Inflammatory cytokine production and specific antibody responses to lipopolysaccharide from endodontopathic black-pigmented bacteria in patients with multilesional periapical periodontitis

An overview of systematic reviews on endotoxins in endodontic infections and the effectiveness of root canal therapy in its removal

Background The objective of this overview was to synthesise the current evidence on the role of endotoxins in endodontics infections and to evaluate the effectiveness of endodontic procedures in its removal using information from published systematic reviews.Methods Electronic databases Medline, Scopus, Embase, Cochrane Library and Google Scholar were searched for reviews published up to July 2021. Systematic reviews on endotoxins based on clinical and/or observational studies were included. The quality of systematic reviews was assessed with the AMSTAR2 tool.Results A total of five systematic reviews were selected, of which two reviews were of high quality. A significantly higher level of endotoxins were found in teeth with exudation, teeth with a previous episode of pain and pain on percussion. Chemomechanical preparation of root canals significantly reduce endotoxin levels. Calcium hydroxide intracanal medication in symptomatic teeth was significantly effective in endotoxin reduction (standardised mean difference -1.051 [95% confidence interval -2.039 to -0.063]; p <0.05; I2 = 83.3%; certainty of evidence = very low). Multiple session root canal treatment in teeth with symptomatic apical periodontitis was significantly more effective in endotoxins/lipopolysaccharides removal than single-session treatment.Conclusion Limited quality of evidence showed a significant association of endotoxins in infected teeth with clinical symptoms. Conventional chemomechanical preparation of root canals and intracanal medication were unable to eliminate endotoxins from the root canal system. Future evolution of effective disinfection therapies is warranted.

Pathological and Therapeutic Approach to Endotoxin-Secreting Bacteria Involved in Periodontal Disease

It is widely recognized that periodontal disease is an inflammatory entity of infectious origin, in which the immune activation of the host leads to the destruction of the supporting tissues of the tooth. Periodontal pathogenic bacteria like Porphyromonas gingivalis, that belongs to the complex net of oral microflora, exhibits a toxicogenic potential by releasing endotoxins, which are the lipopolysaccharide component (LPS) available in the outer cell wall of Gram-negative bacteria. Endotoxins are released into the tissues causing damage after the cell is lysed. There are three well-defined regions in the LPS: one of them, the lipid A, has a lipidic nature, and the other two, the Core and the O-antigen, have a glycosidic nature, all of them with independent and synergistic functions. Lipid A is the "bioactive center" of LPS, responsible for its toxicity, and shows great variability along bacteria. In general, endotoxins have specific receptors at the cells, causing a wide immunoinflammatory response by inducing the release of pro-inflammatory cytokines and the production of matrix metalloproteinases. This response is not coordinated, favoring the dissemination of LPS through blood vessels, as well as binding mainly to Toll-like receptor 4 (TLR4) expressed in the host cells, leading to the destruction of the tissues and the detrimental effect in some systemic pathologies. Lipid A can also act as a TLRs antagonist eliciting immune deregulation. Although bacterial endotoxins have been extensively studied clinically and in a laboratory, their effects on the oral cavity and particularly on periodontium deserve special attention since they affect the connective tissue that supports the tooth, and can be linked to advanced medical conditions. This review addresses the distribution of endotoxins associated with periodontal pathogenic bacteria and its relationship with systemic diseases, as well as the effect of some therapeutic alternatives.

Blockade of fatty acid signalling inhibits lipopolysaccharide-induced macrophage recruitment and progression of apical periodontitis

AIM

To examine the role of palmitic acid in lipopolysaccharide (LPS)-stimulated chemotaxis of macrophages and the potential contribution of saturated fatty acid in signalling during the pathogenesis of apical periodontitis.

METHODOLOGY

J774, a mouse macrophage cell line, was used in the experiments. After treatment with LPS, proteolytic maturation of sterol regulatory element-binding protein-1c (SREBP-1c) and expression of fatty acid synthase (FASN) were examined by Western analysis. Levels of palmitic acid were measured by reverse phase-high performance liquid chromatography-mass spectrometry. Knockdown of SREBP-1c and FASN was accomplished by small interfering RNA technology. Secretion of CC-chemokine ligand 2 (CCL2) and cellular chemotaxis were assessed by enzyme-linked immunosorbent assay and transwell migration assay, respectively. Sulfo-N-succinimidyl oleate (SSO) treatment was used to inhibit fatty acid signalling in vitro and also in a rat model of apical periodontitis. All data were first subjected to Levene's test. In vitro data were then analysed using ANOVA followed by Tukey's multiple comparison test. Data from animal experiments were analysed by independent t-tests. The significant level was set at 0.05.

RESULTS

LPS stimulated proteolytic maturation of SREBP-1c and FASN expression in macrophages and significantly enhanced palmitic acid synthesis (P < 0.05). Knockdown of SREBP-1c attenuated LPS-enhanced FASN expression. Knockdown of FASN significantly suppressed LPS-enhanced palmitic acid synthesis (P < 0.05). LPS and exogenous palmitic acid significantly enhanced CCL2 secretion and macrophage chemotaxis (all P < 0.05). Inhibition of FASN expression significantly alleviated LPS-augmented CCL2 secretion (P < 0.05). SSO significantly suppressed CCL2 secretion and macrophage chemotaxis augmented by LPS and palmitic acid (all P < 0.05). In a rat model of induced apical periodontitis, SSO treatment significantly attenuated progression of apical periodontitis and macrophage recruitment (all P < 0.05).

CONCLUSIONS

LPS/SREBP-1c/FASN/palmitic acid signalling contributed to tissue destruction caused by bacterial infection. Modulation of lipid metabolism and signalling may be helpful for the management of apical periodontitis.

Comparison of the effectiveness of single- and multiple-sessions disinfection protocols against endotoxins in root canal infections: systematic review and meta-analysis

This systematic review (SR) addressed the following common clinical question: What is more effective in reducing or eliminating endotoxin in endodontic infections—single or multiple-session treatments using calcium hydroxide medications? Literature searches of Medline/PubMed, Embase, Cochrane Library, Scielo, Science Direct, Web of Knowledge, Scopus, and Google Scholar databases. Two reviewers independently assessed the eligibility for inclusion, extracted data, and evaluated the quality of the studies using the risk of bias tools. Electronic searches resulted in 358 articles, of which 32 studies were included for full-text assessment, and nine were included in this review. Meta-analysis pooling all the nine studies revealed lower levels of endotoxin for multiple-session treatment (P < 0.001). The sub-group analysis indicated no difference between single-session and 7 days of Ca(OH)₂ medication (SMD − 0.32; P = 0.22). However, 14-days (I² = 80.5%, P < 0.001) and 30-days (I² = 78.9%, P < 0.01) of Ca(OH)₂ medication was more effective than single-session treatment (both, p < 0.001). Overall, Overall, this SR provides evidence to support that multiple-session disinfection protocols with the placement of Ca(OH)₂ medications are more effective in reducing the levels of endotoxin from root canal infections compared to single-session when applied for 14 and 30 days.

Resolution of Nasal Sinus Tract after Endodontic Therapy: A Case Report with Microbial Analysis

This case report describes the resolution of a 20-year misdiagnosed nasal sinus tract after root canal therapy with multiple sessions of calcium hydroxide (Ca[OH]₂) intracanal medication. Clinical evaluation, including diagnostic testing and sinus tract tracing, was performed followed by a cone-beam computed tomographic scan and 3-dimensional reconstruction of the apical lesion. Bacteria and endotoxin analyses were performed from the nasal sinus tract and paired root canal infection before (s1) and after instrumentation (s2) and after 7 (s3), 14 (s4), and 21 (s5) days of Ca(OH)₂ medication. The bacteria analysis was performed using the checkerboard DNA-DNA hybridization method and endotoxin quantified by the limulus amebocyte lysate method. A similar microbiota profile was found in the sinus tract and paired root canal infection. No target bacterial species were detected in the root canal at s2, s3, and s5. In contrast, Actinomyces israellii and Eubacterium nodatum were detected at s4. Differences in bacterial detection were found between s1 × s2, s3 × s4, and s4 × s5 (all P < .05). Endotoxin was detected in the root canal at all sampling times. Differences in the levels of endotoxin were found between s1 × s2, s2 × s3, and s3 × s4 (all P < .05).The bacterial analysis revealed similar microbiota profiles present in the nasal sinus tract and paired root canal infection with the participation of a wide variety of gram-positive and -negative species. Additionally, root canal therapy with multiple sessions of Ca(OH)₂ intracanal medication for 21 days was effective in disinfecting the root canal system and resolving the nasal sinus tract.

Does Calcium Hydroxide Reduce Endotoxins in Infected Root Canals? Systematic Review and Meta-analysis

INTRODUCTION

The purpose of this study was to evaluate the potential of endotoxin reduction by comparing the number of lipopolysaccharides (LPSs) before and after the use of calcium hydroxide (Ca[OH]₂) as intracanal medication (ICM).

METHODS

Searches were performed up to June 2020. Clinical and experimental studies comparing the amount of LPSs before and after the use of Ca(OH)₂ as ICM in infected root canals were included. Risks of bias assessment and data extraction were performed. Meta-analysis was conducted by subgrouping according to Ca(OH)₂, the presence of an antimicrobial substance (AS), irrigant solution during chemomechanical preparation (CMP), and the incidence of LPS reduction. The certainty of evidence was determined by the Grading of Recommendations Assessment, Development and Evaluation approach.

RESULTS

Nine studies were included in the qualitative synthesis and 7 in the meta-analysis. Three articles had low risk of bias (RB), 1 had moderate RB, 2 had high RB, and 3 "some concerns." Overall, Ca(OH)₂, with or without AS, reduced mean LPSs before CMP (standardized mean difference [SMD] = -1.087 [confidence interval {CI}, -1.453 to -0.721], P < .001, I² = 58.7%) and after CMP (SMD = -0.919 [CI, -1.156 to -0.682], P < .001, I² = 24.7%). Considering the irrigant solutions, the overall results showed a reduction before (SMD = -1.053 [CI, -1.311 to -0.795], P < .001, I² = 58.7%) and after CMP (SMD = -0.938 [CI, -1.147 to -0.729], P < .001, I² = 24,6%). Analyses presented very low certainty of evidence. The incidence of LPS reduction was 98.9% and 61.7% for Ca(OH)₂ with and without AS, respectively.

CONCLUSIONS

Ca(OH)₂ reduces endotoxin levels when used as ICM but is unable to eliminate LPSs completely independent of the irrigating solution used with very low certainty of evidence.

Effect of lipopolysaccharide on the adherence of human umbilical vein endothelial cells (HUVEC) on a natural substrate

 Polymers are often contaminated with lipopolysaccharides also known as endotoxins. Even small amounts of endotoxins can have strong effects on endothelial cell function so that the endothelialisation of cardiovascular implants might be hampered. An open question is how endothelial cells seeded on a body foreign substrate respond to shear load after adding Lipid A (LPA), the domain, which is responsible for much of the toxicity of gram-negative bacteria, and whether morphological changes of endothelial cells occur.LPA supplementation to the culture medium in increasing concentrations (5, 25 and 50μg/ml) resulted in progressive reductions of the density of adherent HUVEC after shear load (p < 0.001). 48% of the HUVEC in control cultures (0μg/ml LPA) were still adherent after 2 hours of shearing at 6 dyne/cm2, while 80 minutes after addition of 50μg/ml LPA, 88% of the HUVEC had already detached from the substrate and after 100 minutes no more HUVEC were attached.The results demonstrate that endotoxins are of extreme importance for the behavior of HUVEC and that in vivo pathologies can be increasingly simulated in vitro.

Tissue reaction to Aroeira (Myracrodruon urundeuva) extracts associated with microorganisms: an in vivo study

Based on aroeira's (Myracrodruon urundeuva) antimicrobial activity and a future trend to compose intracanal medication, the aim of this study was to assess in vivo inflamatory tissue response to the extracts by edemogenic and histological analysis containing inactivated facultative and anaerobic microorganisms. For edema quantification, eighteen animals were divided into three groups (n = 3, periods: 3 and 6 hours) and 0.2 mL of 1% Evans blue per 100 g of body weight was injected into the penile vein under general anesthesia. After 30 min the animals received a subcutaneous injection in the dorsal region of aqueous or ethanolic extract of aroeira or saline (control) containing inactivated bacteria. Samples were collected, immersed in formamide for 72h, and evaluated by spectrophotometry (630 m). For histological analysis, polyethylene tubes with the extracts were implanted in the dorsal of 30 male rats. Analysis of the fibrous capsule and inflammatory infiltrate were performed after 7 and 30 days. The aqueous extract group induced less edema in both postoperative periods compared to the other groups, but the differences were not significant (p > 0.05). Tissue repair was significantly better after 30 days than after 7 days (p < 0.01). The aqueous solution showed less inflammatory response than the ethanolic solution (p < 0.05), with tendency for better results than control after 7 days. After 30 days, the response to both extracts was similar to control. The aqueous and ethanolic aroeira extracts containing inactivated microorganisms showed a trend for better results than saline, even when associated with microorganisms, and facilitated the tissue repair process.

A potential role for the silent information regulator 2 homologue 1 (SIRT1) in periapical periodontitis

AIM

To investigate the role played by silent information regulator 2 homologue 1 (SIRT1) during angiogenesis of periapical periodontitis.

METHODOLOGY

Periapical granulomas were subjected to dual-colour immunofluorescence imaging and real-time polymerase chain reactions assaying the expression levels of SIRT1, vascular endothelial growth factor (VEGF) and VE-cadherin. The association between Ki-67 and SIRT1 expression was also examined. Human umbilical vein endothelial cells (HUVECs) were treated with a combination of lipopolysaccharide and resveratrol (a SIRT1 activator) or sirtinol (a SIRT1 inhibitor); and the levels of mRNAs encoding SIRT1, VEGF and VE-cadherin were determined. HUVEC tube formation was assayed in the presence of resveratrol or sirtinol. The Mann-Whitney U-test or the Tukey-Kramer test was used for statistical analysis.

RESULTS

Ki-67-expressing cells, including endothelial cells, lay adjacent to SIRT1-expressing cells in periapical granulomas. In addition, SIRT1-expressing cells were detected adjacent to VEGF-expressing cells and VEGF- or VE-cadherin-expressing endothelial cells. SIRT1, VEGF and VE-cadherin mRNA expression levels in periapical granulomas were significantly higher (P = 0.0054, 0.0090 and 0.0090, respectively) than those in healthy gingival tissues. HUVECs treated with resveratrol exhibited significantly higher expression of mRNAs encoding SIRT1, VEGF and VE-cadherin (P = 0.0019, 0.00005 and 0.0045, respectively) compared with controls, but sirtinol inhibited such expression. Resveratrol caused HUVECs to form tube-like structures, whilst sirtinol inhibited this process.

CONCLUSIONS

These findings suggest that SIRT1 may stimulate angiogenesis in periapical granulomas by triggering the proliferation of endothelial cells and inducing VEGF and VE-cadherin expression.

Chemokines in Oral Inflammatory Diseases: Apical Periodontitis and Periodontal Disease

The inflammatory oral diseases are characterized by the persistent migration of polymorphonuclear leukocytes, monocytes, lymphocytes, plasma and mast cells, and osteoblasts and osteoclasts. In the last decade, there has been a great interest in the mediators responsible for the selective recruitment and activation of these cell types at inflammatory sites. Of these mediators, the chemokines have received particular attention in recent years. Chemokine messages are decoded by specific receptors that initiate signal transduction events, leading to a multitude of cellular responses, including chemotaxis and activation of inflammatory and bone cells. However, little is known about their role in the pathogenesis of inflammatory oral diseases. The purpose of this review is to summarize the findings regarding the role of chemokines in periapical and periodontal tissue inflammation, and the integration, into experimental models, of the information about the role of chemokines in human diseases.

Intragingival injection of Porphyromonas gingivalis-derived lipopolysaccharide induces a transient increase in gingival tumour necrosis factor-α, but not interleukin-6, in anaesthetised rats

This study used in vivo microdialysis to examine the effects of intragingival application of lipopolysaccharide (LPS) derived from Porphyromonas gingivalis (Pg-LPS) on gingival tumour necrosis factor (TNF)-α and interleukin (IL)-6 levels in rats. A microdialysis probe with an injection needle attached to the surface of the dialysis membrane was implanted into the gingiva of the upper incisor. For comparison, the effects of LPS derived from Escherichia coli (Ec-LPS) on IL-6 and TNF-α levels were also analysed. Pg-LPS (1 μg/1 μL) or Ec-LPS (1 or 6 μg/1 μL) was applied by microsyringe, with gingival dialysates collected every hour. Enzyme-linked immunosorbent assay (ELISA) revealed that gingival dialysates contained approximately 389 pg·mL⁻¹ of IL-6 basally; basal TNF-α levels were lower than the detection limit of the ELISA. Pg-LPS failed to alter IL-6 levels but markedly increased TNF-α levels, which remained elevated for 2 h after treatment. Neither IL-6 nor TNF-α were affected by Ec-LPS. Reverse transcriptase-polymerase chain reaction (RT-PCR) analysis revealed that the gingiva expresses Toll-like receptor (TLR) 2 and TLR4 mRNA. Immunohistochemical examination showed that TLR2 and TLR4 are expressed by gingival epithelial cells. The present study provides in vivo evidence that locally applied Pg-LPS, but not Ec-LPS, into the gingiva transiently increases gingival TNF-α without affecting IL-6. The present results suggest that TLR2 but not TLR4 expressed on gingival epithelial cells may mediate the Pg-LPS-induced increase in gingival TNF-α in rats.

Calcium Hydroxide Suppresses Porphyromonas endodontalis Lipopolysaccharide–induced Bone Destruction

Porphyromonas endodontalis and its main virulence factor, lipopolysaccharide (LPS), are associated with the development of periapical diseases and alveolar bone loss. Calcium hydroxide is commonly used for endodontic therapy. However, the effects of calcium hydroxide on the virulence of P. endodontalis LPS and the mechanism of P. endodontalis LPS–induced bone destruction are not clear. Calcium hydroxide rescued the P. endodontalis LPS–suppressed viability of MC3T3-E1 cells and activity of nuclear factor-κB (NF-κB) in these cells, resulting in the reduced expression of interleukin-6 and tumor necrosis factor-α. In addition, calcium hydroxide inhibited P. endodontalis LPS–induced osteoclastogenesis by decreasing the activities of NF-κB, p38, and ERK1/2 and the expression of nuclear factor of activated T-cell cytoplasmic 1 in RAW264.7 cells. Calcium hydroxide also rescued the P. endodontalis LPS–induced osteoclastogenesis and bone destruction in mouse calvaria. Taken together, our present results indicate that calcium hydroxide suppressed bone destruction by attenuating the virulence of P. endodontalis LPS on bone cells.

Clinical investigation of the effect of calcium hydroxide intracanal dressing on bacterial lipopolysaccharide reduction from infected root canals

The purpose of this clinical study was to determine the effect of 7 day intracanal dressing with calcium hydroxide on the amount of bacterial lipopolysaccharide (LPS; endotoxin) in human teeth with necrotic and infected pulp and apical periodontitis. Twenty-five single-rooted teeth with necrotic pulps and apical periodontitis were selected. Samples were collected before (S1), after root canal preparation (S2) and after 7 day intracanal dressing with calcium hydroxide (S3). The limulus amoebocyte lysate assay was used to quantify LPS. LPS was present in 100% of the root canals before (S1), after preparation (S2) and after 7 day intracanal dressing (S3). A significant reduction, equal to 29.54%, was found after root canal preparation (P < 0.05). A significant difference (equal to 25.26% reduction) was also detected between S2 and S3 (P < 0.05). Total endotoxin reduction (S3 compared with S1) was found to be 47.34%. Endotoxin concentration of the infected root canals was reduced after root canal preparation and also after 7 days of dressing of canals with calcium hydroxide; however, relatively high values of endotoxin remained in the root canals.

The role of IL-6 on apical periodontitis: a systematic review

The aim of this review was to examine current knowledge of the role of interleukin-6 (IL-6) in apical periodontitis (AP) pathogenesis as an inflammatory or pro-inflammatory cytokine. It also looked at whether IL-6 could serve as a measure for differential diagnosis or as a biomarker that can further predict the progression of bone resorption. A systematic review relating to AP and IL-6 was made via PubMed, BIOSIS, Cochrane, EMBASE and Web of Science databases using keywords and controlled vocabulary. Two independent reviewers first screened titles and abstracts and then the full texts. The reference lists of the identified publications were examined for additional titles. Eighteen papers were studied in total. In vitro studies (n = 6) revealed that IL-6 is present in AP, and its levels are proportional to the size of the periapical lesions. Neutrophils and macrophages resident in these lesions can produce IL-6 in vitro after a bacterial stimulus. Animal studies (n = 5) showed that IL-6 is present in AP and that osteoblasts can produce IL-6 in vivo. On the other hand, two studies using IL-6 knockout mice revealed larger periapical lesions when compared with control groups, demonstrating IL-6's role as an anti-inflammatory cytokine. In human studies (n = 7), IL-6 was identified in AP, and its levels were higher in symptomatic, epithelialized and large lesions than in asymptomatic and small lesions. These data lead to the conclusion that IL-6 may play a pro-inflammatory role, increasing its levels and reabsorbing bone in the presence of infections. When IL-6 is not present, other cytokines such as IL-1 and TNF-α induce bone resorption. Further studies about the relationship between AP development and the cytokine network must be performed to establish the exact role of each cytokine in the inflammatory process.

In vitro evaluation of the action of irrigating solutions associated with intracanal medications on Escherichia coli and its endotoxin in root canals

OBJECTIVE

The purpose of this study was to evaluate the efficacy of auxiliary chemical substances and intracanal medications on Escherichia coli and its endotoxin in root canals.

MATERIAL AND METHODS

Teeth were contaminated with a suspension of E. coli for 14 days and divided into 3 groups according to the auxiliary chemical substance used: G1) 2.5% sodium hypochlorite (NaOCl); G2) 2% chlorhexidine gel (CLX); G3) pyrogen-free solution. After, these groups were subdivided according to the intracanal medication (ICM): A) Calcium hydroxide paste (Calen®), B) polymyxin B, and C) Calcium hydroxide paste+2% CLX gel. For the control group (G4), pyrogen-free saline solution was used without application of intracanal medication. Samples of the root canal content were collected immediately after biomechanical preparation (BMP), at 7 days after BMP, after 14 days of intracanal medication activity, and 7 days after removal of intracanal medication. The following aspects were evaluated for all collections: a) antimicrobial activity; b) quantification of endotoxin by the Limulus Amebocyte Lysate test (LAL). Results were analyzed by the Kruskal-Wallis and Dunn's tests at 5% significance level.

RESULTS

The 2.5% NaOCl and CLX were able to eliminate E. coli from root canal lumen and reduced the amount of endotoxin compared to saline.

CONCLUSIONS

It was concluded that 2.5% NaOCl and CLX were effective in eliminating E. coli. Only the studied intracanal medications were to reduce the amount of endotoxin present in the root canals, regardless of the irrigant used.

Histological analysis of the association between formocresol and endotoxin in the subcutaneous tissue of mice

This study performed a histological analysis of the effect of formocresol associated to endotoxin (LPS) in the subcutaneous connective tissue of mice. Ninety mice were randomly assigned to 3 groups (n=30). Each animal received one plastic tube implant containing endotoxin solution (10 mg/mL), formocresol (original formula) or a mixture of endotoxin and formocresol. The endotoxin and formocresol groups served as controls. The periods of analysis were 7, 15 and 30 days. At each experimental period, tissue samples were collected and submitted to routine processing for histological analysis. Endotoxin and formocresol produced necrosis and chronic inflammation at 7 and 15 days. At 30 days, the endotoxin group showed no necrosis, while in the formocresol group necrosis persisted. The formocresol-endotoxin association produced necrosis and chronic inflammation in the same way as observed with formocresol at all experimental periods. In conclusion, formocresol seems not to be able to inactive the toxic effects of endotoxin in connective tissues.

Eugenol suppressed the expression of lipopolysaccharide-induced proinflammatory mediators in human macrophages

Eugenol is commonly used as an analgesic agent during acute pulpitis and is a major component of root canal sealers. Despite the frequent applications of eugenol in the practice of dentistry, little is known about the role of eugenol under the status of inflammation. This study was aimed to investigate the influence of eugenol on human macrophages (U937) under the stimulation of lipopolysaccharide (LPS). Eugenol was shown to block the release of the bone resorbing mediators, including interleukin-1beta (IL-1beta), tumor necrosis factor-alpha (TNF-alpha), and prostaglandin E2 from LPS-stimulated macrophages. In contrast, eugenol alone did not alter the expression levels of these proinflammatory mediators in macrophages. Consistent with downregulation of bone-resorbing mediators, eugenol suppressed the messenger RNA expression of LPS-induced IL-1beta, TNF-alpha, and cyclooxygenase-2 in macrophages. The results suggest a potential anti-inflammatory effect of eugenol in the acute inflamed pulps and apical periodontitis.

Quantification of endotoxins in necrotic root canals from symptomatic and asymptomatic teeth

The purpose of this investigation was to quantify the concentration of endotoxin in necrotic root canals and investigate the possible relationship between the concentration of endotoxin and endodontic signs and symptoms. Samples were collected from root canals of 50 patients requiring endodontic treatment due to necrosis of the pulpal tissue. Anaerobic techniques were used to determine the number of c.f.u. in each sample. A quantitative chromogenic Limulus amoebocyte lysate assay was used to measure the concentration of endotoxin in each sample. The presence of c.f.u. was detected by culture in all samples (range 10(2)-5x10(6)). In samples from cases of patients with spontaneous pain, the mean c.f.u. was 1.43x10(6) while in asymptomatic cases it was 9.1x10(4). Endotoxin was present in all the samples studied [range 2390.0-22100.0 endotoxin units (EU) ml-1]. The mean concentration of endotoxin in samples from patients with spontaneous pain was 18540.0 EU ml-1 while in asymptomatic cases it was 12030.0 EU ml-1. Asymptomatic cases generally had lower levels of endotoxin (i.e. a negative association). A positive association was found between endotoxin and symptomatic cases (e.g. spontaneous pain, tenderness to percussion, pain on palpation, swelling and purulent exudates). This study showed that endotoxin is present in high concentrations in root canals of symptomatic teeth. There was a positive correlation between the concentration of endotoxin in the root canal and the presence of endodontic signs and symptoms.

Porphyromonas gingivalis lipopolysaccharide induces shedding of syndecan-1 expressed by gingival epithelial cells

Syndecans are constitutively shed from growing epithelial cells as the part of normal cell surface turnover. However, increased serum levels of the soluble syndecan ectodomain have been reported to occur during bacterial infections. The aim of this study was to evaluate the potential of lipopolysaccharide (LPS) from the periodontopathogen Porphyromonas gingivalis to induce the shedding of syndecan-1 expressed by human gingival epithelial cells. We showed that the syndecan-1 ectodomain is constitutively shed from the cell surface of human gingival epithelial cells. This constitutive shedding corresponding to the basal level of soluble syndecan-1 ectodomain was significantly increased when cells were stimulated with P. gingivalis LPS and reached a level comparable to that caused by phorbol myristic acid (PMA), an activator of protein kinase C (PKC) which is well known as a shedding agonist. The syndecan-1 shedding was paralleled by pro-inflammatory cytokine interleukin-1 beta (IL-1beta), IL-6, IL-8, and tumor necrosis factor alpha (TNF-alpha) release. Indeed, secretion of IL-1beta and TNF-alpha increased following stimulation by P. gingivalis LPS and PMA, respectively. When recombinant forms of these proteins were added to the cell culture, they induced a concentration-dependent increase in syndecan-1 ectodomain shedding. A treatment with IL-1beta converting enzyme (ICE) specific inhibitor prevented IL-1beta secretion by epithelial cells stimulated by P. gingivalis LPS and decreased the levels of shed syndecan-1 ectodomain. We also observed that PMA and TNF-alpha stimulated matrix metalloproteinase-9 secretion, whereas IL-1beta and P. gingivalis LPS did not. Our results demonstrated that P. gingivalis LPS stimulated syndecan-1 shedding, a phenomenon that may be mediated in part by IL-1beta, leading to an activation of intracellular signaling pathways different from those involved in PMA stimulation.

Importance of bacterial endotoxin (LPS) in endodontics

New knowledge of the structure and biological activity of endotoxins (LPS) has revolutionized concepts concerning their mechanisms of action and forms of inactivation. Since the 1980's, technological advances in microbiological culture and identification have shown that anaerobic microorganisms, especially Gram-negative, predominate in root canals of teeth with pulp necrosis and radiographically visible chronic periapical lesions. Gram-negative bacteria not only have different factors of virulence and generate sub-products that are toxic to apical and periapical tissues, as also contain endotoxin (LPS) on their cell wall. This is especially important because endotoxin is released during multiplication or bacterial death, causing a series of biological effects that lead to an inflammatory reaction and resorption of mineralized tissues. Thus, due to the role of endotoxin in the pathogenesis of periapical lesions, we reviewed the literature concerning the biological activity of endotoxin and the relevance of its inactivation during treatment of teeth with pulp necrosis and chronic periapical lesion.

Effect of different irrigation solutions and calcium hydroxide on bacterial LPS

AIM

To evaluate the effect of biomechanical preparation with different irrigating solutions and calcium hydroxide dressing in dog root canals containing bacterial endotoxin (lipopolysaccharides; LPS).

METHODOLOGY

One hundred and forty premolar roots from seven dogs were filled with Escherichia coli LPS for 10 days (three roots were lost during histological processing). The following irrigating solutions were used for biomechanical preparation: 1% (group I, n = 20), 2.5% (group II, n = 19) and 5% sodium hypochlorite (group III, n = 19), 2% chlorhexidine digluconate (group IV, n = 20) and physiological saline solution (group V, n = 19). In group VI (n = 20), the LPS solution was maintained in the root canal during the entire experiment and in group VII (n = 20), after biomechanical preparation with saline solution, the root canals were filled with a calcium hydroxide dressing (Calen; control). After 60 days, the animals were sacrificed and the following parameters of periapical disease were evaluated: (a) inflammatory infiltrate, (b) periodontal ligament thickness, (c) cementum resorption and (d) bone resorption. Scores were given and data were analysed statistically with the Kruskal-Wallis and Dunn tests (P < 0.05).

RESULTS

Histopathological evaluation showed that groups I-VI had more inflammatory infiltrate, greater periodontal ligament thickening and greater cementum and bone resorption (P < 0.05) compared to group VII, which received the calcium hydroxide intracanal dressing.

CONCLUSIONS

Biomechanical preparation with the irrigating solutions did not inactivate the effects of the endotoxin but the calcium hydroxide intracanal dressing did appear to inactivate the effects induced by the endotoxin in vivo.

Production of macrophage inflammatory protein (MIP)-1alpha and MIP-1beta by human polymorphonuclear neutrophils stimulated with Porphyromonas endodontalis lipopolysaccharide

This study was undertaken to investigate the capacity of polymorphonuclear neutrophils (PMNs) to secrete Macrophage Inflammatory Protein (MIP)-1alpha and MIP-1beta after stimulation with Porphyromonas endodontalis lipopolysaccharide (LPS). Escherichia coli LPS was used as a positive control. Venous blood was collected and PMNs were isolated from healthy volunteers. Cells were cultured with various concentrations of LPS for different periods of time. Cell supernatants were assayed by enzyme-linked immunosorbent assay. The levels of chemokine secretion in PMNs stimulated with each LPS were found to be significantly higher than in the unstimulated control cells (p < 0.05), and this expression occurred in a time- and dose-dependent manner. E. coli LPS induced higher levels of cytokines than P. endodontalis LPS. These findings demonstrated that P. endodontalis LPS is capable of stimulating PMNs to produce chemotactic cytokines and suggested that PMNs stimulated with P. endodontalis LPS may play a crucial role in the inflammatory and immunopathological reactions of pulpal and periapical diseases.

Evidence for a role of mitogen-activated protein kinases in proliferating and differentiating odontogenic epithelia of inflammatory and developmental cysts

OBJECTIVE

The activation of intracellular signaling cascades involving serine/threonine kinases ERK1/2 has been variably reported either to stimulate or inhibit epithelial cell differentiation in response to extracellular signals. The purpose of our study was to determine the distribution of the signaling molecule ERK1 and its activated form pERK1/2 in the epithelial components of developmental and inflammatory odontogenic cysts in relation to parameters of differentiation and proliferation.

STUDY DESIGN

Thirty samples of dental follicles, dentigerous cysts, and radicular cysts were immunostained with antibodies to ERK1, pERK1/2, and proliferating cell nuclear antigen (a marker for proliferation). The tissues were subclassified according to the pattern of histomorphological differentiation (ie, squamous differentiation) and the proliferation rate of their epithelial components. The significance of differences in the proportion of ERK1- and pERK1/2-expressing cells among the tissue groups was determined by chi-square analysis or Fisher's exact test.

RESULTS

ERK1 and pERK1/2 were found to be expressed in a significantly higher proportion of cells with differentiated and highly proliferating epithelial components, as compared with those of nondifferentiated, quiescent epithelial rests. The epithelium of radicular cysts exhibited the highest proportion of pERK1/2-positive cells. In both dentigerous and radicular cyst samples, pERK1/2 expression was significantly higher in the inflamed tissues.

CONCLUSIONS

These data demonstrate that ERK1 and its active form pERK1/2 are associated with differentiating and actively proliferating epithelia of odontogenic cysts, and are consistent with pERK1/2 involvement in the activation of odontogenic epithelia in response to inflammation.

Effect of calcium hydroxide on bacterial endotoxin in vivo

The aim of this study was the histopathological evaluation of apical and periapical tissues in dog teeth that were submitted to bacterial endotoxin, associated or not with calcium hydroxide. After removal of the pulp from 60 premolars, the teeth were divided into four groups and were filled with bacterial endotoxin (group 1), bacterial endotoxin plus calcium hydroxide (group 2), saline solution (group 3), or had induced periapical lesions with no treatment (group 4). After 30 days, animals were killed and the teeth processed histologically. The inflammatory infiltrate, the thickness of the periodontal ligament, and the presence of resorption areas were similar for groups 1 and 4. Groups 2 and 3 were similar to each other. It can be concluded that the bacterial endotoxin caused a periapical lesion and that calcium hydroxide detoxified the lipopolysaccharides in vivo.

Determination of endotoxins in the vital pulp of human carious teeth: association with pulpal pain

OBJECTIVES

The aims of this investigation were to determine the presence or absence of endotoxins in the pulp of symptomatic and symptom-free human carious teeth, to quantify the amount of endotoxins present, and to associate the presence of endotoxins with the acute pulpal pain.

MATERIAL AND METHODS

Pulpal tissue was sampled from 28 single-rooted carious teeth (15 symptomatic, 13 symptom-free) derived from 28 patients. Samples were also taken from the pulp of 5 noncarious control teeth. During sampling an effort was made to collect an equal weight of pulpal tissue in all cases (approximately 8 mg). The extraction of endotoxins was performed with the use of phenol-water. The assay and quantitative determination of endotoxins was performed with the use of a limulus lysate test. The data were analyzed statistically by using the independent t test.

RESULTS

Endotoxins were detected in pulpal tissues of all carious teeth in the symptomatic (mean average, 0.15773 ng/mL; SD = 0.045811) and symptom-free group (mean average, 0.10723 ng/mL; SD = 0.010925). In noncarious control teeth, endotoxins were not detected. The presence of endotoxins was significantly higher in the group of symptomatic teeth than in the group of symptom-free teeth (P <.001).

CONCLUSIONS

The presence of endotoxins in the pulpal tissue of all the carious teeth indicates that they may play a major role in the pathogenesis of human pulpal diseases. Since a significantly higher level of endotoxins was detected in the pulp of symptomatic carious teeth than in that of symptom-free carious teeth, an association of endotoxins levels with severity of pulpal pain is probable.