Immunoreactive A4 and gamma-trace peptide colocalization in amyloidotic arteriolar lesions in brains of patients with Alzheimer's disease.

Cerebral amyloid angiopathy (CAA) defines a biochemically heterogeneous entity that manifests as effacement of cerebral microvessel walls by a fibrillar material with characteristic tinctorial properties. In biochemical terms, the amyloid that infiltrates blood vessels in CAA is composed of the A4 or beta peptide of Alzheimer's disease (AD), a molecule related to gamma trace or cystatin C (seen in patients with hereditary cerebral hemorrhage with amyloidosis in Iceland, HCHWA-I), or the PrP characteristic of spongiform encephalopathy and scrapie. Using antibodies to synthetic peptides representing portions of the 4.2-kd Alzheimer A4 peptide and the gamma-trace peptide, we immunostained sections of brain from patients with AD, senile dementia of Alzheimer's type, and CAA with associated leukoencephalopathy. Immunohistochemical studies demonstrated colocalization of the A4 and gamma-trace peptides within arteriolar walls, but only rarely in A4 amyloidotic capillaries or senile plaque cores of amyloid. When gamma-tracelike reactivity was noted in capillary walls, it was sometimes noted within the cytoplasm of pericytes. Immunostaining was always more intense when the anti-A4 antibody was used as the primary antibody. Gamma-trace immunostaining was more prominent on the adventitial component of arteriolar walls, whereas A4 staining was usually seen more diffusely throughout the blood vessel wall, especially in the media. Rarely individual pericytelike cells showed prominent gamma-trace immunoreactivity. These findings suggest that A4 and gamma-tracelike molecules may colocalize within arteriolar walls within the brains of patients with AD, and highlight the fact that CAA identified with AD and HCHWA-I are not as biochemically distinct as was assumed previously. Furthermore these findings suggest that other peptidases or protease inhibitors may be found within amyloidotic microvessel walls and may contribute to senile brain change and CAA-related strokes, including hemorrhage and encephalomalacia.     

The 2,6-disubstituted naphthalene derivative FDDNP labeling reliably predicts Congo red birefringence of protein deposits in brain sections of selected human neurodegenerative diseases

Deposition of conformationally altered proteins prominently characterizes pathogenesis and pathomorphology of a number of neurodegenerative disorders. 2-(1-{6-[(2-[F-18]fluoroethyl) (methyl)amino]-2-naphthyl} ethylidene) malononitrile ([F-18]FDDNP), a hydrophobic, viscosity-sensitive, solvent-sensitive, fluorescent imaging probe has been used with positron emission tomography to visualize brain pathology in the living brain of Alzheimer disease (AD) patients. Its non-radiofluorinated analog FDDNP was shown to label senile plaques and neurofibrillary tangles (NFTs) in brain tissue sections. This work aimed at evaluating FDDNP labeling of various protein deposits in fixed, paraffin-embedded brain tissue sections of selected neurodegenerative disorders: AD, cerebral amyloid angiopathy (CAA), transmissible spongiform encephalopathies, progressive supranuclear palsy (PSP), Pick disease (PiD), Parkinson disease, dementia with Lewy bodies, multiple system atrophy (MSA). Cerebral hypertensive vascular hyalinosis (HVH) was used as negative control. Significant agreement between amyloid histochemical properties and FDDNP labeling of the deposits was established. FDDNP labeling showed high positive predictive value for birefringence in senile plaques and NFTs in AD, prion plaques and amyloid deposits in CAA. No FDDNP labeled structures were observed in HVH, PSP, PiD or MSA tissue sections. Our findings may be of significant value for the detection of neuropathological aggregates with [F-18]FDDNP in some of these disorders in the living brain of human subjects.     

Apolipoprotein B immunoreactivity in senile plaque and vascular amyloids and neurofibrillary tangles in the brains of patients with Alzheimer's disease.

Based upon our previous finding of the association of apolipoprotein E (apoE) immunoreactivity with cerebral amyloids and neurofibrillary tangles (NFTs), we examined immunohistochemically whether this is also the case for apolipoprotein B (apoB). Polyclonal antibody to apoB immunosustained senile plaque amyloid, vascular amyloid, subpial amyloid deposits and intracellular NFTs in formalin-fixed, paraffin-embedded brain sections from patients with Alzheimer disease. Hydrated autoclave pretreatment of the sections enhanced the staining of plaque amyloid. The results may suggest a role of apoB in amyloid and NFT formation.     

Brain Parenchymal and Microvascular Amyloid in Alzheimer's Disease

Brains of patients with Alzheimer disease/senile dementia of Alzheimer type (AD/SDAT) develop a progressive accumulation of amyloid, which deposits primarily in the form of characteristic parenchyma!'plaques' (senile or neuritic plaques/SP's) and as mural deposits in the walls of capillaries and arterioles (cerebral amyloid angiopa-thy/CAA). A major component of this amyloid is a small and unique peptide composed of 39–43 amino acids, beta/A4, which is cleaved from a much larger precursor protein (APP) that has several isoforms. Brain amyloid can be detected in autopsy or biopsy brain tissue by classical, immunohistochemical and ultrastructural (including immuno-electron microscopic) methods of varying sensitivity and specificity. Beta/A4 amyloid deposition is remarkably variable (e.g. predominantly parenchyma! or vascular, or a mixture of parenchymal and vascular) among patients with AD/SDAT. Despite its abundance in the brains of AD/SDAT patients, the precise role of beta/A4 in the pathogenesis of the neurological deficit, neocortical atrophy and progressive synapse loss associated with AD/SDAT has yet to be determined. However, mutations in the gene that encodes APP are clearly associated with familial AD syndromes in which there is significant brain amyloid deposition. CAA, in addition to its association with AD/SDAT, can result in hemorrhagic and (possibly) ischemic forms of stroke. Work with recently developed transgenic mice which express large amounts of beta/A4 in the central nervous system is likely to elucidate mechanisms by which the protein is selectively deposited in the brain in a parenchymal or microvascular form, and how it contributes to the pathogenesis of neurodegeneration.     

Abeta is targeted to the vasculature in a mouse model of hereditary cerebral hemorrhage with amyloidosis

The E693Q mutation in the amyloid beta precursor protein (APP) leads to cerebral amyloid angiopathy (CAA), with recurrent cerebral hemorrhagic strokes and dementia. In contrast to Alzheimer disease (AD), the brains of those affected by hereditary cerebral hemorrhage with amyloidosis-Dutch type (HCHWA-D) show few parenchymal amyloid plaques. We found that neuronal overexpression of human E693Q APP in mice (APPDutch mice) caused extensive CAA, smooth muscle cell degeneration, hemorrhages and neuroinflammation. In contrast, overexpression of human wild-type APP (APPwt mice) resulted in predominantly parenchymal amyloidosis, similar to that seen in AD. In APPDutch mice and HCHWA-D human brain, the ratio of the amyloid-beta40 peptide (Abeta40) to Abeta42 was significantly higher than that seen in APPwt mice or AD human brain. Genetically shifting the ratio of AbetaDutch40/AbetaDutch42 toward AbetaDutch42 by crossing APPDutch mice with transgenic mice producing mutated presenilin-1 redistributed the amyloid pathology from the vasculature to the parenchyma. The understanding that different Abeta species can drive amyloid pathology in different cerebral compartments has implications for current anti-amyloid therapeutic strategies. This HCHWA-D mouse model is the first to develop robust CAA in the absence of parenchymal amyloid, highlighting the key role of neuronally produced Abeta to vascular amyloid pathology and emphasizing the differing roles of Abeta40 and Abeta42 in vascular and parenchymal amyloid pathology.     

Dense-core senile plaques in the Flemish variant of Alzheimer's disease are vasocentric

Alzheimer's disease (AD) is characterized by deposition of beta-amyloid (Abeta) in diffuse and senile plaques, and variably in vessels. Mutations in the Abeta-encoding region of the amyloid precursor protein (APP) gene are frequently associated with very severe forms of vascular Abeta deposition, sometimes also accompanied by AD pathology. We earlier described a Flemish APP (A692G) mutation causing a form of early-onset AD with a prominent cerebral amyloid angiopathy and unusually large senile plaque cores. The pathogenic basis of Flemish AD is unknown. By image and mass spectrometric Abeta analyses, we demonstrated that in contrast to other familial AD cases with predominant brain Abeta42, Flemish AD patients predominantly deposit Abeta40. On serial histological section analysis we further showed that the neuritic senile plaques in APP692 brains were centered on vessels. Of a total of 2400 senile plaque cores studied from various brain regions from three patients, 68% enclosed a vessel, whereas the remainder were associated with vascular walls. These observations were confirmed by electron microscopy coupled with examination of serial semi-thin plastic sections, as well as three-dimensional observations by confocal microscopy. Diffuse plaques did not associate with vessels, or with neuritic or inflammatory pathology. Together with earlier in vitro data on APP692, our analyses suggest that the altered biological properties of the Flemish APP and Abeta facilitate progressive Abeta deposition in vascular walls that in addition to causing strokes, initiates formation of dense-core senile plaques in the Flemish variant of AD.     

The copper-peroxide-silver method: a highly sensitive procedure for the demonstration of Alzheimer's disease lesions and for signal intensification in immunocytochemistry.

Ammoniacal silver solutions give striking impregnation of Alzheimer's disease (AD) lesions if sections are pretreated with copper sulfate and hydrogen peroxide. In contrast to most silver impregnation methods, no staining of normal neurites is obtained, and senile plaques (SPs), neurofibrillary tangles (NFTs), and neuropil threads (NTs) are strongly stained in black against a clear background. A sodium acetate wash interposed between the copper sulfate and hydrogen peroxide resulted in suppression of the staining of amyloid lesions. This variant of the basic procedure (CPS-II method), maintains the capacity of the latter (CPS-I method) to strongly impregnate NFTs and NTs. In addition, it clearly delineates the dystrophic neurites of SPs obscured by the strong argyrophilia of the amyloid deposits seen in CPS-I stains. NTs are strongly impregnated with both CPS-I and CPS-II methods and are unmasked from normal neurites, which remain unstained. The staining can be abolished by pretreatment with formic acid and erased with a brief wash in sulfochromic acid. Destained sections can be restained with either method or with immunoperoxidase procedures. CPS staining of previously immunostained tissues produces marked intensification of the diaminobenzidine reaction product. In AD brains, the immunostaining is markedly enhanced and selective when the silver procedure is preceded by formic acid treatment. The selectivity and high sensitivity of the procedure may be useful as a diagnostic tool and of value to study the biogenesis and natural evolution of the brain lesions of AD.(ABSTRACT TRUNCATED AT 250 WORDS)     

Coexistence of Alzheimer's amyloid precursor protein and amyloid protein in cerebral vessel walls

Polyclonal antibodies to synthetic peptides homologous to amino acid residues 45-62, 597-624, and 676-695 of the predicted sequence of Alzheimer's amyloid precursor protein (APP) were used to investigate the site of origin of APP, and the relationship between APP and amyloid protein in Alzheimer's disease (AD) and hereditary cerebral hemorrhage with amyloidosis, Dutch type (HCHWA-D). Cortical sections as well as homogenates of isolated leptomeningeal and cortical microvessels from three patients with AD, two patients with HCHWA-D, and two nondemented controls were probed. In vessel extracts of both groups of patients and the controls, APP was detected as a set of proteins with electrophoretic mobility of 105 to 135 kilodaltons. In cortical sections of all subjects, APP immunoreactivity was found in leptomeningeal and cortical vessel walls. In patients with AD and HCHWA-D, APP and amyloid fibrils coexisted in the same vessels. Moreover, APP immunoreactivity was found in association with 50% of senile plaques in AD brains, but was not evidenced in parenchymal amyloid deposits in patients with HCHWA-D. These data suggest that the vascular system is a source of APP and that the processing of APP into insoluble fibrils in AD and HCHWA-D may take place in situ.     

Transglutaminases and transglutaminase-catalyzed cross-links colocalize with the pathological lesions in Alzheimer's disease brain

Alzheimer's disease (AD) is characterized by pathological lesions, in particular senile plaques (SPs), cerebral amyloid angiopathy (CAA) and neurofibrillary tangles (NFTs), predominantly consisting of self-aggregated proteins amyloid beta (Aβ) and tau, respectively. Transglutaminases (TGs) are inducible enzymes, capable of modifying conformational and/or structural properties of proteins by inducing molecular covalent cross-links. Both Aβ and tau are substrates for TG cross-linking activity, which links TGs to the aggregation process of both proteins in AD brain. The aim of this study was to investigate the association of transglutaminase 1 (TG1), transglutaminase 2 (TG2) and TG-catalyzed cross-links with the pathological lesions of AD using immunohistochemistry. We observed immunoreactivity for TG1, TG2 and TG-catalyzed cross-links in NFTs. In addition, both TG2 and TG-catalyzed cross-links colocalized with Aβ in SPs. Furthermore, both TG2 and TG-catalyzed cross-links were associated with CAA. We conclude that these TGs demonstrate cross-linking activity in AD lesions, which suggests that both TG1 and TG2 are likely involved in the protein aggregation processes underlying the formation of SPs, CAA and/or NFTs in AD brain.     

Negative association between amyloid plaques and cerebral amyloid angiopathy in Alzheimer's disease

Cerebral amyloid angiopathy (CAA) is an important, though still relatively neglected, aspect of the pathology of Alzheimer's disease (AD), and both the source of amyloid beta protein (Abeta) in CAA, and its relationship to senile plaque (SP) Abeta, remain unclear. We have investigated the relationship between Abeta deposition in SP and CAA in four regions of brain from 69 patients with AD in order to gain insight into the pathogenetic mechanism(s) underlying these pathologies. CAA was present to some degree in all 69 patients, with the occipital cortex being affected more often and more severely than frontal, temporal and parietal cortices. By definition, SPs were present in all brain areas in all 69 patients, with greater uniformity of distribution than CAA, though the occipital cortex was less severely affected than the other brain regions. There was no significant (positive) correlation between CAA rating and that of SP for any one cortical region, but on combining data from all four regions there was a significant inverse correlation (P=0.037) between CAA and SP ratings. Such data suggest that the cellular sources and mechanisms leading to Abeta deposition as SP or CAA are likely to differ and may proceed independently of each other.     

Sporadic and familial cerebral amyloid angiopathies

Cerebral amyloid angiopathy (CAA) is the term used to describe deposition of amyloid in the walls of arteries, arterioles and, less often, capillaries and veins of the central nervous system. CAAs are an important cause of cerebral hemorrhage and may also result in ischemic lesions and dementia. A number of amyloid proteins are known to cause CAA. The most common sporadic CAA, caused by A beta deposition, is associated with aging and is a common feature of Alzheimer disease (AD). CAA occurs in several familial conditions, including hereditary cerebral hemorrhage with amyloidosis of Icelandic type caused by deposition of mutant cystatin C, hereditary cerebral hemorrhage with amyloidosis Dutch type and familial AD with deposition of either A beta variants or wild-type A beta, the transthyretin-related meningo-vascular amyloidoses, gelsolin as well as familial prion disease-related CAAs and the recently described BRI2 gene-related CAAs in familial British dementia and familial Danish dementia. This review focuses on the morphological, biochemical, and genetic aspects as well as the clinical significance of CAAs with special emphasis on the BRI2 gene-related cerebrovascular amyloidoses. We also discuss data relevant to the pathomechanism of the different forms of CAA with an emphasis on the most common A beta-related types.     

Concurrent cardiac transthyretin and brain β amyloid accumulation among the older adults: The Hisayama study

Previous studies have revealed risk for cognitive impairment in cardiovascular diseases. We investigated the relationship between degenerative changes of the brain and heart, with reference to Alzheimer's disease (AD) pathologies, cardiac transthyretin amyloid (ATTR) deposition, and cardiac fibrosis. A total of 240 consecutive autopsy cases of a Japanese population-based study were examined. β amyloid (Aβ) of senile plaques, phosphorylated tau protein of neurofibrillary tangles, and ATTR in the hearts were immunohistochemically detected and graded according to the NIH-AA guideline for AD pathology and as Tanskanen reported, respectively. Cerebral amyloid angiopathy (CAA) was graded according to the Vonsattel scale. Cardiac fibrosis was detected by picrosirius red staining, followed by image analysis. Cardiac ATTR deposition occurred after age 75 years and increased in an age-dependent manner. ATTR deposition was more common, and of higher grades, in the dementia cases. We subdivided the cases into two age groups: ≤90 years old (n = 173) and >90 years old (n = 67), which was the mean and median age at death of the AD cases. When adjusted for age and sex, TTR deposition grades correlated with Aβ phase score (A2–3), the Consortium to Establish a Registry for AD score (sparse to frequent), and high Braak stage (V–VI) only in those aged ≤90 years at death. No significant correlation was observed between the cardiac ATTR deposition and CAA stages, or between cardiac fibrosis and AD pathologies. Collectively, AD brain pathology correlated with cardiac TTR deposition among the older adults ≤90 years.     

The role of cystatin C in cerebral amyloid angiopathy and stroke: cell biology and animal models

A variant of the cysteine protease inhibitor, cystatin C, forms amyloid deposited in the cerebral vasculature of patients with hereditary cerebral hemorrhage with amyloidosis, Icelandic type (HCHWA-I), leading to cerebral hemorrhages early in life. However, cystatin C is also implicated in neuronal degenerative diseases in which it does not form the amyloid protein, such as Alzheimer disease (AD). Accumulating data suggest involvement of cystatin C in the pathogenic processes leading to amyloid deposition in cerebral vasculature and most significantly to cerebral hemorrhage in patients with cerebral amyloid angiopathy (CAA). This review focuses on cell culture and animal models used to study the role of cystatin C in these processes.     

Beta-protein amyloid is widely distributed in the central nervous system of patients with Alzheimer''s disease.

To clarify the distribution, morphology, and density of amyloid deposits in patients with Alzheimer's disease (AD), tissue sections from various areas of the central nervous system of 14 patients with AD and from 20 nondemented aged controls were investigated immunohistochemically using anti-beta protein antiserum. beta-protein amyloid deposits were present not only in the cores of the senile plaques and in the vascular wall (amyloid angiopathy), but also in various sized plaque-shaped fibrillary, perivascular, subpial, and subependymal deposits. Amyloid deposits were found mainly in the cerebral cortex in nondemented controls, while in AD they were distributed widely in the regions that were not affected in nondemented controls. The positivity of amyloid deposits in AD was 100% in the cerebral cortex, hippocampus, amygdala, thalamus, caudate nucleus, claustrum, hypothalamus, nucleus basalis of Meynert, and cerebellar cortex. Putamen and brain-stem nuclei were affected frequently, and the spinal cord, dentate nucleus, and globus pallidus were sometimes (less than 50%) affected. This result provides an evidence that Alzheimer's disease is a beta-protein amyloidosis of the central nervous system. An assessment of the distribution of amyloid deposits should prove to be useful for the histopathologic diagnosis of AD.     

Silver staining of senile plaques and neurofibrillary tangles in paraffin sections. A simple and effective method.

A one-step silver staining method using a protective colloidal developer of gelatin and formic acid was originally established for demonstration of argyrophilic nucleolus organizer regions by controlled reduction of silver. We describe here a new application of this silver technique that can easily be performed to demonstrate senile plaques (SP) and neurofibrillary tangles (NFT) on paraffin sections. Preliminary results in ten cases of senile dementia of Alzheimer type and five cases of amyloid congophilic angiopathy showed a reliable demonstration of amyloid and neuritic type SP as well as NFT in all 15 cases. In addition, deposits of perivascular amyloid and areas of fibrillar amyloid, the diffuse type of senile plaques, were revealed. The success seems to depend particularly on the low concentration of formic acid in the developer, which might be the responsible agent for the careful revealing of buried argyrophilic structures in SP and NFT. The staining features were quite similar to those with anti-beta and anti-tau immunostaining. This result suggests a high specificity of this method for extracellular and intraneuronal cerebral amyloid. The detailed staining of delicate morphological structures points to a high sensitivity for cerebral amyloids, senile plaques and neurofibrillary tangles, respectively, by this simple and inexpensive method.     

Thrombin accumulation in brains of patients with Alzheimer's disease.

Thrombin was detected immunohistochemically in brain tissue of Alzheimer's disease (AD) patients and age-matched controls. Positive staining was restricted to vessels and residual plasma in controls but was also present in senile plaques, some diffuse amyloid deposits and neurofibrillary tangles in AD. Positive staining was abolished by absorption of antibody with purified human thrombin but not by absorption with prothrombin. The data suggest that thrombin formation from prothrombin probably takes place in AD brain.     

Capillary cerebral amyloid angiopathy is associated with vessel occlusion and cerebral blood flow disturbances

The role of cerebral amyloid angiopathy (CAA) in the pathogenesis of Alzheimer's disease (AD) is not fully understood. Here, we studied whether CAA is associated with alterations in microvascularisation in transgenic mouse models and in the human brain. APP23 mice at 25–26 months of age exhibited severe CAA in thalamic vessels whereas APP51/16 mice did not. Wild-type littermates were free of CAA. We found CAA-related capillary occlusion within the thalamus of APP23 mice but not in APP51/16 and wild-type mice. Magnetic resonance angiography (MRA) showed blood flow alterations in the thalamic vessels of APP23 mice. CAA-related capillary occlusion in the branches of the thalamoperforating arteries of APP23 mice, thereby, corresponded to the occurrence of blood flow disturbances. Similarly, CAA-related capillary occlusion was observed in the human occipital cortex of AD cases but less frequently in controls. These results indicate that capillary CAA can result in capillary occlusion and is associated with cerebral blood flow disturbances providing an additional mechanism for toxic effects of the amyloid β-protein in AD.     

Cerebral amyloid angiopathy: major contributor or decorative response to Alzheimer's disease pathogenesis

Amyloid deposition within cerebral vessels, or cerebral amyloid angiopathy (CAA), is common in advanced age and even more common in Alzheimer's disease. CAA may be complicated by lobar intracerebral hemorrhage, while rare kindreds of autosomal dominant CAA also show propensity for intracerebral hemorrhage, due to germline mutations in specific amyloidogenic precursor proteins and apparent compromise of structural integrity of the blood vessel wall due to marked amyloid deposition. The relationship between cerebral amyloid angiopathy and cognitive dysfunction, however, is less clear. While cognitive dysfunction in familial CAA is likely related to prodigious amyloid deposits and vascular luminal compromise (e.g., hereditary cerebral hemorrhage with angiopathy-Dutch type (HCHWA-D)), cerebral amyloid angiopathy with intracerebral hemorrhage often presents sporadically in cognitively intact elderly patients. Moreover, while about 80% of subjects with Alzheimer's disease have demonstrable amyloid beta within blood vessel walls at autopsy, the vast majority of these fail to suffer clinically relevant intracerebral hemorrhage during life. The remaining 20% manage to progress and die of their disease with virtual no amyloid within blood vessels. Thus, the role of amyloid beta deposits in cerebral vessels as regards cognitive function on the one hand, and tendency for hemorrhage on the other, remain to be resolved for sporadic late onset Alzheimer's disease and CAA. Recent studies on transgenic APP23 mice suggest a relationship between passive immunization and amyloid angiopathy-associated cerebral hemorrhage, although the mechanism of hemorrhage was unclear from the data presented. We suggest that amyloid accumulation represents a response to chronic stress, and that the neurodegenerative process occurs at the neuronal level, encompassing oxidative stress and aberrant cell cycle activation. As such, CAA represents tissue homeostasis, such that an abrupt perturbation of this balance (e.g., amyloid beta immunization) is deleterious.     

Osteopontin and phospho‐SMAD2/3 are associated with calcification of vessels in D‐CAA,an hereditary cerebral amyloid angiopathy

In severe forms of cerebral amyloid angiopathy (CAA) pathology, vascular calcification has been observed in the cerebral cortex, both in vivo on MRI and CT, and post‐mortem using histopathology. However, the pathomechanisms leading to calcification of CAA‐laden arteries are unknown. Therefore, we investigated the correlation between calcification of cortical arterioles and several potential modulators of vascular calcification using immunohistochemistry in a unique collection of brain material of patients with a hereditary form of CAA, namely hereditary cerebral hemorrhage with amyloidosis‐Dutch type (HCHWA‐D or D‐CAA). We show a topographical association of osteopontin (OPN) and TGFβ signaling factor phospho‐SMAD2/3 (pSMAD2/3) in calcified CAA vessel walls. OPN and pSMAD2/3 gradually accumulate in vessels prior to calcification. Moreover, we found that the vascular accumulation of Collagen 1 (Col1), OPN and pSMAD2/3 immunomarkers correlated with the CAA severity. This was independently of the vessel size, including capillaries in the most severe cases. We propose that calcification of CAA vessels in the observed HCHWA‐D cases may be induced by extracellular OPN trapped in the fibrotic Col1 vessel wall, independently of the presence of vascular amyloid.     

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.