Improved Differential Diagnosis of Alzheimer's Disease by Integrating ELISA and Mass Spectrometry-Based Cerebrospinal Fluid Biomarkers.

BACKGROUND: Alzheimer's disease (AD) is diagnosed based on a clinical evaluation as well as analyses of classical biomarkers: Aß42, total tau (t-tau), and phosphorylated tau (p-tau) in cerebrospinal fluid (CSF). Although the sensitivities and specificities of the classical biomarkers are fairly good for detection of AD, there is still a need to develop novel biochemical markers for early detection of AD. OBJECTIVE: We explored if integration of novel proteins with classical biomarkers in CSF can better discriminate AD from non-AD subjects. METHODS: We applied ELISA, mass spectrometry, and multivariate modeling to investigate classical biomarkers and the CSF proteome in subjects (n = 206) with 76 AD patients, 74 mild cognitive impairment (MCI) patients, 11 frontotemporal dementia (FTD) patients, and 45 non-dementia controls. The MCI patients were followed for 4-9 years and 21 of these converted to AD, whereas 53 remained stable. RESULTS: By combining classical CSF biomarkers with twelve novel markers, the area of the ROC curves (AUROCS) of distinguishing AD and MCI/AD converters from non-AD were 93% and 96%, respectively. The FTDs and non-dementia controls were identified versus all other groups with AUROCS of 96% and 87%, respectively. CONCLUSIONS: Integration of new and classical CSF biomarkers in a model-based approach can improve the identification of AD, FTD, and non-dementia control subjects.

High tau levels in cerebrospinal fluid predict nursing home placement and rapid progression in Alzheimer's disease.

BACKGROUND: Increased concentrations of cerebrospinal fluid (CSF) total tau (t-tau) and phosphorylated tau, as well as decreased amyloid-ß 42 peptide, are biomarkers of Alzheimer's disease (AD) pathology, but few studies have shown an association with AD progression rate. We hypothesized that high CSF tau, as a marker of ongoing neurodegeneration, would predict a more aggressive course of AD, using time to nursing home placement (NHP) as the main outcome. METHODS: Our sample inlcuded 234 patients with mild cognitive impairment (MCI) due to AD (n = 134) or mild to moderate AD (n = 100) who underwent lumbar puncture at a memory clinic and were followed for 2-11 years (median 4.9 years). RESULTS: Individuals with CSF t-tau in the highest quartile (≥900 ng/L) had a higher ratio of NHP, both in the total cohort and in patients with MCI only (adjusted HR 2.17 [95% CI 1.24-3.80]; HR 2.37 [95% CI 1.10-5.09], respectively), than the lowest quartile. The association between high t-tau levels and future steep deterioration was confirmed in analyses with conversion to moderate dementia (HR 1.66; 95% CI 1.08-2.56), rapid decline in Mini Mental State Examination score (≥4-point drop/12 months), and dying in severe dementia as outcomes. CONCLUSIONS: To our knowledge, this is the first study to show that high CSF t-tau levels predict early NHP and conversion to moderate dementia in an AD cohort. Selecting patients with high CSF t-tau, indicating more aggressive neurodegeneration and steeper decline, for AD immunotherapy trials might increase the possibility of showing contrast between active treatment and placebo.

Reduced levels of IgM autoantibodies against N-truncated pyroglutamate Aß in plasma of patients with Alzheimer's disease.

In the present work, we investigated the level of IgM autoantibodies directed against different Aß epitopes as potential diagnostic biomarker for Alzheimer's disease (AD). Anti-Aß autoantibody levels were measured in 75 plasma samples from patients with AD, individuals with mild cognitive impairment (MCI), and healthy age- and sex-matched controls (HC). To validate the presence of anti-Aß IgMs, pooled plasma samples were subjected to gel-filtration analysis. The mean level of pGluAß-IgM (N-terminal truncated starting at position three with pyroglutamate) was significantly decreased in AD patients as compared to HC. In the group of MCI patients there was a significant positive correlation between pGluAß-IgM and cognitive decline analyzed by MMSE (rho = 0.58, d.f. = 13, p = 0.022). These observations indicate that the level of IgM autoantibodies against pGluAß is a promising plasma biomarker for AD and correlates with the cognitive status of individuals at risk to develop AD.

Higher cathepsin B levels in plasma in Alzheimer's disease compared to healthy controls.

Cathepsin B is suggested to be involved in amyloid-ß (Aß) processing and Alzheimer's disease (AD). Studies of cathepsin B levels in plasma and cerebrospinal fluid (CSF) have not been previously performed. We examined cathepsin B levels in plasma and CSF samples in persons with AD, mild cognitive impairment (MCI), and healthy controls in order to test the hypothesis that cathepsin B levels can discriminate persons with AD or MCI from healthy controls. Cathepsin B, Cystatin C, Aß1-40 and Aß1-42, total tau, phosphorylated tau, and albumin levels in plasma and CSF were analyzed by ELISA (Cathepsin B) turbidimetry (cystatin C), xMAP Luminex technology (Aß1-40 and Aß1-42 and tau), and Cobas C501 analyzer (albumin) in persons with AD (n=101), MCI (n=84), and healthy control subjects (n=28). Plasma cathepsin B levels were higher in persons with AD compared to healthy controls, both in unadjusted models and in multivariable models adjusting for age, gender, APOE genotype, cystatin C, and albumin levels: Odds ratio (OR) for AD per 1 SD of plasma cathepsin B; 2.04, 95% confidence interval (CI); 1.01-4.14, p= 0.05. There was no difference between diagnostic groups in cathepsin B levels in CSF: OR for AD per 1 SD of CSF cathepsin B; 0.93, 95% CI; 0.37-2.30, p= 0.87. Plasma cathepsin B levels were higher in persons with AD compared to healthy controls whereas there was no difference between diagnostic groups in cathepsin B levels in CSF. Further investigation of cathepsin B as a predictor of AD is warranted.

Identification of low molecular weight pyroglutamate A{beta} oligomers in Alzheimer disease: a novel tool for therapy and diagnosis.

N-terminally truncated Aß peptides starting with pyroglutamate (AßpE3) represent a major fraction of all Aß peptides in the brain of Alzheimer disease (AD) patients. AßpE3 has a higher aggregation propensity and stability and shows increased toxicity compared with full-length Aß. In the present work, we generated a novel monoclonal antibody (9D5) that selectively recognizes oligomeric assemblies of AßpE3 and studied the potential involvement of oligomeric AßpE3 in vivo using transgenic mouse models as well as human brains from sporadic and familial AD cases. 9D5 showed an unusual staining pattern with almost nondetectable plaques in sporadic AD patients and non-demented controls. Interestingly, in sporadic and familial AD cases prominent intraneuronal and blood vessel staining was observed. Using a novel sandwich ELISA significantly decreased levels of oligomers in plasma samples from patients with AD compared with healthy controls were identified. Moreover, passive immunization of 5XFAD mice with 9D5 significantly reduced overall Aß plaque load and AßpE3 levels, and normalized behavioral deficits. These data indicate that 9D5 is a therapeutically and diagnostically effective monoclonal antibody targeting low molecular weight AßpE3 oligomers.

Cystatin C levels are positively correlated with both Abeta42 and tau levels in cerebrospinal fluid in persons with Alzheimer's disease, mild cognitive impairment, and healthy controls.

Cystatin C is suggested to be involved in neurodegeneration and the development of Alzheimer's disease (AD) by binding to soluble amyloid-beta (Abeta) peptides. Studies of cystatin C levels in cerebrospinal fluid (CSF) in relation to risk of AD are conflicting and relations between cystatin C, Abeta42, and tau levels in CSF in AD, mild cognitive impairment (MCI), and healthy controls are unknown. The objective of this study was to investigate cystatin C, Abeta42, and tau levels in CSF in AD, MCI, and controls. As a secondary aim, the relationships between cystatin C, Abeta42, and tau levels across disease groups were investigated. Cystatin C, Abeta42, total tau, and phosphorylated tau levels in CSF were analyzed by turbidimetry (cystatin C) and xMAP Luminex technology (Abeta and tau) in persons with AD (n=101), MCI (n=84), and healthy control subjects (n=28). Mean cystatin C levels were similar in cases of AD (5.6 micromol/L +/- 1.7), MCI (5.4 micromol/L +/- 1.48), and controls (5.6 micromol/L +/- 1.6). However, CSF cystatin C levels were strongly and positively correlated with total tau and phosphorylated tau levels (r=0.61-0.81, p< 0.0001) and Abeta42 (r=0.35-0.65, p< 0.001) independent of age, gender, and APOE genotype. Mean CSF cystatin C levels did not differ between patients with AD and MCI and healthy controls. Interestingly, cystatin C levels were positively correlated with both tau and Abeta42 levels in CSF independent of age, gender, and APOE genotype.

Oligomerization partially explains the lowering of Abeta42 in Alzheimer's disease cerebrospinal fluid.

BACKGROUND/OBJECTIVE: The lowering of natively analyzed Abeta42 in cerebrospinal fluid (CSF) is used as a diagnostic tool in Alzheimer's disease (AD). The presence of Abeta oligomers can interfere with such analyses causing underestimation of Abeta levels due to epitope masking. The aim was to investigate if the lowering of CSF Abeta42 seen in AD is caused by oligomerization. METHODS: Abeta42 was analyzed under both denaturing and non-denaturing conditions. An Abeta42 oligomer ratio was calculated from these quantifications. The presence of oligomers leads to Abeta42 epitope masking during non-denaturing assays, resulting in a higher ratio. RESULTS: The Abeta42 oligomer ratio was used for the assessment of oligomerized Abeta in human CSF, after being evaluated in transgenic mouse brain homogenates. AD and mild cognitive impairment (MCI) samples displayed the expected decrease in natively measured Abeta42 compared to healthy controls and frontotemporal dementia, but not when analyzing under denaturing conditions. Accordingly, AD and MCI CSF had a higher Abeta42 oligomer ratio in CSF. CONCLUSION: Combining denaturing and non-denaturing quantifications of Abeta42 into an oligomer ratio enables the assessment of Abeta oligomers in biological samples. The increased Abeta42 oligomer ratio for AD and MCI indicates the presence of oligomers in CSF and that the lowering of natively measured Abeta42 is caused by oligomerization.

Systemic inflammation and the risk of Alzheimer's disease and dementia: a prospective population-based study.

Inflammation is suggested to be involved in the pathogenesis of Alzheimer's disease (AD). Serum interleukin-6 (IL-6) and high sensitivity serum reactive protein C (hsCRP) as markers of systemic inflammation were analyzed at two examinations of the ULSAM-study, a longitudinal, community-based study of elderly men (age 70, n = 1062 and age 77, n = 749). In addition, serum amyloid protein A (SAA) and urinary prostaglandin F2alpha (PGF2alpha) metabolite levels were analyzed at age 77 in this cohort. Two serial samples (at ages 70 and 77) were available from 704 individuals. Using Cox regression analyses, associations between serum IL-6, hsCRP, SAA and PGF2alpha metabolite levels and risk of AD, any type of dementia (all-cause dementia) and non-AD dementia were analyzed. On follow-up (median, 11.3 years) in the age 70 cohort, 81 subjects developed AD and 165 subjects developed all-cause dementia. Serum IL-6, hsCRP, SAA, or PGF2alpha levels were not associated with risk of AD. At age 70, high IL-6 levels were associated with an increased risk of non-AD dementia (Hazard ratio 2.21 for above vs. below/at median, 95%confidence interval 1.23-3.95, p-value = 0.008). A longitudinal change in CRP or IL-6 levels was not associated with AD ordementia. In conclusion, Serum IL-6, hsCRP, SAA, and PGF2alpha levels are not associated with the risk of AD. High serum IL-6 levels may be associated with increased risk of non-AD dementia.

Systemic tocopherols and F2-isoprostanes and the risk of Alzheimer's disease and dementia: a prospective population-based study.

Oxidative stress in the brain is suggested to be involved in the pathophysiology of Alzheimer's disease (AD). In this study, serum alpha- and gamma-tocopherol, the two major systemic antioxidants, were analyzed at two examinations of the ULSAM-study, a longitudinal, community-based study of elderly men (age 70, n = 616 and age 77, n = 761). In addition, urinary F2-isoprostane levels, as markers of systemic oxidative stress, were analyzed at the age of 77 in this cohort (n = 679). Cox regression analyses were used to examine associations between serum alpha-, gamma-tocopherol and urinary F2-isoprostane levels and AD, any type of dementia (all-cause dementia) and non-AD dementia. On follow-up (median, 12.3 years), 40 subjects developed AD and 86 subjects developed all-cause dementia. Serum alpha- and gamma-tocopherol or urinary F2-isoprostane levels were not associated with the future risk of AD or dementia. In conclusion, systemic serum alpha- and gamma-tocopherol and urinary F2-isoprostane levels are not associated with the future risk of AD or dementia and do not seem to be useful predictors of clinical AD or dementia.

Circulating immune complexes of Abeta and IgM in plasma of patients with Alzheimer's disease.

It has previously been shown that immune complexes (IC) of a given biomarker with class M immunoglobulins (IgM) provide better performances compared to the unbound biomarker in a number of cancer entities. In the present work, we investigated IC of IgM-Abeta as a potential biomarker for Alzheimer's disease (AD). Abeta-IgM concentration has been measured in 75 plasma samples from patients with AD, individuals with mild cognitive impairment (MCI), and healthy age- and sex-matched controls (HC). To characterize the fractions associated with Abeta, pooled plasma samples were subjected to gel-filtration analysis. Size-separated fractions were analyzed for the presence of Abeta using a sandwich ELISA assay. A strong reactivity was observed in the high molecular weight IgM (>500 kDa) and 150 kDa (IgG) fractions indicating that blood Abeta is strongly associated with antibodies. Using an ELISA assay detecting Abeta-IgM complexes, we observed that high levels of Abeta-IgMs were detectable in HC and MCI patients; however, there was no significant difference to the AD group.

Genetic analysis of Alzheimer's disease in the Uppsala Longitudinal Study of Adult Men.

BACKGROUND/AIMS: Genetic factors influencing common complex conditions have proven difficult to identify, and data from numerous investigations have provided incomplete conclusions as to the identity of these genes. Here we aimed to identify susceptibility genes for late-onset Alzheimer's disease (AD). METHODS: The case-control analysis included samples from 86 AD patients and 404 cognitively healthy controls selected from the Uppsala Longitudinal Study of Adult Men (ULSAM). In the incidence analysis, all 1,088 genotyped ULSAM participants were included. DNA samples from ULSAM participants were analyzed for 2,578 single nucleotide polymorphisms (SNP) within 368 genes. The selection of genes tested for association to AD within this cohort was based on genes previously implicated in conditions with relevance to ULSAM, such as dementia, cardiovascular disease, diabetes and metabolic syndrome, osteoporosis, and cancer. RESULTS/CONCLUSION: Association analysis revealed 82 genes containing at least 1 significant SNP at p < 0.05 with association to AD. Only 20 genes remained significant after a permutation test to correct for multiple comparisons within individual genes. Using publicly available data from 2 genome-wide association (GWA) studies and linkage disequilibrium data from HapMap, we attempted to replicate the AD association identified in ULSAM. In addition to apolipoprotein E, we were able to replicate 5 other genes in both GWA studies at p < 0.05.