Cerebrospinal fluid and blood biomarkers in Alzheimer’s disease

Due to an ever aging society and growing prevalence of Alzheimer’s disease (AD), the challenge to meet social and health care system needs will become increasingly difficult. Unfortunately, a definite ante mortem diagnosis is not possible. Thus, an early diagnosis and identification of AD patients is critical for promising, early pharmacological interventions as well as addressing health care needs. The most advanced and most reliable markers are β-amyloid, total tau and phosphorylated tau in cerebrospinal fluid (CSF). In blood, no single biomarker has been identified despite an intense search over the last decade. The most promising approaches consist of a combination of several blood-based markers increasing the reliability, sensitivity and specificity of the AD diagnosis. However, contradictory data make standardized testing methods in longitudinal and multi-center studies extremely difficult. In this review, we summarize a range of the most promising CSF and blood biomarkers for diagnosing AD.     

Cerebrospinal fluid biomarkers of Alzheimer’s disease

Alzheimer’s disease (AD) is a fatal neurodegenerative disorder that takes about a decade to develop, making early diagnosis possible. Clinically, the diagnosis of AD is complicated, costly, and inaccurate, so it is urgent to find specific biomarkers. Due to its multifactorial nature, a panel of biomarkers for the multiple pathologies of AD, such as cerebral amyloidogenesis, neuronal dysfunction, synapse loss, oxidative stress, and inflammation, are most promising for accurate diagnosis. Highly sensitive and high-throughput proteomic techniques can be applied to develop a panel of novel biomarkers for AD. In this review, we discuss the metabolism and diagnostic performance of the well-established core candidate cerebrospinal fluid (CSF) biomarkers (β-amyloid, total tau, and hyperphosphorylated tau). Meanwhile, novel promising CSF biomarkers, especially those identified by proteomics, updated in the last five years are also extensively discussed. Furthermore, we provide perspectives on how biomarker discovery for AD is evolving.     

Cerebrospinal fluid protein biomarkers for Alzheimer’s disease

The introduction of acetylcholine esterase (AChE) inhibitors as a symptomatic treatment of Alzheimer’s disease (AD) has made patients seek medical advice at an earlier stage of the disease. This has highlighted the importance of diagnostic markers for early AD. However, there is no clinical method to determine which of the patients with mild cognitive impairment (MCI) will progress to AD with dementia, and which have a benign form of MCI without progression. In this paper, the performance of cerebrospinal fluid (CSF) protein biomarkers for AD is reviewed. The diagnostic performance of the three biomarkers, total tau, phospho-tau, and the 42 amino acid form of β-amyloid have been evaluated in numerous studies and their ability to identify incipient AD in MCI cases has also been studied. Some candidate AD biomarkers including ubiquitin, neurofilament proteins, growth-associated protein 43 (neuromodulin), and neuronal thread protein (AD7c) show interesting results but have been less extensively studied. It is concluded that CSF biomarkers may have clinical utility in the differentiation between AD and several important differential diagnoses, including normal aging, depression, alcohol dementia, and Parkinson’s disease, and also in the identification of Creutzfeldt-Jakob disease in cases with rapidly progressive dementia. Early diagnosis of AD is not only of importance to be able to initiate symptomatic treatment with AChE inhibitors, but will be the basis for initiation of treatment with drugs aimed at slowing down or arresting the degenerative process, such as γ-secretase inhibitors, if these prove to affect AD pathology and to have a clinical effect.     

Cerebrospinal fluid analysis in Alzheimer’s disease: technical issues and future developments

Alzheimer’s disease (AD) is a leading cause of morbidity, mortality, and a major epidemic worldwide. Although clinical assessment continues to remain the keystone for patient management and clinical trials, such evaluation has important limitations. In this context, cerebrospinal fluid (CSF) biomarkers are important tools to better identify high-risk individuals, to diagnose AD promptly and accurately, especially at the prodromal mild cognitive impairment stage of the disease, and to effectively prognosticate and treat AD patients. Recent advances in functional genomics, proteomics, metabolomics, and bioinformatics will hopefully revolutionize unbiased inquiries into several putative CSF markers of cerebral pathology that may be concisely informative with regard to the various stages of AD progression through years and decades. Moreover, the identification of efficient drug targets and development of optimal therapeutic strategies for AD will increasingly rely on a better understanding and integration of the systems biology paradigm, which will allow predicting the series of events and resulting responses of the biological network triggered by the introduction of new therapeutic compounds. In this scenario, unbiased systems biology-based diagnostic and prognostic models in AD will consist of relevant comprehensive panels of molecules and key branches of the disease-affected cellular neuronal network. Such characteristic and unbiased biomarkers will more accurately and comprehensively reflect pathophysiology from the early asymptomatic and presymptomatic to the final prodromal and symptomatic clinical stages in individual patients (and their individual genetic disease predisposition), ultimately increasing the chances of success of future disease modifying and preventive treatments.     

Cerebrospinal fluid biomarkers of Alzheimer＇s disease

Alzheimer＇s disease （AD） is a fatal neurodegenerative disorder that takes about a decade to develop, making early diagnosis possible. Clinically, the diagnosis of AD is complicated, costly, and inaccurate, so it is urgent to find specific biomarkers. Due to its multifactorial nature, a panel of biomarkers for the multiple pathologies of AD, such as cerebral amyloidogenesis, neuronal dysfunction, synapse loss, oxidative stress, and inflammation, are most promising for accurate diagnosis. Highly sensitive and high-throughput proteomic techniques can be applied to develop a panel of novel biomarkers for AD. In this review, we discuss the metabolism and diagnostic performance of the well-established core candidate cerebrospinal fluid （CSF） biomarkers （β-amyloid, total tau, and hyperphosphorylated tau）. Meanwhile, novel promising CSF biomarkers, especially those identified by proteomics, updated in the last five years are also extensively discussed. Furthermore, we provide perspectives on how biomarker discovery for AD is evolving.     

Cerebrospinal fluid biomarkers for Alzheimer’s disease: diagnostic performance in a homogeneous mono-center population

The cerebrospinal fluid (CSF) biomarkers amyloid-β (Aβ)(1-42), T-tau, and P-tau have good diagnostic accuracy for clinically diagnosed Alzheimer’s disease (AD). However, in multi-center studies, the predictive values of the CSF biomarkers have been lower, possibly due to differences in procedures for lumbar puncture and CSF handling and storage, and to differences in patient populations, clinical evaluations, and diagnostic procedures. Here we investigate the diagnostic accuracy of CSF biomarkers in a well defined homogeneous mono-center population. We also evaluate an extended panel of amyloid related biomarkers. Sixty consecutive patients admitted for cognitive impairment to a memory clinic were recruited. The participants included patients with AD or mild cognitive impairment (MCI) diagnosed with AD upon follow-up (n = 32), patients with stable MCI (n = 13), patients with other dementias diagnosed at primary evaluation or upon follow-up (n = 15), and healthy controls(n = 20). CSF was analyzed for Aβ(1-42), T-tau, and P-tau, and PA(X-38), Aβ(X-40), Aβ(X-42), sAβPPα, and sAβPPβ. In multivariate analysis, thecore biomarkers Aβ(1-42), T-tau, and P-tau demonstrated a high ability to diagnose AD versus the combined groups of controls and stable MCI, with an area under the receiver operating characteristic curve (AUROC) of 0.97 (95% CI 0.93–1.00, p < 0.0001). The additional biomarkers only marginally increased AUROC to 0.98 (95% CI 0.95–1.00, p < 0.0001), this increase mainly mediated by Aβ(X-42). In conclusion, CSF biomarkers Aβ(1-42), T-tau, and P-tau have very high diagnostic accuracy in a well defined cohort of untreated patients, demonstrating the excellent potency of CSF biomarkers to identify pathological processes in AD when astringent analytical protocol is used.     

Interstitial fluid drainage is impaired in ischemic stroke and Alzheimer’s disease mouse models

The interstitial fluid (ISF) drainage pathway has been hypothesized to underlie the clearance of solutes and metabolites from the brain. Previous work has implicated the perivascular spaces along arteries as the likely route for ISF clearance; however, it has never been demonstrated directly. The accumulation of amyloid β (Aβ) peptides in brain parenchyma is one of the pathological hallmarks of Alzheimer disease (AD), and it is likely related to an imbalance between production and clearance of the peptide. Aβ drainage along perivascular spaces has been postulated to be one of the mechanisms that mediate the peptide clearance from the brain. We therefore devised a novel method to visualize solute clearance in real time in the living mouse brain using laser guided bolus dye injections and multiphoton imaging. This methodology allows high spatial and temporal resolution and revealed the kinetics of ISF clearance. We found that the ISF drains along perivascular spaces of arteries and capillaries but not veins, and its clearance exhibits a bi-exponential profile. ISF drainage requires a functional vasculature, as solute clearance decreased when perfusion was impaired. In addition, reduced solute clearance was observed in transgenic mice with significant vascular amyloid deposition; we suggest the existence of a feed-forward mechanism, by which amyloid deposition promotes further amyloid deposition. This important finding provides a mechanistic link between cerebrovascular disease and Alzheimer disease and suggests that facilitation of Aβ clearance along the perivascular pathway should be considered as a new target for therapeutic approaches to Alzheimer disease and cerebral amyloid angiopathy.     

Platelet phospholipase A<Subscript>2</Subscript> activity in patients with Alzheimer’s disease,vascular dementia and ischemic stroke

Summary Phospholipase A₂ (E.C. 3.1.1.4, PLA₂) plays an essential role in metabolism of membrane phospholipids, it is related to inflammatory reactions, secretion of amyloid precursor protein and activation of NMDA receptor after ischemia. In the present study we investigated PLA₂ activity in platelets from 37 Alzheimer’s disease (AD) patients, 32 vascular dementia (VaD) patients and 32 individuals with ischemic stroke as compared to 27 healthy elderly controls. PLA₂ activity was determined using radiometric assay. Mean platelet PLA₂ activity was increased in individuals with Alzheimer’s disease (p < 0.001). In VaD group the enzyme activity was between the values in AD and controls, these differences being significant from both groups. In the group of patients with ischemic stroke mean PLA₂ activity was higher either 48 h after the stroke or 7 days later (in both cases p < 0.001). The results may be particularly interesting in light of the fact, that inhibitors of PLA₂ activity are known.     

Cerebrospinal fluid markers analysis in the differential diagnosis of dementia with Lewy bodies and Parkinson’s disease dementia

European Archives of Psychiatry and Clinical Neuroscience - Dementia with Lewy bodies (DLB) and Parkinson’s disease dementia (PDD) share a couple of clinical similarities that is often a...     

Cerebrospinal fluid/plasma quotients of essential and non-essential metals in patients with Alzheimer’s disease

In this study, the quotients (Q) between metal concentrations in cerebrospinal fluid (CSF) and plasma were studied in subjects with Alzheimer’s disease (AD) and referents to investigate if the leakage through the blood–CSF barrier (BCB) increased with increased duration and severity of the disease. Concentrations of 18 metals (Mg, Ca, Mn, Fe, Co, Ni, Cu, Zn, Se, Rb, Sr, Mo, Cd, Sn, Sb, Cs, Hg, and Pb) were determined by ICP-MS in plasma and cerebrospinal fluid in 264 patients with AD, and in 54 healthy referents. The quotients Q _Mn, Q _Rb, Q _Sb, Q _Pb and Q _Hg were significantly lower (p ≤ 0.003) and Q _Co significantly higher (p ≤ 0.001) in subjects with AD as compared with the controls. Subjects in a subgroup with more severe AD, showed the same pattern. The metal leakage into CSF did not increase with increased duration and/or severity of the disease. The permeability of BCB varied considerably between the studied metals with low median quotients (Q ≤ 0.02) for Cd, Cu, Sb, Se and Zn and higher median quotients for Ca (Q ~ 0.5) and Mg (Q ~ 1.3), probably partly depending on differences in size and lipophilicity of metal–carrier complexes and specific carrier mechanisms.     

Muscle profile and cognition in patients with Alzheimer’s disease dementia

Introduction

Neurodegenerative disease is one of the main contributing factors affecting muscle atrophy. However, this intriguing brain-muscle axis has been explained by the unsubstantial mechanisms. Although there have been several studies that have evaluated the muscle profile and its relation to cognition in patients with dementia, there is still lack of data using standardized methods and only few published studies on Korean populations. The objective of this study is to evaluate the relationship of muscle mass and strength to cognition in patients with Alzheimer’s disease dementia (AD).

Methods

We recruited 91 patients with probable AD without weakness. We assessed patients’ basic demographic characteristics, vascular risk, body mass index, and global cognitive assessment scores. Muscle mass was measured using body dual-energy X-ray absorptiometry. Muscle strength was assessed by isokinetic knee extensor using an isokinetic device at an angular velocity of 60°/s in nm/kg.

Results

The muscle mass and strength were not related to each other in both male and female groups. Only muscle strength, but not muscle mass, was negatively related to cognition. After adjusting for covariates, the relationship between muscle strength and cognition still remained in the male group, however, was attenuated in the female group.

Conclusions

In patients with AD dementia, abundant muscle mass did not mean strong power. The simple lower-extremity muscle strength assessment is more effective in predicting cognition than a muscle mass measure in male patients.

     

Laboratory biomarkers in Alzheimer’s disease

Diagnosis and monitoring of Alzheimer’s disease and the related dementias have long depended principally on clinical examination, especially cognitive testing. Establishment of biomarkers, which might assist in diagnosis or tracking of disease progression, would be a highly valuable addition to the care of patients. Such biomarkers are potentially available from body fluids and tissues as well as from brain imaging data. As specific disease-modifying therapies for Alzheimer’s disease are developed, biomarkers may improve diagnostic accuracy and facilitate clinical trials, allowing a better gauge of treatment response. In this review, we focus on biomarkers in cerebrospinal fluid and plasma, including measurements of the proteins tau and beta-amyloid.     

Cerebrospinal fluid diagnostic markers correlate with lower plasma copper and ceruloplasmin in patients with Alzheimer’s disease

Summary. Increasing evidence links Alzheimer’s disease (AD) with misbalanced Cu homeostasis. Recently, we have shown that dietary Cu supplementation in a transgenic mouse model for AD increases bioavailable brain Cu levels, restores Cu, Zn-super oxide-1 activity, prevents premature death, and lowers Aβ levels. In the present report we investigated AD patients with normal levels of Aβ42, Tau and Phospho-Tau in the cerebrospinal fluid (CSF) in comparison with AD patients exhibiting aberrant levels in these CSF biomarkers. The influence of these cerebrospinal fluid (CSF) diagnostic markers with primary dependent variables blood Cu, Zn and ceruloplasmin (CB) and secondary with CSF profiles of Cu, Zn and neurotransmitters was determined. Multivariate tests revealed a significant effect of factor diagnostic group (no AD diagnosis in CSF or AD diagnosis in CSF) for variables plasma Cu and CB (F = 4.80; df = 2, 23; p = 0.018). Subsequent univariate tests revealed significantly reduced plasma Cu (−12.7%; F = 7.05; df = 1, 25; p = 0.014) and CB (−14.1%; F = 9.44; df = 1, 24; p = 0.005) levels in patients with aberrant CSF biomarker concentrations. Although only AD patients were included, the reduced plasma Cu and CB levels in patients with a CSF diagnosis of advanced AD supports previous observations that a mild Cu deficiency might contribute to AD progression. The first and second author contributed equally     

Follow-up investigations in cerebrospinal fluid of patients with dementia with Lewy bodies and Alzheimer’s disease

Summary. Measuring proteins in cerebrospinal fluid (CSF) has gained wide acceptance for the differential diagnosis of dementia. Some groups have already extended these investigations in Alzheimers disease (AD) by asking how stable these markers are in follow-up analysis, if they depend on the stage of disease and whether they can be used to monitor the progression and biological effects of treatment. We evaluated 21 patients with dementia with Lewy bodies (DLB) and 19 patients with AD, on two occasions, with regard to levels of tau protein, tau protein phosphorylated at threonine 181 (p-tau), A42, A40 and S-100B protein, using a set of commercially available assays.Tau protein levels were lower in DLB in first and second LP compared to AD and decreased during course of both groups. P-tau levels were increased in AD and DLB and decreased during follow-up. A42 and A40 remained relatively stable during follow-up but we found a slight increase of the median A42 level in DLB, whereas in AD, A42 tends to decrease during follow-up. S-100B protein increased during follow-up in both diseases.The protein dynamics in DLB and AD are relatively similar. S-100B protein may be a useful marker for follow-up in neurodegenerative diseases but has to be analysed in longer follow-up periods. Tau protein may be used to differentiate between DLB and AD.Follow-up CSF analyses are of limited value for the differentiation of AD and DLB. We conclude that more specific markers have to be established for the differentiation and follow-up of these diseases.     

Different mechanisms of corpus callosum atrophy in Alzheimer’s disease and vascular dementia

Abstract. Previous neuroimaging studies have indicated that corpus callosum atrophy in Alzheimers disease (AD) and large vessel occlusive disease (LVOD) is caused by interhemispheric disconnection, namely Wallerian degeneration of interhemispheric commissural nerve fibers originating from pyramidal neurons in the cerebral cortex. However, this hypothesis has not been tested from a neuropathological viewpoint. In the present study, 22 brains with AD (presenile onset, 9; senile onset, 13), 6 brains with Binswangers disease (BD), a form of vascular dementia and 3 brains with LVOD were compared with 6 non-neurological control brains.White matter lesions in the deep white matter and corpus callosum were quantified as a fiber density score by image analysis of myelin-stained sections. Axonal damage and astrogliosis were assessed by immunohistochemistry for amyloid precursor protein and glial fibrillary acidic protein, respectively.The corpus callosum thickness at the anterior part of the body was decreased in AD and LVOD,but not in BD significantly, as compared with the controls. The corpus callosum thickness correlated roughly with brain weight in AD (R = 0.50),and with the severity of deep white matter lesions in BD (R = 0.81). Atrophy of the brain and corpus callosum was more marked in presenile onset AD than in senile onset AD. With immunohistochemistry, the corpus callosum showed axonal damage and gliosis with a decreased fiber density score in BD and LVOD, but not in AD. Thus, corpus callosum atrophy was correlated with brain atrophy in AD, which is relevant to the mechanism of interhemispheric disconnection,whereas corpus callosum lesions in BD were secondary to deep white matter lesions. Corpus callosum atrophy in LVOD may indicate interhemispheric disconnection, but focal ischemic injuries may also be involved.     

Evaluation of CSF-Chlamydia pneumoniae,CSF-tau,and CSF-Abeta42 in Alzheimer’s disease and vascular dementia

The potential role of microbiological factors such as Chlamydia pneumoniae (ChP) in the pathogenesis of neurodegenerative disorders, including Alzheimer's disease (AD) and vascular dementia (VD), has been suggested, but the correctness of this hypothesis still needs to be tested. In this study the appearance of ChP in the cerebrospinal fluid (CSF) of 57 AD and 21 VD patients and in 47 controls (CG) as well as the influence of ChP on the levels of tau protein and Abeta42 were investigated. The frequency of ChP occurrence in the AD patient group (43.9%) was significantly higher (p < 0.001) than in the control group (10.6%). In the case of VD patients, 9.5% of this group was positive for ChP. The presence of ChP DNA in the CSF of patients with AD significantly increases the occurrence of this disease (odds ratio = 7.21). Cerebrospinal fluid Abeta42 levels were significantly lower in patients with AD than in the CG (p < 0.001). Cerebrospinal tau protein was significantly higher in AD vs. CG (p = 0.007). However, no relationships between the presence of the bacterium in CSF and the level of either tau or Abeta42 protein were observed. In conclusion, we may suspect that testing for the presence of ChP in CSF, along with the tau and Abeta42 markers, may be used in the clinic diagnosis of AD.     

Tomm40 polymorphisms in Italian Alzheimer’s disease and frontotemporal dementia patients

Chromosome 19 is one of the several prominent chromosomes related to the risk of developing late-onset Alzheimer’s disease (LOAD) and frontotemporal lobar degeneration (FTLD). However, only Apolipoprotein E (APOE) has been confirmed as a risk factor for both disorders. The aim of this study was to investigate a set of polymorphisms in the translocase of the outer mitochondrial membrane 40 (TOMM40) gene, located in close proximity to APOE, to clarify if the TOMM40 gene may be considered a risk factor for AD and FTLD, independently of APOE status. We performed a case–control study in a dataset of Italian LOAD and FTLD patients, analyzing the following three single-nucleotide polymorphisms (SNPs): rs157580, rs2075650 and rs157581. The analysis was made in 710 Italian subjects: 282 LOAD patients, 156 FTLD patients and 272 healthy subjects. Our results confirm the presence of an association between TOMM40 SNPs and LOAD in our Italian population, suggesting that genetic variations proximate to APOE contributes to the LOAD risk. Genotype and allele distribution of the TOMM40 polymorphisms between the FTLD group and controls did not show any statistical difference. When we analyzed haplotype distribution of the SNPs, taking into account the presence of the APOE allele, we observed a strong association between the ε4 allele and the GAC haplotype both in LOAD and FTLD patients. In contrast, this association did not hold for ε3/GAC. These results demonstrate that the TOMM40 gene does not have an APOE-independent role in the risk of developing LOAD and FTLD.     

Influence of controlled encoding and retrieval facilitation on memory performance of patients with subcortical ischemic vascular dementia and Alzheimer’s disease

Journal of Neurology - Patients with subcortical ischemic vascular dementia (SIVD) perform better than Alzheimer’s disease patients (AD) on the Free and Cued Recall Selective Reminding test...     

Impact of cerebro-spinal fluid biomarkers of Alzheimer’s disease in clinical practice: a multicentric study

CSF biomarkers of Alzheimer’s disease are well validated in clinical research; however, their pragmatic utility in daily practice is still unappreciated. These biomarkers are used in routine practice according to Health Authority Recommendations. In 604 consecutive patients explored for cognitive disorders, questionnaires were prospectively proposed and filled. Before and after CSF biomarker results, clinicians provided a diagnosis and an estimate of their diagnostic confidence. Analysis has compared the frequency of diagnosis before and after CSF biomarker results using the net reclassification improvement (NRI) method. We have evaluated external validity comparing with data of French Bank National of AD (BNA). A total of 561 patients [Alzheimer’s disease (AD), n = 253; non-AD, n = 308] were included (mean age, 68.6 years; women, 52 %). Clinically suspected diagnosis and CSF results were concordant in 65.2 % of cases. When clinical hypothesis and biological results were discordant, a reclassification occurred in favour of CSF biomarkers results in 76.9 %. The NRI was 39.5 %. In addition, the results show a statistically significant improvement in clinician confidence for their diagnosis. In comparison with BNA data, patients were younger and more frequently diagnosed with AD. Clinicians tend to heavily rely on the CSF AD biomarkers results and are more confident in their diagnoses using CSF AD biomarkers. Thus, these biomarkers appear as a key tool in clinical practice.