Using proteomic approach in this study, we sought to identify proteins with heparin affinity associated with rheumatoid arthritis (RA), psoriatic arthritis (PsA) and non-inflammatory arthritis (NIA).
Plasma samples from adult RA, PsA and NIA patients, 20 of each, were collected. After enrichment of proteins with heparin affinity, SDS-PAGE and in-gel digestion with trypsin were performed. Peptides were concentrated, micro-purified, separated and measured by nano-scale HPLC system coupled to a mass spectrometer. Peak lists were generated from raw spectra and searched against human complete proteome set by MaxQuant software. Statistical analysis of protein relative expression levels was done in IPython interactive Python shell using NumPy and Matplotlib libraries. Individual protein impact on the whole dataset correlation was done by excluding one protein at a time and calculating the correlation coefficient of remaining data points.
Three hundred and eighty-four different proteins were identified keeping false discovery rate to 1%, from which 163 were identified in all three conditions. The plasma proteome showed a good correlation between rheumatoid (RA) and psoriatic arthritis (PsA). Out of 10 proteins whose impact on the correlation coefficient fell outside of two standard deviations from the mean, four were up-regulated (complement factor I, complement component C8 beta, glyceraldehyde-3-phosphate dehydrogenase and inter-alpha-trypsin inhibitor heavy chain H1), and two were down-regulated (immunoglobulin heavy chain V-III region BRO, and immunoglobulin J chain), both in PsA and RA by a similar ratio when compared to NIA. The remaining four proteins (Serpin A11, complement factor H-related protein 5, cartilage acidic protein 1 and coagulation factor IX) were down-regulated in PsA and up-regulated in RA when compared to NIA.
We found differently expressed proteins in patients with inflammatory and non-inflammatory rheumatic conditions. Out of 384 proteins with heparin affinity four proteins should be further validated as potential diagnostic biomarkers in patients with RA and PsA.