Hormesis in aging

Peroxisome metabolism and cellular aging

The essential role of peroxisomes in fatty acid oxidation, anaplerotic metabolism, and hydrogen peroxide turnover is well established. Recent findings suggest that these and other related biochemical processes governed by the organelle may also play a critical role in regulating cellular aging. The goal of this review is to summarize and integrate into a model the evidence that peroxisome metabolism actually helps define the replicative and chronological age of a eukaryotic cell. In this model, peroxisomal reactive oxygen species (ROS) are seen as altering organelle biogenesis and function, and eliciting changes in the dynamic communication networks that exist between peroxisomes and other cellular compartments. At low levels, peroxisomal ROS activate an anti-aging program in the cell; at concentrations beyond a specific threshold, a pro-aging course is triggered.

A cold stress applied at various ages can increase resistance to heat and fungal infection in aged Drosophila melanogaster flies

A cold stress applied to young flies can have positive effects on longevity, behavioral aging, and resistance to heat and infection. However, the same mild stress, if applied at older ages, i.e. in frailer flies, could be a strong stress with negative effects. Cold stress was applied at various ages (weeks 1-2, 2-3, 3-4, and 4-5) and its effect on longevity and on resistance at 6 weeks of age to heat or fungal infection was observed. In males, the cold stress had positive effects on longevity and resistance to infection, except when applied at the oldest age. No positive effect on longevity or resistance to infection was detected in cold-stressed females, as already observed in previous experiments using a cold stress at young age only. By contrast, cold stress applied at various ages increased resistance to heat in both sexes. Therefore, a mild stress can have positive effects on longevity and resistance to strong stresses not only when used at a young age, but also at older ages.

Commentary on ‘Resveratrol commonly displays hormesis: Occurrence and biomedical significance’ by Calabrese et al

Resveratrol, a grape skin and red wine-derived polyphenolic phytoalexin, exhibits hormetic action delivering numerous health benefits at lower doses while being detrimental at higher doses. Epidemiologic and clinical trials need to be based on the clear understanding of hormetic health benefits of resveratrol

Xenohormesis: health benefits from an eon of plant stress response evolution

Xenohormesis is a biological principle that explains how environmentally stressed plants produce bioactive compounds that can confer stress resistance and survival benefits to animals that consume them. Animals can piggyback off products of plants' sophisticated stress response which has evolved as a result of their stationary lifestyle. Factors eliciting the plant stress response can judiciously be employed to maximize yield of health-promoting plant compounds. The xenohormetic plant compounds can, when ingested, improve longevity and fitness by activating the animal's cellular stress response and can be applied in drug discovery, drug production, and nutritional enhancement of diet.

Towards a unifying, systems biology understanding of large-scale cellular death and destruction caused by poorly liganded iron: Parkinson's, Huntington's, Alzheimer's, prions, bactericides, chemical toxicology and others as examples

Exposure to a variety of toxins and/or infectious agents leads to disease, degeneration and death, often characterised by circumstances in which cells or tissues do not merely die and cease to function but may be more or less entirely obliterated. It is then legitimate to ask the question as to whether, despite the many kinds of agent involved, there may be at least some unifying mechanisms of such cell death and destruction. I summarise the evidence that in a great many cases, one underlying mechanism, providing major stresses of this type, entails continuing and autocatalytic production (based on positive feedback mechanisms) of hydroxyl radicals via Fenton chemistry involving poorly liganded iron, leading to cell death via apoptosis (probably including via pathways induced by changes in the NF-κB system). While every pathway is in some sense connected to every other one, I highlight the literature evidence suggesting that the degenerative effects of many diseases and toxicological insults converge on iron dysregulation. This highlights specifically the role of iron metabolism, and the detailed speciation of iron, in chemical and other toxicology, and has significant implications for the use of iron chelating substances (probably in partnership with appropriate anti-oxidants) as nutritional or therapeutic agents in inhibiting both the progression of these mainly degenerative diseases and the sequelae of both chronic and acute toxin exposure. The complexity of biochemical networks, especially those involving autocatalytic behaviour and positive feedbacks, means that multiple interventions (e.g. of iron chelators plus antioxidants) are likely to prove most effective. A variety of systems biology approaches, that I summarise, can predict both the mechanisms involved in these cell death pathways and the optimal sites of action for nutritional or pharmacological interventions.

Testing the hormetic nature of homeopathic interventions through stress response pathways

The scientific foundations of hormesis are now well established and include various biochemical and molecular criteria for testing the hormetic nature of chemicals and other modulators. In order to claim homeopathy as being hormetic, it is essential that, in addition to the hormetic biphasic dose response, homeopathic remedies should fulfill one or more molecular criteria. Since stress response pathways, such as heat shock response, antioxidative response, autophagic response and unfolded protein response, are integral components of the physiological hormesis, it is important that homeopathic drugs be tested for these pathways if these are to be considered as hormetins and to cause hormesis.

Lifespan and oxidative stress show a non-linear response to atmospheric oxygen in Drosophila

Oxygen provides the substrate for most ATP production, but also serves as a source of reactive oxygen species (ROS), which can induce cumulative macromolecular oxidative damage and cause aging. Pure oxygen atmospheres (100 kPa) are known to strongly reduce invertebrate lifespan and induce aging-related physiological changes. However, the nature of the relationship between atmospheric oxygen, oxidative stress, and lifespan across a range of oxygen levels is poorly known. Developmental responses are likely to play a strong role, as prior research has shown strong effects of rearing oxygen level on growth, size and respiratory system morphology. In this study, we examined (1) the effect of oxygen on adult longevity and (2) the effect of the oxygen concentration experienced by larvae on adult lifespan by rearing Drosophila melanogaster in three oxygen atmospheres throughout larval development (10, 21 and 40 kPa), then measuring the lifespan of adults in five oxygen tensions (2, 10, 21, 40, 100 kPa). We also assessed the rate of protein carbonyl production for flies kept at 2, 10, 21, 40 and 100 kPa as adults (all larvae reared in normoxia). The rearing of juveniles in varying oxygen treatments affected lifespan in a complex manner, and the effect of different oxygen tensions on adult lifespan was non-linear, with reduced longevity and heightened oxidative stress at extreme high and low atmospheric oxygen levels. Moderate hypoxia (10 kPa) extended maximum, but not mean lifespan.

Ecological processes in a hormetic framework

There is increasing evidence that some non-essential substances or environmental stressors can have stimulatory or beneficial effects at low exposure levels while being toxic at higher levels, and that environmental 'priming' of certain physiological processes can result in their improved functioning in later life. These kinds of nonlinear dose-response relationships are referred to as hormetic responses and have been described across a wide range of organisms (from bacteria to vertebrates), in response to exposure to at least 1000 different chemical and environmental stressors. Although most work in this area has been in the fields of toxicology and human health, the concept of hormesis also has general applicability in ecology and evolutionary biology as it provides an important conceptual link between environmental conditions and organism function - both at the time of initial exposure to stressors and later in life. In this review, we discuss and clarify the different ways in which the term hormesis is used and provide a framework that we hope will be useful for ecologists interested in the fitness consequences of exposure to stressors. By using ecologically relevant examples from the existing literature, we show that hormesis is connected with both acclimation and phenotypic plasticity, and may play an important role in allowing animals to adjust to changing environments.

Resveratrol and cardiovascular health

Resveratrol (3,4',5-trihydroxystilbene) is a member of natural, plant-derived chemicals known as polyphenols and is attracting increased attention due to its diverse health benefits especially in case of cardiovascular disease, cancer, diabetes and neurological problems. Despite impressive gains in diagnosis and treatment, cardiovascular disease (CVD) remains a serious clinical problem and threat to public health. Resveratrol possesses potent antioxidant properties and has been shown to decrease low-density lipoprotein-cholesterol oxidation and platelet aggregation. This compound also possesses a range of additional cardioprotective and vasoprotective properties including antiatherosclerotic and vasorelaxation action. Resveratrol also has the capacity to interact with multiple molecular targets, which involve diverse intracellular pathways. Most well-known is the ability of resveratrol to activate sirtuins, a class of NAD(+)-dependent deacetylase that affect multiple transcription factors and other protein targets. Recently, resveratrol was found to induce autophagy and regenerate myocardial ischemic tissue treated with stem cells. Overall observation indicates that resveratrol has a high therapeutic potentials for the treatment of cardiovascular diseases.

Hormetic responses of thyroid hormone calorigenesis in the liver: Association with oxidative stress

Thyroid hormone (L-3,3',5-triiodothyronine, T(3)) exerts calorigenic effects by accelerating mitochondrial O(2) consumption through transcriptional activation of respiratory genes, with consequent increased reactive oxygen species (ROS) production. In the liver, ROS generation occurs at different sites of hepatocytes and in the respiratory burst of Kupffer cells, triggering the activation of the transcription factors nuclear factor-kappaB, signal transducer and activator of transcription 3, and activating protein 1. Under these conditions, the redox upregulation of Kupffer cell-dependent expression of cytokines [tumor necrosis factor-alpha, interleukin (IL)-1, and IL-6] is achieved, which upon interaction with specific receptors in hepatocytes trigger the expression of antioxidant enzymes (manganese superoxide dismutase, inducible nitric oxide synthase), antiapoptotic proteins (Bcl-2), and acute-phase proteins (haptoglobin, beta-fibrinogen). These responses and the promotion of hepatocyte and Kupffer cell proliferation observed represent hormetic effects re-establishing redox homeostasis, promoting cell survival, and protecting the liver against ischemia-reperfusion (IR) injury. It is proposed that hormesis underlying T(3) action may constitute a novel preconditioning strategy for IR injury during liver surgery in man or in liver transplantation using reduced-size grafts from living donors, considering that (i) with the exception of the controversial ischemic preconditioning, all other studied strategies have failed to reach the clinical setting and (ii) T(3) is a well-tolerated therapeutic agent that either lacks major adverse effects or has minimal and controlled side effects.

Anti-inflammatory heat shock protein 70 genes are positively associated with human survival

A positive relationship between stress tolerance and longevity has been observed in several model systems. That the same correlation is applicable in humans and that it may be open to experimental manipulation for extending human lifespan requires studies on association of stress genes with longevity. The involvement of heat shock protein 70 (Hsp70) in cellular maintenance and repair mechanisms, including its role as an anti-inflammatory protein, makes it a suitable candidate for studying such associations. We have studied the association of three single nucleotide polymorphisms, HSPA1A (-110A>C), HSPA1B (1267A>G), and HSPA1L (2437T>C), present in the three HSP70 genes, with human survival, in a cohort of individuals born in the year 1905. This population cohort is a part of the longitudinal study of Danish nonagenarians. Since DNA samples were already collected in 1998, this gave us the opportunity to perform survival analysis on these subjects. Haplotype relative risk, and genotype relative risk were calculated to measure the effects of haplotypes and genotypes on human survival in a sex-specific manner. A significant association of HSPA1A-AA (RR=3.864; p=0.016) and HSPA1B-AA (RR=2.764; p=0.039) genotypes with poor survival was observed in female subjects. Also the female carriers of haplotype G-C-T had longer survival than the non-carriers (HRR=0.550; p=0.015). On an average, female carriers of the G-C-T haplotype live about one year longer than non-carriers. This result corroborates our previous observations from heat shock response (HSR) study where we had shown that after heat stimulation, mononuclear cells from the carriers of genotype HSPA1L-TT had better HSR than cells with the HSPA1L-CC genotype.

Maternal protein restriction affects gene expression profiles in the kidney at weaning with implications for the regulation of renal function and lifespan

Nutritionally induced alterations in early growth can influence health and disease in later adult life. We have demonstrated previously that low birthweight resulting from maternal protein restriction during pregnancy followed by accelerated growth in rodents was associated with shortened lifespan, whereas protein restriction and slow growth during lactation increased lifespan. Thus early life events can also have a long lasting impact on longevity. In the present study, we show that long-lived PLP (postnatal low protein) mice were protected from developing albuminuria, whereas short-lived recuperated mice demonstrated an age-dependent increase in albuminuria in old age. Microarray analysis of kidneys from 21-day-old mice revealed that gene expression profiles were differentially affected depending on whether protein restriction was imposed during pregnancy or lactation. The differentially expressed genes were involved in diverse biological functions such as cytoprotective functions, vitamin D synthesis, protein homoeostasis, regulation of antioxidant enzymes and cellular senescence. Significantly, up-regulation of Hmox1 (haem oxygenase 1) in kidneys from PLP mice suggests that tissues of long-lived mice are equipped with a better cytoprotective function. In contrast, up-regulation of Nuak2 (NUAK family, SNF1-like kinase 2) and down-regulation of Lonp2 (Lon peptidase 2), Foxo3a (forkhead box O3a), Sod1 (copper/zinc superoxide dismutase) and Sesn1 (sestrin 1) in the kidneys of recuperated offspring suggest that protein homoeostasis and resistance to oxidative stress are compromised, leading to accelerated cellular senescence in these shorter-lived mice.

Genetics vs. entropy: longevity factors suppress the NF-kappaB-driven entropic aging process

Molecular studies in model organisms have identified potent longevity genes which can delay the aging process and extend the lifespan. Longevity factors promote stress resistance and cellular survival. It seems that the aging process itself is not genetically programmed but a random process involving the loss of molecular fidelity and subsequent accumulation of waste products. This age-related increase in cellular entropy is compatible with the disposable soma theory of aging. A large array of host defence systems has been linked to the NF-kappaB system which is an ancient signaling pathway specialized to host defence, e.g. functioning in immune system. Emerging evidence demonstrates that the NF-kappaB system is activated during aging. Oxidative stress and DNA damage increase with aging and elicit a sustained activation of the NF-kappaB system which has negative consequences, e.g. chronic inflammatory response, increase in apoptotic resistance, decline in autophagic cleansing, and tissue atrophy, i.e. processes that enhance the aging process. We will discuss the role of NF-kappaB system in the pro-aging signaling and will emphasize that several longevity factors seem to be inhibitors of NF-kappaB signaling and in that way they can suppress the NF-kappaB-driven entropic host defence catastrophe.

ER stress and hormetic regulation of the aging process

An ability to mount a stress resistance under pressure is a major host defence mechanism and has been a fundamental force during evolution. However, the adaptation capacity clearly declines during aging and this loss of stress resistance accelerates the aging process exposing the organism to degenerative diseases. The effect of stress on organisms seems to be a dose-dependent response, i.e. mild stress induces a stress tolerance and extends the lifespan whereas excessive stress accentuates the aging process. This paradox is known as hormesis in aging research. It is essential to distinguish the intensity of cellular stress and thus mount an appropriate host defence. The endoplasmic reticulum (ER) contains three branches of stress transducers, i.e. IRE1, PERK, and ATF6 pathways, all of which recognize stress-related disturbances in the function of ER. These transducers trigger a complex signaling network which activates an unfolded protein response (UPR). Interestingly, ER stress transducers can distinguish the intensity of ER stress and induce a dose-dependent UPR, either adaptive response to stress or apoptotic cell death. The efficiency of the stress recognition system and UPR signaling declines during aging. We will discuss the role of ER stress in hormetic regulation of aging process and longevity.

Targeting the age-related occurrence, removal, and accumulation of molecular damage by hormesis

Strategies for testing and developing effective means of intervention, prevention, and modulation of aging incorporate means to minimize the occurrence and accumulation of molecular damage, to reduce molecular heterogeneity, and to evaluate the relevance of the type and extent of damage with respect to its role in aging and age-related diseases. One such approach is that of mild stress-induced hormesis, which stimulates maintenance and repair systems and strengthens the homeodynamic space of cells and organisms. Hormesis through mild heat shock, natural and synthetic hormetins, and other stressors brings about several antiaging effects in human fibroblasts, keratinocytes, and telomerase-immortalized bone marrow stem cells. Depending on the cell type, these antiaging hormetic effects include extension of replicative life span, enhanced proteasomal activities, increased chaperone levels, and improved wound healing, angiogenesis, and differentiation. The main molecular pathways for achieving such hormetic effects are through targeting the processes for the repair and removal of molecular damage, which can slow aging.

Longevity mutants do not establish any "new science" of ageing

The biological reasons for ageing are now well known, so it is no longer an unsolved problem in biology. Furthermore, there is only one science of ageing, which is continually advancing. The significance and importance of the mutations that lengthen the lifespan of invertebrates can be assessed only in relationship to previous well-established studies of ageing. The mutant strains of model organisms that increase longevity have altered nutrient signalling pathways similar to the effects of dietary restriction, and so it is likely that there is a shift in the trade-off between reproduction and maintenance of the soma. To believe that the isolation and characterisation of a few invertebrate mutations (as well as those in yeast) will "galvanise" the field and provide new insights into human ageing is an extreme point of view which does not recognize the huge progress in ageing research that has been made in the last 50 years or so.

Inflammation, genetic background and longevity

Ageing is an inexorable intrinsic process that affects all cells, tissues, organs and individuals. Due to a diminished homeostasis and increased organism frailty, ageing causes a reduction of the response to environmental stimuli and, in general, is associated to an increased predisposition to illness and death. Actually, it is characterized by a state of reduced ability to maintain health and general homeodynamics of the organism. A large part of the ageing phenotype is explained by an imbalance between inflammatory and anti-inflammatory networks, which results in the low grade chronic pro-inflammatory status of ageing, "inflamm-ageing". It is strictly linked to immunosenescence, and on the whole they are the major contributory factors to the increased frequency of morbidity and mortality among elderly. Inflamm-ageing is compatible with longevity; even if centenarians have an increased level of inflammatory mediators in comparison to old subjects and they are very frail, they also have high level of anti-inflammatory cytokines together with protective genotypes. Actually, data on case control studies performed in Italian centenarians suggest that a pro-inflammatory genotype is unfavourable to reach extreme longevity in good health and likely favours the onset of age-related diseases such as cardiovascular diseases and Alzheimer's disease, the leading causes of mortality and disability in the elderly. However, many associations between gene variants and longevity have been found only in Italian population. This should not be unexpected, since ageing and longevity are complex traits resulting not only and not exclusively from genetics, but rather from the interactions between genetics, environment and chance.

Effect of osteoporosis treatment on mortality: a meta-analysis

CONTEXT

Fragility fractures cause significant morbidity and mortality. Effective osteoporosis treatment can reduce fracture incidence, but it is not known whether it reduces mortality.

OBJECTIVE

The aim of the study was to determine whether effective osteoporosis treatment reduces mortality.

DATA SOURCES

We searched Medline and the Cochrane Central Register of Trials prior to September 2008, as well as 2000-2008 American Society for Bone and Mineral Research conference abstracts.

STUDY SELECTION

Eligible studies were randomized placebo-controlled trials of approved doses of medications with proven efficacy in preventing both vertebral and nonvertebral fractures, in which the study duration was longer than 12 months and there were more than 10 deaths. Trials of estrogen and selective estrogen receptor modulators were specifically excluded.

DATA EXTRACTION

Data were extracted from the text of the retrieved articles, published meta-analyses, or the Food and Drug Administration web site.

DATA SYNTHESIS

Eight eligible studies of four agents (risedronate, strontium ranelate, zoledronic acid, and denosumab) were included in the primary analysis. During two alendronate studies, the treatment dose changed, and those studies were only included in secondary analyses. In the primary analysis, treatment was associated with an 11% reduction in mortality (relative risk, 0.89; 95% confidence interval, 0.80-0.99; P = 0.036). In the secondary analysis, the results were similar (relative risk, 0.90; 95% confidence interval, 0.81-1.0; P = 0.044). Mortality reduction was not related to age or incidence of hip or nonvertebral fracture, but was greatest in trials conducted in populations with higher mortality rates.

CONCLUSIONS

Treatments for osteoporosis with established vertebral and nonvertebral fracture efficacy reduce mortality in older, frailer individuals with osteoporosis who are at high risk of fracture.

Cellular stress and protein misfolding during aging

Cells are under constant onslaught from several intrinsic and extrinsic stressors, which lead to the occurrence and accumulation of molecular damage, functional impairment, aging, and eventual death. Protein misfolding is both a cause and a consequence of increased cellular stress. An age-related failure of the complex systems for handling protein misfolding results in the accumulation of misfolded and aggregated proteins, and consequent conformational diseases. However, some misfolded proteins have been found to be both toxic and, in some cases, protective, highlighting the various complex, dynamic, and interdependent mechanisms at play. Molecular mechanisms are being elucidated for the occurrence of protein misfolding and for its prevention by chaperones and various pathways of degradation. Insights from the knowledge about proteodynamics are likely to impact future interventional strategies to counter stress and to promote healthy aging by preventing and/or treatment of protein conformational diseases.

When a theory of aging ages badly

According to the widely acknowledged mitochondrial free radical theory of aging (MFRTA), the macromolecular damage that results from the production of toxic reactive oxygen species (ROS) during cellular respiration is the cause of aging. However, although it is clear that oxidative damage increases during aging, the fundamental question regarding whether mitochondrial oxidative stress is in any way causal to the aging process remains unresolved. An increasing number of studies on long-lived vertebrate species, mutants and transgenic animals have seriously challenged the pervasive MFRTA. Here, we describe some of these new results, including those pertaining to the phenotype of the long-lived Mclk1(-/-) mice, which appear irreconcilable with the MFRTA. Thus, we believe that it is reasonable to now consider the MFRTA as refuted and that it is time to use the insight gained by many years of testing this theory to develop new views as to the physiological causes of aging.

Effect of caloric restriction on base-excision repair (BER) in the aging rat brain

Apyrimidinic/apurinic endonuclease (APE) is a key protein involved in the base-excision DNA repair (BER) pathway of oxidative DNA lesions. Using a novel oligonucleotide substrate, we demonstrate that APE activity in the frontal/parietal cortex (F/PCTX), cerebellum, brainstem, midbrain and hypothalamus declined with age in rats on an ad libitum (AL) diet. In contrast, APE activity for these brain regions was approximately 1.5-3 times higher in young, caloric restricted (CR) rats. Despite continuous CR treatment in all animals since six weeks of age, APE activity in the CR group started to decline by middle-age and continued into old age. However, CR maintained APE activity at a level that was significantly higher than that in AL rats across age and in the brain regions examined. Because Western analysis of APE, DNA polymerase beta and DNA ligase III levels in the F/PCTX of both CR and AL rats remained unchanged with age, this suggests that the increased APE activity in CR rats is the result of differential post-translational modification of APE.

Hormesis can and does work in humans

If we accept the validity of the general concept of physiological hormesis as being the phenomenon of achieving health beneficial effects by exposure to mild stress, then hormesis is being applied already and successfully to humans. The evidence for this is the well-demonstrated health benefits of regular and moderate exercise. Mild stress-induced activation of one or more intracellular pathways of stress response are central to this. Experimental studies performed on human cells in culture exposed to mild heat shock and other stresses provide biochemical and molecular evidence in support of the application of hormesis to human systems. Although several issues remain to be resolved by more research with respect to the extent and duration of hormetic exposure, making use of the cellular stress response pathways can facilitate discovering novel hormetins for human applications.

Heat shock-induced three-dimensional-like proliferation of normal human fibroblasts mediated by pressed silk

The aim of this study was to determine the optimal heat treatment conditions for enhancement of pressed silk-mediated 3D-like proliferation of normal human dermal fibroblasts, as well as to determine the responses to heat shock of cells and intracellular signaling pathways. The beginning of 3D-like pattern formation of cells was observed in the second week after the start of the experiment. The mean rates of beginning of 3D-like pattern formation by cells heat-treated at 40 ºC and 43 ºC for 10 min were significantly higher (3.2- and 8.6-fold, respectively) than that of untreated cells. We found that apoptosis had occurred in 7.5% and 50.0% of the cells at one week after heat treatment for 10 min at 43 ºC and 45 ºC, respectively. Western blot analysis demonstrated that phosphorylation of p38 MAPK and that of Hsp27 were markedly increased by heat treatment at 43 ºC for 10 min. The results of an experiment using a p38 MAPK inhibitor and Hsp27 inhibitor suggest that activation of p38 MAPK by heat shock is associated with 3D-like cell proliferation and that Hsp27 contributes to the inhibition of apoptosis. The results of this study should be useful for further studies aimed at elucidation of the physiologic mechanisms underlying thermotherapy.

Modulation of oxidative phosphorylation machinery signifies a prime mode of anti-ageing mechanism of calorie restriction in male rat liver mitochondria

Mitochondria being the major source and target of reactive oxygen species (ROS) play a crucial role during ageing. We analyzed ageing and calorie restriction (CR)-induced changes in abundance of rat liver mitochondrial proteins to understand key aspects behind the age-retarding mechanism of CR. The combination of blue-native (BN) gel system with fluorescence Difference Gel Electrophoresis (DIGE) facilitated an efficient analysis of soluble and membrane proteins, existing as monomers or multi-protein assemblies. Changes in abundance of specific key subunits of respiratory chain complexes I, IV and V, critical for activity and/or assembly of the complexes were identified. CR lowered complex I assembly and complex IV activity, which is discussed as a molecular mechanism to minimize ROS production at mitochondria. Notably, the antioxidant system was found to be least affected. The GSH:GSSG couple could be depicted as a rapid mean to handle the fluctuations in ROS levels led by reversible metabolic shifts. We evaluated the relative significance of ROS generation against quenching. We also observed parallel and unidirectional changes as effect of ageing and CR, in subunits of ATP synthase, cytochrome P450 and glutathione S-transferase. This is the first report on such 'putatively hormetic' ageing-analogous effects of CR, besides the age-retarding ones.

Increased oxidative stress in barn swallows from the Chernobyl region

The Chernobyl nuclear accident produced the largest unintended release of radionuclides in history, with dramatic consequences for humans and other organisms. Exposure to ionizing radiation is known to reduce circulating and stored levels of specific antioxidants in birds and humans, thus potentially increasing oxidative stress. However, overall effects of radioactive exposure on oxidative status have never been investigated in any free ranging vertebrate. We measured plasma antioxidant capacity and concentration of reactive oxygen metabolites in adult barn swallows (Hirundo rustica) from colonies with variable background radiation levels in the Chernobyl region in Ukraine and Belarus. We predicted that antioxidants would decrease while reactive oxygen metabolites would increase with exposure to increasing levels of radiation at the breeding sites. Consistent with this expectation, radiation level positively predicted plasma concentration of reactive oxygen metabolites, whereas no significant covariation was found with non-enzymatic plasma antioxidant capacity. An index of oxidative stress was also larger in barn swallows exposed to high contamination levels. Thus, radioactive contamination appeared to be responsible for the increased generation of reactive oxygen metabolites and the imbalance between reactive oxygen metabolites and non-enzymatic plasma antioxidant capacity.

Hormesis as a pro-healthy aging intervention in human beings?

Hormesis is a phenomenon in which adaptive responses to low doses of otherwise harmful factors (also called mild stressors) make cells and organisms more robust. Aging is a complex and poorly understood process. This review explores the positive effects of hormesis on aging in animal models and human cell cultures, and discusses whether it might apply to humans. As an example, repeated mild heat stress confers anti-aging benefits to normal human cells in culture. Calorie restriction and xenohormetic compounds such as resveratrol, in large part via activation of sirtuins, decrease risk of common age-related conditions, such as cancer, cardiovascular disease, type 2 diabetes, and neurological diseases, so lengthening lifespan. Mild stressors and xenohormetic dietary components have diverse molecular targets and affect many pathways. Despite experimental advances in aging research, findings in humans are still quite limited. Moderate-intensity exercise, weight management and healthy diet ameliorate diseases of aging to increase lifespan and this could involve hormesis.

Hormesis is applicable as a pro-healthy aging intervention in mammals and human beings

The aging of the population brings new health challenges, and in particular, the need to implement suitable pro-healthy aging interventions. This paper discusses the potential of mild stressors inducing hormesis as a lifespan and healthspan extension strategy and how it can be applied to the human. There is some evidence that the anti-aging benefits of lifestyle factors, such as diet, exercise or engaging in activities may be achieved via hormetic regulation. This supports the validity of the concept in human. There are, however, gaps in knowledge and ethical barriers that need to be addressed to establish the suitability of the approach to the clinical context or the general geriatric population. In particular, we need to find out which stressors are safe for use as anti-aging interventions, when they have to be applied to achieve maximal benefits, how their therapeutic potential is altered by changes in the stress system induced by age and pathological conditions, and the extent to which the occurrence of adverse versus positive effects depends on interacting genetic and experiential factors.

Mice deficient in both Mn superoxide dismutase and glutathione peroxidase-1 have increased oxidative damage and a greater incidence of pathology but no reduction in longevity

To test the impact of increased mitochondrial oxidative stress as a mechanism underlying aging and age-related pathologies, we generated mice with a combined deficiency in two mitochondrial-localized antioxidant enzymes, Mn superoxide dismutase (MnSOD) and glutathione peroxidase-1 (Gpx-1). We compared life span, pathology, and oxidative damage in Gpx1(-/-), Sod2(+/-)Gpx1(+/-), Sod2(+/-)Gpx1(-/-), and wild-type control mice. Oxidative damage was elevated in Sod2(+/-)Gpx1(-/-) mice, as shown by increased DNA oxidation in liver and skeletal muscle and increased protein oxidation in brain. Surprisingly, Sod2(+/-)Gpx1(-/-) mice showed no reduction in life span, despite increased levels of oxidative damage. Consistent with the important role for oxidative stress in tumorigenesis during aging, the incidence of neoplasms was significantly increased in the older Sod2(+/-)Gpx1(-/-) mice (28-30 months). Thus, these data do not support a significant role for increased oxidative stress as a result of compromised mitochondrial antioxidant defenses in modulating life span in mice and do not support the oxidative stress theory of aging.

Hormesis: a conversation with a critic

OBJECTIVE

In this commentary I respond to points raised in the commentary by Mushak [Ad hoc and fast forward: the science and control of hormesis growth and development. Environ Health Perspect 117:1333-1338 (2009)], which principally concerns studies by me and my colleagues concerning the frequency of hormesis in toxicology.

DISCUSSION

In this commentary I demonstrate that Mushak's analysis contains critical statistical errors and misunderstandings of statistical concepts that invalidate its conclusions concerning the frequency of hormesis in the toxicologic literature.

CONCLUSIONS

In his commentary Mushak offers no significant new conceptual insights, and his key technical criticisms of hormesis frequency findings are unfounded.

Multiple mild heat-shocks decrease the Gompertz component of mortality in Caenorhabditis elegans

Exposure to mild heat-stress (heat-shock) can significantly increase the life expectancy of the nematode Caenorhabditis elegans. A single heat-shock early in life extends longevity by 20% or more and affects life-long mortality by decreasing initial mortality only; the rate of increase in subsequent mortality (Gompertz component) is unchanged. Repeated mild heat-shocks throughout life have a larger effect on life span than does a single heat-shock early in life. Here, we ask how multiple heat-shocks affect the mortality trajectory in nematodes and find increases of life expectancy of close to 50% and of maximum longevity as well. We examined mortality using large numbers of animals and found that multiple heat-shocks not only decrease initial mortality, but also slow the Gompertz rate of increase in mortality. Thus, multiple heat-shocks have anti-aging hormetic effects and represent an effective approach for modulating aging.

Reduced expression of alpha-1,2-mannosidase I extends lifespan in Drosophila melanogaster and Caenorhabditis elegans

Exposure to sub-lethal levels of stress, or hormesis, was a means to induce longevity. By screening for mutations that enhance resistance to multiple stresses, we identified multiple alleles of alpha-1,2-mannosidase I (mas1) which, in addition to promoting stress resistance, also extended longevity. Longevity enhancement is also observed when mas1 expression is reduced via RNA interference in both Drosophila melanogaster and Caenorhabditis elegans. The screen also identified Edem1 (Edm1), a gene downstream of mas1, as a modulator of lifespan. As double mutants for both mas1 and Edm1 showed no additional longevity enhancement, it appeared that both mutations function within a common pathway to extend lifespan. Molecular analysis of these mutants revealed that the expression of BiP, a putative biomarker of dietary restriction (DR), is down-regulated in response to reductions in mas1 expression. These findings suggested that mutations in mas1 may extend longevity by modulating DR.

Late-onset dietary restriction compensates for age-related increase in oxidative stress and alterations of HSP 70 and synapsin 1 protein levels in male Wistar rats

Numerous reports implicate increased oxidative stress in the functional and structural changes occurring in the brain and other organs as a part of the normal aging process. Dietary restriction (DR) has long been shown to be life-prolonging intervention in several species. This study was aimed to assess the potential efficacy of late-onset short term DR when initiated in 21 months old male wistar rats for 3 months on the antioxidant defense system and lipid peroxidation, cellular stress response protein HSP 70 and synaptic marker protein synapsin 1 in discrete brain regions such as cortex, hypothalamus, and hippocampus as well as liver, kidney and heart from 24 month old rats. Age-associated decline in activities of superoxide dismutase, catalase, glutathione peroxidase, glutathione, and elevated levels of lipid peroxidation was observed in brain and peripheral organ as well as increased expression of HSP 70 and reduction in synapsin 1 was observed in brain studied. Late-onset short term DR was effective in partially restoring the antioxidant status and in decreasing lipid peroxidation level as well as enhancing the expression of HSP 70 and synapsin 1 in aged rats. Late onset short term DR also prevented age-related neurodegeneration as revealed by Fluoro-Jade B staining in hippocampus and cortex regions of rat brain. Thus our current results suggest that DR initiated even in old age has the potential to improve age related decline in body functions.

NF-kappaB signaling in the aging process

INTRODUCTION

The aging process represents a progressive decline in cellular and organism function. Explaining the aging process has given rise to a cornucopia for different theories in which the basic difference has been the question whether aging is genetically regulated or an entropic degeneration process.

DISCUSSION

Different screening techniques have revealed that mammalian aging is associated with the activation of NF-kappaB transcription factor system. The NF-kappaB system is an ancient host defense system concerned with immune responses and different external and internal dangers, such as oxidative and genotoxic stress. NF-kappaB signaling is not only the master regulator of inflammatory responses but can also regulate several homeostatic responses such as apoptosis, autophagy, and tissue atrophy. We will describe how chronic activation of NF-kappaB signaling has the capacity to induce the senescent phenotype associated with aging. Interestingly, several longevity genes such as SIRT1, SIRT6, and FoxOs can clearly suppress NF-kappaB signaling and in this way delay the aging process and extend lifespan.

CONCLUSION

It seems that the aging process is an entropic degeneration process driven by NF-kappaB signaling. This process can be regulated by a variety of longevity genes along with a plethora of other factors such as genetic polymorphism, immune and dietary aspects, and environmental insults.

A perspective on the scientific, philosophical, and policy dimensions of hormesis

The hormesis concept has broad implications for biology and the biomedical sciences. This perspective on hormesis concentrates on toxicology and toxicological risk assessment and secondarily explores observations from other fields. It considers the varied manifestations of hormesis in the context of a broad family of biological stress responses. Evidence for hormesis is reviewed, and the hormesis model is contrasted with more widely accepted dose-response models in toxicology: a linear nonthreshold (LNT) model for mutagenesis and carcinogenesis, and a threshold model for most other toxicologic effects. Scientific, philosophical, and political objections to the hormesis concept are explored, and complications in the hormesis concept are analyzed. The review concludes with a perspective on the current state of hormesis and challenges that the hormesis model poses for risk assessment.

Progress & prospects: gene therapy in aging

Studies performed on various experimental model systems indicate that genetic interventions can increase longevity, even if in a highly protected laboratory condition. Generally, such interventions required partial or complete switching off of the gene and inhibiting the activity of its gene products, which normally have other well-defined roles in metabolic processes. Overexpression of some genes, such as stress response and antioxidant genes, in some model systems also extends their longevity. Such genetic interventions may not be easily applicable to humans without knowing their effects on human growth, development, maturation, reproduction and other characteristics. Studies on the association of single nucleotide polymorphisms and multiple polymorphisms (haplotype) in genes with human longevity have identified several genes whose frequencies increase or decrease with age. Whether genetic redesigning can be achieved in the wake of numerous and complex epigenetic factors that effectively determine the life course and the life span of an individual still appears to be a 'mission impossible'.

Oxidative stress as a mediator of life history trade-offs: mechanisms, measurements and interpretation

The concept of trade-offs is central to our understanding of life-history evolution. The underlying mechanisms, however, have been little studied. Oxidative stress results from a mismatch between the production of damaging reactive oxygen species (ROS) and the organism's capacity to mitigate their damaging effects. Managing oxidative stress is likely to be a major determinant of life histories, as virtually all activities generate ROS. There is a recent burgeoning of interest in how oxidative stress is related to different components of animal performance. The emphasis to date has been on immediate or short-term effects, but there is an increasing realization that oxidative stress will influence life histories over longer time scales. The concept of oxidative stress is currently used somewhat loosely by many ecologists, and the erroneous assumption often made that dietary antioxidants are necessarily the major line of defence against ROS-induced damage. We summarize current knowledge on how oxidative stress occurs and the different methods for measuring it, and highlight where ecologists can be too simplistic in their approach. We critically review the potential role of oxidative stress in mediating life-history trade-offs, and present a framework for formulating appropriate hypotheses and guiding experimental design. We indicate throughout potentially fruitful areas for further research.

Heat stress and hormetin-induced hormesis in human cells: effects on aging, wound healing, angiogenesis, and differentiation

Accumulation of molecular damage and increased molecular heterogeneity are hallmarks of cellular aging. Mild stress-induced hormesis can be an effective way for reducing the accumulation of molecular damage, and thus slowing down aging from within. We have shown that repeated mild heat stress (RMHS) has anti-aging effects on growth and various other cellular and biochemical characteristics of normal human skin fibroblasts and keratinocytes undergoing aging in vitro. RMHS given to human cells increased the basal levels of various chaperones, reduced the accumulation of damaged proteins, stimulated proteasomal activities, increased the cellular resistance to other stresses, enhanced the levels of various antioxidant enzymes, enhanced the activity and amounts of sodium-potassium pump, and increased the phosphorylation-mediated activities of various stress kinases. We have now observed novel hormetic effects of mild heat stress on improving the wound healing capacity of skin fibroblasts and on enhancing the angiogenic ability of endothelial cells. We have also tested potential hormetins, such as curcumin and rosmarinic acid in bringing about their beneficial effects in human cells by inducing stress response pathways involving heat shock proteins and hemeoxygenase HO-1. These data further support the view that mild stress-induced hormesis can be applied for the modulation, intervention and prevention of aging and age-related impairments.

Plant adaptogens increase lifespan and stress resistance in C. elegans

Extracts of plant adaptogens such as Eleutherococcus senticosus (or Acanthopanax senticosus) and Rhodiola rosea can increase stress resistance in several model systems. We now show that both extracts also increase the mean lifespan of the nematode C. elegans in a dose-dependent way. In at least four independent experiments, 250 microg/ml Eleutherococcus (SHE-3) and 10-25 microg/ml Rhodiola (SHR-5) significantly increased life span between 10 and 20% (P < 0.001), increased the maximum lifespan with 2-3 days and postponed the moment when the first individuals in a population die, suggesting a modulation of the ageing process. With higher concentrations, less effect was observed, whereas at the highest concentrations tested (2500 microg/ml Eleutherococcus and 250 microg/ml Rhodiola) a lifespan shortening effect was observed of 15-25% (P < 0.001). Both adaptogen extracts were also able to increase stress resistance in C. elegans: against a relatively short heat shock (35 degrees C during 3 h) as well as chronic heat treatment at 26 degrees C. An increase against chronic oxidative stress conditions was observed in mev-1 mutants, and during exposure of the wild type nematode to paraquat (10 mM) or UV stress, be it less efficiently. Concerning the mode of action: both adaptogens induce translocation of the DAF-16 transcription factor from the cytoplasm into the nucleus, suggesting a reprogramming of transcriptional activities favoring the synthesis of proteins involved in stress resistance (such as the chaperone HSP-16) and longevity. Based on these observations, it is suggested that adaptogens are experienced as mild stressors at the lifespan-enhancing concentrations and thereby induce increased stress resistance and a longer lifespan.

Reductive stress on life span extension in C. elegans

Recently, Schulz and colleagues have contributed to the ongoing controversy on the unproven role of oxidative stress in the aging process in their well-performed study 'Glucose restriction extends Caenorhabditis elegans life span by inducing mitochondrial respiration and increasing oxidative stress' (Cell Metab 2007, 6: 280–293). Here, we suggest an alternative hypothesis that reductive stress can prevent calorie-restriction induced life span extension. We draw attention to this condition as an explanation for some contradictory observations including the deleterious effects from antioxidants.

Valproic acid extends Caenorhabditis elegans lifespan

Aging is an important biological phenomenon and a major contributor to human disease and disability, but no drugs have been demonstrated to delay human aging. Caenorhabditis elegans is a valuable model for studies of animal aging, and the analysis of drugs that extend the lifespan of this animal can elucidate mechanisms of aging and might lead to treatments for age-related disease. By testing drugs that are Food and Drug Administration approved for human use, we discovered that the mood stabilizer and anticonvulsant valproic acid (VA) extended C. elegans lifespan. VA also delayed age-related declines of body movement, indicating that VA delays aging. Valproic acid is a small carboxylic acid that is the most frequently prescribed anticonvulsant drug in humans. A structure-activity analysis demonstrated that the related compound valpromide also extends lifespan. Valproic acid treatment may modulate the insulin/IGF-1 growth factor signaling pathway, because VA promoted dauer larvae formation and DAF-16 nuclear localization. To investigate the mechanism of action of VA in delaying aging, we analyzed the effects of combining VA with other compounds that extend the lifespan of C. elegans. Combined treatment of animals with VA and the heterocyclic anticonvulsant trimethadione caused a lifespan extension that was significantly greater than treatment with either of these drugs alone. These data suggest that the mechanism of action of VA is distinct from that of trimethadione, and demonstrate that lifespan-extending drugs can be combined to produce additive effects.

Increased molecular damage and heterogeneity as the basis of aging

Aging at the molecular level is characterized by the progressive accumulation of molecular damage. The sources of damage act randomly through environmental and metabolically generated free radicals, through spontaneous errors in biochemical reactions, and through nutritional components. However, damage to a macromolecule may depend on its structure, localization and interactions with other macromolecules. Damage to the maintenance and repair pathways comprising homeodynamic machinery leads to age-related failure of homeodynamics, increased molecular heterogeneity, altered cellular functioning, reduced stress tolerance, diseases and ultimate death. Novel approaches for testing and developing effective means of intervention, prevention and modulation of aging involve means to minimize the occurrence and accumulation of molecular damage. Mild stress-induced hormesis by physical, biological and nutritional methods, including hormetins, represents a promising strategy for achieving healthy aging and for preventing age-related diseases.