Reduced glutathione protects human hepatocytes from palmitate-mediated injury by suppressing endoplasmic reticulum stress response.

BACKGROUND/AIMS: The aim of this study was to investigate the protective role of reduced glutathione (GSH) in hepatocytes by suppressing palmitate-induced endoplasmic reticulum (ER) stress.

METHODOLOGY: Human L02 hepatocytes were co-cultured with palmitate and reduced GSH. Cell viability and apoptosis were measured by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay and Annexin V/ PI (propidium iodide) staining with flow cytometry, respectively. Lipid peroxidation was assessed by malonaldehyde (MDA) and oxidized glutathione (GSSG) measurements. Levels of ER stress signaling proteins (phosphorylated PRK-like ER kinase, activating transcription factor 4 and glucose regulating protein 78) as well as Caspase-4 activity were also analyzed.

RESULTS: Palmitate caused an increased lipid peroxidation level and cytotoxic effect in hepatocytes in a concentration-dependent and time-dependent manner. However, a significant cell protective effect was observed after GSH treatment. The protein levels of GRP78, pPERK and AFT4 as well as the mRNA level of ATF4 were significantly increased after palmitate treatment, and these levels decreased after GSH addition. Additionally, Caspase-4 activity significantly increased after palmitate addition and strongly decreased after the addition of GSH.

CONCLUSIONS: ER stress provoked by lipid peroxidation is a key event that mediates palmitate cytotoxicity in hepatocytes. Reduced GSH has a protective effect by suppressing palmitate-induced ER stress.