Retinopathy of prematurity, a disease characterised by aberrant retinal vascular development in premature neonates, is a leading cause of blindness and visual impairment in childhood. This work sought to examine differences in the susceptibility of inbred rat strains to oxygen-induced retinopathy, a model of human retinopathy of prematurity. The overriding aim was to identify genetic factors in rats that might be generalisable to humans. Newborn rats of six different strains were exposed to alternating cycles of hyperoxia and relative hypoxia for fourteen days. Rats were removed to room air and killed for analysis immediately, to assess oxygen-induced retinal vascular attenuation, or four days later to evaluate the extent of hypoxia-induced vasoproliferation. Whole flat-mounted retinae were stained with fluorophore conjugated isolectin GS-IB4, and measurement of vascular area was conducted using fluorescence microscopy and video-image analysis. A hierarchy of susceptibility to the inhibitory effects of cyclic hyperoxia and relative hypoxia on postnatal retinal vascularization was identified for the rat strains studied. Susceptibility to vascular attenuation was predictive of the subsequent risk of vascular morphological abnormalities. Cross-breeding experiments between susceptible and resistant strains demonstrated that the susceptible phenotype was dominantly inherited in an autosomal fashion. These studies confirmed an association between ocular pigmentation and retinopathy risk, however the finding of differential susceptibility amongst albino rat strains implicated factors in addition to those associated with ocular pigmentation. Quantitative real-time reverse transcription-polymerase chain reaction was used to compare the retinal expression of angiogenic factor genes in susceptible and resistant strains with the aim of identifying a genetic basis for the strain difference. Eight angiogenic factor genes were selected for study: vascular endothelial growth factor (VEGF); VEGF receptor 2; angiopoietin 2; Tie2; pigment epithelium-derived factor; erythropoietin; cyclooxygenase-2 and insulin-like growth factor-1. The most notable difference between strains was the expression of vascular endothelial growth factor (VEGF) during the cyclic hyperoxia exposure period - higher VEGF expression was associated with relative resistance to retinopathy. Other differences in retinal angiogenic factor gene expression between strains, such as higher expression of VEGF receptor 2 and angiopoietin 2 in resistant strains, appeared to be secondary to those in VEGF. Following cyclic hyperoxia, the expression pattern of angiogenic factor genes changed - messenger RNA levels of hypoxia-induced genes, including VEGF, VEGF receptor 2, angiopoietin 2 and erythropoietin, were significantly higher in those strains with larger avascular areas, than in those strains that were relatively resistant to retinopathy. These findings provide firm evidence for hereditary risk factors for oxygen-induced retinopathy in the rat. Differences in the regulatory effects of oxygen on VEGF expression appear to be central to the risk of retinopathy. The potential relevance of these hereditary factors is discussed in the context of the human disease.

No description available.

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No. of bitstreams: 1 TeseLAZ.pdf: 5426859 bytes, checksum: 033582b6221f018d86ae920b42835b76 (MD5) Previous issue date: 2016-10-26 / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / For adequate blood supply to match metabolic demand, vertebrates regulate blood pressure (BP) in order to maintain adequate perfusion of target organs avoiding ischemia and tissue damage like edema. Effective short-term BP regulation in anuran amphibians occurs through adjustments in heart rate (HR), peripheral vascular resistance, and changing pulsatile frequency of lymph hearts. In addition, pulmonary ventilation in anurans is directly linked to blood volume homeostasis by facilitating lymph fluid movement back into the cardiovascular system which takes place by changing pressure and volume within anurans' lymphatic sacs. It is apparent that an interaction between baroreflex regulation and breathing control exists in anuran amphibians. In the present study I used pharmacological methods (phenylephrine and sodium nitroprusside; infusion ramp and in bolus methods) to investigate baroreflex sensitivity at different temperatures in the cururu toad Rhinella schneideri. I evaluated the degree to which arterial baroreflex plays a role in pulmonary ventilation in the cururu toad. Baroreflex regulation in the toad R. schneideri was temperature dependent and influenced the toad’s ventilation. Hypotension and hypertension resulted in increases and decreases in HR, respectively, as well as increases and decreases in pulmonary ventilation mainly through adjustments in breathing frequency. In contrast to data from the literature, anuran amphibians seem to defend lower BP events primarily rather than hypertension independent of temperature. Anurans exhibit higher rates of transcapillary fluid filtration which means during hypertension fluid filtration is increased and excess interstitial fluid formation will be reclaimed by an efficient lymphatic system. Therefore, besides pulmonary ventilation's role in matching O2 delivery to demand (e.g. temperatures) in anurans, it also plays a role in BP regulation possibly owing to an interaction between baroreflex control and respiratory areas in the brain. / Para um adequado suprimento sanguíneo de modo a atender as diferentes demandas metabólicas, os vertebrados regulam a pressão arterial (PA) mantendo adequada perfusão dos órgãos evitando assim eventos isquêmicos ou outros danos teciduais, como edema. O controle efetivo da PA a curto prazo em anfíbios anuros se dá por ajustes da frequência cardíaca (FC), resistência vascular periférica e também por ajustes da frequência de pulsação dos corações linfáticos. Além disso, a ventilação pulmonar nos anuros está diretamente associada à homeostase do volume sanguíneo por meio da facilitação do transporte de fluído linfático de volta ao sistema cardiovascular, que se dá por meio da alteração de pressão e volume dos sacos linfáticos. Isso parece sugerir a existência de uma possível interação entre a regulação barorreflexa e o controle da respiração nos anfíbios anuros, como já observado para os mamíferos. No presente estudo utilizamos de um método farmacológico (fenilefrina e nitroprussiato de sódio: infusão em rampa e injeção in bolus) para investigar a sensibilidade barorreflexa em diferentes temperaturas no sapo cururu Rhinella schneideri. Também avaliamos o papel do barorreflexo arterial na modulação da ventilação pulmonar nesta mesma espécie. A regulação barorreflexa no sapo R. schneideri apresentou dependência térmica, além de afetar consideravelmente a ventilação dos sapos. A hipotensão e hipertensão resultaram em aumentos e reduções da FC, respectivamente, bem como na ventilação pulmonar, que se deu prioritariamente por meio de ajustes na frequência respiratória. Ao contrário dos dados da literatura, os anfíbios anuros parecem defender prioritariamente eventos de hipotensão ao invés da hipertensão, independente da temperatura testada. É importante salientar que os anuros apresentam alta taxa de filtração transcapilar, e que durante eventos de PA elevada, um aumento na formação de fluido transcapilar pulmonar seria recrutado por um eficiente sistema linfático, característico dos anuros. Portanto, apesar da função da ventilação pulmonar em corresponder à disponibilidade de O2 em diferentes demandas metabólicas (e.g. temperatura), também parece apresentar participação na regulação da PA, possivelmente devido a uma interação entre o barorreflexo e as áreas respiratórias no sistema nervoso central.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / O oxigênio é importante não só por sua participação no metabolismo energético, mas também por sua conversão em derivados parcialmente reduzidos, as espécies reativas de oxigênio (ERO). ERO participam de funções importantes em diversas vias do metabolismo, entretanto, em concentrações desequilibradamente elevadas deflagram a peroxidação lipídica, processo deletério que forma aldeídos tóxicos, como o 4-hidroxi-2-nonenal (4-HNE). A manutenção de concentrações não deletérias das ERO é realizada por moléculas componentes do sistema antioxidante. Peixes podem ser expostos a grandes variações das concentrações de oxigênio, o que provoca ciclos oxidantes. A maioria dos estudos usa fígado e rim para avaliar estresse oxidante por meio de ensaios das atividades antioxidantes, o que requer o sacrifício dos animais. Contudo, o sangue sofre efeitos das ERO e avaliações no sangue podem permitir o estudo de antioxidantes no mesmo animal, sem a necessidade de sacrifício. Em consequência, foram nossos objetivos estabelecer uma técnica de cateterismo branquial em peixes, a padronização dos ensaios e a avaliação em sangue de componentes do sistema antioxidante de duas espécies de teleósteos em diferentes tensões de oxigênio. Pacus e tilápias foram avaliados em 6,0 mg de O2.L-1 e em hipoxia a 0,5 mg de O2.L-1 por 42 horas . Para os ensaios de hiperoxia os animais foram avaliados em 6,0 mg de O2.L-1, depois de 6 horas em 9,5 mg de O2.L-1 e depois de 30 horas de recuperação a 6,0 mg de O2.L-1. A utilização de materiais para o cateterismo de humanos permitiu a implantação de um acesso branquial. Infelizmente, houve formação de trombo após 24 horas. Mesmo assim, a observação de fluxo sanguíneo no interior da cânula e a sobrevida dos animais testados, confirmam a viabilidade da técnica. Verificamos em sangue uma maior atividade da enzima glutationa S-transferase (GST) sobre o 4-HNE em relação ao 1-cloro-2-dinitrobenzeno (CDNB). Isto reflete a importância de avaliações de atividade de enzimas, como a GST, sobre substratos endógenos. As respostas enzimáticas de tilápias mostraram-se mais sensíveis que as dos pacus quando comparadas em diferentes tensões de oxigênio. / Oxygen is important not only for their role in energy metabolism, but also for its conversion into partially reduced derivatives, the reactive oxygen species (ROS). ROS participate in important roles in several metabolic pathways, however, at concentrations lopsidedly high they trigger lipid peroxidation process to form deleterious toxic aldehydes such as 4-hydroxy-2-nonenal (4-HNE). Maintenance of non deleterious concentrations of ROS molecules is performed by components of the antioxidant system. Fish may be exposed to large variations in the concentrations of oxygen, which causes oxidative cycles. Most studies use liver and kidney to assess oxidative stress through antioxidant activities assay, which requires the sacrifice of animals. However, the blood undergoes effects of ROS and evaluations in blood may allow the study of antioxidants in the same animal, without the need of sacrifice. Consequently, our objectives were to establish a catheterization technique in fish gill, standardization of testing and evaluation of components of blood antioxidant system of two species of teleost in various oxygen tensions. Pacus and tilapias were evaluated at 6.0 mg O2.L-1 hypoxia and 0.5 mg O2.L-1 for 42 hours. For assays of hyperoxia animals were evaluated at 6.0 mg O2.L-1, after 6 hours at 9.5 mg O2.L-1 and after 30 hours recovery at 6.0 mg O2.L-1. The use of materials of human catheterization allowed the implantation of a gill access. Unfortunately, there was thrombus formation after 24 hours. Nevertheless, the observation of blood flow within the cannula and survival of the animals tested, confirm the viability of the technique. We found blood in a higher activity of glutathione S-transferase (GST) on the 4-HNE compared to 1-chloro-2-dinitrobenzene (CDNB). This reflects the importance of assessing the activity of enzymes, such as GST with endogenous substrates. The enzymatic responses of tilapia were more sensitive than those of pacus when compared to different oxygen tensions.

INTRODUÇÃO: Baixos níveis séricos de fator de crescimento insulin-like I (IGF- 1) ao nascimento têm sido considerados um fator de risco para o desenvolvimento da retinopatia da prematuridade em recém-nascidos prematuros de extremo baixo peso. Isto se deve ao seu papel como fator permissivo para o fator de crescimento endotelial vascular (VEGF) exercer sua função no desenvolvimento normal e patológico dos vasos da retina. OBJETIVO: Testar a hipótese de que a administração do JB-1 (um análogo do IGF-1 que inibe de forma potente a auto-fosforilação do receptor do IGF-1 pelo IGF-1) durante a hiperóxia previne a retinopatia induzida por oxigênio em nosso modelo experimental em ratos. MATERIAL E METODOS: Ratos recém-nascidos foram expostos a 50% de oxigênio com três episódios consecutivos de hipóxia (12% de oxigênio) do nascimento ao 14º dia de vida. Os ratos foram tratados com injeções subcutâneas de 1) JB-1 (1g/d) nos três primeiros dias de vida (JB-1 x3); 2) JB- 1(1g/d) por dias alternados do 1º ao 13º dias de vida (JB-1x7) 3) ou volume equivalente de solução salina. Grupos controles foram criados em ar ambiente nas mesmas condições, exceto pelo ciclo de hiperóxia/ hipóxia. Os grupos foram analisados após a exposição ao oxigênio no 14º dia de vida ou deixados em ar ambiente por mais sete dias até o sacrifício, no 21º dia de vida. Determinou-se as dosagens sistêmicas e oculares de fator de crescimento endotelial vascular (VEGF), receptor tipo1 solúvel do fator de crescimento endotelial vascular (sVEGFR-1) e fator de crescimento insulin-like I (IGF-1), associados a análise da vascularização retiniana e do perfil dos genes relacionados à angiogênese retiniana. RESULTADOS: O tratamento com JB-1x3 resultou em supressão efetiva da retinopatia induzida por oxigênio, sem efeitos adversos no crescimento somático e foi associado a um aumento do sVEGFR-1 quando comparado com o JB-1x7. Ao contrário, o tratamento com JB-1x7 durante a exposição ao oxigênio levou à diminuição do peso corpóreo e níveis mais altos de IGF-1 e VEGF relacionados à presença de tortuosidades vasculares e neovascularização retiniana, quando comparado com as retinas que receberam apenas solução salina. CONCLUSÃO: O tratamento curto e sistêmico com JB-1 durante a hiperóxia resultou em prevenção da retinopatia induzida por oxigênio sem restrição do crescimento somático. Novos estudos devem ser realizados para determinar se o JB-1 pode ser usado em recém-nascidos de extremo baixo peso na prevenção da retinopatia da prematuridade / INTRODUCTION: Low serum insulin growth factor (IGF-1) levels at birth is a risk factor for the development of retinopathy of prematurity in extremely low birth weight infants. This may be due to its role as a permissive factor for vascular endothelial growth factor (VEGF) function in normal and pathologic vascular development. OBJECTIVE: To test the hypothesis that JB-1 (an IGF-1 analog that potently inhibits the autophosphorylation of the IGF-1 receptor by IGF-1) administration during hyperoxia prevents oxygen induced retinopathy in our rat model. MATERIAL AND METHODS: Neonatal rats were exposed to 50% oxygen with brief, clustered, hypoxic (12% oxygen) episodes from birth to day 14. The pups were treated with subcutaneus injections of 1) JB-1 (1g/d) on the first, second, and third day (JB-1x3) 2) JB1 (1g/d) on alternate days from first to day 13 (JB- 1x7); or equivalent volume of saline. Control littermates were raised in room air with all conditions identical except for inspired oxygen. Groups were analyzed after hyperoxia/hypoxia cycling on day 14 or allowed to recover in room air until the 21st day. Systemic and ocular VEGF, soluble VEGFR-1, and IGF-1; retinal vasculature and gene profile of retinal angiogenesis were assessed. RESULTS: JB-1x3 treatment resulted in successful suppression of oxygeninduced retinopathy with no adverse effect on anthropometric growth, which was associated with increased sVEGFR-1 compared to JB-1x7. In contrast, intermittent and long exposure to JB-1 (JB-1x7) during the hyperoxia/hypoxia cycling period resulted in decreased body weight and higher ocular IGF-1 and VEGF levels as well as vascular tortuosity and retinal neovascularization compared with saline treated retinas. CONCLUSION: Systemic treatment with JB-1 during hyperoxia results in successful prevention of oxygen-induced retinopathy with little adverse effects on anthropometric growth. Further confirmatory studies are needed to determine whether systemic JB-1 should be used in extremely low birth weight infants to prevent retinopathy of prematurity

Submitted by Renata Lopes (renatasil82@gmail.com) on 2016-05-05T17:26:06Z No. of bitstreams: 1 akinoricardozonagato.pdf: 3623412 bytes, checksum: 052499ef93e153d7b083782377a73cd1 (MD5) / Approved for entry into archive by Adriana Oliveira (adriana.oliveira@ufjf.edu.br) on 2016-06-07T15:40:58Z (GMT) No. of bitstreams: 1 akinoricardozonagato.pdf: 3623412 bytes, checksum: 052499ef93e153d7b083782377a73cd1 (MD5) / Made available in DSpace on 2016-06-07T15:40:58Z (GMT). No. of bitstreams: 1 akinoricardozonagato.pdf: 3623412 bytes, checksum: 052499ef93e153d7b083782377a73cd1 (MD5) Previous issue date: 2016-03-23 / CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / CNPq - Conselho Nacional de Desenvolvimento Científico e Tecnológico / FAPEMIG - Fundação de Amparo à Pesquisa do Estado de Minas Gerais / Estudos prévios têm demonstrado que o dano e estresse oxidativo induzido pela hiperóxia levam ao aumento de interleucina-6 (IL6), fator de necrose tumoral-alfa (TNFα) e fator de crescimento transformador beta (TGFβ) em pulmões de camundongos. Juntos, a IL6 e TGFβ têm sido conhecidos por direcionar a diferenciação do fenótipo para as células T-helper 17 (Th17). No estudo corrente nós testamos a hipótese que a hiperóxia promove a polarização de células T para o fenótipo Th17 na resposta inflamatória aguda das vias aéreas induzida por ovalbumina (OVA). A inflamação das vias aéreas foi induzida em camundongos BALB/c, fêmeas, através da sensibilização intraperitonial e instilação intranasal de OVA, acompanhado de metacolina (MetCo). Depois do ataque com MetCo, os animais foram expostos a condições de hiperóxia em uma câmara de inalação durante 24h. Os animais do grupo controle permaneceram em normóxia ou receberam hidróxido de alumínio em salina tamponada. Depois de 24h de hiperóxia, o número de macrófagos (Mᶲ) e linfócitos diminuiu nos animais com inflamação induzida por OVA, enquanto o número de neutrófilos (PMN) aumentou. Os resultados mostraram que a expressão de Fator de transcrição nuclear derivado de eritróide 2 (Nrf2), óxido nítrico sintase induzida (iNOS), Fator de transcrição Tbet (Tbet) e interleucina-17 (IL17) aumentou depois de 24h de hiperóxia tanto em Mᶲ alveolares quanto em células epiteliais pulmonares, comparados com os animais que permaneceram em ar ambiente e com inflamação induzido por OVA. A hiperóxia, isoladamente, levou ao aumento dos níveis de Fator de necrose tumoral (TNFα) e Quimiocina ligante CC5 (CCL5), enquanto a hiperóxia depois da inflamação por OVA levou a diminuição dos níveis de CCL2. O extravasamento de células inflamatórias peribronquiolar e perivascular foi observado após a inflamação pulmonar e hiperóxia. A hiperóxia promoveu a polarização da resposta imune em direção ao fenótipo Th17, resultando em estresse oxidativo e dano tecidual, e migração de PMN e Mᶲ para os pulmões e vias aéreas. Esses achados sugerem que controlar o estresse oxidativo induzido pela hiperóxia pode contribuir importantemente no controle da inflamação aguda das vias aéreas induzida por OVA. / Previous studies have demonstrated that hyperoxia-induced stress and oxidative damage to the lungs of mice lead to an increase in IL6, TNFα and TGFβ expression. Together, IL6 and TGFβ have been known to direct T cell differentiation towards the TH17 phenotype.In the current study, we tested the hypothesis that hyperoxia promotes the polarization of T cells to the TH17 cell phenotype in response to ovalbumin-induced acute airway inflammation. Airway inflammation was induced in female BALB/c mice by intraperitoneal sensitization and intranasal introduction of ovalbumin, followed by challenge methacholine. After the methacholine challenge, animals were exposed to hyperoxic conditions in an inhalation chamber for 24 h. The controls were subjected to normoxia or aluminum hydroxide dissolved in phosphate buffered saline. After 24 h of hyperoxia, the number of macrophages and lymphocytes decreased in animals with ovalbumin-induced airway inflammation, whereas the number of neutrophils increased after ovalbumin-induced airway inflammation. The results showed that expression of Nrf2, iNOS, Tbet and IL17 increased after 24 of hyperoxia in both alveolar macrophages and in lung epithelial cells, compared with both animals that remained in room air, and animals with ovalbumin-induced airway inflammation. Hyperoxia alone without the induction of airway inflammation lead to increased levels of TNFα and CCL5, whereas hyperoxia after inflammation lead to decreased CCL2 levels. Histological evidence of extravasation of inflammatory cells into the perivascular and peribronchial regions of the lungs was observed after pulmonary inflammation and hyperoxia. Hyperoxia promotes polarization of the immune response towards the TH17 phenotype, resulting in tissue damage associated with oxidative stress, and the migration of neutrophils to the lung and airways. Elucidating the effect of hyperoxia-induced oxidative stress is relevant to preventing or treating ovalbumin-induced acute airway inflammation.

La dysoxie (hypoxie/hyperoxie) résulte de l’inadéquation entre la consommation en oxygène et ses apports, provoquant altérations du métabolisme cellulaire et impact physiopathologique majeur. L’hypoxie et l’inflammation font intervenir les facteurs HIF-1a et NF-kB qui activent le système adénosinergique. L’hypoxie augmente la concentration d’adénosine, entraîne une surexpression d’A2AR et induit une immunosuppression lymphocytaire T. Nous avons fait l‘hypothèse que l’inflammation via NF-kB influençait la suppression lymphocytaire adénosinergique; qu’une hyperhomocystéinémie favoriserait l’inflammation en modifiant la viabilité lymphocytaire; qu’in vivo, la réponse adénosinergique était modulée par l’hyperoxie. Des lymphocytes T ont été soumis à une inflammation (agents mitogènes) et à une hypoxie chimique (CoCl2). Nous avons analysé l’expression de NF-kB, HIF-1α, A2AR et évalué les concentrations en adénosine, adénosine déaminase, AMPc, et homocystéine. Enfin, nous avons étudié les effets de l’hyperoxie/hyperbarie sur la réponse adénosinergique. L’hypoxie stimule la réponse adénosinergique : NF-kB induit HIF-1α qui augmente l’expression d’A2AR, favorisant l’immunosuppression. L’inhibition de NF-kB par H2S bloque l’immunosuppression via HIF-1α/A2AR. In vivo, l’hyperoxie inhibe la réponse adénosinergique via la diminution de l’expression d’A2AR. Hypoxie et hyperoxie ont un effet en miroir sur le système adénosinergique. Manipuler la concentration en O2 permet de piloter système immunitaire et inflammation via A2AR. L’utilisation d’H2S pourrait traiter des pathologies à fort impact en santé publique, tels des troubles cardiovasculaires favorisés par l’hyperhomocystéinémie. / Dysoxia (hypoxia/hyperoxia) results from an impaired balance between oxygen-supply concentration and cellular metabolism causing various disorders. Hypoxia and inflammation involve HIF-1a and NF-kB factors and are linked via the adenosinergic response. Hypoxia increase adenosine concentration and A2A receptors (A2AR) expression which induces T-lymphocyte suppression. We hypothesized that during hypoxia, inflammation influences adenosinergic immunosuppression via NF-kB. As homocysteine promotes inflammation, which is considered as a risk factor, we hypothesized that hyperomocysteinemia affects T-cell viability and adenosinergic response. Effects of hyperoxic and hyperbaric conditions on adenosinergic system remain unclear. NF-kB, HIF-1α, and A2AR expression were studied using T-cells stimulated by mitogens under hypoxic conditions (CoCl2). Adenosine, adenosine deaminase, cAMP concentration and homocysteine metabolism were analyzed. Effect of hyperoxia on the adenosinergic pathway was addressed in a rat model using pressure chambers. HIF-1α production was induced by hypoxia, A2AR expression increased following NF-kB activation that enhanced lymphocyte-suppression. Inhibition of NF-kB by H2S resulted in improved cell-viability by down-regulating A2AR-mediated-immunosuppression. Hyperhomocysteinemia increased H2S production (transsulfuration-pathway). We also found in rat that hyperoxia repressed the adenosinergic response. Manipulating blood oxygen level constitutes an effective mean to control the immune response and inflammation via the adenosinergic system. Acting on A2AR expression via H2S production may control cardiovascular-disorders with high impact on public health.

Title: Verification of the effects of hyperoxia on the result in a test simulating performance in a team sprint on SkiErg skiing simulator. Objectives: The work aims to verify the effect of hyperoxia on the result in a test simulating performance in a team sprint on SkiErg skiing simulator. Methods: This is a qualitative research conducted by comparing hart rate, power in watts and lactate in ten probands. Values measured after inhalation of concentrated oxygen and placebo were compared. Results: There was no positive effect from meansurements of the heart rate, power in watts and lactate after concentration of inhaled oxygen and placebo on the SkiErg simulator. We concluded that the effect of inhalated concentrated oxygen Was in our test statistically insignificant. Keywords: Cross-country skiing, strengh, hyperoxia, heart rate, lactate

The retina is the ocular tissue responsible for the detection of light. Its extensive demand for oxygen, coupled with a concomitant elevated supply, renders this tissue prone to both hypoxia and hyperoxia. In this thesis, we construct mathematical models of the retina, formulated as systems of reaction-diffusion equations, investigating its oxygen-related dynamics in healthy and diseased states. In the healthy state, we model the oxygen distribution across the human retina, examining the efficacy of the protein neuroglobin in the prevention of hypoxia. It has been suggested that neuroglobin could prevent hypoxia, either by transporting oxygen from regions where it is rich to those where it is poor, or by storing oxygen during periods of diminished supply or increased uptake. Numerical solutions demonstrate that neuroglobin may be effective in preventing or alleviating hypoxia via oxygen transport, but that its capacity for oxygen storage is essentially negligible, whilst asymptotic analysis reveals that, contrary to the prevailing assumption, neuroglobin's oxygen affinity is near optimal for oxygen transport. A further asymptotic analysis justifies the common approximation of a piecewise constant oxygen uptake across the retina, placing existing models upon a stronger theoretical foundation. In the diseased state, we explore the effect of hyperoxia upon the progression of the inherited retinal diseases, known collectively as retinitis pigmentosa. Both numerical solutions and asymptotic analyses show that this mechanism may replicate many of the patterns of retinal degeneration seen in vivo, but that others are inaccessible to it, demonstrating both the strengths and weaknesses of the oxygen toxicity hypothesis. It is shown that the wave speed of hyperoxic degeneration is negatively correlated with the local photoreceptor density, high density regions acting as a barrier to the spread of photoreceptor loss. The effects of capillary degeneration and treatment with antioxidants or trophic factors are also investigated, demonstrating that each has the potential to delay, halt or partially reverse photoreceptor loss. In addition to answering questions that are not accessible to experimental investigation, these models generate a number of experimentally testable predictions, forming the first loop in what has the potential to be a fruitful experimental/modelling cycle.

Ce projet illustre cinq études, mettant l'emphase sur le développement d'une nouvelle approche diagnostique cardiovasculaire afin d'évaluer le niveau d’oxygène contenu dans le myocarde ainsi que sa fonction microvasculaire. En combinant une séquence de résonance magnétique cardiovasculaire (RMC) pouvant détecter le niveau d’oxygène (OS), des manœuvres respiratoires ainsi que des analyses de gaz artériels peuvent être utilisés comme procédure non invasive destinée à induire une réponse vasoactive afin d’évaluer la réserve d'oxygénation, une mesure clé de la fonction vasculaire. Le nombre de tests diagnostiques cardiaques prescrits ainsi que les interventions, sont en pleine expansion. L'imagerie et tests non invasifs sont souvent effectués avant l’utilisation de procédures invasives. L'imagerie cardiaque permet d’évaluer la présence ou absence de sténoses coronaires, un important facteur économique dans notre système de soins de santé. Les techniques d'imagerie non invasives fournissent de l’information précise afin d’identifier la présence et l’emplacement du déficit de perfusion chez les patients présentant des symptômes d'ischémie myocardique. Néanmoins, plusieurs techniques actuelles requièrent la nécessité de radiation, d’agents de contraste ou traceurs, sans oublier des protocoles de stress pharmacologiques ou physiques. L’imagerie RMC peut identifier une sténose coronaire significative sans radiation. De nouvelles tendances d’utilisation de RMC visent à développer des techniques diagnostiques qui ne requièrent aucun facteur de stress pharmacologiques ou d’agents de contraste. L'objectif principal de ce projet était de développer et tester une nouvelle technique diagnostique afin d’évaluer la fonction vasculaire coronarienne en utilisant l' OS-RMC, en combinaison avec des manœuvres respiratoires comme stimulus vasoactif. Ensuite, les objectifs, secondaires étaient d’utilisés l’OS-RMC pour évaluer l'oxygénation du myocarde et la réponse coronaire en présence de gaz artériels altérés. Suite aux manœuvres respiratoires la réponse vasculaire a été validée chez un modèle animal pour ensuite être utilisé chez deux volontaires sains et finalement dans une population de patients atteints de maladies cardiovasculaires. Chez le modèle animal, les manœuvres respiratoires ont pu induire un changement significatif, mesuré intrusivement par débit sanguin coronaire. Il a été démontré qu’en présence d'une sténose coronarienne hémodynamiquement significative, l’OS-RMC pouvait détecter un déficit en oxygène du myocarde. Chez l’homme sain, l'application de cette technique en comparaison avec l'adénosine (l’agent standard) pour induire une vasodilatation coronarienne et les manœuvres respiratoires ont pu induire une réponse plus significative en oxygénation dans un myocarde sain. Finalement, nous avons utilisé les manœuvres respiratoires parmi un groupe de patients atteint de maladies coronariennes. Leurs myocardes étant altérées par une sténose coronaire, en conséquence modifiant ainsi leur réponse en oxygénation. Par la suite nous avons évalué les effets des gaz artériels sanguins sur l'oxygénation du myocarde. Ils démontrent que la réponse coronarienne est atténuée au cours de l’hyperoxie, suite à un stimuli d’apnée. Ce phénomène provoque une réduction globale du débit sanguin coronaire et un déficit d'oxygénation dans le modèle animal ayant une sténose lorsqu’un supplément en oxygène est donné. En conclusion, ce travail a permis d'améliorer notre compréhension des nouvelles techniques diagnostiques en imagerie cardiovasculaire. Par ailleurs, nous avons démontré que la combinaison de manœuvres respiratoires et l’imagerie OS-RMC peut fournir une méthode non-invasive et rentable pour évaluer la fonction vasculaire coronarienne régionale et globale. / This project encompasses five studies, which focus on developing a new cardiovascular diagnostic approach for assessing myocardial oxygenation and microvascular function. In combination with oxygenation-sensitive cardiovascular magnetic resonance (OS-CMR) imaging, breathing maneuvers and altered arterial blood gases can be used as a non-invasive method for inducing a vasoactive response to test the oxygenation reserve, a key measurement in vascular function. The number of prescribed cardiac diagnostic tests and interventions is rapidly growing. In particular, imaging and other non-invasive tests are frequently performed prior to invasive procedures. One of the most common uses of cardiac imaging is for the diagnosis of significant coronary artery stenosis, a critical cost factor in today’s health care system. Non-invasive imaging techniques provide the most reliable information for the presence and location of perfusion or oxygenation deficits in patients with symptoms suggestive of myocardial ischemia, yet many current techniques suffer from the need for radiation, contrast agents or tracers, and pharmacological or physical stress protocols. CMR imaging can identify significant coronary artery stenosis without radiation and new trends in CMR research aim to develop diagnostic techniques that do not require any pharmacological stressors or contrast agents. For this project, the primary aim was to develop and test a new diagnostic technique to assess coronary vascular function using OS-CMR in combination with breathing maneuvers as the vasoactive stimulus. Secondary aims then used OS-CMR to assess myocardial oxygenation and the coronary response in the presence of altered arterial blood gases. An animal model was used to validate the vascular response to breathing maneuvers before translating the technique to human subjects into both healthy volunteers, and a patient population with cardiac disease. In the animal models, breathing maneuvers could induce a significant change in invasively measured coronary blood flow and it was demonstrated that in the presence of a haemodynamically significant coronary stenosis, OS-CMR could detect a myocardial oxygen deficit. This technique was then applied in a human model, with healthy participants. In a direct comparison to the infusion of the coronary vasodilator adenosine, which is considered a standard agent for inducing vasodilation in cardiac imaging, breathing maneuvers induced a stronger response in oxygenation of healthy myocardium. The final study then implemented the breathing maneuvers in a patient population with coronary artery disease; in which myocardium compromised by a coronary stenosis had a compromised oxygenation response. Furthermore, the observed effects of arterial blood gases on myocardial oxygenation were assessed. This demonstrated that the coronary response to breath-hold stimuli is attenuated during hyperoxia, and this causes an overall reduction in coronary blood flow, and consequently an oxygenation deficit in a coronary stenosis animal model when supplemental oxygen is provided. In conclusion, this work has improved our understanding of potential new diagnostic techniques for cardiovascular imaging. In particular, it demonstrated that combining breathing maneuvers with oxygenation-sensitive CMR can provide a non-invasive and cost-effective method for assessing global and regional coronary vascular function.