Control of white and brown adipose tissues by the autonomic nervous system

Metabolic remodeling of visceral and subcutaneous white adipose tissue during reacclimation of rats after cold

Deciphering lipid metabolism in white adipose tissue (WAT) depots during weight gain is important to understand the heterogeneity of WAT and its roles in obesity. Here, we examined the expression of key enzymes of lipid metabolism and changes in the morphology of representative visceral (epididymal) and subcutaneous (inguinal) WAT (eWAT and iWAT, respectively)-in adult male rats acclimated to cold (4 ± 1 °C) for 45 days and reacclimated to room temperature (RT, 22 ± 1 °C) for 1, 3, 7, 12, 21, or 45 days. The relative mass of both depots decreased to a similar extent after cold acclimation. However, fatty acid synthase (FAS), glucose-6-phosphate dehydrogenase (G6PDH), and medium-chain acyl-CoA dehydrogenase (ACADM) protein level increased only in eWAT, whereas adipose triglyceride lipase (ATGL) expression increased only in iWAT. During reacclimation, the relative mass of eWAT reached control values on day 12 and that of iWAT on day 45 of reacclimation. The faster recovery of eWAT mass is associated with higher expression of FAS, acetyl-CoA carboxylase (ACC), G6PDH, and ACADM during reacclimation and a delayed increase in ATGL. The absence of an increase in proliferating cell nuclear antigen suggests that the observed depot-specific mass increase is predominantly due to metabolic adjustments. In summary, this study shows a differential rate of visceral and subcutaneous adipose tissue weight regain during post-cold reacclimation of rats at RT. Faster recovery of the visceral WAT as compared to subcutaneous WAT during reacclimation at RT could be attributed to observed differences in the expression patterns of lipid metabolic enzymes.

Lactate induces the development of beige adipocytes via an increase in the level of reactive oxygen species

Recent studies have indicated that lactate acts as a signaling molecule in various tissues. We previously demonstrated that intake of an amino acid mixture combined with exercise synergistically induced beige adipocyte formation in inguinal white adipose tissue (iWAT) in mice. Moreover, plasma lactate levels remained significantly elevated in the amino acid mixture + exercise group even 16 h after exercise, indicating that a lactate-mediated pathway may be involved in the induction of beige adipocyte formation. Against this background, we hypothesized that oral intake of lactate would induce beige adipocyte formation via the lactate signaling pathway without exercise. Furthermore, if oral intake of lactate can produce the same effect as exercise, lactate might be used as a food-derived exercise replacement-factor. Oral intake of lactate (100 mM in drinking water) for 4 weeks significantly induced beige adipocyte formation in iWAT in mice as well as a significant elevation of lactate transporter (monocarboxylic acid transporter 1; MCT1) and lactate dehydrogenase B levels. Administration of lactate to adipocytes significantly increased reactive oxygen species (ROS) and superoxide levels and the NADH/NAD+ ratio. The induction of lactate-mediated uncoupling protein 1 (UCP1) expression and ROS production were significantly suppressed by antioxidant treatment or inhibition of MCT1. However, UCP1 induction was not significantly affected by the inhibition of lactate receptor (hydroxycarboxylic acid receptor 1). These findings suggest that lactate-mediated ROS production induces beige adipocyte formation, and thus oral intake of lactate may confer some benefits of exercise without the need to perform exercise.

Somatosensory innervation of adipose tissues

The increasing prevalence of obesity and type 2 diabetes has led to a greater interest in adipose tissue physiology. Adipose tissue is now understood as an organ with endocrine and thermogenic capacities in addition to its role in fat storage. It plays a critical role in systemic metabolism and energy regulation, and its activity is tightly regulated by the nervous system. Fat is now recognized to receive sympathetic innervation, which transmits information from the brain, as well as sensory innervation, which sends information into the brain. The role of sympathetic innervation in adipose tissue has been extensively studied. However, the extent and the functional significance of sensory innervation have long been unclear. Recent studies have started to reveal that sensory neurons robustly innervate adipose tissue and play an important role in regulating fat activity. This brief review will discuss both historical evidence and recent advances, as well as important remaining questions about the sensory innervation of adipose tissue.

Combination of Exercise and Intake of Amino Acid Mixture Synergistically Induces Beige Adipocyte Formation in Mice

Exercise combined with dietary factors may have significant effects on the suppression of body fat accumulation. Several trials suggest that amino acid mixtures containing alanine, arginine, and phenylalanine (ARF) combined with exercise can significantly reduce body fat accumulation in overweight adults and high-fat diet-induced obesity in mice. We therefore hypothesized that combining ARF and exercise would significantly induce beige adipocyte formation and that this would contribute to reducing body weight, whereas administration of ARF or exercise alone would not. Administration of ARF (1 g/kg body weight, daily) combined with exercise (5 sessions per week) for 4 wk significantly induced formation of beige adipocytes in inguinal white adipose tissue (iWAT) in mice, although ARF or exercise alone did not. Metabolomic analysis showed that plasma lactate concentration was significantly elevated in the exercise+ARF group relative to the exercise group. Furthermore, lactate dehydrogenase B, which increases redox stress by converting lactate to pyruvate in iWAT and triggers induction of uncoupling protein 1 expression was significantly upregulated in iWAT of the exercise+ARF group. These findings demonstrate the unique effect of ARF combined with exercise for inducing beige adipocyte formation, which may be associated with the suggested lactate-mediated pathway. Appropriate mixtures of amino acids could be used as a dietary supplement before exercise and contributed to increasing energy expenditures.

Tears of joy, aesthetic chills and heartwarming feelings: Physiological correlates of Kama Muta

Situations involving increased closeness or exceptional kindness are often labeled as moving or touching and individuals often report bodily symptoms, including tears, goosebumps, and warmth in the body. Recently, the kama muta framework has been proposed as a cross-cultural conceptualization of these experiences. Prior research on kama muta has mostly relied on subjective reports. Thus, our main goal of the present project was to examine the pattern of physiological responses to kama muta inducing videos and compare it to the patterns for the similar, though distinct emotions of sadness and awe. One hundred forty-four Portuguese and Norwegian participants were individually exposed to all three emotion conditions. Several psychophysiological indexes of the autonomic nervous system were collected continuously during exposure, including cardiovascular, respiratory, and electrodermal activity, facial EMG, skin temperature, as well as piloerection and lachrymation using cameras. Overall, the results partly replicated previous findings on being moved experiences and self-report studies. Strong self-reported experiences of kama muta were associated with increased phasic skin conductance, skin temperature, piloerection, and zygomaticus activity, while they were associated with reduced heart rate, respiration rate, and tonic skin conductance. The physiological profile of kama muta was successfully distinguished from sadness and awe, partly corroborating self-report evidence. We obtained no clear evidence of a kama muta association with the occurrence of lachrymation or heart rate variability. Our findings provide a systematic overview of psychophysiological response to experiences of kama muta, and help to inform future research on this emotion and positive emotions in general.

Co-Administration of Curcumin and Artepillin C Induces Development of Brown-Like Adipocytes in Association with Local Norepinephrine Production by Alternatively Activated Macrophages in Mice

Classical brown adipocytes, characterized by interscapular depots, have multilocular fat depots and are known to release excess energy. Recent studies have shown that induction of brown-like adipocytes, also referred to as beige or brite cells, in white adipose tissue (WAT) results in the release of excess energy through mitochondrial heat production via uncoupling protein 1. This has potential a therapeutic strategy for obesity and related diseases as well as classical brown adipocytes. In our previous studies, we found that artepillin C (ArtC, 10 mg/kg body weight), a characteristic constituent of Brazilian propolis, significantly induced the development of brown-like adipocytes in inguinal WAT (iWAT) of mice. Furthermore, we recently demonstrated that curcumin (Cur, 4.5 mg/kg) also significantly induced the development of brown-like adipocytes in mice. The combined administration of several food-derived factors can enhance their bioactivity and reduce their required functional doses. In this study, we showed that co-administration of Cur and ArtC at lower doses (Cur, 1.5 mg/kg; ArtC, 5 mg/kg) additively induce brown-like adipocyte development in mouse iWAT. Moreover, this induction is associated with the localized production of norepinephrine following accumulation of alternatively activated macrophages in iWAT. These findings suggest that co-administration of Cur and ArtC is significantly effective to reduce the dose and enhance the formation of brown-like adipocyte via a unique molecular mechanism.

α-Monoglucosyl Hesperidin but Not Hesperidin Induces Brown-Like Adipocyte Formation and Suppresses White Adipose Tissue Accumulation in Mice

Hesperidin (HES) is a flavanone glycoside found in citrus peel that contributes to its bitter taste. It has low water solubility and poor oral bioavailability. To improve its solubility and bioavailability, α-monoglucosyl hesperidin (αGH) has been synthesized from HES by transglucosylation using cyclodextrin glucanotransferase. Several reports indicate that αGH significantly decreases body fat, but the underlying molecular mechanism remains unclear. We hypothesized that the antiobesity effects of αGH occur through the induced formation of brown-like adipocytes. The present study verified that dietary αGH induces brown-like adipocytes to form in mouse inguinal white adipose tissue (iWAT), thereby significantly decreasing the weight of white adipose tissue (WAT). Furthermore, dietary αGH significantly induced thermogenesis in iWAT. Dietary αGH also significantly suppressed high-fat-diet-induced WAT accumulation in mice, which may be mediated by brown-like adipocyte formation. These results indicate that dietary αGH induces increased energy expenditure by stimulating the formation of brown-like adipocytes.

Highly Dispersible and Bioavailable Curcumin but not Native Curcumin Induces Brown-Like Adipocyte Formation in Mice

SCOPE

The induction of brown-like adipocytes in white adipose tissue (WAT) is a potential therapeutic target for the treatment of obesity and metabolic disorders via the ability of these cells to release excess energy as heat in association with uncoupling protein 1. Some experimental trials suggest that curcumin (a yellow pigment from turmeric) has a suppressive effect on the accumulation of body fat. However, there is little evidence to show that curcumin induces the formation of brown-like adipocytes and the molecular mechanisms involved remain elusive. In addition, in most experimental trials, high doses of curcumin are administered.

METHODS AND RESULTS

Highly dispersible and bioavailable curcumin (HC, i.e., 4.5 mg native curcumin kg^-1 ) but not the same dose of native curcumin induces the formation of brown-like adipocytes in mouse inguinal WAT. Moreover, the formation of brown-like adipocytes induced by HC in inguinal WAT may be mediated by the production of local norepinephrine from accumulated alternatively activated macrophages.

CONCLUSION

These novel findings suggest that curcumin increases energy expenditure by inducing the formation of brown-like adipocytes via a unique molecular mechanism. Importantly, they show that HC has significant bioactive effects in vivo at lower doses of curcumin.

The effects of acute renal denervation on kidney perfusion and metabolism in experimental septic shock

BACKGROUND

Perfusion deficits likely play an important role in the development of renal dysfunction in sepsis. Renal denervation may improve kidney perfusion and metabolism.

METHODS

We randomized 14 female sheep to undergo bilateral surgical renal denervation (n = 7) or sham procedure (n = 7) prior to induction of sepsis. Renal blood flow (RBF) was measured with a pre-calibrated flowprobe. Laser Doppler probes were implanted to measure cortical and medullary perfusion. Cortical glucose, lactate and pyruvate levels were measured using the microdialysis technique. Creatinine clearance was determined. Sepsis was induced by peritonitis and fluid resuscitation was provided to avoid hypovolemia.

RESULTS

RBF and cortical perfusion were higher in the denervated group during the first 6 h after induction of sepsis (P < 0.001 and P < 0.05, respectively), while medullary perfusion decreased similarly in both groups. After hypotension developed, RBF decreased to similar levels in both groups. Cortical pyruvate and lactate levels were lower in the denervated animals (P < 0.001 and P < 0.001, respectively). There were no differences between groups in creatinine clearance, urine output or time to oliguria.

CONCLUSION

Denervation thus caused an early increase in RBF that was distributed towards the kidney cortex. Although associated with an attenuation of early cortical metabolic alterations, denervation failed to prevent the deterioration in renal function.

Deletion of p22phox-dependent oxidative stress in the hypothalamus protects against obesity by modulating 3-adrenergic mechanisms

A role for oxidative stress in the brain has been suggested in the pathogenesis of diet-induced obesity (DIO), although the underlying neural regions and mechanisms remain incompletely defined. We tested the hypothesis that NADPH oxidase-dependent oxidative stress in the paraventricular nucleus (PVN), a hypothalamic energy homeostasis center, contributes to the development of DIO. Cre/LoxP technology was coupled with selective PVN adenoviral microinjection to ablate p22^phox , the obligatory subunit for NADPH oxidase activity, in mice harboring a conditional p22^phox allele. Selective deletion of p22^phox in the PVN protected mice from high-fat DIO independent of changes in food intake or locomotor activity. This was accompanied by β₃-adrenoceptor-dependent increases in energy expenditure, elevations in brown adipose tissue thermogenesis, and browning of white adipose tissue. These data reveal a potentially novel role for brain oxidative stress in the development of DIO by modulating β₃-adrenoceptor mechanisms and point to the PVN as an underlying neural site.

Artepillin C, a Typical Brazilian Propolis-Derived Component, Induces Brown-Like Adipocyte Formation in C3H10T1/2 Cells, Primary Inguinal White Adipose Tissue-Derived Adipocytes, and Mice

Induction of brown-like adipocytes (beige/brite cells) in white adipose tissue (WAT) suggests a new approach for preventing and treating obesity via induction of thermogenesis associated with uncoupling protein 1 (UCP1). However, whether diet-derived factors can directly induce browning of white adipocytes has not been well established. In addition, the underlying mechanism of induction of brown-like adipocytes by diet-derived factors has been unclear. Here, we demonstrate that artepillin C (ArtC), which is a typical Brazilian propolis-derived component, significantly induces brown-like adipocytes in murine C3H10T1/2 cells and primary inguinal WAT (iWAT)-derived adipocytes. This significant induction is due to activation of peroxisome proliferator-activated receptor γ and stabilization of PRD1-BF-1-RIZ1 homologous domain-containing protein-16 (PRDM16). Furthermore, the oral administration of ArtC (10 mg/kg) for 4 weeks significantly induced brown-like adipocytes accompanied by significant expression of UCP1 and PRDM16 proteins in iWAT of mice, and was independent of the β3-adrenergic signaling pathway via the sympathetic nervous system. These findings may provide insight into browning of white adipocytes including the molecular mechanism mediated by dietary factors and demonstrate that ArtC has a novel biological function with regard to increasing energy expenditure by browning of white adipocytes.

Type 2 responses at the interface between immunity and fat metabolism

Adipose tissue resident leukocytes are often cast solely as the effectors of obesity and its attendant pathologies; however, recent observations have demonstrated that these cells support and effect 'healthy' physiologic function as well as pathologic dysfunction. Importantly, these two disparate outcomes are underpinned by similarly disparate immune programs; type 2 responses instruct and promote metabolic normalcy, while type 1 responses drive tissue dysfunction. In this Review, we summarize the literature regarding type 2 immunity's role in adipose tissue physiology and allude to its potential therapeutic implications.

Brown adipose tissue and novel therapeutic approaches to treat metabolic disorders

In humans, 2 functionally different types of adipose tissue coexist: white adipose tissue (WAT) and brown adipose tissue (BAT). WAT is involved in energy storage, whereas BAT is involved in energy expenditure. Increased amounts of WAT may contribute to the development of metabolic disorders, such as obesity-associated type 2 diabetes mellitus and cardiovascular diseases. In contrast, the thermogenic function of BAT allows high consumption of fatty acids because of the activity of uncoupling protein 1 in the internal mitochondrial membrane. Interestingly, obesity reduction and insulin sensitization have been achieved by BAT activation-regeneration in animal models. This review describes the origin, function, and differentiation mechanisms of BAT to identify new therapeutic strategies for the treatment of metabolic disorders related to obesity. On the basis of the animal studies, novel approaches for BAT regeneration combining stem cells from the adipose tissue with active components, such as melatonin, may have potential for the treatment of metabolic disorders in humans.

Transcriptional fingerprinting of "browning" white fat identifies NRG4 as a novel adipokine

Brown adipocytes help to maintain body temperature by the expression of a unique set of genes that facilitate cellular metabolic events including uncoupling protein 1-dependent thermogenesis. The dissipation of energy in brown adipose tissue (BAT) is in stark contrast to white adipose tissue (WAT) which is the body's primary site of energy storage. However, adipose tissue is highly dynamic and upon cold exposure profound changes occur in WAT resulting in a BAT-like phenotype due to the presence of brown-in-white (BRITE) adipocytes. In our recent report, transcription profiling was used to identify the gene expression changes that underlie the browning process as well as the intrinsic differences between BAT and WAT. Neuregulin 4 was categorized as a cold-induced BAT gene encoding an adipokine that signals between adipocytes and nerve cells and likely to have a role in increasing adipose tissue innervation in response to cold.

Neuronal Control of Adaptive Thermogenesis

The obesity epidemic continues rising as a global health challenge, despite the increasing public awareness and the use of lifestyle and medical interventions. The biomedical community is urged to develop new treatments to obesity. Excess energy is stored as fat in white adipose tissue (WAT), dysfunction of which lies at the core of obesity and associated metabolic disorders. By contrast, brown adipose tissue (BAT) burns fat and dissipates chemical energy as heat. The development and activation of "brown-like" adipocytes, also known as beige cells, result in WAT browning and thermogenesis. The recent discovery of brown and beige adipocytes in adult humans has sparked the exploration of the development, regulation, and function of these thermogenic adipocytes. The central nervous system drives the sympathetic nerve activity in BAT and WAT to control heat production and energy homeostasis. This review provides an overview of the integration of thermal, hormonal, and nutritional information on hypothalamic circuits in thermoregulation.

Eosinophils and type 2 cytokine signaling in macrophages orchestrate development of functional beige fat

Beige fat, which expresses the thermogenic protein UCP1, provides a defense against cold and obesity. Although a cold environment is the physiologic stimulus for inducing beige fat in mice and humans, the events that lead from the sensing of cold to the development of beige fat remain poorly understood. Here, we identify the efferent beige fat thermogenic circuit, consisting of eosinophils, type 2 cytokines interleukin (IL)-4/13, and alternatively activated macrophages. Genetic loss of eosinophils or IL-4/13 signaling impairs cold-induced biogenesis of beige fat. Mechanistically, macrophages recruited to cold-stressed subcutaneous white adipose tissue (scWAT) undergo alternative activation to induce tyrosine hydroxylase expression and catecholamine production, factors required for browning of scWAT. Conversely, administration of IL-4 to thermoneutral mice increases beige fat mass and thermogenic capacity to ameliorate pre-established obesity. Together, our findings have uncovered the efferent circuit controlling biogenesis of beige fat and provide support for its targeting to treat obesity.

Hypoxia and adipocyte physiology: implications for adipose tissue dysfunction in obesity

Hypoxia develops in white adipose tissue in obese mice, resulting in changes in adipocyte function that may underpin the dysregulation that leads to obesity-associated disorders. Whether hypoxia occurs in adipose tissue in human obesity is unclear, with recent studies contradicting earlier reports that this was the case. Adipocytes, both murine and human, exhibit extensive functional changes in culture in response to hypoxia, which alters the expression of up to 1,300 genes. These include genes encoding key adipokines such as leptin, interleukin (IL)-6, vascular endothelial growth factor (VEGF), and matrix metalloproteinase-2 (MMP-2), which are upregulated, and adiponectin, which is downregulated. Hypoxia also inhibits the expression of genes linked to oxidative metabolism while stimulating the expression of genes associated with glycolysis. Glucose uptake and lactate release by adipocytes are both stimulated by hypoxia, and insulin sensitivity falls. Preadipocytes and macrophages in adipose tissue also respond to hypoxia. The hypoxia-signaling pathway may provide a new target for the treatment of obesity-associated disorders.

Brown and white adipose tissues: intrinsic differences in gene expression and response to cold exposure in mice

Brown adipocytes dissipate energy, whereas white adipocytes are an energy storage site. We explored the plasticity of different white adipose tissue depots in acquiring a brown phenotype by cold exposure. By comparing cold-induced genes in white fat to those enriched in brown compared with white fat, at thermoneutrality we defined a "brite" transcription signature. We identified the genes, pathways, and promoter regulatory motifs associated with "browning," as these represent novel targets for understanding this process. For example, neuregulin 4 was more highly expressed in brown adipose tissue and upregulated in white fat upon cold exposure, and cell studies showed that it is a neurite outgrowth-promoting adipokine, indicative of a role in increasing adipose tissue innervation in response to cold. A cell culture system that allows us to reproduce the differential properties of the discrete adipose depots was developed to study depot-specific differences at an in vitro level. The key transcriptional events underpinning white adipose tissue to brown transition are important, as they represent an attractive proposition to overcome the detrimental effects associated with metabolic disorders, including obesity and type 2 diabetes.

Endocrine and metabolic signaling in retroperitoneal white adipose tissue remodeling during cold acclimation

The expression profiles of adiponectin, resistin, 5'-AMP-activated protein kinase α (AMPK α ), hypoxia-inducible factor-1 α (HIF-1 α ), and key enzymes of glucose and fatty acid metabolism and oxidative phosphorylation in rat retroperitoneal white adipose tissue (RpWAT) during 45-day cold acclimation were examined. After transient suppression on day 1, adiponectin protein level increased following sustained cold exposure. In parallel, on day 1, the protein level of HIF-1 α was strongly induced and AMPK α suppressed, while afterwards the reverse was seen. What is more, after an initial decrease on day 1, a sequential increase in pyruvate dehydrogenase, acyl-CoA dehydrogenase, cytochrome c oxidase, and ATP synthase and a decrease in acetyl-CoA carboxylase (from day 3) were observed. Similar to adiponectin, protein level of resistin showed a biphasic profile: it increased after days 1, 3, and 7 and decreased below the control after 21 days of cold-acclimation. In summary, the data suggest that adiponectin and resistin are important integrators of RpWAT metabolic response and roles it plays during cold acclimation. It seems that AMPK α mediate adiponectin effects on metabolic remodeling RpWAT during cold acclimation.

Miglitol prevents diet-induced obesity by stimulating brown adipose tissue and energy expenditure independent of preventing the digestion of carbohydrates

Miglitol is an alpha-glucosidase inhibitor that improves post-prandial hyperglycemia, and it is the only drug in its class that enters the bloodstream. Anecdotally, miglitol lowers patient body weight more effectively than other alpha-glucosidase inhibitors, but the precise mechanism has not been addressed. Therefore, we analyzed the anti-obesity effects of miglitol in mice and in the HB2 brown adipocyte cell line. Miglitol prevented diet-induced obesity by stimulating energy expenditure without affecting food intake in mice. Long-term miglitol treatment dose-dependently prevented diet-induced obesity and induced mitochondrial gene expression in brown adipose tissue. The anti-obesity effect was independent of preventing carbohydrate digestion in the gastrointestinal tract. Miglitol effectively stimulated energy expenditure in mice fed a high-fat high-monocarbohydrate diet, and intraperitoneal injection of miglitol was sufficient to stimulate energy expenditure in mice. Acarbose, which is a non-absorbable alpha glucosidase inhibitor, also prevented diet-induced obesity, but through a different mechanism: it did not stimulate energy expenditure, but caused indigestion, leading to less energy absorption. Miglitol promoted adrenergic signaling in brown adipocytes in vitro. These data indicate that circulating miglitol stimulates brown adipose tissue and increases energy expenditure, thereby preventing diet-induced obesity. Further optimizing miglitol's effect on brown adipose tissue could lead to a novel anti-obesity drug.

Perspective: Does brown fat protect against diseases of aging?

The most commonly studied laboratory rodents possess a specialized form of fat called brown adipose tissue (BAT) that generates heat to help maintain body temperature in cold environments. In humans, BAT is abundant during embryonic and early postnatal development, but is absent or present in relatively small amounts in adults where it is located in paracervical and supraclavicular regions. BAT cells can 'burn' fatty acid energy substrates to generate heat because they possess large numbers of mitochondria in which oxidative phosphorylation is uncoupled from ATP production as a result of a transmembrane proton leak mediated by uncoupling protein 1 (UCP1). Studies of rodents in which BAT levels are either increased or decreased have revealed a role for BAT in protection against diet-induced obesity. Data suggest that individuals with low levels of BAT are prone to obesity, insulin resistance and cardiovascular disease, whereas those with higher levels of BAT maintain lower body weights and exhibit superior health as they age. BAT levels decrease during aging, and dietary energy restriction increases BAT activity and protects multiple organ systems including the nervous system against age-related dysfunction and degeneration. Future studies in which the effects of specific manipulations of BAT levels and thermogenic activity on disease processes in animal models (diabetes, cardiovascular disease, cancers, neurodegenerative diseases) are determined will establish if and how BAT affects the development and progression of age-related diseases. Data from animal studies suggest that BAT and mitochondrial uncoupling can be targeted for interventions to prevent and treat obesity and age-related diseases. Examples include: diet and lifestyle changes; specific regimens of mild intermittent stress; drugs that stimulate BAT formation and activity; induction of brown adipose cell progenitors in muscle and other tissues; and transplantation of brown adipose cells.

Norepinephrine and rosiglitazone synergistically induce Elovl3 expression in brown adipocytes

The Elovl3 gene, which putatively encodes for a protein involved in the elongation of saturated and monounsaturated fatty acids in the C20-C24 range, is expressed in murine liver, skin, and brown adipose tissue (BAT). In BAT, Elovl3 is dramatically upregulated during tissue activation in response to cold exposure, and functional data imply that ELOVL3 is a critical enzyme for lipid accumulation in brown adipocytes during the early phase of tissue recruitment. The activation of BAT is controlled by sympathetic nerve activity and norepinephrine release. By using primary cultures of brown adipocytes, we show here that the induced Elovl3 gene expression is synergistically regulated by norepinephrine and the peroxisome proliferator-activated receptor (PPAR) gamma ligand rosiglitazone. In addition, the potency of rosiglitazone to induce Elovl3 expression was several orders of magnitude higher than for the PPARalpha and PPARdelta ligands WY-14643 and L-165041, respectively. The maximal increase in mRNA level by norepinephrine and rosiglitazone is achieved by induced transcription as well as increased mRNA stability, and the whole process requires novel protein synthesis. We conclude that norepinehrine and PPARgamma, despite having different roles in brown adipocyte activation and differentiation, cooperate in expanding the intracellular lipid pool by synergistically stimulating Elovl3 expression.

Brown adipocytes of sucrose-overfed rats treated with corticosterone: A stereological and ultrastructural study

The aim of this study was to examine the effects of short-term corticosterone treatment on brown adipo?cytes of rats overfed with sucrose. Ultrastructural and stereological analysis showed that brown adipocyte components responded to the applied treatment in conformity with their own dynamics and affinity. Although brown adipocytes generally corresponded to thermogenically active cells, some signs of supression of that function, such as mitochondrial degradation and a pattern of lipid accumulation, were noticeable. Taken together, the presented results indicate that a high carbohydrate diet delays the expected inhibitory influence of corticosterone on brown adipose tissue thermogenesis. For the full expression of corticosterone effects, longer treatment is needed.

ELOVL3 is an important component for early onset of lipid recruitment in brown adipose tissue

During the recruitment process of brown adipose tissue, the mRNA level of the fatty acyl chain elongase Elovl3 is elevated more than 200-fold in cold-stressed mice. We have obtained Elovl3-ablated mice and report here that, although cold-acclimated Elovl3-ablated mice experienced an increased heat loss due to impaired skin barrier, they were unable to hyperrecruit their brown adipose tissue. Instead, they used muscle shivering in order to maintain body temperature. Lack of Elovl3 resulted in a transient decrease in the capacity to elongate saturated fatty acyl-CoAs into very long chain fatty acids, concomitantly with the occurrence of reduced levels of arachidic acid (C20:0) and behenic acid (C22:0) in brown adipose tissue during the initial cold stress. This effect on very long chain fatty acid synthesis could be illustrated as a decrease in the condensation activity of the elongation enzyme. In addition, warm-acclimated Elovl3-ablated mice showed diminished ability to accumulate fat and reduced metabolic capacity within the brown fat cells. This points to ELOVL3 as an important regulator of endogenous synthesis of saturated very long chain fatty acids and triglyceride formation in brown adipose tissue during the early phase of the tissue recruitment.

Limits to sustained energy intake IX: a review of hypotheses

Several lines of evidence indicate that animals in the wild may be limited in their maximal rates of energy intake by their intrinsic physiology rather than food availability. Understanding the limits to sustained energy intake is important because this defines an envelope within which animals must trade-off competing activities. In the first part of this review, we consider the initial ideas that propelled this area and experimental evidence connected with them. An early conceptual advance in this field was the idea that energy intake could be centrally limited by aspects of the digestive process, or peripherally limited at the sites of energy utilisation. A model system that has been widely employed to explore these ideas is lactation in small rodents. Initial studies in the late 1980s indicated that energy intake might be centrally limited, but work by Hammond and colleagues in the 1990s suggested that it was more likely that the limits were imposed by capacity of the mammary glands, and other works tended to support this view. This consensus, however, was undermined by studies that showed milk production was higher in mice at low temperatures, suggesting that the capacity of the mammary gland is not a limiting factor. In the second part of the review we consider some additional hypotheses that might explain these conflicting data. These include the heat dissipation limits hypothesis, the seasonal investment hypothesis and the saturated neural control hypothesis. Current evidence with respect to these hypotheses is also reviewed. The limited evidence presently available does not unambiguously support any one of them.

Perceived role of fibre in a healthy diet among Finnish consumers

OBJECTIVE

The aim was to study how Finnish consumers perceive the role of fibre in the diet, which foods are regarded as good sources of fibre and the relationship between the respondents' self-estimated fibre intake and their measured intake.

METHODS

A semistructured interview was conducted with 125 volunteers, including a background information questionnaire and an easy-to-use self-administered paper-and-pencil form estimating fibre intake.

RESULTS

According to the self-administered form about half of the respondents had adequate fibre intake. Among those who estimated their fibre intake as adequate/maybe adequate, only 61% belonged to the highest fibre intake group. Most of the respondents defined their diet as being healthy. The key elements for a healthy diet were 'vegetables', 'low in fat', 'fruit and berries' and 'variety'. Only 5% of the respondents mentioned fibre spontaneously here. However, fibre was considered important for health because of its effect on bowel function and general well-being. The recommended intake of fibre could not be described in nutritional terms, but respondents could identify relevant sources of fibre in the diet.

CONCLUSION

Finnish consumers considered fibre important for health and could recognize the sources of fibre correctly although they did not mention it spontaneously as a part of a healthy diet.

Innervation of mammalian white adipose tissue: implications for the regulation of total body fat

We review the extensive physiological and neuroanatomical evidence for the innervation of white adipose tissue (WAT) by the sympathetic nervous system (SNS) as well as what is known about the sensory innervation of this tissue. The SNS innervation of WAT appears to be a part of the general SNS outflow from the central nervous system, consisting of structures and connections throughout the neural axis. The innervation of WAT by the SNS could play a role in the regulation of total body fat in general, most likely plays an important role in regional differences in lipid mobilization specifically, and may have a trophic affect on WAT. The exact nature of the SNS innervation of WAT is not known but it may involve contact with adipocytes and/or their associated vasculature. We hypothesize that the SNS innervation of WAT is an important contributor to the apparent "regulation" of total body fat.

Effects of fasting and food restriction on sympathetic activity in brown adipose tissue in mice

The activity of the sympathetic nervous system in mice that were either fed ad libitum, food restricted or fasted was estimated by measuring the accumulation of dopamine following the inhibition of dopamine beta-hydroxylase activity. Mice in each group were injected with the dopamine beta-hydroxylase inhibitor 1-cyclohexyl-2-mercaptoimidazole and were exposed to either 30 degrees C (warm) or 4 degrees C (cold). Mice were killed 1 h after the injection. Both heart and brown adipose tissue were then quickly removed and homogenized in ice-cold perchloric acid. Dopamine and noradrenaline were determined using high performance liquid chromatography. Regardless of whether mice were warm or cold exposed, both content and concentration of brown adipose tissue and dopamine were predictably higher in 1-cyclohexyl-2-mercaptoimidazole-injected mice than in non-injected animals. In mice fed ad libitum, post-injection content and concentration of dopamine in both brown adipose tissue and heart were higher in cold-exposed mice than in warm-exposed animals. In food-restricted and fasted mice, post-injection concentrations of dopamine in brown adipose tissue were higher in cold-exposed mice than in warm-exposed animals. In food-restricted and fasted mice there was no difference between warm- and cold-exposed animals with respect to post-injection contents and concentrations of dopamine in heart tissue. In fasted mice there was no difference between warm- and cold-exposed animals in post-injection content of dopamine in brown adipose tissue. This study provides further evidence that fasting, in contrast to food restriction, may blunt the tissue sympathetic nervous system response in brown adipose tissue of cold-exposed mice.

Nucleus tractus solitarii lesions alter the metabolic and hyperthermic response to central prostaglandin E1 in the rat

1. Given that the nucleus tractus solitarii (NTS) may regulate the ability of brown adipose tissue to evoke non-shivering thermogenesis and that brown fat may mediate the rise in whole-body metabolism observed following central pyrogen administration, we assessed whether interruption of baroreceptor afferents coursing though the NTS would interfere with the ability of prostaglandin E1 to evoke a normal fever response profile. 2. Infusion of 150-600 ng of prostaglandin E1 (PGE1) into a lateral cerebral ventricle of the conscious rat resulted in a rise in core temperature, and also an increase in whole-body metabolic rate, brown adipose tissue temperature, arterial blood pressure and heart rate. 3. Following bilateral electrolytic lesions to the NTS, resting core and brown fat temperatures, metabolic rates, blood pressures and heart rates in the NTS-lesioned animals were comparable to control rats. However, the PGE1-evoked increase in metabolic rate, along with the rise in core and brown adipose tissue temperatures and heart rate were attenuated. The pressor response was, however, enhanced, possibly due to the demonstrated interference by the lesions with normal baroreflex control. 4. The findings suggest that the nucleus tractus solitarii region of the rats' brain may be important in mediating the thermogenesis evoked by central PGE1.

Regulation of adipose tissue metabolism in support of lactation

In the dairy cow, adipose tissue lipid accumulates during pregnancy, and catabolism begins prior to parturition and increases dramatically afterward. After peak lactation, body lipid is replenished. The duration and magnitudes of these adaptations depend on milk energy secretion, net energy intake, genotype, and endocrine environment. Recent research efforts have focused on endocrine, genetic, and biochemical mechanisms underlying metabolic adaptations in cows of high production potential. Adipose tissue lipid synthesis is decreased and lipolysis is increased in early lactation. The magnitude and duration of these adaptations are increased in animals either consuming relatively less energy or producing more milk. Adipose tissue is more responsive to catecholamines in early and midlactation and in animals with higher production. This is more of an increase in maximal response than in sensitivity. In vivo and in vitro rates of adipose tissue lipolysis correlate positively with milk energy secretion, whereas lipid synthesis rates correlate with energy intake. Thus, mammary metabolic activity, within and among lactations, correlates with that in adipose tissue. Likely mechanisms include adaptations in receptors for homeostatic signals and modulation of postreceptor responses. Research is needed into neural, genetic, and hormone regulation of nutrient utilization and body fat use and recovery during lactation. Research should describe mechanistic relationships among nutrients in animals of high production as well as investigate cellular and molecular mechanisms suitable to genetic manipulation.

A comparison of norepinephrine- and ACTH-stimulated lipolysis in white and brown adipocytes of female rats

1. Isolated white and brown adipocytes (WFA and BFA) from the rat were compared with respect to their lipolytic responsiveness towards norepinephrine (NE) and adrenocorticotrophic hormone (ACTH). 2. NE yielded a Km value of 702.7 +/- 30.6 nM for WFA and 142.5 +/- 7.2 nM for BFA. The maximum lipolytic response (Vm) was 145.7 +/- 1.2 nmol glycerol/micrograms DNA/90 min for WFA and 23.7 +/- 0.2 nmol glycerol/micrograms DNA/90 min for BFA. 3. ACTH yield Km values of 31.6 +/- 1.5 and 31.9 +/- 3.1 nM for WFA and BFA, respectively. Vm values of 141.9 +/- 1.0 and 34.2 +/- 0.5 nmol glycerol/micrograms DNA/90 min were observed for WFA and BFA, respectively.