Brown Adipose Tissue Fat Research Articles

Detection of brown adipose tissue in rats with acute cold stimulation using quantitative susceptibility mapping.

Detection of brown adipose tissue in rats with acute cold stimulation using quantitative susceptibility mapping.

Lcn2 mediates adipocyte-muscle-tumor communication and hypothermia in pancreatic cancer cachexia

ObjectiveAdipose tissue is the largest endocrine organ. When activated by cancer cells, adipocytes secrete adipocytokines and release fatty acids, which are then transferred to cancer cells and used for structural and biochemical support. How this metabolic symbiosis between cancer cells and adipocytes affects skeletal muscle and thermogenesis during cancer cachexia is unknown. Cancer cachexia is a multiorgan syndrome and how the communication between tissues is established has yet to be determined. We investigated adipose tissue secretory factors and explored their role in crosstalk of adipocytes, muscle, and tumor during pancreatic cancer cachexia. MethodsWe used a pancreatic cancer cachexia mouse model generated by syngenic implantation of pancreatic ductal adenocarcinoma (PDAC) cells (KPC) intraperitoneally into C57BL/6 mice and Lcn2-knockout mice. For in vitro studies, adipocytes (3T3-L1 and primary adipocytes), cachectic cancer cells (Panc0203), non-cachectic cancer cells (Du145 cells), and skeletal muscle cells (C2C12 myoblasts) were used. ResultsTo identify molecules involved in the crosstalk of adipose tissue with muscle and tumors, we treated 3T3-L1 adipocytes with conditioned medium (CM) from cancer cells. Upon screening the secretomes from PDAC-induced adipocytes, several adipocytokines were identified, including lipocalin 2 (Lcn2). We investigated Lcn2 as a potential mediator of cachexia induced by adipocytes in response to PDAC. During tumor progression, mice exhibited a decline in body weight gain, which was accompanied by loss of adipose and muscle tissues. Tumor-harboring mice developed drastic hypothermia because of a dramatic loss of fat in brown adipose tissue (BAT) and suppression of the thermogenesis pathway. We inhibited Lcn2 with an anti-Lcn2 antibody neutralization or genomic ablation in mice. Lcn2 deficiency significantly improved body temperature in tumor-bearing mice, which was supported by the increased expression of Ucp1 and β3-adrenergic receptor in BAT. In addition, Lcn2 inhibition abrogated the loss of fat and muscle in tumor-bearing mice. In contrast to tumor-bearing WT mice, the corresponding Lcn2-knockout mice showed reduced ATGL expression in iWAT and decreased the expression of muscle atrophy molecular markers MuRF-1 and Fbx32. ConclusionsThis study showed that Lcn2 is causally involved in the dysregulation of adipose tissue–muscle-tumor crosstalk during pancreatic cancer cachexia. Therapeutic targets that suppress Lcn2 may minimize the progression of cachexia.

Toward in vivo proof of binding of 18F-labeled inhibitor [18F]TRACK to peripheral tropomyosin receptor kinases

BackgroundTropomyosin receptor kinases (TrkA, TrkB, TrkC) are a family of tyrosine kinases primarily expressed in neuronal cells of the brain. Identification of oncogenic alterations in Trk expression as a driver in multiple tumor types has increased interest in their role in human cancers. Recently, first- and second-generation 11C and 18F-labeled Trk inhibitors, e.g., [18F]TRACK, have been developed. The goal of the present study was to analyze the direct interaction of [18F]TRACK with peripheral Trk receptors in vivo to prove its specificity for use as a functional imaging probe.MethodsIn vitro uptake and competition experiments were carried out using the colorectal cancer cell line KM12. Dynamic PET experiments were performed with [18F]TRACK, either alone or in the presence of amitriptyline, an activator of Trk, entrectinib, a Trk inhibitor, or unlabeled reference compound TRACK in KM12 tumor-bearing athymic nude mice as well as B6129SF2/J and corresponding B6;129S2-Ntrk2tm1Bbd/J mice. Western blot and immunohistochemistry experiments were done with KM12 tumors, brown adipose tissue (BAT), and brain tissue samples.ResultsUptake of [18F]TRACK was increasing over time reaching 208 ± 72% radioactivity per mg protein (n = 6/2) after 60 min incubation time. Entrectinib and TRACK competitively blocked [18F]TRACK uptake in vitro (IC50 30.9 ± 3.6 and 29.4 ± 9.4 nM; both n = 6/2). [18F]TRACK showed uptake into KM12 tumors (SUVmean,60 min 0.43 ± 0.03; n = 6). Tumor-to-muscle ratio reached 0.9 (60 min) and 1.2 (120 min). In TrkB expressing BAT, [18F]TRACK uptake reached SUVmean,60 min 1.32 ± 0.08 (n = 7). Activation of Trk through amitriptyline resulted in a significant radioactivity increase of 21% in KM12 tumor (SUVmean,60 min from 0.53 ± 0.01 to 0.43 ± 0.03; n = 6; p < 0.05) and of 21% in BAT (SUVmean,60 min from 1.32 ± 0.08; n = 5 to 1.59 ± 0.07; n = 6; p < 0.05) respectively. Immunohistochemistry showed TrkB > TrkA expression on BAT fat cells, but TrkA > TrkB in whole brain. WB analysis showed sevenfold higher TrkB expression in BAT versus KM12 tumor tissue.ConclusionThe present data show that radiotracer [18F]TRACK can target peripheral Trk receptors in human KM12 colon cancer as well as brown adipose tissue as confirmed through in vitro and in vivo blocking experiments. Higher TrkB versus TrkA protein expression was detected in brown adipose tissue of mice confirming a peripheral functional role of brain-derived neurotrophic factor in adipose tissue.

Flattening of circadian glucocorticoid oscillations drives acute hyperinsulinemia and adipocyte hypertrophy.

Disruption of circadian glucocorticoid oscillations in Cushing's disease and chronic stress results in obesity and adipocyte hypertrophy, which is believed to be a main source of the harmful effects of obesity. Here, we recapitulate stress due to jet lag or work-life imbalances by flattening glucocorticoid oscillations in mice. Within 3days, mice achieve a metabolic state with persistently high insulin, but surprisingly low glucose and fatty acids in the bloodstream, that precedes a more than 2-fold increase in brown and white adipose tissue mass within 3weeks. Transcriptomic and Cd36-knockout mouse analyses show that hyperinsulinemia-mediated de novo fatty acid synthesis and Cd36-mediated fatty acid uptake drive fat mass increases. Intriguingly, this mechanism by which glucocorticoid flattening causes acute hyperinsulinemia and adipocyte hypertrophy is unexpectedly beneficial in preventing high levels of circulating fatty acids and glucose for weeks, thus serving as a protective response to preserve metabolic health during chronic stress.

Brown Adipose Tissue Volume and Fat Content Are Positively Associated With Whole-Body Adiposity in Young Men-Not in Women.

Human brown adipose tissue (BAT) volume has consistently been claimed to be inversely associated with whole-body adiposity. However, recent advances in the assessment of human BAT suggest that previously reported associations may have been biased. The present cross-sectional study investigates the association of BAT volume, mean radiodensity, and 18F-fluorodeoxyglucose (18F-FDG) uptake (assessed via a static positron emission tomography [PET]-computed tomography [CT] scan after a 2-h personalized cold exposure) with whole-body adiposity (measured by DXA) in 126 young adults (42 men and 84 women; mean ± SD BMI 24.9 ± 4.7 kg/m2). BAT volume, but not 18F-FDG uptake, was positively associated with BMI, fat mass, and visceral adipose tissue (VAT) mass in men but not in women. These associations were independent of the date when the PET-CT was performed, insulin sensitivity, and body surface area. BAT mean radiodensity, an inverse proxy of BAT fat content, was negatively associated with BMI, fat mass, and VAT mass in men and in women. These results refute the widely held belief that human BAT volume is reduced in obese persons, at least in young adults, and suggest that it might even be the opposite in young men.

The effect of mirabegron on energy expenditure and brown adipose tissue in healthy lean South Asian and Europid men.

AimTo compare the effects of cold exposure and the β3‐adrenergic receptor agonist mirabegron on plasma lipids, energy expenditure and brown adipose tissue (BAT) activity in South Asians versus Europids.Materials and MethodsTen lean Dutch South Asian (aged 18‐30 years; body mass index [BMI] 18‐25 kg/m2) and 10 age‐ and BMI‐matched Europid men participated in a randomized, double‐blinded, cross‐over study consisting of three interventions: short‐term (~ 2 hours) cold exposure, mirabegron (200 mg one dose p.o.) and placebo. Before and after each intervention, we performed lipidomic analysis in serum, assessed resting energy expenditure (REE) and skin temperature, and measured BAT fat fraction by magnetic resonance imaging.ResultsIn both ethnicities, cold exposure increased the levels of several serum lipid species, whereas mirabegron only increased free fatty acids. Cold exposure increased lipid oxidation in both ethnicities, while mirabegron increased lipid oxidation in Europids only. Cold exposure and mirabegron enhanced supraclavicular skin temperature in both ethnicities. Cold exposure decreased BAT fat fraction in both ethnicities. After the combination of data from both ethnicities, mirabegron decreased BAT fat fraction compared with placebo.ConclusionsIn South Asians and Europids, cold exposure and mirabegron induced beneficial metabolic effects. When combining both ethnicities, cold exposure and mirabegron increased REE and lipid oxidation, coinciding with a higher supraclavicular skin temperature and lower BAT fat fraction.

Liraglutide decreases energy expenditure and does not affect the fat fraction of supraclavicular brown adipose tissue in patients with type 2 diabetes

Background and aimsSeveral studies have shown that glucagon-like peptide-1 (GLP-1) analogues can affect resting energy expenditure, and preclinical studies suggest that they may activate brown adipose tissue (BAT). The aim of the present study was to investigate the effect of treatment with liraglutide on energy metabolism and BAT fat fraction in patients with type 2 diabetes. Methods and resultsIn a 26-week double-blind, placebo-controlled trial, 50 patients with type 2 diabetes were randomized to treatment with liraglutide (1.8 mg/day) or placebo added to standard care. At baseline and after treatment for 4, 12 and 26 weeks, we assessed resting energy expenditure (REE) by indirect calorimetry. Furthermore, at baseline and after 26 weeks, we determined the fat fraction in the supraclavicular BAT depot using chemical-shift water-fat MRI at 3T. Liraglutide reduced REE after 4 weeks, which persisted after 12 weeks and tended to be present after 26 weeks (week 26 vs baseline: liraglutide −52 ± 128 kcal/day; P = 0.071, placebo +44 ± 144 kcal/day; P = 0.153, between group P = 0.057). Treatment with liraglutide for 26 weeks did not decrease the fat fraction in supraclavicular BAT (−0.4 ± 1.7%; P = 0.447) compared to placebo (−0.4 ± 1.4%; P = 0.420; between group P = 0.911). ConclusionTreatment with liraglutide decreases REE in the first 12 weeks and tends to decrease this after 26 weeks without affecting the fat fraction in the supraclavicular BAT depot. These findings suggest reduction in energy intake rather than an increase in REE to contribute to the liraglutide-induced weight loss. Trial registry numberNCT01761318.

Differentiating brown and white adipose tissues by high-resolution diffusion NMR spectroscopy

There are two types of fat tissues, white adipose tissue (WAT) and brown adipose tissue (BAT), which essentially perform opposite functions in whole body energy metabolism. There is a large interest in identifying novel biophysical properties of WAT and BAT by a quantitative and easy-to-run technique. In this work, we used high-resolution pulsed field gradient diffusion NMR spectroscopy to study the apparent diffusion coefficient (ADC) of fat molecules in rat BAT and WAT samples. The ADC of fat in BAT and WAT from rats fed with a chow diet was compared with that of rats fed with a high-fat diet to monitor how the diffusion properties change due to obesity-associated parameters such as lipid droplet size, fatty acid chain length, and saturation. Feeding a high-fat diet resulted in increased saturation, increased chain lengths, and reduced ADC of fat in WAT. The ADC of fat was lower in BAT relative to WAT in rats fed both chow and high-fat diets. Diffusion of fat was restricted in BAT due to the presence of small multilocular lipid droplets. Our findings indicate that in vivo diffusion might be a potential way for better delineation of BAT and WAT in both lean and obese states.

Differential metabolism of brown adipose tissue in newborn rabbits in relation to position in the litter huddle

Competition for resources can contribute importantly to the early development of individual differences in behavioral and physiological phenotypes. In newborn rabbits, littermates compete for thermally favorable positions within the litter huddle. As brown adipose tissue (BAT) is the principal site of thermogenesis in such altricial young, we investigated differences in rabbit pups’ growth and morphological differences in BAT associated with position within the huddle. We formed three treatment groups (7 litters/group): GI—birth (pups killed at birth); GII—chronic thermal challenge (pups killed after exposure to a moderately cold environmental during postnatal days 1–3); GIII—acute thermal challenge (as for GII but pups killed after an additional 30min exposure to a very cold environment on postnatal day 3). Interscapular BAT was removed at death for histological analysis, and triglyceride concentrations measured in serum. Pups occupying central positions in the huddle had higher skin temperatures, obtained more milk, and were more efficient at converting this into body mass, than pups occupying peripheral positions. There was no significant difference in BAT morphology or triglyceride concentrations between pups at birth, nor between central and peripheral pups chronically exposed to moderate cold until postnatal day 3. However, during acute cold exposure at this age, peripheral pups were less able to maintain their body temperature, they depleted BAT fat reserves almost completely, and they had lower serum concentrations of triglycerides than central pups. These findings confirm the contribution of early sibling relations to individual differences in growth and metabolic processes associated with thermoregulation in newborn rabbits.

Brown Adipose Tissue Quantification in Human Neonates Using Water-Fat Separated MRI

There is a major resurgence of interest in brown adipose tissue (BAT) biology, particularly regarding its determinants and consequences in newborns and infants. Reliable methods for non-invasive BAT measurement in human infants have yet to be demonstrated. The current study first validates methods for quantitative BAT imaging of rodents post mortem followed by BAT excision and re-imaging of excised tissues. Identical methods are then employed in a cohort of in vivo infants to establish the reliability of these measures and provide normative statistics for BAT depot volume and fat fraction. Using multi-echo water-fat MRI, fat- and water-based images of rodents and neonates were acquired and ratios of fat to the combined signal from fat and water (fat signal fraction) were calculated. Neonatal scans (n = 22) were acquired during natural sleep to quantify BAT and WAT deposits for depot volume and fat fraction. Acquisition repeatability was assessed based on multiple scans from the same neonate. Intra- and inter-rater measures of reliability in regional BAT depot volume and fat fraction quantification were determined based on multiple segmentations by two raters. Rodent BAT was characterized as having significantly higher water content than WAT in both in situ as well as ex vivo imaging assessments. Human neonate deposits indicative of bilateral BAT in spinal, supraclavicular and axillary regions were observed. Pairwise, WAT fat fraction was significantly greater than BAT fat fraction throughout the sample (ΔWAT-BAT = 38%, p<10−4). Repeated scans demonstrated a high voxelwise correlation for fat fraction (Rall = 0.99). BAT depot volume and fat fraction measurements showed high intra-rater (ICCBAT,VOL = 0.93, ICCBAT,FF = 0.93) and inter-rater reliability (ICCBAT,VOL = 0.86, ICCBAT,FF = 0.93). This study demonstrates the reliability of using multi-echo water-fat MRI in human neonates for quantification throughout the torso of BAT depot volume and fat fraction measurements.

Tissue-specific effects of 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) on the activity of phosphoenolpyruvate carboxykinase (PEPCK) in rats.

Reduced gluconeogenesis due to decreased activity of key gluconeogenic enzymes in liver, together with feed refusal, has been suggested to play an important role in TCDD-induced lethality in rats. In this study the toxicological significance of reduced gluconeogenesis was further analyzed by studying dose responses and time courses of effects of TCDD on the activity of PEPCK in liver and two other tissues with high specific activity, viz. kidney and brown adipose tissue (BAT). Liver PEPCK activity was significantly decreased from 1 to 32 days after dosing (60 micrograms/kg). A clear dose response was present 8 days after dosing, beginning at a dose of 1 microgram/kg. In contrast to liver, TCDD treatment increased PEPCK activity in kidney and BAT, but only at the two highest doses administered (30 and 60 micrograms/kg). PEPCK activity in kidney began to increase slowly, reaching a maximum on Day 16 and declining thereafter, whereas in BAT the activity was significantly increased already on Day 1 and maximally on Day 4 after dosing. A likely explanation for these tissue-specific effects is in part related to toxicokinetics and in part to homeostatic responses of the organism to the toxic insult of TCDD. High concentrations of TCDD in liver and BAT combined with early responses (1 day after dosing) suggest a direct effect in these organs/tissues, whereas very low concentration and delayed response in kidney indicate an indirect effect. This interesting enzymatic constellation suggests that the reduction in gluconeogenesis due to decreased PEPCK activity in liver is partially counterbalanced by increased gluconeogenesis in kidney as a result of induction of PEPCK in this organ. Induction of PEPCK in BAT, where it is a glyceroneogenic enzyme, provides for the first time a plausible explanation for the initial accumulation of fat in BAT of TCDD-treated rats.

Fat metabolism and heat production in young rabbits.

1. The rates of oxygen consumption were measured in 6-8-day-old rabbits at 34 and 15 degrees C after varying periods of starvation and cold exposure. At the start of the experiment the rabbits had been fasted for 24 hr. Eight rabbits were studied immediately, six after 24 and six after 48 hr in a cold environment (20 degrees C), and twelve after a further 48 hr in a warm environment (34 degrees C). All the animals had a similar increase in oxygen consumption during the final hour of cold exposure (15 degrees C).2. The rabbits kept at 20 degrees C lost 83% of the fat stored in their brown adipose tissue within 24 hr and a further 11% in the next 24 hr. The fat content of white adipose tissue had fallen by 75% at 48 hr. In contrast rabbits kept unfed at 34 degrees C had lost 47% of the fat in brown adipose tissue and 44% of the fat in white adipose tissue after 48 hr.3. In six rabbits subcutaneous thermocouples demonstrated that local heat production continued in brown adipose tissue after 48 hr cold exposure.4. In the rabbits kept at 34 degrees C the final cold exposure caused a large increase in the serum free fatty acid and glycerol concentrations. Much lower concentrations were found in rabbits kept at 20 degrees C.5. The results show that the fat stored in the brown adipose tissue of young rabbits exposed to cold is preferentially used for heat production. When this store of fat is exhausted, brown adipose tissue still produces heat presumably by oxidizing fat and glucose taken from the circulation.