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

Background: 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.

Methods: 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).

Results: 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.

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