Dysregulation of the renin-angiotensin system in vascular dementia.

The renin-angiotensin system (RAS) regulates systemic and cerebral blood flow and is dysregulated in dementia. The major aim of this study was to determine if RAS signalling is dysregulated in vascular dementia. We measured markers of RAS signalling in white matter underlying the frontal and occipital cortex in neuropathologically confirmed cases of vascular dementia (n = 42), Alzheimer's disease (n = 50), mixed AD/VaD (n = 50) and age-matched controls (n = 50). All cases were stratified according to small vessel disease (SVD) severity across both regions. ACE-1 and ACE-2 protein and activity was measured by ELISA and fluorogenic peptide assays respectively, and angiotensin peptide (Ang-II, Ang-III and Ang-(1-7)) levels were measured by ELISA. ACE-1 protein level and enzyme activity, and Ang-II and Ang-III, were elevated in the white matter in vascular dementia in relation to SVD severity. ACE-1 and Ang-II protein levels were inversely related to MAG:PLP1 ratio, a biochemical marker of brain tissue oxygenation that when reduced indicates cerebral hypoperfusion, in a subset of cases. ACE-2 level was elevated in frontal white matter in vascular dementia. Ang-(1-7) level was elevated across all dementia groups compared to age-matched controls but was not related to SVD severity. RAS signalling was not altered in the white matter in Alzheimer's disease. In the overlying frontal cortex, ACE-1 protein was reduced and ACE-2 protein increased in vascular dementia, whereas angiotensin peptide levels were unchanged. These data indicate that RAS signalling is dysregulated in the white matter in vascular dementia and may contribute to the pathogenesis of small vessel disease.

CSF evidence of pericyte damage in Alzheimer's disease is associated with markers of blood-brain barrier dysfunction and disease pathology.

BACKGROUND: We aimed to assess the relationship between levels of a cerebrospinal fluid (CSF) marker of pericyte damage, soluble platelet-derived growth factor receptor ß (sPDGFRß) and CSF markers of blood-brain barrier (BBB) integrity (CSF albumin and CSF/serum albumin ratio) and disease pathology (reduced CSF Aß42 and elevated CSF total and phosphorylated tau) in Alzheimer's disease (AD). METHODS: sPDGFRß and albumin were measured by sandwich ELISA in ante-mortem CSF from 39 AD and 39 age-matched controls that were grouped according to their biomarker profile (i.e. AD cases t-tau > 400 pg/mL, p-tau > 60 pg/mL and Aß42 < 550 pg/mL). sPDGFRß was also measured in matched serum and CSF samples (n = 23) in a separate neurologically normal group for which the CSF/serum albumin ratio had been determined. RESULTS: CSF sPDGFRß level was significantly increased in AD (p = 0.0038) and correlated positively with albumin (r = 0.45, p = 0.007), total tau (r = 0.50, p = 0.0017) and phosphorylated tau (r = 0.41, p = 0.013) in AD but not in controls. CSF sPDGFRß did not correlate with Aß42. Serum and CSF sPDGFRß were positively correlated (r = 0.547, p = 0.0085) in the independent neurologically normal CSF/serum matched samples. CONCLUSIONS: We provide further evidence of an association between pericyte injury and BBB breakdown in AD and novel evidence that a CSF marker of pericyte injury is related to the severity of AD pathology.

Regional differences in effects of APOE ε4 on cognitive impairment in non-demented subjects.

BACKGROUND: The APOE ε4 allele is a risk factor for Alzheimer's disease (AD). APOE ε4 is common in non-demented subjects with cognitive impairment. In both healthy people and people with AD, its prevalence has a north-south gradient across Europe. In the present study, we investigated whether the relation between the APOE ε4 allele and cognitive impairment varied across Northern, Middle and Southern Europe. We also investigated whether a north-south gradient existed in subjects with subjective cognitive impairment (SCI), amnestic mild cognitive impairment (MCI) and non-amnestic MCI. METHODS: Data from 16 centers across Europe were analyzed. RESULTS: A north-south gradient in APOE ε4 prevalence existed in the total sample (62.7% for APOE ε4 carriers in the northern region, 42.1% in the middle region, and 31.5% in the southern region) and in subjects with SCI and amnestic MCI separately. Only in Middle Europe was the APOE ε4 allele significantly associated with poor performance on tests of delayed recall and learning, as well as with the amnestic subtype of MCI. CONCLUSION: The APOE ε4 allele frequencies in subjects with SCI and amnestic MCI have a north-south gradient. The relation between the APOE ε4 allele and cognition is region dependent.

Endothelin-converting enzyme-1 in Alzheimer's disease and vascular dementia.

AIMS: Alzheimer's disease (AD) is believed to be caused by the accumulation of amyloid beta (Aß) peptide within the brain. Endothelin-converting enzyme-1 and 2 (ECE-1 and ECE-2) are expressed in endothelial cells and neurones, respectively, and both cleave 'big endothelin' to produce the vasoconstrictor endothelin-1 (ET-1). ECE-1 and ECE-2 also degrade Aß. AD patients have regionally reduced microvascular blood flow in the brain, with impaired endothelium-dependent relaxation and cerebrovascular autoregulation, and abnormal production of ET-1 has been demonstrated in mice overexpressing amyloid precursor protein. We recently found ECE-2 mRNA and protein to be elevated in the brain in AD. In vitro, expression of ECE-2 was upregulated by Aß. Our aims for this study were to examine expression of ECE-1 (which has 57% homology with ECE-2) in temporal cortex from patients with AD, vascular dementia (VaD) and controls. METHODS: We examined the distribution of ECE-1 with immunohistochemistry, and measured ECE-1 mRNA by real-time polymerase chain reaction (PCR). ECE-1 protein levels were measured by western blot, and results analysed before and after adjustment for factor VIII-related antigen. RESULTS: We showed ECE-1 to be in vascular endothelial cells. We did not find significant differences in ECE-1 mRNA or protein levels (either full-length ECE-1 or the soluble spliced variant, ECE-1sv) in AD or VaD compared with controls. CONCLUSIONS: Our findings suggest that any disease-specific contribution of ECE-1 to the accumulation of Aß or reduction in local microvascular blood flow in AD or VaD is probably small, with abnormal production of ET-1 being more likely to reflect Aß-mediated upregulation of ECE-2.

Ethical aspects of research into Alzheimer disease. A European Delphi Study focused on genetic and non-genetic research.

BACKGROUND: Although genetic research into Alzheimer disease (AD) is increasing, the ethical aspects of this kind of research and the differences between ethical issues related to genetic and non-genetic research into AD have not yet received much attention. OBJECTIVES: (1) To identify and compare the five ethical issues considered most important by surveyed expert panellists in non-genetic and genetic AD research and (2) to compare our empirical findings with ethical issues in genetic research in general as described in the literature. METHOD: A modified Delphi study in two rounds RESULTS: Genetic and non-genetic research into AD generated an approximately equal number of topics with a considerable overlap. Different priorities in the ethics of both types of research were found. Genetic research raised new topics such as "confidentiality of genetic information" and "implications of research for relatives" which changes the impact and application of existing ethical topics such as "informed consent" and is judged to have more impact on both individuals and society. A difference with the results of more theoretical approaches on ethical aspects related to AD research was also found. CONCLUSIONS: Different priorities are given to ethical issues in genetic and non-genetic research. These arise partly because genetic research causes unique and new questions, mostly related to the position of family members and the status of and access to genetic information. Differences found between the results of our empirical study and the more theoretical literature, suggest an additional value for empirical research in medical ethics.

MMP-2, -3 and -9 levels and activity are not related to Abeta load in the frontal cortex in Alzheimer's disease.

Matrix metalloproteinases (MMPs) -2, -3 and -9 are up-regulated in several cell types on exposure to amyloid beta peptide (Abeta) and have Abeta-degrading activity in vitro. The aims of this study were to determine (i) the distribution of MMP-2, -3 and -9 in the cerebral cortex in Alzheimer's disease (AD) and control brains; (ii) whether the levels and activity of these proteases are increased in AD; and (iii) whether their activity is related to Abeta load. In addition, we examined whether promoter polymorphisms in the MMP-3 and -9 genes are associated with AD in the study cohort. Paraffin sections of frontal lobe from AD and control cases were immunostained for MMP-2, -3 and -9 and tissue homogenates used for MMP activity assays. DNA from these cases was genotyped for the MMP-3 5A/6A (-1171) and MMP-9 C-1562T promoter polymorphisms. Immunohistochemistry revealed MMP-3 in plaques and both MMP-3 and -9 around scattered neurones. The levels and activity of all three MMPs were similar in AD and control brains and bore no relationship to Abeta load. Analysis of MMP-3 -1171 5A/6A allele frequencies showed that the 6A allele (with reduced promoter activity) was associated with AD; the MMP-9 C-1562T polymorphism was not. The levels and activities of MMP-2, -3 and -9 are not increased in the frontal cortex in AD and are not related to Abeta load. Our findings suggest that altered expression of these proteases does not make a significant contribution to the accumulation of Abeta in AD.

Angiotensin-converting enzyme (ACE) levels and activity in Alzheimer's disease, and relationship of perivascular ACE-1 to cerebral amyloid angiopathy.

AIMS: Several observations point to the involvement of angiotensin-converting enzyme-1 (ACE-1) in Alzheimer's disease (AD): ACE-1 cleaves amyloid-beta peptide (Abeta) in vitro, the level and activity of ACE-1 are reportedly increased in AD, and variations in the ACE-1 gene are associated with AD. We analysed ACE-1 activity and expression in AD and control brains, particularly in relation to Abeta load and cerebral amyloid angiopathy (CAA). METHODS: ACE-1 activity was measured in the frontal cortex from 58 control and 114 AD cases of known Abeta load and CAA severity. The distribution of ACE-1 was examined immunohistochemically. In five AD cases with absent or mild CAA, five with moderate to severe CAA and five controls with absent or mild CAA, levels of vascular ACE-1 were assessed by quantitative immunofluorescence. RESULTS: ACE-1 activity was increased in AD (P < 0.001) and correlated directly with parenchymal Abeta load (P = 0.05). Immunohistochemistry revealed ACE-1 in neurones and cortical blood vessels - in the intima but most abundant perivascularly. Cases with moderate to severe CAA had significantly more vessel-associated ACE-1 than did those with little or no CAA. Perivascular ACE-1 did not colocalize with Abeta, smooth muscle actin, glial fibrillary acidic protein, collagen IV, vimentin or laminin, but was similarly distributed to extracellular matrix (ECM) proteins fibronectin and decorin. CONCLUSIONS: Our findings indicate that ACE-1 activity is increased in AD, in direct relationship to parenchymal Abeta load. Increased ACE-1, probably of neuronal origin, accumulates perivascularly in severe CAA and colocalizes with vascular ECM. The possible relationship of ACE-1 to the deposition of perivascular ECM remains to be determined.

Caveolin-1 and -2 and their relationship to cerebral amyloid angiopathy in Alzheimer's disease.

Cerebral amyloid angiopathy (CAA) affects over 90% of patients with Alzheimer's disease (AD) and increases the risk of cerebral haemorrhage and infarction. Caveolae--cholesterol-enriched plasmalemmal microinvaginations--are implicated in the production of amyloid beta peptide (Abeta). Caveolin-1 (CAV-1) is essential for the formation of caveolae. Caveolin-2 (CAV-2) is expressed at the plasma membrane only when in a stable hetero-oligomeric complex with CAV-1. CAV-1 and CAV-2 are highly co-expressed by endothelium and smooth muscle. Recent studies suggest that down-regulation of CAV-1 causes a reduction in alpha-secretase activity and consequent accumulation of Abeta. We have used quantitative immunohistochemical techniques to assess the relationship between CAV-1 and CAV-2 with respect to Abeta accumulation in the cerebral vasculature in a series of post mortem brains. CAV-1 and CAV-2 were co-expressed within the tunica media and endothelium of cerebral blood vessels. There were regional differences in CAV-1 immunolabelling, which was significantly greater in the frontal cortex and white matter than in the parietal lobe (in both control and AD cases) or the temporal lobe (in AD alone). However, CAV-1 labelling in AD did not differ from that in controls in any of the three lobes examined. Assessment of CAV-1 labelling in relation to the severity of CAA showed CAV-1 to be significantly increased in the frontal white matter in a subgroup of AD cases with absent/mild CAA compared with controls with absent/mild CAA and to AD cases with moderate/severe CAA, but the latter groups did not show significant differences from one another. CAV-1 labelling did not vary with age, gender, APOE genotype, post mortem delay or brain weight. Only segments of blood vessels with particularly abundant Abeta and extensive loss of smooth muscle actin showed loss of CAV-1 and CAV-2 from the tunica media. Within these vessels endothelial CAV-1 was preserved and discontinuous CAV-2 labelling was noted along the outer aspect of the vessel wall. Our findings suggest that alterations in the expression of vascular CAV-1 and CAV-2 are unlikely to play a role in the development of CAA in AD.

The cardiovascular and respiratory health of people with schizophrenia.

OBJECTIVE: To examine the cardiovascular and respiratory health of people with severe mental illness (SMI) and compare findings with the Health Surveys for England. METHOD: A prospective, multi-centre observational prevalence study of 602 patients with schizophrenia-related psychoses carried out in six locations across the UK over 24 months. RESULTS: Compared with general population subjects, people with SMI reported higher rates of angina and respiratory symptoms and had poor lung function. Much of this increased risk could be explained by lifestyle risk factors; there were increased levels of obesity among younger people with SMI. CONCLUSION: Key indicators of the cardiovascular and respiratory health of people with SMI are poor compared with those of the general population. Care plans should prioritize interventions to attenuate lifestyle risk factors. Evidence of increasing obesity in younger patients is of particular concern, predicting even greater health needs in the future.

Vascular risk and genetics of sporadic late-onset Alzheimer's disease.

In recent years, it is becoming apparent that genes may play an important role in the development of late-onset Alzheimer's disease (LOAD), and genetic studies could unravel new clues. Based on a growing vascular hypothesis for the pathogenesis of LOAD and other dementias, there is increasing interest for environmental and genetic vascular factors. Polymorphisms in different susceptibility genes already implicated in vascular disease risk are now also being suggested as possible genetic markers for increased risk of developing LOAD; however, many of these studies have shown conflicting results. Thus far, the apolipoprotein E (APOE) gene seems to be the only vascular susceptibility factor that is agreed to play a role in the multifactorial pathogenesis of AD although emerging genetic and biological evidence is now strengthening the case for additional inclusion of angiotensin I-converting enzyme 1 (ACE1) into this category. This review will focus on the current knowledge on genetic and nongenetic vascular factors likely to be involved in LOAD, with special emphasis placed on the APOE and ACE1 genes.

APOE epsilon 4 influences the manifestation of Alzheimer's disease in adults with Down's syndrome.

BACKGROUND: Recent studies of the relationship between the apolipoprotein E (APOE) gene and Alzheimer's disease in adults with Down's syndrome have revealed inconsistent results. AIMS: To assess the role of the APOE gene in the manifestation of Alzheimer's disease in adults with Down's syndrome. METHOD: We studied the APOE genotypes of 24 adults with dementia and 33 non-demented adults with Down's syndrome over 35 years of age, and an additional group of 164 non-learning disabled adults. We also carried out a meta-analysis of all previously published studies of association between APOE and Down's syndrome, incorporating the current data. RESULTS: We observed a non-significant excess of APOE epsilon 4 and a reduction of epsilon 2 in adults with dementia compared with non-demented adults with Down's syndrome in our sample. However, meta-analysis showed a significantly higher frequency of epsilon 4 in adults with dementia compared with non-demented adults with Down's syndrome (odds ratio = 2.02, 95% CI 1.33-3.07, P = 0.001), but no significant reduction in the frequency of epsilon 2. CONCLUSIONS: The APOE epsilon 4 allele acts as a risk factor for the age-specific manifestation of Alzheimer's disease in people with Down's syndrome.

The butyrylcholinesterase K variant and susceptibility to Alzheimer's disease.

Previous work has shown an association between the K variant of the butyrylcholinesterase (BCHE) gene and Alzheimer's disease (AD) in patients carrying the epsilon4 allele of ApoE. We attempted to replicate this finding in 181 UK white AD cases and 71 controls. No difference was found in BCHE-K genotypes (p=0.75) or alleles (p=0.70) between patients and controls. Moreover, despite a significant excess of ApoE epsilon4 in patients versus controls (p<0.0001), we found no evidence to support previous reports of an interaction between ApoE and BCHE-K (chi2=1.49, df=4, p=0.83).