Alzheimer's Disease Amyloid Plaques Research Articles

Mostly Separate Distributions of CLAC- versus Aβ40- or Thioflavin S-Reactivities in Senile Plaques Reveal Two Distinct Subpopulations of β-Amyloid Deposits

Collagenous Alzheimer amyloid plaque component (CLAC) is a unique non-Abeta amyloid component of senile plaques (SP) derived from a transmembrane collagen termed CLAC-precursor. Here we characterize the chronological and spatial relationship of CLAC with other features of SP amyloid in the brains of patients with Alzheimer's disease (AD), Down syndrome (DS), and of PSAPP transgenic mice. In AD and DS cerebral cortex, CLAC invariably colocalized with Abeta42 but often lacked Abeta40- or thioflavin S (thioS)-reactivities. Immunoelectron microscopy of CLAC-positive SP showed labeling of fibrils that are more loosely dispersed compared to typical amyloid fibrils in CLAC-negative SP. In DS cerebral cortex, diffuse plaques in young patients were negative for CLAC, whereas a subset of SP became CLAC-positive in patients aged 35 to 50 years, before the appearance of Abeta40. In DS cases over 50 years of age, Abeta40-positive SP dramatically increased, whereas CLAC burden remained at a constant level. In PSAPP transgenic mice, CLAC was positive in the diffuse Abeta deposits surrounding huge-cored plaques. Thus, CLAC and Abeta40 or thioS exhibit mostly separate distribution patterns in SP, suggesting that CLAC is a relatively early component of SP in human brains that may have inhibitory effects against the maturation of SP into beta-sheet-rich amyloid deposits.

Contribution of glial cells to the development of amyloid plaques in Alzheimer’s disease

Amyloid plaques appear early during Alzheimer’s disease (AD), and their development is intimately linked to activated astrocytes and microglia. Astrocytes are capable of accumulating substantial amounts of neuron-derived, amyloid β(1–42) (Aβ42)-positive material and other neuron-specific proteins as a consequence of their debris-clearing role in response to local neurodegeneration. Immunohistochemical analyses have suggested that astrocytes overburdened with these internalized materials can eventually undergo lysis, and radial dispersal of their cytoplasmic contents, including Aβ42, can lead to the deposition of a persistent residue in the form of small, GFAP-rich, astrocytic amyloid plaques, first appearing in the molecular layer of the cerebral cortex. Microglia, most of which appear to be derived from blood monocytes and recruited from local blood vessels, rapidly migrate into and congregate within neuritic and dense-core plaques, but not diffuse plaques. Instead of internalizing and removing Aβ from plaques, microglia appear to contribute to their morphological and chemical evolution by facilitating the conversion of existing soluble and oligomeric Aβ within plaques to the fibrillar form. Aβ fibrillogenesis may occur largely within tiny, tube-like invaginations in the surface plasma membrane of microglia. These results highlight the therapeutic potential of blocking the initial intracellular accumulation of Aβ42 in neurons and astrocytes and inhibiting microglia-mediated assembly of fibrillar Aβ, which is particularly resistant to degradation in Alzheimer brain.

Design and chemical synthesis of a magnetic resonance contrast agent with enhanced in vitro binding, high blood-brain barrier permeability, and in vivo targeting to Alzheimer's disease amyloid plaques.

Molecular imaging is an important new direction in medical diagnosis; however, its success is dependent upon molecular probes that demonstrate selective tissue targeting. We report the design and chemical synthesis of a derivative of human amyloid-beta (Abeta) peptide that is capable of selectively targeting individual amyloid plaques in the brain of Alzheimer's disease transgenic mice after being intravenously injected. This derivative is based on the sequence of the first 30 amino acid residues of Abeta with asparagyl/glutamyl-4-aminobutane residues (N-4ab/Q-4ab) substituted at unique Asp and Glu positions and with Gd-DTPA-aminohexanoic acid covalently attached at the N-terminal Asp. The Gd[N-4ab/Q-4ab]Abeta30 peptide was homogeneous as shown by high-resolution analytical techniques with a mass of +/-4385 Da determined by electrospray ionization mass spectrometry. This diamine- and gadolinium-substituted derivative of Abeta is shown to have enhanced in vitro binding to Alzheimer's disease (AD) amyloid plaques and increased in vivo permeability at the blood-brain barrier because of the unique Asp/Glu substitutions. In addition, specific in vivo targeting to AD amyloid plaques is demonstrated throughout the brain of an APP, PS1 transgenic mouse after intravenous injection. Because of the magnetic resonance (MR) imaging contrast enhancement provided by gadolinium, this derivative should enable the in vivo MR imaging of individual amyloid plaques in the brains of AD animals or patients to allow for early diagnosis and also provide a direct measure of the efficacy of anti-amyloid therapies currently being developed.

Amyloid beta-peptide interactions with neuronal and glial cell plasma membrane: binding sites and implications for Alzheimer's disease.

The extracellular accumulation of amyloid-beta (Abeta) in neuritic plaques is one of the characteristic hallmarks of Alzheimer's disease (AD), a progressive dementing neurodegenerative disorder of the elderly. By virtue of its structure, Abeta is able to bind to a variety of biomolecules, including lipids, proteins and proteoglycans. The binding of the various forms of Abeta (soluble or fibrillar) to plasma membranes has been studied with regard to the direct toxicity of Abeta to neurons, and the activation of a local inflammation phase involving microglia. The binding of Abeta to membrane lipids facilitates Abeta fibrillation, which in turn disturbs the structure and function of the membranes, such as membrane fluidity or the formation of ion channels. A subset of membrane proteins binds Abeta. The serpin-enzyme complex receptor (SEC-R) and the insulin receptor can bind the monomeric form of Abeta. The alpha7nicotinic acetylcholine receptor (alpha7nAChR), integrins, RAGE (receptor for advanced glycosylation end-products) and FPRL1 (formyl peptide receptor-like 1) are able to bind the monomeric and fibrillar forms of Abeta. In addition, APP (amyloid precursor protein), the NMDA-R (N-methyl-D-aspartate receptor), the P75 neurotrophin receptor (P75NTR), the CLAC-P/collagen type XXV (collagen-like Alzheimer amyloid plaque component precursor/collagen XXV), the scavenger receptors A, BI (SR-A, SR-BI) and CD36, a complex involving CD36, alpha6beta1-integrin and CD47 have been reported to bind the fibrillar form of Abeta. Heparan sulfate proteoglycans have also been described as cell-surface binding sites for Abeta. The various effects of Abeta binding to these membrane molecules are discussed.

The lipophilic metal chelator DP-109 reduces amyloid pathology in brains of human β-amyloid precursor protein transgenic mice

Metals such as zinc, copper and iron contribute to aggregation of amyloid-β (Aβ) protein and deposition of amyloid plaques in Alzheimer’s disease (AD). We examined whether the lipophilic metal chelator DP-109 inhibited these events in aged female hAβPP-transgenic Tg2576 mice. Daily gavage administration of DP-109 for 3 months markedly reduced the burden of amyloid plaques and the degree of cerebral amyloid angiopathy in brains, compared to animals receiving vehicle treatment. Moreover, DP-109 treatment appeared to facilitate the transition of Aβ from insoluble to soluble forms in the cerebrum. These results further support the hypothesis that endogenous metals are involved in the deposition of aggregated Aβ in brains of AD patients, and that metal chelators may be useful therapeutic agents in the treatment of AD.

Binding sites of amyloid beta-peptide in cell plasma membrane and implications for Alzheimer's disease.

The binding of amyloid beta peptides (Abeta) to plasma membranes appears to be a promising point of intervention in the events leading to the development of Alzheimer's disease (AD). This binding has been studied as regards the direct toxicity of Abeta on neurons, and the activation of a local inflammation phase involving microglia. By virtue of its structure, Abeta is able to bind to a variety of biomolecules, including lipids, proteoglycans and proteins. This review focuses on the membrane proteins that can mediate the interaction between Abeta and the plasma membranes in AD. On neurons, these are APP (amyloid precursor protein), the NMDA-R (N-methyl-D-aspartate receptor), integrins, the alpha7nicotinic acetylcholine receptor (alpha7nAChR), the P75 neurotrophin receptor (P75NTR) and the CLAC-P/collagen type XXV (collagen-like Alzheimer amyloid plaque component precursor/collagen XXV). On glial cells, FPRL1 (formyl peptide receptor-like 1), the scavenger receptors A, BI (SR-A, SR-BI) and CD36, a complex involving CD36, alpha(6)beta(1)-integrin and CD47, and heparan sulfate proteoglycans have been reported to bind Abeta. It should be noted that integrins, RAGE (receptor for advanced glycosylation end-products), the Serpin-enzyme complex receptor (SEC-R) and the insulin receptor can bind Abeta and are present on neurons and on glial cells. After a presentation of the structure and the function of each of these proteins, the method used to prove their binding to Abeta is described, and the implication of this binding in AD is discussed. Finally, it is underlined that multireceptor complexes containing integrins may be involved in this interaction.

Cyclin-dependent kinase 5--a neuronal killer?

In dividing cells, cyclin-dependent kinases (Cdks) are cell cycle-associated protein kinases that regulate proliferation, differentiation, senescence, and apoptosis. In neurons that no longer divide, deregulation of Cdks, especially Cdk5, occurs in many neurological disorders, including Alzheimer's disease (AD) and Parkinson's disease (PD). Cdk5 is a unique member of the Cdk family because it does not play a critical role in cell cycle progression, and it is not activated by a cyclin. Instead, Cdk5 normally is activated by the regulatory protein p35. This Cdk5/p35 activity has emerged as an important regulator of proper development of the mammalian central nervous system. In vitro studies suggest that aberrant activation of Cdk5 by an endogenous truncated version (p25) of p35 might be a key event in the process of neurodegeneration. One enzyme responsible for cleavage of p35 to form p25 is calpain, a calcium-activated protease that has been shown to be involved in neuronal cell death. Recent studies provided important in vivo evidence that hyperactivation and redistribution of Cdk5 by p25 plays an essential role in the phosphorylation of "pathological" substrates (such as tau) and the cell death of neurons in experimental models of AD and PD. Because amyloid beta peptide, the primary neurotoxic component of amyloid plaques in AD, has been shown to increase the conversion of p35 to p25, aberrant activation of Cdk5 by p25 might be a pathway connecting amyloid beta toxicity to tau hyperphosphorylation in AD.

Neuroinflammatory perspectives on the two faces of Alzheimer's disease.

The amyloid plaques in Alzheimer's disease (AD) brains are co-localized with a broad variety of inflammation-related proteins (complement factors, acute-phase proteins, pro-inflammatory cytokines) and clusters of activated microglia. The present data suggest that Abeta deposits in AD brains are closely associated with a locally induced, non-immune mediated, chronic inflammatory response. Clinicopathological and neuroradiological studies show that activation of microglia is a relatively early pathogenic event that precedes the process of neuropil destruction in AD. Epidemiological studies indicate that polymorphisms of certain cytokines and acute-phase proteins that are colocalized with Abeta plaques, are genetic risk factors of AD. Epidemiological studies have also shown that the use of classical nonsteroidal anti-inflammatory drugs (NSAIDs) can prevent the risk of AD but clinical trials with anti-inflammatory drugs in AD patients were negative. These findings indicate that anti-inflammatory agents can be helpful in the prevention but not in the treatment of AD. So, pathological, genetic and therapeutic studies suggest that inflammatory mechanisms are most likely involved in the early steps of the pathological cascade. In the autosomal dominant inherited forms of AD the primary factor is the increased production of Abeta1-42 resulting into fibrillar Abeta deposition that elicits a brain inflammatory response. The etiology of the sporadic forms is yet unknown but this subtype is considered to be heterogeneous and multifactorial in its pathogenesis. Here we review the evidence that inflammation related events could be a critical etiological factor in certain forms of the sporadic AD.

Amyloid-β is found in drusen from some age-related macular degeneration retinas, but not in drusen from normal retinas

Immunohistochemical staining was performed with three Aβ antibodies on sections from nine normal eyes and nine eyes with age-related macular degeneration (AMD). The AMD eyes included three eyes with early AMD, three eyes with geographic atrophy, and three eyes with exudative disease. Five sections form each eye were evaluated. Aβ-positive deposits in drusen were identified using epifluorescence and confocal microscopy. Antibodies were pre-adsorbed with Aβ peptide to verify specificity. Some sections were also stained with PAS-hematoxylin to aid in identification of morphology. The Aβ antibody was optimized by detection of Aβ in amyloid plaques in Alzheimer’s disease. The Aβ label was blocked by pre-adsorption of antibody with Aβ peptide, verifying specificity. Four of the nine AMD specimens and none of nine controls contained Aβ-positive drusen. Two of the early AMD eyes had a few Aβ-positive drusen, each with a few Aβ-containing vesicles, and two of the geographic atrophy eyes had many Aβ-positive drusen with many Aβ-containing vesicles. In four of the nine eyes with AMD, Aβ was localized to a subset of drusen. Aβ in drusen correlated with the location of degenerating photoreceptors and retinal pigment epithelium.—Hans E. Grossniklaus

Identification of peptides that specifically bind Aβ 1–40 amyloid in vitro and amyloid plaques in Alzheimer's disease brain using phage display

The accumulation of the amyloid-β (Aβ) peptides in amyloid plaques correlates with pathologic changes that occur in the brains of patients with Alzheimer's disease (AD). The ability to directly target reagents to the amyloid form of the Aβ peptide may allow the delivery of neuroprotective agents to make amyloid plaques less toxic, the delivery of amyloid-destroying molecules to eliminate plaques, or the delivery of reagents to prevent amyloid plaque formation. In addition, such reagents may be useful as diagnostic tools to quantitate the extent of amyloid plaque formation in AD patients. As a step toward these goals, we have used phage peptide display technology to identify peptides that bind specifically to the amyloid form of the Aβ 1–40 peptide. Here we identify two 20-amino acid peptides with similar structural features that bind to the amyloid form of Aβ 1–40 but not to monomeric Aβ 1–40. A recombinant form of one of these peptides was produced in Escherichia coli as a fusion protein with thioredoxin. After purification, this reagent bound Aβ 1–40 amyloid in vitro with a K d of 60 nM and specifically labeled amyloid plaques in AD brains. A chemically synthesized version of this peptide also bound Aβ 1–40 amyloid and specifically stained amyloid plaques in AD brain. These peptide sequences represent new potential carrier molecules to deliver medicines to amyloid plaques in AD patients and to image plaques in AD brains.

11C-labeled stilbene derivatives as Aβ-aggregate-specific PET imaging agents for Alzheimer’s disease

A series of stilbene derivatives as potential diagnostic imaging agents targeting amyloid plaques in Alzheimer’s disease (AD) were synthesized and evaluated. The syntheses of the stilbenes were successfully achieved by a simple Wadsworth-Emmons reaction between diethyl (4-nitrobenzyl)phosphonate and 4-methoxybenzaldehyde. 4-N,N-dimethylamino-4′-methyoxy and the corresponding 4-N-monomethylamino-, 4′-hydroxy stilbenes showed good binding affinities towards Aβ aggregates in vitro (K i < 10 nM). The 11C labeled 4-N-methylamino-4′-hydroxystilbene, [ 11C]4, was prepared by 11C methylation of 4-amino-4′-hydroxystilbene. The [ 11C]4 displayed a moderate lipophilicity (log P = 2.36), and showed a very good brain penetration and washout from normal rat brain after an iv injection. In vitro autoradiography of transgenic AD mouse brain sections showed a high specific labeling of β-amyloid plaques, whereas the control sections showed no binding. Taken together the data suggest that a relatively simple stilbene derivative, [ 11C]4, N-[ 11C]methylamino-4′-hydroxystilbene, may be useful as a positron emission tomography (PET) imaging agent for mapping Aβ plaques in the brain of patients with Alzheimer’s disease.

Advanced glycation endproducts and pro-inflammatory cytokines in transgenic Tg2576 mice with amyloid plaque pathology.

Increased expression and altered processing of the amyloid precursor protein (APP) and generation of beta-amyloid peptides is important in the pathogenesis of amyloid plaques in Alzheimer's disease (AD). Transgenic Tg2576 mice overexpressing the Swedish mutation of human APP exhibit beta-amyloid deposition in the neocortex and limbic areas, accompanied by gliosis and dystrophic neurites. However, murine plaques appear to be less cross-linked and the mice show a lower degree of inflammation and neurodegeneration than AD patients. 'Advanced glycation endproducts (AGEs)', formed by reaction of proteins with reactive sugars or dicarbonyl compounds, are able to cross-link proteins and to activate glial cells, and are thus contributing to plaque stability and plaque-induced inflammation in AD. In this study, we analyze the tissue distribution of AGEs and the pro-inflammatory cytokines IL-1beta and TNF-alpha in 24-month-old Tg2576 mice, and compare the AGE distribution in these mice with a younger age group (13 months old) and a typical Alzheimer's disease patient. Around 70% of the amyloid plaque cores in the 24-month-old mice are devoid of AGEs, which might explain their solubility in physiological buffers. Plaque associated glia, which express IL-1beta and TNF-alpha, contain a significant amount of AGEs, suggesting that plaques, i.e. Abeta as its major component, can induce intracellular AGE formation and the expression of the cytokines on its own. In the 13-month-old transgenic mice, AGEs staining can neither be detected in plaques nor in glial cells. In contrast, AGEs are present in high amounts in both plaques and glia in the human AD patient. The data obtained in this show interesting differences between the transgenic mouse model and AD patients, which should be considered using the transgenic approach to test therapeutical strategies to eliminate plaques or to attenuate the inflammatory response in AD.

Cholesterol in Alzheimer's disease and tauopathy.

Cholesterol has been implicated in the pathogenesis of amyloid plaques in Alzheimer's disease (AD) and in the formation of neurofibrillary pathology in Niemann-Pick disease. Several epidemiology studies have implicated high cholesterol as a risk factor for AD and have shown that the use of cholesterol-reducing agents (statins) can be protective against the disease. We and others have shown that cholesterol levels modulate the processing of the amyloid precursor protein (APP) both in vivo and in vitro, affecting the accumulation of A-beta (Abeta) peptides that may directly impact the risk of AD. Mutations in the Niemann-Pick C gene (NPC) result in deficient cholesterol transport/storage. Clinically, Niemann-Pick disease causes a severe childhood lipidosis, with neurodegeneration characterized by the presence of AD-type neurofibrillary tangles (NFTs) composed of hyperphosphorylated tau. Studies of mouse models of NPC show that defects in cellular cholesterol trafficking are associated with enhanced generation of Abeta and the hyperphosphorylation of tau, further implicating the cholesterol homeostasis pathway as a risk factor for amyloidosis.

Molecular Targeting of Alzheimer's Amyloid Plaques for Contrast-Enhanced Magnetic Resonance Imaging

Smart molecular probes for both diagnostic and therapeutic purposes are expected to provide significant advances in clinical medicine and biomedical research. We describe such a probe that targets β-amyloid plaques of Alzheimer's disease and is detectable by magnetic resonance imaging (MRI) because of contrast imparted by gadolinium labeling. Three properties essential for contrast enhancement of β-amyloid plaques on MRI exist in this smart molecular probe, putrescine–gadolinium–amyloid-β peptide: (1) transport across the blood–brain barrier following intravenous injection conferred by the polyamine moiety, (2) binding to plaques with molecular specificity by putrescine–amyloid-β, and (3) magnetic resonance imaging contrast by gadolinium. MRI was performed on ex vivo tissue specimens at 7 T at a spatial resolution approximating plaque size (62.5 μm 3), in order to prove the concept that the probe, when administered intravenously, can selectively enhance plaques. The plaque-to-background tissue contrast-to-noise ratio, which was precisely correlated with histologically stained plaques, was enhanced more than nine-fold in regions of cortex and hippocampus following intravenous administration of this probe in AD transgenic mice. Continuing engineering efforts to improve spatial resolution are underway in MRI, which may enable in vivo imaging at the resolution of individual plaques with this or similar contrast probes. This could enable early diagnosis and also provide a direct measure of the efficacy of anti-amyloid therapies currently being developed.

Methionine 35 Oxidation Reduces Fibril Assembly of the Amyloid Aβ-(1–42) Peptide of Alzheimer's Disease

The major component of amyloid plaques in Alzheimer's disease (AD) is Abeta, a small peptide that has high propensity to assemble as aggregated beta-sheet structures. Using three well established techniques for studying amyloid structure, namely circular dichroism, thioflavin-T fluorescence, and atomic force microscopy, we demonstrate that oxidation of the Met-35 side chain to a methionine sulfoxide (Met-35(ox)) significantly hinders the rate of fibril formation for the 42-residue Abeta-(1-42) at physiological pH. Met-35(ox) also alters the characteristic Abeta fibril morphology and prevents formation of the protofibril, which is a key intermediate in beta-amyloidosis and the associated neurotoxicity. The implications of these results for the biological function and role of Abeta with oxidative stress in AD are discussed.

Conformational changes preceding amyloid-fibril formation of amyloid-beta and stefin B; parallels in pH dependence.

Amyloid beta (A beta) protein is the key component of amyloid plaques in Alzheimer's disease brain whereas stefin B is an intracellular cysteine proteinase inhibitor, broadly distributed in different tissue and recently reported to form amyloid fibrils in vitro. By reducing the pH to 4.6, the native conformation of both polypeptides are changed into less ordered metastable intermediates that are stabilized by formation of the more stable fibrils. In A beta, the Glu at position 11 was found to be responsible for the conformational change at pH 4.6. Metal ions, including copper and zinc, could also induce conformational changes of A beta at neutral pH. The acid modified A beta conformer exhibited protease K resistance, preferential internalization and accumulation in the human glial cells. In stefin B, reducing the pH to pH 3.3 results in another intermediate of the molten-globule type which also leads to amyloid fibril formation. Multiple sequence alignment revealed distinct similarities of A beta (1-42) peptide, stefin B (13 to 61 residues) and prion fragment (90 to 144 residues).

Activation of group II metabotropic glutamate receptors underlies microglial reactivity and neurotoxicity following stimulation with chromogranin A, a peptide up-regulated in Alzheimer's disease.

Regulation of microglial reactivity and neurotoxicity is critical for neuroprotection in neurodegenerative diseases. Here we report that microglia possess functional group II metabotropic glutamate receptors, expressing mRNA and receptor protein for mGlu2 and mGlu3, negatively coupled to adenylate cyclase. Two different agonists of these receptors were able to induce a neurotoxic microglial phenotype which was attenuated by a specific antagonist. Chromogranin A, a secretory peptide expressed in amyloid plaques in Alzheimer's disease, activates microglia to a reactive neurotoxic phenotype. Chromogranin A-induced microglial activation and subsequent neurotoxicity may also involve an underlying stimulation of group II metabotropic glutamate receptors since their inhibition reduced chromogranin A-induced microglial reactivity and neurotoxicity. These results show that selective inhibition of microglial group II metabotropic glutamate receptors has a positive impact on neuronal survival, and may prove a therapeutic target in Alzheimer's disease.

Additive effects of amyloid β fragment and interleukin-1β on interleukin-6 secretion in rat primary glial cultures

The main constituent of the Alzheimer amyloid plaques is the amyloid beta (Abeta) peptide shown to activate glial cells in vitro. Activated glial cells are believed to contribute to neurotoxicity through production of inflammatory cytokines, such as interleukin-1 (IL-1), chemokines and neurotoxic substances. The IL-1 system has been proposed to play a role in neurodegenerative processes and can in turn induce expression of other cytokines such as IL-6. Recently, association of IL-1 and IL-6 gene polymorphism with Alzheimer's disease was reported, suggesting that these cytokines may play an important role in the development of the disease. In this study, rat primary mixed glial cells were treated with IL-1beta, Abeta(1-42) or Abeta(25-35). As expected the different treatments all resulted in activation of the transcription factor NFkappaB observed by electrophoretic mobility shift assay. Significant increases in IL-1beta and IL-6 mRNA levels, as analysed by reverse transcriptase-polymerase chain reaction (RT-PCR), were detected after the different treatments. In addition, increased secretion of IL-6 was detected by ELISA after 96 h exposure in response to IL-1beta, Abeta(1-42) or Abeta(25-35). When cells were exposed to both IL-1beta and Abeta(25-35) additive effects were observed. This supports that the effect of Abeta can be potentiated by concurrent exposure to inflammatory cytokines and that the IL-1 system is not necessary for Abeta effects on IL-6 expression in agreement with previous studies.

Benzofuran derivatives as Aβ-aggregate-specific imaging agents for Alzheimer’s disease

The purpose of this study is to develop potential I-123 labeled diagnostic imaging agents targeting amyloid plaques in Alzheimer’s disease (AD). Formation and accumulation of aggregates of beta-amyloid (Aβ) peptides in the brain are critical factors in the development and progression of AD. Small molecule-based benzofuran derivatives were designed and synthesized. Both 5- and 6-iodobenzofuran derivatives displayed excellent competition for I-125 TZDM binding to Aβ40 aggregates with K i values in the subnanomolar range. The radioiodinated ligands, with a high specific activity, were successfully prepared through an iododestannylation reaction from the corresponding tributyltin derivatives using hydrogen peroxide as the oxidant in high yields (60–80%) and with high radiochemical purities (greater than 95%). After an iv injection, all four radioiodinated ligands displayed high brain uptakes ranging from 0.5 to 1.5% initial dose/organ in normal mice. The radioactivity washed out from the mouse brain slowly (less than 50% at 2 h post injection), suggesting high in vivo non-specific binding. In conclusion, the benzofuran ligands displayed excellent binding affinity for Aβ aggregates. The long retention of these ligands in the normal mouse brain suggests that there may be high binding for these probes in the brain not associated with Aβ plaques. Additional modifications are necessary to improve the in vivo imaging properties for plaque detection.

Perturbed sphingomyelin metabolism and accumulation of ceramides and cholesterol esters in Alzheimer's disease and ALS

Alzheimer's disease (AD) and amyotrophic lateral sclerosis (ALS) involve selective degeneration of neurons involved in learning and memory (hippocampal and cortical neurons) and movement (spinal cord motor neurons), respectively. In each disorder and increase in oxidative stress is believed to render neurons vulnerable to excitotoxicity and apoptosis. We report abnormalities in sphingolipid and cholesterol metabolism in brain tissue of AD patients and a mouse model of AD (APP mutant mice), and in spinal cords of ALS patients and a transgenic mouse model of ALS (Cu/Zn‐SOD mutant mice), characterized by increased levels of sphingomyelin, long‐chain ceramides and cholesterol esters. In the mouse models these abnormalities precede the clinical phenotype. Exposure of cultured hippocampal neurons to amyloid β‐peptide (the neurotoxic component of amyloid plaques in AD) and of cultured motor neurons to oxidative insults, increases the accumulation of sphingomyelin, ceramides and cholesterol esters. Pharmacological inhibition of sphingomyelin synthesis prevents accumulation of ceramides and cholesterol esters and protects hippocampal and motor neurons against death induced by insults relevant to AD and ALS. These findings suggest links between oxidative stress, altered sphingolipid and cholesterol metabolism and the pathogenesis of AD and ALS. Our data also identify novel targets for therapeutic intervention in neurodegenerative disorders.