Open AccessInterleukin‐1‐Mediated phospholipid breakdown and arachidonic acid release in human synovial cells
Author(s) -
Angel Juana,
Colard Odile,
Chevy Françoise,
Fournier Catherine
Publication year - 1993
Publication title -
arthritis & rheumatism
Language(s) - English
Resource type - Journals
eISSN - 1529-0131
pISSN - 0004-3591
DOI - 10.1002/art.1780360205
Subject(s) - phospholipase a2 , arachidonic acid , phospholipid , phospholipase a , phosphatidylinositol , chemistry , prostaglandin e2 , biochemistry , phosphatidylcholine , phospholipase , synovial fluid , lipid signaling , synovial membrane , phospholipase c , intracellular , microbiology and biotechnology , enzyme , endocrinology , biology , medicine , arthritis , signal transduction , osteoarthritis , alternative medicine , pathology , membrane
Objective. Interleukin‐1 (IL‐1), an important mediator contributing to joint destruction in rheumatoid arthritis, is known to stimulate the release of arachidonic acid (AA) and prostaglandin E 2 (PGE 2 ) from adherent synoviocytes. To study the intracellular pathways involved in these functions, we stimulated cultures of human synovial cells with recombinant IL‐1β. Methods. AA liberation was measured after labeling synovial cells with 3 H‐AA, and PGE 2 levels were determined by high performance liquid chromatography or radioimmunoassay. Identification of 3 H‐AA‐labeled phospholipids was performed by thin layer chromatography. Cell‐associated phospholipase A 2 (PLA 2 ) enzymatic activity was determined by an assay with cell‐free systems and exogenous substrates. Results. Stimulation of synovial cells with recombinant IL‐1β induced a decrease in phosphatidylcholine (PC), phosphatidylinositol (PI), and phosphatidylethanolamine (PE), and a marked increase in cell‐associated PLA 2 activity as compared with controls. In the presence of either quinacrine, an inhibitor of PLA 2 pathway activation, or neomycin, which binds to PI mono‐ and biphosphate thus blocking their degradation by phospholipases, AA and PGE 2 secretion were reduced in a dose‐dependent manner. Kinetic studies revealed that quinacrine had little blocking activity on the IL‐1‐mediated AA release after 1 hour of stimulation but completely abolished it after 5 or 8 hours. In contrast, neomycin exerted a partial but significant inhibitory effect from the first hour of stimulation onward. Addition of quinacrine was also demonstrated to abolish the IL‐1‐induced hydrolysis of PC and PE but not PI, indicating that PC and PE are the preferred substrates for PLA 2 enzymatic activity in human synovial cells. Conclusion. Our findings strongly suggest that AA and PGE 2 production by IL‐1‐triggered synoviocytes are largely dependent upon PLA 2 ‐mediated hydrolysis of PC and PE and to a lesser extent upon the earlier degradation of PI.