Localization of 3-nitrotyrosine to rheumatoid and normal synovium

Objective. To determine the localization of 3-nitrotyrosine (3-NT), a footp rint marker of peroxynitrite (ONOO-) and other reactive nitrogen species, t o the inflamed human synovium and to compare this with normal synovial and nonsynovial tissue of human and animal origin. Methods. Monoclonal and polyclonal antibodies were used to investigate for 3-NT, inducible nitric oxide synthase (iNOS), macrophage marker CD68, and t he vascular smooth muscle marker alpha -actin by avidin-biotin immunocytoch emistry. Results. In the inflamed synovium, 3-NT was found in the vascular smooth mu scle and macrophages. In normal human synovium, 3-NT was present in the vas cular smooth muscle and some lining cells and was not associated with immun oreactivity for iNOS. Similarly, 3-NT could be demonstrated in the vascular smooth muscle cells of normal rats and iNOS knockout mice. It was not pres ent in the vascular smooth muscle of healthy, nonsynovial tissue. Conclusion. The synovial vasculature in histologically, normal human and na ive rodent synovium was alone among the normal tissues studied in exhibitin g iNOS-independent immunoreactivity for 3-NT. These findings suggest a phys iologic role for ONOO- in normal synovial vascular function.