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

The adiponectin receptor agonist AdipoAI attenuates periodontitis in diabetic rats by inhibiting gingival fibroblast-induced macrophage migration

BACKGROUND AND PURPOSE

Low-grade inflammation, a common feature of both diabetes and periodontitis, partly accounts for the complexity and refractoriness of diabetes-associated periodontitis. Adiponectin (APN), the most abundant adipokine in human blood, has been widely reported to have anti-inflammatory functions. Herein, we investigated the ability of an APN receptor agonist, AdipoAI, to alleviate diabetes-associated periodontitis. Furthermore, we revealed the possible mechanism underlying its anti-inflammatory effects.

EXPERIMENTAL APPROACH

The maxillary first molar of Zucker diabetic fatty (ZDF) rats was ligated to construct a diabetes-associated periodontitis model, and rats were administered AdipoAI by gavage. We examined diabetes-related indexes, pathological changes in insulin target organs, alveolar bone resorption and systemic and local inflammation. In vitro, transwell assays were used to evaluate monocyte/macrophage migration induced by human gingival fibroblasts (hGFs) with/without AdipoAI treatment. Additionally, we examined chemokine expression levels in hGFs and hGF-induced monocyte/macrophage migration upon siRNA knockdown of Adiponectin receptor expression. Expression of Adipo1/Adipo2 receptors and inflammation-related signalling pathways were examined by IHC and WB, followed by confirmation with an NF-κB P65 inhibitor (BAY 11-7082).

KEY RESULTS

AdipoAI lowered fasting blood glucose and serum insulin in ZDF rats and alleviated inflammation in insulin target tissues. Locally, AdipoAI reduced alveolar bone absorption and gingival inflammation. Mechanistically, AdipoAI inhibited hGF-induced monocyte/macrophage migration by reducing CCL2 secretion. In hGFs, AdipoAI attenuated LPS-induced activation of NF-κB P65 and CCL2 expression, which was dependent on the Adipo receptor 1.

CONCLUSION AND IMPLICATIONS

AdipoAI, with its ability to alleviate inflammatory damage in tissues, is a candidate for diabetes-associated periodontitis treatment.

Analysis of Endothelin-1 Concentrations in Individuals with Periodontitis

Endothelin 1 (ET-1) has been shown to have a key role in homeostasis and function of endothelium and maybe fundamental in the relationship between coronary heart disease (CHD) and periodontitis. In this trial, we assessed the influence on serum and salivary ET-1 levels of gingival health, CHD, periodontitis, or a combination of periodontitis-CHD. Clinical and periodontal parameters, were collected from periodontitis patients (n = 34), CHD patients (n = 34), periodontitis + CHD patients (n = 34), and from healthy patients (n = 34) together with saliva and serum samples. The median concentrations of salivary and serum ET-1 were significantly higher in the CHD patients [serum: 1.4(1.1-1.6) pg/ml; saliva 1.2 (0.9-1.6) µmol/g, p < 0.01] and in the periodontitis + CHD patients [serum: 1.7 (1.2-21.8) pg/ml; salivary 1.4(1-1.6) µmol/g, p < 0.001] respect to periodontitis and control patients. Through a univariate regression analysis, c-reactive protein (CRP) and CHD (both p < 0.001) and periodontitis (p = 0.029) were statistically correlated with ET-1 in serum. The multivariate regression analysis demonstrated that only CRP was the statistically predictor of ET-1 in serum(p < 0.001). The multivariate regression analysis in saliva demonstrated that, regarding ET-1 levels the only predictor were CRP (p < 0.001) and total cholesterol (p = 0.042). The present study evidenced that subjects with CHD and periodontitis plus CHD had higher serum and salivary levels of ET-1 compared to subjects with periodontitis and healthy controls. Moreover, only CRP remained a major predictor of increased ET-1 concentrations in both serum and saliva.

Physical Exercise Improves Glycemic and Inflammatory Profile and Attenuates Progression of Periodontitis in Diabetic Rats (HFD/STZ)

The authors aimed to evaluate the effects of physical exercise on the metabolism and progression of periodontal disease (PD), induced by ligature in diabetic rats induced by high fat diet and streptozotocin (HFD/STZ). Diabetes Mellitus (DM) was induced by four weeks of a hyperlipidic diet associated with a single low-dose of streptozotocin (35 mg/kg/animal). The exercise groups swam for 60 min/day for eight weeks (five times/week). In the last two weeks of exercise, a ligature was placed around the right and left mandibular first molars. The authors determined alveolar bone loss by morphometry. Blood biochemical profile and serum levels of IL-10 and TNF-α were evaluated by colorimetric and enzyme-linked immunosorbent assays (ELISA), respectively. The diabetic animals subjected to exercise showed decreased alveolar bone loss, lower glycemia, triacylglycerols and glycosylated hemoglobin levels than the controls. Total cholesterol and its fractions (High density lipoprotein—HDL-c, Low density lipoprotein—LDL-c and Very low density lipoprotein—VLDL-c) remained similar among the groups. Animals with PD showed higher levels of TNF-α and lower levels of IL-10, when compared to animals without PD. In diabetic animals with PD, physical exercise decreased TNF-α levels and increased IL-10 levels as well as the IL10/TNF-α ratio. In conclusion, eight weeks of physical exercise improved glycemic control and systemic inflammatory profile, and attenuated alveolar bone loss in rats with DM and PD.

[Beneficial effect of periodontal therapy on insulin resistance and lipid metabolism in obese rats with periodontitis]

OBJECTIVE

To investigate the effect of periodontal therapy in controlling periodontitis and on insulin resistance and lipid metabolism in obese rats with periodontitis.

METHODS

Sprague-Dawley rats were randomized into normal group (group C), obese group (group O), periodontitis combined with obesity group (group P) and periodontal treatment group (group T). The obese rats in groups P and T were subjected to ligation of the maxillary second molar with silk thread to induce experimental periodontitis, and the rats in group T received periodontal therapy after the ligation. All the rats were sacrificed at the age of 24 weeks for measurement of blood lipids, insulin and blood glucose levels, and insulin resistance index (HOMA-IR) was calculated. The expressions of insulin receptor substrate-1 (IRS-1) and IRS-2 in the liver tissues were detected using real-time quantitative polymerase chain reaction (RT-PCR).

RESULTS

Compared with the obese rats in group O, the rats in group P showed significantly higher HOMA-IR and LDL-C and lower expressions of IRS-1 and IRS-2 mRNA expression and HDL-C level (P<0.05). Compared with those in group P, the mRNA expressions of IRS-1 and IRS-2 and HDL-C level were significantly increased and LDL-C level, TC level and HOMA-IR were all decreased in group T (P<0.05), but the level of TG was comparable between the two groups. Pathological examination revealed lessened inflammatory cell infiltration and tissue destruction in the upper jaw of the rats in group T; the rats in group P presented with the most obvious upper jaw destruction and steatosis and inflammatory cell infiltration in the liver.

CONCLUSION

Periodontal inflammation can downregulate the expression of IRS-1 and IRS-2 and increase insulin resistance and dyslipidemia in obese rats. Periodontal therapy produces a beneficial effect in improving insulin resistance and reducing dyslipidemia in obese rats.

Comparison of Serum Levels of Endothelin-1 in Chronic Periodontitis Patients Before and After Treatment

INTRODUCTION

Endothelin-1 (ET-1) is a potent vasoconstrictive peptide with multi functional activity in various systemic diseases. Previous studies indicate the detection of ET-1 in gingival tissues and gingival crevicular fluid.

AIM

The aim of this study was to estimate the serum ET-1 levels in clinically healthy subjects and subjects with chronic periodontitis, before and after treatment, and correlate it with the clinical parameters.

MATERIALS AND METHODS

A total of 44 patients were included in the study. Group I comprised of 20 subjects with clinically healthy periodontium. Group II comprised of 24 subjects with chronic periodontitis. Group III comprised of same Group II subjects following periodontal management. Serum samples were collected from the subjects and an Enzyme Linked Immunosorbent Assay (ELISA) was done to estimate the ET-1 levels. The ET-1 levels were then correlated among the three groups with the clinical parameters namely, Plaque Index (PI), Sulcus Bleeding Index (SBI), probing pocket depth, clinical attachment loss and Periodontally Inflamed Surface Area (PISA). The independent t-test and paired t-test were used for comparison of clinical parameters and Pearson's correlation coefficient test was used for correlating the ET-1 levels.

RESULTS

ET-1 levels in chronic periodontitis subjects were significantly higher compared to healthy subjects (p<0.001). However, the clinical parameters did not statistically correlate with the ET-1 levels. There was a significant decrease in ET-1 levels following treatment (p<0.001).

CONCLUSION

Serum ET-1 is increased in chronic periodontitis and reduces after periodontal therapy. Further studies are required to establish ET-1 as a biomarker for periodontal disease.

Co-culture of bone marrow stem cells and macrophages indicates intermediate mechanism between local inflammation and innate immune system in diabetic periodontitis

Diabetic periodontitis (DP), which has been shown to cause alveolar bone loss, is among the most common complications associated with diabetes. The precise mechanisms underlying alveolar bone loss in patients with DP remain unclear. Therefore, the present study established a co-culture system of bone marrow stem cells (BMSCs) and macrophages, in order to investigate the potential mechanisms underlying DP-associated alveolar bone loss in vitro. In addition, Porphyromonas gingivalis (PG) periodontal infection and high glucose levels were used to induce DP in mice. The present study evaluated the protein expression levels of various chemokines and the migration of BMSCs and macrophages. The protein expression levels of extracellular signal-regulated kinase 1 and 2, c-Jun N-terminal kinase and p38 mitogen-activated protein kinase (MAPK) were significantly increased in the BMSCs exposed to high glucose and PG, which may have been due to the activation of MAPK. In addition, DP induction in mice was associated with the release of chemokine (C-C motif) ligand 2 (CCL2) from BMSCs and the secretion of chemokine (C-C Motif) receptor 2 (CCR2) and tumor necrosis factor-α from macrophages, which was associated in turn with enhanced adhesion and chemotaxis of macrophages. The results of the present study suggested that DP led to the upregulation of CCL2 in the periodontal tissues and enhanced macrophage infiltration via the CCL2/CCR2 axis, which in turn promoted alveolar bone loss.

The enduring importance of animal models in understanding periodontal disease

Whereas no single animal model can reproduce the complexity of periodontitis, different aspects of the disease can be addressed by distinct models. Despite their limitations, animal models are essential for testing the biological significance of in vitro findings and for establishing cause-and-effect relationships relevant to clinical observations, which are typically correlative. We provide evidence that animal-based studies have generated a durable framework for dissecting the mechanistic basis of periodontitis. These studies have solidified the etiologic role of bacteria in initiating the inflammatory response that leads to periodontal bone loss and have identified key mediators (IL-1, TNF, prostaglandins, complement, RANKL) that induce inflammatory breakdown. Moreover, animal studies suggest that dysbiosis, rather than individual bacterial species, are important in initiating periodontal bone loss and have introduced the concept that organisms previously considered commensals can play important roles as accessory pathogens or pathobionts. These studies have also provided insight as to how systemic conditions, such as diabetes or leukocyte adhesion deficiency, contribute to tissue destruction. In addition, animal studies have identified and been useful in testing therapeutic targets.

Vaspin: a new adipokine correlating the levels of crevicular fluid and tear fluid in periodontitis and obesity

AIM

In the present study, we investigated the levels of vaspin in gingival crevicular fluid (GCF) and tear fluid in obese patients with chronic periodontitis (CP), and sought to find an association, if any.

METHODS

Forty patients (20 males and 20 females) with moderate-severe CP were selected based on their clinical parameters of gingival index, probing depth (PD), clinical attachment level (CAL), bleeding on probing, body mass index (BMI), and waist circumference, and divided into four groups (n = 10/group): group 1 (healthy non-obese), group 2 (healthy obese), group 3 (non-obese with CP), and group 4 (obese with CP). GCF and tear fluid vaspin levels were estimated by enzyme-linked immunosorbent assay.

RESULTS

The mean vaspin concentration both in GCF and tear fluid was greater for group 4 (1.84 ± 0.03) and (1.98 ± 0.08), followed by groups 3 (1.35 ± 0.03 and 1.50 ± 0.06), 2 (0.95 ± 0.26 and 1.27 ± 0.51), and then 1 (0.65 ± 0.02 and 0.75 ± 0.02), respectively. Mean vaspin levels correlated with BMI, CAL, and PD. The association between GCF and tear fluid vaspin concentration was also statistically significant (P < 0.001).

CONCLUSION

Vaspin can be a novel biomarker connecting inflammatory marker for the systemic inflammatory response in obesity and CP.

Occlusal disharmony accelerates the initiation of atherosclerosis in apoE knockout rats

Background

Psychosocial stress is one of the risk factors for atherosclerosis. As occlusal disharmony induces psychological stress, we hypothesized that psychological stress by occlusal disharmony accelerates atherosclerosis. The aim of this study was to investigate the effects of occlusal disharmony on the initiation of atherosclerosis in apolipoprotein E (apoE) knockout rats.

Methods

Fourteen male apoE-knockout rats (age; 8 weeks) (Sprague–Dawley strain background) were divided into two groups of seven rats: the occlusal disharmony group and the no treatment (control) group. In the occlusal disharmony group, the maxillary molar cusps were cut off for the 8-week experimental period.

Results

In the occlusal disharmony group, the percentages of the area of total aortic lumen occupied by plaques and lipid were significantly higher than those in the control group (p < 0.05, t-test). The occlusal disharmony group also showed significantly higher serum levels of very low-density lipoprotein-cholesterol (VLDL) and low-density lipoprotein-cholesterol (LDL), plasma levels of corticosterone (1.9, 1.3 and 1.3 times, respectively), higher aortic protein expression levels of vascular cell adhesion molecule-1 (VCAM1) and intercellular adhesion molecule-1 (ICAM1) (1.5 and 1.4 times, respectively), and higher aortic gene expression of levels of VCAM1 and Toll-like receptor 4 (TLR4) (1.9 and 4.3 times, respectively), as compared to the control group (p < 0.05). However, there were no significant differences in serum levels of oxidized LDL, reactive oxygen metabolites and C-reactive protein between the two groups.

Conclusion

In apoE knockout rats, occlusal disharmony may induce VCAM1, ICAM1 and TLR4 expression and accelerate the initiation of atherosclerosis.

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.

25-Hydroxyvitamin D3 attenuates experimental periodontitis through downregulation of TLR4 and JAK1/STAT3 signaling in diabetic mice

Vitamin D has been known to be closely associated with diabetes and periodontitis while the underlying mechanism has yet to be clarified. The present study aimed to discover the effect of 25-hydroxyvitamin D3 (25-OHD3) on glycemic control and periodontal health in mice with periodontitis superimposed on experimental diabetes (known as diabetic periodontitis). We showed that 25-OHD3 intraperitoneal injection attenuated diabetic periodontitis by reducing serum fasting blood glucose, glycosylated hemoglobin and TNF-α levels, which led to decreased alveolar bone loss. Immunohistochemical staining and western blot analysis of gingival epithelia revealed that vitamin D receptor (VDR) expression was enhanced upon 25-OHD3 treatment, while toll-like receptor 4 (TLR4) expression was reduced. The expressions of Janus family kinase (JAK) 1 and signal transducer and activator of transcription (STAT) 3 as well as their phosphorylation were inhibited in gingival epithelia of diabetic periodontitis mice, whereas the expression and phosphorylation of STAT1 remained unchanged. These results suggest that 25-OHD3 could improve diabetic periodontitis through downregulation of TLR4 and JAK1/STAT3 signaling in the gingival epithelium. Our study extends the previous findings on the regulation of diabetes with periodontitis, and may also provide a potential therapy for the patients with this disease.

Experimental periodontitis promotes transient vascular inflammation and endothelial dysfunction

OBJECTIVES

This study aimed to evaluate the systemic inflammatory response and cardiovascular changes induced by experimental periodontitis in rats.

DESIGN

Experimental periodontitis was induced by placing a cotton ligature around the cervix of both sides of mandibular first molars and maxillary second molars in each male rat. Sham-operated rats had the ligature removed immediately after the procedure. Seven, 14 or 28 days after procedure, the effects of acetylcholine, sodium nitroprusside and phenylephrine were evaluated on blood pressure, aortic rings and isolated and perfused mesenteric bed. The blood was obtained for plasma Interleukin-6 (IL-6), C-reactive protein (CRP) and lipid evaluation. The mesenteric vessels were obtained to evaluate superoxide production and nitric oxide synthase 3 (NOS-3) expression.

RESULTS

Ligature induced periodontitis reduced endothelium-dependent vasodilatation, a hallmark of endothelial dysfunction. This effect was associated with an increase in systemic inflammatory markers (IL-6 and CRP), worsens on lipid profile, increased vascular superoxide production and reduced NOS-3 expression. It is interesting to note that many of these effects were transitory.

CONCLUSION

Periodontitis induced a transient systemic and vascular inflammation which leads to endothelial dysfunction, an initial step for cardiovascular diseases. Moreover, the animal model of periodontitis used here may represent a valuable tool for studying the relationship between periodontitis and endothelial dysfunction.

Pathogenesis of antineutrophil cytoplasmic autoantibody-associated small-vessel vasculitis

Clinical, in vitro, and experimental animal observations indicate that antineutrophil cytoplasmic autoantibodies (ANCA) are pathogenic. The genesis of the ANCA autoimmune response is a multifactorial process that includes genetic predisposition, environmental adjuvant factors, an initiating antigen, and failure of T cell regulation. ANCA activate primed neutrophils (and monocytes) by binding to certain antigens expressed on the surface of neutrophils in specific inflammatory microenvironments. ANCA-activated neutrophils activate the alternative complement pathway, establishing an inflammatory amplification loop. The acute injury elicits an innate inflammatory response that recruits monocytes and T lymphocytes, which replace the neutrophils that have undergone karyorrhexis during acute inflammation. Extravascular granulomatous inflammation may be initiated by ANCA-induced activation of extravascular neutrophils, causing tissue necrosis and fibrin formation, which would elicit an influx of monocytes that transform into macrophages and multinucleated giant cells. Over time, the neutrophil-rich acute necrotizing lesions cause the accumulation of more lymphocytes, monocytes, and macrophages and produce typical granulomatous inflammation.

Periodontitis as a novel contributor of adipose tissue inflammation promotes insulin resistance in a rat model

BACKGROUND

Recent studies have indicated that the chronic low-grade inflammation induced by periodontitis is related to obesity and type 2 diabetes mellitus. The purpose of this study is to investigate the effects of periodontitis on obesity-related adipose tissue inflammation and subsequent systemic insulin resistance in a rat model.

METHODS

Thirty-two rats were divided into four groups of eight: 1) obese rats with periodontitis (combination group); 2) obese rats without periodontitis (obesity group); 3) normal rats with periodontitis (periodontitis group); and 4) normal rats without periodontitis (control group). Monosodium glutamate was used to induce obesity during the early postnatal period. Periodontitis was induced by ligatures for 8 weeks. Morphologic features of white adipose tissue (WAT) and islets were observed, and fasting plasma glucose and insulin concentrations and homeostasis model assessment for insulin (HOMA-IR) were measured at 5 months. Differences among groups were compared with the Fisher post hoc least significant difference test.

RESULTS

A slight increase of stromal vascular fractions (SVFs) and macrophage infiltration in the WAT of the periodontitis group was observed. Significant proliferation of SVFs and macrophage infiltration were induced in the combination group. HOMA-IR scores in the combination and periodontitis groups were higher than in the obesity and control groups, respectively. The disturbance of islet architecture was consistent with a high HOMA-IR score in the combination group.

CONCLUSIONS

Periodontitis induced initial stages of WAT inflammation and acted as a contributing factor to exacerbate proinflammatory phenotype of WAT and promote the development of insulin resistance in the obese rat model.

Periodontitis and insulin resistance: casual or causal relationship?

Insulin resistance (IR) is now considered as a chronic and low level inflammatory condition. It is closely related to altered glucose tolerance, hypertriglyceridemia, abdominal obesity, and coronary heart disease. IR is accompanied by the increase in the levels of inflammatory cytokines like interleukin-1 and 6, tumor necrosis factor-α. These inflammatory cytokines also play a crucial part in pathogenesis and progression of insulin resistance. Periodontitis is the commonest of oral diseases, affecting tooth investing tissues. Pro-inflammatory cytokines are released in the disease process of periodontitis. Periodontitis can be attributed with exacerbation of IR. Data in the literature supports a "two way relationship" between diabetes and periodontitis. Periodontitis is asymptomatic in the initial stages of disease process and it often escapes diagnosis. This review presents the blurred nexus between periodontitis and IR, underlining the pathophysiology of the insidious link. The knowledge of the association between periodontitis and IR can be valuable in planning effectual treatment modalities for subjects with altered glucose homeostasis and diabetics. Presently, the studies supporting this association are miniscule. Further studies are mandatory to substantiate the role of periodontitis in the deterioration of IR.

Occlusal disharmony increases amyloid-β in the rat hippocampus

Amyloid-β plays a causative role in Alzheimer's disease. Occlusal disharmony causes chronic psychological stress, and psychological stress increases amyloid-β accumulation. The purpose of the present study was to investigate whether occlusal disharmony-induced psychological stress affects the accumulation of amyloid-β and its related gene expressions in the rat hippocampus. Eight-week-old male Wistar rats (n = 18) were divided into three groups of six rats each: (1) a control group that received no treatment for 8 weeks; (2) an occlusal disharmony group that underwent cutoff maxillary molar cusps for 8 weeks; and (3) a recovered group that underwent cutoff maxillary molar cusps for 4 weeks followed by recovery for 4 weeks. Occlusal disharmony increased plasma corticosterone levels in a time-dependent manner. Levels of amyloid-β 40 and 42, glucocorticoid receptor (Gr) protein, and cleaved caspase 3 (Casp3) as well as gene expressions of amyloid precursor protein, beta-secretase, Casp3, and Gr in the hippocampus in the occlusal disharmony group were significantly higher than those in the control group (P < 0.016). These findings were significantly improved by recovery of occlusion (P < 0.016). These results indicate that psychological stress induced by occlusal disharmony reversibly induces amyloid-β 40 and 42 in the rat hippocampus through the glucocorticoid signal.