The aim of this study was to investigate the effects of S. horneri (Sargassum horneri) extracts on PA (Palmitic acid)-induced ER stress (Endoplasmic reticulum stress) in HepG2 cells. Antioxidant activity of the S. horneri extract was evaluated, reactive oxygen species (ROS) production activities of the extracts were measured in hydrogen peroxide (H2O2)-stressed HepG2 cells. HepG2 cells were treated with S. horneri extract or palmitic acid to measure cell viability by WST analysis. In addition, to investigate the effective induction of ER stress and the effects of S. horneri, ER stress-related genes such as ATF4 (Activating Transcription Factor 4), XBP1s (X-box binding protein), CHOP (C/EBP homologous protein), and GRP78 (Growth arrest and DNA damage-inducible 34) were examined by RT-PCR, and expression and activation levels of IRE1α(Inositol-Requiring Enzyme-1α), eIF2α(Eukaryotic translation Initiation Factor 2 alpha submit), and CHOP were examined by western blot analysis. In the results of mRNA and protein expression, palmitic acid significantly increases the expression of genes related to ER stress as well as the protein expression levels in 12-hour treatment. Subsequent treatment with S. horneri reduced mRNA expression of ATF4, GRP78, and XBP1s. In addition, protein levels of p-IRE1α, p-elF2α and CHOP were also reduced by treatment with S. horneri. Analysis of sirtuin mRNA expression showed that in S. horneri increased the levels of SIRT2 and SIRT7, which indicates a possible role in reducing the expression of ER stress-related genes.
These data indicate that S. horneri is able to exert an inhibitory effect on ER stress caused by palmitic acid and suggests its potential as an agent of various ER stress-related diseases.