Synovial fluid proteins are required for the induction of interleukin-1ß production by monosodium urate crystals.

OBJECTIVES: Monosodium urate (MSU) crystal deposition in gouty joints promotes the release of inflammatory mediators, in particular interleukin (IL)-1ß. The induction of IL-1ß production by MSU crystals requires a co-stimulus. The objective of this study was to determine which part of the synovial fluid (SF) provides co-stimulation to MSU crystals to induce IL-1ß in macrophages. METHOD: The lipidic fraction (LF) and the protein fraction (PF) were isolated from the SF of patients with arthropathies. The PF was subfractionated according to different molecular weight (MW) ranges. THP-1 cells or human primary monocytes were stimulated with MSU crystals in the presence or absence of SF or SF fractions. IL-1ß and IL-8 production and IL-1ß mRNA expression were assessed by an enzyme-linked immunosorbent assay (ELISA) and quantitative real-time polymerase chain reaction (qPCR). RESULTS: Exposure of monocytes/macrophages to MSU crystals alone induced the moderate release of IL-8 but not of IL-1ß. The production of IL-1ß required the presence of both SF from patients with inflammatory arthritis (SFi) and MSU crystals. SF from patients with non-inflammatory arthritis, that is patients with osteoarthritis (OA), did not affect the IL-1ß production but slightly enhanced the secretion of IL-8. Both MSU crystals and SFi were required for the induction of the IL-1ß transcript, which was not expressed in the presence of either stimulus alone. SFi fractionation demonstrated that the MSU crystal co-stimulus was contained in the PF of SFi with MW > 50 kDa but not in the LF. CONCLUSIONS: This study shows that the SF of inflammatory arthritis patients, including gout patients, contains proteins required for the induction of IL-1ß by MSU crystals in macrophages whereas lipids are not involved.

The active metabolite of leflunomide, A77 1726, inhibits the production of prostaglandin E(2), matrix metalloproteinase 1 and interleukin 6 in human fibroblast-like synoviocytes.

OBJECTIVES: To investigate the effects of the active metabolite of leflunomide, A77 1726, on fibroblast-like synoviocytes. In rheumatoid arthritis (RA) synoviocytes participate in tissue destruction by producing metalloproteinases (MMP), prostaglandin E(2) (PGE(2)) and interleukin (IL) 6, which are involved in extracellular matrix degradation, resorption of the mineral phase and osteoclast-mediated bone resorption. METHODS: Human synoviocytes were stimulated with IL-1alpha or tumour necrosis factor alpha (TNF-alpha) in the presence of A77 1726. Culture supernatants were analysed for production of interstitial collagenase (MMP-1), tissue-inhibitor of metalloproteinases 1 (TIMP-1), PGE(2) and IL-6. Total RNA was isolated and analysed for steady-state levels of MMP-1, cyclooxygenase-2 (COX-2) and IL-6 mRNA. RESULTS: A77 1726 inhibited the production of PGE(2) in synoviocytes activated by TNF-alpha and IL-1alpha with median inhibitory concentrations (IC(50)) of 7 and 3 microM respectively. In contrast, MMP-1 and IL-6 production was inhibited at high A77 1726 concentrations (> 10 microM), whereas TIMP-1 was not affected. The inhibition of MMP-1 and IL-6 production was due to the known inhibitory effect of A77 1726 on pyrimidine synthesis, as it was reversed by the addition of uridine. This did not apply to PGE(2) production, which was inhibited via direct action of A77 1726 on COX-2, as shown by the increasing amount of substrate (arachidonic acid) in the culture medium. CONCLUSION: This study shows that some of the beneficial effect of leflunomide in RA patients may be due to the inhibition of PGE(2), IL-6 and MMP-1 production in synoviocytes. This effect, coupled with its multiple inhibitory effects on T lymphocyte functions, might account for the significant reduction in the rate of disease progression in RA patients treated with leflunomide.