Synergistic effect of interleukin-1 beta and tumor necrosis factor alpha on PGE(2) production by articular chondrocytes does not involve PLA(2) stimulation

This study investigates the ways in which two proinflammatory cytokines, tumor necrosis factor alpha (TNF) and interleulrin-1 beta (IL1), cause increased production of prostaglandin E(2) (PGE(2)) in rabbit articular chondrocytes (RAC). Rabbit articular chondrocytes in primary culture were incubated with IL1, TNF, or both. Arachidonic acid (AA) release, PGE(2) production, and the activities of cytosolic phospholipase A(2) (cPLA(2)), secreted phospholipase A(2) (sPLA(2)), and cyclooxygenase (COX) were measured. The mRNA levels of cPLA(2), sPLA(2), and COX-2 were also measured by Northern blotting, using specific complementary DNA probes. Incubation of IL1-stimulated RAC with TNF further increased PGE(2) production. This synergy did not involve PLA(2) stimulation, as there were no increases in AA release, cPLA(2) and sPLA(2) activities, or mRNA. In contrast, TNF increased the effect of IL1 on COX-2 activity and mRNA level, These results show that TNF and IL1 act in synergy in PGE(2) production in articular chondrocytes. As sPLA(2) and cPLA(2) do not seem to be involved, COX-2 appears to be the best target for a specific anti-inflammatory strategy against cartilage degradation. (C) 1996 Academic Press, Inc.