DIO Rats Research Articles

Reversal of Diet-Induced Obesity Increases Insulin Transport into Cerebrospinal Fluid and Restores Sensitivity to the Anorexic Action of Central Insulin in Male Rats

Diet-induced obesity (DIO) reduces the ability of centrally administered insulin to reduce feeding behavior and also reduces the transport of insulin from the periphery to the central nervous system (CNS). The current study was designed to determine whether reversal of high-fat DIO restores the anorexic efficacy of central insulin and whether this is accompanied by restoration of the compromised insulin transport. Adult male Long-Evans rats were initially maintained on either a low-fat chow diet (LFD) or a high-fat diet (HFD). After 22 weeks, half of the animals on the HFD were changed to the LFD, whereas the other half continued on the HFD for an additional 8 weeks, such that there were 3 groups: 1) a LFD control group (Con; n = 18), 2) a HFD-fed, DIO group (n = 17), and 3) a HFD to LFD, DIO-reversal group (DIO-rev; n = 18). The DIO reversal resulted in a significant reduction of body weight and epididymal fat weight relative to the DIO group. Acute central insulin administration (8 mU) reduced food intake and caused weight loss in Con and DIO-rev but not DIO rats. Fasting cerebrospinal fluid insulin was higher in DIO than Con animals. However, after a peripheral bolus injection of insulin, cerebrospinal fluid insulin increased in Con and DIO-rev rats but not in the DIO group. These data provide support for previous reports that DIO inhibits both the central effects of insulin and insulin's transport to the CNS. Importantly, DIO-rev restored sensitivity to the effects of central insulin on food intake and insulin transport into the CNS.

Anorexic effects of intra-VTA leptin are similar in low-fat and high-fat-fed rats but attenuated in a subgroup of high-fat-fed obese rats

Leptin is an adiposity hormone that plays an important role in regulating food intake and energy homeostasis. This study investigated the effects of a high-fat (HF) and a low-fat, high-carbohydrate/sugar (LF) diet on leptin sensitivity in the ventral tegmental area (VTA) in rats. The animals were exposed to a HF or LF diet for 16weeks. Then the effects of intra-VTA leptin (150 and 500ng/side, unilateral dose) on food intake and body weights were investigated while the animals were maintained on the HF or LF diet. Long-term exposure to the HF or LF diet led to similar body weight gain in these groups. The HF-fed animals consumed a smaller amount of food by weight than the LF-fed animals but both groups consumed the same amount of calories. The bilateral administration of leptin into the VTA decreased food intake (72h) and body weights (48h) to a similar degree in the HF and LF-fed animals. When the HF-fed animals were ranked by body weight gain it was shown that the diet-induced obese rats (HF-fed DIO, upper quartile for weight gain) were less sensitive to the effects of leptin on food intake and body weights than the diet-resistant rats (HF-fed DR, lower quartile for weight gain). A control experiment with fluorescent Cy3-labeled leptin showed that leptin did not spread beyond the borders of the VTA. This study indicates that leptin sensitivity in the VTA is the same in animals that are exposed to a HF or LF diet. However, HF-fed DIO rats are less sensitive to the effects of leptin in the VTA than HF-fed DR rats. Leptin resistance in the VTA might contribute to overeating and weight gain when exposed to a HF diet.

Cerebral Markers of the Serotonergic System in Rat Models of Obesity and After Roux‐en‐Y Gastric Bypass

Food intake and body weight are regulated by a complex system of neural and hormonal signals, of which the anorexigenic neurotransmitter serotonin (5-hydroxytryptamine or 5-HT) is central. In this study, rat models of obesity and weight loss intervention were compared with regard to several 5-HT markers. Using receptor autoradiography, brain regional-densities of the serotonin transporter (SERT) and the 5-HT(2A) and 5-HT(4) receptors were measured in (i) selectively bred polygenic diet-induced obese (pgDIO) rats, (ii) outbred DIO rats, and (iii) Roux-en-Y gastric bypass (RYGB)-operated rats. pgDIO rats had higher 5-HT(4) and 5-HT(2A) receptor binding and lower SERT binding when compared to polygenic diet-resistant (pgDR) rats. The most pronounced difference between pgDIO and pgDR rats was observed in the nucleus accumbens shell (NAcS), a brain region regulating reward aspects of feeding. No differences were found in the 5-HT markers between DIO rats, chow-fed control rats, and DIO rats experiencing a weight loss. The 5-HT markers were also similar in RYGB and sham-operated rats except for a downregulation of 5-HT(2A) receptors in the NAcS. The higher receptor and lower SERT binding in pgDIO as compared to pgDR rats corresponds to what is reported in overweight humans and suggests that the dysfunctions of the 5-HT system associated with overeating or propensity to become overweight are polygenically determined. Our results support that the obesity-prone rat model has high translational value and suggests that susceptibility to develop obesity is associated with changed 5-HT tone in the brain that may also regulate hedonic aspects of feeding.

Although the fatty-acid receptor GPR120 is upregulated in DIO rats and widely expressed in the gut it does not appear to play a key role in the regulation of GLP-1 secretion

Although the fatty-acid receptor GPR120 is upregulated in DIO rats and widely expressed in the gut it does not appear to play a key role in the regulation of GLP-1 secretion

Corrigendum

CorrigendumCorrigendumPublished Online:01 Feb 2011https://doi.org/10.1152/ajpendo.zh1-6178-corr.2011Original articleMoreSectionsPDF (407 KB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations ShareShare onFacebookTwitterLinkedInWeChat Volume 299, December 2010Perello M, Çakir I, Cyr NE, Romero A, Stuart RC, Chiappini F, Hollenberg AN, Nillni EA. Maintenance of the thyroid access during diet-induced obesity in rodents is controlled at the central level; doi:; http://ajpendo.physiology.org/cgi/content/full/299/6/E976.In this article, the wrong Western blot image was placed above the bar graph in Fig. 2C (it was actually the same image that was used in Fig. 2B). A full, revised version of Fig. 2, with the corrected Western blot image, is shown here.Fig. 2.The change in the set point of the hypothalamic-pituitary-thyroid (HPT) axis of DIO rats correlates with plasma leptin and with an increase of pSTAT3 signaling within TRH neurons. A: correlation between serum leptin and serum tiiodothyronine (T3) in lean and DIO rats (r = 0.46 and 0.66 for lean and DIO rats, respectively). Each point represents a measurement from a single animal. B and C: thyroid hormone receptor-β2 (TRβ2) and leptin receptor (ObRb) protein levels were similar in both groups of rats. To perform this, hypothalamic paraventricular nuclei (PVN) were removed from fed lean and DIO rats; proteins were extracted in RIPA lysis buffer, and TRβ2 (60 kDa), ObRb (120 kDa), and β-actin (43 kDa) levels were assayed by Western blot. In addition, brain sections of fed rats were subjected to double immunohistochemistry using anti-pSTAT3 (brown staining) and anti-pro-TRH (red fluorescent staining) antiserum. D: low-magnification images for each individual staining for each group and high-magnification merged images. Arrows point to dual-labeled cells. Scale bars, 50 (low magnification) and 20 μm (high magnification). E: bar graph of the quantitative analysis of the percentage of TRH neurons positive for pSTAT3 in the PVN of fed lean and DIO rats (n = 3 and 5/group). Values are means ± SE. *P < 0.05 vs. lean group.Download figureDownload PowerPointThis article has no references to display. Download PDF Previous Back to Top FiguresReferencesRelatedInformation Collections Related ArticlesMaintenance of the thyroid axis during diet-induced obesity in rodents is controlled at the central level 01 Dec 2010American Journal of Physiology-Endocrinology and Metabolism More from this issue > Volume 300Issue 2February 2011Pages E422-E422 Copyright & PermissionsCopyright © 2011 the American Physiological Societyhttps://doi.org/10.1152/ajpendo.zh1-6178-corr.2011History Published online 1 February 2011 Published in print 1 February 2011 Metrics

Endurance exercise training ameliorates insulin resistance and reticulum stress in adipose and hepatic tissue in obese rats

Obesity-induced endoplasmatic reticulum (ER) stress has been demonstrated to underlie the induction of obesity-induced JNK and NF-κB activation inflammatory responses, and generation of peripheral insulin resistance. On the other hand, exercise has been used as a crucial tool in obese and diabetic patients, and may reduce inflammatory pathway stimulation. However, the ability of exercise training to reverse endoplasmatic reticulum stress in adipose and hepatic tissue in obesity has not been investigated in the literature. Here, we demonstrate that exercise training ameliorates ER stress and insulin resistance in DIO-induced rats. Rats were fed with standard rodent chow (3,948 kcal kg(-1)) or high-fat diet (5,358 kcal kg(-1)) for 2 months. After that rats were submitted to swimming training (1 h per day, 5 days for week with 5% overload of the body weight for 8 weeks). Samples from epididymal fat and liver were obtained and western blot analysis was performed. Our results showed that swimming protocol reduces pro-inflammatory molecules (JNK, IκB and NF-κB) in adipose and hepatic tissues. In addition, exercise leads to reduction in ER stress, by reducing PERK and eIF2α phosphorylation in these tissues. In parallel, an increase in insulin pathway signaling was observed, as confirmed by increases in IR, IRSs and Akt phosphorylation following exercise training in DIO rats. Thus, results suggest that exercise can reduce ER stress, improving insulin resistance in adipose and hepatic tissue.

Pre-treatment with a DPP-4 Inhibitor is Infarct Sparing in Hearts from Obese, Pre-diabetic Rats

Cardiovascular risk is closely associated with insulin resistance and type 2 diabetes. Therapy based on the actions of GLP-1 is currently seen as a novel approach to treat this disease. The aims of this study was therefore to use an animal model to determine whether (i) pre-treatment of obese, insulin resistant but pre-diabetic rats with a DPP4 inhibitor, PFK275-055, could protect the heart from ischaemia/reperfusion injury and (ii) the possible mechanisms involved in such protection. Obese, pre-diabetic rats (DIO) were treated for 4 weeks with 10 mg/kg/day of the DPP4 inhibitor PFK275-055. Ex vivo perfusion was used to subject hearts to ischaemia/reperfusion to determine infarct size, functional recovery and post-ischaemic activation of proteins associated with cardiac protection. Adult ventricular cardiomyocytes were isolated to determine insulin sensitivity. Other assessments included body weight, intra-peritoneal fat weight, insulin and GLP-1 levels as well as histological evaluation of the pancreata. Results showed that DIO animals had higher body mass and intra-peritoneal fat mass than chow-fed animals. They presented with elevated plasma insulin levels and lower GLP-1 levels. Treatment with the DPP4 inhibitor resulted in smaller infarct size development in hearts from DIO rats after ischaemia/reperfusion accompanied by activation of cardioprotective kinases. GLP-1 levels were elevated and plasma insulin levels lower after treatment. In addition, the beta-cell to alpha-cell ratio of the pancreas was improved. We conclude that treatment with PFK275-055 for 4 weeks protected the heart against ischaemia/reperfusion injury, elevated GLP-1 levels and improved metabolic control in obese, pre-diabetic rats.

Synaptic input organization of the melanocortin system predicts diet-induced hypothalamic reactive gliosis and obesity

The neuronal circuits involved in the regulation of feeding behavior and energy expenditure are soft-wired, reflecting the relative activity of the postsynaptic neuronal system, including the anorexigenic proopiomelanocortin (POMC)-expressing cells of the arcuate nucleus. We analyzed the synaptic input organization of the melanocortin system in lean rats that were vulnerable (DIO) or resistant (DR) to diet-induced obesity. We found a distinct difference in the quantitative and qualitative synaptology of POMC cells between DIO and DR animals, with a significantly greater number of inhibitory inputs in the POMC neurons in DIO rats compared with DR rats. When exposed to a high-fat diet (HFD), the POMC cells of DIO animals lost synapses, whereas those of DR rats recruited connections. In both DIO rats and mice, the HFD-triggered loss of synapses on POMC neurons was associated with increased glial ensheathment of the POMC perikarya. The altered synaptic organization of HFD-fed animals promoted increased POMC tone and a decrease in the stimulatory connections onto the neighboring neuropeptide Y (NPY) cells. Exposure to HFD was associated with reactive gliosis, and this affected the structure of the blood-brain barrier such that the POMC and NPY cell bodies and dendrites became less accessible to blood vessels. Taken together, these data suggest that consumption of an HFD has a major impact on the cytoarchitecture of the arcuate nucleus in vulnerable subjects, with changes that might be irreversible due to reactive gliosis.

Diet-induced obesity, exogenous leptin-, and MADB106 tumor cell challenge affect tissue leukocyte distribution and serum levels of cytokines in F344 rats

The adipocyte-derived catabolic protein leptin alters cell-mediated immunity and cytokine crosstalk. This may provide new insights into the altered immune response, seen in obese individuals. Therefore, we determined the tissue distribution of immune cells in diet-induced obese (dio) and normal weight F344 rats challenged with MADB106 tumor cells or leptin. Immune cell distribution in blood (by FACS analysis) and tissues (NK cells in spleen and liver, immunohistologically) as well as pro-inflammatory cytokines (IL-6, TNF-α; by flow cytometry) were investigated in 28 normal weight and 28 dio rats (n=4-6/group). Pro-inflammatory cytokines were increased 3-fold for IL-6 and 7-fold for TNF-α in obese animals. Higher numbers of blood monocytes and NK cells were found in obese as compared to normal weight animals. In dio rats challenged with leptin and MADB106 tumor cells, monocyte numbers were decreased as compared to the obese control animals. Immunohistochemistry revealed an altered NK cell distribution in a compartment-, treatment-, and bodyweight-specific manner. In conclusion, our data reveal a distinct distribution pattern of monocytes and NK cells in dio rats as compared to normal weight littermates and an additional modulatory effect of a leptin- and MADB106 tumor cell challenge.

W1863 Functional Characteristics of Calcium and Potassium Channels in Diet Induced Obese (Dio) Rats

W1863 Functional Characteristics of Calcium and Potassium Channels in Diet Induced Obese (Dio) Rats

The anorexigenic effects of metformin involve increases in hypothalamic leptin receptor expression

Metformin demonstrates anorectic effects in vivo and inhibits neuropeptide Y expression in cultured hypothalamic neurons. Here we investigated the mechanisms implicated in the modulation of feeding by metformin in animals rendered obese by long-term high-fat diet (diet-induced obesity [DIO]) and in animals resistant to obesity (diet resistant [DR]). Male Long-Evans rats were kept on normal chow feeding (controls) or on high-fat diet (DIO, DR) for 6 months. Afterward, rats were treated 14 days with metformin (75 mg/kg) or isotonic sodium chloride solution and killed. Energy efficiency, metabolic parameters, and gene expression were analyzed at the end of the high-fat diet period and after 14 days of metformin treatment. At the end of the high-fat diet period, despite higher leptin levels, DIO rats had higher levels of hypothalamic neuropeptide Y expression than DR or control rats, suggesting a central leptin resistance. In DIO but also in DR rats, metformin treatment induced significant reductions of food intake accompanied by decreases in body weight. Interestingly, the weight loss achieved by metformin was correlated with pretreatment plasma leptin levels. This effect was paralleled by a stimulation of the expression of the leptin receptor gene (ObRb) in the arcuate nucleus. These data identify the hypothalamic ObRb as a gene modulated after metformin treatment and suggest that the anorectic effects of the drug are potentially mediated via an increase in the central sensitivity to leptin. Thus, they provide a rationale for novel therapeutic approaches associating leptin and metformin in the treatment of obesity.

Insulin Secretagogue Bioactivity of Finger Citron Fruit (Citrus medicaL. var.SarcodactylisHort, Rutaceae)

Finger citron [Citrus medica L. var. Sarcodactylis Hort, Rutaceae] (FC) fruits, widely cultivated in Japan, the southern provinces of China and Taiwan, are commonly used as functional vegetables and preserved as sweetmeats. Previously we identified the major compounds in essential oils (% in EO) of FC fruits to be d-limonene (51.24), gamma-terpenene (33.71), alpha-pinene (3.40), and beta-pinene (2.88). Documented evidence on its insulin secretion characteristics is still lacking. In parallel to compositional analysis, we performed in vivo the safety, hypoglycemic, and antidiabetic tests in Sprague-Dawley-SPF rats and Wistar DIO rats respectively. By kinetic analysis on the hypoglycemic patterns of the intraperitoneal glucose tolerance (IPGTT) and the insulin-glucose tolerance tests (IGTT), its insulin secretagogue effect was confirmed. In conclusion, FC fruits that concomitantly possess insulin secretagogue and slimming effects would be very beneficial to type 2 diabetes mellitus patients.

Glutamate permeability at the blood-brain barrier in insulinopenic and insulin-resistant rats

The influence of diabetes on brain glutamate (GLU) uptake was studied in insulinopenic (streptozotocin [STZ]) and insulin-resistant (diet-induced obesity [DIO]) rat models of diabetes. In the STZ study, adult male Sprague-Dawley rats were treated with STZ (65 mg/kg intravenously) or vehicle and studied 3 weeks later. The STZ rats had elevated plasma levels of glucose, ketone bodies, and branched-chain amino acids; brain uptake of GLU was very low in both STZ and control rats, examined under conditions of normal and greatly elevated (by intravenous infusion) plasma GLU concentrations. In the DIO study, rats ingested a palatable, high-energy diet for 2 weeks and were then divided into weight tertiles: rats in the heaviest tertile were designated DIO; rats in the lightest tertile, diet-resistant (DR); and rats in the intermediate tertile, controls. The DIO and DR rats continued to consume the high-energy diet for 4 more weeks, whereas the control rats were switched to standard rat chow. All rats were studied at 6 weeks (subgroups were examined under conditions of normal or elevated plasma GLU concentrations). The DIO rats ate more food and were heavier than the DR or control rats and had higher plasma leptin levels and insulin-glucose ratios. In all diet groups, the blood-brain barrier showed very low GLU penetration and was unaffected by plasma GLU concentration. Brain GLU uptake also did not differ among the diet groups. Together, the results indicate that the blood-brain barrier remains intact to the penetration of GLU in 2 models of diabetes under the conditions examined.

Pioglitazone, but not balaglitazone, negatively affects bone formation rates in male dio rats

Pioglitazone, but not balaglitazone, negatively affects bone formation rates in male dio rats

Three weeks of post-weaning exercise in DIO rats fed HE diet increases central leptin sensitivity and hypothalamic 125leptin receptor binding

Three weeks of post-weaning exercise in DIO rats fed HE diet increases central leptin sensitivity and hypothalamic 125leptin receptor binding

Hypertension in the diet induced obese rat is independent of body weight gain

This study tested the hypothesis that the elevated mean arterial pressure (MAP) observed in the diet induced obese rats (DIO) on normal chow diet is associated with early life weight gain. A radiotelemetry transmitter was implanted in the femoral artery of 4 week old DIO and diet resistant (DR) rats for measurements of MAP and heart rate (HR) over a four week period. All rats were maintained on a normal diet. At 5 weeks, MAP was higher in DIO vs. DR rats (97±1 vs. 89±1 mm Hg, p&lt;0.05), while body weight was not different (DIO: 133±5 gms and DR: 127±2 gms, p&gt;0.05). At 9 weeks, MAP was still significantly elevated (DIO: 114±1 mmHg vs. DR: 103±1 mmHg), but the DIO rats weighed more than the DR rats (336±12 vs. 300±6 gms, p&lt;0.05). At 9 weeks, there was no difference in plasma renin activity (4.0±0.6 vs. 3.5±0.6 ng/ml/hr, p&gt;0.05), aldosterone (82±24 vs. 55±19 pg/ml, p&gt;0.05) and leptin (3.0±0.2 vs. 3.4±0.4 pg/ml, p&gt;0.05). MAP response to ganglionic blockade was similar between the two groups of rats (−43±2 vs. –37±2 mmHg). However, plasma insulin was significantly elevated in the DIO compared to the DR rats (DIO: 1.9±0.2 pg/ml vs. DR: 1.5±0.1 pg/ml). In conclusion, hypertension in DIO rats precedes an enhanced weight gain suggesting that genetic factors predetermine the hypertensive phenotype independent of body weight.

A weight loss formula, WL2, alters gene expressions in endocrine organs of DIO rats

We reported altered gene expressions in liver, muscle and adipose tissues, improving glucose, lipid and energy metabolisms, in response to WL2 therapy (FASEB J 21:A1352 &amp; 21:A329, 2007). We further explored via microarray analysis the effects of WL2 (1.5g/kg for 10wks; n=20) in gene expressions in adrenal gland (AG), thyroid (T), hypothalamus (HT) and pituitary (P) of DIO rats. Along with significantly less gain of body weight, gene expressions were altered in many metabolic pathways in WL2 treated rats, as compared to controls (all p&lt;0.05): (1) up‐regulated: a 3‐fold increase in gene expressions of calcitonin/calcitonin related polypeptide (Calca) in P, and a 68% increase in gene expressions of somatostatin receptor 2 (Sstr2) in AG; (2) down‐regulated: cannabinoid receptor family members (Cnr1, Cnr2) in AG, HT and P, all pro‐inflammation factors in endocrine organs, and thyroid hormone receptor in HT (−30%). Our data suggest that the weight loss by WL2 is a multi‐target outcome through alterations of multiple metabolic pathways, including regulating endocrine functions towards optimization of glucose, lipid, and energy metabolisms and anti‐inflammation.

Different functional responsibility of the small intestine to high-fat/high-energy diet determined the expression of obesity-prone and obesity-resistant phenotypes in rats

The objective of the present experiment was to assess the involvement of small intestine in expression of susceptibility or resistance to the high-fat/high-energy diet. The investigation was carried out in adult male Sprague-Dawley rats fed either standard laboratory diet (3.2 kcal/g, 9.5 % fat) or high-fat (HF) diet (4.04 kcal/g, 30 % fat) for 4 weeks as well as in HF rats that were retrospectively designated on the bases of their higher or lower weight gain as sensitive (DIO) or resistant (DR) to obesity. Our results revealed in HF group significant increase in energy intake, food efficiency, weight gain and Lee s index of obesity. Moreover, in comparison with controls, a significantly increased duodenal and jejunal alkaline phosphatase (AP) and alpha-glucosidase activity as well as hypertrophy of jejunal mucosa (increased protein/DNA ratio) were observed in HF fed rats. In contrast, intestinal function was inversely related to energy intake or to the development of adiposity in DIO vs. DR rats. The DR rats had significantly greater AP and alpha-glucosidase activity and more pronounced suppression of energy intake than obese DIO rats. It indicates that the increase of enzyme activities and the lowered effectiveness of nutrient absorption might be a significant factor preventing the expression of obesity proneness. This information contributes to a better understanding of a complex interaction between HF diet feeding and small intestinal adaptability, which determines the energy homeostasis and predict the ability to resist or develop obesity in these phenotypes.

Rewired to be thin? When exercise hits the brain

in this issue of the American Journal of Physiology—Regulatory, Comparative and Integrative Physiology , the article by Patterson et al. ([17][1]) demonstrates that just 3 wk of voluntary exercise in the postnatal period mitigates weight gain in obesity-prone rats for at least 10 wk after

Reduced capacity for fatty acid oxidation in rats with inherited susceptibility to diet-induced obesity

High-fat, energy-dense diets promote weight gain and obesity in humans and other animals, but the mechanisms underlying such diet-induced obesity remain elusive. To determine whether a reduced capacity to oxidize fat is involved in the etiology of diet-induced obesity, we examined different measures of fatty acid oxidation in rats selectively bred for susceptibility (DIO) or resistance (DR) to dietary obesity before and after they were fed a high-fat diet and became obese. DIO rats eating a low-fat diet oxidized less dietary fatty acid in vivo and had lower levels of plasma ketone bodies during fasting compared with DR rats. Lean DIO rats fed a low-fat diet showed reduced liver messenger RNA expression of CD36, which transports fatty acids across cell membranes, and long-chain acyl-coenzyme A dehydrogenase (ACADL), which catalyzes the first step in the mitochondrial β-oxidation of fatty acids. The deficit in CD36 and ACADL messenger RNA expression was also seen in obese DIO rats that had been eating a high-fat diet and, in addition, was accompanied by reduced expression of liver carnitine palmitoyl transferase I, the enzyme that mediates transport of long-chain fatty acids into mitochondria. No differences were found in the expression of liver enzymes involved in fat synthesis; however, in muscle, DIO rats fed the low-fat, but not high-fat, diet showed greater expression of diacylglycerol O-acyltransferase 1 and lipoprotein lipase than did DR rats. Expression of muscle enzymes involved in fatty acid oxidation was similar in the 2 groups. These findings provide a metabolic mechanism for the development of diet-induced obesity and thus suggest potential targets for intervention strategies to treat or prevent it.