(+)-Lipoic Acid Reduces Lipotoxicity and Regulates Mitochondrial Homeostasis and Energy Balance in an In Vitro Model of Liver Steatosis

Abstract

Non-alcoholic fatty liver disease (NAFLD) is characterized by the accumulation of lipids within hepatocytes, which compromises liver functionality following mitochondrial dysfunction and increased production of reactive oxygen species (ROS). Lipoic acid is one of the prosthetic groups of the pyruvate dehydrogenase complex also known for its ability to confer protection from oxidative damage because of its antioxidant properties. In this study, we aimed to investigate the effects of lipoic acid on lipotoxicity and mitochondrial dynamics in an in vitro model of liver steatosis. HepG2 cells were treated with palmitic acid and oleic acid (1:2) to induce steatosis, without and with 1 and 5 µM lipoic acid. Following treatments, cell proliferation and lipid droplets accumulation were evaluated. Mitochondrial functions were assessed through the evaluation of membrane potential, MitoTracker Red staining, expression of genes of the mitochondrial quality control, and analysis of energy metabolism by HPLC and Seahorse. We showed that lipoic acid treatment restored membrane potential to values comparable to control cells, as well as protected cells from mitochondrial fragmentation following PA:OA treatment. Furthermore, our data showed that lipoic acid was able to determine an increase in the expression of mitochondrial fusion genes and a decrease in mitochondrial fission genes, as well as to restore the bioenergetics of cells after treatment with palmitic acid and oleic acid. In conclusion, our data suggest that lipoic acid reduces lipotoxicity and improves mitochondrial functions in an in vitro model of steatosis, thus providing a potentially valuable pharmacological tool for NAFLD treatment.

Comparison of HepaRG and HepG2 cell lines to model mitochondrial respiratory adaptations in non‑alcoholic fatty liver disease

“…On the other hand, herein, the FFA-treated HepG2 cells exhibited a decreased mitochondrial respiration, increased ROS production [2 mM OA/PA (1/1)], mitochondrial fragmentation and TAG accumulation, with no change in MMP and cell death. The findings demonstrating a decreased mitochondrial respiration in FFA-treated HepG2 cells are in accordance with those of previous studies, although the findings regarding lipotoxicity are inconsistent ( 15 , 16 , 45 , 48 ).…”

“…On the other hand, it was surprising to observe that a significant decline in mitochondrial respiration in FFA-treated HepG2 cells did not result in more severe mitochondria damage and decreased cell viability. It is possible that the methods used to evaluate cell death in the present study may not have been as sensitive as those used in previous studies ( 45 , 48 ). Of note, the study by Doczi et al ( 63 ) demonstrated that the viability of HepG2 cells was not decreased by the complete inhibition of mitochondrial respiration.…”

“…Although excessive mitochondrial fragmentation is detrimental, it is also associated with adaptive responses as it activates fatty acid β-oxidation and mitophagy ( 62 ). Exposure to FFAs has been shown to be associated with increased mitochondrial fission proteins and decreased fusion proteins in HepG2 cells ( 44 , 45 , 48 ). For HepaRG cells, 24-h exposure to FFAs was ideal as it allowed the authors to capture the coexistence of physiologically incompatible processes (in the long run), such as stimulated mitochondrial respiration and mitochondrial damage.…”