Abstract
We have shown that feeding cod protein, which is rich in anti-inflammatory arginine, glycine, and taurine, may beneficially modulate the inflammatory response during recovery following skeletal muscle injury; however it is unknown if these amino acids are responsible for this effect. This study was designed to assess whether supplementing casein with an amino acid mixture composed of arginine, glycine, taurine and lysine, matching their respective levels in cod protein, may account for the anti-inflammatory effect of cod protein. Male Wistar rats were fed isoenergetic diets containing either casein, cod protein, or casein supplemented with L-arginine (0.45%), glycine (0.43%), L-taurine (0.17%) and L-lysine (0.44%) (casein+). After 21 days of ad libitum feeding, one tibialis anterior muscle was injured with 200 µl bupivacaine while the saline-injected contra-lateral tibialis anterior was served as sham. Cod protein and casein+ similarly modulated the inflammation as they decreased COX-2 level at day 2 post-injury (cod protein, p=0.014; casein+, p=0.029) and ED1+ macrophage density at days 2 (cod protein, p=0.012; casein+, p<0.0001), 5 (cod protein, p=0.001; casein+, p<0.0001) and 14 (cod protein, p<0.0001; casein+, p<0.0001) post-injury, and increased ED2+ macrophage density at days 5 (cod protein, p<0.0001; casein+, p=0.006), 14 (cod protein, p=0.001; casein+, p<0.002) and 28 (cod protein, p<0.009; casein+, p<0.005) post-injury compared with casein. Furthermore, cod protein up-regulated (p=0.037) whereas casein+ tended to up-regulate (p=0.062) myogenin expression at day 5 post-injury compared with casein. In the cod protein-fed group, these changes resulted in greater muscle mass at days 14 (p=0.002), and 28 (p=0.001) post-injury and larger myofiber cross-sectional area at day 28 post-injury compared with casein (p=0.012). No such effects were observed with casein+. These data indicate that anti-inflammatory actions of cod protein, contrary to its effect on muscle mass recovery, are driven by its high levels of arginine, glycine, taurine and lysine.
Highlights
Skeletal muscle injury leads to changes in tissue morphology and function that may last for several weeks [1,2]
Both the cod protein and casein+ diets reduced the percentage of centrally nucleated fibers (CNF) compared to the casein diet (p=0.025), while no significant difference was found between the cod protein and casein+ diets (Figure 1B)
Data from the present study strongly suggest that the combination of arginine, glycine, taurine and lysine in cod protein was responsible for the modulation of inflammation in rat skeletal muscle after injury
Summary
Skeletal muscle injury leads to changes in tissue morphology and function that may last for several weeks [1,2]. The progression of muscle repair is likely to be modulated by dietary proteins providing essential and nonessential amino acids, modulating inflammation and protein anabolism. In this respect, feeding cod protein has been found to facilitate skeletal muscle regeneration, notably through improving the inflammatory response [5]. Muscle inflammation after injury results in a rapid early response by neutrophils, followed by sequential increases in ED1+ and ED2+-macrophages [6] The latter is pivotal in orchestrating tissue repair and remodelling [1]. Behind the noteworthy importance of scavenging cell debris for subsequent repair, excessive accumulation of neutrophils and ED1+-macrophages may delay the resolution of inflammation [7,8]. Previous findings in mice reported that immunodepletion of neutrophils and invading macrophages can substantially reduce muscle damages [9,10], indicating that limiting the action of neutrophils and ED1+-cells would be beneficial for muscle repair
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