Cerebrospinal Fluid Sediments as a Novel Tool for Potential Biomarkers of Neurodegenerative Diseases

Cerebrospinal fluid (CSF) biomarkers for neurodegenerative diseases have been extensively studied over the years. However, CSF samples are routinely centrifuged, and the resulting sediment or pellet is typically discarded to remove cellular debris and high-density particles. This standard practice raises a critical question: Could these discarded sediments harbour potential biomarkers? The aim of the present study is to demonstrate that CSF sediments contain specific brain-derived components and thus to substantiate the possible presence of biomarkers within these sediments. To this end, we analysed post-mortem CSF samples of one patient with neuropathologically confirmed Alzheimer's disease (AD) and one patient with confirmed progressive supranuclear palsy (PSP). CSF pellets were studied using transmission and scanning electron microscopy techniques (TEM and SEM, respectively), along with compositional analysis through SEM combined with energy-dispersive X-ray spectroscopy (SEM-EDX), as well as immunofluorescence and histochemical analyses on semithin pellet sections. We observed that, among others, CSF pellets contain brain-derived structures such as wasteosomes and psammoma bodies. Furthermore, we also found disease-relevant proteins, including tau and Aβ42 in the AD sediment and tau in the PSP sediment. Although further studies are required, the study of CSF pellets could open new avenues for biomarker discovery in neurodegenerative diseases.