Cysteine aggravates palmitate-induced cell death in hepatocytes

Lipotoxicity, defined as cell death induced by excessive fatty acids, especially saturated fatty acids, is critically involved in the development of non-alcoholic steatohepatitis (NASH). Recent studies report that plasma cysteine concentrations is elevated in the subjects with either alcoholic steatohepatitis (ASH) or NASH than normal subjects. The present study was conducted to determine if elevation of cysteine could be a deleterious factor in palmitate-induced hepatocyte cell death.

HepG2 and Hep3B cells were treated with palmitate with/without the inclusion of cysteine in the media for 24h. The effects of cysteine inclusion on palmitate induced cell death were determined by lactate dehydrogenase (LDH) release and MTT assay. Oxidative stress was evaluated by intracellular glutathione (GSH) level, malondialdehyde (MDA) formation, and DCFH-DA assay. Western blotting was performed to detect the changes of endoplasmic reticulum(ER) stress markers: C/EBP homologous transcription factor (CHOP), GRP-78, and phosphorylated c-jun N-terminal kinase (p-JNK).

Elevated intracellular cysteine aggravates hepatocytes to palmitate-induced cell death. Enhancement of ER stress, specifically increased activation of JNK pathway, contributed to this cell death process.

Increase of plasma cysteine levels, as observed in both ASH and NASH patients, may play a pathological role in the development of the liver diseases. Manipulation of dietary amino acid supplementation could be a therapeutic choice.