Immunohistochemical study of cerebral amyloid angiopathy: use of an antiserum to a synthetic 28-amino-acid peptide fragment of the Alzheimer's disease amyloid precursor

Emerging concepts in Alzheimer's disease

Alzheimer's disease/senile dementia of the Alzheimer type (AD/SDAT) is the most common neuropathologic substrate of dementia. It is characterized by synapse loss (predominantly within neocortex) as well as deposition of certain distinctive lesions (the result of protein misfolding) throughout the brain. The latter include senile plaques, composed mainly of an amyloid (Aβ) core and a neuritic component; neurofibrillary tangles, composed predominantly of hyperphosphorylated tau; and cerebral amyloid angiopathy, a microangiopathy affecting both cerebral cortical capillaries and arterioles and resulting from Aβ deposition within their walls or (in the case of capillaries) immediately adjacent brain parenchyma. In this article, I discuss the hypothesized role these lesions play in causing cerebral dysfunction, as well as CSF and neuroimaging biomarkers (for dementia) that are especially relevant as immunotherapeutic approaches are being developed to remove Aβ from the brain parenchyma. In addition, I address the role of neuropathology in characterizing the sequelae of new AD/SDAT therapies and helping to validate CSF and neuroimaging biomarkers of disease. Comorbidity of AD/SDAT and various types of cerebrovascular disease is a major theme in dementia research, especially as cognitive impairment develops in the oldest old, who are especially vulnerable to ischemic and hemorrhagic brain lesions.

Pathologic lesions in neurodegenerative diseases

This chapter will discuss two of the most widely used approaches to assessing brain structure: neuroimaging and neuropathology. Whereas neuropathologic approaches to studying the central nervous system have been utilized for many decades and have provided insights into morphologic correlates of dementia for over 100 years, accurate structural imaging techniques "blossomed" with the development and refinement of computerized tomographic scanning and magnetic resonance imaging (MRI), beginning in the late 1970s. As Alzheimer disease progresses over time, there is progressive atrophy of the hippocampus and neocortex--this can be quantified and regional accentuation of the atrophy can be evaluated using quantitative MRI scanning. Furthermore, ligands for amyloid proteins have recently been developed--these can be used in positron emission tomography studies to localize amyloid proteins, and (in theory) study the dynamics of their deposition (and clearance) within the brain over time. Neuropathologic studies of the brain, using highly specific antibodies, can demonstrate synapse loss and the deposition of proteins important in AD progression--specifically ABeta and phosphor-tau. Finally, neuropathologic assessment of (autopsy) brain specimens can provide important correlation with sophisticated neuroimaging techniques.

Neurovascular changes measured by time-of-flight MR angiography in cholesterol-fed rabbits with cortical amyloid beta-peptide accumulation

PURPOSE

To test the hypothesis that narrowing of cranial blood vessels in cholesterol-fed rabbits is a function of the duration of the high cholesterol diet. Such neurovascular changes, caused by elevated serum cholesterol, are linked to stroke and Alzheimer's disease risk.

MATERIALS AND METHODS

Four groups of New Zealand White rabbits were studied. Six were fed a normal diet, 19 were fed a 2% cholesterol diet with 0.12 ppm copper in the drinking water for 8 weeks, 10 weeks, or 12 weeks. Time-of-flight (TOF) MR angiography (MRA) at 3 Tesla was used to measure arterial diameters in 11 vessels. Previously published data for amyloid beta-peptide (Abeta) accumulation in the brains measured postmortem were correlated to vessel diameters. Ventricular volumes of rabbits were measured on group-averaged data.

RESULTS

Several vessel diameters decreased with cholesterol diet duration. The posterior communicating arteries showed the largest significant effect. Abeta accumulation was inversely correlated with arterial diameter. Ventricular volumes between the normal diet and 12 weeks cholesterol-fed groups were not significantly different.

CONCLUSION

Reduction in vessel diameter of medium-sized vessels but not large vessels was measured in these hypercholesterolemic rabbits. The vessel diameter narrowing and cortical Abeta deposition occurred before measurable ventricular enlargement.

The diagnostic relevance of cerebral amyloid angiopathy in the setting of forensic pathology - a report of two cases and review of the literature

The neuropathological features seen in two cases with cerebral amyloid angiopathy (CAA) are presented. An 85-year-old woman was found comatose at home and died on the way to the hospital. The cause of death was an intracerebral hemorrhage (ICH) in the right parietal lobe. A 93-year-old woman with a history of traumatic subarachnoid hemorrhage was operated on for a chronic subdural hematoma. Intraoperatively, she developed severe ICH and died. The cause of death was an ICH in the parieto-occipital lobe. The morphology of the vessels was studied on differently stained sections and the neuropathological findings of the surrounding brain tissue were investigated. The affected vessels showed the characteristic alterations seen in CAA and included vascular amyloid deposition, fibrinoid necrosis, double-barrel lumen, splitting of the internal elastic lamina, defects of the vessel wall, and microaneurysms. Visualization of beta-amyloid protein was performed by histological and immunohistochemical methods. The immunohistochemistry for beta-amyloid was more sensitive and yielded better results compared with Congo red. In cases of ICH, CAA has to be considered in the differential diagnosis. Besides the use of Congo red stain, the application of beta-amyloid immunohistochemistry is requested to reliably make the diagnosis of CAA. Additional staining with a modified silver impregnation technique (AgNOR) is useful to detect associated neurodegenerative changes.

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 parenchymal 'plaques' (senile or neuritic plaques/SP's) and as mural deposits in the walls of capillaries and arterioles (cerebral amyloid angiopathy /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 parenchymal 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 or deposited in the brain in a parenchymal or microvascular form, and how it contributes to the pathogenesis of neurodegeneration.

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.

Autosomal dominant arteriopathic leuko-encephalopathy and Alzheimer's disease

A 49-year-old man suffered from progressive dementia and seizures leading to death after 2 years. CT scans showed severe cortical-subcortical atrophy and hypodensity of the white matter. His father had died at about the same age with similar clinical signs. Two sisters and one brother were also affected. Neuropathological study revealed predominant involvement of the cerebral white matter with myelin loss, gliosis and type I lacunes. The small arteries and arterioles of the white matter and basal ganglia, and, to a lesser extent those of the subarachnoidal space, displayed fibrosis and replacement of the media by an eosinophilic, PAS positive, Congo Red negative, granular substance. Electron microscopy showed swollen myocytes surrounded by collagen, elastin and a compact electron-dense material. Immunofluorescence using antibodies against IgA, IgG, IgM, C1q and C3 stained the abnormal media weakly. In the cortex, there were diffuse senile plaques and neurofibrillary tangles. Immunohistochemistry demonstrated beta/A4 positive material in cortical senile plaques but not in arterial walls. Adventitial macrophages were, however, immunoreactive for gamma-trace. Systemic arterioles were normal. The vascular changes and leukoencephalopathy are comparable to those described in 'Cerebral Autosomal Dominant Arteriopathy with Subcortical Infarcts and Leukoencephalopathy' (CADASIL). Similar vascular changes were also observed in nonfamilial cases. An association with Alzheimer changes in the cortex has not been described previously. The relationship between both diseases and the role of each in the causation of the dementia is unclear.

Blood-brain glucose transfer in the mouse

The intracarotid injection method has been utilized to examine blood-brain barrier (BBB) glucose transport in normal mice, and after a 2-day fast. In anesthetized mice, cerebral blood flow (CBF) rates were reduced from 0.86 ml.min-1 x gm-1 in control to 0.80 ml.min-1 x gm-1 in fasted animals (p > 0.05). Brain Uptake Indices were significantly (p < 0.05) higher in fasted (plasma glucose = 4.7 mM) than control (plasma glucose = 6.5 mM) mice, while plasma glucose was significantly lower. The maximal velocity (Vmax) for glucose transport was 1562 +/- 303 nmoles.min-1 x g-1, and the half-saturation constant (Km =) 6.67 +/- 1.46 mM in normally fed mice. In fasted mice the Vmax was 2053 +/- 393 nmoles.min-1 x g-1 (p > 0.05), and the half-saturation constant (Km =) 7.40 +/- 1.60 mM (not significant, P > 0.05). A rabbit polyclonal antiserum to a synthetic peptide encoding the 13 C-terminal amino acids of the human erythrocyte glucose transporter (GLUT-1) immunocytochemically confirmed that the mouse brain capillary endothelial glucose transporter is a GLUT-1 transporter, and immunoreactivity was similar in brain endothelia from fed and fasted animals. In conclusion, after a 2-day fast in the mouse, we saw significant reductions in forebrain weight (7%), and plasma glucose levels (27%). Increased brain glucose extraction (25%, p < 0.05), and a 22% increase in the unsaturated permeability-surface area product (p < 0.05) was also observed.

Ubiquitin in cerebral amyloid angiopathy

Immunohistological findings in cerebral blood vessels of 4 cases with cerebral amyloid angiopathy (CAA) were compared with those of 4 Alzheimer's (AD) cases. A panel of antibodies against 2 neurofilament subunits (BF10 and RT97), a microtubule-associated protein (TAU) and ubiquitin were used. CAA cases showed a strong immunoreactivity for ubiquitin in blood vessel wall. Senile plaques (SPs) in CAA cases showed strong ubiquitin positivity but the central amyloid core was negative. AD brains showed immunoreactivity with all antibodies in SPs and neurofibrillary tangles (NFTs); blood vessels were consistently negative for ubiquitin. Control brains showed few SPs and NFTs; these were positive for ubiquitin, but blood vessels were negative. These results indicate that vascular amyloid deposition in CAA and AD may have different pathophysiological mechanisms.

Alzheimer's disease or plaque disease? Two cases at the frontier of a definition

Atypical dementias confront the adequacy of current diagnostic concepts. The two patients with atypical dementia syndromes described here shared common postmortem features of numerous neocortical neuritic (senile) plaques and microvascular amyloid, sparing of hippocampus and substantia nigra, and the virtual absence of neurofibrillary tangles. Microscopically, the two differed only by the presence of a few subcortical Lewy bodies in case 1. These similar morphologic features were associated with dramatically different clinical presentations. In the first patient, visual hallucinations, Capgras' syndrome, cognitive slowing, myoclonus, parkinsonism, and primitive reflexes evolved over 3 years. Memory and language were relatively spared. In the second, dysphagia, nonfluent aphasia, hypophonia, motor perseveration, and a severe disorder of attention developed during this 18-month illness. At autopsy, an unrecognized colon malignancy was found. Despite high neuritic plaque counts in cortex, neither the clinical nor the pathologic criteria for Alzheimer's disease adequately describe either case. The cases will be examined first as clinical, then as neuropathologic, entities. From this approach, we conclude that a specific clinical dementia syndrome may be expressed by several neuropathologic "diseases" and that a variety of clinical syndromes may represent a single neuropathologic diagnosis. This strategy identifies a conceptual dichotomy between Alzheimer's syndrome and postmortem Alzheimer's disease. Meticulous clinical and neuropathologic observation is essential in advancing an understanding of the relationship between the two.

Morphological substrates of infantile spasms: studies based on surgically resected cerebral tissue

Extensive surgical resections of neocortical cerebral tissue (including hemispherectomies) from 13 infants and children with infantile spasms showed that 12 of 13 specimens contained either malformative and dysplastic lesions of the cortex and white matter (sometimes with associated hamartomatous proliferation of globular cells), or destructive lesions possibly acquired as a result of anoxic-ischemic injury, or a combination of the two. In brain tissue from 4 patients, coarse neuronal cytoplasmic fibrils resembling neurofibrillary tangles were seen in areas of dysplastic brain on silver-stained (Bielschowsky technique) sections. Immunohistochemical (immunoperoxidase) study of cortical lesions containing globular cells employing primary antibodies to glial fibrillary acidic protein and synaptophysin as markers of astrocytic and neuronal differentiation, respectively, revealed that many cells showed astrocytic and/or neuronal features, suggesting the local proliferation of primitive or multipotential neuroectodermal cells as one substrate for this seizure disorder. Morphological abnormalities of a severe degree and wide extent in the resected tissue (e.g., in one patient with hemimegalencephaly) often showed features to suggest that they may represent variants of tuberous sclerosis. These most likely result from abnormal movement and/or local proliferation of neuroectodermal precursors that have migrated from the germinal matrix to the cortical mantle. Cellular, molecular and neurophysiological study of these abnormalities is likely to yield information about basic molecular mechanisms of brain malformation and injury important in the pathogenesis of infantile spasms and other forms of focal or generalized epilepsy.

Cerebral amyloid angiopathy and granulomatous angiitis: immunohistochemical study using antibodies to the Alzheimer A4 peptide

Neuropathologic study of an 82-year-old male who died from massive cerebral hemorrhage showed extensive amyloid angiopathy, with morphologic and immunohistochemical characteristics similar to those observed in Alzheimer's disease, associated with granulomatous angiitis, including the presence of numerous giant cells. Some of the giant cells contained, in their cytoplasm, congophilic material immunoreactive for the Alzheimer A4 peptide, supporting the hypothesis that the granulomatous angiitis may, in part, represent a foreign body reaction to A4 amyloid deposition.

Antibodies raised against different portions of A4 protein identify a subset of plaques in Down's syndrome

Antisera were raised to peptides corresponding to residues 1-10 and 12-28 of the published sequence of A4 protein, a 42/43 amino acid long peptide isolated from the brains of patients with Down's syndrome and Alzheimer's disease. Immunohistochemical studies performed on sections of temporal lobe from 12 cases of Down's syndrome showed that the number of senile plaques in the molecular layer of the dentate gyrus which were identified by antibody to A4(1-10) was only 23% (range 11-53%) of that recognised by antibody to A4(12-28). This observation has important consequences for both the diagnosis and the pathogenesis of Down's syndrome and Alzheimer's disease.

Immunohistochemical study of cerebral amyloid angiopathy. III. Widespread Alzheimer A4 peptide in cerebral microvessel walls colocalizes with gamma trace in patients with leukoencephalopathy

Brain tissue from 11 patients with cerebral amyloid angiopathy, changes of Alzheimer's disease, and variable degrees of subcortical leukoencephalopathy was examined by immunohistochemical methods, using primary antibodies to peptide segments representing portions of the Alzheimer A4 (beta-) peptide or gamma-trace peptide (seen most commonly in Icelandic patients with cerebral hemorrhage (hereditary cerebral hemorrhage with amyloidosis [HCHWA-I]). Variable A4 immunostaining was seen within cortical (and rarely white matter) parenchyma in the form of senile plaques (with or without central cores), and within capillary and arteriolar walls. Within individual patients, A4 deposits were often primarily parenchymal or vascular, and when they were vascular they tended to be more prominent in arteriolar than in capillary wall segments. Perivascular A4 deposits were often detected around strongly immunoreactive microvessels. Gamma-trace immunoreactivity was noted in many A4-positive microvessel walls, but staining was always less intense than with the anti-A4 antibody. We conclude that patients with severe cerebral amyloid angiopathy may show wide variation in the severity and topography of A4 deposits within brain parenchyma. A4 may colocalize with gamma-trace peptide, suggesting that A4 and gamma-trace forms of cerebral amyloid angiopathy may not be as biochemically distinctive as has been suggested. Other proteases or protease inhibitors may contribute to the pathogenesis of cerebral amyloid angiopathy or cerebral amyloid angiopathy-related stroke syndromes.

Stroke related to cerebral amyloid angiopathy: the significance of systemic vascular disease

A retrospective postmortem analysis of 25 cases of cerebral amyloid angiopathy (CAA) in the setting of Alzheimer's disease or senile dementia of the Alzheimer type (AD/SDAT) is reported. Seven patients experienced clinically significant cerebral infarcts or hemorrhages or both. There was no statistically significant difference in the incidence of infarcts or hemorrhages in hypertensive and nonhypertensive patients. Hypertension does not appear to be an additional risk factor in the causation of cerebral infarct or hemorrhage associated with CAA in the setting of AD/SDAT. Just over half of patients with CAA and significant ischemic and/or hemorrhagic brain lesions showed atherosclerosis of the circle of Willis, sometimes in the context of severe disseminated atheromatous disease.