Chronic mirabegron treatment increases human brown fat, HDL cholesterol, and insulin sensitivity

BCAA-nitrogen flux in brown fat controls metabolic health independent of thermogenesis

Brown adipose tissue (BAT) is best known for thermogenesis. Rodent studies demonstrated that enhanced BAT thermogenesis is tightly associated with increased energy expenditure, reduced body weight, and improved glucose homeostasis. However, human BAT is protective against type 2 diabetes, independent of body weight. The mechanism underlying this dissociation remains unclear. Here, we report that impaired mitochondrial catabolism of branched-chain amino acids (BCAAs) in BAT, by deleting mitochondrial BCAA carriers (MBCs), caused systemic insulin resistance without affecting energy expenditure and body weight. Brown adipocytes catabolized BCAA in the mitochondria as nitrogen donors for the biosynthesis of non-essential amino acids and glutathione. Impaired mitochondrial BCAA-nitrogen flux in BAT resulted in increased oxidative stress, decreased hepatic insulin signaling, and decreased circulating BCAA-derived metabolites. A high-fat diet attenuated BCAA-nitrogen flux and metabolite synthesis in BAT, whereas cold-activated BAT enhanced the synthesis. This work uncovers a metabolite-mediated pathway through which BAT controls metabolic health beyond thermogenesis.

Lipids, apolipoproteins and gestational diabetes mellitus: a Mendelian randomization study

BACKGROUND

This study investigates the causal relationship between lipid traits and GDM in an effort to better understand the aetiology of GDM.

METHODS

Employing a two-sample Mendelian Randomization (MR) framework, we used Single Nucleotide Polymorphisms (SNPs) as instrumental variables to examine the impact of lipids and apolipoproteins on GDM. The research comprised univariable and multivariable MR analyses, with a prime focus on individual and combined effects of lipid-related traits. Statistical techniques included the fixed-effect inverse variance weighted (IVW) method and supplementary methods such as MR-Egger for comprehensive assessment.

RESULTS

Our findings revealed the following significant associations: apoA-I and HDL cholesterol were inversely correlated with GDM risk, while triglycerides showed a positive correlation. In multivariable analysis, apoA-I consistently exhibited a strong causal link with GDM, even after adjusting for other lipids and Body Mass Index (BMI).

CONCLUSION

The study demonstrates a significant causal relationship between apoA-I and GDM risk.

Adrenoceptor Desensitization: Current Understanding of Mechanisms

G-protein coupled receptors (GPCRs) transduce a wide range of extracellular signals. They are key players in the majority of biologic functions including vision, olfaction, chemotaxis, and immunity. However, as essential as most of them are to body function and homeostasis, overactivation of GPCRs has been implicated in many pathologic diseases such as cancer, asthma, and heart failure (HF). Therefore, an important feature of G protein signaling systems is the ability to control GPCR responsiveness, and one key process to control overstimulation involves initiating receptor desensitization. A number of steps are appreciated in the desensitization process, including cell surface receptor phosphorylation, internalization, and downregulation. Rapid or short-term desensitization occurs within minutes and involves receptor phosphorylation via the action of intracellular protein kinases, the binding of β-arrestins, and the consequent uncoupling of GPCRs from their cognate heterotrimeric G proteins. On the other hand, long-term desensitization occurs over hours to days and involves receptor downregulation or a decrease in cell surface receptor protein level. Of the proteins involved in this biologic phenomenon, β-arrestins play a particularly significant role in both short- and long-term desensitization mechanisms. In addition, β-arrestins are involved in the phenomenon of biased agonism, where the biased ligand preferentially activates one of several downstream signaling pathways, leading to altered cellular responses. In this context, this review discusses the different patterns of desensitization of the α 1-, α 2- and the β adrenoceptors and highlights the role of β-arrestins in regulating physiologic responsiveness through desensitization and biased agonism. SIGNIFICANCE STATEMENT: A sophisticated network of proteins orchestrates the molecular regulation of GPCR activity. Adrenoceptors are GPCRs that play vast roles in many physiological processes. Without tightly controlled desensitization of these receptors, homeostatic imbalance may ensue, thus precipitating various diseases. Here, we critically appraise the mechanisms implicated in adrenoceptor desensitization. A better understanding of these mechanisms helps identify new druggable targets within the GPCR desensitization machinery and opens exciting therapeutic fronts in the treatment of several pathologies.

The effects of the β1-adrenergic receptor antagonist bisoprolol administration on mirabegron-stimulated human brown adipose tissue thermogenesis

AIM

Pharmacological stimulation of human brown adipose tissue (BAT) has been hindered by ineffective activation or undesirable off-target effects. Oral administration of the maximal allowable dose of mirabegron (200 mg), a β3-adrenergic receptor (β3-AR) agonist, has been effective in stimulating BAT thermogenesis and whole-body energy expenditure. However, this has been accompanied by undesirable cardiovascular effects. Therefore, we hypothesized that combining mirabegron with a β1-AR antagonist could suppress these unwanted effects and increase the stimulation of the β3-AR and β2-AR in BAT.

METHODS

We performed a randomized crossover trial (NCT04823442) in 8 lean men. Mirabegron (200 mg) was administered orally with or without the β1-AR antagonist bisoprolol (10 mg). Dynamic [11C]-acetate and 2-deoxy-2-[18F]fluoro-d-glucose PET/CT scans were performed sequentially after oral administration of mirabegron ± bisoprolol.

RESULTS

Compared to room temperature, mirabegron alone increased BAT oxidative metabolism (0.84 ± 0.46 vs. 1.79 ± 0.91 min-1, p = 0.0433), but not when combined with bisoprolol. The metabolic rate of glucose in BAT, measured using [18F]FDG PET, was significantly higher with mirabegron than mirabegron with bisoprolol (24 ± 10 vs. 16 ± 8 nmol/g/min, p = 0.0284). Bisoprolol inhibited the mirabegron-induced increase in systolic blood pressure and heart rate.

CONCLUSION

The administration of bisoprolol decreases the adverse cardiovascular effects of mirabegron. However, the provided dose also blunted the mirabegron-stimulated increase in BAT lipolysis, thermogenesis, and glucose uptake. The attenuation in BAT blood flow induced by the large dose of bisoprolol may have limited BAT thermogenesis.

Genetic evidence for involvement of β2-adrenergic receptor in brown adipose tissue thermogenesis in humans

BACKGROUND

Sympathetic activation of brown adipose tissue (BAT) thermogenesis can ameliorate obesity and related metabolic abnormalities. However, crucial subtypes of the β-adrenergic receptor (AR), as well as effects of its genetic variants on functions of BAT, remains unclear in humans. We conducted association analyses of genes encoding β-ARs and BAT activity in human adults.

METHODS

Single nucleotide polymorphisms (SNPs) in β1-, β2-, and β3-AR genes (ADRB1, ADRB2, and ADRB3) were tested for the association with BAT activity under mild cold exposure (19 °C, 2 h) in 399 healthy Japanese adults. BAT activity was measured using fluorodeoxyglucose-positron emission tomography and computed tomography (FDG-PET/CT). To validate the results, we assessed the effects of SNPs in the two independent populations comprising 277 healthy East Asian adults using near-infrared time-resolved spectroscopy (NIRTRS) or infrared thermography (IRT). Effects of SNPs on physiological responses to intensive cold exposure were tested in 42 healthy Japanese adult males using an artificial climate chamber.

RESULTS

We found a significant association between a functional SNP (rs1042718) in ADRB2 and BAT activity assessed with FDG-PET/CT (p < 0.001). This SNP also showed an association with cold-induced thermogenesis in the population subset. Furthermore, the association was replicated in the two other independent populations; BAT activity was evaluated by NIRTRS or IRT (p < 0.05). This SNP did not show associations with oxygen consumption and cold-induced thermogenesis under intensive cold exposure, suggesting the irrelevance of shivering thermogenesis. The SNPs of ADRB1 and ADRB3 were not associated with these BAT-related traits.

CONCLUSIONS

The present study supports the importance of β2-AR in the sympathetic regulation of BAT thermogenesis in humans. The present collection of DNA samples is the largest to which information on the donor's BAT activity has been assigned and can serve as a reference for further in-depth understanding of human BAT function.

The Different Shades of Thermogenic Adipose Tissue

PURPOSE OF REVIEW

By providing a concise overview of adipose tissue types, elucidating the regulation of adipose thermogenic capacity in both physiological contexts and chronic wasting diseases (a protracted hypermetabolic state that precipitates sustained catabolism and consequent progressive corporeal atrophy), and most importantly, delving into the ongoing discourse regarding the role of adipose tissue thermogenic activation in chronic wasting diseases, this review aims to provide researchers with a comprehensive understanding of the field.

RECENT FINDINGS

Adipose tissue, traditionally classified as white, brown, and beige (brite) based on its thermogenic activity and potential, is intricately regulated by complex mechanisms in response to exercise or cold exposure. This regulation is adipose depot-specific and dependent on the duration of exposure. Excessive thermogenic activation of adipose tissue has been observed in chronic wasting diseases and has been considered a pathological factor that accelerates disease progression. However, this conclusion may be confounded by the detrimental effects of excessive lipolysis. Recent research also suggests that such activation may play a beneficial role in the early stages of chronic wasting disease and provide potential therapeutic effects. A more comprehensive understanding of the changes in adipose tissue thermogenesis under physiological and pathological conditions, as well as the underlying regulatory mechanisms, is essential for the development of novel interventions to improve health and prevent disease.

Olodaterol promotes thermogenesis in brown adipocytes via regulation of the β2-AR/cAMP/PKA signaling pathway

The escalating incidence of metabolic pathologies such as obesity and diabetes mellitus underscores the imperative for innovative therapeutics targeting lipid metabolism modulation. Within this context, augmenting thermogenic processes in adipose cells emerges as a viable therapeutic approach. Given the limitations of previous β3-adrenergic receptor (β3-AR) agonist treatments in human diseases, there is an increasing focus on therapies targeting the β2-adrenergic receptor (β2-AR). Olodaterol (OLO) is a potent β2-AR agonist that is a potential novel pharmacological candidate in this area. Our study explores the role and underlying mechanisms of OLO in enhancing brown adipose thermogenesis, providing robust evidence from in vitro and in vivo studies. OLO demonstrated a dose-dependent enhancement of lipolysis, notably increasing the expression of Uncoupling Protein 1 (UCP1) and raising the rate of oxygen consumption in primary brown adipocytes. This suggests a significant increase in thermogenic potential and energy expenditure. The administration of OLO to murine models noticeably enhanced cold-induced nonshivering thermogenesis. OLO elevated UCP1 expression in the brown adipose tissue of mice. Furthermore, it promoted brown adipocyte thermogenesis by activating the β2-AR/cAMP/PKA signaling cascades according to RNA sequencing, western blotting, and molecular docking analysis. This investigation underscores the therapeutic potential of OLO for metabolic ailments and sheds light on the intricate molecular dynamics of adipocyte thermogenesis, laying the groundwork for future targeted therapeutic interventions in human metabolic disorders.

Healthy Aging in Times of Extreme Temperatures: Biomedical Approaches

Climate extremes and rising energy prices present interconnected global health risks. Technical solutions can be supplemented with biomedical approaches to promote healthy longevity in hot and cold conditions. In summer, reducing basal metabolic rate through mild caloric restriction or CR mimetics, such as resveratrol, can potentially be used to lower body temperature. In winter, activating brown adipose tissue (BAT) for non-shivering thermogenesis and improved metabolic health can help adaptation to colder environments. Catechins found in green tea and in other food could be alternatives to drugs for these purposes. This review examines and discusses the biomedical evidence supporting the use of CR mimetics and BAT activators for health benefits amid increasingly extreme temperatures.

Futile cycles: Emerging utility from apparent futility

Futile cycles are biological phenomena where two opposing biochemical reactions run simultaneously, resulting in a net energy loss without appreciable productivity. Such a state was presumed to be a biological aberration and thus deemed an energy-wasting "futile" cycle. However, multiple pieces of evidence suggest that biological utilities emerge from futile cycles. A few established functions of futile cycles are to control metabolic sensitivity, modulate energy homeostasis, and drive adaptive thermogenesis. Yet, the physiological regulation, implication, and pathological relevance of most futile cycles remain poorly studied. In this review, we highlight the abundance and versatility of futile cycles and propose a classification scheme. We further discuss the energetic implications of various futile cycles and their impact on basal metabolic rate, their bona fide and tentative pathophysiological implications, and putative drug interactions.

Futile lipid cycling: from biochemistry to physiology

In the healthy state, the fat stored in our body isn't just inert. Rather, it is dynamically mobilized to maintain an adequate concentration of fatty acids (FAs) in our bloodstream. Our body tends to produce excess FAs to ensure that the FA availability is not limiting. The surplus FAs are actively re-esterified into glycerides, initiating a cycle of breakdown and resynthesis of glycerides. This cycle consumes energy without generating a new product and is commonly referred to as the 'futile lipid cycle' or the glyceride/FA cycle. Contrary to the notion that it's a wasteful process, it turns out this cycle is crucial for systemic metabolic homeostasis. It acts as a control point in intra-adipocyte and inter-organ cross-talk, a metabolic rheostat, an energy sensor and a lipid diversifying mechanism. In this Review, we discuss the metabolic regulation and physiological implications of the glyceride/FA cycle and its mechanistic underpinnings.

Parallel control of cold-triggered adipocyte thermogenesis by UCP1 and CKB

That uncoupling protein 1 (UCP1) is the sole mediator of adipocyte thermogenesis is a conventional viewpoint that has primarily been inferred from the attenuation of the thermogenic output of mice genetically lacking Ucp1 from birth (germline Ucp1-/-). However, germline Ucp1-/- mice harbor secondary changes within brown adipose tissue. To mitigate these potentially confounding ancillary changes, we constructed mice with inducible adipocyte-selective Ucp1 disruption. We find that, although germline Ucp1-/- mice succumb to cold-induced hypothermia with complete penetrance, most mice with the inducible deletion of Ucp1 maintain homeothermy in the cold. However, inducible adipocyte-selective co-deletion of Ucp1 and creatine kinase b (Ckb, an effector of UCP1-independent thermogenesis) exacerbates cold intolerance. Following UCP1 deletion or UCP1/CKB co-deletion from mature adipocytes, moderate cold exposure triggers the regeneration of mature brown adipocytes that coordinately restore UCP1 and CKB expression. Our findings suggest that thermogenic adipocytes utilize non-paralogous protein redundancy-through UCP1 and CKB-to promote cold-induced energy dissipation.

A Synergistic Botanical Composition Increases Resting Energy Expenditure and Reduces Adiposity in High-Fat Diet-Fed Rats

OBJECTIVE

An imbalance between dietary energy intake and energy expenditure may result in body fat gain or obesity. Increasing resting energy expenditure (REE) is an attractive strategy for managing body fat gain. The objective of the current study was to generate proof-of-concept data on a synergistic composition (LN19183) of Citrus aurantifolia fruit rind (CA) and Theobroma cacao seed (TC) extracts to increase REE and reduce body fat gain in a high-fat diet (HFD)-fed rats.

METHOD

In in vitro cell-based experiments, CA, TC, or LN19183 were tested for fibroblast growth factor 21 (FGF-21) production from 3T3-L1 mouse adipocytes. Uncoupling protein 1 (UCP-1) and beta3-adrenergic receptor (β3-AR) protein expressions in LN19183-treated 3T3-L1 lysates were also tested. The 56-day in vivo study in male Sprague Dawley (SD) rats (age: 12-14 weeks; body weight [b.w.]: 115-197 g) contained 2 phases of 28 days each of induction and supplementation. Seven rats received a regular rodent diet (RD) over 56 days. In the induction phase, 21 rats received HFD; in the supplementation phase, the obese rats (n = 7) received either HFD alone or in concurrence with a daily oral dose of either 100 or 250 mg/kg b.w. of LN19183 for 28 days.

RESULTS

In 3T3-L1 adipocytes, LN19183 synergistically increased FGF-21 production and dose-dependently increased β3-AR and UCP-1 protein expression. In HFD-fed rats, both doses of LN19183 supplementation significantly (p < 0.05) decreased the body weight gain, total fat mass, and liver weight and increased (p < 0.05) REE. High-dose LN19183 also significantly (p < 0.05) increased fat oxidation and UCP-1 protein expression in white fat tissue and reduced liver triglyceride (TG) level. LN19183-supplemented groups substantially reduced serum TG and glucose levels compared to the HFD rats.

CONCLUSIONS

LN19183 reduces body fat mass and weight gain via increased REE and fat oxidation in HFD-fed obese rats.

Obesity - Standards, trends and advances

Obesity continues to be a significant global health concern, giving rise to various complications. This review article explores the current standards and emerging innovations in diagnosing and treating obesity, including recent disease name change, staging system or therapeutic goals. This narrative review has been based on recent scientific articles from PubMed database, limiting the scope of topics to current standards and upcoming developments and breakthroughs in the diagnosis and treatment of obesity. The educational and informative nature of the review has been maintained in order to make the information presented accessible to both researchers and clinical practitioners. The recognition of diverse obesity phenotypes has prompted a paradigm shift towards a complex and patient-centered approach to diagnosis and therapy. Pharmacotherapy for obesity is evolving rapidly, with ongoing research focusing on novel molecular targets and metabolic pathways. Promising developments include dual or triple incretin analogs, oral incretin drugs, neurotransmitter-based therapies, muscle mass-increasing treatments, and therapies targeting visceral adipose tissue browning. Despite current evidence-based international standards, the field of obesity diagnosis and treatment continues to expand, with new diagnostic tools and pharmacotherapies potentially replacing current practices. Therapeutic management should be tailored to individual patients, considering obesity phenotype, health status, lifestyle, and preferences. Looking ahead, the future holds promising opportunities for obesity management, but further research is required to assess the efficacy and safety of emerging therapies. A multifactorial and personalized approach will be pivotal in addressing the diverse challenges posed by obesity.

Effects of mirabegron on brown adipose tissue and metabolism in humans: A systematic review and meta-analysis

BACKGROUND

Brown adipose tissue (BAT) has emerged as a potential therapeutic target for metabolic disorders due to its thermogenic and anti-obesity properties. β3-adrenergic receptor (β3-AR) agonists have also gained attention as potential agents for BAT activation and metabolic regulation. Mirabegron, a selective β3-AR-agonist used clinically for overactive bladder syndrome, has been explored for its utility in metabolic disorders. However, the controversy surrounding the ability of mirabegron to activate BAT to accelerate metabolism requires further investigation. The aim of this systematic review is to characterize comprehensively the impact of mirabegron on human BAT and its metabolism.

METHODS

We searched PubMed Central, Web of Science, Embase, and Cochrane Library databases for relevant papers published from the date of database inception to March 2023 for systematic reviews and meta-analyses. We extracted data on primary outcome indicators such as BAT volume, BAT activity, body temperature, and resting energy expenditure (REE), as well as secondary outcome indicators such as heart rate (HR), diastolic blood pressure (DBP), systolic blood pressure (SBP), non-esterified fatty acids (NEFA), blood glucose, and blood insulin from relevant studies. For studies that did not provide suitable data for meta-analysis, we used narrative data synthesis. For studies that provided suitable data for meta-analysis, we conducted meta-analysis using RevMan 5.4 software.

RESULTS

We reviewed 10 papers and included 6 in our meta-analysis. Our findings revealed no significant changes in BAT volume (p = 0.72) or blood glucose (p = 0.52) with mirabegron when compared to the placebo or pre-dose population. However, patients showed significant increases in BAT activity (p < 0.01), blood NEFA (p < 0.01), body temperature (p < 0.01), REE (p < 0.01), HR (p < 0.01), DBP (p < 0.01), SBP (p = 0.25), and blood insulin (p < 0.01).

CONCLUSION

Through our meta-analysis of 6 papers, we found that mirabegron has the potential to increase human BAT activity, REE, NEFA content, body temperature, HR, blood pressure, and blood insulin content. These effects may lead to reductions in blood glucose levels in obese/overweight and diabetic patients. Additionally, the activation of BAT by mirabegron could represent a novel approach for treating obesity, diabetes, and cardiovascular disease.

TRIAL REGISTRATION NUMBER AND DATE

CRD42023413446, 04/11/2023.

Drugs of the future for diarrhea-predominant irritable bowel syndrome: an overview of current investigational drugs

INTRODUCTION

Irritable bowel syndrome (IBS) has a significant impact on society and quality of life. Current treatments are ineffective, and new investigational drugs are necessary.

AREAS COVERED

Numerous potential therapies are developing, targeting different areas such as cannabinoid signaling, opioid receptors, tachykinin (NK2) receptors, β3-adrenergic receptors, intestinal microbiota, inflammation, and 5HT receptors. Clinical trial evidence has shown that loperamide, eluxadoline, alosetron, ramosetron, bile acid sequestrants, and rifaximin can modulate GI alterations and benefit patients with IBS-D. Among the potential therapies, ibodutant, ibudilast, blautix, BOS-589, solabegron, vibegron, olorinab, ebastine, and ORP-101 have demonstrated possible effects but remain confirmed.

EXPERT OPINION

Individuals with IBS-D require cost-effective treatment options that do not impede their productivity or that of their caregivers. This is necessary for consistent healthcare and improved quality of life. Therefore, we should focus on developing new, efficient, and affordable medications for IBS-D. The government, insurers, and society must recognize this need and collaborate to ensure its fulfillment.

NG ,NG -Dimethylarginine Dimethylaminohydrolase 1 Expression Is Dispensable for Cold- or Diet-Induced Thermogenesis

The strategy to activate thermogenic adipocytes has therapeutic potential to overcome obesity as they dissipate surplus energy as heat through various mechanisms. NG,NG-dimethylarginine dimethylaminohydrolases (DDAHs) are enzymes involved in the nitric oxide-protein kinase G signaling axis which increases thermogenic gene expression. However, the role of DDAHs in thermogenic adipocytes has not been elucidated. The adipocyte-specific Ddah1 knockout mice are generated by crossing Ddah1fl/fl mice with adiponectin Cre recombinase mice. Adipocyte-specific DDAH1 overexpressing mice are generated using adeno-associated virus-double-floxed inverse open reading frame (AAV-DIO) system. These mice are analyzed under basal, cold exposure, or high-fat diet (HFD) conditions. Primary inguinal white adipose tissue cells from adipocyte-specific Ddah1 knockout mice expressed comparable amounts of Ucp1 mRNA. Adipocyte-specific DDAH1 overexpressing mice do not exhibit enhanced activation of thermogenic adipocytes. In addition, when these mice are exposed to cold environment or fed an HFD, their body temperature/weight and thermogenesis-related gene and protein expressions are unchanged. These findings indicate that DDAH1 does not play a role in either cold- or diet-induced thermogenesis. Therefore, adipocyte targeting DDAH1 gene therapy for the treatment of obesity is unlikely to be effective.

Ubiquitin ligase RNF20 coordinates sequential adipose thermogenesis with brown and beige fat-specific substrates

In mammals, brown adipose tissue (BAT) and inguinal white adipose tissue (iWAT) execute sequential thermogenesis to maintain body temperature during cold stimuli. BAT rapidly generates heat through brown adipocyte activation, and further iWAT gradually stimulates beige fat cell differentiation upon prolonged cold challenges. However, fat depot-specific regulatory mechanisms for thermogenic activation of two fat depots are poorly understood. Here, we demonstrate that E3 ubiquitin ligase RNF20 orchestrates adipose thermogenesis with BAT- and iWAT-specific substrates. Upon cold stimuli, BAT RNF20 is rapidly downregulated, resulting in GABPα protein elevation by controlling protein stability, which stimulates thermogenic gene expression. Accordingly, BAT-specific Rnf20 suppression potentiates BAT thermogenic activity via GABPα upregulation. Moreover, upon prolonged cold stimuli, iWAT RNF20 is gradually upregulated to promote de novo beige adipogenesis. Mechanistically, iWAT RNF20 mediates NCoR1 protein degradation, rather than GABPα, to activate PPARγ. Together, current findings propose fat depot-specific regulatory mechanisms for temporal activation of adipose thermogenesis.

ATF4 expression in thermogenic adipocytes is required for cold-induced thermogenesis in mice via FGF21-independent mechanisms

In brown adipose tissue (BAT), short-term cold exposure induces the activating transcription factor 4 (ATF4), and its downstream target fibroblast growth factor 21 (FGF21). Induction of ATF4 in BAT in response to mitochondrial stress is required for thermoregulation, partially by increasing FGF21 expression. In the present study, we tested the hypothesis that Atf4 and Fgf21 induction in BAT are both required for BAT thermogenesis under physiological stress by generating mice selectively lacking either Atf4 (ATF4 BKO) or Fgf21 (FGF21 BKO) in UCP1-expressing adipocytes. After 3 days of cold exposure, core body temperature was significantly reduced in ad-libitum-fed ATF4 BKO mice, which correlated with Fgf21 downregulation in brown and beige adipocytes, and impaired browning of white adipose tissue. Conversely, despite having reduced browning, FGF21 BKO mice had preserved core body temperature after cold exposure. Mechanistically, ATF4, but not FGF21, regulates amino acid import and metabolism in response to cold, likely contributing to BAT thermogenic capacity under ad libitum-fed conditions. Importantly, under fasting conditions, both ATF4 and FGF21 were required for thermogenesis in cold-exposed mice. Thus, ATF4 regulates BAT thermogenesis under fed conditions likely in a FGF21-independent manner, in part via increased amino acid uptake and metabolism.

Brown adipose tissue-derived metabolites and their role in regulating metabolism

The discovery and rejuvenation of metabolically active brown adipose tissue (BAT) in adult humans have offered a new approach to treat obesity and metabolic diseases. Beyond its accomplished role in adaptive thermogenesis, BAT secretes signaling molecules known as "batokines", which are instrumental in regulating whole-body metabolism via autocrine, paracrine, and endocrine action. In addition to the intrinsic BAT metabolite-oxidizing activity, the endocrine functions of these molecules may help to explain the association between BAT activity and a healthy systemic metabolic profile. Herein, we review the evidence that underscores the significance of BAT-derived metabolites, especially highlighting their role in controlling physiological and metabolic processes involving thermogenesis, substrate metabolism, and other essential biological processes. The conversation extends to their capacity to enhance energy expenditure and mitigate features of obesity and its related metabolic complications. Thus, metabolites derived from BAT may provide new avenues for the discovery of metabolic health-promoting drugs with far-reaching impacts. This review aims to dissect the complexities of the secretory role of BAT in modulating local and systemic metabolism in metabolic health and disease.

Sweet swell of burning fat: emerging role of high-density lipoprotein in energy homeostasis

PURPOSE OF REVIEW

Metabolism of lipids and lipoproteins, including high-density lipoprotein (HDL), plays a central role in energy homeostasis. Mechanisms underlying the relationship between energy homeostasis and HDL however remain poorly studied.

RECENT FINDINGS

Available evidence reveals that HDL is implicated in energy homeostasis. Circulating high-density lipoprotein-cholesterol (HDL-C) levels are affected by energy production, raising with increasing resting metabolic rate. Lipolysis of triglycerides as a source of energy decreases plasma levels of remnant cholesterol, increases levels of HDL-C, and can be cardioprotective. Switch to preferential energy production from carbohydrates exerts opposite effects.

SUMMARY

Low HDL-C may represent a biomarker of inefficient energy production from fats. HDL-C-raising can be beneficial when it reflects enhanced energy production from burning fat.

Is the β3-Adrenoceptor a Valid Target for the Treatment of Obesity and/or Type 2 Diabetes?

β3-Adrenoceptors mediate several functions in rodents that could be beneficial for the treatment of obesity and type 2 diabetes. This includes promotion of insulin release from the pancreas, cellular glucose uptake, lipolysis, and thermogenesis in brown adipose tissue. In combination, they lead to a reduction of body weight in several rodent models including ob/ob mice and Zucker diabetic fatty rats. These findings stimulated drug development programs in various pharmaceutical companies, and at least nine β3-adrenoceptor agonists have been tested in clinical trials. However, all of these projects were discontinued due to the lack of clinically relevant changes in body weight. Following a concise historical account of discoveries leading to such drug development programs we discuss species differences that explain why β3-adrenoceptors are not a meaningful drug target for the treatment of obesity and type 2 diabetes in humans.

Mirabegron displays anticancer effects by globally browning adipose tissues

Metabolic reprogramming in malignant cells is a hallmark of cancer that relies on augmented glycolytic metabolism to support their growth, invasion, and metastasis. However, the impact of global adipose metabolism on tumor growth and the drug development by targeting adipose metabolism remain largely unexplored. Here we show that a therapeutic paradigm of drugs is effective for treating various cancer types by browning adipose tissues. Mirabegron, a clinically available drug for overactive bladders, displays potent anticancer effects in various animal cancer models, including untreatable cancers such as pancreatic ductal adenocarcinoma and hepatocellular carcinoma, via the browning of adipose tissues. Genetic deletion of the uncoupling protein 1, a key thermogenic protein in adipose tissues, ablates the anticancer effect. Similarly, the removal of brown adipose tissue, which is responsible for non-shivering thermogenesis, attenuates the anticancer activity of mirabegron. These findings demonstrate that mirabegron represents a paradigm of anticancer drugs with a distinct mechanism for the effective treatment of multiple cancers.

Mirabegron, a Selective β3-Adrenergic Receptor Agonist, as a Potential Anti-Obesity Drug

Obesity is becoming a global health epidemic. Brown and "beige" adipose tissue may produce heat, leading to energy expenditure enhancement and weight loss. Mirabegron, a selective β3-adrenergic receptor agonist, has been found to be effective as a brown adipose tissue activator, a "beige" cells stimulator and a metabolic homeostasis controller in animal and human studies. Although in animal studies, administration of mirabegron led to obesity improvement, significant weight loss in obese patients after mirabegron treatment has not been demonstrated so far, which may be associated with the too-short duration of the trials and the small number of participants in the studies. In humans, the most effective treatment for adipose tissue stimulation was high doses of mirabegron; however, cardiovascular side effects may limit the use of such doses, so the long-term safety must be evaluated. In cases of tachycardia or blood pressure elevation, the co-administration of a β1-adrenergic receptor blocker may be useful. It should be checked whether smaller doses of mirabegron, taken for a longer time, will be sufficient to stimulate brown and "beige" adipose tissue, leading to weight loss. The introduction of mirabegron into obesity treatment in the future will require long-term trials with larger numbers of subjects, to assess mirabegron efficacy, tolerability, and safety.

Pharmacological modulation of adaptive thermogenesis: new clues for obesity management?

BACKGROUND

Adaptive thermogenesis represents the main mechanism through which the body generates heat in response to external stimuli, a phenomenon that includes shivering and non-shivering thermogenesis. The non-shivering thermogenesis is mainly exploited by adipose tissue characterized by a brown aspect, which specializes in energy dissipation. A decreased amount of brown adipose tissue has been observed in ageing and chronic illnesses such as obesity, a worldwide health problem characterized by dysfunctional adipose tissue expansion and associated cardiometabolic complications. In the last decades, the discovery of a trans-differentiation mechanism ("browning") within white adipose tissue depots, leading to the generation of brown-like cells, allowed to explore new natural and synthetic compounds able to favour this process and thus enhance thermogenesis with the aim of counteracting obesity. Based on recent findings, brown adipose tissue-activating agents could represent another option in addition to appetite inhibitors and inhibitors of nutrient absorption for obesity treatment.

PURPOSE

This review investigates the main molecules involved in the physiological (e.g. incretin hormones) and pharmacological (e.g. β3-adrenergic receptors agonists, thyroid receptor agonists, farnesoid X receptor agonists, glucagon-like peptide-1, and glucagon receptor agonists) modulation of adaptive thermogenesis and the signalling mechanisms involved.

Repurposing the β3-Adrenergic Receptor Agonist Mirabegron in Patients With Structural Cardiac Disease: The Beta3-LVH Phase 2b Randomized Clinical Trial

Importance

Left ventricular (LV) hypertrophy contributes to the onset and progression of heart failure (HF), particularly for patients with pre-HF (stage B) for whom no treatment has yet proven effective to prevent transition to overt HF (stage C). The β3-adrenergic receptors (β3ARs) may represent a new target, as their activation attenuates LV remodeling.

Objective

To determine whether activation of β3ARs by repurposing a β3AR agonist, mirabegron, is safe and effective in preventing progression of LV hypertrophy and diastolic dysfunction among patients with pre- or mild HF.

Design, Setting, and Participants

The Beta3-LVH prospective, triple-blind, placebo-controlled phase 2b randomized clinical trial enrolled patients between September 12, 2016, and February 26, 2021, with a follow-up of 12 months. The trial was conducted at 10 academic hospitals in 8 countries across Europe (Germany, Poland, France, Belgium, Italy, Portugal, Greece, and the UK). Patients aged 18 years or older with or without HF symptoms (maximum New York Heart Association class II) were screened for the presence of LV hypertrophy (increased LV mass index [LVMI] of ≥95 g/m2 for women or ≥115 g/m2 for men) or maximum wall thickness of 13 mm or greater using echocardiography. Data analysis was performed in August 2022.

Intervention

Participants were randomly assigned (1:1) to mirabegron (50 mg/d) or placebo, stratified by the presence of atrial fibrillation and/or type 2 diabetes, for 12 months.

Main Outcomes and Measures

The primary end points were LVMI determined using cardiac magnetic resonance imaging and LV diastolic function (early diastolic tissue Doppler velocity [E/e'] ratio assessed using Doppler echocardiography) at 12 months. Patients with at least 1 valid measurement of either primary end point were included in the primary analysis. Safety was assessed for all patients who received at least 1 dose of study medication.

Results

Of the 380 patients screened, 296 were enrolled in the trial. There were 147 patients randomized to mirabegron (116 men [79%]; mean [SD] age, 64.0 [10.2] years) and 149 to placebo (112 men [75%]; mean [SD] age, 62.2 [10.9] years). All patients were included in the primary intention-to-treat analysis. At 12 months, the baseline and covariate-adjusted differences between groups included a 1.3-g/m2 increase in LVMI (95% CI, -0.15 to 2.74; P = .08) and a -0.15 decrease in E/e' (95% CI, -0.69 to 0.4; P = .60). A total of 213 adverse events (AEs) occurred in 82 mirabegron-treated patients (including 31 serious AEs in 19 patients) and 215 AEs occurred in 88 placebo-treated patients (including 30 serious AEs in 22 patients). No deaths occurred during the trial.

Conclusions

In this study, mirabegron therapy had a neutral effect on LV mass or diastolic function over 12 months among patients who had structural heart disease with no or mild HF symptoms.

Trial Registration

ClinicalTrials.gov Identifier: NCT02599480.

Angiotensin II type 2 receptor as a novel activator of brown adipose tissue in obesity

The angiotensin II type 2 receptor (AT2R) exerts vasorelaxant, anti-inflammatory, and antioxidant properties. In obesity, its activation counterbalances the adverse cardiovascular effects of angiotensin II mediated by the AT1R. Preliminary results indicate that it also promotes brown adipocyte differentiation in vitro. Our hypothesis is that AT2R activation could increase BAT mass and activity in obesity. Five-week-old male C57BL/6J mice were fed a standard or a high-fat (HF) diet for 6 weeks. Half of the animals were treated with compound 21 (C21), a selective AT2R agonist, (1 mg/kg/day) in the drinking water. Electron transport chain (ETC), oxidative phosphorylation, and UCP1 proteins were measured in the interscapular BAT (iBAT) and thoracic perivascular adipose tissue (tPVAT) as well as inflammatory and oxidative parameters. Differentiation and oxygen consumption rate (OCR) in the presence of C21 was tested in brown preadipocytes. In vitro, C21-differentiated brown adipocytes showed an AT2R-dependent increase of differentiation markers (Ucp1, Cidea, Pparg) and increased basal and H+ leak-linked OCR. In vivo, HF-C21 mice showed increased iBAT mass compared to HF animals. Both their iBAT and tPVAT showed higher protein levels of the ETC protein complexes and UCP1, together with a reduction of inflammatory and oxidative markers. The activation of the AT2R increases BAT mass, mitochondrial activity, and reduces markers of tissue inflammation and oxidative stress in obesity. Therefore, insulin reduction and better vascular responses are achieved. Thus, the activation of the protective arm of the renin-angiotensin system arises as a promising tool in the treatment of obesity.

Promoting metabolic inefficiency for metabolic disease

Recent advances in pharmacotherapies that promote appetite suppression have shown remarkable weight loss. Therapies targeting energy expenditure lag behind, and as such none have yet been identified to be safe and efficacious for sustaining negative energy balance toward weight loss. Multiple energy dissipating pathways have been identified in adipose tissue and muscle. The molecular effectors of some of these pathways have been identified, but much is still left to be learned about their regulation. Understanding the molecular underpinnings of metabolic inefficiency in adipose tissue and muscle is required if these pathways are to be therapeutically targeted in the context of obesity and obesity-accelerated diseases.

HDAC11 inhibition triggers bimodal thermogenic pathways to circumvent adipocyte catecholamine resistance

Stimulation of adipocyte β-adrenergic receptors (β-ARs) induces expression of uncoupling protein 1 (UCP1), promoting nonshivering thermogenesis. Association of β-ARs with a lysine-myristoylated form of A kinase-anchoring protein 12 (AKAP12, also known as gravin-α) is required for downstream signaling that culminates in UCP1 induction. Conversely, demyristoylation of gravin-α by histone deacetylase 11 (HDAC11) suppresses this pathway. Whether inhibition of HDAC11 in adipocytes is sufficient to drive UCP1 expression independently of β-ARs is not known. Here, we demonstrate that adipocyte-specific deletion of HDAC11 in mice leads to robust induction of UCP1 in adipose tissue (AT), resulting in increased body temperature. These effects are mimicked by treating mice in vivo or human AT ex vivo with an HDAC11-selective inhibitor, FT895. FT895 triggers biphasic, gravin-α myristoylation-dependent induction of UCP1 protein expression, with a noncanonical acute response that is posttranscriptional and independent of protein kinase A (PKA), and a delayed response requiring PKA activity and new Ucp1 mRNA synthesis. Remarkably, HDAC11 inhibition promotes UCP1 expression even in models of adipocyte catecholamine resistance where β-AR signaling is blocked. These findings define cell-autonomous, multimodal roles for HDAC11 as a suppressor of thermogenesis, and highlight the potential of inhibiting HDAC11 to therapeutically alter AT phenotype independently of β-AR stimulation.

Impact of estrogens on resting energy expenditure: A systematic review

The fear of weight gain is one of the main reasons for women not to initiate or to early discontinue hormonal contraception or menopausal hormone therapy. Resting energy expenditure is by far the largest component and the most important determinant of total energy expenditure. Given that low resting energy expenditure is a confirmed predictive factor for weight gain and consecutively for the development of obesity, research into the influence of sex steroids on resting energy expenditure is a particularly exciting area. The objective of this systematic review was to evaluate the effects of medication with natural and synthetic estrogens on resting energy expenditure in healthy normal weight and overweight women. Through complex systematic literature searches, a total of 10 studies were identified that investigated the effects of medication with estrogens on resting energy expenditure. Our results demonstrate that estrogen administration increases resting energy expenditure by up to +208 kcal per day in the context of contraception and by up to +222 kcal per day in the context of menopausal hormone therapy, suggesting a preventive effect of circulating estrogen levels and estrogen administration on weight gain and obesity development.

Cold-stimulated brown adipose tissue activation is related to changes in serum metabolites relevant to NAD+ metabolism in humans

Cold-induced brown adipose tissue (BAT) activation is considered to improve metabolic health. In murine BAT, cold increases the fundamental molecule for mitochondrial function, nicotinamide adenine dinucleotide (NAD+), but limited knowledge of NAD+ metabolism during cold in human BAT metabolism exists. We show that cold increases the serum metabolites of the NAD+ salvage pathway (nicotinamide and 1-methylnicotinamide) in humans. Additionally, individuals with cold-stimulated BAT activation have decreased levels of metabolites from the de novo NAD+ biosynthesis pathway (tryptophan, kynurenine). Serum nicotinamide correlates positively with cold-stimulated BAT activation, whereas tryptophan and kynurenine correlate negatively. Furthermore, the expression of genes involved in NAD+ biosynthesis in BAT is related to markers of metabolic health. Our data indicate that cold increases serum tryptophan conversion to nicotinamide to be further utilized by BAT. We conclude that NAD+ metabolism is activated upon cold in humans and is probably regulated in a coordinated fashion by several tissues.

Brown Fat and Nutrition: Implications for Nutritional Interventions

Brown and beige adipocytes are renowned for their unique ability to generate heat through a mechanism known as thermogenesis. This process can be induced by exposure to cold, hormonal signals, drugs, and dietary factors. The activation of these thermogenic adipocytes holds promise for improving glucose metabolism, reducing fat accumulation, and enhancing insulin sensitivity. However, the translation of preclinical findings into effective clinical therapies poses challenges, warranting further research to identify the molecular mechanisms underlying the differentiation and function of brown and beige adipocytes. Consequently, research has focused on the development of drugs, such as mirabegron, ephedrine, and thyroid hormone, that mimic the effects of cold exposure to activate brown fat activity. Additionally, nutritional interventions have been explored as an alternative approach to minimize potential side effects. Brown fat and beige fat have emerged as promising targets for addressing nutritional imbalances, with the potential to develop strategies for mitigating the impact of metabolic diseases. Understanding the influence of nutritional factors on brown fat activity can facilitate the development of strategies to promote its activation and mitigate metabolic disorders.

ATF4 Expression in Thermogenic Adipocytes is Required for Cold-Induced Thermogenesis in Mice via FGF21-Independent Mechanisms

In brown adipose tissue (BAT), short-term cold exposure induces the activating transcription factor 4 (ATF4), and its downstream target fibroblast growth factor 21 (FGF21). Induction of ATF4 in BAT in response to mitochondrial stress is required for thermoregulation, partially via upregulation of FGF21. In the present study, we tested the hypothesis that Atf4 and Fgf21 induction in BAT are both required for BAT thermogenesis by generating mice selectively lacking either Atf4 ( ATF4 BKO ) or Fgf21 (FGF21 BKO) in UCP1-expressing adipocytes. After 3 days of cold exposure, core body temperature was significantly reduced in ad-libitum -fed ATF4 BKO mice, which correlated with Fgf21 downregulation in brown and beige adipocytes, and impaired browning of white adipose tissue (WAT). Conversely, despite having reduced browning, FGF21 BKO mice had preserved core body temperature after cold exposure. Mechanistically, ATF4, but not FGF21, regulates amino acid import and metabolism in response to cold, likely contributing to BAT thermogenic capacity under ad libitum -fed conditions. Importantly, under fasting conditions, both ATF4 and FGF21 were required for thermogenesis in cold-exposed mice. Thus, ATF4 regulates BAT thermogenesis by activating amino acid metabolism in BAT in a FGF21-independent manner.

A Systematic Review and Meta-Analysis of Free Triiodothyronine (FT3) Levels in Humans Depending on Seasonal Air Temperature Changes: Is the Variation in FT3 Levels Related to Nonshivering Thermogenesis?

Thyroid hormones play a crucial role in regulating normal development, growth, and metabolic function. However, the controversy surrounding seasonal changes in free triiodothyronine (FT3) levels remains unresolved. Therefore, the aim of this study was to conduct a systematic review and meta-analysis of variations in FT3 levels in relation to seasonal air temperatures in the context of current knowledge about its role in nonshivering thermogenesis. Ten eligible articles with a total of 336,755 participants were included in the meta-analysis. The studies were categorized into two groups based on the air temperature: "Cold winter", where the winter temperature fell below 0 °C, and "Warm winter", where the winter temperature was above 0 °C. The analysis revealed that in cold regions, FT3 levels decreased in winter compared to summer (I2 = 57%, p < 0.001), whereas in warm regions, FT3 levels increased during winter (I2 = 28%, p < 0.001). These findings suggest that seasonal variations in FT3 levels are likely to be influenced by the winter temperature. Considering the important role of the FT3 in the nonshivering thermogenesis process, we assume that this observed pattern is probably related to the differences in use of thyroid hormones in the brown adipose tissue during adaptive thermogenesis, which may depend on intensity of cold exposure.

Breaking down silos: the multifaceted nature of obesity and the future of weight management

The continued global increase in the prevalence of obesity prompted a meeting at the Royal Society of London investigating causal mechanisms of the disease, 'Causes of obesity: theories, conjectures, and evidence' in October 2022. Evidence presented indicates areas of obesity science where there have been advancements, including an increased understanding of biological and physiological processes of weight gain and maintenance, yet it is clear there is still debate on the relative contribution of plausible causes of the modern obesity epidemic. Consensus was reached that obesity is not a reflection of diminished willpower, but rather the confluence of multiple, complex factors. As such, addressing obesity requires multifactorial prevention and treatment strategies. The accumulated evidence suggests that a continued focus primarily on individual-level contributors will be suboptimal in promoting weight management at the population level. Here, we consider individual biological and physiological processes within the broader context of sociodemographic and sociocultural exposures as well as environmental changes to optimize research priorities and public health efforts. This requires a consideration of a systems-level approach that efficiently addresses both systemic and group-specific environmental determinants, including psychosocial factors, that often serve as a barrier to otherwise efficacious prevention and treatment options. This article is part of a discussion meeting issue 'Causes of obesity: theories, conjectures and evidence (Part I)'.

Loss of cAMP Signaling in CD11c Immune Cells Protects Against Diet-Induced Obesity

In obesity, CD11c+ innate immune cells are recruited to adipose tissue and create an inflammatory state that causes both insulin and catecholamine resistance. We found that ablation of Gnas, the gene that encodes Gαs, in CD11c expressing cells protects mice from obesity, glucose intolerance, and insulin resistance. Transplantation studies showed that the lean phenotype was conferred by bone marrow-derived cells and did not require adaptive immunity. Loss of cAMP signaling was associated with increased adipose tissue norepinephrine and cAMP signaling, and prevention of catecholamine resistance. The adipose tissue had reduced expression of catecholamine transport and degradation enzymes, suggesting that the elevated norepinephrine resulted from decreased catabolism. Collectively, our results identified an important role for cAMP signaling in CD11c+ innate immune cells in whole-body metabolism by controlling norepinephrine levels in white adipose tissue, modulating catecholamine-induced lipolysis and increasing thermogenesis, which, together, created a lean phenotype.

ARTICLE HIGHLIGHTS

We undertook this study to understand how immune cells communicate with adipocytes, specifically, whether cAMP signaling in the immune cell and the adipocyte are connected. We identified a reciprocal interaction between CD11c+ innate immune cells and adipocytes in which high cAMP signaling in the immune cell compartment induces low cAMP signaling in adipocytes and vice versa. This interaction regulates lipolysis in adipocytes and inflammation in immune cells, resulting in either a lean, obesity-resistant, and insulin-sensitive phenotype, or an obese, insulin-resistant phenotype.

Adipose Tissue and Metabolic Health

In this review, we provide a brief synopsis of the connections between adipose tissue and metabolic health and highlight some recent developments in understanding and exploiting adipocyte biology. Adipose tissue plays critical roles in the regulation of systemic glucose and lipid metabolism and secretes bioactive molecules possessing endocrine, paracrine, and autocrine functions. Dysfunctional adipose tissue has a detrimental impact on metabolic health and is intimately involved in key aspects of metabolic diseases such as insulin resistance, lipid overload, inflammation, and organelle stress. Differences in the distribution of fat depots and adipose characteristics relate to divergent degrees of metabolic dysfunction found in metabolically healthy and unhealthy obese individuals. Thermogenic adipocytes increase energy expenditure via mitochondrial uncoupling or adenosine triphosphate-consuming futile substrate cycles, while functioning as a metabolic sink and participating in crosstalk with other metabolic organs. Manipulation of adipose tissue provides a wealth of opportunities to intervene and combat the progression of associated metabolic diseases. We discuss current treatment modalities for obesity including incretin hormone analogs and touch upon emerging strategies with therapeutic potential including exosome-based therapy, pharmacological activation of brown and beige adipocyte thermogenesis, and administration or inhibition of adipocyte-derived factors.

Sympathetic Nervous System and Atherosclerosis

Atherosclerosis is characterized by the narrowing of the arterial lumen due to subendothelial lipid accumulation, with hypercholesterolemia being a major risk factor. Despite the recent advances in effective lipid-lowering therapies, atherosclerosis remains the leading cause of mortality globally, highlighting the need for additional therapeutic strategies. Accumulating evidence suggests that the sympathetic nervous system plays an important role in atherosclerosis. In this article, we reviewed the sympathetic innervation in the vasculature, norepinephrine synthesis and metabolism, sympathetic activity measurement, and common signaling pathways of sympathetic activation. The focus of this paper was to review the effectiveness of pharmacological antagonists or agonists of adrenoceptors (α1, α2, β1, β2, and β3) and renal denervation on atherosclerosis. All five types of adrenoceptors are present in arterial blood vessels. α1 blockers inhibit atherosclerosis but increase the risk of heart failure while α2 agonism may protect against atherosclerosis and newer generations of β blockers and β3 agonists are promising therapies against atherosclerosis; however, new randomized controlled trials are warranted to investigate the effectiveness of these therapies in atherosclerosis inhibition and cardiovascular risk reduction in the future. The role of renal denervation in atherosclerosis inhibition in humans is yet to be established.

Latest advances in the regulatory genes of adipocyte thermogenesis

An energy imbalance cause obesity: more energy intake or less energy expenditure, or both. Obesity could be the origin of many metabolic disorders, such as type 2 diabetes and cardiovascular disease. UCP1 (uncoupling protein1), which is highly and exclusively expressed in the thermogenic adipocytes, including beige and brown adipocytes, can dissipate proton motive force into heat without producing ATP to increase energy expenditure. It is an attractive strategy to combat obesity and its related metabolic disorders by increasing non-shivering adipocyte thermogenesis. Adipocyte thermogenesis has recently been reported to be regulated by several new genes. This work provided novel and potential targets to activate adipocyte thermogenesis and resist obesity, such as secreted proteins ADISSP and EMC10, enzyme SSU72, etc. In this review, we have summarized the latest research on adipocyte thermogenesis regulation to shed more light on this topic.

ScreenDMT reveals linoleic acid diols replicably associate with BMI and stimulate adipocyte calcium fluxes

Activating brown adipose tissue (BAT) improves systemic metabolism, making it a promising target for metabolic syndrome. BAT is activated by 12, 13-dihydroxy-9Z-octadecenoic acid (12, 13-diHOME), which we previously identified to be inversely associated with BMI and which directly improves metabolism in multiple tissues. Here we profile plasma lipidomics from a cohort of 83 people and test which lipids' association with BMI replicates in a concordant direction using our novel tool ScreenDMT, whose power and validity we demonstrate via mathematical proofs and simulations. We find that the linoleic acid diols 12, 13-diHOME and 9, 10-diHOME both replicably inversely associate with BMI and mechanistically activate calcium fluxes in mouse brown and white adipocytes in vitro, which implicates this pathway and 9, 10-diHOME as candidate therapeutic targets. ScreenDMT can be applied to test directional mediation, directional replication, and qualitative interactions, such as identifying biomarkers whose association is shared (replication) or opposite (qualitative interaction) across diverse populations.

The serotonin transporter sustains human brown adipose tissue thermogenesis

Activation of brown adipose tissue (BAT) in humans is a strategy to treat obesity and metabolic disease. Here we show that the serotonin transporter (SERT), encoded by SLC6A4, prevents serotonin-mediated suppression of human BAT function. RNA sequencing of human primary brown and white adipocytes shows that SLC6A4 is highly expressed in human, but not murine, brown adipocytes and BAT. Serotonin decreases uncoupled respiration and reduces uncoupling protein 1 via the 5-HT2B receptor. SERT inhibition by the selective serotonin reuptake inhibitor (SSRI) sertraline prevents uptake of extracellular serotonin, thereby potentiating serotonin's suppressive effect on brown adipocytes. Furthermore, we see that sertraline reduces BAT activation in healthy volunteers, and SSRI-treated patients demonstrate no 18F-fluorodeoxyglucose uptake by BAT at room temperature, unlike matched controls. Inhibition of BAT thermogenesis may contribute to SSRI-induced weight gain and metabolic dysfunction, and reducing peripheral serotonin action may be an approach to treat obesity and metabolic disease.

Obese Adipocytes Have Altered Redox Homeostasis with Metabolic Consequences

White and brown adipose tissues are organized to form a real organ, the adipose organ, in mice and humans. White adipocytes of obese animals and humans are hypertrophic. This condition is accompanied by a series of organelle alterations and stress of the endoplasmic reticulum. This stress is mainly due to reactive oxygen species activity and accumulation, lending to NLRP3 inflammasome activation. This last causes death of adipocytes by pyroptosis and the formation of large cellular debris that must be removed by macrophages. During their chronic scavenging activity, macrophages produce several secretory products that have collateral consequences, including interference with insulin receptor activity, causing insulin resistance. The latter is accompanied by an increased noradrenergic inhibitory innervation of Langerhans islets with de-differentiation of beta cells and type 2 diabetes. The whitening of brown adipocytes could explain the different critical death size of visceral adipocytes and offer an explanation for the worse clinical consequence of visceral fat accumulation. White to brown transdifferentiation has been proven in mice and humans. Considering the energy-dispersing activity of brown adipose tissue, transdifferentiation opens new therapeutic perspectives for obesity and related disorders.

Inhibition of AXL receptor tyrosine kinase enhances brown adipose tissue functionality in mice

The current obesity epidemic and high prevalence of metabolic diseases necessitate efficacious and safe treatments. Brown adipose tissue in this context is a promising target with the potential to increase energy expenditure, however no pharmacological treatments activating brown adipose tissue are currently available. Here, we identify AXL receptor tyrosine kinase as a regulator of adipose function. Pharmacological and genetic inhibition of AXL enhance thermogenic capacity of brown and white adipocytes, in vitro and in vivo. Mechanistically, these effects are mediated through inhibition of PI3K/AKT/PDE signaling pathway, resulting in induction of nuclear FOXO1 localization and increased intracellular cAMP levels via PDE3/4 inhibition and subsequent stimulation of the PKA-ATF2 pathway. In line with this, both constitutive Axl deletion as well as inducible adipocyte-specific Axl deletion protect animals from diet-induced obesity concomitant with increases in energy expenditure. Based on these data, we propose AXL receptor as a target for the treatment of obesity.

Mirabegron alleviates acetic acid-induced colitis in rats: role of adiponectin and GSTM1/GSH detoxification pathway

The prevalence of the debilitating chronic disease ulcerative colitis (UC) is increasing significantly. Mirabegron is a selective beta-3 adrenergic receptor (β-3 AR) agonist used to treat an overactive bladder. Previous reports have demonstrated the antidiarrheal effect of β-3AR agonists. Therefore, the current study aims to investigate the potential symptomatic effects of mirabegron on an experimental colitis model. The effects of oral administration of mirabegron (10mg/kg) for seven days on rats receiving intra-rectal acetic acid instillation on the sixth day were examined using adult male Wistar rats. Sulfasalazine was utilized as a reference medication. Gross, microscopic, and biochemical observations of the experimental colitis were performed. The quantity and mucin content of goblet cells were found to have significantly decreased in the colitis group. In the colons of rats administered mirabegron, the number of goblet cells and the optical density of its mucin content increased. Mirabegron's ability to increase adiponectin in serum and decrease glutathione, GSTM1, and catalase in the colon may account for its protective effects. In addition, mirabegron decreased the expression of the proteins caspase-3 and NF-κB p65. It also prevented the activation of their upstream signaling receptors TLR4 and p-AKT by acetic acid administration. In conclusion, mirabegron prevented acetic acid-induced colitis in rats, possibly due to its antioxidant, anti-inflammatory, and antiapoptotic properties.

18F-FDG PET/CT technology for the assessment of brown adipose tissue: an updated review

INTRODUCTION

This review provides an update of 18 F-fluorodeoxyglucose ([18F] FDG) for Brown adipose tissue (BAT) activity quantification, whose role is not completely understood.

AREAS COVERED

We conducted an unstructured search of the literature for any studies employing the [18F] FDG PET in BAT assessment. We explored BAT quantification both in healthy individuals and in different pathologies, after cold exposure and as a metabolic biomarker. The assessment of possible BAT modulators by using [18F] FDG PET is shown. Further PET tracers and novel developments for BAT assessments are also described.

EXPERT OPINION

Further PET tracers and imaging modalities are under investigation, but the [18F] FDG PET is currently the method of choice for the evaluation of BAT and further multicentric trials are needed for a better understanding of the BAT physiopathology, also after cold stimuli. The modulation of BAT activity, assessed by [18F] FDG PET imaging, seems a promising tool for the management of conditions such as obesity and type 2 diabetes. Moreover, an interesting possible correlation of BAT activation with prognostic [18F] FDG PET indices in cancer patients should be assessed with further multicentric trials.

Clinical pharmacology of β-3 adrenergic receptor agonists for cardiovascular diseases

INTRODUCTION

Few agonists of the third isotype of beta-adrenergic receptors, the β3-adrenoreceptor, are currently used clinically, and new agonists are under development for the treatment of overactive bladder disease. As the receptor is expressed in human cardiac and vascular tissues, it is important to understand their beneficial (or adverse) effect(s) on these targets.

AREAS COVERED

We discuss the most recent results of clinical trials testing the benefit and safety of β3-adrenoreceptor activation on cardiovascular outcomes in light of current knowledge on the receptor biology, genetic polymorphisms, and agonist pharmacology.

EXPERT OPINION

While evidence from small clinical trials is limited so far, the β3-agonist, mirabegron seems to be safe in patients at high cardiovascular risk but produces benefits on selected cardiovascular outcomes only at higher than standard doses. Activation of cardiovascular β3-adrenoreceptors deserves to be tested with more potent agonists, such as vibegron.

Adipocyte G Protein-Coupled Receptors as Potential Targets for Novel Antidiabetic Drugs

The functional state of adipocytes plays a central role in regulating numerous important metabolic functions, including energy and glucose homeostasis. While white adipocytes store excess calories as fat (triglycerides) and release free fatty acids as a fuel source in times of need, brown and beige adipocytes (so-called thermogenic adipocytes) convert chemical energy stored in substrates (e.g., fatty acids or glucose) into heat, thus promoting energy expenditure. Like all other cell types, adipocytes express many G protein-coupled receptors (GPCRs) that are linked to four major functional classes of heterotrimeric G proteins (Gs, Gi/o, Gq/11, and G12/13). During the past few years, novel experimental approaches, including the use of chemogenetic strategies, have led to a series of important new findings regarding the metabolic consequences of activating or inhibiting distinct GPCR/G protein signaling pathways in white, brown, and beige adipocytes. This novel information should guide the development of novel drugs capable of modulating the activity of specific adipocyte GPCR signaling pathways for the treatment of obesity, type 2 diabetes, and related metabolic disorders.

Subclinical Reactive Hypoglycemia with Low Glucose Effectiveness-Why We Cannot Stop Snacking despite Gaining Weight

Obesity has grown worldwide owing to modern obesogenic lifestyles, including frequent snacking. Recently, we studied continuous glucose monitoring in obese/overweight men without diabetes and found that half of them exhibit glucose levels less than 70 mg/dL after a 75-g oral glucose load without notable hypoglycemic symptoms. Interestingly, people with "subclinical reactive hypoglycemia (SRH)" snack more frequently than those without it. Since the ingestion of sugary snacks or drinks could further induce SRH, a vicious cycle of "Snacking begets snacking via SRH" can be formed. Glucose effectiveness (Sg) is an insulin-independent mechanism that contributes to most of the whole-body glucose disposal after an oral glucose load in people without diabetes. Our recent data suggest that both higher and lower Sg are associated with SRH, while the latter but not the former is linked to snacking habits, obesity, and dysglycemia. The present review addresses the possible role of SRH in snacking habits in people with obesity/overweight, taking Sg into account. It is concluded that, for those with low Sg, SRH can be regarded as a link between snacking and obesity. Prevention of SRH by raising Sg might be key to controlling snacking habits and body weight.

360-Degree Perspectives on Obesity

Alarming statistics show that the number of people affected by excessive weight has surpassed 2 billion, representing approximately 30% of the world's population. The aim of this review is to provide a comprehensive overview of one of the most serious public health problems, considering that obesity requires an integrative approach that takes into account its complex etiology, including genetic, environmental, and lifestyle factors. Only an understanding of the connections between the many contributors to obesity and the synergy between treatment interventions can ensure satisfactory outcomes in reducing obesity. Mechanisms such as oxidative stress, chronic inflammation, and dysbiosis play a crucial role in the pathogenesis of obesity and its associated complications. Compounding factors such as the deleterious effects of stress, the novel challenge posed by the obesogenic digital (food) environment, and the stigma associated with obesity should not be overlooked. Preclinical research in animal models has been instrumental in elucidating these mechanisms, and translation into clinical practice has provided promising therapeutic options, including epigenetic approaches, pharmacotherapy, and bariatric surgery. However, more studies are necessary to discover new compounds that target key metabolic pathways, innovative ways to deliver the drugs, the optimal combinations of lifestyle interventions with allopathic treatments, and, last but not least, emerging biological markers for effective monitoring. With each passing day, the obesity crisis tightens its grip, threatening not only individual lives but also burdening healthcare systems and societies at large. It is high time we took action as we confront the urgent imperative to address this escalating global health challenge head-on.