Beneficial Effects Of Caloric Restriction Research Articles

Glutathione is necessary to ensure benefits of calorie restriction during ageing in Saccharomyces cerevisiae

Calorie restriction increases longevity of mammals and yeasts but this mechanism remains unclear. In this study, the role of glutathione on lifespan extension induced by calorie restriction was investigated by using a Saccharomyces cerevisiae strain deficient in glutathione synthesis ( gsh1). We observed an increase in chronological lifespan of calorie-restricted gsh1 mutant cells, compared to WT (wild type) strain, which was associated with a reduction in the levels of oxidative stress biomarkers. The gsh1 strain showed an increase in cell yield under calorie restriction that was associated with a higher pyruvate kinase activity and a reduction in oxygen consumption and aconitase activity. This indicates that the respiratory metabolism is decreased in gsh1 mutant cells. The lifespan extension of gsh1 mutant cells did not represent an advantage at long term, since old cells of gsh1 strain showed a higher frequency of petite mutants. In addition, aged WT cells outlast aged gsh1 mutant cells in direct competition assays in a fresh medium. These results suggest that glutathione is required for the beneficial effects of calorie restriction on cellular longevity.

Increased aerobic metabolism is essential for the beneficial effects of caloric restriction on yeast life span

Calorie restriction is a dietary regimen capable of extending life span in a variety of multicellular organisms. A yeast model of calorie restriction has been developed in which limiting the concentration of glucose in the growth media of Saccharomyces cerevisiae leads to enhanced replicative and chronological longevity. Since S. cerevisiae are Crabtree-positive cells that present repression of aerobic catabolism when grown in high glucose concentrations, we investigated if this phenomenon participates in life span regulation in yeast. S. cerevisiae only exhibited an increase in chronological life span when incubated in limited concentrations of glucose. Limitation of galactose, raffinose or glycerol plus ethanol as substrates did not enhance life span. Furthermore, in Kluyveromyces lactis, a Crabtree-negative yeast, glucose limitation did not promote an enhancement of respiratory capacity nor a decrease in reactive oxygen species formation, as is characteristic of conditions of caloric restriction in S. cerevisiae. In addition, K. lactis did not present an increase in longevity when incubated in lower glucose concentrations. Altogether, our results indicate that release from repression of aerobic catabolism is essential for the beneficial effects of glucose limitation in the yeast calorie restriction model. Potential parallels between these changes in yeast and hormonal regulation of respiratory rates in animals are discussed.

Trans-Resveratrol: A Magical Elixir of Eternal Youth?

Trans-resveratrol or (E)-resveratrol [3,4',5 trihydroxy-trans-stilbene, t-RESV or (E)-RESV] is a natural component of Vitis vinifera L. (Vitaceae), abundant in the skin of grapes (but not in the flesh) and in the leaf epidermis and present in wines (especially red wines). In in vitro, ex vivo and in vivo experiments, t-RESV exhibits a number of biological activities, including anti inflammatory, antioxidant, platelet antiaggregatory and anticarcinogenic properties, and modulation of lipoprotein metabolism. Some of these activities have been implicated in the cardiovascular protective effects attributed to t-RESV and to red wine. Prior to 2002 there had been no previous studies describing the potential effects of t-RESV on the lifespan extension. However, in the last 5 years, several researchers have reported that t-RESV is a potent activator of sirtuin enzymatic activity, mimics the beneficial effects of caloric restriction (CR), retards the aging process and increases longevity in a number of organisms from different phyla such as yeasts, worms, flies and short-lived fish. In addition, t-RESV seems to be effective in delaying the onset of a variety of age-related diseases in mammals (e.g.: rodents). Therefore, this review will basically focus on the possible role of t-RESV to extend life duration and on some of the mechanisms by which t-RESV may act as an anti-aging agent.

Low Sirt1 expression, which is upregulated by fasting, in human adipose tissue from obese women

Calorie restriction increases the life span in a number of different organisms. This effect is dependent upon activation of the Sirt1 enzyme, and many of the beneficial effects of calorie restriction can be mimicked using resveratrol, which activates the Sirt1 enzyme. Nothing is known about this system in human adipose tissue; therefore, we investigated this system in human adipose tissue. Sirt1 mRNA was measured in adipose tissue biopsies from human volunteers before and after 6 days of total fasting. In addition, adipose tissue from lean and obese individuals was compared and in vitro investigations were performed. Long-term total fasting (6 days) of nine human volunteers increased Sirt1 mRNA expression in subcutaneous adipose tissue more than twofold (0.197-0.454 arbitrary units, P<0.05). Likewise, lean women (n=12) had more than twofold higher Sirt1 expression in subcutaneous adipose tissue compared to obese women (n=12; 0.33-0.73 arbitrary units, P<0.05). Sirt1 was equally expressed in the stroma-vascular fraction and the isolated adipocyte fraction. Finally, in vitro, we demonstrated that resveratrol (a Sirt1 activator) significantly enhanced the lipolytic effect of epinephrine in human adipose tissue (P<0.05). Human adipose tissue contains Sirt1 and the expression of Sirt1 can be regulated by calorie restriction as in other species. Furthermore, we demonstrated that resveratrol affects human fat-cell metabolism similar to the effects in rodents (that is, increased epinephrine induced lipolysis). These findings indicated that the beneficial effects of calorie restriction in humans might involve the activation of Sirt1. Thus, based on these findings, we propose that Sirt1 might play important roles for the beneficial effects of calorie restriction in humans.

Pituitary growth hormone suppression reduces resistin expression and enhances insulin effectiveness: Relationship with caloric restriction

Caloric restriction (CR) retards various age-dependent disorders, increases lifespan, and improves insulin activity in laboratory animals. Recently, adipocytes were found to act together as an active endocrine organ that produces various hormones called adipocytokines. The peripheral and central activities of these adipocytokines have been suggested to mediate the anti-aging effects of CR. Here, we tested this notion by analyzing the effect of CR and suppression of growth hormone/insulin-like growth factor-I (GH/IGF-I) axis on the expression of resistin, adiponectin, and adipsin genes by rat white adipose tissue (WAT). We found that CR and GH/IGF-I suppression markedly downregulated resistin gene expression. We also found plasma resistin levels correlated positively with pituitary GH mRNA expression levels. Our observations suggest that CR reduces resistin expression and increases insulin effectiveness in a GH/IGF-I-dependent manner. The beneficial effects of CR and GH/IGF-I suppression appear to be mediated, at least in part, by changes in glucose metabolism that result from reductions in plasma resistin levels.

What is Xenohormesis?

Polyphenols such as resveratrol and quercetin, which are produced by stressed plants, activate sirtuin enzymes and extend the lifespan of fungi and animals, ostensibly by mimicking the beneficial effects of caloric restriction. This observation raises an interesting question: Why should foreign molecules that are non-nutritive and seemingly unrelated to any endogenous molecule modulate the same biochemical pathways that mediate the response to an energy deficit? A possible explanation is that the sirtuin enzymes have evolved to respond to plant stress molecules as indicators of an impending deterioration of the environment. This idea has become known as the Xenohormesis Hypothesis, the name stemming from a combination of the prefix xeno-(for stranger) with hormesis (a protective response induced by mild stress). Here we review the evidence for xenohormesis in a broader context, taking into account the diverse spectrum of phytochemicals to which animals are exposed. We also consider alternative hypotheses that may explain some of the beneficial effects of plant-based foods. We suggest that xenohormesis, defined as an adaptive response in the physiology of an organism to molecular cues that are neither nutritive nor direct stressors, most likely occurs at some level. Whether this can fully or partially account for the beneficial effects of resveratrol and other phytochemicals remains to be seen. However, there is already sufficient cause to re-evaluate the relationship between complex organisms, including humans and their food.

Silencing Metabolic Disorders by Novel SIRT1 Activators

SIRT1, a NAD(+)-dependent protein deacetylase that regulates transcription factors involved in key cellular processes, has been implicated as a mediator of the beneficial effects of calorie restriction. In a recent issue of Nature, Milne et al. (2007) describe novel potent activators of SIRT1, whose administration to insulin-resistant animals improves glucose homeostasis.

The Ischemic Heart

Caloric restriction has emerged as an effective strategy for lengthening lifespan in a variety of species.1 In mammals, one mechanism for this phenomenon may be the prevention of detrimental age-related alterations in cellular function1 and presumably subsequent improvement in organ function. The effects of caloric restriction on the heart, at least in rats and mice, involve a number of changes in gene expression that are beneficial to the aged cardiomyocyte2 and/or protect the heart from ischemic injury.3 Although it is likely that all of the beneficial mediators of caloric restriction have not been identified, a number of proteins in the mammalian sirtuin family may play key roles in the regulation of health and longevity.4 In addition, recent evidence has suggested that alterations in whole-body energy metabolism contribute to the beneficial effects of caloric restriction.5 Indeed, caloric restriction in mammals leads to loss of adipose tissue and dramatically alters the action of this endocrine organ.6 As such, caloric restriction contributes to changes in adipose tissue–derived hormone (adipokine) secretion, which can govern whole-body metabolism.7 Furthermore, studies using isolated cardiac myocytes suggest that these adipokines may exert direct end-organ effects that are independent from alterations in whole-body metabolism.8–10 One adipokine that is significantly increased during caloric restriction is adiponectin.11 Previous work has shown that adiponectin exerts a host of protective effects on the cardiovascular system12 and as such may be an essential component mediating the effects of caloric restriction. Article p 2809 The focus on adiponectin in the cardiovascular system has been due largely to the fact that in humans, circulating adiponectin levels are negatively correlated with increased body mass index.13 Because increased body mass index is associated with a number of obesity-linked disorders, including cardiovascular disease, the reduction in serum …

Role of Insulin and Growth Hormone/Insulin-Like Growth Factor-I Signaling in Lifespan Extension: Rodent Longevity Models for Studying Aging and Calorie Restriction

Insulin/insulin-like growth factor-I (IGF-I) pathways are recognized as critical signaling pathways involved in the control of lifespans in lower organisms to mammals. Caloric restriction (CR) reduces plasma concentration of insulin, growth hormone (GH), and IGF-I. CR retards various age-dependent disorders such as nuerodegenerative diseases and extends lifespan in laboratory rodents. These beneficial effects of CR are partly mimicked in spontaneous or genetically engineered rodent models of reduced insulin and GH/IGF-I axis. Most of these long-living rodents show increased insulin sensitivity; however, recent study has revealed that some other rodents show normal or reduced insulin sensitivity. Thus, increased insulin sensitivity might be not prerequisite for lifespan extension in insulin/GH/IGF-I altered longevity rodent models. These results highlighted that, for lifespan extension, the intracellular signaling molecules of insulin/GH/IGF-I pathways might be more important than actual peripheral or systemic insulin action.

Is Sirt1 a miracle bullet for longevity?

The Sir2 (silent information regulator 2) family of nicotinamide adenine dinucleotide-dependent deacetylases has been implicated in the regulation of aging and longevity across a wide variety of organisms. Although controversial, Sir2 proteins have also been implicated as key mediators for the beneficial effects of caloric restriction (CR) on aging and longevity. In this issue, Bordone et al. report that transgenic mice in which the mammalian Sir2 ortholog Sirt1 is overexpressed mimic the physiological changes in response to CR. These findings have important implications for the development of CR mimetics and perhaps also for lifespan extension.

Sirtuins in mammals: insights into their biological function

Sirtuins are a conserved family of proteins found in all domains of life. The first known sirtuin, Sir2 (silent information regulator 2) of Saccharomyces cerevisiae, from which the family derives its name, regulates ribosomal DNA recombination, gene silencing, DNA repair, chromosomal stability and longevity. Sir2 homologues also modulate lifespan in worms and flies, and may underlie the beneficial effects of caloric restriction, the only regimen that slows aging and extends lifespan of most classes of organism, including mammals. Sirtuins have gained considerable attention for their impact on mammalian physiology, since they may provide novel targets for treating diseases associated with aging and perhaps extend human lifespan. In this review we describe our current understanding of the biological function of the seven mammalian sirtuins, SIRT1-7, and we will also discuss their potential as mediators of caloric restriction and as pharmacological targets to delay and treat human age-related diseases.

Could pathogens be nutrients for lymphoid cells?

Metabolic and immune systems are very important for a living organism to survive. Since they play crucial roles in maintaining homeostasis, both systems work interdependently. In metabolic disorders like obesity and related diseases, lot of reports have been published about immune system impairment. In addition, in the case of malnutrition and calorie restriction, immune system is affected through several mechanisms. Different from the current point of view, I propose an unusual way of thinking about the relationship between immune and metabolic systems. The nutrient-based ecosystemic balance; the simple desires and rules like feeding or reproduction underlying very complex relations among species; the beneficial effects of caloric restriction; and the similarities between the pathways contributing obesity and infection made me look from a different perspective. Based on ecology and systems thinking, the present hypotheses suggest that pathologic organisms could be a kind of dietary source for lymphoid cells. If it is true, it will bring new and hopeful insights to all events related to metabolic and immune systems. At first, new mechanisms could be improved to defeat unbeatable organisms like Mycobacterium tuberculosis or HIV. The unphagocytosed organisms could be unknown tastes for our body's defenders. For example, the lymphoid cells could be classified as virovores, bacterivores, or fungivores like herbivores, and carnivores. Secondly, this basic relation could be used to solve huge problems caused by obesity related disorders like diabetes, because insulin would play more important roles for lymphoid cells while regulating the blood glucose level if the hypothesis is true. And the persistence of hyperglycemia would mainly effect lymphoid cells according to the current hypothesis.

Resveratrol improves health and survival of mice on a high-calorie diet

Resveratrol (3,5,4'-trihydroxystilbene) extends the lifespan of diverse species including Saccharomyces cerevisiae, Caenorhabditis elegans and Drosophila melanogaster. In these organisms, lifespan extension is dependent on Sir2, a conserved deacetylase proposed to underlie the beneficial effects of caloric restriction. Here we show that resveratrol shifts the physiology of middle-aged mice on a high-calorie diet towards that of mice on a standard diet and significantly increases their survival. Resveratrol produces changes associated with longer lifespan, including increased insulin sensitivity, reduced insulin-like growth factor-1 (IGF-I) levels, increased AMP-activated protein kinase (AMPK) and peroxisome proliferator-activated receptor-gamma coactivator 1alpha (PGC-1alpha) activity, increased mitochondrial number, and improved motor function. Parametric analysis of gene set enrichment revealed that resveratrol opposed the effects of the high-calorie diet in 144 out of 153 significantly altered pathways. These data show that improving general health in mammals using small molecules is an attainable goal, and point to new approaches for treating obesity-related disorders and diseases of ageing.

Coordinated multitissue transcriptional and plasma metabonomic profiles following acute caloric restriction in mice

Caloric restriction (CR) increases healthy life span in a range of organisms. The underlying mechanisms are not understood but appear to include changes in gene expression, protein function, and metabolism. Recent studies demonstrate that acute CR alters mortality rates within days in flies. Multitissue transcriptional changes and concomitant metabolic responses to acute CR have not been described. We generated whole genome RNA transcript profiles in liver, skeletal muscle, colon, and hypothalamus and simultaneously measured plasma metabolites using proton nuclear magnetic resonance in mice subjected to acute CR. Liver and muscle showed increased gene expressions associated with fatty acid metabolism and a reduction in those involved in hepatic lipid biosynthesis. Glucogenic amino acids increased in plasma, and gene expression for hepatic gluconeogenesis was enhanced. Increased expression of genes for hormone-mediated signaling and decreased expression of genes involved in protein binding and development occurred in hypothalamus. Cell proliferation genes were decreased and cellular transport genes increased in colon. Acute CR captured many, but not all, hepatic transcriptional changes of long-term CR. Our findings demonstrate a clear transcriptional response across multiple tissues during acute CR, with congruent plasma metabolite changes. Liver and muscle switched gene expression away from energetically expensive biosynthetic processes toward energy conservation and utilization processes, including fatty acid metabolism and gluconeogenesis. Both muscle and colon switched gene expression away from cellular proliferation. Mice undergoing acute CR rapidly adopt many transcriptional and metabolic changes of long-term CR, suggesting that the beneficial effects of CR may require only a short-term reduction in caloric intake.

Cardiovascular disease could be contained based on currently available data!

Largely due to better control of infectious diseases and significant advances in biomedical research, life expectancy worldwide has increased dramatically in the last three decades. However, as the average age of the population has risen, the incidence of chronic age-related diseases such as arthritis, Alzheimer's, Parkinson's, cardiovascular disease, cancer, osteoporosis, benign prostatic hyperplasia, and late-onset diabetes have increased and have become serious public health problem, as well. The etiology of these disorders is still incompletely understood, therefore, neither preventive strategies nor long-term effective treatment modalities are available for these disorders. In keeping with the aforementioned, the ultimate goal in cardiovascular research is to prevent the onset of cardiovascular episodes and thereby allow successful ageing without morbidity and cognitive decline. Herein, I argue that cardiovascular episodes could be contained with relatively simple approaches. Cardiovascular disorder is characterized by cellular and molecular changes that are commonplace in age-related diseases in other organ system, such alterations include increased level of oxidative stress, perturbed energy metabolism, and "horror autotoxicus" largely brought about by the perturbation of ubiquitin -proteasome system, and excessive oxidative stress damage to the cardiac muscle cells and tissues, and cross-reactions of specific antibodies against human heat shock protein 60 with that of mycobacterial heat shock protein 65. "Horror autotoxicus", a Latin expression, is a term coined by Paul Ehrlich at the turn of the last century to describe autoimmunity to self, or the attack of "self" by immune system, which ultimately results to autoimmune condition. Based on the currently available data, the risk of cardiovascular episodes and several other age-related disorders, including cancer, Alzheimer's disease and diabetes, is known to be influenced by the nature and level of food intake. Now, a wealth of scientific data from studies of rodents and monkeys has documented the significant beneficial effects of calorie restriction (CR) or dietary restriction (DR), and multiple antioxidant agents in extending life span and reducing the incidence of progeroid-related diseases. Reduced levels of cellular oxidative stress, protection of genome from deleterious damage, detoxification of toxic molecules, and enhancement of energy homeostasis, contribute to the beneficial effects of dietary restriction and multiple antioxidant agents. Recent findings suggest that employment of DR and multiple antioxidant agents (including, catalase, glutathione peroxidase, CuZn superoxide dismutase, and Mn superoxide dismutase = enzymes forming the primary defense against oxygen toxicity), and ozone therapy may mount an effective resistance to pathogenic factors relevant to the pathogenesis of cardiovascular episodes. Hence, while further studies will be needed to establish the extent to which CR and multiple antioxidant agents will reduce incidence of cardiovascular episodes in humans, it would seem prudent to recommend CR and multiple antioxidant agents as widely applicable preventive approach for cardiovascular disorders and other progeroid-related disorders.

STRESS AND SURVIVAL: POSSIBLE ROLE OF SIRT1 IN THE DIENCEPHALON DURING FASTING

Sirtuins (SIRT), a novel family of NAD-dependent deacetylases, is known to mediate caloric restriction-induced extension of life span. They have also been implicated in preventing oxidative damage during stress, thus conferring neuroprotection during times of adversity. Alternate day fasting has been shown to equal or better most beneficial effects observed with caloric restriction. We hypothesized that fasting-induced beneficial effects could also be mediated through alterations in SIRT1 expression. To investigate this hypothesis, we fasted sexually mature female chicken (Hyline W36 strain) for 48 h. The diencephalon of the brain, which includes the hypothalamus, is known to mediate several of the beneficial effects of caloric restriction. We harvested the diencephalon and other non-neuronal tissues such as the liver, pituitary and adipose tissue. SIRT1 mRNA expression was measured in these tissues using quantitative real time-PCR. Fasting induced a significant increase (0.006±0.000025; p<0.05) in the relative SIRT1 mRNA expression normalized to β-actin in the diencephalon when compared to ad-libitum fed controls (0.004±0.000024). In contrast, SIRT1 mRNA expression decreased significantly in adipose tissue of fasted chicken compared to the controls. Fasting did not affect SIRT-1 mRNA expression in the liver and pituitary. It is concluded that fasting-induced augmentation of SIRT-1 mRNA expression in the diencephalon might play a role in mediating the beneficial effects of fasting.

Proteomics analysis provides insight into caloric restriction mediated oxidation and expression of brain proteins associated with age-related impaired cellular processes: Mitochondrial dysfunction, glutamate dysregulation and impaired protein synthesis

Age-related impairment of functionality of the central nervous system (CNS) is associated with increased susceptibility to develop many neurodegenerative diseases. Increased oxidative stress in the CNS of aged animals is manifested by increased protein oxidation, which is believed to contribute to the age-related learning and memory deficits. Glutamate dysregulation, mitochondrial dysfunction and impaired protein synthesis are observed in aged brains, along with increased protein oxidation. Interestingly, all of these age-related cellular alterations can be improved by caloric restriction (CR), which can also improve the plasticity and recovery of the CNS. Although the beneficial effects of CR on brains are well established, the mechanism(s) of its action remains unclear. In order to gain insight into the mechanism of CR in the brain, we located the brain regions that are benefited the most from reduced oxidative stress by CR. Along with other brain regions, striatum (ST) showed significantly decreased bulk protein carbonyl levels and hippocampus (HP) showed decreased bulk protein 3-nitrotyrosine (3-NT) levels in CR aged rats when compared to those of age matched controls. To determine which proteins were oxidatively modified in these brain regions, we used parallel proteomics approach to identify the proteins that are altered in oxidation and expression. The specific carbonyl levels of pyruvate kinase M2 (PKM2), α-enolase (ENO1), inositol monophosphatase (INSP1), and F1-ATPase Chain B (ATP-F1B) were significantly decreased in ST of aged CR rats. In contrast, the expression levels of phosphoglycerate kinase 1 (PKG1), inosine monophosphate cyclohydrolase (IMPCH) and F1-ATPase Chain A (ATP-F1A) were significantly increased in the ST of CR rats. In the hippocampus of CR rats, the specific 3-NT levels of malate dehydrogenase (MDH), phosphoglycerate kinase 1 (PKG1) and 14-3-3 zeta protein were significantly decreased and expression levels of DLP1 splice variant 1 (DLP1), mitochondrial aconitase (ACO2), dihydrolipoamide dehydrogenase (DLDH), neuroprotective peptide H3 (NPH3), and eukaryotic translation initiation factor 5A (eIF-5A) are increased. Moreover, an unnamed protein product (UNP1) with similar sequence to initiation factor 2 (IF-2) was decreased in the HP of CR rats. Our data support the hypothesis that CR induces a mild metabolic stress response by increasing the production of neurotrophic proteins, therefore, priming neurons against apoptosis. Moreover, our study shows that the improvement of glutamate dysregulation, mitochondrial dysfunction and protein synthesis by CR is, at least partially, due to the CR-mediated alteration of the oxidation or the expression of PKM2, ENO1, INSP1, ATP-F1B, PKG1, IMPCH, ATP-F1A MDH, PKG1 and 14-3-3 zeta protein, DLP1, ACO2, DLDH, NPH3, eIF-5A and UNP1. This study provides valuable insights into the mechanisms of the beneficial factors on brain aging by CR.

Molecular events in kidney ageing

Ageing of the kidney is a problem of clinical and basic interest. The problem of renal dysfunction and end-stage renal disease is a major burden on the health system, and old donor age is a major limitation on the use of donor organs and on survival of transplanted kidneys. Moreover, stresses linked to nephropathies, postoperative stress, inflammation and allograft rejection can lead to premature senescence of renal cells thus accelerating organ atrophy. Age-related and disease or stress-related nephron loss could reflect both the limited ability of epithelial cells to repair and replicate in the face of environmental stresses, and limitations on the number of cell replications caused by telomere shortening. Therefore, elucidating cellular senescence mechanisms is relevant to kidney diseases and kidney transplantation. Recent findings suggest additive effects of replicative and environmental stress-induced senescence in cellular and organ ageing. In particular, ATM/p53/p21 and Ras/p38/p16 pathways have been shown to co-contribute to the overall cellular senescence, which is caused by extrinsic and intrinsic stimuli. Moreover, the role of epigenetic factors, including protein acylation/deacetylation, chromatin remodeling or caloric restriction, is the focus of recent studies on ageing and senescence. Despite significant progress, cellular senescence is still better understood in vitro than in vivo. So far, p16 remains the best marker of chronological age in the kidney, and can be considered as an indicator of premature senescence caused by stresses or disease. The beneficial effects of caloric restriction on organ ageing and the role of histone acetylation in pathologic states in rodents are of considerable interest, and deserve future studies.

The diet restriction paradigm: a brief review of the effects of every-other-day feeding

It has been known since the early 1900s that restriction of dietary intake relative to the ad libitum (AL) level increases stress resistance, cancer resistance, and longevity in many species. Studies investigating these phenomena have used three paradigms for dietary restriction. In the first, the AL intake of a control group is measured, and an experimental group is fed less than that amount in a specified proportion, e.g., 40%. In the second, food is provided AL to both the control and experimental groups: however, the experimental group is subjected to periods of fasting. Recent studies using this paradigm provide food every other day (EOD). Both of these paradigms have been in use since the early 1900s. A third paradigm that combines them was developed in the early 1970s: one or more days of fasting separate the provision of a limited amount of food. It was assumed for many years that the physiological responses to these paradigms were due exclusively to a net decrease in energy intake. Recently, however, it was found that some species and strains of laboratory animals, when fed AL every other day, are capable of gorging so that their net weekly intake is not greatly decreased. Despite having only a small deficit in energy intake relative to control levels, however, these animals experience enhanced longevity and stress resistance is enhanced in comparison to AL controls as much in animals enduring daily restriction of diet. These observations warrant renewed interest in this paradigm and suggest that comparisons of the paradigms and their effects can be used to determine which factors are critical to the beneficial effects of caloric restriction.

Higher Respiratory Activity Decreases Mitochondrial Reactive Oxygen Release and Increases Life Span in Saccharomyces cerevisiae

Increased replicative longevity in Saccharomyces cerevisiae because of calorie restriction has been linked to enhanced mitochondrial respiratory activity. Here we have further investigated how mitochondrial respiration affects yeast life span. We found that calorie restriction by growth in low glucose increased respiration but decreased mitochondrial reactive oxygen species production relative to oxygen consumption. Calorie restriction also enhanced chronological life span. The beneficial effects of calorie restriction on mitochondrial respiration, reactive oxygen species release, and replicative and chronological life span could be mimicked by uncoupling agents such as dinitrophenol. Conversely, chronological life span decreased in cells treated with antimycin (which strongly increases mitochondrial reactive oxygen species generation) or in yeast mutants null for mitochondrial superoxide dismutase (which removes superoxide radicals) and for RTG2 (which participates in retrograde feedback signaling between mitochondria and the nucleus). These results suggest that yeast aging is linked to changes in mitochondrial metabolism and oxidative stress and that mild mitochondrial uncoupling can increase both chronological and replicative life span.