Increased melatonin in oral mucosal tissue of oral lichen planus (OLP) patients: A possible link between melatonin and its role in oral mucosal inflammation

Melatonin alleviates oral epithelial cell inflammation via Keap1/Nrf2 signaling

BACKGROUND

Oral mucosal diseases manifest primarily as inflammatory conditions. These diseases affect approximately half a billion people worldwide.

OBJECTIVE

Novel and effective strategies for treating inflammatory diseases of the oral mucosa have great potential for improving patient outcomes, and warrant study.

METHODS

The impact of melatonin on inflammation was investigated using RAW264.7 macrophages and HOEC and HSC-3 oral epithelial cells.

RESULTS

Melatonin decreased macrophage-induced inflammation by acting through the melatonin receptor MTNR1A. Additionally, melatonin mitigated macrophage-induced inflammation in oral epithelial cells. Importantly, the results demonstrated that the effects of melatonin on oral epithelial inflammation were mediated through the KEAP1/Nrf2 signaling pathway.

CONCLUSION

These findings will contribute to the development of innovative therapies for inflammatory conditions affecting the oral epithelium.

Melatonin and oral diseases: possible therapeutic roles based on cellular mechanisms

Oral diseases, including periodontal disorders, oral cancer, periodontitis, and mucositis are the major challenges for both patients and healthcare providers. These conditions often involve inflammation, oxidative stress, and impaired cellular processes, leading to symptoms ranging from discomfort to severe debilitation. Conventional treatments for such oral diseases exhibit constraints, prompting the investigation of innovative therapeutic approaches. Considering the anti-inflammatory, anti-oxidant, and anti-cancer effects of melatonin, this study was carried out to investigate the potential protective effects of melatonin in mitigating the severity of oral diseases. Studies indicate that melatonin influences the differentiation of periodontal stem cells, inhibits oral cancer progression, reduces inflammation associated with periodontitis, and alleviates the severity of oral mucositis. Melatonin has demonstrated potential efficacy in both preclinical and clinical investigations; however, findings are frequently heterogeneous and contingent upon contextual factors. This review provides a comprehensiveoverview of current state of knowledge in this domain, elucidating the multifaceted role that melatonin may assume in combatingoral diseases. Further research should be directed toward determining the most effective dosing, timing, and administration methods for melatonin-based therapies for oral diseases.

Melatonin antagonizes lipopolysaccharide-induced pulpal fibroblast responses

Background

Pulpal inflammation is known to be mediated by multiple signaling pathways. However, whether melatonin plays regulatory roles in pulpal inflammation remains unclear. This study aimed at elucidating an in situ expression of melatonin and its receptors in human pulpal tissues, and the contribution of melatonin on the antagonism of lipopolysaccharide (LPS)-infected pulpal fibroblasts.

Methods

Melatonin expression in pulpal tissues harvested from healthy teeth was investigated by immunohistochemical staining. Its receptors, melatonin receptor 1 (MT1) and melatonin receptor 2 (MT2), were also immunostained in pulpal tissues isolated from healthy teeth and inflamed teeth diagnosed with irreversible pulpitis. Morphometric analysis was subsequently performed. After LPS infection of cultured pulpal fibroblasts, cyclo-oxygenase (COX) and interleukin-1 β (IL-1 β) transcripts were examined by using reverse transcription-polymerase chain reaction (RT-PCR). Analysis of mRNA expression was performed to investigate an antagonism of LPS stimulation by melatonin via COX and IL-1 β induction. Mann-Whitney U test and One-way ANOVA were used for statistical analysis to determine a significance level.

Results

Melatonin was expressed in healthy pulpal tissue within the odontoblastic zone, cell-rich zone, and in the pulpal connective tissue. Furthermore, in health, strong MT1 and MT2 expression was distributed similarly in all 3 pulpal zones. In contrast, during disease, expression of MT2 was reduced in inflamed pulpal tissues (P-value< 0.001), but not MT1 (P-value = 0.559). Co-culturing of melatonin with LPS resulted in the reduction of COX-2 and IL-1 β expression in primary pulpal fibroblasts, indicating that melatonin may play an antagonistic role to LPS infection in pulpal fibroblasts.

Conclusions

Human dental pulp abundantly expressed melatonin and its receptors MT1 and MT2 in the odontoblastic layers and pulpal connective tissue layers. Melatonin exerted antagonistic activity against LPS-mediated COX-2 and IL-1 β induction in pulpal fibroblasts, suggesting its therapeutic potential for pulpal inflammation and a possible role of pulpal melatonin in an immunomodulation via functional melatonin receptors expressed in dental pulp.

Dietary Fatty Acids and Other Nutrients in Relation to Inflammation and Particularly to Oral Mucosa Inflammation. A Literature Review

Oral mucosa is site of inflammatory process development. When they are chronic, they provide a microenvironment based on cytokines and inflammatory mediators that contribute to cancer initiation, progression, invasion, and metastasis. Certain dietary fatty acids (FAs) have immunomodulatory, inflammatory, and antiinflammatory effects. This review examined the literature on inflammation, mainly referred to the oral mucosa, and its association with dietary FAs and other nutrients. A Pubmed search of studies published in English until June 2018 was carried out. N-3 FAs have shown immunomodulatory and antiinflammatory activity in certain human diseases. These FAs and their mediators may inhibit inflammation, angiogenesis, and cancer via multiple mechanisms. Studies on cellular models of murine and human intestinal mucosa indicate association between dietary n-3 FA intake and the inflammatory state of mucosa membranes. Nevertheless scarce information on the association between dietary FAs and oral inflammation could be found. Based on the evidence, we hypothesize that n-3 FAs reduce the oral mucosa inflammation thus decreasing the risk of developing precancerous lesions and cancer. Molecular and clinical studies referred to this topic should be carried out as a contribution to the oral cancer prevention.

New evidence of connections between increased O-GlcNAcylation and inflammasome in the oral mucosa of patients with oral lichen planus

Oral lichen planus (OLP) is considered a chronic inflammatory immune-mediated disease of the oral mucosa. Immunopathogenesis of OLP is thought to be associated with cell-mediated immune dysregulation. O-GlcNAcylation is a form of reversible glycosylation. It has been demonstrated that O-GlcNAcylation promoted nuclear factor kappa B (NF-κB) signalling. Activation of NF-кB can induce expression of nucleotide-binding domain-like receptor family pyrin domain containing 3 (NLRP3) inflammasome, which is a large intracellular multi-protein complex involving an immune response. Dysregulated expression of the NLRP3 inflammasome was reported to be associated with autoinflammatory diseases. No integrative studies between O-GlcNAcylation and NLRP3 inflammasome in OLP patients have been reported. The present study aimed to determine the immunohistochemical expression of O-GlcNAcylation, NF-κB signalling molecules and NLRP3 inflammasome in oral mucosae of OLP patients. Oral tissue samples were collected from 30 OLP patients and 30 healthy individuals. Immunohistochemical staining and analyses of immunostaining scores were performed to evaluate expression of O-GlcNAcylation, NF-κB signalling molecules and NLRP3 inflammasome. According to observations in this study, significantly higher levels of O-GlcNAcylation, NF-κB signalling molecules and NLRP3 inflammasome were demonstrated in OLP patients compared with control subjects (P < 0·001). Positive correlations among O-GlcNAcylation, NF-κB signalling molecules and NLRP3 inflammasome were also observed in OLP samples (P < 0·01). In conclusion, the present study provides supportive evidence that increased O-GlcNAcylation is associated with increased expression of NLRP3 inflammasome via the NF-κB signalling pathway. These findings provide a new perspective on immunopathogenesis of OLP in relation to autoinflammation.