Effect of citrulline on muscle protein turnover in an in vitro model of muscle catabolism

Abstract Muscle net catabolism, as seen after severe trauma or sepsis or in post-operative situations, is mediated by hormones, such as cortisol, and pro-inflammatory cytokines, such as tumor necrosis factor alpha (TNF-α). Specific amino acids (AAs) may be able to limit this muscle mass loss. Citrulline (Cit) stimulates muscle protein synthesis in various situations, but there are few data on hypercatabolic situations, and its effects on protein breakdown are unknown. Our aim was to assess the effect of Cit on protein turnover in an in vitro model of muscle hypercatabolism. Myotubes derived from C2C12 myoblasts were treated with 150 nM dexamethasone (DEX), 10 ng/ml TNF-α, or 0.006% ethanol (as control, CON) for 24 h. Myotubes were then incubated with or without 5 mM Cit for 6 h. Muscle protein synthesis rate (PSR) was evaluated by the surface sensing of translation (SUnSET) method and by l -[3,5-3H]tyrosine (Tyr) incorporation. Muscle protein breakdown rate (PBR) was evaluated from Tyr release into culture medium. Cit action was analyzed by non-parametric Kruskal-Wallis and Mann-Whitney tests. Cit treatment significantly increased PSR compared with the DEX group or TNF-α group (SUnSET method; DEX+CIT vs. DEX, p = 0.03 and TNF-α+CIT vs. TNF-α, p = 0.05), and significantly decreased PBR in the CON and DEX groups (CON+CIT vs. CON p = 0.05 and DEX + Cit vs. DEX, p = 0.05). Cit treatment regulated muscle protein turnover in an in vitro model of muscle net catabolism. It would be of interest to explore the underlying mechanisms.