Assessment of the Correlation and Diagnostic Accuracy between Cerebrospinal Fluid and Plasma Alzheimer's Disease Biomarkers: A Comparison of the Lumipulse and Simoa Platforms.

We compared the clinical and analytical performance of Alzheimer's disease (AD) plasma biomarkers measured using the single-molecule array (Simoa) and Lumipulse platforms. We quantified the plasma levels of amyloid beta 42 (Aß42), Aß40, phosphorylated tau (Ptau181), and total tau biomarkers in 81 patients with mild cognitive impairment (MCI), 30 with AD, and 16 with non-AD dementia. We found a strong correlation between the Simoa and Lumipulse methods. Concerning the clinical diagnosis, Simoa Ptau181/Aß42 (AUC 0.739, 95% CI 0.592-0.887) and Lumipulse Aß42 and Ptau181/Aß42 (AUC 0.735, 95% CI 0.589-0.882 and AUC 0.733, 95% CI 0.567-0.900) had the highest discriminating power. However, their power was significantly lower than that of CSF Aß42/Aß40, as measured by Lumipulse (AUC 0.879, 95% CI 0.766-0.992). Simoa Ptau181 and Lumipulse Ptau181/Aß42 were the markers most consistent with the CSF Aß42/Aß40 status (AUC 0.801, 95% CI 0.712-0.890 vs. AUC 0.870, 95% CI 0.806-0.934, respectively) at the ≥2.127 and ≥0.084 cut-offs, respectively. The performance of the Simoa and Lumipulse plasma AD assays is weaker than that of CSF AD biomarkers. At present, the analysed AD plasma biomarkers may be useful for screening to reduce the number of lumbar punctures in the clinical setting.

New plasma LC-MS/MS assays for the quantitation of beta-amyloid peptides and identification of apolipoprotein E proteoforms for Alzheimer's disease risk assessment.

Early detection of Alzheimer's disease (AD) represents an unmet clinical need. Beta-amyloid (Aß) plays an important role in AD pathology, and the Aß42/40 peptide ratio is a good indicator for amyloid deposition. In addition, variants of the apolipoprotein E (APOE) gene are associated with variable AD risk. Here, we describe the development and validation of high-throughput liquid chromatography-tandem mass spectrometry (LC-MS/MS) assays for plasma Aß40 and Aß42 quantitation, as well as apolipoprotein E (ApoE) proteotype determination as a surrogate for APOE genotype. Aß40 and Aß42 were simultaneously immunoprecipitated from plasma, proteolytically digested, and quantitated by LC-MS/MS. ApoE proteotype status was qualitatively assessed by targeting tryptic peptides from the ApoE2, ApoE3, and ApoE4 proteoforms. Both assays were validated according to the Clinical and Laboratory Standards Institute (CLSI) guidelines. Within-run precision was 1.8%-4.2% (Aß40), 1.9%-7.2% (Aß42), and 2.6%-8.3% (Aß42/40 ratio). Between-run precision was 3.5%-5.9% (Aß40), 3.8%-8.0% (Aß42), and 3.3%-8.7% (Aß42/40 ratio). Both Aß40 and Aß42 were linear from 10 to 2500 pg/mL. Identified ApoE proteotypes had 100% concordance with APOE genotypes. We have developed a precise, accurate, and sensitive high-throughput LC-MS/MS assay for plasma Aß40, Aß42, and proteoforms of ApoE.

Is blood pTau a reliable indicator of the CSF status? A narrative review.

BACKGROUND: The identification of biomarkers for the early diagnosis of Alzheimer's disease (AD) is a crucial goal of the current research. Blood biomarkers are less invasive, easier to obtain and achievable by a cheaper means than those on cerebrospinal fluid (CSF) and significantly more economic than functional neuroimaging investigations; thus, a great interest is focused on blood isoforms of the phosphorylated Tau protein (pTau), indicators of ongoing tau pathology (i.e. neurofibrillary tangles, NFTs, an AD neuropathological hallmark) in the central nervous system (CNS). However, current data often highlight discordant results about the ability of blood pTau to predict CSF status. OBJECTIVE: We aim to synthesise the studies that compared pTau levels on CSF and blood to assess their correlation in AD continuum. METHODS: We performed a narrative literature review using, first, MEDLINE (via PubMed) by means of MeSH terms, and then, we expanded the reults by means of Scopus and Web of Sciences to be as inclusive as possible. Finally, we added work following an expert opinion. Only papers presenting original data on pTau values on both blood and CSF were included. RESULTS: The 33 included studies show an extreme heterogeneity in terms of pTau isoform (pTau181, 217 and 231), laboratory methods, diagnostic criteria and choice of comparison groups. Most studies evaluated plasma pTau181, while data on other isoforms and serum are scarcer. DISCUSSION: Most papers identify a correlation between CSF and blood measurements. Furthermore, even when not specified, it is often possible to show an increase in blood pTau values as AD-related damage progresses in the AD continuum and higher values in AD than in other neurodegenerative diseases. Notably, plasma pTau231 seems the first biomarker to look for in the earliest and pre-clinical stages, quickly followed by pTau217 and, finally, by pTau181. CONCLUSIONS: Our results encourage the use of blood pTau for the early identification of patients with AD continuum.

Plasma isoprostanoids assessment as Alzheimer's disease progression biomarkers.

Alzheimer's Disease (AD) is the most common neurodegenerative disease worldwide. So, there is a need to identify AD early diagnosis and monitoring biomarkers in blood samples. The aim of this study was to analyse the utility of lipid peroxidation biomarkers in AD progression evaluation. Participants (n = 19) were diagnosed with AD at early stages (Time 0, T0), and they were re-evaluated 2 years later (Time 1, T1). Plasma biomarkers from AD patients were determined at both times. Some analytes, such as dihomo-isoprostanes (17-epi-17-F2t-dihomo-IsoP, 17-F2t-dihomo-IsoP, Ent-7(RS)-7-F2t-dihomo-IsoP), and neuroprostanes (10-epi-10-F4t-NeuroP) showed very high probability of showing an increasing trend over time. Baseline values allowed to develop an affordable preliminary regression model to predict long-term cognitive status. So, some lipid peroxidation biomarkers would deserve consideration as useful progression AD biomarkers. The developed prediction model would constitute an important minimally invasive approach in AD personalized prognosis and perhaps could have some interest also in experimental treatments evaluation.

A Sensitive and Cost-Effective Chemiluminescence ELISA for Measurement of Amyloid-ß 1-42 Peptide in Human Plasma.

BACKGROUND: Amyloid-ß42 (Aß42) is associated with plaque formation in the brain of patients with Alzheimer's disease (AD). Studies have suggested the potential utility of plasma Aß42 levels in the diagnosis, and in longitudinal study of AD pathology. Conventional ELISAs are used to measure Aß42 levels in plasma but are not sensitive enough to quantitate low levels. Although ultrasensitive assays like single molecule array or immunoprecipitation-mass spectrometry have been developed to quantitate plasma Aß42 levels, the high cost of instruments and reagents limit their use. OBJECTIVE: We hypothesized that a sensitive and cost-effective chemiluminescence (CL) immunoassay could be developed to detect low Aß42 levels in human plasma. METHODS: We developed a sandwich ELISA using high affinity rabbit monoclonal antibody specific to Aß42. The sensitivity of the assay was increased using CL substrate to quantitate low levels of Aß42 in plasma. We examined the levels in plasma from 13 AD, 25 Down syndrome (DS), and 50 elderly controls. RESULTS: The measurement range of the assay was 0.25 to 500 pg/ml. The limit of detection was 1 pg/ml. All AD, DS, and 45 of 50 control plasma showed measurable Aß42 levels. CONCLUSION: This assay detects low levels of Aß42 in plasma and does not need any expensive equipment or reagents. It offers a preferred alternative to ultrasensitive assays. Since the antibodies, peptide, and substrate are commercially available, the assay is well suited for academic or diagnostic laboratories, and has a potential for the diagnosis of AD or in clinical trials.

Serum Tau Proteins as Potential Biomarkers for the Assessment of Alzheimer's Disease Progression.

Total tau (t-tau) and phosphorylated tau (p-tau) protein elevations in cerebrospinal fluid (CFS) are well-established hallmarks of Alzheimer's disease (AD), while the associations of serum t-tau and p-tau levels with AD have been inconsistent across studies. To identify more accessible non-invasive AD biomarkers, we measured serum tau proteins and associations with cognitive function in age-matched controls (AMC, n = 26), mild cognitive impairment group (MCI, n = 30), and mild-AD group (n = 20) according to the Mini-mental State Examination (MMSE), Clinical Dementia Rating (CDR), and Global Deterioration Scale (GDS) scores. Serum t-tau, but not p-tau, was significantly higher in the mild-AD group than AMC subjects (p < 0.05), and there were significant correlations of serum t-tau with MMSE and GDS scores. Receiver operating characteristic (ROC) analysis distinguished mild-AD from AMC subjects with moderate sensitivity and specificity (AUC = 0.675). We speculated that tau proteins in neuronal cell-derived exosomes (NEX) isolated from serum would be more strongly associated with brain tau levels and disease characteristics, as these exosomes can penetrate the blood-brain barrier. Indeed, ELISA and Western blotting indicated that both NEX t-tau and p-tau (S202) were significantly higher in the mild-AD group compared to AMC (p < 0.05) and MCI groups (p < 0.01). In contrast, serum amyloid ß (Aß1-42) was lower in the mild-AD group compared to MCI groups (p < 0.001). During the 4-year follow-up, NEX t-tau and p-tau (S202) levels were correlated with the changes in GDS and MMSE scores. In JNPL3 transgenic (Tg) mice expressing a human tau mutation, t-tau and p-tau expression levels in NEX increased with neuropathological progression, and NEX tau was correlated with tau in brain tissue exosomes (tEX), suggesting that tau proteins reach the circulation via exosomes. Taken together, our data suggest that serum tau proteins, especially NEX tau proteins, are useful biomarkers for monitoring AD progression.

Mini Nutritional Assessment May Identify a Dual Pattern of Perturbed Plasma Amino Acids in Patients with Alzheimer's Disease: A Window to Metabolic and Physical Rehabilitation?

Conflicting results about alterations of plasma amino acid (AA) levels are reported in subjects with Alzheimer's disease (AD). The current study aimed to provide more homogeneous AA profiles and correlations between AAs and cognitive tests. Venous plasma AAs were measured in 54 fasting patients with AD (37 males, 17 females; 74.63 ± 8.03 yrs; 3.2 ± 1.9 yrs from symptom onset). Seventeen matched subjects without neurodegenerative symptoms (NNDS) served as a control group (C-NNDS). Patients were tested for short-term verbal memory and attention capacity and stratified for nutritional state (Mini Nutritional Assessment, MNA). Compared to C-NNDS, patients exhibited lower plasma levels of aspartic acid and taurine (p < 0.0001) and higher 3-methylhistidine (p < 0.0001), which were independent of patients' MNA. In comparison to normonourished AD, the patients at risk of and with malnutrition showed a tendency towards lower ratios of Essential AAs/Total AAs, Branched-chain AAs/Total AAs, and Branched-chain AAs/Essential AAs. Serine and histidine were positively correlated with verbal memory and attention capacity deficits, respectively. Total AAs negatively correlated with attention capacity deficits. Stratifying patients with AD for MNA may identify a dual pattern of altered AAs, one due to AD per se and the other linked to nutritional state. Significant correlations were observed between several AAs and cognitive tests.

Effects of vitamin D in an animal model of Alzheimer's disease: behavioral assessment with biochemical investigation of Hippocampus and serum.

Regulatory role of vitamin D (VitD) in cognitive memory and learning has been proposed. Here, we examine the behavioral and biochemical effects of VitD in Alzheimer's disease (AD), as the most common form of dementia, in male Wistar rats. Animals (n = 48) were randomly divided into six groups: control, sham solvent, sham surgery, VitD (by intraperitoneal injection), AD (receiving intrahippocampal injection of amyloid-beta peptide, Aß), and combination of VitD and Aß. Learning and memory functions were investigated through the passive avoidance and the Morris water maze (MWM) tasks. Moreover, oxidative stress biomarkers including total antioxidant capacity (TAC), total thiol groups (TTG), lipid peroxidation (LPO), and DNA damage were assessed in hippocampus and serum. In passive avoidance task, Aß significantly impaired the step-through latency and time in dark compartment. It also increased escape latency and time spent in the target quadrant in the MWM. VitD administration attenuated the Aß-induced memory impairment in passive avoidance and MWM tests. Furthermore, VitD reduced deleterious biochemical effect of Aß by enhancing the levels of TAC and TTG in addition to decreasing LPO and DNA damage levels in both hippocampus and serum. We showed, for the first time, that VitD administration improves the impaired Aß-induced memory and that, by acting as a strong antioxidant, it can attenuate the stress oxidative biomarkers in hippocampus and serum of rats with AD. Altogether, our results provide evidence for further application of VitD in neurodegenerative disorders such as AD to enlighten the involved mechanisms.

Concordance between the assessment of Aß42, T-tau, and P-T181-tau in peripheral blood neuronal-derived exosomes and cerebrospinal fluid.

INTRODUCTION: Neuronal-derived exosomal Aß42, T-tau, and P-T181-tau have been demonstrated to be biomarkers of Alzheimer's disease (AD). However, no study has assessed the association of Aß42, T-tau, and P-T181-tau between exosomes and CSF. METHODS: This was a multicenter study with two-stage design. The subjects included 28 AD patients, 25 aMCI patients, and 29 controls in the discovery stage; the results of which were confirmed in the validation stage (73 AD, 71 aMCI, and 72 controls). RESULTS: The exosomal concentrations of Aß42, T-tau, and P-T181-tau in AD group were higher than those in aMCI and control groups (all P < .001). The level of each exosomal biomarker was highly correlated with that in CSF. DISCUSSION: This study verified the agreement between CSF and blood exosomal biomarkers and confirmed that exosomal Aß42, T-tau, and P-T181-tau have the same capacity as those in CSF for the diagnosis of AD and aMCI.

Assessment of lipid peroxidation and artificial neural network models in early Alzheimer Disease diagnosis.

OBJECTIVE: Lipid peroxidation constitutes a molecular mechanism involved in early Alzheimer Disease (AD) stages, and artificial neural network (ANN) analysis is a promising non-linear regression model, characterized by its high flexibility and utility in clinical diagnosis. ANN simulates neuron learning procedures and it could provide good diagnostic performances in this complex and heterogeneous disease compared with linear regression analysis. DESIGN AND METHODS: In our study, a new set of lipid peroxidation compounds were determined in urine and plasma samples from patients diagnosed with early Alzheimer Disease (n = 70) and healthy controls (n = 26) by means of ultra-performance liquid chromatography coupled with tandem mass-spectrometry. Then, a model based on ANN was developed to classify groups of participants. RESULTS: The diagnostic performances obtained using an ANN model for each biological matrix were compared with the corresponding linear regression model based on partial least squares (PLS), and with the non-linear (radial and polynomial) support vector machine (SVM) models. Better accuracy, in terms of receiver operating characteristic-area under curve (ROC-AUC), was obtained for the ANN models (ROC-AUC 0.882 in plasma and 0.839 in urine) than for PLS and SVM models. CONCLUSION: Lipid peroxidation and ANN constitute a useful approach to establish a reliable diagnosis when the prognosis is complex, multidimensional and non-linear.

The sociodemographic characteristics and dietary and blood plasma fatty acid profiles of elderly Saudi women with Alzheimer disease.

BACKGROUND: Alzheimer's disease (AD) is a progressive neurodegenerative disease, and due to various physiological and psychological factors the patients are at risk of nutritional insufficiencies. The purpose of this study was to assess the dietary fatty acid intake and its effect on plasma fatty acids in elderly Saudi women and to compare the differences in their food and plasma fatty acid profile on the basis of their residence. METHODS: A total of 76 elderly women (50-100 years) were recruited through a random sampling method. A structured proforma was designed to gather information related to their age, income, dietary habits, and presence of any disease and awareness of AD. A 24-h dietary recall method for 3 days and food frequency questionnaire, concentrating on fish consumption and consumption of foods rich in ω-3 fatty acids, which was planned by dietitians, was used for dietary assessment. The gathered data were then analyzed using food processor software. The blood samples were collected to determine plasma fatty acids. RESULTS: The mean age of women diagnosed with AD was more than 75 years, and the prevalence of illiteracy was higher among AD subjects. As compared to the AD group, the concentration of LA and total ω-6 was significantly (p ≤ 0.05) higher in the control group from both recruitment sites [National Guard Health Affairs, King Abdulaziz Medical City, Riyadh (NGH) and Social Welfare Homes for the Elderly (SWH)]. Similarly, the concentrations of EPA, DHA, and ω-3 were also slightly higher in the control group at both sites, but the difference between the control and AD subjects was only significant (p ≤ 0.05) in subjects from NGH. We found no significant difference in the ω-6/ ω-3 ratio between groups. Also, no significant difference was found in the mean level of the plasma fatty acid when comparing the control and AD groups. The concentration of DHA in controls only and AA, EPA and ω-6 in both control and AD were significant (although weakly) correlated with their respective dietary intakes. No correlations were found between the intake of 18 C precursors (LA and ALA) and plasma levels of their long chain derivatives (AA, EPA, and DHA). Education, income, overall health status and the concentration of various fatty acids from food was higher and better in subjects from SWH than NGH. The lower plasma level indicates lower impaired systemic availability of several nutrients. CONCLUSION: We found that dietary intervention might play a role in the prevention of AD.

Assessment of Plasma Total Tau Level as a Predictive Biomarker for Dementia and Related Endophenotypes.

Importance: Blood-based biomarkers have the potential to improve the identification of persons with the greatest dementia risk for inclusion in dementia prevention trials through low-cost and minimally invasive screening. Objective: To investigate the use of plasma total tau as a blood biomarker for dementia and related endophenotypes. Design, Setting, and Participants: This prospective cohort study used data from the US community-based Framingham Heart Study with replication in the Memento study, a multicenter cohort of persons with mild cognitive impairment or subjective cognitive complaints recruited from memory clinics across France. Total tau levels were measured from stored plasma samples in Framingham Heart Study participants during 2004 to 2011. Dementia follow-up occurred across a median of 6 years (interquartile range, 5-8 years) for persons 65 years and older who were dementia free at baseline. Plasma and/or cerebrospinal fluid samples were obtained from Memento study participants from April 19, 2011, to June 22, 2016. Dementia follow-up took place over a median of 4 years (interquartile range, 3-5 years). Data analysis was performed from January to November 2018. Exposures: Plasma total tau level measured using single-molecule array technology. Main Outcomes and Measures: Incidence of dementia of any cause (all dementia) and dementia due to clinical Alzheimer disease (AD dementia). Results: Among the 1453 participants in the Framingham dementia study sample, the mean (SD) age was 75 (7) years; 792 (54.5%) were female. Among the 367 individuals in the replication cohort, the mean (SD) age was 69 (9) years; 217 (59.1%) were female. Of 134 cases of incident all dementia in the Framingham sample, 105 were AD dementia. After adjustment for age and sex, each SD unit increase in the log of plasma total tau level was associated with a 35% increase in AD dementia risk (hazard ratio [HR], 1.35; 95% CI, 1.10-1.67). The addition of plasma total tau to a model including age and sex improved the stratification of participants for risk of AD dementia (net reclassification improvement, 0.382; 95% CI, 0.030-0.716). Higher plasma total tau level was associated with poorer cognition across 7 cognitive tasks (P < .05) and smaller hippocampi (hippocampal volume: ß [SE] = 0.002 [0.001]; P = .003) as well as neurofibrillary tangles (ß [SE] = 0.95 [0.45]; P = .04) and microinfarcts (odds ratio, 3.04; 95% CI, 1.26-7.37) at autopsy. In the replication cohort, plasma total tau level weakly correlated with cerebrospinal fluid total tau level (Spearman correlation coefficient, 0.16; P = .07), but plasma total tau was at least as strongly associated with incident AD dementia as cerebrospinal fluid total tau (log plasma total tau: HR, 2.33; 95% CI, 1.00-5.48; log cerebrospinal fluid total tau: HR, 2.14; 95% CI, 1.33-3.44) after adjustment for age and sex. Conclusions and Relevance: The findings suggest that plasma total tau levels may improve the prediction of future dementia, are associated with dementia endophenotypes, and may be used as a biomarker for risk stratification in dementia prevention trials.

A two-step immunoassay for the simultaneous assessment of Aß38, Aß40 and Aß42 in human blood plasma supports the Aß42/Aß40 ratio as a promising biomarker candidate of Alzheimer's disease.

BACKGROUND: The quantification of amyloid-beta (Aß) peptides in blood plasma as potential biomarkers of Alzheimer's disease (AD) is hampered by very low Aß concentrations and the presence of matrix components that may interfere with the measurements. METHODS: We developed a two-step immunoassay for the simultaneous measurement of the relative levels of Aß38, Aß40 and Aß42 in human EDTA plasma. The assay was employed for the study of 23 patients with dementia of the Alzheimer's type (AD-D) and 17 patients with dementia due to other reasons (OD). We examined relationships with the clinical diagnosis, cerebral Aß load as quantified by amyloid-positron emission tomography, apolipoprotein E genotype, Aß levels and Tau protein in cerebrospinal fluid. RESULTS: Preconcentration of plasma Aß peptides by immunoprecipitation substantially facilitated their immunological measurements. The Aß42/Aß40 and Aß42/Aß38 ratios were statistically significantly lower in the AD-D patients than in the OD group. The areas under the receiver operating characteristic curves reached 0.87 for the Aß42/Aß40 ratio and 0.80 for the Aß42/Aß38 ratio. CONCLUSIONS: The measurement of plasma Aß peptides with an immunological assay can be improved by preconcentration via immunoprecipitation with an antibody against the Aß amino-terminus and elution of the captured peptides by heating in a mild detergent-containing buffer. Our findings support the Aß42/Aß40 ratio in blood plasma as a promising AD biomarker candidate which correlates significantly with the validated core biomarkers of AD. Further studies will be needed for technical advancement of the assay and validation of the biomarker findings.

High performance plasma amyloid-ß biomarkers for Alzheimer's disease.

To facilitate clinical trials of disease-modifying therapies for Alzheimer's disease, which are expected to be most efficacious at the earliest and mildest stages of the disease, supportive biomarker information is necessary. The only validated methods for identifying amyloid-ß deposition in the brain-the earliest pathological signature of Alzheimer's disease-are amyloid-ß positron-emission tomography (PET) imaging or measurement of amyloid-ß in cerebrospinal fluid. Therefore, a minimally invasive, cost-effective blood-based biomarker is desirable. Despite much effort, to our knowledge, no study has validated the clinical utility of blood-based amyloid-ß markers. Here we demonstrate the measurement of high-performance plasma amyloid-ß biomarkers by immunoprecipitation coupled with mass spectrometry. The ability of amyloid-ß precursor protein (APP)669-711/amyloid-ß (Aß)1-42 and Aß1-40/Aß1-42 ratios, and their composites, to predict individual brain amyloid-ß-positive or -negative status was determined by amyloid-ß-PET imaging and tested using two independent data sets: a discovery data set (Japan, n = 121) and a validation data set (Australia, n = 252 including 111 individuals diagnosed using 11C-labelled Pittsburgh compound-B (PIB)-PET and 141 using other ligands). Both data sets included cognitively normal individuals, individuals with mild cognitive impairment and individuals with Alzheimer's disease. All test biomarkers showed high performance when predicting brain amyloid-ß burden. In particular, the composite biomarker showed very high areas under the receiver operating characteristic curves (AUCs) in both data sets (discovery, 96.7%, n = 121 and validation, 94.1%, n = 111) with an accuracy approximately equal to 90% when using PIB-PET as a standard of truth. Furthermore, test biomarkers were correlated with amyloid-ß-PET burden and levels of Aß1-42 in cerebrospinal fluid. These results demonstrate the potential clinical utility of plasma biomarkers in predicting brain amyloid-ß burden at an individual level. These plasma biomarkers also have cost-benefit and scalability advantages over current techniques, potentially enabling broader clinical access and efficient population screening.

Assessment of kallikrein 6 as a cross-sectional and longitudinal biomarker for Alzheimer's disease.

BACKGROUND: Kallikrein 6 (KLK6) is known to be an age-related protease expressed at high levels in the central nervous system. It was previously shown to be involved in proteolysis of extracellular proteins implicated in neurodegenerative diseases such as Alzheimer's disease (AD), prompting validation of KLK6 as a potential biomarker of disease. However, analyses of both plasma and cerebrospinal fluid (CSF) levels of KLK6 in patients with AD have been inconclusive. We present a detailed analysis of KLK6 in plasma and CSF in two separate cohorts in a cross-sectional and a longitudinal clinical setting. METHODS: The cross-sectional cohort included control subjects without dementia and patients with AD, and the longitudinal cohort included patients with MCI and patients with AD followed over a 2-year period. Plasma and CSF levels of KLK6 were quantified by use of a previously developed and validated enzyme-linked immunosorbent assay. Statistical analyses were performed to compare KLK6 levels between diagnostic groups and to identify potential associations between KLK6 level, age, apolipoprotein E (APOE) genotype, total apoE level and the classical CSF AD biomarkers. RESULTS: In the cross-sectional setting, KLK6 levels in plasma but not in CSF were significantly higher in the AD group than in control subjects. CSF but not plasma KLK6 levels were positively correlated with age in both the cross-sectional and longitudinal settings. In both cohorts, the CSF KLK6 levels were significantly and positively correlated with the CSF levels of core AD biomarkers. Total plasma and CSF apoE levels were positively associated with KLK6 in the cross-sectional study. Finally, during the 2-year monitoring period of the longitudinal cohort, CSF KLK6 levels increased with disease progression over time in the investigated patient groups. CONCLUSIONS: In two separate cohorts we have confirmed the previously reported correlation between age and CSF levels of KLK6. Increased plasma KLK6 levels in patients with AD with a more advanced disease stage suggest KLK6 as a potential biomarker in patients with AD with more severe dementia. Significant correlations between KLK6 levels and core CSF AD biomarkers suggest molecular links between KLK6 and AD-related pathological processes.

Oxidative Stress Assessment in Alzheimer's Disease: A Clinic Setting Study.

BACKGROUND: Oxidative stress (OS) is a physiological age-related brain process, dramatically overexpressed in neurodegenerative disorders like Alzheimer's disease (AD). Nevertheless, the pathophysiological role of OS in AD pathology has not been clarified yet. OS as a biomarker for AD is a controversial issue. A comparison of previous data is difficult due to a remarkable methodological variability. Most of the previous studies have shown higher levels of OS markers and lower antioxidant power in patients with dementia when compared to mild cognitive impairment (MCI) and healthy controls. METHODS: We followed a strict protocol in order to limit intrasite variability of OS assessment. In addition, we have taken into account possible confounding factors. RESULTS: In agreement with previous reports, we found both lower plasmatic OS and higher plasmatic antioxidant defenses when comparing patients with AD having dementia that is stably treated to patients with MCI-AD. DISCUSSION: A speculative hypothesis based on correlative data is provided.

Assessment of serum uric acid as risk factor for tauopathies.

Low levels of serum uric acid (UA) are a risk factor for many neurodegenerative diseases but the role of UA in tauopathies has not been yet fully evaluated. In this study, we assessed the risk associated with serum UA levels in a large group of patients with tauopathies, either primary or secondary. The mean serum UA concentrations of 111 patients with tauopathies (TAU), including 41 with progressive supranuclear palsy (PSP), 45 with Alzheimer's disease (AD) and 25 with frontotemporal dementia (FTD) were compared to that of 130 controls (CTL). The association between serum UA and TAU condition, PSP, AD and FTD was calculated as odd ratio (OR) adjusted for age and gender. A cut-off value of serum UA was finally obtained to predict subjects at risk for TAU. The serum UA levels in TAU and PSP, AD and FTD subgroups were similar, and significantly lower than CTL. Linear regression revealed inverse relationships between UA and TAU (OR = 0.610), PSP (OR = 0.626), AD (OR = 0.685) and FTD (OR = 0.577). The cut-off value of 4.35 mg/dl (AUC = 0.655) discriminates TAU from CTL, although with poor specificity and sensitivity. Low concentrations of serum UA represent a common risk factor for different tauopathies (PSP, FTD and AD). These findings may represent a starting point for preventive strategies or novel therapeutic approaches in this group of severe neurodegenerative diseases.

Combined assessment of DYRK1A, BDNF and homocysteine levels as diagnostic marker for Alzheimer's disease.

Early identification of Alzheimer's disease (AD) risk factors would aid development of interventions to delay the onset of dementia, but current biomarkers are invasive and/or costly to assess. Validated plasma biomarkers would circumvent these challenges. We previously identified the kinase DYRK1A in plasma. To validate DYRK1A as a biomarker for AD diagnosis, we assessed the levels of DYRK1A and the related markers brain-derived neurotrophic factor (BDNF) and homocysteine in two unrelated AD patient cohorts with age-matched controls. Receiver-operating characteristic curves and logistic regression analyses showed that combined assessment of DYRK1A, BDNF and homocysteine has a sensitivity of 0.952, a specificity of 0.889 and an accuracy of 0.933 in testing for AD. The blood levels of these markers provide a diagnosis assessment profile. Combined assessment of these three markers outperforms most of the previous markers and could become a useful substitute to the current panel of AD biomarkers. These results associate a decreased level of DYRK1A with AD and challenge the use of DYRK1A inhibitors in peripheral tissues as treatment. These measures will be useful for diagnosis purposes.