Similar metabolic responses to calorie restriction in lean and obese Zucker rats

Energy Restriction Suppresses Muscle Protein Synthesis, and High Protein Diets Extend Protein Half-Lives Across the Muscle Proteome in Obese Female Zucker Rats

BACKGROUND

Effects of high protein (HP) diets and prolonged energy restriction (ER) on integrated muscle protein kinetics have not been determined.

OBJECTIVE

The objective of this study was to measure protein kinetics in response to prolonged ER and HP on muscle protein synthesis (MPS; absolute rates of synthesis) and muscle protein breakdown (MPB; half-lives) for proteins across the muscle proteome.

METHODS

Female 6-wk-old obese Zucker rats (Leprfa+/fa+, n = 48) were randomly assigned to one of four diets for 10 wk: ad libitum-standard protein (AL-SP; 15% kcal from protein), AL-HP (35% kcal from protein), ER-SP, and ER-HP (both fed 60% feed consumed by AL-SP). During week 10, heavy/deuterated water (2H2O) was administered by intraperitoneal injection, and isotopic steady-state was maintained via 2H2O in drinking water. Rats were euthanized after 1 wk, and mixed-MPS as well as fractional replacement rate (FRR), relative concentrations, and half-lives of individual muscle proteins were quantified in the gastrocnemius. Data were analyzed using 2-factor (energy × protein) ANOVAs and 2-tailed t-tests or binomial tests as appropriate.

RESULTS

Absolute MPS was lower in ER than AL for mixed-MPS (-29.6%; P < 0.001) and MPS of most proteins measured [23/26 myofibrillar, 48/60 cytoplasmic, and 46/60 mitochondrial (P < 0.05)], corresponding with lower gastrocnemius mass in ER compared with AL (-29.4%; P < 0.001). Although mixed-muscle protein half-life was not different between groups, prolonged half-lives were observed for most individual proteins in HP compared with SP in ER and AL (P < 0.001), corresponding with greater gastrocnemius mass in HP than SP (+5.3%; P = 0.043).

CONCLUSIONS

ER decreased absolute bulk MPS and most individual MPS rates compared with AL, and HP prolonged half-lives of most proteins across the proteome. These data suggest that HP, independent of energy intake, may reduce MPB, and reductions in MPS may contribute to lower gastrocnemius mass during ER by reducing protein deposition in obese female Zucker rats.

Taurine Improves Lipid Metabolism and Increases Resistance to Oxidative Stress

Calorie restriction (CR) by 30-40% decreases morbidity of age-related diseases and prolongs the lifespan of various laboratory animal species. Taurine (2-aminoethanesulfonic acid) is an important nutrient for lipid metabolism as it conjugates bile acids. Here, we investigated how taurine supplementation induces effects similar to the CR beneficial effects. Sprague Dawley rats were fed a diet containing different taurine concentrations (0, 0.5, 1.0, 3.0, 5.0%) to analyze the effects on growth, blood, and hepatic parameters. Rats fed a 5% taurine-supplemented diet showed a significant decrease in visceral fat weight, compared with control rats. Moreover, there were significant decreases in the serum total cholesterol, hepatic cholesterol and triglyceride concentrations in the taurine-supplemented groups compared with the control group in a dose-dependent manner. These results were associated with decreased mRNA expression of fatty acid synthase, and increased mRNA expression of carnitine palmitoyltransferase 1α. C57BL/6 mice were fed a 5.0% taurine-supplemented diet, and their response to 3-nitropropionic acid-induced oxidative stress was analyzed. The rate of weight loss due to oxidative stress decreased and the survival rate significantly increased in the taurine-supplemented groups compared with the control group. Finally, cells were treated with 100 μM taurine and their resistance to UV-induced oxidative stress was analyzed. We found that the p53-Chk1 pathway was less activated in taurine-treated cells compared with control cells. Furthermore, damage to cells evaluated by oxidative stress indicators revealed a reduction in oxidative damage with taurine treatment. These findings suggest that taurine partially acts as a CR mimetic.

Effects of rikkunshito supplementation on resistance to oxidative stress and lifespan in mice

AIM

Caloric restriction (CR), which limits the caloric intake to 60-70% of ad libitum (AL) amounts in various experimental animals, delays aging and extends the lifespan. We previously showed that neuropeptide Y (NPY), an appetite-stimulating peptide, is essential for the anti-oxidative and life-extending effects of CR. Here, we investigated whether a Japanese traditional herbal medicine, rikkunshito (RKT), which induces NPY activation, has CR-like life-extending effects.

METHODS

First, we evaluated the life-extending activity of RKT by examining the effect of long-term RKT administration on wild-type and NPY knockout mice. Furthermore, we tested whether RKT enhances CR-mediated beneficial effects under AL conditions with a normal diet and under mild CR conditions with a high-fat diet. We then used 3-nitropropionic acid or doxorubicin to induce oxidative stress, and analyzed the differences in survival rate, weight loss, gene expression and cellular oxidative damage among groups.

RESULTS

RKT administration did not extend the lifespan of wild-type or NPY knockout mice. In the oxidative stress models, RKT treatment upregulated anti-oxidative gene expression in the liver. Furthermore, RKT administration reduced the oxidative damage in the liver compared to the CR conditions alone. However, on induction of oxidative stress by 3-nitropropionic acid or doxorubicin, RKT administration did not affect the survival rate.

CONCLUSIONS

These results show that RKT administration only partially mimics the effects of CR at the cellular level, but not at the organismal level to increase the lifespan of mice. Geriatr Gerontol Int 2019; ••: ••-••.

Ghrelin mediated neuroprotection - A possible therapy for Parkinson's disease?

Parkinson's disease is a common age-related neurodegenerative disorder affecting 10 million people worldwide, but the mechanisms underlying its pathogenesis are still unclear. The disease is characterised by dopamine nerve cell loss in the mid-brain and intra-cellular accumulation of α-synuclein that results in motor and non-motor dysfunction. In this review, we discuss the neuroprotective effects of the stomach hormone, ghrelin, in models of Parkinson's disease. Recent findings suggest that it may modulate mitochondrial function and autophagic clearance of impaired organelle in response to changes in cellular energy balance. We consider the putative cellular mechanisms underlying ghrelin-action and the possible role of ghrelin mimetics in slowing or preventing Parkinson's disease progression. This article is part of the Special Issue entitled 'Metabolic Impairment as Risk Factors for Neurodegenerative Disorders.'

Energy homeostasis in leptin deficient Lepob/ob mice

Maintenance of reduced body weight is associated both with reduced energy expenditure per unit metabolic mass and increased hunger in mice and humans. Lowered circulating leptin concentration, due to decreased fat mass, provides a primary signal for this response. However, leptin deficient (Lep^ob/ob) mice (and leptin receptor deficient Zucker rats) reduce energy expenditure following weight reduction by a necessarily non-leptin dependent mechanisms. To identify these mechanisms, Lep^ob/ob mice were fed ad libitum (AL group; n = 21) or restricted to 3 kilocalories of chow per day (CR group, n = 21). After losing 20% of initial weight (in approximately 2 weeks), the CR mice were stabilized at 80% of initial body weight for two weeks by titrated refeeding, and then released from food restriction. CR mice conserved energy (-17% below predicted based on body mass and composition during the day; -52% at night); and, when released to ad libitum feeding, CR mice regained fat and lean mass (to AL levels) within 5 weeks. CR mice did so while their ad libitum caloric intake was equal to that of the AL animals. While calorically restricted, the CR mice had a significantly lower respiratory exchange ratio (RER = 0.89) compared to AL (0.94); after release to ad libitum feeding, RER was significantly higher (1.03) than in the AL group (0.93), consistent with their anabolic state. These results confirm that, in congenitally leptin deficient animals, leptin is not required for compensatory reduction in energy expenditure accompanying weight loss, but suggest that the hyperphagia of the weight-reduced state is leptin-dependent.

Soluble Fermentable Dietary Fibre (Pectin) Decreases Caloric Intake, Adiposity and Lipidaemia in High-Fat Diet-Induced Obese Rats

Consumption of a high fat diet promotes obesity and poor metabolic health, both of which may be improved by decreasing caloric intake. Satiety-inducing ingredients such as dietary fibre may be beneficial and this study investigates in diet-induced obese (DIO) rats the effects of high or low fat diet with or without soluble fermentable fibre (pectin). In two independently replicated experiments, young adult male DIO rats that had been reared on high fat diet (HF; 45% energy from fat) were given HF, low fat diet (LF; 10% energy from fat), HF with 10% w/w pectin (HF+P), or LF with 10% w/w pectin (LF+P) ad libitum for 4 weeks (n = 8/group/experiment). Food intake, body weight, body composition (by magnetic resonance imaging), plasma hormones, and plasma and liver lipid concentrations were measured. Caloric intake and body weight gain were greatest in HF, lower in LF and HF+P, and lowest in the LF+P group. Body fat mass increased in HF, was maintained in LF, but decreased significantly in LF+P and HF+P groups. Final plasma leptin, insulin, total cholesterol and triglycerides were lower, and plasma satiety hormone PYY concentrations were higher, in LF+P and HF+P than in LF and HF groups, respectively. Total fat and triglyceride concentrations in liver were greatest in HF, lower in LF and HF+P, and lowest in the LF+P group. Therefore, the inclusion of soluble fibre in a high fat (or low fat) diet promoted increased satiety and decreased caloric intake, weight gain, adiposity, lipidaemia, leptinaemia and insulinaemia. These data support the potential of fermentable dietary fibre for weight loss and improving metabolic health in obesity.

Differential expression of hypothalamic, metabolic and inflammatory genes in response to short-term calorie restriction in juvenile obese- and lean-prone JCR rats

Background:

Childhood obesity is an important early predictor of adult obesity and associated comorbidities. Common forms of obesity are underpinned by both environmental and genetic factors. However, the rising prevalence of obesity in genetically stable populations strongly suggests that contemporary lifestyle is a premier factor to the disease. In pediatric population, the current treatment/prevention options for obesity are lifestyle interventions such as caloric restriction (CR) and increase physical activity. In obese individuals, CR improves many metabolic parameters in peripheral tissues. Little is known about the effect of CR on the hypothalamus. This study aimed to assess the effect of CR on hypothalamic metabolic gene expression of young obese- and lean-prone animals.

Methods:

Male juvenile JCR:LA-cp obese-prone rats were freely fed (Obese-FF) or pair fed (Obese-FR) to lean-prone, free-feeding animals (Lean-FF). A group of lean-prone rats (Lean-FR) were matched for relative average degree of CR to Obese-FR rats.

Results:

In free-feeding conditions, obese-prone rats consumed more energy than lean-prone rats (P<0.001) and showed greater increases in body weight, fat mass, plasma glucose, insulin and lipids (P<0.01). These metabolic differences were associated with alterations of feeding-related neuropeptides expression in the hypothalamus, as well as pro-inflammatory cytokines and oxidative stress markers. When submitted to the same degree of CR, the two genotypes responded differently; hypothalamic inflammatory and oxidative stress gene expression was improved in Obese-FR, while it was worsened in Lean-FR rats.

Conclusions:

We demonstrate in JCR rats that the metabolic and inflammatory response of the brain to CR is genotype dependent.

TRAMP prostate tumor growth is slowed by walnut diets through altered IGF-1 levels, energy pathways, and cholesterol metabolism

Dietary changes could potentially reduce prostate cancer morbidity and mortality. Transgenic adenocarcinoma of the mouse prostate (TRAMP) prostate tumor responses to a 100 g of fat/kg diet (whole walnuts, walnut oil, and other oils; balanced for macronutrients, tocopherols [α-and γ]) for 18 weeks ad libitum were assessed. TRAMP mice (n=17 per group) were fed diets with 100 g fat from either whole walnuts (diet group WW), walnut-like fat (diet group WLF, oils blended to match walnut's fatty acid profile), or as walnut oil (diet group WO, pressed from the same walnuts as WW). Fasted plasma glucose was from tail vein blood, blood was obtained by cardiac puncture, and plasma stored frozen until analysis. Prostate (genitourinary intact [GUI]) was weighed and stored frozen at -80°C. Plasma triglyceride, lipoprotein cholesterol, plasma multianalyte levels (Myriad RBM Rat Metabolic MAP), prostate (GUI), tissue metabolites (Metabolon, Inc., Durham, NC, USA), and mRNA (by Illumina NGS) were determined. The prostate tumor size, plasma insulin-like growth factor-1 (IGF-1), high density lipoprotein, and total cholesterol all decreased significantly (P<.05) in both WW and WO compared to WLF. Both WW and WO versus WLF showed increased insulin sensitivity (Homeostasis Model Assessment [HOMA]), and tissue metabolomics found reduced glucose-6-phosphate, succinylcarnitine, and 4-hydroxybutyrate in these groups suggesting effects on cellular energy status. Tissue mRNA levels also showed changes suggestive of altered glucose metabolism with WW and WO diet groups having increased PCK1 and CIDEC mRNA expression, known for their roles in gluconeogenesis and increased insulin sensitivity, respectively. WW and WO group tissues also had increased MSMB mRNa a tumor suppressor and decreased COX-2 mRNA, both reported to inhibit prostate tumor growth. Walnuts reduced prostate tumor growth by affecting energy metabolism along with decreased plasma IGF-1 and cholesterol. These effects are not due to the walnut's N-3 fatty acids, but due to component(s) found in the walnut's fat component.

Chronological analysis of caloric restriction-induced alteration of fatty acid biosynthesis in white adipose tissue of rats

The beneficial actions of caloric restriction (CR) could be mediated in part by metabolic remodeling of white adipose tissue (WAT). Recently, we suggested that CR for 6 months increased the expressions of proteins involved in de novo fatty acid (FA) biosynthesis in WAT of 9-month-old rats. Herein, we compared the CR-induced chronological alterations of the expression of mRNAs and/or proteins involved in FA biosynthesis in the WAT and liver of rats subjected to CR starting from 3 months of age and their age-matched controls fed ad libitum. The findings suggested that CR was more effective on FA biosynthesis in WAT than in liver. In WAT, CR markedly increased the expressions of mRNAs and/or proteins involved in FA biosynthesis, including sterol regulatory element-binding protein 1c (SREBP1c), a master transcriptional regulator of FA biosynthesis, throughout the experimental period. Interestingly, the CR-enhanced upregulation was temporally attenuated at 5 months of age. CR markedly increased the nuclear phosphorylated form of Akt only at 3.5 months of age. In contrast, CR significantly reduced the expression of leptin at 9 months of age. The CR-induced upregulation was not observed in obese fa/fa Zucker rats homozygous for nonfunctional leptin receptor. Collectively, these data indicate that the V-shaped chronological alterations in WAT are regulated via SREBP1c, which is probably activated by CR duration-dependent modulation of both insulin and leptin signaling.

20 years of leptin: role of leptin in energy homeostasis in humans

The hyperphagia, low sympathetic nervous system tone, and decreased circulating concentrations of bioactive thyroid hormones that are common to states of congenital leptin deficiency and hypoleptinemia following and during weight loss suggest that the major physiological function of leptin is to signal states of negative energy balance and decreased energy stores. In weight-reduced humans, these phenotypes together with pronounced hypometabolism and increased parasympathetic nervous system tone create the optimal circumstance for weight regain. Based on the weight loss induced by leptin administration in states of leptin deficiency (obese) and observed similarity of phenotypes in states of congenital and dietary-induced states of hypoleptinemia (reduced obese), it has been suggested that exogenous leptin could potentially be useful in initiating, promoting, and sustaining weight reduction. However, the responses of human beings to exogenous leptin administration are dependent not only on extant energy stores but also on energy balance. Leptin administration to humans at usual weight has little, if any, effect on body weight while leptin administration during weight loss mitigates hunger, especially if given in supraphysiological doses during severe caloric restriction. Leptin repletion is most effective following weight loss by dietary restriction. In this state of weight stability but reduced energy stores, leptin at least partially reverses many of the metabolic, autonomic, neuroendocrine, and behavioral adaptations that favor weight regain. The major physiological function of leptin is to signal states of negative energy balance and decreased energy stores. Leptin, and pharmacotherapies affecting leptin signaling pathways, is likely to be most useful in sustaining weight loss.

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.

A key role for neuropeptide Y in lifespan extension and cancer suppression via dietary restriction

Knowledge of genes essential for the life-extending effect of dietary restriction (DR) in mammals is incomplete. In this study, we found that neuropeptide Y (Npy), which mediates physiological adaptations to energy deficits, is an essential link between DR and longevity in mice. The lifespan-prolonging effect of lifelong 30% DR was attenuated in Npy-null mice, as was the effect on the occurrence of spontaneous tumors and oxidative stress responses in comparison to wild-type mice. In contrast, the physiological processes activated during adaptation to DR, including inhibition of anabolic signaling molecules (insulin and insulin-like growth factor-1), modulation of adipokine and corticosterone levels, and preferential fatty acid oxidation, were unaffected by the absence of Npy. These results suggest a key role for Npy in mediating the effects of DR. We also provide evidence that most of the physiological adaptations to DR could be achieved in mice without Npy.

Calorie restriction attenuates cardiac remodeling and diastolic dysfunction in a rat model of metabolic syndrome

Calorie restriction (CR) can modulate the features of obesity-related metabolic and cardiovascular diseases. We have recently characterized DahlS.Z-Lepr(fa)/Lepr(fa) (DS/obese) rats, derived from a cross between Dahl salt-sensitive and Zucker rats, as a new animal model of metabolic syndrome. DS/obese rats develop hypertension and manifest left ventricular remodeling and diastolic dysfunction, as well as increased cardiac oxidative stress and inflammation. We have now investigated the effects of CR on cardiac pathophysiology in DS/obese rats. DS/obese rats were fed either normal laboratory chow ad libitum or a calorie-restricted diet (65% of the average food intake for ad libitum) from 9 to 13 weeks. Age-matched homozygous lean (DahlS.Z-Lepr(+)/Lepr(+) or DS/lean) littermates served as controls. CR reduced body weight in both DS/obese and DS/lean rats, as well as attenuated the development of hypertension in DS/obese rats without affecting blood pressure in DS/lean rats. CR also reduced body fat content, ameliorated left ventricular hypertrophy, fibrosis, and diastolic dysfunction, and attenuated cardiac oxidative stress and inflammation in DS/obese rats. In addition, it increased serum adiponectin concentration, as well as downregulated the expression of angiotensin-converting enzyme and angiotensin II type 1A receptor genes in the heart of DS/obese rats. Our results thus show that CR attenuated obesity and hypertension, as well as left ventricular remodeling and diastolic dysfunction in DS/obese rats, with these latter effects being associated with reduced cardiac oxidative stress and inflammation.

Greater insulin sensitivity in calorie restricted rats occurs with unaltered circulating levels of several important myokines and cytokines

Calorie restriction (CR; ~60% of ad libitum, AL intake) has been associated with substantial alterations in body composition and insulin sensitivity. Recently, several proteins that are secreted by nontraditional endocrine tissues, including skeletal muscle and other tissues, have been discovered to modulate energy metabolism, body composition, and insulin sensitivity. The aim of this study was to characterize the influence of CR by rats on plasma levels of six of these newly recognized metabolic hormones (BDNF, FGF21, IL-1β, myonectin, myostatin, and irisin). Body composition of 9-month old male Fischer-344/Brown Norway rats (AL and CR groups) was determined by nuclear magnetic resonance. Blood sampled from the carotid artery of unanesthetized rats was used to measure concentrations of glucose and plasma proteins. As expected, CR versus AL rats had significantly altered body composition (reduced percent fat mass, increased percent lean mass) and significantly improved insulin sensitivity (based on the homeostasis model assessment-estimated insulin resistance index). Also consistent with previous reports, CR compared to AL rats had significantly greater plasma levels of adiponectin and corticosterone. However, there were no significant diet-related differences in plasma levels of BDNF, FGF21, IL-1β, myonectin, myostatin, or irisin. In conclusion, these results indicate that alterations in plasma concentration of these six secreted proteins are not essential for the CR-related improvement in insulin sensitivity in rats.

Calorie restriction with a high-fat diet effectively attenuated inflammatory response and oxidative stress-related markers in obese tissues of the high diet fed rats

Obesity characterized by increased mass of adipose tissue leads to systemic inflammation. Calorie restriction (CR) improves parameters associated with immune response and antioxidant defense. We hypothesized that CR with a high fat diet (HFCR) regulates local and systemic inflammation and oxidative stress damage in a high fat diet induced obesity (HF group). We investigated effect of HFCR on inflammation and oxidative stress-related markers in liver and adipose tissues as well as adipokines in plasma. HFCR lowered liver triglyceride levels, total cholesterol levels, and the plasma leptin/adiponectin ratio to normal levels and improved glucose tolerance. HFCR also improved fatty liver and normalized adipocyte size and morphology. HFCR reduced lipid peroxidation and decreased the expression levels of inducible nitric oxide synthetase, cyclooxygenase-2, NF-E2-related factor, and heme oxygenase-1 in the liver. Moreover, HFCR suppressed the expression levels of C- reactive protein and manganese superoxide dismutase in the adipose tissue in the HF group. These results suggest that HFCR may have beneficial effects on inflammation and oxidative stress as well as lipid profiles in the HF diet induced obesity. Moreover, HFCR may be a good way to increase compliance in obese patients and to prevent obesity induced complications without changes in dietary pattern.

Fasting and postprandial conditions affect both fatty acids and lipid compositions in the hypothalamus and fat-soluble vitamins in the serum of male rats

The purpose of this study was to examine the effects of fasting and re-feeding on lipid derivative patterns in the hypothalamus, and on vitamin, cholesterol and malondialdehyde (MDA) levels in serum. Adult male Wistar albino rats were assigned (n = 6/group) as follows: normally-fed controls (CON), fasted for 24 h (24F), fasted for 48 h (48F), and fed normally for 2 d after fasting for 48 h (FAF). Biochemical measures were analyzed by gas chromatography (GC) and high performance liquid chromatography (HPLC). Our results demonstrate that hypothalamic saturated fatty acid (C16:0, C18:0) levels were lower, and unsaturated fatty acid (C22:6 n-3, C22:4 n-6, C20:4 n-6) levels were higher, in the 48F and FAF groups than in CON (). In addition, hypothalamic monounsaturated fatty acid (MUFA) levels were lower, and polyunsaturated fatty acids (PUFA) levels were higher, in 24F than in CON. Total hypothalamic lipids in both 24F and 48F were higher than CON, and cholesterol was elevated in the hypothalami of all experimental groups as compared to CON. Serum malondialdehyde was higher in fasted and FAF groups; 24F and 48F also had higher serum cholesterol levels, than CON (, ). Serum α-tocoferol, retinol and vitamin C values were lower in 48F than CON (). In conclusion, we demonstrate that feeding state can significantly alter brain fatty acid and lipid derivative levels, and serum concentrations of cholesterol and vitamins. These changes may consequently influence lipid peroxidation, fatty acid synthase or desaturase system in hypothalamic fields.

Development of calorie restriction mimetics as therapeutics for obesity, diabetes, inflammatory and neurodegenerative diseases

Calorie restriction (CR) is the most robust intervention that decreases morbidity and mortality, and thereby increases the lifespan of many organisms. Although the signaling pathways involved in the beneficial effects of CR are not yet fully understood. Several candidate pathways and key molecules have been identified. The effects of CR are highly conserved from lower organisms such as yeast to higher mammals such as rodents and monkeys. Recent studies have also demonstrated beneficial effects of CR in humans, although we need much longer studies to evaluate whether CR also increases the lifespan of humans. In reality, it is difficult for us to conduct CR interventions in humans because the subjects must be kept in a state of hunger and the duration of this state needed to achieve a clinically meaningful effect is still unknown. Thus, research in this field is focusing on the development of molecules that mimic the beneficial effects of CR without reducing food intake. Some of these candidate molecules include plant-derived functional chemicals (phyto-chemicals), synthetic small molecules, and endocrine molecules such as adipokines. Several studies have already shown that this research field may yield novel drugs for the treatment of age-related diseases such as diabetes. In this article, we describe the target pathways, candidate molecules, and strategies to develop CR mimetics.

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.

Ghrelin neutralization during fasting-refeeding cycle impairs the recuperation of body weight and alters hepatic energy metabolism

Ghrelin, a hormone whose levels increase during food deprivation, plays a pivotal role in the regulation of food intake, energy metabolism and storage, as well as in insulin sensitivity. Here, we investigated the effects of acyl-ghrelin neutralization with the acyl-ghrelin-binding compound NOX-B11(2) during the fasting-refeeding cycle. Our data demonstrate that ghrelin neutralization with NOX-B11(2) impairs recuperation of lost body weight after food deprivation. Analysis of enzymes involved in glucose and lipid metabolism in liver of fed, fasted and refed rats revealed that neutralization of acyl-ghrelin resulted in minor decreases in the enzymes of glycolytic and lipogenic pathways during fasting. However, during refeeding these enzymes as well as glycogen levels recovered more slowly when acyl-ghrelin was blocked. The high levels of ghrelin in response to food deprivation may contribute to an adequate decrease in hepatic glycolytic and lipogenic enzymes and aid in the recovery of body weight and energetic reserves once food becomes available after the fasting period.

Impaired hypothalamic regulation of endocrine function and delayed counterregulatory response to hypoglycemia in Magel2-null mice

Hypothalamic dysfunction may underlie endocrine abnormalities in Prader-Willi syndrome (PWS), a genetic disorder that features GH deficiency, obesity, and infertility. One of the genes typically inactivated in PWS, MAGEL2, is highly expressed in the hypothalamus. Mice deficient for Magel2 are obese with increased fat mass and decreased lean mass and have blunted circadian rhythm. Here, we demonstrate that Magel2-null mice have abnormalities of hypothalamic endocrine axes that recapitulate phenotypes in PWS. Magel2-null mice had elevated basal corticosterone levels, and although male Magel2-null mice had an intact corticosterone response to restraint and to insulin-induced hypoglycemia, female Magel2-null mice failed to respond to hypoglycemia with increased corticosterone. After insulin-induced hypoglycemia, Magel2-null mice of both sexes became more profoundly hypoglycemic, and female mice were slower to recover euglycemia, suggesting an impaired hypothalamic counterregulatory response. GH insufficiency can produce abnormal body composition, such as that seen in PWS and in Magel2-null mice. Male Magel2-null mice had Igf-I levels similar to control littermates. Female Magel2-null mice had low Igf-I levels and reduced GH release in response to stimulation with ghrelin. Female Magel2-null mice did respond to GHRH, suggesting that their GH deficiency has a hypothalamic rather than pituitary origin. Female Magel2-null mice also had higher serum adiponectin than expected, considering their increased fat mass, and thyroid (T(4)) levels were low. Together, these findings strongly suggest that loss of MAGEL2 contributes to endocrine dysfunction of hypothalamic origin in individuals with PWS.

Unilateral neuromodulation of the ventromedial hypothalamus of the rat through deep brain stimulation

This study offers evidence that long-term deep brain stimulation of the ventromedial hypothalamus (VMH) can alter weight gain in mammals without affecting feeding behavior. Animals stimulated unilaterally at high frequencies of 150 or 500 Hz demonstrated increased CO(2) production that decreased from prestimulation levels after the stimulation was removed. Animals stimulated for up to 6 weeks gained weight at a lower rate than normal animals or animals implanted with an electrode but not stimulated. Stimulated animals exhibited normal food and water consumption. A significant decrease in efficiency was observed during stimulation that coincided with an increase in the amount of feces produced. Whereas the weight of control animals was significantly different from week to week, the weight of stimulated animals did not change accordingly. These data suggest that the VMH may be a viable target for long-term deep brain stimulation for modulation of the neural mechanisms of metabolism. The potential therapeutic effects of deep brain stimulation of the hypothalamus are discussed.

Effects of periodontitis on aortic insulin resistance in an obese rat model

The combination of obesity and its associated risk factors, such as insulin resistance and inflammation, results in the development of atherosclerosis. However, the effects of periodontitis on atherosclerosis in an obese body remain unclear. The aim of the study was to investigate the effects of ligature-induced periodontitis in Zucker fatty rats on initiation of atherosclerosis by evaluating aortic insulin resistance. Zucker fatty rats (n=24) were divided into two groups. In the periodontitis group, periodontitis was ligature-induced for 4 weeks, whereas the control group was left unligated. After the 4-week experimental period, descending aorta was used for measuring the levels of lipid deposits, immunohistochemical analysis, and evaluation of gene expression. Levels of serum C-reactive protein (CRP), tumor necrosis factor-alpha (TNF-alpha), and insulin were also measured. Rats in the periodontitis group had significantly enhanced lipid deposits in the aorta, but not in the control group. Expression of suppressor of cytokine signaling 3, vascular cell adhesion molecule 1, reactive oxygen species, nitrotyrosine, and endothelin-1 in the periodontitis group was more intense than that in the control group. Significantly decreased levels of phosphatidylinositol 3-kinase (Pi3k) catalytic beta-polypeptide (Pi3kcb), Pi3kp85, and insulin receptor substrate 1 and 2 were observed in the periodontitis group. Levels of serum CRP and TNF-alpha were significantly increased in the periodontitis group. Under insulin-stimulated conditions, aorta in the periodontitis group altered the Akt phosphorylation. Periodontitis in obesity induced the initial stage of atherosclerosis and disturbed aortic insulin signaling.