Rhythmic, reciprocal ghrelin and leptin signaling: new insight in the development of obesity

Rhythmic leptin is required for weight gain from circadian desynchronized feeding in the mouse

The neuroendocrine and metabolic effects of leptin have been extensively researched since the discovery, and the later identification, of the leptin gene mutated within the ob/ob mouse. Leptin is required for optimal health in a number of physiological systems (e.g. fertility, bone density, body weight regulation). Despite the extensive leptin literature and many observations of leptin's cyclical pattern over the 24-hour day, few studies have specifically examined how the circadian rhythm of leptin may be essential to leptin signaling and health. Here we present data indicating that a rhythmic leptin profile (e.g. 1 peak every 24 hours) leads to excessive weight gain during desynchronized feeding whereas non-rhythmic leptin provided in a continuous manner does not lead to excessive body weight gain under similar feeding conditions. This study suggests that feeding time can interact with leptin's endogenous rhythm to influence metabolic signals, specifically leading to excessive body weight gains during 'wrongly' timed feeding.

An approximation to the temporal order in endogenous circadian rhythms of genes implicated in human adipose tissue metabolism

Although it is well established that human adipose tissue (AT) shows circadian rhythmicity, published studies have been discussed as if tissues or systems showed only one or few circadian rhythms at a time. To provide an overall view of the internal temporal order of circadian rhythms in human AT including genes implicated in metabolic processes such as energy intake and expenditure, insulin resistance, adipocyte differentiation, dyslipidemia, and body fat distribution. Visceral and subcutaneous abdominal AT biopsies (n=6) were obtained from morbid obese women (BMI≥40 kg/m(2) ). To investigate rhythmic expression pattern, AT explants were cultured during 24-h and gene expression was analyzed at the following times: 08:00, 14:00, 20:00, 02:00 h using quantitative real-time PCR. Clock genes, glucocorticoid metabolism-related genes, leptin, adiponectin and their receptors were studied. Significant differences were found both in achrophases and relative-amplitude among genes (P<0.05). Amplitude of most genes rhythms was high (>30%). When interpreting the phase map of gene expression in both depots, data indicated that circadian rhythmicity of the genes studied followed a predictable physiological pattern, particularly for subcutaneous AT. Interesting are the relationships between adiponectin, leptin, and glucocorticoid metabolism-related genes circadian profiles. Their metabolic significance is discussed. Visceral AT behaved in a different way than subcutaneous for most of the genes studied. For every gene, protein mRNA levels fluctuated during the day in synchrony with its receptors. We have provided an overall view of the internal temporal order of circadian rhythms in human adipose tissue.

Pivotal role of leptin-hypothalamus signaling in the etiology of diabetes uncovered by gene therapy: a new therapeutic intervention?

The incidence of diabetes mellitus has soared to epidemic proportion worldwide. The debilitating chronic hyperglycemia is caused by either lack of insulin as in diabetes type 1 or its ineffectiveness as in diabetes type 2. Frequent replacement of insulin with or without insulin analogs for optimum glycemic control are the conventional cumbersome therapies. Recent application of leptin gene transfer technology has uncovered the participation of adipocytes-derived leptin-dependent hypothalamic neural signaling in glucose homeostasis and demonstrated that a breakdown in this communication due to leptin insufficiency in the hypothalamus underlies the etiology of chronic hyperglycemia. Reinstatement of central leptin sufficiency by hyperleptinemia produced either by intravenous leptin infusion or a single systemic injection of recombinant adenovirus vector encoding leptin gene suppressed hyperglycemia and evoked euglycemia only transiently in rodent models of diabetes type 1. In contrast, stable restoration of leptin sufficiency, solely in the hypothalamus, with biologically active leptin transduced by an intracerebroventicular injection of recombinant adeno-associated virus vector encoding leptin gene (rAAV-lep) abolished hyperglycemia and imposed euglycemia through the extended duration of experiment by stimulating glucose disposal in the periphery in models of diabetes type 1. Further, similar hypothalamic leptin transgene expression abrogated chronic hyperglycemia and hyperinsulinemia, the predisposing risk factors of the age and environmentally acquired diabetes type 2, and instituted euglycemia by independently activating relays that stimulate glucose metabolism and repress hyperinsulinemia and improve insulin sensitivity in the periphery. Consequently, this durable antidiabetic efficacy of one time rAAV-lep neurotherapy offers a potential novel substitute for insulin therapy following preclinical trials in subhuman primates and humans.

Effect of feeding regimens on circadian rhythms: implications for aging and longevity

Increased longevity and improved health can be achieved in mammals by two feeding regimens, caloric restriction (CR), which limits the amount of daily calorie intake, and intermittent fasting (IF), which allows the food to be available ad libitum every other day. The precise mechanisms mediating these beneficial effects are still unresolved. Resetting the circadian clock is another intervention that can lead to increased life span and well being, while clock disruption is associated with aging and morbidity. Currently, a large body of evidence links circadian rhythms with metabolism and feeding regimens. In particular, CR, and possibly also IF, can entrain the master clock located in the suprachiasmatic nuclei (SCN) of the brain hypothalamus. These findings raise the hypothesis that the beneficial effects exerted by these feeding regimens could be mediated, at least in part, through resetting of the circadian clock, thus leading to synchrony in metabolism and physiology. This hypothesis is reinforced by a transgenic mouse model showing spontaneously reduced eating alongside robust circadian rhythms and increased life span. This review will summarize recent findings concerning the relationships between feeding regimens, circadian rhythms, and metabolism with implications for ageing attenuation and life span extension.

Appetite regulation: the central role of melatonin in Danio rerio

Melatonin is the hormonal mediator of photoperiodic information to the central nervous system in vertebrates and allows the regulation of energy homeostasis through the establishment of a proper balance between energy intake and energy expenditure. The aim of this study was to evaluate the role of melatonin in appetite central control analyzing the involvement of this hormone in the regulation of feeding behavior in the zebrafish Danio rerio. For this purpose, the effect of two different melatonin doses (100nM and 1μM) administered for 10 days, via water, to zebrafish adults was evaluated at both physiological and molecular level and the effect of melatonin was considered in relation to the most prominent systems involved in appetite regulation. For the first time, in fact, melatonin control of food intake by the modulation of leptin, MC4R, ghrelin, NPY and CB1 gene expression was evaluated. The results obtained indicate that melatonin significantly reduces food intake and the reduction is in agreement with the changes observed at molecular level. A significant increase in genes codifying for molecules involved in feeding inhibition, such as leptin and MC4R, and a significant reduction in the major orexigenic signals including ghrelin, NPY and CB1 are showed here. Taken together these results support the idea that melatonin falls fully into the complex network of signals that regulate food intake thus playing a key role in central appetite regulation.

The circadian clock and metabolism

Mammals have developed an endogenous circadian clock located in the SCN (suprachiasmatic nuclei) of the anterior hypothalamus that responds to the environmental light–dark cycle. Human homoeostatic systems have adapted to daily changes in a way that the body anticipates the sleep and activity periods. Similar clocks have been found in peripheral tissues, such as the liver, intestine and adipose tissue. Recently it has been found that the circadian clock regulates cellular and physiological functions in addition to the expression and/or activity of enzymes and hormones involved in metabolism. In turn, key metabolic enzymes and transcription activators interact with and affect the core clock mechanism. Animals with mutations in clock genes that disrupt cellular rhythmicity have provided evidence to the relationship between the circadian clock and metabolic homoeostasis. The present review will summarize recent findings concerning the relationship between metabolism and circadian rhythms.

Food addiction and obesity: evidence from bench to bedside

Obesity has become a major health problem and epidemic. However, much of the current debate has been fractious and etiologies of obesity have been attributed to eating behavior or fast food, personality issues, depression, addiction, or genetics. One of the interesting new hypotheses for epidemic obesity is food addiction, which is associated with both substance-related disorder and eating disorder. Accumulating evidences have shown that there are many shared neural and hormonal pathways as well as distinct differences that may help researchers find why certain individuals overeat and become obese. Functional neuroimaging studies have further revealed that good or great smelling, looking, tasting, and reinforcing food has characteristics similar to that of drugs of abuse. Many of the brain changes reported for hedonic eating and obesity are also seen in various forms of addictions. Most importantly, overeating and obesity may have an acquired drive like drug addiction with respect to motivation and incentive; craving, wanting, and liking occur after early and repeated exposures to stimuli. The acquired drive for great food and relative weakness of the satiety signal would cause an imbalance between the drive and hunger/reward centers in the brain and their regulation.

Body weight, metabolism and clock genes

Biological rhythms are present in the lives of almost all organisms ranging from plants to more evolved creatures. These oscillations allow the anticipation of many physiological and behavioral mechanisms thus enabling coordination of rhythms in a timely manner, adaption to environmental changes and more efficient organization of the cellular processes responsible for survival of both the individual and the species. Many components of energy homeostasis exhibit circadian rhythms, which are regulated by central (suprachiasmatic nucleus) and peripheral (located in other tissues) circadian clocks. Adipocyte plays an important role in the regulation of energy homeostasis, the signaling of satiety and cellular differentiation and proliferation. Also, the adipocyte circadian clock is probably involved in the control of many of these functions. Thus, circadian clocks are implicated in the control of energy balance, feeding behavior and consequently in the regulation of body weight. In this regard, alterations in clock genes and rhythms can interfere with the complex mechanism of metabolic and hormonal anticipation, contributing to multifactorial diseases such as obesity and diabetes. The aim of this review was to define circadian clocks by describing their functioning and role in the whole body and in adipocyte metabolism, as well as their influence on body weight control and the development of obesity.

Chronobiological aspects of nutrition, metabolic syndrome and obesity

The present review starts from the classical physiological and nutritional studies related with food intake control, digestion, transport and absorption of nutrients. It continues with studies related with the metabolism of adipose tissue, and finish with modern experiments in genetics and molecular biology - all from a fresh, chronobiological point of view. Obesity will be explained as a fault in the circadian system, as pathology associated with "chronodisruption". The main gaps in chronobiological research related to obesity will be also identified and chronobiological-based therapies will be proposed in order to allow the resetting of the circadian rhythm among obese subjects.

Food for thoughts: feeding time and hormonal secretion

Many daily cycles are imposed on us by our environment, such as alternating days and nights, temperature fluctuations or rhythms in food availability. When food is accessible every day at the same time, animals will adapt their physiology and behaviour to match the daily meal. They will anticipate the access to food by waking up and being active in the hours prior to feeding, foraging for food. Adaptation of physiology to changing conditions of food availability is not only evident at the behavioural level, but also for hormonal systems. Thus, corticosteroids, melatonin, leptin/ghrelin, insulin/glucagon, orexins and thyroid hormones, which show rhythmic profiles of secretion in ad libitum feeding conditions, are sensitive to increase and/or depletion in energy supplies and will be influenced when food sources are limited or available at unusual times. The present review reports the influence of restricted feeding schedules on secretion profiles of diverse hormones compared to normal ad libitum feeding conditions in rodents. In the end, the interplay between these systems and their response to environmental challenges will allow the animal to maintain their fitness for survival.

Metabolism and circadian rhythms--implications for obesity

Obesity has become a serious public health problem and a major risk factor for the development of illnesses, such as insulin resistance and hypertension. Human homeostatic systems have adapted to daily changes in light and dark in a way that the body anticipates the sleep and activity periods. Mammals have developed an endogenous circadian clock located in the suprachiasmatic nuclei of the anterior hypothalamus that responds to the environmental light-dark cycle. Similar clocks have been found in peripheral tissues, such as the liver, intestine, and adipose tissue, regulating cellular and physiological functions. The circadian clock has been reported to regulate metabolism and energy homeostasis in the liver and other peripheral tissues. This is achieved by mediating the expression and/or activity of certain metabolic enzymes and transport systems. In return, key metabolic enzymes and transcription activators interact with and affect the core clock mechanism. In addition, the core clock mechanism has been shown to be linked with lipogenic and adipogenic pathways. Animals with mutations in clock genes that disrupt cellular rhythmicity have provided evidence for the relationship between the circadian clock and metabolic homeostasis. In addition, clinical studies in shift workers and obese patients accentuate the link between the circadian clock and metabolism. This review will focus on the interconnection between the circadian clock and metabolism, with implications for obesity and how the circadian clock is influenced by hormones, nutrients, and timed meals.

Gene expression profiles of a mouse congenic strain carrying an obesity susceptibility QTL under obesigenic diets

Genetic factors are strongly involved in the development of obesity, likely through the interactions of susceptibility genes with obesigenic environments, such as high-fat, high-sucrose (HFS) diets. Previously, we have established a mouse congenic strain on C57BL/6 J background, carrying an obesity quantitative trait locus (QTL), tabw2, derived from obese diabetic TALLYHO/JngJ mice. The tabw2 congenic mice exhibit increased adiposity and hyperleptinemia, which becomes exacerbated upon feeding HFS diets. In this study, we conducted genome-wide gene expression profiling to evaluate differentially expressed genes between tabw2 and control mice fed HFS diets, which may lead to identification of candidate genes as well as insights into the mechanisms underlying obesity mediated by tabw2. Both tabw2 congenic mice and control mice were fed HFS diets for 10 weeks beginning at 4 weeks of age, and total RNA was isolated from liver and adipose tissue. Whole-genome microarray analysis was performed and verified by real-time quantitative RT-PCR. At False Discovery Rate adjusted P < 0.05, 1026 genes were up-regulated and 308 down-regulated in liver, whereas 393 were up-regulated and 187 down-regulated in adipose tissue in tabw2 congenic mice compared to controls. Within the tabw2 QTL interval, 70 genes exhibited differential expression in either liver or adipose tissue. A comprehensive pathway analysis revealed a number of biological pathways that may be perturbed in the diet-induced obesity mediated by tabw2.

Appetite and gastrointestinal motility: role of ghrelin-family peptides

Eating disorders, obesity and cachexia endanger the lives of millions of people worldwide. Fortunately, in last decade, there has been a rapid and substantial progress toward uncovering the molecular and neural mechanisms by which energy imbalance develops. In 1999, ghrelin was identified as the first orexigenic gut-derived peptide. It stimulates appetite and controls the gastric motility and the acid secretion through the activation of the growth hormone secretagogue-receptor. After the discovery of ghrelin, other forms of ghrelin-related proteins were isolated from the rat stomach. The unmodified des-n-octanoyl form (des-acyl ghrelin) and the recent obestatin act through distinct receptors and contrarily to acyl ghrelin, show an anorexigenic activity. The finding that these three peptide hormones derive from the same precursor exert opposing physiological actions, highlights the importance of post-translational regulatory mechanisms. Further investigations are required to highlight the complexity of ghrelin physiology in order to better understand the mechanisms regulating the energy balance and provide a successful treatment of eating disorders, obesity and cachexia.

Effect of a high-fat diet on 24-hour pattern of circulating adipocytokines in rats

We have shown a significant disruption of 24-h pattern of plasma pituitary, adrenal, and gonadal hormones in high-fat-fed rats. Our objective was to assess the effect of a high-fat diet (35% fat) on mean levels and 24-h pattern of several adipocytokines in rats. A normal diet-fed rats (4% fat) were used as controls. When body weight of high-fat-fed rats attained values about 25% higher than controls (after 66 days of treatment), the animals were killed at six different time intervals throughout a 24-h cycle. Plasma concentrations of insulin, adiponectin, interleukin (IL)-1, leptin, ghrelin, plasminogen activator inhibitor-1 (PAI-1), and monocyte chemoattractant protein-1 (MCP-1) were measured in a multianalyte profiling by using the Luminex-100 system. Tumor necrosis factor alpha (TNFalpha) and IL-6 were measured by enzyme-linked immunosorbent assay. A significant hyperglycemia developed in high-fat-fed rats, together with a significant increase in plasma insulin. Mean levels of plasma adiponectin, IL-1, IL-6, TNFalpha, and leptin augmented, and ghrelin decreased, in high-fat-fed rats. The normal daily pattern of plasma insulin, adiponectin, IL-1, IL-6, TNFalpha, leptin, ghrelin, and MCP-1 became disrupted in high-fat-fed rats. The results indicate that a high-fat diet may bring about signs of insulin resistance and mild inflammation in rats, together with the disruption in daily variations of circulating insulin and ghrelin, and of several adipocytokines including leptin, adiponectin, IL-1, IL-6, TNFalpha, and MCP-1.

Adolescents' sleep behaviors and perceptions of sleep

BACKGROUND

Sleep duration affects the health of children and adolescents. Shorter sleep durations have been associated with poorer academic performance, unintentional injuries, and obesity in adolescents. This study extends our understanding of how adolescents perceive and deal with their sleep issues.

METHODS

General education classes were randomly selected from a convenience sample of three high schools in the Midwest. Three hundred eighty-four ninth- to twelfth-grade students (57%) completed a self-administered valid and reliable questionnaire on sleep behaviors and perceptions of sleep.

RESULTS

Most respondents (91.9%) obtained inadequate sleep (<or= 9 hours) on most school nights of the week, with 10% reporting less than 6 hours of sleep each week night. The majority indicated that not getting enough sleep had the following effects on them: being more tired during the day (93.7%), having difficulty paying attention (83.6%), lower grades (60.8%), increase in stress (59.0%), and having difficulty getting along with others (57.7%). Some students reported engaging in harmful behaviors to help them sleep: taking sleeping pills (6.0%), smoking a cigarette to relax (5.7%), and drinking alcohol in the evening (2.9%). Students who received fewer hours of sleep were significantly more likely to report being stressed (p = .02) and were more likely to be overweight (p = .04).

CONCLUSIONS

Inadequate sleep time may be contributing to adolescent health problems such as increased stress and obesity. Findings indicate a need for sleep hygiene education for adolescents and their parents. A long-term solution to chronic sleep deprivation among high school students could include delaying high school start times, such as was done successfully in the Minneapolis Public School District.

Disruption in the leptin-NPY link underlies the pandemic of diabetes and metabolic syndrome: new therapeutic approaches

Multidisciplinary research from my and my colleagues' laboratory has shown that disruption at various levels of leptin signaling to the interactive hypothalamic network of neuropeptide Y (NPY) and cohorts contributes to the antecedent pathophysiologic sequelae of the disease cluster of the metabolic syndrome. Disruptions in NPY signaling due to high or low abundance of NPY and cognate receptors dysregulate the homeostatic milieu to promote hyperinsulinemia, hyperglycemia, fat accrual, and overt diabetes. Hyperleptinemia induced by consumption of energy-rich diets inhibits leptin transport across the blood-brain barrier and thereby produces leptin insufficiency in the hypothalamus. Sustained leptin insufficiency results in loss of hypothalamic restraint on pancreatic insulin secretion and diminished glucose metabolism and energy expenditure. This chain of events culminates in hyperinsulinemia, hyperglycemia, and diabetes. Our recent studies have shown that increasing the supply of leptin centrally by gene therapy reinstates the restraint on hypothalamic NPY signaling and ameliorates diabetes and the attendant disease cluster of the metabolic syndrome. Thus, newer therapies that would enhance leptin transport across the blood-brain barrier in a timely manner or reinstate leptin restraint on NPY signaling through central leptin gene therapy or pharmacologically with leptin mimetics are likely to curtail the pathophysiologic sequelae of diabetes and related ailments of the metabolic syndrome.

Sex-associated differences in the leptin and ghrelin systems related with the induction of hyperphagia under high-fat diet exposure in rats

Leptin and ghrelin are known to be main hormones involved in the control of food intake, with opposing effects. Here we have explored whether changes in the leptin and ghrelin system are involved in the long-term effects of high-fat (HF) diet feeding in rats and whether sex-associated differences exist. Male and female Wistar rats were fed until the age of 6 months with a normal-fat (NF) or an HF-diet. Food intake and body weight were followed. Gastric and serum levels of leptin and ghrelin, and mRNA levels of leptin (in stomach and adipose tissue), ghrelin (in stomach), and NPY, POMC, and leptin and ghrelin receptors (OB-Rb and GHS-R) (in the hypothalamus) were measured. In both males and females, total caloric intake and body weight were greater under the HF-diet feeding. In females, circulating ghrelin levels and leptin mRNA expression in the stomach were higher under HF-diet. HF-diet feeding also resulted in higher hypothalamic NPY/POMC mRNA levels, more marked in females, and in lower OB-Rb mRNA levels, more marked in males. In addition, in females, serum ghrelin levels correlated positively with hypothalamic NPY mRNA levels, and these with caloric intake. In males, hypothalamic OB-Rb mRNA levels correlated positively with POMC mRNA levels and these correlated negatively with caloric intake and with body weight. These data reflect differences between sexes in the effects of HF-diet feeding on food intake control systems, suggesting an impairment of the anorexigenic leptin-POMC system in males and an over-stimulation of the orexigenic ghrelin-NPY system in females.

[Relation between sleep and obesity: a literature review]

Reduction in sleep time has become an endemic condition in modern society and current literature has found important epidemiological associations between damage in the habitual standard of sleep and obesity. On this basis, the present revision analyzed the role of sleep and its alteration in the promotion of obesity. Diverse studies indicate that subjects that sleep less have greater possibility of becoming obese, and the shortening of sleep increases the leptin/ghrelin reason, generating increase of the appetite and hunger. This can be associated to the biggest caloric intake and promotion of obesity. An adequate standard of sleep becomes basic for the regulation of body mass and must be stimulated by health professionals.

Body weight and plasma levels of ghrelin and leptin during treatment with olanzapine

Although enhanced appetite and weight gain are potential side effects of treatment with antipsychotic agents, particularly olanzapine and clozapine, the mechanisms underlying these side effects are poorly understood. Leptin and ghrelin were recently identified as hormones that play crucial roles in the regulation of energy balance and glucose metabolism. To elucidate relationships between weight change and plasma levels of ghrelin and leptin, we investigated the circulating ghrelin and leptin levels and body weight during olanzapine treatment. Twenty-four patients with schizophrenia were examined during 6-month administration of olanzapine. Ghrelin, leptin, weight and body mass index (BMI) were measured before and after 2, 4, 8, 12, 16, and 24 weeks of olanzapine treatment. The concentration of glucose and various lipid metabolic parameters were measured at baseline and at 24 weeks. Significant increases in weight, BMI and leptin were observed at week 24. On the other hand, the serum levels of ghrelin decreased significantly after olanzapine treatment. In addition, the level of ghrelin was negatively correlated with the leptin level, BMI and weight. The leptin level was positively correlated with both BMI and weight. Ghrelin is associated with metabolic changes, in combination with leptin, during olanzapine treatment. However, further large-scale and longitudinal studies are warranted to elucidate the metabolic changes involving ghrelin, leptin and insulin during treatment with antipsychotics.

Photoperiod influences the central effects of ghrelin on food intake, GH and LH secretion in sheep

Ghrelin is a circulating peptide, primarily secreted by the gut, that has reported actions within the hypothalamo-pituitary axis to stimulate food intake, inhibit GnRH/LH secretion and stimulate GH secretion in monogastric species. Here, we examine responses to centrally administered ghrelin in a seasonal ruminant. Estradiol-implanted castrated male sheep with indwelling intracerebroventricular (i.c.v.) cannulae were kept with unrestricted food for 16 weeks in long day photoperiod (LD, 16 h light/day) then 16 weeks in short days (SD, 8 h light/day). In week 16 of each photoperiod they were given a control (saline) i.c.v. injection on day 1 and ghrelin i.c.v. injection on day 2. Mean circulating endogenous plasma ghrelin concentrations showed no diurnal pattern and were similar between the photoperiods. Central ghrelin injection increased voluntary food intake 2-fold in the first hour after administration in LD but not in SD, decreased LH pulse frequency and amplitude in SD but not in LD, and stimulated GH release in both photoperiods, although there was a 1.5-fold larger response in LD. Therefore, central injection of ghrelin to sheep acutely stimulated food intake in LD, suppressed reproductive neuroendocrine output in SD, and stimulated GH secretion irrespective of photoperiod, although more pronounced in LD. These data indicate that photoperiod can influence hypothalamic appetite and reproductive neuroendocrine responses to ghrelin in seasonal species.

Central leptin insufficiency syndrome: an interactive etiology for obesity, metabolic and neural diseases and for designing new therapeutic interventions

This review critically reappraises recent scientific evidence concerning central leptin insufficiency versus leptin resistance formulations to explain metabolic and neural disorders resulting from subnormal or defective leptin signaling in various sites in the brain. Research at various fronts to unravel the complexities of the neurobiology of leptin is surveyed to provide a comprehensive account of the neural and metabolic effects of environmentally imposed fluctuations in leptin availability at brain sites and the outcome of newer technology to restore leptin signaling in a site-specific manner. The cumulative new knowledge favors a unified central leptin insufficiency syndrome over the, in vogue, central resistance hypothesis to explain the global adverse impact of deficient leptin signaling in the brain. Furthermore, the leptin insufficiency syndrome delineates a novel role of leptin in the hypothalamus in restraining rhythmic pancreatic insulin secretion while concomitantly enhancing glucose metabolism and non-shivering thermogenic energy expenditure, sequelae that would otherwise promote fat accrual to store excess energy resulting from consumption of energy-enriched diets. A concerted effort should now focus on development of newer technologies for delivery of leptin or leptin mimetics to specifically target neural pathways for remediation of diverse ailments encompassing the central leptin insufficiency syndrome.

Increased acylated plasma ghrelin, but improved lipid profiles 24-h after consumption of carob pulp preparation rich in dietary fibre and polyphenols

We have recently shown that a polyphenol-rich insoluble dietary fibre preparation from carob pulp (Ceratonia siliqua L; carob fibre) decreased postprandial acylated ghrelin, TAG and NEFA during an acute liquid meal challenge test. However, delayed effects of carob fibre consumption are unknown. Therefore, a randomized controlled crossover study in nineteen healthy volunteers consuming foods with or without 50 g carob fibre was conducted. On the subsequent day (day 2), glucose, TAG, total and acylated ghrelin as well as insulin, NEFA and leptin were assessed at baseline and at timed intervals for 300 min after ingestion of standardized bread. Consumption of carob fibre-enriched foods did not affect fasting concentrations of glucose, TAG, total ghrelin, NEFA, insulin and leptin. Fasting acylated ghrelin was increased on the day subsequent to carob fibre consumption compared with control (P = 0.046). After consumption of the standard bread on day 2, glucose response (P = 0.029) was increased, and TAG (P = 0.033) and NEFA (P < 0.001) responses were decreased compared with control. Postprandial responses of total and acylated ghrelin, insulin and leptin on day 2 were unaffected by carob fibre consumption the previous day. In conclusion, an increase in total and acylated plasma ghrelin accompanied by enhanced lipid metabolism after carob fibre consumption suggests higher lipid utilization and suppressed lipolysis on the day subsequent to carob fibre consumption. However, elevated glucose levels after carob fibre consumption need to be addressed in future studies.

Ghrelin effects on the circadian system of mice

The orexigenic peptide ghrelin stimulates both food intake and growth hormone release and is synthesized in the stomach and in hypothalamic areas involved in feeding control. The suprachiasmatic nuclei of the hypothalamus (SCN) control most circadian rhythms, although there is evidence that some oscillators, such as food-entrainable oscillators, can drive activity rhythms even after SCN ablation. Ghrelin levels exhibit a circadian rhythm and closely follow feeding schedules, making this peptide a putative candidate for food-related entraining signals. We examined the response of the SCN to ghrelin treatments in vitro, by means of electrophysiological and bioluminescence recordings, and in vivo, by assessing effects on the phase of locomotor activity rhythms. Ghrelin applied at circadian time 6 in vitro to cultured SCN slices induced an approximately 3 h phase advance. In addition, ghrelin phase advanced the rhythm of PER2::LUC (Period2::Luciferase) expression in cultured SCN explants from mPer2(Luc) transgenic mice. In vivo, intraperitoneal administration of ghrelin or a synthetic analog, growth hormone-releasing protein-6 (GHRP-6), to ad libitum fed animals failed to alter circadian phase. When injected after 30 h of food deprivation, GHRP-6 induced a phase advance compared with saline-injected animals. These results indicate that ghrelin may play a role in the circadian system by exerting a direct action on the SCN and that the system as a whole may become sensitive to ghrelin and other feeding-related neuropeptides under conditions of food restriction.

Early causes of child obesity and implications for prevention

Child obesity is becoming a serious public health concern, and major research effort is being devoted both to understand its aetiology and to improve the effectiveness of prevention strategies. Early growth patterns, both prenatally and postnatally, are emerging as important markers of later obesity risk, with rapid neonatal weight gain a clear risk factor for later obesity and metabolic syndrome. Thus, in two distinct senses child obesity is a growing problem. The paper summarises current evidence on growth pattern and obesity, relating it to infant feeding practice and appetite regulation, and highlights the areas in which public health interventions are feasible. Of the conclusions drawn, one involves a futuristic solution to child obesity where neonates are given an infusion of the hormone leptin to reset their appetite regulation.

Circadian rhythms in the development of obesity: potential role for the circadian clock within the adipocyte

Obesity is one of the most profound public health problems today, and simplistic explanations based on excessive nutritional consumption or lack of physical activity are inadequate to account for this dramatic and literal growth in our world population. Recent reports have suggested that disruptions in sleep patterns, often linked to our '24-h' lifestyle, are associated with increased body fat and altered metabolism, although the cause-effect relationship for these associations has yet to be elucidated. Abnormal sleep/wake patterns likely alter intracellular circadian clocks, which are molecular mechanisms that enable the cell/tissue/organism to anticipate diurnal variations in its environment. The environment may include circulating levels of nutrients (e.g. glucose, fatty acids and triglycerides) and various hormones (e.g. insulin, glucocorticoids). As such, alterations in this molecular mechanism, in particular within the adipocyte, likely induce metabolic changes that may potentiate disrupted metabolism, adipose accumulation and/or obesity. Although diurnal variations in adipokines and adipose tissue metabolism have been observed, little is known regarding the molecular mechanisms that influence these events.

To subjugate NPY is to improve the quality of life and live longer

The interactive network of neuropeptide Y (NPY) and cohorts is necessary for integrating the hypothalamic regulation of appetite and energy expenditure with the endocrine and neuroendocrine systems on a daily basis. Genetic and environmental factors that produce an insufficiency of leptin restraint on NPY and cognate receptors deregulate the homeostasis to engender various life-threatening risk factors. Recent studies from our laboratory show that neurotherapy consisting of a single central administration of recombinant adeno-associated virus vector encoding the leptin gene can repress the hypothalamic NPY system for the lifetime of rodents. A major benefit of this stable tonic restraint is deceleration of pathophysiologic sequalae that shorten life span. These include suppression of weight gain, fat accumulation, circulating adipokines, amelioration of major symptoms of metabolic syndrome, improved reproduction and bone health. Thus, sustained repression of NPY signaling in the hypothalamus by leptin transgene expression can improve the quality of life and extend longevity.

Neuroendocrine actions and regulation of hypothalamic neuropeptide Y during lactation

The expression of neuropeptide Y (NPY) and its co-messenger, agouti-related peptide (AgRP), in arcuate neurons of the hypothalamus is increased during lactation in rats. Our research has been addressing the questions of the physiological actions of these peptides during lactation and the physiological signals associated with lactation that result in increased expression of their genes. Our studies indicate that NPY and AgRP exert pleiotropic actions during lactation that help integrate neuroendocrine regulation of energy balance with controls over anterior and posterior pituitary hormone secretion. Further, reciprocal signaling to the NPY/AgRP system by leptin and ghrelin is responsible for the changes in expression of these hypothalamic peptides in lactating animals, and thus, may contribute to regulation of food intake and the various neuroendocrine adaptations of lactation.

Hypothalamic clamp on insulin release by leptin-transgene expression

The effects of sustained leptin action locally in the hypothalamus on the functional link between fat accrual and insulin secretion after chronic high fat diet (HFD) consumption in leptin-deficient ob/ob mice, and on the post-prandial insulin response in rats consuming regular chow diet (RCD), was examined in this study. A single intracerebroventricular (icv) injection of recombinant adeno-associated virus vector encoding leptin gene (rAAV-lep) enhanced hypothalamic leptin-transgene expression in ob/ob mice consuming RCD and suppressed the time-related weight gain and fat accumulation concomitant with abrogation of hyperinsulinemia and enhanced glucose tolerance. This increased hypothalamic leptin-transgene expression continued to impose insulinopenia and increased glucose tolerance but was ineffective in suppressing weight gain and fat accumulation after these mice were switched to chronic HFD consumption. A similar icv rAAV-lep pretreatment in rats consuming RCD markedly attenuated the post-prandial rise in insulin release concomitant with suppressed weight and fat depots. These results show for the first time that a sustained hypothalamic leptin action can stably clamp pancreatic insulin secretion independent of the status of fat accrual engendered by diets of varying caloric enrichment. Thus, the efficacy of increased leptin afferent signaling in the hypothalamus to persistently restrain pancreatic insulin release and insulin resistance can be explored as an adjunct therapeutic modality to alleviate pathophysiological derrangements that confer type 2 diabetes.

Ghrelin: a hormone regulating food intake and energy homeostasis

Regulation of energy homeostasis requires precise coordination between peripheral nutrient-sensing molecules and central regulatory networks. Ghrelin is a twenty-eight-amino acid orexigenic peptide acylated at the serine 3 position mainly with an n-octanoic acid, which is produced mainly in the stomach. It is the endogenous ligand of the growth hormone secretagogue (GHS) receptors. Since plasma ghrelin levels are strictly dependent on recent food intake, this hormone plays an essential role in appetite and meal initiation. In addition, ghrelin is involved in the regulation of energy homeostasis. The ghrelin gene is composed of four exons and three introns and renders a diversity of orexigenic peptides as well as des-acyl ghrelin and obestatin, which exhibit anorexigenic properties. Ghrelin stimulates the synthesis of neuropeptide Y (NPY) and agouti-related protein (AgRP) in the arcuate nucleus neurons of the hypothalamus and hindbrain, which in turn enhance food intake. Ghrelin-expressing neurons modulate the action of both orexigenic NPY/AgRP and anorexigenic pro-opiomelanocortin neurons. AMP-activated protein kinase is activated by ghrelin in the hypothalamus, which contributes to lower intracellular long-chain fatty acids, and this appears to be the molecular signal for the expression of NPY and AgRP. Recent data suggest that ghrelin has an important role in the regulation of leptin and insulin secretion and vice versa. The present paper updates the effects of ghrelin on the control of energy homeostasis and reviews the molecular mechanisms of ghrelin synthesis, as well as interaction with GHS receptors and signalling. Relationships with leptin and insulin in the regulation of energy homeostasis are addressed.

Leptin transgene expression in the hypothalamus enforces euglycemia in diabetic, insulin-deficient nonobese Akita mice and leptin-deficient obese ob/ob mice

We have tested the hypothesis that sustained leptin action in the hypothalamus alone can engender and maintain euglycemia in wild type mice and in two monogenic diabetic models, the insulin-deficient nonobese Akita mice and the hyperinsulinemic leptin-deficient obese, ob/ob mice. A single intracerebroventricular injection of recombinant adeno-associated virus vector encoding leptin (rAAV-lep) enhanced leptin transgene expression in the hypothalamus without any evidence of leptin leakage to the peripheral circulation, and promptly reinstated euglycemia that persisted along with severe insulinopenia in all three genotypes through the 7-week period of observation. A comparative evaluation of known etiologic factors of hyperglycemia showed that this long-term benefit on glucose homeostasis was not due to diminished energy consumption, weight and adiposity, but was conferred by at least two mechanisms operating simultaneously, enhanced glucose metabolism to meet the demand for the rAAV-lep induced increased non-shivering thermogenesis mediated by brown adipose tissue and insulin hypersensitivity. These findings endorse the hypothesis that increased leptin action locally in the hypothalamus can impose euglycemia independent of pancreatic insulin, and central leptin reinforcement may serve as a newer adjunct therapy to treat type 1 and type 2 diabetes.

Central leptin gene therapy blocks ovariectomy-induced adiposity

OBJECTIVE

In this study, we tested the hypothesis that insufficiency of leptin restraint in the hypothalamus is responsible for promoting weight gain and adiposity after ovariectomy (ovx). Whether increasing leptin transgene expression can overcome the diminution in leptin restraint was evaluated in ovx rats.

RESEARCH METHODS AND PROCEDURES

Enhanced leptin or green fluorescent protein (GFP; control) transgene expression was induced by a single intracerebroventricular injection of recombinant adeno-associated viral vector encoding either leptin gene (rAAV-lep) or GFP gene (rAAV-GFP; control) in acutely and chronically ovx rats. Body weight and food intake responses were monitored weekly. White adipose tissue (WAT) mass and serum levels of WAT-derived hormones, leptin, and adiponectin were analyzed at termination of the experiments.

RESULTS AND DISCUSSION

An increase in leptin transgene expression in the hypothalamus initiated soon after ovx blocked hyperphagia and body weight gain and markedly suppressed WAT mass and adipokines, leptin, and adiponectin. Similar suppression of weight gain and adiposity and serum leptin and adiponectin levels after intracerebroventricular rAAV-lep injection in chronically ovx rats were observed concomitant with unchanged daily food intake. These findings are consistent with the hypothesis that in the absence of ovarian steroids, the existent insufficiency of leptin restraint at the hypothalamic level can be overcome with ectopic leptin expression, thereby reinstating central control on weight and adiposity.

Increased leptin expression in the dorsal vagal complex suppresses adiposity without affecting energy intake and metabolic hormones

OBJECTIVE

Increased leptin transgene expression locally in hypothalamic sites suppresses weight and energy intake, enhances thermogenic energy expenditure, and differentially modulates metabolic hormones for an extended period. We evaluated whether a similar localized expression of leptin transgene in the dorsal vagal complex (DVC) in the caudal brain stem that also displays the biologically relevant leptin receptor would reproduce these varied responses and thus demonstrate functional connectivity between the hypothalamus and DVC.

RESEARCH METHODS AND PROCEDURES

Adult female rats were microinjected with a recombinant adeno-associated virus encoding either rat leptin or green fluorescent protein gene (control) in the DVC. Food intake and body weight were monitored weekly, and metabolic variables were analyzed at the end of 10 weeks.

RESULTS AND DISCUSSION

Increased leptin transgene expression in the DVC suppressed the time-related increase in body weight accompanied by a transient decrease in food intake at week 1 post-injection and little effect on thermogenic energy expenditure. That suppression of weight was due to decreased adiposity is shown by the markedly suppressed white adipose tissue-derived hormones, leptin and adiponectin. Circulating concentrations of pancreatic insulin, gastric ghrelin, and glucose levels were unchanged. This segregation of the varied effects of leptin expression in hypothalamic sites vs. DVC endorses the view that among the various endocrine organs under sympathetic nervous system control, only those leptin-activated neural circuits in the hypothalamus that suppress weight and adiposity on a long-term basis transverse through DVC en route to white adipose tissue.

Fasting ghrelin does not predict food intake after short-term energy restriction

OBJECTIVE

To study the role of ghrelin as a hunger signal during energy restriction and to test the hypothesis that changes in fasting leptin concentrations during energy restriction are associated with changes in fasting ghrelin concentrations.

RESEARCH METHODS AND PROCEDURES

Thirty-five healthy, lean men (23 +/- 3 years of age; BMI: 22.3 +/- 1.6 kg/m(2)) participated in a controlled intervention study. Fasting ghrelin and leptin concentrations were measured before and after 2 days of 62% energy restriction and after a 2-day period of ad libitum food intake. Energy intake during the latter period was assessed.

RESULTS

On average, ghrelin concentrations did not change (0.05 mug/liter; 95% confidence interval, -0.03; 0.12) during energy restriction. Changes in ghrelin concentration during energy restriction were not associated with energy intake during the ad libitum period (r = 0.07; not significant). Ad libitum energy intake was, however, associated with the change in ghrelin concentrations during the same period (r = -0.34; p = 0.05). Ghrelin and leptin concentrations were not associated. In addition, the ratio of percentage changes in ghrelin and leptin during energy restriction was not correlated with ad libitum food intake after energy restriction (r = -0.26; p = 0.14).

DISCUSSION

Fasting ghrelin concentrations did not rise after a 2-day energy restriction regimen. Moreover, changes in ghrelin concentrations during energy restriction were not associated with subsequent ad libitum food intake, suggesting that fasting ghrelin does not act as a hunger signal to the brain. The data did not support our hypothesis that leptin suppresses ghrelin levels.

Subjugation of hypothalamic NPY and cohorts with central leptin gene therapy alleviates dyslipidemia, insulin resistance, and obesity for life-time

An interactive network comprised of neuropeptide Y (NPY) and cohorts is obligatory in the hypothalamic integration of appetite and energy expenditure on a minute-to-minute basis. High or low abundance of NPY and cognate receptors dysregulates the homeostatic milieu engendering hyperphagia, decreased energy expenditure, obesity and attendant metabolic syndrome cluster of dyslipidemia, glucose intolerance, insulin resistance and hyperinsulinemia, risk factors for type II diabetes and cardiovascular diseases. Increasing the supply of the endogenous repressor hormone leptin locally in the hypothalamus with the aid of leptin gene therapy, blocked age-related and dietary obesities, and the sequential development of dyslipidemia, hyperglycemia, and insulin resistance. Thus, sustained repression of NPY signaling with increased leptin selectively in the hypothalamus can avert environmental obesity and the risks of metabolic diseases.

O papel dos hormônios leptina e grelina na gênese da obesidade

A prevalência da obesidade está aumentando e estudos prospectivos mostram que, em 2025, o Brasil será o quinto país do mundo a apresentar problemas de obesidade em sua população. A etiologia da obesidade não é de fácil identificação, uma vez que a mesma é caracterizada como uma doença multifatorial, ou seja, diversos fatores estão envolvidos em sua gênese, incluindo fatores genéticos, psicológicos, metabólicos e ambientais. Pesquisas recentes na área de metabolismo mostram que o adipócito é capaz de sintetizar várias substâncias e, diferentemente do que se supunha anteriormente, o tecido adiposo não é apenas um sítio de armazenamento de triglicérides, é hoje considerado um órgão endócrino. Dentre as diversas substâncias sintetizadas pelo adipócito, destacam-se a adiponectina, a angiotensina e a leptina. A leptina é um petídeo que desempenha importante papel na regulação da ingestão alimentar e no gasto energético, gerando um aumento na queima de energia e diminuindo a ingestão alimentar. Além dos avanços no estudo da célula adiposa, um novo hormôrnio relacionado ao metabolismo foi descoberto recentemente, a grelina. A grelina é um peptídeo produzido nas células do estômago, e está diretamente envolvida na regulação do balanço energético a curto prazo. Assim, este artigo abordará o papel da leptina e da grelina no controle do peso corporal e as limitações que ainda existem para tratar a obesidade em humanos.

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.

Central leptin differentially modulates ultradian secretory patterns of insulin, leptin and ghrelin independent of effects on food intake and body weight

We tested the hypothesis that leptin acts centrally to differentially modulate the ultradian communication of leptin, insulin and ghrelin with the hypothalamus. The ultradian fluctuation of these hormones in plasma after central leptin gene therapy was analyzed. Increased leptin transgene expression in the hypothalamus significantly decreased energy intake and body weight concomitant with severe hypoleptinemia and hypoinsulinemia resulting from drastically suppressed peak heights with unchanged frequency discharge of these hormones. Ghrelin secretion was, however, increased solely due to increased pulse amplitude. In pair-fed control rats leptin and ghrelin secretion was unchanged. In conclusion, independent of restraint on caloric intake and weight, leptin acting centrally modulates only the pulse amplitude of ultradian rhythmicity of the three afferent signals involved in the hypothalamic integration of energy balance. Since rhythmic discharge patterns dictate target response of hormones, these findings reveal a novel hypothalamic action of leptin in the pathophysiology of the obesity-dependent metabolic syndrome.

Gene-transfer technology: a preventive neurotherapy to curb obesity, ameliorate metabolic syndrome and extend life expectancy

Leptin insufficiency at crucial target sites in the hypothalamic circuitries that integrate energy intake and expenditure underlies abnormal rates of fat accumulation. The payload of this "fat burden" is metabolic syndrome, a cluster of life-threatening metabolic afflictions, and a shorter lifespan. Currently available therapies employed to combat obesity have disadvantages such as poor compliance for lifestyle modification or transient effectiveness and undesirable side-effects of pharmacological interventions. Recent studies suggest that neurotherapy comprising a single central administration of recombinant adeno-associated virus vector encoding the leptin gene severely depletes fat and ameliorates the major symptoms of metabolic syndrome for extended periods in rodents. These persistent benefits avert the deleterious impact of the "fat burden" and extend life expectancy. Thus, the novel approach of central gene-transfer technology has distinct advantages over current therapies and has the potential to correct or slow the progression of inherited or acquired hypothalamic diseases.

High-fat diet-induced ultradian leptin and insulin hypersecretion are absent in obesity-resistant rats

OBJECTIVE

Sprague-Dawley rats fed a high-fat diet (HFD) are either obesity prone (OP) or obesity resistant (OR). We tested the hypothesis that differences in the ultradian rhythmic patterns of insulin and ghrelin in OP vs. OR rats promote obesity in OP rats.

RESEARCH METHODS AND PROCEDURES

Rats were fed regular chow or an HFD, and ultradian fluctuations in leptin, insulin, and ghrelin were analyzed in blood samples collected at 5-minute intervals from intrajugular cannulae of freely moving rats.

RESULTS

Regular chow feeding resulted in a slow weight gain accompanied by small increases in insulin and leptin and a decrease in ghrelin discharge, with only the pulse amplitude significantly altered. Similar changes were observed in OR rats, despite HFD consumption. In contrast, OP rats exhibited a high rate of weight gain and marked hyperinsulinemia, hyperleptinemia, and hypoghrelinemia; amplitude was altered, but frequency was stable. In a short-term experiment, HFD elicited similar secretory patterns of smaller magnitude even in the absence of weight gain.

DISCUSSION

We showed that three hormonal signals of disparate origin involved in energy homeostasis were secreted in discrete episodes, and only the pulse amplitude component was vulnerable to age and HFD consumption. Increases in insulin and leptin and decreases in ghrelin pulse amplitude caused by HFD were exaggerated in OP rats relative to OR rats and preceded the weight increase. These findings show that a distinct genetic predisposition in the endocrine organs of OR rats confers protection against high-fat intake-induced ultradian hypersecretion of obesity-promoting hormonal signals.

Suppression of fat deposition for the life time with gene therapy

Unexpended energy is stored as fat in the body and increased rate of fat accretion culminates in obesity. Obesity increases the risks of many diseases several folds and shortens life span. A progressive deficit in the central feedback effects of leptin, a peptide produced by fat cells and hypothalamus, results in increased weight gain and obesity. This article summarizes our experimental findings to show that a stable increase in leptin availability in the hypothalamus alone with the aid of leptin gene therapy suppresses fat accretion and metabolic hormones for nearly the lifetime of laboratory rodents. Consequently, central leptin gene therapy is a novel modality that offers a viable therapeutic option to reduce fat depots and attendant metabolic sequelae implicated in obesity-related illnesses.

Brain somatic cross-talk: ghrelin, leptin and ultimate challengers of obesity

Energy balance is largely regulated by the central nervous system (CNS), which senses metabolic status from a wide range of humoral and neural signals, and controls energy intake. Accumulating evidence supports the model that stimulation of leptin- and ghrelin-responsive pathways, including the central melanocortin system, in the hypothalamus, contributes to the maintenance of body weight. Ghrelin is the brain-gut peptide with growth hormone-releasing and appetite-inducing activities. It is mainly secreted from the stomach and acts as an afferent signal to the hypothalamus and hindbrain. Leptin, the adipocyte hormone, is believed to tonically act as an afferent signal from adipose tissue to the brain, in particular hypothalamus, as a part of negative feedback loop regulating the size of energy stores and energy balance. Dysregulation of these pathways is a marker of changes in energy balance. Ghrelin is negatively correlated with weight and obese subjects have lower ghrelin levels than lean subjects, consistent with a compensatory rather than causal role for ghrelin in obesity. On the contrary, circulating leptin levels correlate in proportion to adiposity being high in obesity suggesting that human obesity is associated with insensitivity to leptin. The leptin resistance in diet-induced obesity emphasizes that environmental factors can modulate leptin sensitivity. It is speculated that through hypothalamic/pituitary axis ghrelin and leptin operate as a metabolic switch. Ghrelin actually transfers information from the stomach to the hypothalamus in cooperation with leptin and provides calories that growth hormone (GH) needs for growth and repair. Pharmacological manipulations of circulating hormone levels may work well in "cheating" the brain regarding information from the periphery. It might also be necessary to combine two or three agents to fight obesity. A combination of drugs that decrease preprandial appetite (ghrelin antagonist) and increase post-prandial satiety (gut hormone fragment peptide YY 3-36) might have a chance of achieving sustained weight loss. The administration of exogenous satiety hormone peptide YY 3-36 (PYY) may prevent the action of appetite-stimulating hypothalamic circuits on the anorexigenic melanocortin pathways.

Stimulation of appetite by ghrelin is regulated by leptin restraint: peripheral and central sites of action

A reciprocal rhythmic pattern of 2 afferent hormonal signals, anorexigenic leptin and orexigenic ghrelin, imparts rhythmicity to the neuropeptide Y (NPY) system, the final common pathway for appetite expression in the hypothalamus. We now show that leptin inhibits both the secretion of gastric ghrelin and the stimulation of feeding by ghrelin. We propose that this dual leptin restraint is the major regulatory arm of the feedback communication between the periphery and the hypothalamus for weight homeostasis, and disruption in the rhythmic communication at any locus in the leptin-ghrelin-NPY feedback loop impels loss of hypothalamic control, leading to abnormal weight gain and obesity.

Perigestational suppression of weight gain with central leptin gene therapy results in lower weight F1 generation

The efficacy of central leptin therapy on weight homeostasis through various phases of reproduction, pregnancy outcome and postnatal, prepubertal and pubertal growth of offspring was assessed. Enhanced leptin transgene expression after a single intracerebroventricular injection of recombinant adeno-associated virus vector encoding the leptin gene (rAAV-lep) decreased calorie intake and weight in adult nulliparous female rats. rAAV-lep treated rats conceived normally, displayed unremarkable pregnancy rate, parturition and delivered normal sized litters. Significantly lower weight was maintained through gestation, lactation, and post-lactation periods. The maintenance of a modest weight reduction was accompanied by voluntarily reduced calorie intake, increased thermogenic energy expenditure, decreased adiposity as reflected by drastically reduced leptin levels, and suppressed insulin and insulin-like growth factor 1 levels through lactation and post-lactation in rAAV-lep treated dams. The offspring at birth weighed significantly less than those of controls and this lower weight range was sustained during postnatal, prepubertal, pubertal and adult (3 months old) periods, contemporaneous with metabolic circulating hormones in the normal range. For the first time we show the persistent efficacy of central leptin gene therapy to suppress weight gain through all phases of reproduction, lactation and post-lactation in dams and reveal the potential imprinting link to producing lower weight in the F1 generation.

A reassessment of the role of serotonergic system in the control of feeding behavior

The role of serotonergic system in the feeding behavior was appraised by electrolytic lesions in the dorsal raphe nucleus (DRN) and administration of para-chlorophenylalanine (PCPA, 3 mg/5 microl, icv). Chronic evaluations were accomplished through 120 and 360 days in PCPA-injected and DRN-lesioned rats, respectively. Acute food intake was evaluated in fasted rats and submitted to injection of PCPA and hydroxytryptophan (LHTP, 30 mg/kg, ip). DRN-lesioned rats exhibited 22-80% increase in food intake up to sixth month, whereas the obesity was evident and sustained by whole period. In PCPA-injected rats was observed an initial increase in the food intake followed by hypophagy from 25th to 30th day and a transitory increase of body weight from 5th to 60th day. In the acute study, the LHTP reverted partially the PCPA-induced increase in food intake of fasted rats suggesting a sustained capacity of decarboxylation of precursor by serotonergic neurons. Slow restoration of the levels of food intake in DRN-lesioned rats reveals a neuroplasticity in the systems that regulate feeding behavior. A plateau on the body weight curve in lesioned rats possibly represents the establishment of a new and higher set point of energetic balance.

Role of adiposity hormones in the mouse during fasting and winter-acclimatization

The influence of fasting and winter-acclimatization (cold and short-day acclimatization) on mouse plasma leptin, ghrelin, growth hormone (GH) and melatonin concentrations was determined from blood samples taken at mid-day and midnight. A 16-h fast decreased the plasma leptin but almost doubled the plasma ghrelin concentrations which contribute to energy saving, appetite stimulation and, in the case of leptin, to inhibition of reproduction. Winter-acclimatization did not affect plasma ghrelin concentrations, whereas leptin decreased to the same level as in fasting. The low leptin concentrations possibly enable an increased caloric intake for the purpose of thermogenesis. Fasting and winter-acclimatization seemed to abolish the diurnal leptin rhythm, but had no effect on that of ghrelin. Plasma melatonin concentration correlated negatively with ghrelin, suggesting a possible role for melatonin in the regulation of ghrelin concentration. SNS-activity and insulin appear to be the main regulators of leptin plasma concentration in the mouse, rather than melatonin as in some seasonal mammals. Interestingly, endogenous ghrelin did not stimulate GH secretion, which is a well-documented reaction to exogenous ghrelin injections.

Ghrelin: more than a natural GH secretagogue and/or an orexigenic factor

Ghrelin, an acylated peptide produced predominantly by the stomach, has been discovered to be a natural ligand of the growth hormone secretagogue receptor type 1a (GHS-R1a). Ghrelin has recently attracted considerable interest as a new orexigenic factor. However, ghrelin exerts several other neuroendocrine, metabolic and also nonendocrine actions that are explained by the widespread distribution of ghrelin and GHS-R expression. The likely existence of GHS-R subtypes and evidence that the neuroendocrine actions, but not all the other actions, of ghrelin depend on its acylation in serine-3 revealed a system whose complexity had not been completely explored by studying synthetic GHS. Ghrelin secretion is mainly regulated by metabolic signals and, in turn, the modulatory action of ghrelin on the control of food intake and energy metabolism seems to be among its most important biological actions. However, according to a recent study, ghrelin-null mice are neither anorectics nor dwarfs and this evidence clearly depicts a remarkable difference from leptin null mice. Nevertheless, the original and fascinating story of ghrelin, as well as its potential pathophysiological implications in endocrinology and internal medicine, is not definitively cancelled by these data as GHS-R1a null aged mice show significant alterations in body composition and growth, in glucose metabolism, cardiac function and contextual memory. Besides potential clinical implications for natural or synthetic ghrelin analogues acting as agonists or antagonists, there are several open questions awaiting an answer. How many ghrelin receptor subtypes exist? Is ghrelin 'the' or just 'a' GHS-R ligand? That is, are there other natural GHS-R ligands? Is there a functional balance between acylated and unacylated ghrelin forms, potentially with different actions? Within the next few years suitable answers to these questions will probably be found, making it possible to gain a better knowledge of ghrelin's potential clinical perspectives.

Differential effects of methamphetamine on expression of neuropeptide Y mRNA in hypothalamus and on serum leptin and ghrelin concentrations in ad libitum-fed and schedule-fed rats

Relatively little is known concerning the interaction of psychostimulants with hypothalamic neuropeptide systems or metabolic hormones implicated in regulation of energy balance. The present studies tested whether methamphetamine alters the expression of neuropeptide Y (NPY) and agouti-related peptide (AgRP), two important orexigenic neuropeptides, or proopiomelanocortin (POMC), the precursor for the anorexigenic peptide alpha-melanocyte-stimulating hormone, or the secretion of leptin, insulin and ghrelin, concomitant with inhibition of food intake. Female rats were either fed ad libitum (AL) or placed on a scheduled feeding (SF) regimen, with access to food limited to 4 h/day. Administration of (+/-)-methamphetamine (7.5 mg/kg, i.p.) 2 h prior to food presentation significantly inhibited food intake in SF animals, but did not affect intake in AL animals. In a separate study, AL and SF animals were killed just prior to expected food presentation, and expression of NPY, AgRP and POMC mRNAs in hypothalamus was determined using in situ hybridisation; concentrations of leptin, insulin and ghrelin in serum were determined with radioimmunoassays. In saline-treated, SF controls, NPY and AgRP mRNA expression in arcuate nucleus and serum ghrelin were significantly elevated, and serum leptin and insulin were significantly reduced. Methamphetamine reversed the up-regulation of NPY mRNA expression observed in the SF condition, without affecting AgRP mRNA or the serum concentrations of metabolic hormones. However, in AL animals, NPY mRNA expression in arcuate and dorsomedial nuclei was significantly increased by methamphetamine, which also reduced serum leptin and insulin and increased serum ghrelin concentrations. These findings suggest that the inhibition of NPY expression in SF animals may be a mechanism underlying the anorexigenic effect of methamphetamine seen in this condition. The increase in NPY expression produced by methamphetamine in AL animals may be mediated by the ability of this drug to decrease secretion of leptin and insulin and increase secretion of ghrelin.

Aged neuropeptide Y transgenic rats are resistant to acute stress but maintain spatial and non-spatial learning

The behavioral phenotype of five-month-old rats overexpressing neuropeptide Y (NPY) has previously been described [Proc Natl Acad Sci USA 97 (2000) 12852]. In this transgenic rat model, there is central overexpression of prepro-NPY mRNA and NPY peptide in the hippocampus and hypothalamus and decreased Y1 binding sites within the hippocampus. These molecular and neurochemical events led to altered anxiety profile and learning abilities in NPY-overexpressing rats. In the present study, anxiety and learning/memory related behaviors were examined in one-year-old NPY-transgenic rats in order to assess any behavioral changes that may have occurred during the aging process. As observed in 5-month-old overexpressing rats, aged NPY-transgenic animals are resistant to acute physical restraint stress measured by the elevated-plus maze and demonstrate anxiolytic-like activity in the open field. However, in contrast to data in young rats, there was no significant difference between aged wildtype and NPY-transgenic animals in relation to spatial and non-spatial memory as indicated by the (allo- and ego-centric) Morris water maze and object recognition test. It would thus appear that the anxiolytic-like profile observed in young NPY-overexpressing rats is maintained in older animals providing further evidence for a role for NPY in anxious behaviors. However, the cognitive deficits observed in young rats do not appear to occur in older animals suggesting the existence of compensatory mechanisms leading to a reversal of the learning deficits noted in younger animals. These results also provide additional evidence for the mechanistic dissociation between anxiety and cognition-related behaviors modulated by NPY.

Circulating ghrelin levels and central ghrelin receptor expression are elevated in response to food deprivation in a seasonal mammal (Phodopus sungorus)

Ghrelin is an endogenous ligand for the growth hormone secretagogue receptor (GHSR). However, the functional interaction of ligand and receptor is not very well understood. We demonstrate that GHSR mRNA is up-regulated after food deprivation (48 h) in the hypothalamic arcuate nucleus and ventromedial nucleus of the seasonal Siberian hamster, Phodopus sungorus. This increase is accompanied by a two-fold elevation of circulating ghrelin concentration. Chronic changes in feeding state imposed by food restriction over a period of 12 weeks during long day-length induced increased GHSR gene expression, whereas food restriction for 6 weeks had no effect. Phodopus sungorus reveals remarkable seasonal changes in body weight, fat mass and circulating leptin levels. Ghrelin is generally regarded as having opposing effects on appetite and body weight with respect to those exhibited by leptin. However, our study revealed that seasonal adaptations were not accompanied by changes in either GHSR gene expression or circulating ghrelin concentration. Therefore, we suggest that ghrelin only plays a minor role in modulating long-term seasonal body weight cycles. Our findings imply that ghrelin predominantly acts as a short-term regulator of feeding.