Amyloid PET imaging: applications beyond Alzheimer's disease

Clinical outcomes up to 9 years after [18F]flutemetamol amyloid-PET in a symptomatic memory clinic population

BACKGROUND

Previous studies demonstrated increases in diagnostic confidence and change in patient management after amyloid-PET. However, studies investigating longitudinal outcomes over an extended period of time are limited. Therefore, we aimed to investigate clinical outcomes up to 9 years after amyloid-PET to support the clinical validity of the imaging technique.

METHODS

We analyzed longitudinal data from 200 patients (Mage = 61.8, 45.5% female, MMMSE = 23.3) suspected of early-onset dementia that underwent [18F]flutemetamol-PET. Baseline amyloid status was determined through visual read (VR). Information on mortality was available with a mean follow-up of 6.7 years (range = 1.1-9.3). In a subset of 108 patients, longitudinal cognitive scores and clinical etiological diagnosis (eDx) at least 1 year after amyloid-PET acquisition were available (M = 3.06 years, range = 1.00-7.02). VR - and VR + patients were compared on mortality rates with Cox Hazard's model, prevalence of stable eDx using chi-square test, and longitudinal cognition with linear mixed models. Neuropathological data was available for 4 patients (mean delay = 3.59 ± 1.82 years, range = 1.2-6.3).

RESULTS

At baseline, 184 (92.0%) patients were considered to have dementia. The majority of VR + patients had a primary etiological diagnosis of AD (122/128, 95.3%), while the VR - group consisted mostly of non-AD etiologies, most commonly frontotemporal lobar degeneration (30/72, 40.2%). Overall mortality rate was 48.5% and did not differ between VR - and VR + patients. eDx at follow-up was consistent with baseline diagnosis for 92/108 (85.2%) patients, with most changes observed in VR - cases (VR -  = 14/35, 40% vs VR +  = 2/73, 2.7%, χ2 = 26.03, p < 0.001), who at no time received an AD diagnosis. VR + patients declined faster than VR - patients based on MMSE (β =  - 1.17, p = 0.004), episodic memory (β =  - 0.78, p = 0.003), fluency (β =  - 1.44, p < 0.001), and attention scores (β = 16.76, p = 0.03). Amyloid-PET assessment was in line with post-mortem confirmation in all cases; two cases were VR + and showed widespread AD pathology, while the other two cases were VR - and showed limited amyloid pathology.

CONCLUSION

In a symptomatic population, we observed that amyloid-status did not impact mortality rates, but is predictive of cognitive functioning over time across several domains. Also, we show particular validity for a negative amyloid-PET assessment, as these patients did not receive an AD diagnosis at follow-up.

What is New in Nuclear Medicine Imaging for Dementia

Advances in the molecular biology, pathology and genetics of Alzheimer's disease (AD) and other degenerative dementias have led to the development of biomarkers specific to these diseases and radiotracers that are used in nuclear medicine. Imaging and non-imaging markers have enabled very early recognition of these diseases and have caused significant changes in their definitions. Amyloid positron emission tomography (PET) and tau PET, which are molecular imaging methods, [F18]fluorodeoxyglucose (FDG) PET showing the glucose metabolism pattern in the brain, dopamine transporter single photon emission computerized tomography (SPECT) that marks dopaminergic terminals are valuable tools for early recognition and differentiation of AD and its atypical variants, frontotemporal dementias and dementia with Lewy bodies. These imaging methods, which have different advantages over each other, have different indications for use and sometimes provide complementary information. In addition, research on radiotracers targeting neuroinflammation, astrocytes, synaptic density, and cholinergic terminals is ongoing. In this review, routinely used and newly developed nuclear imaging methods in AD and other neurodegenerative dementias, the agents used and their diagnostic features will be presented together with case examples.

Solitary Isolated Dural Metastasis From Lung Adenocarcinoma Mimicking Meningioma

ABSTRACT

Solitary isolated dural metastasis is extremely rare. Distinguishing solitary dural metastasis from meningioma based on radiological findings can be challenging. We describe MRI and FDG PET/CT findings in 2 cases of histologically proved solitary isolated dural metastasis from lung adenocarcinoma. Enhanced brain MRI of the 2 cases showed parafalcine extra-axial, dural-based tumors with hypervascularity mimicking meningioma. Preoperative FDG PET/CT was performed in one case with a known history of lung adenocarcinoma showing intense FDG uptake of the parafalcine tumor. Postoperative FDG PET/CT was performed in the other case showing solitary lung tumor, suggestive of the primary tumor.

Development and in vivo Evaluation of Hydroxy-α-Sanshool Intranasal Liposomes as a Potential Remedial Treatment for Alzheimer’s Disease

Purpose

Hydroxy-α-sanshool (HAS) improves cognitive dysfunction, but its structural instability has limited its clinical application. The present study was conducted to investigate the optimal formulation of hydroxy-α-sanshool liposomes (HAS-LPs) and its effect on ameliorating learning and memory disorders in an Alzheimer’s disease (AD) model.

Methods

In this study, HAS was prepared as HAS-LP using a thin film dispersion method. After selecting the optimal preparation conditions, HAS-LP was characterized using transmission electron microscopy (TEM) and by measuring the zeta potential, particle size, and in vitro drug release. Next, evaluated the effect of HAS-LP on the rat nasal mucosa and then applied it to AD mice. By performing behaviour experiments, pathological test and related pharmacokinetic parameters, we explored its effect on attenuating learning and memory impairment in mice.

Results

When the mass ratio of HAS:cholesterol:soybean lecithin was 1:4:16 and 15 mL of ultrapure water were added, the highest encapsulation efficiency and drug loading were obtained. HAS-LP had a particle size of 181.77 nm, a polydispersity index of 0.207 and a zeta potential of −53.8 mV, and it remained stable at 25 °C for 1 week and 4 °C for 8 weeks. Moreover, HAS-LP exhibited slow drug release and was highly consistent with the Higuchi release model. HAS-LP was not significantly toxic to the nasal mucosa and effectively alleviated D-galactose-induced learning memory deficits and protected mouse hippocampal neuronal cells. HAS-LP was highly enriched in plasma and brain tissue after administration via the nasal route and obtained some ability to target the brain.

Conclusion

HAS encapsulated in soybean lecithin and cholesterol was successfully developed, suggesting that treatment with the nanoparticles might reverse some AD symptoms. Therefore, these nanoparticles might be used as promising new candidates for the delivery of HAS to treat AD.

Positron Emission Tomography in Animal Models of Alzheimer's Disease Amyloidosis: Translational Implications

Animal models of Alzheimer's disease amyloidosis that recapitulate cerebral amyloid-beta pathology have been widely used in preclinical research and have greatly enabled the mechanistic understanding of Alzheimer's disease and the development of therapeutics. Comprehensive deep phenotyping of the pathophysiological and biochemical features in these animal models is essential. Recent advances in positron emission tomography have allowed the non-invasive visualization of the alterations in the brain of animal models and in patients with Alzheimer's disease. These tools have facilitated our understanding of disease mechanisms and provided longitudinal monitoring of treatment effects in animal models of Alzheimer's disease amyloidosis. In this review, we focus on recent positron emission tomography studies of cerebral amyloid-beta accumulation, hypoglucose metabolism, synaptic and neurotransmitter receptor deficits (cholinergic and glutamatergic system), blood-brain barrier impairment, and neuroinflammation (microgliosis and astrocytosis) in animal models of Alzheimer's disease amyloidosis. We further propose the emerging targets and tracers for reflecting the pathophysiological changes and discuss outstanding challenges in disease animal models and future outlook in the on-chip characterization of imaging biomarkers towards clinical translation.

18F-florbetapir PET as a marker of myelin integrity across the Alzheimer's disease spectrum

Purpose

Recent evidence suggests that PET imaging with amyloid-β (Aβ) tracers can be used to assess myelin integrity in cerebral white matter (WM). Alzheimer’s disease (AD) is characterized by myelin changes that are believed to occur early in the disease course. Nevertheless, the extent to which demyelination, as measured with Aβ PET, contributes to AD progression remains unexplored.

Methods

Participants with concurrent ¹⁸F-florbetapir (FBP) PET, MRI, and cerebrospinal fluid (CSF) examinations were included (241 cognitively normal, 347 Aβ-positive cognitively impaired, and 207 Aβ-negative cognitively impaired subjects). A subset of these participants had also available diffusion tensor imaging (DTI) images (n = 195). We investigated cross-sectional associations of FBP retention in the white matter (WM) with MRI-based markers of WM degeneration, AD clinical progression, and fluid biomarkers. In longitudinal analyses, we used linear mixed models to assess whether FBP retention in normal-appearing WM (NAWM) predicted progression of WM hyperintensity (WMH) burden and clinical decline.

Results

In AD-continuum individuals, FBP retention in NAWM was (1) higher compared with WMH regions, (2) associated with DTI-based measures of WM integrity, and (3) associated with longitudinal progression of WMH burden. FBP uptake in WM decreased across the AD continuum and with increasingly abnormal CSF biomarkers of AD. Furthermore, FBP retention in the WM was associated with large-calibre axon degeneration as reflected by abnormal plasma neurofilament light chain levels. Low FBP uptake in NAWM predicted clinical decline in preclinical and prodromal AD, independent of demographics, global cortical Aβ, and WMH burden. Most of these associations were also observed in Aβ-negative cognitively impaired individuals.

Conclusion

These results support the hypothesis that FBP retention in the WM is myelin-related. Demyelination levels progressed across the AD continuum and were associated with clinical progression at early stages, suggesting that this pathologic process might be a relevant degenerative feature in the disease course.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00259-021-05493-y.

Validation of amyloid PET positivity thresholds in centiloids: a multisite PET study approach

Background

Inconsistent positivity thresholds, image analysis pipelines, and quantitative outcomes are key challenges of multisite studies using more than one β-amyloid (Aβ) radiotracer in positron emission tomography (PET). Variability related to these factors contributes to disagreement and lack of replicability in research and clinical trials. To address these problems and promote Aβ PET harmonization, we used [¹⁸F]florbetaben (FBB) and [¹⁸F]florbetapir (FBP) data from the Alzheimer’s Disease Neuroimaging Initiative (ADNI) to derive (1) standardized Centiloid (CL) transformations and (2) internally consistent positivity thresholds based on separate young control samples.

Methods

We analyzed Aβ PET data using a native-space, automated image processing pipeline that is used for PET quantification in many large, multisite AD studies and trials and made available to the research community. With this pipeline, we derived SUVR-to-CL transformations using the Global Alzheimer’s Association Interactive Network data; we used reference regions for cross-sectional (whole cerebellum) and longitudinal (subcortical white matter, brain stem, whole cerebellum) analyses. Finally, we developed a FBB positivity threshold using an independent young control sample (N=62) with methods parallel to our existing FBP positivity threshold and validated the FBB threshold using a data-driven approach in ADNI participants (N=295).

Results

The FBB threshold based on the young sample (1.08; 18 CL) was consistent with that of the data-driven approach (1.10; 21 CL), and the existing FBP threshold converted to CL with the derived transformation (1.11; 20 CL). The following equations can be used to convert whole cerebellum- (cross-sectional) and composite- (longitudinal) normalized FBB and FBP data quantified with the native-space pipeline to CL units:

[¹⁸F]FBB: CL_{whole cerebellum} = 157.15 × SUVR_FBB − 151.87; threshold=1.08, 18 CL

[¹⁸F]FBP: CL_{whole cerebellum} = 188.22 × SUVR_FBP − 189.16; threshold=1.11, 20 CL

[¹⁸F]FBB: CL_composite = 244.20 × SUVR_FBB − 170.80

[¹⁸F]FBP: CL_composite = 300.66 × SUVR_FBP − 208.84

Conclusions

FBB and FBP positivity thresholds derived from independent young control samples and quantified using an automated, native-space approach result in similar CL values. These findings are applicable to thousands of available and anticipated outcomes analyzed using this pipeline and shared with the scientific community. This work demonstrates the feasibility of harmonized PET acquisition and analysis in multisite PET studies and internal consistency of positivity thresholds in standardized units.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13195-021-00836-1.

Multimodality Imaging of Dementia: Clinical Importance and Role of Integrated Anatomic and Molecular Imaging

Neurodegenerative diseases are a devastating group of disorders that can be difficult to accurately diagnose. Although these disorders are difficult to manage owing to relatively limited treatment options, an early and correct diagnosis can help with managing symptoms and coping with the later stages of these disease processes. Both anatomic structural imaging and physiologic molecular imaging have evolved to a state in which these neurodegenerative processes can be identified relatively early with high accuracy. To determine the underlying disease, the radiologist should understand the different distributions and pathophysiologic processes involved. High-spatial-resolution MRI allows detection of subtle morphologic changes, as well as potential complications and alternate diagnoses, while molecular imaging allows visualization of altered function or abnormal increased or decreased concentration of disease-specific markers. These methodologies are complementary. Appropriate workup and interpretation of diagnostic studies require an integrated, multimodality, multidisciplinary approach. This article reviews the protocols and findings at MRI and nuclear medicine imaging, including with the use of flurodeoxyglucose, amyloid tracers, and dopaminergic transporter imaging (ioflupane). The pathophysiology of some of the major neurodegenerative processes and their clinical presentations are also reviewed; this information is critical to understand how these imaging modalities work, and it aids in the integration of clinical data to help synthesize a final diagnosis. Radiologists and nuclear medicine physicians aiming to include the evaluation of neurodegenerative diseases in their practice should be aware of and familiar with the multiple imaging modalities available and how using these modalities is essential in the multidisciplinary management of patients with neurodegenerative diseases.^©RSNA, 2020.

Positron Emission Tomography (PET) and Neuroimaging in the Personalized Approach to Neurodegenerative Causes of Dementia

Generally, dementia should be considered an acquired syndrome, with multiple possible causes, rather than a specific disease in itself. The leading causes of dementia are neurodegenerative and non-neurodegenerative alterations. Nevertheless, the neurodegenerative group of diseases that lead to cognitive impairment and dementia includes multiple possibilities or mixed pathologies with personalized treatment management for each cause, even if Alzheimer's disease is the most common pathology. Therefore, an accurate differential diagnosis is mandatory in order to select the most appropriate therapy approach. The role of personalized assessment in the treatment of dementia is rapidly growing. Neuroimaging is an essential tool for differential diagnosis of multiple causes of dementia and allows a personalized diagnostic and therapeutic protocol based on risk factors that may improve treatment management, especially in early diagnosis during the prodromal stage. The utility of structural and functional imaging could be increased by standardization of acquisition and analysis methods and by the development of algorithms for automated assessment. The aim of this review is to focus on the most commonly used tracers for differential diagnosis in the dementia field. Particularly, we aim to explore ¹⁸F Fluorodeoxyglucose (FDG) and amyloid positron emission tomography (PET) imaging in Alzheimer's disease and in other neurodegenerative causes of dementia.

Multitracer model for staging cortical amyloid deposition using PET imaging

OBJECTIVE

To develop and evaluate a model for staging cortical amyloid deposition using PET with high generalizability.

METHODS

Three thousand twenty-seven individuals (1,763 cognitively unimpaired [CU], 658 impaired, 467 with Alzheimer disease [AD] dementia, 111 with non-AD dementia, and 28 with missing diagnosis) from 6 cohorts (European Medical Information Framework for AD, Alzheimer's and Family, Alzheimer's Biomarkers in Daily Practice, Amsterdam Dementia Cohort, Open Access Series of Imaging Studies [OASIS]-3, Alzheimer's Disease Neuroimaging Initiative [ADNI]) who underwent amyloid PET were retrospectively included; 1,049 individuals had follow-up scans. With application of dataset-specific cutoffs to global standard uptake value ratio (SUVr) values from 27 regions, single-tracer and pooled multitracer regional rankings were constructed from the frequency of abnormality across 400 CU individuals (100 per tracer). The pooled multitracer ranking was used to create a staging model consisting of 4 clusters of regions because it displayed a high and consistent correlation with each single-tracer ranking. Relationships between amyloid stage, clinical variables, and longitudinal cognitive decline were investigated.

RESULTS

SUVr abnormality was most frequently observed in cingulate, followed by orbitofrontal, precuneal, and insular cortices and then the associative, temporal, and occipital regions. Abnormal amyloid levels based on binary global SUVr classification were observed in 1.0%, 5.5%, 17.9%, 90.0%, and 100.0% of individuals in stage 0 to 4, respectively. Baseline stage predicted decline in Mini-Mental State Examination (MMSE) score (ADNI: n = 867, F = 67.37, p < 0.001; OASIS: n = 475, F = 9.12, p < 0.001) and faster progression toward an MMSE score ≤25 (ADNI: n = 787, hazard ratio [HR]stage1 2.00, HRstage2 3.53, HRstage3 4.55, HRstage4 9.91, p < 0.001; OASIS: n = 469, HRstage4 4.80, p < 0.001).

CONCLUSION

The pooled multitracer staging model successfully classified the level of amyloid burden in >3,000 individuals across cohorts and radiotracers and detects preglobal amyloid burden and distinct risk profiles of cognitive decline within globally amyloid-positive individuals.

Quantification of cardiac amyloid with [18F]Flutemetamol in patients with V30M hereditary transthyretin amyloidosis

Background: Hereditary transthyretin amyloid (ATTRv) is a systemic amyloidosis with mainly neurological and cardiac symptoms. The aim of this study was to evaluate the outcome of [¹⁸F]Flutemetamol PET/CT-scan of the heart in long-term survivors with ATTRV30M amyloidosis.Methods: Twenty-one patients with ATTRV30M amyloidosis and predominantly neurological symptoms, mainly negative on cardiac ^99mtechnetium-3,3-diphosphono-1,2-propanodicarboxylic acid (DPD)-scintigraphy, were examined with a dynamic [¹⁸F]Flutemetamol PET/CT-scan. Five patients suffering from Alzheimer's disease and one healthy individual served as controls. Volumes of interests were drawn over the intraventricular septum, lateral wall of the left ventricle and free wall of the right ventricle. Clinical records were reviewed for data from previous completed DPD-scintigraphy of the heart and echocardiography.Results: Patients with ATTRv amyloidosis had a higher cardiac uptake than the control-group in all analysed regions of the heart and could be identified with high accuracy (sensitivity 88%, specificity 100%) in static image acquisition at 30 or 60 min. We found no correlation between cardiac [¹⁸F]Flutemetamol uptake and clinical variables.Conclusion: In this small study of selected patients, cardiac [¹⁸F]Flutemetamol PET/CT could differentiate between healthy individuals and patients with ATTRV30M. [¹⁸F]Flutemetamol PET/CT imaging of amyloidosis in patients with a negative DPD-scintigraphy has a potential as a diagnostic method.

Nuclear medicine and molecular imaging advances in the 21st century

Currently, Nuclear Medicine has a clearly defined role in clinical practice due to its usefulness in many medical disciplines. It provides relevant diagnostic and therapeutic options leading to patients' healthcare and quality of life improvement. During the first two decades of the 21stt century, the number of Nuclear Medicine procedures increased considerably.Clinical and research advances in Nuclear Medicine and Molecular Imaging have been based on developments in radiopharmaceuticals and equipment, namely, the introduction of multimodality imaging. In addition, new therapeutic applications of radiopharmaceuticals, mainly in oncology, are underway.This review will focus on radiopharmaceuticals for positron emission tomography (PET), in particular, those labeled with Fluorine-18 and Gallium-68. Multimodality as a key player in clinical practice led to the development of new detector technology and combined efforts to improve resolution. The concept of dual probe (a single molecule labeled with a radionuclide for single photon emission computed tomography)/positron emission tomography and a light emitter for optical imaging) is gaining increasing acceptance, especially in minimally invasive radioguided surgery. The expansion of theranostics, using the same molecule for diagnosis (γ or positron emitter) and therapy (β minus or α emitter) is reshaping personalized medicine.Upcoming research and development efforts will lead to an even wider array of indications for Nuclear Medicine both in diagnosis and treatment.

Cardiac amyloidosis imaging with amyloid positron emission tomography: A systematic review and meta-analysis

BACKGROUND

Recent progress in amyloid positron emission tomography (PET) has enabled the targeted imaging of cardiac amyloidosis with accuracy. We performed a systematic review and meta-analysis on the diagnostic performance of cardiac amyloidosis using amyloid PET.

METHODS

A systematic search was performed using key words: cardiac amyloidosis, amyloid, and PET. We estimated the pooled sensitivity, specificity, positive and negative likelihood ratio (LR), and diagnostic odds ratio (DOR). Furthermore, the semiquantitative parameters of PET were evaluated to diagnose cardiac amyloidosis and discern its type [systemic light chain amyloidosis (AL) vs transthyretin amyloidosis (ATTR)] using the pooled standardized mean difference (SMD).

RESULTS

In total, six eligible studies with a total of 98 subjects were included in this meta-analysis. The pooled sensitivity was 0.95, the specificity was 0.98, positive LR was 10.130, negative LR was 0.1, and DOR was 148.83. The semiquantitative parameters of amyloid PET showed significantly higher values for cardiac amyloidosis patients than those for controls (pooled SMD = 1.42; P < .001), and in AL than ATTR (pooled SMD = 0.96; P < .001).

CONCLUSION

Amyloid PET imaging can be a useful method for diagnosing cardiac amyloidosis. The semiquantitative parameters of amyloid PET can help diagnose cardiac amyloidosis and discern its type.

Amyloid PET findings in multiple sclerosis are associated with cognitive decline at 18 months

OBJECTIVE

To study the clinical, cognitive, and radiological progression of a cohort of patients with MS, taking into account the amyloid PET with 18F-florbetaben analyses.

METHODS

Twenty-nine patients with MS were assessed with longitudinal structural MRI and a clinical and comprehensive neuropsychological protocol, with a mean interval between assessments of 18 ± 3.31 months. 18F-florbetaben PET was performed at baseline. Uptake was analysed in demyelinating plaques (DWM) and normal-appearing white matter (NAWM). Results were correlated with clinical, cognitive and MRI data.

RESULTS

Patients with cognitive decline over the follow-up period showed a lower standardised uptake value ratio in NAWM and lower thalamic volume and a higher lesion load in the baseline MRI. Myelin status was correlated with EDSS and cognitive tests mainly evaluating visuospatial function and working memory. Lower uptake in NAWM at baseline was also associated with a growth in white matter lesion volume over time.

CONCLUSIONS

Lower white matter uptake in amyloid PET is associated with cognitive decline and an increase in white matter lesion volume during the follow-up. Our study suggests that 18F-florbetaben may be a useful biomarker in assessing myelin status in MS, understanding MS pathophysiology, and predicting cognitive outcomes.

A new perspective for advanced positron emission tomography-based molecular imaging in neurodegenerative proteinopathies

Recent studies in neurodegenerative conditions have increasingly highlighted that the same neuropathology can trigger different clinical phenotypes or, vice-versa, that similar phenotypes can be triggered by different neuropathologies. This evidence has called for the adoption of a pathology spectrum-based approach to study neurodegenerative proteinopathies. These conditions share brain deposition of abnormal protein aggregates, leading to aberrant biochemical, metabolic, functional, and structural changes. Positron emission tomography (PET) is a well-recognized and unique tool for the in vivo assessment of brain neuropathology, and novel PET techniques are emerging for the study of specific protein species. Today, key applications of PET range from early research and clinical diagnostic tools to their use in clinical trials for both participants screening and outcome evaluation. This position article critically reviews the role of distinct PET molecular tracers for different neurodegenerative proteinopathies, highlighting their strengths, weaknesses, and opportunities, with special emphasis on methodological challenges and future applications.

Regional hypometabolism in the 3xTg mouse model of Alzheimer's disease

Alzheimer's disease (AD) is a progressive age-related neurodegenerative disease. Although neurofibrillary tangles and amyloid beta are classic hallmarks of AD, the earliest deficits in AD progression may be caused by unknown factors. One suspected factor has to do with brain energy metabolism. To investigate this factor, brain metabolic activity in 3xTg-AD mice and age-matched controls were measured with FDG-PET. Significant hypometabolic changes (p < .01) in brain metabolism were detected in the cortical piriform and insular regions of AD brains relative to controls. These regions are associated with olfaction, which is a potential clinical marker for AD progression as well as neurogenesis. The activity of the terminal component of the mitochondrial respiratory chain (complex IV) and the expression of complex I-V were significantly decreased (p < .05), suggesting that impaired metabolic activity coupled with impaired oxidative phosphorylation leads to decreased mitochondrial bioenergetics and subsequent Neurodegeneration. Although there is an association between neuroinflammatory pathological markers (microglial) and hypometabolism in AD, there was no association found between neuropathological (Aβ, tau, and astrocytes) and functional changes in AD sensitive brain regions, also suggesting that brain hypometabolism occurs prior to AD pathology. Therefore, targeting metabolic mechanisms in cortical piriform and insular regions at early stages may be a promising approach for preventing, slowing, and/or blocking the onset of AD and preserving neurogenesis.

[18F]Amylovis as a Potential PET Probe for β-Amyloid Plaque: Synthesis, In Silico, In vitro and In vivo Evaluations

BACKGROUND

Alzheimer's disease (AD) is the most common form of dementia. Neuroimaging methods have widened the horizons for AD diagnosis and therapy. The goals of this work are the synthesis of 2-(3-fluoropropyl)-6-methoxynaphthalene (5) and its [18F]-radiolabeled counterpart ([18F]Amylovis), the in silico and in vitro comparative evaluations of [18F]Amylovis and [11C]Pittsburg compound B (PIB) and the in vivo preclinical evaluation of [18F]Amylovis in transgenic and wild mice.

METHODS

Iron-catalysis cross coupling reaction, followed by fluorination and radiofluorination steps were carried out to obtain 5 and 18F-Amylovis. Protein/Aß plaques binding, biodistribution, PET/CT Imaging and immunohistochemical studies were conducted in healthy/transgenic mice.

RESULTS

The synthesis of 5 was successful obtained. Comparative in silico studies predicting that 5 should have affinity to the Aβ-peptide, mainly through π-π interactions. According to a dynamic simulation study the ligand-Aβ peptide complexes are stable in simulation-time (ΔG = -5.31 kcal/mol). [18F]Amylovis was obtained with satisfactory yield, high radiochemical purity and specific activity. The [18F]Amylovis log Poct/PBS value suggests its potential ability for crossing the blood brain barrier (BBB). According to in vitro assays, [18F]Amylovis has an adequate stability in time. Higher affinity to Aβ plaques were found for [18F]Amylovis (Kd 0.16 nmol/L) than PIB (Kd 8.86 nmol/L) in brain serial sections of 3xTg-AD mice. Biodistribution in healthy mice showed that [18F]Amylovis crosses the BBB with rapid uptake (7 %ID/g at 5 min) and good washout (0.11±0.03 %ID/g at 60 min). Comparative PET dynamic studies of [18F]Amylovis in healthy and transgenic APPSwe/PS1dE9 mice, revealed a significant high uptake in the mice model.

CONCLUSION

The in silico, in vitro and in vivo results justify that [18F]Amylovis should be studied as a promissory PET imaging agent to detect the presence of Aβ senile plaques.

Investigation of the quantitative accuracy of low-dose amyloid and tau PET imaging

With the increasing incidence of dementia worldwide, the frequent use of amyloid and tau positron emission tomography imaging requires low-dose protocols for the differential diagnoses of various neurodegenerative diseases and the monitoring of disease progression. In this study, we investigated the feasibility to reduce the PET dose without a significant loss of quantitative accuracy in 3D dynamic row action maximum likelihood algorithm-reconstructed PET images using [¹¹C]PIB and [¹⁸F]THK5351. Eighteen cognitively normal young controls, cognitively normal elderly controls, and patients with probable Alzheimer's disease (n = 6 each), were included. Reduced doses were simulated by randomly sampling half and quarter of the full counts in list mode data for one independent realization at each simulated dose. Bias was evaluated between the reduced dose from the full dose of standardized uptake value ratio (SUVR), distribution volume ratio (DVR) from reference Logan, and non-displaceable binding potential (BP_ND) from simplified reference tissue model (SRTM). DVR yielded the least bias at low dose compared to SUVR and BP_ND, and thus, is highly recommended. The dose of [¹⁸F]THK5351 and [¹¹C]PIB can be reduced to a quarter of the full dose using DVR for evaluation, whereas the dose can only be reduced to half and a quarter of the full dose for [¹⁸F]THK5351 and [¹¹C]PIB using SUVR. BP_ND showed inconsistent trend and large bias at low dose. The feasibility of dose reduction was dependent on the selected parameters of interest, reconstruction algorithms, reference regions, and to a lesser degree by motion effects.

White Matter Reference Region in PET Studies of 11C-Pittsburgh Compound B Uptake: Effects of Age and Amyloid-β Deposition

Amyloid-β (Aβ) deposition as seen on PET using an Aβ-binding agent is a critical diagnostic biomarker for Alzheimer disease (AD). Some reports suggest using white matter (WM) as a reference region for quantification of serial Aβ PET studies; however, nonspecific WM retention in Aβ PET in people with dementia or cognitively unimpaired (CU) has been widely reported and is poorly understood. Methods: To investigate the suitability of WM as a reference region and the factors affecting WM 11C-Pittsburgh compound B (11C-PiB) uptake variability, we conducted a retrospective study on 2 large datasets: a longitudinal study of participants (n = 577) who were CU, had mild cognitive impairment, or had dementia likely due to AD; and a cross-sectional study of single-scan PET imaging in CU subjects (n = 1,349). In the longitudinal study, annual changes in WM 11C-PiB uptake were assessed, and in the cross-sectional study, WM 11C-PiB uptake was assessed relative to subject age. Results: Overall, we found that WM 11C-PiB uptake showed age-related increases, which varied with the WM regions selected. Further, variable annual WM 11C-PiB uptake changes were seen with different gray matter (GM) 11C-PiB baseline uptake levels. Conclusion: WM binding increases with age and varies with GM 11C-PiB. These correlations should be considered when using WM for normalization in 11C-PiB PET studies. The cerebellar crus1+crus2 showed no increase with age and cerebellar GM+WM showed minimal increase, supporting their use as reference regions for cross-sectional studies comparing wide age spans. In longitudinal studies, the increase in WM uptake may be minimal in the short-term and thus using WM as a reference region in these studies seems reasonable. However, as participants age, the findings may be affected by changes in WM uptake. Changes in WM 11C-PiB uptake may relate to disease progression, warranting examination of the causes of WM 11C-PiB uptake.

A Systematic Review of Positron Emission Tomography of Tau, Amyloid Beta, and Neuroinflammation in Chronic Traumatic Encephalopathy: The Evidence To Date

Chronic traumatic encephalopathy (CTE) is associated with pathological changes, yet detecting these changes during life has proven elusive. Positron emission tomography (PET) offers the potential for identifying such pathology. Few studies have been completed to date and their approaches and results have been diverse. It was the objective of this review to systematically examine relevant research using ligands for PET that bind to identified pathology in CTE. We focused on identification of patterns of binding and addressing gaps in knowledge of PET imaging for CTE. A comprehensive literature search was conducted. Data used were published on or before May 22, 2017. As the extant literature is limited, any peer-reviewed article assessing military, contact sports athletes, or professional fighters was considered for inclusion. The main outcomes were regional binding to brain regions identified through control comparisons or through clinical metrics (e.g., standardized uptake volume ratios). A total of 1207 papers were identified for review, of which six met inclusion criteria. Meta-analyses were planned but were deemed inappropriate given the small number of studies identified. Methodological concerns in these initial papers included small sample sizes, lack of a control comparison, use of nonstandard statistical procedures to quantify data, and interpretation of potentially off-target binding areas. Across studies, the hippocampi, amygdalae, and midbrain had reasonably consistent increased uptake. Evidence for increased uptake in cortical regions was less consistent. The evidence suggests that the field of PET imaging in those at risk for CTE remains nascent. As the field evolves to include more stringent studies, ligands for PET may prove an important tool in identifying CTE in vivo.

A simulation study on the impact of the blood flow-dependent component in [18F]AV45 SUVR in Alzheimer's disease

Background

Increased brain uptake on [¹⁸F]AV45 PET is a biomarker for Alzheimer’s disease (AD). The standardised uptake value ratio (SUVR) is widely used for quantification but is subject to variability. Here we evaluate how SUVR of a cortical target region is affected by blood flow changes in the target and two frequently used reference regions.

Methods

Regional baseline time-activity curves (TACs) were simulated based on metabolite-corrected plasma input functions and pharmacokinetic parameters obtained from our previously acquired data in healthy control (HC; n = 10), amnestic mild cognitive impairment (aMCI; n = 15) and AD cohorts (n = 9). Blood flow changes were simulated by altering the regional tracer delivery rate K1 (and clearance rate k2) between -40% and +40% from its regional baseline value in the target region and/or cerebellar grey (CB) or subcortical white matter (WM) reference regions. The corresponding change in SUVR was calculated at 50–60 min post-injection.

Results

A -40% blood flow reduction in the target resulted in an increased SUVR^target (e.g. SUVR^precuneus: +10.0±5% in HC, +2.5±2% in AD), irrespective of the used reference region. A -40% blood flow reduction in the WM reference region increased SUVR_WM (+11.5±4% in HC, +13.5±3% in AD) while a blood flow reduction in CB decreased SUVR_CB (-9.5±6% in HC, -5.5±2% in AD), irrespective of the used target region. A -40% flow reduction in both the precuneus and reference WM (i.e., global flow change) induced an increased SUVR (+22.5±8% in HC, +16.0±4% in AD). When considering reference CB instead, SUVR was decreased by less than -5% (both in HC and AD).

Conclusion

Blood flow changes introduce alterations in [¹⁸F]AV45 PET SUVR. Flow reductions in the CB and WM reference regions resulted in a decreased and increased SUVR of the target, respectively. SUVR was more affected by global blood flow changes when considering WM instead of CB normalization.

Clinical Applications of Small-molecule PET Radiotracers: Current Progress and Future Outlook

Radiotracers, or radiopharmaceuticals, are bioactive molecules tagged with a radionuclide used for diagnostic imaging or radiotherapy and, when a positron-emitting radionuclide is chosen, the radiotracers are used for PET imaging. The development of novel PET radiotracers in many ways parallels the development of new pharmaceuticals, and small molecules dominate research and development pipelines in both disciplines. The 4 decades since the introduction of [¹⁸F]FDG have seen the development of many small molecule PET radiotracers. Ten have been approved by the US Food and Drug Administration as of 2016, whereas hundreds more are being evaluated clinically. These radiotracers are being used in personalized medicine and to support drug discovery programs where they are greatly improving our understanding of and ability to treat diseases across many areas of medicine including neuroscience, cardiovascular medicine, and oncology.

[Amyloid positron-emission-tomography with [18 F]-florbetaben in the diagnostic workup of dementia patients]

BACKGROUND

To this day the definite diagnosis of Alzheimer's disease still relies on post-mortem histopathological detection of neurofibrillary tangles and beta-amyloid deposits. Amyloid positron emission tomography (PET) is a new diagnostic tool that enables the in vivo quantification of pathological beta-amyloid deposits. The aim of the current study was to evaluate to what extent ¹⁸F-florbetaben-PET (FBB-PET) influences the diagnosis of patients with dementia.

MATERIAL AND METHODS

Imaging with FBB-PET was performed on 33 patients from our outpatient department for cognitive neurology. Beforehand all patients underwent a comprehensive clinical, neuropsychiatric and laboratory examination as well as imaging by means of magnetic resonance imaging (MRI) and fluorodeoxyglucose-PET. The working diagnoses before and after FBB-PET imaging were compared.

RESULTS

17 out of 33 patients were scored as FBB-PET positive. In four cases the initial diagnosis had to be changed to Alzheimer's disease (three cases) and cerebral amyloid angiopathy (one case) due to the positive FBB-PET scan. 16 patients showed a negative FBB-PET scan. In three patients the initial diagnosis of Alzheimer's disease could be ruled out due to the negative FBB-PET scan. Overall, in 7 out of 33 examined patients the initial diagnosis had to be changed because of the findings of the FBB-PET scan. In 24 patients the initial diagnosis was confirmed by the results of the FBB-PET scan.

CONCLUSION

Amyloid-PET is currently no standard procedure in the diagnosis of dementia; however, it can be a helpful additional diagnostic tool when used according to the "Appropriate Use Criteria" and the S3 guidelines on dementia in cases of unclear clinical presentation, atypically early age of onset as well as in patients with persistent or progressive unexplained mild cognitive impairment. By facilitating early diagnosis amyloid-PET imaging allows patient selection for therapeutic drug trials.

Correlation of Cerebral Microbleed Distribution to Amyloid Burden in Patients with Primary Intracerebral Hemorrhage

The underlying pathology of cerebral microbleeds (CMBs) with mixed lobar and deep distribution remains contentious. The aim of this study was to correlate CMBs distribution to β-amyloid burden in patients with primary intracerebral hemorrhage (ICH). Fourty-seven ICH patients underwent magnetic resonance susceptibility-weighted imaging and ¹¹C-Pittsburgh Compound B positron emission tomography. The amyloid burden was expressed as standardized uptake value ratio with reference to cerebellum, and presented as median (interquartile range). Patients were categorized into the lobar, mixed (both lobar and deep regions), and deep types of CMB. Comparing the lobar (17%), mixed (59.6%) and deep (23.4%) CMB types, the global amyloid burden was significantly higher in the mixed type than the deep type (1.10 [1.03–1.25] vs 1.00 [0.97–1.09], p = 0.011), but lower than in the lobar type (1.48 [1.18–1.50], p = 0.048). On multivariable analysis, the ratio of lobar to deep CMB number was positively correlated with global (p = 0.028) and occipital (p = 0.031) amyloid burden. In primary ICH, patients with lobar and mixed CMB types are associated with increased amyloid burden than patients with deep type. The ratio of lobar to deep CMB number is an independent indicator of cerebral β-amyloid deposition.

Magnetic resonance imaging and positron emission tomography in the diagnosis of neurodegenerative dementias

Neuroimaging, both with magnetic resonance imaging (MRI) and positron emission tomography (PET), has gained a pivotal role in the diagnosis of primary neurodegenerative diseases. These two techniques are used as biomarkers of both pathology and progression of Alzheimer's disease (AD) and to differentiate AD from other neurodegenerative diseases. MRI is able to identify structural changes including patterns of atrophy characterizing neurodegenerative diseases, and to distinguish these from other causes of cognitive impairment, e.g. infarcts, space-occupying lesions and hydrocephalus. PET is widely used to identify regional patterns of glucose utilization, since distinct patterns of distribution of cerebral glucose metabolism are related to different subtypes of neurodegenerative dementia. The use of PET in mild cognitive impairment, though controversial, is deemed helpful for predicting conversion to dementia and the dementia clinical subtype. Recently, new radiopharmaceuticals for the in vivo imaging of amyloid burden have been licensed and more tracers are being developed for the assessment of tauopathies and inflammatory processes, which may underlie the onset of the amyloid cascade. At present, the cerebral amyloid burden, imaged with PET, may help to exclude the presence of AD as well as forecast its possible onset. Finally PET imaging may be particularly useful in ongoing clinical trials for the development of dementia treatments. In the near future, the use of the above methods, in accordance with specific guidelines, along with the use of effective treatments will likely lead to more timely and successful treatment of neurodegenerative dementias.

Potential biomarkers and novel pharmacological targets in protein aggregation-related neurodegenerative diseases

The aggregation of specific proteins plays a pivotal role in the etiopathogenesis of several neurodegenerative diseases (NDs). β-Amyloid (Aβ) peptide-containing plaques and intraneuronal neurofibrillary tangles composed of hyperphosphorylated protein tau are the two main neuropathological lesions in Alzheimer's disease. Meanwhile, Parkinson's disease is defined by the presence of intraneuronal inclusions (Lewy bodies), in which α-synuclein (α-syn) has been identified as a major protein component. The current literature provides considerable insights into the mechanisms underlying oligomeric-related neurodegeneration, as well as the relationship between protein aggregation and ND, thus facilitating the development of novel putative biomarkers and/or pharmacological targets. Recently, α-syn, tau and Aβ have been shown to interact each other or with other "pathological proteins" to form toxic heteroaggregates. These latest findings are overcoming the concept that each neurodegenerative disease is related to the misfolding of a single specific protein. In this review, potential opportunities and pharmacological approaches targeting α-syn, tau and Aβ and their oligomeric forms are highlighted with examples from recent studies. Protein aggregation as a biomarker of NDs, in both the brain and peripheral fluids, is deeply explored. Finally, the relationship between biomarker establishment and assessment and their use as diagnostics or therapeutic targets are discussed.

18F-Florbetaben: A New Tool for Amyloidosis Staging?

We report the case of a 73-year-old man with a documented (renal biopsy) light-chain amyloidosis (AL) imaged with F-AV-1 (F-florbetaben) compared with a volunteer. A cardiac amyloidosis was suspected. As it was an AL and not a transthyretin amyloidosis, F-FDG and F-florbetaben PET/CT were preferred to bone scan. F-FDG scintigraphy showed a focal cardiac hypermetabolism. In addition of the heart, F-florbetaben scintigraphy showed an intense spleen and thyroid pathologic uptake and a moderate salivary gland and kidney uptake. F-florbetaben PET/CT appears to be useful for staging systemic amyloidosis.

Neuroimaging of deployment-associated traumatic brain injury (TBI) with a focus on mild TBI (mTBI) since 2009

OBJECTIVES

A substantial body of recent research has aimed to better understand the clinical sequelae of military trauma through the application of advanced brain imaging procedures in Veteran populations. The primary objective of this review was to highlight a portion of these recent studies to demonstrate how imaging tools can be used to understand military-associated brain injury.

METHODS

We focus here on the phenomenon of mild traumatic brain injury (mTBI) given its high prevalence in the Veteran population and current recognition of the need to better understand the clinical implications of this trauma. This is intended to provide readers with an initial exposure to the field of neuroimaging of mTBI with a brief introduction to the concept of traumatic brain injury, followed by a summary of the major imaging techniques that have been applied to the study of mTBI.

RESULTS

Taken together, the collection of studies reviewed demonstrates a clear role for neuroimaging towards understanding the various neural consequences of mTBI as well as the clinical complications of such brain changes.

CONCLUSIONS

This information must be considered in the larger context of research into mTBI, including the potentially unique nature of blast exposure and the long-term consequences of mTBI.

Cystatin C in aging and in Alzheimer's disease

Under normal conditions, the function of catalytically active proteases is regulated, in part, by their endogenous inhibitors, and any change in the synthesis and/or function of a protease or its endogenous inhibitors may result in inappropriate protease activity. Altered proteolysis as a result of an imbalance between active proteases and their endogenous inhibitors can occur during normal aging, and such changes have also been associated with multiple neuronal diseases, including Amyotrophic Lateral Sclerosis (ALS), rare heritable neurodegenerative disorders, ischemia, some forms of epilepsy, and Alzheimer's disease (AD). One of the most extensively studied endogenous inhibitor is the cysteine-protease inhibitor cystatin C (CysC). Changes in the expression and secretion of CysC in the brain have been described in various neurological disorders and in animal models of neurodegeneration, underscoring a role for CysC in these conditions. In the brain, multiple in vitro and in vivo findings have demonstrated that CysC plays protective roles via pathways that depend upon the inhibition of endosomal-lysosomal pathway cysteine proteases, such as cathepsin B (Cat B), via the induction of cellular autophagy, via the induction of cell proliferation, or via the inhibition of amyloid-β (Aβ) aggregation. We review the data demonstrating the protective roles of CysC under conditions of neuronal challenge and the protective pathways induced by CysC under various conditions. Beyond highlighting the essential role that balanced proteolytic activity plays in supporting normal brain aging, these findings suggest that CysC is a therapeutic candidate that can potentially prevent brain damage and neurodegeneration.

Amyloid-β deposition and regional grey matter atrophy rates in dementia with Lewy bodies

Alzheimer's disease pathology frequently coexists with Lewy body disease at autopsy in patients with probable dementia with Lewy bodies. More than half of patients with probable dementia with Lewy bodies have high amyloid-β deposition as measured with 11C-Pittsburgh compound B binding on positron emission tomography. Biomarkers of amyloid-β deposition precede neurodegeneration on magnetic resonance imaging during the progression of Alzheimer's disease, but little is known about how amyloid-β deposition relates to longitudinal progression of atrophy in patients with probable dementia with Lewy bodies. We investigated the associations between baseline 11C-Pittsburgh compound B binding on positron emission tomography and the longitudinal rates of grey matter atrophy in a cohort of clinically diagnosed patients with dementia with Lewy bodies (n = 20), who were consecutively recruited to the Mayo Clinic Alzheimer's Disease Research Centre. All patients underwent 11C-Pittsburgh compound B positron emission tomography and magnetic resonance imaging examinations at baseline. Follow-up magnetic resonance imaging was performed after a mean (standard deviation) interval of 2.5 (1.1) years. Regional grey matter loss was determined on three-dimensional T1-weighted magnetic resonance imaging with the tensor-based morphometry-symmetric normalization technique. Linear regression was performed between baseline 11C-Pittsburgh compound B standard unit value ratio and longitudinal change in regional grey matter volumes from an in-house modified atlas. We identified significant associations between greater baseline 11C-Pittsburgh compound B standard unit value ratio and greater grey matter loss over time in the posterior cingulate gyrus, lateral and medial temporal lobe, and occipital lobe as well as caudate and putamen nuclei, after adjusting for age (P < 0.05). Greater baseline 11C-Pittsburgh compound B standard unit value ratio was also associated with greater ventricular expansion rates (P < 0.01) and greater worsening over time in Clinical Dementia Rating Scale, sum of boxes (P = 0.02). In conclusion, in patients with probable dementia with Lewy bodies, higher amyloid-β deposition at baseline is predictive of faster neurodegeneration in the cortex and also in the striatum. This distribution is suggestive of possible interactions among amyloid-β, tau and α-synuclein aggregates, which needs further investigation. Furthermore, higher amyloid-β deposition at baseline predicts a faster clinical decline over time in patients with probable dementia with Lewy bodies.

New protein deposition tracers in the pipeline

Traditional nuclear medicine ligands were designed to target cellular receptors or transporters with a binding pocket and a defined structure-activity relationship. More recently, tracers have been developed to target pathological protein aggregations, which have less well-defined structure-activity relationships. Aggregations of proteins such as tau, α-synuclein, and β-amyloid (Aβ) have been identified in neurodegenerative diseases, including Alzheimer's disease (AD) and other dementias, and Parkinson's disease (PD). Indeed, Aβ deposition is a hallmark of AD, and detection methods have evolved from coloured dyes to modern 18F-labelled positron emission tomography (PET) tracers. Such tracers are becoming increasingly established in routine clinical practice for evaluation of Aβ neuritic plaque density in the brains of adults who are being evaluated for AD and other causes of cognitive impairment. While similar in structure, there are key differences between the available compounds in terms of dosing/dosimetry, pharmacokinetics, and interpretation of visual reads. In the future, quantification of Aβ-PET may further improve its utility. Tracers are now being developed for evaluation of tau protein, which is associated with decreased cognitive function and neurodegenerative changes in AD, and is implicated in the pathogenesis of other neurodegenerative diseases. While no compound has yet been approved for tau imaging in clinical use, it is a very active area of research. Development of tau tracers comprises in-depth characterisation of existing radiotracers, clinical validation, a better understanding of uptake patterns, test-retest/dosimetry data, and neuropathological correlations with PET. Tau imaging may allow early, more accurate diagnosis, and monitoring of disease progression, in a range of conditions. Another marker for which imaging modalities are needed is α-synuclein, which has potential for conditions including PD and dementia with Lewy bodies. Efforts to develop a suitable tracer are ongoing, but are still in their infancy. In conclusion, several PET tracers for detection of pathological protein depositions are now available for clinical use, particularly PET tracers that bind to Aβ plaques. Tau-PET tracers are currently in clinical development, and α-synuclein protein deposition tracers are at early stage of research. These tracers will continue to change our understanding of complex disease processes.

Brain imaging of neurovascular dysfunction in Alzheimer's disease

Neurovascular dysfunction, including blood-brain barrier (BBB) breakdown and cerebral blood flow (CBF) dysregulation and reduction, are increasingly recognized to contribute to Alzheimer's disease (AD). The spatial and temporal relationships between different pathophysiological events during preclinical stages of AD, including cerebrovascular dysfunction and pathology, amyloid and tau pathology, and brain structural and functional changes remain, however, still unclear. Recent advances in neuroimaging techniques, i.e., magnetic resonance imaging (MRI) and positron emission tomography (PET), offer new possibilities to understand how the human brain works in health and disease. This includes methods to detect subtle regional changes in the cerebrovascular system integrity. Here, we focus on the neurovascular imaging techniques to evaluate regional BBB permeability (dynamic contrast-enhanced MRI), regional CBF changes (arterial spin labeling- and functional-MRI), vascular pathology (structural MRI), and cerebral metabolism (PET) in the living human brain, and examine how they can inform about neurovascular dysfunction and vascular pathophysiology in dementia and AD. Altogether, these neuroimaging approaches will continue to elucidate the spatio-temporal progression of vascular and neurodegenerative processes in dementia and AD and how they relate to each other.

Amyloid Proteins and Their Role in Multiple Sclerosis. Considerations in the Use of Amyloid-PET Imaging

Thioflavin T derivatives are used in positron-emission tomography (PET) studies to detect amyloid protein deposits in patients with Alzheimer disease. These tracers bind extensively to white matter, which suggests that they may be useful in studies of multiple sclerosis (MS), and that proteins resulting from proteolytic processing of the amyloid precursor protein (APP) may contribute to MS. This article reviews data from both clinical and preclinical studies addressing the role of these proteins, whether they are detected in CSF studies or using PET imaging. APP is widely expressed in demyelinated axons and may have a protective effect in MS and in experimental allergic encephalomyelitis in animals. Several mechanisms associated with this increased expression may affect the degree of remyelination in MS. Amyloid-PET imaging may help determine the degree of demyelination and provide information on the molecular changes linked to APP proteolytic processing experienced by patients with MS.

PET imaging in neurology: Alzheimer's and Parkinson's diseases

PET studies play an important role in the early detection of Alzheimer's and Parkinson's diseases (AD and PD). Fluorine-18 fluorodeoxyglucose (F-FDG) PET imaging of regional cerebral glucose metabolism and PET amyloid imaging are the two major PET studies for AD. F-FDG PET is highly sensitive for the early diagnosis of AD, in predicting conversion from mild cognitive impairment to AD, and in differentiating AD from other dementias. PET amyloid imaging is positive in the majority of patients with AD. Negative amyloid PET reduces the likelihood of AD. The main limitations of PET amyloid imaging is its high positivity in the normal elderly population and in other medical conditions with amyloid pathologies. Various PET tracers are available to assess motor and cognitive dysfunctions in PD. PET tracers targeting presynaptic dopaminergic function (F-DOPA, radiolabeled PET tracers assessing the availability of dopamine transporters and vesicular monoamine transporters) and postsynaptic dopamine receptors are used to assess motor dysfunction in PD. PET tracers, particularly dopamine transporters, are highly sensitive in the early diagnosis of PD. Uptake of PET tracers in the striatum is inversely correlated with disease severity. PET is valuable in differentiating PD from other movement disorders. PET studies, particularly F-FDG PET, help to evaluate cortical metabolism in PD patients with cognitive dysfunction and dementia.

Discovery of a novel fluorescent probe for the sensitive detection of β-amyloid deposits

Here we reported the development of the first photoinduced electron transfer (PeT) probe (1) to directly locate β-amyloid aggregates (Aβ plaques) in the brain without the need of post-washing procedures. The probe showed a high affinity for Aβ aggregates with a Kd value of 3.5nM. It is weakly emissive by itself with its fluorescence quenched by electron transfer from PeT donor to the excited fluorophore. But selective binding to Aβ plaques would attenuate the PeT process and restore the fluorescence, therefore facilitating the tracking of Aβ plaques. The probe is advantageous in that its fluorescence is environment-less-sensitive and no washing procedure is required to provide high contrast fluorescent signal when applied to stain brain tissues. As a proof of concept, its application has been exemplified by staining Aβ plaques in slices of brain tissue from double transgenic (APP/PS1) mice of Alzheimer's disease.

Structure–activity relationships of radioiodinated diphenyl derivatives with different conjugated double bonds as ligands for α-synuclein aggregates

We investigated the structure–activity relationships of radioiodinated diphenyl (IDP) derivatives with different conjugated double bonds as ligands for α-syn aggregates.

Effects of acupuncture at HT7 on glucose metabolism in a rat model of Alzheimer's disease: an 18F-FDG-PET study

Objective

To explore the effects of acupuncture at HT7 on different cerebral regions in a rat model of Alzheimer's disease (AD) with the application of ¹⁸F-2-fluoro-deoxy-D-glucose positron emission tomography (FDG-PET).

Methods

Sixty Wistar rats were included after undergoing a Y-maze electric sensitivity test. Ten rats were used as a healthy control group. The remaining 50 rats were injected stereotaxically with ibotenic acid into the right nucleus basalis magnocellularis and injected intraperitoneally with D-galactose. AD was successfully modelled in 36 rats, which were randomly divided into three groups (n=12 each): the AD group, which remained untreated; the AD+HT7 group, which received 20 sessions of acupuncture at HT7 over 1 month; and the AD+Sham group, which received acupuncture at a distant non-acupuncture point. Total reaction time (TRT) was measured by Y-maze and ¹⁸F-FDG-PET scans were conducted on day 1 and 30. PET images were processed with Statistical Parametric Mapping 8.0.

Results

Pre-treatment, TRT was greater in all AD groups versus controls (mean±SD 24.10±2.48 vs 41.34±5.00 s). Post-treatment, TRT was shortened in AD+HT7 versus AD+Sham and AD groups (p<0.0001, two-way analysis of variance). Glucose metabolic activity in the hippocampus, thalamus, hypothalamus, frontal lobe, and temporal lobe was decreased in AD rats compared with healthy controls and relatively elevated after HT7 acupuncture. Compared with sham acupuncture, HT7 needling had a greater positive influence on brain glucose metabolism.

Conclusions

Needling at HT7 can improve memory ability and cerebral glucose metabolic activity of the hippocampus, thalamus, hypothalamus, and frontal/temporal lobes in an AD rat model.

Amyloid PET imaging in multiple sclerosis: an (18)F-florbetaben study

Background

Positron emission tomography (PET) images with amyloid tracers show normal uptake in healthy white matter, which suggests that amyloid tracers are potentially useful for studying such white matter diseases as multiple sclerosis (MS).

Methods

Twelve patients diagnosed with MS (5 with RRMS, 5 with SPMS, and 2 with PPMS) and 3 healthy controls underwent studies with MRI and ¹⁸F-florbetaben-PET imaging. Images were preprocessed using Statistical Parametric Mapping software. We analysed ¹⁸F-florbetaben uptake in demyelinating plaques (appearing as hyperintense lesions in FLAIR sequences), in normal-appearing white matter, and in grey matter.

Results

Mean standardized uptake value relative to cerebellum was higher in normally appearing white matter (NAWM) (1.51 ± 0.12) than in damaged white matter (DWM) (1.24 ± 0.12; P = .002). Mean percentage of change between NAWM and DWM was −17.56 % ± 6.22 %. This percentage of change correlated negatively with EDSS scores (r = −0.61, p < .05) and with age (r = −0.83, p < 0.01). Progressive forms of MS showed a more pronounced reduction of the uptake in DWM in comparison to relapsing-remitting form.

Conclusions

Uptake of ¹⁸F-florbetaben in damaged white matter is lower than that occurring in normally-appearing white matter. These findings indicate that amyloid tracers may be useful in studies of MS, although further research is needed to evaluate the utility of amyloid-PET in monitoring MS progression.

Electronic supplementary material

The online version of this article (doi:10.1186/s12883-015-0502-2) contains supplementary material, which is available to authorized users.

Early-Phase 11C-PiB PET in Amyloid Angiopathy-Related Symptomatic Cerebral Hemorrhage: Potential Diagnostic Value?

Although late-phase (>35min post-administration) 11C-PiB-PET has good sensitivity in cerebral amyloid angiopathy (CAA), its specificity is poor due to frequently high uptake in healthy aged subjects. By detecting perfusion-like abnormalities, early-phase 11C-PiB-PET might add diagnostic value. Early-frame (1-6min) 11C-PiB-PET was obtained in 11 non-demented patients with probable CAA-related symptomatic lobar intracerebral haemorrhage (70±7yrs), 9 age-matched healthy controls (HCs) and 10 HCs <55yrs. There was a significant decrease in early-phase atrophy-corrected whole-cortex SUV relative to cerebellar vermis (SUVR) in the CAA vs age-matched HC group. None of the age-matched controls fell below the lower 95% confidence limit derived from the young HCs, while 6/11 CAA patients did (sensitivity = 55%, specificity = 100%). Combining both early- and late-phase 11C-PiB data did not change the sensitivity and specificity of late-phase PiB, but combined early- and late-phase positivity entails a very high suspicion of underlying Aβ-related clinical disorder, i.e., CAA or Alzheimer disease (AD). In order to clarify this ambiguity, we then show that the occipital/posterior cingulate ratio is markedly lower in CAA than in AD (N = 7). These pilot data suggest that early-phase 11C-PiB-PET may not only add to late-phase PiB-PET with respect to the unclear situation of late-phase positivity, but also help differentiate CAA from AD.

Brain catecholamine depletion and motor impairment in a Th knock-in mouse with type B tyrosine hydroxylase deficiency

Tyrosine hydroxylase catalyses the hydroxylation of L-tyrosine to l-DOPA, the rate-limiting step in the synthesis of catecholamines. Mutations in the TH gene encoding tyrosine hydroxylase are associated with the autosomal recessive disorder tyrosine hydroxylase deficiency, which manifests phenotypes varying from infantile parkinsonism and DOPA-responsive dystonia, also termed type A, to complex encephalopathy with perinatal onset, termed type B. We generated homozygous Th knock-in mice with the mutation Th-p.R203H, equivalent to the most recurrent human mutation associated with type B tyrosine hydroxylase deficiency (TH-p.R233H), often unresponsive to l-DOPA treatment. The Th knock-in mice showed normal survival and food intake, but hypotension, hypokinesia, reduced motor coordination, wide-based gate and catalepsy. This phenotype was associated with a gradual loss of central catecholamines and the serious manifestations of motor impairment presented diurnal fluctuation but did not improve with standard l-DOPA treatment. The mutant tyrosine hydroxylase enzyme was unstable and exhibited deficient stabilization by catecholamines, leading to decline of brain tyrosine hydroxylase-immunoreactivity in the Th knock-in mice. In fact the substantia nigra presented an almost normal level of mutant tyrosine hydroxylase protein but distinct absence of the enzyme was observed in the striatum, indicating a mutation-associated mislocalization of tyrosine hydroxylase in the nigrostriatal pathway. This hypomorphic mouse model thus provides understanding on pathomechanisms in type B tyrosine hydroxylase deficiency and a platform for the evaluation of novel therapeutics for movement disorders with loss of dopaminergic input to the striatum.

Synthesis of a PET tau tracer [(11)C]PBB3 for imaging of Alzheimer's disease

The authentic standard PBB3 and its precursor N-desmethyl-PBB3 as well as TBS-protected N-desmethyl-PBB3 precursor for radiolabeling were synthesized from 5-bromo-2-nitropyridine, acrolein diethyl acetal, 6-methoxy-2-methylbenzothiazole, and diethylchlorophosphate with overall chemical yield 1% in six steps, 2% in five steps, and 1% in six steps, respectively. [(11)C]PBB3 was prepared from either desmethyl-PBB3 or TBS-protected desmethyl-PBB3 with [(11)C]CH3OTf through N-[(11)C]methylation and isolated by HPLC combined with SPE in 20-25% and 15-20% radiochemical yield, respectively, based on [(11)C]CO2 and decay corrected to end of bombardment (EOB). The radiochemical purity was >99%, and the specific activity at EOB was 370-1110 GBq/μmol with a total synthesis time of ~40-min from EOB.