Occludin is overexpressed in Alzheimer's disease and vascular dementia

The tight junctions (TJs) are key players in the control of blood-brain barrier (BBB) properties, the most complex TJs in the vascular system being found in the endothelial cells of brain capillaries. One of the main TJs proteins is occludin, which anchors plasma membranes of neighbour cells and is present in large amounts in the brain endothelia. Previous studies demonstrated that disruption of BBB in various pathological situations associates with changes in occludin expression, and this change could be responsible for malfunction of BBB. Therefore in this study, applying an immunohistochemical approach, we decided to explore the occludin expression in frontal cortex (FC) and basal ganglia in ageing control, Alzheimer's disease (AD), and vascular dementia (VD) brains, as far as all these pathologies associate microangiopathy and disruption of BBB. Strikingly, we found selected neurons, astrocytes and oligodendrocytes expressing occludin, in all cases studied. To estimate the number of occludin-expressing neurons, we applied a stereological approach with random systematic sampling and the unbiased optical fractionator method. We report here a significant increase in ratio of occludin-expressing neurons in FC and basal ganglia regions in both AD and VD as compared to ageing controls. Within the cerebral cortex, occludin was selectively expressed by pyramidal neurons, which are the ones responsible for cognitive processes and affected by AD pathology. Our findings could be important in unravelling new pathogenic pathways in dementia disorders and new functions of occludin and TJs.     

Cerebrospinal fluid tau, A beta, and phosphorylated tau protein for the diagnosis of Alzheimer's disease

The diagnosis of AD is still largely based on exclusion criteria of secondary causes and other forms of dementia with similar clinical pictures, than the diagnostic accuracy of AD is low. Improved methods of early diagnosis are needed, particularly because drugs treatment is more effective in the early stages of the disease. Recent research focused the attention to biochemical diagnostic markers (biomarkers) and according to the proposal of a consensus group on biomarkers, three candidate CSF markers reflecting the pathological AD processes, have recently been identified: total tau protein (t-tau), amyloid beta(1-42) protein (A beta42), and tau protein phosphorylated at AD-specific epitopes (p-tau). Several articles report reduced CSF levels of A beta42 and increased CSF levels of t-tau and p-tau in AD; the sensitivity and specificity of these data are able for discrimination of AD patients from controls. However, the specificity for other dementias is low. According to the literature analysis reported in the present review, we can conclude that the combination of the CSF markers and their ratios may significantly increase the specificity and the accuracy of AD diagnosis.     

"Closing-in" phenomenon in Alzheimer's disease and subcortical vascular dementia

Background  

The 'closing-in' phenomenon is defined as a tendency to close in on a model while copying it. This is one of several constructional apraxia observed in dementia, particularly in Alzheimer's disease (AD). The aim of this study was to investigate the usefulness of it in the differential diagnosis of AD and subcortical vascular dementia (SVD) and to clarify the factors associated with it.     

Genetic markers for diagnosis and pathogenesis of Alzheimer's disease

Alzheimer's disease (AD) is the most common form of dementia in the elderly and represents an important and increasing clinical challenge in terms of diagnosis and treatment. Mutations in the genes encoding amyloid precursor protein (APP), presenilin 1 (PSEN1) and presenilin 2 (PSEN2) are responsible for early-onset autosomal dominant AD. The ε4 allele of the apolipoprotein E (APOE) gene has been recognized as a major genetic risk factor for the more common, complex, late-onset AD. Fibrillar deposits by phosphorylated tau are also a key pathological feature of AD. The retromer complex also has been reported to late-onset AD. More recently, genome-wide association studies (GWASs) identified putative novel candidate genes associated with late-onset AD. Lastly, several studies showed that circulating microRNAs (miRNAs) in the cerebrospinal fluid (CSF) and blood serum of AD patients can be used as biomarkers in AD diagnosis. This review addresses the advances and challenges in determining genetic and diagnostic markers for complex AD pathogenesis.     

Cerebrospinal fluid acetylcholinesterase changes after treatment with donepezil in patients with Alzheimer's disease

We analyzed whether donepezil differently influences acetylcholinesterase (AChE) variants from cerebrospinal fluid (CSF) in patients with Alzheimer's disease (AD) after long-term treatment. Overall CSF-AChE activity in AD patients before treatment was not different from controls, but the ratio between the major tetrameric form, G(4), and the smaller G(1) and G(2) species was significantly lower. AChE levels at study outset were found to correlate positively with beta-amyloid (1-42) (Abeta42). When patients were re-examined after 12 months treatment with donepezil, there was a remarkable increase in both the G(4) and the lighter species of CSF AChE. As compared with placebo, donepezil caused decreases in the percentage of AChE that failed to bind to the lectin concanavalin A and the antibody AE1. These non-binding species comprised primarily a small subset of G(1) and G(2) forms. In treated patients, these light variants were the only subset of CSF AChE that correlated with CSF-Abeta42 levels. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis showed that a 77-kDa band, attributed in part to inactive AChE, was lower in AD patients than in controls. Unlike enzyme activity, the intensity of this band did not increase after donepezil treatment. The varying responses of different AChE species to ChE-I treatment suggest different modes of regulation, which may have therapeutic implications.     

Potential therapeutic targets of huperzine A for Alzheimer's disease and vascular dementia

Huperzine A (HupA), a novel Lycopodium alkaloid isolated from Chinese folk medicine Huperzia serrata (Qian Ceng Ta), is a potent, selective and well-tolerated inhibitor of acetylcholinesterase (AChE). It has been proven to significantly improve the learning and memory impairment in Alzheimer's disease (AD) and vascular dementia (VaD) patients in China. Interestingly, our recent data indicate that HupA also possesses other protective functions. This paper will give an overview on the protective effects of HupA, which includes regulating beta-amyloid precursor protein (APP) metabolism, protecting against Abeta-mediated oxidative stress, apoptosis and mitochondrial dysfunction, as well as anti-inflammation. The multiple neuroprotective effects of HupA might yield additional beneficial effects in AD and VaD therapy.     

Cerebrospinal fluid S100B is elevated in the earlier stages of Alzheimer's disease

Postmortem demonstration of increased expression of biologically active S100B in Alzheimer's disease (AD) and its relation to progression of neuropathological changes across the cortical regions suggests involvement of this astrocytic cytokine in the pathophysiology of AD. The hypothesis that the overexpression of S100B in Alzheimer brain is related to the progression of clinical symptoms was addressed in living persons by measuring S100B concentrations in cerebrospinal fluid (CSF) from AD patients with a broad range of clinical dementia severity and from healthy older persons. The effect of normal aging on CSF S100B concentrations also was estimated. CSF S100B did not differ between all 68 AD subjects (0.98±0.09 ng/ml (mean±S.E.M.)) and 25 healthy older subjects (0.81±0.13 ng/ml). When AD subjects were divided into mild/moderate stage and advanced stage clinical dementia severity by the established Clinical Dementia Rating Scale (CDR) criteria, S100B was significantly higher in the 46 mild/moderate stage AD subjects (1.17±0.11 ng/ml) than in either the 22 advanced stage AD subjects (0.60±0.12 ng/ml) or the healthy older subjects. Consistent with higher CSF S100B in mild to moderate AD, there was a significant correlation among all AD subjects between CSF S100B and cognitive status as measured by the Mini Mental State Exam (MMSE) score. CSF S100B did not differ between healthy older subjects and healthy young subjects. These results suggest increased CNS expression of S100B in the earlier stages of AD, and are consistent with a role for S100B in the initiation and/or facilitation of neuritic plaque formation in AD brain.     

Cerebrospinal fluid and plasma corticotropin-releasing hormone in senile dementia.

Cerebrospinal fluid (CSF) levels of corticotropin-releasing hormone (CRH) and ACTH, and plasma levels of CRH, ACTH and cortisol were determined in samples taken simultaneously from 28 patients with dementia including senile dementia of the Alzheimer type (SDAT), multi-infarct dementia (MID), dementia following a cerebrovascular accident (CVD), and the borderline-to-normal state. CRH levels in CSF were significantly reduced in patients with SDAT and CVD, but not in those with MID, as compared with the borderline cases. ACTH levels in CSF were significantly reduced in the patients with SDAT compared to those with MID. Reduced CRH levels in CSF were found in the patients who showed severe dementia and poor activities of daily living (ADL). Plasma levels of CRH, ACTH and cortisol were normal and were not significantly different among the four groups of patients. CRH levels in CSF were positively correlated with ACTH levels in CSF, but not with the levels of plasma CRH, ACTH or cortisol. Plasma CRH levels were positively correlated with plasma ACTH levels. These results suggest that: 1) abnormalities in the extrahypothalamic CRH system play a role in the pathophysiology of senile dementia, which may not be specific to SDAT; 2) CSF CRH is correlated with the severity of dementia and ADL; 3) the levels of CRH in CSF and plasma are independent, and 4) the plasma CRH reflects, at least in part, the activity of the hypothalamic CRH regulating the secretion of pituitary ACTH.     

A novel peptidomics approach to detect markers of Alzheimer's disease in cerebrospinal fluid

Sensitive and specific diagnosis and monitoring of disease progression are of prime importance to develop new therapies for Alzheimer's disease patients. Although the diagnostic accuracy, verified by pathological examination is high, it is currently not possible to diagnose Alzheimer's disease with a high degree of certainty until relatively late in the disease process. Here, we have undertaken a peptidome analysis of postmortem cerebrospinal fluid of neuropathologically confirmed Alzheimer's disease patients and non-demented controls using a combination of methods and technologies. This includes novel sample preparation based on the enrichment of endogenous, proteolytically derived peptides as well as peptides non-covalently bound to abundant proteins. We observed differences in peptide profiles associated with Alzheimer's disease in the endogenous peptide fraction and in the protein-bound peptide fraction. The discriminating peptides in the unbound peptide fraction were identified as VGF nerve growth factor inducible precursor, and complement C4 precursor, whereas the discriminating peptides in the protein-bound fraction were identified as VGF nerve growth factor inducible precursor, and alpha-2-HS-glycoprotein.     

The association of a cystatin C gene polymorphism with late-onset Alzheimer's disease and vascular dementia

A polymorphism in the cystatin C (CST3) gene was suggested to associate with Alzheimer's disease (AD). In the present study we attempted to determine the association between CST3 polymorphism and AD or vascular dementia (VD), and whether such effects are dependent of the APOE4 allele. The polymorphisms of CST3 genotype were determined using polymerase chain reactions (PCR) followed by gel electrophoresis in 124 AD, 70 VD, and 115 control individuals. No statistical difference in CST3B allele frequencies was observed among all three groups. Associations between CST3B/B genotype and AD patients older than 75-year-old, or VD patients younger than 75-year-old were evident. The APOE4 allele alone significantly increased the odds for the developing AD, but not VD. A logistic regression analysis revealed that either CST3 or its interaction with APOE4 were not significant predictors of AD. However, a synergistic association of CST3 and APOE4 alleles was observed in predicting VD patients. These results suggest that CST3 might interact with APOE4 on conferring vascular pathologies.     

Studies of neuroimmune markers in Alzheimer's disease

Based on a suspected role of the immune system in the pathophysiology of Alzheimer's disease (AD) and the new discoveries of neuroimmune networks, the investigation of certain neuroimmune markers was performed in AD patients, healthy controls, and disease controls. In agreement with our previous immunological research on AD, the assessment of additional immune parameters revealed abnormalities of both cellular and humoral immunity in several AD patients. These include:

1. Enhanced production of cytokines, such as interleukin-1 (IL-1), interleukin-2 (IL-2), and interleukin-6 (IL-6);
2. Increase plasma level of CD8-positive lymphocyte derived soluble CD8 (sCD8) antigen; and
3. Increased incidence of autoantibodies to brain myelin basic protein (MBP) and thymic cells.

As analyzed by flow cytometry and enzyme immunoassay, the peripheral blood immunocytes from AD patients showed a significant increase in the expression of the brain-derived S-100 protein. In the cell proliferation assay, the blood immunocytes from healthy subjects responded to stimulation with beta-amyloid protein (βAP), but this response was absent in AD patients. The initial results of our research suggest that the studies of specific markers of the neuroimmune axis may be potentially important for the new development of diagnostic and therapeutic strategies for AD.     

The impact of cerebrospinal fluid biomarkers on the diagnosis of Alzheimer's disease

The cerebrospinal fluid (CSF) biomarkers β-amyloid(1-42) (Aβ(1-42)), total tau protein (T-tau), and tau phosphorylated at threonine 181 (P-tau(181P)) are gradually finding their way into routine clinical practice as an affirmative diagnostic tool for Alzheimer's disease (AD). These biomarkers have also been implemented in the revised diagnostic criteria for AD. The combination of the CSF biomarkers Aβ(1-42), T-tau, and P-tau(181P) leads to high (around 80%) levels of sensitivity, specificity, and diagnostic accuracy for discrimination between AD and controls (including psychiatric disorders like depression) and can be applied for diagnosing AD in the predementia phases of the disease (mild cognitive impairment). The added value of CSF biomarkers could lie within those cases in which the clinical diagnostic work-up is not able to discriminate between AD and non-AD dementias. However, their discriminatory power for the differential diagnosis of dementia is suboptimal. Other CSF biomarkers, especially those that are reflective of the pathology of non-AD dementia etiologies, could improve the accuracy of differential dementia diagnosis. CSF biomarkers will be of help to establish a correct and early AD diagnosis, even in the preclinical stages of the disease, which will be of importance once disease-modifying drugs for AD become available. Variation in biomarker measurements still jeopardize the introduction of CSF biomarkers into routine clinical practice and clinical trials, but several national and international standardization initiatives are ongoing.     

Prevalence of Alzheimer's disease and vascular dementia: association with education. The Rotterdam study.

OBJECTIVE--To estimate the prevalence of dementia and its subtypes in the general population and examine the relation of the disease to education. DESIGN--Population based cross sectional study. SETTING--Ommoord, a suburb of Rotterdam. SUBJECTS--7528 participants of the Rotterdam study aged 55-106 years. RESULTS--474 cases of dementia were detected, giving an overall prevalence of 6.3%. Prevalence ranged from 0.4% (5/1181 subjects) at age 55-59 years to 43.2% (19/44) at 95 years and over. Alzheimer''s disease was the main subdiagnosis (339 cases; 72%); it was also the main cause of the pronounced increase in dementia with age. The relative proportion of vascular dementia (76 cases; 16%), Parkinson''s disease dementia (30; 6%), and other dementias (24; 5%) decreased with age. A substantially higher prevalence of dementia was found in subjects with a low level of education. The association with education was not due to confounding by cardiovascular disease. CONCLUSIONS--The prevalence of dementia increases exponentially with age. About one third of the population aged 85 and over has dementia. Three quarters of all dementia is due to Alzheimer''s disease. In this study an inverse dose-response relation was found between education and dementia--in particular, Alzheimer''s disease.     

Haptoglobin types and subtypes in Alzheimer's disease and senile dementia

Summary The haptoglobin subtypes were studied in 120 patients with the clinical diagnosis of Alzheimer's disease or senile dementia. As compared with two control groups an increase of both the Hp^1F and Hp^1S genotypes was observed. The abnormal haptoglobin subtype distribution was most striking in those patients with an early onset of the dementia.

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Zusammenfassung Bei 120 Patienten, bei denen eine Alzheimersche Krankheit oder eine senile Demenz diagnostiziert wurde, haben wir die Haptoglobinuntergruppen bestimmt. Im Vergleich zu zwei Kontrollgruppen stellten wir fest, daß die Frequenz des Vorkommens der Hp^1F-und Hp^1S-Genotypen erhöht war. Diese abnorme Haptoglobinuntergruppenverteilung was bei Kranken mit einem frühzeitigen Auftreten der Demenz am markantesten ausgeprägt.

     

A panel of cerebrospinal fluid potential biomarkers for the diagnosis of Alzheimer's disease

The diagnosis of Alzheimer's disease (AD), the most common form of dementia in the general population, usually relies upon the presence of typical clinical features and structural changes on brain magnetic resonance imaging. Over the last decade, a number of biological abnormalities have been reported in the cerebrospinal fluid (CSF) of AD patients, in particular altered levels of the tau protein and the 1-42 fragment of the amyloid precursor protein. These, however, have not yet proved sensitive and specific enough to be included in the diagnostic criteria for AD, leaving plenty of room for the search of novel biomarkers. The present study describes the analysis of CSF polypeptides by a protein-chip array technology called surface enhanced laser desorption/ionization-time of flight-mass spectrometry (SELDI-TOF-MS). Using this approach, we detected statistically significant quantitative differences (p < 0.05) regarding four overexpressed and one underexpressed polypeptides in the CSF of AD patients as compared to healthy controls. Four of them were further purified by strong anionic exchange chromatography (SAX) and identified by MS analysis as cystatin C, two beta-2-microglobulin isoforms, an unknown 7.7 kDa polypeptide, and a 4.8 kDa VGF polypeptide. The combination of the five polypeptides for the diagnosis of AD allowed to classified six AD patients out of the nine included in this study and all the ten controls, which means in this small cohort that the specificity and sensitivity are 100% and 66%, respectively. This study, based on the protein-chip array technology, demonstrates the presence in the CSF of novel potential biomarkers for AD, which may be used for the diagnosis and perhaps the assessment of the severity and progression of the disease.     

Blood markers of oxidative stress in Alzheimer's disease

Alzheimer's disease (AD) represents a highly common form of dementia, but can be diagnosed in the earlier stages before dementia onset. Early diagnosis is crucial for successful therapeutic intervention. The introduction of new diagnostic biomarkers for AD is aimed at detecting underlying brain pathology. These biomarkers reflect structural or biochemical changes related to AD. Examination of cerebrospinal fluid has many drawbacks; therefore, the search for sensitive and specific blood markers is ongoing. Investigation is mainly focused on upstream processes, among which oxidative stress in the brain is of particular interest. Products of oxidative stress may diffuse into the blood and evaluating them can contribute to diagnosis of AD. However, results of blood oxidative stress markers are not consistent among various studies, as documented in this review. To find a specific biochemical marker for AD, we should concentrate on specific metabolic products formed in the brain. Specific fluorescent intermediates of brain lipid peroxidation may represent such candidates as the composition of brain phospholipids is unique. They are small lipophilic molecules and can diffuse into the blood stream, where they can then be detected. We propose that these fluorescent products are potential candidates for blood biomarkers of AD.