Rat Adipose Research Articles

Large Litter Rearing Enhances Leptin Sensitivity and Protects Selectively Bred Diet-induced Obese Rats from Becoming Obese

Abstract Because rearing rats in large litters (LLs) protects them from becoming obese, we postulated that LL rearing would protect rats selectively bred to develop diet-induced obesity (DIO) from becoming obese by overcoming their inborn central leptin resistance. Male and female DIO rats were raised in normal litters (10 pups/dam) or LLs (16 pups/dam) and assessed for anatomical, biochemical, and functional aspects of leptin sensitivity at various ages when fed low-fat chow or a 31% fat high-energy (HE) diet. LL rearing reduced plasma leptin levels by postnatal d 2 (P) 2 and body weight gain by P8. At P16, LL DIO neonates had increased arcuate nucleus (ARC) binding of leptin to its extracellular receptors and at P28 an associated increase of their agouti-related peptide and α-MSH axonal projections to the paraventricular nucleus. Reduced body weight persisted and was associated with increased ARC leptin receptor binding and sensitivity to the anorectic effects of leptin, reduced adiposity, and enhanced insulin sensitivity in LL DIO rats fed chow until 10 wk of age. The enhanced ARC leptin receptor binding and reduced adiposity of LL DIO rats persisted after an additional 5 wk on the HE diet. Female LL DIO rats had similar reductions in weight gain on both chow and HE diet vs. normal litter DIO rats. We postulate that LL rearing enhances DIO leptin sensitivity by lowering plasma leptin levels and thereby increasing leptin receptor availability and that this both enhances the ARC-paraventricular nucleus pathway development and protects them from becoming obese.

Basal Plasma Levels of Insulin, Leptin, Ghrelin, and Amylin Do Not Signal Adiposity in Rats Recovering from Forced Overweight

This study examined how adiposity signals are related to adiposity during recovery from forced overweight (OW). Rats were rendered OW by chronic intragastric overfeeding (OW). Overfeeding was stopped when OW rats reached 126-129% of saline-infused normal-weight (NW) rats. Adipose tissue (AT) mass was estimated by computed tomography, and blood was drawn from chronic atrial cannulas throughout. Basal levels (i.e. after 2-3 h fasts late in the diurnal phase) of the hypothesized adiposity signals insulin, leptin, ghrelin, and amylin were assayed. OW rats gained approximately 130 g more body weight (BW) and approximately 100 g more AT mass during overfeeding. Plasma levels of insulin and leptin increased, whereas those of ghrelin decreased, linearly with AT mass; amylin did not change reliably. During recovery, OW rats' BW and AT mass decreased but were still elevated vs. NW rats after 39 d. OW rats' insulin returned to NW levels on d 1 of recovery and decreased below NW levels thereafter. Leptin was no longer elevated after d 8 of recovery. Ghrelin and amylin did not change reliably during recovery. Although AT mass decreased in OW rats during each intermeasurement interval between d 0 and d 23 of recovery, insulin and leptin did so during only the first interval (d 0-5). Insulin and leptin levels were exponentially related to AT mass during recovery. These data indicate that basal insulin, leptin, ghrelin, and amylin do not encode AT mass in rats dynamically regulating BW and adiposity during recovery from OW.

Dietary naringenin increases hepatic peroxisome proliferators–activated receptor α protein expression and decreases plasma triglyceride and adiposity in rats

Naringenin, a flavonoid present in grapefruit, has recently been shown to exert hypolipidemic and hypocholesterolemic effects, which has a particular importance for protecting against chronic diseases. However, the lipid-lowering potential of naringenin at the concentrations in the dietary range and its underlying mechanisms have yet to be fully elucidated. The aim of the present study was (1) to investigate the effects of dietary naringenin on plasma and hepatic triglyceride and cholesterol levels and on adipose deposition in rat and (2) to determine the contribution of hepatic peroxisome proliferators-activated receptor α (PPARα) expression to fatty acid oxidation. Male Long-Evans hooded rats were fed a diet supplemented with naringenin (0.003, 0.006, and 0.012%) for 6weeks. We analyzed plasma and hepatic lipid contents and determined the protein expression of PPARα, carnitine-palmitoyl transferase 1L (CPT-1), and uncoupling protein 2 (UCP2), all of which are critical genes for fatty acid oxidation. Naringenin supplementation caused a significant reduction in the amount of total triglyceride and cholesterol in plasma and liver. In addition, naringenin supplementation lowered adiposity and triglyceride contents in parametrial adipose tissue. Naringenin-fed animals showed a significant increase in PPARα protein expression in the liver. Furthermore, expression of CPT-1 and UCP2, both of which are known to be regulated by PPARα, was markedly enhanced by naringenin treatment. Our results indicate that the activation of PPARα transcription factor and upregulation of its fatty acid oxidation target genes by dietary naringenin may contribute to the hypolipidemic and anti-adiposity effects in vivo.

Olanzepine-induced adiposity in female rats

Olanzepine-induced adiposity in female rats

Circadian and age-associated differences in feeding and spontaneous physical activity contribute to reduced adiposity in obesity resistant rats

Circadian and age-associated differences in feeding and spontaneous physical activity contribute to reduced adiposity in obesity resistant rats

Sibutramine Effects on the Reproductive Performance of Pregnant Overweight and Non-Overweight rats

It is well established that sibutramine produces weight loss and is used frequently in women of childbearing age. However, the potential adverse consequences attributed to sibutramine use by women who may become pregnant is not known. It was thus of interest to determine the effects of sibutramine on the reproductive performance of pregnant rats. Overweight as well as non-overweight female Wistar rats were treated with sibutramine (6 mg/kg) orally, daily for 15 d and then mated with normal male rats. Pregnancy was confirmed and treatment continued with sibutramine until d 14 of pregnancy. On d 20 of pregnancy all rats were anesthetized for determination of various maternal and fetal parameters. There was a significant maternal weight reduction at the end of pregnancy in the non-overweight drug-treated group compared to the control (non-overweight, no drug). Sibutramine alone and overweight condition alone produced a significant increase in postimplantation loss and placental index. In the overweight with or without sibutramine groups a significant decrease in fetal weight was noted. Data suggest that sibutramine alone or the condition of excess weight in the absence of drugs produced impaired reproductive performance. However, treatment of overweight rats with sibutramine did not further exacerbate fetal loss compared to sibutramine alone or the effects noted with excess weight alone.

Viscous dietary fibers reduce visceral adiposity, lower oxidative stress and improve glucose control in ZDF rats

Viscous dietary fibers have been shown to blunt the postprandial rise in blood glucose. Previous studies in this lab have suggested that viscous dietary fibers decrease adiposity in rats with little or no change in body weight. The aim of this study was to examine the effect of consumption of viscous dietary fibers, hydroxypropyl methylcellulose (HPMC) and β‐glucans (Sustagrain), in an obese diabetic rat model. Zucker Diabetic Fatty (ZDF) rats and their lean counterparts (n=12) were fed diets containing either 5% non‐viscous cellulose, low viscosity (LV) HPMC, high viscosity (HV) HPMC or 40% Sustagrain flour. After 6 weeks of feeding, the HV HPMC group had a reduced percentage epididymal fat pad weight (visceral fat) compared to the other ZDF groups, but no differences in percentage inguinal (subcutaneous) fat pad weights were found. Fasting plasma leptin did not differ among the ZDF groups. Rats fed HPMC and Sustagrain had lower percent glycated hemoglobin and kidney weights than the cellulose group, indicating improved glycemic control. Urinary 8‐isoprostane concentrations in the ZDF cellulose, LV HPMC and Sustagrain groups were significantly higher than the lean group, but HV HPMC and lean groups did not differ. These results indicate that consumption of viscous dietary fiber can lower visceral adiposity and oxidative stress and improve diabetic control in ZDF rats. (Supported by the MN Agric Exp Station)Grant Funding Source: MN Agric Exp Station/CHE Administative Fund

Mechanisms of impaired acetylcholine‐mediated vasodilation in overweight rats

The current study was designed to examine the early effects of increased adiposity in adult male Sprague‐Dawley rats fed either a high sucrose (HSD) or high fat diet (HFD) for 6 weeks. Initial studies examined pathways involved in acetylcholine (ACh)‐mediated vasodilation which is typically thought to act through increased production of the vasodilator nitric oxide (NO). Similar to obese animals, HSD and HFD‐fed rats developed impaired ACh‐mediated vasodilation in isolated mesenteric arteries compared to chow fed controls that was normalized by antioxidants. Unlike chow controls, inhibition of NO did not further impair vasodilation in the HSD or HFD groups suggesting that ACh may activate pathways distinct from NO in these settings. To examine smooth muscle sensitivity to NO, arteries were exposed to increasing concentrations of the NO donor sodium nitroprusside (10−11 to 10−3M). We found that HSD and HFD reduced smooth muscle sensitivity to NO. These data suggest that increased ROS scavenging of NO coupled with diminished VSM reactivity minimizes the role of NO in vasodilation following HSD or HFD which is partially compensated by activation of parallel vasodilatory pathways.

Pioglitazone improves lipid and insulin levels in overweight rats on a high cholesterol and fructose diet by decreasing hepatic inflammation.

Nutrient overload leads to obesity and insulin resistance. Pioglitazone, a selective peroxisome proliferator-activated receptor (PPAR)gamma agonist, is currently used to manage insulin resistance, but the specific molecular mechanisms activated by PPARgamma are not yet fully understood. Recent studies suggest the involvement of suppressor of cytokine signalling (SOCS)-3 in the pathogenesis of insulin resistance. This study aimed to investigate the hepatic signalling pathway activated by PPARgamma activation in a non-genetic insulin-resistant animal model. Male Wistar rats were maintained on a high-cholesterol fructose (HCF) diet for 15 weeks. Pioglitazone (3 mg x kg(-1)) was administered orally for the last 4 weeks of this diet. At the end of the treatment, serum was collected for biochemical analysis. Levels of PPARgamma, SOCS-3, pro-inflammatory markers, insulin receptor substrate-2 and Akt/glycogen synthase kinase-3beta phosphorylation were assessed in rat liver. Rats fed the HCF diet exhibited hyperlipidemia, hyperinsulinemia, impaired glucose tolerance and insulin resistance. Pioglitazone administration evoked a significant improvement in lipid metabolism and insulin responsiveness. This was accompanied by reduced hepatic expression of SOCS-3, interleukin-6, tumour necrosis factor-alpha and markers of neutrophil infiltration. Diet-induced PPARgamma expression was unaffected by the pioglitazone treatment. Chronic pioglitazone administration reduced hepatic inflammatory responses in rats fed a HCF diet. These effects were associated with changes in hepatic expression of SOCS-3, which may be a crucial link between the reduced local inflammation and the improved insulin signalling.

Site-specific modulation of white adipose tissue lipid metabolism by oleoyl-estrone and/or rosiglitazone in overweight rats

In spite of their shared decrease of insulin resistance, oleoyl-estrone [OE], and rosiglitazone show diverging effects on body fat mass and distribution. In this study, we studied whether their effects on white adipose tissue [WAT] were due to a shared or synergistic mechanism of action. Combined effects of OE and rosiglitazone 10-day treatment on WAT lipid, cell mass/number, and the expression of key lipid metabolism and regulatory agents were studied using an adult male overweight rat model. OE decreased WAT cell mass and lipids, parameters not changed by rosiglitazone. The effects of OE and--specially--rosiglitazone were more marked in small-cell WAT (i.e., mesenteric and subcutaneous sites) than in larger cell WAT (retroperitoneal and perigonadal). OE decreased the expressions in WAT of lipogenic enzymes, lipoprotein lipase, PPARs, and SREBP1c, effects symmetrically reversed by rosiglitazone. OE showed no effects on hormone-sensitive lipase expression, which was increased by rosiglitazone. OE strongly inhibited WAT lipogenesis, leaving lipolysis unchanged, thus unbalancing (and helping mobilize) WAT lipid stores. Rosiglitazone acted practically only on small-cell WAT sites, where it favored lipogenesis, but also stimulated lipolysis, which resulted in limited changes in lipid stores. Combination of OE and rosiglitazone induced less fat loss than OE alone.

Effect of Mild Intermittent Hypoxia on Glucose Tolerance, Muscle Morphology and AMPK-PGC-1α Signaling

The main goal of this study was to investigate the long-term effect of daily 8-hour mild intermittent hypoxia (14-15% O2) on glucose tolerance and muscle morphology of Sprague-Dawley rats. The involvement of AMPK-PGC-1alpha-VEGF signaling pathways in the skeletal muscle was also determined during the first 8 hours of hypoxia. We found that mRNA levels of VEGF and PGC-1alpha were significantly increased above control after 8-h mild hypoxia without a change in AMPK phosphorylation. After 8 weeks of mild intermittent hypoxia treatment, plasma glucose and insulin levels in oral glucose tolerance test (OGTT), epididymal fat mass, and body weight were significantly lower compared to the control group. While soleus muscle weight was not changed, capillary and fiber densities in the hypoxia group were 33% and 35% above the control suggesting reorganization of muscle fibers. In conclusion, our data provide strong evidence that long-term mild intermittent hypoxia decreases the diffusion distance of glucose and insulin across muscle fibers, and decreases adiposity in rats. These changes may account for the improved glucose tolerance observed following the 8-week hypoxia treatment, and provides grounds for investigating the development of a mild non-pharmacological intervention in the treatment of obesity and type 2 diabetes.

Pathways affected by 3,5-diiodo-l-thyronine in liver of high fat-fed rats: Evidence from two-dimensional electrophoresis, blue-native PAGE, and mass spectrometry

3,5-Diiodo-l-thyronine (T2) powerfully reduces adiposity in rats fed a high-fat diet (HFD), stimulating (in the liver) fatty acid oxidation and mitochondrial uncoupling, and strongly counteracting steatosis, a condition commonly associated with diet-induced obesity. Proteomics offer unique possibilities for the investigation of changes in the levels and modifications of proteins. Here, combining 2D-E, mass spectrometry, and blue native (BN) PAGE, we studied how the subcellular hepatic phenotype responds to HFD and T2-treatment. By identifying differentially expressed proteins and analyzing their interrelation [using the Ingenuity Pathway Analysis (IPA) platform], we obtained an integrated view of the phenotypic/metabolic adaptations occurring in the liver proteome during HFD with or without T2-treatment. Interestingly, T2 counteracted several HFD-induced changes, mostly in mitochondria. BN-PAGE and subsequent in-gel activity analysis of OXPHOS complexes revealed a modified profile of individual complexes in HFD mitochondria vs. normal ones. This pattern was re-normalized in mitochondria from T2-treated HFD animals. These data indicate that in HFD rats, the effects of T2 on the liver proteome cause it to resemble that associated with a non-steatotic condition. The identified metabolic pathways (mainly at the mitochondrial level) may be responsible for the beneficial effects of T2 on liver adiposity and metabolism.

Gene expression modulation of liver energy metabolism by oleoyl-oestrone in overweight rats

We intended to determine how the liver copes with the massive handling of lipids induced by OE (oleoyl-oestrone), as well as to characterize and differentiate the actual OE effects from those that may be only the consequence of decreased food intake. Thus we used male rats treated with oral OE (10 nmol/g per day) compared with a vehicle only PF (pair-fed) group and controls fed ad libitum (vehicle only). Plasma parameters, and total liver lipids, glycogen, DNA and total mRNA were measured. RNA was extracted and used for real-time PCR analysis of the gene expression of enzymes and regulatory factors of liver energy metabolism. Most hepatic proteins showed similar gene expressions in OE and controls, but the differences widened between OE and PF rats, showing that OE effects could not be merely attributed to a lower energy intake. The liver of OE-treated rats largely maintained its ability to mobilize glucose for the synthesis of fats; this was achieved in part by a peculiar combination of regulative modifications that facilitate both fatty acid disposal and restrained glucose utilization under conditions of limited food supply but ample availability of internal energy stores. In conclusion, the results presented suggest that the effect of OE on liver metabolism may be (at least in part) mediated through an insulin-sensitivity-dependent modulation of the expression of SREBP-1c (sterol-regulatory-element-binding protein-1c), resulting in the unique combined effect of mildly increased (or maintained) glucose disposal but also limited enhancement of lipogenesis.

Gene expression modulation of rat liver cholesterol metabolism by oleoyl-estrone

Since oleoyl-estrone (OE) decreases circulating cholesterol in the rat, we analyzed the response to OE treatment of hepatic gene expressions related with cholesterol metabolism. Male overweight rats treated with oral OE (10 nmol/g daily) were compared with a pair-fed (PF) group and controls fed ad libitum. Serum parameters and liver lipid and cholesterol contents were measured. Total tissue RNA was used for real-time PCR analysis of the gene expression of enzymes and regulatory factors of liver cholesterol metabolism. Cholesterol-7α-hydroxylase and ABC transporter A1 protein levels were estimated by Western blot. Pair-feeding and OE treatment reduced the expression of 3-hydroxy-3-methyl-glutaryl-CoA synthase. OE increased the expression of the LDL receptor. Cholesterol disposal, through bile acids synthesis, was increased in PF and more markedly in OE rats. Gene expressions of the ABC transporter A1 and apolipoproteins A1 and E were increased in OE rats. The expression of liver X receptor was lower in PF than in OE and controls. The rapid disappearance of circulating cholesterol elicited by OE is consequence of: (1) decreased mevalonate pathway activity, (2) a higher expression of the LDL-receptor, and (3) the activation of the oxidation of cholesterol to form bile acids as a consequence of the higher cholesterol concentrations found in liver, also affected by energy availability.

Oleoyl-estrone increases adrenal corticosteroid synthesis gene expression in overweight male rats

Oleoyl-estrone (OE) induces a marked loss of body fat in rats by maintaining energy expenditure, body protein and blood glucose despite decreasing food intake. OE increases glucocorticoids, but they arrest OE lipid-mobilization. We studied here whether OE induces a direct effect on adrenal glands function as part of this feedback regulation. Dietary overweight male rats were given oral 10nmol/g OE gavages for ten days. A group (PF) of pair-fed to OE rats, and controls received vehicle-only gavages. OE rats lost slightly more body than PF, but had larger adrenal glands. Tissue corticosterone levels, and gene expressions for glucocorticoid-synthesizing enzymes were increased in OE versus controls and PF; thus, we assumed that adrenal growth affected essentially its cortex since OE also lowered the expression of the medullar catecholamine synthesis enzyme genes. Serum corticosterone was higher in PF than in OE and controls, but liver expression of corticosteroid-disposing steroid 5alpha-reductase was 3x larger in OE than PF and controls. Circulating glucocorticoids changed little under OE, in spite of higher adrenal gland and liver content, hinting at modulation of glucocorticoid turnover as instrumental in their purported increased activity. In conclusion, we have observed that OE considerable enhanced the expression of the genes controlling the synthesis of glucocorticoids from cholesterol in the rat and increasing the adrenal glands' corticosterone, size and cellularity, but also the liver disposal of corticosteroids, suggesting that OE increases corticosterone synthesis and degradation (i.e. serum turnover), a process not driven by limited energy availability but directly related to the administration of OE.

Study on the Feasibility of Bacterial Cellulose as Tissue Engineering Scaffold

OBJECTIVE: As a kind of nanometer natural material, bacterial cellulose (BC) has been widely used in the field of food processing, paper making, pharmaceutical science, etc. In recent years, it is found that there is a good application potentiality of BC used in the medical science, especially in the field of regeneration medicine. There are some reports about BC being used in tissue engineering. It is of great necessity to investigate its tissue compatibility. In this research, the cell compatibility of BC was studied by using the method of cell-culturing combined with rat adipose- derived stem cells (ADSCs) as the seed cells. MATERIAL and METHODS: BC membranes were prepared by Key Laboratory of Industrial Microbiology, Ministry of Education, Tianjin University of Science and Technology. The average pore size and porosity of it were 0.8-3.5μm and 93％, respectively. The ADSCs were isolated from the fat pad located in pars inguinalis of 3-weeks Wistar rats by using type II collagenase and then cultured using DMED medium contained 10% new-born calf serum. The status of cell growth was observed everyday. The cell growth curve was determined by MTT method and stem cell phenotype was identified by flow cytometry. Cells in exponential phase of growth were planted on the surface of BC membrane which had been sterilized beforehand by steam at 121°C for 20 min at cell density of 3.0×105cells/mL. The cell-BC compound was cultured by using DMED medium contained 10% new-born calf serum. The growth status and the biological characterization of ADSCs cultured on the BC were determined at different culture time. RESULTS: Most ADSCs primary cultured in vitro showed fusiform shape when they were cultured for 72 hours. The amount of the cells increased along with the culture time and confluenced at 7 days. The exponential phase of growth of primary cultured ADSCs in vitro appeared when they were cultured for 3 to 9 days. The result of flow cytometry showed that ADSCs could express the stem cell symbol. The portait section of cell-BC compound were made after 10 days cultured in vitro. It was shown that ADSCs compact grew on the surface of BC. CONCLUSION: It is indicated that ADSCs grew on the BC membrane still retain the biological activity of stem cell and BC has good biocompatibility. It might be further studied for BC as tissue engineering scaffold.

Identification of Hydroxylated Metabolites of Hexabromocyclododecane in Wildlife and 28-days Exposed Wistar Rats

We studied the presence of hydroxylated metabolites of hexabromocyclododecane (HBCD) in three wildlife species (tern egg, seal, and flounder) and in Wistar rats exposed to 30 and 100 mg HBCD/kg bw/day for 28 days. A nondestructive extraction, fractionation, and cleanup method was developed to separate the hydroxylated HBCD metabolites from the biotic sample matrix. Four different groups of hydroxylated HBCD metabolites were identified in rat adipose, liver, lung, and muscle tissues by liquid and gas chromatography (LC and GC) combined with mass spectrometry (MS): monohydroxy metabolites of HBCD, pentabromocyclododecene (PBCDe), tetrabromocyclododecene (TBCDe), and dihydroxy-HBCD. Dihydroxy-PBCDe was identified by GC-MS but could not be confirmed by LCMS. Debromination of HBCD to PBCDe was another metabolic pathway observed. In tern eggs from the Western Scheldt the monohydroxy-HBCD was found and in the blubber of harbor seal (Wadden Sea) the monohydroxy metabolites of HBCD and PBCDe were found. No hydroxylated metabolites were detected in the tissue of flounder (Wadden Sea). To our knowledge, this is the first study to identify different hydroxylated metabolite groups of HBCD in rat and wildlife samples.

Plasma levels of ‘adiposity signals’ do not reflect adiposity in rats compensating for under- or over-weight

Plasma levels of ‘adiposity signals’ do not reflect adiposity in rats compensating for under- or over-weight

Effects of intermittent intraperitoneal infusion of exendin-4 and PYY(3–36) on food intake and adiposity in diet-induced obese rats

Effects of intermittent intraperitoneal infusion of exendin-4 and PYY(3–36) on food intake and adiposity in diet-induced obese rats

Oleoyl-oestrone inhibits lipogenic, but maintains thermogenic, gene expression of brown adipose tissue in overweight rats

In the present study we intended to determine how BAT (brown adipose tissue) maintained thermogenesis under treatment with OE (oleoyl-oestrone), a powerful slimming hormone that sheds off body lipid but maintains the metabolic rate. Overweight male rats were subjected to daily gavages of 10 nmol/g of OE or vehicle (control) for 10 days. A PF (pair-fed) vehicle-receiving group was used to discount the effects attributable to energy availability limitation. Interscapular BAT mass, lipid, DNA, mRNA and the RT-PCR (real-time PCR) expression of lipid and energy metabolism genes for enzymes and regulatory proteins were measured. BAT mass and lipid were decreased in OE and PF, with the latter showing a marked reduction in tissue mRNA. Maintenance of perilipin gene expression in PF and OE rats despite the loss of lipid suggests the preservation of the vacuolar interactive surface, a critical factor for thermogenic responsiveness. OE and, to a lesser extent, PF maintained the expression of genes controlling lipolysis and fatty acid oxidation, but markedly decreased the expression of those genes involved in lipogenic and acyl-glycerol synthesis. OE did not affect UCP1 (uncoupling protein 1) (decreased in PF), beta(3) adrenergic receptors or hormone-sensitive lipase gene mRNAs, which may translate in maintaining a full thermogenic system potential. OE rats were able to maintain a less energetically stressed BAT (probably through glucose utilization) than PF rats. These changes were not paralleled in PF rats, in which lower thermogenesis and glucose preservation resulted in a heavier toll on internal fat stores. Thus the mechanism of action of OE is more complex and tissue-specific than previously assumed.