Reactive Oxygen Species Participation in Experimentally Induced Arthritis of the Temporomandibular Joint in Rats

In the temporomandibular joint (TMJ), it has been hypothesized that mechanical stresses lead to the oxidative stress of articular tissues. It has also been postulated that cells pertinent to arthritis-including endothelial cells and synovial cells-when stimulated by mechanical stresses and/or pro-inflammatory cytokines, promote oxidative damage. To determine the involvement of reactive oxygen species (ROS) in the diseased joint, we studied the generation of ROS in synovial fluid (SF) from interleukin-1alpha (IL-1alpha)-induced TMJ arthritis by electron spin resonance (ESR) spectroscopy, using 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-1alpha into the TMJ; control rats were treated with normal saline solution. 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 adduct. The ESR signal intensity of the hydroxyl radical-DMPO spin adduct in the SF from IL-1-treated rats was significantly higher than that from the control rats (P < 0.01). The results of ESR study also showed that hydroxyl radical (HO*) was increased in a time-dependent fashion in the presence of superoxide anion radical (O2*-) scavenger superoxide dismutase (SOD); the formation of DMPO-HO* was strongly inhibited by the iron chelater deferoxamine. We could measure higher levels of free iron (Fe2- and Fe3-) in the SF from TMJ arthritis than in that from controls (P < 0.05). Analysis of the data 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 O2*- can subsequently result 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 ROS in IL-1-induced TMJ arthritis.