A diterpene derivative enhanced insulin signaling induced by high glucose level in HepG2 cells.

The predominant feature of type 2 diabetes is insulin resistance. Identifying a drug able to reduce insulin resistance is an urgent requirement. ent-3α-Formylabieta-8(14),13(15)-dien-16,12β-olide had been identified as a new diterpene derivative which showed anticancer activity. This study explores the hypoglycemic effect of ent-3α-formylabieta-8(14),13(15)-dien-16,12β-olide and studied its mechanism. The insulin response of HepG2 cells following ent-3α-formylabieta-8(14),13(15)-dien-16,12β-olide treatment, as a model for liver cancer cells, was assessed. The results demonstrated that hyperglycemia resulted in a significant increase in the levels of insulin receptor substrate-1 (IRS-1) serine phosphorylation and decrease in Akt phosphorylation. High glucose also inhibited the phosphorylation of insulin-dependent GSK3β. ent-3α-Formylabieta-8(14),13(15)-dien-16,12β-olide treatment improved the effect of insulin on the phosphorylation of IRS-1 Ser307. In addition, this study demonstrated that the effect of ent-3α-formylabieta-8(14),13(15)-dien-16,12β-olide was dependent on the activation of AMP-activated protein kinase. Collectively, experimental data indicated an association between insulin resistance and hyperglycemia in HepG2 cells, and that ent-3α-formylabieta-8(14),13(15)-dien-16,12β-olide reduces IRS-1 Ser307 phosphorylation via activating AMPK, thereby decreasing the insulin signaling blockade.