Central and peripheral effects of chronic food restriction and weight restoration in the rat

Satiety Associated with Calorie Restriction and Time-Restricted Feeding: Central Neuroendocrine Integration

This review focuses on summarizing current knowledge on how time-restricted feeding (TRF) and continuous caloric restriction (CR) affect central neuroendocrine systems involved in regulating satiety. Several interconnected regions of the hypothalamus, brainstem, and cortical areas of the brain are involved in the regulation of satiety. Following CR and TRF, the increase in hunger and reduction in satiety signals of the melanocortin system [neuropeptide Y (NPY), proopiomelanocortin (POMC), and agouti-related peptide (AgRP)] appear similar between CR and TRF protocols, as do the dopaminergic responses in the mesocorticolimbic circuit. However, ghrelin and leptin signaling via the melanocortin system appears to improve energy balance signals and reduce hyperphagia following TRF, which has not been reported in CR. In addition to satiety systems, CR and TRF also influence circadian rhythms. CR influences the suprachiasmatic nucleus (SCN) or the primary circadian clock as seen by increased clock gene expression. In contrast, TRF appears to affect both the SCN and the peripheral clocks, as seen by phasic changes in the non-SCN (potentially the elusive food entrainable oscillator) and metabolic clocks. The peripheral clocks are influenced by the primary circadian clock but are also entrained by food timing, sleep timing, and other lifestyle parameters, which can supersede the metabolic processes that are regulated by the primary circadian clock. Taken together, TRF influences hunger/satiety, energy balance systems, and circadian rhythms, suggesting a role for adherence to CR in the long run if implemented using the TRF approach. However, these suggestions are based on only a few studies, and future investigations that use standardized protocols for the evaluation of the effect of these diet patterns (time, duration, meal composition, sufficiently powered) are necessary to verify these preliminary observations.

A role for leptin and ghrelin in the augmentation of heroin seeking induced by chronic food restriction

RATIONAL

Caloric restriction increases the risk of relapse in abstinent drug users. Hormones involved in the regulation of energy balance and food intake, such as leptin and ghrelin, are implicated in drug-related behaviors.

OBJECTIVES

We investigated the role of leptin and ghrelin in the augmentation of heroin seeking induced by chronic food restriction.

METHODS

Rats self-administered heroin (0.1 mg/kg/infusion) for 10 days followed by 14 days of drug withdrawal. During withdrawal, rats were food restricted to 90% of their original body weight or were given free access to food. In experiment 1, we measured the plasma concentrations of leptin and ghrelin following heroin self-administration and withdrawal. In experiment 2, leptin was administered centrally (2.0 or 4.0 μg; i.c.v.) prior to a heroin-seeking test under extinction conditions. High density of both leptin and ghrelin receptors was previously identified in the ventral tegmental area (VTA), suggesting a direct effect on reward and motivation. Hence, we administered leptin (experiment 3; 0.125 or 0.250 μg/side), or ghrelin receptor antagonist JMV 2959 (experiment 4; 2.0 or 10.0 μg/side) directly into the VTA prior to the heroin-seeking test.

RESULTS

Chronic food restriction significantly decreased plasma levels of leptin and elevated plasma levels of ghrelin. Central administration of leptin had no statistically significant effect on heroin seeking. Intra-VTA administration of either leptin or JMV 2959 dose-dependently and selectively decreased heroin seeking in the food-restricted rats.

CONCLUSIONS

Leptin and ghrelin transmission in the VTA can modulate the augmentation of heroin seeking induced by chronic food restriction.

Caloric restriction alters the hormonal profile and testicular metabolome, resulting in alterations of sperm head morphology

Energy homeostasis is crucial for all physiological processes. Thus, when there is low energy intake, negative health effects may arise, including in reproductive function. We propose to study whether caloric restriction (CR) changes testicular metabolic profile and ultimately sperm quality. Male Wistar rats (n = 12) were randomized into a CR group fed with 30% fewer calories than weight-matched, ad libitum-fed animals (control group). Circulating hormonal profile, testicular glucagon-like peptide-1 (GLP-1), ghrelin and leptin receptors expression, and sperm parameters were analyzed. Testicular metabolite abundance and glycolysis-related enzymes were studied by NMR and Western blot, respectively. Oxidative stress markers were analyzed in testicular tissue and spermatozoa. Expressions of mitochondrial complexes and mitochondrial biogenesis in testes were determined. CR induced changes in body weight along with altered GLP-1, ghrelin, and leptin circulating levels. In testes, CR led to changes in receptor expression that followed those of the hormone levels; modified testicular metabolome, particularly amino acid content; and decreased oxidative stress-induced damage in testis and spermatozoa, although sperm head defects increased. In sum, CR induced changes in body weight, altering circulating hormonal profile and testicular metabolome and increasing sperm head defects. Ultimately, our data highlight that conditions of CR may compromise male fertility.

Examining weight suppression as a transdiagnostic factor influencing illness trajectory in bulimic eating disorders

Recent research indicates that weight suppression (WS: defined as the difference between highest lifetime and current weight) prospectively predicts illness trajectory across eating disorders characterized by binge eating, including AN binge-purge subtype (ANbp), bulimia nervosa (BN), and binge eating disorder (BED), collectively referred to as bulimic eating disorders. Through a series of studies, we have developed a model to explain the link between WS and illness trajectory in bulimic eating disorders. Our model posits that WS contributes to reduced circulating leptin, which leads to reduced postprandial glucagon-like peptide 1 (GLP-1) response. Diminished leptin and GLP-1 function contribute to alterations in two reward-related constructs in the Research Domain Criteria (RDoC): reward value/effort and reward satiation. Respectively, these changes increase drive/motivation to consume food and decrease ability for food consumption to lead to a state of satiation/satisfaction. Combined, these alterations increase risk for experiencing large, out-of-control binge-eating episodes. The following review presents evidence that contributed to the development of this model as well as preliminary findings from an on-going project funded to test this model.

Regulation of Agouti-Related Protein and Pro-Opiomelanocortin Gene Expression in the Avian Arcuate Nucleus

The arcuate nucleus is generally conserved across vertebrate taxa in its neuroanatomy and neuropeptide expression. Gene expression of agouti-related protein (AGRP), neuropeptide Y (NPY), pro-opiomelanocortin (POMC), and cocaine- and amphetamine-regulated transcript (CART) has been established in the arcuate nucleus of several bird species and co-localization demonstrated for AGRP and NPY. The proteins encoded by these genes exert comparable effects on food intake in birds after central administration to those seen in other vertebrates, with AGRP and NPY being orexigenic and CART and α-melanocyte-stimulating hormone anorexigenic. We have focused on the measurement of arcuate nucleus AGRP and POMC expression in several avian models in relation to the regulation of energy balance, incubation, stress, and growth. AGRP mRNA and POMC mRNA are, respectively, up- and downregulated after energy deprivation and restriction. This suggests that coordinated changes in the activity of AGRP and POMC neurons help to drive the homeostatic response to replace depleted energy stores in birds as in other vertebrates. While AGRP and POMC expression are generally positively and negatively correlated with food intake, respectively, we review here situations in some avian models in which AGRP gene expression is dissociated from the level of food intake and may have an influence on growth independent of changes in appetite. This suggests the possibility that the central melanocortin system exerts more pleiotropic functions in birds. While the neuroanatomical arrangement of AGRP and POMC neurons and the sensitivity of their activity to nutritional state appear generally conserved with other vertebrates, detailed knowledge is lacking of the key nutritional feedback signals acting on the avian arcuate nucleus and there appear to be significant differences between birds and mammals. In particular, recently identified avian leptin genes show differences between bird species in their tissue expression patterns and appear less closely linked in their expression to nutritional state. It is presently uncertain how the regulation of the central melanocortin system in birds is brought about in the situation of the apparently reduced importance of leptin and ghrelin compared to mammals.

Food-Restriction Lowers the Acoustic Startle Response in both Male and Female Rats, and, in Combination with Acute Ghrelin Injection, Abolishes the Expression of Fear-Potentiated Startle in Male Rats

Food restriction has been reported to reduce anxiety-like behaviour in male rats, whereas the effects of food restriction on anxiety in female rats are less clear. Ghrelin is a peptide hormone produced and secreted in the stomach that stimulates food intake and is considered to play a role in reward and emotional responses such as fear expression. Under food restriction, endogenous ghrelin levels increase. In the present study, we examined the effect of moderate food restriction (80% of ad libitum fed weight), with or without an acute application of a small dose of exogenous ghrelin intended to cause an immediate hunger response, on the expression of the acoustic startle reflex (ASR). This was carried out under basal conditions (baseline ASR to 90- and 95-dB noise bursts), and in the presence of a light cue associated with a mild foot-shock, as measured by fear-potentiated startle, which compares the proportional change in ASR in the presence of the conditioned stimulus. The results obtained show that food-restriction reduces basal ASR in both male and female rats, apart from any concomitant change in motor activity, suggesting that food-restriction reduces anxiety levels in both sexes. In addition, the data show that food-restriction reduces fear-potentiated startle in male but not female rats. Acute ghrelin injection, prior to fear-potentiated startle testing, eliminates the expression of fear-potentiated startle in food-restricted male rats alone, suggesting a role for ghrelin in the reduction of fear expression in food-restricted male rats. These data imply that, although food-restriction decreases anxiety in both sexes, learned fear responses remain intact after food-restriction in female but not male rats.

Metabolic Benefit of Chronic Caloric Restriction and Activation of Hypothalamic AGRP/NPY Neurons in Male Mice Is Independent of Ghrelin

Aging is associated with attenuated ghrelin signaling. During aging, chronic caloric restriction (CR) produces health benefits accompanied by enhanced ghrelin production. Ghrelin receptor (GH secretagogue receptor 1a) agonists administered to aging rodents and humans restore the young adult phenotype; therefore, we tested the hypothesis that the metabolic benefits of CR are mediated by endogenous ghrelin. Three month-old male mice lacking ghrelin (Ghrelin-/-) or ghrelin receptor (Ghsr-/-), and their wild-type (WT) littermates were randomly assigned to 2 groups: ad libitum (AL) fed and CR, where 40% food restriction was introduced gradually to allow Ghrelin-/- and Ghsr-/- mice to metabolically adapt and avoid severe hypoglycemia. Twelve months later, plasma ghrelin, metabolic parameters, ambulatory activity, hypothalamic and liver gene expression, as well as body composition were measured. CR increased plasma ghrelin and des-acyl ghrelin concentrations in WT and Ghsr-/- mice. CR of WT, Ghsr-/-, and Ghrelin-/- mice markedly improved metabolic flexibility, enhanced ambulatory activity, and reduced adiposity. Inactivation of Ghrelin or Ghsr had no effect on AL food intake or food anticipatory behavior. In contrast to the widely held belief that endogenous ghrelin regulates food intake, CR increased expression of hypothalamic Agrp and Npy, with reduced expression of Pomc across genotypes. In the AL context, ablation of ghrelin signaling markedly inhibited liver steatosis, which correlated with reduced Pparγ expression and enhanced Irs2 expression. Although CR and administration of GH secretagogue receptor 1a agonists both benefit the aging phenotype, we conclude the benefits of chronic CR are a consequence of enhanced metabolic flexibility independent of endogenous ghrelin or des-acyl ghrelin signaling.

Differential gene regulation of GHSR signaling pathway in the arcuate nucleus and NPY neurons by fasting, diet-induced obesity, and 17β-estradiol

Ghrelin's receptor, growth hormone secretagogue receptor (GHSR), is highly expressed in the arcuate nucleus (ARC) and in neuropeptide Y (NPY) neurons. Fasting, diet-induced obesity (DIO), and 17β-estradiol (E2) influence ARC Ghsr expression. It is unknown if these effects occur in NPY neurons. Therefore, we examined the expression of Npy, Agrp, and GHSR signaling pathway genes after fasting, DIO, and E2 replacement in ARC and pools of NPY neurons. In males, fasting increased ARC Ghsr and NPY Foxo1 but decreased NPY Ucp2. In males, DIO decreased ARC and NPY Ghsr and Cpt1c. In fed females, E2 increased Agrp, Ghsr, Cpt1c, and Foxo1 in ARC. In NPY pools, E2 decreased Foxo1 in fed females but increased Foxo1 in fasted females. DIO in females suppressed Agrp and augmented Cpt1c in NPY neurons. In summary, genes involved in GHSR signaling are differentially regulated between the ARC and NPY neurons in a sex-dependent manner.

Effects of a novel MC4R agonist on maintenance of reduced body weight in diet-induced obese mice

OBJECTIVE

The physiology of the weight-reduced (WR) state suggests that pharmacologic agents affecting energy homeostasis may have greater efficacy in WR individuals. Our aim was to establish a protocol that allows for evaluation of efficacy of weight maintenance agents and to assess the effectiveness of AZD2820, a novel melanocortin 4 receptor (MC4R) agonist in such a paradigm.

METHODS

MC4R agonist was administered in stratified doses to mice who were either fed high-fat diet ad libitum (AL) throughout the study; or stabilized at a 20% reduced body weight (BW), administered the drug for 4 weeks, and thereafter released from caloric restriction while continuing to receive the drug (WR).

RESULTS

After release of WR mice to AL feeding, the high-dose group (53.4 nmol/day) regained 12.4% less BW than their vehicle-treated controls since the beginning of drug treatment. In WR mice, 10.8 nmol/day of the agonist was sufficient to maintain these animals at 95.1% of initial BW versus 53.4 nmol/day required to maintain the BW of AL animals (94.5%).

CONCLUSIONS

In the WR state, the MC4R agonist was comparably efficacious to a five-fold higher dose in the AL state. This protocol provides a model for evaluating the mechanisms and quantitative efficacy of weight-maintenance strategies and agents.

Hypothalamic agouti-related protein expression is affected by both acute and chronic experience of food restriction and re-feeding in chickens

The central melanocortin system is conserved across vertebrates. However, in birds, little is known about how energy balance influences orexigenic agouti-related protein (AGRP) and anorexigenic pro-opiomelanocortin (POMC) expression, despite the fact that commercial food restriction is critical to the efficient production of poultry meat. To enable contrasts to be made, in broiler-breeder chickens, between levels of food restriction, between birds with the same body weight but different feeding experience, and between birds moved from restricted feeding to ad lib. feeding for different periods, five groups of hens were established between 6 and 12 weeks of age with different combinations of food restriction and release from restriction. AGRP and neuropeptide Y expression in the basal hypothalamus was significantly increased by chronic restriction but only AGRP mRNA levels reflected recent feeding experience: hens at the same body weight that had recently been on ad lib. feeding showed lower expression than restricted birds. AGRP expression also distinguished between hens released from restriction to ad lib. feeding for different periods. By contrast, POMC and cocaine- and amphetamine-regulated transcript mRNA levels were not different. These results showed that AGRP mRNA not only reflected differences between a bird's weight and its potential weight or set point, but also discriminated between differing feeding histories of birds at the same body weight. Therefore, AGRP expression potentially provides an integrated measure of food intake experience and an objective tool to assess a bird's perception of satiety in feeding regimes for improved poultry welfare.

Environment, leptin sensitivity, and hypothalamic plasticity

Regulation of feeding behavior has been a crucial step in the interplay between leptin and the arcuate nucleus of the hypothalamus (ARC). On one hand, the basic mechanisms regulating central and peripheral action of leptin are becoming increasingly clear. On the other hand, knowledge on how brain sensitivity to leptin can be modulated is only beginning to accumulate. This point is of paramount importance if one considers that pathologically obese subjects have high levels of plasmatic leptin. A possible strategy for exploring neural plasticity in the ARC is to act on environmental stimuli. This can be achieved with various protocols, namely, physical exercise, high-fat diet, caloric restriction, and environmental enrichment. Use of these protocols can, in turn, be exploited to isolate key molecules with translational potential. In the present review, we summarize present knowledge about the mechanisms of plasticity induced by the environment in the ARC. In addition, we also address the role of leptin in extrahypothalamic plasticity, in order to propose an integrated view of how a single diffusible factor can regulate diverse brain functions.

Systemic α-melanocyte-stimulating hormone administration decreases arthritis-induced anorexia and muscle wasting

Rheumatoid cachexia is associated with rheumatoid arthritis and it increases mortality and morbidity. Adjuvant-induced arthritis is an experimental model of rheumatoid arthritis that causes anorexia and muscle wasting. α-Melanocyte-stimulating hormone (α-MSH) has anti-inflammatory actions, and it is able to decrease inflammation in several inflammatory diseases including experimental arthritis. In this study we tested whether systemic α-MSH treatment is able to ameliorate cachexia in arthritic rats. On day 8 after adjuvant injection control and arthritic rats were treated with α-MSH (50 μg/rat ip) twice a day, until day 16 when all rats were euthanized. Arthritis decreased food intake, but it increased hypothalamic expression of neuropeptide Y (NPY) and Agouti-related peptides (AgRP) as well as interleukin-1β (IL-1β) and cyclooxygenase-2 (COX-2) mRNA. In arthritic rats, α-MSH decreased the external signs of arthritis and increased food intake (P < 0.01). In addition, α-MSH decreased hypothalamic expression of IL-1β, COX-2, proopiomelanocortin, and prohormone-converting (PC) enzymes PC1/3 and PC2 mRNA in arthritic rats. In control rats, α-MSH did not modify food intake or hypothalamic expression of aforementioned mRNA. α-MSH prevented arthritis-induced increase in gastrocnemius COX-2, muscle-specific RING-finger protein-1 (MuRF1), and atrogin-1 expression, and it increased fast myofiber size. In conclusion our data show that in arthritic rats peripheral α-MSH treatment has an anti-cachectic action increasing food intake and decreasing muscle wasting.

Intermittent fasting dietary restriction regimen negatively influences reproduction in young rats: a study of hypothalamo-hypophysial-gonadal axis

Nutritional infertility is very common in societies where women fail to eat enough to match their energy expenditure and such females often present as clinical cases of anorexia nervosa. The cellular and molecular mechanisms that link energy balance and central regulation of reproduction are still not well understood. Peripheral hormones such as estradiol, testosterone and leptin, as well as neuropeptides like kisspeptin and neuropeptides Y (NPY) play a potential role in regulation of reproduction and energy balance with their primary target converging on the hypothalamic median eminence-arcuate region. The present study was aimed to explore the effects of negative energy state resulting from intermittent fasting dietary restriction (IF-DR) regimen on complete hypothalamo-hypophysial-gonadal axis in Wistar strain young female and male rats. Significant changes in body weight, blood glucose, estrous cyclicity and serum estradiol, testosterone and LH level indicated the negative role of IF-DR regimen on reproduction in these young animals. Further, it was elucidated whether serum level of metabolic hormone, leptin plays a mechanistic role in suppressing hypothalamo-hypophysial-gonadal (HPG) axis via energy regulators, kisspeptin and NPY in rats on IF-DR regimen. We also studied the effect of IF-DR regimen on structural remodeling of GnRH axon terminals in median eminence region of hypothalamus along with the glial cell marker, GFAP and neuronal plasticity marker, PSA-NCAM using immunostaining, Western blotting and RT-PCR. Together these data suggest that IF-DR regimen negatively influences reproduction in young animals due to its adverse effects on complete hypothalamus-hypophysial-gonadal axis and may explain underlying mechanism(s) to understand the clinical basis of nutritional infertility.

Serum leptin is not correlated with body fat in severe food restriction

Leptin is an adipose-derived hormone with established roles in energy balance that can impact the response to refeeding after malnutrition. Although the amount of circulating leptin has traditionally been associated with the amount of adipose tissue, controversy exists as to whether this relationship is constant in both humans and animals and over a wide range of body composition. Our objective was to evaluate whether the leptin - body fat ratio is constant in the range of healthy to low body mass in female Wistar rats. Eight ad libitum fed (C) and eight food-restricted (FR) rats were compared over a period of four weeks. FR rats attained the target 75% of baseline body mass after the first two weeks, which was maintained for the remaining two weeks. Serum leptin and IGF-1 (ELISA) and body composition (DXA) were measured at baseline (t(0)) and once weekly for the remainder of the study (t(1)-t(4)). The leptin - body fat ratio was reduced during the two-week period of weight loss (t(0) = 0.036 ± 0.016 (ng·mL(-1))·g(-1) vs. t(1) = 0.010 ± 0.004 (ng·mL(-1))·g(-1) and t(2) = 0.015 ± 0.007 (ng·mL(-1))·g(-1), p < 0.05). Leptin concentration plateaued at its nadir (~0.24 (ng·mL(-1))·g(-1)) at fat mass < 22 g. IGF-1 was correlated with lean mass (r = 0.45, p < 0.05) and fat mass (r = 0.58, p < 0.05), regardless of body mass. We concluded that the leptin - body fat ratio was reduced early in food restriction and the correlation between these two variables was absent at low body fat.

You are what you eat: influence of type and amount of food consumed on central dopamine systems and the behavioral effects of direct- and indirect-acting dopamine receptor agonists

The important role of dopamine (DA) in mediating feeding behavior and the positive reinforcing effects of some drugs is well recognized. Less widely studied is how feeding conditions might impact the sensitivity of drugs acting on DA systems. Food restriction, for example, has often been the focus of aging and longevity studies; however, other studies have demonstrated that mild food restriction markedly increases sensitivity to direct- and indirect-acting DA receptor agonists. Moreover, it is becoming clear that not only the amount of food, but the type of food, is an important factor in modifying the effects of drugs. Given the increased consumption of high fat and sugary foods, studies are exploring how consumption of highly palatable food impacts DA neurochemistry and the effects of drugs acting on these systems. For example, eating high fat chow increases sensitivity to some behavioral effects of direct- as well as indirect-acting DA receptor agonists. A compelling mechanistic possibility is that central DA pathways that mediate the effects of some drugs are regulated by one or more of the endocrine hormones (e.g. insulin) that undergo marked changes during food restriction or after consuming high fat or sugary foods. Although traditionally recognized as an important signaling molecule in regulating energy homeostasis, insulin can also regulate DA neurochemistry. Because direct- and indirect-acting DA receptor drugs are used therapeutically and some are abused, a better understanding of how food intake impacts response to these drugs would likely facilitate improved treatment of clinical disorders and provide information that would be relevant to the causes of vulnerability to abuse drugs. This article is part of a Special Issue entitled 'Central Control of Food Intake'.

Influence of body weight and type of chow on the sensitivity of rats to the behavioral effects of the direct-acting dopamine-receptor agonist quinpirole

RATIONALE

Amount and type of food can alter dopamine systems and sensitivity to drugs acting on those systems.

OBJECTIVES

This study examined whether changes in body weight, food type, or both body weight and food type contribute to these effects.

METHODS

Rats had free or restricted access (increasing, decreasing, or maintaining body weight) to standard (5.7% fat) or high-fat (34.3%) chow.

RESULTS

In rats gaining weight with restricted or free access to high-fat chow, both limbs of the quinpirole yawning dose-response curve (0.0032-0.32 mg/kg) shifted leftward compared with rats eating standard chow. Restricting access to standard or high-fat chow (maintaining or decreasing body weight) decreased or eliminated quinpirole-induced yawning; within 1 week of resuming free feeding, sensitivity to quinpirole was restored, although the descending limb of the dose-response curve was shifted leftward in rats eating high-fat chow. These are not likely pharmacokinetic differences because quinpirole-induced hypothermia was not different among groups. PG01037 and L-741,626 antagonized the ascending and descending limbs of the quinpirole dose-response curve in rats eating high-fat chow, indicating D3 and D2 receptor mediation, respectively. Rats eating high-fat chow also developed insulin resistance.

CONCLUSIONS

These results show that amount and type of chow alter sensitivity to a direct-acting dopamine-receptor agonist with the impact of each factor depending on whether body weight increases, decreases, or is maintained. These data demonstrate that feeding conditions, perhaps related to insulin and insulin sensitivity, profoundly impact the actions of drugs acting on dopamine systems.

Biology's response to dieting: the impetus for weight regain

Dieting is the most common approach to losing weight for the majority of obese and overweight individuals. Restricting intake leads to weight loss in the short term, but, by itself, dieting has a relatively poor success rate for long-term weight reduction. Most obese people eventually regain the weight they have worked so hard to lose. Weight regain has emerged as one of the most significant obstacles for obesity therapeutics, undoubtedly perpetuating the epidemic of excess weight that now affects more than 60% of U.S. adults. In this review, we summarize the evidence of biology's role in the problem of weight regain. Biology's impact is first placed in context with other pressures known to affect body weight. Then, the biological adaptations to an energy-restricted, low-fat diet that are known to occur in the overweight and obese are reviewed, and an integrative picture of energy homeostasis after long-term weight reduction and during weight regain is presented. Finally, a novel model is proposed to explain the persistence of the "energy depletion" signal during the dynamic metabolic state of weight regain, when traditional adiposity signals no longer reflect stored energy in the periphery. The preponderance of evidence would suggest that the biological response to weight loss involves comprehensive, persistent, and redundant adaptations in energy homeostasis and that these adaptations underlie the high recidivism rate in obesity therapeutics. To be successful in the long term, our strategies for preventing weight regain may need to be just as comprehensive, persistent, and redundant, as the biological adaptations they are attempting to counter.

Central nervous system lipocalin-type prostaglandin D2-synthase is correlated with orexigenic neuropeptides, visceral adiposity and markers of the hypothalamic-pituitary-adrenal axis in obese humans

Lipocalin-type prostaglandin D2-synthase (L-PGDS) is the main producer of prostaglandin D2 (PGD2) in the central nervous system (CNS). Animal data suggest effects of central nervous L-PGDS in the regulation of food intake and obesity. No human data are available. We hypothesised that a role for CNS L-PGDS in metabolic function in humans would be reflected by correlations with known orexigenic neuropeptides. Cerebrospinal fluid (CSF) and serum samples were retrieved from 26 subjects in a weight loss study, comprising a 3-week dietary lead-in followed by 12-weeks of leptin or placebo treatment. At baseline, CSF L-PGDS was positively correlated with neuropeptide Y (NPY) (ρ = 0.695, P < 0.001, n = 26) and galanin (ρ = 0.651, P < 0.001) as well as visceral adipose tissue (ρ = 0.415, P = 0.035). Furthermore, CSF L-PGDS was inversely correlated with CSF leptin (ρ = -0.529, P = 0.005) and tended to correlate inversely with s.c. adipose tissue (ρ = -0.346, P = 0.084). As reported earlier, leptin treatment had no effect on weight loss and did not affect CSF L-PGDS or NPY levels compared to placebo. After weight loss, the change of CSF L-PGDS was significantly correlated with the change of CSF NPY levels (ρ = 0.604, P = 0.004, n = 21). Because of the correlation between baseline CSF L-PGDS levels and visceral adipose tissue, we examined associations with hypothalamic-pituitary-adrenal (HPA) axis components. Baseline CSF L-PGDS was correlated with corticotrophin-releasing hormone (ρ = 0.764, P < 0.001) and β-endorphin (ρ = 0.491, P < 0.001). By contrast, serum L-PGDS was not correlated with any of the measured variables either at baseline or after treatment. In summary, CSF L-PGDS was correlated with orexigenic neuropeptides, visceral fat distribution and central HPA axis mediators. The importance of these findings is unclear but could suggest a role for CSF L-PGDS in the regulation of visceral obesity by interaction with the neuroendocrine circuits regulating appetite and fat distribution. Further interventional studies will be needed to characterise these interactions in more detail.

Effects of chronic weight perturbation on energy homeostasis and brain structure in mice

Maintenance of reduced body weight in lean and obese human subjects results in the persistent decrease in energy expenditure below what can be accounted for by changes in body mass and composition. Genetic and developmental factors may determine a central nervous system (CNS)-mediated minimum threshold of somatic energy stores below which behavioral and metabolic compensations for weight loss are invoked. A critical question is whether this threshold can be altered by environmental influences and by what mechanisms such alterations might be achieved. We examined the bioenergetic, behavioral, and CNS structural responses to weight reduction of diet-induced obese (DIO) and never-obese (CON) C57BL/6J male mice. We found that weight-reduced (WR) DIO-WR and CON-WR animals showed reductions in energy expenditure, adjusted for body mass and composition, comparable (-10-15%) to those seen in human subjects. The proportion of excitatory synapses on arcuate nucleus proopiomelanocortin neurons was decreased by ∼50% in both DIO-WR and CON-WR mice. These data suggest that prolonged maintenance of an elevated body weight (fat) alters energy homeostatic systems to defend a higher level of body fat. The synaptic changes could provide a neural substrate for the disproportionate decline in energy expenditure in weight-reduced individuals. This response to chronic weight elevation may also occur in humans. The mouse model described here could help to identify the molecular/cellular mechanisms underlying both the defense mechanisms against sustained weight loss and the upward resetting of those mechanisms following sustained weight gain.

Leptin signaling in the failing and mechanically unloaded human heart

BACKGROUND

Increased circulating leptin is present in human heart failure, and leptin deficiency is linked to worse outcomes in chronic ischemic injury. In the present observational study, we tested the hypothesis that cardiac leptin production and signaling are increased in the failing human heart, and that mechanical unloading with a ventricular assist device (VAD) reverses these changes.

METHODS AND RESULTS

All studies were performed using human cardiac tissue obtained from (1) hearts not matched for transplantation (nonfailing), (2) at the time of cardiac transplant (failing), or (3) paired samples at the time of VAD implant (pre-VAD) and removal (post-VAD). The expression of brain naturetic peptide, leptin, leptin receptor, and tumor necrosis factor alpha mRNA was measured, and the protein expression of leptin and its receptor was examined by Western blot and immunofluorescent staining of cardiac sections. The assessment of leptin signaling was performed by measuring the phosphorylation state of the leptin receptor. The phosphorylation state of signal transducer and activator of transcription-3 and AMP-activated kinase proteins were also measured. All data are expressed as mean+/-SEM with a statistical significance in failing relative to nonfailing groups determined by Student independent t test, and the significance between pre- and post-VAD groups determined by paired t test. In failing human hearts, the mRNA expressions of leptin and its receptor were increased 5.4+/-0.3-fold (P<0.05) and 4.5+/-0.3-fold (P<0.05), respectively, with similar changes in protein. The phosphorylation state of both the leptin receptor and signal transducer and activator of transcription-3 proteins were increased 1.4+/-0.1-fold (P<0.05), and the level of phosphorylated AMP-activated kinase protein was increased 1.9+/-0.2-fold (P<0.05). Mechanical unloading of the failing human heart with a VAD resulted in no change in tumor necrosis factor alpha expression but a marked decrease in leptin production to 1.7+/-0.1% (P<0.05) and leptin receptor expression to 3.0+/-0.2% (P<0.05) of pre-VAD levels. Phosphorylation of the leptin receptor, signal transducer and activator of transcription-3, and AMP-activated kinase were also decreased to 45+/-7%, 75+/-8%, and 58+/-8% of pre-VAD values, respectively (P<0.05 for all values).

CONCLUSIONS

These results indicate that the failing human heart increases expression of leptin and its receptor and that mechanical unloading downregulates this increase. Further, a cardioprotective role for leptin in the failing human heart is suggested through the activation of signal transducer and activator of transcription-3 and AMP-activated kinase signaling.