INHIBITION OF EXTRACELLULAR RELEASE OF PROINFLAMMATORY SECRETORY PHOSPHOLIPASE A(2) (SPLA(2)) BY SULFASALAZINE - A NOVEL MECHANISM OF ANTIINFLAMMATORY ACTIVITY

Sulfasalazine is widely used in rheumatoid arthritis and inflammatory bowel diseases. The mechanisms of its activity have not been elucidate d. In leukocytes, sulfasalazine and its analogue, CL 42A, inhibited th e formation of leukotrienes and possibly of the second messenger compo unds at the level of phospholipase C. Partial inhibition of interleuki n-1 beta (IL-1 beta), IL-6 and tumor necrosis factor a (TNF a) was als o found. Since the synthesis of eicosanoids is induced by phospholipas e A(2) and since secretory phospholipase A(2) (sPLA(2)) is proinflamma tory, we investigated the impact of sulfasalazine and related compound s 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) a nd 200 mu M, respectively. Split products of sulfasalazine, 5-aminosal icylic acid (400 mu M) and sulfapyridine (400 mu M), had no impact. Th e effect of sulfasalazine and CL 42A was evident regardless of whether the cells were stimulated with IL-1 beta/TNF-alpha, lipopolysaccharid e/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 i ntracellular sPLA(2) protein as tested by western blot; however, enzym atic activity of PLA(2) in disrupted cells was definitely increased. T hus, the impact is on the post-transcriptional release of sPLA(2) rath er than on the synthesis. There was also an increase in the extracellu lar release of prostaglandin E-2 from FRCO exposed to sulfasalazine or to CL 42A. In contrast, sulfasalazine had no effect an the extracellu lar 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 Els evier Science Inc.