Oxidant stress reduces insulin responsiveness in 3T3-L1 adipocytes

Increased oxidant stress has been suggested to occur in diabetes and to contribute to the development of late diabetic complications. Whether oxidant stress plays a role in the development or progression of insulin resistance is not known. In this study we hypothesized that exposing 3T3-L1 adipocytes to prolonged micromolar concentrations of H₂O₂ would reduce their acute metabolic responses to insulin stimulation. 3T3-L1 adipocytes exposed to 25 mU/ml glucose oxidase (GO) for 18 h exhibited a threefold increase in basal 2-deoxyglucose (2-DG) uptake activity. However, net increase in 2-DG uptake activity after acute insulin (100 nM) stimulation was 355 ± 56 pmol · mg protein^-1 · min^-1 in control vs. 198 ± 41 pmol · mg protein^-1 · min^-1 in GO-pretreated cells (P < 0.05). Basal lipogenesis activity was significantly enhanced by GO, but acute insulin stimulation resulted in significantly reduced lipogenesis activity (29 ± 4 vs. 11 ± 1 nmol glucose/well for control and 50 mU/ml GO, respectively, P = 0.001). Glycogen synthase a activity was reduced by GO (78 ± 1 vs. 43 ± 2 pmol UDP-glucose · mg protein^-1 · min^-1, P = 0.03), whereas insulin stimulation of glycogen synthase was reduced, exhibiting a right shift in the insulin dose- response curve. These effects of GO were associated with increased GLUT-1 and reduced GLUT-4 protein and mRNA content. In conclusion, our data suggest that oxidant stress alters glucose transporters expression and insulin-stimulated metabolism in 3T3-L1 adipocytes.