Reactive oxygen species participation in experimentally induced arthritis of the temporomandibular joint in rats

In the temporomandibular joint (TMJ), it has been hypothesized that mechani cal stresses lead to the oxidative stress of articular tissues. It has also been postulated that cells pertinent to arthritis-including endothelial ce lls and synovial cells-when stimulated by mechanical stresses and/or pro-in flammatory cytokines, promote oxidative damage. To determine the involvemen t of reactive oxygen species (ROS) in the diseased joint, we studied the ge neration of ROS in synovial fluid (SF) from interleukin-1 alpha (IL-1 alpha )-induced TMJ arthritis by electron spin resonance (ESR) spectroscopy, usin g the spin trap 5,5-dimethyl-1-pyrroline N-oxide (DMPO). The TMJ arthritis was experimentally induced in rats by the injection of human recombinant IL -1 alpha into the TMJ; control rats were treated with normal saline solutio n. We found that the detected radicals in the collected SF were identified as a 1:2:2:1 quartet, characteristic of the hydroxyl radical-DMPO spin addu ct. The ESR signal intensity of the hydroxyl radical-DMPO spin adduct in th e SF from IL-1-treated rats was significantly higher than that from the con trol rats (P < 0.01). The results of ESR study also showed that hydroxyl ra dical (HO.) was increased in a time-dependent fashion in the presence of su peroxide anion radical (O-2(.)) scavenger superoxide dismutase (SOD); the f ormation of DMPO-HO. was strongly inhibited by the iron chelater deferoxami ne. We could measure higher level of free iron (Fe2+ and Fe3+) in the SF fr om TMJ arthritis than in that from controls (P < 0.05). Analysis of the dat a obtained from the present study suggests that the HO. radical detected in SF from IL-1-induced TMJ arthritis is generated via a modified Haber-Weiss reaction (biological Fenton reaction) in which O-2(.) can subsequently res ult in the production of H2O2 through dismutation reaction by SOD. Thus, HO . may be generated from the reaction of resultant H2O2 with free iron ions. The results presented here provide the first evidence of involvement of RO S in IL-1-induced TMJ arthritis.