Platelet Tau Protein as a Potential Peripheral Biomarker in Alzheimer's Disease: An Explorative Study

Background: Cerebrospinal fluid (CSF) measures of tau and amyloid proteins have now been largely accepted to be a diagnostic tool to aid the clinical diagnosis of Alzheimer's disease (AD), but CSF is not routinely obtained in most clinical settings. There is a need, therefore, to uncover additional readily accessible peripheral biomarkers that will enable comprehensive detection of AD-specific proteins in blood and blood derivates. Objectives: Blood platelets contain proteins found in neuronal cell lines, including tau protein. Since tau protein is a characteristic of AD-neuropathology, platelet tau protein may be closely related to the central nervous process occurring in neurodegeneration. Method: Platelets from 25 AD and 26 control subjects were analysed for the microtubule-binding and C-terminal region, as well as two tau phosphorylation sites (Ser202/Thr205 and Thr181). Results: Tau protein measures did not discriminate between AD and control individuals. However, subjects with MMSE 24-27 had elevated C-terminal end tau protein (p=0.049) compared to those with MMSE >27, whereas older AD subjects (>80 years) showed higher t-tau protein in comparison to younger AD (<80 years; p=0.009) and control (<80 years; p=0.011) participants. Conclusions: These initial findings not only confirm that platelet tau protein can be measured, but also indicate that platelet tau measures merit further study as they may be useful in indicating early stages of cognitive impairment. Further studies on larger number of participants are needed to confirm our findings.