Implication of circulating irisin levels with brown adipose tissue and sarcopenia in humans.
BACKGROUND
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.


OBJECTIVE
To assess the association of circulating irisin concentrations with brown adipose tissue (BAT) and/or sarcopenia in humans.


METHODS
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.


RESULTS
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.


CONCLUSIONS
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.
Division of Endocrinology and Metabolism, Department of Internal Medicine, College of Medicine (H.Y.C., H.C.H., H.J.Y., S.Y.B., K.M.C.), Korea University, Seoul 136-701, Korea; Department of Nuclear Medicine, College of Medicine (S.K.), Korea University, Seoul 136-701, Korea; AdipoGen, Inc (J.W.P., N.S.L., B.-S.Y.), Incheon 406-840, Korea; Department of Biostatistics, College of Medicine (S.W.H.), Korea University, Seoul 136-701, Korea; and Section of Endocrinology (J.Y.H., C.S.M.), VA Boston Healthcare System, Harvard Medical School, Boston, Massachusetts 02130.
Hae Yoon
HY
Choi
Sungeun
S
Kim
Ji Woo
JW
Park
Nam Seok
NS
Lee
Soon Young
SY
Hwang
Joo Young
JY
Huh
Ho Cheol
HC
Hong
Hye Jin
HJ
Yoo
Sei Hyun
SH
Baik
Byung-Soo
BS
Youn
Christos S
CS
Mantzoros
Kyung Mook
KM
Choi
D015502:Absorptiometry, Photon; D002001:Adipose Tissue, Brown / Q000033:anatomy & histology* / Q000000981:diagnostic imaging; D052436:Adipose Tissue, White / Q000033:anatomy & histology / Q000000981:diagnostic imaging; D000328:Adult; D001823:Body Composition; D015992:Body Mass Index; D015331:Cohort Studies; D005260:Female; D005353:Fibronectins / Q000097:blood*; D019788:Fluorodeoxyglucose F18; D006801:Humans; D008297:Male; D018482:Muscle, Skeletal / Q000473:pathology; D009765:Obesity / Q000097:blood* / Q000000981:diagnostic imaging / Q000453:epidemiology; D049268:Positron-Emission Tomography; D055948:Sarcopenia / Q000097:blood* / Q000000981:diagnostic imaging / Q000453:epidemiology / Q000209:etiology
C577593:FNDC5 protein, human; D005353:Fibronectins; D019788:Fluorodeoxyglucose F18