Peripheral signals conveying metabolic information to the brain: short-term and long-term regulation of food intake and energy homeostasis

Pre- and post- prandial appetite hormone levels in normal weight and severely obese women

Background

Appetite is affected by many factors including the hormones leptin, ghrelin and adiponectin. Ghrelin stimulates hunger, leptin promotes satiety, and adiponectin affects insulin response. This study was designed to test whether the pre- and postprandial response of key appetite hormones differs in normal weight (NW) and severely obese (SO) women.

Methods

Twenty three women ages 25–50 were recruited for this study including 10 NW (BMI = 23.1 ± 1.3 kg/m²) and 13 SO (BMI = 44.5 ± 7.1 kg/m²). The study was conducted in a hospital-based clinical research centre. Following a 12-hour fast, participants had a baseline blood draw, consumed a moderately high carbohydrate meal (60% carbohydrate, 20% protein, 20% fat) based on body weight. Postprandially, participants had six blood samples drawn at 0, 15, 30, 60, 90, and 120 minutes. Primary measures included pre- and post-prandial total ghrelin, leptin, adiponectin and insulin. A repeated measures general linear model was used to evaluate the hormone changes by group and time (significance p ≤ 0.05).

Results

There were significant differences between the NW and the SO for all hormones in the preprandial fasting state. The postprandial responses between the SO versus NW revealed: higher leptin (p < 0.0001), lower adiponectin (p = 0.04), trend for lower ghrelin (p = 0.06) and insulin was not different (p = 0.26). Postprandial responses over time between the SO versus NW: higher leptin (p < 0.001), lower ghrelin and adiponectin (p = 0.004, p = 0.015, respectively), and trend for higher insulin (p = 0.06).

Conclusion

This study indicates that significant differences in both pre- and selected post- prandial levels of leptin, ghrelin, adiponectin and insulin exist between NW and SO women. Improving our understanding of the biochemical mechanisms accounting for these differences in appetite hormones among individuals with varying body size and adiposity should aid in the development of future therapies to prevent and treat obesity.

Influência de alimentos líquidos e sólidos no controle do apetite

Este trabalho discute o papel dos alimentos líquidos e sólidos na ingestão alimentar, fundamentando-se em uma revisão crítica sobre o assunto. Utilizaram-se os principais bancos de dados nacionais e internacionais em saúde, entre eles, Medline/PubMed, Web of Science, Lilacs, SciELO. A busca bibliográfica compreendeu o período de 1980 a 2008. Os resultados atuais das pesquisas indicam que o estado físico do alimento pode influenciar o consumo alimentar, tanto a curto quanto a longo prazo, e que os alimentos líquidos exercem um menor poder sacietógeno, em comparação aos sólidos. Os possíveis mecanismos envolvidos nesse fraco controle do apetite pelos líquidos são: falta de mastigação, fase cefálica da ingestão menos pronunciada, esvaziamento gástrico mais rápido e fatores cognitivos. Conclui-se que o uso de alimentos líquidos, em especial bebidas energéticas, deve ser moderado tanto na prevenção como no tratamento da obesidade.

Leptin receptor gene expression and number in the brain are regulated by leptin level and nutritional status

Hormone potency depends on receptor availability, regulated via gene expression and receptor trafficking. To ascertain how central leptin receptors are regulated, the effects of leptin challenge, high-fat diet, fasting and refeeding were measured on leptin receptor number and gene expression. These were measured using quantitative (125)I-labelled leptin in vitro autoradiography and in situ hybridisation, respectively. Ob-R (all forms of leptin receptor) expression in the choroid plexus (CP) was unchanged by high-fat diet or leptin challenge, whereas fasting increased but refeeding failed to decrease expression. (125)I-labelled leptin binding to the CP was increased by fasting and returned to basal levels on refeeding. (125)I-Labelled leptin was reduced by leptin challenge and increased by high-fat feeding. Ob-Rb (signalling form) in the arcuate (ARC) and ventromedial (VMH) nuclei was increased after fasting and decreased by refeeding. Leptin challenge increased Ob-Rb expression in the ARC, but not after high-fat feeding. In general, changes in gene expression in the ARC and VMH appeared to be largely due to changes in area rather than density of labelling, indicating that the number of cells expressing Ob-Rb was the parameter that contributed most to these changes. Leptin stimulation of suppressor of cytokine signalling 3 (SOCS3), a marker of stimulation of the Janus kinase/signal transducer and activator of transcription 3 (JAK/STAT3) pathway, was unchanged after high-fat diet. Thus, early loss of leptin sensitivity after high-fat feeding is unrelated to down-regulation of leptin receptor expression or number and does not involve the JAK/STAT pathway. The effect of leptin to decrease (125)I-labelled leptin binding and the loss of ability of leptin to up-regulate Ob-Rb expression in the ARC after high-fat feeding offer potential mechanisms for the development of leptin insensitivity in response to both hyperleptinaemia and high-fat diet.

Dietary sweeteners containing fructose: overview of a workshop on the state of the science

The occurrence and impact of fructose in the American food supply has garnered much recent attention in the popular press as well as the scientific community. This paper provides an overview of a workshop cosponsored by the International Life Sciences Institute North America and the USDA, Agricultural Research Service, titled "State of the Science on Dietary Sweeteners Containing Fructose." Papers in the workshop addressed the chemical composition and properties of dietary sweeteners that contain fructose, the sources and amount of fructose in the American diet, and the metabolism of fructose in the human body. Further, the authors of each paper assessed the strength of the existing data linking dietary fructose intake and risk for overweight, metabolic syndrome, type 2 diabetes mellitus, cardiovascular disease, and other disorders. The assessment considered factors in study design, including the amount fed, the food form, the length of the study, the characteristics of the subjects, the specific methodology, and other potential confounders including diet. In addition to papers assessing the basic science of fructose, some papers also addressed consumer concern about sugars and fructose in the diet, the way fructose and other sugars are presented in the media, and the resulting confusion of consumers about fructose and other sugars in the diet. The purpose of the papers in the aggregate was to clarify what data exist about fructose and what the gaps are in the data and to help both scientists and consumers understand issues surrounding fructose in the food supply.

A dietary fat excess alters metabolic and neuroendocrine responses before the onset of metabolic diseases

Early changes in neuroendocrine pathways are essential in the development of metabolic pathologies. Thus, it is important to have a better understanding of the signals involved in their initiation. Long-term consumption of high-fat diets induces insulin resistance, obesity, diabetes. Here, we have investigated early neural and endocrine events in the hypothalamus and hippocampus induced by a short-term high fat, low carbohydrate diet in adult male Wistar rats. The release of serotonin, which is closely associated with the actions of insulin and leptin, was measured, by electrochemical detection following reverse-phase liquid chromatography (HPLC), in the extracellular space of the medial hypothalamus and the dorsal hippocampus in samples obtained from non-anesthetized animals, by microdialysis. The high-fat diet had a specific effect on the hypothalamus. Serotonin release induced by food intake was reduced after 1 week, and effectively ceased after 6 weeks of the diet. After 1 week, there was an increased gene expression of the insulin receptor and the insulin receptor substrates IRS1 and IRS2, as measured by real-time PCR. After 6 weeks of diet, insulin gene expression increased. Leptinemia increased in all cases. This new data support the concept that high-fat diets, in addition to have peripheral effects, cause a rapid alteration in specific central mechanisms involved in energy and glucose homeostasis. The changes in the gene expression of insulin and signaling elements represent possible adaptations aimed at counterbalancing the reduced responsiveness of the serotonergic system to nutritional signals and maintaining homeostasis.

Effects of weight loss on visceral and abdominal subcutaneous adipose tissue blood-flow and insulin-mediated glucose uptake in healthy obese subjects

OBJECTIVE

Rapid weight loss with very-low-calorie diet (VLCD) is known to improve insulin sensitivity and decrease adipose tissue masses. The aim was to investigate the effects of VLCD on adipose tissue regional glucose uptake (rGU) and perfusion and their association with adipokines.

RESEARCH DESIGN AND METHODS

Sixteen healthy obese (body mass index 33+/-1.1 kg/m(2)) subjects underwent VLCD for 6 weeks. RGU and perfusion were measured using [(18)F]-fluoro-deoxy-glucose, [(15)O]H(2)O and positron emission tomography.

RESULTS

Blood-flow and rGU expressed per gram of adipose tissue were higher in visceral fat compared to abdominal subcutaneous fat (P<0.01 for both). Dieting decreased weight by 11+/-0.9 kg (P<0.0001). Visceral adipose fat decreased by 25% (P<0.001) and abdominal subcutaneous fat by 16% (P<0.001). Whole body insulin sensitivity increased by 33% (P<0.01). Perfusion of both fat depots decreased (P<0.001), while rGU remained unchanged. Among the adipokines, leptin and interleukin-6 levels seemed to be associated with abdominal subcutaneous and intra-abdominal adipose tissue insulin resistance but not with adipose tissue perfusion.

CONCLUSIONS

Abdominal adipose tissue perfusion and rGU are not related in obesity. Rapid weight loss decreases perfusion through adipose tissue depots but has no influence on rGU demonstrating the 'sink' role of adipose tissue.

Bovine gene polymorphisms related to fat deposition and meat tenderness

Leptin, thyroglobulin and diacylglycerol O-acyltransferase play important roles in fat metabolism. Fat deposition has an influence on meat quality and consumers' choice. The aim of this study was to determine allele and genotype frequencies of polymorphisms of the bovine genes, which encode leptin (LEP), thyroglobulin (TG) and diacylglycerol O-acyltransferase (DGAT1). A further objective was to establish the effects of these polymorphisms on meat characteristics. We genotyped 147 animals belonging to the Nelore (Bos indicus), Canchim (5/8 Bos taurus + 3/8 Bos indicus), Rubia Gallega X Nelore (1/2 Bos taurus + 1/2 Bos indicus), Brangus Three-way cross (9/16 Bos taurus + 7/16 Bos indicus) and Braunvieh Three-way cross (3/4 Bos taurus + 1/4 Bos indicus) breeds. Backfat thickness, total lipids, marbling score, ribeye area and shear force were fitted, using the General Linear Model (GLM) procedure of the SAS software. The least square means of genotypes and genetic groups were compared using Tukey's test. Allele frequencies vary among the genetic groups, depending on Bos indicus versus Bos taurus influence. The LEP polymorphism segregates in pure Bos indicus Nelore animals, which is a new finding. The T allele of TG is fixed in Nelore, and DGAT1 segregates in all groups, but the frequency of allele A is lower in Nelore animals. The results showed no association between the genotypes and traits studied, but a genetic group effect on these traits was found. So, the genetic background remains relevant for fat deposition and meat tenderness, but the gene markers developed for Bos taurus may be insufficient for Bos indicus.

Anterograde transneuronal viral tract tracing reveals central sensory circuits from white adipose tissue

The origins of the sympathetic nervous system (SNS) innervation of white adipose tissue (WAT) have been defined using the transneuronal viral retrograde tract tracer, pseudorabies virus. Activation of this SNS innervation is acknowledged as the principal initiator of WAT lipolysis. The central control of WAT lipolysis may require neural feedback to a brain-SNS-WAT circuit via WAT afferents. Indeed, conventional tract tracing studies have demonstrated that peripheral pseudounipolar dorsal root ganglion (DRG) sensory cells innervate WAT. The central nervous system projections of WAT afferents remain uncharted, however, and form the focus of the present study. We used the H129 strain of the herpes simplex virus-1 (HSV-1), an anterograde transneuronal viral tract tracer, to define the afferent circuits projecting from WAT to the central nervous system. Siberian hamster inguinal (IWAT) or epididymal WAT was injected with H129 and the neuraxis processed for HSV-1 immunoreactivity. We found substantial overlap in the pattern of WAT sensory afferent projections with multiple SNS outflow sites along the neuraxis, suggesting the possibility of WAT sensory-SNS circuits that could regulate WAT SNS drive and thereby lipolysis. Previously, we demonstrated that systemic 2-deoxy-d-glucose (2DG) elicited increases in the SNS drive to IWAT. Here, we show that systemic 2DG administration also significantly increases multiunit spike activity arising from decentralized IWAT afferents. Collectively, these data provide structural and functional support for the existence of a sensory WAT pathway to the brain, important in the negative feedback control of lipid mobilization.

Glycemia and insulinemia evaluation after high-sucrose and high-fat diets in lean and overweight/obese women

The study investigates the effect of weight-maintaining high-sucrose (HSD) and high-fat (HFD) diets on plasma glucose and insulin concentrations in lean and obese women, and verifies the correlation between insulin profile and body composition. Lean (G1 group, n=6, BMI= 21.4 (20.2-22.8) kg/m2) and overweight/obese (G2 group, n=6, BMI 28.6 (25.1-32.1) kg/m2) women participated in the study. HSD (59% total carbohydrate with 23% sucrose; 28% lipid) or HFD (42% total carbohydrate with 1.3% sucrose; 45% lipid) diets were consumed under free-living conditions for 14 days. Anthropometry and body composition were assessed before and after HSD and HFD diets following-up. Fasting and postprandial (at 30, 60, 180 and 240 min) glucose and insulin were determined. HOMA-IR and QUICK index were also calculated. Fasting and postprandial glucose and insulin concentration did not differ significantly between groups or diets. However, there was a positive and significant correlation between plasma fasting and postprandial insulin concentrations and BMI, percentage of total body fat (% TBF) and HOMA-IR index. In addition, carbohydrate and sucrose intake presented a positive and significant correlation with insulin concentration and HOMA-IR at 180 min postprandial, after adjusting for energy intake and % TBF (p<0.05). These results suggest that altering the profile of the macronutrients in the diet can modify glycemia and insulinemia homeostasis, regardless of energy intake and adiposity. On the other hand, the overweight/obese women can maintain a stable metabolic profile with the habitual diet.

High-fructose corn syrup, energy intake, and appetite regulation

High-fructose corn syrup (HFCS) has been implicated in excess weight gain through mechanisms seen in some acute feeding studies and by virtue of its abundance in the food supply during years of increasing obesity. Compared with pure glucose, fructose is thought to be associated with insufficient secretion of insulin and leptin and suppression of ghrelin. However, when HFCS is compared with sucrose, the more commonly consumed sweetener, such differences are not apparent, and appetite and energy intake do not differ in the short-term. Longer-term studies on connections between HFCS, potential mechanisms, and body weight have not been conducted. The main objective of this review was to examine collective data on associations between consumption of HFCS and energy balance, with particular focus on energy intake and its regulation.

Endocrine and metabolic effects of consuming beverages sweetened with fructose, glucose, sucrose, or high-fructose corn syrup

Our laboratory has investigated 2 hypotheses regarding the effects of fructose consumption: 1) the endocrine effects of fructose consumption favor a positive energy balance, and 2) fructose consumption promotes the development of an atherogenic lipid profile. In previous short- and long-term studies, we showed that consumption of fructose-sweetened beverages with 3 meals results in lower 24-h plasma concentrations of glucose, insulin, and leptin in humans than does consumption of glucose-sweetened beverages. We have also tested whether prolonged consumption of high-fructose diets leads to increased caloric intake or decreased energy expenditure, thereby contributing to weight gain and obesity. Results from a study conducted in rhesus monkeys produced equivocal results. Carefully controlled and adequately powered long-term studies are needed to address these hypotheses. In both short- and long-term studies, we showed that consumption of fructose-sweetened beverages substantially increases postprandial triacylglycerol concentrations compared with glucose-sweetened beverages. In the long-term studies, apolipoprotein B concentrations were also increased in subjects consuming fructose, but not in those consuming glucose. Data from a short-term study comparing consumption of beverages sweetened with fructose, glucose, high-fructose corn syrup, and sucrose suggest that high-fructose corn syrup and sucrose increase postprandial triacylglycerol to an extent comparable with that induced by 100% fructose alone. Increased consumption of fructose-sweetened beverages along with increased prevalence of obesity, metabolic syndrome, and type 2 diabetes underscore the importance of investigating the metabolic consequences of fructose consumption in carefully controlled experiments.

Hypophagia induced by glucocorticoid deficiency is associated with an increased activation of satiety-related responses

Glucocorticoids have major effects on food intake, demonstrated by the decrease of food intake following adrenalectomy. Satiety signals are relayed to the nucleus of the solitary tract (NTS), which has reciprocal projections with the arcuate nucleus (ARC) and paraventricular nucleus (PVN) of the hypothalamus. We evaluated the effects of glucocorticoids on the activation of hypothalamic and NTS neurons induced by food intake in rats subjected to adrenalectomy (ADX) or sham surgery 7 days before the experiments. One-half of ADX animals received corticosterone (ADX+B) in the drinking water (B: 25 mg/l). Fos/tyrosine hydroxylase (TH), Fos/corticotrophin-releasing factor (CRF) and Fos immunoreactivity were assessed in the NTS, PVN, and ARC, respectively. Food intake and body weight were reduced in the ADX group compared with sham and ADX+B groups. Fos and Fos/TH in the NTS, Fos, and Fos/CRF immunoreactive neurons in the PVN and Fos in the ARC were increased after refeeding, with higher number in the ADX group, compared with sham and ADX+B groups. CCK administration showed no hypophagic effect on ADX group despite a similar increase of Fos/TH immunoreactive neurons in the NTS compared with sham and ADX+B groups, suggesting that CCK alone cannot further increase the anorexigenic effect induced by glucocorticoid deficiency. The present data indicate that glucocorticoid withdrawal reduced food intake, which was associated with higher activation of ARC, CRF neurons of the PVN, and catecholaminergic neurons of the NTS. In the absence of glucocorticoids, satiety signals elicited during a meal lead to an augmented activation of brain stem and hypothalamic pathways.

Leptin and its metabolic interactions: an update

Obesity results from an abnormal accumulation of fat in the white adipose tissue. Recent research utilizing genetic models of obesity in rodents has implicated a major role of leptin as a controller of obesity. Leptin is a 167-amino acid peptide hormone encoded by the obesity gene (ob), which is secreted by adipocytes and plays an important role in regulating food intake, energy expenditure and adiposity. Leptin receptors (OB-R) are expressed in the central nervous system mainly in afferent satiety centres of hypothalamus and in peripheral organs such as adipose tissues, skeletal muscles, pancreatic beta-cells and liver, thus indicating the autocrine and paracrine role of leptin in energy regulation. In human beings, a highly organized circadian pattern of leptin secretion is observed with peak levels in the midnight probably resulting from cumulative hyperinsulinemia of entire day. Leptin has a dual role in weight maintenance. Leptin reflects total body adipose tissue mass whereas in conditions of negative and positive energy balance, the dynamic changes in plasma leptin concentration function as a sensor of energy balance and influence the efferent energy regulation pathways. Many effects of leptin on metabolism are mediated by interaction with Insulin and also by synergistic action with cholecystokinin. Besides physiological roles, leptin may influence pathological conditions like obesity-associated atherosclerosis, oxidative stress and cancers. The purpose of the present review is to summarize the important aspects of the biology, actions, and regulation of leptin and to serve as an update of new information.

Body energy homeostasis

Evidence for the regulation of body energy is reviewed from the homeostatic perspective of Claude Bernard and Walter Cannon. The complementary roles of food intake and energy expenditure in the maintenance and defense of energy balance are considered. Particular attention is paid to the roles adjustments in energy expenditure play in this process and to recent investigations identifying their metabolic underpinnings. This is followed by a consideration of the many newly identified signals of body energy status and the pathways and feedback loops they utilize to inform the central regulating system. Finally, various naturally occurring and experimentally induced alterations in the regulated level of body energy are described and discussed. It is concluded that, though early investigators did not expressly consider energy a regulated feature of the milieu interieur, more recent research has provided a sound basis for judging the regulation of body energy to be another homeostatic process.

The relative impact of chronic food restriction and acute food deprivation on plasma hormone levels and hypothalamic neuropeptide expression

Our understanding of the central regulation of food intake and body weight has increased tremendously through implication of a high number of neuropeptides. However, lack of all-embracing studies have made comparison difficult in the past. The objective of this study was to demonstrate the relative importance of the different neuropeptides in terms of involvement in appetite regulatory mechanisms. We quantified expression levels of 21 hypothalamic neuropeptides and circulating levels of leptin, insulin, corticosterone, adrenocorticotropic hormone, ghrelin and adiponectin in rats after acute food deprivation and chronic food restriction using validated quantitative real-time PCR and hormone measurements. Body weight, insulin and leptin were reduced whereas corticosterone was increased by both acute food deprivation and chronic food restriction. Our results confirmed the relative importance in body weight homeostasis of neuropeptide Y and proopiomelanocortin, which were increased and decreased as predicted. The expression of other neuropeptides previously attributed central roles in body weight homeostasis, e.g. melanin-concentrating hormone and orexin, appeared to be less affected by the treatments. Moreover, the expression of dynorphin, galanin-like peptide and neuropeptide B was dramatically reduced after both treatments. This suggests that the latter neuropeptides--although previously known to be involved in body weight homeostasis--may be of unexpected importance in states of negative energy balance.

Long-term effects of ghrelin and ghrelin receptor agonists on energy balance in rats

Ghrelin, an endogenous ligand of the growth hormone secretagogue receptor (GHS-R), is the only circulating agent to powerfully promote a positive energy balance. Such action is mediated predominantly by central nervous system pathways controlling food intake, energy expenditure, and nutrient partitioning. The ghrelin pathway may therefore offer therapeutic potential for the treatment of catabolic states. However, the potency of the endogenous hormone ghrelin is limited due to a short half-life and the fragility of its bioactivity ensuring acylation at serine 3. Therefore, we tested the metabolic effects of two recently generated GHS-R agonists, BIM-28125 and BIM-28131, compared with ghrelin. All agents were administered continuously for 1 mo in doses of 50 and 500 nmol x kg(-1) x day(-1) using implanted subcutaneous minipumps in rats. High-dose treatment with single agonists or ghrelin increased body weight gain by promoting fat mass, whereas BIM-28131 was the only one also increasing lean mass significantly. Food intake increased during treatment with BIM-28131 or ghrelin, whereas no effects on energy expenditure were detected. With the lower dose, only BIM-28131 had a significant effect on body weight. This also held true when the compound was administered by subcutaneous injection three times/day. No symptoms or signs of undesired effects were observed in any of the studies or treated groups. These results characterize BIM-28131 as a promising GHS-R agonist with an attractive action profile for the treatment of catabolic disease states such as cachexia.

Effect of antipsychotics on peptides involved in energy balance in drug-naive psychotic patients after 1 year of treatment

Weight gain has become one of the most common and concerning side effects of antipsychotic treatment. The mechanisms whereby antipsychotics induce weight gain are not known. It has been suggested that peptides related to food intake and energy balance could play a role in weight gain secondary to antipsychotic therapy. To better understand the pathophysiology of antipsychotic-induced weight gain, we studied the effects of 3 antipsychotic drugs (haloperidol, olanzapine, and risperidone) on peptides involved in energy balance (insulin, ghrelin, leptin, adiponectin, visfatin, and resistin) in a population of drug-naive patients with first episode of psychosis.A significant increase in weight (10.16 kg [SD, 8.30 kg]; P < 0.001), body mass index (3.56 kg/m [SD, 2.89 kg/m]; P < 0.001), and fasting insulin (3.93 muU/mL [SD, 3.93 muU/mL]; P = 0.028), leptin (6.76 ng/mL [SD, 7.21 ng/mL]; P < 0.001), and ghrelin (15.47 fmol/mL [SD, 47.90 fmol/mL]; P = 0.009) plasma levels were observed. The increments in insulin and leptin concentrations were highly correlated with the increment in weight and body mass index and seem to be a consequence of the higher fat stores. The unexpected increase in ghrelin levels might be related with the causal mechanism of weight gain induced by antipsychotics. Finally, the 3 antipsychotics had similar effects in all parameters evaluated.

The endogenous CCK mediation of electroacupuncture stimulation-induced satiety in rats

A major satiety hormone, cholecystokinin (CCK) is well known to be released by electroacupuncture (EA) stimulation at certain body sites which elicits profound psychophysiological responses. Previous clinical and animal studies have shown that EA stimulation reduces food intake and body weight in both normal and obese subjects. The aim of the present study was to elucidate the satiety effect of EA stimulation and its mechanism related to CCK in rats. Here we show that EA stimulation at "Zusanli" (ST36) acupoint significantly reduced 30-min and 60-min food intake in 48-h fasted Sprague-Dawley rats, and such effect was reversed by a lorglumide (CCK-1 receptor antagonist, 10mg/kg, i.p.) pretreatment. The ST36 EA stimulation-induced satiety was not observed in CCK-1 receptor knockout, Otsuka Long-Evans Tokushima Fatty rats, but in their controls, Long-Evans Tokushima Otsuka rats. Subdiaphragmatic vagotomy also blocked the satiety effect of ST36 EA stimulation in Sprague-Dawley rats. These results suggest that ST36 EA stimulation elicits satiety in rats and this is mediated by the endogenous CCK signaling pathway.

Hormones of the gut-brain axis as targets for the treatment of upper gastrointestinal disorders

The concept of the gut forming the centre of an integrated gut-brain-energy axis - modulating appetite, metabolism and digestion - opens up new paradigms for drugs that can tackle multiple symptoms in complex upper gastrointestinal disorders. These include eating disorders, nausea and vomiting, gastroesophageal reflux disease, gastroparesis, dyspepsia and irritable bowel syndrome. The hormones that modulate gastric motility represent targets for gastric prokinetic drugs, and peptides that modify eating behaviours may be targeted to develop drugs that reduce nausea, a currently poorly treated condition. The gut-brain axis may therefore provide a range of therapeutic opportunities that deliver a more holistic treatment of upper gastrointestinal disorders.

Metformin, arterial function, intima-media thickness and nitroxidation in metabolic syndrome: the mefisto study

1. Metabolic syndrome (MS) is one of the greatest public health problems in Mexico, where more than 75% of adults in urban populations are overweight or obese. Metabolic syndrome has several comorbidities, which result in a high cardiometabolic risk. 2. Some of the vasopathogenic phenomena in MS are caused by nitroxidant stress, secondary to cardiometabolic dysfunction. 3. The action of metformin to diminish or control MS remains a matter of debate. 4. In the present study, 60 patients with at least three diagnostic criteria for MS were divided into two groups. Both groups received similar dietary counselling, but one group was given 850 mg metformin daily. 5. The variables assessed were body mass index, waist circumference, systolic and diastolic blood pressures (SBP and DBP, respectively), total cholesterol (TC), high- and low-density lipoprotein-cholesterol, triglycerides (TG), fasting glucose, nitroxidant metabolites (free carbonyls, malondialdehyde, dityrosines and advanced oxidative protein products (AOPP)), nitric oxide (NO), carotid vascular stiffness, carotid intima-media thickness (IMT) and C-reactive protein (CRP). 6. After 1 year follow up, both groups reported weight loss, as well as decreases in waist circumference, SBP and DBP. 7. Patients on metformin exhibited reductions in TC and IMT and there were marked changes in nitroxidation: levels of carbonyls, dityrosines and AOPP were reduced, whereas those of NO were increased, indicating better endothelial function. In addition, in patients given metformin, CRP levels decreased. 8. In conclusion, metformin has a considerable beneficial effect on nitroxidation, endothelial function and IMT in patients with MS.

Brain insulin, energy and glucose homeostasis; genes, environment and metabolic pathologies

The central nervous system is essential in maintaining energy and glucose homeostasis. In both animals and humans, efficient cerebral insulin signalling is a pivotal control element in these pathophysiological processes. The action of insulin in the brain is under a multilevel control via metabolic, endocrine and neural signals induced by nutrients, integrated mainly by the hypothalamus. Of particular interest is the interaction of insulin with the anabolic and catabolic neuroregulators. The anorexic peptides insulin, leptin and the neurotransmitter serotonin share common signalling pathways involved in food intake, in particular the insulin receptor substrate, phosphatidylinositol-3-kinase (PI3K) pathway. The dialogue of neurotransmitters and peptides via this signalling pathway is potentially of major importance in the pathophysiology of the brain in general and specifically in the regulation of feeding behaviour. At this time, a new concept in the aetiopathology of type 2 diabetes is immerging. This concept proposes that the combination of defective pancreatic beta-cell function and insulin resistance not only in classical insulin target tissues but in every tissue, contributes to the onset of the disease. It highlights the importance of the disruption of cerebral insulin signal transmission and its direct relation to metabolic diseases. Impaired brain insulin signalling, a link coupling obesity to diabetes, may be related to either genetic factors, or environmental factors such as stress, over or under-feeding and unbalanced diets: such factors may work either independently or in concert. Current approaches used for the prevention and treatment of type 2 diabetes are not adequately effective. Most of the anti-diabetic therapies induce many adverse effects, in particular obesity, and thus may initiate a vicious cycle of problems. In order to develop new, more efficient, preventive and therapeutic strategies for metabolic pathologies, there is an urgent need for increased understanding of the complexity of insulin signalling in the brain and on the interactive, central and peripheral effects of insulin.

Enteroendocrine cells: a site of 'taste' in gastrointestinal chemosensing

PURPOSE OF REVIEW

This review discusses the role of enteroendocrine cells of the gastrointestinal tract as chemoreceptors that sense lumen contents and induce changes in gastrointestinal function and food intake through the release of signaling substances acting on a variety of targets locally or at a distance.

RECENT FINDINGS

Recent evidence supports the concept that chemosensing in the gut involves G protein-coupled receptors and effectors that are known to mediate gustatory signals in the oral cavity. These include sweet-taste and bitter-taste receptors, and their associated G proteins, which are expressed in the gastrointestinal mucosa, including selected populations of enteroendocrine cells. In addition, taste receptor agonists elicit a secretory response in enteroendocrine cells in vitro and in animals in vivo, and induce neuronal activation.

SUMMARY

Taste-signaling molecules expressed in the gastrointestinal mucosa might participate in the functional detection of nutrients and harmful substances in the lumen and prepare the gut to absorb them or initiate a protective response. They might also participate in the control of food intake through the activation of gut-brain neural pathways. These findings provide a new dimension to unraveling the regulatory circuits initiated by luminal contents of the gastrointestinal tract.

Can artificial sweeteners help control body weight and prevent obesity?

The possible role played by artificial sweeteners in the long-term maintenance of body weight is considered. Although artificial sweeteners can play a role in a short-term energy-controlled diet, the evidence that they are helpful over a longer period is limited. In those in the recommended weight range there is evidence of compensation; that is, the consumption of low-energy foods is followed by an increased energy intake to make up the lost energy. Energy compensation is more likely in those not displaying dietary restraint. The desire to remove sugar from the diet reflects an assumption that its intake is associated with obesity. However, the consumption of energy-dense food, that almost entirely reflects a high fat and low water content, is the best predictor of obesity. Diets offering a high proportion of energy in the form of carbohydrate tend to contain low levels of fat. There are several reports that the use of artificial sweeteners leads to an increased consumption of fat. The weak ability of fat to satisfy hunger makes it easy to overeat fatty foods; in contrast, carbohydrates promote a feeling of ‘fullness’. Various short-term studies have found that carbohydrate consumed as a liquid, rather than a solid, is more likely to result in weight gain.

No differences in satiety or energy intake after high-fructose corn syrup, sucrose, or milk preloads

BACKGROUND

It is unclear whether energy-containing drinks, especially those sweetened with high-fructose corn syrup (HFCS), promote positive energy balance and thereby play a role in the development of obesity.

OBJECTIVE

The objective was to examine the satiating effects of HFCS and sucrose in comparison with milk and a diet drink.

DESIGN

The effects of four 800-mL drinks [corrected] containing no energy or 1.5 MJ from sucrose, HFCS, or milk on satiety were assessed, first in 15 men and 15 women with a mean (+/-SD) body mass index (BMI; in kg/m(2)) of 22.1 +/- 1.9 according to visual analogue scales (VAS) and blood variables and second in 20 men and 20 women (BMI: 22.4 +/- 2.1) according to ingestion of a standardized ad libitum meal (granola cereal + yogurt, 10.1 kJ/g).

RESULTS

Fifty minutes after consumption of the 1.5-MJ preload drinks containing sucrose, HFCS, or milk, 170%-mm VAS changes in satiety were observed. Glucagon-like peptide 1 (GLP-1) (P < 0.001) and ghrelin (P < 0.05) concentrations changed accordingly. Compensatory energy intake did not differ significantly between the 3 preloads and ranged from 30% to 45%. Energy intake compensations were related to satiety (r = 0.35, P < 0.05). No differences were observed between the effects of the sucrose- and HFCS-containing drinks on changes in VAS and on insulin, glucose, GLP-1, and ghrelin concentrations. Changes in appetite VAS ratings were a function of changes in GLP-1, ghrelin, insulin, and glucose concentrations.

CONCLUSION

Energy balance consequences of HFCS-sweetened soft drinks are not different from those of other isoenergetic drinks, eg, a sucrose-drink or milk.

Chronobiology in the endocrine system

Biological signaling occurs in a complex web with participation and interaction of the central nervous system, the autonomous nervous system, the endocrine glands, peripheral endocrine tissues including the intestinal tract and adipose tissue, and the immune system. All of these show an intricate time structure with rhythms and pulsatile variations in multiple frequencies. Circadian (about 24-hour) and circannual (about 1-year) rhythms are kept in step with the cyclic environmental surrounding by the timing and length of the daily light span. Rhythmicity of many endocrine variables is essential for their efficacy and, even in some instances, for the qualitative nature of their effects. Indeed, the continuous administration of certain hormones and their synthetic analogues may show substantially different effects than expected. In the design of drug-delivery systems and treatment schedules involving directly or indirectly the endocrine system, consideration of the human time organization is essential. A large amount of information on the endocrine time structure has accumulated, some of which is discussed in this review.

Genome-wide scan of plasma cholecystokinin in baboons shows linkage to human chromosome 17

OBJECTIVE

Cholecystokinin (CCK) is known to inhibit food intake and is an important signal for controlling meal volume, indicating a possible role in weight regulation. Our objective was to investigate genetic influences on plasma CCK in baboons.

RESEARCH METHODS AND PROCEDURES

Subjects were 376 baboons (males = 113, females = 263) from the Southwest National Primate Research Center, housed at the Southwest Foundation for Biomedical Research, San Antonio, Texas. Anthropometric and biochemical parameters were analyzed. Genetic effects on plasma CCK were estimated by the maximum likelihood-based variance components method implemented in the software program SOLAR (Sequential Oligogenic Linkage Analysis Routines).

RESULTS

Male baboons (32.7 +/- 6 kg) were much heavier than females (20.2 +/- 4 kg). Similarly, mean (+/- standard deviation) plasma CCK values were also higher in male baboons (13.8 +/- 6 pM) than female baboons (12.5 +/- 4 pM). Significant heritabilities were observed for plasma CCK (0.14 +/- 0.1, p < 0.05), body weight (h2 = 0.62 +/- 0.15, p < 10(-8)), and glucose (h2 = 0.68 +/- 0.17, p < 10(-7)). A genome-wide scan of plasma CCK detected a strong signal for a quantitative trait locus (QTL) on chromosome 17p12-13 [logarithm of the odds (LOD) = 3.1] near marker D17S804. Suggestive evidence of a second QTL was observed on chromosome 4q34-35 (LOD = 2.3) near marker D4S2374.

DISCUSSION

A substantial contribution of additive genetic effects to the variation in plasma levels of CCK was demonstrated in baboons. The identification of a QTL for plasma CCK on chromosome 17p is significant, as several obesity-related traits such as BMI, leptin, adiponectin, and acylation stimulating protein have already been mapped to this region.

Avenues of communication between the brain and tissues/organs involved in energy homeostasis

Obesity is a rapidly increasing public health concern worldwide as a major risk factor for numerous disorders, including diabetes, hypertension and heart disease. Despite remarkable advances in obesity research over the past 10 years, the molecular mechanisms underlying obesity are still not completely understood. To maintain systemic energy homeostasis, it is important that organs/tissues communicate metabolic information among each other. Obesity-related disorders can be thought of as resulting from dysregulation of this inter-tissue communication. This system has both afferent sensing components and efferent effecter limbs. The afferent signals consist of not only humoral factors, such as nutrients (glucose, fatty acids and amino acids) and adipocytokines (leptin, adiponectin and so on), but also autonomic afferent nerve systems. Both converge on brain centers, most importantly within the hypothalamus, where the signals are integrated, and the direction and magnitude of efferent responses are determined. The efferent elements of this physiological system include those regulating energy inputs and outputs, i.e. food intake and metabolic rates. In this review, we will summarize recent advances in research on metabolic information avenues to the brain, which are important for energy homeostasis.

Gastric/intestinal electrical stimulation modulates appetite regulatory peptide hormones in the stomach and duodenum in rats

BACKGROUND

Gastric/intestinal electrical stimulation (GIES) has been used to suppress appetite in the treatment of obesity with promising results. However, the mechanisms by which GIES benefits obese patients are not completely understood. This study investigated the acute effects of GIES on gastric and intestinal tissue levels of peptide hormones related to satiety and appetite in rats.

METHODS

32 rats were divided into 4 groups: 1) sham stimulation, 2) gastric electrical stimulation (GES) with pulse trains, 3) GES with long pulse, and 4) duodenal electrical stimulation (DES) with pulse trains. After 2 hours of GIES, the rats were sacrificed immediately, and gastric fundus, duodenum and distal colon were harvested and extracted. Hormone levels of ghrelin, obestatin, cholecystokinin-8 (CCK-8) and peptide YY (PYY) were measured by radioimmunoassay (RIA).

RESULTS

1) The mean gastric fundus ghrelin level was 1789.04+/-362.81 pg/mg in the sham stimulation and significantly decreased with GES of pulse trains (597.85+/-195.33 pg/mg, P=0.012), GES of long pulse (754.6+/-282.6 pg/mg, P=0.039) and DES (731.69+/-110.84 pg/mg, P=0.037). 2) The mean duodenal CCK-8 concentration was 413.27+/-42.14 pg/mg in the sham stimulation and significantly increased by DES (762.6+/-98.75 pg/mg, P=0.013) but not in others. 3) Neither gastric obestatin nor distal colonic PYY was altered by any of GES or DES.

CONCLUSIONS

GIES significantly impacts appetite-related peptide hormones in gastric and duodenal tissues. Acute GIES-induced manipulation of gut peptide hormones related to appetite and satiety is a nonpharmacologic, well-tolerated clinical procedure that could substantially contribute to the successful treatment and long-term management of obesity.

Fructose consumption and moderate zinc deficiency influence growth and adipocyte metabolism in young rats prone to adult-onset obesity

The effects of low zinc, high fructose diet on growth and adipocyte metabolism were examined in rats. At 28 days of age, animals were assigned to diets either adequate in zinc (30 ppm) with water (AZW) or fructose solution (AZF), or low in zinc (5 ppm) with water (LZW) or fructose solution (LZF). Body weight and food and fructose solution intake were measured three times a week. Blood samples were collected at baseline, 4 weeks, and 8 weeks, and energy expenditure was measured. The rats were killed at 12 weeks. Adipocytes were cultured in medium containing C14-glucose and physiological insulin concentrations. The animals in the LZF group consumed less energy and gained less weight than the other groups. Serum zinc concentrations were lower in the LZF than the AZF group. Energy expenditure over a 24-h period did not differ between groups; however, the respiratory quotient in the fed state was higher in the groups consuming fructose solution than in those consuming water. The mesenteric adipocytes from the animals in the LZF group utilized more glucose. Thus, the addition of fructose to a LZ diet reduced energy intake and growth and altered adipocyte fuel metabolism in young growing rats.

Getting to the bottom of feeding behaviour: who's on top?

Traditionally there has been a tendency to focus on peripheral "bottom-up" feeding-related signals and their resulting downstream actions on hypothalamic centers when studying the feeding behaviour of animals. A problem with this hierarchal approach emerges especially with respect to acquiring a human model attempting to explain what is ultimately a distributed control of feeding and energy balance. This review focuses on illuminating the means by which we have come to understand the complexities of feeding, and takes the next step in an attempt to propose a distinctive top-down view of this composite behaviour. It is argued that in evolutionary terms humans demonstrate behaviours unique to all species as represented by an expanded forebrain and the resultant psychological "non-homeostatic" mediators of feeding. Emphasis is placed on a distributionist "two-tier" model, arguing that traditional short-term (cholescystokinin, ghrelin, peptide YY, glucagon-like peptide 1, etc.) and long-term (insulin and leptin) feeding signals may be actively suppressed by the nested nuclei and projections of cortical-limbic brain areas. It is the motivational state (dependent on depletion-repletion signals of hunger and satiety) that in turn has the capability to modulate how rewarding or how palatable a food item may be perceived; thus, both sides of the two-tiered model of feeding behaviour are complimentary and interdependent all at once. In the end, this paper is both commentary and critical review. This synthesis purports that as evolutionary processes spawned consciousness, the psychology of hunger and the present-day discordance of gene-environment interaction forever changed the feeding behaviour of Homo sapiens.

Role of Appetite-Regulating Peptides in Alcohol Craving: An Analysis in Respect to Subtypes and Different Consumption Patterns in Alcoholism

BACKGROUND

A role of appetite-regulating peptides like leptin and ghrelin in the neurobiology of alcohol craving has been proposed by several studies. Aim of this analysis was to search for differences regarding an association between these peptides and alcohol craving with respect to different subtypes and beverage consumption patterns in patients with alcohol dependence.

METHODS

We analyzed a sample of 188 patients at admission for alcohol detoxification regarding leptin and ghrelin (n=117) serum levels. Craving was measured using the Obsessive Compulsive Drinking Scale (OCDS). Patients were classified according to Lesch's typology of alcohol dependence and according to their preferred type of alcoholic beverage (beer, wine, spirits).

RESULTS

Using general linear models to analyze a possible interaction between subtypes and leptin/ghrelin levels with respect to craving, we found a significant positive association for leptin in patients of Lesch's types 1 and 2, and in patients consuming beer or wine. Ghrelin levels showed a significant trend regarding an association with craving in patients of Lesch's type 1. In the other subgroups we found no significant results.

CONCLUSIONS

Our findings show that appetite-regulating peptides may be of special importance regarding alcohol craving in subtypes of patients. This may explicate at least in part previous contradictory findings.

Exercise-induced alterations in plasma concentrations of ghrelin, adiponectin, leptin, glucose, insulin, and cortisol in horses

Six Standardbred (STB) mares (11+/-2 years, 521+/-77 kg; means+/-SD) performed an exercise trial (EX) where they underwent an incremental exercise test (GXT) as well as a parallel control trial (CON) to test the hypothesis that short-term, high intensity exercise would alter plasma concentrations of glucose, leptin, adiponectin, ghrelin, insulin and cortisol. Plasma samples were taken before (0 min), during (last 10s at 6, 8m/s, and the velocity eliciting VO(2max)), and after exercise (2, 10, 30, 60 min; 12 and 24h post-GXT). A second set of blood samples was collected before and after an afternoon meal given at 1515 h (at 1500, 1514, 1530, and 1545 h). Data were analyzed using ANOVA for repeated measures and Tukey's test. During the GXT, there were no changes (P>0.05) in the plasma concentrations of glucose, leptin, adiponectin or ghrelin. However, there was a 29% increase (P<0.05) in mean plasma cortisol concentration and a 35% decrease (P<0.05) in mean plasma insulin concentration. Substantial increases (P<0.05) in the mean plasma concentrations of glucose and cortisol of 36% and 102%, respectively, were seen in the EX trial during the first 60 min post-GXT. Plasma leptin concentration, measured at the 24h post-GXT time point, was 20% lower (P<0.05) during the EX trial compared with the parallel time point in the standing control (CON) trial. Plasma ghrelin concentration was 37% lower (P<0.05) in the EX trial compared with CON before and after the afternoon meal, but was 43% higher (P<0.05) 12h post-GXT. There were no differences between EX and CON for plasma concentrations of insulin or adiponectin during recovery. It was concluded that short-term high intensity exercise alters plasma leptin and ghrelin concentrations in STB mares post-exercise, which may signal the exercised animals to alter energy intake.

Effects of high-fructose corn syrup and sucrose consumption on circulating glucose, insulin, leptin, and ghrelin and on appetite in normal-weight women

OBJECTIVE

Fructose has been implicated in obesity, partly due to lack of insulin-mediated leptin stimulation and ghrelin suppression. Most work has examined effects of pure fructose, rather than high-fructose corn syrup (HFCS), the most commonly consumed form of fructose. This study examined effects of beverages sweetened with HFCS or sucrose (Suc), when consumed with mixed meals, on blood glucose, insulin, leptin, ghrelin, and appetite.

METHODS

Thirty lean women were studied on two randomized 2-d visits during which HFCS- and Suc-sweetened beverages were consumed as 30% of energy on isocaloric diets during day 1 while blood was sampled. On day 2, food was eaten ad libitum. Subjects rated appetite at designated times throughout visits.

RESULTS

No significant differences between the two sweeteners were seen in fasting plasma glucose, insulin, leptin, and ghrelin (P > 0.05). The within-day variation in all four items was not different between the two visits (P > 0.05). Net areas under the curve were similar for glucose, insulin, and leptin (P > 0.05). There were no differences in energy or macronutrient intake on day 2. The only appetite variable that differed between sweeteners was desire to eat, which had a higher area under the curve the day after Suc compared with HFCS.

CONCLUSION

These short-term results suggest that, when fructose is consumed in the form of HFCS, the measured metabolic responses do not differ from Suc in lean women. Further research is required to examine appetite responses and to determine if these findings hold true for obese individuals, males, or longer periods.

Sleep and metabolic control: waking to a problem?

1. The aim of the present review is to outline: (i) the association between sleep and metabolism; (ii) how sleep duration influences the development of disease; and (iii) how sex differences, ageing and obesity may potentially influence the relationship between sleep, metabolic control and subsequent disease. 2. Sleep is associated with a number of endocrine changes, including a change in insulin action in healthy young individuals. Sleep duration shows a prospective U-shaped relationship with all-cause mortality, cardiovascular disease and Type 2 diabetes. 3. Chronic sleep restriction is becoming more common. Experimental sleep restriction impedes daytime glucose control and increases appetite. 4. The sex hormones oestrogen and testosterone influence sleep duration and quality and may account for sex differences in the prevalence of sleep-related disorders. 5. Ageing is associated with a decreased sleep duration, decreased muscle mass and impaired insulin action. 6. Obesity impairs insulin action and is associated with the incidence and severity of obstructive sleep apnoea. 7. Sleep plays an integral role in metabolic control. Consequently, insufficient sleep may represent a modifiable risk factor for the development of Type 2 diabetes. The challenge ahead is to identify how sex differences, ageing and obesity could potentially influence the relationship between sleep and metabolism.

Appetite control after weight loss: what is the role of bloodborne peptides?

The literature presented in this paper argues that our limited ability to maintain energy balance in a weight-reduced state is the product of our difficulty in compensating for the weight loss-induced reduction in total energy expenditure. The end result, translated into the overwhelming complexity of preserving long-term weight loss, is presented as being a consequence of compromised appetite control. Given the present-day food landscape and the resultant susceptibility to passive overconsumption, the focus of this review will be on the peripheral (“bottom-up”) signals (leptin, PYY, ghrelin, and GLP-1) and the evidence highlighting their influence on feeding behaviour. As we continue studying paradigms of body mass reduction, specifically the data emerging from patients of bariatric surgery, it is becoming clearer that counter-regulatory adaptations, possibly through down-(leptin, PYY, and GLP-1) or upregulation (ghrelin) of peptides, have an impact on energy balance. In itself, food deprivation influences some of the peptides that ultimately provide the physiological input for the overt expression of feeding behaviour; these peripheral adaptations are expected to serve as feeding cues — cues that, in the end, can serve to compromise the maintenance of energy balance. In a potentially novel intervention to increase compliance to long-term reductions in energy intake, it is proposed that manipulating the pattern of food intake to favourably alter the profile of gastrointestinal peptides would lead to better dietary control.

Liquid calories, sugar, and body weight

The consumption of sugar-sweetened beverages has been linked to rising rates of obesity in the United States. The standard explanation is that energy-containing liquids are less satiating than are solid foods. However, purely physiologic mechanisms do not fully account for the proposed links between liquid sugar energy and body weight change. First, a reevaluation of published epidemiologic studies of consumption of sweetened beverages and overweight shows that most such studies either are cross-sectional or are based on passive surveillance of temporal trends and thus permit no conclusions about causal links. Second, research evidence comparing the short-term satiating power of different types of liquids and of solids remains inconclusive. Numerous clinical studies have shown that sugar-containing liquids, when consumed in place of usual meals, can lead to a significant and sustained weight loss. The principal ingredient of liquid meal replacement shakes is sugar, often high-fructose corn syrup, which is present in amounts comparable to those in soft drinks. Far from suppressing satiety, one such liquid shake is marketed on the grounds that it helps control hunger and prevents hunger longer when consumed for the purpose of weight loss. These inconsistencies raise the question whether the issue of sugars and body weight should continue to be framed purely in metabolic or physiologic terms. The effect of sugar consumption on body weight can also depend on behavioral intent, context, and the mode of use, availability, and cost of sweetened liquids.

Changes in body composition in women over six years at midlife: ovarian and chronological aging

CONTEXT

Understanding the menopause association with body weight is important because excess weight increases risk for stroke, incident cardiovascular disease, cardiovascular mortality, and all-cause mortality among the middle-aged.

OBJECTIVE

The objective of this study was to examine chronological age and ovarian age and consider how these could influence body size and composition in midlife women.

DESIGN AND SETTING

The Study of Women's Health Across the Nation is a longitudinal, community-based study. This report uses data from the Michigan Study of Women's Health Across the Nation site.

PARTICIPANTS

Participants were 543 premenopausal or early perimenopausal African-American and Caucasian women aged 42-52 yr at baseline examination.

MAIN OUTCOME MEASURES

Waist circumference, fat mass and skeletal muscle mass, from bioelectrical impedance, were assessed in seven annual serial measures. Annual FSH values were assayed by ELISA. The final menstrual period was defined retrospectively after 12 months of amenorrhea.

RESULTS

There was an absolute cumulative 6-yr increase in fat mass of 3.4 kg and a 6-yr decrease in skeletal muscle mass of approximately 0.23 kg. There was an absolute cumulative 6-yr increase of approximately 5.7 cm in waist circumference. The (log)FSH change was positively correlated with (log)(fat mass) change. Waist circumference increased over the time period, but 1 yr after final menstrual period, the rate of increase slowed. Fat mass continued to increase with no change in rate.

CONCLUSIONS

Both time (chronological aging) and ovarian aging contributed to substantial changes in body composition (fat and skeletal muscle mass) and waist circumference. These changes have important ramifications for establishing a metabolic environment that can be healthy or unhealthy.

Vagus nerve stimulation acutely alters food craving in adults with depression

Vagus nerve stimulation (VNS) is now available as a treatment for epilepsy and treatment-resistant depression. The vagus nerve plays a central role in satiety and short-term regulation of food intake and research suggests a relationship between VNS and weight loss. The underlying mechanisms of this relationship are unknown. The purpose of the current study was to determine whether acute cervical VNS might temporarily alter food cravings. Thirty-three participants were recruited for three groups; depression VNS, depression non-VNS, and healthy controls. Participants viewed 22 computerized images of foods twice in one session and completed ratings for food cravings after each image. The VNS participants' devices were turned on for one viewing of an image and off for the other (randomized order). Participants were blind to VNS condition (on versus off). Acute VNS device activation was associated with a significant change in cravings-ratings for sweet foods. A significant proportion of variability in VNS-related changes in cravings was accounted for by patients' clinical VNS device settings, acute level of depression, and body mass. Further studies are warranted addressing how acute or chronic VNS might modify eating behavior and weight.

Changes in inflammatory biomarkers following one-year of moderate resistance training in overweight women

BACKGROUND

Overweight individuals commonly demonstrate elevated levels of inflammatory and cell adhesion molecules. Elevated levels of inflammation and adhesion have been implicated in the pathogenesis of cardiovascular disease. Aerobic exercise has been shown to be effective in altering specific biomarkers of inflammation and cell adhesion; however, little is known regarding the effects of resistance training (RT) on these biomarkers. This study examined the effects of 1 year of moderate-intensity RT on biomarkers of inflammation and adhesion in healthy, overweight women.

METHODS AND RESULTS

Participants included 28 (12 control, 16 RT) overweight (body mass index>or=25 kg/m2) women, aged 25-44 years, studied before and after 1 year of RT. C-reactive protein (CRP), interleukin-6 (IL-6), adiponectin, intracellular adhesion molecule-1, vascular cell adhesion molecule-1 and E-selectin were measured by standard enzyme-linked immunosorbent assays. Body composition, blood pressure, fasting blood lipids, glucose and insulin also were assessed. There were no significant changes in blood pressure, fasting blood lipids, glucose or insulin levels in either group after 1 year. There was also no change in body mass or fat mass in either group; however, there was a significant increase in lean body mass (P<0.05) in the RT group. Both CRP (P<0.01) and adiponectin (P<0.01) demonstrated significant improvements in the RT group, with no change in IL-6. Conversely, there were no associated changes in the biomarkers of cell adhesion in either group.

CONCLUSIONS

This study demonstrates that moderate-intensity RT significantly results in modest improvements of inflammatory markers without affecting cell adhesion molecules in overweight women.

The anorexia of aging

Malnutrition in the elderly is one of the greatest threats to health, well-being and autonomy, it is therefore crucial to understand and to contrast the causal factors of inadequate energy intake. This review focuses on the mechanisms of the so-called 'anorexia of aging'. In recent years, it has been shown that elderly subjects have abnormal peripheral signal patterns and alterations in central hypothalamic control relays. Negative feedback from impaired gastric motility, exaggerated long-term adiposity signals (leptin, insulin) and postprandial anorexigenic signals (CCK, PYY) seem to prevail over the central feeding drive. If nutritional strategies of intervention are to be improved, these data need to be taken into account.

Restricted access to food, but not sucrose, saccharine, or salt, synchronizes the expression of Period2 protein in the limbic forebrain

Restricted feeding schedules (RF) in which daily access to food is limited to a few hours each day can entrain the rhythms of expression of circadian clock genes in the brain and periphery in rodents. The critical factors mediating the effect of RF on rhythms of clock gene expression are unknown. Previously, we demonstrated that daytime RF shifts the phase of expression of the clock protein, Period2 (PER2) in the oval nucleus of the bed nucleus of the stria terminalis in rats kept on a 12-h light/dark cycle, and restored the rhythm of PER2 expression in rats housed in constant light. We now report that RF also modifies the rhythms of PER2 expression in the central and basolateral nuclei of the amygdala and in the dentate gyrus, such that all three areas become synchronized, peaking 12 h after the time of food presentation. Daily limited access to sucrose or saccharine in freely fed rats or scheduled access to saline in sodium-deprived rats had no effect on these PER2 rhythms. Thus, it would appear that the rhythms of PER2 in limbic forebrain structures are sensitive to signals that arise from the alleviation of a negative metabolic state associated with scheduled feeding and that access to rewarding substances in the absence of food deprivation or metabolic challenges, per se, is not sufficient to alter the rhythms of PER2 expression in these regions.

Food intake and reward mechanisms in patients with schizophrenia: implications for metabolic disturbances and treatment with second-generation antipsychotic agents

Obesity is highly prevalent among patients with schizophrenia and is associated with detrimental health consequences. Although excessive consumption of fast food and pharmacotherapy with such second-generation antipsychotic agents (SGAs) as clozapine and olanzapine has been implicated in the schizophrenia/obesity comorbidity, the pathophysiology of this link remains unclear. Here, we propose a mechanism based on brain reward function, a relevant etiologic factor in both schizophrenia and overeating. A comprehensive literature search on neurobiology of schizophrenia and of eating behavior was performed. The collected articles were critically reviewed and relevant data were extracted and summarized within four key areas: (1) energy homeostasis, (2) food reward and hedonics, (3) reward function in schizophrenia, and (4) metabolic effects of the SGAs. A mesolimbic hyperdopaminergic state may render motivational/incentive reward system insensitive to low salience/palatability food. This, together with poor cognitive control from hypofunctional prefrontal cortex and enhanced hedonic impact of food, owing to exaggerated opioidergic drive (clinically manifested as pain insensitivity), may underlie unhealthy eating habits in patients with schizophrenia. Treatment with SGAs purportedly improves dopamine-mediated reward aspects, but at the cost of increased appetite and worsened or at least not improved opiodergic capacity. These effects can further deteriorate eating patterns. Pathophysiological and therapeutic implications of these insights need further validation via prospective clinical trials and neuroimaging studies.

Globular adiponectin augments insulin secretion from pancreatic islet beta cells at high glucose concentrations

Adiponectin plays an important role in improving insulin resistance and preventing atherosclerosis. However it has been rarely reported that adiponectin influences insulin secretion because its receptor was identified in human islet beta cells. In order to investigate the direct effect of adiponectin on pancreatic islet beta cells, we performed an insulin secretion test in purified rat islets, which were incubated with adiponectin (100 ng/mL) at low (3.3 mM) and high (16.7 mM) glucose concentrations. Furthermore, cell lysates were extracted from the adiponectin-treated islets for p-AMPKalpha assay. RTPCR and immunohistochemical examination showed both adiponectin receptor 1 (AdipoR1) and receptor 2 (AdipoR2) were expressed in islet cells and AdipoR1 was predominantly expressed. Insulin secretion was significantly increased in the presence of adiponectin for 6 h at high glucose concentration. Meanwhile, the levels of phosphorylated AMPK increased with adiponectin treatment at high glucose concentrations. It is concluded that adiponectin augments insulin secretion from pancreatic islet beta cells at high glucose concentration through AMPK activation.

Leptin contributes to slower weight gain in juvenile rodents on a ketogenic diet

The ketogenic diet (KD) is an efficacious therapy for medically refractory childhood epilepsy that also slows weight gain. We tested the hypothesis that the KD slows weight gain via neurohormones involved in energy homeostasis. We found that juvenile rodents fed a KD had slower weight gain than those fed a standard diet (SD). Rats fed a KD had higher serum leptin levels and lower insulin levels compared with those fed an SD. We investigated the increase in leptin further because this change was the only one consistent with slower weight gain. Although rats fed the SD experienced slower weight gain when calorie restricted, they had serum leptin levels similar to those fed the SD ad libitum. Furthermore, leptin deficient (ob/ob) and leptin receptor deficient (db/db) mice did not show slower weight gain on the KD. All animals on the KD had elevated serum beta-hydroxybutyrate (betaHB) levels. Thus, ketosis is insufficient and a functioning leptin signaling system appears necessary for the KD to slow weight gain. The increase in leptin may contribute to the anticonvulsant effects of the KD.

Physiological evidence for the involvement of peptide YY in the regulation of energy homeostasis in humans

OBJECTIVE

To explore the potential role of the endogenous peptide YY (PYY) in the long-term regulation of body weight and energy homeostasis.

RESEARCH METHODS AND PROCEDURES

Fasting and postprandial plasma PYY concentrations were measured after an overnight fast and 30 to 180 minutes after a standardized meal in 29 (21 men/8 women) non-diabetic subjects, 16 of whom had a follow-up visit 10.8 +/- 1.4 months later. Ratings of hunger and satiety were collected using visual analog scales. Resting metabolic rate (RMR) (15-hour RMR) and respiratory quotient (RQ) were assessed using a respiratory chamber.

RESULTS

Fasting PYY concentrations were negatively correlated with various markers of adiposity and negatively associated with 15-hour RMR (r = -0.46, p = 0.01). Postprandial changes in PYY (area under the curve) were positively associated with postprandial changes in ratings of satiety (r = 0.47, p = 0.01). The maximal PYY concentrations achieved after the meal (peak PYY) were negatively associated with 24-hour RQ (r = -0.41, p = 0.03). Prospectively, the peak PYY concentrations were negatively associated with changes in body weight (r = -0.58, p = 0.01).

DISCUSSION

Our data indicate that the endogenous PYY may be involved in the long-term regulation of body weight. It seems that this long-term effect was not exclusively driven by the modulation of food intake but also by the control of energy expenditure and lipid metabolism.