OP0348 Mass spectrometry imaging analysis of synovium differentiate patients with psoriatic and rheumatoid arthritis
Authors: B. Rocha, B. Cillero-Pastor, C. Ruiz-Romero, A. Cuervo, R.M. Heeren, J.D. Cañete, F.J. Blanco
Journal: Annals of the Rheumatic Diseases (2018)

<h3>Background</h3> Rheumatoid arthritis (RA) and Psoriatic arthritis (PsA) are systemic inflammatory diseases characterised by a chronic form of arthritis, often leading to irreversible joint damage. Both are highly heterogeneous and complex disorders, presenting major challenges in diagnosis and treatment. The signs and symptoms of RA and PsA are similar especially at the earlier phases of the disease, so it can be difficult to distinguish them on clinical grounds. Lipids and metabolites have been associated with pathological events in both diseases as contributors of the inflammation process. Accordingly, the local lipidome and metabolome from the inflamed tissue may be more reliable in predicting the disease status than the current diagnostic methods, since the synovium is one of the main target tissues of both pathologies. <h3>Objectives</h3> To identify lipid and metabolic profiles in the synovium using Mass Spectrometry Imaging (MSI) that would have the potential to distinguish between patients with RA and PsA. <h3>Methods</h3> Synovium biopsies from 25 patients with PsA, 21 with RA (16 seropositive and 5 seronegative) and 10 with IA (Indeterminate arthritis) were included. Tissue sections were deposited on conductive slides and coated with different matrices for lipid and metabolite extraction. MALDI images were acquired on a rapifleX MALDI Tissuetyper time-of-flight instrument. Multivariate data analysis was used to look for the lipids and metabolites with the highest differences among groups. <h3>Results</h3> MALDI-MSI revealed differential lipid and metabolic profiles among all compared groups. Discriminant analysis (DA) performed on lipid data acquired in positive ion mode displayed a good separation of patients with PsA and RA, especially seropositive RA (figure 1A). PsA showed higher lipid content, mainly phospholipids and sphingolipids, compared to seropositive RA (figure 1B and 1C). Some of them showed a specific localization within tissue. Experiments performed in negative ion mode showed that phosphatidylinositols and phosphatidic acids content varied among groups. Accordingly, DA allowed the separation of PsA from RA and IA patients, mainly from seronegative RA. PsA and RA groups were also distinguished based on synovium metabolic signatures. Sugars including <i>N</i>-acetylhexosamine 6-sulfate (<i>m/z</i> 282.0276), glucuronic acid 1-phosphate (<i>m/z</i> 273.0026) and <i>N</i>-acetylneuraminic acid (<i>m/z</i> 290.0876) displayed a stronger intensity in RA synovium when compared to PsA. <h3>Conclusions</h3> For the first time, PsA and RA synovial membranes have been classified by MALDI-MSI. PsA synovium was characterised by a higher content of phospholipids compared to seronegative and seropositive RA. However, sugar metabolites displayed a stronger intensity in RA synovium when compared to PsA. Metabolic and lipid signatures here reported could support clinical decision-making in the diagnosis of RA and PsA. <h3>Disclosure of Interest</h3> None declared