OA16 Identification of surrogate serum proteomic biomarkers associated with ultrasound power Doppler in psoriatic arthritis

Abstract

Abstract Background/Aims An area of key unmet need in psoriatic arthritis (PsA) is the identification of biomarker(s) which predict those likely to respond to a specific therapy; in order to achieve that, an objective measure of disease activity would be ideal. Ultrasound power Doppler (PD) is a semi-quantitative measure of inflammation. However, ultrasound is time-consuming and requires specific expertise, whereas a blood-based surrogate biomarker of PD would be easier to apply clinically, and could serve as an objective outcome measure of response. Our aim is to identify proteomic biomarkers associated with PD in PsA patients. Methods Twenty-six patients with PsA (fulfilling CASPAR criteria) were recruited prospectively. All underwent 66-joint ultrasound examination and presence of PD was recorded. There were 7 patients without PD(-) and 19 with PD(+) detectable in at least 1 joint. Proteomics data for 1,073 proteins were generated using sequential window acquisition of all theoretical fragment ion spectra mass spectrometry (SWATH MS). Proteins with high levels of missing data were filtered (>30%) followed by random forest analysis. Differentially expressed proteins (DEPs) based on PD status were identified. Protein-protein interaction network analysis was performed using the search tool for retrieval of interacting genes (STRING), Kyoto Encyclopedia of Genes and Genomes (KEGG) and gene ontology (GO). Results Following pre-processing, 553 proteins were available for analysis. Seventeen DEPs were identified (p-values <0.05) (Table 1). Among these, ERAP2, an enzyme involved in MHC-I ligand processing and a known risk factor for inflammatory diseases, had the largest fold change (-0.64 95%CI -1.20 to -0.07, p = 0.03). Network analysis revealed that the 17 DEPs were significantly enriched (p < 0.001) in the PD+ group. KEGG pathway analysis identified the association of the DEPs in leukocyte transendothelial migration (strength 1.5 FDR=0.04). GO analysis of the DEPs revealed involvement in immunoglobulin receptor binding (strength 2.28 FDR=0.03). Conclusion We identified several potential serum proteomic biomarkers correlated with disease activity, as assessed by the presence of PD, in PsA; these provide insights into the biological mechanisms underlying synovitis in PsA. Validation in a larger cohort and functional studies are required to determine the role of these proteins in mediating inflammation in PsA. Disclosure R.M. Hum: None. N. Nair: None. S.F. Ling: None. A. Barton: None. P. Ho: None. D. Plant: None.