Diet-induced Obese Rodents Research Articles

Impact of Obesity on Development and Progression of Mammary Tumors in Preclinical Models of Breast Cancer

Overweight and/or obesity are known risk factors for postmenopausal breast cancer. More recently increased body weight has also been associated with poor prognosis for premenopausal breast cancer. This relationship has primarily been identified through epidemiological studies. Additional information from in vitro studies has also been produced in attempts to delineate mechanisms of action for the association of obesity and body weight and breast cancer. This approach has identified potential growth factors such as insulin, leptin, estrogen and IGF-I which are reported to be modulated by body weight changes. However, in vitro studies are limited in scope and frequently use non-physiological concentrations of growth factors, while long follow-up is needed for human studies. Preclinical animal models provide an intermediary approach to investigate the impact of body weight and potential growth factors on mammary/breast tumor development and progression. Here results of a number of studies addressing this issue are presented. In the majority of the studies either genetically-obese or diet-induced obese rodent models have been used to investigate spontaneous, transgenic and carcinogen-induced mammary tumor development. To study tumor progression the major focus has been allograft studies in mice with either genetic or dietary-induced obesity. In general, obesity has been demonstrated to shorten mammary tumor latency and to impact tumor pathology. However, in rodents with defects in leptin and other growth factors the impact of obesity is not as straightforward. Future studies using more physiologically relevant obesity models and clearly distinguishing diet composition from body weight effects will be important in continuing to understand the factors associated with body weight's impact on mammary/breast cancer development and progression.

Role of oxytocin signaling in the regulation of body weight

Obesity and its associated metabolic disorders are growing health concerns in the US and worldwide. In the US alone, more than two-thirds of the adult population is classified as either overweight or obese [1], highlighting the need to develop new, effective treatments for these conditions. Whereas the hormone oxytocin is well known for its peripheral effects on uterine contraction during parturition and milk ejection during lactation, release of oxytocin from somatodendrites and axonal terminals within the central nervous system (CNS) is implicated in both the formation of prosocial behaviors and in the control of energy balance. Recent findings demonstrate that chronic administration of oxytocin reduces food intake and body weight in diet-induced obese (DIO) and genetically obese rodents with impaired or defective leptin signaling. Importantly, chronic systemic administration of oxytocin out to 6weeks recapitulates the effects of central administration on body weight loss in DIO rodents at doses that do not result in the development of tolerance. Furthermore, these effects are coupled with induction of Fos (a marker of neuronal activation) in hindbrain areas (e.g. dorsal vagal complex (DVC)) linked to the control of meal size and forebrain areas (e.g. hypothalamus, amygdala) linked to the regulation of food intake and body weight. This review assesses the potential central and peripheral targets by which oxytocin may inhibit body weight gain, its regulation by anorexigenic and orexigenic signals, and its potential use as a therapy that can circumvent leptin resistance and reverse the behavioral and metabolic abnormalities associated with DIO and genetically obese models.

Hepatic glycogen cycling contributes to glucose lowering effects of the glucokinase activator LCZ960

Glucokinase (GK) acts as a glucose sensor by facilitating glucose phosphorylation into glucose-6-phosphate (G6P) in the liver and pancreas, the two key target tissues. LCZ960, a glucokinase activator exerts a stimulatory effect on GK activity in hepatocytes in vitro. This study aimed to verify in vivo that LCZ960 stimulates glucose uptake primarily through a mechanism involving hepatic GK activation. Acute and chronic LCZ960 treatment-induced changes in glycemia and hepatic glucose turnover were measured in high fat diet-induced obese (DIO) mice and rats. G6P production and glycogen cycling were quantified by 13C-MR spectroscopy during a [1-13C]glucose infusion, followed by a pulse-chase with [12C]glucose to mimic postprandial conditions in rats. Acute treatment with LCZ960 dose-dependently reduced blood glucose without causing hypoglycemia in DIO mice. Chronic LCZ960 treatment maintained normoglycemia and improved glucose tolerance without increased insulin secretion in DIO mice and rats. In rats, LCZ960 stimulated a 240% increase (P<0.05) in the glycogen synthase flux. However, due to a much higher glycogen breakdown (LCZ960: 48±15 vs control: 4±1μmol/kg/min, P<0.05), this translated to only a 46% (ns) increase in glycogen storage (Vsyn net, LCZ960: 64±26 vs control: 43±6μmol/kg/min). Despite a 4-fold increase in hepatic glycogen turnover (LCZ960: 36.0±5.5% vs control: 8.3±2.0%), LCZ960 did not impact glucose-stimulated G6P accumulation. LCZ960 did not cause hypoglycemia in DIO rodents. Under hyperglycemic conditions, LCZ960 induced a robust increase in hepatic glycogen cycling. Since net hepatic glycogen storage is diminished in type 2 diabetes patients, stimulation of glycogen synthesis may contribute to the anti-hyperglycemic properties of glucokinase activation.

A dairy‐based high calcium diet improves glucose homeostasis and reduces steatosis in the context of preexisting obesity

High dietary calcium (Ca) in the context of a dairy food matrix has been shown to reduce obesity development and associated inflammation in diet-induced obese (DIO) rodents. The influence of Ca and dairy on these phenotypes in the context of preexisting obesity is not known. Furthermore, interpretations have been confounded historically by differences in body weight gain among DIO animals fed dairy-based protein or high Ca. Adiposity along with associated metabolic and inflammatory outcomes were measured in DIO mice previously fattened for 12 week on a soy protein-based obesogenic high fat diet (45% energy, 0.5% adequate Ca), then fed one of three high fat diets (n = 29-30/group) for an additional 8 week: control (same as lead-in diet), high-Ca (1.5% Ca), or high-Ca + nonfat dry milk (NFDM). Mice fed high-Ca + NFDM had modestly, but significantly, attenuated weight gain compared to mice fed high-Ca or versus controls (P < 0.001), whereas mice fed high-Ca alone had increased weight gain compared to controls (P < 0.001). Total measured adipose depot weights between groups were similar, as were white adipose tissue inflammation and macrophage infiltration markers (e.g. TNFα, IL-6, CD68 mRNAs). Mice fed high-Ca + NFDM had significantly improved glucose tolerance following a glucose tolerance test, and markedly lower liver triglycerides compared to high-Ca and control groups. Improved metabolic phenotypes in prefattened DIO mice following provision of a diet enriched with dairy-based protein and carbohydrates appeared to be driven by non-Ca components of dairy and were observed despite minimal differences in body weight or adiposity.

Diet‐Induced Models of Obesity (DIO) in Rodents

Obesity results from a complex interplay between a susceptible genotype and an environment that both promotes increased caloric intake and enables sustained decreases in energy expenditure. One commonly employed approach to modeling obesity in preclinical species is the diet-induced obese (DIO) rodent. Here, theoretical and practical considerations for producing obese rodents via dietary manipulation, and for assessing drug-induced changes in food intake and body weight are described. Based on these considerations, a standardized protocol for diet-induced obesity in both mouse and rat is provided and sample data from these models are also described.

2071 HYPEROXALURIA AND NEPHROPATHY IN OBESE RATS FOLLOWING RYGB

You have accessJournal of UrologyStone Disease: Basic Research I1 Apr 20122071 HYPEROXALURIA AND NEPHROPATHY IN OBESE RATS FOLLOWING RYGB Shannon Moore, Marguerite Hatch, Amandeep Chadda, Bryce Bergeron, Mary Reinhard, and Benjamin Canales Shannon MooreShannon Moore Gainesville, FL More articles by this author , Marguerite HatchMarguerite Hatch Gainesville, FL More articles by this author , Amandeep ChaddaAmandeep Chadda Gainesville, FL More articles by this author , Bryce BergeronBryce Bergeron Gainesville, FL More articles by this author , Mary ReinhardMary Reinhard Gainesville, FL More articles by this author , and Benjamin CanalesBenjamin Canales Gainesville, FL More articles by this author View All Author Informationhttps://doi.org/10.1016/j.juro.2012.02.2237AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookTwitterLinked InEmail INTRODUCTION AND OBJECTIVES Hyperoxaluria is a common yet poorly understood complication of Roux-en-Y gastric bypass (RYGB) surgery, portending high calcium oxalate stone risk and oxalate nephropathy. To better define the effect of bariatric surgery on renal physiology, in particular hyperoxaluria, we performed RYGB in diet-induced obese (DIO) rodents and compare urinary oxalate excretion and renal histology to sham pair-fed (PF) and sham obese (SO) controls on both normal and high oxalate diets. METHODS Three-week old male Sprague-Dawley rats, given 60% high fat diet for 20 weeks, were randomized to sham procedure with gastric mobilization without transection or RYGB utilizing a stapled stomach pouch and hand-sewn 30 cm biliopancreatic and 10 cm Roux limbs. After 3 weeks of post-surgical recovery, animals were assigned to no oxalate/40% fat (No OX) or 1.5% potassium oxalate/40% fat (High OX) diets for 10 or 20 weeks. SO rats continued on diet ad libitum while sham PF rats ingested a similar amount of food as a paired-RYGB rat from the previous day. Daily weights and food intake were recorded. Urine studies for oxalate were collected at baseline and every 5 weeks. At study endpoint, renal histology was assessed using a quantitative glomerular and tubular scoring system by an experienced veterinary pathologist. RESULTS RYGB rodents had significant reductions in body weight at 10 weeks (n=8; 136 ± 7 gm, p<0.001) and 20 weeks (n=5; 174 ± 14 gm, p<0.001) compared to PF and SO controls (n=18). Urine oxalate was slightly higher than baseline in No OX RYGB animals (mean 9.2 ± 3 μmol/day; p=0.07) and unchanged in PF and SO animals on both No and High OX diets (mean 4.6 ± 1.74 μmol/day; p=0.36). High OX RYGB rats had significantly elevated urinary oxalate at 10 weeks (13 ± 9 μmol/day; p=0.05), 15 weeks (48 ± 21 μmol/day; p<0.001), and 20 weeks (51 ± 16 μmol/day; p<0.001). Additionally, regardless of diet, 10 and 20 week RYGB animals had more glomerular and tubular lesions and received higher glomerular and tubular lesion scores compared to SO and sham PF controls (p<0.001). CONCLUSIONS RYGB rodents on high oxalate diet long-term had a 10 fold increase in urinary oxalate compared to weight, age, and diet-matched controls. Irrespective of urinary oxalate levels, RYGB in this DIO rodent model is associated with sustained weight loss and progressive glomerular and tubular nephropathy, suggesting that the observed renal damage is occurring through pathways other than oxalate. Prospective studies are underway to better define the injurious mechanisms in this model. © 2012 by American Urological Association Education and Research, Inc.FiguresReferencesRelatedDetails Volume 187Issue 4SApril 2012Page: e835 Peer Review Report Advertisement Copyright & Permissions© 2012 by American Urological Association Education and Research, Inc.MetricsAuthor Information Shannon Moore Gainesville, FL More articles by this author Marguerite Hatch Gainesville, FL More articles by this author Amandeep Chadda Gainesville, FL More articles by this author Bryce Bergeron Gainesville, FL More articles by this author Mary Reinhard Gainesville, FL More articles by this author Benjamin Canales Gainesville, FL More articles by this author Expand All Advertisement Advertisement PDF downloadLoading ...

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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

Bypassing the Duodenum Does Not Improve Insulin Resistance Associated With Diet-Induced Obesity in Rodents

Roux-en-y gastric bypass (RYGB) surgery rapidly improves glucose tolerance and reverses insulin resistance in obese patients. It has been hypothesized that this effect is mediated by the diversion of nutrients from the proximal small intestine. We utilized duodenal-jejunal bypass (DJB) as a modification of gastric bypass to determine the effect of nutrient diversion from the foregut without gastric restriction on insulin resistance in obese rats. The effects of DJB or Sham surgery on glucose homeostasis were determined in both high-fat-fed Long-Evans and Wistar rats. Body weight and food intake were measured weekly postoperatively, and body composition was monitored before and after surgery. Glucose tolerance was tested before and as early as 1 month postoperation; additionally, in Wistar rats, insulin sensitivity was determined by a hyperinsulinemic-euglycemic clamp (HIEC). DJB did not affect body weight, body composition, glucose tolerance, or insulin concentrations over the period of the study. The average glucose infusion rate (GIR) during the HIEC was 6.2 ± 1.16 mg/kg/min for Sham rats compared to 7.2 ± 1.71 mg/kg/min for DJB rats (P = 0.62), and neither endogenous glucose production (EGP; P = 0.81) nor glucose utilization (glucose disappearance (R(d)), P = 0.59) differed between DJB and Sham rats. DJB does not affect insulin resistance induced by a high-fat diet in Long-Evans and Wistar rats. These data suggest that duodenal bypass alone is an insufficient mechanism to alter insulin sensitivity independent of weight loss in obese, nondiabetic rodents.

Correlations between Hippocampal Neurogenesis and Metabolic Indices in Adult Nonhuman Primates

Increased neurogenesis in feeding centers of the murine hypothalamus is associated with weight loss in diet-induced obese rodents (Kokoeva et al., 2005 and Matrisciano et al., 2010), but this relationship has not been examined in other species. Postmortem hippocampal neurogenesis rates and premortem metabolic parameters were statistically analyzed in 8 chow-fed colony-reared adult bonnet macaques. Dentate gyrus neurogenesis, reflected by the immature neuronal marker, doublecortin (DCX), and expression of the antiapoptotic gene factor, B-cell lymphoma 2 (BCL-2), but not the precursor proliferation mitotic marker, Ki67, was inversely correlated with body weight and crown-rump length. DCX and BCL-2 each correlated positively with blood glucose level and lipid ratio (total cholesterol/high-density lipoprotein). This study demonstrates that markers of dentate gyrus neuroplasticity correlate with metabolic parameters in primates.

Maintenance of the thyroid axis during diet-induced obesity in rodents is controlled at the central level

The hypothalamic-pituitary-thyroid (HPT) axis is a major contributor in maintaining energy expenditure and body weight, and the adipocyte hormone leptin regulates this axis by increasing TRH levels in the fed state. Leptin stimulates TRH directly in the hypothalamic paraventricular nucleus (PVN; direct pathway) and indirectly by regulating proopiomelnocortin neurons in the hypothalamic arcuate nucleus (ARC; indirect pathway). Whereas the indirect pathway is fully functional in lean animals, it is inactive during diet-induced obesity (DIO) because of the establishment of leptin resistance. Despite this, the HPT axis activity in obese humans and rodents remains within the normal levels or slightly higher. Therefore, in this study, we aimed to determine the mechanism(s) by which the HPT axis is still active despite leptin resistance. With a combination of using the Sprague-Dawley rat physiological model and the Zuker rat that bears a mutation in the leptin receptor, we were able to demonstrate that under DIO conditions the HPT axis is regulated at the central level, but only through the direct pathway of leptin action on TRH neurons. Deiodinase enzymes, which are present in many tissues and responsible for converting thyroid hormones, were not statistically different between lean and DIO animals. These data suggest that the increase in T(4/3) seen in obese animals is due mostly to central leptin action. We also found that T(3) feedback inhibition on the prepro-TRH gene is controlled partially by leptin-induced pSTAT3 signaling via the TRH promoter. This interactive relationship between T(3) and pSTAT3 signaling appears essential to maintain the HPT axis at normal levels in conditions such as obesity.

Bypassing the duodenum does not improve insulin resistance associated with diet-induced obesity in rodents

Bypassing the duodenum does not improve insulin resistance associated with diet-induced obesity in rodents

Subcutaneous oxyntomodulin analogue administration reduces body weight in lean and obese rodents

To determine the efficacy of a long-acting oxyntomodulin (OXM) analogue, OXM6421, in inhibiting food intake and decreasing body weight in lean and diet-induced obese (DIO) rodents. The glucagon-like peptide-1 (GLP-1) receptor binding affinity and efficacy, sensitivity to enzymatic degradation in vitro and persistence in the circulation after peripheral administration were investigated for OXM6421 and compared with native OXM. The chronic effect of OXM6421 on food intake, body weight and energy expenditure was examined in lean rats, and its anti-obesity potential was evaluated in DIO mice. OXM6421 showed enhanced GLP-1 receptor binding affinity and cyclic adenosine monophosphate (cAMP) stimulation, and higher resistance to enzymatic degradation by dipeptidyl peptidase IV (DPP-IV) and neutral endopeptidase (NEP) compared with native OXM. OXM6421 persisted longer in the circulation than OXM after peripheral administration. Acute administration of OXM6421 potently inhibited food intake in lean rodents, with cumulative effects lasting up to 24 h. In lean rats, daily subcutaneous (s.c.) administration of OXM6421 caused greater weight loss than the pair-fed animals, and a higher rate of oxygen consumption than both the pair-fed and the saline controls. In DIO mice, continuous s.c. infusion of OXM6421 resulted in a significant weight loss, accompanied by an improvement in glucose homeostasis and an increase in circulating adiponectin levels. Once-daily s.c. administration of OXM6421 for 21 days caused sustained weight loss in DIO mice. OXM6421 induces negative energy balance in both lean and obese rodents, suggesting that long-acting OXM analogues may represent a potential therapy for obesity.

Diet-induced obesity alters behavior as well as serum levels of corticosterone in F344 rats

Obesity is an increasing socio-economic health problem. Diet-induced obese (DIO) rodents are widely used as a model of obesity in humans. However, there is no comprehensive data about the behavioral phenotype of DIO rodents. Therefore, the aim of the present study was to determine whether a high-fat-diet changes behavioral patterns of DIO Fischer 344 (F344) rats in comparison with lean littermates. The behavioral tests (homecage, holeboard, social interaction, and hotplate) were performed in 28 normal-weight and 28 male DIO F344 rats (mean age: 16 weeks) and revealed a significantly higher level of anxiety- and aggression-related parameters in obese rats, whereas their pain threshold was significantly lower. Fitting to a different behavioral response, basal corticosterone levels (measured by RIA) of obese animals were significantly elevated (16.0 ng/ml vs. 12.5 ng/ml; p < 0.01). We conclude that obese rats differ in various aspects from their lean littermates. The altered behavioral characteristics displayed by DIO F344 rats have to be considered in further experiments involving DIO rodents.

Enhanced Weight Loss With Pramlintide/Metreleptin: An Integrated Neurohormonal Approach to Obesity Pharmacotherapy

The neurohormonal control of body weight involves a complex interplay between long-term adiposity signals (e.g., leptin), and short-term satiation signals (e.g., amylin). In diet-induced obese (DIO) rodents, amylin/leptin combination treatment led to marked, synergistic, fat-specific weight loss. To evaluate the weight-lowering effect of combined amylin/leptin agonism (with pramlintide/metreleptin) in human obesity, a 24-week, randomized, double-blind, active-drug-controlled, proof-of-concept study was conducted in obese or overweight subjects (N = 177; 63% female; 39 +/- 8 years; BMI 32.0 +/- 2.1 kg/m(2); 93.3 +/- 13.2 kg; mean +/- s.d.). After a 4-week lead-in period with pramlintide (180 microg b.i.d. for 2 weeks, 360 microg b.i.d. thereafter) and diet (40% calorie deficit), subjects achieving 2-8% weight loss were randomized 1:2:2 to 20 weeks of treatment with metreleptin (5 mg b.i.d.), pramlintide (360 microg b.i.d.), or pramlintide/metreleptin (360 microg/5 mg b.i.d.). Combination treatment with pramlintide/metreleptin led to significantly greater weight loss from enrollment to week 20 (-12.7 +/- 0.9%; least squares mean +/- s.e.) than treatment with pramlintide (-8.4 +/- 0.9%; P < 0.001) or metreleptin (-8.2 +/- 1.3%; P < 0.01) alone (evaluable, N = 93). The greater reduction in body weight was significant as early as week 4, and weight loss continued throughout the study, without evidence of a plateau. The most common adverse events with pramlintide/metreleptin were injection site events and nausea, which were mostly mild to moderate and decreased over time. These results support further development of pramlintide/metreleptin as a novel, integrated neurohormonal approach to obesity pharmacotherapy.

GRP78 expression inhibits insulin and ER stress–induced SREBP-1c activation and reduces hepatic steatosis in mice

Hepatic steatosis is present in insulin-resistant obese rodents and is concomitant with active lipogenesis. Hepatic lipogenesis depends on the insulin-induced activation of the transcription factor SREBP-1c. Despite prevailing insulin resistance, SREBP-1c is activated in the livers of genetically and diet-induced obese rodents. Recent studies have reported the presence of an ER stress response in the livers of obese ob/ob mice. To assess whether ER stress promotes SREBP-1c activation and thus contributes to lipogenesis, we overexpressed the chaperone glucose-regulated protein 78 (GRP78) in the livers of ob/ob mice using an adenoviral vector. GRP78 overexpression reduced ER stress markers and inhibited SREBP-1c cleavage and the expression of SREBP-1c and SREBP-2 target genes. Furthermore, hepatic triglyceride and cholesterol contents were reduced, and insulin sensitivity improved, in GRP78-injected mice. These metabolic improvements were likely mediated by restoration of IRS-2 expression and tyrosine phosphorylation. Interestingly, GRP78 overexpression also inhibited insulin-induced SREBP-1c cleavage in cultured primary hepatocytes. These findings demonstrate that GRP78 inhibits both insulin-dependent and ER stress-dependent SREBP-1c proteolytic cleavage and explain the role of ER stress in hepatic steatosis in obese rodents.

Peptide YY: Food for thought

Obtaining a fuller understanding of gut hormones as mediators of appetite regulation and energy homeostasis has never been so important with obesity rates increasing at pandemic proportions. The role of the gut hormone peptide YY 3–36 (PYY3–36) in particular has sparked interest since the discovery of its anorectic effect in obese rodents and humans. Fasting circulating PYY concentrations correlate negatively with BMI and waist circumference in humans, whilst postprandial PYY levels predict subsequent changes in weight over a period of at least 6 months. Furthermore, Pyy null mice demonstrate increased adiposity and hyperphagia, which is reversed by exogenous PYY3–36. Chronic administration of PYY3–36 to diet-induced obese rodents has shown a dose-dependent reduction in adiposity. Taken in concert, these findings suggest that the PYY system may hold significant potential in the treatment and prevention of obesity.

Amylin-Mediated Restoration of Leptin Responsiveness in Diet-Induced Obesity: Magnitude and Mechanisms

Previously, we reported that combination treatment with rat amylin (100 microg/kg.d) and murine leptin (500 microg/kg.d) elicited greater inhibition of food intake and greater body weight loss in diet-induced obese rats than predicted by the sum of the monotherapy conditions, a finding consistent with amylin-induced restoration of leptin responsiveness. In the present study, a 3 x 4 factorial design was used to formally test for a synergistic interaction, using lower dose ranges of amylin (0, 10, and 50 microg/kg.d) and leptin (0, 5, 25, and 125 microg/kg.d), on food intake and body weight after 4 wk continuous infusion. Response surface methodology analysis revealed significant synergistic anorexigenic (P < 0.05) and body weight-lowering (P < 0.05) effects of amylin/leptin combination treatment, with up to 15% weight loss at doses considerably lower than previously reported. Pair-feeding (PF) experiments demonstrated that reduction of food intake was the predominant mechanism for amylin/leptin-mediated weight loss. However, fat loss was 2-fold greater in amylin/leptin-treated rats than PF controls. Furthermore, amylin/leptin-mediated weight loss was not accompanied by the counterregulatory decrease in energy expenditure and chronic shift toward carbohydrate (rather than fat) utilization observed with PF. Hepatic gene expression analyses revealed that 28 d treatment with amylin/leptin (but not PF) was associated with reduced expression of genes involved in hepatic lipogenesis (Scd1 and Fasn mRNA) and increased expression of genes involved in lipid utilization (Pck1 mRNA). We conclude that amylin/leptin interact synergistically to reduce body weight and adiposity in diet-induced obese rodents through a number of anorexigenic and metabolic effects.

Assessment of Diet‐induced Obese Rats as an Obesity Model by Comparative Functional Genomics

We applied a comparative functional genomics approach to evaluate whether diet-induced obese (DIO) rats serve as an effective obesity model. Gene-expression profiles of epididymal fat from DIO and lean rats were generated using microarrays and compared with the published array data of obese and non-obese human subcutaneous adipocytes. Caloric intake and fuel efficiency were significantly higher in DIO rats, which resulted in increased body weight and adiposity. Circulating glucose, cholesterol, triglyceride, insulin, and leptin levels in DIO rats were significantly higher than those in the lean controls. DIO rats also exhibited impaired insulin sensitivity. A direct comparison of gene-expression profiles from DIO and lean rats and those from obese and non-obese humans revealed that global gene-expression patterns in DIO rat fat resemble those of obese human adipocytes. Differentially expressed genes between obese and non-obese subjects in both human and rat studies were identified and associated with biological pathways by mapping genes to Gene Ontology (GO) categories. Immune response-related genes and angiogenesis-related genes exhibited significant upregulation in both obese humans and DIO rats when compared with non-obese controls. However, genes in fatty acid metabolism and oxidation exhibited a broad downregulation only in obese human adipocytes but not in DIO rat epididymal fat. Our study based on gene-expression profiling suggested that DIO rats in general represent an appropriate obesity model. However, the discrepancies in gene-expression alterations between DIO rats and obese humans, particularly in the metabolic pathways, may explain the limitations of using DIO rodent models in obesity research and drug discovery.

The Long Form of the Leptin Receptor Regulates STAT5 and Ribosomal Protein S6 via Alternate Mechanisms

The action of leptin via the long form of its receptor (LepRb) is central to the control of body energy homeostasis and neuroendocrine function, but the mechanisms by which LepRb regulates intracellular signaling have remained incompletely understood. Here we demonstrate that leptin stimulates the phosphorylation of STAT5 and ribosomal protein S6 in the hypothalamic arcuate nucleus in mice. In cultured cells, we investigate the mechanisms by which leptin regulates each of these pathways. Our analysis reveals a dominant role for LepRb Tyr(1077) (which we demonstrate to be phosphorylated during receptor activation) and a secondary role for LepRb Tyr(1138) in the acute phosphorylation of STAT5a and STAT5b. Tyr(1138) and STAT3 attenuate STAT5-dependent transcription over the long-term, however. In contrast, Tyr(985) (the LepRb phosphorylation site required for ERK activation) mediates the phosphorylation of the ribosomal S6 kinase (RSK) and S6, as well as cap-dependent translation. Thus, these data demonstrate the phosphorylation of Tyr(1077) on LepRb during receptor activation, substantiate the hypothalamic regulation of STAT5 and S6 by leptin, and define the alternate LepRb signaling pathways that mediate each of these signals and their effects in cultured cells. Dissecting the contributions of these individual pathways to leptin action will be important for our ultimate understanding of the processes that regulate energy balance in vivo.

Combination therapy with amylin and PYY(3–36) in diet-induced obese rats: A response surface analysis.

Amylin (from pancreatic B-cells), and PYY(3–36) (from ileal L-cells) are both released following a meal and act as short-term satiety signals. Peripheral administration of the individual peptide hormones has been shown to reduce food intake (FI) and body weight (BW) in rodent models. We recently demonstrated that the combination of amylin and PYY(3–36) appeared to exert additive FI- and BW-lowering effects in diet-induced obese (DIO) rodents. In the present study, we extended these findings by using a 4×3 factorial design (n=5/group) to define the interaction of a range of doses of amylin (0, 4, 20, 100 μg/kg/d) and PYY(3–36) (0, 200, 400 μg/kg/d) on FI and BW loss following 2-week subcutaneous (SC) infusion in DIO rats. This design enabled us to formally test for statistical additivity or synergy using Response Surface Methodology (RSM), where p-values less than 0.05 indicate synergy and non-significant p-values suggest additivity. At 2 weeks, the RSM showed that (1) cumulative FI (% vehicle-corrected±SEM) was synergistically reduced across the combinations (p=0.022) by up to 54.7±1.1% and, (2) BW (% vehicle corrected±SEM) was additively reduced (p=0.27) across the combinations by up to 15.6±0.9%. Our results formally confirm that in DIO rats, amylin and PYY(3–36) have additive effects for BW loss, mediated in part via a synergistic suppression of food intake. These preclinical findings point to the need for further studies to investigate the potential utility of integrated neurohormonal approaches for the treatment of obesity.