Proinflammatory agents, IL-8 and IL-10, upregulate inducible nitric oxide synthase expression and nitric oxide production in avian osteoclast-like cells

Exercise and osteoimmunology in bone remodeling

Bones can form the scaffolding of the body, support the organism, coordinate somatic movements, and control mineral homeostasis and hematopoiesis. The immune system plays immune supervisory, defensive, and regulatory roles in the organism, which mainly consists of immune organs (spleen, bone marrow, tonsils, lymph nodes, etc.), immune cells (granulocytes, platelets, lymphocytes, etc.), and immune molecules (immune factors, interferons, interleukins, tumor necrosis factors, etc.). Bone and the immune system have long been considered two distinct fields of study, and the bone marrow, as a shared microenvironment between the bone and the immune system, closely links the two. Osteoimmunology organically combines bone and the immune system, elucidates the role of the immune system in bone, and creatively emphasizes its interdisciplinary characteristics and the function of immune cells and factors in maintaining bone homeostasis, providing new perspectives for skeletal-related field research. In recent years, bone immunology has gradually become a hot spot in the study of bone-related diseases. As a new branch of immunology, bone immunology emphasizes that the immune system can directly or indirectly affect bones through the RANKL/RANK/OPG signaling pathway, IL family, TNF-α, TGF-β, and IFN-γ. These effects are of great significance for understanding inflammatory bone loss caused by various autoimmune or infectious diseases. In addition, as an external environment that plays an important role in immunity and bone, this study pays attention to the role of exercise-mediated bone immunity in bone reconstruction.

Insights into the functional role of grass carp IL-8 in head kidney leukocytes: pro-inflammatory effects and signalling mechanisms

Interleukin-8 (IL-8) is a critical chemokine regulating immune cells' chemotaxis as well as their physiological or pathological activations. In fish cells, recombinant IL-8 proteins induced transcriptions of pro-inflammatory cytokines. Nonetheless, the exact mechanisms underlying the function of fish IL-8 as a pro-inflammatory cytokine are still unclear. In this paper, the authors first prepared recombinant grass carp IL-8 (rgcIL-8) using an Escherichia coli expression system, and later confirmed rgcIL-8 increased gene expression of il8, il1β and tumour necrosis factor alpha (tnfα) in grass carp head kidney leukocytes (HKLs). Using signalling pathway inhibitors, the authors showed that rgcIL-8 regulated transcriptions of pro-inflammatory cytokines via MAPK and/or NF-κB signalling pathways. They cloned gcIL-8-specific receptor CXCR1 and subsequently discovered that gcIL-8 could increase the activity of NF-κB and the transcription of IL-1β via CXCR1. Simultaneously, antibody neutralization assay showed that endogenous IL-8 is partially relevant to the self-regulation of IL-1β. Moreover, rgcIL-8 led to the expression of inducible nitric oxide synthase gene, causing an accumulation of nitric oxide in the culture medium of HKLs, suggesting the potential of gcIL-8 to mediate inflammatory response. This study not only enriched the function of IL-8 in teleost but also revealed it as a potential target for the inflammatory control in grass carp.

Nitric oxide and bone: The phoenix rises again

The involvement of nitric oxide (NO) in preventing bone loss has long been hypothesized, but despite decades of research the mechanisms remain obscure. In this issue of the JCI, Jin et al. explored NO deficiency using human cell and mouse models that lacked argininosuccinate lyase (ASL), the enzyme involved in synthesizing arginine and NO production. Osteoblasts that did not express ASL produced less NO and failed to differentiate. Notably, in the context of Asl deficiency, heterozygous deletion of caveolin 1, which normally inhibits NO synthesis, restored NO production, osteoblast differentiation, glycolysis, and bone mass. These experiments suggest that ASL regulates arginine synthesis in osteoblasts, which leads to enhanced NO production and increased glucose metabolism. After a period when research slowed, these studies, like the legendary phoenix, renew the exploration of NO in bone biology, and provide exciting translational potential.

Cytokines and Bone: Osteoimmunology

Cytokines and hematopoietic growth factors have traditionally been thought of as regulators of the development and function of immune and blood cells. However, an ever-expanding number of these factors have been discovered to have major effects on bone cells and the development of the skeleton in health and disease (Table 1). In addition, several cytokines have been directly linked to the development of osteoporosis in both animal models and in patients. In order to understand the mechanisms regulating bone cells and how this may be dysregulated in disease states, it is necessary to appreciate the diverse effects that cytokines and inflammation have on osteoblasts, osteoclasts, and bone mass. This chapter provides a broad overview of this topic with extensive references so that, if desired, readers can access specific references to delve into individual topics in greater detail.

Cytochrome c oxidase dysfunction enhances phagocytic function and osteoclast formation in macrophages

The mitochondria-to-nucleus retrograde signaling (MtRS) pathway aids in cellular adaptation to stress. We earlier reported that the Ca2+- and calcineurin-dependent MtRS induces macrophage differentiation to bone-resorbing osteoclasts. However, mechanisms through which macrophages sense and respond to cellular stress remain unclear. Here, we induced mitochondrial stress in macrophages by knockdown (KD) of subunits IVi1 or Vb of cytochrome c oxidase (CcO). Whereas both IVi1 and Vb KD impair CcO activity, IVi1 KD cells produced higher levels of cellular and mitochondrial reactive oxygen species with increased glycolysis. Additionally, IVi1 KD induced the activation of MtRS factors NF-κB, NFAT2, and C/EBPδ as well as inflammatory cytokines, NOS 2, increased phagocytic activity, and a greater osteoclast differentiation potential at suboptimal RANK-L concentrations. The osteoclastogenesis in IVi1 KD cells was reversed fully with an IL-6 inhibitor LMT-28, whereas there was minimal rescue of the enhanced phagocytosis in these cells. In agreement with our findings in cultured macrophages, primary bone marrow-derived macrophages from MPV17-/- mice, a model for mitochondrial dysfunction, also showed higher propensity for osteoclast formation. This is the first report showing that CcO dysfunction affects inflammatory pathways, phagocytic function, and osteoclastogenesis.-Angireddy, R., Kazmi, H. R., Srinivasan, S., Sun, L., Iqbal, J., Fuchs, S. Y., Guha, M., Kijima, T., Yuen, T., Zaidi, M., Avadhani, N. G. Cytochrome c oxidase dysfunction enhances phagocytic function and osteoclast formation in macrophages.

Screening for potential genes associated with bone overgrowth after mid-shaft femur fracture in a rat model

Background

We investigated the underlying molecular mechanisms of bone overgrowth after femoral fracture by using high-throughput bioinformatics approaches.

Methods

The gene expression profile of GSE3298 (accession number) was obtained from the Gene Expression Omnibus database. Sixteen femoral growth plate samples, including nine samples without fracture and seven fracture samples for seven time points, were used for analysis. The Limma package was applied to identify differentially expressed genes (DEGs) between fractured and intact samples. The DAVID online tool was used for Gene ontology functional and pathway enrichment analysis. A protein-protein interaction (PPI) network established by String software was used to identify interactions between significant DEGs, and network modules were detected using plug-in MCODE. Additionally, a transcription regulatory network was constructed based on the ENCODE Project and PPI network.

Results

A total of 680 DEGs were screened in fractured femoral growth plate samples compared with controls, including 238 up- and 442 down-regulated genes. These DEGs were significantly involved in the calcium signaling pathway and cancer pathway. A PPI network was constructed with 167 nodes and 233 edges, and module analysis demonstrated that CCL2, CSF2, NOS2, and DLC1 may stimulate bone overgrowth after femoral fracture via anti-apoptosis-related functions. A transcription regulatory network was constructed with 387 interacting pairs, and overlapping nodes were significantly enriched in intracellular signaling cascade and regulation of cell proliferation, among others.

Conclusions

Bone overgrowth was associated with changes in the expression of identified DEGs such as CCL2, NOS2, CSF2, and DLC1 in the femoral head. They may be important in regulating bone overgrowth via the anti-apoptosis of osteoblasts.

Electronic supplementary material

The online version of this article (doi:10.1186/s13018-017-0510-6) contains supplementary material, which is available to authorized users.

Osteoimmunology in orthodontic tooth movement

The skeletal and immune systems share a multitude of regulatory molecules, including cytokines, receptors, signaling molecules, and signaling transducers, thereby mutually influencing each other. In recent years, several novel insights have been attained that have enhanced our current understanding of the detailed mechanisms of osteoimmunology. In orthodontic tooth movement, immune responses mediated by periodontal tissue under mechanical force induce the generation of inflammatory responses with consequent alveolar bone resorption, and many regulators are involved in this process. In this review, we take a closer look at the cellular/molecular mechanisms and signaling involved in osteoimmunology and at relevant research progress in the context of the field of orthodontic tooth movement.

Osteoimmunology and the influence of pro-inflammatory cytokines on osteoclasts

Bone and immune system are functionally interconnected. Immune and bone cells derive from same progenitors in the bone marrow, they share a common microenvironment and are being influenced by similar mediators. The evidence on increased bone resorption associated with inappropriate activation of T cells such as during inflammation, is well established. However, the molecular mechanisms beyond this clinical observation have begun to be intensively studied with the advancement of osteoimmunology. Now days, we have firm evidence on the influence of numerous proinflammatory cytokines on bone cells, with the majority of data focused on osteoclasts, the bone resorbing cells. It has been shown that some proinflammatory cytokines could possess osteoclastogenic and/or anti-osteoclastogenic properties and can target osteoclasts directly or via receptor activator of nuclear factor κB (RANK)/RANK ligand(RANKL)/osteoprotegerin (OPG) system. Several studies have reported opposing data regarding (anti)osteoclastogenic properties of these cytokines.

Therefore, the first part of this review is summarizing current evidence on the influence of pro-inflammatory cytokines on osteoclasts and thus on bone resorption. In the second part, the evidence on the role of pro-inflammatory cytokines in osteoporosis and osteoarthritis is reviewed to show that unravelling the mechanisms beyond such complex bone diseases, is almost impossible without considering skeletal and immune systems as an indivisible integrated system.

Anti-inflammatory effect of ethyl acetate extract from Cissus quadrangularis Linn may be involved with induction of heme oxygenase-1 and suppression of NF-κB activation

AIM OF THE STUDY

Cissus quadrangularis (family: Vitaceae) has been widely used in traditional herbal medicine for the treatment of hemorrhoids, gastric ulcers and bone healing. In the present study, we determined the anti-inflammatory activity and the molecular mechanism of the ethyl acetate extract of Cissus quadrangularis stem (CQE) in LPS-stimulated RAW 264.7 macrophage cells.

MATERIALS AND METHODS

The inhibitory effect of CQE on LPS-induced nitric oxide (NO) production was evaluated in conditioned media. Cell viability was monitored by MTT assay. Protein and mRNA expressions were determined by RT-PCR and Western blotting analysis, respectively.

RESULTS

CQE potently inhibited lipopolysaccharide (LPS)-induced nitric oxide (NO) production in RAW 264.7 macrophage cells in a dose-dependent manner. The mRNA and protein expressions of inducible nitric oxide synthase (iNOS) were suppressed also by CQE as was p65 NF-κB nuclear translocation. Further study demonstrated that CQE by itself induced heme oxygenase-1 (HO-1) gene expression at the protein and mRNA levels in dose- and time-dependent manner. In addition, the inhibitory effects of CQE on NO production were abrogated by a HO-1 inhibitor, zinc protoporphyrin IX (ZnPP).

CONCLUSIONS

Collectively, these results suggest that CQE exerts an anti-inflammatory effect in macrophages, at least in part, through the induction of HO-1 expression. These findings provide the scientific rationale for anti-inflammatory therapeutic use of Cissus quadrangularis stem.

Osteoimmunology: cytokines and the skeletal system

It has become clear that complex interactions underlie the relationship between the skeletal and immune systems. This is particularly true for the development of immune cells in the bone marrow as well as the functions of bone cells in skeletal homeostasis and pathologies. Because these two disciplines developed independently, investigators with an interest in either often do not fully appreciate the influence of the other system on the functions of the tissue that they are studying. With these issues in mind, this review will focus on several key areas that are mediated by crosstalk between the bone and immune systems. A more complete appreciation of the interactions between immune and bone cells should lead to better therapeutic strategies for diseases that affect either or both systems.

Osteoimmunology: interactions of the bone and immune system

Bone and the immune system are both complex tissues that respectively regulate the skeleton and the body's response to invading pathogens. It has now become clear that these organ systems often interact in their function. This is particularly true for the development of immune cells in the bone marrow and for the function of bone cells in health and disease. Because these two disciplines developed independently, investigators in each don't always fully appreciate the significance that the other system has on the function of the tissue they are studying. This review is meant to provide a broad overview of the many ways that bone and immune cells interact so that a better understanding of the role that each plays in the development and function of the other can develop. It is hoped that an appreciation of the interactions of these two organ systems will lead to better therapeutics for diseases that affect either or both.

Necessity of inositol (1,4,5)-trisphosphate receptor 1 and mu-calpain in NO-induced osteoclast motility

In skeletal remodeling, osteoclasts degrade bone, detach and move to new locations. Mechanical stretch and estrogen regulate osteoclast motility via nitric oxide (NO). We have found previously that NO stimulates guanylyl cyclase, activating the cGMP-dependent protein kinase 1 (PKG1), reversibly terminating osteoclast matrix degradation and attachment, and initiating motility. The PKG1 substrate vasodilator-stimulated protein (VASP), a membrane-attachment-related protein found in complexes with the integrin alphavbeta3 in adherent osteoclasts, was also required for motility. Here, we studied downstream mechanisms by which the NO-dependent pathway mediates osteoclast relocation. We found that NO-stimulated motility is dependent on activation of the Ca(2+)-activated proteinase mu-calpain. RNA interference (RNAi) showed that NO-dependent activation of mu-calpain also requires PKG1 and VASP. Inhibition of Src kinases, which are involved in the regulation of adhesion complexes, also abolished NO-stimulated calpain activity. Pharmacological inhibition and RNAi showed that calpain activation in this process is mediated by the inositol (1,4,5)-trisphosphate receptor 1 [Ins(1,4,5)P(3)R1] Ca(2+) channel. We conclude that NO-induced motility in osteoclasts requires regulated Ca(2+) release, which activates mu-calpain. This occurs via the Ins(1,4,5)P(3)R1.

Single-cell analysis divides bovine monocyte-derived dendritic cells into subsets expressing either high or low levels of inducible nitric oxide synthase

Dendritic cells (DC) are important cells at the interface between innate and adaptive immunity. DC have a key role in antigen processing and presentation to T cells. Effector functions of DC related to innate immunity have not been explored extensively. We show that bovine monocyte-derived DC (mDC) express inducible nitric oxide synthase (iNOS) mRNA and protein and produce NO upon triggering with interferon-gamma (IFN-gamma) and heat-killed Listeria monocytogenes (HKLM). An immunocytochemical analysis revealed that a sizeable subset (20-60%) copiously expresses iNOS (iNOShi) upon IFN-gamma/HKLM triggering, whereas the other subset expressed low levels of iNOS (iNOSlo). Monocyte-derived macrophages (mMphi) are more homogeneous with regard to iNOS expression. The number of cells within the iNOSlo mDC subset is considerably larger than the number of dead cells or cells unresponsive to IFN-gamma/HKLM. The large majority of cells translocated p65 to the nucleus upon triggering by IFN-gamma/HKLM. A contamination of mDC with iNOS-expressing mMphi was excluded as follows. (i) Cell surface marker analysis suggested that mDC were relatively homogeneous, and no evidence for a contaminating subset expressing macrophage markers (e.g. high levels of CD14) was obtained. (ii) iNOS expression was stronger in iNOShi mDC than in mMphi. The use of maturation-promoting stimuli revealed only subtle phenotypic differences between immature and mature DC in cattle. Nevertheless, these stimuli promoted development of considerably fewer iNOShi mDC upon triggering with IFN-gamma/HKLM. Immunocytochemical results showed that although a significant proportion of cells expressed iNOS only or TNF only upon triggering with IFN-gamma/HKLM, a significant number of cells expressed both iNOS and TNF, suggesting that TNF and iNOS producing (TIP) DC are present within bovine mDC populations obtained in vitro.

RANKL stimulates inducible nitric-oxide synthase expression and nitric oxide production in developing osteoclasts. An autocrine negative feedback mechanism triggered by RANKL-induced interferon-beta via NF-kappaB that restrains osteoclastogenesis and bone resorption

Nitric oxide (NO) is a multifunctional signaling molecule and a key vasculoprotective and potential osteoprotective factor. NO regulates normal bone remodeling and pathological bone loss in part through affecting the recruitment, formation, and activity of bone-resorbing osteoclasts. Using murine RAW 264.7 and primary bone marrow cells or osteoclasts formed from them by receptor activator of NF-kappaB ligand (RANKL) differentiation, we found that inducible nitric-oxide synthase (iNOS) expression and NO generation were stimulated by interferon (IFN)-gamma or lipopolysaccharide, but not by interleukin-1 or tumor necrosis factor-alpha. Surprisingly, iNOS expression and NO release were also triggered by RANKL. This response was time- and dose-dependent, required NF-kappaB activation and new protein synthesis, and was specifically blocked by the RANKL decoy receptor osteoprotegerin. Preventing RANKL-induced NO (via iNOS-selective inhibition or use of marrow cells from iNOS-/- mice) increased osteoclast formation and bone pit resorption, indicating that such NO normally restrains RANKL-mediated osteoclastogenesis. Additional studies suggested that RANKL-induced NO inhibition of osteoclast formation does not occur via NO activation of a cGMP pathway. Because IFN-beta is also a RANKL-induced autocrine negative feedback inhibitor that limits osteoclastogenesis, we investigated whether IFN-beta is involved in this novel RANKL/iNOS/NO autoregulatory pathway. IFN-beta was induced by RANKL and stimulated iNOS expression and NO release, and a neutralizing antibody to IFN-beta inhibited iNOS/NO elevation in response to RANKL, thereby enhancing osteoclast formation. Thus, RANKL-induced IFN-beta triggers iNOS/NO as an important negative feedback signal during osteoclastogenesis. Specifically targeting this novel autoregulatory pathway may provide new therapeutic approaches to combat various osteolytic bone diseases.

Autocrine and paracrine nitric oxide regulate attachment of human osteoclasts

Nitric oxide (NO) can reduce bone loss in chronic bone diseases. NO inhibits or kills osteoclasts, but the mechanism of action of NO in human bone turnover is not clear. To address this, we studied effects of NO on attachment and motility of human osteoclasts on mineralized and tissue culture substrates under defined conditions. Osteoclasts were differentiated in vitro from CD14 selected monocytes in RANKL and CSF-1, and characterized by cathepsin K expression, tartrate-resistant acid phosphatase (TRAP) activity, acid secretion, and lacunar resorption. Cell attachment was labeled with monoclonal antibody 23C6, specific for a binding domain of a key osteoclast attachment protein, the CD51/CD61 integrin dimer (alpha(v)beta(3)), with or without cell permeabilization. A ring of integrin attachment during bone degradation delimits an extracellular acid compartment, while alpha(v)beta(3) forms focal attachments on non-resorbable substrates. On resorbable substrate but not non-resorbable substrate, alpha(v)beta(3) labeling required cell permeabilization, in keeping with the membrane-matrix apposition that excludes large molecules and allows extracellular acidification. Acid secretion was labeled with the fluorescent weak base indicator lysotracker. NO donors, S-nitroso-N-acetyl penicillamine (SNAP) or sodium nitroprusside (SNP), downmodulated acid secretion simultaneously with cytoskeletal rearrangement, with alpha(v)beta(3) redistributed to a discontinuous pattern that labeled, on bone substrate, without membrane permeabilization. These effects were reversible, and an inhibitor of NO synthesis, N(G)-monomethyl-L-arginine (l-NMMA), increased acid secretion and decreased heterogeneity of attachment structures, showing that NO is an autocrine regulator of attachment. A hydrolysis-resistant activating cGMP analog 8-(4-chlorophenylthio)guanosine-3',5'-cyclic monophosphate replicated effects of NO donors, while an inhibiting analog, 8-(4-chlorophenylthio)guanosine-3',5'-cyclic monophosphorothioate, Rp-isomer, opposed them. On tissue culture or mineralized substrates, NO or cGMP analogs directly regulated motility; after washout cells reattached and survived for days. We conclude that NO is produced by human osteoclasts and regulates acid secretion and cellular motility, in keeping with autocrine and paracrine NO regulation of the resorption cycle.

HIV-1 gp120 stimulates proinflammatory cytokine-mediated pain facilitation via activation of nitric oxide synthase-I (nNOS)

It has become clear that spinal cord glia (microglia and astrocytes) importantly contribute to the creation of exaggerated pain responses. One model used to study this is peri-spinal (intrathecal, i.t.) administration of gp120, an envelope protein of HIV-1 known to activate glia. Previous studies demonstrated that i.t. gp120 produces pain facilitation via the release of glial proinflammatory cytokines. The present series of studies tested whether spinal nitric oxide (NO) contributes to i.t. gp120-induced mechanical allodynia and, if so, what effect NO has on spinal proinflammatory cytokines. gp120 stimulation of acutely isolated lumbar dorsal spinal cords released NO as well as proinflammatory cytokines (tumor necrosis factor-alpha, interleukin-1beta (IL1), interleukin-6 (IL6)), thus identifying NO as a candidate mediator of gp120-induced behavioral effects. Behaviorally, identical effects were observed when gp120-induced mechanical allodynia was challenged by i.t. pre-treatment with either a broad-spectrum nitric oxide synthase (NOS) inhibitor (L-NAME) or 7-NINA, a selective inhibitor of NOS type-I (nNOS). Both abolished gp120-induced mechanical allodynia. While the literature pre-dominantly documents that proinflammatory cytokines stimulate the production of NO rather than the reverse, here we show that gp120-induced NO increases proinflammatory cytokine mRNA levels (RT-PCR) and both protein expression and protein release (serial ELISA). Furthermore, gp120 increases mRNA for IL1 converting enzyme and matrix metalloproteinase-9, enzymes responsible for activation and release of proinflammatory cytokines.

Study of host-pathogen interactions to identify sustainable vaccine strategies to Marek's disease

Marek's disease virus is a highly cell-associated, lymphotropic alpha-herpesvirus that causes paralysis and neoplastic disease in chickens. The disease has been contained by vaccination with attenuated viruses and provides the first evidence for a malignant cancer being controlled by an antiviral vaccine. Marek's disease pathogenesis is complex, involving cytolytic and latent infection of lymphoid cells and oncogenic transformation of CD4+ T cells in susceptible chickens. Innate and adaptive immune responses develop in response to infection, but infection of lymphocytes results in immunosuppressive effects. The remarkable ability of MDV to escape immune responses by interacting with, and down-regulating, some key aspects of the immune system will be discussed in the context of genetic resistance. Resistance conferred by vaccination and the implications of targeting replicative stages of the virus will also be examined.

Comparison of the response of primary human blood monocytes and the U937 human monocytic cell line to two different sizes of alumina ceramic particles

It is well recognized that wear particles derived from orthopaedic implants have the potential to induce inflammation, which may eventually lead to aseptic loosening of the artificial joint. We hypothesized that alumina ceramic particles of different sizes cause a differential cytokine response by human monocytes. To test this hypothesis a human monocytic cell line (U937) and primary human blood monocytes obtained from healthy volunteers were exposed to ceramic particles within the range known to be generated in vivo. Cellular responses were measured by quantifying the relative gene expression of 12 different cytokines using TAQman Real-Time Polymerase Chain Reaction (RT-PCR). Our results demonstrate that at a particle to cell ratio of 100:1, 0.5 microm ceramic particles consistently provoked higher amounts of Interleukin-1alpha (IL-1alpha), IL-1beta, IL-8, IL-10 and Tumor necrosis factor-alpha (TNF-alpha) steady state mRNA by U937 cells. As expected, the variability of cytokine expression in primary blood monocytes was much higher compared to the cell line however, a similar trend was observed. These results show a differential response to ceramic particle size, which may imply that 0.5 microm particles are less biocompatible. New ceramic implants can be designed to generate a known particle size range in vivo. Implant materials of this type may induce relatively lower levels of production of inflammatory cytokines resulting in a reduced incidence of failure due to aseptic loosening.

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

This experiment was undertaken to determine the role of macrophage-derived nitric oxide (NO) in mediating lipopolysaccharide (LPS)-induced bone resorption by using an in vitro co-culture system and an in vivo model of infectious bone resorption. Our results demonstrated that LPS stimulated the expression of inducible nitric oxide synthase (iNOS) and tumor necrosis factor (TNF)-a mRNAs and nitrite synthesis in the J774 mouse macrophage cell line but not in the UMR-106 (rat) and MC3T3-E1 (mouse) osteoblast cell lines. Conditioned media (CM) from LPS-stimulated J774 triggered only low to moderate levels of iNOS mRNAs in MC3T3-E1 and a trivial effect in UMR-106. On the other hand, CM induced matrix metalloproteinase-1 (MMP-1) gene expression in both osteoblast cell lines. The NOS inhibitor N(G)-monomethyl-L-arginine (L-NMMA) did not alter this effect in MC3T3-E1 and UMR-106, whereas TNF-a antibody diminished the CM-induced MMP-1 gene expression in both cell lines. Interestingly, SNAP, a NO donor, although by itself is not a MMP-1 stimulator for UMR-106, augmented the TNF-alpha-stimulated MMP-1 mRNA production in UMR-106. In a J774/UMR-106 co-culture system, LPS stimulated significant MMP-1 gene expression in UMR-106, and this upregulation was abolished by L-NMMA and TNF-alpha antibodies. Immunohistochemical analysis in a rat model of infectious bone resorption (periapical lesion) showed co-distributions of iNOS+ macrophages and MMP-1+ osteoblasts around the osteolytic areas. Administration of L-NMMA markedly reduced the extent of bone loss and the percentage of MMP-1-synthesizing osteoblasts. These data suggest that NO derived from macrophages after LPS stimulation may enhance bone loss by augmenting the cytokine-induced MMP-1 production in osteoblasts.

Apoptosis of rat gastric mucosa and of primary cultures of gastric epithelial cells by indomethacin: role of inducible nitric oxide synthase and interleukin-8

In order to gain insights into indomethacin-induced gastric injury, rats were fed with indomethacin (20 mg/kg), or alternatively, the primary cultures of rat gastric epithelial cells were cultured with different doses of indomethacin (1-1000 microM). Light microscopy, electron microscopy, fluorescence microscopy, TdT-mediated dUTP-biotin nick end labelling staining, ssDNA staining and DNA fragmentation assay were employed to evaluate the levels of gastric injury and apoptosis. Cells expressing inducible nitric oxide synthase (iNOS) and interleukin (IL)-8 were localized at the rat gastric mucosa by immunohistochemistry. Administration of indomethacin to rats caused apoptosis and injury of the gastric mucosal epithelial cells. Indomethacin also induced apoptosis of primary cultures of gastric epithelial cells in a dose-dependent manner. Cells expressing iNOS and IL-8 were detected at and around the sites of gastric injury in the indomethacin-fed rats, but not in the control rats. The induction of apoptosis by indomethacin in the primary cultures of gastric epithelial cells suggests that the direct apoptotic capacity of indomethacin. iNOS and IL-8 may be involved in this process.

Induction of nitric oxide synthase during Japanese encephalitis virus infection: evidence of protective role

The ability of Japanese encephalitis virus (JEV) and JEV-induced macrophage-derived factor (MDF) to modulate nitric oxide synthase (NOS) activity in brain and tumor necrosis factor-alpha (TNF-alpha) and the possible antiviral role of NOS during JEV infection were investigated. NOS activity and particularly that of the inducible form of NOS (iNOS) was significantly enhanced in JEV or JEV-induced MDF-treated mice. Following JEV infection, total NOS activity in brain was gradually increased from Day 3 and reached a peak on Day 6. MDF-induced NOS activity and iNOS activity were dose dependent and maximum activity was observed at 1 h after treatment. The response was sensitive to anti-MDF antibody treatment and N(G)-monomethyl-L-arginine (L-NMMA), an inhibitor of NOS. Pretreatment of JEV-infected mice with L-NMMA increased the mortality as evident from reduced mean survival time (MST, 11.8 days) compared to placebo treated JEV-infected mice (MST, 17 days). The enhanced level of TNF-alpha observed in the early phase of JEV infection correlated well with the enhanced activity of iNOS. These observations thus provide evidence of the protective role of iNOS during JEV infection and indicate that iNOS may be a key mediator in host innate immune response to infection.

Expression of cytokine genes in Marek's disease virus-infected chickens and chicken embryo fibroblast cultures

The role of cytokines in the pathogenesis and immunity of Marek's disease (MD), a herpesvirus-induced T-cell lymphoma in chickens, is poorly understood. Two different experiments were used to examine the potential role of particular cytokines in the pathogenesis and immune responses of MD. First, chicken embryo fibroblasts (CEF) were stimulated with lipopolysaccharide (LPS) and/or recombinant chicken interferon-gamma (rChIFN-gamma) and used to develop techniques for examining transcription of IFN-alpha, IFN-gamma, inducible nitric oxide synthase (iNOS), interleukin (IL)-1beta, IL-2, IL-6 and IL-8 by reverse transcription-polymerase chain reaction (RT-PCR). Addition of LPS and/or rChIFN-gamma resulted in the up-regulation of mRNA for iNOS, IL-1beta and IL-6, while IFN-gamma was up-regulated by LPS alone. IL-2 was down-regulated by the treatments. Second, to determine the effects of Marek's disease herpesvirus (MDV) infection on cytokine transcription in vivo, chickens were infected with MDV at 21 days of age and examined at 7 days post-infection (p.i.) (exp. 1) or were infected with MDV at 1 day of age and examined from 3 to 15 days p.i. (exp. 2). In MDV-infected chickens, IFN-gamma transcription was up-regulated as early as 3 days p.i. until the termination of the experiment at 15 days p.i., while iNOS and IL-1beta were up-regulated between 6 and 15 days p.i. Infection of 1-day-old chicks increased levels of mRNA for IFN-gamma and iNOS between 16- and 64-fold at 9 days p.i. These results suggest that IFN-gamma and iNOS may play an important role in the pathogenesis of MD.

Antiviral effect of nitric oxide during Japanese encephalitis virus infection

The ability of Japanese encephalitis virus (JEV) and JEV-induced macrophage derived neutrophil chemotactic factor (MDF) to produce nitric oxide (NO), and the possible antiviral effect of NO during JEV infection, was investigated. Splenic macrophages of JEV infected mice produced maximum NO in vivo at day 7 post infection, and in vitro at 24 h after JEV stimulation. MDF-induced NO production was dose dependent and maximal at 60 min after MDF treatment. The response was sensitive to anti-MDF antibody treatment and the nitric oxide synthase inhibitor NG-monomethyl-L-arginine (L-NMMA). Pretreatment of mice with L-NMMA increased the mortality to 100% in JEV infected mice in vivo and inhibited NO production in vitro, while MDF stimulated macrophages inhibited virus replication with high levels of NO production. MDF treatment increased the survival rate of JEV infected mice. The findings thus demonstrate that MDF induces production of NO during JEV infection, which has an antiviral effect. This may be one of the important mechanisms of natural immunity in controlling the initial stages of JEV infection.

Decreased nitric oxide levels stimulate osteoclastogenesis and bone resorption both in vitro and in vivo on the chick chorioallantoic membrane in association with neoangiogenesis

High nitric oxide (NO) levels inhibit osteoclast (OC)-mediated bone resorption in vivo and in vitro, and nitrate donors protect against estrogen-deficient bone loss in postmenopausal women. Conversely, decreased NO production potentiates OC bone resorption in vitro and is associated with in vivo bone loss in rats and humans. Previously, we reported that bone sections from rats administered aminoguanidine (AG), a selective inhibitor of NO production via inducible NO synthase, exhibited both increased OC resorptive activity as well as greater numbers of OC. Here, we investigated further whether AG promoted osteoclastogenesis, in addition to stimulating mature OC function, using a modified in vivo chick chorioallantoic membrane (CAM) system and an in vitro chick bone marrow OC-like cell developmental model. AG, focally administered in small agarose plugs placed directly adjacent to a bone chip implanted on the CAM, dose-dependently elicited neoangiogenesis while stimulating the number, size, and bone pit resorptive activity of individual OC ectopically formed in vivo. In addition to enhancing OC precursor recruitment via neoangiogenesis, AG also exerted other vascular-independent effects on osteoclastogenesis. Thus, AG promoted the in vitro fusion and formation from bone marrow precursor cells of larger OC-like cells that contained more nuclei per cell and exhibited multiple OC differentiation markers. AG stimulated development was inversely correlated with declining medium nitrite levels. In contrast, three different NO donors each dose-dependently inhibited in vitro OC-like cell development while raising medium nitrite levels. Therefore, NO sensitively regulates OC-mediated bone resorption through affecting OC recruitment (angiogenesis), formation (fusion and differentiation), and bone resorptive activity in vitro and in vivo. Possibly, the stimulation of neoangiogenesis and OC-mediated bone remodeling via AG or other pro-angiogenic agents may find clinical applications in reconstructive surgery, fracture repair, or the treatment of avascular necrosis.

Essential role of nitric oxide and interferon-gamma for tumor immunotherapy with interleukin-10

Several laboratories have reported anti-tumor activity for high levels of interleukin-10 (IL-10) expressed as a transgene or administered as recombinant protein. The authors have reported a positive correlation for nitric oxide production and anti-tumor activity of IL-10 in a murine model of breast cancer. In the current study, they sought evidence of a mechanistic role for nitric oxide in IL-10-mediated tumor growth inhibition. They wanted to determine whether pharmacologic inhibition of nitric oxide synthase (NOS) activity reverses the therapeutic effect of IL-10. Administration of either of two NOS inhibitors, aminoguanidine (AG) or L-lysine,N6-1-iminoethyl-dihydrochloride, appears to abrogate in part the tumor growth inhibition observed when IL-10 is overexpressed as a transgene in two murine mammary tumor cell lines. Nitric oxide levels were assessed at the tumor site by measuring nitrosylated heme levels by electron spin resonance spectroscopy. Nitric oxide hemoglobin levels were lower in tumors from aminoguanidine-treated mice, indicating that effective inhibition of nitric oxide production occurred at the tumor site. Previous investigations showed that the inducible form of NOS protein (iNOS), but not constitutive NOS, was expressed at higher levels in IL-10-expressing tumors. Because iNOS is regulated at the transcriptional level, the authors compared iNOS mRNA levels in IL-10 and control tumors. Northern analysis revealed strong iNOS message expression in all six IL-10-expressing tumors examined, whereas message was faintly detected in parental or 66-neo tumors. The inducible form of NOS is responsive to induction by interferon-gamma (IFN-gamma). The role of IFN-gamma in IL-10-mediated tumor inhibition and iNOS mRNA induction was determined. When tumors were transplanted to IFN-gamma mutant mice, the tumor-inhibitory activity of IL-10 was lost. Furthermore, iNOS mRNA was no longer induced in the absence of host expression of IFN-gamma. These data indicate that nitric oxide contributes to the anti-tumor activity of IL-10 and that expression of iNOS in this context depends on IFN-gamma.

Paradoxical priming effects of IL-10 on cytokine production

IL-10 is a well-known immunosuppressive and/or anti-inflammatory cytokine. However, we report in vitro experimental studies in which IL-10 primed leukocytes and led to an enhanced production of tumor necrosis factor (TNF) upon further stimulation by lipopolysaccharide (LPS). Monocytes and peripheral blood mononuclear cells (PBMC) prepared from whole blood maintained for 20 h at 37 degrees C in the presence of recombinant human IL-10 had an enhanced capacity to produce TNF in response to LPS. In addition to TNF, LPS-induced IL-6 and spontaneous IL-1ra production were also enhanced. When isolated PBMC were first cultured for 20 h in the presence of IL-10 on Teflon to prevent adherence, washed to remove IL-10 and then further cultured in plastic dishes for an additional 20 h in the presence of LPS or IL-1beta, an enhanced release of TNF was observed. This was not the case when PBMC were pre-cultured in plastic multidishes in the presence of IL-10. TNF mRNA expression induced by LPS was decreased when the pre-treatment of PBMC with IL-10 was performed on plastic, whereas this was not the case when cells were pre-cultured with IL-10 on Teflon. Furthermore, NFkappaB translocation following LPS activation was higher after IL-10 pre-treatment on Teflon than on plastic. Interestingly, an enhanced frequency of CD16 and CD68(+) cells among the CD14(+) cells was observed in the presence of IL-10, independently of the pre-culture conditions of the PBMC. Altogether, these results indicate that the IL-10-induced up-regulation of cytokine production depends on the prevention of monocyte adherence by red cells in the whole blood assays or by cultures of PBMC on Teflon. In contrast, the adherence parameter has no effect on the IL-10-induced modulation of some monocyte surface markers.

Nuclear and cytosolic calcium changes in osteoclasts stimulated with ATP and integrin-binding peptide

Cytosolic calcium modulates the activity of osteoclasts, large multinucleate cells that resorb bone. Nuclear events, such as gene transcription, are also calcium-regulated in these cells, and fluorescence imaging has suggested that calcium signals produced by some stimuli are specifically targeted to, or amplified within, osteoclast nuclei. We used two alternative techniques of dye loading to examine the changes of intracellular calcium induced in rat osteoclasts by three stimuli. Osteoclasts loaded with the calcium indicator Fura-2 by the acetoxymethyl (AM) ester technique appeared to display marked nuclear calcium amplification. During stimulation with integrin-binding peptides, ATP, or high extracellular calcium, fluorescence ratios recorded from the nuclei rose higher than did ratios recorded from extranuclear regions. In contrast, nuclear calcium amplification was not observed after AM loading in the presence of the anion transport inhibitor sulfinpyrazone, nor in osteoclasts injected with Fura-2 conjugated to a high MW dextran. In these cells, nuclear fluorescence ratios were equal to the extranuclear values at all times: upon stimulation by an agonist, the nuclear and cytosolic calcium concentrations increased by the same amount. The calcium changes seen in stimulated osteoclasts can no longer be taken as evidence for the general validity of the phenomenon of nuclear calcium amplification.

Interleukin-10 gene transfer inhibits murine mammary tumors and elevates nitric oxide

Transfection of cDNA for IL-10 into line 66.1 murine mammary tumor cells results in marked suppression of tumor growth and metastasis. Others have reported that nitric oxide has potent antitumor activity and IL-10 is known to regulate the inducible isoform of nitric oxide synthase (iNOS) expressed in macrophages. We identified nitric oxide production in mammary tumors as indicated by electron paramagnetic resonance detection of nitric oxide-hemoglobin (NO-Hb). IL-10 expression resulted in elevated levels of NO-Hb in mammary tumors. Immunohistochemical examination of mammary tumors for iNOS protein revealed few positively staining cells in parental or control neo-transfected tumors but strong iNOS staining in all IL-10 transfected tumors, consistent with the NO-Hb data. To determine if mammary epithelial tumor cells themselves, express nitric oxide synthase activity, cultured tumor cells were treated with pro-inflammatory cytokines and nitrite accumulation was assessed in the conditioned medium. All IL-10 producing cell lines accumulated uM concentrations of nitrite in response to short term (24 hr) cytokine stimulation. Cells not expressing IL-10 (parental and neo-transfectants) accumulated no nitrite under similar culture conditions. After longer stimulation (48 hr), parental and 66-neo cells accumulated lower amounts of nitrite. IL-10 gene transfer is associated with increased iNOS protein expression and enzymatic activity detected both in vitro and in vivo. Our findings suggest that the antimetastatic and antitumor activity of IL-10 is related to enhanced production of nitric oxide.

Molecular cloning and expression of inducible nitric oxide synthase in chick embryonic ventricular myocytes

OBJECTIVE

Inducible nitric oxide synthase (iNOS) has been implicated to contribute to myocardial dysfunction in various settings, but considerable species differences have been noted in the levels of iNOS expression and its function in several tissues. The aim of this study was to elucidate evolutional changes in myocardial iNOS expression and function.

METHODS

An iNOS cDNA clone was isolated by RT-PCR from the 10-day old cultured chick embryonic ventricular myocytes stimulated with 10 micrograms/ml of lipopolysaccharide. Expression of the iNOS mRNA was analyzed with Northern blot analysis and RNase protection assay. The iNOS activity was estimated from conversion rates of L-arginine to L-citrulline and intracellular cGMP contents were measured with radioimmunoassay. Furthermore, both [Ca2+]i (fluorescent dye indo-1) and cell contraction (video motion detector) were simultaneously recorded.

RESULTS

Aside from the primer sequences, the insert (1026 bp) of the cDNA clone showed 66.4% identity at the deduced amino acid level to the human iNOS cDNAs. Northern blot analysis revealed that chicken iNOS mRNA of approximately 4.5 kb was induced by lipopolysaccharide within 6 h in the cultured myocytes. RNase protection assay also showed that lipopolysaccharide provoked 14.6 +/- 5.1-fold increases (n = 6, p < 0.05) in the iNOS mRNA signals within 6 h. The iNOS activity (+300%, P < 0.05) as well as the intracellular cGMP contents (+75%, P < 0.01) were significantly augmented in the lipopolysaccharide-stimulated cells. Both the cell contraction and [Ca2+]i were significantly reduced after the administration of a large amount (10 mM) of L-arginine in the myocytes pretreated with both lipopolysaccharide and NG-monomethyl-L-arginine (100 microM).

CONCLUSION

As like as the nucleotide and amino acid sequences, the myocardial effects of the iNOS may also be evolutionary conserved.

Protective effects of mercaptoethylguanidine, a selective inhibitor of inducible nitric oxide synthase, in ligature-induced periodontitis in the rat

1. Excessive production of nitric oxide (NO), and the generation of peroxynitrite have been implicated in various proinflammatory conditions. In the present study, using mercaptoethylguanidine (MEG), a selective inhibitor of iNOS and a peroxynitrite scavenger, we investigated the role of iNOS and peroxynitrite in a rat model of periodontitis. 2. Periodontitis was produced in rat by a ligature of 2/0 braided silk placed around the cervix of the lower left 1st molar. Animals were then divided into two groups: one group of rats was treated with MEG (30 mg kg(-1), i.p., 4 times per day for 8 days), animals in the other group received vehicle. At day 8, the gingivomucosal tissue encircling the mandibular 1st molars was removed on both sides from ligated and sham operated animals for inducible nitric oxide synthase (iNOS) activity assay and for immunocytochemistry with anti-iNOS serum. Plasma extravasation was measured with the Evans blue technique. Alveolar bone loss was measured with a videomicroscopy. 3. Ligation caused a significant, more than 3 fold increase in the gingival iNOS activity, whereas it did not affect iNOS activity on the contralateral side, when compared to sham-operated animals. Immunohistochemical analysis revealed iNOS-positive macrophages, lymphocytes and PMNs in the connective tissue and immunoreactive layers of epithelium on side of the ligature, and only a few iNOS reactive connective tissue cells on the contralateral side [corrected]. Ligation significantly increased Evans blue extravasation in gingivomucosal tissue and alveolar bone destruction compared to the contralateral side. MEG treatment significantly reduced the plasma extravasation and bone destruction. 4. The present results demonstrated that ligature-induced periodontitis increases local NO production and that MEG treatment protects against the associated extravasation and bone destruction. Based on the present data, we propose that enhanced formation of NO and peroxynitrite plays a significant role in the pathogenesis of periodontitis.

Role of nitric oxide in the physiopathology of pain

Many painful disorders, including joint dysfunctions such as rheumatoid arthritis (RA) or temporomandibular joint disorders (TMD), are associated with hyperthermia of the overlying skin. The same is true of certain intractable chronic pain conditions, such as chronic orofacial pain, which may be associated with TMD. We suggest that this skin hyperthermia, caused by regional vasodilation, is induced by extravascular nitric oxide (NO). Extravascular NO can be produced in the affected joint by osteoblasts, chondrocytes, and macrophages, by mechanical stimulation of endothelial cells, or by stimulated neurons. In view of a strong correlation between pain and skin hyperthermia in these disorders, and the evidence that NO enhances the sensitivity of peripheral nociceptors, we also suggest that at least this kind of pain is associated with excessive local level of NO. This hypothesis can be verified by dynamic area telethermometry, assessing the effect of NO on the sympathetic nervous function. This mechanism, which is in line with the general role of NO as a mediator between different organ systems, also may be relevant to any pain associated with enhanced immune response. Clinical implications of the proposed mechanism are discussed.

Ca2+ or phorbol ester but not inflammatory stimuli elevate inducible nitric oxide synthase messenger ribonucleic acid and nitric oxide (NO) release in avian osteoclasts: autocrine NO mediates Ca2+-inhibited bone resorption

Osteoclast bone resorption is essential for normal calcium homeostasis and is therefore tightly controlled by calciotropic hormones and local modulatory cytokines and factors. Among these is nitric oxide (NO), a multifunctional free radical that potently inhibits osteoclast bone resorption in vitro and in vivo. Previous findings led us to propose that NO might serve as an autocrine, as well as paracrine, regulator of osteoclast function. This premise was investigated using isolated bone-resorptive avian osteoclasts and focusing on the inducible isoform of NO synthase (iNOS) responsible for inflammatory stimulated high-level NO synthesis in other cells. Avian osteoclasts expressed both iNOS messenger RNA (mRNA) and protein. However, inflammatory cytokines that induce iNOS mRNA, protein, and NO in other cells did not do so in avian osteoclasts, consistent with the known role of inflammatory stimuli in promoting osteoclast resorption and localized bone loss. In searching for potential modulators of osteoclast iNOS, protein kinase C activation [by phorbol 12-myristate 13-acetate (PMA)] and intracellular Ca2+ rises (A23187) were each found to elevate osteoclast iNOS mRNA and protein levels, while increasing NO release and reducing osteoclast bone resorption. The iNOS selective inhibitor aminoguanidine suppressed stimulated osteoclast NO production elicited by either signal, but reversed only the resorption inhibition due to raised Ca2+. Thus, whereas additional inhibitory signals are presumably coproduced in osteoclasts treated with PMA, osteoclast iNOS-derived NO may act as an autocrine signal to mediate Ca2+-inhibited bone resorption. These findings document for the first time an iNOS whose mRNA levels are regulated by Ca2+ or PMA, but not inflammatory stimuli, and the autocrine production of NO as a Ca2+ sensing signal to suppress osteoclast bone resorption. The unusual regulation of osteoclast iNOS makes it a potentially attractive target for designing novel therapeutic agents to alleviate excessive bone loss.

Nitric oxide acts in conjunction with proinflammatory cytokines to promote cell death in osteoblasts

Proinflammatory cytokines such as tumor necrosis factor-alpha (TNF-alpha), interferon-gamma (IFN-gamma), and interleukin-1 beta are known modulators of bone remodeling in vitro and in vivo. The same cytokines induce the production of nitric oxide (NO) in various cell types, including osteoblasts and osteoclasts, and NO has recently been implicated in the regulation of bone resorption. We investigated the relationship between NO levels and cell viability in MC3T3-E1, a well-characterized osteoblastic cell line. NO donors at high concentrations (> or = 0.5 mM) produce a significant cytotoxic effect over a 48 h period. Various combinations of the three cytokines strongly promote endogenous NO production, and high NO levels are correlated with the loss of cell viability. Although TNF-alpha produces NO-independent cytotoxicity, NO greatly enhances this cytotoxic effect. Human and mouse TNF-alpha differ in their cytotoxic effects, and human TNF-alpha induces lower levels of NO production. In cocultures of RAW 264.7 mouse macrophages stimulated with lipopolysaccharide and IFN-gamma, and untreated MC3T3-E1 osteoblasts, addition of anti-TNF-alpha antibody and inhibition of NO synthesis have additive, protective effects on osteoblast viability. NO cytotoxicity involves an apoptotic mechanism. Our results underline the importance of NO and TNF-alpha as cytotoxic mediators in the osseous microenvironment and might explain the observed deficiency of bone formation in inflammatory sites.