Brown adipose tissue activation in humans increases plasma levels of lipid mediators

CONTEXT

Activation of brown adipose tissue (BAT) thermogenesis improves insulin sensitivity and is beneficial in obesity. Emerging evidence indicates that BAT activation increases lipid mediators that play autocrine and endocrine roles to regulate metabolism and inflammation.

OBJECTIVE

The goal of the study was to determine the relationship between two distinct approaches of BAT activation (cold exposure and mirabegron treatment) with lipid mediators in humans.

METHODS

Healthy female subjects (n = 14) were treated with β3-adrenergic receptor agonist mirabegron (100 mg) daily for 28 days. A subset of female subjects (n = 8) was additionally exposed to cold temperatures (14-16°C) for 2 hours using a cooling vest prior to initiating mirabegron treatment.

MAIN OUTCOME MEASURES

A panel of lipid mediators was assessed in plasma using targeted liquid chromatography-tandem mass spectrometry, and their relationship to anthropometric and metabolic parameters was determined.

RESULTS

Activation of BAT with cold exposure acutely increased levels of lipoxygenase and cyclooxygenase products, including 12-hydroxyeicosapentaenoic acid (HEPE), 12-hydroxyeicosatetraenoic acid (HETE), 5-HETE, 14-hydroxydocosahexaenoic acid (HDHA), an isomer of maresin 2 (MaR2), 17-HDHA, protectin D1 (PD1), and prostaglandin E2 (PGE2). Mirabegron treatment similarly increased these products acutely, although levels of some mediators were blunted after chronic mirabegron treatment. Selected lipid mediators, including a MaR2 isomer, 17-HDHA, 5-HETE, and 15-HETE, positively correlated with non-esterified fatty acids and negatively correlated with the respiratory quotient, while PD1, 15-HETE, and 5-HETE positively correlated with adiponectin.

CONCLUSION

These results indicate that selected lipid mediators may serve as biomarkers of BAT activation.

Brown adipose tissue CoQ deficiency activates the integrated stress response and FGF21-dependent mitohormesis

Coenzyme Q (CoQ) is essential for mitochondrial respiration and required for thermogenic activity in brown adipose tissues (BAT). CoQ deficiency leads to a wide range of pathological manifestations, but mechanistic consequences of CoQ deficiency in specific tissues, such as BAT, remain poorly understood. Here, we show that pharmacological or genetic CoQ deficiency in BAT leads to stress signals causing accumulation of cytosolic mitochondrial RNAs and activation of the eIF2α kinase PKR, resulting in activation of the integrated stress response (ISR) with suppression of UCP1 but induction of FGF21 expression. Strikingly, despite diminished UCP1 levels, BAT CoQ deficiency displays increased whole-body metabolic rates at room temperature and thermoneutrality resulting in decreased weight gain on high-fat diets (HFD). In line with enhanced metabolic rates, BAT and inguinal white adipose tissue (iWAT) interorgan crosstalk caused increased browning of iWAT in BAT-specific CoQ deficient animals. This mitohormesis-like effect depends on the ATF4-FGF21 axis and BAT-secreted FGF21, revealing an unexpected role for CoQ in the modulation of whole-body energy expenditure with wide-ranging implications for primary and secondary CoQ deficiencies.

"Turning up the heat": Role of neurotrophic batokines in the postnatal maturation and remodelling of brown adipose tissue in deer mice

Activation of brown adipose tissue (BAT) thermogenesis impacts energy balance and must be tightly regulated. Several neurotrophic factors, expressed in BAT of adult laboratory rodents, have been implicated in remodelling the sympathetic neural network to enhance thermogenesis (e.g., NGF, NRG4 and S100b). Here, we compare for the first time the relative roles of three neurotropic 'batokines' in establishing/remodelling innervation during postnatal development and adult cold stress. We used lab-reared P. maniculatus, which rely heavily on BAT-based thermogenesis for survival in the wild, beginning between postnatal days (P) 8 and 10. BAT sympathetic innervation was enhanced from P6-10, and exogenous NGF, NRG4, and S100b stimulated neurite outgrowth from P6 sympathetic neurons. Endogenous BAT protein stores and/or gene expression of NRG4, S100b, and calsyntenin-3ß (which regulates S100b secretion), remained high and constant during development. However, endogenous NGF was low and ngf mRNA was undetectable. Conditioned media (CM) from cultured P10 BAT slices stimulated neurite outgrowth from sympathetic neurons in vitro that was inhibited by antibodies against all three growth factors. P10 CM had significant amounts of secreted NRG4 and S100b protein, but not NGF. By contrast, BAT slices from cold-acclimated adults released significant amounts of all three factors relative to thermoneutral controls. These data suggest that while neurotrophic batokines regulate sympathetic innervation in vivo, their relative contributions differ depending on life stage. They also provide novel insight into the regulation of BAT remodelling and BAT's secretory role, which are both critical to our understanding of mammalian energy homeostasis.

β-caryophyllene ameliorated obesity-associated airway hyperresponsiveness through some non-conventional targets

BACKGROUND

Obesity worsens airway hyperresponsiveness (AHR) in asthmatic subjects by up-regulating macrophage polarization that leads to excessive secretion of pro-inflammatory adipokines from white adipose tissue followed by generation of oxidative stress in the respiratory system. Treatment through conventional signaling pathways proved to be inadequate in obese asthmatics, so a therapeutical approach through a non-conventional pathway may prove to be effective.

PURPOSE

This study aimed to investigate the efficacy of a FDA-approved food additive, β-caryophyllene (BCP) in obesity-associated AHR.

METHOD

A repertoire of protein expression, cytokine and adiponectin estimation, oxidative stress assays, histopathology, and fluorescence immune-histochemistry were performed to assess the efficacy of BCP in C57BL/6 mice model of obesity-associated AHR. Additionally, human adipocyte was utilized to study the effect of BCP on macrophage polarization in Boyden chamber cell culture inserts.

RESULTS

Obesity-associated AHR is ameliorated by administration of BCP by inhibition of the macrophage polarization by activation of AMPKα, Nrf2/HO-1 and AdipoR1 and AdipoR2 signaling pathway, up-regulation of adiponectin, GLP-1, IFN-γ, SOD, catalase and down-regulation of NF-κB, leptin, IL-4, TNF, and IL-1β. Browning of eWAT by induction of thermogenesis and activation of melanocortin pathway also contributed to the amelioration of obesity-associated AHR. We conclude that BCP ameliorated the obesity-associated AHR via inhibition of macrophage polarization, activation of AMPKα, Nrf2/HO-1, and up-regulation of AdipoR1 and AdipoR2 expression and down-regulation of NFκB expression in lung of animal.

CONCLUSION

Being an FDA-approved food additive, BCP may prove to be a safe and potential agent against obesity-associated AHR.

Non-shivering Thermogenesis Signalling Regulation and Potential Therapeutic Applications of Brown Adipose Tissue

In mammals, thermogenic organs exist in the body that increase heat production and enhance energy regulation. Because brown adipose tissue (BAT) consumes energy and generates heat, increasing energy expenditure via BAT might be a potential strategy for new treatments for obesity and obesity-related diseases. Thermogenic differentiation affects normal adipose tissue generation, emphasizing the critical role that common transcriptional regulation factors might play in common characteristics and sources. An understanding of thermogenic differentiation and related factors could help in developing ways to improve obesity indirectly or directly through targeting of specific signalling pathways. Many studies have shown that the active components of various natural products promote thermogenesis through various signalling pathways. This article reviews recent major advances in this field, including those in the cyclic adenosine monophosphate-protein kinase A (cAMP-PKA), cyclic guanosine monophosphate-GMP-dependent protein kinase G (cGMP-AKT), AMP-activated protein kinase (AMPK), mammalian target of rapamycin (mTOR), transforming growth factor-β/bone morphogenic protein (TGF-β/BMP), transient receptor potential (TRP), Wnt, nuclear factor-κ-light-chain-enhancer of activated B cells (NF-κΒ), Notch and Hedgehog (Hh) signalling pathways in brown and brown-like adipose tissue. To provide effective information for future research on weight-loss nutraceuticals or drugs, this review also highlights the natural products and their active ingredients that have been reported in recent years to affect thermogenesis and thus contribute to weight loss via the above signalling pathways.

Mirabegron: The most promising adipose tissue beiging agent

Accumulation of white adipose tissue (WAT) underlies the obesity epidemic, leading to current therapeutic techniques that are being investigated for their ability to activate/“beige” this tissue. Adipose tissue (AT) beiging has been reported through intermittent cold exposure (CE), exercise, and β3‐Adrenergic Receptor (β3AR) agonists. But how AT beiging can help in the treatment of metabolic disorders like obesity and type 2 diabetes (T2D) remains largely unexplored. This review summarizes recent research on the use of β3AR agonist, mirabegron (Myrbetriq®), in stimulating beiging in AT. Researchers have only recently been able to determine the optimal therapeutic dose of mirabegron for inducing beiging in subcutaneous/ inguinal WAT, where the benefits of AT activation are evident without the undesired cardiovascular side effects. To determine whether the effects that mirabegron elicits are metabolically beneficial, a comparison of the undisputed findings resulting from intermittent CE‐induced beiging and the disputed findings from exercise‐induced beiging was conducted. Given the recent in vivo animal and clinical studies, the understanding of how mirabegron can be metabolically beneficial for both lean and obese individuals is more clearly understood. These studies have demonstrated that circulating adipokines, glucose metabolism, and lipid droplet (LD) size are all positively affected by mirabegron administration. Recent studies have also demonstrated that mirabegron has similar outcomes to intermittent CE and displays more direct evidence for beiging than those produced with exercise. With these current findings, mirabegron is considered the most promising and safest β3AR agonist currently available that has the potential to be used in the therapeutic treatment of metabolic disorders, and future studies into its interaction with different conditions may prove to be useful as part of a treatment plan in combination with a healthy diet and exercise.

Supplementary prenatal copper increases plasma triiodothyronine and brown adipose tissue uncoupling protein-1 gene expression but depresses thermogenesis in newborn lambs

Objective

We tested the hypothesis that increasing dietary copper (Cu) to gravid ewes would enhance brown adipose tissue (BAT) thermogenesis in their offspring.

Methods

Twin-bearing ewes were assigned on d 70 of gestation to diets containing 3, 10, or 20 ppm dietary Cu (n = 8 per group). Twin lambs were assigned at birth to a cold (6°C) or warm (28°C) environmental chamber for 48 h. Blood was collected from ewes and from lambs and perirenal BAT was collected after 48 h in the environmental chambers.

Results

Prenatal Cu exposure increased ewe plasma triiodothyronine (T3) and thyroxine concentration (T4) (p < 0.01) but prenatal Cu exposure had no effect on lamb plasma concentrations of T3, T4, glucose, or nonesterified fatty acid concentration (p ≥ 0.08). The high level of prenatal Cu exposure depressed 48-h rectal temperature (p = 0.03). Cold exposure decreased BAT norepinephrine (NE) and increased BAT dopamine (p ≤ 0.01), but prenatal Cu exposure had no effect on BAT cytochrome C oxidase activity or BAT NE or dopamine (p ≥ 0.07). However, BAT of lambs from high-Cu ewes maintained higher uncoupling protein-1 (UCP1) gene expression than BAT of lambs from low- and medium-Cu ewes following warm or cold exposure in environmental chambers (p = 0.02). Cold exposure caused near depletion of BAT lipid by 48 h (p < 0.001), increased BAT cytochrome c oxidase activity (p < 0.01), and depressed plasma fatty acid concentrations (p < 0.001).

Conclusion

Although prenatal Cu exposure increased BAT UCP1 expression during warm and cold exposure, prenatal cold Cu exposure depressed 48-h rectal temperature. Cold exposure decreased BAT lipid content by over 80% and decreased lamb plasma fatty acid concentration by over 40%, indicating that fuel reserves for thermogenesis were nearly depleted by 48 h of cold exposure.

β -Lapachone Regulates Obesity through Modulating Thermogenesis in Brown Adipose Tissue and Adipocytes: Role of AMPK Signaling Pathway

Activation of brown adipose tissue (BAT) has been proposed as a promising target against obesity due to its increased capacity for thermogenesis. In this study, we explored the effect of β -Lapachone ( β L), a compound obtained from the bark of the lapacho tree, against obesity. In vivo administration of β L into either high fat diet (HFD)-induced obese C57BL6 mice and genetically obese Lepr -∕- mice prevented body weight gain, which was associated with tissue weight loss of white adipose tissue (WAT). In addition, β L elevated thermogenic proteins including uncoupling protein 1 (UCP1) and mitochondrial count in BAT and human adipose tissue-derived mesenchymal stem cells (hAMSCs). β L also induced AMP-activated protein kinase (AMPK) phosphorylation, subsequent upregulation of acetyl-CoA carboxylase (ACC) and UCP1, and these effects were diminished by AMPK inhibitor compound C, suggesting that AMPK underlies the effects of β L. Mitogen-activated protein kinase pathways participated in the thermogenesis of β L, specifically p38, c-Jun N-terminal kinase (JNK) and extracellular signal-regulated kinase 1/2 (ERK1/2) were activated by β L treatment in hAMSCs. Additionally, inhibitors of p38/JNK/ERK1/2 abrogated the activity of β L. Taken together, β L exerts anti-obese effects by inducing thermogenesis mediated by AMPK signaling pathway, suggesting that β L may have a potential therapeutic implication of obesity. Taken together, β L exerts anti-obese effects by not only inducing thermogenesis on brown adipocytes but also inducing the browning of white adipocytes. The anti-obese effect of β L is mediated by AMPK signaling pathway, suggesting that β L may have potential therapeutic implication of obesity.

Glucocorticoid Receptor and Adipocyte Biology

Glucocorticoids are steroid hormones that play a key role in metabolic adaptations during stress, such as fasting and starvation, in order to maintain plasma glucose levels. Excess and chronic glucocorticoid exposure, however, causes metabolic syndrome including insulin resistance, dyslipidemia, and hyperglycemia. Studies in animal models of metabolic disorders frequently demonstrate that suppressing glucocorticoid signaling improves insulin sensitivity and metabolic profiles. Glucocorticoids convey their signals through an intracellular glucocorticoid receptor (GR), which is a transcriptional regulator. The adipocyte is one cell type that contributes to whole body metabolic homeostasis under the influence of GR. Glucocorticoids' functions on adipose tissues are complex. Depending on various physiological or pathophysiological states as well as distinct fat depots, glucocorticoids can either increase or decrease lipid storage in adipose tissues. In rodents, glucocorticoids have been shown to reduce the thermogenic activity of brown adipocytes. However, in human acute glucocorticoid exposure, glucocorticoids act to promote thermogenesis. In this article, we will review the recent studies on the mechanisms underlying the complex metabolic functions of GR in adipocytes. These include studies of the metabolic outcomes of adipocyte specific GR knockout mice and identification of novel GR primary target genes that mediate glucocorticoid action in adipocytes.

Melinjo (Gnetum gnemon L.) seed extract induces uncoupling protein 1 expression in brown fat and protects mice against diet-induced obesity, inflammation, and insulin resistance

Dietary supplementation with melinjo (Gnetum gnemon L.) seed extract (MSE) has been proposed as an anti-obesity strategy. However, it remains unclear how MSE modulates energy balance. We tested the hypothesis that dietary MSE reduces energy intake and/or increases physical activity and metabolic thermogenesis in brown and white adipose tissue (BAT and WAT) in mice. Twenty-four C57BL/6 J mice were provided with normal diet, high-fat diet (HFD), or HFD with 1% MSE added, for 17 weeks. Food intake, spontaneous locomotor activity, hepatic triglyceride (TG) content, and blood parameters were examined. Mitochondrial thermogenesis-associated molecule and inflammatory marker expression levels in BAT and WAT were examined by quantitative PCR and western blotting. Dietary MSE did not affect energy intake or spontaneous locomotor activity, but significantly suppressed HFD-induced fat accumulation, hyperglycemia, and hyperinsulinemia. Homeostasis model assessment of insulin resistance score and hepatic TG content were both lower in the MSE-supplemented HFD-fed group than in the HFD-fed group, indicating reduced insulin resistance and a less fatty liver. Dietary MSE upregulated thermogenic uncoupling protein 1 (UCP1) and mitochondrial marker cytochrome c oxidase subunit IV protein expression in BAT; this was closely associated with sirtuin 1 mRNA induction. mRNAs of adipose inflammatory markers, such as monocyte chemotactic 1 and interleukin-1, were induced by HFD but suppressed by MSE. Considering that UCP1 protein expression is the most physiologically relevant parameter to assess the thermogenic capacities of BAT, our results indicate that dietary MSE supplementation induces BAT thermogenesis and reduces obesity-associated adipose tissue inflammation, hepatic steatosis, and insulin resistance.

Diabetes incidence and glucose intolerance prevalence increase with higher outdoor temperature

OBJECTIVE

Rising global temperatures might contribute to the current worldwide diabetes epidemic, as higher ambient temperature can negatively impact glucose metabolism via a reduction in brown adipose tissue activity. Therefore, we examined the association between outdoor temperature and diabetes incidence in the USA as well as the prevalence of glucose intolerance worldwide.

RESEARCH DESIGN AND METHODS

Using meta-regression, we determined the association between mean annual temperature and diabetes incidence during 1996-2009 for each US state separately. Subsequently, results were pooled in a meta-analysis. On a global scale, we performed a meta-regression analysis to assess the association between mean annual temperature and the prevalence of glucose intolerance.

RESULTS

We demonstrated that, on average, per 1°C increase in temperature, age-adjusted diabetes incidence increased with 0.314 (95% CI 0.194 to 0.434) per 1000. Similarly, the worldwide prevalence of glucose intolerance increased by 0.170% (95% CI 0.107% to 0.234%) per 1°C rise in temperature. These associations persisted after adjustment for obesity.

CONCLUSIONS

Our findings indicate that the diabetes incidence rate in the USA and prevalence of glucose intolerance worldwide increase with higher outdoor temperature.

Lipocalin 2 regulates brown fat activation via a nonadrenergic activation mechanism

In this study, we report that lipocalin 2 (Lcn2), a recently characterized adipokine/cytokine, is a novel regulator of brown adipose tissue (BAT) activation by modulating the adrenergic independent p38 MAPK-PGC-1α-UCP1 pathway. Global Lcn2 knock-out (Lcn2(-/-)) mice have defective BAT thermogenic activation caused by cold stimulation and decreased BAT activity under high fat diet-induced obesity. Nevertheless, Lcn2(-/-) mice maintain normal sympathetic nervous system activation as evidenced by normal catecholamine release and lipolytic activity in response to cold stimulation. Further studies showed that Lcn2 deficiency impairs peroxisomal and mitochondrial oxidation of lipids and attenuates cold-induced Pgc1a and Ucp1 expression and p38 MAPK phosphorylation in BAT. Moreover, in vitro studies showed that Lcn2 deficiency reduces the thermogenic activity of brown adipocytes. Lcn2(-/-) differentiated brown adipocytes have significantly decreased expression levels of brown fat markers, decreased p38 MAPK phosphorylation, and decreased mitochondrial oxidation capacity. However, Lcn2(-/-) brown adipocytes have normal norepinephrine-stimulated p38 MAPK and hormone-sensitive lipase phosphorylation and Pgc1a and Ucp1 expression, suggesting an intact β-adrenergic signaling activation. More intriguingly, recombinant Lcn2 was able to significantly stimulate p38 MAPK phosphorylation in brown adipocytes. Activating peroxisome proliferator-activated receptor γ, a downstream effector of PGC-1α, by thiazolidinedione administration fully reverses the BAT function of Lcn2(-/-) mice. Our findings provide evidence for the novel role Lcn2 plays in oxidative metabolism and BAT activation via an adrenergic independent mechanism.

The chemical uncoupler 2,4-dinitrophenol (DNP) protects against diet-induced obesity and improves energy homeostasis in mice at thermoneutrality

The chemical uncoupler 2,4-dinitrophenol (DNP) was an effective and widely used weight loss drug in the early 1930s. However, the physiology of DNP has not been studied in detail because toxicity, including hyperthermia and death, reduced interest in the clinical use of chemical uncouplers. To investigate DNP action, mice fed a high fat diet and housed at 30 °C (to minimize facultative thermogenesis) were treated with 800 mg/liter DNP in drinking water. DNP treatment increased energy expenditure by ∼ 17%, but did not change food intake. DNP-treated mice weighed 26% less than controls after 2 months of treatment due to decreased fat mass, without a change in lean mass. DNP improved glucose tolerance and reduced hepatic steatosis without observed toxicity. DNP treatment also reduced circulating T3 and T4 levels, Ucp1 expression, and brown adipose tissue activity, demonstrating that DNP-mediated heat generation substituted for brown adipose tissue thermogenesis. At 22 °C, a typical vivarium temperature that is below thermoneutrality, DNP treatment had no effect on body weight, adiposity, or glucose homeostasis. Thus, environmental temperature should be considered when assessing an anti-obesity drug in mice, particularly agents acting on energy expenditure. Furthermore, the beneficial effects of DNP suggest that chemical uncouplers deserve further investigation for the treatment of obesity and its comorbidities.

Ambient Temperature and Obesity

Homeotherms maintain an optimal body temperature that is most often above their environment or ambient temperature. As ambient temperature decreases, energy expenditure (and energy intake) must increase to maintain thermal homeostasis. With the wide spread adoption of climate control, humans in modern society are buffered from temperature extremes and spend an increasing amount of time in a thermally comfortable state where energetic demands are minimized. This is hypothesized to contribute to the contemporary increase in obesity rates. Studies reporting exposures of animals and humans to different ambient temperatures are discussed. Additional consideration is given to the potentially altered metabolic and physiologic responses in obese versus lean subjects at a given temperature. The data suggest that ambient temperature is a significant contributor to both energy intake and energy expenditure, and that this variable should be more thoroughly explored in future studies as a potential contributor to obesity susceptibility.