1,25-dihydroxyvitamin D3 suppresses lipopolysaccharide-induced interleukin-6 production through aryl hydrocarbon receptor/nuclear factor-κB signaling in oral epithelial cells

NAT10 regulates the LPS-induced inflammatory response via the NOX2-ROS-NF-κB pathway in macrophages

Periodontitis is a chronic osteolytic inflammatory disease resulting from complex dynamic interactions among bacterial pathogens and the host immune response. Macrophages play a vital role in the pathogenesis of periodontitis by triggering periodontal inflammation and inducing periodontium destruction. N-Acetyltransferase 10 (NAT10) is an acetyltransferase that has been shown to catalyse N4-acetylcytidine (ac4C) mRNA modification and is related to cellular pathophysiological processes, including the inflammatory immune response. Nevertheless, whether NAT10 regulates the inflammatory response of macrophages in periodontitis remains unclear. In this study, the expression of NAT10 in macrophages was found to decrease during LPS-induced inflammation. NAT10 knockdown significantly reduced the generation of inflammatory factors, while NAT10 overexpression had the opposite effect. RNA sequencing revealed that the differentially expressed genes were enriched in the NF-κB signalling pathway and oxidative stress. Both the NF-κB inhibitor Bay11-7082 and the ROS scavenger N-acetyl-L-cysteine (NAC) could reverse the upregulation of inflammatory factors. NAC inhibited the phosphorylation of NF-κB, but Bay11-7082 had no effect on the production of ROS in NAT10-overexpressing cells, suggesting that NAT10 activated the LPS-induced NF-κB signalling pathway by regulating ROS generation. Furthermore, the expression and stability of Nox2 was promoted after NAT10 overexpression, indicating that Nox2 may be a potential target of NAT10. In vivo, the NAT10 inhibitor Remodelin reduced macrophage infiltration and bone resorption in ligature-induced periodontitis mice. In summary, these results showed that NAT10 accelerated LPS-induced inflammation via the NOX2-ROS-NF-κB pathway in macrophages and that its inhibitor Remodelin might be of potential therapeutic significance in periodontitis treatment.

Enamel Matrix Derivative Suppresses Chemokine Expression in Oral Epithelial Cells

Epithelial cells in periodontitis patients increasingly express chemokines, suggesting their active involvement in the inflammatory process. Enamel matrix derivative (EMD) is an extract of porcine fetal tooth germs clinically applied to support the regrowth of periodontal tissues. Periodontal regeneration might benefit from the potential anti-inflammatory activity of EMD for epithelial cells. Our aim was, therefore, to set up a bioassay where chemokine expression is initiated in the HSC2 oral squamous carcinoma cell line and then test EMD for its capacity to lower the inflammatory response. To establish the bioassay, HSC2 cells being exposed to TNFα and LPS from E. coli (Escherichia coli) or P. gingivalis (Porphyromonas gingivalis) were subjected to RNAseq. Here, TNFα but not LPS caused a robust increase of chemokines, including CXCL1, CXCL2, CXCL8, CCL5, and CCL20 in HSC2 cells. Polymerase chain reaction confirmed the increased expression of the respective chemokines in cells exposed to TNFα and IL-1β. Under these conditions, EMD reduced the expression of all chemokines at the transcriptional level and CXCL8 by immunoassay. The TGF-β receptor type I kinase-inhibitor SB431542 reversed the anti-inflammatory activity. Moreover, EMD-activated TGF-β-canonical signaling was visualized by phosphorylation of smad3 and nuclear translocation of smad2/3 in HSC2 cells and blocked by SB431542. This observation was confirmed with primary oral epithelial cells where EMD significantly lowered the SB431542-dependent expression of CXCL8. In summary, our findings suggest that TGF-β signaling mediates the effects of EMD to lower the forced expression of chemokines in oral epithelial cells.

The role of vitamin D in periodontal health and disease

Vitamin D plays an essential role in calcium and bone metabolism, immune regulation and possesses profound anti-inflammatory effects. Evidence suggests that low serum vitamin D is associated with increased severity of periodontitis, a chronic inflammatory condition characterised by destruction of the supporting tissues surrounding the tooth, which has several shared risk factors with other chronic non-communicable diseases. The biological functions of vitamin D are mediated by its strong anti-microbial, anti-inflammatory, and host modulatory properties. Experimental periodontitis models involving targeted deletion of 1α-hydroxylase, the enzyme responsible for the conversion of inactive substrate to active 1,25(OH)₂ D₃ (calcitriol), showed augmented alveolar bone loss and gingival inflammation. Vitamin D receptor (VDR) gene polymorphisms have also been associated with increased severity of periodontitis. Thus, the involvement of vitamin D in the pathogenesis of periodontitis is biological plausible. Clinical studies have consistently demonstrated an inverse relationship between serum 25OHD₃ and periodontal disease inflammation. However, due to the paucity of well-designed longitudinal studies, there is less support for the impact of vitamin D status on periodontal disease progression and tooth loss. The evidence emphasises the importance of maintaining vitamin D sufficiency in supporting periodontal health. This review aims to first examine the biological mechanisms by which vitamin D might influence the pathogenesis of periodontal disease and second, discuss the clinical evidence which implicate the role of vitamin D in periodontal disease.

The Critical Role of Acyl Hydrocarbon Receptor on the Combined Benefits of Postbiotic Propionate on Active Vitamin D3-Orchestrated Innate Immunity in Salmonella Colitis

Our recent study observed the combined beneficial effects of postbiotic butyrate on active vitamin D3-orchestrated innate immunity to Salmonella Colitis. There is increasing interest in the role of acyl hydrocarbon receptor (AhR) on colitis and innate immunity. Therefore, we investigated the involvement of AhR in the effects. Salmonella colitis model is conducted with 6-8 w/o male C57BL/6 mice: Streptomycin (20 mg/mouse p.o.)-pretreated C57BL/6 mice were mock infected with sterile PBS or infected orally with 1 × 10⁸ CFU of an S. typhimurium wild-type strain SL1344 for 48 h. Before and after the colitis induction, mice were oral gavage with active vitamin D3 0.2 μg/25 g mice (VD3) and/or postbiotics propionate (PP), in the absence of the presence of intraperitoneal injection of AhR inhibitor for 4 and 7 days, respectively. We observed AhR inhibitor counteracted the synergistic effects of PP and VD3 on reducing the severity of Salmonella colitis and body weight loss in C57BL/6 mice, reducing the cecal inflammatory but enhancing antimicrobial peptide mRNAs expression, and reducing the bacterial translocation in liver/spleen, compared to single treatment. It suggests the involvement of AhR on the synergistic effects of postbiotics PP and VD3 on the antibacterial and anti-inflammatory responses in Salmonella colitis and the potential biological treatment of Salmonella colitis.

Chronic Kidney Disease and Periodontitis Interplay-A Narrative Review

Periodontitis (PO), a chronic microbially-induced inflammation of the supporting tissues of the tooth, is linked to various systemic diseases. We analyze its bidirectional relationship to chronic kidney disease (CKD), a major health-care problem with impressive excess mortality. Overwhelming associative relationship between CKD and PO are analyzed. Major pathophysiologic mechanisms that link CKD to PO are then presented: systemic inflammation, endothelial dysfunction, and imbalance of oxidative stress characteristic of CKD have a role in PO development and might influence escape mechanisms of oral microbiota. Subclinical local and systemic inflammation induced by PO might influence in turn CKD outcomes. Homeostatic changes induced by CKD such as mineral bone disorders, acidosis, uremic milieu, or poor salivary flow are also relevant for the occurrence of PO. There is insufficient evidence to recommend a standardized diagnostic and therapeutic approach regarding association of PO to CKD.

The Impact of Chronic Kidney Disease on Nutritional Status and Its Possible Relation with Oral Diseases

Several studies have demonstrated a strong relation between periodontal diseases and chronic kidney disease (CKD). The main mechanisms at the base of this link are malnutrition, vitamin dysregulation, especially of B-group vitamins and of C and D vitamins, oxidative stress, metabolic acidosis and low-grade inflammation. In particular, in hemodialysis (HD) adult patients, an impairment of nutritional status has been observed, induced not only by the HD procedures themselves, but also due to numerous CKD-related comorbidities. The alteration of nutritional assessment induces systemic manifestations that have repercussions on oral health, like oral microbiota dysbiosis, slow healing of wounds related to hypovitaminosis C, and an alteration of the supporting bone structures of the oral cavity related to metabolic acidosis and vitamin D deficiency. Low-grade inflammation has been observed to characterize periodontal diseases locally and, in a systemic manner, CKD contributes to the amplification of the pathological process, bidirectionally. Therefore, CKD and oral disease patients should be managed by a multidisciplinary professional team that can evaluate the possible co-presence of these two pathological conditions, that negatively influence each other, and set up therapeutic strategies to treat them. Once these patients have been identified, they should be included in a follow-up program, characterized by periodic checks in order to manage these pathological conditions.

Tryptophan Metabolites and Aryl Hydrocarbon Receptor in Severe Acute Respiratory Syndrome, Coronavirus-2 (SARS-CoV-2) Pathophysiology

The metabolism of tryptophan is intimately associated with the differential regulation of diverse physiological processes, including in the regulation of responses to severe acute respiratory syndrome, coronavirus-2 (SARS-CoV-2) infection that underpins the COVID-19 pandemic. Two important products of tryptophan metabolism, viz kynurenine and interleukin (IL)4-inducible1 (IL41)-driven indole 3 pyruvate (I3P), activate the aryl hydrocarbon receptor (AhR), thereby altering the nature of immune responses to SARS-CoV-2 infection. AhR activation dysregulates the initial pro-inflammatory cytokines production driven by neutrophils, macrophages, and mast cells, whilst AhR activation suppresses the endogenous antiviral responses of natural killer cells and CD8+ T cells. Such immune responses become further dysregulated by the increased and prolonged pro-inflammatory cytokine suppression of pineal melatonin production coupled to increased gut dysbiosis and gut permeability. The suppression of pineal melatonin and gut microbiome-derived butyrate, coupled to an increase in circulating lipopolysaccharide (LPS) further dysregulates the immune response. The AhR mediates its effects via alterations in the regulation of mitochondrial function in immune cells. The increased risk of severe/fatal SARS-CoV-2 infection by high risk conditions, such as elderly age, obesity, and diabetes are mediated by these conditions having expression levels of melatonin, AhR, butyrate, and LPS that are closer to those driven by SARS-CoV-2 infection. This has a number of future research and treatment implications, including the utilization of melatonin and nutraceuticals that inhibit the AhR, including the polyphenols, epigallocatechin gallate (EGCG), and resveratrol.

Vitamin D Deficiency and Oral Health: A Comprehensive Review

Vitamin D (VD) levels have been gaining growing attention in Oral Health. During growth and adulthood, VD deficiency (VDD) is associated with a wide variety of oral health disorders, and impaired VD synthesis may expedite some of these conditions. In children, severe VDD can induce defective tooth mineralization, resulting in dentin and enamel defects. As a consequence, these defects may increase the risk of the onset and progression of dental caries. Further, VDD has been associated with higher prevalence of periodontitis and gingival inflammation, and several recent preclinical and clinical studies have unveiled potential pathways through which Vitamin D may interact with the periodontium. VDD correction through supplementation may contribute to a successful treatment of periodontitis; however, alveolar bone regeneration procedures performed in baseline VDD patients seem more prone to failure. Vitamin D may also be linked with some oral pathology entities such as certain oral cancers and events of osteonecrosis of the jaw. This review aims to provide comprehensive evidence of how VD levels should be considered to promote good oral health, and to summarize how VDD may hamper oral development and its role in certain oral conditions.