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

ANNEXIN I is a glucocorticoid-induced mediator with anti-inflammatory activity in animal models of arthritis. We studied the effects of a bioactive annex in I peptide, ac 2–26, dexamethasone (DEX), and interleukin- 1β (IL-1β) on phospholipase A_2 (PLA_2) and cyclooxygenase (COX) activities and pros taglandin E_2 (PGE_2) r elease in cultur ed human fibroblast-like synoviocytes (FLS). Annex in I binding sites on human osteoarthritic (OA) FLS were detected by ligand binding flow cytometry. PLA_2 activity was measured us in g ^3H-arachidonic acid re lease, PGE_2 release and COX activity by ELISA, and COX2 content by flow cytometry. Annex in I binding sites were present on human OA FLS. Anne x in I peptide ac 2–26 exerted a significant concentration-dependent inhibition of FLS constitutive PLA2 activity, which was reversed by IL- 1β. In contrast, DEX inhibited IL-1β -induced PLA_2 activity but not constitutive activity. DEX but not annex in I peptide inhibited IL-1β -induced PGE_2 release. COX activity and COX_2 expression were significantly increased by IL-1β. Annex in I peptide demonstrated no inhibition of constitutive or IL- 1β-induced COX activity. DEX exerted a concentration- dependent inhibition of IL-1β -induced but not constitutive COX activity. Uncoupling of inhibition of PLA_2 and COX by annex 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 PLA_2 activity suggests a glucocorticoid-independent role for annex in I in auto regulation of arachidonic acid production. The lack of effect of annex in I on cytokine-induced PGE_2 production suggests PGE_2-independent mechanisms for the anti-inflammatory effects of annex in I in vivo.