A new procedure for detecting brain-specific proteins in cerebrospinal fluid

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Abstract
We have developed a new procedure, including three affinity chromatography steps, micro-reversed phase high pressure liquid chromatography (mR-HPLC) and Western blotting/mass spectrometric analysis to study central nervous system (CNS) specific proteins in human cerebrospinal fluid (CSF) in order to find biochemical markers for neuronal and synaptic function and pathology in degenerative brain disorders. After the three affinity chromatography steps, intended to remove interfering serum proteins from CSF, mR-HPLC revealed four major peaks, which by both Western blotting and mass spectrometric analyses were found to correspond to β2-microglobulin, cystatin C, transthyretin (TTR) and asialotransferrin. When comparing these peaks in CSF from Alzheimer's disease (AD) patients and age-matched healthy controls, a reduction of the brain-specific TTR was found. Therefore we quantified TTR in CSF and serum samples from 8 patients with early onset AD (EAD), 18 patients with late onset AD (LAD), 8 patients with vascular dementia (VAD) and 18 healthy individuals using a nephelometric method. CSF-TTR was divided into barrier-dependent and barrier-independent TTR. The barrier-independent i.e. brain-specific TTR was significantly reduced in the EAD group compared to the controls. Transthyretin has been found to be present in the senile plaques in AD, and to specifically bind to β/A4 protein, the major component of the amyloid deposits in AD. Therefore, the reduction of the transthyretin-isoform in CSF in AD may reflect an absorption of transthyretin to the amyloid deposits in the senile plaques.