Mibefradil reduces hepatic glucose output in HepG2 cells via Ca2+/calmodulin-dependent protein kinase II-dependent Akt/forkhead box O1signaling

The effects and underlying mechanisms of mibefradil on gluconeogenesis and glycogenesis were investigated using insulin-resistant HepG2 human hepatocellular carcinoma cells and a mouse model of type 2 diabetes mellitus (T2DM). HepG2 cells were divided into one of four groups: control, palmitate (PA)-induced insulin-resistance (0.25 mM), low-concentration mibefradil (0.025 μM), or high-concentration mibefradil (0.05 μM). Glycogen synthesis and glucose consumption were evaluated in these HepG2 cells, and quantitative polymerase chain reaction (qPCR) and western blotting techniques were used to detect expression of forkhead box O1 (FoxO1), phosphoenolpyruvate carboxykinase (PEPCK), and glucose 6-phosphatase (G6Pase). Intracellular calcium concentrations were determined using Fluo-4 AM, and phosphorylation levels of calmodulin-dependent protein kinase II (CaMKII), protein kinase B (Akt) and FoxO1were detected by western blotting. Immunofluorescence was used for the localization and quantification of FoxO1.In vitro results were verified using a mouse model of T2DM. In HepG2 cells and mouse liver tissues, mibefradil decreased PA-induced cytoplasmic calcium levels and CaMKII phosphorylation, but increased the phosphorylation of Akt and FoxO1, thereby contributing to the cytoplasmic localization of FoxO1. Additionally, mibefradil alleviated PA-induced glucose output and insulin resistance through increased glucose consumption and glycogen synthesis, while decreasing the expression of key gluconeogenesis enzymes, including PEPCK and G6Pase. Mibefradil may help to control blood sugar levels by reducing glucose output and insulin resistance, and the mechanism of action may involve the Ca2+-CaMKII-dependent Akt/FoxO1 signaling pathway.