Mass spectrometry was used to study blood samples from patients with amyotrophic lateral sclerosis (ALS) and healthy controls. Addenbrooke's cognitive examination-III (ACE-III) was used to test for cognitive impairment (CI). Nano liquid chromatography and time of flight mass spectrometry (MS) were performed on samples from 42 ALS patients and 18 healthy controls. SWATH™ proteomic analysis was utilized to look for differences between groups. Western blot analysis was used to study levels of 4 proteins, selected as being of possible interest in ALS, in the MS discovery cohort and a second validation group of 10 ALS patients and 10 healthy controls. INGENUITY PATHWAY ANALYSIS (IPA) was applied to the final proteomic data. Between ALS patients and controls, there were significant differences in the expression of 30 proteins. Between controls and ALS patients without CI, there were significant differences in 15 proteins. Between controls and ALS patients with CI, there were significant differences in 32 proteins. Changes in levels of gelsolin, clusterin, and CD5L were validated by using western blot analysis in the discovery cohort. Changes in the expression of gelsolin, clusterin, and ficolin 3 were replicated in a validation group. In ALS, the LXR/RXR and coagulation pathways were downregulated whereas the complement pathway was upregulated. The proteomic data were used to produce two new networks, centered on IL1 and on NFkB, which showed altered levels in ALS. This study highlights the usefulness of MS of blood samples as a tool to study ALS.
Keywords: Amyotrophic lateral sclerosis; biomarker; clusterin; cognitive impairment; gelsolin; lipid metabolism; proteomics.