Periodontal disease is an inflammatory disease caused by pathogenic oral microorganisms that leads to the destruction of alveolar bone and connective tissues around the teeth. Although many studies have shown that periodontal disease is a risk factor for systemic diseases, such as type 2 diabetes and cardiovascular diseases, the relationship between nonalcoholic fatty liver disease (NAFLD) and periodontal disease has not yet been clarified. Thus, the purpose of this review was to reveal the relationship between NAFLD and periodontal disease based on epidemiological studies, basic research, and immunology. Many cross-sectional and prospective epidemiological studies have indicated that periodontal disease is a risk factor for NAFLD. An in vivo animal model revealed that infection with periodontopathic bacteria accelerates the progression of NAFLD accompanied by enhanced steatosis. Moreover, the detection of periodontopathic bacteria in the liver may demonstrate that the bacteria have a direct impact on NAFLD. Furthermore, Porphyromonas gingivalis lipopolysaccharide induces inflammation and accumulation of intracellular lipids in hepatocytes. Th17 may be a key molecule for explaining the relationship between periodontal disease and NAFLD. In this review, we attempted to establish that oral health is essential for systemic health, especially in patients with NAFLD.

Periodontal disease is a chronic inflammatory disease caused by periodontal bacteria. Recently, periodontal phototherapy, treatment using various types of lasers, has attracted attention. Photobiomodulation, the biological effect of low-power laser irradiation, has been widely studied. Although many types of lasers are applied in periodontal phototherapy, molecular biological effects of laser irradiation on cells in periodontal tissues are unclear. Here, we have summarized the molecular biological effects of diode, Nd:YAG, Er:YAG, Er,Cr:YSGG, and CO₂ lasers irradiation on cells in periodontal tissues. Photobiomodulation by laser irradiation enhanced cell proliferation and calcification in osteoblasts with altering gene expression. Positive effects were observed in fibroblasts on the proliferation, migration, and secretion of chemokines/cytokines. Laser irradiation suppressed gene expression related to inflammation in osteoblasts, fibroblasts, human periodontal ligament cells (hPDLCs), and endothelial cells. Furthermore, recent studies have revealed that laser irradiation affects cell differentiation in hPDLCs and stem cells. Additionally, some studies have also investigated the effects of laser irradiation on endothelial cells, cementoblasts, epithelial cells, osteoclasts, and osteocytes. The appropriate irradiation power was different for each laser apparatus and targeted cells. Thus, through this review, we tried to shed light on basic research that would ultimately lead to clinical application of periodontal phototherapy in the future.

Kataoka A, et al. J Periodontal Implant Sci. 2021 Aug;51(4):226-238. https://doi.org/10.5051/jpis.2006040302

Small extracellular vesicles (sEVs) derived from mesenchymal stem/stromal cells (MSCs) contain microRNAs (miRNAs) that can modulate the cellular behavior of recipient cells. Human periodontal ligament mesenchymal stem/stromal cells (hPDL-MSCs) are a unique MSC population involved in periodontal tissue regeneration; however, the specific miRNAs that regulate their proliferative and differentiation–related properties remain incompletely understood. In this study, we profiled miRNAs enriched in sEVs secreted by highly proliferative human PDL-MSCs and identified hsa-let-7c-3p as a candidate regulator of hPDL-MSC behavior. Functional assays demonstrated that hsa-let-7c-3p enhanced proliferative and migratory behavior, reflected by an approximately 1.5-fold increase in metabolic activity and a 2-fold increase in migration, while suppressing osteogenic differentiation, with approximately 50% reductions in alkaline phosphatase activity and mineralization. To identify functionally relevant downstream targets, we intersected AGO2-RIP-seq–enriched transcripts, RNA-seq–defined genes altered by hsa-let-7c-3p overexpression, and in silico target predictions, identifying NT5E/CD73 as a candidate downstream target with experimental validation. Furthermore, NT5E knockdown partially phenocopied the effects of hsa-let-7c-3p overexpression on hPDL-MSC proliferation, migration, and osteogenic differentiation, supporting a functional link between hsa-let-7c-3p and NT5E/CD73. These findings highlight hsa-let-7c-3p as an underexplored sEV-associated 3p miRNA strand that restrains the proliferation-to-osteogenesis transition of hPDL-MSCs and identify NT5E/CD73 as a functionally relevant downstream target. Clinical trial number. Not applicable.