Localization of 3-nitrotyrosine to rheumatoid and normal synovium

Objective. To determine the localization of 3-nitrotyrosine (3-NT), a footprint marker of peroxynitrite (ONOO-) and other reactive nitrogen species, to 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 the vascular smooth muscle marker alpha -actin by avidin-biotin immunocytochemistry. Results. In the inflamed synovium, 3-NT was found in the vascular smooth muscle and macrophages. In normal human synovium, 3-NT was present in the vascular smooth muscle and some lining cells and was not associated with immunoreactivity for iNOS. Similarly, 3-NT could be demonstrated in the vascular smooth muscle cells of normal rats and iNOS knockout mice. It was not present in the vascular smooth muscle of healthy, nonsynovial tissue. Conclusion. The synovial vasculature in histologically, normal human and naive rodent synovium was alone among the normal tissues studied in exhibiting iNOS-independent immunoreactivity for 3-NT. These findings suggest a physiologic role for ONOO- in normal synovial vascular function.