Malaria is prevalent in over 100 countries which is populated by half of the world’s population and culminates in approximately one million deaths per annum, 85% of which occurs in sub-Saharan Africa. The combined resistance of the mosquitoes and parasites to the currently available pesticides and antimalarial chemotherapeutic agents requires the concerted effort of scientists in the malaria field to identify and develop novel mechanisms to curb this deadly disease. In this study, a thorough understanding of the role players in the polyamine pathway of the parasite was obtained, which could aid future studies in the development of novel inhibitory compounds against these validated drug targets. The uniquely bifunctional S-adenosylmethionine decarboxylase/ornithine decarboxylase (AdoMetDC/ODC) of Plasmodium falciparum forms an important controlling node between the polyamine and methionine metabolic pathways. It has been speculated that the unique bifunctional association of the rate-limiting enzymes allows for the concerted regulation of the respective enzyme activities resulting in polyamine synthesis as per requirement for the rapidly proliferating parasite while the methionine levels are strictly controlled for their role in the methylation status. The results of this study showed that the enzyme activities of the bifunctional complex are indeed coordinated and subtle conformational changes induced by complex formation is suggested to result in these altered kinetics of the individual AdoMetDC and ODC domains. Studies also showed that the identification of the interaction sites between the domains, which allows for communication across the complex, may be targeted for specific interference with the enzyme activities. Furthermore, these studies showed that the current knowledge on the different subclasses of the AdoMetDC family should be re-evaluated since P. falciparum AdoMetDC shows diverse properties from orthologues and therefore points towards a novel grouping of the plasmodial protein. The extensive biochemical and biophysical studies on AdoMetDC has also provided important avenues for the crystallisation and solving of this protein’s 3D structure for subsequent structure-based identification of drug-like lead compounds against AdoMetDC activity. The application of structure-based drug design on malarial proteins was additionally investigated and consequently proved that the rational design of lead inhibitory compounds can provide important scaffold structures for the identification of the key aspects that are required for the successful inhibition of a specific drug target. Spermidine synthase, with its intricate catalytic mechanism involving two substrate binding sites for the products of the reactions catalysed by AdoMetDC/ODC, was used to computationally identify compounds that could bind within its active site. Subsequent testing of the compounds identified with a dynamic receptor-based pharmacophore model showed promising inhibitory results on both recombinant protein and in vitro parasite levels. The confirmation of the predicted interaction sites and identification of aspects to improve inhibitor interaction was subsequently investigated at atomic resolution with X-ray protein crystallography. The outcome of this doctoral study shows the benefit in applying a multidisciplinary and multinational approach for studying drug targets within the malaria parasite, which has led to a thorough understanding of the targets on both biochemical and structural levels for future drug design studies. / Thesis (PhD)--University of Pretoria, 2011. / Biochemistry / unrestricted

A Araucaria angustifolia é uma conífera nativa do Brasil. Em função da sua intensa exploração florestal, a espécie ocupa apenas 2% de sua vegetação natural. Neste sistema, a aplicação de técnicas biotecnológicas, como a embriogênese somática, podem ser integradas a programas de melhoramento genético e conservação. A similaridade entre a embriogênese somática e zigótica, tem sido utilizada para o estabelecimento de estudos visando o aperfeiçoamento do cultivo in vitro dos embriões somáticos, bem como para um maior conhecimento dos aspectos moleculares e fisiológicos que regulam a embriogênese. O metabolismo de poliaminas (PAs), mais especificamente putrescina, espermidina e espermina, tem se mostrado como fundamental para a compreensão e evolução da embriogênese zigótica e somática. Entretanto, a biossíntese das PAs e seu envolvimento nos vários processos biológicos que regulam a embriogênese, são pouco conhecidas em coníferas. Inserido nessa perspectiva, o presente trabalho teve como objetivo o estudo do metabolismo de PAs durante três estádios de desenvolvimento da semente (contendo as fases da embriogênese inicial até a tardia) e na proliferação de linhagens embriogênicas com diferentes potenciais embriogênicos de A. angustifolia. Foram investigados: a) os perfis de PAs (livres e conjugadas) e aminoácidos; b) determinação da via preferencial da biossíntese de putrescina, através da atividade enzimática da arginina descarboxilase (ADC) e ornitina descarboxilase (ODC); c) identificação e caracterização do padrão de expressão dos genes envolvidos no metabolismo de PAs; e d) a identificação das relações entre os perfis de PAs e aminoácidos presentes nas sementes das matrizes, e sua potencial influência nas fases de indução, proliferação e maturação dos embriões somáticos. Durante a embriogênese zigótica, a expressão dos genes AaADC (arginina descarboxilase) e AaSAMDC (S-adenosilmetionina descarboxilase) aumentaram no estádio cotiledonar, juntamente com o aumento de PAs. A biossíntese da putrescina é realizada preferencialmente via ADC, enquanto que a citrulina foi o principal aminoácido presente nas sementes. Em relação ao metabolismo de PAs nas culturas embriogênicas, os dados obtidos demonstraram que a arginina e ornitina parecem ter diferentes funções em cada linhagem testada. Na linhagem com alto potencial embriogênico, a arginina parece estar associada com a ativação dos genes relacionados ao catabolismo de PAs (AaPAO2, AaCuAO e AaALDH), enquanto que esse efeito não foi observado na linhagem bloqueada. A ODC tem uma maior atividade na linhagem responsiva, enquanto que na linhagem bloqueada, as atividades da ADC e ODC são similares. Dependendo da matriz foram observados diferentes perfis de PAs e aminoácidos, sendo estes perfis relacionados com as taxas de indução, proliferação e desenvolvimento dos embriões somáticos. Putrescina total, ornitina e asparagina foram os metabólitos diferencialmente identificados entre as matrizes, os quais podem ser propostos como marcadores bioquímicos para a seleção de matrizes com alto potencial para a embriogênese somática. Os resultados obtidos fornecem informações relevantes e inéditas sobre o metabolismo de PAs e aminoácidos na embriogênese zigótica e somática de A. angustifolia, bem como fornece novos subsídios para o aprimoramento das condições artificiais utilizadas para o desenvolvimento dos embriões somáticos / The Araucaria angustifolia is a native conifer species of Brazil. Due to its intense exploitation, the species cover only 2% of its original forest area. In this system, biotechnological tools, like somatic embryogenesis, may be integrated into breeding and conservation programs. The similarity between zygotic and somatic embryogenesis have been used to establishment of studies in order to optimization of somatic embryos in vitro culture, as well as for a better understanding of physiologic and molecular aspects that modulates the embryogenesis. The metabolism of polyamines (PAs), specifically putrescine, spermidine and spermine, has been demonstrated as fundamental for the comprehension and evolution of zygotic and somatic embryogenesis. However, the biosynthetic pathways of PAs and their involvement in various biological process that regulate the embryogenesis are little known in conifers. Inserted in this perspective, the aim of the current work was to study the metabolism of PAs during three seeds development stages (containing the early till late embryogenesis phases) and in proliferation of cell lines with different embryogenic potential of A. angustifolia. Were investigated: a) PAs (free and conjugated) and amino acids profiles; b) determination of preferential pathway for putrescine biosynthesis, through enzymatic activity of arginine decarboxylase (ADC) and ornithine decarboxylase (ODC); c) identification and characterization of gene expression profile of genes related to metabolism of PAs; and d) identification of the relationship between PAs and amino acids profiles in seeds of mother plants, and their potential influence in initiation, proliferation and maturation phases of somatic embryos. During the zygotic embryogenesis, AaADC (arginine decarboxylase) and AaSAMDC (S-adenosylmethionine decarboxylase) genes were up-regulated at cotyledonary stage along with the increasing of PAs. The biosynthesis of putrescine is performed preferentially by ADC pathway, while citrulline was the main amino acid recorded during the seed development. Regarding the metabolism of PAs in embryogenic cultures, the data demonstrated that arginine and ornithine seem to have different functions in each cell line tested. In cell line with high embryogenic potential, arginine seems to be associated to activation of genes related to PAs catabolism (AaPAO2, AaCuAO e AaALDH), while in blocked cell line this effect was not observed. ODC has a higher enzymatic activity in responsive cell line, while in blocked cell line, both ADC and ODC activities are similar. Depending of mother plant, were observed different PAs and amino acids profiles, being these profiles related with the rate of initiation, proliferation and maturation of somatic embryos. Total putrescine, ornithine and asparagine were the differentially metabolites identified between the mother plants, which can be proposed as biochemical marker to select mother plant with high potential to somatic embryogenesis. The results obtained provide relevant and inedited information about the metabolism of PAs and amino acids in zygotic and somatic embryogenesis of A. angustifolia, as well as provide news subsidies for optimization of in vitro conditions for somatic embryos development

Molecular aspects of nitrogen metabolism in vertebrates is an interesting area of physiology and evolution to explore due to the different ways in which animals excrete nitrogenous waste as they transition from an aquatic to a terrestrial lifestyle. Two main products of nitrogen metabolism in fishes are ammonia and urea. Ammonia is produced during protein catabolism and build up of ammonia is toxic. Some aquatic vertebrates convert ammonia into a less toxic compound urea via de novo synthesis through the ornithine-urea cycle (O-UC). Five enzymes are involved in the O-UC: carbamoyl phosphate synthetase (CPS), ornithine carbamoyl transferase (OCT), argininosuccinate synthetase (ASS), argininosuccinate lyase (ASL), and arginase (ARG). An accessory enzyme, glutamine synthetase (GS) also participates in the "fish-type" O-UC. Teleosts excrete ammonia passively over their gills into the aquatic environment. The teleost, Opsanus beta, has been shown to increase urea production after 48 hours of crowding. This thesis explored how crowding stress affected nitrogen metabolite levels of ammonia and urea and O-UC gene expression and enzyme activity in O. beta. Lungfishes while in an aquatic environment avoid ammonia toxicity by releasing excess ammonia across their gills, but when stranded on land they produce urea through the O-UC. Urea production via the O-UC has a metabolic cost of at least four ATP molecules. This thesis explored the response of a lungfish, Protopterus annectens, to six days of aerial exposure and re-immersion conditions by measuring concentrations of O-UC mRNA expression and enzyme activity and nitrogen metabolites ammonia and urea. CPS acts as the entry point to the O-UC and based on enzymatic studies, most aquatic vertebrates utilize one isoform of this enzyme (CPSIII) while terrestrial vertebrates utilize a different isoform of this enzyme (CPSI). Lungfishes are a particularly interesting group of air-breathing fishes, not only because of their link to the origins of tetrapods, but also because CPS I may have originated within this group. Both CPS III and CPS I have been enzymatically described within this group. This thesis uses phylogenetics to investigate how CPS nucleotide sequences in lungfishes evolved compared to other vertebrates.

Las poliaminas regulan procesos de crecimiento y diferenciación celular, y su desregulación está relacionada con diferentes patologías incluyendo el cáncer. Las antizimas (AZs) de ornitina descarboxilasa (ODC) inhiben tanto su biosíntesis, como su captación, regulando los niveles intracelulares de poliaminas. En esta tesis se ha caracterizado una nueva proteína inhibidora de antizimas (AZIN2) que posee alta homología con ODC y el inhibidor de antizimas previamente conocido (AZIN1). Esta nueva proteína está desprovista de actividad enzimática, pero es capaz de revertir la acción que las tres antizimas conocidas ejercen sobre la actividad ODC y la captación de poliaminas. A diferencia de sus proteínas homólogas, AZIN2 se localiza subcelularmente en el ERGIC, y se expresa específicamente en cerebro y testículo, pero de forma muy abundante en espermátidas y espermatozoides, al igual que AZ3, indicando que estas dos proteínas juegan un importante papel regulando los niveles de poliaminas durante la espermiogénesis. / Polyamines regulate cell growth and differentiation, and the alteration of their homeostasis is related to different diseases, including cancer. Ornithine decarboxylase (ODC) antizymes (AZs) regulate polyamine levels by inhibiting both their biosynthesis and the cellular uptake. In this work, a new ODC paralogue has been characterized as a novel antizyme inhibitor protein that has been named AZIN2. This protein lacks decarboxylating activity, but it is able to reverse the action of any of the three antizymes on ODC activity and polyamine uptake. Unlike its homologue proteins ODC and AZIN1, AZIN2 is located in the ERGIC, and it is specifically expressed in brain and testes. The abundant expression in spermatids and spermatozoa, concomitantly with AZ3, suggests that both proteins may play an important role in regulating polyamine levels during spermiogenesis

Diss. med. dent. Zürich. / Literaturverz.

Fundação de Amparo a Pesquisa no Estado do Rio Grande do Sul / Gout attack is characterized severe joint pain and inflammation with concomitant accumulation of monosodium urate (MSU) crystals. However, gout and the mechanisms responsible for the acute attacks are poorly understood, leading to improper treatment of the patient and reducing the quality of life. Polyamines (putrescine, spermidine and spermine) are involved in inflammatory nociceptive processes and have not been investigated to date. Therefore, the aim of the present study was to investigate the involvement of polyamines in the development of acute gout attack. Arthritis score, a compound measure of joint compromise that considers edema formation, erythema and paw position, mechanical hyperalgesia and inflammatory parameters were measured in an acute gout attack model in male mice induced by intra-articular (i.a.) injection of MSU, H2O2, phorbol 12-myristate 13-acetate (PMA), L-ornithine or polyamines (putrescine, spermidine, spermine). All these algogenic agents increased arthritis score in a dose-dependent manner with ED50 of 0.73 (0.4-1.1) mg/site for MSU, 2.3 (1.5-3.5) μmol/site for H2O2, 3.5 (2.1-5.6) nmol/site for PMA, 0.6 (0.3-1.1) μmol/site for L-ornithine, 0.8 (0.4-1.7) μmol/site for putrescine, 3.6 (2.6-5.1) μmol/site for spermidine and 0.1 (0.06-0.2) μmol/site for spermine. All tested algogenic agents caused joint edema and nociception, except putrescine, which increased only arthritis score. α-Difluoromethylornithine (DFMO; ornithine decarboxylase ODC - inhibitor, i.a.) prevented MSU-, H2O2-, PMA-, L-ornithine-induced nociception, but not edema. On the other hand, DFMO did not prevent spermine-induced edema and nociception. DFMO prevented MSU-induced increase of ODC activity. Our results indicate that polyamines contribute to acute gout attacks, suggesting that inhibitors of polyamine synthesis may be potential therapeutic agents for the treatment and prophylaxis of gout. / O ataque agudo de gota é caracterizado por dor intensa e inflamação combinados com o acúmulo de cristais de urato monossódico (MSU). No entanto, a gota e os mecanismos responsáveis pelos ataques agudos ainda estão mal compreendidos, levando ao tratamento inadequado dos pacientes e reduzindo a qualidade de vida. As poliaminas (putrescina, espermidina e espermina) estão envolvidas em processos nociceptivos inflamatórios, e não foram investigadas até o momento, por conseguinte, o objetivo do presente estudo foi investigar o envolvimento das poliaminas no desenvolvimento do ataque de gota aguda em camundongos. Para isso, o escore de artrite (conjunto de somatórios de medidas que considera a formação de edema, eritema e posição da pata tratada do animal), hiperalgesia mecânica e parâmetros inflamatórios foram medidos em um modelo de ataque agudo de gota em camundongos machos, induzidos por uma injeção intra-articular de (i.a.) MSU, H2O2, forbol 12-miristato 13-acetato (PMA), L-ornitina ou poliaminas (putrescina, espermidina, espermina). Todos os agentes algogênicos aumentaram o escore de artrite de um modo dose dependente com um DE50 de 0,73 (0,4-1,1) mg/sitio de MSU, 2,3 (1,5-3,5) μmol/sitio de H2O2, 3,5 (2,1-5,6) nmol/sitio para PMA, 0,6 (0,3-1,1) μmol/sitio para a L-ornitina, 0,8 (0,4-1,7) μmol/sitio para a putrescina, 3,6 (2,6-5,1) μmol/sitio para a espermidina e 0,1 (0,06-0,2) μmol/sitio para espermina. Todos os agentes algogênicos testados causaram edema articular e nocicepção, exceto a putrescina, que aumentou apenas o escore de artrite. α-Difluorometilornitina (DFMO; inibidor da ornitina descarboxilase - ODC) preveniu a nocicepção induzida por: MSU, H2O2, PMA, L-ornitina, mas não o edema. Por outro lado, DFMO não preveniu a nocicepção e o edema induzido por espermina. DFMO preveniu o aumento da atividade da ODC induzido por MSU. Os nossos resultados indicam que as poliaminas estão envolvidas no ataque agudo de gota, sugerindo que os inibidores da síntese de poliaminas podem ser potenciais agentes terapêuticos para o tratamento e profilaxia da gota.

An exceptionally important stress response of Pseudomonas putida strains to toxic chemicals is the induction of efflux pumps that extrude solvents, as well as other toxicants, into the surrounding medium. However, the bacterial tolerance mechanisms are still not fully understood, thus in this thesis metabolomic approaches were used to detect and identify metabolites involved in P. putida DOT-T1E tolerance to abiotic stresses, in particular focussing on the role of efflux pumps. To elucidate any metabolome alterations several strains of P. putida, including the wild type DOT-T1E, and the efflux pump knockouts DOT-T1E-PS28 and DOT-T1E-18, were challenged with different levels of propranolol. Fourier-transform infrared (FT-IR) spectroscopy, which provided a rapid, high-throughput metabolic fingerprint of P. putida strains, was used to investigate any phenotypic changes resulting from exposure to propranolol. FT-IR data illustrated phenotypic changes associated with the presence of propranolol within the cell that could be assigned to the bacterial protein components. To complement this phenotypic fingerprinting approach metabolic profiling on the same samples was performed using gas chromatography mass spectrometry (GC-MS) to identify metabolites of interest during growth of bacteria following this toxic perturbation with propranolol. GC-MS revealed significant changes in ornithine levels which can be directly linked to bacterial tolerance mechanisms, and alterations in the levels of several other metabolites which were also modified in response to propranolol exposure. Moreover, the effect of the organic solvent toluene was also investigated using the same approach. Examination of FT-IR data indicated that protein and fatty acids were the most affected components of P. putida strains due to the presence of toluene within the cell. Moreover, application of GC-MS allowed for the identification and quantification of several metabolites which were differentially produced or consumed in the presence of toluene. To investigate the role of efflux pumps in P. putida DOT-T1E, several analytical techniques were employed including Raman spectroscopy, gas and liquid chromatography to identify and quantify the level of propranolol or toluene in P. putida cells. These analyses showed that propranolol and toluene accumulated in the mutant P. putida DOT-T1E-18 (lacking the TtgABC pump) at higher levels in comparison with the levels found in the wild-type DOT-T1E and the mutant DOT-T1E-PS28 (lacking the TtgGHI pump), indicating the key role of efflux pumps in solvent tolerance. Furthermore, the effect of Mg2+ and Ca2+ on the stabilisation of the toluene tolerance of P. putida DOT-T1E strains was examined in order to elucidate whether divalent cations interact with efflux pumps or other resistant mechanisms to improve solvent tolerance. FT-IR analysis suggested that the influence of divalent cations on the stabilisation of the toluene tolerance could be due to the contribution of metal ions towards other tolerance mechanisms such as lipopolysaccharide (LPS) instead of enhancing the activity of efflux pumps. In conclusion, this thesis presents evidence that phenotypic fingerprinting and metabolic profiling approaches in combination with chemometric methods can generate valuable information on phenotypic responses occurring within microbial cultures subjected to abiotic stress.

Thèse numérisée par la Direction des bibliothèques de l'Université de Montréal. / Hepatic encephalopathy (HE) is a neuropsychiatric disorder occurring in both acute and chronic liver diseases. Depending on the duration and degree of hepatic dysfunction, HE may be present as one of two major types; portal-systemic encephalopathy (PSE) (chronic liver failure) and fulminant hepatic failure (FHF) (acute liver failure). Hyperammonemia is a key feature of both PSE and FHF and it is strongly suggested that ammonia toxicity is implicated directly or indirectly in the pathogenesis of both forms of HE. The present thesis comprises 5 articles demonstrating various aspects of the pathophysiology and new approaches to the treatment of HE. In chapter 2.1; article 1, using in vivo microdialysis, brain extracellular glutamate levels were found to be increased in correlation with arterial ammonia levels and the degree of neurological impairment in rats with FHF due to liver devascularization. N-methyl-D-aspartate (NMDA) receptor binding was found to be unchanged in rats with liver devascularization compared to control rats. Treatments for both forms of HE continue to focus on ammonia-lowering strategies. When administered to portacaval shunted (PCS) rats, L-ornithine-Laspartate (OA), two substrates of the urea cycle, was observed to result in a lowering of plasma ammonia and increased plasma urea levels as well as protection against ammonia-induced coma (chapter 2.2; article 2). In acute liver failure, peripheral ammonia is removed via muscle glutamine synthetase (GS). This was confirmed in the study (chapter 2.3; article 3) in rats with liver devascularization where OA also lowered plasma ammonia and protected rats against coma and brain edema. GS activity in muscle was increased following OA treatment. Mild hypothermia was shown to be protective against coma and brain edema in rats with liver devascularization (chapter 2.5; article 5). In mildly hypothermie rats, plasma ammonia levels were unaffected whereas cerebrospinal fluid (CSF) ammonia levels were lowered suggesting that hypothermia prevents increased ammonia uptake into brain. This protective effect was associated with a decrease in extracellular brain glutamate levels, supporting the proposal that glutamate may be implicated in the pathogenesis of brain edema in FHF. Although the precise pathophysiologic mechanisms responsible for HE in FHF are not completely understood, an increased glutamatergic neurotransmission could contribute to this phenomenon. Another potential neurotoxin, manganese, is believed to be implicated in the pathogenesis of PSE. Manganese levels were found to be increased in both autopsied brain tissue from patients and in brain tissue from experimental animal models of PSE (chapter 2.4; article 4). It is suggested that manganese deposition is responsible for the signal hyperintensities on T1-weighted magnetic resonance (MR) images and the extrapyramidal symptoms found in PSE. / L'encéphalopathie hépatique (EH) est un désordre neuropsychiatrique que l'on retrouve soit dans la période aiguë ou la phase chronique d'une maladie du foie. Ainsi, selon la durée de l'atteinte hépatique, l'EH peut se présenter de 2 façons : la première étant l'encéphalopathie porto-systémique et la seconde l'encéphalopathie rencontrée au cours des hépatites fulminantes. L'encéphalopathie porto-systémique est secondaire à la dérivation portosystémique du sang veineux tel que rencontré spontanément lors de l'hypertension portale ou soit suite à une anastomose portocave chirurgicale ou radiologique (shunt intra-hépatique porto systémique transjugulaire ou TIPS). Cliniquement, l'EH portosystémique est un syndrome neurologique qui se développe lentement; le stade précoce est souvent peu apparent et se caractérise par des modifications du cycle du sommeil ainsi que des changements mineurs de personnalité. Une baisse du niveau d’attention ainsi qu'une incoordination musculaire apparaissent ensuite, progressant lentement vers la léthargie, la stupeur et le coma. Du point de vue anatomopathologique, l'EH porto-systémique est caractérisée par une astrocytose sans évidence d'altérations neuronales structurelles. L'hyperammonémie est une caractéristique importante de l'EH portosystémique et de l'encéphalopathie aiguë des hépatites fulminantes. Il est admis que l'ammoniaque est impliquée directement et/ou indirectement dans la pathogénèse dans ces deux types d'EH. À forte concentration, l'ammoniaque a le potentiel d'affecter le système nerveux central de diverses façons. Il y a d'abord un effet direct de l'ion ammonium sur la neurotransmission inhibitrice ou excitatrice ainsi qu'une inhibition de l'enzyme a-cétoglutarate déshydrogénase dans le cycle de Krebs, ce qui a comme conséquence directe d'altérer le métabolisme énergétique du cerveau. Cependant, le métabolisme énergétique du cerveau ne semble affecté que dans les stades très avancés de l'EH porto-systémique ou d'encéphalopathie aiguë des hépatites fulminantes. L'insuffisance hépatique chronique se traduit par une augmentation des concentrations de manganèse dans le sang et le cerveau. Une sélectivité des dépôts de manganèse est l'hypothèse la plus probable afin d'expliquer les signaux hyperintenses localisés dans le pallidum tel que démontré par l'imagerie par résonance magnétique chez les patients cirrhotiques. La section 2.5 démontre que les dépôts de manganèse sont augmentés dans les globus pallidus prélevés à partir d’autopsie du tissu cérébral chez des patients cirrhotiques. La concentration de manganèse est aussi élevée dans le globus pallidus dans deux modèles animaux d'insuffisance hépatique chronique. De plus, une corrélation a été établie entre le degré de dérivation porto-systémique et la quantité de dépôts de manganèse. Au contraire, le manganèse cérébral n'est pas augmenté dans un modèle animal d'hépatite fulminante, ce qui suggère que l'accumulation découle de l'insuffisance hépatique chronique, plus particulièrement suite à une dérivation porto-systémique. L'EH est caractérisée par des perturbations de plusieurs systèmes de neurotransmission cérébrale. Le système glutamatergique est celui qui a été le plus étudié et on croit qu'il est impliqué dans la pathogénèse de l'EH. Des nouveaux traitements sont requis pour traiter ou stabiliser l'EH chez les patients atteints d'EH porto-systémique ou d'encéphalopathie aiguë afin d'augmenter la période de temps nécessaire pour pouvoir effectuer une transplantation. Les traitements actuels sont soit inefficaces ou comportent des effets secondaires très néfastes. Afin de traiter l'EH porto-systémique, on préconise comme thérapie des stratégies axées sur la diminution de l'ammoniaque sérique. La L-ornithine-L-aspartate (OA) est composée de deux substrats du cycle de l'urée qui se sont avérés efficaces pour réduire l'ammoniaque et améliorer les symptômes cliniques chez des patients hyperammonémiques ayant une EH portosystémique. Nous avons démontré un effet protecteur de l'OA sur le coma précipité par une infusion d'ammoniaque chez des rats ayant une dérivation porto-cave. L'effet protecteur s'accompagne d'une réduction significative de l'ammoniaque plasmatique ainsi que d'une augmentation significative de l'urée plasmatique, ce qui suggère que la réduction de la concentration plasmatique de l'ammoniaque est en partie le résultat d'une augmentation de la synthèse d'urée par le foie. Nous croyons aussi que l'OA peut, par l'intermédiaire des transaminases, mener à la production de trois molécules de glutamate. Ce substrat (le glutamate) peut ensuite stimuler l'activité de la glutamine synthétase dans les muscles, le foie et le cerveau pour ainsi former de la glutamine. Cette possibilité est soutenue par l'augmentation du glutamate et de la glutamine dans le plasma et le liquide céphalo-rachidien (LCR). Contrairement à l'EH porto-systémique, l’insuffisance hépatique fulminante (HF) progresse très rapidement en quelques heures ou jours seulement, vers un état mental altéré, la stupeur et finalement le coma. Les convulsions sont rares mais des myoclonies sont souvent rencontrées avant le coma. Dans cette condition, le taux de mortalité est élevé et la mort est souvent causée par une hernie du tronc cérébral secondaire à une hypertension intracrânienne causée par un oedème cérébral massif. L'oedème cellulaire des astrocytes est fréquemment observé mais l'astrocytose Alzheimer de Type II (voir insuffisance hépatique chronique) n'est pas une caractéristique neuropathologique de l'hépatite fulminante. L'ammoniaque est aussi incriminée dans la physiopathologie de ce type d'encéphalopathie. Afin d'élucider davantage la pathophysiologie de l'encéphalopathie des HF, nous avons mesuré, par le biais d'une microdialyse cérébrale in vivo, les concentrations extracellulaires des acides aminés dans le cortex frontal de rats atteints d'HF induite par dévascularisation hépatique afin d'établir une relation avec le degré d'atteinte neurologique. Dans ce modèle, on retrouve un oedème cérébral accompagné d'une augmentation de l'eau, tel que mesurée dans le cortex frontal. Les concentrations extracellulaires de glutamate sont significativement élevées trois heures avant le début du stade précoma et continuent à augmenter jusqu'à l'état comateux. Ces données suggèrent que l'HF mène à une augmentation de la libération de glutamate et/ou une diminution de la recapture du glutamate de l'espace extracellulaire. Récemment, des études sur le tissu cérébral de rats encéphalopathiques suite à une HF ont révélé une diminution de la concentration protéique et de l'expression génique de GLT-1, un transporteur astrocytaire du glutamate. L'augmentation de la production de la glutamine via la glutamine synthétase est aussi possiblement impliquée dans la pathogénèse de ce type d'encéphalopathie. Cependant, l'augmentation constante des concentrations de glutamine extracellulaire n'est pas corrélée avec la sévérité de l'encéphalopathie. Ceci suggère que la glutamine joue un rôle plutôt mineur dans la pathogénèse de l'oedème cérébral. Les traitements de l'encéphalopathie des HF sont axés sur le contrôle de l'hypertension intracrânienne. La transplantation hépatique demeure le traitement ultime mais d'autres traitements sont nécessaires afin de prolonger la vie des patients en attente de transplantation. Des stratégies visant à diminuer les taux d'ammoniaque ont été développées depuis qu'une étude récente a démontré que la survenue d'hernie cérébrale chez les patients souffrant d'HF était corrélée à la concentration artérielle d'ammoniaque. Nous avons démontré que l'infusion d'OA chez des rats ayant subi une dévascularisation hépatique entraînait un délai significatif avant l'apparition du coma, et une diminution significative de l'ammoniaque du plasma et du LCR comparativement aux contrôles. Cette diminution d'ammoniaque était accompagnée d'une réduction du contenu cérébral en eau. Le glutamate et la glutamine plasmatiques furent aussi significativement augmentés et puisque le cycle de l'urée est non-fonctionnel dans un foie dévascularisé, la réduction d'ammoniaque ne pouvait donc être induite que par la stimulation de la glutamine synthétase des muscles squelettiques. Le glutamate présent dans le LCR diminue parallèlement à la réduction du contenu cérébral en eau. Un autre des traitements qui fut récemment développé pour contrôler l'encéphalopathie des HF est l'hypothermie modérée. En réduisant la température corporelle de rats ayant subi une dévascularisation hépatique à 34°C, nous avons démontré un effet protecteur de cette procédure sur l'apparition du coma et de l'oedème cérébral. Les niveaux des acides aminés furent aussi mesurés en utilisant la méthode de microdialyse cérébrale in vivo et nous avons démontré une diminution du glutamate extracellulaire chez les rats protégés par l’hypothermie. Les mécanismes possiblement impliqués dans l'action bénéfique de l'hypothermie modérée incluent la diminution du transfert de l'ammoniaque sanguin vers le cerveau et la diminution des concentrations extracellulaires cérébrales d'acides aminés excitateurs tels que le glutamate. Ces résultats ajoutent davantage de crédibilité à la notion que la disponibilité élevée du glutamate dans l'espace extracellulaire et donc, une neurotransmission glutamatergique élevée, est impliquée dans la pathogénèse de certaines des complications cérébrales rencontrées au cours de l'HF. Ces résultats appuient aussi l'hypothèse que l'hypothermie modérée peut s'avérer une méthode efficace de prévention de l'encéphalopathie et de l'oedème cérébral, deux complications cérébrales très sévères de l'HF.

Reaktion von Arginin mit Abbauprodukten 1,4-verknüpfter Disaccharide Im Verlauf der Reaktion von Arginin mit Abbauprodukten 1,4-glycosidisch verknüpfter Disaccharide entsteht ein Hauptderivatisierungsprodukt des Arginins, welches aus Inkubationsansätzen von Lactose mit N-(tert-Butoxycarbonyl)-L-arginin (Boc-Arg) bzw. N-a-Hippuryl-L-arginin (Hip-Arg) isoliert und als N-d-[5-(3-Hydroxypropyl)-4-oxo-imidazolon-2-yl]-L-ornithin (PIO) identifiziert werden konnte. PIO stellt ein spezifisches Reaktionsprodukt von Arginin mit Abbauprodukten 1,4-glycosidisch verknüpfter Disaccharide dar. Zum Nachweis des Precursors von PIO wurden die Bildung und der Abbau von 1,2-Dicarbonylverbindungen in Inkubationsansätzen von Lactose mit und ohne Hip-Arg nach der Hitzebehandlung mit o-Phenylendiamin untersucht. Es zeigte sich, dass ein als 1,2-Dicarbonylverbindung identifiziertes Abbauprodukt von Lactose nur in Abwesenheit von der Aminokomponente (Hip-Arg) als Hauptabbauprodukt bestimmbar war. Nach Isolierung dieser 1,2-Dicarbonylverbindung in Form ihres stabilen Chinoxalin-Derivates und der Strukturaufklärung ist es gelungen, dieses Hauptabbauprodukt der Lactose als (3'-Hydroxypropyl)-chinoxalin also das Chinoxalin der 3,4-Didesoxypentosulose (3,4-DDPs) zu identifizieren. Bestimmung von 1,2-Dicarbonylverbindungen in Lebensmitteln Glyoxal (GO), Methylglyoxal (MGO), 3-Desoxyglucosulose (3-DG) und 3-Desoxypentosulose (3-DPs) konnten nach Umsetzung mit o-Phenylendiamin erstmals in Milch- und Milchprodukten quantifiziert werden. Für Glyoxal wurden Gehalte von 0,06 bis 3,5 mg/ l und für Methylglyoxal von 0,2 bis 4,7 mg/ l bestimmt. 3-Desoxyglucosulose wurde mit Gehalten von 0,7 bis 3,5 mg/ l und 3-Desoxypentosulose von 0,1 bis 4,7 mg/ l bestimmt. Des Weiteren erfolgte die Bestimmung von Glyoxal, Methylglyoxal und 3-Desoxyglucosulose in käuflich erworbenen deutschen Honigen, in Honigen des Imkerverbandes Dresden und in neuseeländischen Honigen. Im Vergleich zu den Milchprodukten wurden deutlich höhere Gesamtgehalte an 1,2-Dicarbonylverbindungen (124 bis 1550 mg/ kg) bestimmt. Für 3-Desoxyglucosulose wurden 119 bis 1451 mg/ kg, für Glyoxal 0,2 bis 4,6 mg/ kg und für Methylglyoxal 0,5 bis 743 mg/ kg ermittelt. Ein Zusammenhang zwischen hohen Gehalten an 1,2-Dicarbonylverbindungen und der antibakteriellen Aktivität der Honige wurde untersucht. Hier stellten die neuseeländischen Manuka-Honige (Manuka: Leptospermum scoparium, Teebaum) den Schwerpunkt der Untersuchung dar. Für die untersuchten Manuka-Honige konnten ungewöhnlich hohe Gehalte an Methylglyoxal bestimmt werden (von 347 bis 743 mg/ kg). Von 12 verschiedenen Honigen deutscher und neuseeländischer Herkunft konnten nur Manuka-Honige als antibakteriell wirksam eingestuft werden. Bezogen auf den Gehalt an Methylglyoxal liegen die MIC-Werte für Staphylococcus aureus bei 1,5 mmol/ l für Manuka-Honig (35 % v/v), 1,4 mmol/ l für Manuka-Honig "active" (30 % v/v), 1,1 mmol/ l für Manuka-Honig UMF 10+ (25 % v/v) bzw. 1,8 mmol/ l für Manuka-Honig UMF 20+ (20 % v/v). Es zeigte sich, dass die antibakterielle Aktivität des Honigs unmittelbar auf den Methylglyoxal-Gehalt zurückführbar war.

The rising number of the population that present with major depressive disorder has intensified the need to identify and elucidate new biological markers for the diagnosis and treatment of depression. Depression presents with evidence of changes in the nitric oxide (NO) pathway. In this study, levels of various endogenous markers of the NO cascade, viz. nitrite (NO2–), asymmetrical dimethylarginine (ADMA) and arginase II activity, were investigated in the Flinders Sensitive Line (FSL) rat, a genetic animal model of depression. The aim of the current study was to determine if there are differences between these markers in the plasma of the FSL rat compared to its healthy control, the (Flinders Resistant Line) FRL rat, with the possibility of considering their use as biomarkers of depression. Nitrite was chosen as metabolite over nitrate (NO3–) because the dietary intake of nitrite and/or nitrate does not significantly affect nitrite (NO2–) levels in plasma. Although this is of no significance if applied to rats, it is an important factor to be considered when doing clinical studies. For neurochemical determination of nitrite a sensitive fluorometric reversed phase high–performance liquid chromatographic (HPLC) assay was developed to analyze nitrite in human and rat plasma. Derivatization of sample nitrite was performed with 2,3–diaminonaphthalene (DAN) followed by the quantification of the stable and highly fluorescent product, 2,3–naphthotriazole (NAT). Determination of arginase II activity was performed by measuring L–arginine and L–ornithine concentrations in the plasma, while ADMA was measured simultaneously with L–arginine and L–ornithine using liquid chromatography/tandem mass spectrometry, or LC/MS/MS. Plasma nitrite levels of FSL rats were significantly decreased compared to plasma nitrite levels in the FRL rat, but neither the levels of ADMA nor arginase II activity showed a significant difference between the FSL and FRL rat groups. From these results it is concluded that in accordance with previous studies, the NO pathway plays an important role in the pathophysiology of depression, as depicted in the differences found between plasma nitrite levels in the FSL rat compared to its healthy control. / Thesis (M.Sc. (Pharmacology))--North-West University, Potchefstroom Campus, 2011.