PEMFs mediate an up-regulation of A2A and A3 receptors related to an increase of their functional activities in bovine chondrocytes and fibroblast-like synoviocytes. No differences are present in adenosine affinity and in the drug-receptor interactions. Our data could be used as a trigger to future studies addressed to PEMFs and adenosine therapeutic intervention in inflammatory joint diseases.

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This study supports anti-inflammatory activities of A(1) and A(2A) adenosine receptors and EMFs in bovine SFs. EMF activity appears mediated by an EMF-induced up-regulation of A(2A) receptors. Biophysical and/or pharmacological modulation of adenosine pathways may play an important role to control joint inflammation.

Low-energy, low-frequency pulsed electromagnetic fields (PEMFs) can induce cell proliferation in several cell culture models. In this work we analysed the proliferative response of human articular chondrocytes, cultured in medium containing 10% FBS, following prolonged exposure to PEMFs (75 Hz, 2.3 mT), currently used in the treatment of some orthopaedic pathologies. In particular, we investigated the dependence of the proliferative effects on the cell density, the availability of growth factors and the exposure lengths. We observed that PEMFs can induce cell proliferation of low density chondrocyte cultures for a long time (6 days), when fresh serum is added again in the culture medium. In the same conditions, in high density cultures, the PEMF-induced increase in cell proliferation was observed only in the first three days of exposure. The data presented in this study show that the availability of growth factors and the environmental constrictions strongly condition the cellular proliferative response to PEMFs.

The results of this study show that EMF can act in concert with IGF-I in stimulating PG synthesis in bovine articular cartilage explants. As this effect is not maintained in chondrocyte monolayers, the native cell-matrix interactions in the tissue may be fundamental in driving the EMF effects. These data suggest that in vivo the combination of both EMF and IGF may exert a more chondroprotective effect than either treatment alone on articular cartilage.

Synovial fibroblasts (SFs) contribute to the development of osteoarthritis (OA) by the secretion of a wide range of pro-inflammatory mediators, including cytokines and lipid mediators of inflammation. Previous studies suggest that electromagnetic fields (EMFs) may represent a potential therapeutic approach to limit cartilage degradation and control inflammation associated to OA, and that they may act through the adenosine pathway. Therefore, we investigated whether EMFs might modulate inflammatory activities of human SFs from OA patients (OASFs) treated with interleukin-1β (IL-1β), and the possible involvement of adenosine receptors (ARs) in mediating EMF effects. EMF exposure induced a selective increase in A(2A) and A(3) ARs. These increases were associated to changes in cAMP levels, indicating that ARs were functionally active also in EMF-exposed cells. Functional data obtained in the presence of selective A(2A) and A(3) adenosine agonists and antagonists showed that EMFs inhibit the release of prostaglandin E(2) (PGE(2)) and the proinflammatory cytokines interleukin-6 (IL-6) and interleukin-8 (IL-8), while stimulating the release of interleukin-10 (IL-10), an antinflammatory cytokine. These effects seem to be mediated by the EMF-induced upregulation of A(2A) and A(3) ARs. No effects of EMFs or ARs have been observed on matrix degrading enzyme production. In conclusion, this study shows that EMFs display anti-inflammatory effects in human OASFs, and that these EMF-induced effects are in part mediated by the adenosine pathway, specifically by the A(2A) and A(3) AR activation. Taken together, these results open new clinical perspectives to the control of inflammation associated to joint diseases.

Background and purpose:Adenosine is an endogenous modulator, interacting with four G-protein coupled receptors (A1, A2A, A2B and A3) and acts as a potent inhibitor of inflammatory processes in several tissues. So far, the functional effects modulated by adenosine receptors on human synoviocytes have not been investigated in detail. We evaluated mRNA, the protein levels, the functional role of adenosine receptors and their pharmacological modulation in human synoviocytes. Experimental approach: mRNA, Western blotting, saturation and competition binding experiments, cyclic AMP, p38 mitogen-activated protein kinases (MAPKs) and nuclear factor (NF)-kB activation, tumour necrosis factor a (TNF-a) and interleukin-8 (IL-8) release were assessed in human synoviocytes isolated from patients with osteoarthritis. Key results: mRNA and protein for A1, A2A, A2B and A3 adenosine receptors are expressed in human synoviocytes. Standard adenosine agonists and antagonists showed affinity values in the nanomolar range and were coupled to stimulation or inhibition of adenylyl cyclase. Activation of A2A and A3 adenosine receptors inhibited p38 MAPK and NF-kB pathways, an effect abolished by selective adenosine antagonists. A2A and A3 receptor agonists decreased TNF-a and IL-8 production. The phosphoinositide 3-kinase or Gs pathways were involved in the functional responses of A3 or A2A adenosine receptors. Synoviocyte A1 and A2B adenosine receptors were not implicated in the inflammatory process whereas stimulation of A2A and A3 adenosine receptors was closely associated with a down-regulation of the inflammatory status. Conclusions and implications:These results indicate that A2A and A3 adenosine receptors may represent a potential target in therapeutic modulation of joint inflammation.