Resolvin D2 Induces Resolution of Periapical Inflammation and Promotes Healing of Periapical Lesions in Rat Periapical Periodontitis

Effects of aged garlic extract on experimental periodontitis in mice

Aged garlic extract (AGE) has been reported to exert anti-inflammatory effects. AGE has been recently found to reduce the inflammatory symptoms of periodontitis, a widespread chronic inflammatory disease caused by oral bacterial infection. However, the mechanisms underlying these effects remain unclear. In the present study, it was aimed to determine the effects of AGE on experimental periodontitis and the related inflammatory factors. AGE (2 g/kg/day) was orally administered to 15 mice during the experimental period, while a control group consisted of 15 mice that received pure water. A total of 3 days after initiation of administration, the left maxillary second molar was ligated with a 5-0 silk thread for 7 days. Blood biochemical tests were performed to monitor the systemic effects of AGE. Alveolar bone loss was measured morphometrically using a stereomicroscope, and reverse transcription-quantitative PCR was performed to assay mRNAs of proinflammatory cytokines in gingival tissues. A histological survey was also performed to identify osteoclasts in periodontitis lesions (five mice per group). The total protein and albumin levels showed no significant differences between the AGE and control groups. However, ligation-induced bone resorption was lower in the AGE group than in the control group (P=0.01). Additionally, ligature increased the mRNA expression of inflammatory cytokines, whereas AGE administration tended to suppress them. Remarkably, tumor necrosis factor gene expression was significantly suppressed (P=0.04). The number of osteoclasts in periodontitis lesions was reduced in the AGE-treated group. These results indicate that AGE prevents alveolar bone loss by suppressing the inflammatory responses related to osteoclast differentiation in the periodontal tissue. Further research is needed to elucidate the role of AGE in reducing inflammatory bone resorption.

Increased Prevalence of Periapical Lesions in Osteoporosis Patients: A Systematic Review

Assessing scientific literature about prevalence of periapical lesions in individuals with osteoporosis in comparison to those without osteoporosis. Systematic searches were conducted up to November 24th, 2023 in Cochrane Library, EMBASE, MEDLINE/PubMed, SCOPUS, Web of Science and Grey Literature Reports databases. Only observational studies were included. The ROBINS-E tool, a revised Cochrane instrument for assessing bias in nonrandomized exposure studies, was employed. The Grading of Recommendations Assessment, Development, and Evaluation (GRADE) tool was utilized to evaluate the certainty of the evidence. From 484 studies, three were included. One of them was categorized as having an exceptionally high risk of bias, while two were deemed to have certain concerns. Two studies reported that osteoporotic patients may have more chances to present a periapical lesion compared to non-osteoporotic patients. One study reported no differences between groups. The GRADE analysis indicated a markedly low level of certainty in the evidence. The present review indicates that osteoporotic patients may present more periapical lesions compared to non-osteoporotic patients. This statement should be cautiously interpreted and further well-designed studies are needed. (EEJ-2023-09-123).

FTO-associated osteoclastogenesis promotes alveolar bone resorption in apical periodontitis male rat via the HK1/USP14/RANK pathway

Alveolar bone resorption (ABR) is a key pathological manifestation in the development of apical periodontitis (AP) and contributes to the AP-associated tooth loss among AP patients in the clinic. However, the underlying mechanism of ABR development is largely unknown. Here we show, the total levels of N6-methyladenosine (m6A) were reduced in AP male rat alveolar bone tissues and BMDM-derived osteoclasts (OC), which was associated with the up-regulation of obesity-associated protein (FTO). Subsequently FTO-mediated hexokinase (HK1) demethylation modification enhancing glycolytic pathway that stabilizes receptor activator of NF-κB (RANK) protein via the deubiquitination activity of ubiquitin-specific protease 14 (USP14), which further promotes osteoclastogenesis to participate in the AP-related ABR development. Finally, Dac51 (an FTO inhibitor) and 2-DG (an HK1 inhibitor) both exhibit the inhibitory activity of osteoclastogenesis. Our current study reveals a molecular mechanism on osteoclastogenesis-related ABR and provides a therapeutic target of AP via modulating the FTO/HK1/USP14/RANK axis.

The Involvement of Resolvins in Pathological Mechanisms of Periodontal Disease Associated with Type 2 Diabetes: A Narrative Review

Resolvins are specialized pro-resolving mediators (SPMs) derived from omega-3 fatty acids that play a critical role in resolving inflammation and restoring tissues to a state of health after an immune response. Their role in chronic inflammatory conditions highlights their importance in maintaining a balance between an effective immune response and the resolution of inflammation to prevent tissue damage. Periodontal disease is a chronic inflammatory condition affecting the tissues surrounding the teeth, leading to gum damage and bone loss. Chronic inflammation in periodontal disease can exacerbate systemic inflammation and influence other conditions, such as diabetes. There is a bidirectional relationship between diabetes and periodontal disease, as both are characterized by chronic inflammation and exacerbate systemic and oral health complications. This narrative review aims to synthesize the current knowledge on how resolvins influence inflammatory pathways and the tissue repair mechanism in periodontal disease in patients with type 2 diabetes. Furthermore, this review serves as a foundation for developing targeted therapeutic strategies, addressing the pressing need for effective treatments that consider both systemic and oral health outcomes.

The resolvin D2 and omega-3 polyunsaturated fatty acid as a new possible therapeutic approach for inflammatory bowel diseases

Inflammatory bowel diseases (IBD) are idiopathic disorders characterized by chronic gastrointestinal inflammation. Given conventional therapies' adverse effects and clinical failures, novel approaches are being investigated. Recent studies have highlighted the role of specialized pro-resolving lipid mediators (SPMs) in the active resolution of chronic inflammation. In this regard, omega-3 fatty acid-derived Resolvin D2 (RvD2) appears to play a protective role in the pathophysiology of IBD. Therefore, we characterized the RvD2 pathway and its receptor expression in the intestinal mucosa of experimental colitis induced by dextran sulfate sodium. We also evaluated the preventive impact of an omega-3-enriched diet and the therapeutic efficacy of RvD2 compared with anti-TNF-α treatment. We found an increase in TNFα and IL22 expression and decreased levels of enzymes involved in RvD2 biosynthesis, such as PLA2, 15-LOX, 5-LOX, and its receptor GPR18 in experimental colitis. Omega-3 supplementation reduced the Disease Activity Index (DAI), weight loss, colonic shortening, and inflammation. These results and the increased IL-10 transcriptional levels after RvD2 treatment suggest that this mediator attenuated experimental colitis. These results enhance our understanding of the molecular mechanisms involved in the exacerbated inflammatory response present in experimental colitis and suggest that RvD2 and its omega-3 precursor offer a promising therapeutic approach for IBD.

Impact of Specialized Pro-Resolving Lipid Mediators on Craniofacial and Alveolar Bone Regeneration: Scoping Review

Craniofacial bone defects caused by tumors, trauma, long-term tooth loss, or periodontal disease are a major challenge in the field of tissue engineering. In periodontitis and peri-implantitis, reconstructive therapy is also a major challenge for the dental surgeon. Lipoxins, resolvins, protectins, and maresins, known as specialized pro-resolving lipid mediators (SPMs), have been widely studied in the field of dental, oral, and craniofacial research for bone regeneration for their actions in restoring tissue homeostasis and promoting tissue healing and regeneration. Therefore, this study focuses on a survey of the use of SPMs for craniofacial and alveolar bone regeneration. Thus, electronic searches of five databases were performed to identify pre-clinical studies that evaluated the actions of SMPs on craniofacial and alveolar bone regeneration. Of the 523 articles retrieved from the electronic databases, 19 were included in the analysis. Resolvin (Rv) E1 was the mostly assessed SPM (n=8), followed by maresins (Ma) R1 (n=3), lipoxins (Lx) A4 (n=3), RvD1 (n=3), RvD2 (n=1), LxB4 (n=1), and maresin (M)-CTR3 (n=1). Meta-analysis showed that SPMs increased the newly formed bone by 14.85% compared to the control group (p<0.00001), decreased the area of the remaining defect by 0.35 mm2 (p<0.00001), and decreased the linear distance between the defect to the bone crest by 0.53 mm (p<0.00001). RvE1 reduced inflammatory bone resorption in periodontal defects and calvarial osteolysis and enhanced bone regeneration when RvE1 was combined with a bovine bone graft. RvD2 induced active resolution of inflammation and tissue regeneration in periapical lesions, while RvD1 controlled the inflammatory microenvironment in calvarial defects in rats, promoting bone healing and angiogenesis. MaR1 induced the proliferation and migration of mesenchymal stem cells, osteogenesis, and angiogenesis in calvarial defects, and benzo (b)-LxA4 and LxA4 promoted bone regeneration calvarial and alveolar bone defects in rats, inducing regeneration under inflammatory conditions. In summary, SPMs have emerged as pivotal contributors to the resolution of inflammation and the facilitation of bone neoformation within craniofacial and alveolar bone defects. These results are based on pre-clinical studies, in vivo and in vitro, and provide an updated review regarding the impact of SPMs in tissue engineering.

Naringin dihydrochalcone alleviates sepsis-induced acute lung injury via improving gut microbial homeostasis and activating GPR18 receptor

Acute lung injury (ALI) is a life-threatening disease characterized by severe lung inflammation and intestinal microbiota disorder. The GPR18 receptor has been demonstrated to be a potential therapeutic target against ALI. Extracting Naringin dihydrochalcone (NDC) from the life-sustaining orange peel is known for its diverse anti-inflammatory properties, yet the specific action target remains uncertain. In the present study, we identified NDC as a potential agonist of the GPR18 receptor using virtual screening and investigated the pharmacological effects of NDC on sepsis-induced acute lung injury in rats and explored underlying mechanisms. In in vivo experiments, CLP-induced ALI model was established by cecum puncture and treated with NDC gavage one hour prior to drug administration, lung histopathology and inflammatory cytokines were evaluated, and feces were subjected to 16s rRNA sequencing and untargeted metabolomics analysis. In in vitro experiments, the anti-inflammatory properties were exerted by evaluating NDC targeting the GPR18 receptor to inhibit lipopolysaccharide (LPS)-induced secretion of TNF-α, IL-6, IL-1β and activation of inflammatory signaling pathways in MH-S cells. Our findings showed that NDC significantly ameliorated lung damage and pro-inflammatory cytokine levels (TNF-α, IL-6, IL-1β) in both cells and lung tissues via inhibiting the activation of STAT3, NF-κB, and NLRP3 inflammatory signaling pathways through GRP18 receptor activation. In addition, NDC can also partly reverse the imbalance of gut microbiota composition caused by CLP via increasing the proportion of Firmicutes/Bacteroidetes and Lactobacillus and decreasing the relative abundance of Proteobacteria. Meanwhile, the fecal metabolites in the NDC treatment group also significantly were changed, including decreased secretion of Phenylalanin, Glycine, and bile secretion, and increased secretion of Lysine. In conclusion, these findings suggest that NDC can alleviate sepsis-induced ALI via improving gut microbial homeostasis and metabolism and mitigate inflammation via activating GPR18 receptor. In conclusion, the results indicate that NDC, derived from the typical orange peel of food, could significantly contribute to development by enhancing intestinal microbial balance and metabolic processes, and reducing inflammation by activating the GPR18 receptor, thus mitigating sepsis-induced ALI and expanding the range of functional foods.

Resolvin D2-induced reparative dentin and pulp stem cells after pulpotomy in a rat model

Introduction

Vital pulp therapy (VPT) is performed to preserve dental pulp. However, the biocompatibility of the existing materials is of concern. Therefore, novel materials that can induce pulp healing without adverse effects need to be developed. Resolvin D2 (RvD2), one of specialized pro-resolving mediators, can resolve inflammation and promote the healing of periapical lesions. Therefore, RvD2 may be suitable for use in VPT. In the present study, we evaluated the efficacy of RvD2 against VPT using in vivo and in vitro models.

Methods

First molars of eight-week-old male Sprague-Dawley rats were used for pulpotomy. They were then divided into three treatment groups: RvD2, phosphate-buffered saline, and calcium hydroxide groups. Treatment results were assessed using radiological, histological, and immunohistochemical (GPR18, TNF-α, Ki67, VEGF, TGF-β, CD44, CD90, and TRPA1) analyses. Dental pulp-derived cells were treated with RvD2 in vitro and analyzed using cell-proliferation and cell-migration assays, real-time PCR (Gpr18, Tnf-α, Il-1β, Tgf-β, Vegf, Nanog, and Trpa1), ELISA (VEGF and TGF-β), immunocytochemistry (TRPA1), and flow cytometry (dental pulp stem cells: DPSCs).

Results

The formation of calcified tissue in the pulp was observed in the RvD2 and calcium hydroxide groups. RvD2 inhibited inflammation in dental pulp cells. RvD2 promoted cell proliferation and migration and the expression of TGF-β and VEGF in vitro and in vivo. RvD2 increased the number of DPSCs. In addition, RvD2 suppressed TRPA1 expression as a pain receptor.

Conclusion

RvD2 induced the formation of reparative dentin, anti-inflammatory effects, and decreased pain, along with the proliferation of DPSCs via the expression of VEGF and TGF-β, on the pulp surface in pulpotomy models.

Dental Pulp Cell Transplantation Combined with Regenerative Endodontic Procedures Promotes Dentin Matrix Formation in Mature Mouse Molars

Regenerative endodontic procedures (REPs) are promising for dental pulp tissue regeneration; however, their application in permanent teeth remains challenging. We assessed the potential combination of an REP and local dental pulp cell (DPC) transplantation in the mature molars of C57BL/6 mice with (REP + DPC group) or without (REP group) transplantation of DPCs from green fluorescent protein (GFP) transgenic mice. After 4 weeks, the regenerated tissue was evaluated by micro-computed tomography and histological analyses to detect odontoblasts, vasculogenesis, and neurogenesis. DPCs were assessed for mesenchymal and pluripotency markers. Four weeks after the REP, the molars showed no signs of periapical lesions, and both the REP and REP + DPC groups exhibited a pulp-like tissue composed of a cellular matrix with vessels surrounded by an eosin-stained acellular matrix that resembled hard tissue. However, the REP + DPC group had a broader cellular matrix and uniquely contained odontoblast-like cells co-expressing GFP. Vasculogenesis and neurogenesis were detected in both groups, with the former being more prominent in the REP + DPC group. Overall, the REP was achieved in mature mouse molars and DPC transplantation improved the outcomes by inducing the formation of odontoblast-like cells and greater vasculogenesis.

Effectiveness of Calcium Hydroxide and Gingerols Mixture as a Novel Obturation Material for Infected Root in Primary Teeth: A Randomized Clinical Trial

Introduction

The tendency to use dental materials of plant origin is one of the prevailing trends in dentistry to reduce exposure to materials that could have some toxic impact in the long term.

Objective

To evaluate the efficacy of calcium hydroxide combined with gingerols (Ginge-Cal) as a novel obturation material for treating infected primary teeth and decreasing the recurrence of infection.

Materials and Methods

The study was conducted on 30 lower primary molars with infected pulp for children aged 4-8 years. The sample was randomly divided into two groups depending on the tested obturation material: Ginge-Cal group and the Metapex group. The evaluation was done by different parameters clinically and radiographically at various intervals up to 12 months.

Results

Based on chi-squared and McNamara's test with a 5% significance level, the clinical results indicated that Ginge-Cal group was more effective than the Metapex group in reducing or eliminating pain (P=0.467) after 1 week, sensitivity to percussion (P=0.090) at 3 months of follow-up, purulent swelling (P=0.444) at 6 and 9 months of follow-up, fistula, and tooth mobility. The radiographic results, based on the periapical and furcation area radiolucency at 12 months of follow-up, favored Ginge-Cal group over the Metapex group (P=0.683), (P=0.456), respectively. There were no statistically significant differences in pathological root resorption and periodontal space. The differences within the Ginge-Cal group were directly influenced by the time intervals in a statistically significant manner, ranging from (P=0.004) to (P < 0.001). The success percentage was 87.5% for Ginge-Cal group and 64.3% for Metapex group.

Conclusions

Ginge-Cal can be considered a promising material for treating the infected root canal when used as an obturation material for the infected root canal. This trial is registered with NCT05181813.

RvE1 Promotes Axin2+ Cell Regeneration and Reduces Bacterial Invasion

Vital pulp therapy and root canal therapy (RCT) are the dominant treatment for irreversible pulpitis. While the success rate of these procedures is favorable, they have some limitations. For instance, RCT leads to removing significant dentin in the coronal third of the tooth that increases root-fracture risk, which forces tooth removal. The ideal therapeutic goal is dental pulp regeneration, which is not achievable with RCT. Specialized proresolving mediators (SPMs) are well known for inflammatory resolution. The resolution of inflammation and tissue restoration or regeneration is a dynamic and continuous process. SPMs not only have potent immune-modulating functions but also effectively promote tissue homeostasis and regeneration. Resolvins have been shown to promote dental pulp regeneration. The purpose of this study was to explore further the cellular target of Resolvin E1 (RvE1) therapy in dental pulp regeneration and the impact of RvE1 in infected pulps. We investigated the actions of RvE1 on experimentally exposed pulps with or without microbial infection in an Axin2Cre-Dox;Ai14 genetically defined mouse model. Our results showed RvE1 promoted Axin2-tdTomato+ cell expansion and odontoblastic differentiation after direct pulp capping in the mouse, which we used to mimic reversible pulpitis cases in the clinic. In cultured mouse dental pulp stem cells (mDPSCs), RvE1 facilitated Axin2-tdTomato+ cell proliferation and odontoblastic differentiation and also rescued impaired functions after lipopolysaccharide stimulation. In infected pulps exposed to the oral environment for 24 h, RvE1 suppressed inflammatory infiltration, reduced bacterial invasion in root canals, and prevented the development of apical periodontitis, while its proregenerative impact was limited. Collectively, topical treatment with RvE1 facilitated dental pulp regenerative properties by promoting Axin2-expressing cell proliferation and differentiation. It also modulated the resolution of inflammation, reduced infection severity, and prevented apical periodontitis, presenting RvE1 as a novel therapeutic for treating endodontic diseases.

Resolvin D2 activates anti-inflammatory microglia via restoring autophagy flux and alleviate neuropathic pain following spinal cord injury in rats

Spinal cord injury (SCI) is a fatal and intractable disease accompanied by the comorbidity of chronic neuropathic pain. Here, we purposed to explore the therapeutic effect and the underlying mechanism of Resolvin D2 (RvD2) on neuropathic pain after SCI. The in vivo model of traumatic SCI rats was established. Primary microglia isolated from neonatal rats were induced by TNF-α in vitro. The locomotor ability was assessed by the Basso-Beattie-Besnahan score. Hargreaves methods and Von Frey fibrofilaments were used to evaluate the symptoms of neuropathic pain including allodynia and hyperalgesia in rats. The cytotoxicity of RvD2 was evaluated by MTT assay. ELISA kit was applied to access the levels of inflammatory factors. And the expression levels of related mRNA and proteins were determined by qRT-PCR, western blotting and immunofluorescence staining. The targeting relationship between miR-155 and PTEN was verified by dual-luciferase reporter (DLR) assay. We found that RvD2 mitigated locomotor dysfunction, allodynia and hyperalgesia of SCI rats. In addition, RvD2 treatment suppressed pro-inflammatory phenotype but promoted anti-inflammatory differentiation in microglia. Furthermore, RvD2 treatment inhibited the upregulated expression level of miR-155 which was caused by NF-κB activation and then recovered the autophagy flux via targeting PTEN, thereby relieving the inflammatory response in the TNF-α-induced primary microglia. In summary, RvD2 treatment could recover the autophagy flux via suppressing NF-κB-modulated miR-155 expression to activate anti-inflammatory microglia and then inhibit the inflammatory response and even mitigate neuropathic pain following SCI.

Resolvin D2 and its receptor GPR18 in cardiovascular and metabolic diseases: A promising biomarker and therapeutic target

Accumulating evidence suggests that inflammation plays an important role in the pathophysiology of the initiation and progression of cardiovascular and metabolic diseases (CVMDs). Anti-inflammation strategies and those that promote inflammation resolution have gradually become potential therapeutic approaches for CVMDs. Resolvin D2 (RvD2), a specialized pro-resolving mediator, exerts anti-inflammatory and pro-resolution effects through its receptor GPR18, a G protein-coupled receptor. Recently, the RvD2/GPR18 axis has received more attention due to its protective role in CVMDs, including atherosclerosis, hypertension, ischaemiareperfusion, and diabetes. Here, we introduce basic information about RvD2 and GPR18, summarize their roles in different immune cells, and review the therapeutic potential of the RvD2/GPR18 axis in CVMDs. In summary, RvD2 and its receptor GPR18 play an important role in the occurrence and development of CVMDs and are potential biomarkers and therapeutic targets.

Beyond Macromolecules: Extracellular Vesicles as Regulators of Inflammatory Diseases

Inflammation is the defense mechanism of the immune system against harmful stimuli such as pathogens, toxic compounds, damaged cells, radiation, etc., and is characterized by tissue redness, swelling, heat generation, pain, and loss of tissue functions. Inflammation is essential in the recruitment of immune cells at the site of infection, which not only aids in the elimination of the cause, but also initiates the healing process. However, prolonged inflammation often brings about several chronic inflammatory disorders; hence, a balance between the pro- and anti-inflammatory responses is essential in order to eliminate the cause while producing the least damage to the host. A growing body of evidence indicates that extracellular vesicles (EVs) play a major role in cell-cell communication via the transfer of bioactive molecules in the form of proteins, lipids, DNA, RNAs, miRNAs, etc., between the cells. The present review provides a brief classification of the EVs followed by a detailed description of how EVs contribute to the pathogenesis of various inflammation-associated diseases and their implications as a therapeutic measure. The latter part of the review also highlights how EVs act as a bridging entity in blood coagulation disorders and associated inflammation. The findings illustrated in the present review may open a new therapeutic window to target EV-associated inflammatory responses, thereby minimizing the negative outcomes.

The Role of Apical Periodontitis Disease in the Development of Bisphosphonate-Related Osteonecrosis of the Jaw: An Animal Study

BACKGROUND

Microorganisms and their by-products are responsible for establishing pulpal and periapical diseases. Healing is compromised in patients under bisphosphonate therapy, and the presence of periapical infections can potentially lead to the development of medication-related osteonecrosis of the jaw (MRONJ). This work aimed to evaluate if bisphosphonate therapy is a risk factor for MRONJ development in the presence of periapical lesions.

METHODS

Two groups of 10 female Wistar rats were used. The experimental group received zoledronate (0.1 mg/kg) intraperitoneally, and the control received a saline solution, three times a week for three weeks. One week after the last injection, apical periodontitis was induced through pulpal exposure in the mandibular first molars. Twenty-one days later, the animals were intravenously injected with ^99mTc-HMDP, and the radioactivity uptake by mandibular specimens was counted. In addition, sample radiographs and a histological examination were performed.

RESULTS

The bone loss was higher in the control group when compared to the experimental group (p = 0.027). ^99mTc-HMDP uptake in the control was reduced compared with the experimental group, although without statistical significance.

CONCLUSIONS

In the presence of zoledronate therapy, apical periodontitis does not increase the risk of MRONJ development, and periapical lesions have lower bone resorption when compared to the control group.

Specialized Pro-Resolving Lipid Mediators: Endogenous Roles and Pharmacological Activities in Infections

During an infection, inflammation mobilizes immune cells to eliminate the pathogen and protect the host. However, inflammation can be detrimental when exacerbated and/or chronic. The resolution phase of the inflammatory process is actively orchestrated by the specialized pro-resolving lipid mediators (SPMs), generated from omega-3 and -6 polyunsaturated fatty acids (PUFAs) that bind to different G-protein coupled receptors to exert their activity. As immunoresolvents, SPMs regulate the influx of leukocytes to the inflammatory site, reduce cytokine and chemokine levels, promote bacterial clearance, inhibit the export of viral transcripts, enhance efferocytosis, stimulate tissue healing, and lower antibiotic requirements. Metabolomic studies have evaluated SPM levels in patients and animals during infection, and temporal regulation of SPMs seems to be essential to properly coordinate a response against the microorganism. In this review, we summarize the current knowledge on SPM biosynthesis and classifications, endogenous production profiles and their effects in animal models of bacterial, viral and parasitic infections.

Resolution of inflammation in oral diseases

The resolution of inflammation is an essential endogenous process that protects host tissues from an exaggerated chronic inflammatory response. Multiple interactions between host cells and resident oral microbiome regulate the protective functions that lead to inflammation in the oral cavity. Failure of appropriate regulation of inflammation can lead to chronic inflammatory diseases that result from an imbalance between pro-inflammatory and pro-resolution mediators. Thus, failure of the host to resolve inflammation can be considered an essential pathological mechanism for progression from the late stages of acute inflammation to a chronic inflammatory response. Specialized pro-resolving mediators (SPMs), which are essential polyunsaturated fatty acid (PUFA)-derived autacoid mediators, aid in regulating the endogenous inflammation resolving process by stimulating immune cell-mediated clearance of apoptotic polymorphonuclear neutrophils, cellular debris, and microbes, restricting further neutrophil tissue infiltration, and counter-regulating pro-inflammatory cytokine production. The SPM superfamily contains four specialized lipid mediator families: lipoxins, resolvins, protectins, and maresins that can activate resolution pathways. Understanding the crosstalk between resolution signals in the tissue response to injury has therapeutic application potential for preventing, maintaining, and regenerating chronically damaged tissues. Here, we discuss the fundamental concepts of resolution as an active biochemical process, novel concepts demonstrating the role of resolution mediators in tissue regeneration in periodontal and pulpal diseases, and future directions for therapeutic applications with particular emphasis on periodontal therapy.

[Akt2 inhibitor promotes M2 macrophage polarization in rats with periapical inflammation by reducing miR-155-5p expression]

OBJECTIVE

To investigate the effect of Akt2 inhibitor on macrophage polarization in the periapical tissue in a rat model of periapical inflammation.

METHODS

Rat models of periapical inflammation were established in 28 normal SD rats by opening the pulp cavity of the mandibular first molars, followed by injection of normal saline and Akt2 inhibitor into the left and right medullary cavities, respectively. Four rats without any treatment served as the healthy control group. At 7, 14, 21 and 28 days after modeling, 7 rat models and 1 control rat were randomly selected for observation of inflammatory infiltration in the periapical tissues by X-ray and HE staining. Immunohistochemistry was used to detect the expression and localization of Akt2, macrophages and the inflammatory mediators. RT-PCR was performed to detect the mRNA expressions of Akt2, CD86, CD163, inflammatory mediators, miR-155-5p and C/EBPβ to analyze the changes in macrophage polarization.

RESULTS

X-ray and HE staining showed that periapical inflammation was the most obvious at 21 days after modeling in the rats. Immunohistochemistry and RT-PCR showed that compared with those in the control rats, the expressions of Akt2, CD86, CD163, miR-155-5p, C/EBPβ, and IL-10 increased significantly in the rat models at 21 days (P < 0.05). Compared with saline treatment, treatment with the Akt2 inhibitor significantly decreased the expression levels of Akt2, CD86, miR-155-5p and IL-6 and the ratio of CD86+M1/CD163+M2 macrophages (P < 0.05) and increased the expression levels of CD163, C/EBPβ and IL-10 in the rat models (P < 0.05).

CONCLUSION

Inhibition of Akt2 can delay the progression of periapical inflammation in rats and promote M2 macrophage polarization in the periapical inflammatory microenvironment possibly by reducing miR-155-5p expression and activating the expression of C/EBPβ in the Akt signaling pathway.

Recent Advances in Apical Periodontitis Treatment: A Narrative Review

Apical periodontitis is an inflammatory response caused by pulp infection. It induces bone resorption in the apical and periapical regions of the tooth. The most conservative approach to treat this condition is nonsurgical endodontic treatment. However, clinical failure has been reported with this approach; thus, alternative procedures are required. This review highlights recent literature regarding advanced approaches for the treatment of apical periodontitis. Various therapies, including biological medications, antioxidants, specialized pro-resolving lipid mediators, and stem cell therapy, have been tested to increase the success rate of treatment for apical periodontitis. Some of these approaches remain in the in vivo phase of research, while others have just entered the translational research phase to validate clinical application. However, a detailed understanding of the molecular mechanisms that occur during development of the immunoinflammatory reaction in apical periodontitis remains unclear. The aim of this review was to summarize advanced approaches for the treatment of apical periodontitis. Further research can confirm the potential of these alternative nonsurgical endodontic treatment approaches.

Targeting Angiogenesis via Resolution of Inflammation

Angiogenesis, the growth of new blood vessels, plays a critical role in tissue repair and regeneration, as well as in cancer. A paradigm shift is emerging in our understanding of the resolution of inflammation as an active biochemical process with the discovery of novel endogenous specialized pro-resolving mediators (SPMs), including resolvins. Angiogenesis and the resolution of inflammation are critical interdependent processes. Disrupted inflammation resolution can accelerate tumor growth, which is angiogenesis-dependent. SPMs, including resolvins and lipoxins, inhibit physiologic and pathological angiogenesis at nanogram concentrations. The failure of resolution of inflammation is an emerging hallmark of angiogenesis-dependent diseases including arthritis, psoriasis, diabetic retinopathy, age-related macular degeneration, inflammatory bowel disease, atherosclerosis, endometriosis, Alzheimer's disease, and cancer. Whereas therapeutic angiogenesis repairs tissue damage (e.g., limb ischemia), inhibition of pathological angiogenesis suppresses tumor growth and other non-neoplastic diseases such as retinopathies. Stimulation of resolution of inflammation via pro-resolving lipid mediators promotes the repair of tissue damage and wound healing, accelerates tissue regeneration, and inhibits cancer. Here we provide an overview of the mechanisms of cross talk between angiogenesis and inflammation resolution in chronic inflammation-driven diseases. Stimulating the resolution of inflammation via pro-resolving lipid mediators has emerged as a promising new field to treat angiogenic diseases.

Selenium ameliorates inflammation by decreasing autophagic flux and mitogen-activated protein kinase signalling on experimentally induced rat periapical lesions

AIM

To reveal the molecular mechanisms that targets mitogen-activated protein kinase (MAPK) signalling and the autophagic flux and to investigate the possible effects of the systemic administration of selenium (Se) on experimentally induced rat periapical lesions.

METHODOLOGY

Thirty adult Sprague-Dawley rats were divided equally into negative control, positive control and Se groups. In the positive control and Se groups, the pulp chambers of their mandibular first molars were exposed to the oral environment to induce periapical lesions The Se group received daily intraperitoneal injections of Se at a dose of 0.1 mg kg^-1 . After 28 days, the amount of bone destruction; severity of inflammation; penetration of microorganisms along the root canal; collagen degradation in periodontal ligament; interleukin (IL)-6, hypoxia-inducible factor-1 (HIF-1), cyclooxygenase-2 (COX-2) and caspase-3 expression; autophagic flux; and p38 MAPK signalling were evaluated using radiographic, histopathological, Gram staining, picrosirius red stain, immunohistochemical, quantitative real-time polymerase chain (qRT-PCR) and Western blot methods, respectively. These data were analysed through the Kruskal-Wallis and Dunnett's tests (p < .05).

RESULTS

The area of radiographic periapical bone loss, histopathological scores, the area of periapical bone loss and the scores for the bacteria localisation, the intensity of immunohistochemical staining for IL-6, HIF-1, COX-2 and caspase-3 in the Se group was significantly less than those of the positive control group (p < .01). The mRNA expression levels of Beclin-1, Atg3, Atg5, Atg7 and Atg16L1 were lower in the Se group than in the positive control group (p < .01). The protein expressions of Beclin-1, Atg5 and LC3-II, the phosphorylation ratio of the p38 MAPK and the ratios of LC3II/LC3I were significantly higher (p < .05) in the positive control and Se groups. On the contrary, the expression of the p62/SQSTM1 protein was significantly lower (p < .05) in the positive control and Se groups than in the negative control group.

CONCLUSION

The induction of periapical lesions in rats increased autophagic flux and activated p38 MAPK signal transduction processes. Se suppressed the inflammatory process, reduced bone destruction and both the autophagic flux and p38 MAPK activation.

Formyl peptide receptor 2 as a potential therapeutic target for inflammatory bowel disease

Inflammatory bowel disease (IBD) is a global health burden whose existing treatment is largely dependent on anti-inflammatory agents. Despite showing some therapeutic actions, their clinical efficacy and adverse events are unacceptable. Resolution as an active and orchestrated phase of inflammation involves improper inflammatory response with three key triggers, specialized pro-resolving mediators (SPMs), neutrophils and phagocyte efferocytosis. The formyl peptide receptor 2 (FPR2/ALX) is a human G protein-coupled receptor capable of binding SPMs and participates in the resolution process. This receptor has been implicated in several inflammatory diseases and its association with mouse model of IBD was established in some resolution-related studies. Here, we give an overview of three reported FPR2/ALX agonists highlighting their respective roles in pro-resolving strategies.

Roles of Resolvins in Chronic Inflammatory Response

An inflammatory response is beneficial to the organism, while an excessive uncontrolled inflammatory response can lead to the nonspecific killing of tissue cells. Therefore, promoting the resolution of inflammation is an important mechanism for protecting an organism suffering from chronic inflammatory diseases. Resolvins are a series of endogenous lipid mediums and have the functions of inhibiting a leukocyte infiltration, increasing macrophagocyte phagocytosis, regulating cytokines, and alleviating inflammatory pain. By promoting the inflammation resolution, resolvins play an irreplaceable role throughout the pathological process of some joint inflammation, neuroinflammation, vascular inflammation, and tissue inflammation. Although a large number of experiments have been conducted to study different subtypes of resolvins in different directions, the differences in the action targets between the different subtypes are rarely compared. Hence, this paper reviews the generation of resolvins, the characteristics of resolvins, and the actions of resolvins under a chronic inflammatory response and clinical translation of resolvins for the treatment of chronic inflammatory diseases.

CD4+-mediated colitis in mice is independent of the GPR183 and GPR18 pathways

Colitis is characterized by an exacerbated intestinal immune response, but the genetic and other mechanisms regulating immune activation remain incompletely understood. In order to identify new pathways leading to colitis, we sought to identify genes with increased expression in the colons of patients that also are near loci identified by genome wide association studies (GWAS) associated with IBD risk. One such SNP, rs9557195 was of particular interest because it is within an intron of G-protein-coupled receptor (GPR) 183, known to be important for lymphocyte migration. Furthermore, this SNP is in close proximity to the gene encoding another G-protein coupled receptor, GPR18. Analyzing publicly available datasets, we found transcripts of GPR183 and GPR18 to be increased in colon biopsies from ulcerative colitis and Crohn's disease patients, and GPR183 was even more increased in patients resistant to TNF treatment. Expression of both genes also was increased in mouse models of colitis. Therefore, our aim was to understand if increased expression of these GPRs in the intestine is related to disease severity in colitis models. Here we investigated the role of these receptors in the T cell transfer model and the dextran sulfate sodium model. In the T cell transfer model, GPR183 expression on donor T cells, as well as on other cell types in the Rag-/- recipients, was not essential for severe colitis induction. Furthermore, deficiency in Rag-/- mice for the enzyme that synthesizes a cholesterol metabolite that is a major ligand for GPR183 also did not affect disease. Similarly, lack of GPR18 expression in T cells or other cell types did not affect colitis pathogenesis in the T cell transfer or in the dextran sulfate sodium model. Therefore, despite increased expression of transcripts for these genes in the intestine during inflammation in humans and mice, they are not required for disease severity in mouse models of colitis induced by chemical injury or T cell cytokines, perhaps due to redundancy in mechanisms important for homing and survival of lymphocytes to the inflamed intestine.

Comparison of the biomechanical differences in the occlusal movement of wild-type and BMP9 knockout mice with apical periodontitis

Apical periodontitis is a common clinical disease caused by bacteria; bacterial metabolites can cause an imbalance in bone homeostasis, bone mass reduction, and tooth loss. Bone resorption in apical periodontitis causes a concentration of stress in the tooth and periodontal tissues during occlusion, which aggravates the disease. Emerging evidence indicates that bone morphogenetic protein 9 (BMP9), also known as growth differentiation factor 2(Gdf2), may play an important role in tooth and dentoalveolar development. Herein, we investigated the role of BMP9 in the development of apical periodontitis and its effects on the biomechanics of dentoalveolar bone. Apical periodontitis models were established in five BMP9 knockout (KO) mice and five C57BL/6 WT (wild-type) mice. At baseline and 14, 28, and 42 days after modeling, in vivo micro-computed tomography analysis and three-dimensional (3D) reconstruction were performed to evaluate the apical lesion in each mouse, and confirm that the animal models were successfully established. Finite element analysis (FEA) was performed to study the stress and strain at the alveolar fossa of each mouse under the same vertical and lateral stress. FEA revealed that the stress and strain at the alveolar fossa of each mouse gradually concentrated on the tooth cervix. The stress and strain at the tooth cervix gradually increased with time but were decreased at day 42. Under the same lingual loading, the maximum differences of the stress and strain at the tooth root in KO mice were greater than those in WT mice. Thus, these findings demonstrate that BMP9 could affect the biomechanical response of the alveolar fossa at the tooth root in mice with apical periodontitis. Moreover, the effects of BMP9 on the biomechanical response of the alveolar bone may be site-dependent. Overall, this work contributes to an improved understanding of the pathogenesis of apical periodontitis and may inform the development of new treatment strategies for apical periodontitis.

GPR18 Agonist Resolvin D2 Reduces Early Brain Injury in a Rat Model of Subarachnoid Hemorrhage by Multiple Protective Mechanisms

Early brain injury (EBI) is the early phase of secondary complications arising from subarachnoid hemorrhage (SAH). G protein-coupled receptor 18 (GPR18) can exert neuroprotective effects during ischemia. In this study, we investigated the roles of GPR18 in different brain regions during EBI using a GPR18 agonist, resolvin D2 (RvD2). Location and dynamics of GPR18 expression were assessed by immunohistochemistry and western blotting in a rat model of SAH based on endovascular perforation. RvD2 was given intranasally at 1 h after SAH, and SAH grade, brain water content and behavior were assayed before sacrifice. TUNEL and dihydroethidium staining of the cortex were performed at 24 h after SAH. Selected brain regions were also examined for pathway related proteins using immunofluorescence and Western blotting. We found that GPR18 was expressed in meninges, hypothalamus, cortex and white matter before EBI. After SAH, GPR18 expression was increased in meninges and hypothalamus but decreased in cortex and white matter. RvD2 improved neurological scores and brain edema after SAH. RvD2 attenuated mast cell degranulation and reduced expression of chymase and tryptase expression in the meninges. In the hypothalamus, RvD2 attenuated inflammation, increased expression of proopiomelanocortin and interleukin-10, as well as decreased expression of nerve peptide Y and tumor necrosis factor-α. In cortex, RvD2 alleviated oxidative stress and apoptosis, and protected the blood-brain barrier. RvD2 also ameliorated white matter injury by elevating myelin basic protein and suppressing amyloid precursor protein. Our results suggest that GPR18 may help protect multiple brain regions during EBI, particularly in the cortex and hypothalamus. Upregulating GPR18 by RvD2 may improve neurological functions in different brain regions via multiple mechanisms.

Local immunomodulatory effects of intracanal medications in apical periodontitis

The immune system is an extremely complex biological network that plays a crucial role in the hemostasis of periapical tissue, pathogenesis of apical periodontitis (AP) as well as periapical tissue healing. The successful elimination of microbial infections remains a significant challenge, mostly due to the ever-growing development of antimicrobial-resistant pathogens. The bacterial endurance in the root canal system contributes to features ranging from altered post-treatment healing to exacerbation of chronic periradicular immune response, that compromise the outcome of endodontic treatment. A highly effective strategy for combating infectious diseases and the associated inflammation-mediated tissue damage is to modulate the host immune response in conjunction with antimicrobial therapy. There are several medications currently used in endodontic treatment, however, they suffer various levels of microbial resistance and do not deliver all the required characteristics to simultaneously address both intracanal bacteria and periapical inflammation. Interaction of antimicrobial agents with the immune system can impact its function, leading to immune-suppressive or immune-stimulatory effects. The group of non-conventional antimicrobial medications, such as antimicrobial peptides, propolis, and nanomaterials, are agents that provide strong antimicrobial effectiveness and concomitant immunomodulatory and/or reparative effect, without any host tissue damages. Herein, we provide an overview of local immune modulation in AP and a comprehensive review of the immunomodulatory effect of antimicrobials intracanal medications applied in endodontics with specific emphasis on the antimicrobial nanomaterial-based approaches that provide immunomodulatory potential for successful clinical deployment in endodontics.

Resolvins as a Treatment Modality in Experimental Periodontitis: A Systematic Review of Preclinical Studies

This systematic review aimed to assess scientific data of existing literature to identify the efficacy of resolvins (Rv) in the treatment of periodontitis. The electronic databases, Web of Science (WOS), Medline/PubMed, The Cochrane Library, Scopus, and Saudi digital library (SDL), were searched for eligible studies in the field of periodontics. A thorough analysis of the retrieved literature provided five articles that were assessed and included in this systematic review. The quality of these studies was assessed by updated Essential Animal Research: Reporting of In-Vivo Experiments (ARRIVE) guidelines. The five included studies were published between 2005 and 2018 and investigated resolvins as a treatment approach in experimental periodontitis of animals. Among the study animals employed, New Zealand white rabbits were used in three studies, Wistar rats and Albino mice in two studies, respectively. Four studies have evaluated eicosapentaenoic acid-derived RvE1, and one study evaluated docosahexaenoic acid-derived RvD2. Oral-topical application of Rv was followed in four studies, and intra-peritoneal Rv injection was administered in one study. The study duration in these studies have ranged between 4-12 weeks, and the Rv dose was between 0.1 μg to 0.5 μg. One study evaluated the influence of RvE1 topical application on both the prevention and treatment of experimental periodontitis. Resolvins (RvE1 and RvD2) have been studied in periodontitis-induced animal models to assess their potential role in periodontal inflammation resolution. There are promising preclinical data of using resolvins as a treatment modality in experimental periodontitis. Resolvins have been demonstrated to inhibit the destructive inflammatory process and alveolar bone loss in laboratory-induced periodontitis under controlled experimental conditions.

Nature of the Interplay Between Periodontal Diseases and COVID-19

The coronavirus disease 2019 (COVID-19) is mostly a mild condition, however, in some patients, it could progress into a severe and even fatal disease. Recent studies have shown that COVID-19 infection and severity could be associated with the presence of periodontitis, one of the most prevalent chronic diseases. This association could be explained by the fact that periodontitis and COVID-19 share some common risk factors that included chronic diseases, such as diabetes and hypertension as well as conditions such as age, sex, and genetic variants. Another possible explanation could be the systemic inflammation and the aspiration of periodontopathogens seen in patients with periodontitis, which could have a synergism with the virus or compromise the reaction of the body against COVID-19. This narrative review explores the nature of these associations, the evidence behind them, and their implications.

Apoptotic cell-derived metabolites in efferocytosis-mediated resolution of inflammation

The resolution of inflammation, as part of standard host defense mechanism, is the process to guarantee timely termination of inflammatory responses and eventual restoration of tissue homeostasis . It is mainly achieved via efferocytosis, during which pro-resolving macrophages clear apoptotic neutrophils at the inflammatory site. Unfortunately, impaired resolution can be the leading cause of chronic inflammatory disorders and some autoimmune diseases. Existing studies have provided relatively comprehensive understandings about the recognition and uptake of apoptotic neutrophils by macrophages during early phases of efferocytosis. However, lack of information concerns macrophage metabolism of apoptotic cell-derived metabolites after being released from phagolysosomes or the relationship between such metabolism and efferocytosis. Notwithstanding, three recent studies have revealed macrophage metabolism of cholesterol, fatty acids and arginine, as well as their respective functions in the context of inflammation-resolution. This review provides an overview of the resolution of inflammation, efferocytosis and the key players involved, followed by a focus on the metabolism of apoptotic cell-derived metabolites within efferocytes. Hypotheses of more potential apoptotic cell-derived metabolites and their possible roles in the resolution are also formulated. Understanding the effect of these metabolites further advances the concept that apoptotic cells act as active players to regulate resolution, and also suggests novel therapeutic strategies for diseases driven by defective resolution and even cancer that may be treated through enhanced efferocytosis.

Resolvin-D2 targets myogenic cells and improves muscle regeneration in Duchenne muscular dystrophy

Lack of dystrophin causes muscle degeneration, which is exacerbated by chronic inflammation and reduced regenerative capacity of muscle stem cells in Duchenne Muscular Dystrophy (DMD). To date, glucocorticoids remain the gold standard for the treatment of DMD. These drugs are able to slow down the progression of the disease and increase lifespan by dampening the chronic and excessive inflammatory process; however, they also have numerous harmful side effects that hamper their therapeutic potential. Here, we investigated Resolvin-D2 as a new therapeutic alternative having the potential to target multiple key features contributing to the disease progression. Our in vitro findings showed that Resolvin-D2 promotes the switch of macrophages toward their anti-inflammatory phenotype and increases their secretion of pro-myogenic factors. Moreover, Resolvin-D2 directly targets myogenic cells and promotes their differentiation and the expansion of the pool of myogenic progenitor cells leading to increased myogenesis. These effects are ablated when the receptor Gpr18 is knocked-out, knocked-down, or blocked by the pharmacological antagonist O-1918. Using different mouse models of DMD, we showed that Resolvin-D2 targets both inflammation and myogenesis leading to enhanced muscle function compared to glucocorticoids. Overall, this preclinical study has identified a new therapeutic approach that is more potent than the gold-standard treatment for DMD.

Resolvin D2 suppresses NLRP3 inflammasome by promoting autophagy in macrophages

Inflammasome, a multiprotein complex that regulates interleukin (IL)-1β secretion and pyroptosis, participates in numerous inflammatory diseases, including sepsis, atherosclerosis and type-2 diabetes. Investigating the inflammasome regulation is therefore crucial to understand the inflammasome activation and develop treatment for the related diseases. In addition, it remains unknown how the inflammasome is naturally suppressed during the inflammatory process. The present study aimed to investigate the role of resolvin D2 (RvD2), an innate suppressor of inflammation produced from essential ω3-polyunsaturated fatty acids, in the activation of the inflammasome via in vitro and in vivo experiments. The effects of RvD2 on the cytokine production of inflammasome-related peritonitis were determined, and the NLRP3 inflammasome activation was investigated in the presence of RvD2. Moreover, the potential mechanisms underlying RvD2 in NLRP3 inflammasome regulation through autophagy and proteasome were investigated. The results of the present study demonstrated that RvD2 suppressed inflammasome-mediated peritonitis in vivo and regulated the NLR family pyrin domain containing 3 (NLRP3) inflammasome, but not in absent in melanoma 2 (AIM2), NLR family CARD domain containing 4 (NLRC4) inflammasomes. Mechanistically, RvD2 was found to promote the degradation of NLRP3 through autophagy, and the inhibition of autophagy could reverse the RvD2-mediated suppression of NLRP3 inflammasome in vitro and partially reverse the inflammasome-mediated peritonitis in vivo. In summary, the present study reported the negative regulation of NLRP3 inflammasome activation by RvD2. The findings from this study may extend the knowledge of the innate regulation of inflammasome and highlight a possible target for inflammasome-related diseases.

Matrix stiffness regulates bone repair by modulating 12-lipoxygenase-mediated early inflammation

Lipid metabolism in macrophages has been increasingly emphasized in exerting an anti-inflammatory effect and accelerating fracture healing. 12-lipoxygenase (12-LOX) is expressed in several cell types, including macrophages, and oxidizes polyunsaturated fatty acids (PUFAs) to generate both pro- and anti-inflammatory lipid mediators, of which the n-3 PUFAs play an important part in tissue homeostasis/fibrosis. Although mechanical factor regulates the lipid metabolic axis of inflammatory cells, specifically matrix stiffness influences macrophages metabolic responses, little is known about how matrix stiffness affects the 12-LOX-mediated early inflammation in bone repair. In the present study, demineralized bone matrix (DBM) scaffolds with different matrix stiffness were constructed by controlling the duration of decalcification (0 h (control), 1 h (high), 12 h (medium), and 5 d (low)) to repair the defected rat skull. The expression of inflammatory cytokines and macrophages polarization were analyzed. The lipid metabolites and lipid mediators' biosynthesis by matrix stiffness-regulated were further detected. The results showed that the low matrix stiffness could polarize macrophages into an anti-inflammatory phenotype, promote the expression of anti-inflammatory cytokines and specialized pro-resolving lipid mediators (SPMs) biosynthesis beneficial for the osteogenesis of mesenchymal stem cells (MSCs). After treated with ML355, the expression of anti-inflammatory cytokines/proteins and SPMs biosynthesis in macrophages cultured on low-matrix stiffness scaffolds were repressed, and there were almost no statistical differences among all groups. Findings from this study support that matrix stiffness regulates bone repair by modulating 12-LOX-mediated early inflammation, which suggest a direct mechanical impact of matrix stiffness on macrophages lipid metabolism and provide a new insight into the clinical application of SPMs for bone regeneration.

Specialized pro-resolving lipid mediators in endodontics: a narrative review

Endodontics is the branch of dentistry concerned with the morphology, physiology, and pathology of the human dental pulp and periradicular tissues. Human dental pulp is a highly dynamic tissue equipped with a network of resident immunocompetent cells that play major roles in the defense against pathogens and during tissue injury. However, the efficiency of these mechanisms during dental pulp inflammation (pulpitis) varies due to anatomical and physiological restrictions. Uncontrolled, excessive, or unresolved inflammation can lead to pulp tissue necrosis and subsequent bone infections called apical periodontitis. In most cases, pulpitis treatment consists of total pulp removal. Although this strategy has a good success rate, this treatment has some drawbacks (lack of defense mechanisms, loss of healing capacities, incomplete formation of the root in young patients). In a sizeable number of clinical situations, the decision to perform pulp extirpation and endodontic treatment is justifiable by the lack of therapeutic tools that could otherwise limit the immune/inflammatory process. In the past few decades, many studies have demonstrated that the resolution of acute inflammation is necessary to avoid the development of chronic inflammation and to promote repair or regeneration. This active process is orchestrated by Specialized Pro-resolving lipid Mediators (SPMs), including lipoxins, resolvins, protectins and maresins. Interestingly, SPMs do not have direct anti-inflammatory effects by inhibiting or directly blocking this process but can actively reduce neutrophil infiltration into inflamed tissues, enhance efferocytosis and bacterial phagocytosis by monocytes and macrophages and simultaneously inhibit inflammatory cytokine production. Experimental clinical application of SPMs has shown promising result in a wide range of inflammatory diseases, such as renal fibrosis, cerebral ischemia, marginal periodontitis, and cancer; the potential of SPMs in endodontic therapy has recently been explored. In this review, our objective was to analyze the involvement and potential use of SPMs in endodontic therapies with an emphasis on SPM delivery systems to effectively administer SPMs into the dental pulp space.

Novel selective agonist of GPR18, PSB-KK-1415 exerts potent anti-inflammatory and anti-nociceptive activities in animal models of intestinal inflammation and inflammatory pain

BACKGROUND

GPR18 is a recently deorphanized receptor which was reported to act with several endogenous cannabinoid ligands. Here, we aimed to describe the role of GPR18 in intestinal inflammation and inflammatory pain.

METHODS

The anti-inflammatory activity of selective GPR18 agonist, PSB-KK-1415, and antagonist, PSB-CB5, was characterized in semi-chronic and chronic mouse models of colitis induced by 2,4,6-trinitrobenzenesulfonic acid (TNBS). The extent of inflammation was evaluated based on the macroscopic and microscopic scores, quantification of myeloperoxidase (MPO) activity, and Western blot analyses of tumor necrosis factor-α (TNF-α) and interleukin-6 in colonic tissue. The expression of GPR18 in colonic samples from patients with Crohn's disease (CD) was quantified using real-time PCR. The anti-nociceptive potential of the agonist in intestinal inflammation was evaluated in the mouse model of inflammatory pain.

KEY RESULTS

In semi-chronic colitis, PSB-KK-1415 reduced macroscopic score (1.79 ± 0.22 vs. 2.61 ± 0.48), expression of TNF-α (1.89 ± 0.36 vs. 2.83 ± 0.64), and microscopic score (5.00 ± 0.33 vs. 6.45 ± 0.40), all compared to mice with colitis. In chronic colitis, PSB-KK-1415 decreased macroscopic score (3.33 ± 1.26 vs. 4.00 ± 1.32) and MPO activity (32.23 ± 8.51 vs. 41.33 ± 11.64) compared to inflamed mice. In the mouse model of inflammatory pain, PSB-KK-1415 decreased the number of pain-induced behaviors in both, controls (32.60 ± 2.54 vs. 58.00 ± 6.24) and inflamed mice (60.83 ± 2.85 vs. 85.00 ± 5.77) compared to animals without treatment with PSB-KK-1415 (P < 0.005 for both). Lastly, we showed an increased expression of GPR18 in CD patients compared to healthy controls (3.77 ± 1.46 vs. 2.38 ± 0.66, p = 0.87).

CONCLUSIONS & INFERENCES

We showed that GPR18 is worth considering as a potential treatment target in intestinal inflammation and inflammatory pain.

Nanozymes go oral: nanocatalytic medicine facilitates dental health

Nanozymes are multi-functional nanomaterials with enzyme-like activity, which rapidly won a place in biomedicine due to their number of nanocatalytic materials types and applications. Yan and Gao first discovered horseradish peroxidase-like activity in ferromagnetic nanoparticles in 2007. With the joint efforts of many scientists, a new concept-nanocatalytic medicine-is emerging. Nanozymes overcome the inherent disadvantages of natural enzymes, such as poor environmental stability, high production costs, difficult storage and so on. Their progress in dentistry is following the advancement of materials science. The oral research and application of nanozymes is becoming a new branch of nanocatalytic medicine. In order to highlight the great contribution of nanozymes facilitating dental health, we first review the overall research progress of multi-functional nanozymes in oral related diseases, including treating dental caries, dental pulp diseases, oral ulcers and peri-implantitis; the monitoring of oral cancer, oral bacteria and ions; and the regeneration of soft and hard tissue. Additionally, we also propose the challenges remaining for nanozymes in terms of their research and application, and mention future concerns. We believe that the new catalytic nanomaterials will play important roles in dentistry in the future.

Proresolving Mediators in Endodontics: A Systematic Review

INTRODUCTION

Proresolving lipid mediators are specialized molecules (SPMs) involved in the active resolution of the inflammatory process by regulating tissue homeostasis. The aim of this study was to investigate the scientific literature to assess the potential of SPMs as an adjunct in the treatment of endodontic infection.

METHODS

Three electronic databases (PubMed, Web of Science, and Scopus) were searched from their inception until February 2020 (PROSPERO CRD42020164743). Supplemental research was performed by screening the references of the relevant studies eligible for inclusion. A quality assessment of animal studies was performed using the Animal Research: Reporting of In Vivo Experiments guidelines, whereas the Systematic Review Centre for Laboratory animal Experimentation Risk of Bias tool was used to assess the risk of bias.

RESULTS

A total of 3295 records were screened, and 8 articles meeting the criteria were included for this qualitative review. The eligible studies showed a high to moderate overall quality and a low to moderate risk of bias. SPMs positively affected the development of pulpitis and apical periodontitis in experimental animal models. The early treatment of pulpitis with the topical application of SPMs was beneficial to control inflammation within 24 hours from contamination. In addition, SPMs delivered within the root canals after disinfection were found effective in promoting periapical healing.

CONCLUSIONS

Our findings suggest that SPMs may play a role in the inception and treatment of pulpal-periapical diseases, and they should be considered for future research for developing new therapeutics as an adjunct to endodontic treatment.

Specialized proresolving mediators in infection and lung injury

Specialized proresolving mediators (SPMs) are endogenous lipid metabolites of long-chain polyunsaturated fatty acids that are involved in promoting the resolution of inflammation. Many disease conditions characterized by excessive inflammation have impaired or altered SPM biosynthesis, which may lead to chronic, unresolved inflammation. Exogenous administration of SPMs in infectious conditions has been shown to be effective at improving infection clearance and survival in preclinical models. SPMs have also shown tremendous promise in the context of inflammatory lung conditions, such as acute respiratory distress syndrome and chronic obstructive pulmonary disease, mostly in preclinical settings. To date, SPMs have not been studied in the context of the novel Coronavirus, severe acute respiratory syndrome Coronavirus-2 (SARS-CoV-2), however their preclinical efficacy in combatting infections and improving acute respiratory distress suggest they may be a valuable resource in the fight against Coronavirus disease-19 (COVID-19). Overall, while the research on SPMs is still evolving, they may offer a novel therapeutic option for inflammatory conditions.

Endogenous antisense walR RNA modulates biofilm organization and pathogenicity of Enterococcus faecalis

Enterococcus faecalis (E. faecalis) is regarded as the major pathogen for persistent periapical periodontitis. The aim of the present study was to investigate the role of antisense walR RNA in the regulation of adjacent downstream genes. Reverse transcription-PCR assays were performed to validate walR. Adjacent downstream genes walK, EF1195, EF1196, and EF1197 were co-transcribed and detect antisense walR RNA. Northern blotting and 5'-rapid amplification of cDNA ends (5'-RACE) assays were conducted to detect and confirm a novel walR antisense (ASwalR) RNA. ASwalR overexpression mutants were constructed, and the biofilm biomass was determined using a crystal violet microtiter assay. The present study detected and confirmed a 550-bp noncoding antisense RNA with the potential to attenuate the activities of the essential response regulator WalR. The levels of antisense walR RNA transcripts were inversely associated with the production of WalR protein. It was showed that overexpression of ASwalR leads to reduced biofilm formation and exopolysaccharide synthesis. Furthermore, the pathogenicity of E. faecalis was markedly decreased by ASwalR overexpression in an in vivo periapical periodontitis model. In summary, the present study detected a novel antisense walR RNA that leads to a reduction in biofilm formation and the pathogenicity of E. faecalis. Collectively, the data suggest a role for ASwalR as a post-transcriptional modulator of the WalR regulator in E. faecalis.

Clinical influence of calcium hydroxide and N-acetylcysteine on the levels of resolvins E1 and D2 in apical periodontitis

AIM

To investigate the presence of resolvins E1 (RvE1) and D2 (RvD2) in teeth with primary endodontic infections and apical periodontitis, and to assess the influence of calcium hydroxide medication [Ca(OH)₂ ], in association with 2% chlorhexidine gel (2% CHX gel), and N-acetylcysteine (NAC) on the levels of RvE1 and RvD2 in periapical tissues.

METHODOLOGY

Thirty-six single-rooted teeth with primary endodontic infections and apical periodontitis were selected and randomly divided into three groups according to the medication: [Ca(OH)₂ ] + saline solution (SSL) [Ca(OH)₂  + SSL group] (n = 12), Ca(OH)₂  + 2% chlorhexidine gel [Ca(OH)₂  + 2% CHX gel group] (n = 12) and NAC [NAC group] (n = 12). Samples were collected from the periapical interstitial fluid at two different sampling times: before (S1) and after 14 days of intracanal medications (S2). Resolvins were measured using the enzyme-linked immunosorbent assay. Data were analysed using paired t-test, Wilcoxon test and Kruskal-Wallis test, followed by Dunn's post hoc test; all statistical tests were performed at a significance level of 5%.

RESULTS

RvE1 and RvD2 were detected in 100% of the samples (36/36) at S1 and S2. Ca(OH)₂ medication did not increase the levels of RvE1 or RvD2 (both P > 0.05); however, NAC significantly increased the levels of RvE1 and RvD2 after 14 days of treatment (P < 0.05).

CONCLUSIONS

RvE1 and RvD2 were detected in periapical tissues from teeth with root canal infections. Moreover, calcium hydroxide medication did not increase the levels of resolvins in apical periodontitis. In contrast, the use of NAC intracanal medication significantly increased the levels of RvE1 and RvD2 after 14 days of treatment.

Therapeutic Exploitation of GPR18: Beyond the Cannabinoids?

GPR18 is a G-protein-coupled receptor that belongs to the orphan class A family. Even though it shares low sequence homology with the cannabinoid receptors CB₁R and CB₂R, a growing body of research suggests its relationship with the endocannabinoid system, not only because it is able to recognize cannabinoid ligands but also because of its expression and ability to heteromerize with CBRs. In this review, we aim to analyze the biological relevance, reported modulators, and structural features of GPR18. In order to guide future drug design in this field, highlights from molecular modeling of GPR18 will be provided.

Specialized pro-resolving mediator network: an update on production and actions

Today, persistent and uncontrolled inflammation is appreciated to play a pivotal role in many diseases, such as cardiovascular diseases, neurodegenerative diseases, metabolic syndrome and many other diseases of public health concern (e.g. Coronavirus Disease 2019 (COVID-19) and periodontal disease). The ideal response to initial challenge in humans is a self-limited inflammatory response leading to complete resolution. The resolution phase is now widely recognized as a biosynthetically active process, governed by a superfamily of endogenous chemical mediators that stimulate resolution of inflammatory responses, namely specialized proresolving mediators (SPMs). Because resolution is the natural ideal response, the SPMs have gained attention. SPMs are mediators that include ω-6 arachidonic acid-derived lipoxins, ω-3 eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA)-derived resolvins, protectins and maresins, cysteinyl-SPMs, as well as n-3 docosapentaenoic acid (DPA)-derived SPMs. These novel immunoresolvents, their biosynthetic pathways and receptors have proven to promote resolution of inflammation, clearance of microbes, reduce pain and promote tissue regeneration via specific cellular and molecular mechanisms. As of 17 August, 2020, PubMed.gov reported >1170 publications for resolvins, confirming their potent protective actions from many laboratories worldwide. Since this field is rapidly expanding, we provide a short update of advances within 2-3 years from human and preclinical animal studies, together with the structural-functional elucidation of SPMs and identification of novel SPM receptors. These new discoveries indicate that SPMs, their pathways and receptors could provide a basis for new approaches for treating inflammation-associated diseases and for stimulating tissue regeneration via resolution pharmacology and precision nutrition.

Resolvin D2 prevents inflammation and oxidative stress in the retina of streptozocin-induced diabetic mice

Diabetic retinopathy is the main ocular complication of diabetes mellitus. The aim of this study was to investigate the protective effect and mechanism of resolvin D2 (RvD2) on diabetic retinopathy. Streptozocin-induced C57/BJ diabetic mice were divided into three groups: normal control, diabetes mellitus, and diabetes plus RvD2 treatment. After three months of diabetic model induction, exogenous RvD2 was injected, monthly for three months, into the vitreous cavity of mice in the diabetic treatment group. Retinal vascular leakage, ganglion cell apoptosis, inflammatory factor expression, and oxidative stress factors were detected one month after the last injection. The levels of retinal vascular leakage and ganglion cell apoptosis in diabetic mice treated with RvD2 were significantly lower than those in untreated diabetic mice, as were the retinal levels of inflammatory factors and oxidative stress. In conclusion, RvD2 might be used as a retinal protective factor for diabetes mellitus by reducing inflammation and oxidative stress.

High Mobility Group Box 1 Expression in Oral Inflammation and Regeneration

High mobility group box 1 (HMGB1) is a non-histone DNA-binding protein of about 30 kDa. It is released from a variety of cells into the extracellular milieu in response to inflammatory stimuli and acts on specific cell-surface receptors, such as receptors for advanced glycation end-products (RAGE), Toll-like receptor (TLR)2, TLR4, with or without forming a complex with other molecules. HMGB1 mediates various mechanisms such as inflammation, cell migration, proliferation, and differentiation. On the other hand, HMGB1 enhances chemotaxis acting through the C-X-C motif chemokine ligand (CXCL)12/C-X-C chemokine receptor (CXCR)4 axis and is involved in regeneration. In the oral cavity, high levels of HMGB1 have been detected in the gingival tissue from periodontitis and peri-implantitis patients, and it has been shown that secreted HMGB1 induces pro-inflammatory cytokine expression, such as interleukin (IL)-1β, IL-6, and tumor necrosis factor (TNF)-α, which prolong inflammation. In contrast, wound healing after tooth extraction or titanium dental implant osseointegration requires an initial acute inflammation, which is regulated by secreted HMGB1. This indicates that secreted HMGB1 regulates angiogenesis and bone remodeling by osteoclast and osteoblast activation and promotes bone healing in oral tissue repair. Therefore, HMGB1 can prolong inflammation in the periodontal tissue and, conversely, can regenerate or repair damaged tissues in the oral cavity. In this review, we highlight the role of HMGB1 in the oral cavity by comparing its function and regulation with its function in other diseases. We also discuss the necessity for further studies in this field to provide more specific scientific evidence for dentistry.

Design and Synthesis of Benzene Congeners of Resolvin E2, a Proresolving Lipid Mediator, as Its Stable Equivalents

Resolvins (Rvs) are highly potent anti-inflammatory lipid mediators that are chemically and biologically unstable because of their polyunsaturated structures. To address this issue, we designed benzene congeners of RvE2, i.e., o-, m-, and p-BZ-RvE2s, as stable equivalents of RvE2 by replacing the unstable skipped diene moiety with a benzene ring on the basis of computational conformation studies and synthesized these congeners via a short common route through two Stille couplings. o-BZ-RvE2 exhibited more potent anti-inflammatory activity and much higher metabolic stability than RvE2. Thus, o-BZ-RvE2 was identified as a stable equivalent of RvE2, which is useful as a lead for anti-inflammatory drugs with a new mechanism of action as well as a biotool for investigating RvE2-mediated inflammation resolving pathways.

Nano-graphene oxide with antisense walR RNA inhibits the pathogenicity of Enterococcus faecalis in periapical periodontitis

Background/purpose

Enterococcus faecalis (E. faecalis) is considered a predominant pathogen for persistent periapical infections. Antisense walR (ASwalR) RNA was reported to inhibit the biofilm formation and sensitized E. faecalis to calcium hydroxide medication. The aims of this study were to investigate whether the graphene oxide (GO) nanosheets could be used to enhance antibacterial activity of ASwalR RNA for E. faecalis in periapical periodontitis.

Materials and methods

We developed a graphene-based plasmid transformation system by loading antisense walR plasmid with GO-polyethylenimine (PEI) complexes (GO-PEI-ASwalR). The particle size distributions and zeta-potential of the GO-PEI-ASwalR were evaluated. Then, ASwalR plasmids were labeled with gene encoding enhanced green fluorescent protein (ASwalR-eGFP). The transformation efficiencies and the bacterial viability of E. faecalis were evaluated by confocal laser scanning microscopy. Quantitative real-time PCR assays were used to investigate the expressions of E. faecalis virulent genes after transformed by GO-PEI-ASwalR. Also, the antibacterial properties of the GO-PEI-ASwalR were validated in the rat periapical periodontitis model.

Results

We showed that GO-PEI could efficiently deliver the ASwalR plasmid into E. faecalis cell. GO-PEI-ASwalR significantly reduced virulent-associated gene expressions. Furthermore, GO-PEI-ASwalR suppressed biofilm aggregation and improved bactericidal effects using infected canal models in vitro. In four-weeks periapical infective rat models, the GO-PEI-ASwalR strains remarkably reduced the periapical lesion size.

Conclusion

Transformation efficiency and antibacterial prosperity of ASwalR can be marked improved by GO-PEI based delivery system for E. faecalis infections.

Estrogen deficiency aggravates apical periodontitis by regulating NLRP3/caspase-1/IL-1β axis

Estrogen plays critical roles in apical periodontitis and subsequent bone loss, however the mechanism is not clear yet. In this study, we aimed to study the underlying mechanism of estrogen in apical periodontitis using both clinic samples and animal model. Clinically, as estrogen physiologically declines in elder female patients (premenopausal verses postmenopausal patients), we found that the expression level of NLRP3/Caspase-1/IL-1β signaling pathway was elevated in the infected apical tissues of postmenopausal patients as compared to the premenopausal patients, suggesting that this pathway is involved in the estrogen-mediated apical periodontitis. Furthermore, by analyzing the well-established OVX (estrogen deficiency model) animal model, we confirmed that the expression level of NLRP3/Caspase-1/IL-1β signaling pathway was also elevated in the infection areas of apical periodontitis in OVX animals. Importantly, as the periodontitis progressed, the subsequent bone loss was aggravated significantly. Thus, taken all these data together, our results demonstrated that the NLRP3/Caspase-1/IL-1β signaling pathway is involved in the estrogen-mediated apical periodontitis and the consequent bone loss in both human being and animal model. This study may provide a potential target for female apical periodontitis therapy.