title: Reduced skeletal muscle oxidative capacity and elevated ceramide but not diacylglycerol content in severe obesity.
abstract: OBJECTIVE
  The link between a reduced capacity for skeletal muscle mitochondrial fatty acid oxidation (FAO) and lipotoxicity in human insulin resistance has been the subject of intense debate. The objective of this study was to investigate whether reduced FAO is associated with elevated acyl CoA, ceramide, and diacylglycerol (DAG) in severely obese insulin resistant subjects.
  
  
  METHODS
  Muscle biopsies were conducted in lean (L, 22.6 ± 0.5 kg/m(2) , n = 8), Class I (CI, 32.1 ± 0.4 kg/m(2) , n = 7) and Class II&III obese (CII&III, 45.6 ± 1.1 kg/m(2) , n = 15) women for acyl CoA, sphingolipid and DAG profiling. Intramyocellular triglyceride (IMTG) content was determined by histology. FAO was assessed by incubating muscle homogenates with [1-C]palmitate and measuring CO2 production. Cardiolipin content was quantified as an index of mitochondrial content. Lipid metabolism proteins, DGAT1, PLIN5, and PNPLA2 were quantified in biopsy samples by western blot.
  
  
  RESULTS
  CII&III were more insulin resistant (HOMA-IR: 4.5 ± 0.5 vs. 1.1 ± 0.1, P < 0.001), and had lower FAO (∼58%, P = 0.007) and cardiolipin content (∼31%, P = 0.013) compared to L. IMTG was elevated in CI (P = 0.04) and CII&III (P = 0.04) compared to L. Sphingolipid content was higher in CII&III compared to L (13.6 ± 1.1 vs. 10.3 ± 0.5 pmol/mg, P = 0.031) whereas DAG content was not different among groups. DGAT1 was elevated in CII&III, and PLIN5 was elevated in CI compared to L.
  
  
  CONCLUSIONS
  Severe obesity is associated with reduced muscle oxidative capacity and occurs concomitantly with elevated IMTG, ceramide and insulin resistance.
authors.affiliation: Department of Health and Physical Activity, School of Education, University of Pittsburgh, Pittsburgh, PA 15213, USA; Division of Endocrinology and Metabolism, Department of Medicine, University of Pittsburgh, Pittsburgh, PA 15213, USA.
authors.forename: P M
authors.initials: PM
authors.lastname: Coen
authors.forename: K C
authors.initials: KC
authors.lastname: Hames
authors.forename: E M
authors.initials: EM
authors.lastname: Leachman
authors.forename: J P
authors.initials: JP
authors.lastname: DeLany
authors.forename: V B
authors.initials: VB
authors.lastname: Ritov
authors.forename: E V
authors.initials: EV
authors.lastname: Menshikova
authors.forename: J J
authors.initials: JJ
authors.lastname: Dubé
authors.forename: M
authors.initials: M
authors.lastname: Stefanovic-Racic
authors.forename: F G S
authors.initials: FG
authors.lastname: Toledo
authors.forename: B H
authors.initials: BH
authors.lastname: Goodpaster
mesh_terms: D000328:Adult; D001823:Body Composition; D016022:Case-Control Studies; D002518:Ceramides / Q000378:metabolism*; D051048:Diacylglycerol O-Acyltransferase / Q000235:genetics / Q000378:metabolism; D004075:Diglycerides / Q000378:metabolism*; D005260:Female; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism; D008049:Lipase / Q000235:genetics / Q000378:metabolism; D050356:Lipid Metabolism / Q000235:genetics; D008875:Middle Aged; D009124:Muscle Proteins / Q000235:genetics / Q000378:metabolism; D018482:Muscle, Skeletal / Q000378:metabolism* / Q000473:pathology; D009767:Obesity, Morbid / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D010084:Oxidation-Reduction; D000070797:Perilipin-5; D000217:Acyltransferases
chemical_list: D002518:Ceramides; D051048:Diacylglycerol O-Acyltransferase; D004075:Diglycerides; D047908:Intracellular Signaling Peptides and Proteins; D008049:Lipase; D009124:Muscle Proteins; D000070797:Perilipin-5; C544352:PLIN5 protein, human; C494881:DGAT1 protein, human; C494794:PNPLA2 protein, human; D000217:Acyltransferases