title: Impaired myocardial fatty acid oxidation and reduced protein expression of retinoid X receptor-alpha in pacing-induced heart failure.
abstract: BACKGROUND
  The nuclear receptors peroxisome proliferator-activated receptor-alpha (PPARalpha) and retinoid X receptor alpha (RXRalpha) stimulate the expression of key enzymes of free fatty acid (FFA) oxidation. We tested the hypothesis that the altered metabolic phenotype of the failing heart involves changes in the protein expression of PPARalpha and RXRalpha.
  
  
  RESULTS
  Cardiac substrate uptake and oxidation were measured in 8 conscious, chronically instrumented dogs with decompensated pacing-induced heart failure and in 8 normal dogs by infusing 3 isotopically labeled substrates: 3H-oleate, 14C-glucose, and 13C-lactate. Although myocardial O2 consumption was not different between the 2 groups, the rate of oxidation of FFA was lower (2.8+/-0.6 versus 4.7+/-0.3 micromol x min(-1) x 100g(-1)) and of glucose was higher (4.6+/-1.0 versus 1.8+/-0.5 micromol x min(-1) x 100g(-1)) in failing compared with normal hearts (P<0.05). The rates of lactate uptake and lactate output were not significantly different between the 2 groups. In left ventricular tissue from failing hearts, the activity of 2 key enzymes of FFA oxidation was significantly reduced: carnitine palmitoyl transferase-I (0.54+/-0.04 versus 0.66+/-0.04 micromol x min(-1) x g(-1)) and medium chain acyl-coenzyme A dehydrogenase (MCAD; 1.8+/-0.1 versus 2.9+/-0.3 micromol x min(-1) x g(-1)). Consistently, the protein expression of MCAD and of RXRalpha were significantly reduced by 38% in failing hearts, but the expression of PPARalpha was not different. Moreover, there were significant correlations between the expression of RXRalpha and the expression and activity of MCAD.
  
  
  CONCLUSIONS
  Our results provide the first evidence for a link between the reduced expression of RXRalpha and the switch in metabolic phenotype in severe heart failure.
authors.affiliation: Department of Physiology, New York Medical College, Valhalla, NY 10595, USA.
authors.forename: Juan Carlos
authors.initials: JC
authors.lastname: Osorio
authors.forename: William C
authors.initials: WC
authors.lastname: Stanley
authors.forename: Axel
authors.initials: A
authors.lastname: Linke
authors.forename: Michele
authors.initials: M
authors.lastname: Castellari
authors.forename: Quy N
authors.initials: QN
authors.lastname: Diep
authors.forename: Ashish R
authors.initials: AR
authors.lastname: Panchal
authors.forename: Thomas H
authors.initials: TH
authors.lastname: Hintze
authors.forename: Gary D
authors.initials: GD
authors.lastname: Lopaschuk
authors.forename: Fabio A
authors.initials: FA
authors.lastname: Recchia
mesh_terms: D000103:Acetyl-CoA Carboxylase / Q000032:analysis; D042964:Acyl-CoA Dehydrogenase; D000818:Animals; D002247:Carbon Isotopes; D002250:Carbon Radioisotopes; D002262:Carboxy-Lyases / Q000032:analysis; D002304:Cardiac Pacing, Artificial; D002334:Carnitine O-Palmitoyltransferase / Q000032:analysis; D004195:Disease Models, Animal; D004285:Dogs; D004789:Enzyme Activation; D044943:Fatty Acid Desaturases / Q000032:analysis; D005227:Fatty Acids / Q000378:metabolism*; D005947:Glucose / Q000378:metabolism / Q000493:pharmacokinetics; D006333:Heart Failure / Q000378:metabolism* / Q000473:pathology; D006439:Hemodynamics; D019344:Lactic Acid / Q000378:metabolism / Q000493:pharmacokinetics; D008297:Male; D008929:Mitochondria, Heart / Q000201:enzymology; D009206:Myocardium / Q000737:chemistry / Q000378:metabolism* / Q000473:pathology; D019301:Oleic Acid / Q000378:metabolism / Q000493:pharmacokinetics; D010084:Oxidation-Reduction; D020033:Protein Isoforms / Q000378:metabolism; D018160:Receptors, Cytoplasmic and Nuclear / Q000032:analysis / Q000378:metabolism; D018168:Receptors, Retinoic Acid / Q000032:analysis / Q000378:metabolism*; D047488:Retinoid X Receptors; D014157:Transcription Factors / Q000032:analysis / Q000378:metabolism*; D014316:Tritium
chemical_list: D002247:Carbon Isotopes; D002250:Carbon Radioisotopes; D005227:Fatty Acids; D020033:Protein Isoforms; D018160:Receptors, Cytoplasmic and Nuclear; D018168:Receptors, Retinoic Acid; D047488:Retinoid X Receptors; D014157:Transcription Factors; D014316:Tritium; D019301:Oleic Acid; D019344:Lactic Acid; D044943:Fatty Acid Desaturases; D042964:Acyl-CoA Dehydrogenase; D002334:Carnitine O-Palmitoyltransferase; D002262:Carboxy-Lyases; C021532:malonyl-CoA decarboxylase; D000103:Acetyl-CoA Carboxylase; D005947:Glucose