title: Concentration-dependent dual effects of hydrogen peroxide on insulin signal transduction in H4IIEC hepatocytes.
abstract: BACKGROUND
  Oxidative stress induced by the accumulation of reactive oxygen species (ROS) has a causal role in the development of insulin resistance, whereas ROS themselves function as intracellular second messengers that promote insulin signal transduction. ROS can act both positively and negatively on insulin signaling, but the molecular mechanisms controlling these dual actions of ROS are not fully understood.
  
  
  RESULTS
  Here, we directly treated H4IIEC hepatocytes with hydrogen peroxide (H2O2), a representative membrane-permeable oxidant and the most abundant ROS in cells, to identify the key factors determining whether ROS impair or enhance intracellular insulin signaling. Treatment with high concentrations of H2O2 (25-50 µM) for 3 h reduced insulin-stimulated Akt phosphorylation, and increased the phosphorylation of both JNK and its substrate c-Jun. In contrast, lower concentrations of H2O2 (5-10 µM) enhanced insulin-stimulated phosphorylation of Akt. Moreover, lower concentrations suppressed PTP1B activity, suggesting that JNK and phosphatases such as PTP1B may play roles in determining the thresholds for the diametrical effects of H2O2 on cellular insulin signaling. Pretreatment with antioxidant N-acetyl-L-cysteine (10 mM) canceled the signal-promoting action of low H2O2 (5 µM), and it canceled out further impairment of insulin of insulin signaling induced by high H₂O₂ (25 µM).
  
  
  CONCLUSIONS
  Our results demonstrate that depending on its concentration, H2O2 can have the positive or negative effect on insulin signal transduction in H4IIEC hepatocytes, suggesting that the concentration of intracellular ROS may be a major factor in determining whether ROS impair or enhance insulin signaling.
authors.affiliation: Department of Disease Control and Homeostasis, Kanazawa University Graduate School of Medical Science, Kanazawa, Japan.
authors.forename: Satoshi
authors.initials: S
authors.lastname: Iwakami
authors.forename: Hirofumi
authors.initials: H
authors.lastname: Misu
authors.forename: Takashi
authors.initials: T
authors.lastname: Takeda
authors.forename: Makoto
authors.initials: M
authors.lastname: Sugimori
authors.forename: Seiichi
authors.initials: S
authors.lastname: Matsugo
authors.forename: Shuichi
authors.initials: S
authors.lastname: Kaneko
authors.forename: Toshinari
authors.initials: T
authors.lastname: Takamura
mesh_terms: D000111:Acetylcysteine / Q000494:pharmacology*; D000818:Animals; D015153:Blotting, Western; D002478:Cells, Cultured; D022781:Hepatocytes / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D006861:Hydrogen Peroxide / Q000494:pharmacology*; D007328:Insulin / Q000494:pharmacology*; D048031:JNK Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D016877:Oxidants / Q000494:pharmacology*; D018384:Oxidative Stress / Q000187:drug effects; D010766:Phosphorylation / Q000187:drug effects; D054562:Protein Tyrosine Phosphatase, Non-Receptor Type 1 / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D051381:Rats; D017382:Reactive Oxygen Species / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects*
chemical_list: D007328:Insulin; D016877:Oxidants; D017382:Reactive Oxygen Species; D006861:Hydrogen Peroxide; D051057:Proto-Oncogene Proteins c-akt; D048031:JNK Mitogen-Activated Protein Kinases; D054562:Protein Tyrosine Phosphatase, Non-Receptor Type 1; C516610:Ptpn1 protein, rat; D000111:Acetylcysteine
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