Effect of dietary restriction on age-related increase of liver susceptibility to peroxidation in rats

Impact of Intermittent Fasting and Dietary Restriction on Redox State, Energetic Metabolism, and Liver Injury in Common Bile Duct Ligation Model

The aim of this work was to test whether we can treat cholestasis with dietary approaches applied after the onset of the disease. The effects of intermittent fasting and dietary restriction on liver damage caused by common bile duct ligation (BDL) in rats were studied, with particular attention paid to changes in the activity of enzymes of energy metabolism and antioxidant protection. Morphological changes in liver tissue and serum markers of liver damage were assessed in rats with BDL kept for one month on ad libitum diet, intermittent fasting, or 35% dietary restriction. We studied parameters of glucose metabolism (activity of glycolysis and gluconeogenesis enzymes), TCA cycle, and indicators of oxidative stress and redox status of the liver tissue. Dietary restriction resulted in an increase in gluconeogenesis activity, antioxidant capacity, and autophagy activation. When implemented after BDL, none of the dietary restriction protocols reduced the level of oxidative stress, detrimental morphological and biochemical alterations, or the fibrosis progression. Thus, under severe damage and oxidative stress developing in cholestasis, dietary restrictions are not hepatoprotective and can only be used in a pre-treatment mode.

Lipocalin 2 regulates mitochondrial phospholipidome remodeling, dynamics, and function in brown adipose tissue in male mice

Mitochondrial function is vital for energy metabolism in thermogenic adipocytes. Impaired mitochondrial bioenergetics in brown adipocytes are linked to disrupted thermogenesis and energy balance in obesity and aging. Phospholipid cardiolipin (CL) and phosphatidic acid (PA) jointly regulate mitochondrial membrane architecture and dynamics, with mitochondria-associated endoplasmic reticulum membranes (MAMs) serving as the platform for phospholipid biosynthesis and metabolism. However, little is known about the regulators of MAM phospholipid metabolism and their connection to mitochondrial function. We discover that LCN2 is a PA binding protein recruited to the MAM during inflammation and metabolic stimulation. Lcn2 deficiency disrupts mitochondrial fusion-fission balance and alters the acyl-chain composition of mitochondrial phospholipids in brown adipose tissue (BAT) of male mice. Lcn2 KO male mice exhibit an increase in the levels of CLs containing long-chain polyunsaturated fatty acids (LC-PUFA), a decrease in CLs containing monounsaturated fatty acids, resulting in mitochondrial dysfunction. This dysfunction triggers compensatory activation of peroxisomal function and the biosynthesis of LC-PUFA-containing plasmalogens in BAT. Additionally, Lcn2 deficiency alters PA production, correlating with changes in PA-regulated phospholipid-metabolizing enzymes and the mTOR signaling pathway. In conclusion, LCN2 plays a critical role in the acyl-chain remodeling of phospholipids and mitochondrial bioenergetics by regulating PA production and its function in activating signaling pathways.

Effects of Aging and Methionine Restriction on Rat Kidney Metabolome

Methionine restriction (MetR) in animal models extends maximum longevity and seems to promote renoprotection by attenuating kidney injury. MetR has also been proven to affect several metabolic pathways including lipid metabolism. However, there is a lack of studies about the effect of MetR at old age on the kidney metabolome. In view of this, a mass spectrometry-based high-throughput metabolomic and lipidomic profiling was undertaken of renal cortex samples of three groups of male rats-An 8-month-old Adult group, a 26-month-old Aged group, and a MetR group that also comprised of 26-month-old rats but were subjected to an 80% MetR diet for 7 weeks. Additionally, markers of mitochondrial stress and protein oxidative damage were analyzed by mass spectrometry. Our results showed minor changes during aging in the renal cortex metabolome, with less than 59 differential metabolites between the Adult and Aged groups, which represents about 4% of changes in the kidney metabolome. Among the compounds identified are glycerolipids and lipid species derived from arachidonic acid metabolism. MetR at old age preferentially induces lipid changes affecting glycerophospholipids, docosanoids, and eicosanoids. No significant differences were observed between the experimental groups in the markers of mitochondrial stress and tissue protein damage. More than rejuvenation, MetR seems to induce a metabolic reprogramming.

Linking Lipid Metabolism to Chromatin Regulation in Aging

The lifespan of an organism is strongly influenced by environmental factors (including diet) and by internal factors (notably reproductive status). Lipid metabolism is critical for adaptation to external conditions or reproduction. Interestingly, specific lipid profiles are associated with longevity, and increased uptake of certain lipids extends longevity in Caenorhabditis elegans and ameliorates disease phenotypes in humans. How lipids impact longevity, and how lipid metabolism is regulated during aging, is just beginning to be unraveled. This review describes recent advances in the regulation and role of lipids in longevity, focusing on the interaction between lipid metabolism and chromatin states in aging and age-related diseases.

Carbohydrate restriction ameliorates nephropathy by reducing oxidative stress and upregulating HIF-1α levels in type-1 diabetic rats

Background

Carbohydrate restricted diet regimen is widely accepted as therapeutic approach for the treatment of kidney disease associated with type-2 diabetes, obesity and hypertensive disorders. The present study tested the influence of carbohydrate-energy restricted diet (CR) on type-1 diabetes induced renal dysfunction, hypoxia and structural alterations against diabetic rat group fed control diet (ad libitium).

Methods

Male wistar rats weighing between 180 and 190 g were subjected to 30% carbohydrate energy restricted diet (CR) and diabetes was induced by administration of streptozotocin (45 mg/kg., i.p). Assessment of renal function was done after 4 weeks by determining the serum levels of creatinine, BUN, proteinuria. Oxidative stress was determined by estimating the reduced glutathione, malonaldehyde levels, catalase activity and extent of renal hypoxia by estimating the HIF-1α levels in kidney tissue homogenates. Histological studies were conducted on kidney sections using hematoxylin and eosin, periodic acid-schiff staining.

Results

Diabetic rats exhibited marked hyperglycemia and renal dysfunction developed in diabetic rats fed control diet (ad libitium) as shown by significantly elevated levels of serum creatinine, BUN and massive proteinuria after 4 weeks period. CR diet treatment in diabetic rats significantly lowered hyperglycemia, reversed the above renal functional abnormalities, reduced oxidative stress and enhanced HIF-1α levels. Furthermore histological examination of kidney sections from CR diet treated diabetic rat group showed absence of glomerular hypertrophy, mesangial expansion and tubular vacoulations.

Conclusion

Our results demonstrated that CR diet treatment in diabetic rats attenuated renal damage by reducing oxidative stress and preventing the development of hypoxia by up-regulating HIF-1α levels.

Perspectives on the membrane fatty acid unsaturation/pacemaker hypotheses of metabolism and aging

The membrane pacemaker hypotheses of metabolism and aging are distinct, but interrelated hypotheses positing that increases in unsaturation of lipids within membranes are correlated with increasing basal metabolic rate and decreasing longevity, respectively. The two hypotheses each have evidence that either supports or contradicts them, but consensus has failed to emerge. In this review, we identify sources of weakness of previous studies supporting and contradicting these hypotheses and suggest different methods and lines of inquiry. The link between fatty acyl composition of membranes and membrane-bound protein activity is a central tenet of the membrane pacemaker hypothesis of metabolism, but the mechanism by which unsaturation would change protein activity is not well defined and, whereas fatty acid desaturases have been put forward by some as the mechanism behind evolutionary differences in fatty acyl composition of phospholipids among organisms, there have been no studies to differentiate whether desaturases have been more affected by natural selection on aging and metabolic rate than have elongases or acyltransferases. Past analyses have been hampered by potentially incorrect estimates of the peroxidizability of lipids and longevity of study animals, and by the confounding effect of phylogeny. According to some authors, body mass may also be a confounding effect that should be taken into account, though this is not universally accepted. Further research on this subject should focus more on mechanisms and take weaknesses of past studies into account.

Physiological underpinnings associated with differences in pace of life and metabolic rate in north temperate and neotropical birds

Animal life-history traits fall within limited ecological space with animals that have high reproductive rates having short lives, a continuum referred to as a "slow-fast" life-history axis. Animals of the same body mass at the slow end of the life-history continuum are characterized by low annual reproductive output and low mortality rate, such as is found in many tropical birds, whereas at the fast end, rates of reproduction and mortality are high, as in temperate birds. These differences in life-history traits are thought to result from trade-offs between investment in reproduction or self-maintenance as mediated by the biotic and abiotic environment. Thus, tropical and temperate birds provide a unique system to examine physiological consequences of life-history trade-offs at opposing ends of the "pace of life" spectrum. We have explored the implications of these trade-offs at several levels of physiological organization including whole-animal, organ systems, and cells. Tropical birds tend to have higher survival, slower growth, lower rates of whole-animal basal metabolic rate and peak metabolic rate, and smaller metabolically active organs compared with temperate birds. At the cellular level, primary dermal fibroblasts from tropical birds tend to have lower cellular metabolic rates and appear to be more resistant to oxidative cell stress than those of temperate birds. However, at the subcellular level, lipid peroxidation rates, a measure of the ability of lipid molecules within the cell membranes to thwart the propagation of oxidative damage, appear not to be different between tropical and temperate species. Nevertheless, lipids in mitochondrial membranes of tropical birds tend to have increased concentrations of plasmalogens (phospholipids with antioxidant properties), and decreased concentrations of cardiolipin (a complex phospholipid in the electron transport chain) compared with temperate birds.

Linkages between mitochondrial lipids and life history in temperate and tropical birds

Temperate birds tend to have a fast pace of life and short life spans with high reproductive output, whereas tropical birds tend to have a slower pace of life, invest fewer resources in reproduction, and have higher adult survival rates. How these differences in life history at the organismal level are rooted in differences at the cellular level is a major focus of current research. Here, we cultured fibroblasts from phylogenetically paired tropical and temperate species, isolated mitochondria from each, and compared their mitochondrial membrane lipids. We also correlated the amounts of these lipids with an important life history parameter, clutch size. We found that tropical birds tended to have less mitochondrial lipid per cell, especially less cardiolipin per cell, suggesting that cells from tropical birds have fewer mitochondria or less inner mitochondrial membrane per cell. We also found that the mitochondria of tropical birds and the species with the smallest clutch sizes had higher amounts of plasmalogens, a lipid that could serve as an antioxidant. Overall, our findings are consistent with the idea that there are underlying molecular and cellular physiological traits that could account for the differences in whole-animal physiology between animals with different life histories.

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.

Comparison of rat liver and brain proteasomes for oxidative stress-induced inactivation: Influence of ageing and dietary restriction

The present study examined brain and liver derived proteasome complexes to elucidate if there is a differential susceptibility in proteasome complexes from these tissues to undergo inactivation following exposure to oxidative stressors. It then examined the influence of ageing and dietary restriction (DR) on the observed proteasome inactivation. Studies used a filtration based methodology that allows for enrichment of proteasome complexes with less tissue than is required for traditional chromatography procedures. The results indicate that the brain has much lower levels of overall proteasome activity and exhibits increased sensitivity to hydrogen peroxide mediated inactivation as compared to proteasome complexes derived from the liver. Interestingly, the brain proteasome complexes did not appear to have increased susceptibility to 4-hydroxynonenal (HNE)-induced inactivation. Surprisingly, ageing and DR induced minimal effects on oxidative stress mediated proteasome inhibition. These results indicate that the brain not only has lower levels of proteasome activity compared to the liver, but is also more susceptible to inactivation following exposure to some (but certainly not all) oxidative stressors. This data also suggest that ageing and DR may not significantly modulate the resistance of the proteasome to inactivation in some experimental settings.

Aging and survival: the genetics of life span extension by dietary restriction

Reducing food intake to induce undernutrition but not malnutrition extends the life spans of multiple species, ranging from single-celled organisms to mammals. This increase in longevity by dietary restriction (DR) is coupled to profound beneficial effects on age-related pathology. Historically, much of the work on DR has been undertaken using rodent models, and 70 years of research has revealed much about the physiological changes DR induces. However, little is known about the genetic pathways that regulate the DR response and whether or not they are conserved between species. Elucidating these pathways may facilitate the design of targeted pharmaceutical treatments for a range of age-related pathologies. Here, we discuss how recent work in nonmammalian model organisms has revealed new insight into the genetics of DR and how the discovery of DR-specific transcription factors will advance our understanding of this phenomenon.

Age-related increase of superoxide generation in the brains of mammals and birds

Oxidative stress, an imbalance between endogenous levels of oxygen radicals and antioxidative defense, increases with aging. However, it is not clear which of these two factors is the more critical. To clarify the production of oxygen radicals increases with age, we examined oxygen radical-dependent chemiluminescent signals in ex vivo brain slices using a novel photonic imaging method. The chemiluminescent intensity was significantly decreased by the membrane permeable superoxide dismutase (SOD)/catalase mimic, but not by Cu,Zn-SOD. Inhibitors for complex I, III, and IV of the mitochondrial electron transport chain transiently enhanced the chemiluminescent signal. The superoxide-dependent chemiluminescent intensity in senescence accelerated mouse (SAM) brain tissues increases with age. Moreover, the slope of the age-dependent increase was steeper in SAMP10, a strain characterized by a short lifespan and atrophy in the frontal cerebral cortex, than the senescence-resistant strain SAMR1, which has a longer lifespan. An increase in chemiluminescence with age was also observed in C57/BL6 mice, Wistar rats, and pigeons, although levels of chemiluminescence were lower in the pigeons than murines. The rate of age-related increases of superoxide-dependent chemiluminescence was inversely related to the maximum lifespan of the animals. The activity of superoxide dismutase was unchanged during the aging process in the brain. This suggested that superoxide production itself may increase with age. We speculated that reactive oxygen may be a signal to determine the aging process.

Molecular mechanisms involved in the hormonal prevention of aging in the rat

Previous data from our group have provided support for the role of GH, melatonin and estrogens in the prevention of aging of several physiological parameters from bone, liver metabolism, vascular activity, the central nervous system (CNS), the immune system and the skin. In the present work data on the molecular mechanisms involved are presented. A total of 140 male and female rats have been submitted to different treatments over 10 weeks, between 22 and 24 months of age. Males have been treated with GH and melatonin. Females were divided in two groups: intact and castrated at 12 months of age. The first group was treated with GH and melatonin and the second with the two latter compounds and additionally with estradiol and Phytosoya. Aging was associated with a reduction in the number of neurons of the hylus of the dentate gyrus of the hippocampus and with a reduction of neurogenesis. GH treatment increased the number of neurons but did not increase neurogenesis thus suggesting a reduction of apoptosis. This was supported by the reduction in nucleosomes and the increase in Bcl2 observed in cerebral homogenates together with an increase in sirtuin2 and a reduction of caspases 9 and 3. Melatonin, estrogen and Phytosoya treatments increased neurogenesis but did not enhance the total number of neurons. Aging induced a significant increase in mitochondrial nitric oxide in the hepatocytes, together with a reduction in the mitochondrial fraction content in cytochrome C and an increase of this compound in the cytosolic fraction. Reductions of glutathione peroxidase and glutathione S-transferase were also detected, thus indicating oxidative stress and possibly apoptosis. Treatment for 2.5 months of old rats with GH and melatonin were able to significantly and favourably affect age-induced deteriorations, thus reducing oxidative damage. Keratinocytes obtained from old rats in primary culture showed an increase in lipoperoxides, caspases 8 and 3 as well as a reduction in Bcl2 leading to enhanced number of nucleosomes that was also restored upon treatments with GH and melatonin. In conclusion, GH and melatonin treatment seem to have beneficial effects against age-induced damage in the CNS the liver and the skin through molecular mechanisms reducing oxidative stress and apoptosis.

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.

Hypoxia-related lipid peroxidation: Evidences, implications and approaches

Hypoxia may be intensified by concurrent oxidative stress. Lack of oxygen in relation to aerobic ATP requirements, as hypoxia has been defined, goes along with an increased generation of reactive oxygen species (ROS). Polyunsaturated fatty acids (PUFAs) range among the molecules most susceptible to ROS. Oxidative breakdown of n-3 PUFAs may compromise not only membrane lipid matrix dynamics, and hence structure and function of membrane-associated proteins like enzymes, receptors, and transporters, but also gene expression. Eicosapentaenoic acid depletion, products of lipid peroxidation (LP), as well as, lack of oxygen may combine in exacerbating activity of nuclear factor kappa B (NFkappaB), an ubiquitous pro-inflammatory and anti-apoptotic transcription factor. Field studies at high altitude show malondialdehyde (MDA) content in exhaled breath condensate (EBC) of mountaineers to correlate with Lake Louis score of acute mountain sickness. A pathogenic role of LP in hypoxia can therefore be expected. By control of LP, some species seem to cope more efficiently than others with naturally occurring hypoxia. Limitation of potential pro-inflammatory effects of hypoxia-related LP by an adequate provision of n-3 PUFAs and antioxidants may contribute to increase survival under conditions where oxygen is lacking in relation to aerobic ATP requirements. A need for antioxidant intervention, however, should be weighed against the ROS requirement for triggering adaptive processes in response to an increased demand of oxygen.

Effect of exogenous administration of melatonin and growth hormone on pro-antioxidant functions of the liver in aging male rats

Aging is accompanied by changes in the morphology and physiology of organs and tissues, such as the liver. This process might be due to the accumulation of oxidative damage induced by reactive oxygen (ROS) and reactive nitrogen species (RNS). Hepatocytes are very rich in mitochondria and have a high respiratory rate, so they are exposed to large amounts of ROS and permanent oxidative stress. Twenty-four male Wistar rats of 22 months of age were divided into three groups. One group remained untreated and acted as the control group. The second was treated with growth hormone (GH) (2 mg/kg/d sc) and the third was submitted to treatment wit 1 mg/kg/d of melatonin in the drinking water. A group of 2-months-old male rats was used as young controls. After 10 wk of treatment the rats were killed by decapitation, and the liver was dissected and homogenized. Mitochondrial, cytosolic and microsomal fractions were obtained and cytochrome C, glutathione peroxidase, s-transferase and nitric oxide (NO) were measured. Aging induced a significant increase in mitochondrial nitric oxide. An increase in cytochrome C in the cytosolic fraction and a reduction in the mitochondrial fraction with age was also observed. Both GH and melatonin treatments significantly reduced the enhanced measures and increased the reduced values. A reduction in glutathione peroxidase and glutathione S-transferase was found in old control rats when compared with the group of young animals. Treatment for 2.5 months of old rats with GH and melatonin were able to increase the enzymes reaching values similar to those found in young animals. In conclusion, GH and melatonin treatment seems to have beneficial effects against age-induced damage in the liver.

Calorie Restriction in Mice: Effects on Body Composition, Daily Activity, Metabolic Rate, Mitochondrial Reactive Oxygen Species Production, and Membrane Fatty Acid Composition

Different levels of calorie restriction (CR) (125, 85, 50, or 40 kcal/wk for 1, 3, and 6 months) were examined in mice by using the paradigm of Weindruch and colleagues. Lean and total body mass increased on 125 and 85 kcal/wk, but there was negligible growth on low-energy intake. There was no CR-induced reduction in either daily activity or mass-specific metabolic rate. There was no CR-effect on in vitro reactive oxygen species production by liver or muscle mitochondria at 3 months, but after 6 months the effect was significantly reduced in liver mitochondria from 40 kcal/wk mice compared to 125 kcal/wk mice. Changes in the fatty acid composition of phospholipids from liver, kidneys, heart, brain, and skeletal muscle were observed following 1 month of CR.

Effect of isoflavone administration on age-related hepatocyte changes in old ovariectomized femal Wistar rats

Aging seems to be due to the accumulation of oxidative damage in cells and molecules. On the other hand, menopause and ovariectomy induce deleterious effects on different organs and systems that have been shown to be counteracted by estrogens and in a not so evident form also with phytoestrogens. The present study has investigated whether the administration of a commercial soy extract that contains approximately 10% isoflavones was able to modify some parameters related to oxidative stress and inflammation in hepatocytes isolated from old ovariectomized female Wistar rats. Eighteen 22-month-old animals that had been previously ovariectomized at 12 months of age were divided into four groups: ovariectomized control rats, estradiol-treated ovariectomized females and ovariectomized rats treated with isoflavones. Six intact female rats of 2 months of age were used as reference group. Hepatocytes were isolated and cultured, and carbon monoxide (CO) and nitric oxide (NO) release, as well as adenosyl triphosphate (ATP), cyclic guanosyl monophosphate (cGMP), phosphatidylcholine (PC) and lipid peroxide (LPO) content of cells were evaluated. Uterus was also removed and weighed. Hepatocytes isolated from old ovariectomized rats showed a decrease in ATP content as compared to young animals. Age also induced an increase in LPO cell content. NO, CO and cGMP were augmented with age, and PC synthesis showed a dramatic reduction. Treatment with either estradiol or isoflavones were able to improve all the mentioned parameters altered in hepatocytes isolated from old ovariectomized rats, and the magnitude of the improvement was similar for both treatments. Ovariectomy induced a significant reduction in uterine weight, which was significantly counteracted by estradiol treatment but not by isoflavone administration. In conclusion, the administration of a soy extract containing isoflavones seems to prevent oxidative changes in hepatocytes isolated from old ovariectomized female rats, without modifying uterus weight.

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 O(2) 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.

The plasma membrane redox system in aging

Oxidative stress over time leads to the accumulation of damaged macromolecules and to profound physiological changes that are associated with several age-related diseases. The plasma membrane redox system (PMRS) appears to attenuate oxidative stress acting as a compensatory mechanism during the aging process. The PMRS appears to play a protective role during mitochondrial dysfunction to provide cells with a survival mechanism by lowering oxidative stress. The PMRS accomplishes this by producing more NAD(+) for glycolytic ATP production via transfer of electrons from intracellular reducing equivalents to extracelluar acceptors. Ubiquinone and alpha-tocopherol are key antioxidant molecules in the plasma membrane that are affected by aging and can be up-regulated by dietary interventions such as calorie restriction (CR). Up-regulation of PMRS activity leads to cell survival and membrane homeostasis under stress conditions and during calorie restriction. Further studies of the PMRS may provide not only additional information on the mechanisms involved in aging and CR, but may provide therapeutic targets for the prevention and treatment of age-related diseases.

Minireview: the role of oxidative stress in relation to caloric restriction and longevity

Reduction of caloric intake without malnutrition is one of the most consistent experimental interventions that increases mean and maximum life spans in different species. For over 70 yr, caloric restriction has been studied, and during the last years the number of investigations on such nutritional intervention and aging has dramatically increased. Because caloric restriction decreases the aging rate, it constitutes an excellent approach to better understand the mechanisms underlying the aging process. Various investigations have reported reductions in steady-state oxidative damage to proteins, lipids, and DNA in animals subjected to restricted caloric intake. Most interestingly, several investigations have reported that these decreases in oxidative damage are related to a lowering of mitochondrial free radical generation rate in various tissues of the restricted animals. Thus, similar to what has been described for long-lived animals in comparative studies, a decrease in mitochondrial free radical generation has been suggested to be one of the main determinants of the extended life span observed in restricted animals. In this study we review recent reports of caloric restriction and longevity, focusing on mitochondrial oxidative stress and the proposed mechanisms leading to an extended longevity in calorie-restricted animals.

Effects of caloric restriction on post-spawning death of ayu

Caloric restriction (CR) is the only established intervention that extends life span in mammals, insects and nematodes. One of the hypotheses suggested that most of the effects of CR on aging may be due to reduced oxidative stress at the cellular level. It was known that ayu (Plecoglossus altivelis) produced ROS higher than other fish and that the life span of ayu is only one year. The present study attempts to quantify age-associated changes of the degree of attenuation on oxidative damage and hormonal homeostases in CR. The levels of 8-OHdG as the oxidative DNA damage level and the caspase-9/6, -3-like activities as the induction factors of apoptosis with aging in brain and liver were surveyed. Caspase-like activities in brain and liver were reduced by CR, while CR had no influence on DNA damage level. However, life span of ayu was not prolonged by CR. These results suggested that there would be factors determining life span of ayu other than CR and apoptosis.

Mouse liver plasma membrane redox system activity is altered by aging and modulated by calorie restriction

Caloric restriction (CR) is known as the only non-genetic method proven to slow the rate of aging and extend lifespan in animals. Free radicals production emerges from normal metabolic activity and generates the accumulation of oxidized macromolecules, one of the main characteristics of aging. Due to its central role in cell bioenergetics, a great interest has been paid to CR-induced modifications in mitochondria, where CR has been suggested to decrease reactive oxygen species production. The plasma membrane contains a trans-membrane redox system (PMRS) that provides electrons to recycle lipophilic antioxidants, such as α-tocopherol and coenzyme Q (CoQ), and to modulate cytosolic redox homeostasis. In the present study, we have investigated age differences in the PMRS in mouse liver and their modulation by CR. Aging induced a decrease in the ratio of CoQ10/CoQ9 and α-tocopherol in liver PM from AL-fed mice that was attenuated by CR. CoQ-dependent NAD(P)H dehydrogenases highly increased in CR old mice liver PMs. On the other hand, the CoQ-independent NADH-FCN reductase activity increased in AL-fed animals; whereas, in mice under CR this activity did not change during aging. Our results suggest that liver PMRS activity changes during aging and that CR modulates these changes. By this mechanism CR maintains a higher antioxidant capacity in liver PM of old animals by increasing the activity of CoQ-dependent reductases. Also, the putative role of PMRS in the modulation of redox homeostasis of cytosol is implicated.

On the importance of fatty acid composition of membranes for aging

The membrane pacemaker theory of aging is an extension of the oxidative stress theory of aging. It emphasises variation in the fatty acid composition of membranes as an important influence on lipid peroxidation and consequently on the rate of aging and determination of lifespan. The products of lipid peroxidation are reactive molecules and thus potent damagers of other cellular molecules. It is suggested that the feedback effects of these peroxidation products on the oxidative stress experienced by cells is an important part of the aging process. The large variation in the chemical susceptibility of individual fatty acids to peroxidation coupled with the known differences in membrane composition between species can explain the different lifespans of species, especially the difference between mammals and birds as well as the body-size-related variation in lifespan within mammals and birds. Lifespan extension by calorie-restriction can also be explained by changes in membrane fatty acid composition which result in membranes more resistant to peroxidation. It is suggested that lifespan extension by reduced insulin/IGF signalling may also be mediated by changes in membrane fatty acid composition.

Effect of melatonin administration on parameters related to oxidative damage in hepatocytes isolated from old Wistar rats

Aging induces changes in several organs and tissues, such as the liver, and this process might be due to oxidative damage caused by free radicals and inflammatory mediators. Melatonin is a secretory product with well-known antioxidant properties. The aim of this study was to investigate the effect of melatonin administration on age-induced alterations in hepatocytes. Twenty-two-month old male Wistar rats were treated with oral melatonin for 10 wk. At the end of the treatment, hepatocytes were isolated and cultured, and different parameters were measured in both cells and medium. Aging induced a significant increase in lipid peroxidation, nitric oxide, carbon monoxide and cyclic guanosyl-monophosphate, as well as a reduction in adenosine triphosphate content and phosphatidylcholine synthesis when compared to young animals. Melatonin administration significantly ameliorated all these age-related changes in males. Melatonin administration seems to exert beneficial effects against age-induced changes in hepatocytes.

Effect of recombinant human growth hormone on age-related hepatocyte changes in old male and female Wistar rats

Aging induces changes in several organs, such as the liver, and this process might be due to damage caused by free radicals and inflammatory mediators. The growth hormone (GH)/insulin-like growth factor-1 (IGF-1) axis shows a reduction with age, and this fact could be associated with some age-related changes. The aim of this study was to investigate the effect of GH administration on age-induced alterations in hepatocytes. Two and twenty two month-old male and female Wistar rats were used. Old rats were treated with human recombinant GH for 10 wk. At the end of the treatment, hepatocytes were isolated from the liver and cultured, and different parameters were measured in cells and medium. Plasma IGF-1 was also measured. Aging significantly decreased plasma IGF-1 in males. In females, plasma IGF-1 was also reduced, but not significantly. GH treatment restored plasma IGF-1 levels to values similar to young males. Aging was associated with a significant increase in lipid peroxidation (LPO), nitric oxide (NO), carbon monoxide (CO) and cyclic guanosyl-monophosphate (cGMP), as well as a reduction in adenosyl triphosphate (ATP) and phosphatidylcholine (PC) synthesis. GH administration partially prevented all these changes in males. In females, some of the parameters were significantly improved by GH (ATP, CO, cGMP), while others showed a tendency to improvement, although differences did not reach significance. In conclusion, GH administration could exert beneficial effects against age-related changes in hepatocytes, mainly in males.

Effect of ageing and caloric restriction on specific markers of protein oxidative damage and membrane peroxidizability in rat liver mitochondria

To gain insight into the anti-ageing mechanisms of caloric restriction (CR), liver mitochondria were isolated from male Brown-Norway rats of different ages (fully fed control and CR) and various specific markers of non-enzymatic protein modification (by oxidative, glyco- and lipoxidative-reactions) were measured by GC/MS and Western blotting. A membrane peroxidizability index (PI) was calculated from the fatty acid profiles. Between 6 and 18 months of age, there were significant decreases in the concentration of all markers of damage in mitochondria from both the fully fed and CR groups. In contrast, between the ages of 18 and 28 months, there were significant increases in the concentrations of all markers of damage. In mitochondria from both fully fed and CR groups, there were significant increases in N-epsilon (Nepsilon)-(carboxymethyl)lysine (CML) and N-epsilon-(malondialdehyde)lysine (MDAL) between 6 and 28 months of age. In general, damage tended to be lower in mitochondria from CR animals, but the effects were not significant, except for the concentration of N-epsilon-(carboxymethyl)lysine at 28 months of age. PI increased steadily and significantly with age in fully fed animals, whilst CR induced a significant decrease in this index at 28 months of age. It is concluded that for male rats of the Brown-Norway strain, and mitochondria from liver (i) old (but not mature) age is associated with an increased membrane PI and protein oxidative damage and (ii) CR does not lead to a general reversion in age-related protein damage, but it does prevent the age-induced increase in PI very late in life.

Calorie restriction attenuates age-related alterations in the plasma membrane antioxidant system in rat liver

Aging is associated with increased production of reactive oxygen species and oxidation-induced damage to intracellular structures and membranes. Caloric restriction (CR) is the only non-genetic method proven to extend lifespan in mammals. Although the mechanisms of CR remain to be clearly elucidated, reductions in oxidative stress have been shown to increase lifespan in several model systems. Oxidative stress can be attenuated by CR. Mitochondria and plasma membrane (PM) are normal sources of free radicals. The PM has a trans-membrane redox system that provides electrons to recycle lipophilic antioxidants, such as alpha-tocopherol and coenzyme Q (CoQ). The idea developed in this study is that the PM is intimately involved in cellular physiology controlling the relationship of the cell to its environment. PM is the key for protecting cellular integrity during aging. Specifically, we have investigated age-related alterations and the effects of CR in the trans-PM redox (antioxidant) system in rat liver. We found that age-related declines in the ratio of CoQ(10)/CoQ(9) and alpha-tocopherol in liver PM were attenuated by CR compared to those fed ad libitum (AL). CoQ-dependent NAD(P)H dehydrogenases were increased in CR old rat liver PMs. As a consequence, the liver PM of CR old rats was more resistant to oxidative stress-induced lipid peroxidation than AL rats. Thus, our results suggest that CR induces a higher capacity to oxidize NAD(P)H in the PM of old rat livers and as a result, a higher resistance to oxidative stress-induced damage.

Life, death and membrane bilayers

Membrane bilayers are essential elements of life, and the synthesis of the hydrocarbons that make up membrane bilayers may have preceded the appearance of life on Earth. Membrane-associated processes are significant components of metabolism, and the acyl composition of membrane bilayers is associated with metabolic activity in a predictable manner. This has resulted in the "membrane pacemaker" theory of metabolism, which proposes that the relative balance between monounsaturated and long-chain polyunsaturated acyl chains in membrane bilayers is a fundamental determinant of metabolic rate of a species. The omega-3 polyunsaturated docosahexaenoate is an especially important component of membranes in this regard. Whilst it is suggested that the physical properties of membrane polyunsaturates are important with respect to their influence on metabolic rate, it is their chemistry that is important in aging. Membrane acyl composition is related to maximum lifespan in mammals and birds, probably via their role in lipid peroxidation. Calorie restriction modifies acyl composition of membrane bilayers and is associated with decreased membrane lipid peroxidation and lifespan extension. The membrane pacemaker theory of metabolism has given birth to the membrane pacemaker hypothesis of aging, which will require further investigation.

Food restriction and fish oil suppress atherogenic risk factors in lupus-prone (NZB x NZW) F1 mice

Atherosclerosis-mediated coronary artery disease is a significant cause of mortality in lupus patients. Both an activated immune system and hyperlipidemia are implicated in the pathogenesis of the atherosclerotic lesions of lupus. In this study, the increases in anticardiolipin antibodies, total cholesterol, and LDL cholesterol with age were significantly lowered by fish oil and food restriction, either alone or in combination. Food restriction also significantly decreased the elevation in anti-dsDNA antibody production seen with age in ad libitum groups. Interestingly, effects of food restriction and fish oil on both lipid profile and autoantibody production were seen from a young age. Accumulation of leukocytes in the blood vessels and deposition of IgG in the glomerular mesangium also were suppressed by food restriction. Thus, beneficial effects of fish oil and food restriction on lupus nephritis and survival could be, at least in part, due to their selective effect on atherogenic risk factors.