Critical evaluation of the free radical theory of aging. A proposal for the oxidative stress hypothesis

Cellular mechanisms of cardioprotection by calorie restriction: state of the science and future perspectives

Evidence from animal models and preliminary studies in humans indicates that calorie restriction (CR) delays cardiac aging and can prevent cardiovascular disease. These effects are mediated by a wide spectrum of biochemical and cellular adaptations, including redox homeostasis, mitochondrial function, inflammation, apoptosis, and autophagy. Despite the beneficial effects of CR, its large-scale implementation is challenged by applicability issues as well as health concerns. However, preclinical studies indicate that specific compounds, such as resveratrol, may mimic many of the effects of CR, thus potentially obviating the need for drastic food intake reductions. Results from ongoing clinical trials will reveal whether the intriguing alternative of CR mimetics represents a safe and effective strategy to promote cardiovascular health and delay cardiac aging in humans.

Age-related differences in inflammatory markers in men: contribution of visceral adiposity

As visceral adipose tissue (AT) accumulation and inflammatory markers are known to increase with age, we examined whether this age-related change in regional AT distribution could contribute to the increase in the concentration of some inflammatory markers found with age. Two hundred eight healthy men aged 18.6 to 72.2 years and covering a wide range of adiposity values (body mass index, 18.5-39.3 kg/m(2)) were studied. Plasma C-reactive protein (CRP), interleukin-6 (IL-6), and tumor necrosis factor-alpha (TNF-alpha) levels were measured by enzyme-linked immunosorbent assay. Anthropometric characteristics such as height, weight, and waist girth were measured; and body mass index was calculated. Cross-sectional areas of abdominal AT were obtained at L4-L5 by computed tomography. Fasting blood samples were collected to determine a complete lipoprotein lipid profile, and a 75-g oral glucose tolerance test was performed. Overall, visceral AT accumulation was positively correlated with age (r = 0.51, P < .0001) as well as with plasma CRP (r = 0.39, P < .0001), IL-6 (r = 0.32, P < .0001), and TNF-alpha (r = 0.14, P < .05) levels. A significant positive relationship was also observed between age and CRP (r = 0.36, P < .0001), IL-6 (r = 0.39, P < .0001), or TNF-alpha (r = 0.15, P < .05) concentrations. As middle-aged men were characterized by higher CRP (1.32 [25th percentile, 0.71; 75th percentile, 2.71] vs 0.66 [0.36, 1.62] mg/L, P < .0001) and IL-6 (1.60 [1.09, 2.28] vs 1.12 [0.77, 1.60] pg/mL, P < .0001) levels as well as by a greater amount of visceral AT (P < .0001) than young men, we have individually matched 43 young men (age, 28.6 +/- 5.82 years) with 43 middle-aged men (age, 57.6 +/- 5.15 years) on the basis of their visceral AT. Matching for visceral AT eliminated the difference between middle-aged men and younger adult men in inflammatory markers. These results suggest that the age-related variation in CRP and IL-6 is largely explained by differences in visceral AT.

Molecular inflammation: underpinnings of aging and age-related diseases

Recent scientific studies have advanced the notion of chronic inflammation as a major risk factor underlying aging and age-related diseases. In this review, low-grade, unresolved, molecular inflammation is described as an underlying mechanism of aging and age-related diseases, which may serve as a bridge between normal aging and age-related pathological processes. Accumulated data strongly suggest that continuous (chronic) upregulation of pro-inflammatory mediators (e.g., TNF-alpha, IL-1beta, IL-6, COX-2, iNOS) are induced during the aging process due to an age-related redox imbalance that activates many pro-inflammatory signaling pathways, including the NF-kappaB signaling pathway. These pro-inflammatory molecular events are discussed in relation to their role as basic mechanisms underlying aging and age-related diseases. Further, the anti-inflammatory actions of aging-retarding caloric restriction and exercise are reviewed. Thus, the purpose of this review is to describe the molecular roles of age-related physiological functional declines and the accompanying chronic diseases associated with aging. This new view on the role of molecular inflammation as a mechanism of aging and age-related pathogenesis can provide insights into potential interventions that may affect the aging process and reduce age-related diseases, thereby promoting healthy longevity.

Differential oxidative stress response in young children and the elderly following exposure to PM(2.5)

OBJECTIVES

The mechanism of the adverse health effects of ambient particulate matter on humans has not been well-investigated despite many epidemiologic association studies. Measurement of personal exposure to particulate pollutants and relevant biological effect markers are necessary in order to investigate the mechanism of adverse health effects, particularly in fragile populations considered to be more susceptible to the effects of pollutants.

METHODS

We measured personal exposure to PM(2.5) and examined oxidative stress using urinary malondialdehyde three times in 51 preschoolers and 38 elderly subjects. A linear mixed-effects model was used to estimate PM(2.5) effects on urinary MDA levels.

RESULTS

Average personal exposure of the children and elderly to PM(2.5) was 80.5 +/- 29.9 and 20.7 +/- 12.7 mug/m(3), respectively. Mean urinary MDA level in the children and the elderly was 3.6 +/- 1.9 and 4.0 +/- 1.6 mumol/g creatinine. For elderly subjects the PM(2.5) level was significantly associated with urinary MDA after adjusting for age, sex, BMI, passive smoking, day-care facility site, alcohol consumption, cigarette smoking, and medical history (heart disease, hypertension and bronchial asthma). However, there was no significant relationship for children.

CONCLUSIONS

The elderly were more susceptible than young children to oxidative stress as a result of ambient exposure to PM(2.5). Identification of oxidative stress induced by PM(2.5) explains the mechanism of adverse health effects such as cardiovascular or respiratory diseases, particularly in the elderly.

Antioxidant activity of L-adrenaline: a structure-activity insight

L-adrenaline belongs to a group of the compounds known as catecholamines, which play an important role in the regulation of physiological process in living organisms. The antioxidant activity and antioxidant mechanism of L-adrenaline was clarified using various in vitro antioxidant assays including 1,1-diphenyl-2-picryl-hydrazyl (DPPH), 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS), N,N-dimethyl-p-phenylenediamine (DMPD(+)), and superoxide anion radicals (O(2)(-)) scavenging activity, hydrogen peroxide (H(2)O(2)), total antioxidant activity, ferric ions (Fe(3+)) and cupric ions (Cu(2+)) reducing ability, ferrous ions (Fe(2+)) chelating activity. L-adrenaline inhibited 74.2% lipid peroxidation of a linoleic acid emulsion at 30 microg/mL concentration. On the other hand, butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), alpha-tocopherol and trolox displayed 83.3, 82.1, 68.1 and 81.3% inhibition on the peroxidation of linoleic acid emulsion at the same concentration, respectively. BHA, BHT, alpha-tocopherol and trolox were used as reference antioxidants and radical scavenger compounds. Moreover, this study will bring an innovation for further studies related to antioxidant properties of L-adrenaline. According to present study, L-adrenaline had effective in vitro antioxidant and radical scavenging activity.

Plasma antioxidants and human aging: a study on healthy elderly Tunisian population

The aging has been described by several theories. It was proposed that free radicals are the major factor involved in this process. This gave birth to the free radical theory of aging. This current theory provides the most popular explanation for how aging occurs at the biochemical/molecular level. Ever since 1956, this theory has received widespread attention and a large body of evidence has been accumulated in support of its hypotheses which were subsequently refined. The free radical theory of aging postulates that age-associated reductions in physiological functions are caused by an irreversible accumulation of oxidative alterations to macromolecules. This accumulation increases with age and is associated with the life expectancy of organisms. Moreover, this theory suggests the existence of an imbalance between reactive oxygen species (ROS)-producing pathways and (ROS)-scavenging pathways, which is responsible for the generation of oxidative stress syndrome. In this article, we evaluate the antioxidant status in a population of healthy elderly Tunisians in comparison with a group of healthy young Tunisian subjects. This study sets out to investigate the age-related changes in glutathione peroxidase (GPx), superoxide dismutase (SOD) activities, and in total antioxidant status (TAS) of human plasma. We have concluded that healthy aging is accompanied with a disturbed antioxidant status.

Molecular mechanisms of life- and health-span extension: role of calorie restriction and exercise intervention

The aging process results in a gradual and progressive structural deterioration of biomolecular and cellular compartments and is associated with many pathological conditions, including cardiovascular disease, stroke, Alzheimer's disease, osteoporosis, sarcopenia, and liver dysfunction. Concomitantly, each of these conditions is associated with progressive functional decline, loss of independence, and ultimately disability. Because disabled individuals require care in outpatient or home care settings, and in light of the social, emotional, and fiscal burden associated with caring for an ever-increasing elderly population, research in geriatric medicine has recently focused on the biological mechanisms that are involved in the progression towards functional decline and disability to better design treatment and intervention strategies. Although not completely understood, the mechanisms underlying the aging process may partly involve inflammatory processes, oxidative damage, mitochondrial dysfunction, and apoptotic tissue degeneration. These hypotheses are based on epidemiological evidence and data from animal models of aging, as well as interventional studies. Findings from these studies have identified possible strategies to decrease the incidence of age-related diseases and delay the aging process. For example, lifelong exercise is known to extend mean life-span, whereas calorie restriction (CR) increases both mean and maximum life-span in a variety of species. Optimal application of these intervention strategies in the elderly may positively affect health-related outcomes and possibly longevity. Therefore, the scope of this article is to (i) provide an interpretation of various theories of aging from a "health-span" perspective; (ii) describe interventional testing in animals (CR and exercise); and (iii) provide a translational interpretation of these data.

Analysis of age-associated changes in mitochondrial free radical generation by rat testis

Throughout spermatogenesis, mitochondria undergo a morphological and functional differentiation. Mitochondria are involved in the production of reactive oxygen species (ROS), considered one of the mediators of ageing. Particularly, lipid peroxidation is regarded as a major phenomenon by which ROS can impair cellular function. In the present study, we examined the production of superoxide anion, superoxide dismutase activity and the effect of Fe(2+)/ascorbate induced-lipid peroxidation on the respiratory chain activities of testis mitochondria throughout the process of spermatogenesis and ageing. Mitochondria from rat testes generated superoxide anion, mainly using NADH as substrate, which increased according to age. The activity of SOD is age-dependent and greatly stimulated during the first wave of spermatogenesis, but decreases in adulthood and old age. TBARS concentration was also markedly increased by ageing. The activity of mitochondrial respiratory chain complexes is differentially affected by oxidative stress induced by iron/ascorbate, succinate-dehydrogenase activity being less vulnerable than that of NADH-dehydrogenase and cytochrome c oxidase. The data suggest that ageing is accompanied by reduced activity of SOD, leading to excessive oxidative stress and enhanced lipid peroxidation that compromises the functionality of the electron transport chain. The data support the concept that mitochondrial function is an important determinant in ageing.

Neuroglobin protects PC12 cells against beta-amyloid-induced cell injury

Excessive accumulation of amyloid beta (Abeta) has been proposed as a pivotal event in the pathogenesis of Alzheimer's disease. Possible mechanisms underlying Abeta-induced neuronal cytotoxicity include excess production of reactive oxidative species (ROS) and apoptosis. Neuroglobin (Ngb), a newly discovered globin in vertebrates that exhibits neuroprotective functions, may have a potential role in scavenging ROS. To examine the potential protective role of Ngb in Abeta-induced cytotoxicity, PC12 cells were treated with Abeta (1-42 fragment) for 24h. Abeta treatments increased ROS production in PC12 cells. Overexpression of Ngb but not Ngb mutant in the PC12 cells significantly attenuated Abeta-induced ROS production and lipids peroxidation. Furthermore, overexpression of Ngb also attenuated Abeta-induced mitochondrial dysfunction and apoptosis, and promoted cell survival in PC12 cells. Therefore, Ngb may act as an intracellular ROS scavenger, and such antioxidant properties may play a protective role against Abeta-induced cell injury.

Effect of aging and caloric restriction on the mitochondrial proteome

The rat mitochondrial proteome was analyzed using two-dimensional polyacrylamide gel electrophoresis (2-D PAGE), and proteins altered by age or caloric restriction (CR) were identified using mass spectrometry. Of 2061 mitochondrial proteins analyzed in the three tissues, a significant change with age occurred in 25 liver proteins (19 increased, 6 decreased), 3 heart proteins (1 increased, 2 decreased), and 5 skeletal muscle proteins (all increased). CR prevented the age-related change in the level of one liver mitochondrial protein, altered the levels of four proteins (one increased, three decreased) from heart, and one protein (decreased) from skeletal muscle. Identification of the proteins that changed with age or CR revealed that they were varied among the three tissues, that is, not one mitochondrial protein was changed, in common, by age or CR in any tissue studied. Thus, the effect of age on the mitochondrial proteome appears to be tissue-specific, and CR has a minor effect on age-related protein changes.

Ageing effects on the expression of cell defence genes after UVA irradiation in human male cutaneous fibroblasts using cDNA arrays

Ageing is a multifactorial process in which reactive oxygen species (ROS) are thought to be implicated. ROS cause oxidative alterations on cell constituents, and damage accumulation can lead to mutations in DNA. Modulation of gene expression during ageing is now quite documented but results are often controversial and/or incomplete. As ultraviolet A is one of the exogenous factors involved in skin ageing, by the production of ROS, we further document the modifications in gene expression during ageing process and response to an oxidative stress. For this purpose, we used a cDNA macroarray containing 82 genes related to cell defence, essentially represented by antioxidant and DNA repair proteins. Ageing-associated gene expression was assessed in normal skin human fibroblasts from three age groups: children (n=4), adults (n=4) and olders (n=3), at the basal state and after a 5J/cm2 UVA irradiation. Analysis revealed that 22 genes were never detected, whereas certain were always expressed such as those related to antioxidant defence, extracellular matrix (ECM) regulator and XPC. Transcripts related to ECM, MMP1 and MMP3 were increased with age and after UVA irradiation, independently of age. It appeared that transcripts involved in the redox status control (TXN and APEX) decreased as a function of age, at the basal state and after irradiation, respectively. Most of transcripts involved in DNA repair were not detected but repression of POLD1 in the adult group and induction of XRCC5 and LIG4 were observed after UVA irradiation, as a function of age. In the basal state, the transcript of GAS1, regulator of cell cycle arrest in G1 phase was found to be decreased with age. HMOX1 increased after UVA irradiation. In conclusion, the decrease in expression of some antioxidant system, cell cycle control gene and extracellular matrix enzymes, particularly after UV exposure can explain the occurrence of photoaging.

The essential mechanisms of aging: Irreparable damage accumulation of biochemical side-reactions

Explanations on aging mechanisms have now become unexpectedly complicated. However, it is gradually accepted that 'senescence is a collective consequence of both inheritance and environment'. Based on the achievements of biological and medical research in related fields, we pinpoint in this review that although aging is mainly considered a physiological (non-pathological) process, the biochemical structure of aged organisms is deranged, or 'sick' at the molecular level. The free radical/glycation induced carbonyl stress, the key culprit to form crosslinks, has been identified to cause stable cyclic conjugates of mainly protein-based aggregates implying entropy increase (the Second Law of Thermodynamics) during aging. When combining such key aging processes with age pigment biochemistry, a general picture of aging process can be figured out, as the main clues and results are available. In this review we also propose for the first time that by focusing on 'process' rather than on 'causes' (damages), we can then get a clear view of aging mechanisms. Through rational thinking and critical analysis, we conclude that the accumulation of irreparable damages and alternations caused by spontaneous biological side-reactions seems to be the essential and profound nature of higher animals' aging mechanisms.

Oxidative stress-mediated macromolecular damage and dwindle in antioxidant status in aged rat brain regions: Role of l-carnitine and dl-α-lipoic acid

BACKGROUND

The free radical theory of aging has significant relevance in a number of age-related neurological disorders. Too many free radicals create cellular pollution that shuts down energy levels. They have also been implicated in the loss of physiological functioning associated with the aging of post mitotic cells such as the brain. The activities of enzymatic antioxidative defenses decrease in rat brain may be possible causes of age-associated increase in oxidative damage to macromolecules.

METHODS

We determined whether DL-alpha-lipoic acid (100 mg/kg body weight/day), and L-carnitine (300 mg/kg body weight/day) together when administered for 30 days declines the rate of oxidative stress-mediated macromolecular damages such as lipid peroxidation (LPO), protein carbonyl (PCO) and DNA protein cross-links in different anatomic regions (cortex, striatum and hippocampus). The activities of antioxidant enzymes in programmed aging were evaluated in the cortex, striatum and hippocampus of young and aged rat brain regions.

RESULTS

Aged rats elicited a significant decline in the antioxidant status and increase in LPO, PCO and DNA protein cross-links as compared to young rats in all the 3 brain regions. The increase in LPO, PCO and DNA protein cross-links were (35.8%, 35.6%, 43.5%) in cortex, (32.5%, 40.3%, 29.8%) in striatum and (62.7%, 42.4%, 34.9%) in hippocampus, respectively, in aged rats as compared to young rats. Co-supplementation of carnitine and lipoic acid was found to be effective in reducing brain regional LPO, PCO and DNA protein cross-links and in increasing the activities of enzymatic antioxidants in aged rats to near normalcy.

CONCLUSION

The combination of l-carnitine and lipoic acid overcame the oxidative stress induced rate of lipid peroxidation, protein carbonyl formation, accumulation of DNA protein cross-links and deficits in antioxidant enzyme activities in various brain regions of aged rats.

Adaptive mechanisms to oxidative stress during aging

Whether or not oxidative stress is the cause of the aging process, as proposed by the oxidative stress theory of aging remains unknown; but accumulated evidence overwhelmingly identifies increased oxidative stress with age as a source of damage to cellular structure and function. From an evolutionary perspective, the utilization of oxygen as a life supporting means makes oxidative stress an inescapable part of an organism's biological system. The inseparability of oxidative stress from the biological system can be viewed as an adaptive response that all aerobic organisms undergo to ward-off the potentially harmful effects of oxygen and its derivatives, including free radicals. The organism's adaptive mechanisms include an intricate network of defenses that regulate and guard against any over-acting oxidative reactions to ensure its survival. This review discusses and illustrates several adaptive responses at various levels (from gene regulation to physical exercise) that organisms use as part of their survival strategy.

Proteomic Analysis of Nitrated and 4-Hydroxy-2-Nonenal-Modified Serum Proteins During Aging

Using proteomic techniques, we investigated peroxynitrite (ONOO-) and 4-hydroxy-2-nonenal (HNE) modified serum proteins from young and old Fischer 344 rats. Two-dimensional gel electrophoresis/western blot analysis of nitrotyrosine and HNE-histidine revealed that serum proteins were differentially modified by ONOO- and HNE. Among them, 16 of the modified proteins, identified by matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF MS), are involved in blood coagulation, lipid transport, blood pressure regulation, and protease inhibition. Furthermore, nitration and HNE adduction were found to increase with age, lending support to the oxidative stress hypothesis of aging. Our data showed that proteomic techniques can be valuable tools in the study of protein profiling modifications during aging.

The molecular inflammatory process in aging

Emerging pathological evidence indicates that major chronic aging-related diseases such as atherosclerosis, arthritis, dementia, osteoporosis, and cardiovascular diseases, are inflammation-related. In this review, inflammation is examined as a possible underlying basis for the molecular alterations that link aging and age-related pathological processes. A proposal for the molecular inflammation hypothesis of the aging views the redox derangement that occurs during aging as the major factor for increased risk for age-related inflammation. Accumulated data strongly indicate the activation of redox-sensitive transcription factors and dysregulated gene expression under the age-related oxidative stress seems to be the major culprits. Key players involved in the inflammatory process are the age-related upregulation of NF-kappaB, IL-1beta, IL-6, TNFalpha, cyclooxygenase-2, adhesion molecules, and inducible NO synthase. Furthermore, data are presented on the molecular events involved in age-related NF-kappaB activation and phosphorylation by IkappaB kinase/NIK and MAPKs. Experimental data on anti-aging calorie restriction (CR) for its antiinflammatory efficacy by suppressing the upregulated proinflammatory mediators will be reviewed. Also, the involvement of another super family of transcription factors, PPARs (PPARalpha, gamma) as regulators of proinflammatory responses and NF-kappaB signaling pathway is described as well as a discussion on the physiological significance of a well-maintained balance between NF-kappaB and PPARs.

Glutathione peroxidase 4 protects cortical neurons from oxidative injury and amyloid toxicity

Polyunsaturated fatty acids (PUFA) in membrane lipids are prone to attack by reactive oxygen species (ROS), and the resulting lipid peroxidation can cause injury and death of cells. Glutathione peroxidase 4 (Gpx4) is an antioxidant defense enzyme that can directly detoxify lipid hydroperoxides generated by ROS. Overexpression of Gpx4 has been shown to be protective against oxidative damage in several cell lines. We examined in this study the stress response of neurons with increased expression of Gpx4, because neurons are especially vulnerable to oxidative injury as a result of their high content of PUFA. Our results show that primary culture cortical neurons derived from Gpx4 transgenic mice, which had increased expression of Gpx4, had increased cell survival and reduced level of apoptosis after exposure to t-butyl hydroperoxide and hydrogen peroxide. We also studied the protective role of Gpx4 against beta-amyloid toxicity, because beta-amyloid-induced neural toxicity is believed to be mediated through lipid peroxidation. Primary culture cortical neurons from Gpx4 transgenic mice had significantly less cell toxicity than their wild-type counterparts after exposure to Abeta25-35 and Abeta1-40 peptides, and apoptosis induced by Abeta25-35 was attenuated in neurons from Gpx4 transgenic mice. Our data demonstrate that overexpression of Gpx4 protects neurons against oxidative injury and beta-amyloid-induced cytotoxicity.

Membrane alteration as a basis of aging and the protective effects of calorie restriction

As has been experimentally determined, oxidative modification to biological systems can be extensive, although the identification and stochiometric relation of the reactive species that cause these alterations have not been fully elucidated. In this review, arguments are presented to support the notion that the combined effects of membrane lipid peroxidation and its by-products, reactive aldehydes are likely responsible for membrane-associated functional declines during aging. As evidence for a systemic response to overall oxidative stress, the molecular inflammation hypothesis of aging is discussed by considering that the activation of inflammatory genes act as a bridge linking normal aging to pathological processes.

Rejuvenation of antioxidant system in central nervous system of aged rats by grape seed extract

Oxidative stress is considered as a major risk factor that contributes to age-related increase in lipid peroxidation and declined antioxidants in the central nervous system during aging. Grape seed extract, one of the bioflavonoid, is widely used for its medicinal properties. In the present study, we evaluated the role of grape seed extract on lipid peroxidation and antioxidant status in discrete regions of the central nervous system of young and aged rats. Male albino rats of Wistar strain were divided into four groups: Group I-control young rats, Group II-young rats treated with grape seed extract (100 mg/kg body weight) for 30 days, Group III-aged control rats and Group IV-aged rats supplemented with grape seed extract (100 mg/kg body weight) for 30 days. Age-associated increase in lipid peroxidation was observed in the spinal cord, cerebral cortex, striatum and the hippocampus regions of aged rats (Group III). Activities of antioxidant enzymes like superoxide dismutase, catalase, glutathione peroxidase and levels of non-enzymic antioxidants like reduced glutathione, Vitamin C and Vitamin E were found to be significantly decreased in all the brain regions studied in aged rats when compared to young rats. However, normalized lipid peroxidation and antioxidant defenses were reported in the grape seed extract-supplemented aged rats. These findings demonstrated that grape seed extract enhanced the antioxidant status and decreased the incidence of free radical-induced lipid peroxidation in the central nervous system of aged rats.

Exploring the processing continuum of single-word comprehension in aphasia

This study investigated the vulnerability of lexical processing in individuals with aphasia. Though classical teaching of aphasia syndromes holds that people with Broca's aphasia have intact comprehension at the single-word level, the nature and extent of this purported sparing were explored under suboptimal processing conditions. A combination of acoustic distortions (low-pass filtering and time compression) was used to probe for "break points" in lexical comprehension in a group of individuals with aphasia. Results suggest that accurate and efficient lexical processing is vulnerable to suboptimal listening climates, and that processing under these conditions reveals the continuous nature of the impairment of linguistic behaviors observed in individuals with aphasia.

The role of omega-3 long-chain polyunsaturated fatty acids in health and disease of the retina

In this work we advance the hypothesis that omega-3 (omega-3) long-chain polyunsaturated fatty acids (LCPUFAs) exhibit cytoprotective and cytotherapeutic actions contributing to a number of anti-angiogenic and neuroprotective mechanisms within the retina. omega-3 LCPUFAs may modulate metabolic processes and attenuate effects of environmental exposures that activate molecules implicated in pathogenesis of vasoproliferative and neurodegenerative retinal diseases. These processes and exposures include ischemia, chronic light exposure, oxidative stress, inflammation, cellular signaling mechanisms, and aging. A number of bioactive molecules within the retina affect, and are effected by such conditions. These molecules operate within complex systems and include compounds classified as eicosanoids, angiogenic factors, matrix metalloproteinases, reactive oxygen species, cyclic nucleotides, neurotransmitters and neuromodulators, pro-inflammatory and immunoregulatory cytokines, and inflammatory phospholipids. We discuss the relationship of LCPUFAs with these bioactivators and bioactive compounds in the context of three blinding retinal diseases of public health significance that exhibit both vascular and neural pathology. How is omega-3 LCPUFA status related to retinal structure and function? Docosahexaenoic acid (DHA), a major dietary omega-3 LCPUFA, is also a major structural lipid of retinal photoreceptor outer segment membranes. Biophysical and biochemical properties of DHA may affect photoreceptor membrane function by altering permeability, fluidity, thickness, and lipid phase properties. Tissue DHA status affects retinal cell signaling mechanisms involved in phototransduction. DHA may operate in signaling cascades to enhance activation of membrane-bound retinal proteins and may also be involved in rhodopsin regeneration. Tissue DHA insufficiency is associated with alterations in retinal function. Visual processing deficits have been ameliorated with DHA supplementation in some cases. What evidence exists to suggest that LCPUFAs modulate factors and processes implicated in diseases of the vascular and neural retina? Tissue status of LCPUFAs is modifiable by and dependent upon dietary intake. Certain LCPUFAs are selectively accreted and efficiently conserved within the neural retina. On the most basic level, omega-3 LCPUFAs influence retinal cell gene expression, cellular differentiation, and cellular survival. DHA activates a number of nuclear hormone receptors that operate as transcription factors for molecules that modulate reduction-oxidation-sensitive and proinflammatory genes; these include the peroxisome proliferator-activated receptor-alpha (PPAR-alpha) and the retinoid X receptor. In the case of PPAR-alpha, this action is thought to prevent endothelial cell dysfunction and vascular remodeling through inhibition of: vascular smooth muscle cell proliferation, inducible nitric oxide synthase production, interleukin-1 induced cyclooxygenase (COX)-2 production, and thrombin-induced endothelin 1 production. Research on model systems demonstrates that omega-3 LCPUFAs also have the capacity to affect production and activation of angiogenic growth factors, arachidonic acid (AA)-based vasoregulatory eicosanoids, and MMPs. Eicosapentaenoic acid (EPA), a substrate for DHA, is the parent fatty acid for a family of eicosanoids that have the potential to affect AA-derived eicosanoids implicated in abnormal retinal neovascularization, vascular permeability, and inflammation. EPA depresses vascular endothelial growth factor (VEGF)-specific tyrosine kinase receptor activation and expression. VEGF plays an essential role in induction of: endothelial cell migration and proliferation, microvascular permeability, endothelial cell release of metalloproteinases and interstitial collagenases, and endothelial cell tube formation. The mechanism of VEGF receptor down-regulation is believed to occur at the tyrosine kinase nuclear factor-kappa B (NFkappaB). NFkappaB is a nuclear transcription factor that up-regulates COX-2 expression, intracellular adhesion molecule, thrombin, and nitric oxide synthase. All four factors are associated with vascular instability. COX-2 drives conversion of AA to a number angiogenic and proinflammatory eicosanoids. Our general conclusion is that there is consistent evidence to suggest that omega-3 LCPUFAs may act in a protective role against ischemia-, light-, oxygen-, inflammatory-, and age-associated pathology of the vascular and neural retina.

Ageing and subcellular distribution of mitochondria: role of mitochondrial DNA deletions and energy production

The rapid growing population of elderly illustrates the importance of understanding the mechanisms responsible for ageing and the detrimental effects on health associated with increasing age. One of the primary mechanisms may be because of the accumulation of mtDNA damage and oxidative damage with age. Previous studies have examined this correlation in post-mitotic tissues such as skeletal muscle, heart and brain with decreased mitochondrial function, such as enzymatic activities of the electron transport chain and ATP production. However, regional differences in the subcellular location of mitochondria exist and most studies have failed to differentiate the effects of these two autonomous fractions, the subsarcolemmal and intermyofibrillar populations. Hence, while future research attempts to explain the mechanisms responsible for ageing in the mitochondrion, it should also take into account the independent pathways of these two distinctly different populations.

Transgenic mice overexpressing glutathione peroxidase 4 are protected against oxidative stress-induced apoptosis

Glutathione peroxidase 4 (Gpx4) is uniquely involved in the detoxification of oxidative damage to membrane lipids. Our previous studies showed that Gpx4 is essential for mouse survival and that Gpx4 deficiency makes cells vulnerable to oxidative injury. In the present study, we generated two lines of transgenic mice overexpressing Gpx4 (Tg(GPX4) mice) using a genomic clone containing the human GPX4 gene. Both lines of Tg-(GPX4) mice, Tg5 and Tg6, had elevated levels of Gpx4 (mRNA and protein) in all tissues investigated, and overexpression of Gpx4 did not cause alterations in activities of glutathione peroxidase 1, catalase, Cu/Zn superoxide dismutase, and manganese superoxide dismutase. The human GPX4 transgene rescued the lethal phenotype of null mutation of the mouse Gpx4 gene, indicating that the transgene can replace the essential role of mouse Gpx4 in mouse development. Cell death induced by t-butylhydroperoxide and diquat was significantly less in murine embryonic fibroblasts from Tg(GPX4) mice compared with wild type mice. Liver damage and lipid peroxidation induced by diquat were reduced significantly in Tg(GPX4) mice. In addition, diquat-induced apoptosis was decreased in Tg(GPX4) mice, as evidenced by attenuated caspase-3 activation and reduced cytochrome c release from mitochondria. These data demonstrate that Gpx4 plays a role in vivo in the mechanism of apoptosis induced by oxidative stress that most likely occurs through oxidative damage to mitochondrial phospholipids such as cardiolipin.

Vascular Aging: Molecular Modulation of the Prostanoid Cascade by Calorie Restriction

The relevance of prostanoids to inflammation, thrombosis, and cardiovascular diseases is well known. The present study attempts to explore age effects on prostanoids and their biosynthesis cascade. Results from comparing prostanoid levels between young (6 months) and old (24 months) Fischer 344 rats showed rises of prostaglandin E2 (PGE2), PGI2, and thromboxane A2 (TXA2) levels in the old rats. Correlating evidence showed gene expression up-regulation of several prostanoid synthase enzymes in old rat aorta. Further, we found that expression of the antioxidant enzyme glutathione peroxidase was raised by age in the aorta, while superoxide dismutase and catalase expression showed no significant change during aging in the aorta. Moreover, calorie restriction (CR) was found to attenuate age-related prostanoid changes by suppressing inflammatory activities. In conclusion, the data from this study indicated that age-related increases in prostanoids and their biosynthesis might be closely associated with a weakened antioxidant capacity.

Proteomic analysis of post-mitochondrial fractions of young and old rat kidney

Proteomic analysis is defined as the characterization of the entire set of proteins encoded by a genome. Two-dimensional (2D) electrophoresis and matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF MS) are key technologies used in proteomic analysis to gain information about protein expression profiles and post-translational modifications. Knowledge about aging processes can be gained by recognizing changes in protein expression. Thus, to better understand the aging process through protein profiling, post-mitochondrial (PM) fractions of young (13-month) and old (31-month) male Fischer 344 rat kidney were differentially analyzed by 2D. We detected a total number of 380 spots on 2D gel images. Among them, 167 spots showed 2-fold significant alterations (p<0.05) between young and old PM fractions. Further, 103 proteins were identified by MALDI-TOF MS. The PM fraction of aged rat kidney showed increases in antioxidative and proteolytic proteins and decreases in cytoskeletal proteins. In addition, we found age-related changes in transport and homeostasis proteins. Thus, our results demonstrated that proteomic analysis can be effectively applied to the assessment of the age status of protein expression, and thereby provide valuable information on age-related changes of proteome.

Age-dependent generation of reactive oxygen species in the skin of live hairless rats exposed to UVA light

Aging proceeds by highly complicated biochemical processes, in which the involvement of the reactive oxygen species (ROS) and free radicals has been implicated. Although the relationship between UV-induced photoaging and ROS generation has been proposed, it has been difficult to establish direct proof of the generation of ROS in the skin under UV exposure. Recently, we reported finding endogenously generated ROS in the skin of live mice after UVA light exposure by a method of in vivo chemiluminescent detection, in which superoxide anion radical (*O2-) and singlet oxygen species (1O2) are contributed. In light of the results, we tried to understand the age-dependent changes in ROS generation in the skin of hairless rats under UVA exposure. Chemiluminescent levels due to ROS in the untreated and UVA-exposed skin decreased age dependently, and the signal intensities in old rats were significantly lower than those in young rats. However, the ratios of chemiluminescent intensities in the UVA-exposed skin to those in the untreated skin were significantly enhanced in an age-dependent manner. These results suggest that the antioxidative ability against ROS generation in the skin, possessed by antioxidant enzymes and low molecular weight antioxidants, is lowered age dependently.

Effect of DL-alpha-lipoic acid on the status of lipid peroxidation and antioxidant enzymes in various brain regions of aged rats

The effect of DL-alpha-lipoic acid on lipid peroxidation and antioxidant enzymes were evaluated in various brain regions of young and aged rats. Lipoate contents of discrete brain regions were also measured. In aged rats, the activities of superoxide dismutase, glutathione peroxidase, glutathione reductase and glucose-6-phosphate dehydrogenase were low whereas thiobarbituric acid reactive substances were found to be high. Catalase activity in various brain regions was little altered in aged rats. Lipoic acid an antioxidant was administered intraperitoneally (100mg/kg body weight per day) for 7 and 14 days. Lipoate administered aged rats showed a duration dependent reduction in the level of lipid peroxidation and elevation in the activities of antioxidant enzymes. There was a rise in the level of lipoate in aged rats after supplementation of lipoate in all the brain regions examined. From our results we conclude that lipoate supplementation had a beneficial effect in both preventing and reversing abnormalities in ageing brain. This beneficial effect was associated with normalization of lipid peroxidation and partial restoration in the activities of various enzymatic antioxidants suggesting that lipoate supplementation could improve brain antioxidant functions in the elderly.

Effect of L-carnitine on brain lipid peroxidation and antioxidant enzymes in old rats

The effect of L-carnitine on lipid peroxidation and enzymatic antioxidants, such as superoxide dismutase, catalase, and glutathione peroxidase, was evaluated in brain regions of young and old rats. In all brain regions except the hypothalamus, lipid peroxidation was higher for old rats than for young control rats. The activity of superoxide dismutase, glutathione peroxidase, and catalase was lower in the striatum, cerebral cortex, and hippocampus, but no difference was observed in the hypothalamus and cerebellum. L-Carnitine administration (intraperitoneally) prevented thiobarbituric acid-reactive substance formation in the cerebral cortex, cerebellum, hypothalamus, hippocampus, and striatum of 24-month-old rats. Administration of L-carnitine reversed the age-associated changes in a duration-dependent manner. Results suggest that the neuroprotective effect on the brains in old rats was achieved by the elevation of antioxidants with L-carnitine.

Bacterial peptide methionine sulphoxide reductase: co-induction with glutathione S-transferase during chemical stress conditions

Peptide methionine sulphoxide reductase (MsrA; EC 1.8.4.6) is a ubiquitous enzyme catalysing the reduction of methionine sulphoxide to methionine in proteins, while the glutathione S-transferases (GSTs) are a major family of detoxification enzymes. A gene homologous to MsrA was identified in a chromosomal fragment from the bacterium Ochrobactrum anthropi, and this gene is located just downstream of a GST gene identified previously (OaGST) [Favaloro, Tamburro, Angelucci, De Luca, Melino, Di Ilio and Rotilio (1998) Biochem. J. 335, 573-579]. This raises the question of whether the products of these two genes may be involved in a common cellular protection function. To test this hypothesis, the hypothetical MsrA protein has been overexpressed in Escherichia coli as a functional 51 kDa GST fusion protein. Following cleavage with thrombin and purification, the soluble 24 kDa protein showed MsrA activity with N-acetylmethionine sulphoxide as substrate, as well as with other sulphoxide compounds. Therefore polyclonal antibodies were raised against the recombinant protein, and the modulation of MsrA in this bacterium, grown in the presence of different stimulants simulating several stress conditions, was investigated. The level of expression of MsrA was detected both by measuring the mRNA level and by immunoblotting experiments, in addition to measuring its catalytic activity. MsrA is a constitutive enzyme which is also inducible by chemical stress involving phenolic compounds such as phenol and 4-chlorophenol. Recently we reported that the GST of this bacterium, like MsrA, is only modulated by toxic chemical compounds [Favaloro, Tamburro, Trofino, Bologna, Rotilio and Heipieper (2000) Biochem. J. 346, 553-559]; therefore this is the first indication of a co-induction of the MsrA and GST enzymes during chemical stress.

Oxidative stress and vascular aging

In attempt to meet tissue demands for proper blood flow, the vasculature alters its structure, simultaneously responding to both physical and chemical stresses. Substantial information has emerged in this field of study, particularly concerning the roles of the endothelium and smooth muscle cells in relation to signaling pathways for mechanotransduction. As a first line of defense upon exposure to various stressors, the endothelium and smooth muscle cells respond with adaptive cellular modifications. One prime example of these modifications is the cellular response to oxidative stress as evidenced by accumulated data. A recent proposal of the inflammatory hypothesis of vascular aging emphasized that stress-induced vascular aging may be the primary event that underlies the general aging phenomenon of systemic dysfunction.

The nitrite/collagen reaction: non-enzymatic nitration as a model system for age-related damage

The effects of age seen in long-lived connective tissue proteins are thought to be the result of post-translational modifications by reactive molecules. One such molecule is the nitrite ion. Human nitrite exposure results predominately from endogenous production of nitric oxide as well as inhalation of cigarette smoke and ingestion of cured meats. Although nitrite reactions with various proteins have been studied previously with regard to carcinogenesis, the specific reaction with collagen and its role in age-related damage has never been examined. We describe the reaction of nitrite with type I collagen at neutral pH and body temperature. The incubation of collagen with nitrite results in an increase in cross-linking, the accumulation of a yellow chromophore, and a depletion of tyrosine residues. Similar changes also are found in aged human collagen. In addition, 3-nitro-tyrosine, which has recently been used as a marker for peroxynitrite mediated damage, is produced from this reaction. Thus, we propose non-enzymatic nitration as an in vitro model system for human collagen age-related damage.

Iron chlorin e6 scavenges hydroxyl radical and protects human endothelial cells against hydrogen peroxide toxicity

Iron chlorin e6 (FeCe6) has recently been proposed to be potentially antimutagenic and antioxidative. However, the antioxidant property of FeCe6 has not been elucidated in detail. In this study, we investigated the ability of FeCe6 to scavenge hydroxyl radical and to protect biomolecules and mammalian cells from oxidative stress-mediated damage. In electron spin resonance (ESR) experiments, FeCe6 showed excellent hydroxyl radical scavenging activity, whereas its iron-deficient molecule, chlorin e6 (Ce6) showed little effect. FeCe6 also significantly reduced hydroxyl radical-induced thiobarbituric acid reactive substance (TBARS) formation and benzoate hydroxylation in a dose-dependent manner. The rate constant for reaction between FeCe6 and hydroxyl radical was measured as 8.5 x 10(10) M(-1) s(-1) by deoxyribose degradation method, and this value was much higher than that of most hydroxyl radical scavengers. Superoxide dismutase (SOD) activity of FeCe6 was also confirmed by ESR study and cytochrome c reduction assay, but its in vitro activity appeared to be less efficient in comparison with other well-known SOD mimics. In addition, FeCe6 appreciably diminished hydroxyl radical-induced DNA single-strand breakage and protein degradation in Fe-catalyzed and Cu-catalyzed Fenton systems, and it significantly protected human endothelial cells against hydrogen peroxide (H2O2) toxicity. These results suggest that FeCe6 is a novel hydroxyl radical scavenger and may be useful for preventing oxidative injury in biological systems.

Gene expression of cyclooxygenase in the aging heart

Cyclooxygenase (COX) is the key rate-limiting enzyme in the prostaglandin synthetic pathway. Two isoforms of COX have been identified: a constitutive COX-1 and an inducible COX-2, which is activated in response to various stimuli. We investigated the changes of COX-1 and COX-2 in rat heart during aging. We measured the age-related changes in the mRNA and protein levels of COX by using reverse-transcription polymerase chain reaction and Western blotting, respectively. COX-2 mRNA and protein levels increased with age, whereas those of COX-1 showed no change. The COX activity determined by prostaglandin E(2) production increased with age. Because the COX-catalyzed arachidonate cascade is an important source of reactive oxygen species (ROS) generation, changes in ROS generation and lipid peroxidation were also assessed. The amount of ROS generated by the COX pathway increased with age, as did the total ROS generation and lipid peroxidation. These results show that COX-2 activity increases with age, partially because of elevated transcriptional expression and protein content, and they suggest that increased COX-2 can play a role in oxidative alterations in the aged heart.

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

Dietary restriction (DR) increases life span and decreases age-related diseases in experimental animals. It has received a great deal of attention in connection with the relationship between aging, nutrition, and oxidative stress because oxidative injury in several organ systems is a prominent feature in aging. We investigated the possibility that DR can protect vulnerable liver lipids against age-related increases of peroxidation. Male Fischer 344 rats fed ad libitum (AL) or dietarily restricted (maintained on 60% of AL food intake) were killed by decapitation at 4 (young) or 12 mon (adult) of age. Phosphatidylcholine hydroperoxide (PCOOH) concentration of liver was determined using a chemiluminescent high-performance liquid chromatographic method. Liver PCOOH increased with age in adult rats, but less of an increase of PCOOH was seen in DR rats, which is consistent with results on production of thiobarbituric acid-reactive substances and oxygen-derived free radicals. No significant differences were found in liver superoxide dismutase and catalase activity between AL and DR groups of young and adult rats. Liver triglyceride and cholesterol contents were lower in DR than AL rats at 12 mon. Fatty acid compositions of phosphatidylcholine and phosphatidylethanolamine indicated that the ratio of (20:3n-6 + 20:4n-6)/18:2n-6, an index of linoleic acid (18:2n-6) desaturation, was lower in DR than in AL rats. We concluded that DR suppresses age-related oxidative damage in liver by modulating the amount of lipid as well as fatty acid composition.

Correlation of fatty acid unsaturation of the major liver mitochondrial phospholipid classes in mammals to their maximum life span potential

Free radical damage is considered a determinant factor in the rate of aging. Unsaturated fatty acids are the tissue macromolecules that are most sensitive to oxidative damage. Therefore, the presence of low proportions of fatty acid unsaturation is expected in the tissues of long-lived animals. Accordingly, the fatty acid compositions of the major liver mitochondrial phospholipid classes from eight mammals, ranging in maximum life span potential (MLSP) from 3.5 to 46 yr, show that the total number of double bonds is inversely correlated with MLSP in both phosphatidylcholine (PtdCho) and phosphatidylethanolamine (PtdEtn) (r = 0.757, P < 0.03, and r = 0.862, P < 0.006, respectively), but not in cardiolipin (P = 0.323). This is due not to a low content of unsaturated fatty acids in long-lived animals, but mainly to a redistribution between kinds of fatty acids on PtdCho and PtdEtn, shifting from arachidonic (r = 0.911, P < 0.002, and r = 0.681, P = 0.05, respectively), docosahexaenoic (r = 0.931 and r = 0.965, P < 0.0001, respectively) and palmitic (r = 0.944 and r = 0.974, P < 0.0001, respectively) acids to linoleic acid (r = 0.942, P < 0.0001, for PtdCho; and r = 0.957, P < 0.0001, for PtdEtn). For cardiolipin, only arachidonic acid showed a significantly inverse correlation with MLSP (r = 0.904, P < 0.002). This pattern strongly suggests the presence of a species-specific desaturation pathway and deacylation-reacylation cycle in determining the mitochondrial membrane composition, maintaining a low degree of fatty acid unsaturation in long-lived animals.

Effects of caloric restriction on skeletal muscle mitochondrial proton leak in aging rats

Long-term caloric restriction (CR) retards aging processes and increases maximum life span. We investigated the influence of CR on mitochondrial proton leaks in rat skeletal muscle. Because CR lowers oxidative damage to mitochondrial membrane lipids and proteins, we hypothesized that leak would be lower in mitochondria from old CR rats than in age-matched controls. Three groups (n = 12) were studied: 4-month-old "young" control rats (body weight: 404 g +/- 7 SEM), 33-month-old CR rats (body weight: 262 g +/- 3), and 33-month-old control rats (body weight: 446 g +/- 5). CR rats received 67% of the energy intake of old control rats, with adequate intakes of all essential nutrients. Maximum leak-dependent O2 consumption (State 4) was 23% lower in CR rats than in age-matched controls, whereas protonmotive force values were similar, supporting our hypothesis. The overall kinetics of leak were similar between the two groups of old rats; in the young, kinetics indicated higher protonmotive force values. The latter indication is consistent with aging-induced alterations in proton leak kinetics that are independent of dietary intervention. There was no influence of age or diet on serum T4 level, whereas T3 was lower in young than in old control rats. These results support and extend the oxidative stress hypothesis of aging.

The biochemistry of aging

Although philosophers and scientists have long been interested in the aging process, general interest in this fascinating and highly important topic was minimal before the 1960s. In recent decades, however, interest in aging has greatly accelerated, not only since the elderly form an ever-increasing percentage of the population, but because they utilize a significant proportion of the national expenditures. In addition, many people have come to the realization that one can now lead a very happy, active, and productive life well beyond the usual retirement age. Scientifically, aging is an extremely complex, multifactorial process, and numerous aging theories have been proposed; the most important of these are probably the genomic and free radical theories. Although it is abundantly clear that our genes influence aging and longevity, exactly how this takes place on a chemical level is only partially understood. For example, what kinds of genes are these, and what proteins do they control? Certainly they include, among others, those that regulate the processes of somatic maintenance and repair, such as the stress-response systems. The accelerated aging syndromes (i.e., Hutchinson-Gilford, Werner's, and Down's syndromes) are genetically controlled, and studies of them have decidedly increased our understanding of aging. In addition, C. elegans and D. melanogaster are important systems for studying aging. This is especially true for the former, in which the age-1 mutant has been shown to greatly increase the life span over the wild-type strain. This genetic mutation results in increased activities of the antioxidative enzymes, Cu-Zn superoxide dismutase and catalase. Thus, the genomic and free radical theories are closely linked. In addition, trisomy 21 (Down's syndrome) is characterized by a significantly shortened life span; it is also plagued by increased oxidative stress which results in various free radical-related disturbances. Exactly how this extra chromosome results in an increased production of reactive oxygen species is, however, only partially understood. There is considerable additional indirect evidence supporting the free radical theory of aging. Not only are several major age-associated diseases clearly affected by increased oxidative stress (atherosclerosis, cancer, etc.), but the fact that there are numerous natural protective mechanisms to prevent oxyradical-induced cellular damage speaks loudly that this theory has a key role in aging [the presence of superoxide dismutase, catalase, glutathione peroxidase, and glutathione reductase, among others; various important intrinsic (uric acid, bilirubin, -SH proteins, glutathione, etc.) and extrinsic (vitamins C, E, carotenoids, flavonoids, etc.) antioxidants; and metal chelating proteins to prevent Fenton and Haber-Weiss chemistry]. In addition, a major part of the free radical theory involves the damaging role of reactive oxygen species and various toxins on mitochondria. These lead to numerous mitochondrial DNA mutations which result in a progressive reduction in energy output, significantly below that needed in body tissues. This can result in various signs of aging, such as loss of memory, hearing, vision, and stamina. Oxidative stress also inactivates critical enzymes and other proteins. In addition to these factors, caloric restriction is the only known method that increases the life span of rodents; studies currently underway suggest that this also applies to primates, and presumably to humans. Certainly, oxidative stress plays an important role here, although other, as yet unknown, factors are also presumably involved. Exactly how the other major theories (i.e., immune, neuroendocrine, somatic mutation, error catastrophe) control aging is more difficult to define. The immune and neuroendocrine systems clearly deteriorate with age. (ABSTRACT TRUNCATED)

Alterations of antioxidant enzymes and oxidative stress markers in aging

In accordance with the present state of scientific knowledge, the excessive production of free radicals in the organism, and the imbalance between the concentrations of these and the antioxidant defenses may be related to processes such as aging and several diseases. The aging process has been described by various theories. In particular, the free radical theory of aging has received widespread attention which proposes that deleterious actions of free radicals are responsible for the functional deterioration associated with aging. Although, the relationship between lipid peroxidation and aging have been investigated extensively, the studies have produced conflicting results. To investigate the correlation between the oxidative stress and aging, we have determined the levels of lipid peroxidation expressed as thiobarbituric acid reactive substances (TBARS; MDA) and conjugated dien; oxidative protein damage as indicated by carbonyl content and activities of antioxidant enzymes including superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPx) in a sample of 100 healthy men and women ranging in age from 20 to 70years. In addition, vitamin E, C levels, reduced glutathione and sulphydryl content were determined. The oxidation end product of nitric oxide (nitrate) was also studied to investigate any role of nitrogen radicals in aging. Our data show that there is an age related increase in lipid peroxidation expressed as MDA and oxidative protein damage as indicated by carbonyl content. Aging is not linked to a decline in antioxidant enzymes except GPx. Our data suggests that the level of oxidative stress increase cannot entirely be attributed to a decrease in the activities of antioxidant defense system and probably various factors may contribute to this process.

Low fatty acid unsaturation: a mechanism for lowered lipoperoxidative modification of tissue proteins in mammalian species with long life spans

Carbonyl compounds generated by the nonenzymatic oxidation of polyunsaturated fatty acids react with nucleophilic groups in proteins, leading to their modification. It has not been tested whether fatty acid unsaturation is related to steady-state levels of lipoxidation-derived protein modification in vivo. A low fatty acid unsaturation, hence a low protein lipoxidation, in tissues of longevous animals would be consistent with the free radical theory of aging, because membrane lipids increase their sensitivity to oxidative damage as a function of their degree of unsaturation. To evaluate the relationship between fatty acid composition, protein lipoxidation, and maximum life span (MLSP), we analyzed liver fatty acids and proteins from seven mammalian species, ranging in MLSP from 3.5 to 46 years. The results show that the peroxidizability index of fatty acids and the sensitivity to in vitro lipid peroxidation are negatively correlated with the MLSP. Based on gas chromatography and mass spectroscopy analyses, liver proteins of all these species contain malondialdehyde-lysine and Nepsilon-carboxymethyllysine adducts, two biomarkers of protein lipoxidation. The steady-state levels of malondialdehyde-lysine and Nepsilon-carboxymethyl lysine are directly related to the peroxidizability index and inversely related to the MLSP. We propose that a low degree of fatty acid unsaturation may have been selected in longevous mammals to protect their tissue lipids and proteins against oxidative damage while maintaining an appropriate environment for membrane function.

[Alzheimer's disease: from pathology to preventive methods?]

INTRODUCTION

Sporadic Alzheimer's disease is the most frequent form of dementia and appears to be associated with increasing age and certain genetic and environmental factors. Some studies have recently been published on potential protective factors.

CURRENT KNOWLEDGE AND KEY POINTS

Several genes appear to be involved; one of the most common is the ApoE4 allele on chromosome 19. The physiopathology is not elucidated, but recent studies have shown a protective effect for NSAIDs, estrogen, nutritional factors (vitamins E, B6 and B12) as well as some biochemical amino acids (homocysteine).

FUTURE PROSPECTS AND PROJECTS

Interventional studies are now in progress and some preventive approaches will soon be available.

Alzheimer disease: protective factors

Approximately 6-8% of all persons aged >65 y have Alzheimer disease and the prevalence of the disease is increasing. Any intervention strategy aimed at decreasing risks or delaying the onset of the disease will therefore have a substantial effect on health care costs. Nutrition seems to be one of the factors that may play a protective role in Alzheimer disease. Many studies suggest that oxidative stress and the accumulation of free radicals are involved in the pathophysiology of the disease. Several studies have shown the existence of a correlation between cognitive skills and the serum concentrations of folate, vitamin B-12, vitamin B-6, and, more recently, homocysteine. However, nutritional factors have to be studied not alone but with the other factors related to Alzheimer disease: genetics, estrogen, antiinflammatory drug use, and socioeconomic variables. The objective of this article was to review recent studies in this field.

Site-specific DNA damage at GGG sequence by oxidative stress may accelerate telomere shortening

Telomere shortening during human aging has been reported to be accelerated by oxidative stress. We investigated the mechanism of telomere shortening by oxidative stress. H2O2 plus Cu(II) caused predominant DNA damage at the 5' site of 5'-GGG-3' in the telomere sequence. Furthermore, H2O2 plus Cu(II) induced 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG) formation in telomere sequences more efficiently than that in non-telomere sequences. NO plus O2- efficiently caused base alteration at the 5' site of 5'-GGG-3' in the telomere sequence. It is concluded that the site-specific DNA damage at the GGG sequence by oxidative stress may play an important role in increasing the rate of telomere shortening with aging.

Altered levels of primary antioxidant enzymes in progeria skin fibroblasts

Free radicals are involved in the aging process. In this study, the profile of primary antioxidant enzymes that scavenge reactive oxygen species (ROS) was examined for the first time in human skin fibroblasts from progeria, a premature aging disease. Altered levels of antioxidant enzymes were found in progeria cells. Basal levels of MnSOD were decreased in progeria cells as well as a blunted induction in response to chronic stress. This change may contribute to the accelerated aging process in progeria cells. In contrast, the levels of CuZnSOD showed no progeria-related change. Two H2O2 removing enzymes demonstrated a significant reduction in progeria cells: only 50% of normal CAT activity and 30% of normal GPX activity can be detected in progeria cells. This diminished H2O2 removing capacity in progeria cells may lead to an imbalance of intracellular ROS and therefore may play an important role in the development of progeria.

Endogenous oxidative damage of mtDNA

Almost a decade ago, based on analytical measurements of the oxidative DNA adduct 8-oxo-deoxyguanosine (oxo8dG), it was reported that mitochondrial DNA suffers greater endogenous oxidative damage than nuclear DNA. The subsequent discovery that somatic deletions of mitochondrial DNA occur in humans, and that they do so to the greatest extent in metabolically active tissues, strengthened the hypothesis that mitochondrial DNA is particularly susceptible to endogenous oxidative attack. This hypothesis was (and is) appealing for a number of reasons. Nevertheless, solid direct support for the hypothesis is lacking. Since the initial measurements, attempts to repeat the observation of greater oxidation of mitochondrial DNA have resulted in a range of measurements that spans over four orders of magnitude. Moreover, this range includes values that are as low as published values for nuclear DNA. In the last 2 years or so, it has become apparent that the quantification of oxidative DNA adducts is prone to artifactual oxidation. We have reported that the analysis of small quantities of DNA may be particularly susceptible to such interference. Because yields of mitochondrial DNA are generally low, a systematic artifact associated with low quantities of DNA may have elevated the apparent level of adduct oxo8dG in mitochondrial DNA relative to nuclear DNA in some studies. Whatever the cause for the experimental variation, the huge disparity between published measurements of oxidative damage makes it impossible to conclude that mitochondrial DNA suffers greater oxidation than nuclear DNA. Despite the present confusion, however, there are reasons to hypothesize that this is indeed the case. We briefly describe methods being developed by a number of workers that are likely to surmount current obstacles and allow the hypothesis to be tested definitively.

Structural and functional changes in proteins induced by free radical-mediated oxidative stress and protective action of the antioxidants N-tert-butyl-alpha-phenylnitrone and vitamin E

The free radical theory of aging proposes that reactive oxygen species (ROS) cause oxidative damage over the lifetime of the subject. It is the cumulative and potentially increasing amount of accumulated damage that accounts for the dysfunctions and pathologies seen in normal aging. We have previously demonstrated that both normal rodent brain aging and normal human brain aging are associated with an increase in oxidative modification of proteins and in changes in plasma membrane lipids. Several lines of investigation indicate that one of the likely sources of ROS is the mitochondria. There is an increase in oxidative damage to the mitochondrial genome in aging and a decreased expression of mitochondrial mRNA in aging. We have used a multidisciplinary approach to the characterization of the changes that occur in aging and in the modeling of brain aging, both in vitro and in vivo. Exposure of rodents to acute normobaric hyperoxia for up to 24 h results in oxidative modifications in cytosolic proteins and loss of activity for the oxidation-sensitive enzymes glutamine synthetase and creatine kinase. Cytoskeletal protein spin labeling also reveals synaptosomal membrane protein oxidation following hyperoxia. These changes are similar to the changes seen in senescent brains, compared to young adult controls. The antioxidant spin-trapping compound N-tert-butyl-alpha-phenylnitrone (PBN) was effective in preventing all of these changes. In a related study, we characterized the changes in brain protein spin labeling and cytosolic enzyme activity in a series of phenotypically selected senescence-accelerated mice (SAMP), compared to a resistant line (SAMR1) that was derived from the same original parents. In general, the SAM mice demonstrated greater oxidative changes in brain proteins. In a sequel study, a group of mice from the SAMP8-sensitive line were compared to the SAMR1-resistant mice following 14 days of daily PBN treatment at a dose of 30 mg/kg. PBN treatment resulted in an improvement in the cytoskeletal protein labeling toward that of the normal control line (SAMR1). The results of these and related studies indicate that the changes in brain function seen in several different studies may be related to the progressive oxidation of critical brain proteins and lipids. These components may be critical targets for the beneficial effects of gerontotherapeutics both in normal aging and in disease of aging.

Mitochondrial aging: open questions

Interest in the role of mitochondria in aging has intensified in recent years. This focus on mitochondria originated in part from the free radical theory of aging, which argues that oxidative damage plays a key role in degenerative senescence. Among the numerous mechanisms known to generate oxidants, leakage of the superoxide anion and hydrogen peroxide from the mitochondrial electron transport chain are of particular interest, due to the correlation between species-specific metabolic rate ("rate of living") and life span. Phenomenological studies of mitochondrial function long ago noted a decline in mitochondrial function with age, and on-going research continues to add to this body of knowledge. The extranuclear somatic mutation theory of aging proposes that the accumulation of mutations in the mitochondrial genome may be responsible in part for the mitochondrial phenomenology of aging. Recent studies of mitochondrial DNA (mtDNA) deletions have shown that they increase with age in humans and other mammals. Currently, there exist numerous important and fundamental questions surrounding mitochondria and aging. Among these are (1) How important are mitochondrial oxidants in determining overall cellular oxidative stress? (2) What are the mechanisms of mitochondrial oxidant generation? (3) How are lesions and mutations in mtDNA formed? (4) How important are mtDNA lesions and mutations in causing mitochondrial dysfunction? (5) How are mitochondria regulated, and how does this regulation change during aging? (6) What are the dynamics of mitochondrial turnover? (7) What is the relationship between mitochondrial damage and lipofuscinogenesis? (8) What are the relationships among mitochondria, apopotosis, and aging? and (9) How can mitochondrial function (ATP generation and the establishment of a membrane potential) and dysfunction (oxidant generation) be modulated and degenerative senescence thereby treated?