Mitochondrial free radical production and aging in mammals and birds

High resistance to lipid peroxidation of bird heart mitochondria and microsomes: Effects of mass and maximum lifespan

The aim of this investigation was to study the connection between body size, fatty acid composition and sensitivity to lipid peroxidation of heart mitochondria and microsomes isolated from different size bird species: manon (Lonchura striata), quail (Coturnix coturnix var japonica), pigeon (Columba livia), duck (Cairina moschata) and goose (Anser anser), representing a 372-fold range of body mass. Fatty acids of total lipids were determined using gas chromatography and lipid peroxidation was evaluated with a chemiluminescence assay. The fatty acids present in heart organelles of the different bird species analyzed showed a small number of significant allometric trends. In mitochondria, from the individual fatty acid data, palmitoleic acid (C16:1 n7) increased allometrically (r=0.878), while stearic acid (C18:0) was negatively related to body mass (r=-0.903). Interestingly, none of the calculated fatty acid variables, the average fatty acid saturated, monounsaturated, polyunsaturated (PUFA) and the unsaturation index (UI) was established to show significant body size-related variations. In heart microsomes, the content of C18:0 was significantly smaller (r=-0.970) in the birds of greater size. A significant allometric increase in linoleic acid (C18:2 n6) (r=0.986), polyunsaturated (r=0.990) and UI (r=0.904) was observed in the larger birds. The total n6 fatty acids of heart mitochondria did not show significant differences when it was correlated to body mass of the birds. Moreover, positive allometric relationships were shown for microsomes. The total n3 fatty acids of heart mitochondria and microsomes indicated no significant correlations to body mass of birds. The C16:1 n7, C18:0 in mitochondria and C18:0, C18:2 n6, PUFA, UI and PUFA n6 in microsomes showed significant differences when they were correlated to maximum life span (MLSP) of birds. As light emission=chemiluminescence originated from heart organelles was not statistically significant, a lack of correlation between the sensitivity to lipid peroxidation and body size or maximum life span was obtained. These results indicate that the high resistance of bird hearts to the attack by free radicals is body size-independent and would be related to the preservation of cardiac function.

3,5-diiodo-l-thyronine, by modulating mitochondrial functions, reverses hepatic fat accumulation in rats fed a high-fat diet

BACKGROUND/AIMS

Mitochondrial dysfunction is central to the physiopathology of steatosis and/or non-alcoholic fatty liver disease. In this study on rats we investigated whether 3,5-diiodo-l-thyronine (T2), a biologically active iodothyronine, acting at mitochondrial level is able to reverse hepatic steatosis after its induction through a high-fat diet.

METHODS

Hepatic steatosis was induced by long-term high-fat feeding of rats for six weeks which were then fed the same high-fat diet for the next 4 weeks and were simultaneously treated or not treated with T2. Histological analyses were performed on liver sections (by staining with Sudan black B). In liver mitochondria fatty acid oxidation rate, mitochondrial efficiency (by measuring proton conductance) and mitochondrial oxidative stress (by measuring H(2)O(2) release, aconitase and SOD activity) were detected.

RESULTS

Stained sections showed that T2 treatment reduced hepatic fatty accumulation induced by a high-fat diet. At the mitochondrial level, the fatty acid oxidation rate and carnitine palmitoyl transferase activity were enhanced by T2 treatment. Moreover, by stimulating mitochondrial uncoupling, T2 caused less efficient utilization of fatty acid substrates and ameliorated mitochondrial oxidative stress.

CONCLUSION

These data demonstrate that T2, by activating mitochondrial processes, markedly reverses hepatic steatosis in vivo.

Oxygen sensitivity of mitochondrial reactive oxygen species generation depends on metabolic conditions

The mitochondrial generation of reactive oxygen species (ROS) plays a central role in many cell signaling pathways, but debate still surrounds its regulation by factors, such as substrate availability, [O2] and metabolic state. Previously, we showed that in isolated mitochondria respiring on succinate, ROS generation was a hyperbolic function of [O2]. In the current study, we used a wide variety of substrates and inhibitors to probe the O2 sensitivity of mitochondrial ROS generation under different metabolic conditions. From such data, the apparent Km for O2 of putative ROS-generating sites within mitochondria was estimated as follows: 0.2, 0.9, 2.0, and 5.0 microM O2 for the complex I flavin site, complex I electron backflow, complex III QO site, and electron transfer flavoprotein quinone oxidoreductase of beta-oxidation, respectively. Differential effects of respiratory inhibitors on ROS generation were also observed at varying [O2]. Based on these data, we hypothesize that at physiological [O2], complex I is a significant source of ROS, whereas the electron transfer flavoprotein quinone oxidoreductase may only contribute to ROS generation at very high [O2]. Furthermore, we suggest that previous discrepancies in the assignment of effects of inhibitors on ROS may be due to differences in experimental [O2]. Finally, the data set (see supplemental material) may be useful in the mathematical modeling of mitochondrial metabolism.

Examining the mechanisms responsible for lower ROS release rates in liver mitochondria from the long-lived house sparrow (Passer domesticus) and big brown bat (Eptesicus fuscus) compared to the short-lived mouse (Mus musculus)

Lower ROS release rate in long-lived species is likely caused by decreased reduction of electron transport chain (ETC) complexes, but how this is achieved remains largely unknown. We compared liver mitochondrial H(2)O(2) release rates among endotherms of comparable size and metabolic rate: house sparrow and big brown bat (both long-lived) and house mouse (short-lived). We hypothesized that low ROS release rates in long-lived species result from (i) lower mitochondrial respiration rate, (ii) increased mitochondrial proton conductance ('uncoupling to survive'), and/or (iii) increased ETC oxidative capacity ('spare oxidative capacity'). H(2)O(2) release rate was 70% lower in bats than mice despite similar respiration rates. Consistent with 'uncoupling to survive', proton leakiness was 3-fold higher in bats at membrane potentials above 130mV. Basal H(2)O(2) release rate and respiration rates were 2-fold higher in sparrows than mice. Consistent with 'spare oxidative capacity', subsaturating succinate decreased H(2)O(2) release rate in sparrows but not mice. Moreover, succinate:Cytochrome c oxidoreductase activity was 3-fold higher in sparrows, and ETC inhibitors increased ROS release rate 20-27-fold in sparrows (with glutamate or subsaturating succinate) but only 4-5-fold in mice. Taken together these data suggest that complexes I and III are less reduced under physiological conditions in sparrows. We conclude that different long-lived species may use distinct mechanisms to lower mitochondrial ROS release rate.

Assessment of environmental stress in Parablennius sanguinolentus (Pallas, 1814) of the Sicilian Ionian coast

The blenny Parablennius sanguinolentus was selected as a useful bioindicator of environmental pollution. Chemical parameters in water and sediments from three different sampling sites along the Sicilian Ionian coast were determined and metal concentrations in fish muscle were measured. DNA fragmentation and oxidation in erythrocytes and hepatocytes was determined by the Comet assay and HSP70 expression levels were evaluated in the liver. The results show an increased level of chromium in sediments and high polycyclic aromatic hydrocarbon (PAH) concentrations in water at one site. The bioaccumulation of metals in muscle tissue shows high concentrations of lead in some samples. A high percentage of DNA damage in blood and liver cells, as well as high hepatic levels of HSP70, were found in all the sites. The results demonstrate the usefulness of an integrated chemical and biological approach for the determination of environmental stress.

The proteasome and its role in the degradation of oxidized proteins

The generation of free radicals and the resulting oxidative modification of cell structures are omnipresent in mammalian cells. This includes the permanent oxidation of proteins leading to the disruption of the protein structure and an impaired functionality. In consequence, these oxidized proteins have to be removed in order to prevent serious metabolic disturbances. The most important cellular proteolytic system responsible for the removal of oxidized proteins is the proteasomal system. For normal functioning, the proteasomal system needs the coordinated interaction of numerous components. This review describes the fundamental functions of the 20S "core" proteasome, its regulators, and the roles of the proteasomal system beyond the removal of oxidized proteins in mammalian cells.

An attempt to prevent senescence: a mitochondrial approach

Antioxidants specifically addressed to mitochondria have been studied to determine if they can decelerate senescence of organisms. For this purpose, a project has been established with participation of several research groups from Russia and some other countries. This paper summarizes the first results of the project. A new type of compounds (SkQs) comprising plastoquinone (an antioxidant moiety), a penetrating cation, and a decane or pentane linker has been synthesized. Using planar bilayer phospholipid membrane (BLM), we selected SkQ derivatives with the highest permeability, namely plastoquinonyl-decyl-triphenylphosphonium (SkQ1), plastoquinonyl-decyl-rhodamine 19 (SkQR1), and methylplastoquinonyldecyltriphenylphosphonium (SkQ3). Anti- and prooxidant properties of these substances and also of ubiquinonyl-decyl-triphenylphosphonium (MitoQ) were tested in aqueous solution, detergent micelles, liposomes, BLM, isolated mitochondria, and cell cultures. In mitochondria, micromolar cationic quinone derivatives were found to be prooxidants, but at lower (sub-micromolar) concentrations they displayed antioxidant activity that decreases in the series SkQ1=SkQR1>SkQ3>MitoQ. SkQ1 was reduced by mitochondrial respiratory chain, i.e. it is a rechargeable antioxidant. Nanomolar SkQ1 specifically prevented oxidation of mitochondrial cardiolipin. In cell cultures, SkQR1, a fluorescent SkQ derivative, stained only one type of organelles, namely mitochondria. Extremely low concentrations of SkQ1 or SkQR1 arrested H(2)O(2)-induced apoptosis in human fibroblasts and HeLa cells. Higher concentrations of SkQ are required to block necrosis initiated by reactive oxygen species (ROS). In the fungus Podospora anserina, the crustacean Ceriodaphnia affinis, Drosophila, and mice, SkQ1 prolonged lifespan, being especially effective at early and middle stages of aging. In mammals, the effect of SkQs on aging was accompanied by inhibition of development of such age-related diseases and traits as cataract, retinopathy, glaucoma, balding, canities, osteoporosis, involution of the thymus, hypothermia, torpor, peroxidation of lipids and proteins, etc. SkQ1 manifested a strong therapeutic action on some already pronounced retinopathies, in particular, congenital retinal dysplasia. With drops containing 250 nM SkQ1, vision was restored to 67 of 89 animals (dogs, cats, and horses) that became blind because of a retinopathy. Instillation of SkQ1-containing drops prevented the loss of sight in rabbits with experimental uveitis and restored vision to animals that had already become blind. A favorable effect of the same drops was also achieved in experimental glaucoma in rabbits. Moreover, the SkQ1 pretreatment of rats significantly decreased the H(2)O(2) or ischemia-induced arrhythmia of the isolated heart. SkQs strongly reduced the damaged area in myocardial infarction or stroke and prevented the death of animals from kidney ischemia. In p53(-/-) mice, 5 nmol/kgxday SkQ1 decreased the ROS level in the spleen and inhibited appearance of lymphomas to the same degree as million-fold higher concentration of conventional antioxidant NAC. Thus, SkQs look promising as potential tools for treatment of senescence and age-related diseases.

Comparative and alternative approaches and novel animal models for aging research: introduction to special issue

This special issue of AGE showcases powerful alternative or unconventional approaches to basic aging research, including the use of exceptionally long-lived animal model species and comparative methods from evolutionary biology. In this opening paper, we introduce several of these alternative aging research themes, including the comparative phylogenetic approach. This approach applies modern inferential methods for dissecting basic physiological and biochemical mechanisms correlated with phenotypic traits including longevity, slow aging, sustained somatic maintenance, and repair of molecular damage. Comparative methods can be used to assess the general relevance of specific aging mechanisms--including oxidative processes--to diverse animal species, as well as to assess their potential clinical relevance to humans and other mammals. We also introduce several other novel, underexploited approaches with particular relevance to biogerontology, including the use of model animal species or strains that retain natural genetic heterogeneity, studies of effects of infectious disease and parasites on aging and responses to caloric restriction, studies of reproductive aging, and naturally occurring sex differences in aging. We emphasize the importance of drawing inferences from aging phenomena in laboratory studies that can be applied to clinically relevant aging syndromes in long-lived, outbred animals, including humans.

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.

Gender and age-dependent differences in the mitochondrial apoptogenic pathway in Alzheimer's disease

Age-related mitochondrial oxidative stress is highly gender dependent. The aim of this study was to determine the role of gender in the mitochondrial contribution to neuronal apoptosis in Alzheimer's disease (AD). We used mitochondria isolated from brains of Wistar rats to study the toxicity of ss-amyloid peptide (Ass), and found that it increases mitochondrial peroxide production, nitration and oxidation of proteins, and release of cytochrome c. The toxic effects occurred in young males and in old females but not in young females, indicating their resistance to Ass. This resistance was abolished with age. These toxic effects of Ass were prevented by heme. Our findings provide a molecular mechanism for the contribution of Abeta to the mitochondrial dysfunction and oxidative stress seen in AD, as well as for the mitochondria-dependent pathway of apoptosis in AD. Gender and age-related differences seen in the development of AD can also be partially explained.

An allometric study of fatty acids and sensitivity to lipid peroxidation of brain microsomes and mitochondria isolated from different bird species

The objective of this investigation was to examine the relationship between body size, fatty acid composition and sensitivity to lipid peroxidation of mitochondria and microsomes isolated from the brain of different size bird species: manon, quail, pigeon, duck and goose, representing a 372-fold range of body mass. Fatty acids of total lipids were determined using gas chromatography and lipid peroxidation was evaluated using a chemiluminescence assay. The allometric study of the fatty acids present in brain mitochondria and microsomes of the different bird species showed a small number of significant allometric trends. In mitochondria the percentage of monounsaturated fatty acids, was significantly lower in the larger birds (r=-0.965; P<0.008). The significant allometric increase in 18:2 n-6; linoleic acid (r=0.986; P<0.0143), polyunsaturated (r=0.993; P<0.007) and total unsaturated (r=0.966; P<0.034) in brain microsomes but not in mitochondria may indicate a preferential incorporation of this fatty acid in the brain endoplasmic reticulum of the larger bird species. The brain of all birds studied had a high content of docosahexaenoic acid. However brain mitochondria but not microsomes isolated from all the birds analyzed showed a significant decrease of arachidonic and docosahexaenoic acids during lipid peroxidation. The allometric analyses of chemiluminescence were not statistically significant. In conclusion our results show absence of correlation between the sensitivity to lipid peroxidation of brain mitochondria and microsomes with body size and maximum life span.

Interrelated influence of superoxides and free fatty acids over mitochondrial uncoupling in skeletal muscle

Mitochondrial uncoupling protein 3 (UCP(3))-mediated uncoupling has been postulated to depend on several factors, including superoxides, free fatty acids (FFAs), and fatty acid hydroperoxides and/or their derivatives. We investigated whether there is an interrelation between endogenous mitochondrial superoxides and fatty acids in inducing skeletal muscle mitochondrial uncoupling, and we speculated on the possible involvement of UCP(3) in this process. In the absence of FFAs, no differences in proton-leak kinetic were detected between succinate-energized mitochondria respiring in the absence or presence of rotenone, despite a large difference in complex I superoxide production. The addition of either arachidic acid or arachidonic acid induced an increase in proton-leak kinetic, with arachidonic acid having the more marked effect. The uncoupling effect of arachidic acid was independent of the presence of GDP, rotenone and vitamin E, while that of arachidonic acid was dependent on these factors. These data demonstrate that FFA and O(2-) play interrelated roles in inducing mitochondrial uncoupling, and we hypothesize that a likely formation of mitochondrial fatty acid hydroperoxides is a key event in the arachidonic acid-induced GDP-dependent inhibition of mitochondrial uncoupling.

Ischemic defects in the electron transport chain increase the production of reactive oxygen species from isolated rat heart mitochondria

Cardiac ischemia decreases complex III activity, cytochrome c content, and respiration through cytochrome oxidase in subsarcolemmal mitochondria (SSM) and interfibrillar mitochondria (IFM). The reversible blockade of electron transport with amobarbital during ischemia protects mitochondrial respiration and decreases myocardial injury during reperfusion. These findings support that mitochondrial damage occurs during ischemia and contributes to myocardial injury during reperfusion. The current study addressed whether ischemic damage to the electron transport chain (ETC) increased the net production of reactive oxygen species (ROS) from mitochondria. SSM and IFM were isolated from 6-mo-old Fisher 344 rat hearts following 25 min global ischemia or following 40 min of perfusion alone as controls. H2O2release from SSM and IFM was measured using the amplex red assay. With glutamate as a complex I substrate, the net production of H2O2was increased by 178 ± 14% and 179 ± 17% in SSM and IFM ( n = 9), respectively, following ischemia compared with controls ( n = 8). With succinate as substrate in the presence of rotenone, H2O2increased by 272 ± 22% and 171 ± 21% in SSM and IFM, respectively, after ischemia. Inhibitors of electron transport were used to assess maximal ROS production. Inhibition of complex I with rotenone increased H2O2production by 179 ± 24% and 155 ± 14% in SSM and IFM, respectively, following ischemia. Ischemia also increased the antimycin A-stimulated production of H2O2from complex III. Thus ischemic damage to the ETC increased both the capacity and the net production of H2O2from complex I and complex III and sets the stage for an increase in ROS production during reperfusion as a mechanism of cardiac injury.

Exceptional longevity in songbirds is associated with high rates of evolution of cytochrome b, suggesting selection for reduced generation of free radicals

In animals, longevity (maximal lifespan) is inversely related to mass-specific basal metabolic rates. However, contrary to expectation, in several mammalian taxa, exceptional longevity is associated with high basal metabolic rate, and also fast evolution of mtDNA-coded proteins. The association of these traits was suggested to result from adaptive selection of mutations in mtDNA-coded proteins, which accelerates basal respiration, thus inhibiting the generation of reactive oxygen species that constrain longevity. In birds, all the genera with high rate of cytochrome b evolution are songbirds (oscines). Within the songbirds group, both longevity residuals and lifetime expenditure of energy are positively correlated with the rate of cytochrome b evolution. Moreover, within the large songbirds family Fringillidae (true finches) mass-specific basal metabolic rates, longevity,longevity residuals and lifetime expenditure of energy are all positively correlated with the rate of evolution of cytochrome b. In Serinus, a genus of finches (canaries) that exhibits the highest rate of cytochrome b evolution, and the highest values of exceptional longevity and lifetime expenditure of energy in all birds, many of the substitutions in cytochrome b are clustered around Qi, a ubiquinone binding site adjacent to the mitochondrial matrix, apparently selected to increase the rate of ubiquinone reduction. We therefore suggest that, in songbirds, the accelerated evolution of cytochrome binvolved selection of mutations that reduce the generation of reactive oxygen species, thus contributing to the evolution of exceptional longevity, and possibly also exceptional long-term memory, which is necessary for learning songs.

Public and private mechanisms of life extension in Caenorhabditis elegans

Model organisms have been widely used to study the ageing phenomenon in order to learn about human ageing. Although the phylogenetic diversity between vertebrates and some of the most commonly used model systems could hardly be greater, several mechanisms of life extension are public (common characteristic in divergent species) and likely share a common ancestry. Dietary restriction, reduced IGF-signaling and, seemingly, reduced ROS-induced damage are the best known mechanisms for extending longevity in a variety of organisms. In this review, we summarize the knowledge of ageing in the nematode Caenorhabditis elegans and compare the mechanisms of life extension with knowledge from other model organisms.

Sympatric Drosophila simulans flies with distinct mtDNA show difference in mitochondrial respiration and electron transport

The role of mitochondrial DNA (mtDNA) in mitochondrial metabolism is understudied yet humans harboring specific mtDNA types age at dissimilar rates, are unequally susceptible to various diseases, and differentially adapt to various environmental conditions. This study compares mitochondrial respiration, proton leak and electron transport of Drosophila simulans males with distinct mtDNA haplogroups (siII and -III) that were collected in sympatry in Kenya. Despite the large divergence among haplogroups there is very low intrahaplogroup variation and no correlated variation in the nuclear genome has been detected. We show that repeatable bioenergetic differences exist between 11d old males harboring siII and siIII mtDNA. Males with siIII mtDNA showed higher (i) state 3 respiration rates from isolated mitochondria for both complex I and complex III based substrates, and (ii) complex IV (cytochrome c oxidase) activity. Males harboring siIII mtDNA had lower (i) hydrogen peroxide formation by both complexes I and III, (ii) proton leak from isolated mitochondria, (iii) mitochondrial ATPase activity, and (iv) mitochondrial cytochrome content. In combination, the results suggest that mitochondria isolated from siIII mtDNA harboring males have more efficient metabolism than siII mtDNA harboring males.

Simultaneous age-related depolarization of mitochondrial membrane potential and increased mitochondrial reactive oxygen species production correlate with age-related glutamate excitotoxicity in rat hippocampal neurons

Mitochondria are implicated in glutamate excitotoxicity by causing bioenergetic collapse, loss of Ca(2+) homeostasis, and generation of reactive oxygen species (ROS), all of which become increasingly important clinically with age. Little is known about how aging affects the relative importance of mitochondrial membrane potential (DeltaPsi(m)) and ROS production. To determine aging affects on DeltaPsi(m) and ROS production in individual somal and axonal/dendritic mitochondria, we compared ROS production while simultaneously monitoring DeltaPsi(m) before and after glutamate treatment of live neurons from embryonic (day 18), middle-aged (9-12 months), and old (24 months) rats. At rest, old neuronal mitochondria 1) showed a higher rate of ROS production that was particularly strong in axonal/dendritic mitochondria relative to that in middle-age neurons, 2) were more depolarized in comparison with neurons of other ages, and 3) showed no differences in ROS or DeltaPsi(m) as a function of distance from the nucleus. All DeltaPsi(m) grouped into three classes of high (less than -120 mV), medium (-85 to -120 mV), and low (greater than -85 mV) polarization that shifted toward the lower classes with age at rest. Glutamate exposure dramatically depolarized the DeltaPsi(m) in parallel with greatly increased ROS production, with a surprising absence of an effect of age or distance from the nucleus on these mitochondrial parameters. These data suggest that old neurons are more susceptible to glutamate excitotoxicity because of an insidious depolarization of DeltaPsi(m) and rate of ROS generation at rest that lead to catastrophic failure of phosphorylative and reductive energy supplies under stress.

Non-enzymatic lipid peroxidation of microsomes and mitochondria from liver, heart and brain of the bird Lonchura striata: relationship with fatty acid composition

The aim of this study was to examine the fatty acid composition and non-enzymatic lipid peroxidation (LP) of mitochondria and microsomes obtained from liver, heart and brain of Lonchura striata. The percentage of total unsaturated fatty acid was approximately 30-60% in the organelles from all tissues studied. Brain mitochondria and both organelles of liver exhibited the highest percentage of polyunsaturated fatty acid (PUFA) (30 and 18%, respectively). The arachidonic acid (AA) content was 7% in mitochondria of liver and brain and 3% in heart mitochondria. The percentage of docosahexanoic acid (DHA) was 8% in brain mitochondria and approximately 2-3% in heart and liver mitochondria. The peroxidizability index (PI) of brain mitochondria and both organelles from liver was higher than that of organelles from heart and brain microsomes. Liver organelles and brain mitochondria were affected by LP, as indicated by the increase in chemiluminescence and a decrease of AA and DHA. These changes were not observed during LP of brain microsomes and both organelles from heart. These results indicate: 1) PI positively correlates with PUFA percentage and LP; 2) The resistance to LP detected in heart organelles would contribute to the cardiac protection against oxidative damage.

Oxidative phosphorylation and aging

This review addresses the data that support the presence and contribution of decreased mitochondrial oxidative phosphorylation during aging to impaired cellular metabolism. Aging impairs substrate oxidation, decreases cellular energy production and increases the production of reactive intermediates that are toxic to the cell. First, the basic principles of mitochondrial oxidative physiology are briefly reviewed. Second, the focus on the relationship of altered mitochondrial respiration to the increased production of reactive oxygen species that are employed by the "rate of living" and the "uncoupling to survive" theories of aging are discussed. Third, the impairment of function of respiration in aging is reviewed using an organ-based approach in mammalian systems. Fourth, the current state of knowledge regarding aging-induced alterations in the composition and function of key mitochondrial constituents is addressed. Model organisms, including C. elegans and D. melanogaster are included where pertinent. Fifth, these defects are related to knowledge regarding the production of reactive oxygen species from specific sites of the electron transport chain.

The relationship between uric acid and its oxidative product allantoin: a potential indicator for the evaluation of oxidative stress in birds

Uric acid is the main nitrogenous waste product in birds but it is also known to be a potent antioxidant. Hominoid primates and birds lack the enzyme urate oxidase, which oxidizes uric acid to allantoin. Consequently, the presence of allantoin in their plasma results from non-enzymatic oxidation. In humans, the allantoin to uric acid ratio in plasma increases during oxidative stress, thus this ratio has been suggested to be an in vivo marker for oxidative stress in humans. We measured the concentrations of uric acid and allantoin in the plasma and ureteral urine of white-crowned sparrows (Zonotrichia leucophrys gambelii) at rest, immediately after 30 min of exercise in a hop/hover wheel, and after 1 h of recovery. The plasma allantoin concentration and the allantoin to uric acid ratio did not increase during exercise but we found a positive relationship between the concentrations of uric acid and allantoin in the plasma and in the ureteral urine in the three activity phases. In the plasma, the slope of the regression describing the above positive relationships was significantly higher immediately after activity. We suggest that the slope indicates the rate of uric acid oxidation and that during activity this rate increases as a result of higher production of free radicals. The present study demonstrates that allantoin is present in the plasma and in the ureteral urine of white-crowned sparrows and therefore might be useful as an indicator of oxidative stress in birds.

[Ageing free radicals and cellular stress]

A number of theories have attempted to account for ageing processes in various species. Following the << rate of living >> theory of Pearl, Harman suggested fifty years ago that the accumulation of oxidants could explain the alteration of physical and cognitive functions with ageing. Oxygen metabolism leads to reactive species, including free radicals, which tend to oxidize surrounding molecules such as DNA, proteins and lipids. As a consequence various functions of cells and tissues can be altered, leading to DNA instability, protein denaturation and accumulation of lipid byproducts. Oxidative stress is an adaptive process which is triggered upon oxidant accumulation and which comprises the induction of protective and survival functions. Experimental evidence suggests that the ageing organism is in a state of oxidative stress, which supports the free radical theory. A number of other theories have been proposed ; some of these are actually compatible with the free radical theory. Caloric restriction is among the best models to increase life span in many species. While the relationship between caloric restriction and corrected metabolic rate is controversial, the decrease in ROS production by mitochondria appears to be experimentally supported. The ROS and mitochondrial theories of ageing appear to be compatible. Genetic models of increased life span, particularly those affecting the Foxo pathway, are usually accompanied by an increased resistance to oxidative insult. The free radical theory is not consistent with programmed senescence theories involving the cell division dependent decrease in telomere length ; however, oxidants are known to alter telomere structure. An appealing view of the role of oxidative stress in ageing is the trade-off principle which states that a phenotypic trait can be evolutionarily conserved because of its positive effects on development, growth or fertility, and despite its negative effect on somatic functions and ageing. It is likely that most cellular stresses which comprise adaptive and toxic functions follow such a rule.

Flight activity, mortality rates, and lipoxidative damage in Drosophila

In this study, the effect of flight activity on mortality rates and lipoxidative damage in Drosophila was determined to identify mechanisms through which oxidative damage affects life span. The results showed that flies allowed flying throughout life had higher mortality rates and decreased median and maximum life spans compared to controls. The mortality rate of the flight activity group could be lowered, but not completely reversed by switching to control conditions; and the accrued oxidative damage could not be eliminated. The levels of reactive oxygen species produced by mitochondria isolated from high activity and control flies did not differ significantly. However, the high activity flies had altered membrane fatty acid compositions, which made them prone to increased lipid peroxidation. The effect of flight activity on insect life span differs considerably from the beneficial effects of exercise in mammals; these differences may be caused by physiological differences between the two taxa.

A low degree of fatty acid unsaturation leads to high resistance to lipid peroxidation in mitochondria and microsomes of different organs of quail (Coturnix coturnix japonica)

Birds -- particularly long-lived species -- have special adaptations for preventing tissue damage caused by reactive oxygen species. The objective of the present study was to analyse the fatty acid composition and non-enzymatic lipid peroxidation of mitochondria and microsomes obtained from liver, heart and brain of quail (Coturnix coturnix japonica), a short-lived bird. Fatty acids located in total lipids of rat liver, heart and brain mitochondria and microsomes were determined using gas chromatography and lipid peroxidation was evaluated using a chemiluminescence assay. The unsaturated fatty acid content found in mitochondria and microsomes of all tissue examined was approximately 50 and 40%, respectively with a prevalence of C18:1 n9. The C18:2 n6 content in brain mitochondria was significantly lower as compared to liver and heart mitochondria. Whereas the C20:4 n6 content in mitochondria from all tissues examined and brain microsomes was approximately 6%, liver and heart microsomes exhibited lower values. C22:6 n3 was absent in liver mitochondria, very low content in liver microsomes and heart organelles (between 0.5 and 1%) and high content in brain organelles, with mitochondria having the highest value (11%). Whereas liver and heart organelles were not affected when subjected to lipid peroxidation, brain mitochondria were highly affected, as indicated by the increase in chemiluminescence and a considerable decrease of C20:4 n6 and C22:6 n3. These results indicate that a low degree of fatty acid unsaturation in liver and heart organelles of quail, a short-lived bird, may confer advantage by decreasing their sensitivity to lipid peroxidation process.

The effect of dietary restriction on mitochondrial protein density and flight muscle mitochondrial morphology in Drosophila

Dietary restriction (DR) extends life span in diverse organisms and may do so by attenuating production of mitochondrial reactive oxygen species (ROS). However, measurements of ROS production from isolated mitochondria of organisms subjected to DR have produced inconsistent results. In the fruit fly Drosophila, DR does not reduce production of ROS from isolated mitochondria. In this study, we used Drosophila to test whether DR lowered mitochondrial density. We assessed mitochondrial densities of flies on DR and Control diets using (a) the activities of mitochondrial enzymes and (b) electron microscopy. Both methods showed no overall effect of DR on mitochondrial density; however, mitochondrial enzyme activities and morphology differed significantly between DR and Control flies. We concluded that life-span extension by DR in Drosophila is not mediated through a reduction in mitochondrial density. If DR in Drosophila extends life span by reducing ROS production, then it does so through mechanisms that operate only in vivo.

Oxidative damage and age-related functional declines

Most organisms experience progressive declines in physiological function as they age. Since this senescence of function is thought to underlie the decrease in quality of life in addition to the increase in susceptibility to disease and death associated with aging, identifying the mechanisms involved would be highly beneficial. One of the leading mechanistic theories for aging is the oxidative damage hypothesis. A number of studies in a variety of species support a strong link between oxidative damage and life span determination. The role of oxidative damage in functional senescence has also been investigated, albeit not as comprehensively. Here, we review these investigations. Several studies show that the age-related loss of a number of functions is associated with an accrual of oxidative damage in the tissues mediating those functions. Additionally, treatments that increase the accumulation of oxidative damage with age frequently exacerbate functional losses. Moreover, treatments that reduce the accumulation of oxidative damage often attenuate or delay the loss of function associated with aging. These data provide the foundation for a link between oxidative damage and functional senescence, thereby supporting the oxidative damage hypothesis of aging within the context of age-related functional decline.

Fat intake reverses the beneficial effects of low caloric intake on skeletal muscle mitochondrial H(2)O(2) production

Food restriction is the most effective modulator of oxidative stress and it is believed that a reduction in caloric intake per se is responsible for the reduced generation of reactive oxygen species (ROS) by mitochondria. Hydrogen peroxide (H(2)O(2)) generation and oxygen consumption (O(2)) by skeletal muscle mitochondria were determined in a peculiar strain of rats (Lou/C) characterized by a self-low-caloric intake and a dietary preference for fat. These rats were fed either with a standard high-carbohydrate (HC) or a high-fat (HF) diet and the results were compared to those measured in Wistar rats fed a HC diet. H(2)O(2) production was significantly reduced in Lou/C rats fed a HC diet; this effect was not due to a lower O(2) consumption but rather to a decrease in rotenone-sensitive NADH-ubiquinone oxidoreductase activity and increased expression of uncoupling proteins 2 and 3. The reduced H(2)O(2) generation displayed by Lou/C rats was accompanied by a significant inhibition of permeability transition pore (PTP) opening. H(2)O(2) production was restored and PTP inhibition was relieved when Lou/C rats were allowed to eat a HF diet, suggesting that the reduced oxidative stress provided by low caloric intake is lost when fat proportion in the diet is increased.

Rise in Insulin Resistance Is Associated With Escalated Telomere Attrition

Background— Insulin resistance predisposes to cardiovascular disease and shortens human lifespan. We therefore tested the hypothesis that a rise in insulin resistance in concert with gain in body mass is associated with accelerated white blood cell telomere attrition.

Methods and Results— We measured white blood cell telomere dynamics and age-related changes in insulin resistance and body mass index in young adults of the Bogalusa Heart Study. Over 10.1 to 12.8 years, the relative changes in telomere length were correlated with the homeostasis model assessment of insulin resistance ( r =−0.531, P <0.001) and changes in the body mass index ( r =−0.423, P <0.001).

Conclusions— These findings provide the first tangible nexus of telomere biology with insulin resistance and adiposity in humans.

Thyroid-hormone effects on putative biochemical pathways involved in UCP3 activation in rat skeletal muscle mitochondria

In vitro, uncoupling protein 3 (UCP3)-mediated uncoupling requires cofactors [e.g., superoxides, coenzyme Q (CoQ) and fatty acids (FA)] or their derivatives, but it is not yet clear whether or how such activators interact with each other under given physiological or pathophysiological conditions. Since triiodothyronine (T3) stimulates lipid metabolism, UCP3 expression and mitochondrial uncoupling, we examined its effects on some biochemical pathways that may underlie UCP3-mediated uncoupling. T3-treated rats (Hyper) showed increased mitochondrial lipid-oxidation rates, increased expression and activity of enzymes involved in lipid handling and increased mitochondrial superoxide production and CoQ levels. Despite the higher mitochondrial superoxide production in Hyper, euthyroid and hyperthyroid mitochondria showed no differences in proton-conductance when FA were chelated by bovine serum albumin. However, mitochondria from Hyper showed a palmitoyl-carnitine-induced and GDP-inhibited increased proton-conductance in the presence of carboxyatractylate. We suggest that T3 stimulates the UCP3 activity in vivo by affecting the complex network of biochemical pathways underlying the UCP3 activation.

Physiological cost of tolerance to toxicants in the European flounder Platichthys flesus, along the French Atlantic Coast

Physiological and genetic responses of flounder Platichthys flesus populations were investigated along the French Atlantic Coast in one moderately contaminated estuary (Ster) and three contaminated estuaries (Seine, Loire and Gironde). The focus of this study was to explore the relationship between stress resistance and energetic trade-offs, in order to detect possible differential physiological capacities or performances between individuals carrying particular alleles or genotypes (allozyme data) characterised as "tolerant" or "sensitive". A general reduction of the relative fecundity, the growth rate and the condition factor was highlighted in contaminated fish populations, suggesting that survival in such polluted systems implies energetic costs for fish thus reducing the energy available for particular functions. A lower observed heterozygosity was also detected in contaminated populations with respect to the Ster, suggesting a general decrease in genetic variability in response to chemical stress (with an exception for the Seine estuary). This study confirmed the previously detected relationship between PGM 85, AAT1 95 alleles and reduced DNA damage in contaminated fish [Marchand, J., Tanguy, A., Laroche, J., Quiniou, L., Moraga, D., 2003. Responses of European flounder Platichthys flesus populations to contamination in different estuaries along the Atlantic coast of France. Mar. Ecol. Prog. Ser. 260, 273-284] and furthermore suggested that, reduced fecundity and condition factor associated to the individuals carrying the previous alleles, were also reflecting the cost of resistance to stress in polluted populations. The cost of tolerance to stress as well as the high gene flow from neighbouring populations less exposed to contamination may explain the apparently moderate increase of the suspected "tolerant" alleles in contaminated flounder populations.

Lifespan and mitochondrial control of neurodegeneration

We examine the allometric (comparative scaling) relationships between rates of neurodegeneration resulting from equivalent mutations in a diverse group of genes from five mammalian species with different maximum lifespan potentials. In both retina and brain, rates of neurodegeneration vary by as much as two orders of magnitude and are strongly correlated with maximum lifespan potential and rates of formation of mitochondrial reactive oxygen and nitrogen species (RONS). Cell death in these disorders is directly or indirectly regulated by the intrinsic mitochondrial cell death pathway. Mitochondria are the main source of RONS production and integrate cellular stress signals to coordinate the intrinsic pathway. We propose that these two functions are intimately related and that steady-state RONS-mediated signaling or damage to the mitochondrial stress-integration machinery is the principal factor setting the probability of cell death in response to a diverse range of cellular stressors. This provides a new and unifying framework for investigating neurodegenerative disorders.

Short-term caloric restriction and sites of oxygen radical generation in kidney and skeletal muscle mitochondria

Mitochondrial free radical generation is believed to be one of the principal factors determining aging rate, and complexes I and III have been described as the main sources of reactive oxygen species (ROS) within mitochondria in heart, brain, and liver. Moreover, complex I ROS generation of heart and liver mitochondria seems especially linked to aging rate both in comparative studies between animals with different longevities and in caloric restriction models. Caloric restriction (CR) is a well-documented manipulation that extends mean and maximum longevity. One of the factors that appears to be involved in such life span extension is the reduction in mitochondrial free radical generation at complex I. We have performed two parallel investigations, one studying the effect of short-term CR on oxygen radical generation in kidney and skeletal muscle (gastrocnemius) mitochondria and a second one regarding location of mitochondrial ROS-generating sites in these same tissues. In the former study, no effect of short-term caloric restriction was observed in mitochondrial free radical generation in either kidney or skeletal muscle. The latter study ruled out complex II as a principal source of free radicals in kidney and in skeletal muscle mitochondria, and, similar to previous investigations in heart and liver organelles, the main free radical generators were located at complexes I and III within the electron transport system.

Pharmacological management of persistent pain in older patients

OBJECTIVES

The purpose of this manuscript is to foster understanding of the unique attributes of aging as they relate to the treatment of persistent pain in order to improve care of older patients.

METHODS

: A thorough review of pertinent recent literature, including clinical guidelines, provided the materials from which this synthesis is drawn.

RESULTS

Several unique attributes of aging are identified that should be taken into account in order to provide safe and effective pharmacotherapy for older patients with persistent pain.

DISCUSSION

Adherence to contemporary clinical guidelines should serve to promote improved outcomes in older patients who suffer from ongoing and debilitating pain. Since outcomes studies are lacking, attention to principles of care as they apply to this particular population is advised. Since each patient's experience and response to drug therapy will be unique, individualized assessment that incorporates an analysis of the patient's physiological state (comorbidities and concurrent drug therapies), a determination of realistic goals, and monitoring of outcomes on a regular basis will provide the optimum balance between benefits and risks of analgesic pharmacotherapy.

Isolation of long-lived mutants in Caenorhabditis elegans using selection for resistance to juglone

The accumulation of molecular damage from attack by reactive oxygen species is one cause of aging. Therefore, some mutant organisms showing increased resistance to reactive oxygen species should live longer. We show that selection for Caenorhabditis elegans mutants that are resistant to juglone, a reactive oxygen species-generating compound, leads to the identification of long-lived mutants. Indeed, four of six resistant mutants isolated were also long-lived. This study illustrates once more the strong relationship between oxidative stress and the aging processes.

Lack of Correlation between Mitochondrial Reactive Oxygen Species Production and Life Span inDrosophila

The free radical theory of aging proposes that mitochondrial production of reactive oxygen species (ROS) determines the rate of aging. Supporting this hypothesis, longer-lived species produce fewer ROS than shorter-lived ones, and calorically restricted rodents live longer and produce fewer ROS than controls. We studied such correlation in Drosophila melanogaster in caloric restriction and in mutant flies overexpressing the mitochondrial adenine nucleotide translocase (ANT). Caloric restriction extended life span, but there was no significant difference in mitochondrial ROS production compared with controls. ANT overexpressers had significantly lower ROS production (because they had lower membrane potential), but their life span was not extended compared to wild type. Our results show two examples in which mitochondrial ROS production and life span are not correlated.

A unifying view of ageing and disease: the double-agent theory

The quest for therapies based on molecular genetics (pharmacogenomics, DNA microarrays, etc.) drives pharmaceutical research into individual diseases of old age, but has failed to deliver an unequivocal clinical breakthrough. Attempts to treat most age-related diseases using antioxidant supplements have been equally disappointing, despite the clear benefits of a healthy diet. The double-agent theory is a new, unifying synthesis that draws on flaws in three leading theories of ageing. It argues that there is a tradeoff between oxidative stress as a critical redox signal that marshals genetic defences against physiological stress (such as infection) and oxidative stress as a cause of ageing and age-related disease. The stress response and ageing are linked by redox-sensitive transcription factors, such as NFkappaB. Ageing is a function of rising intracellular oxidative stress, rather than chronological time, but this relationship is obscured because free-radical leakage from mitochondria also tends to rise with age. Mitochondrial leakage produces a genetic response which mirrors that following infection, but because mitochondrial leakage is continuous the shift in gene expression is persistent, leading to the chronic inflammation characteristic of old age. Age-related diseases are thus the price we pay for redox control of stress-gene expression. Because the selective pressure favouring the stress response in youth is stronger than that penalising degenerative diseases after reproductive decline, we may be homeostatically refractory to antioxidant supplements that 'swamp' the redox switch. Furthermore, because genetic selection takes place predominantly in the reductive homeostatic environment of youth, alleles associated with age-related diseases are not inherently damaging (they do not inevitably express a negative effect over time), but are simply less effective in the oxidising conditions of old age. Gene therapies for age-related diseases are unlikely to succeed unless oxidative stress can be controlled physiologically, thereby altering the activity and function of potentially hundreds of genes.

Mitochondria, reactive oxygen species and longevity: some lessons from the Barja group

To demonstrate that an uncoupling of respiration and phosphorylation, measured in vitro, reflects an in vivo situation, we badly need in vivo measurements of some uncoupling-linked parameters. The importance of this assertion is illustrated by studies of Barja and co-workers. A lower rate of H(2)O(2) production by mitochondria isolated from long-lived birds compared with short-lived mammals of the same body weight (see publications by Barja's and Sohal's groups) could be explained by (i) an in vivo difference or (ii) an in vitro artefact. In both cases, the reason for lower H(2)O(2) production may well be the same, i.e. a mild uncoupling of respiration in avian mitochondria showing lowered respiratory control. Again, this should be due to an in vivo operation of some bird-specific natural uncouplers (the first case) or stronger in vitro damage to the avian mitochondria during their isolation and incubation (the second). The latter possibility seemed more probable when Barja and co-workers revealed that the level of antioxidants in birds is lower than in mammals. However, further studies by the same group showed that the degree of unsaturation of fatty acids in birds is lower than in mammals, indicating a greater resistance of avian mitochondria to oxidative damage in vitro. Indeed, it was found that lipid peroxidation in isolated avian mitochondria occurs at a much lower rate than in mammals. More importantly, the in vivo level of peroxidation of lipids and proteins appears to be lower in birds than in mammals. Thus, it seems probable that longer lifespan of birds really does correlate with a slower rate of production of H2O2 by mitochondria in vivo.

Lysosomes and brain aging in mammals

Hypotheses about the factors controlling the rate of brain aging are usually derived from 1) correlates of maximum life span across mammals or 2) investigations into the causes of age-related neuropathologies in humans. With regard to the former, the strong correlation between metabolic rate and longevity prompted a variety of free radical hypotheses of aging. There is also evidence that brain size affects life span independently of body metabolism rates. The second approach has led to a diverse array of pathogenic mechanisms and, importantly for the development of general hypotheses, the discovery of animal analogues. The present paper discusses the possibility that age-associated lysosomal dysfunction constitutes a generalized mammalian phenomenon that accounts for specific features of the aged human brain. Immunocytochemical studies using rats and dogs have identified lysosomal changes that begin early in adulthood and are most pronounced in brain areas known to be particularly vulnerable to age-related pathogenesis in humans. Experimentally induced lysosomal dysfunction in cultured brain slices from rats and mutant mice triggers a wide array of changes associated with the aged human brain, including meganeurites and intraneuronal tangles. Finally, there is evidence that at least some forms of proteolysis decrease with increasing brain size across the mammals. The above observations lead to the suggestion that the expansion of neuronal arborizations that occurred in conjunction with increases in brain size secondarily slowed both neuronal metabolism and protein turnover. These events could have served to reduce the rate at which lysosomes (and other organelles) fail.

Cerebrometabolic abnormalities in Alzheimer's disease

Extensive, replicated evidence in patients in vivo and in Alzheimer (AD) tissues in vitro indicates that impaired brain metabolism is one of the cardinal and essentially invariable events in AD. The degree of impairment in brain metabolism is proportional to the degree of clinical disability, both in vivo and in vitro. The 'cerebrometabolic lesion' cannot be attributed to 'slower thinking' or 'brain atrophy', because of quantitative considerations and because the metabolic lesion precedes the development of neuropsychological abnormalities or decreases in brain mass detectable by modern imaging techniques. The causes of the cerebrometabolic lesion in AD are not well defined. Free radicals seem likely to be involved, including free radicals generated from Alzheimer amyloid. Thus, the importance of the cerebrometabolic lesion is entirely compatible with most versions of the widely accepted 'amyloid cascade hypothesis' of AD. A variety of plausible, redundantly documented mechanisms are compatible with the proposal that the cerebrometabolic lesion is a proximate cause of the clinical disability in AD. In agreement with these findings, recent attempts to treat the cerebrometabolic lesion in AD have given encouraging preliminary results. The cerebrometabolic lesion in AD deserves further study.

Ischemia–reperfusion injury in the aged heart: role of mitochondria

The aged heart sustains greater injury during ischemia and reperfusion compared to the adult heart. Aging decreases oxidative phosphorylation and the activity of complexes III and IV only in interfibrillar mitochondria (IFM) that reside among the myofibrils, whereas subsarcolemmal mitochondria (SSM), located beneath the plasma membrane, remain unaltered. The peptide subunit composition of complexes III and IV is intact in aging. The aging defect in complex IV is in the inner membrane lipid environment. The defect in complex III is within the ubiquinol binding site of the cytochrome b subunit. Following ischemia, in the aged heart both SSM and IFM sustain additional decreases in complex III and complex IV activity. In contrast to the aging defect, with ischemia the subunits of complex IV appear to be damaged. Ischemia inactivates the iron-sulfur peptide subunit in complex III. Mitochondria are the major source of the reactive oxygen species that are generated during myocardial ischemia. Complex III is the major site of mitochondrial oxyradical production during ischemia in the adult heart. The role of complex III in the oxidative damage sustained by the aged heart during ischemia, as well as the potential contribution of aging defects in electron transport to ischemic damage in the aged heart, deserves further study. We propose that following ischemic damage to the electron transport chain, the production and release of reactive oxygen species increases from mitochondria in the aged heart, leading to additional damage during reperfusion.

Birds as long-lived animal models for the study of aging

Despite their high lifetime energy expenditures, most birds can be characterized as long-lived homeotherms with moderately slow aging. A growing body of research confirms the prediction that birds have special adaptations for preventing aging-related oxidative and glycoxidative damage. Nonetheless, biogerontologists have been slow to develop avian laboratory models. A number of domestic poultry and cage bird species represent either established or very promising animal models for studies of basic aging processes and their prevention, including degenerative neurobiological, behavioral and reproductive processes. Several kinds of birds have also been used in studies of cellular resistance to oxidative stressors in vitro. Results of preliminary studies on chickens and quail suggest that caloric restriction may extend the reproductive life span of hens, but its long-term effects on life span remain unstudied. Birds' innate anti-aging mechanisms may actually make them more suitable in some respects as models of longevity than short-lived laboratory rodents, and bird studies may ultimately reveal routes for therapeutic intervention in diseases of human aging and infertility.

The general case for redox control of wound repair

The orthodox view has been that reactive oxygen species are primarily damaging to cells. There is general agreement that while high (3%) doses of H(2)O(2) may serve as a clinical disinfectant, its overall effect on healing is not positive. Current work shows that at very low concentrations, reactive oxygen species may regulate cellular signaling pathways by redox-dependent mechanisms. Recent discoveries show that almost all cells of the wound microenvironment contain specialized enzymes that utilize O(2) to generate reactive oxygen species. Numerous aspects of wound healing are subject to redox control. An understanding of how endogenous reactive oxygen species are generated in wound-related cells may influence the healing process and could result in new redox-based therapeutic strategies. Current results with growth factor therapy of wounds have not met clinical expectations. Many of these growth factors, such as platelet-derived growth factor, rely on reactive oxygen species for functioning. Redox-based strategies may serve as effective adjuncts to jump-start healing of chronic wounds. The understanding of wound-site redox biology is also likely to provide novel insights into the fundamental mechanisms that would help to optimize conditions for oxygen therapy. While a window of therapeutic opportunity seems to exist under conditions of low concentrations of reactive oxygen species, high levels may complicate regeneration and remodeling of nascent tissue.

Superoxide and hydrogen peroxide production by Drosophila mitochondria

Drosophila melanogaster is a key model organism for genetic investigation of the role of free radicals in aging, but biochemical understanding is lacking. Superoxide production by Drosophila mitochondria was measured fluorometrically as hydrogen peroxide, using its dependence on substrates, inhibitors, and added superoxide dismutase to determine sites of production and their topology. Glycerol 3-phosphate dehydrogenase and center o of complex III in the presence of antimycin had the greatest maximum capacities to generate superoxide on the cytosolic side of the inner membrane. Complex I had significant capacity on the matrix side. Center i of complex III, cytochrome c, and complex IV produced no superoxide. Native superoxide generation by isolated mitochondria was also measured without added inhibitors. There was a high rate of superoxide production with sn-glycerol 3-phosphate as substrate; two-thirds mostly from glycerol 3-phosphate dehydrogenase on the cytosolic side and one-third on the matrix side from complex I following reverse electron transport. There was little superoxide production from any site with NADH-linked substrate. Superoxide production by complex I following reverse electron flow from glycerol 3-phosphate was particularly sensitive to membrane potential, decreasing 70% when potential decreased 10 mV, showing that mild uncoupling lowers superoxide production in the matrix very effectively.

Mitochondrial localization of reactive oxygen species by dihydrofluorescein probes

Mitochondria are the main source of reactive oxygen species (ROS). The aim of this work was to verify the ROS generation in situ in HeLa cells exposed to prooxidants and antioxidants (menadione, tert-butyl hydroperoxide, antimycin A, vitamin E, N-acetyl-L-cysteine, and butylated hydroxytoluene) using the ROS-sensitive probes 6-carboxy-2',7'-dichlorodihydrofluorescein diacetate di-acetomethyl ester (DCDHF) and dihydrofluorescein diacetate (DHF). Mitochondria were counterstained with the potential-sensitive probe tetramethylrhodamine methyl ester perchlorate (TMRM). Both DCDHF and DHF were able to detect the presence of ROS in mitochondria, though with distinct morphological features. DCDHF fluorescence was invariably blurred, smudged, and spread over the cytoplasm surrounding the major mitochondrial clusters. On the contrary, DHF fluorescence was sharp and delineated thin filaments which corresponded in all details to TMRM-stained mitochondria. These data suggest that DCDHF does not reach the mitochondrial matrix but is oxidized by ROS released by mitochondria in the cytosol. On the other hand, DHF enters mitochondria and reacts with ROS released in the matrix. Cytosolic (DCDHF+) ROS but not matrix (DHF+) ROS, were significantly decreased by vitamin E. N-acetyl-L-cysteine was effective in reducing DCDHF and DHF photooxidation in the medium, but was unable to reduce intracellular ROS. ROS generation was accompanied by partial mitochondrial depolarization.

Effects of age and caloric restriction on glutathione redox state in mice

The main purpose of this study was to determine whether the aging process in the mouse is associated with a pro-oxidizing shift in the redox state of glutathione and whether restriction of caloric intake, which results in the extension of life span, retards such a shift. Amounts of reduced and oxidized forms of glutathione (GSH and GSSG, respectively) and protein-glutathione mixed disulfides (protein-SSG) were measured in homogenates and mitochondria of liver, kidney, heart, brain, eye, and testis of 4, 10, 22, and 26 month old ad libitum-fed (AL) mice and 22 month old mice fed a diet containing 40% fewer calories than the AL group from the age of 4 months. The concentrations of GSH, GSSG, and protein-SSG vary greatly (approximately 10-, 30-, and 9-fold, respectively) from one tissue to another. During aging, the ratios of GSH:GSSG in mitochondria and tissue homogenates decreased, primarily due to elevations in GSSG content, while the protein-SSG content increased significantly. Glutathione redox potential in mitochondria became less negative, i.e., more pro-oxidizing, as the animal aged. Caloric restriction (CR) lowered the GSSG and protein-SSG content. Results suggest that the aging process in the mouse is associated with a gradual pro-oxidizing shift in the glutathione redox state and that CR attenuates this shift.

Growth, telomere dynamics and successful and unsuccessful human aging

This paper links mass trajectories with telomere dynamics to construct theoretical models of successful and unsuccessful aging in human beings. It couples parameters of telomere length in somatic cells, as expressed by the terminal restriction fragment (TRF), at birth and the rate of telomere attrition thereafter with nonlinear models of somatic growth to predict the probability of surviving disease free, based on the assumption that telomere length in replicating somatic cells is a surrogate indicator of aging determinants in humans. The models capture aspects of individual variation in successful and unsuccessful aging and the long-term consequences of rapid growth early in life.