Ο ρόλος των ελεύθερων λιπαρών οξέων και του οξειδωτικού στρες στην ανάπτυξη μη αλκοολικής στεατοηπατίτιδας (Doctoral thesis)
Ιnappropriate accumulation of excess lipids into liver cells, in the form of lipid droplets, has been proposed to lead to dysfunction of hepatocytes and, consequently, to serious pathological complications (lipotoxicity). Nonalcoholic fatty liver disease (NAFLD) is a term used to characterize a spectrum of pathological changes ranging from simple fatty infiltration (steatosis) to hepatic steatosis accompanied with inflammation, fibrosis, and cirrhosis (non-alcoholic steatohepatitis, NASH). Despite the high prevalence of NAFLD and its potential for serious complications, the underlying molecular mechanisms that determine the progression to liver damage remain poorly understood and need further investigation. The aim of the present study was to create a model of the two hit hypothesis, using human hepatocytes in culture, in order to investigate the role of free fatty acids and oxidative stess in the process of lipotoxicity. In detail, HepG2 human liver cells were exposed to stearate, oleate, or mixtures of the two fatty acids and the effects on cell proliferation and viability, reactive oxygen species (ROS) generation, induction of ER stress and apoptosis and lipid droplet accumulation, were evaluated. It was observed that: a) stearate, but not oleate, inhibited cell proliferation and induced cell death, b) stearate-induced cell death had the characteristics of ER stress- and mitochondrial-mediated apoptosis, c) stearate-treated cells did not produce ROS and untreated and fatty acid-treated cells were equally sensitive against DNA damage, induced by subsequent exposure to hydrogen peroxide, d) the capacity of cells to produce and accumulate triglycerides in the form of lipid droplets was hindered at an early phase following exposure to stearate, while it proceeded normally in oleate-treated cells, e) Co-administration of oleate restored the ability of stearate-treated cells for triglyceride synthesis and lipid droplet formation and protected cells from stearate-induced toxicity at all steps, e) activation of stearate, in the form of stearoyl-CoA, was a necessary step for the manifestation of toxicity. Collectively, the data suggest that oxidative stress does not represent a significant contributor in saturated fatty acid-induced liver toxicity. The results indicate that it is not free stearate per se, but one or more of its specific metabolic products, with different properties than oleate metabolites, which are responsible for inducing cell toxicity. It is proposed that these saturated lipid intermediates of stearate hinder and then interrupt the process of triglyceride synthesis in endoplasmic reticulum (ER) membranes and induce ER stress, leading ultimately in mitochondrial-mediated apoptotic cell death. Co-administration of oleate appears to modulate the physical properties of these metabolites, inhibiting in this way their toxic effect. In conclusion, it is suggested that interruption of triglyceride synthesis constitutes the key initiating event, in the process of saturated fatty acid-induced lipotoxicity
|Institution and School/Department of submitter:||Πανεπιστήμιο Ιωαννίνων Σχολή Ιατρικής Τμήμα Ιατρικής Τομέας Λειτουργικός - Κλινικοεργαστηριακός Εργαστήριο Βιολογικής Χημείας|
|Keywords:||Ήπαρ,Μη αλκολική λιπώδης εκφύλιση του,Στεατοηπατίτιδα, μη αλκοολική,Λιποτοξικότητα,Λιποαπόπτωση,Λιπαρά οξέα, κορεσμένα ελεύθερα,Λιπαρά οξέα, μονοκόρεστα ελεύθερα,Στρές ενδοπλασματικού δικτύου,Οξειδωτικό στρες|
|Appears in Collections:||Διδακτορικές Διατριβές|
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