Identificación de alteraciones metabólicas y marcadores moleculares asociados a la ingesta prolongada de dietas desequilibradas

Abstract

The intake of diets with an unbalanced macronutrient composition has increased over the years. This rise is due to general changes in the diet of Western societies (increased consumption of fats and proteins) and a growing tendency to reduce the quantity of carbohydrates in the diet, increasing therefore the proportion of fats and/ or proteins, in order to maintain body weight. These dietary patterns could be increasing the risk of suffering health problems. In this thesis we have characterised the metabolic effect of chronic intake of macronutrient unbalanced diets, either rich in fats or proteins, administered to rats in isocaloric quantity to a control diet in order to avoid the over-consumption associated to high-fat diets. Animals fed an isocaloric diet rich in fats, even though they did not present obesity, showed alterations related to the metabolic syndrome such as increased adiposity, insulin resistance and an increase in inflammatory markers. This is known as the “thin outside, fat inside” or “metabolically obese normalweight” (MONW) phenotype. In the case of the animals fed the high-protein diet, body weight was reduced, as were serum cholesterol levels. However, the lower body weight observed was not due to a reduced fat content, but to a lower content of body water. These animals also presented signs that evidence an increased pathologic risk, such as increased levels of inflammatory markers and an increase in renal size. An effect seen in both unbalanced diets was the increase in triglyceride deposition in the liver, being a risk factor for the development of hepatic conditions and metabolic syndrome. Through massive gene analysis (microarray), we identified alterations in the hepatic molecular environment which could explain the major accumulation of fats in this organ after the intake of unbalanced diets. Furthermore, the data of the transcriptomic analysis in the liver allowed the caracterization of gene expression patterns that could enhance the risk of suffering conditions, such as the case of the increased expression of the Krt23 gene in the liver of MONW animals, which has been defined in humans as a marker of steatohepatitis development and hepatocarcinoma progression. On the other hand, we have described that the long-term intake of unbalanced diets has a major impact on gene expression profile in peripheral blood mononuclear cells (PBMC), and therefore these could be used as biomarkers for dietetic imbalances. A microarray study showed that the immune response was the most affected metabolic pathway, being inhibited or increased in PBMC of MONW animals or highprotein fed animals, respectively. Moreover, PBMC are able to reflect the adaptive changes in key homeostatic organs in order to deal with the lower content of carbohydrates in both diets or of the higher content in proteins in the case of the high-protein. We have also described a set of 7 genes whose expression changes in an equal manner with both types of unbalanced diets, and which could be used as a metabolic print in order to identify alterations in macronutrient equilibrium that could lead to metabolic and health alterations. Finally, we have identified the increased gene expression of Cpt1a in PBMC as an early biomarker of unbalanced dietary intake associated to future alterations in health, being mainly indicative of an increased risk of ectopic fat accumulation in the liver and of metabolic syndrome. In conclusion, our research provides new results regarding the harmful effects on health of long-term intake of macronutrient unbalanced diets. Our results put forward the importance of an early detection of individuals with dietary imbalances, and therefore the use of PBMC as biomarkers of nutritional unbalances associated to future metabolic alterations proves useful