Reduction in asymmetrical dimethylarginine, an endogenous nitric oxide synthase inhibitor, in the cerebrospinal fluid during aging and in patients with Alzheimer's disease

To investigate the significance of nitric oxide (NO) -mediated neuron death in aging and Alzheimer's disease (AD), the concentration of asymmetrical dimethylarginine (ADMA), an endogenous NO synthase inhibitor, in the cerebrospinal fluid was determined in neurologically normal controls and patients with AD. The ADMA concentration significantly decreased with age, whereas the arginine concentration was unaltered. In patients with AD, the ADMA concentration was significantly decreased, compared with controls of a similar age (-48%, P=0.0001), and it significantly decreased with decreasing cognitive functions (r(s)=0.58, P<0.05), whereas the arginine concentration did not change. These findings suggest that ADMA may play an important role in regulating NO synthesis in brain aging and AD.     

Increased tau in the cerebrospinal fluid of patients with frontotemporal dementia and Alzheimer's disease

Cerebrospinal fluid (CSF) concentrations of tau protein were measured using an enzyme-linked immunosorbent assay which measures both normal and hyperphosphorylated tau. Levels of CSF tau were measured in 17 patients with Alzheimer's disease and 23 patients with frontotemporal dementia, and were compared to age-matched healthy controls. The CSF tau concentration in control subjects was 198+/-49 pg/ml and no relationship was found between age and CSF tau concentrations in these subjects. CSF tau concentrations were significantly raised in patients with both Alzheimer's disease and frontotemporal dementia when compared to healthy controls (802+/-381 pg/ml, P<0.001; 612+/-382 pg/ml, P<0.05, respectively). In neither disease did CSF tau correlate with disease severity as assessed by the Mini Mental State Examination score (MMSE). This study shows that CSF tau is significantly raised in patients with frontotemporal dementia.     

Alterations of visual search strategy in Alzheimer's disease and aging

Visual search, characterized by eye fixation patterns, was examined in 8 patients with Alzheimer's disease (AD), 8 cognitively intact, age-matched individuals, and 8 young control participants as they searched for a number among a nonlinear array of letters on a large computer screen. Among the 3 groups, target detection accuracy differed and detection time increased linearly. There were more fixations, and fixation duration was significantly longer in the AD patients than in the other 2 groups. These factors contributed to the lengthening of target detection time. This qualitative difference in the architecture of visual search between AD and aging may reflect a specific deficit in the disengagement of visual spatial attention, a prolongation of saccade initiation, or inefficiency in planning a search strategy.     

Increased protein glycation in cerebrospinal fluid of Alzheimer's disease

Accumulation of advanced glycation end products occurs in the brain with ageing and was proposed to be involved in pathogenesis of Alzheimer's disease. We studied changes in the level of an early glycation product, an Amadori product, in cerebrospinal fluid (CSF) in ageing and in late-onset Alzheimer's disease. The work was carried out on 99 consecutive patients. The concentration of Amadori product in CSF correlated with CSF glucose concentration but was not changed with age (n = 70). In contrast, level of CSF Amadori product was 1.7-fold higher in Alzheimer's disease patients (n = 29) as compared with non-demented age-matched control group (n = 20; P < 0.0005), although CSF glucose concentration was similar in both groups (4.1 +/- 1.3 vs. 3.8 +/- 0.6 mmol/liter, resp.). An increased accumulation of Amadori products was found in all major proteins of CSF of Alzheimer's disease including albumin, apolipoprotein E and transthyretin. We propose that the increased early glycation of CSF proteins in the Alzheimer's patients may stimulate the formation and the consequent deposition of advanced glycation end products as well as oxidative stress in the brain.     

Elevated cerebrospinal fluid sphingomyelin levels in prodromal Alzheimer's disease

Alzheimer's disease (AD) is the most common neurodegenerative disorder, but still without known disease mechanism, proper treatment and efficient diagnostic tools for an early stage diagnosis. There is increasing evidence that lipids, especially cholesterol and sphingolipids, may play a role in pathological processes that occur in the AD brain even in very early stages of the disease. However, lipid changes in cerebrospinal fluid (CSF) of individuals with AD have not been well studied. In previous work, we developed a reproducible and sensitive nano-HPLC-MS method for CSF phospholipids screening and conducted a pilot study to find potential phospholipid changes in CSF from individuals with AD dementia. We observed a slight increase (24%) of sphingomyelin (SM) in CSF samples from patients with probable AD compared to non-demented controls. The goal of this work was to validate our findings and to analyze how SM CSF levels change in different stages of AD from prodromal to mild and moderate AD. We found significantly increased SM levels (50.4±11.2%, p=0.003) in the CSF from individuals with prodromal AD compared to cognitively normal controls, but no change in CSF SM levels between mild and moderate AD groups and cognitively normal controls. These results suggest that alterations in the SM metabolism may contribute to early pathological processes leading to AD.     

Aging and Alzheimer's disease: protease inhibitors in cerebrospinal fluid

Recent advances suggested that proteases and their inhibitors could be implicated in the genesis and/or maturation of insoluble deposits associated with Alzheimer's disease (AD). This study was designed to measure the level of alpha 1-antichymotrypsin (ACT) and alpha 1-antitrypsin (AT) in cerebrospinal fluid (CSF) of patients with AD and nondemented humans at various ages. Our analysis failed to demonstrate a significant relationship between inhibitor content and disease. However, a positive correlation was observed between age and the ACT level for the normal control group. Such observation suggests a specific association of ACT with the mechanisms of brain aging.     

Alterations of Ca-responsive proteins within cholinergic neurons in aging and Alzheimer's disease

The molecular basis of selective neuronal vulnerability in Alzheimer's disease (AD) remains poorly understood. Using basal forebrain cholinergic neurons (BFCNs) as a model and immunohistochemistry, we have demonstrated significant age-related loss of the calcium-binding protein calbindin-D_28K (CB) from BFCN, which was associated with tangle formation and degeneration in AD. Here, we determined alterations in RNA and protein for CB and the Ca²⁺-responsive proteins Ca²⁺/calmodulin-dependent protein kinase I (CaMKI), growth-associated protein-43 (GAP43), and calpain in the BF. We observed progressive downregulation of CB and CaMKI RNA in laser-captured BFCN in the normal-aged-AD continuum. We also detected progressive loss of CB, CaMKIδ, and GAP43 proteins in BF homogenates in aging and AD. Activated μ-calpain, a calcium-sensitive protease that degrades CaMKI and GAP43, was significantly increased in the normal aged BF and was 10 times higher in AD BF. Overactivation of μ-calpain was confirmed using proteolytic fragments of its substrate spectrin. Substantial age- and AD-related alterations in Ca²⁺-sensing proteins most likely contribute to selective vulnerability of BFCN to degeneration in AD.     

Increased bilirubins and their derivatives in cerebrospinal fluid in Alzheimer's disease

Bilirubin, an efficient antioxidant, is the end product of the heme cleavage pathway, which is catalyzed by heme oxygenase (HO) and biliverdin reductase. Although an inducible form of HO is overexpressed in the Alzheimer's disease (AD) brain, it has not been determined whether bilirubin metabolism is actually activated or not. In this study, we measured CSF-bilirubins and their derivatives using an enzyme-linked immunosorbent assay with two kinds of anti-bilirubin monoclonal antibodies, designated 24G7 and 5M2. In AD patients, the levels of CSF bilirubin derivatives increased significantly compared with those of controls. This increase was not due to the increased permeability of the blood-brain barrier, because the levels of unconjugated bilirubin were not different between AD and controls. These data may reflect the increase of degraded bilirubin metabolites in the AD brain derived from the scavenging reaction against chronic oxidative stress.     

Ex vivo lumbar and post mortem ventricular cerebrospinal fluid substance P-immunoreactivity in Alzheimer's disease patients

The concentration of substance P-immunoreactivity (SPIR) in ex vivo lumbar cerebrospinal fluid (CSF) of patients with probable Alzheimer's disease (AD), non-Alzheimer dementias, neurological patients without dementia and control subjects was determined using a sensitive and specific competitive enzyme-immunoassay. There were no significant differences between AD patients and the other groups, but patients with late onset AD (>65 years) showed significantly higher levels of SPIR than patients with early onset (<65 years) and controls. In post mortem ventricular fluid, SPIR levels of all groups were lower compared with the lumbar compartment, but without significant group differences. It is concluded that CSF SPIR may not serve as a diagnostic marker for AD, but possibly could reflect immunological or neuroprotective processes modulated by substance P in late onset AD patients.     

Levels of alpha- and beta-secretase cleaved amyloid precursor protein in the cerebrospinal fluid of Alzheimer's disease patients

A- and D-type K+ channels (KA and KD channels) have unique physiological properties that play important roles in the integration of excitatory post synaptic potentials (EPSPs) in neuronal dendrites. These functions were analyzed using a computer program, NEURON, to simulate high-frequency sequential synaptic inputs, that can induce long-term potentiation (LTP). We paid close attention to the stability of the reduction of sequential EPSPs. When either KA or KD channels were included in models, the EPSP reduction ratios were less stable than containing both KA and KD channels. When both KA and KD channels were present in the model, the variance of EPSP reduction ratios was significantly smaller in comparison with that in the presence of either KA or KD channels alone. We thus concluded that the co-existence of KA and KD channels is necessary to produce stable EPSPs during the high-frequency synaptic stimulation necessary for induction of LTP.     

Abnormal proteins in the cerebrospinal fluid of patients with Creutzfeldt-Jakob disease

We studied more than 300 cerebrospinal fluid proteins from 21 patients with Creutzfeldt-Jakob disease. We also examined cerebrospinal fluid from 100 normal controls and more than 400 patients with various neurologic disorders other than Creutzfeldt-Jakob disease. Four abnormal proteins that were identified in the patients with Creutzfeldt-Jakob disease were absent in the normal persons. Two of these proteins (Mr [relative molecular mass], 40,000; pl [isoelectric point], 5.7 and Mr 40,000; pl 5.9) were also present in some patients with multiple sclerosis, herpes simplex encephalitis, schizophrenia, Parkinson's disease, or Guillain-Barré or Beh?et's syndrome. Two proteins (Mr 26,000; pl 5.2 and Mr 29,000; pl 5.1) were present in all patients with Creutzfeldt-Jakob disease and in 5 of 10 patients with herpes simplex encephalitis, but in none of the other control groups. A subsequent blinded study of these cerebrospinal fluid proteins from patients with Creutzfeldt-Jakob disease, Alzheimer's disease, Huntington's disease, multi-infarct dementia, parkinsonism dementia of Guam, or the specific dementia of the acquired immunodeficiency syndrome resulted in the ability to distinguish all cases of Creutzfeldt-Jakob disease from the other types of dementia. Although the identity and origin of the abnormal spinal fluid proteins are not yet known, these preliminary results suggest that their presence may help in the diagnosis of Creutzfeldt-Jakob disease.     

Reduced cerebrospinal fluid estradiol levels are associated with increased beta-amyloid levels in female patients with Alzheimer's disease.

Recent in-vitro studies indicate that estrogens such as 17beta-estradiol (E2) may decrease the production of beta-amyloid 1-42 (Abeta42), a peptide central for the formation of senile plaques in Alzheimer's disease (AD). To test this hypothesis in a clinical study, cerebrospinal fluid levels of E2 were compared between 30 female AD patients and 11 female patients with non-dementing diseases such as major depression and investigated with respect to beta-amyloid 1-40 and Abeta42 levels. E2 levels were significantly (P<0.05) lower in the AD group than in controls; within the AD group E2 levels were inversely correlated with Abeta42 concentrations (r=-0.36, P=0.05). This is the first clinical study providing evidence for an influence of E2 on Abeta42 metabolism in vivo. This observation corresponds to the putative beneficial effects of estrogen replacement therapy on the development and course of AD.     

Complement 3 and factor h in human cerebrospinal fluid in Parkinson's disease, Alzheimer's disease, and multiple-system atrophy

Complement activation, a key component of neuroinflammation, has been reported in both Parkinson's disease (PD) and Alzheimer's disease (AD). However, it is unclear whether complement activation and neuroinflammation in general are distinctly different from each another in major neurodegenerative disorders. In the present study, cerebrospinal fluid complement 3 (C3) and factor H (FH) were measured and evaluated together with amyloid-β(42) (Aβ(42)), which in recent investigations was decreased in patients with PD, in particular those with cognitive impairment. The study included 345 participants: 126 patients with PD at various stages with or without cognitive impairment, 50 with AD, and 32 with multiple-system atrophy, and 137 healthy control individuals. In addition to changes in Aβ(42) concentrations, there were clear differences in the patterns of complement profiles among neurodegenerative disorders. The C3/FH ratio demonstrated high sensitivity and specificity in differentiating patients with multiple-system atrophy from those with AD or PD and control individuals. In addition, the C3/Aβ(42) and FH/Aβ(42) ratios not only correlated with PD severity approximated using the Unified Parkinson's Disease Rating Scale but also with the presence of cognitive impairment or dementia in PD. Both C3 and FH correlated with the severity of impairment in AD as indicated using Mini-Mental State Examination scores.     

Tau phosphorylation pathway genes and cerebrospinal fluid tau levels in Alzheimer's disease

Alzheimer's disease (AD) is characterized by the presence in the brain of amyloid plaques, consisting predominately of the amyloid β peptide (Aβ), and neurofibrillary tangles, consisting primarily of tau. Hyper-phosphorylated-tau (p-tau) contributes to neuronal damage, and both p-tau and total-tau (t-tau) levels are elevated in AD cerebrospinal fluid (CSF) compared to cognitively normal controls. Our hypothesis was that increased ratios of CSF phosphorylated-tau levels relative to total-tau levels correlate with regulatory region genetic variation of kinase or phosphatase genes biologically associated with the phosphorylation status of tau. Eighteen SNPs located within 5' and 3' regions of 5 kinase and 4 phosphatase genes, as well as two SNPs within regulatory regions of the MAPT gene were chosen for this analysis. The study sample consisted of 101 AD patients and 169 cognitively normal controls. Rs7768046 in the FYN kinase gene and rs913275 in the PPP2R4 phosphatase gene were both associated with CSF p-tau and t-tau levels in AD. These SNPs were also differentially associated with either CSF t-tau (rs7768046) or CSF p-tau (rs913275) relative to t-tau levels in AD compared to controls. These results suggest that rs7768046 and rs913275 both influence CSF tau levels in an AD-associated manner. ? 2012 Wiley Periodicals, Inc.     

Increased cerebrospinal fluid levels of transforming growth factor-beta1 in Alzheimer's disease

Accumulation of beta-amyloid (Abeta) in senile plaques in specific brain regions is a key event in the development of Alzheimer's disease (AD). Expression of transforming growth factor-beta1 (TGF-beta1), a regulator of brain responses to inflammation and injury, has been correlated with Abeta accumulation, aggregation and clearance in transgenic mice and increased production of amyloid precursor protein (APP) followed by Abeta generation in murine and human astrocyte cultures. Here, we compared TGF-beta1 levels in cerebrospinal fluid (CSF) from 20 AD patients and 20 healthy controls and correlated TGF-beta1 to intrathecal levels of the amyloidogenic 42-amino acid fragment of Abeta (Abeta42). AD patients had higher concentration of TGF-beta1 than controls (P = 0.002). Moreover, TGF-beta1 levels were negatively correlated to Abeta42 levels in the whole material (cases and controls, r = -0.35; P = 0.020), although this correlation failed to reach significance in the AD group alone (r = -0.38; P = 0.099). Taken together, the data indicate that TGF-beta1 plays a role in the processes that affect amyloid metabolism in AD.     

MicroRNAs in Alzheimer's disease: differential expression in hippocampus and cell-free cerebrospinal fluid

MicroRNAs (miRNAs) are small, noncoding RNAs that function in complex networks to regulate protein expression. In the brain, they are involved in development and synaptic plasticity. In this study, we aimed to identify miRNAs with a differential expression in either hippocampus or cerebrospinal fluid (CSF) from Alzheimer's disease (AD) patients and age-matched nondemented control subjects using quantitative polymerase chain reaction. In hippocampus, we also differentiated between AD patients with an intermediate stage, according to Braak III/IV stage, and a late stage, characterized according to Braak VI stage. Eight selected miRNAs were analyzed in hippocampus, and the expression of miR-16, miR-34c, miR-107, miR-128a, and miR-146a were differentially regulated. In CSF, out of 8 selected miRNAs only miR-16 and miR-146a could be reliably detected. In addition, we identified an effect of blood contamination on the CSF levels of miR-16, miR-24, and miR-146a. For group comparisons, we therefore selected CSF samples absent of, or containing only low numbers of blood cells. Levels of miR-146a were significantly decreased in CSF of AD patients. In conclusion, the abnormal expression of several miRNAs in hippocampus of intermediate- and late-stage AD patients suggests their involvement in AD pathogenesis, and low levels of miR-146a in CSF were associated with AD.     

The effect of increased concentrations of homocysteine on the concentration of (E)-4-hydroxy-2-nonenal in the plasma and cerebrospinal fluid of patients with Alzheimer's disease

There is evidence that increased blood concentrations of homocysteine may be a risk factor for Alzheimer's disease. (E)-4-hydroxy-2-nonenal (HNE) is a neurotoxic product of lipid peroxidation that is increased in the ventricular fluid and brains of patients with Alzheimer's disease. We measured the concentrations of homocysteine, HNE, vitamin B(12) and folate in the plasma of 27 patients with Alzheimer's disease and 25 control subjects. There was a statistically significant increase in the plasma concentration of homocysteine (P < 0.001) and HNE (P < 0.001) in the Alzheimer's disease patients compared to the control group. There was a significant decrease in the plasma concentration of vitamin B(12) (P < 0.001) and folate (P = 0.002) in the Alzheimer's group compared to the controls. There was a significant positive correlation between the plasma concentrations of homocysteine and HNE in the patients with Alzheimer's disease (r = 0.661, P < 0.001). A significant negative correlation was found between the plasma concentration of homocysteine and the plasma concentrations of vitamin B(12) (r = -0.605, P = 0.0006) and folate (r = 0.586, P = 0.001). We also measured the concentrations of homocysteine, HNE, vitamin B(12) and folate in the cerebrospinal fluid (CSF) of 8 patients with Alzheimer's disease compared to 6 control subjects. The concentrations of homocysteine (P = 0.032) and HNE (P = 0.001) were significantly higher in the CSF of Alzheimer's patients than in the control subjects. There were significant positive correlations between the CSF concentrations of homocysteine and HNE (r = 0.924, P = 0.001). There was also a significant positive correlation between the plasma concentration of homocysteine and the CSF concentrations of homocysteine (r = 0.850, P = 0.007) and HNE (r = 0.092, P = 0.002). These results demonstrate that there is a relationship between increased homocysteine concentrations and increased HNE concentrations in Alzheimer's disease.     

White matter integrity is associated with cerebrospinal fluid markers of Alzheimer's disease in normal adults

We explored whether white matter (WM) integrity in cognitively normal (CN) older adults is associated with cerebrospinal fluid (CSF) markers of Alzheimer's disease pathology. Twenty CN older adults underwent lumbar puncture and magnetic resonance imaging within a few days of each other. Analysis of diffusion tensor imaging data involved a priori region of interest and voxelwise approaches. The region of interest results revealed a positive correlation between CSF measures of amyloid-beta (Aβ₄₂ and Aβ₄₂/p-Tau₁₈₁) and WM integrity in the fornix, a relationship which persisted after controlling for hippocampal volume and fornix volume. Lower WM integrity in the same portion of the fornix was also associated with reduced performance on the Digit Symbol test. Subsequent exploratory voxelwise analyses indicated a positive correlation between CSF Aβ₄₂/p-Tau₁₈₁ and WM integrity in bilateral portions of the fornix, superior longitudinal fasciculus, inferior fronto-occipital fasciculus, and in the corpus callosum and left inferior longitudinal fasciculus. Our results link lower WM microstructural integrity in CN older adults with CSF biomarkers of Alzheimer's disease and suggest that this association in the fornix may be independent of volumetric measures.     

Distinctive alterations of the cingulum bundle during aging and Alzheimer's disease

Brain imaging studies have revealed frontal disruption during aging and parieto-temporal disruption during Alzheimer's disease (AD). The present study aims at developing a specific method based on precise anatomical landmarks for assessing the integrity all along the course of the cingulum bundle, so as to determine if it presents the classical aging and AD dissociation. Five regions of interest (ROIs) were placed on fractional anisotropy (FA) maps all along the cingulum in 15 young (Gyoung), 15 70-year-old (Gold), and 15 AD subjects (Galz). An age-related decrease of FA occurred in the anterior part of the bundle. Moreover, a specific alteration of the supero-posterior region of the cingulum during AD was observed since mean FA values as well as mean number of fibers were significantly decreased in Galz compared to Gold and Gyoung. This multiple ROIs placement allows for revealing distinctive alterations of the cingulum bundle during aging and AD, which could constitute the anatomical basis for the distinctive functional disconnection recently described in the literature using functional connectivity at rest.