Annexin I and dexamethasone effects on phospholipase and cyclooxygenase activity in human synoviocytes

ANNEXIN I is a glucocorticoid-induced me diator with anti-inflammatory acti vity in animal models of arthritis. We studied the effects of a bioactive a nnex in I peptide, ac 2-26, dexamethasone (DEX), and interleukin- 1 beta (I L-1 beta) on phospholipase A(2) (PLA(2)) and cyclooxygenase (COX) activitie s and prostaglandin E-2 (PGE(2)) release in cultured human fibroblast-like synoviocytes (FLS). Annex in I binding sites on human osteoarthritic (OA) F LS were detected by ligand binding flow cytometry. PLA(2) activity was meas ured using H-3-arachidonic acid release, PGE(2) release and COX activity by ELISA, and COX2 content by flow cyto metry. Annex in I binding sites were present on human OA FLS. Annex in I peptide ac 2-26 exerted a significant c oncentration-dependent inhibition of FLS constitutive PLA(2) activity, whic h was reversed by IL-1 beta. In contrast, DEX inhibited IL-1 beta -induced PLA(2) activity but not constitutive activity. DEX but not annex in I pepti de inhibited IL-1 beta -induced PGE(2) release. COX activity and COX2 expre ssion were significantly increased by IL-1 beta. Annex in I peptide demonst rated no inhibition of constitutive or IL-1 beta -induced COX activity. DEX exerted a concentration-dependent inhibition of IL-1 beta -induced but not constitutive COX activity. Uncoupling of inhibition of PLA(2) and COX by a nnex in I and DEX support the hypothesis that COX is rate-limiting for PGE( 2) synthesis in FLS. The effect of annex in I but not DEX on constitutive P LA(2) activity suggests a glucocorticoid-independent role for annex in I in auto regulation of arachidonic acid production. The lack of effect of anne x in I on cytokine-induced PGE(2) production suggests PGE(2)-independent me chanisms for th eantiinflammatory effects of annex in I in vivo.