Age-associated, oxidatively modified proteins: A critical evaluation

Age associated oxidative damage in lymphocytes

Lymphocytes are an important immunological cell and have been played a significant role in acquired immune system; hence, may play in pivotal role in immunosenescence. Oxidative stress has been reported to increase in elderly subjects, possibly arising from an uncontrolled production of free radicals with aging and decreased antioxidant defenses. This study was aimed to evaluate the level of lipid-protein damage and antioxidant status in lymphocytes of healthy individuals to correlate between oxidative damage with the aging process. Twenty healthy individuals of each age group (11-20; 21-30; 31-40; 41-50; and 51-60 years) were selected randomly. Blood samples were drawn by medical practitioner and lymphocytes were isolated from blood samples. Malondialdehyde (MDA), protein carbonyls (PC) level were evaluated to determine the lipid and protein damage in lymphocytes. Superoxide dismutase (SOD), catalase (CAT), glutathione and glutathione dependent enzymes were estimated to evaluate the antioxidant status in the lymphocytes. Increased MDA and PC levels strongly support the increased oxidative damage in elderly subject than young subjects. The results indicated that, balance of oxidant and antioxidant systems in lymphocytes shifts in favor of accelerated oxidative damage during aging. Thus oxidative stress in lymphocytes may particular interest in aging and may play important role in immunosenescence.

Oxidative Stress in the Developing Rat Brain due to Production of Reactive Oxygen and Nitrogen Species

Oxidative stress after birth led us to localize reactive oxygen and nitrogen species (RONS) production in the developing rat brain. Brains were assessed a day prenatally and on postnatal days 1, 2, 4, 8, 14, 30, and 60. Oxidation of dihydroethidium detected superoxide; 6-carboxy-2',7'-dichlorodihydrofluorescein diacetate revealed hydrogen peroxide; immunohistochemical proof of nitrotyrosine and carboxyethyllysine detected peroxynitrite formation and lipid peroxidation, respectively. Blue autofluorescence detected protein oxidation. The foetuses showed moderate RONS production, which changed cyclically during further development. The periods and sites of peak production of individual RONS differed, suggesting independent generation. On day 1, neuronal/glial RONS production decreased indicating that increased oxygen concentration after birth did not cause oxidative stress. Dramatic changes in the amount and the sites of RONS production occurred on day 4. Nitrotyrosine detection reached its maximum. Day 14 represented other vast alterations in RONS generation. Superoxide production in arachnoidal membrane reached its peak. From this day on, the internal elastic laminae of blood vessels revealed the blue autofluorescence. The adult animals produced moderate levels of superoxide; all other markers reached their minimum. There was a strong correlation between detection of nitrotyrosine and carboxyethyllysine probably caused by lipid peroxidation initiated with RONS.

Toxicity assessment and comparison between two types of iron oxide nanoparticles in Mytilus galloprovincialis

Nanoparticles (NPs), due to their increased application and production, are being released into the environment with unpredictable impact on the physiology of marine organisms, as well as on entire ecosystems and upcoming effects on human health. The aim of the present study was to evaluate and compare the oxidative responses of the mussel Mytilus galloprovincialis after exposure to iron oxide NPs and to iron oxide NPs incorporated into zeolite for 1, 3 and 7 days. Our results showed that both effectors induced changes on animal physiology by causing oxidative stress in hemocytes of exposed mussels compared to control animals. This was shown by the significant increase in reactive oxygen species (ROS) production, protein carbonylation, lipid peroxidation, ubiquitin conjugates and DNA damage. In addition an increase in prooxidant levels as measured by the prooxidant-antioxidant balance (PAB) assay was observed in exposed mussels' hemolymph. The results show that ROS, DNA damage, protein and lipid oxidation, ubiquitin conjugates and PAB could constitute, after further investigation, reliable biomarkers for the evaluation of pollution or other environmental stressors. In addition, more studies are needed in order to ensure the safety of these NPs on various biomedical applications, since it is critical to design NPs that they meet the demands of application without causing cellular toxicity.

Cytochrome P450-2E1 promotes aging-related hepatic steatosis, apoptosis and fibrosis through increased nitroxidative stress

The role of ethanol-inducible cytochrome P450-2E1 (CYP2E1) in promoting aging-dependent hepatic disease is unknown and thus was investigated in this study. Young (7 weeks) and aged female (16 months old) wild-type (WT) and Cyp2e1-null mice were used in this study to evaluate age-dependent changes in liver histology, steatosis, apoptosis, fibrosis and many nitroxidative stress parameters. Liver histology showed that aged WT mice exhibited markedly elevated hepatocyte vacuolation, ballooning degeneration, and inflammatory cell infiltration compared to all other groups. These changes were accompanied with significantly higher hepatic triglyceride and serum cholesterol in aged WT mice although serum ALT and insulin resistance were not significantly altered. Aged WT mice showed the highest rates of hepatocyte apoptosis and hepatic fibrosis. Further, the highest levels of hepatic hydrogen peroxide, lipid peroxidation, protein carbonylation, nitration, and oxidative DNA damage were observed in aged WT mice. These increases in the aged WT mice were accompanied by increased levels of mitochondrial nitroxidative stress and alteration of mitochondrial complex III and IV proteins in aged WT mice, although hepatic ATP levels seems to be unchanged. In contrast, the aging-related nitroxidative changes were very low in aged Cyp2e1-null mice. These results suggest that CYP2E1 is important in causing aging-dependent hepatic steatosis, apoptosis and fibrosis possibly through increasing nitroxidative stress and that CYP2E1 could be a potential target for translational research in preventing aging-related liver disease.

Reactive oxygen species induce Cox-2 expression via TAK1 activation in synovial fibroblast cells

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Oxidative stress in the arthritis joint is involved in generating mediators for inflammation.

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Oxidative stress-induced expression of Cox-2 was mediated by MAPKs and NF-κB.

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ROS-induced MAPKs and NF-κB were attenuated by inhibition of MAPKKK TAK1.

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Inhibition of TAK1 activity resulted in reduced expression of Cox-2 and PGE2.

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ROS-induced TAK1 activation and Cox-2 expression was inhibited by antioxidants N-acetyl cysteamine and hyaluronic acid.

Oxidative stress within the arthritis joint has been indicated to be involved in generating mediators for tissue degeneration and inflammation. COX-2 is a mediator in inflammatory action, pain and some catabolic reactions in inflamed tissues. Here, we demonstrated a direct relationship between oxidative stress and Cox-2 expression in the bovine synovial fibroblasts. Furthermore, we elucidated a novel mechanism, in which oxidative stress induced phosphorylation of MAPKs and NF-κB through TAK1 activation and resulted in increased Cox-2 and prostaglandin E2 expression. Finally, we demonstrated that ROS-induced Cox-2 expression was inhibited by supplementation of an antioxidant such as N-acetyl cysteamine and hyaluronic acid in vitro and in vivo. From these results, we conclude that oxidative stress is an important factor for generation of Cox-2 in synovial fibroblasts and thus its neutralization may be an effective strategy in palliative therapy for chronic joint diseases.

Molecular alterations in proteasomes of rat liver during aging result in altered proteolytic activities

Aging induces alterations of tissue protein homoeostasis. To investigate one of the major systems catalysing intracellular protein degradation we have purified 20S proteasomes from rat liver of young (2 months) and aged (23 months) animals and separated them into three subpopulations containing different types of intermediate proteasomes with standard- and immuno-subunits. The smallest subpopulation ΙΙΙ and the major subpopulation Ι comprised proteasomes containing immuno-subunits β1i and β5i beside small amounts of standard-subunits, whereas proteasomes of subpopulation ΙΙ contained only β5i beside standard-subunits. In favour of a relative increase of the major subpopulation Ι, subpopulation ΙΙ and ΙΙΙ were reduced for about 55 % and 80 %, respectively, in aged rats. Furthermore, in all three 20S proteasome subpopulations from aged animals standard-active site subunits were replaced by immuno-subunits. Overall, this transformation resulted in a relative increase of immuno-subunit-containing proteasomes, paralleled by reduced activity towards short fluorogenic peptide substrates. However, depending on the substrate their hydrolysing activity of long polypeptide substrates was significantly higher or unchanged. Furthermore, our data revealed an altered MHC class I antigen-processing efficiency of 20S proteasomes from liver of aged rats. We therefore suggest that the age-related intramolecular alteration of hepatic proteasomes modifies its cleavage preferences without a general decrease of its activity. Such modifications could have implications on protein homeostasis as well as on MHC class I antigen presentation as part of the immunosenescence process.

The redox stress hypothesis of aging

The main objective of this review is to examine the role of endogenous reactive oxygen/nitrogen species (ROS) in the aging process. Until relatively recently, ROS were considered to be potentially toxic by-products of aerobic metabolism, which, if not eliminated, may inflict structural damage on various macromolecules. Accrual of such damage over time was postulated to be responsible for the physiological deterioration in the postreproductive phase of life and eventually the death of the organism. This "structural damage-based oxidative stress" hypothesis has received support from the age-associated increases in the rate of ROS production and the steady-state amounts of oxidized macromolecules; however, there are increasing indications that structural damage alone is insufficient to satisfactorily explain the age-associated functional losses. The level of oxidative damage accrued during aging often does not match the magnitude of functional losses. Although experimental augmentation of antioxidant defenses tends to enhance resistance to induced oxidative stress, such manipulations are generally ineffective in the extension of life span of long-lived strains of animals. More recently, in a major conceptual shift, ROS have been found to be physiologically vital for signal transduction, gene regulation, and redox regulation, among others, implying that their complete elimination would be harmful. An alternative notion, advocated here, termed the "redox stress hypothesis," proposes that aging-associated functional losses are primarily caused by a progressive pro-oxidizing shift in the redox state of the cells, which leads to the overoxidation of redox-sensitive protein thiols and the consequent disruption of the redox-regulated signaling mechanisms.

Generation of hydrogen peroxide in the developing rat heart: the role of elastin metabolism

Reports describing production of reactive oxygen species in neonatal heart are missing. As lysyl oxidase is potentially important source of H(2)O(2), we studied its role during ontogenic development of rat heart. H(2)O(2) was detected in thin sections of developing rat heart by fluorescence microscopy with the use of fluorescence probe 2'-7'-dichlorofluorescin. The experimental design comprised foetuses 21 days after conception, and then the animals sampled on the 1st, 4th, 7th, 10th, 15th, 30th and 60th day after birth. We also used 7-month-old animals as an example of ageing effects. Since the day 4 on, H(2)O(2) was produced only extracellularly up to the day 15, between days 30 and 60 intracellular production was detected as well, and in 7-month-old animals only extracellular production was observed. The specific inhibitors of lysyl oxidase almost completely quenched the H(2)O(2)-dependent fluorescence. Starting from day 7, blue autofluorescence specific to oxidized proteins developed in the vessel wall. Intracellular blue autofluorescence specific to autoxidation products developed after day 30. Chloroform extraction diminished the intracellular blue fluorescence, leaving the extracellular fluorescence intact. This confirmed the protein nature of the fluorophores. Lysyl oxidase is significant source of H(2)O(2) in the heart vessel wall during development and H(2)O(2) oxidatively modifies elastin producing protein blue autofluorescence.

Beneficial biochemical outcomes of late-onset dietary restriction in rodents

Dietary restriction (DR) or caloric restriction (CR) is the well-established means to retard aging, leading to prolongation of mean and maximum life span in many animal models. We have been interested in the possibility of extending the span of health of elderly people rather than increasing longevity, and therefore studied the effects of DR/CR initiated late in life in rodent models. We restricted food for 2-3.5 months in mice or rats of middle or old ages, which would perhaps be equivalent to 50-70 years of age in humans. We found that: (1) Potentially harmful altered proteins were reduced in the animals' tissues. (2) Extended half-life of protein in aged animals was shortened in mouse hepatocytes, suggesting improved protein turnover. (3) Reduced proteasome activity was upregulated in rat liver and skeletal muscle. (4) Protein carbonyls were decreased in rat liver mitochondria and skeletal muscle cytoplasm, and also oxidative DNA damage was reduced in rat liver nucleus, suggesting amelioration of oxidative stress. (5) Reduced apo A-IV and C-III metabolism in aged mouse was restored, suggesting increase in reduced fatty acid mobilization. (6) The carbonyl modification in histones that was paradoxically reduced in aged rat was increased to the level of a young animal, suggesting restoration of reduced transcription. These findings in rodents suggest a possibility that DR/CR is beneficial if applied in middle-aged or early senescent obese people. We argue, however, that application of late life DR/CR can be harmful if practiced in people who are already eating modestly.

Senescence Marker Protein-30 Protects Mice Lungs from Oxidative Stress, Aging, and Smoking

RATIONALE

Senescence marker protein-30 (SMP30) is a multifunctional protein providing protection to cellular functions from age-associated deterioration. We previously reported that SMP30 knockout (SMP30Y/-) mice are capable of being novel models for senile lung with age-related airspace enlargement and enhanced susceptibility to harmful stimuli.

OBJECTIVES

Aging and smoking are considered as major contributing factors for the development of pulmonary emphysema. We evaluated whether SMP30Y/- mice are susceptible to oxidative stress associated with aging and smoking.

METHODS

Age-related changes of protein carbonyls in lung tissues from the wild-type (SMP30Y/+) and SMP30Y/- mice were evaluated. Both strains were exposed to cigarette smoke for 8 wk. Histopathologic and morphologic evaluations of the lungs, protein carbonyls and malondialdehyde in the lung tissues, total glutathione content in the bronchoalveolar lavage fluid, and degree of apoptosis of lung cells were determined.

MEASUREMENTS AND MAIN RESULTS

In the lungs of SMP30Y/- mice, protein carbonyls tended to increase with aging and were significantly higher than the age-matched SMP30Y/+ mice. Cigarette smoke exposure generated marked airspace enlargement (23.3% increase of the mean linear intercepts) with significant parenchymal destruction in the SMP30Y/- mice but not in the SMP30Y/+ mice (5.4%). The protein carbonyls, malondialdehyde, total glutathione, and apoptosis of lung cells were significantly increased after 8-wk exposure to cigarette smoke in the SMP30Y/- mice.

CONCLUSIONS

Our results suggest that SMP30 protects mice lungs from oxidative stress associated with aging and smoking. The SMP30Y/- mice could be useful animal models for investigating age-related lung diseases, including cigarette smoke-induced pulmonary emphysema.

Molecular biomarkers of oxidative stress in aquatic organisms in relation to toxic environmental pollutants

The potential of oxygen free radicals and other reactive oxygen species (ROS) to damage tissues and cellular components, called oxidative stress, in biological systems has become a topic of significant interest for environmental toxicology studies. The balance between prooxidant endogenous and exogenous factors (i.e., environmental pollutants) and antioxidant defenses (enzymatic and nonenzymatic) in biological systems can be used to assess toxic effects under stressful environmental conditions, especially oxidative damage induced by different classes of chemical pollutants. The role of these antioxidant systems and their sensitivity can be of great importance in environmental toxicology studies. In the past decade, numerous studies on the effects of oxidative stress caused by some environmental pollutants in terrestrial and aquatic species were published. Increased numbers of agricultural and industrial chemicals are entering the aquatic environment and being taken up into tissues of aquatic organisms. Transition metals, polycyclic aromatic hydrocarbons, organochlorine and organophosphate pesticides, polychlorinated biphenyls, dioxins, and other xenobiotics play important roles in the mechanistic aspects of oxidative damage. Such a diverse array of pollutants stimulate a variety of toxicity mechanisms, such as oxidative damage to membrane lipids, DNA, and proteins and changes to antioxidant enzymes. Although there are considerable gaps in our knowledge of cellular damage, response mechanisms, repair processes, and disease etiology in biological systems, free radical reactions and the production of toxic ROS are known to be responsible for a variety of oxidative damages leading to adverse health effects and diseases. In the past decade, mammalian species were used as models for the study of molecular biomarkers of oxidative stress caused by environmental pollutants to elucidate the mechanisms underlying cellular oxidative damage and to study the adverse effects of some environmental pollutants with oxidative potential in chronic exposure and/or sublethal concentrations. This review summarizes current knowledge and advances in the understanding of such oxidative processes in biological systems. This knowledge is extended to specific applications in aquatic organisms because of their sensitivity to oxidative pollutants, their filtration capacity, and their potential for environmental toxicology studies.

Carbonyl modification in rat liver histones: decrease with age and increase by dietary restriction

We studied carbonylation, a form of oxidative modification of proteins, of histones in rat livers. Histones H1, H2B/H2A, and H3 were significantly carbonylated but the modification was almost undetectable in H4. Contrary to the generally accepted view of increased protein carbonylation with age, the modification of histones was significantly lower in old (30-month-old) than in young (5-month-old) animals. Dietary restriction of older animals for 2 months resulted in increase in carbonylation comparable to that at the young level. These findings may have physiological implications in chromatin structure/function in aging and beneficial effects of DR by influencing transcription, replication, and/or repair activities.

Three layer functional model and energy exchange concept of aging process

Relying on a certain degree of abstraction, we can propose that no particular distinction exists between animate or living matter and inanimate matter. While focusing attention on some specifics, the dividing line between the two can be drawn. The most apparent distinction is in the level of structural and functional organization with the dissimilar streams of 'energy flow' between the observed entity and the surrounding environment. In essence, living matter is created from inanimate matter which is organized to contain internal intense energy processes and maintain lower intensity energy exchange processes with the environment. Taking internal and external energy processes into account, we contend in this paper that living matter can be referred to as matter of dissipative structure, with this structure assumed to be a common quality of all living creatures and living matter in general. Interruption of internal energy conversion processes and terminating the controlled energy exchange with the environment leads to degeneration of dissipative structure and reduction of the same to inanimate matter, (gas, liquid and/or solid inanimate substances), and ultimately what can be called 'death.' This concept of what we call dissipative nature can be extended from living organisms to social groups of animals, to mankind. An analogy based on the organization of matter provides a basis for a functional model of living entities. The models relies on the parallels among the three central structures of any cell (nucleus, cytoplasm and outer membrane) and the human body (central organs, body fluids along with the connective tissues, and external skin integument). This three-part structural organization may be observed almost universally in nature. It can be observed from the atomic structure to the planetary and intergalactic organizations. This similarity is corroborated by the membrane theory applied to living organisms. According to the energy nature of living matter and the proposed functional model, the decreased integrity of a human body's external envelope membrane is a first cause of the structural degradation and aging of the entire organism. The aging process than progresses externally to internally, as in single cell organisms, suggesting that much of the efforts towards the restoration and maintenance of the mechanisms responsible for structural development should be focused accordingly, on the membrane, i.e., the skin. Numerous reports indicate that all parts of the human body, like: bones, blood with blood vessels, muscles, skin, and so on, have some ability for restoration. Therefore, actual revival of not only aging tissue of the human body's membrane, but the entire human body enclosed within, with all internal organs, might be expected. We assess several aging theories within the context of our model and provide suggestions on how to activate the body's own anti-aging mechanisms and increase longevity. This paper presents some analogies and some distinctions that exist between the living dissipative structure matter and inanimate matter, discusses the aging process and proposes certain aging reversal solutions.

Age-related increases in plasma malondialdehyde and protein carbonyl levels and lymphocyte DNA damage in elderly subjects

OBJECTIVES

Increased oxidative stress has been hypothesized to play an important role in the aging process. A role for oxidative damage in normal aging is supported by studies in experimental animals, but there is limited evidence in humans. To investigate the relationship between the oxidative stress and aging in humans, we determined lipid and protein oxidation in plasma as well as DNA damage in lymphocytes in young and elderly subjects.

DESIGN AND METHODS

55 healthy subjects were divided into young (21-40 years) and elderly (61-85 years) groups. Plasma malondialdehyde (MDA), protein carbonyl (PC) levels, and grade of DNA damage in lymphocytes using comet assay as well as total ferric reducing antioxidant power (FRAP) in plasma were determined in young and elderly subjects.

RESULTS

Plasma MDA and PC levels were found to be increased in plasma of elderly subjects as compared to young subjects. Increases in endogenous and H2O2-induced DNA damage were also observed in lymphocytes of elderly subjects. In addition, we detected a significant decrease in FRAP values in elderly subjects. Plasma MDA, PC levels and endogenous and H2O2-induced DNA damage were positively correlated with aging, but negatively with FRAP values.

CONCLUSION

We evaluated MDA, PC levels and lymphocyte DNA damage altogether in both young and elderly subjects for the first time. The results of this study strongly support the presence of increased oxidative stress in elderly subjects.

Effect of aging and late onset dietary restriction on antioxidant enzymes and proteasome activities, and protein carbonylation of rat skeletal muscle and tendon

Many studies have shown that lifelong dietary restriction (DR) can retard aging processes. Very few reports, however, are found that examined the effect of late onset DR on biochemical parameters in aging animals [Goto, S., Takahashi, R., Araki, S., Nakamoto, H., 2002b. Dietary restriction initiated in late adulthood can reverse age-related alterations of protein and protein metabolism. Ann. NY Acad. Sci. 959, 50-56]. We studied the effect of every-other-day feeding, initiated at the age of 26.5 months and continued for 3.5 months, on antioxidant enzymes, protein carbonyls, and proteasomes of the gastrocnemius muscle and tendon in rats. Age-related increase in the activity and content of Cu, Zn-SOD and the content of Mn-SOD was attenuated by the DR in both tissues. The same was true for glutathione peroxidase and catalase activities. Significant increase with age in protein reactive carbonyl derivatives (RCD) in the tendon was noted that was partially reversed by the DR. No significant change of RCD, however, was observed in the skeletal muscle. The age-related and DR-induced changes of the RCD in the tendon appeared to be associated with proteasome activity that decreases with age and increases by the DR. It is suggested that the late onset DR can have beneficial effects on the locomotive functions by reducing age-associated potentially detrimental oxidative protein damage in the tendon.

Importance of individuality in oxidative stress and aging

Tight linkage between aging and oxidative stress is indicated by the observations that reactive oxygen species generated under various conditions of oxidative stress are able to oxidize nucleic acids, proteins, and lipids and that aging is associated with the accumulation of oxidized forms of cellular constituents, and also by the fact that there is an inverse relationship between the maximum life span of organisms and the age-related accumulation of oxidative damage. Nevertheless, validity of the oxidative stress hypothesis of aging is questioned by (i) the failure to establish a causal relationship between aging and oxidative damage and (ii) lack of a consistent correlation between the accumulation of oxidative damage and aging. The present discussion is focused on the complexity of the aging process and suggests that discrepancies between various studies in this area are likely due to the fact that aging is not a single process and that the lack of consistent experimental results is partly explained by individual variations. Even so, there is overwhelming support for a dominant role of oxidative stress in the aging of some individuals.

Dietary restriction initiated in late adulthood can reverse age-related alterations of protein and protein metabolism

Many reports have been published on the effects of lifelong dietary restriction (DR) on a variety of parameters such as life span, carcinogenesis, immunosenescence, memory function, and oxidative stress. There is, however, limited available information on the effect of late onset DR that might have potential application to intervene in human aging. We have investigated the effect of DR initiated late in life on protein and protein degradation. Two months of DR in 23.5-month-old mice significantly reduced heat-labile altered proteins in the liver, kidney, and brain. DR reversed the age-associated increase in the half-life of proteins, suggesting that the dwelling time of the proteins is reduced in DR animals. In accordance with this observation, the activity of proteasome, which is suggested to be responsible for degradation of altered proteins, was found increased in the liver of rats 30 months of age subjected to 3.5 months of DR. Thus, DR can increase turnover of proteins, thereby possibly attenuating potentially harmful consequences by altered proteins. Likewise, DR in old rats reduced carbonylated proteins in liver mitochondria, although the effect was not observed in cytosolic proteins. Fasting induced apoA-IV synthesis in the liver of young mice for efficient mobilization of stored tissue fats, while it occurred only marginally in the old. DR for 2 months from 23 months of age partially restored inducibility of this protein, suggesting the beneficial effect of DR. Taking all these findings together, it is conceivable that DR conducted in old age can be beneficial not only to retard age-related functional decline but also to restore functional activity in young rodents. Interestingly, recent evidence that involves DNA array gene expression analysis supports the findings on the age-related decrease in protein turnover and its reversion by late-onset DR.

Carnosine, the anti-ageing, anti-oxidant dipeptide, may react with protein carbonyl groups

Carnosine (beta-alanyl-L-histidine) is a physiological dipeptide which can delay ageing and rejuvenate senescent cultured human fibroblasts. Carnosine's anti-oxidant, free radical- and metal ion-scavenging activities cannot adequately explain these effects. Previous studies showed that carnosine reacts with small carbonyl compounds (aldehydes and ketones) and protects macromolecules against their cross-linking actions. Ageing is associated with accumulation of carbonyl groups on proteins. We consider here whether carnosine reacts with protein carbonyl groups. Our evidence indicates that carnosine can react non-enzymically with protein carbonyl groups, a process termed 'carnosinylation'. We propose that similar reactions could occur in cultured fibroblasts and in vivo. A preliminary experiment suggesting that carnosine is effective in vivo is presented; it suppressed diabetes-associated increase in blood pressure in fructose-fed rats, an observation consistent with carnosine's anti-glycating actions. We speculate that: (i) carnosine's apparent anti-ageing actions result, partly, from its ability to react with carbonyl groups on glycated/oxidised proteins and other molecules; (ii) this reaction, termed 'carnosinylation,' inhibits cross-linking of glycoxidised proteins to normal macromolecules; and (iii) carnosinylation could affect the fate of glycoxidised polypeptides.

Single bout of exercise eliminates the immobilization-induced oxidative stress in rat brain

We were interested in the effects of immobilization (IM), a single bout of exercise (E) and immobilization followed by exercise (EIM) on memory and oxidative damage of macromolecules in hippocampus of rat brain. Eight hours of IM resulted in impairment of passive avoidance test (memory retrieval deficit) and increased latency to start locomotion in an open-field test. Two hours of swimming did not significantly alter the memory retrieval deficit and latency, while the EIM group had longer latency and similar memory than control and E groups. The oxidative damage of lipids, proteins and nuclear DNA increased significantly in IM group and no increase was observed in E and EIM animals. The activity of proteasome was not altered in any groups. The activity of glutamine synthetase (GS) was decreased in IM group (P < 0.05), this down regulation was not observed in E and EIM groups. These data suggest that oxidative damage of macromolecules is associated with impaired cognitive function. Single bout of exercise after immobilization eliminates the oxidative damage of macromolecules and normalizes memory function, probably by its ability to restore the activity level of GS and eliminate the consequences of immobilization-induced prolonged efflux of glutamate.

Regular exercise improves cognitive function and decreases oxidative damage in rat brain

The biochemical mechanisms by which regular exercise significantly benefits health and well being, including improved cognitive function, are not well understood. Four-week-old (young) and 14-month-old (middle aged) Wistar rats were randomly assigned to young control and young exercised, middle-aged control and middle-aged exercised groups. Exercise groups were exposed to a swimming regime of 1 h a day, 5 days a week for 9 weeks. The passive avoidance test showed that middle-aged exercised rats had significantly (P<0.05) better short- (24 h) and long-term (72 h) memory than aged-matched control rats. Conditioned pole-jumping avoidance learning was improved markedly in both age groups by exercise. Brain thiobarbituric acid-reactive substances and 8-hydroxy-2'deoxyguanosine content in the DNA did not change significantly, while the protein carbonyl levels decreased significantly (P<0.05) in both exercised groups. This decrease was accompanied by an increase in the chymotrypsin-like activity of proteasome complex in the exercised groups, whereas trypsin-like activity did not differ significantly between all groups. The DT-diaphorase activity increased significantly (P<0.05) in the brain of young exercised animals. These data show that swimming training improves some cognitive functions in rats, with parallel attenuation of the accumulation of oxidatively damaged proteins.

Regular training modulates the accumulation of reactive carbonyl derivatives in mitochondrial and cytosolic fractions of rat skeletal muscle

The oxygen flux into the mitochondria of skeletal muscle increases with exercise. However, the extent of oxidative damage to mitochondrial proteins of skeletal muscle has only been estimated. We studied the alteration of reactive carbonyl derivatives (RCD) in mitochondrial and cytosolic fractions of skeletal muscle following 9 weeks of swimming training in rats. The RCD content of mitochondria was significantly elevated compared with the cytosolic fraction of both control and exercised animals. Accumulation of RCD in muscle mitochondria of the exercised group was also significantly elevated (P < 0.05). On the other hand, alteration of the accumulation of RCD was not apparent in the cytosolic fraction of skeletal muscle. The activity of proteasome complex, however, was increased in the cytosolic fraction of exercised muscle (P < 0.05). The data suggest that mitochondria of skeletal muscle accumulate significantly larger amounts of RCD than the cytosolic fraction and the tendency of the accumulation varies in cell fractions. Exercise training increases the accumulation of protein damage in mitochondria of skeletal muscle but cytosolic proteins are protected by increased activity of proteasome complex and possibly by other antioxidant enzymes.

Dehydroascorbic acid irreversibly inhibits hexokinase activity

The oxidized form of vitamin C (dehydroascorbic acid, DHA) completely and irreversibly inactivates recombinant human hexokinase type I, in a pseudo-first order fashion. The inactivation reaction occurs without saturation, indicating that DHA does not form a reversible complex with hexokinase. Further characterization of this response revealed that the inactivation does not require oxygen and that dithiothreitol, while able to prevent the DHA-mediated loss of enzyme activity, failed to restore the activity of the DHA-inhibited enzyme. Inactivation was not associated with cleavage of the peptide chain or cross-linking. The decay in enzymatic activity was however both dependent on deprotonation of a residue with an alkaline pKa and associated with covalent binding of DHA to the protein. In addition, inactivation of hexokinase decreased or increased, respectively, in the presence of the substrates glucose or MgATP. Finally, amino acid analysis of the DHA-modified hexokinase revealed a decrease of cysteine residues. Taken together, the above results are consistent with the possibility that covalent binding of the reagent with a thiol group of cysteine is a critical event for the DHA-mediated loss of hexokinase activity.

Vitellogenin-6 is a major carbonylated protein in aged nematode, Caenorhabditis elegans

Recently we found that protein carbonyl content increases with age in wild-type as well as long- and short-lived Caenorhabditis elegans nematodes in inverse correlation with life span (Adachi et al., J. Gerontol. 53A, B240-B244, 1998; Yasuda et al., J. Gerontol. 54A, B47-B51, 1999). In the present study, we investigated carbonyl modification of individual proteins in young and old wild-type nematodes by two-dimensional immunoblot using antibodies against 2, 4-dinitrophenylhydrazones. A protein with apparent molecular weight of 110 kDa was found to be a major carbonylated protein in aged animals. Amino acid sequence of peptide fragments of the protein was identical to that of vitellogenin-6, a yolk protein synthesized in and secreted from the intestine during egg-laying stage. Although the function(s) of the protein in aged nematodes is unclear, we suggest that the protein may have a role to protect other cellular components from oxidation because of its metal binding capacity.

Carbonylated proteins in aging and exercise: immunoblot approaches

Protein carbonyls were studied in aging and exercise by immunoblot followed by one- or two-dimensional polyacrylamide gel electrophoresis using antibodies against 2,4-dinitrophenylhydrazones. Proteins of rat kidneys exhibited significant age-related increase in the amount of carbonyl while those of the brain and liver did not. Major carbonylated proteins in the kidney included serum albumin. In nematodes in which protein carbonyls increased with age, one of the carbonylated proteins was identified as vitellogenin, an egg-yolk protein. A possible biological significance of this protein present in abundance even after egg-laying stages is discussed in terms of protection against oxidative stress. Exhaustive exercise induced significant increase in the carbonylation of selected but unidentified proteins in the lung. This oxidative stress might be caused by xanthine oxidase in this tissue and hypoxanthine derived from ATP-depleted muscles. Exercise at high altitude caused higher carbonylation of the skeletal muscle proteins, most notably a protein likely to be actin, than that at sea level but no significant difference was observed in lipid peroxidation. These studies emphasize the value of immunoblot analysis of tissue protein carbonyls in a variety of situations where oxidative stress is likely involved.

Substrates of hexokinase, glucose-6-phosphate dehydrogenase, and glyceraldehyde-3-phosphate dehydrogenase prevent the inhibitory response induced by ascorbic acid/iron and dehydroascorbic acid in rabbit erythrocytes

Exposure of intact rabbit erythrocytes or erythrocyte lysates to ascorbic acid/FeCl3 in a glucose-free saline promoted a rapid decline in reduced glutathione and this response was paralleled by inactivation of hexokinase. Under the same conditions, the activity of the enzymes glyceraldehyde-3-phosphate dehydrogenase and glucose-6-phosphate dehydrogenase did not show appreciablevariations in intact cells, but was severely inhibited in the cell-free system. Similar results were obtained by replacing ascorbic acid/FeCl3 with dehydroascorbic acid. In addition, both treatments effectively inhibited the activity of purified hexokinase as well as those of glucose-6-phosphate dehydrogenase and glyceraldehyde-3-phosphate dehydrogenase. Further studies using the cell-free system indicated that the inhibition of enzyme activities elicited by either of the two treatments was effectively counteracted by the specific substrates of these enzymes. The fact that the hexokinase substrate glucose freely permeates the plasma membrane, unlike the substrates of glucose-6-phosphate dehydrogenase and glyceraldehyde-3-phosphatedehydrogenase, explains the selective inhibition of hexokinase observed in intact cells. The above results also indicate that dehydroascorbic acid is an inhibitor of these enzymes and strongly suggest that it is at least in part responsible for the effects mediated by the cocktail ascorbic acid/FeCl3.

Formation of carbonyls during attack on insulin by submolar amounts of hypochlorite

Bovine insulin was reacted at pH 4.0 with submolar amounts of hypochlorite. At least one molecule of insulin was modified per two molecules of hypochlorite added, as estimated by HPLC of native and modified insulin. About 5% of the hypochlorite-modified insulin reacted with dinitrophenylhydrazine (DNPH), a reagent which specifically labels carbonyl groups. The major DNPH-labeled product was isolated from the native insulin on reverse-phase HPLC, using trifluoroacetic acid/water/acetonitrile gradients. The UV spectrum of the major peak on the HPLC diode-array detector was representative of DNPH adducts, with lambda max = 365 nm. Several methods, including total amino acid analysis, tryptic digestion, and collision-induced dissociation-electrospray MS, indicate that the major carbonyl in the DNPH-labeled product was on the amino-terminal phenylalanine of the insulin B-chain. Amino acid analysis indicated that tyrosine was also degraded by hypochlorite, but we could not detect a carbonyl group formed at tyrosine. These findings suggest that the terminal amino groups of proteins are highly vulnerable to carbonyl formation during hypochlorite attack. The use of relatively low amounts of active oxygen species (such as hypochlorite), followed by chromatographic isolation of the protein labeled with a carbonyl-specific reagent, can be a useful approach to the study of reactive sites on proteins.

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.