Effects of an adenosine kinase inhibitor and an adenosine deaminase inhibitor on accumulation of extracellular adenosine by equine articular chondrocytes.
OBJECTIVE
To investigate accumulation of extracellular adenosine (ADO) by equine articular chondrocytes and to compare effects of adenosine kinase inhibition and adenosine deaminase inhibition on the amount of nitric oxide (NO) produced by lipopolysaccharide (LPS)-stimulated chondrocytes.


METHODS
Articular cartilage from metacarpophalangeal and metatarsophalangeal joints of 14 horses.


METHODS
Chondrocytes were cultured as monolayers, and cells were incubated with LPS, the adenosine kinase inhibitor 5'-iodotubercidin (ITU), or the adenosine deaminase inhibitor erythro-9-(2-hydroxy-3-nonyl)adenine hydrochloride (EHNA). Concentrations of ADO in cell supernatants were measured by use of reverse-phase high-performance liquid chromatography. Effect of inhibition of enzymatic metabolism of ADO on induced NO production was evaluated by exposing cells to a combination of LPS and ITU or LPS and EHNA.


RESULTS
Articular chondrocytes accumulated extracellular ADO when exposed to LPS or ITU. Chondrocytes exposed to ITU accumulated ADO in a time-dependent manner. Unstimulated chondrocytes did not accumulate ADO. Similarly, EHNA alone did not produce detectable ADO concentrations; however, addition of EHNA and ITU resulted in a synergistic effect on accumulation of ADO. Lipopolysaccharide-induced NO production was more effectively suppressed by exposure to ITU than to EHNA CONCLUSIONS AND CLINICAL RELEVANCE: Equine articular chondrocytes release ADO in response to the proinflammatory stimulus of bacterial LPS. Inhibition of the metabolism of ADO increases accumulation of extracellular ADO. Autocrine release of ADO from chondrocytes may play a role in the cellular response to tissue damage in arthritic conditions, and pharmacologic modulation of these pathways in joints of arthritic horses could be a potential method of therapy.
Tesch
Anthony M
AM
Department of Surgical and Radiological Sciences, School of Veterinary Medicine, University of California, Davis 95616, USA.
MacDonald
Melinda H
MH
Kollias-Baker
Cynthia
C
Benton
Hilary P
HP
D000225:Adenine / Q000031:analogs & derivatives* / Q000494:pharmacology; D000241:Adenosine / Q000378:metabolism*; D000243:Adenosine Deaminase / Q000378:metabolism; D058892:Adenosine Deaminase Inhibitors; D000248:Adenosine Kinase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D000818:Animals; D002358:Cartilage, Articular / Q000166:cytology / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D019902:Chondrocytes / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D006736:Horses / Q000378:metabolism*; D008070:Lipopolysaccharides / Q000378:metabolism; D009569:Nitric Oxide / Q000096:biosynthesis; D009573:Nitrites / Q000032:analysis; D014372:Tubercidin / Q000031:analogs & derivatives / Q000494:pharmacology
D058892:Adenosine Deaminase Inhibitors; D004791:Enzyme Inhibitors; D008070:Lipopolysaccharides; D009573:Nitrites; D009569:Nitric Oxide; C010192:9-(2-hydroxy-3-nonyl)adenine; D000248:Adenosine Kinase; D000243:Adenosine Deaminase; D000225:Adenine; D000241:Adenosine; D014372:Tubercidin