Bacterial invasion in experimental gingivitis in man

Metabolism of serine/glycine lipids by human gingival cells in culture

Porphyromonas gingivalis produces five classes of serine/glycine lipids that are recovered in lipid extracts from periodontitis-afflicted teeth and diseased gingival tissues, particularly at sites of periodontitis. Because these lipids are recovered in diseased gingival tissues, the purpose of the present study was to evaluate the capacity of cultured human gingival fibroblasts (HGF), keratinocytes, and macrophages to hydrolyze these lipids. We hypothesize that one or more of these cell types will hydrolyze the serine/glycine lipids. The primary aim was to treat these cell types for increasing time in culture with individual highly enriched serine/glycine lipid preparations. At specified times, cells and culture media samples were harvested and extracted for hydrolysis products. The serine/glycine lipids and hydrolysis products were quantified using liquid chromatography-mass spectrometry (LC-MS) and free fatty acids were quantified using gas chromatograph-mass spectrometer. LC-MS analysis used two different mass spectrometric methods. This study revealed that treatment of HGF or macrophage (THP1) cells with lipid (L) 654 resulted in breakdown to L342 and subsequent release into culture medium. However, L654 was converted only to L567 in gingival keratinocytes. By contrast, L1256 was converted to L654 by fibroblasts and macrophages but no further hydrolysis or release into medium was observed. Gingival keratinocytes showed no hydrolysis of L1256 to smaller lipid products but because L1256 was not recovered in these cells, it is not clear what hydrolysis products are produced from L1256. Although primary cultures of gingival fibroblasts and macrophages are capable of hydrolyzing specific serine/glycine lipids, prior analysis of lipid extracts from diseased gingival tissues revealed significantly elevated levels of L1256 in diseased tissues. These results suggest that the hydrolysis of bacterial lipids in gingival tissues may reduce the levels of specific lipids, but the hydrolysis of L1256 is not sufficiently rapid to prevent significant accumulation at periodontal disease sites.

Tumor necrosis factor-alpha inhibits osteogenic differentiation of pre-osteoblasts by downregulation of EphB4 signaling via activated nuclear factor-kappaB signaling pathway

BACKGROUND AND OBJECTIVE

The majority of experiments show that tumor necrosis factor-alpha (TNF-α) inhibits osteogenic differentiation of mesenchymal stem cells and pre-osteoblasts by activated nuclear factor-kappaB (NF-κB) signaling. However, the underlying mechanisms by which NF-κB signaling inhibits osteogenic differentiation are not fully understood. The aim of the present study was to investigate whether EphB4 signaling inhibition mediates the effects of TNF-α-activated NF-κB signaling on osteogenic differentiation of pre-osteoblasts.

MATERIAL AND METHODS

Murine MC3T3-E1 pre-osteoblasts were treated with 10 ng/mL of TNF-α. NF-κB inhibitor, pyrrolidine dithiocarbamate, was used to achieve NF-κB signaling inhibition. EphB4 signaling was activated using ephrinB2-fc. The mRNA expressions of runt related transcription factor 2 (Runx2), bone sialoprotein (BSP) and EphB4 were determined using reverse transcription-polymerase chain reaction. The protein levels of Runx2, BSP, Col Ia1, osteopontin, EphB4, p-NF-κB p65 and NF-κB p65 were evaluated using western blot assays. Alkaline phosphatase (ALP) activity in MC3T3-E1 cells was evaluated by ALP activity kit, and mineral nodule formation was evaluated by Alizarin Red S staining.

RESULTS

TNF-α inhibited EphB4 expression, while it suppressed Runx2, BSP expression from gene and protein levels as well as ALP activity and mineral nodule formation in MC3T3-E1 cells. Activation of EphB4 signaling by ephrinB2-fc promoted osteogenic differentiation of MC3T3-E1 cells, whereas TNF-α impaired the osteogenic differentiation enhanced by ephrinB2-fc. Pyrrolidine dithiocarbamate blocked the activation of NF-κB signaling induced by TNF-α, while it prevented the downregulation of Runx2, BSP and EphB4, induced by TNF-α.

CONCLUSION

TNF-α inhibits osteogenic differentiation of pre-osteoblasts by downregulation of EphB4 signaling via activated NF-κB signaling pathway.

Experimental gingivitis induces systemic inflammatory markers in young healthy individuals: a single-subject interventional study

Objectives

We here investigated whether experimental gingivitis enhances systemic markers of inflammation which are also known as surrogate markers of atherosclerotic plaque development.

Background

Gingivitis is a low-level oral infection induced by bacterial deposits with a high prevalence within Western populations. A potential link between the more severe oral disease periodontitis and cardiovascular disease has already been shown.

Methods

37 non-smoking young volunteers with no inflammatory disease or any cardiovascular risk factors participated in this single-subject interventional study with an intra-individual control. Intentionally experimental oral inflammation was induced by the interruption of oral hygiene for 21 days, followed by a 21-days resolving phase after reinitiation of oral hygiene. Primary outcome measures at baseline, day 21 and 42 were concentrations of hsCRP, IL-6, and MCP-1, as well as adhesion capacity and oxLDL uptake of isolated blood monocytes.

Results

The partial cessation of oral hygiene procedures was followed by the significant increase of gingival bleeding (34.0%, P<0.0001). This local inflammation was associated with a systemic increase in hsCRP (0.24 mg/L, P = 0.038), IL-6 (12.52 ng/L, P = 0.0002) and MCP-1 (9.10 ng/l, P = 0.124) in peripheral blood samples between baseline and day 21, which decreased at day 42. Monocytes showed an enhanced adherence to endothelial cells and increased foam cell formation after oxLDL uptake (P<0.050) at day 21 of gingivitis.

Conclusions

Bacterial-induced gingival low-level inflammation induced a systemic increase in inflammatory markers. Dental hygiene almost completely reversed this experimental inflammatory process, suggesting that appropriate dental prophylaxis may also limit systemic markers of inflammation in subjects with natural gingivitis. International Clinical Trials Register Platform of the World Health Organization, registry number: DRKS00003366, URL: http://apps.who.int/trialsearch/Default.aspx

Proteomic analysis of a noninvasive human model of acute inflammation and its resolution: the twenty-one day gingivitis model

The 21-day experimental gingivitis model, an established noninvasive model of inflammation in response to increasing bacterial accumulation in humans, is designed to enable the study of both the induction and resolution of inflammation. Here, we have analyzed gingival crevicular fluid, an oral fluid comprising a serum transudate and tissue exudates, by LC-MS/MS using Fourier transform ion cyclotron resonance mass spectrometry and iTRAQ isobaric mass tags, to establish meta-proteomic profiles of inflammation-induced changes in proteins in healthy young volunteers. Across the course of experimentally induced gingivitis, we identified 16 bacterial and 186 human proteins. Although abundances of the bacterial proteins identified did not vary temporally, Fusobacterium outer membrane proteins were detected. Fusobacterium species have previously been associated with periodontal health or disease. The human proteins identified spanned a wide range of compartments (both extracellular and intracellular) and functions, including serum proteins, proteins displaying antibacterial properties, and proteins with functions associated with cellular transcription, DNA binding, the cytoskeleton, cell adhesion, and cilia. PolySNAP3 clustering software was used in a multilayered analytical approach. Clusters of proteins that associated with changes to the clinical parameters included neuronal and synapse associated proteins.

Porphyromonas gingivalis RgpA-Kgp proteinase-adhesin complexes penetrate gingival tissue and induce proinflammatory cytokines or apoptosis in a concentration-dependent manner

The RgpA-Kgp proteinase-adhesin complexes of Porphyromonas gingivalis were observed, using immunostaining, in human gingival tissue associated with periodontitis but not in healthy tissue. The staining pattern suggested a concentration gradient from the subgingival plaque into the subjacent gingival connective tissue. Intense immunostaining was observed in areas displaying gross disturbance of tissue architecture. P. gingivalis cells and the RgpA-Kgp complexes at low concentrations were shown to stimulate secretory intercellular adhesion molecule 1, interleukin-8 (IL-8), IL-6, and macrophage chemoattractant protein secretion from cultured human epithelial (KB) and fibroblast (MRC-5) cells. However, at high concentrations a reduction in the level of these mediators was observed. In contrast, macrophage inflammatory protein 1alpha and IL-1alpha were stimulated only at high P. gingivalis cell concentrations. P. gingivalis cells and the RgpA-Kgp complexes were shown to induce apoptosis in KB and MRC-5 cells in a time- and dose-dependent manner. These data suggest that the RgpA-Kgp complexes penetrate the gingival connective tissue; at low concentrations distal from the plaque the complexes stimulate the secretion of proinflammatory mediators, while at high concentrations proximal to the plaque they induce apoptosis and attenuate the secretion of proinflammatory mediators.

Actinobacillus actinomycetemcomitans suppresses rat natural killer cell activity in vivo

OBJECTIVE

To examine the immune suppressive effect of Actinobacillus actinomycetemcomitans (Aa) on rat natural killer (NK) cell activity in vivo.

MATERIAL AND METHODS

Sprague Dawley rats were given Aa in 2 different manners: (i) by mixing Aa with food at a dose of 10(8) cells/rat/day for 3 months; or (ii) by a single i.m. injection of live Aa at doses of 10(6) and 10(7) cells/rat/day. NK cell activity was measured by means of a 51Cr-release assay using YAC-1 tumor cells as targets.

RESULTS

Rats that had been infected by Aa mixed with food experienced significant suppression of their NK cell activity; this reached approximately =50% of control values at 2 and 3 months post-Aa infection. The suppression in NK cell activity was related to decreases in the extent of conjugate formation between effectors and YAC-1 target tumor cells (51.7%) and the extent of lysis of target cells (75.7%). The results also showed that addition of an admixture of Aa-treated NK cells to the control NK cells caused 75% and 53% decreases in activity at effector:target ratios of 25:1 and 50:1, respectively. In addition, a significant increase in the extent of T-suppressor cells (154.8% of control) was detected at 3 months post-Aa infection. In contrast, the single injection of live bacteria resulted in a remarkable, dose-dependent inhibition of NK cell activity (55% and 71% at doses of 10(6) and 10(7) cells/rat/day, respectively) as early as 2 days post-treatment. This also reflected significant suppression in the effector:target conjugate formation ratio (52% of control). The data also revealed a 150-188% increase in the number of splenic lymphocytes post-Aa injection. These effects were transient and normal levels were re-established by the fifth day

CONCLUSION

Aa treatment causes suppression of NK cell activity and the mode of action may be due to induction of T-suppressor cells or dilution of NK cells with other lymphoid cell populations. The degree of suppression is affected by the way in which Aa is introduced to the host. These results may contribute to the understanding of how Aa evades host defense.

Occurrence of invading bacteria in radicular dentin of periodontally diseased teeth: microbiological findings

Bacterial invasion in roots of periodontally diseased teeth, which has been recently documented using cultural and microscopic techniques, may be important in the pathogenesis of periodontal disease. The purpose of this investigation was to determine the occurrence and the species of invading bacteria in radicular dentin of periodontally diseased teeth. Samples were taken from the middle layer of radicular dentin of 26 periodontally diseased teeth. 14 healthy teeth were used as controls. Dentin samples were cultured anaerobically. The chosen methodology allowed the determination of the numbers of bacteria present in both deeper and outer part of dentinal tubules, and the bacterial concentration in dentin samples, expressed as colony forming units per mg of tissue (CFU/mg). Invading bacteria was detected in 14 (53.8%) samples from periodontally diseased teeth. The bacterial concentration ranged from 831.84 to 11971.3 CFU/mg (mean+/-standard deviation: 3043.15+/-2763.13). Micro-organisms identified included putative periodontal pathogens such as Prevotella intermedia, Porphyromonas gingivalis, Fusobacterium nucleatum, Bacteroides forsythus, Peptostreptococcus micros and Streptococcus intermedius. These findings suggest that radicular dentin could act as bacterial reservoir from which periodontal pathogens can recolonize treated periodontal pockets, contributing to the failure of therapy and recurrence of disease.

Physiopathology of primary periodontitis associated with plaque. Microbial and host factors. A review. Part 1

Microbial factors involved in the genesis of periodontitis include colonization, bacterial penetration of the epithelium, multiplication and invasive-destructive capacity. Colonization of the gingival sulcus is related, to a certain extent, to supragingival plaque. Bacterial multiplication is induced by nutrients in the gingival fluid, and nutrients produced by degradative and excretory microbial activity. Invasion and destruction are mediated by exotoxins, structural elements of the bacteria, enzymes, metabolites, polyclonal lymphocyte activity, fibroblastic cytotoxicity, and leukocyte chemotactic inhibition.

The periodontally-involved root surface

Recent years have seen much research on the periodontally-involved root surface. Many of these studies have produced results which suggest that plaque contaminants of the root surface are only superficially placed, and capable of being removed by gentle means. Further research has attested to the difficulties in rendering periodontally-involved root surfaces free of calculus deposits by instrumentation, yet clinical studies show that periodontal disease can be managed by root planing. It is concluded that root surface debridement is best assessed on the basis of the healing response and that it should aim to disrupt plaque on and remove plaque from the periodontally-involved root surface rather than to remove part of the root surface itself.

Reviewing nonsurgical periodontal therapy

Selection of the appropriate case and clinical competency in treatment modalities results in success in nonsurgical periodontal therapy. The patient with early periodontitis with significant local factors in the form of professionally accessible plaque and calculus is the most receptive to nonsurgical periodontal treatment. The clinician must make decisions centering around the important question, "Can the patient, or moreover, can the therapist delivering the debridement, gain access to the microbial subgingival plaque on a frequent basis below the host defense threshold of the respective patient?" If the answer is "yes," nonsurgical periodontal therapy will be rewarding. If the answer is "no," other modalities such as periodontal surgery must be instituted.

Report of the Committee on Scientific Investigation of the American Academy of Restorative Dentistry

Dental research continued to grow during 1988. Unfortunately the quality does not always parallel the quantity of publications. This report obviously does not encompass all of the literature but focuses on studies that are related to trends and to matters that are considered controversial. Likewise the particular interests of the members of the American Academy of Restorative Dentistry were taken into consideration. The subjects covered include periodontics, preventive dentistry, bulp biology, craniomandibular disorders, ceramics, color in restorative dentistry, and dental materials.

Intragingival occurrence of Actinobacillus actinomycetemcomitans and Bacteroides gingivalis in active destructive periodontal lesions

A total of six active and six nonactive sites from six untreated periodontitis patients were examined for intragingival presence of Actinobacillus actinomycetemcomitans and Bacteroides gingivalis. The active destructive periodontal disease was determined by the "tolerance method." The method of immunoperoxidase was used in the identification of intragingival microorganisms in active and nonactive periodontal sites. Light microscopic sections of gingival tissues consecutive to those with gram stain, revealing presence of bacteria (substantiated by electron microscopy), were stained with peroxidase-labeled antibodies against A. actinomycetemcomitans and B. gingivalis. B. gingivalis was found to be significantly elevated in the connective tissue of active sites when compared to nonactive sites. A statistically significant border-line difference was found between active and nonactive sites in the connective tissue invaded by A. actinomycetemcomitans. Our findings plus the well established periodontopathic potential of A. actinomycetemcomitans and B. gingivalis support the concept that these bacteria are important invasive pathogenic agents in periodontitis.