Editors' ChoiceTemperature Regulation

What’s Up with BAT?

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Science Translational Medicine  14 Mar 2012:
Vol. 4, Issue 125, pp. 125ec45
DOI: 10.1126/scitranslmed.3003954

Even in cold climates, humans maintain a constant body temperature by producing heat internally through increased metabolism and shivering. In small mammals such as rats and mice, brown adipose tissue (BAT) contributes to nonshivering thermogenesis through uncoupling of respiration from adenosine 5´-triphosphate synthesis, generating heat. Whether this occurs in humans is not known. Until recently, there was even doubt that BAT existed in the adult human.

18F-fluorodeoxyglucose, a glucose analog, is taken up into hot spots within the neck, thorax, and shoulder regions of adult humans, as seen with positron emission tomography (PET) and computed tomography (CT). These regions contain adipocytes that express uncoupling protein 1, indicating the presence of BAT. To test whether these adipocytes function metabolically as genuine BAT and contribute to heat production, Ouellet and colleagues investigated their contribution to cold-induced thermogenesis. They administered radiolabeled metabolites to six healthy men and followed the progress of the metabolites with PET/CT imaging. Cold exposure increased the uptake of glucose and nonesterified fatty acids, an important combustion substrate for thermogenesis, into the supraclavicular hot spots. On the basis of the tissue kinetics of 11C-acetate, a marker of tissue oxidative activity, the authors proved that oxidative metabolism in human BAT is activated during exposure to cold, increasing the subjects’ whole-body metabolism by 80% on average with a minimum of muscle-mediated shivering thermogenesis.

This study documents the presence of metabolically active BAT in healthy adult humans. A wide variability in the volume and activity of BAT among the subjects was seemingly a result of factors other than age, sex, and body weight. Identification of these factors might pave the way for pharmacological intervention—a way to burn excess calories and improve metabolic homeostasis, without being cold!

V. Ouellet et al., Brown adipose tissue oxidative metabolism contributes to energy expenditure during acute cold exposure in humans. J. Clin. Invest. 122, 545–552 (2012). [Abstract]

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