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We reported previously that higher doses (150–250 μM) of silibinin enhanced fission and inhibited fusion of mitochondria, accompanying apoptosis of double-positive breast cancer cell line MCF-7 cells and triple-negative breast cancer cell line MDA-MB-231 cells. We report here three important questions yet unclarified in the previous study; 1) Whether enhanced fission of mitochondria by the treatment of silibinin leads to mitophagy, 2) Whether mitophagy positively contributes to apoptosis and 3) Whether estrogen receptor-positive (ER+) MCF-7 cells and estrogen receptor-negative (ER−) MDA-MB-231 cells are affected in a different way by silibinin treatment, since silibinin often works through ERs signaling pathway. Mitophagy driven by Pink1/Parkin signaling, plays an important role in eliminating damaged mitochondria. Indeed, increased expression of Pink1 and the recruitment of Parkin and LC3-II to mitochondria by the treatment with silibinin account for silibinin induction of mitophagy. In this study, the effects of mitochondrial division inhibitor 1 (mdivi-1) and small interfering RNA targeting dynamin-related protein 1 (DRP1) were examined to reveal the effect of mitochondrial fission on mitophagy. As expected, mdivi-1 or siRNA targeting DRP1 reversed silibinin-induced mitochondrial fission due to down-regulation in the expression of DRP1. Inhibition of mitochondrial fission by mdivi-1 prevented induction of mitophagy as well as autophagy in both MCF-7 and MDA-MB-231 cells, indicating that silibinin-induced mitochondrial fission leads to mitophagy. Inhibition of mitochondrial fission efficiently prevented silibinin-induced apoptosis in MCF-7 and MDA-MB-231 cells in our previous work, and the second point of the present study, inhibition of mitophagy by Pink1 or Parkin knockdown increased silibinin-induced apoptosis of these cells, respectively, suggesting that the mitophagy induced by silibinin treatment serves as a cytoprotective effect, resulting in reduction of apoptosis of cancer cells in both cells. In the third point, we studied whether estrogen receptors (ERs) played a role in silibinin-induced mitophagy and apoptosis in MCF-7 and MDA-MB-231 cells. ERα and ERβ are not involved in silibinin-induced mitophagic process in MCF-7 and MDA-MB-231 cells. These findings demonstrated that silibinin induced mitochondria fission leads to mitophagy, which attenuates silibinin-induced apoptosis not through ERs-Pink1 or -Parkin pathway in MCF-7 and MDA-MB-231. [ABSTRACT FROM AUTHOR]

Type 2 diabetes (T2DM) is induced by the abundance of glucose and lipids, which causes glucolipotoxicity to the pancreatic β-cells. Silibinin is a natural flavonoid possessing the regulatory activity on insulin production and therapeutic activity in diabetic mice; however, its effect on glucolipotoxicity is not fully explained. This in vitro study investigates the effects of silibinin on palmitic acid (PA) and high glucose (HG)-induced cell loss and ferroptosis of rat insulinoma INS-1 cells. In the cells treated with PA and HG, expressions of glucose transporter 4 (Glut4) and carnitine acyltransferase I (CPT1) for β-oxidation of fatty acids are reduced. Mitochondria are the metabolic organelles for glucose and fatty acids. The mitochondrial membrane potential (MMP) and ATP production were decreased, while the ROS level was elevated in the cells treated with PA and HG, indicating an induction of mitochondrial disorder. Cell loss was partially rescued by ferroptosis inhibition, suggesting an involvement of ferroptosis in the cells treated with PA and HG. More importantly, the increases in total iron, lipid ROS, MDA and COX-2, and the decrease in ferroptosis inhibitory molecules GSH, GPX4 and FSP1 appeared in the cells treated with PA and HG, confirming the occurrence of ferroptosis. Moreover, PINK1/parkin-mediated mitophagy, a vital process for selective elimination of damaged mitochondria, was blocked. Interestingly, silibinin rescued the mitochondria, restricted the ferroptosis and restored the mitophagy. By using the pharmacological stimulator and inhibitor of mitophagy, and si-RNA transfection to silence PINK1 expression, silibinin's protective effect against ferroptosis caused by PA and HG treatment was found to depend on mitophagy. Collectively, our current study reveals the new mechanisms for the protection of silibinin against the injury of INS-1 cells treated with PA and HG, elucidates the participation of ferroptosis in glucolipotoxicity, highlighting the involvement of mitophagy in defense against ferroptotic cell death. [Display omitted] • Silibinin improves the mitochondrial function in INS-1 cells treated with palmitic acid and high glucose. • Silibinin alleviates the reduction of PINK1/parkin-mediated mitophagy in INS-1 cells treated with palmitic acid and high glucose. • Silibinin attenuates ferroptosis in INS-1 cells treated with palmitic acid and high glucose. • Silibinin-induced mitophagy negatively regulates ferroptosis in INS-1 cells treated with palmitic acid and high glucose. [ABSTRACT FROM AUTHOR]