Effects of lifelong moderate caloric restriction on levels of neuropeptide Y, proopiomelanocortin, and galanin mRNA

Activity of the Hypothalamic Melanocortin System Decreases in Middle-Aged and Increases in Old Rats

Appearance of middle-aged obesity and aging anorexia both in humans and rodents suggests a role for regulatory alterations. Hypothalamic melanocortin agonist, α-melanocyte-stimulating hormone (α-MSH) produced in the arcuate nucleus (ARC), reduces body weight via inducing hypermetabolism and anorexia mainly through melanocortin 4 receptors (MC4Rs) in the paraventricular nucleus (PVN). Orexigenic ARC-derived agouti-related protein (AgRP) is an inverse agonist on MC4R in the PVN. Previously, we demonstrated that characteristic age-related shifts in the catabolic effects of α-MSH may contribute both to middle-aged obesity and aging anorexia. Responsiveness to α-MSH decreases in middle-aged rats compared with young adults, whereas in old age it rises again significantly. We hypothesized corresponding age-related dynamics of endogenous melanocortins. Therefore, we quantified mRNA gene expression and peptide or protein level of α-MSH, AgRP, and MC4R in the ARC and PVN of male Wistar rats of five age groups (from young to old). Immunofluorescence and quantitative reverse transcriptase polymerase chain reaction were applied. α-MSH and MC4R immunoreactivities in the ARC and PVN declined in middle-aged and increased together with their expressions in aging rats. AgRP gene expression but not its immunoreactivity increased in aging rats. Our results demonstrate that age-dependent changes of endogenous melanocortins contribute to middle-aged obesity and aging anorexia.

Mechanisms of the anorexia of aging-a review

Many, even healthy, older people fail to adequately regulate food intake and experience loss of weight. Aging-associated changes in the regulation of appetite and the lack of hunger have been termed as the anorexia of aging. The etiology of the anorexia of aging is multi-factorial and includes a combination of physiological changes associated with aging (decline in smell and taste, reduced central and peripheral drive to eat, delayed gastric emptying), pathological conditions (depression, dementia, somatic diseases, medications and iatrogenic interventions, oral-health status), and social factors (poverty, loneliness). However, exact mechanisms of the anorexia of aging remain to be elucidated. Many neurobiological mechanisms may be secondary to age-related changes in body composition and not associated with anorexia per se. Therefore, further studies on pathophysiological mechanisms of the anorexia of aging should employ accurate measurement of body fat and lean mass. The anorexia of aging is associated with protein-energy malnutrition, sarcopenia, frailty, functional deterioration, morbidity, and mortality. Since this symptom can lead to dramatic consequences, early identification and effective interventions are needed. One of the most important goals in the geriatric care is to optimize nutritional status of the elderly.

A New Strategy Using Rikkunshito to Treat Anorexia and Gastrointestinal Dysfunction

Because the clinical condition of gastrointestinal dysfunction, including functional dyspepsia, involves tangled combinations of pathologies, there are some cases of insufficient curative efficacy. Thus, traditional herbal medicines (Kampo medicines) uniquely developed in Japan are thought to contribute to medical treatment for upper gastrointestinal symptoms. Rikkunshito is a Kampo medicine often used to treat dyspeptic symptoms. Over the past few years, several studies have investigated the efficacy of rikkunshito for dysmotility, for example, upper abdominal complaints, in animals and humans. Rikkunshito ameliorated the decrease in gastric motility and anorexia in cisplatin-treated rats, stress-loaded mice, and selective serotonin reuptake inhibitor-treated rats by enhancing plasma ghrelin levels via serotonin2B/2C receptor antagonism. In addition, rikkunshito ameliorated the decrease in food intake in aged mice and stress-loaded decreased gastric motility via enhanced ghrelin receptor signaling. Several clinical studies revealed that rikkunshito was effective in ameliorating upper gastrointestinal symptoms, including dyspepsia, epigastric pain, and postprandial fullness. In this review, we discuss these studies and propose additional evidence-based research that may promote the clinical use of Kampo medicines, particularly rikkunshito, for treating anorexia and gastrointestinal dysfunction.

The homeostatic role of neuropeptide Y in immune function and its impact on mood and behaviour

Neuropeptide Y (NPY), one of the most abundant peptides in the nervous system, exerts its effects via five receptor types, termed Y1, Y2, Y4, Y5 and Y6. NPY's pleiotropic functions comprise the regulation of brain activity, mood, stress coping, ingestion, digestion, metabolism, vascular and immune function. Nerve-derived NPY directly affects immune cells while NPY also acts as a paracrine and autocrine immune mediator, because immune cells themselves are capable of producing and releasing NPY. NPY is able to induce immune activation or suppression, depending on a myriad of factors such as the Y receptors activated and cell types involved. There is an intricate relationship between psychological stress, mood disorders and the immune system. While stress represents a risk factor for the development of mood disorders, it exhibits diverse actions on the immune system as well. Conversely, inflammation is regarded as an internal stressor and is increasingly recognized to contribute to the pathogenesis of mood and metabolic disorders. Intriguingly, the cerebral NPY system has been found to protect against distinct disturbances in response to immune challenge, attenuating the sickness response and preventing the development of depression. Thus, NPY plays an important homeostatic role in balancing disturbances of physiological systems caused by peripheral immune challenge. This implication is particularly evident in the brain in which NPY counteracts the negative impact of immune challenge on mood, emotional processing and stress resilience. NPY thus acts as a unique signalling molecule in the interaction of the immune system with the brain in health and disease.

Calorie restriction increases lipopolysaccharide-induced neuropeptide Y immunolabeling and reduces microglial cell area in the arcuate hypothalamic nucleus

Calorie restriction (CR) increases longevity and elicits many health promoting benefits including delaying immunosenescence and reducing the incidence of age-related diseases. Although the mechanisms underlying the health-enhancing effects of CR are not known, a likely contributing factor is alterations in immune system functioning. CR suppresses lipopolysaccharide (LPS)-induced release of pro-inflammatory cytokines, blocks LPS-induced fever, and shifts hypothalamic signaling pathways to an anti-inflammatory bias. Furthermore, we have recently shown that CR attenuates LPS-stimulated microglial activation in the hypothalamic arcuate nucleus (ARC), a brain region containing neurons that synthesize neuropeptide Y (NPY), an orexigenic neuropeptide that is upregulated by a CR diet and has anti-inflammatory properties. To determine if increased NPY expression in the ARC following CR was associated with changes in microglial activation, a set of brain sections from mice that were exposed to 50% CR or ad libitum feeding for 28 days before being injected with LPS were immunostained for NPY. The density of NPY-immunolabeling was assessed across the rostrocaudal extent of the ARC and hypothalamic paraventricular nucleus (PVN). An adjacent set of sections were immunostained for ionized calcium-binding adapter molecule-1 (Iba1) and immunostained microglia in the ARC were digitally reconstructed to investigate the effects of CR on microglial morphology. We demonstrated that exposure to CR increased NPY expression in the ARC, but not the PVN. Digital reconstruction of microglia revealed that LPS increased Iba1 intensity in ad libitum fed mice but had no effect on Iba1 intensity in CR mice. CR also decreased the size of ARC microglial cells following LPS. Correlational analyses revealed strong associations between NPY and body temperature, and body temperature and microglia area. Together these results suggest that CR-induced changes in NPY are not directly involved in the suppression of LPS-induced microglial activation, however, NPY may indirectly affect microglial morphology through changes in body temperature.

Age versus nutritional state in the development of central leptin resistance

Leptin, a catabolic adiposity signal acts in the hypothalamus via suppressing food intake and inducing hypermetabolism. Age and obesity are accompanied by leptin resistance. The present study aimed to clarify which components of the catabolic leptin effects are influenced most strongly by aging and which ones by nutritional state-induced alterations in body composition. In our biotelemetric study the effects of a 7-day intracerebroventricular leptin infusion on various parameters of energy balance (food intake, body weight, oxygen consumption, heart rate and body temperature) were analyzed in male Wistar rats of different age-groups (from 3 to 24 months) and nutritional states (normally fed, diet-induced obese and calorie-restricted). Leptin resistance of older animals affected hypermetabolic actions, whereas leptin induced anorexia in all age-groups. Weight reducing effect of leptin diminished in middle-aged and aging animals to become significant again in the oldest group. In diet-induced obese rats leptin-induced hypermetabolism of the young rats and hypermetabolism plus anorexia of the aging ones were suppressed. Calorie-restriction reduced body weight and fat mass to a similar extent in all age-groups. It strongly enhanced leptin-induced hypermetabolism at all ages and prevented the manifestation of anorexigenic actions of leptin with the exception of the oldest group. This latter finding suggests an unexpected increase of responsiveness to anorexigenic leptin actions in old rats. Accordingly, anorexia and hypermetabolism change in disparate ways with aging. Nutritional state predominantly influences hypermetabolic leptin actions. Resistance to both hypermetabolic and anorexigenic actions were promoted by obesity, while calorie-restriction enhanced responsiveness to leptin, especially in old rats.

Calorie restriction attenuates LPS-induced sickness behavior and shifts hypothalamic signaling pathways to an anti-inflammatory bias

Calorie restriction (CR) has been demonstrated to alter cytokine levels; however, its potential to modify sickness behavior (fever, anorexia, cachexia) has not. The effect of CR on sickness behavior was examined in male C57BL/6J mice fed ad libitum or restricted 25% (CR25%) or restricted 50% (CR50%) in food intake for 28 days and injected with 50 μg/kg of LPS on day 29. Changes in body temperature, locomotor activity, body weight, and food intake were determined. A separate cohort of mice were fed ad libitum or CR50% for 28 days, and hypothalamic mRNA expression of inhibitory factor κB-α (IκB-α), cyclooxygenase-2 (COX-2), prostaglandin E(2) (PGE(2)), suppressor of cytokine signaling 3 (SOCS3), IL-10, neuropeptide Y (NPY), leptin, proopiomelanocortin (POMC), and corticotrophin-releasing hormone (CRH) were determined at 0, 2, and 4 h post-LPS. CR50% mice did not develop fevers, whereas the CR25% mice displayed a fever shorter in duration but with the same peak as the controls. Both CR25% and CR50% mice showed no sign of anorexia and reduced cachexia after LPS administration. Hypothalamic mRNA expression of NPY and CRH were both increased by severalfold in CR50% animals preinjection compared with controls. The CR50% mice did not demonstrate the expected rise in hypothalamic mRNA expression of COX-2, microsomal prostaglandin E synthase-1, POMC, or CRH 2 h post-LPS, and leptin expression was decreased at this time point. Increases in SOCS3, IL-10, and IκB-α expression in CR50% animals were enhanced compared with ad libitum-fed controls at 4 h post-LPS. CR results in a suppression of sickness behavior in a dose-dependent manner, which may be due to CR attenuating proinflammatory pathways and enhancing anti-inflammatory pathways.

Rikkunshito ameliorates the aging-associated decrease in ghrelin receptor reactivity via phosphodiesterase III inhibition

Aging is associated with decreased food intake, a phenomenon termed the anorexia of aging. In this study, we sought to clarify changes in peripheral and central appetite-related factors in aged mice. Furthermore, we investigated the effects of rikkunshito, a traditional Japanese medicine, on age-related anorexia. C57BL/6J mice that were 6 or 75 wk old were studied. We investigated changes in food intake, ghrelin and leptin levels, and the expression of appetite-related genes with age. In addition, we verified the effects of ghrelin, rikkunshito, phosphodiesterase 3 (PDE3), and phosphoinositide 3-kinase inhibitors on appetite. Food intake was significantly decreased in 75-wk-old mice compared with the 6-wk-old mice. In 75-wk-old mice, plasma acylated ghrelin levels under fasting conditions were lower than in 6-wk-old mice, whereas leptin levels under feeding conditions were substantially higher. The expression levels of hypothalamic preproghrelin under feeding conditions and the expression levels of neuropeptide Y and agouti-related protein under fasting conditions were lower compared with those of the 6-wk-old mice. Ghrelin supplementation (33 microg/kg) failed to increase food intake in 75-wk-old mice. Conversely, oral administration of LY294002, a phosphoinositide 3-kinase inhibitor, and cilostamide, a PDE3 inhibitor, increased food intake in 75-wk-old mice. Moreover, rikkunshito increased food intake in aged mice. The components of rikkunshito (nobiletin, isoliquiritigenin, and heptamethoxyflavone) had inhibitory effects on PDE3. These results suggest that dysregulation of ghrelin secretion and ghrelin resistance in the appetite control system occurred in aged mice and that rikkunshito ameliorated aging-associated anorexia via inhibition of PDE3.

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

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

Early hypothalamic response to age-dependent gene expression by calorie restriction

Molecular events linking the initial detection of calorie restriction (CR) to changes in gene expression throughout the organism that ultimately retard aging in CR animals are unknown. This study measured changes in gene expression induced by CR and by aging in the hypothalamus, which likely plays a central role in the initial perception of and response to CR. Hypothalamic expression profiling was done in young (4-6 months) ad libitum fed (AL), young CR (2.5-4.5 months of CR), and old (26-28 months) AL male C57BL/6 mice. CR altered the expression of 137 genes and aging altered 1222. Only 8 age-related genes were oppositely regulated by CR. To test whether reduced plasma glucose is a signal in altering hypothalamic gene expression, we examined GLUT4 transgenic mice (C57BL/6 background; 4-6 months), which have reduced plasma glucose similar to that of CR mice. Twenty-seven genes differed between transgenic and non-transgenic mice; nine of these were only altered by CR. The decreased plasma glucose had a limited role in CR mediated hypothalamic gene expression.

Endocrinology of anorexia of ageing

Appetite and food intake decrease with normal ageing, predisposing to the development of under-nutrition. Under-nutrition is common in older people and has been implicated in the development and progression of chronic diseases commonly affecting the elderly, as well as in increasing mortality. An understanding of the factors that contribute to the physiological and pathological declines in food intake in older people is likely to aid in the development of effective forms of prevention and treatment. Ageing affects many of the endocrine factors involved in the control of appetite and feeding but few studies have been performed in humans to clarify these changes. Possible hormonal causes of the anorexia of ageing include increased activity of cholecystokinin, leptin and various cytokines and reduced activity of ghrelin and testosterone.

Age-associated changes in hypothalamic and pituitary neuroendocrine gene expression in the rat

A cDNA membrane array displaying 1183 probes was used to detect hypothalamic and pituitary changes in gene expression accompanying ageing and age-associated pituitary macroadenomas. Four groups of male Sprague-Dawley rats (3-, 15-, 24-month-old and 24-month-old with prolactinoma) were compared in two independent hybridizations. cDNA array data were confirmed and completed by comparative reverse transcriptase-polymerase chain reaction on selected genes. The expression of 454 and 116 mRNAs was detected in hypothalamus and pituitary, respectively. Growth hormone (GH) mRNA alone represented 85% of total gene expression in the gland of young rats, and other pituitary hormone transcripts 2.8%, while melanin-concentrating hormone (MCH) mRNA, the most expressed neuropeptide transcript involved in neuroendocrine regulation, accounted for only 0.8% of total hypothalamic transcripts. The proportion of genes modified in the hypothalamus and pituitary was rather modest: 1.5% and 5.2%, respectively, for ageing per se, and 1.1% and 5.2% for age-associated macroprolactinomas. Among pituitary specific RNAs, GH mRNA expression was notably decreased with age. At the hypothalamic level, expression of genes directly involved in GH regulation, such as somatostatin and growth hormone-releasing hormone, was not altered, while neuropeptide transcripts involved in feeding behaviour [orexin/hypocretin, MCH, pro-opiomelanocortin (POMC), cocaine- and amphetamine-regulated transcript (CART)] were significantly altered. In addition, a few ubiquitous transcripts (hnRNP-K, PFKm, CCND 2, calponin and set) were differently affected in both tissues. Modifications in hypothalamic orexigenic (orexin, MCH) and anorexigenic (POMC, CART) gene expression are in keeping with an age-associated decrease in energy consumption but a higher one in the presence of macroprolactinomas.

Anti-aging effects of caloric restriction: Involvement of neuroendocrine adaptation by peripheral signaling

Many hormonal signals from peripheral tissues contribute to the regulation of energy homeostasis and food intake. These regulators including leptin, insulin, and ghrelin, modulate the orexigenic and anorexigenic neuropeptide expression in hypothalamic nuclei. The anti-aging effects of caloric restriction have been explained from an evolutional viewpoint of the adaptive response of the neuroendocrine and metabolic response systems to maximize survival during periods of food shortage. In organisms, excess energy is stored in adipose tissues as a triglyceride preparation for such survival situations. Adipose tissue has recently been recognized as an endocrine organ, and leptin, as secreted by adipocyte, seems to be an especially important factor for the adaptive response to fasting and neuroendocrine alterations under caloric restriction. In this review, we discuss the potential involvement of neuroendocrine modulators in longevity and the anti-aging effects of caloric restriction.

Opioid receptor blockade in rat nucleus tractus solitarius alters amygdala dynorphin gene expression

It has been suggested that an opioidergic feeding pathway exists between the nucleus of the solitary tract (NTS) and the central nucleus of the amygdala. We studied the following three groups of rats: 1) artificial cerebrospinal fluid (CSF) infused in the NTS, 2) naltrexone (100 microg/day) infused for 13 days in the NTS, and 3) artificial CSF infused in the NTS of rats pair fed to the naltrexone-infused group. Naltrexone administration resulted in a decrease in body weight and food intake. Also, naltrexone infusion increased dynorphin, but not enkephalin, gene expression in the amygdala, independent of the naltrexone-induced reduction in food intake. Gene expression of neuropeptide Y in the arcuate nucleus and neuropeptide Y peptide levels in the paraventricular nucleus did not change because of naltrexone infusion. However, naltrexone induced an increase in serum leptin compared with pair-fed controls. Thus chronic administration of naltrexone in the NTS increased dynorphin gene expression in the amygdala, further supporting an opioidergic feeding pathway between these two brain sites.

Leptin signaling and aging: insight from caloric restriction

Organisms have evolved neuroendocrine and metabolic response systems to enhance survival during periods of food shortage, which occur frequently in nature. The anti-aging effect of caloric restriction (CR) might derive from these adaptive responses to maximize organism survival. The present article discusses the potential role for leptin, a hormone secreted from adipocytes, as a key signal that induces the adaptive responses relevant to CR. Evidence indicates that a CR-induced reduction of the plasma leptin concentration suppresses the gonadal, somatotropic, and thyroidal axes, and activates the adrenal axis. Metabolic adaptation, a shift in fuel utilization mainly conducted in the liver, seems to require leptin signaling. Although alternative signaling pathways might also mediate the anti-aging effects of CR, leptin signaling could be a substantial pathway involved in these effects. Molecular dissection of the mechanisms underlying the effects of CR will contribute to a better understanding of the aging process, leading to the extension of a healthy lifespan in humans.

Parasites flicking the NPY gene on the host's switchboard: why NPY?

It was investigated whether up-regulation of the NPY gene by the schistosome Trichobilharzia ocellata in its snail host Lymnaea stagnalis redirects the host's energy flows. We cloned the cDNA encoding Lymnaea NPY (LyNPY), purified and sequenced the peptide, and used synthesized peptide for physiological and morphological studies. Increasing the LyNPY titer in nonparasitized snails (mimicking parasitosis) by 1) implantation of slow-release pellets and 2) injections suppressed reproductive activity and reduced growth in a dose- and time-dependent manner without affecting food intake. When the LyNPY titer was back to normal, reproduction and growth were resumed, coinciding with a transient increase of food intake serving to replenish glycogen stores. Observations on double-immunostained whole mount preparations of brains support these data. A close association was found between LyNPY-positive axons and axons both from ovulation hormone-producing neurons and molluscan insulin-like peptide-producing neurons involved in regulation of growth. As no synaptic(-like) contacts were observed, it is supposed that LyNPY acts nonsynaptically. No morphological interaction was found between LyNPY-positive axons and motoneurons innervating the feeding apparatus. Our data explain why it is an advantageous strategy for endoparasites to up-regulate the highly conserved NPY gene in their host.

The role of galanin in feeding behavior

Galanin inhibits food consumption in satiated rats. Discovered relatively recently, galanin is a 29-amino-acid neuropeptide, not homologous with any other known peptide. Three G-protein-linked galanin receptor subtypes have been cloned. This review summarizes the mechanisms by which exogenously administered galanin may stimulate ingestion, discusses pharmacological and genetic investigations of the role of endogenous galanin on feeding and body weight, and speculates on the therapeutic potential of non-peptide galanin receptor antagonists for the treatment of appetite disorders.