Cynarin Counteracts Lipotoxicity in Pancreatic β-Cells Via Inhibiting Palmitate-Induced Apoptosis and Linoleic Acid-Provoked Ferroptosis.

Lipotoxicity has raised intense public concerns for its cytotoxicity and associated chronic diseases. Pancreatic β-cells are highly susceptible to lipotoxicity, since the excessive lipids may produce massive reactive oxygen species (ROS), cause severe oxidative stress, induce the dysfunction of endoplasmic reticulum (ER), damage lipid membranes and trigger the eventual cell death. This study explored the mechanism of cynarine (CYN) in preventing rat pancreatic cells (RINm5F) from the cytotoxicity induced by representative fatty acids, palmitate (PA, physiologically abundant) and linoleic acid (LA, prevalent in Western-style diets). In 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay, CYN administration significantly enhanced the viability of pancreatic β cells exposed to PA or LA, validating its protective efficacy against lipotoxicity in RINm5F cells. Further experiments demonstrated that CYN treatment prevented PA-treated beta cells from apoptosis by quenching the intracellular ROS, ameliorating the cellular damages of lipid peroxidation, mitigating cellular calcium dysregulation, suppressing crucial ER stress mediator proteins' expression, attenuating aberrant sub-G1 cell population, and inhibiting the expression of key proapoptotic proteins. In the β cells stressed by LA, CYN treatment efficiently abrogated the abnormal elevation of cellular ferric iron content, inhibited lipid peroxidation, improved the declined GSH content, enhanced the expression of glutathione peroxidase 4, and thereby alleviated the LA-provoked ferroptosis. The findings provide experimental evidence for employing CYN as a preferential antagonist to intervene in lipotoxicity and relevant diseases like diabetes mellitus.