title: Chronic α-hydroxyisocaproic acid treatment improves muscle recovery after immobilization-induced atrophy.
abstract: Muscle disuse atrophy is observed routinely in patients recovering from traumatic injury and can be either generalized resulting from extended bed rest or localized resulting from single-limb immobilization. The present study addressed the hypothesis that a diet containing 5% α-hydroxyisocaproic acid (α-HICA), a leucine (Leu) metabolite, will slow the loss and/or improve recovery of muscle mass in response to disuse. Adult 14-wk-old male Wistar rats were provided a control diet or an isonitrogenous isocaloric diet containing either 5% α-HICA or Leu. Disuse atrophy was produced by unilateral hindlimb immobilization ("casting") for 7 days and the contralateral muscle used as control. Rats were also casted for 7 days and permitted to recover for 7 or 14 days. Casting decreased gastrocnemius mass, which was associated with both a reduction in protein synthesis and S6K1 phosphorylation as well as enhanced proteasome activity and increased atrogin-1 and MuRF1 mRNA. Although neither α-HICA nor Leu prevented the casting-induced muscle atrophy, the decreased muscle protein synthesis was not observed in α-HICA-treated rats. Neither α-HICA nor Leu altered the increased proteasome activity and atrogene expression observed with immobilization. After 14 days of recovery, muscle mass had returned to control values only in the rats fed α-HICA, and this was associated with a sustained increase in protein synthesis and phosphorylation of S6K1 and 4E-BP1 of previously immobilized muscle. Proteasome activity and atrogene mRNA content were at control levels after 14 days and not affected by either treatment. These data suggest that whereas α-HICA does not slow the loss of muscle produced by disuse, it does speed recovery at least in part by maintaining an increased rate of protein synthesis.
authors.affiliation: Department of Cellular and Molecular Physiology, Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033, USA. clang@psu.edu
authors.forename: Charles H
authors.initials: CH
authors.lastname: Lang
authors.forename: Anne
authors.initials: A
authors.lastname: Pruznak
authors.forename: Maithili
authors.initials: M
authors.lastname: Navaratnarajah
authors.forename: Kristina A
authors.initials: KA
authors.lastname: Rankine
authors.forename: Gina
authors.initials: G
authors.lastname: Deiter
authors.forename: Hugues
authors.initials: H
authors.lastname: Magne
authors.forename: Elizabeth A
authors.initials: EA
authors.lastname: Offord
authors.forename: Denis
authors.initials: D
authors.lastname: Breuillé
mesh_terms: D000596:Amino Acids / Q000097:blood; D000818:Animals; D001284:Atrophy; D015153:Blotting, Western; D001835:Body Weight / Q000187:drug effects; D002208:Caproates / Q000494:pharmacology*; D004032:Diet; D004435:Eating / Q000187:drug effects; D023381:Endpoint Determination; D007103:Immobilization / Q000009:adverse effects*; D007700:Kinetics; D007930:Leucine / Q000494:pharmacology; D008297:Male; D009124:Muscle Proteins / Q000096:biosynthesis; D018482:Muscle, Skeletal / Q000187:drug effects* / Q000473:pathology*; D009929:Organ Size / Q000187:drug effects; D046988:Proteasome Endopeptidase Complex / Q000187:drug effects / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D060888:Real-Time Polymerase Chain Reaction; D020127:Recovery of Function / Q000187:drug effects*
chemical_list: D000596:Amino Acids; D002208:Caproates; D009124:Muscle Proteins; C019419:alpha-hydroxyisocaproic acid; D046988:Proteasome Endopeptidase Complex; D007930:Leucine
keywords: disuse; leucine; mammalian target of rapamycin; protein degradation; protein synthesis