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

Theabrownin remodels the circadian rhythm disorder of intestinal microbiota induced by a high-fat diet to alleviate obesity in mice

The intestinal microbiota undergoes diurnal compositional and functional oscillations within a day, which affect the metabolic homeostasis of the host and exacerbate the occurrence of obesity. TB has the effect of reducing body weight and lipid accumulation, but the mechanism of improving obesity caused by a high-fat diet based on the circadian rhythm of intestinal microorganisms has not been clarified. In this study, we used multi-omics and imaging approaches to investigate the mechanism of TB in alleviating obesity in mice based on the circadian rhythm of gut microbiota. The results showed that TB could significantly regulate the levels and rhythmic expression of serum lipid indicators (TG, TC, LDL) and serum hormones (MT, FT3, LEP, CORT). The number of intestinal microbiota colonizing the colonic epithelium underwent daily fluctuations. TB remodeled the rhythmic oscillation of gut microbes (i.e., Lachnospiraceae_NK4A136_group, Alistipes, etc.), including the number, composition, abundance and rhythmic expression of the biogeographic localization of microbes. TB notably reduced the levels of 16 bile acids (TCA, THDCA, TCDA, GHDCA, T-α-MCA, etc.) and restored the balance of bile acid metabolism. It was found that TB may mitigate high-fat diet-induced obesity in mice by reshaping the circadian rhythm of the gut microbiome and regulating bile acid metabolism.

Gut microbiota and eating behaviour in circadian syndrome

Eating behaviour and circadian rhythms are closely related. The type, timing, and quantity of food consumed, and host circadian rhythms, directly influence the intestinal microbiota, which in turn impacts host circadian rhythms and regulates food intake beyond homeostatic eating. This Opinion discusses the impact of food intake and circadian disruptions induced by an obesogenic environment on gut-brain axis signalling. We also explore potential mechanisms underlying the effects of altered gut microbiota on food intake behaviour and circadian rhythmicity. Understanding the crosstalk between gut microbiota, circadian rhythms, and unhealthy eating behaviour is crucial to addressing the obesity epidemic, which remains one of the biggest societal challenges of our time.

Leptin and ghrelin dynamics: unraveling their influence on food intake, energy balance, and the pathophysiology of type 2 diabetes mellitus

Purpose

Type 2 diabetes mellitus (T2DM) is a chronic metabolic disorder characterized by insulin resistance and impaired glucose homeostasis. In recent years, there has been growing interest in the role of hunger and satiety hormones such as ghrelin and leptin in the development and progression of T2DM. In this context, the present literature review aims to provide a comprehensive overview of the current understanding of how ghrelin and leptin influences food intake and maintain energy balance and its implications in the pathophysiology of T2DM.

Methods

A thorough literature search was performed using PubMed and Google Scholar to choose the studies that associated leptin and ghrelin with T2DM. Original articles and reviews were included, letters to editors and case reports were excluded.

Results

This narrative review article provides a comprehensive summary on mechanism of action of leptin and ghrelin, its association with obesity and T2DM, how they regulate energy and glucose homeostasis and potential therapeutic implications of leptin and ghrelin in managing T2DM.

Conclusion

Ghrelin, known for its appetite-stimulating effects, and leptin, a hormone involved in the regulation of energy balance, have been implicated in insulin resistance and glucose metabolism. Understanding the complexities of ghrelin and leptin interactions in the context of T2DM may offer insights into novel therapeutic strategies for this prevalent metabolic disorder. Further research is warranted to elucidate the molecular mechanisms underlying these hormone actions and to explore their clinical implications for T2DM prevention and management.

Long-duration leptin transgene expression in dorsal vagal complex does not alter bone parameters in female Sprague Dawley rats

The hypothalamus and dorsal vagal complex (DVC) are both important for integration of signals that regulate energy balance. Increased leptin transgene expression in either the hypothalamus or DVC of female rats was shown to decrease white adipose tissue and circulating levels of leptin and adiponectin. However, in contrast to hypothalamus, leptin transgene expression in the DVC had no effect on food intake, circulating insulin, ghrelin and glucose, nor on thermogenic energy expenditure. These findings imply different roles for hypothalamus and DVC in leptin signaling. Leptin signaling is required for normal bone accrual and turnover. Leptin transgene expression in the hypothalamus normalized the skeletal phenotype of leptin-deficient ob/ob mice but had no long-duration (≥10 weeks) effects on the skeleton of leptin-replete rats. The goal of this investigation was to determine the long-duration effects of leptin transgene expression in the DVC on the skeleton of leptin-replete rats. To accomplish this goal, we analyzed bone from three-month-old female rats that were microinjected with recombinant adeno-associated virus encoding either rat leptin (rAAV-Leptin, n = 6) or green fluorescent protein (rAAV-GFP, control, n = 5) gene. Representative bones from the appendicular (femur) and axial (3rd lumbar vertebra) skeleton were evaluated following 10 weeks of treatment. Selectively increasing leptin transgene expression in the DVC had no effect on femur cortical or cancellous bone microarchitecture. Additionally, increasing leptin transgene expression had no effect on vertebral osteoblast-lined or osteoclast-lined bone perimeter or marrow adiposity. Taken together, the findings suggest that activation of leptin receptors in the DVC has minimal specific effects on the skeleton of leptin-replete female rats.

Repeated photodynamic therapy using a chlorin e6-embedded device to prolong the therapeutic effects on obesity

OBJECTIVE

This study aimed to investigate the efficacy and safety of repeated photodynamic therapy (PDT) with a chlorin e6 (Ce6)-embedded intragastric satiety-inducing device (ISD) to maintain therapeutic effects of obesity in a juvenile pig.

METHODS

The Ce6-embedded ISD was fabricated with a dipping method. Twelve pigs were divided into four groups of three and were administered control, single, biweekly, or weekly PDT, respectively. The therapeutic effects were assessed by comparing the results of phototoxicity, endoscopy, fluoroscopy, hormone and weight changes, and histological examination.

RESULTS

The percentage of total body weight gain was significantly suppressed in PDT-treated pigs compared with control pigs (all p < 0.001). This suppression persisted in the repeated PDT groups, but percentage of total body weight gain gradually increased when PDT was stopped. Ghrelin levels in the PDT-treated groups were significantly lower and leptin levels were significantly higher than those in the control group (all p < 0.05). Inflammatory cell infiltration, collagen, TUNEL, and anti-ghrelin-positive deposition in the weekly group were significantly higher than those in the control, single, and biweekly groups (all p < 0.01).

CONCLUSIONS

Repeated and periodic PDT was technically feasible and safe and successfully maintained the therapeutic effects against obesity while eliminating the indwelling time and reducing ISD-related complications in pigs.

Misalignment of Circadian Rhythms in Diet-Induced Obesity

The biological clocks of the circadian timing system coordinate cellular and physiological processes and synchronize them with daily cycles. While the central clock in the suprachiasmatic nucleus (SCN) is mainly synchronized by the light/dark cycles, the peripheral clocks react to other stimuli, including the feeding/fasting state, nutrients, sleep-wake cycles, and physical activity. During the disruption of circadian rhythms due to genetic mutations or social and occupational obligations, incorrect arrangement between the internal clock system and environmental rhythms leads to the development of obesity. Desynchronization between the central and peripheral clocks by altered timing of food intake and diet composition leads to uncoupling of the peripheral clocks from the central pacemaker and to the development of metabolic disorders. The strong coupling of the SCN to the light-dark cycle creates a situation of misalignment when food is ingested during the "wrong" time of day. Food-anticipatory activity is mediated by a self-sustained circadian timing, and its principal component is a food-entrainable oscillator. Modifying the time of feeding alone greatly affects body weight, whereas ketogenic diet (KD) influences circadian biology, through the modulation of clock gene expression. Night-eating behavior is one of the causes of circadian disruption, and night eaters have compulsive and uncontrolled eating with severe obesity. By contrast, time-restricted eating (TRE) restores circadian rhythms through maintaining an appropriate daily rhythm of the eating-fasting cycle. The hypothalamus has a crucial role in the regulation of energy balance rather than food intake. While circadian locomotor output cycles kaput (CLOCK) expression levels increase with high-fat diet-induced obesity, peroxisome proliferator-activated receptor-alpha (PPARα) increases the transcriptional level of brain and muscle aryl hydrocarbon receptor nuclear translocator (ARNT)-like 1 (BMAL1) in obese subjects. In this context, effective timing of chronotherapies aiming to correct SCN-driven rhythms depends on an accurate assessment of the SCN phase. In fact, in a multi-oscillator system, local rhythmicity and its disruption reflects the disruption of either local clocks or central clocks, thus imposing rhythmicity on those local tissues, whereas misalignment of peripheral oscillators is due to exosome-based intercellular communication.Consequently, disruption of clock genes results in dyslipidemia, insulin resistance, and obesity, while light exposure during the daytime, food intake during the daytime, and sleeping during the biological night promote circadian alignment between the central and peripheral clocks. Thus, shift work is associated with an increased risk of obesity, diabetes, and cardiovascular diseases because of unusual eating times as well as unusual light exposure and disruption of the circadian rhythm.

Subcutaneous adipose tissue circadian gene expression: Relationship with insulin sensitivity, obesity, and the effect of weight-reducing dietary intervention

OBJECTIVE

The circadian rhythms are controlled by the central clock in the hypothalamic suprachiasmatic nuclei and by the peripheral clocks in tissues, including adipose tissue. The adipose tissue circadian clock may be associated with the regulation of insulin action; however, human data are limited. The aim of this study was to analyze the expression of subcutaneous adipose tissue circadian genes as they relate to obesity and insulin sensitivity before and after diet-induced weight loss.

METHODS

The study group comprised 38 individuals who were overweight or obese. The individuals completed a 12-wk dietary intervention program. Hyperinsulinemic-euglycemic clamp and subcutaneous adipose tissue biopsy were performed before and after the program. Sixteen normal weight individuals were examined at baseline and served as a control group.

RESULTS

At baseline, individuals who were overweight/obese had lower adipose tissue expression of NR1D1, NR1D2, DBP, PER1, and PER2 than normal weight individuals. The expression of ARNTL, CLOCK, and CRY did not differ between the groups. A weight-reducing dietary intervention resulted in an increase in the expression of adipose tissue NR1D2 and DBP, which was positively related to insulin sensitivity both before (in the entire study group and in the subgroup of overweight/obese individuals) and after the dietary intervention.

CONCLUSIONS

Adipose tissue circadian gene expression is decreased in obesity and this decrease may be partially reversed by dietary intervention. Among circadian genes, NR1D2 and DBP seem to be specifically associated with insulin action.

Environmental light exposure and mealtime regularity: Implications for human health

Light exposure and mealtime act as cues to the human circadian rhythm, which subsequently regulates various physiological functions in the body. However, modernization alters lifestyles, with changes to social and work-related activities independent of the natural light-dark cycle. This review summarizes the role of light exposure and regular mealtime on bodily processes and, ultimately, metabolic health. Various aspects of light are reviewed, including the type of light (natural/artificial), intensity (lux), spectral composition, time of exposure (night/day), and exposure duration. Further, the possible relationship between light exposure and mealtime irregularity is discussed as a function affecting metabolic health. In essence, research evidence suggests that mealtime regularity and light exposure habits based on the natural occurring light-dark cycle are essential for metabolic health in relation to an aligned circadian rhythm.

Relations among sweet taste preference, body mass index, and use of E-cigarettes for weight control motives in young adults

While weight control is anecdotally reported as a motive for e-cigarette use, empirical evidence on correlates of weight control vaping motives is largely absent. This study evaluated main effect and interactive associations of body mass index (BMI) and sweet taste food preference-a construct defined by difficulty resisting sweet foods and consuming foods for mood regulation- with e-cigarette weight control motives among young adult e-cigarette users. Young adults (N = 99; 35% women) between the ages of 18-35 who currently used e-cigarettes ≥1 day/week for ≥1 month were recruited in Los Angeles, CA in January-August 2016. Participants completed an e-cigarette product appeal experiment that also involved questionnaire-based measures of vaping motives and participant characteristics, which are this paper's focus. Regression analysis of e-cigarette use for weight control motive outcomes revealed no main effect of BMI, a significant main effect positive association for sweet taste food preference, and a BMI x sweet taste preference interactive relation. The interaction was underpinned by a positive association between sweet taste preference and use of e-cigarettes for weight control at mean and + 1SD levels of BMI and no relation at -1SD BMI levels. Higher sweet taste preference might increase use of e-cigarettes for weight control, particularly in young adults with higher weight. Taking into account sweet taste preference might be useful in interventions promoting healthy weight control strategies instead of e-cigarette use to address overweight/obesity in young adults.

Hypothesis paper: electroacupuncture targeting the gut-brain axis to modulate neurocognitive determinants of eating behavior-toward a proof of concept in the obese minipig model

Acupuncture has thousands of years of history and perspective for the treatment of many health problems and disorders. Beneficial effects of acupuncture on obesity have been demonstrated at various levels in animals and clinical trials, with almost no adverse effect, even when combined with local electrical stimulation, i.e., electroacupuncture (EA), a way to potentiate the effects of acupuncture. However, there is still scattered evidence about the impact of EA on brain functions related to the control of eating behavior, and notably on the gut-brain axis mechanisms involved in these putative central modulations. During the past 10 years, we have described a convincing diet-induced obese minipig model, and successfully implemented brain imaging and neurocognitive approaches to challenge mechanistic hypotheses and innovative therapeutic strategies. In the present article, we propose to confront the current literature on the acupuncture and EA effects on the gut-brain axis and obesity with the latest developments in nutrition and neuroscience research using the minipig model. Our aims are to (a) elaborate functional hypotheses on the gut-brain mechanisms underlying EA effects on obesity, and especially on the role of the vagus nerve, and (b) present the rational for testing these hypotheses in the minipig model.

Circadian regulation of appetite and time restricted feeding

The circadian system plays an important role in the temporal regulation of metabolic processes as well as food intake to ensure energy efficiency. The 'master' clock is located within the superchiasmatic nucleus and receives input from the retina so that it can be entrained by the light:dark cycle. In turn, the master clock entrains other clocks in the central nervous system, including areas involved in energy homeostasis such as the arcuate nucleus, and the periphery (e.g. adipose tissue and the gastrointestinal tract). This master clock is reinforced by other zeitgebers such as the timing of food intake and activity. If these zeitgebers desynchronise, such as occurs in high fat diet-induced obesity or shift work conditions, it can lead to a misalignment of circadian clocks, disruption of metabolic processes and the development of metabolic disorders. The timing of food intake is a strong zeitgeber, particularly in the gastrointestinal tract, and therefore time restricted feeding offers potential for the treatment of diet and shift work induced metabolic disorders. This review will focus on the role of the circadian system in food intake regulation and the effect of environment factors, such as high fat diet feeding or shift work, on the temporal regulation of food intake along with the benefits of time restricted feeding.

Evidence for a Coupled Oscillator Model of Endocrine Ultradian Rhythms

Whereas long-period temporal structures in endocrine dynamics have been well studied, endocrine rhythms on the scale of hours are relatively unexplored. The study of these ultradian rhythms (URs) has remained nascent, in part, because a theoretical framework unifying ultradian patterns across systems has not been established. The present overview proposes a conceptual coupled oscillator network model of URs in which oscillating hormonal outputs, or nodes, are connected by edges representing the strength of node-node coupling. We propose that variable-strength coupling exists both within and across classic hormonal axes. Because coupled oscillators synchronize, such a model implies that changes across hormonal systems could be inferred by surveying accessible nodes in the network. This implication would at once simplify the study of URs and open new avenues of exploration into conditions affecting coupling. In support of this proposed framework, we review mammalian evidence for (1) URs of the gut-brain axis and the hypothalamo-pituitary-thyroid, -adrenal, and -gonadal axes, (2) UR coupling within and across these axes; and (3) the relation of these URs to body temperature. URs across these systems exhibit behavior broadly consistent with a coupled oscillator network, maintaining both consistent URs and coupling within and across axes. This model may aid the exploration of mammalian physiology at high temporal resolution and improve the understanding of endocrine system dynamics within individuals.

The Circadian Clock in White and Brown Adipose Tissue: Mechanistic, Endocrine, and Clinical Aspects

Obesity is a major risk factor for the development of illnesses, such as insulin resistance and hypertension, and has become a serious public health problem. Mammals have developed a circadian clock located in the hypothalamic suprachiasmatic nuclei (SCN) that responds to the environmental light-dark cycle. Clocks similar to the one located in the SCN are found in peripheral tissues, such as the kidney, liver, and adipose tissue. The circadian clock regulates metabolism and energy homeostasis in peripheral tissues by mediating activity and/or expression of key metabolic enzymes and transport systems. Knockouts or mutations in clock genes that lead to disruption of cellular rhythmicity have provided evidence to the tight link between the circadian clock and metabolism. In addition, key proteins play a dual role in regulating the core clock mechanism, as well as adipose tissue metabolism, and link circadian rhythms with lipogenesis and lipolysis. Adipose tissues are distinguished as white, brown, and beige (or brite), each with unique metabolic characteristics. Recently, the role of the circadian clock in regulating the differentiation into the different adipose tissues has been investigated. In this review, the role of clock proteins and the downstream signaling pathways in white, brown, and brite adipose tissue function and differentiation will be reviewed. In addition, chronodisruption and metabolic disorders and clinical aspects of circadian adiposity will be addressed.

Biologic Agents Are Associated with Excessive Weight Gain in Children with Inflammatory Bowel Disease

BACKGROUND

Children with active inflammatory bowel disease (IBD) are frequently underweight. Anti-tumor necrosis factor (anti-TNF) agents may induce remission and restore growth. However, its use in other autoimmune diseases has been associated with excess weight gain. Our aim was to examine whether children with IBD could experience excess weight gain.

METHODS

A centralized diagnostic index identified pediatric IBD patients evaluated at our institution who received anti-TNF therapy for at least 1 year between August 1998 and December 2013. Anthropometric data were collected at time of anti-TNF initiation and annually. Excess weight gain was defined as ΔBMI SDS (standard deviation score) where patients were (1) reclassified from "normal" to "overweight/obese," (2) "overweight" to "obese," or (2) a final BMI SDS >0 and ΔSDS >0.5.

RESULTS

During the study period, 268 children received anti-TNF therapy. Of these, 69 had sufficient follow-up for a median of 29.3 months. Median age at first anti-TNF dose was 12.8 years. At baseline, mean weight SDS was -0.7 (SD 1.4), while mean BMI SDS was -0.6 (1.3). Using baseline BMI SDS, 11.6% were overweight/obese. At last follow-up (LFU), however, the mean ΔBMI SDS was 0.50 (p < 0.0001). However, 10 (17%) patients had excess weight gain at LFU; 3 patients were reclassified from "normal" to "obese," and 7 had a final BMI SDS >0 and ΔSDS >0.5.

CONCLUSIONS

Pediatric patients with IBD may experience excess weight gain when treated with anti-TNF agents. Monitoring for this side effect is warranted.

Circadian CLOCK gene polymorphisms in relation to sleep patterns and obesity in African Americans: findings from the Jackson heart study

BACKGROUND

Circadian rhythms regulate key biological processes and the dysregulation of the intrinsic clock mechanism affects sleep patterns and obesity onset. The CLOCK (circadian locomotor output cycles protein kaput) gene encodes a core transcription factor of the molecular circadian clock influencing diverse metabolic pathways, including glucose and lipid homeostasis. The primary objective of this study was to evaluate the associations between CLOCK single nucleotide polymorphisms (SNPs) and body mass index (BMI). We also evaluated the association of SNPs with BMI related factors such as sleep duration and quality, adiponectin and leptin, in 2962 participants (1116 men and 1810 women) from the Jackson Heart Study. Genotype data for the selected 23 CLOCK gene SNPS was obtained by imputation with IMPUTE2 software and reference phase data from the 1000 genome project. Genetic analyses were conducted with PLINK RESULTS: We found a significant association between the CLOCK SNP rs2070062 and sleep duration, participants carriers of the T allele showed significantly shorter sleep duration compared to non-carriers after the adjustment for individual proportions of European ancestry (PEA), socio economic status (SES), body mass index (BMI), alcohol consumption and smoking status that reach the significance threshold after multiple testing correction. In addition, we found nominal associations of the CLOCK SNP rs6853192 with longer sleep duration and the rs6820823, rs3792603 and rs11726609 with BMI. However, these associations did not reach the significance threshold after correction for multiple testing.

CONCLUSIONS

In this work, CLOCK gene variants were associated with sleep duration and BMI suggesting that the effects of these polymorphisms on circadian rhythmicity may affect sleep duration and body weight regulation in Africans Americans.

Circadian Rhythms in Diet-Induced Obesity

The biological clocks of the circadian timing system coordinate cellular and physiological processes and synchronizes these with daily cycles, feeding patterns also regulates circadian clocks. The clock genes and adipocytokines show circadian rhythmicity. Dysfunction of these genes are involved in the alteration of these adipokines during the development of obesity. Food availability promotes the stimuli associated with food intake which is a circadian oscillator outside of the suprachiasmatic nucleus (SCN). Its circadian rhythm is arranged with the predictable daily mealtimes. Food anticipatory activity is mediated by a self-sustained circadian timing and its principal component is food entrained oscillator. However, the hypothalamus has a crucial role in the regulation of energy balance rather than food intake. Fatty acids or their metabolites can modulate neuronal activity by brain nutrient-sensing neurons involved in the regulation of energy and glucose homeostasis. The timing of three-meal schedules indicates close association with the plasma levels of insulin and preceding food availability. Desynchronization between the central and peripheral clocks by altered timing of food intake and diet composition can lead to uncoupling of peripheral clocks from the central pacemaker and to the development of metabolic disorders. Metabolic dysfunction is associated with circadian disturbances at both central and peripheral levels and, eventual disruption of circadian clock functioning can lead to obesity. While CLOCK expression levels are increased with high fat diet-induced obesity, peroxisome proliferator-activated receptor (PPAR) alpha increases the transcriptional level of brain and muscle ARNT-like 1 (BMAL1) in obese subjects. Consequently, disruption of clock genes results in dyslipidemia, insulin resistance and obesity. Modifying the time of feeding alone can greatly affect body weight. Changes in the circadian clock are associated with temporal alterations in feeding behavior and increased weight gain. Thus, shift work is associated with increased risk for obesity, diabetes and cardio-vascular diseases as a result of unusual eating time and disruption of circadian rhythm.

Effects of different periods of paradoxical sleep deprivation and sleep recovery on lipid and glucose metabolism and appetite hormones in rats

Sleep has a fundamental role in the regulation of energy balance, and it is an essential and natural process whose precise impacts on health and disease have not yet been fully elucidated. The aim of this study was to assess the consequences of different periods of paradoxical sleep deprivation (PSD) and recovery from PSD on lipid profile, oral glucose tolerance test (OGTT) results, and changes in insulin, corticosterone, ghrelin, and leptin concentrations. Three-month-old male Wistar rats weighing 250–350 g were submitted to 24, 96, or 192 h of PSD or 192 h of PSD with 480 h of recovery. The PSD was induced by the multiple platforms method. Subsequently, the animals were submitted to an OGTT. One day later, the animals were killed and the levels of triglycerides, total cholesterol, lipoproteins (low-density lipoprotein, very-low-density lipoprotein, and high-density lipoprotein), insulin, ghrelin, leptin, and corticosterone in plasma were quantified. There was a progressive decrease in body weight with increasing duration of PSD. The PSD induced basal hypoglycemia over all time periods evaluated. Evaluation of areas under the curve revealed progressive hypoglycemia only after 96 and 192 h of PSD. There was an increase in corticosterone levels after 192 h of PSD. We conclude that PSD induces alterations in metabolism that are reversed after a recovery period of 20 days.

Circadian rhythms in glucose and lipid metabolism in nocturnal and diurnal mammals

Most aspects of energy metabolism display clear variations during day and night. This daily rhythmicity of metabolic functions, including hormone release, is governed by a circadian system that consists of the master clock in the suprachiasmatic nuclei of the hypothalamus (SCN) and many secondary clocks in the brain and peripheral organs. The SCN control peripheral timing via the autonomic and neuroendocrine system, as well as via behavioral outputs. The sleep-wake cycle, the feeding/fasting rhythm and most hormonal rhythms, including that of leptin, ghrelin and glucocorticoids, usually show an opposite phase (relative to the light-dark cycle) in diurnal and nocturnal species. By contrast, the SCN clock is most active at the same astronomical times in these two categories of mammals. Moreover, in both species, pineal melatonin is secreted only at night. In this review we describe the current knowledge on the regulation of glucose and lipid metabolism by central and peripheral clock mechanisms. Most experimental knowledge comes from studies in nocturnal laboratory rodents. Nevertheless, we will also mention some relevant findings in diurnal mammals, including humans. It will become clear that as a consequence of the tight connections between the circadian clock system and energy metabolism, circadian clock impairments (e.g., mutations or knock-out of clock genes) and circadian clock misalignments (such as during shift work and chronic jet-lag) have an adverse effect on energy metabolism, that may trigger or enhancing obese and diabetic symptoms.

Neuroendocrine regulation of lactation and milk production

Prolactin (PRL) released from lactotrophs of the anterior pituitary gland in response to the suckling by the offspring is the major hormonal signal responsible for stimulation of milk synthesis in the mammary glands. PRL secretion is under chronic inhibition exerted by dopamine (DA), which is released from neurons of the arcuate nucleus of the hypothalamus into the hypophyseal portal vasculature. Suckling by the young activates ascending systems that decrease the release of DA from this system, resulting in enhanced responsiveness to one or more PRL-releasing hormones, such as thyrotropin-releasing hormone. The neuropeptide oxytocin (OT), synthesized in magnocellular neurons of the hypothalamic supraoptic, paraventricular, and several accessory nuclei, is responsible for contracting the myoepithelial cells of the mammary gland to produce milk ejection. Electrophysiological recordings demonstrate that shortly before each milk ejection, the entire neurosecretory OT population fires a synchronized burst of action potentials (the milk ejection burst), resulting in release of OT from nerve terminals in the neurohypophysis. Both of these neuroendocrine systems undergo alterations in late gestation that prepare them for the secretory demands of lactation, and that reduce their responsiveness to stimuli other than suckling, especially physical stressors. The demands of milk synthesis and release produce a condition of negative energy balance in the suckled mother, and, in laboratory rodents, are accompanied by a dramatic hyperphagia. The reduction in secretion of the adipocyte hormone, leptin, a hallmark of negative energy balance, may be an important endocrine signal to hypothalamic systems that integrate lactation-associated food intake with neuroendocrine systems.

Circadian metabolism in the light of evolution

Circadian rhythm, or daily oscillation, of behaviors and biological processes is a fundamental feature of mammalian physiology that has developed over hundreds of thousands of years under the continuous evolutionary pressure of energy conservation and efficiency. Evolution has fine-tuned the body's clock to anticipate and respond to numerous environmental cues in order to maintain homeostatic balance and promote survival. However, we now live in a society in which these classic circadian entrainment stimuli have been dramatically altered from the conditions under which the clock machinery was originally set. A bombardment of artificial lighting, heating, and cooling systems that maintain constant ambient temperature; sedentary lifestyle; and the availability of inexpensive, high-calorie foods has threatened even the most powerful and ancient circadian programming mechanisms. Such environmental changes have contributed to the recent staggering elevation in lifestyle-influenced pathologies, including cancer, cardiovascular disease, depression, obesity, and diabetes. This review scrutinizes the role of the body's internal clocks in the hard-wiring of circadian networks that have evolved to achieve energetic balance and adaptability, and it discusses potential therapeutic strategies to reset clock metabolic control to modern time for the benefit of human health.

Connectivity Study of the Neuromechanism of Acute Acupuncture Needling during fMRI in "Overweight" Subjects

This functional connectivity study depicts how acupoints ST 36 and SP 9 and their sham acupoints acutely act on blood glucose (GLU), core body temperature (CBT), hunger, and sensations pertaining to needling (De-qi) via the limbic system and dopamine (DA) to affect various brain areas in fasting, adult, and "overweight" Chinese males using functional magnetic resonance imaging. Functional connectivity (FC) analysis utilized the amygdala (AMY) and hypothalamus (HYP) as regions of interest (ROIs) in the discrete cosine transform and seed correlation analysis methods. There was a significant difference in the spatial patterns of the distinct brain regions between groups. Correlation results showed that increased HYP-hippocampus FC after ACU was positively correlated with ACU-induced change in CBT; increased HYP-putamen-insula FC after ACU was positively correlated with ACU-induced change in GLU; and increased HYP-anterior cingulate cortex FC after ACU was positively correlated with ACU-induced change in HUNGER suggesting that increased DA modulation during ACU was probably associated with increased poststimulation limbic system and spinothalamic tract connectivity. Decreased HYP-thalamus FC after ACU was negatively correlated or anticorrelated with ACU-induced change in HUNGER suggesting that increased DA modulation during ACU was possibly associated with decreased poststimulation limbic system and spinothalamic tract connectivity. No correlation was found for min SHAM. This was an important study in addressing acute acupuncture effects and neural pathways involving physiology and appetite regulation in overweight individuals.

Effectual comparison of quinoa and amaranth supplemented diets in controlling appetite; a biochemical study in rats

The objective of this study was to assess the efficacy of two current cynosure protein substitutes; quinoa and amaranth in controlling short term food intake and satiety in rats. Experimental rats were allotted to three groups (n = 8 per group) and fed with diets containing casein, quinoa and amaranth as major protein sources, with casein diet kept as control. At the end of the experiment it was observed that the rats ingesting quinoa and amaranth supplemented diets exhibited lesser food intake (p < 0.01) and lesser body weight gain significantly in amaranth (p < 0.05) as compared to control. They seemed to bring down plasma ghrelin levels while meliorating plasma leptin and cholecystokinin (CCK) levels postprandially (p < 0.01). Although both quinoa diet and amaranth diet were effective in improving blood glucose response and maintaining plasma free fatty acids (FFA) and general lipid profiles subsequently after the meal, amaranth diet showed significant effects when compared to control and amaranth diets. There was 15 % improvement in blood glucose profile in the amaranth group with respect to the control at 90 min, where as there was only 3.4 % improvement in the quinoa group. These findings provide a scientific rationale to consider incorporation of these modest cereals in a diet meant to fight against growing obesity and poverty.

Effects of Wen Dan Tang on insomnia-related anxiety and levels of the brain-gut peptide Ghrelin

Ghrelin, a brain-gut peptide that induces anxiety and other abnormal emotions, contributes to the effects of insomnia on emotional behavior. In contrast, the traditional Chinese Medicine remedy Wen Dan Tang reduces insomnia-related anxiety, which may perhaps correspond to changes in the brain-gut axis. This suggests a possible relationship between Wen Dan Tang's pharmacological mechanism and the brain-gut axis. Based on this hypothesis, a sleep-deprived rat model was induced and Wen Dan Tang was administered using oral gavage during model establishment. Wen Dan Tang significantly reduced insomnia-related anxiety and prevented Ghrelin level decreases following sleep deprivation, especially in the hypothalamus. Increased expression of Ghrelin receptor mRNA in the hypothalamus was also observed, suggesting that reduced anxiety may be a result of Wen Dan Tang's regulation of Ghrelin-Ghrelin receptors.

Episodic hormone secretion: a comparison of the basis of pulsatile secretion of insulin and GnRH

Rhythms govern many endocrine functions. Examples of such rhythmic systems include the insulin-secreting pancreatic beta-cell, which regulates blood glucose, and the gonadotropin-releasing hormone (GnRH) neuron, which governs reproductive function. Although serving very different functions within the body, these cell types share many important features. Both GnRH neurons and beta-cells, for instance, are hypothesized to generate at least two rhythms endogenously: (1) a burst firing electrical rhythm and (2) a slower rhythm involving metabolic or other intracellular processes. This review discusses the importance of hormone rhythms to both physiology and disease and compares and contrasts the rhythms generated by each system.

Leptin expression is rhythmic in brain and liver of goldfish (Carassius auratus). Role of feeding time

Daily rhythms of feeding regulators are currently arousing research interest due to the relevance of the temporal harmony of endocrine regulators for growth and welfare in vertebrates. However, it is unknown the leptin circadian pattern in fish. The aim of this study is to investigate if leptin (gLep-aI and gLep-aII) expression is rhythmic in goldfish (Carassius auratus) liver and brain, and if such rhythms are driven by feeding time through a food entrainable oscillator. Fish maintained under 12-h light:12-h dark photoperiod and a scheduled feeding time showed 24-h locomotor activity and glycaemia rhythms. Moreover, hepatic gLep-aI and brain gLep-aI and gLep-aII expression were rhythmic with different daily profiles, showing a postprandial increase of leptin expression in the liver but not in the brain. Under constant light and different feeding regimes (scheduled fed at 10:00, 22:00 or randomly fed), feeding time synchronized daily rhythms in locomotor activity, glycaemia and clock gene expression (gPer1a, gPer3 and gCry3), but the rhythmic expression of hepatic gLep-aI and brain gLep-aII only remained in fed fish at 10:00. In summary, daily rhythms of leptin expression in goldfish are differently regulated at central and peripheral level, and they are not directly driven by clock genes. The role of food entrained oscillators on leptin expression rhythms in fish remains to be demonstrated.

Ghrelin and leptin levels of sojourners and acclimatized lowlanders at high altitude

The circulatory levels of two appetite regulatory hormones i.e. leptin and ghrelin were estimated in sojourners and acclimatized subjects to investigate their possible role in high altitude (HA) induced anorexia. A group of 30 lowlanders who had never visited HA were inducted to a height of 3600 m by air and after 48 h they were further taken to an altitude of 4300 m by road. Blood samples were collected after 48 h stay at 3600 m and again after 48 h and 7 days of stay at 4300 m during 0700-0730 h. There was a decrease in energy intake (850 kcal/day) of sojourners, which resulted in loss of body weight by 2.12 kg at HA. At an altitude of 4300 m there was a significant increase in leptin over basal levels (54.9%, p < 0.001) at 48 h that persisted even after 7 days of stay at this altitude. Ghrelin levels of sojourners decreased by more than 30% in comparison to basal values at 48 h of ascent to HA. Leptin levels of acclimatized lowlanders were also higher in comparison with control group (acclimatized group 7.6 + 0.6 ng/ml vs. control 5.6 + 0.5 ng/ml, p < 0.01, n = 50).

Circadian aspects of energy metabolism and aging

Life span extension has been a goal of research for several decades. Resetting circadian rhythms leads to well being and increased life span, while clock disruption is associated with increased morbidity accelerated aging. Increased longevity and improved health can be achieved by different feeding regimens that reset circadian rhythms and may lead to better synchrony in metabolism and physiology. This review focuses on the circadian aspects of energy metabolism and their relationship with aging in mammals.

Leptin-sensitive neurons in the arcuate nucleus integrate activity and temperature circadian rhythms and anticipatory responses to food restriction

Previously, we investigated the role of neuropeptide Y and leptin-sensitive networks in the mediobasal hypothalamus in sleep and feeding and found profound homeostatic and circadian deficits with an intact suprachiasmatic nucleus. We propose that the arcuate nuclei (Arc) are required for the integration of homeostatic circadian systems, including temperature and activity. We tested this hypothesis using saporin toxin conjugated to leptin (Lep-SAP) injected into Arc in rats. Lep-SAP rats became obese and hyperphagic and progressed through a dynamic phase to a static phase of growth. Circadian rhythms were examined over 49 days during the static phase. Rats were maintained on a 12:12-h light-dark (LD) schedule for 13 days and, thereafter, maintained in continuous dark (DD). After the first 13 days of DD, food was restricted to 4 h/day for 10 days. We found that the activity of Lep-SAP rats was arrhythmic in DD, but that food anticipatory activity was, nevertheless, entrainable to the restricted feeding schedule, and the entrained rhythm persisted during the subsequent 3-day fast in DD. Thus, for activity, the circuitry for the light-entrainable oscillator, but not for the food-entrainable oscillator, was disabled by the Arc lesion. In contrast, temperature remained rhythmic in DD in the Lep-SAP rats and did not entrain to restricted feeding. We conclude that the leptin-sensitive network that includes the Arc is required for entrainment of activity by photic cues and entrainment of temperature by food, but is not required for entrainment of activity by food or temperature by photic cues.

Circannual changes in stress and feeding hormones and their effect on food-seeking behaviors

Seasonal fluctuations in food availability show a tight association with seasonal variations in body weight and food intake. Seasonal variations in food intake, energy storage, and expenditure appear to be a widespread phenomenon suggesting they may have evolved in anticipation for changing environmental demands. These cycles appear to be driven by changes in external daylength acting on neuroendocrine pathways. A number of neuroendocrine pathways, two of which are the endocrine mechanisms underlying feeding and stress, appear to show seasonal changes in both their circulating levels and reactivity. As such, variation in the level or reactivity to these hormones may be crucial factors in the control of seasonal variations in food-seeking behaviors. The present review examines the relationship between feeding behavior and seasonal changes in circulating hormones. We hypothesize that seasonal changes in circulating levels of glucocorticoids and the feeding-related hormones ghrelin and leptin contribute to seasonal fluctuations in feeding-related behaviors. This review will focus on the seasonal circulating levels of these hormones as well as sensitivity to these hormones in the modulation of food-seeking behaviors.

Differential regulation of adipokines may influence migratory behavior in the white-throated sparrow (Zonotrichia albicollis)

White-throated sparrows increase fat deposits during pre-migratory periods and rely on these fat stores to fuel migration. Adipose tissue produces hormones and signaling factors in a rhythmic fashion and may be controlled by a clock in adipose tissue or driven by a master clock in the brain. The master clock may convey photoperiodic information from the environment to adipose tissue to facilitate pre-migratory fattening, and adipose tissue may, in turn, release adipokines to indicate the extent of fat energy stores. Here, we present evidence that a change in signal from the adipokines adiponectin and visfatin may act to indicate body condition, thereby influencing an individual's decision to commence migratory flight, or to delay until adequate fat stores are acquired. We quantified plasma adiponectin and visfatin levels across the day in captive birds held under constant photoperiod. The circadian profiles of plasma adiponectin in non-migrating birds were approximately inverse the profiles from migrating birds. Adiponectin levels were positively correlated to body fat, and body fat was inversely related to the appearance of nocturnal migratory restlessness. Visfatin levels were constant across the day and did not correlate with fat deposits; however, a reduction in plasma visfatin concentration occurred during the migratory period. The data suggest that a significant change in the biological control of adipokine expression exists between the two migratory conditions and we propose a role for adiponectin, visfatin and adipose clocks in the regulation of migratory behaviors.

Reduced preprandial dipping accounts for rapid elevation of blood pressure and renal sympathetic nerve activity in rabbits fed a high-fat diet

Consumption of a high-fat diet (HFD) by rabbits results in increased blood pressure (BP), heart rate (HR), and renal sympathetic nerve activity (RSNA) within 1 wk. Here, we determined how early this activation occurred and whether it was related to changes in cardiovascular and neural 24-h rhythms. Rabbits were meal-fed a HFD for 3 wks, then a normal-fat diet (NFD) for 1 wk. BP, HR, and RSNA were measured daily in the home cage via implanted telemeters. Baseline BP, HR, and RSNA over 24 h were 71 ± 1 mm Hg, 205 ± 4 beats/min and 7 ± 1 normalized units (nu). The 24-h pattern was entrained to the feeding cycle and values increased from preprandial minimum to postprandial maximum by 4 ± 1 mm Hg, 51 ± 6 beats/min, and 1.6 ± .6 nu each day. Feeding of a HFD markedly diminished the preprandial dip after 2 d (79-125% of control; p < 0.05) and this reduction lasted for 3 wks of HFD. Twenty-four-hour BP, HR, and RSNA concurrently increased by 2%, 18%, and 22%, respectively. Loss of preprandial dipping accounted for all of the BP increase and 50% of the RSNA increase over 3 wks and the 24-h rhythm became entrained to the light-dark cycle. Resumption of a NFD did not alter the BP preprandial dip. Thus, elevated BP induced by a HFD and mediated by increased sympathetic nerve activity results from a reduction in preprandial dipping, from the first day. Increased calories, glucose, insulin, and leptin may account for early changes, whereas long-term loss of dipping may be related to increased sensitivity of sympathetic pathways.

Circadian rhythms, metabolism, and insulin sensitivity: transcriptional networks in animal models

Homeostatic systems have adapted to respond to the diurnal light/dark cycle. Numerous physiological pathways, including metabolism, are coordinated by this 24-h cycle. Animals with mutations in clock genes show abnormal glucose and lipid metabolism, indicating a critical relationship between the circadian clock and metabolism. Energy homeostasis is achieved through circadian regulation of the expression and activity of several key metabolic enzymes. Temporal organization of tissue metabolism is coordinated by reciprocal cross-talk between the core clock mechanism and key metabolic enzymes and transcriptional activators. The aim of this review is to define the role of the circadian clock in the regulation of insulin sensitivity by describing the interconnection between the circadian clock and metabolic pathways.

The suprachiasmatic nucleus controls circadian energy metabolism and hepatic insulin sensitivity

Disturbances in the circadian system are associated with the development of type 2 diabetes mellitus. Here, we studied the direct contribution of the suprachiasmatic nucleus (SCN), the central pacemaker in the circadian system, in the development of insulin resistance. Exclusive bilateral SCN lesions in male C57Bl/6J mice, as verified by immunochemistry, showed a small but significant increase in body weight (+17%), which was accounted for by an increase in fat mass. In contrast, mice with collateral damage to the ventromedial hypothalamus and paraventricular nucleus showed severe obesity and insulin resistance. Mice with exclusive SCN ablation revealed a loss of circadian rhythm in activity, oxygen consumption, and food intake. Hyperinsulinemic-euglycemic clamp analysis 8 weeks after lesioning showed that the glucose infusion rate was significantly lower in SCN lesioned mice compared with sham-operated mice (-63%). Although insulin potently inhibited endogenous glucose production (-84%), this was greatly reduced in SCN lesioned mice (-7%), indicating severe hepatic insulin resistance. Our data show that SCN malfunctioning plays an important role in the disturbance of energy balance and suggest that an absence of central clock activity, in a genetically intact animal, may lead to the development of insulin resistance.

Glutamate release mediates leptin action on energy expenditure

Restricting energy expenditure is an adaptive response to food shortage. Despite being insulated with massive amount of fat tissues, leptin-deficient mice lose the ability to maintain their body temperature and develop deep hypothermia, which can be suppressed by exogenous leptin, suggesting an important role for leptin in energy expenditure regulation. However, the mechanism underlying the leptin action is not clear. We generated mice with disruption of glutamate release from leptin receptor-expressing neurons by deleting vesicular glutamate transporter 2 in these neurons, and found that these mice developed mild obesity purely due to reduced energy expenditure, exhibited bouts of rapidly reduced energy expenditure, body temperature and locomotion. In addition, these mice exhibited lower energy expenditure and body temperature in response to fasting and were defective in leptin-mediated thermogenic action in brown adipose tissues. Taken together, our results identify a role for glutamate release in mediating leptin action on energy expenditure.

Circadian clocks and metabolism

Circadian clocks maintain periodicity in internal cycles of behavior, physiology, and metabolism, enabling organisms to anticipate the 24-h rotation of the Earth. In mammals, circadian integration of metabolic systems optimizes energy harvesting and utilization across the light/dark cycle. Disruption of clock genes has recently been linked to sleep disorders and to the development of cardiometabolic disease. Conversely, aberrant nutrient signaling affects circadian rhythms of behavior. This chapter reviews the emerging relationship between the molecular clock and metabolic systems and examines evidence that circadian disruption exerts deleterious consequences on human health.

Circadian rhythms and obesity in mammals

Obesity has become a serious public health problem and a major risk factor for the development of illnesses, such as insulin resistance and hypertension. Attempts to understand the causes of obesity and develop new therapeutic strategies have mostly focused on caloric intake and energy expenditure. Recent studies have shown that the circadian clock controls energy homeostasis by regulating the circadian expression and/or activity of enzymes, hormones, and transport systems involved in metabolism. Moreover, disruption of circadian rhythms leads to obesity and metabolic disorders. Therefore, it is plausible that resetting of the circadian clock can be used as a new approach to attenuate obesity. Feeding regimens, such as restricted feeding (RF), calorie restriction (CR), and intermittent fasting (IF), provide a time cue and reset the circadian clock and lead to better health. In contrast, high-fat (HF) diet leads to disrupted circadian expression of metabolic factors and obesity. This paper focuses on circadian rhythms and their link to obesity.

Meal time shift disturbs circadian rhythmicity along with metabolic and behavioral alterations in mice

In modern society, growing numbers of people are engaged in various forms of shift works or trans-meridian travels. Such circadian misalignment is known to disturb endogenous diurnal rhythms, which may lead to harmful physiological consequences including metabolic syndrome, obesity, cancer, cardiovascular disorders, and gastric disorders as well as other physical and mental disorders. However, the precise mechanism(s) underlying these changes are yet unclear. The present work, therefore examined the effects of 6 h advance or delay of usual meal time on diurnal rhythmicities in home cage activity (HCA), body temperature (BT), blood metabolic markers, glucose homeostasis, and expression of genes that are involved in cholesterol homeostasis by feeding young adult male mice in a time-restrictive manner. Delay of meal time caused locomotive hyperactivity in a significant portion (42%) of subjects, while 6 h advance caused a torpor-like symptom during the late scotophase. Accordingly, daily rhythms of blood glucose and triglyceride were differentially affected by time-restrictive feeding regimen with concurrent metabolic alterations. Along with these physiological changes, time-restrictive feeding also influenced the circadian expression patterns of low density lipoprotein receptor (LDLR) as well as most LDLR regulatory factors. Strikingly, chronic advance of meal time induced insulin resistance, while chronic delay significantly elevated blood glucose levels. Taken together, our findings indicate that persistent shifts in usual meal time impact the diurnal rhythms of carbohydrate and lipid metabolisms in addition to HCA and BT, thereby posing critical implications for the health and diseases of shift workers.

Nutrient sensing and the circadian clock

The circadian system synchronizes behavioral and physiologic processes with daily changes in the external light-dark cycle, optimizing energetic cycles with the rising and setting of the sun. Molecular clocks are organized hierarchically, with neural clocks orchestrating the daily switch between periods of feeding and fasting, and peripheral clocks generating 24h oscillations of energy storage and utilization. Recent studies indicate that clocks respond to nutrient signals and that a high-fat diet influences the period of locomotor activity under free-running conditions, a core property of the clock. A major goal is to identify the molecular basis for the reciprocal relation between metabolic and circadian pathways. Here the role of peptidergic hormones and macromolecules as nutrient signals integrating circadian and metabolic systems is highlighted.

The role of the circadian clock system in nutrition and metabolism

Mammals have an endogenous timing system in the suprachiasmatic nuclei (SCN) of the hypothalamic region of the brain. This internal clock system is composed of an intracellular feedback loop that drives the expression of molecular components and their constitutive protein products to oscillate over a period of about 24 h (hence the term 'circadian'). These circadian oscillations bring about rhythmic changes in downstream molecular pathways and physiological processes such as those involved in nutrition and metabolism. It is now emerging that the molecular components of the clock system are also found within the cells of peripheral tissues, including the gastrointestinal tract, liver and pancreas. The present review examines their role in regulating nutritional and metabolic processes. In turn, metabolic status and feeding cycles are able to feed back onto the circadian clock in the SCN and in peripheral tissues. This feedback mechanism maintains the integrity and temporal coordination between various components of the circadian clock system. Thus, alterations in environmental cues could disrupt normal clock function, which may have profound effects on the health and well-being of an individual.

Expression of clock genes in human subcutaneous and visceral adipose tissues

Disrupted circadian rhythms are associated with obesity and metabolic alterations, but little is known about the participation of peripheral circadian clock machinery in these processes. The aim of the present study was to analyze RNA expression of clock genes in subcutaneous (SAT) and visceral (VAT) adipose tissues of male and female subjects in AM (morning) and PM (afternoon) periods, and its interactions with body mass index (BMI). Ninety-one subjects (41 ± 11 yrs of age) presenting a wide range of BMI (21.4 to 48.6 kg/m(2)) were included. SAT and VAT biopsies were obtained from patients undergoing abdominal surgeries. Clock genes expressions were evaluated by qRT-PCR. The only clock gene that showed higher expression (p < .0001) in SAT in comparison to VAT was PER1 of female (372%) and male (326%) subjects. Different patterns of expression between the AM and PM periods were observed, in particular REV-ERBα, which was reduced (p < .05) at the PM period in SAT and VAT of both women and men (women: ∼53% lower; men: ∼78% lower), whereas CLOCK expression was not altered. Relationships between clock genes were different in SAT vs. VAT. BMI was negatively correlated with SATPER1 (r = -.549; p = .001) and SATPER2 (r = -.613; p = .0001) and positively with VATCLOCK (r = .541; p = .001) and VATBMAL1 (r = .468; p = .007) only in women. These data suggest that the circadian clock machinery of adipose tissue depots differs between female and male subjects, with a sex-specific effect observed for some genes. BMI correlated with clock genes, but at this moment it is not possible to establish the cause-effect relationship.

Chronobiological Effects on Obesity

The development of obesity is the consequence of a multitude of complex interactions between both genetic and environmental factors. It has been suggested that the dramatic increase in the prevalence of obesity over the past 30 years has been the result of environmental changes that have enabled the full realization of genetic susceptibility present in the population. Among the many environmental alterations that have occurred in our recent history is the ever-increasing dyssynchrony between natural cycles of light/dark and altered patterns of sleep/wake and eating behavior associated with our "24-hour" lifestyle. An extensive research literature has established clear links between increased risk for obesity and both sleep deprivation and shift work, and our understanding of the consequences of such dyssynchrony at the molecular level is beginning to emerge. Studies linking alterations in cellular circadian clocks to metabolic dysfunction point to the increasing importance of chronobiology in obesity etiology.

Circadian rhythms, aging, and life span in mammals

Resetting the circadian clock leads to well being and increased life span, whereas clock disruption is associated with aging and morbidity. Increased longevity and improved health can be achieved by different feeding regimens that reset circadian rhythms and may lead to better synchrony in metabolism and physiology. This review focuses on recent findings concerning the relationships between circadian rhythms, aging attenuation, and life-span extension in mammals.

Neuroendocrine and metabolic activities of ghrelin gene products

Acylated ghrelin (AG) is a 28 amino acid gastric peptide a natural ligand for the growth hormone secretagogue (GHS) receptor type 1a (GHS-R1a), endowed with GH-secreting and orexigenic properties. Besides, ghrelin exerts several peripheral metabolic actions, including modulation of glucose homeostasis and stimulation of adipogenesis. Notably, AG administration causes hyperglycemia in rodents as in humans. Ghrelin pleiotropy is supported by a widespread expression of the ghrelin gene, of GHS-R1a and other unknown ghrelin binding sites. The existence of alternative receptors for AG, of several natural ligands for GHS-R1a and of acylation-independent ghrelin non-neuroendocrine activities, suggests that there might be a complex 'ghrelin system' not yet completely explored. Moreover, the patho-physiological implications of unacylated ghrelin (UAG), and obestatin (Ob), the other two ghrelin gene-derived peptides, need to be clarified. Within the next few years, we may better understand the 'ghrelin system', where we might envisage clinical applications.