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

Abstract

Objective: Muscle net catabolism, as seen after severe trauma or sepsis or in postoperative situations, is mediated by hormones (e.g., cortisol) and proinflammatory cytokines (e.g., tumor necrosis factor alpha [TNF-α]). Specific amino acids may be able to limit this muscle mass loss. Citrulline (CIT) stimulates muscle protein synthesis in various situations, but little data exist on hypercatabolic situations and the 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.

Methods: 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. Subsequently, myotubes were incubated with or without 5 mM CIT for 6 h. Muscle protein synthesis rate was evaluated by the surface sensing of translation method and by l-[3,5-³H]tyrosine (Tyr) incorporation. The muscle protein breakdown rate was evaluated from Tyr release into culture medium. CIT action was analyzed by non-parametric Kruskal-Wallis and Mann-Whitney tests.

Results: CIT treatment significantly increased protein synthesis rates compared with the DEX or TNF-α group (surface sensing of translation method; DEX + CIT versus DEX; P = 0.03 and TNF-α+CIT versus TNF-α; P = 0.05) and significantly decreased protein breakdown rate in the CON and DEX groups (CON + CIT versus CON; P = 0.05 and DEX + CIT versus DEX; P = 0.05).

Conclusions: CIT treatment regulated muscle protein turnover in an in vitro model of muscle net catabolism. Exploring the underlying mechanisms would also be of interest.

Keywords: Citrulline; Cytokines; Glucocorticoids; Muscle hypercatabolism; Protein turnover.