Evaluation of the effects of natural and synthetic compounds on lipid accumulation and inflammation in hepatocytes, endotheliocytes and adipocytes.

Obesity is a condition characterized by an excessive accumulation of body fat, especially at the visceral level, which causes serious damage to health. Obesity is caused, in most cases, by unhealthy lifestyles (on the one hand, a high-calorie diet, and on the other, reduced or no physical activity). From an etiological point of view obesity is a multifactorial disease associated with various pathological conditions such as insulin resistance, type 2 diabetes mellitus, hypertension, atherosclerosis and non-alcoholic liver steatosis (NAFLD). Obesity is currently one of the most important public health problems in the world, as its prevalence is constantly increasing. Obesity therefore represents one of the main challenges in the field of research which, on one side, studies the cellular/tissutal mechanisms involved in the development and progression of the disease at the level of the different organs and, on the other side, tries to identify natural and synthetic compounds for the treatment of this condition, to be associated with diet and adequate physical activity. This PhD thesis is part of this context, with the aim of studying, first, the molecular mechanisms associated with excessive fat accumulation in different cell types representative of the tissues involved in obesity, then to identify and study natural compounds (of plant origin or otherwise endogenous) that may have beneficial effects on the cellular models developed. For this purpose, the following cellular models of NAFLD, adipose tissue hypertrophy (obesity) and endothelial dysfunction (atherosclerosis) have been developed and used: • An in vitro model of NAFLD consisting of rat hepatoma cells treated with different steatogenic agents in order to mimic in vitro the steps of the progression of NAFLD in vivo from simple steatosis to steatohepatitis. • An in vitro model of atherosclerosis, consisting of human umbilical vein endothelial cells exposed to a mixture of fatty acids. • An in vitro model of adipocytic hypertrophy, represented by mouse pre-adipocytes treated with a mixture of adipogenic substances and then with long chain fatty acids to induce a picture of hypertrophy in vitro. Starting from the different cellular models mentioned above, the research activity has been focused on the study of the possible beneficial effects of different compounds: • Silybin, a natural molecule, that represents the main component of silymarin, an extract from Silybum marianum. Starting from previous studies, both clinical and animal, which suggested a potential beneficial effect of silybin on the liver, this thesis investigated the effects and molecular mechanisms of this molecule treatment in the in vitro model of NAFLD. • S-Adenosylmethionine (SAMe), an endogenous molecule that acts as the main donor of methyl groups at the cellular level. Previous studies had observed that low levels of SAMe in the liver are related to pathological organ conditions. In this thesis it was evaluated whether and by what molecular mechanisms SAMe could improve a condition of liver steatosis and endothelial dysfunction using the two in vitro models. The results have shown that: (i) the three in vitro cellular systems developed duing this thesis work represent a good model of the different physio-pathological conditions of interest, liver steatosis (NAFLD), endothelial dysfunction (atherosclerosis) and adipocytic hypertrophy (obesity); (ii) both silybin and SAMe have significant beneficial properties. In particular, both compounds have demonstrated an anti-steatotic and antioxidant effect in the in vitro model of liver steatosis. SAMe also showed significant antioxidant and cytoprotective activity on dysfunctional endothelial cells. In conclusion, we can say that the three models developed and used in this thesis represent a good in vitro experimental model for the study of molecular and biochemical mechanisms involved in complex pathological conditions and that they can be effectively used for the study of possible natural compounds to be used as nutraceuticals.