OP0244 High Expression of Prostaglandin E2 in Zygapophyseal Joints of Patients with Ankylosing Spondylitis and Osteoarthritis

Background A study by Poddubnyy et al. showed that a high NSAIDs intake over 2 years is associated with retarded radiographic spinal progression in AS [1] suggesting that NSAIDs might prevent new bone formation in patients with ankylosing spondylitis (AS). Objectives In order to determine prostaglandin E 2 (PGE 2 ) expression at sites of bone remodeling we performed an immunohistochemical study analyzing PGE 2 expressing cells in zygapophyseal joints of AS patients in comparison to autopsy controls and patients with osteoarthritis (OA). Methods PGE 2 was determined in zygapophyseal joints from 13 AS, 11 OA patients and 10 controls (autopsies without spinal diseases). Immunohistochemistry was performed to detect PGE 2 + cells per total cell number at four different sites: within hyaline cartilage, subchondral bone plate, trabecular bone and fibrous tissue replacing subchondral bone marrow. Results About 50 percent of the chondrocytes expressed prostaglandin E 2 in autopsy controls. While PGE 2 expression in chondrocytes of OA patients was significantly increased compared to controls (p=0.0015), a trend towards increased numbers of PGE 2 + chondrocytes was also found in AS patients (p=0.1095). For osteocytes within the subchondral bone plate and the trabecular bone a similar trend was seen: more osteocytes were PGE 2 positive in joints of AS patients (41.80±16.42%; 41.16±21.15%) and OA patients (44.82±15.47%; 49.25±16.32%) patients than in controls (20.33±16.69%; 32.18±18.88%). Fibrous tissue, replacing the subchondral bone marrow and invading the subchondral bone plate, is a typical feature of AS and OA joints, but not seen in controls. Here we found that more than 80 percent of the cells expressed PGE 2 (AS 84.82±9.00%; OA 87.88±13.38%), without differences between AS and OA patients (p=0.1902). Conclusions PGE 2 is highly expressed within zygapophyseal joints, including the cells of cartilagineous and bony regions. However also within the fibrous tissue high expression rates were detected suggesting that PGE 2 is expressed by many cell types within joints which could be potentially targeted by a NSAID therapy. In spite of the knowledge that NSAIDs are highly effective in reduction of symptoms such as pain and therefore represent a first-line therapy in AS and OA [2, 3], further studies are required to determine the impact of PGE 2 on the function and differentiation of cells potentially involved in aberrant new bone formation in AS and OA. References Poddubnyy D, Rudwaleit M, Haibel H, Listing J, Marker-Hermann E, Zeidler H, et al. Effect of non-steroidal anti-inflammatory drugs on radiographic spinal progression in patients with axial spondyloarthritis: results from the German Spondyloarthritis Inception Cohort. Annals of the rheumatic diseases. 2012 Oct; 71(10):1616-1622. Poddubnyy D, van der Heijde D. Therapeutic controversies in spondyloarthritis: nonsteroidal anti-inflammatory drugs. Rheumatic diseases clinics of North America. 2012 Aug; 38(3):601-611. Stam W, Jansen J, Taylor S. Efficacy of etoricoxib, celecoxib, lumiracoxib, non-selective NSAIDs, and acetaminophen in osteoarthritis: a mixed treatment comparison. The open rheumatology journal. 2012; 6:6-20. Disclosure of Interest None Declared