Pia Davidsson

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.

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.

Cerebrospinal fluid tau protein as a biochemical marker for Alzheimer’s disease: a community based follow up study

OBJECTIVES Biochemical markers for Alzheimer’s disease would be of great value, especially to help in diagnosis early in the course of the disease. A pronounced increase in CSF tau protein (CSF-tau) is found in most patients with Alzheimer’s disease. However, the specificity has to be further studied, as an increase in CSF-tau has also been found in other dementias, especially in vascular dementia. As most previous CSF studies have been based on selected inpatients, it was considered of special interest to examine the diagnostic potential of CSF-tau in a community population based sample of consecutive patients with dementia. Such patient material has been examined at the Piteå River Valley Hospital in Northern Sweden since 1986, and includes all those with memory disturbances in the community. The aim was also to study if an increase in CSF-tau is found early in the disease process, and whether CSF-tau changes during the progression of disease. METHODS Participants: Community population based sample of 75 demented patients (43 with Alzheimer’s disease, 21 with vascular dementia, and 11 with mixed Alzheimer’s disease/vascular dementia), 18 healthy subjects, and 18 neurological controls. A follow up investigation (including analysis of a new CSF sample) was performed in all patients after about one year. MAIN OUTCOME MEASURES Concentrations of total (both normal tau and PHF-tau) tau in CSF, clinical measures (duration and severity of dementia), and apoE polymorphism. RESULTS CSF-tau was markedly increased in Alzheimer’s disease, 41/43 (95%) patients had values above the cut off level (mean+2 SD) in controls (306 pg/ml). High CSF-tau concentrations were also found in most patients with vascular dementia, preferentially in patients with vascular dementia without progressive leukoaraiosis on CT, whereas patients with vascular dementia with progressive leukoaraiosis had normal CSF-tau. Concentrations of CSF-tau were stable at one year follow up in both patients with Alzheimer’s disease and patients with vascular dementia, and there was no correlation between CSF-tau and either duration or severity of dementia. CONCLUSIONS The findings confirm the high sensitivity of CSF-tau for the diagnosis of Alzheimer’s disease, but high CSF-tau was also found in vascular dementia, resulting in a lower specificity. However, high CSF-tau is preferentially found in patients with vascular dementia without progressive leukoaraiosis, which may constitute a group with concomitant Alzheimer’s disease pathology. High CSF-tau may be present during the whole course of the disease in Alzheimer’s disease. Possibly, therefore, the same high CSF-tau concentrations may be present before the onset of clinical dementia. Follow up studies on such patients will tell whether analysis of CSF-tau is useful as a biochemical marker for early Alzheimer’s disease.

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.

Proteome analysis of cerebrospinal fluid proteins in Alzheimer patients

&NA; By comparing the CSF proteome between Alzheimer disease (AD) patients and controls it may be possible to identify proteins that play a role in the disease process and thus to study the pathogenesis of AD. We used mini‐gel technology in a two‐dimensional electrophoresis procedure, sensitive SYPRO Ruby staining and mass spectrometry for clinical screening of disease‐influenced CSF proteins in 15 AD patients and 12 controls. The levels of six proteins and their isoforms, including proapolipoprotein, apolipoprotein E, &bgr;‐2 microglobulin, retinol‐binding protein, transthyretin, and ubiquitin, were significantly altered in CSF of AD patients. The most prominently altered proteins were the apolipoproteins, especially proapolipoprotein.

Sensitivity, specificity, and stability of CSF-tau in AD in a community-based patient sample

OBJECTIVE To evaluate the sensitivity and specificity of CSF-tau in clinical practice as a diagnostic marker for AD compared with normal aging and depression, to study the stability of CSF-tau in longitudinal samples, and to determine whether CSF-tau levels are influenced by different covariates such as gender, age, duration or severity of disease, or possession of the APOE-epsilon4 allele. METHODS Consecutive AD patients from a community-based sample were studied, including 407 patients with AD (274 with probable AD and 133 with possible AD), 28 patients with depression, and 65 healthy elderly control subjects. A follow-up lumbar puncture was performed in 192 AD patients after approximately 1 year. CSF-tau was determined using a sandwich ELISA, which was run as a routine clinical neurochemical analysis. RESULTS CSF-tau was increased in probable (690+/-341 pg/mL; p < 0.0001) and possible (661+/-447 pg/mL; p < 0.0001) AD, but not in depression (231+/-110 pg/mL) compared with control subjects (227+/-101 pg/mL). Receiver operating characteristics analysis showed that a cutoff level of 302 pg/mL resulted in a sensitivity of 93% (95% CI, 90-96%) and a specificity of 86% (95% CI, 75-94%), with an area under the curve of 0.95 to discriminate AD from control subjects. Within the AD group, CSF-tau did not differ significantly between baseline and follow-up investigations, and was relatively stable between baseline and 1-year follow-up levels, with a coefficient of variation of 21.0%. High CSF-tau levels were also found in most AD patients with very short duration of dementia, and with Mini-Mental State Examination scores >23 (n = 205). In total, 193 of 205 patients (sensitivity, 94%) had a CSF-tau level higher than 302 pg/mL. CONCLUSIONS CSF-tau has a high sensitivity and specificity to differentiate AD from normal aging and depression, as demonstrated in a large community-based series of consecutive AD patients during which analyses were run continually in a clinical neurochemical laboratory. The increase in CSF-tau is found very early in the disease process in AD, is stable over time, and has a low interindividual variation on repeated sampling. Although high CSF-tau is found in some neurologic conditions (e.g., stroke), these findings suggest that CSF-tau may be of use to help in differentiating AD from normal aging and depression, especially early in the course of the disease, when the symptoms are vague and the diagnosis is especially difficult.

Cerebrospinal Fluid Beta-Amyloid 42 Is Reduced before the Onset of Sporadic Dementia: A Population-Based Study in 85-Year-Olds

Deposition of β-amyloid (Aβ) is an early pathogenic event in Alzheimer’s disease (AD). We measured Aβ42 and Aβ40 in cerebrospinal fluid (CSF) in a population-based sample of 85-year-olds, 27 demented and 35 non-demented. During the following 3 years, 7 of the 35 non-demented individuals had developed dementia, while 28 remained non-demented. Reduced CSF levels of both Aβ42 (p = 0.001) and Aβ40 (p = 0.0001) were found in patients with manifest AD and vascular dementia at the age of 85. Non-demented individuals who developed dementia during follow-up had lower levels of CSF- Aβ42 (p = 0.003), but not CSF-Aβ40 (p = 0.96), than those who remained non-demented. The odds ratio for development of dementia was 8.2 (p = 0.027) for individuals in the lower 50th percentile of CSF-Aβ42, while none of those in the highest 33rd percentile of CSF-Aβ42 developed dementia during follow-up. There were no significant differences between carriers and non-carriers of the apolipoprotein E Ε4 allele regarding CSF-Aβ42or CSF-Aβ40.Our study suggests that low CSF-Aβ42 is found also in an unselected population-based sample of old demented patients and provides the first evidence of a disturbance in the metabolism of Aβ, specifically involving Aβ42, before the onset of clinical symptoms in AD.

Cerebrospinal fluid levels of total-tau, phospho-tau and Aβ42 predicts development of Alzheimer's disease in patients with mild cognitive impairment

Cerebrospinal fluid (CSF) biochemical diagnostic markers may be valuable to help in the diagnosis early in the course of Alzheimers disease (AD), especially in the phase before clinically overt dementia, i.e. in patients with mild cognitive impairment (MCI). We studied 44 patients with MCI who, at 1‐year follow‐up investigation, had progressed to AD with dementia, and 32 controls. Three CSF biomarkers related to the central pathogenic processes in AD were analysed, including CSF total‐tau (T‐tau) (as a marker for neuronal degeneration), CSF phospho‐tau (P‐tau) (as a marker for hyperphosphorylation of tau and possibly for the formation of neurofibrillary tangles), and CSF Aβ42 (as a marker for Aβ metabolism, and possibly for the formation of senile plaques). At baseline, 35/44 (79.5%) of the MCI patients had high CSF T‐tau, 31/44 (70.4%) high CSF P‐tau, while 34/44 (77.3%) had low CSF‐Aβ42 levels. The positive likelihood ratio was 8.45 for CSF T‐tau, 7.49 for CSF P‐tau and 8.20 for CSF Aβ42. These findings suggest that these CSF‐markers are abnormal before the onset of clinical dementia, and that they may help to identify MCI patients that will progress to AD. CSF diagnostic markers will be especially important when drugs with potential effects on the progression of AD (e.g. γ‐secretase inhibitors) will reach the clinical phase.