MyD88 knockout mice develop initial enlarged periapical lesions with increased numbers of neutrophils

The effects of NLRP3 inflammasome inhibition or knockout in experimental apical periodontitis induced in mice

OBJECTIVE

To evaluate the effects of NLRP3 inflammasome inhibition or knockout in experimental apical periodontitis (AP) induced in mice.

METHODS

The experimental AP was induced by pulpal exposure. To evaluate NLRP3-specific inhibitor medication (MCC950), WT mice received intraperitoneal injections, while the control received PBS (n = 10). In addition, to evaluate NLRP3 knockout, 35 wild-type (WT) and 35 NLRP3-/- mice were divided into a control group (without pulpal exposure, n = 5) and three experimental groups: after 2, 14 and 42 days after pulpal exposure (n = 10). Microscopic and molecular analyzes were carried out using a significance level of 5%.

RESULTS

Exposure to MCC950 did not affect the periapical lesion size after 14 days (P = 0.584). However, exposed mice had a lower expression of IL-1β, IL-18 and caspase-1 (P = 0.010, 0.016 and 0.002, respectively). Moreover, NLRP3-/- mice showed a smaller periapical lesion after 14 and 42 days (P = 0.023 and 0.031, respectively), as well as a lower expression of IL-1β after 42 days (P < 0.001), of IL-18 and caspase-1 after 14 (P < 0.001 and 0.035, respectively) and 42 days (P = 0.002 and 0.002, respectively). NLRP3-/- mice also showed a lower mRNA for Il-1β, Il-18 and Casp1 after 2 (P = 0.002, 0.036 and 0.001, respectively) and 14 days (P = 0.002, 0.002 and 0.001, respectively).

CONCLUSIONS

NLRP3 inflammasome inhibition or knockout can attenuate the inflammatory events that result in the periapical lesion (AP) formation after pulpal exposure in mice.

CLINICAL RELEVANCE

The NLRP3 inflammasome may be a therapeutic target for AP, and new approaches may verify the impact of its inhibition (through intracanal medications or filling materials) on the bone repair process and treatment success.

TLR2 agonist prevents the progression of periapical lesions in mice by reducing osteoclast activity and regulating the frequency of Tregs

AIM

To evaluate the role of regulatory T lymphocytes (Tregs) in the presence or absence of the synthetic ligand Pam3Cys during the progression of periapical lesion in wild-type (WT) and toll-like receptor 2 knockout (TLR2KO) mice.

METHODOLOGY

A total of 130 C57BL/6 male WT and TLR2KO mice were allocated into control (n = 5) and experimental (periapical lesion induction) (n = 10) groups. In specific groups (WT+Pam3cys and TLR2KO+Pam3cys), the synthetic ligand Pam3cys was administered intraperitoneally every 7 days, according to the experimental period (14, 21 and 42 days). At the end of those periods, the animals were euthanized, and the mandible and the spleen were submitted to histotechnical processing. Mandible histological sections were analysed by haematoxylin and eosin, TRAP histoenzymology and immunohistochemistry (FOXP3, RANK, RANKL and OPG). Spleen sections were analysed by immunohistochemistry (FOXP3).

RESULTS

The inflammatory infiltrate and bone resorption were more intense in the TLR2KO group compared to the WT group. The animals that received the Pam3cys had smaller periapical lesions when compared to the animals that did not receive the ligand (p < .05). TLR2KO animals showed a significant increase in the number of osteoclasts when compared to TLR2KO+Pam3cys group (p < .05). At 21 days, the WT+Pam3cys group had a lower number of osteoclasts when compared to the WT animals (p = .02). FOXP3 expression was more intense in the WT+Pam3cys groups when compared to the WT animals in the 42 days (p = .03). In the spleen analysis, the WT+Pam3cys group also had a higher expression of FOXP3 when compared to the WT animals at 14 and 42 days (p = .02). Concerning RANKL, there was a reduction in staining in the KOTLR2+Pam3cys groups at 21 and 42 days (p = .03) and a higher binding ratio between RANK/RANKL in animals that did not receive the ligand.

CONCLUSION

Administration of the Pam3cys increased the proliferation of Tregs, showed by FOXP3 expression and prevented the progression of the periapical lesion in WT mice. On the other hand, in the TLR2KO animals, Treg expression was lower with larger areas of periapical lesions. Finally, systemic administration of the Pam3cys in KO animals was able to limit the deleterious effects of the absence of the TLR2 receptor.

Effect of systemic administration of Bifidobacterium animalis subsp. lactis HN019 on apical periodontitis

This study aimed to evaluate the effect of Bifidobacterium animalis subsp. lactis (B. lactis) HN019 in drinking water on the development of apical periodontitis (AP) in rats. In total 60 animals were divided into a control group (sound teeth); Group I - regular water without AP; Group II - probiotic water without AP; Group III - regular water with AP; Group IV - probiotic water with AP. AP was induced after 3 days in the control groups and after 7, 21, and 42 days in groups III and IV. The animals were euthanized, and the mandibles were subjected to histotechnical processing. Samples were stained with hematoxylin & eosin (H&E) to identify root canal features, apical and periapical regions. Additionally, histoenzymology was performed to detect osteoclasts, immunohistochemistry was used to identify osteoclastogenesis markers, and the Brown & Brenn technique was applied for microbiological analysis. The data were analyzed using GraphPad Prism 8.0.1 with a significance level of 5%. Although no statistical differences were observed, the groups administered with probiotics showed better conditions in terms of histological aspects seen microscopically. Furthermore, there were no differences in the number of osteoclasts (p > 0.05). The RANKL marker was not found in the probiotic group at 42 days, unlike in group III.

A novel experimental model to investigate fungal involvement shows expression of Dectin-1 in periapical lesion pathogenesis

BACKGROUND

Candida albicans is linked to persistent endodontic lesions. However, the recognition receptor that identifies it is not explored previously.

OBJECTIVES

The aim of this study was to (1) establish a zymosan-induced model of apical periodontitis in mouse, (2) observe the expression of Dectin-1 and its possible relationship with toll-like receptor (TLR) 2 and (3) observe relationship between Osteopontin (OPN) and inflammatory cytokines.

METHODS

A total of 138 Naval Medical Research Institute (NMRI) mice were randomly divided into; Experimental Group n = 69 and Zymosan Group n = 69. Periapical periodontitis was developed in right maxillary molar. The animals were sacrificed at 7, 21 and 42 days. Bone blocks containing the mesial root (n = 15 for qRT-PCR, n = 45 for enzyme-linked immune sorbent assay (ELISA)) were collected for mRNA expression and ELISA. While whole maxilla (n = 3 from each time interval) were used for histology and immunohistochemical analysis. One way analysis of variance (ANOVA) and Tuckey's posthoc was used for statistical analysis at p ≤ .05.

RESULTS

TLR-2, Dectin-1 and TLR4-positive cells was detected at all time intervals in both groups. A strong positive correlation was observed between TLR-2 and Dectin-1 in both lesions (regular r = .680, p = .015, zymosan (r = .861, p < .001)). A significant correlation was found between OPN and tumour necrosis factor-alpha (TNF-α) in zymosan lesion (r = .827, p = .001).

CONCLUSIONS

Immune cells of inflamed periapical tissue expressed Dectin-1 receptor in response to the microbial challenge from infected root canals and showed positive correlation with TLR-2 and OPN suggesting a possible receptor collaboration mediated by OPN. The expression of OPN and TNF-α showed positive correlation in response to fungal antigen, indicating a possible relationship.

Absence of tumor necrosis factor receptor 1 inhibits osteoclast activity in apical dental resorption caused by endodontic infection in mice

INTRODUCTION

To evaluate osteoclastogenesis and dental resorption resulting from endodontic infection in wild-type (WT) and tumor necrosis factor receptor 1 genetically deficient (TNFR1 KO) mice.

METHODS

After approval by the Ethics Committee on the use of Animals, 40 mice were distributed into two experimental groups based on periods: 14 days (n=10 WT mice; n=10 TNFR1 KO mice) and 42 days (n=10 WT mice; n=10 TNFR1 KO mice). After these periods, morphometrics analysis was done using bright field and fluorescence microscopy and tartrate-resistant acid phosphatase histoenzymology to identify osteoclasts. One-way analysis of variance followed by Tukey's post-hoc test was used for the statistical analysis (a=0.05).

RESULTS

WT mice in the 42-day period had a greater resorption in the apical region distal root of the first molar than TNFR1 KO mice (p<0.05). On the other hand, TNFR1 KO mice showed a smaller number of osteoclasts on the dental surface than WT mice (p<0.05).

CONCLUSION

WT mice had more extensive bone and apical dental resorptions and a larger number of osteoclasts on the tooth surface than TNFR1 KO mice.

Genetic, Cellular and Molecular Aspects involved in Apical Periodontitis

The development, establishment and repair of apical periodontitis (AP) is dependent of several factors, which include host susceptibility, microbial infection, immune response, quality of root canal treatment and organism's ability to repair. The understanding of genetic contributions to the risk of developing AP and presenting persistent AP has been extensively explored in modern Endodontics. Thus, this article aims to provide a review of the literature regarding the biochemical mediators involved in immune response signaling, osteoclastogenesis and bone neoformation, as the genetic components involved in the development and repair of AP. A narrative review of the literature was performed through a PUBMED/MEDLINE search and a hand search of the major AP textbooks. The knowledge regarding the cells, receptors and molecules involved in the host's immune-inflammatory response during the progression of AP added to the knowledge of bone biology allows the identification of factors inherent to the host that can interfere both in the progression and in the repair of these lesions. The main outcomes of studies evaluated in the review that investigated the correlation between genetic polymorphisms and AP in the last five years, demonstrate that genetic factors of the individual are involved in the success of root canal treatment. The discussion of this review gives subsides that may help to glimpse the development of new therapies based on the identification of therapeutic targets and the development of materials and techniques aimed at acting at the molecular level for clinical, radiographic and histological success of root canal treatment.

Single nucleotide polymorphisms as a predisposing factor for the development of apical periodontitis-An umbrella review

BACKGROUND

The interaction between heredity and different environmental factors in the modification of apical periodontitis (AP) susceptibility and prediction of its progression remain poorly elucidated.

OBJECTIVES

This umbrella review aimed to (i) analyse the available relevant systematic reviews in an attempt to determine the association between genotype and allelic distribution of different single-nucleotide polymorphisms (SNPs) and the development of AP, (ii) report deficiencies and gaps in knowledge in this area and (iii) present recommendations to conduct future clinical studies and systematic reviews.

METHODS

A literature search was conducted using Clarivate Analytics' Web of Science, Scopus, PubMed and Cochrane Database of Systematic Reviews, from inception to October 2021, with no language restrictions, including a grey literature search. Systematic reviews with/without meta-analysis evaluating genotype and allelic distribution of different SNPs between adult patients with/ without AP were included. All other type of studies were excluded. The methodological quality was assessed using the A MeaSurement Tool to Assess systematic Reviews (AMSTAR)-2 tool. Two independent reviewers were involved in study selection, data extraction and appraising the included reviews; disagreements were resolved by a third reviewer.

RESULTS

The current study includes five systematic reviews. Three reviews performed meta-analysis. Three reviews were graded by AMSTAR 2 as 'critically low' quality, whereas the other two were graded as 'low' and 'moderate' quality. Two reviews indicated that carriers of specific genotypes and alleles of tumour necrosis factor-alpha (TNF-α) -308 G > A and interleukin 1-beta (IL-1β) + 3954 C/T gene polymorphisms are more susceptible to an acute and persistent form of AP. However, high heterogeneity was observed.

DISCUSSION

The statistical heterogeneity within included systematic reviews was a consequence of clinical and methodological diversity amongst primary studies. Although some of the included reviews suggested that carriers of specific genotype and/or allele of TNF-α -308 G > A and IL-1β + 3954 C/T SNPs are more susceptible to AP, their conclusions should be interpreted with caution.

CONCLUSIONS

No candidate genes could be identified as a definitive genetic risk or protective factor for the development and progression of AP, and further high-quality genome-wide association studies are warranted.

M1 and M2 macrophages phenotypes modulation after stimuli with materials used in endodontic treatment

The aim of this study was to evaluate the M1 and M2 macrophage modulation after stimuli with different materials used during endodontic treatment. In bone marrow-derived macrophage cell culture, from males C57BL/6 wild-type (WT) mice, gene expression analysis of markers to M1 and M2 macrophages was performed by qRT-PCR (Cxcl10, CxCL9, iNOS, Arg1, Chil3, Retnla and MRC1) and cytokine quantification by Luminex® (GM-CSF, IL-10, IL-6, IL-1β and TNF-α) after exposure to the five endodontic sealers: AH Plus, Sealapex Xpress, Endosequence BC Sealer, BioRoot RCS and a calcium hydroxide-based paste. For normal values, ANOVA test was used, followed by Tukey post-test. For non-normal values, the Kruskall-Wallis test was used. BioRootTM RCS and EndoSequence BC SealerTM stimulated the highest expression of markers for M1 macrophages, while calcium hydroxide-based paste stimulated the lowest expression of these gene markers. For M2 protein markers, BioRootTM RCS presented the highest stimulation while calcium hydroxide-based paste also presented the lowest stimulation. It was concluded that all the evaluated filling materials increased the genetic expression of pro- and anti-inflammatory markers: TNF-α and IL-10 respectively. The others proinflammatory mediators showed differences against the filling materials. However, this process did not induce the inflammatory response polarization, resulting in a hybrid macrophage.

Anti-inflammatory and antiresorptive functions of melatonin on experimentally induced periapical lesions

AIM

To investigate the effects of systemically administered melatonin on inflammation and alveolar bone resorption in rats with experimentally induced periapical lesions.

METHODOLOGY

Thirty adult Sprague Dawley rats were divided equally into negative, positive control and melatonin groups. The pulp chambers of their mandibular first molars were exposed to the oral environment to induce experimental periapical lesions in the positive control and melatonin groups. The melatonin group received daily intraperitoneal injections of melatonin at a dose of 10 mg kg^-1 . After 21 days, the animals were euthanized; the hemi-mandible parts were prepared for radiological, histopathological, immunohistochemical (IL-1β, RANK, RANKL, OPG and tartrate-resistant acid phosphatase (TRAP) and Brown-Brenn (bacteria) evaluations. Data were analysed by Kruskal-Wallis (for non-parametric data) and one-way anova tests (for parametric data) (P < 0.05).

RESULTS

The area of radiographic periapical bone loss was significantly smaller in rats that were given daily intraperitoneal injections of melatonin (P < 0.01). The histopathological scores of the melatonin group were significantly lower than those of positive control group (P < 0.01). Histomorphometrically, the area of periapical bone loss in the melatonin group was significantly smaller than the positive control group (P < 0.01). The expression of IL1-β, RANK and RANKL was significantly higher in the positive control group, whereas OPG was significantly higher in the melatonin group (P < 0.01). The number of osteoclasts was significantly greater in the positive control group by TRAP staining analyses (P < 0.01). The scores for bacteria localization using Brown-Brenn staining in the melatonin group was significantly lower than that of the positive control group (P < 0.01).

CONCLUSIONS

Melatonin demonstrated antiresorptive effects on bone associated with experimentally induced periapical lesions in rats via its anti-inflammatory activity. Further studies are necessary to evaluate its possible effects on the healing of periapical lesions.

MMP2 and MMP9 are Associated with Apical Periodontitis Progression and Might be Modulated by TLR2 and MyD88

The aim of this study was to evaluate the expression of MMP2 and MMP9 during apical periodontitis (AP) progression in TLR2 (TLR2 KO) and in MyD88 (MyD88 KO) knockout mice compared to wild type (WT) mice. AP was induced in mandibular first molars of TLR2 KO (n= 18), MyD88 KO (n= 18), and WT mice (n= 18). After 7, 21, and 42 days, the animals were euthanized and the jaws were dissected and subjected to histotechnical processing. Subsequent sections were stained by immunohistochemistry and evaluated for detection of MMP2 and MMP9. Statistical analysis of the semi-quantitative analysis of immunohistochemistry was performed using chi-square test (α = 0.05). In the initial periods of AP progression, an increased expression of MMP9 in the TLR2 KO and MyD88 KO mice was observed. In the final periods of AP progression, a reduction of MMP2 expression and an increase of MMP9 expression in the TLR2 KO mice were observed. MMP2 and MMP9 production was modulated for TLR2 and MyD88 during apical periodontitis progression.

Immunohistochemical and mRNA expression of RANK, RANKL, OPG, TLR2 and MyD88 during apical periodontitis progression in mice

Objective

To evaluate and correlate, in the same research, the mRNA expression and the staining of RANK, RANKL, OPG, TLR2 and MyD88 by immunohistochemistry in the apical periodontitis (AP) progression in mice.

Material and Methods

AP was induced in the lower first molars of thirty-five C57BL/6 mice. They were assigned to four groups according to their euthanasia periods (G0, G7, G21 and G42). The jaws were removed and subjected to histotechnical processing, immunohistochemistry and real-time reverse transcription-PCR (qRT-PCR). Data were analyzed with parametric and nonparametric tests (α=0.05).

Results

An increase of positive immunoreactivity for RANK, RANKL, OPG, TLR2 and MyD88 was observed over time (p<0.05). The RANKL expression was different between the groups G0 and G42, G21 and G42 (p=0.006), with G42 presenting the higher expression in both comparations. The OPG expression was statistically different between the groups G0 and G7, G7 and G21 and G7 and G42 (p<0.001), with G7 presenting higher expression in all the time points. The TLR2 expression was different between the groups G0 and G42 (p=0.03), with G42 showing the higher expression. The MyD88 expression presented a statistical significant difference between groups G7, G21 and G42 compared with G0 (p=0.01), with G0 presenting the smallest expression in all the comparisons. The Tnfrsf11/Tnfrsf11b (RANKL/OPG) ratio increased with the AP progression (p=0.002). A moderate positive correlation between MyD88 and RANKL (r=0.42; p=0.03) and between MyD88 and TLR2 (r=0.48; p<0.0001) was observed.

Conclusion

The expression of the RANK, RANKL, OPG, MyD88 and TLR2 proteins as well as the ratio Tnfrsf11/Tnfrsf11b (RANKL/OPG) increased with AP progression. There was also a moderate positive correlation between the expression Myd88-Tnfrsf11 and Tlr2-Myd88, suggesting the relevance of Tlr2-Myd88 in bone loss due to bacterial infection.

Apical Negative Pressure irrigation presents tissue compatibility in immature teeth

Aim:

To compare the apical negative pressure irrigation (ANP) with conventional irrigation in the teeth of immature dogs with apical periodontitis.

Methods:

Fifty-two immature pre-molar root canals were randomly assigned into 4 groups: ANP (n=15); conventional irrigation (n=17); healthy teeth (control) (n = 10); and teeth with untreated apical periodontitis (control) (n=10). After induction of apical periodontitis, teeth were instrumented using EndoVac^® (apical negative pressure irrigation) or conventional irrigation. The animals were euthanized after 90 days. The sections were stained by HE and analyzed under conventional and fluorescence microscopy. TRAP histoenzymology was also performed. Statistical analyses were performed with the significance level set at 5%.

Results:

There was difference in the histopathological parameters between ANP and conventional groups (p<0.05). The ANP group showed a predominance of low magnitude inflammatory infiltrate, a smaller periodontal ligament, and lower mineralized tissue resorption. There were no differences in the periapical lesion extensions between the ANP and conventional groups (p>0.05). However, a lower number of osteoclasts was observed in the ANP group (p<0.05).

Conclusion:

The EndoVac^® irrigation system presented better biological results and more advanced repair process in immature teeth with apical periodontitis than the conventional irrigation system, confirming the hypothesis.

MyD88 is an essential component of retinoic acid-induced differentiation in human pluripotent embryonal carcinoma cells

We have previously reported that myeloid differentiation primary response gene 88 (MyD88) is downregulated during all-trans retinoic acid (RA)-induced differentiation of pluripotent NTera2 human embryonal carcinoma cells (hECCs), whereas its maintained expression is associated with RA differentiation resistance in nullipotent 2102Ep hECCs. MyD88 is the main adapter for toll-like receptor (TLR) signalling, where it determines the secretion of chemokines and cytokines in response to pathogens. In this study, we report that loss of MyD88 is essential for RA-facilitated differentiation of hECCs. Functional analysis using a specific MyD88 peptide inhibitor (PepInh) demonstrated that high MyD88 expression in the self-renewal state inhibits the expression of a specific set of HOX genes. In NTera2 cells, MyD88 is downregulated during RA-induced differentiation, a mechanism that could be broadly replicated by MyD88 PepInh treatment of 2102Ep cells. Notably, MyD88 inhibition transitioned 2102Ep cells into a stable, self-renewing state that appears to be primed for differentiation upon addition of RA. At a molecular level, MyD88 inhibition combined with RA treatment upregulated HOX, RA signalling and TLR signalling genes. These events permit differentiation through a standard downregulation of Oct4-Sox2-Nanog mechanism. In line with its role in regulating secretion of specific proteins, conditioned media experiments demonstrated that differentiated (MyD88 low) NTera2 cell media was sufficient to differentiate NTera2 cells. Protein array analysis indicated that this was owing to secretion of factors known to regulate angiogenesis, neurogenesis and all three branches of TGF-β Superfamily signalling. Collectively, these data offer new insights into RA controlled differentiation of pluripotent cells, with notable parallels to the ground state model of embryonic stem cell self-renewal. These data may provide insights to facilitate improved differentiation protocols for regenerative medicine and differentiation-therapies in cancer treatment.

Three-Dimensional Micro-Computed Tomography Analyses of Induced Periapical Lesions in Transgenic Mice

The aim of this study was to evaluate the three-dimensional (3D) parameters given by the micro-computed tomography (µCT) analysis of experimentally induced periapical lesions in wild type (WT) and knockout mice for the interleukin 22 (IL-22 KO). Periapical lesions were induced in the mandibular first molars of wild type and IL-22 KO mice (n = 12 teeth/group). The animals were euthanized after the experimental periods of 7, 21 and 42 days. The mandibles were removed and exposed to µCT scanning. The analyses were performed by the CTAn software for the tree-dimensional parameters: Tissue Volume (TV), Lesion Volume (LV), Tissue Surface (TS), Lesion Surface (LS), Intersection Surface (IS), and Trabecular Pattern factor (Tb.Pf). After that, the tissue was subjected to routine histologic procedures and to immunohistochemistry analysis. Statistical analysis was performed in the GraphPad software. A t-test was used to compare the differences between the groups with significance level of 5%. The evaluation of the 3D parameters showed statistical significant difference between the groups only at the latest period of periapical lesion development (42 days), for the TV, LV, TS, LS and IS parameters. The immunohistochemistry evaluation confirmed the immunostaining for IL-22 only in the WT mice, surrounding the periapical lesion. There were no differences regarding the trabecular alveolar bone (Tb.Pf) that could influence the lesion development. In conclusion, the 3D parameters showed that the absence of IL-22 leads to detectable differences at 42 days of lesion progression, resulting in smaller periapical lesions.

Correlation Between Histomorphometric and Micro-computed Tomography Analysis of Periapical Lesions in Mice Model

Periapical lesions are processes mediated from bacterial invasion on the pulp tissue, which results in inflammatory process and bone resorption. Animal models have been used for the study of cell interactions and inflammatory responses involved in periapical lesion. The use of different methods for morphometric evaluation of this lesion has been reported. However, due to the limitation of 2D methods, computerized microtomography (µCT) has been indicated. Therefore, the aim of this study was to evaluate the correlation between the histomorphometric measures of periapical lesions and the µCT analysis obtained in an animal experimental model. Briefly, the periapical lesions were induced by pulp exposal and after the experimental periods (7, 21 and 42 days) the mice were euthanized. The mandibles were evaluated under the µCT scanning and then were subjected to the routine histologic procedures, stained with hematoxilin and eosin. The periapical lesions were measured by the specific softwares of each technique. A weak correlation among the histomorphometric measurement and the 2D µCT analysis (r(2)= .204) and between the histomorphometric measurement and the 3D µCT analysis (r(2)= .237) was observed. A strong correlation between the 2D and 3D µCT analysis (r(2)= .867) was observed. Thereby, it can be concluded that the µCT is a method that allows a precise volumetric scanning and represents an important tool for morphometric evaluation.