Protective effects of mercaptoethylguanidine, a selective inhibitor of inducible nitric oxide synthase, in ligature‐induced periodontitis in the rat

Abstract

1 Excessive production of nitric oxide (NO), and the generation of peroxynitrite have been implicated in various proin¯ammatory conditions. In the present study, using mercaptoethylguanidine (MEG), a selective inhibitor of iNOS and a peroxynitrite scavenger, we investigated the role of iNOS and peroxynitrite in a rat model of periodontitis. 2 Periodontitis was produced in rat by a ligature of 2/0 braided silk placed around the cervix of the lower left 1st molar. Animals were then divided into two groups: one group of rats was treated with MEG (30 mg kg 71 , i.p., 4 times per day for 8 days), animals in the other group received vehicle. At day 8, the gingivomucosal tissue encircling the mandibular 1st molars was removed on both sides from ligated and sham operated animals for inducible nitric oxide synthase (iNOS) activity assay and for immunocytochemistry with anti-iNOS serum. Plasma extravasation was measured with the Evans blue technique. Alveolar bone loss was measured with a videomicroscopy. 3 Ligation caused a signi®cant, more than 3 fold increase in the gingival iNOS activity, whereas it did not a ect iNOS activity on the contralateral side, when compared to sham-operated animals. Immunohistochemical analysis revealed iNOS-positive macrophages, lymphocytes and PMNs in the connective tissue and immunoreactive basal layers of epithelium on side of the ligature, and only a few iNOS-negative connective tissue cells on the contralateral side. Ligation signi®cantly increased Evans blue extravasation in gingivomucosal tissue and alveolar bone destruction compared to the contralateral side. MEG treatment signi®cantly reduced the plasma extravasation and bone destruction. 4 The present results demonstrated that ligature-induced periodontitis increases local NO production and that MEG treatment protects against the associated extravasation and bone destruction. Based on the present data, we propose that enhanced formation of NO and peroxynitrite plays a signi®cant role in the pathogenesis of periodontitis.

Nitric oxide in gingival crevicular fluid and nitric oxide synthase expression in the gingiva of patients with sickle cell disease

“…iNOS activity was reported to increase in ligatureinduced periodontitis [27], experimental periodontitis [30], and chronic periodontitis [20,26,31]. Higher levels of iNOS expression were observed in chronic periodontitis tissues than in clinically healthy gingival tissues [20,23,26,27,31] and a previous study of ours showed that iNOS increased in the gingival tissue of aggressive periodontitis patients (unpublished data). In various animal models iNOS was susceptible to infections by a variety of pathogens [32][33][34][35].…”

“…NO has been implicated in the pathogenesis of apical infection [45], periapical granulomas [46], and inflamed human dental pulp [47]. Increased iNOS expression in gingiva was shown in periodontitis [20,22,26,28,31], ligature-induced periodontitis [27], experimental periodontitis [30,46], inflamed gingiva [23], localized aggressive periodontitis [21], and recently by our group in aggressive periodontitis (unpublished data).…”

“…NO synthesis and iNOS activity increase in inflamed periodontal tissues [20,[25][26][27][28] as a result of macrophage infiltration in periodontal tissues [29]. The literature includes only a few studies that evaluated iNOS activity in inflamed periodontal tissues.…”

Efficacy of subantimicrobial-dose doxycycline against nitrosative stress in chronic periodontitis

“…Since large amounts of NO are toxic, NO has been implicated in the pathophysiology of several inflammatory conditions [9][10][11][12] . In such diseases, under conditions of high and sustained NO production, reactive nitrogen oxide species (RNS) (such as nitrogen dioxide, NO 2 ; dinitrogen trioxide, N 2 O 3 ; and peroxynitrite, ONOO -) are formed by reactions with reactive oxygen species (ROS), and may result in nitrosative or oxidative stress [13,14] . Some experimental and clinical evidence indicates that pharmacological inhibition of iNOS triggers anti-inflammatory responses, which may be of clinical use [12,13] .…”

“…Some experimental and clinical evidence indicates that pharmacological inhibition of iNOS triggers anti-inflammatory responses, which may be of clinical use [12,13] . Furthermore, since NO can interact with other inflammatory mediators, it may be part of a system of dual or multiple inhibitors of the inflammatory cascade [14] . Based on these assumptions, the aim of this study was to locally and systemically assess the effect of adjunctive SDD treatment on nitrosative stress in moderate to advanced chronic periodontitis.…”