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.     

Site specific changes of redox metabolism in adipose tissue of obese Zucker rats

Adipose tissues are differently involved in lipid metabolism and obesity according to their type and location. Increasing reports stress on the impact of redox metabolism on obesity and metabolic syndrome. The aim of this work is to investigate the site-specific redox metabolism in three different adipose tissues and its changes occurring in obesity. We analysed enzymatic and non-enzymatic parameters, and focused on the reduced/oxidized glutathione and coenzyme Q couples. In lean compared with obese non-diabetic Zucker rats, interscapular brown fat seems well protected against oxidative stress and epididymal adipose tissue shows a more reduced glutathione redox state, associated with a higher susceptibility to lipophilic oxidative stress than inguinal adipose tissue. Epididymal adipose tissue redox metabolism significantly differs from inguinal one by its limited redox metabolism adaptation. Our results demonstrate site-specific managements of reactive oxygen species metabolism in obese Zucker rats. These results are not consistent with the classic deciphering of inflammatory situation and produce a new conception of the redox parameters implication in the development of the metabolic syndrome.     

Glucose tolerance and insulin action in monosodium glutamate (MSG) obese exercise-trained rats

The present study was designed to evaluate the effects of chronic aerobic exercise (swimming, 1h/day, 5 days/week, with an overload of 5% body weight) on glucose metabolism in obese male Wistar rats. Hypothalamic obesity was induced through administration of monosodium glutamate (MSG) at 4 mg/g of body weight every other day from birth to 14 days old. Fourteen weeks after drug administration, the rats were separated into two groups: MSG-S (sedentary) and MSG-T (swimming for 10 weeks). Rats of the same age and strain, receiving saline in place of MSG, were used as control (C), and subdivided into two groups: C-S and C-T. At the end of the experimental period, an oral glucose tolerance test was performed and serum glucose (AG) and insulin (AI) were evaluated. A constant for serum glucose decrease (Kitt) in response to exogenous insulin was calculated. Soleus muscle strips and adipose tissue samples were incubated and insulin stimulated glucose uptake determined. No differences were observed in AG among the 4 groups. MSG-S rats showed higher Al (418%) and lower Kitt (92.3%) than C-S rats. T-rats showed higher glucose uptake by muscle (224.0%) and adipose tissues (94.1%) than S-rats. Among trained rats, glucose uptake by muscle was higher in MSG-T (5.4%) than in C-T, while the opposite was observed in adipose tissue (39% higher in C-T). Chronic aerobic exercise was able to improve glucose tolerance and reduce insulin resistance in MSG-obese rats. These effects were associated to an increase in glucose uptake by muscle and adipose tissue in response to insulin.     

Effect of adrenalectomy on the activity of small intestine enzymes in monosodium glutamate obese rats

It is well known that adrenalectomy (ADX) reverses the eating and energy balance disturbances in a variety of models of obesity associated with elevated food intake. We have previously demonstrated enhanced functional activity in the small intestine of neonatally monosodium glutamate-treated (MSG) obese rats despite the absence of overeating and we concluded that these changes might also contribute to the development of MSG obesity. The objective of the present experiments was to investigate whether ADX would affect the small intestinal functions and whether their changes would counteract attenuation or prevention of obesity development in MSG rats. Therefore the investigation was carried out in MSG-obese Wistar male rats and untreated intact rats adrenalectomized on day 40, as well as in lean littermates of MSG rats and intact rats subjected to Sham-ADX surgery. All animals had free access to a standard pellet diet after weaning. At the age of 80 days, body mass, body fat content and food consumption as well as changes of the brush-border-bound duodenal and jejunal alkaline phosphatase (AP), the dipeptidyl(amino)peptidase IV (DPP IV) and maltase activity were measured. During the postoperative period, ADX resulted in a significant decrease of mass gain in both MSG and control rats (P<0.05). ADX fully prevented the development of obesity in MSG rats (significantly decreased epididymal+retroperitoneal fat pad mass, P<0.05) and increased mean daily food intake (P<0.001). These effects were only minimal in the ADX controls suggesting that enhanced adrenal secretion is involved in the expression of MSG obesity and its complications. The AP activity in obese MSG rats was increased by about 21 % (P<0.01) in both intestinal segments when compared to the lean controls, whereas no parallel variations in the activities of DPP IV and maltase were observed in the intestinal parts mentioned. In MSG rats, ADX significantly reduced the AP activity in the duodenum and jejunum (P<0.01). A similar tendency was also seen in the DPP IV activity of adrenalectomized MSG rats as well as in lean control rats. Nevertheless, no significant effect of adrenal withdrawal on maltase activity was found. These results indicate that the decrease of enzyme activities in the small intestine and the different effectiveness of nutrient absorption might be a significant factor preventing the development of excess adiposity in glutamate-treated rats. This information contributes to a better understanding of the importance of small intestinal function for the development of obesity and its maintenance in later life.     

Effect of fasting and refeeding on duodenal alkaline phosphatase activity in monosodium glutamate obese rats

In the present work the effects of fasting and refeeding on fat pad weight and alkaline phosphatase activity in the brush border of individual duodenal enterocytes have been evaluated in male Wistar rats with obesity induced by monosodium glutamate (MSG) treatment during the early postnatal period. Neonatal rats were treated subcutaneously with MSG (2 mg/g b.w.) or saline (controls) for 4 days after birth. At 4 months of age, two types of experiments were performed. In the first experiment rats, were submitted to 3 or 6 days lasting food deprivation. In the second experiment the rats were refed for 3 or 6 days ad libitum or restrictedly (60% of pre-fasting intake) after a 6 day-fasting period. Fasting and refeeding influenced the body fat and function of the duodenum in MSG-treated rats differently as compared to the controls. However, alkaline phosphatase activity and the weight of epididymal and retroperitoneal fat depots were significantly increased in MSG obese rats (P<0.001) during all the periods examined. While 3 days of food deprivation resulted in both groups in a similar loss of adipose tissue weight and alkaline phosphatase activity, the decrements of these parameters after 6 days of fasting were lower in obese rats suggesting that their capacity to spare body fat stores was enhanced. After 3 days of ad libitum refeeding, a more marked adaptational increase of food consumption and also a significantly increased alkaline phosphatase activity above the pre-fasting level (P<0.01) was observed in the MSG-treated rats. Consequently, a more rapid body fat restoration was demonstrated in these animals. Refeeding of rats at 60% of the pre-fasting intake level resulted in a significant increase of alkaline phosphatase activity in both the MSG and control group; moreover, as food restriction continued, MSG-treated rats tended to further increase the enzyme activity. Our results revealed that MSG treatment of neonatal rats may significantly change the intestinal functions. Permanently increased alkaline phosphatase activity observed in MSG obese rats during all investigated periods suggests that this functional alteration is probably not a consequence of actual nutritional variation but could be a component of regulatory mechanisms maintaining their obesity at critical values.     

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.     

Insulin secretion in monosodium glutamate (MSG) obese rats submitted to aerobic exercise training

The present study was designed to evaluate the effects of aerobic exercise training on glucose tolerance and insulin secretion of obese male Wistar rats (monosodium glutamate [MSG] administration, 4 mg/g-body weight, each other day, from birth to the 14th day). Fourteen weeks after the drug administration, the rats were separated into two groups: MSG-S (sedentary) and MSG-T (T = swimming, 1 h/day, 5 days/week, with an overload of 5% body weight for 10 weeks). Rats of the same age and strain injected with saline were used as control (C) and subdivided into two groups: C-S and C-T. Insulin and glucose responses during an oral glucose tolerance test (GTT) were evaluated by the estimation of the total areas under serum insulin (AI) and glucose (AG) curves. Glucose-induced insulin secretion by isolated pancreatic islets was also evaluated. MSG-S rats showed higher AI than C-rats while MSG-T rats presented lower AI than MSG-S rats. No differences in AG were observed among the 4 groups. Pancreatic islets from MSG-rats showed higher insulin secretion in response to low (2.8) and moderate (8.3 mM) concentrations of glucose than those from their control counterparts and no differences were observed between MSG-S and MSG-T rats. These results provide evidences that the hyperinsulinemia at low or moderate glucose concentrations observed in MSG-obese rats is, at least in part, a consequence of direct hypersecretion of the B cells and that chronic aerobic exercise is able to partially counteract the hyperinsulinemic state of these animals without disrupting glucose homeostasis.     

Morpholigic and physiologic repercussions of partial removal of brown adipose tissue in rats acclimated to different temperatures]

Rats were chronically acclimated to 28 degrees C or 5 degrees C or submitted to daily variations of ambiant temperature. Ten or thirty days after removal of about 40% of the total brown adipose tissue (whole interscapular and 25% of abdominal tissues), the weight of the different pads of brown adipose tissue, thyroid and adrenals were determined. In all the groups, there was a large decrease of brown adipose tissue weight for the first ten days due to the shock following the operation. Then, the brown adipose tissue weight was restaured and, only in constant cold accliclimated rats, compensative hypertrophies of axillary and thoracic brown adipose tissue were found. Adrenals weight was significantly increased after the operation; in the two groups of cold acclimated rats, that increase was still significant one month later. However, the corticosterone production rate was not increased. These results are discussed in relation to the physiolocical role of brown adipose tissue in cold acclimated animals.     

APM/CD13 and FOS in the hypothalamus of monosodium glutamate obese and food deprived rats

Protein (western blotting) and gene (PCR) expressions, catalytic activity of puromycin-insensitive membrane-bound neutral aminopeptidase (APM/CD13) and in situ regional distribution of CD13 and FOS immunoreactivity (ir) were evaluated in the hypothalamus of monosodium glutamate obese (MSG) and/or food deprived (FD) rats in order to investigate their possible interplay with metabolic functions. Variations in protein and gene expressions of CD13 relative to controls coincided in the hypothalamus of MSG and MSG-FD (decreased 2- to 17-fold). Compared with controls, the reduction of hypothalamic CD13 content reflected a negative balance in its regional distribution in the supraoptic, paraventricular, periventricular and arcuate nuclei. CD13-ir increased in the supraoptic nucleus in MSG (2.5-fold) and decreased in the paraventricular nucleus (2-fold) together with FOS-ir (1.5-fold) in FD. In MSG-FD, FOS-ir decreased (7-fold) in the paraventricular nucleus, while CD13-ir decreased in the periventricular (5.6-fold) and the arcuate (3.7-fold) nuclei. It was noteworthy that all these changes of CD13 were not related to catalytic activity of APM. Data suggested that hypothalamic CD13 plays a role in the regulation of energy metabolism not by means of APM enzyme activity.     

Effect of cholecystokinin on feeding is attenuated in monosodium glutamate obese mice

Treatment of newborn mice with monosodium glutamate (MSG) is neurotoxic for hypothalamic arcuate nucleus (ARC) and causes obesity. In the MSG-treated 16-week-old NMRI mice, we detected specific ablation of ARC neuronal cells, 8 times higher fat to body mass ratio but unchanged body mass compared to controls, advanced hyperglycemia and hyperinsulinemia--both more pronounced in males, and hyperleptinemia--more severe in females. After fasting, the MSG-treated mice showed attenuated food intake compared to controls. Cholecystokinin octapeptide, which decreased food intake in a dose-dependent manner in 24 h fasted controls, did not significantly affect food intake in the MSG-treated animals. We propose that the obesity-related changes in the feeding behavior of the MSG-treated obese mice were the result of missing leptin and insulin receptors in ARC and consequent altered neuropeptide signaling. This makes the MSG model suitable for clarifying generally the central control of food intake.     

Microarray analysis after adipose derived mesenchymal stem cells injection in monosodium iodoacetate-induced osteoarthritis rats

Osteoarthritis (OA) is a degenerative joint disease characterized by abrasion, and ultimately, destruction of the articular cartilage and trabecular bone loss. OA is still considered a devastating disease, which requires an aggressive therapeutic approach. Despite the therapeutic potential of human adipose-derived mesenchymal stem cells (AD-MSCs), the molecular parameters needed to define the “stemness” remain largely unknown. Using high-density oligonucleotide microarrays, the differential gene expression profiles between a fraction of human adipose-derived (AD) mononuclear cells and its MSC subpopulation were obtained. Of particular interest was a subset of 58 genes preferentially expressed at sevenfold or higher in the group treated with human AD-MSCs. This subset contained numerous genes involved in the inflammatory response, immune response, lipid metabolism, cell death, cell proliferation, and DNA repair. Additionally, four protein networks were constructed. The interaction network consisted of 46 proteins encoded by up-regulated genes. However, the interaction network also consisted of 38 proteins encoded by down-regulated genes. My results provide a basis for a more reproducible and reliable quality control using genotypic analysis for the definition of human AD-MSCs. Therefore, these results will provide a basis for studies on molecular mechanisms controlling the core properties of human MSCs.     

Differential adipose tissue inflammatory state in obese nondiabetic Zucker fatty rats compared to obese diabetic zucker diabetic fatty rats

Adipose tissue (AT) inflammation is linked to the pathogenesis of diabetes in obesity. Here, we compare the AT inflammatory state of 2 animal models of obesity and obesity plus diabetes, respectively. Obese nondiabetic ZF rats exhibited a trend towards increased proportions of CD11b positive cells in the adipose tissue stroma vascular fraction suggesting a state of increased AT inflammation compared to their lean littermates, but no alterations in systemic inflammatory parameters. In contrast, obese diabetic ZDF rats exhibited systemic as well as local AT inflammation with elevated levels of circulating Regulated upon Activation, Normal T-cell Expressed and Secreted Protein (Rantes), interleukin 1β (IL-1β) and monocyte chemotactic protein 1 (MCP-1), and an increased infiltration of adipose tissue CD11b positive cells. Our data provide a novel phenotypic characterisation of 2 common metabolic animal models and suggest an association of obesity with local inflammation in adipose tissue, and an association of diabetes with local inflammation in adipose tissue plus systemic inflammation. AT inflammation in obesity might therefore initiate a process that above a certain limits finally results in systemic inflammation and diabetes.     

Effects of exercise training on brown adipose tissue thermogenesis in ovariectomized obese rats

The effect of exercise training on brown adipose tissue (BAT) thermogenesis was studied by measuring cytochrome oxidase activity, as a marker of mitochondrial abundance, mitochondrial guanosine-5'-diphosphate (GDP) binding, as an indicator of thermogenic activity and oxygen consumption in BAT in ovariectomized (OVX) obese rats and sham-operated rats. Six-week exercise training significantly suppressed body weight gain in OVX rats to the level of sedentary control rats, although food intake in exercise trained OVX rats increased more than in the sedentary OVX rats. Exercise training increased cytochrome oxidase activity, mitochondrial GDP binding and oxygen consumption in BAT in OVX rats, which were reduced in a sedentary condition, as well as in the control rats. These results suggest that exercise training potentiates BAT thermogenesis, which may contribute to the reduction of body weight in OVX obese rats.     

Brown adipose tissue in morbidly obese subjects

Background

Cold-stimulated adaptive thermogenesis in brown adipose tissue (BAT) to increase energy expenditure is suggested as a possible therapeutic target for the treatment of obesity. We have recently shown high prevalence of BAT in adult humans, which was inversely related to body mass index (BMI) and body fat percentage (BF%), suggesting that obesity is associated with lower BAT activity. Here, we examined BAT activity in morbidly obese subjects and its role in cold-induced thermogenesis (CIT) after applying a personalized cooling protocol. We hypothesize that morbidly obese subjects show reduced BAT activity upon cold exposure.

Methods and Findings

After applying a personalized cooling protocol for maximal non-shivering conditions, BAT activity was determined using positron-emission tomography and computed tomography (PET-CT). Cold-induced BAT activity was detected in three out of 15 morbidly obese subjects. Combined with results from lean to morbidly obese subjects (n = 39) from previous study, the collective data show a highly significant correlation between BAT activity and body composition (P<0.001), respectively explaining 64% and 60% of the variance in BMI (r = 0.8; P<0.001) and BF% (r = 0.75; P<0.001). Obese individuals demonstrate a blunted CIT combined with low BAT activity. Only in BAT-positive subjects (n = 26) mean energy expenditure was increased significantly upon cold exposure (51.5±6.7 J/s versus 44.0±5.1 J/s, P = 0.001), and the increase was significantly higher compared to BAT-negative subjects (+15.5±8.9% versus +3.6±8.9%, P = 0.001), indicating a role for BAT in CIT in humans.

Conclusions

This study shows that in an extremely large range of body compositions, BAT activity is highly correlated with BMI and BF%. BAT-positive subjects showed higher CIT, indicating that BAT is also in humans involved in adaptive thermogenesis. Increasing BAT activity could be a therapeutic target in (morbid) obesity.     

Gene expression profiles of adipose tissue of high-fat diet-induced obese rats by cDNA microarrays

To better understand the molecular basis of dietary obesity, we examined adipose tissue genes differentially expressed in a well-characterized rat model of high-fat diet (HFD)-induced obesity using cDNA microarrays. Male Sprague–Dawley rats were fed either the HFD or the normal diet. Seven weeks later, the weights of obese models (362.92 ± 39.65 g) were significantly higher than those of normal control rats (315.22 ± 42.30 g, P < 0.01) and the wet weights of adipose tissue of rats fed with HFD (9.29 ± 5.14 g) were significantly higher than those of normal control rats (4.09 ± 2.69 g, P < 0.01), which confirmed the successful preparation of obese models. cDNA microarrays containing 9 216 genes/Ests were used to investigate gene expression of adipose tissue. Autoradiographic analysis showed that 532, 154, and 22 genes were differently expressed over 2-, 3-, and 5-fold, respectively. The analysis of gene expression profiles indicated that 276 genes were up-regulated and 432 genes were down-regulated in response to HFD-induced obesity. Different clusters of genes associated with lipid metabolism, extracellular matrix, signal transduction, cytoskeleton, cell apoptosis, etc., such as VLCS-H2, DGAT, ACADVL, PHYH, SCD, ACACA, ACS, MMP-2, MMP-15, CD38, CAMK2D, CACNA1F, CAPZA2, TMOD3, ARPC2, KNS2, TPM1, MAPK8, GADD45B, DAXX, TOK-1, PRKACA, STAT6, were concerned.     

Type 2 diabetes mellitus in obese mouse model induced by monosodium glutamate.

The number of diabetic patients is increasing every year, and new model animals are required to study the diverse aspects of this disease. An experimental obese animal model has reportedly been obtained by injecting monosodium glutamate (MSG) to a mouse. We found that ICR-MSG mice on which the same method was used developed glycosuria. Both female and male mice were observed to be obese but had no polyphagia, and were glycosuric by 29 weeks of age, with males having an especially high rate of incidence (70.0%). Their blood concentrations of glucose, insulin, total cholesterol, and triglycerides were higher than in the control mice at 29 weeks. These high concentrations appeared in younger males more often than in females, and were severe in adult males. Also, the mice at 54 weeks of age showed obvious obesity and increased concentrations of glucose, insulin, and total cholesterol in the blood. The pathological study of ICR-MSG female and male mice at 29 weeks of age showed hypertrophy of the pancreatic islet. This was also observed in most of these mice at 54 weeks. It was recognized as a continuation of the condition of diabetes mellitus. From the above results, these mice are considered to be useful as new experimental model animals developing a high rate of obese type 2 (non-insulin dependent) diabetes mellitus without polyphagia.     

Decreased rate of fatty acid synthesis in brown adipose tissue of hypothalamic obese rats

Intranuclear coinjection of the late SV40 KpnI/BclI DNA fragment and the early promotor/enhancer HpaII/BglI DNA segment into permissive monkey and non-permissive mouse cells allows late SV40 gene expression without T-antigen synthesis and DNA replication. These conditions were chosen to analyse the effect of DNA methylation on V-antigen synthesis detached from the process of DNA replication. We found that in vitro methylation of a single cytosine nucleotide proximal to the major late mRNA cap site by the HpaII methylase does not block capsid protein synthesis. This result is in contrast to reported data obtained in Xenopus laevis oocyte injection experiments [(1982) Proc. Natl. Acad. Sci. USA 79, 5142-5146].