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Background The oral cavity serves as an entrance to the body and is therefore exposed to various exogenous stimuli, including mechanical forces, chemical agents, and bacterial components. The oral mucosa responds to these stimuli to maintain homeostasis and good oral health. The transient receptor potential vanilloid 1 (TRPV1) ion channel functions as an environment-sensing protein and is involved in a wide variety of cellular responses. Recent studies have revealed that epithelial TRPV1 ion channels in the oral cavity play pivotal roles in several pathophysiological conditions. In this review, we summarize the features of epithelial TRPV1 channels in the oral cavity and focus on their cellular function and pathogenicity with reference to related findings in other organs and tissues. Highlight TRPV1 channels are widely expressed in epithelial cells in the oral cavity and play pivotal roles in fundamental cellular processes and disease progression. Conclusion This review suggests that oral epithelial TRPV1 contributes to several cellular functions such as cell proliferation, barrier function, and inflammation. Further understanding of the characteristics of epithelial TRPV1 in the oral cavity may provide new insights into the prevention or treatment of diseases.

Laminin, a basement membrane heterotrimeric glycoprotein composed of α/β/γ subunits, has important tissue-specific functions in the control of cellular behavior. Our recent study showed the colocalization of CD163+ M2-like macrophages with Schwann cells in human dental pulp, leading us to hypothesize that the laminin isoform of Schwann cells is associated with CD163 expression. The present study investigated the distribution of laminin isoforms in human dental pulp and the underlying mechanisms that affect macrophage phenotypes. Immunofluorescence analysis indicated that blood vessels were exclusively positive for laminin α4 and α5, whereas laminin α2 was associated with Schwann cells. Unexpectedly, laminin α3/laminin-332 (α3β3γ2) was detected on lymphatic vessels. In intact and carious teeth, CD163+ cells were associated with laminin α2, whereas CD206 single-positive cells were present inside, outside, and along blood vessels. In vitro incubation of THP-1 macrophages in plates coated with laminin-211/511 or its functionally analogous E8 fragments of α-chain (E8-α) indicated that cell shapes differed between macrophages grown on laminin-211/E8-α2 and macrophages grown on laminin-511/E8-α5. Laminin-211/E8-α2–coated plates upregulated CD163 expression, compared with laminin-511/E8-α5–coated plates. Integrin α3– and integrin α6–neutralizing Abs altered the shape of THP-1 macrophages and upregulated mRNA levels of CD206 and CD163 in macrophages grown on laminin-511; the neutralizing Abs did not affect macrophages grown on laminin-211. These findings suggest that laminin isoforms differentially regulate macrophage behavior via distinct integrin–laminin affinities. Of note, laminin-332 is expressed by pulpal lymphatic vessels, the existence of which has been debated; laminin-211 might have a role in maintaining CD163 expression on macrophages.

BACKGROUND The bioactive metabolite KetoC, generated by intestinal bacteria, exerts various beneficial effects. Nevertheless, its function in the pathogenesis of periodontitis remains unclear. Here, we investigated the effect of KetoC in a mouse model of periodontitis and explored the underlying mechanism. METHODS Thirty-one 8-week-old male C57BL/6N mice were randomly divided into four groups (non-ligation, non-ligation + KetoC, ligation + Porphyromonas gingivalis, and ligation + P. gingivalis + KetoC) (n = 7/8 mice/group) and given a daily oral gavage of KetoC (15 mg/mL) or vehicle for 2 weeks. To induce periodontitis, a 5-0 silk ligature was placed on the maxillary left second molar on day 7, and P. gingivalis W83 (109 colony-forming unit [CFU]) was administered orally every 3 days. On day 14, all mice were euthanized. Alveolar bone destruction was determined from the level of the cemento-enamel junction to the alveolar bone crest. Moreover, bone loss level was confirmed from gingival tissue sections stained with hematoxylin and eosin. The presence of P. gingivalis was quantified using real-time polymerase chain reaction. In vitro, the bacteriostatic and bactericidal effects of KetoC were assessed by analyzing its suppressive activity on the proliferation of P. gingivalis and using a live/dead bacterial staining kit, respectively. A double-bond-deficient metabolite (KetoB) was then used to investigate the importance of double-bond structure in the antimicrobial activity of KetoC on P. gingivalis. RESULTS In vivo, KetoC attenuated alveolar bone destruction and suppressed P. gingivalis in the periodontitis group. In vitro, KetoC (but not KetoB) downregulated the proliferation and viability of P. gingivalis in a dose-dependent manner. CONCLUSIONS KetoC reduced alveolar bone destruction in a periodontitis model via its antimicrobial function. Therefore, this bioactive metabolite may be valuable in clinical applications to support periodontal therapy.

Objective Food-derived bioactive peptides have been reported to exhibit various beneficial effects, including anti-microbial, anti-inflammatory, and anti-oxidant properties. Oxidative stress has been implicated in the development of several inflammatory diseases such as periodontal disease. However, the anti-oxidative effect of food-derived bioactive peptides in gingival epithelial cells (GECs) is unknown. Therefore, we examined the bioactivity of the peptides in GECs. Design Food-derived peptide fractionations derived from rice bran, rice endosperm, corn, and soy were screened for anti-oxidative effects using anti-oxidant response element (ARE)-luciferase–transfected HEK 293 cells. The induction of anti-oxidation–related genes and proteins in GECs by the fractions were examined by quantitative PCR and Western blotting, respectively. Then, the fraction-mediated anti-oxidative effects were examined by measuring intracellular reactive oxygen species (ROS) levels using flow cytometry. Furthermore, the anti-oxidative response-related cellular signaling pathways were analyzed via Western blotting. Results Although treatment with the food-derived peptides alone did not activate anti-oxidative responses, co-treatment with sulforaphane (SFN; a potent anti-oxidant) and certain food-derived peptides enhanced anti-oxidative responses in ARE-luciferase–transfected HEK 293 cells. The fractions augmented heme oxygenase-1 mRNA and protein expression in GECs. The percentage of ROS-positive cells was significantly decreased by co-treatment with SFN and peptide fractions derived from rice bran. Furthermore, the involvement of both nuclear factor erythroid 2-related factor 2 (Nrf2) and extracellular signal-regulated kinase (ERK) in the enhancement of anti-oxidative responses was demonstrated by Western blotting. Conclusions Peptides derived from rice bran enhances SFN-induced anti-oxidative responses in GECs through ERK–Nrf2–ARE signaling.

Objective This study aimed to evaluate the effects of ingested periodontal pathogens on experimental colitis in mice and to elucidate its underlying mechanisms. Background Inflammatory bowel disease (IBD) is defined as a chronic intestinal inflammation that results in damage to the gastrointestinal tract. Epidemiological studies have shown an association between IBD and periodontitis. Although a large number of ingested oral bacteria reach gastrointestinal tract constantly, the effect of ingested periodontal pathogens on intestinal inflammation is still unknown. Methods Experimental colitis was induced by inclusion of dextran sodium sulfate solution in drinking water of the mice. Major periodontal pathogens (Porphyromonas gingivalis, Prevotella intermedia, and Fusobacterium nucleatum) were administered orally every day during the experiment. The severity of colitis between the groups was compared. In vitro studies of the intestinal epithelial cell line were conducted to explore the molecular mechanisms by which periodontal pathogens affect the development of colitis. Results The oral administration of P. gingivalis significantly increased the severity of colitis when compared to other pathogens in the DSS-induced colitis model. The ingested P. gingivalis disrupted the colonic epithelial barrier by decreasing the expression of tight junction proteins in vivo. In vitro permeability assays using the intestinal epithelial cell line suggested the P. gingivalis-specific epithelial barrier disruption. The possible involvement of gingipains in the exacerbation of colitis was implied by using P. gingivalis lacking gingipains. Conclusion Porphyromonas gingivalis exacerbates gastrointestinal inflammation by directly interacting with the intestinal epithelial barrier in a susceptible host.

The gingival epithelium acts as a physical barrier to separate the biofilm from the gingival tissue, providing the first line of defense against bacterial invasion in periodontal disease. Disruption of the gingival epithelial barrier, and the subsequent penetration of exogenous pathogens into the host tissues, triggers an inflammatory response, establishing chronic infection. Currently, more than 700 different bacterial species have been identified in the oral cavity, some of which are known to be periodontopathic. These bacteria contribute to epithelial barrier dysfunction in the gingiva by producing several virulence factors. However, some bacteria in the oral cavity appear to be beneficial, helping gingival epithelial cells maintain their integrity and barrier function. This review aims to discuss current findings regarding microorganism interactions and epithelial barrier function in the oral cavity, with reference to investigations in the gut, where this interaction has been extensively studied.

Background and objectives Recent evidence suggests that oral bacteria can affect extra-oral diseases by modulating aspects of the gut environment such as the microbiome, metabolome, and immune profiles. However, differences in the effects of different types of oral bacteria, particularly periodontopathic and health-associated bacteria, remain elusive. Materials and methods Five-week-old germ-free mice were orally administered with either periodontopathic bacteria as oral pathobionts (Porphyromonas gingivalis, Filifactor alocis, and Fusobacterium nucleatum) or bacteria associated with periodontal health (Actinomyces naeslundii, Streptococcus mitis, and Veillonella rogosae) twice a week for five weeks. The presence of all bacterial species in the feces and the livers of the mice was analyzed via polymerase chain reaction (PCR), using specific primers for 16S rRNA genes. Alveolar bone resorption was evaluated histologically. The expression profiles of various genes in the liver and small intestine were analyzed using real-time PCR. Sera were analyzed to determine the levels of antibodies and endotoxin. The proportions of T helper 17 (Th17) and regulatory T (Treg) cells in mesenteric lymph nodes and Peyer's patches were analyzed using flow cytometry. Results Neither of the types of bacteria administered in this experiment induced alveolar bone resorption. All bacteria elicited some degree of systemic antibody response in the mice, although the response to S. mitis was not obvious. The response to P. gingivalis and V. rogosae was strongest. Generally, the health-associated bacteria but not the periodontitis-associated bacteria were detected in fecal samples. Interestingly, only Fusobacterium nucleatum DNA was detected in the liver, despite that live Fusobacterium nucleatum were not detected in the liver. The levels of interleukin-17 in the intestine and genes related to lipid accumulation in the liver were significantly higher in the mice that received periodontitis-associated bacteria. In addition, expression of the gene associated with endoplasmic reticulum stress was higher and that of the gene controlling circadian rhythm was lower in the periodontitis group. There was no difference in serum endotoxin, T-cell phenotypes in the lymphatic tissues, or genes related to the gut barrier. Conclusion Oral administration of periodontitis-associated bacteria can induce pathological changes in the liver and intestine that are implicated in the process of periodontitis. These findings further support the importance of the oral–gut connection.

Objective Oxidative stress, which is defined as an imbalance between pro-oxidant and antioxidant systems, has been implicated in the development and/or progression of several inflammatory diseases, including periodontal disease. The reactive oxygen species (ROS) are the primary inducers of oxidative stress. In the induction of cytoprotective enzymes, the nuclear factor erythroid 2-related factor 2 (Nrf2)/antioxidant response element (ARE) signaling in antioxidant systems takes a main role. Notably, 10-oxo-trans-11-octadecenoic acid (KetoC), known as a bioactive metabolite generated by intestinal microorganisms, has been reported to have beneficial effects on several biological responses. Therefore, we investigated the antioxidant effect of KetoC on gingival epithelial cells (GECs) in this present study. Methods An SV40-T antigen-transformed human gingival epithelial cell line (Epi4) was used for experiments. The alteration of anti-oxidative stress related genes was analyzed by qPCR. The cellular ROS levels were evaluated by flow cytometry. To explore its molecular mechanisms, ARE promotor activity was analyzed by luciferase assay; the involvement of mitogen-activated protein kinase (MAPK) and G protein-coupled receptor 120 (GPR120) were evaluated by Western blotting and luciferase assay, respectively. Results KetoC significantly increased the expression of antioxidant-related genes in GECs. The level of ROS was significantly inhibited by the pretreatment of KetoC. Extracellular signal-regulated kinase (ERK) phosphorylation by KetoC promoted both the nuclear translocation of Nrf2 and its binding to the ARE in GECs. Further, GPR120 regulated the activation of KetoC induced-Nrf2-ARE signaling. Conclusion KetoC exerts a protective function against the oxidative stress in GECs through GPR120-dependent ERK-Nrf2-ARE signaling.