Brown adipose tissue improves whole-body glucose homeostasis and insulin sensitivity in humans

Fluvastatin Reduces Glucose Tolerance in Healthy Young Individuals Independently of Cold Induced BAT Activity

BACKGROUND

Statins are commonly prescribed for primary and secondary prevention of atherosclerotic disease. They reduce cholesterol biosynthesis by inhibiting hydroxymethylglutaryl-coenzyme A-reductase (HMG-CoA-reductase) and therefore mevalonate synthesis. Several studies reported a small, but significant increase in the diagnosis of diabetes mellitus with statin treatment. The molecular mechanisms behind this adverse effect are not yet fully understood. Brown adipose tissue (BAT), which plays a role in thermogenesis, has been associated with a reduced risk of insulin resistance. Statins inhibit adipose tissue browning and have been negatively linked to the presence of BAT in humans. We therefore speculated that inhibition of BAT by statins contributes to increased insulin resistance in humans.

METHODS

A prospective study was conducted in 17 young, healthy men. After screening whether significant cold-induced thermogenesis (CIT) was present, participants underwent glucose tolerance testing (oGTT) and assessment of BAT activity by FDG-PET/MRI after cold-exposure and treatment with a β3-agonist. Fluvastatin 2x40mg per day was then administered for two weeks and oGTT and FDG-PET/MRI were repeated.

RESULTS

Two weeks of fluvastatin treatment led to a significant increase in glucose area under the curve (AUC) during oGTT (p=0.02), reduction in total cholesterol and LDL cholesterol (both p<0.0001). Insulin AUC (p=0.26), resting energy expenditure (REE) (p=0.44) and diet induced thermogenesis (DIT) (p=0.27) did not change significantly. The Matsuda index, as an indicator of insulin sensitivity, was lower after fluvastatin intake, but the difference was not statistically significant (p=0.09). As parameters of BAT activity, mean standard uptake value (SUV_mean) (p=0.12), volume (p=0.49) and total glycolysis (p=0.74) did not change significantly during the intervention. Matsuda index, was inversely related to SUV_mean and the respiratory exchange ratio (RER) (both R^{2 =} 0.44, p=0.005) at baseline, but not after administration of fluvastatin (R^{2 =} 0.08, p=0.29, and R^{2 =} 0.14, p=0.16, respectively).

CONCLUSIONS

Treatment with fluvastatin for two weeks reduced serum lipid levels but increased glucose AUC in young, healthy men, indicating reduced glucose tolerance. This was not associated with changes in cold-induced BAT activity.

Peripheral Administration of NMU Promotes White Adipose Tissue Beiging and Improves Glucose Tolerance

PURPOSE

Targeting white adipose tissue (WAT) beiging has been proposed as an effective way to increase thermogenesis and improve glucose metabolism. Neuromedin U (NMU) is a neuropeptide that could increase energy expenditure, while its effects on WAT beiging and glucose homeostasis remain to be investigated.

METHODS

Male C57BL/6 mice were fed with high fat diet (HFD) to induce obesity and hyperglycemia and then treated with chronic subcutaneous injection of NMU. Body weight and food intake were recorded daily. After 14 days of injection, intraperitoneal glucose tolerance tests and 18F-fluorodeoxyglucose micro-positron emission tomography/computed tomography (18F-FDG micro-PET/CT) scans were conducted. Subcutaneous WAT (sWAT) and interscapular brown adipose tissue were collected for the evaluation of adipocyte size, expression of uncoupling protein 1 (Ucp1), and other thermogenic-related genes. Stromal vascular fraction of subcutaneous WAT was extracted for the measurement of type 2 innate lymphocytes (ILC2s) proportions.

RESULTS

Glucose tolerance was markedly improved by peripherally administered NMU. Micro-PET/CT suggested that NMU promoted WAT beiging, which was further confirmed by haematoxylin and eosin (H&E) staining and immunohistochemistry. In diet-induced-obese (DIO) mice, NMU activated thermogenic-related genes in WAT. In addition, NMU stimulated ILC2s in the stromal vascular fraction of WAT.

CONCLUSION

Taken together, our study indicates that peripheral administration of NMU is a potential therapeutic strategy for the promotion of WAT beiging and the improvement of impaired glucose tolerance.

Activated brown adipose tissue and its relationship to adiposity and metabolic markers: an exploratory study

Objective: To explore relationships between PET/CT characteristics of cold-activated brown adipose tissue (BAT), measures of adiposity and metabolic markers.Methods: We conducted a post-hoc analysis of a study which utilized PET/CT to characterize BAT. 25 men ages 18-24 (BMI 19.4 to 35.9 kg/m2) were studied. Fasting blood samples were collected. Body composition was measured using DXA. An individualized cooling protocol was utilized to activate BAT prior to imaging with PET/CT.Results: There was an inverse relationship between fasting serum glucose and BAT volume (r = -0.40, p = 0.048). A marginally significant inverse relationship was also noted between fasting glucose and total BAT activity (r = -0.40, p = 0.05). In addition, a positive correlation was observed between serum FGF21 and SUVmax (r = 0.51, p = 0.01). No significant correlations were noted for measures of BAT activity or volume and other indicators of adiposity or glucose metabolism.Conclusions: The presence of active BAT may be associated with lower fasting glucose in young men. BAT activity may also be correlated with levels of FGF21, suggesting that BAT may lower glucose levels via an FGF21 dependent pathway. Further studies are needed to clarify mechanisms by which BAT may impact glucose metabolism.

Relationship between environmental temperature and the diagnosis and treatment of gestational diabetes mellitus: An observational retrospective study

INTRODUCTION

Environmental temperature has been described to affect plasma glucose levels after oral glucose tolerance testing (OGTT).

AIMS

We evaluated the relationship between seasons and environmental temperature and gestational diabetes mellitus (GDM) diagnosis and treatment.

METHODS

We analyzed data from 2374 women retrospectively. GDM was diagnosed in 473 patients by a 100-g OGTT. OGTT results and needing of insulin therapy were evaluated in relation to seasons and environmental temperature (mean temperature and temperature change) the day of the OGTT and the preceding 14 and 28 days.

RESULTS

We found significant seasonal differences in the percentage of GDM: 24.4% in summer vs. 15.6% in autumn (p < 0.01). The odds ratio (OR) for being diagnosed with GDM was 1.78 in summer relative to autumn, after controlling for age. A higher mean temperature the day of the OGTT and the preceding 14 and 28 days increased the risk of being diagnosed with GDM the months in which temperature was rising (March-August) but not the months in which temperature was decreasing (September-February). We observed a negative correlation between temperature and fasting glucose and a positive correlation with post-load glucose. Neither the season nor the environmental temperature affected the risk of requiring insulin therapy.

CONCLUSIONS

There is a higher prevalence of GDM diagnosis at warmer seasons and at rising temperatures the 2-4 weeks prior to the OGTT. The impact of temperature is different between fasting and post-load glucose.

Peripheral Innervation in the Regulation of Glucose Homeostasis

Precise regulation of circulating glucose is crucial for human health and ensures a sufficient supply to the brain, which relies almost exclusively on glucose for metabolic energy. Glucose homeostasis is coordinated by hormone-secreting endocrine cells in the pancreas, as well as glucose utilization and production in peripheral metabolic tissues including the liver, muscle, and adipose tissue. Glucose-regulatory tissues receive dense innervation from sympathetic, parasympathetic, and sensory fibers. In this review, we summarize the functions of peripheral nerves in glucose regulation and metabolism. Dynamic changes in peripheral innervation have also been observed in animal models of obesity and diabetes. Together, these studies highlight the importance of peripheral nerves as a new therapeutic target for metabolic disorders.

Control of Adipose Cell Browning and Its Therapeutic Potential

Adipose tissue is the largest endocrine organ in humans and has an important influence on many physiological processes throughout life. An increasing number of studies have described the different phenotypic characteristics of fat cells in adults. Perhaps one of the most important properties of fat cells is their ability to adapt to different environmental and nutritional conditions. Hypothalamic neural circuits receive peripheral signals from temperature, physical activity or nutrients and stimulate the metabolism of white fat cells. During this process, changes in lipid inclusion occur, and the number of mitochondria increases, giving these cells functional properties similar to those of brown fat cells. Recently, beige fat cells have been studied for their potential role in the regulation of obesity and insulin resistance. In this context, it is important to understand the embryonic origin of beige adipocytes, the response of adipocyte to environmental changes or modifications within the body and their ability to transdifferentiate to elucidate the roles of these cells for their potential use in therapeutic strategies for obesity and metabolic diseases. In this review, we discuss the origins of the different fat cells and the possible therapeutic properties of beige fat cells.

Sinapic acid induces the expression of thermogenic signature genes and lipolysis through activation of PKA/CREB signaling in brown adipocytes

Lipid accumulation in white adipose tissue is the key contributor to the obesity and orchestrates numerous metabolic health problems such as type 2 diabetes, hypertension, atherosclerosis, and cancer. Nonetheless, the prevention and treatment of obesity are still inadequate. Recently, scientists found that brown adipose tissue (BAT) in adult humans has functions that are diametrically opposite to those of white adipose tissue and that BAT holds promise for a new strategy to counteract obesity. In this study, we evaluated the potential of sinapic acid (SA) to promote the thermogenic program and lipolysis in BAT. SA treatment of brown adipocytes induced the expression of brown-adipocyte activation–related genes such as Ucp1, Pgc-1α, and Prdm16. Furthermore, structural analysis and western blot revealed that SA upregulates protein kinase A (PKA) phosphorylation with competitive inhibition by a pan-PKA inhibitor, H89. SA binds to the adenosine triphosphate (ATP) site on the PKA catalytic subunit where H89 binds specifically. PKA-cat-α1 gene–silencing experiments confirmed that SA activates the thermogenic program via a mechanism involving PKA and cyclic AMP response element–binding protein (CREB) signaling. Moreover, SA treatment promoted lipolysis via a PKA/p38-mediated pathway. Our findings may allow us to open a new avenue of strategies against obesity and need further investigation.

A comparative genomics multitool for scientific discovery and conservation

The Zoonomia Project is investigating the genomics of shared and specialized traits in eutherian mammals. Here we provide genome assemblies for 131 species, of which all but 9 are previously uncharacterized, and describe a whole-genome alignment of 240 species of considerable phylogenetic diversity, comprising representatives from more than 80% of mammalian families. We find that regions of reduced genetic diversity are more abundant in species at a high risk of extinction, discern signals of evolutionary selection at high resolution and provide insights from individual reference genomes. By prioritizing phylogenetic diversity and making data available quickly and without restriction, the Zoonomia Project aims to support biological discovery, medical research and the conservation of biodiversity.

A whole-genome alignment of 240 phylogenetically diverse species of eutherian mammal—including 131 previously uncharacterized species—from the Zoonomia Project provides data that support biological discovery, medical research and conservation.

Spermidine ameliorates high-fat diet-induced hepatic steatosis and adipose tissue inflammation in preexisting obese mice

AIMS

The therapeutic effects of spermidine on preexisting obese mice have been not fully elucidated. In this study, we assessed the anti-obesity impact of spermidine on high-fat diet (HFD)-induced obese mice.

MAIN METHODS

C57BL/6J mice were fed a HFD for 16 weeks to induce obesity, and then treated with or without spermidine via drinking water for additional 8 weeks. The contributions of spermidine in regulating obesity phenotypes and metabolic syndrome were further evaluated.

KEY FINDINGS

Spermidine administration lowered fat mass and plasma lipid profile in HFD-induced obese mice without affecting body weight. In addition, spermidine attenuated hepatic steatosis by regulating lipid metabolism and enhancing antioxidant capacity. Moreover, spermidine reduced adipose tissue inflammation by decreasing inflammatory cytokine and chemokines expression, and these results might contributed to the enhanced thermogenic gene expression in brown adipose tissue. Furthermore, spermidine treatment enhanced gut barrier function by up-regulating tight junction- and mucin-related gene expression.

SIGNIFICANCE

Spermidine-mediated protective impacts involve the regulation of lipid metabolism, inflammation response, gut barrier function and thermogenesis. These findings demonstrate that spermidine has potentials in treating obesity.

FGF15/19 is required for adipose tissue plasticity in response to thermogenic adaptations

Objective

To determine the role of enterokine FGF15/19 in adipose tissue thermogenic adaptations.

Methods

Circulating FGF19 and gene expression (qRT-PCR) levels were assessed in subcutaneous adipose tissue from obese human patients. Effects of experimentally increased FGF15 and FGF19 levels in vivo were determined in mice using adenoviral and adeno-associated vectors. Adipose tissues were characterized in FGF15-null mice under distinct cold-related thermogenic challenges. The analyses spanned metabolic profiling, tissue characterization, histology, gene expression, and immunoblot assays.

Results

In humans, FGF19 levels are directly associated with UCP1 gene expression in subcutaneous adipose tissue. Experimental increases in FGF15 or FGF19 induced white fat browning in mice as demonstrated by the appearance of multilocular beige cells and markers indicative of a beige phenotype, including increased UCP1 protein levels. Mice lacking FGF15 showed markedly impaired white adipose tissue browning and a mild reduction in parameters indicative of BAT activity in response to cold-induced environmental thermogenic challenges. This was concomitant with signs of altered systemic metabolism, such as reduced glucose tolerance and impaired cold-induced insulin sensitization.

Conclusions

Enterokine FGF15/19 is a key factor required for adipose tissue plasticity in response to thermogenic adaptations.

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Circulating FGF19 levels correlate positively with signs of fat browning in humans.

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Adaptive adipose tissue browning in response to cold is impaired in mice lacking FGF15.

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Experimentally induced increase in FGF15 or FGF19 promotes fat browning in mice.

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FGF15/19 signaling is required for thermogenic challenge-induced plasticity of adipose tissue.

Total-body PET Imaging: A New Frontier for the Assessment of Metabolic Disease and Obesity

Obesity and associated metabolic syndrome are a global public health issue. Understanding the pathophysiology of this systemic disease is of critical importance for the development of future therapeutic interventions to improve clinical outcomes. The multiorgan nature of the pathophysiology of obesity presents a unique challenge. Total-body PET imaging, either static or dynamic, provides a vital set of tools to study organ crosstalk. The visualization and quantification of tissue metabolic kinetics with total-body PET in health and disease provides essential information to better understand disease physiology and potentially develop diagnostic and therapeutic modalities.

Lipid Droplets in Brown Adipose Tissue Are Dispensable for Cold-Induced Thermogenesis

Brown adipocytes store metabolic energy as triglycerides (TGs) in lipid droplets (LDs). Fatty acids released from brown adipocyte LDs by lipolysis are thought to activate and fuel UCP1-mediated thermogenesis. Here, we test this hypothesis by preventing fatty acid storage in murine brown adipocytes through brown adipose tissue (BAT)-specific deletions of the TG synthesis enzymes DGAT1 and DGAT2 (BA-DGAT KO). Despite the absence of TGs in brown adipocytes, BAT is functional, and BA-DGAT-KO mice maintain euthermia during acute or chronic cold exposure. As apparent adaptations to the lack of TG, brown adipocytes of BA-DGAT-KO mice appear to use circulating glucose and fatty acids, and stored glycogen, to fuel thermogenesis. Moreover, BA-DGAT-KO mice are resistant to diet-induced glucose intolerance, likely because of increased glucose disposal by BAT. We conclude that TGs in BAT are dispensable for its contribution to cold-induced thermogenesis, at least when other fuel sources are available.

Brown adipose tissue recruitment in a rodent model of severe burns

BACKGROUND

Severe burns results in a prolonged hypermetabolic response. Brown adipose tissue (BAT), abundant in uncoupling protein 1 (UCP1), plays a key role in non-shivering thermogenesis. We set out to determine if BAT is recruited in response to severe burns.

METHODS

Male balb-c mice underwent scald burns on approximately 20-25% of their total body surface. BAT was harvested from the interscapular fat pad of sham and burned mice at 3h, 24h, 4 days, and 10 days after injury. High-resolution respirometry was used to determine mitochondrial respiratory function in BAT. BAT protein concentration, and mitochondrial enzyme activity were also determined.

RESULTS

Respiration increased in BAT of burned mice, peaking at 24h after injury (after injury, P<0.001). While UCP1 independent respiration was not significantly altered by burn, UCP1 dependent respiration increased >2-fold at 24h after injury when compared to the 3h and sham group (P<0.01). Normalized to citrate synthase activity, total uncoupled (P<0.05) and UCP1 dependent (P<0.01) respiration remained elevated at 24h after injury.

CONCLUSIONS

We show a time-dependent recruitment of rodent BAT in response to severe burns. Given recent reports that humans, including patients with severe burns, have functional BAT, these data support a role for BAT in the hypermetabolic response to severe burns.

Aging and Immunometabolic Adaptations to Thermogenesis

Brown and subcutaneous adipose tissues play a key role in non-shivering thermogenesis both in mice and human, and their activation by adrenergic stimuli promotes energy expenditure, reduces adiposity, and protects against age-related metabolic diseases such as type 2 diabetes (T2D). Low-grade inflammation and insulin resistance characterize T2D. Even though the decline of thermogenic adipose tissues is well-established during ageing, the mechanisms by which this event affects immune system and contributes to the development of T2D is still poorly defined. It is emerging that activation of thermogenic adipose tissues promotes type 2 immunity skewing, limiting type 1 inflammation. Of note, metabolic substrates sustaining type 1 inflammation (e.g. glucose and succinate) are also used by activated adipocytes to promote thermogenesis. Keeping in mind this aspect, a nutrient competition between adipocytes and adipose tissue immune cell infiltrates could be envisaged. Herein, we reviewed the metabolic rewiring of adipocytes during thermogenesis in order to give important insight into the anti-inflammatory role of thermogenic adipose tissues and delineate how their decline during ageing may favor the setting of low-grade inflammatory states that predispose to type 2 diabetes in elderly. A brief description about the contribution of adipokines secreted by thermogenic adipocytes in modulation of immune cell activation is also provided. Finally, we have outlined experimental flow chart procedures and provided technical advices to investigate the physiological processes leading to thermogenic adipose tissue impairment that are behind the immunometabolic decline during aging.

Decreased UCP-1 expression in beige adipocytes from adipose-derived stem cells of type 2 diabetes patients associates with mitochondrial ROS accumulation during obesity

OBJECTIVE

Adipose derived stem cells (ADSC) are defective in metabolic disorders in various functionalities and properties including differentiation, multipotent state, metabolism and immunomodulation. However, the role of ADSC beiging potential in promoting of type 2 diabetes mellitus (T2DM) development remains unclear. Here we uncover association between potential of subcutaneous ADSC to beige differentiation and T2DM in patients with obesity.

METHODS

ADSC were isolated from subcutaneous adipose tissue of patients with long morbid obesity (BMI > 35 kg/m2) and normal glucose tolerance (NGT) or T2DM. ADSC were differentiated into white or beige adipocytes and levels of thermogenic markers, lipid metabolism and electron transport chain (ETC) genes was analyzed by Western blotting and RT-PCR. ROS production was estimated by fluorescent microscopy.

RESULTS

We have shown decreased UCP-1 expression in beige adipocytes from T2DM patients. Nevertheless, signal and expression activities of lipolysis were equal in NGT and T2DM beige adipocytes. Expression analysis of ETC genes also has not shown any statistically significant differences. Interestingly, we revealed increased mitochondrial ROS production in T2DM beige adipocytes during beige differentiation.

CONCLUSIONS

In summary, compromised UCP1 expression in beige adipocytes of T2DM patients may cause increase of mitochondrial ROS. Elevated oxidative level is liable to act as damaging mechanism leading to insulin resistance or, alternatively, serve as compensatory mechanism for thermogenesis activation.

Dot1l interacts with Zc3h10 to activate Ucp1 and other thermogenic genes

Brown adipose tissue is a metabolically beneficial organ capable of dissipating chemical energy into heat, thereby increasing energy expenditure. Here, we identify Dot1l, the only known H3K79 methyltransferase, as an interacting partner of Zc3h10 that transcriptionally activates the Ucp1 promoter and other BAT genes. Through a direct interaction, Dot1l is recruited by Zc3h10 to the promoter regions of thermogenic genes to function as a coactivator by methylating H3K79. We also show that Dot1l is induced during brown fat cell differentiation and by cold exposure and that Dot1l and its H3K79 methyltransferase activity is required for thermogenic gene program. Furthermore, we demonstrate that Dot1l ablation in mice using Ucp1-Cre prevents activation of Ucp1 and other target genes to reduce thermogenic capacity and energy expenditure, promoting adiposity. Hence, Dot1l plays a critical role in the thermogenic program and may present as a future target for obesity therapeutics.

Functional characterization of human brown adipose tissue metabolism

Brown adipose tissue (BAT) has long been described according to its histological features as a multilocular, lipid-containing tissue, light brown in color, that is also responsive to the cold and found especially in hibernating mammals and human infants. Its presence in both hibernators and human infants, combined with its function as a heat-generating organ, raised many questions about its role in humans. Early characterizations of the tissue in humans focused on its progressive atrophy with age and its apparent importance for cold-exposed workers. However, the use of positron emission tomography (PET) with the glucose tracer [18F]fluorodeoxyglucose ([18F]FDG) made it possible to begin characterizing the possible function of BAT in adult humans, and whether it could play a role in the prevention or treatment of obesity and type 2 diabetes (T2D). This review focuses on the in vivo functional characterization of human BAT, the methodological approaches applied to examine these features and addresses critical gaps that remain in moving the field forward. Specifically, we describe the anatomical and biomolecular features of human BAT, the modalities and applications of non-invasive tools such as PET and magnetic resonance imaging coupled with spectroscopy (MRI/MRS) to study BAT morphology and function in vivo, and finally describe the functional characteristics of human BAT that have only been possible through the development and application of such tools.

Seasonality of gestational diabetes mellitus and maternal blood glucose levels: Evidence from Taiwan

Previous studies have indicated that the prevalence of gestational diabetes mellitus (GDM) was related to the season. However, there was no relevant information in Asia. The aim of this study was to determine whether there was seasonality of GDM and maternal blood glucose level in Taiwanese women.A total of 6396 pregnancies were enrolled between 2012 and 2014 in this retrospective study. A 2-step approach according to the Carpenter-Coustan criteria was used for GDM diagnosis. A generalized linear mixed model was used to estimate the effect of season on GDM diagnosis by adjusting for age, prepregnancy body mass index, parity, history of GDM, fetal sex, and the rate of weight gain.During the study period, 418 (6.5%) pregnancies were diagnosed as GDM. The model demonstrated an increased prevalence of GDM in spring and summer (odds ratio: 1.59, 95% confidence interval: 1.13-2.24; odds ratio: 1.59, 95% confidence interval: 1.14-2.23, respectively) compared to winter. For the glucose level variation, the model demonstrated an increase of 2.56 mg/dL glucose in the 50-g glucose challenge test in summer compared to winter. In glucose challenge test-positive pregnancies, the season also had an effect on the results of the 100-g 1-h, 2-h, and 3-h oral glucose tolerance tests, but no effect on the 100-g fasting oral glucose tolerance tests.GDM prevalence in Taiwan presents seasonal variation, with the highest risk during spring and summer due to post-glucose load level variations. These findings could serve as reference data for countries in Southeast Asia or areas with a similar climate.

Brown Adipose Expansion and Remission of Glycemic Dysfunction in Obese SM/J Mice

We leverage the SM/J mouse to understand glycemic control in obesity. High-fat-fed SM/J mice initially develop poor glucose homeostasis relative to controls. Strikingly, their glycemic dysfunction resolves by 30 weeks of age despite persistent obesity. The mice dramatically expand their brown adipose depots as they resolve glycemic dysfunction. This occurs naturally and spontaneously on a high-fat diet, with no temperature or genetic manipulation. Removal of the brown adipose depot impairs insulin sensitivity, indicating that the expanded tissue is functioning as an insulin-stimulated glucose sink. We describe morphological, physiological, and transcriptomic changes that occur during the brown adipose expansion and remission of glycemic dysfunction, and focus on Sfrp1 (secreted frizzled-related protein 1) as a compelling candidate that may underlie this phenomenon. Understanding how the expanded brown adipose contributes to glycemic control in SM/J mice will open the door for innovative therapies aimed at improving metabolic complications in obesity.

Contribution of perfusion to the 11 C-acetate signal in brown adipose tissue assessed by DCE-MRI and 68 Ga-DOTA PET in a rat model

PURPOSE

Determine if dynamic contrast enhanced (DCE) -MRI and/or 68 gallium 1,4,7,10-tetraazacyclododecane N, N', N″, N‴-tretraacetic acid (⁶⁸ Ga-DOTA) positron emission tomography (PET) can assess perfusion in rat brown adipose tissue (BAT). Evaluate changes in perfusion between cold-stimulated and heat-inhibited BAT. Determine if the ¹¹ C-acetate pharmacokinetic model can be constrained with perfusion information to improve assessment of BAT oxidative metabolism.

METHODS

Rats were split into three groups. In group 1 (N = 6), DCE-MRI with gadobutrol was compared directly to ⁶⁸ Ga-DOTA PET following exposure to 10 °C for 48 h. ¹¹ C-Acetate PET was also performed to assess oxidation. In group 2 (N = 4), only ⁶⁸ Ga-DOTA PET was acquired following exposure to 10 °C for 48 h. Finally, in group 3 (N = 10), perfusion was assessed with DCE-MRI in rats exposed to 10 °C or 30 °C for 48 h, and oxidation was measured with ¹¹ C-acetate. Perfusion was quantified with a two-compartment pharmacokinetic model, while oxidation was assessed by a four-compartment model.

RESULTS

DCE-MRI and ⁶⁸ Ga-DOTA PET provided similar perfusion measures, but a decrease in the perfusion signal was noted with longer imaging sessions. Exposure to 10 °C or 30 °C did not affect the perfusion measures, but the ¹¹ C-acetate signal increased in BAT at 10 °C. Without prior information about blood volume, the ¹¹ C-acetate compartment model overestimated blood volume and underestimated oxidation in 10 °C BAT.

CONCLUSION

Precise assessment of oxidation via ¹¹ C-acetate PET requires prior information about blood volume which can be obtained by DCE-MRI or ⁶⁸ Ga-DOTA PET. Since perfusion can change rapidly, simultaneous PET-MRI would be preferred.

Plasma Docosahexaenoic Acid and Eicosapentaenoic Acid Concentrations Are Positively Associated with Brown Adipose Tissue Activity in Humans

Brown adipose tissue (BAT) activation is a possible therapeutic strategy to increase energy expenditure and improve metabolic homeostasis in obesity. Recent studies have revealed novel interactions between BAT and circulating lipid species—in particular, the non-esterified fatty acid (NEFA) and oxylipin lipid classes. This study aimed to identify individual lipid species that may be associated with cold-stimulated BAT activity in humans. A panel of 44 NEFA and 41 oxylipin species were measured using mass-spectrometry-based lipidomics in the plasma of fourteen healthy male participants before and after 90 min of mild cold exposure. Lipid measures were correlated with BAT activity measured via ¹⁸F-fluorodeoxyglucose ([¹⁸F]FDG) positron emission tomography/computed tomography (PET/CT), along with norepinephrine (NE) concentration (a surrogate marker of sympathetic activity). The study identified a significant increase in total NEFA concentration following cold exposure that was positively associated with NE concentration change. Individually, 33 NEFA and 11 oxylipin species increased significantly in response to cold exposure. The concentration of the omega-3 NEFA, docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) at baseline was significantly associated with BAT activity, and the cold-induced change in 18 NEFA species was significantly associated with BAT activity. No significant associations were identified between BAT activity and oxylipins.

Intact vitamin A transport is critical for cold-mediated adipose tissue browning and thermogenesis

Objective

Transformation of white into brown fat (“browning”) reduces obesity in many preclinical models and holds great promise as a therapeutic concept in metabolic disease. Vitamin A metabolites (retinoids) have been linked to thermogenic programming of adipose tissue; however, the physiologic importance of systemic retinoid transport for adipose tissue browning and adaptive thermogenesis is unknown.

Methods

We performed cold exposure studies in mice and humans and used a genetic model of defective vitamin A transport, the retinol binding protein deficient (Rbp^−/-) mouse, to study the effects of cooling on systemic vitamin A and the relevance of intact retinoid transport on cold-induced adipose tissue browning.

Results

We show that cold stimulation in mice and humans leads to an increase in circulating retinol and its plasma transporter, Rbp. In Rbp^−/- mice, thermogenic programming of adipocytes and oxidative mitochondrial function are dramatically impaired in subcutaneous white fat, which renders Rbp^−/- mice more cold-sensitive. In contrast, retinol stimulation in primary human adipocytes promotes thermogenic gene expression and mitochondrial respiration. In humans, cold-mediated retinol increase is associated with a shift in oxidative substrate metabolism suggestive of higher lipid utilisation.

Conclusions

Systemic vitamin A levels are regulated by cold exposure in mice and humans, and intact retinoid transport is essential for cold-induced adipose tissue browning and adaptive thermogenesis.

Pinealectomy increases thermogenesis and decreases lipogenesis

The present study was designed to determine the effects of pineal gland-derived melatonin on obesity by employing a rat pinealectomy (Pnx) model. After 10 weeks of a high-fat diet, rats received sham or Pnx surgery followed by a normal chow diet for 10 weeks. Reverse transcription-quantitative PCR, western blotting analysis, immunohistochemistry and ELISA were used to determine the effects of Pnx. Pnx decreased the expression of melatonin receptor (MTNR)1A and MTNR1B, in brown adipose tissues (BAT) and white adipose tissues (WAT). Pnx rats showed increased insulin sensitivity compared with those that received sham surgery. Leptin levels were significantly decreased in the serum of the Pnx group. In addition, Pnx stimulated thermogenic genes in BAT and attenuated lipogenic genes in both WAT and the liver. Histological analyses revealed a marked decrease in the size of lipid droplets and increased expression of uncoupling protein 1 in BAT. In the liver of the Pnx group, the size and number of lipid droplets had also decreased. In conclusion, the results presented in the current study suggested that Pnx increases thermogenesis in BAT and decreases lipogenesis in WAT and the liver.

Effects of Nutrition/Diet on Brown Adipose Tissue in Humans: A Systematic Review and Meta-Analysis

BACKGROUND

Brown adipose tissue (BAT) provides a minor contribution to diet-induced thermogenesis (DIT)-the metabolic response to food consumption. Increased BAT activity is generally considered beneficial for mammalian metabolism and has been associated with favorable health outcomes. The aim of the current systematic review was to explore whether nutritional factors and/or diet affect human BAT activity.

METHODS

We searched PubMed Central, Embase and Cochrane Library (trials) to conduct this systematic review (PROSPERO protocol: CRD42018082323).

RESULTS

We included 24 eligible papers that studied a total of 2785 participants. We found no mean differences in standardized uptake value of BAT following a single meal or after 6 weeks of L-Arginine supplementation. Resting energy expenditure (REE), however, was increased following a single meal and after supplementation of capsinoid and catechin when compared to a control condition (Z = 2.41, p = 0.02; mean difference = 102.47 (95% CI = 19.28-185.67)).

CONCLUSIONS

Human BAT activity was not significantly affected by nutrition/diet. Moreover, REE was only increased in response to a single meal, but it is unlikely that this was due to increased BAT activity. BAT activity assessments in response to the chronic effect of food should be considered along with other factors such as body composition and/or environmental temperature.

KMT5c modulates adipocyte thermogenesis by regulating Trp53 expression

Brown and beige adipocytes harbor the thermogenic capacity to adapt to environmental thermal or nutritional changes. Histone methylation is an essential epigenetic modification involved in the modulation of nonshivering thermogenesis in adipocytes. Here, we describe a molecular network leading by KMT5c, a H4K20 methyltransferase, that regulates adipocyte thermogenesis and systemic energy expenditure. The expression of Kmt5c is dramatically induced by a β3-adrenergic signaling cascade in both brown and beige fat cells. Depleting Kmt5c in adipocytes in vivo leads to a decreased expression of thermogenic genes in both brown and subcutaneous (s.c.) fat tissues. These mice are prone to high-fat-diet-induced obesity and develop glucose intolerance. Enhanced transformation related protein 53 (Trp53) expression in Kmt5c knockout (KO) mice, that is due to the decreased repressive mark H4K20me3 on its proximal promoter, is responsible for the metabolic phenotypes. Together, these findings reveal the physiological role for KMT5c-mediated H4K20 methylation in the maintenance and activation of the thermogenic program in adipocytes.

Mulberry Leaf Flavonoids Improve Milk Production, Antioxidant, and Metabolic Status of Water Buffaloes

This study was aimed to evaluate the effect of mulberry leaf flavonoids (MLF) on oxidative stress, metabolic hormones, and milk production in Murrah buffaloes. Forty multiparous Murrah buffaloes (4 ± 1 lactations) with similar body weight (average 600 ± 50 Kg) and stage of lactation (90 ± 20 d) were randomly selected for this trial. Four treatment groups (10 buffaloes per group) with different doses of MLF included; control (0 g/d), MLF15 (15 g/d), MLF30 (30 g/d), and MLF45 (45 g/d). Buffaloes were fed with total mix ration consisting of grass (Pennisetum purpureum schum), brewery's grain and concentrate mixture for 5 weeks. Meteorological data including ambient temperature and relative humidity were recorded using the online dust monitoring system to calculate temperature-humidity index (THI). After 1 week of the adaptation, milk yield was recorded daily while physiological parameters (respiratory rate, rectal, and body surface temperature), and milk composition were measured weekly. At the end of the trial, blood samples were collected to analyze serum metabolic hormones including estradiol (E2), growth hormone (GH), prolactin (PRL), Tri-iodothyronine (T3), and Thyroxine (T4). Moreover, serum heat shock proteins (HSP), antioxidants enzymes including malondialdehyde (MDA), total antioxidant capacity (T-AOC), superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GSH-Px) and blood biochemical indices were also analyzed. Results revealed a decrease (P = 0.012) in serum MDA level while increasing (P < 0.01) the HSP and serum GHS-Px contents in supplemented buffaloes. Treatment showed a linear and quadratic decrease (p = 0.001) in the serum T-AOC while reducing CAT contents linearly (p = 0.012) as compared to the control. However, no effect of treatment on serum SOD content was observed. Treatment resulted a linear increase (p = 0.001) in serum GH and PRL hormones while increasing serum E2 levels linearly (P < 0.001) and quadratically (P = 0.025). Treatment increased (p = 0.038) the daily milk yield as compared to the control. However, increase (P < 0.05) in serum T3 and T4 contents, fat corrected milk (4%) and milk protein (%) was observed only in MLF45. Moreover, we observed no change in serum biochemical indices except insulin which linearly increased (p = 0.002) in MLF45. Our findings indicated that MLF at 45 g per day is an appropriate level to enhance milk performance and alleviate heat stress in buffaloes.

Molecular insights into therapeutic promise of targeting of Wnt/β-catenin signaling pathway in obesity

Obesity is a curable disorder which is a global health concern, linked to an excess amount of fat. It is caused by inherited and environmental factors and can be grim to maintain through dieting only. The importance of peculiar Wnt/β-catenin signaling has directed considerable efforts in the future production of therapeutic approaches in metabolic complications, including obesity. The article aims to examine the prospects of Wnt/β-catenin signaling cascade in obesity via directing effects of Wnt/β-catenin cascade in regulating appetite. A deep research on the literature available to date, for Wnt/β-catenin cascade in obesity is conducted using various medical databases like PubMed, MEDLINE from the internet. The articles published in English language were mainly preferred. Obesity has developed endemic worldwide, which initiates various obesity-related comorbidities. Obesity is implied by excessive deposition of fat primarily in the adipose tissue. Numerous studies have shown the vital impact of the Wnt/β-catenin signaling pathway in the growth of body part and biological homeostasis, while latent data illustrate the inherited variations in the Wnt/β-catenin cascade, correlating to several complications. The current article enlightens the stimulation of the Wnt/β-catenin cascade in obesity, mainly depot-explicit impact among adipose tissue during high caloric intake regulation and WAT browning event. Taken all together these data illustrate Wnt/β-catenin signaling cascade subsidizes to obesity promoted insulin resistance independent proliferation of adipose tissue.

Hypothalamic CDK4 regulates thermogenesis by modulating sympathetic innervation of adipose tissues

This study investigated the role of CDK4 in the oxidative metabolism of brown adipose tissue (BAT). BAT from Cdk4^−/− mice exhibited fewer lipids and increased mitochondrial volume and expression of canonical thermogenic genes, rendering these mice more resistant to cold exposure. Interestingly, these effects were not BAT cell‐autonomous but rather driven by increased sympathetic innervation. In particular, the ventromedial hypothalamus (VMH) is known to modulate BAT activation via the sympathetic nervous system. We thus examined the effects of VMH neuron‐specific Cdk4 deletion. These mice display increased sympathetic innervation and enhanced cold tolerance, similar to Cdk4^−/− mice, in addition to browning of scWAT. Overall, we provide evidence showing that CDK4 modulates thermogenesis by regulating sympathetic innervation of adipose tissue depots through hypothalamic nuclei, including the VMH. This demonstrates that CDK4 not only negatively regulates oxidative pathways, but also modulates the central regulation of metabolism through its action in the brain.

Lipocalin-2 deficiency may predispose to the progression of spontaneous age-related adiposity in mice

Lipocalin-2 (Lcn2) is an innate immune protein elevated by several orders of magnitude in various inflammatory conditions including aging and obesity. Recent studies have shown that Lcn2 is secreted by adipocytes in response to inflammation and is categorized as a new adipokine cross-linking innate immunity and metabolic disorders including obesity. However, the involvement of Lcn2 and its function during the progression of obesity is largely unknown. Recently, browning of white adipose tissue (WAT) has gained attention as a therapeutic strategy to combat obesity. Herein, we have shown that treatment of mature 3T3-L1 adipocytes with recombinant Lcn2 (rec-Lcn2) resulted in the up-regulation of thermogenic and beige/brown markers (UCP1, PRDM16, ZIC-1 and TBX1) and increased mitochondrial activity. Additionally, global Lcn2 genetic knockout (Lcn2KO) mice exhibited accelerated weight gain and visceral fat deposition with age, when compared to wild type (WT) mice. Taken together, both in vitro and in vivo studies suggest that Lcn2 is a naturally occurring adipokine, and may serve as an anti-obesity agent by upregulating the thermogenic markers resulting in the browning of WAT. Therefore, Lcn2 and its downstream signaling pathways could be a potential therapeutic target for obesity.

Loss of Uncoupling Protein 3 Attenuates Western Diet-Induced Obesity, Systemic Inflammation, and Insulin Resistance in Rats

OBJECTIVE

Uncoupling protein 3 (UCP3) is a mitochondrial carrier related to fatty acid metabolism. Although gene variants of UCP3 are associated with human obesity, their contribution to increased adiposity remains unclear. This study investigated the impact that loss of UCP3 has on diet-induced obesity in rats.

METHODS

Male UCP3 knockout rats (ucp3^-/- ) and wild-type littermates (ucp3^+/+ ) were fed a high-fat, high-carbohydrate Western diet for 21 weeks. Body composition was analyzed by EchoMRI. Whole-body insulin sensitivity and rates of tissue glucose uptake were determined by using hyperinsulinemic-euglycemic clamp. Changes in tissue physiology were interrogated by microscopy and RNA sequencing.

RESULTS

Loss of UCP3 decreased fat mass gain, white adipocytes size, and systemic inflammation. The ucp3^-/- rats also exhibited preserved insulin sensitivity and increased glucose uptake in interscapular brown adipose tissue (iBAT). Brown adipocytes from ucp3^-/- rats were protected from cellular degeneration caused by lipid accumulation and from reactive oxygen species-induced protein sulfonation. Increased glutathione levels in iBAT from ucp3^-/- rats were linked to upregulation of genes encoding enzymes from the transsulfuration pathway in that tissue.

CONCLUSIONS

Loss of UCP3 partially protects rats from diet-induced obesity. This phenotype is related to induction of a compensatory antioxidant mechanism and prevention of iBAT whitening.

Adropin stimulates proliferation but suppresses differentiation in rat primary brown preadipocytes

Adropin is a peptide hormone encoded by Energy Homeostasis Associated (Enho) gene. Adropin modulates glucose and lipid metabolism, and adiposity. Recently, we found that adropin suppresses differentiation of rodent white preadipocytes into mature fat cells. By contrast, the role of adropin in controlling brown adipogenesis is largely unknown. Therefore, in the present study we evaluated the effects of adropin on proliferation and differentiation of adipocyte precursor cells in rats. Brown adipocyte precursor cells were isolated from male Wistar rats. Cell replication was measured by BrdU incorporation. Gene expression was studied using real time PCR. Protein phosphorylation and production was assessed by Western blot. Lipid accumulation was evaluated by Oil Red O staining. Colorimetric kits were used to evaluate glycerol and free fatty acids release. We report here that adropin stimulates proliferation of brown preadipocytes. Moreover, in brown preadipocytes, adropin suppresses mRNA expression of adipogenic genes (C/ebpα, C/ebpβ, Pgc1α, Pparγ and Prdm16) during differentiation process. In addition, adropin suppresses UCP1 protein production in brown adipocytes. Finally, adropin reduces intracellular lipid content in brown adipocytes. These results indicate that adropin stimulates proliferation of brown preadipocytes and suppresses their differentiation into mature adipocytes.

Deficiency of bone morphogenetic protein-3b induces metabolic syndrome and increases adipogenesis

Bone morphogenetic protein (BMP) receptor signaling is critical for the regulation of the endocrine system and cardiovascular structure and function. The objective of this study was to investigate whether Bmp3b, a glycoprotein synthetized and secreted by adipose tissue, is necessary to regulate glucose and lipid metabolism, adipogenesis, and cardiovascular remodeling. Over the course of 4 mo, Bmp3b-knockout (Bmp3b^-/-) mice gained more weight than wild-type (WT) mice. The plasma levels of cholesterol and triglycerides were higher in Bmp3b^-/- mice than in WT mice. Bmp3b^-/- mice developed insulin resistance and glucose intolerance. The basal heart rate was higher in Bmp3b^-/- mice than in WT mice, and echocardiography revealed eccentric remodeling in Bmp3b^-/- mice. The expression of adipogenesis-related genes in white adipose tissue was higher in Bmp3b^-/- mice than in WT control mice. In vitro studies showed that Bmp3b modulates the activity of the C/ebpα promoter, an effect mediated by Smad2/3. The results of this study suggest that Bmp3b is necessary for the maintenance of homeostasis in terms of age-related weight gain, glucose metabolism, and left ventricular (LV) remodeling and function. Interventions that increase the level or function of BMP3b may decrease cardiovascular risk and pathological cardiac remodeling.

Comparison of [18F]FDG PET/CT with magnetic resonance imaging for the assessment of human brown adipose tissue activity

Background

Brown adipose tissue (BAT) is a thermogenic tissue which can generate heat in response to mild cold exposure. As it constitutes a promising target in the fight against obesity, we need reliable techniques to quantify its activity in response to therapeutic interventions. The current standard for the quantification of BAT activity is [¹⁸F]FDG PET/CT. Various sequences in magnetic resonance imaging (MRI), including those measuring its relative fat content (fat fraction), have been proposed and evaluated in small proof-of-principle studies, showing diverging results. Here, we systematically compare the predictive value of adipose tissue fat fraction measured by MRI to the results of [¹⁸F]FDG PET/CT.

Methods

We analyzed the diagnostic reliability of MRI measured fat fraction (FF) for the estimation of human BAT activity in two cohorts of healthy volunteers participating in two prospective clinical trials (NCT03189511, NCT03269747). In both cohorts, BAT activity was stimulated by mild cold exposure. In cohort 1, we performed [¹⁸F]FDG PET/MRI; in cohort 2, we used [¹⁸F]FDG PET/CT followed by MRI. Fat fraction was determined by 2-point Dixon and 6-point Dixon measurement, respectively. Fat fraction values were compared to SUV_mean in the corresponding tissue depot by simple linear regression.

Results

In total, 33 male participants with a mean age of 23.9 years and a mean BMI of 22.8 kg/m² were recruited. In 32 participants, active BAT was visible. On an intra-individual level, FF was significantly lower in high-SUV areas compared to low-SUV areas (cohort 1: p < 0.0001 and cohort 2: p = 0.0002). The FF of the supraclavicular adipose tissue depot was inversely related to its metabolic activity (SUVmean) in both cohorts (cohort 1: R² = 0.18, p = 0.09 and cohort 2: R² = 0.42, p = 0.009).

Conclusion

MRI FF explains only about 40% of the variation in BAT glucose uptake. Thus, it can currently not be used to substitute [¹⁸F] FDG PET-based imaging for quantification of BAT activity.

Trial registration

ClinicalTrials.gov. NCT03189511, registered on June 17, 2017, actual study start date was on May 31, 2017, retrospectively registered. NCT03269747, registered on September 01, 2017.

The colorful versatility of adipocytes: white-to-brown transdifferentiation and its therapeutic potential in humans

Brown and brite adipocytes contribute to energy expenditure through nonshivering thermogenesis. Though these cell types are thought to arise primarily from the de novo differentiation of precursor cells, their abundance is also controlled through the transdifferentiation of mature white adipocytes. Here, we review recent advances in our understanding of the regulation of white-to-brown transdifferentiation, as well as the conversion of brown and brite adipocytes to dormant, white-like fat cells. Converting mature white adipocytes into brite cells or reactivating dormant brown and brite adipocytes has emerged as a strategy to ameliorate human metabolic disorders. We analyze the evidence of learning from mice and how they translate to humans to ultimately scrutinize the relevance of this concept. Moreover, we estimate that converting a small percentage of existing white fat mass in obese subjects into active brite adipocytes could be sufficient to achieve meaningful benefits in metabolism. In conclusion, novel browning agents have to be identified before adipocyte transdifferentiation can be realized as a safe and efficacious therapy.

Biomarkers of Browning in Cold Exposed Siberian Adults

Cold-exposure promotes energy expenditure by inducing brown adipose tissue (BAT) thermogenesis, which over time, is also sustained by browning, the appearance, or increase, of brown-like cells into white fat depots. Identification of circulating markers reflecting BAT activity and browning is crucial to study this phenomenon and its triggers, also holding possible implications for the therapy of obesity and metabolic diseases. Using RT-qPCR, we evaluated the peripheral blood mononuclear cells (PBMC) expression profile of regulators of BAT activity (CIDEA, PRDM16), white adipocytes browning (HOXC9 and SLC27A1), and fatty acid β-oxidation (CPT1A) in 150 Siberian healthy miners living at extremely cold temperatures compared to 29 healthy subjects living in thermoneutral conditions. Anthropometric parameters, glucose, and lipid profiles were also assessed. The cold-exposed group showed significantly lower weight, BMI, hip circumference, and PBMC expression of CIDEA, but higher expression of HOXC9 and higher circulating glucose compared to controls. Within the cold-exposed group, BMI, total cholesterol, and the atherogenic coefficient were lower in individuals exposed to low temperatures for a longer time. In conclusion, human PBMC expresses the brown adipocytes marker CIDEA and the browning marker HOXC9, which, varying according to cold-exposure, possibly reflect changes in BAT activation and white fat browning.

The regulation of glucose and lipid homeostasis via PLTP as a mediator of BAT-liver communication

While brown adipose tissue (BAT) is well-recognized for its ability to dissipate energy in the form of heat, recent studies suggest multifaced roles of BAT in the regulation of glucose and lipid homeostasis beyond stimulating thermogenesis. One of the functions involves interorgan communication with metabolic organs, such as the liver, through BAT-derived secretory factors, a.k.a., batokine. However, the identity and the roles of such mediators remain insufficiently understood. Here, we employed proteomics and transcriptomics in human thermogenic adipocytes and identified previously unappreciated batokines, including phospholipid transfer protein (PLTP). We found that increased circulating levels of PLTP, via systemic or BAT-specific overexpression, significantly improve glucose tolerance and insulin sensitivity, increased energy expenditure, and decrease the circulating levels of cholesterol, phospholipids, and sphingolipids. Such changes were accompanied by increased bile acids in the circulation, which in turn enhances glucose uptake and thermogenesis in BAT. Our data suggest that PLTP is a batokine that contributes to the regulation of systemic glucose and lipid homeostasis as a mediator of BAT-liver interorgan communication.

Regulation of thermogenic adipocytes during fasting and cold

Cold exposure activates brown and brown-like adipocytes that dissipate large amounts of glucose and fatty acids via uncoupling protein 1 (UCP1) to drive non-shivering thermogenesis (NST). Evidence for the existence of these thermogenic adipocytes in adult humans gave rise to a renaissance in research on brown adipose tissue, establishing it as linchpin of energy homeostasis and metabolic health. Besides low ambient temperature, shortage or excess of food affect thermoregulation. Upon high caloric meals thermogenic adipocytes burn excess calories and maintain energy balance. In contrast, in conditions of nutrient deprivation, counter-regulatory mechanisms prevent thermogenic adipocytes from "wasting" energy substrates that need to be conserved. In this review, we discuss cell-autonomous mechanisms, metabolites, and hormones that modify NST in response to nutrient fluctuations. In particular, we focus on how thermogenic adipocytes balance thermogenesis with systemic energy homeostasis during fasting periods.

The Presence of Active Brown Adipose Tissue Determines Cold-Induced Energy Expenditure and Oxylipin Profiles in Humans

BACKGROUND

Accumulating evidence links brown adipose tissue (BAT) to increased cold-induced energy expenditure (CIEE) and regulation of lipid metabolism in humans. BAT has also been proposed as a novel source for biologically active lipid mediators including polyunsaturated fatty acids (PUFAs) and oxylipins. However, little is known about cold-mediated differences in energy expenditure and various lipid species between individuals with detectable BAT positive (BATpos) and those without BAT negative (BATneg).

METHODS

Here we investigated a unique cohort of matched BATpos and BATneg individuals identified by 18F-fluorodeoxyglucose positron emission tomography combined with computed tomography ([18F]-FDG PET/CT). BAT function, CIEE, and circulating oxylipins, were analyzed before and after short-term cold exposure using [18F]-FDG PET/CT, indirect calorimetry, and high-resolution mass spectrometry, respectively.

RESULTS

We found that active BAT is the major determinant of CIEE since only BATpos individuals experienced significantly increased energy expenditure in response to cold. A single bout of moderate cold exposure resulted in the dissipation of an additional 20 kcal excess energy in BATpos but not in BATneg individuals. The presence of BAT was associated with a unique systemic PUFA and oxylipin profile characterized by increased levels of anti-inflammatory omega-3 fatty acids as well as cytochrome P450 products but decreased concentrations of some proinflammatory hydroxyeicosatetraenoic acids when compared with BATneg individuals. Notably, cold exposure raised circulating levels of various lipids, including the recently identified BAT-derived circulating factors (BATokines) DiHOME and 12-HEPE, only in BATpos individuals.

CONCLUSIONS

In summary, our data emphasize that BAT in humans is a major contributor toward cold-mediated energy dissipation and a critical organ in the regulation of the systemic lipid pool.

Cold Exposure Distinctively Modulates Parathyroid and Thyroid Hormones in Cold-Acclimatized and Non-Acclimatized Humans

Cold-induced activation of thermogenesis modulates energy metabolism, but the role of humoral mediators is not completely understood. We aimed to investigate the role of parathyroid and thyroid hormones in acute and adaptive response to cold in humans. Examinations were performed before/after 15 minutes of ice-water swimming (n = 15) or 120 to 150 minutes of cold-induced nonshivering thermogenesis (NST) applied to cold-acclimatized (n = 6) or non-acclimatized (n = 11) individuals. Deep-neck brown adipose tissue (BAT) was collected from non-acclimatized patients undergoing elective neck surgery (n = 36). Seasonal variations in metabolic/hormonal parameters of ice-water swimmers were evaluated. We found that in ice-water swimmers, PTH and TSH increased and free T3, T4 decreased after a 15-minute winter swim, whereas NST-inducing cold exposure failed to regulate PTH and free T4 and lowered TSH and free T3. Ice-water swimming-induced increase in PTH correlated negatively with systemic calcium and positively with phosphorus. In non-acclimatized men, NST-inducing cold decreased PTH and TSH. Positive correlation between systemic levels of PTH and whole-body metabolic preference for lipids as well as BAT volume was found across the 2 populations. Moreover, NST-cooling protocol-induced changes in metabolic preference for lipids correlated positively with changes in PTH. Finally, variability in circulating PTH correlated positively with UCP1/UCP1, PPARGC1A, and DIO2 in BAT from neck surgery patients. Our data suggest that regulation of PTH and thyroid hormones during cold exposure in humans varies by cold acclimatization level and/or cold stimulus intensity. Possible role of PTH in NST is indicated by its positive relationships with whole-body metabolic preference for lipids, BAT volume, and UCP1 content.

The Role of Exercise in the Interplay between Myokines, Hepatokines, Osteokines, Adipokines, and Modulation of Inflammation for Energy Substrate Redistribution and Fat Mass Loss: A Review

Exercise is an effective strategy for preventing and treating obesity and its related cardiometabolic disorders, resulting in significant loss of body fat mass, white adipose tissue browning, redistribution of energy substrates, optimization of global energy expenditure, enhancement of hypothalamic circuits that control appetite-satiety and energy expenditure, and decreased systemic inflammation and insulin resistance. Novel exercise-inducible soluble factors, including myokines, hepatokines, and osteokines, and immune cytokines and adipokines are hypothesized to play an important role in the body's response to exercise. To our knowledge, no review has provided a comprehensive integrative overview of these novel molecular players and the mechanisms involved in the redistribution of metabolic fuel during and after exercise, the loss of weight and fat mass, and reduced inflammation. In this review, we explain the potential role of these exercise-inducible factors, namely myokines, such as irisin, IL-6, IL-15, METRNL, BAIBA, and myostatin, and hepatokines, in particular selenoprotein P, fetuin A, FGF21, ANGPTL4, and follistatin. We also describe the function of osteokines, specifically osteocalcin, and of adipokines such as leptin, adiponectin, and resistin. We also emphasize an integrative overview of the pleiotropic mechanisms, the metabolic pathways, and the inter-organ crosstalk involved in energy expenditure, fat mass loss, reduced inflammation, and healthy weight induced by exercise.

Leucine Potentiates Glucose-mediated 18F-FDG Uptake in Brown Adipose Tissue via β-Adrenergic Activation

Significant depots of brown adipose tissue (BAT) have been identified in many adult humans through positron emission tomography (PET), with the amount of BAT being inversely correlated with obesity. As dietary activation of BAT has implications for whole body glucose metabolism, leucine was used in the present study to determine its ability to promote BAT activation resulting in increased glucose uptake. In order to assess this, 2-deoxy-2-(fluorine-18)fluoro-d-glucose (¹⁸F-FDG) uptake was measured in C57BL/6 mice using microPET after treatment with leucine, glucose, or both in interscapular BAT (IBAT). Pretreatment with propranolol (PRP) was used to determine the role of β-adrenergic activation in glucose and leucine-mediated ¹⁸F-FDG uptake. Analysis of maximum standardized uptake values (SUV_MAX) determined that glucose administration increased ¹⁸F-FDG uptake in IBAT by 25.3%. While leucine did not promote ¹⁸F-FDG uptake alone, it did potentiate glucose-mediated ¹⁸F-FDG uptake, increasing ¹⁸F-FDG uptake in IBAT by 22.5%, compared to glucose alone. Pretreatment with PRP prevented the increase in IBAT ¹⁸F-FDG uptake following the combination of glucose and leucine administration. These data suggest that leucine is effective in promoting BAT ¹⁸F-FDG uptake through β-adrenergic activation in combination with glucose.

HCBP6 deficiency exacerbates glucose and lipid metabolism disorders in non-alcoholic fatty liver mice

BACKGROUND

Non-alcoholic fatty liver disease (NAFLD), which often accompanied by metabolic syndrome, such as obesity, diabetes and dyslipidemia, has become a global health problem. Our previous results show that HCV core protein binding protein 6 (HCBP6) could maintain the triglyceride homeostasis in liver cells. However, the role of HCBP6 in NAFLD and its associated metabolic disorders remains incompletely understood.

METHODS

Hepatic HCBP6 expression was determined by qRT-PCR, Western blot and immunohistochemistry analysis. HCBP6 knockout (HCBP6-KO) mice were constructed and fed a high-fat diet (HFD) to induce NAFLD. The effects of HCBP6 on glucose and lipid metabolism were measured by HE staining, qRT-PCR, Western blot and GTT. Wild-type and HCBP6-KO mice kept on a HFD were treated with ginsenosides Rh2, and HE staining and GTT were used to study the function of Rh2 in metabolism disorders.

RESULTS

HCBP6 is reduced in HFD-fed mice. HCBP6 deficiency increased the body weight, aggravated fatty liver and deteriorated lipid homeostasis as well as glucose homeostasis in HFD-induced mouse model of NAFLD. Moreover, HCBP6-KO mice failed to maintain body temperature upon cold challenge. Mechanistically, HCBP6 could regulate lipolysis and fatty acid oxidation via activation of AMKP in vivo. In addition, HCBP6 expression was upregulated by ginsenosides Rh2. Accordingly, ginsenosides Rh2 administrations improved HFD-induced fatty liver and glucose tolerance.

CONCLUSIONS

These findings indicated that HCBP6 is essential in maintaining lipid and glucose homeostasis and body temperature. HCBP6 augmented by ginsenosides Rh2 may be a promising therapeutic strategy for the treatment of metabolic disorders in NAFLD mice.

Gastric banding-associated weight loss diminishes hepatic Tsukushi expression

Obesity has emerged as a substantial global healthcare issue that is frequently associated with insulin resistance and non-alcoholic fatty liver disease (NAFLD). Tsukushi (TSK), a liver-derived molecule, was recently identified as a major driver of NAFLD. Laparoscopic adjustable gastric banding (LAGB) has proven effective in reducing body weight and improving NAFLD. We therefore aimed to investigate the relation between LAGB-induced weight loss and TSK expression. Twenty-six obese patients undergoing LAGB were included in the study and metabolic parameters were assessed before (t0) and six months after LAGB (t6). The expression of TSK in liver and subcutaneous adipose tissue (AT) specimens was determined at both time points. To unravel regulatory mechanisms of TSK expression, human peripheral blood mononuclear cells (PBMCs) were stimulated with pro-inflammatory cytokines and TSK mRNA levels were analyzed by quantitative polymerase chain reaction. LAGB induced pronounced weight loss which was paralleled by amelioration of metabolic disturbances and histologically defined NAFLD. While hepatic TSK expression was markedly decreased after LAGB, adipose tissue TSK expression remained comparable to baseline. The decline in hepatic TSK expression after LAGB positively correlated with weight loss and the reduction in BMI, and negatively correlated with NAFLD activity score (NAS). In human PBMCs, pro-inflammatory cytokines such as IL-1β and TNFα induced the expression of TSK. In conclusion, LAGB-induced weight loss reduces hepatic TSK expression. Inhibiting TSK might represent a promising target for treating NAFLD in the future.

Comprehensive proteomics and functional annotation of mouse brown adipose tissue

Knowledge about the mouse brown adipose tissue (BAT) proteome can provide a deeper understanding of the function of mammalian BAT. Herein, a comprehensive analysis of interscapular BAT from C57BL/6J female mice was conducted by 2DLC and high-resolution mass spectrometry to construct a comprehensive proteome dataset of mouse BAT proteins. A total of 4949 nonredundant proteins were identified, and 4495 were quantified using the iBAQ method. According to the iBAQ values, the BAT proteome was divided into high-, middle- and low-abundance proteins. The functions of the high-abundance proteins were mainly related to glucose and fatty acid oxidation to produce heat for thermoregulation, while the functions of the middle- and low-abundance proteins were mainly related to protein synthesis and apoptosis, respectively. Additionally, 497 proteins were predicted to have signal peptides using SignalP4 software, and 75 were confirmed in previous studies. This study, for the first time, comprehensively profiled and functionally annotated the BAT proteome. This study will be helpful for future studies focused on biomarker identification and BAT molecular mechanisms.

Cold-Activated Brown Adipose Tissue is Associated with Less Cardiometabolic Dysfunction in Young Adults with Obesity

OBJECTIVE

This study aimed to test the hypothesis that young adults with obesity and cold-activated brown adipose tissue (BAT) are less likely to have metabolic dysfunction (dyslipidemia, insulin resistance, and hypertension) than those without cold-activated BAT. Previous studies have noted a potentially protective effect of BAT and higher adiponectin/leptin ratios, but they have acknowledged that the clinical implications of these findings remain uncertain.

METHODS

Twenty-one females and twenty-three males with obesity (BMI ≥ 30 kg/m² ) underwent a 2-hour cooling protocol before ¹⁸ F-fluorodeoxyglucose (¹⁸ F-FDG)-positron emission tomography/x-ray computed tomography scan to determine the prevalence, volume, and ¹⁸ F-FDG uptake of cold-activated BAT.

RESULTS

Cold-activated BAT was identified in 43% of participants (11 female, 8 male); females had greater ¹⁸ F-FDG uptake. Those with cold-activated BAT had a lesser degree of metabolic dysfunction. Cold-activated BAT volume correlated with triglycerides (inversely) and adiponectin (concordantly). Body-mass-adjusted cold-activated BAT activity correlated with high-density lipoprotein cholesterol (concordantly). Males with cold-activated BAT had lower leptin and higher adiponectin/leptin ratio.

CONCLUSIONS

A high prevalence of cold-activated BAT was found in the study participants. BAT could be important in decreasing metabolic dysfunction among young adults with obesity, making it a potential target for treating metabolically unhealthy obesity.

Do Bariatric Surgeries Enhance Brown/Beige Adipose Tissue Thermogenesis?

Bariatric surgeries induce marked and durable weight loss in individuals with morbid obesity through powerful effects on both food intake and energy expenditure. While alterations in gut-brain communication are increasingly implicated in the improved eating behavior following bariatric surgeries, less is known about the mechanistic basis for energy expenditure changes. Brown adipose tissue (BAT) and beige adipose tissue (BeAT) have emerged as major regulators of whole-body energy metabolism in humans as well as in rodents due to their ability to convert the chemical energy in circulating glucose and fatty acids into heat. In this Review, we critically discuss the steadily growing evidence from preclinical and clinical studies suggesting that Roux-en-Y gastric bypass (RYGB) and vertical sleeve gastrectomy (VSG), the two most commonly performed bariatric surgeries, enhance BAT/BeAT thermogenesis. We address the documented mechanisms, highlight study limitations and finish by outlining unanswered questions in the subject. Further understanding how and to what extent bariatric surgeries enhance BAT/BeAT thermogenesis may not only aid in the development of improved obesity pharmacotherapies that safely and optimally target both sides of the energy balance equation, but also in the development of novel hyperglycemia and/or hyperlipidemia pharmacotherapies.

A population-based study on the prevalence of gestational diabetes mellitus in association with temperature in Taiwan

BACKGROUND

Previous studies showing seasonal clustering of gestational diabetes mellitus (GDM) were conducted in the temperate or frigid zones and mostly included pregnant Caucasian women. This study aims to investigate the association of ambient temperature with prevalence of GDM in Taiwan, a sub-tropic country.

METHODS

This population-based cohort study comprised women (n = 371,131) who gave births between 2013 and 2014; of which, 43,538 (11.7%) were diagnosed with GDM. The mean daily temperature and difference in temperature within a day was calculated over a 35-day period prior to GDM diagnosis or the first day of the 27th gestational week (for non-GDM subjects). Multiple logistic regression models with generalized estimation equation were performed to estimate the adjusted odds ratio (aOR) and 95% confidence interval (CI) of GDM in association with temperature.

RESULTS

After controlling for potential confounders, summer and fall were associated with higher risk of GDM diagnosis, with aOR [95% CI] of 1.05 [1.04-1.07] and 1.04 [1.02-1.06] in reference to winter. Additionally, an increase of 1 °C from 14 °C to 27 °C was associated with an aOR of 1.03 [1.02-1.03]. The aOR greatly increased to 1.54 [1.48-1.60] after 28 °C. An increase of 1 °C difference within a day was associated with a reduced aOR at 0.90 [0.87-0.92].

CONCLUSION

A higher prevalence of GDM was associated with a higher daily temperature, but with a smaller difference in temperature within a day.

Feeding brown fat: dietary phytochemicals targeting non-shivering thermogenesis to control body weight

Excessive adipose accumulation, which is the main driver for the development of secondary metabolic complications, has reached epidemic proportions and combined pharmaceutical, educational and nutritional approaches are required to reverse the current rise in global obesity prevalence rates. Brown adipose tissue (BAT) is a unique organ able to dissipate energy and thus a promising target to enhance BMR to counteract a positive energy balance. In addition, active BAT might support body weight maintenance after weight loss to prevent/reduce relapse. Natural products deliver valuable bioactive compounds that have historically helped to alleviate disease symptoms. Interest in recent years has focused on identifying nutritional constituents that are able to induce BAT activity and thereby enhance energy expenditure. This review provides a summary of selected dietary phytochemicals, including isoflavones, catechins, stilbenes, the flavonoids quercetin, luteolin and resveratrol as well as the alkaloids berberine and capsaicin. Most of the discussed phytochemicals act through distinct molecular pathways e.g. sympathetic nerve activation, AMP-kinase signalling, SIRT1 activity or stimulation of oestrogen receptors. Thus, it might be possible to utilise this multitude of pathways to co-activate BAT using a fine-tuned combination of foods or combined nutritional supplements.