Elevated cerebrospinal fluid tau levels: implications for the early diagnosis of Alzheimer's disease

The Inflammasome Adaptor Protein ASC in Mild Cognitive Impairment and Alzheimer's Disease

Mild cognitive impairment (MCI) is characterized by memory loss in the absence of dementia and is considered the translational stage between normal aging and early Alzheimer’s disease (AD). Patients with MCI have a greater risk of advancing to AD. Thus, identifying early markers of MCI has the potential to increase the therapeutic window to treat and manage the disease. Protein levels of the inflammasome signaling proteins apoptosis-associated speck-like protein containing a caspase recruitment domain (ASC) and interleukin (IL)-18 were analyzed in the serum of patients with MCI, AD and healthy age-matched donors as possible biomarkers, as well as levels of soluble amyloid precursor proteins α/β (sAPP α/β) and neurofilament light (NfL). Cut-off points and positive and negative predictive values, as well as receiver operator characteristic (ROC) curves, likelihood ratios and accuracy were determined for these proteins. Although the levels of ASC were higher in MCI and AD than in age-matched controls, protein levels of ASC were higher in MCI than in AD cases. For control vs. MCI, the area under the curve (AUC) for ASC was 0.974, with a cut-off point of 264.9 pg/mL. These data were comparable to the AUC for sAPP α and β of 0.9687 and 0.9068, respectively, as well as 0.7734 for NfL. Moreover, similar results were obtained for control vs. AD and MCI vs. AD. These results indicate that ASC is a promising biomarker of MCI and AD.

[Biomarkers, mild cognitive impairment and early diagnosis of Alzheimer's disease]

Elderly people are concerned about changes in their cognitive functioning. Since cholinergic therapies for Alzheimer's disease have been developed and become widely accepted, elderly people have come to visit clinics to seek medical advice about whether such a subtle change in cognitive ability may represent an early manifestation of Alzheimer's disease (AD). If they are likely to develop dementia or AD, they want to receive immediate medical treatment as soon as possible to prevent further loss of cognitive functioning so that they can live independently as long as possible. The first priority in the clinical application of a biomarker is that biomarker should contribute to early diagnosis of dementia. Among such biomarkers, we believe that cerebrospinal fluid markers and functional brain imaging are clinically the most applicable procedures. Since 1993, we have collected 623 cerebrospinal fluid (CSF) samples at The Tohoku University Hospital for evaluation of dementia (age: 42-93). We found that CSF/phospho-tau measures produced the most adequate sensitivity (85.2%) and specificity (85.0%) in the diagnosis of AD as a sole bio-marker. The CSF levels of A beta 1-42 showed a strong positive correlation with the Mini-mental state examination score and brain glucose metabolism by positron emission tomography. The baseline levels of both total-tau and phospho-tau in CSF increased in approximately 70% of patients with mild cognitive impairment who later developed AD, suggesting that pathological change in the brain might start years before dementia becomes clinically manifested. A combined use of CSF-tau and IMP-SPECT improved the predictability of the transition from mild cognitive impairment into AD.

Cerebrospinal fluid amyloid beta(1-42) levels in the mild cognitive impairment stage of Alzheimer's disease

Cerebrospinal fluid (CSF) levels of amyloid beta-protein ending at amino acid position 42 (CSF-A beta(1-42)) and CSF-tau levels were quantified by sandwich ELISAs in 19 patients with mild cognitive impairment (MCI) who eventually developed Alzheimer's disease (AD) on follow-up as well as in 15 age-matched normal controls and 54 AD patients at diverse stages of the disease. In the present study, the annual conversion rate was approximately 15%. The CSF-A beta(1-42) levels did not differ significantly between the normal control group and the MCI group, however, these values declined significantly once AD became clinically overt. In contrast to CSF-Abeta(1-42), CSF-tau levels were significantly increased in the MCI stage, and these values continued to be elevated thereafter, indicating that increased levels of CSF-tau may help in detecting MCI subjects who are predicted to develop AD. We propose that CSF-tau and CSF-A beta(1-42) must be used as two distinct biomarkers that should be applied appropriately in clinical settings.

CSF phosphorylated tau protein and mild cognitive impairment: a prospective study

Cerebrospinal fluid (CSF) tau protein phosphorylated at both Thr231 and Ser235 sites (CSF/phospho-tau(231-235)) and total tau (CSF/total-tau) were quantified by sandwich ELISA in 20 patients with mild cognitive impairment (MCI) who eventually developed AD on follow-up as well as seven memory complainers with no objective memory loss. 13/20 (65%) of the MCI patients had high CSF/total-tau and detectable levels of CSF/phospho-tau(231-235), whereas these markers were low and under a detectable level in all of the memory complainers. Although either a total-tau, phospho-tau measurement or a combination of these can help in predicting if MCI will develop AD, our results suggest that the pathogenic steps of AD may be at the stage that finally leads to an accumulation of abnormally phosphorylated tau and neuron death, at least in some brain areas, when MCI patients present with the earliest detectable clinical symptoms of dementia.

Recent advances in dementia research in Japan: Alzheimer-type dementia

In a previous article, recent reports by Japanese researchers on non-Alzheimer-type degenerative dementias were reviewed. In the present article, recent Japanese reports on Alzheimer-type dementia (ATD) are reviewed. Alzheimer-type dementia has received great attention and has been studied from various viewpoints in Japan as well as in Europe and the Americas. In Japan, although it was believed that vascular dementia was the most frequent dementia in the elderly, ATD has recently been shown to be the most predominant type of dementia. Such a great number of papers on ATD have been reported in Japan that mainly the clinical, neuropathological, biochemical and molecular biological research papers alone are reviewed here.

Effect of genetic risk factors and disease progression on the cerebrospinal fluid tau levels in Alzheimer's disease

OBJECTIVE

This study was undertaken to gain insights into the clinical utility of measuring cerebrospinal fluid tau protein (CSF-tau) to aid in the diagnosis of Alzheimer's disease (AD).

SETTING

AD patients from Tohoku University Hospital, Sendai Japan were sampled.

SUBJECTS AND METHODS

CSF-tau levels were examined by sandwich enzyme-linked immunosorbent assay in a total of 62 patients carrying different alpha 1-antichymotrypsin (ACT) and presenilin-1 (PS-1) polymorphic alleles. Further, the CSF-tau levels were followed up on two occasions during the progression of the disease in 17 AD patients.

RESULTS

There was no evident gradient for tau protein in CSF. Neither the ACT/A allele nor the PS-1/1 allele affected the CSF-tau levels. Although CSF-tau levels changed to a variable extent over time, the CSF-tau levels were significantly increased (P < .01) during the follow-up period. Three of the AD patients demonstrated decreasing values, whereas 14 patients showed increasing values. Finally, these temporal changes in CSF-tau levels were not influenced by the apolipoprotein E epsilon 4, ACT/A or PS-1/1 alleles during the progression of AD.

CONCLUSION

Regardless of the mechanisms leading to the degeneration of neurons in AD, our findings provide further evidences that monitoring CSF-tau levels may provide useful information about AD irrespective of the background of genetic risks and disease progression.

Biological markers for the clinical diagnosis of Alzheimer's disease

There is a compelling need to develop biological marker(s) to confirm a clinical diagnosis of Alzheimer's disease (AD) during life in order to unequivocally identify AD patients for emerging therapeutic interventions. This review describes recent advances in the development of diagnostic marker(s) for AD. They include polymorphism of apolipoprotein E (ApoE) and alpha 1-antichymotrypsin as well as cerebrospinal fluid (CSF) tau and CSF-amyloid beta-protein levels, skin biopsy, and pupil dilatation assay by anti-cholinergic agent. In conclusion, ApoE genotyping should not be used as a sole diagnostic test for AD, and that monitoring of CSF-tau appeared to be most promising and reliable diagnostic aid.