Relationship between antioxidant defenses and longevity in different mammalian species

Open-minded scepticism: inferring the causal mechanisms of human ageing from genetic perturbations

Given the myriad of age-related changes and the many proposed mechanistic theories of ageing, a major problem in gerontology is distinguishing causes from effects. This review aims to identify and evaluate those mechanisms which have gathered experimental support in favour of seeing them as a cause rather than an effect of ageing. Recent results related to energy metabolism and ageing, the free radical and the DNA damage theories of ageing are reviewed and their predictions evaluated through a systems biology rationale. Crucial in this approach are genetic manipulations in animal models that enable researchers to discriminate causes from effects of ageing and focus on the causal structure of human ageing. Based on a system-level interpretation, the GH/IGF-1 axis appears the most likely explanation for caloric restriction and a possible causal mechanism of human ageing. Although much work remains to fully understand the human ageing process, there is little evidence that free radicals are a causal factor in mammalian ageing, though they may be involved in signalling pathways related to ageing. On the other hand, studying how the DNA machinery affects ageing appears a promising avenue for disclosing the human ageing process.

Mitochondrial superoxide: production, biological effects, and activation of uncoupling proteins

Mitochondria are potent producers of cellular superoxide, from complexes I and III of the electron transport chain, and mitochondrial superoxide production is a major cause of the cellular oxidative damage that may underlie degradative diseases and aging. This superoxide production is very sensitive to the proton motive force, so it can be strongly decreased by mild uncoupling. Superoxide and the lipid peroxidation products it engenders, including hydroxyalkenals such as hydroxynonenal, are potent activators of proton conductance by mitochondrial uncoupling proteins such as UCP2 and UCP3, although the mechanism of activation has yet to be established. These observations suggest a hypothesis for the main, ancestral function of uncoupling proteins: to cause mild uncoupling and so diminish mitochondrial superoxide production, hence protecting against disease and oxidative damage at the expense of a small loss of energy. We review the growing evidence for this hypothesis, in mitochondria, in cells, and in vivo. More recently evolved roles of uncoupling proteins are in adaptive thermogenesis (UCP1) and perhaps as part of a signaling pathway to regulate insulin secretion in pancreatic beta cells (UCP2).

Free radical-dependent nuclear localization of Bcl-2 in the central nervous system of aged rats is not associated with Bcl-2-mediated protection from apoptosis

We have previously reported that Bcl-2 is up-regulated in the CNS of aged F344 rats as a consequence of oxidative stress. In addition to increased levels of expression, we now report that there is a subcellular redistribution of Bcl-2 in the CNS of aged F344 rats. Using western blotting, we found Bcl-2 predominantly located in the cytosol of young rats. However, in aged rats Bcl-2 was found primarily in the nucleus. This distribution, in the hippocampus and cerebellum, was reversed by treatment with the nitrone spin trap N-tert-butyl-alpha-phenylnitrone (PBN). Paradoxically, PBN treatment in young rats had the opposite effect, changing Bcl-2 from predominantly cytosolic to nuclear. We also detected an increase in Bax in aged hippocampal samples (both nuclear and cytosolic), which was reversed by treatment with PBN. The distribution of Bcl-2 and Bax in the cytosol of aged rats dramatically decreased the Bcl-2/Bax ratio, a probable indicator of neuronal vulnerability, which was restored upon treatment with PBN. In order to assess the effect of nuclear association of Bcl-2 we used PC12 cells stably transfected with a Bcl-2 construct to which we added the nuclear localization sequence of the SV40 large T antigen to the N-terminus which resulted in nuclear targeting of Bcl-2. Measurement of cell death using lactate dehydrogenase assays showed that, contrary to wild-type Bcl-2, Bcl-2 localized to the nucleus was not effective in protecting cells from treatment with 250 microm H2O2. These results suggest that nuclear localization of Bcl-2 observed in the aged CNS may not reflect a protective mechanism against oxidative stress, a major component of age-associated CNS impairments.

Selected contribution: Carotid body as a model for aging studies: is there a link between oxygen and aging?

The carotid body (CB) is the site in the body that triggers awareness of changes in blood oxygen pressure. Aging is characterized by a decrease in oxygen supply to tissues, in reduction of tissue Po2, and in the activity of several enzymes and metabolic factors. The ventilatory response to hypoxia is attenuated with aging related to the age-dependent structure modifications including the basal reduction of oxygen requirements. The aged CB shows an increase in extracellular matrix, a reduction in number and volume of type I cells, and a reduction in volume of mitochondria that was consistent with and similar to that during chronic hypoxia; this phenomenon seems to operate also during aging as shown by the reduced volume of mitochondria in the aged CB. During chronic hypoxia, CB hypertrophy is less evident in aged CB than in young CB. Therefore, hypoxia and aging seem to share some type of link at different cell sites. CB represents an experimental model adequate for studying aging processes because of its high blood flow and metabolism, and thus it serves as a means to understanding the oxygen modulation of the aging process.

Protein oxidation in aging: endoplasmic reticulum as a target

Oxidatively modified proteins have been shown to correlate with the age of an organism or its tissues. An increase in tissue-susceptibility to experimentally induced protein oxidation not only depends on tissue type and age, but also on the maximum lifespan potential of the species. A general, although tissue dependent, decline in anti-oxidative defenses during aging may very well be responsible for this difference in vulnerability. In addition, the level of protein modifications also depends on the nature and the subcellular localization of the proteins involved. Damage to the endoplasmic reticulum (ER), and its subsequent impaired functionality may be involved in the process of aging. This is suggested by; (1) an upregulation of ER stress-response chaperones, (2) a preferential oxidation of ER-resident proteins and, (3) a disturbance of calcium homeostasis. Therefore, this review will focus on the putative involvement of the oxidized endoplasmic reticulum in the process of aging.

Sex-dependent antioxidant enzyme activities and lipid peroxidation in ageing mouse brain

We investigated whether oxidant status and antioxidant enzyme activities during ageing of mouse brain are regulated in sex-dependent manner. In the homogenate from the brain of 1, 4, 10 and 18 months old male and female CBA mice, lipid peroxidation (LPO), total superoxide dismutase (tSOD), catalase (CAT) and glutathione peroxidase (Gpx) were determined. LPO was age- and sex-related, favoring males over females throughout the lifespan with the peak in both sexes at 10 months of age. Throughout ageing, no difference in tSOD activity between male and female brains was observed, except in immature 1 month old mice. Gender-related difference in Gpx activity was observed, with higher level in females comparing to males, reaching statistical significance in senescent (18 months old) animals. CAT activity was drastically changed with ageing in both the male and female brain. We found different age associated trends in CAT activity in males and females: decreased with age in males and increased with age in females. Taken together, the present findings indicate that brains of female mice have lower oxidant and higher antioxidant capacity mostly related to CAT and to a lesser extent to Gpx activity.

Pair-wise linear and 3D nonlinear relationships between the liver antioxidant enzyme activities and the rate of body oxygen consumption in mice

Relationships between the rate of body oxygen consumption (VO2) and the liver key antioxidant enzyme activities were assessed in female CBA mice. The pair-wise linear regression and correlation demonstrated significant correlative links between VO2 and activity of catalase (CAT). Nonlinear 3D plotting revealed a complementary pattern of CAT and glutathione peroxidase (GP) relation. CAT activity was elevated in mice with proportionally high VO2 and superoxide dismutase (SOD), whereas GP activity was high in animals with low or disproportional VO2 and SOD.

Rate of generation of oxidative stress-related damage and animal longevity

Comparative studies about the relationship between endogenous antioxidant and pro-oxidant factors and maximum longevity of different animal species are reviewed. The majority of studies on antioxidant supplementation indicate that it can increase mean survival without changing maximum longevity. On the other hand, endogenous antioxidants are negatively correlated with maximum longevity. The same is true for the rates of mitochondrial oxygen radical generation, oxidative damage to mitochondrial DNA, and the degree of fatty acid unsaturation of cellular membranes in postmitotic tissues. The lower rate of mitochondrial oxygen radical generation of long-lived animals in relation to that of short-lived ones can be a primary cause of their slow aging rate. This is secondarily complemented in long-lived animals with low rates of lipid peroxidation due to their low degrees of fatty acid unsaturation. These two traits suggest that the rate of generation of endogenous oxidative damage determines, at least in part, the rate of aging in animals.

Antioxidant gene expression in active and sedentary house mice (Mus domesticus) selected for high voluntary wheel-running behavior

We present liver mRNA levels of the two antioxidant enzymes catalase (CAT) and Mn-superoxide dismutase (SOD2) in four treatment groups of house mice assayed by RNase protection at 20 months of age. These groups were mice from four replicate selection and four replicate control lines from the sixteenth generation of selective breeding for high voluntary wheel running, housed with or without running wheels from age 3 weeks through 20 months. Exercising control females had induced CAT expression; SOD2 exhibited a similar pattern in females from two of the four control lines. Exercising male mice had induced CAT expression, but not SOD2 expression, irrespective of genetic background. We discuss these results with respect to both evolutionary (genetic) and training (exercise-induced) adaptations and explore predictions of these results in relation to the oxidative-damage theory of senescence.

Role of oxidative stress and protein oxidation in the aging process

The hypothesis is that the rate of oxygen consumption and the ensuing accrual of molecular oxidative damage constitute a fundamental mechanism governing the rate of aging is supported by several lines of evidence: (i) life spans of cold blooded animals and mammals with unstable basal metabolic rate (BMR) are extended and oxidative damage (OxD) is attenuated by an experimental decrease in metabolic rate; (ii) single gene mutations in Drosophila and Caenorhabditis elegans that extend life span almost invariably result in a generalized slowing of physiological activities, albeit via different mechanisms, affecting a decrease in OxD; (iii) caloric restriction decreases body temperature and OxD; and, (iv) results of studies on the effects of transgenic overexpressions of antioxidant enzymes are generally supportive, but quite ambiguous. It is suggested that oxidative damage to proteins plays a crucial role in aging because oxidized proteins lose catalytic function and are preferentially hydrolyzed. It is hypothesized that oxidative damage to specific proteins constitutes one of the mechanisms linking oxidative stress/damage and age-associated losses in physiological functions.

Endogenous oxidative stress: relationship to aging, longevity and caloric restriction

Available studies are consistent with the possibility that oxygen radicals endogenously produced by mitochondria are causally involved in the determination of the rate of aging in homeothermic vertebrates. Oxidative damage to tissue macromolecules seems to increase during aging. The rate of mitochondrial oxygen radical generation of post-mitotic tissues is negatively correlated with animal longevity. In agreement with this, long-lived animals show lower levels of oxidative damage in their mitochondrial DNA (mtDNA) than short-lived ones, whereas this does not occur in nuclear DNA (nDNA). Caloric restriction, which decreases the rate of aging, also decreases mitochondrial oxygen radical generation and oxidative damage to mitochondrial DNA. This decrease in free radical generation occurs in complex I and is due to a decrease in the degree of electronic reduction of the complex I free radical generator, similarly to what has been described in various cases in long-lived animals. These results suggest that similar mechanisms have been used to extend longevity through decreases in oxidative stress in caloric restriction and during the evolution of species with different longevities.

Living fast, dying when? The link between aging and energetics

The idea that aging should be linked to energy expenditure has a long history that can be traced to the late 1800s and the industrial revolution. Machines that are run fast wear out more quickly, so the notion was born that humans and animals might experience similar fates: the faster they live (expressed as greater energy expenditure), the sooner they die. Evidence supporting the "rate-of-living" theory was gleaned from the scaling of resting metabolism and life span as functions of body mass. The product of these factors yields a mass-invariant term, equivalent to the "amount of living." There are at least four problems with this evidence, which are summarized and reviewed in this communication: 1) life span is a poor measure of aging, 2) resting metabolism is a poor measure of energy expenditure, 3) the effects are confounded by body mass and 4) the comparisons made are not phylogenetically independent. We demonstrate that there is a poor association between resting metabolic rate (RMR) and daily energy expenditure (DEE) measured using the doubly labeled water (DLW) method at the level of species. Nevertheless, the scaling relation between DEE and body mass still has the same scaling exponent as the RMR and body mass relationship. Thus, if we use DEE rather than RMR in the analysis, the rate-of-living ideas are still supported. Data for 13 species of small mammal were obtained, where energy demands by DLW and longevity were reliably known. In these species, there was a strong negative relationship between residual longevity and residual DEE, both with the effects of body mass removed (r(2) = 0.763, F = 32.1, P < 0.001). Hence, the association of energy demands and life span is not attributed to the confounding effects of body size. We subjected these latter data to an analysis that extracts phylogenetically independent contrasts, and the relationship remained significant (r(2) = 0.815, F = 39.74, P < 0.001). Small mammals that live fast really do die young. However, there are very large differences between species in the amounts of living that each enjoy and these disparities are even greater when other taxa are included in the comparisons. Such differences are incompatible with the "rate-of-living" theory. However, the link between energetics and aging across species is reconcilable within the framework of the "free-radical damage hypothesis" and the "disposable soma hypothesis." Within species one might anticipate the rate-of-living model would be more appropriate. We reviewed data generated from three different sources to evaluate whether this were so, studies in which metabolic rate is experimentally increased and impacts on life span followed, studies of caloric restriction and studies where links between natural variation in metabolism and life span are sought. This review reveals that there might be contrasting effects of resting and nonresting energy expenditure on aging, with increases in the former being protective and increases in the latter being harmful.

Response of Sod-2 enzyme activity to selection for high voluntary wheel running

The objective of this study was to examine the correlated response of anti-oxidant enzyme activity to selective breeding for increased voluntary wheel running in house mice. Activity of liver superoxide dismutase-2 (Sod-2), a free radical scavenger, was measured in four groups of mice. 'Active' individuals were housed in cages with attached wheels for 8 weeks beginning at weaning; 'sedentary' individuals were housed in cages with attached wheels that were prevented from rotating. Both of these treatments were applied to male and female mice from generation 14 of a replicated artificial selection experiment, which is composed of four lines selected for high wheel running and four randomly bred lines that serve as controls. In females, Sod-2 activity was significantly lower in selected vs control animals, regardless of presence/absence of a free-turning wheel. This difference suggests a trade-off between early-age voluntary wheel-running activity and Sod-2 activity. In males, Sod-2 activity was significantly affected by an interaction between selection group and activity group, with males from selected lines having lower Sod-2 activity relative to control males only in the sedentary treatment. These negative correlated responses of Sod-2 activity to selection on wheel running are discussed in the context of antagonistic pleiotropy models of aging and with respect to potential effects on lifespan.

Ageing and the free radical theory

The free radical theory proposes that ageing is the cumulative result of oxidative damage to the cells and tissues of the body that arises primarily as a result of aerobic metabolism. Several lines of evidence have been used to support this hypothesis including the claims that: (1) variation in species life span is correlated with metabolic rate and protective antioxidant activity; (2) enhanced expression of antioxidative enzymes in experimental animals can produce a significant increase in longevity; (3) cellular levels of free radical damage increases with age; and (4) reduced calorie intake leads to a decline in the production of reactive oxygen species and an increase in life span. The free radical theory may also be used to explain many of the structural features that develop with ageing including the lipid peroxidation of membranes, formation of age pigments, cross-linkage of proteins, DNA damage and decline of mitochondrial function. Despite this, many uncertainties concerning the role of oxidative damage in ageing remain and alternative explanations cannot be ruled out. Free radicals only occur in trace quantities in biological tissues, their cellular levels and actions cannot be measured in vivo, and definitive proof that oxidised molecules are the primary cause of ageing is lacking. Moreover, ageing is also likely to be a multifactorial process and not reducible to any one single cause. Thus, despite its positive features, the evidence for the free radical theory is either correlative or inconclusive.

Increased infarct size and exacerbated apoptosis in the glutathione peroxidase-1 (Gpx-1) knockout mouse brain in response to ischemia/reperfusion injury

Glutathione peroxidase is an antioxidant enzyme that is involved in the control of cellular oxidative state. Recently, unregulated oxidative state has been implicated as detrimental to neural cell viability and involved in both acute and chronic neurodegeneration. In this study we have addressed the importance of a functional glutathione peroxidase in a mouse ischemia/reperfusion model. Two hours of focal cerebral ischemia followed by 24 h of reperfusion was induced via the intraluminal suture method. Infarct volume was increased three-fold in the glutathione peroxidase-1 (Gpx-1) -/- mouse compared with the wild-type mouse; this was mirrored by an increase in the level of apoptosis found at 24 h in the Gpx-1 -/- mouse compared with the wild-type mouse. Neuronal deficit scores correlated to the histologic data. We also found that activated caspase-3 expression is present at an earlier time point in the Gpx-1 -/- mice when compared with the wild-type mice, which suggests an enhanced susceptibility to apoptosis in the Gpx-1 -/- mouse. This is the first known report of such a dramatic increase, both temporally and in level of apoptosis in a mouse stroke model. Our results suggest that Gpx-1 plays an important regulatory role in the protection of neural cells in response to the extreme oxidative stress that is released during ischemia/reperfusion injury.

Oxidative-stress-dependent up-regulation of Bcl-2 expression in the central nervous system of aged Fisher-344 rats

Oxidative stress has been shown to play a role in aging and in neurodegenerative disorders. Some of the consequences of oxidative stress are DNA base modifications, lipid peroxidation, and protein modifications such as formation of carbonyls and nitrotyrosine. These events may play a role in apoptosis, another factor in aging and neurodegeneration, in response to uncompensated oxidative stress. Bcl-2 is a mitochondrial protein that protects neurons from apoptotic stimuli including oxidative stress. Using immunohistochemistry and western blot analysis, here we show that Bcl-2 is up-regulated in the hippocampus and cerebellum of aged (24 months) Fisher 344 rats. Treatment with the free radical spin trap N-tert-butyl-alpha-phenylnitrone (PBN) effectively reverses this age-dependent Bcl-2 up-regulation indicating that this response is redox sensitive. This conclusion was further supported by inducing the same regional Bcl-2 up-regulation in young (3 months) Fisher 344 rats exposed to 100% normobaric O(2) for 48 h. Our results indicate that Bcl-2 expression is increased in the aged brain, possibly as a consequence of oxidative stress challenges. These results also illustrate the effectiveness of antioxidants in reversing age-related changes in the CNS and support further research to investigate their use in aging and in age-related neurodegenerative disorders.

Improved cardiac performance after ischemia in aged rats supplemented with vitamin E and alpha-lipoic acid

The purpose of these experiments was to examine the effects of dietary antioxidant supplementation with vitamin E (VE) and alpha-lipoic acid (alpha-LA) on biochemical and physiological responses to in vivo myocardial ischemia-reperfusion (I-R) in aged rats. Male Fischer-334 rats (18 mo old) were assigned to either 1) a control diet (CON) or 2) a VE and alpha-LA supplemented diet (ANTIOX). After a 14-wk feeding period, animals in each group underwent an in vivo I-R protocol (25 min of myocardial ischemia and 15 min of reperfusion). During reperfusion, peak arterial pressure was significantly higher (P < 0.05) in ANTIOX animals compared with CON diet animals. I-R resulted in a significant increase (P < 0.05) in myocardial lipid peroxidation in CON diet animals but not in ANTIOX animals. Compared with ANTIOX animals, heart homogenates from CON animals experienced significantly less (P < 0.05) oxidative damage when exposed to five different in vitro radical producing systems. These data indicate that dietary supplementation with VE and alpha-LA protects the aged rat heart from I-R-induced lipid peroxidation by scavenging numerous reactive oxygen species. Importantly, this protection is associated with improved cardiac performance during reperfusion.

Decreased mitochondrial hydrogen peroxide release in transgenic Drosophila melanogaster expressing intramitochondrial catalase

The objective of this study was to develop strategies for manipulating oxidative stress transgenically in a multicellular organism. Ectopic catalase was introduced into the mitochondrial matrix, which is the main intracellular site of H2O2 formation and where catalase is normally absent. Transgenic Drosophila melanogaster were generated by microinjection of a P element construct, containing the genomic catalase sequence of Drosophila, with the mitochondrial leader sequence of ornithine aminotransferase inserted upstream of the coding region. Total catalase activities in whole-body homogenates of 10-day-old flies from four transgenic lines were approximately 30-160% higher than those from the parental and four vector-only control lines. Expression of catalase in the mitochondrial matrix was confirmed by immunoblotting and catalase activity assays. Mitochondrial release of H2O2 was decreased by approximately 90% in the transgenic lines when compared to levels in vector-only controls. This in vivo system provides a novel model for examining the functional significance of decreased mitochondrial H2O2 release.

The flux of free radical attack through mitochondrial DNA is related to aging rate

Aging is a progressive and universal process originated endogenously which manifests best in post-mitotic cells. Available data indicate that the relation between oxidative stress and aging is due to the presence of low rates of mitochondrial free radical production and low degrees of fatty acid unsaturation of cellular membranes in the post-mitotic tissues of long-lived animals in relation to those of short-lived ones. Recent research shows that long-lived animals also have lower steady-state levels of oxidative damage in the mitochondrial DNA (mtDNA) of post-mitotic cells than short-lived species. This study shows that the flux of free radical attack to mtDNA is higher in short- than in long-lived animals, and proposes that this is a main determinant of the rate of accumulation of mtDNA mutations, and thus the rate of aging. This implies that aging has been slowed evolutionarily by mechanisms that decrease the generation of endogenous damage rather than try to intercept damaging agents, or to repair the damage already inflicted. The first kind of mechanisms are more efficient and less energetically expensive. Free radicals of mitochondrial origin, oxidative damage to DNA, evolution of aging rate, and possibilities and consequences of their future modification are also discussed.

Current issues concerning the role of oxidative stress in aging: a perspective

The main tenet of the oxidative stress hypothesis of aging is that accrual of molecular oxidative damage is the principal causal factor in the senescence-related loss of ability to maintain homeostasis. This hypothesis has garnered a considerable amount of supportive correlational evidence, which is now being extended experimentally in transgenic Drosophila over-expressing antioxidative defense enzymes. Some of these studies have reported extensions of life span, while others have not. Interpretation of life spans in poikilotherms is complicated by a number of factors, including the interrelationship between metabolic rate and longevity. The life spans of poikilotherms can be extended multi-fold by reducing the metabolic rate but without affecting the metabolic potential, i.e., the total amount of energy expended during life. A hypometabolic state in poikilotherms also enhances stress resistance and activities of antioxidative enzymes. It is emphasized that extension of life span without simultaneously increasing metabolic potential is of questionable biological significance.

Monograph: reassessment of human cancer risk of aldrin/dieldrin

In 1987, the US Environmental Protection Agency (EPA) classified aldrin and dieldrin as category B2 carcinogens, i.e. probable human carcinogens, based largely on the increase in liver tumors in mice fed either organochlorine insecticide. At that date, the relevant epidemiology was deemed inadequate to influence the cancer risk assessment. More time has now elapsed since early exposures of manufacturing workers to aldrin/dieldrin; therefore, updated epidemiological data possess more power to detect exposure-related differences in cancer risk and mortality. Also, recent experimental studies provide a plausible mode of action to explain the mouse specificity of dieldrin-induced hepatocarcinogenesis and call into question the relevance of this activity to human cancer risk. This monograph places this new information within the historic and current perspectives of human cancer risk assessment, including EPA's 1996 Proposed Guidelines for Carcinogen Risk Assessment. Updated epidemiological studies of manufacturing workers in which lifetime exposures to aldrin/dieldrin have been quantified do not indicate increased mortality or cancer risk. In fact, at the middle range of exposures, there is evidence of a decrease in both mortality from all causes and cancer. Recent experimental studies indicate that dieldrin-induced hepatocarcinogenesis in mice occurs through a nongenotoxic mode of action, in which the slow oxidative metabolism of dieldrin is accompanied by an increased production of reactive oxygen species, depletion of hepatic antioxidant defenses (particularly alpha-tocopherol), and peroxidation of liver lipids. Dieldrin-induced oxidative stress or its sequelae apparently result in modulation of gene expression that favors expansion of initiated mouse, but not rat, liver cells; thus, dieldrin acts as a nongenotoxic promoter/accelerator of background liver tumorigenesis in the mouse. Within the framework of EPA's Proposed Guidelines for Carcinogen Risk Assessment, it is proposed that the most appropriate cancer risk descriptor for aldrin/dieldrin, relating to the mouse liver tumor response, is 'not likely a human carcinogen', a descriptor consistent with the example of phenobarbital cited by EPA.

MAO inhibitors and oxidant stress in aging brain tissue

The process of aging presents itself with various alterations in physiological events. Among many theories, the free radical (FR) theory of aging which reflects the FR damage to cellular components is accepted as one of the most important theories. Recently, the increases in catecholamine metabolism in aging have also attracted attention, and monoamine oxidase (MAO), a key enzyme in this process has been extensively studied. The aim of this study was to assess the role of FR species via MAO, a possible source of FRs, in physiological aging by determining the lipid peroxidation products (LPP) (malondialdehyde, diene conjugates) and antioxidant enzyme levels (superoxide dismutase (SOD) and catalase (CAT) in young (3 months old, n=10) and aging (16-18 months old, n=10) rat brain tissues of Swiss male albino rats. In the second part of the study, the same parameters were determined after the acute administration of MAO inhibitors (deprenyl and pargyline, 25 mg/kg i.p.) to investigate whether these agents have any beneficial effects in reducing oxidant stress via inhibition of MAO. In old rat brains, MAO activities showed a significant increase (P=0.000) in addition to an insignificant increase in LPP, while SOD (P=0.007) and CAT activities showed a decrease with advancing age. After the acute administration of both deprenyl and pargyline, a significant decrease in the MAO activities of both young (P=0.0002 for each) and aging rats (P=0.0002 for deprenyl and P=0.0001 for pargyline) were observed. It was noted that deprenyl causes a significant increase in CAT activity (P<0.05) but a significant decrease in SOD activity (P<0.05) in young rats, while it causes only a significant increase in SOD activity in aging rats (P<0.05). Both deprenyl and pargyline cause a significant decrease in conjugated diene levels of aging rats (P<0.05). These results confirm the role of catecholamine oxidation and MAO activity as one of the causative factors in increased oxidant stress during aging. By reducing the oxidant stress observed in aging brain, MAO inhibitors, especially deprenyl, may contribute to the control of the aging process.

Profile of reactive oxygen species generation and antioxidative mechanisms in the maturing rat kidney

The antioxidative potential and reactive oxygen species generation were assessed in rat kidney during early critical periods of development and maturation. Superoxide anion generation was found to be low in kidney during early postnatal days of development, whereas hydrogen peroxide levels remained unaltered during development. The levels of thiobarbituric acid reactive substances and protein carbonyls in developing kidney were higher during early postnatal days, up to 26 days after birth, compared to the adult levels. Kidney sulphydryl contents were significantly less during early periods (9 days postnatally) of development compared to adults but attain adult value by postnatal day 26. The levels of ascorbic acid and ceruloplasmin were also higher in developing kidney than in adults. Among enzymic antioxidants, the levels of glutathione peroxidase (GPx) enzyme in developing kidney were high during the early developmental period of the study as compared to adults; however, superoxide dismutase (SOD), catalase (CAT) and glutathione reductase (GR) were found to be significantly low at early postnatal days up to 16 days of age, which subsequently attained maturational level by the age of 26 days. The levels of antioxidant enzymes and sulphydryl contents in the developing kidney during early periods after birth are low but they increase subsequently with increasing age. Therefore, the present finding suggests that immature kidneys are in a highly dynamic stage of development during the early period and are equipped with antioxidative defence mechanisms that may have a predominant role in protecting against oxidative challenge.

Variability of oxygen radical absorbance capacity (ORAC) in different animal species

The oxygen radical absorbance capacity (ORAC) was measured both in whole (ORAC-T) and deproteinized (ORAC-AS) plasma samples of human, pig, cow, rabbit, dog, cat, sheep, horse, dolphin, turkey, guinea-hen and chicken. In the 12 species, ORAC-T data, expressed as micromoles of peroxyl radicals trapped by 11 of sample, were found scattered between 8,600 and 23,000 micromol/l. The species with the highest ORAC-T values were cat among mammals and chicken among avies. ORAC-AS values ranged between 600 and 2000 micromol/l, with the highest values found in dolphin and sheep among mammals, while chicken was first among avies. In the 12 species, the relative contribution of ORAC-AS in relation to ORAC-T ranged from 5% to 20%. Protein SH-groups and uric acid were measured in plasma of all species, but no significant correlation was found between thiols and ORAC-T values or between uric acid and ORAC-AS values. Our results show that: (1) the ORAC method is reproducible and sensitive enough to be used in the comparison of the peroxyl-radical absorbance capacity of protein and non-protein plasma components in different animal species; (2) both in mammals and in avies, there is a deep intra-class heterogeneity of ORAC-T and ORAC-AS values; (3) by considering most species, plasma proteins and lipoproteins account for about 85-90% of the overall peroxyl-radical trapping capacity. In the dolphin only, the protein contribution decreases to 80%; (4) uric acid accounts for about one-half of the ORAC-AS value in human, guinea-hen and for about one-third in chicken, while it provides a very limited contribution in other species. We conclude that species with the highest ORAC-T, like cat and chicken, or with the highest ORAC-AS, like dolphin, are interesting models to study the reasons of such a marked antioxidant defense in the plasma.

Mice with a homozygous null mutation for the most abundant glutathione peroxidase, Gpx1, show increased susceptibility to the oxidative stress-inducing agents paraquat and hydrogen peroxide

Glutathione peroxidases have been thought to function in cellular antioxidant defense. However, some recent studies on Gpx1 knockout (-/-) mice have failed to show a role for Gpx1 under conditions of oxidative stress such as hyperbaric oxygen and the exposure of eye lenses to high levels of H2O2. These findings have, unexpectedly, raised the issue of the role of Gpx1, especially under conditions of oxidative stress. Here we demonstrate a role for Gpx1 in protection against oxidative stress by showing that Gpx1 (-/-) mice are highly sensitive to the oxidant paraquat. Lethality was already detected within 24 h in mice exposed to paraquat at 10 mg.kg-1 (approximately (1)/(7) the LD50 of wild-type controls). The effects of paraquat were dose-related. In the 30 mg.kg-1-treated group, 100% of mice died within 5 h, whereas the controls showed no evidence of toxicity. We further demonstrate that paraquat transcriptionally up-regulates Gpx1 in normal cells, reinforcing a role for Gpx1 in protection against paraquat toxicity. Finally, we show that cortical neurons from Gpx1 (-/-) mice are more susceptible to H2O2; 30% of neurons from Gpx1 (-/-) mice were killed when exposed to 65 microM H2O2, whereas the wild-type controls were unaffected. These data establish a function for Gpx1 in protection against some oxidative stressors and in protection of neurons against H2O2. Further, they emphasize the need to elucidate the role of Gpx1 in protection against different oxidative stressors and in different disease states and suggest that Gpx1 (-/-) mice may be valuable for studying the role of H2O2 in neurodegenerative disorders.

The free radical theory of aging matures

The free radical theory of aging, conceived in 1956, has turned 40 and is rapidly attracting the interest of the mainstream of biological research. From its origins in radiation biology, through a decade or so of dormancy and two decades of steady phenomenological research, it has attracted an increasing number of scientists from an expanding circle of fields. During the past decade, several lines of evidence have convinced a number of scientists that oxidants play an important role in aging. (For the sake of simplicity, we use the term oxidant to refer to all "reactive oxygen species," including O2-., H2O2, and .OH, even though the former often acts as a reductant and produces oxidants indirectly.) The pace and scope of research in the last few years have been particularly impressive and diverse. The only disadvantage of the current intellectual ferment is the difficulty in digesting the literature. Therefore, we have systematically reviewed the status of the free radical theory, by categorizing the literature in terms of the various types of experiments that have been performed. These include phenomenological measurements of age-associated oxidative stress, interspecies comparisons, dietary restriction, the manipulation of metabolic activity and oxygen tension, treatment with dietary and pharmacological antioxidants, in vitro senescence, classical and population genetics, molecular genetics, transgenic organisms, the study of human diseases of aging, epidemiological studies, and the ongoing elucidation of the role of active oxygen in biology.

The origins of human ageing

The origins of human ageing are to be found in the origins and evolution of senescence as a general feature in the life histories of higher animals. Ageing is an intriguing problem in evolutionary biology because a trait that limits the duration of life, including the fertile period, has a negative impact on Darwinian fitness. Current theory suggests that senescence occurs because the force of natural selection declines with age and because longevity is only acquired at some metabolic cost. In effect, organisms may trade late survival for enhanced reproductive investments in earlier life. The comparative study of ageing supports the general evolutionary theory and reveals that human senescence, while broadly similar to senescence in other mammalian species, has distinct features, such as menopause, that may derive from the interplay of biological and social evolution.

Development and age-associated differences in electron transport potential and consequences for oxidant generation

We determined the activities of NADH dehydrogenase (ND), succinate dehydrogenase, and cytochrome c oxidase (COX) in 29 skin fibroblast lines established from donors ranging in age from 12 gestational weeks to 94 years. The results of this study demonstrate that all three of the enzyme activities examined are greater in adult-derived fibroblasts than in the fetal cell lines. The ratio of enzyme activities that control electron entry into and exit from the electron transport chain varied directly with lucigenin-detected chemiluminescence (an indicator of .O2- generation) and inversely with H2O2 generation. These results indicate a clear difference in the predominant oxidant species generated during fetal and adult stages of life. We also examined the mRNA abundances of different components of the electron transport chain complexes. We observed higher abundances of mitochondrial encoded mRNAs (COX 1 and ND 4) in cell lines established from adults than in fetal cells. No differences in the mRNA abundances of the nuclear encoded sequences (COX 4 and ND 51) were observed in fetal and postnatal-derived lines. Succinate dehydrogenase mRNA abundance was greater in cell lines established from postnatal donors than in fetal cell lines. No significant differences between cell lines established from young and old adults were detected in any of the parameters examined.

Age-associated increase in ferritin content of male rat liver: implication for diquat-mediated oxidative injury

Our previous studies in rat hepatocytes demonstrated an age-dependent increase in sensitivity to diquat-induced cytotoxicity, possibly as a result of increased iron availability. The present study was conducted to determine whether quantitative or qualitative changes in hepatic ferritin occur as a consequence of aging and whether diquat-mediated oxidation is intensified by elevated ferritin concentrations. Hepatic ferritins were isolated from male Fischer 344 rats ages 5, 15, and 25 months. Age-associated increases were observed in amounts of ferritin protein and ferritin iron per gram of liver, but there were no differences in proportions of H to L subunits or in rates of diquat-mediated iron release. The consequences of a threefold increase in ferritin content for diquat-mediated lipid peroxidation and protein carbonyl formation were examined in microsomal incubation systems. The addition of isolated rat liver ferritin augmented diquat-mediated oxidative damage in a time- and concentration-dependent manner, and the inclusion of deferoxamine completely inhibited the stimulation by ferritin. The results indicate that availability of ferritin iron is an important determinant of diquat-mediated oxidative injury and support the hypothesis that elevated hepatic ferritin content is responsible, at least in part, for the age-associated enhancement of diquat-induced toxicity.

Comparison of age-related differences in expression of phospholipid hydroperoxide glutathione peroxidase mRNA and activity in various tissues of pigs

Phospholipid hydroperoxide glutathione peroxidase (PHGPX) is the second identified Se-dependent intracellular glutathione peroxidase (PHGPX) that reduces phospholipid hydroperoxides. The objective of this study was to determine the developmental regulation of PHGPX expression in tissues of neonatal, weanling and finishing pigs (Sus scrofa) compared with the expression of the classic Se-dependent cellular glutathione peroxidase (GPX) and the Se-independent enzyme, glutathione S-transferase (GST). Eight different tissues were collected from Se-adequate male pigs aged 1, 28 and 180 days, and supernatant of the tissue homogenate was assayed for PHGPX, GPX and GST activities by using phosphatidylcholine hydroperoxide, hydrogen peroxide and 1-chloro-2,4-dinitrobenzene as substrate, respectively. Total RNA was isolated from four tissues and assayed for PHGPX mRNA expression. Both mRNA and activity expression of PHGPX in most assayed tissues was increased as pigs became older (P < 0.05), but increases in PHGPX mRNA levels between ages did not fully account for all changes in activity. Expression of GPX activity was increased more than that of PHGPX between day 1 and day 28 (P < 0.0001). Expression of GST activity in various tissues was also affected by age (P < 0.01) but lacked a consistent relationship with the changes in GPX and PHGPX activity. Tissue-specific patterns of developmental expression of these enzymes may be related to the susceptibility of organs to pro-oxidant injuries. In conclusion, expression of PHGPX mRNA and activity in various tissues of pigs is developmentally increased over ages, and the pattern is somewhat different from that of GPX.

DNA adducts and chronic degenerative disease. Pathogenetic relevance and implications in preventive medicine

Chronic degenerative diseases are the leading causes of death in developed countries. Their control is exceedingly difficult due to their multiplicity and diversity, the interconnection with a network of multiple risk factors and protective factors, the long latency and multistep pathogenesis, and the multifocal localization. Adducts to nuclear DNA are biomarkers evaluating the biologically effective dose, reflecting an enhanced risk of developing a mutation-related disease more realistically than the external exposure dose. The localization and accumulation of these promutagenic lesions in different organs are the composite result of several factors, including (a) toxicokinetics (first-pass effect); (b) local and distant metabolism; (c) efficiency and fidelity of DNA repair; and (d) cell proliferation rate. The last factor will affect not only the dilution of DNA adducts but also the possible evolution towards either destructive processes, such as emphysema or cardiomyopathies, or proliferative processes, such as benign or malignant tumors at various sites. They also include heart tumors affecting fetal myocytes after transplacental exposure to DNA-binding agents, blood vessel tumors, and atherosclerotic plaques. In this article, particular emphasis is given to molecular alterations in the heart, which is the preferential target for the formation of DNA adducts in smokers, and in human aorta, where an extensive molecular epidemiology project is documenting the systematic presence of adducts to the nuclear DNA of smooth muscle cells from atherosclerotic lesions, and their significant correlation with known atherogenic risk factors. Exocyclic DNA adducts resulting from lipid peroxidation, and age-related indigenous adducts (I-compounds) may also originate from endogenous sources, chronic infections and infestations, and inflammatory processes. Type II I-compounds are bulky DNA lesions resulting from oxidative stress, whereas type II-compounds are presumably normal DNA modifications, which display positive correlations with median life span and are decreased in cancer and other pathological conditions. Profiles of type II-compounds strongly depend on diet and are related to the antidegenerative effects of caloric/ dietary restriction. Even broader is the possible meaning of adducts to mitochondrial DNA, which have been detected in rodents exposed to genotoxic agents and complex mixtures, as well as in untreated rodents, in larger amounts when compared to the nuclear DNA of the same cells. Mutations in mitochondrial DNA increase the number of oxidative phosphorylation-defective cells, especially in energy-requiring postmitotic tissues such as brain, heart and skeletal muscle, thereby playing an important role in aging and a variety of chronic degenerative diseases. A decreased formation of DNA adducts is an indicator of reduced risk of developing the associated disease. Therefore, these molecular dosimeters can be used as biomarkers in the prevention of chronic degenerative diseases, pursued either by avoiding exposure to adduct-forming agents or by using chemopreventive agents. Interventions addressed to the human organism by means of dietary measures or pharmacological agents have encountered a broad consensus in the area of cardiovascular diseases, and are deserving a growing interest also in cancer prevention. The efficacy of chemopreventive agents can be assessed by evaluating inhibition of nuclear DNA or mitochondrial DNA adduct formation in vitro, in animal models, and in phase II clinical trials in high-risk individuals.

Reducing equivalents in the aging process

Reducing equivalents may play a major role in the aging process. These metabolites are responsible for the endogenous redox potential in the living cell which is kept under tight regulation. Among their various roles is the ability to donate electrons to reactive oxygen species and by doing so to scavenge them. Most of the reducing equivalents in the cell are molecules with low molecular weights, such as glutathione and NADH which are synthesized by the cell. Other members of this group, such as uric acid are produced as waste products, while others, such as ascorbic acid and tocopherol, are derived from the diet. We studied the role of these equivalents in the aging process in various rat tissues. We demonstrated that the reducing power of a tissue may reflect its antioxidant activity. We used cyclic voltammeter methodology in order to evaluate the overall reducing power of tissue homogenates and other biological fluids. It was found that reducing power changes during the aging process in a bell-shaped manner in liver, lungs and kidneys, but not in heart and brain. We also showed that skin possesses strong reducing power which decreases dramatically with age. A non-invasive procedure to evaluate the oxidation status and the antioxidant activity of skin was developed. Using this method we demonstrated that there is an accumulation of organic peroxide in old skin compared to young skin, supporting the free radical hypothesis of aging.

Age-related changes in the peroxyl radical scavenging capacity of human plasma

Aging and the diseases that typically follow with increasing age, notably atherosclerosis and cancer, are often proposed to be involved in increased oxidative stress. Animal studies, on the other hand, show no clear-cut pattern of age-related changes in enzymatic antioxidant defences. In this study we have demonstrated that total peroxyl radical scavenging antioxidant capacity (TRAP) in human plasma changes with age. We also found that among the antioxidants in human plasma there exists a major fraction of so far unidentified antioxidant(s). A chemiluminescent TRAP assay was used to determine the presence of peroxyl radical scavenging antioxidants in human plasma. The material consisted of 87 healthy volunteers, aged 20-96 years, who used no regular medication, vitamins, or trace elements. In females, total antioxidant capacity increased significantly during the life span. The increase in TRAP was mainly due to unidentified antioxidants. In males, TRAP increased until age 51-74, and then significantly decreased. The decrease observed among males was also due to the sharp decline in the concentration of unidentified antioxidants.

The effect of ethanol and/or food restriction on coenzyme Q in liver in rats

The individual and combined effects of ethanol and lovastatin on rats and their prevention by supplemental coenzyme Q10 (CoQ10) was studied. The ethanol and lovastatin findings are reported elsewhere. This paper focuses on the food restriction which occurred in rats fed 35% of energy as ethanol and those control rats pair-fed to the 35% of energy as ethanol group. Six groups of rats received 35% of energy as ethanol (with or without lovastatin and/or CoQ10 treatment). One group served as a 0% ethanol ad libitum control and one 0% ethanol control group was pair-fed to the 35% ethanol group. Rats receiving 35% of energy as ethanol and their pair-fed controls consumed 83% of the energy/day consumed by the ad libitum controls. This was consistent regardless of lovastatin or CoQ10 treatment. Weight gains were 84% of control. The energy reduction was consistently associated with a substantial (48%+) increase in liver CoQ9 concentrations. Reports by others of associations between food restriction and increased longevity in rodents has focused on a decrease in oxidant damage in tissues of food restricted animals. The increase in CoQ levels in the food restricted animals would result in an increase in antioxidant protection and might explain the observed increases in longevity.

Correlational analysis in comparative gerontology: an examination of some problems

Correlation coefficients are widely used in comparative gerontology. However, due to many pitfalls, only a poor knowledge can be gained from these studies in many cases. For instance, a few variables gathered from few species may be used, with no attention to possible confounding variables giving spurious correlations. This article describes some of these problems and proposes to use more thoroughly multivariate analysis in comparative gerontology.

Oxidative injury and potential use of antioxidants in schizophrenia

There is increasing evidence that oxidative injury contributes to pathophysiology of schizophrenia, indicated by the increased lipid peroxidation products in plasma and CSF, and altered levels of both enzymatic and non-enzymatic antioxidants in chronic and drug-naive first-episode schizophrenic patients. The increased plasma lipid peroxidation is also supported by concomitant lower levels of esterified polyunsaturated essential fatty acids of red blood cell plasma membrane phospholipids. Because membrane phospholipids play a critical role in neuronal signal transduction, oxidative damage of these lipids may contribute to the proposed altered neurotransmitter receptor-mediated signal transduction and thereby alter information processing in schizophrenia. Adjunctive treatment with antioxidants (e.g. vitamins E and C, beta-carotene and quinones) at the initial stages of illness may prevent further oxidative injury and thereby ameliorate and prevent further possible deterioration of associated neurological and behavioral deficits in schizophrenia.

Relationship between susceptibility to protein oxidation, aging, and maximum life span potential of different species

The main objective of this study was to determine whether antioxidative potential of the tissues plays a role in the aging process. Antioxidative potential was ascertained as the susceptibility of tissues to undergo protein oxidation, manifested as protein carbonyls, in response to acute oxidative stress, induced by exposure to x-rays. Brain homogenates from 22-month-old rats were more susceptible to oxidative stress than those from three-month-old rats. Brain was more susceptible to oxidative damage than the heart. A comparison of the susceptibility of brain and heart homogenates in five different species (mouse, rat, rabbit, pig, and pigeon) indicated that maximum life span potential of the species was inversely related to their susceptibility to acute oxidative stress.

Free radical pathology and antioxidant defense in schizophrenia: a review

There is increasing evidence that free radical-mediated CNS neuronal dysfunction is involved in the pathophysiology of schizophrenia. Free radicals (oxyradicals, such as superoxide, hydroxyl ions, and nitric oxide) cause cell injury when they are generated in excess or the antioxidant defense is impaired. Both of these processes seem to be affected in schizophrenia. Evidence of excessive oxyradical generation is premised on the assumption that there is increased catecholamine turnover, though there is little direct evidence to support such a view, which is further accentuated by neuroleptic treatment. However, antioxidant enzymes (superoxide dismutase, SOD; glutathione peroxidase, GSHPx; and catalase, CAT) which are constitutively expressed in all tissues, are found to be altered in erythrocytes of schizophrenic patients. Also, possible oxyradical-mediated injury to CNS is suggested by increased lipid peroxidation products in cerebrospinal fluid and plasma, and reduced membrane polyunsaturated fatty acids (PUFAs) in the brain and RBC plasma membranes. The brain is more vulnerable to oxyradical-mediated injury,because its membranes are preferentially enriched in oxyradical sensitive PUFAs, and damaged adult neurons cannot be replaced. In addition to their pathological role, oxyradicals have critical physiological functions in neuronal development, differentiation, and signal transduction, all of which may be altered in some cases of schizophrenia. It may be possible to define cellular injury processes, investigate underlying dynamic regulatory molecular processes, and find ways to prevent these injury processes using peripheral cell models, e.g., red blood cells, lymphocytes and cultured skin fibroblasts. Information on the clinical implications of these processes are valuable for developing new and innovative therapeutic strategies for schizophrenia.

The beneficial effects of dietary restriction: reduced oxidative damage and enhanced apoptosis

There is compelling evidence for the central role of oxidative damage in the aging process and for the participation of reactive oxygen species in tumor initiation and promotion. Caloric restriction (CR) or energy restriction retards age-associated increases in mitochondrial free-radical production and reduces the accumulation of oxidatively damaged cell components. CR has also been shown to slow down age-related declines in various repair capabilities, including some types of DNA repair. It is proposed that inhibitors of mitochondrial electron transport and/or uncouplers of oxidative phosphorylation (rotenone, amytal, amiodarone, valinomycin, etc.), when used at extremely low doses, could mimic the effects of CR in model systems. The objective is to lower mitochondrial free-radical production by decreasing the fraction of electron carriers in the reduced state. In addition to a variety of other effects, CR has been shown to increase the rate of apoptosis, particularly in preneoplastic cells, and in general, to promote elevated levels of free glucocorticoids (GCs). GCs are known to induce tissue-specific apoptosis and to upregulate gap-junction-mediated intercellular communication (GJIC). Tumor promoters like phorbol esters have the opposite effect, in that they inhibit both the process of apoptosis and GJIC. The enzyme poly (ADP-ribose) polymerase (PARP) is thought to play a central role in apoptosis, in a manner that has been highly conserved in evolution. There is good evidence that the apoptosis-associated Ca/Mg-dependent DNA endonuclease is maintained in a latent form by being poly (ADP-ribosylated). Apoptosis would require the removal of this polymer from the endonuclease, and, most likely, its removal from topoisomerase II and histone H1 as well. The role of poly (ADP-ribose) in apoptosis, carcinogenesis, and aging could be studied by the use of modulators of PARP activity (3-aminobenzamide, 3-nitrosobenzamide, 1% ethanol, etc.), inhibitors of poly ADP-ribose) glycohydrolase activity (ethacridine, 43 degrees C, etc.), and inhibitors of the PARP-specific protease (interleukin-1 beta converting enzyme (ICE)-like protease). Also, it would be of interest to determine if CR can decrease the half-life of poly (ADP-ribose), upregulate GJIC, and modulate the activities of PARP, the glycohydrolase, and the PARP-specific protease, factors potentially important in these processes.

Developmental changes of antioxidant enzymes in kidney and liver from rats

The five principal antioxidant enzymes superoxide dismutase, catalase, glutathione peroxidase, glutathione-S-transferase, glutathione reductase in the kidney and liver, and the total hepatic glutathione were determined in rats of different ages (1, 2, 3, 6, and 12 months). Variance analysis proved the effect of age on the measured enzymes in the respective organ with the exception of glutathione S-transferase. The behavior of the enzymes was not uniform, and there were both increased and decreased changes in the two organs. A clear correlation between cellular antioxidative capacity and the age-specific processes of growing or aging could not be seen. A far more complicated network of interactions has to be assumed.

Aging reduces postischemic recovery of coronary endothelial function

The aging process is known to be associated with profound changes in the heart. To determine whether resistance of coronary endothelial and vascular smooth muscle function to ischemia may be related to age, four groups of rats (n = 6 in each group) of different ages (1, 5, 15, and 26 months) were subjected to cardioplegic arrest for 4 hours at 4 degrees C. The postischemic basal release of nitric oxide by endothelium, as assessed by the percentage loss of coronary flow in response to 0.5 mmol/L L-monomethylarginine, an inhibitor of nitric oxide synthase, was as follows: (mean +/- standard error of the mean): 87.1% +/- 1.7%, 81.2% +/- 2.3%, 79.6% +/- 1.9%, and 74.9% +/- 2.4% in groups 1, 2, 3, and 4, respectively. Stimulated release of nitric oxide, as assessed by percentage increase of coronary flow to 10(-5) mmol/L 5-hydroxytryptamine, an endothelium-dependent vasodilator, was as follows (mean +/- standard error of the mean): 88.3% +/- 1.5%, 83.4% +/- 2.4%, 71.1% +/- 2.7%, and 63.1% +/- 3.3% in groups 1, 2, 3, and 4, respectively. Significant differences were found between each group (p < 0.05) for both basal and stimulated release of nitric oxide. Vascular smooth muscle function, as assessed by the percentage increase in coronary flow in response to glyceryl trinitrate, an endothelium-independent vasodilator, was (mean +/- standard error of the mean): 96.7% +/- 2.1%, 92.3% +/- 5.2%, 92.9% +/- 5.0%, and 98.1% +/- 2.4% in groups 1, 2, 3, and 4 respectively. No significant difference was found between groups (p = not significant). In a protocol mimicking conditions for transplantation, the postischemic recovery of the basal and stimulated release of nitric oxide, but not vascular smooth muscle function, diminished with age.

Expression and regulation of superoxide dismutase activity in human skin fibroblasts from donors of different ages

We have determined the activities, protein, and mRNA abundances as well as the level of transcriptional activation of two intracellular forms of the free radical metabolizing enzyme superoxide dismutase in 29 human skin fibroblast lines established from donors of different ages. SOD-1 (a copper and zinc containing form of SOD) and SOD-2 (a manganese containing form of the enzyme) activities were both observed to be significantly lower in cell lines derived from fetal skin than in lines established from postnatal skin (ages 17-94 years). The percent of total activity contributed by SOD-1 decreased in an age-associated manner from approximately 50% in the fetal lines to less than 20% in lines established from old tissue donors. All of the cell lines were screened to exclude the possibility that they contained a polymorphism known to influence SOD-2 activity. Northern blot analysis revealed three SOD-1 mRNA transcripts that were 0.5, 0.7, and 1.9 kb in length. Although SOD-1 protein abundance was lower in fetal lines than in lines derived from postnatal donors, SOD-1 mRNA abundance did not differ between fetal cells and cell lines derived from young donors. SOD-2 protein abundance and mRNA abundance were both significantly lower in fetal lines than in postnatal lines. No postnatal age-dependent differences were observed in any of the SOD-2 parameters examined. Nuclear run-on analysis revealed that fetal cell lines exhibited a lower level of transcriptional initiation for SOD-1 than postnatal lines. The transcription of SOD-2 was readily detected in postnatal lines, but undetectable in fetal lines. These results are consistent with multiple levels of control for SOD-1 expression and with a strong transcriptional influence on SOD-2 expression.

Age-related changes in antioxidant enzymes, superoxide dismutase, catalase, glutathione peroxidase and glutathione in different regions of mouse brain

It has been proposed that neurodegenerative processes of aging are associated with the generation of reactive oxygen species (ROS) during cellular metabolism. These reactive oxygen species are scavenged by antioxidant enzymes in biological systems. The present study was designed to determine the selective distribution of the antioxidant enzymes superoxide dismutase, catalase and glutathione peroxidase activity and reduced glutathione (GSH) levels in different regions of the C57BL/6N mouse brain and to determine if any alterations occurred with age. Catalase activity did not show any significant change except in cerebellum. Activity of superoxide dismutase was increased with age in all regions of the brain except in hippocampus of 2-yr-old mice. The glutathione peroxidase activity in the caudate nucleus increased in all regions of the brain, however, the activity did not change at one, six and 12 months. A significant increasing pattern of glutathione content was found in the cerebellum and brain stem with age. These data demonstrate that although the level of antioxidant enzymes varied in different regions of the brain, overall the enzyme activities tend to increase with age.

Mitochondrial superoxide and hydrogen peroxide generation, protein oxidative damage, and longevity in different species of flies

The objective of this study was to further elucidate the role of oxidative stress in the aging process by determining whether or not the rates of mitochondrial superoxide anion radical and hydrogen peroxide (H2O2) production, the activity of cytochrome c oxidase, and the concentration of protein carbonyls are correlated with the life span potential of different species. A comparison was made among five different species of dipteran flies, namely, Drosophila melanogaster (fruit fly), Musca domestica (house fly), Sarcophaga bullata (flesh fly), Calliphora vicina (blow fly) and Phaenecia sericata (a species of blow flies), which range more than 2-fold in their life span potentials. The average life span potential of these species was found to be inversely correlated with the rates of mitochondrial superoxide and H2O2 production and with the level of protein carbonyls, and to be directly related to the activity of cytochrome c oxidase. The significance of these findings in context of the validity of the oxidative stress hypothesis of aging is discussed. It is inferred that longer life span potential in these insect species is associated with relatively low levels of oxidant generation and oxidative molecular damage. These results accord with our previous findings on different mammalian species.

Mitochondrial decay in aging

Several mitochondrial functions decline with age. The contributing factors include, the intrinsic rate of proton leakage across the inner mitochondrial membrane (a correlate of oxidant formation), decreased membrane fluidity, and decreased levels and function of cardiolipin, which supports the function of many of the proteins of the inner mitochondrial membrane. Oxidants generated by mitochondria appear to be the major source of the oxidative lesions that accumulate with age. Evidence supports the suggestion that age-associated accumulation of mitochondrial deficits due to oxidative damage is likely to be a major contributor to cellular, tissue, and organismal aging.