Brain parenchymal and microvascular amyloid in Alzheimer's disease

Permeability of proteins at the blood-brain barrier in the normal adult mouse and double transgenic mouse model of Alzheimer's disease

The permeability of albumin, insulin, and human A beta 1--40 at the blood-brain barrier (BBB) was determined in the normal adult mouse (B6/SJL) and in the double transgenic Alzheimer mouse (APP, PS1) by using an I.V. bolus injection technique to quantify the permeability coefficient-surface area (PS) product for each protein after correction for the residual plasma volume (V(p)) occupied by the protein in the blood vessels of different brain regions using a second aliquot of the same protein radiolabeled with a different isotope of iodine ((125)I vs (131)I) as a vascular space marker. This technology for quantifying BBB permeability of proteins was adapted from the rat to the mouse and involved catheterizing the femoral artery and vein of the mouse instead of the brachial artery and vein as for the rat. Because of the smaller blood volume in the mouse, serial sampling (20 microl) of blood from the femoral artery of the mouse was performed and directly TCA precipitated to generate a whole blood washout curve for the intact protein. When similar blood sampling techniques were used in the rat, the PS values for albumin and insulin at the BBB were similar in these two species. In the double transgenic mouse, the V(p) values for albumin were significantly increased 1.4- to 1.6-fold in five of six brain regions compared to the normal adult mouse, which indicated increased adherence of albumin to vessel walls. As a result, the PS values were significantly decreased, from 1.4- to 3.2-fold, which likely reflected decreased transport of albumin by passive diffusion. In contrast, insulin, which is taken up into the brain by a receptor-mediated transport mechanism at the BBB, showed no significant difference in the V(p) values but a significant increase in the PS values in four of six brain regions. This suggests a compensatory mechanism in the Alzheimer's transgenic brain whereby there is an increased permeability to insulin at the BBB. Surprisingly, there was no significant difference in the V(p) or PS values for human A beta 1--40 at the BBB in the double transgenic Alzheimer mouse at 24, 32, or 52 weeks of age, when there is both significant A beta levels in the plasma and amyloid burden in the brains of these animals. These data suggest that there is not an alteration in permeability to human A beta 1--40 at the BBB with increasing amyloid burden in the double transgenic Alzheimer mouse. Although these observations suggest structural alterations at the BBB, they do not support the concept of extensive BBB damage with substantial increases in BBB permeability in Alzheimer's disease.

Exogenous A beta1-40 reproduces cerebrovascular alterations resulting from amyloid precursor protein overexpression in mice

Transgenic mice overexpressing the amyloid precursor protein (APP) have a profound impairment in endothelium-dependent cerebrovascular responses that is counteracted by the superoxide scavenger superoxide dismutase (SOD). The authors investigated whether the amyloid-beta peptide (A beta) is responsible for the cerebrovascular effects of APP overexpression. Cerebral blood flow (CBF) was monitored by a laser-Doppler flowmeter in anesthetized-ventilated mice equipped with a cranial window. Superfusion of A beta1-40 on the neocortex reduced resting CBF in a dose-dependent fashion (-29% +/- 7% at 5 micromol/L) and attenuated the increase in CBF produced by the endothelium-dependent vasodilators acetylcholine (-41% +/- 8%), bradykinin (-39% +/- 9%), and the calcium ionophore A23187 (-37% +/- 5%). A beta1-40 did not influence the CBF increases produced by the endothelium-independent vasodilators S-nitroso-N-acetylpenicillamine and hypercapnia. In contrast, A beta1-42 did not attenuate resting CBF or the CBF increases produced by endothelium-dependent vasodilators. Cerebrovascular effects of A beta1-40 were reversed by the superoxide scavengers SOD or MnTBAP. Furthermore, substitution of methionine 35 with norleucine, a mutation that blocks the ability of A beta to generate reactive oxygen species, abolished A beta1-40 vasoactivity. The authors conclude that A beta1-40, but not A beta1-42, reproduces the cerebrovascular alterations observed in APP transgenics. Thus, A beta1-40 could play a role in the cerebrovascular alterations observed in Alzheimer's dementia.

Neuropathologic substrates of ischemic vascular dementia

Ischemic vascular dementia (IVD) is a relatively uncommon entity, in the course of which multiple ischemic brain lesions result in progressive cognitive and memory impairment. Ischemic brain lesions may also aggravate the neuropsychologic deficit of Alzheimer disease (AD). In this review we summarize our experience based upon autopsy examination of the central nervous system in 20 patients (age range 68-92 years) enrolled in a longitudinal investigation of structural, neurochemical, functional neuroimaging, and neuropsychologic components of IVD, especially dementia associated with cerebral microvascular disease. While cystic infarcts were present in the CNS of 5 patients, the most commonly observed neuropathologic abnormalities were lacunar infarcts and microinfarcts--both types of lesion were encountered in over half of patients' brains. Evidence of (remote) hippocampal injury was found in 11/20 patients. Severe atherosclerosis and arterio/ arteriolosclerosis were both associated with the occurrence of multiple lacunar infarcts. Pronounced cerebral amyloid angiopathy (CAA) was noted in a single patient, who also showed other microscopic changes of severe AD. While fairly unusual as a nosologic entity, IVD appears to correlate with widespread small ischemic lesions distributed throughout the CNS. We furthermore propose an approach to quantifying the burden of ischemic vascular and parenchymal disease that may be associated with a dementia syndrome. A brief review of neuropathologic features of vascular dementia (both familial and sporadic) is presented.

Cerebral beta amyloid angiopathy is a risk factor for cerebral ischemic infarction. A case control study in human brain biopsies

Cerebral amyloid angiopathy (CAA) is conspicuous for its association with Alzheimer disease (AD) and as a cause of lobar hemorrhages in the elderly, but its role in cerebral infarction is less clear. There is evidence that CAA may also be a risk factor for ischemic infarction in AD. To further investigate CAA as a risk factor for infarction, we studied 108 cases of recent cerebral or cerebellar infarction diagnosed in tissue samples obtained from surgical material. There were 69 males and 39 females with a mean age of 52 yr (range 1-86). The majority of biopsies were obtained from the frontal and parietal lobes. Radiological studies demonstrated a lesion confined to a vascular distribution in 12 of the 17 (71%) cases examined. Microscopic sections stained with hematoxylin and eosin revealed complete, organizing infarction in 107 cases with areas of coagulative necrosis, anoxic-ischemic neuronal injury, inflammation, macrophages, vascular proliferation, gliosis, and swollen axons. One case showed an incomplete infarct. Most cases also exhibited a minor hemorrhagic component with hemosiderin and hematoidin pigments. CAA, defined as amyloid deposition in the walls of leptomeningeal and parenchymal arteries, was found by immunohistochemical stains for beta amyloid in 14 (13%) cases of complete cerebral infarct. Cortical beta amyloid plaques were found by immunohistochemistry in 19 (17%) cases. Cerebral or cerebellar tissues containing cortex and leptomeninges obtained from 136 patients with a mean age of 52 yr (range 1-85) during surgical procedures for diagnosis of primary or metastatic neoplasms and demyelinating lesions were used as age-matched controls. In this control group, CAA was found in 5 (3.7%) and beta amyloid plaques in 19 (14%). The results indicate that CAA, but not beta amyloid plaque formation, is significantly more common in patients with ischemic cerebral infarction than in age-matched controls with nonvascular lesions (odds ratio 3.8; 95% confidence interval 1.3-10.9; p < 0.01). Our results indicate that CAA is a risk factor for ischemic cerebral infarction in the population studied.

Abeta 1-40-related reduction in functional hyperemia in mouse neocortex during somatosensory activation

Peptides derived from proteolytic processing of the beta-amyloid precursor protein (APP), including the amyloid-beta peptide (Abeta), play a critical role in the pathogenesis of Alzheimer's dementia. We report that transgenic mice overexpressing APP and Abeta have a profound attenuation in the increase in neocortical blood flow elicited by somatosensory activation. The impairment is highly correlated with brain Abeta concentration and is reproduced in normal mice by topical neocortical application of exogenous Abeta1-40 but not Abeta1-42. Overexpression of M146L mutant presenilin-1 in APP mice enhances the production of Abeta1-42 severalfold, but it does not produce a commensurate attenuation of the hyperemic response. APP and Abeta overexpression do not diminish the intensity of neural activation, as reflected by the increase in somatosensory cortex glucose usage. Thus, Abeta-induced alterations in functional hyperemia produce a potentially deleterious mismatch between substrate delivery and energy demands imposed by neural activity.

Cerebral amyloid angiopathy: accumulation of A beta in interstitial fluid drainage pathways in Alzheimer's disease

Cerebral amyloid angiopathy (CAA) is characterized by the accumulation of beta-amyloid (A beta) peptides in the walls of arteries both in the cortex and meninges. Here, we test the hypothesis that CAA results from the progressive accumulation of A beta in the perivascular interstitial fluid drainage pathways of the brain. Experimental studies have shown that interstitial fluid (ISF) from the rat brain flows along periarterial spaces to join the cerebrospinal fluid (CSF) to drain to cervical lymph nodes. Such lymphatic drainage plays a key role in B-cell and T-cell mediated immunity of the brain. Anatomical studies have defined periarterial ISF drainage pathways in the human brain that are homologous with the lymphatic pathways in the rat brain but are largely separate from the CSF. Periarterial channels in the brain in man are in continuity with those of leptomeningeal arteries and can be traced from the brain to the extracranial portions of the internal carotid arteries related to deep cervical lymph nodes. The pattern of deposition of A beta in senile plaques and in CAA suggests that A beta accumulates in pericapillary and periarterial ISF drainage pathways. A beta could accumulate in CAA due to either (i) increased production of A beta, (ii) reduced solubility of A beta peptides, or (iii) impedance of drainage of A beta along periarterial ISF drainage pathways within the brain and leptomeninges due to aging factors in cerebral arteries. Elucidation of factors that reduce elimination of A beta via perivascular drainage pathways may lead to their rectification and to new strategies for treatment of Alzheimer's disease.

Toxicity of Dutch (E22Q) and Flemish (A21G) mutant amyloid beta proteins to human cerebral microvessel and aortic smooth muscle cells

BACKGROUND AND PURPOSE

Cerebral amyloid angiopathy (CAA) is characterized by the deposition of amyloid beta protein (Abeta) in cortical and leptomeningeal vessels of patients with Alzheimer's disease and hereditary cerebral hemorrhage with amyloidosis, Dutch type. Smooth muscle cells (SMC) from cerebral microvessels (MV) are of particular interest as a site of Abeta-related injury because CAA is much more pronounced in the tunica media of cortical arterioles than meningeal arteries. Patients carrying point mutations at residues 22 (E22Q) and 21 (A21G) of Abeta show severe CAA with various degrees of brain parenchymal Abeta deposition. The purpose of this study was to investigate the effects of 2 mutant E22Q- and A21G-Abeta peptides on MV and aortic SMC. MERHODS: SMC were isolated from human cerebral MV and aorta. Cell morphology, viability, and proliferation as parameters of Abeta toxicity were investigated after 3 days of peptide treatment by trypan blue exclusion and [(3)H]thymidine incorporation.

RESULTS

E22Q-Abeta induced significant decreased cellular proliferation and viability, as well as obvious degeneration of both MV and aortic SMC. A21G-Abeta and wild-type Abeta did not cause significant toxicity, as judged by cell morphology, viability, or cell proliferation, on either type of SMC.

CONCLUSIONS

E22Q-Abeta induced greater toxicity in all parameters than A21G-Abeta and wild-type Abeta with respect to both MV and aortic SMC. A21G-Abeta did not show a significant toxic effect on MV and aortic SMC. This differential effect may be linked to cell type-specific processing and metabolism of mutant forms of Abeta. Mutations in amyloid precursor protein may lead to CAA by different pathogenetic mechanisms or share an unknown property that distinguishes them from wild-type Abeta.

Chronic overproduction of transforming growth factor-beta1 by astrocytes promotes Alzheimer's disease-like microvascular degeneration in transgenic mice

Cerebrovascular amyloid deposition and microvascular degeneration are frequently associated with Alzheimer's disease (AD), but the etiology and pathogenetic role of these abnormalities are unknown. Recently, transforming growth factor-beta1 (TGF-beta1) was implicated in cerebrovascular amyloid formation in transgenic mice with astroglial overproduction of TGF-beta1 and in AD. We tested whether TGF-beta1 overproduction induces AD-like cerebrovascular degeneration and analyzed how cerebrovascular abnormalities develop over time in TGF-beta1-transgenic mice. In cerebral microvessels from 3- to 4-month-old TGF-beta1-transgenic mice, which display a prominent perivascular astrocytosis, levels of the basement membrane proteins perlecan and fibronectin were severalfold higher than in vessels from nontransgenic mice. Consistent with this increase, cortical capillary basement membranes of TGF-beta1 mice were significantly thickened. These changes preceded amyloid deposition, which began at around 6 months of age. In 9- and 18-month-old TGF-beta1 mice, various degenerative changes in microvascular cells of the brain were observed. Endothelial cells were thinner and displayed abnormal, microvilli-like protrusions as well as occasional condensation of chromatin, and pericytes occupied smaller areas in capillary profiles than in nontransgenic controls. Similar cerebrovascular abnormalities have been reported in AD. We conclude that chronic overproduction of TGF-beta1 triggers an accumulation of basement membrane proteins and results in AD-like cerebrovascular amyloidosis and microvascular degeneration. Closely related processes may induce cerebrovascular pathology in AD.

Amyloid beta precursor protein-mRNA is expressed throughout cerebral vessel walls

To determine the presence and distribution of cerebrovascular Abeta production we investigated amyloid beta precursor protein (AbetaPP)-mRNA expression by RNA in situ hybridization in patients with hereditary cerebral hemorrhage with amyloidosis, Dutch type, Alzheimer disease and controls. In all subjects, AbetaPP-mRNA was expressed in endothelial cells, smooth muscle cells, adventitial cells and brain pericytes and/or perivascular cells. Meningeal cells also expressed AbetaPP-mRNA. AbetaPP was detected in endothelial cells, smooth muscle cells and adventitial cells. The demonstration of AbetaPP-mRNA at all vascular sites where amyloid formation can occur supports an important contribution of locally derived Abeta to cerebrovascular amyloidosis.

Gelsolin-related spinal and cerebral amyloid angiopathy

Gelsolin-related amyloidosis (familial amyloidosis, Finnish type) is a rare disorder, reported worldwide in kindreds carrying a G654A or G654T gelsolin gene mutation. Facial palsy, mild peripheral neuropathy, and corneal lattice dystrophy are characteristic, but atrophic bulbar palsy, ataxia of gait, and minor cognitive impairment may occur. In histological and immunohistochemical studies of the central nervous system in 4 patients with a G654A gelsolin mutation, we found widespread spinal, cerebral, and meningeal amyloid angiopathy, with deposition of gelsolin-related amyloid (AGel). Marked extravascular deposits occurred in the dura, spinal nerve roots, and sensory ganglia. The amyloid deposits were also variably immunoreactive for apolipoprotein E (ApoE), alpha1-antichymotrypsin (alpha1-ACT), and cystatin C (Cys C). Cerebral perivascular fibrinogen immunoreactivity was occasionally noted. The patients showed posterior column degeneration and diffuse loss of myelin in the centrum semiovale with perivascular accentuation. Postmortem magnetic resonance imaging, performed on 1 patient, showed white matter lesions, colocalizing with the histological abnormalities. Our study shows that deposition of AGel in the spinal and cerebral blood vessel walls, meninges, as well as spinal nerve roots and sensory ganglia is an essential feature of this form of systemic amyloidosis and may contribute to the central nervous system symptoms.

Cerebral amyloid angiopathy: amyloid beta accumulates in putative interstitial fluid drainage pathways in Alzheimer's disease

Cerebral amyloid angiopathy in Alzheimer's disease is characterized by deposition of amyloid beta (Abeta) in cortical and leptomeningeal vessel walls. Although it has been suggested that Abeta is derived from vascular smooth muscle, deposition of Abeta is not seen in larger cerebral vessel walls nor in extracranial vessels. In the present study, we examine evidence for the hypothesis that Abeta is deposited in periarterial interstitial fluid drainage pathways of the brain in Alzheimer's disease and that this contributes significantly to cerebral amyloid angiopathy. There is firm evidence in animals for drainage of interstitial fluid from the brain to cervical lymph nodes along periarterial spaces; similar periarterial channels exist in humans. Biochemical study of 6 brains without Alzheimer's disease revealed a pool of soluble Abeta in the cortex. Histology and immunocytochemistry of 17 brains with Alzheimer's disease showed that Abeta accumulates five times more frequently around arteries than around veins, with selective involvement of smaller arteries. Initial deposits of Abeta occur at the periphery of arteries at the site of the putative interstitial fluid drainage pathways. These observations support the hypothesis that Abeta is deposited in periarterial interstitial fluid drainage pathways of the brain and contributes significantly to cerebral amyloid angiopathy in Alzheimer's disease.

Neuropathology of aging

The brain undergoes many gross and histopathologic changes with advancing age. Some of the changes seen with aging are also found in demented individuals, especially patients with Alzheimer's disease. The extent to which Alzheimer's disease and aging are truly different processes remains to be determined. The morphologic features that seem most clearly to distinguish between aging and Alzheimer's disease are the neurofibrillary tangles and senile plaques. The distinction can be further refined by determining the immunocytochemical and ultrastructural composition of the degenerating nerve processes in the neuritic plaques.

Molecular pathogenesis of sporadic and familial forms of Alzheimer's disease

Our understanding of the pathogenesis of Alzheimer's disease (AD) comes primarily from the study of rare inherited forms of the disease. Mutations that cause familial AD appear to act by a common mechanism: that of increasing production of A beta 42/43, one of the family of A beta peptides deposited in senile plaques. However, increased A beta 42/43 production has not been demonstrated to occur in most cases of sporadic AD, suggesting that genetic and environmental factors acting at other stages of the disease process can modify the risk for disease. Such factors most likely include those affecting A beta aggregation or clearance, the inflammatory response, cerebrovascular disease, or susceptibility of neurons to injury. Identifying these factors will lead to a better understanding of the etiology of the disease and provide additional targets for therapeutic intervention.

Amyloidomas of the nervous system: a monoclonal B-cell disorder with monotypic amyloid light chain lambda amyloid production

BACKGROUND

Amyloidomas or localized tumor-like amyloid deposits rarely affect the nervous system. To the authors' knowledge, no comprehensive studies on central and peripheral nervous system amyloidomas have been published. The amyloid subtype of amyloidomas of the nervous system only recently was characterized and almost invariably was found to be of amyloid light chain (AL) lambda type. The nature of the plasma cell population responsible for AL amyloid production has not been investigated further.

METHODS

The current analysis included the clinical findings, neuroimaging characteristics, and pathology of seven amyloidomas (four cerebral and three involving peripheral nerves). All were subjected to histochemical staining (Congo red, thioflavine S) and to immunohistochemical study using primary antibodies detecting serum amyloid component P, serum amyloid protein A (SAA), transthyretin, beta2 microglobulin (beta2m), and free immunoglobulin (Ig) light chain. For the detection of mRNA of light chain Ig, fluorescein-conjugated kappa and lambda mRNA oligonucleotide probes were used. For the assessment of B-cell clonality, polymerase chain reaction (PCR) was applied on extracted DNA from two cases using VH FRIII and JH primers. Two cases were assessed ultrastructurally.

RESULTS

All amyloidomas were organ restricted and unrelated to systemic amyloidosis. The clinical symptoms of the cerebral lesions were nonspecific, whereas neurologic deficits were noted in the distribution of the involved peripheral nerves. Cerebral deposits, either solitary or multiple, were associated spatially with the choroid plexus and secondarily extended into white matter. All peripheral nerve amyloidomas involved the gasserian ganglion of the trigeminal nerve. Imaging by computed tomography and magnetic resonance imaging scans revealed hyperdense and contrast-enhancing mass lesions unassociated with significant edema. Immunohistochemically, the amyloid was present in the interstitium and within the walls of the intralesional vessels, was invariably of AL lambda subtype, and was negative for free Ig kappa light chains, SAA, transthyretin, and beta2m. Plasma cells along the perivascular sheaths and occasionally squeezed between amyloid masses showed no cytologic atypia. In situ hybridization for Ig light chain mRNA reflected a massive preponderance of lambda-producing cells. PCR revealed monoclonal rearrangement of the heavy chain Ig gene.

CONCLUSIONS

The results of the current study provide strong support for the concept that amyloidomas of the nervous system are neoplasms of an AL lambda-producing B-cell clone capable of terminal differentiation. Nevertheless, all seven patients lacked clinical evidence of an aggressive or systemic lymphoplasmacytic neoplasm. Unlike plasmacytomas, the relatively indolent course of most nervous system amyloidomas is reminiscent of the similarly indolent biologic behavior of extranodal, low grade B-cell lymphoma of mucosa-associated lymphoid tissue (MALT) type.

Giant cell arteritis in association with cerebral amyloid angiopathy: immunohistochemical and molecular studies

Giant cell arteritis (GCA) usually manifests as a transmural vascular infiltrate of mononuclear and multinucleated giant cells (MNGC). We describe six patients with GCA associated with severe cerebral amyloid angiopathy (CAA), all with cerebral hemorrhage or varying degrees of cerebral infarct, and histological evidence of Alzheimer's disease (cortical CAA often predominating over senile plaques and neurofibrillary tangles). One case showed mostly cortical involvement (with old microhemorrhages), and the others were primarily leptomeningeal (with involvement of the underlying cortex and extensive encephalomalacia of adjacent brain). Many vessels with CAA exhibited a pronounced adventitial and perivascular infiltrate of lymphocytes, histiocytes, and MNGC. Immunohistochemical staining showed deposition of beta/A4 peptide primarily in the thickened media of CAA vessels, and within the cytoplasm of MNGC--suggesting phagocytosis of insoluble peptide. Cystatin C antibody stained vascular amyloid and diffusely highlighted astrocytic and MNGC cytoplasm. HAM56-positive macrophages were frequently seen around amyloid-laden vessels. Anti-smooth muscle actin immunohistochemistry suggests the occurrence of medial destruction by amyloid, with relative preservation of intimal cells. Ultrastructural studies performed in one case confirmed the presence of intracytoplasmic amyloid in MNGC. The GCA seen in these cases of CAA most likely represents a foreign body response to amyloid proteins, causing secondary destruction of the vessel wall. DNA from brain tissues of five affected patients was examined to assess whether mutations were present in exon 17 of the APP gene or exon 2 of the cystatin C gene, a finding that might explain the foreign body giant cell response to amyloid proteins in these cases. However, restriction fragment mapping of amplified gene segments showed that previously described mutations were not present in these cases.

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.

Amyloid-beta protein angiopathies masquerading as Alzheimer's disease?

Current evidence from genetic and epidemiological studies supports the view that Alzheimer's disease (AD) is a heterogeneous disorder. While the disease is pathologically defined by the presence of specified lesions in form of amyloid plaques and neurofibrillary tangles within the parenchyma, other features of pathology are often either neglected or considered coincidental. Our studies suggest that cerebrovascular pathology is inherently part of the disorder, which could be an important factor in a cause or effect manner. We have recently identified subjects having died with severe amyloid beta (A beta) protein cerebral amyloid angiopathy (CAA) in the absence of a profound Alzheimer pathology. These subjects, diagnosed with dementia had a late onset disease and were found at autopsy to exhibit severe CAA but paucity of typical AD changes. Immunocytochemical studies showed numerous microvascular abnormalities as well as characteristic degeneration of the vascular smooth muscle in both surface and intracortical vessels. The pathology was also characterized by occasional intracerebral hemorrhages and multiple infarcts. Further assessment of the abnormalities and amyloid infiltrated cerebral vessels with antibodies to the carboxyl terminus of A beta indicated that the longer, more pathogenic form of A beta(1-42) was found to be highly associated with intracerebral hemorrhages. Our observations suggest that these mild AD cases with a predominantly vascular pathology are variants of AD and bear resemblance to the familial Dutch and Flemish versions of cerebral amyloidosis. We propose that AD is a group of diseases with a variable pathology analogous to the prion diseases, in which a vascular variant also exists.

High frequency of apolipoprotein E epsilon 2 allele in hemorrhage due to cerebral amyloid angiopathy

From the somewhat conflicting published data on apolipoprotein E (apoE) genotype in hemorrhage due to cerebral amyloid angiopathy (CAA), it is unclear whether apoE genotype influences the risk of CAA-related hemorrhage independently of its association with concomitant Alzheimer's disease (AD). We determined the apoE genotypes of 36 patients presenting with cerebral hemorrhage associated with histologically confirmed CAA. The frequency of apoE epsilon 2 was 0.25 and the frequency of apoE epsilon 4 was 0.18. Patients with CAA-related hemorrhage and concomitant AD pathology (CERAD criteria, n = 17) had a high apoE epsilon 4 frequency, close to that in AD cases without hemorrhage. Patients in whom CAA-related hemorrhage occurred in the absence of significant AD pathology (n = 13) had an apoE epsilon 4 frequency somewhat lower than non-AD controls without hemorrhage. However, in CAA-related hemorrhage, the apoE epsilon 2 frequency was high regardless of whether significant AD pathology was present. We conclude that whereas possession of apoE epsilon 2 may be a risk factor for cerebral hemorrhage due to CAA, apoE epsilon 4 is a risk factor for concomitant AD but not an independent risk factor for CAA-related hemorrhage.

A beta deposition inhibitor screen using synthetic amyloid

The formation, growth, and maturation of brain amyloid "senile" plaques are essential pathological processes in Alzheimer's disease (AD) and key targets for therapeutic intervention. The process of in vitro deposition of A beta at physiological concentrations onto plaques in AD brain preparations has been well characterized, but is cumbersome for drug discovery. We describe here a high-through put screen for inhibitors of A beta deposition onto a synthetic template (synthaloid) of fibrillar A beta immobilized in a polymer matrix. Synthaloid is indistinguishable from plaques in AD brain (the natural template) in deposition kinetics, pH profile, and structure-activity relationships for both A beta analogs and inhibitors. Synthaloid, in contrast to current A beta aggregation screens, accurately predicted inhibitor potency for A beta deposition onto AD cortex preparations, validating its use in searching for agents that can slow the progression of AD and exposing a previously inaccessible target for drug discovery.

Microvascular degeneration in hereditary cystatin C amyloid angiopathy of the brain

Hereditary cystatin C amyloid angiopathy (HCCAA), an autosomal dominant form of cerebral amyloid angiopathy (CAA) occurring primarily in Iceland, is characterized by a variant cystatin C amyloid deposition in the walls of cerebral parenchymal and leptomeningeal vessels. Cystatin C is also found to colocalize with amyloid beta/A4 protein in cerebral vessel walls of patients with Alzheimer's disease (AD), sporadic CAA, and hereditary cerebral hemorrhage with amyloidosis, Dutch type (HCHWA-D). The abundance of cystatin C deposition in cerebral blood vessel walls suggests that cellular elements of the vessel wall itself may play a role in its deposition. Microvascular changes in the brains of HCCAA patients were investigated by single- and double-label immunohistochemistry. We found that cystatin C amyloid immunoreactivity was present not only in cerebral cortical and leptomeningeal vessels, but also in white matter parenchymal vessels. Cystatin C deposition was more prominent in the media of parenchymal vessels and in the adventitia of leptomeningeal vessels. Smooth muscle (sm) cells were few or could not be identified within vessel walls showing extensive cystatin C deposition, suggesting progressive loss of these cells as cystatin C accumulates. However, in less severely affected vessels, cystatin C was present in cells that also had the phenotype of sm, suggesting that sm cells synthesize or process cystatin C. Cystatin C immunoreactivity was in addition, detected in some neuronal cell bodies throughout the cortex in patients with HCCAA and AD-related CAA. Our results indicate that cellular components of the vessel walls may play an important role in cystatin C deposition, as they do in beta/A4 deposition in AD-related CAA. Cystatin C deposition within the vascular media and adventitia, with associated vessel wall injury as manifested by sm cell loss, represents microvascular degeneration that leads to cerebral hemorrhage.

Cystatin C. Icelandic-like mutation in an animal model of cerebrovascular beta-amyloidosis

BACKGROUND AND PURPOSE

Cerebral amyloid angiopathy (CAA) occurs as a sporadic disorder in aged humans, as a frequent component of Alzheimer's disease, or in hereditary cerebral hemorrhage with amyloidosis (HCHWA). The primary histological locus of cerebral amyloid deposition varies in aged humans and in different species of nonhuman primates. In aged rhesus monkeys, amyloid deposition occurs most frequently in senile plaques, whereas in aged squirrel monkeys CAA is more common. We hypothesized that the preponderance of CAA in squirrel monkeys is related to a species-specific amino acid change in cystatin C, a cysteine protease inhibitor, similar to the Leu68Gln substitution found in the amyloid protein of Icelandic patients with HCHWA-I, also termed hereditary cystatin C amyloid angiopathy.

METHODS

We performed immunohistochemical analyses of brain sections of aged squirrel and rhesus monkeys with anti-amyloid-beta and anti-cystatin C antibodies and sequenced the cystatin C cDNA of these monkeys.

RESULTS

Cerebral amyloid in aged squirrel and rhesus monkeys, previously shown to be immunoreactive with anti-amyloid-beta anti-bodies, reacts also with antibodies to cystatin C. While the predicted amino acid sequence in rhesus monkeys differs from the human sequence by four residues, that of the squirrel monkeys has seven additional amino acid substitutions, one of which is Leu68Met.

CONCLUSIONS

The presence of a mutation in squirrel monkeys similar to the one found in HCHWA-I suggests that alterations in cystatin C may influence the likelihood that amyloid will be deposited in the walls of cerebral blood vessels. These observations support the utilization of the monkeys as models to study CAA.