Role of poly(ADP-ribose) polymerase activation in the pathogenesis of periodontitis in diabetes.

AIM: The aetiology of progressive periodontitis in diabetes has not yet been elucidated. We previously demonstrated that nitrosative stress is increased in diabetic rats with periodontitis. Nitrosative stress induces poly(ADP-ribose) polymerase (PARP) activation. Here, we demonstrated the involvement of PARP activation in diabetic periodontitis and detailed the therapeutic effects of PARP inhibitor. MATERIALS AND METHODS: Experimental periodontitis was induced by placing a nylon thread ligature. Half of the normal and diabetic rats received the PARP inhibitor, 1,5-isoquinolinediol, for 2 weeks. Gingival PARP activation was detected by immunostaining for poly(ADP-ribose). Periodontitis was evaluated by gingival inflammatory cell infiltration, inflammatory gene expressions and micro-CT analyses. RESULTS: Although both periodontitis and the presence of diabetes increased PARP activation in the gingiva, diabetic rats with periodontitis had the highest activation of PARP. Diabetic rats with periodontitis also showed significant increases in monocyte/macrophage invasion into the gingiva, inflammatory gene expressions, nitrotyrosine-positive cells in the gingiva and alveolar bone loss, all of which were suppressed by treatment with the PARP inhibitor. CONCLUSIONS: These results indicate the involvement of PARP activation in the pathogenesis and aggravation of periodontal disease in diabetes and suggest the therapeutic potential of PARP inhibition for treating periodontal disease, especially in patients with diabetes.

Glucagon-Like Peptide-1 Receptor Agonist Liraglutide Ameliorates the Development of Periodontitis.

Periodontitis is one of the diabetic complications due to its high morbidity and severity in patients with diabetes. The prevention of periodontitis is especially important in diabetic patients because the relationship between diabetes and periodontitis is bidirectional. Here, we evaluated the impacts of glucagon-like peptide-1 (GLP-1) receptor agonist liraglutide on the amelioration of periodontitis. Five-wk-old Male Sprague-Dawley (SD) rats (n = 30) were divided into 3 groups: normal, periodontitis, and periodontitis with liraglutide treatment groups. Periodontitis was induced by ligature around the maxillary second molar in SD rats. Half of the rats were administered liraglutide for 2 weeks. Periodontitis was evaluated by histological staining, gene expressions of inflammatory cytokines in gingiva, and microcomputed tomography. Periodontitis increased inflammatory cell infiltration, macrophage accumulation, and gene expressions of tumor necrosis factor-α and inducible nitric oxide synthase in the gingiva, all of which were ameliorated by liraglutide. Liraglutide decreased M1 macrophages but did not affect M2 macrophages in periodontitis. Moreover, ligature-induced alveolar bone resorption was ameliorated by liraglutide. Liraglutide treatment also reduced osteoclasts on the alveolar bone surface. These results highlight the beyond glucose-lowering effects of liraglutide on the treatment of periodontitis.

Therapeutic potential for insulin on type 1 diabetes-associated periodontitis: Analysis of experimental periodontitis in streptozotocin-induced diabetic rats.

AIMS/INTRODUCTION: The association between diabetes and periodontal disease is considered to be bidirectional. However, there is still controversy surrounding the relationship between periodontal disease and type 1 diabetes. We investigated whether insulin improves periodontitis without any local treatments for periodontitis under type 1 diabetes conditions using the ligature-induced experimental periodontitis model. MATERIALS AND METHODS: Type 1 diabetic rats were induced by streptozotocin injection. Experimental periodontitis was induced by ligature in normal and diabetic rats. Half of the diabetic rats were treated with insulin. Two weeks after the ligature, periodontitis was evaluated. RESULTS: Insulin treatment significantly improved inflammatory cell infiltration and inflammatory cytokine gene expression, leading to suppression of alveolar bone loss, in the periodontitis of diabetic rats. Insulin also suppressed the periodontitis-increased nitric oxide synthase-positive cells in periodontal tissue of the diabetic rats. Even without induction of periodontitis, diabetic rats showed decreased gingival blood flow and an increased number of nitric oxide synthase-positive cells in the gingiva and alveolar bone loss compared with normal rats, all of which were ameliorated by insulin treatment. We further confirmed that insulin directly suppressed lipopolysaccharide-induced inflammatory cytokine expressions in THP-1 cells. CONCLUSIONS: There were abnormalities of periodontal tissue even without the induction of periodontitis in streptozotocin-induced diabetic rats. Insulin treatment significantly ameliorated periodontitis without local periodontitis treatment in diabetic rats. These data suggest the therapeutic impacts of insulin on periodontitis in type 1 diabetes.

Anti-inflammatory role of glucose-dependent insulinotropic polypeptide in periodontitis.

AIMS/INTRODUCTION: The involvement of glucose-dependent insulinotropic polypeptide (GIP) on inflammation was explored in atherosclerosis and adipose tissue. Periodontal disease is a chronic inflammatory disease, and is considered one of the diabetic complications. In the present study, to examine the effect of GIP on periodontitis, we induced experimental periodontitis in glucose-dependent insulinotropic polypeptide receptor-knockout mice (GIPRKO). We also investigated the anti-inflammatory effect of GIP in a culture system. MATERIALS AND METHODS: Experimental periodontitis was induced by ligature wire in GIPRKO and C57BL/C mice. Two weeks after the ligature, immunohistological evaluation and inflammatory messenger ribonucleic acid expression in the gingiva was examined. To elucidate the role of GIP in inflammation, the effects of GIP on lipopolysaccharide-induced gene expressions in THP-1 cells were evaluated. RESULTS: Periodontitis increased inflammatory cell infiltration, macrophage accumulation and tumor necrosis factor-α and nitric oxide synthase gene expressions in the gingiva. Periodontitis in GIPRKO showed a marked increase of inflammatory cells in the gingivomucosal tissue. Mac-1-positive macrophages and the inflammatory gene expressions were significantly increased in periodontitis in GIPRKO compared with C57BL/C mice periodontitis. Immunohistochemical staining confirmed that GIP receptors were expressed in residual and infiltrated Mac-1-positive macrophages. The in vitro study showed that GIP suppressed lipopolysaccharide-induced tumor necrosis factor-α and nitric oxide synthase gene expression in a dose-dependent manner. Furthermore, the inhibitory effect of GIP on lipopolysaccharide-induced inflammatory gene expressions was at least partially through cyclic adenosine monophosphate/protein kinase A pathway. CONCLUSIONS: These results suggest the beneficial effects of GIP on periodontal disease. In diabetic patients, GIP is expected to have a direct anti-inflammatory effect on periodontitis in addition to its glucose-lowering effect.

Periodontitis-activated monocytes/macrophages cause aortic inflammation.

A relationship between periodontal disease and atherosclerosis has been suggested by epidemiological studies. Ligature-induced experimental periodontitis is an adequate model for clinical periodontitis, which starts from plaque accumulation, followed by inflammation in the periodontal tissue. Here we have demonstrated using a ligature-induced periodontitis model that periodontitis activates monocytes/macrophages, which subsequently circulate in the blood and adhere to vascular endothelial cells without altering the serum TNF-α concentration. Adherent monocytes/macrophages induced NF-κB activation and VCAM-1 expression in the endothelium and increased the expression of the TNF-α signaling cascade in the aorta. Peripheral blood-derived mononuclear cells from rats with experimental periodontitis showed enhanced adhesion and increased NF-κB/VCAM-1 in cultured vascular endothelial cells. Our results suggest that periodontitis triggers the initial pathogenesis of atherosclerosis, inflammation of the vasculature, through activating monocytes/macrophages.