Irisin - a myokine potentially bridging muscle and fat tissue in cachexia.

We read with great interest the recent article reporting muscle atrophy in heart failure animal models by Matsuo et al.1 Cachexia is characterized by loss of muscle mass with or without fat mass.2 Also, in patients with heart failure, muscle, fat and even bone loss were shown and reported to be associated with worse outcome.3,4 Although studies in muscle wasting attract much attention in heart failure,5 cross-talk among these three different tissues has been increasingly investigated and discussed6 as Matsuo et al. stated them in Introduction of this article.1 Large number of muscle biomarkers are in development7–10 and mentioned in several issues of Journal of Cachexia, Sarcopenia and Muscle. Under these circumstances, myokines including irisin, myostatin, interleukin-6, follistatin, and so on, which are produced by muscle tissue and affect other organs, are highlighted as both biomarkers and hormonal substances, which may have therapeutic implication.11 Irisin has been investigated as a key myokine, which has a bridging potential between muscle and fat.12,13 There are a number of articles reporting the plasma levels of irisin in patients with diabetes,14 chronic kidney disease,15 and myocardial infarction.16 However, there is almost no data about irisin levels in heart failure patients. In addition, recent reports have just been casting some doubt on the detection methods for human plasma irisin.17,18 In this context, further clinical studies in heart failure patients performed with improved assays are needed.