title: Methylglyoxal impairs insulin signalling and insulin action on glucose-induced insulin secretion in the pancreatic beta cell line INS-1E.
abstract: OBJECTIVE
  Chronic hyperglycaemia aggravates insulin resistance, at least in part, by increasing the formation of advanced glycation end-products (AGEs). Methylglyoxal (MGO) is the most reactive AGE precursor and its abnormal accumulation participates in damage in various tissues and organs. Here we investigated the ability of MGO to interfere with insulin signalling and to affect beta cell functions in the INS-1E beta cell line.
  
  
  METHODS
  INS-1E cells were incubated with MGO and then exposed to insulin or to glucose. Western blotting was used to study signalling pathways, and real-time PCR to analyse gene expression; insulin levels were determined by radioimmunoassay.
  
  
  RESULTS
  Non-cytotoxic MGO concentrations inhibited insulin-induced IRS tyrosine phosphorylation and phosphatidylinositol 3-kinase (PI3K)/protein kinase B (PKB) pathway activation independently from reactive oxygen species (ROS) production. Concomitantly, formation of AGE adducts on immunoprecipitated IRS was observed. Aminoguanidine reversed MGO inhibitory effects and the formation of AGE adducts on IRS. Further, the insulin- and glucose-induced expression of Ins1, Gck and Pdx1 mRNA was abolished by MGO. Finally, MGO blocked glucose-induced insulin secretion and PI3K/PKB pathway activation. These MGO effects were abolished by LiCl, which inhibits glycogen synthase kinase-3 (GSK-3).
  
  
  CONCLUSIONS
  MGO exerted major damaging effects on INS-1E cells impairing both insulin action and secretion. An important actor in these noxious MGO effects appears to be GSK-3. In conclusion, MGO participates not only in the pathogenesis of the debilitating complications of type 2 diabetes, but also in worsening of the diabetic state by favouring beta cell failure.
authors.affiliation: Dipartimento di Biologia e Patologia Cellulare e Molecolare and Istituto di Endocrinologia ed Oncologia Sperimentale del Consiglio Nazionale delle Ricerche, Università degli Studi di Napoli Federico II, Naples, Italy.
authors.forename: F
authors.initials: F
authors.lastname: Fiory
authors.forename: A
authors.initials: A
authors.lastname: Lombardi
authors.forename: C
authors.initials: C
authors.lastname: Miele
authors.forename: J
authors.initials: J
authors.lastname: Giudicelli
authors.forename: F
authors.initials: F
authors.lastname: Beguinot
authors.forename: E
authors.initials: E
authors.lastname: Van Obberghen
mesh_terms: D000818:Animals; D001692:Biological Transport; D002460:Cell Line; D005786:Gene Expression Regulation / Q000187:drug effects; D005941:Glucokinase / Q000235:genetics / Q000378:metabolism; D005947:Glucose / Q000378:metabolism*; D017127:Glycation End Products, Advanced / Q000378:metabolism; D038362:Glycogen Synthase Kinase 3 / Q000037:antagonists & inhibitors; D018398:Homeodomain Proteins / Q000235:genetics / Q000378:metabolism; D007328:Insulin / Q000235:genetics / Q000378:metabolism*; D055504:Insulin Receptor Substrate Proteins; D000078790:Insulin Secretion; D050417:Insulin-Secreting Cells / Q000187:drug effects / Q000378:metabolism*; D010766:Phosphorylation / Q000187:drug effects; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D011499:Protein Processing, Post-Translational / Q000187:drug effects; D011765:Pyruvaldehyde / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017382:Reactive Oxygen Species / Q000378:metabolism; D055571:Secretory Pathway / Q000187:drug effects; D015398:Signal Transduction / Q000187:drug effects; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism
chemical_list: D017127:Glycation End Products, Advanced; D018398:Homeodomain Proteins; D007328:Insulin; D055504:Insulin Receptor Substrate Proteins; D047428:Protein Kinase Inhibitors; D012333:RNA, Messenger; D017382:Reactive Oxygen Species; D015534:Trans-Activators; C084010:pancreatic and duodenal homeobox 1 protein; D011765:Pyruvaldehyde; D005941:Glucokinase; D038362:Glycogen Synthase Kinase 3; D005947:Glucose