Hypothalamic-pituitary-adrenal axis activation by experimental periodontal disease in rats

Mental health and periodontal and peri-implant diseases

Mental health disorders, particularly depression and anxiety, affect a significant number of the global population. Several pathophysiological pathways for these disorders have been identified, including the hypothalamic-pituitary-adrenal axis, autonomic nervous system, and the immune system. In addition, life events, environmental factors, and lifestyle affect the onset, progression, and recurrence of mental health disorders. These may all overlap with periodontal and/or peri-implant disease. Mental health disorders are associated with more severe periodontal disease and, in some cases, poorer healing outcomes to nonsurgical periodontal therapy. They can result in behavior modification, such as poor oral hygiene practices, tobacco smoking, and alcohol abuse, which are also risk factors for periodontal disease and, therefore, may have a contributory effect. Stress has immunomodulatory effects regulating immune cell numbers and function, as well as proinflammatory cytokine production. Stress markers such as cortisol and catecholamines may modulate periodontal bacterial growth and the expression of virulence factors. Stress and some mental health disorders are accompanied by a low-grade chronic inflammation that may be involved in their relationship with periodontal disease and vice versa. Although the gut microbiome interacting with the central nervous system (gut-brain axis) is thought to play a significant role in mental illness, less is understood about the role of the oral microbiome. The evidence for mental health disorders on implant outcomes is lacking, but may mainly be through behaviourial changes. Through lack of compliance withoral hygiene and maintenance visits, peri-implant health can be affected. Increased smoking and risk of periodontal disease may also affect implant outcomes. Selective serotonin reuptake inhibitors have been linked with higher implant failure. They have an anabolic effect on bone, reducing turnover, which could account for the increased loss.

Influence of vitamin E and carcass feeding supplementation on fecal glucocorticoid and androgen metabolites in male black-footed ferrets (Mustela nigripes)

In recent years, the ex situ population of the endangered black-footed ferret (Mustela nigripes; ferret) has experienced a decline in normal sperm morphology (from 50% to 20%), which may be linked to inbreeding depression and/or a dietary change. We examined the effects of adding carcass and vitamin E to the diet on stress and reproductive biomarkers in male ferrets (n = 42 males including 16 juveniles and 26 adults) housed at the U.S. Fish and Wildlife National Black-footed Ferret Conservation Center (Carr, CO, USA). Fecal samples (3x/week) were collected from November and December (pre-breeding season, no diet change), February through May (breeding season, diet change) and June (post-breeding season, diet change) and analyzed for fecal glucocorticoid metabolites (FGM) via a corticosterone enzyme immunoassay (EIA). A subset of samples from adult males (n = 15) were analyzed for fecal androgen metabolites (FAM) via a testosterone EIA. We first used a linear mixed effects model to identify the important fixed effects among meat treatment, vitamin E treatment, age class (juvenile or adult), and all possible interactions on each hormone. We then examined the important factor’s effects across seasons using the non-parametric Friedman test. We found that age did not influence (p = 0.33) FGMs; however there was a significant effect of meat treatment on FGM (p = 0.04) and an effect of vitamin E on FAMs (p<0.10). When fed carcass, FGMs declined (p<0.001) from pre- to the during the breeding season time period, but was similar (p>0.05) between during and post-breeding season periods. Males that were not fed carcass had higher (p<0.05) FGMs during the breeding season compared to pre- and post-breeding season and FGMs were lower (p<0.05) in the post-breeding season compared to pre-breeding season. Males fed with carcass had lower (p<0.001) FGM than males that were not fed carcass during both the pre-breeding and the breeding season but not during the post-breeding season (p>0.05). Males supplemented with vitamin E had higher (p<0.001) FAM than non-supplemented males during the breeding season only. For both groups, FAM was highest (p<0.05) during the breeding season. In conclusion, adding carcass to the diet can reduce glucocorticoid production and adding vitamin E can increase testosterone during the breeding season, which may influence reproductive success.

Diet-induced Generalized Periodontitis in Lewis Rats

Periodontitis is an important public health concern worldwide. Because rodents from the genus Rattus are resistant to spontaneous periodontitis, experimental periodontitis must be initiated by mechanical procedures and interventions. Due to their exacerbated Th1 response and imbalanced Th17 regulatory T-cell responses, Lewis rats are highly susceptible to inducible inflammatory and autoimmune diseases. We hypothesized that feeding Lewis rats a diet high in sucrose and casein (HSC) would alter the oral microenvironment and induce inflammation and the development of periodontitis lesions without mechanical intervention. A baseline group (BSL, n = 8) was euthanized at age 6 wk. Beginning at 6 wk of age, 2 groups of Lewis rats were fed standard (STD, n = 12) or HSC (n = 20) chow and euthanized at 29 wk of age. We evaluated the degree of periodontitis through histology and μCT of maxillae and mandibles. The HSC-induced inflammatory response of periodontal tissues was assessed by using immunohistochemistry. Gene expression analysis of inflammatory cytokines associated with Th1 and Th17 responses, innate immunity cytokines, and tissue damage in response to bacteria were assessed also. The potential systemic effects of HSC diet were evaluated by assessing body composition and bone densitometry endpoints; serum leptin and insulin concentrations; and gene expression of inflammatory cytokines in the liver. Placing Lewis rats on HSC diet for 24 wk induced a host Th1-immune response in periodontal tissues and mild to moderate, generalized periodontitis characterized by inflammatory cell infiltration (predominantly T cells and macrophages), osteoclast resorption of alveolar bone, and hyperplasia and migration of the gingival epithelium. HSC-fed Lewis rats developed periodontitis without mechanical intervention in the oral cavity and in the absence of any noteworthy metabolic abnormalities. Consequently, the rat model we described here may be a promising approach for modeling mild to moderate periodontitis that is similar in presentation to the human disease.

Stress, Cortisol, and Periodontitis in a Population Aged 50 Years and Over

Periodontitis and its relationship with psycho-neuro-immunological variables, such as psychological stress and cortisol, have been little explored. The objective of this study was to evaluate the extent and severity of chronic periodontitis and its association with the levels of salivary cortisol and the scores obtained with a stress questionnaire in a population aged 50 years and over. We studied 235 individuals in a cross-sectional study. They answered the Lipp’s Inventory of Stress Symptoms for Adults, were instructed to collect three saliva samples for cortisol analysis, and were examined for evaluation for periodontitis. Based on logistic regression, cortisol levels were positively associated with the following outcomes: means of clinical attachment level (CAL) > = 4 mm [OR = 5.1, 95%CI (1.2, 20.7)]; 30% of sites with CAL > = 5 mm [OR = 6.9, 95%CI (1.7, 27.1)]; and 26% of sites with probing depth > = 4 mm [OR = 10.7, 95%CI (1.9, 54.1)] after adjustment for confounding variables. The results suggest that cortisol levels were positively associated with the extent and severity of periodontitis.

The expression of 11β-hydroxysteroid dehydrogenase type 1 is increased in experimental periodontitis in rats

Background

The involvement of 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1), which converts inactive glucocorticoids into active glucocorticoids intracellularly, in metabolic diseases and chronic inflammatory diseases has been elucidated. We recently reported that an increase in 11β-HSD1 expression was associated with chronic periodontitis in humans irrespective of obesity. To further clarify the role of 11β-HSD1 in chronic periodontitis, the expression of 11β-HSD1 was investigated in experimental periodontitis model in rats.

Methods

Experimental periodontitis was induced by silk ligature of left maxillary second molars of 7-week-old male Wistar rats, and periodontal tissues were collected at day 3. The expression of 11β-HSD1, 11β-HSD2, and TNFα mRNA was examined using real time reverse transcription-polymerase chain reaction. The expression of TNFα was used as an indicator of inflammation. Thus, the rats in which the levels of TNFα mRNA were increased in the ligature-induced periodontitis compared with the control were analysed.

Results

The findings demonstrated that the expression of 11β-HSD1 mRNA was significantly increased in experimental periodontitis compared with the control. The increase in the levels of 11β-HSD1 mRNA in the ligature-induced periodontitis compared with the control was positively correlated with that of TNFα mRNA. On the other hand, the expression of 11β-HSD2 mRNA, which inactivates glucocorticoids, was slightly decreased in experimental periodontitis. Therefore, the ratio of 11β-HSD1 versus 11β-HSD2 mRNA was significantly higher in experimental periodontitis than in the control.

Conclusions

These results suggest that the increased expression of 11β-HSD1, which would result in the increased levels of intracellular glucocorticoids, may play a role in the pathophysiology of experimental periodontitis.

The increased ratio of 11β-hydroxysteroid dehydrogenase type 1 versus 11β-hydroxysteroid dehydrogenase type 2 in chronic periodontitis irrespective of obesity

11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1), which converts inactive cortisone to active cortisol, has been reported to play an important role in metabolic diseases as well as chronic inflammatory diseases. The involvement of 11β-HSD1 in chronic periodontitis was investigated in the present study. The relationship between the levels of 11β-HSD1, chronic periodontitis, and body mass index (BMI) was analyzed. The expression of 11β-HSD1 mRNA was significantly higher in the chronic periodontitis group than in the control group. Since the expression of 11β-HSD2, which converts active cortisol to inactive cortisone, was slightly lower in the chronic periodontitis group than in the controls, the ratio of 11β-HSD1 versus 11β-HSD2 was significantly higher in the chronic periodontitis group than in the controls. A correlation was not observed between BMI and the level of 11β-HSD1 or between BMI and the ratio of 11β-HSD1 versus 11β-HSD2. These results suggested that an increase in the ratio of 11β-HSD1 versus 11β-HSD2 was associated with chronic periodontitis irrespective of obesity.

Maternal Deprivation of Lewis Rat Pups Increases the Severity of Experi-mental Periodontitis in Adulthood

Background and Objective:

Early life adverse events may influence susceptibility/resistance to chronic inflammatory diseases later in life by permanently dysregulating brain-controlled immune-regulatory systems. We have investigated the impact of infant-mother separation during early postnatal life on the severity of experimental periodontitis, as well as systemic stress and immune responses, in adulthood.

Material and Methods:

Pups of periodontitis resistant Lewis rats were separated from their mothers for 3 h daily during postnatal days 2-14 (termed maternal deprivation; MD), separated for 15 min daily during the same time period (termed handling; HD), or left undisturbed. As adults, their behaviour was tested in a novel stressful situation, and ligature-induced periodontitis applied for 21 days. Two h before sacrifice all rats were exposed to a gram-negative bacterial lipopolysaccharide (LPS) challenge to induce a robust immune and stress response.

Results:

Compared to undisturbed controls, MD rats developed significantly more periodontal bone loss as adults, whereas HD rats showed a tendency to less disease. MD and HD rats exhibited depression-like behaviour in a novel open field test, while MD rats showed higher glucocorticoid receptor (Gr) expression in the hippocampus, and HD rats had altered methylation of genes involved in the expression of hippocampal Gr. LPS provoked a significantly lower increase in circulating levels of the cytokine TGF-1β in MD and HD rats, but there were no significant differences in levels of the stress hormone corticosterone.

Conclusion:

Stressful environmental exposures in very early life may alter immune responses in a manner that influences susceptibility/resistance to periodontitis.

Effect of chronic stress on ligature-induced periodontitis in inbred and noninbred rats: a radiographic study

AIM

The aim was to compare the effect of chronic stress on ligature-induced periodontitis in inbred and noninbred female rats by means of a radiographic study.

MATERIALS AND METHODS

Adult Lewis (inbred) and Wistar (non-inbred) rats were used and divided into the following groups: Ligature/Stress Lewis Group (LSLG, n = 8); Ligature/Stress Wistar Group (LSWG, n = 8); Ligature Lewis Group (LLG, n = 8) and Ligature Wistar Group (LWG, n = 8). The animals were anesthetized and a silk thread was continuously kept around their second upper right molar. Then, groups LSLG and LSWG were subjected to physical stress test (physical restraint for 12 hours). After 15 days of ligature placement, the animals were euthanized. The right hemimaxilla was kept in formalin solution for 48 hours. Radiographs of the hemimaxillae were obtained using the parallelism technique and subsequently submitted to a standardized radiographic processing. The examiner was blinded to the groups and calibrated. The bone height level was measured and the data were subjected to statistical analysis (ANOVA, Tukey, p < 0.05).

RESULTS

LSWG showed bone destruction significantly higher than that of LSLG (32.1 ± 1.45 mm and 23.6 mm ± 2.13, respectively). Similarly, LWG showed bone destruction significantly higher than that of LLG (28.6 ± 1.18 mm and 25.2 ± 2.76 mm, respectively).

CONCLUSION

Inbred rats (Lewis) are less susceptible to the effects of chronic stress than are noninbred rats (Wistar) in relation to ligature-induced periodontitis.

CLINICAL SIGNIFICANCE

Epidemiological studies have shown a relationship between stress and periodontitis. One of the major difficulties of this type of research is the bias of the exact diagnosis of the patient's emotional state. Inbred lines animals have standards-specific neuroendocrine, this allows answers about the susceptibility of periodontal disease, making knowledge applicable in future clinical trials.

Effects of long-term exposure of 3,4-methylenedioxymethamphetamine (MDMA; "ecstasy") on neuronal transmitter transport, brain immuno-regulatory systems and progression of experimental periodontitis in rats

The present study was designed to investigate the effects of long-term exposure (4 weeks) to the widely used narcotic drug and putative neurotoxicant 3,4-methylenedioxymetamphetamine (MDMA; "ecstasy") on neuronal transmitter transport and progression of experimental periodontitis in male Wistar rats. The rats were exposed to MDMA (10mg/kg/day i.p.) or saline five days a week for four consecutive weeks. Exposure to MDMA induced a significant reduction in the synaptosomal reuptake of serotonin, while the uptake of dopamine was significantly increased 24h after the last injection of MDMA. In contrast, the synaptosomal uptake of noradrenaline and the vesicular uptake through the vesicular monoamine transporter 2 were not affected. In the experiments of periodontitis development, ligature-induced periodontitis was induced three days prior to MDMA administration. Compared to controls, MDMA-treated rats developed significantly more periodontitis. In conclusion, our results show that long-term exposure to MDMA affects the serotonergic and dopaminergic transport systems in the rat brain and increased the susceptibility to the psychosomatic ailment periodontitis following disturbances of brain immune-regulatory systems. These results are interesting with respect to recent research showing that changes in neurotransmitter signalling may alter the reactivity of brain-controlled immunoregulatory systems controlling pathogenic microorganisms colonizing mucosal surfaces.

Chronic treatment with the glucocorticoid receptor antagonist RU486 inhibits diabetes-induced enhancement of experimental periodontitis

BACKGROUND AND OBJECTIVE

Chronic hypothalamic-pituitary-adrenal (HPA) axis hyperactivity and excessive glucocorticoid hormone release have been associated with diabetes, altered immune responses and increased susceptibility to periodontitis. In the present study we tested the impact of streptozotocin (STZ)-induced diabetes on ligature-induced periodontitis and the effect of subsequent treatment with the glucocorticoid receptor (GR) antagonist, RU486.

MATERIAL AND METHODS

A single dose of STZ [45 mg/kg, intraperitoneally (i.p.)] or vehicle was given 10 d before induction of ligature-induced periodontitis and implantation subcutaneously of a drug pellet containing the GR antagonist, RU486, or a placebo pellet. Periodontitis was assessed when the ligatures had been in place for 21 d. Two hours before decapitation all rats received gram-negative bacterial lipopolysaccharide (LPS) (150 μg/kg, i.p.) to induce a robust immune and stress response.

RESULTS

Compared with control rats, STZ-treated rats developed significantly more periodontal bone loss, and RU486 treatment of STZ -treated rats significantly inhibited this effect. STZ-treated rats also showed significantly higher levels of the HPA axis-derived hormone, corticosterone, as well as of the proinflammatory cytokine, tumor necrosis factor-alpha (TNF-α), but lower levels of the anti-inflammatory cytokines interleukin-10 (IL-10) and transforming growth factor-1beta (TGF-1β) after LPS stimulation. GR blockade had no statistically significant effects on these measurements in diabetic rats, but tended to enhance the levels of TNF-α and TGF-1β, and reduce the levels of IL-10 and blood glucose.

CONCLUSION

In diabetic subjects, excessive GR activation as a result of chronic high levels of glucocorticoid hormones may alter immune-system responses in a manner that may increase the susceptibility to periodontitis.

The effect of stress on periodontitis: A clinicobiochemical study

BACKGROUND

Clinical and epidemiological data suggest that negative life experience events, like depression, may contribute to an increased susceptibility to periodontal disease.

AIM

To study the association between psychological stress and chronic periodontitis.

MATERIALS AND METHODS

One hundred and eleven dentate individuals, of age 40 years and above, were selected. The clinical examination included, the number of teeth present, plaque index, Probing Pocket Depth, and Clinical Attachment Level. Assessment of Psychological stress levels were done by a questionnaire and were correlated with salivary cortisol levels, which were estimated biochemically by using the Enzyme-Linked Immunosorbent Assay (ELISA) method.

RESULTS

Statistical analysis was done by using the student 't' test and Mann Whitney test. According to our observation, chronic periodontitis showed a significant correlation with hypercortisolemia (P<0.0001), work tension (P=0.04), economic problems (P<0.0001), clinical stress syndrome (P<0.0001), plaque index (P<0.0001), and unsecured job (P=0.003).

CONCLUSION

Stress may be considered as an important risk factor for periodontal disease. Routine salivary cortisol assessment may be an economical and useful diagnostic marker to rule out stress in periodontitis patients.

Oral treatment with complement factor C5a receptor (CD88) antagonists inhibits experimental periodontitis in rats

BACKGROUND AND OBJECTIVE

The complement activation product 5a (C5a) is a potent mediator of the innate immune response to infection, and may thus also importantly determine the development of periodontitis. The present study was designed to explore the effect of several novel, potent and orally active C5a receptor (CD88) antagonists (C5aRAs) on the development of ligature-induced periodontitis in an animal model.

MATERIAL AND METHODS

Three different cyclic peptide C5aRAs, termed PMX205, PMX218 and PMX273, were investigated. Four groups of Wistar rats (n = 10 in each group) were used. Starting 3 d before induction of experimental periodontitis, rats either received one of the C5aRas (1-2 mg/kg) in the drinking water or received drinking water only. Periodontitis was assessed when the ligatures had been in place for 14 d.

RESULTS

Compared with control rats, PMX205- and PMX218-treated rats had significantly reduced periodontal bone loss.

CONCLUSION

The findings suggest that complement activation, and particularly C5a generation, may play a significant role in the development and progression of periodontitis. Blockade of the major C5a receptor, CD88, with specific inhibitors such as PMX205, may offer novel treatment options for periodontitis.

Systemic chemical desensitization of peptidergic sensory neurons with resiniferatoxin inhibits experimental periodontitis

Background and objective:

The immune system is an important player in the pathophysiology of periodontitis. The brain controls immune responses via neural and hormonal pathways, and brain-neuro-endocrine dysregulation may be a central determinant for pathogenesis. Our current knowledge also emphasizes the central role of sensory nerves. In line with this, we wanted to investigate how desensitization of peptidergic sensory neurons influences the progression of ligature-induced periodontitis, and, furthermore, how selected cytokine and stress hormone responses to Gram-negative bacterial lipopolysaccharide (LPS) stimulation are affected.

Material and methods:

Resiniferatoxin (RTX; 50 μg/kg) or vehicle was injected subcutaneously on days 1, 2, and 3 in stress high responding and periodontitis-susceptible Fischer 344 rats. Periodontitis was induced 2 days thereafter. Progression of the disease was assessed after the ligatures had been in place for 20 days. Two h before decapitation all rats received LPS (150 μg/kg i.p.) to induce a robust immune and stress response.

Results:

Desensitization with RTX significantly reduced bone loss as measured by digital X-rays. LPS provoked a significantly higher increase in serum levels of the pro-inflammatory cytokine tumour necrosis factor (TNF)-α, but lower serum levels of the anti-inflammatory cytokine interleukin (IL)-10 and the stress hormone corticosterone.

Conclusions:

In this model RTX-induced chemical desensitization of sensory peptidergic neurons attenuated ligature-induced periodontitis and promoted a shift towards stronger pro-inflammatory cytokine and weaker stress hormone responses to LPS. The results may partly be explained by the attenuated transmission of immuno-inflammatory signals to the brain. In turn, this may weaken the anti-inflammatory brain-derived pathways.

Evidence that metyrapone in the presence of inflammation modulates cytokine mRNA expression

OBJECTIVE

Metyrapone (MT) has been used clinically to decrease glucocorticoid levels in human and animal studies. However, the potential effects of MT in the presence of inflammation are poorly understood. Thus, the aim of this study was to evaluate the effects of the administration of MT on the mRNA levels of pro-inflammatory cytokines in the presence of inflammation induced by the well-established model of ligature-induced periodontitis in rats.

MATERIAL AND METHODS

Sixty animals were randomly assigned into three experimental groups of 20 rats each: G1-control; G2-periodontal disease (PD) induced by cotton ligature; G3-PD associated with 3 daily doses of MT (50mg/kg/3×3h). After 30 days, all animals were killed by decapitation. Blood samples were taken and the concentrations of corticosterone and catecholamines measured. Marginal tissues around ligated and non-ligated teeth were harvested and gene expression was assessed by quantitative polymerase chain reaction technique (qPCR). Moreover, the area of interradicular bone loss (ABL) was histometrically determined.

RESULTS

Data analysis showed that: (i) ligature placement resulted in a significant ABL, as compared to non-ligated sites of G1 group; (ii) mRNA levels of all the pro-inflammatory factors assessed (INF-γ, TNF-α, IL-1β and IL-6) were increased in the PD group (G2) (p<0.05) when compared to G1; (iii) there were no significant differences in corticosterone and catecholamine plasmatic levels between the three groups; (iv) MT administration, in the presence of inflammation, induces an increased ABL and significantly increased mRNA levels of all pro-inflammatory cytokines analyzed (p<0.05).

CONCLUSION

Within the limits of this study, it can be concluded that MT in the presence of inflammation may modulate expression of pro-inflammatory cytokines, regardless of its effect on plasma corticosterone levels.

Effect of neonatal clomipramine in the pathogenesis of ligature-induced periodontitis in Lewis rats

OBJECTIVE

The aim of this study was to verify the association between an endogenous depression model and the development of ligature-induced periodontitis in rats.

MATERIAL AND METHODS

Nine male Lewis rats received 30 mg/kg clomipramine from neonatal day 8 to day 21 (depressed group), while 13 control Lewis rats were left untouched (control group). On day 150, ligatures were placed around the 2nd upper molars in both groups, i.e. the contralateral molar of the intra-group control. On day 190, the rats were killed and the maxillae were defleshed. The distance between the cemento-enamel junction and the alveolar bone crest was measured by a blinded examiner using standardized digital photographs.

RESULTS

The depressed rats showed hyperactivity in open field on day 142 and greater attempts to escape on day 143 compared to controls. The other behavioral data did not show statistically significant differences between the groups (Mann-Whitney, p>0.05). In teeth with ligature, mean alveolar bone loss varied from 0.51 to 0.60 and from 0.63 to 0.64 mm for tests and controls, respectively (t-test, p>0.05). In teeth without ligature, these values varied from 0.38 to 0.43 and 0.42 to 0.45 mm in the test and control groups, respectively (t-test, p>0.05).

CONCLUSION

Induced depression did not alter ligature-induced bone loss in Lewis rats.

Hydrocortisone Affects the Expression of Matrix Metalloproteinases (MMP-1, -2, -3, -7, and -11) and Tissue Inhibitor of Matrix Metalloproteinases (TIMP-1) in Human Gingival Fibroblasts

BACKGROUND

There is a positive correlation between the course of periodontal disease and psychosocial stress status. Stress leads to activation of the hypothalamic-pituitary-adrenal axis, resulting in increased cortisol release. The present study evaluates the effect of two different hydrocortisone concentrations on mRNA expression of matrix metalloproteinases (MMPs) and tissue inhibitor of matrix metalloproteinases (TIMPs) in cultured, human gingival fibroblasts.

METHODS

Gingival fibroblasts were stimulated with 10(-7) or 10(-9) M hydrocortisone for 24 hours; untreated cells served as controls. Alterations in the expression of MMP-1, -2, -3, -7, -11 and TIMP-1 and -2 were evaluated using real-time polymerase chain reaction and Western blotting. beta-actin mRNA expression was used as a reference to normalize gene expression.

RESULTS

Although the higher hydrocortisone concentration upregulated MMP-1, -2, -7, -11, and TIMP-1 (P <0.05) expression, the lower concentration induced downregulation or diminished upregulation. The lower hydrocortisone concentration induced a 23-fold increase in MMP-3 gene expression, whereas the higher concentration induced less upregulation; however, protein expression was regulated similarly by both hydrocortisone concentrations. The effect of hydrocortisone on TIMP-2 expression was not significant (P >0.05).

CONCLUSIONS

Hydrocortisone produced a dose-dependent regulation of MMP and TIMP expression. The higher hydrocortisone concentration significantly upregulated expression of MMP-1, -2, -7, and -11 and TIMP-1 in human gingival fibroblasts, which may constitute a mechanism underlying the increased periodontal breakdown associated with psychosocial stress status.

Cocaine and amphetamine regulated transcript (CART) and the stress response

CART is expressed abundantly in the hypothalamic paraventricular nucleus and locus coeruleus, major corticotropin releasing factor (CRF) and noradrenaline sources, respectively. There is a bidirectional relation between CART and hypothalamo-pituitary-adrenal axis activity. CART stimulates CRF, adrenocorticotropic hormone and glucocorticoid secretion, whereas CRF and glucocorticoids increase the transcriptional activity of the CART gene; adrenalectomy declines CART expression in the hypothalamus. Stress exposure modulates CART expression in hypothalamus and amygdala in rat brain in a region and sex specific manner. CART may be a mediator peptide in the interaction between stress, drug abuse, and feeding. The review discusses the established role of CART as it relates to the stress response.

Enhanced susceptibility to periodontitis in an animal model of depression: reversed by chronic treatment with the anti-depressant tianeptine

OBJECTIVE

To test the hypothesis that the olfactory bulbectomy model of depression in rats could influence susceptibility to ligature-induced periodontitis, and that chronic treatment with the anti-depressant drug tianeptine could attenuate this effect.

MATERIAL AND METHODS

Tianeptine was given twice daily (10 mg/kg, i.p.) during the entire experiment, starting 29 days before induction of olfactory bulbectomy and periodontitis. Olfactory bulbectomized (OB) rats and sham-operated rats were given saline in a similar manner. Periodontal disease was assessed when the ligatures had been in place for 21 days. Two hours before decapitation, rats were injected with lipopolysaccharide (LPS;100 microg/kg, i.p.) to induce a robust immune and stress response.

RESULTS

Compared with sham-operated controls, OB rats developed significantly more periodontal bone loss, exhibited characteristic behavioural responses in a novel open field test, and showed a decreased expression of glucocorticoid receptors (GRs) in the hippocampus. LPS provoked a significantly larger increase in circulating levels of the stress hormone corticosterone and the cytokine transformation growth factor (TGF)-1beta but smaller tumour necrosis factor (TNF)-alpha levels. Tianeptine treatment of OB rats significantly inhibited peridodontal bone loss, normalized behavioural responses, enhanced TGF-1beta levels, and abolished TNF-alpha decrease, but did not attenuate the increased corticosterone response and the decreased hippocampal GR expression.

CONCLUSIONS

These experimental results are consistent with an emerging literature showing that life stress, anxiety, depression, pathological grief, and poor coping behaviour may dysregulate regulatory mechanisms within the brain involved in immune regulation, and thereby alter immune responses and influence the susceptibility/resistance to inflammatory disorders.

Neonatal dexamethasone and chronic tianeptine treatment inhibit ligature-induced periodontitis in adult rats

OBJECTIVE

The responsiveness of the hypothalamic-pituitary-adrenal (HPA) axis has been found to play a significant role for susceptibility and resistance to periodontal disease. In the present study we have investigated the effects of two different treatment strategies, which have been found to down-regulate the HPA axis, on ligature-induced periodontitis.

METHODS

In experiment 1, newborn rats were treated with the synthetic glucocorticoid hormone dexamethasone-21-phosphate, which permanently down-regulates HPA axis responsiveness. In experiment 2, adult rats were treated with the novel antidepressant drug tianeptine, which opposes the action of stress. Periodontitis was inflicted upon all rats. Just before decapitation the animals received gram-negative bacterial lipopolysaccharide (LPS) to induce a robust immune and HPA axis response.

RESULTS

Compared to the saline-treated control rats, dexamethasone-treated rats had significantly less periodontal bone loss (p < 0.01), reduced expression of glucocorticoid receptors in the hippocampus (p < 0.001), lower corticosterone (p=0.01) and higher plasma levels of the cytokine tumor necrosis factor (TNF)-alpha (p < 0.05) after LPS challenge. Also the tianeptine-treated rats showed significantly reduced periodontal bone loss (p=0.01), enhanced plasma levels of TNF-alpha (p < 0.05), and transforming growth factor-1beta (p < 0.01), whereas no significant difference was found in corticosterone levels.

CONCLUSION

An individual's responsiveness to danger signals, whether they are of immunological, chemical, or psychological origin, may be an important factor for explaining variability in susceptibility to periodontal disease. The results may provide new insight into the mechanisms of periodontal disease development, and open new vistas for disease prevention.

Chemical sympathectomy inhibits periodontal disease in Fischer 344 rats

OBJECTIVE

The responsiveness of the sympathetic nervous system (SNS) and the hypothalamic--pituitary--adrenal (HPA) axis plays a major role in immune regulation and for the outcome of infections and inflammatory disorders. This study was designed to investigate whether chemical SNS denervation with the noradrenaline-selective neurotoxic drug 6-hydroxydopamine (6-OHDA), which destroys peripheral noradrenaline terminals, would influence immune responses to Gram-negative bacterial lipopolysaccharide (LPS) stimulation, and the progression of ligature-induced periodontal disease in Fischer 344 rats.

MATERIAL AND METHODS

6-OHDA (40--60 microg/kg) or vehicle was injected intraperitoneally (i.p.) on days 1, 3 and 5, 10 days before application of the ligatures, and thereafter weekly in doses of 80 microg/kg. Periodontal disease was assessed when the ligatures had been in place for 49 days. At 24 and 2 h before decapitation, all rats received LPS (150 microg/kg i.p.) to induce a robust immune and HPA axis response.

RESULTS

The 6-OHDA-treated rats showed significantly reduced bone loss as measured by digital X-rays (p< 0.01), and enhanced levels of the cytokines transforming growth factor-beta (p=0.05) and interleukin-6 (p=0.05), as well as the HPA axis derived hormone corticosterone (p=0.01), induced by LPS stimulation.

CONCLUSIONS

6-OHDA-induced chemical sympathectomy inhibits ligature-induced periodontal disease in this model. This effect may be attributable to the well-documented ability of the SNS to regulate immune system function primarily via the adrenergic neurotransmitter noradrenaline released at sympathetic nerve terminals. The enhanced HPA axis activation may be a compensatory response that reduces the T helper (Th)2 to Th1 skewing effect of treatment with 6-OHDA.

Soluble beta-1,3/1,6-glucan from yeast inhibits experimental periodontal disease in Wistar rats

OBJECTIVE

We have investigated whether a purified immunomodulatory water soluble beta-1,3/1,6-glucan isolated from the cell wall of Bakers yeast, Saccharomyces cerevisiae, would influence the progression of ligature-induced periodontal disease, and to modulate accompanying cytokine and hypothalamic-pituitary-adrenal (HPA) axis responses to a lipopolysaccharide (LPS) challenge.

MATERIAL AND METHODS

beta-1,3/1,6-glucan (10 mg/kg/day) was given in the drinking water to Wistar rats during the entire experiment, starting 14 days before disease induction, while control rats were given tap water only. Periodontal disease was assessed when the ligatures had been in place for 35 days.

RESULTS

Orally administered soluble beta-1,3/1,6-glucan significantly reduced periodontal bone loss as measured on digital X-rays (p=0,026). Glucan-treated rats also showed a significantly enhanced plasma level of the HPA axis-driven hormone corticosterone (p=0.047), and of the cytokine transforming growth factor-1beta (p=0.032), as well as a tendency to enhanced IL-10 (p=0.106), induced by intra-peritoneally administered LPS.

CONCLUSION

Soluble beta-1,3/1,6-glucan administered by the oral route diminishes ligature-induced periodontal bone loss in this model. This effect may be attributable to the well documented ability of beta-1,3/1,6-glucan to stimulate macrophage phagocytosis and to skew the T helper (Th)1/Th2 balance towards Th1 and T regulatory responses. The HPA axis may play a significant role in beta-1,3/1,6-glucan induced immune modulation.

Chronic treatment with the glutamate receptor antagonist MK-801 alters periodontal disease susceptibility

OBJECTIVE

Previous experiments in rats suggest that hypothalamic-pituitary-adrenal (HPA) axis over-responsiveness, which leads to increased secretion of immunoregulatory glucocorticoid hormones, increases periodontal disease susceptibility, whereas HPA axis under-responsiveness is associated with increased resistance to the disease. The present study was designed to investigate whether MK-801 (dizocilipine malate), an antagonist of the glutamate receptor N-methyl-D-aspartate (NMDA) in the brain, which has been found to play an important role in the regulation of the HPA axis, would influence the outcome of experimental ligature-induced periodontal disease in a rat model.

METHODS

Experimental periodontal disease was induced in periodontal disease susceptible and HPA axis high-responding Fischer 344 rats 2 days before chronic treatment with MK-801(1 mg/kg intraperitoneally). The periodontal breakdown was assessed after the ligatures had been in place for 23 days. Following intraperitoneal Gram-negative bacterial lipopolysaccharide stimulation (Escherichia coli, 250 microg/kg), concentrations of glucocorticoid receptors (GRs) in the hippocampus, and levels of the cytokine tumour necrosis factor alpha (TNF-alpha), as well as the HPA axis-derived hormone corticosterone, were measured in serum.

RESULTS

Compared to vehicle-treated controls, MK-801-treated rats had significantly increased periodontal tissue destruction (p < 0.01). MK-801-treated rats also showed significantly increased expression of GRs in the hippocampus (p < 0.05), elevated levels of corticosterone (p < 0.001) and reduced levels of TNF-alpha (p < 0.01) in serum 2 h after lipopolysaccharide stimulation.

CONCLUSION

These findings may implicate glutamate receptor-dependent mechanisms in periodontal disease, and support the concept of a bidirectional immune-brain-immune regulatory network with importance for periodontal health and disease.

Chronic glycine treatment inhibits ligature-induced periodontal disease in Wistar rats

OBJECTIVE

Dysregulation of immune and stress responses plays a significant role for the development and progression of inflammatory diseases, including periodontal disease. The non-essential amino acid glycine modulates immune and central nervous system (CNS) responses, and has been shown to beneficially affect tissue destructive inflammatory conditions. The purpose of this study was to test the ability of orally administered glycine to influence periodontal disease progression, as well as immune and hypothalamic-pituitary-adrenal (HPA) responses following lipopolysaccharide stimulation.

METHODS

Glycine was supplied in the drinking water during the whole experiment to male Wistar rats, starting 3 days before the induction of experimental ligature-induced periodontal disease. Control rats were given tap water only. The periodontal breakdown was assessed after the ligatures had been in place for 34 days. Following intraperitonal lipopolysaccharide stimulation, concentrations of the proximal cytokines tumour necrosis factor-alpha (TNF-alpha) and interleukin-10, as well as the HPA axis-derived hormone corticosterone, were measured in blood serum.

RESULTS

Orally administered glycine significantly reduced periodontal bone loss as measured by digital X-rays (p = 0.007). Bone loss was negatively correlated with increased serum glycine, whereas no significant relationship was found with TNF-alpha, interleukin-10, or corticosterone.

CONCLUSION

Chronic ingestion of glycine supplied in the drinking water significantly reduced periodontal bone loss. No effect of glycine on immune and HPA-axis responses was revealed. Further studies are needed to clarify the mechanisms of action.

Effect of Restraint Stress on the Progression of Experimental Periodontitis in Rats

BACKGROUND

A hypothesis of an increased risk for destructive periodontal diseases due to psychological stress has long been promoted. However, the research on stress and periodontal disease is still in its infancy. One of the reasons is thought to be that there is no suitable animal model for investigating the relationship.

METHODS

One hundred male Wistar rats were included. A nylon ligature was placed around the second right maxillary molars. The animals were then divided into group S, exposed to a restraint stress for 12 hours/day for up to 10 days, and group N, controls. Ten animals were sacrificed on days 2, 4, 6, 8, and 10. Blood samples were taken, and the blood glucose level and the concentrations of adrenocorticotropic hormone, corticosterone, and adrenaline were measured as the markers of stress. The atrophies of the thymus and the spleen were measured. The furcation area of the second maxillary molars was examined histologically and histometrically.

RESULTS

In group S, all values of stress markers were increased, and the thymus and the spleen were atrophied. Whereas group N showed only slight alveolar bone resorption, a marked alveolar bone resorption occurred in group S between days 8 and 10. An increase in beaded nerve terminals occurred around the vessels in the furcation area of group S.

CONCLUSION

The results of the present study suggest that the restraint stress modulates the progression of periodontal inflammation and that this rat model is suitable for investigating the association between stress and periodontal disease.

Oral treatment with SRP299 (killed Mycobacterium vaccae ) inhibits experimental periodontal disease in Wistar rats

OBJECTIVE

Mycobacterium vaccae injected subcutaneously was previously shown to prevent and treat ligature-induced periodontal disease (PD) in Wistar rats (Breivik & Rook 2000, 2002). Since mycobacteria are readily taken up via Peyer's patches in the intestine, we have now tested the ability of oral SRP299 (killed M. vaccae) to prevent ligature-enhanced PD in Wistar rats, and to modulate the accompanying cytokine and corticosterone responses.

MATERIAL AND METHODS

A single oral dose of SRP299 (1 mg) was given 14 days before the application of ligatures. PD was assessed when the ligatures had been in place for 56 days.

RESULTS

Oral SRP299 reduced bone loss (p = 0.036, X-ray; p = 0.061, histometry) and fibre loss, both on the ligatured (p = 0.0047) and control (p = 0.005) sides, and also reduced the level of TNF-alpha (p = 0.0137) and corticosterone (p = 0.048) induced by intraperitoneal endotoxin lipopolysaccharide (LPS).

CONCLUSIONS

SRP299 administered by the oral route diminishes ligature-induced bone and fibre loss in this model. This effect may be attributable to the known ability of SRP299 to evoke regulatory T cells, although the mechanism could not be investigated in this study. Treated rats also had less excitable hypothalamo-pituitary-adrenal (HPA) axes. HPA axis overactivity is a known risk factor in human PD. Trials of SRP299 in human PD are now justified.

Effects of hippocampal lesioning on experimental periodontitis in Wistar rats

The hippocampus, which is a brain structure involved in learning and memory processes, plays a key role in the feedback regulation of the hypothalamic-pituitary-adrenal (HPA) axis and autonomic sympathetic nervous system, and the subsequent secretion of immuno-modulatory hormones in response to pathogenic microorganisms. Dysregulation of these brain-neuroendocrine-immune regulatory networks, which act in concert to maintain homeostasis, is found to be of critical importance to the host defence against pathogens, as well as susceptibility to diseases, including periodontal disease. The present study was designed to determine the effects of hippocampal lesioning on the progression of periodontitis. Experimental ligature-induced periodontitis was induced in 16 Wistar rats, which were bilaterally lesioned in their hippocampal region with an aspiration technique that is well documented to impair learning and memory, as well as in 15 sham-operated control rats. The disease progression was evaluated radiographically and histometrically. The results revealed that the hippocampal lesioned rats developed significantly more destruction of the periodontium than did the sham-operated controls. This finding supports recent studies that indicate that inappropriate brain-neuroendocrine regulation of inflammatory responses to infectious agents may play an important role in disease susceptibility and progression.

Postnatal lipopolysaccharide-induced illness predisposes to periodontal disease in adulthood

The long-term consequences of neonatal lipopolysaccharide (LPS) exposure on adult behavioral and neuroendocrine stress responsiveness as well as on the clinical course of periodontal disease were assessed in male Lewis rats. At 3 and 5 days of age, pups were administered either saline (SHAM) or LPS or were left undisturbed. After postnatal treatment, mothers licked LPS-treated pups significantly more. In adult LPS rats of 3-5 months of age, home cage activity indicated changes of the diurnal rhythmicity. Furthermore, SHAM- and LPS-treated animals displayed treatment-specific signs of increased anxiety in social interaction, elevated plus maze, holeboard, and open field tests. At 7 months of age, a dramatic increase of periodontal fiber loss in LPS rats was associated with increased plasma interleukin-6 levels. In contrast, SHAM treatment caused high plasma interferon-gamma cytokine levels and protective effects in periodontal disease. Parameters of the response to novelty were significantly correlated with later disease susceptibility. Thus, LPS-induced early postnatal illness modulates the adult behavioral responsiveness to stress and predisposes to periodontal disease.

Postnatally induced differences in adult pain sensitivity depend on genetics, gender and specific experiences: reversal of maternal deprivation effects by additional postnatal tactile stimulation or chronic imipramine treatment

Postnatal endotoxin exposure, handling or maternal deprivation produce long-lasting individual differences in various neuroendocrine and behavioural responses. However, the impact of postnatal experiences on adult pain sensitivity and its reversibility by postnatal additional tactile stimulation or antidepressants in adulthood is not well understood. Therefore, postnatal endotoxin application as a model for infection, maternal deprivation as a model for depression, and postnatal handling as a model for stimulation were compared with respect to the effects on pain sensitivity in adult Fischer 344 (F344) and Lewis (LEW) rats. Handling increased hot plate latencies in adult F344 and LEW rats, while maternal deprivation shortened hot plate latencies only in LEW rats. Prophylactic treatment strategies, such as tactile stimulation of the dorsal neck region of pups directly after maternal deprivation, or chronic treatment of adult maternally deprived rats using imipramine, successfully provide protection against the maternal deprivation-induced shortening of hot plate latencies. Thus, there is considerable specificity of certain postnatal experiences in modulating adult pain sensitivity and the maternal deprivation-induced hyperalgesia is reversible by different interventional regimes. These findings may explain some of the individual differences in pain sensitivity of humans and the differential efficacy of antidepressants in pain syndromes.

Manipulations in maternal environment reverse periodontitis in genetically predisposed rats

The predisposition to develop periodontitis is partly genetically determined in humans as well as in animals. Here we demonstrate, however, that early manipulations in the maternal environment of an animal (rat) model of periodontitis can fully reverse the genetic predisposition to develop periodontitis at adult age.

Influence of restraint stress on ligature-induced periodontitis in rats

The influence of stress on periodontal breakdown in Wistar rats was analyzed during experimental periodontitis, induced by placing silk ligatures around the maxillary right second molar teeth. The rats were divided into three groups with 10 animals in each; the first group was exposed to restraint stress for 12 h d(-1) for a period of 4 wk; the second group was exposed to restraint stress for 2.5 h d(-1) for a period of 4 wk; the third group served as a control group. Ligation for 4 wk resulted in an accelerated periodontal degradation, whereas the restraint stress by itself had no significant effect. Combined stress and ligation resulted in a significantly higher attachment loss and alveolar bone resorption than either treatment alone, while no differences were seen between the two stress regimens. After 4 wk, a reduced body weight was found in both restrained groups of rats and a reduced weight of the thymus in the rats restrained for 12 h d(-1), while no changes were observed in the weight or composition of the suprarenal glands. We conclude that stress alone does not result in periodontal disease but may modulate the pathophysiological processes of already present periodontal inflammation, resulting in accelerated degradation of periodontal tissues.