Periapical inflammatory responses and their modulation

Cytokine production in response to endodontic infection in germ-free mice

This study evaluated the cytokine profiles (type 1 or type 2) that are triggered by and modulate endodontic periapical infections in the root canal system of germ-free mice. Microorganisms isolated from two patients with pulpal necrosis were inoculated into two groups of experimental animals: group I (Gemella morbillorum) and group II (Bifidobacterium adolescentis, Fusobacterium nucleatum and Clostridium butyricum). In vitro, G. morbillorum induced type 1 cytokine synthesis, while the modulation processed in vivo seemed to have the opposite effect, with a reduction in the basal levels of IL-12 and IFN-gamma, IL-4-independent down-modulation. In vitro, microorganisms from group II, in poly-infection, induced a reduction of type 1 cytokine levels from day 10 to day 20, which seemed to be modulated via IL-4. In vivo, however, a predominance of the immune response to one species over the others occurred.

Evaluating IL-2 levels in human pulp tissue

In murine and human CD4+ T cell populations, there are three subpopulations of T helper cell types. Hahn et al. demonstrated the ratio of CD4/ CD8 + cells significantly increases in inflamed dental pulps compared with normal pulps. Elevated levels of interleukin (IL)-2 have been detected in inflamed dental pulps and the level of IL-2 could be used as a marker for inflammation. In this study, levels of IL-2 were evaluated by using a human IL-2 cytokine assay kit on 80 samples of freshly extracted human pulp tissue. Applying standard diagnostic procedures, the tissue samples were clinically categorized into one of three experimental groups. The results demonstrated that there were no significant differences between the concentrations of IL-2 in any of the experimental groups. Our findings are different from results reported previously. Further investigation is warranted to determine if a correlation exists between the concentration of IL-2 or other interleukins and the degree of inflammation present in the dental pulp.

Periapical lesion development in rats inhibited by dexamethasone

Bone resorption is one of the hallmarks of inflammatory periapical lesions and is mediated by cytokines. Recent insights into the immunobiology of these lesions indicate that pharmacological modulation of their bone resorbing activity may be possible. Periapical lesions were induced in rats by occlusal exposure of the pulps of their lower first molars. The size of the resulting lesions was followed-up and evaluated by image analysis of their radiographs. The lesions increased with time, and the average area of their radiographic images reached 2.18 (+/- 0.33) mm2 by day 21. Systemic dexamethasone treatment (0.5 mg/kg, every third day) inhibited the growth of the periapical lesions, which reached an average area of 1.63 (+/- 0.30) (p < 0.01). These results support the hypothesis that bone resorption in periapical inflammatory lesions may be pharmacologically down regulated.

Pathologic interactions in pulpal and periodontal tissues

Both endodontic and periodontal disease are caused by a mixed anaerobic infection. The pathways for the spread of bacteria between pulpal and periodontal tissues have been discussed with controversy. This article is an attempt to provide a rational approach to the perio-endo/endo-perio question based on a review of the relevant literature. In the light of evidence, clinical concepts for the diagnosis and treatment of lesions involving both periodontal and pulpal tissues are discussed.

Mice lacking monocyte chemoattractant protein 1 have enhanced susceptibility to an interstitial polymicrobial infection due to impaired monocyte recruitment

Monocyte chemoattractant protein 1 (MCP-1) is an important chemokine that induces monocyte recruitment in a number of different pathologies, including infection. To investigate the role of MCP-1 in protecting a host from a chronic interstitial polymicrobial infection, dental pulps of MCP-1(-/-) mice and controls were inoculated with six different oral pathogens. In this model the recruitment of leukocytes and the impact of a genetic deletion on the susceptibility to infection can be accurately assessed by measuring the progression of soft tissue necrosis and osteolytic lesion formation. The absence of MCP-1 significantly impaired the recruitment of monocytes, which at later time points was threefold higher in the wild-type mice than in MCP-1(-/-) mice (P < 0.05). The consequence was significantly enhanced rates of soft tissue necrosis and bone resorption (P < 0.05). We also determined that the MCP-1(-/-) mice were able to recruit polymorphonuclear leukocytes (PMNs) to a similar or greater extent as controls and to produce equivalent levels of Porphyromonas gingivalis-specific total immunoglobulin G (IgG) and IgG1. These results point to the importance of MCP-1 expression and monocyte recruitment in antibacterial defense and demonstrate that antibacterial defense is not due to an indirect effect on PMN recruitment or modulation of the adaptive immune response.

Reduction in intracanal bacteria during root canal preparation with and without apical enlargement

AIM

To compare in vitro intracanal bacterial reduction using nickel-titanium rotary instruments with and without apical enlargement.

METHODOLOGY

Thirty-eight palatal roots of maxillary molar teeth, with mature apices were subdivided according to lengths and then randomly assigned to two experimental and one control groups. The roots were sterilized and then reinfected with Enterococcus faecalis, which served as a bacteriological marker. All roots in the experimental groups were prepared in a step-down sequence with engine-driven GT rotary files at 350 rpm. In experimental group A (n = 16) additional apical enlargement to ISO size 35 was performed. In group B (n = 16) a serial step-back technique was followed with no apical enlargement. This was combined in groups A and B with irrigation with NaOCl and EDTA. In the control group (group C, n = 6) irrigation only was carried out, with no mechanical preparation. Samples were then taken from the root canals to determine the numbers of remaining bacteria.

RESULTS

In groups A and B, 15 (94%) and 13 (81%) specimens were rendered bacteria-free, respectively. In the control group C none of the specimens were bacteria-free. There was a significant difference (P < 0.001) in the antibacterial effects of experimental and control regimens. There was, however, no significant difference (P = 0.276) between the preparation methods used in the experimental groups.

CONCLUSIONS

There was no significant difference in intracanal bacterial reduction when Ni-Ti GT rotary preparation with NaOCl and EDTA irrigation was used with or without apical enlargement preparation technique. It may therefore not be necessary to remove dentine in the apical part of the root canal when a suitable coronal taper is achieved to allow satisfactory irrigation of the root canal system with antimicrobial agents.

Vascular endothelial growth factor (VEGF) expression in healthy and inflamed human dental pulps

Vascular endothelial growth factor (VEGF) is a glycoprotein that has the capability to increase vascular proliferation and permeability. VEGF has been found to be expressed in several different types of tumors, and it may contribute to the progression of malignant tumors. Immunostaining for VEGF and factor VIII was performed in normal healthy pulps and in irreversible pulpitis. In both cases the vessels were always positive for VEGF. Our immunohistochemical data show that the expression of VEGF was strongly positive in the inflammatory infiltrate in irreversible pulpitis. VEGF expression in the stromal cells in healthy pulps ranged from 20 to 100% (with a mean of 68.82), and in irreversible pulpitis ranged from 0 to 100% (with a mean of 62.35%); this difference was statistically significant (p = 0.05). This down-regulation in the stromal cells in irreversible pulpitis could be due to the presence, in a low compliance system such as the dental pulp, of inflammatory infiltrate. VEGF is probably a factor implicated in the etiology and progression of pulpitis. The microvessel density in healthy pulps was 90.00 +/- 27.5, while, in irreversible pulpitis, it was 56.68 +/- 21.15. This difference was statistically significant (p = 0.001). The decrease in microvessel density in irreversible pulpitis could be related to failing vascular function and blood flow decrease.

Periapical lesion progression and cytokine expression in an LPS hyporesponsive model

AIM

The purpose of this study was to compare periapical lesion progression and the expression of the bone modulating cytokines IL-1alpha, TNF-alpha, IL-4, IL-6 and IL-11 in periapical lesions of normal and C3H/HeJ (LPS hyporesponsive) mice.

METHODOLOGY

Pulps of both mandibular first molars from C3H/HeJ and BALB/c (normal) mice were exposed and inoculated with normal mouse oral microorganisms for 2, 4, 6, and 8 weeks. After euthanasia, specimens were prepared for histological examination. A quantitative evaluation of the lesional area and immunohistochemical stain counts was performed.

RESULTS

There were no statistically significant differences in progression of periapical lesions for both mouse strains with time (two-factor ANOVA, P > 0.05). The immunohistochemical staining revealed no overall differences between the two strains in levels of expression of the cytokines (P > 0.05). IL-11 expression did not change from control levels in BALB/c mice, but correlated with the expression of IL-6 and IL-4 in C3H/HeJ mice.

CONCLUSION

Responsiveness to LPS may not be significant in the pathogenesis of periapical lesions and in cytokine expression within the lesions, when the lesions are induced by non-specific oral flora.

Implantation of bacteria from human pulpal necrosis and translocation from root canals in gnotobiotic mice

The aim of this study was to determine whether microorganisms recovered from infected human root canals were able to survive and translocate to a local lymph node when experimentally inoculated into the root canal system of germ-free mice. The microorganisms isolated from two patients with pulpal necrosis were inoculated in two groups of experimental animals; group I (Gemella morbillorum) and group II (Bifidobacterium adolescentis, Fusobacterium nucleatum, and Clostridium butyricum). G. morbillorum showed the highest frequency of colonization and translocation to the draining lymph node. In group II only F. nucleatum and C. butyricum colonized and translocated when inoculated in tri-association. When the bacteria from group II were inoculated in monoinfection all three species colonized the root canal of germ-free mice and translocated to the draining lymph node, but with different frequencies. We conclude that selective mechanisms occur in which some bacterial species are fit to survive, multiply, and translocate in the germ-free mouse model.

An immunoelectron-microscopic study of class II major histocompatibility complex molecule-expressing macrophages and dendritic cells in experimental rat periapical lesions

Previous studies have demonstrated that heterogeneous populations of class II major histocompatibility complex (MHC) molecule-expressing non-lymphoid cells, ultrastructurally classified as macrophages and dendritic cell (DC) cell-like cells, comprise the major immune cell population in experimental periapical lesions in rat molars. In this study, the temporal changes in relative proportions of the two types of cells were examined, on the hypothesis that they are involved in different aspects of the pathogenesis of the lesions. The lesions were induced by making surgical pulp exposures in mandibular first molars of 5-week-old Wistar rats. Observation periods were set at 0 (normal), 3, 14, 28, and 56 days. Non-lymphoid cells immunoreactive to OX6 (reactive to class II MHC molecules) were classified as macrophages and DC cell-like cells according to their ultrastructure, and the frequencies of the two types of cells were assessed at each time-point. ED1 (reactive to nearly all macrophages and DCs) was also used to identify macrophages and DC cell-like cells. At 3 days, most OX6+ cells and ED1+ cells in the periapical tissue had the ultrastructural appearance of newly recruited macrophages. At 14 days, when the lesion was actively expanding, there were significantly more OX6+ macrophages than OX6+ DC cell-like cells (P<0.01). However, at 28 days, when lesion expansion had ceased, DC cell-like cells significantly outnumbered OX6+ macrophages (P<0.01); this remained constant at 56 days. Cell-to-cell contact between OX6+ non-lymphoid cells and OX6- lymphocytes, suggesting a functional interaction, was most frequently seen at 28 days. These results support the notion that class II MHC molecule-expressing macrophages play some part in the initial lesion expansion, and suggest that DC cell-like cells may primarily be involved in immune defence against perpetuated antigenic challenges following lesion stabilization.

Effect of interleukin-6 deficiency on the formation of periapical lesions after pulp exposure in mice

OBJECTIVE

The multifunctional cytokine interleukin-6 (IL-6) has actions on multiple cell types, including promotion of the development of immune cells and osteoclasts. Periapical inflammation as the result of root canal infection is characterized by the accumulation of inflammatory cells and bone resorption. The effect of IL-6 on periapical lesion formation after pulpal infection is unknown. We sought to determine whether deletion of IL-6 affects periapical lesion formation after pulp exposure.

METHODS

Molar pulps of homozygous IL-6 knock-out mice (IL-6(-/-), strain B6, 129-Il6tm1Koe ) and wild-type mice (IL-6(+/+)) were exposed, and the mice were killed at 1, 2, 3, 5, and 8 weeks after the exposure. Mouse jaws were decalcified and prepared for histologic examination of periapical lesions.

RESULTS

The IL-6(-/-) mice developed larger periapical lesions more rapidly than did the IL-6(+/+) mice.

CONCLUSIONS

IL-6 deletion promoted periapical lesion development.

Aspartate aminotransferase activity in human healthy and inflamed dental pulps

Aspartate aminotransferase (AST) seems to be an important mediator of inflammatory processes. Its role in the progression and detection of inflammatory periodontal disease has been increasingly recognized in recent years. In the present study AST activity was analyzed in normal healthy human dental pulps, in reversible pulpitis, and in irreversible pulpitis. Enzymatic AST activity showed that the control values for the healthy pulps were 4.8 +/- 0.7 units/mg of pulp tissue. In reversible pulpitis specimens the AST activity increased to 7.98 +/- 2.1 units/mg of pulp tissue. In irreversible pulpitis specimens the values decreased to 2.28 +/- 1.7 units/mg of pulp tissue. Differences between the groups (control versus reversible pulpitis and reversible pulpitis versus irreversible pulpitis) were statistically significant (p = 0.0015). These results could point to a role of AST in the early events that lead to development of pulpal inflammation.

Interleukin-6 deficiency increases inflammatory bone destruction

Periapical bone destruction occurs as a consequence of pulpal infection. In previous studies, we showed that interleukin-1 (IL-1) is the primary stimulator of bone destruction in this model. IL-6 is a pleiotropic cytokine that is induced in these infections and has both pro- and anti-inflammatory activities. In the present study, we determined the role of IL-6 in regulating IL-1 expression and bone resorption. The first molars of IL-6 knockouts (IL-6(-/-)) and wild-type mice were subjected to surgical pulp exposure and infection with a mixture of four common pulpal pathogens, including Prevotella intermedia, Fusobacterium nucleatum, Peptostreptococcus micros, and Streptococcus intermedius. Mice were killed after 21 days, and bone destruction and cytokine expression were determined. Surprisingly, bone destruction was significantly increased in IL-6(-/-) mice versus that in wild-type mice (by 30%; P < 0.001). In a second experiment, the effects of chronic (IL-6(-/-)) IL-6 deficiency and short-term IL-6 deficiency induced by in vivo antibody neutralization were determined. Both IL-6(-/-) (30%; P < 0.001) and anti-IL-6 antibody-treated mice (40%; P < 0.05) exhibited increased periapical bone resorption, compared to wild-type controls. The increased bone resorption in IL-6-deficient animals correlated with increases in osteoclast numbers, as well as with elevated expression of bone-resorptive cytokines IL-1alpha and IL-1beta, in periapical lesions and with decreased expression of the anti-inflammatory cytokine IL-10. These data demonstrate that endogenous IL-6 expression has significant anti-inflammatory effects in modulating infection-stimulated bone destruction in vivo.

Tumor necrosis factor-alpha and transforming growth factor-beta1 in chronic periapical lesions

OBJECTIVE

Proinflammatory cytokines are involved in the pathogenesis of periapical lesions. The purpose of this study was to evaluate the presence of the cytokines tumor necrosis factor-alpha (TNF-alpha) and transforming growth factor-beta(1) (TGF-beta(1)) in periapical pathosis and to determine their relationship to the size of the lesions.

STUDY DESIGN

One tooth from each of 25 patients was root-end resected, and the periapical lesion was collected. The amounts of TNF-alpha and TGF-beta(1) were assessed by enzyme-linked immunosorbent assay.

RESULTS

TGF-beta(1) was detected in 21 of 25 lesions. In samples with scar tissue, no TGF-beta(1) activity was detected. A statistically significant correlation was found between TGF-beta(1) per milligram of tissue and the diameter of the lesions. TNF-alpha was detected in only 2 samples.

CONCLUSIONS

TGF-beta(1) was present in periapical granulomas and cysts but not in lesions with scar tissue. The correlation between the amount of TGF-beta(1) per milligram of tissue and the size of the lesion was significant.

IL-10, but not IL-4, suppresses infection-stimulated bone resorption in vivo

Periapical bone resorption occurs following infection of the dental pulp and is mediated mainly by IL-1alpha in the murine model. The production and activity of IL-1alpha is modulated by a network of regulatory cytokines, including those produced by Th1 (pro-inflammatory) and Th2 (anti-inflammatory) subset T cells. This study was designed to assess the functional role of the Th2-type cytokines IL-4 and IL-10 in infection-stimulated bone resorption in vivo. The dental pulps of the first molars were exposed and infected with a mixture of four common endodontic pathogens, and bone destruction was determined by micro-computed tomography at sacrifice on day 21. The results demonstrate that IL-10(-/-) mice had significantly greater infection-stimulated bone resorption in vivo compared with wild-type mice (p < 0.001), whereas IL-4(-/-) exhibited no increased resorption. IL-10(-/-) had markedly elevated IL-1alpha production within periapical inflammatory tissues (>10-fold) compared with wild type (p < 0.01), whereas IL-4(-/-) exhibited decreased IL-1alpha production (p < 0.05). IL-10 also suppressed IL-1alpha production by macrophages in a dose-dependent fashion in vitro, whereas IL-4 had weak and variable effects. We conclude that IL-10, but not IL-4, is an important endogenous suppressor of infection-stimulated bone resorption in vivo, likely acting via inhibition of IL-1alpha expression.

In vitro evidence that lipopolysaccharide of an oral pathogen leaks from root-end filled teeth

AIM

The ability to achieve a complete apical seal of the root canal system is thought to be important in the success of non-surgical and surgical endodontics. The aim of this study was to establish whether or not root-end filled teeth allow leakage of lipopolysaccharide (LPS) from a known oral pathogen in vitro.

METHODOLOGY

Lipopolysaccharide (LPS) from a virulent strain of Prophyromonas gingivalis (P. gingivalis) (A7436 from patient with refractory periodontitis), was isolated by the Westphall and Jann technique, dialysed extensively, lyophilyzed, resuspended in distilled water and analysed by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). Root canals from 10 teeth were instrumented endodontically and the apical 3 mm of resected roots were filled with gutta-percha. The teeth were mounted in 12 mL polypropylene vials by using sticky wax and root surfaces were covered with two layers of nail varnish. Teeth were filled with 3.3 mg mL-1 LPS and the vials filled with 11 mL of Tris Buffered Saline (TBS) containing 0.05% sodium azide. Both positive and negative controls were run in parallel with the experimental specimens. Aliquots were removed each day and subjected to slot blot analysis to quantitate the amount of LPS that had leaked into the bottom of the vials. The density of slots was analyzed using a laser densitometer and regression analysis was used to generate a standard curve, confidence intervals and experimental values.

RESULTS

The data indicated that teeth obturated apically with gutta-percha leaked, whilst no LPS leakage was detected in teeth covered completely with nail varnish (P < 0.05).

CONCLUSIONS

In vitro teeth with gutta-percha root-end fills can permit leakage of LPS from an identified oral pathogen.

Expression of bone-resorptive and regulatory cytokines in murine periapical inflammation

Periapical bone destruction earlier was shown to be mediated primarily by interleukin (IL)-1alpha in a rat model. The production and action of IL-1alpha is in turn potentially modulated by a network of cytokines, which are produced by infiltrating T-helper type 1 (Th1) and type 2 (Th2) lymphocytes, and resident connective tissue cells within the lesion. This study was designed to examine the kinetics of expression of 10 cytokines in experimentally induced murine periapical lesions, including bone-resorptive [IL-1alpha, tumour necrosis factor alpha (TNFalpha), IL-6, IL-11], Th1-type [IL-2, IL-12, interferon-gamma (IFNgamma)] and Th2-type (IL-4, IL-6, IL-10, IL-13) mediators. Cytokine mRNA expression was assessed qualitatively by reverse transcription-polymerase chain reaction, and cytokine proteins quantified by enzyme-linked immunosorbent assay. IL-1alpha and TNFalpha protein and mRNA were highly expressed, beginning on day 7, and increased to day 28. IL-6 increased to day 14 and then declined, whereas the expression of IL-11 was not modulated by pulp exposure. Most of the Th1-type cytokines, including IL-2, IL-12, and IFNgamma, showed an increase in mRNA and/or protein expression in periapical lesions after pulpal exposure; the expression of Th2-type cytokines was similarly increased, but had declined at the latest time-point (day 28), suggesting possible inhibition by Th1-type mediators. Significant correlations were observed between levels of IL-1alpha and Th1-derived pro-inflammatory mediators IL-2, IL-12, TNFalpha, and IFNgamma. There was a lack of correlation between IL-1alpha and Th2-type anti-inflammatory mediators, including IL-4, -6, and -10. These results indicate that a cytokine network is activated in the periapex in response to bacterial infection, and that Th1-modulated pro-inflammatory pathways may predominate during periapical bone destruction.