Effect of Aminoguanidine in Ligature-induced Periodontitis in Rats

Systemic use of selective iNOS inhibitor 1400W or non-selective NOS inhibitor l-NAME differently affects systemic nitric oxide formation after oral Porphyromonas gingivalis inoculation in mice

OBJECTIVE

Nitric oxide synthase (NOS) inhibitors are reported to protect against the local tissue damage in gingivitis and periodontal disease by reducing nitroxidative stress during inflammation, but their systemic effects are not well investigated.

DESIGN

NOS inhibitors systemic effects were investigated in a murine chronic oral inoculation model using live Porphyromonas gingivalis ATCC 33277 (0.3 ml; 10(9)cfu/ml) or sterile broth (0.3 ml). Organ nitric oxide (NO) and plasma nitrite/nitrate (NOx) were determined in mice treated with non-selective NOS inhibitor l-NAME (50mg/kg/24h i.p.) or selective iNOS inhibitor 1400W (10mg/kg/6h i.p.) for the last 5 days of the experiment. Differences between groups were evaluated by nonparametric Wilcoxon's rank-sum one-sided two-sample test and the results compared to those obtained from sham-treated (sterile broth) sham-inoculated animals (water for injection i.p./6h).

RESULTS

Repeated ingestion of P. gingivalis resulted in generalized production of NO in organs and NOx in plasma, the levels of both typically being reduced in P. gingivalis-inoculated-1400W-treated mice, whilst the use of l-NAME was largerly ineffective, even promoting NO/NOx formation. Application of either inhibitor to sham-inoculated animals enhanced NO/NOx formation, due only in part to the repeated i.p. injections.

CONCLUSIONS

The systemic use of 1400W or l-NAME differently affects systemic nitric oxide formation in mice orally challenged with P. gingivalis, but the sequelae of such an intervention should be evaluated further.

Effects of periodontitis on aortic insulin resistance in an obese rat model

The combination of obesity and its associated risk factors, such as insulin resistance and inflammation, results in the development of atherosclerosis. However, the effects of periodontitis on atherosclerosis in an obese body remain unclear. The aim of the study was to investigate the effects of ligature-induced periodontitis in Zucker fatty rats on initiation of atherosclerosis by evaluating aortic insulin resistance. Zucker fatty rats (n=24) were divided into two groups. In the periodontitis group, periodontitis was ligature-induced for 4 weeks, whereas the control group was left unligated. After the 4-week experimental period, descending aorta was used for measuring the levels of lipid deposits, immunohistochemical analysis, and evaluation of gene expression. Levels of serum C-reactive protein (CRP), tumor necrosis factor-alpha (TNF-alpha), and insulin were also measured. Rats in the periodontitis group had significantly enhanced lipid deposits in the aorta, but not in the control group. Expression of suppressor of cytokine signaling 3, vascular cell adhesion molecule 1, reactive oxygen species, nitrotyrosine, and endothelin-1 in the periodontitis group was more intense than that in the control group. Significantly decreased levels of phosphatidylinositol 3-kinase (Pi3k) catalytic beta-polypeptide (Pi3kcb), Pi3kp85, and insulin receptor substrate 1 and 2 were observed in the periodontitis group. Levels of serum CRP and TNF-alpha were significantly increased in the periodontitis group. Under insulin-stimulated conditions, aorta in the periodontitis group altered the Akt phosphorylation. Periodontitis in obesity induced the initial stage of atherosclerosis and disturbed aortic insulin signaling.

FSH aggravates periodontitis-related bone loss in ovariectomized rats

Alveolar bone loss is one of the prominent pathologic and clinical features of periodontitis. Recently, the direct effect of follicle-stimulating hormone (FSH) on bone resorption has been demonstrated. However, the effect of FSH on alveolar bone loss remains unknown. This study tested the hypothesis that FSH would exacerbate periodontitis-related alveolar bone loss. Experimental periodontitis was induced in ovariectomized rats, and the rats were treated with extrinsic FSH or its inhibitor, leuprorelin. After mandibles were collected, we performed morphological examinations to evaluate bone loss, enzyme histochemical tests for osteoclasts, and immunohistochemical examinations for FSH receptor (FSHR). The results showed that FSH significantly increased alveolar bone resorption compared with non-FSH-treated ovariectomized rats (P < 0.05), and the number of FSHR-positive cells was positively correlated with alveolar bone loss area (r = 0.682, P < 0.01). Our results suggested that FSH can aggravate alveolar bone loss by FSHR, independent of estrogen.

Nitric oxide production by a human osteoblast cell line stimulated with Aggregatibacter actinomycetemcomitans lipopolysaccharide

BACKGROUND/AIM

Human osteoblasts induced by inflammatory stimuli express an inducible nitric oxide synthase (iNOS). The aim of the present study was to test the hypothesis that Aggregatibacter actinomycetemcomitans lipopolysaccharide stimulates the production of nitric oxide (NO) by a human osteoblast-like cell line (HOS cells).

METHODS

Cells were stimulated directly with A. actinomycetemcomitans lipopolysaccharide or pretreated with the following l-NIL (an iNOS inhibitor), anti-CD14, Toll-like receptor 2 (TLR2), or TLR4 antibody before stimulation with A. actinomycetemcomitans lipopolysaccharide. The role of the cyclic nucleotides was assessed by pretreating the cells with the following; ODQ (a guanylyl cyclase inhibitor); SQ22536 (an adenylyl cyclase inhibitor); db-cAMP (a cyclic adenosine monophosphate analog); br-cGMP (a cyclic guanosine monophosphate analog); forskolin (an adenylyl cyclase activator), IBMX [a non-specific phosphodiesterase (PDE) inhibitor], or KT5720 [a protein kinase A (PKA) inhibitor]. The cells were also preincubated with genistein [a protein tyrosine kinase (PTK) inhibitor], bisindolylmaleimide [a protein kinase C (PKC) inhibitor], BPB [a phospholipase A2 (PLA2) inhibitor], and NDGA (a lipoxygenase inhibitor). The iNOS activity and nitrite production in the cell cultures were determined spectrophotometrically.

RESULTS

The results showed that A. actinomycetemcomitans lipopolysaccharide stimulated both iNOS activity and nitrite production by HOS cells; this was reduced by l-NIL, anti-CD14, or anti-TLR4 antibody, SQ22536, KT5720, genistein, bisindolylmaleimde, BPB, and NDGA, but was enhanced by db-cAMP, IBMX, and forskolin.

CONCLUSION

These results therefore suggest that A. actinomycetemcomitans lipopolysaccharide may induce the production of NO by HOS cells via a CD14-TLR4 molecule complex, a cAMP-PKA pathway, as well as by a PTK, PKC, PLA2, and lipoxygenase-dependent mechanism.

Histometric analysis of ligature-induced periodontitis in rats: a comparison of histological section planes

The purpose of this study was to analyze the histometry of ligature-induced periodontitis in rats at different histological section depths. Sixteen male adult Wistar rats were randomly assigned to two groups: ligature and control. In the ligature group, rats received a sterile 4/0 silk ligature around the maxillary right 2nd molar. Thirty serial sections containing the 1st and 2nd molars, in which the coronal and root pulp, cementoenamel junction (CEJ) in the mesial side of the 2nd molar, interproximal alveolar bone and connective fiber attachment were clearly visible, were selected for histometric analysis. The histological sections were clustered in groups of 10 sections corresponding the buccal (B), central (C) and lingual (L) regions of the of periodontal tissue samples. The distance between the CEJ in the mesial side of the 2nd molar and the attached periodontal ligament fibers (CEJ-PL) as well as the distance between the CEJ and the alveolar bone crest (CEJ-BC) were determined. From CEJ-PL and CEJ-BC distances measured for each specimen, the measurements obtained in the B, L and C regions were recorded individually and together. Data were submitted to statistical analysis. Significant differences (p<0.001) were observed between the control and ligature groups regarding CEJ-PL (0.05 mm and 0.26 mm, respectively) and CEJ-BC (0.47 mm and 0.77 mm, respectively) measurements. Regarding the depth of the buccal, central and lingual planes, the means of CEJ-PL and CEJ-BC of both groups showed no statistically significant differences (p>0.05). In conclusion, the selection of 10 serial sections of the central region of periodontal tissue samples at any depth can be considered as representative for the evaluation of periodontal ligament fiber attachment and bone loss in ligature-induced periodontitis in rats.

Porphyromonas gingivalis, gamma interferon, and a proapoptotic fibronectin matrix form a synergistic trio that induces c-Jun N-terminal kinase 1-mediated nitric oxide generation and cell death

During infection and inflammation, bacterial and inflammatory proteases break down extracellular matrices into macromolecular fragments. Fibronectin fragments are associated with disease severity in arthritis and periodontitis. The mechanisms by which these fragments contribute to disease pathogenesis are unclear. One likely mechanism is that fibronectin fragments induce apoptosis of resident cells, which can be further modulated by nitric oxide. Nitric oxide levels are increased at inflammatory sites in periodontitis patients. The aim of this study was to examine whether a proapoptotic fibronectin matrix (AFn) exerts its action by inducing nitric oxide and whether priming by bacterial and inflammatory components exacerbates this mechanism. Our data demonstrate that AFn increased the levels of nitric oxide and inducible nitric oxide synthase (iNOS) dose and time dependently in periodontal ligament (PDL) cells. These effects and apoptosis were inhibited by iNOS suppression and enhanced by iNOS overexpression. Nitric oxide and iNOS induction were paralleled by increased c-Jun N-terminal kinase 1 (JNK-1) phosphorylation. JNK-1 overexpression enhanced the expression of nitric oxide and iNOS, whereas inhibiting JNK-1 by small interfering RNA or a kinase mutant reversed these findings. Priming PDL cells with Porphyromonas gingivalis, its lipopolysaccharide (LPS), or gamma interferon (IFN-gamma) further increased nitric oxide levels and apoptosis. Escherichia coli and Streptococcus mutans induced lesser effects. Gingival fibroblasts and neutrophils responded to a lesser degree to these stimuli, whereas keratinocytes were resistant to apoptosis. Thus, proapoptotic matrices trigger nitric oxide release via JNK-1, promoting further apoptosis in host cells. LPS and IFN-gamma accentuate this mechanism, suggesting that during inflammation, the affected matrices and bacterial and inflammatory components combined exert a greater pathogenic effect on host cells.

COX-2 inhibition decreases VEGF expression and alveolar bone loss during the progression of experimental periodontitis in rats

BACKGROUND

Vascular endothelial growth factor (VEGF) is a macromolecule of importance in inflammation that has been implicated in periodontitis. The aims of this study were to investigate VEGF expression during the progression of periodontal disease and to evaluate the effect of a preferential cyclooxygenase (COX)-2 inhibitor meloxicam on VEGF expression and alveolar bone loss in experimentally induced periodontitis.

METHODS

A total of 120 Wistar rats were randomly separated into groups 1 (control) and 2 (meloxicam, 3 mg/kg/day, intraperitoneally, for 3, 7, 14, or 30 days). Silk ligatures were placed at the gingival margin level of the lower right first molar of all rats. VEGF expression was assessed by reverse transcription-polymerase chain reaction (RT-PCR), Western blot (WB), and immunohistochemical (IHC) analyses. The hemiarcades were processed for histopathologic analysis. RT-PCR and WB results were submitted to analysis of variance, the Tukey test, and Pearson correlation analysis (P <0.05).

RESULTS

A reduction in alveolar bone resorption was observed in the meloxicam-treated group compared to the control group at all periods studied. There was a positive correlation between COX-2 mRNA and VEGF mRNA in the gingival tissues and periodontal disease (R = 0.80; P = 0.026). Meloxicam significantly reduced the increased mRNA VEGF expression in diseased tissues after 14 days of treatment (P = 0.023). Some alterations in VEGF receptor 1 mRNA expression were observed, but these were not statistically significant. VEGF protein expression in WB experiments was significantly higher in diseased sites compared to healthy sites (P <0.05). After 14 days of treatment with meloxicam, an important decrease in VEGF protein expression was detected in diseased tissues (P = 0.08). Qualitative IHC analysis revealed that VEGF protein expression was higher in diseased tissues and decreased in tissues from rats treated with meloxicam.

CONCLUSIONS

The present data suggest an important role for VEGF in the progression of periodontal disease. Systemic therapy with meloxicam can modify the progression of experimentally induced periodontitis in rats by reducing VEGF expression and alveolar bone loss.

Effects of Ethanol Consumption on Periodontal Inflammation in Rats

Studies suggest a correlation between ethanol consumption and periodontal disease. We hypothesized that elevated levels of blood reactive oxygen species following ethanol consumption may increase inflammation in periodontal tissue. Rats were divided into 4 groups (6–7 rats/group). Two groups were fed an ethanol-containing liquid diet, and 2 groups were fed a pair-fed control diet. In one of each dietary group, periodontitis was ligature-induced, while the other group was left unligated. Chronic ethanol feeding alone decreased the ratio of reduced/oxidized glutathione and increased 8-hydroxydeoxy-guanosine and tumor necrosis factor (TNF)-α levels in the gingiva. Blood hydroperoxides were also increased. In ligature-induced periodontitis lesions, ethanol feeding enhanced polymorpho-nuclear leukocyte infiltration and TNF-α expression. The results suggest that chronic alcohol consumption increased periodontal inflammation, oxidative damage, and TNF-α production and had an additive effect on polymorphonuclear leukocyte infiltration and gingival oxidative damage, increasing the severity of periodontal inflammation in the ligature model.

Nitric oxide levels in saliva increase with severity of chronic periodontitis

The aims of this study were to compare nitric oxide (NO) levels in stimulated whole saliva from individuals with and without generalized chronic periodontitis (GCP), and to evaluate correlations between these levels with a clinical diagnostic parameter. According to specific criteria, 30 individuals were divided into three groups: one comprising individuals without periodontitis (GC), a second comprising individuals with moderate GCP (GM), and a third comprising individuals with advanced GCP (GA). Samples were collected and NO levels measured. NO in the GCP group (GM: 7.78 microM; GA: 15.79 microM) was higher than in the GC group (5.86 microM). NO levels in the GA group were significantly higher (P < 0.0001) than in the GC group, and could also differentiate (P < 0.0001) the moderate and advanced forms of the disease. In addition, positive correlations between NO level and the number of teeth with a probing depth of > or = 4 mm (r = 0.54) and > or = 7 mm (r = 0.68) were observed. In conclusion, NO levels are elevated in individuals with GPC and are correlated with a periodontal clinical parameter. These results reveal that this form of periodontal disease and its severity are related to salivary nitrite concentration, indicating that NO may serve as a potential biological marker for detection and/or monitoring of GCP.

Morphologic evaluation and expression of matrix metalloproteinases-2 and 9 and nitric oxide during experimental periodontal disease in rat

The immunopathologic and inflammatory mechanisms involved in periodontal disease (PD) include the participation of host resident, inflammatory cells and chemical mediators. Metalloproteinases (MMPs) and nitric oxide (NO) play essential role in extracellular matrix turnover of periodontal tissue destruction. In this study, by means of RT-PCR through semi-quantitative densitometric scanning methods, the expression of MMPs -2 and -9 and inducible NO synthase (iNOS) was temporally and spatially investigated during the destructive mechanisms of experimentally induced PD in rats. Samples from different periods were microscopically analyzed and compared with the contralateral side (control). Our results showed significant expression of MMP-9 and iNOS in tissues affected by PD, as compared with controls, three days after PD induction, simultaneously with the beginning of alveolar bone loss. At 7 days post induction, only the MMP-9 mRNA presented a significantly higher expression, as compared with the respective controls. Thus, in the rat ligature-induced PD, MMP-9 and iNOS might importantly participate in the early stages of the disease, including inflammatory cell migration, tissue destruction and alveolar bone resorption. Also, we may suggest that the exuberant presence of PMNs may be related to the important expression of iNOS and MMP-9 found at 3 days post induction.

Total antioxidant status and 8-hydroxy-2'-deoxyguanosine levels in gingival and peripheral blood of periodontitis patients

INTRODUCTION

The aim of this study was to determine 8-OHdG concentration as a biomarker of oxidant-induced DNA damage and to assess total antioxidant status (TAS) in gingival and peripheral blood during periodontal lesion.

MATERIALS AND METHODS

The study included 56 untreated periodontitis patients (26 with aggressive periodontitis, and 30 with chronic periodontitis (CP). The control group consisted of 25 healthy volunteers without pathological changes in the periodontium. Competitive ELISA was used to measure 8-OHdG. A colorimetric method based on the reduction of ABTSo+ radical cation generation was used to measure TAS.

RESULTS

Significantly higher 8-OHdG concentrations were detected in the gingival blood in both groups of patients with periodontitis than in the control group. Subjects with CP had significantly decreased TAS levels in the gingival blood compared with the control group. A significantly decreased TAS level in the peripheral blood in both patient groups compared with the control group was found. Significant positive correlation between TAS levels in venous and gingival blood in all the periodontitis patients and in the CP group was observed.

CONCLUSIONS

The oxidative burst in periodontitis may lead to significant local damage to nucleic acids. The significantly decreased TAS level in the gingival blood of CP patients compared with the healthy subjects suggests the possibility of a significant decrease in local antioxidant system capacity during the course of periodontitis. The decreased TAS level in the peripheral blood in the group of all patients with periodontitis may be one of the pathogenic mechanisms underlying the links between periodontal disease and several systemic diseases for which periodontitis is regarded as a independent risk factor.

Milk basic protein increases alveolar bone formation in rat experimental periodontitis

BACKGROUND AND OBJECTIVE

It is conceivable that the active components extracted from milk whey protein (i.e. milk basic protein, MBP) stimulate bone formation and suppress bone resorption. Periodontitis is characterized by excessive alveolar bone resorption. We examined whether milk basic protein could recover alveolar bone loss in rat experimental periodontitis.

MATERIAL AND METHODS

A nylon ligature was placed around the cervix of molars in 8-wk-old male Fischer rats for 20 d. Then, the ligature was removed and a powder diet containing 0.2 or 1.0% milk basic protein was provided daily for another 45-90 d. On days 45 and 90, the maxillae were extracted and analyzed using microcomputerized tomography (micro-CT), followed by histological analysis.

RESULTS

Micro-CT images showed that alveolar bone resorption was severely induced around the molar by the 20-d ligature procedure. Treatment with high-dose milk basic protein (1.0%) clearly recovered ligature-induced alveolar bone resorption on days 45 and 90, whereas low-dose milk basic protein (0.2%) did not show such a clear effect. Histological examination clarified that the osteoid thickness of alveolar bone was dose dependently increased by milk basic protein treatment for 90 d.

CONCLUSION

These findings suggest that a systemic administration of milk basic protein may be effective for the recovery of alveolar bone loss in periodontitis.

5-aminoisoquinolin-1(2H)-one, a water-soluble poly (ADP-ribose) polymerase (PARP) inhibitor reduces the evolution of experimental periodontitis in rats

BACKGROUND

Poly (ADP-ribose) polymerase (PARP), a nuclear enzyme activated by strand breaks in DNA, plays an important role in the tissue injury associated with ischaemia-reperfusion and inflammation. Recent studies have demonstrated that PARP activation plays a crucial role in the pathogenesis of acute periodontal injury.

AIM

We have investigated the effect of 5-aminoisoquinolin-1(2H)-one (5-AIQ), a water-soluble PARP inhibitor, in a rat model of periodontitis.

MATERIALS AND METHODS

Periodontitis was induced in rats by placing a 2/0 braided silk ligature around the lower left first molar. At day eight, the gingivomucosal tissue encircling the mandibular first molar was removed for biochemical and histological analysis.

RESULTS AND CONCLUSIONS

Ligation significantly induced an increased neutrophil infiltration and a positive staining for PARP activation. Ligation significantly increased Evans blue extravasation in gingivomucosal tissue and alveolar bone destruction. Intraperitonial injection of 5-aminoisoquinolin-1(2H)-one (5-AIQ) (5 mg/kg daily for eight days) significantly decreased all of the parameters of inflammation as described above. This suggests that inhibition of PARP may represent a novel approach for the treatment of periodontal disease.

Effects of etanercept, a tumour necrosis factor-alpha antagonist, in an experimental model of periodontitis in rats

BACKGROUND AND PURPOSE

Etanercept is a tumour necrosis factor antagonist with anti-inflammatory effects. The aim of our study was to evaluate, for the first time, the therapeutic efficacy of in vivo inhibition of TNF-alpha in an experimental model of periodontitis.

EXPERIMENTAL APPROACH

Periodontitis was induced in adult male Sprague-Dawley rats by placing a nylon thread ligature around the lower 1st molars. Etanercept was administered at a dose of 5 mg kg-1, s.c., after placement of the ligature.

KEY RESULTS

Periodontitis in rats resulted in an inflammatory process characterized by oedema, neutrophil infiltration and cytokine production that was followed by the recruitment of other inflammatory cells, production of a range of inflammatory mediators, tissue damage, apoptosis and disease. Treatment of the rats with etanercept (5 mg kg-1, s.c., after placement of the ligature) significantly reduced the degree of (1) periodontitis inflammation and tissue injury (histological score), (2) infiltration of neutrophils (MPO evaluation), (3) iNOS (the expression of nitrotyrosine and cytokines (eg TNF-alpha)) and (4) apoptosis (Bax and Bcl-2 expression).

CONCLUSIONS AND IMPLICATIONS

Taken together, our results clearly demonstrate that treatment with etanercept reduces the development of inflammation and tissue injury, events associated with periodontitis.

Rosiglitazone reduces the evolution of experimental periodontitis in the rat

The peroxisome proliferator-activated receptor-gamma (PPAR-gamma) receptor appears to play a pivotal role in the regulation of cellular proliferation and inflammation. Recent evidence also suggests that rosiglitazone, a PPAR-gamma agonist, reduces acute and chronic inflammation. We hypothesized that rosiglitazone would attenuate periodontal inflammation. In the present study, we investigated the effects of rosiglitazone in a rat model of ligature-induced periodontitis. At day 8, ligation significantly induced an increase in neutrophil infiltration, as well as of gingivomucosal tissue expression of iNOS, nitrotyrosine formation, and poly (ADP-ribose) polymerase activation. Ligation significantly increased Evans blue extravasation in gingivomucosal tissue and alveolar bone destruction. Intraperitoneal injection of rosiglitazone (10 mg/kg 10% DMSO daily for 8 days) significantly decreased all of the parameters of inflammation, as described above. Analysis of these data demonstrated that rosiglitazone exerted an anti-inflammatory role during experimental periodontitis, and was able to ameliorate the tissue damage associated with ligature-induced periodontitis.

Pyrrolidine dithiocarbamate reduced experimental periodontitis

Nuclear factor-kappaB (NF-kappaB) is a transcription factor which plays a pivotal role in the induction of genes involved in physiological processes as well as in the response to injury and inflammation. Dithiocarbamates are antioxidants which are potent inhibitors of NF-kappaB. We postulated that pyrrolidine dithiocarbamate (PDTC) would attenuate inflammation. In the present study, we have investigated the effects of PDTC, in a rat model of periodontitis. Periodontitis was induced in rats by placing around the lower left first molar a 2/0 braided silk. At day eight the gingivomucosal tissue encircling the mandibular first molar was removed for biochemical and histological analysis. At day eight ligations significantly induced an increase neutrophil infiltration as well as the gingivomucosal tissue expression of TNF-alpha and iNOS as well as nitrotyrosine formation and poly (ADP-ribose) polymerase activation. Ligation significantly increased Evans blue extravasation in gingivomucosal tissue and alveolar bone destruction. Intraperitonial injection of PDTC (10 mg/kg daily for eight days) significantly reduced all of the parameters of inflammation as described above. These data demonstrate that PDTC exerts an anti-inflammatory role during experimental periodontitis and is able to ameliorate the tissue damage associated with ligature-induced periodontitis.

Cloricromene, a coumarine derivative, reduced the development of periodontitis in rats

Recent studies have demonstrated that cloricromene, a coumarin derivative, exerts protective effects in models of inflammation and shock. Tumour necrosis factor plays a pivotal role in the induction of genes involved in physiological processes, as well as in the response to inflammation. We investigated the effect of cloricromene in a rat model of periodontitis. Periodontitis was induced in rats by placing a 2/0 braided silk ligature around the lower left first molar. At day 8 the gingivomucosal tissue encircling the mandibular first molar was removed for evaluation of tumour necrosis factor production, neutrophil infiltration, tissue permeability, nitrotyrosine formation, poly (ADP-ribose) polymerase activation, radiography and histology. Ligation significantly induced an increased tumour necrosis factor production, neutrophil infiltration and a positive staining for nitrotyrosine formation and poly (ADP-ribose) polymerase activation. Ligation significantly increased Evans blue extravasation in gingivomucosal tissue and alveolar bone erosion as evaluated by radiography analysis. Intraperitonal injection of cloricromene (10 mg/kg daily for 8 days) significantly decreased all of the parameters of inflammation as described above. This suggests that cloricromene treatment, which reduced tumour necrosis factor production, may be of benefit in the treatment of periodontitis.

Inhibition of Experimental Gingivitis in Beagle Dogs With Topical Mercaptoalkylguanidines

BACKGROUND

Nitric oxide is a free radical produced in host tissues by constitutive and inducible forms of the enzyme nitric oxide synthase. Nitric oxide plays physiological roles, but it is also involved in the pathophysiology of several inflammatory conditions, including arthritis, ulcerative colitis, and circulatory shock. Local increases in inducible nitric oxide synthase (iNOS) and reactive nitrogen products have also been demonstrated in humans and animals with periodontal disease. This masked, randomized, placebo-controlled preclinical investigation examined the effect of two mercaptoalkylguanidines, mercaptoethylguanidine (MEG) and guanidinoethyldisulfide (GED), which are iNOS inhibitors and reactive nitrogen scavenging compounds, on the development of experimental gingivitis in beagle dogs.

METHODS

Fifteen female, 1-year-old beagles first completed a 2-week dose-escalation experiment during which a maximum tolerated dose was determined for MEG and GED gels. Thereafter, all animals were brought to optimal gingival health by mechanical scaling, followed by rigorous daily toothbrushing over a 4-week washout period. Experimental gingivitis was then induced, with cessation of plaque control and institution of a soft diet over 8 weeks. Beagles randomly received 0.3% MEG, 0.3% GED, or placebo (vehicle) gels, topically applied twice daily to premolar teeth. Gingival inflammation, bleeding tendency, and supragingival plaque were clinically measured at baseline and at 2, 3, 4, 6, and 8 weeks. Comparisons among groups and between group pairs (active versus placebo) were made using Kruskal-Wallis tests.

RESULTS

From baseline to day 7, all groups expressed similar indices. Thereafter, significant and time-dependent increases in the plaque index (PI), gingival index (GI), and percentage of bleeding on probing (%BOP) were observed in placebo-treated beagles. Mean GI scores for beagles treated with GED or MEG gels remained at or below baseline levels for the entire treatment period. At weeks 2, 3, 4, and 8, GI scores were significantly lower for MEG and GED groups compared to the placebo group (P<0.05). In addition, MEG and GED gels significantly reduced gingival bleeding responses by 8 weeks (P<0.05). Although placebo-treated beagles demonstrated %BOP scores of 43% at week 8, GED- and MEG-treated beagles exhibited %BOP scores of 21% and 26%, respectively. Since no statistical difference among PI scores was noted for any of the time points, neither mercaptoalkylguanidine appeared to affect supragingival plaque levels.

CONCLUSION

The data from this preclinical study indicate that mercaptoalkylguanidines, topically administered, may significantly reduce experimental gingivitis in the beagle dog.

Effects of Tempol, a membrane-permeable radical scavenger, in a rodent model periodontitis

BACKGROUND

Recent studies have demonstrated that Tempol (4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl), a cell membrane-permeable radical scavenger, exerts protective effects in various models of inflammation and shock. Reactive oxygen species (ROS) plays a pivotal role in the induction of genes involved in physiological processes as well as in the response to inflammation.

AIM

We have investigated the effect of Tempol in a rat model of periodontitis.

MATERIALS AND METHODS

Periodontitis was induced in rats by placing a 2/0 braided silk ligature around the lower left first molar. At day 8, the gingivomucosal tissue encircling the mandibular first molar was removed for evaluation of neutrophils infiltration, tissue permeability, nitrotyrosine formation, poly-(ADP-ribose) polymerase (PARP) activation, radiography and histology.

RESULTS AND CONCLUSIONS

Legation significantly induced an increased neutrophil infiltration and a positive staining for nitrotyrosine formation and PARP activation. Ligation significantly increased Evans blue extravasation in gingivomucosal tissue and alveolar bone erosion as evaluated by radiography analysis. Intraperitonial injection of Tempol (10 mg/kg daily for 8 days) significantly decreased all of the parameters of inflammation as described above. This suggests that antioxidant therapies, which interfere with ROS, may be of benefit in the treatment of periodontitis.

Nitric oxide synthase inhibition prevents alveolar bone resorption in experimental periodontitis in rats

BACKGROUND

Periodontitis is the most frequent cause of tooth loss in adults. Nitric oxide (NO) has been linked to bone resorption mechanisms during inflammation processes. The aim of this study was to investigate the effect of NOS (NO synthase) inhibitors in the alveolar bone loss in an experimental periodontitis disease (EPD) model.

METHODS

Wistar rats were subjected to a ligature placement around the second upper left molars and were sacrificed at 11 days. Alveolar bone loss was evaluated by the sum of distances between the cusp tips and the alveolar bone along the axis of each molar root, subtracting from the contralateral side. Histopathological analysis was based on cell influx, alveolar bone, and cementum integrity. Leukogram was performed at 6 hours and 1, 7, and 11 days after the EPD induction. Groups were treated with the NOS inhibitors, aminoguanidine (AG) (2.5 to 10 mg/kg/d), or L-arginine methyl ester (L-NAME, 5 to 20 mg/kg/d) intraperitoneally (i.p.), 1 hour before the EPD induction and daily for 11 days. Controls received only saline (EPD group). As controls for L-NAME specificity, groups were co-treated with either L-arginine (150 to 600 mg/kg/d) or D-arginine (600 mg/kg/d) and L-NAME (20 mg/kg/d). Different groups were used for morphometric and histopathological analysis.

RESULTS

Both L-NAME and AG significantly and dose-dependently inhibited the alveolar bone loss as compared to EPD group. L-NAME (20 mg/kg/d) reduced the alveolar bone loss by 50%, whereas AG (5 mg/kg/d) reduced it by 47% compared to EPD. This result was coupled to a significant reduction of cell influx to the periodontium, as well as to the preservation of alveolar bone and cementum, seen at histopathology, for both compounds. The co-administration of L-arginine, but not of D-arginine reversed L-NAME effects.

CONCLUSION

These data provide evidence that NOS inhibitors prevent inflammatory bone resorption in experimental periodontitis.

Reduced development of experimental periodontitis by treatment with M40403, a superoxide dismutase mimetic

M40403, [manganese(II)dichloro[(4R,9R,14R,19R)-3,10,13,20,26 pentaazatetracyclo[20.3.1.0.(4,9)0(14,19)]hexacosa-1(26),-22(23),24-triene]], is a low-molecular-weight, synthetic, manganese-containing superoxide dismutase mimetic that removes superoxide anions without interfering with other reactive species known to be involved in inflammatory responses (e.g., nitric oxide, NO and peroxynitrite, ONOO-). As such, M40403 represents an important pharmacological tool to dissect the roles of superoxide anion in acute and chronic inflammation. For this purpose, the pharmacological profile of M40403 was evaluated in a rat model of periodontitis. Periodontitis was induced in rats by placing a 2/0 braided silk around the lower left first molar. On day 8 the gingivomucosal tissue encircling the first molar was removed for biochemical and histological analysis. Ligation significantly increased inducible nitric oxide synthase activity and expression, and gingival tissue revealed increased neutrophil infiltration, lipid peroxidation and positive staining for nitrotyrosine formation and poly (ADP-ribose) polymerase activation. Ligation significantly increased Evans blue extravasation in gingivomucosal tissue and alveolar bone destruction. Intraperitoneal injection of M40403 (10 mg/kg daily for 8 days) significantly decreased all of the above-described markers of inflammation. This suggests compounds that inhibit the generation of superoxide anion, such as M40403 may be potentially useful for the treatment of periodontitis.