Experimental stress suppresses recruitment of macrophages but enhanced their P. gingivalis LPS-stimulated secretion of nitric oxide

Evaluation of hydrocortisone as a strain-dependent growth-regulator of Porphyromonasgingivalis

OBJECTIVE

Porphyromonas gingivalis is an oral key pathogen and known to be very diverse in geno- and phenotypes. It is a fastidious bacterium with low O₂-tolerance and 3-7 days of incubation are necessary. With growing interest in the field of microbial endocrinology we explored the potential growth-stimulating effect of hydrocortisone (HC, synonym cortisol) on P. gingivalis cultures.

MATERIAL AND METHODS

Six different P. gingivalis strains were pre-incubated in supplemented Brain-Heart-Infusion broth under appropriate conditions for 24 h, diluted and transferred into microplates. A newly developed and semi-automated spectrophotometric measurement in triplicate, applying a SpectraMax i3x microplate reader at an optical density of 600 nm, was conducted to test growth differences between test group (exposed to a supplement of either 1.25, 2.5, 5, 10, or 20 μg/ml of hydrocortisone) and control group over 48 h of anaerobic incubation (O₂ ≤ 1%). Furthermore, strains were also incubated on HC-supplemented blood agar to test for a possible growth-stimulating effect on solid media.

RESULTS

HC significantly stimulated the lag-phase growth of four out of six P. gingivalis strains. Our data suggest a concentration-dependent growth stimulatory effect of HC between 2.5 and 5 μg/ml, while below 1.25 μg/ml and above 10 μg/ml HC either did not stimulate or inhibited growth.

CONCLUSIONS

HC could reduce the incubation time when isolating P. gingivalis from clinical samples and could boost low biomass cultivations especially during their lag-phase. The growth-modulating effect might be via modulation of virulence factors/quorum sensing gene expression or by reactive oxygen species(ROS)-capturing during early stages of bacterial growth. Further experiments are necessary to explain the mechanism behind our observations.

Periodontal diseases and depression: A pre-clinical in vivo study

AIM

To analyse, through a pre-clinical in vivo model, the possible mechanisms linking depression and periodontitis at behavioural, microbiological and molecular levels.

MATERIALS AND METHODS

Periodontitis (P) was induced in Wistar:Han rats (oral gavages with Porphyromonas gingivalis and Fusobacterium nucleatum) during 12 weeks, followed by a 3-week period of Chronic Mild Stress (CMS) induction. Four groups (n = 12 rats/group) were obtained: periodontitis and CMS (P+CMS+); periodontitis without CMS; CMS without periodontitis; and control. Periodontal clinical variables, alveolar bone levels (ABL), depressive-like behaviour, microbial counts and expression of inflammatory mediators in plasma and brain frontal cortex (FC), were measured. ANOVA tests were applied.

RESULTS

The highest values for ABL occurred in the P+CMS+ group, which also presented the highest expression of pro-inflammatory mediators (TNF-α, IL-1β and NF-kB) in frontal cortex, related to the lipoprotein APOA1-mediated transport of bacterial lipopolysaccharide to the brain and the detection of F. nucleatum in the brain parenchyma. A dysregulation of the hypothalamic-pituitary-adrenal stress axis, reflected by the increase in plasma corticosterone and glucocorticoid receptor levels in FC, was also found in this group.

CONCLUSIONS

Neuroinflammation induced by F. nucleatum (through a leaky mouth) might act as the linking mechanism between periodontal diseases and depression.

Environmental factors and periodontal microbiome

Periodontal diseases are chronic inflammatory, multifactorial diseases where the major triggering factors for disease onset are bacteria and their toxins, but the major part of tissue destruction occurs as a result of host response towards the periodontal microbiome. Periodontal microbiome consists of a wide range of microorganisms including obligate and facultative anaerobes. In health, there is a dynamic balance between the host, environment, and the microbiome. Environmental factors, mainly tobacco smoking and psychological stress, disrupt the symbiotic relationship. Tobacco smoke and its components alter the bacterial surface and functions such as growth. Psychological stressors and stress hormones may affect the outcome of an infection by changing the virulence factors and/or host response. This review aims to provide currently available data on the effects of the major environmental factors on the periodontal microbiome.

Effects of forced alcohol intake associated with chronic stress on the severity of periodontitis: an animal model study

This study histometrically evaluated the effect of forced alcohol intake by stressed animals on the severity of ligature-induced periodontitis in rats. Thirty-two rats were randomly divided in four groups: group GAL—alcohol and ligature; group GASL—alcohol, chronic physical stress, and ligature; GNC—negative control; GPC—positive control. GAL and GASL received 20% ethanol ad libitum, and GNC received water ad libitum for 60 days. After 24 hours of exposition to alcohol intake—by GAL and GASL—immobilization was applied as a chronic stressor in the GASL group for a two-month period, six times a week, in random hours. The means of the respective groups were statistically compared (Analysis of Variance and Tukey tests, P < 0.05). The most severe periodontal breakdown was observed in nonstressed animals which drank alcohol (GAL), followed by stressed animals exposed to alcohol (GASL). GASL did not differ from the positive control group (GPC). The negative control group showed the lowest values of periodontal breakdown (P < 0.05). Conclusions. Non-stressed alcohol consumer animals showed the most severe pattern of periodontal breakdown. Although stressed animals which were forced to drink alcohol showed poorer periodontal status than the negative controls, their results were similar to those of positive controls.

Immune response of macrophages from young and aged mice to the oral pathogenic bacterium Porphyromonas gingivalis

Periodontal disease is a chronic inflammatory gum disease that in severe cases leads to tooth loss. Porphyromonas gingivalis (Pg) is a bacterium closely associated with generalized forms of periodontal disease. Clinical onset of generalized periodontal disease commonly presents in individuals over the age of 40. Little is known regarding the effect of aging on inflammation associated with periodontal disease. In the present study we examined the immune response of bone marrow derived macrophages (BMM) from young (2-months) and aged (1-year and 2-years) mice to Pg strain 381. Pg induced robust expression of cytokines; tumor necrosis factor (TNF)-α, interleukin (IL)-6, and IL-10, chemokines; neutrophil chemoattractant protein (KC), macrophage colony stimulating factor (MCP)-1, macrophage inflammatory protein (MIP)-1α and regulated upon activation normal T cell expressed and secreted (RANTES), as well as nitric oxide (NO, measured as nitrite), and prostaglandin E2 (PGE2) from BMM of young mice. BMM from the 2-year age group produced significantly less TNF-α, IL-6 and NO in response to Pg as compared with BMM from 2-months and 1-year of age. We did not observe any difference in the levels of IL-1β, IL-10 and PGE2 produced by BMM in response to Pg. BMM from 2-months and 1-year of age produced similar levels of all chemokines measured with the exception of MCP-1, which was reduced in BMM from 1-year of age. BMM from the 2-year group produced significantly less MCP-1 and MIP-1α compared with 2-months and 1-year age groups. No difference in RANTES production was observed between age groups. Employing a Pg attenuated mutant, deficient in major fimbriae (Pg DPG3), we observed reduced ability of the mutant to stimulate inflammatory mediator expression from BMMs as compared to Pg 381, irrespective of age. Taken together these results support senescence as an important facet of the reduced immunological response observed by BMM of aged host to the periodontal pathogen Pg.

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.

NEUROPEPTIDES AND NEUROGENIC MECHANISMS IN ORAL AND PERIODONTAL INFLAMMATION

It is generally accepted that the nervous system contributes to the pathophysiology of peripheral inflammation, and a neurogenic component has been implicated in many inflammatory diseases, including periodontitis. Neurogenic inflammation should be regarded as a protective mechanism, which forms the first line of defense and protects tissue integrity. However, severe or prolonged noxious stimulation may result in the inflammatory response mediating injury rather than facilitating repair. This review focuses on the accumulating evidence suggesting that neuropeptides have a pivotal role in the complex cascade of chemical activity associated with periodontal inflammation. An overview of neuropeptide synthesis and release introduces the role of neuropeptides and their interactions with other inflammatory factors, which ultimately lead to neurogenic inflammation. The biological effects of the neuropeptides substance P (SP), calcitonin gene-related peptide (CGRP), vasoactive intestinal polypeptide (VIP), and neuropeptide Y (NPY) are summarized, and evidence for their involvement in the localized inflammatory lesions which characterize periodontitis is presented. In this context, the role of CGRP in bone metabolism is described in more detail. Recent research highlighting the role of the nervous system in suppressing pain and inflammation is also discussed.

Regulation of nitric oxide production from macrophages by lipopolysaccharide and catecholamines

Catecholamines are elaborated in stress responses to mediate vasoconstriction, and elevate systemic vascular resistance and blood pressure. They are elaborated in disorders such as sepsis, cocaine abuse, and cardiovascular disease. The aim of the study was to determine whether catecholamines affect nitric oxide (NO) production, as NO is a vasodilator and counteracts the harmful effects of catecholamines. RAW264.7 macrophage cells were cultured with lipopolysaccharide (LPS)+/-epinephrine, norepinephrine, and dopamine at 5x10(-6)M concentrations for 24h. Supernatants were harvested for measuring NO by spectrophotometry using the Greiss reagent and cells were harvested for detecting inducible NO synthase (iNOS) by Western blot. NO production in RAW 264.7 macrophages was increased significantly by addition of LPS (0.5-10ng/ml) in a dose-dependent fashion. The NO production induced by LPS was further enhanced by epinephrine and norepinephrine, and to a lesser extent by dopamine. These increases in NO correlated with expression of iNOS protein in these cells. The enhancing effect of iNOS synthesis by epinephrine and norepinephrine on LPS-induced macrophages was down regulated by beta-adrenoceptor antagonist, propranolol, and dexamethasone. The results suggest that catecholamines have a synergic effect on LPS in induction of iNOS synthesis and NO production, and this may mediate some of the vascular effects of infection. These data support a novel role for catecholamines in disorders such as septic shock and cocaine use, and indicate that beta-adrenoceptor antagonists and glucocorticoids may be used therapeutically for modulation of the catecholamine-NO axis in disease states.

Nitric oxide synthesis and severity of human periodontal disease

The expression of the inducible nitric oxide synthase enzyme (iNOS) is a response to an inflammatory stimulus and produces a large amount of nitric oxide (NO), which may act as a cytotoxic molecule against the invading microorganism and may be related to both harmful and beneficial effects to tissues.

OBJECTIVE AND MATERIAL AND METHODS

In order to further characterize the presence of NO in human periodontal disease, we undertook a quantitative study of iNOS positive cells in samples of clinically healthy gingival tissues, plaque-induced gingivitis and localized chronic periodontitis using immunohistochemistry.

RESULTS

A significant increase in the number of iNOS+ cells mm-2 was found in the samples of the gingivitis and periodontitis compared with those of the control. In all groups most of the polymorphonuclear cells showed intense immunoreactivity for iNOS independent of the disease stage, and the percentage of iNOS+ polymorphonuclear cells increased significantly in periodontal disease when compared with the control.

CONCLUSION

Our results indicate that iNOS increases in the presence of periodontal disease. In addition, our findings suggest that polymorphonuclear cells present an additional activation pathway in periodontal disease, expressing significant iNOS and probably representing an important source of NO in human periodontal disease that has not been previously reported.