Behavior of different soot combustion catalysts under NOx/O2. Importance of the catalyst���soot contact

Four different catalysts (Pt/Al2O3, Ce0.8Zr0.2O2, PrO2���x and SrTiCuO3) have been investigated on a laboratory scale to evaluate their potential as diesel soot combustion catalysts under different experimental conditions, which simulate the situation found in a continuous regeneration technology trap (dual-bed configuration of catalyst and soot) or a catalyst-coated filter system (single-bed configuration, both catalyst and soot particles mixed under loose-contact mode). Under dual-bed configuration, the behavior of the catalysts towards soot combustion are very similar, despite the differences observed in the NO2 production profiles. However, under single-bed configuration, there are important differences in the soot combustion activities and in the NO2 slip profiles. The configurations chosen have an enormous impact on CO/(CO + CO2) ratios of combustion products as well. The most active catalyst under NOx + O2 is PrO2���x combining a high contribution of active oxygen-assisted soot combustion as well as high NO2 production activity along the catalytic bed.

Catalytic performance of CuO/Ce0.8Zr0.2O2 loaded onto SiC-DPF in NOx-assisted combustion of diesel soot

This work presents a comparative study between the catalytic performance of the 2% CuO/ceria-zirconia powder catalyst and the same catalyst supported on silicon carbide DPF (Diesel Particulate Filter) towards NO oxidation reaction and soot combustion reaction. The ceria-zirconia catalyst was prepared by the co-precipitation method and 2 wt% copper was incorporated by the incipient wetness impregnation method. The catalyst was incorporated onto the ceramic support using a simple and organic solvent-free procedure by a simply dipping the DPF into an aqueous solution of the catalyst. The powder catalyst has been characterized using N2 adsorption at ���196 ��C, XRD and Raman Spectroscopy; whereas the catalytic coating morphology has been evaluated by SEM and the mechanical stability by an adherence test. Both catalyst configurations were tested for NO oxidation to NO2 and for soot combustion under NOx/O2. The results revealed that incorporation of the very active copper/ceria-zirconia catalyst onto SiC-DPF has been successfully achieved by a simple coating procedure. Furthermore, the catalytic coating has shown suitable mechanical, chemical and thermal stability. A satisfactory catalytic performance of the catalytic-coated filter was reached towards the NO oxidation reaction. Moreover, it was proved that the catalytic coating is stable and the corresponding coated DPF can be reused for several cycles of NO oxidation without a significant decrease in its activity. Finally, it was verified that the loose-contact mode is a good choice to simulate the catalytic performance of this active phase in a real diesel particulate filter.

Preparation, characterisation and testing of CuO/Ce0.8Zr0.2O2 catalysts for NO oxidation to NO2 and mild temperature diesel soot combustion

CuO/ceria-zirconia catalysts have been prepared, deeply characterised (N2 adsorption���desorption isotherms at ���196 ��C, XRD, Raman spectroscopy, XPS, TEM and H2-TPR) and tested for NO oxidation to NO2 in TPR conditions, and for soot combustion at mild temperature (400 ��C) in a NOx/O2 stream. The behaviour has been compared to that of a reference Pt/alumina commercial catalyst. The ceria-zirconia support was prepared by the co-precipitation method, and different amounts of copper (0.5, 1, 2, 4 and 6 wt%) were loaded by incipient wetness impregnation. The results revealed that copper is well-dispersed onto the ceria-zirconia support for the catalysts with low copper loading and CuO particles were only identified by XRD in samples with 4 and 6% of copper. A very low loading of copper increases significantly the activity for the NO oxidation to NO2 with regard to the ceria-zirconia support and an optimum was found for a 4% CuO/ceria-zirconia composition, showing a very high activity (54% at 348 ��C). The soot combustion rate at 400 ��C obtained with the 2% CuO/ceria-zirconia catalyst is slightly lower to that of 1% Pt/alumina in terms of mass of catalyst but higher in terms of price of catalyst.

Potential of Cu���saponite catalysts for soot combustion

H��� and Na���saponite supports have been prepared by several synthesis approaches. 5% Cu/saponite catalysts have been prepared and tested for soot combustion in a NOx + O2 + N2 gas flow and with soot and catalyst mixed in loose contact mode. XRD, FT-IR, N2 adsorption and TEM characterization results revealed that the use of either surfactant or microwaves during the synthesis led to delamination of the saponite support, yielding high surface area and small crystallite size materials. The degree of delamination affected further copper oxide dispersion and soot combustion capacity of the Cu/saponite catalysts. All Cu/saponite catalysts were active for soot combustion, and the NO2-assisted mechanism seemed to prevail. The best activity was achieved with copper oxide supported on a Na���saponite prepared at pH 13 and with surfactant. This best activity was attributed to the efficient copper oxide dispersion on the high surface area delaminated saponite (603 m2 g���1) and to the presence of Na. Copper oxide reduction in H2-TPR experiments occurred at lower temperature for the Na-containing catalysts than for the H-containing counterparts, and all Cu/Na���saponite catalysts were more active for soot combustion than the corresponding Cu/H���saponite catalysts.

Effect of the CeZrNd mixed oxide synthesis method in the catalytic combustion of soot

Ce0.64Zr0.27Nd0.09O�� mixed oxides have been prepared by three different methods (nitrates calcination, coprecipitation and microemulsion), characterized by N2 adsorption, XRD, H2-TPR, Raman spectroscopy and XPS, and tested for soot combustion in NOx/O2. The catalyst prepared by microemulsion method is the most active one, which is related to its high surface area (147 m2/g) and low crystallite size (6 nm), and the lowest activity was obtained with the catalyst prepared by coprecipitation (74 m2/g; 9 nm). The catalyst prepared by nitrates precursors calcination is slightly less active to that prepared by microemulsion, but the synthesis procedure is very straightforward and surfactants or other chemicals are not required, being very convenient for scaling up and practical utilization. The high activity of the catalyst prepared by nitrates calcination can be attributed to the better introduction of Nd cations into the parent ceria framework than on catalysts prepared by coprecipitation and microemulsion, which promotes the creation of more oxygen vacancies.

Opportunities for ceria-based mixed oxides versus commercial platinum-based catalysts in the soot combustion reaction. Mechanistic implications

The aim of this paper is to study the activities of ceria���zirconia and copper/ceria���zirconia catalysts, comparing with a commercial platinum/alumina catalyst, for soot combustion reaction under different gas atmospheres and loose contact mode (simulating diesel exhaust conditions), in order to analyse the kinetics and to deduce mechanistic implications. Activity tests were performed under isothermal and TPR conditions. The NO oxidation to NO2 was studied as well. It was checked that mass transfer limitations were not influencing the rate measurements. Global activation energies for the catalysed and non-catalysed soot combustion were calculated and properly discussed. The results reveal that ceria-based catalysts greatly enhance their activities under NOx/O2 between 425 ��C and 450 ��C, due to the ���active oxygen���-assisted soot combustion. Remarkably, copper/ceria���zirconia shows a slightly higher soot combustion rate than the Pt-based catalyst (under NOx/O2, at 450 ��C).

Aportaci��n a la investigaci��n sobe la reducci��n de las emisiones de NOx en grupos diesel utilizados para generaci��n de energ��a el��ctrica

Programa de doctorado: Energ��a y Medio Ambiente

Isotopic study of ceria-catalyzed soot oxidation in the presence of NOx

The ceria-catalyzed soot oxidation mechanism has been studied by a pulse technique with labeled O2 in the absence and presence of NO, using ceria���soot mixtures prepared in the loose contact mode. In the absence of soot, the ceria-catalyzed oxidation of NO to NO2 takes place with ceria oxygen and not with gas-phase O2. However, the oxygen exchange process between gas-phase O2 and ceria oxygen (to yield back O2, but with oxygen atoms coming from ceria) prevailed with regard to the ceria-catalyzed oxidation of NO to NO2. Gas-phase O2 did not react directly with soot when pulsed to a soot���ceria loose contact mixture. Instead, ceria oxygen is transferred to soot (this step does not require gas-phase molecular oxygen to be present), and gas-phase O2 fills up the vacancies created on the oxide in a further step. The transfer of oxygen between ceria and soot occurred directly in the absence of NO. However, in the presence of NO, NO2 is expected to be additionally generated by ceria oxygen oxidation, which also reacts with soot. The main reaction products of the ceria-catalyzed soot oxidation reaction with NO/O2 were CO2 and NO. Additionally, evidence of the reduction of NOx to N2 was found.

Weekend/weekday differences in concentrations of ozone, nox, and non-methane hydrocarbon in the metropolitan area of S��o Paulo

Ozone and inhalable particulate matter are the major air pollutants in the Metropolitan Area of S��o Paulo, Brazil, a region that has more than 19 million inhabitants and approximately 7 million registered vehicles. Proximity of roadways, adjacent land use, and local circulation are just some of the factors that can affect the results of monitoring of pollutant concentrations. The so-called weekend effect (higher ozone concentrations on weekends than on weekdays) might be related to the fact that concentrations of ozone precursors, such as nitrogen oxides (NOx) and Non Methane-Hydrocarbon (NMHC), are relatively lower on weekends. This phenomenon has been reported in some areas of the United States since the 1970s. The differences between the concentrations of ozone in period of weekend and weekday, were obtained from analysis of data hourly average of CETESB for 2004, studied the precursors to the formation of troposphere ozone, the meteorological variables and traffic profile for RMSP. Because of the proximity to sources of emissions from the station Pinheiros showed higher concentrations of NO and NO�� and greater variations to the periods weekend and weekday. With fewer vehicles circulating during the weekend, and consequently less emission of pollutants, it has cleaner air and less concentration of NO and NO��, there is the ideal setting to the formation of troposphere ozone, despite the lower concentration of NO��. The proximity with the source emissions, aided by the increased availability of solar radiation and the presence of ozone precursors, were factors conditions for the occurrence of weekend effect.

Cross-Talk Between Mitochondria and NADPH Oxidase: Effects of Mild Mitochondrial Dysfunction on Angiotensin II-Mediated Increase in Nox Isoform Expression and Activity in Vascular Smooth Muscle Cells

Mitochondria and NADPH oxidase activation are concomitantly involved in pathogenesis of many vascular diseases. However, possible cross-talk between those ROS-generating systems is unclear. We induced mild mitochondrial dysfunction due to mitochondrial DNA damage after 24 h incubation of rabbit aortic smooth muscle (VSMC) with 250 ng/mL ethidium bromide (EtBr). VSMC remained viable and had 29% less oxygen consumption, 16% greater baseline hydrogen peroxide, and unchanged glutathione levels. Serum-stimulated proliferation was unaltered at 24 h. Although PCR amplification of several mtDNA sequences was preserved, D-Loop mtDNA region showed distinct amplification of shorter products after EtBr. Such evidence for DNA damage was further enhanced after angiotensin-II (AngII) incubation. Remarkably, the normally observed increase in VSMC membrane fraction NADPH oxidase activity after AngII was completely abrogated after EtBr, together with failure to upregulate Nox1 mRNA expression. Conversely, basal Nox4 mRNA expression increased 1.6-fold, while being unresponsive to AngII. Similar loss in AngII redox response occurred after 24 h antimycin-A incubation. Enhanced Nox4 expression was unassociated with endoplasmic reticulum stress markers. Protein disulfide isomerase, an NADPH oxidase regulator, exhibited increased expression and inverted pattern of migration to membrane fraction after EtBr. These results unravel functionally relevant cross-talk between mitochondria and NADPH oxidase, which markedly affects redox responses to AngII. Antioxid Redox Signal 11, 1265-1278.

Development of composite adsorbents of carbon and intercalated clay for N2 and O2 adsorption: A preliminary study

Composite adsorbents of carbon and alumina intercalated montmorillonite were prepared and characterized by adsorption of N-2 and O-2 at various temperatures. The effects of pyrolysis, temperature, heating rate, subsequent degassing, and doping of cations and anions were investigated. The adsorption capacities of the composite adsorbents developed at higher temperatures (0 and -79 degrees C) are found to be larger than those of normal alumina pillared clays. The experimental results showed that the framework of these adsorbents is made of alumina particles and clay sheets while the pyrolyzed carbon distributes in the space of interlayers and interpillars. The pores between the carbon particles, clay sheets, and alumina pillars are very narrow with very strong adsorption forces, leading to enhanced adsorption capacities at 0 and -79 degrees C. The composite adsorbents exhibit features similar to those of carbonaceous adsorbents. Their pore structures, adsorption capacities, and selectivities to oxygen can be tailored by a controlled degassing procedure. Meanwhile, ions can be doped into the adsorbents to modify their adsorption properties, as usually observed for oxide adsorbents like zeolite and pillared clays. Such flexibility in pore structure tailoring is a potential advantage of the composite adsorbents developed for their adsorption and separation applications. (C) 1999 Academic Press.

Plasma nitrate/nitrite (NOx) is not a useful biomarker to predict inherent cardiopulmonary bypass inflammatory response

Background and Aim: There were strong evidences that nitric oxide has capital importance in the progressive vasodilatation associated with varied circulatory shock forms, including systemic inflammatory response syndrome (SIRS), in patients undergoing cardiac surgeries for cardiopulmonary bypass (CPB). If CPB procedures, per se, are the inciting stimulus for inflammation, plasma nitrate/nitrite (NOx) excretion would be expected to be higher in these patients rather than in patients operated without CPB. In consequence, we hypothesized that increased levels of NOx would be predictive for vasoplegic syndrome. Methods: Thirty patients were assigned to three groups: Group 1-coronary artery bypass graft (CABG) roller pump CPB; Group 2-CABG centrifugal vortex pump CPB; and Group 3-heart valve surgery roller pump CPB. Sampling of venous blood for chemiluminescence plasma NOx dosage was achieved at the following time points: (1) before anesthesia induction; (2) after anesthesia induction; (3) before heparin infusion; (4) after heparin infusion; (5) CPB-30 minutes; (6) CPB-60 minutes; (7) before protamine infusion; (8) after protamine infusion; and (9) on return to the recovery area. Results: There were no intergroup differences regarding age and anesthetic regimen, and the number of arteries grafted was not different between the CABG groups. There were no NOx statistic differences, neither among the three groups of patients or among the surgery time. In addition, there was no correlation among NOx, lactate, and hemoglobin. Conclusions: Considering the inflammatory process intrinsic to CPB, this study reinforces the idea that plasma NOx is not useful as a biomarker of inflammatory response onset, which may or may not lead to SIRS and/or vasoplegic syndrome.

O2/CO2-sensitive cyclic AMP-signalling pathway in peripheral chemoreceptors

RESUMO: O corpo carot��deo (CB) �� um pequeno ��rg��o sens��vel a varia����es na PaO2, PaCO2 e pH. As c��lulas tipo I (c��lulas gl��micas) do corpo carot��deo, as unidades sensoriais deste ��rg��o, libertam neurotransmissores em resposta ��s varia����es dos gases arteriais. Estes neurotransmissores atuam quer em recetores pr��-sin��pticos, localizados nas c��lulas tipo I, quer em recetores p��ssin��pticos, localizados nas termina����es do nervo do seio carot��deo, ou em ambos. A activa����o dos recetores pr��-sin��pticos modula a atividade do corpo carot��deo, enquanto que, a activa����o dos recetores p��s-sin��pticos, de carater excitat��rio, desencadeia um aumento da frequ��ncia de descarga das fibras do CSN, com subsequente despolariza����o dos neur��nios do g��nglio petroso, e posterior despolariza����o de um grupo espec��fico de neur��nios do centro respirat��rio central, desencadeando, como resposta final, hiperventila����o. Estes recetores pr��- e p��s-sin��pticos podem ser classificados em ionotr��picos ou metabotr��picos, estando os ��ltimos acoplados a adenilatos ciclases transmembranares (tmAC). O mecanismo exato pelo qual as varia����es dos gases arteriais s��o detetadas pelo CB n��o se encontra ainda completamente elucidado, mas tem sido sugerido que altera����es nos n��veis de cAMP estejam associadas ao mecanismo de dete����o de varia����es de O2 e CO2. Os n��veis de cAMP podem ser regulados atrav��s da sua via de s��ntese, mediada por dois tipos de adenilatos ciclases: tmAC sens��vel aos eurotransmissores e adenilato ciclase sol��vel (sAC)sens��vel a varia����es de HCO3/CO2, e pela sua via de degrada����o mediada por fosfodiesterases. A via de degrada����o do cAMP pode ser manipulada farmacologicamente, funcionando enquanto alvo terap��utico para o tratamento de patologias do foro respirat��rio (e.g. asma, hipertens��o pulmonar, doen��a pulmonar obstructiva cr��nica e apneia do sono), que induzem um aumento da actividade do CB.O trabalho descrito nesta disserta����o partiu da hip��tese de que a actividade do CB �� manipulada por f��rmacos, que interferem com a via de sinaliza����o do cAMP, tendo sido nosso objectivo geral, investigar o papel do cAMP na quimiotransdu����o do CB de rato, e determinar se a actividade dos enzimas respons��veis pela via de sinaliza����o do cAMP �� ou n��o regulada por varia����es de O2/CO2. Assim, a relev��ncia deste trabalho �� a de estudar e identificar poss��veis alvos moleculares (sAC, isoformas de tmAC e PDE) com potencial para serem usados no tratamento de patologias relacionadas com o controlo respirat��rio. A primeira parte do presente trabalho, centrou-se na caracteriza����o farmacol��gica da PDE4 no CB e em tecidos n��o quimiorecetores (e.g. g��nglio cervical superior e art��rias car��tidas), e na observa����o do efeito de hip��xia aguda na acumula����o dos n��veis de cAMP, induzidos pelos inibidores de PDE, nestes tecidos. A quantifica����o de cAMP foi efectuada por t��cnica imunoenzim��tica (EIA), tendo sido elaboradas curvas de dose-resposta para os efeitos de inibidores, n��o espec��ficos (IBMX) e espec��ficos para a PDE2 e PDE4 (EHNA, Rolipram e Ro 20-1724), nos n��veis de cAMP acumulados, em situa����es de norm��xia (20%O2/5%CO2) e hip��xia (5%O2/5%CO2). A caracteriza����o das PDE no g��nglio cervical superior foi aprofundada, utilizando-se a t��cnica de transfer��ncia de energia de resson��ncia por fluoresc��ncia (FRET) em culturas prim��rias de neur��nios, na presen��a de inibidores n��o espec��ficos (IBMX) e espec��ficos para a PDE3 e PDE4 (milrinone e rolipram, respetivamente). Foram igualmente estudadas, atrav��s de RT-qPCR, as altera����es na express��o de PDE3A-B e PDE4A-D, no g��nglio cervical superior, em resposta a diferentes percentagens de oxig��nio. Na segunda parte do trabalho investigou-se a via de s��ntese do cAMP no CB em resposta a varia����es na concentra����o de HCO3/CO2. Em concreto, o protocolo experimental centrou-se na caracteriza����o da sAC, dado que a sua actividade �� regulada por varia����es de HCO3/CO2. A caracteriza����o da express��o e regula����o da sAC, em resposta a varia����es de HCO3/CO2 ,foi efectuada no CB e em tecidos n��o quimioreceptores perif��ricos (e.g. g��nglio cervical superior, petroso e nodoso) por qRT-PCR. A actividade deste enzima foi caracterizada indirectamente atrav��s da quantifica����o dos n��veis de cAMP (quantifica����o por EIA), induzidos por diferentes concentra����es de HCO3/CO2, na presen��a de MDL-12,33-A, um inibidore da tmAC. A express��o das isoformas da tmAC no CB e g��nglio petroso foi determinada por RT-qPCR. Adicionalmente, estud��mos a contribui����o relativa da tmAC e sAC no mecanismo de sensibilidade ao CO2 no CB. Para o efeito foram estudadas as altera����es: 1) nos n��veis de cAMP (quantificado por EIA) na presen��a de diferentes concentra����es de HCO3/CO2 e ao longo do tempo (5-30 min); 2) na ativa����o da prote��na cinase A (PKA, FRET baseado em sensores) em c��lulas tipo I do CB; e 3) na frequ��ncia de descarga do CSN (registos) na presen��a e aus��ncia de ativadores e inibidores da sAC,tmAC e PKA. Por ��ltimo, foi caracterizada a express��o e actividade da sAC nos quimioreceptors centrais (locus ceruleus, rafe e medula ventro-lateral) atrav��s de t��cnicas de RT-qPCR e EIA. A express��o das isoformas da tmAC foi aprofundada no locus coeruleus atrav��s de RT-qPCR. Por fim, compar��mos a contribui����o da tmAC e sAC nos n��veis de cAMP no locus coeruleus em condi����es de normocapnia e hipercapnia.O nosso trabalho teve os seguintes resultados principais: 1) PDE4 est�� funcional no corpo carot��deo, art��rias car��tidas e g��nglio cervical superior de rato, embora a PDE2 s�� se encontre funcional neste ��ltimo; 2) Os efeitos dos inibidores de PDE nos n��veis de acumula����o de cAMP foram exacerbados em situa����es de hip��xia aguda no CB e art��rias car��tidas, mas foram atenuados no g��nglio cervical superior; 3) No g��nglio cervical superior, diferentes tipos de c��lulas apresentaram uma caracteriza����o espec��fica de PDEs, sugerindo uma subpopula����o de c��lulas neste g��nglio com fun����es fisiol��gicas distintas; 4) Embora todas as isoformas de PDE4 e PDE3 estivessem presentes no g��nglio, a PDE3a, PDE4b e a PDE4d foram as isoformas mais expressas. Por outro lado, incuba����es de g��nglio cervical superior, em diferentes percentagens de oxig��nio, n��o alteraram (n��o regularam) significativamente a express��o das diferentes isoformas de PDE neste ��rg��o; 5) a sAC encontra-se expressa e funcional no CB e nos quimiorecetores centrais estudados (locus coeruleus, rafe e medula ventrolateral). A sAC apresenta maior express��o no CB comparativamente aos restantes org��os estudados, exceptuando os test��culos, org��o controlo. Varia����es de HCO3/CO2 de 0/0 para 24/5 aumentaram os n��veis de cAMP no CB e quimiorecetores centrais, tendo sido o aumento mais significativo observado no CB. Concentra����es acima dos 24mM HCO3/5%CO2 n��o induziram altera����es nos n��veis de cAMP, sugerindo que a actividade da sAC se encontra saturada em condi����es fisiol��gicas (normocapnia) e que este enzima n��o desempenha qualquer papel na dete����o de situa����es de hipercapnia; 6) No CB, a express��o das isoformas tmAC1, tmAC4, tmAC6 e tmAC9 �� mais elevada comparativamente �� express��o da sAC; 7) Utilizamos diferentes inibidores da tmAC (MDL 12-330A, 500��M, 2���5���-ddADO, 30-300��M, SQ 22536, 200��M) e da sAC (KH7, 10-100��M) para estudar a contribui����o relativa destes enzimas na acumula����o do cAMP no CB. Tanto a tmAC como a sAC contribuem para a acumula����o dos n��veis de cAMP em condi����es de hipercapnia. Contudo, existe um maior efeito destes inibidores nas condi����es de 12 mM HCO3/2.5%CO2 do que em condi����es de normocapnia e hipercapnia, sugerindo um papel relevante destes enzimas na atividade do CB em situa����es de hipocapnia; 8) N��o se observaram varia����es nos n��veis de cAMP em resposta a diferentes concentra����es de HCO3/CO2 ao longo do tempo (5-30 min). O efeito inibit��rio induzido por ddADO e KH7 foi sobrepon��vel ap��s 5 ou 30 minutos de incuba����o em todas as concentra����es de HCO3/CO2 estudadas; 9) Por ��ltimo, verificou-se um aumento na frequ��ncia da descarga do nervo do seio carot��deo entre as condi����es de normocapnia e hipercapnia ac��dica. Ao contr��rio do KH7 (10��M), o 2���5���-ddADO reduziu significativamente a frequ��ncia de descarga do nervo, quer em condi����es de normocapnia quer de hipercapnia ac��dica. Contudo, n��o se verificou aumento na frequ��ncia de descarga do nervo entre normocapnia e hipercapnia isoh��drica, sugerindo que a sensibilidade �� hipercapnia no CB �� mediada por varia����es de pH. Em conclus��o, os resultados decorrentes deste trabalho permitiram demonstrar que, embora os enzimas que medeiam a via de sinaliza����o do cAMP possam ser bons alvos terap��uticos em condi����es particulares, a sua actividade n��o �� espec��fica para o CB. Os resultados sugerem ainda que o cAMP n��o �� um mediador espec��fico da transdu����o �� hipercapnia neste org��o. Contudo, os nossos resultados demonstraram que os n��veis de cAMP s��o mais elevados em condi����es fisiol��gicas, o que sugere que o cAMP possa ter uma fun����o homeost��tica neste org��o. Por ��ltimo, o presente trabalho demonstrou que os aumentos de cAMP descritos por outros em condi����es de hipercapnia, n��o s��o observ��veis quando o pH se encontra controlado. ------------------ ABSTRACT: The work presented in this dissertation was aimed to establish how specific is cAMP-signaling pathways in the CB mainly in different CO2 conditions and how O2 concentrations alter/drives the manipulation of cAMP signaling in the CB. The experimental studies included in this thesis sought to investigate the role of cAMP in the rat CB chemotransduction mechanisms and to determine whether the enzymes that participate in cAMP signal transduction in the CB are regulated by O2/CO2. We characterized the enzymes involved in the cAMP-signaling pathway in the CB (sAC, tmAC, PDE) under different O2/CO2 conditions. Our results demonstrated that many of these enzymes are involved in CO2/O2 sensing and while they may be useful in treating conditions with alterations in CO2/O2 sensing,they will not be specific to chemoreception within the CB: 1) PDE4 is ubiquitously expressed in CB and non-chemoreceptor related tissues and their affinity to inhibitors change with O2 tensions in both CB and carotid arteries, and 2) sAC and tmAC are expressed in peripheral and central chemo- and non-chemoreceptor tissues and their effect on cAMP levels do not change between normocapnic and isohydric hypercapnic conditions. Our results provide evidence against a specific role of cAMP as a mediator for O2 and CO2 chemotransduction in the rat CB and emphasized the role of pH in CO2 sensitivity of the CB. Furthermore, our results demonstrate that cAMP levels are maintained higher under physiological conditions, supporting recent finding from our lab, which all together suggests that cAMP has a homeostatic function in this organ.

Modellierung der Ru��- und NOx-Emissionen des Dieselmotors

Diesel Engine, Soot- and NOx-Emissions, Potency Product Approaches, zero-dimensional Models, optical and thermodynamical Methods, semi-empirical, Combustion Strategy, Injection Rate Shape

Role of NOX enzymes in phagocyte response and signaling upon Chlamydia infection

Les membres de l'ordre des Chlamydiales peuvent infecter un choix ��tendu d'animaux, insectes, et protistes. Comme toutes bact��ries intracellulaires obligatoires, les Chlamydiales ont besoin d'une cellule h��te pour se r��pliquer. Chaque fois qu'une cellule est infect��e une lutte commence entre les m��canismes de d��fense de la cellule et l'arsenal de facteurs de virulence de la bact��rie. Dans cette th��se nous nous sommes int��ress��s �� d��terminer le r��le de deux m��canismes de l'immunit�� inn��e de l'h��te. En premier, nous avons ��tudi�� les NADPH oxidases, une source de mol��cules superoxydantes (MSO). Leur r��le dans la restriction de la r��plication de Waddlia chondrophila et Estrella iausannensis a ��t�� ��tudi�� dans l'organisme mod��le Dictyostelium discoideum et les macrophages humains. Diff��rentes prot��ines Nox ��taient n��cessaires pour contr��ler la r��plication de W. chondrophila ou E. Iausannensis. De plus, nous avons d��termin�� que parmi les Chlamydiales, cinq esp��ces poss��daient une catalase. Cette enzyme peut d��grader l'eau oxyg��n��e, une MSO. L'activit�� de la catalase a ��t�� d��montr��e in vitro et dans les corps ��l��mentaires. Avant de pouvoir ��tudier le r��le de NOX2 dans des macrophages infect��s avec E. Iausannensis, nous avons d�� ��tablir la capacit�� de la bact��rie �� se r��pliquer clans les macrophages avec son trafic intracellulaire. Le deuxi��me m��canisme d'immunit�� inn��e que nous avons ��tudi�� est l'autophagie. Dans les cellules infect��es l'autophagie permet de dig��rer les bact��ries envahissantes. Deux prot��ines de la voie autophagique (Atg1 et Atg8) jouent un r��le dans la restriction de la croissance de W. chondrophila dans D. discoideum. D'avantage d'��tudes sur l'immunit�� inn��e et les bact��ries apparent��s aux Chlamydia sont indispensables, car les r��ponses paraissent ��tre sp��cifiques pour chaque esp��ce. - Members of the Chlamydiales order are able to infect a large variety of animals, insects, and protists. These obligate intracellular bacteria require a host cell for replication. Each time a cell is infected a struggle begins between the virulence arsenal of the bacteria and the defense mechanisms activated by the host. Each bacterial species will exhibit a selection of virulence factors that will allow it to overcome the defense of the host in some species, but not others. In this thesis we were interested in dissecting the role of two host innate immunity mechanisms. First we determined the role of NADPH oxidases, a source of reactive oxygen species (ROS), in restricting replication of Waddlia chondrophila and EstreHa lausannensis in the model organism Dictyostelium discoideum and human macrophages. Different Nox proteins were required to restrict growth of W. chondrophila and E. lausannensis. Additionally, we determined that five Chlamydia- related bacterial species encode for catalase, an enzyme that is able to degrade hydrogen peroxide, a ROS. The activity of the catalase was demonstrated in vitro and in elementary bodies. To study the role of NOX2 in macrophages for E. lausannensis we first had to determine the ability of E. lausannensis to grow in macrophages. Besides demonstrating its replication we also determined the intracellular trafficking of E. lausannensis. The second innate immunity mechanism studied was autophagy. Through autophagy bacteria can be targeted to degradation. Atg1 and Atg8, two autophagic proteins appeared restrict W. chondrophila replication in D. discoideum. More studies on innate immunity and Chlamydia-related bacteria are required. It appears that the responses to innate immunity are species specific and it will be difficult to generalize data obtained for W. chondrophila to the Chlamydiales order.