ELISA-quantitation of phosphorylated tau protein in the Alzheimer's disease brain.

A reliable, sensitive and specific sandwich ELISA for the quantitation of paired helical filament (PHF) tau in human brain was developed using well-defined monoclonal antibodies. We examined rapid-autopsy-derived brain tissue from 21 neuropathologically confirmed Alzheimer's disease (AD) patients and 14 nondemented controls, matched for age, sex and postmortem delay times. We demonstrated significant elevations of phosphorylated tau levels in the frontal and parietal cortex as well as in the hippocampus of AD patients as compared to the nondemented controls. No difference was observed in the cerebellum. Phosphorylated tau levels measured by ELISA were significantly correlated with the presence or absence of neurofibrillary tangles.

Histological markers in nasal mucosa of patients with Alzheimer's disease.

Neuropathological changes such as dystrophic neurites and the presence of abnormal tau protein in the olfactory system, including primary sensory cells and nerve fibres have previously been demonstrated in nasal mucosa tissue of patients with Alzheimer's disease (AD). These changes were detected in autopsy-derived material from histopathologically confirmed AD cases as well as in biopsy tissue from clinical severely ill AD patients. To investigate the potential usefulness for the early diagnosis of AD, we obtained biopsy tissue from olfactory mucosa from 5 clinically mild to moderate AD patients and stained for the presence of tau or beta-amyloid by immunocytochemistry using a panel of specific antibodies. No positive staining was found in any of the cases. For comparison, post-mortem olfactory tissue from AD patients with severe neuropathological changes (widespread neurofibrillary tangles and amyloid in the brain) was investigated. In these severe cases, tau immunoreactivity was found in fine nerve fibres in the lamina propria and in a few olfactory epithelial cells. These results are consistent with other reports showing that cytoskeletal changes and tau pathology in the olfactory epithelium are not primary (or specific) features of AD and may occur predominantly in late stages of the disease.

Increased blood mercury levels in patients with Alzheimer's disease.

Alzheimer's disease (AD) is a common neurodegenerative disorder that leads to dementia and death. In addition to several genetic parameters, various environmental factors may influence the risk of getting AD. In order to test whether blood levels of the heavy metal mercury are increased in AD, we measured blood mercury concentrations in AD patients (n = 33), and compared them to age-matched control patients with major depression (MD) (n = 45), as well as to an additional control group of patients with various non-psychiatric disorders (n = 65). Blood mercury levels were more than two-fold higher in AD patients as compared to both control groups (p = 0.0005, and p = 0.0000, respectively). In early onset AD patients (n = 13), blood mercury levels were almost three-fold higher as compared to controls (p = 0.0002, and p = 0.0000, respectively). These increases were unrelated to the patients' dental status. Linear regression analysis of blood mercury concentrations and CSF levels of amyloid beta-peptide (A beta) revealed a significant correlation of these measures in AD patients (n = 15, r = 0.7440, p = 0.0015, Pearson type of correlation). These results demonstrate elevated blood levels of mercury in AD, and they suggest that this increase of mercury levels is associated with high CSF levels of A beta, whereas tau levels were unrelated. Possible explanations of increased blood mercury levels in AD include yet unidentified environmental sources or release from brain tissue with the advance in neuronal death.

Cerebrospinal fluid levels of amyloid precursor protein and amyloid beta-peptide in Alzheimer's disease and major depression - inverse correlation with dementia severity.

Alzheimer's disease (AD) is the most common neurodegenerative disorder characterized by progressive dementia that ultimately leads to death. Histopathological hallmarks of AD include brain amyloid deposits and neurofibrillary tangles. Major depression is a frequent diagnosis in every gerontopsychiatric clinic that sees patients with both cognitive and affective disorders. Many depressed patients, in fact, are clinically characterized by cognitive impairments. Thus, an assay that excludes - or confirms - probable AD in cognitively impaired patients is desirable. Such assays may use protein markers that are derived from such histopathologically relevant molecules as the amyloid precursor protein (APP) and its derivatives including the amyloid beta-peptides (Abeta). To evaluate the differential diagnostic properties of cerebrospinal fluid (CSF) Abeta and secreted soluble ectodomain (APPs), we quantitated CSF levels of these measures in AD patients and compared them to age-matched control patients with major depression. CSF levels of APPs and Abeta were similar in patients with AD or major depression, and the apolipoprotein E genotype had no influence on CSF levels of Abeta in AD patients. Measurement of Abeta peptide using a novel zinc/copper capture ELISA that detects aggregated Abeta peptides as well demonstrated similar levels in AD and major depression. In AD patients, CSF levels of total Abeta (Abeta1-40 plus Abeta1-42) were inversely correlated with a functional measure of dementia severity (NOSGER), suggesting that CSF levels of Abeta decrease with advancing severity of AD. Thus, CSF levels of Abeta are not useful for the differentiation of AD from major depression. However, CSF levels of Abeta reflect the severity of dementia and may be useful as biological markers of the stage of the disease.

Dependence of cerebrospinal fluid Tau protein levels on apolipoprotein E4 allele frequency in patients with Alzheimer's disease.

Consistent pathological hallmarks of Alzheimer's disease (AD) are the formation of brain amyloid and neurofibrillary tangles (NFTs). Levels of the major protein component of NFTs, the microtubule associated protein Tau, were shown to be increased in cerebrospinal fluid (CSF) of AD patients as compared to age-matched controls. The presence of apolipoprotein E-epsilon 4 allele (APOE4) is a risk factor for sporadic and familial late-onset AD. ApoE may interact with the binding of Tau to microtubules and Tau phosphorylation in an isoform-specific manner. We investigated whether direct evidence of an isoform-specific interaction of apoE and Tau can be demonstrated in the CSF of live AD patients. We measured the apoE genotype and CSF levels of Tau in 19 patients with probable AD and 12 age-matched control subjects. We found that CSF levels of Tau increase with increasing APOE allele frequency (Spearman rank correlation, zeta = 2.71, P = 0.007). This finding may be in agreement with reports of a lesser binding of apoE4 to Tau, compared to apoE2 and apoE3, resulting in higher levels of unbound Tau in CSF.

Interleukin-6 (IL-6) and soluble forms of IL-6 receptors are not altered in cerebrospinal fluid of Alzheimer's disease patients.

We quantitated interleukin-6 (IL-6), soluble IL-6 receptor (sIL-6R) and soluble form of the IL-6 signal-transducing protein gp130 (sgp130) in cerebrospinal fluid (CSF) of patients with Alzheimer's disease (AD) (n = 17) and control subjects (n = 18) using sensitive enzyme-linked immunosorbent assays (ELISA). Our results show that none of the parameters examined was significantly different in CSF of AD patients as compared to control age-matched non-demented patients. We conclude that CSF levels of IL-6 and their soluble receptors do not necessarily reflect local changes of the IL-6 system that has been shown to be involved in neurodegenerative events occurring in AD. Levels of sgp130 are substantially high (approximately 100 ng/ml) in the CSF of all individuals probably representing a high antagonistic potential.