Bile acids have been studied for many years for their role in either promoting (Deoxycholic Acid) or suppressing (Ursodeoxycholic Acid) colon tumor development in animal models. However, the molecular mechanisms of both DCA's and UDCA's biological effects in colon tumorigenesis is still unclear. The cholesterol-like composition of bile acids and evidence of deregulating signal transduction pathways, such as the p42/44 MAP kinase cascade, led us to identify the plasma membrane as a target for bile acid-mediated effects. Specifically, plasma membrane microdomains such as lipid rafts and caveolae are particularly capable of altering mitogenic signaling due to have their role as platforms to concentrate receptors and assemble signal transduction machinery. In this study I tested the hypothesis that the growth suppressive effects of UDCA are mediated by stimulating membrane microdomains to activate protein degradation machinery to facilitate the down-regulation of receptor tyrosine kinase activity. We found that UDCA suppresses EGF-induced ERK activation, promotes interactions between EGFR and Caveolin-1 membrane fractions, whereas DCA causes redistribution. EGFR proteins that are localized to membrane fractions in the UDCA treated cells are extensively ubiquitinylated and we present evidence that this yields recruitment of the ubiquitin ligase c-Cbl to membrane fractions. UDCA increases the rate of EGFR degradation, whereas DCA sustains its' stability. I present evidence that UDCA's growth inhibitory effects on colon cancer cells may be mediated by recruitment of protein degradation machinery to membrane domains that are enriched with signaling receptors, a mechanism which has not been previously described. Importantly, I demonstrate for the first time a novel mechanism by which UDCA promotes growth inhibition, through increasing the rates of degradation of EGFR, thereby down-regulating mitogenic signaling in the cell. These experiments show exciting insights into the mechanism of bile acids and represent potential mechanisms for other chemopreventive agents.

Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.

Charles University in Prague Faculty of Pharmacy in Hradec Králové Department of Pharmacology & Toxicology Student: Alžbeta Horvátová Supervisor: prof. PharmDr. Petr Pávek PhD. Title of diploma thesis: Anti-inflammatory effects of ursodeoxycholyl lysophosphatidylethanolamide on THP-1 human macrophages via Toll-like receptor 4 Nonalcoholic steatohepatitis (NASH) became the most common liver disease in developed countries. It is well-known that the level of protectant phosphatidylcholine (PC) is decreased in NASH. The bile acid-phospholipid conjugate ursodeoxycholyl lysophosphatidylethanolamide (UDCA-LPE) was designed in order to specifically deliver PC to hepatocytes. However, previous studies have proved that UDCA-LPE possesses its proper hepatoprotectant capacity and exhibits anti-apoptotic, anti-inflammatory, anti-fibrotic properties and also improved steatosis and hyperlipidaemia in various models in vivo. These effects may be mediated secondary through modulation of immune system. Therefore, in order to dissect if UDCA-LPE directly influences immune cells in vitro, release of pro-inflammatory cytokines TNFα, IL-6 and IL-1β in LPS-induced THP-1-derived human macrophages was measured by ELISA. Moreover, effects of UDCA-LPE on MAPK signalling pathways and nuclear translocation of NFκB were...

La stéatohépatite non alcoolique (NASH) est une pathologie du foie dont l’amplitude et les répercussions sont de plus en plus préoccupantes dans le monde médical ou biomédical. Elle est associée à l’obésité, au syndrome métabolique et au diabète sucré de type II. La recherche de la thérapie optimale pour le NASH est un domaine en plein essor puisqu’aucun traitement n’est suffisamment efficace à ce jour. La présente étude fait le point sur de nouvelles possibilités de traitements qui se sont avérés efficaces pour contrer les différentes lésions métaboliques et cellulaires rencontrées dans un modèle in vivo chez le rat où le NASH est induit par l’ingestion d’une diète riche en gras. Cette étude démontre, tout d’abord, que les traitements durant six semaines avec l’acide ursodéoxycholique (UDCA) et son dérivé le NCX 1000, possédant des propriétés donatrices de monoxyde d’azote, à doses équimolaires, protègent de manière équivalente le foie contre le stress oxydatif, l’hyperinsulinémie, l’inflammation et la fibrose causés par la stéatohépatite. De plus, la combinaison d’une plus faible dose de NCX 1000 avec un antioxydant lipophile tel que la vitamine E offre une protection similaire, particulièrement au niveau des paramètres du stress oxydatif. Par ailleurs, l’étude illustre aussi que la silibinine, composé polyphénolique actif du chardon marie (Silybum marianum) et utilisé en traitement pendant 5 semaines, possède un pouvoir hépatoprotecteur, des propriétés antioxydantes et un effet hypoinsulinémique dans ce modèle de stéatohépatite d’origine nutritionnelle. Le potentiel thérapeutique de ces composés en fait des candidats de choix pour le traitement du NASH qui méritent de faire l’objet d’études cliniques poussées. / Nonalcoholic steatohepatitis (NASH) is a serious liver condition related to the metabolic syndrome, obesity, and type II diabetes mellitus whose prevalence is drastically rising in developed countries and worldwide. Several remedies were investigated for the treatment of NASH but an efficient therapy has yet to be developed. In the present study, we explored novel therapeutic possibilities that were thought to be effective for the treatment of experimental high-fat diet-induced NASH the in rat. Our results show that a chronic six week treatment with a high dose of NCX 1000, a derivative of ursodeoxycholic acid (UDCA) with nitric oxide (NO) donating properties, is efficient at reversing steatosis, oxidative stress, inflammation, insulin resistance and fibrosis; major hallmarks of experimental NASH. We also demonstrated that the mother molecule, UDCA, is as efficacious in controlling the same parameters at equimolar doses. Moreover, our study demonstrates that NCX 1000 at lower doses can exert similar potent properties when combined with lipophilic antioxidants like vitamin E. On the other hand, we found that a 5-week treatment with silibinin, the major active component of milk thistle extract, improved liver steatosis and inflammation and decreased NASH-induced oxidative stress, insulin resistance, and fibrosis. These compounds have therefore the potential for being developed for the treatment of NASH. Clinical evidences are needed.

La stéatohépatite non alcoolique (NASH) est une pathologie du foie dont l’amplitude et les répercussions sont de plus en plus préoccupantes dans le monde médical ou biomédical. Elle est associée à l’obésité, au syndrome métabolique et au diabète sucré de type II. La recherche de la thérapie optimale pour le NASH est un domaine en plein essor puisqu’aucun traitement n’est suffisamment efficace à ce jour. La présente étude fait le point sur de nouvelles possibilités de traitements qui se sont avérés efficaces pour contrer les différentes lésions métaboliques et cellulaires rencontrées dans un modèle in vivo chez le rat où le NASH est induit par l’ingestion d’une diète riche en gras. Cette étude démontre, tout d’abord, que les traitements durant six semaines avec l’acide ursodéoxycholique (UDCA) et son dérivé le NCX 1000, possédant des propriétés donatrices de monoxyde d’azote, à doses équimolaires, protègent de manière équivalente le foie contre le stress oxydatif, l’hyperinsulinémie, l’inflammation et la fibrose causés par la stéatohépatite. De plus, la combinaison d’une plus faible dose de NCX 1000 avec un antioxydant lipophile tel que la vitamine E offre une protection similaire, particulièrement au niveau des paramètres du stress oxydatif. Par ailleurs, l’étude illustre aussi que la silibinine, composé polyphénolique actif du chardon marie (Silybum marianum) et utilisé en traitement pendant 5 semaines, possède un pouvoir hépatoprotecteur, des propriétés antioxydantes et un effet hypoinsulinémique dans ce modèle de stéatohépatite d’origine nutritionnelle. Le potentiel thérapeutique de ces composés en fait des candidats de choix pour le traitement du NASH qui méritent de faire l’objet d’études cliniques poussées. / Nonalcoholic steatohepatitis (NASH) is a serious liver condition related to the metabolic syndrome, obesity, and type II diabetes mellitus whose prevalence is drastically rising in developed countries and worldwide. Several remedies were investigated for the treatment of NASH but an efficient therapy has yet to be developed. In the present study, we explored novel therapeutic possibilities that were thought to be effective for the treatment of experimental high-fat diet-induced NASH the in rat. Our results show that a chronic six week treatment with a high dose of NCX 1000, a derivative of ursodeoxycholic acid (UDCA) with nitric oxide (NO) donating properties, is efficient at reversing steatosis, oxidative stress, inflammation, insulin resistance and fibrosis; major hallmarks of experimental NASH. We also demonstrated that the mother molecule, UDCA, is as efficacious in controlling the same parameters at equimolar doses. Moreover, our study demonstrates that NCX 1000 at lower doses can exert similar potent properties when combined with lipophilic antioxidants like vitamin E. On the other hand, we found that a 5-week treatment with silibinin, the major active component of milk thistle extract, improved liver steatosis and inflammation and decreased NASH-induced oxidative stress, insulin resistance, and fibrosis. These compounds have therefore the potential for being developed for the treatment of NASH. Clinical evidences are needed.