Cerebral Amyloid-β Research Articles

Cerebral β‐amyloid detected by Pittsburgh compound B positron emission topography predisposes to recombinant tissue plasminogen activator‐related hemorrhage

Cerebral amyloid angiopathy (CAA) may be an important predisposing factor for the hemorrhagic complications of recombinant tissue-type plasminogen activator (rt-PA) therapy. We studied patients treated within 3 hours of onset of ischemic stroke with rt-PA using positron emission tomography to compare Pittsburgh compound B (PiB) (a cerebral β-amyloid ligand) retention in those with and without parenchymal hemorrhage (PH) and normal controls. Neocortical PiB retention was higher among patients with PH compared with patients without PH and normal controls, suggesting underlying CAA as a predisposing factor for rt-PA-related hemorrhage. This finding may provide an impetus for the development of a more practical rapid pretreatment screening technique.

99mTc/Re complexes based on flavone and aurone as SPECT probes for imaging cerebral β-amyloid plaques

Two 99mTc/Re complexes based on flavone and aurone were tested as potential probes for imaging β-amyloid plaques using single photon emission computed tomography. Both 99mTc-labeled derivatives showed higher affinity for Aβ(1–42) aggregates than did 99mTc-BAT. In sections of brain tissue from an animal model of AD, the Re-flavone derivative 9 and Re-aurone derivative 19 intensely stained β-amyloid plaques. In biodistribution experiments using normal mice, 99mTc-labeled flavone and aurone displayed similar radioactivity pharmacokinetics. With additional modifications to improve their brain uptake, 99mTc complexes based on the flavone or aurone scaffold may serve as probes for imaging cerebral β-amyloid plaques.

High-definition characterization of cerebral β-amyloid angiopathy in Alzheimer's disease

The occurrence and progression of cerebral β-amyloid angiopathy and β-amyloid plaques in sporadic Alzheimer's disease may be attributed to aging-related deficiencies in β-amyloid drainage along cerebral perivascular pathways. To elucidate high-definition characteristics of cerebral β-amyloid deposition, we performed immunogold silver staining for β-amyloid-40 and β-amyloid-42 on semithin LR White-embedded tissue sections from 7 Alzheimer's disease/severe cerebral β-amyloid angiopathy, 9 Alzheimer's disease/mild cerebral β-amyloid angiopathy, 5 old control, and 4 young control autopsy brains. In vessel walls, β-amyloid-40 and β-amyloid-42 deposits were unevenly distributed along the adventitia and among the medial smooth muscle cells. β-Amyloid-40 immunoreactivity appeared greater than that of β-amyloid-42 in vessel walls, with β-amyloid-42 being preferentially located on their abluminal regions. In capillary walls, either β-amyloid-40 or β-amyloid-42 deposits or both were present in 6 of 7 severe cerebral β-amyloid angiopathy and in 1 of 9 mild cerebral β-amyloid angiopathy cases, with a marked variation in thickness and focally abluminal excrescences. In 5 of 7 severe cerebral β-amyloid angiopathy cases, a subset of β-amyloid-laden capillaries revealed either β-amyloid-40 or β-amyloid-42 deposits or both radiating from their walls into the surrounding neuropil ("pericapillary deposits"). No vascular β-amyloid-40 or β-amyloid-42 deposits were observed in any of the controls. In conclusion, the patterns of β-amyloid-42 and β-amyloid-40 immunoreactivity in vessel walls suggest that β-amyloid deposits occur in the vascular basement membranes along cerebral perivascular drainage pathways, extending from cortical capillaries to leptomeningeal arteries. The presence of pericapillary β-amyloid deposits suggests that a subset of β-amyloid plaques originate from β-amyloid-laden capillaries, particularly in Alzheimer's disease brains that exhibit preferential capillary involvement by cerebral β-amyloid angiopathy.

Novel Benzofurans with (99m)Tc Complexes as Probes for Imaging Cerebral β-Amyloid Plaques.

Two novel benzofuran derivatives coupled with (99m)Tc complexes were tested as probes for imaging cerebral β-amyloid plaques using single photon emission tomography. Although both derivatives bound to Aβ(1-42) aggregates, (99m)Tc-BAT-BF showed higher affinity than (99m)Tc-MAMA-BF. In sections of brain tissue from an animal model of AD, (99m)Tc-BAT-BF clearly labeled β-amyloid plaques. In biodistribution experiments using normal mice, (99m)Tc-BAT-BF displayed high uptake soon after its injection and washed out from the brain rapidly, a highly desirable feature for an imaging agent. (99m)Tc-BAT-BF may be a potential probe for imaging β-amyloid plaques in Alzheimer's brains.

Development of dual functional SPECT/fluorescent probes for imaging cerebral β-amyloid plaques

The imaging of β-amyloid (Aβ) aggregates in the brain may lead to the early detection of Alzheimer’s disease (AD) and monitoring of the progression and effectiveness of treatment. The purpose of this study was to develop dual modality SPECT and fluorescent probes based on boron dipyrromethane (BODIPY) as a core structure. We designed and synthesized an 125I-labeled derivative of BODIPY (BODIPY7). BODIPY7 had a K i value of 108 nM for Aβ(1–42) aggregates and exhibited peaks of absorption/emission at 606/613 nm. It detected Aβ plaques in sections of brain tissue from an animal model of AD and displayed low uptake in the brain and high uptake in the liver in normal mice. Although additional modifications of the BODIPY scaffold are necessary to improve brain uptake, these results should aid the development of dual functional SPECT/fluorescent probes for the imaging of Aβ plaques in the brain.

Cognitive Decline and Brain Volume Loss as Signatures of Cerebral Amyloid-β Peptide Deposition Identified With Pittsburgh Compound B

To examine the relation of amyloid-beta peptide (Abeta) levels in the cerebral cortex with structural brain integrity and cognitive performance in cognitively healthy older people. Longitudinal study from May 22, 1985, through October 15, 2008. Washington University Alzheimer Disease Research Center. A total of 135 individuals aged 65 to 88 years with a Clinical Dementia Rating of 0. The relations between mean cortical carbon 11 ((11)C)-labeled Pittsburgh compound B (PiB) binding potential values, proportional to the density of fibrillar Abeta binding sites in the brain, concurrent regional brain volumes as assessed by magnetic resonance imaging, and both concurrent and longitudinal cognitive performance in multiple domains. Elevated cerebral Abeta levels, in some cases comparable to those seen in individuals with Alzheimer disease, were observed in 29 participants, who also had smaller regional volumes in the hippocampus, temporal neocortex, anterior cingulate, and posterior cingulate. Concurrent cognitive performance was unrelated to Abeta levels but was related to regional brain volumes with the exception of the caudate. Longitudinal cognitive decline in episodic and working memory and visuospatial ability was associated with elevated Abeta levels and decreased hippocampal volume. The in vivo measure of cerebral amyloidosis known as [(11)C]PiB is associated with cross-sectional regionally specific brain atrophy and longitudinal cognitive decline in multiple cognitive domains that occur before the clinical diagnosis of Alzheimer disease. These findings contribute to the understanding of the cognitive and structural consequences of Abeta levels in cognitively healthy older adults.

Deficient high-affinity binding of Pittsburgh compound B in a case of Alzheimer’s disease

Radiolabeled Pittsburgh compound B (PIB) is a benzothiazole imaging agent that usually binds with high affinity, specificity, and stoichiometry to cerebral beta-amyloid (Abeta) in patients with Alzheimer's disease. Among a cohort of ten AD subjects examined postmortem, we describe a case of idiopathic, end-stage Alzheimer's disease with heavy Abeta deposition yet substantially diminished high-affinity binding of (3)H-PIB to cortical homogenates and unfixed cryosections. Cortical tissue samples were analyzed by immunohistochemistry, electron microscopy, ELISA, immunoblotting, MALDI-TOF mass spectrometry, in vitro (3)H-PIB binding and (3)H-PIB autoradiography. The PIB-refractory subject met the histopathological criteria for AD. However, cortical tissue from this case contained more vascular beta-amyloidosis, higher levels of insoluble Abeta40 and Abeta42, and a higher ratio of Abeta40:Abeta42 than did tissue from the nine comparison AD cases. Furthermore, cerebral Abeta from the PIB-refractory subject displayed an unusual distribution of low- and high-molecular weight Abeta oligomers, as well as a distinct pattern of N- and C-terminally truncated Abeta peptides in both the soluble and insoluble cortical extracts. Genetically, the patient was apolipoprotein-E3/4 heterozygous, and exhibited no known AD-associated mutations in the genes for the beta-amyloid precursor protein, presenilin1 or presenilin2. Our findings suggest that PIB may differentially recognize polymorphic forms of multimeric Abeta in humans with Alzheimer's disease. In addition, while the prevalence of PIB-refractory cases in the general AD population remains to be determined, the paucity of high-affinity binding sites in this AD case cautions that minimal PIB retention in positron-emission tomography scans of demented patients may not always rule out the presence of Alzheimer-type Abeta pathology.

Synthetic Abeta 1-40 oligomers impair recognition memory in mice

Alzheimer disease (AD) is a neurodegenerative pathology characterized by cerebral β-amyloid (Aβ) deposits, neurofibrillary tangles, early synaptic dysfunction and subsequent memory loss. Aβ oligomers, rather than fibrils, were proposed to play a major role in the neurodegeneration. Various forms of Aβ oligomers extracted from the brain were shown to induce synaptic failure and cognitive impairment. Aβ oligomers inhibited the long-term potentiation (LTP) process, a paradigm measuring synaptic plasticity, and induced loss of dendritic spines which represent synaptic connections in the formation of new memory traces. The present study was aimed to investigate, in vivo, the effect of synthetic Aβ1-40 monomer, small oligomers and higher aggregates, in mice tested in the object recognition task. Aβ oligomers were covalently stabilized using the photo-induced-cross-linking technique. Two hours following Aβ1-40 (1.0 μM) intracerebroventricle (icv) injection, mice underwent to the familiarization phase on day 1 and to the memory test phase on day 2. Memory abilities were determined calculating the discrimination index. Our findings show that only Aβ1-40 oligomers have the ability to impair long-term recognition memory. Moreover, we demonstrated that this effect was reverted by an icv pretreatment with the 4G8 anti-Aβ antibody. Our findings demonstrate, in vivo, that beside Aβ1-42 also synthetic Aβ1-40 oligomers have toxic effects on cognitive processes. Furthermore, the ability of the Aβ specific antibody to revert Aβ1-40-mediated cognitive impairment, supports the immunotherapy as useful strategy in the AD pathology.

Synthetic Abeta 1-40 oligomers impair recognition memory in mice

Alzheimer disease (AD) is a neurodegenerative pathology characterized by cerebral β-amyloid (Aβ) deposits, neurofibrillary tangles, early synaptic dysfunction and subsequent memory loss. Aβ oligomers, rather than fibrils, were proposed to play a major role in the neurodegeneration. Various forms of Aβ oligomers extracted from the brain were shown to induce synaptic failure and cognitive impairment. Aβ oligomers inhibited the long-term potentiation (LTP) process, a paradigm measuring synaptic plasticity, and induced loss of dendritic spines which represent synaptic connections in the formation of new memory traces. The present study was aimed to investigate, in vivo, the effect of synthetic Aβ1-40 monomer, small oligomers and higher aggregates, in mice tested in the object recognition task. Aβ oligomers were covalently stabilized using the photo-induced-cross-linking technique. Two hours following Aβ1-40 (1.0 μM) intracerebroventricle (icv) injection, mice underwent to the familiarization phase on day 1 and to the memory test phase on day 2. Memory abilities were determined calculating the discrimination index. Our findings show that only Aβ1-40 oligomers have the ability to impair long-term recognition memory. Moreover, we demonstrated that this effect was reverted by an icv pretreatment with the 4G8 anti-Aβ antibody. Our findings demonstrate, in vivo, that beside Aβ1-42 also synthetic Aβ1-40 oligomers have toxic effects on cognitive processes. Furthermore, the ability of the Aβ specific antibody to revert Aβ1-40-mediated cognitive impairment, supports the immunotherapy as useful strategy in the AD pathology.

Transgenic Alzheimer mice in a semi-naturalistic environment: More plaques, yet not compromised in daily life

The behaviour of transgenic animals modelling human diseases such as Alzheimer's disease (AD) is typically characterised in artificial apparatuses rather than labour-intensively observing their spontaneous behaviour in the home environment. Here we report on an in-depth behavioural characterisation of the day-to-day life of a murine model for AD living in a large (6.6 m 2) semi-naturalistic indoor enclosure. In a genotype-blind investigation, 40 different behavioural patterns of wildtype and transgenic animals were recorded at early ages, before plaques can be found in the brains of the transgenic mice; and later in life, when these mice are known to exhibit AD-like plaques. Basal stress hormone levels (corticosterone) and cerebral amyloid-β depositions were determined, and compared with individually and group-housed mice from non-enriched standard cages. Semi-naturalistically housed transgenics could not be differentiated from wildtypes by their behavioural profiles nor by basal levels of corticosterone. Surprisingly, the brains of these transgenics revealed an even more pronounced plaque load than controls from standard-housing conditions. Behavioural traits are known to involve gene–environment interactions. Here we show for the first time that despite high β-amyloid plaque load the day-to-day life of AD mice is not compromised when the genetic predisposition interacts with a generous physically and socially enriched environment.

Blood pressure and the risk for dementia—A double edged sword

Alzheimer's disease (AD) and vascular dementia (VaD) are important causes of cognitive decline in the elderly. As a result of the aging population, the incidence of dementia is expected to increase substantially over the coming decades. Many studies have identified that vascular risk factors are implicated in the pathogenesis of both AD and VaD. Longitudinal studies have suggested that high blood pressure in midlife is associated with a higher incidence of both AD and VaD in later life. The association appears weaker for hypertension in later life. Some studies also suggest that hypotension; especially low diastolic blood pressure in late-life is also associated with an increased risk of AD. Long-standing hypertension may lead to severe atherosclerosis and impaired cerebrovascular autoregulation. A decline in blood pressure in later life may contribute to diminished cerebral perfusion. The subsequent ischaemic state may lead to increased cerebral β-amyloid accumulation.

Age-dependent and -independent behavioral deficits in Tg2576 mice

The Tg2576 mouse model of excessive cerebral β-amyloid deposition is now more than a decade old, yet consensus as to its exact characteristics and utility as a model of Alzheimer's disease is still lacking. Four different cohorts of control and Tg2576 mice, aged approximately 3, 9, 13 and 21 months, were therefore subjected to a battery of tests, principally to assess cognitive and species-typical behaviors. A novel test, the paddling Y-maze, demonstrated an age-dependent deficit in 10 and 14, but not 3 month Tg2576 mice, also in aged (21 month) control mice. However, in many other cognitive tests few Tg2576-related deficits could be shown. This frequently seemed attributable to poor performance of control mice. Tests of species-typical behaviors showed that Tg2576 mice had a deficit in burrowing behavior at all ages. An age-independent deficit was also seen in nest construction, but only when mice were group-housed; most individually housed mice in either group made reasonable nests. Overall, the results suggested that these Tg2576 mice are not a simple, suitable or reliable model for routine screening of treatments for Alzheimer's disease. However, this model might perform better behaviorally on a different genetic background.

BACE1 gene deletion: Impact on behavioral function in a model of Alzheimer's disease

Accumulation of cerebral amyloid-β (Aβ) has been implicated as a putative causal factor in the development of Alzheimer's disease (AD). Transgenic mice like the PDAPP line overexpress human mutant Amyloid Precursor Protein (hAPP) and recapitulate many features of AD, including amyloid neuropathology and cognitive deficits. Inhibition of the β-site aspartyl cleaving enzyme (BACE1) enzyme responsible for the first proteolytic cleavage that ultimately generates Aβ has been proposed as a strategy for AD therapy. To assess the theoretical repercussions of β-secretase activity reduction in an in vivo model of AD, BACE1 −/− mice bred to the PDAPP line were examined in a series of behavioral tasks. Although BACE1 gene ablation abolished hAβ accumulation, BACE1 −/− mice had unexpected sensorimotor impairments, spatial memory deficits, and displayed seizures, phenotypes which were severe on the PDAPP background. These results suggest that while excess Aβ is functionally pathological, BACE1-mediated processing of APP and other substrates play a role in “normal” learning, memory and sensorimotor processes.

Transcutaneous β-amyloid immunization reduces cerebral β-amyloid deposits without T cell infiltration and microhemorrhage

Alzheimer's disease (AD) immunotherapy accomplished by vaccination with beta-amyloid (Abeta) peptide has proved efficacious in AD mouse models. However, "active" Abeta vaccination strategies for the treatment of cerebral amyloidosis without concurrent induction of detrimental side effects are lacking. We have developed a transcutaneous (t.c.) Abeta vaccination approach and evaluated efficacy and monitored for deleterious side effects, including meningoencephalitis and microhemorrhage, in WT mice and a transgenic mouse model of AD. We demonstrate that t.c. immunization of WT mice with aggregated Abeta(1-42) plus the adjuvant cholera toxin (CT) results in high-titer Abeta antibodies (mainly of the Ig G1 class) and Abeta(1-42)-specific splenocyte immune responses. Confocal microscopy of the t.c. immunization site revealed Langerhans cells in areas of the skin containing the Abeta(1-42) immunogen, suggesting that these unique innate immune cells participate in Abeta(1-42) antigen processing. To evaluate the efficacy of t.c. immunization in reducing cerebral amyloidosis, transgenic PSAPP (APPsw, PSEN1dE9) mice were immunized with aggregated Abeta(1-42) peptide plus CT. Similar to WT mice, PSAPP mice showed high Abeta antibody titers. Most importantly, t.c. immunization with Abeta(1-42) plus CT resulted in significant decreases in cerebral Abeta(1-40,42) levels coincident with increased circulating levels of Abeta(1-40,42), suggesting brain-to-blood efflux of Abeta. Reduction in cerebral amyloidosis was not associated with deleterious side effects, including brain T cell infiltration or cerebral microhemorrhage. Together, these data suggest that t.c. immunization constitutes an effective and potentially safe treatment strategy for AD.

Subcutaneous Nogo Receptor Removes Brain Amyloid-β and Improves Spatial Memory in Alzheimer's Transgenic Mice

The production and aggregation of cerebral amyloid-beta (Abeta) peptide are thought to play a causal role in Alzheimer's disease (AD). Previously, we found that the Nogo-66 receptor (NgR) interacts physically with both Abeta and the amyloid precursor protein (APP). The inverse correlation of Abeta levels with NgR levels within the brain may reflect regulation of Abeta production and/or Abeta clearance. Here, we assess the potential therapeutic benefit of peripheral NgR-mediated Abeta clearance in APPswe/PSEN-1deltaE9 transgenic mice. Through site-directed mutagenesis, we demonstrate that the central 15-28 aa of Abeta associate with specific surface-accessible patches on the leucine-rich repeat concave side of the solenoid structure of NgR. In transgenic mice, subcutaneous NgR(310)ecto-Fc treatment reduces brain Abeta plaque load while increasing the relative levels of serum Abeta. These changes in Abeta are correlated with improved spatial memory in the radial arm water maze. The benefits of peripheral NgR administration are evident when therapy is initiated after disease onset. Thus, the peripheral association of NgR(310)ecto-Fc with central Abeta residues provides an effective therapeutic approach for AD.

Intracellular Aβ and cognitive deficits precede β-amyloid deposition in transgenic arcAβ mice

The brain pathology of Alzheimer's disease is characterized by abnormally aggregated Aβ in extracellular β-amyloid plaques and along blood vessel walls, but the relation to intracellular Aβ remains unclear. To address the role of intracellular Aβ deposition in vivo, we expressed human APP with the combined Swedish and Arctic mutations in mice (arcAβ mice). Intracellular punctate deposits of Aβ occurred concomitantly with robust cognitive impairments at the age of 6 months before the onset of β-amyloid plaque formation and cerebral β-amyloid angiopathy. β-Amyloid plaques from arcAβ mice had distinct dense-core morphologies with blood vessels appearing as seeding origins, suggesting reduced clearance of Aβ across blood vessels in arcAβ mice. The co-incidence of intracellular Aβ deposits with behavioral deficits support an early role of intracellular Aβ in the pathophysiological cascade leading to β-amyloid formation and functional impairment.

Human apoB overexpression and a high-cholesterol diet differently modify the brain APP metabolism in the transgenic mouse model of atherosclerosis

Epidemiological and biochemical data suggest a link between the cholesterol metabolism, the amyloid precursor protein (APP) processing and the increased cerebral β-amyloid (Aβ) deposition in Alzheimer's disease (AD). The individual and combined effects of a high-cholesterol (HC) diet and the overexpression of the human apoB-100 gene were therefore examined on the cerebral expression and processing of APP in homozygous apoB-100 transgenic mice [Tg (apoB +/+)], a validated model of atherosclerosis. When fed with 2% cholesterol for 17 weeks, only the wild-type mice exhibited significantly increased APP695 (123%) and APP770 (138%) mRNA levels in the cortex. The HC diet-induced hypercholesterolemia significantly increased the APP isoform levels in the membrane-bound fraction, not only in the wild-type animals (114%), but also in the Tg apoB +/+ group (171%). The overexpression of human apoB-100 gene by the liver alone reduced the brain APP isoform levels in the membrane-bound fraction (78%), whereas the levels were increased by the combined effect of HC and the overexpression of the human apoB-100 gene (134%). The protein kinase C and β-secretase protein levels were not altered by the individual or combined effects of these two factors. Our data indicate that the two atherogenic factors, the HC diet and the overexpression of the human apoB-100 gene by the liver, could exert different effects on the processing and expression of APP in the mice brain.

A 50-Year-Old Man With Acute-Onset Generalized Seizure

A 50-Year-Old Man With Acute-Onset Generalized Seizure

The Cerebral β-Amyloid Angiopathies: Hereditary and Sporadic

We review the clinical, radiologic, and neuropathologic features of the hereditary and sporadic forms of cerebral amyloid angiopathy (CAA) associated with vascular deposition of the beta-amyloid peptide. Amino acid substitutions at 4 sites in the beta-amyloid precursor protein, all situated within the beta-amyloid peptide sequence itself, have been shown to cause heritable forms of CAA. The vascular diseases caused by these mutations are associated primarily with cerebral hemorrhages, white matter lesions, and cognitive impairment, and only variable extents of the plaque and neurofibrillary pathologies characteristic of Alzheimer disease. Sporadic CAA typically presents 20 or more years later than hereditary CAA, but is otherwise characterized by a comparable constellation of recurrent cerebral hemorrhages, white matter lesions, and cognitive impairment. The clinical, radiologic and pathologic similarities between hereditary and sporadic CAA suggest that important lessons for this common age-related process can be learned from the mechanisms by which mutation makes beta-amyloid tropic or toxic to vessels.

Mechanism of Cerebral β-Amyloid Angiopathy: Murine and Cellular Models

Cerebral amyloid angiopathy of the beta-amyloid type (Abeta-CAA) is a risk factor for hemorrhagic stroke and independently is believed to contribute to dementia. Naturally occurring animal models of Abeta-CAA are scarce and not well suited for the laboratory. To this end, a variety of transgenic mouse models have been developed that, similar to cerebral Abeta-amyloidosis in humans, develop either Abeta-CAA only or both Abeta-CAA and parenchymal amyloid, or primarily parenchymal amyloid with only scarce Abeta-CAA. The lessons learned from these mouse models are: i) Abeta-CAA alone is sufficient to induce cerebral hemorrhage and associate pathologies including neuroinflammation, ii) the origin of vascular amyloid is mainly neuronal, iii) Abeta-CAA results largely from impaired Abeta clearance, iv) a high ratio Abeta40:42 favors vascular over parenchymal amyloidosis, and v) genetic risk factors such as ApoE modulate Abeta-CAA and CAA-induced hemorrhages. Therapeutic strategies to inhibit Abeta-CAA are poor at the present time. Once Abeta-CAA is present current Abeta immunotherapy strategies have failed to clear vascular amyloid and even run the risk of serious side effects. Despite this progress in deciphering the pathomechanism of Abeta-CAA, with these first generation mouse models of Abeta-CAA, refining these models is needed and will help to understand the emerging importance of Abeta-CAA for dementia and to develop biomarkers and therapeutic strategies.