Thesis (M. S.)--Mechanical Engineering, Georgia Institute of Technology, 2006. / Ansari, Armin, Committee Member ; Wang, C.-K. Chris, Committee Member ; Hertel, Nolan, Committee Chair.

Thesis (Ph. D.)--University of Texas at Austin, 2005. / Vita. Includes bibliographical references.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1989. / Cover title. Includes bibliographical references (p. 253-256).

Presented as Plain's Thesis (Ph. D.)--University of Wisconsin--Madison, 1940. / Reprinted from Physical review, vol. 57, no. 3 (1 Feb. 1940). Includes bibliographical references.

Thesis (Ph.D.)--Baylor University, 2006. / Includes bibliographic references (p. 163-189).

Th.--Astrophys.--Toulouse 3, 1982. N°: 1045.

The interactions of gamma-rays with matter have been studied for many years and there are accurate mathematical representations of the physical processes involved. Tabulations of the total interaction cross-section and of the major constituent processes have been produced which have an uncertainty of a few percent. In recent years the development of the tomographic scanner, first at EMI and then worldwide, has lead to the measurement of material interaction cross-sections with a precision of less than one percent, which is much less than the available tabulations. The form of the tabulations has also meant that data points must be interpolated from standard energy values, and so a large data base must be maintained if the values are stored on a computer. This is a time consuming and fairly inefficient process, especially if a micro-computer is used for the data base. In 1981 a compact, portable computer program was developed for the calculation of total interaction cross-sections (Jackson and Hawkes (1981)), which reproduced the tabulated data with a high precision (typically better than 0.5%) over a wide range of atomic number (1 < Z < 54) and energy (15 < E < 1500 keV). Although the computer code reproduces the theoretical data with high precision, the uncertainty in the original data is relatively large, this has prompted this experimental study to determine the agreement of the theoretical data values with experimental measurements. The precision desired from the experiments at the outset was 1%, which has been achieved in some, although not all, of the results presented here. The range of atomic number and gamma-ray energies of the materials tested in this study are from carbon (Z=6) to lead (Z=82) and from 15 to 1500 keV. This range has been determined largely by the sources and samples that have been available within the department, but it also represents the range of materials and energies that have been used in the industrial tomography group within this department. Isotopic sources and high resolution solid state detectors have been used to measure total cross-sections for the twelve elements used and up to 25 energies per sample (depending on the range of thicknesses available for the material). Many repeat runs have been done on each sample to increase the precision of the measurements presented here. The use of total interaction cross-sections for materials analysis has also been investigated for several situations and these are discussed and it is shown which methodsare possible and which are not with the precision used in these experiments. This study has to be seen as part of an ongoing process of experimentally producing total interaction cross-sections of higher and higher precision for comparison with theoretical formulations so that a deeper understanding of the underlying processes can be obtained. Within that framework some directions for future work have been outlined which will benefit from further study and a more detailed exploration.

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Doctor en Farmacología / Diversos estudios clínicos han revelado que las tiazolidinedionas, fármacos para el tratamiento de la diabetes de tipo 2 y resistencia a insulina, podrían reducir la morbimortalidad cardiovascular. Su mecanismo de acción es a través de la activación de los Receptores Activados por Proliferadores Peroxisomales (PPARs), los cuales son factores transcripcionales activados por ligandos. En el sistema cardiovascular, los PPARs se expresan de forma variable y juegan un importante papel en la regulación del metabolismo energético y en la respuesta inflamatoria. Durante diversos estados patológicos como por ejemplo en el infarto al miocardio, el tratamiento con tiazolidinedionas ha mostrado efectos cardioprotectores ya que reducen la hipertrofia y el área infartada y atenúan la respuesta inflamatoria cardiaca. Estos antecedentes sugieren un importante papel de PPARγ durante el remodelado cardiaco, proceso fisiopatológico que consiste en un cambio estructural y funcional del tejido, caracterizado por fibrosis, hipertrofia y pérdida progresiva de los cardiomiocitos. Se ha sugerido que la apoptosis es el principal mecanismo de muerte celular en el corazón pero últimamente se ha avanzado en los estudios de la participación de la autofagia o “muerte programada de tipo II”. Sin embargo, la autofagia se describió inicialmente como un proceso fisiológico clave para la sobrevida celular durante la privación de aminoácidos, diferenciación celular y desarrollo. Consiste en un proceso dinámico y programado que procede con el secuestro de proteínas citoplasmáticas y organelos enteros dentro de vacuolas de doble membrana, que posteriormente se fusionan con los lisosomas formando los autolisosomas. Todos estos elementos capturados en las vacuolas son degradados por proteasas lisosomales y removidos de la célula por exocitosis. Evidencias recientes han mostrado que los agonistas de PPARγ podrían inducir la autofagia en algunas líneas celulares. Sin embargo, aún no queda claro si la autofagia es realmente un proceso de muerte o un mecanismo de sobrevida celular. Dado que prácticamente se desconoce si la activación de PPARγ regula la autofagia cardiaca, en esta tesis se postuló como hipótesis que “El agonista farmacológico de PPARγ rosiglitazona induce la autofagia del cardiomiocito, protegiéndolo de la muerte”. Los objetivos específicos propuestos fueron: • Estudiar in vitro el efecto de agonistas farmacológicos de PPARα y/o PPARγ en la viabilidad del cardiomiocito de rata. • Determinar si rosiglitazona induce autofagia en el cardiomiocito y si ésta se relaciona con sobrevida celular. • Investigar si la estimulación con rosiglitazona afecta la viabilidad de cardiomiocitos expuestos a estrés nutricional, estrés hiperosmótico o a isquemia/reperfusión simulada. El modelo experimental utilizado fue cultivo primario de cardiomiocitos de ratas neonatas tratados con rosigllitazona en un rango creciente de concentraciones y de tiempo. La autofagia se evaluó mediante procesamiento de la proteína LC3 endógena, cambio en la distribución y degradación de la proteína GFP-LC3 en cardiomiocitos transducidos con el adenovirus GFP-LC3. Los resultados mostraron que PPARγ está presente en cardiomiocitos de ratas y que es transcripcionalmente activo, lo cual se demostró mediante un plasmidio reportero que contiene el elemento de respuesta para este factor transcripcional. Además, rosiglitazona estimuló temprana y progresivamente la autofagia en los cultivos primarios de cardiomiocitos, determinada por el procesamiento de la proteína endógena LC3-I, efecto similar al observado en repuesta al tratamiento con rapamicina. Rosiglitazona también incrementó la distribución punteada de LC3-GFP, sin embargo no disminuyó la fluorescencia de la proteína LC3-GFP en los cardiomiocitos transducidos con el adenovirus LC3-GFP. Por otra parte, rosiglitazona no modificó de forma significativa los niveles intracelulares de ATP y ni afectó la viabilidad basal del cardiomiocito. El tratamiento con gemfibrozilo, tampoco modificó su viabilidad. Para determinar si la inducción de autofagia tiene un efecto en la viabilidad del cardiomiocito, los cultivos celulares se expusieron a estrés mecánico por hiperosmolaridad y se midió la viabilidad. El estrés hiperosmótico indujo de manera rápida y potente la muerte de las células cardiacas. Sin embargo, rosiglitazona y gemfibrozilo no previnieron este efecto. La muerte de las células cardiacas inducida por el estrés hiperosmótico es mediante apoptosis, lo que se demostró la evaluación por citometría de flujo de la subpoblación G1 en células permeabilizadas y tratadas con yoduro de propidio y determinación de potencial mitocondrial. Rosiglitazona y gemfibrozilo no previnieron la apoptosis del cardiomiocito inducida por estrés hiperosmótico. Rosiglitazona tampoco bloqueó la muerte celular inducida por isquemia y reperfusión simulada. Finalmente, los resultados obtenidos con el desarrollo de esta tesis permiten concluir que rosiglitazona induce la autofagia del cardiomiocito pero que ésta es insuficiente para modificar la viabilidad celular / Clinical studies showed that thiazolidinediones, drugs used for type 2 diabetes and insulin resistance treatment, can reduce cardiovascular morbid and mortality. These compounds are highly specific ligands of peroxisome proliferator-activator receptor gamma (PPARγ), a nuclear hormone receptor superfamily member. PPARs are variably expressed in the cardiovascular system and play an important role in both energetic metabolism regulation and inflammation response. In myocardial infarct, treatment with thiazolidinediones has cardioprotective effects reducing cardiac hypertrophy, infarcted area and inflammatory response. These data suggest an important role of PPARγ during cardiac remodeling. Remodeling is a physiopathological alteration in heart structure and function characterized by cardiomyocytes fibrosis, hypertrophy and death. Apoptosis has been described as the main cardiac cell death mechanism. However, recent studies have also described the participation of autophagy, also known as type II programmed cell death. Autophagy was first described as an adaptative physiological process during amino acids starvation. It has also been described its participation in cellular differentiation and development. Autophagy consists in the sequestration of cytoplasm portions and organelles within double membrane vesicles, named autophagosomes. These vesicles were subsequently fused with lysosomes forming the autofagosomes. All elements captured in these vesicles are degraded by lysosomal proteases and removed by exocytosis. Recent evidence has shown that PPARγ agonists could induce autophagy in some cells lines. However, is not clear whether autophagy is a mechanism for cell survival or death. Based on these antecedents we postulated the following hypothesis: “The pharmacological PPARγ agonist, rosiglitazone, induces cardiomyocyte autophagy protecting them from cell death”. The specific aims were: • To study in vitro the effects of PPARα and PPARγ pharmacological agonists on neonatal rat cardiomyocytes. • To determine whether rosiglitazone induces autophagy in cardiomyocyte and whether this process is related with cell viability. • To investigate if the stimulation with rosiglitazone affects cardiomyocyte viability when exposed to nutritional stress, hyperosmotic stress and simulated ischemia/reperfusion. The experimental models were primary cultures of neonatal rat cardiomyocytes treated with rosiglitazone at different concentrations and times. Autophagy was evaluated by endogenous LC3-I processing, and by change in adenoviral expressing GFP-LC3 distribution and degradation. Results showed that PPARγ is expressed and is transcriptionally active in neonatal rat cardiomyocytes as determined by western blot and activity of PPAR reporter plasmid. Furthermore, rosiglitazone stimulated early and progressively cardiac autophagy as determined by endogenous LC3-I processing. This effect was similar to that induced by rapamycin. Rosiglitazone also increased the GFP-LC3 punctuated pattern, but without decreasing GFP-LC3 fluorescence. On the other hand, rosiglitazone neither affects ATP levels nor viability of cardiomyocytes. Gemfibrozil treatment, also did not affect cardiomyocyte viability. To determine whether autophagy affects cardiomyocyte viability, cultured cells were exposed to hyperosmotic stress in the presence or absence of rosiglitazone or gemfobrozil, and viability was measured. Hyperosmotic stress induced a rapid decrease in cardiomyocyte viability. Cardiomyocyte death was also achieved by simulated ischemia/reperfusiom. Neither rosiglitazone nor gemfibrozil prevented cardiomyocyte death induced by both procedures. Hyperosmotic stress-induced cell death was characterized as apoptosis, as determined by mitochondrial potential decay and DNA fragmentation visualized by sub G1 population in propidium iodide-treated cells followed flow cytometry. Both rosiglitazone and gemfibrozil did not prevent the hyperosmotic stress-induced apoptosis. Finally, these results allow us to conclude that rosiglitazone induces cardiomyocyte autophagy but this process does not affect cardiomyocyte viability