Energy dissipation in brown adipose tissue: from mice to men

White-to-Beige and Back: Adipocyte Conversion and Transcriptional Reprogramming

Obesity has become a pandemic, as currently more than half a billion people worldwide are obese. The etiology of obesity is multifactorial, and combines a contribution of hereditary and behavioral factors, such as nutritional inadequacy, along with the influences of environment and reduced physical activity. Two types of adipose tissue widely known are white and brown. While white adipose tissue functions predominantly as a key energy storage, brown adipose tissue has a greater mass of mitochondria and expresses the uncoupling protein 1 (UCP1) gene, which allows thermogenesis and rapid catabolism. Even though white and brown adipocytes are of different origin, activation of the brown adipocyte differentiation program in white adipose tissue cells forces them to transdifferentiate into "beige" adipocytes, characterized by thermogenesis and intensive lipolysis. Nowadays, researchers in the field of small molecule medicinal chemistry and gene therapy are making efforts to develop new drugs that effectively overcome insulin resistance and counteract obesity. Here, we discuss various aspects of white-to-beige conversion, adipose tissue catabolic re-activation, and non-shivering thermogenesis.

Are MTV and TLG Accurate for Quantifying the Intensity of Brown Adipose Tissue Activation?

Recent research has suggested that one novel mechanism of action for anti-obesity medications is to stimulate the activation of brown adipose tissue (BAT). 18FDG PET/CT remains the gold standard for defining and quantifying BAT. SUVmax is the most often used quantification tool in clinical practice. However, this parameter does not reflect the entire BAT volume. As a potential method for precisely evaluating BAT, we have utilised metabolic tumour volume (MTV) and total lesion glycolysis (TLG) to answer the question: Are MTV and TLG accurate in quantifying the intensity of BAT activation? After analysing the total number of oncological 18F-FDG PET/CT scans between 2021-2023, we selected patients with active BAT. Based on the BAT SUVmax, the patients were divided into BAT-moderate activation (MA) vs. BAT-high activation (HA). Furthermore, we statistically analysed the accuracy of TLG and MTV in assessing BAT activation intensity. The results showed that both parameters increased their predictive value regarding BAT activation, and presented a significantly high sensitivity and specificity for the correct classification of BAT activation intensity. To conclude, these parameters could be important indicators with increased accuracy for classifying BAT expression, and could bring additional information about the volume of BAT to complement the limitations of the SUVmax.

Mechanisms of Action of Bariatric Surgery on Body Weight Regulation

Bariatric surgery is an effective treatment modality for obesity and obesity-associated complications. Weight loss after bariatric surgery was initially attributed to anatomic restriction or reduced energy absorption, but now it is understood that surgery treats obesity by influencing the subcortical areas of the brain to lower adipose tissue mass. There are three major phases of this process: initially the weight loss phase, followed by a phase where weight loss is maintained, and in a subset of patients a phase where weight is regained. These phases are characterized by altered appetitive behavior together with changes in energy expenditure. The mechanisms associated with the rearrangement of the gastrointestinal tract include central appetite control, release of gut peptides, change in microbiota and bile acids. However, the exact combination and timing of signals remain largely unknown.

Oxidative and DNA damage in obese patients undergoing bariatric surgery: A one-year follow-up study

The pathogenesis of obesity and related comorbidities has long been associated with oxidative stress. The excess of adipose tissue contributes to the production of free radicals that sustain both a local and a systemic chronic inflammatory state, whereas its reduction can bring to an improvement in inflammation and oxidative stress. In our work, using the fluorescent lipid probe BODIPY® 581/591 C11 and the γH2AX foci assay, a well-known marker of DNA double strand breaks (DSB), we evaluated the extent of cell membrane oxidation and DNA damage in peripheral blood lymphocytes of normal weight (NW) controls and obese patients sampled before and after bariatric surgery. Compared to NW controls, we observed a marked increase in both the frequencies of oxidized cells or nuclei exhibiting phosphorylation of histone H2AX in preoperatory obese patients. After bariatric surgery, obese patients, resampled over one-year follow-up, improved oxidative damage and reduced the presence of DSB. In conclusion, the present study highlights the importance for obese patients undergoing bariatric surgery to also monitor these molecular markers during their postoperative follow-up.

Bioactive dietary components-Anti-obesity effects related to energy metabolism and inflammation

Obesity is the result of the long-term energy imbalance between the excess calories consumed and the few calories expended. Reducing the intake of energy dense foods (fats, sugars), and strategies such as fasting and caloric restriction can promote body weight loss. Not only energy in terms of calories, but also the specific composition of the diet can affect the way the food is absorbed and how its energy is stored, used or dissipated. Recent research has shown that bioactive components of food, such as polyphenols and vitamins, can influence obesity and its pathologic complications such as insulin resistance, inflammation and metabolic syndrome. Individual micronutrients can influence lipid turnover but for long-term effects on weight stability, dietary patterns containing several micronutrients may be required. At the molecular level, these molecules modulate signaling and the expression of genes that are involved in the regulation of energy intake, lipid metabolism, adipogenesis into white, beige and brown adipose tissue, thermogenesis, lipotoxicity, adipo/cytokine synthesis, and inflammation. Higher concentrations of these molecules can be reached in the intestine, where they can modulate the composition and action of the microbiome. In this review, the molecular mechanisms by which bioactive compounds and vitamins modulate energy metabolism, inflammation and obesity are discussed.

Mechanisms of Weight Loss After Obesity Surgery

Obesity surgery remains the most effective treatment for obesity and its complications. Weight loss was initially attributed to decreased energy absorption from the gut but has since been linked to reduced appetitive behavior and potentially increased energy expenditure. Implicated mechanisms associating rearrangement of the gastrointestinal tract with these metabolic outcomes include central appetite control, release of gut peptides, change in microbiota, and bile acids. However, the exact combination and timing of signals remain largely unknown. In this review, we survey recent research investigating these mechanisms, and seek to provide insights on unanswered questions over how weight loss is achieved following bariatric surgery which may eventually lead to safer, nonsurgical weight-loss interventions or combinations of medications with surgery.

Nipple Hibernoma in a Dog: A Case Report With Literature Review

This report provides a clinical, histological, and immunohistochemical description of an unusual hibernoma (pale cell variant) in the subepidermal area of the nipple of a six-year-old bitch. Furthermore, an extensive literature review of hibernomas in animals was made. Physical examination revealed a nodular lesion in the subepidermal area of the third nipple of the left mammary chain. The histopathological findings included lobules of round to oval cells with abundant pale to eosinophilic cytoplasm, containing one or multiple optically empty vacuoles, consistent with nipple hibernoma. Immunohistochemically, the neoplastic cells were negative for cytokeratin AE1/AE3 and p53 but showed strong immunoreaction for vimentin and uncoupling protein-1, thus confirming the brown adipose tissue origin. Local recurrence was not detected after 18 months of follow-up. Hibernomas are rare and benign neoplastic lesions, originating from brown adipose tissue. Due to their histological and molecular resemblance with liposarcoma, a correct diagnosis of these neoplasms is required. In addition, the literature review suggests that hibernomas may present different features, according to species.

3-N-butylphthalide protects against high-fat-diet-induced obesity in C57BL/6 mice and increases metabolism in lipid-accumulating cells

Obesity is one of the world's largest health problems, and 3-N-butylphthalide (NBP), a bioactive compound in celery, has been used in dieting and weight management programs. In this study, NBP prevented high-fat-diet-induced weight gain, reduced the food efficiency ratio, altered the blood biochemical profile, and reduced the obesity-related index. NBP reduced adiposity, white fat depots, liver weight, and hepatic steatosis in obese mice. NBP ameliorated the diabetic state by decreasing glucose levels and improving glucose and insulin tolerance. NBP increased uncoupling protein-1 expression in white adipose tissue and upregulated thermogenesis by enhancing mitochondrial respiration. NBP inhibited white adipocyte development by prohibiting lipid accumulation in human adipose-derived stem cells. NBP increased free fatty acid uptake and the oxygen consumption rate in beige adipocytes. Our results suggest that NBP could be used as functional natural supplement against obesity and its associated disorders.

β3-Adrenergic receptor agonist treats rotator cuff fatty infiltration by activating beige fat in mice

BACKGROUND

Rotator cuff (RC) muscle atrophy and fatty infiltration (FI) are independent factors correlated with failure of attempted tendon repair in larger RC tears. However, there is no effective treatment for RC muscle atrophy and FI at this time. The recent discovery of beige adipose tissue (BAT) in adults shed light on a new avenue in treating obesity and excessive fat deposition by promoting BAT activity. The goal of this study was to define the role of intramuscular BAT in RC muscle FI and the effect of β₃-adrenergic receptor agonists in treating RC muscle FI by promoting BAT activity.

MATERIALS AND METHODS

Three-month-old wild-type C57BL/6J, platelet derived growth factor receptor-alpha (PDGFRα) green fluorescent protein (GFP) reporter and uncoupling protein 1 (UCP-1) knockout mice underwent a unilateral RC injury procedure, which included supraspinatus (SS) and infraspinatus tendon resection and suprascapular nerve transection. To stimulate BAT activity, amibegron, a selective β₃-adrenergic receptor agonist, was administered to C57BL/6J mice either on the same day as surgery or 6 weeks after surgery through daily intraperitoneal injections. Gait analysis was conducted to measure forelimb function at 6 weeks or 12 weeks (in groups receiving delayed amibegron treatment) after surgery. Animals were killed humanely at 6 weeks (or 12 weeks for delayed amibegron groups) after surgery. SS muscles were harvested and analyzed histologically and biochemically.

RESULTS

Histologic analysis of SS muscles from PDGFRα-GFP reporter mice showed that PDGFRα-positive fibroadipogenic progenitors in RC muscle expressed UCP-1, a hallmark of BAT during the development of FI after RC tears. Impairing BAT activity by knocking out UCP-1 resulted in more severe muscle atrophy and FI with inferior forelimb function in UCP-1 knockout mice compared with wild-type mice. Promoting BAT activity with amibegron significantly reduced muscle atrophy and FI after RC tears and improved forelimb function. Delayed treatment with amibegron reversed muscle atrophy and FI in muscle.

CONCLUSIONS

Fat accumulated in muscle after RC tears possesses BAT characteristics. Impairing BAT activity results in worse RC muscle atrophy and FI. Amibegron reduces and reverses RC atrophy and FI by promoting BAT activity.

Epidermal Acyl-CoA-binding protein is indispensable for systemic energy homeostasis

OBJECTIVES

The skin is the largest sensory organ of the human body and plays a fundamental role in regulating body temperature. However, adaptive alterations in skin functions and morphology have only vaguely been associated with physiological responses to cold stress or sensation of ambient temperatures. We previously found that loss of acyl-CoA-binding protein (ACBP) in keratinocytes upregulates lipolysis in white adipose tissue and alters hepatic lipid metabolism, suggesting a link between epidermal barrier functions and systemic energy metabolism.

METHODS

To assess the physiological responses to loss of ACBP in keratinocytes in detail, we used full-body ACBP-/- and skin-specific ACBP-/- knockout mice to clarify how loss of ACBP affects 1) energy expenditure by indirect calorimetry, 2) response to high-fat feeding and a high oral glucose load, and 3) expression of brown-selective gene programs by quantitative PCR in inguinal WAT (iWAT). To further elucidate the role of the epidermal barrier in systemic energy metabolism, we included mice with defects in skin structural proteins (ma/ma Flgft/ft) in these studies.

RESULTS

We show that the ACBP-/- mice and skin-specific ACBP-/- knockout mice exhibited increased energy expenditure, increased food intake, browning of the iWAT, and resistance to diet-induced obesity. The metabolic phenotype, including browning of the iWAT, was reversed by housing the mice at thermoneutrality (30 °C) or pharmacological β-adrenergic blocking. Interestingly, these findings were phenocopied in flaky tail mice (ma/ma Flgft/ft). Taken together, we demonstrate that a compromised epidermal barrier induces a β-adrenergic response that increases energy expenditure and browning of the white adipose tissue to maintain a normal body temperature.

CONCLUSIONS

Our findings show that the epidermal barrier plays a key role in maintaining systemic metabolic homeostasis. Thus, regulation of epidermal barrier functions warrants further attention to understand the regulation of systemic metabolism in further detail.

Metabolic and energetic benefits of microRNA-22 inhibition

INTRODUCTION

We previously demonstrated in primary cultures of human subcutaneous adipocytes and in a mouse model of diet-induced obesity that specific microRNA-22-3p antagomirs produce a significant reduction of fat mass and an improvement of several metabolic parameters. These effects are related to the activation of target genes such as KDM3A, KDM6B, PPARA, PPARGC1B and SIRT1 involved in lipid catabolism, thermogenesis, insulin sensitivity and glucose homeostasis.

RESEARCH DESIGN AND METHODS

We now report a dedicated study exploring over the course of 3 months the metabolic and energetic effects of subcutaneous administration of our first miR-22-3p antagomir drug candidate (APT-110) in adult C57BL/6 male mice. Body composition, various blood parameters and energy expenditure were measured at several timepoints between week 12 and week 27 of age.

RESULTS

Weekly subcutaneous injections of APT-110 for 12 weeks produced a sustained increase of energy expenditure as early as day 11 of treatment, a significant fat mass reduction, but no change of appetite nor physical activity. Insulin sensitivity as well as circulating glucose, cholesterol and leptin were improved. There was a dramatic reduction of liver steatosis after 3 months of active treatment. RNA sequencing revealed an activation of lipid metabolism pathways in a tissue-specific manner.

CONCLUSIONS

These original findings suggest that microRNA-22-3p inhibition could lead to a potent treatment of fat accumulation, insulin resistance, and related complex metabolic disorders such as obesity, type 2 diabetes mellitus and non-alcoholic fatty liver disease.

An indispensable role for dynamin-related protein 1 in beige and brown adipogenesis

Emerging evidence indicates that proper mitochondrial dynamics are critical for adipocyte differentiation and functional thermogenic capacity. We found that the mitochondrial fission protein dynamin-related protein 1 (DRP1, also known as DNML1) is highly expressed in brown adipose tissue compared to expression in white adipose tissue, and these expression levels increase during brown adipocyte differentiation. Our results reveal that the inhibition of DRP1 using mdivi-1 mitigates beige adipocyte differentiation and differentiation-associated mitochondrial biogenesis. We found that DRP1 is essential for the induction of the early-phase beige adipogenic transcriptional program. Intriguingly, inhibition of DRP1 is dispensable following the induction of beige adipogenesis and adipogenesis-associated mitochondrial biogenesis. Altogether, we demonstrate that DRP1 in preadipocytes plays an essential role in beige and brown adipogenesis.This article has an associated First Person interview with the first author of the paper.

DUODENAL-JEJUNAL BYPASS REDUCES LIPID ACCUMULATION IN THE BROWN ADIPOSE TISSUE OF HYPOTHALAMIC OBESE RATS

BACKGROUND

Effects of duodenal-jejunal bypass surgery (DJB) on the proliferation of nuclei and the area of adipocytes in the brown adipose tissue of obese rats. Thermogenic activity in the brown adipose tissue (BAT) of obese individuals is reduced, and this condition may be modified by bariatric surgery (BS).

AIM

To characterize fat deposition in BAT from hypothalamic obese (HyO) rats submitted to duodenal-jejunal-bypass (DJB) surgery.

METHODS

For induction of hypothalamic obesity, newborn male Wistar rats were treated with subcutaneous injections of monosodium glutamate (MSG). The control (CTL) group received saline solution. At 90 days, the HyO rats were submitted to DJB or sham operation, generating the HyO-DJB and HyO-SHAM groups. At 270 days, the rats were euthanized, and the BAT was weighed and submitted to histological analysis.

RESULTS

Compared to BAT from CTL animals, the BAT from HyO-SHAM rats displayed increased weight, hypertrophy with greater lipid accumulation and a reduction in nucleus number. DJB effectively increased nucleus number and normalized lipid deposition in the BAT of HyO-SHAM rats, similar to that observed in CTL animals.

CONCLUSION

DJB surgery avoided excessive lipid deposition in the BAT of hypothalamic obese rats, suggesting that this procedure could reactivate thermogenesis in BAT, and contribute to increase energy expenditure.

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.

BCL6 regulates brown adipocyte dormancy to maintain thermogenic reserve and fitness

During exposure to environmental cold, brown adipocytes protect against hypothermia by generating heat (thermogenesis). In warm environments, brown adipocytes become inactive or dormant but still maintain their identity and thermogenic capacity, allowing rapid reactivation of thermogenesis upon subsequent cold exposure. Our understanding of the dormant state and its regulation is very limited. Here, we show that the transcription factor B cell leukemia/lymphoma 6 (BCL6) is specifically required for maintenance of thermogenic capacity during dormancy in brown adipocytes. Mechanistically, BCL6 drives a gene expression program that promotes survival, fatty acid oxidation, and uncoupled respiration. Thus, unlike other transcription factors that regulate cold-induced thermogenesis, BCL6 is specifically required for maintaining thermogenic fitness during adaptation to environmental warmth.

Brown adipocytes provide a metabolic defense against environmental cold but become dormant as mammals habituate to warm environments. Although dormancy is a regulated response in brown adipocytes to environmental warmth, its transcriptional mechanisms and functional importance are unknown. Here, we identify B cell leukemia/lymphoma 6 (BCL6) as a critical regulator of dormancy in brown adipocytes but not for their commitment, differentiation, or cold-induced activation. In a temperature-dependent manner, BCL6 suppresses apoptosis, fatty acid storage, and coupled respiration to maintain thermogenic fitness during dormancy. Mechanistically, BCL6 remodels the epigenome of brown adipocytes to enforce brown and oppose white adipocyte cellular identity. Thus, unlike other thermogenic regulators, BCL6 is specifically required for maintaining thermogenic fitness when mammals acclimate to environmental warmth.

Resveratrol regulates skeletal muscle fibers switching through the AdipoR1-AMPK-PGC-1α pathway

This study was conducted to investigate the effect and underlying mechanism of Resveratrol (RES) in regulating skeletal muscle fiber-type switching.

T Cells in Adipose Tissue in Aging

Similar to obesity, aging is associated with visceral adiposity and insulin resistance. Inflammation in adipose tissue, mainly evidenced by increased accumulation and proinflammatory polarization of T cells and macrophages, has been well-documented in obesity and may contribute to the associated metabolic dysfunctions including insulin resistance. Studies show that increased inflammation, including inflammation in adipose tissue, also occurs in aging, so-called "inflamm-aging." Aging-associated inflammation in adipose tissue has some similarities but also differences compared to obesity-related inflammation. In particular, conventional T cells are elevated in adipose tissue in both obesity and aging and have been implicated in metabolic functions in obesity. However, the changes and also possibly functions of regulatory T cells (Treg) in adipose tissue are different in aging and obesity. In this review, we will summarize recent advances in research on the changes of these immune cells in adipose tissue with aging and obesity and discuss their possible contributions to metabolism and the potential of these immune cells as novel therapeutic targets for prevention and treatment of metabolic diseases associated with aging or obesity.

The chemokine system and its role in obesity

The chemokine system is a complex arrangement of molecules that attract leukocytes to the site of injury or inflammation. This chemotactic behavior gives the system the name "Chemokine." The intricate and redundant nature of the chemokine system has made it a subject of ongoing scientific investigation. Obesity is characterized as low-grade systemic or chronic inflammation that is responsible for the release of cytokines, adipokines, and chemokines. Excessive tissue fat expansion triggers the release of chemokines, which in turn attract various leukocytes and activate the resident immune surveillance system, eventually leading to worsening of obesity and other related comorbidities. To date, 50 chemokines and 20 chemokine receptors that belong to the G-protein-coupled receptor family have been discovered, and over the past two decades, the physiological and pathological roles of many of these chemokines and their receptors have been elucidated. The objective of this review is to present an update on the link between chemokines and obesity under the light of recent knowledge.

Dietary polyphenols and their roles in fat browning

Discovery of the presence of brown adipose tissue (BAT) in newborn babies and adult humans, especially constitutively active brown fat or inducible beige fat, has led to the investigation of strategies employing BAT aimed at the development of novel therapeutic avenues for combating obesity and diabetes. Such antiobesity therapeutic tools include pharmaceutical and nutraceutical dietary polyphenols. Although there have been emerging notable advances in knowledge of and an increased amount of research related to brown and beige adipocyte developmental lineages and transcriptional regulators, current knowledge regarding whether and how food factors and environmental modifiers of BAT influence thermogenesis has not been extensively investigated. Therefore, in this review, we summarized recent updates on the exploration of dietary polyphenols while paying attention to the activation of BAT and thermogenesis. Specifically, we summarized findings pertaining to BAT metabolism, white adipose tissue (WAT) browning and thermogenic function of polyphenols (e.g., flavan-3-ols, green tea catechins, resveratrol, capsaicin/capsinoids, curcumin, thymol, chrysin, quercetin and berberine) that may foster a relatively safe and effective therapeutic option to improve metabolic health. We also deciphered the underlying proposed mechanisms through which these dietary polyphenols facilitate BAT activity and WAT browning. Characterization of thermogenic dietary factors may offer novel insight enabling revision of nutritional intervention strategies aimed at obesity and diabetes prevention and management. Moreover, identification of polyphenolic dietary factors among plant-derived natural compounds may provide information that facilitates nutritional intervention strategies against obesity, diabetes and metabolic syndrome.

Brown Adipose Tissue Controls Skeletal Muscle Function via the Secretion of Myostatin

Skeletal muscle and brown adipose tissue (BAT) are functionally linked, as exercise increases browning via secretion of myokines. It is unknown whether BAT affects muscle function. Here, we find that loss of the transcription factor IRF4 in BAT (BATI4KO) reduces exercise capacity, mitochondrial function, ribosomal protein synthesis, and mTOR signaling in muscle and causes tubular aggregate formation. Loss of IRF4 induces myogenic gene expression in BAT, including the secreted factor myostatin, a known inhibitor of muscle function. Reducing myostatin via neutralizing antibodies or soluble receptor rescues the exercise capacity of BATI4KO mice. In addition, overexpression of IRF4 in brown adipocytes reduces serum myostatin and increases exercise capacity in muscle. Finally, mice housed at thermoneutrality have reduced IRF4 in BAT, lower exercise capacity, and elevated serum myostatin; these abnormalities are corrected by excising BAT. Collectively, our data point to an unsuspected level of BAT-muscle crosstalk driven by IRF4 and myostatin.

Cross-sectional areas of deep/core veins are smaller at lower core body temperatures

The cardiovascular system plays a crucial role in thermoregulation. Deep core veins, due to their large size and role in returning blood to the heart, are an important part of this system. The response of veins to increasing core temperature has not been adequately studied in vivo. Our objective was to noninvasively quantify in C57BL/6 mice the response of artery-vein pairs to increases in body temperature. Adult male mice were anesthetized and underwent magnetic resonance imaging. Data were acquired from three colocalized vessel pairs (the neck [carotid/jugular], torso [aorta/inferior vena cava (IVC)], periphery [femoral artery/vein]) at core temperatures of 35, 36, 37, and 38°C. Cross-sectional area increased with increasing temperature for all vessels, excluding the carotid. Average area of the jugular, aorta, femoral artery, and vein linearly increased with temperature (0.10, 0.017, 0.017, and 0.027 mm2 /°C, respectively; P < 0.05). On average, the IVC has the largest venous response for area (18.2%/°C, vs. jugular 9.0 and femoral 10.9%/°C). Increases in core temperature from 35 to 38 °C resulted in an increase in contact length between the aorta/IVC of 29.3% (P = 0.007) and between the femoral artery/vein of 28.0% (P = 0.03). Previously unidentified increases in the IVC area due to increasing core temperature are biologically important because they may affect conductive and convective heat transfer. Vascular response to temperature varied based on location and vessel type. Leveraging noninvasive methodology to quantify vascular responses to temperature could be combined with bioheat modeling to improve understanding of thermoregulation.

Comparison of the sympathetic stimulatory abilities of B-type procyanidins based on induction of uncoupling protein-1 in brown adipose tissue (BAT) and increased plasma catecholamine (CA) in mice

OBJECTIVES

We previously found that elevated energy expenditure following a single oral dose of flavan 3-ols (FL), a mixture of catechins and B type procyanidins, is caused by sympathetic nerve activation. In the present study, we compared the activity of the FL components (-)-epicatechin (EC; monomer), procyanidin B2 (B2; dimer), procyanidin C1 (C1; trimer), cinnamtannin A2 (A2; tetramer), and more than pentamer fraction (P5).

METHODS

Male ICR mice were treated with a single oral dose of FL, EC, B2, C1, A2, or P5. The animals were sacrificed and blood and brown adipose tissue (BAT) sampled. The plasma catecholamine (CA) levels and BAT uncoupling protein (UCP)-1 mRNA expression were determined.

RESULTS

A single dose of 10 mg/kg FL significantly increased plasma CA and UCP-1 mRNA levels. B2, C1, and A2, but not EC and P5 (all at 1 mg/kg), significantly increased plasma adrenaline levels. Plasma noradrenaline was significantly elevated by B2 and A2, but not by EC, C1, or P5. UCP-1 mRNA levels were significantly increased by C1 and P5. In the dose response study of A2, 10-3 mg/kg A2 increased UCP-1 mRNA levels significantly, but not 10-2 and 10-1 mg/kg A2. In addition, combination treatment with 10-1 mg/kg A2 and yohimbine, an α2 adrenalin blocker, remarkably increased UCP-1 mRNA levels.

CONCLUSION

These results suggest that FL and its components, except EC, increase UCP-1 mRNA and plasma CA with varying efficacy.

CD8+ T cells in beige adipogenesis and energy homeostasis

Although accumulation of lymphocytes in the white adipose tissue (WAT) in obesity is linked to insulin resistance, it remains unclear whether lymphocytes also participate in the regulation of energy homeostasis in the WAT. Here, we demonstrate enhanced energy dissipation in Rag1-/- mice, increased catecholaminergic input to subcutaneous WAT, and significant beige adipogenesis. Adoptive transfer experiments demonstrated that CD8+ T cell deficiency accounts for the enhanced beige adipogenesis in Rag1-/- mice. Consistently, we identified that CD8-/- mice also presented with enhanced beige adipogenesis. The inhibitory effect of CD8+ T cells on beige adipogenesis was reversed by blockade of IFN-γ. All together, our findings identify an effect of CD8+ T cells in regulating energy dissipation in lean WAT, mediated by IFN-γ modulation of the abundance of resident immune cells and of local catecholaminergic activity. Our results provide a plausible explanation for the clinical signs of metabolic dysfunction in diseases characterized by altered CD8+ T cell abundance and suggest targeting of CD8+ T cells as a promising therapeutic approach for obesity and other diseases with altered energy homeostasis.

The Nile Rat (Arvicanthis niloticus) as a Superior Carbohydrate-Sensitive Model for Type 2 Diabetes Mellitus (T2DM)

Type II diabetes mellitus (T2DM) is a multifactorial disease involving complex genetic and environmental interactions. No single animal model has so far mirrored all the characteristics or complications of diabetes in humans. Since this disease represents a chronic nutritional insult based on a diet bearing a high glycemic load, the ideal model should recapitulate the underlying dietary issues. Most rodent models have three shortcomings: (1) they are genetically or chemically modified to produce diabetes; (2) unlike humans, most require high-fat feeding; (3) and they take too long to develop diabetes. By contrast, Nile rats develop diabetes rapidly (8-10 weeks) with high-carbohydrate (hiCHO) diets, similar to humans, and are protected by high fat (with low glycemic load) intake. This review describes diabetes progression in the Nile rat, including various aspects of breeding, feeding, and handling for best experimental outcomes. The diabetes is characterized by a striking genetic permissiveness influencing hyperphagia and hyperinsulinemia; random blood glucose is the best index of disease progression; and kidney failure with chronic morbidity and death are outcomes, all of which mimic uncontrolled T2DM in humans. Non-alcoholic fatty liver disease (NAFLD), also described in diabetic humans, results from hepatic triglyceride and cholesterol accumulation associated with rising blood glucose. Protection is afforded by low glycemic load diets rich in certain fibers or polyphenols. Accordingly, the Nile rat provides a unique opportunity to identify the nutritional factors and underlying genetic and molecular mechanisms that characterize human T2DM.

Insulin selectively reduces mitochondrial uncoupling in brown adipose tissue in mice

The purpose of the present study was to determine the effects of prolonged hyperinsulinemia on mitochondrial respiration and uncoupling in distinct adipose tissue depots. Sixteen-week-old male mice were injected daily with placebo or insulin to induce an artificial hyperinsulinemia for 28 days. Following the treatment period, mitochondrial respiration and degree of uncoupling were determined in permeabilized perirenal, inguinal, and interscapular adipose tissue. White adipose tissue (WAT) mitochondria (inguinal and perirenal) respire at substantially lower rates compared with brown adipose tissue (BAT). Insulin treatment resulted in a significant reduction in mitochondrial respiration in inguinal WAT (iWAT) and interscapular BAT (iBAT), but not in perirenal WAT (pWAT). Furthermore, these changes were accompanied by an insulin-induced reduction in UCP-1 (uncoupling protein 1) and PGC-1α in iWAT and iBAT only, but not in pWAT or skeletal muscle. Compared with adipose tissue mitochondria in placebo conditions, adipose tissue from hyperinsulinemic mice manifested a site-specific reduction in mitochondrial respiration probably as a result of reduced uncoupling. These results may help explain weight gain so commonly seen with insulin treatment in type 2 diabetes mellitus.

Correlation of Brown Adipose Tissue with Other Body Fat Compartments and Patient Characteristics: A Retrospective Analysis in a Large Patient Cohort Using PET/CT

RATIONALE AND OBJECTIVES

The objective of this study was to assess the relationship of brown adipose tissue (BAT) activity with different fat compartments of the body, body mass index (BMI), outdoor temperature, thyroid-stimulating hormone (TSH) levels, blood glucose, age, and sex in a large patient population using F-18-fluordesoxyglucose positron emission tomography-computer tomography (FDG-PET/CT) scans obtained under thermoneutral conditions.

MATERIALS AND METHODS

FDG-PET/CT scans of 4852 patients were retrospectively analyzed for BAT activity. The volumes of the different fat compartments visceral adipose tissue (VAT), subcutaneous adipose tissue (SCAT), and liver fat, were assessed by computed tomography. Age, sex, TSH levels, blood glucose levels, BMI, primary disease, and the outdoor temperature were determined. Multiple linear regression analyses were performed to identify independent relationships between the parameters.

RESULTS

The VAT, SCAT, and liver fat content were lower in BAT-positive patients than in BAT-negative patients (each P < 0.0001). BAT-positive patients had a lower BMI (P < 0.0001) and were more often female (P < 0.0001), younger (P < 0.0001), and had higher TSH levels (P = 0.0002), whereas the outdoor temperature and the blood glucose level were not different compared to BAT-negative patients. Age, sex, VAT, and SCAT were independent factors related to BAT.

CONCLUSIONS

Age, sex, and VAT are the most important determinants of BAT activity under thermoneutral conditions. VAT reflects the association between BAT activity and body fat mass more clearly than BMI. The strength of the association between VAT and BAT decreases during aging in men, but increases in women. This may indicate a different importance of BAT activity for obesity in men and in women.

Phytol stimulates the browning of white adipocytes through the activation of AMP-activated protein kinase (AMPK) α in mice fed high-fat diet

In vivo and in vitro studies show that phytol stimulates the browning of mice iWAT and formation of brown-like adipocytes in the differentiated 3T3-L1 through the activation of the AMPKα signaling pathway.

A thermal gradient modulates the oxidative metabolism and growth of human keratinocytes

During their spatial and differentiative progression, keratinocytes face a thermal gradient, from 37 °C in the proliferating basal layer to 32 °C found in skin surface. In our study, we hypothesized that this difference in temperature must be balanced by increasing the heat produced during respiratory activity. We demonstrated that at 33 °C human primary keratinocytes and HaCaT cells raised mitochondrial energy metabolism, but not glycolytic activity. At 33 °C, the increased mitochondrial ATP synthesis was associated with a strong induction of the modulator of the respiratory chain estrogen receptor β, whereas uncoupling protein 1 expression was not changed. The enhanced mitochondrial oxidative metabolism was accompanied by a remarkable reduction in proliferation. These results suggest that environmental temperature can modulate the energy metabolism and proliferation of human keratinocytes.

Effects of nicotine on homeostatic and hedonic components of food intake

Chronic tobacco use leads to nicotine addiction that is characterized by exaggerated urges to use the drug despite the accompanying negative health and socioeconomic burdens. Interestingly, nicotine users are found to be leaner than the general population. Review of the existing literature revealed that nicotine affects energy homeostasis and food consumption via altering the activity of neurons containing orexigenic and anorexigenic peptides in the brain. Hypothalamus is one of the critical brain areas that regulates energy balance via the action of these neuropeptides. The equilibrium between these two groups of peptides can be shifted by nicotine leading to decreased food intake and weight loss. The aim of this article is to review the existing literature on the effect of nicotine on food intake and energy homeostasis and report on the changes that nicotine brings about in the level of these peptides and their receptors that may explain changes in food intake and body weight induced by nicotine. Furthermore, we review the effect of nicotine on the hedonic aspect of food intake. Finally, we discuss the involvement of different subtypes of nicotinic acetylcholine receptors in the regulatory action of nicotine on food intake and energy homeostasis.

Beiging of white adipose tissue as a therapeutic strategy for weight loss in humans

An imbalance between energy intake and expenditure leads to obesity. Adiposity associated with obesity progressively causes inflammation, type 2 diabetes, hypertension, hyperlipidemia and cardiovascular disease. Excessive dietary intake of fat results in its accumulation and storage in the white adipose tissue (WAT), whereas energy expenditure by fat utilization and oxidation predominately occurs in the brown adipose tissue (BAT). Recently, the presence of a third type of fat, referred to as beige or brite (brown in white), has been recognized in certain kinds of WAT depots. It has been suggested that WAT can undergo the process of browning in response to stimuli that induce and enhance the expression of thermogenes characteristic of those typically associated with brown fat. The resultant beige or brite cells enhance energy expenditure by reducing lipids stored within adipose tissue. This has created significant excitement towards the development of a promising strategy to induce browning/beiging in WAT to combat the growing epidemic of obesity. This review systematically describes differential locations and functions of WAT and BAT, mechanisms of beiging of WAT and a concise analysis of drug molecules and natural products that activate the browning phenomenon in vitro and in vivo. This review also discusses potential approaches for targeting WAT with compounds for site-specific beiging induction. Overall, there are numerous mechanisms that govern browning of WAT. There are a variety of newly identified targets whereby potential molecules can promote beiging of WAT and thereby combat obesity.

Targeting the NO/superoxide ratio in adipose tissue: relevance to obesity and diabetes management

Insulin sensitivity and metabolic homeostasis depend on the capacity of adipose tissue to take up and utilize excess glucose and fatty acids. The key aspects that determine the fuel-buffering capacity of adipose tissue depend on the physiological levels of the small redox molecule, nitric oxide (NO). In addition to impairment of NO synthesis, excessive formation of the superoxide anion (О2•- ) in adipose tissue may be an important interfering factor diverting the signalling of NO and other reactive oxygen and nitrogen species in obesity, resulting in metabolic dysfunction of adipose tissue over time. Besides its role in relief from superoxide burst, enhanced NO signalling may be responsible for the therapeutic benefits of different superoxide dismutase mimetics, in obesity and experimental diabetes models. This review summarizes the role of NO in adipose tissue and highlights the effects of NO/О2•- ratio 'teetering' as a promising pharmacological target in the metabolic syndrome.

LINKED ARTICLES

This article is part of a themed section on Redox Biology and Oxidative Stress in Health and Disease. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v174.12/issuetoc.

Dietary Factors Promoting Brown and Beige Fat Development and Thermogenesis

Brown adipose tissue (BAT) is a specialized fat tissue that has a high capacity to dissociate cellular respiration from ATP utilization, resulting in the release of stored energy as heat. Adult humans possess a substantial amount of BAT in the form of constitutively active brown fat or inducible beige fat. BAT activity in humans is inversely correlated with adiposity, blood glucose concentrations, and insulin sensitivity; this suggests that strategies aimed at BAT-mediated bioenergetics are an attractive therapeutic target in combating the continuing epidemic of obesity and diabetes. Despite advances in knowledge regarding the developmental lineage and transcriptional regulators of brown and beige adipocytes, our current understanding of environmental modifiers of BAT thermogenesis, such as diet, is limited. In this review, we consolidated the latest research on dietary molecules that may serve to promote BAT thermogenesis. Here, we summarized the thermogenic function of selected phytochemicals (e.g., capsaicin, resveratrol, curcumin, green tea, and berberine), dietary fatty acids (e.g., fish oil and conjugated linoleic acids), and all-trans retinoic acid, a vitamin A metabolite. We also delineated the proposed mechanisms whereby these dietary molecules promote BAT activity and/or browning of white adipose tissue. Characterizing thermogenic dietary factors may offer novel insight into revising nutritional intervention strategies aimed at obesity and diabetes prevention and management.

Resveratrol enhances brown adipocyte formation and function by activating AMP-activated protein kinase (AMPK) α1 in mice fed high-fat diet

SCOPE

Enhancing the formation and function of brown adipose tissue (BAT) increases thermogenesis and hence reduces obesity. Thus, we investigate the effects of resveratrol (Resv) on brown adipocyte formation and function in mouse interscapular BAT (iBAT).

METHODS AND RESULTS

CD1 mice and stromal vascular cells (SVCs) isolated from iBAT were treated with Resv. Expression of brown adipogenic and thermogenic markers, and involvement of AMP-activated protein kinase (AMPK)α1 were assessed. In vivo, Resv-enhanced expression of brown adipogenic markers, PR domain-containing 16 (PRDM16) and thermogenic genes, uncoupling protein 1 (UCP1) and cytochrome C in iBAT, along with smaller lipid droplets, elevated AMPKα activity and increased oxygen consumption. Meanwhile, Resv promoted expression of PRDM16, UCP1, PGC1α, cytochrome C and pyruvate dehydrogenase (PDH) in differentiated iBAT SVCs, suggesting that Resv enhanced brown adipocyte formation and function in vitro. In addition, Resv stimulated AMPKα and oxygen consumption in differentiated iBAT SVCs. However, the promotional effects of Resv were diminished by AMPK inhibition or AMPKα1 knockout, implying the involvement of AMPKα1 in this process.

CONCLUSION

Resv enhanced brown adipocyte formation and thermogenic function in mouse iBAT by promoting the expression of brown adipogenic markers via activating AMPKα1, which contributed to the anti-obesity effects of Resv.

Can Resistance Exercise Alter Irisin Levels and Expression Profiles of FNDC5 and UCP1 in Rats?

Background

Irisin is a new myokine secreted from the skeletal muscle and appears to affect the metabolism of adipose tissue.

Objectives

The mechanisms of cellular and molecular identification by which exercise training exerts its benefits remain unclear and are under investigation.

Methods

We examined the effect of 8-week resistance exercise on plasma irisin levels and expression profiles of muscle FNDC5 and subcutaneous adipose tissue UCP1 in male rats. Sixteen adult male rats were divided into two groups, control (n = 8) and exercise training (n = 8) groups. The training group received exercise for 3 days/week on a specific ladder (120 cm height) with a carrying load of 50% of body weight, which was attached to their tails.

Results

The weight of the load was gradually increased during the training sessions, ultimately reaching 200% of the body weight of rats in the final week. There were three sets of five repetitions with a 3-min rest between each set of exercise sessions and 1 minute between repetitions. Plasma irisin levels and relative mRNA expression of the genes UCP1 and FNDC5 were assessed. The results demonstrated a significant increase in the irisin levels after 8 weeks of resistance exercise (P < 0.001, t = 4.48). The relative expression of FNDC5 (P < 0.001, t = 6.18) and UCP1 genes (P < 0.001, t = 13.91) was also significantly increased.

Conclusions

Therefore, we can conclude from this study that resistance exercise may improve body composition possibly through increased thermogenesis in white adipose tissue through the secretion of irisin.

Room temperature housing results in premature cancellous bone loss in growing female mice: implications for the mouse as a preclinical model for age-related bone loss

Room temperature housing (22 °C) results in premature cancellous bone loss in female mice. The bone loss was prevented by housing mice at thermoneutral temperature (32 °C). Thermogenesis differs markedly between mice and humans and mild cold stress induced by standard room temperature housing may introduce an unrecognized confounding variable into preclinical studies.

INTRODUCTION

Female mice are often used as preclinical models for osteoporosis but, in contrast to humans, mice exhibit cancellous bone loss during growth. Mice are routinely housed at room temperature (18-23 °C), a strategy that exaggerates physiological differences in thermoregulation between mice (obligatory daily heterotherms) and humans (homeotherms). The purpose of this investigation was to assess whether housing female mice at thermoneutral (temperature range where the basal rate of energy production is at equilibrium with heat loss) alters bone growth, turnover and microarchitecture.

METHODS

Growing (4-week-old) female C57BL/6J and C3H/HeJ mice were housed at either 22 or 32 °C for up to 18 weeks.

RESULTS

C57BL/6J mice housed at 22 °C experienced a 62 % cancellous bone loss from the distal femur metaphysis during the interval from 8 to 18 weeks of age and lesser bone loss from the distal femur epiphysis, whereas cancellous and cortical bone mass in 32 °C-housed mice were unchanged or increased. The impact of thermoneutral housing on cancellous bone was not limited to C57BL/6J mice as C3H/HeJ mice exhibited a similar skeletal response. The beneficial effects of thermoneutral housing on cancellous bone were associated with decreased Ucp1 gene expression in brown adipose tissue, increased bone marrow adiposity, higher rates of bone formation, higher expression levels of osteogenic genes and locally decreased bone resorption.

CONCLUSIONS

Housing female mice at 22 °C resulted in premature cancellous bone loss. Failure to account for species differences in thermoregulation may seriously confound interpretation of studies utilizing mice as preclinical models for osteoporosis.

Preclinical In vivo Imaging for Fat Tissue Identification, Quantification, and Functional Characterization

Localization, differentiation, and quantitative assessment of fat tissues have always collected the interest of researchers. Nowadays, these topics are even more relevant as obesity (the excess of fat tissue) is considered a real pathology requiring in some cases pharmacological and surgical approaches. Several weight loss medications, acting either on the metabolism or on the central nervous system, are currently under preclinical or clinical investigation. Animal models of obesity have been developed and are widely used in pharmaceutical research. The assessment of candidate drugs in animal models requires non-invasive methods for longitudinal assessment of efficacy, the main outcome being the amount of body fat. Fat tissues can be either quantified in the entire animal or localized and measured in selected organs/regions of the body. Fat tissues are characterized by peculiar contrast in several imaging modalities as for example Magnetic Resonance Imaging (MRI) that can distinguish between fat and water protons thank to their different magnetic resonance properties. Since fat tissues have higher carbon/hydrogen content than other soft tissues and bones, they can be easily assessed by Computed Tomography (CT) as well. Interestingly, MRI also discriminates between white and brown adipose tissue (BAT); the latter has long been regarded as a potential target for anti-obesity drugs because of its ability to enhance energy consumption through increased thermogenesis. Positron Emission Tomography (PET) performed with 18F-FDG as glucose analog radiotracer reflects well the metabolic rate in body tissues and consequently is the technique of choice for studies of BAT metabolism. This review will focus on the main, non-invasive imaging techniques (MRI, CT, and PET) that are fundamental for the assessment, quantification and functional characterization of fat deposits in small laboratory animals. The contribution of optical techniques, which are currently regarded with increasing interest, will be also briefly described. For each technique the physical principles of signal detection will be overviewed and some relevant studies will be summarized. Far from being exhaustive, this review has the purpose to highlight some strategies that can be adopted for the in vivo identification, quantification, and functional characterization of adipose tissues mainly from the point of view of biophysics and physiology.

Perinatal Licensing of Thermogenesis by IL-33 and ST2

For placental mammals, the transition from the in utero maternal environment to postnatal life requires the activation of thermogenesis to maintain their core temperature. This is primarily accomplished by induction of uncoupling protein 1 (UCP1) in brown and beige adipocytes, the principal sites for uncoupled respiration. Despite its importance, how placental mammals license their thermogenic adipocytes to participate in postnatal uncoupled respiration is not known. Here, we provide evidence that the "alarmin" IL-33, a nuclear cytokine that activates type 2 immune responses, licenses brown and beige adipocytes for uncoupled respiration. We find that, in absence of IL-33 or ST2, beige and brown adipocytes develop normally but fail to express an appropriately spliced form of Ucp1 mRNA, resulting in absence of UCP1 protein and impairment in uncoupled respiration and thermoregulation. Together, these data suggest that IL-33 and ST2 function as a developmental switch to license thermogenesis during the perinatal period. PAPERCLIP.

Capsaicin induces browning of white adipose tissue and counters obesity by activating TRPV1 channel-dependent mechanisms

BACKGROUND AND PURPOSE

The growing epidemic of obesity and metabolic diseases necessitates the development of novel strategies to prevent and treat such diseases. Current research suggests that browning of white adipose tissue (WAT) promotes energy expenditure to counter obesity. Recent research suggests that activation of the TRPV1 channels counters obesity. However, the mechanism by which activation of TRPV1 channels counters obesity still remains unclear.

EXPERIMENTAL APPROACH

We evaluated the effect of dietary capsaicin to induce a browning program in WAT by activating TRPV1 channels to prevent diet-induced obesity using wild-type and TRPV1(-/-) mouse models. We performed experiments using preadipocytes and fat pads from these mice.

KEY RESULTS

Capsaicin stimulated the expression of brown fat-specific thermogenic uncoupling protein-1 and bone morphogenetic protein-8b in WAT. Capsaicin triggered browning of WAT by promoting sirtuin-1 expression and activity via TRPV1 channel-dependent elevation of intracellular Ca(2) (+) and phosphorylation of Ca(2) (+) /calmodulin-activated protein kinase II and AMP-activated kinase. Capsaicin increased the expression of PPARγ 1 coactivator α and enhanced metabolic and ambulatory activity. Further, capsaicin stimulated sirtuin-1-dependent deacetylation of PPARγ and the transcription factor PRDM-16 and facilitated PPARγ-PRDM-16 interaction to induce browning of WAT. Dietary capsaicin did not protect TRPV1(-/-) mice from obesity.

CONCLUSIONS AND INTERPRETATIONS

Our results show for the first time that activation of TRPV1 channels by dietary capsaicin triggers browning of WAT to counteract obesity. Our results suggest that activation of TRPV1 channels is a promising strategy to counter obesity.

Supraclavicular skin temperature and BAT activity in lean healthy adults

The 'gold standard' for measuring brown adipose tissue (BAT) in humans is [(18)F]FDG-PET/CT-imaging. With this technique subjects are exposed to ionizing radiation and are therefore limited in the number of scans that can be performed. We investigated the relation between supraclavicular skin temperatures and BAT activity values using a strictly temperature-controlled air-cooling protocol. Data of 36 male subjects was analyzed. BAT activity was evaluated by [(18)F]FDG-PET/CT-imaging and skin temperature was measured by means of wireless temperature sensors. Supraclavicular skin temperature dropped less compared to skin temperatures at other sites (all P values <0.01). A significant positive correlation was found between the change in supraclavicular skin temperature with BAT activity (R (2) 0.23), and the change in supraclavicular skin temperature and non-shivering thermogenesis (R (2) 0.18, both P values <0.01). The correlations indicate that supraclavicular skin temperature (changes) can potentially be used as a qualitative measure of BAT activity and BAT thermogenesis.

A worm of one's own: how helminths modulate host adipose tissue function and metabolism

Parasitic helminths have coexisted with human beings throughout time. Success in eradicating helminths has limited helminth-induced morbidity and mortality but is also correlated with increasing rates of 'western' diseases, including metabolic syndrome and type 2 diabetes. Recent studies in mice describe how type 2 immune cells, traditionally associated with helminth infection, maintain adipose tissue homeostasis and promote adipose tissue beiging, protecting against obesity and metabolic dysfunction. Here, we review these studies and discuss how helminths and helminth-derived molecules may modulate these physiologic pathways to improve metabolic functions in specific tissues, such as adipose and liver, as well as at the whole-organism level.

The gut microbiota in human energy homeostasis and obesity

Numerous studies of rodents suggest that the gut microbiota populations are sensitive to genetic and environmental influences, and can produce or influence afferent signals that directly or indirectly impinge on energy homeostatic systems affecting both energy balance (weight gain or loss) and energy stores. Fecal transplants from obese and lean human, and from mouse donors to gnotobiotic mice, result in adoption of the donor somatotype by the formerly germ-free rodents. Thus, the microbiota is certainly implicated in the development of obesity, adiposity-related comorbidities, and the response to interventions designed to achieve sustained weight reduction in mice. More studies are needed to determine whether the microbiota plays a similarly potent role in human body-weight regulation and obesity.

Regulation of brown fat by AMP-activated protein kinase

Novel strategies are needed to reduce the obesity epidemic. One promising strategy is activation of brown adipose tissue (BAT), either via the brain or directly, which increases energy expenditure by combustion of fatty acids (FAs) into heat. The enzyme complex AMP-activated protein kinase (AMPK) is crucially involved in energy metabolism and is highly expressed in both brain and BAT, regulating thermogenesis. As a general rule, BAT activity and energy expenditure are increased either by suppression of AMPK activity in the brain, resulting in enhanced sympathetic outflow towards BAT, or by activation of AMPK in BAT. Targeting AMPK may thus hold therapeutic potential for the treatment of obesity and related disorders.

Functional modification of adipocytes by grape seed extract impairs their pro-tumorigenic signaling on colon cancer stem cells and the daughter cancer cells

With global rise in obesity, it is imperative that we identify obesity-driven factors that increase growth and progression of colorectal cancer (CRC), and also discover and develop agents with anti-CRC efficacy under obese conditions. Here in, we investigated grape seed extract (GSE), a well-defined agent with both preventive and anti-CRC efficacy, for its potential to impair pro-tumorigenic signaling of adipocytes on CRC/colon cancer stem cells (CSCs) and associated molecular mechanisms, to control CRC under obese conditions. GSE treatment significantly decreased the growth and invasion promoting effects of both mouse and human adipocytes on CRC cells. Moreover, GSE exerted a direct inhibitory effect, as well as it strongly reduced the growth promoting signals of adipocytes, on colon CSCs. These GSE effects were associated with a decrease in both mRNA and protein levels of various CSC-associated molecules. Notably, GSE effects on adipocytes were not due to changes in lipid content, but by inducing the ‘browning’ of adipocytes as evidenced by an increase in UCP-1 mRNA level and mitochondriogenesis. Together, these findings, for the first time, suggest the ability of GSE to induce ‘brown remodeling’ of white adipocytes, which causes functional modification of adipocytes thus impairing their pro-tumorigenic signals on colon CSCs/CRC cells.

The future of brown adipose tissues in the treatment of type 2 diabetes

The recent recognition that humans possess active depots of brown adipose tissue has boosted the interest in this tissue as a potential target for the prevention and treatment of obesity and related metabolic disorders. Furthermore, it was also revealed that brown adipose tissue (BAT) in humans may consist of so-called beige or brite adipocytes. So far, cold exposure is recognised as the strongest activator of BAT in humans, but there is much ongoing research focused on finding alternative activators of BAT. The consequences of long-term BAT activation and/or cold exposure on metabolic health are still unknown, and this represents an area of intensive research. This is one of a series of commentaries under the banner '50 years forward', giving personal opinions on future perspectives in diabetes, to celebrate the 50th anniversary of Diabetologia (1965-2015).

Brown adipose tissue as a therapeutic target for human obesity

Brown adipose tissue (BAT) is the major site of sympathetically activated adaptive thermogenesis during cold exposure and after spontaneous hyperphagia, thereby controlling whole-body energy expenditure and body fat. Recent radionuclide studies have 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 is lower in older and obese individuals. The inverse relationship between the BAT activity and body fatness suggests that BAT, because of its energy dissipating activity, is protective against body fat accumulation. In fact, either repeated cold exposure or daily ingestion of some food ingredients acting on transient receptor potential channels recruited BAT in association with increased energy expenditure and decreased body fat even in individuals with low BAT activities before the treatment. Thus, BAT is a promising therapeutic target for combating human obesity and related metabolic disorders.

Circulating irisin concentrations in rat models of thyroid dysfunction -- effect of exercise

OBJECTIVES

The speculation that the myokine irisin could regulate whole body energy expenditure led to the anticipation that irisin may have therapeutic potential in metabolic diseases. Regulation of irisin under conditions of metabolic derangements in altered thyroid status, and the changes in irisin response to exercise remain to be investigated.

METHODS

Serum irisin concentration was measured in sixty male Wistar rats subjected to either sedentary life or 8-week chronic swimming exercise after induction of hyper- or hypothyroidism (10 rats/group). The effect of acute exercise on serum irisin was assessed in 10 additional rats subjected once to forced swimming against a load (5% of body weight) and compared to sedentary rats.

RESULTS

Serum irisin was significantly higher in both sedentary hyper- and hypothyroid rats (by 45%, p<0.001, and 30%, p<0.001, respectively) versus euthyroid controls. Serum irisin also increased after acute exercise (p<0.001 versus sedentary control). Chronic training episodes failed to significantly alter serum irisin in all thyroid hormone profiles. Serum irisin correlated positively with serum creatine kinase (r=0.45, p<0.001) and with muscle and liver concentrations of malondialdehyde (r=0.50 and r=0.47 respectively, p<0.001 for both), and negatively with muscle and liver content of reduced glutathione (r=-0.34, p=0.003 and r=-0.28, p=0.018 respectively) in pooled groups. However, significance of these associations was waived when analyzing each group separately. Serum irisin was not associated with skeletal muscle mass, insulin resistance, blood glucose, lipids or TSH.

CONCLUSIONS

Both hyper- and hypothyroidism are associated with up-regulation of serum irisin in male rats, possibly as a response to oxidative damage and/or myopathy observed in both conditions. Acute exercise, which is also associated with oxidative stress, increases serum irisin. No obvious association was detected linking serum irisin to metabolic abnormalities in thyroid dysfunction.