Streptococcus gordonii induces bone resorption by increasing osteoclast differentiation and reducing osteoblast differentiation

Detection of Enterococcus faecalis and the red complex bacteria analyzed by the Checkerboard technique for DNA-DNA hybridization in endodontic infections: A systematic review and meta-analysis

Endodontic infections include conditions such as pulp necrosis, apical periodontitis, abscesses, granulomas, and periapical cysts. Detection of pathogenic microorganisms responsible for these diseases is essential for accurate diagnosis and future therapy. Enterococcus faecalis, Porphyromonas gingivalis, Tannerella forsythia, and Treponema denticola were analyzed qualitatively and quantitatively using the Checkerboard methodology for DNA-DNA hybridizations as a bacterial identification tool. Clinical investigations have shown a significant frequency of these microorganisms. The present systematic review and meta-analysis aimed to determine the prevalence of E. faecalis and red complex bacteria (RCB) (P. gingivalis, T. forsythia, and T. denticola) analyzed by the Checkerboard DNA-DNA hybridization technique in endodontic infections. This systematic literature review followed the Preferred Reporting Items for Systematic Reviews and Meta-analysis (PRISMA) guidelines-electronic databases: PubMed, Scopus, ScienceDirect, Web of Science, and Google Scholar. Statistical analysis was performed using STATA V.15 software. Seventeen articles were included, of which a total of 620 samples were evaluated. Five hundred sixty-seven samples were taken from infected root canals, 34 samples from periradicular tissues, and 27 samples from periapical abscesses of infected teeth. The prevalence of E. faecalis in endodontic infections in all studies was 74 %, of P. gingivalis was 63 %, of T. forsythia 46 %, and of T. denticola 58 %. The presence of bacteria such as E. faecalis reduces the efficiency of endodontic therapy and leads to recurring infections. It is recognized that "RCB" can be identified in endodontic lesions; however, they are not usually prominent. The DNA-DNA hybridization approach is critical for identifying bacteria and detecting difficult-to-culture microorganisms, making it a helpful and cost-effective tool for directing personalized endodontic treatments.

Heat-killed Lancefieldella Rimae Induces Bone Resorption by Promoting Osteoclast Differentiation

INTRODUCTION

Apical periodontitis, mainly caused by bacterial infection in the dental pulp, is often accompanied by abscess, periapical inflammation, and alveolar bone loss. Lancefieldella rimae has been detected in the root canals of patients with apical periodontitis. Here, we investigated whether L. rimae is associated with bone resorption.

METHODS

L. rimae was anaerobically cultured and heat-killed (HKLr). A mouse calvarial implantation model was used to determine the bone resorption in vivo. Committed osteoclasts prepared from C57BL/6 wild-type or Toll-like receptor 2 (TLR2)-deficient mice were differentiated into mature osteoclasts in the presence or absence of HKLr. The mRNA expression of tartrate-resistant acid phosphatase (TRAP), ATPase H+ transporting V0 subunit D2, cathepsin K, interleukin-6, tumor necrosis factor-α, and glyceraldehyde 3-phosphate dehydrogenase was quantified using real-time reverse transcription-polymerase chain reaction. The protein levels of c-Fos and NFATc1 were determined by Western blot analysis.

RESULTS

Implantation of HKLr onto the mouse calvaria induced the bone destruction with an increase of TRAP-positive areas. While HKLr enhanced the differentiation of osteoclasts, this effect was not observed in TLR2-deficient osteoclasts. HKLr dose-dependently increased the mRNA expression of genes associated with osteoclast differentiation including TRAP, ATPase H+ transporting V0 subunit D2, and cathepsin K. In addition, HKLr enhanced the expression of c-Fos and NFATc1, which are important transcription factors for osteoclast differentiation. Moreover, HKLr increased the expression of interleukin-6 and tumor necrosis factor-α.

CONCLUSION

L. rimae induces bone resorption by enhancing osteoclast differentiation through the TLR2 signaling pathway, implying that L. rimae is a causative agent responsible for the alveolar bone resorption accompanying apical periodontitis.

Preventing bisphosphonate induced osteonecrosis of the jaw with a polyguanidine conjugate (GuaDex): A promising new approach

Osteonecrosis of the jaw (ONJ) is a relatively rare side effect after prolonged use of bisphosphonates, which are drugs used to treat bone resorption in osteoporosis and certain cancers. This study introduces a novel ONJ model in rats by combining exposure to bisphosphonates, oral surgery, and bacterial inoculation. Potential ONJ preventive effects of polyguanidine (GuaDex) or antibiotics were evaluated. The study consisted of twenty-four male Wistar rats were divided into four groups. Groups 1 to 3 were given weekly doses of i.v. Zoledronic acid (ZA), four weeks before and two weeks after an osteotomy procedure on their left mandibular first molar. Group 4 was a negative control. Streptococcus gordonii bacteria were introduced into the osteotomy pulp chamber and via the food for seven days. On day eight, the rats were given different treatments. Group 1 was given a GuaDex injection into the osteotomy socket, Group 2 was given an intramuscular (i.m.) injection of clindamycin, Group 3 (positive control) was given an i.m. injection of saline, and Group 4 was given an i.m. injection of saline. Blood samples were taken two weeks after the osteotomy procedure, after which the rats were euthanized. Bone healing, bone mineral density, histology, and blood status were analyzed. The results showed that Group 1 (GuaDex) had no ONJ, extensive ongoing bone regeneration, active healing activity, vascularization, and no presence of bacteria. Group 2 (clindamycin) showed early stages of ONJ, avascular areas, and bacteria. Group 3 showed stages of ONJ, inflammatory infiltrates, defective healing, and bacterial presence, and Group 4 had normal healing activity and no bacterial presence. Conclusion: ZA treatment and bacterial inoculation after tooth extraction inhibited bone remodeling/healing and induced ONJ characteristic lesions in the rats. Only GuaDex apparently prevented ONJ development, stimulated bone remodeling, and provided an antimicrobial effect.

NLRP3 inflammasome activity and periodontal disease pathogenesis-A bidirectional relationship

OBJECTIVE

Periodontitis is an inflammatory oral disease that occurs as a result of the damaging effects of the immune response against the subgingival microflora. Among the mechanisms involved, the nucleotide-binding oligomerization domain, leucine-rich repeat-containing proteins family member NLRP3 (NLR family pyrin domain-containing 3), proposed as the key regulator of macrophage-induced inflammation, is strongly associated with periodontal disease due to the bacterial activators. This paper aimed to present key general concepts of NLRP3 inflammasome activation and regulation in periodontal disease.

METHOD

A narrative review was conducted in order to depict the current knowledge on the relationship between NLRP3 inflammasome activity and periodontal disease. In vitro and in situ studies were retrieved and commented based on their relevance in the field.

RESULTS

The NLRP3 inflammasome activity stimulated by periodontal microbiota drive periodontal disease pathogenesis and progression. This occurs through the release of proinflammatory cytokines IL-1β, IL-18, and DAMPs (damage-associated molecular pattern molecules) following inflammasome activation. Moreover, the tissue expression of NLRP3 is dysregulated by oral microbiota, further exacerbating periodontal inflammation.

CONCLUSION

The review provides new insights into the relationship between the NLRP3 inflammasome activity and periodontal disease pathogenesis, highlighting the roles and regulatory mechanism of inflammatory molecules involved in the disease process.

Oral Propolis Nanoemulsions Modulate Gut Microbiota to Balance Bone Remodeling for Enhanced Osteoporosis Therapy

The discovery of the bone-gut axis linking bone metabolism to gut microbiota (GM) dysbiosis has revolutionized our understanding of managing degenerative skeletal diseases. Targeting GM regulation has emerged as a promising approach to osteoporosis treatment. Herein, we develop propolis nanoemulsions (PNEs) with enhanced gastrointestinal stability and oral bioavailability for GM-based osteoporosis therapy. Orally administered PNEs exhibit superior antiosteoporosis efficacy in an ovariectomized (OVX) mouse model by modulating the GM structure and metabolites and restoring the intestinal barrier function. Multiomics analysis reveals that a reduction in Streptococcus abundance and an increase in the GM metabolite l-arginine are key factors in osteoporosis management. These changes suppress osteoclast activity and enhance osteoblast function, leading to balanced bone remodeling and, thus, significant antiosteoporotic effects via the gut-bone axis. Our results deepen insights into the intricate relationship between GM and bone remodeling, suggesting a promising strategy that maintains the homeostasis of the GM structure and metabolite for osteoporosis treatment.

Experimental Inoculation of Aggregatibacter actinomycetemcomitans and Streptococcus gordonii and Its Impact on Alveolar Bone Loss and Oral and Gut Microbiomes

Oral bacteria are implicated not only in oral diseases but also in gut dysbiosis and inflammatory conditions throughout the body. The periodontal pathogen Aggregatibacter actinomycetemcomitans (Aa) often occurs in complex oral biofilms with Streptococcus gordonii (Sg), and this interaction might influence the pathogenic potential of this pathogen. This study aims to assess the impact of oral inoculation with Aa, Sg, and their association (Aa+Sg) on alveolar bone loss, oral microbiome, and their potential effects on intestinal health in a murine model. Sg and/or Aa were orally administered to C57Bl/6 mice, three times per week, for 4 weeks. Aa was also injected into the gingiva three times during the initial experimental week. After 30 days, alveolar bone loss, expression of genes related to inflammation and mucosal permeability in the intestine, serum LPS levels, and the composition of oral and intestinal microbiomes were determined. Alveolar bone resorption was detected in Aa, Sg, and Aa+Sg groups, although Aa bone levels did not differ from that of the SHAM-inoculated group. Il-1β expression was upregulated in the Aa group relative to the other infected groups, while Il-6 expression was downregulated in infected groups. Aa or Sg downregulated the expression of tight junction genes Cldn 1, Cldn 2, Ocdn, and Zo-1 whereas infection with Aa+Sg led to their upregulation, except for Cldn 1. Aa was detected in the oral biofilm of the Aa+Sg group but not in the gut. Infections altered oral and gut microbiomes. The oral biofilm of the Aa group showed increased abundance of Gammaproteobacteria, Enterobacterales, and Alloprevotella, while Sg administration enhanced the abundance of Alloprevotella and Rothia. The gut microbiome of infected groups showed reduced abundance of Erysipelotrichaceae. Infection with Aa or Sg disrupts both oral and gut microbiomes, impacting oral and gut homeostasis. While the combination of Aa with Sg promotes Aa survival in the oral cavity, it mitigates the adverse effects of Aa in the gut, suggesting a beneficial role of Sg associations in gut health.

The impacts of oral and gut microbiota on alveolar bone loss in periodontitis

Periodontitis, a chronic infectious disease, primarily arises from infections and the invasion of periodontal pathogens. This condition is typified by alveolar bone loss resulting from host immune responses and inflammatory reactions. Periodontal pathogens trigger aberrant inflammatory reactions within periodontal tissues, thereby exacerbating the progression of periodontitis. Simultaneously, these pathogens and metabolites stimulate osteoclast differentiation, which leads to alveolar bone resorption. Moreover, a range of systemic diseases, including diabetes, postmenopausal osteoporosis, obesity and inflammatory bowel disease, can contribute to the development and progression of periodontitis. Many studies have underscored the pivotal role of gut microbiota in bone health through the gut-alveolar bone axis. The circulation may facilitate the transfer of gut pathogens or metabolites to distant alveolar bone, which in turn regulates bone homeostasis. Additionally, gut pathogens can elicit gut immune responses and direct immune cells to remote organs, potentially exacerbating periodontitis. This review summarizes the influence of oral microbiota on the development of periodontitis as well as the association between gut microbiota and periodontitis. By uncovering potential mechanisms of the gut-bone axis, this analysis provides novel insights for the targeted treatment of pathogenic bacteria in periodontitis.

Inflammatory macrophages exploited by oral streptococcus increase IL-1B release via NLRP6 inflammasome

Chronic inflammatory periodontal disease develops in part from the infiltration of a large number of classically activated inflammatory macrophages that release inflammatory cytokines important for disease progression, including inflammasome-dependent interleukin (IL)-1β. Streptococcus gordonii is a normally commensal oral microorganism; while not causative, recent evidence indicates that commensal oral microbes are required for the full development of periodontal disease. We have recently reported that inflammatory macrophages counterintuitively allow for the increased survival of phagocytosed S. gordonii over nonactivated or alternatively activated macrophages. This survival is dependent on increased reactive oxygen species production within the phagosome of the inflammatory macrophages, and resistance by the bacterium and can result in S. gordonii damaging the phagolysosomes. Here, we show that activated macrophages infected with live S. gordonii release more IL-1β than non-activated macrophages infected with either live or dead S. gordonii, and that the survival of oral Streptococci are more dependent on macrophage activation than other Gram positive microbes, both classical pathogens and commensals. We also find that S. gordonii-dependent inflammatory macrophage inflammasome activation requires the cytoplasmic NLRP6. Overall, our results suggest S. gordonii is capable of evading immune destruction, increasing inflammatory mediators, and increasing inflammatory macrophage response, and that this ability is increased under conditions of inflammation. This work reveals additional mechanisms by which normally commensal oral streptococci-macrophage interactions can change, resulting in increased release of mature IL-1β, potentially contributing to an environment that perpetuates inflammation.

Metformin Reduces Bone Resorption in Apical Periodontitis Through Regulation of Osteoblast and Osteoclast Differentiation

INTRODUCTION

We have previously demonstrated that auxiliary metformin therapy promotes healing of apical periodontitis. Here we aimed to investigate the effects of metformin on osteoblast differentiation and osteoclast formation in cultured cells and rat apical periodontitis.

METHODS

Murine pre-osteoblasts MC3T3-E1 and macrophages RAW264.7 were cultured under hypoxia (2% oxygen) or normoxia (21% oxygen) and stimulated with receptor activator of nuclear factor-κB ligand (RANKL) when indicated. Metformin was added to the cultures to evaluate its anti-hypoxic effects. Expressions of osteoblast differentiation regulator runt-related transcription factor 2 (RUNX2), RANKL, and osteoclast marker tartrate-resistant acid phosphatase (TRAP) were assessed by Western blot. Apical periodontitis was induced in mandibular first molars of 10 Sprague-Dawley rats. Root canal therapy with or without metformin supplement was performed. Periapical bone resorption was measured by micro-computed tomography. Immunohistochemistry was used to examine RUNX2, RANKL, and TRAP expressions.

RESULTS

Hypoxia suppressed RUNX2 expression and enhanced RANKL synthesis in pre-osteoblasts. TRAP production increased in macrophages after hypoxia and/or RANKL stimulation. Metformin reversed hypoxia-induced RUNX2 suppression and RANKL synthesis in pre-osteoblasts. Metformin also inhibited hypoxia and RANKL-enhanced TRAP synthesis in macrophages. Intracanal metformin diminished bone loss in rat apical periodontitis. Comparing with vehicle control, cells lining bone surfaces in metformin-treated lesions had significantly stronger expression of RUNX2 and decreased synthesis of RANKL and TRAP.

CONCLUSIONS

Alleviation of bone resorption by intracanal metformin was associated with enhanced osteoblast differentiation and diminished osteoclast formation in rat apical periodontitis. Our results endorsed the role of metformin as an effective medicament for inflammatory bone diseases.

A Review on Saliva-Based Health Diagnostics: Biomarker Selection and Future Directions

The human body has a unique way of saying when something is wrong with it. The molecules in the body fluids can be helpful in the early detection of diseases by enabling health and preventing disease progression. These biomarkers enabling better healthcare are becoming an extensive area of research interest. Biosensors that detect these biomarkers are becoming the future, especially Point Of Care (POC) biosensors that remove the need to be physically present in the hospital. Detection of complex and systemic diseases using biosensors has a long way to go. Saliva-based biosensors are gaining attention among body fluids due to their non-invasive collection and ability to detect periodontal disease and identify systemic diseases. The possibility of saliva-based diagnostic biosensors has gained much publicity, with companies sending home kits for ancestry prediction. Saliva-based testing for covid 19 has revealed effective clinical use and relevance of the economic collection. Based on universal biomarkers, the detection of systemic diseases is a booming research arena. Lots of research on saliva-based biosensors is available, but it still poses challenges and limitations as POC devices. This review paper talks about the relevance of saliva and its usefulness as a biosensor. Also, it has recommendations that need to be considered to enable it as a possible diagnostic tool.

Graphical Abstract

Oral Commensal Streptococci: Gatekeepers of the Oral Cavity

Oral commensal streptococci are primary colonizers of the oral cavity. These streptococci produce many adhesins, metabolites, and antimicrobials that modulate microbial succession and diversity within the oral cavity. Often, oral commensal streptococci antagonize cariogenic and periodontal pathogens such as Streptococcus mutans and Porphyromonas gingivalis, respectively. Mechanisms of antagonism are varied and range from the generation of hydrogen peroxide, competitive metabolite scavenging, the generation of reactive nitrogen intermediates, and bacteriocin production. Furthermore, several oral commensal streptococci have been shown to alter the host immune response at steady state and in response to oral pathogens. Collectively, these features highlight the remarkable ability of oral commensal streptococci to regulate the structure and function of the oral microbiome. In this review, we discuss mechanisms used by oral commensal streptococci to interact with diverse oral pathogens, both physically and through the production of antimicrobials. Finally, we conclude by exploring the critical roles of oral commensal streptococci in modulating the host immune response and maintaining health and homeostasis.

Effects of extracellular vesicles derived from oral bacteria on osteoclast differentiation and activation

Dysbiosis of the oral microbiota plays an important role in the progression of periodontitis, which is characterized by chronic inflammation and alveolar bone loss, and associated with systemic diseases. Bacterial extracellular vesicles (EVs) contain various bioactive molecules and show diverse effects on host environments depending on the bacterial species. Recently, we reported that EVs derived from Filifactor alocis, a Gram-positive periodontal pathogen, had osteoclastogenic activity. In the present study, we analysed the osteoclastogenic potency and immunostimulatory activity of EVs derived from the Gram-negative periodontal pathogens Porphyromonas gingivalis and Tannerella forsythia, the oral commensal bacterium Streptococcus oralis, and the gut probiotic strain Lactobacillus reuteri. Bacterial EVs were purified by density gradient ultracentrifugation using OptiPrep (iodixanol) reagent. EVs from P. gingivalis, T. forsythia, and S. oralis increased osteoclast differentiation and osteoclstogenic cytokine expression in osteoclast precursors, whereas EVs from L. reuteri did not. EVs from P. gingivalis, T. forsythia, and S. oralis preferentially activated Toll-like receptor 2 (TLR2) rather than TLR4 or TLR9, and induced osteoclastogenesis mainly through TLR2. The osteoclastogenic effects of EVs from P. gingivalis and T. forsythia were reduced by both lipoprotein lipase and polymyxin B, an inhibitor of lipopolysaccharide (LPS), while the osteoclastogenic effects of EVs from S. oralis were reduced by lipoprotein lipase alone. These results demonstrate that EVs from periodontal pathogens and oral commensal have osteoclastogenic activity through TLR2 activation by lipoproteins and/or LPS.

The Relationship Between Osteoporosis and Intestinal Microbes in the Henan Province of China

Osteoporosis (OP) is a chronic disease in the elderly, and China is entering an aging demographic trend. In recent years, increasing evidence has demonstrated that probiotics can treat osteoporosis. This study aimed to explore the relevant mechanisms and to validate the beneficial effect on osteoporosis by high-throughput metagenome-wide gene sequencing in humans. In this study, compared with controls, several species had altered abundances, and specific functional pathways were found in the OP group. At the species level, the species that had increased in OP individuals were positively correlated to bone resorption markers and negatively correlated to 25-OH-D3 and bone formation markers, with Streptococcus sanguinis showing the strongest relevance, followed by Streptococcus gordonii, Actinomyces odontolyticus, and Olsenella unclassified. Additionally, Actinomyces graevenitzii, enriched in the OP group, was positively correlated to inflammation indicators that included white blood cell (WBC), neutrophil count (NEC), and the neutrophil-to-lymphocyte ratio (NLR) (p < 0.05). Conversely, the levels of Akkermansia muciniphila, Bacteroides eggerthii, Bacteroides fragilis, Bacteroides uniformis, and Butyricimonas synergistic were increased in the control group, which had a negative correlation with bone resorption markers and positive correlation with bone formation markers and 25-OH-D3. Additionally, Bacteroides fragilis had a negative correlation with inflammation indicators (WBC, NEC, and NLR) and the above pathways (p < 0.05). Functional prediction revealed that 106 metabolic pathways, enriched in the OP group, were significantly higher than in the control group (p < 0.05). In particular, pathways related to LPS biosynthesis, phytate degradation, lactate acid, and ethanol fermentation were more abundant in the OP group than in the control and were positively related to WBC and NEC. Taken together, several species with altered abundances and specific functional pathways were found in OP individuals. The role of phytases in OP provides novel epidemiological evidence to elucidate the underlying microbiota-relevant mechanisms in bone mineralization and should be explored further.

Induction of Apoptotic Cell Death by Oral Streptococci in Human Periodontal Ligament Cells

Initiation and progression of oral infectious diseases are associated with streptococcal species. Bacterial infection induces inflammatory responses together with reactive oxygen species (ROS), often causing cell death and tissue damage in the host. In the present study, we investigated the effects of oral streptococci on cytotoxicity and ROS production in human periodontal ligament (PDL) cells. Streptococcus gordonii showed cell cytotoxicity in a dose- and time-dependent manner. The cytotoxicity might be due to apoptosis since S. gordonii increased annexin V-positive cells, and the cytotoxicity was reduced by an apoptosis inhibitor, Z-VAD-FMK. Other oral streptococci such as Streptococcus mitis, Streptococcus sanguinis, and Streptococcus sobrinus also induced apoptosis, whereas Streptococcus mutans did not. All streptococci tested except S. mutans triggered ROS production in human PDL cells. Interestingly, however, streptococci-induced apoptosis appears to be ROS-independent, as the cell death induced by S. gordonii was not recovered by the ROS inhibitor, resveratrol or n-acetylcysteine. Instead, hydrogen peroxide (H₂O₂) appears to be important for the cytotoxic effects of streptococci since most oral streptococci except S. mutans generated H₂O₂, and the cytotoxicity was dramatically reduced by catalase. Furthermore, streptococcal lipoproteins are involved in cytotoxicity, as we observed that cytotoxicity induced by the lipoprotein-deficient S. gordonii mutant was less potent than that by the wild-type and was attenuated by anti-TLR2-neutralizing antibody. Indeed, lipoproteins purified from S. gordonii alone were sufficient to induce cytotoxicity. Notably, S. gordonii lipoproteins did not induce H₂O₂ or ROS but cooperatively induced cell death when co-treated with H₂O₂. Taken together, these results suggest that most oral streptococci except S. mutans efficiently induce damage to human PDL cells by inducing apoptotic cell death with bacterial H₂O₂ and lipoproteins, which might contribute to the progression of oral infectious diseases such as apical periodontitis.

Colorectal cancer cells promote osteoclastogenesis and bone destruction through regulating EGF/ERK/CCL3 pathway

Bone metastasis of colorectal cancer (CRC) cells leads to osteolysis. Aberrant activation of osteoclasts is responsible for bone resorption in tumor. In general, bone marrow-derived monocytes (BMMs) differentiate into osteoclasts, however, how CRC cells interact with BMMs and how to regulate the differentiation is elusive. We here report that CRC cells promote bone resorption in bone metastasis. Transcriptomic profiling revealed CCL3 up-regulated in MC-38 conditional medium treated BMMs. Further investigation demonstrated that CCL3 produced by BMMs facilitated cell infusion and thus promoted the osteoclastogenesis. In addition, CRC cells derived EGF stimulated the production of CCL3 in BMMs through activation of ERK/CREB pathway. Blockage of EGF or CCL3 can efficiently attenuate the osteolysis in bone metastasis of CRC.

Streptococcus gordonii: Pathogenesis and Host Response to Its Cell Wall Components

Streptococcus gordonii, a Gram-positive bacterium, is a commensal bacterium that is commonly found in the skin, oral cavity, and intestine. It is also known as an opportunistic pathogen that can cause local or systemic diseases, such as apical periodontitis and infective endocarditis. S. gordonii, an early colonizer, easily attaches to host tissues, including tooth surfaces and heart valves, forming biofilms. S. gordonii penetrates into root canals and blood streams, subsequently interacting with various host immune and non-immune cells. The cell wall components of S. gordonii, which include lipoteichoic acids, lipoproteins, serine-rich repeat adhesins, peptidoglycans, and cell wall proteins, are recognizable by individual host receptors. They are involved in virulence and immunoregulatory processes causing host inflammatory responses. Therefore, S.gordonii cell wall components act as virulence factors that often progressively develop diseases through overwhelming host responses. This review provides an overview of S. gordonii, and how its cell wall components could contribute to the pathogenesis and development of therapeutic strategies.