Role of dha supplementation and physical exercise on non-alcoholic fatty liver disease markers in aged obese female mice and postmenopausal women

Resumen

The main objective of this PhD dissertation was to investigate the effects of n-3 PUFA supplementation or physical exercise, alone or in combination, on the mechanisms involved in non-alcoholic fatty liver disease (NAFLD) development in aged obese female mice and to study their effects on NAFLD-risk biomarkers in overweight/obese postmenopausal women. Chapter 1 aimed to conduct a systematic review of the effects of n-3 PUFA supplementation on oxidative stress biomarkers and on NAFLD/NASH human adults. The systematic review illustrated that it remains controversial whether n-3 PUFA are effective to counteract oxidative stress in humans. Indeed, the heterogeneity in population, treatment duration, doses and methods to assess oxidative stress in the trials reviewed prevent any definitive conclusions. Moreover, the review suggested that n-3 PUFA supplementation maybe effective in the early stages of NAFLD, but not in patients with more severe NAFLD or NASH. Chapter 2 and 3 analyzed the effects of long-term DHA rich n-3 PUFA supplementation or physical treadmill exercise, alone or in combination on the progression of HFD-induced hepatic steatosis, as well as the potential mechanisms involved in 18 months old obese female mice. Chapter 2 showed that the DHA-rich diet reduced liver steatosis in diet-induced obese (DIO) mice, decreasing lipogenic genes (Dgat2, Scd1, Srebp1c), and upregulating lipid catabolism genes (Hsl/Acox) expression. A similar pattern was observed in the DIO+exercise group. The combination of DHA+exercise potentiated an increase in Cpt1α and Pparα genes, and AMPK activation, key regulators of fatty acid oxidation (FAO). Exercise, alone or in combination with DHA, significantly reversed the induction of proinflammatory genes (Mcp1, Il6, Tnfα, Tlr4) in DIO mice. DHA supplementation was effective in preventing the alterations induced by the HFD in endoplasmic reticulum stress-related genes (Ern1/Xbp1) and autophagy markers (LC3II/I ratio, p62, Atg7). Chapter 3 showed that long-term exercise, especially when combined with DHA supplementation upregulated hepatic Sirt1 mRNA levels, which were positively correlated with FAO genes, and negatively correlated with lipogenic and proinflammatory genes. Unlike Sirt1, hepatic Foxo1 mRNA expression was increased in DIO mice, and positively associated with liver TG content, and the expression of lipogenic and pro-inflammatory genes. In overweight/obese postmenopausal women, correlations between SIRT1 and FOXO1 mRNA expression in PBMCs and several NAFLD risk indexes/biomarkers, and the regulatory effect of a 16-week DHA-rich n-3 PUFA supplementation and/or a progressive resistance training programme were studied (Chapter 3). Results showed that FOXO1 mRNA levels negatively correlated with NAFLD risk indexes (HSI and ZJU), while no significant correlations were observed for SIRT1 with any biomarker/index of NAFLD. After 16-week intervention, nearly all intervention groups showed reduced NAFLD biomarkers and NAFLD risk indexes in parallel with a body fat mass reduction. However, neither DHA-rich n-3 PUFA supplementation nor resistance training induced significant effects as compared to placebo or non-trained groups. Interestingly, DHA-rich supplementation promoted a significant upregulation of FOXO1 expression in PBMCs as compared to the placebo supplemented groups, and the changes in FOXO1 expression were positively correlated with baseline FLI, HSI indexes. Moreover, resistance training promoted an upregulation of SIRT1 expression in PBMCs, while no correlations were found between changes in SIRT1 and changes or initial levels of NAFLD indexes.