Skeletal Muscle Myokine Expression in Critical Illness, Association With Outcome and Impact of Therapeutic Interventions

Context Muscle expresses and secretes several myokines that bring about benefits in distant organs. Objective We investigated the impact of critical illness on muscular expression of irisin, kynurenine aminotransferases, and amylase; association with clinical outcome; and impact of interventions that attenuate muscle wasting/weakness. Methods We studied critically ill patients who participated in 2 randomized controlled trials (EPaNIC/NESCI) and documented time profiles in critically ill mice. Included in the study were 174 intensive care unit (ICU) patients (day 8 +/- 1) vs 19 matched controls, and 60 mice subjected to surgery/sepsis vs 60 pair-fed healthy mice. Interventions studied included 7-day neuromuscular electrical stimulation (NMES), and withholding parenteral nutrition (PN) in the first ICU week (late PN) vs early PN. The main outcome measures were FNDC5 (irisin- precursor), KYAT1, KYAT3, and amylase mRNA expression in skeletal muscle. Results Critically ill patients showed 34% to 80% lower mRNA expression of FNDC5, KYAT1, and amylases than controls (P < .0001). Critically ill mice showed time-dependent reductions in all mRNAs compared with healthy mice (P <= .04). The lower FNDC5 expression in patients was independently associated with a higher ICU mortality (P = .015) and ICU-acquired weakness (P = .012), whereas the lower amylase expression in ICU survivors was independently associated with a longer ICU stay (P = .0060). Lower amylase expression was independently associated with a lower risk of death (P = .048), and lower KYAT1 expression with a lower risk of weakness (P = .022). NMES increased FNDC5 expression compared with unstimulated muscle (P = .016), and late PN patients had a higher KYAT1 expression than early PN patients (P = .022). Conclusion Expression of the studied myokines was affected by critical illness and associated with clinical outcomes, with limited effects of interventions that attenuate muscle wasting or weakness.

Automated summary

This study investigated the impact of critical illness on muscular expression of irisin, kynurenine aminotransferases, and amylase, and their association with clinical outcomes, as well as the effects of interventions that attenuate muscle wasting/weakness. The findings showed that critically ill patients had lower mRNA expression levels of FNDC5, KYAT1, and amylase compared to controls. Lower expression of FNDC5 was associated with higher ICU mortality and ICU-acquired weakness, while lower amylase expression was associated with longer ICU stay. Lower KYAT1 expression was associated with a lower risk of weakness. The study also found that neuromuscular electrical stimulation increased FNDC5 expression and that late parenteral nutrition patients had higher KYAT1 expression compared to early parenteral nutrition patients.