Papel de diferentes antioxidantes naturales en la regulación de la función y biogénesis mitocondrialposible implicación en la obesidad

Abstract

Non-alcoholic steatosis is an important hepatic complication of obesity linked to mitochondrial dysfunction and oxidative stress. In this context, the sirtuin family has been demonstrated to play an important role in the regulation of mitochondrial function and in the activation of antioxidant defenses. Lipoic acid (LA) has been reported to have beneficial effects on mitochondrial function and to attenuate oxidative stress. In this thesis, the potential protective effect of LA supplementation against the development of non-alcoholic steatosis associated with a long-term high-fat diet feeding and the potential mechanisms involved in these effects were analyzed. Particularly, I researched the effects of LA on the modulation of mitochondrial defenses through the sirtuin pathway. To achieved these objectives, male Wistar rats were fed a standard diet (C, n=10), a high-fat diet (OB, n=10) and a high-fat diet supplemented with LA (OLIP, n=10). A group pair-fed to the latter group (PFO, n=6) was also included. LA prevents hepatic triglyceride accumulation and liver damage in rats fed on a high-fat diet, through the modulation of genes involved in lipogenesis and mitochondrial â-oxidation, and by improving insulin sensitivity. Moreover, this molecule showed an inhibitory action on electron transport chain complexes activities and ATP synthesis, and reduced significantly energy efficiency. By contrast, LA induces an increase in mitochondrial copy number and in Ucp2 gene expression. Moreover, LA prevents liver oxidative damage through the inhibition of hydroperoxide production and the stimulation of mitochondrial antioxidant defenses. LA treatment up-regulated manganese superoxide dismutase and glutathione peroxidase activities, and increased the GSH:GSSG ratio and UCP2 mRNA levels. Moreover, this molecule reduced oxidative damage in mitochondrial DNA and increased mitochondrial copy number. LA treatment decreased the acetylation levels of Foxo3a and PGC1â through the stimulation of SIRT3 and SIRT1. In summary, our results demonstrate that the beneficial effects of LA supplementation on hepatic steatosis could be mediated by its ability to restore the oxidative balance by increasing antioxidant defenses through the deacetylation of Foxo3a and PGC1â by SIRT1 and SIRT3. Finally, the novelty and importance of this study is the finding of how lipoic acid modulates some of the mitochondrial processes involved in energy homeostasis. The reduction in mitochondrial energy efficiency could also explain, at least in part, the beneficial effects of lipoic acid not only in fatty liver but also in preventing excessive body weight gain.