title: Endogenous formation of Nε-(carboxymethyl)lysine is increased in fatty livers and induces inflammatory markers in an in vitro model of hepatic steatosis.
abstract: OBJECTIVE
  Increased lipid peroxidation and inflammation are major factors in the pathogenesis of nonalcoholic fatty liver disease (NAFLD). A lipoxidation product that could play a role in the induction of hepatic inflammation is N(ε)-(carboxymethyl)lysine (CML). The aim of the present study was to investigate the relationship between steatosis and CML and to study the role of CML in hepatic inflammation.
  
  
  METHODS
  We included 74 obese individuals, which were categorized into 3 groups according to the grade of hepatic steatosis. CML accumulation in liver biopsies was assessed by immunohistochemistry and plasma CML levels were measured by mass spectrometry. Plasma CML levels were also determined in the hepatic artery, portal, and hepatic vein of 22 individuals, and CML fluxes across the liver were calculated. Hepatocyte cell lines were used to study CML formation during intracellular lipid accumulation and the effect of CML on pro-inflammatory cytokine expression. Gene expression levels of the inflammatory markers were determined in liver biopsies of the obese individuals.
  
  
  RESULTS
  CML accumulation was significantly associated with the grade of hepatic steatosis, the grade of hepatic inflammation, and gene expression levels of inflammatory markers PAI-1, IL-8, and CRP. Analysis of CML fluxes showed no release/uptake of CML by the liver. Lipid accumulation in hepatocytes, induced by incubation with fatty acids, was associated with increased CML formation and expression of the receptor for advanced glycation endproducts (RAGE), PAI-1, IL-8, IL-6, and CRP. Pyridoxamine and aminoguanidine inhibited the endogenous CML formation and the increased RAGE, PAI-1, IL-8, IL-6, and CRP expression. Incubation of hepatocytes with CML-albumin increased the expression of RAGE, PAI-1, and IL-6, which was inhibited by an antibody against RAGE.
  
  
  CONCLUSIONS
  Accumulation of CML and a CML-upregulated RAGE-dependent inflammatory response in steatotic livers may play an important role in hepatic steatosis and in the pathogenesis of NAFLD.
authors: Department of Internal Medicine, Laboratory of Metabolism and Vascular Medicine, Maastricht University Medical Center, Maastricht, The Netherlands.
authors: Katrien H J
authors: KH
authors: Gaens
authors: Petra M G
authors: PM
authors: Niessen
authors: Sander S
authors: SS
authors: Rensen
authors: Wim A
authors: WA
authors: Buurman
authors: Jan Willem M
authors: JW
authors: Greve
authors: Ann
authors: A
authors: Driessen
authors: Marcel G M
authors: MG
authors: Wolfs
authors: Marten H
authors: MH
authors: Hofker
authors: Johanne G
authors: JG
authors: Bloemen
authors: Cornelis H
authors: CH
authors: Dejong
authors: Coen D A
authors: CD
authors: Stehouwer
authors: Casper G
authors: CG
authors: Schalkwijk
mesh_terms: D000368:Aged; D015415:Biomarkers / Q000378:metabolism; D001706:Biopsy; D016207:Cytokines / Q000235:genetics / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005234:Fatty Liver / Q000276:immunology* / Q000378:metabolism* / Q000473:pathology; D005260:Female; D015870:Gene Expression / Q000276:immunology; D006146:Guanidines / Q000494:pharmacology; D056945:Hep G2 Cells; D022781:Hepatocytes / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D006801:Humans; D066298:In Vitro Techniques; D008099:Liver / Q000276:immunology* / Q000378:metabolism* / Q000473:pathology; D008239:Lysine / Q000031:analogs & derivatives* / Q000096:biosynthesis / Q000378:metabolism; D008297:Male; D008875:Middle Aged; D065626:Non-alcoholic Fatty Liver Disease; D009765:Obesity / Q000276:immunology / Q000378:metabolism / Q000473:pathology; D011733:Pyridoxamine / Q000494:pharmacology; D014803:Vitamin B Complex / Q000494:pharmacology
chemical_list: D015415:Biomarkers; D016207:Cytokines; D004791:Enzyme Inhibitors; D006146:Guanidines; D014803:Vitamin B Complex; D011733:Pyridoxamine; C048496:N(6)-carboxymethyllysine; D008239:Lysine; C004479:pimagedine