MRI Reveals Human Brown Adipose Tissue Is Rapidly Activated in Response to Cold

Abstract

Context In rodents, cold exposure induces the activation of brown adipose tissue (BAT) and the induction of intracellular triacylglycerol (TAG) lipolysis. However, in humans, the kinetics of supraclavicular (SCV) BAT activation and the potential importance of TAG stores remain poorly defined. Objective To determine the time course of BAT activation and changes in intracellular TAG using MRI assessment of the SCV (i.e., BAT depot) and fat in the posterior neck region (i.e., non-BAT). Design Cross-sectional. Setting Clinical research center. Patients or Other Participants Twelve healthy male volunteers aged 18 to 29 years [body mass index = 24.7 ± 2.8 kg/m2 and body fat percentage = 25.0% ± 7.4% (both, mean ± SD)]. Intervention(s) Standardized whole-body cold exposure (180 minutes at 18°C) and immediate rewarming (30 minutes at 32°C). Main Outcome Measure(s) Proton density fat fraction (PDFF) and T2* of the SCV and posterior neck fat pads. Acquisitions occurred at 5- to 15-minute intervals during cooling and subsequent warming. Results SCV PDFF declined significantly after only 10 minutes of cold exposure [−1.6% (SE: 0.44%; P = 0.007)] and continued to decline until 35 minutes, after which time it remained stable until 180 minutes. A similar time course was also observed for SCV T2*. In the posterior neck fat (non-BAT), there were no cold-induced changes in PDFF or T2*. Rewarming did not result in a change in SCV PDFF or T2*. Conclusions The rapid cold-induced decline in SCV PDFF suggests that in humans BAT is activated quickly in response to cold and that TAG is a primary substrate.

Energy Expenditure and Macronutrient Oxidation in Response to an Individualized Nonshivering Cooling Protocol

“…Therefore, it is plausible to speculate that BAT is the main contributor to CIT at initial stages of mild cold exposure, whereas the muscle contribution to CIT would increase progressively, therefore balancing the contribution of CHOox and FATox. This hypothesis is supported by recent studies showing that BAT is rapidly activated upon cold exposure and seems to stabilize after 35 minutes of cold exposure (51‐53). Moreover, we previously reported a high prevalence of BAT in study 1 (88% BAT‐positive, BAT volume = 94.4 ± 59.6 mL), as measured by static 18 F‐flurodeoxyglucose positron emission tomography/computed tomography scanning after 2 hours of personalized cold exposure (23,54); therefore, BAT thermogenesis was likely induced during the mild cold exposure.…”

Metabolic Improvement via Enhancing Thermogenic Fat-Mediated Non-shivering Thermogenesis: From Rodents to Humans

“…The differences between these methods are shown in Table 1. MRI can be used to assess the intracellular triglyceride depletion of human BAT by measuring fat content before and after BAT activation (37). Unlike PET/CT, MRI does not require radiation.…”

Substrate Utilization by Brown Adipose Tissue: What’s Hot and What’s Not?

“…Although BAT lipid content acutely decreases following cold activation this does not further change during prolonged cold exposure, suggesting that intracellular triglycerides are constantly replenished ( Figure 1 ) ( 22 , 59 ). As discussed above, glucose may contribute to this either through glyceroneogenesis and/or de novo lipogenesis.…”