title: Leucine-enriched essential amino acids attenuate inflammation in rat muscle and enhance muscle repair after eccentric contraction.
abstract: Eccentric exercise results in prolonged muscle damage that may lead to muscle dysfunction. Although inflammation is essential to recover from muscle damage, excessive inflammation may also induce secondary damage, and should thus be suppressed. In this study, we investigated the effect of leucine-enriched essential amino acids on muscle inflammation and recovery after eccentric contraction. These amino acids are known to stimulate muscle protein synthesis via mammalian target of rapamycin (mTOR), which, is also considered to alleviate inflammation. Five sets of 10 eccentric contractions were induced by electrical stimulation in the tibialis anterior muscle of male SpragueDawley rats (8-9 weeks old) under anesthesia. Animals received a 1 g/kg dose of a mixture containing 40 % leucine and 60 % other essential amino acids or distilled water once a day throughout the experiment. Muscle dysfunction was assessed based on isometric dorsiflexion torque, while inflammation was evaluated by histochemistry. Gene expression of inflammatory cytokines and myogenic regulatory factors was also measured. We found that leucine-enriched essential amino acids restored full muscle function within 14 days, at which point rats treated with distilled water had not fully recovered. Indeed, muscle function was stronger 3 days after eccentric contraction in rats treated with amino acids than in those treated with distilled water. The amino acid mix also alleviated expression of interleukin-6 and impeded infiltration of inflammatory cells into muscle, but did not suppress expression of myogenic regulatory factors. These results suggest that leucine-enriched amino acids accelerate recovery from muscle damage by preventing excessive inflammation.
authors.affiliation: Frontier Research Laboratories, Institute for Innovation, Ajinomoto Co., Inc., Kawasaki, Kanagawa, Japan. hiroyuki_kato@ajinomoto.com.
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Kato
authors.affiliation: Frontier Research Laboratories, Institute for Innovation, Ajinomoto Co., Inc., Kawasaki, Kanagawa, Japan.
authors.forename: Kyoko
authors.initials: K
authors.lastname: Miura
authors.affiliation: Frontier Research Laboratories, Institute for Innovation, Ajinomoto Co., Inc., Kawasaki, Kanagawa, Japan.
authors.forename: Sayako
authors.initials: S
authors.lastname: Nakano
authors.affiliation: Frontier Research Laboratories, Institute for Innovation, Ajinomoto Co., Inc., Kawasaki, Kanagawa, Japan.
authors.forename: Katsuya
authors.initials: K
authors.lastname: Suzuki
authors.affiliation: Frontier Research Laboratories, Institute for Innovation, Ajinomoto Co., Inc., Kawasaki, Kanagawa, Japan.
authors.forename: Makoto
authors.initials: M
authors.lastname: Bannai
authors.affiliation: Frontier Research Laboratories, Institute for Innovation, Ajinomoto Co., Inc., Kawasaki, Kanagawa, Japan.
authors.forename: Yoshiko
authors.initials: Y
authors.lastname: Inoue
mesh_terms: D000818:Animals; D016207:Cytokines / Q000378:metabolism; D007249:Inflammation / Q000188:drug therapy / Q000378:metabolism; D007537:Isometric Contraction / Q000187:drug effects*; D007930:Leucine / Q000494:pharmacology*; D008297:Male; D018482:Muscle, Skeletal / Q000378:metabolism* / Q000503:physiopathology; D051381:Rats; D017207:Rats, Sprague-Dawley; D058570:TOR Serine-Threonine Kinases / Q000096:biosynthesis
chemical_list: D016207:Cytokines; C546845:mTOR protein, rat; D058570:TOR Serine-Threonine Kinases; D007930:Leucine
keywords: Eccentric contractions; Inflammation; Interleukin-6; Leucine-enriched essential amino acids; Mammalian target of rapamycin; Muscle repair