Effect of caloric restriction on mitochondrial reactive oxygen species production and bioenergetics: reversal by insulin

Mitigating the effects of time in the heart and liver: the variable effects of short- and long-term caloric restriction

Caloric restriction (CR) is known for its anti-aging benefits, partly due to reduced oxidative stress and enhanced antioxidant defense. However, CR outcomes vary based on its intensity, timing, and duration. This study explored CR's effects on antioxidant activity in the heart and liver of male Wistar rats during aging. We investigated two CR paradigms: long-term CR (LTCR), started early in life, and short-term CR (STCR), initiated in middle or old age for 3 months. Contrary to previous findings of short-term CR deleterious effects of on the nervous system, our results revealed increased levels of key antioxidants after STCR. More specifically, we found an increase in GSH-Px and GSH under STCR that was particularly pronounced in the liver, while an increase in CAT and GR activities was observed in the heart of the STCR groups. Catalase was characterized as an enzyme particularly responsive to CR, as its activity was also increased in both the liver and heart after long-term caloric restriction. Our results highlight a significant tissue-specific response to CR and contribute to our understanding of the dynamic effects of CR, which in turn has implications for refining its therapeutic potential in combating age-related decline.

Rate of body weight gain during early gestation in F0 beef heifers has effects that extend multigenerationally to the F2 fetuses

Our aim was to investigate the effects of maternal (F0) body weight (BW) gain during the first 84 d of gestation on body composition, ovarian reserve, and hormonal and metabolic parameters of breeding-age F1 heifers, as well as the BW and morphometry of F2 fetuses. The study also evaluated the effect of maternal BW gain (F0) on the mRNA relative abundance of the small intestine of both F1 heifers and F2 fetuses. Crossbred Angus heifers (F0; n = 100) were managed to gain 0.20 kg/d (low gain [LG], n = 50) or 0.75 kg/d (moderate gain [MG], n = 50) for the first 84 d of gestation. Subsequently, F0 dams were managed on a common forage-based diet for the rest of gestation until the weaning of the F1 offspring. At 15 mo of age, a subset of F1 heifers was randomly selected for the current experiment (n = 8 LG and n = 8 MG). Heifers were bred via artificial insemination (AI; day 0), then harvested on day 84 of gestation. On days -10, 42, and 84, BW was recorded, and blood was collected and analyzed for concentrations of glucose, non-esterified fatty acids, progesterone, insulin, and insulin-like growth factor-1. The weight of F1 carcasses, organs, gravid uteri, and F2 fetuses and organs were recorded at harvest. Visible follicles were counted on F1 ovaries at harvest, and histology was used to count microscopic follicles. Liver and jejunal samples from F1 heifers were collected to measure tissue oxygen consumption and jejunal samples from F1 heifers and F2 fetuses were collected for mRNA relative abundance analysis. BW of F1 heifers from MG dams tended to be 12 kg greater (P = 0.06) than for F1 heifers from LG dams. Concentrations of glucose were greater (P = 0.03) in F1 heifers from the MG group, with no differences in other blood metabolites or follicular populations (P ≥ 0.16). Interestingly, mammary glands were heavier (P = 0.05), and placentas and body depth tended to be heavier and greater, respectively (P ≤ 0.10), for F2 fetuses from F0 LG heifers. Oxygen consumption in the liver and jejunum, as well as mRNA relative abundance in the jejunum of F1 heifers, were not affected by F0 rate of gain (P ≥ 0.16). However, the NDUFC1, SDHA, UQCR1, and PPARG genes were upregulated (P ≤ 0.05) in the jejunum of F2 fetuses from the LG group. In conclusion, BW gain of F0 heifers during early gestation exerts subtle effects on pre-breeding BW and blood metabolites in F1 offspring, with impacts present in F2 placenta, mammary gland, and intestine.

Dietary Energy Restriction Ameliorates Cognitive Impairment in a Mouse Model of Traumatic Brain Injury

Traumatic brain injury (TBI) is one of the most common causes of neurological damage in young people. It was previously reported that dietary restriction, by either intermittent fasting (IF) or daily caloric restriction (CR), could protect neurons against dysfunction and degeneration in animal models of stroke and Parkinson's disease. Recently, several studies have shown that the protein Sirtuin 1 (SIRT1) plays a significant role in the induced neuroprotection following dietary restriction. In the present study, we found a significant reduction of SIRT1 levels in the cortex and hippocampus in a mouse model of mild weight-drop closed head TBI. This reduction was prevented in mice maintained on IF (alternate day fasting) and CR initiated after the head trauma. Hippocampus-dependent learning and memory (measured using a novel object recognition test) was impaired 30 days post-injury in mice fed ad libitum, but not in mice in the IF and CR groups. These results suggest a clinical potential for IF and/or CR as an intervention to reduce brain damage and improve functional outcome in TBI patients.

Adaptive Physiological and Morphological Adjustments Mediated by Intestinal Stem Cells in Response to Food Availability in Mice

Several studies have evaluated plastic changes in the morphology of the digestive tract in rodents subjected to caloric restriction or restricted availability. Nevertheless, studies that link these morphological responses to physiological consequences are scarce. In order to investigate short-term plastic responses in the intestine, we acclimated adult Mus musculus (BALB/c) males for 20 days to four distinctive treatments: two caloric regimens (ad libitum and 60% of calorie ingestion) and two levels of periodicity of the regimens (continuous and stochastic treatment). At the end of the treatment we analyzed the cell proliferation and cell death dynamics of small intestinal crypts in these animals. In addition, we measured organ masses and lengths, hydrolytic digestive enzyme activities, and energy output from feces. Finally, in order to explore the metabolic changes generated by these dietary conditions we assessed the catabolic activity (i.e., enzymes) of the liver. Our results show that individuals acclimated to a continuous and 60% regimen presented longer intestines in comparison to the other treatments. Indeed, their intestines grew with a rate of 0.22 cm/day, generating a significant caloric reduction in the content of their feces. Besides, both mass and intestinal lengths were predicted strongly by the stabilization coefficient of BrdU+ proliferating cells per crypt, the latter correlating positively with the activity of n-aminopeptidases. Interestingly, by using pharmacological inhibition of the kinase mammalian target of rapamycin complex 1 (mTORC1) by Rapamycin, we were able to recapitulate similar changes in the proliferation dynamics of intestinal stem cells. Based on our results, we propose that the impact of caloric restriction on macroscopic variation in morphology and functional changes in digestive n-aminopeptidases occurs through synchronization in the proliferation rate of stem and/or progenitor cells located in the small intestinal crypts and requires mTORC1 as a key mediator. Hence, we suggest that an excessive stem and progenitor activity could result in increased crypts branching and might therefore underlie the reported intestinal tissue expansion in response to short-term caloric restriction. Summarizing, we demonstrate for the first time that short-term caloric restriction induces changes in the level of cell proliferation dynamics explaining in part digestive tract plasticity in adaptive performance.

Stem cell rejuvenation and the role of autophagy in age retardation by caloric restriction: An update

Stem cells being pluripotent in nature can differentiate into a wide array of specific cells and asymmetrically divide to produce new ones but may undergo aging by themselves. Aging has both quantitative and qualitative effects on stem cells, and could eventually restrain them from replenishing into progenitor cells. Reactive oxygen species (ROS) accumulated in the aging cells could not only block the cell cycle but also affect autophagy by damaging the mitochondria. Autophagy could eliminate redundant production of ROS in aging stem cells and helps to maintain the proliferation capacity by restraining the expression of p16^INK4a. Current studies showed that improving autophagy could restore the regenerative ability of aging stem cells. Therefore, it is important for an organism to maintain the appropriate autophagy. Caloric restriction (CR) was shown to retard the stem cell aging by a certain basic level of autophagy, suggesting that CR was an effective way to extend longevity in mammals. However, little is known about the underlying mechanisms. In this review, we tried to explore the molecular mechanisms on how CR induces appropriate autophagy to restore aging stem cell regenerative ability.

Production of superoxide and hydrogen peroxide from specific mitochondrial sites under different bioenergetic conditions

Mitochondrial production of superoxide and hydrogen peroxide is potentially important in cell signaling and disease. Eleven distinct mitochondrial sites that differ markedly in capacity are known to leak electrons to oxygen to produce O₂^̇̄ and/or H₂O₂ We discuss their contributions to O₂^̇̄/H₂O₂ production under native conditions in mitochondria oxidizing different substrates and in conditions mimicking physical exercise and the changes in their capacities after caloric restriction. We review the use of S1QELs and S3QELs, suppressors of mitochondrial O₂^̇̄/H₂O₂ generation that do not inhibit oxidative phosphorylation, as tools to characterize the contributions of specific sites in situ and in vivo.

Liver metabolic changes induced by conjugated linoleic acid in calorie-restricted rats

OBJECTIVE

Complexes like conjugated linoleic acid (CLA) reduce the percentage of body fat by increasing energy expenditure, fat oxidation, or both. The aim of this study was to verify if CLA is able to mimic caloric restriction (CR), and determine the effects of CLA on liver metabolic profile of young adult male Wistar rats.

MATERIALS AND METHODS

We divided 36 animals into the following groups: 1) Control; 2) CLA (1% of daily food intake, 21 days, orogastric intubation); 3) Restr (fed 60% of the diet offered to controls); and 4) CLA Restr. Liver tissues were processed for biochemical and molecular or mitochondrial isolation (differential centrifugation) and blood samples were collected for biochemical analyses.

RESULTS

Treatment of the animals for 21 days with 1% CLA alone or combined with CR increased liver weight and respiration rates of liver mitochondria suggesting significant mitochondrial uncoupling. We observed a decrease in adipose tissue leading to insulin resistance, hyperinsulinemia, and hepatic steatosis due to increased liver cholesterol and triacylglycerol levels, but no significant effects on body mass. The expression of hepatic cellular connexins (43 and 26) was significantly higher in the CLA group compared with the Control or Restr groups.

CONCLUSION

CLA does not seem to be a safe compound to induce mass loss because it upregulates the mRNA expression of connexins and induces hepatic mitochondrial changes and lipids disorders.

The influence of dietary fat source on liver and skeletal muscle mitochondrial modifications and lifespan changes in calorie-restricted mice

The Membrane Theory of Aging proposes that lifespan is inversely related to the level of unsaturation in membrane phospholipids. Calorie restriction (CR) without malnutrition extends lifespan in many model organisms, which may be related to alterations in membrane phospholipids fatty acids. During the last few years our research focused on studying how altering the predominant fat source affects the outcome of CR in mice. We have established four dietary groups: one control group fed 95 % of a pre-determined ad libitum intake (in order to prevent obesity), and three CR groups fed 40 % less than ad libitum intake. Lipid source for the control and one of the CR groups was soybean oil (high in n-6 PUFA) whereas the two remaining CR groups were fed diets containing fish oil (high in n-3 PUFA), or lard (high in saturated and monounsaturated fatty acids). Dietary intervention periods ranged from 1 to 18 months. We performed a longitudinal lifespan study and a cross-sectional study set up to evaluate several mitochondrial parameters which included fatty acid composition, H(+) leak, activities of electron transport chain enzymes, ROS generation, lipid peroxidation, mitochondrial ultrastructure, and mitochondrial apoptotic signaling in liver and skeletal muscle. These approaches applied to different cohorts of mice have independently indicated that lard as a fat source often maximizes the effects of 40 % CR on mice. These effects could be due to significant increases of monounsaturated fatty acids levels, in accordance with the Membrane Theory of Aging.

Diet impact on mitochondrial bioenergetics and dynamics

Diet induced obesity is associated with impaired mitochondrial function and dynamic behavior. Mitochondria are highly dynamic organelles and the balance in fusion/fission is strictly associated with their bioenergetics. Fusion processes are associated with the optimization of mitochondrial function, whereas fission processes are associated with the removal of damaged mitochondria. In diet-induced obesity, impaired mitochondrial function and increased fission processes were found in liver and skeletal muscle. Diverse dietary fat sources differently affect mitochondrial dynamics and bioenergetics. In contrast to saturated fatty acids, omega 3 polyunsaturated fatty acids induce fusion processes and improve mitochondrial function. Moreover, the pro-longevity effect of caloric restriction has been correlated with changes in mitochondrial dynamics leading to decreased cell oxidative injury. Noteworthy, emerging findings revealed an important role for mitochondrial dynamics within neuronal populations involved in central regulation of body energy balance. In conclusion, mitochondrial dynamic processes with their strict interconnection with mitochondrial bioenergetics are involved in energy balance and diet impact on metabolic tissues.

Caloric restriction and the aging process: a critique

The main objective of this review is to provide an appraisal of the current status of the relationship between energy intake and the life span of animals. The concept that a reduction in food intake, or caloric restriction (CR), retards the aging process, delays the age-associated decline in physiological fitness, and extends the life span of organisms of diverse phylogenetic groups is one of the leading paradigms in gerontology. However, emerging evidence disputes some of the primary tenets of this conception. One disparity is that the CR-related increase in longevity is not universal and may not even be shared among different strains of the same species. A further misgiving is that the control animals, fed ad libitum (AL), become overweight and prone to early onset of diseases and death, and thus may not be the ideal control animals for studies concerned with comparisons of longevity. Reexamination of body weight and longevity data from a study involving over 60,000 mice and rats, conducted by a National Institute on Aging-sponsored project, suggests that CR-related increase in life span of specific genotypes is directly related to the gain in body weight under the AL feeding regimen. Additionally, CR in mammals and "dietary restriction" in organisms such as Drosophila are dissimilar phenomena, albeit they are often presented to be the very same. The latter involves a reduction in yeast rather than caloric intake, which is inconsistent with the notion of a common, conserved mechanism of CR action in different species. Although specific mechanisms by which CR affects longevity are not well understood, existing evidence supports the view that CR increases the life span of those particular genotypes that develop energy imbalance owing to AL feeding. In such groups, CR lowers body temperature, rate of metabolism, and oxidant production and retards the age-related pro-oxidizing shift in the redox state.

The effects of dietary restriction on oxidative stress in rodents

Oxidative stress is observed during aging and in numerous age-related diseases. Dietary restriction (DR) is a regimen that protects against disease and extends life span in multiple species. However, it is unknown how DR mediates its protective effects. One prominent and consistent effect of DR in a number of systems is the ability to reduce oxidative stress and damage. The purpose of this review is to comprehensively examine the hypothesis that dietary restriction reduces oxidative stress in rodents by decreasing reactive oxygen species (ROS) production and increasing antioxidant enzyme activity, leading to an overall reduction of oxidative damage to macromolecules. The literature reveals that the effects of DR on oxidative stress are complex and likely influenced by a variety of factors, including sex, species, tissue examined, types of ROS and antioxidant enzymes examined, and duration of DR. Here we present a comprehensive review of the existing literature on the effect of DR on mitochondrial ROS generation, antioxidant enzymes, and oxidative damage. In a majority of studies, dietary restriction had little effect on mitochondrial ROS production or antioxidant activity. On the other hand, DR decreased oxidative damage in the majority of cases. Although the effects of DR on endogenous antioxidants are mixed, we find that glutathione levels are the most likely antioxidant to be increased by dietary restriction, which supports the emerging redox-stress hypothesis of aging.

The influence of dietary lipid composition on skeletal muscle mitochondria from mice following eight months of calorie restriction

Calorie restriction (CR) has been shown to decrease reactive oxygen species (ROS) production and retard aging in a variety of species. It has been proposed that alterations in membrane saturation are central to these actions of CR. As a step towards testing this theory, mice were assigned to 4 dietary groups (control and 3 CR groups) and fed AIN-93G diets at 95 % (control) or 60 % (CR) of ad libitum for 8 months. To manipulate membrane composition, the primary dietary fats for the CR groups were soybean oil (also used in the control diet), fish oil or lard. Skeletal muscle mitochondrial lipid composition, proton leak, and H(2)O(2) production were measured. Phospholipid fatty acid composition in CR mice was altered in a manner that reflected the n-3 and n-6 fatty acid profiles of their respective dietary lipid sources. Dietary lipid composition did not alter proton leak kinetics between the CR groups. However, the capacity of mitochondrial complex III to produce ROS was decreased in the CR lard compared to the other CR groups. The results of this study indicate that dietary lipid composition can influence ROS production in muscle mitochondria of CR mice. It remains to be determined if lard or other dietary oils can maximize the CR-induced decreases in ROS production.

Thermoregulatory, cardiovascular, and metabolic responses to mild caloric restriction in the Brown Norway rat

Caloric restriction (CR) has been demonstrated to prolong the life span of a variety of species. CR-induced reduction in core temperature (Tc) is considered a key mechanism responsible for prolonging life span in rodents; however, little is known about the regulation of CR-induced hypothermia as a function of the circadian cycle. We assessed how mild CR that resulted in a 10% reduction in body weight affected the 24 h patterns of Tc as well as heart rate (HR) and motor activity (MA) of the Brown Norway rat. Telemetered rats were allowed to feed for 20 weeks ad libitum (AL) or given a CR diet. Tc, HR, and MA of CR rats exhibited nocturnal reductions and diurnal elevations, opposite to that of AL rats. The effects of CR appeared to peak at ∼4 weeks. Metabolic rate (MR) and respiratory exchange ratio (RER) were measured overnight after 18 weeks of CR. MR and RER were elevated markedly at the time of feeding in CR rats and then declined during the night. We found that the pattern of Tc was altered with CR, characterized by elimination of high nocturnal Tc's typically observed in AL animals. In terms of mechanisms to prolong life span in CR animals, we suggest that the shift in the pattern of Tc during CR (i.e., elimination of high Tc's) may be as critical as the overall mean reduction in Tc. Future studies should address how the time of feeding may affect the thermoregulatory response in calorically restricted rats.

Mitochondria as a source of reactive oxygen and nitrogen species: from molecular mechanisms to human health

Mitochondrially generated reactive oxygen species are involved in a myriad of signaling and damaging pathways in different tissues. In addition, mitochondria are an important target of reactive oxygen and nitrogen species. Here, we discuss basic mechanisms of mitochondrial oxidant generation and removal and the main factors affecting mitochondrial redox balance. We also discuss the interaction between mitochondrial reactive oxygen and nitrogen species, and the involvement of these oxidants in mitochondrial diseases, cancer, neurological, and cardiovascular disorders.

Facts and controversies in our understanding of how caloric restriction impacts the mitochondrion

Caloric restriction (CR) has pronounced benefits in promoting healthy aging. Amongst the most frequently implicated physiological mechanisms implicated in this benefit is altered mitochondrial function. Whereas a reduction in mitochondrial reactive oxygen species (ROS) production is a widely consistent effect of CR, an increase in mitochondrial biogenesis, which is accepted by many as fact, is contradicted on several levels, most critically by a lack of increase in mitochondrial protein synthesis rate in vivo. Furthermore, an increase in PGC-1α protein and markers of mitochondrial content with CR is a highly variable observation between studies. On the other hand, deacetylation of several mitochondrial proteins by the sirtuin, Sirt3, is an increasingly reported observation and at least so far, this observation is consistent between studies. Notwithstanding this point, the controversies evident in the published literature underscore the significant questions that remain in our understanding of how CR impacts the mitochondrion and suggest we have yet to fully understand the complexities herein.

The influence of dietary lipid composition on liver mitochondria from mice following 1 month of calorie restriction

To investigate the role mitochondrial membrane lipids play in the actions of CR (calorie restriction), C57BL/6 mice were assigned to four groups (control and three 40% CR groups) and the CR groups were fed diets containing soya bean oil (also in the control diet), fish oil or lard. The fatty acid composition of the major mitochondrial phospholipid classes, proton leak and H₂O₂ production were measured in liver mitochondria following 1 month of CR. The results indicate that mitochondrial phospholipid fatty acids reflect the PUFA (polyunsaturated fatty acid) profile of the dietary lipid sources. CR significantly decreased the capacity of ROS (reactive oxygen species) production by Complex III but did not markedly alter proton leak and ETC (electron transport chain) enzyme activities. Within the CR regimens, the CR-fish group had decreased ROS production by both Complexes I and III, and increased proton leak when compared with the other CR groups. The CR-lard group showed the lowest proton leak compared with the other CR groups. The ETC enzyme activity measurements in the CR regimens showed that Complex I activity was decreased in both the CR-fish and CR-lard groups. Moreover, the CR-fish group also had lower Complex II activity compared with the other CR groups. These results indicate that dietary lipid composition does influence liver mitochondrial phospholipid composition, ROS production, proton leak and ETC enzyme activities in CR animals.

Chronic caloric restriction preserves mitochondrial function in senescence without increasing mitochondrial biogenesis

Caloric restriction (CR) mitigates many detrimental effects of aging and prolongs life span. CR has been suggested to increase mitochondrial biogenesis, thereby attenuating age-related declines in mitochondrial function, a concept that is challenged by recent studies. Here we show that lifelong CR in mice prevents age-related loss of mitochondrial oxidative capacity and efficiency, measured in isolated mitochondria and permeabilized muscle fibers. We find that these beneficial effects of CR occur without increasing mitochondrial abundance. Whole-genome expression profiling and large-scale proteomic surveys revealed expression patterns inconsistent with increased mitochondrial biogenesis, which is further supported by lower mitochondrial protein synthesis with CR. We find that CR decreases oxidant emission, increases antioxidant scavenging, and minimizes oxidative damage to DNA and protein. These results demonstrate that CR preserves mitochondrial function by protecting the integrity and function of existing cellular components rather than by increasing mitochondrial biogenesis.

Caloric restriction and redox state: does this diet increase or decrease oxidant production?

Calorie restriction (CR) is well established to enhance the lifespan of a wide variety of organisms, although the mechanisms are still being uncovered. Recently, some authors have suggested that CR acts through hormesis, enhancing the production of reactive oxygen species (ROS), activating stress response pathways, and increasing lifespan. Here, we review the literature on the effects of CR and redox state. We find that there is no evidence in rodent models of CR that an increase in ROS production occurs. Furthermore, results in Caenorhabditis elegans and Saccharomyces cerevisiae suggesting that CR increases intracellular ROS are questionable, and probably cannot be resolved until adequate, artifact free, tools for real-time, quantitative, and selective measurements of intracellular ROS are developed. Overall, the largest body of work indicates that CR improves redox state, although it seems improbable that a global improvement in redox state is the mechanism through which CR enhances lifespan.

The influence of dietary lipid composition on skeletal muscle mitochondria from mice following 1 month of calorie restriction

To investigate the role mitochondrial membrane lipids play in the actions of calorie restriction (CR), C57BL/6 mice were assigned to four groups (control and three 40% CR groups) and fed diets containing soybean oil (also in the control diet), fish oil, or lard. The fatty acid composition of the major mitochondrial phospholipid classes, proton leak, and H(2)O(2) production were measured in muscle mitochondria following 1 month of CR. The results indicate that phospholipid fatty acids reflected the polyunsaturated fatty acid profile of the dietary lipid sources. Capacity for Complex I- and III-linked H(2)O(2) production was decreased with CR, although there was no difference between CR groups. The CR lard group had lower proton leak than all other groups. The results indicate that a decreased degree of unsaturation in muscle mitochondrial membranes is not required for reduced H(2)O(2) production with CR. However, dietary lipids do have some influence on proton leak with CR.

Mitochondrial therapeutics for cardioprotection

Mitochondria represent approximately one-third of the mass of the heart and play a critical role in maintaining cellular function-however, they are also a potent source of free radicals and pro-apoptotic factors. As such, maintaining mitochondrial homeostasis is essential to cell survival. As the dominant source of ATP, continuous quality control is mandatory to ensure their ongoing optimal function. Mitochondrial quality control is accomplished by the dynamic interplay of fusion, fission, autophagy, and mitochondrial biogenesis. This review examines these processes in the heart and considers their role in the context of ischemia-reperfusion injury. Interventions that modulate mitochondrial turnover, including pharmacologic agents, exercise, and caloric restriction are discussed as a means to improve mitochondrial quality control, ameliorate cardiovascular dysfunction, and enhance longevity.

Caloric restriction increases adiponectin expression by adipose tissue and prevents the inhibitory effect of insulin on circulating adiponectin in rats

Aging is associated with redistribution of body fat and the development of insulin resistance. White adipose tissue emerges as an important organ in controlling life span. Caloric restriction (CR) delays the rate of aging possibly modulated partly by altering the amount and function of adipose tissue. Adiponectin is a major adipose-derived adipokine that has anti-inflammatory and insulin-sensitizing properties. This study examined the effects of CR on adiposity and gene expression of adiponectin, its receptors (AdipoR1 and AdipoR2) in adipose tissue and in isolated adipocytes of Brown Norway rats that had undergone CR for 4 months or fed ad libitum. The study also determined plasma concentrations of adiponectin and insulin in these animals and whether insulin infusion for 7 days affects adiponectin expression and its circulating concentrations under CR conditions. CR markedly reduced body weight as anticipated, epididymal fat mass and adipocyte size. CR led to an increase in plasma free fatty acid and glycerol (both twofold), and adipose triglyceride lipase messenger RNA (mRNA) in adipose tissue and isolated adipocytes (both >2-fold). Adiponectin mRNA levels were elevated in adipose tissue and adipocytes (both >2-fold) as was plasma adiponectin concentration (2.8-fold) in CR rats. However, CR did not alter tissue or cellular AdipoR1 and AdipoR2 expression. Seven days of insulin infusion decreased adiponectin mRNA in adipose tissue but did not reverse the CR-induced up-regulation of circulating adiponectin levels. Our results suggest that the benefits of CR could be, at least in part, dependent on enhanced expression and secretion of adiponectin by adipocytes.

Caloric restriction influences hydrogen peroxide generation in mitochondrial sub-populations from mouse liver

Calorie restriction (CR) has been shown to decrease H(2)O(2) production in liver mitochondria, although it is not known if this is due to uniform changes in all mitochondria or changes in particular mitochondrial sub-populations. To address this issue, liver mitochondria from control and CR mice were fractionated using differential centrifugation at 1,000 g, 3,000 g and 10,000 g into distinct populations labeled as M1, M3 and M10, respectively. Mitochondrial protein levels, respiration and H(2)O(2) production were measured in each fraction. CR resulted in a decrease in total protein (mg) in each fraction, although this difference disappeared when adjusted for liver weight (mg protein/g liver weight). No differences in respiration (State 3 or 4) were observed between control and CR mice in any of the mitochondrial fractions. CR decreased H(2)O(2) production in all fractions when mitochondria respired on succinate (Succ), succ+antimycin A (Succ+AA) or pyruvate/malate+rotenone (P/M+ROT). Thus, CR decreased reactive oxygen species (ROS) production under conditions which stimulate mitochondrial complex I ROS production under both forward (P/M+ROT) and backward (Succ & Succ+AA) electron flow. The results indicate that CR decreases H(2)O(2) production in all liver mitochondrial fractions due to a decrease in capacity for ROS production by complex I of the electron transport chain.

Mild mitochondrial uncoupling and calorie restriction increase fasting eNOS, akt and mitochondrial biogenesis

Enhanced mitochondrial biogenesis promoted by eNOS activation is believed to play a central role in the beneficial effects of calorie restriction (CR). Since treatment of mice with dinitrophenol (DNP) promotes health and lifespan benefits similar to those observed in CR, we hypothesized that it could also impact biogenesis. We found that DNP and CR increase citrate synthase activity, PGC-1α, cytochrome c oxidase and mitofusin-2 expression, as well as fasting plasma levels of NO^• products. In addition, eNOS and Akt phosphorylation in skeletal muscle and visceral adipose tissue was activated in fasting CR and DNP animals. Overall, our results indicate that systemic mild uncoupling activates eNOS and Akt-dependent pathways leading to mitochondrial biogenesis.

Mitochondrial ROS production correlates with, but does not directly regulate lifespan in Drosophila

The Mitochondrial Free Radical Theory of Aging (MFRTA) is currently one of the most widely accepted theories used to explain aging. From MFRTA three basic predictions can be made: long-lived individuals or species should produce fewer mitochondrial Reactive Oxygen Species (mtROS) than short-lived individuals or species; a decrease in mtROS production will increase lifespan; and an increase in mtROS production will decrease lifespan. It is possible to add a further fourth prediction: if ROS is controlling longevity separating these parameters through selection would be impossible. These predictions have been tested in Drosophila melanogaster. Firstly, we studied levels of mtROS production and lifespan of three wild-type strains of Drosophila, Oregon R, Canton S and Dahomey. Oregon R flies live the longest and produce significantly fewer mtROS than both Canton S and Dahomey. These results are therefore in accordance with the first prediction. A new transgenic Drosophila model expressing the Ciona intestinalis Alternative Oxidase (AOX) was used to test the second prediction. In fungi and plants, AOX expression regulates both free radical production and lifespan. In Drosophila, AOX expression decreases mtROS production, but does not increase lifespan. This result contradicts the second prediction of MFRTA. The third prediction was tested in flies mutant for the gene dj-1beta. These flies are characterized by an age-associated decline in locomotor function and increased levels of mtROS production. Nevertheless, dj-1beta mutant flies do not display decreased lifespan, which again is in contradiction with MFRTA. In our final experiment we utilized flies with DAH mitochondrial DNA in an OR nuclear background, and OR mitochondrial DNA in DAH nuclear background. From this, Mitochondrial DNA does not control free radical production, but it does determine longevity of females independently of mtROS production. In summary, these results do not systematically support the predictions of the MFRTA. Accordingly, MFRTA should be revised to accommodate these findings.

Mitochondrial redox metabolism: aging, longevity and dietary effects

Mitochondrial redox metabolism has long been considered to play important roles in mammalian aging and the development of age-related pathologies in the major oxidative organs. Both genetic and dietary manipulations of mitochondrial redox metabolism have been associated with the extension of lifespan. Here we provide a broad overview of the circumstantial evidence showing associations between mitochondrial reactive oxygen species (ROS) metabolism, aging and longevity. We address most aspects of mitochondrial ROS metabolism, from superoxide production, to ROS detoxification and the repair/removal of ROS-mediated macromolecular damage. Finally, we discuss the effects of dietary manipulations (e.g. caloric restriction, methionine restriction), dietary deficiencies (e.g. folate) and dietary supplementation (e.g. resveratrol) on mitochondrial ROS metabolism and lifespan.

Mitochondrial function as a determinant of life span

Average human life expectancy has progressively increased over many decades largely due to improvements in nutrition, vaccination, antimicrobial agents, and effective treatment/prevention of cardiovascular disease, cancer, etc. Maximal life span, in contrast, has changed very little. Caloric restriction (CR) increases maximal life span in many species, in concert with improvements in mitochondrial function. These effects have yet to be demonstrated in humans, and the duration and level of CR required to extend life span in animals is not realistic in humans. Physical activity (voluntary exercise) continues to hold much promise for increasing healthy life expectancy in humans, but remains to show any impact to increase maximal life span. However, longevity in Caenorhabditis elegans is related to activity levels, possibly through maintenance of mitochondrial function throughout the life span. In humans, we reported a progressive decline in muscle mitochondrial DNA abundance and protein synthesis with age. Other investigators also noted age-related declines in muscle mitochondrial function, which are related to peak oxygen uptake. Long-term aerobic exercise largely prevented age-related declines in mitochondrial DNA abundance and function in humans and may increase spontaneous activity levels in mice. Notwithstanding, the impact of aerobic exercise and activity levels on maximal life span is uncertain. It is proposed that age-related declines in mitochondrial content and function not only affect physical function, but also play a major role in regulation of life span. Regular aerobic exercise and prevention of adiposity by healthy diet may increase healthy life expectancy and prolong life span through beneficial effects at the level of the mitochondrion.

Mitochondria and reactive oxygen species

Mitochondria are a quantitatively relevant source of reactive oxygen species (ROS) in the majority of cell types. Here we review the sources and metabolism of ROS in this organelle, including the conditions that regulate the production of these species, such as mild uncoupling, oxygen tension, respiratory inhibition, Ca2+ and K+ transport, and mitochondrial content and morphology. We discuss substrate-, tissue-, and organism-specific characteristics of mitochondrial oxidant generation. Several aspects of the physiological and pathological roles of mitochondrial ROS production are also addressed.

Anti-oxidative and anti-inflammatory vasoprotective effects of caloric restriction in aging: role of circulating factors and SIRT1

Endothelial dysfunction, oxidative stress and inflammation are associated with vascular aging and promote the development of cardiovascular disease. Caloric restriction (CR) mitigates conditions associated with aging, but its effects on vascular dysfunction during aging remain poorly defined. To determine whether CR exerts vasoprotective effects in aging, aortas of ad libitum (AL) fed young and aged and CR-aged F344 rats were compared. Aging in AL-rats was associated with impaired acetylcholine-induced relaxation, vascular oxidative stress and increased NF-kappaB activity. Lifelong CR significantly improved endothelial function, attenuated vascular ROS production, inhibited NF-kappaB activity and down-regulated inflammatory genes. To elucidate the role of circulating factors in mediation of the vasoprotective effects of CR, we determined whether sera obtained from CR animals can confer anti-oxidant and anti-inflammatory effects in cultured coronary arterial endothelial cells (CAECs), mimicking the effects of CR. In CAECs cultured in the presence of AL serum TNFalpha elicited oxidative stress, NF-kappaB activation and inflammatory gene expression. By contrast, treatment of CAECs with CR serum attenuated TNFalpha-induced ROS generation and prevented NF-kappaB activation and induction of inflammatory genes. siRNA knockdown of SIRT1 mitigated the anti-oxidant and anti-inflammatory effects of CR serum. CR exerts anti-oxidant and anti-inflammatory vascular effects, which are likely mediated by circulating factors, in part, via a SIRT1-dependent pathway.

Why eating less keeps mitochondria working in aged skeletal muscle

The mechanisms by which caloric restriction preserves skeletal muscle health with aging continue to be explored; however, mounting evidence points toward a convergence of effects at the level of the mitochondrion. Specifically, caloric restriction reduces mitochondrial reactive oxygen species production and promotes mitochondrial renewal via enhanced drive on mitochondrial biogenesis and autophagy.

Neurochemistry, neuropathology, and heredity in SAMP8: a mouse model of senescence

The SAMP8 strain spontaneously develops learning and memory deficits with characteristics of aging, and is a good model for studying the mechanism of cognitive dysfunction with age. Oxidative stress occurs systemically in SAMP8 from early on in life and increases with aging. Neuropathological changes such as the deposition of A beta, hyperphosphorylation of tau, impaired development of dendritic spines, and sponge formation, and neurochemical changes were found in the SAMP8 brain. These changes may be partially mediated by oxidative stress. Oxidative damage is a major factor in neurodegenerative disorders and aging. A decline in the respiratory control ratio suggesting mitochondrial dysfunction was found in the brain of SAMP8. The rise in oxidative stress following mitochondrial dysfunction may trigger neuropathological and neurochemical changes, disrupting the development of neural networks in the brain in SAMP8.

Effect of every-other-day fasting on spontaneous chromosomal damage in rat's bone-marrow cells

Dietary restriction in experimental rodents, either by calorie restriction (CR) or by every-other-day fasting (EODF), was shown to protect against cancer and increase lifespan. One of the suggested hypotheses to explain the beneficial effects of dietary restriction is that the diet stabilizes the integrity of the genetic information. The effects of EODF on the spontaneous frequency of sister chromatid exchanges (SCE) and chromosomal aberrations (CA) were examined in bone-marrow cells of 3-mo-old Wistar male rats. After 12 wk of EODF diet, significant reduction in the frequency of SCE and total number of CA was observed. Data indicate a protective effect of EODF diet against spontaneous mutations in rats.

Sarcopenia of aging: underlying cellular mechanisms and protection by calorie restriction

Sarcopenia, the loss of muscle mass and function, is a common feature of aging and impacts on individual health and quality of life. Several cellular mechanisms have been involved in the pathogenesis of this syndrome, including mitochondrial dysfunction, altered apoptotic and autophagic signaling, and, more recently, trace metal dyshomeostasis. Calorie restriction (CR) without malnutrition has been shown to ameliorate the age-related loss of muscle mass in a variety a species. Mechanisms of protection span from preservation of mitochondrial functional and structural integrity to mitochondrial biogenesis, reduction of oxidative stress, and favorable modulation of apoptotic and autophagic signaling pathways. Importantly, preliminary evidence indicates that moderate CR may promote muscle mitochondrial biogenesis in middle-aged human subjects. Further research is warranted to investigate whether CR may represent a safe and efficient strategy to delay the onset and mitigate the progression of sarcopenia in older adults.

Caloric restriction optimizes the proteasome pathway with aging in rat plantaris muscle: implications for sarcopenia

To gain insight into the significance of alterations in the proteasome pathway for sarcopenia and its attenuation by calorie restriction, we examined protein oxidation and components of the proteasome pathway in plantaris muscle in 8-, 30-, and 35-mo-old ad libitum-fed (AL) rats; and in 8-, 35-, and 40-mo-old calorie-restricted (CR) rats. We hypothesized that CR rats would exhibit a lesser accumulation of protein carbonyls with aging and that this would be associated with a better maintenance of skeletal muscle proteasome activity and function with aging. Consistent with this view, whereas AL rats had a significant increase in protein carbonylation with aging, there was no such increase in CR rats. Protein levels of the ubiquitin ligases MuRF1 and MAFbx increased similarly with aging in both AL and CR rats. On the other hand, chymotrypsin-like activity of the proteasome increased with aging more gradually in CR rats, and this increase was paralleled by increases in the expression of the C2 subunit in both groups, suggesting that differences in activity were not related to differences in proteasome function with aging. Interestingly, the plot of muscle mass vs. proteasome activity showed that the oldest animals in both diets had a lower muscle mass than would be predicted by their proteasome activity, suggesting that other factors explain the acceleration of sarcopenia at advanced age. Since calorie restriction better protects skeletal muscle function than muscle mass with aging (Hepple RT, Baker DJ, Kaczor JJ, Krause DJ, FASEB J 19: 1320–1322, 2005), and our current results show that this protection of function is associated with a prevention of oxidative protein damage accumulation, we suggest that calorie restriction optimizes the proteasome pathway to preserve skeletal muscle function at the expense of modest muscle atrophy.

Effect of aging, caloric restriction, and uncoupling protein 3 (UCP3) on mitochondrial proton leak in mice

Mitochondrial proton leak may modulate reactive oxygen species (ROS) production and play a role in aging. The purpose of this study was to determine proton leak across the life span in skeletal mitochondria from calorie-restricted and UCP2/3 overexpressing mice. Proton leak in isolated mitochondria and markers of oxidative stress in whole tissue were measured in female C57BL/6J mice fed ad-libitum (WT-Control) or a 30% calorie-restricted (WT-CR) diet, and in mice overexpressing UCP2 and UCP3 (Positive-TG), their non-overexpressing littermates (Negative-TG) and UCP3 knockout mice (UCP3KO). Proton leak in WT-CR mice was lower than that of control mice at 8 and 26 months of age. The Positive-TG mice had greater proton leak than the Negative-TG and UCP3KO mice at 8 months of age, but this difference disappeared by 19 and 26 months. Lipid peroxidation was generally lower in WT-CR vs. WT-Control mice and UCP3KO mice had greater concentrations of T-BARS (thiobarbituric acid reactive substances, a measure of lipid peroxidation) than did Positive-TG and Negative-TG. The results of this study indicate that sustained increases in muscle mitochondrial proton leak are not responsible for alterations in life span with calorie restriction or UCP3 overexpression in mice. However, UCP3 may contribute to the actions of CR through mechanisms distinct from increasing basal proton leak.

The neuroprotective properties of calorie restriction, the ketogenic diet, and ketone bodies

Both calorie restriction and the ketogenic diet possess broad therapeutic potential in various clinical settings and in various animal models of neurological disease. Following calorie restriction or consumption of a ketogenic diet, there is notable improvement in mitochondrial function, a decrease in the expression of apoptotic and inflammatory mediators and an increase in the activity of neurotrophic factors. However, despite these intriguing observations, it is not yet clear which of these mechanisms account for the observed neuroprotective effects. Furthermore, limited compliance and concern for adverse effects hamper efforts at broader clinical application. Recent research aimed at identifying compounds that can reproduce, at least partially, the neuroprotective effects of the diets with less demanding changes to food intake suggests that ketone bodies might represent an appropriate candidate. Ketone bodies protect neurons against multiple types of neuronal injury and are associated with mitochondrial effects similar to those described during calorie restriction or ketogenic diet treatment. The present review summarizes the neuroprotective effects of calorie restriction, of the ketogenic diet and of ketone bodies, and compares their putative mechanisms of action.

Mild mitochondrial uncoupling in mice affects energy metabolism, redox balance and longevity

Caloric restriction is the most effective non-genetic intervention to enhance lifespan known to date. A major research interest has been the development of therapeutic strategies capable of promoting the beneficial results of this dietary regimen. In this sense, we propose that compounds that decrease the efficiency of energy conversion, such as mitochondrial uncouplers, can be caloric restriction mimetics. Treatment of mice with low doses of the protonophore 2,4-dinitrophenol promotes enhanced tissue respiratory rates, improved serological glucose, triglyceride and insulin levels, decrease of reactive oxygen species levels and tissue DNA and protein oxidation, as well as reduced body weight. Importantly, 2,4-dinitrophenol-treated animals also presented enhanced longevity. Our results demonstrate that mild mitochondrial uncoupling is a highly effective in vivo antioxidant strategy, and describe the first therapeutic intervention capable of effectively reproducing the physiological, metabolic and lifespan effects of caloric restriction in healthy mammals.

Modulation of age-induced apoptotic signaling and cellular remodeling by exercise and calorie restriction in skeletal muscle

Aging is inevitably associated with a progressive loss of muscle mass and strength, a condition also known as sarcopenia of aging. Although the precise mechanisms underlying this syndrome have not been completely elucidated, recent studies point toward several key cellular mechanisms that could contribute to age-associated muscle loss. Among these, mitochondrial dysfunction and deregulation of apoptotic signaling have emerged as critical players in the onset and progression of sarcopenia. Interestingly, calorie restriction, a well-known antiaging intervention, and, more recently, exercise training have been shown to beneficially affect both mitochondrial function and apoptotic signaling in skeletal muscle from young and old animals. Preliminary observations also indicate that even a small (8%) reduction in food intake may still provide protective effects against sarcopenia and cellular remodeling in aging skeletal muscle, with the advantage of being more applicable to human subjects than the traditional 30-40% restriction regimen. The most recent evidence on the relevance of skeletal muscle apoptosis to sarcopenia, as well as its modulation by calorie restriction and exercise, is reviewed.

Life and death: metabolic rate, membrane composition, and life span of animals

Maximum life span differences among animal species exceed life span variation achieved by experimental manipulation by orders of magnitude. The differences in the characteristic maximum life span of species was initially proposed to be due to variation in mass-specific rate of metabolism. This is called the rate-of-living theory of aging and lies at the base of the oxidative-stress theory of aging, currently the most generally accepted explanation of aging. However, the rate-of-living theory of aging while helpful is not completely adequate in explaining the maximum life span. Recently, it has been discovered that the fatty acid composition of cell membranes varies systematically between species, and this underlies the variation in their metabolic rate. When combined with the fact that 1) the products of lipid peroxidation are powerful reactive molecular species, and 2) that fatty acids differ dramatically in their susceptibility to peroxidation, membrane fatty acid composition provides a mechanistic explanation of the variation in maximum life span among animal species. When the connection between metabolic rate and life span was first proposed a century ago, it was not known that membrane composition varies between species. Many of the exceptions to the rate-of-living theory appear explicable when the particular membrane fatty acid composition is considered for each case. Here we review the links between metabolic rate and maximum life span of mammals and birds as well as the linking role of membrane fatty acid composition in determining the maximum life span. The more limited information for ectothermic animals and treatments that extend life span (e.g., caloric restriction) are also reviewed.

Sexual dimorphism in liver mitochondrial oxidative capacity is conserved under caloric restriction conditions

Caloric restriction (CR) without malnutrition has been shown to increase maximal life span and delay the rate of aging in a wide range of species. It has been proposed that reduction in energy expenditure and oxidative damage may explain the life-extending effect of CR. Sex-related differences also have been shown to influence longevity and energy expenditure in many mammalian species. The aim of the present study was to determine the sex-related differences in rat liver mitochondrial machinery, bioenergetics, and oxidative balance in response to short-term CR. Mitochondria were isolated from 6-mo-old male and female Wistar rats fed ad libitum or subjected to 40% CR for 3 mo. Mitochondrial O2 consumption, activities of the oxidative phosphorylation system (complexes I, III, IV, and V), antioxidative activities [MnSOD, glutathione peroxidase (GPx)], mitochondrial DNA and protein content, mitochondrial H2O2 production, and markers of oxidative damage, as well as cytochrome C oxidase and mitochondrial transcription factor A levels, were measured. Female rats showed a higher oxidative capacity and GPx activity than males. This sexual dimorphism was not modified by CR. Restricted rats showed slightly increased oxygen consumption, complex III activity, and GPx antioxidant activity together with lower levels of oxidative damage. In conclusion, the sexual dimorphism in liver mitochondrial oxidative capacity was unaffected by CR, with females showing higher mitochondrial functionality and ROS protection than males.

Reduced TOR signaling extends chronological life span via increased respiration and upregulation of mitochondrial gene expression

The relationships between mitochondrial respiration, reactive oxygen species (ROS), and life span are complex and remain controversial. Inhibition of the target of rapamycin (TOR) signaling pathway extends life span in several model organisms. We show here that deletion of the TOR1 gene extends chronological life span in Saccharomyces cerevisiae, primarily by increasing mitochondrial respiration via enhanced translation of mtDNA-encoded oxidative phosphorylation complex subunits. Unlike previously reported pathways regulating chronological life span, we demonstrate that deletion of TOR1 delays aging independently of the antioxidant gene SOD2. Furthermore, wild-type and tor1 null strains differ in life span only when respiration competent and grown in normoxia in the presence of glucose. We propose that inhibition of TOR signaling causes derepression of respiration during growth in glucose and that the subsequent increase in mitochondrial oxygen consumption limits intracellular oxygen and ROS-mediated damage during glycolytic growth, leading to lower cellular ROS and extension of chronological life span.

Nicotinamide extends replicative lifespan of human cells

We found that an ongoing application of nicotinamide to normal human fibroblasts not only attenuated expression of the aging phenotype but also increased their replicative lifespan, causing a greater than 1.6-fold increase in the number of population doublings. Although nicotinamide by itself does not act as an antioxidant, the cells cultured in the presence of nicotinamide exhibited reduced levels of reactive oxygen species (ROS) and oxidative damage products associated with cellular senescence, and a decelerated telomere shortening rate without a detectable increase in telomerase activity. Furthermore, in the treated cells growing beyond the original Hayflick limit, the levels of p53, p21WAF1, and phospho-Rb proteins were similar to those in actively proliferating cells. The nicotinamide treatment caused a decrease in ATP levels, which was stably maintained until the delayed senescence point. Nicotinamide-treated cells also maintained high mitochondrial membrane potential but a lower respiration rate and superoxide anion level. Taken together, in contrast to its demonstrated pro-aging effect in yeast, nicotinamide extends the lifespan of human fibroblasts, possibly through reduction in mitochondrial activity and ROS production.