Butyrate, a bacterial metabolite, induces apoptosis and autophagic cell death in gingival epithelial cells

High-Throughput Combined Analysis of Saliva Microbiota and Metabolomic Profile in Chinese Periodontitis Patients: A Pilot Study

The onset and progression of periodontitis involves complicated interactions between the dysbiotic oral microbiota and disrupted host immune-inflammatory response, which can be mirrored by the changes in salivary metabolites profile. This pilot study sought to examine the saliva microbiome and metabolome in the Chinese population by the combined approach of 16s rRNA sequencing and high-throughput targeted metabolomics to discover potential cues for host-microbe metabolic interactions. Unstimulated whole saliva samples were collected from eighteen Stage III and IV periodontitis patients and thirteen healthy subjects. Full-mouth periodontal parameters were recorded. The taxonomic composition of microbiota was obtained by 16s rRNA sequencing, and the metabolites were identified and measured by ultra-high performance liquid chromatography and mass spectrometry-based metabolomic analysis. The oral microbiota composition displayed marked changes where the abundance of 93 microbial taxa differed significantly between the periodontitis and healthy group. Targeted metabolomics identified 103 differential metabolites between the patients and healthy individuals. Functional enrichment analysis demonstrated the upregulation of protein digestion and absorption, histidine metabolism, and nicotinate and nicotinamide metabolism pathways in the dysbiotic microbiota, while the ferroptosis, tryptophan metabolism, glutathione metabolism, and carbon metabolism pathways were upregulated in the patients. Correlation analysis confirmed positive relationships between the clinical parameters, pathogen abundances, and disease-related metabolite levels. The integral analysis of the saliva microbiome and metabolome yielded an accurate presentation of the dysbiotic oral microbiome and functional alterations in host-microbe metabolism. The microbial and metabolic profiling of the saliva could be a potential tool in the diagnosis, prognosis evaluation, and pathogenesis study of periodontitis.

Periodontopathogen-Related Cell Autophagy-A Double-Edged Sword

The periodontium is a highly organized ecosystem, and the imbalance between oral microorganisms and host defense leads to periodontal diseases. The periodontal pathogens, mainly Gram-negative anaerobic bacteria, colonize the periodontal niches or enter the blood circulation, resulting in periodontal tissue destruction and distal organ damage. This phenomenon links periodontitis with various systemic conditions, including cardiovascular diseases, malignant tumors, steatohepatitis, and Alzheimer's disease. Autophagy is an evolutionarily conserved cellular self-degradation process essential for eliminating internalized pathogens. Nowadays, increasing studies have been carried out in cells derived from periodontal tissues, immune system, and distant organs to investigate the relationship between periodontal pathogen infection and autophagy-related activities. On one hand, as a vital part of innate and adaptive immunity, autophagy actively participates in host resistance to periodontal bacterial infection. On the other, certain periodontal pathogens exploit autophagic vesicles or pathways to evade immune surveillance, therefore achieving survival within host cells. This review provides an overview of the autophagy process and focuses on periodontopathogen-related autophagy and their involvements in cells of different tissue origins, so as to comprehensively understand the role of autophagy in the occurrence and development of periodontal diseases and various periodontitis-associated systemic illnesses.

Reactive oxygen species generation required for autophagy induction during butyrate- or propionate-induced release of damage-associated molecular patterns from dying gingival epithelial Ca9-22 cells

PURPOSE

Bacterial cells in mature dental plaque produce a high concentration of short-chain fatty acids (SCFAs) such as butyrate and propionate. SCFA-treatment on human gingival epithelial Ca9-22 cells induced cell death. However, the exact mechanism underlying cell death remains unclear. In this study, the relationship between reactive oxygen species (ROS) and autophagy induction during SCFA-induced cell death was examined.

METHODS

Human gingival epithelial Ca9-22 cells were treated with butyrate or propionate to induce cell death and the number of dead cells were measured using SYTOX-green dye. A siRNA for ATG5 and N-acetylcysteine (NAC) were used for autophagy reduction and ROS-scavenging, respectively. Release of damage-associated molecular patterns (DAMPs) such as Sin3A-associated protein 130 (SAP130) and high-mobility group box 1 (HMGB1) were detected using western blot.

RESULTS

Reducing autophagy significantly suppressed SCFA-induced Ca9-22 cell death. ROS generation was observed upon SCFA treatment, and scavenging ROS with NAC decreased cell death. NAC also reduced the SCFA-induced increase in microtubule-associated protein 1 light chain 3B (LC3B)-I and LC3B-II, and mitigated the release of DAMPs.

CONCLUSION

The findings suggest that ROS generation is necessary for autophagy, which is required for SCFA-induced cell death and accompanying DAMP release.

The interplay between gingival crevicular fluid microbiome and metabolomic profile in intensively treated people with type 1 diabetes - a combined metagenomic/metabolomic approach cross-sectional study

Aims

This study aimed to assess the gingival crevicular fluid (GCF) microbiome and metabolome of adults with type 1 diabetes (T1D) treated with continuous subcutaneous insulin infusion (CSII).

Methods

In this cross-sectional study, the GCF of adults with T1D treated with CSII and non-diabetic controls were sampled, and metagenomic/metabolomic analyses were performed.

Results

In total, 65 participants with T1D and 45 healthy controls with a mean age of 27.05 ± 5.95 years were investigated. There were 22 cases of mild gingivitis (G) in the T1D group. There were no differences considering the Shannon and Chao indices and β-diversity between people with T1D and G, with T1D without G, and healthy controls. Differential taxa were identified, which were mainly enriched in people with T1D and G. Acetic acid concentration was higher in people with T1D, regardless of the presence of G, than in healthy controls. Propionic acid was higher in people with T1D and G than in healthy controls. Isobutyric and isovaleric acid levels were higher in individuals with T1D and G than in the other two subgroups. The concentration of valeric acid was lower and that of caproic acid was higher in people with T1D (regardless of gingival status) than in healthy controls.

Conclusions

The identification of early changes in periodontal tissues by targeting the microbiome and metabolome could potentially enable effective prevention and initial treatment of periodontal disease in people with T1D.

The Complicated Relationship of Short-Chain Fatty Acids and Oral Microbiome: A Narrative Review

The human oral microbiome has emerged as a focal point of research due to its profound implications for human health. The involvement of short-chain fatty acids in oral microbiome composition, oral health, and chronic inflammation is gaining increasing attention. In this narrative review, the results of early in vitro, in vivo, and pilot clinical studies and research projects are presented in order to define the boundaries of this new complicated issue. According to the results, the current research data are disputable and ambiguous. When investigating the role of SCFAs in human health and disease, it is crucial to distinguish between their local GI effects and the systemic influences. Locally, SCFAs are a part of normal oral microbiota metabolism, but the increased formation of SCFAs usually attribute to dysbiosis; excess SCFAs participate in the development of local oral diseases and in oral biota gut colonization and dysbiosis. On the other hand, a number of studies have established the positive impact of SCFAs on human health as a whole, including the reduction of chronic systemic inflammation, improvement of metabolic processes, and decrease of some types of cancer incidence. Thus, a complex and sophisticated approach with consideration of origin and localization for SCFA function assessment is demanded. Therefore, more research, especially clinical research, is needed to investigate the complicated relationship of SCFAs with health and disease and their potential role in prevention and treatment.

Metaproteomics Characterizes the Human Gingival Crevicular Fluid Microbiome Function in Periodontitis

Periodontitis is the leading cause of tooth loss in adults worldwide. The human proteome and metaproteome characterization of periodontitis is not clearly understood. Gingival crevicular fluid samples were collected from eight periodontitis and eight healthy subjects. Both the human and microbial proteins were characterized by liquid chromatography coupled with high-resolution mass spectrometry. A total of 570 human proteins were found differentially expressed, which were primarily associated with inflammatory response, cell death, cellular junction, and fatty acid metabolism. For the metaproteome, 51 genera were identified, and 10 genera were found highly expressed in periodontitis, while 11 genera were downregulated. The analysis showed that microbial proteins related to butyrate metabolism were upregulated in periodontitis cases. In particular, correlation analysis showed that the expression of host proteins related to inflammatory response, cell death, cellular junction, and lipid metabolism correlates with the alteration of metaproteins, which reflect the changes of molecular function during the occurrence of periodontitis. This study showed that the gingival crevicular fluid human proteome and metaproteome could reflect the characteristics of periodontitis. This might benefit the understanding of the periodontitis mechanism.

Catestatin: Antimicrobial Functions and Potential Therapeutics

The rapid increase in drug-resistant and multidrug-resistant infections poses a serious challenge to antimicrobial therapies, and has created a global health crisis. Since antimicrobial peptides (AMPs) have escaped bacterial resistance throughout evolution, AMPs are a category of potential alternatives for antibiotic-resistant "superbugs". The Chromogranin A (CgA)-derived peptide Catestatin (CST: hCgA352-372; bCgA344-364) was initially identified in 1997 as an acute nicotinic-cholinergic antagonist. Subsequently, CST was established as a pleiotropic hormone. In 2005, it was reported that N-terminal 15 amino acids of bovine CST (bCST1-15 aka cateslytin) exert antibacterial, antifungal, and antiyeast effects without showing any hemolytic effects. In 2017, D-bCST1-15 (where L-amino acids were changed to D-amino acids) was shown to exert very effective antimicrobial effects against various bacterial strains. Beyond antimicrobial effects, D-bCST1-15 potentiated (additive/synergistic) antibacterial effects of cefotaxime, amoxicillin, and methicillin. Furthermore, D-bCST1-15 neither triggered bacterial resistance nor elicited cytokine release. The present review will highlight the antimicrobial effects of CST, bCST1-15 (aka cateslytin), D-bCST1-15, and human variants of CST (Gly364Ser-CST and Pro370Leu-CST); evolutionary conservation of CST in mammals; and their potential as a therapy for antibiotic-resistant "superbugs".

Oral Microbiome Community Composition in Head and Neck Squamous Cell Carcinoma

The impact of the oral microbiome on head and neck cancer pathogenesis and outcomes requires further study. 16s rRNA was isolated and amplified from pre-treatment oral wash samples for 52 cases and 102 controls. The sequences were binned into operational taxonomic units (OTUs) at the genus level. Diversity metrics and significant associations between OTUs and case status were assessed. The samples were binned into community types using Dirichlet multinomial models, and survival outcomes were assessed by community type. Twelve OTUs from the phyla Firmicutes, Proteobacteria, and Acinetobacter were found to differ significantly between the cases and the controls. Beta-diversity was significantly higher between the cases than between the controls (p < 0.01). Two community types were identified based on the predominant sets of OTUs within our study population. The community type with a higher abundance of periodontitis-associated bacteria was more likely to be present in the cases (p < 0.01), in older patients (p < 0.01), and in smokers (p < 0.01). Significant differences between the cases and the controls in community type, beta-diversity, and OTUs indicate that the oral microbiome may play a role in HNSCC.

Autophagy as a potential mechanism underlying the biological effect of 1,25-Dihydroxyvitamin D3 on periodontitis: a narrative review

The major active form of vitamin D, 1,25-dihydroxyvitamin D3 (1,25D3), is known for its wide bioactivity in periodontal tissues. Although the exact mechanisms underlying its protective action against periodontitis remain unclear, recent studies have shown that 1,25D3 regulates autophagy. Autophagy is vital for intracellular pathogen invasion control, inflammation regulation, and bone metabolic balance in periodontal tissue homeostasis, and its regulation could be an interesting pathway for future periodontal studies. Since vitamin D deficiency is a worldwide health problem, its role as a potential regulator of autophagy provides new insights into periodontal diseases. Based on this premise, this narrative literature review aimed to investigate the possible connection between 1,25D3 and autophagy in periodontitis. A comprehensive literature search was conducted on PubMed using the following keywords (e.g., vitamin D, autophagy, periodontitis, pathogens, epithelial cells, immunity, inflammation, and bone loss). In this review, the latest studies on the protective action of 1,25D3 against periodontitis and the regulation of autophagy by 1,25D3 are summarized, and the potential role of 1,25D3-activated autophagy in the pathogenesis of periodontitis is analyzed. 1,25D3 can exert a protective effect against periodontitis through different signaling pathways in the pathogenesis of periodontitis, and at least part of this regulatory effect is achieved through the activation of the autophagic response. This review will help clarify the relationship between 1,25D3 and autophagy in the homeostasis of periodontal tissues and provide perspectives for researchers to optimize prevention and treatment strategies in the future.

Analysis of subgingival micro-organisms based on multi-omics and Treg/Th17 balance in type 2 diabetes with/without periodontitis

Type 2 diabetes mellitus (T2DM) and periodontitis are common and interrelated diseases, resulting in altered host response microbiota. The subgingival micro-organisms play a key role in periodontitis pathogenesis. To assess the shift of subgingival microbiome and metabolome in T2DM, we performed an analysis of the subgingival microbiome in patients with T2DM (n = 20) compared with non-diabetes (ND) subjects (n = 21). Furthermore, patients were subdivided into 10 T2DM with periodontitis (DP), 10 T2DM without periodontitis (DNP), 10 periodontitis (P), and 11 healthy control (H) groups. 16SrRNA gene sequencing combined with ultra high-performance liquid chromatography-mass spectrometry (UHPLC-MS) based metabolomics was performed in all participants. T lymphocyte immunity was analyzed by flow cytometry. Furthermore, the network relationship among subgingival micro-organisms, metabolites, blood glucose level, and T lymphocyte immunity were analyzed. The results showed that the difference of the subgingival microbiome from healthy to periodontitis status was less prominent in T2DM compared with ND, though the clinical signs of disease were similar. The bacteria Eubacterium nodatum group, Filifactor, Fretibacterium, Peptostreptococcus, and Desulfovibrio, amongst others, may be important in the pathopoiesia of periodontitis in the T2DM state. In addition, some dominant bacteria showed network relationships. The Treg/Th17 ratio was lower in the DP and DNP groups than in the P and H groups-though that of P was lower than for H. The percentage of CD4+/CD8+ PD1 and CD8+ PDL1 was higher in the DP and DNP groups than in the H group; the percentage of CD8+ PDL1 was higher in the DP than P groups. Subgingival micro-organisms in periodontitis had a significant metabolic shift in terms of their signature metabolites. Butyrate metabolism and phenylalanine metabolism may play a role in the pathogenesis of periodontitis with/without T2DM. Specifically, biphenyl degradation, tryptophan metabolism, and the two-component system may play important roles in periodontitis with T2DM. Lastly, the network relationship among subgingival micro-organisms, metabolites, blood glucose level, and T lymphocyte immunity were unbalanced. This study identified the changes in the subgingival microbiome associated with periodontitis in T2DM, as well as the associated network between bacterial flora, metabolism dysbiosis, and immune regulation.

Proof-of-Principle Study Suggesting Potential Anti-Inflammatory Activity of Butyrate and Propionate in Periodontal Cells

Short-chain fatty acids (SCFAs) are potent immune modulators present in the gingival crevicular fluid. It is therefore likely that SCFAs exert a role in periodontal health and disease. To better understand how SCFAs can module inflammation, we screened acetic acid, propionic acid, and butyric acid for their potential ability to lower the inflammatory response of macrophages, gingival fibroblasts, and oral epithelial cells in vitro. To this end, RAW 264.7 and primary macrophages were exposed to LPSs from Porphyromonas gingivalis (P. gingivalis) with and without the SCFAs. Moreover, gingival fibroblasts and HSC2 oral epithelial cells were exposed to IL1β and TNFα with and without the SCFAs. We report here that butyrate was effective in reducing the lipopolysaccharide (LPS)-induced expression of IL6 and chemokine (C-X-C motif) ligand 2 (CXCL2) in the RAW 264.7 and primary macrophages. Butyrate also reduced the IL1β and TNFα-induced expression of IL8, chemokine (C-X-C motif) ligand 1 (CXCL1), and CXCL2 in gingival fibroblasts. Likewise, butyrate lowered the induced expression of CXCL1 and CXCL2, but not IL8, in HSC2 cells. Butyrate further caused a reduction of p65 nuclear translocation in RAW 264.7 macrophages, gingival fibroblasts, and HSC2 cells. Propionate and acetate partially lowered the inflammatory response in vitro but did not reach the level of significance. These findings suggest that not only macrophages, but also gingival fibroblasts and oral epithelial cells are susceptive to the anti-inflammatory activity of butyrate.

The Effect of Short-Chain Fatty Acids on Growth of Cryptosporidium parvum In Vitro

In a previous study, we observed an increase in the severity of cryptosporidial infection corresponding to decreased levels of short-chain fatty acids (SCFAs). Therefore, we decided to examine the effect of SCFAs on Cryptosporidium growth in human ileocecal adenocarcinoma (HTC-8) cells. HTC-8 cells were infected with 1 × 105 C. parvum oocysts. After 48 h of incubation with selected SCFAs, cells were fixed and labeled with monoclonal antibody directed to all intracellular stages, and the number of parasites was quantitated using a fluorescent microscope. Acetate, butyrate, propionate and valproate significantly inhibited growth, with an EC50 between 4 and 10 mM. Additionally, when combined, butyrate, acetate and propionate showed increased efficacy. Butyrate also inhibited growth when incubated with sporozoites prior to infection of host cell monolayers. In addition, we looked at possible mechanisms of action of inhibition. A combination of C. parvum infection and butyrate treatment led to increases in apoptosis and certain inflammatory cytokines. We conclude that acetate, propionate and butyrate have direct inhibitory activities in host cells against C. parvum, and butyrate can also affect sporozoite infectivity directly. While not preventing infection, SCFAs may help in keeping the infection low or in check.

PINK1 mediated mitophagy attenuates early apoptosis of gingival epithelial cells induced by high glucose

BACKGROUND

Oxidative stress mediated by hyperglycemia damages cell-reparative processes such as mitophagy. Down-regulation of mitophagy is considered to be a susceptible factor for diabetes mellitus (DM) and its complications. However, the role of mitophagy in DM-associated periodontitis has not been fully elucidated. Apoptosis of human gingival epithelial cells (hGECs) is one of the representative events of DM-associated periodontitis. Thus, this study aimed to investigate PTEN-induced putative kinase 1 (PINK1)-mediated mitophagy activated in the process of high glucose (HG)-induced hGECs apoptosis.

METHODS

For dose-response studies, hGECs were incubated in different concentrations of glucose (5.5, 15, 25, and 50 mmol/L) for 48 h. Then, hGECs were challenged with 25 mmol/L glucose for 12 h and 48 h, respectively. Apoptosis was detected by TdT-mediated dUTP nick end labeling (TUNEL), caspase 9 and mitochondrial membrane potential (MMP). Subsequently, autophagy was evaluated by estimating P62, LC3 II mRNA levels, LC3 fluorescent puncta and LC3-II/I ratio. Meanwhile, the involvement of PINK1-mediated mitophagy was assessed by qRT-PCR, western blotting and immunofluorescence. Finally, hGECs were transfected with shPINK1 and analyzed by MMP, caspase 9 and annexin V-FITC apoptosis.

RESULTS

The number of TUNEL-positive cells and caspase 9 protein were significantly increased in cells challenged with HG (25 mmol/L) for 48 h (HG 48 h). MMP was impaired both at HG 12 h and HG 48 h, but the degree of depolarization was more serious at HG 48 h. The autophagy improved as the amount of LC3 II increased and p62 decreased in HG 12 h. During this process, HG 12 h treatment induced PINK1-mediated mitophagy. PINK1 silencing with HG 12 h resulted in MMP depolarization and cell apoptosis.

CONCLUSIONS

These results suggested that loss of the PINK1 gene may cause mitochondrial dysfunction and increase sensitivity to HG-induced apoptosis of hGECs at the early stage. PINK1 mediated mitophagy attenuates early apoptosis of gingival epithelial cells induced by high glucose.

Butyric acid modulates periodontal nociception in Porphyromonas gingivalis-induced periodontitis

PURPOSE

Periodontitis progresses with chronic inflammation, without periodontal pain. However, the underlying mechanisms are not well known. Here, the involvement of butyric acid (BA) in periodontal pain sensitivity in Porphyromonas gingivalis (P. gingivalis)-induced periodontitis was examined.

METHODS

P. gingivalis was inoculated into the ligature which was tied around the molar (P. gingivalis-L) and the gingival mechanical head withdrawal threshold (MHWT) was measured. Following P. gingivalis-L, the expressions of orphan G protein-coupled receptor 41 (GPR41) in trigeminal ganglion (TG) neurons were examined. The amount of gingival BA was analyzed following the P. gingivalis-L and the changes in the MHWT in complete Freund's adjuvant (CFA)-injected gingival tissue by gingival BA were examined. The changes in the MHWT following P. gingivalis-L by gingival GPR41 antagonist (HA) were examined.

RESULTS

No change in the MHWT was observed, GPR41-immunoreactive TG neurons were increased following P. gingivalis-L. The gingival BA amount increased following P. gingivalis-L, and the gingival BA suppressed the decrease in MHWT following CFA. HA decreased MHWT following P. gingivalis-L.

CONCLUSION

Gingival BA modulates periodontal mechanical nociception via GPR41 signaling in P. gingivalis-L-induced periodontitis.

Autophagy in aging-related oral diseases

Autophagy is an intracellular degradation mechanism that allows recycling of organelles and macromolecules. Autophagic function increases metabolite availability modulating metabolic pathways, differentiation and cell survival. The oral environment is composed of several structures, including mineralized and soft tissues, which are formed by complex interactions between epithelial and mesenchymal cells. With aging, increased prevalence of oral diseases such as periodontitis, oral cancer and periapical lesions are observed in humans. These aging-related oral diseases are chronic conditions that alter the epithelial-mesenchymal homeostasis, disrupting the oral tissue architecture affecting the quality of life of the patients. Given that autophagy levels are reduced with age, the purpose of this review is to discuss the link between autophagy and age-related oral diseases.

Patterns of subgingival microbiota in different periodontal phenotypes

OBJECTIVES

To compare the subgingival microbiota of patients with aggressive (AgP) or chronic periodontitis (CP) to healthy (H), non-periodontitis patients as well as to explore their relevant associations to different host genetic variants.

METHODS

Following clinical examination, blood and subgingival plaque sampling of 471 study participants (125 AgP, 121 CP, 225 H), subgingival community analysis was performed by next generation sequencing of the 16S rRNA. Microbial data from 266 participants (75 AgP, 95 CP, 98 H) were available for analysis. SNPs in the IL6, IL6R and FTO gene were selected for genetic marker analyses.

RESULTS

Combined periodontitis patients (AgP + CP), particularly those classified with AgP, exhibited lower alpha- and beta- diversity. Several genera (including Peptostreptococcaceae, Filifactor, Desulfobulbus, Tannerella and Lachnospiracee) and species were over-abundant in combined periodontitis vs. healthy individuals, while other genera such as Prevotella or Dialister were found to be more abundant in healthy cases. The only genus with difference in abundance between AgP and CP was Granulicatella. No associations between IL6, IL6RA and FTO genetic variants and microbial findings were detected.

CONCLUSION

This study suggests that limited microbial differences existed between AgP and CP and challenges the current notion that periodontitis is associated with increased subgingival microbial diversity compared with periodontal health.

CLINICAL SIGNIFICANCE

The findings of this study cast some doubts on the notion that the dysbiosis characteristic of periodontal disease is expressed as increased microbial diversity.

Gut-Bone Axis: A Non-Negligible Contributor to Periodontitis

Periodontitis is a polymicrobial infectious disease characterized by alveolar bone loss. Systemic diseases or local infections, such as diabetes, postmenopausal osteoporosis, obesity, and inflammatory bowel disease, promote the development and progression of periodontitis. Accumulating evidences have revealed the pivotal effects of gut microbiota on bone health via gut-alveolar-bone axis. Gut pathogens or metabolites may translocate to distant alveolar bone via circulation and regulate bone homeostasis. In addition, gut pathogens can induce aberrant gut immune responses and subsequent homing of immunocytes to distant organs, contributing to pathological bone loss. Gut microbial translocation also enhances systemic inflammation and induces trained myelopoiesis in the bone marrow, which potentially aggravates periodontitis. Furthermore, gut microbiota possibly affects bone health via regulating the production of hormone or hormone-like substances. In this review, we discussed the links between gut microbiota and periodontitis, with a particular focus on the underlying mechanisms of gut-bone axis by which systemic diseases or local infections contribute to the pathogenesis of periodontitis.

Nicotine regulates autophagy of human periodontal ligament cells through α7 nAchR that promotes secretion of inflammatory factors IL-1β and IL-8

Background

Nicotine is an important risk factor and the main toxic component associated with periodontitis. However, the mechanism of nicotine induced periodontitis is not clear. To investigated the mechanism through which nicotine regulates autophagy of human periodontal ligament cells (hPDLCs) through the alpha7 nicotinic acetylcholine receptor (α7 nAChR) and how autophagy further regulates the release of IL-1β and IL-8 secretion in hPDLCs.

Methods

HPDLCs were obtained from root of extracted teeth and pre-incubated in alpha-bungarotoxin (α-BTX) or 3-Methyladenine (3-MA), followed by culturing in nicotine. We used a variety of experimental detection techniques including western blotting, immunofluorescence, enzyme-linked immunosorbent assay (ELISA), transmission electron microscopy (TEM) and RT-qPCR to assess the expression of the LC3 protein, autolysosome, and release of IL-1β and IL-8 from hPDLCs.

Results

Western blots, immunofluorescence and TEM results found that the nicotine significantly increased the autophagy expression in hPDLCs that was time and concentration dependent and reversed by α-BTX treatment (p < 0.05). RT-qPCR and ELISA results revealed a noticeable rise in the release of inflammatory factors IL-1β and IL-8 from hPDLCs in response to nicotine. RT-qPCR and ELISA results showed that nicotine can significantly up-regulate the release of inflammatory factors IL-1β and IL-8 in hPDLCs, and this effect can be inhibited by 3-MA (p < 0.05).

Conclusions

Nicotine regulated autophagy of hPDLCs through α7 nAChR and in turn the regulation of the release of inflammatory factors 1L-1β and 1L-8 by hPDLCs.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12903-021-01894-5.

Comparison of the modulatory effects of three structurally similar potential prebiotic substrates on an in vitro multi-species oral biofilm

Previous research identified potential prebiotic substrates for oral health like the structural analogues N-acetyl-D-mannosamine (NADM) and N-acetyl-D-glucosamine (NADG). The main hypothesis of the current study was twofold. Firstly, it was hypothesized that the modulatory effects of NADM are not limited to changes in multi-species oral biofilm composition, but also include effects on metabolism, virulence, and inflammatory potential. Secondly, the presence and orientation of their N-acetyl group could play a role. Therefore, a comparison was made between the effects of NADM, NADG and D-(+)-mannose on multi-species oral biofilms. Besides a beneficial compositional shift, NADM-treated biofilms also showed an altered metabolism, a reduced virulence and a decreased inflammatory potential. At a substrate concentration of 1 M, these effects were pronounced for all biofilm aspects, whereas at ~ 0.05 M (1%_(w/v)) only the effects on virulence were pronounced. When comparing between substrates, both the presence and orientation of the N-acetyl group played a role. However, this was generally only at 1 M and dependent on the biofilm aspect. Overall, NADM was found to have different effects at two concentrations that beneficially modulate in vitro multi-species oral biofilm composition, metabolism, virulence and inflammatory potential. The presence and orientation of the N-acetyl group influenced these effects.

Resolving the Contradictory Functions of Lysine Decarboxylase and Butyrate in Periodontal and Intestinal Diseases

Periodontal disease is a common, bacterially mediated health problem worldwide. Mastication (chewing) repeatedly traumatizes the gingiva and periodontium, causing traces of inflammatory exudate, gingival crevicular fluid (GCF), to appear in crevices between the teeth and gingiva. Inadequate tooth cleaning causes a dentally adherent microbial biofilm composed of commensal salivary bacteria to appear around these crevices where many bacteria grow better on GCF than in saliva. We reported that lysine decarboxylase (Ldc) from Eikenella corrodens depletes the GCF of lysine by converting it to cadaverine and carbon dioxide. Lysine is an amino acid essential for the integrity and continuous renewal of dentally attached epithelium acting as a barrier to microbial products. Unless removed regularly by oral hygiene, bacterial products invade the lysine-deprived dental attachment where they stimulate inflammation that enhances GCF exudation. Cadaverine increases and supports the development of a butyrate-producing microbiome that utilizes the increased GCF substrates to slowly destroy the periodontium (dysbiosis). A long-standing paradox is that acid-induced Ldc and butyrate production support a commensal (probiotic) microbiome in the intestine. Here, we describe how the different physiologies of the respective tissues explain how the different Ldc and butyrate functions impact the progression and control of these two chronic diseases.

Potential prebiotic substrates modulate composition, metabolism, virulence and inflammatory potential of an in vitro multi-species oral biofilm

Background: Modulation of the commensal oral microbiota constitutes a promising preventive/therapeutic approach in oral healthcare. The use of prebiotics for maintaining/restoring the health-associated homeostasis of the oral microbiota has become an important research topic.

Aims: This study hypothesised that in vitro 14-species oral biofilms can be modulated by (in)direct stimulation of beneficial/commensal bacteria with new potential prebiotic substrates tested at 1 M and 1%_(w/v), resulting in more host-compatible biofilms with fewer pathogens, decreased virulence and less inflammatory potential.

Methods: Established biofilms were repeatedly rinsed with N-acetyl-D-glucosamine, α-D-lactose, D-(+)-trehalose or D-(+)-raffinose at 1 M or 1%_(w/v). Biofilm composition, metabolic profile, virulence and inflammatory potential were eventually determined.

Results: Repeated rinsing caused a shift towards a more health-associated microbiological composition, an altered metabolic profile, often downregulated virulence gene expression and decreased the inflammatory potential on oral keratinocytes. At 1 M, the substrates had pronounced effects on all biofilm aspects, whereas at 1%_(w/v) they had a pronounced effect on virulence gene expression and a limited effect on inflammatory potential.

Conclusion: Overall, this study identified four new potential prebiotic substrates that exhibit different modulatory effects at two different concentrations that cause in vitro multi-species oral biofilms to become more host-compatible.

Effect of Butyric Acid in the Proliferation and Migration of Junctional Epithelium in the Progression of Periodontitis: An In Vitro Study

Purpose: To elucidate the effects of butyric acid (BA), a metabolite of bacteria involved in periodontitis, and a possible enhancer of the junctional epithelial cells. Methods: A murine junctional epithelial cell line, JE-1, was used to assess the effects of sodium butyrate (NaB) as BA. Cell proliferation, migration and attachment were analyzed. Additionally, gene and promoter expression analysis was performed, i.e., cap analysis of gene expression (CAGE) and gene ontology (GO) term enrichment analysis. Results: NaB affected junctional epithelial cell proliferation, migration and attachment. A high concentration of NaB caused cell death and a low concentration tended to promote migration and adhesion. CAGE analysis revealed 75 upregulated and 96 downregulated genes in the cells after 0.2 mM NaB stimulation for 3 h. Regarding GO term enrichment, the genes upregulated >4-fold participated predominantly in cell migration and proliferation. The results of this study suggest that BA produced from periodontopathic bacteria is involved in periodontal tissue destruction at high concentrations. Furthermore, at low concentrations, BA potentially participates in periodontal disease progression by increasing proliferation, migration and attachment of the junctional epithelium and thereby increasing epithelial down-growth.

High Fat Diet Dysbiotic Mechanism of Decreased Gingival Blood Flow

The gut microbiome has a very important role in human health and its influence on the development of numerous diseases is well known. In this study, we investigated the effect of high fat diet (HFD) on the onset of dysbiosis, gingival blood flow decreases, and the periodontal matrix remodeling. We established a dysbiosis model (HFD group) and probiotic model by Lactobacillus rhamnosus GG (LGG) treatment for 12weeks. Fecal samples were collected 24h before mice sacrificing, while short chain fatty acids (SCFA) analysis, DNA extraction, and sequencing for metagenomic analysis were performed afterwards. After sacrificing the animals, we collected periodontal tissues and conducted comprehensive morphological and genetic analyses. While HFD reduced Bacteroidetes, SCFA, and gingival blood flow, this type of diet increased Firmicutes, lipopolysaccharide (LPS) binding protein, TLR4, pro-inflammatory cytokines (TNF-α, IL-1β, and IL-6), matrix metalloproteinases (MMP-2 and MMP-9) expression, and also altered markers of bone resorption (OPG and RANKL). However, LGG treatment mitigated these effects. Thus, it was observed that HFD increased molecular remodeling via inflammation, matrix degradation, and functional remodeling and consequently cause reduced gingival blood flow. All of these changes may lead to the alveolar bone loss and the development of periodontal disease.

Hydrogen sulfide exacerbated periodontal inflammation and induced autophagy in experimental periodontitis

Hydrogen sulfide (H₂S), the metabolite produced by gram-negative bacteria, is present in deep periodontal pockets of periodontitis patients at high concentrations. The harsh conditions in the diseased periodontium may stimulate a local autophagy response. However, how H₂S participates in pathogenesis and whether H₂S induces autophagy in periodontitis remain partially unknown. In this article, we determined the role of the slow-releasing H₂S donor GYY4137 in experimental periodontitis and its possible regulation in autophagy involved. We found that GYY4137 dose-dependently decreased cell viability and increased the level of proinflammatory cytokines in LPS-stimulated human periodontal ligament cells (HPDLCs). Topically applied GYY4137 also exacerbated periodontal inflammation and alveolar bone loss in ligature-induced rats. Moreover, GYY4137 activated autophagy by upregulating the expression levels of the autophagy-related proteins LC3 and Beclin-1 and downregulating P62 in LPS-treated HPDLCs and inflamed periodontal tissues. Blocking autophagy with 3-methyladenine resulted in further increased expression of proinflammatory cytokines in LPS- and GYY4137-induced HPDLCs. Our results indicate that GYY4137 exerted proinflammatory effects and promoted autophagy in periodontitis, and the induced autophagy may function as a cytoprotective mechanism to prevent excessive inflammation.

Reactive oxygen species-dependent release of damage-associated molecular patterns from human gingival epithelial Ca9-22 cells during butyrate or propionate exposure

Treating the gingival epithelial Ca9-22 cell with butyrate, a short-chain fatty acid (SCFA) produced by bacteria within mature dental plaque, induces necrotic cellular death. In this report, it was examined whether SCFA-mediated cellular death is accompanied by a release of damage-associated molecular patterns (DAMPs). In addition, the role of reactive oxygen species (ROS) in the release of DAMPs was evaluated. Human gingival epithelial Ca9-22 cells were treated with butyrate or propionate. The amounts of dead cells were then measured using SYTOX-green dye. Released DAMPs were detected by western blot. The role of ROS scavengers, ascorbic acid and N-acetylcysteine, on DAMP-release was evaluated. Dose and time-dependent induction of Ca9-22 cell death was observed during butyrate and propionate treatments. This was accompanied by the release of DAMPs. Ascorbic acid or N-acetylcysteine reduced cellular death and inhibited DAMP-release induced by exposure to butyrate or propionate. These data collectively suggest that SCFA-induced death of gingival epithelial Ca9-22 cells and accompanying release of DAMPs are dependent on ROS.

CXXC5 orchestrates Stat3/Erk/Akt signaling networks to modulate P. gingivalis-elicited autophagy in cementoblasts

The keystone pathogen Porphyromonas gingivalis (P. gingivalis) elicits inflammation and autophagy in periodontal tissues. Transcription factor CXXC-type zinc finger protein 5 (CXXC5) and various signals are sensitive to P. gingivalis invasion. Herein, we investigated the P. gingivalis-elicited autophagy activity, the contribution of CXXC5, and the involvement of signals in cementoblasts, tooth root surface cells crucial in periodontal and periapical regions. After coculture with P. gingivalis, cementoblasts exhibited inflammatory cytokine increase, light chain 3(LC3)-I/II conversion, autophagosome activation, and CXXC5 reduction. Cementoblasts with loss and gain of CXXC5 were developed. CXXC5 silencing suppressed autophagy and inflammation, thereby partially compensating for the effects of P. gingivalis, and vice versa. We then screened potential signals and verified the positive participation of Stat3/Akt/Erk networks through specific inhibitor employment. P. gingivalis and CXXC5 induced autophagy through Beclin1 and Atg5 activation. Intriguingly, Annexin V/PI assay and EdU detection revealed that P. gingivalis promoted apoptosis and repressed cell proliferation. In sum, coculture with P. gingivalis enhanced autophagy activity in cementoblasts, which was partially suppressed by CXXC5 downregulation and mediated by Jak/Stat3, PI3K-Akt, and Erk1/2 signaling. This process probably influenced cell apoptosis and proliferation.

Epigenetic regulation of inflammation in periodontitis: cellular mechanisms and therapeutic potential

Epigenetic mechanisms, namely DNA and histone modifications, are critical regulators of immunity and inflammation which have emerged as potential targets for immunomodulating therapies. The prevalence and significant morbidity of periodontitis, in combination with accumulating evidence that genetic, environmental and lifestyle factors cannot fully explain the susceptibility of individuals to disease development, have driven interest in epigenetic regulation as an important factor in periodontitis pathogenesis. Aberrant promoter methylation profiles of genes involved in inflammatory activation, including TLR2, PTGS2, IFNG, IL6, IL8, and TNF, have been observed in the gingival tissue, peripheral blood or buccal mucosa from patients with periodontitis, correlating with changes in expression and disease severity. The expression of enzymes that regulate histone acetylation, in particular histone deacetylases (HDACs), is also dysregulated in periodontitis-affected gingival tissue. Infection of gingival epithelial cells, gingival fibroblasts and periodontal ligament cells with the oral pathogens Porphyromonas gingivalis or Treponema denticola induces alterations in expression and activity of chromatin-modifying enzymes, as well as site-specific and global changes in DNA methylation profiles and in histone acetylation and methylation marks. These epigenetic changes are associated with excessive production of inflammatory cytokines, chemokines, and matrix-degrading enzymes that can be suppressed by small molecule inhibitors of HDACs (HDACi) or DNA methyltransferases. HDACi and inhibitors of bromodomain-containing BET proteins ameliorate inflammation, osteoclastogenesis, and alveolar bone resorption in animal models of periodontitis, suggesting their clinical potential as host modulation therapeutic agents. However, broader application of epigenomic methods will be required to create a comprehensive map of epigenetic changes in periodontitis. The integration of functional studies with global analyses of the epigenetic landscape will provide critical information on the therapeutic and diagnostic potential of epigenetics in periodontal disease.

Autophagy and its significance in periodontal disease

Autophagy is an evolutionarily conserved process essential for cellular homeostasis and human health. As a lysosome-dependent degradation pathway, autophagy acts as a modulator of the pathogenesis of diverse diseases. The relationship between autophagy and oral diseases has been explored in recent years, and there is increasing interest in the role of autophagy in periodontal disease. Periodontal disease is a prevalent chronic inflammatory disorder characterized by the destruction of periodontal tissues. It is initiated through pathogenic bacterial infection and interacts with the host immune defense, leading to inflammation and alveolar bone resorption. In this review, we outline the machinery of autophagy and present an overview of work on the significance of autophagy in regulating pathogen invasion, the immune response, inflammation, and alveolar bone homeostasis of periodontal disease. Existing data provide support for the importance of autophagy as a multi-dimensional regulator in the pathogenesis of periodontal disease and demonstrate the importance of future research on the potential roles of autophagy in periodontal disease.

A double-edged sword: Role of butyrate in the oral cavity and the gut

Butyrate, a four-carbon short-chain fatty acid (SCFA), is a metabolite of anaerobic bacteria. Butyrate has primarily been described as an energy substance in the studies on the digestive tract. The multiple mechanisms of its protective function in the gut and on underlying diseases (including metabolic diseases, diseases of the nervous system, and osteoporosis) via interaction with intestinal epithelial cells and immune cells have been well documented. There are many butyrogenic bacteria in the oral cavity as well. As essential components of the oral microbiome, periodontal pathogens are also able to generate butyrate when undergoing metabolism. Considerable evidence has indicated that butyrate plays an essential role in the initiation and perpetuation of periodontitis. However, butyrate is considered to participate in the pro-inflammatory activities in periodontal tissue and the reactivation of latent viruses. In this review, we focused on the production and biological impact of butyrate in both intestine and oral cavity and explained the possible pathway of various diseases that were engaged by butyrate. Finally, we suggested two hypotheses, which may give a better understanding of the significantly different functions of butyrate in different organs (i.e., the expanded butyrate paradox).

Periodontitis-level butyrate-induced ferroptosis in periodontal ligament fibroblasts by activation of ferritinophagy

Loss of periodontal ligament fibroblasts (PDLFs) is one critical issue for regenerating lost periodontal tissues. A wide variety of regulated cell death pathways, such as apoptosis, pyroptosis, and necroptosis have been proposed in the periodontitis development. The aim of the present study was to explore whether long-term periodontitis-level butyrate may trigger ferroptosis, a newly characterized iron-dependent regulated cell death in PDLFs. Here, we showed that long-term treatment of butyrate, an important short-chain fatty acid in the periodontal pocket, induces the cargo receptor nuclear receptor coactivator 4 (NCOA4)-mediated ferritinophagy and ferroptosis in PDLFs. Butyrate-induced iron accumulation, reactive oxygen species (ROS) generation, glutathione depletion and lipid peroxidation in PDLFs, and the butyrate-induced ferroptosis can be blocked by the lipid peroxide scavenger ferrostatin-1. The NCOA4-mediated ferritinophagy is dependent on p38/hypoxia inducible factor-1α (HIF-1α) pathway activation as well as Bromodomain-containing protein (BRD) 4 and cyclin-dependent kinase 9 (CDK9) coordination. These lines of evidence provide a new mechanistic insight into the mechanism of loss of PDLFs during periodontitis development, showing that periodontitis-level butyrate disrupted iron homeostasis by activation of NCOA4-mediated ferritinophagy, leading to ferroptosis in PDLFs.

Establishment and use of a three-dimensional ameloblastoma culture model to study the effects of butyric acid on the transcription of growth factors and laminin β3

OBJECTIVE

This study aimed to establish a three-dimensional (3D) culture method for ameloblastoma cell lines and to use the model to investigate the effect of butyric acid (BA), a periodontopathic bacterial metabolite, on the malignant transformation of ameloblastoma.

DESIGN

Three ameloblastoma cell lines (HAM1, HAM2, and HAM3) established from the same tumor were used in this study. A 3D culture model was established in low absorption dishes and was incubated for 48 h. The effects of BA on the transcription of growth factors and LMβ3 were examined by real-time reverse transcription PCR. Various BA concentrations (0.02, 0.2, 2, and 20 mM) were used to stimulate the cell cultures for 6 and 12 h.

RESULTS

A 3D culture model was established. Gene expression levels of epithelial growth factor (EGF), transforming growth factor beta 1 (TGFβ1), and laminin β3 (LMβ3) were higher in 3D than in 2D cultures. Cell morphology in 3D cultures did not change, while the transcription levels of EGF, TGFβ1, and LMβ3 were upregulated by BA in all cell lines.

CONCLUSION

The 3D culture model is more responsive to BA than the 2D culture model, and there is a possibility that the malignancy and progression of ameloblastoma via laminin 332 (LM332) is mediated by BA.

Gingival tissue autophagy pathway gene expression profiles in periodontitis and aging

OBJECTIVE

We hypothesized that autophagy-related genes will be differentially expressed in periodontitis, suggesting an impaired gingival autophagic response associated with disease.

BACKGROUND

Autophagy is a cellular physiologic mechanism to maintain tissue homeostasis, while deficient autophagic responses increase inflammation and susceptibility to infection.

METHODS

Rhesus monkeys [<3 years to 23 years of age (n = 34)] were examined for periodontal health and naturally occurring periodontitis. Gingival tissues samples were obtained from healthy or diseased sites, total RNA was isolated, and the Rhesus Gene Chip 1.0 ST (Affymetrix) was used for gene expression analysis of 150 autophagy-related genes.

RESULTS

Comparison of expression levels with adult healthy tissues demonstrated a rather limited number of individual genes that were significantly different across the age-groups. In contrast, with periodontitis in the adults and aged animals, about 15% of the genes were significantly increased or decreased. The differences were reflected in the mTOR complex (5/12), ULK1/ATG1 complex (5/9), PI3K complex (5/21), ATG9 complex (2/7), ATG12 conjugation/LC3 lipidation (7/22), and lysosome fusion/vesicle degradation [LF/VD (5/10)] activities within the broader autophagic pathway. The genes most greatly altered in gingival tissues of naturally occurring periodontitis were identified in the ATG12 and LF/VD pathways that approximated 50% of the genes in each of those categories. While healthy gingival aging did not appear to reflect altered autophagy gene expression, substantial differences were noted with periodontitis irrespective of the age of the animals. Future studies into the role of autophagy in periodontitis and could offer potential new therapeutic strategies to prevent and/or treat periodontal disease.

Effects of Short-Chain Fatty Acids on Human Oral Epithelial Cells and the Potential Impact on Periodontal Disease: A Systematic Review of In Vitro Studies

Short-chain fatty acids (SCFA), bacterial metabolites released from dental biofilm, are supposed to target the oral epithelium. There is, however, no consensus on how SCFA affect the oral epithelial cells. The objective of the present study was to systematically review the available in vitro evidence of the impact of SCFA on human oral epithelial cells in the context of periodontal disease. A comprehensive electronic search using five databases along with a grey literature search was performed. In vitro studies that evaluated the effects of SCFA on human oral epithelial cells were eligible for inclusion. Risk of bias was assessed by the University of Bristol's tool for assessing risk of bias in cell culture studies. Certainty in cumulative evidence was evaluated using GRADE criteria (grading of recommendations assessment, development, and evaluation). Of 3591 records identified, 10 were eligible for inclusion. A meta-analysis was not possible due to the heterogeneity between the studies. The risk of bias across the studies was considered "serious" due to the presence of methodological biases. Despite these limitations, this review showed that SCFA negatively affect the viability of oral epithelial cells by activating a series of cellular events that includes apoptosis, autophagy, and pyroptosis. SCFA impair the integrity and presumably the transmigration of leucocytes through the epithelial layer by changing junctional and adhesion protein expression, respectively. SCFA also affect the expression of chemokines and cytokines in oral epithelial cells. Future research needs to identify the underlying signaling cascades and to translate the in vitro findings into preclinical models.

Butyrate Decreases ICAM-1 Expression in Human Oral Squamous Cell Carcinoma Cells

Short-chain fatty acids (SCFA) are bacterial metabolites that can be found in periodontal pockets. The expression of adhesion molecules such as intercellular adhesion molecule-1 (ICAM-1) within the epithelium pocket is considered to be a key event for the selective transmigration of leucocytes towards the gingival sulcus. However, the impact of SCFA on ICAM-1 expression by oral epithelial cells remains unclear. We therefore exposed the oral squamous carcinoma cell line HSC-2, primary oral epithelial cells and human gingival fibroblasts to SCFA, namely acetate, propionate and butyrate, and stimulated with known inducers of ICAM-1 such as interleukin-1-beta (IL1β) and tumor necrosis factor-alfa (TNFα). We report here that butyrate but not acetate or propionate significantly suppressed the cytokine-induced ICAM-1 expression in HSC-2 epithelial cells and primary epithelial cells. The G-protein coupled receptor-43 (GPR43/ FFAR2) agonist but not the histone deacetylase inhibitor, trichostatin A, mimicked the butyrate effects. Butyrate also attenuated the nuclear translocation of p65 into the nucleus on HSC-2 cells. The decrease of ICAM-1 was independent of Nrf2/HO-1 signaling and phosphorylation of JNK and p38. Nevertheless, butyrate could not reverse an ongoing cytokine-induced ICAM-1 expression in HSC-2 cells. Overall, these observations suggest that butyrate can attenuate cytokine-induced ICAM-1 expression in cells with epithelial origin.

Butyrate rather than LPS subverts gingival epithelial homeostasis by downregulation of intercellular junctions and triggering pyroptosis

AIM

To investigate the effects of sodium butyrate (NaB) and lipopolysaccharide (LPS) on gingival epithelial barrier.

MATERIAL AND METHODS

We cultured human primary gingival epithelial cells and investigated the effects of NaB and LPS on gingival epithelial barrier and involved mechanisms at in vitro and in vivo levels by immunostaining, confocal microscopy, field emission scanning electron microscopy (FE-SEM), transmission electronic microscopy (TEM), transepithelial electrical resistance (TEER), FTIC-dextran flux, flow cytometry, real-time PCR and Western blot assays.

RESULTS

Our results showed that NaB, rather than LPS, destroyed the epithelial barrier by breaking down cell-cell junctions and triggering gingival epithelial cell pyroptosis with characteristic morphological changes, including swollen cells, large bubbles, pore formation in the plasma membrane and subcellular organelles changes. The upregulated expression of pyroptosis-related markers, caspase-3 and gasdermin-E (GSDME) contributed to this effect. Pyroptosis aroused by NaB is a pro-inflammatory cell death. Pyroptotic cell death provoked inflammatory responses by upregulation of IL-8 and MCP-1, and releasing intracellular contents into the extracellular microenvironment after pyroptotic rupture of the plasma membrane.

CONCLUSIONS

Our new findings indicate that butyrate is a potent destructive factor of gingival epithelial barrier and pro-inflammatory mediator, which shed a new light on our understanding of periodontitis initiation.

Species-Level Salivary Microbial Indicators of Well-Resolved Periodontitis: A Preliminary Investigation

Objective: To profile the salivary microbiomes of a Hong Kong Chinese cohort at a species-level resolution and determine species that discriminated clinically resolved periodontitis from periodontally healthy cases. Methods: Salivary microbiomes of 35 Hong Kong Chinese subjects' under routine supportive dental care were analyzed. All subjects had been treated for any dental caries or periodontal disease with all restorative treatment completed at least 1 year ago and had ≤3 residual pockets. They were categorized based on a past diagnosis of chronic periodontitis into "healthy" (H) or "periodontitis" (P) categories. Unstimulated whole saliva was collected, genomic DNA was isolated, and high throughput Illumina MiSeq sequencing of 16S rRNA (V3-V4) gene amplicons was performed. The sequences were assigned taxonomy at the species level by using a BLASTN based algorithm that used a combined reference database of HOMD RefSeqV14.51, HOMD RefSeqExtended V1.1 and GreenGeneGold. Species-level OTUs were subjected to downstream analysis in QIIME and R. For P and H group comparisons, community diversity measures were compared, differentially abundant species were determined using DESeq2, and disease indicator species were determined using multi-level pattern analysis within the R package "indicspecies." Results: P subjects were significantly older than H subjects (p = 0.003) but not significantly different in their BOP scores (p = 0.82). No significant differences were noted in alpha diversity measures after adjusting for age, gender, and BOP or in the beta diversity estimates. Four species; Treponema sp. oral taxon 237, TM7 sp. Oral Taxon A56, Prevotella sp. oral taxon 314, Prevotella sp. oral taxon 304, and Capnocytophaga leadbetteri were significantly more abundant in P than in the H group. Indicator species analysis showed 7 significant indicators species of P group. Fusobacterium sp oral taxon 370 was the sole positive indicator of P group (positive predictive value = 0.9, p = 0.04). Significant indicators of the H category were Leptotrichia buccalis, Corynebacterium matruchotii, Leptotrichia hofstadii, and Streptococcus intermedius. Conclusion: This exploratory study showed salivary microbial species could discriminate treated, well-maintained chronic periodontitis from healthy controls with similar gingival inflammation levels. The findings suggest that certain salivary microbiome features may identify periodontitis-susceptible individuals despite clinical disease resolution.

Importance of Virulence Factors for the Persistence of Oral Bacteria in the Inflamed Gingival Crevice and in the Pathogenesis of Periodontal Disease

Periodontitis is a chronic inflammation that develops due to a destructive tissue response to prolonged inflammation and a disturbed homeostasis (dysbiosis) in the interplay between the microorganisms of the dental biofilm and the host. The infectious nature of the microbes associated with periodontitis is unclear, as is the role of specific bacterial species and virulence factors that interfere with the host defense and tissue repair. This review highlights the impact of classical virulence factors, such as exotoxins, endotoxins, fimbriae and capsule, but also aims to emphasize the often-neglected cascade of metabolic products (e.g., those generated by anaerobic and proteolytic metabolism) that are produced by the bacterial phenotypes that survive and thrive in deep, inflamed periodontal pockets. This metabolic activity of the microbes aggravates the inflammatory response from a low-grade physiologic (homeostatic) inflammation (i.e., gingivitis) into more destructive or tissue remodeling processes in periodontitis. That bacteria associated with periodontitis are linked with a number of systemic diseases of importance in clinical medicine is highlighted and exemplified with rheumatoid arthritis, The unclear significance of a number of potential "virulence factors" that contribute to the pathogenicity of specific bacterial species in the complex biofilm-host interaction clinically is discussed in this review.

[Role of autophagy in the pathogenesis of periodontitis]

Periodontitis is a chronic inflammatory disease of periodontal tissues initiated by oral biofilm. Cellular autophagy is an effective weapon against bacterial infection. Recent studies have shown that autophagy not only promotes the removal of bacteria and toxins from infected cells, but also helps to suppress the inflammatory response to maintain the homeostasis of intracellular environment, which is closely related to the development of periodontitis. Here, we reviewed the relationship between autophagy and periodontitis from three aspects: the interactions between autophagy and periodontal pathogen infection, the regulation of autophagy and immune inflammatory responses, and the relationship between autophagy and alveolar bone metabolism. We aim to provide ideas for further study on the mechanisms of autophagy and periodontitis, and ultimately contribute to a better prevention and treatment of periodontitis.

Association network analysis identifies enzymatic components of gut microbiota that significantly differ between colorectal cancer patients and healthy controls

The human gut microbiota plays a major role in maintaining human health and was recently recognized as a promising target for disease prevention and treatment. Many diseases are traceable to microbiota dysbiosis, implicating altered gut microbial ecosystems, or, in many cases, disrupted microbial enzymes carrying out essential physio-biochemical reactions. Thus, the changes of essential microbial enzyme levels may predict human disorders. With the rapid development of high-throughput sequencing technologies, metagenomics analysis has emerged as an important method to explore the microbial communities in the human body, as well as their functionalities. In this study, we analyzed 156 gut metagenomics samples from patients with colorectal cancer (CRC) and adenoma, as well as that from healthy controls. We estimated the abundance of microbial enzymes using the HMP Unified Metabolic Analysis Network method and identified the differentially abundant enzymes between CRCs and controls. We constructed enzymatic association networks using the extended local similarity analysis algorithm. We identified CRC-associated enzymic changes by analyzing the topological features of the enzymatic association networks, including the clustering coefficient, the betweenness centrality, and the closeness centrality of network nodes. The network topology of enzymatic association network exhibited a difference between the healthy and the CRC environments. The ABC (ATP binding cassette) transporter and small subunit ribosomal protein S19 enzymes, had the highest clustering coefficient in the healthy enzymatic networks. In contrast, the Adenosylhomocysteinase enzyme had the highest clustering coefficient in the CRC enzymatic networks. These enzymic and metabolic differences may serve as risk predictors for CRCs and are worthy of further research.

MicroRNA-214 contributes to regulation of necroptosis via targeting ATF4 in diabetes-associated periodontitis

Diabetes and periodontal diseases have a mutual promoting relationship that induces severe tissue damage and cell death. The potential roles of microRNAs (miRNAs) and the type of cell death involved in diabetes-associated periodontitis are obscure. The gingival tissues of patients were obtained and MC3T3-E1 cells were costimulated with high glucose and lipopolysaccharide (LPS). Osseous morphometric analysis was evaluated with micro-CT, and histological characteristics were measured by hematoxylin/eosin and immunohistochemical staining. Cytokine secretion was confirmed by enzyme-linked immunosorbent assay, and reactive oxygen species (ROS) was measured using a DCFH-DA probe kit. Gene expression was measured by real-time quantitative reverse transcription PCR (qRT-PCR), and protein expression was assessed by Western blot and immunofluorescence analysis. The miR-214 level, receptor-interacting serine-threonine protein (RIP) 1, RIP3, and phospho-mixed lineage kinase domain-like (p-MLKL) protein expression were elevated in the inflamed gingival tissues of diabetes-associated periodontitis patients, with activating transcription factor 4 (ATF4) expression showing the opposite effect. The high glucose (22 mM) could not induce significant increase of RIP1, RIP3, and p-MLKL; however, the high glucose and LPS (500-1000 ng/mL) cotreatment resulted in increase in the number of RIP1, RIP3, and p-MLKL in MC3T3-E1 cells. NAC (ROS inhibitor) inhibited RIP1, RIP3, and increased ATF4; however, necrostatin-1 (Nec-1) (RIP1 inhibitor) specifically inhibited the protein expression of RIP1 and RIP3 and had no influence on ATF4. The use of antagomir-214 suppressed the expression of miR-214, RIP1, RIP3, and p-MLKL, but increased ATF4 protein level in glucose and LPS-induced cells. ATF4 knockdown by ATF4 small interfering RNA offset the effect of antagomir-214. RIP1- and RIP3-dependent necroptosis was confirmed in the inflamed gingival tissues of diabetes-associated periodontitis patients and high glucose- and LPS- cotreated cells. It was suggested that miR-214-targeted ATF4 participated in the regulation of necroptosis in vivo and in vitro.

Necrostatin-1 promotes ectopic periodontal tissue like structure regeneration in LPS-treated PDLSCs

Necroptosis is a programmed necrosis, regulated by receptor interacting protein kinase 1(RIP1) and receptor interacting protein kinase 3(RIP3), and could be inhibited by necrostatin-1(Nec-1) specifically. This study aims to evaluate the effect of Nec-1 on LPS-treated periodontal ligament stem cells (PDLSCs). In the research, three groups were established: normal cultured PDLSCs, Porphyromonas gingivalis (Pg)-LPS stimulated PDLSCs and Pg-LPS+Nec-1 treated PDLSCs. The expression of RIP1 and RIP3 and osteogenic differentiation of PDLSCs in three groups were analyzed. Then, we constructed cell aggregates (CA) using PDLSCs, then PDLSCs-CA were combined with Bio-Oss in three groups were transplanted subcutaneously in nude mice to assess their potentials of periodontal tissue regeneration. The results showed that RIP1 and RIP3 were fully expressed in Pg-LPS stimulated PDLSCs and the level increased significantly. Nec-1 inhibited RIP1-RIP3 interaction, and further inhibited necroptosis of PDLSCs in inflammatory state. Moreover, Nec-1 pretreatment ameliorates the osteogenic differentiation of LPS-treated PDLSCs and can effectively promote the cementum like structure ectopic regenerative ability of PDLSCs in nude mice. These findings show RIP1/RIP3-mediated necroptosis is an important mechanism of cell death in PDLSCs. Nec-1 has a protective effect in reducing cell death and promotes ectopic periodontal tissue like structure regeneration by inhibiting necroptosis. Nec-1 is a hopeful therapeutic agent which protects cells from necroptosis and ameliorates functional outcome.

Receptor-Interacting Protein 3/Caspase-8 May Regulate Inflammatory Response and Promote Tissue Regeneration in the Periodontal Microenvironment

Background

Periodontal ligament stem cells (PDLSCs) possess characteristics of multi-potential differentiation and immuno-modulation, and PDLSCs-mediated periodontal tissue regeneration is regarded as a hopeful method for periodontitis treatment. Recent studies demonstrated that RIP3 and caspase8 regulate bacteria-induced innate immune response and programmed necrosis, which is also called necroptosis. This study aimed to determine the role of the RIP3/Caspase8 signal pathway on necroptosis of PDLSCs under the inflammatory microenvironment, both in vitro and in vivo.

Material/Methods

PDLSCs were cultured, and transmission electron microscopy and flow cytometry were used to detect necroptosis. PCR, ALP, and Alizarin Red S staining were used to assess the effect of necroptosis on osteogenesis differentiation of PDLSCs in vitro, while HE and Masson staining were taken after the nude mouse subcutaneous transplant experiment.

Results

Our research indicates that RIP3/caspase8 can regulate the immune response of PDLSCs, and blockade of RIP3/caspase8 can protect the biological characteristics of the PDLSCs, effectively promoting periodontal tissue regeneration in the inflammatory microenvironment.

Conclusions

Inhibiting RIP3/caspase8 can effectively promote periodontal tissue regeneration in the inflammatory microenvironment.

Epigenetic regulation in bacterial infections: targeting histone deacetylases

Pathogens have developed sophisticated strategies to evade the immune response, among which manipulation of host cellular epigenetic mechanisms plays a prominent role. In the last decade, modulation of histone acetylation in host cells has emerged as an efficient strategy of bacterial immune evasion. Virulence factors and metabolic products of pathogenic microorganisms alter expression and activity of histone acetyltransferases (HATs) and histone deacetylases (HDACs) to suppress transcription of host defense genes through epigenetic changes in histone acetylation marks. This new avenue of pathogen-host interactions is particularly important in light of introduction of HDAC inhibitors into clinical practice. Considerable effort is currently being applied to better understand the effects of HDAC inhibitors on the quality of immune responses to pathogens and to characterize the therapeutic potential of these compounds in microbial infections. In this review, we will discuss the recently discovered mechanisms utilized by bacteria to facilitate their survival within infected hosts through subversion of the host acetylation system and the effects of acetylation modulators, including HDAC inhibitors and bromodomain-containing BET protein inhibitors, on innate immune responses against microbial pathogens. Integration of these two lines of experimental evidence provides critical information on the perspectives of epigenetic therapies targeting protein acetylation in infectious diseases.

The Role of Reactive Oxygen Species and Autophagy in Periodontitis and Their Potential Linkage

Periodontitis is a chronic inflammatory disease that causes damage to periodontal tissues, which include the gingiva, periodontal ligament, and alveolar bone. The major cause of periodontal tissue destruction is an inappropriate host response to microorganisms and their products. Specifically, a homeostatic imbalance between reactive oxygen species (ROS) and antioxidant defense systems has been implicated in the pathogenesis of periodontitis. Elevated levels of ROS acting as intracellular signal transducers result in autophagy, which plays a dual role in periodontitis by promoting cell death or blocking apoptosis in infected cells. Autophagy can also regulate ROS generation and scavenging. Investigations are ongoing to elucidate the crosstalk mechanisms between ROS and autophagy. Here, we review the physiological and pathological roles of ROS and autophagy in periodontal tissues. The redox-sensitive pathways related to autophagy, such as mTORC1, Beclin 1, and the Atg12-Atg5 complex, are explored in depth to provide a comprehensive overview of the crosstalk between ROS and autophagy. Based on the current evidence, we suggest that a potential linkage between ROS and autophagy is involved in the pathogenesis of periodontitis.

Comparative In silico Analysis of Butyrate Production Pathways in Gut Commensals and Pathogens

Biosynthesis of butyrate by commensal bacteria plays a crucial role in maintenance of human gut health while dysbiosis in gut microbiome has been linked to several enteric disorders. Contrastingly, butyrate shows cytotoxic effects in patients with oral diseases like periodontal infections and oral cancer. In addition to these host associations, few syntrophic bacteria couple butyrate degradation with sulfate reduction and methane production. Thus, it becomes imperative to understand the distribution of butyrate metabolism pathways and delineate differences in substrate utilization between pathogens and commensals. The bacteria utilize four pathways for butyrate production with different initial substrates (Pyruvate, 4-aminobutyrate, Glutarate and Lysine) which follow a polyphyletic distribution. A comprehensive mining of complete/draft bacterial genomes indicated conserved juxtaposed genomic arrangement in all these pathways. This gene context information was utilized for an accurate annotation of butyrate production pathways in bacterial genomes. Interestingly, our analysis showed that inspite of a beneficial impact of butyrate in gut, not only commensals, but a few gut pathogens also possess butyrogenic pathways. The results further illustrated that all the gut commensal bacteria (Faecalibacterium, Roseburia, Butyrivibrio, and commensal species of Clostridia etc) ferment pyruvate for butyrate production. On the contrary, the butyrogenic gut pathogen Fusobacterium utilizes different amino acid metabolism pathways like those for Glutamate (4-aminobutyrate and Glutarate) and Lysine for butyrogenesis which leads to a concomitant release of harmful by-products like ammonia in the process. The findings in this study indicate that commensals and pathogens in gut have divergently evolved to produce butyrate using distinct pathways. No such evolutionary selection was observed in oral pathogens (Porphyromonas and Filifactor) which showed presence of pyruvate as well as amino acid fermenting pathways which might be because the final product butyrate is itself known to be cytotoxic in oral diseases. This differential utilization of butyrogenic pathways in gut pathogens and commensals has an enormous ecological impact taking into consideration the immense influence of butyrate on different disorders in humans. The results of this study can potentially guide bioengineering experiments to design therapeutics/probiotics by manipulation of butyrate biosynthesis gene clusters in bacteria.

Autophagy and its implication in human oral diseases

Macroautophagy/autophagy is a conserved lysosomal degradation process essential for cell physiology and human health. By regulating apoptosis, inflammation, pathogen clearance, immune response and other cellular processes, autophagy acts as a modulator of pathogenesis and is a potential therapeutic target in diverse diseases. With regard to oral disease, autophagy can be problematic either when it is activated or impaired, because this process is involved in diverse functions, depending on the specific disease and its level of progression. In particular, activated autophagy functions as a cytoprotective mechanism under environmental stress conditions, which regulates tumor growth and mediates resistance to anticancer treatment in established tumors. During infections and inflammation, activated autophagy selectively delivers microbial antigens to the immune systems, and is therefore connected to the elimination of intracellular pathogens. Impaired autophagy contributes to oxidative stress, genomic instability, chronic tissue damage, inflammation and tumorigenesis, and is involved in aberrant bacterial clearance and immune priming. Hence, substantial progress in the study of autophagy provides new insights into the pathogenesis of oral diseases. This review outlines the mechanisms of autophagy, and highlights the emerging roles of this process in oral cancer, periapical lesions, periodontal diseases, and oral candidiasis.

Programmed cell death in periodontitis: recent advances and future perspectives

Periodontitis is a highly prevalent infectious disease, characterized by destruction of the periodontium, and is the main cause of tooth loss. Periodontitis is initiated by periodontal pathogens, while other risk factors including smoking, stress, and systemic diseases aggravate its progression. Periodontitis affects many people worldwide, but the molecular mechanisms by which pathogens and risk factors destroy the periodontium are unclear. Programmed cell death (PCD), different from necrosis, is an active cell death mediated by a cascade of gene expression events and can be mainly classified into apoptosis, autophagy, necroptosis, and pyroptosis. Although PCD is involved in many inflammatory diseases, its correlation with periodontitis is unclear. After reviewing the relevant published articles, we found that apoptosis has indeed been reported to play a role in periodontitis. However, the role of autophagy in periodontitis needs further verification. Additionally, implication of necroptosis or pyroptosis in periodontitis remains unknown. Therefore, we recommend future studies, which will unravel the pivotal role of PCD in periodontitis, allowing us to prevent, diagnose, and treat the disease, as well as predict its outcomes.