The chemical biology of nitric oxide: implications in cellular signaling

Redox control of protein-DNA interactions: from molecular mechanisms to significance in signal transduction, gene expression, and DNA replication

Protein-DNA interactions play a key role in the regulation of major cellular metabolic pathways, including gene expression, genome replication, and genomic stability. They are mediated through the interactions of regulatory proteins with their specific DNA-binding sites at promoters, enhancers, and replication origins in the genome. Redox signaling regulates these protein-DNA interactions using reactive oxygen species and reactive nitrogen species that interact with cysteine residues at target proteins and their regulators. This review describes the redox-mediated regulation of several master regulators of gene expression that control the induction and suppression of hundreds of genes in the genome, regulating multiple metabolic pathways, which are involved in cell growth, development, differentiation, and survival, as well as in the function of the immune system and cellular response to intracellular and extracellular stimuli. It also discusses the role of redox signaling in protein-DNA interactions that regulate DNA replication. Specificity of redox regulation is discussed, as well as the mechanisms providing several levels of redox-mediated regulation, from direct control of DNA-binding domains through the indirect control, mediated by release of negative regulators, regulation of redox-sensitive protein kinases, intracellular trafficking, and chromatin remodeling.

Part I. Development of a model system for studying nitric oxide in tumors: high nitric oxide-adapted head and neck squamous cell carcinoma cell lines

The free radical nitric oxide (NO) is over-expressed in many tumors, including head and neck squamous cell carcinomas (HNSCC); however, the role NO plays in tumor pathophysiology is still not well understood. We, herein, report the development of an in vitro model system which can be used to probe the role of NO in the carcinogenesis of HNSCC. Five HNSCC cell lines were adapted to a high NO (HNO) environment by gradually introducing increasing concentrations of DETA-NONOate, a nitrogen-based NO donor, to cell media. The adaptation process was carried out until a sufficiently high enough donor concentration was reached which enabled the HNO cells to survive and grow, but which was lethal to the original, unadapted ("parent") cells. The adapted HNO cells exhibited analogous morphology to the parent cells, but grew better than their corresponding parent cells in normal media, on soft agar, and in the presence of hydrogen peroxide, an oxygen-based free radical donor. These results indicate that the HNO cell lines are unique and possess biologically different properties than the parent cell lines from which they originated. The HNO/parent cell lines developed herein may be used as a model system to better understand the role NO plays in HNSCC carcinogenesis.

Low concentrations of nitric oxide delay the differentiation of embryonic stem cells and promote their survival

Nitric oxide (NO) is an intracellular messenger in several cell systems, but its contribution to embryonic stem cell (ESC) biology has not been characterized. Exposure of ESCs to low concentrations (2-20 μM) of the NO donor diethylenetriamine NO adduct confers protection from apoptosis elicited by leukaemia inhibitory factor (LIF) withdrawal. NO blocked caspase 3 activation, PARP degradation, downregulation of the pro-apoptotic genes Casp7, Casp9, Bax and Bak1 and upregulation of the anti-apoptotic genes Bcl-2 111, Bcl-2 and Birc6. These effects were also observed in cells overexpressing eNOS. Exposure of LIF-deprived mESCs to low NO prevented the loss of expression of self-renewal genes (Oct4, Nanog and Sox2) and the SSEA marker. Moreover, NO blocked the differentiation process promoted by the absence of LIF and bFGF in mouse and human ESCs. NO treatment decreased the expression of differentiation markers, such as Brachyury, Gata6 and Gata4. Constitutive overexpression of eNOS in cells exposed to LIF deprivation maintained the expression of self-renewal markers, whereas the differentiation genes were repressed. These effects were reversed by addition of the NOS inhibitor L-NMMA. Altogether, the data suggest that low NO has a role in the regulation of ESC differentiation by delaying the entry into differentiation, arresting the loss of self-renewal markers and promoting cell survival by inhibiting apoptosis.

Clinical Relevance of Nitric Oxide Metabolites and Nitrative Stress in Thrombotic Primary Antiphospholipid Syndrome

Objective.

To assess the role of nitrite (NO2−), nitrate (NO3−), and nitrative stress in thrombotic primary antiphospholipid syndrome (PAPS).

Methods.

We investigated 46 patients with PAPS: 21 asymptomatic but persistent carriers of antiphospholipid antibodies (PCaPL), 38 patients with inherited thrombophilia (IT), 33 patients with systemic lupus erythematosus (SLE), and 29 healthy controls (CTR). IgG anticardiolipin (aCL), IgG anti-beta2-glycoprotein I (anti-ß2-GPI), IgG anti-high density lipoprotein (aHDL), IgG anti-apolipoprotein A-I (aApoA-I), crude nitrotyrosine (NT) (an indicator of nitrative stress), and high sensitivity C-reactive protein (CRP) were measured by immunoassays. Plasma nitrite (NO2−), nitrate (NO3−), and total antioxidant capacity (TAC) were measured by colorimetric spectroscopic assays.

Results.

Average plasma NO2−was lower in PAPS, PCaPL, and IT (p < 0.0001); average NO3−was highest in SLE (p < 0.0001), whereas average NT was higher in PAPS and SLE (p = 0.01). In thrombotic PAPS, IgG aCL titer and number of vascular occlusions negatively predicted NO2−(p = 0.03 and p = 0.001, respectively), whereas arterial occlusions and smoking positively predicted NO3−(p = 0.05 and p = 0.005), and CRP positively predicted NT (p = 0.004). In the PCaPL group IgG aCL negatively predicted NO3−(p = 0.03). In the SLE group IgG aCL negatively predicted NO2−(p = 0.03) and NO3−(p = 0.02).

Conclusion.

PAPS is characterized by decreased NO2−in relation to type and number of vascular occlusions and to aPL titers. Nitrative stress and low grade inflammation are linked phenomena in PAPS and may have implications for thrombosis and atherosclerosis.

Dietary hyperglycemia, glycemic index and metabolic retinal diseases

The glycemic index (GI) indicates how fast blood glucose is raised after consuming a carbohydrate-containing food. Human metabolic studies indicate that GI is related to patho-physiological responses after meals. Compared with a low-GI meal, a high-GI meal is characterized with hyperglycemia during the early postprandial stage (0-2h) and a compensatory hyperlipidemia associated with counter-regulatory hormone responses during late postprandial stage (4-6h). Over the past three decades, several human health disorders have been related to GI. The strongest relationship suggests that consuming low-GI foods prevents diabetic complications. Diabetic retinopathy (DR) is a complication of diabetes. In this aspect, GI appears to be useful as a practical guideline to help diabetic people choose foods. Abundant epidemiological evidence also indicates positive associations between GI and risk for type 2 diabetes, cardiovascular disease, and more recently, age-related macular degeneration (AMD) in people without diabetes. Although data from randomized controlled intervention trials are scanty, these observations are strongly supported by evolving molecular mechanisms which explain the pathogenesis of hyperglycemia. This wide range of evidence implies that dietary hyperglycemia is etiologically related to human aging and diseases, including DR and AMD. In this context, these diseases can be considered as metabolic retinal diseases. Molecular theories that explain hyperglycemic pathogenesis involve a mitochondria-associated pathway and four glycolysis-associated pathways, including advanced glycation end products formation, protein kinase C activation, polyol pathway, and hexosamine pathway. While the four glycolysis-associated pathways appear to be universal for both normoxic and hypoxic conditions, the mitochondria-associated mechanism appears to be most relevant to the hyperglycemic, normoxic pathogenesis. For diseases that affect tissues with highly active metabolism and that frequently face challenge from low oxygen tension, such as retina in which metabolism is determined by both glucose and oxygen homeostases, these theories appear to be insufficient. Several lines of evidence indicate that the retina is particularly vulnerable when hypoxia coincides with hyperglycemia. We propose a novel hyperglycemic, hypoxia-inducible factor (HIF) pathway, to complement the current theories regarding hyperglycemic pathogenesis. HIF is a transcription complex that responds to decrease oxygen in the cellular environment. In addition to playing a significant role in the regulation of glucose metabolism, under hyperglycemia HIF has been shown to increase the expression of HIF-inducible genes, such as vascular endothelial growth factor (VEGF) leading to angiogenesis. To this extent, we suggest that HIF can also be described as a hyperglycemia-inducible factor. In summary, while management of dietary GI appears to be an effective intervention for the prevention of metabolic diseases, specifically AMD and DR, more interventional data is needed to evaluate the efficacy of GI management. There is an urgent need to develop reliable biomarkers of exposure, surrogate endpoints, as well as susceptibility for GI. These insights would also be helpful in deciphering the detailed hyperglycemia-related biochemical mechanisms for the development of new therapeutic agents.

Inorganic nitrite and chronic tissue ischaemia: a novel therapeutic modality for peripheral vascular diseases

Ischaemic tissue damage represents the ultimate form of tissue pathophysiology due to cardiovascular disease, which is the leading cause of morbidity and mortality across the globe. A significant amount of basic research and clinical investigation has been focused on identifying cellular and molecular pathways to alleviate tissue damage and dysfunction due to ischaemia and subsequent reperfusion. Over many years, the gaseous molecule nitric oxide (NO) has emerged as an important regulator of cardiovascular health as well as protector against tissue ischaemia and reperfusion injury. However, clinical translation of NO therapy for these pathophysiological conditions has not been realized for various reasons. Work from our laboratory and several others suggests that a new form of NO-associated therapy may be possible through the use of nitrite anion (sodium nitrite), a prodrug which can be reduced to NO in ischaemic tissues. In this manner, nitrite anion serves as a highly selective NO donor in ischaemic tissues without substantially altering otherwise normal tissue. This surprising and novel discovery has reinvigorated hopes for effectively restoring NO bioavailability in vulnerable tissues while continuing to reveal the complexity of NO biology and metabolism within the cardiovascular system. However, some concerns may exist regarding the effect of nitrite on carcinogenesis. This review highlights the emergence of nitrite anion as a selective NO prodrug for ischaemic tissue disorders and discusses the potential therapeutic utility of this agent for peripheral vascular disease.

Hypoxia inducible factor-1α accumulation in steatotic liver preservation: Role of nitric oxide

AIM: To examine the relevance of hypoxia inducible factor (HIF-1) and nitric oxide (NO) on the preservation of fatty liver against cold ischemia-reperfusion injury (IRI).

METHODS: We used an isolated perfused rat liver model and we evaluated HIF-1α in steatotic and non-steatotic livers preserved for 24 h at 4°C in University of Wisconsin and IGL-1 solutions, and then subjected to 2 h of normothermic reperfusion. After normoxic reperfusion, liver enzymes, bile production, bromosulfophthalein clearance, as well as HIF-1α and NO [endothelial NO synthase (eNOS) activity and nitrites/nitrates] were also measured. Other factors associated with the higher susceptibility of steatotic livers to IRI, such as mitochondrial damage and vascular resistance were evaluated.

RESULTS: A significant increase in HIF-1α was found in steatotic and non-steatotic livers preserved in IGL-1 after cold storage. Livers preserved in IGL-1 showed a significant attenuation of liver injury and improvement in liver function parameters. These benefits were enhanced by the addition of trimetazidine (an anti-ischemic drug), which induces NO and eNOS activation, to IGL-1 solution. In normoxic reperfusion, the presence of NO favors HIF-1α accumulation, promoting also the activation of other cytoprotective genes, such as heme-oxygenase-1.

CONCLUSION: We found evidence for the role of the HIF-1α/NO system in fatty liver preservation, especially when IGL-1 solution is used.

Nitration of the tumor suppressor protein p53 at tyrosine 327 promotes p53 oligomerization and activation

Previous studies demonstrate that nitric oxide (NO) promotes p53 transcriptional activity by a classical DNA damage responsive mechanism involving activation of ATM/ATR and phosphorylation of p53. These studies intentionally used high doses of NO donors to achieve the maximum DNA damage. However, lower concentrations of NO donors also stimulate rapid and unequivocal nuclear retention of p53 but apparently do not require ATM/ATR-dependent p53 phosphorylation or total p53 protein accumulation. To identify possible mechanisms for p53 activation at low NO levels, the role of Tyr nitration in p53 activation was evaluated. Low concentrations of the NO donor, DETA NONOate (<200 microM), exclusively nitrate Tyr327 within the tetramerization domain promoting p53 oligomerization, nuclear accumulation, and increased DNA-binding activity without p53 Ser15 phosphorylation. Molecular modeling indicates that nitration of one Tyr327 stabilizes the dimer by about 2.67 kcal mol(-1). Significant quantitative and qualitative differences in the patterns of p53-target gene modulation by low (50 microM), non-DNA-damaging and high (500 microM), DNA-damaging NO donor concentrations were shown. These results demonstrate a new posttranslational mechanism for modulating p53 transcriptional activity responsive to low NO concentrations and independent of DNA damage signaling.

Regulatory effects of nitric oxide on Src kinase, FAK, p130Cas, and receptor protein tyrosine phosphatase alpha (PTP-alpha): a role for the cellular redox environment

The role of NO in regulating the focal adhesion proteins, Src, FAK, p130 Cas, and PTP-alpha, was investigated. Fibroblasts expressing PTP-alpha (PTP-alpha(WT) cells), fibroblasts "knockout" for PTP-alpha (PTP-alpha(-/-) cells), and "rescued" "knockout" fibroblasts (PTP-alpha A5/3 cells) were stimulated with either S-nitroso-N-acetylpenicillamine (SNAP) or fetal bovine serum (FBS). FBS increased inducible NO synthase in both cell lines. Activation of Src mediated either by SNAP or by FBS occurred independent of dephosphorylation of Tyr527 in PTP-alpha(-/-) cells. Both stimuli promoted dephosphorylation of Tyr527 and activation of Src kinase in PTP-alpha(WT) cells. NO-mediated activation of Src kinase affected the activities of FAK and p130Cas and was dependent on the expression of PTP-alpha. Analogous to tyrosine phosphorylation, SNAP and FBS stimulated differential generation of NO and S-nitrosylation of Src kinase in both cell lines. Incubation with SNAP resulted in higher levels of NO and S-nitrosylation of immunoprecipitated Src in PTP-alpha(-/-) cells (oxidizing redox environment) as compared with the levels of NO and S-nitrosylated Src in PTP-alpha(WT) cells (reducing redox environment). SNAP differentially stimulated cell proliferation of both cell lines is dependent on the intracellular redox environment, Src activity, and PTP-alpha expression. This dependence also is observed with FBS-stimulated cell migration.

Development of nitrosyl ruthenium complex-loaded lipid carriers for topical administration: improvement in skin stability and in nitric oxide release by visible light irradiation

The prominent nitric oxide (NO) donor [Ru(terpy)(bdqi)NO](PF(6))(3) has been synthesized and evaluated with respect to noteworthy biological effects due to its NO photorelease, including vascular relaxation and melanoma cell culture toxicity. The potential for delivering NO in therapeutic quantities is tenable since the nitrosyl ruthenium complex (NRC) must first reach the "target tissue" and then release the NO upon stimulus. In this context, NRC-loaded lipid carriers were developed and characterized to further explore its topical administration for applications such as skin cancer treatment. NRC-loaded solid lipid nanoparticles (SLN) and nanostructured lipid carriers were prepared via the microemulsification method, with average diameters of 275+/-15 nm and 211+/-31 nm and zeta potentials of -40.7+/-10.4 mV and -50.0+/-7.5 mV, respectively. In vitro kinetic studies of NRC release from nanoparticles showed sustained release of NRC from the lipid carriers and illustrated the influence of the release medium and the lyophilization process. Stability studies showed that NO is released from NRC as a function of temperature and time and due to skin contact. The encapsulation of NRC in SLN followed by its lyophilization, significantly improved the complex stability. Furthermore, of particular interest was the fact that in the NO photorelease study, the NO release from the NRC-loaded SLN was approximately twice that of just NRC in solution. NRC-loaded SLN performs well enough at releasing and protecting NO degradation in vitro that it is a promising carrier for topical delivery of NO.

New insights into fatty liver preservation using Institute Georges Lopez preservation solution

Institute Georges Lopez preservation solution (IGL-1) has been demonstrated to be useful for fatty liver preservation. The mechanisms responsible for this effective graft protection against ischemia-reperfusion injury are pivotal actions on generation of nitric oxide a diffusible molecule with vasodilator properties, that facilitates the up-regulation of other well-known cytoprotective genes, such as hypoxia-inducible factor-1 alpha (HIF-1alpha) and heme-oxygenase 1 (HO-1). During normoxic reperfusion, the presence of nitric oxide permits HIF-1alpha accumulation to inhibit prolyl-hydoxylases, thus promoting an additional overexpression of the HO-1 in steatotic and nonsteatotic graft livers preserved in IGL-1.

Efeito da inibição da óxido nítrico sintase induzível na capacitação in vitro de espermatozoides bovinos

Avaliaram-se o papel do óxido nítrico (NO) por meio da inibição da enzima óxido nítrico sintase induzível (iNOS), após a adição da aminoguanidina (AG), na motilidade, no vigor e na integridade da membrana plasmática nos tempos de 15, 60, 120, 180, 240 e 300min e a atividade mitocondrial e a capacitação de espermatozoides bovinos após 300min de cultivo. Adicionaram-se diferentes concentrações (0,001, 0,01 e 0,1M) de AG durante a capacitação induzida pela heparina e 500μM de nitroprussiato de sódio (SNP, doador de NO) à concentração deletéria. A adição de 0,1M de AG diminuiu a motilidade e o vigor espermático e a integridade da membrana (P<0,05). A adição de SNP ao meio de cultivo com 0,1M de AG somente reverteu a integridade da membrana após 300min. A inibição da síntese de NO pela adição de AG não alterou a atividade mitocondrial. A percentagem de oócitos penetrados com espermatozoides tratados com 0,01 e 0,1M de AG diminuiu 20,3 e 100%, respectivamente, em relação aos não tratados (controle) (P<0,05), contudo houve aumento de 15% na percentagem de oócitos desnudados penetrados com espermatozoides capacitados em presença de 0,1M de AG. Conclui-se que a inibição da síntese de NO pela AG diminuiu a qualidade espermática durante a capacitação de espermatozoides bovinos in vitro, exceto a atividade mitocondrial. Somente a integridade da membrana foi revertida após adição de NO, sugerindo diferentes vias de ação do NO na qualidade espermática ao longo da capacitação in vitro de espermatozoides bovinos.

Myocardial fibrosis is unaltered by long-term administration of L-arginine in dystrophin deficient mdx mice: a histomorphometric analysis

Cardiac failure secondary to myocardial fibrosis (MF) significantly contributes to death in Duchenne muscular dystrophy (DMD), a fatal form of muscle disease. In aging, the mdx mice, an animal model of DMD, MF is similar to that observed in humans. Nitric oxide-based therapy has been proposed to retard MF in DMD and a candidate is L-arginine (L-arg). In this study we evaluated the effects of long-term therapy with L-arg in the MF of mdx mice. mdx mice (6 months old) were treated with L-arg in drinking water. Control mdx mice received water only. After 15 months of treatment, hearts were stained with Masson's trichrome for analysis of MF and with hematoxilyn and eosin for analysis of inflammation and cardiomyocyte damage. We observed that MF was not affected (29.5 +/- 2.5% of MF area for control vs 31.4 +/- 2% for L-arginine-treated animals; P > 0.05). The density of inflammatory cells was reduced (169 +/- 12 cells/mm 2 in control vs 102 +/- 9 cells/mm 2 in L-arg-treated; P < 0.05). The present study shows that long-term administration of L-arg is not effective in retarding MF in mdx dystrophinopathy.

Growth hormone releasing hormone induces the expression of nitric oxide synthase

Growth hormone releasing hormone (GHRH) and its receptors are expressed in a wide variety of human tumours and established cancer cell lines and are involved in carcinogenesis. In addition, GHRH antagonists exert an antitumour activity in experimental cancer models. Recent studies indicate that the mechanisms involved in the mediation of the effects of GHRH include the regulation of the metabolism of the reactive oxygen species. This work demonstrates the expression of GHRH receptors and GHRH in the A549 human lung cancer cell line and shows that the mitogenic effect of GHRH in these cells is dependent on the activation of the extracellular receptor kinase (ERK)1/2 pathway. The action of GHRH can be suppressed by GHRH antagonist MZ-5-156 and mitogen activated protein kinase (MAPK) inhibitor PD 098059. These results are reflected in the effect in the proliferating cell nuclear antigen. In addition, our study shows that GHRH increases the expression of the inducible nitric oxide synthase, an enzyme which is strongly involved in various human diseases, including cancer and augments key intracellular regulators of its expression, such as pNF (nuclear factor)κBp50 and cyclooxygenase 2. GHRH antagonist MZ-5-156 counteracts the effects of GHRH in these studies, indicating that this class of peptide antagonists may be useful for the treatment of diseases related to increased oxidative and nitrosative stress.

Long-term adaptation of breast tumor cell lines to high concentrations of nitric oxide

Nitric oxide (NO), a free radical, has been implicated in the biology of human cancers, including breast cancer, yet it is still unclear how NO affects tumor development and propagation. We herein gradually adapted four human breast adenocarcinoma cell lines (BT-20, Hs578T, T-47D, and MCF-7) to increasing concentrations of the NO donor DETA-NONOate up to 600 muM. The resulting model system consisted of a set of fully adapted high nitric oxide ("HNO") cell lines that are biologically different from the "parent" cell lines from which they originated. Although each of the four parent and HNO cell lines had identical morphologic appearance, the HNO cells grew faster than their corresponding parent cells and were resistant to both nitrogen- and oxygen-based free radicals. These cell lines serve as a novel tool to study the role of NO in breast cancer progression and potentially can be used to predict the therapeutic response leading to more efficient therapeutic regimens.

Oxidative metabolism, ROS and NO under oxygen deprivation

Oxygen deprivation, in line with other stress conditions, is accompanied by reactive oxygen (ROS) and nitrogen species (RNS) formation and is characterised by a set of metabolic changes collectively named as the 'oxidative stress response'. The controversial induction of oxidative metabolism under the lack of oxygen is necessitated by ROS and RNS signaling in the induction of adaptive responses, and inevitably results in oxidative damage. To prevent detrimental effects of oxidative stress, the levels of ROS and NO are tightly controlled on transcriptional, translational and metabolic levels. Hypoxia triggers the induction of genes responsible for ROS and NO handling and utilization (respiratory burst oxidase, non-symbiotic hemoglobins, several cytochromes P450, mitochondrial dehydrogenases, and antioxidant-related transcripts). The level of oxygen in the tissue is also under metabolic control via multiple mechanisms: Regulation of glycolytic and fermentation pathways to manage pyruvate availability for respiration, and adjustment of mitochondrial electron flow through NO and ROS balance. Both adaptive strategies are controlled by energy status and aim to decrease the respiratory capacity and to postpone complete anoxia. Besides local oxygen concentration, ROS and RNS formation is controlled by an array of antioxidants. Hypoxic treatment leads to the upregulation of multiple transcripts associated with ascorbate, glutathione and thioredoxin metabolism. The production of ROS and NO is an integral part of the response to oxygen deprivation which encompasses several levels of metabolic regulation to sustain redox signaling and to prevent oxidative damage.

Electrochemical nitric oxide sensors for physiological measurements

The important biological roles of nitric oxide (NO) have prompted the development of analytical techniques capable of sensitive and selective detection of NO. Electrochemical sensing, more than any other NO detection method, embodies the parameters necessary for quantifying NO in challenging physiological environments such as blood and the brain. In this tutorial review, we provide a broad overview of the field of electrochemical NO sensors, including design, fabrication, and analytical performance characteristics. Both electrochemical sensors and biological applications are detailed.

Hemoglobin encapsulation in vesicles retards NO and CO binding and O2 release when perfused through narrow gas-permeable tubes

Intravenous administration of cell-free Hb induces vasoconstriction and circulatory disorders, presumably because of the intrinsic affinities to endogenous nitric oxide (NO) and carbon monoxide (CO) as vasorelaxation factors and because of the facilitated O2 release that might induce autoregulatory vasoconstriction. We examined these gas reactions when Hb-containing solutions of four kinds were perfused through artificial narrow tubes at a practical Hb concentration (10 g/dl). Purified Hb solution, polymerized bovine Hb (PolyBHb), encapsulated Hb [Hb-vesicles (HbV), 279 nm], and red blood cells (RBCs) were perfused through a gas-permeable narrow tube (25 μm inner diameter) at 1 mm/s centerline velocity. The level of reactions was determined microscopically based on the visible-light absorption spectrum of Hb. When the tube was immersed in NO and CO atmospheres, both NO binding and CO binding of deoxygenated Hb (deoxy-Hb) and PolyBHb in the tube was faster than those of HbV and RBCs, and HbV and RBCs showed almost identical binding rates. When the tube was immersed in a N2 atmosphere, oxygenated Hb and PolyBHb showed much faster O2 release than did HbV and RBCs. PolyBHb showed a faster reaction than Hb because of the lower O2 affinity of PolyBHb than Hb. The diffusion process of the particles was simulated using Navier-Stokes and Maxwell-Stefan equations. Results clarified that small Hb (6 nm) diffuses laterally and mixes rapidly. However, the large-dimension HbV shows no such rapid diffusion. The purely physicochemical differences in diffusivity of the particles and the resulting reactivity with gas molecules are one factor inducing biological vasoconstriction of Hb-based oxygen carriers.

The biology of reactive intermediates in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is an autoimmune syndrome marked by autoantibody production. Innate immunity is essential to transform humoral autoimmunity into the clinical lupus phenotype. Nitric oxide (NO) is a membrane- permeable signaling molecule involved in a broad array of biologic processes through its ability to modify proteins, lipids, and DNA and alter their function and immunogenicity. The literature regarding mechanisms through which NO regulates inflammation and cell survival is filled with contradictory findings. However, the effects of NO on cellular processes depend on its concentration and its interaction with reactive oxygen. Understanding this interaction will be essential to determine mechanisms through which reactive intermediates induce cellular autoimmunity and contribute to a sustained innate immune response and organ damage in SLE.

FoxO3a governs early microglial proliferation and employs mitochondrial depolarization with caspase 3, 8, and 9 cleavage during oxidant induced apoptosis

Microglia of the central nervous system have a dual role in the ability to influence the survival of neighboring cells. During inflammatory cell activation, microglia can lead to the disposal of toxic cellular products and permit tissue regeneration, but microglia also may lead to cellular destruction with phagocytic removal. For these reasons, it is essential to elucidate not only the underlying pathways that control microglial activation and proliferation, but also the factors that determine microglial survival. In this regard, we investigated in the EOC 2 microglial cell line with an oxygen-glucose deprivation (OGD) injury model of oxidative stress the role of the "O" class forkhead transcription factor FoxO3a that in some scenarios is closely linked to immune system function. We demonstrate that FoxO3a is a necessary element in the control of early and late apoptotic injury programs that involve membrane phosphatidylserine externalization and nuclear DNA degradation, since transient knockdown of FoxO3a in microglia preserves cellular survival 24 hours following OGD exposure. However, prior to the onset of apoptotic injury, FoxO3a facilitates the activation and proliferation of microglia as early as 3 hours following OGD exposure that occurs in conjunction with the trafficking of the unphosphorylated and active post-translational form of FoxO3a from the cytoplasm to the cell nucleus. FoxO3a also can modulate apoptotic mitochondrial signal transduction pathways in microglia, since transient knockdown of FoxO3a prevents mitochondrial membrane depolarization as well as the release of cytochrome c during OGD. Control of this apoptotic cascade also extends to progressive caspase activation as early as 1 hour following OGD exposure. The presence of FoxO3a is necessary for the expression of cleaved (active) caspase 3, 8, and 9, since loss of FoxO3a abrogates the induction of caspase activity. Interestingly, elimination of FoxO3a reduced caspase 9 activity to a lesser extent than that noted with caspase 3 and 8 activities, suggesting that FoxO3a in relation to caspase 9 may be more reliant upon other signal transduction pathways potentially independent from caspase 3 and 8.

Differential effects of reactive nitrogen species on DNA base excision repair initiated by the alkyladenine DNA glycosylase

Chronic generation of reactive nitrogen species (RNS) can cause DNA damage and may also directly modify DNA repair proteins. RNS-modified DNA is repaired predominantly by the base excision repair (BER) pathway, which includes the alkyladenine DNA glycosylase (AAG). The AAG active site contains several tyrosines and cysteines that are potential sites for modification by RNS. In vitro, we demonstrate that RNS differentially alter AAG activity depending on the site and type of modification. Nitration of tyrosine 162 impaired 1,N(6)-ethenoadenine (epsilonA)-excision activity, whereas nitrosation of cysteine 167 increased epsilonA excision. To understand the effects of RNS on BER in vivo, we examined intestinal adenomas for levels of inducible nitric oxide synthase (iNOS) and AAG. A striking correlation between AAG and iNOS expression was observed (r = 0.76, P = 0.00002). Interestingly, there was no correlation between changes in AAG levels and enzymatic activity. We found AAG to be nitrated in human adenomas, suggesting that this RNS modification is relevant in the human disease. Expression of key downstream components of BER, apurinic/apyrimidinic endonuclease 1 (APE1) and DNA polymerase beta (POLbeta), was also examined. POLbeta protein was increased in nearly all adenomas compared with adjacent non-tumor tissues, whereas APE1 expression was only increased in approximately half of the adenomas and also was relocalized to the cytoplasm in adenomas. Collectively, the results suggest that BER is dysregulated in colon adenomas. RNS-induced posttranslational modification of AAG is one mechanism of BER dysregulation, and the type of modification may define the role of AAG during carcinogenesis.

B1 cells produce nitric oxide in response to a series of toll-like receptor ligands

The effect of a series of toll-like receptor (TLR) ligands on the production of nitric oxide (NO) in mouse B1 cells was examined by using CD5(+) IgM(+) WEHI 231 cells. The stimulation with a series of TLR ligands, which were Pam3Csk4 for TLR1/2, poly I:C for TLR3, lipopolysaccharide (LPS) for TLR4, imiquimod for TLR7 and CpG DNA for TLR9, resulted in enhanced NO production via augmented expression of an inducible type of NO synthase (iNOS). LPS was most potent for the enhancement of NO production, followed by poly I:C and Pam3Csk4. Imiquimod and CpG DNA led to slight NO production. The LPS-induced NO production was dependent on MyD88-dependent pathway consisting of nuclear factor (NF)-kappaB and a series of mitogen-activated protein kinases (MAPKs). Further, it was also dependent on the MyD88-independent pathway consisting of toll-IL-1R domain-containing adaptor-inducing IFN-beta (TRIF) and interferon regulatory factor (IRF)-3. Physiologic peritoneal B1 cells also produced NO via the iNOS expression in response to LPS. The immunological significance of TLR ligands-induced NO production in B1 cells is discussed.

Heterogeneity of microglial activation in the innate immune response in the brain

The immune response in the brain has been widely investigated and while many studies have focused on the proinflammatory cytotoxic response, the brain's innate immune system demonstrates significant heterogeneity. Microglia, like other tissue macrophages, participate in repair and resolution processes after infection or injury to restore normal tissue homeostasis. This review examines the mechanisms that lead to reduction of self-toxicity and to repair and restructuring of the damaged extracellular matrix in the brain. Part of the resolution process involves switching macrophage functional activation to include reduction of proinflammatory mediators, increased production and release of anti-inflammatory cytokines, and production of cytoactive factors involved in repair and reconstruction of the damaged brain. Two partially overlapping and complimentary functional macrophage states have been identified and are called alternative activation and acquired deactivation. The immunosuppressive and repair processes of each of these states and how alternative activation and acquired deactivation participate in chronic neuroinflammation in the brain are discussed.

Thrombospondin-1/CD47 blockade following ischemia-reperfusion injury is tissue protective

BACKGROUND

Nitric oxide has prosurvival effects that can limit ischemia-reperfusion injuries. However, the matrix glycoprotein thrombospondin-1 is induced following ischemia-reperfusion injury and limits nitric oxide signaling by engaging its cell surface receptor CD47. In this article, the authors examine whether postinjury blocking of this inhibitory signal can protect from ischemia-reperfusion injury in a rat flap model.

METHODS

A total of 40 tissue flaps were created in rats based solely on the deep inferior epigastric vessels. Microvascular clamps were used to create 45 minutes of ischemia time to the flaps. The flaps were then treated using a monoclonal antibody to CD47 or an isotype-matched control immunoglobulin G1 5 or 30 minutes after clamp removal. Twenty-four or 72 hours postoperatively, the necrotic area of the flap was determined, and serum, deep inferior epigastric vessels, and flaps were harvested for analysis from five rats in each respective group.

RESULTS

Treatment with a CD47 antibody 5 minutes after reperfusion significantly reduces flap necrosis compared with immunoglobulin G1 control (9 percent versus 43 percent; p < 0.01). The protective effect is even more dramatic when treatment is delayed until 30 minutes after reperfusion (10 percent versus 88 percent for control; p < 0.01). Markers of neutrophil and endothelial cell activation along with total leukocytes are reduced in CD47 antibody-treated flaps, as are tissue malondialdehyde levels. Levels of cyclic guanosine monophosphate are elevated 72 hours postoperatively in the CD47 antibody-treated deep inferior epigastric vessels versus the control flaps.

CONCLUSIONS

Therapies targeting the thrombospondin-1 receptor CD47 offer potential for increasing tissue survival in ischemia-reperfusion injuries. The ability to protect when given after ischemia-reperfusion injury enables a broader clinical applicability.

Formation of nitric oxide from nitrite by the ferriheme b protein nitrophorin 7

Recently, the conversion of nitrite into NO by certain heme proteins, in particular hemoglobin, gained much interest as a physiologically important source of NO in human tissue. However, in an aqueous environment, nitrite reduction at an iron porphyrin occurs either through oxidation of ferroheme to ferriheme or with the assistance of a second substrate molecule. Here we report on the reduction of nitrite in the absence of a second substrate at the heme center of the ferriheme protein nitrophorin 7 (NP7) resulting in the formation of NO and restoration of the ferriheme center. The product was spectroscopically characterized, in particular by resonance Raman and FT-IR spectroscopy. Performing the reaction in the presence of the NO trap 2-(4-trimethylammonio)phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl 3-oxide (TMA-PTIO) revealed that continuous NO production is possible, i.e., that NP7 is fully restored upon a single turnover. Thus, NP7 is the first case of a b-type heme that performs reduction of nitrite as a single substrate out of the iron(III) state.

Resveratrol: its biologic targets and functional activity

The polyphenolic phytoalexin resveratrol (RSV) and its analogues have received tremendous attention over the past couple of decades because of a number of reports highlighting their benefits in vitro and in vivo in a variety of human disease models, including cardio- and neuroprotection, immune regulation, and cancer chemoprevention. These studies have underscored the high degree of diversity in terms of the signaling networks and cellular effector mechanisms that are affected by RSV. The activity of RSV has been linked to cell-surface receptors, membrane signaling pathways, intracellular signal-transduction machinery, nuclear receptors, gene transcription, and metabolic pathways. The promise shown by RSV has prompted heightened interest in studies aimed at translating these observations to clinical settings. In this review, we present a comprehensive account of the basic chemistry of RSV, its bioavailability, and its multiple intracellular target proteins and signaling pathways.

Activity-dependent regulation of synapses by retrograde messengers

Throughout the brain, postsynaptic neurons release substances from their cell bodies and dendrites that regulate the strength of the synapses they receive. Diverse chemical messengers have been implicated in retrograde signaling from postsynaptic neurons to presynaptic boutons. Here, we provide an overview of the signaling systems that lead to rapid changes in synaptic strength. We consider the capabilities, specializations, and physiological roles of each type of signaling system.

Molecular hydrogen suppresses FcepsilonRI-mediated signal transduction and prevents degranulation of mast cells

Molecular hydrogen ameliorates oxidative stress-associated diseases in animal models. We found that oral intake of hydrogen-rich water abolishes an immediate-type allergic reaction in mice. Using rat RBL-2H3 mast cells, we demonstrated that hydrogen attenuates phosphorylation of the FcepsilonRI-associated Lyn and its downstream signal transduction, which subsequently inhibits the NADPH oxidase activity and reduces the generation of hydrogen peroxide. We also found that inhibition of NADPH oxidase attenuates phosphorylation of Lyn in mast cells, indicating the presence of a feed-forward loop that potentiates the allergic responses. Hydrogen accordingly inhibits all tested signaling molecule(s) in the loop. Hydrogen effects have been solely ascribed to exclusive removal of hydroxyl radical. In the immediate-type allergic reaction, hydrogen exerts its beneficial effect not by its radical scavenging activity but by modulating a specific signaling pathway. Effects of hydrogen in other diseases are possibly mediated by modulation of yet unidentified signaling pathways. Our studies also suggest that hydrogen is a gaseous signaling molecule like nitric oxide.

The vitamin nicotinamide: translating nutrition into clinical care

Nicotinamide, the amide form of vitamin B(3) (niacin), is changed to its mononucleotide compound with the enzyme nicotinic acide/nicotinamide adenylyltransferase, and participates in the cellular energy metabolism that directly impacts normal physiology. However, nicotinamide also influences oxidative stress and modulates multiple pathways tied to both cellular survival and death. During disorders that include immune system dysfunction, diabetes, and aging-related diseases, nicotinamide is a robust cytoprotectant that blocks cellular inflammatory cell activation, early apoptotic phosphatidylserine exposure, and late nuclear DNA degradation. Nicotinamide relies upon unique cellular pathways that involve forkhead transcription factors, sirtuins, protein kinase B (Akt), Bad, caspases, and poly (ADP-ribose) polymerase that may offer a fine line with determining cellular longevity, cell survival, and unwanted cancer progression. If one is cognizant of the these considerations, it becomes evident that nicotinamide holds great potential for multiple disease entities, but the development of new therapeutic strategies rests heavily upon the elucidation of the novel cellular pathways that nicotinamide closely governs.

Rapeseed protein in a high-fat mixed meal alleviates postprandial systemic and vascular oxidative stress and prevents vascular endothelial dysfunction in healthy rats

High-saturated fat and high-sucrose meals induce vascular endothelial dysfunction, the early hallmark of atherogenesis. The impact of dietary protein on vascular homeostasis remains misunderstood. In this study, we investigated whether rapeseed protein, an emergent arginine- and cysteine-rich protein, can acutely modulate the onset of adverse effects induced by a high-saturated fat meal (HFM). In a series of crossover experiments, healthy rats received 3 HFM (saturated fat: 60%; sucrose: 20%; protein: 20% energy) with the protein source being either total milk protein (MP; control), rapeseed protein (RP), or MP supplemented with cysteine and arginine to the same level as in RP (MP+AA). Endothelium-related vascular reactivity, measured as an acetylcholine-induced transient decrease in blood pressure, and plasma triglycerides, hydroperoxides, cyclic GMP (cGMP), and free 3-nitrotyrosine were measured before and 2, 4, and 6 h after meals. Superoxide anion production, expressed as ethidine fluorescence, was measured in the aorta 6 h after meals. Whereas plasma triglycerides rose similarly in all meals, the decrease in vascular reactivity after MP was attenuated after MP+AA and entirely prevented after RP. The type of meal had no consistent effect on plasma cGMP and free 3-nitrotyrosine over the postprandial period. The postprandial increase in plasma hydroperoxides differed according to the meal, and concentrations were 43% lower 6 h after MP+AA and RP than after MP. Aortic superoxide anion production was 36% lower 6 h after RP than MP. These results show that substituting rapeseed protein for milk protein markedly reduces vascular and oxidative disturbances induced by an HFM and this may be mediated in part by cysteine and arginine.

Comparing the chemical biology of NO and HNO

For the past couple of decades nitric oxide (NO) and nitroxyl (HNO) have been extensively studied due to the important role they play in many physiological and/or pharmacological processes. Many researchers have reported important signaling pathways as well as mechanisms of action of these species, showing direct and indirect effects depending on the environment. Both NO and HNO can react with, among others, metals, proteins, thiols and heme proteins via unique and distinct chemistry leading to improvement of some clinical conditions. Understanding the basic chemistry of NO and HNO and distinguishing their mechanisms of action as well as methods of detection are crucial for understanding the current and potential clinical applications. In this review, we summarize some of the most important findings regarding NO and HNO chemistry, revealing some of the possible mechanisms of their beneficial actions.

Bench-to-bedside review: nitric oxide in critical illness--update 2008

Nitric oxide (NO) is a unique and nearly ubiquitous molecule that is widely utilized as a signaling molecule in cells throughout the body. NO is highly diffusible, labile, and multiply reactive, suiting it well for its role as an important regulator of a number of diverse biologic processes, including vascular tone and permeability, platelet adhesion, neurotransmission, and mitochondrial respiration. NO can protect cells against antioxidant injury, can inhibit leukocyte adhesion, and can participate in antimicrobial defense, but can also have deleterious effects, including inhibition of enzyme function, promotion of DNA damage, and activation of inflammatory processes. This molecule's chemistry dictates its biologic activity, which can be both direct and indirect. In addition, NO has bimodal effects in a number of cells, maintaining homeostasis at low doses, and participating in pathophysiology in others. Perturbation of NO regulation is involved in the most important and prevalent disease processes in critical care units, including sepsis, acute lung injury, and multiple organ failure. Given that NO is ubiquitous, highly diffusible, and promiscuously reactive, its regulation is complex. The NO concentration, kinetics, and localization, both inside and outside the cell, are clearly crucial factors. In the present update we review a selection of studies that have yielded important information on these complex but important issues. Interpretation of these and other studies aimed at elucidating physiologic and pathophysiologic roles of NO must take this complexity into account. A full review of the role of NO in these diseases is beyond the scope of the current manuscript; the present article will focus on recent advances in understanding the complex role of NO in health and disease.

Enhanced tolerance against early and late apoptotic oxidative stress in mammalian neurons through nicotinamidase and sirtuin mediated pathways

Focus upon therapeutic strategies that intersect between pathways that govern cellular metabolism and cellular survival may offer the greatest impact for the treatment of a number of neurodegenerative and metabolic disorders, such as diabetes mellitus. In this regard, we investigated the role of a Drosophila nicotinamidase (DN) in mammalian SH-SY5Y neuronal cells during oxidative stress. We demonstrate that during free radical exposure to nitric oxide generators DN neuronal expression significantly increased cell survival and blocked cellular membrane injury. Furthermore, DN neuronal expression prevented both apoptotic late DNA degradation and early phosphatidylserine exposure that may serve to modulate inflammatory cell activation in vivo. Nicotinamidase activity that limited nicotinamide cellular concentrations appeared to be necessary for DN neuroprotection, since application of progressive nicotinamide concentrations could abrogate the benefits of DN expression during oxidative stress. Pathways that involved sirtuin activation and SIRT1 were suggested to be vital, at least in part, for DN to confer protection through a series of studies. First, application of resveratrol increased cell survival during oxidative stress either alone or in conjunction with the expression of DN to a similar degree, suggesting that DN may rely upon SIRT1 activation to foster neuronal protection. Second, the overexpression of either SIRT1 or DN in neurons prevented apoptotic injury specifically in neurons expressing these proteins during oxidative stress, advancing the premise that DN and SIRT1 may employ similar pathways for neuronal protection. Third, inhibition of sirtuin activity with sirtinol was detrimental to neuronal survival during oxidative stress and prevented neuronal protection during overexpression of DN or SIRT1, further supporting that SIRT1 activity may be necessary for DN neuroprotection during oxidative stress. Implementation of further work to elucidate the cellular mechanisms that govern nicotinamidase activity in mammalian cells may offer novel avenues for the treatment of disorders tied to oxidative stress and cellular metabolic dysfunction.

Discovery of highly potent and selective inhibitors of neuronal nitric oxide synthase by fragment hopping

Selective inhibition of neuronal nitric oxide synthase (nNOS) has been shown to prevent brain injury and is important for the treatment of various neurodegenerative disorders. This study shows that not only greater inhibitory potency and isozyme selectivity but more druglike properties can be achieved by fragment hopping. On the basis of the structure of lead molecule 6, fragment hopping effectively extracted the minimal pharmacophoric elements in the active site of nNOS for ligand hydrophobic and steric interactions and generated appropriate lipophilic fragments for lead optimization. More potent and selective inhibitors with better druglike properties were obtained within the design of 20 derivatives (compounds 7-26). Our structure-based inhibitor design for nNOS and SAR analysis reveal the robustness and efficiency of fragment hopping in lead discovery and structural optimization, which implicates a broad application of this approach to many other therapeutic targets for which known druglike small-molecule modulators are still limited.