999 resultados para Óxido nítrico sintase Teses
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O cncer destaca-se pela alta incidncia e mortalidade. Os tratamentos atualmente usados so agressivos e no especficos, com isso cresce a busca por novas drogas. Uma substncia que vem despertando muito interesse so as zelitas, minerais com caracterstica porosa e estrutura conhecida. Estas possuem aes como adjuvante de vacinas, imunomoduladores e imunoestimuladores, o que desperta o interesse em estuda-las no modelo antitumoral. O presente estudo avaliou o efeito antitumoral e imunomodulador da zelita natural clinoptilolita e da zelita comercial, utilizando um modelo de cncer mamrio (Tumor de Ehrlich). Para tanto a zelita natural foi caracterizada (Microscopia Eletrnica de Varredura e Difrao de raio X), realizada avaliao da viabilidade celular (ensaio de MTT), determinada a produo de xido nítrico por macrfagos peritoneais, quantificao de citocinas (ELISA) e avaliao do crescimento tumoral. As zelitas natural e comercial apresentaram elevada ativao de macrfagos, e no produziram quantidades significativas de NO. A zelita natural apresentou citotoxicidade frente ao Tumor de Ehrlich em duas concentraes testadas (5 e 25 mg/ml). No houve liberao significativa da citocina IL-10, no entanto os grupos que foram reestimulados com zelita natural apresentaram maior liberao de IL-1 e TNF-. Nos testes in vivo, a zelita comercial foi a nica que apresentou inibio tumoral frente ao Tumor de Ehrlich, sendo necessrios estudos mais aprofundados para definir a sua atividade antitumoral nesse tipo celular.
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Fundao de Amparo Pesquisa do Estado de So Paulo (FAPESP)
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Conselho Nacional de Desenvolvimento Cientfico e Tecnolgico (CNPq)
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O cncer destaca-se pela alta incidncia e mortalidade. Os tratamentos atualmente usados so agressivos e no especficos, com isso cresce a busca por novas drogas. Uma substncia que vem despertando muito interesse so as zelitas, minerais com caracterstica porosa e estrutura conhecida. Estas possuem aes como adjuvante de vacinas, imunomoduladores e imunoestimuladores, o que desperta o interesse em estuda-las no modelo antitumoral. O presente estudo avaliou o efeito antitumoral e imunomodulador da zelita natural clinoptilolita e da zelita comercial, utilizando um modelo de cncer mamrio (Tumor de Ehrlich). Para tanto a zelita natural foi caracterizada (Microscopia Eletrnica de Varredura e Difrao de raio X), realizada avaliao da viabilidade celular (ensaio de MTT), determinada a produo de xido nítrico por macrfagos peritoneais, quantificao de citocinas (ELISA) e avaliao do crescimento tumoral. As zelitas natural e comercial apresentaram elevada ativao de macrfagos, e no produziram quantidades significativas de NO. A zelita natural apresentou citotoxicidade frente ao Tumor de Ehrlich em duas concentraes testadas (5 e 25 mg/ml). No houve liberao significativa da citocina IL-10, no entanto os grupos que foram reestimulados com zelita natural apresentaram maior liberao de IL-1 e TNF-. Nos testes in vivo, a zelita comercial foi a nica que apresentou inibio tumoral frente ao Tumor de Ehrlich, sendo necessrios estudos mais aprofundados para definir a sua atividade antitumoral nesse tipo celular.
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Fundao de Amparo Pesquisa do Estado de So Paulo (FAPESP)
Inhibition of iNOS induces antidepressant-like effects in mice: Pharmacological and genetic evidence
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Recent evidence has suggested that systemic administration of non-selective NOS inhibitors induces antidepressant-like effects in animal models. However, the precise involvement of the different NOS isoforms (neuronal-nNOS and inducible-iNOS) in these effects has not been clearly defined yet. Considering that mediators of the inflammatory response, that are able to induce iNOS expression, can be increased by exposure to stress, the aim of the present study was to investigate iNOS involvement in stress-induced behavioral consequences in the forced swimming test (FST), an animal model sensitive to antidepressant drugs. Therefore, we investigated the effects induced by systemic injection of aminoguanidine (preferential iNOS inhibitor), 1400W (selective iNOS inhibitor) or n-propyl-L-arginine (NPA, selective nNOS inhibitor) in mice submitted to the FST. We also investigated the behavior of mice with genetic deletion of iNOS (knockout) submitted to the FST. Aminoguanidine significantly decreased the immobility time (IT) in the FST. 1400W but not NPA, when administered at equivalent doses considering the magnitude of their Ki values for iNOS and nNOS, respectively, reduced the IT, thus suggesting that aminoguanidine-induced effects would be due to selective iNOS inhibition. Similarly, iNOS KO presented decreased IT in the FST when compared to wild-type mice. These results are the first to show that selective inhibition of iNOS or its knockdown induces antidepressant-like effects, therefore suggesting that iNOS-mediated NO synthesis is involved in the modulation of stress-induced behavioral consequences. Moreover, they further support NO involvement in the neurobiology of depression. This article is part of a Special Issue entitled 'Anxiety and Depression'. (C) 2011 Elsevier Ltd. All rights reserved.
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The aim of this study was to compare the in vitro cytotoxicity of white mineral trioxide aggregate (MTA), MTA Fillapex and Portland cement (PC) on human cultured periodontal ligament fibroblasts. Periodontal ligament fibroblast culture was established and the cells were used for cytotoxic tests after the fourth passage. Cell density was set at 1.25 X10 4 cells/well in 96-well plates. Endodontic material extracts were prepared by placing sealer/cement specimens (5X3mm) in 1mL of culture medium for 72 h. The extracts were then serially two-fold diluted and inserted into the cell-seeded wells for 24, 48 and 72 h. MTT assay was employed for analysis of cell viability. Cell supernatants were tested for nitric oxide using the Griess reagent system. MTA presented cytotoxic effect in undiluted extracts at 24 and 72 h. MTA Fillapex presented the highest cytotoxic levels with important cell viability reduction for pure extracts and at and dilutions. In this study, PC did not induce alterations in fibroblast viability. Nitric oxide was detected in extract-treated cell supernatants and also in the extracts only, suggesting presence of nitrite in the soluble content of the tested materials. In the present study, MTA Fillapex displayed the highest cytotoxic effect on periodontal ligament fibroblasts followed by white MTA and PC.
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For the last 40 years, schizophrenia has been considered to be the result primarily of a dysfunction in brain dopaminergic pathways. In this review, it is described and discussed findings concerning nitric oxide-mediated neurotransmission in schizophrenia. Studies were searched in PubMed, SciELO, and LILACS using the terms schizophrenia and nitric oxide plasma levels or nitric oxide serum levels, with no time limit. The reference lists of selected articles were also hand-searched for additional articles. From 15 potential reports, 10 were eligible to be included in the review and meta-analysis. These studies included a total of 505 patients with schizophrenia and 339 healthy volunteers. No significant difference was found between patients and healthy controls regarding total nitrite plasma/serum levels (effect size g = 0.285, 95%CI = -0.205 to 0.774, p = 0.254). However, when studies with patients under antipsychotic treatment were examined separately, there was a significant difference between patients and healthy volunteers (effect size g = 0.663, 95%CI = 0.365 to 0.961, p < 0.001), showing that patients under treatment have higher levels of plasma/serum nitric oxide than controls. These results suggest that antipsychotics increase nitric oxide plasma/serum levels and that the nitrergic pathway would be a fertile target for the development of new treatments for patients with schizophrenia.
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The activation of the transient receptor potential vanilloid type 1 channel (TRPV1) has been correlated with oxidative and nitrosative stress and cell death in the nervous system. Our previous results indicate that TRPV1 activation in the adult retina can lead to constitutive and inducible nitric oxide synthase-dependent protein nitration and apoptosis. In this report, we have investigated the potential effects of TRPV1 channel activation on nitric oxide synthase (NOS) expression and function, and the putative participation of ionotropic glutamate receptors in retinal TRPV1-induced protein nitration, lipid peroxidation, and DNA fragmentation. Intravitreal injections of the classical TRPV1 agonist capsaicin up-regulated the protein expression of the inducible and endothelial NOS isoforms. Using 4,5-diaminofluorescein diacetate for nitric oxide (NO) imaging, we found that capsaicin also increased the production of NO in retinal blood vessels. Processes and perikarya of TRPV1-expressing neurons in the inner nuclear layer of the retina were found in the vicinity of nNOS-positive neurons, but those two proteins did not colocalize. Retinal explants exposed to capsaicin presented high protein nitration, lipid peroxidation, and cell death, which were observed in the inner nuclear and plexiform layers and in ganglion cells. This effect was partially blocked by AP-5, a NMDA glutamate receptor antagonist, but not by CNQX, an AMPA/kainate receptor antagonist. These data support a potential role for TRPV1 channels in physiopathological retinal processes mediated by NO, which at least in part involve glutamate release.
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Background: Nitric oxide synthase (NOS) is essential for the synthesis of nitric oxide (NO), a non-conventional neurotransmitter with an important role in synaptic plasticity underlying processes of hippocampus-dependent memory and in the regulation of biological clocks and circadian rhythms. Many studies have shown that both the NOS cytosolic protein content and its enzymatic activity present a circadian variation in different regions of the rodent brain, including the hippocampus. The present study investigated the daily variation of NOS enzymatic activity and the cytosolic content of nNOS in the hippocampus of pigeons. Results: Adult pigeons kept under a skeleton photoperiod were assigned to six different groups. Homogenates of the hippocampus obtained at six different times-of-day were used for NOS analyses. Both iNOS activity and nNOS cytosolic protein concentrations were highest during the subjective light phase and lowest in the subjective dark phase of the circadian period. ANOVA showed significant time differences for iNOS enzymatic activity (p < 0.05) and for nNOS protein content (p < 0.05) in the hippocampus. A significant daily rhythm for both iNOS and nNOS was confirmed by analysis with the Cosinor method (p < 0.05). The present findings indicate that the enzymatic activity of iNOS and content of nNOS protein in the hippocampus of pigeons exhibit a daily rhythm, with acrophase values occurring during the behavioral activity phase. Conclusions: The data corroborate the reports on circadian variation of NOS in the mammalian hippocampus and can be considered indicative of a dynamic interaction between hippocampus-dependent processes and circadian clock mechanisms.
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Bronchial hyperresponsiveness is a hallmark of asthma and many factors modulate bronchoconstriction episodes. A potential correlation of formaldehyde (FA) inhalation and asthma has been observed; however, the exact role of FA remains controversial. We investigated the effects of FA inhalation on Ovalbumin (OVA) sensitisation using a parameter of respiratory mechanics. The involvement of nitric oxide (NO) and cyclooxygenase-derived products were also evaluated. The rats were submitted, or not, to FA inhalation (1%, 90 min/day, 3 days) and were OVA-sensitised and challenged 14 days later. Our data showed that previous FA exposure in allergic rats reduced bronchial responsiveness, respiratory resistance (Rrs) and elastance (Ers) to methacholine. FA exposure in allergic rats also increased the iNOS gene expression and reduced COX-1. L-NAME treatment exacerbated the bronchial hyporesponsiveness and did not modify the Ers and Rrs, while Indomethacin partially reversed all of the parameters studied. The L-NAME and Indomethacin treatments reduced leukotriene B4 levels while they increased thromboxane B2 and prostaglandin E2. In conclusion, FA exposure prior to OVA sensitisation reduces the respiratory mechanics and the interaction of NO and PGE2 may be representing a compensatory mechanism in order to protect the lung from bronchoconstriction effects.
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La nefropata obstructiva puede ser un desorden renal complejo de tratar debido al severo cuadro inflamatorio, desbalance oxidativo, apoptosis y fibrosis. Estudios previos sostienen que rosuvastatina (Ros) podra tener utilidad como una opcin teraputica en enfermedades renales que cursaran con apoptosis y fibrosis. Objetivo: Evaluar los posibles efectos antiapoptticos y antifibrticos de Ros durante la obstruccin ureteral unilateral en ratas neonatas. Materiales y Mtodos: Ratas Wistar neonatas de 48 hs. de vida fueron intervenidas quirrgicamente (grupo experimental) o no (grupo control). Ambos grupos fueron subdivididos en tratadas o no tratadas con Ros (10mg / kg por da) va oral durante 14 das. Posteriormente se procedi a nefrectomizar y procesar las cortezas renales para determinar por RT-PCR las expresiones de genes: xido nítrico sintasa inducible (iNOS), factor promotor gnico de chaperonas (hsf1), protena de shock trmico (hsp70), bax, bcL2, wt1, p53, snail, protena morfognica del hueso (bmp7), caderina E, factor transformador de crecimiento (tgf-) y factor de necrosis tumoral (tnf-). Resultados: La obstruccin ureteral unilateral neonatal indujo una marcada fibrosis y apoptosis, mientras que el tratamiento con Ros modul el patrn de genes fibrticos y apoptticos mediante disminucin de la expresin de bmp7, caderina E, wt1, p53 y bcl2; adems indujo una cada en la expresin de los genes profibrticos y proapoptticos (bax, tnf- y tgf-). El anlisis de los resultados presentados, permiten sugerir que la proteccin renal de rosuvastatina durante nefropata obstructiva de ratas neonatas estara asociado a la interaccin entre hsp70 y la biodisponibilidad del xido nítrico con el concomitante descenso en genes pro-apoptticos.
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En el paradigma clsico, los efectos biolgicos de la radiacin ionizante se atribuyen al dao en el ADN inducido en cada clula irradiada. La demostracin de efectos de vecindad causados por radiacin ionizante (EVIR) ha generado un cambio profundo en la concepcin actual de la radiobiologa. Los EVIR son aquellos efectos causados por la radiacin que se producen en clulas que no han sido irradiadas. Diversos avances tcnicos, en particular el empleo de microhaces, han permitido estudiar los EVIR in vitro. Se conocen dos vas por las cuales las clulas irradiadas pueden comunicarse con las no irradiadas, a saber: mediante uniones especializadas (nexos) que comunican los citoplasmas de clulas adyacentes, y mediante la secrecin de factores solubles al medio extracelular. Estos factores incluyen varias citokinas y especies reactivas del oxgeno y nitrgeno. Las vas de sealizacin en las clulas afectadas involucran en particular la activacin de protena kinasas activadas por mitgenos (MAPK) y del factor de transcripcin NFciclooxigenasa 2, sintasa de xido nítrico 2 y NAD(P)H oxidasa. Los EVIR pueden causar mutaciones puntuales y cambios epigenticos. Los efectos sobre las vas de sealizacin pueden persistir indefinidamente e incluso transmitirse a la descendencia. Paradjicamente, en ciertas condiciones los EVIR pueden ser adaptativos, es decir que tornan a las clulas afectadas ms resistentes a la radiacin. La adaptacin exige sntesis de protenas y mejora la capacidad celular de reparar el ADN y resistir el estrs oxidativo. Los EVIR tambin se han demostrado in vivo. Por tanto, pueden tener implicaciones importantes en radioterapia, tanto para mejorar la eficacia teraputica como para reducir la incidencia de efectos adversos. Asimismo, su mejor conocimiento puede influenciar las normas internacionales de radioproteccin.
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El xido nitroso (N2O) es un potente gas de efecto invernadero (GHG) proveniente mayoritariamente de la fertilizacin nitrogenada de los suelos agrcolas. Identificar estrategias de manejo de la fertilizacin que reduzcan estas emisiones sin suponer un descenso de los rendimientos es vital tanto a nivel econmico como medioambiental. Con ese propsito, en esta Tesis se han evaluado: (i) estrategias de manejo directo de la fertilizacin (inhibidores de la nitrificacin/ureasa); y (ii) interacciones de los fertilizantes con (1) el manejo del agua, (2) residuos de cosecha y (3) diferentes especies de plantas. Para conseguirlo se llevaron a cabo meta-anlisis, incubaciones de laboratorio, ensayos en invernadero y experimentos de campo. Los inhibidores de la nitrificacin y de la actividad ureasa se proponen habitualmente como medidas para reducir las prdidas de nitrgeno (N), por lo que su aplicacin estara asociada al uso eficiente del N por parte de los cultivos (NUE). Sin embargo, su efecto sobre los rendimientos es variable. Con el objetivo de evaluar en una primera fase su efectividad para incrementar el NUE y la productividad de los cultivos, se llev a cabo un meta-anlisis. Los inhibidores de la nitrificacin dicyandiamide (DCD) y 3,4-dimetilepyrazol phosphate (DMPP) y el inhibidor de la ureasa N-(n-butyl) thiophosphoric triamide (NBPT) fueron seleccionados para el anlisis ya que generalmente son considerados las mejores opciones disponibles comercialmente. Nuestros resultados mostraron que su uso puede ser recomendado con el fin de incrementar tanto el rendimiento del cultivo como el NUE (incremento medio del 7.5% y 12.9%, respectivamente). Sin embargo, se observ que su efectividad depende en gran medida de los factores medioambientales y de manejo de los estudios evaluados. Una mayor respuesta fue encontrada en suelos de textura gruesa, sistemas irrigados y/o en cultivos que reciben altas tasas de fertilizante nitrogenado. En suelos alcalinos (pH 8), el inhibidor de la ureasa NBPT produjo el mayor efecto. Dado que su uso representa un coste adicional para los agricultores, entender las mejores prcticas que permitan maximizar su efectividad es necesario para posteriormente realizar comparaciones efectivas con otras prcticas que incrementen la productividad de los cultivos y el NUE. En base a los resultados del meta-anlisis, se seleccion el NBPT como un inhibidor con gran potencial. Inicialmente desarrollado para reducir la volatilizacin de amoniaco (NH3), en los ltimos aos algunos investigadores han demostrado en estudios de campo un efecto mitigador de este inhibidor sobre las prdidas de N2O provenientes de suelos fertilizados bajo condiciones de baja humedad del suelo. Dada la alta variabilidad de los experimentos de campo, donde la humedad del suelo cambia rpidamente, ha sido imposible entender mecansticamente el potencial de los inhibidores de la ureasa (UIs) para reducir emisiones de N2O y su dependencia con respecto al porcentaje de poros llenos de agua del suelo (WFPS). Por lo tanto se realiz una incubacin en laboratorio con el propsito de evaluar cul es el principal mecanismo bitico tras las emisiones de N2O cuando se aplican UIs bajo diferentes condiciones de humedad del suelo (40, 60 y 80% WFPS), y para analizar hasta qu punto el WFPS regula el efecto del inhibidor sobre las emisiones de N2O. Un segundo UI (i.e. PPDA) fue utilizado para comparar el efecto del NBPT con el de otro inhibidor de la ureasa disponible comercialmente; esto nos permiti comprobar si el efecto de NBPT es especfico de ese inhibidor o no. Las emisiones de N2O al 40% WFPS fueron despreciables, siendo significativamente ms bajas que las de todos los tratamientos fertilizantes al 60 y 80% WFPS. Comparado con la urea sin inhibidor, NBPT+U redujo las emisiones de N2O al 60% WFPS pero no tuvo efecto al 80% WFPS. La aplicacin de PPDA increment significativamente las emisiones con respecto a la urea al 80% WFPS mientras que no se encontr un efecto significativo al 60% WFPS. Al 80% WFPS la desnitrificacin fue la principal fuente de las emisiones de N2O en todos los tratamientos mientras que al 60% tanto la nitrificacin como la desnitrificacin tuvieron un papel relevante. Estos resultados muestran que un correcto manejo del NBPT puede suponer una estrategia efectiva para mitigar las emisiones de N2O. Con el objetivo de trasladar nuestros resultados de los estudios previos a condiciones de campo reales, se desarroll un experimento en el que se evalu la efectividad del NBPT para reducir prdidas de N y aumentar la productividad durante un cultivo de cebada (Hordeum vulgare L.) en secano Mediterrneo. Se determin el rendimiento del cultivo, las concentraciones de N mineral del suelo, el carbono orgnico disuelto (DOC), el potencial de desnitrificacin, y los flujos de NH3, N2O y xido nítrico (NO). La adicin del inhibidor redujo las emisiones de NH3 durante los 30 das posteriores a la aplicacin de urea en un 58% y las emisiones netas de N2O y NO durante los 95 das posteriores a la aplicacin de urea en un 86 y 88%, respectivamente. El uso de NBPT tambin increment el rendimiento en grano en un 5% y el consumo de N en un 6%, aunque ninguno de estos incrementos fue estadsticamente significativo. Bajo las condiciones experimentales dadas, estos resultados demuestran el potencial del inhibidor de la ureasa NBPT para mitigar las emisiones de NH3, N2O y NO provenientes de suelos arables fertilizados con urea, mediante la ralentizacin de la hidrlisis de la urea y posterior liberacin de menores concentraciones de NH4 + a la capa superior del suelo. El riego por goteo combinado con la aplicacin dividida de fertilizante nitrogenado disuelto en el agua de riego (i.e. fertirriego por goteo) se considera normalmente una prctica eficiente para el uso del agua y de los nutrientes. Algunos de los principales factores (WFPS, NH4 + y NO3 -) que regulan las emisiones de GHGs (i.e. N2O, CO2 y CH4) y NO pueden ser fcilmente manipulados por medio del fertirriego por goteo sin que se generen disminuciones del rendimiento. Con ese propsito se evaluaron opciones de manejo para reducir estas emisiones en un experimento de campo durante un cultivo de meln (Cucumis melo L.). Los tratamientos incluyeron distintas frecuencias de riego (semanal/diario) y tipos de fertilizantes nitrogenados (urea/nitrato clcico) aplicados por fertirriego. Fertirrigar con urea en lugar de nitrato clcico aument las emisiones de N2O y NO por un factor de 2.4 y 2.9, respectivamente (P < 0.005). El riego diario redujo las emisiones de NO un 42% (P < 0.005) pero aument las emisiones de CO2 un 21% (P < 0.05) comparado con el riego semanal. Analizando el Poder de Calentamiento global en base al rendimiento as como los factores de emisin del NO, concluimos que el fertirriego semanal con un fertilizante de tipo nítrico es la mejor opcin para combinar productividad agronmica con sostenibilidad medioambiental en este tipo de agroecosistemas. Los suelos agrcolas en las reas semiridas Mediterrneas se caracterizan por su bajo contenido en materia orgnica y bajos niveles de fertilidad. La aplicacin de residuos de cosecha y/o abonos es una alternativa sostenible y eficiente desde el punto de vista econmico para superar este problema. Sin embargo, estas prcticas podran inducir cambios importantes en las emisiones de N2O de estos agroecosistemas, con impactos adicionales en las emisiones de CO2. En este contexto se llev a cabo un experimento de campo durante un cultivo de cebada (Hordeum vulgare L.) bajo condiciones Mediterrneas para evaluar el efecto de combinar residuos de cosecha de maz con distintos inputs de fertilizantes nitrogenados (purn de cerdo y/o urea) en estas emisiones. La incorporacin de rastrojo de maz increment las emisiones de N2O durante el periodo experimental un 105%. Sin embargo, las emisiones de NO se redujeron significativamente en las parcelas enmendadas con rastrojo. La sustitucin parcial de urea por purn de cerdo redujo las emisiones netas de N2O un 46 y 39%, con y sin incorporacin de residuo de cosecha respectivamente. Las emisiones netas de NO se redujeron un 38 y un 17% para estos mismos tratamientos. El ratio molar DOC:NO3 - demostr predecir consistentemente las emisiones de N2O y NO. El efecto principal de la interaccin entre el fertilizante nitrogenado y el rastrojo de maz se dio a los 4-6 meses de su aplicacin, generando un aumento del N2O y una disminucin del NO. La sustitucin de urea por purn de cerdo puede considerarse una buena estrategia de manejo dado que el uso de este residuo orgnico redujo las emisiones de xidos de N. Los pastos de todo el mundo proveen numerosos servicios ecosistmicos pero tambin suponen una importante fuente de emisin de N2O, especialmente en respuesta a la deposicin de N proveniente del ganado mientras pasta. Para explorar el papel de las plantas como mediadoras de estas emisiones, se analiz si las emisiones de N2O dependen de la riqueza en especies herbceas y/o de la composicin especfica de especies, en ausencia y presencia de una deposicin de orina. Las hiptesis fueron: 1) las emisiones de N2O tienen una relacin negativa con la productividad de las plantas; 2) mezclas de cuatro especies generan menores emisiones que monocultivos (dado que su productividad ser mayor); 3) las emisiones son menores en combinaciones de especies con distinta morfologa radicular y alta biomasa de raz; y 4) la identidad de las especies clave para reducir el N2O depende de si hay orina o no. Se establecieron monocultivos y mezclas de dos y cuatro especies comunes en pastos con rasgos funcionales divergentes: Lolium perenne L. (Lp), Festuca arundinacea Schreb. (Fa), Phleum pratense L. (Php) y Poa trivialis L. (Pt), y se cuantificaron las emisiones de N2O durante 42 das. No se encontr relacin entre la riqueza en especies y las emisiones de N2O. Sin embargo, estas emisiones fueron significativamente menores en ciertas combinaciones de especies. En ausencia de orina, las comunidades de plantas Fa+Php actuaron como un sumidero de N2O, mientras que los monocultivos de estas especies constituyeron una fuente de N2O. Con aplicacin de orina la comunidad Lp+Pt redujo (P < 0.001) las emisiones de N2O un 44% comparado con los monocultivos de Lp. Las reducciones de N2O encontradas en ciertas combinaciones de especies pudieron explicarse por una productividad total mayor y por una complementariedad en la morfologa radicular. Este estudio muestra que la composicin de especies herbceas es un componente clave que define las emisiones de N2O de los ecosistemas de pasto. La seleccin de combinaciones de plantas especficas en base a la deposicin de N esperada puede, por lo tanto, ser clave para la mitigacin de las emisiones de N2O. ABSTRACT Nitrous oxide (N2O) is a potent greenhouse gas (GHG) directly linked to applications of nitrogen (N) fertilizers to agricultural soils. Identifying mitigation strategies for these emissions based on fertilizer management without incurring in yield penalties is of economic and environmental concern. With that aim, this Thesis evaluated: (i) the use of nitrification and urease inhibitors; and (ii) interactions of N fertilizers with (1) water management, (2) crop residues and (3) plant species richness/identity. Meta-analysis, laboratory incubations, greenhouse mesocosm and field experiments were carried out in order to understand and develop effective mitigation strategies. Nitrification and urease inhibitors are proposed as means to reduce N losses, thereby increasing crop nitrogen use efficiency (NUE). However, their effect on crop yield is variable. A meta-analysis was initially conducted to evaluate their effectiveness at increasing NUE and crop productivity. Commonly used nitrification inhibitors (dicyandiamide (DCD) and 3,4-dimethylepyrazole phosphate (DMPP)) and the urease inhibitor N-(n-butyl) thiophosphoric triamide (NBPT) were selected for analysis as they are generally considered the best available options. Our results show that their use can be recommended in order to increase both crop yields and NUE (grand mean increase of 7.5% and 12.9%, respectively). However, their effectiveness was dependent on the environmental and management factors of the studies evaluated. Larger responses were found in coarse-textured soils, irrigated systems and/or crops receiving high nitrogen fertilizer rates. In alkaline soils (pH 8), the urease inhibitor NBPT produced the largest effect size. Given that their use represents an additional cost for farmers, understanding the best management practices to maximize their effectiveness is paramount to allow effective comparison with other practices that increase crop productivity and NUE. Based on the meta-analysis results, NBPT was identified as a mitigation option with large potential. Urease inhibitors (UIs) have shown to promote high N use efficiency by reducing ammonia (NH3) volatilization. In the last few years, however, some field researches have shown an effective mitigation of UIs over N2O losses from fertilized soils under conditions of low soil moisture. Given the inherent high variability of field experiments where soil moisture content changes rapidly, it has been impossible to mechanistically understand the potential of UIs to reduce N2O emissions and its dependency on the soil water-filled pore space (WFPS). An incubation experiment was carried out aiming to assess what is the main biotic mechanism behind N2O emission when UIs are applied under different soil moisture conditions (40, 60 and 80% WFPS), and to analyze to what extent the soil WFPS regulates the effect of the inhibitor over N2O emissions. A second UI (i.e. PPDA) was also used aiming to compare the effect of NBPT with that of another commercially available urease inhibitor; this allowed us to see if the effect of NBPT was inhibitor-specific or not. The N2O emissions at 40% WFPS were almost negligible, being significantly lower from all fertilized treatments than that produced at 60 and 80% WFPS. Compared to urea alone, NBPT+U reduced the N2O emissions at 60% WFPS but had no effect at 80% WFPS. The application of PPDA significantly increased the emissions with respect to U at 80% WFPS whereas no significant effect was found at 60% WFPS. At 80% WFPS denitrification was the main source of N2O emissions for all treatments. Both nitrification and denitrification had a determinant role on these emissions at 60% WFPS. These results suggest that adequate management of the UI NBPT can provide, under certain soil conditions, an opportunity for N2O mitigation. We translated our previous results to realistic field conditions by means of a field experiment with a barley crop (Hordeum vulgare L.) under rainfed Mediterranean conditions in which we evaluated the effectiveness of NBPT to reduce N losses and increase crop yields. Crop yield, soil mineral N concentrations, dissolved organic carbon (DOC), denitrification potential, NH3, N2O and nitric oxide (NO) fluxes were measured during the growing season. The inclusion of the inhibitor reduced NH3 emissions in the 30 d following urea application by 58% and net N2O and NO emissions in the 95 d following urea application by 86 and 88%, respectively. NBPT addition also increased grain yield by 5% and N uptake by 6%, although neither increase was statistically significant. Under the experimental conditions presented here, these results demonstrate the potential of the urease inhibitor NBPT in abating NH3, N2O and NO emissions from arable soils fertilized with urea, slowing urea hydrolysis and releasing lower concentrations of NH4 + to the upper soil layer. Drip irrigation combined with split application of N fertilizer dissolved in the irrigation water (i.e. drip fertigation) is commonly considered best management practice for water and nutrient efficiency. Some of the main factors (WFPS, NH4 + and NO3 -) regulating the emissions of GHGs (i.e. N2O, carbon dioxide (CO2) and methane (CH4)) and NO can easily be manipulated by drip fertigation without yield penalties. In this study, we tested management options to reduce these emissions in a field experiment with a melon (Cucumis melo L.) crop. Treatments included drip irrigation frequency (weekly/daily) and type of N fertilizer (urea/calcium nitrate) applied by fertigation. Crop yield, environmental parameters, soil mineral N concentrations, N2O, NO, CH4, and CO2 fluxes were measured during the growing season. Fertigation with urea instead of calcium nitrate increased N2O and NO emissions by a factor of 2.4 and 2.9, respectively (P < 0.005). Daily irrigation reduced NO emissions by 42% (P < 0.005) but increased CO2 emissions by 21% (P < 0.05) compared with weekly irrigation. Based on yield-scaled Global Warming Potential as well as NO emission factors, we conclude that weekly fertigation with a NO3 --based fertilizer is the best option to combine agronomic productivity with environmental sustainability. Agricultural soils in semiarid Mediterranean areas are characterized by low organic matter contents and low fertility levels. Application of crop residues and/or manures as amendments is a cost-effective and sustainable alternative to overcome this problem. However, these management practices may induce important changes in the nitrogen oxide emissions from these agroecosystems, with additional impacts on CO2 emissions. In this context, a field experiment was carried out with a barley (Hordeum vulgare L.) crop under Mediterranean conditions to evaluate the effect of combining maize (Zea mays L.) residues and N fertilizer inputs (organic and/or mineral) on these emissions. Crop yield and N uptake, soil mineral N concentrations, dissolved organic carbon (DOC), denitrification capacity, N2O, NO and CO2 fluxes were measured during the growing season. The incorporation of maize stover increased N2O emissions during the experimental period by c. 105 %. Conversely, NO emissions were significantly reduced in the plots amended with crop residues. The partial substitution of urea by pig slurry reduced net N2O emissions by 46 and 39 %, with and without the incorporation of crop residues respectively. Net emissions of NO were reduced 38 and 17 % for the same treatments. Molar DOC:NO3 - ratio was found to be a robust predictor of N2O and NO fluxes. The main effect of the interaction between crop residue and N fertilizer application occurred in the medium term (4-6 month after application), enhancing N2O emissions and decreasing NO emissions as consequence of residue incorporation. The substitution of urea by pig slurry can be considered a good management strategy since N2O and NO emissions were reduced by the use of the organic residue. Grassland ecosystems worldwide provide many important ecosystem services but they also function as a major source of N2O, especially in response to N deposition by grazing animals. In order to explore the role of plants as mediators of these emissions, we tested whether and how N2O emissions are dependent on grass species richness and/or specific grass species composition in the absence and presence of urine deposition. We hypothesized that: 1) N2O emissions relate negatively to plant productivity; 2) four-species mixtures have lower emissions than monocultures (as they are expected to be more productive); 3) emissions are lowest in combinations of species with diverging root morphology and high root biomass; and 4) the identity of the key species that reduce N2O emissions is dependent on urine deposition. We established monocultures and two- and four-species mixtures of common grass species with diverging functional traits: Lolium perenne L. (Lp), Festuca arundinacea Schreb. (Fa), Phleum pratense L. (Php) and Poa trivialis L. (Pt), and quantified N2O emissions for 42 days. We found no relation between plant species richness and N2O emissions. However, N2O emissions were significantly reduced in specific plant species combinations. In the absence of urine, plant communities of Fa+Php acted as a sink for N2O, whereas the monocultures of these species constituted a N2O source. With urine application Lp+Pt plant communities reduced (P < 0.001) N2O emissions by 44% compared to monocultures of Lp. Reductions in N2O emissions by species mixtures could be explained by total biomass productivity and by complementarity in root morphology. Our study shows that plant species composition is a key component underlying N2O emissions from grassland ecosystems. Selection of specific grass species combinations in the context of the expected nitrogen deposition regimes may therefore provide a key management practice for mitigation of N2O emissions.
Resumo:
Trypanosoma cruzi es el agente causal de la enfermedad de Chagas, un problema de salud importante en Amrica Latina, as como tambin en Amrica Central, ya que causa infeccin crnica afectando a millones de personas [1]. Durante esta enfermedad se han descripto varias alteraciones de la respuesta inmune, entre ellas una severa inmunosupresin durante la etapa aguda de la infeccin, tanto en humanos como en ratones. Clulas T provenientes de ratones infectados activadas in vitro, muestran reduccin en la respuesta proliferativa a mitgenos, caracterstica de un estado de inmunosupresin [2-4]. La falla del sistema inmune durante estadios tempranos de la infeccin probablemente colabore con la diseminacin y el establecimiento del parsito. Un gran nmero de estudios se han focalizado en la identificacin de mecanismos moleculares responsables del fenmeno de inmunosupresin, entre los mecanismos citados se ha demostrado presencia de clulas supresoras [5-9], factores inmunosupresores presentes en el parsito [2, 3, 10-13], produccin excesiva de xido nítrico [14], disminuida produccin de IL-2 y reducida expresin del receptor de IL2 en clulas de bazo de animales infectados [9, 15-17]. Muchos de estos mecanismos han sido exhaustivamente investigados, sin embargo no est del todo claro si existen mecanismos adicionales involucrados en la inmunosupresin de la clula T. Adicionalmente, en los ltimos aos nuevas molculas que median la regulacin negativa de la clula T, entre las cuales estn PD-1/PD1-L [18], arginasa [19] y E3 ubiquitina ligasas [20-22], han sido reportadas durante inmunosupresin en diversas infecciones.
