Srage as biomarker for COPD, introducing novel LC-MS-based methods for the quantification of serum srage levels

Abstract

Rationale: Soluble RAGE (sRAGE) is a promising biomarker for COPD and an attractive target for biomarker validation studies. Validated, reliable and clinically applicable biomarkers are needed for the early detection of COPD, identification of clinically relevant subgroups of COPD and for the selection of subjects for clinical trials. The circulating levels of sRAGE are decreased in COPD patients compared to both smoking and non-smoking controls, and are even further decreased during COPD exacerbations. Furthermore, the serum levels of sRAGE associate with neutrophilic airway inflammation, decline in FEV1, and emphysema. Methods: To date, most studies use commercially available ELISA kits for measurements of sRAGE, which have limited accuracy and reproducibility. Here, we present two novel liquid chromatography-mass spectrometry (LC-MS) methods for the quantification of sRAGE in serum. Our first approach measures the free, unbound fraction of sRAGE using an immunoaffinity enrichment-based method as sample preparation, comparable to the ELISA. Our second approach is an antibody-free method based on strong cation exchange solid-phase extraction, which likely measures the total sRAGE fraction. Both sample preparation methods are followed by LC-MS analysis in the multiple reaction monitoring mode. Results: Using the immunoaffinity enrichment-based method we are able to detect and quantify sRAGE in human serum over a large range (0.1-10 ng/mL) with high precision and accuracy (CV