FRI0166 Characterisation of phosphodiesterase 4 (PDE4) blockade in the synovium of psoriatic arthritis patients: a focus on synovial invasiveness and t-cell polyfunctionality
Authors: S.M. Wade, M. Canavan, T. McGarry, S.C. Wade, D.J. Veale, U. Fearon
Journal: Annals of the Rheumatic Diseases (2018)

<h3>Background</h3> Owing to the multi-faceted nature of the pathogenesis of psoriatic arthritis (PsA), the development of multi-targeted agents has been an area of intensive research. Such agents include the phosphodiesterase 4 (PDE4) inhibitors, Rolipram and Apremilast, which elevate intracellular cAMP levels to modulate a number of anti-inflammatory mechanisms. However, the effect of PDE4 blockade within the complex inflammatory environment of the inflamed synovium remains to be elucidated. <h3>Objectives</h3> To characterise the effect of PDE4 blockade in PsA using <i>ex vivo</i> synovial whole tissue explants and synovial single cell suspensions reflective of the complex synovial micro-environment. <h3>Methods</h3> <i>Ex-vivo</i> PsA whole tissue synovial explants were cultured in the presence of PDE4 inhibitor, Rolipram, for 24 hour. The expression of pro-inflammatory mediators were quantified by ELISA and MSD multiplex. A 21 day synovial explant matrigel model was utilised to examine synovial fibroblast (SFC) invasiveness to allow for a long-term assessment. For the characterisation of synovial T-cells, synovial explants were digested and cultured in the presence of Rolipram for 8 hours, stimulated and stained for surface and intracellular T-cell markers. Cell surface expression of CD161 was used to identify Th17 lineage (CD161 +Th17 and exTh17 cells) or non-Th17 lineage (CD161-) Th1 cells. SPICE analysis was utilised to determine the proportions of mono- and polyfunctional T-cells, which were correlated with disease activity scores. <h3>Results</h3> Rolipram treatment inhibited the spontaneous secretion of inflammatory mediators IL-6, IL-8, MCP-1 and MMP-1 (all p&lt;0.05), with a parallel increase in IL-10 expression. Under DMSO control conditions, a significant increase in SFC outgrowths from PsA explants (indicative of SFC invasiveness) was observed from day 8–21 (all p&lt;0.05), effects of which were significantly decreased in the presence of Rolipram (all p&lt;0.05). A comparative analysis of T cells in PsA PBMC and synovial tissue revealed an enrichment of Th1 (p&lt;0.05), Th17 (p=0.06) and exTh17 (p&lt;0.05) cells in PsA synovial tissue, which displayed distinct polyfunctional cytokine profiles, in particular Th17 cells, as compared to matched PBMC. The frequency of polyfunctional triple positive GM-CSF/TNF/IL-17 and or IFNy producing Th1 (r=0.8, p&lt;0.05), Th17 (r=0.6, p&lt;0.16) and exTh17 (r=0.9, p&lt;0.05) cells positively correlated with PsA disease activity, suggesting an important role of T-cell polyfunctionality in PsA synovial pathogenesis. Analysis of synovial tissue cell suspensions and matched PBMC cultured in the presence of Rolipram showed a significant decrease in the proportion of these triple positivesynovial T cells compared to DMSO (p&lt;0.05), suggesting that PDE4 blockade can effectively targets the polyfunctional hyper-pathogenic synovial T cells in PsA, particularly polyfunctional CD8 +T cells and Th17 lineage, Th17 and exTh17 cells. <h3>Conclusions</h3> PDE4 blockade mediates broad anti-inflammatory mechanisms in PsA synovial tissue through the reduced expression of pro-inflammatory mediators, decreased invasiveness and reduced T cell polyfunctionality. We also demonstrate the feasibility of using <i>ex vivo</i> models to determine "<i>in situ</i> like" assessments of therapeutic agents and further our understanding of disease pathogenesis. <h3>Disclosure of Interest</h3> None declared