title: Alanyl-glutamine prevents muscle atrophy and glutamine synthetase induction by glucocorticoids.
abstract: The aims of this work were to establish whether glutamine infusion via alanyl-glutamine dipeptide provides effective therapy against muscle atrophy from glucorticoids and whether the glucocorticoid induction of glutamine synthetase (GS) is downregulated by dipeptide supplementation. Rats were given hydrocortisone 21-acetate or the dosing vehicle and were infused with alanine (AA) or alanyl-glutamine (AG) at the same concentrations and rates (1.15 mumol.min-1.100 g body wt-1, 0.75 ml/h) for 7 days. Compared with AA infusion in hormone-treated animals, AG infusion prevented total body and fast-twitch muscle mass losses by over 70%. Glucocorticoid treatment did not reduce muscle glutamine levels. Higher serum glutamine was found in the AG-infused (1.72 +/- 0.28 mumol/ml) compared with the AA-infused group (1.32 +/- 0.06 mumol/ml), but muscle glutamine concentrations were not elevated by AG infusion. Following glucocorticoid injections, GS enzyme activity was increased by two- to threefold in plantaris, fast-twitch white (superficial quadriceps), and fast-twitch red (deep quadriceps) muscle/fiber types of the AA group. Similarly, GS mRNA was elevated by 3.3- to 4.1-fold in these same muscles of hormone-treated, AA-infused rats. AG infusion diminished glucocorticoid effects on GS enzyme activity to 52-65% and on GS mRNA to 31-37% of the values with AA infusion. These results provide firsthand evidence of atrophy prevention from a catabolic state using glutamine in dipeptide form. Despite higher serum and muscle alanine levels with AA infusion than with AG infusion, alanine alone is not a sufficient stimulus to counteract muscle atrophy. The AG-induced muscle sparing is accompanied by diminished expression of a glucocorticoid-inducible gene in skeletal muscle. However, glutamine regulation of GS appears complex and may involve more regulators than muscle glutamine concentration alone.
authors.affiliation: School of Kinesiology, University of Illinois at Chicago 60608-1516, USA.
authors.forename: R C
authors.initials: RC
authors.lastname: Hickson
authors.forename: L E
authors.initials: LE
authors.lastname: Wegrzyn
authors.forename: D F
authors.initials: DF
authors.lastname: Osborne
authors.forename: I E
authors.initials: IE
authors.lastname: Karl
mesh_terms: D000409:Alanine / Q000378:metabolism; D000818:Animals; D001835:Body Weight; D004151:Dipeptides / Q000494:pharmacology*; D004790:Enzyme Induction / Q000187:drug effects; D005260:Female; D005938:Glucocorticoids / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D005974:Glutamate-Ammonia Ligase / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D018656:Muscle Fibers, Fast-Twitch / Q000378:metabolism; D018482:Muscle, Skeletal / Q000033:anatomy & histology / Q000378:metabolism; D009133:Muscular Atrophy / Q000139:chemically induced / Q000517:prevention & control*; D009929:Organ Size; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D004151:Dipeptides; D005938:Glucocorticoids; D012333:RNA, Messenger; D005974:Glutamate-Ammonia Ligase; D000409:Alanine; C054122:alanylglutamine