Calorie restriction lowers body temperature in rhesus monkeys, consistent with a postulated anti-aging mechanism in rodents

Molecules affecting hypothalamic control of core body temperature in response to calorie intake

Core body temperature (CBT) and calorie intake are main components of energy homeostasis and two important regulators of health, longevity, and aging. In homeotherms, CBT can be influenced by calorie intake as food deprivation or calorie restriction (CR) lowers CBT whereas feeding has hyperthermic effects. The finding that in mice CBT prolonged lifespan independently of CR, suggested that the mechanisms modulating CBT may represent important regulators of aging. Here we summarize the current knowledge on the signaling molecules and their receptors that participate in the regulation of CBT responses to calorie intake. These include hypothalamic neuropeptides regulating feeding but also energy expenditure via modulation of thermogenesis. We also report studies indicating that nutrient signals can contribute to regulation of CBT by direct action on hypothalamic preoptic warm-sensitive neurons that in turn regulate adaptive thermogenesis and hence CBT. Finally, we show the role played by two orphans G protein-coupled receptor: GPR50 and GPR83, that were recently demonstrated to regulate temperature-dependent energy expenditure.

Metabolic and neuropsychiatric effects of calorie restriction and sirtuins

Most living organisms, including humans, age. Over time the ability to do physical and intellectual work deteriorates, and susceptibility to infectious, metabolic, and neurodegenerative diseases increases, which leads to general fitness decline and ultimately to death. Work in model organisms has demonstrated that genetic and environmental manipulations can prevent numerous age-associated diseases, improve health at advanced age, and increase life span. Calorie restriction (CR) (consumption of a diet with fewer calories but containing all the essential nutrients) is the most robust manipulation, genetic or environmental, to extend longevity and improve health parameters in laboratory animals. However, outside of the protected laboratory environment, the effects of CR are much less certain. Understanding the molecular mechanisms of CR may lead to the development of novel therapies to combat diseases of aging and to improve the quality of life. Sirtuins, a family of NAD(+)-dependent enzymes, mediate a number of metabolic and behavioral responses to CR and are intriguing targets for pharmaceutical interventions. We review the molecular understanding of CR; the role of sirtuins in CR; and the effects of sirtuins on physiology, mood, and behavior.

Of mice and men: the benefits of caloric restriction, exercise, and mimetics

During aging there is an increasing imbalance of energy intake and expenditure resulting in obesity, frailty, and metabolic disorders. For decades, research has shown that caloric restriction (CR) and exercise can postpone detrimental aspects of aging. These two interventions invoke a similar physiological signature involving pathways associated with stress responses and mitochondrial homeostasis. Nonetheless, CR is able to delay aging processes that result in an increase of both mean and maximum lifespan, whereas exercise primarily increases healthspan. Due to the strict dietary regime necessary to achieve the beneficial effects of CR, most studies to date have focused on rodents and non-human primates. As a consequence, there is vast interest in the development of compounds such as resveratrol, metformin and rapamycin that would activate the same metabolic- and stress-response pathways induced by these interventions without actually restricting caloric intake. Therefore the scope of this review is to (i) describe the benefits of CR and exercise in healthy individuals, (ii) discuss the role of these interventions in the diseased state, and (iii) examine some of the promising pharmacological alternatives such as CR- and exercise-mimetics.

A general model for ontogenetic growth under food restriction

Food restriction (FR) retards animals' growth. Understanding the underlying mechanisms of this phenomenon is important to conceptual problems in life-history theory, as well as to applied problems in animal husbandry and biomedicine. Despite a considerable amount of empirical data published since the 1930s, there is no relevant general theoretical framework that predicts how animals vary their energy budgets and life-history traits under FR. In this paper, we develop such a general quantitative model based on fundamental principles of metabolic energy allocation during ontogeny. This model predicts growth curves under varying conditions of FR, such as the compensatory growth, different age at which FR begins, its degree and its duration. Our model gives a quantitative explanation for the counterintuitive phenomenon that under FR, lower body temperature and lower metabolism lead to faster growth and larger adult size. This model also predicts that the animals experiencing FR reach the same fraction of their adult mass at the same age as their ad libitum counterparts. All predictions are well supported by empirical data from mammals and birds of varying body size, under different conditions of FR.

Calorie restriction and stroke

Stroke, a major cause of disability and mortality in the elderly, occurs when a cerebral blood vessel is occluded or ruptured, resulting in ischemic damage and death of brain cells. The injury mechanism involves metabolic and oxidative stress, excitotoxicity, apoptosis and inflammatory processes, including activation of glial cells and infiltration of leukocytes. In animal models, dietary energy restriction, by daily calorie reduction (CR) or intermittent fasting (IF), extends lifespan and decreases the development of age-related diseases. Dietary energy restriction may also benefit neurons, as suggested by experimental evidence showing that CR and IF protect neurons against degeneration in animal models. Recent findings by our group and others suggest the possibility that dietary energy restriction may protect against stroke induced brain injury, in part by inducing the expression of neurotrophic factors, such as brain-derived neurotrophic factor (BDNF) and basic fibroblast growth factor (bFGF); protein chaperones, including heat shock protein 70 (Hsp70) and glucose regulated protein 78 (GRP78); antioxidant enzymes, such as superoxide dismutases (SOD) and heme oxygenase-1 (HO-1), silent information regulator T1 (SIRT1), uncoupling proteins and anti-inflammatory cytokines. This article discusses the protective mechanisms activated by dietary energy restriction in ischemic stroke.

Metformin as a geroprotector

Abstract Geroprotectors are drugs that decrease the rate of aging and therefore extend life span. Metformin has been described as a geroprotector, and several studies have shown that metformin can slow down the rate of aging. The mechanisms behind the geroprotective effect of metformin are less established. The goal of this review is to investigate the evidence for the geroprotective effect of metformin and to describe the possible mechanisms behind it.

Long-term calorie restriction, but not endurance exercise, lowers core body temperature in humans

Reduction of body temperature has been proposed to contribute to the increased lifespan in calorie restricted animals and mice overexpressing the uncoupling protein-2 in hypocretin neurons. However, nothing is known regarding the long-term effects of calorie restriction (CR) with adequate nutrition on body temperature in humans. In this study, 24-hour core body temperature was measured every minute by using ingested telemetric capsules in 24 men and women (mean age 53.7±9.4 yrs) consuming a CR diet for an average of 6 years, 24 age- and sex-matched sedentary (WD) and 24 body fat-matched exercise-trained (EX) volunteers, who were eating Western diets. The CR and EX groups were significantly leaner than the WD group. Energy intake was lower in the CR group (1769±348 kcal/d) than in the WD (2302±668 kcal/d) and EX (2798±760 kcal/d) groups (P<0.0001). Mean 24-hour, day-time and night-time core body temperatures were all significantly lower in the CR group than in the WD and EX groups (P≤0.01). Long-term CR with adequate nutrition in lean and weight-stable healthy humans is associated with a sustained reduction in core body temperature, similar to that found in CR rodents and monkeys. This adaptation is likely due to CR itself, rather than to leanness, and may be involved in slowing the rate of aging.

Lifespan and glucose metabolism in insulin receptor mutant mice

Insulin/insulin-like growth factor type 1 signaling regulates lifespan and resistance to oxidative stress in worms, flies, and mammals. In a previous study, we revealed that insulin receptor (IR) mutant mice, which carry a homologous mutation found in the long-lived daf-2 mutant of Caenorhabditis elegans, showed enhanced resistance to oxidative stress cooperatively modulated by sex hormones and dietary signals (Baba et al., (2005)). We herein investigated the lifespan of IR mutant mice to evaluate the biological significance of insulin signaling in mice. Under normoxia, mutant male mice had a lifespan comparable to that of wild-type male mice. IR mutant female mice also showed a lifespan similar to that of wild-type female mice, in spite of the fact that the IR mutant female mice acquired more resistance to oxidative stress than IR mutant male mice. On the other hand, IR mutant male and female mice both showed insulin resistance with hyperinsulinemia, but they did not develop hyperglycemia throughout their entire lifespan. These data indicate that the IR mutation does not impact the lifespan in mice, thus suggesting that insulin signaling might have a limited effect on the lifespan of mice.

Calorie restriction and prevention of age-associated chronic disease

Life expectancy in the world has increased dramatically during the last century; the number of older adults is expected to rise while the number of youths will decline in the near future. This demographic shift has considerable public health and economic implications since aging is associated with the development of serious chronic diseases. Calorie restriction (CR) is the most effective nutritional intervention for slowing aging and preventing chronic disease in rodents. In non-human and human primates, CR with adequate nutrition protects against abdominal obesity, diabetes, hypertension and cardiovascular diseases. Cancer morbidity and mortality are also diminished in CR monkeys, and data obtained from individuals practicing long-term CR show a reduction of metabolic and hormonal factors associated with increased cancer risk.

A general life history theory for effects of caloric restriction on health maintenance

Background

Caloric restriction (CR) has been shown to keep organisms in a relatively youthful and healthy state compared to ad libitum fed counterparts, as well as to extend the lifespan of a diverse set of organisms. Several attempts have been made to understand the underlying mechanisms from the viewpoint of energy tradeoffs in organisms' life histories. However, most models are based on assumptions which are difficult to justify, or are endowed with free-adjusting parameters whose biological relevancy is unclear.

Results

In this paper, we derive a general quantitative, predictive model based on physiological data for endotherms. We test the hypothesis that an animal's state of health is correlated with biological mechanisms responsible for the maintenance of that animal's functional integrities. Such mechanisms require energy. By suppressing animals' caloric energy supply and biomass synthesis, CR alters animals' energy allocation strategies and channels additional energy to those maintenance mechanisms, therefore enhancing their performance. Our model corroborates the observation that CR's effects on health maintenance are positively correlated with the degree and duration of CR. Furthermore, our model shows that CR's effects on health maintenance are negatively correlated to the temperature drop observed in endothermic animals, and is positively correlated to animals' body masses. These predictions can be tested by further experimental research.

Conclusion

Our model reveals how animals will alter their energy budget when food availability is low, and offers better understanding of the tradeoffs between growth and somatic maintenance; therefore shedding new light on aging research from an energetic viewpoint.

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.

Phenotyping small animals as models for the human metabolic syndrome: thermoneutrality matters

It is standard practice in preclinical biomedical research to house mammalian model organisms at an ambient temperature substantially below the thermoneutral zone. These experimental studies are performed using animals that are chronically challenged by mild cold stress. This condition increases food intake, metabolic rate, sympathetic activity, blood pressure and heart rate. Furthermore, this condition alters the behavioral and physiological responses to drug administration, energy restriction and overfeeding. This paper will review these observations, which must be understood in the context of phenotyping small mammals to enhance our understanding of the biology of human disease.

Lipid overaccumulation and drastic insulin resistance in adult catch-up growth rats induced by nutrition promotion after undernutrition

This study was designed to explore the metabolic changes resulting from catch-up growth in adult (CUGA) induced by varying degrees of nutrition promotion after undernutrition and to confirm whether these changes are transient or not. The CUGA models were developed on rats refed on intakes of normal chow or high-fat diet after a period of caloric restriction. The growth of the rats measured by body weight and length stagnated during caloric restriction and then rapidly accelerated following refeeding. Catch-up growth in adult resulted in an increase in intramuscular and intrahepatic lipid content, visceral fat deposition, and insulin resistance, which is consistent with a transient rise in food efficiency during the early stage of refeeding. In addition, ectopic lipid deposition, visceral fat accumulation, and insulin resistance were more severe in rats refed the high-fat diet than rats refed the normal chow. These findings suggest that CUGA induced by rapid nutrition promotion could result in persistent lipid overaccumulation (increased visceral fat and ectopic lipid deposition) and drastic systemic insulin resistance. The effects of CUGA on metabolic characteristics are dependent on the type of diet that is used for refeeding, especially on the amount of fat intake.

Caloric restriction and longevity: effects of reduced body temperature

Caloric restriction (CR) causes a reduction in body temperature (T(b)) which is suggested to contribute to changes that increase lifespan. Moreover, low T(b) has been shown to improve health and longevity independent of CR. In this review we examine the connections between CR, T(b) and mechanisms that influence longevity and ageing. Recent findings regarding the overlapping mechanisms of CR and T(b) that benefit longevity are discussed, including changes in body composition, hormone regulation, and gene expression, as well as reductions in low-level inflammation and reactive oxygen species-induced molecular damage. This information is summarized in a model describing how CR and low T(b), both synergistically and independently, increase lifespan. Moreover, the nascent notion that the rate of ageing may be pre-programmed in response to environmental influences at critical periods of early development is also considered. Based on current evidence, it is concluded that low T(b) plays an integral role in mediating the effects of CR on health and longevity, and that low T(b) may exert independent biological changes that increase lifespan. Our understanding of the overlap between CR- and T(b)-mediated longevity remains incomplete and should be explored in future research.

Calorie restriction and aging in nonhuman primates

In the 75 years since the seminal observation of Clive McCay that restriction of calorie intake extends the lifespan of rats, a great deal has been learned about the effects of calorie restriction (CR; reduced intake of a nutritious diet) on aging in various short-lived animal models. Studies have demonstrated many beneficial effects of CR on health, the rate of aging, and longevity. Two prospective investigations of the effects of CR on long-lived nonhuman primate (NHP) species began nearly 25 years ago and are still under way. This review presents the design, methods, and main findings of these and other important contributing studies, which have generally revealed beneficial effects of CR on physiological function and the retardation of disease consistent with studies in other species. Specifically, prolonged CR appears to extend the lifespan of rhesus monkeys, which exhibited lower body fat; slower rate of muscle loss with age; lower incidence of neoplasia, cardiovascular disease, type 2 diabetes mellitus, and endometriosis; improved insulin sensitivity and glucose tolerance; and no apparent adverse effect on bone health, as well as a reduction in total energy expenditure. In addition, there are no reports of deleterious effects of CR on reproductive endpoints, and brain morphology is preserved by CR. Adrenal and thyroid hormone profiles are inconsistently affected. More research is needed to delineate the mechanisms of the desirable outcomes of CR and to develop interventions that can produce similar beneficial outcomes for humans. This research offers tremendous potential for producing novel insights into aging and risk of disease.

Body temperature as a mouse pharmacodynamic response to bombesin receptor subtype-3 agonists and other potential obesity treatments

Treatment of rodents with a bombesin receptor subtype-3 (BRS-3) agonist reduces food intake and increases fasting metabolic rate, causing weight loss with continued treatment. In small mammals, core body temperature (T(b)) is regulated in part by nutritional status, with a reduced T(b) during fasting. We report that fed Brs3 knockout mice have a lower T(b), which is discordant with their nutritional status. Treatment of wild-type mice with a BRS-3 agonist increased T(b), more so when the baseline T(b) was reduced such as by fasting or during the inactive phase of the light cycle. With repeated BRS-3 agonist dosing, the T(b) increase attenuated despite continued weight loss efficacy. The increase in T(b) was not prevented by inhibitors of prostaglandin E (PGE) production but was partially reduced by a β-adrenergic blocker. These results demonstrate that BRS-3 has a role in body temperature regulation, presumably secondary to its effect on energy metabolism, including effects on sympathetic tone. By making use of this phenomenon, the reversal of the fasting T(b) reduction was developed into a sensitive single-dose pharmacodynamic assay for BRS-3 agonism and other antiobesity compounds acting by various mechanisms, including sibutramine, cannabinoid-1, and melanin-concentrating hormone-1 receptor blockers, and melanocortin, β₃-adrenergic, and cholecystokinin-1 receptor agonists. These drugs increased both the fasted T(b) and the fasted, resting metabolic rates. The T(b) assay is a robust, information-rich assay that is simpler and has a greater throughput than measuring metabolic rate and is a practical, effective tool for drug discovery.

Design and conduct of the CALERIE study: comprehensive assessment of the long-term effects of reducing intake of energy

BACKGROUND

In a robust and consistent manner, sustained caloric restriction (CR) has been shown to retard the aging process in a variety of animal species. Nonhuman primate studies suggest that CR may have similar effects in longer-lived species. The CALERIE (Comprehensive Assessment of the Long-term Effects of Reducing Intake of Energy) research program is the first systematic investigation of CR in nonobese human beings. In the phase 2 study, it is hypothesized that 2 years of sustained CR, involving a 25% reduction of ad libitum energy intake, results in beneficial effects similar to those observed in animal studies. This article presents the design and implementation of this study.

METHODS

The study is a multicenter, parallel-group, randomized controlled trial. A sample of 225 participants (22.0 ≤ body mass index [BMI] < 28.0 kg/m(2)) is being enrolled with 2:1 allocation to CR.

RESULTS

An intensive dietary and behavioral intervention was developed to achieve 25% CR and sustain it over the 2 years. Adherence is monitored using a doubly labeled water technique. Primary outcomes are resting metabolic rate and core temperature, and are assessed at baseline and at 6-month intervals. Secondary outcomes address oxyradical formation, cardiovascular risk markers, insulin sensitivity and secretion, immune function, neuroendocrine function, quality of life and cognitive function. Biologic materials are stored in a central repository.

CONCLUSIONS

An intricate protocol has been developed to conduct this study. Procedures have been implemented to safeguard the integrity of the data and the conclusions drawn. The results will provide insight into the detrimental changes associated with the human aging process and how CR mitigates these effects.

The sirtuins in the pathogenesis of cancer

Aging is the natural trace that time leaves behind on life during blossom and maturation, culminating in senescence and death. This process is accompanied by a decline in the healthy function of multiple organ systems, leading to increased incidence and mortality from diseases such as diabetes, cancer, cardiovascular disease, and neurodegeneration. Based on the fact that both sirtuin expression and activity appear to be upregulated in some types of cancer while they are being downregulated in others, there is quite some controversy stirring up as to the role of sirtuins, acting as cancer suppressors in some cases while under other circumstances they may promote cellular malignancy. It is therefore currently quite unclear as to what extent and under which particular circumstances sirtuin activators and/or inhibitors will find their place in the treatment of age-related disease and cancer. In this review, we take an effort to bring together the highlights of sirtuin research in order to shed some light on the mechanistic impact that sirtuins have on the pathogenesis of cellular malignancy.

Metabolic depression and increased reactive oxygen species production by isolated mitochondria at moderately lower temperatures

Temperature (T) reduction increases lifespan, but the mechanisms are not understood. Because reactive oxygen species (ROS) contribute to aging, we hypothesized that lowering T might decrease mitochondrial ROS production. We measured respiratory response and ROS production in isolated mitochondria at 32, 35, and 37 °C. Lowering T decreased the rates of resting (state 4) and phosphorylating (state 3) respiration phases. Surprisingly, this respiratory slowdown was associated with an increase of ROS production and hydrogen peroxide release and with elevation of the mitochondrial membrane potential, ΔΨ(m). We also found that at lower T mitochondria produced more carbon-centered lipid radicals, a species known to activate uncoupling proteins. These data indicate that reduced mitochondrial ROS production is not one of the mechanisms mediating lifespan extension at lower T. They suggest instead that increased ROS leakage may mediate mitochondrial responses to hypothermia.

Neurodegenerative diseases: exercising toward neurogenesis and neuroregeneration

Currently, there is still no effective therapy for neurodegenerative diseases (NDD) such as Alzheimer's disease (AD) and Parkinson's disease (PD) despite intensive research and on-going clinical trials. Collectively, these diseases account for the bulk of health care burden associated with age-related neurodegenerative disorders. There is therefore an urgent need to further research into the molecular pathogenesis, histological differentiation, and clinical management of NDD. Importantly, there is also an urgency to understand the similarities and differences between these two diseases so as to identify the common or different upstream and downstream signaling pathways. In this review, the role iron play in NDD will be highlighted, as iron is key to a common underlying pathway in the production of oxidative stress. There is increasing evidence to suggest that oxidative stress predisposed cells to undergo damage to DNA, protein and lipid, and as such a common factor involved in the pathogenesis of AD and PD. The challenge then is to minimize elevated and uncontrolled oxidative stress levels while not affecting basal iron metabolism, as iron plays vital roles in sustaining cellular function. However, overload of iron results in increased oxidative stress due to the Fenton reaction. We discuss evidence to suggest that sustained exercise and diet restriction may be ways to slow the rate of neurodegeneration, by perhaps promoting neurogenesis or antioxidant-related pathways. It is also our intention to cover NDD in a broad sense, in the context of basic and clinical sciences to cater for both clinician's and the scientist's needs, and to highlight current research investigating exercise as a therapeutic or preventive measure.

Calorie restriction: what recent results suggest for the future of ageing research

BACKGROUND

Calorie Restriction (CR) research has expanded rapidly over the past few decades and CR remains the most highly reproducible, environmental intervention to improve health and extend lifespan in animal studies. Although many model organisms have consistently demonstrated positive responses to CR, it remains to be shown whether CR will extend lifespan in humans. Additionally, the current environment of excess caloric consumption and high incidence of overweight/obesity illustrate the improbable nature of the long-term adoption of a CR lifestyle by a significant proportion of the human population. Thus, the search for substances that can reproduce the beneficial physiologic responses of CR without a requisite calorie intake reduction, termed CR mimetics (CRMs), has gained momentum.

MATERIAL AND METHODS

Recent articles describing health and lifespan results of CR in nonhuman primates and short-term human studies are discussed. Additional consideration is given to the rapidly expanding search for CRMs.

RESULTS

The first results from a long-term, randomized, controlled CR study in nonhuman primates showing statistically significant benefits on longevity have now been reported. Additionally, positive results from short-term, randomized, controlled CR studies in humans are suggestive of potential health and longevity gains, while test of proposed CRMs (including rapamycin, resveratrol, 2-deoxyglucose and metformin) have shown both positive and mixed results in rodents.

CONCLUSION

Whether current positive results will translate into longevity gains for humans remains an open question. However, the apparent health benefits that have been observed with CR suggest that regardless of longevity gains, the promotion of healthy ageing and disease prevention may be attainable.

A rapidly occurring compensatory decrease in physical activity counteracts diet-induced weight loss in female monkeys

To study changes in energy balance occurring during the initial phases of dieting, 18 adult ovariectomized female monkeys were placed on a low-fat diet, and available calories were reduced by 30% compared with baseline consumption for 1 mo. Surprisingly, there was not significant weight loss; however, daily activity level (measured by accelerometry) decreased soon after diet initiation and reached statistical significance by the 4th wk of dieting (18 +/- 5.6% decrease, P = 0.02). During a 2nd mo of dieting, available calories were reduced by 60% compared with baseline consumption, leading to 6.4 +/- 1.7% weight loss and further suppression of activity. Metabolic rate decreased by 68 +/- 12 kcal/day, with decreased activity accounting for 41 +/- 9 kcal/day, and the metabolic activity of the weight lost accounting for 21 +/- 5 kcal/day. A second group of three monkeys was trained to run on a treadmill for 1 h/day, 5 days/wk, at 80% maximal capacity, leading to increased calorie expenditure of 69.6 +/- 10.7 kcal/day (equivalent to 49 kcal/day for 7 days). We conclude that a diet-induced decrease in physical activity is the primary mechanism the body uses to defend against diet-induced weight loss, and undertaking a level of exercise that is recommended to counteract weight gain and promote weight loss is able to prevent the compensatory decrease in physical activity-associated energy expenditure that slows diet-induced weight loss.

Impact of Moderate Calorie Restriction on the Reproductive Neuroendocrine Axis of Male Rhesus Macaques

The impact of moderate calorie restriction on reproductive neuroendocrine function was investigated in young adult male rhesus macaques (Macaca mulatta). The animals were subjected to either 30% calorie restriction (CR; n=5), or were fed a standard control diet (CON; n=5), starting during their peripubertal period. Plasma LH and testosterone concentrations were examined after 7 years of differential dietary treatment, and were found to be similar in both groups, both during the day and during the night. Microarray profiling of pituitary gland and testicular gene expression was performed after 8 years of treatment, using GeneChip® Rhesus Macaque Genome Arrays (Affymetrix), and showed very little effect of caloric restriction. Using a 1.5-fold difference threshold, our microarray analysis revealed differential expression of only 145 probesets in the pituitary gland and 260 in the testes, out of a total of >54,000. Semi-quantitative RT-PCR performed on pituitary gland mRNA corroborated the microarray findings for selected modulated genes, including TSH receptor (TSHR) and sperm-specific antigen 2 (SSFA2). Most notably, significantly lower expression of TSH receptor mRNA was observed in the pituitary of CR compared to CON animals. Also, significantly lower expression of the glycoprotein hormone alpha subunit (CGA) was observed in CR animals, and this finding was further corroborated using quantitative real-time RT-PCR. No significant diet-induced changes were detected in the testis for genes associated with reproduction, circadian clocks, or oxidative stress. There is mounting evidence that CR may promote health and longevity in a wide range of organisms, including nonhuman primates. Importantly, our data suggest that moderate CR has no obvious lasting detrimental effect on the reproductive neuroendocrine axis of long-lived primates, and has only a modest influence on pituitary and testicular gene expression.

Hypothalamic and dietary control of temperature-mediated longevity

Temperature is an important modulator of longevity and aging in both poikilotherms and homeotherm animals. In homeotherms, temperature homeostasis is regulated primarily in the preoptic area (POA) of the hypothalamus. This region receives and integrates peripheral, central and environmental signals and maintains a nearly constant core body temperature (T(core)) by regulating the autonomic and hormonal control of heat production and heat dissipation. Temperature sensitive neurons found in the POA are considered key elements of the neuronal circuitry modulating these effects. Nutrient homeostasis is also a hypothalamically regulated modulator of aging as well as one of the signals that can influence T(core) in homeotherms. Investigating the mechanisms of the regulation of nutrient and temperature homeostasis in the hypothalamus is important to understanding how these two elements of energy homeostasis influence longevity and aging as well as how aging can affect hypothalamic homeostatic mechanisms.

Ambient temperature influences aging in an annual fish (Nothobranchius rachovii)

Extending lifespan by lowering ambient temperature in the habitat has been shown in a variety of organisms. Its mechanism, however, remains elusive. In this study, we examined the survivorship and the aging process of the annual fish (Nothobranchius rachovii) reared under high (30 degrees C), moderate (25 degrees C) and low (20 degrees C) ambient temperatures. The results showed that low ambient temperatures prolong survivorship, whereas high ambient temperatures shorten survivorship. At low ambient temperature, expression of senescence-associated beta-galactosidase, lipofuscin, reactive oxygen species, lipid peroxidation, protein oxidation, mitochondrial density and ADP/ATP ratio were reduced compared with those reared at high and moderate temperatures, whereas catalase activity, Mn-superoxide dismutase activities, mitochondrial membrane potential and the levels of ATP, ADP, Sirt1 and Forkhead box O expression were elevated. The expression levels of Hsp70 and CIRP showed no significant difference under any of the ambient temperatures tested. We concluded that cellular metabolism, energy utilization and gene expression are altered at lower ambient temperature, which is associated with the extension of lifespan of the annual fish.

Could Sirt1-mediated epigenetic effects contribute to the longevity response to dietary restriction and be mimicked by other dietary interventions?

Dietary restriction (DR) increases lifespan in a range of evolutionarily distinct species. The polyphenol resveratrol may be a dietary mimetic of some effects of DR. The pivotal role of the mammalian histone deacetylase (HDAC) Sirt1, and its homologue in other organisms, in mediating the effects of both DR and resveratrol on lifespan/ageing suggests it may be the common conduit through which these dietary interventions influence ageing. We propose the novel hypothesis that effects of DR relevant to lifespan extension include maintenance of DNA methylation patterns through Sirt1-mediated epigenetic effects, and proffer the view that dietary components, including resveratrol, may mimic these actions.

Caloric restriction, SIRT1 and longevity

More than 70 years after its initial report, caloric restriction stands strong as the most consistent non-pharmacological intervention increasing lifespan and protecting against metabolic disease. Among the different mechanisms by which caloric restriction might act, Sir2/SIRT1 (Silent information regulator 2/Silent information regulator T1) has been the focus of much attention because of its ability to integrate sensing of the metabolic status with adaptive transcriptional outputs. This review focuses on gathered evidence suggesting that Sir2/SIRT1 is a key mediator of the beneficial effects of caloric restriction and addresses the main questions that still need to be answered to consolidate this hypothesis.

Effect of acute and chronic caloric restriction and metabolic glucoprivation on spontaneous physical activity in obesity-prone and obesity-resistant rats

Caloric restriction (CR) and metabolic glucoprivation affect spontaneous physical activity (SPA), but it's unknown whether these treatments similarly affect SPA in selectively bred obesity-prone (OP) and -resistant (OR) rats. OR rats have greater basal SPA and are more responsive to treatments that modulate SPA, such as orexin A administration. We hypothesized that OR rats would be more sensitive to other treatments modulating SPA. To test this, continuous 24-h SPA was measured before and during acute (24 h) and chronic (8 wk) CR in OR, OP, and Sprague-Dawley rats. Pharmacological glucoprivation was produced by injection of 2-deoxyglucose (2-DG), and SPA was measured 5 h postinjection. Acute CR increased SPA in all groups; however, the effect was dependent on the index of SPA and time interval during the 24-h time period. In contrast to OR rats, chronic CR increased distance traveled, ambulatory episodes, and time spent in ambulation and stereotypy during the time interval preceding anticipation of food in OP and Sprague-Dawley rats. Although the effects of 2-DG treatment on SPA were minimal, OR rats had significantly greater SPA than OP and Sprague-Dawley rats independent of treatment. That chronic CR failed to result in significant changes in SPA in OR rats suggests that these rats may be especially unresponsive to treatments modulating feeding. This insensitivity coupled with elevated basal SPA levels may in part mediate phenotypic traits of lean rats.

The scientific basis of caloric restriction leading to longer life

PURPOSE OF THE REVIEW

The present review discusses the current state of knowledge regarding the effects of calorie restriction in modulating metabolism and aging.

RECENT FINDINGS

There are currently no interventions or gene manipulations that can prevent, stop or reverse the aging process. However, there are a number of interventions that can slow down aging and prolong maximal lifespan up to 60% in experimental animals. Long-term calorie restriction without malnutrition and reduced function mutations in the insulin/IGF-1 signaling pathway are the most robust interventions known to increase maximal lifespan and healthspan in rodents. Although it is currently not known if long-term calorie restriction with adequate nutrition extends maximal lifespan in humans, we do know that long-term calorie restriction without malnutrition results in some of the same metabolic and hormonal adaptations related to longevity in calorie restriction rodents. Moreover, calorie restriction with adequate nutrition protects against obesity, type 2 diabetes, hypertension and atherosclerosis, which are leading causes of morbidity, disability and mortality.

SUMMARY

More studies are needed to elucidate the molecular mechanisms underlying the beneficial effects of calorie restriction in humans and to characterize new markers of aging/longevity that can assist clinicians in predicting mortality and morbidity of the general population.

Life span extension in mice by food restriction depends on an energy imbalance

In this study, our main objective was to determine whether energy restriction (ER) affects the rate of oxygen consumption of mice transiently or lastingly and whether metabolic rate plays a role in the ER-related extension of life span. We compared rates of resting oxygen consumption between C57BL/6 mice, whose life span is prolonged by ER, and the DBA/2 mice where it is not, at 6 and 23 mo of age, following 40% ER for 2 and 19 mo, respectively. Mice of the 2 strains that consumed food ad libitum (AL) had a similar body mass at the age of 4 mo and consumed similar amounts of food throughout the experiment; however, the body weight subsequently significantly increased (20%) in the C57BL/6 mice but did not increase significantly in the DBA/2 mice. The resting rate of oxygen consumption was normalized as per g body weight, lean body mass, organ weight, and per mouse. The resting rate of oxygen consumption at 6 mo was significantly higher in AL DBA/2 mice than the AL C57BL/6 mice for all of the criteria except organ weight. A similar difference in AL mice of the 2 strains was present at 23 mo when resting oxygen consumption was normalized to body weight. Resting oxygen consumption was lowered by ER in both age groups of each strain according to all 4 criteria used for normalization, except body weight in the C57BL/6 mice. The effect of ER on resting oxygen consumption was thus neither transient nor age or strain dependent. Our results suggest that ER-induced extension of life span occurs in the mouse genotype in which there is a positive imbalance between energy intake and energy expenditure.

Endocrine alterations in response to calorie restriction in humans

This review focuses on research involving calorie restriction (CR) in humans and the resulting changes observed in endocrine and neuroendocrine systems. Special emphasis is given to the clinical science studies designed to investigate the effects of controlled, high-quality, energy-restricted diets on both biomarkers of longevity and on the development of chronic diseases of human aging. Prolonged CR has been shown to extend both the median and maximal lifespan in a variety of lower species such as yeast, worms, fish, rats and mice. The biological mechanisms of this lifespan extension via CR are not fully elucidated, but possibly involve significant alterations in energy metabolism, oxidative damage, insulin sensitivity and functional changes in both neuroendocrine and autonomic nervous systems. Most of the difficulty in characterizing the systemic endocrine and neuroendocrine changes with aging and CR is due to the limited capability to collect large and multiple blood samples from small animals, which are usually shorter lived, and hence the most studied. Ongoing studies of prolonged CR in humans are now making it possible to analyze changes in the "biomarkers of aging" to unravel some of the mechanisms of its anti-aging phenomenon. With the incremental expansion of research endeavors in the area of energy restriction, data on the effects of CR in non-human primates and human subjects are becoming more accessible. Detailed analyses from controlled human trials involving long-term CR will allow investigators to link observed alterations from body composition and endocrine systems down to changes in molecular pathways and gene expression, with their possible effects on aging.

Caloric restriction improves memory in elderly humans

Animal studies suggest that diets low in calories and rich in unsaturated fatty acids (UFA) are beneficial for cognitive function in age. Here, we tested in a prospective interventional design whether the same effects can be induced in humans. Fifty healthy, normal- to overweight elderly subjects (29 females, mean age 60.5 years, mean body mass index 28 kg/m(2)) were stratified into 3 groups: (i) caloric restriction (30% reduction), (ii) relative increased intake of UFAs (20% increase, unchanged total fat), and (iii) control. Before and after 3 months of intervention, memory performance was assessed under standardized conditions. We found a significant increase in verbal memory scores after caloric restriction (mean increase 20%; P < 0.001), which was correlated with decreases in fasting plasma levels of insulin and high sensitive C-reactive protein, most pronounced in subjects with best adherence to the diet (all r values < -0.8; all P values <0.05). Levels of brain-derived neurotrophic factor remained unchanged. No significant memory changes were observed in the other 2 groups. This interventional trial demonstrates beneficial effects of caloric restriction on memory performance in healthy elderly subjects. Mechanisms underlying this improvement might include higher synaptic plasticity and stimulation of neurofacilitatory pathways in the brain because of improved insulin sensitivity and reduced inflammatory activity. Our study may help to generate novel prevention strategies to maintain cognitive functions into old age.

Resveratrol treatment in mice does not elicit the bradycardia and hypothermia associated with calorie restriction

Dietary supplementation with resveratrol may produce calorie restriction-like effects on metabolic and longevity endpoints in mice. In this study, we sought to determine whether resveratrol treatment elicited other hallmark changes associated with calorie restriction, namely bradycardia and decreased body temperature. We found that during short-term treatment, wild-type mice on a calorie-restricted diet experienced significant decreases in both heart rate and body temperature after only 1 day whereas those receiving resveratrol exhibited no such change after 1 wk. We also used ob/ob mice to study the effects of long-term treatment because previous studies had indicated the therapeutic value of resveratrol against the linked morbidities of obesity and diabetes. After 12 wk, resveratrol treatment had produced no changes in either heart rate or body temperature. Strikingly, and in contrast to previous findings, we found that resveratrol-treated mice had significantly reduced endurance in a treadmill test. Quantitative reverse transcriptase-polymerase chain reaction suggested that a proposed target of resveratrol, Sirt1, was activated in resveratrol-treated ob/ob mice. Thus, we conclude that the bradycardia and hypothermia associated with calorie restriction occur through mechanisms unaffected by the actions of resveratrol and that further studies are needed to examine the differential effects of resveratrol in a leptin-deficient background.

Energy expenditure in chow-fed female non-human primates of various weights

BACKGROUND

Until now no technology has been available to study energy metabolism in monkeys. The objective of this study was to determine daily energy expenditures (EE) and respiratory quotients (RQ) in female monkeys of various body weights and ages.

METHODS

16 socially reared Bonnet Macaque female monkeys [5.5 +/- 1.4 kg body weight, modified BMI (length measurement from head to base of the tail) = 28.8 +/- 6.7 kg/crown-rump length, m2 and 11.7 +/- 4.6 years] were placed in the primate Enhanced Metabolic Testing Activity Chamber (Model 3000a, EMTAC Inc. Santa Barbara, CA) for 22-hour measurements of EE (kcal/kg) and RQ (VCO2/VO2). All were fed monkey chow (4.03 kcal/g) ad-libitum under a 12/12 hour light/dark cycle. Metabolic data were corrected for differences in body weight. Results were divided into day (8-hours), dark (12 hours) and morning (2-hours) periods. Data analysis was conducted utilizing SPSS (Version 13).

RESULTS

Modified BMI negatively correlated with 22-hour energy expenditure in all monkeys (r = -0.80, p < 0.01). The large variability of daily energy intake (4.5 to 102.0 kcal/kg) necessitated division into two groups, non-eaters (< 13 kcal/kg) and eaters (> 23 kcal/kg). There were reductions (p < 0.05) in both 22-hour and dark period RQs in the "non-eaters" in comparison to those who were "eaters". Monkeys were also classified as "lean" (modified BMI < 25) or "obese" (modified BMI > 30). The obese group had lower EE (p < 0.05) during each time period and over the entire 22-hours (p < 0.05), in comparison to their lean counterparts.

CONCLUSION

The EMTAC proved to be a valuable tool for metabolic measurements in monkeys. The accuracy and sensitivity of the instrument allowed detection of subtle metabolic changes in relation to energy intake. Moreover, there is an association between a reduction of energy expenditure and a gain in body weight.

Differential gender effects of a reduced-calorie diet on systemic inflammatory and immune parameters in nonhuman primates

BACKGROUND AND OBJECTIVE

Dietary manipulation, including caloric restriction, has been shown to impact host response capabilities significantly, particularly in association with aging. This investigation compared systemic inflammatory and immune-response molecules in rhesus monkeys (Macaca mulatta).

MATERIAL AND METHODS

Monkeys on continuous long-term calorie-restricted diets and a matched group of animals on a control ad libitum diet, were examined for systemic response profiles including the effects of both gender and aging.

RESULTS

The results demonstrated that haptoglobin and alpha1-antiglycoprotein levels were elevated in the serum of male monkeys. Serum IgG responses to Campylobacter rectus, Actinobacillus actinomycetemcomitans and Porphyromonas gingivalis were significantly elevated in female monkeys. While only the antibody to Fusobacterium nucleatum was significantly affected by the calorie-restricted diet in female monkeys, antibody levels to Prevotella intermedia, C. rectus and Treponema denticola demonstrated a similar trend.

CONCLUSION

In this investigation, only certain serum antibody levels were influenced by the age of male animals, which was seemingly related to increasing clinical disease in this gender. More generally, analytes were modulated by gender and/or diet in this oral model system of mucosal microbial challenge.

Metabolic consequences of pregnancy-associated plasma protein-A deficiency in mice: exploring possible relationship to the longevity phenotype

Mice born with the deletion of the gene for pregnancy-associated plasma protein-A (PAPP-A), a model of reduced local IGF activity, live approximately 30% longer than their wild-type (WT) littermates. In this study, we investigated metabolic consequences of PAPP-A gene deletion and possible relationship to lifespan extension. Specifically, we determined whether 18-month-old PAPP-A knockout (KO) mice when compared with their WT littermates have reduced energy expenditure and/or altered glucose-insulin sensitivity. Food intake, and total energy expenditure and resting energy expenditure as measured by calorimetry were not different between PAPP-A KO and WT mice when subjected to the analysis of covariance with body weight as the covariate. However, there was an increase in spontaneous physical activity in PAPP-A KO mice. Both WT and PAPP-A KO mice exhibited mild insulin resistance with age, as assessed by fasting glucose/insulin ratios. Oral glucose tolerance and insulin sensitivity were not significantly different between the two groups of mice, although there appeared to be a decrease in the average size of the pancreatic islets in PAPP-A KO mice. Thus, neither reduced 'rate of living' nor altered glucose-insulin homeostasis can be considered key determinants of the enhanced longevity of PAPP-A KO mice. These findings are discussed in the context of those from other long-lived mouse models.

The effects of a calorie-reduced diet on periodontal inflammation and disease in a non-human primate model

BACKGROUND

Low-calorie diets are commonplace for reducing body weight. However, no information is available on the effects of a reduced-calorie diet on periodontal inflammation and disease. The purpose of this study was to evaluate the clinical effects of a long-term calorie-restriction (CR) diet on periodontitis in an animal model of periodontitis.

METHODS

Periodontitis was induced in 55 young, healthy, adult rhesus monkeys (Macaca mulatta) by tying 2.0 silk ligatures at the gingival margins of maxillary premolar/molar teeth. Animals on a CR diet (30% CR; N = 23) were compared to ad libitum diet controls (N = 32). Clinical measures, including the plaque index (PI), probing depth (PD), clinical attachment level (CAL), modified gingival index (GI), and bleeding on probing (BOP) were recorded at baseline and 1, 2, and 3 months after ligature placement.

RESULTS

Significant effects of CR were observed on the development of inflammation and the progression of periodontal destruction in this model. Compared to controls, CR resulted in a significant reduction in ligature-induced GI (P <0.0001), BOP (P <0.0015), PD (P <0.0016), and CAL (P <0.0038). Periodontal destruction, as measured by CAL, progressed significantly more slowly in the CR animals than in the controls (P <0.001).

CONCLUSIONS

These clinical findings are consistent with available evidence that CR has anti-inflammatory effects. Moreover, these experimental findings are the first observations, to the best of our knowledge, that CR dampens the inflammatory response and reduces active periodontal breakdown associated with an acute microbial challenge.

Considerations on temperature, longevity and aging

A modest reduction in body temperature prolongs longevity and may retard aging in both poikilotherm and homeotherm animals. Some of the possible mechanisms mediating these effects are considered here with respect to major aging models and theories.

Role of dFOXO in lifespan extension by dietary restriction in Drosophila melanogaster: not required, but its activity modulates the response

Dietary restriction (DR) increases lifespan in diverse organisms. However, the mechanisms by which DR increases survival are unclear. The insulin/IGF-like signaling (IIS) pathway has been implicated in the response to DR in some studies, while in others it has appeared to play little or no role. We used the fruitfly Drosophila melanogaster to investigate the responses to DR of flies mutant for the transcription factor dFOXO, the main transcription factor target of IIS. We found that lifespan extension by DR does not require dFOXO. However, flies with dFOXO overexpressed in the adult fat body showed an altered response to DR and behaved as though partially dietarily restricted. These results suggest that, although DR extends lifespan of flies in the absence of dFOXO, the presence of active dFOXO modulates the response to DR, possibly by modifying expression of its target genes, and may therefore mediate the normal response to DR.

Calorie restriction and cardiometabolic health

An epidemic of overweight/obesity and type 2 diabetes, caused by overeating nutrient-poor energy-dense foods and a sedentary lifestyle, is spreading rapidly throughout the world. Abdominal obesity represents a serious threat to health because it increases the risk of developing many chronic diseases, including cardiovascular disease and cancer. Calorie restriction (CR) with adequate nutrition improves cardiometabolic health, prevents tumorigenesis and increases life span in experimental animals. The purpose of this review is to evaluate the metabolic and clinical implications of CR with adequate nutrition in humans, within the context of data obtained in animal models. It is unlikely that information regarding the effect of CR on maximal life span in humans will become available in the foreseeable future. In young and middle-aged healthy individuals, however, CR causes many of the same cardiometabolic adaptations that occur in long-lived CR rodents, including decreased metabolic, hormonal and inflammatory risk factors for diabetes, hypertension, cardiovascular disease and cancer. Unraveling the mechanisms that link calorie intake and body composition with metabolism and aging will be a major step in understanding the age-dependency of a wide range of human diseases and will also contribute to improve the general quality of life at old ages.

Daily meal timing is not necessary for resetting the main circadian clock by calorie restriction

In rodents, entrainment and/or resetting by feeding of the central circadian clock, the suprachiasmatic nucleus (SCN), is more efficient when food cues arise from a timed calorie restriction. Because timed calorie restriction is associated with a single meal each day at the same time, its resetting properties on the SCN possibly depend on a combination of meal time-giving cues and hypocaloric conditions per se. To exclude any effect of daily meal timing in resetting by calorie restriction, the present study employed a model of ultradian feeding schedules, divided into six meals with different durations of food access (6 x 8-min versus 6 x 12-min meal schedule) every 4 h over the 24-h cycle. The effects of such an ultradian calorie restriction were evaluated on the rhythms of wheel-running activity (WRA) and body temperature (Tb) in rats. The results indicate that daily/circadian rhythms of WRA and Tb were shifted by a hypocaloric feeding distributed in six ultradian short meals (i.e. 6 x 8-min meal schedule), showing both phase advances and delays. The magnitude of phase shifts was positively correlated with body weight loss and level of day-time behavioural activity. By contrast, rats fed daily with six ultradian meals long enough (i.e. 6 x 12-min meal schedule) to prevent body weight loss, showed only small, if any, phase shifts in WRA and Tb rhythms. The results obtained reveal the potency of calorie restriction to reset the SCN clock without synchronisation to daily meal timing, highlighting functional links between metabolism, calorie restriction and the circadian timing system.

Effect of long-term caloric restriction on oxygen consumption and body temperature in two different strains of mice

The hypothesis, that a decrease in metabolic rate mediates the life span prolonging effect of caloric restriction (CR), was tested using two strains of mice, one of which, C57BL/6, exhibits life span extension as a result of CR, while the other, DBA/2, shows little or no effect. Comparisons of the rate of resting oxygen consumption and body temperature were made between the strains after they were fed ad libitum (AL) or maintained under 40% CR, from 4 to 16 months of age. Ad libitum-fed mice of the two strains weighed the same when young and consumed similar amounts of food throughout the experiment; however, the C57BL/6 mice weighed 25% more than DBA/2 mice at 15 months of age. The rate of oxygen consumption was normalized as per gram body weight, lean body mass or organ weight as well as per animal. The body temperature and the rate of oxygen consumption, expressed according to all of the four criteria, were decreased in the DBA/2 mice following CR. The C57BL/6 mice also showed a CR-related decrease in body temperature and in the rate of oxygen consumption per animal and when normalized according to lean body mass or organ weight. The results of this study indicate that CR indeed lowers the rate of metabolism; however, this effect by CR does not necessarily entail the prolongation of the life span of mice.