Guillermo Sanchez‐Delgado

Objective The study objective was to investigate the effect of cold exposure on the plasma levels of five potential human brown adipokines (chemokine ligand 14 [CXCL14], growth differentiation factor 15 [GDF15], fibroblast growth factor 21 [FGF21], interleukin 6 [IL6], and bone morphogenic protein 8b [BMP8b]) and to study whether such cold‐induced effects are related to brown adipose tissue (BAT) volume, activity, or radiodensity in young humans. Methods Plasma levels of brown adipokines were measured before and 1 h and 2 h after starting an individualized cold exposure in 30 young adults (60% women, 21.9 ± 2.3 y; 24.9 ± 5.1 kg/m 2 ). BAT volume, 18 F‐fluorodeoxyglucose uptake, and radiodensity were assessed by a static positron emission tomography‐computerized tomography scan after cold exposure. Results Cold exposure increased the concentration of CXCL14 (Δ2h = 0.58 ± 0.98 ng/mL; p = 0.007), GDF15 (Δ2h = 19.63 ± 46.2 pg/mL; p = 0.013), FGF21 (Δ2h = 33.72 ± 55.13 pg/mL; p = 0.003), and IL6 (Δ1h = 1.98 ± 3.56 pg/mL; p = 0.048) and reduced BMP8b (Δ2h = −37.12 ± 83.53 pg/mL; p = 0.022). The cold‐induced increase in plasma FGF21 was positively associated with BAT volume (Δ2h: β = 0.456; R 2 = 0.307; p = 0.001), but not with 18 F‐fluorodeoxyglucose uptake or radiodensity. None of the changes in the other studied brown adipokines was related to BAT volume, activity, or radiodensity. Conclusions Cold exposure modulates plasma levels of several potential brown adipokines in humans, whereas only cold‐induced changes in FGF21 levels are associated with BAT volume. These findings suggest that human BAT might contribute to the circulatory pool of FGF21.