Nitric oxide promotes infectious bone resorption by enhancing cytokine-stimulated interstitial collagenase synthesis in osteoblasts

Role of nitric oxide in orthodontic tooth movement (Review)

Nitric oxide (NO) is an ubiquitous signaling molecule that mediates numerous cellular processes associated with cardiovascular, nervous and immune systems. NO also plays an essential role in bone homeostasis regulation. The present review article summarized the effects of NO on bone metabolism during orthodontic tooth movement in order to provide insight into the regulatory role of NO in orthodontic tooth movement. Orthodontic tooth movement is a process in which the periodontal tissue and alveolar bone are reconstructed due to the effect of orthodontic forces. Accumulating evidence has indicated that NO and its downstream signaling molecule, cyclic guanosine monophosphate (cGMP), mediate the mechanical signals during orthodontic-related bone remodeling, and exert complex effects on osteogenesis and osteoclastogenesis. NO has a regulatory effect on the cellular activities and functional states of osteoclasts, osteocytes and periodontal ligament fibroblasts involved in orthodontic tooth movement. Variations of NO synthase (NOS) expression levels and NO production in periodontal tissues or gingival crevicular fluid (GCF) have been found on the tension and compression sides during tooth movement in both orthodontic animal models and patients. Furthermore, NO precursor and NOS inhibitor administration increased and reduced the tooth movement in animal models, respectively. Further research is required in order to further elucidate the underlying mechanisms and the clinical application prospect of NO in orthodontic tooth movement.

The Role of Reactive Oxygen Species and Nitric Oxide in the Inhibition of Trichophyton rubrum Growth by HaCaT Cells

Trichophyton rubrum (T. rubrum) is one of the most important agents of dermatophyte infection in humans. The aim of this experiment was to evaluate the effect of HaCaT cells on T. rubrum, investigate the responsible mechanism of action, and explore the role of reactive oxygen species (ROS) and nitric oxide (NO) in the inhibition of T. rubrum growth by HaCaT cells. The viability of fungi treated with HaCaT cells alone and with HaCaT cells combined with pretreatment with the NADPH oxidase inhibitor (DPI) or the nitric oxide synthase (NOS) inhibitor L-NMMA was determined by enumerating the colony-forming units. NOS, ROS, and NO levels were quantified using fluorescent probes. The levels of the NOS inhibitor asymmetric dimethylarginine (ADMA) were determined by enzyme-linked immunosorbent assay (ELISA). Micromorphology was observed using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). In addition, fungal keratinase activity was assessed by measuring dye release from keratin azure. In vitro fungal viability, keratinase activity, and ADMA content decreased after HaCaT cell intervention, whereas the levels of ROS, NO, and NOS increased. The micromorphology was abnormal. Fungi pretreated with DPI and L-NMMA exhibited opposite effects. HaCaT cells inhibited the growth and pathogenicity of T. rubrum in vitro. A suggested mechanism is that ROS and NO play an important role in the inhibition of T. rubrum growth by HaCaT cells.

Intracanal Metformin Promotes Healing of Apical Periodontitis via Suppressing Inducible Nitric Oxide Synthase Expression and Monocyte Recruitment

INTRODUCTION

We have previously shown that intracanal metformin ameliorates apical periodontitis, partially by modulation of osteoblast apoptosis. The action of metformin on other cell types pertinent to the development of apical periodontitis needs to be examined. In the present study, we aimed to analyze whether its effects on the expression of inducible nitric oxide synthase (iNOS) and monocyte recruitment contribute to the therapeutic effect on apical periodontitis.

METHODS

Lipopolysaccharide (LPS)-induced expression of iNOS in a human monocytic cell line, Mono-Mac-6, was assessed by Western blot. The amount of nitrite in culture medium was assessed to quantify nitric oxide (NO) production. C-C motif chemokine ligand-2 (CCL-2) synthesis was measured by enzyme-linked immunosorbent assay. Experimental apical periodontitis in rats was treated with root canal debridement with or without intracanal metformin medication. Lesion progression was assessed by conventional radiography and micro-computed tomographic imaging. Cellular expression of iNOS and the number of monocytes/macrophages were assessed by immunohistochemistry.

RESULTS

Metformin suppressed LPS-induced iNOS and NO production by monocytes. More importantly, metformin inhibited LPS-enhanced CCL-2 synthesis through modulation of the iNOS/NO pathway. Intracanal metformin reduced bone resorption associated with apical periodontitis and suppressed iNOS expression and monocyte recruitment.

CONCLUSIONS

Our results confirmed the therapeutic efficacy of intracanal metformin for apical periodontitis. Suppression of monocyte recruitment through modulation of iNOS expression and NO production is an important mechanism underlying the beneficial effect of metformin.

Participation of endotoxin in root canal infections: A systematic review and meta-analysis

This systematic review and meta-analysis aimed to evaluate the relationship between endotoxin levels and presence of clinical signs/symptoms and radiographic features in patients with endodontic infection. Electronic searches were performed on Medline/PubMed, Embase, Cochrane Library, Scielo, Science Direct, Web of Knowledge and Scopus databases for identification of relevant studies published up to December 2016. Grey literature was searched in Google Scholar. The selected literature was reviewed independently by two authors. Clinical studies evaluating the levels of endotoxin and the presence of clinical and radiographic features were included in this review. In order to determine the relationship between endotoxin levels and presence of clinical signs/symptoms and radiographic features meta-analyses were performed. Among the 385 articles identified in the initial search, 30 were included for full-text appraisal and only eight studies met the inclusion criteria for this systematic review. Meta-analysis revealed that individuals having teeth with tenderness to percussion (TTP) (P = 0.04; I² 57%) and previous episode of pain (PEP) (P = 0.001; I² 81%) had higher levels of endotoxin than their counterparts. Size of radiographic lesion >2 mm (P = 0.02; I² 68%) and presence of root canal exudation (EX) (P = 0.0007; I² 0%) were associated with higher levels of endotoxin. This systematic review and meta-analyses provided a strong evidence that endotoxin are related with the presence of clinical signs/symptoms and radiographic features in patients with endodontic infection.

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.

Evaluation of interleukin-1β level and oxidative status in gingival crevicular fluid during rapid maxillary expansion

OBJECTIVES

The levels of interleukin-1β (IL-1β), nitric oxide (NO), total antioxidant capacity (TAC), and total oxidant status (TOS) in gingival crevicular fluid (GCF) were determined during rapid maxillary expansion (RME) treatment.

MATERIALS AND METHODS

Fourteen patients (10-13 years old) were included. A modified hyrax appliance was used for the treatment. After periodontal parameters were recorded, GCF was collected from the first molars at each observation [T1:baseline:14 days after periodontal prophylaxis and instructions; T2:1 day later hyrax inserted, at passive position; T3:1 week later; after the first activation; T4:after 2 × 1/4 activation; T5:after 7 × 1/4 activation; T6:after 14 × 1/4 activation; T7:retention period on the 1 st month; and T8:retention period on the 3rd month].

RESULTS

Although the levels of IL1-β, NO, and PD increased significantly from T1 to T2, the GI, BOP%, and PI remained unchanged throughout treatment. GCF volume at buccal and palatal surfaces increased significantly from T1 to T4, T6, T7, and T8. The parameters in GCF and TAC levels were not only higher at palatal side in comparison with buccal, but also TOS levels increased at both buccal and palatal sides.

CONCLUSIONS

In this study, the differences of oxidative status and IL-1β levels during RME treatment could be attributable to orthopedic effect of the heavy forces on maxilla and minimal orthodontic forces on teeth applied by the RME apparatus.

Effects of rosuvastatin on inducible nitric oxide synthase in rats with hyperlipidaemia and periodontitis

BACKGROUND AND OBJECTIVE

Nitric oxide is a free radical that is synthesized from l-arginine by nitric oxide synthase (NOS). The level of inducible NOS (iNOS) in gingiva with periodontitis is higher than that in healthy gingiva. The aim of this study was to evaluate the effects of rosuvastatin administration on alveolar bone loss (ABL) and iNOS(+) cell counts in gingival tissues in rats with ligature-induced experimental periodontitis with/without hyperlipidaemia.

MATERIAL AND METHODS

The rats were randomly divided into seven groups: Hy (cholesterol-added diet/water administration); HyP (cholesterol-added diet/periodontitis/water administration); HyPR (cholesterol-added diet/periodontitis/rosuvastatin administration); P (standard diet/periodontitis/water administration); PR (standard diet/periodontitis/rosuvastatin administration); C (standard diet/water administration); and R (standard diet/rosuvastatin administration). Experimental periodontitis was induced with silk ligatures, and rosuvastatin/water was administered to rats by oral gavage for the last 2 weeks of the 8-week study. After the rats were killed in week 8, histomorphometric and histological analyses were performed. Immunostained iNOS(+) cells were counted in the gingival samples and the Mann-Whitney U-test was used for statistical analysis.

RESULTS

The experimental groups exhibited increases in total cholesterol and low-density lipoprotein, except for Groups C and R. The cholesterol-added diet induced ABL in Group Hy. Of the periodontitis groups, the lowest ABL was found in Group PR. While there was a significant difference in ABL between Groups P (0.82 ± 0.15 mm) and PR (0.70 ± 0.21 mm) receiving a standard diet (P < .05), no difference was observed between Groups HyP (0.77 ± 0.07 mm) and HyPR (0.76 ± 0.11 mm) receiving a cholesterol-added diet (P ˃ .05). Rosuvastatin significantly reduced expression of iNOS in Groups PR (18.40 ± 2.31%) and HyPR (24.00 ± 4.83%) compared with Group P (30.90 ± 2.42%; P < .001). However, a larger number of iNOS(+) cells was found in Group HyPR than in Group PR (P < .001).

CONCLUSION

Administration of rosuvastatin reduced gingival iNOS expression in ligature-induced periodontitis with/without hyperlipidaemia. It also led to significant differences in ABL in rats with periodontitis, except when periodontitis was associated with hyperlipidaemia. These findings could provide an important contribution in further studies to evaluate the role of rosuvastatin as a host modulatory agent in the pathogenesis of periodontal diseases.

Antimicrobial and immunomodulatory activity of host defense peptides, clavanins and LL-37, in vitro: An endodontic perspective

Endodontic treatment is mainly based on root canal disinfection and its failure may be motivated by microbial resistance. Endodontic therapy can be benefitted by host defense peptides (HDPs), which are multifunctional molecules that act against persistent infection and inflammation. This study aimed to evaluate the antimicrobial, cytotoxic and immunomodulatory activity of several HDPs, namely clavanin A, clavanin A modified (MO) and LL-37, compared to intracanal medication Ca(OH)₂. HDPs and Ca(OH)₂ were evaluated by: (1) antimicrobial assays against Candida albicans and Enterococcus faecalis, (2) cytotoxicity assays and (3) cytokine tumor necrosis factor (TNF)-α, monocyte chemoattractant protein (MCP)-1, interleukin (IL)-1α, IL-6, IL-10 and IL-12 and nitric oxide (NO) production by RAW 264.7 cells incubated with or without heat-killed (HK) C. albicans or E. faecalis combined or not with interferon-γ. The minimum inhibitory concentration (MIC) was established only for E. faecalis (LL-37, 57μM). Considering cytotoxicity, clavanin MO was able to reduce cell viability in many groups and demonstrated lowest LC₅₀. The Ca(OH)₂ up-regulated the production of MCP-1, TNF-α, IL-12 and IL-6 and down-regulated IL-1α, IL-10 and NO. Clavanins up-regulated the TNF-α and NO and down-regulated IL-10 production. LL-37 demonstrated up-regulation of IL-6 and TNF-α production and down-regulation in IL-10 and NO production. In conclusion, LL-37 demonstrated better antibacterial potential. In addition, Ca(OH)₂ demonstrated a proinflammatory response, while the HDPs modulated the inflammatory response from non-interference with the active cytokines in the osteoclastogenesis process, probably promoting the health of periradicular tissues.

Exogenous nitric oxide enhances calcification in embryonic stem cell-derived osteogenic cultures

While the involvement of nitric oxide in bone formation, homeostasis and healing has been extensively characterized, its role in directing pluripotent stem cells to the osteogenic lineage has not been described. Yet, the identification of chemical inducers that improve differentiation output to a particular lineage is highly valuable to the development of such cells for the cell-based treatment of osteo-degenerative diseases. This study aimed at investigating the instructive role of nitric oxide (NO) and its synthesizing enzymes on embryonic stem cell (ESC) osteogenic differentiation. Our findings showed that NO levels may support osteogenesis, but that the effect of nitric oxide on osteoblast differentiation may be specific to a particular time phase during the development of osteoblasts in vitro. Endogenously, nitric oxide was specifically secreted by osteogenic cultures during the calcification period. Simultaneously, messenger RNAs for both the endothelial and inducible nitric oxide synthase isoforms (eNOS and iNOS) were upregulated during this late phase development. However, the specific eNOS inhibitor L-N(5)-(1-Iminoethyl)ornithine dihydrochloride attenuated calcification more so than the specific iNOS inhibitor diphenyleneiodonium. Exogenous stage-specific supplementation of culture medium with the NO donor S-nitroso-N-acetyl-penicillamine increased the percentage of cells differentiating into osteoblasts and enhanced calcification. Our results point to a primary role for eNOS as a pro-osteogenic trigger in ESC differentiation and expand on the variety of supplements that may be used to direct ESC fate to the osteogenic lineage, which will be important in the development of cell-based therapies for osteo-degenerative diseases.

Immune Response Profile against Persistent Endodontic Pathogens Candida albicans and Enterococcus faecalis In Vitro

INTRODUCTION

Persistent microorganisms such as Candida albicans and Enterococcus faecalis might be directly related to endodontic treatment failure. The host response to these microorganisms impairs the reestablishment of intraradicular and periradicular health.

METHODS

The present investigation evaluated the expression of inflammatory mediators produced by RAW 264.7 cells in the presence of heat-killed antigens (HK) C. albicans and E. faecalis. Cultures of RAW cells were stimulated with both antigens in the presence or absence of recombinant interferon (rIFN)-γ. Parameters of cell viability, production of nitric oxide (NO), as well as the synthesis of interleukin (IL)-1α, IL-6, IL-10, IL-12, monocyte chemotactic protein-1, and tumor necrosis factor (TNF)-α were analyzed.

RESULTS

Results demonstrated that cell viability was especially reduced in antigens and rIFN-γ-stimulated groups. Groups stimulated with HK C. albicans upregulated IL-10 production. Otherwise, the addition of rIFN-γ to HK C. albicans upregulated TNF-α and NO production. Groups stimulated with HK E. faecalis upregulated TNF-α production. HK E. faecalis and rIFN-γ upregulated TNF-α and NO synthesis. The production of other cytokines remained unchanged by all stimuli.

CONCLUSIONS

Knowledge regarding the host mechanism of response to microorganisms that perpetuate endodontic infection and the periradicular lesions can contribute to optimization of endodontic therapy. The mentioned inflammatory mediators and virulence factors involved in endodontic failure might guide lesion progression and also be targets in the development of disinfectant and immunomodulatory agents.

The expression of a nitric oxide derivative, tissue inhibitors of metalloproteinase-3, and tissue inhibitors of metalloproteinase-4 in chronic periodontitis with type 2 diabetes mellitus

Purpose

The purpose of this study was to analyze the expression of inducible nitric oxide synthases (iNOS), tissue inhibitors of metalloproteinase (TIMP)-3, and TIMP-4 in the gingival tissues of periodontal patients with or without type 2 diabetes mellitus (DM).

Methods

Depending on the patient's systemic condition and clinical criteria of the gingiva, each gingival sample was classified into one of three groups. Sixteen clinically, systemically healthy patients (group 1), 16 periodontal patients (group 2), and 16 periodontal patients with DM (group 3) were included. Tissue samples in each group were collected, prepared, and analyzed by western blotting. Quantification of the relative amount of TIMP-3, TIMP-4, and iNOS was performed.

Results

The expression levels of iNOS and TIMP-3 both increased in group 1, group 2, and group 3 in increasing order, and were significantly higher in both group 2 and group 3 as compared to group 1 (P<0.05). The expression levels of TIMP-4 increased in the same order, but significantly increased in group 2 as compared to group 1, in group 3 as compared to group 1, and group 3 as compared to group 2 (P<0.05).

Conclusions

This study demonstrated that iNOS, TIMP-3, and TIMP-4 might be involved in the progression of periodontal inflammation associated with type 2 DM. It is thought that further study of these factors can be applied practically for the diagnosis and control of periodontitis in diabetics.

An in vitro study of osteoblast vitality influenced by the vitamins C and E

Vitamin C and vitamin E are known as important cellular antioxidants and are involved in several other non-antioxidant processes. Generally vitamin C and vitamin E are not synthesized by humans and therefore have to be applied by nutrition. The absence or deficiency of the vitamins can lead to several dysfunctions and even diseases (e.g. scurvy). The main interest in this study is that vitamin C and E are known to influence bone formation, e.g. vitamin C plays the key role in the synthesis of collagen, the major component of the extracellular bone matrix.

In the present study we evaluate the effect of ascorbic acid (vitamin C) and α-tocopherol (vitamin E) on the proliferation and differentiation of primary bovine osteoblasts in vitro. Starting from standard growth medium we minimized the foetal calf serum to reduce their stimulatory effect on proliferation.

An improved growth and an increased synthesis of the extracellular matrix proteins collagen type I, osteonectin and osteocalcin was observed while increasing the ascorbic acid concentration up to 200 μg/ml. Furthermore the effects of α-tocopherol on cell growth and cell differentiation were examined, whereby neither improved growth nor increased synthesis of the extracellular matrix proteins collagen type I, osteonectin and osteocalcin were detected.

Further investigations are necessary to target at better supportive effect of vitamins on bone regeneration, and healing.

NO-β-catenin crosstalk modulates primitive streak formation prior to embryonic stem cell osteogenic differentiation

Nitric oxide (NO) has been shown to play a crucial role in bone formation in vivo. We sought to determine the temporal effect of NO on murine embryonic stem cells (ESCs) under culture conditions that promote osteogenesis. Expression profiles of NO pathway members and osteoblast-specific markers were analyzed using appropriate assays. We found that NO was supportive of osteogenesis specifically during an early phase of in vitro development (days 3-5). Furthermore, ESCs stably overexpressing the inducible NO synthase showed accelerated and enhanced osteogenesis in vitro and in bone explant cultures. To determine the role of NO in early lineage commitment, a stage in ESC differentiation equivalent to primitive streak formation in vivo, ESCs were transfected with a T-brachyury-GFP reporter. Expression levels of T-brachyury and one of its upstream regulators, β-catenin, the major effector in the canonical Wnt pathway, were responsive to NO levels in differentiating primitive streak-like cells. Our results indicate that NO may be involved in early differentiation through regulation of β-catenin and T-brachyury, controlling the specification of primitive-streak-like cells, which may continue through differentiation to later become osteoblasts.

iNOS-derived nitric oxide stimulates osteoclast activity and alveolar bone loss in ligature-induced periodontitis in rats

BACKGROUND

Inflammatory stimuli activate inducible nitric oxide synthase (iNOS) in a variety of cell types, including osteoclasts (OC) and osteoblasts, resulting in sustained NO production. In this study, we evaluate the alveolar bone loss in rats with periodontitis under long-term iNOS inhibition, and the differentiation and activity of OC from iNOS-knockout (KO) mice in vitro.

METHODS

Oral aminoguanidine (an iNOS inhibitor) or water treatment was started 2 weeks before induction of periodontitis. Rats were sacrificed 3, 7, or 14 days after ligature placement, and alveolar bone loss was evaluated. In vitro OC culture experiments were also performed to study the differentiation of freshly isolated bone marrow cells from both iNOS KO and wild-type C57BL/6 mice. OC were counted 6 days later after tartrate-resistant acid phosphatase staining (a marker of osteoclast identity), and bone resorption activity was assessed by counting the number of resorption pits on dentin disks.

RESULTS

Rats with ligature showed progressive and significant alveolar bone loss compared to sham animals, and aminoguanidine treatment significantly inhibited ligature-induced bone loss at 7 and 14 days after the induction. In comparison to bone marrow cells from wild-type mice, cells from iNOS KO mice showed decreased OC growth and the resulting OC covered a smaller culture dish area and generated fewer resorption pit counts.

CONCLUSION

Our results demonstrate that iNOS inhibition prevents alveolar bone loss in a rat model of ligature-induced periodontitis, thus confirming that iNOS-derived NO plays a crucial role in the pathogenesis of periodontitis, probably by stimulating OC differentiation and activity.

The roles of TNFR1 in lipopolysaccharide-induced bone loss: dual effects of TNFR1 on bone metabolism via osteoclastogenesis and osteoblast survival

LPS (lipopolysaccharide), a major constituent of Gram-negative bacteria, regulates proliferation and differentiation of osteoclasts directly or indirectly. This study sought to investigate the functions of the RANK/RANKL pathway in LPS-induced bone loss in vivo. Wild-type mice or TNFR1-/- mice were injected LPS with or without osteoprotegerin (OPG) and analyzed histologically. Bone volume was reduced by LPS injection in all groups, and OPG administration prevented the LPS-induced bone loss regardless of genotypes. LPS-induced enhancement of osteoclastogenesis in wild-type mice was blocked by OPG administration. LPS or OPG did not affect osteoclastogenesis in TNFR1-/- mice. Interestingly, osteoblast surface was remarkably reduced in LPS-treated TNFR1-/- mice as a result of enhanced osteoblast apoptosis. TRAIL, induced by TNF-alpha in BMC, triggered apoptosis of primary osteoblast only when TNFR1 signal was ablated in vitro. In conclusion, RANK signaling plays a prominent role in osteoclastogenesis downstream of LPS. Furthermore, TNFR1 regulates bone metabolism through not only the regulation of osteoclast differentiation but also osteoblast survival.

The role of Toll-like receptors 2 and 4 on reactive oxygen species and nitric oxide production by macrophage cells stimulated with root canal pathogens

INTRODUCTION

Periapical lesions arise as a result of the activation and interaction of the host immune responses against root canal infection. Recently identified Toll-like receptors (TLR) seem to be involved in the recognition and development of immune responses against a myriad of microorganisms. However, very little information is available on the role of TLR in the induction of periapical lesions.

METHOD

The role of TLR-2 and TLR-4 in the activation of murine macrophages stimulated using Fusobacterium nucleatum and Peptostreptococcus anaerobius was investigated. The production of nitric oxide (NO) and reactive oxygen species (ROS) was assessed.

RESULTS

The results demonstrate that TLR-2 and TLR-4 are involved in the production of ROS by activated macrophages. The microorganisms induced similar levels of NO production by TLR-2-competent and TLR-2-deficient macrophages, regardless of the addition of interferon-gamma (IFN-gamma), ruling out a role for TLR-2 in the NO production induced by these bacteria. Only P. anaerobius induced NO production by TLR-4-competent macrophages without the addition of IFN-gamma. However, after IFN-gamma addition, F. nucleatum induced macrophage NO production. Therefore, NO production stimulated by IFN-gamma and these microorganisms seems to be TLR-4-independent.

CONCLUSION

TLR-2 seems to be involved in the induction of ROS production by macrophages in response to prevalent root canal bacteria, while only F. nucleatum induced ROS production by TLR-4-competent macrophages. Both microorganisms significantly induced large amounts of NO independent of TLR-2 and TLR-4. We conclude that microorganisms may participate in the induction and progression of periapical lesions through NO and ROS production by activated macrophages.

Exposure to pro-inflammatory cytokines upregulates MMP-9 synthesis by mesenchymal stem cells-derived osteoprogenitors

An intimate interplay exists between the bone and the immune system, which has been recently termed osteoimmunology. The activity of immune cells affects the intrinsic balance of bone mineralization and resorption carried out by the opposing actions of osteoblasts and osteoclasts. The aim of this study was to determine the possible interaction between inflammatory-induced conditions and matrix metalloproteinases-2,-9 (MMP-2,-9) synthesis and secretion by bone marrow-derived osteoprogenitor cells during advanced stages of osteogenesis. Rat bone marrow-derived mesenchymal stem cells (MSCs) were cultured in the presence of osteogenic supplements in order to direct the cells towards the osteogenic differentiation lineage. At the late stages of osteogenesis, assessed by histochemistry, immunohistochemistry and RT-PCR, cultures were exposed to pro-inflammatory cytokines, tumor necrosis factor-alpha (TNF-alpha) and interleukin-1 alpha (IL-1 alpha). Biochemical, histochemical and molecular biology techniques were used to discern the influence of pro-inflammatory cytokines on MMP-2,-9 synthesis and secretion. Results indicated that MMP-9 synthesis and secretion were significantly induced after exposure to the cytokines (TNF-alpha, IL-1 alpha) treatment, while MMP-2 levels remained unchanged. These results indicate that in response to inflammatory processes, osteoblasts, in addition to osteoclasts, can also be involved and contribute to the process of active bone resorption by secretion and activation of MMPs.

Role of Sandhika: A Polyherbal Formulation on MC3T3-E1 Osteoblast-like Cells

Sandhika is a polyherbal formulation, (water soluble fraction of Commiphora mukul, Boswellia serrata, Semecarpus anacardium and Strychnos nux vomica), which has been in clinical use in India for last 20 years. Its modified formulation BHUx has shown specific inhibition of cyclooxygenase (COX)-2 and lipoxygenase (LOX)-15 and has prevented diet-induced atherosclerosis in rabbits. In order to explore the possibility of the use of Sandhika for the management of osteoporosis, we have examined its influence on MC3T3-E1 osteoblast-like cells in presence of lipopolysaccharide (1 microg/ml) in terms of calcium nodule formation and alkaline phosphatase activity. MC3T3-E1 osteoblast-like cells (80% confluence in 6-well plates) were treated with water extract of Sandhika, for 10 days, in the concentration range of 0.5 to 16 mg/ml final concentration, in presence of LPS. Media was changed on every third day and culture supernatant was collected after every change to assess the alkaline phosphatase activity and on the tenth day, cells were washed and stained with "Alizarin S" for visualization of calcium nodules by using Meta Morph software (Universal Imaging, Downingtown, PA). The results showed significant enhancement in calcium nodule formation in the dose dependent manner up to 2 mg/ml, followed by gradual decrease at higher concentrations. This change was accompanied with the increase in the alkaline phosphatase activity in these plates, indicating a potential anabolic effect of this polyherbal formulation on osteoblast-like cells under inflammatory conditions induced by LPS.

Nitric oxide promotes the progression of periapical lesion via inducing macrophage and osteoblast apoptosis

This study aimed to elucidate the modulation by nitric oxide (NO) of the apoptosis of macrophages and osteoblasts, the essential cellular components in the development of periapical lesions. Lipopolysaccharide (LPS) induced prominent nitrite synthesis in J774 mouse macrophage cell lines. Exposure to LPS induced obvious apoptosis in J774 cells, whereas transient transfection with murine inducible nitric oxide synthase (iNOS), small interfering RNA (siRNA) diminished this effect. Tumor necrosis factor-alpha (TNF-alpha) and S-nitroso-N-acetyl-DL-penicillamine (SNAP) (a NO donor) triggered apoptosis in UMR-106 rat osteoblastic cell lines and a synergistic effect was noted when TNF-alpha and SNAP were added to the medium together. Administration of siRNAs for c-Fos and c-Jun: components of activator protein-1 (AP-1) and transforming growth factor-beta1 attenuated the combined effect markedly. Terminal deoxynucleotidyl transferase-mediated nick end-labeling (TUNEL) stain in a rat model of induced periapical lesion showed positive apoptotic signals in macrophages and osteoblasts. Administration of N(G)-monomethyl-l-arginine markedly diminished the extent of bone loss and the amounts of apoptotic macrophages and osteoblasts. In conclusion, NO mediates LPS-stimulated apoptosis of macrophages. It also induces osteoblast apoptosis and augments the pro-apoptotic effect of cytokines. Inhibition of NO synthesis in vivo attenuates apoptosis and the size of periapical lesions. Taken together, these results suggest that NO may promote the progression of periapical lesion by inducing the apoptosis of macrophages and osteoblasts.

Synthesis of Nitric Oxide in Human Osteoblasts in Response to Physiologic Stimulation of Electrotherapy

Electrotherapy for bone healing, remodeling and wound healing may be mediated by modulation of nitric oxide (NO). Using NO-specific fluorophore (DAF-2), we report here that application of non-invasive, physiologic electrical stimulation induces NO synthesis in human osteoblasts, and that such NO generation is comparable to that induced by estrogen treatment. For example, application of a sinusoidal 1 Hz, 2 V/cm (peak to peak) electrical stimulation (ES) increases NO-bound DAF-2 fluorescence intensity by a 2-fold within 60 min exposure by activating nitric oxide synthase (NOS). Increase in the NO level is found to depend critically on the frequency and strength of ES. While the frequency of 1 Hz ES seems optimal, the ES strength >0.5 V/cm is required to induce significant NO increase, however. Nitric oxide synthesis in response to ES is completely prevented by blocking estrogen receptors using a competitive inhibitor, suggesting that NO generation is likely initiated by activation of estrogen receptors at the cell surface. Based on these findings, physiologic stimulation of electrotherapy appears to represent a potential non-invasive, non-genomic, and novel physical technique that could be used to regulate NO-mediated bone density and facilitate bone remodeling without adverse effects associated with hormone therapy.

Supplemental arginine and high-dose folate may promote bone health by supporting the activity of endothelial-type nitric oxide synthase in bone

The endothelial isoform of NO synthase promotes maintenance of bone density by stimulating osteoblastic activity while inhibiting bone catabolism; it appears to be a key mediator of the anabolic effects of mechanical loading, estrogens, and statin therapy on bone. This enzyme is susceptible to competitive inhibition by elevated systemic levels of asymmetric dimethylarginine (ADMA) encountered in vascular disorders associated with endotheliopathy; it may not be coincidental that reduced bone density has been observed in subjects afflicted with many of these disorders. Supplemental arginine has the potential to offset this adverse effect of ADMA. Superoxide production by osteoclasts may also impair bone NO synthase activity by oxidizing its cofactor tetrahydrobiopterin; high-dose folate has been shown to compensate for endothelial deficiency of this cofactor by effectively "pinch hitting" for it. These considerations suggest that supplementation with arginine as well as high-dose folate might aid maintenance of bone density by helping to preserve optimal NO synthase activity in bone cells.

Vitamin E provides protection for bone in mature hindlimb unloaded male rats

The deleterious effects of skeletal unloading on bone mass and strength may, in part, result from increased production of oxygen-derived free radicals and proinflammatory cytokines. This study was designed to evaluate the ability of vitamin E (alpha-tocopherol), a free-radical scavenger with antiinflammatory properties, to protect against bone loss caused by skeletal unloading in mature male Sprague-Dawley rats. A 2 x 3 factorial design was used with either hindlimb unloading (HU) or normal loading (ambulatory; AMB), and low-dose (LD; 15 IU/kg diet), adequate-dose (AD; 75 IU/kg diet), or high-dose (HD; 500 IU/kg diet) vitamin E (DL-alpha-tocopherol acetate). To optimize the effects of vitamin E on bone, dietary treatments were initiated 9 weeks prior to unloading and continued during the 4-week unloading period, at which time animals were euthanized and blood and tissue samples were collected. Serum vitamin E was dose-dependently increased, confirming the vitamin E status of animals. The HD treatment improved oxidation parameters, as indicated by elevated serum ferric-reducing ability and a trend toward reducing tissue lipid peroxidation. Histomorphometric analysis of the distal femur revealed significant reductions in trabecular thickness (TbTh), double-labeled surface (dLS/BS), and rate of bone formation to bone volume (BFR/BV) due by HU. AMB animals on the HD diet and HU animals on the LD diet had reduced bone surface normalized to tissue volume (BS/TV) and trabecular number (TbN); however, the HD vitamin E protected against these changes in the HU animals. Our findings suggest that vitamin E supplementation provides modest bone protective effects during skeletal unloading.

Effects of 17 beta-estradiol on the expression of interstitial collagenases-8 and -13 (MMP-8 and MMP-13) and tissue inhibitor of metalloproteinase-1 (TIMP-1) in ovariectomized rat osteoblastic cells

Estrogen plays an important role in maintaining normal bone metabolism via the direct or indirect regulation of bone cells. Osteoblastic cells, as the target cells of estrogen, can secrete multiple matrix metalloproteinases (MMPs) that participate in bone remodeling. It has been demonstrated that bone loss induced by estrogen deficiency is closely related to the abnormal expression of multiple MMPs in osteoblastic cells. However, the regulating action of estrogen on the expression of interstitial collagenases MMP-8 and MMP-13 in osteoblastic cells in vivo remains unclear. We used an ovariectomized osteoporotic rat model to analyze the changes in the histomorphometric parameters of bone after and without treatment with 17beta-estradiol (E(2)); We also used immunohistochemistry and in situ hybridization to observe changes in the expression of mRNA and the proteins MMP-8, MMP-13 and TIMP-1 in osteoblastic cells in rat proximal tibia. In this study, we found that in the ovariectomized rat the expression of MMP-13 mRNA and protein increased markedly, whereas the expression of MMP-8 and TIMP-1 mRNA and protein did not change significantly. Our analysis showed that the expression of MMP-13 protein was correlated positively to bone trabecular separation, osteoid surface area, and negatively to trabecular numbers and the percentage of trabecula bone volume/total tissue volume. Our results suggest that MMP-13 plays an important role in estrogen deficiency-induced bone loss, while estrogen can inhibit bone resorption and reduce bone turnover rate by down-regulating the expression of MMP-13 in osteoblastic cells.

Agastache rugosa leaf extract inhibits the iNOS expression in ROS 17/2.8 cells activated with TNF-α and IL-1β

It has been suggested that nitric oxide (NO) derived from inducible nitric oxide synthase (iNOS) may act as a mediator of cytokine-induced effects on bone turn-over. NO is also recognized as an important factor in bone remodeling, i.e., participating in osteoblast apoptosis in an arthritic joint. The components of Agastache rugosa are known to have many pharmacological activities. In the present study, we investigated the effects of Agastache rugosa leaf extract (ELAR) on NO production and the iNOS expression in ROS 17/2.8 cells activated by a mixture of inflammatory cytokines including TNF-alpha and IL-1beta. A preincubation with ELAR significantly and concentration-dependently reduced the expression of iNOS protein in ROS 17/2.8 cells activated with the cytokine mixture. Consequently, the NO production was also significantly reduced by ELAR with an IC50 of 0.75 mg/mL. The inhibitory mechanism of iNOS induction by ELAR prevented the activation and translocation of NF-kappaB (p65) to the nucleus from the cytosol fraction. Furthermore, ELAR concentration-dependently reduced the cellular toxicity induced by sodium nitroprusside, an NO-donor. These results suggest that ELAR may be beneficial in NO-mediated inflammatory conditions such as osteoporosis.

Inducible nitric oxide synthase mediates bone development and P. gingivalis-induced alveolar bone loss

The role of inducible nitric oxide synthase (iNOS) in bone development and bacterially induced periodontal bone loss was examined using mice with targeted mutation of the iNOS gene. Femurs of iNOS KO mice showed 30% and 9% higher bone mineral density compared to wild type (WT) at 4 and 9 weeks of age, respectively. Micro-computed tomography revealed that cortical thickness and cortical bone density is increased in the absence of iNOS, while trabecular bone thickness and bone density remains unchanged. Histochemical analysis using TRAP staining showed that osteoclast numbers are lower by 25% in iNOS KO femurs compared to WT femurs. When bone marrow cells were stimulated with M-CSF and RANKL in vitro, iNOS KO cultures developed 51% fewer TRAP-positive multinuclear cells compared to WT cultures. When similar cultures were grown on dentine discs, resorption pit area was decreased by 54% in iNOS KO cultures. Gene expression studies showed that iNOS expression is induced by M-CSF and RANKL in WT bone marrow cultures, while no iNOS transcript was detected in iNOS KO. No compensatory change was detected in the expression of neuronal or endothelial NOS isoforms. There was no difference in RANK and osteoprotegerin expression between iNOS KO and WT bone marrow cultures after M-CSF and RANKL-treatment, while Traf6 expression was significantly lower in the absence of iNOS. In the alveolar bone of the maxilla, the distance between the cementoenamel junction and the alveolar bone crest was larger in iNOS KO compared to WT mice from 6 to 14 weeks of age, indicating a developmental effect of iNOS in oral tissues. Oral administration of the periodontal pathogen Porphyromonas gingivalis caused alveolar bone loss in the maxilla of WT mice, but failed to do so in iNOS KO mice. Expression of the osteoclast marker cathepsin K was 25% lower in iNOS KO alveolar bone. These data indicate that iNOS promotes bone resorption during bone development as well as after bacterial infection, and that iNOS is an important signal for normal osteoclast differentiation.

Mitochondrial redox control of matrix metalloproteinases

Reactive oxygen species (ROS) are constantly generated in aerobic organisms during normal metabolism and in response to both internal and external stimuli. Imbalances in the production and removal of ROS have been hypothesized to play a causative role in numerous disease pathologies such as cancer, ischemia/reperfusion injury, and degenerative diseases such as photoaging, atherosclerosis, arthritis, and neurodegeneration. A feature often associated with these diseases is a malfunctioning of the connective tissue remodeling process due to increased activity of extracellular matrix-degrading metalloproteinases (MMPs). This review summarizes the evidence that implicates ROS as key regulators of MMP production and the importance of these interactions in disease pathologies.

Locally Applied Isosorbide Decreases Bone Resorption in Experimental Periodontitis in Rats

BACKGROUND

The role of nitric oxide (NO) on bone metabolism is controversial, since it can either stimulate bone formation or resorption. We investigated the effect of local administration of the NO donor isosorbide in an experimental periodontal disease model.

METHODS

Wistar rats were subjected to a ligature placement around the cervix of the right second upper molar and were sacrificed after 11 days. Alveolar bone loss was measured in one quadrant as the sum of the distances between the cuspid tip and the alveolar bone along the axis of each molar root, which was subtracted from the contralateral side, used as unligated control. The semiquantitative histopathological scale of the periodontium was based on cell infiltration and alveolar bone and cementum integrity. Groups were treated with a gel containing 1% or 5% isosorbide applied to the vestibular side of the molar gingiva 1 hour before the placement of the ligature and then twice daily until sacrifice. Controls included one group subjected to periodontitis and no treatment (NT) and another that received the gel containing just the vehicle (V).

RESULTS

The application of the vehicle gel produced an increase of the alveolar bone resorption, without altering the inflammatory changes, compared to the NT group. The 5% isosorbide produced a significant reduction of the alveolar bone resorption, compared to V and NT. This reduction was confirmed by histological analysis, showing less inflammatory cell infiltration and preservation of the cementum and the alveolar process.

CONCLUSION

Local application of isosorbide reduces alveolar bone resorption in experimental periodontal disease in rats, suggesting a local anti-inflammatory effect of isosorbide.

Therapeutic interventions targeting the nitric oxide system: current and potential uses in obstetrics, bone disease and erectile dysfunction

Nitric oxide is involved in a countless number of physiological processes and is known to have cytoprotective as well as cytotoxic effects. Increased knowledge about the multifaceted role of nitric oxide in a variety of disease states has led to the design of multiple treatment strategies involving the nitric oxide system. The current review focuses on recent research advances in the fields of obstetrics, bone disease and erectile dysfunction that have led to current or potential future therapies involving nitric oxide.

Effects of matrix metalloproteinase inhibitors on bone resorption and orthodontic tooth movement

Matrix metalloproteinases are involved in the regulation of bone remodeling. The hypothesis that matrix metalloproteinase inhibitors may be useful for experimentally limiting orthodontic tooth movement, a process involving perturbations of normal bone remodeling, was tested. General matrix metalloproteinase inhibitors limited the resorption of bone slices by mouse marrow cultures stimulated by calcitriol, parathyroid hormone, and basic-fibroblast growth factor. Pre-coating dentin slices with short arginine-glycine aspartic acid (RGD) peptides, but not arginine-glycine-glutamic acid (RGE) controls, restored bone resorption in the presence of matrix metalloproteinase inhibitors. Orthodontic tooth movement was inhibited by local delivery of Ilomastat, a general matrix metalloproteinase inhibitor, with the use of ethylene-vinyl-acetate (ELVAX) 40, a non-biodegradable, non-inflammatory sustained-release polymer. This study shows that orthodontic tooth movement can be inhibited with the use of matrix metalloproteinase inhibitors, and suggests a mechanistic link between matrix metalloproteinase activity and the production of RGD peptides.