Differential modulation of the hepatocellular metabolome, cytoprotective and inflammatory responses due to endotoxemia and lipotoxicity

Abstract

The present work aimed to examine the primary mechanisms of liver damage, namely the impact of gut-derived endotoxins along the gut–liver axis and adipose-derived free fatty acids along the adipose–liver axis. These processes are known to play a significant role in the development of hepatic inflammation and steatosis. Although possible overlapping in the pathogenesis was expected, these processes have unique pathophysiological consequences. Therefore, we used HepG2 cells as a model system to investigate the impact of lipopolysaccharides (LPS) and free fatty acid (FFA; albumin conjugated palmitic acid) on the intracellular metabolome. Although both LPS and FFA triggered the expression of nuclear factor κB (NFκB)-dependent inflammation, only LPS treatment was able to trigger a Toll-like receptor 4 (TLR4) dependent response. The intracellular cytoprotective enzymatic levels (catalase, peroxidase, glutathione) were increased due to FFA but lowered due to LPS. The free-radical neutralizing efficacies of cell-free metabolites of FFA-treated cells were better than those of the LPS-treated ones. The use of untargeted metabolomics allowed for the identification of distinct metabolic pathway enrichments, providing further insights into the differential effects of LPS and FFA on the metabolism of hepatocytes. Collectively, the current study highlights the distinct impacts of endotoxemia and lipotoxicity on the metabolome of hepatocytes, hence offering valuable insights into hepatocellular function.