SYNOVIOCYTES BUT NOT ARTICULAR CHONDROCYTES RELEASE FREE RADICALS AFTER REPETITIVE CYCLES OF ANOXIA/REOXYGENATION: AN ELECTRON SPIN RESONANCE STUDY.

Objective : We investigated if short recurrent periods of anoxia/reoxygenation (A/R), mimicking the in vivo conditions of hypoxia, could stimulate the production of free radicals by synoviocytes and chondrocytes.
Material and Methods : Synoviocytes (immortalised rabbit line HIG-82 and equine synoviocytes isolated from synovial membranes of the stifle joint) and chondrocytes (isolated from the same equine joint) were cultured for 48 hours. The respiration rate of the cells (107 cells/assay) was studied by oxymetry and the free radical production monitored by electron spin resonance (ESR) in the presence of the spin trap (-[-4-pyridyl 1-oxide]-N-tert butyl nitrone)/ethanol mixture (2%v/v). The A/R consisted of three periods of 20 minutes anoxia, each anoxia period being followed by re-oxygenation. Oxygen consumption by the cells was measured before starting the anoxia/reoxygenation cycles and after each reoxygenation. At the end of the last A/R period, the cells were transferred into the ESR flat cell and in the cavity, and the free radical formation was monitored.
Results : The equine chondrocytes showed a low respiration rate, weakly affected by A/R and no production of free radicals (n=3). Synoviocytes showed a higher respiration rate (at least 20 times higher) which was affected by recurrent A/R (decrease of the slope of oxygen consumption), and a free radical production as evidenced by the appearance of the 4-POBN/EtOH adducts (n=6).
Conclusions :These observations suggest that synoviocytes, but not chondrocytes, responded to repeated anoxia-reoxygenation conditions by the production of free radicals. Synoviocytes could thus be responsible for the production of free radicals in the joints, what could be an important factor in the onset of osteoarthritis.