Objective: To study activation of intracellular pathways depending on nuclear factor kappa B (NFkappaB) and mitogen activated kinases (MAPK) in the synovium of patients with psoriatic arthritis before and after treatment with etanercept.
Methods: Synovial biopsies were obtained by needle arthroscopy of the knee in 9 patients with active psoriatic arthritis before the initiation of etanercept. Follow-up biopsies were taken in the same knee after 6 months. Synovitis was studied by histology. Pathway activation was studied by immunofluorescense for phosphorylated ERK, phosphorylated p38, phosphorylated JNK or phosphorylated inhibitor of kappa B (IkappaBalpha) using digital image analysis.
Results: Histological severity scores were significantly reduced after etanercept treatment. Activation of NFkappaB signaling was found in the lining layer, and in infiltrating and peri-vascular cells in the sublining zone. Activated p38 was present in both lining and sublining layer. In the sublining layer, positive cells were found in inflammatory infiltrates, in perivascular zones and in the endothelium. Activated ERK was mainly present in the sublining layer, both in mononuclear cell infiltrates and perivascularly. Occasional positive cells were found in the lining layer. Activation of JNK was recognized in cells of the lining layer, in some of the sublining cell infiltrates and the perivascular compartment.
Conclusions: Etanercept therapy resulted in a significant decrease in NFkappaB, JNK and ERK, but not in p38 activation. Persistent activation of these pathways, albeit reduced, may trigger positive feedback loops and flares of arthritis after cessation of etanercept.