Keynote: mechanisms of senescence--complificationists versus simplificationists

Vegetables and Their Bioactive Compounds as Anti-Aging Drugs

Aging is a continuous process over time that is mainly related to natural alterations in mechanical–biological processes. This phenomenon is due to several factors, including the time and energy of biological processes. Aging can be attributed to biological factors such as oxidative stress, cell longevity, and stem cell senescence. Currently, aging is associated with several diseases, such as neurodegenerative diseases, cancer, and other diseases related to oxidative stress. In addition, certain natural molecules, including those derived from vegetables, have shown the ability to delay the aging process. Their effects are linked to different mechanisms of action, such as tissue regeneration and the activation of longevity and anti-senescence genes. The present work discusses the impact of vegetables, and bioactive compounds isolated from vegetables, against the physiological and pathological aging process and accompanying human diseases.

Sensory perception and aging in model systems: from the outside in

Sensory systems provide organisms from bacteria to humans with the ability to interact with the world. Numerous senses have evolved that allow animals to detect and decode cues from sources in both their external and internal environments. Recent advances in understanding the central mechanisms by which the brains of simple organisms evaluate different cues and initiate behavioral decisions, coupled with observations that sensory manipulations are capable of altering organismal lifespan, have opened the door for powerful new research into aging. Although direct links between sensory perception and aging have been established only recently, here we discuss these initial discoveries and evaluate the potential for different forms of sensory processing to modulate lifespan across taxa. Harnessing the neurobiology of simple model systems to study the biological impact of sensory experiences will yield insights into the broad influence of sensory perception in mammals and may help uncover new mechanisms of healthy aging.

The new biology of ageing

Human life expectancy in developed countries has increased steadily for over 150 years, through improvements in public health and lifestyle. More people are hence living long enough to suffer age-related loss of function and disease, and there is a need to improve the health of older people. Ageing is a complex process of damage accumulation, and has been viewed as experimentally and medically intractable. This view has been reinforced by the realization that ageing is a disadvantageous trait that evolves as a side effect of mutation accumulation or a benefit to the young, because of the decline in the force of natural selection at later ages. However, important recent discoveries are that mutations in single genes can extend lifespan of laboratory model organisms and that the mechanisms involved are conserved across large evolutionary distances, including to mammals. These mutations keep the animals functional and pathology-free to later ages, and they can protect against specific ageing-related diseases, including neurodegenerative disease and cancer. Preliminary indications suggest that these new findings from the laboratory may well also apply to humans. Translating these discoveries into medical treatments poses new challenges, including changing clinical thinking towards broad-spectrum, preventative medicine and finding novel routes to drug development.

Chemical Complexity and the Genetics of Aging

We examine how aging is impacted by various chemical challenges that organisms face and by the molecular mechanisms that have evolved to regulate lifespan in response to them. For example, environmental information, which is detected and processed through sensory systems, can modulate lifespan by providing information about the presence and quality of food as well as presence and density of conspecifics and predators. In addition, the diverse forms of molecular damage that result from constant exposure to damaging chemicals that are generated from the environment and from metabolism pose an informatic and energetic challenge for detoxification systems, which are important in ensuring longevity. Finally, systems of innate immunity are vital for recognizing and combating pathogens but are also seen as of increasing importance in causing the aging process. Integrating ideas of molecular mechanism with context derived from evolutionary considerations will lead to exciting new insights into the evolution of aging.

Decrease in the lgl tumor suppressor dose in Drosophila increases survival and longevity in stress conditions

Recent studies suggest that downregulation of tumor suppressor genes might not only favor cancer development but also postpone organisms' aging and increase longevity. However, there is lack of population-based studies directly supporting this idea. We studied the lgl lethal alleles which are widespread in natural Drosophila populations. We demonstrate, for the first time, that animals heterozygous on the loss-of-function lgl tumor suppressor gene display a clear pre-adult viability advantage under stressful conditions (high 29 degrees C and low 16 degrees C temperatures). We found also the survival and longevity advantage effect of the lgl loss-of-function in the temperature stress conditions. The main features of this longevity influence are following. First, the lgl-dependent life span increase is sex-dependent; in all experimental combinations males are more sensitive than females of relevant genotypes. Second, the effect is stronger under the life-shortening temperature stress, 29 degrees C, where the hormesis was demonstrated. Third, the favoring effect of reduced dosage of tumor suppressor displays clearly in old but not young animals, delaying aging. Forth, the maternal or epigenetic inheritance of thermotolerance from mother to offspring appears to strengthen the observed longevity effects. One possible explanation of this stress-adaptive effect of reduced tumor suppressor dose might be a better resistance of Drosophila post-mitotic cells to a stress-associated apoptosis at old ages.

Do longevity mutants always show trade-offs?

A number of genetic mutations that substantially increase longevity have been discovered in model organisms. Although these long-lived mutants have provided many insights into the factors that affect longevity, the results from such studies should be interpreted with caution. In particular, at least some of these mutations may be poor guides to human medical intervention because they often have deleterious side effects on important biological functions.

Dementia-free centenarians

BACKGROUND

A small percentage of centenarians, about 15-25%, are functionally cognitively intact. Among those who are not cognitively intact at 100, approximately 90% delayed the onset of clinically evident impairment at least until the average age of 92 yr.

OBJECTIVE

To review current and past findings related to the prevalence and incidence of dementia amongst the exceptionally long-lived.

METHODS

Findings from the various centenarian studies, world-wide, are reviewed.

RESULTS

Neuropsychological and neuropathological correlations thus far suggest that there are centenarians who demonstrate no evidence of neurodegenerative disease. There also appear to be centenarians who despite the substantial presence of neuropathological markers of Alzheimer's disease did not meet clinical criteria for having dementia, thus suggesting the existence of cognitive reserve. Epigenic studies suggest a significant familial component to these survival advantages.

CONCLUSION

Centenarians are of scientific interest as a human model of relative resistance to dementia.

Single nucleotide polymorphisms: aging and diseases

Differences of more than 3 million nucleotides can bee seen comparing the genomes of two individuals as a result of single nucleotide polymorphism (SNP). More and more SNPs can be identified and it seems that these alterations are behind of several biological phenomena. Personal differences in these nucleotides result for example in elevated disease susceptibilities, that is, certain nucleotides are more frequent in patients suffering from different diseases comparing to the healthy population. SNPs may cause substantial alterations in the cells, e.g. the enzyme activity of the respective gene changes, but in other cases the effects of the SNPs are not so pronounced. Later results indicate that SNPs can be rendered to individuals living a longer life than the average. Perhaps these results will not directly lead to the lengthening of the maximal life span; however, genes that play an important role in the aging process could be identified. In this respect SNPs are important factors in determining the information level of the cells of individuals which determines the maximal life span (I. Semsei On the nature of aging. Mech. Ageing Dev . 2000; 117: 93-108), in turn SNP is one of the factors that determine the aging process. Since there are certain age-related diseases, the discovery and the description of the SNPs as a function of age and diseases may result in a better understanding of the common roots of aging and those diseases.

Selected contribution: long-lived Drosophila melanogaster lines exhibit normal metabolic rates

The use of model organisms, such as Drosophila melanogaster, provides a powerful method for studying mechanisms of aging. Here we report on a large set of recombinant inbred (RI) D. melanogaster lines that exhibit approximately a fivefold range of average adult longevities. Understanding the factors responsible for the differences in longevity, particularly the characteristics of the longest-lived lines, can provide fundamental insights into the mechanistic correlates of aging. In ectothermic organisms, longevity is often inversely correlated with metabolic rate, suggesting the a priori hypothesis that long-lived lines will have low resting metabolic rates. We conducted approximately 6000 measurements of CO2 production in individual male flies aged 5, 16, 29, and 47 days postemergence and simultaneously measured the weight of individual flies and life spans in populations of each line. Even though there was a wide range of longevities, there was no evidence of an inverse relationship between the variables. The increased longevity of long-lived lines is not mediated through reduction of metabolic activity. In Drosophila, it is possible to both maintain a normal metabolic rate and achieve long life. These results are evaluated in the context of 100 years of research on the relationship between metabolic rate and life span.

Genetics of exceptional longevity

Centenarians exist at the extreme of life expectancy and are rare. A number of pedigree and molecular genetic studies indicate that a significant component of exceptional longevity is genetically influenced. Furthermore, the recent discovery of a genetic locus on chromosome 4 indicates the powerful potential of studying centenarians for genetic factors that significantly modulate aging and susceptibility to age-related diseases. These studies include siblings and children of centenarians. Siblings have a significantly increased propensity to achieve exceptional old age and have half the mortality risk of their birth cohort from young adulthood through extreme old age. The children of centenarians are emerging as a promising model for the genetic and phenotypic study of aging relatively slowly and the delay and perhaps escape of important age-related diseases.

Functional genomics of ageing

Ageing is the most complex phenotype currently known, since it becomes manifest in all organs and tissues, affects an organism's entire physiology, impacts function at all levels and increases susceptibility to all major chronic diseases. Insight into the molecular and cellular targets of the ageing process would offer the unprecedented opportunity to postpone and prevent some, if not all, of its deteriorative aspects by preventive and therapeutic means. Thus far, our understanding of the causes of ageing is limited. To an important extent this is due to our inability, in the past, to study ageing systems. Instead, ample information has been gathered about individual cellular components at various ages, but this has not allowed a clear understanding of the integrated genomic circuits that control mechanisms of ageing, survival and stress responses. With the emergence of functional genomics, we finally have the opportunity to study ageing in a comprehensive manner, as a function of the dynamic network of genes that determines the physiology of an individual organism over time.

The influence of metabolic rate on longevity in the nematode Caenorhabditis elegans

Much of the recent interest in aging research is due to the discovery of genes in a variety of model organisms that appear to modulate aging. A large amount of research has focused on the use of such long-lived mutants to examine the fundamental causes of aging. While model organisms do offer many advantages for studying aging, it also critical to consider the limitations of these systems. In particular, ectothermic (poikilothermic) organisms can tolerate a much larger metabolic depression than humans. Thus, considering only chronological longevity when assaying for long-lived mutants provides a limited perspective on the mechanisms by which longevity is increased. In order to provide true insight into the aging process additional physiological processes, such as metabolic rate, must also be assayed. This is especially true in the nematode Caenorhabditis elegans, which can naturally enter into a metabolically reduced state in which it survives many times longer than its usual lifetime. Currently it is seen as controversial if long-lived C. elegans mutants retain normal metabolic function. Resolving this issue requires accurately measuring the metabolic rate of C. elegans under conditions that minimize environmental stress. Additionally, the relatively small size of C. elegans requires the use of sensitive methodologies when determining metabolic rates. Several studies indicating that long-lived C. elegans mutants have normal metabolic rates may be flawed due to the use of inappropriate measurement conditions and techniques. Comparisons of metabolic rate between long-lived and wild-type C. elegans under more optimized conditions indicate that the extended longevity of at least some long-lived C. elegans mutants may be due to a reduction in metabolic rate, rather than an alteration of a metabolically independent genetic mechanism specific to aging.

Metabolism and aging in the nematode Caenorhabditis elegans

Research into the causes of aging has greatly increased in recent years. Much of this interest is due to the discovery of genes in a variety of model organisms that appear to modulate aging. Studies of long-lived mutants can potentially provide valuable insights into the fundamental mechanisms of aging. While there are many advantages to the use of model organisms to study aging it is also important to consider the limitations of these systems, particularly because ectothermic (poikilothermic) organisms can survive a far greater metabolic depression than humans. As such, the consideration of only chronological longevity when assaying for long-lived mutants provides a limited perspective on the mechanisms by which longevity is increased. Additional physiological processes, such as metabolic rate, must also be assayed to provide true insight into the aging process. This is especially true in the nematode Caenorhabditis elegans, which has the natural ability to enter into a metabolically reduced state in which it can survive many times longer than its normal lifetime. The extended longevity of at least some long-lived C. elegans mutants may be due to a reduction in metabolic rate, rather than an alteration of a metabolically independent genetic mechanism specific for aging.

An exact law can test biological theories of mortality

Wild animals rarely grow old, and die due to extrinsic hazards. So, natural selection favors genes with good early effects even when they lead to senescence and death at later ages. This implies the Medawar accumulation of late-acting deleterious effects and Williams-Kirkwood life-history trade-off: mortality of a generation strongly depends on its early age life history. Human and protected animal populations live in evolutionary unprecedented conditions, and survive to old age. Quantitative analysis of their mortality establishes that in such conditions a dominant fraction of mortality yields an exact law. In contrast to mortality, the law is biologically non-specific (i.e. independent of genotypes, phenotypes, life history, old age diseases, and all other relevant factors, describing the population and its environment from conception to the age of death). It is universal for species as remote as humans and flies and may lead to the formulation of a biologically non-specific thermodynamic mechanism of mortality. The law predicts that mortality may be significantly decreased and reversed to its value at a much younger age. The reversal is consistent with demographic data. For instance, Swedish females, born in 1916, at 48 years restored the mortality rate they had at 20; Japanese females, born in 1927, at 28 restored the life expectancy they had 8 years earlier. The law quantitatively tests mortality theories and establishes their limitations.

Law of universal mortality

Mortality is arguably the best statistically quantified biological phenomenon. This allows for a physical approach to its study. I establish that in well protected populations, a dominant fraction of mortality at a given age depends on a single parameter only. Such invariance to any other time and space changes is known only in general relativity. It is so mathematically restrictive that, with no other knowledge of experimental data, it is sufficient to predict the exact law. It is universal for species as remote as humans and flies. The law unravels its biologically nonspecific thermodynamic mechanism. It implies that within a couple of years human mortality may be reset to its value at a much younger age. The reversal (albeit not yet as rapid) is consistent with demographic data. For instance, Swedish females, born in 1916, at 48 yr restored their mortality rate 28 yr earlier. The law and its other predictions and implications are also verified. The universal law suggests that a dominant fraction of mortality in well protected populations is just a by-product, which may be eliminated. Total mortality can be significantly decreased.