Iron contributes to hepatocyte insulin resistance in a cell model of nonalcoholic fatty liver disease

Abstract

Increased body iron stores are associated with increased severity of nonalcoholic fatty liver disease (NAFLD). To clarify the role(s) of iron in NAFLD, this study investigated its effects on surrogate disease markers in AML12 hepatocytes: reactive oxygen species (ROS), stress kinase activation, and insulin resistance. Control AML12 cells defined baseline ROS levels (dichlorodihydro‐fluorescein fluorescence) and maximum insulin response (phospho‐activation of protein kinase B: EC50 near 1 nM insulin, maximum at 100 nM). Treatment with 50 μM iron (given with the lipophilic chelator 8‐hydroxyquinoline) increased ROS levels 8‐fold (p<0.01) and elevated phospho‐jnk and phospho‐p38. This was accompanied by a 33% decrease in response to 10 nM insulin (p<0.01). Under conditions in which fat accumulation alone had little or no effect on ROS levels or insulin response, cells pre‐loaded with stearic acid appeared sensitized to iron (ROS increased 18‐fold (p<0.01); insulin response decreased 51% vs. control), while cells treated with oleic acid appeared partially protected from iron (ROS levels increased 5‐fold (p<0.01); insulin response decreased 24%). We conclude NAFLD progression in this in vitro model is best recapitulated by the combined effects of saturated fat and iron. Studies to further define iron‐sensitive signaling pathways and evaluate novel therapies are justified. Supported by NIH grant AT03448.