Citrulline enhances myofibrillar constituents expression of skeletal muscle and induces a switch in muscle energy metabolism in malnourished aged rats

Abstract

Citrulline (Cit) actions on muscle metabolism remain unclear. Those latter were investigated using a proteomic approach on Tibialis muscles from male Sprague-Dawley rats. At 23 months of age, rats were either fed ad libitum (AL group) or subjected to dietary restriction for 12 weeks. At the end of the restriction period, one group of rats was euthanized (R group) and two groups were refed for one week with a standard diet supplemented with nonessential amino acids group or Cit (CIT group). Results of the proteomic approach were validated using targeted Western blot analysis and assessment of gene expression of the related genes. Maximal activities of the key enzymes involved in mitochondrial functioning were also determined. Cit supplementation results in a significant increase in the protein expression of the main myofibrillar constituents and of a few enzymes involved in glycogenolysis and glycolysis (CIT vs. AL and R, p < 0.05). Conversely, the expression of oxidative enzymes from Krebs cycle and mitochondrial respiratory chain was significantly decreased (CIT vs. AL, p < 0.05). However, maximal activities of key enzymes of mitochondrial metabolism were not significantly affected, except for complex 1 which presented an increased activity (CIT vs. AL and R, p < 0.05). In conclusion, Cit supplementation increases expression of the main myofibrillar proteins and seems to induce a switch in muscle energy metabolism, from aerobia toward anaerobia.

Citrulline Supplementation Induces Changes in Body Composition and Limits Age-Related Metabolic Changes in Healthy Male Rats

“…Electrophoresis of myosin heavy chain (MyHC; tibialis) was performed as previously described (7). Relative levels of MyHC proteins (percent of total) were determined by densitometry (ImageJ; http:// imagej.nih.gov/ij/).…”

“…Tibialis anterior muscles of 4 rats in each group (i.e., the NEAA and CIT groups) were used to perform proteomic analysis and define different protein expression profiles. Proteins from the tibialis anterior muscles were extracted as described by Faure et al (7). 12 Abbreviations used: AA, amino acid; AID/APOBEC5, activation induced deaminase/apolipoprotein B editing complex 5; APOBEC2, apoB mRNA editing enzyme, catalytic polypeptide-like 2; AU, arbitrary unit; CD, conjugated diene; CIT, citrulline; Cy2, cyanine dyes 2; Cy3, cyanine dyes 3; Cy5, cyanine dyes 5; DIGE, difference gel electrophoresis; EDL, extensor digitorum longus; mTORC1, mammalian target of rapamycin complex 1; MyHC, myosin heavy chain; Nd1, NADH dehydrogenase subunit 1; Ndufb6, NADH dehydrogenase (ubiquinone) 1 b subcomplex, 6; Ndufb8, NADH dehydrogenase (ubiquinone) 1 b subcomplex, 8; NEAA, nonessential amino acid; rpS6, S2 ribosomal protein; Tfam, mitochondrial transcription factor A; 2D, 2-dimensional; 4E-BP1, 4E-binding protein 1.…”

“…Nutritional interventions have proven disappointing so far (5), but citrulline has recently emerged as a new candidate with very high potential (6). One week of oral citrulline supplementation increases muscle protein synthesis, mass, strength, and mobility in old malnourished rats (7)(8)(9), and this effect is specifically focused on contractile proteins (7). Citrulline is also one of the most potent scavengers of the hydroxyl radical and a known first-line defense allowing specific decomposition of free hydroxyl radical (10,11).…”

An increased need for dietary cysteine in support of glutathione synthesis may underlie the increased risk for mortality associated with low protein intake in the elderly

“…This anabolic effect is clearest in the context of underfeeding and reflects an increased rate of synthesis of muscle myofibrillar proteins and glycolytic enzymes (Osowska et al 2006;Faure et al 2013). Data are inconsistent as to whether muscle-specific activation of mTORC1 activity plays a role in this effect; it is also unknown whether this effect is mediated by arginine or NO (Moinard et al 2015;Cynober et al 2013) In healthy human volunteers fed a low-protein diet, postabsorptive administration of citrulline, in comparison to equal intakes of a mixture of non-essential amino acids, increases the fractional synthesis rate of mixed muscle protein (Jourdan et al 2015).…”

Citrulline directly modulates muscle protein synthesis via the PI3K/MAPK/4E-BP1 pathway in a malnourished state: evidence from in vivo, ex vivo, and in vitro studies

“…CIT has also emerged as an important regulator of nitrogen homeostasis in both humans and animals, as reviewed recently (6). For example, in pioneering work, we used a model of aged malnourished rats to demonstrate that CIT-enriched diet stimulated muscle protein synthesis (MPS) (ϩ80%), and led to a net muscle protein gain (ϩ20%) (10,33). Interestingly, this metabolic effect was accompanied by muscle histological change and an increase in maximum strength as well as increased traction in treated animals (11).…”