Free radical theory of aging: an update: increasing the functional life span

Mass spectrometry-based survey of age-associated protein carbonylation in rat brain mitochondria

There is a body of evidence lending credence to the idea that oxidative stress may be responsible for age-related deleterious changes in brain function, and that protein carbonylation is a potential marker for such changes. An investigation of oxidative damage to mitochondrial proteins from aged rat brains was done using gel electrophoresis coupled with carbonylation-specific immunostaining. Six proteins that appeared to be susceptible to oxidative modification were identified by in-gel trypsin digestion followed by matrix-assisted laser desorption/ionization mass spectrometry and tandem mass spectrometry. Two subunits of the H(+)-transporting ATP synthase, adenine nucleotide translocator, voltage-dependent anion channel, glutamate oxaloacetate transaminase, and aconitase were identified as likely targets of age-associated carbonylation.

Alterations in antioxidant enzymes during aging in humans

The oxidative stress theory of aging offers the best mechanistic elucidation of the aging phenomenon and other age-related diseases. The susceptibility of an individual depends on the antioxidant status of the body. In humans, the antioxidant system includes a number of antioxidant enzymes such as superoxide dismutase (SOD) and catalase (CAT), nonenzymatic antioxidants such as glutathione (GSH), protein -SH, ascorbic acid, and uric acid, and dietary antioxidants. Antioxidant enzymes form the first line of defense against reactive oxygen species. In an earlier report, we showed that the plasma antioxidant potential in humans decreases as a function of age and that there are compensatory mechanisms operating in the body which are induced to maintain the antioxidant capacity during aging. In the present study, we report the relationship between human aging and antioxidant enzymes SOD and CAT; we also correlate the activity of these enzymes with the antioxidant capacity of the plasma. Our results show a significantly higher plasma SOD and CAT activity in older individuals than in younger individuals. The induction in activity of SOD and CAT during human aging may be a compensatory response of the individual to an increased oxidative stress.

Reduced mitochondrial SOD displays mortality characteristics reminiscent of natural aging

Manganese superoxide dismutase (MnSOD or SOD2) is a key mitochondrial enzymatic antioxidant. Arguably the most striking phenotype associated with complete loss of SOD2 in flies and mice is shortened life span. To further explore the role of SOD2 in protecting animals from aging and age-associated pathology, we generated a unique collection of Drosophila mutants that progressively reduce SOD2 expression and function. Mitochondrial aconitase activity was substantially reduced in the Sod2 mutants, suggesting that SOD2 normally ensures the functional capacity of mitochondria. Flies with severe reductions in SOD2 expression exhibited accelerated senescence of olfactory behavior as well as precocious neurodegeneration and DNA strand breakage in neurons. Furthermore, life span was progressively shortened and age-dependent mortality was increased in conjunction with reduced SOD2 expression, while initial mortality and developmental viability were unaffected. Interestingly, life span and age-dependent mortality varied exponentially with SOD2 activity, indicating that there might normally be a surplus of this enzyme for protecting animals from premature death. Our data support a model in which disruption of the protective effects of SOD2 on mitochondria manifests as profound changes in behavioral and demographic aging as well as exacerbated age-related pathology in the nervous system.

Oxidative stress modulation and T cell activation

During the immune response T cell function is influenced by extrinsic factors, some of which lead to increased protein and DNA damage and are thought to play a role in age-related immune dysfunction. Damage is in part due to reactive oxygen species produced as a result of aerobic metabolism during a vigorous immune response, but in the in vitro models commonly used to study human immunity may also be due to culturing cells under hyperoxic conditions, i.e., in air. Reactive oxygen species (ROS) are ubiquitously generated but an imbalance between ROS production and protection against ROS may severely affect T cell activation. Controlling and modulating oxidative stress in the extracellular milieu may influence T cell signalling and activation. Here, we discuss the relevance of oxidative stress modulation to prevent T cell dysfunction. We draw attention to some technical, but critical, aspects of T cell culture under hyperoxic conditions.

Estrogen suppresses brain mitochondrial oxidative stress in female and male rats

Mitochondria are a major source of reactive oxygen species (ROS) and oxidative stress, key contributors to aging and neurodegenerative disorders. We report that gonadal hormones influence brain mitochondrial ROS production in both females and males. Initial experiments showed that estrogen decreases mitochondrial superoxide production in a receptor-mediated manner, as measured by MitoSOX fluorescence in differentiated PC-12 cells. We then assessed in vivo effects of gonadal hormones on brain mitochondrial oxidative stress in female and male rats. Brain mitochondria were isolated to measure a functional indicator of ROS, i.e., activity of the ROS-sensitive mitochondrial enzyme, aconitase. Gonadectomy of both males and females caused a decrease in aconitase activity, suggesting that endogenous gonadal hormones influence mitochondrial ROS production in the brain. In vivo treatment of gonadectomized animals with testosterone or dihydrotestosterone (DHT) had no effect, but estrogen replacement significantly increased aconitase activity in brain mitochondria from both female and male rats. This indicates that estrogen decreases brain mitochondrial ROS production in vivo. Sex hormone treatments did not affect protein levels of brain mitochondrial uncoupling proteins (UCP-2, 4, and 5). However, estrogen did increase the activity, but not the levels, of manganese superoxide dismutase (MnSOD), the mitochondrial enzyme that catalyzes superoxide radical breakdown, in brain mitochondria from both female and male rats. Thus, in contrast to the lack of effect of androgens on mitochondrial ROS, estrogen suppression of mitochondrial oxidative stress may influence neurological disease incidence and progression in both females and males.

'In vitro' protective effect of a hydrophilic vitamin E analogue on the decrease in levels of elongation factor 2 in conditions of oxidative stress

BACKGROUND

Protein synthesis is inhibited by oxidative stress. Among the possible causes of this inhibition are the modifications of elongation factor 2 (eEF-2), the protein that catalyzes the translocation of the ribosome through mRNA. eEF-2 is extremely sensitive to oxidative stress caused mainly by lipid peroxidant compounds such as cumene hydroperoxide (CH).

OBJECTIVE

The purpose of this study was to determine whether the antioxidant Trolox prevents the effect of CH on the levels of hepatic eEF-2.

METHODS

The effect was determined in liver homogenates treated with both compounds. Lipid peroxides and carbonyl content were also measured.

RESULTS

The results show that Trolox at certain doses prevents the decrease in the level of eEF-2 caused by CH.

CONCLUSION

Under oxidative stress circumstances, vitamin E can prevent the effect of oxidations on relevant biological processes such as protein synthesis.

Theories of biological aging: genes, proteins, and free radicals

Traditional categorization of theories of aging into programmed and stochastic ones is outdated and obsolete. Biological aging is considered to occur mainly during the period of survival beyond the natural or essential lifespan (ELS) in Darwinian terms. Organisms survive to achieve ELS by virtue of genetically determined longevity assuring maintenance and repair systems (MRS). Aging at the molecular level is characterized by the progressive accumulation of molecular damage caused by environmental and metabolically generated free radicals, by spontaneous errors in biochemical reactions, and by nutritional components. Damages in the MRS and other pathways lead to age-related failure of MRS, molecular heterogeneity, cellular dysfunctioning, reduced stress tolerance, diseases and ultimate death. A unified theory of biological aging in terms of failure of homeodynamics comprising of MRS, and involving genes, milieu and chance, is acquiring a definitive shape and wider acceptance. Such a theory also establishes the basis for testing and developing effective means of intervention, prevention and modulation of aging.

Age-dependent accumulation of mtDNA mutations in murine hematopoietic stem cells is modulated by the nuclear genetic background

Alterations in mitochondrial DNA (mtDNA) and consequent loss of mitochondrial function underlie the mitochondrial theory of aging. In this study, we systematically analyzed the mtDNA control region somatic mutation pattern in 2864 single hematopoietic stem cells (HSCs) and progenitors, isolated by flow cytometry sorting on Lin(-)Kit(+)CD34(-) parameters from young and old C57BL/6 (B6) and BALB/cBy (BALB) mice, to test the hypothesis that the accumulated mtDNA mutations in HSCs were strain-correlated and associated with HSC functional senescence during aging. An increased level of mtDNA mutations in single HSCs was observed in old B6 when compared with young B6 mice (P=0.003); in contrast, no significant age-dependent accumulation of mutations was observed in BALB mice (old versus young, P=0.202) and the level of mutations in both young and old BALB mice was close to that of old B6 mice (P>0.280). Cellular reactive oxygen species (ROS) in mouse HSCs could not be correlated with the level of mtDNA mutations in these cells, although B6 mice had a higher proportion of ROS(-) cells when compared with the BALB mice. Propagation assays of single HSCs showed B6 cells form larger colonies compared with cells from BALB mice, irrespective of age and mtDNA mutation load. We infer from our data that age-related mtDNA somatic mutation accumulation in mouse HSCs is influenced by the nuclear genetic background and that these mutations may not obviously correlate to either cellular ROS content or HSC senescence.

Comparative approaches to facilitate the discovery of prolongevity interventions: effects of tocopherols on lifespan of three invertebrate species

Many compounds hold promise for pharmacologic manipulation of aging. However, such claims are difficult to investigate due to time and budget constraints. Here, we took a comparative approach, using short-lived invertebrate species, to directly test the effects of two tocopherols (Vitamin E) on longevity. gamma-Tocopherol represents the most abundant tocopherol in the Western diet, while alpha-tocopherol is selectively enriched in human plasma. Both isoforms demonstrate antioxidant activity and are proposed to have anti-aging activities. We compared the effects of alpha- and gamma-tocopherol supplementation on lifespan in three invertebrate species. gamma-Tocopherol, but not alpha-tocopherol, slightly extended lifespan in nematodes, but neither significantly affected lifespan in two fly species. This study shows that a comparative approach, utilizing multiple invertebrate species, can increase the robustness of invertebrate-based pilot screens for prolongevity interventions.

The mitochondrial energy transduction system and the aging process

Aged mammalian tissues show a decreased capacity to produce ATP by oxidative phosphorylation due to dysfunctional mitochondria. The mitochondrial content of rat brain and liver is not reduced in aging and the impairment of mitochondrial function is due to decreased rates of electron transfer by the selectively diminished activities of complexes I and IV. Inner membrane H(+) impermeability and F(1)-ATP synthase activity are only slightly affected by aging. Dysfunctional mitochondria in aged rodents are characterized, besides decreased electron transfer and O(2) uptake, by an increased content of oxidation products of phospholipids, proteins and DNA, a decreased membrane potential, and increased size and fragility. Free radical-mediated oxidations are determining factors of mitochondrial dysfunction and turnover, cell apoptosis, tissue function, and lifespan. Inner membrane enzyme activities, such as those of complexes I and IV and mitochondrial nitric oxide synthase, decrease upon aging and afford aging markers. The activities of these three enzymes in mice brain are linearly correlated with neurological performance, as determined by the tightrope and the T-maze tests. The same enzymatic activities correlated positively with mice survival and negatively with the mitochondrial content of lipid and protein oxidation products. Conditions that increase survival, as vitamin E dietary supplementation, caloric restriction, high spontaneous neurological activity, and moderate physical exercise, ameliorate mitochondrial dysfunction in aged brain and liver. The pleiotropic signaling of mitochondrial H(2)O(2) and nitric oxide diffusion to the cytosol seems modified in aged animals and to contribute to the decreased mitochondrial biogenesis in old animals.