Mass spectrometry quantitation of multicomponent protein biomarker panels of Alzheimer's disease

Clusterin, complement C3, complement C3a, serum amyloid P component (SAP), alpha-2-macroglobulin (A2M), gelsolin, fibrinogen gamma-chain (FGG) and complement factor H (CFH) have emerged as candidate AD biomarkers from discovery exercises using twodimensional gel electrophoresis and TMT labeling technologies (Hye et al., 2006; Thambisetty et al., 2010; Guntert et al., 2010). Furthermore, possession of the apolipoprotein E (Apo E) E4 allele is the only unequivocal genetic risk factor known to-date for late-onset AD and the protein expression of this genetic association may translate as an AD biomarker. The expression levels and absolute quantitative amounts of these proteins across large patient populations have yet to be described. We have now developed two mass spectrometry assay methods based on using isotopically labelled synthetic peptides (TMT-SRM) or a whole plasma digest reference (TMTOrbi) to assess candidate biomarker levels in plasma and present the results from the analysis of a subset of samples from an extensive, well characterised cohort of AD, MCI and Control patients.