Rapid Discovery of Putative Protein Biomarkers of Traumatic Brain Injury by SDS–PAGE–Capillary Liquid Chromatography–Tandem Mass Spectrometry

We report the rapid discovery of putative protein biomarkers of traumatic brain injury (TBI) by SDS–PAGE–capillary liquid chromatography–tandem mass spectrometry (SDS–PAGE–Capillary LC–MS²). Ipsilateral hippocampus (IH) samples were collected from naive rats and rats subjected to controlled cortical impact (a rodent model of TBI). Protein database searching with 15,558 uninterpreted MS² spectra, collected in 3 days via data-dependent capillary LC-MS² of pooled cyanine dye-labeled samples separated by SDS-PAGE, identified more than 306 unique proteins. Differential proteomic analysis revealed differences in protein sequence coverage for 170 mammalian proteins (57 in naive only, 74 in injured only, and 39 of 64 in both), suggesting these are putative biomarkers of TBI. Confidence in our results was obtained by the presence of several known biomarkers of TBI (including αII-spectrin, brain creatine kinase, and neuron-specific enolase) in our data set. These results show that SDS-PAGE prior to in vitro proteolysis and capillary LC-MS² is a promising strategy for the rapid discovery of putative protein biomarkers associated with a specific physiological state (i.e., TBI) without a priori knowledge of the molecules involved.