Objective. To determine the relationship between hypoxia and the expression of Ets-1 and hypoxiainducible factor 1␣ (HIF-1␣) in both normal and inflamed joints. Adjuvant-induced arthritis (AIA) was used as the model system, since it mirrors many aspects of the pathology of rheumatoid arthritis.Methods. Adjuvant arthritis was induced in a group of 10 female Lewis rats. A second group of 10 uninjected female Lewis rats served as naive controls. When a maximum clinical joint score was achieved in the AIA group, all 20 rats were injected with the specific hypoxic cell marker Hypoxyprobe-1 and subsequently killed. Hypoxyprobe-1 adducts, Ets-1, and HIF-1␣ were localized in the joints of the hind feet from these groups using immunohistochemistry.Results. Compared with the joints from control rats, inflamed joints contained markedly more cells with Hypoxyprobe-1 adduct immunoreactivity, Ets-1-immunoreactive nuclei, and nuclear immunoreactivity for both Ets-1 and HIF-1␣.Conclusion. Our results demonstrate the presence of hypoxia in inflamed joints in this experimental model of arthritis. The colocalization of Ets-1 and HIF-1␣ in these hypoxic areas suggests that hypoxia may induce Ets-1 and HIF-1␣ expression during joint inflammation.

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Background: Nitric oxide and superoxide radical production are both increased in rheumatoid arthritis. They avidly react with each other to form the strong oxidating and nitrating substance peroxynitrite. We investigated the presence and distribution of 3nitrotyrosine (3NT), a marker of exposure to peroxynitrite and other reactive nitrogen species, in inflamed and normal synovium from humans and rodents. Method: Standard alkaline-phosphatase immunohisto-chemistry with rabbit polyclonal antibody to 3NT, was used on on synovial specimens from rheumatoid patients (n=13), taken at time of replacement arthroplasty; and from individuals (n=7) with mechanical knee symptoms, undergoing diagnostic arthroscopy. Furthcrmorc, we examined normal synovial and non-synovial tissue from post-mortem specimens (n=3) and a pathological specimen library; from immersion-and perfusion-fixed Wistar rats (n=3) and from wildtype-and iNOS-knock-out mice (n=3; 2 respectively). Appropriate controls included pre-incubation of antibody with authentic 3NT and pre-treatment of sections with hydrogen sulphite. Cell lineage was confirmed, using antibodies to CD68 and =-actin. Results: Inflamed human synovium showed 3NT-immunoreactivity (-ir) mainly in macrophages and vascular smooth muscle, codistributing with immunoreactivity for iNOS The arthroscopic and post-mortem synovia were histologically normal and also showed 3NT-ir in the majority of vascular smooth muscle, that did not colocalise with iNOS-ir. All normal rodent synovia demonstrated identical 3NT-ir in vascular smooth muscle. We found no 3NT-ir in vascular smooth muscle from any of the examined normal nonsynovial human and rodent specimens (eg: skin, intestine, colon, liver, meninges). Conclusion: 3NT-ir is present in the vascular smooth muscle of normal as well as inflamed synovium. In the normal synovium this finding appears exclusive to the synovium, independent of the presence of iNOS and not due to early postmortem change. This suggests a physiological and tissue-specific role for reactive nitrogen species, such as peroxynitrite, in the synovial vasculature.