Lípids de la dieta i càncer de mama experimental: Anàlisi del metabolisme i l’apoptosi tumoral.

Abstract

Breast cancer (BC) is the most common malignant tumor in women worldwide, with diet, and especially dietary lipids, having an etiological role. We have previously observed a differential effect of high-fat diets on experimental mammary carcinogenesis (clearly stimulating from the high-corn oil diet, with a weak influence from the high-extra virgin olive oil EVOO diet), through different mechanisms such as modifications in the expression of metabolism and/or apoptotic genes. Metabolic reprogramming and apoptosis avoidance are crucial hallmarks of cancer development. The main goal of this thesis was to investigate the effect of high-fat diets and their components on experimental mammary carcinogenesis and elucidate the mechanisms involved, especially in metabolism and apoptosis, through in vivo and in vitro approaches. For the in vivo studies, the experimental model of mammary cancer induced with DMBA in rats was used. Animals were fed with a low-fat diet (LF), with a high corn oil diet from weaning (HOO) or after induction (LF-HCO), and with a high EVOO diet from weaning (HOO) or after induction (LF-HOO). Data from carcinogenesis and anatomopathological parameters to validate and extend results regarding the differential effect of high-fat diets on carcinogenesis was used. Tumor molecular analysis was performed at mRNA, protein, or enzymatic levels, and metabolome was characterized by 1H-Nuclear Magnetic Resonance (NMR) spectroscopy. Regarding the in vitro assays, two cell lines representing different molecular subtypes of breast cancer (MDA-MB-231 and MCF-7) were used. The effects of different oil components on viability, apoptosis and metabolomic profile were determined. Tumor molecular analysis of enzymes of the main metabolic pathways has shown that the EVOO-enriched diet increased glucose and mitochondrial metabolism. This metabolic reprogramming did not reflect clinical and morphological characteristics of tumors (lower degree in the EVOO groups). This data suggested that metabolic changes without the context of other pathways, such as proliferation or apoptosis, may not reflect tumor malignancy. Further analysis using untargeted metabolomics showed changes in tumor lipid composition. The high corn oil diet (rich in polyunsaturated fatty acids PUFA n 6) increased total PUFA and linoleic acid while decreasing monounsaturated fatty acids (MUFA). On the contrary, tumors from high EVOO groups were similar to those of the control group. These differences were concordant with the different effect of diets on carcinogenesis, suggesting that tumor lipid composition play a role in malignancy. Moreover, the levels of apoptotic proteins in the tumors were studied, finding that the high-EVOO diet modulated several cell death pathways. This suggested that EVOO may exert a beneficial effect modulating apoptosis. Secondly, in vitro analyses were designed to elucidate the role of the components of high-fat diets. The treatment of MDA-MB-231 and MCF-7 cells with polyphenols (Hydroxytyrosol HT , Luteolin LUT and Oleuropein) diminished cell viability and increased apoptosis, whereas fatty acids treatment (oleic and linoleic acid) had no significant effect. Next, changes in BC cell metabolome induced with HT and LUT were characterized, revealing extensive metabolic reprogramming. Although some effects were observed in both cell lines, others were markedly depending on the type of cell, underscoring the significance of metabolic context in cancer metabolomics studies. In summary, the results suggest a beneficial effect of EVOO on breast cancer risk and disease progression, through multiple mechanisms like the modulation of metabolism and favoring a pro-apoptotic environment in the tumors. These effects would be mediated by various components, especially the minor compounds, which highlight the importance of the type but also the quality of the oil consumed. The relevance of nutritional factors is that they are modifiable, which highlights the importance of improving dietary habits, especially in relation to lipid intake, in the prevention and fight against breast cancer.

Date of Award	25 Jul 2023
Original language	Catalan
Supervisor	Raquel Moral Cabrera (Director)