Oxidative stress induced by intermittent hypoxia exacerbates lipid accumulation and inflammation in a cell model of non-alcoholic steatohepatitis

Abstract

Background/Aims: The prevalence of obstructive sleep apnea (OSA) is high in patients with non-alcoholic fatty liver disease (NAFLD) and NASH is a progressive hallmark of the pathogenesis of NAFLD. Chronic intermittent hypoxia is associated with recurrent episodes of oxygen desaturation and reoxygenation in OSA patients, leading to excessive production of reactive oxygen species (ROS). The causal link between OSA and NAFLD is not known and the mechanistic effect of intermittent hypoxia (IH) on the pathogenesis of NAFLD remains elusive. Here we tested the hypothesis that IH-induced oxidative stress aggravates lipid accumulation and inflammation induced by sodium palmitate in HepG2 cells. Materials and Methods: HepG2 cells were treated with sodium palmitate or vehicle under normoxia (Nx) or IH condition for 72 hours in the present or absence of a ROS scavenger MnTBAP. Cell viability was detected by MTT assay and intracellular lipid deposit was examined by oil red staining. Lipid peroxidation was measured by malondialdehyde (MDA) assay and levels of reactive oxygen species (ROS) were detected by CM-H2DCFDA staining. The expressions of pro-inflammatory cytokines (IL-1β, TNF-α, IL-6), fatty acid uptake-associated genes (caveolin-1 and FATP5), fatty acid synthesis genes (SREBP1 and ACC1) and fatty acid β-oxidation gene ACOX were determined by real-time PCR.

Results: Results showed that sodium palmitate increased lipid deposit in the cells and it also decreased cell viability. The effect of sodium palmitate was more prominent in the group co-treated with hypoxia. Levels of MDA and ROS and the expressions of IL-1β, TNF-α, IL-6 and caveolin-1, but not FATP5, were significantly increased in the palmitate- or hypoxia-treated group and were remarkably elevated in the co-treated group. These effects were abolished by MnTBAP treatment. In addition, levels of the expression of ACOX, SREBP1 and ACC1 were significantly lowered in the cells treated with palmitate or hypoxia and the expressions were much less in the cotreated group. Treatment of MnTBAP prevented the decreased expression of ACOX but had no effect on the SREBP1 and ACC1 expression. Conclusion: IH-induced oxidative stress exacerbates lipid accumulation and inflammation induced by sodium palmitate in HepG2 cells, probably mediated by an increase in lipid uptake and a decrease in the fatty acid β-oxidation.