Lipid accumulation in multi-walled carbon nanotube-exposed HepG2 cells: Possible role of lipophagy pathway

Nanoparticle (NP) exposure might promote hepatic steatosis, but relatively few studies investigated the influence of multi-walled carbon nanotubes (MWCNTs) on lipid accumulation in hepatocytes in vitro. This study investigated lipid accumulation and the possible role of lipophagy (autophagic degradation of lipid droplets) in MWCNT-exposed HepG2 cells. Pristine (XFM19) and carboxylated MWCNTs (XFM21) were internalized, accompanying cytotoxicity, lysosomal destabilization, and intracellular reactive oxygen species (ROS) production. Compared with XFM21, XFM19 promoted lipid accumulation in HepG2 cells more effectively, which was further enhanced by pre-incubation with autophagy inhibitor NH4Cl. In addition, MWCNTs increased the expression of lipophagy genes PLIN2 and BECN1 but decreased that of ATG7. The expression of endoplasmic reticulum (ER) stress regulators, namely DDIT3, HSPA5, and XBP-1s, was also altered in MWCNT exposed HepG2 cells. Combined, these results suggested that MWCNT exposure might promote lipid accumulation in hepatocytes probably through the modulation of lipophagy pathway.