Summary Brown fat defends against hypothermia and obesity through thermogenesis mediated by mitochondrial UCP1. Recent data suggest that there are two distinct types of brown fat: classical brown fat derived from a myf-5 cellular lineage and UCP1-positive cells that emerge in white fat from a non-myf-5 lineage. Here we report the cloning of “beige” cells from murine white fat depots. Beige cells resemble white fat cells in having extremely low basal expression of UCP1, but like classical brown fat, they respond to cyclic AMP stimulation with high UCP1 expression and respiration rates. Beige cells have a gene expression pattern distinct from either white or brown fat and are preferentially sensitive to the polypeptide hormone irisin. Finally, we show that deposits of brown fat previously observed in adult humans are composed of beige adipose cells. These data illustrate a new cell type with therapeutic potential in mouse and human.

Using positron-emission tomography (PET), we found that cold-induced glucose uptake was increased by a factor of 15 in paracervical and supraclavicular adipose tissue in five healthy subjects. We obtained biopsy specimens of this tissue from the first three consecutive subjects and documented messenger RNA (mRNA) and protein levels of the brown-adipocyte marker, uncoupling protein 1 (UCP1). Together with morphologic assessment, which showed numerous multilocular, intracellular lipid droplets, and with the results of biochemical analysis, these findings document the presence of substantial amounts of metabolically active brown adipose tissue in healthy adult humans.

We investigated the metabolism of human brown adipose tissue (BAT) in healthy subjects by determining its cold-induced and insulin-stimulated glucose uptake and blood flow (perfusion) using positron emission tomography (PET) combined with computed tomography (CT). Second, we assessed gene expression in human BAT and white adipose tissue (WAT). Glucose uptake was induced 12-fold in BAT by cold, accompanied by doubling of perfusion. We found a positive association between whole-body energy expenditure and BAT perfusion. Insulin enhanced glucose uptake 5-fold in BAT independently of its perfusion, while the effect on WAT was weaker. The gene expression level of insulin-sensitive glucose transporter GLUT4 was also higher in BAT as compared to WAT. In conclusion, BAT appears to be differently activated by insulin and cold; in response to insulin, BAT displays high glucose uptake without increased perfusion, but when activated by cold, it dissipates energy in a perfusion-dependent manner.

clinicaltrials.gov Identifier: NCT00793143.

Based on the seminal observation by Cannon and Nedergaard 1 that human PET scans sometimes depicted a symmetric cold induced uptake of FDG-glucose, three independent studies, published in April 2009, demonstrated metabolically highly active brown adipose tissue (BAT) in adult humans [2][3][4] . Subsequent investigations demonstrated an inverse association of obesity and type 2 diabetes mellitus and the presence of active BAT [5][6][7] . A unique characteristic of BAT is the expression of uncoupling protein 1 (UCP1, also known as thermogenin). Activation of this transmembrane protein by fatty acids in response to adrenergic signaling short-circuits the inner mitochondrial membrane's proton gradient thereby uncoupling oxidative phosphorylation from ATP synthesis. Hence, chemical energy stored in the gradient is dissipated as heat allowing for efficient direct thermogenesis without shivering 8 . This adaptive defense against cold has been examined extensively in rodents and many aspects of BAT development and function have been elucidated. In rodents it is evident 3 that not only the distinct thermogenic BAT organ located in the interscapular region (iBAT) consists of brown adipocytes, but that a second type of brown adipocytes, so-called beige or brite cells can appear in white adipose tissue (WAT) depots in response to cold or 3-adrenergic stimuli 9,10 . Recently, lineage tracing experiments revealed that the two cell types have a different developmental origin 11 . While classical brown adipocytes and skeletal muscle cells arise from precursors in the dermomyotome 12 , beige/brite cells seem to originate from endothelial and perivascular cells within WAT depots [13][14][15] . A recent study by Wu et al suggests that the previously described depots of human BAT are of the beige/brite type and raises the question whether humans altogether lack classical brown adipocytes 16 , this has also been the topic of a recent review 17 . Histomorphological studies performed in the 1970s indicated the existence of brown adipocytes within the interscapular region in human infants and that these disappeared with age 18 . Using a combination of high resolution imaging techniques and morphological and biochemical analyses, we tested the hypothesis that human infants, like small mammals, possess an anatomically distinguishable iBAT depot consisting of classical brown adipocytes, a cell type so far not proven to exist in humans.In an attempt to visualize potential iBAT in humans we performed post mortem MR imaging of eight human infants. Using the fat fraction method 19 we did not only identify BAT depots in the supraclavicular region, but importantly also a fat depot in the interscapular region presenting with an intermediate fat fraction as opposed to the high fat fraction of the surrounding subcutaneous WAT (Supplementary Fig. 1). Using a three dimensional reconstruction we were able to compute the volume of the tissue depot with an average (±SD) volume of 3.6±2.4 ml. Figure 1 displays a representative reconstruction of the iBAT...

The posttreatment basal GH concentration less than 2.5 microg/liter in acromegalic patients is associated with a normal lifespan. Excess mortality is confined to poorly controlled patients and possibly those who have received conventional radiotherapy.

The accumulation of triglyceride in and around the myocardium of moderately obese individuals is significant, and it is related to FFA exposure, generalized ectopic fat excess, and peripheral vascular resistance. These changes precede LV overload and hypertrophy.

Neurochemical pathways involved in pathological overeating and obesity are poorly understood. Although previous studies have shown increased -opioid receptor (MOR) and decreased dopamine D 2 receptor (D 2 R) availability in addictive disorders, the role that these systems play in human obesity still remains unclear. We studied 13 morbidly obese women [mean body mass index (BMI), 42 kg/m 2 ] and 14 nonobese age-matched women, and measured brain MOR and D 2 R availability using PET with selective radioligands [11 C]carfentanil and [11 C]raclopride, respectively. We also used quantitative meta-analytic techniques to pool previous evidence on the effects of obesity on altered D 2 R availability. Morbidly obese subjects had significantly lower MOR availability than control subjects in brain regions relevant for reward processing, including ventral striatum, insula, and thalamus. Moreover, in these areas, BMI correlated negatively with MOR availability. Striatal MOR availability was also negatively associated with self-reported food addiction and restrained eating patterns. There were no significant differences in D 2 R availability between obese and nonobese subjects in any brain region. Meta-analysis confirmed that current evidence for altered D 2 R availability in obesity is only modest. Obesity appears to have unique neurobiological underpinnings in the reward circuit, whereby it is more similar to opioid addiction than to other addictive disorders. The opioid system modulates motivation and reward processing, and low -opioid availability may promote overeating to compensate decreased hedonic responses in this system. Behavioral and pharmacological strategies for recovering opioidergic function might thus be critical to curb the obesity epidemic.