Total α-synuclein levels in human blood cells, CSF, and saliva determined by a lipid-ELISA.

The validity of α-synuclein (α-Syn) as a biomarker for Parkinson's disease (PD) is still under investigation. Conventional methods for capture and quantitation of α-Syn protein in human samples are primarily based on anti-α-Syn antibodies. Specific and competent antibodies were raised against α-Syn. However, capture by anti-α-Syn antibodies may be limited to specific epitope recognition, attributed to protein structure or post-translational modifications. Hence, antibody-based methods for α-Syn capture raise a concern regarding their efficacy to detect the intracellular, unfolded α-Syn pool. An alternative is α-Syn capture by membrane lipids, i.e., to utilize the biochemical property of α-Syn to specifically bind membrane lipids and acquire a characteristic structure following binding. We determined α-Syn levels in human samples using immobilized lipids for α-Syn capture. The lipids used for α-Syn capture consist of phosphatidyl inositol (PI), phosphatidyl serine (PS), and phosphatidyl ethanolamine (PE). Addition of mono-sialoganglioside, GM1 ganglioside, to the immobilized lipids significantly improved α-Syn detection. Following capture, the lipid-bound α-Syn was detected using an anti-α-Syn antibody. Total α-Syn levels in whole blood cells (WBC), cerebrospinal fluid (CSF), and saliva were determined by the lipid-ELISA method.