Clinical validity of increased cortical binding of tau ligands of the THK family and PBB3 on PET as biomarkers for Alzheimer's disease in the context of a structured 5-phase development framework.

PURPOSE: The research community has focused on defining reliable biomarkers for the early detection of the pathological hallmarks of Alzheimer's disease (AD). In 2017, the Geneva AD Biomarker Roadmap initiative adapted the framework for the systematic validation of oncological biomarkers to AD, with the aim to accelerate their development and implementation in clinical practice. The aim of this work was to assess the validation status of tau PET ligands of the THK family and PBB3 as imaging biomarkers for AD, based on the Biomarker Roadmap methodology. METHODS: A panel of experts in AD biomarkers convened in November 2019 at a 2-day workshop in Geneva. The level of clinical validity of tau PET ligands of the THK family and PBB3 was assessed based on the 5-phase development framework before the meeting and discussed during the workshop. RESULTS: PET radioligands of the THK family discriminate well between healthy controls and patients with AD dementia (phase 2; partly achieved) and recent evidence suggests an accurate diagnostic accuracy at the mild cognitive impairment (MCI) stage of the disease (phase 3; partly achieved). The phases 2 and 3 were considered not achieved for PBB3 since no evidence exists about the ligand's diagnostic accuracy. Preliminary evidence exists about the secondary aims of each phase for all ligands. CONCLUSION: Much work remains for completing the aims of phases 2 and 3 and replicating the available evidence. However, it is unlikely that the validation process for these tracers will be completed, given the presence of off-target binding and the development of second-generation tracers with improved binding and pharmacokinetic properties.

Strategic roadmap for an early diagnosis of Alzheimer's disease based on biomarkers.

The diagnosis of Alzheimer's disease can be improved by the use of biological measures. Biomarkers of functional impairment, neuronal loss, and protein deposition that can be assessed by neuroimaging (ie, MRI and PET) or CSF analysis are increasingly being used to diagnose Alzheimer's disease in research studies and specialist clinical settings. However, the validation of the clinical usefulness of these biomarkers is incomplete, and that is hampering reimbursement for these tests by health insurance providers, their widespread clinical implementation, and improvements in quality of health care. We have developed a strategic five-phase roadmap to foster the clinical validation of biomarkers in Alzheimer's disease, adapted from the approach for cancer biomarkers. Sufficient evidence of analytical validity (phase 1 of a structured framework adapted from oncology) is available for all biomarkers, but their clinical validity (phases 2 and 3) and clinical utility (phases 4 and 5) are incomplete. To complete these phases, research priorities include the standardisation of the readout of these assays and thresholds for normality, the evaluation of their performance in detecting early disease, the development of diagnostic algorithms comprising combinations of biomarkers, and the development of clinical guidelines for the use of biomarkers in qualified memory clinics.

Clinical validity of brain fluorodeoxyglucose positron emission tomography as a biomarker for Alzheimer's disease in the context of a structured 5-phase development framework.

The use of Alzheimer's disease (AD) biomarkers is supported in diagnostic criteria, but their maturity for clinical routine is still debated. Here, we evaluate brain fluorodeoxyglucose positron emission tomography (FDG PET), a measure of cerebral glucose metabolism, as a biomarker to identify clinical and prodromal AD according to the framework suggested for biomarkers in oncology, using homogenous criteria with other biomarkers addressed in parallel reviews. FDG PET has fully achieved phase 1 (rational for use) and most of phase 2 (ability to discriminate AD subjects from healthy controls or other forms of dementia) aims. Phase 3 aims (early detection ability) are partly achieved. Phase 4 studies (routine use in prodromal patients) are ongoing, and only preliminary results can be extrapolated from retrospective observations. Phase 5 studies (quantify impact and costs) have not been performed. The results of this study show that specific efforts are needed to complete phase 3 evidence, in particular comparing and combining FDG PET with other biomarkers, and to properly design phase 4 prospective studies as a basis for phase 5 evaluations.

Clinical validity of increased cortical uptake of amyloid ligands on PET as a biomarker for Alzheimer's disease in the context of a structured 5-phase development framework.

The use of biomarkers has been proposed for diagnosing Alzheimer's disease in recent criteria, but some biomarkers have not been sufficiently investigated to justify their routine clinical use. Here, we evaluate in a literature review the clinical validity of amyloid positron emission tomography (PET) imaging using a structured framework developed for the assessment of oncological biomarkers. Homogenous criteria have been addressed in reviews of other Alzheimer's disease biomarkers. There is adequate evidence that the main aims of phases 1 (rationale for use) and 2 (discriminative ability) have been achieved. The aims of phase 3 (early detection ability) have been partly achieved, while phase 4 studies (performance in representative mild cognitive impairment patients) are currently ongoing. Phase 5 studies (quantification of impact and costs) are still to come. This review highlights the priorities to be pursued to enable the proper use of amyloid PET imaging in a clinical setting. Future investigations will primarily be large, phase 4 studies that will assess the utility of amyloid PET imaging in routine clinical practice.

Amyloid tracers binding sites in autosomal dominant and sporadic Alzheimer's disease.

INTRODUCTION: Amyloid imaging has been integrated into diagnostic criteria for Alzheimer's disease (AD). How amyloid tracers binding differ for different tracer structures and amyloid-ß aggregates in autosomal dominant AD (ADAD) and sporadic AD is unclear. METHODS: Binding properties of different amyloid tracers were examined in brain homogenates from six ADAD with APPswe, PS1 M146V, and PS1 EΔ9 mutations, 13 sporadic AD, and 14 control cases. RESULTS: 3H-PIB, 3H-florbetaben, 3H-AZD2184, and BTA-1 shared a high- and a varying low-affinity binding site in the frontal cortex of sporadic AD. AZD2184 detected another binding site (affinity 33 nM) in the frontal cortex of ADAD. The 3H-AZD2184 and 3H-PIB binding were significantly higher in the striatum of ADAD compared to sporadic AD and control. Polyphenol resveratrol showed strongest inhibition on 3H-AZD84 binding followed by 3H-florbetaben and minimal on 3H-PIB. DISCUSSION: This study implies amyloid tracers of different structures detect different sites on amyloid-ß fibrils or conformations.

Pittsburgh compound B imaging and cerebrospinal fluid amyloid-ß in a multicentre European memory clinic study.

The aim of this study was to assess the agreement between data on cerebral amyloidosis, derived using Pittsburgh compound B positron emission tomography and (i) multi-laboratory INNOTEST enzyme linked immunosorbent assay derived cerebrospinal fluid concentrations of amyloid-ß42; (ii) centrally measured cerebrospinal fluid amyloid-ß42 using a Meso Scale Discovery enzyme linked immunosorbent assay; and (iii) cerebrospinal fluid amyloid-ß42 centrally measured using an antibody-independent mass spectrometry-based reference method. Moreover, we examined the hypothesis that discordance between amyloid biomarker measurements may be due to interindividual differences in total amyloid-ß production, by using the ratio of amyloid-ß42 to amyloid-ß40 Our study population consisted of 243 subjects from seven centres belonging to the Biomarkers for Alzheimer's and Parkinson's Disease Initiative, and included subjects with normal cognition and patients with mild cognitive impairment, Alzheimer's disease dementia, frontotemporal dementia, and vascular dementia. All had Pittsburgh compound B positron emission tomography data, cerebrospinal fluid INNOTEST amyloid-ß42 values, and cerebrospinal fluid samples available for reanalysis. Cerebrospinal fluid samples were reanalysed (amyloid-ß42 and amyloid-ß40) using Meso Scale Discovery electrochemiluminescence enzyme linked immunosorbent assay technology, and a novel, antibody-independent, mass spectrometry reference method. Pittsburgh compound B standardized uptake value ratio results were scaled using the Centiloid method. Concordance between Meso Scale Discovery/mass spectrometry reference measurement procedure findings and Pittsburgh compound B was high in subjects with mild cognitive impairment and Alzheimer's disease, while more variable results were observed for cognitively normal and non-Alzheimer's disease groups. Agreement between Pittsburgh compound B classification and Meso Scale Discovery/mass spectrometry reference measurement procedure findings was further improved when using amyloid-ß42/40 Agreement between Pittsburgh compound B visual ratings and Centiloids was near complete. Despite improved agreement between Pittsburgh compound B and centrally analysed cerebrospinal fluid, a minority of subjects showed discordant findings. While future studies are needed, our results suggest that amyloid biomarker results may not be interchangeable in some individuals.

Targeted delivery of nerve growth factor to the cholinergic basal forebrain of Alzheimer's disease patients: application of a second-generation encapsulated cell biodelivery device.

BACKGROUND: Targeted delivery of nerve growth factor (NGF) has emerged as a potential therapy for Alzheimer's disease (AD) due to its regenerative effects on basal forebrain cholinergic neurons. This hypothesis has been tested in patients with AD using encapsulated cell biodelivery of NGF (NGF-ECB) in a first-in-human study. We report our results from a third-dose cohort of patients receiving second-generation NGF-ECB implants with improved NGF secretion. METHODS: Four patients with mild to moderate AD were recruited to participate in an open-label, phase Ib dose escalation study with a 6-month duration. Each patient underwent stereotactic implant surgery with four NGF-ECB implants targeted at the cholinergic basal forebrain. The NGF secretion of the second-generation implants was improved by using the Sleeping Beauty transposon gene expression technology and an improved three-dimensional internal scaffolding, resulting in production of about 10 ng NGF/device/day. RESULTS: All patients underwent successful implant procedures without complications, and all patients completed the study, including implant removal after 6 months. Upon removal, 13 of 16 implants released NGF, 8 implants released NGF at the same rate or higher than before the implant procedure, and 3 implants failed to release detectable amounts of NGF. Of 16 adverse events, none was NGF-, or implant-related. Changes from baseline values of cholinergic markers in cerebrospinal fluid (CSF) correlated with cortical nicotinic receptor expression and Mini Mental State Examination score. Levels of neurofilament light chain (NFL) protein increased in CSF after NGF-ECB implant, while glial fibrillary acidic protein (GFAP) remained stable. CONCLUSIONS: The data derived from this patient cohort demonstrate the safety and tolerability of sustained NGF release by a second-generation NGF-ECB implant to the basal forebrain, with uneventful surgical implant and removal of NGF-ECB implants in a new dosing cohort of four patients with AD. TRIAL REGISTRATION: ClinicalTrials.gov identifier: NCT01163825 . Registered on 14 Jul 2010.

Neural Stem Cell Transplant-Induced Effect on Neurogenesis and Cognition in Alzheimer Tg2576 Mice Is Inhibited by Concomitant Treatment with Amyloid-Lowering or Cholinergic α7 Nicotinic Receptor Drugs.

Stimulating regeneration in the brain has the potential to rescue neuronal networks and counteract progressive pathological changes in Alzheimer's disease (AD). This study investigated whether drugs with different mechanisms of action could enhance neurogenesis and improve cognition in mice receiving human neural stem cell (hNSC) transplants. Six- to nine-month-old AD Tg2576 mice were treated for five weeks with the amyloid-modulatory and neurotrophic drug (+)-phenserine or with the partial α7 nicotinic receptor (nAChR) agonist JN403, combined with bilateral intrahippocampal hNSC transplantation. We observed improved spatial memory in hNSC-transplanted non-drug-treated Tg2576 mice but not in those receiving drugs, and this was accompanied by an increased number of Doublecortin- (DCX-) positive cells in the dentate gyrus, a surrogate marker for newly generated neurons. Treatment with (+)-phenserine did however improve graft survival in the hippocampus. An accumulation of α7 nAChR-expressing astrocytes was observed around the injection site, suggesting their involvement in repair and scarring processes. Interestingly, JN403 treatment decreased the number of α7 nAChR-expressing astrocytes, correlating with a reduction in the number of DCX-positive cells in the dentate gyrus. We conclude that transplanting hNSCs enhances endogenous neurogenesis and prevents further cognitive deterioration in Tg2576 mice, while simultaneous treatments with (+)-phenserine or JN403 result in countertherapeutic effects.

Prediction of AD dementia by biomarkers following the NIA-AA and IWG diagnostic criteria in MCI patients from three European memory clinics.

INTRODUCTION: Proposed diagnostic criteria (international working group and National Institute on Aging and Alzheimer's Association) for Alzheimer's disease (AD) include markers of amyloidosis (abnormal cerebrospinal fluid [CSF] amyloid beta [Aß]42) and neurodegeneration (hippocampal atrophy, temporo-parietal hypometabolism on [18F]-fluorodeoxyglucose-positron emission tomography (FDG-PET), and abnormal CSF tau). We aim to compare the accuracy of these biomarkers, individually and in combination, in predicting AD among mild cognitive impairment (MCI) patients. METHODS: In 73 MCI patients, followed to ascertain AD progression, markers were measured. Sensitivity and specificity, positive (LR+) and negative (LR-) likelihood ratios, and crude and adjusted hazard ratios were computed. RESULTS: Twenty-nine MCI patients progressed and 44 remained stable. Positivity to any marker achieved the lowest LR- (0.0), whereas the combination Aß42 plus FDG-PET achieved the highest LR+ (6.45). In a survival analysis, positivity to any marker was associated with 100% conversion rate, whereas negativity to all markers was associated with 100% stability. DISCUSSION: The best criteria combined amyloidosis and neurodegeneration biomarkers, whereas the individual biomarker with the best performance was FDG-PET.

The use of biomarkers for the etiologic diagnosis of MCI in Europe: an EADC survey.

We investigated the use of Alzheimer's disease (AD) biomarkers in European Alzheimer's Disease Consortium centers and assessed their perceived usefulness for the etiologic diagnosis of mild cognitive impairment (MCI). We surveyed availability, frequency of use, and confidence in diagnostic usefulness of markers of brain amyloidosis (amyloid positron emission tomography [PET], cerebrospinal fluid [CSF] Aß42) and neurodegeneration (medial temporal atrophy [MTA] on MR, fluorodeoxyglucose positron emission tomography [FDG-PET], CSF tau). The most frequently used biomarker is visually rated MTA (75% of the 37 responders reported using it "always/frequently") followed by CSF markers (22%), FDG-PET (16%), and amyloid-PET (3%). Only 45% of responders perceive MTA as contributing to diagnostic confidence, where the contribution was rated as "moderate". Seventy-nine percent of responders felt "very/extremely" comfortable delivering a diagnosis of MCI due to AD when both amyloid and neuronal injury biomarkers were abnormal (P < .02 versus any individual biomarker). Responders largely agreed that a combination of amyloidosis and neuronal injury biomarkers was a strongly indicative AD signature.

³H-deprenyl and ³H-PIB autoradiography show different laminar distributions of astroglia and fibrillar ß-amyloid in Alzheimer brain.

BACKGROUND: The pathological features in Alzheimer's disease (AD) brain include the accumulation and deposition of ß-amyloid (Aß), activation of astrocytes and microglia and disruption of cholinergic neurotransmission. Since the topographical characteristics of these different pathological processes in AD brain and how these relate to each other is not clear, this motivated further exploration using binding studies in postmortem brain with molecular imaging tracers. This information could aid the development of specific biomarkers to accurately chart disease progression. RESULTS: In vitro binding assays demonstrated increased [³H]-PIB (fibrillar Aß) and [³H]-PK11195 (activated microglia) binding in the frontal cortex (FC) and hippocampus (HIP), as well as increased binding of [³H]-L-deprenyl (activated astrocytes) in the HIP, but a decreased [³H]-nicotine (α4ß2 nicotinic acetylcholine receptor (nAChR)) binding in the FC of AD cases compared to age-matched controls. Quantitative autoradiography binding studies were also performed to investigate the regional laminar distributions of [³H]-L-deprenyl, [³H]-PIB as well as [¹²5I]-α-bungarotoxin (α7 nAChRs) and [³H]-nicotine in hemisphere brain of a typical AD case. A clear lamination pattern was observed with high [³H]-PIB binding in all layers and [³H]-deprenyl in superficial layers of the FC. In contrast, [³H]-PIB showed low binding to fibrillar Aß, but [³H]-deprenyl high binding to activated astrocytes throughout the HIP. The [³H]-PIB binding was also low and the [³H]-deprenyl binding high in all layers of the medial temporal gyrus and insular cortex in comparison to the frontal cortex. Low [³H]-nicotine binding was observed in all layers of the frontal cortex in comparison to layers in the medial temporal gyrus, insular cortex and hippocampus. Immunohistochemical detection in the AD case revealed abundant glial fibrillary acidic protein positive (GFAP+) reactive astrocytes and α7 nAChR expressing GFAP+ astrocytes both in the vicinity and surrounding Aß neuritic plaques in the FC and HIP. Although fewer Aß plaques were observed in the HIP, some hippocampal GFAP+ astrocytes contained Aß-positive (6 F/3D) granules within their somata. CONCLUSIONS: Astrocytosis shows a distinct regional pattern in AD brain compared to fibrillar Aß, suggesting that different types of astrocytes may be associated with the pathophysiological processes in AD.

Functional variability in butyrylcholinesterase activity regulates intrathecal cytokine and astroglial biomarker profiles in patients with Alzheimer's disease.

Butyrylcholinesterase (BuChE) activity is associated with activated astrocytes in Alzheimer's disease brain. The BuChE-K variant exhibits 30%-60% reduced acetylcholine (ACh) hydrolyzing capacity. Considering the increasing evidence of an immune-regulatory role of ACh, we investigated if genetic heterogeneity in BuChE affects cerebrospinal fluid (CSF) biomarkers of inflammation and cholinoceptive glial function. Alzheimer's disease patients (n = 179) were BCHE-K-genotyped. Proteomic and enzymatic analyses were performed on CSF and/or plasma. BuChE genotype was linked with differential CSF levels of glial fibrillary acidic protein, S100B, interleukin-1ß, and tumor necrosis factor (TNF)-α. BCHE-K noncarriers displayed 100%-150% higher glial fibrillary acidic protein and 64%-110% higher S100B than BCHE-K carriers, who, in contrast, had 40%-80% higher interleukin-1ß and 21%-27% higher TNF-α compared with noncarriers. A high level of CSF BuChE enzymatic phenotype also significantly correlated with higher CSF levels of astroglial markers and several factors of the innate complement system, but lower levels of proinflammatory cytokines. These individuals also displayed beneficial paraclinical and clinical findings, such as high cerebral glucose utilization, low ß-amyloid load, and less severe progression of clinical symptoms. In vitro analysis on human astrocytes confirmed the involvement of a regulated BuChE status in the astroglial responses to TNF-α and ACh. Histochemical analysis in a rat model of nerve injury-induced neuroinflammation, showed focal assembly of astroglial cells in proximity of BuChE-immunolabeled sites. In conclusion, these results suggest that BuChE enzymatic activity plays an important role in regulating intrinsic inflammation and activity of cholinoceptive glial cells and that this might be of clinical relevance. The dissociation between astroglial markers and inflammatory cytokines indicates that a proper activation and maintenance of astroglial function is a beneficial response, rather than a disease-driving mechanism. Further studies are needed to explore the therapeutic potential of manipulating BuChE activity or astroglial functional status.

Age-dependent neuroplasticity mechanisms in Alzheimer Tg2576 mice following modulation of brain amyloid-ß levels.

The objective of this study was to investigate the effects of modulating brain amyloid-ß (Aß) levels at different stages of amyloid pathology on synaptic function, inflammatory cell changes and hippocampal neurogenesis, i.e. processes perturbed in Alzheimer's disease (AD). Young (4- to 6-month-old) and older (15- to 18-month-old) APP(SWE) transgenic (Tg2576) mice were treated with the AD candidate drug (+)-phenserine for 16 consecutive days. We found significant reductions in insoluble Aß1-42 levels in the cortices of both young and older transgenic mice, while significant reductions in soluble Aß1-42 levels and insoluble Aß1-40 levels were only found in animals aged 15-18 months. Autoradiography binding with the amyloid ligand Pittsburgh Compound B ((3)H-PIB) revealed a trend for reduced fibrillar Aß deposition in the brains of older phenserine-treated Tg2576 mice. Phenserine treatment increased cortical synaptophysin levels in younger mice, while decreased interleukin-1ß and increased monocyte chemoattractant protein-1 and tumor necrosis factor-alpha levels were detected in the cortices of older mice. The reduction in Aß1-42 levels was associated with an increased number of bromodeoxyuridine-positive proliferating cells in the hippocampi of both young and older Tg2576 mice. To determine whether the increased cell proliferation was accompanied by increased neuronal production, the endogenous early neuronal marker doublecortin (DCX) was examined in the dentate gyrus (DG) using immunohistochemical detection. Although no changes in the total number of DCX(+)-expressing neurons were detected in the DG in Tg2576 mice at either age following (+)-phenserine treatment, dendritic arborization was increased in differentiating neurons in young Tg2576 mice. Collectively, these findings indicate that reducing Aß1-42 levels in Tg2576 mice at an early pathological stage affects synaptic function by modulating the maturation and plasticity of newborn neurons in the brain. In contrast, lowering Aß levels in Tg2576 mice when Aß plaque pathology is prominent mainly alters the levels of proinflammatory cytokines and chemokines.

Prediction of dementia in MCI patients based on core diagnostic markers for Alzheimer disease.

OBJECTIVES: The current model of Alzheimer disease (AD) stipulates that brain amyloidosis biomarkers turn abnormal earliest, followed by cortical hypometabolism, and finally brain atrophy ones. The aim of this study is to provide clinical evidence of the model in patients with mild cognitive impairment (MCI). METHODS: A total of 73 patients with MCI from 3 European memory clinics were included. Brain amyloidosis was assessed by CSF Aß42 concentration, cortical metabolism by an index of temporoparietal hypometabolism on FDG-PET, and brain atrophy by automated hippocampal volume. Patients were divided into groups based on biomarker positivity: 1) Aß42- FDG-PET- Hippo-, 2) Aß42+ FDG-PET- Hippo-, 3) Aß42 + FDG-PET + Hippo-, 4) Aß42 + FDG-PET+ Hippo+, and 5) any other combination not in line with the model. Measures of validity were prevalence of group 5, increasing incidence of progression to dementia with increasing biological severity, and decreasing conversion time. RESULTS: When patients with MCI underwent clinical follow-up, 29 progressed to dementia, while 44 remained stable. A total of 26% of patients were in group 5. Incident dementia was increasing with greater biological severity in groups 1 to 5 from 4% to 27%, 64%, and 100% (p for trend < 0.0001), and occurred increasingly earlier (p for trend = 0.024). CONCLUSIONS: The core biomarker pattern is in line with the current pathophysiologic model of AD. Fully normal and fully abnormal pattern is associated with exceptional and universal development of dementia. Cases not in line might be due to atypical neurobiology or inaccurate thresholds for biomarker (ab)normality.

Neurotrophic and neuroprotective actions of (-)- and (+)-phenserine, candidate drugs for Alzheimer's disease.

Neuronal dysfunction and demise together with a reduction in neurogenesis are cardinal features of Alzheimer's disease (AD) induced by a combination of oxidative stress, toxic amyloid-ß peptide (Aß) and a loss of trophic factor support. Amelioration of these was assessed with the Aß lowering AD experimental drugs (+)-phenserine and (-)-phenserine in neuronal cultures, and actions in mice were evaluated with (+)-phenserine. Both experimental drugs together with the metabolite N1-norphenserine induced neurotrophic actions in human SH-SY5Y cells that were mediated by the protein kinase C (PKC) and extracellular signal-regulated kinases (ERK) pathways, were evident in cells expressing amyloid precursor protein Swedish mutation (APP(SWE)), and retained in the presence of Aß and oxidative stress challenge. (+)-Phenserine, together with its (-) enantiomer as well as its N1- and N8-norphenserine and N1,N8-bisnorphenserine metabolites, likewise provided neuroprotective activity against oxidative stress and glutamate toxicity via the PKC and ERK pathways. These neurotrophic and neuroprotective actions were evident in primary cultures of subventricular zone (SVZ) neural progenitor cells, whose neurosphere size and survival were augmented by (+)-phenserine. Translation of these effects in vivo was assessed in wild type and AD APPswe transgenic (Tg2576) mice by doublecortin (DCX) immunohistochemical analysis of neurogenesis in the SVZ, which was significantly elevated by 16 day systemic (+)-phenserine treatment, in the presence of a (+)-phenserine-induced elevation in brain- derived neurotrophic factor (BDNF).

Encapsulated cell biodelivery of nerve growth factor to the Basal forebrain in patients with Alzheimer's disease.

BACKGROUND/AIMS: Degeneration of cholinergic neurons in the basal forebrain correlates with cognitive decline in patients with Alzheimer's disease (AD). Targeted delivery of exogenous nerve growth factor (NGF) has emerged as a potential AD therapy due to its regenerative effects on the basal forebrain cholinergic neurons in AD animal models. Here we report the results of a first-in-man study of encapsulated cell (EC) biodelivery of NGF to the basal forebrain of AD patients with the primary objective to explore safety and tolerability. METHODS: This was an open-label, 12-month study in 6 AD patients. Patients were implanted stereotactically with EC-NGF biodelivery devices targeting the basal forebrain. Patients were monitored with respect to safety, tolerability, disease progression and implant functionality. RESULTS: All patients were implanted successfully with bilateral single or double implants without complications or signs of toxicity. No adverse events were related to NGF or the device. All patients completed the study, including removal of implants at 12 months. Positive findings in cognition, EEG and nicotinic receptor binding in 2 of 6 patients were detected. CONCLUSIONS: This study demonstrates that surgical implantation and removal of EC-NGF biodelivery to the basal forebrain in AD patients is safe, well tolerated and feasible.

The use of PIB-PET as a dual pathological and functional biomarker in AD.

Amyloid imaging with positron emission tomography (PET) is presently used in Alzheimer's disease (AD) research. In this study we investigated the possibility to use early frames (ePIB) of the PIB scans as a rough index of CBF by comparing normalised early PIB values with cerebral glucose metabolism (rCMRglc). PIB-PET and FDG-PET were performed in 37 AD patients, 21 subjects with mild cognitive impairment (MCI) and 6 healthy controls (HC). The patients were divided based on their PIB retention (amyloid load) as either PIB positive (PIB+) or PIB negative (PIB-). Data of the unidirectional influx K(1) from a subset of the subjects including 7 AD patients and 3 HC was used for correlative analysis. Data was analysed using regions of interest (ROI) analysis. A strong, positive correlation was observed across brain regions between K(1) and ePIB (r=0.70; p≤0.001). The ePIB values were significantly lower in the posterior cingulate (p≤0.001) and the parietal cortices (p=0.002) in PIB+ subjects compared to PIB-, although the group difference were stronger for rCMRglc in cortical areas (p≤0.001). Strong positive correlations between ePIB and rCMRglc were observed in all cortical regions analysed, especially in the posterior cingulate and parietal cortices (p≤0.001). A single dynamic PIB-PET scan may provide information about pathological and functional changes (amyloidosis and impaired blood flow). This might be important for diagnosis of AD, enrichment of patients in clinical trials and evaluation of treatment effects. This article is part of a Special Issue entitled: Imaging Brain Aging and Neurodegenerative disease.

Different ß-amyloid oligomer assemblies in Alzheimer brains correlate with age of disease onset and impaired cholinergic activity.

In this study, we examined the relationship between various ß-amyloid (Aß) oligomer assemblies in autopsy brain with the levels of fibrillar Aß and cholinergic synaptic function. Brain tissues obtained from the frontal cortex of 14 Alzheimer's disease (AD) patients grouped into early-onset AD (EOAD) and late-onset AD (LOAD) and 12 age-matched control subjects were used to extract and quantify Aß oligomers in soluble (TBS), detergent soluble (TBST), and insoluble (GuHCl) fractions. The predominant oligomeric Aß assemblies detected were dodecamers, decamers, and pentamers, and different patterns of expression were observed between EOAD and LOAD patients. There was no association between any of the detected Aß oligomer assemblies and fibrillar Aß levels measured by N-methyl[(3)H] 2-(40-methylaminophenyl)-6-hydroxy-benzothiazole ([(3)H]PIB) binding. Levels of pentamers in the soluble fraction significantly correlated with a reduction in choline acetyltransferase activity in AD patients. The number of nicotinic acetylcholine receptors negatively correlated with the total amount of Aß oligomers in the insoluble fraction in EOAD patients, and with decamers in the soluble fraction in LOAD patients. These novel findings suggest that distinct Aß oligomers induce impairment of cholinergic neurotransmission in AD pathogenesis.

Functional interactions of fibrillar and oligomeric amyloid-ß with alpha7 nicotinic receptors in Alzheimer's disease.

Amyloid-ß (Aß) peptides in the brain of patients with Alzheimer's disease (AD) assemble into various aggregation forms that differ in size, structure, and functional properties. Previous studies have shown that Aß binds to nicotinic acetylcholine receptors (nAChRs) and activates signaling cascades that result in the disruption of synaptic functions. These findings suggest a possible link between impaired cholinergic neurotransmitter function in AD and Aß pathogenesis. However, it is not yet known how the different Aß assemblies interact with specific nAChR subtypes. In the present study, we demonstrate that neurotoxicity in neuronal cells in culture induced by fibrillar Aß(1-40) is prevented through an α7 nAChR-dependent mechanism. The α7 nAChR agonists varenicline and JN403 increased binding of the amyloid ligand [³H]PIB to fibrillar Aß in AD frontal cortex autopsy tissue. This suggests that the presence of nAChR agonists may inhibit interaction of Aß with α7 nAChRs and prevent the formation of Aß/α7 nAChR complexes. This interaction was confirmed in binding assays with [¹²5I]Aß(1-40) and α7 nAChRs in autopsy brain tissue homogenates from the frontal cortex. The functional effects of Aß fibrils and oligomers on nAChRs were examined by measuring intracellular calcium ([Ca(2+)](i) levels. Oligomeric, but not fibrillar Aß(1-40), increased [Ca(2+)](i) in neuronal cells, and this effect was attenuated by varenicline. Our findings demonstrate that fibrillar Aß exerts neurotoxic effects mediated partly through a blockade of α7 nAChRs, whilst oligomeric Aß may act as a ligand activating α7 nAChRs, thereby stimulating downstream signaling pathways.

Β-amyloid 1-42 oligomers impair function of human embryonic stem cell-derived forebrain cholinergic neurons.

Cognitive impairment in Alzheimer's disease (AD) patients is associated with a decline in the levels of growth factors, impairment of axonal transport and marked degeneration of basal forebrain cholinergic neurons (BFCNs). Neurogenesis persists in the adult human brain, and the stimulation of regenerative processes in the CNS is an attractive prospect for neuroreplacement therapy in neurodegenerative diseases such as AD. Currently, it is still not clear how the pathophysiological environment in the AD brain affects stem cell biology. Previous studies investigating the effects of the ß-amyloid (Aß) peptide on neurogenesis have been inconclusive, since both neurogenic and neurotoxic effects on progenitor cell populations have been reported. In this study, we treated pluripotent human embryonic stem (hES) cells with nerve growth factor (NGF) as well as with fibrillar and oligomeric Aß1-40 and Aß1-42 (nM-µM concentrations) and thereafter studied the differentiation in vitro during 28-35 days. The process applied real time quantitative PCR, immunocytochemistry as well as functional studies of intracellular calcium signaling. Treatment with NGF promoted the differentiation into functionally mature BFCNs. In comparison to untreated cells, oligomeric Aß1-40 increased the number of functional neurons, whereas oligomeric Aß1-42 suppressed the number of functional neurons. Interestingly, oligomeric Aß exposure did not influence the number of hES cell-derived neurons compared with untreated cells, while in contrast fibrillar Aß1-40 and Aß1-42 induced gliogenesis. These findings indicate that Aß1-42 oligomers may impair the function of stem cell-derived neurons. We propose that it may be possible for future AD therapies to promote the maturation of functional stem cell-derived neurons by altering the brain microenvironment with trophic support and by targeting different aggregation forms of Aß.