Deep Proteome Profiling of Circulating Granulocytes Reveals Bactericidal/Permeability-Increasing Protein as a Biomarker for Severe Atherosclerotic Coronary Stenosis

Coronary atherosclerosis represents the major cause of
death in
Western societies. As atherosclerosis typically progresses over years
without giving rise to clinical symptoms, biomarkers are urgently
needed to identify patients at risk. Over the past decade, evidence
has accumulated suggesting cross-talk between the diseased vasculature
and cells of the innate immune system. We therefore employed proteomics
to search for biomarkers associated with severe atherosclerotic coronary
lumen stenosis in circulating leukocytes. In a two-phase approach,
we first performed in-depth quantitative profiling of the granulocyte
proteome on a small pooled cohort of patients suffering from chronic
(sub)­total coronary occlusion and matched control patients using stable
isotope peptide labeling, two-dimensional LC–MS/MS and data-dependent
decision tree fragmentation. Over 3000 proteins were quantified, among
which 57 candidate biomarker proteins remained after stringent filtering.
The most promising biomarker candidates were subsequently verified
in the individual samples of the discovery cohort using label-free,
single-run LC–MS/MS analysis, as well as in an independent
verification cohort of 25 patients with total coronary occlusion (CTO)
and 19 matched controls. Our data reveal bactericidal/permeability-increasing
protein (BPI) as a promising biomarker for severe atherosclerotic
coronary stenosis, being down-regulated in circulating granulocytes
of CTO patients.