Transgenic study of energy homeostasis equation: implications and confounding influences

Low Basal CB2R in Dopamine Neurons and Microglia Influences Cannabinoid Tetrad Effects

There are two well-characterized cannabinoid receptors (CB1R and CB2R and other candidates): the central nervous system (CNS) enriched CB1R and peripheral tissue enriched CB2R with a wide dynamic range of expression levels in different cell types of human tissues. Hepatocytes and neurons express low baseline CB1R and CB2R, respectively, and their cell-type-specific functions are not well defined. Here we report inducible expression of CB1R in the liver by high-fat and high sugar diet and CB2R in cortical neurons by methamphetamine. While there is less controversy about hepatocyte CB1R, the presence of functional neuronal CB2R is still debated to date. We found that neuron CB2R basal expression was higher than that of hepatocyte CB1R by measuring mRNA levels of specific isoform CB2A in neurons isolated by fluorescence-activated cell sorting (FACS) and CB1A in hepatocytes isolated by collagenase perfusion of liver. For in vivo studies, we generated hepatocyte, dopaminergic neuron, and microglia-specific conditional knockout mice (Abl-Cnr1Δ, Dat-Cnr2Δ, and Cx3cr1-Cnr2Δ) of CB1R and CB2R by crossing Cnr1f/f and Cnr2f/f strains to Abl-Cre, Dat-Cre, and Cx3cr1-Cre deleter mouse strains, respectively. Our data reveals that neuron and microglia CB2Rs are involved in the "tetrad" effects of the mixed agonist WIN 55212-2, CB1R selective agonist arachidonyl-2'-chloroethylamide (ACEA), and CB2R selective agonist JWH133. Dat-Cnr2Δ and Cx3cr1-Cnr2Δ mice showed genotypic differences in hypomobility, hypothermia, analgesia, and catalepsy induced by the synthetic cannabinoids. Alcohol conditioned place preference was abolished in DAT-Cnr2Δ mice and remained intact in Cx3cr1-Cnr2Δ mice in comparison to WT mice. These Cre-loxP recombinant mouse lines provide unique approaches in cannabinoid research for dissecting the complex endocannabinoid system that is implicated in many chronic disorders.

Metabolism disrupting chemicals and metabolic disorders

The recent epidemics of metabolic diseases, obesity, type 2 diabetes(T2D), liver lipid disorders and metabolic syndrome have largely been attributed to genetic background and changes in diet, exercise and aging. However, there is now considerable evidence that other environmental factors may contribute to the rapid increase in the incidence of these metabolic diseases. This review will examine changes to the incidence of obesity, T2D and non-alcoholic fatty liver disease (NAFLD), the contribution of genetics to these disorders and describe the role of the endocrine system in these metabolic disorders. It will then specifically focus on the role of endocrine disrupting chemicals (EDCs) in the etiology of obesity, T2D and NAFLD while finally integrating the information on EDCs on multiple metabolic disorders that could lead to metabolic syndrome. We will specifically examine evidence linking EDC exposures during critical periods of development with metabolic diseases that manifest later in life and across generations.

A non-canonical function of telomerase RNA in the regulation of developmental myelopoiesis in zebrafish

Dyskeratosis congenita (DC) is an inherited disorder with mutations affecting telomerase or telomeric proteins. DC patients usually die of bone marrow failure. Here we show that genetic depletion of the telomerase RNA component (TR) in the zebrafish results in impaired myelopoiesis, despite normal development of haematopoietic stem cells (HSCs). The neutropenia caused by TR depletion is independent of telomere length and telomerase activity. Genetic analysis shows that TR modulates the myeloid-erythroid fate decision by controlling the levels of the master myeloid and erythroid transcription factors spi1 and gata1, respectively. The alteration in spi1 and gata1 levels occurs through stimulation of gcsf and mcsf. Our model of TR deficiency in the zebrafish illuminates the non-canonical roles of TR, and could establish therapeutic targets for DC.

Tnfa signaling through tnfr2 protects skin against oxidative stress-induced inflammation

A new zebrafish model of skin inflammatory disease explains new-onset and worsening psoriasis and lichen planus in patients receiving anti-TNFα therapy.

TNFα overexpression has been associated with several chronic inflammatory diseases, including psoriasis, lichen planus, rheumatoid arthritis, and inflammatory bowel disease. Paradoxically, numerous studies have reported new-onset psoriasis and lichen planus following TNFα antagonist therapy. Here, we show that genetic inhibition of Tnfa and Tnfr2 in zebrafish results in the mobilization of neutrophils to the skin. Using combinations of fluorescent reporter transgenes, fluorescence microscopy, and flow cytometry, we identified the local production of dual oxidase 1 (Duox1)-derived H₂O₂ by Tnfa- and Tnfr2-deficient keratinocytes as a trigger for the activation of the master inflammation transcription factor NF-κB, which then promotes the induction of genes encoding pro-inflammatory molecules. In addition, pharmacological inhibition of Duox1 completely abrogated skin inflammation, placing Duox1-derived H₂O₂ upstream of this positive feedback inflammatory loop. Strikingly, DUOX1 was drastically induced in the skin lesions of psoriasis and lichen planus patients. These results reveal a crucial role for TNFα/TNFR2 axis in the protection of the skin against DUOX1-mediated oxidative stress and could establish new therapeutic targets for skin inflammatory disorders.

Psoriasis and lichen planus are chronic, debilitating skin diseases that affect millions of people worldwide. TNFα is a multifunctional cytokine that mediates acute and chronic inflammation. While TNFα antagonist therapy is used for autoimmune or chronic inflammatory diseases, such as inflammatory bowel disease (IBD), numerous studies have reported new-onset psoriasis and lichen planus following such therapy. We have used the unique advantages of the zebrafish embryo to identify a novel phenotype that mirrors this unexplained and paradoxical onset of psoriasis and lichen planus. We found that depletion of Tnfa or its receptor Tnfr2 caused skin inflammation and hyperproliferation of keratinocytes through the activation of a Duox1/H₂O₂/NF-κB positive feedback inflammatory loop. Strikingly, DUOX1 was drastically induced in the skin lesions of psoriasis and lichen planus patients, and pharmacological inhibition of Duox1 abrogated skin inflammation, placing Duox1-derived H₂O₂ upstream of this inflammatory loop. Our results suggest that therapies targeting DUOX1 and H₂O₂ could provide innovative approaches to the management of skin inflammatory disorders.

Metabolic disruption in male mice due to fetal exposure to low but not high doses of bisphenol A (BPA): evidence for effects on body weight, food intake, adipocytes, leptin, adiponectin, insulin and glucose regulation

Exposure to bisphenol A (BPA) is implicated in many aspects of metabolic disease in humans and experimental animals. We fed pregnant CD-1 mice BPA at doses ranging from 5 to 50,000μg/kg/day, spanning 10-fold below the reference dose to 10-fold above the currently predicted no adverse effect level (NOAEL). At BPA doses below the NOAEL that resulted in average unconjugated BPA between 2 and 200pg/ml in fetal serum (AUC0-24h), we observed significant effects in adult male offspring: an age-related change in food intake, an increase in body weight and liver weight, abdominal adipocyte mass, number and volume, and in serum leptin and insulin, but a decrease in serum adiponectin and in glucose tolerance. For most of these outcomes non-monotonic dose-response relationships were observed; the highest BPA dose did not produce a significant effect for any outcome. A 0.1-μg/kg/day dose of DES resulted in some but not all low-dose BPA outcomes.

Cancer cachexia--pathophysiology and management

About half of all cancer patients show a syndrome of cachexia, characterized by anorexia and loss of adipose tissue and skeletal muscle mass. Cachexia can have a profound impact on quality of life, symptom burden, and a patient's sense of dignity. It is a very serious complication, as weight loss during cancer treatment is associated with more chemotherapy-related side effects, fewer completed cycles of chemotherapy, and decreased survival rates. Numerous cytokines have been postulated to play a role in the etiology of cancer cachexia. Cytokines can elicit effects that mimic leptin signaling and suppress orexigenic ghrelin and neuropeptide Y (NPY) signaling, inducing sustained anorexia and cachexia not accompanied by the usual compensatory response. Furthermore, cytokines have been implicated in the induction of cancer-related muscle wasting. Cytokine-induced skeletal muscle wasting is probably a multifactorial process, which involves a protein synthesis inhibition, an increase in protein degradation, or a combination of both. The best treatment of the cachectic syndrome is a multifactorial approach. Many drugs including appetite stimulants, thalidomide, cytokine inhibitors, steroids, nonsteroidal anti-inflammatory drugs, branched-chain amino acids, eicosapentaenoic acid, and antiserotoninergic drugs have been proposed and used in clinical trials, while others are still under investigation using experimental animals. There is a growing awareness of the positive impact of supportive care measures and development of promising novel pharmaceutical agents for cachexia. While there has been great progress in understanding the underlying biological mechanisms of cachexia, health care providers must also recognize the psychosocial and biomedical impact cachexia can have.

Effects of peripherally administered neuromedin U on energy and glucose homeostasis

Neuromedin U (NMU) is a highly conserved peptide reported to modulate energy homeostasis. Pharmacological studies have shown that centrally administered NMU inhibits food intake, reduces body weight, and increases energy expenditure. NMU-deficient mice develop obesity, whereas transgenic mice overexpressing NMU become lean and hypophagic. Two high-affinity NMU receptors, NMUR1 and NMUR2, have been identified. NMUR1 is found primarily in the periphery and NMUR2 primarily in the brain, where it mediates the anorectic effects of centrally administered NMU. Given the broad expression pattern of NMU, we evaluated whether peripheral administration of NMU has effects on energy homeostasis. We observed that acute and chronic peripheral administration of NMU in rodents dose-dependently reduced food intake and body weight and that these effects required NMUR1. The anorectic effects of NMU appeared to be partly mediated by vagal afferents. NMU treatment also increased core body temperature and metabolic rate in mice, suggesting that peripheral NMU modulates energy expenditure. Additionally, peripheral administration of NMU significantly improved glucose excursion. Collectively, these data suggest that NMU functions as a peripheral regulator of energy and glucose homeostasis and the development of NMUR1 agonists may be an effective treatment for diabetes and obesity.

Cachexia, malnutrition, the refeeding syndrome, and lessons from Goldilocks

Cachexia has plagued clinicians for centuries. Although all cachexia is related to malnutrition, cachexia associated with malignant diseases differs from starvation cachexia in that it is more recalcitrant to nutritional therapy. All cachexia responds to judicious nutritional support; however, cancer cachexia worsens autonomously as the disease advances and cannot be arrested or reversed by any known form of nutrition, hormonal, or pharmacologic therapy. Cachexia must be treated cautiously to avoid overfeeding syndrome, which may result in serious or dangerous complications or death.

Characterization of 7- and 19-month-old Tg2576 mice using multimodal in vivo imaging: limitations as a translatable model of Alzheimer's disease

With 90% of neuroscience clinical trials failing to see efficacy, there is a clear need for the development of disease biomarkers that can improve the ability to predict human Alzheimer's disease (AD) trial outcomes from animal studies. Several lines of evidence, including genetic susceptibility and disease studies, suggest the utility of fluorodeoxyglucose positron emission tomography (FDG-PET) as a potential biomarker with congruency between humans and animal models. For example, early in AD, patients present with decreased glucose metabolism in the entorhinal cortex and several regions of the brain associated with disease pathology and cognitive decline. While several of the commonly used AD mouse models fail to show all the hallmarks of the disease or the limbic to cortical trajectory, there has not been a systematic evaluation of imaging-derived biomarkers across animal models of AD, contrary to what has been achieved in recent years in the Alzheimer's Disease Neuroimaging Initiative (ADNI) (Miller, 2009). If animal AD models were found to mimic endpoints that correlate with the disease onset, progression, and relapse, then the identification of such markers in animal models could afford the field a translational tool to help bridge the preclinical-clinical gap. Using a combination of FDG-PET and functional magnetic resonance imaging (fMRI), we examined the Tg2576 mouse for global and regional measures of brain glucose metabolism at 7 and 19 months of age. In experiment 1 we observed that at younger ages, when some plaque burden and cognitive deficits have been reported, Tg2576 mice showed hypermetabolism as assessed with FDG-PET. This hypermetabolism decreased with age to levels similar to wild type (WT) counterparts such that the 19-month-old transgenic (Tg) mice did not differ from age matched WTs. In experiment 2, using cerebral blood volume (CBV) fMRI, we demonstrated that the hypermetabolism observed in Tg mice at 7 months could not be explained by changes in hemodynamic parameters as no differences were observed when compared with WTs. Taken together, these data identify brain hypermetabolism in Tg2576 mice which cannot be accounted for by changes in vascular compliance. Instead, the hypermetabolism may reflect a neuronal compensatory mechanism. Our data are discussed in the context of disease biomarker identification and target validation, suggesting little or no utility for translational based studies using Tg2576 mice.

Immunotoxin-induced ablation of melanopsin retinal ganglion cells in a non-murine mammalian model

In mammals, non-image-forming visual functions, including circadian photoentrainment and the pupillary light reflex, are thought to be mediated by the combination of rods, cones, and the melanopsin-expressing intrinsically photosensitive retinal ganglion cells (ipRGCs). Although several genetic models have been developed to clarify the individual roles of the rod, cone, and ipRGC systems in mediating non-image visual function, assessing the in vivo role(s) of the ipRGCs has been complicated by the possibility of ontogenetic issues in these genetically modified animal models. In the present study, we describe the development and validation of an immunotoxin that specifically targets the ipRGC population in the mature mammalian retina. This ipRGC immunotoxin, consisting of saporin conjugated to a melanopsin polyclonal antibody, was evaluated with respect to its effectiveness and specificity in depleting the ipRGC population in the fully developed rat retina. The results showed that the ipRGC toxin rapidly and permanently depleted approximately 70% of the ipRGC population, without inducing appreciable changes in the cell number or morphology of any of the non-melanopsin-containing retinal cell populations investigated. These findings suggest that the newly developed ipRGC immunotoxin provides a potent method for achieving relatively rapid, permanent, and selective depletion of the ipRGC population in a non-murine model system. The development of this ipRGC-ablation method is the next step in elucidating the role of ipRGCs in mediating non-visual and circadian light-resetting responses in a wide range of non-murine mammalian models.

The antiobesity effects of centrally administered neuromedin U and neuromedin S are mediated predominantly by the neuromedin U receptor 2 (NMUR2)

Neuromedin U (NMU) and neuromedin S (NMS) are structurally related neuropeptides that have been reported to modulate energy homeostasis. Pharmacological data have shown that NMU and NMS inhibit food intake when administered centrally and that NMU increases energy expenditure. Additionally, NMU-deficient mice develop obesity, whereas transgenic mice overexpressing NMU are lean and hypophagic. Two high-affinity NMU/NMS receptors, NMUR1 and NMUR2, have been identified. NMUR1 is predominantly expressed in the periphery, whereas NMUR2 is predominantly expressed in the brain, suggesting that the effects of centrally administered NMU and NMS are mediated by NMUR2. To evaluate the role of NMUR2 in the regulation of energy homeostasis, we characterized NMUR2-deficient (Nmur2(-/-)) mice. Nmur2(-/-) mice exhibited a modest resistance to diet-induced obesity that was at least in part due to reduced food intake. Acute central administration of NMU and NMS reduced food intake in wild-type but not in Nmur2(-/-) mice. The effects on activity and core temperature induced by centrally administered NMU were also absent in Nmur2(-/-) mice. Moreover, chronic central administration of NMU and NMS evoked significant reductions in body weight and sustained reductions in food intake in mice. In contrast, Nmur2(-/-) mice were largely resistant to these effects. Collectively, these data demonstrate that the anorectic and weight-reducing actions of centrally administered NMU and NMS are mediated predominantly by NMUR2, suggesting that NMUR2-selective agonists may be useful for the treatment of obesity.

Feeding behaviour in galanin knockout mice supports a role of galanin in fat intake and preference

It has been widely suggested that saturated fat consumption has fuelled the current obesity epidemic. Macronutrient choices appear to be important not only as potential factors influencing obesity, but also independently as risk factors for diabetes, cardiovascular disease and cancer. The neuropeptide galanin has previously been implicated in the regulation of fat intake, although its precise role has been contested. The present study investigated mice with targeted knockout of the galanin gene (GKO). We demonstrate that, when only a high fat diet (HFD) was available, wild-type (WT) animals consumed significantly more energy than the GKO mice (89.85 +/- 4.57 kJ/day versus 76.84 +/- 3.55 kJ/day, P < 0.001, n = 17 versus 15). Consistent with this, WT animals gained more body weight when fed the HFD than GKO animals (3.48 +/- 0.44 g versus 2.02 +/- 0.62 g, P < 0.001, n = 17 versus 15). In a macronutrient choice scenario, WT mice ate almost three-fold more fat than GKO animals (0.63 +/- 0.02 g versus 0.23 +/- 0.01 g, P < 0.001, n = 18 versus 24). Chronic administration of galanin by mini-osmotic pumps into the lateral ventricle of GKO animals partially reversed the fat avoidance phenotype. Fat intake was significantly lower in the phosphate-buffered saline-treated GKO group compared to galanin-treated GKO animals (0.32 +/- 0.01 g versus 0.38 +/- 0.01 g, P < 0.005, n = 17 versus 17). These data are compatible with the hypothesis that galanin specifically regulates fat intake, and implies that an antagonist to one or more of the galanin receptor subtype(s) may be of use in the treatment of some forms of obesity.

Is it time to reassess the BDNF hypothesis of depression?

The brain-derived neurotrophic factor (BDNF) hypothesis of depression postulates that a loss of BDNF is directly involved in the pathophysiology of depression, and that its restoration may underlie the therapeutic efficacy of antidepressant treatment. While this theory has received considerable experimental support, an increasing number of studies have generated evidence which is not only inconsistent, but also directly contradicts the hypothesis. This article provides a critical review of the clinical and preclinical studies which have been responsible for this controversy, outlining pharmacological, behavioural and genetic evidence which demonstrates the contrasting role of BDNF in regulating mood and antidepressant effects throughout the brain. I will also review key studies, both human and animal, which have investigated the association of a BDNF single-nucleotide polymorphism (Val66Met) with depression pathogenesis, and detail the number of inconsistencies which also afflict this novel area of BDNF research. The article will conclude by discussing why now is a critical time to reassess the original BDNF hypothesis of depression, and look towards the formation of new models that can provide a more valid account of the complex relationships between growth factors, mood disorders and their treatment.

Therapeutic potential of histamine H3 receptor agonist for the treatment of obesity and diabetes mellitus

Histamine H3 receptors (H3Rs) are located on the presynaptic membranes and cell soma of histamine neurons, where they negatively regulate the synthesis and release of histamine. In addition, H3Rs are also located on nonhistaminergic neurons, acting as heteroreceptors to regulate the releases of other amines such as dopamine, serotonin, and norepinephrine. The present study investigated the effects of H3R ligands on appetite and body-weight regulation by using WT and H3R-deficient mice (H3RKO), because brain histamine plays a pivotal role in energy homeostasis. The results showed that thioperamide, an H3R inverse agonist, increases, whereas imetit, an H3R agonist, decreases appetite and body weight in diet-induced obese (DiO) WT mice. Moreover, in DiO WT mice, but not in DiO H3RKO mice, imetit reduced fat mass, plasma concentrations of leptin and insulin, and hepatic triglyceride content. The anorexigenic effects of imetit were associated with a reduction in histamine release, but a comparable reduction in histamine release with alpha-fluoromethylhistidine, an inhibitor of histamine synthesis, increased appetite. Moreover, the anorexigenic effects of imetit were independent of the melanocortin system, because imetit comparably reduced appetite in melanocortin 3 and 4 receptor-deficient mice. The results provide roles of H3Rs in energy homeostasis and suggest a therapeutic potential for H3R agonists in the treatment of obesity and diabetes mellitus.

A genetic approach for investigating vagal sensory roles in regulation of gastrointestinal function and food intake

Sensory innervation of the gastrointestinal (GI) tract by the vagus nerve plays important roles in regulation of GI function and feeding behavior. This innervation is composed of a large number of sensory pathways, each arising from a different population of sensory receptors. Progress in understanding the functions of these pathways has been impeded by their close association with vagal efferent, sympathetic, and enteric systems, which makes it difficult to selectively label or manipulate them. We suggest that a genetic approach may overcome these barriers. To illustrate the potential value of this strategy, as well as to gain insights into its application, investigations of CNS pathways and peripheral tissues involved in energy balance that benefited from the use of gene manipulations are reviewed. Next, our studies examining the feasibility of using mutations of developmental genes for manipulating individual vagal afferent pathways are reviewed. These experiments characterized mechanoreceptor morphology, density and distribution, and feeding patterns in four viable mutant mouse strains. In each strain a single population of vagal mechanoreceptors innervating the muscle wall of the GI tract was altered, and was associated with selective effects on feeding patterns, thus supporting the feasibility of this strategy. However, two limitations of this approach must be addressed for it to achieve its full potential. First, mutation effects in tissues outside the GI tract can contribute to changes in GI function or feeding. Additionally, knockouts of developmental genes are often lethal, preventing analysis of mature innervation and ingestive behavior. To address these issues, we propose to develop conditional gene knockouts restricted to specific GI tract tissues. Two genes of interest are brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT-3), which are essential for vagal afferent development. Creating conditional knockouts of these genes requires knowledge of their GI tract expression during development, which little is known about. Preliminary investigation revealed that during development BDNF and NT-3 are each expressed in several GI tract regions, and that their expression patterns overlap in some tissues, but are distinct in others. Importantly, GI tissues that express BDNF or NT-3 are innervated by vagal afferents, and expression of these neurotrophins occurs during the periods of axon invasion and receptor formation, consistent with roles for BDNF or NT-3 in these processes and in receptor survival. These results provide a basis for targeting BDNF or NT-3 knockouts to specific GI tract tissues, and potentially altering vagal afferent innervation only in that tissue (e.g., smooth muscle vs. mucosa). Conditional BDNF or NT-3 knockouts that are successful in selectively altering a vagal GI afferent pathway will be valuable for developing an understanding of that pathway's roles in GI function and food intake.

High-fat hyperphagia in neurotrophin-4 deficient mice reveals potential role of vagal intestinal sensory innervation in long-term controls of food intake

Neurotrophin-4 (NT-4) deficient mice exhibit substantial loss of intestinal vagal afferent innervation and short-term deficits in feeding behavior, suggesting reduced satiation. However, they do not show long-term changes in feeding or body weight because of compensatory behaviors. The present study examined whether high-fat hyperphagia induction would overcome compensation and reveal long-term effects associated with the reduced vagal sensory innervation of NT-4 mutants. First, modifications of a feeding schedule previously developed in rats were examined in wild-type mice to identify the regimen most effective at producing hyperphagia. The most successful schedule, which was run for 26 days, included access to a 43%-fat diet and pelleted chow every other day and access to only powdered chow on the alternate days. On high-fat access days mice consumed 25% more calories than mice with continuous daily access to the same high-fat diet and pelleted chow. This feeding regimen also induced hyperphagia in NT-4 deficient mice and their wild-type controls: on high-fat exposure days mutants consumed 35% more calories relative to continuous-access mutants, and wild types ate 25% more than continuous-access wild types. Moreover, on high-fat access days the alternating NT-4 mutants significantly increased caloric intake by 9% compared to alternating wild types. Thus, high-fat hyperphagia appeared to override compensation, permitting short-term changes in meal consumption by mutants that accrued into long-term changes in total daily food intake. This raises the possibility that intestinal vagal sensory innervation contributes to long-term, as well as to short-term regulation of food intake.

Pharmaceutical approaches to the treatment of obesity

The recent increase in pharmaceutical companies' efforts toward the treatment of obesity reflects recognition of the related health risks, the growth of knowledge about mechanisms that control energy balance, and the potential market for new compounds. The current patent literature gives a picture of the targets that are available for pharmaceutical intervention; these include signals of satiety and signals related to fat storage that act in the hypothalamus. The regulation of energy use and storage in adipocytes and the reduction of intestinal absorption of energy are also pharmaceutical focus areas. The multiplicity of targets illustrates not only the many potential approaches to the treatment of obesity but also the complexity and redundancy of the processes that regulate energy storage in the body.

Blockade of the Leptin-Sensitive Pathway Markedly Reduces Alcohol Consumption in Mice

BACKGROUND

The neuropeptide leptin links adipose stores with hypothalamic centers and serves as an endocrine signal involved in the regulation of appetite (and possibly in the endorphinergic modulation of the drug reward system). Increased plasma leptin has been observed at the onset of alcohol withdrawal in humans, and ethanol consumption after withdrawal was increased by injection of leptin in mice. We addressed the role of leptin in alcohol-related behaviors by studying ethanol consumption in two strains of spontaneously mutant mice that lack leptin (ob/ob) or the leptin receptor (db/db).

METHODS

Two strains of mutant leptin-deficient (ob/ob) or leptin-resistant (db/db) mice were tested in a two-bottle-choice paradigm and were compared with wild-type (C57BL/6 inbred strain) mice. The effects of leptin injection on voluntary ethanol intake have been investigated in ob/ob and C57BL/6 mice.

RESULTS

Males and females of both mutant strains showed a significantly lower preference for alcohol in a two-bottle-choice paradigm compared with wild-type mice. Male ob/ob mice demonstrated slightly higher avoidance of bitter taste, and females of the both mutant strains showed a reduced preference for saccharin solutions. Administration of leptin (1 mg/kg intraperitoneally, daily for 8 days) altered body weight but failed to increase the preference for ethanol in ob/ob mice; i.e., we could not correct the effects of leptin deficiency on alcohol consumption by the injection of leptin. Also, there were no differences between the effects of leptin (1 mg/kg intraperitoneally, daily for 8 days) and saline injections on alcohol consumption in C57BL/6 mice.

CONCLUSIONS

These data show that blockade of the leptin pathway markedly decreases the preference for alcohol intake, but this decrease may be the result of compensatory or developmental changes in other systems rather than a more direct effect of leptin on alcohol consumption.

Ghrelin, appetite, and gastric motility: the emerging role of the stomach as an endocrine organ

Recent progress in the field of energy homeostasis was triggered by the discovery of adipocyte hormone leptin and revealed a complex regulatory neuroendocrine network. A late addition is the novel stomach hormone ghrelin, which is an endogenous agonist at the growth hormone secretagogne receptor and is the motilin-related family of regulatory peptides. In addition to its ability to stimulate GH secretion and gastric motility, ghrelin stimulates appetite and induces a positive energy balance leading to body weight gain. Leptin and ghrelin are complementary, yet antagonistic, signals reflecting acute and chronic changes in energy balance, the effects of which are mediated by hypothalamic neuropeptides such as neuropeptide Y and agouti-related peptide. Endocrine and vagal afferent pathways are involved in these actions of ghrelin and leptin. Ghrelin is a novel neuroendocrine signal possessing a wide spectrum of biological activities that illustrates the importance of the stomach in providing input into the brain. Defective ghrelin signaling from the stomach could contribute to abnormalities in energy balance, growth, and associated gastrointestinal and neuroendocrine functions.

Leptin treatment ameliorates anxiety in ob/ob obese mice

We investigated whether or not administered leptin influences anxiety-like behavior in ob/ob mice. Repeated intraperitoneal administrations of leptin were continued for 5 days. Anxiety was assessed in the standard elevated plus maze. Body weight was measured daily. Repeated administrations of leptin significantly increased the percentage of the total number of entries in the open arms and the number of total entries. The body weight was significantly reduced by 13.2% after treatment. Leptin treatment ameliorated not only obesity but also anxiety in ob/ob mice. Our results indicate that the treatment of obesity may lead to the solution of psychological problems.

Obesity--a chronic health problem in cloned mice?

The majority of cloned animals derived by nuclear transfer die during gestation and display neonatal abnormalities. However, because of the long generation interval of cloned animal species, the long-term consequences of cloning on health have been difficult to access. Recent studies in mice have provided evidence that cloned animals might have chronic health problems such as obesity. Obesity in cloned mice is likely to reflect epigenetic abnormalities that arise partly from inadequate nuclear programming; these obese mice display a unique phenotype that is suggestive of a defect other than malfunction of the leptin-melanocortin system, which occurs in most rodent models of obesity and in human obesity.

What we have learned about cachexia in gastrointestinal cancer

It is appreciated widely by clinicians that significant malnutrition accompanies malignant processes in approximately 50% of patients and eventually leads to severe wasting which accounts for approximately 30% of cancer-related deaths overall, 30-50% of deaths in patients with gastrointestinal tract cancers, and up to 80% of deaths in patients with advanced pancreatic cancer. The body wasting known as cancer cachexia is a complex syndrome characterized by progressive tissue depletion and decreased nutrient intake that is manifested clinically as inexplicable, recalcitrant anorexia and inexorable host weight loss. Decreased nutritional intake, increased metabolic expenditure and dysfunctional metabolic processes, including hormonal and cytokine-related abnormalities, all appear to play roles in the development of cancer cachexia. Although this condition of advanced protein-calorie malnutrition, sometimes described as the cancer anorexia-cachexia syndrome, is not entirely understood, it appears to be multifactorial, is a major cause of morbidity and mortality in cancer patients, and ultimately leads to death. Therapeutic interventions have met with little success, and, regardless of tremendous efforts throughout the decades, the exact nature of the mediators responsible for cancer cachexia remain elusive. The pathogenesis of cancer cachexia appears to be related to proinflammatory cytokines, alterations in the neuroendocrine axis and tumor-derived catabolic factors. Despite trials of conventional and/or aggressive nutritional support by a myriad of feeding techniques, patients with cancer cachexia have failed to gain consistent significant benefits in terms of weight gain, functional ability, quality of life or survival. Additionally, attempts to ameliorate the abnormal clinical and metabolic features of cancer cachexia with a variety of pharmacologic agents have met with only limited success. Either until cancer of the gastrointestinal tract can be cured or until it is possible to identify the exact causes and mechanisms of the cancer cachexia syndrome, the most realistic and practical options currently are directed toward minimizing adverse gastrointestinal side effects or complications of the malignant process and/or therapy, as well as increasing appetite, food intake and nutrient utilization in an effort to enhance quality of life and improve survival.

Orexin reverses cholecystokinin-induced reduction in feeding

AIM

This study was designed to investigate the effect of orexin on anorexia induced by cholecystokinin (CCK),a peripheral satiety signal.

METHODS

We administered orexin A (0.01-1 nmol/mouse) and CCK-8 (3 nmol/mouse) to mice. Food intake was measured at different time-points: 20 min, 1, 2 and 4 h post-intracerebroventricular (i.c.v.) or intraperitoneal (i.p.) administrations.

RESULTS

Intracerebroventricular-administered orexin significantly increased food intake in a dose-dependent manner. The inhibitory effect of i.p.-administered CCK-8 on food intake was significantly negated by the simultaneous i.c.v. injection of orexin in a dose-dependent manner.

CONCLUSIONS

Orexin reversed the CCK-induced loss of appetite. Our results indicate that orexin might be a promising target for pharmacological intervention in the treatment of anorexia and cachexia induced by various diseases.

Reduced voluntary activity precedes adult-onset obesity in Nhlh2 knockout mice

Targeted deletion of the neuronal basic helix-loop-helix transcription factor Nhlh2 results in adult-onset obesity in mice. Measurement of body weight and body composition in animals aged 3-25 weeks indicates that while male and female Nhlh2 knockout (N2KO) animals both show adult-onset obesity, the time frame for development of obesity is different, with females becoming obese by 7 weeks of age and males becoming obese by 10 weeks of age. Heterozygous (HET) animals also become obese but with a slower onset, indicating a dosage effect for the activity of the Nhlh2 transcription factor. Food intake, body temperature, and voluntary activity were measured in both preobese and obese N2KO, HET, and wild-type (WT) animals to determine which factors contributed to weight gain. While increased food intake and decreased body temperature were found in older obese N2KO animals, only reduced physical activity preceded the onset of obesity in N2KO mice. N2KO animals had no deficit in either circadian rhythm or balance and motor control, indicating that reduced voluntary activity is the result of a behavioral change. These data demonstrate a role for the Nhlh2 transcription factor in controlling genes important to energy expenditure, and more specifically voluntary physical activity of animals.

Anorexia in space and possible etiologies: an overview

Space travelers experience a flight duration-dependent loss in weight and body mass while in a microgravity environment, despite the absence of increased energy expenditure. Anorexia in space can lead to in-flight caloric deficits of 1330 kcal per 70 kg astronaut per day in the presence of abundant food and has a critical effect on endurance and performance. Microgravity, alterations in the light-and-dark cycle, and exposure to radiation energy are the environmental stresses believed to influence appetite, food intake, and gastrointestinal function during space flight. Review of data and recent studies in rodents during microgravity showed a release of stress hormones and complex neuroendocrine and physiologic changes involving the modulation of hypothalamic activity, food intake-related hormones, and cytokines. The shift of dietary preference to carbohydrates, which occurs in astronauts, denotes a stress physiologic response and augments free-plasma tryptophan concentration in the brain, the precursor of the potent anorexic agent, serotonin (5-HT). Alterations of other neuroendocrine mediators, including corticotropin-releasing factor (CRF), coordinate the stress response, leading to a decrease in appetite and gastrointestinal function. Our laboratories used the antiorthostatic tail-suspension technique to successfully mimic some of these anorexia-related stress responses and to directly demonstrate the role of 5-HT in microgravity-related decreased food intake and delayed gastric emptying. Further rodent studies from our laboratories demonstrated the adverse effect of altered dark-and-light cycles on food intake and body weight. Radiation energy, through its documented effects on appetite, probably contributes to the decreased caloric intake by astronauts. Modulation of hypothalamic activity, 5-HT, and CRF play a critical role in anorexia related to microgravity and circadian rhythm alterations. Specific gene knockout mice (e.g., 5-HT or CRF and their respective receptors) may prove fruitful in defining the pathways by which anorexia in space occurs. An understanding of these pathophysiologic problems as they relate to appetite, food intake, gastric emptying and gastrointestinal function, sufficiently to derive successful practical solutions, may lead to a quantitative enhancement of physiologic well-being and performance status, serving as a productive countermeasure in space.

Emerging functions of neuropeptide Y Y(2) receptors in the brain

The Y(2) receptor is the predominant neuropeptide Y (NPY) receptor subtype in the brain. Y(2) receptor mRNA is discretely distributed in the brain, including specific subregions of the hippocampus and the hypothalamus, and is largely consistent with the distribution of Y(2) receptor protein demonstrated by radioligand-binding methods. Y(2) receptor-mediated effects have been reported principally based on the observations using the C-terminal fragments of NPY. Recent studies indicate an involvement of the receptor in food intake, gastrointestinal motility, cardiovascular regulation, and neuronal excitability. Very recently, Y(2) receptor selective antagonist has been developed and Y(2) receptor-deficient animals have been created. These new pharmacological tools will help to clarify the roles of this receptor in brain functions.