Irisin and Testosterone in Men with Metabolic Syndrome

The beneficial effects of testosterone on the metabolism and body composition of men are well established but the exact mechanisms of these effects are not clearly understood. A potential explanation might lie in the hormones, secreted from skeletal muscles, named myokines. One such myokine, irisin, has been shown to also have potential beneficial metabolic effects. The aim of this pilot study was to evaluate the association of serum testosterone with circulating serum irisin levels in men with metabolic syndrome. A total 128 men with metabolic syndrome (MS) based on the IDF criteria participated in the study. Irisin serum concentration was determined by means of ELISA. Mean age +/- SD of the study participants was 51.8 +/- 8.3 years. Seventy percent of the subjects had type 2 diabetes mellitus. Circulating irisin was inversely associated with serum testosterone (r=-0.279, p<0.01) and was significantly higher in subjects with hypogonadism - mean +/- SD 252.0 +/- 147.1 vs.172.9 +/- 92.2ng/ml (p=0.002). ROC analysis of serum irisin value was determined for distinguishing subjects with hypogonadism (AUC=0.670). In a multiple linear regression model with BMI, FPG, age, and irisin, only BMI (=beta-0.228, p=0.004) and irisin (beta=-0.170, p=0.045) were variables independently associated with testosterone concentrations. Irisin is negatively associated with serum testosterone in our population sample of men with MS. This might suggest a possible involvement of myokines and testosterone with regards to the human metabolism. As no such data on this association has been reported in the literature thus far, further prospective studies are required to elucidate this correlation.