Essential role of Nrf2 in the protective effect of lipoic acid against lipoapoptosis in hepatocytes

et al.Excess of saturated free fatty acids, such as palmitic acid (PA), in hepatocytes has been implicated in nonalcoholic fatty liver disease. α-Lipoic acid (LA) is an antioxidant that protects against oxidative stress conditions. We have investigated the effects of LA in the early activation of oxidative and endoplasmic reticulum stress, lipid accumulation, and Nrf2-mediated antioxidant defenses in hepatocytes treated with PA or in rats fed a high-fat diet. In primary human hepatocytes, a lipotoxic concentration of PA triggered endoplasmic reticulum stress, induced the apoptotic transcription factor CHOP, and increased the percentage of apoptotic cells. Cotreatment with LA prevented these effects. Similar results were found in mouse hepatocytes in which LA attenuated PA-mediated activation of caspase 3 and reduced lipid accumulation by decreasing PA uptake and increasing fatty acid oxidation and lipophagy, thereby preventing lipoapoptosis. Moreover, LA augmented the proliferation capacity of hepatocytes after PA challenge. Antioxidant effects of LA ameliorated reactive oxygen species production and endoplasmic reticulum stress and protected against mitochondrial apoptosis in hepatocytes treated with PA. Cotreatment with PA and LA induced an early nuclear translocation of Nrf2 and activated antioxidant enzymes, whereas reduction of Nrf2 by siRNA abolished the benefit of LA on PA-induced lipoapoptosis. Importantly, posttreatment with LA reversed the established damage induced by PA in hepatocytes, as well as preventing obesity-induced oxidative stress and lipoapoptosis in rat liver. In conclusion, our work has revealed that in hepatocytes, Nrf2 is an essential early player in the rescue of oxidative stress by LA leading to protection against PA-mediated lipoapoptosis.We acknowledge the following grant support: SAF2012-33283 (Ministry of Economy and Competitiveness, MINECO, Spain), Comunidad de Madrid S2010/BMD-2423, EFSD and Amylin Paul Langerhans Grant, and Centro de Investigación Biomédica en Red de Diabetes y Enfermedades Metabólicas Asociadas (ISCIII, Spain) to A.M.V.; SAF2010-17822 (MINECO, Spain) and Centro de Investigación Biomédica en Red de Enfermedades Neurodegenerativas (ISCIII, Spain) to A.C.; PI09/0185 (ISCIII, Spain) and Centro de Investigación Biomédica en Red de Enfermedades Hepáticas y Digestivas (ISCIII, Spain) to J.M.; Línea especial “Nutrición, Obesidad y Salud” (University of Navarra LE/97) and AGL2006-04716/ALI and AGL2009-10873/ALI (Ministry of Science and Innovation, Spain) and Centro de Investigación Biomédica en Red de Fisiopatología de la Obesidad y Nutrición (ISCIII, Spain) to D.S., J.A.M., and M.J.M.; SAF2013-45887-R to L.H. and SAF2011-30520-C02-01 to D.S. (MINECO, Spain), Generalitat de Catalunya (2014SGR-465 to D.S.); and EFSD/Lilly and EFSD/Janssen and L’Oréal-UNESCO research fellowships to L.H. M.W. is the recipient of a Ciência sem Fronteiras–CNPq fellowship (237976/2012-9). M.P.V. holds a scholarship from Instituto de Salud Carlos III (ISCIII, Ministry of Health, Spain).Peer Reviewe