Ultrastructure of capillary plaque-like degeneration in senile dementia. Mechanism of amyloid production

A History of Senile Plaques: From Alzheimer to Amyloid Imaging

Senile plaques have been studied in postmortem brains for more than 120 years and the resultant knowledge has not only helped us understand the etiology and pathogenesis of Alzheimer disease (AD), but has also pointed to possible modes of prevention and treatment. Within the last 15 years, it has become possible to image plaques in living subjects. This is arguably the single greatest advance in AD research since the identification of the Aβ peptide as the major plaque constituent. The limitations and potentialities of amyloid imaging are still not completely clear but are perhaps best glimpsed through the perspective gained from the accumulated postmortem histological studies. The basic morphological classification of plaques into neuritic, cored and diffuse has been supplemented by sophisticated immunohistochemical and biochemical analyses and increasingly detailed mapping of plaque brain distribution. Changes in plaque classification and staging have in turn contributed to changes in the definition and diagnostic criteria for AD. All of this information continues to be tested by clinicopathological correlations and it is through the insights thereby gained that we will best be able to employ the powerful tool of amyloid imaging.

Idebenone: When an antioxidant is not an antioxidant

Idebenone is a well described drug that was initially developed against dementia. The current literature widely portrays this molecule as a potent antioxidant and CoQ₁₀ analogue. While numerous papers seem to support this view, a closer look indicates that the pharmacokinetics of idebenone do not support these claims. A major discrepancy between achievable tissue levels, especially in target tissues such as the brain, and doses required to show the proposed effects, significantly questions our current understanding. This review explains how this has happened and highlights the discrepancies in the current literature. More importantly, based on some recent discoveries, a new framework is presented that can explain the mode of action of this molecule and can align formerly contradictory results. Finally, this new appreciation of the molecular activities of idebenone provides a rational approach to test idebenone in novel indications that might have not been considered previously for this drug.

Targeting vascular amyloid in arterioles of Alzheimer disease transgenic mice with amyloid β protein antibody-coated nanoparticles

The relevance of cerebral amyloid angiopathy (CAA) to the pathogenesis of Alzheimer disease (AD) and dementia in general emphasizes the importance of developing novel targeting approaches for detecting and treating cerebrovascular amyloid (CVA) deposits. We developed a nanoparticle-based technology that uses a monoclonal antibody against fibrillar human amyloid-β42 that is surface coated onto a functionalized phospholipid monolayer. We demonstrate that this conjugated nanoparticle binds to CVA deposits in arterioles of AD transgenic mice (Tg2576) after infusion into the external carotid artery using 3 different approaches. The first 2 approaches use a blood vessel enrichment of homogenized brain and a leptomeningeal vessel preparation from thin tangential brain slices from the surface of the cerebral cortex. Targeting of CVA by the antibody-coated nanoparticle was visualized using fluorescent lissamine rhodamine-labeled phospholipids in the nanoparticles, which were compared with fluorescent staining of the endothelial cells and amyloid deposits using confocal laser scanning microscopy. The third approach used high-field strength magnetic resonance imaging of antibody-coated iron oxide nanoparticles after infusion into the external carotid artery. Dark foci of contrast enhancement in cortical arterioles were observed in T2*-weighted images of ex vivo AD mouse brains that correlated histologically with CVA deposits. The targeting ability of these nanoparticles to CVA provides opportunities for the prevention and treatment of CAA.

Vascular pathology in Alzheimer's disease

Histopathologically, numerous senile plaques and neurofibrillary tangles were remarkably observed in the brain with Alzheimer's disease. At the same time, so much simple atrophy of nerve cells was evident under light microscopy.Electron microscopical observations of serial sections revealed that small blood vessels, including capillaries, had a deep relationship to the amyloid fibrils which formed the senile plaques and they had fallen into degenerative states. The vascular feet of the astroglial cells surrounding small blood vessels showed degenerative features, and many nerve cells in this area either showed various degrees of degeneration or apparently were destroyed. The atrophy of the brain with Alzheimer's disease is considered to be caused by the amyloid angiopathy of small blood vessels and the degeneration of capillaries and vascular feet. These findings strongly suggest that the major causal mechanism of Alzheimer's disease is an alteration of the blood-brain barrier. Morphology is an expression of both the structure and the function of organs in the living body. Based on this viewpoint, this review article emphasizes that the morphological changes to small blood vessels in the brain with Alzheimer's disease convey crucial information and clues for solving the underlying mechanism that causes the disease.

Altered morphology and 3D architecture of brain vasculature in a mouse model for Alzheimer's disease

Substantial evidence from epidemiological, pathological, and clinical reports suggests that vascular factors are critical in the pathogenesis of Alzheimer's disease (AD), and changes in blood flow are currently the most reliable indicators of the disease. We previously reported that older APP23 transgenic (tg) mice have significant blood flow alterations correlated with structural modifications of blood vessels. For the present study, our objective was to analyze the age-dependent morphological and architectural changes of the cerebral vasculature of APP23 tg mice. To visualize the 3D arrangement of the entire brain vasculature, we used vascular corrosion casts. Already at young ages, when typically parenchymal amyloid plaques are not yet present, APP23 tg mice had significant alterations, particularly of the microvasculature, often accompanied by small deposits attached to the vessels. In older animals, vasculature abruptly ended at amyloid plaques, resulting in holes. Often, small deposits were sitting near or at the end of truncated vessels. Between such holes, the surrounding vascular array appeared more dense and showed features typical for angiogenesis. We propose that small amyloid aggregates associated with the microvasculature lead to morphological and architectural alterations of the vasculature, resulting in altered local blood flow. The characteristic early onset of vascular alterations suggests that imaging blood flow and/or vasculature architecture could be used as a tool for early diagnosis of the disease and to monitor therapies.

Ultrastructure of the cells forming amyloid fibers in Alzheimer disease and scrapie

Ultrastructural, three-dimensional reconstruction of cells surrounding the amyloid star in classical plaques in Alzheimer disease (AD) and histochemical studies of the cells associated with the deposits of amyloid fibers in scrapie were carried out. These studies showed that in both diseases, the fibers appear within the smooth endoplasmic reticulum (ER) and infoldings of cytoplasmic membranes of microglia/macrophages. Additional information about the site of formation of the amyloid fibers derives from histochemical studies of the localization of nucleoside diphosphatase (NDPase) activity. In normal microglia, this enzyme is associated with smooth ER and cell membranes. In the cells that form amyloid fibers, the NDPase activity is associated with the newly formed amyloid fibers within the distended cisternae of ER and the finger-like cytoplasmic projections. In the center of the amyloid star, the NDPase activity disappears. The presence of NDPase-positive amyloid fibers in the same location, where the enzyme is found in non-amyloid-forming cells, further supports our conclusion that the microglia/macrophages are the source of amyloid deposits. These studies also show that in spite of the differences in the proteins that produce the amyloid fibers in AD and scrapie, in both diseases, the microglia/macrophages play a key role in amyloid formation.

Vascular pathology in Alzheimer's disease

This report briefly describes the morphological examination in several types of senile plaques made by using serial sections for both light and electron microscopy in order to observe the relationship between senile plaques and cerebral microvessels.

Two types of sporadic cerebral amyloid angiopathy

Cerebral amyloid angiopathy (CAA) is a type of beta-amyloidosis that occurs in leptomeningeal and cortical vessels of the elderly. In a sample of 41 CAA cases including 16 Alzheimer disease (AD) cases and 28 controls, we show that 2 types of sporadic CAA exist: The first type is characterized by immunohistochemically detectable amyloid beta-protein (Abeta) in cortical capillaries, leptomeningeal and cortical arteries, arterioles, veins, and venules. It is referred to here as CAA-Type 1. The second type of CAA also exhibits immunohistochemically detectable Abeta deposits in leptomeningeal and cortical vessels, with the exception of cortical capillaries. This type is termed CAA-Type 2. In cases with CAA-Type 1, the frequency of the apolipoprotein E (ApoE) epsilon4 allele is more than 4 times greater than in CAA-Type 2 cases and in controls. CAA-Type 2 cases have a higher epsilon2 allele frequency than CAA-Type 1 cases and controls. The ratio of CAA-Type 2 to CAA-Type 1 cases does not shift significantly with respect to the severity of AD-related beta-amyloidosis, with respect to degrees of CAA-severity, or with increasing age. Therefore, CAA-Type 1 is unlikely to be the late stage of CAA-Type 2; rather, they represent 2 different entities. Since both the ApoE epsilon2 and the epsilon4 allele are known to be risk factors for CAA, we can assign the risk factor ApoE epsilon4 to a distinct morphological type of CAA. The ApoE epsilon4 allele constitutes a risk factor for CAA-Type 1 and, as such, for neuropil-associated dyshoric vascular Abeta deposition in capillaries, whereas the e2 allele does not. CAA-Type 2 is not associated with the epsilon4 allele as a risk factor but shows a higher epsilon2 allele frequency than CAA-Type 1 cases and controls in our sample.

Role of blood vessels in producing pathological changes in the brain with Alzheimer's disease

Vascular factors have been shown to be highly involved in the deposition of the amyloid beta-protein (A beta) in the brain of Alzheimer's disease (AD). However, the detailed mechanism remains unknown. Here, we showed that more numerous deposits of A beta 40 and A beta 42 in the brain were found in AD patients than in controls. Together with evidence of no difference in the level of A beta 40 and A beta 42 in sera between sporadic AD and controls, a certain dysfunction of the blood-brain barrier could induce an abnormal transport of A beta from sera to the parenchyma in AD. In addition, vascular A beta deposits and mature A beta plaques stained by Congo red in AD brains contained more A beta 40 than A beta 42, whereas Congo red-negative immature plaques mainly consisted of A beta 42. Our confocal laser scanning microscopy demonstrated an intimate relationship between A beta 40 and the vascular network. The amount of mature plaques but not that of immature plaques was reportedly correlated with the severity of dementia in AD patients. These results suggest that serum-derived A beta 40 and/or A beta 42 cause A beta 40 deposition in and around blood vessels through unknown but possible mechanisms such as (1) endocytosis of A beta 40, (2) selective transport A beta 40 and A beta 42 into blood vessels and the parenchyma, respectively, and (3) proteolysis of A beta 42 into A beta 40 induced by a putative carboxyl dipeptidase in blood vessels including vascular feet, which is involved in A beta fibrillation and cognitive deterioration in the patients. Therefore, the accumulation of A beta 40 associated with blood vessels may play a critical role in the development of AD.

Basement membranes, microfibrils and beta amyloid fibrillogenesis in Alzheimer's disease: high resolution ultrastructural findings

It is known that beta amyloid fibrils are deposited at the basement membrane of the cerebromicrovasculature in the brains of patients with Alzheimer's disease, and the assembly of the fibrils may be in continuation with the core of senile plaques. The fibrils accumulate in a manner similar to that in which microfibrils accumulate in the glomerular basement membrane of the rat kidney during long-term experimental diabetes, and in the alveolar-capillary basement membrane of the normal lung. beta amyloid fibrils in-situ are known to be about 10 nm wide tubular structures and they closely resemble connective tissue microfibrils. Our recent high resolution ultrastructural studies combined with immunogold labeling demonstrated that beta amyloid fibrils in-situ are indeed microfibril-like structures, and the beta protein is associated with their surface in the form of loose assemblies of 1 nm wide flexible filaments. Thus, the result of this study indicates that in-situ a major component of the beta amyloid deposit is the microfibril-like structure. The elucidation of the mechanism of cerebral beta amyloid fibrillogenesis in Alzheimer's disease may therefore require understanding the mechanism of 'normal' microfibrils biogenesis.

Animal models of cerebral beta-amyloid angiopathy

Cerebral amyloid angiopathy (CAA) is a significant risk factor for hemorrhagic stroke in the elderly, and occurs as a sporadic disorder, as a frequent component of Alzheimer's disease, and in several rare, hereditary conditions. The most common type of amyloid found in the vasculature of the brain is beta-amyloid (A beta), the same peptide that occurs in senile plaques. A paucity of animal models has hindered the experimental analysis of CAA. Several transgenic mouse models of cerebral beta-amyloidosis have now been reported, but only one appears to develop significant cerebrovascular amyloid. However, well-characterized models of naturally occurring CAA, particularly aged dogs and non-human primates, have contributed unique insights into the biology of vascular amyloid in recent years. Some non-human primate species have a predilection for developing CAA; the squirrel monkey (Saimiri sciureus), for example, is particularly likely to manifest beta-amyloid deposition in the cerebral blood vessels with age, whereas the rhesus monkey (Macaca mulatta) develops more abundant parenchymal amyloid. These animals have been used to test in vivo beta-amyloid labeling strategies with monoclonal antibodies and radiolabeled A beta. Species-differences in the predominant site of A beta deposition also can be exploited to evaluate factors that direct amyloid selectively to a particular tissue compartment of the brain. For example, the cysteine protease inhibitor, cystatin C, in squirrel monkeys has an amino acid substitution that is similar to the mutant substitution found in some humans with a hereditary form of cystatin C amyloid angiopathy, possibly explaining the predisposition of squirrel monkeys to CAA. The existing animal models have shown considerable utility in deciphering the pathobiology of CAA, and in testing strategies that could be used to diagnose and treat this disorder in humans.

Electron microscopy of amyloid fibrils and microvessels

Senile plaques and microvessels in the cortices of brains with Alzheimer's disease were examined using serial sections under light and electron microscopes. In addition, observations were carried out by using an immunostaining method. The results obtained were as follows: (1) Every senile, plaque contains some amyloid fibrils, and many senile plaques have degenerated capillaries with amyloid fibrils. (2) Amyloid fibrils without senile plaques continue directly to the capillaries. (3) A considerable number of preamyloids are observed surrounding the capillaries when a methenamine silver stain is used. (4) Alpha 1-antichymotrypsin is found in amyloid fibrils, endothelial cells, and vascular feet or astrocytic processes. Our findings strongly suggest that amyloid fibrils forming senile plaques have a close relationship to the capillaries. Moreover, a protease inhibitor, such as alpha 1-antichymotrypsin, could possibly play an important role in producing the amyloid fibrils.

Microvasculature in brain biopsy specimens from patients with Alzheimer's disease: an immunohistochemical and ultrastructural study

Brain biopsy specimens from five patients with Alzheimer's disease obtained in the course of a trial of intracerebroventricular bethanechol were studied by immunohistochemical (antibody to A4 peptide) and ultrastructural techniques, with particular emphasis on the microvessels. In some cases, numbers of A4-immunoreactive lesions (senile plaques) correlated well with numbers of plaques demonstrable by silver stains. Prominent A4-immunoreactive amyloid angiopathy was seen in one patient. The patient with severe cerebral amyloid angiopathy (CAA) showed extensive arteriolar deposition of amyloid filaments with apparent destruction of the media but remarkably intact endothelium. A cell of origin for amyloid filaments was not apparent, although close proximity to smooth muscle cell remnants in the arteriolar media suggested this as one possible cell of origin. Frequent vessels showed medial or adventitial collagen deposition, even when the amount of amyloid was minimal or negligible. Thus relatively severe CAA can exist in the absence of overt endothelial injury, although related studies on this tissue indicate definite abnormalities of the blood-brain barrier. Conversely, destruction of smooth muscle cells and collagen deposition in vessel walls may be the cellular correlates of arteriolar weakening that can lead to CAA-related brain hemorrhage.

The distribution of α1-antichymotrypsin and amyloid production in the brain in Alzheimer’s disease

In this immunohistopathological study alpha 1-antichymotrypsin, which is barely demonstrable in the normal brain, was found in amyloid fibrils, endothelial cells and the cytoplasm of astroglial cells in brains from patients with Alzheimer's disease. Amyloid precursors stained with methenamine silver were arrayed mainly along the membranes, and amyloid fibrils, which stained densely with anti-alpha 1-antichymotrypsin, were in direct contact with the fibrous structures connecting with the membranes of vascular feet or astrocytic processes. From the above findings, alpha 1-antichymotrypsin seems to play a role in the production of amyloid fibrils in Alzheimer's disease.

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

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 invaginations 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 beta-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.

Morphological study of amyloid fibrils and preamyloid deposits in the brain with Alzheimer's disease

In addition to the ultrastructural study of amyloid fibrils, amyloid fibrils and preamyloid in the brain which had the fine ultrastructure of a well-preserved neuropil were examined using methenamine silver stain by light and electron microscope. In serial sections, amyloid fibrils in extracellular spaces continued directly to the capillaries. Using methenamine silver stain, silver granules were deposited at the amyloid fibrils and in extracellular spaces forming diffuse plaques. Many silver granules in the extracellular spaces seemed to strain preamyloid surrounding the capillaries. These findings to indicate that the capillaries have an important role in the formation of amyloid fibrils at least in some senile plaques.

Morphological changes of blood vessels in the brain with Alzheimer's disease

Morphological changes of microvessels in the cerebral cortices of Alzheimer's disease and control brains were examined. From several parts of the brains, all of the vessels in blocks of tissues were isolated with ultrasound treatment and mesh filtration, and were observed by light microscopy. The results obtained were as follows: There was no difference between the relatively large arteries of the brains with Alzheimer's disease and the control brains. However, in the Alzheimer's brain irregular shapes of blood vessels and degenerated smooth muscle cells of a single layer were observed in the terminal arterioles. In the capillaries, focal constrictions and irregular shapes were observed. In addition to these changes, the nuclei of endothelial cells were irregular and unclear. These findings seem to indicate that the degeneration of microvessels in the brain of Alzheimer's disease might have occurred at the terminal arterioles and the capillaries.

A quantitative study of the coincidence of blood vessels and A4 protein deposits in Alzheimer's disease

The spatial relationship between A4 protein deposits and blood vessels in the brains of 6 elderly cases of Alzheimer's disease has been investigated. Sections were taken from medial temporal cortex and were double immunostained for A4 protein and type IV collagen, the latter being employed as a marker of blood vessels. By comparing the observed area of vessel overlying A4 deposit with that predicted from the product of A4 deposit and blood vessel area fractions it is shown that, contrary to expectations, the likelihood of a vessel co-inciding with an A4 deposit is less than would be expected by chance. It would therefore appear that the previously described positive association between A4 deposits and blood vessels reflects the abundance of A4 and the high vascularity of the cortex rather than any specific correlation between the two features.

Vascular changes in the brains with Alzheimer's disease

Sections of temporal and occipital cortex from 14 patients with Alzheimer's disease were examined by light and electron microscopy. Especially, areas without senile plaques or neurofibrillary degeneration were examined in detail. The initial change in the cerebral cortex occurred in the capillaries. The endothelial cells demonstrated degeneration with hypertrophic distorted basement membranes and swelling of the vascular feet. Lipochromes were found in the processes and cell bodies of the astrocytes. A decrease in the number of nerve cells and their processes noted in the cortices may be due to primary vascular degeneration. Severe dementia in Alzheimer's disease may be related to the histopathological findings of diffusely destroyed nerve cells and their processes.

Ultrastructure of senile plaque using thick sections in the brain with Alzheimer's disease

The subjects used in the present study consisted of 8 cases with Alzheimer's disease. Senile plaques which seemed to have no relation with the capillaries were examined in thick serial sections (3,000-5,000 A) by electron microscope. The results obtained were as follows: All of those senile plaques had amyloid angiopathy with amyloid fibrils and these amyloid fibrils formed the main elements of senile plaques. From these findings, it was confirmed that the amyloid fibrils in all plaques are produced from the capillaries.

Ultrastructural studies of the cells forming amyloid fibers in classical plaques

Three-dimensional reconstruction and ultrastructural studies of classical plaques from the cortex of patients with Alzheimer's disease showed that microglial cells of the plaques are the amyloid-forming cells. The amyloid star of the single plaque represents the product of five or six microglial cells covering about 80% of the amyloid star surface. The amyloid fibers appear to be formed within altered cisterns of the endoplasmic reticulum. Distended cisterns form channels filled with amyloid fibers. Numerous vesicles derived from the Golgi apparatus appear to be attached to or fused with the amyloid-filled channels. Reconstruction of the amyloid star and the microglia cell pole that forms the amyloid star reveals three different zones of distribution of cytoplasmic organelles and amyloid deposits. The peripheral zone comprises channels filled with loosely packed amyloid fibers arranged in a parallel manner. The transient zone consists of a mixture of fusing amyloid channels and products of disintegration of cytoplasmic pockets, dense bodies and fragments of cellular membranes. The core of the amyloid star is composed of condensed, densely packed amyloid fibers that are free of cellular debris. Formation of the three zones supports the idea that the microglia/macrophages are not phagocytes but instead are the cells manufacturing the amyloid fibers.

Ultrastructural study of senile plaques and microvessels in the brain with Alzheimer's disease and Down's syndrome

This study examined the relation between amyloid fibrils and senile plaques in brains of patients with Alzheimer's disease. All the senile plaques contained some amyloid fibrils, which seemed to be produced in the basement membranes of capillary endothelial cells and projecting into surrounding parenchyma. Even when amyloid fibrils could not be seen in senile plaques using light microscopy, at least one degenerate capillary containing amyloid fibrils was found when serial sections were examined by electron microscopy. Amyloid fibrils consisted of hollow rods and were composed of filaments arranged as a tightly coiled helix, each turn comprising five globular subunits. Many capillaries and microvessels showed degenerative changes. Many terminal arterioles had smooth muscle cells with an irregular shape and arrangement, often showing a series of focal constrictions. The findings suggest that the capillary degeneration with the formation of amyloid fibrils may be a primary change in the genesis of senile plaques. Furthermore, degenerative changes in the microvessels may also be an important factor in the loss of neurons in the brain of subjects with Alzheimer's disease.

Morphological changes of microvessels in the brain with Alzheimer's disease

The pathological changes of microvessels in the cerebral cortex in Alzheimer's disease were examined at the ultrastructural level. With transmission electron microscopy (TEM), the endothelial cells of many capillaries and their pericytes exhibited atrophy and swelling with a narrowed lumen. The capillary basal laminas were thickened and tortuous. After isolation of the microvessels by ultrasonic treatment and collagenase digestion, the vascular wall structure was viewed by scanning electron microscopy (SEM). Most of the terminal arterioles had smooth muscle cells with an irregular shape and arrangement and often showed a series of focal constrictions. In some areas, the capillaries were arrayed in a bundle and terminated with tapered ends. Associated with the microvessels were fine filaments which may represent amyloid fibrils. The findings indicate that diffuse atrophy and the deletion of nerve cells in the cerebral cortex might be caused, at least partly, by a circulatory disturbance through the pathomorphologically changed microvessels.

Ultrastructural heterogeneity in cerebral amyloid of Alzheimer's disease

Cerebral amyloid deposits from five patients with presenile or senile cerebral disease of the Alzheimer type were stained with uranyl acetate and lead citrate or with periodic acid-thiocarbohydrazide-silver proteinate, and examined with traditional high-resolution electron microscopy and with a goniometer tilting stage. In addition to a carbohydrate-rich matrix, we also consistently found local cell-derived vesicles within plaque and dyshoric amyloid. The most likely source for these vesicles appeared to be degenerate neurites. Amyloid fibrils were intimately associated with plasmalemmata, particularly those of degenerate neurites, which supported a neuronal origin for the amyloid fibril of Alzheimer's disease.

Ultrastructural changes of blood vessels in the cerebral cortex in Alzheimer's disease

Several parts of the cerebral cortices in five brains from patients with Alzheimer's disease were examined by light and electron microscopes. The results obtained are as follows: The initial change of the cerebral cortex in the brain occurred in the small blood vessel and capillary. The endothelial cell of the blood vessel fell into a degenerated state with swelling of the vascular feet and astroglial cells. The change in a great number of nerve cells and their processes diffusely observed in the cortices were nonspecific and could be due to primary vascular degeneration. Severe dementia in Alzheimer's disease seemed to be well explained by the histopathological findings of diffusely destroyed nerve cells and their processes. From this, Alzheimer's disease can be speculated to be a disease caused by progressive capillary degeneration.

Ultrastructure of amyloid fibrils in Alzheimer's disease and Down's syndrome

Amyloid fibrils in brains of patients with Alzheimer's disease and Down's syndrome were examined by light and electron microscopy. In addition, replicas of amyloid fibrils produced by a quick freezing method from the brain of a patient with Down's syndrome were examined by electron microscopy. The amyloid fibrils were shown to consist of hollow rods. These were composed of filaments arranged as a tightly coiled helix, each turn of which consisted of five globular subunits. This structure appears to be similar to the prion filament observed in Creutzfeldt-Jakob disease (CJD). The possibility therefore arises that amyloid fibrils in Alzheimer's disease and Down's syndrome may be related to the transmissible agents responsible for diseases such as CJD, kuru and Gerstmann-Sträussler Syndrome (GSS).

Ultrastructural studies of amyloid fibrils and senile plaques in human brain

Amyloid fibrils and senile plaques in brains with Alzheimer's disease, senile dementia and Down's syndrome were examined by light and electron microscopy. In addition, replicas of amyloid fibrils, made by a quick freezing method from a brain with Down's syndrome, were examined. All amyloid masses forming the cores of senile plaques consisted of numerous amyloid fibrils spreading from the walls of small blood vessels to the surrounding parenchyma. The amyloid fibrils ran in various directions, forming bundle-like groups in a geometrical array. They appeared as rods with hollow structures consisting of an array of globular units in the replicas, while they showed bead-like structure in the tissue specimens of 500-nm thick sections. The ultrastructure of replicas reveals a new finding on the structure of amyloid fibrils in the human brain.

The relationship between senile plaques and cerebral blood vessels in Alzheimer's disease and senile dementia. Morphological mechanism of senile plaque production

Several kinds of senile plaque found in 6 brains (4 from patients with Alzheimer's disease and 2 from patients with senile dementia) were examined in serial sections by light electron microscopy. The results obtained were as follows. All the senile plaques contained at least some amyloid fibrils, and these seemed to be produced at the basement membranes of capillary endothelial cells and projected into the surrounding parenchyma. Even when the senile plaques themselves appeared to lack amyloid fibrils by light microscopy, at least one degenerable capillary containing amyloid fibrils was demonstrable when serial sections were examined ultrastructurally. The findings described above suggest that the amyloid fibrils which form the cores of the several kinds of senile plaque, seem to be produced at the basement membrane of the endothelial cell. It is speculated that the capillary degeneration with the formation of amyloid fibrils may be primary change in the genesis of senile plaques.

Observations of amyloid angiopathy and senile plaques by the scanning electron microscope

Blood vessels with amyloid angiopathy and senile plaques in the cortices of the brains with Alzheimer's disease and senile dementia were observed by means of a scanning electron microscope. the results obtained were as follows: The blood vessels with amyloid angiopathy were surrounded by solid substances. The senile plaques consisted of rough solid substances, contained degenerated cell processes, and almost all plaques existed around the degenerated capillaries with amyloid angiopathy. From the above described findings, we suggest that the senile plaque has an extremely cose relationship to the capillary which had undergone amyloid angiopathy.

Electron-microscopical study on senile plaques in Alzheimer's disease

The cerebral cortex taken post mortem from a case of Alzheimer's disease was examined especially with regard to the relation between blood vessels and senile plaques. Many senile plaques had central cores, composed of such matter as degenerated blood vessels and basement membranes with abundant amyloid fibrils. The components of senile plaques seemed to be degenerated neuronal and glial tissue compressed by developed basement membranes and amyloid fibrils. From this we would like to emphasize that senile plaques seem to be caused by amyloid fibrils and degenerated capillaries.

Paraproteinosis and amyloidosis of the cerebral vessels and senile plaques

A case is reported of progressive dementia and a terminal picture of generalized tetaniform contractures. The relationship of the generalized tetaniform contractures to the stiff-man syndrome is discussed. Morphologically, diffuse amyloid deposition was found in the pial and cortical vessels, accompanied by amyloid deposition in the senile plaques in the cortical and cerebellar cortex. Apart from the typical staining and ultrastructural aspects of amyloid, a deposition of material was observed, corresponding in optical and electron microscopy to a paraprotein. This case demonstrated not only the relationship between the deposition of amyloid and the formation of senile plaques, but also sustains the direct connection between amyloid in senile plaques and the paraprotein substances deriving from the blood. The probable relationship between the unusual deposition of paraproteins in the vessels and nervous system and the treatment with immunoglobulins is discussed.

Cerebrovascular amyloidosis with cerebral hemorrhage

More than 1400 necropsies performed on patients with either a nontraumatic cerebral hemorrhage (400 cases) or with dementia over the age of 55 (1010 cases), or both, have been reviewed. There were 15 cases in which a cerebral hemorrhage had occurred together with cerebral amyloid angiopathy all of whom had been demented. Eight of the 15 patients were hypertensive. The 7 non-hypertensives showing only the amyloid change included two cases of "atypical" Alzheimer's disease with acute neurological features, and 5 cases of senile dementia (aged 72 to 78 years) coupled with focal neurological disorders. In the hypertensive patients, aged 67 to 86 years, with a progressive dementing syndrome and acute neurological signs, multiple ball-like hemorrhages (7 cases) and/or cerebral hematomas (3 cases) were associated with a combination of amyloid and hyalinar (hypertensive) angiopathy, often affecting segments of the same pial and cortical vessels. From these data and recent reports on lethal cerebral hemorrhage occurring spontaneously or after neurosurgical procedures in demented old people, cerebral amyloid angiopathy, which is not necessarily associated with systemic amyloidosis or severe (pre)senile cerebral degeneration, may be considered a rare but important cause of cerebral hemorrhage in the aged. The "vascular" type of presenile dementia, occasionally complicated by focal cerebrovascular lesions or bleeds, is considered a variant of Alzheimer's disease. The mechanism leading to formation of cerebral amyloid is unknown.