The Effect of Dexamethasone, Adrenergic and Cholinergic Receptor Agonists on Phospholipid Metabolism in Human Osteoarthritic Synoviocytes.

Phospholipids (PLs) possess the unique ability to contribute to synovial joint lubrication. The aim of our study was to determine for the first time the effect of dexamethasone and some adrenergic and cholinergic agonists on the biosynthesis and release of PLs from human fibroblast-like synoviocytes (FLS). Osteoarthritic human knee FLS were treated with dexamethasone, terbutaline, epinephrine, carbachol, and pilocarpine, or the glucocorticoid receptor antagonist RU 486. Simultaneously PL biosynthesis was determined through the incorporation of stable isotope-labeled precursors into PLs. Radioactive isotope-labeled precursors were used to radiolabel PLs for the subsequent quantification of their release into nutrient media. Lipids were extracted and quantified using electrospray ionization tandem mass spectrometry or liquid scintillation counting. Dexamethasone significantly decreased the biosynthesis of phosphatidylcholine, phosphatidylethanolamine (PE), PE-based plasmalogen, and sphingomyelin. The addition of RU 486 abolished these effects. A release of PLs from FLS into nutrient media was not recognized by any of the tested agents. None of the adrenergic or cholinergic receptor agonists modulated the PL biosynthesis. We demonstrate for the first time an inhibitory effect of dexamethasone on the PL biosynthesis of FLS from human knees. Moreover, our study indicates that the PL metabolism of synovial joints and lungs are differently regulated.

Growth factors regulate phospholipid biosynthesis in human fibroblast-like synoviocytes obtained from osteoarthritic knees.

Elevated levels of growth factors and phospholipids (PLs) have been found in osteoarthritic synovial fluid (SF), although the metabolic regulation of PLs is currently unknown. This study aimed to determine the effects of growth factors on the biosynthesis of PLs by fibroblast-like synoviocytes (FLS) obtained from human osteoarthritic knee joints. Electrospray ionization tandem mass spectrometry was applied to analyse the newly synthesized PLs. In the presence of stable isotope-labelled PL precursors, cultured FLS were treated with either transforming growth factor-ß1 (TGF-ß1), bone morphogenetic protein (BMP)-2, BMP-4, BMP-7 or insulin-like growth factor-1 (IGF-1) alone or in combination with specific inhibitors of cell signalling pathways. TGF-ß1 and IGF-1 markedly stimulated the biosynthesis of phosphatidylcholine (PC) before sphingomyelin (SM) and lysophosphatidylcholine (LPC) species were stimulated. BMPs elaborated less pronounced effects. The BMPs tested have different potentials to induce the biosynthesis of phosphatidylethanolamine (PE) and PE-based plasmalogens. Our study shows for the first time that TGF-ß1 and IGF-1 substantially regulate the biosynthesis of PC, SM and LPC in human FLS. The functional consequences of elevated levels of PLs require additional study. The BMPs tested may be joint protective in that they upregulate PE-based plasmalogens that function as endogenous antioxidants against reactive oxygen species.