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Heterocyclic amines (HCAs) are mutagens generated when cooking meat for prolonged periods of time or until well-done. 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. It is well known that HCAs require hepatic bioactivation by cytochrome P450 1A2 (CYP1A2) and N-acetyltransferase 2 (NAT2). NAT2 expresses a well-defined genetic polymorphism in humans that, depending on the combination of NAT2 alleles, correlate to rapid, intermediate, or slow acetylator phenotypes that exhibit differential metabolism of aromatic amines and HCAs. We hypothesize that HCAs will induce insulin resistance and disrupt energy homeostasis in human hepatocytes, and that the effect will be dependent on NAT2 genetic polymorphism. HCA treatment on human hepatocytes induced insulin resistance, glucose production, and expression of several key genes involved in gluconeogenesis, and these effects were more apparent in rapid NAT2 acetylator hepatocytes than in slow. Additionally, HCAs lead to neutral lipid accumulation and increased levels of triglycerides, cholesterol, and free fatty acids, in addition to dysregulated expression of genes involved in lipid homeostasis. Potential mechanisms of HCA-induced insulin resistance and disrupted energy homeostasis were also explored. HCAs increased JNK activity, a well-known mechanism of hepatic insulin resistance, and blocking JNK activity restored insulin signaling in HCA-treated hepatocytes. Additionally, HCAs led to increased reactive oxygen species and induction of TNF, indicating oxidative stress and inflammation as potential mechanisms of insulin resistance. An RNA-sequencing study also indicated endoplasmic reticulum stress as a potential mechanism. Taken together, the findings presented here indicate that HCAs lead to insulin resistance and dysregulation of energy homeostasis in human hepatocytes, and that these outcomes are differentially affected by NAT2 genetic polymorphism. These studies provide insight into the novel role of HCAs in the development of conditions associated with metabolic syndrome and fatty liver, and elucidate the crucial need to consider the gene-environmental interactions when investigating these conditions.

Heterocyclic amines (HCAs) are formed when cooking meats at high temperatures or for long periods of time, and their major metabolic pathway includes hepatic N‑hydroxylation by CYP1A2 followed by O-acetylation by N-acetyltransferase 2 (NAT2). NAT2 is a highly polymorphic gene involved in metabolism of drugs and xenobiotics, and its single nucleotide polymorphisms (SNPs) produce phenotypes characterized as slow, intermediate, or rapid acetylator. Recent studies have documented associations between HCAs and insulin resistance and between certain NAT2 phenotypes and insulin resistance. In this study, we demonstrated that NAT2 activity and exposure to certain HCAs may alter cellular glucose and lipid homeostasis. Additionally, these results demonstrate changes in sensitivity to insulin following exposure to some HCAs. These findings are significant because they indicate a genetic component (NAT2 polymorphism) and an environmental component (dietary HCA exposure via consumption of cooked meat) in the pathogenesis of insulin resistance in hepatocytes of human origin.