Evidence for reactive nitrogen species formation in the gingivomucosal tissue.

An increase in nitric oxide production has been demonstrated in periodontitis. Here we investigated the potential role of nitric-oxide-derived nitrating species (such as peroxynitrite) in a rat model of ligature-induced periodontitis. Formation of 3-nitrotyrosine, the stable product formed from tyrosine reacting with nitric-oxide-derived nitrating species, was detected in the gingivomucosal tissue. 3-Nitrotyrosine immunohistochemical analysis revealed a significant elevation in the number of immunopositive leukocytes, and higher immunoreactivity of the gingival ligaments and epithelium in the ligated than in the contralateral (control) side. On both sides, several 3-nitrotyrosine-positive bands and, on the ligated side, a unique 52-kDa 3-nitrotyrosine-positive band were detected by Western blot. However, in the sterile gingivomucosal tissue of rat pups, no 3-nitrotyrosine or inducible nitric oxide synthase immunoreactivity was found. Analysis of these data suggests that resident bacteria of the gingivomucosal tissue induce an increase in reactive nitrogen species, which is greatly enhanced by plaque formation in periodontitis.