Amelioration of Insulin Resistance by Scopoletin in High-Glucose-Induced, Insulin-Resistant HepG2 Cells

Abstract

Insulin resistance plays an important role in the development of type 2 diabetes mellitus. Scopoletin, a phenolic coumarin, is reported to regulate hyperglycemia and diabetes. To examine its effect on insulin resistance, we treated high-glucose-induced, insulin-resistant HepG2 cells with scopoletin and measured phosphatidylinositol 3-kinase (PI3 K)-linked protein kinase B (Akt/PKB) phosphorylation. Scopoletin significantly stimulated the reactivation of insulin-mediated Akt/PKB phosphorylation. This effect was blocked by LY294002, a specific PI3 K inhibitor. The ability of scopoletin to activate insulin-mediated Akt/PKB was greater than that of rosiglitazone, a thiazolidinedione, and scopoletin was less adipogenic than rosiglitazone, as shown by the extent of lipid accumulation in differentiated adipocytes. Scopoletin increased the gene expression of both peroxisome proliferator-activated receptor γ2 (PPARγ2), a target receptor for rosiglitazone, and adipocyte-specific fatty acid binding protein, but not to the level induced by rosiglitazone. However, the PPARγ2 protein level was increased equally by rosiglitazone and scopoletin in differentiated adipocytes. Our results suggest that scopoletin can ameliorate insulin resistance in part by upregulating PPARγ2 expression. With its lower adipogenic property, scopoletin may be a useful candidate for managing metabolic disorders, including type 2 diabetes mellitus.