GLUCOCORTICOID INHIBITION OF ADJUVANT ARTHRITIS SYNOVIAL MACROPHAGE NITRIC-OXIDE PRODUCTION - ROLE OF LIPOCORTIN-1

Nitric oxide (NO) is a mediator of inflammatory injury which is inhibi ted by glucocorticoids and is implicated in rheumatoid (RA) and adjuva nt arthritis (AA). The glucocorticoid-induced antiinflammatory molecul e lipocortin 1 is expressed in RA synovium, but the effects of lipocor tin 1 on synovial inflammation have been little studied. We investigat ed the effects of glucocorticoids and lipocortin 1 on inducible NO syn thase (iNOS) and glucocorticoids on the induction of lipocortin 1 in A A synovial macrophages, NO production was measured by Griess assay in supernatants of day 14 AA rat synovial explants and of synovial macrop hages purified from enzyme-digested synovium and treated with lipopoly saccharide (LPS) 1 mu g/ml, dexamethasone (DEX) 10(-7)M, and anti-lipo cortin 1 MoAb. iNOS and lipocortin 1 expression were detected by flow cytometry using specific MoAb. Cell surface lipocortin was determined by Western blot. NO was produced by all AA synovial explants and NO wa s released by cultured synovial macrophages (14.5 +/- 2.1 mu mol/24h). iNOS was detected in synovial macrophages (ED-1(+)) by permeabilizati on flow cytometry. LPS increased synovial macrophage NO release (P < 0 .0001) and iNOS expression (P = 0.04). DEX inhibited constitutive (P = 0.002) and LPS-induced (P < 0.001) NO release and iNOS expression (P = 0.03). DEX inhibition of synovial macrophage NO was associated with induction of cell surface and intracellular lipocortin 1. Anti-lipocor tin 1 MoAb treatment reduced the inhibition of NO release by DEX (P = 0.002), but had no effect on iNOS expression. These findings demonstra te a role for lipocortin 1 in the inhibition by glucocorticoids of AA synovial macrophage iNOS activity.