Melatonin fails to modulate immune parameters influenced by calorie restriction in aging Fischer 344 rats

The aim of this study was to determine if long-term treatment with melatonin (MEL), a purported anti-aging agent, was as effective as calorie restriction (CR) in modulating immune parameters in aging Fischer 344 male rats. Splenic lymphocytes were isolated from 17-month-old rats that, beginning at 6 weeks of age, were treated with MEL (4 or 16 microg/ml in drinking water) and from 17-month-old rats fed ad libitum (AL) or rats fed a CR diet (55% of AL intake). The number of splenic T cell populations and T cell subsets was measured by flow cytometry, the proliferative response of splenocytes to Concanavalin A (Con A) and lipopolysaccharide (LPS) was measured by [(3)H]thymidine incorporation, and the induction of cytokine production (IL-2 and IFN-gamma) was measured by ELISA assay. In addition, the level of the natural killer (NK) cell activity was assessed by fluorimetric assay. CR rats had a higher number of lymphocytes expressing the na?ve T cell marker (CD3 OX22) than AL rats (P < 0.05). CR rats also showed greater induction of proliferative response, IL-2 and IFN-gamma levels following Con A simulation, and NK cell activity than AL rats (P < 0.05). MEL-treated rats did not differ from AL rats in any of these parameters or in any other measurement. These results indicate that MEL treatment is unable to modulate immune function in a manner comparable with that of CR.     

Influence of aging and long-term caloric restriction on oxygen radical generation and oxidative DNA damage in rat liver mitochondria

The effect of long-term caloric restriction and aging on the rates of mitochondrial H2O2 production and oxygen consumption as well as on oxidative damage to nuclear (nDNA) and mitochondrial DNA (mtDNA) was studied in rat liver tissue. Long-term caloric restriction significantly decreased H2O2 production of rat liver mitochondria (47% reduction) and significantly reduced oxidative damage to mtDNA (46% reduction) with no changes in nDNA. The decrease in ROS production was located at complex I because it only took place with complex I-linked substrates (pyruvate/malate) but not with complex II-linked substrates (succinate). The mechanism responsible for that decrease in ROS production was not a decrease in mitochondrial oxygen consumption because it did not change after long-term restriction. Instead, the caloric restricted mitochondria released less ROS per unit electron flow, due to a decrease in the reduction degree of the complex I generator. On the other hand, increased ROS production with aging in state 3 was observed in succinate-supplemented mitochondria because old control animals were unable to suppress H2O2 production during the energy transition from state 4 to state 3. The levels of 8-oxodG in mtDNA increased with age in old animals and this increase was abolished by caloric restriction. These results support the idea that caloric restriction reduces the aging rate at least in part by decreasing the rate of mitochondrial ROS production and so, the rate of oxidative attack to biological macromolecules like mtDNA.     

Effect of vitamin C on lipid hydroperoxides and carbonyl groups content of rat plasma depending on age and acute heat exposure

Free radicals produced during hyperthermic stress and aging are thought to play an important role in the degenerative process. To investigate the correlation between oxidative damages caused by acute heat exposure or aging, and the protective effect of vitamin C in vivo, we determined the levels of oxidative protein damage, lipid peroxidation, content of endogenous ascorbic acid, and glutathione in the plasma of young and old Wistar rats, subjected or not-subjected to acute heat stress. The results showed that the level of oxidative protein damage (measured as carbonyl content) in plasma was significantly higher in elderly and in heat-exposed animals. Vitamin C treatment led to inhibition on carbonyl production much more pronounced in young heat-exposed than in aged heat-exposed rats. Aging and acute heat exposure correlated positively with increased production of lipid hydroperoxides in rats plasma, but there were no significant differences in lipid hydroperoxides levels between young and old heat-exposed rats, depending on the treatment with vitamin C. Multiple backward regression analysis showed ascorbic acid to be the only determining variable of lipid hydroperoxides levels in unexposed rats. It was concluded that aging and heat exposure instigate an increase of lipid peroxidation and protein oxidation in rat plasma, while vitamin C supplementation significantly counteracts these changes.     

Effects of fasting on oxidative stress in rat liver mitochondria

While moderate caloric restriction has beneficial effects on animal health state, fasting may be harmful. The present investigation was designed to test how fasting affects oxidative stress, and to find out whether the effects are opposite to those previously found in caloric restriction studies. We have focused on one of the main determinants of aging rate: the rate of mitochondrial free radical generation. Different parameters related to lipid and protein oxidative damage were also analyzed. Liver mitochondria from rats subjected to 72 h of fasting leaked more electrons per unit of O₂ consumed at complex III, than mitochondria from ad libitum fed rats. This increased leak led to a higher free radical generation under state 3 respiration using succinate as substrate. Regarding lipids, fasting altered fatty acid composition of hepatic membranes, increasing the double bond and the peroxidizability indexes. In accordance with this, we observed that hepatic membranes from the fasted animals were more sensitive to lipid peroxidation. Hepatic protein oxidative damage was also increased in fasted rats. Thus, the levels of oxidative modifications, produced either indirectly by reactive carbonyl compounds (N^epsilon- malondialdehyde-lysine), or directly through amino acid oxidation (glutamic and aminoadipic semialdehydes) were elevated due to the fasting treatment in both liver tissue and liver mitochondria. The current study shows that severe food deprivation increases oxidative stress in rat liver, at least in part, by increasing mitochondrial free radical generation during state 3 respiration and by increasing the sensitivity of hepatic membranes to oxidative damage, suggesting that fasting and caloric restriction have different effects on liver mitochondrial oxidative stress.     

Protein Restriction Without Strong Caloric Restriction Decreases Mitochondrial Oxygen Radical Production and Oxidative DNA Damage in Rat Liver

Previous studies have shown that caloric restriction decreases mitochondrial oxygen radical production and oxidative DNA damage in rat organs, which can be linked to the slowing of aging rate induced by this regime. These two characteristics are also typical of long-lived animals. However, it has never been investigated if those decreases are linked to the decrease in the intake of calories themselves or to decreases in specific dietary components. In this study the possible role of the dietary protein was investigated. Using semipurified diets, the ingestion of proteins of Wistar rats was decreased by 40% below that of controls while the other dietary components were ingested at the same level as in animals fed ad libitum. After seven weeks in this regime the liver of the protein restricted animals showed 30–40% decreases in mitochondrial production of reactive oxygen species (ROS) and in oxidative damage to nuclear and mitochondrial DNA. The decreases in ROS generation occurred specifically at complex~I. They also occurred without changes in mitochondrial oxygen consumption. Instead, there was a decrease in the percent free radical leak (the percentage of total electron flow leading to ROS generation in the respiratory chain). These results are strikingly similar to those previously obtained after 40% caloric restriction in the liver of Wistar rats. Thus, the results suggest that part of the decrease in aging rate induced by caloric restriction can be due to the decreased intake of proteins acting through decreases in mitochondrial ROS production and oxidative DNA damage. Interestingly, these tissue oxidative stress-linked parameters can be lowered by restricting only the intake of dietary protein, probably a more feasible option than caloric restriction for adult humans.     

Effects of fasting on oxidative stress in rat liver mitochondria

While moderate caloric restriction has beneficial effects on animal health state, fasting may be harmful. The present investigation was designed to test how fasting affects oxidative stress, and to find out whether the effects are opposite to those previously found in caloric restriction studies. We have focused on one of the main determinants of aging rate: the rate of mitochondrial free radical generation. Different parameters related to lipid and protein oxidative damage were also analyzed. Liver mitochondria from rats subjected to 72 h of fasting leaked more electrons per unit of O₂ consumed at complex III, than mitochondria from ad libitum fed rats. This increased leak led to a higher free radical generation under state 3 respiration using succinate as substrate. Regarding lipids, fasting altered fatty acid composition of hepatic membranes, increasing the double bond and the peroxidizability indexes. In accordance with this, we observed that hepatic membranes from the fasted animals were more sensitive to lipid peroxidation. Hepatic protein oxidative damage was also increased in fasted rats. Thus, the levels of oxidative modifications, produced either indirectly by reactive carbonyl compounds (N^epsilon- malondialdehyde-lysine), or directly through amino acid oxidation (glutamic and aminoadipic semialdehydes) were elevated due to the fasting treatment in both liver tissue and liver mitochondria. The current study shows that severe food deprivation increases oxidative stress in rat liver, at least in part, by increasing mitochondrial free radical generation during state 3 respiration and by increasing the sensitivity of hepatic membranes to oxidative damage, suggesting that fasting and caloric restriction have different effects on liver mitochondrial oxidative stress.     

Aging sensitizes toward ROS formation and lipid peroxidation in PS1M146L transgenic mice

Mutations in the presenilins (PS) account for the majority of familial Alzheimer disease (FAD) cases. To test the hypothesis that oxidative stress can underlie the deleterious effects of presenilin mutations, we analyzed lipid peroxidation products (4-hydroxynonenal (HNE) and malondialdehyde) and antioxidant defenses in brain tissue and levels of reactive oxygen species (ROS) in splenic lymphocytes from transgenic mice bearing human PS1 with the M146L mutation (PS1M146L) compared to those from mice transgenic for wild-type human PS1 (PS1wt) and nontransgenic littermate control mice. In brain tissue, HNE levels were increased only in aged (19-22 months) PS1M146L transgenic animals compared to PS1wt mice and not in young (3-4 months) or middle-aged mice (13-15 months). Similarly, in splenic lymphocytes expressing the transgenic PS1 proteins, mitochondrial and cytosolic ROS levels were elevated to 142.1 and 120.5% relative to controls only in cells from aged PS1M146L animals. Additionally, brain tissue HNE levels were positively correlated with mitochondrial ROS levels in splenic lymphocytes, indicating that oxidative stress can be detected in different tissues of PS1 transgenic mice. Antioxidant defenses (activities of antioxidant enzymes Cu/Zn-SOD, GPx, or GR) or susceptibility to in vitro oxidative stimulation was unaltered. In summary, these results demonstrate that the PS1M146L mutation increases mitochondrial ROS formation and oxidative damage in aged mice. Hence, oxidative stress caused by the combined effects of aging and PS1 mutations may be causative for triggering neurodegenerative events in FAD patients.     

Lifelong caloric restriction prevents age-induced oxidative stress in the sympathoadrenal system of Fischer 344 x Brown Norway rats

Aging is associated with oxidative damage and an imbalance in redox signaling in a variety of tissues, yet little is known about the extent of age-induced oxidative stress in the sympathoadrenal system. Lifelong caloric restriction has been shown to lower levels of oxidative stress and slow the aging process. Therefore, the aims of this study were twofold: (1) to investigate the effect of aging on oxidative stress in the adrenal medulla and hypothalamus and (2) determine if lifelong 40% caloric restriction (CR) reverses the adverse effects of age-induced oxidative stress in the sympathetic adrenomedullary system. Adult (18 months) and very old (38 months) male Fischer 344 x Brown Norway rats were divided into ad libitum or 40% CR groups and parameters of oxidative stress were analyzed in the adrenal medulla and the hypothalamus. A significant age-dependent increase in lipid peroxidation (+20%, P < 0.05) and tyrosine nitration (+111%, P < 0.001) were observed in the adrenal medulla while age resulted in a reduction in the protein expression of key antioxidant enzymes, CuZnSOD (−27%, P < 0.01) and catalase (−27%, P < 0.05) in the hypothalamus. Lifelong CR completely prevented the age-induced increase in lipid peroxidation in the adrenal medulla and restored the age-related decline in antioxidant enzymes in the hypothalamus. These data indicate that aging results in a significant increase in oxidative stress in the sympathoadrenal system. Importantly, lifelong CR restored the age-related changes in oxidative stress in the adrenal medulla and hypothalamus. Caloric restriction could be a potential non-pharmacological intervention to prevent increased oxidative stress in the sympathetic adrenomedullary system with age.     

Effect of dietary ghee – the anhydrous milk fat on lymphocytes in rats

Lymphocytes are important components of the immune system. Dietary lipids affect the functioning of the immune system. Changes in the lipid composition of the lymphocyte membrane is a case in point. Membrane structural changes are reflected in the altered function of the cell. Lymphocyte proliferation and lymphocyte rosetting are membrane associated phenomena. Ghee, is a clarified butter product, commonly used in the Indian diet. It is rich in saturated fatty acids and also contain oxysterols which are generated on prolonged heating of ghee. Male weanling rats were fed 2.5% (of the total fat levels) of fresh or thermally oxidized ghee for a period of 8 weeks. The control rats were fed groundnut oil. Lipid composition of lymphocytes in ghee fed rats showed changes. In vitro lipid peroxidation of lymphocyte membranes increased by 26% in oxidized ghee fed rats. Na⁺K⁺ ATPase activity was decreased in oxidized ghee fed rats (18%). Lymphocyte proliferation was reduced in ghee fed rats (32%), compared to the controls, irrespective of the mitogens used (ConA or PHA), or the tissue (splenocytes or peripheral blood lymphocytes). Oxysterols present in oxidized ghee are the likely agents inhibiting lymphoproliferation. Rosetting of lymphocytes decreased in the fresh ghee fed rats by 16% and in oxidized ghee fed rats by 25%. Membrane fluidity declined in the oxidized ghee fed rats. It is concluded that feeding ghee results in decreased proliferation of lymphocytes. Also, feeding oxidised ghee results in decreased proliferation of lymphocytes through alterations in the structure of the lymphocyte membranes in the rat.     

Carbohydrate restriction does not change mitochondrial free radical generation and oxidative DNA damage

Many previous investigations have consistently reported that caloric restriction (40%), which increases maximum longevity, decreases mitochondrial reactive species (ROS) generation and oxidative damage to mitochondrial DNA (mtDNA) in laboratory rodents. These decreases take place in rat liver after only seven weeks of caloric restriction. Moreover, it has been found that seven weeks of 40% protein restriction, independently of caloric restriction, also decrease these two parameters, whereas they are not changed after seven weeks of 40% lipid restriction. This is interesting since it is known that protein restriction can extend longevity in rodents, whereas lipid restriction does not have such effect. However, before concluding that the ameliorating effects of caloric restriction on mitochondrial oxidative stress are due to restriction in protein intake, studies on the third energetic component of the diet, carbohydrates, are needed. In the present study, using semipurified diets, the carbohydrate ingestion of male Wistar rats was decreased by 40% below controls without changing the level of intake of the other dietary components. After seven weeks of treatment the liver mitochondria of the carbohydrate restricted animals did not show changes in the rate of mitochondrial ROS production, mitochondrial oxygen consumption or percent free radical leak with any substrate (complex I- or complex II-linked) studied. In agreement with this, the levels of oxidative damage in hepatic mtDNA and nuclear DNA were not modified in carbohydrate restricted animals. Oxidative damage in mtDNA was one order of magnitude higher than that in nuclear DNA in both dietary groups. These results, together with previous ones, discard lipids and carbohydrates, and indicate that the lowered ingestion of dietary proteins is responsible for the decrease in mitochondrial ROS production and oxidative damage in mtDNA that occurs during caloric restriction.     

Attenuation of plasma dyslipidemia and oxidative damage by dietary caloric restriction in streptozotocin-induced diabetic rats

Oxidative stress has been proposed as the pathogenic mechanism linking insulin resistance with endothelial dysfunction during diabetes. The present study investigated the attenuation of plasma dyslipidemia and oxidative damage by caloric restriction in experimental diabetes. Forty male Wistar rats were divided into ad libitum and calorie-restricted groups. The calorie-restricted group was subjected to 30% caloric restriction for 63 days before induction of diabetes to 50% of both groups. Caloric restriction significantly (p<0.01) reduced the body weights, reactive oxygen species (ROS), catalase, total cholesterol levels and non-significantly reduced SOD activities in non-diabetic and diabetic rats. Caloric restriction was also found to improve blood glucose levels, glycated hemoglobin, malondialdehyde, triglyceride, oxidized glutathione and reduced glutathione levels and significantly (p<0.05) increased GPx and GR activities in the experimental animals. The non-diabetic rats fed ad libitum had the most significant increases in body weight which could be due to dyslipidemia. These results indicate that dietary caloric restriction attenuates the oxidative damage and dyslipidemia exacerbated during diabetes as evidenced by the significant reduction in their body weights, ROS, total cholesterol levels and the increases in GPx activity and redox status.     

Aging Increases N epsilon -(Carboxymethyl)lysine and Caloric Restriction Decreases N epsilon -(Carboxyethyl)lysine and N epsilon -(Malondialdehyde)lysine in Rat Heart Mitochondrial Proteins

The present investigation studies the effect of aging, short-term and long-term caloric restriction on four different markers of oxidative, glycoxidative or lipoxidative damage to heart mitochondrial proteins: protein carbonyls (measured by ELISA); N epsilon -(carboxyethyl)lysine (CEL), N epsilon -(carboxymethyl)lysine (CML), and N epsilon -(malondialdehyde)lysine (MDA-lys) measured by gas chromatography/mass spectrometry. Aging increased the steady state level of CML in rat heart mitochondria without changing the levels of the other three markers of protein damage. Short-term caloric restriction (six weeks) did not change any of the parameters measured. However, long-term (one year) caloric restriction decreased CEL and MDA-lys in heart mitochondria and did not change protein carbonyls and CML levels. The decrease in MDA-lys was not due to changes in the sensitivity of mitochondrial lipids to peroxidation since the measurements of the fatty acid composition showed that the total number of fatty acid double bonds was not changed by caloric restriction. The decrease in CEL and MDA-lys in caloric restriction agrees with the previously and consistently described finding that caloric restriction agrees with the previously and consistently described finding that caloric restriction lowers the rate of generation of reactive oxygen species (ROS) in rodent heart mitochondria, although in the case of CEL a caloric restriction-induced lowering of glycaemia can also be involved. The CEL and MDA-lys results support the notion that caloric restriction decreases oxidative stress-derived damage to heart mitochondrial proteins.     

Relationship between antioxidant potential and oxidative damage to lipids, proteins and DNA in aged rats

Oxidative stress has been implicated to play a major role in aging and age-related diseases. In the present study, we investigated the effects of aging on the total antioxidant capacity, uric acid, lipid peroxidation, total sulfhydryl group content and damage to DNA in adult (6 months), old (15 months) and senescent (26 months) male Wistar rats. The antioxidant capacity, determined by phycoerythrin-based TRAP method (total peroxyl radical-trapping potential) was significantly decreased in the plasma and myocardium of old and senescent rats, whereas plasma level of uric acid was elevated in 26-month-old rats. Age-related decline in plasma and heart antioxidant capacity was accompanied by a significant loss in total sulfhydryl group content, increased lipid peroxidation and higher DNA damage in lymphocytes. Correlations between TRAP and oxidative damage to lipids, proteins and DNA suggest that the decline in antioxidant status may play an important role in age-related accumulation of cell damage caused by reactive oxygen species.     

Aging increases Nepsilon-(carboxymethyl)lysine and caloric restriction decreases Nepsilon-(carboxyethyl)lysine and Nepsilon-(malondialdehyde)lysine in rat heart mitochondrial proteins

The present investigation studies the effect of aging, short-term and long-term caloric restriction on four different markers of oxidative, glycoxidative or lipoxidative damage to heart mitochondrial proteins: protein carbonyls (measured by ELISA); N epsilon -(carboxyethyl)lysine (CEL), N epsilon -(carboxymethyl)lysine (CML), and N epsilon -(malondialdehyde)lysine (MDA-lys) measured by gas chromatography/mass spectrometry. Aging increased the steady state level of CML in rat heart mitochondria without changing the levels of the other three markers of protein damage. Short-term caloric restriction (six weeks) did not change any of the parameters measured. However, long-term (one year) caloric restriction decreased CEL and MDA-lys in heart mitochondria and did not change protein carbonyls and CML levels. The decrease in MDA-lys was not due to changes in the sensitivity of mitochondrial lipids to peroxidation since the measurements of the fatty acid composition showed that the total number of fatty acid double bonds was not changed by caloric restriction. The decrease in CEL and MDA-lys in caloric restriction agrees with the previously and consistently described finding that caloric restriction agrees with the previously and consistently described finding that caloric restriction lowers the rate of generation of reactive oxygen species (ROS) in rodent heart mitochondria, although in the case of CEL a caloric restriction-induced lowering of glycaemia can also be involved. The CEL and MDA-lys results support the notion that caloric restriction decreases oxidative stress-derived damage to heart mitochondrial proteins.     

Biochemical and enzymatic characterization of thymic and splenic lymphocyte plasma membranes from inbred rats.

Purified splenic and thymic lymphocytes from the ACI and F344 strains of inbred rats were disrupted by controlled hypotonic treatment, and their plasma membranes were prepared by sucrose density gradient centrifugation. The plasma membrane preparations were highly purified as judged by the structural appearance of the smooth membrane vesicles, by the 10- to 15-fold enrichment of 5'-nucleotidase, which cytochemically localized exclusively in the plasma membranes of intact lymphocytes, by the high cholesterol to phospholipid molar ratio (0.7-1.0), and by the very low specific activities of the enzymes associated predominantly with mitochondria, lysosomes, and endoplasmic reticulum. The protein and the lipid contents of the membranes were 48-55 and 37-48%, respectively. The total lipid content of plasma membranes was characteristically higher in thymic than splenic lymphocytes from both ACI and F344 strains. The specific activity of 5'-nucleotidase was similar in splenic lymphocyte membranes of the ACI strain, and in both the thymic and splenic lymphocyte membranes of the F344 strain. In contrast, the thymic lymphocyte membranes in the ACI strain showed half as much 5'-nucleotidase specific activity. Cytochemical results indicated that the 5'-nucleotidase is located on the outside surface of the lymphocyte plasma membranes.     

Dietary caloric restriction improves the redox status at the onset of diabetes in hepatocytes of streptozotocin-induced diabetic rats

Enhanced production of free radicals and oxidative stress induced by hyperglycemia play a central role in the pathogenesis of diabetes and its complications. This study assessed the attenuation by dietary caloric restriction on the oxidative and lipid peroxidative effects of diabetes in the liver through reduction in body and organ weights and concomitant metabolic changes. Three-month-old male Wistar rats were subjected to ad libitum feeding and 30% caloric restriction for 9 weeks before induction of diabetes by intraperitoneal injection of 35 mg/kg body weight streptozotocin. The animals were sacrificed 2 weeks after streptozotocin treatment depicting the onset of diabetes. Caloric restriction significantly reduced the organ weights (p<0.01), malondialdehyde (p<0.01) and catalase activity (p<0.01), but significantly increased glutathione reductase activity (p<0.01), and GSH/GSSG ratios (p<0.05). Caloric restriction also non-significantly reduced reactive oxygen species, superoxide dismutase and oxidized glutathione but increased glutathione peroxidase activity and reduced glutathione levels in the diabetic rats. Our data indicate a decrease in lipid peroxidation, improvement in the antioxidant defense systems and restoration of the redox status in the liver by caloric restriction. Therefore, this could provide a non-invasive antioxidant therapy early in diabetes to prevent the development of the complications associated with the disease.     

Preventive effect of safranal against oxidative damage in aged male rat brain

An imbalance between production of reactive oxygen species (ROS) and its elimination by antioxidant defense system in the body has been implicated for causes of aging and neurodegenerative diseases. This study was design to assess the changes in activities of antioxidant enzymes (superoxide dismutase (SOD), glutathione-S-transferase (GST), catalase), lipid peroxidation and reduced glutathione (GSH) levels in the brain of 2, 10 and 20 month old rats, and to determine the effect of safranal on the status of selected oxidative stress indices in the 10 and 20 month old rats. The aged rats (10 and 20 months) were given intraperitoneal injections of safranal (0.5 mg/kg day) daily for one month. The results of this study demonstrated that aging caused significant increase in the level of lipid peroxidation as well decrease in the GSH level and activities of SOD and GST in the brain of aging rats. The results of this study showed that safranal ameliorated the increased lipid peroxidation level as well as decreased GSH content of the brain of 10 and 20 month old rats. In addition, safranal treatment to the 20 month old rats, which restored the SOD and GST activities. In conclusion, safranal can be effective to protect susceptible aged brain from oxidative damage by increasing antioxidant defenses.     

Caloric restriction prevents age-associated accrual of oxidative damage to mouse skeletal muscle mitochondria

The purpose of this study was to understand the nature of the causes underlying the senescence-related decline in skeletal muscle mass and performance. Protein and lipid oxidative damage to upper hindlimb skeletal muscle mitochondria was compared between mice fed ad libitum and those restricted to 40% fewer calories—a regimen that increases life span by 30–40% and attenuates the senescence-associated decrement in skeletal muscle mass and function. Oxidative damage to mitochondrial proteins, measured as amounts of protein carbonyls and loss of protein sulfhydryl content, and to mitochondrial lipids, determined as concentration of thiobarbituric acid reactive substances, significantly increased with age in the ad libitum-fed (AL) C57BL/6 mice. The rate of superoxide anion radical generation by submitochondrial particles increased whereas the activities of antioxidative enzymes superoxide dismutase, catalase, and glutathione peroxidase in muscle homogenates remained unaltered with age in the AL group. In calorically-restricted (CR) mice there was no age-associated increase in mitochondrial protein or lipid oxidative damage, or in superoxide anion radical generation. Crossover studies, involving the transfer of 18- to 22-month-old mice fed on the AL regimen to the CR regimen, and vice versa, indicated that the mitochondrial oxidative damage could not be reversed by CR or induced by AL feeding within a time frame of 6 weeks. Results of this study indicate that mitochondria in skeletal muscles accumulate significant amounts of oxidative damage during aging. Although such damage is largely irreversible, it can be prevented by restriction of caloric intake.     

Cardiac mitochondrial bioenergetics, oxidative stress, and aging

Mitochondria have been a central focus of several theories of aging as a result of their critical role in bioenergetics, oxidant production, and regulation of cell death. A decline in cardiac mitochondrial function coupled with the accumulation of oxidative damage to macromolecules may be causal to the decline in cardiac performance with age. In contrast, regular physical activity and lifelong caloric restriction can prevent oxidative stress, delay the onset of morbidity, increase life span, and reduce the risk of developing several pathological conditions. The health benefits of life long exercise and caloric restriction may be, at least partially, due to a reduction in the chronic amount of mitochondrial oxidant production. In addition, the available data suggest that chronic exercise may serve to enhance antioxidant enzyme activities, and augment certain repair/removal pathways, thereby reducing the amount of oxidative tissue damage. However, the characterization of age-related changes to cardiac mitochondria has been complicated by the fact that two distinct populations of mitochondria exist in the myocardium: subsarcolemmal mitochondria and interfibrillar mitochondria. Several studies now suggest the importance of studying both mitochondrial populations when attempting to elucidate the contribution of mitochondrial dysfunction to myocardial aging. The role that mitochondrial dysfunction and oxidative stress play in contributing to cardiac aging will be discussed along with the use of lifelong exercise and calorie restriction as countermeasures to aging. superoxide anion; longevity; postmitotic; calorie restriction; subsarcolemmal, interfibrillar, exercise     

Mitochondria and Organismal Longevity

Mitochondria are essential for various biological processes including cellular energy production. The oxidative stress theory of aging proposes that mitochondria play key roles in aging by generating reactive oxygen species (ROS), which indiscriminately damage macromolecules and lead to an age-dependent decline in biological function. However, recent studies show that increased levels of ROS or inhibition of mitochondrial function can actually delay aging and increase lifespan. The aim of this review is to summarize recent findings regarding the role of mitochondria in organismal aging processes. We will discuss how mitochondria contribute to evolutionarily conserved longevity pathways, including mild inhibition of respiration, dietary restriction, and target of rapamycin (TOR) signaling.