Effects of 5−Lipoxygenase Inhibitors on Interleukin Production by Human Synovial Tissues in Organ Culture: Comparison with Interleukin−1−synthesis Inhibitors

Abstract

Abstract Prostaglandins and leukotrienes differentially regulate the production of interleukin−1 (IL−1) in monocytes. It was, therefore, decided to investigate the effects of some 5−lipoxygenase inhibitors compared with standard IL−1−synthesis inhibitors on the production of IL−1 by human synovial tissue explants in organ culture. Human synovial (from hip/knee arthroplasty) or porcine tibio-tarsal joint synovial explants were incubated in organ culture in Dulbecco's Modified Eagle's Medium + 5% foetal calf serum in the presence of the test compounds or solvents (controls), or media alone for 1−5 days. Total bioactive IL−1 was assayed in the medium (following serial dilution or with polyethylene glycol 8000 added in some assays to remove inhibitors) using the D−10 T-cell bioassay. Some assays of interleukins 1α, 1β, 6 or 8 were performed by ELISA. Of the 5−lipoxygenase inhibitors investigated, MK-886 (3−(1−(4−chlorobenzyl)−3-tert-butyl-thio−5−isopropylindol−2−yl)−2,2−dimethyl propanoic acid), L−656,224 ((7−chloro−2−[4−methoxypenyl]methyl)−3−methyl−5−propyl−4−benzofuranol), PF−5901 and tepoxalin were the most potent inhibitors of IL−1 production. While the PF−5901 was effective at 5–30 μM and tepoxalin was effective at 1−10 μM, the others were the most potent having minimal inhibitory activity in the range of 0.01−0.1 μM. The presumed IL−1−synthesis inhibitors, tenidap and IX−207,887, were inactive at concentrations of 30−50 μM. Leukotriene B4 (1−100 ng mL−1) added to MK−886 (5 μM)-treated cultures reversed the inhibitory effects of the latter on IL−1, confirming the role of 5−lipoxygenase products in the regulation of IL−1 production. Addition of polyethylene glycol 8000 to MK−886−treated cultures eliminated the inhibitory effects of this drug, suggesting that this drug exerts its effects by promoting production of IL−1 inhibitors. MK−886 also inhibited synovial production of two other pleiotrophic cytokines which it regulates, IL−6 and IL−8. The results suggest that some 5−lipoxygenase inhibitors may be usefully employed in regulating production of those interleukins involved in joint cartilage destruction.