Tea catechins enhance the mRNA expression of uncoupling protein 1 in rat brown adipose tissue

The modulatory effect of oat on brain-derived neurotrophic factor, orexigenic neuropeptides, and dopaminergic signaling in obesity-induced rat model: a comparative study to orlistat

BACKGROUND

Obesity is a non-communicable complex disease that is the fifth leading cause of death worldwide. According to a novel viewpoint, the brain plays a significant role in the central regulation of satiety and energy homeostasis. Because of its rich nutritional profile and versatile uses, oat (Avena sativa) is one of the most popular functional foods recommended by many nutritionists. The anti-obesity effect of oat was hypothesized, focusing on the brain as the target organ. In the current study, the interplay between brain biomarkers, obesity, and its related complications was evaluated in diet-induced obese rats for 25 weeks, in which 60 adult male white albino Wistar rats were divided into three control and seven treatment groups given oat extracts in a dose-dependent manner.

RESULTS

Oat significantly improved obesity-related metabolic complications. In terms of brain function, oat significantly increased dopaminergic signaling, brain-derived neurotrophic factor levels, vaspin, irisin, and uncoupling protein-1 brain levels, while decreasing the expression of agouti-related peptide and neuropeptide Y (P-value < 0.05).

CONCLUSION

The current study proposes oat supplementation as a new conceptual framework with numerous implications for hedonic and homeostatic mechanisms that control satiety. © 2024 Society of Chemical Industry.

Keys to the switch of fat burning: stimuli that trigger the uncoupling protein 1 (UCP1) activation in adipose tissue

As one of the main pathogenic factors of cardiovascular and cerebrovascular diseases, the incidence of metabolic diseases such as adiposity and metabolic dysfunction-associated steatotic liver disease (MASLD) is increasing annually. It is urgent and crucial to find more therapeutic targets to treat these diseases. Mainly expressed in brown adipocytes, mitochondrial uncoupling protein 1 (UCP1) is key to the thermogenesis of classical brown adipose tissue (BAT). Furthermore, white adipose tissue (WAT) is likely to express more UCP1 and subsequently acquire the ability to undergo thermogenesis under certain stimuli. Therefore, targeting and activating UCP1 to promote increased BAT thermogenesis and browning of WAT are helpful in treating metabolic diseases, such as adiposity and MASLD. In this case, the stimuli that activate UCP1 are emerging. Therefore, we summarize the thermogenic stimuli that have activated UCP1 in recent decades, among which cold exposure is one of the stimuli first discovered to activate BAT thermogenesis. As a convenient and efficient therapy with few side effects and good metabolic benefits, physical exercise can also activate the expression of UCP1 in adipose tissue. Notably, for the first time, we have summarized and demonstrated the stimuli of traditional Chinese medicines that can activate UCP1, such as acupuncture, Chinese herbal formulas, and Chinese medicinal herbs. Moreover, pharmacological agents, functional foods, food ingredients, and the gut microbiota are also commonly associated with regulating and activating UCP1. The identification and analysis of UCP1 stimuli can greatly facilitate our understanding of adipose tissue thermogenesis, including the browning of WAT. Thus, it is more conducive to further research and therapy for glucose and lipid metabolism disorders.

Browning of Adipocytes: A Potential Therapeutic Approach to Obesity

The increasing prevalence of overweight and obesity suggests that current strategies based on diet, exercise, and pharmacological knowledge are not sufficient to tackle this epidemic. Obesity results from a high caloric intake and energy storage, the latter by white adipose tissue (WAT), and when neither are counterbalanced by an equally high energy expenditure. As a matter of fact, current research is focused on developing new strategies to increase energy expenditure. Against this background, brown adipose tissue (BAT), whose importance has recently been re-evaluated via the use of modern positron emission techniques (PET), is receiving a great deal of attention from research institutions worldwide, as its main function is to dissipate energy in the form of heat via a process called thermogenesis. A substantial reduction in BAT occurs during normal growth in humans and hence it is not easily exploitable. In recent years, scientific research has made great strides and investigated strategies that focus on expanding BAT and activating the existing BAT. The present review summarizes current knowledge about the various molecules that can be used to promote white-to-brown adipose tissue conversion and energy expenditure in order to assess the potential role of thermogenic nutraceuticals. This includes tools that could represent, in the future, a valid weapon against the obesity epidemic.

Brown Adipose Tissue-A Translational Perspective

Brown adipose tissue (BAT) displays the unique capacity to generate heat through uncoupled oxidative phosphorylation that makes it a very attractive therapeutic target for cardiometabolic diseases. Here, we review BAT cellular metabolism, its regulation by the central nervous and endocrine systems and circulating metabolites, the plausible roles of this tissue in human thermoregulation, energy balance, and cardiometabolic disorders, and the current knowledge on its pharmacological stimulation in humans. The current definition and measurement of BAT in human studies relies almost exclusively on BAT glucose uptake from positron emission tomography with 18F-fluorodeoxiglucose, which can be dissociated from BAT thermogenic activity, as for example in insulin-resistant states. The most important energy substrate for BAT thermogenesis is its intracellular fatty acid content mobilized from sympathetic stimulation of intracellular triglyceride lipolysis. This lipolytic BAT response is intertwined with that of white adipose (WAT) and other metabolic tissues, and cannot be independently stimulated with the drugs tested thus far. BAT is an interesting and biologically plausible target that has yet to be fully and selectively activated to increase the body's thermogenic response and shift energy balance. The field of human BAT research is in need of methods able to directly, specifically, and reliably measure BAT thermogenic capacity while also tracking the related thermogenic responses in WAT and other tissues. Until this is achieved, uncertainty will remain about the role played by this fascinating tissue in human cardiometabolic diseases.

Cellular Stress Response (Hormesis) in Response to Bioactive Nutraceuticals with Relevance to Alzheimer Disease

Significance: Alzheimer's disease (AD) is the most common form of dementia associated with aging. As the large Baby Boomer population ages, risk of developing AD increases significantly, and this portion of the population will increase significantly over the next several decades. Recent Advances: Research suggests that a delay in the age of onset by 5 years can dramatically decrease both the incidence and cost of AD. In this review, the role of nuclear factor erythroid 2-related factor 2 (Nrf2) in AD is examined in the context of heme oxygenase-1 (HO-1) and biliverdin reductase-A (BVR-A) and the beneficial potential of selected bioactive nutraceuticals. Critical Issues: Nrf2, a transcription factor that binds to enhancer sequences in antioxidant response elements (ARE) of DNA, is significantly decreased in AD brain. Downstream targets of Nrf2 include, among other proteins, HO-1. BVR-A is activated when biliverdin is produced. Both HO-1 and BVR-A also are oxidatively or nitrosatively modified in AD brain and in its earlier stage, amnestic mild cognitive impairment (MCI), contributing to the oxidative stress, altered insulin signaling, and cellular damage observed in the pathogenesis and progression of AD. Bioactive nutraceuticals exhibit anti-inflammatory, antioxidant, and neuroprotective properties and are potential topics of future clinical research. Specifically, ferulic acid ethyl ester, sulforaphane, epigallocatechin-3-gallate, and resveratrol target Nrf2 and have shown potential to delay the progression of AD in animal models and in some studies involving MCI patients. Future Directions: Understanding the regulation of Nrf2 and its downstream targets can potentially elucidate therapeutic options for delaying the progression of AD. Antioxid. Redox Signal. 38, 643-669.

Nutraceuticals in Brown Adipose Tissue Activation

Obesity and its associated comorbidities have become pandemic, and challenge the global healthcare system. Lifestyle changes, nutritional interventions and phamaceuticals should be differently combined in a personalized strategy to tackle such a public health burden. Altered brown adipose tissue (BAT) function contributes to the pathophysiology of obesity and glucose metabolism dysfunctions. BAT thermogenic activity burns glucose and fatty acids to produce heat through uncoupled respiration, and can dissipate the excessive calorie intake, reduce glycemia and circulate fatty acids released from white adipose tissue. Thus, BAT activity is expected to contribute to whole body energy homeostasis and protect against obesity, diabetes and alterations in lipid profile. To date, pharmacological therapies aimed at activating brown fat have failed in clinical trials, due to cardiovascular side effects or scarce efficacy. On the other hand, several studies have identified plant-derived chemical compounds capable of stimulating BAT thermogenesis in animal models, suggesting the translational applications of dietary supplements to fight adipose tissue dysfunctions. This review describes several nutraceuticals with thermogenic properties and provides indications, at a molecular level, of the regulation of the adipocyte thermogenesis by the mentioned phytochemicals.

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

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

The Role and Regulatory Mechanism of Brown Adipose Tissue Activation in Diet-Induced Thermogenesis in Health and Diseases

Brown adipose tissue (BAT) has been considered a vital organ in response to non-shivering adaptive thermogenesis, which could be activated during cold exposure through the sympathetic nervous system (SNS) or under postprandial conditions contributing to diet-induced thermogenesis (DIT). Humans prefer to live within their thermal comfort or neutral zone with minimal energy expenditure created by wearing clothing, making shelters, or using an air conditioner to regulate their ambient temperature; thereby, DIT would become an important mechanism to counter-regulate energy intake and lipid accumulation. In addition, there has been a long interest in the intriguing possibility that a defect in DIT predisposes one to obesity and other metabolic diseases. Due to the recent advances in methodology to evaluate the functional activity of BAT and DIT, this updated review will focus on the role and regulatory mechanism of BAT biology in DIT in health and diseases and whether these mechanisms are applicable to humans.

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

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

Green tea aqueous extract (GTAE) prevents high-fat diet-induced obesity by activating fat browning

Adipose browning leads to increased energy expenditure and reduced adiposity and has, therefore, become an attractive therapeutic strategy for obesity. In this study, we elucidated the effect of green tea aqueous extract (GTAE) on the browning of inguinal white adipose tissue (Ing-WAT) and brown adipose tissue (BAT) in high-fat diet (HFD)-fed mice. The main phytochemical components identified in GTAE through high-performance liquid chromatography (HPLC) included (-)-gallocatechin, (-)-epigallocatechin, (-)-catechin, (-)-epigallocatechin-3-gallate, caffeine, (-)-epicatechin, (-)-gallocatechin gallate, and (-)-epicatechin-3-gallate. Daily supplementation with 1% GTAE for 12 weeks markedly reduced bodyweight gain, systemic inflammation, oxidative stress, and improved insulin resistance. Additionally, histological analysis revealed that dietary supplementation with 1% GTAE reversed HFD-induced adipocyte size and hepatic steatosis. These effects were associated with activation of browning in the Ing-WAT and BAT, which mediate systemic metabolic dysfunction in HFD-fed mice. Taken together, our data support the use of GTAE, a natural product, for the attenuation of obesity through the activation of fat browning.

Food phenolics stimulate adipocyte browning via regulating gut microecology

Fat browning has piqued the interest of researchers as a potential target for treating obesity and related metabolic disorders. Recruitment of brown adipocytes leads to enhanced energy dissipation and reduced adiposity, thus facilitating the maintenance of metabolic homeostasis. Evidence is increasing to support the crucial roles of polyphenols and gut microecology in turning fat "brown". However, it is not clear whether the intestinal microecology is involved in polyphenol-mediated regulation of adipose browning, so this concept is worthy of exploration. In this review, we summarize the current knowledge, mostly from studies with murine models, supporting the concept that the effects of food phenolics on brown fat activation and white fat browning can be attributed to their regulatory actions on gut microecology, including microbial community profile, gut metabolites, and gut-derived hormones. Furthermore, the potential underlying pathways involved are also discussed. Basically, understanding gut microecology paves the way to determine the underlying roles and mechanisms of food phenolics in adipose browning.

On the Validity of Adipogenic Cell Lines as Model Systems for Browning Processes: In Authentic Brown, Brite/Beige, and White Preadipocytes, There is No Cell-Autonomous Thermogenic Recruitment by Green Tea Compounds

The potential ability of nutritional compounds to induce or enhance the browning of adipocytes has attracted large interest as a workable means of combatting the obesity epidemic. Green tea compounds are discussed as such inducers of an enhanced thermogenic capacity and activity. However, the cell-autonomous effects of green tea compounds on adipocytes have until now only been demonstrated in adipogenic cell lines (3T3-L1 and 3T3-F442A), i.e., cells of undefined tissue lineage. In this study, we examine the ability of green tea compounds to cell-autonomously induce thermogenic recruitment in authentic brown and brite/beige adipocytes in vitro. In primary brown adipocytes, the green tea compounds suppressed basal UCP1 gene expression, and there was no positive interaction between the compounds and adrenergic stimulation. In white adipocytes, green tea compounds decreased both basal and norepinephrine-induced UCP1 mRNA levels, and this was associated with the suppression of cell differentiation, indicated by reduced lipogenic gene expression and lipid accumulation. A lack of interaction between rosiglitazone and green tea compounds suggests that the green tea compounds do not directly interact with the PPARγ pathway. We conclude that there is a negative effect of the green tea compounds on basal UCP1 gene expression, in both brown and white primary adipocytes, in contrast to the positive effects earlier reported from studies in adipogenic cell lines. We posit that the epigenetic status of the adipogenic cell lines is fundamentally different from that of genuine brown and white adipocytes, reflected, e.g., in several-thousand-fold differences in UCP1 gene expression levels. Thus, results obtained with adipogenic cell lines cannot unreservedly be extrapolated as being relevant for authentic effects in brown and white adipocytes. We suggest that this conclusion can be of general concern for studies attempting to establish physiologically relevant cell-autonomous effects.

A Standardized Aframomum melegueta Seed Extract Regulates Browning of White Adipose Tissue in High-Fat Diet Model Mice

Thermogenesis-mediated energy expenditure is a promising strategy to combat obesity. Aframomum melegueta commonly known as grains of paradise (GP) is a popular spice with medicinal attributes in promoting health. We have demonstrated the thermogenic effects of a standardized A melegueta seed extract (AMSE) containing not <10% 6-paradol in high fat diet-fed (HFD) mice. The 6-week oral ingestion of 20 and 40 mg/kg AMSE significantly limited the weight gain, improved the brown adipose tissue (BAT) activity in HFD mice. Interestingly, AMSE markedly induced the beige adipocytes in epididymal white adipose tissue (eWAT). AMSE treatment led to the upregulation of marker proteins i.e., uncoupling protein 1 (UCP1), peroxisome proliferator-activated receptor-gamma-coactivator 1-alpha (PGC-1α), and peroxisome proliferator-activated receptor gamma (PPARγ) in eWAT and BAT. Our findings add to the current understanding of the thermogenic potentials of GP seed extract and report that the extract can stimulate the browning of WATs in addition to enhanced BAT activity. AMSE requires clinical validation to be explored as a dietary supplement/functional ingredient with thermogenic effect in food and beverages.

Activation of Brown Adipose Tissue and Promotion of White Adipose Tissue Browning by Plant-based Dietary Components in Rodents: A Systematic Review

Activation of brown adipose tissue (BAT) and promotion of white adipose tissue (WAT) browning is considered a potential tool to combat obesity and cardiometabolic disorders. The use of plant-based dietary components has become one of the most used strategies for activating BAT and promoting WAT browning in rodents. The main reason is because plant-based dietary components are usually recognized as safe when the dose is properly adjusted, and they can easily be administrated by being added to the diet or dissolved in water. The present systematic review aimed to study the effects of plant-based dietary components on activation of BAT and promotion of WAT browning in rodents. A systematic search of PubMed and Scopus (from 1978 to 2019) identified eligible studies. Studies assessing the effects of plant-based dietary components added to diet and/or water on uncoupling protein 1 (UCP1) expression in BAT and/or WAT were included. Studies that used dietary components of animal origin, did not specify the effects on UCP1, or were conducted in other species different from mice or rats were excluded. Of 3919 studies identified in the initial screening, 146 studies were finally included in the review. We found that tea extract catechins, resveratrol, capsaicin and capsinoids, cacao extract flavanols, and quercetin were the most studied components. Scientific evidence suggests that some of these dietary components activate BAT and promote WAT browning via activation of the AMP-activated protein kinase (AMPK) and sirtuin 1 (SIRT1) pathways. These findings reveal that there is strong scientific evidence supporting the use of plant-based dietary components to activate BAT and promote WAT browning in rodents and thus to potentially combat obesity and cardiometabolic disorders.

Natural Antioxidant Application on Fat Accumulation: Preclinical Evidence

Obesity represents one of the most important challenges in the contemporary world that must be overcome. Different pathological consequences of these physical conditions have been studied for more than 30 years. The most nagging effects were found early in the cardiovascular system. However, later, its negative impact was also investigated in several other organs. Damage at cellular structures due to overexpression of reactive oxygen species together with mechanisms that cause under-production of antioxidants leads to the development of obesity-related complications. In this view, the negative results of oxidant molecules due to obesity were studied in various districts of the body. In the last ten years, scientific literature has reported reasonable evidence regarding natural and synthetic compounds' supplementation, which showed benefits in reducing oxidative stress and inflammatory processes in animal models of obesity. This article attempts to clarify the role of oxidative stress due to obesity and the opposing role of antioxidants to counter it, reported in preclinical studies. This analysis aims to clear-up different mechanisms that lead to the build-up of pro-oxidants during obesity and how various molecules of different origins hinder this phenomenon, behaving as antioxidants.

Role of Dietary Polyphenols in Adipose Tissue Browning: A Narrative Review

Lifestyle modifications such as energy restriction and increased physical activity are highly effective in the management of obesity. However, adherence to these therapeutic approaches is poor. On the other hand, synthetic drugs used for obesity control are plagued by adverse effects. Despite these failures, adipose tissue is still an attractive therapeutic target for novel molecules, and thus, the characterisation of new and safer anti-obesity drugs is of significant interest. For this reason, in recent years, phenolic constituents of diverse plants have drawn much attention due to their health-promoting properties, opening new research lines related to brown adipose tissue activation and white adipose tissue (WAT) browning. The goal is to increase energy expenditure levels through thermogenic activity activation by multiple factors, like polyphenols. The suggested mechanisms by which polyphenols can modulate thermogenesis include Nor-epinephrine/Catechol-O-Methyl-Transferase (NE/COMT) inhibition, PPARγ co-activator alpha (PGC-1α)-dependent pathways activation, and mitochondrial biogenesis, among others. Although polyphenols such as quercetin, catechins, chrysin, luteolin, curcumin, resveratrol, gallic acid, and lignans have shown a positive effect on Non-Shivering Thermogenesis and WAT browning, most of them have only been active in murine models or in vitro systems, and their reproducibility in humans has to be proved. Probably in the future, an approach that includes these compounds as part of the nutritional regimen in conjunction with physical exercise, pharmacological and surgical therapy, would allow modulating a pathophysiological mechanism that is still elusive.

Effect of Acute and Chronic Dietary Supplementation with Green Tea Catechins on Resting Metabolic Rate, Energy Expenditure and Respiratory Quotient: A Systematic Review

The consumption of green tea catechins (GTC) is associated with modulations of fat metabolism and consequent weight loss. The aim of this systematic review was to investigate the effect of GTC on resting metabolic rate (RMR), energy expenditure (EE), and respiratory quotient (RQ). Eligible studies considered both the chronic and acute intake of GTC-based supplements, with epigallocatechin gallate (EGCG) doses ranging between 100–800 mg. Findings from 15 studies (n = 499 participants) lasting 8–12 weeks (for chronic consumption) or 1–3 days (for acute intake) are summarized. This review reveals the positive effects of GTC supplementation on RQ values (272 subjects). Regarding the effects of acute and chronic GTC supplementation on RMR (244 subjects) and EE (255 subjects), the results did not allow for a definitive conclusion, even though they were promising, because some reported a positive improvement (two studies revealed an increase in RMR: one demonstrated an RMR increase of 43.82 kcal/day and another demonstrated an increase of 260.8 kcal/day, mainly when subjects were also engaged in resistance training exercise). Considering GTC daily dose supplementation, studies in which modifications of energetic parameters occurred, in particular RQ reduction, considered GTC low doses (100–300 mg). GTC may be useful for improving metabolic profiles. Further investigations are needed to better define adequate doses of supplementation.

A Mix of Natural Bioactive Compounds Reduces Fat Accumulation and Modulates Gene Expression in the Adipose Tissue of Obese Rats Fed a Cafeteria Diet

Scientists are focusing on bioactive ingredients to counteract obesity. We evaluated whether a mix containing grape seed proanthocyanidin extract (GSPE), anthocyanins, conjugated linoleic acid (CLA), and chicken feet hydrolysate (CFH) could reduce body fat mass and also determined which mechanisms in the white adipose tissue (WAT) and the brown adipose tissue (BAT) were affected by the treatment. The mix or vehicle (VH) were administered for three weeks to obese rats fed a cafeteria (CAF) diet. Biometric measures, indirect calorimetry, and gene expression in WAT and BAT were analyzed as was the histology of the inguinal WAT (IWAT). The individual compounds were also tested in the 3T3-L1 cell line. The mix treatment resulted in a significant 15% reduction in fat (25.01 ± 0.91 g) compared to VH treatment (21.19 ± 1.59 g), and the calorimetry results indicated a significant increase in energy expenditure and fat oxidation. We observed a significant downregulation of Fasn mRNA and an upregulation of Atgl and Hsl mRNA in adipose depots in the group treated with the mix. The IWAT showed a tendency of reduction in the number of adipocytes, although no differences in the total adipocyte area were found. GSPE and anthocyanins modulated the lipid content and downregulated the gene and protein levels of Fasn compared to the untreated group in 3T3-L1 cells. In conclusion, this mix is a promising treatment against obesity, reducing the WAT of obese rats fed a CAF diet, increasing energy expenditure and fat oxidation, and modifying the expression of genes involved in lipid metabolism of the adipose tissue.

Induction of Adipose Tissue Browning as a Strategy to Combat Obesity

The ongoing obesity pandemic generates a constant need to develop new therapeutic strategies to restore the energy balance. Therefore, the concept of activating brown adipose tissue (BAT) in order to increase energy expenditure has been revived. In mammals, two developmentally distinct types of brown adipocytes exist; the classical or constitutive BAT that arises during embryogenesis, and the beige adipose tissue that is recruited postnatally within white adipose tissue (WAT) in the process called browning. Research of recent years has significantly increased our understanding of the mechanisms involved in BAT activation and WAT browning. They also allowed for the identification of critical molecules and critical steps of both processes and, therefore, many new therapeutic targets. Several non-pharmacological approaches, as well as chemical compounds aiming at the induction of WAT browning and BAT activation, have been tested in vitro as well as in animal models of genetically determined and/or diet-induced obesity. The therapeutic potential of some of these strategies has also been tested in humans. In this review, we summarize present concepts regarding potential therapeutic targets in the process of BAT activation and WAT browning and available strategies aiming at them.

Investigating Anti-Obesity Effects by Oral Administration of Aloe vera Gel Extract (AVGE): Possible Involvement in Activation of Brown Adipose Tissue (BAT)

The aim of this study is to investigate the mechanism of anti-obesity effects of Aloe vera gel extract (AVGE) containing Aloe sterols. Previously, we reported that oral intake of Aloe vera components has an anti-diabetic and anti-obesity effect. This study was designed to assess the role of brown adipose tissue (BAT) in the anti-obesity effect of AVGE. Six-week-old male mice were divided into three groups; STD (standard diet), HFD (60% high fat diet) and AVGE (60% high fat diet with AVGE treatment). During 11 wk of AVGE administration, body weight has been monitored. Tissue samples were obtained to be measured the weight and evaluated the gene expressions. Mice treated with AVGE had suppressed body weight, and liver and fat weight gain. To investigate BAT activation, we measured the expression of mRNA related to BAT thermogenesis. Mice in the AVGE group had higher expression of Ucp1, Adrb3, and Cidea in BAT compared to HFD. Next, to investigate the possibility that AVGE induced hepatic FGF21, which is an important factor for nutrient and energy homeostasis including BAT regulation, in vitro study was conducted. HepG2 cell stimulated by AVGE were highly expressed FGF21. These results suggested that BAT activation partially contributes to mechanism of anti-obesity effect of Aloe sterols in diet-induced obesity (DIO) models. However, further study is needed to determine the predominant mechanism.

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

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

Brown Adipose Tissue, Diet-Induced Thermogenesis, and Thermogenic Food Ingredients: From Mice to Men

Since the recent rediscovery of brown adipose tissue (BAT) in adult humans, this thermogenic tissue has been attracting increasing interest. The inverse relationship between BAT activity and body fatness suggests that BAT, because of its energy dissipating activity, is protective against body fat accumulation. Cold exposure activates and recruits BAT, resulting in increased energy expenditure and decreased body fatness. The stimulatory effects of cold exposure are mediated through transient receptor potential (TRP) channels and the sympathetic nervous system (SNS). Most TRP members also function as chemesthetic receptors for various food ingredients, and indeed, agonists of TRP vanilloid 1 such as capsaicin and its analog capsinoids mimic the effects of cold exposure to decrease body fatness through the activation and recruitment of BAT. The antiobesity effect of other food ingredients including tea catechins may be attributable, at least in part, to the activation of the TRP-SNS-BAT axis. BAT is also involved in the facultative thermogenesis induced by meal intake, referred to as diet-induced thermogenesis (DIT), which is a significant component of the total energy expenditure in our daily lives. Emerging evidence suggests a crucial role for the SNS in BAT-associated DIT, particularly during the early phase, but several gut-derived humoral factors may also participate in meal-induced BAT activation. One intriguing factor is bile acids, which activate BAT directly through Takeda G-protein receptor 5 (TGR5) in brown adipocytes. Given the apparent beneficial effects of some TRP agonists and bile acids on whole-body substrate and energy metabolism, the TRP/TGR5-BAT axis represents a promising target for combating obesity and related metabolic disorders in humans.

Near-Infrared Time-Resolved Spectroscopy for Assessing Brown Adipose Tissue Density in Humans: A Review

Brown adipose tissue (BAT) mediates adaptive thermogenesis upon food intake and cold exposure, thus potentially contributing to the prevention of lifestyle-related diseases. ¹⁸F-fluorodeoxyglucose (FDG)-positron emission tomography (PET) with computed tomography (CT) (¹⁸FDG-PET/CT) is a standard method for assessing BAT activity and volume in humans. ¹⁸FDG-PET/CT has several limitations, including high device cost and ionizing radiation and acute cold exposure necessary to maximally stimulate BAT activity. In contrast, near-infrared spectroscopy (NIRS) has been used for measuring changes in O₂-dependent light absorption in the tissue in a non-invasive manner, without using radiation. Among NIRS, time-resolved NIRS (NIR_TRS) can quantify the concentrations of oxygenated and deoxygenated hemoglobin ([oxy-Hb] and [deoxy-Hb], respectively) by emitting ultrashort (100 ps) light pulses and counts photons, which are scattered and absorbed in the tissue. The basis for assessing BAT density (BAT-d) using NIR_TRS is that the vascular density in the supraclavicular region, as estimated using Hb concentration, is higher in BAT than in white adipose tissue. In contrast, relatively low-cost continuous wavelength NIRS (NIR_CWS) is employed for measuring relative changes in oxygenation in tissues. In this review, we provide evidence for the validity of NIR_TRS and NIR_CWS in estimating human BAT characteristics. The indicators (Ind_NIRS) examined were [oxy-Hb]_sup, [deoxy-Hb]_sup, total hemoglobin [total-Hb]_sup, Hb O₂ saturation (StO_2sup), and reduced scattering coefficient ( μs sup' ) in the supraclavicular region, as determined by NIR_TRS, and relative changes in corresponding parameters, as determined by NIR_CWS. The evidence comprises the relationships between the Ind_NIRS investigated and those determined by ¹⁸FDG-PET/CT; the correlation between the Ind_NIRS and cold-induced thermogenesis; the relationship of the Ind_NIRS to parameters measured by ¹⁸FDG-PET/CT, which responded to seasonal temperature fluctuations; the relationship of the Ind_NIRS and plasma lipid metabolites; the analogy of the Ind_NIRS to chronological and anthropometric data; and changes in the Ind_NIRS following thermogenic food supplementation. The [total-Hb]_sup and [oxy-Hb]_sup determined by NIR_TRS, but not parameters determined by NIR_CWS, exhibited significant correlations with cold-induced thermogenesis parameters and plasma androgens in men in winter or analogies to ¹⁸FDG-PET. We conclude that NIR_TRS can provide useful information for assessing BAT-d in a simple, rapid, non-invasive way, although further validation study is still needed.

Catechins and Caffeine Promote Lipid Metabolism and Heat Production Through the Transformation of Differentiated 3T3-L1 Adipocytes from White to Beige Adipocytes

To elucidate effects of catechins and caffeine on lipid metabolism in adipocytes and identify the mechanism of action, differentiated 3T3-L1 adipocytes were incubated in culture media containing catechins at 1, 2.5, 5, and 10 µg/mL and caffeine at 50 and 100 µg/mL, singly or in combination, for 8 days. Intracellular lipid accumulation and glycerol-3-phosphate dehydrogenase activity were strongly suppressed by catechins and caffeine combination treatment. The mRNA expression of PPARɤ, GLUT4, HSL, UCP-1, and TMEM26 were significantly increased in the combined groups. These findings suggest that the combined treatment inhibited lipid synthesis and improved lipid metabolism in adipocytes. Moreover, it was indicated that the differentiated 3T3-L1 adipocytes could be transformed from white adipocytes to beige-like adipocytes by catechins and caffeine, and accordingly that this transformation could promote calorigenic action. PRACTICAL APPLICATION: In this study, we revealed that the combined treatment of catechins and caffeine inhibited lipid synthesis and improved lipid metabolism in adipocytes. Moreover, the treatment may contribute to the transforming from white adipocytes to beige-like adipocytes, which could strongly promote calorigenic action.

Plant-Based Diets in the Reduction of Body Fat: Physiological Effects and Biochemical Insights

Obesity affects over one-third of Americans and increases the risk of cardiovascular disease and type II diabetes. Interventional trials have consistently demonstrated that consumption of plant-based diets reduces body fat in overweight and obese subjects, even when controlling for energy intake. Nonetheless, the mechanisms underlying this effect have not been well-defined. This review discusses six major dietary mechanisms that may lead to reduced body fat. These include (1) reduced caloric density, (2) improved gut microbiota symbiosis, (3) increased insulin sensitivity, (4) reduced trimethylamine-N-oxide (TMAO), (5) activation of peroxisome proliferator-activated receptors (PPARs), and (6) over-expression of mitochondrial uncoupling proteins. Collectively, these factors improve satiety and increase energy expenditure leading to reduced body weight.

Programming mediated by fatty acids affects uncoupling protein 1 (UCP-1) in brown adipose tissue

Brown adipose tissue (BAT) has recently been given more attention for the part it plays in obesity. BAT can generate great amounts of heat through thermogenesis by the activation of uncoupling protein 1 (UCP-1), which can be regulated by many environmental factors such as diet. Moreover, the build-up of BAT relates to maternal nutritional changes during pregnancy and lactation. However, at present, there is a limited number of studies looking at maternal nutrition and BAT development, and it seems that the research trend in this field has been considerably declining since the 1980s. There is much to discover yet about the role of different fatty acids on the development of BAT and the activation of UCP-1 during the fetal and the postnatal periods of life. A better understanding of the impact of nutritional intervention on the epigenetic regulation of BAT could lead to new preventive care for metabolic diseases such as obesity. It is important to know in which circumstances lipids could programme BAT during pregnancy and lactation. The modification of maternal dietary fatty acids, amount and composition, during pregnancy and lactation might be a promising strategy for the prevention of obesity in the offspring and future generations.

Flavonoids as inducers of white adipose tissue browning and thermogenesis: signalling pathways and molecular triggers

Background

Flavonoids are a class of plant and fungus secondary metabolites and are the most common group of polyphenolic compounds in the human diet. In recent studies, flavonoids have been shown to induce browning of white adipocytes, increase energy consumption, inhibit high-fat diet (HFD)-induced obesity and improve metabolic status. Promoting the activity of brown adipose tissue (BAT) and inducing white adipose tissue (WAT) browning are promising means to increase energy expenditure and improve glucose and lipid metabolism. This review summarizes recent advances in the knowledge of flavonoid compounds and their metabolites.

Methods

We searched the following databases for all research related to flavonoids and WAT browning published through March 2019: PubMed, MEDLINE, EMBASE, and the Web of Science. All included studies are summarized and listed in Table 1.

Result

We summarized the effects of flavonoids on fat metabolism and the specific underlying mechanisms in sub-categories. Flavonoids activated the sympathetic nervous system (SNS), promoted the release of adrenaline and thyroid hormones to increase thermogenesis and induced WAT browning through the AMPK-PGC-1α/Sirt1 and PPAR signalling pathways. Flavonoids may also promote brown preadipocyte differentiation, inhibit apoptosis and produce inflammatory factors in BAT.

Conclusion

Flavonoids induced WAT browning and activated BAT to increase energy consumption and non-shivering thermogenesis, thus inhibiting weight gain and preventing metabolic diseases.

The effects of green tea on lipid metabolism and its potential applications for obesity and related metabolic disorders - An existing update

Obesity is one of the top global issues, which induces several serious health consequences both physically and mentally, such as type 2 diabetes, cardiovascular diseases, dyslipidemia, eating disorders, depression and stress. However, the effective therapy to prevent and treat obesity and overweight, up to now, cannot be found nowadays. Several methods/medicines namely diet control, energy balance, environmental changes, genetic and stem cell therapies, new drugs/chemicals have been extensively studied to enhance the ability to control bodyweight and prevent obesity. Of all the aforementioned methods, green tea, used as a daily beverage, has shown beneficial impacts for the health, especially its anti-obesity effects. Available evidence shows that green tea can interrupt lipid emulsification, reduce adipocyte differentiation, increase thermogenesis, and reduce food intake, thus green tea improves the systemic metabolism and decreases fat mass. Here, we highlight and sum up the update investigations of anti-obesity effect of green tea as well as discuss the potential application of them for preventing obesity and its related metabolic disorders.

Food Ingredients Involved in White-to-Brown Adipose Tissue Conversion and in Calorie Burning

Obesity is the consequence of chronic positive energy balance and considered a leading risk factor for cardiovascular and metabolic diseases. Due to its epidemic trends among children and adults, there is an increasing interest in implementing new therapeutic interventions to tackle overweight and obesity. Activation of brown adipose tissue (BAT) represents today a promising strategy to enhance energy expenditure (EE) through heat production. More recently, “browning” of white adipose tissue (WAT) has gained increasing attention in research area as an alternative method in stimulating energy dissipation. This minireview aims to summarize the current knowledge of some dietary compounds that have been shown to promote BAT activation and WAT browning with subsequent beneficial health effects.

Flavonoids, Potential Bioactive Compounds, and Non-Shivering Thermogenesis

Obesity results from the body having either high energy intake or low energy expenditure. Based on this energy equation, scientists have focused on increasing energy expenditure to prevent abnormal fat accumulation. Activating the human thermogenic system that regulates body temperature, particularly non-shivering thermogenesis in either brown or white adipose tissue, has been suggested as a promising solution to increase energy expenditure. Together with the increasing interest in understanding the mechanism by which plant-derived dietary compounds prevent obesity, flavonoids were recently shown to have the potential to regulate non-shivering thermogenesis. In this article, we review the latest research on flavonoid derivatives that increase energy expenditure through non-shivering thermogenesis.

Ginsenoside Rg1 promotes browning by inducing UCP1 expression and mitochondrial activity in 3T3-L1 and subcutaneous white adipocytes

Background

Panax ginseng Meyer is known as a conventional herbal medicine, and ginsenoside Rg1, a steroid glycoside, is one of its components. Although Rg1 has been proved to have an antiobesity effect, the mechanism of this effect and whether it involves adipose browning have not been elucidated.

Methods

3T3-L1 and subcutaneous white adipocytes from mice were used to access the thermogenic effect of Rg1. Adipose mitochondria and uncoupling protein 1 (UCP1) expression were analyzed by immunofluorescence. Protein level and mRNA of UCP1 were also evaluated by Western blotting and real-time polymerase chain reaction, respectively.

Results

Rg1 dramatically enhanced expression of brown adipocyte–specific markers, such as UCP1 and fatty acid oxidation genes, including carnitine palmitoyltransferase 1. In addition, it modulated lipid metabolism, activated 5′ adenosine monophosphate (AMP)-activated protein kinase, and promoted lipid droplet dispersion.

Conclusions

Rg1 increases UCP1 expression and mitochondrial biogenesis in 3T3-L1 and subcutaneous white adipose cells isolated from C57BL/6 mice. We suggest that Rg1 exerts its antiobesity effects by promoting adipocyte browning through activation of the AMP-activated protein kinase pathway.

Cyanidin-3-O-β-glucoside regulates the activation and the secretion of adipokines from brown adipose tissue and alleviates diet induced fatty liver

AIM

Cyanidin-3-O-β-glucoside (Cy-3-G) the most abundant monomer of anthocyanins has multiple protective effects on many diseases. To date, whether Cy-3-G could regulate the function of brown adipose tissue (BAT) is still unclear and whether this regulation could influence the secretion of adipokines from BAT to prevent non-alcoholic fatty liver disease (NAFLD) indirectly remains to be explored. In this study we investigated the effect of Cy-3-G on BAT and the potential role of Cy-3-G to prevent fatty liver through regulating the secretion of BAT.

METHODS

Male C57BL/6 J mice were fed with a high fat high cholesterol (HFC) diet with or without 200 mg/kg B.W Cy-3-G for 8 weeks. In in vitro experiments, the differentiated brown adipocytes (BAC) and C3H10T1/2 clone8 cells were treated with 0.2 mM palmitate with or without Cy-3-G for 72 or 96 h. Then the culture media of C3H10T1/2 clone8 cells were collected for measuring the adipokines secretion by immunoblot assay and were applied to culture HepG2 cells or LO2 cells for 24 h. Lipid accumulation in HepG2 cells or LO2 cells were evaluated by oil red O staining.

RESULTS

Here we found that Cy-3-G regulated the activation of BAT and the expression of adipokines in BAT which were disrupted by HFC diet and alleviated diet induced fatty liver in mice. In in vitro experiments, Cy-3-G inhibited the release of adipokines including extracellular nicotinamide phosphoribosyltransferase (eNAMPT) and fibroblast growth factor 21 (FGF21) from differentiated C3H10T1/2 clone8 cells induced by palmitate, which was accompanied by a reduction of lipid accumulation in HepG2 cells and LO2 cells cultured by the corresponding collected media of C3H10T1/2 clone8 cells.

CONCLUSIONS

These results indicate that Cy-3-G can regulate the thermogenic and secretory functions of BAT. Furthermore, our data suggest that the protective effect of Cy-3-G on hepatic lipid accumulation is probably via regulating the secretion of adipokines from BAT.

Guarana (Paullinia cupana) Stimulates Mitochondrial Biogenesis in Mice Fed High-Fat Diet

The aim of this study was to evaluate the effects of guarana on mitochondrial biogenesis in a high-fat diet (HFD)-fed mice. C57BL6J mice were divided in two groups: high-fat diet HFD and high-fat diet + guarana (HFD-GUA). Both groups received HFD and water ad libitum and the HFD-GUA group also received a daily gavage of guarana (1 g/kg weight). Body weight and food intake was measured weekly. Glycemic, triglyceride, and cholesterol levels were determined. VO₂ and energy expenditure (EE) were determined by indirect calorimetry. Gene expression was evaluated by real-time PCR and protein content by western blotting. The HFD-GUA group presented lower body weight, subcutaneous, retroperitoneal, visceral, and epididyimal adipose tissue depots, and glycemic and triglyceride levels, with no change in food intake and cholesterol levels. Furthermore, the HFD-GUA group presented an increase in VO₂ and basal energy expenditure (EE), as well as Pgc1α, Creb1, Ampka1, Nrf1, Nrf2, and Sirt1 expression in the muscle and brown adipose tissue. In addition, the HFD-GUA group presented an increase in mtDNA (mitochondrial deoxyribonucleic acid) content in the muscle when compared to the HFD group. Thus, our data showed that guarana leads to an increase in energetic metabolism and stimulates mitochondrial biogenesis, contributing to control of weight gain, even when associated with high-fat diet.

Translational Aspects of Brown Fat Activation by Food-Derived Stimulants

Since the rediscovery of brown adipose tissue (BAT) in humans, its energy-dissipating ability has been well-recognized. The negative correlations of BAT activity with adiposity and insulin sensitivity provided an obvious rationale for discerning reliable and practical strategies for stimulating BAT. Though cold exposure or use of pharmacological adrenomimetics can activate BAT, they may have adverse effects. Therefore, determining alternative stimulants of BAT with lower risks such as commonly used food ingredients is highly desirable. Recent observations revealed that chemical activation of temperature-sensitive transient receptor potential (TRP) channels by food ingredients can recruit BAT in humans. Furthermore, animal studies have identified several food-derived stimulants of BAT acting through multiple mechanisms distinct from a TRP-mediated process. Dietary compounds acting as an activator of Sirtuin 1, a critical regulator of mitochondrial biogenesis and brown adipocyte differentiation, are one such class of promising food-derived BAT activators in humans. While the individual effects of various dietary factors are increasingly established in a laboratory setting, the potential synergistic effects of multiple stimulants on BAT remain to be tested in a clinical environment. These investigations may support the development of efficient, flexible dietary regimens capable of boosting BAT thermogenesis.

Phenolic compounds as natural and multifunctional anti-obesity agents: A review

Prevalence of obesity worldwide has reached pandemic proportions. Despite the increasing evidence in the implication of phenolic compounds in obesity management, the real effect is not completely understood. The available in vitro and in vivo studies have demonstrated the implication of phenolic compounds in: lowering food intake, decreasing lipogenesis, increasing lipolysis, stimulating fatty acids β-oxidation, inhibiting adipocyte differentiation and growth, attenuating inflammatory responses and suppress oxidative stress. This review encompasses the most recent evidence in the anti-obesity effect of phenolic compounds from plants to different nutraceuticals and functional foods based on the in vitro, in vivo and clinical studies. For that, this review has been focused on popular plant-based products highly consumed today such as cocoa, cinnamon, and olive oil, beverages such as red wine, tea (green, white and black tea) and Hibiscus sabdariffa L. tea, among others.

Cyanidin-3-glucoside increases whole body energy metabolism by upregulating brown adipose tissue mitochondrial function

SCOPE

Obesity develops when energy intake exceeds energy expenditure. Promoting brown adipose tissue (BAT) formation and function increases energy expenditure and may protect against obesity. Cyanidin-3-glucoside (C3G) is an anthocyanin compound that occurs naturally in many fruits and vegetables. In this study, we investigated the effect and mechanism of C3G on the prevention of obesity.

METHODS AND RESULTS

Db/db mice received C3G dissolved in drinking water for 16 wk; drinking water served as the vehicle treatment. The total body weight, energy intake, metabolic rate, and physical activity were measured. The lipid droplets, gene expression and protein expression were evaluated by histochemical staining, real-time PCR, and western blots. We found that C3G increased energy expenditure, limited weight gain, maintained glucose homeostasis, reversed hepatic steatosis, improved cold tolerance, and enhanced BAT activity in obese db/db mice. C3G also induces brown-like adipocytes (beige) formation in subcutaneous white adipose tissue (sWAT) of db/db mice model. We also found that C3G potently regulates the transcription of uncoupling protein 1 (UCP1) both in BAT and sWAT through increasing mitochondrial number and function.

CONCLUSION

Our results suggest that C3G plays a role in regulating systemic energy balance, which may have potential therapeutic implications for the prevention and control of obesity.

A polyphenolic extract from green tea leaves activates fat browning in high-fat-diet-induced obese mice

Fat browning has emerged as an attractive target for the treatment of obesity and related metabolic disorders. Its activation leads to increased energy expenditure and reduced adiposity, thus contributing to a better energy homeostasis. Green tea extracts (GTEs) were shown to attenuate obesity and low-grade inflammation and to induce the lipolytic pathway in the white adipose tissue (WAT) of mice fed a high-fat diet. The aim of the present study was to determine whether the antiobesity effect of an extract from green tea leaves was associated with the activation of browning in the WAT and/or the inhibition of whitening in the brown adipose tissue (BAT) in HF-diet induced obese mice. Mice were fed a control diet or an HF diet supplemented with or without 0.5% polyphenolic GTE for 8 weeks. GTE supplementation significantly reduced HF-induced adiposity (WAT and BAT) and HF-induced inflammation in WAT. Histological analysis revealed that GTE reduced the adipocyte size in the WAT and the lipid droplet size in the BAT. Markers of browning were induced in the WAT upon GTE treatment, whereas markers of HF-induced whitening were reduced in the BAT. These results suggest that browning activation in the WAT and whitening reduction in the BAT by the GTE could participate to the improvement of metabolic and inflammatory disorders mediated by GTE upon HF diet. Our study emphasizes the importance of using GTE as a nutritional tool to activate browning and to decrease fat storage in all adipose tissues, which attenuate obesity.

Polyphenols and Their Role in Obesity Management: A Systematic Review of Randomized Clinical Trials

Polyphenols have been suggested to reduce body weight and modify body composition through different mechanisms. These effects have been extensively studied in animals and in vitro and to a lesser extent in humans. The aim of this review is to consider the association between polyphenols and body weight status by focusing on human intervention studies. We conducted a systematic literature search in MEDLINE (via EBSCOhost), ProQuest CENTRAL, and Cochrane CENTRAL without time restrictions. Randomized controlled trials assessing the effect of polyphenols on weight and/or body composition in the overweight and/or obese population were included. Nineteen studies met our inclusion criteria. Results suggest that further research is required before supporting a potential role of polyphenols in reducing weight in overweight and obese individuals (nine studies showed a significant decrease in weight by a mean of 1.47 ± 0.58 kg). Nevertheless, several studies indicated that polyphenols might be effective in preventing small increases in weight during periods of overfeeding rather than reducing weight as such. The outcomes noted do not yet support polyphenol supplementation as a complementary approach in weight loss diets. Further larger trials with a duration of 12 months or more are needed to elucidate the effect of polyphenols on body weight status. Copyright © 2017 John Wiley & Sons, Ltd.

Dietary Factors Promoting Brown and Beige Fat Development and Thermogenesis

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

Phenyl-γ-valerolactones, flavan-3-ol colonic metabolites, protect brown adipocytes from oxidative stress without affecting their differentiation or function

SCOPE

Consumption of products rich in flavan-3-ols, such as tea and cocoa, has been associated with decreased obesity, partially dependent on their capacity to enhance energy expenditure. Despite these phenolics having been reported to increase the thermogenic program in brown and white adipose tissue, flavan-3-ols are vastly metabolised in vivo to phenyl-γ-valerolactones. Therefore, we hypothesize that phenyl-γ-valerolactones may directly stimulate the differentiation and the activation of brown adipocytes.

METHODS AND RESULTS

Immortalized brown pre-adipocytes were differentiated in presence of (R)-5-(3',4'-dihydroxyphenyl)-γ-valerolactone (VL1), (R)-5-(3´-hydroxyphenyl)-γ-valerolactone-4'-O-sulphate (VL2), (R)-5-phenyl-γ-valerolactone-3´,4´-di-O-sulphate (VL3), at concentrations of 2 or 10μM, whereas fully differentiated brown adipocyte were treated acutely (6-24h). None of the treatments regulated the expression levels of the uncouple protein 1, nor of the main transcription factors involved in brown adipogenesis. Similarly, mitochondrial content was unchanged after treatments. Moreover these compounds did not display peroxisome proliferator-activated receptor γ-agonist activity, as evaluated by luciferase assay, and did not enhance norepinephrine-stimulated lipolysis in mature adipocytes. However, both VL1 and VL2 prevented oxidative stress caused by H₂ O₂ .

CONCLUSION

Phenyl-γ-valerolactones and their sulphated forms do not influence brown adipocyte development or function at physiological or supraphysiological doses in vitro, but they are active protecting brown adipocytes from increased reactive oxygen species production.

Tea catechin and caffeine activate brown adipose tissue and increase cold-induced thermogenic capacity in humans

Background: The thermogenic effects of green tea catechin have been repeatedly reported, but their mechanisms are poorly understood.Objective: The aim of this study was to investigate the acute and chronic effects of catechin on brown adipose tissue (BAT), a site specialized for nonshivering thermogenesis, in humans.Design: Fifteen healthy male volunteers underwent fluorodeoxyglucose-positron emission tomography to assess BAT activity. To examine the acute catechin effect, whole-body energy expenditure (EE) after a single oral ingestion of a beverage containing 615 mg catechin and 77 mg caffeine (catechin beverage) was measured. Next, to investigate the chronic catechin effects, 10 men with low BAT activity were enrolled. Before and after ingestion of the catechin beverage 2 times/d for 5 wk, cold-induced thermogenesis (CIT) after 2 h of cold exposure at 19°C, which is proportional to BAT activity, was examined. Both the acute and chronic trials were single-blinded, randomized, placebo-controlled, season-matched crossover studies.Results: A single ingestion of the catechin beverage increased EE in 9 subjects who had metabolically active BAT (mean ± SEM: +15.24 ± 1.48 kcal, P < 0.01) but not in 6 subjects who had negligible activities (mean ± SEM: +3.42 ± 2.68 kcal). The ingestion of a placebo beverage containing 82 mg caffeine produced a smaller and comparative EE response in the 2 subject groups. Multivariate regression analysis revealed a significant interaction between BAT and catechin on EE (β = 0.496, P = 0.003). Daily ingestion of the catechin beverage elevated mean ± SEM CIT (from 92.0 ± 26.5 to 197.9 ± 27.7 kcal/d; P = 0.009), whereas the placebo beverage did not change it.Conclusion: Orally ingested tea catechin with caffeine acutely increases EE associated with increased BAT activity and chronically elevates nonshivering CIT, probably because of the recruitment of BAT, in humans. These trials were registered at www.umin.ac.jp/ctr/ as UMIN000016361.

Daily ingestion of catechin-rich beverage increases brown adipose tissue density and decreases extramyocellular lipids in healthy young women

Purpose

Brown adipose tissue (BAT) contributes to the regulation of non-shivering thermogenesis and adiposity. Increasing BAT has recently attracted much attention as a countermeasure to obesity. Animal studies have shown that prolonged catechin treatment increases uncoupling protein 1, a thermogenic protein in BAT. On the other hand, supportable evidence in human is lacking. Thus, the purpose of this study was to examine whether BAT increases after catechin ingestion in humans.

Methods

Twenty-two healthy young women were given either a catechin-rich (540 mg/day; catechin) or placebo beverage every day for 12 weeks in a double-blind design. BAT density was measured using near-infrared time-resolved spectroscopy (NIR_TRS), visceral fat area were measured using magnetic resonance imaging, extramyocellular lipids (EMCL) using proton magnetic resonance spectroscopy, and body fat mass using dual-energy X-ray absorptiometry scans.

Results

BAT density was significantly increased (18.8 %), and EMCL was decreased (17.4 %) after the 12-week ingestion. There was a significant negative correlation between the changes in BAT density and those in EMCL (r = −0.66, P < 0.05). There were no notable changes in other parameters.

Conclusions

In conclusion, prolonged ingestion of a catechin-rich beverage increases the BAT density in parallel with a decrease in EMCL.

Activation and recruitment of brown adipose tissue by cold exposure and food ingredients in humans

Since the recent re-discovery of brown adipose tissue (BAT) in adult humans, this thermogenic tissue has attracted increasing interest. The inverse relationship between the BAT activity and body fatness suggests that BAT, because of its energy dissipating activity, is protective against body fat accumulation. Cold exposure activates and recruits BAT in association with increased energy expenditure and decreased body fatness. The stimulatory effects of cold are mediated through transient receptor potential channels (TRP), most of which are also chemesthetic receptors for various food ingredients. In fact, capsaicin and its analog capsinoids, representative agonists of TRPV1, mimic the effects of cold to decrease body fatness through the activation and recruitment of BAT. The anti-obesity effect of some other food ingredients including tea catechins may also be attributable to the activation of the TRP-BAT axis. Thus, BAT is a promising target for combating obesity and related metabolic disorders in humans.

Capsaicin and Related Food Ingredients Reducing Body Fat Through the Activation of TRP and Brown Fat Thermogenesis

Brown adipose tissue (BAT) is a site of sympathetically activated adaptive nonshivering thermogenesis, thereby being involved in the regulation of energy balance and body fatness. Recent radionuclide imaging studies have revealed the existence of metabolically active BAT in adult humans. Human BAT is activated by acute cold exposure and contributes to cold-induced increase in whole-body energy expenditure. The metabolic activity of BAT is lower in older and obese individuals. The inverse relationship between the BAT activity and body fatness suggests that BAT, because of its energy dissipating activity, is protective against body fat accumulation. In fact, repeated cold exposure recruits BAT in association with increased energy expenditure and decreased body fatness. The stimulatory effects of cold are mediated through the activation of transient receptor potential (TRP) channels, most of which are also chemesthetic receptors for various naturally occurring substances including herbal plants and food ingredients. Capsaicin and its analog capsinoids, representative agonists of TRPV1, mimic the effects of cold to decrease body fatness through the activation and recruitment of BAT. The well-known antiobesity effect of green tea catechins is also attributable to the activation of the sympathetic nerve and BAT system. Thus, BAT is a promising target for combating obesity and related metabolic disorders in humans.

Oolong, black and pu-erh tea suppresses adiposity in mice via activation of AMP-activated protein kinase

It is well known that tea has a variety of beneficial impacts on human health, including anti-obesity effects. It is well documented that green tea and its constituent catechins suppress obesity, but the effects of other types of tea on obesity and the potential mechanisms involved are not yet fully understood. In this study, we investigated the suppression of adiposity by oolong, black and pu-erh tea and characterized the underlying molecular mechanism in vivo. We found that the consumption of oolong, black or pu-erh tea for a period of one week significantly decreased visceral fat without affecting body weight in male ICR mice. On a mechanistic level, the consumption of tea enhanced the phosphorylation of AMP-activated protein kinase (AMPK) in white adipose tissue (WAT). This was accompanied by the induction of WAT protein levels of uncoupling protein 1 and insulin-like growth factor binding protein 1. Our results indicate that oolong, black and pu-erh tea, and in particular, black tea, suppresses adiposity via phosphorylation of the key metabolic regulator AMPK and increases browning of WAT.