Volatile Anesthetic-Induced Skeletal Muscle Atrophy in Mice and Murine-Derived Myotubes: The Role of the Akt Pathway

Volatile anesthetics are gaining attention as sedatives in intensive care units. Sedation is a significant risk factor for skeletal muscle atrophy and weakness in critically ill patients; however, volatile anesthetics' influence on skeletal muscle atrophy remains unclear. Therefore, we investigated their effects on skeletal muscle mass using a murine-derived muscle cell line and mice.

C2C12 myotubes were exposed to isoflurane or sevoflurane. Myotube diameter was assessed using immunofluorescence. The expression levels of Atrogin-1, MuRF1, and LC3-II and phosphorylation levels of p70 S6K and Akt were analyzed to evaluate protein degradation and synthesis. To determine whether these effects were mediated through the Akt pathway, experiments with insulin-like growth factor 1 (IGF-1) were performed. Furthermore, mice skeletal muscle exposed to isoflurane or sevoflurane were compared with control mice and short-term immobility mice induced by sciatic nerve denervation (DN) or hindlimb suspension (HS).

Exposure of C2C12 myotubes to 2.8% isoflurane or 5.0% sevoflurane reduced the myotube diameter by 14.4 µm (95% confidential interval [CI], 11.7-17.1, P < .001) and 13.2 µm (95% CI, 10.1-16.2, P < .001), respectively. Exposure to 2.8% isoflurane increased the expressions of Atrogin-1 (2.9-fold [95% CI, 2.1- to 3.8-fold], P < .001), MuRF1 (3.1-fold [95% CI, 2.4- to 3.8-fold], P < .001), and LC3-II (1.6-fold [95% CI, 1.4- to 1.8-fold], P < .001), whereas decreasing phosphorylation of p70 S6K (0.3-fold [95% CI, 0.2- to 0.4-fold], P < .001) and Akt (0.4-fold [95% CI, 0.3- to 0.5-fold], P < .001). Exposure to 5.0% sevoflurane resulted in similar effects. Additionally, IGF-1 counteracted the effects of isoflurane on myotube mass. In mice skeletal muscle, exposure to 1% isoflurane or 1.5% sevoflurane decreased Akt phosphorylation (isoflurane: 0.4-fold [95% CI, 0.1- to 0.8-fold], P = .003; sevoflurane: 0.5-fold [95% CI, 0.4- to 0.6-fold], P = .011) and increased the expression levels of Atrogin-1 (isoflurane: 4.1-fold [95% CI, 3.2- to 5.1-fold], P < .001; sevoflurane: 2.3-fold [95% CI, 1.1- to 3.5-fold], P = .026), MuRF1 (isoflurane: 2.7-fold [95% CI, 1.3- to 4.1-fold], P = .01; sevoflurane: 2.3-fold [95% CI, 1.0- to 3.7-fold], P = .022), and LC3-II (isoflurane: 1.9-fold [95% CI, 0.9- to 3.0-fold], P = .045; sevoflurane: 1.5-fold [95% CI, 1.4- to 1.6-fold], P < .001) while decreasing p70 S6K phosphorylation (isoflurane: 0.5-fold [95% CI, 0.4- to 0.6-fold], P = .013; sevoflurane: 0.7-fold [95% CI, 0.6- to 0.8-fold], P = .008) compared with DN. Similar results were observed when comparing between isoflurane or sevoflurane exposure and HS.

Volatile anesthetics induce skeletal muscle atrophy by downregulating the Akt pathway, suggesting they may exacerbate skeletal muscle atrophy beyond immobility effects.