title: Effects of adenosine on bacterial lipopolysaccharide- and interleukin 1-induced nitric oxide release from equine articular chondrocytes.
abstract: OBJECTIVE
  To determine whether adenosine influences the in vitro release of nitric oxide (NO) from differentiated primary equine articular chondrocytes.
  
  
  METHODS
  Articular cartilage harvested from the metacarpophalangeal and metatarsophalangeal joints of 11 horses (3 to 11 years old) without history or clinical signs of joint disease.
  
  
  METHODS
  Chondrocytes were isolated, plated at a high density (10(5) cells/well), and treated with adenosine, the adenosine receptor agonist 5'-N-ethylcarboxamidoadenosine (NECA), bradykinin, or other agents that modify secondary messenger pathways alone or in combination with bacterial lipopolysaccharide (LPS) or recombinant human interleukin-1alpha (rhIL-1alpha). Nitric oxide release was measured indirectly by use of the Griess reaction and was expressed as micromol of nitrite in the supernatant/microg of protein in the cell layer. Inducible nitric oxide synthase (iNOS) activity was determined by measuring the conversion of radiolabeled arginine to radiolabeled citrulline.
  
  
  RESULTS
  Treatment of chondrocytes with adenosine alone had no significant effect on NO release. However, adenosine and NECA inhibited LPS- and rhIL-1alpha-induced NO release. This response was mimicked by forskolin, which acts to increase adenylate cyclase activity, but not by the calcium ionophore A23187 Treatment of chondrocytes with phorbol myristate acetate, which acts to increase protein kinase C activity, potentiated LPS-induced NO release. Adenosine treatment also significantly inhibited the LPS-induced increase in iNOS activity.
  
  
  CONCLUSIONS
  Adenosine and the nonspecific adenosine receptor agonist NECA inhibited inflammatory mediator-induced release of NO from equine articular chondrocytes. Modulation of adenosine receptor-mediated pathways may offer novel methods for treatment of inflammation in horses with joint disease.
authors.affiliation: Department of Anatomy, Physiology and Cell Biology, School of Veterinary Medicine, University of California, Davis 95616, USA.
authors.forename: Hilary P
authors.initials: HP
authors.lastname: Benton
authors.forename: Melinda H
authors.initials: MH
authors.lastname: MacDonald
authors.forename: Anthony M
authors.initials: AM
authors.lastname: Tesch
mesh_terms: D000241:Adenosine / Q000494:pharmacology*; D019830:Adenosine-5'-(N-ethylcarboxamide) / Q000494:pharmacology; D000818:Animals; D001920:Bradykinin / Q000494:pharmacology; D000001:Calcimycin / Q000494:pharmacology; D002358:Cartilage, Articular / Q000187:drug effects / Q000201:enzymology*; D002478:Cells, Cultured; D019902:Chondrocytes / Q000187:drug effects / Q000201:enzymology*; D004347:Drug Interactions; D006736:Horses / Q000378:metabolism*; D007375:Interleukin-1 / Q000494:pharmacology*; D007476:Ionophores / Q000494:pharmacology; D008070:Lipopolysaccharides / Q000494:pharmacology*; D019001:Nitric Oxide Synthase / Q000378:metabolism*; D052247:Nitric Oxide Synthase Type II; D011493:Protein Kinase C / Q000378:metabolism; D058906:Purinergic P1 Receptor Agonists
chemical_list: D007375:Interleukin-1; D007476:Ionophores; D008070:Lipopolysaccharides; D058906:Purinergic P1 Receptor Agonists; D019830:Adenosine-5'-(N-ethylcarboxamide); D000001:Calcimycin; D019001:Nitric Oxide Synthase; D052247:Nitric Oxide Synthase Type II; D011493:Protein Kinase C; D000241:Adenosine; D001920:Bradykinin