Non-pharmacological and pharmacological strategies of brown adipose tissue recruitment in humans

Different Protein Sources Enhance 18FDG-PET/MR Uptake of Brown Adipocytes in Male Subjects

Background: The unique ability of brown adipocytes to increase metabolic rate suggests that they could be targeted as an obesity treatment. Objective: The objective of the study was to search for new dietary factors that may enhance brown adipose tissue (BAT) activity. Methods: The study group comprised 28 healthy non-smoking males, aged 21–42 years old. All volunteers underwent a physical examination and a 75 g oral glucose tolerance test (75g-OGTT). Serum atrial and brain natriuretic peptide (ANP, BNP), PRD1-BF1-RIZ1 homologous domain containing 16 (PRDM16) and eukaryotic translation initiation factor 4E (eIF4E) measurements were taken, and 3-day food intake diaries were completed. Body composition measurements were assessed using dual-energy X-ray absorptiometry (DXA) scanning and bioimpedance methods. An fluorodeoxyglucose-18 (FDG-18) uptake in BAT was assessed by positron emission tomography/magnetic resonance (PET/MR) in all participants after 2 h cold exposure. The results were adjusted for age, daily energy intake, and DXA lean mass. Results: Subjects with detectable BAT (BAT⁽⁺⁾) were characterized by a higher percentage of energy obtained from dietary protein and fat and higher muscle mass (p = 0.01, p = 0.02 and p = 0.04, respectively). In the BAT⁽⁺⁾ group, animal protein intake was positively associated (p= 0.04), whereas the plant protein intake negatively correlated with BAT activity (p = 0.03). Additionally, the presence of BAT was inversely associated with BNP concentration in the 2 h of cold exposure (p = 0.002). Conclusion: The outcomes of our study suggest that different macronutrient consumption may be a new way to modulate BAT activity leading to weight reduction.

Thyroid Hormone Abuse in Elite Sports: The Regulatory Challenge

Abuse of androgens and erythropoietin has led to hormones being the most effective and frequent class of ergogenic substances prohibited in elite sports by the World Anti-Doping Agency (WADA). At present, thyroid hormone (TH) abuse is not prohibited, but its prevalence among elite athletes and nonprohibited status remains controversial. A corollary of prohibiting hormones for elite sports is that endocrinologists must be aware of a professional athlete's risk of disqualification for using prohibited hormones and/or to certify Therapeutic Use Exemptions, which allow individual athletes to use prohibited substances for valid medical indications. This narrative review considers the status of TH within the framework of the WADA Code criteria for prohibiting substances, which requires meeting 2 of 3 equally important criteria of potential performance enhancement, harmfulness to health, and violation of the spirit of sport. In considering the valid clinical uses of TH, the prevalence of TH use among young adults, the reason why some athletes seek to use TH, and the pathophysiology of sought-after and adverse effects of TH abuse, together with the challenges of detecting TH abuse, it can be concluded that, on the basis of present data, prohibition of TH in elite sport is neither justified nor feasible.

PET/MRI-evaluated brown adipose tissue activity may be related to dietary MUFA and omega-6 fatty acids intake

An investigation of new ways to activate brown adipose tissue (BAT) is highly valuable, as it is a possible tool for obesity prevention and treatment. The aim of our study was to evaluate the relationships between dietary intake and BAT activity. The study group comprised 28 healthy non-smoking males aged 21–42 years. All volunteers underwent a physical examination and 75-g OGTT and completed 3-day food intake diaries to evaluate macronutrients and fatty acid intake. Body composition measurements were assessed using DXA scanning. An FDG-18 PET/MR was performed to visualize BAT activity. Brown adipose tissue was detected in 18 subjects (67% normal-weight individuals and 33% overweight/obese). The presence of BAT corresponded with a lower visceral adipose tissue (VAT) content (p = 0.04, after adjustment for age, daily kcal intake, and DXA Lean mass). We noted significantly lower omega-6 fatty acids (p = 0.03) and MUFA (p = 0.02) intake in subjects with detected BAT activity after adjustment for age, daily average kcal intake, and DXA Lean mass, whereas omega-3 fatty acids intake was comparable between the two groups. BAT presence was positively associated with the concentration of serum IL-6 (p = 0.01) during cold exposure. Our results show that BAT activity may be related to daily omega-6 fatty acids intake.

Ovariectomy-Induced Hepatic Lipid and Cytochrome P450 Dysmetabolism Precedes Serum Dyslipidemia

Ovarian hormone deficiency leads to increased body weight, visceral adiposity, fatty liver and disorders associated with menopausal metabolic syndrome. To better understand the underlying mechanisms of these disorders in their early phases of development, we investigated the effect of ovariectomy on lipid and glucose metabolism. Compared to sham-operated controls, ovariectomized Wistar female rats markedly increased whole body and visceral adipose tissue weight (p ˂ 0.05) and exhibited insulin resistance in peripheral tissues. Severe hepatic triglyceride accumulation (p ˂ 0.001) after ovariectomy preceded changes in both serum lipids and glucose intolerance, reflecting alterations in some CYP proteins. Increased CYP2E1 (p ˂ 0.05) and decreased CYP4A (p ˂ 0.001) after ovariectomy reduced fatty acid oxidation and induced hepatic steatosis. Decreased triglyceride metabolism and secretion from the liver contributed to hepatic triglyceride accumulation in response to ovariectomy. In addition, interscapular brown adipose tissue of ovariectomized rats exhibited decreased fatty acid oxidation (p ˂ 0.01), lipogenesis (p ˂ 0.05) and lipolysis (p ˂ 0.05) despite an increase in tissue weight. The results provide evidence that impaired hepatic triglycerides and dysregulation of some CYP450 proteins may have been involved in the development of hepatic steatosis. The low metabolic activity of brown adipose tissue may have contributed to visceral adiposity as well as triglyceride accumulation during the postmenopausal period.

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.

Depot-specific UCP1 expression in human white adipose tissue and its association with obesity-related markers

BACKGROUND

This study investigated depot-specific mRNA expression of uncoupling protein 1 (UCP1) in human white adipose tissue (WAT) and its association with obesity-related markers.

METHODS

We recruited 39 normal-weight, 41 nondiabetic obese, and 22 diabetic obese women. We measured UCP1 mRNA expression in abdominal visceral adipose tissue (VAT) and subcutaneous adipose tissue (SAT), and investigated the associations between UCP1 mRNA expression in VAT and SAT, and obesity-related markers including mRNA expression of leptin, adiponectin, CCAAT-enhancer-binding protein homologous protein (CHOP), and positive regulatory domain-containing protein 16 (PRDM16). We also evaluated UCP1 mRNA expression in differentiated human white adipocytes after treatment with various stressors and metabolic improvement agents in vitro.

RESULTS

UCP1 mRNA in VAT was significantly higher than in SAT in all groups. UCP1 mRNA in SAT was negatively correlated with BMI, total abdominal fat area, visceral fat area, blood pressure, fasting glucose, insulin, HOMA-IR score, triglyceride, hsCRP, fasting leptin levels, and adipocyte size. UCP1 mRNA in SAT was positively correlated with fasting adiponectin levels. UCP1 mRNA in VAT was negatively correlated with visceral-to-subcutaneous fat ratio (VSR), fasting glucose, and triglyceride levels. In SAT, UCP1 mRNA was negatively correlated with mRNA expression of leptin and CHOP, and positively correlated with mRNA expression of adiponectin. The expression of PRDM16 was positively correlated with UCP1 mRNA in both VAT and SAT. UCP1 mRNA expression in differentiated human white adipocytes was significantly reduced after incubation with thapsigargin, tunicamycin, homocysteine, TNF-α, or IL-β, and significantly increased after incubation with exendin 4, dapagliflozin, and telmisartan.

CONCLUSIONS

This study demonstrated depot-specific mRNA expression of UCP1 and its association with obesity-related markers in human WAT. UCP1 mRNA in human white adipocytes was suppressed by inflammatory agents and enhanced by metabolic improvement agents. UCP1 in human WAT might participate in the pathogenesis of obesity-related metabolic diseases.

Brown and Brite: The Fat Soldiers in the Anti-obesity Fight

Brown adipose tissue (BAT) is proposed to maintain thermal homeostasis through dissipation of chemical energy as heat by the uncoupling proteins (UCPs) present in their mitochondria. The recent demonstration of the presence of BAT in humans has invigorated research in this area. The research has provided many new insights into the biology and functioning of this tissue and the biological implications of its altered activities. Another finding of interest is browning of white adipose tissue (WAT) resulting in what is known as beige/brite cells, which have increased mitochondrial proteins and UCPs. In general, it has been observed that the activation of BAT is associated with various physiological improvements such as a reduction in blood glucose levels increased resting energy expenditure and reduced weight. Given the similar physiological functions of BAT and beige/ brite cells and the higher mass of WAT compared to BAT, it is likely that increasing the brite/beige cells in WATs may also lead to greater metabolic benefits. However, development of treatments targeting brown fat or WAT browning would require not only a substantial understanding of the biology of these tissues but also the effect of altering their activity levels on whole body metabolism and physiology. In this review, we present evidence from recent literature on the substrates utilized by BAT, regulation of BAT activity and browning by circulating molecules. We also present dietary and pharmacological activators of brown and beige/brite adipose tissue and the effect of physical exercise on BAT activity and browning.

Repeated cold exposures protect a mouse model of Alzheimer's disease against cold-induced tau phosphorylation

Objective

Old age is associated with a rise in the incidence of Alzheimer's disease (AD) but also with thermoregulatory deficits. Indicative of a link between the two, hypothermia induces tau hyperphosphorylation. The 3xTg-AD mouse model not only develops tau and amyloid pathologies in the brain but also metabolic and thermoregulatory deficits. Brown adipose tissue (BAT) is the main thermogenic driver in mammals, and its stimulation counteracts metabolic deficits in rodents and humans. We thus investigated whether BAT stimulation impedes AD neuropathology.

Methods

15-month-old 3xTg-AD mice were subjected to repeated short cold exposures (RSCE), consisting of 4-hour sessions of cold exposure (4 °C), five times per week for four weeks, compared to animals kept at housing temperature.

Results

First, we confirmed that 3xTg-AD RSCE-trained mice exhibited BAT thermogenesis and improved glucose tolerance. RSCE-trained mice were completely resistant to tau hyperphosphorylation in the hippocampus induced by a 24-hour cold challenge. Finally, RSCE increased plasma levels of fibroblast growth factor 21 (FGF21), a batokine, which inversely correlated with hippocampal tau phosphorylation.

Conclusions

Overall, BAT stimulation through RSCE improved metabolic deficits and completely blocked cold-induced tau hyperphosphorylation in the 3xTg-AD mouse model of AD neuropathology. These results suggest that improving thermogenesis could exert a therapeutic effect in AD.

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Cold acclimation increases brown adipose tissue thermogenesis in old 3xTg-AD mice.

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Cold acclimation improved glucose tolerance in old 3xTg-AD mice.

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Enhanced thermogenesis protects against cold-induced brain tau phosphorylation.

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Repeated cold exposures increased plasmatic levels of fibroblast growth factor 21.

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Peripheral fibroblast growth factor 21 levels correlate with tau phosphorylation.

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.

Estrogen-Related Receptors Mediate the Adaptive Response of Brown Adipose Tissue to Adrenergic Stimulation

Adrenergic stimulation of brown adipose tissue (BAT) induces acute and long-term responses. The acute adrenergic response activates thermogenesis by uncoupling oxidative phosphorylation and enabling increased substrate oxidation. Long-term, adrenergic signaling remodels BAT, inducing adaptive transcriptional changes that expand thermogenic capacity. Here, we show that the estrogen-related receptors alpha and gamma (ERRα, ERRγ) are collectively critical effectors of adrenergically stimulated transcriptional reprogramming of BAT. Mice lacking adipose ERRs (ERRαγ^Ad−/−) have reduced oxidative and thermogenic capacity and rapidly become hypothermic when exposed to cold. ERRαγ^Ad−/− mice treated long term with a β₃-adrenergic agonist fail to expand oxidative or thermogenic capacity and do not increase energy expenditure in response to norepinephrine (NE). Furthermore, ERRαγ^Ad−/− mice fed a high-fat diet do not lose weight or show improved glucose tolerance when dosed with β₃-adrenergic agonists. The molecular basis of these defects is the finding that ERRs mediate the bulk of the transcriptional response to adrenergic stimulation.

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Adipose ERRs collectively control brown fat oxidative and thermogenic capacity

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Adipose ERRs are essential for BAT remodeling induced by β-adrenergic agonism

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ERRs control the bulk of the transcriptional response to adrenergic stimulation

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Mice that lack adipose ERRs show no metabolic benefits of β-adrenergic agonism

Both hypothyroidism and hyperthyroidism increase plasma irisin levels in rats

Background A recently discovered hormone, irisin is accepted to be significantly involved in the regulation of body weight. Thyroid functions may be, directly or indirectly, associated with irisin. Aim The aim of the present study is to determine the effect of experimental thyroid dysfunction on irisin levels in rats. Methods The study registered 40 adult male Sprague-Dawley rats, which were allocated to groups as follows: 1. Control; 2. Hypothyroidism induced by injection of 10 mg/kg/day intraperitoneal propylthiouracil (PTU) for 3 weeks; 3. Hypothyroidism (PTU 2 weeks) + L-thyroxin (1.5 mg/kg/day for 1 week); 4. Hyperthyroidism induced in rats by 3-week thyroxin (0.3 mg/kg/day); 5. Hyperthyroidism + PTU. At the end of the study, blood samples were collected to quantify free triiodothyronine (FT3), free triiodothyronine (FT4) and irisin levels. Results FT3 and FT4 levels were reduced in hypothyroidism and were significantly elevated in hyperthyroidism (p < 0.001). Irisin values, on the other hand, were found to be elevated in both hypothyroidism and hyperthyroidism groups (p < 0.001). Conclusion The results of the study suggest that irisin values increase in thyroid dysfunction, hypo- and hyperthyroidism, and that when hypothyroidism is corrected by thyroxin administration and hyperthyroidism by PTU injection, plasma irisin values go back to normal.

Meeting report of the 2016 bone marrow adiposity meeting

There is considerable interest in the physiology and pathology, as well as the cellular and molecular biology, of bone marrow adipose tissue (BMAT). Because bone marrow adiposity is linked not only to systemic energy metabolism, but also to both bone marrow and musculoskeletal disorders, this biologic compartment has become of major interest to investigators from diverse disciplines. Bone marrow adiposity represents a virtual multi-tissue endocrine organ, which encompasses cells from multiple developmental lineages (e.g., mesenchymal, myeloid, lymphoid) and occupies all the non-osseous and non-cartilaginous space within long bones. A number of research groups are now focusing on bone marrow adiposity to understand a range of clinical afflictions associated with bone marrow disorders and to consider mechanisms-based strategies for future therapies.

Potent long-acting rhFGF21 analog for treatment of diabetic nephropathy in db/db and DIO mice

Background

Fibroblast growth factor 21 (FGF21) is an endocrine-acting hormone that has the potential to treat diabetic nephropathy. However, development of FGF21 into a therapeutic has been hindered due to its low intrinsic bio-stability. In our previous study, we have developed a recombinant human FGF21 (rhFGF21) variant by site-directed mutagenesis and solid-phase PEGylation, which retained its biological function. The aim of this study is to elucidate whether the therapeutic effect of PEGylated rhFGF21 (PEG-rhFGF21) on diabetic nephropathy in DIO (diet induced obesity) mice is more significant than rhFGF21 in vivo.

Results

After administration with rhFGF21 and PEG-rhFGF21 for 2 months, biochemical data and histological examination showed that PEG-rhFGF21 significantly lowered lipid levels in the kidney, decreased urine albumin/creatinine ratio (ACR) and improved mesangial expansion, demonstrating that PEG-rhFGF21 was more efficacious in ameliorating functional and morphological abnormalities induced by diabetic nephropathy in db/db and DIO mice.

Conclusions

Our findings suggest that PEG-rhFGF21 treatment is more effective in treating diabetic nephropathy than rhFGF21, through enhancements of systemic metabolic alterations and anti-inflammatory mechanisms. These findings help provide a theoretical basis to develop more long-acting and efficacious protein drugs for diabetic nephropathy.

Thyroid hormone acting via TRβ induces expression of browning genes in mouse bone marrow adipose tissue

PURPOSE

Mutant hypothyroid mouse models have recently shown that thyroid hormone is critical for skeletal development during an important prepubertal growth period. Additionally, thyroid hormone negatively regulates total body fat, consistent with the well-established effects of thyroid hormone on energy and fat metabolism. Since bone marrow mesenchymal stromal cells differentiate into both adipocytes and osteoblasts and a relationship between bone marrow adipogenesis and osteogenesis has been predicted, we hypothesized thyroid hormone deficiency during the postnatal growth period increases marrow adiposity in mice.

METHODS

Marrow adiposity in TH-deficient (Tshr ^-/-) mice treated with T3/T4, TH receptor β-specific agonist GC-1, or vehicle control was evaluated via dual-energy X-ray absorptiometry and osmium micro-computed tomography. To further examine the mechanism for thyroid hormone regulation of marrow adiposity, we used real-time RT-PCR to measure the effects of thyroid hormone on adipocyte differentiation markers in primary mouse bone marrow mesenchymal stromal cells and two mouse cell lines in vitro and in Tshr ^-/- mice in vivo.

RESULTS

Marrow adiposity increased >20% (P < 0.01) in Tshr ^-/- mice at 3 weeks of age, and treatment with T3/T4 when serum thyroid hormone normally increases (day 5-14) rescued this phenotype. Furthermore, GC-1 rescued this phenotype equally well, suggesting this thyroid hormone effect is in part mediated via TRβ signaling. Treatment of bone marrow mesenchymal stromal or ST2 cells with T3 or GC-1 significantly increased expression of several brown/beige fat markers. Moreover, injection of T3/T4 increased browning-specific markers in white fat of Tshr ^-/- mice.

CONCLUSIONS

These data suggest that thyroid hormone regulation of marrow adiposity is mediated at least in part via activation of TRβ signaling.

Kinase Inactive Tyrosine Kinase (Tyk2) Supports Differentiation of Brown Fat Cells

It has been known for decades that brown adipose tissue (BAT) plays a central role in maintaining body temperature in hibernating animals and human infants. Recently, it has become evident that there are also depots of brown fat in adult humans, and the mass of brown fat is inversely correlated with body weight. There are a variety of transcription factors implicated in the differentiation of classical Myf5+ brown preadipocytes, one of the most important of which is PRDM16. We have recently identified that in addition to PRDM16, the tyrosine kinase Tyk2 and the STAT3 transcription factor are required for the differentiation of Myf5 positive brown preadipocytes both in cell culture and in mice. Tyk2 is a member of the Jak family of tyrosine kinases, which are activated by exposure of cells to different cytokines and growth factors. In this study we report the surprising observation that a mutated form of Tyk2, which lacks tyrosine kinase activity (Tyk2KD) restores differentiation of brown preadipocytes in vitro as well as in Tyk2-/- mice. Furthermore, expression of the Tyk2KD transgene in brown fat reverses the obese phenotype of Tyk2-/- animals. Treatment of cells with Jak-selective inhibitors suggests that the mechanism by which Tyk2KD functions to restore BAT differentiation is by dimerizing with kinase active Jak1 or Jak2. These results indicate that there are redundant mechanisms by which members of the Jak family can contribute to differentiation of BAT.

A combined docosahexaenoic acid–thyroid hormone protocol upregulates rat liver β-Klotho expression and downstream components of FGF21 signaling as a potential novel approach to metabolic stress conditions

We study the mechanism of how liver preconditioning by a DHA and triiodothyronine combined protocol underlies peroxisome-proliferator activated receptor α (PPARα)-fibroblast growth factor 21 (FGF21) upregulation.

Lipopolysaccharide-binding protein is a negative regulator of adipose tissue browning in mice and humans

AIMS/HYPOTHESIS

Adipocyte lipopolysaccharide-binding protein (LBP) biosynthesis is associated with obesity-induced adipose tissue dysfunction. Our purpose was to study the role of LBP in regulating the browning of adipose tissue.

METHODS

Adult mice were maintained at 4°C for 3 weeks or treated with the β3-adrenergic agonist, CL316,243, for 1 week to induce the browning of white fat. Precursor cells from brown and white adipose tissues were cultured under differentiation-inducing conditions to yield brown and beige/brite adipocytes, respectively. In vitro, Lbp was knocked down in 3T3-L1 adipocytes, and cells were treated with recombinant LBP or co-cultured in transwells with control 3T3-L1 adipocytes. Wild-type and Lbp-null mice, fed a standard or high fat diet (HFD) for 15 weeks, were also used in investigations. In humans, subcutaneous and visceral adipose tissue samples were obtained from a cohort of morbidly obese participants.

RESULTS

The induction of white fat browning by exposure of mice to cold or CL316,243 treatment was strongly associated with decreased Lbp mRNA expression in white adipose tissue. The acquisition of the beige/brite phenotype in cultured cells was associated with downregulation of Lbp. Moreover, silencing of Lbp induced the expression of brown fat-related genes in adipocytes, whereas LBP treatment reversed this effect. Lbp-null mice exhibited the spontaneous induction of subcutaneous adipose tissue browning, as evidenced by a remarkable increase in Ucp1 and Dio2 gene expression and the appearance of multivacuolar adipocyte clusters. The amount of brown adipose tissue, and brown adipose tissue activity were also increased in Lbp-null mice. These changes were associated with decreased weight gain in Lbp-null mice and protection against HFD-induced inflammatory responses, as shown by reduced IL-6 levels. However, rather than improving glucose homeostasis, these effects led to glucose intolerance and insulin resistance.

CONCLUSIONS/INTERPRETATION

LBP is identified as a negative regulator of the browning process, which is likely to contribute to the obesity-promoting action of LBP. The deleterious metabolic effects of LBP deletion are compatible with the concept that the appropriate regulation of inflammatory pathways is necessary for a healthy systemic metabolic profile, regardless of body weight regulation.

Brown and Beige Adipose Tissue: Therapy for Obesity and Its Comorbidities?

Overweight and obesity are global health problems placing an ever-increasing demand on health care systems. Brown adipose tissue (BAT) is present in significant amounts in adults. BAT has potential as a fuel for oxidation and dissipation as heat production, which makes it an attractive target for obesity therapy. BAT activation results in increased energy expenditure via thermogenesis. The role of BAT/beige adipocyte activation on whole body energy homeostasis, body weight management/regulation, and whole body glucose and lipid homeostasis remains unproven. This paper reviews knowledge on brown/beige adipocytes in energy expenditure and how it may impact obesity therapy and its comorbidities.

Classification of Therapeutic and Experimental Drugs for Brown Adipose Tissue Activation: Potential Treatment Strategies for Diabetes and Obesity

OBJECTIVE

Increasing efforts are being made towards pharmacologic activation of brown adipose tissue (BAT) in animals and humans for potential use in the treatment of obesity and diabetes. We and others have reported a number of animal studies using either experimental or therapeutic drugs. There are now efforts to translate these findings to human studies. The goal of this review is to evaluate the various drugs currently being used that have the potential for BAT activation.

METHODS

Drugs were classified into 4 classes based on their mechanism of action. Class 1 drugs include the use of β3 adrenoceptor agonists for BAT activation. Class 2 drugs include drugs that affect norepinephrine levels and activate BAT with the potential of reducing obesity. Class 3 includes activators of peroxisome proliferator-activated receptor-γ in pursuit of lowering blood sugar, weight loss and diabetes and finally Class 4 includes natural products and other emerging drugs with limited information on BAT activation and their effects on diabetes and weight loss.

RESULTS

Class 1 drugs are high BAT activators followed by Class 2 and 3. Some of these drugs have now been extended to diabetes and obesity animal models and human BAT studies. Drugs in Class 3 are used clinically for Type 2 diabetes, but the extent of BAT involvement is unclear.

CONCLUSION

Further studies on the efficacy of these drugs in diabetes and measuring their effects on BAT activation using noninvasive imaging will help in establishing a clinical role of BAT.