Background: N-3 polyunsaturated fatty acids, such as docosahexaenoic acid (DHA; 22:6n-3), has clinical significance in the prevention and reversal of nonalcoholic steatohepatitis (NASH). However, the precious mechanism underlying remains unclear. The inflammasome, a multiprotein complex formed by NOD-like receptor (NLR) family members, has been recently shown to be activated in NASH and promote the cleavage of the pro-inflammatory cytokines to their maturation forms.
Methods: HepG2 cells were exposed to different dose of PA for 24 h with or without the preincubation of 50 mu M DHA for another 24 h and then lipid deposition was assessed with Oil red O staining and intracellular triglyceride (TG) determination. Secretory levels of inflammatory cytokines and Caspase-1 activity were determined by ELISA assays. Gene expression and protein levels were determined by quantitative RCR and western blotting, respectively.
Results: Palmitate (PA) dose-dependently increased lipid accumulation, TG content and induced the secretion of interleukin-1 beta (IL-1 beta), IL-18, TNF-alpha and MCP-1 from HepG2 cells. Preincubation with DHA significantly alleviated PA-induced lipid accumulation and inflammatory agents. DHA was also found to attenuate PA-induced NOD-like receptor protein 4 (NLRC4) mRNA expression. Furthermore, PA induced caspase-1 activation in a dose-dependent manner, resulting in exacerbating of procaspase-1 and pro-IL-1 beta processing. Knockdown of NLRC4 partially abrogated PA-induced caspase-1 activation and IL-1 beta maturation and completely abolished these events in the presence of DHA.
Conclusions: Our findings indicate DHA attenuates PA-induced lipid accumulation and inflammation through suppressing NLRC4 inflammasome activation, caspase-1 activation and IL-1 beta cleavage.

Docosahexaenoic acid; Inflammation; Lipid accumulation; Nonalcoholic steatohepatitis; NLRC4 inflammasome; Palmitate

Sun Yat-sen University