Types of cerebrovascular lesions associated with severe cerebral amyloid angiopathy in Alzheimer's disease

Protective effect of scallop-derived plasmalogen against vascular dysfunction, via the pSTAT3/PIM1/NFATc1 axis, in a novel mouse model of Alzheimer's disease with cerebral hypoperfusion

A strong relationship between Alzheimer's disease (AD) and vascular dysfunction has been the focus of increasing attention in aging societies. In the present study, we examined the long-term effect of scallop-derived plasmalogen (sPlas) on vascular remodeling-related proteins in the brain of an AD with cerebral hypoperfusion (HP) mouse model. We demonstrated, for the first time, that cerebral HP activated the axis of the receptor for advanced glycation endproducts (RAGE)/phosphorylated signal transducer and activator of transcription 3 (pSTAT3)/provirus integration site for Moloney murine leukemia virus 1 (PIM1)/nuclear factor of activated T cells 1 (NFATc1), accounting for such cerebral vascular remodeling. Moreover, we also found that cerebral HP accelerated pSTAT3-mediated astrogliosis and activation of the nucleotide-binding domain and leucine-rich repeat protein 3 (NLRP3) inflammasome, probably leading to cognitive decline. On the other hand, sPlas treatment attenuated the activation of the pSTAT3/PIM1/NFATc1 axis independent of RAGE and significantly suppressed NLRP3 inflammasome activation, demonstrating the beneficial effect on AD.

The influence of cerebrovascular disease in dementia with Lewy bodies and Parkinson's disease dementia

INTRODUCTION

Lewy body dementia (LBD), including dementia with Lewy bodies (DLB) and Parkinson's disease dementia (PDD), is a common form of neurodegenerative dementia. The frequency and influence of comorbid cerebrovascular disease is not understood but has potentially important clinical management implications.

METHODS

A systematic literature search was conducted (Medline and Embase) for studies including participants with DLB and/or PDD assessing cerebrovascular lesions (imaging and pathological studies). They included white matter changes, cerebral amyloid angiopathy (CAA), cerebral microbleeds (CMB), macroscopic infarcts, micro-infarcts and intracerebral haemorrhage.

RESULTS

Of 4411 articles, 63 studies were included. Cerebrovascular lesions commonly studied included white matter changes (41 studies) and CMB (18 studies). There was an increased severity of white matter changes on magnetic resonance imaging (visualized as white matter hyperintensities, WMH), but not neuropathology, in LBD compared to PD without dementia and age-matched controls. CMB prevalence in DLB was highly variable but broadly similar to Alzheimer's disease (AD) (0-48%), with a lobar predominance. No relationship was found between large cortical or small subcortical infarcts or intracerebral haemorrhage and presence of LBD.

CONCLUSION

The underlying mechanisms of WMH in LBD require further exploration, as their increased severity in LBD was not supported by neuropathological examination of white matter. CMB in LBD had a similar prevalence as AD. There is a need for larger studies assessing the influence of cerebrovascular lesions on clinical symptoms, disease progression and outcomes.

Frontal white matter lesions in Alzheimer's disease are associated with both small vessel disease and AD-associated cortical pathology

Cerebral white matter lesions (WML) encompass axonal loss and demyelination and are assumed to be associated with small vessel disease (SVD)-related ischaemia. However, our previous study in the parietal lobe white matter revealed that WML in Alzheimer's disease (AD) are linked with degenerative axonal loss secondary to the deposition of cortical AD pathology. Furthermore, neuroimaging data suggest that pathomechanisms for the development of WML differ between anterior and posterior lobes with AD-associated degenerative mechanism driving posterior white matter disruption, and both AD-associated degenerative and vascular mechanisms contributed to anterior matter disruption. In this pilot study, we used human post-mortem brain tissue to investigate the composition and aetiology of frontal WML from AD and non-demented controls to determine if frontal WML are SVD-associated and to reveal any regional differences in the pathogenesis of WML. Frontal WML tissue sections from 40 human post-mortem brains (AD, n = 19; controls, n = 21) were quantitatively assessed for demyelination, axonal loss, cortical hyperphosphorylated tau (HPτ) and amyloid-beta (Aβ) burden, and arteriolosclerosis as a measure of SVD. Biochemical assessment included Wallerian degeneration-associated protease calpain and the myelin-associated glycoprotein to proteolipid protein ratio as a measure of ante-mortem ischaemia. Arteriolosclerosis severity was found to be associated with and a significant predictor of frontal WML severity in both AD and non-demented controls. Interesting, frontal axonal loss was also associated with HPτ and calpain levels were associated with increasing Aβ burden in the AD group, suggestive of an additional degenerative influence. To conclude, this pilot data suggest that frontal WML in AD may result from both increased arteriolosclerosis and AD-associated degenerative changes. These preliminary findings in combination with previously published data tentatively indicate regional differences in the aetiology of WML in AD, which should be considered in the clinical diagnosis of dementia subtypes: posterior WML maybe associated with degenerative mechanisms secondary to AD pathology, while anterior WML could be associated with both SVD-associated and degenerative mechanisms.

Association between cortical microinfarcts and total small vessel disease burden in cerebral amyloid angiopathy on 3-Tesla magnetic resonance imaging

BACKGROUND AND PURPOSE

Cortical microinfarcts (CMIs) are frequently found in the brains of patients with advanced cerebral amyloid angiopathy (CAA) at autopsy. The small vessel disease (SVD) score for CAA (i.e., the CAA-SVD score) has been proposed to evaluate the severity of CAA-associated vasculopathic changes by a combination of magnetic resonance imaging (MRI) markers. The aim of this study was to examine the association between total CAA-SVD score and features of CMIs on in vivo 3-Tesla MRI.

METHODS

Eighty patients with probable CAA were retrospectively analyzed. Lobar cerebral microbleeds, cortical superficial siderosis, enlargement of perivascular space in the centrum semiovale and white matter hyperintensity were collectively assessed, and the total CAA-SVD score was calculated. The presence of CMI was also examined.

RESULTS

Of the 80 patients, 13 (16.25%) had CMIs. CMIs were detected more frequently in the parietal and occipital lobes. A positive correlation was found between total CAA-SVD score and prevalence of CMI (ρ = 0.943; p = 0.005). Total CAA-SVD score was significantly higher in patients with CMIs than in those without (p = 0.009). In a multivariable logistic regression analysis, the presence of CMIs was significantly associated with total CAA-SVD score (odds ratio 2.318 [95% confidence interval 1.228-4.376]; p = 0.01, per each additional point).

CONCLUSIONS

The presence of CMIs with a high CAA-SVD score could be an indicator of more severe amyloid-associated vasculopathic changes in patients with probable CAA.

Cerebral Amyloid Angiopathy: Similarity in African-Americans and Caucasians with Alzheimer's Disease

Cerebral amyloid angiopathy (CAA) of the Aβ type is variably present in the brains of patients with Alzheimer's disease (AD). CAA contributes to cognitive decline and increases the risk of lobar hemorrhage; because both AD-typical dementia and lobar hemorrhage are more common in African-Americans than in Caucasians, we postulated that African-Americans with AD might be particularly susceptible to CAA. To test this hypothesis, we analyzed CAA histopathologically in the large vessels and capillaries of autopsy-derived frontal, temporal, parietal, and occipital cortical samples from African-Americans (n = 18) and Caucasians (n = 19) with end-stage AD. In the combined cohort of 37 subjects, 22% of the subjects had severe CAA in large vessels, and 11% had severe CAA in capillaries. However, the prevalence and histopathologic characteristics of CAA were similar in the African-Americans and Caucasians. This conclusion was substantiated in an independent sample from the National Alzheimer's Coordinating Center database, in which the degree of CAA was comparable in 1,554 Caucasians and 68 African-Americans with end-stage AD. These findings support a growing consensus that the fundamental histopathologic features of AD are largely impartial to the race of the afflicted.

Blood-Brain Barrier Leakage and Microvascular Lesions in Cerebral Amyloid Angiopathy

Background and Purpose- Cerebral amyloid angiopathy (CAA) is a common small vessel disease that independently effects cognition in older individuals. The pathophysiology of CAA and CAA-related bleeding remains poorly understood. In this postmortem study, we explored whether blood-brain barrier leakage is associated with CAA and microvascular lesions. Methods- Eleven CAA cases (median [IQR] age=69 years [65-79 years], 8 males) and 7 cases without neurological disease or brain lesions (median [IQR] age=77 years [68-92 years], 4 males) were analyzed. Cortical sections were sampled from each lobe, and IgG and fibrin extravasation (markers of blood-brain barrier leakage) were assessed with immunohistochemistry. We hypothesized that IgG and fibrin extravasation would be increased in CAA cases compared with controls, that this would be more pronounced in parietooccipital brain regions compared with frontotemporal brain regions in parallel with the posterior predilection of CAA, and would be associated with CAA severity and number of cerebral microbleeds and cerebral microinfarcts counted on ex vivo magnetic resonance imaging of the intact brain hemisphere. Results- Our results demonstrated increased IgG positivity in the frontotemporal ( P=0.044) and parietooccipital ( P=0.001) cortex in CAA cases compared with controls. Within CAA cases, both fibrin and IgG positivity were increased in parietooccipital brain regions compared with frontotemporal brain regions ( P=0.005 and P=0.006, respectively). The percentage of positive vessels for fibrin and IgG was associated with the percentage of amyloid-β-positive vessels (Spearman ρ=0.71, P=0.015 and Spearman ρ=0.73, P=0.011, respectively). Moreover, the percentage of fibrin and IgG-positive vessels, but not amyloid-β-positive vessels, was associated with the number of cerebral microbleeds on magnetic resonance imaging (Spearman ρ=0.77, P=0.005 and Spearman ρ=0.70, P=0.017, respectively). Finally, we observed fibrin deposition in walls of vessels involved in cerebral microbleeds. Conclusions- Our results raise the possibility that blood-brain barrier leakage may be a contributory mechanism for CAA-related brain injury.

Signal Change of Acute Cortical and Juxtacortical Microinfarction on Follow-Up MRI

BACKGROUND AND PURPOSE

Although the clinical importance of cortical microinfarcts has become well-recognized recently, the evolution of cortical microinfarcts on MR imaging is not fully understood. The aim of this study was to examine the temporal changes in acute cortical microinfarcts using susceptibility-weighted imaging and conventional MR imaging.

MATERIALS AND METHODS

Patients with acute infarcts located in the cortical and/or juxtacortical region measuring ≤10 mm in axial diameter based on diffusion-weighted imaging who had a follow-up 3T MR imaging were retrospectively included in the study. All lesions did not show hypointensity on initial T2*WI. For cortical and/or juxtacortical microinfarcts detected on initial DWI, 2 neuroradiologists evaluated the follow-up MR imaging (T2WI, FLAIR, T2*WI, and SWI) and assessed lesion signal intensities and locations (cortical microinfarcts or microinfarcts with juxtacortical white matter involvement).

RESULTS

On initial DWI, 2 radiologists observed 180 cortical and/or juxtacortical microinfarcts in 35 MR imaging examinations in 25 patients; on follow-up, the neuroradiologists identified 29 cortical microinfarcts (16%) on T2WI, 9 (5%) on FLAIR, 4 (2%) on T2*, and 97 (54%) on SWI. All cortical microinfarcts detected with any follow-up MR imaging showed hyperintensity on T2WI/FLAIR and/or hypointensity on T2*WI and SWI.

CONCLUSIONS

SWI revealed conversion (paramagnetic susceptibility changes) of acute cortical microinfarcts, suggesting that a substantial number of cortical microinfarcts may contain hemorrhagic components.

Parietal white matter lesions in Alzheimer's disease are associated with cortical neurodegenerative pathology, but not with small vessel disease

Cerebral white matter lesions (WML) encompass axonal loss and demyelination, and the pathogenesis is assumed to be small vessel disease (SVD)-related ischemia. However, WML may also result from the activation of Wallerian degeneration as a consequence of cortical Alzheimer's disease (AD) pathology, i.e. hyperphosphorylated tau (HPτ) and amyloid-beta (Aβ) deposition. WML seen in AD have a posterior predominance compared to non-demented individuals but it is unclear whether the pathological and molecular signatures of WML differ between these two groups. We investigated differences in the composition and aetiology of parietal WML from AD and non-demented controls. Parietal WML tissue from 55 human post-mortem brains (AD, n = 27; non-demented controls, n = 28) were quantitatively assessed for axonal loss and demyelination, as well as for cortical HPτ and Aβ burden and SVD. Biochemical assessment included Wallerian degeneration protease calpain and the myelin-associated glycoprotein (MAG) to proteolipid protein (PLP) ratio (MAG:PLP) as a measure of hypoperfusion. WML severity was associated with both axonal loss and demyelination in AD, but only with demyelination in controls. Calpain was significantly increased in WML tissue in AD, whereas MAG:PLP was significantly reduced in controls. Calpain levels were associated with increasing amounts of cortical AD-pathology but not SVD. We conclude that parietal WML seen in AD differ in their pathological composition and aetiology compared to WML seen in aged controls: WML seen in AD may be associated with Wallerian degeneration that is triggered by cortical AD-pathology, whereas WML in aged controls are due to ischaemia. Hence, parietal WML as seen on MRI should not invariably be interpreted as a surrogate biomarker for SVD as they may be indicative of cortical AD-pathology, and therefore, AD should also be considered as the main underlying cause for cognitive impairment in cases with parietal WML.

Association of cortical microinfarcts and cerebral small vessel pathology in the ageing brain

AIMS

Cortical microinfarcts (CMI) are frequently observed in the ageing brain independent of cognitive decline, but their aetiology is not fully elucidated. To examine the potential role of different vessel pathologies, including cerebral amyloid angiopathy (CAA), arteriolosclerosis-hyalinosis and thromboembolism in the development of CMI, we examined 80 autopsy cases with more than one CMI on routine neuropathological examination.

METHODS

Pial and intracortical vessels around CMI were assessed for their integrity with haematoxylin-eosin staining and antibodies against amyloid-β protein and fibrinogen using a semiquantitative four-level rating scale (absent to severe) in the hippocampus, and the frontal, temporal and occipital cortex. Four histological categories of changes were defined: CAA, vessel pathology other than CAA, thromboembolism and absence of vessel pathology near CMI.

RESULTS

A differential distribution of microvascular pathology was observed depending on brain regions. In the occipital cortex, CAA was commonly associated with CMI. In contrast, in the hippocampus and the frontal cortex, cases without any vascular pathology in pial and intracortical vessels were significantly more frequent.

CONCLUSIONS

The aetiology of CMI differs depending on brain location. CAA may play a role principally in the occipital cortex. The large number of intact vessels around the CMI (mainly in the frontal cortex and hippocampus) raises the possibility that pathologies other than structural microangiopathy, including hypoperfusion/arterial hypotension or large vessel atherosclerosis, play a role in the development of microvascular lesions. These results are relevant in the context of aetiopathogenesis of vascular changes associated with conditions like vascular dementia.

Update on Vascular Dementia

Vascular dementia (VaD) is a major contributor to the dementia syndrome and is described as having problems with reasoning, planning, judgment, and memory caused by impaired blood flow to the brain and damage to the blood vessels resulting from events such as stroke. There are a variety of etiologies that contribute to the development of vascular cognitive impairment and VaD, and these are often associated with other dementia-related pathologies such as Alzheimer disease. The diagnosis of VaD is difficult due to the number and types of lesions and their locations in the brain. Factors that increase the risk of vascular diseases such as stroke, high blood pressure, high cholesterol, and smoking also raise the risk of VaD. Therefore, controlling these risk factors can help lower the chances of developing VaD. This update describes the subtypes of VaD, with details of their complex presentation, associated pathological lesions, and issues with diagnosis, prevention, and treatment.

Cerebral amyloid angiopathy and its co-occurrence with Alzheimer's disease and other cerebrovascular neuropathologic changes

We examined the relationship between cerebral amyloid angiopathy (CAA), Alzheimer's disease neuropathologic changes, other vascular brain pathologies, and cognition in a large multicenter autopsy sample. Data were obtained from the National Alzheimer's Coordinating Center on autopsied subjects (N = 3976) who died between 2002 and 2012. Descriptive statistics and multivariable regression models estimated the associations between CAA and other pathologies, and between CAA severity and cognitive test scores proximal to death. CAA tended to co-occur with Alzheimer's disease neuropathologic changes but a minority of cases were discrepant. CAA was absent in 22% (n = 520) of subjects with frequent neuritic plaques but present in 20.9% (n = 91) of subjects with no neuritic plaques. In subjects with no/sparse neuritic plaques, nonhemorrhagic brain infarcts were more common in those with CAA pathology than without (p = 0.007). In subjects without the APOE ε4 allele, CAA severity was associated with lower cognition proximal to death, factoring in other pathologies. The presence of CAA in patients without Alzheimer's disease may indicate a distinct cerebrovascular condition.

The overlap between vascular disease and Alzheimer's disease--lessons from pathology

Recent epidemiological and clinico-pathological data indicate considerable overlap between cerebrovascular disease (CVD) and Alzheimer's disease (AD) and suggest additive or synergistic effects of both pathologies on cognitive decline. The most frequent vascular pathologies in the aging brain and in AD are cerebral amyloid angiopathy and small vessel disease. Up to 84% of aged subjects show morphological substrates of CVD in addition to AD pathology. AD brains with minor CVD, similar to pure vascular dementia, show subcortical vascular lesions in about two-thirds, while in mixed type dementia (AD plus vascular dementia), multiple larger infarcts are more frequent. Small infarcts in patients with full-blown AD have no impact on cognitive decline but are overwhelmed by the severity of Alzheimer pathology, while in early stages of AD, cerebrovascular lesions may influence and promote cognitive impairment, lowering the threshold for clinically overt dementia. Further studies are warranted to elucidate the many hitherto unanswered questions regarding the overlap between CVD and AD as well as the impact of both CVD and AD pathologies on the development and progression of dementia.

The relationship between cerebral amyloid angiopathy and cortical microinfarcts in brain ageing and Alzheimer's disease

AIMS

Cerebral amyloid angiopathy (CAA) represents the deposition of amyloid β protein (Aβ) in the meningeal and intracerebral vessels. It is often observed as an accompanying lesion of Alzheimer's disease (AD) or in the brain of elderly individuals even in the absence of dementia. CAA is largely age-dependent. In subjects with severe CAA a higher frequency of vascular lesions has been reported. The goal of our study was to define the frequency and distribution of CAA in a 1-year autopsy population (91 cases) from the Department of Internal Medicine, Rehabilitation, and Geriatrics, Geneva.

MATERIALS AND METHODS

Five brain regions were examined, including the hippocampus, and the inferior temporal, frontal, parietal and occipital cortex, using an antibody against Aβ, and simultaneously assessing the severity of AD-type pathology with Braak stages for neurofibrillary tangles identified with an anti-tau antibody. In parallel, the relationships of CAA with vascular brain lesions were established.

RESULTS

CAA was present in 53.8% of the studied population, even in cases without AD (50.6%). The strongest correlation was seen between CAA and age, followed by the severity of amyloid plaques deposition. Microinfarcts were more frequent in cases with CAA; however, our results did not confirm a correlation between these parameters.

CONCLUSION

The present data show that CAA plays a role in the development of microvascular lesions in the ageing brain, but cannot be considered as the most important factor in this vascular pathology, suggesting that other mechanisms also contribute importantly to the pathogenesis of microvascular changes.

Alzheimer's disease pathology in the neocortex and hippocampus of the western lowland gorilla (Gorilla gorilla gorilla)

The two major histopathologic hallmarks of Alzheimer's disease (AD) are amyloid beta protein (Aβ) plaques and neurofibrillary tangles (NFT). Aβ pathology is a common feature in the aged nonhuman primate brain, whereas NFT are found almost exclusively in humans. Few studies have examined AD-related pathology in great apes, which are the closest phylogenetic relatives of humans. In the present study, we examined Aβ and tau-like lesions in the neocortex and hippocampus of aged male and female western lowland gorillas using immunohistochemistry and histochemistry. Analysis revealed an age-related increase in Aβ-immunoreactive plaques and vasculature in the gorilla brain. Aβ plaques were more abundant in the neocortex and hippocampus of females, whereas Aβ-positive blood vessels were more widespread in male gorillas. Plaques were also Aβ40-, Aβ42-, and Aβ oligomer-immunoreactive, but only weakly thioflavine S- or 6-CN-PiB-positive in both sexes, indicative of the less fibrillar (diffuse) nature of Aβ plaques in gorillas. Although phosphorylated neurofilament immunostaining revealed a few dystrophic neurites and neurons, choline acetyltransferase-immunoreactive fibers were not dystrophic. Neurons stained for the tau marker Alz50 were found in the neocortex and hippocampus of gorillas at all ages. Occasional Alz50-, MC1-, and AT8-immunoreactive astrocyte and oligodendrocyte coiled bodies and neuritic clusters were seen in the neocortex and hippocampus of the oldest gorillas. This study demonstrates the spontaneous presence of both Aβ plaques and tau-like lesions in the neocortex and hippocampus in old male and female western lowland gorillas, placing this species at relevance in the context of AD research.

Cerebral microinfarcts: a systematic review of neuropathological studies

Vascular cognitive impairment is an umbrella term for cognitive dysfunction associated with and presumed to be caused by vascular brain damage. Autopsy studies have identified microinfarcts as an important neuropathological correlate of vascular cognitive impairment that escapes detection by conventional magnetic resonance imaging (MRI). As a frame of reference for future high-resolution MRI studies, we systematically reviewed the literature on neuropathological studies on cerebral microinfarcts in the context of vascular disease, vascular risk factors, cognitive decline and dementia. We identified 32 original patient studies involving 10,515 people. The overall picture is that microinfarcts are common, particularly in patients with vascular dementia (weighted average 62%), Alzheimer's disease (43%), and demented patients with both Alzheimer-type and cerebrovascular pathology (33%) compared with nondemented older individuals (24%). In many patients, multiple microinfarcts were detected. Microinfarcts are described as minute foci with neuronal loss, gliosis, pallor, or more cystic lesions. They are found in all brain regions, possibly more so in the cerebral cortex, particularly in watershed areas. Reported sizes vary from 50 μm to a few mm, which is within the detection limit of current high-resolution MRI. Detection of these lesions in vivo would have a high potential for future pathophysiological studies in vascular cognitive impairment.

Review: sporadic cerebral amyloid angiopathy

Cerebral amyloid angiopathy (CAA) may result from focal to widespread amyloid-β protein (Aβ) deposition within leptomeningeal and intracortical cerebral blood vessels. In addition, pericapillary Aβ refers to Aβ depositions in the glia limitans and adjacent neuropil, whereas in capillary CAA Aβ depositions are present in the capillary wall. CAA may cause lobar intracerebral haemorrhages and microbleeds. Hypoperfusion and reduced vascular autoregulation due to CAA might cause infarcts and white matter lesions. CAA thus causes vascular lesions that potentially lead to (vascular) dementia and may further contribute to dementia by impeding the clearance of solutes out of the brain and transport of nutrients across the blood brain barrier. Severe CAA is an independent risk factor for cognitive decline. The clinical diagnosis of CAA is based on the assessment of associated cerebrovascular lesions. In addition, perivascular spaces in the white matter and reduced concentrations of both Aβ(40) and Aβ(42) in cerebrospinal fluid may prove to be suggestive for CAA. Transgenic mouse models that overexpress human Aβ precursor protein show parenchymal Aβ and CAA, thus corroborating the current concept of CAA pathogenesis: neuronal Aβ enters the perivascular drainage pathway and may accumulate in vessel walls due to increased amounts and/or decreased clearance of Aβ, respectively. We suggest that pericapillary Aβ represents early impairment of the perivascular drainage pathway while capillary CAA is associated with decreased transendothelial clearance of Aβ. CAA plays an important role in the multimorbid condition of the ageing brain but its contribution to neurodegeneration remains to be elucidated.

Cerebral microinfarcts associated with severe cerebral beta-amyloid angiopathy

Cerebral amyloid angiopathy (CAA) is common in elderly individuals, especially those affected with Alzheimer's disease. Eighteen brains with severe SCAA (SCAA) were compared with 21 brains with mild CAA (MCAA) to investigate whether the presence of SCAA in the brains of demented patients was associated with a higher burden of old microinfarcts than those with MCAA. Immunohistochemistry for CD68 was employed to highlight old microinfarcts in tissue blocks from various brain regions. Old microinfarcts, manually counted by light microscopy, were present in 14 of 18 SCAA brains and in 7 of 21 MCAA brains (P = 0.01, two-tailed Fisher's exact test). The average number of old microinfarcts across geographic regions in each brain ranged from 0 to 1.95 (mean rank 24.94, sum of ranks 449) in the SCAA group, and from 0 to 0.35 (mean rank 15.76, sum of ranks 331) in the MCAA group (P = 0.008, two-tailed Mann-Whitney U-test). Frequent old microinfarcts in demented individuals with severe CAA may contribute a vascular component to the cognitive impairment in these patients.

Prevalence and impact of vascular and Alzheimer pathologies in Lewy body disease

Whereas the prevalence and impact of vascular pathology in Alzheimer diease (AD) are well established, the role of vascular and Alzheimer pathologies in the progression of neurodegeneration and cognitive impairment in Parkinson disease (PD) is under discussion. A retrospective clinico-pathologic study of 100 patients with autopsy proven PD (including 44 cases with dementia/PDD) and 20 cases of dementia with Lewy bodies (DLB) confirmed essential clinical (duration of illness, Mini-Mental State Examination/MMSE, age at death) and morphologic differences between these groups; Lewy body Braak scores and Alzheimer pathologies (neuritic Braak stage, cortical Abeta plaque load, and generalized cerebral amyloid angiopathy or CAA) were significantly higher/more severe in DLB and PDD than in PD without dementia. Duration of illness showed no association to any of the examined pathologic parameters, while there was a moderate association between LB scores and neuritic Braak stages, the latter significantly increasing with age. Significant association between cerebrovascular lesions and neuritic Braak stage was seen in PDD but not in PD subjects without dementia. These data suggest an influence of Alzheimer-related lesions on the progression of the neurodegenerative process and, in particular, on cognitive decline in both PDD and DLB. On the other hand, both these factors in PD and DLB appear to be largely independent from coexistent vascular pathology, except in cases with severe cerebrovascular lesions or those related to neuritic AD pathology. Assessment of ApoE genotype in a small number of cases showed no significant differences in the severity of Abeta plaque load and CAA except for much lower intensities in non-demented epsilon3/3 patients. Despite increasing evidence suggesting synergistic reactions between alpha-synuclein (alphaSyn), tau and Abeta-peptides, the major protein markers of both AD and Lewy body diseases, and of both vascular pathology and AD, the molecular background and pathophysiological impact of these pathologies on the progression of neurodegeneration and development of cognitive decline in PD await further elucidation.

Cerebral amyloid angiopathy in Lewy body disease

While Alzheimer and Lewy body pathologies are discussed as major substrates of dementia in Parkinson's disease (PD/Lewy body disease of brainstem type), the incidence and impact of cerebral amyloid angiopathy (CAA) and its association with cognitive decline in PD and dementia with Lewy bodies (DLB) are unknown. The severity of CAA and other Alzheimer lesions were assessed in 68 cases of autopsy-confirmed PD, 32 of them with dementia (PDD), and in 20 cases of DLB. PDD patients were significantly older than those without dementia (mean age 84.5 vs 77.6 years; p < 0.01), the age of DLB patients was in between both groups (mean 80.0 years), while duration of disease was DLB < PDD < PD (mean 6.5 vs 8.5 and 14.3 years). PDD patients had a significantly higher neuritic Braak stage (mean 4.2 vs 2.4, p < 0.01), significantly higher cortical amyloid beta (Abeta) load, capillary cerebral amyloid angiopathy (CapCAA) and generalized CAA than those without dementia (mild CapCAA in 22% vs moderate to severe CapCAA in 87%; mild generalized CAA in 5.5% vs moderate to severe generalized CAA in 82%). Mean PD stage was higher in both DLB and PDD than in PD (mean 5.2 vs 4.5 and 4.0, respectively): Mean neuritic Braak stage in DLB was 3.4, severe Abeta plaque load was seen in 95%, moderate to severe CapCAA in 90% and mild to severe generalized CAA in 70%. This and other recent studies imply an association of CAA with cognitive decline in both PD/PDD and DLB, particularly in cases with concomitant AD-type pathology.

Topographical distribution of cerebral amyloid angiopathy and its effect on cognitive decline are influenced by Alzheimer disease pathology

Cerebral amyloid angiopathy (CAA) is defined by beta-amyloid peptide (Abeta) depositions in cerebral vessels and is associated with Alzheimer disease (AD). It has been suggested that severe CAA is an independent risk factor for cognitive decline. 171 autopsy brains underwent standardized neuropathological assessment, the patients age ranged from 54 to 104 years (mean age: 83.9 years, +/-9.2, 59.6% female, 56.1% clinically demented). Using immunohistochemistry, the severity of Abeta depositions in vessels was assessed semiquantitatively in the frontal, frontobasal, hippocampal, and occipital region, respectively. CAA was present in 117 cases (68.4%), with the occipital region being affected significantly stronger than other regions. The overall incidence of CAA was significantly higher in cases with high grade neuritic AD pathology (ADP) compared to those with low grade or no ADP. The severity of CAA significantly increased with increasing ADP, with CAA in the occipital region increasing significantly stronger than that in other regions. The association of CAA and clinical dementia failed to remain statistically significant when adjusting for concomitant ADP. However, in cases devoid of any ADP CAA was significantly associated with the presence of clinical dementia. These results indicate a strong association of AD with CAA, but do not unequivocally support reports suggesting CAA to be an independent risk factor for cognitive decline, except for a subgroup of demented patients lacking any ADP.

The enigma of vascular cognitive disorder and vascular dementia

The prevalence, morphology and pathogenesis of vascular dementia (VaD), recently termed vascular cognitive impairment, are a matter of discussion, and currently used clinical diagnostic criteria show moderate sensitivity (average 50%) and variable specificity (range 64-98%). In Western clinic-based series, VaD is suggested in 8-10% of cognitively impaired aged subjects. Its prevalence in autopsy series varies from 0.03 to 58%, with reasonable values of 8-15%, while in Japan it is seen in 22-35%. Neuropathologic changes associated with cognitive impairment include multifocal and/or diffuse disease and focal lesions: multi-infarct encephalopathy, white matter lesions or arteriosclerotic subcortical (leuko)encephalopathy, multilacunar state, mixed cortico-subcortical type, borderline/watershed lesions, rare granular cortical atrophy, post-ischemic encephalopathy and hippocampal sclerosis. They result from systemic, cardiac and local large or small vessel disease. Recent data indicate that cognitive decline is commonly associated with widespread small ischemic/vascular lesions (microinfarcts, lacunes) throughout the brain with predominant involvement of subcortical and functionally important brain areas. Their pathogenesis is multifactorial, and their pathophysiology affects neuronal networks involved in cognition, memory, behavior and executive functioning. Vascular lesions often coexist with Alzheimer disease (AD) and other pathologies. Minor cerebrovascular lesions, except for severe amyloid angiopathy, appear not essential for cognitive decline in full-blown AD, while both mild Alzheimer pathology and small vessel disease may interact synergistically. The lesion pattern of "pure" VaD, related to arteriosclerosis and microangiopathies, differs from that in mixed-type dementia (AD with vascular encephalopathy), more often showing large infarcts, which suggests different pathogenesis of both types of lesions. Due to the high variability of cerebrovascular pathology and its causative factors, no validated neuropathologic criteria for VaD are available, and a large variability across laboratories still exists in the procedures for morphologic examination and histology techniques.

Clinical phenotypes of Cerebral Amyloid Angiopathy

The term Cerebral Amyloid Angiopathy (CAA) is used to describe the pathological changes occurring in cerebral blood vessels, both leptomeningeal and cortical that result from the deposition of amyloid proteins. This CNS vasculopathy is associated with a spectrum of clinical phenotypes that include both ischemic and hemorrhagic presentations. Dementia, cognitive impairment and transient neurological symptoms or signs are also being increasingly recognized as part of the CAA clinical spectrum. This review covers the clinical, pathological and neuroimaging aspects of CAA.

Prevalence and impact of cerebrovascular pathology in Alzheimer's disease and parkinsonism

OBJECTIVE

To study the prevalence and impact of cerebrovascular lesions (CVL) in Alzheimer's disease (AD) and their effects on cognitive impairment.

MATERIAL AND METHODS

In study I, the prevalence of vascular lesions in a prospective series of 244 autopsy-proved AD cases (mean age 83.1+/-8.4 years) and 230 age-matched non-demented controls was examined using immunochemistry and current morphological diagnostic criteria. In study II, in 100 consecutive autopsy cases (mean age 84.3+/-9.3 years), the incidence of general and capillary cerebral amyloid angiopathy (CAA, CapCAA) was examined.

RESULTS

In study I, AD cases showed significantly more frequent CVL than age-matched controls without differences in the Braak stages, but the severity of CAA was significantly higher in AD brain with associated vascular lesions. In study II, CAA was more frequent in demented than in non-demented patients, but did neither correlate with high-grade AD pathology nor with clinical dementia, whereas CapCAA correlated with both dementia and high Braak stages; the severity of both types of CAA showed only low correlation with each other.

CONCLUSIONS

The present data and other studies confirm the importance of CVL in AD and Parkinson's disease without considerable impact on cognitive impairment in progressed stages of AD, and the close association of CapCAA but not of general CAA with clinical dementia and AD pathology.

Relative paucity of tau accumulation in the small areas with abundant Abeta42-positive capillary amyloid angiopathy within a given cortical region in the brain of patients with Alzheimer pathology

Cerebral amyloid angiopathy (CAA) is a manifestation of amyloid beta-protein (Abeta) accumulation in the elderly as well as in patients with Alzheimer's disease (AD). Two types of CAA have been noted, based on the type of vasculature in which Abeta is deposited: cerebral capillary amyloid angiopathy (capCAA) and non-capCAA. Non-capCAA is a common form of CAA that consists of Abeta deposited in arteries and arterioles. Recent information on Abeta metabolism in the brain suggests that non-capCAA is associated with Abeta secretion into the cerebrospinal fluid via the perivascular space, whereas capCAA is associated with Abeta removal to blood plasma via the capillary endothelium. Abeta40, a major and relatively soluble Abeta isoform, is deposited predominantly in non-capCAA, and Abeta42, which is insoluble and associated more closely than Abeta40 with AD, is deposited predominantly in capCAA. Studying small areas of microscopic size within a given cortical region, we found an inverse association of capCAA and senile plaques. We also found a relative paucity of tau pathology in the small areas with abundant capCAA compared with the small areas with abundant senile plaques within a cortical region with the same cytoarchitecture. We suppose that both capCAA and senile plaques indicate high Abeta42 in the neuropil but that only Abeta42 in the form of insoluble deposits in senile plaques promotes tau abnormality.

Sporadic cerebral amyloid angiopathy: pathology, clinical implications, and possible pathomechanisms

Cerebral amyloid angiopathy (CAA) was observed for the first time nearly 100 years ago and systematically described in 1938. It is a common finding in elderly individuals, defined by beta-amyloid peptide (Abeta) depositions in cerebral blood vessels, and associated with Alzheimer's disease (AD). A variety of genetic mutations cause hereditary forms of CAA; in this review, however, only the sporadic variant of CAA is considered. In CAA, Abeta depositions primarily occur in the abluminal portion of the tunica media, and with increasing severity all layers of the blood vessel wall are infiltrated and an additional spread of Abeta into the surrounding neuropil may be seen (i.e., dyshoric changes). CAA is most pronounced in the occipital lobe and its distribution is usually patchy. The relationship between CAA and AD is poorly understood; however, low positive correlations between the severity of both CAA and AD pathology have been observed. CAA is a frequent cause of (warfarin-associated) intracerebral hemorrhage, and the diagnosis of probable CAA-related hemorrhage can be made during life with high accuracy. Both APOE-epsilon4 and APOE-epsilon2 are risk factors for CAA, while only APOE-epsilon2 increases the risk for hemorrhage in CAA. Although the role of CAA as an independent risk factor for cognitive decline is unclear, severe CAA is likely to lower the threshold for clinically overt dementia in neurodegenerative diseases. As for the origin of Abeta in CAA, it may be both produced by smooth muscle cells (vessel wall) and derived from neurons in the course of perivascular drainage.

Alzheimer's disease pathology influences severity and topographical distribution of cerebral amyloid angiopathy

Cerebral amyloid angiopathy (CAA) is defined by beta-amyloid peptide (Abeta) depositions in cerebral vessels and is associated with Alzheimer's disease (AD). The relationship between sporadic CAA and AD, and the origin of Abeta in CAA are poorly understood. The aim of our study was to investigate the relationship between CAA and AD. Autopsy brains (n=113, 61.1% female, 55.8% clinically demented, age range 54-102 years, mean +/- SE 83.5+/-0.93 years) underwent standardized neuropathological assessment. CAA was evaluated in frontal, frontobasal, hippocampal, and occipital regions. Using immunohistochemistry, the severity of Abeta deposition in vessels was assessed semiquantitatively for each region separately. Evaluation of APOE genotype in 53 cases using real-time PCR showed significant correlations with severe AD pathology and CAA. CAA was present in 77 cases (68.1%), with the occipital region being affected significantly more often and more severely than other regions (P<0.01). Of brains without AD pathology 23.5% revealed CAA, whereas 24% with AD pathology showed no CAA. In concordance with other studies, the severity of both AD pathology and CAA showed a low, but significant correlation. This correlation, however, was only caused by the significant increase of occipital CAA with increasing AD pathology (P<0.01), and was independent of APOE genotype. Our results suggest that progressing AD pathology not only increases the severity of CAA, but also shifts its topographical distribution towards the occipital cortex.

Matrix metalloproteinase-9 in cerebral-amyloid-angiopathy-related hemorrhage

Spontaneous intracerebral hemorrhage (ICH) is one of the most recognized complications of cerebral amyloid angiopathy (CAA), but little is known about the molecular pathogenesis of this life-threatening complication. In this review, we present preliminary evidence which suggests that the extracellular-matrix-degrading protease, matrix metalloproteinase-9 (MMP-9), may play a role in the development of spontaneous ICH resulting from CAA. The amyloid-beta peptide (Abeta) induced the synthesis, cellular release, and activation of MMP-9 in murine cerebral endothelial cells (CECs), resulting in increased extracellular matrix (ECM) degradation. Furthermore, in a mouse model of CAA (APPsw transgenic mice), MMP-9 immunoreactivity was observed in amyloid-laden cerebral vessels in aged APPsw mice but not in young APPsw or aged wild-type mice. More extensive MMP-9 immunostaining was present in amyloid-laden vessels with evidence of microhemorrhage. These results suggest that increased vascular MMP-9 expression, stimulated by Abeta, may play a role in the pathogenesis of spontaneous intracerebral hemorrhage (ICH) in patients with CAA.

Prevalence and pathogenic role of cerebrovascular lesions in Alzheimer disease

Cerebrovascular lesions in Alzheimer disease (AD) being significantly more frequent than in nondemented elderly subjects suggest overlaps and synergistic effects between both pathologies. Examination of a consecutive series of autopsy-proven AD cases and age-matched controls revealed a higher frequency of vascular lesions and of cerebral amyloid angiopathy (CAA) in AD (57.34% vs. 33.2% and 94.1% vs. 33.3%, respectively). These and previous data on vascular pathology in Parkinson disease emphasize its importance in these disorders. A study comparing the frequency and extent of general CAA and capillary CAA (CapCAA) in the postmortem frontal cortex of cases with high and low Braak stages showed no correlation between general CAA and dementia, only a low one with other vascular lesions except for cerebral hemorrhages. However, it was higher in AD than in controls with vascular pathology. The severity of CapCAA not correlating with general CAA showed high correlation with AD pathology, suggesting different pathogenesis of both types of CAA. Its elucidation may have implications for new therapeutic strategies. Considering the variability of vascular pathology in both AD and aged brains, the mechanisms behind their interactions are largely unknown, and further studies are needed to clarify their impact on cognitive impairment.

Passive immunotherapy against Abeta in aged APP-transgenic mice reverses cognitive deficits and depletes parenchymal amyloid deposits in spite of increased vascular amyloid and microhemorrhage

Background

Anti-Aβ immunotherapy in transgenic mice reduces both diffuse and compact amyloid deposits, improves memory function and clears early-stage phospho-tau aggregates. As most Alzheimer disease cases occur well past midlife, the current study examined adoptive transfer of anti-Aβ antibodies to 19- and 23-month old APP-transgenic mice.

Methods

We investigated the effects of weekly anti-Aβ antibody treatment on radial-arm water-maze performance, parenchymal and vascular amyloid loads, and the presence of microhemorrhage in the brain. 19-month-old mice were treated for 1, 2 or 3 months while 23-month-old mice were treated for 5 months. Only the 23-month-old mice were subject to radial-arm water-maze testing.

Results

After 3 months of weekly injections, this passive immunization protocol completely reversed learning and memory deficits in these mice, a benefit that was undiminished after 5 months of treatment. Dramatic reductions of diffuse Aβ immunostaining and parenchymal Congophilic amyloid deposits were observed after five months, indicating that even well-established amyloid deposits are susceptible to immunotherapy. However, cerebral amyloid angiopathy increased substantially with immunotherapy, and some deposits were associated with microhemorrhage. Reanalysis of results collected from an earlier time-course study demonstrated that these increases in vascular deposits were dependent on the duration of immunotherapy.

Conclusions

The cognitive benefits of passive immunotherapy persist in spite of the presence of vascular amyloid and small hemorrhages. These data suggest that clinical trials evaluating such treatments will require precautions to minimize potential adverse events associated with microhemorrhage.

Cerebral amyloid angiopathy in aged Chinese: a clinico-neuropathological study

To investigate the prevalence and clinico-neuropathological characteristics of cerebral amyloid angiopathy (CAA) in aged Chinese and its relationship to dementia and cerebrovascular lesions, we examined 362 archived brains of elderly with immunohistochemical staining for beta-amyloid peptide and Congo red, Bodian and Luxol fast blue stains. We found that: (1) CAA appeared in 31.7% examined brains without sexual preponderance, and the incidence increased with age; (2) the frontal lobe was most frequently involved in CAA, followed by occipital and parietal lobe; (3) subcortical white matter and cerebellum dentate nucleus areas may also be affected by CAA; (4) CAA has a close relationship to Alzheimer's disease and multiple cerebrovascular lesions; (5) CAA alone may result in dementia.

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.

Relationship between severe amyloid angiopathy, apolipoprotein E genotype, and vascular lesions in Alzheimer's disease

In this brief review, we aim to describe the complex relationship between cerebral amyloid angiopathy (CAA), apolipoprotein E (ApoE), and cerebrovascular lesions in Alzheimer's disease (AD). First, we review the evidence that CAA is associated with, and may cause, specific types of vascular lesions (VLs). In addition to being a leading cause of lobar hemorrhages in the elderly, CAA has been implicated as a likely cause of small infarcts, microinfarcts, and incomplete infarctions in the deep white matter. We also review the role that ApoE4 (the major genetic risk factor for AD) has in predisposing toward CAA, coronary artery disease, and possibly toward cerebrovascular disease. Last, we provide evidence that the association between CAA and VLs is not a spurious one due to an increase in the ApoE4 genotype. Even within patient groups with the same ApoE genotype (specifically, E4/4 homozygotes and E3/3 homozygotes), our recent analyses have found significant increases in VLs in association with severe CAA. We discuss the implications of this finding as advancing a pathogenic role for severe CAA in producing many of the VLs commonly found in AD cases.