Mechanism Of Nitric Oxide Production Research Articles

Multiple Ways of Nitric Oxide Production in Plants and Its Functional Activity under Abiotic Stress Conditions.

Nitric oxide (NO) is an endogenous signaling molecule that plays an important role in plant ontogenesis and responses to different stresses. The most widespread abiotic stress factors limiting significantly plant growth and crop yield are drought, salinity, hypo-, hyperthermia, and an excess of heavy metal (HM) ions. Data on the accumulation of endogenous NO under stress factors and on the alleviation of their negative effects under exogenous NO treatments indicate the perspectives of its practical application to improve stress resistance and plant productivity. This requires fundamental knowledge of the NO metabolism and the mechanisms of its biological action in plants. NO generation occurs in plants by two main alternative mechanisms: oxidative or reductive, in spontaneous or enzymatic reactions. NO participates in plant development by controlling the processes of seed germination, vegetative growth, morphogenesis, flower transition, fruit ripening, and senescence. Under stressful conditions, NO contributes to antioxidant protection, osmotic adjustment, normalization of water balance, regulation of cellular ion homeostasis, maintenance of photosynthetic reactions, and growth processes of plants. NO can exert regulative action by inducing posttranslational modifications (PTMs) of proteins changing the activity of different enzymes or transcriptional factors, modulating the expression of huge amounts of genes, including those related to stress tolerance. This review summarizes the current data concerning molecular mechanisms of NO production and its activity in plants during regulation of their life cycle and adaptation to drought, salinity, temperature stress, and HM ions.

Pleiotropic Functions of Nitric Oxide Produced by Ascorbate for the Prevention and Mitigation of COVID-19: A Revaluation of Pauling's Vitamin C Therapy.

Linus Pauling, who was awarded the Nobel Prize in Chemistry, suggested that a high dose of vitamin C (l-ascorbic acid) might work as a prevention or treatment for the common cold. Vitamin C therapy was tested in clinical trials, but clear evidence was not found at that time. Although Pauling's proposal has been strongly criticized for a long time, vitamin C therapy has continued to be tested as a treatment for a variety of diseases, including coronavirus infectious disease 2019 (COVID-19). The pathogen of COVID-19, SARS-CoV-2, belongs to the β-coronavirus lineage, which includes human coronavirus, severe acute respiratory syndrome (SARS), and Middle East respiratory syndrome (MERS). This review intends to shed new light on vitamin C antiviral activity that may prevent SARS-CoV-2 infection through the chemical production of nitric oxide (NO). NO is a gaseous free radical that is largely produced by the enzyme NO synthase (NOS) in cells. NO produced by upper epidermal cells contributes to the inactivation of viruses and bacteria contained in air or aerosols. In addition to enzymatic production, NO can be generated by the chemical reduction of inorganic nitrite (NO2-), an alternative mechanism for NO production in living organisms. Dietary vitamin C, largely contained in fruits and vegetables, can reduce the nitrite in saliva to produce NO in the oral cavity when chewing foods. In the stomach, salivary nitrite can also be reduced to NO by vitamin C secreted from the epidermal cells of the stomach. The strong acidic pH of gastric juice facilitates the chemical reduction of salivary nitrite to produce NO. Vitamin C contributes in multiple ways to the host innate immune system as a first-line defense mechanism against pathogens. Highlighting chemical NO production by vitamin C, we suggest that controversies on the therapeutic effects of vitamin C in previous clinical trials may partly be due to less appreciation of the pleiotropic functions of vitamin C as a universal bioreductant.

Nitric Oxide Production and Regulation in the Teleost Cardiovascular System.

Nitric Oxide (NO) is a free radical with numerous critical signaling roles in vertebrate physiology. Similar to mammals, in the teleost system the generation of sufficient amounts of NO is critical for the physiological function of the cardiovascular system. At the same time, NO amounts are strictly controlled and kept within basal levels to protect cells from NO toxicity. Changes in oxygen tension highly influence NO bioavailability and can modulate the mechanisms involved in maintaining the NO balance. While NO production and signaling appears to have general similarities with mammalian systems, the wide range of environmental adaptations made by fish, particularly with regards to differing oxygen availabilities in aquatic habitats, creates a foundation for a variety of in vivo models characterized by different implications of NO production and signaling. In this review, we present the biology of NO in the teleost cardiovascular system and summarize the mechanisms of NO production and signaling with a special emphasis on the role of globin proteins in NO metabolism.

Understanding the Cellular Sources of the Fractional Exhaled Nitric Oxide (FeNO) and Its Role as a Biomarker of Type 2 Inflammation in Asthma.

Fractional exhaled nitric oxide (FeNO) has gained great clinical importance as a biomarker of type 2 inflammation in chronic airway diseases such as asthma. FeNO originates primarily in the bronchial epithelium and is produced in large quantities by the enzyme inducible nitric oxide synthase (iNOS). It should be noted that nitric oxide (NO) produced at femtomolar to picomolar levels is fundamental for respiratory physiology. This basal production is induced in the bronchial epithelium by interferon gamma (IFNγ) via Janus kinases (JAK)/STAT-1 signaling. However, when there is an increase in the expression of type 2 inflammatory cytokines such as IL-4 and IL-13, the STAT-6 pathway is activated, leading to overexpression of iNOS and consequently to an overproduction of airway NO. Increased NO levels contributes to bronchial hyperreactivity and mucus hypersecretion, increases vascular permeability, reduces ciliary heartbeat, and promotes free radical production, airway inflammation, and tissue damage. In asthmatic patients, FeNO levels usually rise above 25 parts per billion (ppb) and its follow-up helps to define asthma phenotype and to monitor the effectiveness of corticosteroid treatment and adherence to treatment. FeNO is also very useful to identify those severe asthma patients that might benefit of personalized therapies with monoclonal antibodies. In this review, we revised the cellular and molecular mechanisms of NO production in the airway and its relevance as a biomarker of type 2 inflammation in asthma.

Choline Acetyltransferase Administration Decrease Blood Pressure in a Murine Model of Hypertension

Despite significant advances in anti-hypertensive therapy, more than half of hypertensive patients fail to control their blood pressure. The estimated morbidity associated with hypertension is over 30% worldwide, and many hypertensive patients progressively develop cardiovascular disease and chronic kidney disease. Thus, the development of novel antihypertensive therapies is required. Acetylcholine, released by cholinergic neurons and lymphocytes, is a major mediator of endothelium-dependent, arterial smooth muscle relaxation that decreases blood pressure. Here, we assessed the effects of choline acetyltransferase (ChAT), a rate-limiting enzyme in acetylcholine biosynthesis, on decreasing arterial blood pressure in a preclinical model of hypertension. Hypertension was induced in mice using subcutaneous infusion of angiotensin II via osmotic mini-pumps. A single injection of ChAT beginning as late as two weeks after induction of hypertension decreases mean arterial blood pressure (MAP) (121 ± 4 mmHg vehicle vs 107 ± 8 mmHg ChAT, p = 0.06). Acetylcholine acts on muscarinic receptors on endothelial cells and produces arterial relaxation by activating endothelial nitric oxide (NO) synthase that produces NO from L-arginine. To investigate whether ChAT administration stimulates these mechanisms of NO production, we pretreated mice with NOS inhibitor Nω -nitro-L-arginine methyl ester (L-NAME), and measured blood pressure following administration of ChAT. Administration of L-NAME significantly attenuates ChAT-mediated decrease in blood pressure (4.3 ± 6.1 %MAP × h vs25.4 ± 4.9 %MAP × h, p = 0.02). To increase the stability and decrease the immunogenicity of the exogenous ChAT, the protein was PEGylated by covalently coupling polyethylene glycol with ChAT. Activity analysis revealed that PEGylated ChAT (PEG-ChAT) retains enzymatic activity. A single intraperitoneal administration of PEG-ChAT significantly reduces MAP as compared to vehicle injection (121 ± 4.5 mmHg vehicle vs 102 ± 4 mmHg PEG-ChAT 1 mg/kg, p = 0.01). Finally, administration of ChAT and PEG-ChAT during the sleep cycle produces a robust decrease in arterial blood pressure. These observations present administration of ChAT as a novel therapeutic strategy for preventing the progression of established hypertension.

Nitric Oxide as a Target for Phytochemicals in Anti-Neuroinflammatory Prevention Therapy.

Nitric oxide (NO) is a neurotransmitter that mediates the activation and inhibition of inflammatory cascades. Even though physiological NO is required for defense against various pathogens, excessive NO can trigger inflammatory signaling and cell death through reactive nitrogen species-induced oxidative stress. Excessive NO production by activated microglial cells is specifically associated with neuroinflammatory and neurodegenerative conditions, such as Alzheimer’s and Parkinson’s disease, amyotrophic lateral sclerosis, ischemia, hypoxia, multiple sclerosis, and other afflictions of the central nervous system (CNS). Therefore, controlling excessive NO production is a desirable therapeutic strategy for managing various neuroinflammatory disorders. Recently, phytochemicals have attracted considerable attention because of their potential to counteract excessive NO production in CNS disorders. Moreover, phytochemicals and nutraceuticals are typically safe and effective. In this review, we discuss the mechanisms of NO production and its involvement in various neurological disorders, and we revisit a number of recently identified phytochemicals which may act as NO inhibitors. This review may help identify novel potent anti-inflammatory agents that can downregulate NO, specifically during neuroinflammation and neurodegeneration.

Differential nitric oxide induced by Mycobacterium bovis and BCG leading to dendritic cells apoptosis in a caspase dependent manner

Dendritic cells (DCs) are critical for both innate and adaptive immunity. Meanwhile, nitric oxide (NO) is a member of reactive nitrogen species (RNS) generally considered to play a key role in the bactericidal process in innate immunity against Mycobacterium tuberculosis complex infection. The present study therefore investigated the mechanism of NO production in murine DCs induced by Mycobacterium bovis (M.bovis) and its attenuated strain Bacillus Calmette-Guérin (BCG) infection. The expression of genes Slc7A1, Slc7A2, iNOS, and ArgI essential to NO synthesis was up-regulated in M.bovis/BCG infected DCs. IFN-γ addition further increased, while the iNOS inhibitor L-NMMA significantly inhibited their expression. Accordingly, the end products of arginine metabolism, NO and urea, were found to be significantly increased. In addition, BCG induced significantly higher levels of apoptosis in DCs compared to M.bovis shown by higher levels of DNA fragmentation using flow cytometry and release of mitochondrial Cytochrome C, and up-regulation of the genes caspase-3, caspase-8, caspase-9 and dffa critical to apoptosis by qRT-PCR detection and western blot analysis. Furthermore, IFN-γ increased, but L-NMMA decreased apoptosis of M.bovis/BCG infected DCs. In addition, mycobacterial intracellular survival was significantly reduced by IFN-γ treatment in BCG infected DCs, while slightly increased by L-NMMA treatment. Taken altogether, our data show that NO synthesis was differentially increased and associated with apoptosis in M.bovis/BCG infected DCs. These findings may significantly contribute to elucidate the pathogenesis of M.bovis.

The catalytic mechanism for NO production by the mitochondrial enzyme, sulfite oxidase.

Recently, Guenter Schwarz and colleagues published an elegant study in the Biochemical Journal (2019) 476, 1805-1815 which combines kinetic and spectroscopic studies with protein engineering to provide a mechanism for sulfite oxidase (SO)-catalyzed nitrite reduction that yields nitric oxide (NO). This work is noteworthy as it demonstrates that (i) for NO generation, both sulfite and nitrite must bind to the same molybdenum (Mo) center; (ii) upon sulfite reduction, Mo is reduced from +6 (MoVI) to +4 (MoIV) and MoIV reduces nitrite to NO yielding MoV; (iii) the heme moiety, linked to the Mo-center by an 11 amino acid residue tether, gets reduced by intramolecular electron transfer (IET) resulting in MoV being oxidized to MoVI; (iv) the reduced heme transfers its electron to a second nitrite molecule converting it to NO; (v) the authors demonstrate steady-state NO production in the presence of the natural electron acceptor cytochrome c; (vi) Finally, the authors use protein engineering to shorten the heme tether to reduce the heme-Mo-center distance with the aim of increasing NO production. Consequently, the rate of IET to cytochrome c is decreased but the enzymatic turnover rate for NO production is increased by ∼10-fold. This paper is unique as it provides strong evidence for a novel mechanism for steady-state NO production for human mitochondrial SO and serves as a potential template for studying NO production mechanisms in other enzymes by integrating the information gained from enzyme kinetics with EPR and UV/vis spectroscopy and protein engineering.

Aged biochar stimulated ammonia-oxidizing archaea and bacteria-derived N2O and NO production in an acidic vegetable soil

Both nitrous oxide (N2O) and nitric oxide (NO) emissions are typically high in greenhouse-based high N input vegetable soils. Biochar amendment has been widely recommended for mitigating soil N2O emissions in agriculture. However, knowledge of the regulatory mechanisms of fresh and aged biochar for both N2O and NO production during ammonia oxidation is lacking. Two vegetable soils with different pH values were used in aerobic incubation experiments with 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl 3-oxide (PTIO), 1-octyne and acetylene. The relative importance of ammonia-oxidizing archaea (AOA) and bacteria (AOB) to N2O and NO production was investigated as influenced by fresh and aged biochar amendments. The results showed that AOA dominated N2O production in acidic soil, while AOB dominated N2O production in alkaline soil. Aged biochar stimulated both AOA- and AOB-derived N2O and NO production by 84.8 and 340%, respectively, in acidic soil but only increased AOA-derived N2O and NO production in alkaline soil. Fresh biochar amendment increased AOA- and AOB-derived NO in acidic soil and AOA-derived NO in alkaline soil but had negligible effects on AOA- and AOB-derived N2O in both soils. Fresh biochar decreased AOA-amoA but increased AOB-amoA gene abundances in acidic soil, whereas aged biochar increased AOA- and AOB-amoA gene abundances in both soils. These findings improved our understanding of N2O and NO production mechanisms under different biochar amendments in alkaline and acidic vegetable soils.

Nonstatistical Dissociation Dynamics of Nitroaromatic Chromophores.

Organic carbon in the atmosphere is emitted from biogenic and anthropogenic sources and plays a key role in atmospheric chemistry, air quality, and climate. Recent studies have identified several of the major nitroaromatic chromophores embedded in organic "brown carbon" (BrC) aerosols. Indeed, nitroaromatic chromophores are responsible for the enhanced solar absorption of BrC aerosols, extending into the near UV (300-400 nm) and visible regions. Furthermore, BrC chromophores serve as temporary reservoirs of important oxidizing intermediates including hydroxyl (OH) and nitric oxide (NO) radicals that are released upon electronic excitation. The present work represents the first study of the 355 nm photolysis of known BrC chromophores ortho-nitrophenol and 2-nitroresorcinol, as well as the prototypical nitroaromatic, nitrobenzene. Experiments are carried out in a pulsed supersonic jet expansion with velocity map imaging of NO X2Π (ν″ = 0, J″) fragments to report on the photodissociation dynamics. The total kinetic energy release (TKER) distributions and the NO X2Π (ν″ = 0, J″) product state distributions deviate significantly from Prior simulations, indicating that energy is partitioned nonstatistically following dissociation. Experiments are conducted in tandem with complementary calculations using multireference Møller-Plesset second-order perturbation theory (MRMPT2) for stationary points obtained by using multiconfiguration self-consistent field (MCSCF) with an aug-cc-pVDZ basis on the ground and lowest energy triplet electronic states. Furthermore, insights into the partitioning of energy upon photodissociation are achieved by using relaxed scans at the MCSCF/aug-cc-pVDZ level of theory. As a whole, the results suggest that upon excitation to S1, all three nitroaromatics share a common overall mechanism for NO production involving isomerization of the nitro group, nonradiative relaxation to S0, and dissociation to form rotationally hot NO.

Effect of Visible Light on Vasospasticity of Post-Subarachnoid Hemorrhage Cerebrospinal Fluid.

Background and Objective Cerebral vasospasm (CV) is a serious complication of subarachnoid hemorrhage (SAH) with high morbidity and mortality rates. The mechanism of CV has not been determined. There are many theories related to this unsolved issue, one of which supports CV as a two-stage phenomenon from a pathophysiologic perspective. The first stage consists of inhibition of neuronal nitric oxide synthase by oxyhemoglobin, which results in a decrease of nitric oxide (NO) production. The second stage consists of an increase in the levels of asymmetric dimethylarginine through bilirubin oxidation products (BOXes), which are oxidized by-products of hemoglobin metabolism. These in turn inhibit endothelial nitric oxide synthase (eNOS), which results in the blockage of the second NO production mechanism. BOXes are sensitive to visible light, as is their precursor bilirubin. The hypothesis of CV prevention using the photosensitivity of BOXes was tested in this study. Material and Methods Cerebrospinal fluid (CSF) obtained from two patients with SAH was divided in half and either exposed to a standard dose of visible light or not exposed to any light. The CSF was spectrophotometrically investigated and the concentration of BOXes was measured. A comparison between CSF samples exposed to light and not exposed to light was made. Using two groups of 16 rats each, the vasospastic effect of the CSF exposed and not exposed to light on arteries of the cortical surface was measured. The cortex was exposed using the cranial window. Results Spectrophotometric analysis revealed that the concentration of BOXes in the CSF decreased significantly after being exposed to visible light (p < 0.001). There was a significant difference of the vasospastic effect of CSF on exposed cortical arteries (p < 0.001). Conclusion The concentration of BOXes and the vasospastic effect of CSF taken from patients with SAH were significantly reduced after being exposed to visible light if compared with CSF not exposed to light.

Nitric oxide signaling in yeast.

As a cellular signaling molecule, nitric oxide (NO) is widely conserved from microorganisms, such as bacteria, yeasts, and fungi, to higher eukaryotes including plants and mammals. NO is mainly produced by NO synthase (NOS) or nitrite reductase (NIR) activity. There are several NO detoxification systems, including NO dioxygenase (NOD) and S-nitrosoglutathione reductase (GSNOR). NO homeostasis based on the balance between NO synthesis and degradation is important for the regulation of its physiological functions because an excess level of NO causes nitrosative stress due to the high reactivity of NO and NO-derived compounds. In yeast, NO may be involved in stress responses, but NO and its signaling have been poorly understood due to the lack of mammalian NOS orthologs in the genome. Even though the activities of NOS and NIR have been observed in yeast cells, the gene encoding NOS and the NO production mechanism catalyzed by NIR remain unclear. On the other hand, yeast cells employ NOD and GSNOR to maintain an intracellular redox balance following endogenous NO production, exogenous NO treatment, or environmental stresses. This article reviews NO metabolism (synthesis, degradation) and its regulation in yeast. The physiological roles of NO in yeast, including the oxidative stress response, are also discussed here. Such investigations into NO signaling are essential for understanding the NO-dependent genetic and physiological modulations. In addition to being responsible for the pathology and pharmacology of various degenerative diseases, NO signaling may be a potential target for the construction and engineering of industrial yeast strains.

Methane/hydrogen fueling a spark-ignition engine for studying NO, CO and HC emissions with a research CFD code

Emissions of nitric oxide (NO), carbon monoxide (CO), and unburned hydrocarbons (HC) and their reaction mechanisms are investigated in a spark-ignition (SI) engine fueled with methane/hydrogen blends (hydrogen 30% by vol.). This analysis considers engine load variation through a variable equivalence ratio, with the application of an in-house research, three-dimensional computational fluid dynamics code (3D-CFD) for detailed in-cylinder simulations. The code’s combustion model includes the thermal NO mechanism, and other alternative NO production mechanisms, such as via the NNH and N2O species formation and the prompt NO mechanisms. Moreover, two CO formation models have been added, using two and three chemical equations, and their results are compared in order to identify the most appropriate for such combustion processes. Finally, no additional HC formation model is included, as HC emissions are directly calculated by the code escorted by the contribution of unburned fuel from the crevice regions, in which a phenomenological model is applied. Focus is also given on the spatial NO, CO and HC production pattern inside the cylinder during combustion and expansion periods. The numerical results are then compared with available measured data, in order to validate these emission formation models and investigate the production paths at such conditions and for variable equivalence ratio. The NO predictions are adequate and well captured, while the trend of CO and HC is adequately predicted especially for high equivalence ratio. The overall outcome is a numerical tool capable to predict with detail the in-cylinder processes and examine the local gas properties during flame propagation and pollutant emissions inside the combustion chamber for this case of high technological interest.

Investigation of nitric oxide emission mechanisms in a SI engine fueled with methane/hydrogen blends using a research CFD code

The reaction mechanisms of nitric oxide (NO) emissions are investigated in a spark-ignition (SI) engine fueled with hydrogen/methane blends, for variable equivalence ratio (load variation) and variable hydrogen content. For that purpose, a research three-dimensional computational fluid dynamics code (3D-CFD) is applied, being capable of simulating in high detail the in–cylinder processes. The combustion model of the CFD code includes not only the thermal NO mechanism, widely known as ’Zeldovich mechanism’, but also other alternative NO production mechanisms. Therefore, the NO emission modeling has been enhanced here with the addition of other production paths, such as via the NNH and N2O species formation and the prompt NO mechanism. The NNH path has been shown to be favored at lean and low-temperature combustion conditions especially when hydrogen is present, whereas the N2O path becomes important for lean flames irrespectively of the fuel used. Prompt NO becomes important in stoichiometric and fuel-rich conditions and is also examined here to evaluate its contribution to the NO emissions. Focus is also directed on the local/spatial NO production pattern at each location in the cylinder during the combustion and expansion periods. The calculations are compared with available measurements, in order to quantify the use of these alternative production paths at such conditions and applications. In all cases, the thermal NO mechanism is the dominant production path. On the other hand, with lean flames it has been observed that the N2O path produces significant amount of NO, while the contribution of the NNH mechanism is small, but it is recommended to be also considered in the calculations for increasing the accuracy of the results. The prompt NO is not favored at such conditions, even for the stoichiometric case, and could be even omitted from the combustion model.

Physiological implications of arginine metabolism in plants.

Nitrogen is a limiting resource for plant growth in most terrestrial habitats since large amounts of nitrogen are needed to synthesize nucleic acids and proteins. Among the 21 proteinogenic amino acids, arginine has the highest nitrogen to carbon ratio, which makes it especially suitable as a storage form of organic nitrogen. Synthesis in chloroplasts via ornithine is apparently the only operational pathway to provide arginine in plants, and the rate of arginine synthesis is tightly regulated by various feedback mechanisms in accordance with the overall nutritional status. While several steps of arginine biosynthesis still remain poorly characterized in plants, much wider attention has been paid to inter- and intracellular arginine transport as well as arginine-derived metabolites. A role of arginine as alternative source besides glutamate for proline biosynthesis is still discussed controversially and may be prevented by differential subcellular localization of enzymes. Apparently, arginine is a precursor for nitric oxide (NO), although the molecular mechanism of NO production from arginine remains unclear in higher plants. In contrast, conversion of arginine to polyamines is well documented, and in several plant species also ornithine can serve as a precursor for polyamines. Both NO and polyamines play crucial roles in regulating developmental processes as well as responses to biotic and abiotic stress. It is thus conceivable that arginine catabolism serves on the one hand to mobilize nitrogen storages, while on the other hand it may be used to fine-tune development and defense mechanisms against stress. This review summarizes the recent advances in our knowledge about arginine metabolism, with a special focus on the model plant Arabidopsis thaliana, and pinpoints still unresolved critical questions.

Unravelling the reactive oxygen and reactive nitrogen signalling networks in plants.

Unravelling the reactive oxygen and reactive nitrogen signalling networks in plants.

Lack of neuronal nitric oxide synthase results in attention deficit hyperactivity disorder-like behaviors in mice.

Nitric oxide (NO) is an important molecule for the proper development and function of the central nervous system. In this study, we investigated the behavioral alterations in the neuronal NO synthase knockout mice (NOS1 KO) with a deficient NO production mechanism in the brain, characterizing it as a potential rodent model for attention deficit hyperactivity disorder (ADHD). NOS1 KO exhibited higher locomotor activity than their wildtype counterparts in a novel environment, as measured by open field (OF) test. In a 2-way active avoidance paradigm (TWAA), we found sex-dependent effects, where male KO displayed deficits in avoidance and escape behavior, sustained higher incidences of shuttle crossings, and higher incidences of intertrial interval crossings, suggesting learning, and/or performance impairments. On the other hand, female KO demonstrated few deficits in TWAA. Molsidomine (MSD), a NO donor, rescued TWAA deficits in male KO when acutely administered before training. In a passive avoidance paradigm, KO of both sexes displayed significantly shorter step-through latencies after training. Further, abnormal spontaneous motor activity rhythms were found in the KO during the dark phase of the day, indicating dysregulation of rhythmic activities. These data indicate that NOS1 KO mimics certain ADHD-like behaviors and could potentially serve as a novel rodent model for ADHD.

Slow attractive canonical invariant manifolds for reactive systems

We analyze the efficacy of a standard manifold-based reduction method used to simplify reaction dynamics and find conditions under which the reduction can succeed and fail. In the standard reduction, a heteroclinic trajectory linking saddle and sink equilibria is taken as a candidate reduced manifold which we call a Canonical Invariant Manifold (CIM). We develop and exercise analytic tools for studying the local behavior of trajectories near the CIM. In so doing, we find conditions under which nearby trajectories are attracted to the CIM (ACIM) as well as conditions for which the dynamics on the ACIM are slow (SACIM). The method is demonstrated on a (1) simple model problem, (2) Zel’dovich mechanism for nitric oxide production, and (3) hydrogen–air system. For systems that evolve in a three-dimensional composition space, we find that normal stretching away from the CIM in a volume-shrinking vector field is admitted and that depending on the magnitude of the local rotation rate, may or may not render the CIM to be attractive. The success and failure of the candidate CIM as a SACIM is displayed for the model system. Results for the Zel’dovich mechanism and hydrogen–air systems are less definitive, though for specific conditions a SACIM is identified for both systems.

Endothelial-Specific Notch Blockade Inhibits Vascular Function and Tumor Growth through an eNOS-Dependent Mechanism

Notch signaling is important for tumor angiogenesis induced by vascular endothelial growth factor A. Blockade of the Notch ligand Dll4 inhibits tumor growth in a paradoxical way. Dll4 inhibition increases endothelial cell sprouting, but vessels show reduced perfusion. The reason for this lack of perfusion is not currently understood. Here we report that inhibition of Notch signaling in endothelial cell using an inducible binary transgenic system limits VEGFA-driven tumor growth and causes endothelial dysfunction. Neither excessive endothelial cell sprouting nor defects of pericyte abundance accompanied the inhibition of tumor growth and functional vasculature. However, biochemical and functional analysis revealed that endothelial nitric oxide production is decreased by Notch inhibition. Treatment with the soluble guanylate cyclase activator BAY41-2272, a vasorelaxing agent that acts downstream of endothelial nitric oxide synthase (eNOS) by directly activating its soluble guanylyl cyclase receptor, rescued blood vessel function and tumor growth. We show that reduction in nitric oxide signaling is an early alteration induced by Notch inhibition and suggest that lack of functional vessels observed with Notch inhibition is secondary to inhibition of nitric oxide signaling. Coculture and tumor growth assays reveal that Notch-mediated nitric oxide production in endothelial cell requires VEGFA signaling. Together, our data support that eNOS inhibition is responsible for the tumor growth and vascular function defects induced by endothelial Notch inhibition. This study uncovers a novel mechanism of nitric oxide production in endothelial cells in tumors, with implications for understanding the peculiar character of tumor blood vessels.

Nitric oxide production by Peromyscus yucatanicus (Rodentia) infected with Leishmania (Leishmania) mexicana.

Peromyscus yucatanicus (Rodentia: Cricetidae) is a primary reservoir of Leishmania (Leishmania) mexicana (Kinetoplastida: Trypanosomatidae). Nitric oxide (NO) generally plays a crucial role in the containment and elimination of Leishmania. The aim of this study was to determine the amount of NO produced by P. yucatanicus infected with L. (L.) mexicana. Subclinical and clinical infections were established in P. yucatanicus through inoculation with 1 x 10 2 and 2.5 x 10 6 promastigotes, respectively. Peritoneal macrophages were cultured alone or co-cultured with lymphocytes with or without soluble Leishmania antigen. The level of NO production was determined using the Griess reaction. The amount of NO produced was significantly higher (p ≤ 0.0001) in co-cultured macrophages and lymphocytes than in macrophages cultured alone. No differences in NO production were found between P. yucatanicus with subclinical L. (L.) mexicana infections and animals with clinical infections. These results support the hypothesis that the immunological mechanisms of NO production in P. yucatanicus are similar to those described in mouse models of leishmaniasis and, despite NO production, P. yucatanicus is unable to clear the parasite infection.