Hugo Vanderstichele

Deficiency of presenilin-1 inhibits the normal cleavage of amyloid precursor protein.

Point mutations in the presenilin-1 gene (PS1) are a major cause of familial Alzheimers disease. They result in a selective increase in the production of the amyloidogenic peptide amyloid-β(1–42) by proteolytic processing of the amyloid precursor protein (APP). Here we investigate whether PS1 is also involved in normal APP processing in neuronal cultures derived from PS1-deficient mouse embryos. Cleavage by α- and β-secretase of the extracellular domain of APP was not affected by the absence of PS1, whereas cleavage by γ-secretase of the transmembrane domain of APP was prevented, causing carboxyl-terminal fragments of APP to accumulate and a fivefold drop in the production of amyloid peptide. Pulse-chase experiments indicated that PS1 deficiency specifically decreased the turnover of the membrane-associated fragments of APP. As in the regulation of cholesterol metabolism by proteolysis of a membrane-bound transcription factor, PS1 appears to facilitate a proteolytic activity that cleaves the integral membrane domain of APP. Our results indicate that mutations in PS1 that manifest clinically cause a gain of function and that inhibition of PS1 activity is a potential target for anti-amyloidogenic therapy in Alzheimers disease.

Cerebrospinal Fluid Biomarker Signature in Alzheimer’s Disease Neuroimaging Initiative Subjects

Develop a cerebrospinal fluid biomarker signature for mild Alzheimers disease (AD) in Alzheimers Disease Neuroimaging Initiative (ADNI) subjects.

Improved discrimination of AD patients using β-amyloid(1-42) and tau levels in CSF

Objective: To evaluate CSF levels of β-amyloid(1-42) (Aβ42) alone and in combination with CSF tau for distinguishing AD from other conditions. Methods: At 10 centers in Europe and the United States, 150 CSF samples from AD patients were analyzed and compared with 100 CSF samples from healthy volunteers or patients with disorders not associated with pathologic conditions of the brain (CON), 84 patients with other neurologic disorders (ND), and 79 patients with non-Alzheimer types of dementia (NAD). Sandwich ELISA techniques were used on site for measuring Aβ42 and tau. Results: Median levels of Aβ42 in CSF were significantly lower in AD (487 pg/mL) than in CON (849 pg/mL; p = 0.001), ND (643 pg/mL; p = 0.001), and NAD (603 pg/mL; p = 0.001). Discrimination of AD from CON and ND was significantly improved by the combined assessment of Aβ42 and tau. At 85% sensitivity, specificity of the combined test was 86% (95% CI: 81% to 91%) compared with 55% (95% CI: 47% to 62%) for Aβ42 alone and 65% (95% CI: 58% to 72%) for tau. The combined test at 85% sensitivity was 58% (95% CI: 47% to 69%) specific for NAD. The APOE e4 gene load was negatively correlated with Aβ42 levels not only in AD but also in NAD. Conclusions: The combined measure of CSF Aβ42 and tau meets the requirements for clinical use in discriminating AD from normal aging and specific neurologic disorders.

Quantification of tau phosphorylated at threonine 181 in human cerebrospinal fluid : a sandwich ELISA with a synthetic phosphopeptide for standardization

Hyperphosphorylation of the microtubule-associated protein tau is specifically found in those brain cells affected in several tauopathies. Tau has also been consistently found to be present in the cerebrospinal fluid (CSF). Here we report the quantification in CSF of tau phosphorylated at Thr 181 using an immunoassay with a synthetic peptide for standardization. The choice of the peptide was based on fine mapping of a phospho-dependent antibody, AT270 (P(176)PAPKT(p)P(132))and a human specific tau antibody, HT7 (P(159)PGQK(163)). CSF-phospho-tau levels were increased in Alzheimer patients (23.5+/-10.1 pM, P<0.01) compared with age-matched controls (15.9+/-5.7 pM), while decreased in patients with frontotemporal dementia (8.6+/-3.9 pM; P<0.01). In every diagnostic group, a highly significant correlation was found between total tau and phospho-tau (Alzheimers disease, r(2)=0.73; frontotemporal dementia, r(2)=0.43; Control, r(2)=0.42), suggesting that the degree of phosphorylation of CSF-tau changes in different clinical conditions.

Standardization of measurement of beta-amyloid(1-42) in cerebrospinal fluid and plasma

The standardization and clinical validation of the measurement of β–amyloid. (Aβ42) in cerebrospinal fluid (CSF), plasma and urine is described using a commercially available sandwich–type ELISA with 2 IF12 and 3D6 as monoclonal antibodies. The INNOTEST™ β–amyloid(1–42) allows the specific and reliable measurement of (1–42) amyloid peptides in CSF and plasma. The Aβ42 concentrations in serum and urine were below the detection limit. In plasma, no differences were found in Aβ42 levels between controls and patients with different neurodegenerative disorders (Alzheimers disease (AD), Lewy body disease (LED), others). In contrast, CSF–Aβ42 concentrations were lower in AD and LBD patients as compared to controls. No correlation was found in AD patients between CSF and plasma concentrations of Aβ42 or between CSF Aβ42 levels and blood–brain–barrier function. The quantitative outcome of the test is in part dependent on confounding factors such as tube type, freeze/thaw cycles, temperature of incubation, standard preparation protocol, and antibody selection. Notwithstanding these aspects, it emerged that Aβ42 is a useful biochemical marker for the diagnosis of AD patients, but there is a need for an international Aβ standard, a universally accepted protocol for CSF preparation, and a thorough evaluation of assay performance in function of the boundary conditions.

Transient increase in total tau but not phospho-tau in human cerebrospinal fluid after acute stroke

An increase in cerebrospinal fluid (CSF)-total-tau, and recently also in CSF-phospho-tau, has been found in Alzheimers disease (AD). However, the mechanisms for these changes are not known. We examined longitudinal CSF samples from nine patients with acute stroke. As compared with baseline levels (day 0-1), CSF-total-tau showed an increase at day 2-3 (179%; P=0.018), day 7-9 (257%; P=0.003), and after 3 weeks (425%; P=0.002) and returned to normal levels after 3-5 months (140%; NS). In contrast, there was no significant change in CSF-phospho-tau. These findings suggest that total tau and phospho-tau in CSF reflect different pathogenic processes in the brain; total-tau the degree of neuronal damage and phospho-tau the phosphorylation state of tau and thus possibly the formation of neurofibrillary tangles.

The Alzheimer's Association external quality control program for cerebrospinal fluid biomarkers.

The cerebrospinal fluid (CSF) biomarkers amyloid β (Aβ)‐42, total‐tau (T‐tau), and phosphorylated‐tau (P‐tau) demonstrate good diagnostic accuracy for Alzheimers disease (AD). However, there are large variations in biomarker measurements between studies, and between and within laboratories. The Alzheimers Association has initiated a global quality control program to estimate and monitor variability of measurements, quantify batch‐to‐batch assay variations, and identify sources of variability. In this article, we present the results from the first two rounds of the program.

Cerebrospinal fluid tau and Abeta42 as predictors of development of Alzheimer's disease in patients with mild cognitive impairment.

We studied CSF-tau and CSF-Abeta42 in 16 patients with mild cognitive impairment (MCI) who at follow-up investigations 6-27 months later had progressed to Alzheimers disease (AD) with dementia. For comparison, we studied 15 age-matched healthy individuals. At baseline, 14/16 (88%) of MCI patients had high CSF-tau and/or low CSF-Abeta42 levels. These findings show that these CSF-markers are abnormal before the onset of clinical dementia and that they may help to identify MCI patients that will develop AD. This is especially important when drugs with potential effects on the progression of AD will reach the clinical phase.

CSF levels of tau, beta-amyloid(1-42) and GAP-43 in frontotemporal dementia, other types of dementia and normal aging

Summary. Cerebrospinal fluid (CSF) levels of tau, β-amyloid1–42 and growth-associated protein 43 (GAP-43) were studied in patients with frontotemporal dementia (FTD; n = 17), Alzheimers disease (AD; n = 60), subcortical white-matter dementia (SWD; n = 24), Parkinsons disease (PD; n = 23) and dysthymia (n = 19) and in age-matched controls (n = 32). CSF-tau was significantly increased only in AD, and CSF-β-amyloid1–42 was significantly decreased in AD and SWD as compared to controls, and in AD compared to FTD. CSF-GAP-43 was significantly decreased only in PD. The GAP-43/tau ratio was decreased in all the patient groups except the dysthymia group compared to controls. A positive correlation was found between CSF-GAP-43 and CSF-tau in all groups. The results suggest normal levels of CSF-tau and CSF-β-amyloid1–42 in FTD, which will aid in the clinical separation of FTD from AD. In SWD, decreased levels of CSF-β-amyloid1–42 suggest concomitant involvement of vascular and amyloid protein mechanisms.

Evaluation of plasma A beta 40 and A beta 42 as predictors of conversion to Alzheimer's disease in patients with mild cognitive impairment

Numerous studies have shown a marked decrease of beta-amyloid(42) (Abeta(42)) in the cerebrospinal fluid (CSF) of patients with incipient Alzheimers disease (AD). However, studies on Abeta in plasma are contradictory, and show very marginal differences between patients and controls. Here, we analyzed plasma samples using a new multiplex immunoassay for simultaneous analysis of Abeta(1-40), Abeta(n-40), Abeta(1-42), and Abeta(n-42). The plasma samples were obtained at baseline from two independent cohorts of patients with mild cognitive impairment (MCI) and age-matched controls. In the first cohort, 41% of the 117 MCI cases converted to AD during a clinical follow-up period of 4-7 years. In the second cohort, 14% of the 110 MCI subjects developed AD during a clinical follow-up period of 2-4 years. None of the plasma Abeta isoforms differed between MCI patients that subsequently developed AD and healthy controls or stable MCI patients. The Cox proportional hazards model did not reveal any differences in the probability of progression from MCI to AD related to plasma Abeta levels. In contrast, low levels of Abeta(1-42) in CSF were strongly associated with increased risk of future AD. The absence of a change in plasma Abeta in incipient AD, despite the marked change in CSF, may be explained by the lack of a correlation between the levels of Abeta(1-42) in CSF and plasma. In conclusion, the results show that CSF biomarkers are better predictors of progression to AD than plasma Abeta isoforms.