title: Obesity Appears to Be Associated With Altered Muscle Protein Synthetic and Breakdown Responses to Increased Nutrient Delivery in Older Men, but Not Reduced Muscle Mass or Contractile Function.
abstract: Obesity is increasing, yet despite the necessity of maintaining muscle mass and function with age, the effect of obesity on muscle protein turnover in older adults remains unknown. Eleven obese (BMI 31.9 ± 1.1 kg · m(-2)) and 15 healthy-weight (BMI 23.4 ± 0.3 kg · m(-2)) older men (55-75 years old) participated in a study that determined muscle protein synthesis (MPS) and leg protein breakdown (LPB) under postabsorptive (hypoinsulinemic-euglycemic clamp) and postprandial (hyperinsulinemic hyperaminoacidemic-euglycemic clamp) conditions. Obesity was associated with systemic inflammation, greater leg fat mass, and patterns of mRNA expression consistent with muscle deconditioning, whereas leg lean mass, strength, and work done during maximal exercise were no different. Under postabsorptive conditions, MPS and LPB were equivalent between groups, whereas insulin and amino acid administration increased MPS in only healthy-weight subjects and was associated with lower leg glucose disposal (LGD) (63%) in obese men. Blunting of MPS in the obese men was offset by an apparent decline in LPB, which was absent in healthy-weight subjects. Lower postprandial LGD in obese subjects and blunting of MPS responses to amino acids suggest that obesity in older adults is associated with diminished muscle metabolic quality. This does not, however, appear to be associated with lower leg lean mass or strength.
authors.affiliation: MRC Arthritis Research UK Centre for Musculoskeletal Ageing Research, School of Life Sciences, University of Nottingham Medical School, Queen's Medical Centre, Nottingham, U.K.
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Murton
authors.affiliation: MRC Arthritis Research UK Centre for Musculoskeletal Ageing Research, School of Life Sciences, University of Nottingham Medical School, Queen's Medical Centre, Nottingham, U.K.
authors.forename: Kanagaraj
authors.initials: K
authors.lastname: Marimuthu
authors.affiliation: MRC Arthritis Research UK Centre for Musculoskeletal Ageing Research, School of Life Sciences, University of Nottingham Medical School, Queen's Medical Centre, Nottingham, U.K.
authors.forename: Joanne E
authors.initials: JE
authors.lastname: Mallinson
authors.affiliation: MRC Arthritis Research UK Centre for Musculoskeletal Ageing Research, School of Medicine, Division of Medical Sciences and Graduate Entry Medicine, Royal Derby Hospital, Derby, U.K.
authors.forename: Anna L
authors.initials: AL
authors.lastname: Selby
authors.affiliation: MRC Arthritis Research UK Centre for Musculoskeletal Ageing Research, School of Medicine, Division of Medical Sciences and Graduate Entry Medicine, Royal Derby Hospital, Derby, U.K.
authors.forename: Kenneth
authors.initials: K
authors.lastname: Smith
authors.affiliation: MRC Arthritis Research UK Centre for Musculoskeletal Ageing Research, School of Life Sciences, University of Nottingham Medical School, Queen's Medical Centre, Nottingham, U.K.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Rennie
authors.affiliation: MRC Arthritis Research UK Centre for Musculoskeletal Ageing Research, School of Life Sciences, University of Nottingham Medical School, Queen's Medical Centre, Nottingham, U.K. paul.greenhaff@nottingham.ac.uk.
authors.forename: Paul L
authors.initials: PL
authors.lastname: Greenhaff
mesh_terms: D054392:Adipokines / Q000378:metabolism; D000273:Adipose Tissue / Q000378:metabolism*; D000368:Aged; D000596:Amino Acids / Q000494:pharmacology; D001284:Atrophy; D016022:Case-Control Studies; D020869:Gene Expression Profiling; D015309:Glucose Clamp Technique; D006801:Humans; D007004:Hypoglycemic Agents / Q000494:pharmacology; D007249:Inflammation; D007328:Insulin / Q000494:pharmacology; D007866:Leg; D008297:Male; D008875:Middle Aged; D009119:Muscle Contraction; D009124:Muscle Proteins / Q000096:biosynthesis* / Q000187:drug effects; D018482:Muscle, Skeletal / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology; D009765:Obesity / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism*
chemical_list: D054392:Adipokines; D000596:Amino Acids; D007004:Hypoglycemic Agents; D007328:Insulin; D009124:Muscle Proteins; D012333:RNA, Messenger