Human lumbar CSF patterns of Ab peptides were analysed by urea-based b-amyloid sodium dodecyl sulphate polyacrylamide gel electrophoresis with western immunoblot (Ab-SDS-PAGE/immunoblot). A highly conserved pattern of carboxyterminally truncated Ab1-37/38/39 was found in addition to Ab1-40 and Ab1-42. Remarkably, Ab1-38 was present at a higher concentration than Ab1-42, being the second prominent Ab peptide species in CSF. Patients with Alzheimer's disease (AD, n ¼ 12) and patients with chronic inflammatory CNS disease (CID, n ¼ 10) were differentiated by unique CSF Ab peptide patterns from patients with other neuropsychiatric diseases (OND, n ¼ 37). This became evident only when we investigated the amount of Ab peptides relative to their total Ab peptide concentration (Ab1-x%, fractional Ab peptide pattern), which may reflect diseasespecific c-secretase activities. Remarkably, patients with AD and CID shared elevated Ab1-38% 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 e4 alleles resulted in an overall reduction of CSF Ab peptides, which was pronounced for Ab1-42. The severity of dementia was significantly correlated to the fractional Ab peptide pattern but not to the absolute Ab peptide concentrations. Keywords: Alzheimer's disease (AD), b-amyloid protein precursor/metabolism, biological markers, cerebrospinal fluid, 2D-PAGE, western immunoblot.

Alzheimer's disease is an age-related progressive neurodegenerative disorder with an enormous unmet medical need. It is the most common form of dementia affecting approximately 5% of adults over 65 years. In view of our ageing society the number of patients, as well as the economical and social impact, is expected to grow dramatically in the future. Currently available medications appear to be able to produce moderate symptomatic benefits but not to stop disease progression. The search for novel therapeutic approaches targeting the presumed underlying pathogenic mechanisms has been a major focus of research and it is expected that novel medications with disease-modifying properties will emerge from these efforts in the future. In this review, currently available drugs as well as novel therapeutic strategies, in particular those targeting amyloid and tau pathologies, are discussed.

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 Alzheimer's disease, dementia with Lewy bodies (DLB) and Parkinson's 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 Alzheimer's disease, but the discrimination among Alzheimer's 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 Alzheimer's 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—Alzheimer's 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.

Beta-amyloid peptides (A beta peptides) form the main protein component of the amyloid deposits found in the brains of Alzheimer's disease (AD) patients. Soluble A beta peptides, which are proteolytic fragments of the amyloid-precursor protein (APP) are constitutively secreted by cells expressing APP during normal metabolism [1] and are also present in human plasma and cerebrospinal fluid [2]. Missense mutations in Codon 717 of the APP gene are responsible for a small percentage of inherited AD cases (FAD) and increase the amount of A beta peptides containing additional carboxy terminal amino acids (A beta 1-42, A beta 1-43) [3, 4]. Recent findings indicate that FAD mutations in the presenilin 1 and 2 genes also increase the amount of these longer A beta peptides [5]. A beta 1-42 polymerizes more rapidly in vitro [6] than A beta 1-40 and has been identified as the major component of the brain amyloid deposits [7-9]. We recently developed a sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) system [10] for the separation of these two peptides. Here we describe a modified version of the original SDS-PAGE procedure, which allows the separation of A beta 1-40, A beta 1-42, and A beta 1-43 for the first time. Detection of the three A beta peptides in the lower ng and pg range is realized by optimized silver staining or immunoblot procedures. These nonradioactive methods may validate results obtained by ELISA procedures used to study the metabolic fate of APP. They may help to define the neurotoxic potential of the longer A beta peptides in relation to their aggregation state.

An orally bioavailable and blood-brain barrier penetrating analog of the kinase inhibitor K252a was able to prevent the typical motor deficits in the tau (P301L) transgenic mouse model (JNPL3) and markedly reduce soluble aggregated hyperphosphorylated tau. However, neurofibrillary tangle counts were not reduced in the successfully treated cohort, suggesting that the main cytotoxic effects of tau are not exerted by neurofibrillary tangles but by lower molecular mass aggregates of tau. Our findings strongly suggest that abnormal tau hyperphosphorylation plays a critical role in the development of tauopathy and suggest a previously undescribed treatment strategy for neurodegenerative diseases involving tau pathology.Alzheimer's disease ͉ extracellular signal-regulated kinase inhibitor ͉ paired helical filament ͉ tangles

The misfolding of the Amyloid-beta (Aβ) peptide into β-sheet enriched conformations was proposed as an early event in Alzheimer's Disease (AD). Here, the Aβ peptide secondary structure distribution in cerebrospinal fluid (CSF) and blood plasma of 141 patients was measured with an immuno-infrared-sensor. The sensor detected the amide I band, which reflects the overall secondary structure distribution of all Aβ peptides extracted from the body fluid. We observed a significant downshift of the amide I band frequency of Aβ peptides in Dementia Alzheimer type (DAT) patients, which indicated an overall shift to β-sheet. The secondary structure distribution of all Aβ peptides provides a better marker for DAT detection than a single Aβ misfold or the concentration of a specific oligomer. The discrimination between DAT and disease control patients according to the amide I frequency was in excellent agreement with the clinical diagnosis (accuracy 90% for CSF and 84% for blood). The amide I band maximum above or below the decisive marker frequency appears as a novel spectral biomarker candidate of AD. Additionally, a preliminary proof-of-concept study indicated an amide I band shift below the marker band already in patients with mild cognitive impairment due to AD. The presented immuno-IR-sensor method represents a promising, simple, robust, and label-free diagnostic tool for CSF and blood analysis.

Alzheimer’s disease (AD) is an irreversible, devastating neurodegenerative brain disorder characterized by the loss of neurons and subsequent cognitive decline. Despite considerable progress in the understanding of the pathophysiology of AD, the precise molecular mechanisms that cause the disease remain elusive. By now, there is ample evidence that activated microglia have a critical role in the initiation and progression of AD. The present study describes the identification of Glycoprotein nonmetastatic melanoma protein B (GPNMB) as a novel AD-related factor in both transgenic mice and sporadic AD patients by expression profiling, immunohistochemistry and ELISA measurements. We show that GPNMB levels increase in an age-dependent manner in transgenic AD models showing profound cerebral neuron loss and demonstrate that GPNMB co-localizes with a distinct population of IBA1-positive microglia cells that cluster around amyloid plaques. Our data further indicate that GPNMB is part of a microglia activation state that is only present under neurodegenerative conditions and that is characterized by the up-regulation of a subset of genes including TREM2, APOE and CST7. In agreement, we provide in vitro evidence that soluble Aβ has a direct effect on GPNMB expression in an immortalized microglia cell line. Importantly, we show for the first time that GPNMB is elevated in brain samples and cerebrospinal fluid (CSF) of sporadic AD patients when compared to non-demented controls.The current findings indicate that GPNMB represents a novel disease-associated marker that appears to play a role in the neuroinflammatory response of AD.Electronic supplementary materialThe online version of this article (10.1186/s40478-018-0612-3) contains supplementary material, which is available to authorized users.

Cerebrospinal fluid (CSF) concentrations of amyloid-beta (Abeta) 1-38, 1-40, 1-42, total-tau and phospho-tau in samples from 156 patients with Alzheimer's disease (AD) (n = 44), depressive cognitive complainers (DCC, n = 25) and various other forms of non-Alzheimer dementias (NAD, n = 87) were analyzed by electrochemiluminescence and enzyme linked immunosorbent assay, respectively. A significant decrease of CSF Abeta1-42 was the most powerful single marker for differentiation of AD from DCC, yielding accuracies of beyond 85%. Increased p-tau and the ratio Abeta1-42/Abeta1-38 yielded accuracies of beyond 80 and 85%, respectively, to discriminate AD versus NAD. Combining p-tau with Abeta1-42/Abeta1-38 resulted in a sensitivity of 94% for detection of AD and 85% specificity for excluding NAD. Decreased CSF Abeta1-42 represents a core biomarker for AD. The lack of specificity for exclusion of NAD can be most effectively compensated by the ratio Abeta1-42/Abeta1-38. The ratio Abeta1-42/Abeta1-38/p-tau powerfully discriminates AD versus NAD and fulfils the accuracy requirements for an applicable screening and differential diagnostic AD biomarker.