Inhibition of osteoblastic cell differentiation by lipopolysaccharide extract from Porphyromonas gingivalis

Chebulinic acid alleviates LPS-induced inflammatory bone loss by targeting the crosstalk between reactive oxygen species/NFκB signaling in osteoblast cells

Chebulinic acid (CA), a plant ellagitannin derived from Triphala, is reported to exhibit both anti-inflammatory & anti-oxidant activity apart from anti-tumour property. However, its role in inflammatory bone loss conditions was unexplored. We hypothesized that CA may prevent the bone loss under inflammatory conditions induced by lipopolysaccharide (LPS) in 10-week-old male C57BL/6J mice. Micro-CT analysis and histomorphometric evaluations were carried out where it was found that CA significantly improved the bone micro-architectures by enhancing trabecular connectivity and strength of the bone. CA also increased the bone regeneration as examined by calcein labelling and ex-vivo mineralisation along with maintaining the bone serum markers. Further, CA ameliorated the reduction in osteoblast cell differentiation, proliferation and viability after LPS stimulation. DCFDA and Mitosox staining revealed that CA presented remarkable protective effects against LPS treatment by attenuating oxidative stress, both at cellular & mitochondrial levels. In addition, CA significantly decreased the production of pro-inflammatory cytokines, and down-regulated the phosphorylation of NFκB and IκBα, indicating that CA could attenuate the inflammatory impairment to primary osteoblast cells by suppressing the NFkB signalling pathway. Taken together, the protective role of CA against LPS-induced bone loss & inhibitory effect on total ROS levels hold promise as a potential novel therapeutic strategy for the inflammatory diseases in bones.

Locally Delivered Metabolite Derivative Promotes Bone Regeneration in Aged Mice

Repair of large bone defects is still a major challenge, especially for the aged population. One alternative to address this issue is using the biomaterial-mediated bone morphogenetic protein 2 (BMP2) delivery technique, although high-dose BMP2 can cause serious concerns. α-Ketoglutarate (AKG) is a key intermediate in the tricarboxylic acid cycle and emerging as an intriguing antiaging molecule to extend the life/health span in different organisms. While one recent study indicates that the dietary AKG could significantly reduce bone loss and improve bone anabolism in aged mice, the therapeutic potential of AKG for bone regeneration has not been studied so far. Moreover, the poor cell permeability, large dose requirement, and long-term systemic administration of AKG hinder its applications in clinics and cellular mechanism studies. Dimethyl α-ketoglutarate (DMAKG) is a cell-permeable derivative of AKG with promising potential, although its role in osteogenesis is still elusive. Therefore, we aim to study the potential roles of DMAKG for bone regeneration using both in vitro cell culture and in vivo aged mouse models. Compared to AKG, our data indicated that DMAKG could more effectively improve osteoblastic differentiation. In addition, DMAKG significantly reduced adipogenic differentiation and improved osteogenic differentiation of a mouse multipotential mesenchymal stem cell line. Importantly, our result indicated that DMAKG significantly promoted BMP2-induced osteoblastic differentiation and mineralization in vitro. Moreover, DMAKG could not only significantly mitigate lipopolysaccharide (LPS)-stimulated inflammation in macrophages but also largely rescue LPS-inhibited osteoblastic differentiation. Consistently, our in vivo study demonstrated that gelatin scaffold-mediated local release of DMAKG significantly promoted BMP2-induced bone regeneration in aged mice, which is compromised by chronic inflammation and high adipogenesis. Overall, we, for the first time, report that locally delivered metabolite derivative, DMAKG, could improve BMP2-induced bone regeneration in aged mice. Our study suggests DMAKG has a promising therapeutic potential for bone regeneration through modulating local inflammation and stem cell differentiation.

Xanthine Derivative KMUP-1 Attenuates Experimental Periodontitis by Reducing Osteoclast Differentiation and Inflammation

Periodontitis is an inflammatory disease of gum that may predispose to serious systemic complications such as diabetes and cardiovascular diseases. Activation of macrophages and osteoclasts around periodontal tissue can accelerate gum inflammation. In addition, alteration of cyclic nucleotide levels is associated with the severity of periodontitis. Our previous study has shown that KMUP-1, a xanthine derivative exhibiting phosphodiesterase inhibition and soluble guanylyl cyclase activation, can inhibit lipopolysaccharide (LPS)-induced inflammation and receptor activator of nuclear factor kappa-Β ligand (RANKL)-induced osteoclastogenesis. This study was aimed to investigate whether KMUP-1 could attenuate periodontitis both in vitro and in vivo. In vitro, the protective effect of KMUP-1 on inflammation and osteoclastogenesis was investigated in RANKL-primed RAW264.7 cells treated by Porphyromonas gingivalis LPS (PgLPS). The results showed that KMUP-1 attenuated PgLPS-induced osteoclast differentiation as demonstrated by decreased TRAP-positive multinuclear cells and TRAP activity. This reduction of osteoclast differentiation by KMUP-1 was reversed by KT5823, a protein kinase G inhibitor. Similarly, pro-inflammatory cytokine levels induced by PgLPS were inhibited by KMUP-1 in a dose-dependent manner whereas reversed by KT5823. Mechanistically, suppression of MAPKs, PI3K/Akt, and NF-κB signaling pathways and decrease of c-Fos and NFATc1 expression in osteoclast precursors by KMUP-1 may mediate its protective effect. In vivo, two models of periodontitis in rats were induced by gingival injections of PgLPS and ligature placement around molar teeth, respectively. Our results showed that KMUP-1 inhibited alveolar bone loss in both rat models, and this effect mediated at least partly by reduced osteoclastogenesis. In conclusion, our study demonstrated the therapeutic potential of KMUP-1 on periodontitis through suppression of inflammation and osteoclast differentiation.

Microbial-stem cell interactions in periodontal disease

Periodontitis is initiated by hyper-inflammatory responses in the periodontal tissues that generate dysbiotic ecological changes within the microbial communities. As a result, supportive tissues of the tooth are damaged and periodontal attachment is lost. Gingival recession, formation of periodontal pockets with the presence of bleeding, and often suppuration and/or tooth mobility are evident upon clinical examination. These changes may ultimately lead to tooth loss. Mesenchymal stem cells (MSCs) are implicated in controlling periodontal disease progression and have been shown to play a key role in periodontal tissue homeostasis and regeneration. Evidence shows that MSCs interact with subgingival microorganisms and their by-products and modulate the activity of immune cells by either paracrine mechanisms or direct cell-to-cell contact. The aim of this review is to reveal the interactions that take place between microbes and in particular periodontal pathogens and MSCs in order to understand the factors and mechanisms that modulate the regenerative capacity of periodontal tissues and the ability of the host to defend against putative pathogens. The clinical implications of these interactions in terms of anti-inflammatory and paracrine responses of MSCs, anti-microbial properties and alterations in function including their regenerative potential are critically discussed based on literature findings. In addition, future directions to design periodontal research models and study ex vivo the microbial-stem cell interactions are introduced.

Toll-like Receptor 4, Osteoblasts and Leukemogenesis; the Lesson from Acute Myeloid Leukemia

Toll-like receptor 4 (TLR4) is a pattern-recognizing receptor that can bind exogenous and endogenous ligands. It is expressed by acute myeloid leukemia (AML) cells, several bone marrow stromal cells, and nonleukemic cells involved in inflammation. TLR4 can bind a wide range of endogenous ligands that are present in the bone marrow microenvironment. Furthermore, the TLR4-expressing nonleukemic bone marrow cells include various mesenchymal cells, endothelial cells, differentiated myeloid cells, and inflammatory/immunocompetent cells. Osteoblasts are important stem cell supporting cells localized to the stem cell niches, and they support the proliferation and survival of primary AML cells. These supporting effects are mediated by the bidirectional crosstalk between AML cells and supportive osteoblasts through the local cytokine network. Finally, TLR4 is also important for the defense against complicating infections in neutropenic patients, and it seems to be involved in the regulation of inflammatory and immunological reactions in patients treated with allogeneic stem cell transplantation. Thus, TLR4 has direct effects on primary AML cells, and it has indirect effects on the leukemic cells through modulation of their supporting neighboring bone marrow stromal cells (i.e., modulation of stem cell niches, regulation of angiogenesis). Furthermore, in allotransplant recipients TLR4 can modulate inflammatory and potentially antileukemic immune reactivity. The use of TLR4 targeting as an antileukemic treatment will therefore depend both on the biology of the AML cells, the biological context of the AML cells, aging effects reflected both in the AML and the stromal cells and the additional antileukemic treatment combined with HSP90 inhibition.

Regulation of Bone Cell Differentiation and Activation by Microbe-Associated Molecular Patterns

Gut microbiota has emerged as an important regulator of bone homeostasis. In particular, the modulation of innate immunity and bone homeostasis is mediated through the interaction between microbe-associated molecular patterns (MAMPs) and the host pattern recognition receptors including Toll-like receptors and nucleotide-binding oligomerization domains. Pathogenic bacteria such as Porphyromonas gingivalis and Staphylococcus aureus tend to induce bone destruction and cause various inflammatory bone diseases including periodontal diseases, osteomyelitis, and septic arthritis. On the other hand, probiotic bacteria such as Lactobacillus and Bifidobacterium species can prevent bone loss. In addition, bacterial metabolites and various secretory molecules such as short chain fatty acids and cyclic nucleotides can also affect bone homeostasis. This review focuses on the regulation of osteoclast and osteoblast by MAMPs including cell wall components and secretory microbial molecules under in vitro and in vivo conditions. MAMPs could be used as potential molecular targets for treating bone-related diseases such as osteoporosis and periodontal diseases.

lncRNA NEAT1 ameliorates LPS‑induced inflammation in MG63 cells by activating autophagy and suppressing the NLRP3 inflammasome

The mechanisms of inflammation in bone and joint tissue are complex and involve long non‑coding RNAs (lncRNAs), which play an important role in this process. The aim of the present study was to screen out differentially expressed genes in human osteoblasts stimulated by inflammation, and to further explore the mechanisms underlying inflammatory responses and the functional activity of human osteoblasts through bioinformatics methods and in vitro experiments. For this purpose, MG63 cells were stimulated with various concentrations of lipopolysaccharide (LPS) for different periods of time to construct an optimal inflammatory model and RNA sequencing was then performed on these cells. The levels of nuclear enriched abundant transcript 1 (NEAT1), various inflammatory factors, Nod‑like receptor protein 3 (NLRP3) protein and osteogenesis‑related proteins, as well as the levels of cell apoptosis‑ and cell cycle‑related markers were measured in MG63 cells stimulated with LPS, transfected with NEAT1 overexpression plasmid and treated with bexarotene by western blot analysis, RT‑qPCR, immunofluorescence, FISH, TEM and flow cytometry. There were 427 differentially expressed genes in the LPS‑stimulated MG63 cells, in which NEAT1 was significantly downregulated. LPS upregulated the expression of inflammatory cytokines and NLRP3, inhibited the expression of autophagy‑related and osteogenesis‑related proteins, promoted apoptosis and altered the cell cycle, which was partially inhibited by NEAT1 overexpression and promoted by bexarotene. LPS stimulated inflammation in the MG63 cells and inhibited the retinoid X receptor (RXR)‑α to downregulate the expression of NEAT1 and decrease levels of autophagy, which promoted the activation of NLRP3 and the release of inflammatory factors, and impaired the functional activity of osteoblasts, thus promoting the development of inflammation.

Antibacterial, anti-inflammatory, and anti-osteoclastogenic activities of Colocasia antiquorum var. esculenta: Potential applications in preventing and treating periodontal diseases

This study aimed to investigate the inhibitory effects of Colocasia antiquorum var. esculenta (CA) on Porphyromonas gingivalis (P. gingivalis) growth, inflammation, and osteoclastogenesis. CA was effective in inhibiting the growth of P. gingivalis when applied together with an experimental fluoride varnish. CA also significantly decreased the release of interleukin-6, tumor necrosis factor-α, and nitric oxide from lipopolysaccharide-induced RAW 264.7 cells. No significant differences in viability were noted between the cells treated with CA and the controls. In addition, CA significantly attenuated osteoclast differentiation on bone marrow macrophages. In conclusion, CA inhibited the growth of P. gingivalis and showed anti-inflammatory and anti-osteoclastogenic effects. Therefore, CA may have the potential to act as a novel natural agent for preventing periodontitis.

DNA methylation of GJA1, BMP2 and BMP4 in a human cementoblast cell line induced by lipopolysaccharide

AIM

To examine DNA methylation of GJA1, BMP2 and BMP4 in human cementoblasts (HCEM) induced by lipopolysaccharide (LPS).

METHODOLOGY

HCEM were cultured in osteoinduction medium. After 24 h, Escherichia coli LPS (1 μg/mL) was added to the medium, which was changed every 2-3 days. Untreated samples were used as controls. Messenger RNA was extracted after 4 weeks, and quantitative real-time polymerase chain reaction (qRT-PCR) for GJA1, BMP2, BMP4 and DNMT1 was performed. Genomic DNA was extracted after 4 weeks, and quantitative methylation-specific polymerase chain reaction was carried out for GJA1, BMP2 and BMP4. To detect mineralization, alizarin red and alkaline phosphatase staining were performed. The cells were also treated with the DNA methyltransferase inhibitor 5-Aza-2'-deoxycytidine (5Aza) and examined. The significance of differences amongst groups was assessed using a two-way analysis of variance (ANOVA) followed by Bonferroni's multiple comparison test with P < 0.05 being significant.

RESULTS

Decreased expression of mRNA was seen in GJA1, BMP2 and BMP4 after 4 weeks (P < 0.05). DNA hypermethylation was detected in GJA1, BMP2 and BMP4 (P < 0.05). Alizarin red staining and alkaline phosphatase staining revealed decreased mineralization levels in HCEM stimulated with LPS. 5Aza abolished the effects of DNA methylation in HCEM stimulated with LPS.

CONCLUSIONS

These results suggest that long-term LPS stimulation induces DNA methylation of GJA1, BMP2 and BMP4 in HCEM.

Effect of high glucose levels and lipopolysaccharides-induced inflammation on osteoblast mineralization over sandblasted/acid-etched titanium surface

BACKGROUND AND PURPOSE

Poorly controlled diabetes mellitus has been related to higher risk of implant treatment complications due to increased susceptibility to infection and delayed wound healing. Lipopolysaccharides (LPS) stimulate cytokine production leading to chronic inflammation and immunological host response that accentuates the destruction of periodontal tissues. This study aimed to evaluate the effect of different glycemic conditions on secretion and mineralization of bone matrix under sterile inflammation induced by LPS on osteoblasts seeded over sandblasted/acid-etched (SLA) titanium surface.

MATERIALS AND METHODS

Osteoblast cell viability was performed to determine the influence of different glucose concentrations (5.5, 8, 12, and 24 mM), which were chosen to reflect normal, postprandial, and high glucose values, similar to those typically seen in Diabetes mellitus under clinical conditions. Cells were seeded on titanium SLA discs (Straumann AG, Waldenburg, Switzerland) and exposed to glucose concentrations and LPS (1μg/mL) in order to test inflammatory response (qPCR) and mineralization (Alizarin Red staining).

RESULTS

Osteoblast viability was severely decreased when exposed to higher glucose levels (≥12 mM) and LPS (P < .05) compared to control. When the osteoblasts were exposed to LPS and glucose at ≥8 mM, the gene transcripts of inflammatory cytokines were ≈2.5-fold upregulated, while ≤8 mM glucose elicited no significant change compared to control without glucose treatment (P > .05). Osteoblasts exposed to LPS produced sparse extracellular matrix mineralization, especially combined with higher glucose values (≥12 mM), together with decreased calcium deposition compared to control (P < .05).

CONCLUSIONS

High glucose levels combined with LPS inflammatory stimulation elicited an adverse effect on the volume and quality of mineralized hard tissue formation on SLA titanium surfaces in vitro. Hence, both normal glucose levels and infection control including low levels of circulating LPS during initial osseointegration period may be required to increase the success rate of dental implants.

Periodontal Injection of Lipopolysaccharide Promotes Arthritis Development in Mice

This study evaluated the arthritogenic effect of lipopolysaccharide (LPS) in a mouse model of periodontal disease. Periodontitis was induced in wild-type CD1 mice by nine LPS injections (10 or 50 ng) into the maxillary mucosa. Untreated mice or injected with LPS at the tail were used as controls. Two weeks after final inoculation, mice were sacrificed to collect blood, maxilla, and paw samples. Development and progression of periodontitis and arthritis were monitored using clinical assessment, micro-computed tomography (micro-CT), ultrasound (US), and histological analysis. CXCL1, IL-1β, IL-6, TNF-α, and anti-citrullinated peptide antibodies (ACPA) serum levels were determined by enzyme immunoassay. Ankle swelling and inflammation manifested after the 5th periodontal injection of 50 ng of LPS and progressed until the end of experiments. Periodontal injection of 10 ng of LPS and LPS tail injection did not induce paw changes. Therefore, the subsequent assessments were conducted only in mice periodontally injected with 50 ng of LPS. Maxillary micro-CT and histological analysis showed that LPS-induced alveolar bone resorption and vascular proliferation in periodontal tissue, but not inflammation. US and histology revealed increased joint space, leukocyte infiltration, synovial proliferation, and mild cartilage and bone destruction in the paws of mice orally injected. Cytokines and ACPA showed a trend towards an increase in LPS mice. This study shows that arthritis and periodontal disease can co-occur in wild-type mice after periodontal injection of LPS at optimal dose. Our model may be useful to improve the understanding of the mechanisms linking periodontitis and arthritis.

KR-12-a5 Reverses Adverse Effects of Lipopolysaccharides on HBMSC Osteogenic Differentiation by Influencing BMP/Smad and P38 MAPK Signaling Pathways

KR-12-a5 is an analogue of the antimicrobial peptide KR-12. Both of these two agents can play key effects in the treatment of infections such as osteomyelitis. Our previous work demonstrated that the osteogenic differentiation of human bone marrow mesenchymal stem cells (HBMSCs) can be enhanced by KR-12. The present study investigated if KR-12-a5 could reverse the adverse effects of lipopolysaccharides (LPS) on HBMSC osteogenesis and the involved molecular mechanisms. We observed the proliferation, cell cycle, and apoptosis of HBMSCs in the presence of KR-12-a5 by a cell counting kit-8 assay and flow cytometry. The osteogenic differentiation of HBMSCs was studied by alkaline phosphatase, Alizarin Red staining, and quantitative assays. Osteogenic differentiation marker levels were detected using real-time quantitative PCR analysis, which demonstrated that KR-12-a5 treatment reversed the inhibition of osteogenesis. Western blot analysis indicated that LPS-activated P38 mitogen-activated protein kinase (MAPK) signaling was inhibited and BMP/Smad pathway was reactivated after KR-12-a5 treatment under induced osteogenic conditions. Furthermore, flow cytometry results demonstrated that KR-12-a5 relieved LPS-induced oxidative stress. Combining the LPS-treated mouse model results, we proved that KR-12-a5 reversed the adverse effects of LPS on HBMSC osteogenic differentiation by influencing the BMP/Smad and P38 MAPK signaling pathways.

Advanced glycation end-product 2 and Porphyromonas gingivalis lipopolysaccharide increase sclerostin expression in mouse osteocyte-like cells

Sclerostin is a secreted glycoprotein that is mainly expressed in osteocytes, exerts negative effects on bone formation, and is present at elevated levels in diabetes mellitus (DM). Periodontitis is an infectious disease caused by periodontopathic bacteria, a complication of DM, and sometimes associated with severe inflammation and alveolar bone resorption. Advanced glycation end-products (AGEs) are a major pathogen in DM complications and adversely influence periodontitis in DM patients. In the present study, the effects of AGE2 and Porphyromonas gingivalis lipopolysaccharide (P-LPS) on the expression of sclerostin in mouse osteocyte-like cells (MLO-Y4-A2 cells) and its function in osteoblast differentiation were investigated. AGE2 and P-LPS up-regulated the expressions of receptor of AGE (RAGE) and Toll-like receptor 2 (TLR2), respectively, and significantly up-regulated that of sclerostin and interleukin 6 (IL-6) in osteocytes. Sclerostin, RAGE and TLR2 levels were synergistically increased by AGE2 and P-LPS. The siRNAs of RAGE and TLR2 significantly inhibited AGE2- and P-LPS-induced sclerostin expression. AGE2 up-regulated sclerostin expression in osteocyte-like cells via the RAGE, ERK and JNK, and NF-κB signal pathways. On the other hand, P-LPS elevated sclerostin levels via the TLR2, JNK and p38, and NF-κB signal pathways. When osteocytes pre-treated with AGE2 and P-LPS and osteoblastic cells (MC3T3-E1) were co-cultured in the medium with a sclerostin-neutralizing antibody, AGE2- and P-LPS-induced decreases in alkaline phosphatase activity and Runx2 expression in osteoblastic cells were significantly inhibited by the sclerostin-neutralizing antibody. These results suggest that AGE2 and P-LPS influence bone metabolism and inflammation through the regulation of sclerostin expression, and may aggravate periodontitis with DM.

A biological study establishing the endotoxin limit for osteoblast and adipocyte differentiation of human mesenchymal stem cells

INTRODUCTION

Multipotent mesenchymal stem cells (MSCs) are widespread in adult organisms and are implicated in tissue maintenance and repair, regulation of hematopoiesis, and immunologic responses. Human (h)MSCs have applications in tissue engineering, cell-based therapy, and medical devices but it is unclear how they respond to unfavorable conditions, such as hypoxia or inflammation after transplantation in vivo. Although endotoxin testing is required for evaluating the quality and safety of transplanted MSCs, no reports on their dose response to endotoxins are available to establish the limits for in vitro MSC culture systems. In the present study, we aimed to accurately quantify the risk of endotoxin contamination in cell culture systems to establish an acceptable endotoxin limit for the differentiation of hMSC osteoblasts and adipocytes.

METHODS

Three types of bone marrow-derived hMSCs (hMSC-1: 21-year-old, M/B; hMSC-2: 36-year-old, M/B; hMSC-3: 43-year-old, M/C) and adipose-derived stem cells (ADSCs; StemPro Human) were cultured in osteogenic or adipogenic differentiation media, respectively, from commercial kits, containing various concentrations of endotoxin (0.01-100 ng/ml). The degree of adipocyte and osteoblast differentiation was estimated by fluorescent staining of lipid droplets and hydroxyapatite, respectively. To clarify the molecular mechanism underlying the effect of endotoxin on hMSC differentiation, cellular proteins were extracted from cultured cells and subjected to liquid chromatograph-tandem mass spectrometry shotgun proteomics analysis.

RESULTS

Although endotoxin did not effect the adipocyte differentiation of hMSCs, osteoblast differentiation was enhanced by various endotoxin concentrations: over 1 ng/ml, for hMSC-1; 10 ng/ml, for hMSC-2; and 100 ng/ml, for hMSC-3. Proteomic analysis of hMSC-1 cells revealed up-regulation of many proteins related to bone formation. These results suggested that endotoxin enhances the osteoblast differentiation of MSCs depending on the cell type.

CONCLUSIONS

Since endotoxins can affect various cellular functions, an endotoxin limit should be established for in vitro MSC cultures. Its no-observed-adverse-effect level was 0.1 ng/ml based on the effect on the hMSC osteoblast differentiation, but it may not necessarily be the limit for ADSCs.

Role of Toll-Like Receptor 4 on Osteoblast Metabolism and Function

Inflammation is a process whose main function is to fight against invading pathogens or foreign agents. Nonetheless, it is widely accepted that inflammation takes part in multiple processes in a physiological or pathophysiological context. Among these processes the inflammation has been closely related to bone metabolism. It is well-known that in systemic inflammatory diseases such as rheumatoid arthritis the inflammatory environment contributes to the reduction of the bone mineral density. This has been further evidenced in different animals models of osteoporosis where the deletion of key inflammatory molecules dramatically reduced the bone loss. On the contrary, it is also well-known that certain degree of inflammation is required to allow bone fractures healing. In fact, excessive use of anti-inflammatory drugs inhibits bone fracture consolidation. The innate immune responses (IIRs) contribute to the development and maintenance of the inflammation. These responses have been observed in cells of the musculoskeletal system. Chondrocytes and osteoblasts are equipped with the molecular repertoire necessary to setting up these IIR, including the expression of several toll-like receptors. Specifically, toll-like receptor 4 (TLR4) activation in mesenchymal stem cells, osteoblasts, and osteocytes has been involved in catabolic and anabolic process. Accordingly, in this review we have summarized the current knowledge about the physiology of TLR4, including its signaling, and its endogenous agonists. In addition we have focused on its role on osteoblast metabolism and function.

Resveratrol Attenuates Lipopolysaccharides (LPS)-Induced Inhibition of Osteoblast Differentiation in MC3T3-E1 Cells

Background

LPS-inhibited osteoblastic differentiation plays an important role in the pathogenesis of osteomyelitis. Thus, searching for drugs that affect LPS-mediated osteoblastic differentiation may be crucial in developing therapies for osteomyelitis. The purpose of this study was to investigate the role and mechanisms of resveratrol, a natural polyphenol present in red wine, on LPS-inhibited osteoblastic differentiation.

Material/Methods

Cell viability was measured by MMT assay. Mitochondrial ATP levels, membrane potential, and superoxide production were measured to evaluate the effects of LPS and resveratrol on mitochondrial functions in osteoblast-like MC3T3-E1 cells. Osteoblast-related genes, including ALP, OCN, OPN, and RUNX2, were measured by ELISA analysis and RT-PCR in differentiated osteoblast cells treated with LPS and resveratrol. Cellular Sirt1 and PCG-1α levels were measured by Western blot to probe the impact of resveratrol treatment in LPS-stimulated MC3T3-E1 osteoblasts.

Results

The results showed that LPS caused significant mitochondrial dysfunctions of MC3T3-E1 cells in a dose-dependent manner, which were attenuated by resveratrol. Furthermore, LPS markedly decreased the expression of ALP, OCN, OPN, and RUNX2 in MC3T3-E1 cells cultivated in osteoblast differentiation medium, suggesting that LPS inhibited the osteoblastic differentiation of MC3T3-E1 cells. However, resveratrol obviously alleviated the suppressive impact of LPS on osteoblast differentiation. In addition, resveratrol increased expression of Sirt1 and PGC-1α in MC3T3-E1 cells treated with LPS.

Conclusions

Taken together, these results show that resveratrol alleviated the suppression of LPS on osteoblast differentiation by improving, at least in part, mitochondrial function.

Calcitonin gene‑related peptide reduces Porphyromonas gingivalis LPS‑induced TNF‑α release and apoptosis in osteoblasts

Periodontal diseases comprise mixed bacterial infections mainly caused by Gram‑negative anaerobic bacteria. Lipopolysaccharides (LPS) are important virulence factors and periodontal pathogens, which change local cytokine levels and promote osteoblast apoptosis, thereby leading to an imbalance in bone remodeling mechanisms and accelerating bone loss. Calcitonin gene‑related peptide (CGRP) is a vasoactive neuropeptide that is released from sensory nerves and has a positive effect on osteoblast proliferation and differentiation. In addition, this small molecule peptide is an important immune regulator in the inflammatory response. The aim of the present study was to assess the in vitro effects of CGRP on Porphyromonas gingivalis (Pg)LPS‑induced osteoblast apoptosis. Osteoblast cultures were stimulated either with various concentrations of PgLPS (0, 25, 50, 100, 500 and 1,000 ng/ml) for 48 h or with 500 ng/ml PgLPS for various lengths of time (0, 6, 12, 24, 48 and 72 h). The PgLPS‑stimulated cells were pretreated with different concentrations of CGRP (0, 1, 10, 100 and 1,000 nM) and cell viability and apoptotic rates were measured by Cell Counting kit‑8 assays and flow cytometry, respectively. CGRP, cleaved (c)‑Caspase‑8 and c‑Caspase‑3 protein expression levels were analyzed by western blotting. Changes in cytokine expression levels, which included tumor necrosis factor (TNF)‑α, interleukin (IL)‑1β, IL‑6, monocyte chemotactic protein (MCP)‑1 and MCP‑2, were measured by ELISA. PgLPS was demonstrated to inhibit osteoblast viability and promote apoptosis in a time‑ and concentration‑dependent manner. CGRP expression was revealed to reduce PgLPS‑induced cytostatic activity and apoptosis in osteoblasts. CGRP also suppressed the PgLPS‑induced release of TNF‑α and inhibited the activation of c‑Caspase‑3 and c‑Caspase‑8, thus preventing apoptosis in osteoblasts. CGRP may be an important neuropeptide in bone remodeling and may reduce osteoblast apoptosis in inflammatory conditions. These results may provide a solid foundation for CGRP to serve as a new target for the treatment of periodontitis.

A biological study establishing the endotoxin limit for in vitro proliferation of human mesenchymal stem cells

INTRODUCTION

Multipotent mesenchymal stem cells (MSCs) are widespread in adult organisms and are implicated in tissue maintenance and repair, regulation of hematopoiesis, and immunologic responses. Human (h)MSCs have applications in tissue engineering, cell-based therapy, and medical devices but it is unclear how they respond to unfavorable conditions such as hypoxia or inflammation after in vivo transplantation. Although endotoxin testing is a requirement for evaluating the quality and safety of transplanted MSCs, there have been no reports on the dose response to endotoxins to establish limits for in vitro MSC culture systems. The present study aimed to accurately quantify the risk of endotoxin contamination in cell culture systems in order to establish the acceptable endotoxin limit for hMSC proliferation.

METHODS

Three types of bone marrow-derived hMSC (hMSC-1: 21 years, M/B; hMSC-2: 36 years, M/B; hMSC-3: 43 years, M/C) and adipose-derived stem cells (ADSCs; StemPro Human) were cultured in medium from commercial kits containing various concentrations of endotoxin (0.1-1000 ng/ml). The proliferative capacity of cells was estimated by cell counts using a hemocytometer. To clarify the molecular mechanism underlying the effect of endotoxin on hMSCs proliferation, cellular proteins were extracted from cultured cells and subjected to liquid chromatograph-tandem mass spectrometry shotgun proteomics analysis. The expression of Cu/Zn-type superoxide dismutase (SOD1) and Fe/Mn-type superoxide dismutase (SOD2) induced in hMSCs by endotoxin stimulation were evaluated by enzyme-linked immunosorbent assay (ELISA), and the effect of SOD2 on hMSC proliferation was also estimated.

RESULTS

Although there was no change in cell morphology during the culture period, proliferative capacity increased with endotoxin concentration to over 0.1 ng/ml for ADSCs, 1 ng/ml for hMSC-1, and 100 ng/ml for hMSC-2; hMSC-3 proliferation was unaffected by the presence of endotoxin. A proteomic analysis of hMSC-1 revealed that various proteins related to the cell cycle, apoptosis, and host defense against infection were altered by endotoxin stimulation, whereas SOD2 expression was significantly and consistently upregulated during the culture period. The latter was also confirmed by ELISA. Moreover, recombinant SOD2 increased proliferative capacity in hMSC-1 cells in a manner similar to endotoxin. These results suggest that endotoxin protects MSCs from oxidative stress via upregulation of SOD2 to improve cell survival.

CONCLUSIONS

Since endotoxins can affect various cellular functions, an endotoxin limit should be set for in vitro MSC cultures. The lowest observed adverse effect level was determined to be 0.1 ng/ml based on the effect on MSC proliferation.

Porphyromonas gingivalis lipopolysaccharide regulates ephrin/Eph signalling in human periodontal ligament fibroblasts

Objective

EphrinA2‐EphA2 and ephrinB2‐EphB4 critically engage in bidirectional signalling to modulate alveolar bone remodelling. The present study aimed to investigate the effects of lipopolysaccharides (LPS) derived from Porphyromonas gingivalis on ephrin/Eph signalling in periodontal ligament fibroblasts (PDLFs).

Material and Methods

The primary cultured PDLFs were incubated in the absence (as a control) or presence of P. gingivalisLPS at 0.001‐10 μg/mL for 24 hours. The PDLFs were then stimulated with P. gingivalisLPS at the optimal concentration (0.1 μg/mL) for different periods (6‐48 hours). The expression of ephrinA2, ephrinB2, EphA2 and EphB4 was assessed by quantitative reverse‐transcription real‐time polymerase chain reaction and western blotting. The osteoblastic markers alkaline phosphatase, osteocalcin and Runt‐related transcription factor 2 (Runx2), and the osteoclastogenesis‐related factors receptor activator of nuclear factor kappa‐B ligand (RANKL) and osteoprotegerin were also evaluated.

Results

The ephrinA2 and EphA2 expression was upregulated and EphB4 expression was downregulated by stimulation of P. gingivalisLPS. EphrinA2 mRNA expression in the PDLFs was significantly upregulated from 12 to 48 hours (P<.05), whereas EphA2 exhibited no change for the first 24 hours, after which there was a significant increase at 48 hours (P<.05). EphB4 exhibited lower mRNA expression at 12 and 24 hours than did the control (P<.05), but the change was insignificant at 48 hours. In contrast, the expression of ephrinB2 remained unchanged. The expressions of ephrinA2, EphA2, ephrinB2 and EphB4 at the protein level showed a similar pattern to that at the mRNA level. The expression of Runx2 and osteocalcin significantly decreased, whereas that of RANKL/osteoprotegerin increased.

Conclusion

The present study suggest that P. gingivalisLPS would contribute to a dysregulation of bone remodelling, whereby ephrinA2/EphA2 expression is stimulated and EphB4 expression is inhibited.

Plant-derived pectin nanocoatings to prevent inflammatory cellular response of osteoblasts following Porphyromonas gingivalis infection

Background

Bioengineered plant-derived Rhamnogalacturonan-Is (RG-Is) from pectins are potential candidates for surface nanocoating of medical devices. It has recently been reported that RG-I nanocoatings may prevent bacterial infection and improve the biocompatibility of implants. The aim of the study was to evaluate in vitro impact of bioengineered RG-I nanocoatings on osteogenic capacity and proinflammatory cytokine response of murine osteoblasts following Porphyromonas gingivalis infection.

Methods

Murine MC3T3-E1 osteoblasts and isolated primary calvarial osteoblasts from C57BL/6J (B6J osteoblasts) mice were infected with P. gingivalis and incubated on tissue culture polystyrene plates with or without nanocoatings of unmodified RG-Is isolated from potato pulps (PU) or dearabinanated RG-Is (PA). To investigate a behavior of infected osteoblasts cultured on RG-Is cell morphology, proliferation, metabolic activity, mineralization and osteogenic and pro-inflammatory gene expression were examined.

Results

Following P. gingivalis infection, PA, but not PU, significantly promoted MC3T3-E1 and BJ6 osteoblasts proliferation, metabolic activity, and calcium deposition. Moreover, Il-1b, Il-6, TNF-α, and Rankl gene expressions were downregulated in cells cultured on PU and to a higher extent on PA as compared to the corresponding control, whereas Runx, Alpl, Col1a1, and Bglap gene expressions were upregulated vice versa.

Conclusion

Our data clearly showed that pectin RG-Is nanocoating with high content of galactan (PA) reduces the osteoblastic response to P. gingivalis infection in vitro and may, therefore, reduce a risk of inflammation especially in immunocompromised patients with rheumatoid or periodontal disorders.

Cementoblast Gene Expression is Regulated by Porphyromonas gingivalis Lipopolysaccharide Partially via Toll-like Receptor-4/MD-2

Lipopolysaccharides are potent inflammatory mediators considered to contribute to destruction of periodontal tissues. Here, we hypothesized that Porphyromonas gingivalis lipopolysaccharide (P-LPS) treatment would regulate gene expression in murine cementoblasts through Toll-like receptor 4. Real-time (RT)-PCR and Northern blot analysis indicated that P-LPS decreased expression of transcripts for osteocalcin (OCN) and receptor activator of nuclear factor κB ligand (RANKL). In contrast, a dose-dependent up-regulation in mRNA levels for osteopontin (OPN) and osteoprotegerin (OPG) was observed. Similarly, ELISA demonstrated decreased RANKL and increased OPG levels. A monoclonal antibody specific for mouse TLR-4/MD-2 partially neutralized the P-LPS effect on cementoblasts. These results indicate that exposure of cementoblasts to P-LPS can alter cell function by regulating markers of osteoclastic activity ( e.g., RANKL/OPG), thereby potentially affecting the inflammation-associated resorption of mineralized tissues.

Restoring the osteogenic activity of bacterial debris contaminated titanium by doping with magnesium

Bacterial debris can impair the osseointegration of implants and co-doping with magnesium and silver is a promising method to solve this issue.

Enterococcus faecalis attenuates osteogenesis through activation of p38 and ERK1/2 pathways in MC3T3-E1 cells

AIM

To explore the role of Enterococcus faecalis in the proliferation, apoptosis and differentiation of osteoblasts.

METHODOLOGY

Pre-osteoblastic MC3T3-E1 cells were treated with heat-killed E. faecalis ATCC 29212 and clinical E. faecalis P25RC strains, respectively. Cell proliferation, mineralized calcium deposition, alkaline phosphatase (ALP) activity and apoptosis were assessed at various time-points. The expression levels of osteogenic-related genes including ALP, osteocalcin (OC), runt-related protein 2 (Runx2) and collagen type 1 (COL1) were also analysed throughout the duration of the experiment. Additionally, the involvement of mitogen-activated protein kinases (MAPKs) signalling pathways was analysed by Western blotting. In the presence of culture supernatant from E. faecalis-treated murine macrophages, apoptosis of MC3T3-E1 cells was detected with flow cytometry. Data were analysed using analysis of variance (anova), and P < 0.05 was considered significantly different.

RESULTS

E. faecalis significantly inhibited proliferation (P < 0.05) and also significantly induced apoptosis of MC3T3-E1 cells (P < 0.05), whilst differentiation seemed to be unaffected after 7 days of E. faecalis treatment. However, osteogenic differentiation was significantly inhibited with 21-day E. faecalis treatment (P < 0.05). The p38 and ERK1/2 phosphorylation pathways associated with mineral deposition and apoptosis were significantly activated in MC3T3-E1 cells. The culture supernatants from E. faecalis-treated macrophages induced osteoblast apoptosis.

CONCLUSIONS

E. faecalis exerted an inhibitory effect on osteogenesis in pre-osteoblastic MC3T3-E1 cells via phosphorylation of p38 and ERK1/2.

Exposure of periodontal ligament progenitor cells to lipopolysaccharide from Escherichia coli changes osteoblast differentiation pattern

Periodontal ligament mesenchymal stem cells (PDLMSCs) are an important alternative source of adult stem cells and may be applied for periodontal tissue regeneration, neuroregenerative medicine, and heart valve tissue engineering. However, little is known about the impact of bacterial toxins on the biological properties of PDLSMSCs, including self-renewal, differentiation, and synthesis of extracellular matrix.

Expression Profiles of TGF-β and TLR Pathways in Porphyromonas gingivalis and Prevotella intermedia Challenged Osteoblasts

BACKGROUND

The presence of certain oral pathogens at implant sites can hinder the osseointegration process. However, it is unclear how and by what microorganisms it happens.

OBJECTIVES

This study investigated whether the presence of oral pathogens of Porphyromonas gingivalis and Prevotella intermedia individually, play a role in the failure of bone formation by determining the expression profiles of Transforming Growth Factor Beta (TGF-β/Bone Morphogenic Protein (BMP) and Toll-Like Receptor (TLR) pathways in challenged osteoblasts.

MATERIALS AND METHODS

Cell viability of P. gingivalis and P. intermedia challenged osteoblasts were determined by WST assay. Changes in osteoblast morphology and inhibition of mineralization were observed by Scanning Electron Microscopy (SEM) and Von Kossa staining, respectively. Expression of TGF-β and TLR pathway genes on challenged cells were identified by RT profiler array. Both P. gingivalis and P. intermedia challenges resulted in reduced viability and mineralization of osteoblasts.

RESULTS

Viability was reduced to 56.8% (P. gingivalis) and 52.75% (P. intermedia) at 1000 multiplicity. Amongst 48 genes examined, expressions of BMPER, SMAD1, IL8 and NFRKB were found to be highly upregulated by both bacterial challenges (Fold Change > 4).

CONCLUSIONS

P. gingivalis and P. intermedia could play a role in implant failure by changing the expression profiles of genes related to bone formation and resorption.

TLR signaling that induces weak inflammatory response and SHIP1 enhances osteogenic functions

Toll-like receptor (TLR)-mediated inflammatory response could negatively affect bone metabolism. In this study, we determined how osteogenesis is regulated during inflammatory responses that are downstream of TLR signaling. Human primary osteoblasts were cultured in collagen gels. Pam3CSK4 (P3C) and Escherichia coli lipopolysaccharide (EcLPS) were used as TLR2 and TLR4 ligand respectively. Porphyromonas gingivalis LPS having TLR2 activity with either TLR4 agonism (Pg1690) or TLR4 antagonism (Pg1449) and mutant E. coli LPS (LPxE/LPxF/WSK) were used. IL-1β, SH2-containing inositol phosphatase-1 (SHIP1) that has regulatory roles in osteogenesis, alkaline phosphatase and mineralization were analyzed. 3α-Aminocholestane (3AC) was used to inhibit SHIP1. Our results suggest that osteoblasts stimulated by P3C, poorly induced IL-1β but strongly upregulated SHIP1 and enhanced osteogenic mediators. On the contrary, EcLPS significantly induced IL-1β and osteogenic mediators were not induced. While Pg1690 downmodulated osteogenic mediators, Pg1449 enhanced osteogenic responses, suggesting that TLR4 signaling annuls osteogenesis even with TLR2 activity. Interestingly, mutant E. coli LPS that induces weak inflammation upregulated osteogenesis, but SHIP1 was not induced. Moreover, inhibiting SHIP1 significantly upregulated TLR2-mediated inflammatory response and downmodulated osteogenesis. In conclusion, these results suggest that induction of weak inflammatory response through TLR2 (with SHIP1 activity) and mutant TLR4 ligands could enhance osteogenesis.

Lipopolysaccharide (LPS) induces the apoptosis and inhibits osteoblast differentiation through JNK pathway in MC3T3-E1 cells

Bone degradation is a serious complication of chronic inflammatory diseases such as septic arthritis, osteomyelitis, and infected orthopedic implant failure. Up to date, effective therapeutic treatments for bacteria-caused bone destruction are limited. In our previous study, we found that LPS promoted osteoclast differentiation and activity through activation of mitogen-activated protein kinases (MAPKs) pathway such as c-Jun N-terminal kinases (JNK) and extracellular signal regulated kinase (ERK1/2). The current study was to evaluate the mechanism of LPS on the apoptosis and osteoblast differentiation in MC3T3-E1 cells. MC3T3-E1 osteoblasts were non-treated, treated with LPS. After treatment, the cell viability, the activity of alkaline phosphatase (ALP) and caspase-3 were measured. The expressions of osteoblast-specific genes and Bax, Bcl-2, and caspase-3 were determined by real-time quantitative polymerase chain reaction (qPCR). Protein levels of Bax, Bcl-2, caspase-3, and phosphorylation of MAPKs were measured using Western blotting assays. The MAPK signaling pathway was blocked by pretreatment with JNK inhibitor SP600125. LPS treatment induced a significant decrease in cell metabolism, viability, and ALP activity in MC3T3-E1 cells. LPS also significantly decreased mRNA expressions of osteoblast-related genes in MC3T3-E1 cells. On the other hand, LPS significantly upregulated mRNA expressions and protein levels of Bax and caspase-3 as well as activation of caspase-3, whereas decreased Bcl-2 expression in MC3T3-E1 cells. Furthermore, LPS significantly promoted MAPK pathway including the phosphorylation of JNK and the phosphorylation of ERK1/2; moreover, pretreatment with JNK inhibitor not only attenuated both of phosphorylation-JNK and ERK1/2 enhanced by LPS in MC3T3-E1 cells, but also reversed the downregulated expressions of osteoblast-specific genes including ALP and BSP induced by LPS. In conclusion, LPS could induce osteoblast apoptosis and inhibit osteoblast differentiation via activation of JNK pathway.

Quercetin reversed lipopolysaccharide-induced inhibition of osteoblast differentiation through the mitogen‑activated protein kinase pathway in MC3T3-E1 cells

Quercetin, a flavonoid found in onions and other vegetables, has potential inhibitory effects on bone resorption in vivo and in vitro. In our previous study it was identified that quercetin triggered the apoptosis of lipopolysaccharide (LPS)‑induced osteoclasts and inhibited bone resorption. Currently, little information is available detailing the effect of quercetin on osteoblast differentiation and bone formation in bacteria‑induced inflammatory diseases. The present study aimed to investigate the effect of quercetin on osteoblast differentiation in MC3T3‑E1 osteoblasts stimulated with LPS. LPS significantly downregulated the mRNA expression of osteoblast‑related genes in the MC3T3‑E1 cells. By contrast, quercetin significantly restored the LPS‑suppressed mRNA expression of osteoblast‑related genes in a dose‑dependent manner. Quercetin also restored the protein expression of Osterix in MC3T3‑E1 cells suppressed by LPS. Furthermore, quercetin selectively triggered the activation of the mitogen‑activated protein kinase (MAPK) pathway by enhancing the expression of extracellular signal-regulated kinase and reducing the expression of c‑Jun N‑terminal kinase. These data suggest that quercetin reversed the inhibition of osteoblast differentiation induced by LPS through MAPK signaling. These findings suggest that quercetin may be of potential use as a therapeutic agent to restore osteoblast function in bacteria‑induced bone diseases.

Porphyromonas gingivalis infection increases osteoclastic bone resorption and osteoblastic bone formation in a periodontitis mouse model

Background

Porphyromonas gingivalis has been shown to invade osteoblasts and inhibit their differentiation and mineralization in vitro. However, it is unclear if P. gingivalis can invade osteoblasts in vivo and how this would affect alveolar osteoblast/osteoclast dynamics. This study aims to answer these questions using a periodontitis mouse model under repetitive P. gingivalis inoculations.

Methods

For 3-month-old BALB/cByJ female mice, 10⁹ CFU of P. gingivalis were inoculated onto the gingival margin of maxillary molars 4 times at 2-day intervals. After 2 weeks, another 4 inoculations at 2-day intervals were applied. Calcein was injected 7 and 2 days before sacrificing animals to label the newly formed bone. Four weeks after final inoculation, mice were sacrificed and maxilla collected. Immunohistochemistry, micro-CT, and bone histomorphometry were performed on the specimens. Sham infection with only vehicle was the control.

Results

P. gingivalis was found to invade gingival epithelia, periodontal ligament fibroblasts, and alveolar osteoblasts. Micro-CT showed alveolar bone resorption and significant reduction of bone mineral density and content in the infected mice compared to the controls. Bone histomorphometry showed a decrease in osteoblasts, an increase in osteoclasts and bone resorption, and a surprisingly increased osteoblastic bone formation in the infected mice compared to the controls.

Conclusions

P. gingivalis invades alveolar osteoblasts in the periodontitis mouse model and cause alveolar bone loss. Although P. gingivalis appears to suppress osteoblast pool and enhance osteoclastic bone resorption, the bone formation capacity is temporarily elevated in the infected mice, possibly via some anti-microbial compensational mechanisms.

Lipopolysaccharide-regulated production of bone sialoprotein and interleukin-8 in human periodontal ligament fibroblasts: the role of toll-like receptors 2 and 4 and the MAPK pathway

BACKGROUND AND OBJECTIVE

Lipopolysaccharide (LPS) on the cell wall of periodontal pathogens is a major mediator of the inflammatory response and can enhance alveolar bone resorption in periodontitis. Bone sialoprotein is an early marker of osteoblast differentiation. The proinflammatory cytokine, interleukin-8 (IL-8), induces osteoclast differentiation, maturation and maintenance of bone resorption activity. However, the effects of LPS from periodontal pathogens on the expression of bone sialoprotein and IL-8 in human osteoblasts and the mechanism of periodontal bone metabolism regulation are rather unclear. The objectives of this study were to determine the effects of Porphyromonas gingivalis LPS on the production of bone sialoprotein and IL-8 in human periodontal ligament fibroblasts (hPDLFs), and to investigate whether toll-like receptor (TLR) 2, TLR4 and MAPKs pathways are involved in the regulation of production of bone sialoprotein and IL-8 by P. gingivalis LPS.

MATERIAL AND METHODS

The third-generation of hPDLFs were cultured with mineralization-inducing culture medium. After hPDLFs were treated with P. gingivalis LPS, bone sialoprotein and IL-8 mRNA expression were detected using Real time PCR. Then hPDLFs were transiently transfected with siTLR2 or siTLR4 (20 nm) or inhibited by MAPK signaling pathways inhibitors, and then bone sialoprotein and IL-8 mRNA and protein expression were also detected using Real time PCR and western blotting.

RESULTS

Treatments with 0.01 and 0.1 mg/L of P. gingivalis LPS for 8 h up-regulated bone sialoprotein mRNA expression, whereas 10 and 100 mg/L of P. gingivalis LPS induced a significant decrease in the expression of bone sialoprotein mRNA. In contrast, IL8 mRNA levels were increased significantly by 10 mg/L of P. gingivalis LPS. Interestingly, small interfering RNA (siRNA) knock down of the TLR2 and ERK1/2 inhibitor, PD98059, abolished the effects of P. gingivalis LPS on the bone sialoprotein mRNA level, whereas siRNA knock down of the TLR2 and p38 MAPK inhibitor, SB203580, blocked the effect of P. gingivalis LPS on IL-8 in hPDLFs.

CONCLUSION

This study suggests that in hPDLFs, P. gingivalis LPS suppresses bone sialoprotein and enhances IL-8 gene and protein expression via TLR2 and ERK1/2 or the p38 MAPK signaling pathway, respectively.

Porphyromonas gingivalis LPS inhibits osteoblastic differentiation and promotes pro-inflammatory cytokine production in human periodontal ligament stem cells

OBJECTIVE

Porphyromonas gingivalis (P. gingivalis) lipopolysaccharide (LPS) induces pro-inflammatory cytokines, such as interleukin-1 β (IL-1β), IL-6, and IL-8, which induce periodontal tissue destruction. Periodontal ligament stem cells (PDLSCs) play an important role in periodontal tissue regeneration and are expected to have future applications in cellular therapies for periodontitis. However, no studies have examined the effects of P. gingivalis LPS on PDLSCs. The aim of this study was to investigate how P. gingivalis LPS affects the osteoblastic differentiation and pro-inflammatory cytokine production of PDLSCs.

DESIGN

PDLSCs were obtained from healthy adult human mandibular third molars. The identification of PDLSCs was confirmed by immunohistochemical evaluations of the mesenchymal stem cell markers STRO-1 and SSEA-4. Cell proliferation and osteoblastic differentiation were investigated by culturing the PDLSCs in a normal or osteogenic medium with P. gingivalis LPS (0, 1, or 10μg/mL) and then measuring the alkaline phosphatase (ALP) activity and the production of collagen type 1 Alpha 1 (COL1A1), osteocalcin production, and mineralisation. Additionally, we examined the production of IL-1β, IL-6, and IL-8 in the PDLSCs.

RESULTS

P. gingivalis LPS inhibited the ALP activity, COL1A1 and osteocalcin production, and mineralisation in the PDLSCs, which are positive for STRO-1 and SSEA-4. P. gingivalis LPS also promoted cell proliferation and produced IL-1β, IL-6, and IL-8.

CONCLUSIONS

This study provides the first findings that P. gingivalis LPS inhibits osteoblastic differentiation and induces pro-inflammatory cytokines in PDLSCs. These findings will help clarify the relationship between periodontitis and periodontal tissue regeneration.

A critical role for suppressors of cytokine signaling 3 in regulating LPS-induced transcriptional activation of matrix metalloproteinase-13 in osteoblasts

Suppressor of cytokine signaling 3 (SOCS3) is a key regulator of cytokine signaling in macrophages and T cells. Although SOCS3 seems to contribute to the balance between the pro-inflammatory actions of IL-6 family of cytokines and anti-inflammatory signaling of IL-10 by negatively regulating gp130/Jak/Stat3 signal transduction, how and the molecular mechanisms whereby SOCS3 controls the downstream impact of TLR4 are largely unknown and current data are controversial. Furthermore, very little is known regarding SOCS3 function in cells other than myeloid cells and T cells. Our previous study demonstrates that SOCS3 is expressed in osteoblasts and functions as a critical inhibitor of LPS-induced IL-6 expression. However, the function of SOCS3 in osteoblasts remains largely unknown. In the current study, we report for the first time that LPS stimulation of osteoblasts induces the transcriptional activation of matrix metalloproteinase (MMP)-13, a central regulator of bone resorption. Importantly, we demonstrate that SOCS3 overexpression leads to a significant decrease of LPS-induced MMP-13 expression in both primary murine calvariae osteoblasts and a mouse osteoblast-like cell line, MC3T3-E1. Our findings implicate SOCS3 as an important regulatory mediator in bone inflammatory diseases by targeting MMP-13.

Adherent lipopolysaccharide inhibits the osseointegration of orthopedic implants by impairing osteoblast differentiation

Osseointegration is the process by which an orthopedic implant makes direct bone-to-implant contact and is crucial for the long-term function of the implant. Surface contaminants, such as bacterial debris and manufacturing residues, may remain on orthopedic implants after sterilization and impair osseointegration. For example, specific lots of implants that were associated with impaired osseointegration and high failure rates were discovered to have contaminants including bacterial debris. Therefore, the goals of this study were to determine if bacterial debris exists on sterile orthopedic implants and if adherent bacterial debris inhibits the osseointegration of orthopedic implants. We found that debris containing lipopolysaccharide (LPS) from Gram-negative bacteria exists on both sterile craniofacial implants and wrist implants. Levels of bacterial debris vary not only between different lots of implants but within an individual lot. Using our murine model of osseointegration, we found that ultrapure LPS adherent to the implants inhibited bone-to-implant contact and biomechanical pullout measures. Analysis of osseointegration in knock-out mice demonstrated that adherent LPS inhibited osseointegration by signaling through its primary receptor, Toll-like receptor 4, and not by signaling through Toll-like receptor 2. Ultrapure LPS adherent to titanium alloy discs had no detectable effect on early stages of MC3T3-E1 osteogenesis in vitro such as attachment, spreading or growth. However, later stages of osteogenic differentiation and mineralization were inhibited by adherent LPS. Thus, LPS may inhibit osseointegration in part through cell autonomous effects on osteoblasts. These results highlight bacterial debris as a type of surface contaminant that can impair the osseointegration of orthopedic implants.

Gingival crevicular fluid as a periodontal diagnostic indicator--I: Host derived enzymes and tissue breakdown products

Researchers involved in the delivery of periodontal therapy are currently investigating the possible use of oral fluids in the diagnosis of oral diseases and drug development. Substantial improvements have been made in the understanding of the mediators implicated on the initiation, pathogenesis, and progression of periodontitis. This review will analyze the mechanisms involved in the breakdown of periodontal supporting tissues during chronic periodontitis and highlights the potential array of biomarkers present in gingival crevicular fluid (GCF), which may relate to existing or predicted tissue regions undergoing metabolic change.

The role of SH3BP2 in the pathophysiology of cherubism

Cherubism is a rare bone dysplasia that is characterized by symmetrical bone resorption limited to the jaws. Bone lesions are filled with soft fibrous giant cell-rich tissue that can expand and cause severe facial deformity. The disorder typically begins in children at ages of 2-5 years and the bone resorption and facial swelling continues until puberty; in most cases the lesions regress spontaneously thereafter. Most patients with cherubism have germline mutations in the gene encoding SH3BP2, an adapter protein involved in adaptive and innate immune response signaling. A mouse model carrying a Pro416Arg mutation in SH3BP2 develops osteopenia and expansile lytic lesions in bone and some soft tissue organs. In this review we discuss the genetics of cherubism, the biological functions of SH3BP2 and the analysis of the mouse model. The data suggest that the underlying cause for cherubism is a systemic autoinflammatory response to physiologic challenges despite the localized appearance of bone resorption and fibrous expansion to the jaws in humans.

High glucose concentrations alter the biomineralization process in human osteoblastic cells

Diabetes mellitus (DM) may alter bone remodeling, as osteopenia and osteoporosis are among the complications. Moreover, DM increases the risk and severity of chronic inflammatory periodontal disease, in which bone resorption occurs. Broad evidence suggests that chronic inflammation can contribute to the development of DM and its complications. Hyperglycemia is a hallmark of DM that may contribute to sustained inflammation by increasing proinflammatory cytokines, which are known to cause insulin resistance, via toll-like receptor (TLR)-4-mediated mechanisms. However, the mechanisms by which bone-related complications develop in DM are still unknown. Studies done on the effect of high glucose concentrations on osteoblast functions are contradictory because some suggest increases (although others suggest reductions) in the biomineralization process. Therefore, we evaluated the effect of high glucose levels on biomineralization and inflammation markers in a human osteoblastic cell line. Cells were treated with either physiological 5.5 mM or increasing concentrations of glucose up to 24 mM, and we determined the following: i) the quantity and quality of calcium-deposit crystals in culture and ii) the expression of the following: a) proteins associated with the process of biomineralization, b) the receptor activator of nuclear factor kappa-B ligand (RANKL) and osteoprotegerin (OPG), c) cytokines IL1, IL6, IL8, IL10, MCP-1 and TNF alpha, and d) TLR-2, -3, -4 and -9. Our results show that high glucose concentrations (12 mM and particularly 24 mM) alter the biomineralization process in osteoblastic cells and provoke the following: i) a rise in mineralization, ii) an increase in the mRNA expression of RANKL and a decrease of OPG, iii) an increase in the mRNA expression of osteocalcin, bone sialoprotein and the transcription factor Runx2, iv) a diminished quality of the mineral, and v) an increase in the expression of IL1beta, IL6, IL8, MCP-1 and IL10 mRNAs. In addition we found that both high glucose levels and hyperosmotic conditions provoked TLR-2, -3, -4 and -9 overexpression in osteoblastic cells, suggesting that they are susceptible to osmotic stress.

Surface contaminants inhibit osseointegration in a novel murine model

Surface contaminants, such as bacterial debris and manufacturing residues, may remain on orthopedic implants after sterilization procedures and affect osseointegration. The goals of this study were to develop a murine model of osseointegration in order to determine whether removing surface contaminants enhances osseointegration. To develop the murine model, titanium alloy implants were implanted into a unicortical pilot hole in the mid-diaphysis of the femur and osseointegration was measured over a five week time course. Histology, backscatter scanning electron microscopy and X-ray energy dispersive spectroscopy showed areas of bone in intimate physical contact with the implant, confirming osseointegration. Histomorphometric quantification of bone-to-implant contact and peri-implant bone and biomechanical pullout quantification of ultimate force, stiffness and work to failure increased significantly over time, also demonstrating successful osseointegration. We also found that a rigorous cleaning procedure significantly enhances bone-to-implant contact and biomechanical pullout measures by two-fold compared with implants that were autoclaved, as recommended by the manufacturer. The most likely interpretation of these results is that surface contaminants inhibit osseointegration. The results of this study justify the need for the development of better detection and removal techniques for contaminants on orthopedic implants and other medical devices.

Topical and intermittent application of parathyroid hormone recovers alveolar bone loss in rat experimental periodontitis

BACKGROUND AND OBJECTIVE

Periodontitis is characterized by periodontal tissue inflammation and alveolar bone loss. The intermittent administration of parathyroid hormone (PTH), a major regulator of bone remodeling, has been demonstrated to stimulate osteoblastic activity. Although the systemic administration of PTH has been reported to protect against periodontitis-associated bone loss, the effect of the topical administration of PTH is unclear. In this study, the effect of intermittent administration of PTH on osteoblastic differentiation was examined in cultured calvaria cells and then the effect of topical and intermittent administration of PTH was determined by measuring the recovery of alveolar bone loss after inducing experimental periodontitis in rats.

MATERIAL AND METHODS

Alkaline phosphatase activity and bone nodule formation were measured in fetal rat calvaria cells. Experimental periodontitis was induced by placing nylon ligature around rat maxillary molars for 20 d. After ligature removal (day 0), PTH was topically injected into buccal gingiva three times a week for 10 wk. Micro-computed tomography analysis and histological examination were performed on days 35 and 70.

RESULTS

Intermittent exposure of PTH in calvaria cells increased alkaline phosphatase activity and bone nodule formation by 1.4- and 2.4-fold, respectively. Ligature procedures induced marked alveolar bone loss around the molars on day 0 and greater bone recovery was observed in the PTH-treated rats on day 70. An increase in osteoid formation on the surface of alveolar bone was detected in the PTH-treated rats.

CONCLUSION

Intermittent treatment with PTH stimulated osteoblastic differentiation in fetal rat calvaria cell cultures, and topical and intermittent administration of PTH recovered alveolar bone loss in rat experimental periodontitis.