Inhibition of extracellular release of proinflammatory secretory phospholipase A(2) (sPLA(2)) by sulfasalazine - A novel mechanism of anti-inflammatory activity

Sulfasalazine is widely used in rheumatoid arthritis and inflammatory bowel diseases. The mechanisms of its activity have not been elucidated. In leukocytes, sulfasalazine and its analogue, CL 42A, inhibited the formation of leukotrienes and possibly of the second messenger compounds at the level of phospholipase C. Partial inhibition of interleukin-1 beta (IL-1 beta), IL-6 and tumor necrosis factor a (TNF a) was also found. Since the synthesis of eicosanoids is induced by phospholipase A(2) and since secretory phospholipase A(2) (sPLA(2)) is proinflammatory, we investigated the impact of sulfasalazine and related compounds on mRNA, protein synthesis, and release of sPLA(2) from osteoblasts. Sulfasalazine and CL 42A markedly inhibited extracellular release of sPLA(2). The impact of sulfasalazine was evident at 50 mu M (P < 0.001) and maximal at 400 mu M, and that of CL 42A at 10 mu M (P < 0.001) and 200 mu M, respectively. Split products of sulfasalazine, 5-aminosalicylic acid (400 mu M) and sulfapyridine (400 mu M), had no impact. The effect of sulfasalazine and CL 42A was evident regardless of whether the cells were stimulated with IL-1 beta/TNF-alpha, lipopolysaccharide/forskolin, or dibutyryl-cAMP. Sulfasalazine and CL 42A did not alter the level of sPLA(2) mRNA. Exposure of stimulated fetal rat calvaria osteoblasts (FRCO) to sulfasalazine did not show accumulation of the intracellular sPLA(2) protein as tested by western blot; however, enzymatic activity of PLA(2) in disrupted cells was definitely increased. Thus, the impact is on the post-transcriptional release of sPLA(2) rather than on the synthesis. There was also an increase in the extracellular release of prostaglandin E-2 from FRCO exposed to sulfasalazine or to CL 42A. In contrast, sulfasalazine had no effect an the extracellular release of gelatinase from the cells or on mRNA of cytosolic PLA(2) or cyclooxygenase 2. We conclude that the anti-inflammatory activity of sulfasalazine may be related, in part, to the selective inhibition of the extracellular release of proinflammatory sPLA(2). (C) 1997 Elsevier Science Inc.