CSF tau is related to apolipoprotein E genotype in early Alzheimer's disease

Amyloid β-Peptide Effects on Glucose Regulation Are Dependent on Apolipoprotein E Genotype

The apolipoprotein E gene (APOE) confers the greatest genetic risk factor for Alzheimer's disease (AD), wherein the ε4 allele confers an elevated risk compared with the ε3 allele. Biological mechanisms that differ across these alleles have been explored in mouse models wherein the murine Apoe gene has undergone targeted replacement with sequences encoding human ApoE3 or ApoE4 (ApoE-TR mice). Such models have indicated that the two variants of ApoE produce differential effects on energy metabolism, including metabolic syndrome. However, glucose regulation has not been compared in ApoE-TR mice with and without amyloid β-peptide (Aβ) accumulation. We crossed ApoE3-TR and ApoE4-TR mice with a transgenic line that accumulates human Aβ1-42 In male ApoE3-TR mice, introduction of Aβ caused aberrations in glucose tolerance and in membrane translocation of astrocytic glucose transporter 1 (GLUT1). Phosphorylation of Tau at AD-relevant sites was correlated with glucose intolerance. These effects appeared independent of insulin dysregulation and were not observed in females. In ApoE4-TR mice, the addition of Aβ had no significant effects because of a trend toward perturbation of the baseline values.

Genetic Burden for Late-Life Neurodegenerative Disease and Its Association With Early-Life Lipids, Brain, Behavior, and Cognition

BACKGROUND

Genetics play a significant role in the etiology of late-life neurodegenerative diseases like Alzheimer's disease, Parkinson's disease, and frontotemporal dementia. Part of the individual differences in risk for these diseases can be traced back decades before the onset of disease symptoms. Previous studies have shown evidence for plausible links of apolipoprotein E (APOE), the most important genetic marker for Alzheimer's disease, with early-life cognition and neuroimaging markers. We aimed to assess whether genome-wide genetic burden for the aforementioned neurodegenerative diseases plays a role in early-life processes.

METHODS

We studied children from the Generation R Study, a prospective birth cohort. APOE genotypes and polygenic genetic burdens for Alzheimer's disease, Parkinson's disease, and frontotemporal dementia were obtained through genome-wide genotyping. Non-verbal intelligence was assessed through cognitive tests at the research center around the age of 6 years, and educational attainment through a national school performance test around the age of 11 years. The Child Behavior Checklist was administered around the age of 10 years, and data from the anxious/depressed, withdrawn/depressed, and the internalizing behavior problems scales were used. Children participated in a neuroimaging study when they were 10 years old, in which structural brain metrics were obtained. Lipid serum profiles, which may be influenced by APOE genotype, were assessed from venal blood obtained around the age of 6 years. The sample size per analysis varied between 1,641 and 3,650 children due to completeness of data.

RESULTS

We did not find evidence that APOE genotype or the polygenic scores impact on childhood nonverbal intelligence, educational attainment, internalizing behavior, and global brain structural measures including total brain volume and whole brain fractional anisotropy (all p > 0.05). Carriership of the APOE ε2 allele was associated with lower and APOE ε4 with higher low-density lipoprotein cholesterol concentrations when compared to APOE ε3/ε3 carriers.

CONCLUSION

We found no evidence that genetic burden for late-life neurodegenerative diseases associates with early-life cognition, internalizing behavior, or global brain structure.

CSF tau is associated with impaired cortical plasticity, cognitive decline and astrocyte survival only in APOE4-positive Alzheimer's disease

In Alzheimer’s disease (AD) patients, apopoliprotein (APOE) polymorphism is the main genetic factor associated with more aggressive clinical course. However, the interaction between cerebrospinal fluid (CSF) tau protein levels and APOE genotype has been scarcely investigated. A possible key mechanism invokes the dysfunction of synaptic plasticity. We investigated how CSF tau interacts with APOE genotype in AD patients. We firstly explored whether CSF tau levels and APOE genotype influence disease progression and long-term potentiation (LTP)-like cortical plasticity as measured by transcranial magnetic stimulation (TMS) in AD patients. Then, we incubated normal human astrocytes (NHAs) with CSF collected from sub-groups of AD patients to determine whether APOE genotype and CSF biomarkers influence astrocytes survival. LTP-like cortical plasticity differed between AD patients with apolipoprotein E4 (APOE4) and apolipoprotein E3 (APOE3) genotype. Higher CSF tau levels were associated with more impaired LTP-like cortical plasticity and faster disease progression in AD patients with APOE4 but not APOE3 genotype. Apoptotic activity was higher when cells were incubated with CSF from AD patients with APOE4 and high tau levels. CSF tau is detrimental on cortical plasticity, disease progression and astrocyte survival only when associated with APOE4 genotype. This is relevant for new therapeutic approaches targeting tau.

Cerebrospinal fluid biomarkers for Alzheimer's disease in Down syndrome

Down syndrome (DS), present in nearly six million people, is associated with an extremely high risk to develop Alzheimer's disease (AD). Amyloid-β and tau pathology are omnipresent from age 40 years onward, but clinical symptoms do not appear in all DS individuals. Dementia diagnostics is complex in this population, illustrating the great need for predictive biomarkers. Although blood biomarkers have not yet proven useful, cerebrospinal fluid (CSF) biomarkers (low amyloid-β42, high t-tau, and high p-tau) effectively contribute to AD diagnoses in the general population and are increasingly used in clinical practice. Surprisingly, CSF biomarkers have been barely evaluated in DS. Breaking the taboo on CSF analyses would finally allow for the elucidation of its utility in (differential) diagnoses and staging of disease severity. A sensitive and specific biomarker profile for AD in DS would be of paramount importance to daily care, adaptive caregiving, and specific therapeutic interventions.

Combined plasma biomarkers for diagnosing mild cognition impairment and Alzheimer's disease

A highly sensitive immunoassay, the immunomagnetic reduction, is used to measure several biomarkers for plasma that is related to Alzheimer's disease (AD). These biomarkers include Aβ-40, Aβ-42, and tau proteins. The samples are composed of four groups: healthy controls (n=66), mild cognitive impairment (MCI, n=22), very mild dementia (n=23), and mild-to-serve dementia, all due to AD (n=22). It is found that the concentrations of both Aβ-42 and tau protein for the healthy controls are significantly lower than those of all of the other groups. The sensitivity and the specificity of plasma Aβ-42 and tau protein in differentiating MCI from AD are all around 0.9 (0.88-0.97). However, neither plasma Aβ-42 nor tau-protein concentration is an adequate parameter to distinguish MCI from AD. A parameter is proposed, which is the product of plasma Aβ-42 and tau-protein levels, to differentiate MCI from AD. The sensitivity and specificity are found to be 0.80 and 0.82, respectively. It is concluded that the use of combined plasma biomarkers not only allows the differentiation of the healthy controls and patients with AD in both the prodromal phase and the dementia phase, but it also allows AD in the prodromal phase to be distinguished from that in the dementia phase.

Fluid biomarkers for diagnosing dementia: rationale and the Canadian Consensus on Diagnosis and Treatment of Dementia recommendations for Canadian physicians

Fluid biomarkers improve the diagnostic accuracy in dementia and provide an objective measure potentially useful as a therapeutic response in clinical trials. The role of fluid biomarkers in patient care is a rapidly evolving field. Here, we provide a review and recommendations regarding the use of fluid biomarkers in clinical practice as discussed at the Fourth Canadian Consensus Conference on the Diagnosis and Treatment of Dementia (CCCDTD4) convened in Montreal, 4 to 5 May 2012. At present, there is no consensus regarding the optimal methodology for conducting quantification of plasma amyloid-beta (Aβ) peptides. In addition, since there is insufficient evidence supporting clinical applications for plasma Aβ-peptide measures, the CCCDTD4 does not recommended plasma biomarkers either for primary care or for specialists. Evidence for CSF Aβ1-42, total tau and phosphorylated tau in the diagnosis of Alzheimer pathology is much stronger, and can be considered at the tertiary care level for selected cases to improve diagnostic certainty, particularly in those cases presenting atypical clinical features.

Age and apolipoprotein E ε4 effects on neural correlates of odor memory

Alzheimer's disease (AD) affects 5.4 million Americans. Evidence suggests that individuals who are positive for the apolipoprotein E (ApoE) ε4 allele are at higher risk for developing the disease. Studies have also shown that the ε4 allele is linked to olfactory decline. Olfactory functioning may be investigated using olfactory event-related potentials (OERPs). The high temporal resolution of OERPs enables an understanding of the neural correlates of olfactory processing and functioning. This study investigated the effects of age, ApoE ε4 status, response type, and electrode site on OERP latency and amplitude during encoding and retrieval in an odor recognition memory task. The 60 participants were equally divided into 3 age groups matched on ε4 status: younger, middle, and older. Odors were presented using a computer-controlled olfactometer. Participants were notified during encoding that this was a task of odor memory. Results indicated differences in OERP activity as a function of age, ApoE ε4 status, response type, and electrode site. These findings highlight the potential of OERPs to distinguish ε4- and ε4+ individuals and to contribute to an earlier diagnosis of AD.

Cerebrospinal fluid biomarkers of Alzheimer's disease in healthy elderly

Numerous studies have shown that Alzheimer's Disease (AD) pathology begins before the onset of clinical symptoms. Because therapies are likely to be more effective if they are implemented early in the disease progression, it is necessary to identify reliable biomarkers to detect AD pathology in the early stages of the disease, ideally in presymptomatic individuals. Recent research has identified three candidate cerebrospinal fluid (CSF) biomarkers that reflect AD pathology: amyloid beta, total tau protein (t-tau), and tau protein phosphorylated at AD-specific epitopes (p-tau). They are useful in supporting the AD diagnosis and have predictive value for AD when patients are in the stage of mild cognitive impairment (MCI). However, their predictive utility in cognitively healthy subjects is still being evaluated. We conducted a review of studies published between 1993 and 2011 and summarized their findings on the role of CSF biomarkers for AD in healthy elderly.

CSF tau and β-amyloid as biomarkers for mild cognitive impairment

Early diagnosis of Alzheimer s disease (AD) is relevant in order to initiate symptomatic treatment with antidementia drugs. This will be of greater significance if the drugs aimed at slowing down the degenerative process (secondary prevention) prove to affect AD pathology and are clinically effective, such as γ-secretase inhibitors. However, there is currently no clinical assessment to differentiate the patients with mild cognitive impairment (MCI) who will progress to AD from those with a benign form of memory impairment that is part of the normal aging process. Thus, there is great clinical need for diagnostic and predictive biomarkers, as well as biomarkers for classification purposes, to identify incipient AD in MCI subjects. The most promising cerebrospinal fluid (CSF) biomarker candidates are total tau protein (T-tau), phosphorylated tau protein (P-tau), and the 42-andno acid form offi-amyloid (Aβ42), which may, if used in the right clinical context, prove to have sufficient diagnostic accuracy and predictive power to resolve this diagnostic challenge.

Diagnostic Utility of CSF Tau and Aβ(42) in Dementia: A Meta-Analysis

CSF tau and Aβ42 are considered as important markers to diagnose Alzheimer's disease in early stages. Hence, it is important to assess their status in different types of dementia. The main objective of this study was to assess whether these CSF biomarkers can be used to make the differential diagnosis of AD. In the present study, articles published from 1998 till 2009 were taken and meta-analysis was performed to clarify the consistency in trends of biomarkers- CSF tau and Aβ₄₂ in AD and other dementias and whether the same can be used as diagnostic biomarkers for its early diagnosis. 11 out of 60 for CSF tau and 07 out of 40 for CSF Aβ₄₂, dementia case-control studies were selected for final analysis. Descriptive statistics shows that median effect size (raw mean difference) of CSF tau was 429 pg/mL (range: 32 to 910 pg/mL) in AD whereas in Dementia due to other causes (DOC) studies it was 69 pg/mL (range: −53 to 518 pg/mL). Similarly the median effect size of CSF Aβ₄₂ levels was −442 pg/mL (range: −652 to −41.200 pg/mL) whereas in DOC studies it was −193 pg/mL (range: −356 to −33 pg/mL).

Tau as a biomarker of neurodegenerative diseases

The microtubule-associated protein Tau is mainly expressed in neurons of the CNS and is crucial in axonal maintenance and axonal transport. The rationale for Tau as a biomarker of neurodegenerative diseases is that it is a major component of abnormal intraneuronal aggregates observed in numerous tauopathies, including Alzheimer's disease. The molecular diversity of Tau is very useful when analyzing it in the brain or in the peripheral fluids. Immunohistochemical and biochemical characterization of Tau aggregates in the brain allows the postmortem classification and differential diagnosis of tauopathies. As peripheral biomarkers of Alzheimer's disease in the cerebrospinal fluid, Tau proteins are now validated for diagnosis and predictive purposes. For the future, the detailed characterization of Tau in the brain and in peripheral fluids will lead to novel promising biomarkers for differential diagnosis of dementia and monitoring of therapeutics.

Cortical thickness is associated with different apolipoprotein E genotypes in healthy elderly adults

Previous studies have consistently suggested that the varepsilon4 allele of apolipoprotein E (APOE) gene is a major risk factor for Alzheimer's disease (AD). However, whether the varepsilon2 allele, a possible protective factor for AD, will express its protective effect in terms of cortical thickness in healthy elderly carriers is unclear. The goal of this study is to clarify the effects of APOE genotypes on cortical thickness in nondemented elderly subjects. We used 164 healthy, cognitively normal, elderly subjects, who were grouped into varepsilon2 carriers, varepsilon3 homozygotes, and varepsilon4 carriers respectively. The APOE varepsilon2 carriers had a significant thicker (corrected p<0.05) cortical thickness in the superior temporal cortex compared with the varepsilon3 homozygotes. In addition to this area, the APOE varepsilon2 carriers had a significantly thicker region in the dorsolateral prefrontal cortex (corrected p<0.05) than did the varepsilon4 carriers. These findings suggest that the different alleles of the APOE gene have distinct neuroanatomic effects in elderly healthy subjects and may play specific roles in the development of AD.

Olfaction in aging and Alzheimer's disease: event-related potentials to a cross-modal odor-recognition memory task discriminate ApoE epsilon4+ and ApoE epsilon 4- individuals

Alzheimer's disease (AD) is a devastating neurodegenerative condition that affects more than 5 million Americans. Currently, a definitive and unequivocal diagnosis of AD can only be confirmed histopathogically via postmortem autopsy, demonstrating the need for objective measures of cognitive functioning for those at risk for AD. The single most important genetic risk factor of AD is the apolipoprotein E (ApoE) epsilon4 allele. The present study investigated olfactory and cognitive processing deficits in ApoE epsilon4(+) individuals using a cross-modal recognition memory task and an objective electrophysiological measure, the event-related potential (ERP). Ten epsilon4(+) individuals (5 M, 5 F, mean [M]= 75.1 years) and 10 age- and gender-matched epsilon4(-) individuals (5 M, 5 F, M = 71 years) sequentially encoded a set of 16 olfactory stimuli and were subsequently shown names of odors previously presented (targets) or not (foils). EEG activity was recorded from 19 electrodes as participants distinguished targets from foils using a two-button mouse. P3 latencies were significantly longer in epsilon4(+) individuals, and intraclass correlations demonstrated differential activity between the two groups. These findings are consistent with a compensatory hypothesis, which posits that nondemented epsilon4(+) individuals will expend greater effort in cognitive processing or engage in alternative strategies and therefore require greater activation of neural tissue or recruitment of different neural populations. The findings also suggest that cross-modal ERP studies of recognition memory discriminate early neurocognitive changes in ApoE epsilon4(+) and ApoE epsilon4(-) individuals and may contribute to identifying the phenotype of persons who will develop Alzheimer's disease.

Synergistic effect of apolipoprotein E epsilon4 and butyrylcholinesterase K-variant on progression from mild cognitive impairment to Alzheimer's disease

OBJECTIVE

To evaluate the synergistic effects of the apolipoprotein E (APOE) epsilon4 and butyrylcholinesterase K-variant (BCHE-K) alleles on progression to Alzheimer's disease (AD) in individuals with mild cognitive impairment (MCI).

METHODS

This was a post-hoc exploratory analysis from a 3-4-year, randomized, placebo-controlled study of rivastigmine in participants with MCI (InDDEx study). Participants who consented to genetic testing were included in the current analyses. The incidence of progression to AD, cognitive decline and changes in MRI brain volumes were investigated in participants from the placebo arm of the InDDEx study.

RESULTS

Of the 1018 participants in the overall study, 464 were successfully genotyped for both APOE and butyrylcholinesterase. Of these, 68 (14.7%) carried > or =1 APOE epsilon4 and > or =1 BCHE-K allele. The presence of APOE epsilon4 was associated with a significantly higher incidence of progression to AD whereas the presence of BCHE-K had no independent effect on progression. A synergistic effect of the combined presence of APOE epsilon4 and BCHE-K on the time to clinical diagnosis of AD and on MRI brain volumes was seen. Progression to AD and hippocampal volumetric loss was greatest in participants who carried both APOE epsilon4 and BCHE-K alleles and lowest in BCHE-K carriers without the APOE epsilon4 allele.

CONCLUSION

In MCI, the risk of cognitive decline, hippocampal volumetric loss and progression to AD seems to be the greatest in individuals who carry at least one copy of both the BCHE-K and APOE epsilon4 alleles.

CSF tau protein and FDG PET in patients with aging-associated cognitive decline and Alzheimer's disease

INTRODUCTION

In Alzheimer's disease (AD), accelerated neurofibrillary tangle formation occurs which is associated with increased tau protein release into the cerebrospinal fluid (CSF). Recent studies found significantly increased CSF tau already in patients at risk of developing AD, indicating its potential as a biochemical marker of AD. Cerebral glucose metabolism is reduced in frontotemporoparietal and cingulate cortices in patients with mild AD. However, few studies have investigated CSF tau protein and cerebral glucose metabolism changes in patients at risk to develop AD.

METHODS

48 patients with AD, 88 patients with aging-associated cognitive decline (AACD), and 39 healthy controls were included. In all participants, CSF levels of tau were determined by ELISA at baseline and compared between the diagnostic groups. 14 AACD patients and 14 controls underwent (18)F-fluorodeoxyglucose positron emission tomography (FDG PET).

RESULTS

AD patients showed the highest CSF tau levels compared with AACD patients and controls. AACD patients had significantly higher tau levels than the controls but lower than the AD patients. AACD patients were characterized by reduced glucose metabolism in bilateral middle temporal cortex, left posterior cingulate cortex, right angular gyrus, and right precuneus compared with controls.

CONCLUSION

In conclusion, our findings reflect and confirm the clinical judgment of an incipient neurodegenerative disorder in a considerable portion of AACD patients. In patients with AACD, CSF tau levels and cerebral glucose metabolism show an altered pattern comparable with that found in AD and thus may facilitate early diagnosis.

Cerebrospinal fluid tau, Aß, 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.

Cerebrospinal fluid tau and Abeta42 concentrations in healthy subjects: delineation of reference intervals and their limitations

Many limitations and conflicting results have cast serious doubts on the validity of cerebrospinal fluid tau and Abeta42 levels for the biological diagnosis of Alzheimer's disease, particularly extreme variations of the reference limits found by unrelated groups as a consequence of different reference populations used. In this study, we addressed the issue of defining reference limits for cerebrospinal fluid tau and Abeta42 in healthy adult individuals. One hundred and five neurologically intact subjects were enrolled according to strict inclusion criteria, 10 of them with autopsy confirmation of brain integrity. All cerebrospinal fluid samples were similarly and optimally processed as were the dosage methods used and the statistical analyses performed. A robust correlation with age was demonstrated for Abeta42 but not for tau. For tau, we found that an upper cut-off value of 443 ng/l allowed 95% of the subjects to be correctly classified as normal. For Abeta42, a lower cut-off value of 90 ng/l allowed a correct classification of 90% of the subjects. However, a large variance of the reference values, partly explained by the potential contamination of the reference population with presymptomatic dementia patients, may limit the use of reference limits based on living subjects. We propose that the issue of defining reference limits for both cerebrospinal fluid tau and Abeta42 may ultimately be settled by studying large numbers of autopsy-proven neurologically intact individuals only.

CSF markers for Alzheimer's disease: total tau, phospho-tau and Abeta42

Today we have the first therapeutic compounds for treatment of Alzheimer's disease (AD) e.g. acetylcholine esterase inhibitors and in the near future we may expect new compounds such as gamma- and beta-secretase inhibitors. This has demanded increased accuracy in the diagnosis of AD and thus, among other possible approaches, diagnostic markers in the cerebrospinal fluid (CSF) have become a rapidly growing research field. Especially early in the course of the disease, when correct diagnosis is most difficult, such biomarkers would be especially valuable as one might expect the compounds to have the greatest potential of being effective. Two of the defining lesions in AD brains are senile plaques and neurofibrillary tangles with beta-amyloid (Abeta) and tau proteins as the main components respectively. Abeta and tau proteins are secreted to body fluids including plasma and cerebrospinal fluid (CSF). In this paper we review CSF markers for AD, with focus on their role in the clinical diagnosis. Reduced CSF levels of the 42 amino acid form of Abeta (Abeta42) and increased CSF levels of total tau (T-tau) in AD have been found in numerous studies, with high sensitivity figures. However, the specificity against other dementias is lower. The addition of phospho-tau (P-tau) seems to increase the specificity, since normal levels are found in other dementias and in cerebrovascular disease. An increasing number of studies suggests that these CSF markers perform well enough to have a role in the clinical work-up of patients with dementia if used together. We stress that the CSF markers should be combined with the clinical information and brain-imaging techniques.

CSF markers for incipient Alzheimer's disease

Early diagnosis of Alzheimer's disease (AD) is needed to initiate symptomatic treatment with acetylcholinesterase inhibitors, and will be of even greater significance if drugs aimed at slowing down the degenerative process, such as vaccination regimes and beta-secretase and gamma-secretase inhibitors, prove to affect AD pathology and to have clinical effect. However, there is no clinical method to determine in which patients mild cognitive impairment (MCI) will progress to AD with dementia, and in which patients MCI is benign. Hence, there is a great clinical need for biomarkers to identify incipient AD in patients with MCI. The CSF biomarkers total tau protein, phosphorylated tau protein, and the 42 amino-acid residue form of amyloid-beta may, if put in the right clinical context, prove to have high enough diagnostic accuracy to meet this challenge.

Cerebrospinal fluid tau levels in Alzheimer's disease are elevated when compared with vascular dementia but do not correlate with measures of cerebral atrophy

Increased tau levels are a well-established finding in Alzheimer's disease (AD). In contrast, the potential value of tau levels in the differential diagnosis of AD, vascular dementia (VD) and major depression warrants further investigation. The potential impact of psychotropic medication also needs to be established. We investigated cerebrospinal fluid (CSF) tau protein concentrations in 88 patients with AD, 23 patients with VD, 25 patients with major depression and 17 age-paralleled controls without cognitive impairment with respect to important clinical variables, type and dosage of psychotropic medication and cerebral changes as assessed by magnetic resonance imaging (MRI). The AD patients showed significantly elevated tau levels compared with patients with VD or major depression and controls. Tau levels obtained in the VD group were intermediate, with significant differences from both AD patients and patients with major depression and controls. Within the AD group, no significant correlation between tau levels, severity of dementia, age, duration of disease, type and dosage of psychotropic medication or MRI volumetric changes arose. A subgroup of AD patients without increased tau levels was characterized by a significantly larger percentage of patients with presenile onset.

Advances in the development of biomarkers for Alzheimer's disease: from CSF total tau and Abeta(1-42) proteins to phosphorylated tau protein

Advances have been made to establish biological markers of Alzheimer's disease (AD). Measurement of total tau (t-tau) and beta-amyloid(1-42) (Abeta(1-42)) in the cerebrospinal fluid (CSF) seems useful to discriminate early and incipient AD from age-associated memory-impairment, depression, and some secondary dementias. New immunoassays to detect different phosphorylated tau epitopes (p-tau) have recently been developed. P-tau phosphorylated at threonine 231 (p-tau(231)) showed improvements compared to t-tau in the early detection of AD in subjects with mild cognitive impairment. As p-tau(231) declined during the course of AD, it may have potential to track disease progression. Additionally, p-tau(231) improved differential diagnosis between AD, frontotemporal dementia, and geriatric major depression. P-tau phosphorylated at threonine 181 improved diagnostic accuracy between AD and dementia with Lewy bodies. P-tau phosphorylated at serine 199 demonstrated high discriminative power between AD and non-Alzheimer's dementia. P-tau phosphorylated at serine 306/serine 404 improved differential diagnosis between AD and vascular dementia. A comparative study of the different p-tau epitopes is currently under way. In summary, first clinical multi-center studies suggest that measurement of phosphorylated tau proteins may significantly improve early and differential diagnosis and may come close to fulfilling proposed criteria of a biological marker for AD.

CSF markers for pathogenic processes in Alzheimer's disease: diagnostic implications and use in clinical neurochemistry

In view of current (acetylcholine esterase (AChE) inhibitors) and future (e.g. gamma-secretase inhibitors) therapeutic compounds for treatment of Alzheimer's disease (AD), the development and evaluation of cerebrospinal fluid (CSF) biomarkers for AD has become a rapidly growing research field. Diagnostic biomarkers for AD would be especially valuable as aids to diagnosis early in the course of the disease, when correct diagnosis is difficult, and when therapeutic compounds have the greatest potential for being effective. This paper reviews CSF biomarkers for AD, with emphasis on their role in the clinical diagnosis. The two most studied biochemical markers, CSF-tau and CSF-Abeta42, have high sensitivity to identify AD, but the specificity against other dementias is lower. The addition of phosphorylated tau (P-Tau) seems to increase the specificity for the diagnosis of AD, since normal levels are found in both frontotemporal and Lewy body dementia, and in cerebrovascular disease. These CSF markers may be useful as diagnostic aids, especially to discriminate early or incipient AD from age-associated memory impairment, depression, and some secondary dementias.

CSF tau protein and beta-amyloid (1-42) in Alzheimer's disease diagnosis: discrimination from normal ageing and other dementias in the Greek population

Cerebrospinal fluid (CSF) levels of tau protein and amyloid beta(1-42) peptide (Abeta42) have been suggested as possible diagnostic markers of Alzheimer's disease (AD). In order to evaluate their diagnostic potential in clinical practice, we measured tau and Abeta42 levels in the CSF of 49 AD patients, 15 patients with non-AD neurodegenerative dementias (NAND), six patients with vascular dementia (VD) and 49 elderly controls. All the subjects were of Greek origin. A marked increase in tau, a decrease in Abeta42 and a marked increase in the tau/Abeta42 ratio was noted in AD. Abeta42 alone had a specificity of 80% and a sensitivity of 82% in differentiating AD from normal ageing, whilst the corresponding values for differentiating AD from NAND or VD were 80 and 71, or 67 and 82%, respectively. Tau was better in differentiating AD, from normal ageing (specificity 96%, sensitivity 88%), NAND (specificity 93%, sensitivity 71%) and VD (specificity 83%, sensitivity 94%). The tau/Abeta42 ratio achieved values comparable or even better than tau for differentiating AD from normal ageing (specificity 86%, sensitivity 96%) and VD (specificity 83%, sensitivity 90%) and definitely better than any of the candidate markers alone, for differentiating AD from NAND (specificity 100%, sensitivity 71%). Thus, the combined use of CSF tau and Abeta42 in the form of the tau/Abeta42 ratio is a simple, safe and useful adjuvant to clinical criteria for dementia diagnosis.

Cerebral glucose metabolism, cerebrospinal fluid-beta-amyloid1-42 (CSF-Abeta42), tau and apolipoprotein E genotype in long-term rivastigmine and tacrine treated Alzheimer disease (AD) patients

We evaluated cerebral glucose metabolism (CMRglc) and cerebrospinal fluid (CSF) levels of tau and beta-amyloid(1-42) (Abeta42), in relation to apolipoprotein E (ApoE) genotype, in patients with mild Alzheimer disease (AD) treated with rivastigmine (n=11) and tacrine (n=16) for 1 year; and two untreated AD groups. The rivastigmine-treated AD patients showed a significant increase in CMRglc as compared to both tacrine-treated and untreated AD subjects. The rivastigmine-treated AD group showed no change in CSF-tau levels after 1 year, while in contrast a significant increase as seen in tacrine-treated and untreated AD patients. The CSF-tau changes were mainly seen in ApoE epsilon4 carriers. There was no significant change in Abeta42 after 1-year treatment with either rivastigmine or tacrine. This study shows that the two long-term cholinesterase inhibitor treatments exert different effects on biological markers for AD.

CSF total tau, Abeta42 and phosphorylated tau protein as biomarkers for Alzheimer's disease

With the arrival of effective symptomatic treatments and the promise of drugs that may delay progression, we now need to identify Alzheimer's disease (AD) at an early stage of the disease. To diagnose AD earlier and more accurately, attention has been directed toward peripheral biochemical markers. This article reviews promising potential cerebrospinal fluid (CSF) biomarkers for AD focussing on their role in clinical diagnosis. In particular, two biochemical markers, CSF total tau (t-tau) protein and the 42 amino acid form of beta-amyloid (Abeta42), perform satisfactorily enough to achieve a role in the clinical diagnostic settings of patients with dementia together with the cumulative information from basic clinical work-up, genetic screening, and brain imaging. These CSF markers are particularly useful to discriminate early or incipient AD from age-associated memory impairment, depression, and some secondary dementias. In order to discriminate AD from other primary dementia disorders, however, more accurate and specific markers are needed. Preliminary evidence strongly suggests that quantification of tau phosphorylated at specific sites in CSF improves early detection, differential diagnosis, and tracking of disease progression in AD.

Cerebrospinal fluid tau in dementia disorders: a large scale multicenter study by a Japanese study group

A large scale multicenter study of cerebrospinal fluid (CSF) tau levels was conducted to determine the cut-off value, sensitivity and specificity for clinical usage as a biomarker of Alzheimer's disease (AD). Its use for early and differential diagnosis and the factors that increase CSF tau levels were also examined. CSF samples from a total of 1,031 subjects including 366 patients with AD, 168 patients with non-Alzheimer type dementia (NA), 316 patients with non-dementia neurological diseases (ND) and 181 normal controls (NC) were measured using ELISA for tau. The cut-off value of tau, 375 pg/ml, showed 59.1% sensitivity and 89.5% specificity for diagnosis of AD compared with the other groups. The tau levels were increased from the early to late stages of AD. Elevation of CSF tau in the non-tauopathy and tauopathy dementia groups, chronic and acute damage to the cerebrum, and meningeal disturbance were other factors that required attention for clinical practice. Measurement of CSF tau was useful as a biomarker for early and differential diagnosis of AD.

Pathogenic theories and intrathecal analysis of the sporadic form of Alzheimer's disease

Alzheimer's disease (AD) is an age-dependent dementia characterized by progressive loss of cognitive functions and by characteristic pathological changes in the brain: the formation of aggregates extracellularly by beta-amyloid (Abeta) peptide and intracellularly by tau proteins. The disease presents several major diagnostic difficulties: (1) AD develops slowly; (2) analysis of damaged brain tissues is difficult, requiring a biopsy which poses ethical problems; (3) no biochemical markers are available for the diagnosis and monitoring of the disease progression. Since the cerebrospinal fluid (CSF) is in contact with the extracellular space of the brain, many studies have tried to correlate the levels of the intrathecal peptides and amino acids and the development of dementia. The present review analyzes the main results of intrathecal content analyses in light of pathogenic theories proposed to explain the damage associated with AD and observed in the brain of patients by postmortem examination.

Neurofilament protein in cerebrospinal fluid: a marker of white matter changes

The objective of this study was to compare cerebrospinal fluid (CSF) levels of the light subtype of the neurofilament proteins (NFL), tau, and beta-amyloid42 (Abeta42) in individuals with moderate or severe white matter changes (WMC) and in those with mild or no WMC. Twenty-two patients with Alzheimer's disease (AD), nine patients with subcortical vascular dementia (SVD), and 20 normal controls were included in the study. The occurrence of WMC was evaluated by a neuroradiologist using the Blennow-Wallin scale. Thirty-seven subjects had no or only punctate WMC; 14 had moderate to severe WMC. Both diagnostic group and WMC, but not gender or apolipoproteinE E4 inheritance, contributed to the variance in the CSF levels of tau, NFL, and Abeta42. In patients with moderate to severe WMC, CSF NFL (P < 0.01), but not CSF tau or CSF Abeta42, was increased also after correction for age, gender, and degree of cognitive impairment. A comparison between patients and controls with any signs of WMC and those without such signs yielded a similar result: CSF NFL (P < 0.001) was increased in the group with signs of WMC. As in numerous previous studies, we found that CSF tau was increased in AD (P < 0.001) compared with controls. Furthermore, CSF NFL was increased in both AD and SVD compared with controls (P < 0.001 for both). Although diagnostic group seems to be a stronger predictor of the variance found in CSF NFL, a clear association between the presence of WMC and increased CSF NFL was found. Because NFL is located mainly in large myelinated axons, increased CSF NFL in individuals with WMC probably reflects axonal degeneration.

CSF total tau, Abeta42 and phosphorylated tau protein as biomarkers for Alzheimer's disease

With the arrival of effective symptomatic treatments and the promise of drugs that may delay progression, we now need to identify Alzheimer's disease (AD) at an early stage of the disease. To diagnose AD earlier and more accurately, attention has been directed toward peripheral biochemical markers. This article reviews promising potential cerebrospinal fluid (CSF) biomarkers for AD focussing on their role in clinical diagnosis. In particular, two biochemical markers, CSF total tau (t-tau) protein and the 42 amino acid form of beta-amyloid (Abeta42), perform satisfactorily enough to achieve a role in the clinical diagnostic settings of patients with dementia together with the cumulative information from basic clinical work-up, genetic screening, and brain imaging. These CSF markers are particularly useful to discriminate early or incipient AD from age-associated memory impairment, depression, and some secondary dementias. In order to discriminate AD from other primary dementia disorders, however, more accurate and specific markers are needed. Preliminary evidence strongly suggests that quantification of tau phosphorylated at specific sites in CSF improves early detection, differential diagnosis, and tracking of disease progression in AD.

Apolipoprotein E ε4 positive individuals demonstrate delayed olfactory event-related potentials

Apolipoprotein E epsilon4 positive individuals have deficits in the ability to identify and remember odors, as demonstrated by psychophysical measures of olfactory function. The purpose of the present study was to identify olfactory deficits in this population using an objective electrophysiological measure: the olfactory event-related potential (OERP). Olfactory and auditory ERPs were recorded from the Fz, Cz, and Pz electrode sites in 10 epsilon4 positive individuals and 10 age and gender-matched epsilon4 negative individuals in a single-stimulus paradigm. The results indicate: (1) individuals who are positive for the apolipoprotein E epsilon4 allele demonstrated delays (of approximately 100 ms) in the processing of olfactory information compared to those who are epsilon4 negative; (2) OERP latency is more sensitive than psychophysical measures of olfactory function; (3) delays in the cognitive P3 component of the OERP are associated with deficits in the ability to identify an odor; and (4) unlike the moderate ranges found in auditory ERP, OERP latency showed high sensitivity and specificity in classifying epsilon4 positive and negative individuals.

Clinic-based cases with frontotemporal dementia show increased cerebrospinal fluid tau and high apolipoprotein E epsilon4 frequency, but no tau gene mutations

Frontotemporal dementia (FTD) belongs to a group of neurodegenerative disorders known as tauopathies, characterized by intracellular aggregation of hyperphosphorylated tau protein in the brain. Some tauopathies, like Alzheimer's disease (AD), consistently show increased levels of tau protein in cerebrospinal fluid (CSF). However, similar studies in FTD populations have shown variable results, although mutations in the tau gene are identified as causes of disease in certain FTD families. In the present study, a Swedish clinic-based FTD population was investigated with respect to CSF tau levels, apolipoprotein E (APOE) genotype distribution and occurrence of mutations in the tau gene. CSF tau levels were significantly increased among FTD patients (534 +/- 235 pg tau/ml, P < 0.001) (n = 47) compared to controls (316 +/- 137 pg tau/ml) (n = 51). Furthermore, a strong increase in the APOE epsilon4 allele frequency was found in the FTD population, as 52% were epsilon4 carriers, compared to 21% of the controls. However, no mutations in the tau gene were identified. These findings support the present notion of a common pathogenic pathway in the disease processes for several tauopathies, with both APOE epsilon4 and CSF tau being a pathological link between the different disorders. Furthermore, we conclude that mutations in the tau gene are a rare cause of FTD. .

Cytoskeleton proteins in CSF distinguish frontotemporal dementia from AD

OBJECTIVE AND BACKGROUND

To investigate the CSF levels of tau and the light neurofilament protein (NFL) in patients with frontotemporal dementia (FTD) and other common dementia disorders as well as normal control subjects. Both proteins have been implicated in the pathophysiology of FTD.

METHODS

CSF levels of tau and NFL were investigated in 18 patients with FTD, 21 patients with early-onset AD (EAD), 21 patients with late-onset AD (LAD), and 18 age-matched control subjects.

RESULTS

Mean +/- SD CSF NFL levels were increased in patients with FTD (1442 +/- 1183 pg/mL; p < 0.05) and LAD (1006 +/- 727 pg/mL; p < 0.001) compared with control subjects (241 +/- 166 pg/mL) and in LAD compared with EAD (498 +/- 236 pg/mL; p < 0.05), and tended to be increased in FTD compared with EAD. CSF tau levels were increased in EAD (751 +/- 394 pg/mL; p < 0.01) and LAD (699 +/- 319 pg/mL; p < 0.01) compared with control subjects (375 +/- 170 pg/mL), and in EAD (p < 0.001) and LAD (p < 0. 01) compared with FTD (354 +/- 140 pg/mL). CSF NFL correlated positively with degree of cognitive impairment in FTD (r = 0.59; p < 0.05) and LAD (r = 0.61; p < 0.01). No significant differences were found in CSF NFL or CSF tau when comparing patients who did and did not possess the APOE-epsilon4 allele within each diagnostic group.

CONCLUSION

The results suggest a differential involvement of these cytoskeleton proteins in FTD and EAD, with NFL primarily involved in the pathophysiology of FTD and tau in that of EAD. The increase in CSF NFL found in LAD might reflect the white-matter degeneration found in a proportion of LAD cases.

Proteomics in molecular medicine: applications in central nervous systems disorders

Bodily fluids such as cerebrospinal fluid (CSF) and serum can be analysed at the time of presentation and throughout the course of the disease. Changes in the protein composition of CSF may be indicative of altered CNS protein expression pattern with a causative or diagnostic disease link. These findings can be strengthened through subsequent proteomic analysis of specific brain areas implicated in the pathology. New isolation strategies of clinically relevant cellular material such as laser capture microdissection, protein enrichment procedures and proteomic approaches to neuropeptide and neurotransmitter analysis give us the opportunity to map out complex cellular interaction at an unprecedented level of detail. In neurological disorders multiple underlying pathogenic mechanisms as well as an acute and a chronic CNS disease components may require a selective repertoire of molecular targets and biomarkers rather than an individual protein to better define a complex disease. The resulting proteome database bypasses many ambiguities of experimental models and may facilitate pre- and clinical development of more specific disease markers and new selective fast acting therapeutics.

Prediction of deterioration in mild cognitive disorder in old age--neuropsychological and neurochemical parameters of dementia diseases

In normal senescence, an age-related impairment of cognitive function is observed. The difficult clinical question is in which cases of mild cognitive impairment (MCI) will there be a rapid cognitive decline to a dementia syndrome. Two ways to improve prognosis are discussed: neuropsychological tests and analysis of neurochemical markers. First, the question is asked as to whether there are clusters of MCI. Longitudinal neuropsychological data from the Berlin Aging Study (BASE) are presented, a population-based sample of 516 subjects aged 70 to 103 years. There are clusters found that in part match those clusters, which have been identified by a study from Ritchie et al. in 1996. Especially, a cluster of 13.8% of the nondemented participants with a decline in memory performance is observed. The validation of clusters of cognitive performance and decline opens up the possibility of diagnosing distinctive subgroups of MCI to improve prognosis in old age. Second, the existing data concerning the diagnostic laboratory analysis for Alzheimer's disease (AD) are reviewed. Especially, data regarding nerve growth factor (NGF) are reported. In MCI, preliminary data show a correlation between the NGF serum level and cognitive performance. It can be concluded that the combined investigation of neuropsychological functions and cognitive decline, as well as laboratory measurement of neurochemical markers, might allow an improved prognosis for mental health in very old age.

Three-year follow-up of cerebrospinal fluid tau, beta-amyloid 42 and 40 concentrations in Alzheimer's disease

Earlier studies have shown elevated levels of tau protein and decreased levels of amyloid beta42 in cerebrospinal fluid (CSF) from patients with Alzheimer's disease (AD). We investigated the concentrations of Abeta42, Abeta40 and tau in CSF from AD patients on the baseline and after follow-up period of 3 years using ELISA assays. There was a significant decrease of Abeta42 (P<0.05) and Abeta40 (P<0.05) levels with time. AD patients with the duration of the disease 2 years or less at baseline had more pronounced decrease of Abeta42 concentrations compared to those with the duration of the disease more than 2 years at baseline (P<0.05). CSF tau protein concentrations increased in 9/17 but decreased in 8/17 patients. These results suggest that Abeta42 and Abeta40 may be useful in monitoring the long-term progression of AD particularly in the early stages of the disease.

Increased levels of tau-like protein in patients with Down syndrome

Tau-like protein levels from 40 Down syndrome (DS) persons (31-70 years old), 40 non-DS age-matched normal controls, 18 non-DS mentally retarded (MR) persons (26-91 years old), 25 probable Alzheimer disease (AD) patients (55-99 years old) and 24 non-demented elderly controls (54-79 years old) were measured using a sandwich enzyme linked immunosorbent assay. The levels were detected in 22 of 40 DS persons and were significantly higher in DS than any other group (P < 0.0001). There was no relationship between tau-like protein levels and age, gender or apolipoprotein E phenotypes in any of the five groups.

Apolipoprotein E4 accelerates dementia and increases cerebrospinal fluid tau levels in Alzheimer's disease

To examine the effect of apolipoprotein E (ApoE) 4 on the progression of Alzheimer's disease (AD), the clinical course of 33 AD patients (17 cases with ApoE epsilon4 and 16 cases without ApoE epsilon4) was evaluated with the mini-mental state examination (MMSE) and cerebrospinal fluid (CSF) biological markers. The decline of MMSE scores to zero was shortened in the ApoE4 group. During a mean follow-up of 20 months, a significant increase of CSF tau levels was observed in the ApoE4 group. A lower level of CSF A beta1-42(43) was found in both the ApoE4 and non-ApoE4 groups than in age-matched normal controls. The ApoE epsilon4 allele accelerates the progression of dementia and increases the levels of CSF tau in AD patients.

Early diagnostic indices for the prevention of Alzheimer's disease

Recent progress in our understanding of the pathophysiology of Alzheimer's disease (AD) has made it clear that it is a heterogeneous disorder to which both genetic and environmental factors contribute. Therefore, it is unlikely that a single test for the diagnosis of this disease will be developed. Possible candidates for early diagnostic indices have been identified, in addition to biological markers, in the fields of neuropsychology, genetics and neuroimaging. Many studies have indicated that low scores in tests assessing delayed recall predict dementia already years before the actual criteria of dementia are fulfilled. Molecular genetic studies have confirmed that the epsilon4 allele of the apolipoprotein E (APOE) is also a definite risk factor for AD, and other susceptibility genes will probably be identified and confirmed in the near future. Evaluation of the hippocampal atrophy by magnetic resonance imaging (MRI) scans has been reported to be a sensitive and possible specific indicator of mild AD, while possibilities of using functional MRI are currently being explored. A combination of low scores in tests assessing delayed recall, small size of the hippocampus on MRI and APOE epsilon4 might point to a high risk of developing AD. We need extensive follow-up studies to identify which combination of molecular genetic factors and memory test scores supplemented with neuroimaging will prove to be most efficient in diagnosing AD in its preclinical phase, as this is the phase which offers the most promising therapeutic options.

Biological markers for the diagnosis of Alzheimer's disease

A diagnostic test for Alzheimer's disease (AD) based on biochemical markers in the cerebrospinal fluid can help improve diagnostic accuracy, which currently is approximately 90%, leaving every tenth AD patient undiagnosed or falsely diagnosed as having the disease. From all biochemical abnormalities described in AD patients, those related to the hallmark neuropathologic lesions, deposition of amyloid and formation of paired helical filaments mainly consisting of abnormally phosphorylated tau protein, are the most promising and the best documented, even though other markers bear some potential and remain to be further studied. Determining an increase of tau and a reduction of A beta 42 bears satisfactory, even though not absolute specificity for AD and represents a true aid for clinicians in diagnosing AD during the patients lifetime. It remains open if these markers will be helpful for the most challenging goal, diagnosing AD in the preclinical phase, when, according to morphological data, high amounts of these pathological proteins are already deposited in the brain tissue.