Amyloid Beta Derived Diffusible Ligand: Beta Amyloid Ligands: Research Papers

Amyloid Beta Derived Diffusible Ligand: Beta Amyloid Ligands: Research Papers

Sim PL, Heese K. Ligand-Dependent Activation of the Chimeric Tumor Necrosis Factor Receptor-Amyloid Precursor Protein (APP) Reveals Increased APP Processing and Suppressed Neuronal Differentiation. Neurosignals. 2009 Sep 29;18(1):9-23. PubMed Abstract

The beta-amyloid precursor protein (APP) is a type I transmembrane protein whose functions and metabolic processing have been implicated in the pathogenesis of Alzheimer's disease (AD). APP's physical resemblance as a glycosylated receptor and the presence of several conserved motifs which are characteristics of a membrane-associated receptor has prompted interest to study and understand the role of downstream signaling events mediated by the activation of APP during both physiological and pathological conditions. Efforts to elucidate the mechanisms of APP signaling have not been conclusive. In order to further characterize the intracellular signaling activities of APP, we have constructed a chimeric APP receptor which is made up of the extracellular domain of human tumor necrosis factor receptor superfamily, member 1B (TNFRSF1B), the membrane-spanning segment of human APP(770) isoform's beta-cleaved carboxyl-terminal fragment (C99), and the green fluorescent protein (GFP) tagged to the carboxyl-terminus of C99. The mammalian rat pheochromocytoma (PC12) cell line is used as the cellular model for transfection of this TNFRSF1B-APP-GFP (TAF) fusion receptor. Ligand-specific stimulation of this TAF receptor using human recombinant TNF reveals the induction of cytoplasmic TAF phosphorylation on Thr743 (numbering for APP(770) isoform) and an elevated release of APP intracellular domains (AICDs). Time-lapse microscopy shows the trafficking of GFP-tagged AICDs into the nucleus upon TAF receptor activation. The increased presence of AICDs is believed to suppress neuronal differentiation of PC12 cells in response to nerve growth factor treatment, by negatively regulating the levels of p53, cyclin D1 and phosphorylation of the signal transducer and activator of transcription STAT3. Copyright © 2009 S. Karger AG, Basel.

Drew SC, Masters CL, Barnham KJ. Alanine-2 carbonyl is an oxygen ligand in Cu2+ coordination of Alzheimer's disease amyloid-beta peptide--relevance to N-terminally truncated forms. J Am Chem Soc. 2009 Jul 1;131(25):8760-1. PubMed Abstract

Copper interactions with the beta-amyloid peptide (Abeta) are believed to play a role in Alzheimer's disease (AD), in particular due to production of reactive oxygen species and Cu(2+)-mediated oligomerization. To understand the role that copper might play in these processes, a detailed knowledge of the fundamental Cu(2+)/Abeta interactions is essential. To date, the identity of the oxygen ligand(s) involved in Cu(2+) coordination by Abeta has remained unclear. Here, we have used site-specific (13)C and (15)N labeling in conjunction with hyperfine sublevel correlation (HYSCORE) spectroscopy to unambiguously identify the carbonyl of Alanine-2 as an oxygen ligand in one of the pH-dependent Cu(2+) coordination modes of Abeta. Polarization of the carbonyl moiety by Cu(2+) could promote amide hydrolysis and cleavage of the peptide bond between Ala2 and Glu3, providing a chemical mechanism for the generation of truncated Abeta 3-40/42 species found in AD plaques.

Aalto S, Scheinin NM, Kemppainen NM, Någren K, Kailajärvi M, Leinonen M, Scheinin M, Rinne JO. Reproducibility of automated simplified voxel-based analysis of PET amyloid ligand [(11)C]PIB uptake using 30-min scanning data. Eur J Nucl Med Mol Imaging. 2009 Jun 4; PubMed Abstract

PURPOSE: Positron emission tomography (PET) with 11C-labelled Pittsburgh compound B ([11C]PIB) enables the quantitation of beta-amyloid accumulation in the brain of patients with Alzheimer's disease (AD). Voxel-based image analysis techniques conducted in a standard brain space provide an objective, rapid and fully automated method to analyze [11C]PIB PET data. The purpose of this study was to evaluate both region- and voxel-level reproducibility of automated and simplified [11C]PIB quantitation when using only 30 min of imaging data. METHODS: Six AD patients and four healthy controls were scanned twice with an average interval of 6 weeks. To evaluate the feasibility of short scanning (convenient for AD patients), [11C]PIB uptake was quantitated using 30 min of imaging data (60 to 90 min after tracer injection) for region-to-cerebellum ratio calculations. To evaluate the reproducibility, a test-retest design was used to derive absolute variability (VAR) estimates and intraclass correlation coefficients at both region-of-interest (ROI) and voxel level. RESULTS: The reproducibility both at the region level (VAR 0.9-5.5%) and at the voxel level (VAR 4.2-6.4%) was good to excellent. Based on the variability estimates obtained, power calculations indicated that 90% power to obtain statistically significant difference can be achieved using a sample size of five subjects per group when a 15% change from baseline (increase or decrease) in [11C]PIB accumulation in the frontal cortex is anticipated in one group compared to no change in another group. CONCLUSION: Our results showed that an automated analysis method based on an efficient scanning protocol provides reproducible results for [11C]PIB uptake and appears suitable for PET studies aiming at the quantitation of amyloid accumulation in the brain of AD patients for the evaluation of progression and treatment effects.

Johnson AE, Jeppsson F, Sandell J, Wensbo D, Neelissen JA, Juréus A, Ström P, Norman H, Farde L, Svensson SP. AZD2184: a radioligand for sensitive detection of beta-amyloid deposits. J Neurochem. 2009 Mar;108(5):1177-86. PubMed Abstract

The presence of beta-amyloid plaques in brain is a hallmark of Alzheimer's disease (AD) and serves as a biomarker for confirmation of diagnosis postmortem. Positron emission tomography (PET) radioligands such as Pittsburgh compound B ([(11)C]-2-(3-fluoro-4-methylamino-phenyl)-benzothiazol-6-ol) (PIB) binds selectively to beta-amyloid and are promising new tools supporting the clinical diagnoses of AD. In addition, such methodology may be useful for evaluation of new drugs aiming at reduction of amyloid plaque load. The objective of this study is to develop a new amyloid selective PET radioligand with higher signal-to-background ratio when compared with existing amyloid PET ligands. The lead compound, AZD2184, (2-[6-(methylamino)pyridin-3-yl]-1,3-benzothiazol-6-ol) was found to have high affinity for amyloid fibrils in vitro (K(d): 8.4 +/- 1.0 nM). Two minutes after i.v. administration in rats, about 1% of the dose was in brain. In vitro autoradiography on cortical brain sections from amyloid-beta precursor protein/presenilin 1 (APP/PS1) mice and AD patients showed that while [(3)H]AZD2184 and [(3)H]PIB are mutually displaceable, [(3)H]AZD2184 displays a higher signal-to-background ratio primarily by virtue of lower background binding levels. The ratio of binding ability in prefrontal cortex (high plaque load) to subcortical white matter (background) was 4.5 for [(3)H]AZD2184 and 0.8 for [(3)H]PIB at 1 nM. In adjacent cortical sections from APP/PS1 mouse as well as from AD cortical tissue, [(3)H]AZD2184 and antibodies to human beta-amyloid labeled identical structures. In vivo administration of [(3)H]AZD2184 to APP/PS1 mice further showed that [(3)H]AZD2184 labels amyloid deposits with low non-specific background binding. Taken together, the pre-clinical profile of AZD2184 in relation to the reference ligand PIB, suggests that (11)C-labeled AZD2184 is a potential radioligand for PET-visualization of beta-amyloid deposits in the living human brain.

Koivunen J, Verkkoniemi A, Aalto S, Paetau A, Ahonen JP, Viitanen M, Någren K, Rokka J, Haaparanta M, Kalimo H, Rinne JO. PET amyloid ligand [11C]PIB uptake shows predominantly striatal increase in variant Alzheimer's disease. Brain. 2008 Jul;131(Pt 7):1845-53. PubMed Abstract

Variant Alzheimer's disease (VarAD) with spastic paraparesis and presenile dementia is associated with certain mutations of the presenilin 1 (PS-1) gene, particularly those leading to deletion of exon 9 (PS-1Delta E9). VarAD is neuropathologically characterized by the presence of unusually large, Abeta42 positive, non-cored 'cotton wool' plaques (CWPs), also devoid of dystrophic neurites. The aim of the present study was to find out whether [(11)C]PIB would show increased uptake and serve as an in vivo biomarker of amyloid accumulation in VarAD. A further aim was to assess the correspondence of the [(11)C]PIB binding to the amount and type of Abeta deposits in another group of deceased VarAD patients' brains. We studied four patients with VarAD and eight healthy controls with PET using [(11)C]PIB as tracer. Parametric images were computed by calculating the region-to-cerebellum and region-to-pons ratio in each voxel over 60-90 min. Group differences in [(11)C]PIB uptake were analysed with automated region-of-interest (ROI) analysis. [(11)C]PIB uptake was compared to the immunohistochemically demonstrated deposition of Abeta in the brains of another group of four deceased VarAD patients. Patients with VarAD had significantly higher [(11)C] PIB uptake than the control group in the striatum (caudate nucleus and putamen), anterior and posterior cingulate gyrus, occipital cortex and thalamus. In the caudate and putamen [(11)C]PIB uptake, expressed as region-to-cerebellum ratio, was on the average 43% greater than the mean of the control group. The increases in the anterior (28%) and posterior (27%) cingulate gyrus, occipital cortex (21%) and thalamus (14%) were smaller. All VarAD patients showed this similar topographical pattern of increased [(11)C]PIB uptake. The results were essentially similar when the uptake was expressed as region-to-pons ratios. [(11)C]PIB imaging shows increased uptake in patients with VarAD especially in the striatum, and it can be used to detect amyloid accumulation in vivo in these patients. The pattern of increased [(11)C]PIB uptake is different from that described in sporadic Alzheimer's disease and resembles that seen in Alzheimer's disease patients with certain presenilin-1 mutations or amyloid precursor protein gene duplication showing predominantly striatal increase in [(11)C]PIB uptake.

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