Levo-tetrahydropalmatine promotes apoptosis of human hepatocellular carcinoma through switching energy metabolism phenotype via upregulation of mitochondrial reactive oxygen species

Abstract

Mitochondrion is an important organelle that maintains cellular homeostasis and plays a crucial role in determining cell fate. The present study investigated the effect of levo-tetrahydropalmatine(THP) on autophagic flux and energy metabolism phenotype of human hepatocellular carcinoma(HCC) SMMC-7721 and BEL-7402 cells. SMMC-7721 and BEL-7402 cells were treated with THP(100 μmol·L~(-1)) with or without N-acetyl-L-cysteine(NAC, 10 μmol·L~(-1)) for 24 h. The mitochondrial reactive oxygen species(mtROS) was detected by flow cytometry(FCM) with MitoSOX probe and fluorescence microscopy, respectively. Thereafter, autophagic flux was detected by FCM with CYTO-ID probe, and the protein levels of microtubule-associated protein 1 A/1 B-light chain 3-Ⅰ(LC3Ⅰ), LC3Ⅱ, and phosphorylated AMP-activated protein kinase(p-AMPK)/AMPK were measured by Western blot. Mitochondrial respiration was examined by Seahorse XFp assay and cell proliferation by a system. Annexin V-FITC and PI/RNase staining was employed to detect apoptosis of SMMC-7721 and BEL-7402 cells treated with THP and/or NAC. Subsequently, membrane potential was measured with MitoTracker Red CMXRos. Compared with the control group, THP promoted mtROS production and THP combined with NAC attenuated the autophagic flux increase induced by THP alone in SMMC-7721 and BEL-7402 cells. When cells were co-treated with THP and chloroquine(CQ, an autophagy inhibitor), THP further increased mtROS and apoptosis. In addition, THP significantly reduced mitochondrial respiration in terms of mitochondrial basal respiration, ATP production, and maximal respiration. Meanwhile, THP significantly reduced the proliferation index and mitochondrial membrane potential of HCC cells accompanied by the increased apoptosis. This study demonstrates that the up-regulation of mtROS by THP significantly promotes HCC cell autophagy(protective autophagy) and impairs mitochondrial respiration through reprogramming energy metabolism, ultimately inducing the mitochondria-mediated apoptosis of SMMC-7721 and BEL-7402 cells.