Effects of pterostilbene in brown adipose tissue from obese rats

In recent years, much attention has been paid by the scientific community to phenolic compounds as active biomolecules naturally present in foods. Pterostilbene is a resveratrol dimethylether derivative which shows higher bioavailability. The aim of the present study was to analyze the effect of pterostilbene on brown adipose tissue thermogenic markers in a model of genetic obesity, which shows reduced thermogenesis. The experiment was conducted with 30 Zucker (fa/fa) rats that were distributed in three experimental groups: control and two groups orally administered with pterostilbene at 15 and 30 mg/kg body weight/day for 6 weeks. Gene expression of uncoupling protein 1 (Ucp1), peroxisome proliferator-activated receptor γ co-activator 1 α (Pgc-1α), carnitine palmitoyl transferase 1b (Cpt1b), peroxisome proliferator-activated receptor α (Pparα), nuclear respiratory factor 1 (Nfr1), and cyclooxygenase-2 (Cox-2); protein expression of PPARα, PGC-1α, p38 mitogen-activated protein kinase (p38 MAPK), UCP1 and glucose transporter (GLUT4); and enzyme activity of CPT 1b and citrate synthase (CS) were assessed in interscapular brown adipose tissue. With the exception of Pgc-1α expression, all these parameters were significantly increased by pterostilbene administration. These results show for the first time that pterostilbene increases thermogenic and oxidative capacity of brown adipose tissue in obese rats. Whether these effects effectively contribute to the antiobesity properties of these compound needs further research.     

Reduced noradrenaline turnover in brown adipose tissue of lactating rats

Brown adipose tissue properties as well as noradrenaline turnover in the tissue were determined in 15-day lactating rats and virgin controls. Brown adipose tissue thermogenic activity was reduced in lactating rats as shown by a decrease in weight, cytochrome oxidase activity and mitochondrial GDP-binding. The noradrenaline turnover rate was lower in brown adipose tissue from lactating rats. It is suggested that diminished sympathetic activity in brown adipose tissue may be a major cause of the reduced tissue thermogenic activity during lactation.     

Up-regulation of mitochondrial activity and acquirement of brown adipose tissue-like property in the white adipose tissue of fsp27 deficient mice

Fsp27, a member of the Cide family proteins, was shown to localize to lipid droplet and promote lipid storage in adipocytes. We aimed to understand the biological role of Fsp27 in regulating adipose tissue differentiation, insulin sensitivity and energy balance. Fsp27(-/-) mice and Fsp27/lep double deficient mice were generated and we examined the adiposity, whole body metabolism, BAT and WAT morphology, insulin sensitivity, mitochondrial activity, and gene expression changes in these mouse strains. Furthermore, we isolated mouse embryonic fibroblasts (MEFs) from wildtype and Fsp27(-/-) mice, followed by their differentiation into adipocytes in vitro. We found that Fsp27 is expressed in both brown adipose tissue (BAT) and white adipose tissue (WAT) and its levels were significantly elevated in the WAT and liver of leptin-deficient ob/ob mice. Fsp27(-/-) mice had increased energy expenditure, lower levels of plasma triglycerides and free fatty acids. Furthermore, Fsp27(-/-)and Fsp27/lep double-deficient mice are resistant to diet-induced obesity and display increased insulin sensitivity. Moreover, white adipocytes in Fsp27(-/-) mice have reduced triglycerides accumulation and smaller lipid droplets, while levels of mitochondrial proteins, mitochondrial size and activity are dramatically increased. We further demonstrated that BAT-specific genes and key metabolic controlling factors such as FoxC2, PPAR and PGC1alpha were all markedly upregulated. In contrast, factors inhibiting BAT differentiation such as Rb, p107 and RIP140 were down-regulated in the WAT of Fsp27(-/-) mice. Remarkably, Fsp27(-/-) MEFs differentiated in vitro show many brown adipocyte characteristics in the presence of the thyroid hormone triiodothyronine (T3). Our data thus suggest that Fsp27 acts as a novel regulator in vivo to control WAT identity, mitochondrial activity and insulin sensitivity.     

Involvement of the sympathetic nervous system in lipolytic activity in brown adipose tissue of cold acclimated rats

In cold acclimated rats, in vitro, NE led to a significant increase in release of FFA and glycerol in denervated IBAT. In vivo, study of arteriovenous differences showed that the denervated BAT loses its full capacity to utilize FFA and glycerol released by NE. After denervation an increase of blood flow in Sulzer's vein was observed. This effect appeared immediately after intervention whereas the effect on fat metabolism appeared later. In cold acclimated rats, the sympathetic nervous system appears to be an important regulator of fatty acid metabolism in BAT.     

Age-related changes of Renin-Angiotensin system genes in white adipose tissue of rats.

The adipose tissue renin-angiotensin system has been implicated in the regulation of adipocyte growth and differentiation. We studied the influence of age, body weight, total body fat content, anatomical localization, and diet on the expression of angiotensinogen (AGT) and angiotensin II type 1 (AT 1 )-receptor genes in white adipose tissue of normal and postnatal overfed rats. Relative gene expression was measured in epididymal adipose tissue and liver of control and postnatal overfed (PNO) rats at the age of 4, 8, and 12 weeks using real time RT-PCR. Body fat content was determined by carcass analysis. Body weight and body fat content were only significantly greater in PNO rats when compared to control rats at the age of 4 weeks. At the age of 12 weeks, AGT expression was significantly decreased in both tissues. Furthermore, expression of the AT 1 -receptor gene was significantly decreased in liver but not in adipose tissue at 12 weeks of age. Postnatal overfeeding did not influence the expression levels of either gene at any time-point in either liver or adipose tissue. At the age of 24 weeks, AGT expression was significantly greater in epididymal than in subcutaneous adipose tissue, whereas no site-specific differences could be found for the AT 1 -receptor. We conclude that age and depot-specific mechanisms are of more importance for the expression of AGT and AT 1 -receptor genes during the first 12 weeks of age than a short period of overfeeding.     

A protein kinase inhibitor in brown adipose tissue of developing rats

A heat-stable protein was extracted from brown adipose tissue of infant rats that inhibited both purified bovine heart protein kinase and a crude preparation of protein kinase from brown fat. It did not act as an adenosine triphosphatase nor did it exert its effect by proteolytic action. Inhibition of protein kinase was affected in both the presence and the absence of cyclic AMP. Most of the inhibitory activity was present in the 100000g supernatant fraction of tissue homogenates. Inhibitory activity was highest perinatally and it declined 10 days after birth. It is suggested that the protein kinase inhibitor may play a role in regulating cyclic AMP actions.     

Characteristics of diet-induced brown adipose tissue growth and thermogenesis in rats

The characteristics of regional brown (BAT) and white adipose tissue (WAT) growth and of thermogenesis following experimental overfeeding were studied in groups of male Sprague-Dawley rats fed lab chow or cafeteria diets for 8 weeks postweaning. Regional BAT and WAT growth was determined by dissection and weighing, and thermogenesis was characterized by measurements of resting and norepinephrine (NE)-stimulated oxygen consumption, of serum thyroid hormone concentrations, and of 24-hour urinary NE excretion levels. Cafeteria feeding resulted in a 113% increase in total BAT, with the most prominent increases in the interscapular, thoracic, and perirenal regions. Retroperitoneal, epididymal, and omental WAT were significantly greater in cafeteria than in chow-fed rats. Resting oxygen consumption of cafeteria-fed rads increased by 10% and NE excretion by 64% compared to chow-fed controls, while serum T₃ concentrations were nearly doubled in the cafeteria-fed rats. The thermogenic response to NE injection in cafeteria-fed rats was 102% of their resting levels, compared to a 51% increase in the chow-fed controls. The results indicate that increased BAT growth occurs in all primary BAT depots following cafeteria-feeding in rats, and that the greater BAT mass is qualitatively proportional to their greater capacity for non-shivering thermogenesis. Also, the increased NE excretion and greater serum T₃ concentration are consistent with increased sympathetic and thyroidal activity and may in part explain the thermogenic response to diet in the rat.     

Reduced brown adipose tissue thermogenesis of obese rats after ovariectomy

Brown adipose tissue (BAT) thermogenesis was assessed by measuring mitochondrial guanosine diphosphate (GDP) binding, cytochrome oxidase activity and oxygen consumption in ovariectomized (OVX) and sham-operated rats. The food intake and body weight of OVX rats increased more than those of controls and OVX rats became obese. Mitochondrial GDP binding, as an indicator of thermogenic activity, cytochrome oxidase activity, as a marker of mitochondrial abundance, and mitochondrial respiration of BAT in OVX rats were significantly reduced compared with those in controls. And, also, even when OVX rats were restricted in food intake (pair-gained) to produce comparable changes in body weight with sham-controls, or matched in food intake (pair-fed) with sham-controls, these parameters in both pair-gained and pair-fed OVX groups were decreased markedly compared to those in sham-controls. As expected, body weight in pair-fed OVX rats increased significantly more than that in sham-controls. In response to cold exposure, these parameters of OVX rats increased as much as those of controls did. These results suggest that reduced brown adipose tissue thermogenesis might be one of the important factors that are responsible for the development of obesity after OVX.     

Serotonin content of the interscapular brown adipose tissue of growing rats.

In brown fat of newborn rats the serotonin (5HT) content is high during the first five days of life. This may play a part in the lipid repletion of the tissue, lipids being the main fuel for nonshivering thermogenesis. Subsequently 5HT increases more in young rats reared at 16 degrees C than in those reared at 28 degrees C but to a lesser extent than norepinephrine (NE) content. A possible role of 5HT in thermoregulation of the rat during the early postnatal period is discussed.     

Inhibition of the central melanocortin system decreases brown adipose tissue activity

The melanocortin system is an important regulator of energy balance, and melanocortin 4 receptor (MC4R) deficiency is the most common monogenic cause of obesity. We investigated whether the relationship between melanocortin system activity and energy expenditure (EE) is mediated by brown adipose tissue (BAT) activity. Therefore, female APOE*3-Leiden.CETP transgenic mice were fed a Western-type diet for 4 weeks and infused intracerebroventricularly with the melanocortin 3/4 receptor (MC3/4R) antagonist SHU9119 or vehicle for 2 weeks. SHU9119 increased food intake (+30%) and body fat (+50%) and decreased EE by reduction in fat oxidation (−42%). In addition, SHU9119 impaired the uptake of VLDL-TG by BAT. In line with this, SHU9119 decreased uncoupling protein-1 levels in BAT (−60%) and induced large intracellular lipid droplets, indicative of severely disturbed BAT activity. Finally, SHU9119-treated mice pair-fed to the vehicle-treated group still exhibited these effects, indicating that MC4R inhibition impairs BAT activity independent of food intake. These effects were not specific to the APOE*3-Leiden.CETP background as SHU9119 also inhibited BAT activity in wild-type mice. We conclude that inhibition of central MC3/4R signaling impairs BAT function, which is accompanied by reduced EE, thereby promoting adiposity. We anticipate that activation of MC4R is a promising strategy to combat obesity by increasing BAT activity.     

Sympathetic activation of glucose utilization in brown adipose tissue in rats.

The effects of norepinephrine (NE) infusion and surgical denervation or electrical stimulation of the sympathetic nerves on 2-deoxyglucose (2-DG) uptake in interscapular brown adipose tissue (BAT) were investigated in vivo in rats to obtain direct evidence for sympathetic control of glucose utilization in this tissue. 2-DG uptake was rather low in fasted rats, but after refeeding it increased in the BAT as well as the heart, skeletal muscle, and white adipose tissue, in parallel with an increase in plasma insulin level. Cold exposure also enhanced 2-DG uptake in the BAT without the increase in plasma insulin level, while it had no appreciable effect on 2-DG uptake in other tissues. Sympathetic denervation greatly attenuated the stimulatory effect of cold exposure on 2-DG uptake in BAT, but it did not affect the increased 2-DG uptake after refeeding. Electrical stimulation of the sympathetic nerves entering BAT or NE infusion produced a marked increase in 2-DG uptake in BAT without noticeable effects in other tissues. beta-Adrenergic blockade, but not alpha-blockade, abolished the increased 2-DG uptake in BAT. It was concluded that glucose utilization in BAT is activated directly, independently of the action of insulin, by sympathetic nerves via the beta-adrenergic pathway.     

Ventromedial hypothalamic stimulation accelerates norepinephrine turnover in brown adipose tissue of rats

To establish a functional link between the ventromedial hypothalamus (VMH) and brown adipose tissue (BAT), effects of electrical stimulation of the VMH and the lateral hypothalamus (LH) on norepinephrine (NE) turnover in the interscapular BAT were examined in rats. Stimulation of the VMH elicited about 3-fold increase in the rate of NE turnover in BAT, whereas stimulation of the LH had no appreciable effects. The effect of VMH stimulation was abolished after sympathetic ganglion blockade or by surgical sympathetic denervation of BAT. It was concluded that there is a sympathetic nerve-mediated connection between the VMH and BAT, and that stimulation of the VMH induces metabolic activation and heat production in BAT through an increase in sympathetic nerve activity.     

Insulin administration induces capillary growth in brown adipose tissue of heat-exposed rats

• 1.1. An apparent effect of insulin administration on enlargement of interscapular brown adipose tissue (BAT) was found in heat-exposed rats, but not in warm-adapted or cold-acclimated rats.
• 2.2. BAT extracts from the heat-acclimated/insulin-treated (HI) rats notably increased the capillary growth in an in vitro angiogenesis model in which microvascular fragments and myofibroblastic (Mf) cells isolated from lipid tissues were grown in co-culture, although a direct effect of insulin was not high.
• 3.3. BAT extracts from the HI rats stimulated the production of endothelial cell growth factor and collagen by Mf cells.
• 4.4. It is probable that an increased angiogenic activity contributes to the capillary growth and tissue growth in BAT of HI rats.

     

Effects of thyroxine and 3,5,3'-triiodothyronine in brown adipose tissue of rats

Rats of both sexes were either cold acclimated (6 +/- 1 degree C) or treated with thyroxine (T4) or 3,5,3'-triiodothyronine (T3) (500 micrograms/kg body wt daily s.c. for 3 weeks). Wet weight, total proteins, lipids and nucleic acids in the interscapular brown adipose tissue (IBAT) were measured. Values obtained with T4 treatment were similar to those obtained with T3 treatment. T3 is the main thyroidal hormone in the rat and it is formed from T4 deiodination in liver and kidney. As T4-treated rats have not received T3 directly and its IBAT has a similar composition to that of T3-treated rats, it is concluded that peripheral T4 deiodination is governed by the plasma T4 levels. Total proteins and DNA content were similar in cold-acclimated and T3- or T4-treated rats, which is interpreted as thyroidal hormones having an action at these levels.