Hereditary cerebral amyloid angiopathies

Cerebral amyloid angiopathies are defined by the presence of amyloid substance in the walls of cerebral vessels. All amyloid substances have a particular physico-chemical structure, which imparts certain specific staining properties, but the biochemical composition of different amyloid types varies. Different forms of cerebral amyloid angiopathy have been identified, based on the biochemical nature of the protein deposited (e.g. beta-amyloid, cystatin C, transthyretin, gelsolin, amyloid protein Bri, prion protein). Some cerebral amyloid angiopathies are familial; these prompted genetic studies which in turn led to a better understanding of the genes coding for different amyloid proteins. As a group, cerebral amyloid angiopathies have certain neuropathological lesions in common. Infiltration by amyloid substance results in weakening of the small vessel walls and secondary complications responsible for changes such as microinfarcts and miliary haemorrhages in the cerebral cortex, lobar haemorrhages and/or leucoencephalopathy. These changes form the basis of the neurological complications: meningeal and cerebral haemorrhages, transient ischaemic episodes, vascular dementia. However each type of hereditary cerebral amyloid angiopathy has individual clinical and histopathological features reflecting the severity of arterial involvement, the extent of amyloid deposition within or outside the central nervous system, and the association with other neurodegenarative changes.     

Amyloid beta protein toxicity mediated by the formation of amyloid-beta protein precursor complexes

The amyloid-beta protein precursor, a type 1 transmembrane protein, gives rise to the amyloid beta-protein, a neurotoxic peptide postulated to be involved in the pathogenesis of Alzheimer's disease. Here, we show that soluble amyloid beta protein accelerates amyloid precursor protein complex formation, a process that contributes to neuronal cell death. The mechanism of cell death involves the recruitment of caspase-8 to the complex, followed by intracytoplasmic caspase cleavage of amyloid precursor protein. In vivo, the levels of soluble amyloid beta protein correlated with caspase-cleaved fragments of the amyloid precursor protein in brains of Alzheimer's disease subjects. These findings suggest that soluble amyloid beta protein-induced multimerization of the amyloid precursor protein may be another mechanism by which amyloid beta protein contributes to synapse loss and neuronal cell death seen in Alzheimer's disease.     

Amyloid in central nervous system disease

A review is presented of diseases of the central nervous system associated with amyloid deposition. The name amyloid is given to substances with particular physical characteristics which are independent of the chemical constitution of the proteins in the substance. Ideally, a classification of amyloid diseases should be based on the chemical composition of the amyloid deposits; this has only been partially realized. The best documented group of diseases with amyloid deposition in the central nervous system is the group of ‘cerebral β amyloid diseases’, characterized by the deposition of β-protein. This group includes: Alzheimer's disease, sporadic cerebral amyloid angiopathy, Down's syndrome, Parkinson-dementia of Guam, hereditary cerebral hemorrhage with amyloidosis-Dutch type and age-related asymptomatic amyloid angiopathy.     

Permanganate oxidation of senile cerebral amyloid and its relationship to AA protein

Summary Immunoreactivity for AA protein was rarely detected in briefly fixed amyloid of senile plaques and dyshoric angiopathy, but was not observed in Congophilic angiopathy. Plaque and dyshoric amyloid exhibited variable sensitivity to permanganate oxidation; Congophilic angiopathy was resistant to oxidation. In contrast to systemic amyloid composed of AA protein, the rare immunoreactivity of senile cerebral amyloid was lost with prolonged fixation. This study demonstrates that the fibrillar protein of senile cerebral amyloid differs from that of systemic amyloid of AA type.     

Vascular amyloid in the aging central nervous system. Clinico-pathological study and literature review

The clinico-pathological features of five patients with vascular amyloid restricted to the central nervous system are presented. In three normotensive patients, intracerebral hemorrhage was the dramatic manifestation of amyloid angiopathy. In two other cases, one of amyloid in an arteriovenous malformation, the other of amyloid following therapeutic radiation, amyloid deposition was asymptomatic. Clinically, amyloid angiopathy must be considered in the different diagnosis of intracerebral hemorrhage, independent of the presence of dementia. Pathologically, a factor common to the syndrome of cerebrovascular amyloid appears to be locally increased vascular permeability resulting from a variety of previous tissue injuries.     

Systemic amyloid deposition in old age and dementia of Alzheimer type: the relationship of brain amyloid to other amyloid

Summary We investigated amyloid deposition in the brain and other organs in 105 consecutive autopsy cases, aged 59 to 101 years. They consisted of two groups; 15 patients with dementia of Alzheimer type (DAT) and 90 patients without DAT. Amyloid deposition was found in 93% of all cases. The incidence of amyloid deposition increased with age. The number of organs affected with amyloid deposition in each case also increased with age. The incidence of amyloid deposition in each organ was as follows; 88% in pituitary gland, 66% in brain [amyloid of senile plaque (SP) (61%) and/or cerebral amyloid angiopathy (CAA) (56%)], 33% in pancreas, 3% in heart, and less in others. In immunohistochemical studies using the antisera to the various kinds of amyloid or related proteins, amyloid protein was demonstrated in brain amyloids including SP and CAA, but not in others. Cardiac amyloid was positive for prealbumin. Pituitary amyloid and CAA were positive for amyloid P-component. The incidence of brain amyloids in DAT were significantly higher than that in non-DAT. There was no significant difference in the incidence of pituitary and pancreatic amyloid between DAT and non-DAT. In the non-DAT patients, there were significant positive correlations in amyloid deposition between the brain and pituitary gland and between the brain and pancreas. Acceleration of amyloid deposition would be a process confined to the brain in the patients with DAT. The pathogenesis of the accelerated deposition of brain amyloids is discussed from the point of view of amyloidosis.Supported in part by the Research Committee on Primary Amyloidosis, Ministry of Health and Welfare, Japan     

Identification of peptides that specifically bind Abeta1-40 amyloid in vitro and amyloid plaques in Alzheimer''s disease brain using phage display

The accumulation of the amyloid-beta (Abeta) 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 Abeta 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 Abeta(1-40) peptide. Here we identify two 20-amino acid peptides with similar structural features that bind to the amyloid form of Abeta(1-40) but not to monomeric Abeta(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 Abeta(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 Abeta(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.     

Senile plaques in cortex of aged normal monkeys

The density, type, and distributions of cortical senile plaques were determined in 6 aged rhesus monkeys. Plaque densities were highest in prefrontal and temporal cortices and lowest in occipital cortex. Neurite plaques contained many argentophilic neurites and little amyloid, mixed plaques had both neurites and amyloid, and amyloid plaques showed significant amounts of amyloid and fewer numbers of neurites. As total plaque density increased, there was a linear increase in the density of amyloid plaques, suggesting that plaques evolve from neurite, to mixed, to amyloid types.     

Immunohistochemical characterization of cerebrovascular amyloid in 46 autopsied cases using antibodies to beta protein and cystatin C

Using immunohistochemical staining methods with antibodies to amyloid beta protein and human cystatin C, we examined cerebrovascular amyloid protein in the brains from 46 cases with cerebral amyloid angiopathy (seven with Alzheimer's disease, one with Down's syndrome, 18 with intracranial hemorrhage, 10 with cerebral infarction, and 10 elderly patients without any neurologic disorder). All cerebrovascular amyloid deposits in these 46 cases were consistently immunoreactive to anti-beta protein antibody. However, in nine cases some vascular walls with strong beta protein immunoreactivity also reacted less intensely with the anti-cystatin C antiserum. Of these nine cases, seven showed relatively heavy cerebrovascular amyloid deposition, and all seven had suffered a fatal subcortical hemorrhage presumably caused by cerebral amyloid angiopathy. Previous limited studies have suggested that the amyloid protein seen in elderly individuals with cerebral amyloid angiopathy is composed of beta protein. However, subcortical hemorrhage rarely occurs in such individuals. Our study shows that aged patients with different brain disorders commonly suffer from beta protein-type cerebral amyloid angiopathy, and we also suggest that the severity of beta protein-type cerebrovascular amyloid deposition is a fundamental factor in cerebral amyloid angiopathy-induced brain hemorrhage in the elderly. The nature of the cystatin C-immunoreactive substance in some of these vascular lesions is uncertain, but it might conceivably play an additional important role in the pathogenesis of brain hemorrhage in these cases.     

The comparative immunoreactivities of brain amyloids in Alzheimer's disease and scrapie

Summary An antibody was raised to a synthetic peptide corresponding to a published sequence for the first 24 residues of a cerebrovascular amyloid peptide (CVAP). Immunohistochemical staining of tissue sections revealed that the antibody bound extensively to cerebrovascular amyloid in Alzheimer disease (AD/SDAT) and Down's syndrome cases. The antibody bound less extensively to neuritic plaques (primitive and mature) and indetectably to neurofibrillary tangles. The antibody did not label scrapie plaques, scrapie-associated fibrils, or Gerstmann-Sträussler syndrome plaques. Immunoblotting experiments showed that the cerebrovascular amyloid peptide epitopes contaminating the neurofibrillary tangle preparations could be extracted with urea, leaving the neurofibrillary tangles intact. These data confirm that the cerebrovascular amyloid peptide is a component of cerebrovascular amyloid, and suggest that its epitopes are also components of neuritic plaque amyloid. The reduced level of immunostaining on amyloid cores in tissue sections suggests that either the cerebrovascular amyloid peptide epitopes are a minor component of amyloid cores, or that their mode of packing or state of processing in amyloid cores renders them relatively inaccessible to the antibody. We also conclude that the cerebrovascular amyloid peptide is not a component of neurofibrillary tangles. The synthetic cerebrovascular amyloid peptide possesses amyloid-like properties: at neutral pH it forms insoluble aggregates consisting of 5–7-nm fibrils, which form red-green birefringent adducts with Congo red and fluoresce with thioflavine S.Supported by NH Grants Nos. AG04220, NS21349 and GM30800     

Nucleoside diphosphatase (NDPase) activity associated with human β-protein amyloid fibers

Summary Nucleoside diphosphatase (NDPase) activity was studied by electron microscope cytochemistry in surgical specimens obtained from aged human cerebral cortices. The presence of NDPase activity on the surface of the microglial cells (MCs) and especially within the endoplasmic reticulum (ER) cisternae that are filled with amyloid fibers and that are in continuity with the extracellular amyloid deposits in plaques suggests a possible role of this enzyme in final elaboration of amyloid protein. The close structural relationship between MCs and amyloid plaques, suggesting the participation of these cells in the synthesis or final elaboration of amyloid fibers, was observed. The comparison of these observations with previously reported data on the distribution of NDPase in MCs and amyloid fibers in scrapie-infected mouse brain suggests that presumably similar mechanisms are acting in both cases. These observations, as compared with the results of other cytochemical and biochemical studies, also suggest that co-localization of NDPase activity with newly formed amyloid fibers in plaques can be associated with glycosyltransferase activities engaged in the amyloid or amyloid precursor protein glycosylation.     

Hyperforin prevents beta-amyloid neurotoxicity and spatial memory impairments by disaggregation of Alzheimer's amyloid-beta-deposits

The major protein constituent of amyloid deposits in Alzheimer's disease (AD) is the amyloid beta-peptide (Abeta). In the present work, we have determined the effect of hyperforin an acylphloroglucinol compound isolated from Hypericum perforatum (St John's Wort), on Abeta-induced spatial memory impairments and on Abeta neurotoxicity. We report here that hyperforin: (1) decreases amyloid deposit formation in rats injected with amyloid fibrils in the hippocampus; (2) decreases the neuropathological changes and behavioral impairments in a rat model of amyloidosis; (3) prevents Abeta-induced neurotoxicity in hippocampal neurons both from amyloid fibrils and Abeta oligomers, avoiding the increase in reactive oxidative species associated with amyloid toxicity. Both effects could be explained by the capacity of hyperforin to disaggregate amyloid deposits in a dose and time-dependent manner and to decrease Abeta aggregation and amyloid formation. Altogether these evidences suggest that hyperforin may be useful to decrease amyloid burden and toxicity in AD patients, and may be a putative therapeutic agent to fight the disease.     

Characterization of a transthyretin-related amyloid fibril protein from cerebral amyloid angiopathy in type I familial amyloid polyneuropathy.

Recently, it has been reported that transthyretin (TTR)-immunoreactive amyloid deposition with cerebral amyloid angiopathy in central nervous system is a common pathological finding in type I familial amyloid polyneuropathy (FAP). In the present study, we performed isolation and sequence analysis of TTR-related amyloid fibril protein from the meninges of a patient with type I FAP. Purified major amyloid fibril protein had a molecular weight of 15 kDa. Complete sequence analysis revealed that this amyloid fibril protein was a variant TTR with a single amino acid substitution of methionine for valine at position 30. This variant TTR is a previously unrecognized as cerebrovascular amyloid fibril protein. Furthermore, the patients with type I FAP are well known to have the variant TTR in the serum. These suggest that cerebrovascular amyloid fibril protein in type I FAP may derive from a serum precursor.     

Dementia in hereditary cerebral hemorrhage with amyloidosis-Dutch type is associated with cerebral amyloid angiopathy but is independent of plaques and neurofibrillary tangles.

Cerebral amyloid angiopathy is frequently found in demented and nondemented elderly persons, but its contribution to the causation of dementia is unknown. Therefore, we investigated the relation between the amount of cerebral amyloid angiopathy and the presence of dementia in 19 patients with hereditary cerebral hemorrhage with amyloidosis-Dutch type. The advantage of studying hereditary cerebral hemorrhage in amyloidosis-Dutch type is that patients with this disease consistently have severe cerebral amyloid angiopathy with minimal neurofibrillary pathology. The amount of cerebral amyloid angiopathy, as quantified by computerized morphometry, was strongly associated with the presence of dementia independent of neurofibrillary pathology, plaque density, or age. The number of cortical amyloid beta-laden severely stenotic vessels, vessel-within-vessel configurations, and cerebral amyloid angiopathy-associated microvasculopathies was associated with the amount of cerebral amyloid angiopathy and dementia. A semiquantitative score, based on the number of amyloid beta-laden severely stenotic vessels, completely separated demented from nondemented patients. These results suggest that extensive (more than 15 amyloid beta-laden severely stenotic vessels in five frontal cortical sections) cerebral amyloid angiopathy alone is sufficient to cause dementia in hereditary cerebral hemorrhage with amyloidosis-Dutch type. This may have implications for clinicopathological correlations in Alzheimer's disease and other dementias with cerebral amyloid angiopathy.     

Fleecy amyloid deposits in the internal layers of the human entorhinal cortex are comprised of N-terminal truncated fragments of Abeta

The deposition of amyloid in the brain is a hallmark of Alzheimer disease (AD). Amyloid deposits consist of accumulations of beta-amyloid (Abeta), which is a 39-43 amino-acid peptide cleaved from the Abeta-protein precursor (APP). Another cleavage product of APP is the P3-peptide, which consists of the amino acids 17-42 of the Abeta-peptide. In order to study the deposition of N-terminal truncated forms of Abeta in the human entorhinal cortex, serial sections from 16 autopsy cases with AD-related pathology were immunostained with antibodies against Abeta1-40, Abeta1-42, Abeta17-23, and Abeta8-17, as well as with the Campbell-Switzer silver impregnation for amyloid. In the external entorhinal layers (pre-beta and pre-gamma), sharply delineated diffuse plaques were seen. They were labeled by silver impregnation and by all Abeta-antibodies used. By comparison, in the internal layers (pri-alpha, pri-beta, and pri-gamma) blurred, ill-defined clouds of amyloid existed, in addition to sharply delineated diffuse plaques. These clouds of amyloid were termed "fleecy amyloid." Immunohistochemically, fleecy amyloid was stained by Abeta17-23 and Abeta1-42 antibodies, but not with antibodies against Abeta8-17 and Abeta1-40. Using the Campbell-Switzer technique, the fleecy amyloid deposits were found to be fine argyrophilic amyloid fibrils. Thus, the internal entorhinal layers are susceptible to a distinct type of amyloid, namely fleecy amyloid. This fleecy amyloid obviously corresponds to N-terminal truncated fragments of Abeta1-42, probably representing the P3-peptide. These N-terminal truncated fragments of Abeta are capable of creating fine fibrillar "amyloid."     

Further evidence of local ganglioside-dependent amyloid beta-protein assembly in brain

We investigated the molecular mechanism underlying the region-specific deposition of amyloid beta-protein in brains affected with Alzheimer's disease or cerebral amyloid angiopathy. Here, we show that a hereditary variant-type ('Iowa') amyloid beta-protein, which predominantly deposits in the cerebral vessel wall similar to Dutch and Italian-type amyloid beta-proteins, preferably assembles in the presence of GM3 ganglioside. On the basis of our previous findings that first, cerebrovascular smooth muscle cells that provide favorable sites for these variant-type amyloid beta-proteins exclusively express GM3 ganglioside, and second, Dutch and Italian-type amyloid beta-proteins also require GM3 ganglioside for their assembly, our results provide further evidence that local gangliosides play a crucial role in the region-specific amyloid beta-protein deposition in the brain.     

Serial reconstruction of beta-protein amyloid plaques: relationship to microvessels and size distribution.

The suggestion that the amyloid plaques in Alzheimer disease are formed by abnormal leakage from microvessels is mainly based on the finding that many plaques are topographically associated with microvessels. However, because the microvessel network is dense and amyloid plaques are numerous, the frequently observed association may result from chance contact, especially for larger plaques. Therefore, we determined the frequency of this association as a variable of plaque size. If all the amyloid plaques are associated with microvessels, a constant and high rate of association would be expected for all plaque sizes. On the other hand, if the association is a chance contact, larger plaques would show more frequent contact than smaller ones. Sections were double-immunostained for amyloid plaques and microvessels with antibodies raised against beta-protein and collagen type IV, respectively. Amyloid plaques were reconstructed using 12 serial sections (7 microns thick) from the entorhinal cortex of two Alzheimer patients. With reconstruction we determined the size distribution of amyloid plaques as well as the influence of size on vascular association. All the amyloid plaques larger than 42 microns were associated with microvessels, however, the smaller the amyloid plaques, the less frequently they were associated with microvessels. Interestingly, although diffuse amyloid plaques occur in all size classes, core-containing amyloid plaques have a more discrete size. We conclude that the topographical relationship between amyloid deposition and capillaries does not support the leakage theory for amyloid plaque formation.     

Antibody against C-terminal Abeta selectively elevates plasma Abeta

Accumulation of amyloid beta in the brain is a pathological hallmark of Alzheimer's disease, and the reduction of amyloid beta has been proposed as a primary therapeutic target. Mice immunized against amyloid beta and mice infused with anti-amyloid beta antibody (active and passive immunization, respectively) have reduced brain amyloid beta levels, and two mechanisms have been proposed: microglial phagocytosis in the brain and enhancement of amyloid beta efflux by antibodies present in the periphery (sequestration). The optimal antibody for microglial phagocytosis has been shown to be N-terminal-specific antibody; however, the potency of C-terminal-specific antibody in sequestration remains unclear. In this study, we found that anti-amyloid beta 40-specific antibody induces amyloid beta sequestration. These results indicate that C-terminal antibodies may be useful in amyloid beta sequestration therapy.     

Cerebrospinal fluid amyloid β40 is decreased in cerebral amyloid angiopathy

Cerebral amyloid angiopathy is caused by deposition of the amyloid β protein in the cerebral vasculature. In analogy to previous observations in Alzheimer disease, we hypothesized that analysis of amyloid β₄₀ and β₄₂ proteins in the cerebrospinal fluid might serve as a molecular biomarker. We observed strongly decreased cerebrospinal fluid amyloid β₄₀ (p < 0.01 vs controls or Alzheimer disease) and amyloid β₄₂ concentrations (p < 0.001 vs controls and p < 0.05 vs Alzheimer disease) in cerebral amyloid angiopathy patients. The combination of amyloid β₄₂ and total tau discriminated cerebral amyloid angiopathy from controls, with an area under the receiver operator curve of 0.98. Our data are consistent with neuropathological evidence that amyloid β₄₀ as well as amyloid β₄₂ protein are selectively trapped in the cerebral vasculature from interstitial fluid drainage pathways that otherwise transport amyloid β proteins toward the cerebrospinal fluid. Ann Neurol 2009;66:245–249     

Ultrastructural studies of the cells forming amyloid in the cortical vessel wall in Alzheimer's disease

Summary Ultrastructural studies of serial sections of the vessels with amyloid deposits in the brain cortex of patients with Alzheimer's disease showed that cells in the position of pericytes — perivascular cells - and perivascular microglial cells are producers of amyloid fibrils in the vascular wall. Three types of changes from normal are distinguishable in the vessel wall: (1) semicircular or circular thickening of vascular wall containing a large amount of amorphous material and various number of amyloid fibrils, (2) tuberous amyloid deposits containing both amorphous material and amyloid fibrils, some of the fibrils being arranged in strata and others arranged radially, and (3) amyloid star composed of a predominantly radial arrangement of bundles of amyloid fibrils and a less prominent amorphous component. A mixture of amorphous material and amyloid fibrils is present in cell membrane envaginations of perivascular cells, and occasionally perivascular microglial cells. Bundles of amyloid fibrils are found in altered cisternae of the endoplasmic reticulum and in the channels confluent with the infoldings of the plasma membrane of perivascular microglial cells. The amyloid deposition in the wall of the vessel causes degeneration of endothelial cells and the reduction of, and in some vessels obliteration of, the vessel lumen. In areas affected by amyloid angiopathy, extensive degeneration both of the neuropil and of neurons was observed. These changes were accompanied by astrogliosis. This study demonstrates similarities in amyloid formation in amyloid angiopathy and in -amyloid plaques in the neuropil and suggests that cells of the mononuclear phagocyte system of the brain (perivascular cells and perivascular microglia) are engaged in amyloid fibril formation.Supported in part by funds from the New York State Office of Mental Retardation and Developmental Disabilities and a grant from the National Institutes of Health, National Institute of Aging No. PO1-AGO-4220