Heterocyclic amines reduce insulin-induced AKT phosphorylation and induce gluconeogenic gene expression in human hepatocytes.

Abstract

Heterocyclic amines (HCAs) are well-known for their mutagenic properties. One of the major routes of human exposure is through consumption of cooked meat, as certain cooking methods favor formation of HCAs. Recent epidemiological studies reported significant associations between dietary HCA exposure and insulin resistance and type II diabetes. However, no previous studies have examined if HCAs, independent of meat consumption, contributes to pathogenesis of insulin resistance or metabolic disease. In the present study, we have assessed the effect of three HCAs commonly found in cooked meat (2-amino-3,4,8-trimethylimidazo[4,5-f]quinoxaline [MeIQ], 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline [MeIQx], and 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine [PhIP]) on insulin signaling and glucose production. HepG2 or cryopreserved human hepatocytes were treated with 0-50μM of MeIQ, MeIQx, or PhIP for 3days. Treatment of HepG2 cells and hepatocytes with MeIQ and MeIQx resulted in a significant reduction in insulin-induced AKT phosphorylation, suggesting that HCA exposure decreases hepatic insulin signaling. HCA treatment also led to significant increases in expression of gluconeogenic genes, G6PC and PCK1, in both HepG2 and cryopreserved human hepatocytes. Additionally, the level of phosphorylated FOXO1, a transcriptional regulator of gluconeogenesis, was significantly reduced by HCA treatment in hepatocytes. Importantly, HCA treatment of human hepatocytes led to increases in extracellular glucose level in the presence of gluconeogenic substrates, suggesting that HCAs induce hepatic glucose production. The current findings suggest that HCAs induce insulin resistance and promote hepatic glucose production in human hepatocytes. This implicates that exposure to HCAs may lead to the development of type II diabetes or metabolic syndrome.