Search

Neurochemical biomarkers can support the diagnosis of Alzheimer's disease and may facilitate clinical trials. In blood plasma, the ratio of the amyloid-β (Aβ) peptides Aβ-3-40/Aβ1-42 can predict cerebral amyloid-β pathology with high accuracy (Nakamura et al., 2018). Whether or not Aβ-3-40 (aka. amyloid precursor protein (APP) 669-711) is also present in cerebrospinal fluid (CSF) is not clear. Here, we investigated whether Aβ-3-40 can be detected in CSF and to what extent the CSF Aβ-3-40/Aβ42 ratio is able to differentiate between individuals with or without amyloid-β positron emission tomography (PET) evidence of brain amyloid. The occurrence of Aβ-3-40 in human CSF was assessed by immunoprecipitation followed by mass spectrometry. For quantifying the CSF concentrations of Aβ-3-40 in 23 amyloid PET-negative and 17 amyloid PET-positive subjects, we applied a sandwich-type immunoassay. Our findings provide clear evidence of the presence of Aβ-3-40 and Aβ-3-38 in human CSF. While there was no statistically significant difference in the CSF concentration of Aβ-3-40 between the two diagnostic groups, the CSF Aβ-3-40/Aβ42 ratio was increased in the amyloid PET-positive individuals. We conclude that Aβ-3-40 appears to be a regular constituent of CSF and may potentially serve to accentuate the selective decrease in CSF Aβ42 in Alzheimer's disease., (© 2022 The Authors. Journal of Neurochemistry published by John Wiley & Sons Ltd on behalf of International Society for Neurochemistry.)

Blood-based tests for the differential diagnosis of Alzheimer's disease (AD) are under intensive investigation and have shown promising results with regard to Abeta40 and Abeta42 peptide species in incipient AD. Moreover, plasma Abeta40 was suggested as an independent cerebrovascular risk factor candidate. These considerations prompted us to analyse a total of 72 plasma samples in vascular dementias (VAD, n = 15), AD with cerebrovascular disease (AD with CVD, n = 7), AD (n = 15), Parkinson's disease and Parkinson's disease dementia (PD/PDD, n = 20) and 15 patients with depression that served as controls (DC) for distinct plasma amyloid-beta (Abeta) peptide patterns. For the analysis of plasma we used immunoprecipitation followed by the quantitative Abeta-SDS-PAGE/immunoblot. For comparison, CSF tau and Abeta1-42 analyses were performed. The major outcome was an increase in Abeta1-40 in plasma of VAD paralleled by a decrease in the ratio of Abeta1-38/Abeta1-40. The ratio Abeta1-38/Abeta1-40 in plasma enabled contrasts of beyond 85% and 80% for discriminating VAD from DC and all other patients, respectively. In CSF, we confirmed the typical CSF biomarker constellation of increased tau and diminished Abeta1-42 levels for AD. The diagnostic accuracy of plasma Abeta1-38/Abeta1-40 for VAD resembled the accuracy of CSF biomarkers for AD. From the presented results, we consider the ratio of plasma Abeta1-38/Abeta1-40 peptides to be a blood-based biomarker candidate for VAD.

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 beta peptides ending at the amino acid position of 42 (A beta x-42 and A beta 1-42) are widely accepted biomarkers of Alzheimer's disease (AD). However, in subjects with constitutively high- or low-CSF concentrations of total A beta peptides (tA beta), the NDD interpretation might lead to erroneous conclusions as these biomarkers seem to correlate better with the total A beta 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 A beta x-40 concentrations and decreased A beta x-42/x-40 concentration ratio compared with the group of subjects with low CSF A beta x-40 and normal A beta ratio (p<0.001 in both cases). Furthermore, we observed significantly decreased A beta ratio (p<0.01) in the group of subjects with APOE epsilon 4 allele compared with the group of subjects without this allele. Surprisingly, patients with low-A beta x-40 and the decreased A beta ratio characterized with decreased pTau181 (p<0.05), and unaltered total Tau compared with the subjects with high A beta x-40 and the A beta ratio in the normal range. We conclude that the amyloid beta concentration ratio should replace the 'raw' concentrations of corresponding A beta peptides to improve reliability of the neurochemical dementia diagnosis.

Mutations in human presenilin (PS) genes cause aggressive forms of familial Alzheimer's disease. Presenilins are polytopic proteins that harbour the catalytic site of the gamma-secretase complex and cleave many type I transmembrane proteins including beta-amyloid precursor protein (APP), Notch and syndecan 3. Contradictory results have been published concerning whether PS mutations cause 'abnormal' gain or (partial) loss of function of gamma-secretase. To avoid the possibility that wild-type PS confounds the interpretation of the results, we used presenilin-deficient cells to analyse the effects of different clinical mutations on APP, Notch, syndecan 3 and N-cadherin substrate processing, and on gamma-secretase complex formation. A loss in APP and Notch substrate processing at epsilon and S3 cleavage sites was observed with all presenilin mutants, whereas APP processing at the gamma site was affected in variable ways. PS1-Delta9 and PS1-L166P mutations caused a reduction in beta-amyloid peptide Abeta40 production whereas PS1-G384A mutant significantly increased Abeta42. Interestingly PS2, a close homologue of PS1, appeared to be a less efficient producer of Abeta than PS1. Finally, subtle differences in gamma-secretase complex assembly were observed. Overall, our results indicate that the different mutations in PS affect gamma-secretase structure or function in multiple ways.

The interaction of endogenous and exogenous stimulators of innate immunity was examined in primary cultures of mouse microglial cells and macrophages after application of defined Toll-like receptor (TLR) agonists [lipopolysaccharide (LPS) (TLR4), the synthetic lipopeptide Pam3Cys-Ser-Lys4 (Pam3Cys) (TLR2) and single-stranded unmethylated CpG-DNA (CpG) (TLR9)] alone and in combination with amyloid beta peptide (Abeta) 1-40. Abeta1-40 stimulated microglial cells and macrophages primed by interferon-gamma in a dose-dependent manner. Co-administration of Abeta1-40 with LPS or Pam3Cys led to an additive release of nitric oxide (NO) and tumour necrosis factor alpha (TNF-alpha). This may be one reason for the clinical deterioration frequently observed in patients with Alzheimer's disease during infections. In contrast, co-application of Abeta1-40 with CpG led to a substantial decrease of NO and TNF-alpha release compared with stimulation with CpG alone. Abeta1-40 and CpG did not co-localize within the same subcellular compartment, making a direct physicochemical interaction as the cause of the observed antagonism very unlikely. This suggests that not all TLR agonists enhance the stimulatory effect of A beta on innate immunity.

Human lumbar CSF patterns of Abeta peptides were analysed by urea-based beta-amyloid sodium dodecyl sulphate polyacrylamide gel electrophoresis with western immunoblot (Abeta-SDS-PAGE/immunoblot). A highly conserved pattern of carboxyterminally truncated Abeta1-37/38/39 was found in addition to Abeta1-40 and Abeta1-42. Remarkably, Abeta1-38 was present at a higher concentration than Abeta1-42, being the second prominent Abeta peptide species in CSF. Patients with Alzheimer's disease (AD, n = 12) and patients with chronic inflammatory CNS disease (CID, n = 10) were differentiated by unique CSF Abeta peptide patterns from patients with other neuropsychiatric diseases (OND, n = 37). This became evident only when we investigated the amount of Abeta peptides relative to their total Abeta peptide concentration (Abeta1-x%, fractional Abeta peptide pattern), which may reflect disease-specific gamma-secretase activities. Remarkably, patients with AD and CID shared elevated Abeta1-38% values, whereas otherwise the patterns were distinct, allowing separation of AD from CID or OND patients without overlap. The presence of one or two ApoE epsilon4 alleles resulted in an overall reduction of CSF Abeta peptides, which was pronounced for Abeta1-42. The severity of dementia was significantly correlated to the fractional Abeta peptide pattern but not to the absolute Abeta peptide concentrations.