Matured Hop Bittering Components Induce Thermogenesis in Brown Adipose Tissue via Sympathetic Nerve Activity

Current strategies for the management of valuable compounds from hops waste for a circular economy

World beer production generates large volumes of waste discharged with every brew. Recently, new methods of reducing and reusing hops waste: hot trub (HT), and brewer-spent hops (BSH) are being exploited to improve the circular economy processes. This review outlines the current achievements in the management of hops waste. Following an in-depth review of various scientific publications, current strategies are discussed as a sustainable alternative to food waste exploitation and an inexpensive source of valuable compounds. Moreover, key aspects concerning the nutritional value of hops waste and the potential to enhance the functional properties of food and beverages are highlighted. Due to their nutritional composition, hops residues may be used as prospective sources of added-value co-products or additives for food enrichment, especially for products rich in fat, or as a new source of vegetable protein.

Effects of intraduodenal or intragastric administration of a bitter hop extract (Humulus lupulus L.), on upper gut motility, gut hormone secretion and energy intake in healthy-weight men

Gastrointestinal functions, particularly pyloric motility and the gut hormones, cholecystokinin and peptide YY, contribute to the regulation of acute energy intake. Bitter tastants modulate these functions, but may, in higher doses, induce GI symptoms. The aim of this study was to evaluate the effects of both dose and delivery location of a bitter hop extract (BHE) on antropyloroduodenal pressures, plasma cholecystokinin and peptide YY, appetite perceptions, gastrointestinal symptoms and energy intake in healthy-weight men. The study consisted of two consecutive parts, with part A including n = 15, and part B n = 11, healthy, lean men (BMI 22.6 ± 1.1 kg/m², aged 25 ± 3 years). In randomised, double-blind fashion, participants received in part A, BHE in doses of either 100 mg ("ID-BHE-100") or 250 mg ("ID-BHE-250"), or vehicle (canola oil; "ID-control") intraduodenally, or in part B, 250 mg BHE ("IG-BHE-250") or vehicle ("IG-control") intragastrically. Antropyloroduodenal pressures, hormones, appetite and symptoms were measured for 180 min, energy intake from a standardised buffet-meal was quantified subsequently. ID-BHE-250, but not ID-BHE-100, had modest, and transient, effects to stimulate pyloric pressures during the first 90 min (P < 0.05), and peptide YY from t = 60 min (P < 0.05), but did not affect antral or duodenal pressures, cholecystokinin, appetite, gastrointestinal symptoms or energy intake. IG-BHE-250 had no detectable effects. In conclusion, BHE, when administered intraduodenally, in the selected higher dose, modestly affected some appetite-related gastrointestinal functions, but had no detectable effects when given in the lower dose or intragastrically. Thus, BHE, at none of the doses or routes of administration tested, has appetite- or energy intake-suppressant effects.

Humulus lupulus L. extract and its active constituent xanthohumol attenuate oxidative stress and nerve injury induced by iron overload via activating AKT/GSK3β and Nrf2/NQO1 pathways

Hops, the dried female clusters from Humulus lupulus L., have traditionally been used as folk medicines for treating insomnia, neuralgia, and menopausal disorders. However, its pharmacological action on iron overload induced nerve damage has not been investigated. This study aims to evaluate the protective effects of hops extract (HLE) and its active constituent xanthohumol (XAN) on nerve injury induced by iron overload in vivo and in vitro, and to explore its underlying mechanism. The results showed that HLE and XAN significantly improved the memory impairment of iron overload mice, mainly manifested as shortened latency time, increased crossing platform times and spontaneous alternation ratio, and increased the expression of related proteins. Additionally, HLE and XAN significantly increased superoxide dismutase (SOD) and glutathione peroxidase (GSH-PX) activities, and remarkably decreased malondialdehyde (MDA) level in hippocampus. Also, HLE and XAN apparently reduced reactive oxygen species (ROS) content of PC12 cells induced by iron dextran (ID), and improved the oxidative stress level. Moreover, HLE and XAN significantly upregulated the expression of nuclear factor E2-related factor (Nrf2), NAD(P)H quinone oxidoreductase (NQO1), heme oxygenase-1 (HO-1), SOD, phosphorylated AKT (p-AKT), and phosphorylated GSK3β (p-GSK3β) both in hippocampus and PC12 cells. These findings demonstrated the protective effect of HLE and XAN against iron-induced memory impairment, which is attributed to its antioxidant profile by activation of AKT/GSK3β and Nrf2/NQO1 pathways. Also, it was suggested that hops could be a potential candidate for iron overload-related neurological diseases treatment.

An extract of hops (Humulus lupulus L.) modulates gut peptide hormone secretion and reduces energy intake in healthy-weight men: a randomized, crossover clinical trial

BACKGROUND

Gastrointestinal enteroendocrine cells express chemosensory bitter taste receptors that may play an important role in regulating energy intake (EI) and gut function.

OBJECTIVES

To determine the effect of a bitter hop extract (Humulus lupulus L.) on acute EI, appetite, and hormonal responses.

METHODS

Nineteen healthy-weight men completed a randomized 3-treatment, double-blind, crossover study with a 1-wk washout between treatments. Treatments comprised either placebo or 500 mg of hop extract administered in delayed-release capsules (duodenal) at 11:00 h or quick-release capsules (gastric) at 11:30 h. Ad libitum EI was recorded at the lunch (12:00 h) and afternoon snack (14:00 h), with blood samples taken and subjective ratings of appetite, gastrointestinal (GI) discomfort, vitality, meal palatability, and mood assessed throughout the day.

RESULTS

Total ad libitum EI was reduced following both the gastric (4473 kJ; 95% CI: 3811, 5134; P = 0.006) and duodenal (4439 kJ; 95% CI: 3777, 5102; P = 0.004) hop treatments compared with the placebo (5383 kJ; 95% CI: 4722, 6045). Gastric and duodenal treatments stimulated prelunch ghrelin secretion and postprandial cholecystokinin, glucagon-like peptide 1, and peptide YY responses compared with placebo. In contrast, postprandial insulin, glucose-dependent insulinotropic peptide, and pancreatic polypeptide responses were reduced in gastric and duodenal treatments without affecting glycemia. In addition, gastric and duodenal treatments produced small but significant increases in subjective measures of GI discomfort (e.g., nausea, bloating, abdominal discomfort) with mild to severe adverse GI symptoms reported in the gastric treatment only. However, no significant treatment effects were observed for any subjective measures of appetite or meal palatability.

CONCLUSIONS

Both gastric and duodenal delivery of a hop extract modulates the release of hormones involved in appetite and glycemic regulation, providing a potential "bitter brake" on EI in healthy-weight men.

Bitter taste receptor activation by hop-derived bitter components induces gastrointestinal hormone production in enteroendocrine cells

Matured hop bitter acids (MHBA) are bitter acid oxides derived from hops, widely consumed as food ingredients to add bitterness and flavor in beers. Previous studies have suggested a potential gut-brain mechanism in which MHBA simulates enteroendocrine cells to produce cholecystokinin (CCK), a gastrointestinal hormone which activates autonomic nerves, resulting in body fat reduction and cognitive improvement; however, the MHBA recognition site on enteroendocrine cells has not been fully elucidated. In this study, we report that MHBA is recognized by specific human and mouse bitter taste receptors (human TAS2R1, 8, 10 and mouse Tas2r119, 130, 105) using a heterologous receptor expression system in human embryonic kidney 293T cells. In addition, knockdown of each of these receptors using siRNA transfection partially but significantly suppressed an MHBA-induced calcium response and CCK production in enteroendocrine cells. Furthermore, blocking one of the essential taste signaling components, transient receptor potential cation channel subfamily M member 5, remarkably inhibited the MHBA-induced calcium response and CCK production in enteroendocrine cells. Our results demonstrate that specific bitter taste receptor activation by MHBA drives downstream calcium response and CCK production in enteroendocrine cells. These findings reveal a mechanism by which food ingredients derived from hops in beer activate the gut-brain axis for the first time.

Effects of the Non-Alcoholic Fraction of Beer on Abdominal Fat, Osteoporosis, and Body Hydration in Women

Several studies have shown that binge drinking of alcoholic beverages leads to non-desirable outcomes, which have become a serious threat to public health. However, the bioactive compounds in some alcohol-containing beverages might mitigate the negative effects of alcohol. In beer, the variety and concentration of bioactive compounds in the non-alcoholic fraction suggests that its consumption at moderate levels may not only be harmless but could also positively contribute to an improvement of certain physiological states and be also useful in the prevention of different chronic diseases. The present review focuses on the effects of non-alcoholic components of beer on abdominal fat, osteoporosis, and body hydration in women, conditions selected for their relevance to health and aging. Although beer drinking is commonly believed to cause abdominal fat deposition, the available literature indicates this outcome is inconsistent in women. Additionally, the non-alcoholic beer fraction might improve bone health in postmenopausal women, and the effects of beer on body hydration, although still unconfirmed seem promising. Most of the health benefits of beer are due to its bioactive compounds, mainly polyphenols, which are the most studied. As alcohol-free beer also contains these compounds, it may well offer a healthy alternative to beer consumers.

Hop bioactive compounds in prevention of nutrition-related noncommunicable diseases

Nutrition-related noncommunicable diseases (NR-NCDs) such as cardiovascular disease and type 2 diabetes both negatively impact the quality of life of many individuals and generate a substantial burden on society, demonstrating a need for intervention. Phytochemicals are investigated as a potential approach for combating NR-NCDs, and those found in hops have gained increased attention in recent decades. Hops, the strobile of the plant Humulus lupulus, are grown primarily for the brewing industry as they confer taste and increased shelf-life. The bitter acids represent the main compounds of interest for improving beer quality. Additionally, bitter acids as well as the prenylated chalcone xanthohumol, exhibit a wide range of health beneficial properties. This review summarizes those beneficial effects of bitter acids and xanthohumol on NR-NCDs, including inflammatory and immune diseases, obesity and metabolic disorders, as well as cancer prevention.

Improving Effects of Hop-Derived Bitter Acids in Beer on Cognitive Functions: A New Strategy for Vagus Nerve Stimulation

Dementia and cognitive decline are global public health problems. Moderate consumption of alcoholic beverages reduces the risk of dementia and cognitive decline. For instance, resveratrol, a polyphenolic compound found in red wine, has been well studied and reported to prevent dementia and cognitive decline. However, the effects of specific beer constituents on cognitive function have not been investigated in as much detail. In the present review, we discuss the latest reports on the effects and underlying mechanisms of hop-derived bitter acids found in beer. Iso-α-acids (IAAs), the main bitter components of beer, enhance hippocampus-dependent memory and prefrontal cortex-associated cognitive function via dopamine neurotransmission activation. Matured hop bitter acids (MHBAs), oxidized components with β-carbonyl moieties derived from aged hops, also enhance memory functions via norepinephrine neurotransmission-mediated mechanisms. Furthermore, the effects of both IAAs and MHBAs are attenuated by vagotomy, suggesting that these bitter acids enhance cognitive function via vagus nerve stimulation. Moreover, supplementation with IAAs attenuates neuroinflammation and cognitive impairments in various rodent models of neurodegeneration including Alzheimer's disease. Daily supplementation with hop-derived bitter acids (e.g., 35 mg/day of MHBAs) may be a safe and effective strategy to stimulate the vagus nerve and thus enhance cognitive function.

Iso-α-acids and matured hop bitter acids in beer improve obesity-induced cognitive impairment

Dementia and cognitive decline have become public health issues worldwide and life-style-related diseases and obesity have recently been reported as key risk factors. We have recently demonstrated that short-term administration of iso-α-acids (IAAs), hop-derived bitter components of beer, improves spatial and object recognition memory. However, the short-term effects of IAAs on obesity-induced cognitive impairment remain to be investigated. Furthermore, although matured hop bitter acids (MHBAs) are also derived from hops, their effect on obesity-induced cognitive decline remains unknown. In the present study, the short-term administration of IAAs improved memory deficits in high-fat diet (HFD)-fed mice, as assessed in the novel object recognition test (NORT). Dietary MHBAs supplementation administered to HFD-fed mice prevented obesity and improved memory deficits in the NORT. Moreover, the short-term administration of MHBAs improved episodic and spatial reference memory in obese mice. These hop-derived bitter acids may contribute toward improving obesity-induced cognitive impairments.

Abbreviations: IAAs: iso-α-acids; MHBAs: matured hop bitter acids; HFD: high fat diet; NORT: novel object recognition test; NOLT: novel object location test

Matured hop bitter acids improve spatial working and object recognition memory via nicotinic acetylcholine receptors

RATIONALE

Cognitive decline and dementia are major concerns in today's aging society. As limited treatments are available, measures to prevent cognitive decline and dementia are needed. We previously demonstrated that matured hop bitter acids (MHBA), bitter components of beer, increase norepinephrine in the hippocampus and improve memory in amnesia model mice induced by scopolamine (SCP), an antagonist of muscarinic receptor. However, other neurotransmitters involved in the effects of MHBA on memory improvement remain unknown.

OBJECTIVES

This study aimed to assess the role of acetylcholine receptors (AChR) in the effects of MHBA on memory.

METHOD

The involvement of AChR on the effects of MHBA (10 mg/kg) on cognitive function was evaluated using AChR antagonists, SCP, mecamylamine hydrochloride (MEC), a non-competitive antagonist of nicotinic-AChR (nAChR), and methyllycaconitine citrate (MLA), an α7nAChR antagonist, for the Y-maze test and the novel object recognition test (NORT). A separate population of mice, which underwent vagotomy or sham operation, was subjected to NORT to elucidate further mechanism. In addition, the effect of MHBA on acetylcholinesterase (AChE) activity was measured in vitro.

RESULTS

In accordance with previous reports, MHBA improved spontaneous alternations of the Y-maze test in SCP-induced amnesia mice and increased discrimination index evaluated by the NORT in normal mice. On the other hand, treatment with MEC or MLA attenuated the effects of MHBA on memory improvement in the Y-maze test and the NORT. Vagotomized mice also showed attenuated memory enhancement by MHBA in the NORT. In addition, MHBA did not alter AChE activity in vitro.

CONCLUSIONS

The results support the involvement of nAChRs in memory improvement in mice by MHBA. MHBA is thus thought to activate the vagal nerve and enhance hippocampus-dependent memory via nAChRs.

From white to beige adipocytes: therapeutic potential of dietary molecules against obesity and their molecular mechanisms

The global incidence of obesity and its complications continue to rise along with a demand for novel therapeutic approaches. In addition to classic brown adipose tissue (BAT), the formation of brown-like adipocytes called beige adipocytes, within white adipose tissue (WAT), has attracted much attention as a therapeutic target due to its inducible features when stimulated, resulting in the dissipation of extra energy as heat. There are various dietary agents that are able to modulate the beige-development process by interacting with critical molecular signaling cascades, leading to the enhancement of thermogenesis. Although challenges still remain regarding the origin of the beige adipocytes, the crosstalk with activation of BAT and induction of the beiging of white fat may provide attractive potential strategies for management of obesity.

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.

Secretion of a gastrointestinal hormone, cholecystokinin, by hop-derived bitter components activates sympathetic nerves in brown adipose tissue

Matured hop bitter acids (MHBA) are oxidation products from bitter components in hops, which are used widely as food materials to add flavor and bitterness in beer production. Our previous study has shown that MHBA induces thermogenesis in brown adipose tissue (BAT) via sympathetic nerves in rodents and reduces body fat in healthy adults. However, it is unclear how MHBA affects the sympathetic nervous system. In this study, we demonstrate that MHBA treatment of enteroendocrine cells increases Ca²⁺ levels and induces the secretion of the gastrointestinal hormone, cholecystokinin (CCK), in a dose-dependent manner. These effects were eliminated by Ca²⁺ depletion from the medium or blockers of L-type voltage-sensitive Ca²⁺ channels during pretreatment. Induction of CCK secretion by MHBA was also confirmed using isolated rat small intestines. Elevation of the sympathetic nerve activity innervating BAT (BAT-SNA) and BAT temperature by MHBA administration in rats was blocked by pretreatment with a CCK receptor 1 (CCK1R) antagonist. Moreover, the intraperitoneal injection of CCK fragment elevated BAT-SNA, and this increase was blocked by subdiaphragmatic vagotomy. These results demonstrate that MHBA induces CCK secretion in the gastrointestinal tracts and elevates BAT-SNA via CCK1R and vagal afferent nerves. In addition, MHBA increases BAT temperature via CCK1R. Our findings reveal a novel mechanism of the beneficial metabolic effects of food ingredients.

The relationship between the effect of matured hop extract and physical activity on reducing body fat: re-analysis of data from a randomized, double-blind, placebo-controlled parallel group study

BACKGROUND

We recently reported that successive ingestion of matured hop extract (MHE), produced by oxidation of hops, results in a reduction of body fat in healthy overweight participants. A combined effect of MHE and physical activity on body fat has not been investigated. Thus, we re-analyzed data from the previous study to explore the relationship between the effect of MHE and walking as an index of physical activity.

METHODS

This analysis uses existing data from a randomized, double-blind, placebo-controlled parallel group study in which MHE (active) or placebo was given for 12 w to 200 healthy overweight Japanese, from May to December 2014. Correlation between the change in abdominal fat areas at 12 w and the number of steps taken per day was tested by Spearman's correlation coefficient test. The subjects were stratified using the average number of steps per day of Japanese into walking less and walking more subgroups (WL and WM, respectively) as follows: placebo (WL, n = 43; WM, n = 44) and active (WL, n = 49; WM, n = 42). Reductions in total, visceral, and subcutaneous fat area (TFA, VFA and SFA, respectively) were evaluated. The interaction effect between ingestion (active/placebo) and walking (WL/WM) was analyzed using two-way analysis of variance (ANOVA).

RESULTS

There was a significant negative correlation between the change in VFA and daily steps taken in the active group (r = - 0.208, P = 0.048). No significant correlation in TFA or SFA. Although the interaction effect in TFA was not significant, the main effect of ingestion was significant (P = 0.045). In contrast, the interaction effect in VFA was suggested to be synergistic (P = 0.055).

CONCLUSION

The results suggested that MHE ingestion combined with light intensity exercise would induce a greater reduction in VFA which would be beneficial for obese or overweight individuals in reducing obesity and obesity-related diseases.

TRIAL REGISTRATION

UMIN-CTR UMIN000014185 registered 6 June 2014.

Matured Hop-Derived Bitter Components in Beer Improve Hippocampus-Dependent Memory Through Activation of the Vagus Nerve

Improving and maintaining memory function is effective in preventing cognitive decline and dementia. Previously, we demonstrated that iso-α-acids, the hop-derived bitter components in beer, prevent cognitive impairment in an Alzheimer’s disease mouse model. In this report, we investigated the effects of matured hop bitter acids (MHBA) containing components of oxides derived from α- and β-acids, and structurally similar to iso-α-acids, on cognitive function using behavioral pharmacological procedures. MHBA and the representative components of MHBA, 4′-hydroxyallohumulinone (HAH) and 4′-hydroxy-cis-alloisohumulone (HAIH) improved spatial working memory in scopolamine-induced amnesia mice. MHBA also enhanced episodic memory in the novel object recognition test (NORT). The administration of MHBA increased the amount of norepinephrine (NE) and NE release into cerebrospinal fluid (CSF) in hippocampus. The MHBA activity in improving memory function was attenuated by treatment with a β-adrenergic receptor inhibitor. In addition, vagotomized mice did not display the memory improvement induced by MHBA. Together, our results suggest that MHBA improves memory function via stimulation of the vagus nerve and enhancement of NE release in the hippocampus. Vagus nerve activation by the intake of food materials including MHBA may be a safe and effective approach for improving cognitive function.

Genetic, acute and subchronic toxicity studies of matured hop extract produced by extraction from heat-treated hops

It has been demonstrated that successive ingestion of matured hop extract (MHE), produced by extraction from heat-treated hops, results in body fat reduction in animals and humans; however, preclinical safety studies have not been reported. In this study, we conducted in vitro and in vivo safety studies for MHE. Genotoxicity was evaluated using the Ames test, in vitro chromosomal aberration test, and in vivo micronucleus test. To assess acute safety, a single, oral administration of MHE to rats was monitored. Subchronic safety was assessed by repeated feeding with MHE for 90 days. The in vitro chromosomal aberration test was positive at 3,330 μg/mL and 5,000 μg/mL without metabolic activation. However, MHE did not induce any reverse mutation with or without metabolic activation in the Ames test, and no abnormalities were observed at a dose of 2,000 mg/kg body weight in the rat micronucleus test. In the acute and subchronic safety studies, no deaths or toxicological signs were recorded during the observation period. In addition, no changes in body weights, feed/water consumption, clinical signs, ophthalmoscopy, urinalysis, hematology, blood biochemistry, organ weights, or histopathology were observed after repeated administration of MHE. Therefore, the no-observed-adverse-effect-level (NOAEL) of MHE was considered to be over 3,484 and 4,022 mg/kg body weight/day in males and females, respectively. These results indicate that there is no safety concern for MHE in the present preclinical safety study.

β-Eudesmol, an oxygenized sesquiterpene, stimulates appetite via TRPA1 and the autonomic nervous system

Transient receptor potential ankyrin 1 (TRPA1) is a calcium-permeable non-selective cation channel, which is activated by various noxious or irritant substances in nature. TRPA1 activators have been generally recognized as noxious, however, foods and beverages containing TRPA1 activators are preferably consumed; the reasons for this discrepancy are not well understood. We demonstrate that TRPA1 is involved in the stimulatory appetite control mechanism. β-Eudesmol is an oxygenated sesquiterpene contained in medicinal or edible plants which activates TRPA1. Oral administration of β-eudesmol brought significant increments in food intake in rats and elevated plasma ghrelin levels. Gastric vagal nerve activity (GVNA) has been reported to affect feeding behavior. In vivo electrophysiological measurement of GVNA revealed that oral-ingestion of β-eudesmol significantly increased GVNA. This GVNA elevation was eliminated by TRPA1 inhibitor (HC-030031) treatment prior to β-eudesmol administration. The physiological effects of β-eudesmol, for example, incremental increase in food intake, ghrelin elevation and activation of GVNA, were significantly reduced in TRPA1 knockout rats. Our results indicated that β-eudesmol stimulates an increase in appetite through TRPA1, and suggests why TRPA1 activator containing foods and beverages are preferably consumed.

Systems genetic analysis of brown adipose tissue function

Brown adipose tissue (BAT) has been suggested to play an important role in lipid and glucose metabolism in rodents and possibly also in humans. In the current study, we used genetic and correlation analyses in the BXH/HXB recombinant inbred (RI) strains, derived from Brown Norway (BN) and spontaneously hypertensive rats (SHR), to identify genetic determinants of BAT function. Linkage analyses revealed a quantitative trait locus (QTL) associated with interscapular BAT mass on chromosome 4 and two closely linked QTLs associated with glucose oxidation and glucose incorporation into BAT lipids on chromosome 2. Using weighted gene coexpression network analysis (WGCNA) we identified 1,147 gene coexpression modules in the BAT from BXH/HXB rats and mapped their module eigengene QTLs. Through an unsupervised analysis, we identified modules related to BAT relative mass and function. The Coral4.1 coexpression module is associated with BAT relative mass (includes Cd36 highly connected gene), and the Darkseagreen coexpression module is associated with glucose incorporation into BAT lipids (includes Hiat1, Fmo5, and Sort1 highly connected transcripts). Because multiple statistical criteria were used to identify candidate modules, significance thresholds for individual tests were not adjusted for multiple comparisons across modules. In summary, a systems genetic analysis using genomic and quantitative transcriptomic and physiological information has produced confirmation of several known genetic factors and significant insight into novel genetic components functioning in BAT and possibly contributing to traits characteristic of the metabolic syndrome.

Hop Phytochemicals and Their Potential Role in Metabolic Syndrome Prevention and Therapy

Historically, hop cones (Humulus lupulus) have been used since ancient times as a remedy for many ailments and, as a source of polyphenols and bitter acids, is very effective in the treatment of metabolic syndrome (MS). Hop flavonoids, particularly xanthohumol (XN), are substances with hypoglycemic, antihyperlipidemic, and antiobesity activities. Iso-α-acids (IAA) and matured hop bitter acids (MHBA) improve health by influencing lipid metabolism, glucose tolerance, and body weight. The modulatory effect of IAA and MHBA on lipid metabolism may also be responsible for a loss in body weight. These results suggest promising applications for IAA, MHBA, and XN in humans, particularly in the prevention of diet-induced obesity and diabetes.

Difference in intracellular temperature rise between matured and precursor brown adipocytes in response to uncoupler and β-adrenergic agonist stimuli

Brown adipocytes function to maintain body temperature by heat production. However, direct measurement of heat production at a single cell level remains difficult. Here we developed a method to measure the temperature within primary cultured brown adipocytes using a cationic fluorescent polymeric thermometer. Placement of the thermometer within a matured brown adipocyte and a precursor cell enabled the detection of heat production following uncoupler treatment. The increase in the intracellular temperature due to stimulation with a mitochondrial uncoupler was higher in matured brown adipocytes than in precursor cells. Stimulation with a β-adrenergic receptor (β-AR) agonist, norepinephrine, raised the intracellular temperature of matured brown adipocytes to a level comparable to that observed after stimulation with a β3-AR-specific agonist, CL316.243. In contrast, neither β-AR agonist induced an intracellular temperature increase in precursor cells. Further, pretreatment of brown adipocytes with a β3-AR antagonist inhibited the norepinephrine-stimulated elevation of temperature. These results demonstrate that our novel method successfully determined the difference in intracellular temperature increase between matured brown adipocytes and precursor cells in response to stimulation by an uncoupler and β-AR agonists.

Phytochemicals as novel agents for the induction of browning in white adipose tissue

Obesity and its associated metabolic syndrome continue to be a health epidemic in westernized societies and is catching up in the developing world. Despite such increases, little headway has been made to reverse adverse weight gain in the global population. Few medical options exist for the treatment of obesity which points to the necessity for exploration of anti-obesity therapies including pharmaceutical and nutraceutical compounds. Defects in brown adipose tissue, a major energy dissipating organ, has been identified in the obese and is hypothesized to contribute to the overall metabolic deficit observed in obesity. Not surprisingly, considerable attention has been placed on the discovery of methods to activate brown adipose tissue. A variety of plant-derived, natural compounds have shown promise to regulate brown adipose tissue activity and enhance the lipolytic and catabolic potential of white adipose tissue. Through activation of the sympathetic nervous system, thyroid hormone signaling, and transcriptional regulation of metabolism, natural compounds such as capsaicin and resveratrol may provide a relatively safe and effective option to upregulate energy expenditure. Through utilizing the energy dissipating potential of such nutraceutical compounds, the possibility exists to provide a therapeutic solution to correct the energy imbalance that underlines obesity.

Brown adipose tissue: Updates in cellular and molecular biology

Brown adipose tissue (BAT) is mainly composed of adipocytes, it is highly vascularized and innervated, and can be activated in adult humans. Brown adipocytes are responsible for performing non-shivering thermogenesis, which is exclusively mediated by uncoupling protein (UCP) -1 (a protein found in the inner mitochondrial membrane), the hallmark of BAT, responsible for the uncoupling of the proton leakage from the ATP production, therefore, generating heat (i.e. thermogenesis). Besides UCP1, other compounds are essential not only to thermogenesis, but also to the proliferation and differentiation of BAT, including peroxisome proliferator-activated receptor (PPAR) family, PPARgamma coactivator 1 (PGC1)-alpha, and PRD1-BF-1-RIZ1 homologous domain protein containing protein (PRDM) -16. The sympathetic nervous system centrally regulates thermogenesis through norepinephrine, which acts on the adrenergic receptors of BAT. This bound leads to the initialization of the many pathways that may activate thermogenesis in acute and/or chronic ways. In summary, this mini-review aims to demonstrate the latest advances in the knowledge of BAT.

Matured hop extract reduces body fat in healthy overweight humans: a randomized, double-blind, placebo-controlled parallel group study

Background

Hops are the main components of beer that provide flavor and bitterness. Iso-α-acids, the bitter components of beer, have been reported to reduce body fat in humans, but the bitterness induced by effective doses of iso-α-acids precludes their acceptance as a nutrient. The matured hop bitter acids (MHBA) of oxidized hops appear to have a more pleasant bitterness compared to the sharper bitterness of iso-α-acids. While there has been little information concerning the identity of the MHBA compounds and their physiological effects, MHBA was recently found to be primarily composed of oxides derived from α-acids, and structurally similar to iso-α-acids. Here, we investigated the effects of matured hop extract (MHE) containing MHBA on reducing abdominal body fat in healthy subjects with a body mass index (BMI) of 25 to below 30 kg/m², classified as “obese level 1” in Japan or as “overweight” by the WHO.

Trial design

A randomized, double-blind, placebo-controlled parallel group study.

Methods

Two hundred subjects (male and female aged 20 to below 65 years with a BMI of 25 or more and less than 30 kg/m²) were randomly assigned to two groups. During a 12-week ingestion period, the subjects in each group ingested daily 350 mL of test-beverage, either containing MHE (with 35 mg MHBA), i.e. the namely active beverage, or a placebo beverage without MHE. The primary endpoint was reduction of the abdominal fat area as determined by CT scanning after continual ingestion of MHE for 12 weeks.

Results

Compared to the placebo group, a significant reduction was observed in the visceral fat area after 8 and 12 w, and in the total fat area after 12 w in the active group. There was also a concomitant decrease in body fat ratio in the active group compared to the placebo group. No adverse events related to the test beverages or clinically relevant abnormal changes in the circulatory, blood and urine parameters were observed in either group.

Conclusions

The present study suggests that continual ingestion of MHE safely reduces body fat, particularly the abdominal visceral fat of healthy overweight subjects.

Trial registration

UMIN-CTR UMIN000014185

Electronic supplementary material

The online version of this article (doi:10.1186/s12937-016-0144-2) contains supplementary material, which is available to authorized users.