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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
31

Studies about Fusarium infection of emmer and naked barley during grain ripening and the post-harvest period

Trümper, Christina 04 February 2014 (has links)
No description available.
32

Influencia da adição de torta de castanha do Brasil a dieta AIN-93G sobre o crescimento e composição corporea de ratos Wistar / Influence of the addition of Brazil nut cake to the AIN-93G diet on growth and body composition of rats : Brazil nuts deffated cake nutritional characteristics

Poeta, Paula Telles 14 August 2018 (has links)
Orientador: Mario Roberto Marostica Junior / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia de Alimentos / Made available in DSpace on 2018-08-14T08:09:11Z (GMT). No. of bitstreams: 1 Poeta_PaulaTelles.pdf: 385218 bytes, checksum: 2bf4aaf0b22dbeace1a8f8016c3145ef (MD5) Previous issue date: 2009 / Resumo: O objetivo do presente trabalho foi avaliar a qualidade nutricional da castanha do Brasil, enfatizando sua qualidade protéica e aminoacídica, sua composição em ácidos graxos e as alterações na composição corpórea de ratos Wistar decorrentes de sua ingestão em diferentes proporções na forma de torta desengordurada. Assim o estudo se iniciou com o recebimento das amêndoas da castanha do Brasil, provenientes da indústria Juta e CastanhaÒ, localizada na cidade de São Paulo. Em seguida procedeu-se à sua prensagem, utilizando a prensa ERT -60-II da Scott TechÒ, empresa localizada no município de Vinhedo ¿ SP. A composição centesimal das fontes protéicas utilizadas no estudo, torta desengordurada de castanha do Brasil e caseína, (utilizada como proteína padrão) foi determinada. A partir desses dados, foram confeccionadas as dietas dos animais, com 12% de proteína, com base na dieta AIN-93G para roedores. As dietas continham diferentes teores de torta e caseína como fontes de proteína, resultando em quatro dietas diferentes, sendo elas: G1: 100% caseína; G2: 35% torta/ 65%caseína; G3: 25%torta/ 75%caseína; G4: 12.5%torta/ 87.5% caseína. O ensaio biológico contou com 32 animais, divididos em quatro grupos de oito animais cada, mantidos em gaiolas separadas, sob ciclo claro/escuro de 12 horas, com temperatura e umidade controladas, durante o período de 28 dias. O consumo de dieta e o ganho de peso foram monitorados. Nos últimos sete dias do período experimental, os animais foram mantidos em gaiolas metabólicas coletando-se urina e fezes para a determinação dos índices de digestibilidade e valor biológico das dietas em estudo. Ao final do experimento, os animais foram sacrificados por decapitação, seu intestino limpo com soro fisiológico e devolvido à carcaça. As carcaças foram congeladas, fatiadas, liofilizadas e trituradas para posterior análise da composição corpórea. O índice químico utilizado para a avaliação da qualidade protéica foi o escore químico de aminoácidos indispensáveis. Para tal, foi realizada a determinação de aminoácidos nas amostras, através de High Performance Liquid Chromatography (HPLC) e derivatização com fenilisotiocianato (PITC). O escore químico revelou que a castanha do Brasil utilizada neste estudo é deficiente em lisina e treonina; entretanto esta amêndoa é muito rica em metionina+cisteína. Os índices nutricionais determinados foram o PER (quociente de eficência protéica), BN (balanço de nitrogênio), Da (digestibilidade aparente) e VBa (valor biológico aparente). Os resultados encontrados foram valores de PER variando entre 2.1 ± 0.03 e 2.7 ± 0.02; os valores de BN variaram de 1.2 ± 0.13 a 3.61 ± 0.04; a Da apresentou percentuais que variaram de 90.0 ± 0.78 a 95.1 ± 0.12 ; e os percentuais de VB encontrados variaram de 85.7 ± 3.42 a 92.2 ± 1.13. A análise da composição de ácidos graxos presentes no óleo extraído da castanha do Brasil foi realizado por meio de cromatografia gasosa e derivatização com trifluoreto de boro. O resultado revelou 45.3% de ácido graxo oléico e 27.4% de linoléico. A avaliação da composição corpórea variou entre os grupos alimentados com diferentes proporções das fontes de proteína. Redução de até 36.0% na composição de lipídios da carcaça foi observada no grupo G3 comparado com o grupo padrão; aumento dos conteúdos de proteína, cinza e umidade foram também detectados em todos os grupos alimentados com torta desengordurada de castanha do Brasil / Abstract: The objective of this work was the evaluation of the nutritional quality of the Brazil nut defatted cake. Emphases were done on the protein quality, fatty acid composition and the impact of different proportions of defatted cake on fed to Wistar rats. Nuts were received from ¿Juta e CastanhaÒ company¿, placed in São Paulo city, and were pressed using ERT-60-II press, to obtain the cake. The proximate percent composition of the protein sources used in this study (defatted cake and casein) were done. The feeds were formulated with 12% of protein. The casein of AIN rodent diet was partially replaced by defatted cake as follows: G1(100% casein); G2 (35% defatted cake/65% casein); G3 (25% defatted cake/75% casein); G4 (12.5 defatted cake/87.5% casein). For the biological assay, 32 animals were used. They were divided into 4 groups of 8 animals each housed separately with a regime of 12 h dark/light cicle, under controlled temperature and humidity during 28 days. Diet consumption and weight gain were registered. During last 7 days of experiment, the animals were housed in metabolic cages for urine and feces collection in order to determine digestibility and biological value of the studied protein diet. At the end of the experiment, the animals were sacrificed (decapitation), the intestines were removed for cleaning with physiological solution and returned to the respective carcass, which were frozen, sliced, freeze dried and triturated for further analysis. Chemical Score of indispensable amino acids was used in evaluating protein quality. Amino acids were determined using HPLC and derivatization with phenylisothiocyanante (PITC). The amino acid chemical score revealed that Brazil nut is deficient in lysine and threonine; however, the nut is very rich in methionine+cysteine. The nutritional indices used in this work were PER (Protein Efficiency ratio), NB (Nitrogen Balance), AD (Apparent digestibility) and ABV (Apparent Biological Value). The results were: PER>2.0; NB positive to all groups; AD > 90.0%; all ABV > 85.0%. The fatty acids composition of Brazil Nut was determined using gas chromatography and derivatization with boron trifluoride. The extracted oil had 45.3% oleic and 27.4% linoleic acids. The body composition varied among the groups fed different protein sources. Reduction of 36.0% of carcass lipid composition was achieved in G3 group compared to control group; increasing of protein, ash and moisture contents were also detected in all groups fed with defatted cake. For statistical analysis, SAS System, BC, 2001 software was used. ANOVA was applied and averages values were compared using Tukey test (p<5%) / Universidade Estadual de Campi / Nutrição Experimental e Aplicada à Tecnologia de Alimentos / Mestre em Alimentos e Nutrição
33

Plant-based meat substitutes and their nutritional composition : A study on iron content, zinc content, calcium content and protein quality in meatballs and plant-based substitutes and how they contribute to the goal of reaching recommended daily intakes

Thyrén, Linnea January 2020 (has links)
The purpose of this thesis was to study similarities and differences between a meat product and its plant-based substitutes in terms of how they enable people to reach the recommended daily intakes (RDI). The meat product included in the study were meatballs and its substitutes were three different plant-based alternatives. One was mainly based on soy, one on pea protein and one consisted of several different vegetables. The parameters studied were iron, zinc and calcium content as well as protein quality. By analyzing the four different products with flame atomic absorption spectroscopy (FAAS), the mineral content was calculated and protein quality was determined using amino acid analyzis carried out by the laboratory analysis company ALS. The method used to determine protein quality was DIAAS (Digestible Indispensable Amino Acid Score). Example meals and example days were created to visualize any differences and similarities when the products were put in a wider perspective. The results showed that there were differences between the products when they were compared individually, but that the differences were negligible when the products were included in an example meal or example day. This indicates that the products fulfill comparable dietary requirements and that the plant-based products were good substitutes for the meat product. The soy-based product was the best plant-based alternative when it comes to iron content, calcium content and protein quality. However, the soy product and the remaining substitutes reached recommended intakes for the same parameters when included in example days, which shows that the differences between the products are only present when analyzed individually.
34

Structural complexity of the co-chaperone SGTA: a conserved C-terminal region is implicated in dimerization and substrate quality control

Martínez-Lumbreras, S., Krysztofinska, E.M., Thapaliya, A., Spilotros, A., Matak-Vinkovic, D., Salvadori, E., Roboti, P., Nyathi, Yvonne, Muench, J.H., Roessler, M.M., Svergun, D.I., High, S., Isaacson, R.L. 08 June 2020 (has links)
Yes / Protein quality control mechanisms are essential for cell health and involve delivery of proteins to specific cellular compartments for recycling or degradation. In particular, stray hydrophobic proteins are captured in the aqueous cytosol by a co-chaperone, the small glutamine-rich, tetratricopeptide repeat-containing protein alpha (SGTA), which facilitates the correct targeting of tail-anchored membrane proteins, as well as the sorting of membrane and secretory proteins that mislocalize to the cytosol and endoplasmic reticulum-associated degradation. Full-length SGTA has an unusual elongated dimeric structure that has, until now, evaded detailed structural analysis. The Cterminal region of SGTA plays a key role in binding a broad range of hydrophobic substrates, yet in contrast to the well-characterized N-terminal and TPR domains, there is a lack of structural information on the C-terminal domain. In this study, we present new insights into the conformation and organization of distinct domains of SGTA and show that the C-terminal domain possesses a conserved region essential for substrate processing in vivo. We show that the C-terminal domain region is characterized by α-helical propensity and an intrinsic ability to dimerize independently of the N-terminal domain. Based on the properties of different regions of SGTA that are revealed using cell biology, NMR, SAXS, Native MS, and EPR, we observe that its C-terminal domain can dimerize in the full-length protein and propose that this reflects a closed conformation of the substrate-binding domain. Our results provide novel insights into the structural complexity of SGTA and provide a new basis for mechanistic studies of substrate binding and release at the C-terminal region. / MRC New Investigator Research Grant: G0900936; BBSRC grants: BB/L006952/1 and BB/L006510/1; BBSRC grant: BB/N006267/1; Wellcome Trust Investigator Award in Science: 204957/Z/16/Z; BBSRC grant: BB/J014567/1
35

Whole-crop pea-oat silages in dairy production : effects of maturity stage and conservation strategy on fermentation, protein quality, feed intake and milk production /

Rondahl, Tomas, January 2007 (has links) (PDF)
Diss. (sammanfattning) Umeå : Sveriges lantbruksuniv., 2007. / Härtill 3 uppsatser.
36

Respostas biológica, sistêmica e reprodutiva de ratos Wistar alimentados com soja geneticamente modificada resistente ao glifosato / Biological, systemic and reproductive evaluation in Wistar rats feed on genetically modified soybean resistant to the glyphosate.

Venzke, Janaína Guimarães 26 February 2009 (has links)
Made available in DSpace on 2014-08-20T13:32:54Z (GMT). No. of bitstreams: 1 tese_janaina_guimaraes_venzke.pdf: 370814 bytes, checksum: ca6312b2d70800b452ae33ccea99bab6 (MD5) Previous issue date: 2009-02-26 / The most cultivated genetically modified plant in Brazil is the soybean [Glycine max (L.) Merr.] resistant to the systemic herbicide glyphosate. There are 12.3 millions of cultivated hectares. This soybean was obtained through the introduction of the gene that codes for the 5-enolpyruyilshikimic-acid3-phosphate synthase enzyme, (EPSPS, E.C 2.5.1.19, CP4), of the shikimic pathway, resistant to glyphosate that keeps active the aromatic amino acids biosynthetic pathway. To the soybean genetical modification the parameters in law were reviewed and the maximum glyphosate limit permitted in beans that was 0.2 mg/kg was increased to 10 mg/kg to GMRR soybean. Although Brazil is the 3rd biggest worldwide producer, cultivates the GMRR soybean for more than ten years, and represents 50% of the overall production of soybean in Brazil, just a few studies have been conducted in the country to evaluate in biological assays, the impact of this technology on the food quality and safety. Thus, the present work seeks for to evaluate the influence of the genetic modification of the soybean on the nutritional quality, on the possible effects of chronical exposition, as well as the effects on the fertility and the development of Wistar rats and the on the endocrine system. The nutritional quality was evaluated through the protein value, in 30 male rats, just weaned, distributed in five groups, fed along 28 days with the following diets, 10% protein ration GMRR soybean no isogenic, GMRR soybean isogenic, conventional soybean, milk (casein) or for 10 days with a non-protein diet. The weight gain and the food intake of diets did not present statistical relevance. The same behavior was observed in the variables of growth and the nitrogen balance study. In the chronical exposition of 40 male and 39 female rats distributed in four groups that consumed genetically modified soybean no isogenic and isogenic, conventional soybean and the standard group without soybean it signs of systemic toxicity on males have been evident in the neutrophilia, lymphocytopenia in the group conventional soybean compared with the standard group, lymphoid hyperplasia of the lungs in the groups without soybean; the signs of reproductive toxicity through of 8 the increase on relative weight of the tests and epididymis and also through the decrease of the sperm concentration. On the females the effect on the reproductive system became evident through the fertility pregnancy and weaning index. These results point out that the protein quality of the genetically modified soybean is preserved, but there is an association of factors that trigger a probable endocrine disruption. Studies are necessary to elucidate the mechanism of interaction that cause toxicity on males and females fed with conventional soybean and genetically modified soybean that presented detectable glyphosate levels. / A espécie vegetal geneticamente modificada mais cultivada no Brasil é a soja [Glycine max (L.) Merr.] resistente ao herbicida sistêmico pós-emergente glifosato, com 12,3 milhões de hectares cultivados. Essa soja foi obtida pela introdução do gene correspondente à enzima 5-enolpiruvilchiquimato-3-fosfato sintase (EPSPS, E.C 2.5.1.19, CP4), enzima da via de chiquimato, resistente ao glifosato, mantendo ativa a via biossintética de aminoácidos aromáticos. A modificação genética fez com que parâmetros preconizados pela legislação brasileira fossem revistos e o limite máximo permitido de glifosato nos grãos que era de 0,2 mg/kg aumentasse para 10 mg/kg. Embora o Brasil cultive há mais de dez anos a soja resistente ao glifosato e seja o terceiro maior produtor mundial dessa leguminosa, com 50% da produção nacional com genótipos transgênicos, poucos estudos têm sido conduzidos no país com o intuito de avaliar, em ensaios biológicos, o impacto dessa tecnologia sobre o meio ambiente, a qualidade e a segurança do alimento. Sendo assim, o presente trabalho objetivou estudar a influência do consumo de grãos de soja geneticamente modificada resistente ao glifosato (GMRR) isogênica à convencional e não isogênica, tratada com este herbicida, sobre a qualidade nutricional, possíveis efeitos à exposição crônica, bem como efeitos sobre a fertilidade e o desenvolvimento de ratos Wistar e a possibilidade deste, desregular o sistema endócrino. A qualidade nutricional foi avaliada através do valor protéico mediante índices biológicos, em 30 machos recém desmamados, distribuídos em cinco grupos, alimentados por 28 dias com ração contendo 10% de proteína de soja GMRR não isogênica, soja GMRR da isogênica, soja convencional, leite (caseína) ou por 10 dias com ração aproteica. O ganho de massa corporal e o consumo alimentar das dietas não diferiu entre os tratamentos. Esse mesmo comportamento foi observado no que concerne às variáveis de crescimento e índices de balanço nitrogenado. Na exposição crônica de 40 machos e 39 fêmeas distribuídos em 4 grupos que consumiram dietas contendo sojas GMRR (isogênica e não isogênica), soja convencional e grupo padrão sem soja, 6 sinais de toxicidade sistêmica nos machos foram evidenciados na neutrofilia, linfopenia do grupo que consumiu soja convencional em relação ao grupo padrão, e na hiperplasia linfóide dos pulmões nos animais que consumiram soja GMRR e convencional; sinais de toxicidade reprodutiva foram observados através do aumento da massa relativa dos testículos e epidídimos e redução da concentração espermática. Nas fêmeas, os efeitos no sistema reprodutivo foram evidenciados através dos índices de fertilidade, e desmame. Estes resultados indicam que a qualidade protéica da soja modificada geneticamente é preservada, porém há uma associação de fatores que desencadeiam em uma provável desregulação endócrina. Outros estudos são necessários para elucidar o mecanismo de interação que provoca efeitos de toxicidade em machos e fêmeas alimentados com soja convencional e GMRR que apresentam níveis detectáveis de glifosato.
37

Über die potenziell kardioprotektive Rolle des Hitzeschockproteins A4 / The potential cardioprotective role of HSPA4

Gersch, Svante Sören 06 October 2020 (has links)
No description available.
38

THE EFFECTS OF DIETARY PROTEIN ON POSTPRANDIAL ESSENTIAL AMINO ACIDS BIOAVAILABILITY AS A SUBSTRATE FOR PROTEIN ANABOLISM IN YOUNG AND OLDER ADULTS AND ON CARDIOMETABOLIC HEALTH-RELATED OUTCOMES

Gavin Connolly (15331777) 29 April 2023 (has links)
<p>Diet is the number one leading modifiable cause of poor health globally, with poor diets accounting for 10.9 million (22%) of all deaths among adults in 2017. In addition, one of our generation’s forthcoming challenges is the rapid expansion of the population aged 60 years and older. Although people are living longer, there is an associated increase in the prevalence of aged-related chronic diseases and functional impairment, such as cardiometabolic diseases and sarcopenia. As such, dietary components can play a role in positively or negatively influencing the prevention and treatment of chronic cardiometabolic diseases and sarcopenia. One such dietary component is dietary protein, which is essential throughout the life course, from gestation through old age. Evidence supports dietary protein playing an important role in reducing the risk of developing age-related chronic diseases such as sarcopenia and cardiometabolic diseases. </p> <p><em><strong>     Study 1, Chapter 2:</strong></em> The Dietary Guidelines for Americans (DGA) recommends consuming a variety of “Protein Foods” based on “ounce equivalent” (oz-eq) portions. In addition, the 2020-2030 Strategic Plan for NIH Nutrition Research includes to “define the role of nutrition across the lifespan” with an objective to “assess the role of nutrition in older adults to promote healthy aging.” However, there is a paucity of primary research that directly compares EAAs bioavailability between young and older adults consuming the same oz-eq portions of varied Protein Foods. No study has assessed the same oz-eq portions of animal- versus plant-based Protein Foods on essential amino acids (EAAs) bioavailability for protein anabolism in young and older adults. Therefore, we conducted two sequential randomized, investigator-blinded, crossover, acute feeding trials with the same study design; first in a cohort of young adults and second in a cohort of older adults. The primary objective of this project was to assess the effect of consuming two oz-eq portions of animal-based (unprocessed lean pork or whole eggs) vs. plant-based (black beans or sliced almonds) Protein Foods as part of a mixed whole foods meal on plasma EAAs bioavailability for protein anabolism. Consistent with our hypotheses, participant age did not affect postprandial EAAs bioavailability, and consuming a meal with two oz-eq of unprocessed lean pork or whole eggs resulted in greater postprandial EAAs bioavailability compared to a meal with two oz-eq of black beans or raw sliced almonds in 1) young adults; 2) older adults; and 3) young and older adults combined. These findings show on the same oz-eq basis, consuming these animal- vs. plant-based Protein Foods more effectively provide bioavailable EAAs for protein anabolism. </p> <p><em><strong>     Study 2, Chapter 3:</strong></em> Poultry meat is the most consumed type of meat worldwide and in the US. Poultry is generally considered to be a “healthy” meat as it is a high-quality protein source and provides other essential nutrients. However, research assessing poultry and its effects on and relations with chronic diseases in humans is sparse, and the forms of poultry typically consumed in the US, are not necessarily in line with recommendations provided by the DGA. Therefore, we conducted a scoping review to systematically search and chronicle scientific literature pertinent to poultry intake and human health. Main findings from this project were 1) historically, little research, especially randomized diet-controlled feeding trials, has been conducted to understand associations between and effects of consuming poultry products on human health; 2) the majority of research is from observational studies assessing relationships between poultry intake and risks of morbidity and mortality from various types of cancer; 3) a paucity of research exists to support chicken as a health-promoting food in children; and 4) research taking into account poultry product processing and cooking methods is needed. Science and health professionals, the poultry industry, and the public will benefit from new observational and experimental research to address cutting-edge scientific, public policy, and consumer topics pertinent to poultry intake and human health. </p> <p><em><strong>     Study 3, Chapter 4:</strong></em> Emerging research on whey protein supplementation suggests it may be a potential modifier of type 2 diabetes mellitus (T2DM) risk factors, including glucose control. As systematic reviews and/or meta-analyses of randomized controlled trials are gaining importance in nutrition literature, we conducted an umbrella systematic review to search for and chronicle published systematic reviews and/or meta-analyses of randomized controlled trials pertinent to whey protein supplementation and T2DM modifiable risk factors (study 3, Chapter 4). Among the 13 systematic reviews, including 12 meta-analyses critically assessed for this umbrella review, no reviews reported any adverse effects of whey protein on any reported T2DM-related risk factor. Collectively, a preponderance of evidence indicates whey protein supplementation improves multiple clinical indicators of glucose control in apparently healthy adults and those at increased risk for type 2 diabetes mellitus. </p>
39

Ubiquitination assays and protein-protein interactions of E3 ligase CHIP.

De Silva, Anthony Ruvindi Iroshana 06 July 2023 (has links)
No description available.
40

Les abondances naturelles des isotopes stables de l'azote chez le rat : facteurs de variabilité et application pour l'étude des flux azotés et de l'impact métabolique de conditions nutritionnelles et physiopathologiques par modélisation compartimentale. / Natural abundances of stable nitrogen isotopes in rats : their variability and application for the study of body nitrogen fluxes and of the metabolic impact of nutritional and pathophysiological conditions using compartmental modeling.

Poupin, Nathalie 10 January 2013 (has links)
Les abondances relatives naturelles des différents isotopes stables de l'azote (δ15N) varient selon les tissus au sein d'un individu et selon les individus au sein d'une population, et ces différences reflètent à la fois les caractéristiques de structure et de fonctionnement du métabolisme azoté et ses modulations en lien avec des variations des conditions nutritionnelles et physio-pathologiques. Cette thèse vise, à travers une approche couplée d'expérimentation et de modélisation, à mieux caractériser et comprendre les modulations des δ15N des différents pools azotés et à démontrer la capacité des δ15N à fournir des informations sur les flux azotés de l'organisme, leurs valeurs et modulations, qui sont encore mal connus. Nous avons, dans un premier temps, mesuré les δ15N dans plusieurs tissus (intestin, foie, plasma, muscles, rein, peau...) et dans différentes fractions azotées (acides aminés, protéines, urée, NH4) chez le rat, dans différentes conditions nutritionnelles (chez des rats nourris avec des P de qualité différente, les protéines de lait et de soja) ou physiopathologiques (chez des rats présentant ou non un syndrome métabolique, associant insulino-résistance et obésité, après avoir consommé un même régime potentiellement obésogène). Ces données expérimentales nous ont permis (i) de montrer que l'écart de δ15N entre les protéines tissulaires et le régime est plus important lorsque la qualité protéique est moindre, et (ii) de mettre en évidence que, lors de l'initiation précoce d'un syndrome métabolique associant insulino-résistance et obésité, les δ15N de certains pools métaboliques sont modulés et constituent des signatures isotopiques des modulations métaboliques associées. Par ailleurs, grâce à l'analyse par modélisation compartimentale des cinétiques de δ15N mesurées expérimentalement dans les fractions acides aminés et protéines de différents tissus après augmentation du δ15N du régime, nous avons pu estimer les taux de renouvellement protéique tissulaires et explorer la structure et le fonctionnement des échanges entre acides aminés et protéines des différents tissus et comparer leur degré de compartimentation. Enfin, nous avons développé un modèle multi-compartimental reproduisant l'ensemble des flux azotés inter- et intra-organes de l'organisme et rendant compte des variations de δ15N observées. Cette représentation globale du métabolisme azoté fournit une vision novatrice du fonctionnement intégré du métabolisme azoté dont les données éparses de la littérature ne donnaient auparavant qu'une vision parcellaire et fragmentée. Le modèle a permis de reconstituer les mécanismes qui conduisent à l'observation de différences de δ15N entre pools azotés, de mieux comprendre quelles modulations sont les plus susceptibles d'affecter les δ15N, avec quelle amplitude et dans quel sens, et finalement d'expliquer les variations de δ15N mises en évidence expérimentalement en terme de modulation des flux azotés. L'ensemble de nos résultats d'expérimentation et de modélisation démontre la capacité des δ15N à apporter des informations sur les flux métaboliques azotés et souligne l'intérêt prometteur de cette approche nouvelle pour acquérir une compréhension intégrée du système complexe du métabolisme azoté inter- et intra-organes et des processus homéostatiques qui le régulent et de ses dérégulations pré-pathologiques. / Natural abundances of stable nitrogen isotopes vary among tissues within an individual and among individuals within a population, and these differences are linked to the structural and functioning characteristics of the nitrogen metabolism and also to its modulations in response to variations in nutritional and physiological conditions. In this thesis, we developed an approach combining both experimentation and modeling, in order to better characterize and understand the modulations in the δ15N values of various nitrogen metabolic pools, and to show the capacity of the δ15N to provide information regarding the values and modulations of the body nitrogen fluxes, that are still poorly determined. We first measured the δ15N in various tissues (intestine, liver, plasma, muscle, kidney, skin …) and in various nitrogen fractions (amino acids, proteins, urea, NH4) in rats, under different nutritional (i.e. in rats fed with P of distinct quality, that were milk and soy P) or pathophysiological (i.e. in rats that had or not become obese and insulin resistant after being fed a high-fat diet for 10 weeks). From these experimental data, we showed (i) that the tissue nitrogen discrimination (i.e., the difference between tissue and diet δ15N) is higher when the P is of lesser quality, and (ii) that, during the onset of a metabolic syndrome, in the presence of both insulin resistance and obesity, the δ15N differed in some nitrogen pools and thus constitute isotopic signatures of the metabolic impact of such conditions. In this thesis, we also measured the δ15N kinetics in the amino acid and protein fractions of several tissues after a shift in the diet δ15N. The analysis of these kinetics, using a compartimental modeling approach, enabled us to estimate tissue fractional turnover rates and to investigate the structure and the functioning of the protein synthesis and breakdown exchanges in some tissues and their level of compartmentation. Lastly, we developed a multi-compartmental model that describes the various body nitrogen transfers between and within tissues and accounts for the observed δ15N variability. This model of the nitrogen metabolism provides a new and systemic insight of the interactions and modulations of the various nitrogen fluxes, as opposed to the fragmented information available from the literature data. This model enabled us to reconstruct the mechanisms that caused the observed δ15N differences between nitrogen pools, to better understand how they vary, depending on which metabolic modulation and with which amplitude, and finally to hypothesize which nitrogen fluxes alterations are the more likely to be responsible for the δ15N variations that we observed in our experimentations. In conclusion, our experimental and modelling results show that it is feasible to gain information from the δ15N values regarding the metabolic nitrogen fluxes and their modulations, and highlight the interest of this new approach to get an integrated insight into the complex nitrogen metabolic system and a better understanding of the way the various between and within tissues nitrogen fluxes are regulated and altered.

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