High-intensity eccentric training ameliorates muscle wasting in colon 26 tumor-bearing mice

<div><p>Eccentric (ECC) contractions are used to maintain skeletal muscle mass and strength in healthy subjects and patients. Here we investigated the effects of ECC training induced by electrical stimulation (ES) on muscle wasting in colon 26 (C-26) tumor-bearing mice. Mice were divided into four groups: control (CNT), CNT + ECC, C-26, and C-26 + ECC. Cancer cachexia was induced by a subcutaneous injection of C-26 cells and developed for four weeks. In experiment 1, muscle protein synthesis rate and mammalian target of rapamycin complex (mTORC) 1 signaling were investigated six hours after one bout of ECC-ES (2 s contraction given every 6 s, 20°/s, 4 sets of 5 contractions). In experiment 2, ECC-ES training, a total of 14 sessions, was performed every other day starting one day after C-26 injection. Compared to the CNT mice, the gastrocnemius muscle weight was significantly decreased in the tumor-bearing mice. This change was accompanied by a reduction in protein synthesis rate and a marked increase in the expression levels of genes including regulated in development and DNA damage responses (REDD) 1, forkhead box protein O1 (FoxO1), muscle-specific E3 ubiquitin ligases atrogin-1, and muscle ring finger 1 (MuRF-1) mRNA. ECC-ES increased the protein synthesis rate and the phosphorylation levels of p70S6K (Thr389) and rpS6 (Ser240/244), markers for mTORC1 signaling, and reversed an upregulation of MuRF-1 mRNA in muscles from C-26 mice. Our findings suggest that ECC-ES training reduces skeletal muscle atrophy in C-26 tumor-bearing mice through activation of mTORC1 signaling and the inhibition of ubiquitin-proteasome pathway. Thus, ECC-ES training might be used to effectively ameliorate muscle wasting in patients with cancer cachexia.</p></div

Effects of tumor-bearing and/or eccentric training on body and muscle mass in control and colon 26 mice.

<p>Effects of tumor-bearing and/or eccentric training on body and muscle mass in control and colon 26 mice.</p

ECC-ES training activates protein synthesis and the mTORC1 signaling in gastrocnemius muscles from C-26 mice.

<p>(<b><i>A</i></b>) Representative western blots for puromycin, total and phosphorylated p70S6K Thr389 (p-p70S6K) and rpS6 Ser240/244 (p-rpS6) in control (CNT) and C-26 mice at 6 hours after one bout of ECC-ES. The expression levels of puromycin was normalized to the whole proteins in stain-free images (<b><i>B</i></b>). The levels of p-p70S6K (<b><i>C</i></b>) and p-rpS6 (<b><i>D</i></b>) were normalized to total p70S6K and rpS6 content, respectively. Data show mean ± SEM for 5–7 muscles per group. Statistical significance was set at <i>P</i> < 0.05: main effect of *C-26 and ^#ECC; difference versus ^aCNT-untrained and ^bC-26-untrained.</p

Procedure for ECC training.

<p>The foot was placed at 0° of dorsal flexion. Surface electrodes were placed on the front and back surface of lower leg and plantar flexor muscles were stimulated supramaximally (45 V) for 2 s given every 6 s (<b><i>A</i></b>). ECC contractions comprised forced dorsiflexion from 0° to 40° at 20°/s during electrical stimulation. Typical torque traces of plantar flexion and ankle angle of dorsal flexion during eccentric contractions (<b><i>B</i></b>).</p

ECC training inhibits increases in E3 ubiquitin ligase MuRF1 mRNA in gastrocnemius muscles from C-26 bearing mice.

<p>Expression levels of regulated in development and DNA damage responses (REDD) 1 (<b><i>A</i></b>), forkhead box O (FoxO) 1 (<b><i>B</i></b>), atrogin-1 (<b><i>C</i></b>), and muscle ring finger protein 1 (MuRF-1) (<b><i>D</i></b>) mRNA in gastrocnemius muscles from control (CNT) and C-26 mice with or without ECC training. Data show mean ± SEM for 5 muscles per group. Statistical significance was set at <i>P</i> < 0.05: main effect of *C-26 and ^#ECC; difference versus ^aCNT-untrained, ^bC-26-untrained, and ^cCNT-ECC.</p

Superoxide dismutase/catalase mimetic EUK-134 prevents diaphragm muscle weakness in monocrotalin-induced pulmonary hypertension

<div><p>Patients with pulmonary hypertension (PH) suffer from inspiratory insufficiency, which has been associated with intrinsic contractile dysfunction in diaphragm muscle. Here, we examined the role of redox stress in PH-induced diaphragm weakness by using the novel antioxidant, EUK-134. Male Wistar rats were randomly divided into control (CNT), CNT + EUK-134 (CNT + EUK), monocrotaline-induced PH (PH), and PH + EUK groups. PH was induced by a single intraperitoneal injection of monocrotaline (60 mg/kg body weight). EUK-134 (3 mg/kg body weight/day), a cell permeable mimetic of superoxide dismutase (SOD) and catalase, was daily intraperitoneally administered starting one day after induction of PH. After four weeks, diaphragm muscles were excised for mechanical and biochemical analyses. There was a decrease in specific tetanic force in diaphragm bundles from the PH group, which was accompanied by increases in: protein expression of NADPH oxidase 2/gp91phox, SOD2, and catalase; 3-nitrotyrosine content and aggregation of actin; glutathione oxidation. Treatment with EUK-134 prevented the force decrease and the actin modifications in PH diaphragm bundles. These data show that redox stress plays a pivotal role in PH-induced diaphragm weakness. Thus, antioxidant treatment can be a promising strategy for PH patients with inspiratory failure.</p></div