Active leflunomide metabolite inhibits interleukin 1β, tumour necrosis factor α, nitric oxide, and metalloproteinase-3 production in activated human synovial tissue cultures

Background: Leflunomide is now an approved agent for the management of adult rheumatoid arthritis (RA). Its active metabolite A771726 inhibits de novo pyrimidine biosynthesis. Although considered to be an immunosuppressive agent, its mechanism of action remains obscure. Objectives: Evaluation of the leflunomide active metabolite A771726 (LEF) effect on interleukin 1s (IL1s), tumour necrosis factor (TNFα), nitric oxide (NO), and stromelysin (metalloproteinase-3 (MMP-3)) production by activated human synovial tissue in culture. Methods: Synovial tissue was obtained during surgery from patients undergoing total knee replacement owing to RA or osteoarthritis (OA), cut into small pieces, and cultured in Petri dishes with test materials as previously described. IL1s, TNFα, NO, and MMP-3 were measured in the culture media after 48 hours incubation with different doses of LEF by methods previously described. Results: LEF (0.3, 3, and 9 µg/ml) inhibited IL1s production in the presence of lipopolysaccharide (LPS; 3 µg/ml) in a dose dependent manner (p<0.01) at LEF 0.3 µg/ml. TNFα production in the presence of IL1s (1 ng/ml) was also inhibited in a dose dependent manner (p<0.05 at LEF 0.3 µg/ml). NO and MMP-3 production in the presence of LPS (3 µg/ml) was inhibited as well (p<0.01 at LEF 1 µg/ml and at LEF 0.3 µg/ml, respectively). Synovial cell viability evaluated by the tetrazolium salt XTT was unaffected by the LEF concentration used. There was no qualitative difference in the response of OA and RA synovial tissue. Conclusion: Leflunomide may modulate the rheumatoid articular process by inhibition of local production of IL1s, TNFα, NO, and MMP-3.