Oleic acid ameliorates palmitic acid induced hepatocellular lipotoxicity by inhibition of ER stress and pyroptosis.

Background: Pyroptosis is a novel programmed cell death. It is identified as caspase-1 dependent and characterized by plasma-membrane rupture and release of proinflammatory intracellular contents inculuding IL-1 beta and IL-18. Pyroptosis is distinct from other forms of cell death, especially apoptosis that is characterized by nuclear and cytoplasmic condensation and is elicited via activation of a caspase cascade. In pyroptosis, gasdermin D (GSDMD) acts as a major executor, while NLRP3 related inflammasome is closely linked to caspase-1 activation. Given that pyroptosis has played a critical role in the progression of non-alcoholic steatohepatitis (NASH), here, we investigated whether the regulation of pyroptosis activation is responsible for the protective role of monounsaturated oleic acids in the context of hepatocellular lipotoxicity. Methods: Human hepatoma cell line HepG2 cells were exposed to palmitic acid (PA) with or without oleic acids (OA) or/and endoplasmic reticulum (ER) stress inhibitor tauroursodeoxycholic acid (TUDCA) for 24 h. Besides, the cells were treated with the chemical ER stressor tunicamycin (TM) with or without OA for 24 h as well. The expressions of pyroptosis and ER stress related genes or proteins were determined by real-time PCR, Western blot or immunofluorescence. The morphology of pyroptosis was detected by acridine orange and ethidium bromide (AO/EB) staining. The release of IL-1 beta and tumor necrosis factor alpha (TNF-α) was determined by ELISA. Sprague-Dawley (SD) rats were fed with high fat diet (HFD) for 16 w, then, HFD was half replaced by olive oil to observe the protective effects of olive oil. The blood chemistry were analyzed, and the liver histology and the expressions of related genes and proteins were determined in the liver tissues. Results: We demonstrated that PA impaired the cell viability and disturbed the lipid metabolism of HepG2 cells Conclusion: Palmitic acid induced predominant pyroptosis in HepG2 cells, and ER stress may be responsible for the induction of pyroptosis and subsequent cell death. Monounsaturated oleic acids were able to ameliorate hepatocellular lipotoxicity both in vitro and in vivo, and OA mediated inhibition of ER stress and pyroptosis may be the underlying mechanisms.