Evidence for reactive nitrogen species formation in the gingivomucosal tissue

An increase in nitric oxide production has been demonstrated in periodontit is. Here we investigated the potential role of nitric-oxide-derived nitrati ng species (such as peroxynitrite) in a rat model of ligature-induced perio dontitis. Formation of 3-nitrotyrosine, the stable product formed from tyro sine reacting with nitric-oxide-derived nitrating species, was detected in the gingivomucosal tissue. 3-Nitrotyrosine immunohistochemical analysis rev ealed a significant elevation in the number of immunopositive leukocytes, a nd 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-ni trotyrosine-positive band were detected by Western blot. However, in the st erile gingivomucosal. tissue of rat pups, no 3-nitrotyrosine or inducible n itric oxide synthase immunoreactivity was found. Analysis of these data sug gests that resident bacteria of the gingivomucosal tissue induce an increas e in reactive nitrogen species, which is greatly enhanced by plaque formati on in periodontitis.