Chemistry of nitric oxide: biologically relevant aspects

Nitric oxide in kidney transplantation

Kidney transplantation is the treatment of choice for patients with kidney failure. Compared to dialysis therapy, it provides better quality of life and confers significant survival advantage at a relatively lower cost. However, the long-term success of this life-saving intervention is severely hampered by an inexorable clinical problem referred to as ischemia-reperfusion injury (IRI), and increases the incidence of post-transplant complications including loss of renal graft function and death of transplant recipients. Burgeoning evidence shows that nitric oxide (NO), a poisonous gas at high concentrations, and with a historic negative public image as an environmental pollutant, has emerged as a potential candidate that holds clinical promise in mitigating IRI and preventing acute and chronic graft rejection when it is added to kidney preservation solutions at low concentrations or when administered to the kidney donor prior to kidney procurement and to the recipient or to the reperfusion circuit at the start and during reperfusion after renal graft preservation. Interestingly, dysregulated or abnormal endogenous production and metabolism of NO is associated with IRI in kidney transplantation. From experimental and clinical perspectives, this review presents endogenous enzymatic production of NO as well as its exogenous sources, and then discusses protective effects of constitutive nitric oxide synthase (NOS)-derived NO against IRI in kidney transplantation via several signaling pathways. The review also highlights a few isolated studies of renal graft protection by NO produced by inducible NOS.

Inhaled Nitric Oxide in Acute Respiratory Distress Syndrome Subsets: Rationale and Clinical Applications

Acute respiratory distress syndrome (ARDS) is a life-threatening condition, characterized by diffuse inflammatory lung injury. Since the coronavirus disease 2019 (COVID-19) pandemic spread worldwide, the most common cause of ARDS has been the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. Both the COVID-19-associated ARDS and the ARDS related to other causes-also defined as classical ARDS-are burdened by high mortality and morbidity. For these reasons, effective therapeutic interventions are urgently needed. Among them, inhaled nitric oxide (iNO) has been studied in patients with ARDS since 1993 and it is currently under investigation. In this review, we aim at describing the biological and pharmacological rationale of iNO treatment in ARDS by elucidating similarities and differences between classical and COVID-19 ARDS. Thereafter, we present the available evidence on the use of iNO in clinical practice in both types of respiratory failure. Overall, iNO seems a promising agent as it could improve the ventilation/perfusion mismatch, gas exchange impairment, and right ventricular failure, which are reported in ARDS. In addition, iNO may act as a viricidal agent and prevent lung hyperinflammation and thrombosis of the pulmonary vasculature in the specific setting of COVID-19 ARDS. However, the current evidence on the effects of iNO on outcomes is limited and clinical studies are yet to demonstrate any survival benefit by administering iNO in ARDS.

Nitric oxide regulation of cellular metabolism: Adaptive tuning of cellular energy

Nitric oxide can interact with a wide range of proteins including many that are involved in metabolism. In this review we have summarized the effects of NO on glycolysis, fatty acid metabolism, the TCA cycle, and oxidative phosphorylation with reference to skeletal muscle. Low to moderate NO concentrations upregulate glucose and fatty acid oxidation, while higher NO concentrations shift cellular reliance toward a fully glycolytic phenotype. Moderate NO production directly inhibits pyruvate dehydrogenase activity, reducing glucose-derived carbon entry into the TCA cycle and subsequently increasing anaploretic reactions. NO directly inhibits aconitase activity, increasing reliance on glutamine for continued energy production. At higher or prolonged NO exposure, citrate accumulation can inhibit multiple ATP-producing pathways. Reduced TCA flux slows NADH/FADH entry into the ETC. NO can also inhibit the ETC directly, further limiting oxidative phosphorylation. Moderate NO production improves mitochondrial efficiency while improving O2 utilization increasing whole-body energy production. Long-term bioenergetic capacity may be increased because of NO-derived ROS, which participate in adaptive cellular redox signaling through AMPK, PCG1-α, HIF-1, and NF-κB. However, prolonged exposure or high concentrations of NO can result in membrane depolarization and opening of the MPT. In this way NO may serve as a biochemical rheostat matching energy supply with demand for optimal respiratory function.

Inhaled nitric oxide: role in the pathophysiology of cardio-cerebrovascular and respiratory diseases

Nitric oxide (NO) is a key molecule in the biology of human life. NO is involved in the physiology of organ viability and in the pathophysiology of organ dysfunction, respectively. In this narrative review, we aimed at elucidating the mechanisms behind the role of NO in the respiratory and cardio-cerebrovascular systems, in the presence of a healthy or dysfunctional endothelium. NO is a key player in maintaining multiorgan viability with adequate organ blood perfusion. We report on its physiological endogenous production and effects in the circulation and within the lungs, as well as the pathophysiological implication of its disturbances related to NO depletion and excess. The review covers from preclinical information about endogenous NO produced by nitric oxide synthase (NOS) to the potential therapeutic role of exogenous NO (inhaled nitric oxide, iNO). Moreover, the importance of NO in several clinical conditions in critically ill patients such as hypoxemia, pulmonary hypertension, hemolysis, cerebrovascular events and ischemia-reperfusion syndrome is evaluated in preclinical and clinical settings. Accordingly, the mechanism behind the beneficial iNO treatment in hypoxemia and pulmonary hypertension is investigated. Furthermore, investigating the pathophysiology of brain injury, cardiopulmonary bypass, and red blood cell and artificial hemoglobin transfusion provides a focus on the potential role of NO as a protective molecule in multiorgan dysfunction. Finally, the preclinical toxicology of iNO and the antimicrobial role of NO-including its recent investigation on its role against the Sars-CoV2 infection during the COVID-19 pandemic-are described.

Biological Mechanisms of S-Nitrosothiol Formation and Degradation: How Is Specificity of S-Nitrosylation Achieved?

The modification of protein cysteine residues underlies some of the diverse biological functions of nitric oxide (NO) in physiology and disease. The formation of stable nitrosothiols occurs under biologically relevant conditions and time scales. However, the factors that determine the selective nature of this modification remain poorly understood, making it difficult to predict thiol targets and thus construct informatics networks. In this review, the biological chemistry of NO will be considered within the context of nitrosothiol formation and degradation whilst considering how specificity is achieved in this important post-translational modification. Since nitrosothiol formation requires a formal one-electron oxidation, a classification of reaction mechanisms is proposed regarding which species undergoes electron abstraction: NO, thiol or S-NO radical intermediate. Relevant kinetic, thermodynamic and mechanistic considerations will be examined and the impact of sources of NO and the chemical nature of potential reaction targets is also discussed.

Nitric Oxide as a Potential Adjuvant Therapeutic for Neuroblastoma: Effects of NO on Murine N2a Cells

Neuroblastoma, the most common extracranial solid tumor in children, accounts for 15% of all pediatric cancer deaths. Pharmaceutical applications of S-Nitrosylation, which, under normal conditions is involved with a host of epigenetic and embryological development pathways, have exhibited great potential for use as adjuvant therapeutics in the clinical management of cancer. Herein, an evaluation of the impact of nitric oxide (NO) as a potent anticancer agent on murine neuroblastoma cells is presented. Excitingly cell viability, colony formation, and non-carcinogenic cell analysis illustrate the significance and practicality of NO as a cytotoxic anticancer therapeutic. Resazurin, WST-8 (2-(2-methoxy-4-nitrophenyl)-3-(4-nitrophenyl)-5-(2,4-disulfophenyl)-2H-tetrazolium, monosodium salt), and MTT (3-(4,5-Dimethylthiazol-2-yl)-2,5-diphyltetrazolium bromide) assays consistently displayed a moderate, ~20-25% reduction in cell viability after exposure to 1 mM S-Nitrosoglutathione (GSNO). A colony formation assay demonstrated that treated cells no longer exhibited colony formation capacity. Identically GSNO-treated Adult Human Dermal Fibroblasts (HDFa) exhibited no decrease in viability, indicating potential discrimination between neoplastic and normal cells. Collectively, our findings indicate a potential application for NO as an adjuvant therapeutic in the clinical management of neuroblastoma.

Nitric oxide and its derivatives in the cancer battlefield

Elevated levels of reactive nitrogen species, alteration in redox balance and deregulated redox signaling are common hallmarks of cancer progression and chemoresistance. However, depending on the cellular context, distinct reactive nitrogen species are also hypothesized to mediate cytotoxic activity and are thus used in anticancer therapies. We present here the dual face of nitric oxide and its derivatives in cancer biology. Main derivatives of nitric oxide, such as nitrogen dioxide and peroxynitrite cause cell death by inducing protein and lipid peroxidation and/or DNA damage. Moreover, they control the activity of important protein players within the pro- and anti-apoptotic signaling pathways. Thus, the control of intracellular reactive nitrogen species may become a sophisticated tool in anticancer strategies.

Hyaluronan and Hyaluronan Fragments

The glycosaminoglycan hyaluronan (HA) is a key component of the microenvironment surrounding cells. In healthy tissues, HA molecules have extremely high molecular mass and consequently large hydrodynamic volumes. Tethered to the cell surface by clustered receptor proteins, HA molecules crowd each other, as well as other macromolecular species. This leads to severe nonideality in physical properties of the biomatrix, because steric exclusion leads to an increase in effective concentration of the macromolecules. The excluded volume depends on both polymer concentration and hydrodynamic volume/molecular mass. The biomechanical properties of the extracellular matrix, tissue hydration, receptor clustering, and receptor-ligand interactions are strongly affected by the presence of HA and by its molecular mass. In inflammation, reactive oxygen and nitrogen species fragment the HA chains. Depending on the rate of chain degradation relative to the rates of new synthesis and removal of damaged chains, short fragments of the HA molecules can be present at significant levels. Not only are the physical properties of the extracellular matrix affected, but the HA fragments decluster their primary receptors and act as endogenous danger signals. Bioanalytical methods to isolate and quantify HA fragments have been developed to determine profiles of HA content and size in healthy and diseased biological fluids and tissues. These methods have potential use in medical diagnostic tests. Therapeutic agents that modulate signaling by HA fragments show promise in wound healing and tissue repair without fibrosis.

Nitric oxide-mediated sensitization of resistant tumor cells to apoptosis by chemo-immunotherapeutics

The generation of NO by the various NO synthases in normal and malignant tissues is manifested by various biological effects that are involved in the regulation of cell survival, differentiation and cell death. The role of NO in the cytotoxic immune response was first revealed by demonstrating the induction of iNOS in target cells by immune cytokines (e.g. IFN-γ, IL-1, TNF-α, etc.) and resulting in the sensitization of resistant tumor cells to death ligands-induced apoptosis. Endogenous/exogenous NO mediated its immune sensitizing effect by inhibiting NF-κΒ activity and downstream, inactivating the repressor transcription factor YY1, which inhibited both Fas and DR5 expressions. In addition, NO-mediated inhibition of NF-κΒ activity and inhibition downstream of its anti-apoptotic gene targets sensitized the tumor cells to apoptosis by chemotherapeutic drugs. We have identified in tumor cells a dysregulated pro-survival/anti-apoptotic loop consisting of NF-κB/Snail/YY1/RKIP/PTEN and its modification by NO was responsible, in large, for the reversal of chemo and immune resistance and sensitization to apoptotic mechanisms by cytotoxic agents. Moreover, tumor cells treated with exogenous NO donors resulted in the inhibition of NF-κΒ activity via S-nitrosylation of p50 and p65, inhibition of Snail (NF-κΒ target gene), inhibition of transcription repression by S-nitrosylation of YY1 and subsequent inhibition of epithelial-mesenchymal transition (EMT), induction of RKIP (inhibition of the transcription repressor Snail), and induction of PTEN (inhibition of the repressors Snail and YY1). Further, each gene product modified by NO in the loop was involved in chemo-immunosensitization. These above findings demonstrated that NO donors interference in the regulatory circuitry result in chemo-immunosensitization and inhibition of EMT. Overall, these observations suggest the potential anti-tumor therapeutic effect of NO donors in combination with subtoxic chemo-immuno drugs. This combination acts on multiple facets including reversal of chemo-immune resistance, and inhibition of both EMT and metastasis.

Calreticulin Transacetylase mediated activation of human platelet nitric oxide synthase by acetyl group donor compounds

Polyphenols have attracted immense interest because of their diverse biological and pharmacological activities. Surprisingly, not much is documented about the biological activities of acetoxy derivatives of polyphenol called polyphenolic acetates (PA). In our previous reports, we have conclusively established the Calreticulin Transacetylase (CRTAase) catalyzed activation of neuronal nitric oxide synthase (nNOS) and tumor necrosis factor-α (TNF-α) induced nitric oxide synthase (iNOS) by PA. In the present work, specificity of CRTAase to various classes of PA was characterized in human platelet. The effect of PA, on platelet NOS and intracellular cyclic guanosine monophosphate (cGMP), and adenosine diphosphate (ADP)-induced platelet aggregation were studied in an elaborated manner. Platelet CRTAase exhibited differential specificities to polyphenolic acetates upon incubation with l-arginine leading to activation of NOS. The intraplatelet generation of NO was studied by flowcytometry using DCFH-DA. The differential specificities of CRTAase to PA were found to positively correlate with increased production of NO upon incubation of PRP with PA and l-arginine. Further, the inhibitory effect of l-NAME on PA induced NO formation in platelets substantiated the CRTAase catalyzed activation of NOS. The real-time RT-PCR profile of NOS isoforms confirmed the preponderance of eNOS over iNOS in human platelets on treatment with PA. Western blot analysis also reiterated the differential pattern of acetylation of eNOS by PA. PA were also found effective in increasing the intraplatelet cGMP levels and inhibiting ADP-induced platelet aggregation. It is worth mentioning that the effects of PA were found to be in tune with the specificities of platelet CRTAase to PA as the substrates.

Nitric oxide-generating hydrogels inhibit neointima formation

This study evaluated the effects of localized delivery of nitric oxide (NO) from hydrogels covalently modified with S-nitrosocysteine (Cys-NO) on neoinitma formation, a key component of restenosis, in a rat balloon-injury model. Soluble Cys-NO was used in preliminary studies to identify dosage ranges that were able to simultaneously inhibit smooth muscle cell proliferation, enhance endothelial cell proliferation, and reduce platelet adhesion. Photo-cross-linked PEG-based hydrogels were formed with covalently immobilized Cys-NO. These materials release NO for approximately 24 h and can be applied to tissues and photo-cross-linked in situ to form local drug-delivery systems. Localized delivery of NO from hydrogels containing Cys-NO inhibited neointima formation in a rat balloon-injury model by approximately 75% at 14 days.

Ligand specificity of H-NOX domains: from sGC to bacterial NO sensors

Soluble guanylate cyclase (sGC) is a nitric oxide (NO) sensing hemoprotein that has been found in eukaryotes from Drosophila to humans. Prokaryotic proteins with significant homology to the heme domain of sGC have recently been identified through genomic analysis. This family of heme proteins has been named the H-NOX domain, for Heme-Nitric oxide/OXygen binding domain. The key observation from initial studies in this family is that some members, those proteins from most eukaryotes and facultative aerobic prokaryotes, bind NO in a five-coordinate heme complex, but do not bind oxygen (O(2)), the same ligand binding characteristics as sGC. H-NOX family members from obligate aerobic prokaryotes bind O(2) and NO in six-coordinate complexes, similar to the globins and other O(2)-sensing heme proteins. The molecular factors that contribute to these differences in ligand specificity, within a family of sequence related proteins, are the subject of this review.

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.

Possible involvement of nitric oxide and peroxynitrite in the pathogenesis of human vocal polyps and nodules

Nitric oxide (NO) is a molecule involved in multiple functions including vasodilatation, neural transmission, immune response and inflammation. However, the role of NO in the pathophysiology of vocal cord diseases is not clear. The present study investigated the possible involvement of NO and its toxic metabolite, peroxynitrite, in the pathogenesis of vocal polyps and nodules. Vocal polyps and nodules were obtained from patients receiving surgery for their conditions. Immunohistochemistry was applied to evaluate the expression of the inducible form of nitric oxide synthase (iNOS) as well as the production of peroxynitrite represented by the formation of its biological footprint, 3-nitrotyrosine (3-NT). Each section was given a score of 0 to 4 according to the labeling intensity seen, with the highest number representing the highest labeling intensity. The results showed that vocal polyp had an average iNOS labeling score of 3.2, which was significantly higher than the value of 1.9 in vocal nodules. The average labeling score of 3-NT was 2.8 in vocal polyps, which was also significantly higher than the value of 1.8 in vocal nodules. There was also a positive correlation between the level of iNOS expression and the extent of 3-NT formation. These results suggest that increased peroxynitrite production, resulting from increased iNOS expression and NO formation, may have an important pathogenic role in these vocal diseases.

Nitric oxide: NO apoptosis or turning it ON?

Nitric oxide (NO) is known for its diverse activities throughout biology. Among signaling qualities, NO affects cellular decisions of life and death either by turning on apoptotic pathways or by shutting them off. Although copious reports support both notions, the dichotomy of NO actions remains unsolved. Proapoptotic pathways of NO are compatible with established signaling circuits appreciated for mitochondria-dependent roads of death, with some emphasis on the involvement of the tumor suppressor p53 as a target during cell death execution. Antiapoptotic actions of NO are numerous, ranging from an immediate interference with proapoptotic signaling cascades to long-lasting effects based on expression of cell protective proteins with some interest on the ability of NO-redox species to block caspases by S-nitrosylation/S-nitrosation. Summarizing emerging concepts to understand p53 accumulation on the one hand while proposing inhibition of procaspase processing on the other may help to define the pro- versus antiapoptotic roles of NO.

NO and the vasculature: where does it come from and what does it do?

Nitric oxide (NO) is involved in a large number of cellular processes and dysfunctions in NO production have been implicated in many different disease states. In the vasculature NO is released by endothelial cells where it modulates the underlying smooth muscle to regulate vascular tone. Due to the unique chemistry of NO, such as its reactive and free radical nature, it can interact with many different cellular constituents such as thiols and transition metal ions, which determine its cellular actions. In this review we also discuss many of the useful pharmacological tools that have been developed and used extensively to establish the involvement of NO in endothelium-derived relaxations. In addition, the recent literature identifying a potential source of NO in endothelial cells, which is not directly derived from endothelial nitric oxide synthase is examined. Finally, the photorelaxation phenomena, which mediates the release of NO from a vascular smooth muscle NO store, is discussed.

Focusing of nitric oxide mediated nitrosation and oxidative nitrosylation as a consequence of reaction with superoxide

The impact of nitric oxide (NO) synthesis on different biological cascades can rapidly change dependent on the rate of NO formation and composition of the surrounding milieu. With this perspective, we used diaminonaphthalene (DAN) and diaminofluorescein (DAF) to examine the nitrosative chemistry derived from NO and superoxide (O2-) simultaneously generated at nanomolar to low micromolar per minute rates by spermine/NO decomposition and xanthine oxidase-catalyzed oxidation of hypoxanthine, respectively. Fluorescent triazole product formation from DAN and DAF increased as the ratio of O2- to NO approached equimolar, then decreased precipitously as O2- exceeded NO. This pattern was also evident in DAF-loaded MCF-7 carcinoma cells and when stimulated macrophages were used as the NO source. Cyclic voltammetry analysis and inhibition studies by using the N2O3 scavenger azide indicated that DAN- and DAF-triazole could be derived from both oxidative nitrosylation (e.g., DAF radical + NO) and nitrosation (NO+ addition). The latter mechanism predominated with higher rates of NO formation relative to O2-. The effects of oxymyoglobin, superoxide dismutase, and carbon dioxide were examined as potential modulators of reactant availability for the O2- + NO pathway in vivo. The findings suggest that the outcome of NO biosynthesis in a scavenger milieu can be focused by O2- toward formation of NO adducts on nucleophilic residues (e.g., amines, thiols, hydroxyl) through convergent mechanisms involving the intermediacy of nitrogen dioxide. These modifications may be favored in microenvironments where the rate of O2- production is temporally and spatially contemporaneous with nitric oxide synthase activity, but not in excess of NO generation.

Inhaled diazeniumdiolates (NONOates) as selective pulmonary vasodilators

Selective pulmonary vasodilators cause vasodilatation limited to the pulmonary vasculature, within well-ventilated lung regions. Selective pulmonary vasodilators ideally cause only a minimal effect on the systemic circulation and improve ventilation/perfusion matching. NONOates are a novel group of chemical compounds that spontaneously and continuously release nitric oxide under physiological conditions, over periods of up to 24 h. Inhaled NONOates retain the benefits of gaseous nitric oxide without many of its therapeutic disadvantages. This review focuses on the therapeutic potential of inhaled NONOates in pulmonary hypertension, other lung conditions associated with right ventricular dysfunction and in asthma. The potential toxicity of NONOates is also discussed.

Nitric oxide and cell signaling pathways in mitochondrial-dependent apoptosis

Nitric oxide, generated by endogenous nitric oxide synthases or nitric oxide donors, can promote or prevent apoptosis induced by diverse pro-apoptotic stimuli in cell culture models. Both mitochondrial-dependent and -independent apoptotic signaling pathways mediate this dichotomous cellular response to nitric oxide. The molecular mechanisms behind these effects are complex and involve a number of nitrogen oxide-related species that are more reactive than nitric oxide itself. The local cellular environment plays a dynamic role in determining the nature and concentration of these species. Important components of the microenvironment include: the cellular redox state, glutathione, transition metals and the presence of other oxygen- and nitrogen-centered radicals. In particular, redox-sensitive nitrosating species are favorably generated under physiological conditions and capable of modifying multiple cell signaling pathways through reversible S-nitrosation reactions. Cytochrome c release from mitochondria is an important mechanism for the activation of caspase-3 and the initiation of cell death in response to 'intrinsic' pro-apoptotic stimuli, including oxidative and nitrosative stress. In turn, caspases and mitogen associated protein kinases may modulate cytochrome c release through their effects on the Bcl-2 family of proteins. This review will focus on (i) the importance of the cellular environment in determining the fate of nitric oxide and (ii) the ability of S-nitrosation to regulate mitochondrial-dependent apoptosis at the level of mitochondrial bioenergetics, cytochrome c release, caspases, mitogen associated protein kinases, and the Bcl-2 family of proteins.

Nitric oxide reduces the palmitoylation of rat myelin proteolipid protein by an indirect mechanism

Brain slices from 20-day-old rats were incubated with [3H]palmitate for 2 hours in the absence or presence of the NO-donors S-nitroso-N-acetyl-penicillamine (SNAP), ethyl-2-[hydroxyimino]-5-nitro-3-hexeneamide (NOR-3), 4-phenyl-3-furoxan carbonitrile (PFC) and sodium nitroprusside (SNP). Each of these drugs reduced the incorporation of [3H]palmitate into myelin proteolipid protein (PLP) in a concentration-dependent manner, SNP being the most active. The effect of SNAP was prevented by the NO-scavenger PTIO (2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide). Furthermore, decayed-SNAP, sodium nitrite and N- nitrosopyrrolidine were inactive, suggesting that free NO and/or some of its direct oxidation products are the active molecular species. The amount of fatty acids bound to PLP and the rate of deacylation were unaffected by NO. Although NO diminished the number of thiols in brain and myelin proteins, with the formation of both nitrosothiols and disulfides, these changes did not parallel those in PLP acylation. In contrast, NO was effective at reducing the palmitoylation of brain and myelin lipids, and this effect along with that of PLP, was ascribed to a decrease in palmitoyl-CoA levels. The NO-induced reduction in acyl-CoA concentration was due to the decline in ATP levels, while the amount of [3H]palmitate incorporated into the tissue, the activity of palmitoyl-CoA ligase and palmitoyl-CoA hydrolase, and the concentration of CoASH were unaltered by the drugs. Experiments with endogenously-synthesized [18O]fatty acids confirmed that NO affects predominantly the ATP-dependent palmitoylation of PLP. In conclusion, the inhibitory action of NO on the fatty acylation of PLP is indirect and caused by energy depletion.

Nitric oxide and its decomposed derivatives decrease the binding of extracellular-superoxide dismutase to the endothelial cell surface

Extracellular-superoxide dismutase (EC-SOD) is bound to the vascular endothelial cell surface with an affinity for heparan sulfate proteoglycan. The binding of EC-SOD to the human umbilical vein endothelial cell (HUVEC) and bovine aortic endothelial cell surface proteoglycans was significantly decreased by the incubation with S-nitroso-N-acetyl-DL-penicillamine (SNAP) and +/- -N-[(E)-4-ethyl-2-[(Z)-hydroxyimino]-5-nitro-3-hexene-1-yl]-3-pyridine carboxamide (NOR4), potent nitric oxide (NO) donors. NO derived from lipopolysaccharide-stimulated J774 A-1 cells also decreased the binding of EC-SOD to HUVEC, and this decrease was blocked by N(G)-nitro-L-arginine, a nitric oxide synthase inhibitor. SNAP and NOR4 also decreased the binding of EC-SOD to immobilized heparin. Furthermore, the decomposed derivatives of NO donors and sodium nitrite decreased the binding of EC-SOD. These observations suggest that excess NO produced in the inflammatory conditions decreases the binding of EC-SOD to the vascular endothelial cell surface, which results in a loss of the ability to protect the endothelial cell surface from oxidative stress.

Distinction between nitrosating mechanisms within human cells and aqueous solution

The quintessential nitrosating species produced during NO autoxidation is N(2)O(3). Nitrosation of amine, thiol, and hydroxyl residues can modulate critical cell functions. The biological mechanisms that control reactivity of nitrogen oxide species formed during autoxidation of nano- to micromolar levels of NO were examined using the synthetic donor NaEt(2)NN(O)NO (DEA/NO), human tumor cells, and 4,5-diaminofluorescein (DAF). Both the disappearance of NO and formation of nitrosated product from DAF in aerobic aqueous buffer followed second order processes; however, consumption of NO and nitrosation within intact cells were exponential. An optimal ratio of DEA/NO and 2-phenyl-4,4,5,5-tetramethylimidazole-1-oxyl 3-oxide (PTIO) was used to form N(2)O(3) through the intermediacy of NO(2). This route was found to be most reflective of the nitrosative mechanism within intact cells and was distinct from the process that occurred during autoxidation of NO in aqueous media. Manipulation of the endogenous scavengers ascorbate and glutathione indicated that the location, affinity, and concentration of these substances were key determinants in dictating nitrosative susceptibility of molecular targets. Taken together, these findings suggest that the functional effects of nitrosation may be organized to occur within discrete domains or compartments. Nitrosative stress may develop when scavengers are depleted and this architecture becomes compromised. Although NO(2) was not a component of aqueous NO autoxidation, the results suggest that the intermediacy of this species may be a significant factor in the advent of either nitrosation or oxidation chemistry in biological systems.

Role of nitric oxide synthase in the light-induced development of sporangiophores in Phycomyces blakesleeanus

Blue light controls the development of sporangiophores in the zygomycete Phycomyces blakesleeanus Burgeff. Light represses the production of microsporangiophores and enhances the development of macrosporangiophores. Inhibition of the biosynthesis of tetrahydrobiopterin, a cofactor of NO synthase, inhibits this photomorphogenesis. Light induces production of citrulline from arginine in the mycelium and in sporangiophores. The citrulline-forming activity is dependent on NADPH, independent of calcium, and inhibited by NO synthase inhibitors. It is reduced in tetrahydrobiopterin-depleted mycelium. Light induces emission of NO from the developing fungus in the same order of magnitude as citrulline formation from arginine. The NO donor sodium nitroprusside can replace the light effect on sporangiophore development, and inhibitors of NO synthase repress it. We suggest that a fungal NO synthase is involved in sporangiophore development and propose its participation in light signaling.

Nitric oxide disrupts H2O2-dependent activation of nuclear factor kappa B. Role in sensitization of human tumor cells to tumor necrosis factor-alpha -induced cytotoxicity

Tumor necrosis factor alpha (TNF-alpha) exerts its effect by two distinct signaling pathways. It can trigger cytotoxicity in sensitive target cells. TNF-alpha can also promote nuclear factor kappaB (NF-kappaB) activity and regulate the expression of genes that interfere with apoptosis and thus conferring resistance to several apoptotic stimuli. We have observed that interferon-gamma (IFN-gamma) sensitizes human ovarian carcinoma cell lines to TNF-alpha-mediated apoptosis and further, IFN-gamma induces the expression of the inducible nitric-oxide synthase (iNOS) and the generation of nitric oxide (NO). This study examines the role of NO in the sensitization of the ovarian carcinoma cell line AD10 to TNF-alpha-mediated cytotoxicity. Treatment of AD10 cells with the NOS inhibitor l-NMA blocked the IFN-gamma-dependent sensitization whereas NO donors (S-nitroso-N-acetylpenicillamine) sensitized these cells to TNF-alpha cytotoxicity. Analysis of the activation status of NF-kappaB upon treatment with NO donors confirmed the inhibitory role of NO on both the NF-kappaB DNA-binding property and its activation. Moreover, the inhibition of NF-kappaB nuclear translocation by NO donors directly correlated with the intracellular concentration of H(2)O(2) and was reversed by the addition of exogenous H(2)O(2). These findings show that NO might interfere with TNF-alpha-dependent NF-kappaB activation by interacting with O(2) and reducing the generation of H(2)O(2), a potent NF-kappaB activator. Therefore, NO-mediated disruption of NF-kappaB activation results in the removal of anti-apoptotic/resistance signals and sensitizes tumor cells to cytotoxic cytokines like TNF-alpha.

Differential expression of nitric oxide by dermal microvascular endothelial cells from patients with scleroderma

Vascular abnormalities in scleroderma are fundamental to the pathogenesis of this disease. The objective of this study was to characterize dermal microvascular endothelial cells (DMEC) isolated from scleroderma patients with respect to growth and expression of the constitutive form of endothelial nitric oxide synthase (eNOS). DMEC from patients with both systemic sclerosis (SSc) and localized scleroderma (Loc Scl) contained small intact microvascular structures in contrast to single cell isolations obtained from control skin. Immunoaffinity selection on anti-PECAM-1 beads yielded pure populations of DMEC expressing normal markers. While the morphology and initial growth of SSc DMEC closely paralleled control cells, the growth of SSc DMEC decreased with time in culture (doubling time of 3 days vs. 5 days). Expression of ecNOS mRNA was reduced in both Loc Scl and SSc as shown by semi-quantitative RT-PCR (p < 0.001). Western blots showed variable but generally lower ecNOS protein levels and decreased levels of nitrogen oxides in media were found from both SSc and Loc Scl relative to control cells. The results indicate an intrinsic defect in the mechanism of nitric oxide production in DMEC isolated from scleroderma patients and suggest its possible involvement in the pathophysiology of scleroderma.

Is ceruloplasmin an important catalyst for S-nitrosothiol generation in hypercholesterolemia?

Nitric oxide (NO) reacts with thiol-containing biomolecules to form S-nitrosothiols (RSNOs). RSNOs are considered as NO reservoirs as they generate NO by homolytic cleavage. Ceruloplasmin has recently been suggested to have a potent catalytic activity towards RSNO production. Considering that NO activity is impaired in hypercholesterolemia and that RSNOs may act as important NO donors, we investigated the relation between concentrations of ceruloplasmin and RSNOs in plasma of hypercholesterolemic (HC) patients compared to normolipidemic (N) controls. Concentrations of ceruloplasmin (0.36 +/- 0.07 x 0.49 +/- 0.11 mg/dl, N x HC), nitrate (19.10 +/- 12.03 x 40.19 +/- 18.70 microM, N x HC), RSNOs (0.25 +/- 0.20 x 0.54 +/- 0.26 microM, N x HC), nitrated LDL (19.51 +/- 6.98 x 35.29 +/- 17.57 nM nitro-BSA equivalents, N x HC), and cholesteryl ester-derived hydroxy/hydroperoxides (CEOOH, 0.19 +/- 0.06 x 1.46 +/- 0.97 microM) were increased in plasma of HC as compared to N. No difference was found for nitrite levels between the two groups (1.01 +/- 0.53 x 1.02 +/- 0.33 microM, N x HC). The concentrations of RSNOs, nitrate, and nitrated LDL were positively correlated to those of total cholesterol, LDL cholesterol, and apoB. Ceruloplasmin levels were directly correlated to apoB and apoE concentrations. Data suggest that: (i) ceruloplasmin may have a role in the enhancement of RSNOs found in hypercholesterolemia; (ii) the lower NO bioactivity associated with hypercholesterolemia is not related to a RSNOs paucity or a defective NO release from RSNOs; and (iii) the increased nitrotyrosine levels found in hypercholesterolemia indicate that superoxide radicals contribute to inactivation of NO, directly generated by NO synthase or originated by RSNO decomposition.

Nitrosative capacity of macrophages is dependent on nitric-oxide synthase induction signals

Nitrosative stress can occur when reactive nitric oxide (NO) species compromise the function of biomolecules via formation of NO adducts on critical amine and thiol residues. The capacity of inducible nitric-oxide synthase (iNOS) to generate nitrosative stress was investigated in the murine macrophage line ANA-1. Sequential activation with the cytokines IFN-gamma and either tumor necrosis factor-alpha or interleukin-1beta resulted in the induction of iNOS and production of nitrite (20 nM/min) but failed to elicit nitrosation of extracellular 2,3-diaminonapthalene. Stimulation with IFN-gamma and bacterial lipopolysaccharide increased the relative level of iNOS protein and nitrite production of ANA-1 cells 2-fold; however, a substantial level of NO in the media was also observed, and nitrosation of 2,3-diaminonapthalene was increased greater than 30-fold. Selective scavenger compounds suggested that the salient nitrosating mechanism was the NO/O(2) reaction leading to N(2)O(3) formation. These data mimicked the pattern observed with a 5 microM concentration of the synthetic NO donor (Z)-1-[N-ammoniopropyl)-N-(n-propyl)amino]diazen-1-ium -1,2-diolate (PAPA/NO). The NO profiles derived from iNOS can be distinct and depend on the inductive signal cascades. The diverse consequences of NO production in macrophages may reside in the cellular mechanisms that control the ability of iNOS to form N(2)O(3) and elicit nitrosative stress.

Nitric oxide modulates the activity of tobacco aconitase

Recent evidence suggests an important role for nitric oxide (NO) signaling in plant-pathogen interactions. Additional elucidation of the role of NO in plants will require identification of NO targets. Since aconitases are major NO targets in animals, we examined the effect of NO on tobacco (Nicotiana tabacum) aconitase. The tobacco aconitases, like their animal counterparts, were inhibited by NO donors. The cytosolic aconitase in animals, in addition to being a key redox and NO sensor, is converted by NO into an mRNA binding protein (IRP, or iron-regulatory protein) that regulates iron homeostasis. A tobacco cytosolic aconitase gene (NtACO1) whose deduced amino acid sequence shared 61% identity and 76% similarity with the human IRP-1 was cloned. Furthermore, residues involved in mRNA binding by IRP-1 were conserved in NtACO1. These results reveal additional similarities between the NO signaling mechanisms used by plants and animals.

Role of nitric oxide in cancer biology

The role of nitric oxide (NO) in tumorigenesis is multifactorial. NO can participate in the complicated process of carcinogenesis by mediating DNA damage in early phases of tumorigenesis, as well as support tumor progression through the induction of angiogenesis and suppression of the immune response. This paper addresses the effects of NO on transcriptional regulation following DNA damage and cyclooxygenase expression in the multistep process of tumorigenesis.

Formation of nitric oxide-derived oxidants by myeloperoxidase in monocytes: pathways for monocyte-mediated protein nitration and lipid peroxidation In vivo

Protein nitration and lipid peroxidation are implicated in the pathogenesis of atherosclerosis; however, neither the cellular mediators nor the reaction pathways for these events in vivo are established. In the present study, we examined the chemical pathways available to monocytes for generating reactive nitrogen species and explored their potential contribution to the protein nitration and lipid peroxidation of biological targets. Isolated human monocytes activated in media containing physiologically relevant levels of nitrite (NO(2)(-)), a major end product of nitric oxide ((*)NO) metabolism, nitrate apolipoprotein B-100 tyrosine residues and initiate LDL lipid peroxidation. LDL nitration (assessed by gas chromatography-mass spectrometry quantification of nitrotyrosine) and lipid peroxidation (assessed by high-performance liquid chromatography with online tandem mass spectrometric quantification of distinct products) required cell activation and NO(2)(-); occurred in the presence of metal chelators, superoxide dismutase (SOD), and scavengers of hypohalous acids; and was blocked by myeloperoxidase (MPO) inhibitors and catalase. Monocytes activated in the presence of the exogenous (*)NO generator PAPA NONOate (Z-[N-(3-aminopropyl)-N-(n-propyl)amino]diazen-1-ium-1,2- diolate) promoted LDL protein nitration and lipid peroxidation by a combination of pathways. At low rates of (*)NO flux, both protein nitration and lipid peroxidation were inhibited by catalase and peroxidase inhibitors but not SOD, suggesting a role for MPO. As rates of (*)NO flux increased, both nitrotyrosine formation and 9-hydroxy-10,12-octadecadienoate/9-hydroperoxy-10,12-octadecadieno ic acid production by monocytes became insensitive to the presence of catalase or peroxidase inhibitors, but they were increasingly inhibited by SOD and methionine, suggesting a role for peroxynitrite. Collectively, these results demonstrate that monocytes use distinct mechanisms for generating (*)NO-derived oxidants, and they identify MPO as a source of nitrating intermediates in monocytes.

Nitric oxide modulates beta(2)-adrenergic receptor palmitoylation and signaling

To determine whether nitric oxide (NO) modulates the beta-adrenergic signaling pathway, we treated cells expressing beta(2)-adrenergic receptors (beta(2)AR) with the NO donors, 3-morpholinosydnonimine (SIN-1) and 1,2,3,4-oxatriazolium, 5-amino-3-(3-chloro-2-methylphenyl)chloride and determined the intracellular production of cAMP after exposure to beta-adrenergic receptor agonists, cholera toxin and forskolin. NO significantly decreased the potency of the beta-adrenergic agonist, isoproterenol, to stimulate cAMP production without affecting the stimulatory action of forskolin and cholera toxin, which directly activate adenylyl cyclase and G(s), respectively. Treatment with the NO donor increased the guanyl nucleotide-sensitive high affinity constant for the agonist, isoproterenol, thus suggesting that it reduced functional coupling between the receptor and G(s). Stimulation of endogenous NO production by lipopolysaccharide in RAW 264.7 macrophages also caused a significant increase in the EC(50) for isoproterenol-stimulated cAMP production. SIN-1 treatment also led to a reduction in both basal and isoproterenol-stimulated incorporation of [(3)H]palmitate into the beta(2)AR. Signaling through the nonpalmitoylated, Gly(341)beta(2)AR mutant was unchanged by SIN-1 treatment. Given the link between beta(2)AR palmitoylation and its responsiveness to agonist, these results suggest that the primary action of NO was depalmitoylation of the beta(2)AR resulting in decreased signaling through the beta(2)AR.

Serum and urinary concentrations of heparan sulfate in patients with diabetic nephropathy

BACKGROUND

Heparan sulfate (HS) contributes to the negative charge in the glomerular basement membrane (GBM), which may maintain the GBM charge barrier. Changes in sulfation and/or the concentration of HS may be associated with the development of diabetic nephropathy.

METHODS

Using two different antibodies specific for HS chains, one that reacts with the N-sulfated sequences in HS chains (10E4) and the other that reacts with neo-epitope of HS, which occurs after heparitinase digestion of HS chains (3G10), we examined the serum and urinary concentrations of HS by enzyme-linked immunosorbent assay and performed immunohistochemical staining of glomeruli in diabetic patients with and without nephropathy.

RESULTS

The level of urinary excretion of 10E4 binding HS/creatinine clearance was significantly reduced in diabetic patients when compared with that in nondiabetic subjects (P < 0.0001), and the level was more decreased in patients with overt nephropathy than in patients without overt nephropathy. No differences or only small differences were found between these groups in serum and urinary 3G10-binding HS and in serum 10E4-binding HS. Immunohistochemical staining with these antibodies was consistent with the findings in the urine.

CONCLUSIONS

The results suggest that a decreased HS N-sulfation exists in the urine, which may reflect a structural change or an altered processing of HS within the GBM. Because N-sulfation plays a key role in determining the extent of sulfation within the HS chains, the decreased urinary 10E4-binding HS may have potential implications with regard to the development of diabetic nephropathy.

Guanylate cyclase and the .NO/cGMP signaling pathway

Signal transduction with the diatomic radical nitric oxide (NO) is involved in a number of important physiological processes, including smooth muscle relaxation and neurotransmission. Soluble guanylate cyclase (sGC), a heterodimeric enzyme that converts guanosine triphosphate to cyclic guanosine monophosphate, is a critical component of this signaling pathway. sGC is a hemoprotein; it is through the specific interaction of NO with the sGC heme that sGC is activated. Over the last decade, much has been learned about the unique heme environment of sGC and its interaction with ligands like NO and carbon monoxide. This review will focus on the role of sGC in signaling, its relationship to the other nucleotide cyclases, and on what is known about sGC genetics, heme environment and catalysis. The latest understanding in regard to sGC will be incorporated to build a model of sGC structure, activation, catalytic mechanism and deactivation.

Reversible and irreversible hemichrome generation by the oxygenation of nitrosylmyoglobin

The repeated oxygenation/reduction/nitrosylation of nitrosylmyoglobin produces low-spin ferric heme hemichromes which have been characterized by electron spin resonance spectroscopy. The predominant myoglobin hemichrome is a chemically reversible dihistidyl complex identified by the g values 1.53, 2.21, and 2.97. Also present is a low-spin ferric hydroxide derivative which is represented by the g values 1.83, 2.18, and 2.59. The formation of these species goes undetected by UV-vis spectroscopy, but the oxygenation of myoglobin to metmyoglobin is correlated with complete conversion of nitric oxide to nitrate which is released following a clear induction period. These results are interpreted in terms of the intermediates generated during the MbNO oxygenation reaction.

Nitric oxide products degrade chondroitin sulfates

Nitric oxide (NO) is a potent endogenous vasodilator that is elevated in response to inflammation. Inflammation also produces high levels of superoxide, which combines with NO to produce peroxynitrite (PN). We have previously reported that NO degrades heparin and heparan sulfate under acidic conditions and that PN degrades hyaluronan (HA) at neutral pH. Heparin and HA are glycosaminoglycans (GAGs) widely distributed in the extracellular matrix of tissues. Disruption of intestinal GAGs, particularly the chondroitin sulfates, were linked to inflammatory bowel diseases. Chondroitin sulfate A (CSA), chondroitin sulfate B (CSB), and chondroitin sulfate C (CSC) are constituents of the basement membranes of many tissues, including the intestine. The purpose of this study is to determine whether the NO donor S-nitroso-N-acetylpenicillamine (SNAP) and PN can degrade chondroitin sulfates in vitro. The NO donor SNAP (2 mM, pH 4.0) or PN (5 mM, pH 7.4) was incubated for at least 1 week at 37 degrees C with CSA, CSB, or CSC. Breakdown of CSA, CSB, and CSC was assessed by gel filtration chromatography and compared with untreated controls. Percentage degradation was calculated based on the change in peak height compared to the control. SNAP treatment partially degraded CSB and CSC, whereas PN partially degraded all three chondroitin sulfates. Nitric oxide mediated degradation of GAGs, and particularly chondroitin sulfates, may be an important pathway of inflammatory tissue damage.

Muscarinic cholinergic regulation of cardiac myocyte ICa-L is absent in mice with targeted disruption of endothelial nitric oxide synthase

Cardiac myocytes have been shown to express constitutively endothelial nitric oxide synthase (eNOS) (nitric oxide synthase 3), the activation of which has been implicated in the regulation of myocyte L-type voltage-sensitive calcium channel current (ICa-L) and myocyte contractile responsiveness to parasympathetic nervous system signaling, although this implication remains controversial. Therefore, we examined the effect of the muscarinic cholinergic agonist carbachol (CCh) on ICa-L and contractile amplitude in isoproterenol (ISO)-prestimulated ventricular myocytes isolated from adult mice, designated eNOSnull mice, with targeted disruption of the eNOS gene. Although both eNOSnull and wild-type (WT) ventricular myocytes exhibited similar increases in ICa-L in response to ISO, there was no measurable suppression of ICa-L by CCh in cells from eNOSnull mice, in contrast to cells from WT mice. These results were reflected in the absence of an effect of CCh on the positive inotropic effect of ISO in eNOSnull myocytes. Also, unlike myocytes from WT animals, eNOSnull myocytes failed to exhibit an increase in cGMP content in response to CCh. Nevertheless, the pharmacologic nitric oxide donors 3-morpholino-sydnonimine and S-nitroso-acetyl-cystein increased cGMP generation and suppressed ISO-augmented ICa-L in eNOSnull cells, suggesting that the signal transduction pathway(s) downstream of eNOS remained intact. Of importance, activation of the acetylcholine-activated K+ channel by CCh was unaffected in atrial and ventricular eNOSnull myocytes. These results confirm the obligatory role of eNOS in coupling muscarinic receptor activation to cGMP-dependent control of ICa-L in cardiac myocytes.

Biosynthesis and action of nitric oxide in mammalian cells

Nitric oxide (NO) can act as a vasorelaxant, a modulator of neurotransmission and a defence against pathogens. However, under certain conditions, NO can also have damaging effects to cells. Whether NO is useful or harmful depends on its chemical fate, and on the rate and location of its production. Here, we discuss progress in NO chemistry and the enzymology of NO synthases, and we will also attempt to explain its actions in the cardiovascular, nervous and immune systems.

Nitric oxide degradation of heparin and heparan sulphate

NO is a bioactive free radical produced by NO synthase in various tissues including vascular endothelium. One of the degradation products of NO is HNO2, an agent known to degrade heparin and heparan sulphate. This report documents degradation of heparin by cultured endothelial-cell-derived as well as exogenous NO. An exogenous narrow molecular-mass preparation of heparin was recovered from the medium of cultured endothelial cells using strong-anion exchange. In addition, another narrow molecular-mass preparation of heparin was gassed with exogenous NO under argon. Degradation was evaluated by gel-filtration chromatography. Since HNO2 degrades heparin under acidic conditions, the reaction with NO gas was studied under various pH conditions. The results show that the degradation of exogenous heparin by endothelial cells is inhibited by NO synthase inhibitors. Exogenous NO gas at concentrations as low as 400 p.p.m. degrades heparin and heparan sulphate. Exogenous NO degrades heparin at neutral as well as acidic pH. Endothelial-cell-derived NO, as well as exogenous NO gas, did not degrade hyaluronan, an unrelated glycosaminoglycan that resists HNO2 degradation. Peroxynitrite, a metabolic product of the reaction of NO with superoxide, is an agent that degrades hyaluronan; however, peroxynitrite did not degrade heparin. Thus endothelial-cell-derived NO is capable of degrading heparin and heparan sulphate via HNO2 rather than peroxynitrite. These observations may be relevant to various pathophysiological processes in which extracellular matrix is degraded, such as bone development, apoptosis, tissue damage from inflammatory responses and possible release of growth factors and cytokines.

Degradation of hyaluronan by peroxynitrite

Treatment of high-molecular-weight hyaluronan (HA) with peroxynitrite at neutral pH (ONOO-/ONOOH) results in altered mobility on agarose gel electrophoresis, as well as reduced limiting viscosity number. Both effects are consistent with a reduction in HA molecular weight. HA is protected from peroxynitrite attack to varying extents by addition of alternate target molecules. Thiourea is extremely effective as a protective agent, dimethyl sulfoxide is moderately effective, while sodium benzoate and mannitol are slightly effective. A similar pattern of protection is observed when HA is degraded by hydroxyl radical generated by a metal ion/hydrogen peroxide system. On the basis of these observations, peroxynitrite is proposed to have hydroxyl radical-like activity in degrading HA.