Weight loss in adult male Wistar rats by Roux-en-Y gastric bypass is primarily explained by caloric intake reduction and presurgery body weight.

Diets varying in macronutrient composition, energy density, and/or palatability may cause differences in outcome of bariatric surgery. In the present study, rats feeding a healthy low-fat (LF) diet or an obesogenic high-fat/sucrose diet (HF/S) were either subjected to Roux-en-Y gastric bypass surgery (RYGB) or sham surgery, and weight loss trajectories and various energy balance parameters were assessed. Before RYGB, rats eating an HF/S (n = 14) diet increased body weight relative to rats eating an LF diet (n = 20; P < 0.01). After RYGB, absolute weight loss was larger in HF/S (n = 6) relative to LF feeding (n = 6) rats, and this was associated with reduced cumulative energy intake (EI; P < 0.05) and increased locomotor activity (LA; P < 0.05-0.001), finally leading to similar levels of reduced body fat content in HF/S and LF rats 3 wk after surgery. Regression analysis revealed that variation in RYGB-induced body weight loss was best explained by models including 1) postoperative cumulative EI and preoperative body weight (R2 = 0.87) and 2) postoperative cumulative EI and diet (R2 = 0.79), each without significant contribution of LA. Particularly rats on the LF diet became transiently more hypothermic and circadianally arrhythmic following RYGB (i.e., indicators of surgery-associated malaise) than HF/S feeding rats. Our data suggest that relative to feeding an LF diet, continued feeding an HF/S diet does not negatively impact recovery from RYGB surgery, yet it promotes RYGB-induced weight loss. The RYGB-induced weight loss is primarily explained by reduced cumulative EI and higher preoperative body weight, leading to comparably low levels of body fat content in HF/S and LF feeding rats.NEW & NOTEWORTHY Relative to feeding an LF diet, continued feeding an HF/S diet does not negatively impact recovery from RYGB surgery in rats. Relative to feeding an LF diet, continued feeding an HF/S diet promotes RYGB-induced weight loss. The RYGB-induced weight loss is primarily explained by reduced cumulative EI and higher preoperative body weight, leading to comparably low levels of body fat content in HF/S and LF feeding rats.

Laparoscopic Roux-Y-gastric bypass versus laparoscopic one-anastomosis gastric bypass for obesity: clinical & metabolic results of a prospective randomized controlled trial.

BACKGROUND: One anastomosis gastric bypass (OAGB) has been proposed as an effective alternative to the current standard procedure in Switzerland, Roux-en-Y gastric bypass (RYGB). Prospective data comparing both procedures are scarce. Therefore, we performed a non-inferiority randomized controlled trial assessing the effectiveness and safety of these 2 operative techniques. METHOD: Eighty patients were randomized 1:1. OAGB consisted of a very long gastric pouch with a 200 cm biliopancreatic limb, RYGB of a 150 cm ante-colic alimentary and a 60 cm biliopancreatic limb, respectively. Primary endpoint was the percent excess weight loss (%EWL) at 12 months after surgery. RESULTS: Mean %EWL at 12 months was 87.9% (SD24.4) in the RYGB group and 104.1% (SD24.6) in the OAGB group (p = 0.006). There was no mortality. The rate of marginal ulcers was higher in patients with OAGB compared to those with RYGB (p = 0.011), while the total number of late complications did not statistically differ between the two groups. Except for the remission of GERD, which was higher in the RYGB group compared to OAGB, there was no difference between the groups regarding the remission of comorbidities. OAGB showed improved glucose control compared to the RYGB after 1 year (p = 0.001). Furthermore, glucagon-like peptide-1 increase was significantly higher in OAGB at 6 weeks (p = 0.041) and 1 year after surgery (p = 0.029). Quality of life improved after both surgeries, without differences between the groups. CONCLUSIONS: %EWL 1 year after surgery was higher in OAGB than in RYGB. A better glycemic control with a higher increase in GLP-1 was observed after OAGB compared to RYGB. TRIAL REGISTRATION: This trial is registered on ClinicalTrials.gov under the identifier NCT02601092.

Obesity-induced changes in gene expression in feline adipose and skeletal muscle tissue.

Indoor-confined cats are prone to developing obesity due to a sedentary life and an energy intake exceeding energy requirements. As in humans, feline obesity decreases insulin sensitivity and increases the risk of developing feline diabetes mellitus, but the pathophysiological mechanisms are currently poorly understood. Human obesity-related metabolic alterations seem to relate to changes in the expression of genes involved in glucose metabolism, insulin action and inflammation. The objective of the current study was to investigate changes in the expression of genes relating to obesity, glucose metabolism and inflammation in cats with non-experimentally induced obesity. Biopsies from the sartorius muscle and subcutaneous adipose tissue were obtained from 73 healthy, neutered, indoor-confined domestic shorthaired cats ranging from lean to obese. Quantification of obesity-related gene expression levels relative to glyceraldehyde-3-phosphate dehydrogenase was performed by quantitative real-time polymerase chain reaction. A negative association between obesity and adiponectin expression was observed in the adipose tissue (mean ± SD; normal weight, 27.30 × 10-3 ± 77.14 × 10-3 ; overweight, 2.89 × 10-3 ± 0.38 × 10-3 and obese, 2.93 × 10-3 ± 4.20 × 10-3 , p < 0.05). In muscle, the expression of peroxisome proliferative activated receptor-γ2 and plasminogen activator inhibitor-1 was increased in the obese compared to the normal-weight cats, and resistin was increased in the normal-weight compared to the overweight cats. There were no detectable obesity-related changes in the messenger RNA levels of inflammatory cytokines. In conclusion, a possible obesity-related low-grade inflammation caused by increased expression of key proinflammatory regulators was not observed. This could imply that the development of feline obesity and ensuing insulin resistance may not be based on tissue-derived inflammation, but caused by several determining factors, many of which still need further investigation.

Hyperleptinemia as a contributing factor for the impairment of glucose intolerance in obesity.

Obesity has emerged as a major risk factor for insulin resistance leading to the development of type 2 diabetes (T2D). The condition is characterized by high circulating levels of the adipose-derived hormone leptin and a state of chronic low-grade inflammation. Pro-inflammatory signaling in the hypothalamus is associated with a decrease of central leptin- and insulin action leading to impaired systemic glucose tolerance. Intriguingly, leptin not only regulates body weight and glucose homeostasis but also acts as a pro-inflammatory cytokine. Here we demonstrate that increasing leptin levels (62,5 µg/kg/d, PEGylated leptin) in mice fed a high-fat diet (HFD) exacerbated body weight gain and aggravated hypothalamic micro- as well as astrogliosis. In contrast, administration of a predetermined dose of a long-acting leptin antagonist (100 µg/kg/d, PESLAN) chosen to block excessive leptin signaling during diet-induced obesity (DIO) showed the opposite effect and significantly improved glucose tolerance as well as decreased the total number of microglia and astrocytes in the hypothalamus of mice fed HFD. These results suggest that high levels of leptin, such as in obesity, worsen HFD-induced micro-and astrogliosis, whereas the partial reduction of hyperleptinemia in DIO mice may have beneficial metabolic effects and improves hypothalamic gliosis.

Calcitonin receptor antibody validation and expression in the rodent brain.

BACKGROUND AND AIM: Therapeutics that reduce calcitonin gene-related peptide activity are effective migraine treatments. However, gaps remain in our understanding of the molecular mechanisms that link calcitonin gene-related peptide to migraine. The amylin 1 receptor responds potently to calcitonin gene-related peptide, and to the related peptide amylin, but its role in relation to either peptide or to migraine is unclear. We sought to better understand the expression of the amylin 1 receptor protein subunit, the calcitonin receptor, in the rodent brain. METHODS: We profiled three antibodies for immunodetection of calcitonin receptor, using immunocytochemistry, western blotting, and calcitonin receptor conditional knockout mouse tissue. Selected migraine-relevant rat brain regions were then examined for calcitonin receptor-like immunoreactivity. RESULTS: All three antibodies detected calcitonin receptor protein but only one (188/10) produced robust immunostaining in rodent brain, under the conditions used. Calcitonin receptor-like immunoreactivity was apparent in the rat brainstem and midbrain including the locus coeruleus, periaqueductal grey and spinal trigeminal nucleus. CONCLUSIONS: Anti-calcitonin receptor antibodies require comprehensive profiling to ensure confidence in the detection of calcitonin receptor. Using a validated antibody, calcitonin receptor-like immunoreactivity was detected in several brain regions relevant to migraine. Further research is needed to understand the functional consequences of calcitonin receptor expression for calcitonin gene-related peptide or amylin physiology and pathophysiology.

Creating the amylin story.

This paper is based on a presentation given at the Annual Meeting of the Society for the Study of Ingestive Behavior in July 2021 and provides a personal view on some of the milestones in the discovery of amylin as a constituent of pancreatic islet amyloid deposits, as a pancreatic beta-cell hormone, and on its role in physiology and pathophysiology. Only selected effects of amylin are discussed here because we recently published extensive reviews on the physiology and pathophysiology of amylin. Amylin was discovered as the main constituent of islet amyloid that is predominantly found in pancreatic islets in type 2 diabetics. These deposits, and in particular small oligomer aggregates of amylin seem to contribute to the progressive beta-cell damage seen in type 2 diabetics. Amylin is also a physiologically relevant circulating hormone with diverse metabolic functions, e.g. inhibition of eating, of pancreatic glucagon secretion and of gastric emptying. Knowledge of these types of functions and amylin's mechanisms of action lead to the development of amylin analogues that are now among the most promising anti-obesity targets in clinical testing. With this review, I want to give a short overview of 35 exciting years of amylin research.

The Deubiquitinase OTUB1 Is a Key Regulator of Energy Metabolism.

Dysregulated energy metabolism is a major contributor to a multitude of pathologies, including obesity and diabetes. Understanding the regulation of metabolic homeostasis is of utmost importance for the identification of therapeutic targets for the treatment of metabolically driven diseases. We previously identified the deubiquitinase OTUB1 as substrate for the cellular oxygen sensor factor-inhibiting HIF (FIH) with regulatory effects on cellular energy metabolism, but the physiological relevance of OTUB1 is unclear. Here, we report that the induced global deletion of OTUB1 in adult mice (Otub1 iKO) elevated energy expenditure, reduced age-dependent body weight gain, facilitated blood glucose clearance and lowered basal plasma insulin levels. The respiratory exchange ratio was maintained, indicating an unaltered nutrient oxidation. In addition, Otub1 deletion in cells enhanced AKT activity, leading to a larger cell size, higher ATP levels and reduced AMPK phosphorylation. AKT is an integral part of insulin-mediated signaling and Otub1 iKO mice presented with increased AKT phosphorylation following acute insulin administration combined with insulin hypersensitivity. We conclude that OTUB1 is an important regulator of metabolic homeostasis.

Characterization of Antibodies against Receptor Activity-Modifying Protein 1 (RAMP1): A Cautionary Tale.

Calcitonin gene-related peptide (CGRP) is a key component of migraine pathophysiology, yielding effective migraine therapeutics. CGRP receptors contain a core accessory protein subunit: receptor activity-modifying protein 1 (RAMP1). Understanding of RAMP1 expression is incomplete, partly due to the challenges in identifying specific and validated antibody tools. We profiled antibodies for immunodetection of RAMP1 using Western blotting, immunocytochemistry and immunohistochemistry, including using RAMP1 knockout mouse tissue. Most antibodies could detect RAMP1 in Western blotting and immunocytochemistry using transfected cells. Two antibodies (844, ab256575) could detect a RAMP1-like band in Western blots of rodent brain but not RAMP1 knockout mice. However, cross-reactivity with other proteins was evident for all antibodies. This cross-reactivity prevented clear conclusions about RAMP1 anatomical localization, as each antibody detected a distinct pattern of immunoreactivity in rodent brain. We cannot confidently attribute immunoreactivity produced by RAMP1 antibodies (including 844) to the presence of RAMP1 protein in immunohistochemical applications in brain tissue. RAMP1 expression in brain and other tissues therefore needs to be revisited using RAMP1 antibodies that have been comprehensively validated using multiple strategies to establish multiple lines of convincing evidence. As RAMP1 is important for other GPCR/ligand pairings, our results have broader significance beyond the CGRP field.

A selective role for receptor activity-modifying proteins in subchronic action of the amylin selective receptor agonist NN1213 compared with salmon calcitonin on body weight and food intake in male mice.

The role of receptor activity-modifying proteins (RAMPs) in modulating the pharmacological effects of an amylin receptor selective agonist (NN1213) or the dual amylin-calcitonin receptor agonist (DACRA), salmon calcitonin (sCT), was tested in three RAMP KO mouse models, RAMP1, RAMP3 and RAMP1/3 KO. Male wild-type (WT) and knockout (KO) littermate mice were fed a 45% high-fat diet for 20 weeks prior to the 3-week treatment period. A decrease in body weight after NN1213 was observed in all WT mice, whereas sCT had no effect. The absence of RAMP1 had no significant effect on NN1213 efficacy, and sCT was still inactive. However, the absence of RAMP3 impeded NN1213 efficacy but improved sCT efficacy. Similar results were observed in RAMP1/3 KO suggesting that the amylin receptor 3 (AMY3 = CTR + RAMP3) is necessary for NN1213's maximal action on body weight and food intake and that the lack of AMY3 allowed sCT to be active. These results suggest that the chronic use of DACRA such as sCT can have unfavourable effect on body weight loss in mice (which differs from the situation in rats), whereas the use of the amylin receptor selective agonist does not. AMY3 seems to play a crucial role in modulating the action of these two compounds, but in opposite directions. The assessment of a long-term effect of amylin and DACRA in different rodent models is necessary to understand potential physiological beneficial and unfavourable effects on weight loss before its transition to clinical trials.

Whole-brain mapping of amylin-induced neuronal activity in receptor activity-modifying protein 1/3 knockout mice.

The pancreatic hormone amylin plays a central role in regulating energy homeostasis and glycaemic control by stimulating satiation and reducing food reward, making amylin receptor agonists attractive for the treatment of metabolic diseases. Amylin receptors consist of heterodimerized complexes of the calcitonin receptor and receptor-activity modifying proteins subtype 1-3 (RAMP1-3). Neuronal activation in response to amylin dosing has been well characterized, but only in selected regions expressing high levels of RAMPs. The current study identifies global brain-wide changes in response to amylin and by comparing wild type and RAMP1/3 knockout mice reveals the importance of RAMP1/3 in mediating this response. Amylin dosing resulted in neuronal activation as measured by an increase in c-Fos labelled cells in 20 brain regions, altogether making up the circuitry of neuronal appetite regulation (e.g., area postrema (AP), nucleus of the solitary tract (NTS), parabrachial nucleus (PB), and central amygdala (CEA)). c-Fos response was also detected in distinct nuclei across the brain that typically have not been linked with amylin signalling. In RAMP1/3 knockout amylin induced low-level neuronal activation in seven regions, including the AP, NTS and PB, indicating the existence of RAMP1/3-independent mechanisms of amylin response. Under basal conditions RAMP1/3 knockout mice show reduced neuronal activity in the hippocampal formation as well as reduced hippocampal volume, suggesting a role for RAMP1/3 in hippocampal physiology and maintenance. Altogether these data provide a global map of amylin response in the mouse brain and establishes the significance of RAMP1/3 receptors in relaying this response.

Noradrenaline signaling in the LPBN mediates amylin's and salmon calcitonin's hypophagic effect in male rats.

The LPBN (lateral parabrachial nucleus) plays an important role in feeding control. CGRP (calcitonin gene-related peptide) LPBN neurons activation mediates the anorectic effects of different gut-derived peptides, including amylin. Amylin and its long acting analog sCT (salmon calcitonin) exert their anorectic actions primarily by directly activating neurons located in the area postrema (AP). A large proportion of projections from the AP and the adjacent nucleus of the solitary tractNTS to the LPBN, are noradrenergic (NA), and amylin-activated NAAP neurons are critical in mediating amylin's hypophagic effects. Here, we determine the functional role of NAAP amylin activated neurons to activate CGRP and non-CGRP LPBN neurons. To this end, NA was specifically depleted in the rat LPBN through a stereotaxic microinfusion of 6-OHDA, a neurotoxic agent that destroys NA terminals. While amylin (50 µg/kg) and sCT (5 µg/kg) reduced eating in sham-lesioned rats, no reduction in feeding occurred in NA-depleted animals. Further, the amylin-induced c-Fos response in the LPBN and c-Fos/CGRP colocalization were reduced in NA-depleted animals compared to controls. We conclude that AP â†’ LPBN NA signaling, through the activation of LPBN CGRP neurons, mediates part of amylin's hypophagic effect.

Evaluation of Acute Mountain Sickness by Unsedated Transnasal Esophagogastroduodenoscopy at High Altitude.

BACKGROUND & AIMS: It is not clear how rapid ascent to a high altitude causes the gastrointestinal symptoms of acute mountain sickness (AMS). We assessed the incidence of endoscopic lesions in the upper gastrointestinal tract in healthy mountaineers after a rapid ascent to high altitude, their association with symptoms, and their pathogenic mechanisms. METHODS: In a prospective study, 25 mountaineers (10 women; mean age, 43.8 ± 9.5 y) underwent unsedated, transnasal esophagogastroduodenoscopy in Zurich (490 m) and then on 2 test days (days 2 and 4) at a high altitude laboratory in the Alps (Capanna Regina Margherita, 4559 m). Symptoms were assessed using validated instruments for AMS (the acute mountain sickness score and the Lake Louise scoring system) and visual analogue scales (scale, 0-100). Levels of messenger RNAs (mRNAs) in duodenal biopsy specimens were measured by quantitative polymerase chain rection. RESULTS: The follow-up endoscopy at high altitude was performed in 19 of 25 patients on day 2 and in 23 of 25 patients on day 4. The frequency of endoscopic lesions increased from 12% at baseline to 26.3% on day 2 and to 60.9% on day 4 (P < .001). The incidence of ulcer disease increased from 0 at baseline to 10.5% on day 2 and to 21.7% on day 4 (P = .014). Mucosal lesions were associated with lower hunger scores (37.3 vs 67.4 in patients without lesions; P = .012). Subjects with peptic lesions had higher levels of HIF2A mRNA, which encodes a hypoxia-induced transcription factor, and ICAM1 mRNA, which encodes an adhesion molecule, compared with subjects without lesions (fold changes, 1.38 vs 0.63; P = .001; and 1.37 vs 0.66; P = .011, respectively). CONCLUSIONS: In a prospective study of 25 mountaineers, fast ascent to a high altitude resulted in rapid onset of clinically meaningful mucosal lesions and ulcer disease. Duodenal biopsy specimens from these subjects had increased levels of HIF2A mRNA and ICAM1 mRNA, which might contribute to the formation of hypoxia-induced peptic lesions. Further studies are needed of the mechanisms of this process.

Diabetic remission in a cat treated with an implantable pump to deliver insulin.

A diabetic cat was referred because of poor metabolic control and difficulties the owner experienced injecting insulin. A pump, telemetrically controlled with a smartphone, was implanted subcutaneously to deliver insulin. Before implantation, the pump reservoir was filled with a rapid-acting human recombinant insulin. The insulin was administered through continuous infusion or periodic boluses over 2 weeks while the cat was hospitalized and over another 2 weeks after discharge from the hospital. Adjustments of insulin dosage were performed based on blood glucose concentrations measured with a continuous blood monitoring system (CGMS). The cat achieved diabetic remission that is still lasting after 1 year. The treatment protocol adopted in this cat contributed to achieving remission. The owner's unwillingness to inject insulin into an uncooperative cat was circumvented with the implantable pump. Key clinical message: The implantable subcutaneous pump, telemetrically controlled by a smartphone, easily allowed the clinician to modify the type of administration and the amount of insulin delivered; the concurrent use of a CGMS allowed detection of sudden changes in blood glucose while limiting stress to the cat.

Rémission du diabète chez un chat traité avec une pompe implantable pour administrer l'insuline.Un chat diabétique fut référé pour cause de pauvre contrôle métabolique et des difficultés rencontrées par le propriétaire pour injecter l'insuline. Une pompe, contrôlée par télémétrie avec un téléphone intelligent, fut implantée sous-cutané afin d'injecter l'insuline. Avant l'implantation, le réservoir de la pompe fut rempli avec une insuline humaine recombinante à action rapide. L'insuline était administrée par infusion continue ou des bolus périodiques pendant une période de 2 semaines alors que le chat était hospitalisé et pendant un 2 semaines supplémentaires après avoir obtenu son congé de l'hôpital. Des ajustements du dosage de l'insuline furent effectués sur la base des concentrations de glucose sanguin mesurées par un système continu de surveillance du sang (CGMS). Une rémission du diabète fut possible pour ce chat et persiste toujours après 1 an. Le protocole de traitement adopté chez ce chat a contribué à atteindre cette rémission. La réticence du propriétaire à injecter l'insuline chez un chat non-collaborateur fut contournée par une pompe implantable.Message clinique important :La pompe implantable sous-cutanée, contrôlée par télémétrie avec un téléphone intelligent, a facilement permis au clinicien de modifier le type d'administration et la quantité d'insuline donnée; l'utilisation concomitante d'un CGMS a permis la détection de changements soudains dans la glycémie tout en limitant le stress au chat.(Traduit par Dr Serge Messier).

Significant changes in hepatic transcriptome and circulating miRNAs are associated with diet-induced metabolic syndrome in apoE3L.CETP mice.

Long-term exposure to excess dietary fat leads to obesity and the metabolic syndrome (MetS). The purpose of the present study was to identify global changes in liver gene expression and circulating miRNAs in a humanized mouse model of diet-induced MetS. Male apoE3L.CETP mice received a high-fat diet (HFD) or a low-fat diet (LFD) for different time periods and the progression of MetS pathology was monitored. A separate group of mice was divided into responders (R) or nonresponders (NR) and received HFD for 16 weeks. We found that mice receiving the HFD developed manifestations of MetS and displayed an increasing number of differentially expressed transcripts at 4, 8, and 12 weeks compared with mice receiving the LFD. Significantly changed genes were functionally annotated to metabolic diseases and pathway analysis revealed the downregulation of genes in cholesterol and fatty acid biosynthesis and upregulation of genes related to lipid droplet formation, which was in line with the development of hepatic steatosis. In the serum of the apoE3L.CETP mice we identified three miRNAs that were upregulated specifically in the HFD group. We found that responder mice have a distinct gene signature that differentiates them from nonresponders. Comparison of the two diet intervention studies revealed a limited number of common differentially expressed genes but the expression of these common genes was affected in a similar way in both studies. In conclusion, the characteristic hepatic gene signatures and serum miRNAs identified in the present study provide novel insights to MetS pathology and could be exploited for diagnostic or therapeutic purposes.

Body weight-dependent and independent improvement in lipid metabolism after Roux-en-Y gastric bypass in ApoE*3Leiden.CETP mice.

BACKGROUND/OBJECTIVES: The incidence of obesity and metabolic syndrome (MetS) has rapidly increased worldwide. Roux-en-Y gastric bypass (RYGB) achieves long-term weight loss and improves MetS-associated comorbidities. Using a mouse model with a humanized lipoprotein metabolism, we elucidated whether improvements in lipid and glucose metabolism after RYGB surgery are body weight loss-dependent or not. SUBJECTS/METHODS: Male ApoE*3Leiden.CETP (ApoE3L.CETP) mice fed Western type diet for 6 weeks underwent RYGB or Sham surgery. Sham groups were either fed ad libitum or were body weight-matched (BWm) to the RYGB mice to discriminate surgical effects from body weight loss-associated effects. Before and after surgery, plasma was collected to assess the metabolic profile, and glucose tolerance and insulin sensitivity were tested. Twenty days after surgery, mice were sacrificed, and liver was collected to assess metabolic, histological and global gene expression changes after surgery. RESULTS: RYGB induced a marked reduction in body weight, which was also achieved by severe food restriction in BWm mice, and total fat mass compared to Sham ad libitum mice (Sham AL). Total cholesterol, non-high-density lipoprotein cholesterol (non-HDL-C) and ceramide were strongly reduced 20 days after surgery in RYGB compared to BWm mice. Glucose tolerance and insulin sensitivity improved 13 days after surgery similarly in RYGB and BWm mice. Liver histology confirmed lipid reduction in RYGB and BWm mice while the transcriptomics data indicated altered genes expression in lipid metabolism. CONCLUSIONS: RYGB surgery improves glucose metabolism and greatly ameliorates lipid metabolism in part in a body weight-dependent manner. Given that ApoE3L.CETP mice were extensively studied to describe the MetS, and given that RYGB improved ceramide after surgery, our data confirmed the usefulness of ApoE3L.CETP mice after RYGB in deciphering the metabolic improvements to treat the MetS.

Endogenous amylin contributes to birth of microglial cells in arcuate nucleus of hypothalamus and area postrema during fetal development.

Amylin acts in the area postrema (AP) and arcuate nucleus (ARC) to control food intake. Amylin also increases axonal fiber outgrowth from the AP→nucleus tractus solitarius and from ARC→hypothalamic paraventricular nucleus. More recently, exogenous amylin infusion for 4 wk was shown to increase neurogenesis in adult rats in the AP. Furthermore, amylin has been shown to enhance leptin signaling in the ARC and ventromedial nucleus of the hypothalamus (VMN). Thus, we hypothesized that endogenous amylin could be a critical factor in regulating cell birth in the ARC and AP and that amylin could also be involved in the birth of leptin-sensitive neurons. Amylin+/- dams were injected with BrdU at embryonic day 12 and at postnatalday 2; BrdU+ cells were quantified in wild-type (WT) and amylin knockout (KO) mice. The number of BrdU+HuC/D+ neurons was similar in ARC and AP, but the number of BrdU+Iba1+ microglia was significantly decreased in both nuclei. Five-week-old WT and KO littermates were injected with leptin to test whether amylin is involved in the birth of leptin-sensitive neurons. Although there was no difference in the number of BrdU+c-Fos+ neurons in the ARC and dorsomedial nucleus, an increase in BrdU+c-Fos+ neurons was seen in VMN and lateral hypothalamus (LH) in amylin KO mice. In conclusion, these data suggest that during fetal development, endogenous amylin favors the birth of microglial cells in the ARC and AP and that it decreases the birth of leptin-sensitive neurons in the VMN and LH.

Unsilencing of native LepRs in hypothalamic SF1 neurons does not rescue obese phenotype in LepR-deficient mice.

Leptin receptor (LepR) signaling in neurons of the ventromedial nucleus of the hypothalamus (VMH), specifically those expressing steroidogenic factor-1 (SF1), have been proposed to play a key role in controlling energy balance. By crossing LepR-silenced (LepRloxTB) mice with those expressing SF1-Cre, we unsilenced native LepR specifically in the VMH and tested whether SF1 neurons in the VMH are critical mediators of leptin's effect on energy homeostasis. LepRloxTB × SF1-Cre [knockout (KO)/Tg+] mice were metabolically phenotyped and compared with littermate controls that either expressed or were deficient in LepRs. Leptin-induced phosphorylated STAT3 was present in the VMH of KO/Tg+ mice and absent in other hypothalamic nuclei. VMH leptin signaling did not ameliorate obesity resulting from LepR deficiency in chow-fed mice. There was no change in food intake or energy expenditure when comparing complete LepR-null mice with KO/Tg+ mice, nor did KO/Tg+ mice show improved glucose tolerance. The presence of functional LepRs in the VMH mildly enhanced sensitivity to the pancreatic hormone amylin. When maintained on a high-fat diet (HFD), there was no reduction in diet-induced obesity in KO/Tg+ mice, but KO/Tg+ mice had improved glucose tolerance after 7 wk on an HFD compared with LepR-null mice. We conclude that LepR signaling in the VMH alone is not sufficient to correct metabolic dysfunction observed in LepR-null mice.

Phenotypical heterogeneity in responder and nonresponder male ApoE*3Leiden.CETP mice.

The metabolic syndrome (MetS) is a major health issue worldwide and is associated with obesity, insulin resistance, and hypercholesterolemia. Several animal models were used to describe the MetS; however, many of them do not mimic well the MetS pathophysiology in humans. The ApoE*3Leiden.CETP mouse model overcomes part of this limitation, since they have a humanised lipoprotein metabolism and a heterogeneous response to MetS, similar to humans. The reported heterogeneity among them and their common classification refer to responder (R) and nonresponder (NR) mice; R mice show increased body weight, cholesterol, and triglycerides levels, whereas NR mice do not show this expected phenotype when fed a Western type diet. To define better the differences between R and NR mice, we focused on feeding behavior, body weight gain, glucose tolerance, and lipid parameters, and on an extensive pathological examination along with liver histology analysis. Our data confirmed that R mice resemble the pathological features of the human MetS: obesity, dysplipidemia, and glucose intolerance. NR mice do not develop the full dysmetabolic phenotype because of a severe inflammatory hepatic condition, which may heavily affect liver function. We conclude that R and NR mice are metabolically different and that NR mice have indications of severely impaired liver function. Hence, it is critical to identify and separate the respective mice to decrease data heterogeneity. Clinical chemistry and histological analysis should be used to confirm retrospectively the animals' classification. Moreover, we point out that NR mice may not be an appropriate control for studies involving ApoE*3Leiden.CETP R mice. NEW & NOTEWORTHY When compared with some other animal models, ApoE*3Leiden.CETP mice are better models to describe the metabolic syndrome. However, there is phenotypic heterogeneity between "responder" and "nonresponder" mice, the latter showing some evidence of hepatic pathology. A full phenotypic characterization and eventually postmortem analysis of the liver are warranted.

Rodent models of leptin receptor deficiency are less sensitive to amylin.

The pancreatic hormone amylin is released from beta cells following nutrient ingestion and contributes to the control of body weight and glucose homeostasis. Amylin reduces food intake by activating neurons in the area postrema (AP). Amylin was also shown to synergize with the adipokine leptin, with combination therapy producing greater weight loss and food intake reduction than either hormone alone. Although amylin and leptin were initially thought to interact downstream of the AP in the hypothalamus, recent findings show that the two hormones can act on the same AP neurons, suggesting a more direct relationship. The objective of this study was to determine whether amylin action depends on functional leptin signaling. We tested the ability of amylin to induce satiation and to activate its primary target neurons in the AP in two rodent models of LepR deficiency, the db/db mouse and the Zucker diabetic fatty (ZDF) rat. When compared with wild-type (WT) mice, db/db mice exhibited reduced amylin-induced satiation, reduced amylin-induced Fos in the AP, and a lower expression of calcitonin receptor (CTR) protein, the core component of all amylin receptors. ZDF rats also showed no reduction in food intake following amylin treatment; however, unlike the db/db mice, levels of amylin-induced Fos and CTR in the AP were no different than WT rats. Our results suggest that LepR expression is required for the full anorexic effect of amylin; however, the neuronal activation in the AP seems to depend on the type of LepR mutation.

RYGB increases the satiating effect of intrajejunal lipid infusions in female rats.

We used a novel rat model to investigate the physiological bases of early satiation after Roux-en-Y gastric bypass surgery (RYGB). Female rats were subjected to RYGB or sham surgery. Chronic infusion catheters were placed in the Roux limb of RYGB rats and the corresponding anatomical locus of the jejuna of sham-RYGB rats. Rats were also ovariectomized and chronically treated with either estradiol (E2; 2 µg each 4th day SC) or the oil vehicle. Testing was begun 10-12 wk after surgery. Intrajejunal lipid infusions (10 min, 4.4 mL, 8.8 kcal) were performed just before test meals of a low-energy artificially sweetened gel diet (0.1 kcal/g) that RYGB rats ingest avidly. Intrajejunal lipid infusions reduced test-meal size more in RYGB rats than sham-operated rats, indicating that, at least after prolonged adaptation to surgery, the satiating actions of lipids acting intra- or post-jejunally are increased by RYGB and that accelerated meal appearance in the intestines after RYGB is not necessary for this effect. The satiating effects of intrajejunal lipid infusions were similar in E2-and oil-treated rats, suggesting that the effect was not dependent on an activational effect of estrogens. In a second experiment, pretreatment with the cholecystokinin A-receptor antagonist devazepide reduced the satiating effect of intrajejunal lipid infusions in E2-treated RYGB rats. Although these data are preliminary due to the smaller numbers of rats than in the first experiment, they suggest that cholecystokinin-mediated jejunal satiation contributes to early satiation after RYGB in ovariectomized rats with peri-ovulatory levels of estradiol. The results of these experiments may be relevant to understanding RYGB outcome in pre- and postmenopausal women.