Changes in Insulin Signaling and Gluconeogenic Gene Expression in Human Hepatocytes Following Exposure to Heterocyclic Amines

Abstract

Humans are exposed to heterocyclic amine (HCA) mutagens produced in meats cooked at high temperatures or until well-done. A recent epidemiological study documented associations of high HCA intake with increased prevalence of insulin resistance, which is one of the hallmarks of type II diabetes mellitus and metabolic syndrome. However, it is unknown if HCAs directly induce insulin resistance. To investigate the effects of HCA exposure on insulin sensitivity, we subjected HepG2 (hepatocellular carcinoma) cells and primary human hepatocytes to 2-amino-3,4-dimethylimidazo[4,5-f]quinoline (MeIQ) and measured changes in insulin signaling, gluconeogenic gene expression, and glucose production. HepG2 cells were treated with varying concentrations of MeIQ (0-100 μM), then treated with insulin and analyzed for changes in insulin signaling via p-AKT induction on Western blot. MeIQ exposure decreased insulin-induced p-AKT levels in low glucose conditions, suggesting that the cells become insulin resistant in the presence of MeIQ. Additionally, the MeIQ treatment significantly upregulated the transcripts of genes involved in gluconeogenesis (e.g., G6PC and PCK1) in HepG2 cells. Similarly, primary human hepatocytes exposed to MeIQ also showed significant increases in gluconeogenic genes, compared to the vehicle treated cells. These results suggest that MeIQ impairs insulin signaling and potentially induces glucose production in hepatocytes. We then tested if the gene expression changes induced by MeIQ leads to increases in glucose production in primary hepatocytes. Despite upregulation of gluconeogenic genes, there were no significant changes in glucose production between control and MeIQ-treated cells. Future studies will examine whether MeIQ exposure alters the suppressive effects of insulin on gluconeogenic gene expression and glucose production and test additional HCAs. The alterations in insulin signaling and gluconeogenic gene expression following MeIQ exposure in hepatocytes indicate that MeIQ may directly alter insulin sensitivity.