Ghrelin and Body Weight Regulation in the Obese Zucker Rat in Relation to Feeding State and Dark/Light Cycle

Coenzyme A and Its Thioester Pools in Obese Zucker and Zucker Diabetic Fatty Rats

Feeding behavior is closely related to hypothalamic malonyl-CoA level in the brain and diet-induced obesity affects total CoA pools in liver. Herein, we performed a comprehensive analysis of the CoA pools formed in thirteen tissues of Zucker and Zucker diabetic fatty (ZDF) rats. Hypothalamic malonyl-CoA levels in obese rats remained low and were almost the same as those of lean rats, despite obese rats having much higher content of leptin, insulin, and glucose in their sera. Regardless of the fa-genotypes, larger total CoA pools were formed in the livers of ZDF rats and the size of hepatic total CoA pools in Zucker rats showed almost one tenth of the size of ZDF rats. The decreased total CoA pool sizes in Zucker rats was observed in the brown adipose tissues, while ZDF-fatty rats possessed 6% of total CoA pool in the lean rats in response to fa deficiency. This substantially lower CoA content in the obese rats would be disadvantageous to non-shivering thermogenesis. Thus, comparing the intracellular CoA behaviors between Zucker and ZDF rats, as well as the lean and fatty rats of each strain would help to elucidate features of obesity and type 2 diabetes in combination with result (s) of differential gene expression analysis and/or comparative genomics.

Anti-obesity properties of the strain Bifidobacterium animalis subsp. lactis CECT 8145 in Zücker fatty rats

We evaluated the effect of oral administration of Bifidobacterium animalis subsp. lactis CECT 8145 strain in Zücker fatty rats. The Zücker fatty rats were randomly divided into two groups (n=10 each) and administered either B. animalis subsp. lactis CECT 8145 (1010 cfu/day) suspended in skim milk, or skim milk alone (control group). Each treatment was administered in drinking bottles from week 5 until week 17 of age. A lean Zücker rat group (standard group) was included to provide normal values for the Zücker strain. This group was administered skim milk in the drinking bottle for the same experimental period as Zücker fatty rats. Body weight gain was greater in the fatty control group than in the fatty rats treated daily with B. animalis subsp. lactis CECT 8145. Furthermore, dry and liquid food intake significantly decreased in the treated Zücker fatty group and these rats also showed decreased plasma ghrelin levels as compared with the Zücker fatty control group. B. animalis subsp. lactis CECT 8145 intake also decreased plasma tumour necrosis factor-α (a proinflammatory cytokine) and plasma malondialdehyde (a biomarker of oxidative stress). Moreover, the ratio plasma total cholesterol/plasma cholesterol transported by high-density lipoproteins, considered as an index for cardiovascular disease, also significantly decreased in the Zücker fatty rats treated with B. animalis subsp. lactis CECT 8145. By contrast, this bacterial strain significantly increased plasma adiponectin (an insulin-sensitising adipokine), but did not produce significant effects on triglyceride levels or glucose metabolism biomarkers. Although further research is required to confirm B. animalis subsp. lactis CECT 8145 is an efficient anti-obesity treatment in humans, the results obtained in this study are promising and point to the health and anti-obesity properties of this bacterial strain.

Ghrelin-Reactive Immunoglobulins in Conditions of Altered Appetite and Energy Balance

Part of circulating ghrelin is bound to immunoglobulins (Ig) protecting it from degradation and preserving its functional activity. This review summarizes the data on ghrelin- and desacyl-ghrelin-reactive IgG in conditions of altered appetite and energy balance. Plasma levels and affinity kinetics of such IgG were compared in patients with obesity and anorexia nervosa (AN) and in animal models of obesity including ob/ob mice, high-fat diet-induced obese mice, and obese Zucker rats as well as in mice after chronic food restriction and activity-based anorexia and in rats with methotrexate-induced anorexia. We show that plasmatic IgG in both obese humans and animals are characterized by increased affinity for ghrelin. In contrast, patients with AN and anorectic rodents all show lower affinity of ghrelin- and desacyl-ghrelin-reactive IgG, respectively, the changes which were not observed in non-anorectic, chronically starved mice. We also show that affinity of ghrelin-reactive IgG correlate with plasma levels of ghrelin. These data point to common mechanisms underlying modifications of affinity kinetics properties of ghrelin-reactive IgG during chronic alterations of energy balance in humans and rodents and support a functional role of such autoantibodies in ghrelin-mediated regulation of appetite.

An Evaluation of Acylated Ghrelin and Obestatin Levels in Childhood Obesity and Their Association with Insulin Resistance, Metabolic Syndrome, and Oxidative Stress

Background: Ghrelin is a 28-amino acid peptide with an orexigenic property, which is predominantly produced by the stomach. Acylated ghrelin is the active form of this hormone. Obestatin is a 23-amino acid peptide which is produced by post-translational modification of a protein precursor that also produces ghrelin. Obestatin has the opposite effect of ghrelin on food intake. The aim of this study was to evaluate acylated ghrelin and obestatin levels and their ratio in obese and normal-weight children and adolescents, and their association with metabolic syndrome (MetS) parameters. Methods: Serum acyl-ghrelin, obestatin, leptin, insulin, fasting plasma glucose (FPG), lipid profile, and malondialdehyde (MDA) were evaluated in 73 children and adolescents (42 obese and 31 control). Insulin resistance was calculated by a homeostasis model assessment of insulin resistance (HOMA-IR). MetS was determined according to IDF criteria. Results: Acyl-ghrelin levels were significantly lower in obese subjects compared to the control group and lower in obese children with MetS compared to obese subjects without MetS. Obestatin was significantly higher in obese subjects compared to that of the control, but it did not differ significantly among those with or without MetS. Acyl-ghrelin to obestatin ratio was significantly lower in obese subjects compared to that in normal subjects. Acyl-ghrelin showed significant negative and obestatin showed significant positive correlations with body mass index (BMI), BMI Z-score, leptin, insulin, and HOMA-IR. Acyl-ghrelin had a significant negative correlation with MDA as an index of oxidative stress. Conclusion: Ghrelin is decreased and obestatin is elevated in obesity. Both of these hormones are associated with insulin resistance, and ghrelin is associated with oxidative stress. The balance between ghrelin and obestatin seems to be disturbed in obesity.

Voluntary exercise contributed to an amelioration of abnormal feeding behavior, locomotor activity and ghrelin production concomitantly with a weight reduction in high fat diet-induced obese rats

In the present study, effects of voluntary exercise in an obese animal model were investigated in relation to the rhythm of daily activity and ghrelin production. Male Sprague-Dawley rats were fed either a high fat diet (HFD) or a chow diet (CD) from four to 16 weeks old. They were further subdivided into either an exercise group (HFD-Ex, CD-Ex) with a running wheel for three days of every other week or sedentary group (HFD-Se, CD-Se). At 16 weeks old, marked increases in body weight and visceral fat were observed in the HFD-Se group, together with disrupted rhythms of feeding and locomotor activity. The induction of voluntary exercise brought about an effective reduction of weight and fat, and ameliorated abnormal rhythms of activity and feeding in the HFD-Ex rats. Wheel counts as voluntary exercise was greater in HFD-Ex rats than those in CD-Ex rats. The HFD-obese had exhibited a deterioration of ghrelin production, which was restored by the induction of voluntary exercise. These findings demonstrated that abnormal rhythms of feeding and locomotor activity in HFD-obese rats were restored by infrequent voluntary exercise with a concomitant amelioration of the ghrelin production and weight reduction. Because ghrelin is related to food anticipatory activity, it is plausible that ghrelin participates in the circadian rhythm of daily activity including eating behavior. A beneficial effect of voluntary exercise has now been confirmed in terms of the amelioration of the daily rhythms in eating behavior and physical activity in an animal model of obesity.

Modulation of olfactory sensitivity and glucose-sensing by the feeding state in obese Zucker rats

The Zucker fa/fa rat has been widely used as an animal model to study obesity, since it recapitulates most of its behavioral and metabolic dysfunctions, such as hyperphagia, hyperglycemia and insulin resistance. Although it is well established that olfaction is under nutritional and hormonal influences, little is known about the impact of metabolic dysfunctions on olfactory performances and glucose-sensing in the olfactory system of the obese Zucker rat. In the present study, using a behavioral paradigm based on a conditioned olfactory aversion, we have shown that both obese and lean Zucker rats have a better olfactory sensitivity when they are fasted than when they are satiated. Interestingly, the obese Zucker rats displayed a higher olfactory sensitivity than their lean controls. By investigating the molecular mechanisms involved in glucose-sensing in the olfactory system, we demonstrated that sodium-coupled glucose transporters 1 (SGLT1) and insulin dependent glucose transporters 4 (GLUT4) are both expressed in the olfactory bulb (OB). By comparing the expression of GLUT4 and SGLT1 in OB of obese and lean Zucker rats, we found that only SGLT1 is regulated in genotype-dependent manner. Next, we used glucose oxidase biosensors to simultaneously measure in vivo the extracellular fluid glucose concentrations ([Gluc]ECF) in the OB and the cortex. Under metabolic steady state, we have determined that the OB contained twice the amount of glucose found in the cortex. In both regions, the [Gluc]ECF was 2 fold higher in obese rats compared to their lean controls. Under induced dynamic glycemia conditions, insulin injection produced a greater decrease of [Gluc]ECF in the OB than in the cortex. Glucose injection did not affect OB [Gluc]ECF in Zucker fa/fa rats. In conclusion, these results emphasize the importance of glucose for the OB network function and provide strong arguments towards establishing the OB glucose-sensing as a key factor for sensory olfactory processing.

A water-alcohol extract of Citrus grandis whole fruits has beneficial metabolic effects in the obese Zucker rats fed with high fat/high cholesterol diet

Epidemiological studies suggest that citrus fruits and compounds such as flavonoids, limonoids and pectins have health promoting effects. Our aim was to study the effects of Citrus grandis (L.) Osbeck var. tomentosa hort. fruit extract on the energy metabolism. A whole fruit powder from dry water and alcohol extracts of C. grandis containing 19% naringin flavonoid was prepared. The effects of the citrus extract were followed in the obese Zucker rats fed with the HFD. The circulatory levels of GLP-1 decreased significantly by the extract in comparison to the HFD group, whereas the decreased ghrelin levels were reversed. The levels of PYY were decreased in all HFD groups. The leptin amounts decreased but not significantly whereas insulin and amylin were unchanged. The cholesterol and glucose levels were somewhat but not systematically improved in the HFD fed rats. Further studies are needed to identify the active compounds and their mechanisms.

Dietary galacto-oligosaccharides and calcium: effects on energy intake, fat-pad weight and satiety-related, gastrointestinal hormones in rats

Galacto-oligosaccharides (GOS) are carbohydrates that are fermented by colonic microbiota. The present study examined effects of a 3-week dietary enrichment with 6 % (w/w) GOS on parameters of energy balance in forty-three male Wistar rats. GOS was tested with two doses of calcium phosphate (30 and 100 mmol/kg), known to differently affect colonic fermentation. After 17 d, isoenergetic test meals were presented and plasma responses of ghrelin, glucagon-like peptide-1 (GLP-1) and peptide YY (PYY) were measured. On day 21 (study termination) epididymal fat pads and caecum were weighed. Additionally, gastrointestinal mucosal samples and proximal colonic contents were analysed for gene expression (ghrelin, proglucagon and PYY) and fermentation metabolites (SCFA and lactate), respectively. GOS reduced energy intake most prominently during the first week, without provoking compensatory overeating later on (average intake reduction: 14 %). The GOS-fed rats showed increased caecal and reduced fat-pad weight and increased gene expression of the satiety-related peptides, PYY (1.7-fold) and proglucagon (3.5-fold). Pre-meal baseline and post-meal plasma levels of PYY, but not of ghrelin or GLP-1, were higher in GOS-fed rats than in control rats. Ca enrichment resulted in higher energy intake (average 4.5 %). GOS diets increased lactic acid levels and slightly reduced butyric acid in proximal colonic contents. Ca abolished the GOS-related elevation of lactic acid, while increasing propionic acid levels, but did not inhibit GOS-related effects on energy intake, fat-pad weight or gene expression. These results indicate that dietary GOS stimulate a number of physiological mechanisms that can reduce energy intake, regardless of the calcium phosphate content of the diet.

Plasma ghrelin levels and polymorphisms of ghrelin gene in Chinese obese children and adolescents

AIM

To evaluate the role of fasting plasma ghrelin levels [ln(ghrelin)] and polymorphisms of ghrelin gene in Chinese obese children.

METHODS

Genotyping for ghrelin polymorphism was performed in 230 obese and 100 normal weight children. Among them, plasma ghrelin levels were measured in 91 obese and 23 health subjects.

RESULTS

(1) Bivariate correlation analysis showed the ln(ghrelin) was inversely correlated with abnormality of glucose metabolism (r = -0.240, P = 0.023). Stepwise multiple regression analysis showed that abnormality of glucose metabolism was an independent determinant of plasma ghrelin levels (P = 0.023). (2) There was no difference in frequency of Leu72Met polymorphisms between obese and control groups (36.09 vs. 41.00%).

CONCLUSION

Ghrelin is associated with obesity in childhood, especially associated with the glucose homeostasis. Lower ghrelin levels might be a result of obesity, but not a cause of obesity. The Leu72Met polymorphism of ghrelin gene is not associated with obesity and metabolic syndrome in Chinese children.

Plasma ghrelin concentrations change with physiological state in a sciurid hibernator (Spermophilus lateralis)

Ghrelin is a recently discovered hormone which has profound effects on food intake and lipogenesis in mammals. In all mammals studied thus far, plasma ghrelin concentrations are increased before a meal and decrease immediately following a meal; ghrelin levels increase with fasting. The golden-mantled ground squirrel Spermophilus lateralis (also known as Callospermophilus lateralis (see Helgen et al., 2009) is a diurnal hibernator which has a robust annual cycle of body mass gain and loss that is primarily controlled by food intake. We hypothesized that in spring, summer, and autumn, the endogenous ghrelin concentrations of hibernators would be similar to those of non-hibernators, but that during the winter hibernation season, plasma ghrelin concentrations would be low or undetectable. We found that peripherally injected ghrelin significantly increased food intake in June. Plasma ghrelin concentrations were significantly increased through 5 days of fasting during a short-term fast in summer. Over a 24h period, ghrelin concentrations increased at night and decreased during the day with drops corresponding to times when squirrels were eating. In January, ghrelin concentrations are low but measurable even while animals are at low body temperature (Tb). This is the first report of ghrelin concentrations in a non-photoperiodic hibernator. We suggest that ghrelin may be important for the regulation of food intake and the body mass cycle in mammals that hibernate.

Experimental rat models to study the metabolic syndrome

Being the metabolic syndrome a multifactorial condition, it is difficult to find adequate experimental models to study this pathology. The obese Zucker rats, which are homozygous for the fa allele, present abnormalities similar to those seen in human metabolic syndrome and are a widely extended model of insulin resistance. The usefulness of these rats as a model of non-insulin-dependent diabetes mellitus is nevertheless questionable, and they neither can be considered a clear experimental model of hypertension. Some experimental models different from the obese Zucker rats have also been used to study the metabolic syndrome. Some derive from the spontaneously hypertensive rats (SHR). In this context, the most important are the obese SHR, usually named Koletsky rats. Hyperinsulinism, associated with either normal or slightly elevated levels of blood glucose, is present in these animals, but SHR/N-corpulent rats are a more appropriated model of non-insulin-dependent diabetes mellitus. The SHR/NDmc corpulent rats, a subline of SHR/N-corpulent rats, also exhibit metabolic and histopathologic characteristics associated with human metabolic disorders. A new animal model of the metabolic syndrome, stroke-prone-SHR (SHRSP) fatty rats, was obtained by introducing a segment of the mutant leptin receptor gene from the Zucker line heterozygous for the fa gene mutation into the genetic background of the SHRSP. Very recently, it has been developed as a non-obese rat model with hypertension, fatty liver and characteristics of the metabolic syndrome by transgenic overexpression of a sterol-regulatory element-binding protein in the SHR rats. The Wistar Ottawa Karlsburg W rats are also a new strain that develops a nearly complete metabolic syndrome. Moreover, a new experimental model of low-capacity runner rats has also been developed with elevated blood pressure levels together with the other hallmarks of the metabolic syndrome.

KLF4 positively regulates human ghrelin expression

Ghrelin, an endogenous ligand of the GH (growth hormone) secretagogue receptor, influences many metabolic processes including GH secretion, food intake, energy balance, insulin secretion and adipogenesis. Although ghrelin exhibits a variety of biological functions, the mechanism by which ghrelin expression is regulated is unknown. Ghrelin is expressed in the gastrointestinal tract, predominantly in the stomach, as is KLF4 (Krüppel-like factor 4). Therefore we investigated whether ghrelin expression is associated with KLF4, and found that the tissue distribution of ghrelin corresponded with that of KLF4. Furthermore, treatment with butyrate, an inducer of KLF4 expression, stimulated ghrelin expression, and fasting, which induces ghrelin expression, also increased KLF4 expression, suggesting that ghrelin expression is associated with KLF4. Then, we investigated the effects of KLF4 on the human ghrelin-promoter activity and identified a KLF4-responsive region in the promoter. KLF4 expression specifically stimulated human ghrelin-promoter activity in a dose-dependent manner in human gastric-cancer AGS cells. However, this effect was not seen in response to a mutant KLF4 construct. Transfection studies using mutant constructs containing 5'-deletions in the human ghrelin promoter revealed that the KLF4-responsive element is located between -1228 and -1105. Electrophoretic mobility shift assays using oligonucleotides containing -1165/-1146 revealed the binding of KLF4 to the human ghrelin promoter. Finally, deletion of the -1165/-1146 region abrogated KLF4-induced transactivation of the ghrelin promoter. Collectively, these results indicate that KLF4 positively regulates human ghrelin expression via binding to a KLF-responsive region in the promoter.

Suppression of QRFP 43 in the hypothalamic ventromedial nucleus of Long-Evans rats fed a high-fat diet

QRFP 43 is a RFamide peptide present in the ventromedial nucleus (VMN) and lateral hypothalamus. It stimulates food intake in mice and its chronic infusion induces hyperphagia, reduced thermogenesis, and obesity. In this experiment, we measured it in the VMN and lateral hypothalamus of Long-Evans rats fed either a high-fat (HF), control, or low-fat (LF) diet in parallel with plasma leptin, adiposity, and energy intake. After 8weeks of ad libitum diet intake, energy intake of HF rats was similar to that of control rats. In the VMN, QRFP 43 was completely undetectable in HF rats and its tissue concentration in control rats was significantly lower than in LF rats (p<0.03). HF rats had higher levels of leptin than control rats (+24%; p<0.03) and than LF rats (+42%; p<0.002). The QRFP 43 concentration in the VMN was inversely correlated with plasma leptin (r=-0.34; P<0.04) and with the adipogenic index of the diet (p<0.02) but not with insulin. We conclude that the decrease of the orexigenic drive mediated by QRFP 43 could contribute to the normalization of caloric intake in HF diet fed rats. QRFP 43 might play a role downstream of leptin in the regulation of feeding behavior.

The change in ghrelin and obestatin levels in obese children after weight reduction

AIM

To investigate the role of ghrelin and obestatin in obesity mechanisms.

METHODS

A total of 88 obese children and 25 normal children were enrolled. Moreover, 46 obese children took part in a summer camp for weight reduction. Fasting ghrelin, obestatin and other biochemical parameters were measured in all subjects and re-measured in 45 obese children finishing the camp.

RESULTS

The ghrelin levels in the control and obese groups were 67.26 +/- 23.41 pmol/L and 56.53 +/- 15.97 pmol/L with a significant difference (p = 0.039), while the obestatin levels (89.41 +/- 23.63 vs. 83.13 +/- 17.21 pmol/L) were not significantly different (p = 0.083). The ghrelin/obestatin ratio in the controls was significantly higher than that in the obese group (p = 0.014). In the latter, fasting insulin and alanine aminotransferase were independent factors for ghrelin; fasting insulin, weight and gender were independent factors for obestatin and alanine aminotransferase was an independent factor for ghrelin/obestatin. Moreover, ghrelin, obestatin and ghrelin/obestatin increased after weight reduction (p < 0.05, respectively), and the increment in ghrelin and obestatin was associated with a decrement in insulin resistance.

CONCLUSION

These data suggest that ghrelin, obestatin and/or the ghrelin/obestatin ratio are associated with obesity in childhood.

Intraventricular (i3vt) ghrelin increases food intake in fatty Zucker rats

Ghrelin is an orexigenic peptide secreted from the stomach and also made in the brain. Ghrelin receptors are expressed on hypothalamic cells important in appetite and energy balance. We determined that intra-3rd-ventricular (i3vt) ghrelin dose-dependently increases acute (1 and 2 h) food intake in lean and fatty Zucker rats (0, 0.01, 0.1 and 1.0 nmol ghrelin). The percentage increase of food intake in fatty Zucker rats was significantly greater than that in lean rats. Fatty Zucker rats had 4.5 times more ghrelin receptor mRNA in the hypothalamus than lean Zucker rats, suggesting a possible mechanism for the increased sensitivity.

Hypothalamic galanin and early state of hyperphagia in obese Zucker rats

Galanin (GAL) stimulates food intake in normal rats when it is injected in different hypothalamic areas involved in feeding such as the paraventricular and ventromedial nuclei and the lateral hypothalamus. At adulthood, the hyperphagic obese Zucker rat is characterized by a general dysregulation of some important neuropeptides involved in the regulation of food intake including GAL. The aim of this study was to measure GAL in different microdissected brain areas in 2- and 4-week-old lean (FA/-) and obese (fa/fa) male Zucker rats in order to know if GAL actively participates in triggering abnormal feeding behavior in obese rats. There was a significant increase (40%-220%) in GAL concentration with age in the arcuate and dorsomedial nuclei and in the above areas except for the lateral hypothalamus. Genotype differences were observed in the arcuate and paraventricular nuclei only. GAL levels were globally lower in obese than in lean rats (-15% to -25%) and the difference was significant at 2 weeks of age in the paraventricular nucleus and at 4 weeks of age in the arcuate nucleus. In agreement with human observations, these data suggest that GAL is not an early player in the development of overeating.

Neuropeptide Y in normal eating and in genetic and dietary-induced obesity

Neuropeptide Y (NPY) is one the most potent orexigenic peptides found in the brain. It stimulates food intake with a preferential effect on carbohydrate intake. It decreases latency to eat, increases motivation to eat and delays satiety by augmenting meal size. The effects on feeding are mediated through at least two receptors, the Y1 and Y5 receptors. The NPY system for feeding regulation is mostly located in the hypothalamus. It is formed of the arcuate nucleus (ARC), where the peptide is synthesized, and the paraventricular (PVN), dorsomedial (DMN) and ventromedial (VMN) nuclei and perifornical area where it is active. This activity is modulated by the hindbrain and limbic structures. It is dependent on energy availability, e.g. upregulation with food deprivation or restriction, and return to baseline with refeeding. It is also sensitive to diet composition with variable effects of carbohydrates and fats. Leptin signalling and glucose sensing which are directly linked to diet type are the most important factors involved in its regulation. Absence of leptin signalling in obesity models due to gene mutation either at the receptor level, as in the Zucker rat, the Koletsky rat or the db/db mouse, or at the peptide level, as in ob/ob mouse, is associated with increased mRNA abundance, peptide content and/or release in the ARC or PVN. Other genetic obesity models, such as the Otsuka-Long-Evans-Tokushima Fatty rat, the agouti mouse or the tubby mouse, are characterized by a diminution in NPY expression in the ARC nucleus and by a significant increase in the DMN. Further studies are necessary to determine the exact role of NPY in these latter models. Long-term exposure to high-fat or high-energy palatable diets leads to the development of adiposity and is associated with a decrease in hypothalamic NPY content or expression, consistent with the existence of a counter-regulatory mechanism to diminish energy intake and limit obesity development. On the other hand, an overactive NPY system (increased mRNA expression in the ARC associated with an upregulation of the receptors) is characteristic of rats or rodent strains sensitive to dietary-induced obesity. Finally, NPY appears to play an important role in body weight and feeding regulation, and while it does not constitute the only target for drug treatment of obesity, it may nevertheless provide a useful target in conjunction with others.

Ghrelin gene-related peptides modulate rat white adiposity

It is known that ghrelin and des-N-octanoyl (desacyl) ghrelin modulate food intake and adipogenesis in vivo. However, desacyl ghrelin represents the majority of ghrelin forms found in the circulation. The present study explored whether ghrelin gene-derived compounds could modulate, in vitro, adipocyte endocrine function and preadipocyte differentiation. Retroperitoneal (RP) adipocytes were cultured in the absence or presence of either ghrelin or desacyl ghrelin and in combination with either inhibitors of protein synthesis, insulin, dexamethasone (DXM), or GHSR1a antagonist. The results indicate that both ghrelin forms possess a direct leptin-releasing activity (LRA) on RP adipocytes and significantly enhanced adipocyte ob mRNA expression. These activities were related and unrelated to the activation of GHSR1a after coincubation with ghrelin and desacyl ghrelin, respectively. Moreover, desacyl ghrelin facilitated RP preadipocyte differentiation. Desacyl ghrelin enhanced cell lipid content, and PPARgamma2, and LPL mRNAs expression. The LRAs developed by different substances tested followed a rank order: ghrelin > desacyl ghrelin = insulin > or = DXM. Additionally, desacyl ghrelin was able to enhance medium glucose consumption by mature adipocytes in culture. These data strongly support that adipogenesis and adipocyte function are processes directly and positively modulated by ghrelin gene-derived peptides, thus further indicating that, besides their effects on food intake, ghrelin gene-derived peptides could play an important role on adiposity for maintaining homeostasis.

Direct effect of ghrelin on leptin production by cultured rat white adipocytes

OBJECTIVE

Because ghrelin is known to stimulate adipogenesis, we tested whether ghrelin could contribute to the maintenance of homeostasis, directly affecting rat white adipocyte leptin production.

RESEARCH METHODS AND PROCEDURES

Isolated retroperitoneal adipocytes were cultured for 0.5 to 48 hours without (baseline) or with (0.001 to 1 nM) ghrelin alone or in combination with insulin (0.01 to 10 nM) or dexamethasone (1 to 100 nM). Adipocytes were also incubated with ghrelin and inhibitors either of RNA (actinomycin D) or protein synthesis (cycloheximide) or with several concentrations (10 to 1000 nM) of a specific ghrelin antagonist. When cultures were terminated, we evaluated adipocyte leptin secretion and ob mRNA expression.

RESULTS

Our data indicate that ghrelin directly enhanced adipocyte leptin release and ob mRNA expression, that the leptin-releasing activity of ghrelin was additive to the action of both insulin and dexamethasone and was abrogated by protein synthesis inhibitors, and that effects of ghrelin on adipocyte ob mRNA expression and release were blocked by coincubation with the specific growth hormone secretagogue receptor 1a antagonist.

DISCUSSION

Our study supports the ability of ghrelin to enhance white adipose tissue leptin production by a direct receptor-mediated effect. This activity of ghrelin could play a potentially significant role in rapid restoration of homeostasis after food intake.

Current knowledge in the neurophysiologic modulation of obesity

Obesity is today one of the commonest of life-threatening diseases in developed countries and generally results from an imbalance between energy intake and energy expenditure. Although there is increasing evidence for a genetic basis of obesity in some clinical syndromes, this seems to be the cause only in a limited number of patients and obesity is far from being considered as a gene-related disease. Eating is a complex and multifactorial process involving autonomous pathways that transfer sensory and motor information between the entire length of the digestive tract and the central nervous system. Modulation of the amount of energy that we take in as food involves several mechanisms and networks that connect the brain with the gut, this process being key to the regulation of body weight over time, as well as to the modification of long-term eating behaviors. Furthermore, this axis is closely coupled to other systems that are involved in energy homeostasis, namely, food preference, energy expenditure, and lifestyle. The identification of several neuropeptides that modulate eating behavior in various ways, along with studies performed in animal models, have focused attention on the role of these molecules and their clinical implications in the development of obesity in humans.

Peptide S is a novel potent inhibitor of voluntary and fast-induced food intake in rats

Peptide S (NPS or PEPS) and its cognate receptor have been recently identified both in the central nervous system and in the periphery. NPS/PEPS promotes arousal and has potent anxiolytic-like effects when it is injected centrally in mice. In the present experiment, we tested by different approaches its central effects on feeding behaviour in Long-Evans rats. PEPS at doses of 1 and 10 microg injected in the lateral brain ventricle strongly inhibited by more than 50% chow intake in overnight fasted rats with effects of longer duration with the highest dose (P<0.0001). A similar decrease was observed for the spontaneous intake of a high-energy palatable diet (-48%; P<0.0001). This anorexigenic effect was comparable to that induced by corticotropin-releasing hormone in fasted rats at equimolar doses. However, peptide S did not modify food intake stimulated by neuropeptide Y (NPY) at equimolar doses. It also did not affect the fasting concentrations of important modulators of food intake like leptin, ghrelin, and insulin in circulation. This study therefore showed that peptide S is a new potent anorexigenic agent when centrally injected. Its inhibitory action appears to be independent of the NPY, ghrelin, and leptin pathways. Development of peptide S agonists could constitute a new approach for the treatment of obesity.

The role of the small bowel in the regulation of circulating ghrelin levels and food intake in the obese Zucker rat

Circulating levels of ghrelin, a stomach peptide that promotes food intake, rise before and fall after meal. We aimed to investigate whether there is an independent contribution of the small bowel to the regulation of ghrelin and appetite. A duodenal-jejunal bypass (DJB) with preservation of normal gastric volume and exposure to nutrients was performed in 12-wk-old obese Zucker ZDF fa/fa rat. Food intake, weight gain, 48-h fasting, and 24-h refeeding levels of total and acylated ghrelin were measured. The DJB was challenged against gastric banding (GB), diet, and a sham operation in matched animals. Normal controls were age-matched Wistar rats, which underwent either DJB or a sham operation. The Zucker obese animals showed a paradoxical increase of acylated ghrelin levels after refeeding (+30% with respect to fasting levels; P = 0.001), an abnormality that was completely reversed only by the DJB (-30%; P = 0.01) but not after GB, diet, or sham operation. In obese rats, the DJB resulted in significantly less food intake and weight gain compared with both GB (P < 0.05) and sham operation (P < 0.01). In sharp contrast, the DJB did not alter food intake and weight gain in normal rats. The DJB does not physically restrict the flow of food but restores meal-induced suppression of acylated ghrelin and significantly reduces food intake in Zucker obese rats. These findings suggest an independent intestinal contribution to the regulation of the dynamic ghrelin response to eating and the possibility that defective signaling from the proximal bowel could be involved in the pathogenesis of obesity/hyperphagia.

Caloric intake and hypothalamic neurotransmitters in Zucker rats made acutely diabetic with streptozocin

Zucker rats, lean and obese, treated with low dose intraperitoneal injections of streptozocin become hyperglycemic within 24h. Insulin levels fall, although the obese animal remains hyperinsulinemic. Associated with these changes in glucose and insulin there are transient decreases in caloric intake. Macronutrient selection studies show that protein consumption decreases. There is a trend for fat intake to decrease. The levels of hypothalamic neurotransmitters in the lean animals are not altered by streptozocin. The levels of 5-hydroxyindoleacetic acid increases in the streptozocin-treated obese animal in the paraventricular region, ventromedial region and the raphe. Serotonin is also significantly increased in the paraventricular region of the obese rat. These results suggest that acutely, treatment with streptozocin injures pancreatic islets, causing, in turn, decreases in insulin levels so that hyperglycemia ensues in both phenotypes. Associated with these perturbations are decreases in caloric intake. The magnitude of change in insulin levels is much greater in the obese rat. It is hypothesized that in the obese Zucker rat decrements in food intake are mediated by increase in serotonin turnover in the hypothalamus and these changes are related to changes of insulin levels. These data support the concept that circulating insulin affects hypothalamic neurotransmitters.

Influencing the between-feeding and endocrine responses of plasma ghrelin in healthy dogs

OBJECTIVES

Ghrelin has recently been isolated from rat and human stomach as an endogenous ligand for the growth hormone (GH) secretagog receptor. Using beagle dogs, we investigated the distribution of ghrelin in the stomach and its possible role.

METHODS

We examined: (i) GH release in response to ghrelin injection (0.5 or 5 microg/kg, i.v.), (ii) gastric localization of ghrelin-immunostained cells, (iii) changes in daily food consumption after ghrelin injection (3, 10, and 20 microg/kg, i.v.), (iv) plasma ghrelin levels under regular, but restricted feeding conditions, and (v) variations in plasma ghrelin levels in relatively lean, normal and obese dogs.

RESULTS

Administration of ghrelin to dogs promptly increased circulating GH concentrations, although this effect was transitory and was maintained for only 20 min. Ghrelin was localized in the stomach fundus and body, but none was detected in either the pylorus or cardia. Administration of ghrelin at a dose of 20 microg/kg increased the daily food intake of beagle dogs. Plasma ghrelin levels peaked just before meal times, and then returned to basal levels. Obese dogs had higher plasma ghrelin levels than did normal and lean dogs.

CONCLUSIONS

These results indicate that ghrelin is a potent GH secretagog in dogs. The distribution of ghrelin-immunoreactive cells in the canine stomach resembles that of both the murine and human stomach. Ghrelin participates in the control of feeding behavior and energy homeostasis in dogs and may, therefore, be involved in the development of obesity.

Alternate-day fasting in nonobese subjects: effects on body weight, body composition, and energy metabolism

BACKGROUND

Prolonged dietary restriction increases the life span in rodents. Some evidence suggests that alternate-day fasting may also prolong the life span.

OBJECTIVE

Our goal was to determine whether alternate-day fasting is a feasible method of dietary restriction in nonobese humans and whether it improves known biomarkers of longevity.

DESIGN

Nonobese subjects (8 men and 8 women) fasted every other day for 22 d. Body weight, body composition, resting metabolic rate (RMR), respiratory quotient (RQ), temperature, fasting serum glucose, insulin, free fatty acids, and ghrelin were assessed at baseline and after 21 d (12-h fast) and 22 d (36-h fast) of alternate-day fasting. Visual analogue scales were used to assess hunger weekly.

RESULTS

Subjects lost 2.5 +/- 0.5% of their initial body weight (P < 0.001) and 4 +/- 1% of their initial fat mass (P < 0.001). Hunger increased on the first day of fasting and remained elevated (P < 0.001). RMR and RQ did not change significantly from baseline to day 21, but RQ decreased on day 22 (P < 0.001), which resulted in an average daily increase in fat oxidation of > or =15 g. Glucose and ghrelin did not change significantly from baseline with alternate-day fasting, whereas fasting insulin decreased 57 +/- 4% (P < 0.001).

CONCLUSIONS

Alternate-day fasting was feasible in nonobese subjects, and fat oxidation increased. However, hunger on fasting days did not decrease, perhaps indicating the unlikelihood of continuing this diet for extended periods of time. Adding one small meal on a fasting day may make this approach to dietary restriction more acceptable.

Adaptation of ghrelin levels to limit body weight gain in the obese Zucker rat

In this study, we measured the ghrelin, leptin, and insulin variations in lean and obese Zucker fa/fa rats during the acute phase of body weight gain. At 2 months of age, plasma insulin and leptin concentrations in fa/fa rats were, respectively, 470% and 3700% higher than in lean rats (p <0.0001). Plasma ghrelin was significantly lower (-24.6%; p <0.02) than in lean rats. At 6 months of age, ghrelin increased in both genotypes but the difference was no more significant. The inverse correlations existing between ghrelin and either body weight (BW), insulin or leptin at 2 months of age were no more observable in 6-month-old rats. At 6 months of age, the lean rats had the same body weight as the 2-month-old obese rats. In these body weight-matched rats, ghrelin was not correlated with BW but it remained negatively correlated with insulin and leptin. At the same body weight, obese rats had a much lower plasma ghrelin than lean rats (717+/-42 vs. 1754+/-83 pg/ml; p <0.0001). These data indicate that body composition rather than body weight is the primary factor for the down-regulation of the ghrelin system. This down-regulation constitutes a mechanism of defense of the organism against the development of obesity at least during the first part of life.