In vitro Characterization of the Regional Binding Distribution of Amyloid PET Tracer Florbetaben and the Glia Tracers Deprenyl and PK11195 in Autopsy Alzheimer's Brain Tissue.

Background: Emerging evidence indicates a central role of gliosis in Alzheimer's disease (AD) pathophysiology. However, the regional distribution and interaction of astrogliosis and microgliosis in association with amyloid-β (Aβ) still remain uncertain.

Objective: Here we studied the pathological profiles in autopsy AD brain by using specific imaging tracers.

Synthesis and evaluation of 6-(3-[(18)F]fluoro-2-hydroxypropyl)-substituted 2-pyridylbenzothiophenes and 2-pyridylbenzothiazoles as potential PET tracers for imaging Aβ plaques.

3-[(18)F]Fluoro-2-hydroxypropyl substituted compounds were synthesized and evaluated as novel (18)F-labeled PET tracers for imaging Aβ plaque in a living brain. All compounds exhibited high binding affinities toward the synthetic Aβ1-42 aggregate and/or Alzheimer's disease brain homogenate. In the microPET study with normal mice, the 3-[(18)F]fluoro-2-hydroxypropyl substituted compounds resulted in fast brain washout by reducing the lipophilicities of the compounds.

Positron emission tomography imaging of the 18-kDa translocator protein (TSPO) with [18F]FEMPA in Alzheimer's disease patients and control subjects.

Purpose: Imaging of the 18-kDa translocator protein (TSPO) is a potential tool for examining microglial activation and neuroinflammation in early Alzheimer's disease (AD). [(18)F]FEMPA is a novel high-affinity second-generation TSPO radioligand that has displayed suitable pharmacokinetic properties in preclinical studies. The aims of this study were to quantify the binding of [(18)F]FEMPA to TSPO in AD patients and controls and to investigate whether higher [(18)F]FEMPA binding in AD patients than in controls could be detected in vivo.

Alzheimer amyloid peptide aβ42 regulates gene expression of transcription and growth factors.

The pathogenesis of Alzheimer's disease (AD) is characterized by the aggregation of amyloid-β (Aβ) peptides leading to deposition of senile plaques and a progressive decline of cognitive functions, which currently remains the main criterion for its diagnosis. Robust biomarkers for AD do not yet exist, although changes in the cerebrospinal fluid levels of tau and Aβ represent promising candidates in addition to brain imaging and genetic risk profiling. Although concentrations of soluble Aβ42 correlate with symptoms of AD, less is known about the biological activities of Aβ peptides which are generated from the amyloid-β protein precursor.

Specific imaging of inflammation with the 18 kDa translocator protein ligand DPA-714 in animal models of epilepsy and stroke.

Inflammation is a pathophysiological hallmark of many diseases of the brain. Specific imaging of cells and molecules that contribute to cerebral inflammation is therefore highly desirable, both for research and in clinical application. The 18 kDa translocator protein (TSPO) has been established as a suitable target for the detection of activated microglia/macrophages.

Preclinical characterization of a novel class of 18F-labeled PET tracers for amyloid-β.

Unlabelled: Imaging of amyloid-β (Aβ) plaques by PET is more and more integrated into concepts for Alzheimer disease (AD) diagnosis and drug development. The objective of this study was to find novel chemical entities that can be transformed into (18)F-labeled Aβ tracers with favorable brain washout kinetics and low background signal.

Methods: High-throughput screening of a large chemical library was used to identify new ligands for fibrillar aggregates of Aβ(1-42) peptide.

In vitro characterization of [18F]-florbetaben, an Aβ imaging radiotracer.

Purpose: Amyloid-β (Aβ) plaques are a major pathological hallmark of Alzheimer's disease (AD). The noninvasive detection of Aβ plaques may increase the accuracy of clinical diagnosis as well as monitor therapeutic interventions. While [(11)C]-PiB is the most widely used Aβ positron emission tomography (PET) radiotracer, due to the short half-life of (11)C (20 min), its application is limited to centers with an on-site cyclotron and (11)C radiochemistry expertise.

The norepinephrine transporter (NET) radioligand (S,S)-[18F]FMeNER-D2 shows significant decreases in NET density in the human brain in Alzheimer's disease: a post-mortem autoradiographic study.

Earlier post-mortem histological and autoradiographic studies have indicated a reduction of cell numbers in the locus coeruleus (LC) and a corresponding decrease in norepinephrine transporter (NET) in brains obtained from Alzheimer's disease (AD) patients as compared to age-matched healthy controls. In order to test the hypothesis that the regional decrease of NET is a disease specific biomarker in AD and as such, it can be used in PET imaging studies for diagnostic considerations, regional differences in the density of NET in various anatomical structures were measured in whole hemisphere human brain slices obtained from AD patients and age-matched control subjects in a series of autoradiographic experiments using the novel selective PET radioligand for NET (S,S)-[(18)F]FMeNER-D(2). (S,S)-[(18)F]FMeNER-D(2) appears to be a useful imaging biomarker for quantifying the density of NET in various brain structures, including the LC and the thalamus wherein the highest densities are found in physiological conditions.

Induced LC degeneration in APP/PS1 transgenic mice accelerates early cerebral amyloidosis and cognitive deficits.

Degeneration of locus ceruleus neurons and subsequent reduction of norepinephrine concentration in locus ceruleus projection areas represent an early pathological indicator of Alzheimer's disease. In order to model the pathology of the human disease and to study the effects of norepinephrine-depletion on amyloid precursor protein processing, behaviour, and neuroinflammation, locus ceruleus degeneration was induced in mice coexpressing the swedish mutant of the amyloid precursor protein and the presenilin 1 DeltaExon 9 mutant (APP/PS1) using the neurotoxin N-(2-chloroethyl)-N-ethyl-bromo-benzylamine (dsp4) starting treatment at 3 months of age. Norepinephrine transporter immunolabelling demonstrated severe loss of locus ceruleus neurons and loss of cortical norepinephrine transporter starting as early as 4.

Radiation dosimetry of beta-amyloid tracers 11C-PiB and 18F-BAY94-9172.

Unlabelled: Beta-amyloid (Abeta) imaging has great potential to aid in the diagnosis of Alzheimer disease and the development of therapeutics. The radiation dosimetry of Abeta radioligands may influence their application; therefore, we calculated and compared the effective doses (EDs) of 11C-PiB and a new 18F-labeled ligand, 18F-BAY94-9172.

Methods: Attenuation-corrected whole-body scans were performed at 0, 15, 30, 45, and 60 min after injection of 350+/-28 MBq (mean+/-SD) of 11C-PiB in 6 subjects and at 0, 20, 60, 120, and 180 min after injection of 319+/-27 MBq of 18F-BAY94-9172 in 3 subjects.

A comparative autoradiography study in post mortem whole hemisphere human brain slices taken from Alzheimer patients and age-matched controls using two radiolabelled DAA1106 analogues with high affinity to the peripheral benzodiazepine receptor (PBR) system.

The binding of two radiolabelled analogues (N-(5-[125I]Iodo-2-phenoxyphenyl)-N-(2,5-dimethoxybenzyl)acetamide ([125I]desfluoro-DAA1106) and N-(5-[125I]Fluoro-2-phenoxyphenyl)-N-(2-[125I]Iodo-5-methoxybenzyl)acetamide ([125I]desmethoxy-DAA1106) of the peripheral benzodiazepine receptor (PBR) (or TSPO, 18kDa translocator protein) ligand DAA1106 was examined by in vitro autoradiography on human post mortem whole hemisphere brain slices obtained from Alzheimer's disease (AD) patients and age-matched controls. Both [(125)I]desfluoro-IDAA1106 and [(125)I]desmethoxy-IDAA1106 were effectively binding to various brain structures. The binding could be blocked by the unlabelled ligand as well as by other PBR specific ligands.

Imaging of amyloid beta in Alzheimer's disease with 18F-BAY94-9172, a novel PET tracer: proof of mechanism.

Background: Amyloid-beta (Abeta) plaque formation is a hallmark of Alzheimer's disease (AD) and precedes the onset of dementia. Abeta imaging should allow earlier diagnosis, but clinical application is hindered by the short decay half-life of current Abeta-specific ligands. (18)F-BAY94-9172 is an Abeta ligand that, due to the half-life of (18)F, is suitable for clinical use.

Curcumin-derived pyrazoles and isoxazoles: Swiss army knives or blunt tools for Alzheimer's disease?

Curcumin binds to the amyloid beta peptide (Abeta) and inhibits or modulates amyloid precursor protein (APP) metabolism. Therefore, curcumin-derived isoxazoles and pyrazoles were synthesized to minimize the metal chelation properties of curcumin. The decreased rotational freedom and absence of stereoisomers was predicted to enhance affinity toward Abeta(42) aggregates.

Copper-dependent inhibition of human cytochrome c oxidase by a dimeric conformer of amyloid-beta1-42.

In studies of Alzheimer's disease pathogenesis there is an increasing focus on mechanisms of intracellular amyloid-beta (Abeta) generation and toxicity. Here we investigated the inhibitory potential of the 42 amino acid Abeta peptide (Abeta1-42) on activity of electron transport chain enzyme complexes in human mitochondria. We found that synthetic Abeta1-42 specifically inhibited the terminal complex cytochrome c oxidase (COX) in a dose-dependent manner that was dependent on the presence of Cu2+ and specific "aging" of the Abeta1-42 solution.

Highly conserved and disease-specific patterns of carboxyterminally truncated Abeta peptides 1-37/38/39 in addition to 1-40/42 in Alzheimer's disease and in patients with chronic neuroinflammation.

Human lumbar CSF patterns of Abeta peptides were analysed by urea-based beta-amyloid sodium dodecyl sulphate polyacrylamide gel electrophoresis with western immunoblot (Abeta-SDS-PAGE/immunoblot). A highly conserved pattern of carboxyterminally truncated Abeta1-37/38/39 was found in addition to Abeta1-40 and Abeta1-42. Remarkably, Abeta1-38 was present at a higher concentration than Abeta1-42, being the second prominent Abeta peptide species in CSF.

Pulse-chase experiments revealed beta-secretase cleavage from immature full-length amyloid precursor protein harboring the Swedish mutation. Implications for distinct pathways.

The molecular mechanisms of the nonamyloidogenic and the amyloidogenic pathways of the amyloid precursor protein (APP) are unknown, but proteolysis of APP is essential for the generation of beta-amyloid. To study the time-course of C-terminal fragment generation by alpha- and beta-secretase, we expressed the APP751 isoform with the Swedish mutation in the human neuroblastoma cell line SY5Y as previously described (Urmoneit et al., 1995).

Aggregation of A beta Alzheimer's disease-related peptide studied by dynamic light scattering.

The aggregation behavior of the major component of Alzheimer's disease-related, amyloid peptides, Abeta-(1-40) and Abeta-(1-42), was studied in solution using dynamic light scattering. With most solvents employed, we found fibrils coexisting with oligomeric Abeta species. Pronounced differences were observed in aggregation of Abeta-(1-40) and (1-42) sequences in acetonitrile-water mixtures.

Cationic lipids (lipofectamine) and disturbance of cellular cholesterol and sphingomyelin distribution modulates gamma-secretase activity within amyloid precursor protein in vitro.

To study beta-amyloid protein generation we expressed different amyloid precursor protein (APP) isoforms in the human neuroblastoma cell line SY5Y (for details see (1)). Treatment with lipofectamine, an cationic lipid for eucaryotic cell transfection, inhibits gamma-secretase activity and stimulates the physiological APP cleavage by alpha-secretase activity. Beside the MDL inhibitor (2), this is the second agent that shows modulation of gamma-secretase activity in vitro.

Alzheimer's disease betaA4 protein release and amyloid precursor protein sorting are regulated by alternative splicing.

We show here that alternative splicing influences the polarized secretion of amyloid precursor protein (APP) as well as the release of its proteolytic 3-4-kDa fragments betaA4 and p3. In Madin-Darby canine kidney II cells stably transfected with various APP isoforms and APP mutants, APPsec was consistently secreted basolaterally. In contrast, Madin-Darby canine kidney II cells transfected with L-APP677, which occurs naturally by alternative splicing of exon 15, secreted this isoform both apically and basolaterally, while maintaining the basolateral sorting of endogenous APPsec.

Inhibition of beta A4 production by specific modulation of beta-secretase activity.

To study amyloid precursor protein (APP) processing we expressed different APP isoforms with and without the Swedish mutation and the membrane inserted C-terminal 100 residues of APP (SPA4CT) in the human neuroblastoma cell line SY5Y. We show that expression of the Swedish mutation results in a significant production of the amyloidogenic intermediate A4CT, which is further processed by gamma-secretase leading to an overproduction of beta A4. Treatment with methylamine and ammonium chloride, inhibitors interfering with intracellular transport mechanisms, inhibits beta-secretase activity without influencing the physiological APP cleavage by alpha-secretase activity.

Amyloid precursor protein secretion and beta A4 amyloid generation are not mutually exclusive.

The cellular factors regulating the generation of beta A4 from the amyloid precursor protein (APP) are unknown. Protein phosphorylation by protein kinase C (PKC) has been found to influence the processing and metabolism of APP. In this report, we show that in the human neuroblastoma cell line SY5Y, beta A4 generation from full-length APP is not changed by PKC activation whereas production of the non-amyloidogenic secretory fragment (APPsec) and of the C-terminal fragment of beta A4 (p3) are stimulated.

Generation of beta A4 from the amyloid protein precursor and fragments thereof.

The cellular mechanisms underlying the generation of beta A4 in Alzheimer's disease and its relationship to the normal metabolism of the amyloid protein precursor (APP) are unknown. In this report, we show that expression of the C-terminal 100 residues of APP, with (SPA4CT) or without (A4CT) a signal sequence in the N-terminal position, in human neuroblastoma cells results in secretion of a 4 kDa beta A4-like peptide. In A4CT and SPA4CT expressing SY5Y cells, beta A4 generation could not be inhibited by the lysosomotropic amines chloroquine and ammonium chloride but was inhibited by brefeldin A, monensin and methylamine.

Regulation and expression of the Alzheimer's beta/A4 amyloid protein precursor in health, disease, and Down's syndrome.

A four- to fivefold overexpression of the gene for the Alzheimer beta/A4 amyloid precursor protein (APP) in individuals with Down's Syndrome (DS) appears to be responsible for the fifty year earlier onset of Alzheimer's disease (AD) pathology in DS compared to the normal population. It is therefore likely that a deregulated overexpression of the APP gene is a risk factor for the beta/A4 amyloid formation. To test this hypothesis and to get a better understanding of how APP expression is regulated, we studied the 5' control region of the human APP gene, alternative splicing of the 19 APP exons, and APP biogenesis, metabolism and function.

Amyloidogenicity of rodent and human beta A4 sequences.

Previously we have shown that aggregation of the C-terminal 100 residues (A4CT) of the beta A4 amyloid protein precursor (APP) and also of beta A4 itself depends on the presence of metal-catalyzed oxidation systems [T. Dyrks et al. (1988) EMBO J.

Amyloidogenicity of beta A4 and beta A4-bearing amyloid protein precursor fragments by metal-catalyzed oxidation.

Previously we have shown that the COOH-terminal 100 residues (A4CT) of the amyloid protein precursor (APP), which carry the sequence of the amyloid beta A4 protein of Alzheimer's disease at N-terminal position, form highly insoluble aggregates if expressed in the rabbit reticulocyte lysate and analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (Dyrks, T., Weidemann, A., Multhaup, G.