Implication of Circulating Irisin Levels with Brown Adipose Tissue and Sarcopenia in Humans

Abstract

Irisin is an exercise-induced novel myokine that drives brown-fat-like conversion of white adipose tissue and has been suggested to be a promising target for the treatment of obesity-related metabolic disorders. To assess the association of circulating irisin concentrations with brown adipose tissue (BAT) and/or sarcopenia in humans. We examined irisin levels in 40 BAT-positive and 40 BAT-negative women detected by (18)F-fluorodeoxyglucose positron emission tomography ((18)FDG-PET). In a separate study, we also examined 401 subjects with or without sarcopenia defined by skeletal muscle mass index (SMMI) and appendicular skeletal muscle (ASM)/height(2) using dual-energy x-ray absorptiometry. Among 6877 consecutive (18)FDG-PET scans in 4736 subjects, 146 subjects (3.1%) had positive BAT scans. The BAT-detectable group and the matched BAT-undetectable group did not differ in circulating irisin levels measured using two different ELISA kits (P = .747 and P = .160, respectively). Serum irisin levels were not different between individuals with sarcopenia and those without sarcopenia using either kit (P = .305 and P = .569, respectively). Also, serum irisin levels were not different between groups defined by ASM/height(2) using either kit (P = .352 and P = .134, respectively). Although visceral fat area and skeletal muscle mass showed significant difference according to tertiles of SMMI levels, irisin concentrations did not differ. Circulating irisin levels were not different in individuals with detectable BAT or those with sarcopenia compared with control subjects and were not correlated with SMMI.