Nitric oxide at a low concentration protects murine macrophage RAW264 cells against nitric oxide-induced death via cGMP signaling pathway

Evaluation of Antibacterial, Antibiofilm, Antioxidant, and Anti-Inflammatory Activities of Kratom Leaves (Mitragyna speciosa) Fermentation Supernatant Containing Lactobacillus rhamnosus GG

Kratom (Mitragyna speciosa) leaves are commonly used to enhance endurance and treat various diseases. This study evaluated the effect of kratom leaf fermentation with Lactobacillus rhamnosus. Antibacterial activity was investigated against Staphylococcus aureus, methicillin-resistant S. aureus (MRSA), Escherichia coli, and E. coli O157:H7. Biofilm inhibition and eradication assays were also performed. Antioxidant properties were determined by measuring the total phenolic and flavonoid content and DPPH and ABTS scavenging activities. Nitric oxide and TNF-α, IL-1β, and IL-6 expressions in LPS-stimulated RAW 264.7 macrophage cells were also measured. Aqueous kratom extract exhibited promising effects against free radicals and pro-inflammatory cytokines. Notably, all fermented kratoms showed significant antibacterial activity against the tested pathogens and antibiofilm formation by S. aureus and MRSA. Furthermore, the eradication of established biofilms of fermented kratoms was observed in S. aureus (day 2, 50 mg/mL) and E. coli (day 2, 100 mg/mL and day 4, 50 mg/mL). To the best of our knowledge, this study is the first to report that fermented and non-fermented kratoms could be nutraceutical sources of antibacterial, antibiofilm, antioxidant, and anti-inflammatory substances against related diseases and can be applied further in dietary or cosmetic products with health-promoting effects.

Effects of the immune system on muscle regeneration

Muscle regeneration is a complex process orchestrated by multiple steps. Recent findings indicate that inflammatory responses could play central roles in bridging initial muscle injury responses and timely muscle injury reparation. The various types of immune cells and cytokines have crucial roles in muscle regeneration process. In this review, we provide an overview of the functions of acute inflammation in muscle regeneration.

Epigenetic integration of signaling from the regenerative environment

Skeletal muscle has an extraordinary capacity to regenerate itself after injury due to the presence of tissue-resident muscle stem cells. While these muscle stem cells are the primary contributor to the regenerated myofibers, the process occurs in a regenerative microenvironment where multiple different cell types act in a coordinated manner to clear the damaged myofibers and restore tissue homeostasis. In this regenerative environment, immune cells play a well-characterized role in initiating repair by establishing an inflammatory state that permits the removal of dead cells and necrotic muscle tissue at the injury site. More recently, it has come to be appreciated that the immune cells also play a crucial role in communicating with the stem cells within the regenerative environment to help coordinate the timing of repair events through the secretion of cytokines, chemokines, and growth factors. Evidence also suggests that stem cells can help modulate the extent of the inflammatory response by signaling to the immune cells, demonstrating a cross-talk between the different cells in the regenerative environment. Here, we review the current knowledge on the innate immune response to sterile muscle injury and provide insight into the epigenetic mechanisms used by the cells in the regenerative niche to integrate the cellular cross-talk required for efficient muscle repair.

The dominant-negative mitochondrial calcium uniporter subunit MCUb drives macrophage polarization during skeletal muscle regeneration

[Figure: see text].

The Role of Innate and Adaptive Immune Cells in Skeletal Muscle Regeneration

Skeletal muscle regeneration is highly dependent on the inflammatory response. A wide variety of innate and adaptive immune cells orchestrate the complex process of muscle repair. This review provides information about the various types of immune cells and biomolecules that have been shown to mediate muscle regeneration following injury and degenerative diseases. Recently developed cell and drug-based immunomodulatory strategies are highlighted. An improved understanding of the immune response to injured and diseased skeletal muscle will be essential for the development of therapeutic strategies.

Large magnitude of force leads to NO-mediated cell shrinkage in single osteocytes implying an initial apoptotic response

Damage accumulation in the bone under continuous daily loading causes local mechanical overloading known to induce osteocyte apoptosis, which promotes bone resorption to repair bone damage. However, only a few studies have investigated the mechanism of apoptosis in mechanically overloaded osteocytes. As mechanically stimulated osteocytes produce nitric oxide (NO), which triggers apoptosis in various cell types, we aimed to elucidate the mechanism underlying apoptosis in mechanically overloaded osteocytes, focusing on intracellular NO. To investigate the effects of force magnitude on apoptosis and intracellular NO production, we isolated osteocytes from DMP1-EGFP mice and subjected them to quantitative local forces via fibronectin-coated micro beads targeting integrin on the cell surface using a magnetic tweezer. Cell shrinkage was microscopically examined, and intracellular NO production was visualized using DAR-4 M. Mechanical stimulation revealed relationships between force magnitude, apoptosis, and intracellular NO production. The application of a smaller force resulted in no significant cell shrinkage or intracellular NO production; however, a larger force caused a rapid increase in intracellular NO production followed by cell shrinkage. Besides, intracellular NOS (NO synthase) inhibition and NO donation revealed the pro-apoptotic roles of NO in osteocytes. L-NAME (NOS inhibitor)-treated cells displayed no significant shrinkage under a larger force, whereas SNP (NO donor)-treated cells showed cell shrinkage and Annexin V fluorescence, indicating apoptosis. Collectively, our study demonstrates that larger force leads to NO production-mediated osteocyte shrinkage, implying an initial apoptotic response and highlighting the importance of NO production in bone damage.

Skeletal muscle regeneration is modulated by inflammation

Skeletal muscle regeneration is a complex process orchestrated by multiple steps. Recent findings indicate that inflammatory responses could play central roles in bridging initial muscle injury responses and timely muscle injury reparation. The various types of immune cells and cytokines have crucial roles in muscle regeneration process. In this review, we briefly summarise the functions of acute inflammation in muscle regeneration.

THE TRANSLATIONAL POTENTIAL OF THIS ARTICLE

Immune system is closely relevant to the muscle regeneration. Understanding the mechanisms of inflammation in muscle regeneration is therefore critical for the development of effective regenerative, and therapeutic strategies in muscular disorders. This review provides information for muscle regeneration research regarding the effects of inflammation on muscle regeneration.

The role of nitric oxide in metabolic regulation of Dendritic cell immune function

Dendritic cells (DCs) are canonical antigen presenting cells of the immune system and serve as a bridge between innate and adaptive immune responses. When DCs are activated by a stimulus through toll-like receptors (TLRs), DCs undergo a process of maturation defined by cytokine & chemokine secretion, co-stimulatory molecule expression, antigen processing and presentation, and the ability to activate T cells. DC maturation is coupled with an increase in biosynthetic demand, which is fulfilled by a TLR-driven upregulation in glycolytic metabolism. Up-regulation of glycolysis in activated DCs provides these cells with molecular building blocks and cellular energy required for DC activation, and inhibition of glycolysis during initial activation impairs both the survival and effector function of activated DCs. Evidence shows that DC glycolytic upregulation is controlled by two distinct pathways, an early burst of glycolysis that is nitric oxide (NO) -independent, and a sustained commitment to glycolysis in NO-producing DC subsets. This review will address the complex role of NO in regulating DC metabolism and effector function.

Immunobiology of Nitric Oxide and Regulation of Inducible Nitric Oxide Synthase

Nitric oxide (NO) is a bioactive gas that has multiple roles in innate and adaptive immune responses. In macrophages, nitric oxide is produced by inducible nitric oxide synthase upon microbial and cytokine stimulation. It is needed for host defense against pathogens and for immune regulation. This review will summarize the role of NO and iNOS in inflammatory and immune responses and will discuss the regulatory mechanisms that control inducible nitric oxide synthase expression and activity.

Evidence for Detrimental Cross Interactions between Reactive Oxygen and Nitrogen Species in Leber's Hereditary Optic Neuropathy Cells

Here we have collected evidence suggesting that chronic changes in the NO homeostasis and the rise of reactive oxygen species bioavailability can contribute to cell dysfunction in Leber's hereditary optic neuropathy (LHON) patients. We report that peripheral blood mononuclear cells (PBMCs), derived from a female LHON patient with bilateral reduced vision and carrying the pathogenic mutation 11778/ND4, display increased levels of reactive oxygen species (ROS) and reactive nitrogen species (RNS), as revealed by flow cytometry, fluorometric measurements of nitrite/nitrate, and 3-nitrotyrosine immunodetection. Moreover, viability assays with the tetrazolium dye MTT showed that lymphoblasts from the same patient are more sensitive to prolonged NO exposure, leading to cell death. Taken together these findings suggest that oxidative and nitrosative stress cooperatively play an important role in driving LHON pathology when excess NO remains available over time in the cell environment.

Pro-oxidative synergic bactericidal effect of NO: kinetics and inhibition by nitroxides

NO plays diverse roles in physiological and pathological processes, occasionally resulting in opposing effects, particularly in cells subjected to oxidative stress. NO mostly protects eukaryotes against oxidative injury, but was demonstrated to kill prokaryotes synergistically with H2O2. This could be a promising therapeutic avenue. However, recent conflicting findings were reported describing dramatic protective activity of NO. The previous studies of NO effects on prokaryotes applied a transient oxidative stress while arbitrarily checking the residual bacterial viability after 30 or 60min and ignoring the process kinetics. If NO-induced synergy and the oxidative stress are time-dependent, the elucidation of the cell killing kinetics is essential, particularly for survival curves exhibiting a "shoulder" sometimes reflecting sublethal damage as in the linear-quadratic survival models. We studied the kinetics of NO synergic effects on H2O2-induced killing of microbial pathogens. A synergic pro-oxidative activity toward gram-negative and gram-positive cells is demonstrated even at sub-μM/min flux of NO. For certain strains, the synergic effect progressively increased with the duration of cell exposure, and the linear-quadratic survival model best fit the observed survival data. In contrast to the failure of SOD to affect the bactericidal process, nitroxide SOD mimics abrogated the pro-oxidative synergy of NO/H2O2. These cell-permeative antioxidants, which hardly react with diamagnetic species and react neither with NO nor with H2O2, can detoxify redox-active transition metals and catalytically remove intracellular superoxide and nitrogen-derived reactive species such as (•)NO2 or peroxynitrite. The possible mechanism underlying the bactericidal NO synergy under oxidative stress and the potential therapeutic gain are discussed.

Multiple sclerosis: molecular mechanisms and therapeutic opportunities

The pathophysiology of multiple sclerosis (MS) involves several components: redox, inflammatory/autoimmune, vascular, and neurodegenerative. All of them are supported by the intertwined lines of evidence, and none of them should be written off. However, the exact mechanisms of MS initiation, its development, and progression are still elusive, despite the impressive pace by which the data on MS are accumulating. In this review, we will try to integrate the current facts and concepts, focusing on the role of redox changes and various reactive species in MS. Knowing the schedule of initial changes in pathogenic factors and the key turning points, as well as understanding the redox processes involved in MS pathogenesis is the way to enable MS prevention, early treatment, and the development of therapies that target specific pathophysiological components of the heterogeneous mechanisms of MS, which could alleviate the symptoms and hopefully stop MS. Pertinent to this, we will outline (i) redox processes involved in MS initiation; (ii) the role of reactive species in inflammation; (iii) prooxidative changes responsible for neurodegeneration; and (iv) the potential of antioxidative therapy.

Mechanisms of Resolution of Inflammation

The inflammatory response is an integral part of the innate immune mechanism that is triggered in response to a real or perceived threat to tissue homeostasis, with a primary aim of neutralizing infectious agents and initiating repair to damaged tissue. By design, inflammation is a finite process that resolves as soon as the threat of infection abates and sufficient repair to the tissue is complete. Resolution of inflammation involves apoptosis and subsequent clearance of activated inflammatory cells – a tightly regulated event. Chronic inflammation is a characteristic feature in virtually all inflammatory diseases, including atherosclerosis, and it is becoming increasingly clear that derangement of the processes usually involved in resolution of inflammation is an underlying feature of chronic inflammatory conditions. This review will draw on evidence from a range of diseases in which dysregulated inflammation is important, with particular emphasis on cardiovascular disease.

Nitric oxide affects IL-6 expression in human peripheral blood mononuclear cells involving cGMP-dependent modulation of NF-κB activity

Interleukin 6 (IL-6) and nitric oxide (NO) are important mediators of the inflammatory response. We report that in human peripheral blood mononuclear cells (PBMCs), NO exerts a biphasic effect on the expression of IL-6. Using sodium nitroprusside (SNP) and S-nitrosoglutathione (GSNO) as NO-donating compounds, we observed that both mRNA and protein levels of IL-6 increased at lower (≤10μM) and decreased at higher (>100μM) concentrations of NO donors. Changes in the expression of IL-6 correlated with changes in the activity of NF-κB, which increased at lower and decreased at higher concentrations of both NO donors as shown by the electrophoretic mobility shift assay (EMSA). The effects of NO on NF-κB activity were cGMP-dependent because they were reversed in the presence of ODQ, the inhibitor of soluble guanylyl cyclase (sGC), and KT5823, the inhibitor of cGMP-dependent protein kinase (PKG). Moreover, the membrane permeable analog of cGMP (8-Br-cGMP) mimicked the effect of the NO donors. These observations show that NO, depending on its concentration, may act in human PBMCs as a stimulator of IL-6 expression involving the sGC/cGMP/PKG pathway.

Cyclic GMP protects human macrophages against peroxynitrite-induced apoptosis

Background

Nitric oxide (NO) can be both pro- and anti-apoptotic in various cell types, including macrophages. This apparent paradox may result from the actions of NO-related species generated in the microenvironment of the cell, for example the formation of peroxynitrite (ONOO^-). In this study we have examined the ability of NO and ONOO^- to evoke apoptosis in human monocyte-derived macrophages (MDMϕ), and investigated whether preconditioning by cyclic guanosine monophosphate (cGMP) is able to limit apoptosis in this cell type.

Methods

Characterisation of the NO-related species generated by (Z)-1- [2-(2-aminoethyl)-N-(2-ammonioethyl)amino]diazen-1-ium-1,2-diolate (DETA/NO) and 1,2,3,4-oxatriazolium, 5-amino-3-(3,4-dichlorophenyl)-, chloride (GEA-3162) was performed by electrochemistry using an isolated NO electrode and electron paramagnetic resonance (EPR) spectrometry. Mononuclear cells were isolated from peripheral blood of healthy volunteers and cultured to allow differentiation into MDMϕ. Resultant MDMϕ were treated for 24 h with DETA/NO (100 – 1000 μM) or GEA-3162 (10 – 300 μM) in the presence or absence of BAY 41–2272 (1 μM), isobutylmethylxanthine (IBMX; 1 μM), 1H- [1,2,4]oxadiazolo [4,3-a]quinoxalin-1-one (ODQ; 20 μM) or 8-bromo-cGMP (1 mM). Apoptosis in MDMϕ was assessed by flow cytometric analysis of annexin V binding in combination with propidium iodide staining.

Results

Electrochemistry and EPR revealed that DETA/NO liberated free NO radical, whilst GEA-3162 concomitantly released NO and O₂^-, and is therefore a ONOO^- generator. NO (DETA/NO) had no effect on cell viability, but ONOO^- (GEA-3162) caused a concentration-dependent induction of apoptosis in MDMϕ. Preconditioning of MDMϕ with NO in combination with the phosphodiesterase inhibitor, 3-Isobutyl-1-methylxanthine (IBMX), or the NO-independent stimulator of soluble guanylate cyclase, BAY 41–2272, significantly attenuated ONOO^--induced apoptosis in a cGMP-dependent manner.

Conclusion

These results demonstrate disparities between the ability of NO and ONOO^- to induce apoptosis in human MDMϕ. Furthermore, this study provides evidence for a novel cGMP-dependent pre-conditioning mechanism to limit ONOO^--induced apoptosis in human MDMϕ.

The pro-survival pathways of mTOR and protein kinase B target glycogen synthase kinase-3beta and nuclear factor-kappaB to foster endogenous microglial cell protection

Microglia of the central nervous system serve a variety of functions that may ultimately lead to the development or detriment of neighboring neuronal and vascular cells. These scavengers of the nervous system have been associated with a variety of neurodegenerative disorders, but the toxic potential of microglia is equally balanced by the protective nature of these cells to exclude foreign microorganisms and promote new tissue proliferation and reorganization. To this extent, our work outlines a series of endogenous microglial cellular pathways that can constitute protection for microglia against during oxygen-glucose deprivation (OGD). We demonstrate in both primary microglia and the microglial cell line EOC 2 that endogenous microglial protection against OGD relies upon the activation and expression of the phosphatidylinositol 3-kinase pathways of mammalian target of rapamycin (mTOR) and protein kinase B (Akt1), since pharmacological inhibition of mTOR or Akt1 as well as the gene silencing of Akt1 protein expression leads to significantly increased microglial apoptotic cell injury, DNA fragmentation, and membrane phosphatidylserine exposure. The mTOR pathway may offer endogenous protection through mechanisms that do not entirely rely upon inhibition of glycogen synthase kinase-3beta (GSK-3beta) activity while Akt1 appears to converge upon the necessary blockade of GSK-3beta. Closely aligned to these endogenous protective mechanisms is the subcellular presence and nuclear translocation of nuclear factor-kappaB p65 (NF-kappaB p65), since microglial cell injury is significantly increased during the gene silencing of NF-kappaB p65. Elucidating the underlying pathways that can afford endogenous protection and maintain functional integrity of microglia should offer new prospects for the treatment of a broad range of nervous system disorders.

Nitric oxide preconditioning regulates endothelial monolayer integrity via the heat shock protein 90-soluble guanylate cyclase pathway

Large (pathological) amounts of nitric oxide (NO) induce cell injury, whereas low (physiological) NO concentrations often ameliorate cell injury. We tested the hypotheses that pretreatment of endothelial cells with low concentrations of NO (preconditioning) would prevent injury induced by high NO concentrations. Apoptosis, induced in bovine aortic endothelial cells (BAECs) by exposing them to either 4 mM sodium nitroprusside (SNP) or 0.5 mM N-(2-aminoethyl)-N-(2-hydroxy-2-nitrosohydrazino)-1,2-ethylenediamine (spermine NONOate) for 8 h, was abolished by 24-h pretreatment with either 100 microM SNP, 10 microM spermine NONOate, or 100 microM 8-bromo-cGMP (8-Br-cGMP). Repair of BAECs following wounding, measured as the recovery rate of transendothelial electrical resistance, was delayed by 8-h exposure to 4 mM SNP, and this delay was significantly attenuated by 24-h pretreatment with 100 microM SNP. NO preconditioning produced increased association and expression of soluble guanyl cyclase (sGC) and heat shock protein 90 (HSP90). The protective effect of NO preconditioning, but not the injurious effect of 4 mM SNP, was abolished by either a sGC activity inhibitor 1H-[1,2,4]oxadiazolo-[4,3-a]quinoxalin-1-one (ODQ) or a HSP90 binding inhibitor (radicicol) and was mimicked by 8-Br-cGMP. We conclude that preconditioning with a low dose of NO donor accelerates repair and maintains endothelial integrity via a mechanism that includes the HSP90/sGC pathway. HSP90/sGC may thus play a role in the protective effects of NO-generating drugs from injurious stimuli.

Nitric oxide signaling in stretch‐induced apoptosis of neonatal rat cardiomyocytes

Pressure overload associated with hypertension is an important pathological factor leading to heart remodeling and ultimately heart failure partially due to cardiomyocyte apoptosis. Here we show that endogenous NO signaling plays a critical role in mechanical stretch-induced cardiomyocyte apoptosis. Mechanical stretch induced elevated expression of both eNOS and inducible NO synthase (iNOS) and increased synthesis of NO. A sustained increase in iNOS expression was also found in hearts of hypertensive rats in vivo. Blockade of NO signaling by inhibitors of NOS (L-NAME and AMT) or downstream guanylyl cyclase (ODQ) strongly inhibited stretch-induced apoptosis, mitochondria depolarization, and cytochrome c release, suggesting that NO is required in stretch-induced cardiomyocyte apoptosis. The expression of iNOS, but not eNOS, was blocked by L-NAME and ODQ, indicating that the iNOS induction is NO dependent. The initial elevation of NO is likely due to Ca(2+)-dependent activation of eNOS because elimination of intracellular calcium by EGTA-AM inhibited both iNOS induction and NO elevation. Other calcium signaling inhibitors (nifedipine, ryanodine, thapsigargin, and ionic gadolinium) also attenuated the initial NO elevation. These data indicate that mechanical signals initiate Ca(2+)-dependent NO synthesis, which is further amplified by activation of NO-induced iNOS expression, to regulate cardiomyocyte apoptosis.

Nitric oxide/cGMP signaling pathway protects RAW264 cells against nitric oxide-induced apoptosis by inhibiting the activation of p38 mitogen-activated protein kinase

Nitric oxide (NO) induces apoptosis in various cells lines, while activation of the NO/cGMP signaling pathway prevents apoptosis induced by diverse stimuli, including NO. Here, we report the cytoprotective mechanisms of the NO/cGMP signaling pathway against NO-induced apoptosis in a mouse macrophage-like cell line, RAW264. Treatment with sodium nitroprusside (SNP), an NO donor, at a high-toxic concentration (4 mM) stimulated the N-terminal conformational change of Bax and its translocation to mitochondria followed by cytochrome c release and nuclear fragmentation in RAW264 cells. These changes of Bax were attenuated by pretreatment with SNP at a low-nontoxic concentration (100 microM) or dibutyryl cGMP (DBcGMP), a cell-permeable cGMP analogue. SB203580, a p38 mitogen-activated protein kinase (MAP kinase) inhibitor, blocked the effects of 4 mM SNP on Bax translocation and cell viability. Treatment with 4 mM SNP activated p38 MAP kinase and this effect was prevented by pretreatment with 100 microM SNP or DBcGMP. These findings suggest that the NO/cGMP signaling pathway inhibits NO-induced apoptosis of macrophages by suppressing the p38 MAP kinase activation, which results in N-terminal conformational change of Bax and its translocation to mitochondria.

Nitric oxide protects macrophages from hydrogen peroxide-induced apoptosis by inducing the formation of catalase

We investigated the cytoprotective effect of NO on H2O2-induced cell death in mouse macrophage-like cell line RAW264. H2O2-treated cells showed apoptotic features, such as activation of caspase-9 and caspase-3, nuclear fragmentation, and DNA fragmentation. These apoptotic features were significantly inhibited by pretreatment for 24 h with NO donors, sodium nitroprusside and 1-hydroxy-2-oxo-3,3-bis-(2-aminoethyl)-1-triazene, at a low nontoxic concentration. The cytoprotective effect of NO was abrogated by the catalase inhibitor 3-amino-1,2,4-triazole but was not affected by a glutathione synthesis inhibitor, L-buthionine-(S,R)-sulfoximine. NO donors increased the level of catalase and its activity in a concentration-dependent manner. Cycloheximide, a protein synthesis inhibitor, inhibited both the NO-induced increase in the catalase level and the cytoprotective effect of NO. These results indicate that NO at a low concentration protects macrophages from H2O2-induced apoptosis by inducing the production of catalase.

Inhibition of protein synthesis by activation of NMDA receptors in cultured retinal cells: a new mechanism for the regulation of nitric oxide production

The synthesis of nitric oxide (NO) is limited by the intracellular availability of L-arginine. Here we show that stimulation of NMDA receptors promotes an increase of intracellular L-arginine which supports an increase in the production of NO. Although L-[3H]arginine uptake measured in cultured chick retina cells incubated in the presence of cycloheximide (CHX, a protein synthesis inhibitor) was inhibited approximately 75% at equilibrium, quantitative thin-layer chromatography analysis showed that free intracellular L-[3H]arginine was six times higher in CHX-treated than in control cultures. Extracellular L-[3H]citrulline levels increased threefold in CHX-treated groups, an effect blocked by NG-nitro-L-arginine, a NO synthase (NOS) inhibitor. NMDA promoted a 40% increase of free intracellular L-[3H]arginine in control cultures, an effect blocked by the NMDA antagonist 2-amino 5-phosphonovaleric acid. In parallel, NMDA promoted a reduction of 40-50% in the incorporation of 35[S]methionine or L-[3H]arginine into proteins. Western blot analysis revealed that NMDA stimulates the phosphorylation of eukaryotic elongation factor 2 (eEF2, a factor involved in protein translation), an effect inhibited by (+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine maleate (MK801). In conclusion, we have shown that the stimulation of NMDA receptors promotes an inhibition of protein synthesis and a consequent increase of an intracellular L-arginine pool available for the synthesis of NO. This effect seems to be mediated by activation of eEF2 kinase, a calcium/calmodulin-dependent enzyme which specifically phosphorylates and blocks eEF2. The results raise the possibility that NMDA receptor activation stimulates two different calmodulin-dependent enzymes (eEF2 kinase and NOS) reinforcing local NO production by increasing precursor availability together with NOS catalytic activity.

The nitric oxide donor sodium nitroprusside inhibits mineralization in ATDC5 cells

The aim of this study was to test whether the nitric oxide (NO) donor sodium nitroprusside (SNP) has an effect on mineralization in ATDC5 cells. Mineralization in ATDC5 cell culture was induced by addition of beta-glycerophosphate or inorganic phosphate, visualized by staining precipitated calcium with an alizarin red stain, and quantified using atomic absorption spectrometry. SNP was shown to inhibit the mineralization of ADTC5 cells. This inhibition was not affected by inhibitors of guanylyl cyclase nor mimicked by a cyclic guanosine monophosphate (cGMP) analog. Furthermore, SNP did not inhibit phosphate uptake or inhibit apoptosis in ATDC5 cells. These findings indicate that SNP can specifically inhibit matrix mineralization via a cGMP-independent pathway and that the effect is not mediated by inhibition of phosphate transport or apoptosis. These results suggest a preventive role of NO in premature or pathological mineralization.

Fundamental role of nitric oxide in neuritogenesis of PC12h cells

1 We investigated the neuritogenic action of nitric oxide (NO)-generating agents and their mechanisms of action in a subclone of rat pheochromocytoma, PC12h cells. 2 NO donors such as sodium nitroprusside (SNP, 0.05-1 microM), NOR1 (5-100 microM), NOR2 (5-20 microM), NOR3 (5-20 microM), NOR4 (5-100 microM), or S-nitroso-N-acetyl-DL-penicillamine (SNAP, 10-100 microM) significantly induced neurite outgrowth. 3 NOR4-induced neurite outgrowth was accompanied by expression of neurofilament 200 kDa subunit (NF200) protein, an axonal marker, and was significantly inhibited by an NO scavenger, a soluble GC inhibitor, and a PKG inhibitor: 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazole-1-oxyl-3-oxide (carboxy-PTIO, 20-100 microM), 1H-[1,2,4]oxadiazolo[4,3-a] quinoxalin-1-one (ODQ, 100 microM) and KT5823 (0.2-1 microM), respectively. 4 The intracellular cGMP concentration of cells was markedly increased by treatment with NOR4 (100 microM). 5 A mitogen-activated protein kinase (MAPK) kinase inhibitor, PD98059 (10-50 microM), abolished the NOR4-induced neurite outgrowth. In agreement with this observation, NOR4 did phosphorylate extracellular signal-regulated kinase (ERK) 1 and 2, substrates of MAPK kinase. 6 A membrane-permeable cGMP analog, 8-Br-cGMP (1 mM) also induced significant neurite outgrowth. The 8-Br-cGMP-induced neurite outgrowth was almost completely inhibited by both KT5823 (0.5 microM) and PD98059 (50 microM). Moreover, sustained ERK phosphorylation was observed in the 8-Br-cGMP-treated PC12h cells. 7 These results suggest that NO itself has the ability to induce neurite outgrowth and that NO-induced ERK activation involves the NO-cGMP-PKG signaling pathway in PC12h cells.

C-phycocyanin, a very potent and novel platelet aggregation inhibitor from Spirulina platensis

The aim of this study was to systematically examine the inhibitory mechanisms of C-phycocyanin (C-PC), one of the major phycobiliproteins of Spirulina platensis (a blue-green alga), in platelet activation. In this study, C-PC concentration-dependently (0.5-10 nM) inhibited platelet aggregation stimulated by agonists. C-PC (4 and 8 nM) inhibited intracellular Ca2+ mobilization and thromboxane A2 formation but not phosphoinositide breakdown stimulated by collagen (1 microg/mL) in human platelets. In addition, C-PC (4 and 8 nM) markedly increased levels of cyclic GMP and cyclic GMP-induced vasodilator-stimulated phosphoprotein (VASP) Ser(157) phosphorylation. Rapid phosphorylation of a platelet protein of Mw 47,000 (P47), a marker of protein kinase C activation, was triggered by phorbol-12,13-dibutyrate (150 nM). This phosphorylation was markedly inhibited by C-PC (4 and 8 nM). In addition, C-PC (4 and 8 nM) markedly reduced the electron spin resonance (ESR) signal intensity of hydroxyl radicals in collagen (1 microg/mL)-activated platelets. The present study reports on a novel and very potent (in nanomolar concentrations) antiplatelet agent, C-PC, which is involved in the following inhibitory pathways: (1) C-phycocyanin increases cyclic GMP/VASP Ser157 phosphorylation and subsequently inhibits protein kinase C activity, resulting in inhibition of both P47 phosphorylation and intracellular Ca2+ mobilization, and (2) C-PC may inhibit free radicals (such as hydroxyl radicals) released from activated platelets, which ultimately inhibits platelet aggregation. These results strongly indicate that C-PC appears to represent a novel and potential antiplatelet agent for treatment of arterial thromboembolism.

alpha-Naphthoflavone, a potent antiplatelet flavonoid, is mediated through inhibition of phospholipase C activity and stimulation of cyclic GMP formation

The aim of this study was to systematically examine the inhibitory mechanisms of the flavonoid alpha-naphthoflavone (alpha-NF) in platelet activation. In this study, alpha-NF concentration dependently (5-20 microM) inhibited platelet aggregation stimulated by agonists. alpha-NF (5 and 10 microM) inhibited intracellular Ca(2+) mobilization, phosphoinositide breakdown, and thromboxane A(2) formation stimulated by collagen (1 microg/mL) in human platelets. In addition, alpha-NF (5 and 10 microM) markedly increased levels of cyclic GMP and cyclic GMP-induced vasodilator-stimulated phosphoprotein (VASP) Ser(157) phosphorylation. Rapid phosphorylation of a platelet protein of Mr 47,000 (P47), a marker of protein kinase C activation, was triggered by phorbol-12,13-dibutyrate (60 nM). This phosphorylation was markedly inhibited by alpha-NF (5 and 10 microM). However, alpha-NF (5 and 10 microM) did not reduce the electron spin resonance (ESR) signal intensity of hydroxyl radicals in collagen (1 microg/mL)-activated platelets. These results indicate that the antiplatelet activity of alpha-NF may be involved in the following pathways. (1) alpha-NF may inhibit the activation of phospholipase C, followed by inhibition of phosphoinositide breakdown, protein kinase C activation, and thromboxane A(2) formation, thereby leading to inhibition of intracellular Ca(2+) mobilization. (2) alpha-NF also activated the formation of cyclic GMP, resulting in inhibition of platelet aggregation. These results strongly indicate that alpha-NF appears to represent a novel and potent antiplatelet agent for treatment of arterial thromboembolism.

The intimate relation between nitric oxide and superoxide in apoptosis and cell survival

Intra- and intercellular communication in or between cells allows adaptation to changes in the environment. Formation of reactive oxygen (ROS) and nitrogen (RNS) species in response to external insults gained considerable attention in provoking cell demise along an apoptotic subroute of cell death, thus attributing radical formation to pathologies. In close association, stabilization of the tumor suppressor p53 and activation of caspases convey proapoptotic signaling. Complexity was added with the notion that ROS and RNS signals overlap and/or produce synergistic as well as antagonistic effects. With respect to nitric oxide (NO) signaling, it became clear that the molecule is endowed with pro- or antiapoptotic signaling capabilities, depending to some extend on the concentration and cellular context, i.e., ROS generation. Here, some established concepts are summarized that allow an explanation of p53 accumulation under the impact of NO and an understanding of NO-evoked cell protection at the level of caspase inhibition, cyclic GMP formation, or expression of antiapoptotic proteins. In addition, the overlapping sphere of ROS and RNS signaling is recapitulated to appreciate cell physiology/pathology with the notion that marginal changes in the flux rates of either NO or superoxide may shift vital signals used for communication and cell survival into areas of pathology in close association with apoptosis/necrosis.

The mechanism of low-concentration sodium nitroprusside-mediated protection of chondrocyte death

Sodium nitroprusside (SNP), a widely used nitric oxide donor, has recently been shown to mediate chondrocyte apoptosis by generating reactive oxygen species, whereas more potent nitric oxide donors do not induce chondrocyte apoptosis. The present study was performed to investigate the protective effect of a low concentration of SNP upon the cytotoxicity of chondrocytes to higher concentrations of SNP, and to elucidate the underlying mechanism. Human osteoarthritis chondrocytes were cultured as monolayers, and first-passage cells were used for the experiments. Chondrocyte death induced by 1 mM SNP was completely inhibited by pretreating with 0.1 mM SNP. This protective effect of SNP was replicated by the guanosine-3',5'κ-cyclic monophosphate analog, DBcGMP. Protection from chondrocyte death conferred by 0.1 mM SNP was mediated by heme oxygenase 1 (HO-1), as was revealed by the increased expression of HO-1 in 0.1 mM SNP pretreated chondrocytes and by the reversal of this protective effect by the HO-1 inhibitor, zinc protoporphyrin. SNP-mediated chondrocyte protection correlated with the downregulation of both extracellular signal-regulated protein kinase 1/2 and p38 kinase activation. SNP at 0.1 mM induced significant NF-κB activation as revealed by electrophoretic mobility shift assays, and the inhibition of NF-κB by MG132 or Bay 11-7082 nullified 0.1 mM SNP-mediated chondrocyte protection. The upregulation of p53 and the downregulation of Bcl-_XL and Mcl-1 by 1 mM SNP were reversed by 0.1 mM SNP pretreatment at the protein level by western blotting. Our study shows that priming with 0.1 mM SNP confers complete protection against cell death induced by 1 mM SNP in human articular chondrocytes. This protective effect was found to be correlated with the upregulation of both HO-1 and NF-κB and with the concomitant downregulation of both extracellular signal-regulated protein kinase 1/2 and p38 activation.

Nitric oxide and the resolution of inflammation: implications for atherosclerosis

The ubiquitous free radical, nitric oxide (NO), plays an important role in many biological processes including the regulation of the inflammatory response. Alterations in NO synthesis by endogenous systems likely influence inflammatory processes occurring in a wide range of diseases including many in the cardiovascular system (e.g. atherosclerosis). Progression of inflammatory conditions depends not only upon the recruitment and activation of inflammatory cells but also upon their subsequent removal from the inflammatory milieu. Apoptosis, or programmed cell death, is a fundamental process regulating inflammatory cell survival and is critically involved in ensuring the successful resolution of an inflammatory response. Apoptosis results in shutdown of secretory pathways and renders effete, but potentially highly histotoxic, cells instantly recognisable for non-inflammatory clearance by phagocytes (e.g., macrophages). However, dysregulation of apoptosis and phagocytic clearance mechanisms can have drastic consequences for development and resolution of inflammatory processes. In this review we highlight the complexities of NO-mediated regulation of inflammatory cell apoptosis and clearance by phagocytes and discuss the molecular mechanisms controlling these NO mediated effects. We believe that manipulation of pathways involving NO may have previously unrecognised therapeutic potential for limiting or resolving inflammatory and cardiovascular disease.

Nitric Oxide Induces Apoptosis in Mouse C2C12 Myoblast Cells

To investigate whether nitric oxide (NO) induces apoptosis in myoblast cells, the effect of the sodium nitroprusside (SNP), NO donor, on the apoptosis of mouse C2C12 myoblast cells was examined by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, flow cytometry, 4,6-diamidino-2-phenylindole (DAPI) staining, terminal deoxynucleotidyl transferase (TdT)-mediated dUTP nick end labeling (TUNEL) assay, DNA fragmentation assay, reverse transcription-polymerase chain reaction (RT-PCR), Western blot analysis, and caspase-3 enzyme assay. Mouse C2C12 myoblast cells treated with SNP exhibited several apoptotic features. SNP increased p53 expression and bax expression. SNP also enhanced caspase-3 enzyme activity. The data show that NO may induce apoptotic cell death in myoblast cells through the activation of p53-, bax-, and caspase-dependent intracellular death-related pathways.

Inducible nitric oxide synthase upregulates cyclooxygenase-2 in mouse cholangiocytes promoting cell growth

Both inducible nitric oxide (NO) synthase (iNOS) and cyclooxygenase-2 (COX-2) have been implicated in the biliary tract carcinogenesis. However, it is not known whether these inflammatory mediators are induced by interdependent or parallel pathways. Because iNOS activity has been associated with diverse gene expression, the aim of this study was to determine whether iNOS induces COX-2. To address this objective, immortalized, but nonmalignant, murine cholangiocytes, 603B cells were employed for these studies. Both iNOS and COX-2 protein and mRNA were expressed in these cells. However, iNOS inhibition with either N-[3-(aminomethyl) benzyl]acetamidine or stable transfection with an iNOS antisense construct inhibited COX-2 mRNA and protein expression, an effect that was reversed by NO donors. COX-2 mRNA expression in 603B cells was reduced by pharmacological inhibitors of the p38 MAPK and JNK1/2 pathways. In contrast, neither inhibitors of the soluble guanylyl cyclase inhibitor/protein kinase G nor p42/44 MAPK pathways attenuated COX-2 mRNA expression. Finally, 603B cells grew at a rate threefold greater than 603B-iNOS antisense cells. The low growth rate of 603B-iNOS antisense cells could be restored to near that of the parent cell line with exogenous PGE(2.) In conclusion, iNOS induces COX-2 expression in cholangiocytes, which promotes cell growth. COX-2 induction may contribute to iNOS-associated carcinogenesis.