well as novel MR imaging sequences such as arterial spin labeling, MR spectroscopy, diffusion tensor imaging, and resting-state functional MR imaging, may open new pathways toward improved diagnosis of AD even in early stages of disease such as mild cognitive impairment (MCI). This article describes the typical findings of established and new MR imaging procedures in healthy aging, MCI, and AD.

Binding of Congo red to amyloid protofibrils of the Alzheimer Aβ(9-40) peptide probed by molecular dynamics simulations

Congo red (CR) is a commonly used histological amyloid dye and a weak amyloid inhibitor. There is currently no experimentally available structure of CR bound to an amyloid fibril and the binding modes, and the mechanisms governing its inhibitory and optical properties are poorly understood. In this work, we present the first, to our knowledge, atomistically detailed picture of CR binding to protofibrils of the Alzheimer Aβ(9-40) peptide. We identify three major binding modes, with the primary mode residing in the grooves formed by the β-sheets, and observe a restriction of the torsional rotation of the CR molecule upon binding. Our simulations reveal a novel, to our knowledge, electrostatic steering mechanism that plays an important role in the initial recognition and binding of CR to the positively charged surface residues of the fibril. Our simulations provide new, to our knowledge, insights into the striking spectrophotometric and inhibitory properties of CR. In particular, we show that birefringence upon CR binding is due to the anisotropic orientation of the CR dipoles resulting from the spatial ordering of these molecules in the grooves along the fibril axis. The fluorescent enhancement of the bound CR, in turn, is associated with the torsional restriction of this molecule upon binding.

Alzheimer’s disease, cerebrovascular disease, and the β-amyloid cascade

Alzheimer’s disease (AD), considered the commonest neurodegenerative cause of dementia, is associated with hallmark pathologies including extracellular amyloid-β protein (Aβ) deposition in extracellular senile plaques and vessels, and intraneuronal tau deposition as neurofibrillary tangles. Although AD is usually categorized as neurodegeneration distinct from cerebrovascular disease (CVD), studies have shown strong links between AD and CVD. There is evidence that vascular risk factors and CVD may accelerate Aβ 40-42 production/ aggregation/deposition and contribute to the pathology and symptomatology of AD. Aβ deposited along vessels also causes cerebral amyloid angiopathy. Amyloid imaging allows in vivo detection of AD pathology, opening the way for prevention and early treatment, if disease-modifying therapies in the pipeline show safety and efficacy. In this review, we review the role of vascular factors and Aβ, underlining that vascular risk factor management may be important for AD prevention and treatment.

Influence of scan duration on the accuracy of β-amyloid PET with florbetaben in patients with Alzheimer's disease and healthy volunteers

PURPOSE

Florbetaben is a β-amyloid-targeted PET tracer with significant potential for augmenting the toolbox in the clinical diagnosis of Alzheimer's disease (AD). In dementia imaging, shortening of scan duration may simplify future clinical use. The aim of this retrospective study was to investigate the effect of scan duration on diagnostic accuracy.

METHODS

PET scans obtained from 25 AD patients and 25 healthy volunteers (HVs) were analysed. In each subject, scans of three different durations (5, 10 and 20 min; all starting 90 min after injection) were obtained, randomized, and visually assessed by three experts blinded to the subject's identity and group affiliation. Presence/absence of β-amyloid and diagnostic confidence (0-100 %) were scored, and 10 % of the scans were re-read. Further, randomly selected datasets of ten AD patients and ten HVs were quantified using an established VOI-based approach and using a voxel-based approach.

RESULTS

The sensitivity and specificity of the blinded read were 80 % and 96 %, respectively, for all scan durations. Diagnostic confidence was high (97 ± 6 %, 97 ± 6 % and 95 ± 8 % for the 20-min, 10-min and 5-min scans, respectively; n.s.), as was interreader agreement (kappa(20 min) = 0.94, kappa(10 min) = 0.94, kappa(5 min) = 0.89; n.s.). Intrareader agreement was highest for the 20-min scan (kappa = 1.00) and lower for the 10-min scan (kappa = 0.71) and 5-min scan (kappa = 0.80; p = 0.002 and 0.003 vs. the 20-min scan). For all scan durations, composite SUVRs (Cohen's d effect size 4.5, 3.9 and 4.8 for the 5-min, 10-min and 20-min scans; p < 0.0001 each) and individual brain volumes affected by β-amyloid (Cohen's d effect size 1.6, 1.8 and 2.0 for the 5-min, 10-min and 20-min scans; p < 0.005 each) were significantly higher in AD patients than in HVs.

CONCLUSION

Reduction in scan duration did not relevantly affect the accuracy of florbetaben PET scans in discriminating between AD patients and HVs. Thus, a reduction in scan duration seems conceivable for the future clinical use of florbetaben.

On the origin of the stronger binding of PIB over thioflavin T to protofibrils of the Alzheimer amyloid-β peptide: a molecular dynamics study

Pittsburgh compound B (PIB) is a neutral derivative of the fluorescent dye Thioflavin T (ThT), which displays enhanced hydrophobicity and binding affinity to amyloid fibrils. We present molecular dynamics simulations of binding of PIB and ThT to a common cross-β-subunit of the Alzheimer Amyloid-β peptide (Aβ). Our simulations of binding to Aβ(9-40) protofibrils show that PIB, like ThT, selectively binds to the hydrophobic or aromatic surface grooves on the β-sheet surface along the fibril axis. The lack of two methyl groups and charge in PIB not only improves its hydrophobicity but also leads to a deeper insertion of PIB compared to ThT into the surface grooves. This significantly increases the steric, aromatic, and hydrophobic interactions, and hence leads to stronger binding. Simulations on protofibrils consisting of the more-toxic Aβ(17-42) revealed an additional binding mode in which PIB and ThT insert into the channel that forms in the loop region of the protofibril, sandwiched between two sheet layers. Our simulations indicate that the rotation between the two ring parts of the dyes is significantly more restricted when the dyes are bound to the surface of the cross-β-subunits or to the channel inside the Aβ(17-42) cross-β-subunit, compared with free solution. The specific conformations of the dyes are influenced by small chemical modifications (ThT versus PIB) and by the environment in which the dye is placed.

Neuronal dysfunction and disconnection of cortical hubs in non-demented subjects with elevated amyloid burden

Disruption of functional connectivity between brain regions may represent an early functional consequence of β-amyloid pathology prior to clinical Alzheimer's disease. We aimed to investigate if non-demented older individuals with increased amyloid burden demonstrate disruptions of functional whole-brain connectivity in cortical hubs (brain regions typically highly connected to multiple other brain areas) and if these disruptions are associated with neuronal dysfunction as measured with fluorodeoxyglucose-positron emission tomography. In healthy subjects without cognitive symptoms and patients with mild cognitive impairment, we used positron emission tomography to assess amyloid burden and cerebral glucose metabolism, structural magnetic resonance imaging to quantify atrophy and novel resting state functional magnetic resonance imaging processing methods to calculate whole-brain connectivity. Significant disruptions of whole-brain connectivity were found in amyloid-positive patients with mild cognitive impairment in typical cortical hubs (posterior cingulate cortex/precuneus), strongly overlapping with regional hypometabolism. Subtle connectivity disruptions and hypometabolism were already present in amyloid-positive asymptomatic subjects. Voxel-based morphometry measures indicate that these findings were not solely a consequence of regional atrophy. Whole-brain connectivity values and metabolism showed a positive correlation with each other and a negative correlation with amyloid burden. These results indicate that disruption of functional connectivity and hypometabolism may represent early functional consequences of emerging molecular Alzheimer's disease pathology, evolving prior to clinical onset of dementia. The spatial overlap between hypometabolism and disruption of connectivity in cortical hubs points to a particular susceptibility of these regions to early Alzheimer's-type neurodegeneration and may reflect a link between synaptic dysfunction and functional disconnection.

Optimization of automated radiosynthesis of [18F]AV-45: a new PET imaging agent for Alzheimer's disease

INTRODUCTION

Accumulation of β-amyloid (Aβ) aggregates in the brain is linked to the pathogenesis of Alzheimer's disease (AD). Imaging probes targeting these Aβ aggregates in the brain may provide a useful tool to facilitate the diagnosis of AD. Recently, [(18)F]AV-45 ([(18)F]5) demonstrated high binding to the Aβ aggregates in AD patients. To improve the availability of this agent for widespread clinical application, a rapid, fully automated, high-yield, cGMP-compliant radiosynthesis was necessary for production of this probe. We report herein an optimal [(18)F]fluorination, de-protection condition and fully automated radiosynthesis of [(18)F]AV-45 ([(18)F]5) on a radiosynthesis module (BNU F-A2).

METHODS

The preparation of [(18)F]AV-45 ([(18)F]5) was evaluated under different conditions, specifically by employing different precursors (-OTs and -Br as the leaving group), reagents (K222/K(2)CO(3) vs. tributylammonium bicarbonate) and deprotection in different acids. With optimized conditions from these experiments, the automated synthesis of [(18)F]AV-45 ([(18)F]5) was accomplished by using a computer-programmed, standard operating procedure, and was purified on an on-line solid-phase cartridge (Oasis HLB).

RESULTS

The optimized reaction conditions were successfully implemented to an automated nucleophilic fluorination module. The radiochemical purity of [(18)F]AV-45 ([(18)F]5) was >95%, and the automated synthesis yield was 33.6 ± 5.2% (no decay corrected, n=4), 50.1 ± 7.9% (decay corrected) in 50 min at a quantity level of 10-100 mCi (370-3700 MBq). Autoradiography studies of [(18)F]AV-45 ([(18)F]5) using postmortem AD brain and Tg mouse brain sections in the presence of different concentration of "cold" AV-136 showed a relatively low inhibition of in vitro binding of [(18)F]AV-45 ([(18)F]5) to the Aβ plaques (IC50=1-4 μM, a concentration several order of magnitude higher than the expected pseudo carrier concentration in the brain).

CONCLUSIONS

Solid-phase extraction purification and improved labeling conditions were successfully implemented into an automated synthesis module, which is more convenient, highly efficient and simpler in operation than using a semipreparative high-performance liquid chromatography method. This new, automated procedure for preparation of [(18)F]AV-45 ([(18)F]5) is suitable for routine clinical application.