Mirko Bibl

Standardization of preanalytical aspects of cerebrospinal fluid biomarker testing for Alzheimer's disease diagnosis: A consensus paper from the Alzheimer's Biomarkers Standardization Initiative

Numerous studies show that the cerebrospinal fluid biomarkers total tau (T‐tau), tau phosphorylated at threonine 181 (P‐tau181P), and amyloid‐β (1‐42) (Aβ1–42) have high diagnostic accuracy for Alzheimers disease. Variability in concentrations for Aβ1–42, T‐tau, and P‐tau181P drives the need for standardization.

CSF amyloid-β-peptides in Alzheimer's disease, dementia with Lewy bodies and Parkinson's disease dementia

Abstract As the differential diagnosis of dementias based on established clinical criteria is often difficult, biomarkers for applicable diagnostic testing are currently under intensive investigation. Amyloid plaques deposited in the brain of patients suffering from Alzheimers disease, dementia with Lewy bodies (DLB) and Parkinsons disease dementia (PDD) mainly consist of carboxy-terminally elongated forms of amyloid-beta (Aβ) peptides, such as Aβ1–42. Absolute Aβ1–42 levels in CSF have shown diagnostic value for the diagnosis of Alzheimers disease, but the discrimination among Alzheimers disease, DLB and PDD was poor. A recently established quantitative urea-based Aβ-sodium-dodecylsulphate–polyacrylamide-gel-electrophoresis with Western immunoblot (Aβ-SDS–PAGE/immunoblot) revealed a highly conserved Aβ peptide pattern of the carboxy-terminally truncated Aβ peptides 1–37, 1–38, 1–39 in addition to 1–40 and 1–42 in human CSF. We used the Aβ-SDS–PAGE/immunoblot to investigate the CSF of 23 patients with Alzheimers disease, 21 with DLB, 21 with PDD and 23 non-demented disease controls (NDC) for disease-specific alterations of the Aβ peptide patterns in its absolute and relative quantities. The diagnostic groups were matched for age and severity of dementia. The present study is the first attempt to evaluate the meaning of Aβ peptide patterns in CSF for differential diagnosis of the three neurodegenerative diseases—Alzheimers disease, DLB and PDD. The Aβ peptide patterns displayed disease-specific variations and the ratio of the differentially altered Aβ1–42 to the Aβ1–37 levels subsequently discriminated all diagnostic groups from each other at a highly significant level, except DLB from PDD. Additionally, a novel peptide with Aβ-like immunoreactivity was observed constantly in the CSF of all 88 investigated patients. The pronounced percentage increase of this peptide in DLB allowed a highly significant discrimination from PDD. Using a cut-off point of 0.954%, this marker yielded a diagnostic sensitivity and specificity of 81 and 71%, respectively. From several lines of indication, we consider this peptide to represent an oxidized α-helical form of Aβ1–40 (Aβ1–40*). The increased abundance of Aβ1–40* probably reflects a disease-specific alteration of the Aβ1–40 metabolism in DLB. We conclude that Aβ peptide patterns reflect disease-specific pathophysiological pathways of different dementia syndromes as distinct neurochemical phenotypes. Although Aβ peptide patterns failed to fulfil the requirements for a sole biomarker, their combined evaluation with other biomarkers is promising in neurochemical dementia diagnosis. It is noteworthy that DLB and PDD exhibit distinct clinical temporal courses, despite their similar neuropathological appearance. Their distinct molecular phenotypes support the view of different pathophysiological pathways for each of these neurodegenerative diseases.

Amyloid β peptide ratio 42/40 but not Aβ42 correlates with phospho-Tau in patients with low- and high-CSF Aβ40 load

Neurochemical dementia diagnostics (NDD) can significantly improve the clinically based categorization of patients with early dementia disorders, and the cerebrospinal fluid (CSF) concentrations of amyloid β peptides ending at the amino acid position of 42 (Aβx‐42 and Aβ1‐42) are widely accepted biomarkers of Alzheimer’s disease (AD). However, in subjects with constitutively high‐ or low‐CSF concentrations of total Aβ peptides (tAβ), the NDD interpretation might lead to erroneous conclusions as these biomarkers seem to correlate better with the total Aβ load than with the pathological status of a given patient in such cases. In this multicenter study, we found significantly increased CSF concentrations of phosphorylated Tau (pTau181) and total Tau in the group of subjects with high CSF Aβx‐40 concentrations and decreased Aβx‐42/x‐40 concentration ratio compared with the group of subjects with low CSF Aβx‐40 and normal Aβ ratio (p < 0.001 in both cases). Furthermore, we observed significantly decreased Aβ ratio (p < 0.01) in the group of subjects with APOE ε4 allele compared with the group of subjects without this allele. Surprisingly, patients with low‐Aβx‐40 and the decreased Aβ ratio characterized with decreased pTau181 (p < 0.05), and unaltered total Tau compared with the subjects with high Aβx‐40 and the Aβ ratio in the normal range. We conclude that the amyloid β concentration ratio should replace the ‘raw’ concentrations of corresponding Aβ peptides to improve reliability of the neurochemical dementia diagnosis.

Soluble amyloid precursor proteins in the cerebrospinal fluid as novel potential biomarkers of Alzheimer's disease: a multicenter study

In this report, we present the results of a multicenter study to test analytic and diagnostic performance of soluble forms of amyloid precursor proteins α and β (sAPPα and sAPPβ) in the cerebrospinal fluid (CSF) of patients with different forms of dementing conditions. CSF samples were collected from 188 patients with early dementia (mini-mental state examination⩾20 in majority of cases) and mild cognitive impairment (MCI) in 12 gerontopsychiatric centers, and the clinical diagnoses were supported by neurochemical dementia diagnostic (NDD) tools: CSF amyloidβ peptides, Tau and phospho-Tau. sAPPα and sAPPβ were measured with multiplexing method based on electrochemiluminescence. sAPPα and sAPPβ CSF concentrations correlated with each other with very high correlation ratio (R=0.96, P<0.001). We observed highly significantly increased sAPPα and sAPPβ CSF concentrations in patients with NDD characteristic for Alzheimers disease (AD) compared to those with NDD negative results. sAPPα and sAPPβ highly significantly separated patients with AD, whose diagnosis was supported by NDD findings (sAPPα: cutoff, 117.4 ng ml−1, sensitivity, 68%, specificity, 85%, P<0.001; sAPPβ: cutoff, 181.8 ng ml−1, sensitivity, 75%, specificity, 85%, P<0.001), from the patients clinically assessed as having other dementias and supported by NDD untypical for AD. We conclude sAPPα and sAPPβ might be regarded as novel promising biomarkers supporting the clinical diagnosis of AD.

Beta-Amlyoid 1-42 and Tau-Protein in Cerebrospinal Fluid of Patients with Parkinson's Disease Dementia

Measurement of τ-protein and β-amyloid1–42 (Aβ42) in cerebrospinal fluid (CSF) has gained increasing acceptance in the differential diagnosis of Alzheimer’s disease. We investigated CSF τ-protein and Aβ42 concentrations in 73 patients with advanced idiopathic Parkinson’s disease with dementia (PDD) and 23 patients with idiopathic Parkinson’s disease without dementia (PD) and in a comparison group of 41 non-demented neurological patients (CG) using commercially available enzyme-linked-immunoabsorbant-assay (ELISA). τ-Protein levels were statistically significantly higher and Aβ42 lower in the PDD patients compared to PD patients and the CG. This observation was most marked (p < 0.05) in a subgroup of patients with PDD carrying the apolipoprotein genotype Ε3/Ε3. The distribution of the apolipoprotein genotypes in PDD and PD patients was similar to that of the CG. Although a significant difference in τ-protein values was observed between PDD and CG, no diagnostic cut-off value was established. These findings suggest that such protein CSF changes may help to support the clinical diagnosis of cognitive decline in PD and that there may be apolipoprotein-E-isoform-specific differences in CSF protein regulation in advanced PDD.

International quality control survey of neurochemical dementia diagnostics.

UNLABELLED Currently, neurochemical dementia diagnostics (NDD) are increasingly entering routine clinical neurochemistry, offering improved early and differential diagnosis of dementias. However, there is an obvious lack of standardization in pre-analytical sample handling and systematic quality surveys. Therefore, in this study, 14 laboratories in Germany, Austria, and Switzerland were given aliquots of a human cerebrospinal fluid (CSF) sample, and were asked to measure Alzheimers disease (AD) biomarkers (amyloid beta (Abeta) peptides, total Tau protein, and phosphorylated Tau protein (P-tau(181P))) according to their routine protocols. RESULTS The inter-laboratory coefficients of variation of the results obtained by the laboratories participating in this study were in the range of 20-30%. Although the results of this quality control survey are promising, the quality of measurements has to be further optimized.

β-amyloid peptides in cerebrospinal fluid of patients with Creutzfeldt–Jakob disease

Decreased levels of β‐amyloid peptide 1‐42 (Aβ1‐42) in cerebrospinal fluid (CSF) are a characteristic feature of Alzheimers disease (AD) but recently were also observed in Creutzfeldt–Jakob disease (CJD). We analyzed the CSF of patients with CJD, and AD and nondemented controls using a quantitative urea‐based Aβ sodium dodecyl sulfate polyacrylamide gel electrophoresis immunoblot. Like in AD and nondemented controls, we found a highly conserved pattern of carboxyterminally truncated Aβ1‐37/38/39 in addition to Aβ1‐40/42 also in CJD patients. By the introduction of the ratio Aβ1‐39 to Aβ1‐42, CJD and AD can effectively be differentiated. We conclude that the immunoblot shows disease‐specific CSF Aβ peptide patterns in CJD and AD and suppose that measurement of the Aβ peptide pattern seems to be a promising diagnostic tool in the differential diagnosis of dementias. Ann Neurol 2003;54:263–267

Tau protein phosphorylated at threonine 181 in CSF as a neurochemical biomarker in Alzheimer’s disease

Cerebrospinal fluid (CSF) concentrations of total Tau and Tau phosphorylated at threonine (position 181 [pTau181]) were studied with ELISA in a group of carefully selected patients with a neurochemically supported diagnosis of Alzheimer’s disease (AD, n=9; age range, 51–89 yr) and in a group of sex- and age-matched nondemented controls (n=9; age range, 52–81 yr). The concentration of both biomarkers is increased significantly in the AD group (total Tau, p<0.0008; pTau181, p<0.008). A significant correlation between CSF concentrations of both biomarkers is observed (R=0.897; p<0.001). Neither total Tau nor pTau181 correlates with age or degree of memory impairment, and only a tendency is observed between the concentrations of total Tau and Aβ42 in the CSF. Our results further confirm a possible role of pTau181 as a diagnostic tool in AD. The current literature regarding the physiological and pathological role of phosphorylated Tau proteins is reviewed, as well as the role of these proteins as promising biomarkers in the diagnosis of neurodegenerative disorders.

Amyloid β peptides in cerebrospinal fluid as profiled with surface enhanced laser desorption/ionization time-of-flight mass spectrometry: evidence of novel biomarkers in Alzheimer's disease

Abstract Background The advent of new therapeutic avenues for Alzheimers disease (AD) calls for an improved early and differential diagnosis. Methods With surface enhanced laser desorption/ionization time-of-flight mass spectrometry (SELDI-TOF MS), cerebrospinal fluid from patients with AD ( n = 10) and nondemented control subjects ( n = 9) was studied. Results Molecular mass signals were observed corresponding to three novel amyloid beta (Aβ) peptides that have not previously been described, in addition to those previously known, with molecular masses of 4525.1 d, 4846.8 d, and 7755.8 d. The signal-to-noise ratios (S/NR) of Aβ(4525.1) and Aβ(7758.8+2H) were significantly decreased in AD [Aβ(4525.1): median 2.2 and 4.3 in AD and control subjects, respectively, p p p p R = .67, p Conclusions We report evidence of three novel amyloid β peptides that might play an important role in the diagnosis and pathophysiology of Alzheimers disease.

Tau Protein, Aβ42 and S-100B Protein in Cerebrospinal Fluid of Patients with Dementia with Lewy Bodies

The intra vitam diagnosis of dementia with Lewy bodies (DLB) is still based on clinical grounds. So far no technical investigations have been available to support this diagnosis. As for tau protein and β-amyloid(1–42) (Aβ42), promising results for the diagnosis of Alzheimer’s disease (AD) have been reported; we evaluated these markers and S-100B protein in cerebrospinal fluid (CSF), using a set of commercially available assays, of 71 patients with DLB, 67 patients with AD and 41 nondemented controls (NDC) for their differential diagnostic relevance. Patients with DLB showed significantly lower tau protein values compared to AD but with a high overlap of values. More prominent differences were observed in the comparison of DLB patients with all three clinical core features and AD patients. Aβ42 levels were decreased in the DLB and AD groups versus NDC, without significant subgroup differences. S-100B levels were not significantly different between the groups. Tau protein levels in CSF may contribute to the clinical distinction between DLB and AD, but the value of the markers is still limited especially due to mixed pathology. We conclude that more specific markers have to be established for the differentiation of these diseases.