Increase In NOx Production Research Articles

Hybrid rich- and lean-premixed ammonia-hydrogen combustion for mitigation of NOx emissions and thermoacoustic instabilities

The large-scale direct utilization of two carbon-free fuels, ammonia and hydrogen, is currently attracting significant interest in the context of the development of new gas turbine combustion technologies, with paying close attention to the reduction of nitrogen oxides and unburned ammonia emissions. Motivated by recent observations that rich-premixed conditions tend to mitigate excessive NOx emissions from ammonia combustion, and that uniformly blended ammonia-hydrogen fuel/air mixtures tend to increase NOx production exponentially, here we propose a hybrid configuration of hydrogen-doped rich-premixed ammonia-air flames (inner stage) and lean-premixed pure hydrogen-air flames (outer stage) in a radially stratified primary reaction zone. This fuel staging scheme offers a possible mechanism for chemical kinetics-controlled NOx abatement and asymmetry-induced thermoacoustic instability suppression. The relevance and feasibility of the unconventional premixing approach are rigorously evaluated based on detailed measurements of exhaust gas concentrations and self-excited pressure fluctuations, in conjunction with OH*/NH2*/NH* chemiluminescence and OH PLIF imaging measurements. We observe that drastically different non-homogeneous reaction regions can be stably established in a comparatively compact combustion volume without producing negative flame stabilization effects – such as blowoff of less reactive ammonia flames and flashback of more reactive hydrogen flames. As compared with the uniform-blend baseline condition, the hybrid staging method is shown to significantly mitigate total nitrogen oxides emissions, from 7764 to 310 ppmvd (96 % reduction), and achieving an approximately two-fold reduction in dynamic pressure amplitude. Interestingly, hydrogen-enriched rich-premixed ammonia flames are revealed to exhibit anomalous oscillatory states originating from the preferential diffusion of hydrogen molecules and reaction rate-dependent separation of reactive layers, enabling interacting non-homogeneous reaction zones with markedly different characteristic time scales to resist the growth of intense pressure perturbations.

Kinetics modeling of NOx emission of oxygen-enriched and rich-lean-staged ammonia combustion under gas turbine conditions

Though the oxygen enrichment combustion and fuel-rich/quick-mix/fuel-lean (RQL) combustion are respectively effective to improve burning velocity and reduce NOx emissions respectively, their combination feasibility and characteristics for burning ammonia (NH3) need further investigation as oxygen enrichment could increase NOx production. Thus, a kinetic modeling study was conducted on the NOx emission characteristics of an oxygen-enriched and RQL-staged NH3-fired combustor under gas turbine conditions by using the chemical reaction network (CRN) method. The results revealed that NOx emission could be minimized as long as the equivalence ratio (ϕ) in the fuel-rich stage was kept at a certain value according to the oxygen enrichment degree (Ω) in the fuel-rich stage oxidizer, regardless of the Ω in the fuel-lean stage oxidizer. At a higher Ω, low NOx emission was achieved in a wider ϕ range, while the optimal ϕ in the fuel-rich stage became higher and the corresponding NOx emission was lower. This mainly benefited from the stronger NH3 consumption in the fuel-rich stage due to the higher temperature and higher concentration of OH/H radicals. However, a higher Ω in the fuel-rich stage enhanced the thermal NOx formation in the fuel-lean stage. Based on the results of the present study, oxygen-enriched NH3 combustion with a proper ϕ setting in the fuel-rich stage could simultaneously improve the burning intensity and reduce NOx emission for burning NH3 in a gas turbine.

Magnetic field stabilized atmospheric pressure plasma nitrogen fixation: Effect of electric field and gas temperature

In this paper, we investigate the influence of plasma characteristics on nitrogen fixation efficiency and explore the optimization of discharge parameters by utilizing a magnetic field stabilized atmospheric pressure plasma. The gas temperature and electric field of the plasma are maintained at a constant level and can be independently adjusted by controlling the discharge current, gas flow rate, and external magnetic field. The spatial distribution of the gas temperature of the plasma is measured by laser-induced Rayleigh scattering. The results show that reducing the electric field and gas temperature leads to an increase in NOx production. The optimal parameters for nitrogen fixation are identified as a discharge current of 55 mA, a gas flow rate of 6 l·min−1, and an O2 fraction of 40%. These settings result in the lowest recorded energy cost of 2.29 MJ·mol−1 and a NOx concentration of approximately 15 925 ppm. The stable characteristics of the magnetically stabilized atmospheric pressure plasma make it suitable for further investigations into the effect of plasma characteristics on nitrogen fixation.

Optimization of biodiesel production from microalgae and investigation of exhaust emissions and engine performance for biodiesel blended

This paper evaluates the potential of using biodiesel from Dunaliella tertiolecta in the internal combustion engine to reduce emissions and fuel consumption and increase power output. The high cost of microalgae biomass production, the low efficiency of converting biomass into biodiesel and the increase in NOx production and fuel consumption with the combination of biodiesel in high percentages are the problems of this issue. In this article, by using the new solar still desalination/parabolic trough collector/geothermal hybrid system to supply the required water and heat and to investigate the effect of the influencing factors, the efficiency of microalgae production and transesterification process's conversion efficiency were obtained as 1.04 g/L and 80.22%, respectively. The addition of biodiesel from 0% to 20% in the fuel decreased CO, SOx and HC emissions, but CO2 and NOx emissions increased. Also, fuel consumption increased and engine output power decreased. The optimum point was found in order to emit the least emissions and reduce fuel consumption and increase the output power for the composition percentage of 11.5% biodiesel in the fuel.

Dunaliella salina fuel blends as the secondary fuel for the microgas turbine engines: A combustion and emission study

With the increasing demand for fossil fuels causing a decline in oil resources, the development of bio-gasoline has the potential to reduce the dependence of the fuel market on fossil fuels. This paper presents the experimental results of performance and emission characteristics of biofuel in a micro gas turbine engine. The microalgae chosen for this study is Dunaliella salina and different blends includes DB0 (Jet A fuel 100% + Dunaliella salina 0%), DB25 (Jet A fuel 75% + Dunaliella salina 25%) and DB50 (Jet A fuel 50% + Dunaliella salina 50%).All experimental tests were conducted in a small test rig and at different engine speeds as 40000 rpm, 50000 rpm and 60000 rpm. The study analysed the performance metrics including thrust, thrust-specific fuel consumption, thermal efficiency, and emissions. Results showed that blends reduced static thrust and thrust-specific fuel consumption and enhanced thermal efficiency. At 55000 rpm, the DB25 and DB50 reported 3% and 15% reduction in the static thrust. However, 11% and 15% reduction in the TSFC has been noted respectively. The CO and NOx emissions were also reduced with the use of biofuels. There was no observed decrease in NOx production. As the concentration of the microalgae blends increases, the temperature in the combustion chamber also increased, leading to an increase in NOx production. The findings indicate that blending microalgae blends with Jet-A fuel can lower pollutant emissions while retaining the desired thrust level. This research suggests that an optimal blend of the two fuels can be found and that biofuels can be a viable alternative to petroleum-based energy.

Expanding swirl combustor operability on methane-ammonia-air mixtures using a distributed fuel injection technique and inlet air preheating

The necessity to reduce greenhouse gas emissions has prompted the search for carbon-free fuel alternatives. One such carbon-free fuel source that can be used for power generation in a gas turbine-based system is ammonia. Ammonia combustion poses challenges due to reduced flame speed and reactivity, which can be alleviated by addition of methane or natural gas. However, NOx emissions continue to be an issue, which needs resolution before practical consideration of ammonia as a fuel source. One of the potential solutions that has been proposed is a two-stage, rich-lean combustion process to minimize NOx while ensuring complete reactant consumption. This work evaluates the use of two strategies to widen stability limits for swirl combustors operating on premixed methane-ammonia-air mixtures, which would facilitate the two-stage combustion approach. The first strategy involves the use of a distributed fuel injection approach utilizing a novel micro fuel injection swirler to facilitate homogeneous mixing in a highly compact manner while preventing flashback concerns. The second strategy involves use of inlet air preheating to increase flame stability and delay blow-off. The effectiveness of these strategies in expanding combustor operability limits is studied using experiments conducted in a model swirl-combustor setup designed to measure blow-off limits and evaluate exhaust NOx emissions. Complementary numerical simulations, particularly aimed at understanding NOx production pathways, are carried out using a reactor network model, wherein key inputs pertaining to recirculation volume and mass fraction are generated through detailed reacting flow simulations. The influence of the proposed strategies on NOx emissions are studied and underlying reaction pathways leading to NOx production are analyzed. Results of the study indicate that a distributed fuel injection strategy is able to significantly expand stability limits of a swirl combustor operating on methane-ammonia-air mixtures. Inlet air preheating provides additional expansion of stability limits, ≈ 7% for rich and lean blow-off, however, this is accompanied by increased NOx production, up to 14%, which is undesirable from an emissions standpoint. NOx is found to be significantly lower for rich fuel-air mixtures primarily through the effect of NHi reaction pathways responsible for NO consumption facilitated by the presence of excess NH3.

Experimental study of Partially Premixed-Diffusion Turbulent Flame with Circular Plate Bluff Body

This Study presents a parametric study on flame stabilization of partially premixed-diffusion turbulent flame behind the circular bluff body. The effects of the premixing and equivalence fuel ratios on flame temperature distribution and emission variation along the flame axis are investigated. The results indicate that as the premixing ratio increases the residence time and the recirculation zone length increase while the flame length decreases. The axial temperature distribution enhancements at the recirculation zone, and then a decrease towards the flame tip. As the premixed ratio increases the flame average temperature increase while emission measurements indicate a decrease in CO concentration with a slight increase in NOX production along the flame axis.

Control of NOx and other emissions in micro gas turbine combustors fuelled with mixtures of methane and ammonia

Methane–ammonia mixtures have potentials as low-carbon fuels for gas turbines, however significantly high fuel NOx production in their flames present challenges to their application. This study aims to provide deep insight into the physical and chemical processes involved in the formation and control of emissions from the combustion of CH4NH3–air with up to 30% ammonia by heat fraction in gas turbine combustors. Hence, laser diagnostics techniques such as Particle Image Velocimetry (PIV), and Planar Laser Induced Fluorescence (PLIF) imaging, in addition to Fourier Transform Infrared (FTIR) gas analysis were employed to study the flow field, flame structure and emissions characteristics of a micro gas turbine swirl combustor fuelled with CH4NH3–air mixtures. The control of emissions from the flames was further studied using Large Eddy Simulation (LES) of a model swirl combustor. The results show that NOx emissions from premixed CH4NH3–air in single-stage combustion were more than 5000 ppmv at equivalence ratios, Φ = 0.8–1.1, which is about twice more than the values already reported for NH3–air. Trends in NOx emissions correspond with the trends in OH radicals concentration in the combustor owing to the relevance of OH radicals in fuel NOx production. Emissions control leading to significantly low emissions such as 49 ppmv of NOx, 2 ppmv of CO and approximately zero N2O, HCN and NH3 emissions with a 99.8% combustion efficiency was achieved using rich-lean combustion. An optimum Φ of the primary combustion zone for low NOx emission was identified, which varied from 1.30 to 1.35 depending on the ammonia fraction. For Φ richer (leaner) than the optimum Φ, NOx emission increased due to an increase in NOx production in the secondary (primary) combustion zone. Rich-lean combustion of CH4NH3–air emitted less NOx than that of NH3-air because the higher flame speed of CH4NH3–air mixtures ensured lower NOx production in the secondary combustion zone.

Evaluation of operating parameters and fuel composition on knock in large bore two-stroke pipeline engines

Legacy integral compressor engines are crucial to the operation of the North American natural gas pipeline network. Many of these engines are uncontrolled utilizing mechanical scavenging or light turbocharging. The engines typically operate between ∼10 and 20g/bhp-hr of NOx with a minimal knock margin. While suitable for typical pipeline gases, high ethane shale gas can erode the knock margin with the added risk of performance degradation and engine damage. Phase one of the project investigated the impact of variable fuel quality and determined which engine parameters (ignition timing, air manifold temperature, and trapped equivalence ratio) were most effective in preventing and controlling knock. Phase two of the project evaluated the ability of an accelerometer and a NOx emissions sensor to detect engine knock as well as the development of knock prediction models.Testing confirmed elevated fuel ethane could induce continuous engine knock but ignition timing was the most effective method to mitigate engine knock, followed by trapped equivalence ratio. Air manifold temperature did not significantly affect knock onset. When properly tuned, a typical off the shelf accelerometer knock detection system could detect and protect against the onset of knock. Persistent knock lead to a steady increase in NOx production, but NOx values alone were inadequate to detect and protect against knock. The knock prediction models accurately predicted the onset of knock based on ignition timing, trapped equivalence ratio, and fuel composition, suggesting a fundamental relationship between operating parameters and engine knock.

Skeletal Methane–Air Reaction Mechanism for Large Eddy Simulation of Turbulent Microwave-Assisted Combustion

Irradiating a flame via microwave radiation is a plasma-assisted combustion (PAC) technology that can be used to modify the combustion chemical kinetics in order to improve flame stability and to delay lean blow-out. One practical implication is that combustion engines may be able to operate with leaner fuel mixtures and have an improved fuel flexibility capability including biofuels. Furthermore, this technology may assist in reducing thermoacoustic instabilities, which is a phenomenon that may severely damage the engine and increase NOX production. To further understand microwave-assisted combustion, a skeletal kinetic reaction mechanism for methane–air combustion is developed and presented. The mechanism is detailed enough to take into account relevant features, but sufficiently small to be implemented in large eddy simulations (LES) of turbulent combustion. The mechanism consists of a proposed skeletal methane–air reaction mechanism accompanied by subsets for ozone, singlet oxygen, chemionization, and...

Hydrogen Combustion in I.C Engines

The use of hydrogen as a fuel for the internal combustion engine represents an alternative to solve both of the greatest problems related to the use of classic fuels: the limitation of the fossil fuels consumption and the environment pollution. We first describe hydrogen-engine fundamentals by examining the engine-specific properties of hydrogen and topics that are discussed include abnormal combustion (backfire, pre-ignition and knock),emissions of NOx and load control strategies (power output versus NOx tradeoff). Finally, we consider comprehensive overview of the design features of a dedicated hydrogen S.I., Direct-Injection hydrogen fueled internal combustion engine. I. Introduction: At the moment the estimation of the number of motor vehicles is about 800 million. To replace them in a relatively short time by fuel cells is impossible. There are several reasons for converting the gasoline, diesel or natural gas engines to hydrogen fuelled internal combustion engines. ICEs are proven technology, are simple and well-known and the adaptations can be made with a low cost. During the transition period bi-fuel solutions are possible (to run the engine either on gasoline or pure hydrogen). For larger engines (buses, trucks) mixtures of natural gas with hydrogen (about 20%) are easy to exploit. During this transition period, experience can be gained with the production, storage and infrastructure of hydrogen. Currently the hydrogen production is the cheapest through the steam reforming of methane. But CO2 emissions can not be avoided. Renewable energy, e.g. solar power, hydroelectric, tidal, … can give ―CO2-free‖ electricity to electrolyze water to hydrogen. The downside is that these electricity costs are mostly expensive. Interesting is also the application of peak shaving of wind turbine power. Other possibilities are solar thermal, biomass, bacterial… The unique combustion characteristics of hydrogen that allow clean and efficient operation at low engine loads present difficulties at high engine loads. Here, the low ignition energies of hydrogen-air mixtures cause frequent unscheduled combustion events, and high combustion temperatures of mixtures closer to the stoichiometric composition lead to increased NOx production. Both effects, in practical application, limit the power densities of H2ICEs. The recent research thrust and progress on this front is the development of advanced hydrogen engines with improved power densities and reduced NOx emissions at high engine loads.

Reactive Oxygen Species Scavenger, Tempol, Decreases Vasoconstriction after Acute Pulmonary Embolism

Pulmonary vasoconstriction is an important mechanism contributing to the development of pulmonary hypertension after pulmonary embolism (PE) probably due to increased production of reactive oxygen species (ROS). Our aim was to investigate the change of NO production and to determine the effect of ROS scavenger, Tempol, on pulmonary hypertension after PE.Using the model of in vivo pulmonary embolism and isolated, perfused rat lungs we measured the perfusion pressure and its changes after sodium nitroprusside administration and after NO synthase inhibition by L‐NAME.We used 6 groups of Wistar male rats:NN: control group + sodium nitroprusside (SN) (n=5), EN: PE + SN (n=5), TN: Tempol + PE + SN (n=5), NL: control group + L‐Name (n=5), EL: PE + L‐Name (n=5), TL: Tempol + PE + L‐name (n=5). Tempol was administered before PE.PE caused higher pulmonary pressure. Tempol‐treated rats (TN, TL) had significantly lower perfusion pressure than the animals without Tempol (EN, EL). The decrease of perfusion pressure after application of SN was higher in EN than in NN. Administration of L‐Name after PE (EL) increased the pressure more than in the controls (NL). PE also caused increased NOx production.ROS‐induced vasoconstriction contributed to the pulmonary hypertension after PE. Also, PE caused increased production of NO and NOx. Tempol decreased pulmonary hypertension after PE by inhibiting the free radicals production.

NOx Emission Control in Gas Turbines

The increase, in recent years, in the size and efficiency of gas turbines burning natural gas in combined cycle has occurred against a background of tightening environmental legislation on the emission of nitrogen oxides. The higher turbine entry temperatures required for efficiency improvement tend to increase NOX production. To reduce NOX emissions, new engine core configurations with heat management and active systems, as well as advanced combustor technology, have to be investigated. This paper reviews the various approaches adopted by the main gas turbine manufacturers which are achieving low levels of NOX emission from natural gas combustion.

Arginase Inhibition by Ethylacetate Extract ofCaesalpinia sappanLignum Contributes to Activation of Endothelial Nitric Oxide Synthase

Caesalpinia sappan (C. sappan) is a medicinal plant used for promoting blood circulation and removing stasis. During a screening procedure on medicinal plants, the ethylacetate extract of the lignum of C. sappan (CLE) showed inhibitory activity on arginase which has recently been reported as a novel therapeutic target for the treatment of cardiovascular diseases such as atherosclerosis. CLE inhibited arginase II activity prepared from kidney lysate in a dose-dependent manner. In HUVECs, inhibition of arginase activity by CLE reciprocally increased NOx production through enhancement of eNOS dimer stability without any significant changes in the protein levels of eNOS and arginase II expression. Furthermore, CLE-dependent arginase inhibition resulted in increase of NO generation and decrease of superoxide production on endothelium of isolated mice aorta. These results indicate that CLE augments NO production on endothelium through inhibition of arginase activity, and may imply their usefulness for the treatment of cardiovascular diseases associated with endothelial dysfunction.

Piceatannol-3'-O-β-D-glucopyranoside as an active component of rhubarb activates endothelial nitric oxide synthase through inhibition of arginase activity

Arginase competitively inhibits nitric oxide synthase (NOS) via use of the common substrate L-arginine. Arginase II has recently reported as a novel therapeutic target for the treatment of cardiovascular diseases such as atherosclerosis. Here, we demonstrate that piceatannol-3'-O-beta-D-glucopyranoside (PG), a potent component of stilbenes, inhibits the activity of arginase I and II prepared from mouse liver and kidney lysates, respectively, in a dose-dependent manner. In human umbilical vein endothelial cells, incubation of PG markedly blocked arginase activity and increased NOx production, as measured by Griess assay. The PG effect was associated with increase of eNOS dimer ratio, although the protein levels of arginase II or eNOS were not changed. Furthermore, isolated mice aortic rings treated with PG showed inhibited arginase activity that resulted in increased nitric oxide (NO) production upto 78%, as measured using 4-amino-5-methylamino-2',7'-difluorescein (DAF-FM) and a decreased superoxide anions up to 63%, as measured using dihydroethidine (DHE) in the intact endothelium. PG showed IC((50)) value of 11.22 microM and 11.06 microM against arginase I and II, respectively. PG as an arginase inhibitor, therefore, represents a novel molecule for the therapy of cardiovascular diseases derived from endothelial dysfunction and may be used for the design of pharmaceutical compounds.

499 SUSTAINED RELEASE OF SFLT01 IS NECESSARY AND FEASIBLE FOR PROLONGED INTRAARTICULAR DELIVERY TO THE KNEE TO NEUTRALIZE VEGF LOCALLY

498 – Figure 1. NOx (LEFT) and PGE2 (RIGHT) production by AF cells from 4 degenerative human tissue samples after treatment with control media or media with IL-17, IFNγ, or both IL-17 and IFNγ. The values for the media control only were indicated as dotted horizontal lines. (control), TNFα (25 ng/mL), IL17 (10 ng/mL), IFNγ (200 U/mL) or both IL17 and IFNγ. After 72 hours, the supernatant was evaluated for release of nitric oxide (NOx, Griess reaction) and prostaglandin E2 (PGE2, ELISA). One-way ANOVA and post-hoc Dunn’s analysis evaluated differences amongst treatment groups for NOx and PGE2 release (p=0.05). Results: Stimulation of AF cells with IL17 or IFNγ alone did change NOx levels from control values; however, a significant variability in NOx responses was observed across human subjects (Figure 1 left). In the presence of IFNγ costimulant, IL17 induced average 2-fold increase in NOx production above that of IL17 alone (IL17: average NOx = 22 μM, IL17 + IFNγ: NOx = 45 μM, Figure 1 left). In contrast, stimulation with IL17 alone led to a significant elevation in PGE2 levels in all 4 samples (average 14fold increase, Figure 1 right). As for the NOx result, co-stimulation with IL17 and IFNγ led to a large increase in PGE2 release, more than 24-fold over control values (Figure 1 right, IL17 + IFNγ PGE2 release = 1.36 ng/ml; Control PGE2 release = 0.06 ng/ml). In general, the induction of NOx and PGE2 release by IL17 and IFNγ co-stimulation was significantly larger than that due to TNFα stimulation, for which few changes in NOx and a 10-fold increase in PGE2 was observed. Conclusions: The results of this study demonstrate that degenerative human IVD cells may respond to IL17 stimulation with increased production of the inflammatory mediators, PGE2 and NOx, with a more robust effect observed in the presence of IFNγ. Degenerative and herniated IVD explants are known to contain IFNγ, and IFNγ is known to act synergistically with IL17 to promote release of inflammatory mediators in other cell types. This work demonstrates that the responsiveness of IVD cells to IL17 and IFNγ is consistent with other cell types, and suggests a potential role for these cytokines in contributing to IVD pathology.

완전혼합 반응기에서 CH4/Air 예혼합화염의 열손실율에 따른 Nox 생성특성

Abstract The effect of heat loss rate on NOx formation of CH 4 /air premixed flame were examined numerically in a perfectly stirred reactor. The following conclusions were drawn. Under the adiabatic wall condition, an increase in the residence time causes a remarkable increases in NOx emission. Under the heat loss conditions, however, NOx decreases significantly as the heat transfer coefficient and residence time increase. As the heat loss rate increases, Thermal NO mechanism and Re-burning NO mechanism play an important role in the NOx reduction, but Prompt NO mechanism and N 2 O-intermediate NO mechanism lead to the increase in NOx production. Although the NOx formation is actually related to complex NOx mechanism with the changes in the heat transfer coefficient and residence time, it was found that NOx concentration can be represented by independent Thermal NO mechanism. From these results, new NOx correlation combined with the heat loss rate and residence time was suggested for predicting the NOx concentration in a practical CH

ACE-inhibition ameliorates vascular reactivity and delays diabetes outcome in NOD mice

Recently, we have demonstrated a direct correlation among hyperglycaemia, vascular dysfunction and eNOS post-translational regulation in non non-obese diabetic mice (NOD). Here, we evaluate the impact of two ACE-inhibitors therapy, zofenopril and enalapril in NOD mice. Insulin-dependent diabetes mellitus (IDDM) development was monitored weekly through glycosuria measurement. Zofenopril and enalapril were dosed at 0.5 mg/kg/die orally. Animals were sacrificed at different points and aortas used for western blotting or for tissue bath experiments. Bovine aortic endothelial cells in high glucose medium are treated with zofenoprilat or enalaprilat. Cells and supernatant were utilised for western blot analysis and for nitrite/nitrate determination, respectively. In ex-vivo experiments chronic administration of both drugs restored PE-induced contraction but not Isop-induced vasodilatation, however only zofenopril reduced caveolin-1 expression. In vitro, both drugs inhibited caveolin-1 expression and increased NOx production. However, zofenopril caused inhibition of both parameters at a concentration 200 fold lower than enalalpril. In vivo, zofenopril delays the onset of diabetic conditions of about 50%, and ameliorates polyuria. In conclusion our data suggest that ACE-inhibitor therapy may be useful in IDDM, in particular sulphydrylated inhibitor would display a better efficacy especially if administered early on the development of diabetes.

Prostaglandin E2 and Nitric Oxide production by paternal and maternal inherited iNOS in placental tissue in iNOS knockout mice treated with LPS

MATERNAL INHERITED INOS IN PLACENTAL TISSUE IN INOS KNOCKOUT MICE TREATED WITH LPS HIDENORI TAKAHASHI, TOSHIAKI OKAWA, KEIYA FUJIMORI, AKIRA SATO, YURI VEDERNIKOV, GEORGE SAADE, ROBERT GARFIELD, Fukushima Medical University, Obstetrics & Gynecology, Fukushima, Japan, University of Texas Medical Branch at Galveston, Obstetrics & Gynecology, Galveston, Texas OBJECTIVE: To evaluate the effect of paternal or maternal iNOS on prostaglandin E2 (PGE2) and Nitric Oxide (NO) production by placental tissue of pregnant iNOS knockout (iNOSKO) mice and their control mice (C3HeN:C3H) treated with lipopolysaccharide (LPS). STUDY DESIGN: Nonpregnant (NonPreg) iNOSKO(iNOS / ) and C3H(iNOSC/C) and Pregnant (Preg) mice with genetic composition of placenta for mating as (A) male iNOSKO! female iNOSKO; iNOS / , (B) male iNOSKO! femaleC3H; iNOS /Cm, (C) male C3H! female iNOSKO; iNOSCp/ mice on day 14 of gestation were sacrificed 6 hours after intraperitoneal (i.p.) injection of LPS (400 mg/kg) or vehicle (n=8 per group). Uterine rings from NonPreg and Preg were equilibrated in Krebs-Henseleit solution. In some rings from Preg, a piece of placenta was left attached to the uterine wall. One ml sample of the solution was taken after 60 min incubation. The sample was analyzed for PGE2 by radioimmunoassay and NOx production. Statistical analysis was performed using one way ANOVA. RESULTS: (1) PGE2 Production: LPSsignificantly increased PGE2 production in both NonPreg C3H and iNOSKO mice compared without LPS. LPS also increased in placenta attached uterine tissue of all 3 types as (A), (B) and (C). (2)NOx Production: In NonPreg uterine tissue, LPS significantly increased NOx production in both C3H and iNOSKO mice. In Preg placentai tissue, increasing order of magnitude of NOx production without LPS; (A) iNOS( / ) =(C) iNOS ( /Cm)! (B) iNOS(Cp/ ) (p!0.05). LPS significantly increased NOx production in (C) (p!0.01), however, significantly decreased in (B) (p!0.05) and did not change in (A) compared without LPS. CONCLUSION: LPS, a crucial mediator of inflammation and infection, induced PGE2 and NOx production of uterine tissue in NonPreg mice independent of iNOS. However, in Preg mice then presense of the placenta with paternal iNOS decreased NOx production. This study indicates that physiological and pathophysiological iNOS in placental tissue originate from paternal and maternal tissue respectively.

Oxidized Low-Density Lipoprotein–Dependent Endothelial Arginase II Activation Contributes to Impaired Nitric Oxide Signaling

Oxidized low-density lipoprotein (OxLDL) impairs NO signaling and endothelial function, and contributes to the pathogenesis of atherosclerosis. Arginase reciprocally regulates NO levels in endothelial cells by competing with NO synthase for the substrate l-arginine. In human aortic endothelial cells, OxLDL stimulation increased arginase enzyme activity in a time- and dose-dependent manner. Arginase activity reached its maximum as early as 5 minutes, was maintained for a period of more than 48 hours, and was associated with a reciprocal decrease in NO metabolite (NOx [nitrite and nitrate]) production. Furthermore, OxLDL induced arginase II mRNA expression after 4 hours. Small interfering RNA targeted to arginase II decreased both the quantity and the activity of arginase from baseline, prevented OxLDL-dependent increases in arginase activity, and induced an increase in NOx production. Immunofluorescence analysis revealed an association of arginase II with the microtubule cytoskeleton. Microtubule disruption with nocodazole caused a dramatic redistribution of arginase II to a diffuse cytosolic pattern, increased arginase activity, and decreased NOx production, which was restored in the presence of the specific arginase inhibitor (S)-(2-boronoethyl)-l-cysteine (BEC). On the other hand, epothilone B prevented microtubule disruption and inhibited OxLDL-dependent increases in arginase activity and attenuated OxLDL-dependent decreases in NOx. Preincubation of rat aortic rings with OxLDL resulted in an increase in arginase activity and a decrease in NOx production. This was reversed by arginase inhibition with the BEC. Thus, OxLDLs increase arginase activity by a sequence of regulatory events that involve early activation through decreased association with microtubules and a later increase in transcription. Furthermore, increased arginase activity contributes to OxLDL-dependent impairment of NOx production. Arginase, therefore, represents a novel target for therapy in atherosclerosis.