Le p-tert-octylphénol est un produit présent dans l’environnement et issu de la dégradation des alkylphénols éthoxylés. Ce composé a la capacité de se lier au récepteur œstrogénique et d’exercer ainsi un léger effet œstrogénique. Les objectifs de cette étude étaient de 1) développer une méthode d'identification de l'octylphénol dans le sang et les tissus à l'aide de la chromatographie en phase gazeuse jumelée à la spectrométrie de masse, 2) caractériser la toxicocinétique sanguine et tissulaire de l’octylphénol chez le rat Sprague-Dawley mâle et femelle et 3) développer un modèle toxicocinétique à base physiologique permettant de décrire la cinétique sanguine et tissulaire de l’octylphénol inchangé. Pour ce faire, des rats mâle et femelle Sprague-Dawley ont reçu des doses uniques d’octylphénol par les voies intraveineuse, orale et sous-cutanée. Deux autres groupes ont reçu des doses répétées d'octylphénol par voie orale pour une durée de 35 jours consécutifs pour les femelles ou 60 jours pour les mâles. Les concentrations sanguines et tissulaires d’octylphénol ont été mesurées à différents moments après administration à partir d’une méthode d’analyse développée dans nos laboratoires dans le cadre de ce projet. Les expériences impliquant des administrations uniques ont montré que les concentrations sanguines et tissulaires d'octylphénol étaient en général plus élevées chez les femelles que chez les mâles. Des expériences réalisées avec des microsomes hépatiques ont confirmé que ces différences étaient vraisemblablement reliées au métabolisme de l'octylphénol. Les expériences impliquant des administrations répétées ont montré qu'il n'y avait pas d'accumulation d'octylphénol dans l'organisme aux doses étudiées. Les résultats obtenus expérimentalement ont servi à développer et valider un modèle toxicocinétique à base physiologique. Ce modèle a permis de simuler adéquatement les concentrations sanguines et tissulaires d'octylphénol suite à des expositions intraveineuses, orales et sous-cutanées. En conclusion, cette étude a fourni des données essentielles sur la toxicocinétique de l'octylphénol. Ces données sont nécessaires pour établir la relation entre la dose externe et la dose interne et vont contribuer à une meilleure évaluation des risques liés à l'octylphénol. / p-tert-Octylphenol is a degradation product of alkylphenol ethoxylates that can be found in the environment. It has been reported to act as a weak estrogenic compound by binding to the estrogen receptor. This study was undertaken to 1) develop a sensitive method for the determination of octylphenol in blood and various tissues using gas chromatography coupled with detection by mass spectrometry, 2) characterize the blood and tissues toxicokinetics of octylphenol in male and female Sprague-Dawley rats and 3) develop a physiologically-based toxicokinetic model for octylphenol that can describe/predict unchanged blood and tissues octylphenol concentrations in rats. Male and female Sprague-Dawley rats were given a single dose of octylphenol either by oral gavage, intravenous injection or subcutaneous injection. In a repeated dosing experiment, rats were given octylphenol (oral) daily for 35 days (female) or 60 days (male). Blood and tissue samples were collected at various time following the onset of exposure and analyzed for octylphenol content using a method developed in our laboratory. These results showed that blood and tissues octylphenol concentrations were generally higher in female than male rats. Experiments done with rat liver microsomes confirmed that these differences were related to octylphenol metabolism. The results of the repeated exposure study indicate that there is no bioaccumulation of octylphenol at these exposure levels. A physiologically-based pharmacokinetic model for octylphenol was developed and validated using the data obtained in female and male rats. The model simulates adequately blood and tissues octylphenol concentrations following oral, intravenous or subcutaneous exposure. In conclusion, this study provided essential data on the toxicokinetics of octylphenol. These data are essential to predict the relationship between the internal and the external dose of octylphenol and will facilitate the risk assessment of octylphenol in humans.

Dissertation (Ph.D.)--University of South Florida, 2009. / Includes vita. Includes bibliographical references. Also available online.

Dissertation (Ph.D.)--University of South Florida, 2009. / Title from PDF of title page. Document formatted into pages; contains 103 pages. Includes vita. Includes bibliographical references.

A seizure is defined as an abnormal electrical discharge from the brain that results in the affected area losing its normal function and reacting uncontrollably. A particular subset of seizures, known as absence seizures, are characterized by brief, paroxysmal losses of consciousness that are associated with bilaterally synchronous 3 Hz spike and wave discharges (SWDs) on electroencephalography (EEG). The optimal way to understand any disease state is to study it within the human. Unfortunately, well controlled experiments in humans are difficult due to small patient populations, treatment medications which alter the seizure, and the ethical problems associated with invasive experimental procedures. Animal models of absence seizures provide a means of avoiding the above difficulties but the model should mimic, as closely as possible, the human condition. The goal of this thesis was to develop an animal model of absence epilepsy that could be used to explore, non-invasively, the underlying mechanisms of absence seizures. Functional magnetic resonance imaging (fMRI) was used to non-invasively monitor brain activity during absence seizures in various animal models. In this dissertation I report the development of a pharmacological rat model of absence seizures for use in fMRI investigations. Imaging was performed after absence seizure induction using γ-butyrolactone (GBL) and it was found that the cortico-thalamic circuitry, critical for the formation of SWDs, showed robust signal changes consistent with electroencephalographic recordings in the same animals. Since a major disadvantage of the GBL rat model is that it produces acute, drug-induced seizures, a genetic rat model with spontaneous absence seizures was subsequently developed for fMRI. EEG-triggered fMRI was used to identify areas of brain activation during spontaneous SWDs in the epileptic WAG/Rij rat strain under awake conditions. Significant signal changes were apparent in several areas of the cortex and several important nuclei of the thalamus. These results draw an anatomical correlation between areas in which there is increased fMRI signal and those where SWDs have been previously recorded using electrophysiologic techniques. One way in which absences differ between humans and both of these rat models is that the SWD frequency in humans is classically 3 Hz while in rats it varies from 7 to 11 Hz. Marmoset monkeys were found to model the human absence seizure condition better than other animals because GBL administration in these non-human primates results in the formation of 3 Hz SWDs. This monkey model was developed for awake functional imaging and changes in signal intensity in the thalamus and sensorimotor cortex correlated with the onset of 3 Hz SWDs. The change in BOLD signal intensity was bilateral but heterogeneous, affecting some brain areas more than others.

Dissertation (Ph.D.)--University of South Florida, 2007. / Title from PDF of title page. Document formatted into pages; contains 187 pages. Includes vita. Includes bibliographical references.

O desenvolvimento das doenças neurodegenerativas, como a doença de Alzheimer, está associado à presença de agregados proteicos contendo Tau hiperfosforilada (p-Tau). Esta disfunção da Tau leva a prejuízos na homeostase celular. Um mecanismo chave para diminuir e/ou prevenir os danos promovidos pelos agregados contendo Tau seria o estímulo de sua degradação. Neste sentido, a proposta do presente estudo foi analisar a degradação da proteína Tau após aumento da expressão exógena da cochaperona Bag-2, a qual influencia o sistema proteassomal de degradação; bem como avaliar a ativação dos sistemas de degradação, a fim de correlacionar estes sistemas em cultura de células primárias e organotípica do hipocampo de ratos. Os resultados mostraram que a rotenona foi capaz de aumentar os níveis de p-Tau e que a superexpressão de Bag-2, foi eficiente em prevenir e degradar a p-Tau. O mecanismo envolvido neste processo envolve a coordenação dos sistemas proteassomal e lisossomal, já que a Rab7 e a Rab24 (envolvidas na via lisossomal) mostraram-se diminuídas na fase que antecede a agregação proteica, enquanto houve aumento da Rab24 na presença dos agregados proteicos. Com relação ao peptídeo beta amiloide, foi demonstrado tendência de aumento de p-Tau acompanhado de diminuição da atividade proteassomal e lisossomal. O tratamento com PADK (ativador lisossomal) foi capaz de reverter este efeito nestas diferentes condições. A análise da interrelação entre os sistemas mostrou que uma inibição do proteassoma favorece a via lisossomal e que o inverso não se repete. Os resultados sugerem que a modulação das vias de degradação pode ser interessante para o estudo, prevenção e tratamento das doenças neurodegenerativas associadas à agregação de proteínas / Neurodegenerative diseases, such as Alzheimer\'s, are associated to protein inclusions containing hyperphosphorylated Tau (p-Tau). It is well established that Tau dysfunction impairs cell homeostasis. A key mechanism to prevent and/or reduce the damage promoted by aggregates of Tau might be its degradation. In view of this, the aims of the present study are to evaluate p- Tau clearance following exogenous expression of Bag-2, which stimulates proteasome; as well as to analyze the activation of both lysosome and proteasome pathways in order to understand the crosstalk between these two systems in primary and organotypic cultures of rat hippocampus. Results showed that rotenone was able of increasing p-Tau that was prevented and degraded by Bag-2 overexpression. Mechanisms involved in this process involve the coordination of cell degradation systems, depending upon aggregation status, since Rab7 and Rab24 (involved in lysosomal pathway) were decreased before protein aggregation, while Rab24 increased in the presence of protein inclusions. Amyloid-beta peptide also increased p-Tau accompanied by decreased proteasome and lysosome activity. PADK (lysosomal activator) treatment reverted the inhibition promoted by amyloidbeta peptide. Inhibition of proteasome leads to activation of lysosome, but lysosome inhibition does not affect proteasome. Overall, results suggest that targeting degradation pathways might be useful to understand, prevent and treat neurodegenerative diseases associated with protein deposits

O desenvolvimento das doenças neurodegenerativas, como a doença de Alzheimer, está associado à presença de agregados proteicos contendo Tau hiperfosforilada (p-Tau). Esta disfunção da Tau leva a prejuízos na homeostase celular. Um mecanismo chave para diminuir e/ou prevenir os danos promovidos pelos agregados contendo Tau seria o estímulo de sua degradação. Neste sentido, a proposta do presente estudo foi analisar a degradação da proteína Tau após aumento da expressão exógena da cochaperona Bag-2, a qual influencia o sistema proteassomal de degradação; bem como avaliar a ativação dos sistemas de degradação, a fim de correlacionar estes sistemas em cultura de células primárias e organotípica do hipocampo de ratos. Os resultados mostraram que a rotenona foi capaz de aumentar os níveis de p-Tau e que a superexpressão de Bag-2, foi eficiente em prevenir e degradar a p-Tau. O mecanismo envolvido neste processo envolve a coordenação dos sistemas proteassomal e lisossomal, já que a Rab7 e a Rab24 (envolvidas na via lisossomal) mostraram-se diminuídas na fase que antecede a agregação proteica, enquanto houve aumento da Rab24 na presença dos agregados proteicos. Com relação ao peptídeo beta amiloide, foi demonstrado tendência de aumento de p-Tau acompanhado de diminuição da atividade proteassomal e lisossomal. O tratamento com PADK (ativador lisossomal) foi capaz de reverter este efeito nestas diferentes condições. A análise da interrelação entre os sistemas mostrou que uma inibição do proteassoma favorece a via lisossomal e que o inverso não se repete. Os resultados sugerem que a modulação das vias de degradação pode ser interessante para o estudo, prevenção e tratamento das doenças neurodegenerativas associadas à agregação de proteínas / Neurodegenerative diseases, such as Alzheimer\'s, are associated to protein inclusions containing hyperphosphorylated Tau (p-Tau). It is well established that Tau dysfunction impairs cell homeostasis. A key mechanism to prevent and/or reduce the damage promoted by aggregates of Tau might be its degradation. In view of this, the aims of the present study are to evaluate p- Tau clearance following exogenous expression of Bag-2, which stimulates proteasome; as well as to analyze the activation of both lysosome and proteasome pathways in order to understand the crosstalk between these two systems in primary and organotypic cultures of rat hippocampus. Results showed that rotenone was able of increasing p-Tau that was prevented and degraded by Bag-2 overexpression. Mechanisms involved in this process involve the coordination of cell degradation systems, depending upon aggregation status, since Rab7 and Rab24 (involved in lysosomal pathway) were decreased before protein aggregation, while Rab24 increased in the presence of protein inclusions. Amyloid-beta peptide also increased p-Tau accompanied by decreased proteasome and lysosome activity. PADK (lysosomal activator) treatment reverted the inhibition promoted by amyloidbeta peptide. Inhibition of proteasome leads to activation of lysosome, but lysosome inhibition does not affect proteasome. Overall, results suggest that targeting degradation pathways might be useful to understand, prevent and treat neurodegenerative diseases associated with protein deposits