L-Citrulline Protects Skeletal Muscle Cells from Cachectic Stimuli through an iNOS-Dependent Mechanism.

Abstract

Dietary L-citrulline is thought to modulate muscle protein turnover by increasing L-arginine availability. To date, the direct effects of increased L-citrulline concentrations in muscle have been completely neglected. Therefore, we determined the role of L-citrulline in regulating cell size during catabolic conditions by depriving mature C2C12 myotubes of growth factors (serum free; SF) or growth factors and nutrients (HEPES buffered saline; HBS). Cells were treated with L-citrulline or equimolar concentrations of L-arginine (positive control) or L-alanine (negative control) and changes in cell size and protein turnover were assessed. In myotubes incubated in HBS or SF media, L-citrulline improved rates of protein synthesis (HBS: +63%, SF: +37%) and myotube diameter (HBS: +18%, SF: +29%). L-citrulline treatment substantially increased iNOS mRNA expression (SF: 350%, HBS: 750%). The general NOS inhibitor L-NAME and the iNOS specific inhibitor aminoguanidine prevented these effects in both models. Depriving myotubes in SF media of L-arginine or L-leucine, exacerbated wasting which was not attenuated by L-citrulline. The increased iNOS mRNA expression was temporally associated with increases in mRNA of the endogenous antioxidants SOD1, SOD3 and catalase. Furthermore, L-citrulline prevented inflammation (LPS) and oxidative stress (H2O2) induced muscle cell wasting. In conclusion, we demonstrate a novel direct protective effect of L-citrulline on skeletal muscle cell size independent of L-arginine that is mediated through induction of the inducible NOS (iNOS) isoform. This discovery of a nutritional modulator of iNOS mRNA expression in skeletal muscle cells could have substantial implications for the treatment of muscle wasting conditions.

• Authors: Daniel J Ham, Benjamin G Gleeson, Annabel Chee, Dale M Baum, Marissa K Caldow, Gordon S Lynch, René Koopman
• Journal: PloS one (PLoS One) Vol. 10 Issue 10 Pg. e0141572 ( 2015) ISSN: 1932-6203 [Electronic] United States
• PMID: 26513461 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• Antioxidants
• RNA, Messenger
• Citrulline
• Catalase
• Nitric Oxide Synthase Type II
• Sod1 protein, mouse
• Sod3 protein, mouse
• Superoxide Dismutase
• Superoxide Dismutase-1

Topics

• Animals
• Antioxidants (pharmacology)
• Catalase (genetics, metabolism)
• Cell Line
• Citrulline (pharmacology)
• Mice
• Muscle Fibers, Skeletal (drug effects, metabolism)
• Nitric Oxide Synthase Type II (genetics, metabolism)
• Oxidative Stress
• RNA, Messenger (genetics, metabolism)
• Superoxide Dismutase (genetics, metabolism)
• Superoxide Dismutase-1