Adenosine analogs and electromagnetic fields inhibit prostaglandin E2 release in bovine synovial fibroblasts

SummaryObjectiveTo investigate the role of adenosine analogs and electromagnetic field (EMF) stimulation on prostaglandin E2 (PGE2) release and cyclooxygenase-2 (COX-2) expression in bovine synovial fibroblasts (SFs).MethodsSFs isolated from synovia were cultured in monolayer. Saturation and binding experiments were performed by using typical adenosine agonists: N6-cyclohexyladenosine (CHA, A1), 2-[p-(2-carboxyethyl)-phenetyl-amino]-5′-N-ethylcarboxamidoadenosine (CGS 21680, A2A), 5′-N-ethylcarboxamidoadenosine (NECA, non-selective), N6-(3-iodobenzyl)2-chloroadenosine-5′-N-methyluronamide (Cl-IB-MECA, A3). SFs were treated with TNF-α (10 ng/ml) and lipopolysaccharide (LPS) (1 μg/ml) to activate inflammatory response. Adenosine analogs were added to control and TNF-α- or LPS-treated cultures both in the absence and in the presence of adenosine deaminase (ADA) which is used to deplete endogenous adenosine. Parallel cultures were exposed to EMFs (75 Hz, 1.5 mT) during the period in culture (24 h). PGE2 release was measured by immunoassay. COX-2 expression was evaluated by RT-PCR.ResultsTNF-α and LPS stimulated PGE2 release. All adenosine agonists, except for Cl-IB-MECA, significantly inhibited PGE2 production. EMFs inhibited PGE2 production in the absence of adenosine agonists and increased the effects of CHA, CGS 21680 and NECA. In ADA, the inhibition on PGE2 release induced by CHA, CGS and NECA was stronger than in the absence of ADA and the EMF-inhibitory effect was lost. Changes in PGE2 levels were associated to modification of COX-2 expression.ConclusionsThis study supports anti-inflammatory activities of A1 and A2A adenosine receptors and EMFs in bovine SFs. EMF activity appears mediated by an EMF-induced up-regulation of A2A receptors. Biophysical and/or pharmacological modulation of adenosine pathways may play an important role to control joint inflammation.