The human uncoupling protein-1 gene (UCP1): present status and perspectives in obesity research

Recent updates on cold adaptation in population and laboratory studies, including cross-adaptation with nonthermal factors

This review aims to update our understanding of human cold adaptation. First, an overview of the thermoregulatory response to cold is provided, with some recent updates in human brown adipose tissue (BAT). Variation in BAT activity and multiorgan contributions to cold-induced thermogenesis were introduced. We found that individuals with less BAT activity rely more on shivering to compensate for less non-shivering thermogenesis (NST). The mechanisms of cold-induced vasoconstriction are summarized, including the role of arteriovenous anastomoses, adrenergic neural function, and inhibition of the nitric oxide vasodilator pathway. In addition, cold-induced vasodilation (CIVD) during cold immersion of the distal extremities is summarized with some recent updates in physiological mechanism. Furthermore, the cold shock response at the onset of cold immersion is introduced. Next, categorization of cold acclimatization/acclimation into habituation of shivering and metabolic and insulative adaptation are provided, with some recent updates. Especially, the rediscovery of human BAT has clarified metabolic acclimation, where increased NST replace shivering. Then, a greater CIVD response in populations in cold regions has been reported, whereas recent laboratory studies suggest no increase in CIVD after repeated cold exposure. To prevent cold injuries, individuals should not rely on habituation through repeated cold exposure. In addition, habituation to the cold shock response after repeated cold water immersion could help reduce the number of drownings. Furthermore, cross-adaptation between cold and nonthermal factors in the thermoregulatory response is summarized. Recent studies explored the relationship between exercise training and BAT activity, although this remains unresolved, depending on the exercise intensity and environmental conditions. The effects of exercise with cold exposure on the thermoregulatory response to cold are summarized in studies including divers working in cold water. We investigated the effect of exercise training in cold water, which resulted in increased muscle deoxygenation during submaximal exercise and greater anerobic power. Moreover, the effects of a hypoxic environment on cold adaptation are summarized. Elevated basal metabolism and higher distal skin temperature in highlanders could improve their cold tolerance. Finally, factors affecting cold adaptation are discussed. The type of cold adaptation may depend on the specific thermoregulatory responses repeated during the adaptation process.

Wnt10b knockdown promotes UCP1 expression in brown adipose tissue in mice

The effect of Wnt10b overexpression on adipose tissue development has been reported. However, the impact of Wnt10b knockdown on the function of brown adipose tissue (BAT) is yet largely unknown. Here, we used the CRISPR/Cas9 technique to generate Wnt10b-knockdown (Wnt10b+/- ) mice. We compared the development and thermogenic gene expression of interscapular BAT (iBAT) between Wnt10b+/- and Wnt10b+/+ mice under a chow diet, high-fat diet (HFD), and cold exposure conditions. Moreover, the effect of Wnt10b knockdown on brown adipocyte function was tested via in vitro experiments. Results indicated that Wnt10b knockdown decreased the iBAT mass and the brown adipocyte size and enhanced thermogenic gene expression, including UCP1, under chow diet conditions. In addition, Wnt10b+/- mice appeared to be able to maintain their body temperature better than the control in a cold environment, accompanied by higher UCP1 protein expression. Intriguingly, even under HFD conditions, Wnt10b+/- mice still showed higher UCP1 expression, which was associated with an alleviated obesity phenotype. In vitro studies further evidenced the Wnt10b knockdown stimulation of UCP1 expression and suppression of the adipogenic program. This study indicates that Wnt10b knockdown enhances UCP1 expression and inhibits the adipogenic differentiation of brown adipocytes, providing a novel option for therapeutic interventions in adiposity.

n-3 polyunsaturated fatty acids in the regulation of adipose tissue browning and thermogenesis in obesity: Potential relationship with gut microbiota

BACKGROUND

Obesity is a worldwide public health problem characterized by fat tissue accumulation, favouring adipose tissue and metabolic alterations. Increasing energy expenditure (EE) through brown adipose tissue activation and white adipose tissue (WAT) browning has gained relevance as a therapeutic approach. Different bioactive compounds, such as n-3 polyunsaturated fatty acids (PUFA), have been shown to induce those thermogenic effects. This process is regulated by the gut microbiota as well. Nevertheless, obesity is characterized by gut microbiota dysbiosis, which can be restored by weight loss and n-3 PUFA intake, among other factors. Knowledge gap: However, the role of the gut microbiota on the n-3 PUFA effect in inducing thermogenesis in obesity has not been fully elucidated.

OBJECTIVE

This review aims to elucidate the potential implications of this interrelation on WAT browning adiposw sittue (BAT), BAT activity, and EE regulation in obesity models.

Polyphenols and their anti-obesity role mediated by the gut microbiota: a comprehensive review

Obesity is a global public health problem that results in chronic pathologies such as diabetes, cardiovascular diseases, and cancer. The treatment approach based on energy restriction and promotion of physical activity is ineffective in the long term. Due to the high prevalence of this pathology, complementary treatments such as brown adipose tissue activation (BAT) and white adipose tissue browning (WAT) have been proposed. Dietary polyphenols are plant secondary metabolites that can stimulate browning and thermogenesis of adipose tissue. They have also been shown to prevent body weight gain, and decrease systemic inflammation produced by high-fat diets. Ingested dietary polyphenols that reach the colon are metabolized by the gut microbiota (GM), regulating its composition and generating a great array of metabolites. GM is involved in the production of short chain fatty acids and secondary bile salts that regulate energetic metabolism. The alteration in the composition of GM observed in metabolic diseases such as obesity and type 2 diabetes can be attenuated by polyphenols. Recent studies support the hypothesis that GM would mediate WAT browning and BAT thermogenesis activation induced by polyphenol administration. Together, these results indicate that GM in the presence of polyphenols plays a fundamental role in the control of obesity possible through BAT activation.

Anti-Obesity Effects of Artemisia annua Extract in Zucker Fatty Rats and High-Fat Diet Sprague Dawley Rats through Upregulation of Uncoupling Protein 1

Background

Obesity is a widespread disease and is caused mainly by excessive adipocyte differentiation and fat accumulation. Peroxisome proliferation-activated receptor γ (PPARγ) and CCAAT/enhancer-binding proteins (C/EBP) are major components for regulating adipocyte differentiation. Uncoupling protein 1 (UCP1) is a transmembrane protein that can convert white fat to brown adipose tissue. Artemisia annua L. has long been used in East Asia as an herbal drug for anti-oxidant, anti-bacterial, and anti-obesity purposes.

Methods

We investigated the effects of water extracts of A. annua (WEAA) in C3H10T1/2, a mesenchymal stem cell line, by measuring the level of intracellular fat accumulation and the expression of genes associated with adipocyte differentiation. We also evaluated anti-obesity effects of WEAA in Zucker rats, a genetic model for the study of obesity, and in Sprague Dawley rats with high-fat diet (HFD)-induced obesity.

Results

In this study, WEAA reduced the expression levels of PPARγ and C/EBPα in C3H10T1/2 cells, as well as the expression of enzymes that regulate fatty acid metabolism. In the Zucker fatty rat model and the HFD-induced obesity rat model, WEAA significantly decreased adipogenic differentiation and white fat accumulation between the scapulae, in contrast to the brown fat that remained unchanged between the groups. A. annua suppressed the expression of the adipocyte differentiation-promoting genes, while increasing the expression of UCP1.

Conclusion

These results indicated that WEAA could reduce adipocyte differentiation and fat accumulation in in vitro and in vivo model systems, resulting in suppression of obesity and the occurrence of fatty liver due to a HFD.

Obesity and Bone Health: A Complex Link

So far, the connections between obesity and skeleton have been extensively explored, but the results are inconsistent. Obesity is thought to affect bone health through a variety of mechanisms, including body weight, fat volume, bone formation/resorption, proinflammatory cytokines together with bone marrow microenvironment. In this review, we will mainly describe the effects of adipokines secreted by white adipose tissue on bone cells, as well as the interaction between brown adipose tissue, bone marrow adipose tissue, and bone metabolism. Meanwhile, this review also reviews the evidence for the effects of adipose tissue and its distribution on bone mass and bone-related diseases, along with the correlation between different populations with obesity and bone health. And we describe changes in bone metabolism in patients with anorexia nervosa or type 2 diabetes. In summary, all of these findings show that the response of skeleton to obesity is complex and depends on diversified factors, such as mechanical loading, obesity type, the location of adipose tissue, gender, age, bone sites, and secreted cytokines, and that these factors may exert a primary function in bone health.

Thermogenic adipocytes: lineage, function and therapeutic potential

Metabolic inflexibility, defined as the inability to respond or adapt to metabolic demand, is now recognised as a driving factor behind many pathologies associated with obesity and the metabolic syndrome. Adipose tissue plays a pivotal role in the ability of an organism to sense, adapt to and counteract environmental changes. It provides a buffer in times of nutrient excess, a fuel reserve during starvation and the ability to resist cold-stress through non-shivering thermogenesis. Recent advances in single-cell RNA sequencing combined with lineage tracing, transcriptomic and proteomic analyses have identified novel adipocyte progenitors that give rise to specialised adipocytes with diverse functions, some of which have the potential to be exploited therapeutically. This review will highlight the common and distinct functions of well-known adipocyte populations with respect to their lineage and plasticity, as well as introducing the most recent members of the adipocyte family and their roles in whole organism energy homeostasis. Finally, this article will outline some of the more preliminary findings from large data sets generated by single-cell transcriptomics of mouse and human adipose tissue and their implications for the field, both for discovery and for therapy.

Diphyllin Improves High-Fat Diet-Induced Obesity in Mice Through Brown and Beige Adipocytes

Brown adipose tissue (BAT) and beige adipose tissue dissipate metabolic energy and mediate nonshivering thermogenesis, thereby boosting energy expenditure. Increasing the browning of BAT and beige adipose tissue is expected to be a promising strategy for combatting obesity. Through phenotype screening of C3H10-T1/2 mesenchymal stem cells, diphyllin was identified as a promising molecule in promoting brown adipocyte differentiation. In vitro studies revealed that diphyllin promoted C3H10-T1/2 cell and primary brown/beige preadipocyte differentiation and thermogenesis, which resulted increased energy consumption. We synthesized the compound and evaluated its effect on metabolism in vivo. Chronic experiments revealed that mice fed a high-fat diet (HFD) with 100 mg/kg diphyllin had ameliorated oral glucose tolerance and insulin sensitivity and decreased body weight and fat content ratio. Adaptive thermogenesis in HFD-fed mice under cold stimulation and whole-body energy expenditure were augmented after chronic diphyllin treatment. Diphyllin may be involved in regulating the development of brown and beige adipocytes by inhibiting V-ATPase and reducing intracellular autophagy. This study provides new clues for the discovery of anti-obesity molecules from natural products.

Metabolic Benefits of MicroRNA-22 Inhibition

Diabesity is a growing pandemic with substantial health and financial consequences. We are developing microRNA (miRNA)-based drug candidates that transform fat storing adipocytes into fat burning adipocytes (browning effect) to treat metabolic diseases characterized by lipotoxicity. Through phenotypic screening in primary cultures of human subcutaneous adipocytes, we discovered that inhibition of miRNA-22-3p by several complementary antagomirs resulted in increased lipid oxidation, mitochondrial activity, and energy expenditure (EE). These effects may be mediated through activation of target genes like KDM3A, KDM6B, PPARA, PPARGC1B, and SIRT1 involved in lipid catabolism, thermogenesis, and glucose homeostasis. In the model of Diet-Induced Obesity in mice of various ages, weekly subcutaneous injections of various miRNA-22-3p antagomirs produced a significant fat mass reduction, but no change of appetite or body temperature. Insulin sensitivity, as well as circulating glucose and cholesterol levels, was also improved. These original findings suggest that miRNA-22-3p inhibition could become a potent treatment of human obesity and type 2 diabetes mellitus, the so-called diabesity characterized by lipotoxicity and insulin resistance.

Chimonanthus nitens Oliv. leaf extract exerting anti-hyperglycemic activity by modulating GLUT4 and GLUT1 in the skeletal muscle of a diabetic mouse model

The present study aimed to explore the potent molecular mechanisms behind the hypoglycemic effect of Chimonanthus nitens Oliv. leaf extract (COE) in combination with a high-glucose-fat diet-fed and streptozotocin-induced diabetic mouse model. COE (50 and 200 mg per kg body weight per day) was given to the diabetic-model mice by intragastric administration for 4 weeks. It was found that the fasting blood glucose level (FBG), serum insulin level (FINS), and insulin sensitivity index (ISI) were significantly improved in the COE-treated diabetic-model mice. Glucose metabolism genes expression analysis of the skeletal muscle showed that COE exerted a glucose-lowering effect through the following two ways: on the one hand, COE enhanced insulin sensitivity by upregulating the transcription level of GLUT4, and in addition, it enhanced the insulin signaling pathway to promote the translocation of GLUT4 and upregulated thermogenesis genes expression, including PGC-1α and UCP-1; while on the other hand, GLUT1 expression was also increased in both the transcription and translation levels in the presence of COE. These two ways may result in promoting glucose uptake in skeletal muscle, thus leading to the reduction of the blood glucose level. The results suggested that COE ameliorated hyperglycemia in the diabetic-model mice through regulating glucose transporters, and then was likely to increase glucose uptake, which provided more evidence for applying COE to treat anti-hyperglycemia.

Brown fat depots in adult humans remain static in their locations on PET/CT despite changes in seasonality

Active brown adipose tissue (BAT) in humans has been demonstrated through use of positron emission tomography with 2-deoxy-2-(fluorine-18) fluoro-D-glucose integrated with computed tomography (¹⁸F-FDG PET/CT) scans. The aim of our study was to determine whether active human BAT depots shown on ¹⁸F-FDG PET/CT scans remain static in their location over time. This was a retrospective study. Adult human subjects (n = 15) who had had ¹⁸F-FDG PET/CT imaging (n = 38 scans in total) for clinical reasons were included on the basis of ¹⁸F-FDG uptake patterns consistent with BAT activity. For each subject, ¹⁸F-FDG BAT uptake pattern on serial ¹⁸F-FDG PET/CT images was compared to an index ¹⁸F-FDG PET/CT image with the largest demonstrable BAT volume. Object-based colocalization was expressed as Mander's correlation coefficient (where 1 = 100% overlap, 0 = no overlap). Distribution of ¹⁸F-FDG BAT activity over time and across multiple ¹⁸F-FDG BAT scans was equivalent in 60% (n = 9) of the subjects. The degree of consistency in the pattern of ¹⁸F-FDG BAT uptake in each subject over time was greater than expected by chance in 87% (n = 13) of the subjects (pair-wise agreement 75-100%, Fleiss' κ 0.4-1). The degree of BAT colocalization on serial scans was greater than that expected by chance in 93% (n = 14) of the subjects (mean Mander's coefficient 0.81 ± 0.21 [95% CI]). To our knowledge, our study provides the most conclusive evidence to date to support the notion that active BAT depots in humans (volumes and activities of which were measured through use of ¹⁸F-FDG PET/CT scans) remain static in location over sustained periods.

Chimonanthus nitens Oliv. leaf extract exerting anti-hyperglycemic activity by modulating GLUT4 and GLUT1 in the skeletal muscle of a diabetic mouse model

COE supplementation ameliorated hyperglycemia via modulating glucose transporters of the skeletal muscle.

Experimental evidence reveals the UCP1 genotype changes the oxygen consumption attributed to non-shivering thermogenesis in humans

Humans have spread out all over the world adapting to many different cold environments. Recent worldwide genome analyses and animal experiments have reported dozens of genes associated with cold adaptation. The uncoupling protein 1 (UCP1) gene enhances thermogenesis reaction in a physiological process by blocking ATP (adenosine triphosphate) synthesis on a mitochondrial membrane in brown adipose tissues. To our knowledge, no previous studies have shown an association between variants of the UCP1 gene and physiological phenotypes concerning non-shivering thermogenesis (NST) under the condition of low temperature in humans. We showed that the degree of NST for healthy subjects in an artificial climate chamber is significantly different among UCP1 genotypes. Defining the haplotypes covering the UCP1 region (39.4 kb), we found that the frequency of the haplotype with the highest NST was significantly correlated with latitudes and ambient temperature. Thus, the data in this study provide the first evidence that the UCP1 genotype alters the efficiency of NST in humans, and likely supports the hypothesis that the UCP1 gene has been related to cold adaptation in human evolutionary history.

Transcriptional regulation of the uncoupling protein-1 gene

Regulated transcription of the uncoupling protein-1 (UCP1) gene, and subsequent UCP1 protein synthesis, is a hallmark of the acquisition of the differentiated, thermogenically competent status of brown and beige/brite adipocytes, as well as of the responsiveness of brown and beige/brite adipocytes to adaptive regulation of thermogenic activity. The 5' non-coding region of the UCP1 gene contains regulatory elements that confer tissue specificity, differentiation dependence, and neuro-hormonal regulation to UCP1 gene transcription. Two main regions-a distal enhancer and a proximal promoter region-mediate transcriptional regulation through interactions with a plethora of transcription factors, including nuclear hormone receptors and cAMP-responsive transcription factors. Co-regulators, such as PGC-1α, play a pivotal role in the concerted regulation of UCP1 gene transcription. Multiple interactions of transcription factors and co-regulators at the promoter region of the UCP1 gene result in local chromatin remodeling, leading to activation and increased accessibility of RNA polymerase II and subsequent gene transcription. Moreover, a commonly occurring A-to-G polymorphism in close proximity to the UCP1 gene enhancer influences the extent of UCP1 gene transcription. Notably, it has been reported that specific aspects of obesity and associated metabolic diseases are associated with human population variability at this site. On another front, the unique properties of the UCP1 promoter region have been exploited to develop brown adipose tissue-specific gene delivery tools for experimental purposes.

Fibroblast growth factor-21, energy balance and obesity

Fibroblast growth factor (FGF)-21 is an endocrine member of the FGF family with healthy effects on glucose and lipid metabolism. FGF21 reduces glycemia and lipidemia in rodent models of obesity and type 2 diabetes. In addition to its effects improving insulin sensitivity, FGF21 causes weight loss by increasing energy expenditure. Activation of the thermogenic activity of brown adipose tissue and promotion of the appearance of the so-called beige/brite type of brown adipocytes in white fat are considered the main mechanisms underlying the leaning effects of FGF21. Paradoxically, however, obesity in rodents and humans is characterized by high levels of FGF21 in the blood. Some degree of resistance to the actions of FGF21 has been proposed as part of the endocrine alterations in obesity. The resistance in adipose tissue from obese rodents and patients is likely attributable to abnormally low levels of the FGF co-receptor β-Klotho, required for FGF21 cellular action. However, native FGF21 and FGF21 derivatives retain their healthy metabolic and weight-loss effects when used as pharmacological agents to treat obese rodents and humans. FGF21 derivatives or molecules mimicking FGF21 action appear to be interesting candidates for the development of novel anti-obesity drugs designed to increase energy expenditure.

Special Techniques in PET/Computed Tomography Imaging for Evaluation of Head and Neck Cancer

PET with fluorodeoxyglucose F 18 (FDG)/computed tomography (CT) imaging has significantly improved the management of head and neck cancer. FDG, however, is not tumor-specific and various image interpretation pitfalls may occur because of false-positive and -negative causes of FDG uptake. Routine imaging examination of head and neck malignancies does not yield all of the necessary data, even with the most advanced imaging technique. Specific interventions, such as use of different dynamic maneuvers and pharmacologic interventions, may provide useful information about the lesion. This article reviews the use of special techniques in FDG PET/CT imaging and whole-body FDG PET/CT imaging for evaluation of head and neck cancer.

Non-sympathetic control of brown adipose tissue

The thermogenic activity of brown adipose tissue (BAT) in the organism is tightly regulated through different processes, from short-term induction of uncoupling protein-1-mediated mitochondrial proton conductance to complex processes of BAT recruitment, and appearance of the beige/brite adipocytes in white adipose tissue (WAT), the so-called browning process. The sympathetic nervous system is classically recognized as the main mediator of BAT activation. However, novel factors capable of activating BAT through non-sympathetic mechanisms have been recently identified. Among them are members of the bone morphogenetic protein family, with likely autocrine actions, and activators of nuclear hormone receptors, especially vitamin A derivatives. Multiple endocrine factors released by peripheral tissues that act on BAT have also been identified. Some are natriuretic peptides of cardiac origin, whereas others include irisin, originating in skeletal muscle, and fibroblast growth factor-21, mainly produced in the liver. These factors have cell-autonomous effects in brown adipocytes, but indirect effects in vivo that modulate sympathetic activity toward BAT cannot be excluded. Moreover, these factors can affect to different extents such as the activation of existing BAT, the induction of browning in WAT or both. The identification of non-sympathetic controllers of BAT activity is of special biomedical interest as a prerequisite for developing pharmacological tools that influence BAT activity without the side effects of sympathomimetics.

Brown adipose tissue and novel therapeutic approaches to treat metabolic disorders

In humans, 2 functionally different types of adipose tissue coexist: white adipose tissue (WAT) and brown adipose tissue (BAT). WAT is involved in energy storage, whereas BAT is involved in energy expenditure. Increased amounts of WAT may contribute to the development of metabolic disorders, such as obesity-associated type 2 diabetes mellitus and cardiovascular diseases. In contrast, the thermogenic function of BAT allows high consumption of fatty acids because of the activity of uncoupling protein 1 in the internal mitochondrial membrane. Interestingly, obesity reduction and insulin sensitization have been achieved by BAT activation-regeneration in animal models. This review describes the origin, function, and differentiation mechanisms of BAT to identify new therapeutic strategies for the treatment of metabolic disorders related to obesity. On the basis of the animal studies, novel approaches for BAT regeneration combining stem cells from the adipose tissue with active components, such as melatonin, may have potential for the treatment of metabolic disorders in humans.

Thermogenic brown and beige/brite adipogenesis in humans

Evidence from rodents established an important role of brown adipose tissue (BAT) in energy expenditure. Moreover, to sustain thermogenesis, BAT has been shown to be a powerful sink for draining and oxidation of glucose and triglycerides from blood. The potential of BAT activity in protection against obesity and metabolic syndrome is recognized. Recently, an unexpected presence and activity of BAT has been found in adult humans. Here we review the most recent research in this field and, specifically, how new findings apply to humans. Moreover, we seek to clarify the underlying biological processes occurring beyond the burst of new nomenclature in the field. The cell type responsible for thermogenesis, the brown adipocyte, arises from complex developmental processes. In addition to 'classical' brown adipocytes, present in developmentally programmed BAT depots, there are brown adipocytes, named 'brite' (from 'brown-in-white') or 'beige', which appear in response to thermogenic stimuli in white fat due to the so-called 'browning' process. Beige/brite cells appear to be important components of BAT depots in adult humans. In addition to the known control of BAT activity by the sympathetic nervous system, metabolic and hormonal signals originating in muscle or liver (e.g. irisin, FGF21) are recognized as activators of BAT and beige/brite adipocytes.

2-deoxy-2-(18F)fluoro-D-glucose positron emission tomography/computed tomography imaging in paediatric oncology

Positron emission tomography (PET) is a minimally invasive technique which has been well validated for the diagnosis, staging, monitoring of response to therapy, and disease surveillance of adult oncology patients. Traditionally the value of PET and PET/computed tomography (CT) hybrid imaging has been less clearly defined for paediatric oncology. However recent evidence has emerged regarding the diagnostic utility of these modalities, and they are becoming increasingly important tools in the evaluation and monitoring of children with known or suspected malignant disease. Important indications for 2-deoxy-2-(¹⁸F)fluoro-D-glucose (FDG) PET in paediatric oncology include lymphoma, brain tumours, sarcoma, neuroblastoma, Langerhans cell histiocytosis, urogenital tumours and neurofibromatosis type I. This article aims to review current evidence for the use of FDG PET and PET/CT in these indications. Attention will also be given to technical and logistical issues, the description of common imaging pitfalls, and dosimetric concerns as they relate to paediatric oncology.

Fat-constrained 18F-FDG PET reconstruction in hybrid PET/MR imaging

Fusion of information from PET and MR imaging can increase the diagnostic value of both modalities. This work sought to improve (18)F FDG PET image quality by using MR Dixon fat-constrained images to constrain PET image reconstruction to low-fat regions, with the working hypothesis that fatty tissue metabolism is low in glucose consumption.

METHODS

A novel constrained PET reconstruction algorithm was implemented via a modification of the system matrix in list-mode time-of-flight ordered-subsets expectation maximization reconstruction, similar to the way time-of-flight weighting is incorporated. To demonstrate its use in PET/MR imaging, we modeled a constraint based on fat/water-separating Dixon MR images that shift activity away from regions of fat tissue during PET image reconstruction. PET and MR imaging scans of a modified National Electrical Manufacturers Association/International Electrotechnical Commission body phantom simulating body fat/water composition and in vivo experiments on 2 oncology patients were performed on a commercial time-of-flight PET/MR imaging system.

RESULTS

Fat-constrained PET reconstruction visibly and quantitatively increased resolution and contrast between high-uptake and fatty-tissue regions without significantly affecting the images in nonfat regions.

CONCLUSION

The incorporation of MR tissue information, such as fat, in image reconstruction can improve the quality of PET images. The combination of a variety of potential other MR tissue characteristics with PET represents a further justification for merging MR data with PET data in hybrid systems.

White, brite, and brown adipocytes: the evolution and function of a heater organ in mammals

Brown fat is a specialized heater organ in eutherian mammals. In contrast to the energy storage function of white adipocytes, brown adipocytes dissipate nutrient energy by uncoupling of mitochondrial oxidative phosphorylation, which depends on uncoupling protein 1 (UCP1). UCP1, as well as UCP2 and UCP3, belong to the family of mitochondrial carriers inserted into the inner mitochondrial membrane for metabolite trafficking between the matrix and the intermembrane space. UCP1 transports protons into the mitochondrial matrix when activated by a rise in free fatty acid levels in the cell. This UCP1-dependant proton leak drives high oxygen consumption rates in the absence of ATP synthesis and dissipates proton motive force as heat. The enormous heating capacity of brown fat is supported by dense vascularization, high rates of tissue perfusion, and high mitochondrial density in brown adipocytes.

It has been known for more than 50 years that nonshivering thermogenesis in brown fat serves to maintain body temperature of neonates and small mammals in cold environments, and is used by hibernators for arousal from torpor. It has been speculated that the development of brown fat as a new source for nonshivering thermogenesis provided mammals with a unique advantage for survival in the cold. Indeed brown fat and UCP1 is found in ancient groups of mammals, like the afrotherians and marsupials. In the latter, however, the thermogenic function of UCP1 and brown fat has not been demonstrated as of yet. Notably, orthologs of all three mammalian UCP genes are also present in the genomes of bony fishes and in amphibians. Molecular phylogeny reveals a striking increase in the substitution rate of UCP1 between marsupial and eutherian lineages. At present, it seems that UCP1 only gained thermogenic function in brown adipocytes of eutherian mammals, whereas the function of UCP1 and that of the other UCPs in ectotherms remains to be identified.

Evolution of thermogenic function required expression of UCP1 in a brown-adipocyte-like cell equipped with high mitochondrial density embedded in a well-vascularized tissue. Brown-adipocyte-like cells in white adipose tissue, called “brite” (brown-in-white) or “beige” adipocytes, emerge during adipogenesis and in response to cold exposure in anatomically distinct adipose tissue depots of juvenile and adult rodents. These brite adipocytes may resemble the archetypical brown adipocyte in vertebrate evolution. It is therefore of interest to elucidate the molecular mechanisms of brite adipocyte differentiation, study the bioenergetic properties of these cells, and search for the presence of related brown-adipocyte-like cells in nonmammalian vertebrates.

Perirenal (18)F-FDG Uptake in a Patient with a Pheochromocytoma

Increased (18)F-fluorodeoxyglucose (FDG) uptake of brown fat on (18)F-FDG positron emission tomography (PET) originating from physiological activation is a common incidental finding and is usually located in the neck, shoulder, and supraclavicular areas. We present a case of an incidental pheochromocytoma showing diffusely increased (18)F-FDG uptake in bilateral perirenal fat tissue as well as supraclavicular and paravertebral fat tissue on (18)F-FDG PET/CT. The patient had no clinical symptoms except hypertension, and a pheochromocytoma was confirmed in a postsurgical specimen. A pheochromocytoma should be considered a cause in cases of increased (18)F-FDG uptake of perirenal brown fat.

The -3826 A → G variant of the uncoupling protein-1 gene diminishes thermogenesis during acute cold exposure in healthy children

SUMMARY

Uncoupling protein-1 (UCP1) activity in brown adipose tissue increases energy expenditure, and contributes to diet-induced or cold-induced thermogenesis. We previously reported that children with -3826 A → G nucleotide variant of the UCP1 gene had lowered postprandial thermogenesis in response to a high-fat meal. In this study, we investigated whether the UCP1 polymorphism was associated with cold-induced thermogenesis in healthy children. Resting energy expenditure was measured in 19 children (6-10 years) by indirect calorimetry for 30 min under thermoneutral (25 °C) or cold conditions (10 °C) in an environmental chamber. The activity of autonomic nervous system (ANS) was assessed by power spectral analysis of heart rate variability (HRV). Samples of saliva were collected for cortisol determination at the end of the experimental session. Each experiment was performed on 2 consecutive days. Children were genotyped for the UCP1 polymorphism with a PCR-restriction fragment length analysis using buccal samples. During cold exposure, total power of the HRV, an index of the overall ANS activity, as well as the salivary cortisol concentration significantly increased in the children with homozygous (GG) for the UCP1 polymorphism while only cortisol response was found in the carriers of the wild-type (AA) and heterozygous (AG) alleles; however, the GG allele group showed a lower cold-induced thermogenesis compared to the AA + AG group. In conclusion, despite cold-induced autonomic stimulation, the GG allele carriers have a reduced capacity for thermogenesis in response to acute cold exposure, suggesting that such reduced UCP1-linked thermogenesis may have adverse effects on the regulation of body weight.:

Brown adipose tissue as a regulator of energy expenditure and body fat in humans

Brown adipose tissue (BAT) is recognized as the major site of sympathetically activated nonshivering thermogenesis during cold exposure and after spontaneous hyperphagia, thereby controling whole-body energy expenditure and body fat. In adult humans, BAT has long been believed to be absent or negligible, but recent studies using fluorodeoxyglucose-positron emission tomography, in combination with computed tomography, demonstrated the existence of metabolically active BAT in healthy adult humans. Human BAT is activated by acute cold exposure, being positively correlated to cold-induced increases in energy expenditure. The metabolic activity of BAT differs among individuals, being lower in older and obese individuals. Thus, BAT is recognized as a regulator of whole-body energy expenditure and body fat in humans as in small rodents, and a hopeful target combating obesity and related disorders. In fact, there are some food ingredients such as capsaicin and capsinoids, which have potential to activate and recruit BAT via activity on the specific receptor, transient receptor potential channels, thereby increasing energy expenditure and decreasing body fat modestly and consistently.

Regulation of adipocyte autophagy--the potential anti-obesity mechanism of high density lipoprotein and ApolipoproteinA-I

Obesity is reaching epidemic worldwide and is risk factor for cardiovascular disease and type 2 diabetes. Although plasma high density lipoprotein (HDL) and apolipoprotein A-I (apoA-I) are inversely correlated to obesity, whether HDLs have anti-obesity effect remains unclear until a recent study reporting the direct anti-obesity effect of apoA-I and its mimetic peptide. However, the mechanism is not fully understood. Increasing adipose energy expenditure through attainment of brown adipocyte phenotype in white adipose tissue is considered a potential strategy to combat obesity. Specific inhibition of autophagy in adipose tissue is associated with reduced adiposity which is attributed to the attainment of brown adipocyte phenotype in white adipose tissue and the increased energy expenditure. HDL and apoA-I could activate PI3K-Akt-mTORC1 signaling which negatively regulates autophagy. The links between HDL/apoA-I and autophagy brings a new understanding on the anti-obesity effect of HDL and apoA-I.

Impact of UCP1 and β3AR gene polymorphisms on age-related changes in brown adipose tissue and adiposity in humans

BACKGROUND

Brown adipose tissue (BAT) is involved in the regulation of whole-body energy expenditure and adiposity. The activity and prevalence of BAT decrease with age in humans.

OBJECTIVE

To examine the effects of single nucleotide polymorphisms of the genes for uncoupling protein 1 (UCP1) and β3-adrenergic receptor (β3AR), key molecules of BAT thermogenesis, on age-related decline of BAT activity and accumulation of body fat in humans.

METHODS

One hundred ninety-nine healthy volunteers (20-72 years old (y.o.)) underwent fluorodeoxyglucose-positron emission tomography (FDG-PET) and computed tomography (CT) after 2-h cold exposure to assess BAT activity. The visceral and subcutaneous fat areas at the abdominal level were estimated from the CT images. They were genotyped for -3826 A/G polymorphism of the UCP1 gene and 64 Trp/Arg mutation of the β3AR gene.

RESULTS

BAT was detected in 88 subjects out of 199 (44%), more in younger (30 y.o., 55%) than older subjects (>40 y.o., 15%). BAT prevalence of older subjects tended to be lower in the UCP1 G/G group than the A allele group (A/A and A/G), and also in the β3AR Arg allele group (Trp/Arg and Arg/Arg) than the Trp/Trp group. When compared subjects who had two or more base substitutions on the two genes (the 2-4 allele group) with those who had less than two base substitutions (the 0-1 allele group), BAT prevalence was comparable in younger subjects (62% vs 50%) but lower in older subjects (0% vs 24%, P<0.05). Visceral fat area of the 2-4 allele group was higher than that of the 0-1 allele group (P<0.05) in older subjects, but not in younger subjects.

CONCLUSION

UCP1 -3826 A/G and β3AR 64 Trp/Arg substitutions accelerate age-related decrease in BAT activity, and thereby may associate with visceral fat accumulation with age.

Molecular and histological evidence of brown adipose tissue in adult cats

Brown adipose tissue (BAT) can influence glucose, lipid, and energy metabolism in rodents. Active BAT is now known to be present in adult humans, and interventions targeting BAT are being investigated for the treatment of human obesity and disorders of glucose and lipid metabolism. Domestic cats, like humans, are at increasing risk for obesity and diabetes but little is known about the presence and role of BAT in adult cats. The purpose of this study was to determine if brown adipocytes, identifiable by histological features and molecular markers, were present in the fat depots of adult cats. Adipose tissue samples from intrascapular, perirenal, and subcutaneous depots of eleven 8-12 year old cats (6 lean, 5 obese), were analyzed by real-time PCR for brown adipocyte markers uncoupling protein 1 (UCP1) and Type II iodothyronine 5'deiodinase (D2), by histological examination and by immunohistochemistry for UCP1. UCP1 mRNA was detectable in interscapular and subcutaneous depots in all cats, and in the perirenal depot in 10/11 cats. D2 mRNA was detectable in all depots from all cats. Multilocular adipocytes were identified in the interscapular depots of 4/11 cats and these were positive for UCP1 immunoreactivity. The results demonstrate that UCP1-expressing brown adipocytes are present in multiple depots of adult lean and long-term obese cats, even at 8-12 years of age. It is possible that dietary components or pharmacological agents that influence brown fat activity could exert a relevant biological effect in cats.

Ectopic overexpression of porcine DGAT1 increases intramuscular fat content in mouse skeletal muscle

The microsomal enzyme 1, 2-acyl CoA: diacylglyceroltransferase-1 (DGAT1) plays an important role in triglyceride storage in adipose tissue and expresses in skeletal muscle as well. The primary goal of the present study was to investigate the effect of porcine DGAT1 on intramuscular fat (IMF) content of transgenic mice produced by pronuclear microinjection with muscle specific promoter of porcine muscle creatine kinase (MCK). In normal chow-fed diet, 4 month-old male transgenic mice expressed more DGAT1, ACC1, UCP1, and FABP4 mRNAs and proteins in skeletal muscle than control mice by real-time PCR and western blot. No significant changes were detected for ACC2, CD36, ADRP, PPAR gamma and LPL. Triacylglycerol assay and soleus muscle sections showed overexpression of porcine DGAT1 in skeletal muscle increased intramyocellular triglyceride and percent of the total cell surface covered by lipid droplets. Thus, upregulation of porcine DGAT1 in skeletal muscle increases IMF content. The present study may further serve to develop transgenic pigs with higher IMF content and improved meat quality.

Brown fat like gene expression in the epicardial fat depot correlates with circulating HDL-cholesterol and triglycerides in patients with coronary artery disease

BACKGROUND

Recent evidence indicates that epicardial adipose tissue (EAT) expresses uncoupling protein-1 (UCP1), a marker of brown adipocytes. However, the putative effects of the presence of brown adipocytes in EAT remain unknown.

METHODS

The mRNA expression of genes related to brown adipocyte-mediated thermogenesis was measured in the fat samples collected from the epicardial-, mediastinal- and subcutaneous-depots of patients undergoing coronary artery bypass grafting. Both univariate and multivariate analyses were then utilized to determine any association between gene expression and the anthropometrics and fasting blood chemistries of these patients.

RESULTS

EAT exhibited significantly higher expression of UCP1 and cytochrome c oxidase subunit-IV (COX-IV) compared to mediastinal- and subcutaneous-fat depots (P ≤ 0.05). EAT expression of UCP1 (r=0.50), COX-IV (r=0.37) and lipoprotein lipase (LPL) (r=0.58) positively associated with circulating levels of HDL-cholesterol (P ≤ 0.05). In addition, EAT expression of LPL, acyl coA dehydrogenase-short, -medium and -long chain genes associated negatively with circulating TG levels (P ≤ 0.05).

CONCLUSIONS

Abundance of UCP-1 in the EAT relative to other fat depots confirms the presence of brown adipocytes in human EAT. Furthermore, the correlations among the EAT expression of thermogenesis-related genes with the circulating HDL and TG levels indicate that presence of active brown adipocytes shares a functional association with the circulating plasma lipids in humans.

Foxa1 reduces lipid accumulation in human hepatocytes and is down-regulated in nonalcoholic fatty liver

Triglyceride accumulation in nonalcoholic fatty liver (NAFL) results from unbalanced lipid metabolism which, in the liver, is controlled by several transcription factors. The Foxa subfamily of winged helix/forkhead box (Fox) transcription factors comprises three members which play important roles in controlling both metabolism and homeostasis through the regulation of multiple target genes in the liver, pancreas and adipose tissue. In the mouse liver, Foxa2 is repressed by insulin and mediates fasting responses. Unlike Foxa2 however, the role of Foxa1 in the liver has not yet been investigated in detail. In this study, we evaluate the role of Foxa1 in two human liver cell models, primary cultured hepatocytes and HepG2 cells, by adenoviral infection. Moreover, human and rat livers were analyzed to determine Foxa1 regulation in NAFL. Results demonstrate that Foxa1 is a potent inhibitor of hepatic triglyceride synthesis, accumulation and secretion by repressing the expression of multiple target genes of these pathways (e.g., GPAM, DGAT2, MTP, APOB). Moreover, Foxa1 represses the fatty acid transporter protein FATP2 and lowers fatty acid uptake. Foxa1 also increases the breakdown of fatty acids by inducing peroxisomal fatty acid β-oxidation and ketone body synthesis. Finally, Foxa1 is able to largely up-regulate UCP1, thereby dissipating energy and consistently decreasing the mitochondria membrane potential. We also report that human and rat NAFL have a reduced Foxa1 expression, possibly through a protein kinase C-dependent pathway. We conclude that Foxa1 is an antisteatotic factor that coordinately tunes several lipid metabolic pathways to block triglyceride accumulation in hepatocytes. However, Foxa1 is down-regulated in human and rat NAFL and, therefore, increasing Foxa1 levels could protect from steatosis. Altogether, we suggest that Foxa1 could be a novel therapeutic target for NAFL disease and insulin resistance.

Uncoupling protein 1 of brown adipocytes, the only uncoupler: a historical perspective

Uncoupling protein 1 (UCP1), is a unique mitochondrial membranous protein devoted to adaptive thermogenesis, a specialized function performed by brown adipocytes. Whereas the family of mitochondrial metabolite carriers comprises ∼40 members, UCP1 is the only memberable to translocate protons through the inner membrane of brown adipocyte mitochondria. By this process, UCP1 uncouples respiration from ATP synthesis and therefore provokes energy dissipation in the form of heat while, also stimulating high levels of fatty acid oxidation. UCP1 homologs were identified but they are biochemically and physiologically different from UCP1. Thirty five years after its identification, UCP1 still appears as a fascinating component. The recent renewal of the interest in human brown adipose tissue makes UCP1 as a potential target for strategies of treatment of metabolic disorders.

The Association Between the Uncoupling Protein-1 Gene A-3826G Polymorphism and High-density Lipoprotein Cholesterol in A General Japanese Population: A Consideration of the Obesity Status

BACKGROUND

Limited studies have shown inconsistent data about the association between the uncoupling protein 1 (UCP1) gene A-3826G polymorphism and high-density lipoprotein (HDL) cholesterol levels. The present study investigated the association between the A-3826G polymorphism and low HDL-cholesterolemia in non-obese and obese subjects.

METHODS

Anthropometric and biochemical factors, in addition to genotyping by an allele-specific DNA assay, were measured in 294 community-dwelling Japanese subjects (male/female: 127/167, mean age: 65 years). Obesity was defined as a body mass index (BMI) ≥ 25 kg/m(2), and low HDL-cholesterolemia was defined as < 1.04 mmol/L of HDL-cholesterol.

RESULTS

The subjects with the G/G genotype (n = 27) showed a significantly higher prevalence of low HDL-cholesterolemia (37%) than those with the A/A + A/G genotype (13%) in the obese group (n = 102). There was a non-significant difference in the prevalence of low HDL-cholesterolemia between subjects with the G/G genotype (n = 45, 13%) and with the A/A + A/G genotype (15%) in the non-obese group (n = 192). A multivariate-adjusted logistic regression analysis of the presence of low HDL-cholesterolemia revealed that carrying the G/G genotype was an independent and significant factor positively associated with low HDL-cholesterolemia [odds ratio (OR): 6.85, 95% confidence interval (CI): 1.65-28.49] in the obese group, while carrying the G/G genotype exhibited a non-significant but reduced OR, by one-half, for low HDL-cholesterolemia (OR: 0.51, 95% CI: 0.13-1.96) in the non-obese group.

CONCLUSIONS

The obesity status could have opposing impacts on the relationship between the G/G genotype and low HDL-cholesterolemia, providing insight into the need to consider the obesity levels when studying the association between the UCP-1 gene A-3826G polymorphism and HDL-cholesterol.

KEYWORDS

Obesity; Body mass index; HDL-C; Atherosclerotic risk.

PPARs in the Control of Uncoupling Proteins Gene Expression

Uncoupling proteins (UCPs) are mitochondrial membrane transporters involved in the control of energy conversion in mitochondria. Experimental and genetic evidence relate dysfunctions of UCPs with metabolic syndrome and obesity. The PPAR subtypes mediate to a large extent the transcriptional regulation of the UCP genes, with a distinct relevance depending on the UCP gene and the tissue in which it is expressed. UCP1 gene is under the dual control of PPARγ and PPARα in relation to brown adipocyte differentiation and lipid oxidation, respectively. UCP3 gene is regulated by PPARα and PPARδ in the muscle, heart, and adipose tissues. UCP2 gene is also under the control of PPARs even in tissues in which it is the predominantly expressed UCP (eg, the pancreas and liver). This review summarizes the current understanding of the role of PPARs in UCPs gene expression in normal conditions and also in the context of type-2 diabetes or obesity.

Brown adipose tissue 18F-FDG uptake in pediatric PET/CT imaging

Positron emission tomography (PET) using [F-18]2-fluoro-2-deoxyglucose (FDG) fused with CT ((18)F-FDG PET/CT) has been widely adopted in oncological imaging. However, it is known that benign lesions and other metabolically active tissues, such as brown adipose tissue (BAT), can accumulate (18)F-FDG, potentially resulting in false-positive interpretation. Previous studies have reported that (18)F-FDG uptake in BAT is more common in children than in adults. We illustrate BAT FDG uptake in various anatomical locations in children and adolescents. We also review what is known about the effects of patient-related physical attributes and environmental temperatures on BAT FDG uptake, and discuss methods used to reduce BAT FDG uptake on (18)F-FDG PET.

Brown adipose tissue, whole-body energy expenditure, and thermogenesis in healthy adult men

Brown adipose tissue (BAT) can be identified by (18)F-fluorodeoxyglucose (FDG)-positron emission tomography (PET) in adult humans. Thirteen healthy male volunteers aged 20-28 years underwent FDG-PET after 2-h cold exposure at 19 °C with light-clothing and intermittently putting their legs on an ice block. When exposed to cold, 6 out of the 13 subjects showed marked FDG uptake into adipose tissue of the supraclavicular and paraspinal regions (BAT-positive group), whereas the remaining seven showed no detectable uptake (BAT-negative group). The BMI and body fat content were similar in the two groups. Under warm conditions at 27 °C, the energy expenditure of the BAT-positive group estimated by indirect calorimetry was 1,446 ± 97 kcal/day, being comparable with that of the BAT-negative group (1,434 ± 246 kcal/day). After cold exposure, the energy expenditure increased markedly by 410 ± 293 (P < 0.05) and slightly by 42 ± 114 kcal/day (P = 0.37) in the BAT-positive and -negative groups, respectively. A positive correlation (P < 0.05) was found between the cold-induced rise in energy expenditure and the BAT activity quantified from FDG uptake. After cold exposure, the skin temperature in the supraclavicular region close to BAT deposits dropped by 0.14 °C in the BAT-positive group, whereas it dropped more markedly (P < 0.01) by 0.60 °C in the BAT-negative group. The skin temperature drop in other regions apart from BAT deposits was similar in the two groups. These results suggest that BAT is involved in cold-induced increases in whole-body energy expenditure, and, thereby, the control of body temperature and adiposity in adult humans.

Gene expression survey of mitochondrial uncoupling proteins (UCP1/UCP3) in gilthead sea bream (Sparus aurata L.)

The aim of this work is to underline the biological significance of mitochondrial uncoupling proteins (UCPs) in ectothermic fish using the gilthead sea bream (Sparus aurata L.) as an experimental model. A contig of 1,990 bp in length was recognized as a UCP1 ortholog after initial searches in the gilthead sea bream AQUAFIRST database ( http://www.sigenae.org/aquafirst ). Additional searches were performed in skeletal muscle by RT-PCR, and the amplified PCR product was recognized as UCP3 after sequence completion by 5'- and 3'RACE. UCP1 expression was mostly detected in liver, whereas UCP3 transcripts were only found in skeletal and cardiac muscle fibres (white skeletal muscle > red skeletal muscle > heart). Specific gene regulation of UCP1 (liver) and UCP3 (white skeletal muscle) was addressed in physiological models of age, seasonal growth and energy-metabolic unbalances. Both the increase in energy demand (stress confinement) and the reduction in energy supply during adaptive cold response in winter down-regulated UCP1 expression. Conversely, transcript levels of UCP3 were higher with age, seasonal fattening and dietary deficiencies in essential fatty acids leading to the increase in fatty acid flux towards the muscle. This close association between UCP1 and UCP3 with the oxidative and metabolic tissue status is perhaps directly related to the ancestral protein UCP function, and allows the use of UCPs as lipotoxicity markers in ectothermic fish.

Dynamic interactions and cooperative functions of PGC-1alpha and MED1 in TRalpha-mediated activation of the brown-fat-specific UCP-1 gene

PGC-1alpha is an inducible nuclear receptor coactivator with direct functions in both p300-mediated chromatin remodeling and Mediator-dependent transcription in vitro. Here, we have employed the PPARgamma- and TRalpha-activated brown adipose tissue-specific UCP-1 enhancer to investigate mechanistic aspects of PGC-1alpha function. We first demonstrate a cellular role for the PGC-1alpha-interacting MED1 subunit of Mediator in UCP-1 induction, as well as the accumulation of TRalpha, PPARgamma, PGC-1alpha, and MED1 on the UCP-1 enhancer in brown adipocytes. We then use biochemical assays to show that (i) PGC-1alpha is recruited to the TRalpha-RXRalpha-UCP-1 enhancer complex through interaction of an N-terminal LXXLL domain with TRalpha, (ii) MED1/Mediator displaces PGC-1alpha from TRalpha through LXXLL domain competition, and (iii) upon loss of PGC-1alpha-TRalpha interactions, PGC-1alpha remains associated with the enhancer complex through an interaction between PGC-1alpha and MED1 C-terminal domains. These results indicate dynamic MED1-dependent PGC-1alpha interactions related to functions in both chromatin remodeling and the transition to subsequent transcription initiation.

High incidence of metabolically active brown adipose tissue in healthy adult humans: effects of cold exposure and adiposity

OBJECTIVE

The significant roles of brown adipose tissue (BAT) in the regulation of energy expenditure and adiposity are established in small rodents but have been controversial in humans. The objective is to examine the prevalence of metabolically active BAT in healthy adult humans and to clarify the effects of cold exposure and adiposity.

RESEARCH DESIGN AND METHODS

In vivo 2-[(18)F]fluoro-2-deoxyglucose (FDG) uptake into adipose tissue was measured in 56 healthy volunteers (31 male and 25 female subjects) aged 23-65 years by positron emission tomography (PET) combined with X-ray computed tomography (CT).

RESULTS

When exposed to cold (19 degrees C) for 2 h, 17 of 32 younger subjects (aged 23-35 years) and 2 of 24 elderly subjects (aged 38-65 years) showed a substantial FDG uptake into adipose tissue of the supraclavicular and paraspinal regions, whereas they showed no detectable uptake when kept warm (27 degrees C). Histological examinations confirmed the presence of brown adipocytes in these regions. The cold-activated FDG uptake was increased in winter compared with summer (P < 0.001) and was inversely related to BMI (P < 0.001) and total (P < 0.01) and visceral (P < 0.001) fat areas estimated from CT image at the umbilical level.

CONCLUSIONS

Our findings, being against the conventional view, indicate the high incidence of metabolically active BAT in adult humans and suggest a role in the control of body temperature and adiposity.

UCP1 -3826 AG+GG genotypes, adiponectin, and leptin/adiponectin ratio in severe obesity

BACKGROUND AND AIMS

Non-alcoholic fatty liver disease (NAFLD) and metabolic syndrome (MS) are well-recognized complications of obesity. This study was designed to evaluate the role of the UCP1 -3826 A>G polymorphism, adiponectin levels, leptin/adiponectin ratio (L/A), and main biochemical parameters in 102 unrelated severely obese adults [61 females and 41 males, median body mass index (BMI) = 47.8 kg/m2] with NAFLD, with (MS+) or without MS (MS-) from Southern Italy.

SUBJECT AND METHODS

The UCP1 polymorphism was tested by the TaqMan method, main biochemical parameters by routinary methods, adiponectin, and leptin serum levels by enzyme-linked immunosorbent assay. MS was diagnosed according to the American Heart Association criteria, liver steatosis was detected by ultrasound.

RESULTS

MS was present in 53% male and 66% female obese patients. Only total cholesterol (p=0.04 males and p=0.002 females) and L/A ratio (p=0.03 males) differed between MS+ and MS- obese patients. At multivariate analysis, severe liver steatosis was significantly associated with: UCP1 (AG+GG) genotypes [odds ratio-confidence interval (OR-CI): 4.25; 1.12-16.13], MS (OR-CI: 8.47; 1.78-40.25), low adiponectin levels (OR-CI: 0.92; 0.87-0.98), high alanine aminotransferase levels (OR-CI: 1.03; 1.00-1.06), age (ORCI: 1.08; 1.00-1.15), and male gender (OR-CI: 10.78; 1.61- 71.96).

CONCLUSION

In addition to traditional factors, total cholesterol and L/A ratio appear to contribute to MS characterization in severe obesity. Furthermore, the UCP1 (AG+GG) genotypes and low adiponectin levels could predispose to a more severe liver steatosis independently of MS presence. Based on our data, polymorphic UCP1 (AG+GG) obese patients with low adiponectin levels appear to be high-risk subjects for worsening of liver steatosis, a NAFLD, possibly requiring a second-step evaluation by liver biopsy.

Nonshivering thermogenesis without interscapular brown adipose tissue involvement during conditioned fear in the rat

As with other forms of psychological stress, conditioned fear causes an increase in body temperature. The mechanisms underlying this stress-induced hyperthermia are not well understood, but previous research suggests that nonshivering thermogenesis might contribute, as it does during cold exposure. The major source of nonshivering thermogenesis in the rat is brown adipose tissue (BAT), and the largest BAT deposit in that species is in the interscapular area just below the skin. BAT is also under sympathetic control via β-adrenoceptors. If BAT contributes to fear-induced hyperthermia, then the interscapular skin should warm up faster than other skin areas, and this response should be suppressed by the β-adrenoceptor antagonist, propranolol. We tested this noninvasively by infrared thermography. In conscious rats, 30 min of contextual fear caused hyperthermia (as indicated by a +1.5°C increase in lumbar back skin temperature) and increased the difference in temperature between interscapular and lumbar back skin (TiScap − TBack) by +1°C. Propranolol (10 mg/kg ip) completely abolished this hyperthermia; however, the TiScap-TBack increase was not reduced. In contrast, exposure to cold air (4°C) induced a +2.7°C increase in TiScap-TBack, which was reduced to +1°C after propranolol. The results show that conditioned fear-induced hyperthermia is of nonshivering origin and mediated by β-adrenoceptors, but interscapular BAT does not contribute to it and does not appear to be activated, either.