Time to talk SENS: critiquing the immutability of human aging

Combining rejuvenation interventions in rodents: a milestone in biomedical gerontology whose time has come

INTRODUCTION

Longevity research has matured to the point where significantly postponing age-related decline in physical and mental function is now achievable in the laboratory and foreseeable in the clinic. The most promising strategies involve rejuvenation, i.e. reducing biological age, not merely slowing its progression.

AREAS COVERED

We discuss therapeutic strategies for rejuvenation and results achieved thus far, with a focus on in vivo studies. We discuss the implications of interventions which act on mean or maximum lifespan and those showing effects in accelerated disease models. While the focus is on work conducted in mice, we also highlight notable insights in the field from studies in other model organisms.

EXPERT OPINION

Rejuvenation was originally proposed as easier than slowing aging because it targets initially inert changes to tissue structure and composition, rather than trying to disentangle processes that both create aging damage and maintain life. While recent studies support this hypothesis, a true test requires a panel of rejuvenation interventions targeting multiple damage categories simultaneously. Considerations of cost, profitability, and academic significance have dampened enthusiasm for such work, but it is vital. Now is the time for the field to take this key step toward the medical control of aging.

The Divide-and-Conquer Approach to Delaying Age-Related Functional Decline: Where Are We Now?

Over 20 years ago, together with seven illustrious colleagues, the author proposed that efforts to postpone the decline and debilitation of aging might most promisingly be pursued by tackling the various lifelong processes of accumulation of damage through a panel of interventions, rather than seeking a magic bullet that would retard them all. A decade later, this approach was embraced in a paper that rapidly became, and is still, by far the most highly cited publication in the biology of aging this century. Here I survey the progress that the field has made in relation to this philosophy and the challenges that remain.

Turning Back the Clock: A Retrospective Single-Blind Study on Brain Age Change in Response to Nutraceuticals Supplementation vs. Lifestyle Modifications

BACKGROUND

There is a growing consensus that chronological age (CA) is not an accurate indicator of the aging process and that biological age (BA) instead is a better measure of an individual's risk of age-related outcomes and a more accurate predictor of mortality than actual CA. In this context, BA measures the "true" age, which is an integrated result of an individual's level of damage accumulation across all levels of biological organization, along with preserved resources. The BA is plastic and depends upon epigenetics. Brain state is an important factor contributing to health- and lifespan.

METHODS AND OBJECTIVE

Quantitative electroencephalography (qEEG)-derived brain BA (BBA) is a suitable and promising measure of brain aging. In the present study, we aimed to show that BBA can be decelerated or even reversed in humans (N = 89) by using customized programs of nutraceutical compounds or lifestyle changes (mean duration = 13 months).

RESULTS

We observed that BBA was younger than CA in both groups at the end of the intervention. Furthermore, the BBA of the participants in the nutraceuticals group was 2.83 years younger at the endpoint of the intervention compared with their BBA score at the beginning of the intervention, while the BBA of the participants in the lifestyle group was only 0.02 years younger at the end of the intervention. These results were accompanied by improvements in mental-physical health comorbidities in both groups. The pre-intervention BBA score and the sex of the participants were considered confounding factors and analyzed separately.

CONCLUSIONS

Overall, the obtained results support the feasibility of the goal of this study and also provide the first robust evidence that halting and reversal of brain aging are possible in humans within a reasonable (practical) timeframe of approximately one year.

The hyperfunction theory: An emerging paradigm for the biology of aging

The process of senescence (aging) is predominantly determined by the action of wild-type genes. For most organisms, this does not reflect any adaptive function that senescence serves, but rather evolutionary effects of declining selection against genes with deleterious effects later in life. To understand aging requires an account of how evolutionary mechanisms give rise to pathogenic gene action and late-life disease, that integrates evolutionary (ultimate) and mechanistic (proximate) causes into a single explanation. A well-supported evolutionary explanation by G.C. Williams argues that senescence can evolve due to pleiotropic effects of alleles with antagonistic effects on fitness and late-life health (antagonistic pleiotropy, AP). What has remained unclear is how gene action gives rise to late-life disease pathophysiology. One ultimate-proximate account is T.B.L. Kirkwood's disposable soma theory. Based on the hypothesis that stochastic molecular damage causes senescence, this reasons that aging is coupled to reproductive fitness due to preferential investment of resources into reproduction, rather than somatic maintenance. An alternative and more recent ultimate-proximate theory argues that aging is largely caused by programmatic, developmental-type mechanisms. Here ideas about AP and programmatic aging are reviewed, particularly those of M.V. Blagosklonny (the hyperfunction theory) and J.P. de Magalhães (the developmental theory), and their capacity to make sense of diverse experimental findings is assessed.

Emerging rejuvenation strategies-Reducing the biological age

Several interventions have recently emerged that were proposed to reverse rather than just attenuate aging, but the criteria for what it takes to achieve rejuvenation remain controversial. Distinguishing potential rejuvenation therapies from other longevity interventions, such as those that slow down aging, is challenging, and these anti-aging strategies are often referred to interchangeably. We suggest that the prerequisite for a rejuvenation intervention is a robust, sustained, and systemic reduction in biological age, which can be assessed by biomarkers of aging, such as epigenetic clocks. We discuss known and putative rejuvenation interventions and comparatively analyze them to explore underlying mechanisms.

Elementary Laboratory Assays as Biomarkers of Ageing: Support for Treatment of COVID-19?

Youth, working age and the elderly: On a timeline, chronological age (CA) and biological age (BA) may dissociate; nosological entities manifest themselves at different BAs. In determining which disease corresponds to a given age decade, statistical registries of causes of death are unreliable and this does not change with SARS CoV-2 infection. Beyond adolescence, ageing metrics involve estimations of changes in fitness, including prediction models to estimate the number of remaining years left to live. A substantial disparity in biomarker levels and health status of ageing can be observed: the difference in CA and BA in the large cohorts under consideration is glaring. Here, we focus more closely on ageing and senescence metrics in order to make information available for risk analysis non the least with COVID-19, including the most recent risk factors of ABO blood type and 3p21.31 chromosome cluster impacting on C5a and SC5b-9 plasma levels. From the multitude of routine medical laboratory assays, a potentially meaningful set of assays aimed to best reflect the stage of individual senescence; hence risk factors the observational prospective SENIORLABOR study of 1,467 healthy elderly performed since 2009 and similar approaches since 1958 can be instantiated as a network to combine a set of elementary laboratory assays quantifying senescence.

From gerontology to geroscience: a synopsis on ageing

Biological ageing can be tentatively defined as an intrinsic and inevitable degradation of biological function that accumulates over time at every level of biological organisation from molecules to populations. Senescence is characterised by a progressive loss of physiological integrity, leading to impaired function and increased vulnerability to death. With advancing age, all components of the human body undergo these cumulative, universal, progressive, intrinsic and deleterious (CUPID) changes. Although ageing is not a disease per se, age is the main risk factor for the development of a panoply of age-related diseases. From a mechanistic perspective, a myriad of molecular processes and components of ageing can be studied. Some of them seem especially important and they are referred to as the hallmarks of ageing. There is compelling evidence that senescence has evolved as an emergent metaphenomenon that originates in the difficulty in maintaining homeodynamics in biological systems. From an evolutionary perspective, senescence is the inevitable outcome of an evolutionarily derived equilibrium between the amount of resources devoted to somatic maintenance and the amount of resources devoted to sexual reproduction. Single-target, single-molecule and disease-oriented approaches to ageing are severely limited because they neglect the dynamic, interactive and networking nature of life. These limitations notwithstanding, many authors promote single-target and disease-oriented approaches to senescence, e.g. repurposed drugs, claiming that these methods can enhance human health and longevity. Senescence is neither a disease nor a monolithic process. In this review, the limitations of these methods are discussed. The current state of biogerontology is also summarised.

Diet and Botanical Supplementation: Combination Therapy for Healthspan Improvement?

Healthspan science aims to add healthy, functional years to human life. Many different methods of improving healthspan have been investigated, chiefly focusing on just one aspect of an organism's health such as survival. Studies in Drosophila melanogaster have demonstrated that a reversal to a long-abandoned ancestral diet results in improved functional health, particularly at later ages. Meanwhile, pharmaceutical studies have demonstrated that botanical extracts have potent antiaging properties, capable of extending the mean lifespan of D. melanogaster by up to 25%, without a decrease in early fecundity. In this study, we combine these two different approaches to healthspan extension to examine whether a combination of such treatments results in a synergistic or antagonistic effect on Drosophila healthspan. One botanical extract, derived from Rhodiola rosea, mimicked the effects of the ancestral apple diet with better performance at later ages compared with the control. Another extract, derived from Rosa damascena, decreased age-specific survivorship when combined with the apple diet providing support for the "Poisoned Chalice" hypothesis that combinations of various supplements or diets can elicit adverse physiological responses. More experiments in model organisms should be completed researching the effects of combining healthspan-extending substances in various diet backgrounds.

Clinical Evidence for Targeting NAD Therapeutically

Nicotinamide adenine dinucleotide (NAD) pharmacology is a promising class of treatments for age-related conditions that are likely to have a favorable side effect profile for human use, given the widespread use of the NAD precursor vitamin B3 supplements. However, despite several decades of active investigation and numerous possible biochemical mechanisms of action suggested, only a small number of randomized and adequately powered clinical trials of NAD upregulation as a therapeutic strategy have taken place. We conducted a systematic review of the literature, following the PRISMA guidelines, in an attempt to determine whether or not the human clinical trials performed to date support the potential benefits of NAD supplementation in a range of skin, metabolic and age-related conditions. In addition, we sought medical indications that have yielded the most promising results in the limited studies to date. We conclude that promising, yet still speculative, results have been reported for the treatment of psoriasis and enhancement of skeletal muscle activity. However, further trials are required to determine the optimal method of raising NAD levels, identifying the target conditions, and comparisons to the present standard of care for these conditions. Lastly, pharmacological methods that increase NAD levels should also be directly compared to physiological means of raising NAD levels, such as exercise programs and dietary interventions that are tailored to older individuals, and which may be more effective.

A matter of life and longer life

While the major scientific discoveries that would extend the length and health of human lives are not yet here, the research that could create them is already underway. As prospects for a world in which extended and improved lives inches closer into reality, the discourse about what to consider as we move forward grows richer, with corporate executives, ideologues, scientists, theologians, ethicists, investigative journalists, and philosophers taking part in imagining and anticipating the rich array of humanity's possible futures. Drawing from in-depth interviews with key stakeholders (n = 22), we offer empirical insights into key values and beliefs animating the "longevity movement," including what constitutes an ideal human state, the imperative to intervene, and the role of individual liberty and concerns for equality. Emerging from these interviews are common concerns about reducing suffering, preserving diversity in visions of successful aging and how best to promote access to a future that may not remain hypothetical for long.

The Light and Shadow of Senescence and Inflammation in Cardiovascular Pathology and Regenerative Medicine

Recent epidemiologic studies evidence a dramatic increase of cardiovascular diseases, especially associated with the aging of the world population. During aging, the progressive impairment of the cardiovascular functions results from the compromised tissue abilities to protect the heart against stress. At the molecular level, in fact, a gradual weakening of the cellular processes regulating cardiovascular homeostasis occurs in aging cells. Atherosclerosis and heart failure are particularly correlated with aging-related cardiovascular senescence, that is, the inability of cells to progress in the mitotic program until completion of cytokinesis. In this review, we explore the intrinsic and extrinsic causes of cellular senescence and their role in the onset of these cardiovascular pathologies. Additionally, we dissect the effects of aging on the cardiac endogenous and exogenous reservoirs of stem cells. Finally, we offer an overview on the strategies of regenerative medicine that have been advanced in the quest for heart rejuvenation.

Theory and associated phenomenology for intrinsic mortality arising from natural selection

Standard evolutionary theories of aging and mortality, implicitly based on assumptions of spatial averaging, hold that natural selection cannot favor shorter lifespan without direct compensating benefit to individual reproductive success. However, a number of empirical observations appear as exceptions to or are difficult to reconcile with this view, suggesting explicit lifespan control or programmed death mechanisms inconsistent with the classic understanding. Moreover, evolutionary models that take into account the spatial distributions of populations have been shown to exhibit a variety of self-limiting behaviors, maintained through environmental feedback. Here we extend recent work on spatial modeling of lifespan evolution, showing that both theory and phenomenology are consistent with programmed death. Spatial models show that self-limited lifespan robustly results in long-term benefit to a lineage; longer-lived variants may have a reproductive advantage for many generations, but shorter lifespan ultimately confers long-term reproductive advantage through environmental feedback acting on much longer time scales. Numerous model variations produce the same qualitative result, demonstrating insensitivity to detailed assumptions; the key conditions under which self-limited lifespan is favored are spatial extent and locally exhaustible resources. Factors including lower resource availability, higher consumption, and lower dispersal range are associated with evolution of shorter lifespan. A variety of empirical observations can parsimoniously be explained in terms of long-term selective advantage for intrinsic mortality. Classically anomalous empirical data on natural lifespans and intrinsic mortality, including observations of longer lifespan associated with increased predation, and evidence of programmed death in both unicellular and multicellular organisms, are consistent with specific model predictions. The generic nature of the spatial model conditions under which intrinsic mortality is favored suggests a firm theoretical basis for the idea that evolution can quite generally select for shorter lifespan directly.

The aging-disease false dichotomy: understanding senescence as pathology

From a biological perspective aging (senescence) appears to be a form of complex disease syndrome, though this is not the traditional view. This essay aims to foster a realistic understanding of aging by scrutinizing ideas old and new. The conceptual division between aging-related diseases and an underlying, non-pathological aging process underpins various erroneous traditional ideas about aging. Among biogerontologists, another likely error involves the aspiration to treat the entire aging process, which recent advances suggest is somewhat utopian. It also risks neglecting a more modest but realizable goal: to develop preventative treatments that partially protect against aging.

The scientific quest for lasting youth: prospects for curing aging

People have always sought eternal life and everlasting youth. Recent technological breakthroughs and our growing understanding of aging have given strength to the idea that a cure for human aging can eventually be developed. As such, it is crucial to debate the long-term goals and potential impact of the field. Here, I discuss the scientific prospect of eradicating human aging. I argue that curing aging is scientifically possible and not even the most challenging enterprise in the biosciences. Developing the means to abolish aging is also an ethical endeavor because the goal of biomedical research is to allow people to be as healthy as possible for as long as possible. There is no evidence, however, that we are near to developing the technologies permitting radical life extension. One major difficulty in aging research is the time and costs it takes to do experiments and test interventions. I argue that unraveling the functioning of the genome and developing predictive computer models of human biology and disease are essential to increase the accuracy of medical interventions, including in the context of life extension, and exponential growth in informatics and genomics capacity might lead to rapid progress. Nonetheless, developing the tools for significantly modifying human biology is crucial to intervening in a complex process like aging. Yet in spite of advances in areas like regenerative medicine and gene therapy, the development of clinical applications has been slow and this remains a key hurdle for achieving radical life extension in the foreseeable future.

Innovating aging: promises and pitfalls on the road to life extension

One of the main benefits of the dramatic technological progress over the last two centuries is the enormous increase in human life expectancy, which has now reached record highs. After conquering most childhood diseases and a fair fraction of the diseases that plague adulthood, medical technology is now mainly preoccupied by age-related disorders. Further progress is dependent on circumventing the traditional medical focus on individual diseases and instead targeting aging as a whole as the ultimate cause of the health problems that affect humankind at old age. In principle, a major effort to control the gradual accumulation of molecular and cellular damage - considered by many as the ultimate cause of intrinsic aging - may rapidly lead to interventions for regenerating aged and worn-out tissues and organs. While considered impossible by many, there really is no reason to reject this as scientifically implausible. However, as we posit, it is not only scientific progress that is currently a limiting factor, but societal factors that hinder and may ultimately prevent further progress in testing and adopting the many possible interventions to cure aging.

Toward priorities for aging research

The global population is aging, and although age remains the primary risk factor for all major causes of death, no priorities for aging research exist. After reviewing the literature on mortality modeling, we found that different chronic processes underlie mortality before and after reproductive age. To identify priorities in aging research, we propose a simple ranking method that uses the percentage of deaths attributable to each disease for the over 60 population on the basis that, rather than being the result of individual risk factors, these deaths are largely due to underlying senescent processes. Our ranking suggests that vascular aging, led by ischemic heart disease and stroke, is the most important focus for aging research. The availability of funding, however, is not currently aligned with health priorities, and we believe that rectifying this disconnect may improve societal health outcomes.

Healthy aging diets other than the Mediterranean: a focus on the Okinawan diet

The traditional diet in Okinawa is anchored by root vegetables (principally sweet potatoes), green and yellow vegetables, soybean-based foods, and medicinal plants. Marine foods, lean meats, fruit, medicinal garnishes and spices, tea, alcohol are also moderately consumed. Many characteristics of the traditional Okinawan diet are shared with other healthy dietary patterns, including the traditional Mediterranean diet, DASH diet, and Portfolio diet. All these dietary patterns are associated with reduced risk for cardiovascular disease, among other age-associated diseases. Overall, the important shared features of these healthy dietary patterns include: high intake of unrefined carbohydrates, moderate protein intake with emphasis on vegetables/legumes, fish, and lean meats as sources, and a healthy fat profile (higher in mono/polyunsaturated fats, lower in saturated fat; rich in omega-3). The healthy fat intake is likely one mechanism for reducing inflammation, optimizing cholesterol, and other risk factors. Additionally, the lower caloric density of plant-rich diets results in lower caloric intake with concomitant high intake of phytonutrients and antioxidants. Other shared features include low glycemic load, less inflammation and oxidative stress, and potential modulation of aging-related biological pathways. This may reduce risk for chronic age-associated diseases and promote healthy aging and longevity.

Nucleic acid delivery: roles in biogerontological interventions

Prolongation of longevity is a history-long desire of humans. Driven by the genetic contribution to longevity and the remarkable plasticity of healthy lifespan as demonstrated in animal models, arduous efforts have been directed to aging and longevity research over the years. Today, our understanding of lifespan determination is much greater than it was in the past, but administrable interventions for longevity enhancement are still virtually absent. The aim of this article is to highlight the technical gap between basic biogerontological research and intervention development, and to explore the importance of nucleic acid (NA) delivery technologies in bridging the gap. It is hoped that this article can engender more awareness of the roles of NA delivery technologies in biogerontological interventions, particularly NA therapy.

Strategies for engineered negligible senescence

In this viewpoint, we describe the strategies for engineered negligible senescence (SENS) concept--a simple and appealing model for the design of therapeutic interventions able to meaningfully and persistently reverse the deleterious effects of aging. We go on to outline how current or foreseeable biotechnologies could feasibly be employed to repair every currently identified category of pathogenic damage that accumulates over a human lifespan. Then, briefly, we explain why this goal is not only ethically sound, but can in fact be considered to verge on an ethical obligation. Finally, we review recent progress in some key areas of the SENS platform, including proof-of-concept research sponsored by the SENS Foundation, a charity based in California.

Science fact versus SENS foreseeable

Scientists in the various fields of aging share a common goal--the extension of healthy life. However, claiming that the only way to accomplish this is to treat the complications of aging rather than its causes requires more than declarations made by proponents of SENS--it requires empirical research based on the scientific method. As this paper illustrates, it will be difficult to prove that SENS interventions work because the primary result of interest, negligible senescence, is not an outcome variable in empirical tests of SENS.

Zeno's paradox and the faith that technological game-changers are impossible

In their article in this issue, Olshansky and Carnes [Gerontology 2013;59:85-92] spell out in perhaps the most explicit terms yet a view which they have long espoused: that increases in longevity will inevitably slow down in decades to come, since the rate of biomedical progress that everyone agrees would be necessary to avoid such a slowdown is far too dramatic to be plausible. By doing so, they also betray more explicitly than ever before the flaws in their own logic. It is ironic that these flaws, unlike the work they critique, are actually quite closely analogous to the flaws in Zeno's paradox. Since others are offering their own comments on other parts of the article, I shall restrict my remarks on the article to those passages which refer specifically to my own work, together with the conclusion.

The demographic and biomedical case for late-life interventions in aging

The social and medical costs of the biological aging process are high and will rise rapidly in coming decades, creating an enormous challenge to societies worldwide. In recent decades, researchers have expanded their understanding of the underlying deleterious structural and physiological changes (aging damage) that underlie the progressive functional impairments, declining health, and rising mortality of aging humans and other organisms and have been able to intervene in the process in model organisms, even late in life. To preempt a global aging crisis, we advocate an ambitious global initiative to translate these findings into interventions for aging humans, using three complementary approaches to retard, arrest, and even reverse aging damage, extending and even restoring the period of youthful health and functionality of older people.

A history of the future: the emergence of contemporary anti-ageing medicine

The emergence of anti-ageing medicine over the past 20 years has posed tremendous challenges for the understanding of ageing and the concomitant responsibilities of biomedicine. Though highly contentious and loosely organised at best, anti-ageing targets ageing for biomedical intervention. This article examines a history of anti-ageing in the United States from 1993 to 2008, outlining its evolution from a scientific 'backwater' to a field with such promise that many within and outside the field believe efficacious therapies are an inevitability. In large part, the language of anti-ageing has shifted from predictions to expectations; it has become less a question of 'if' and more a question of 'when' and 'how' this rhetorical shift is directly linked with increasing legitimacy constructed upon a complex web of factors including mounting practitioner involvement, research interest, media attention, and popular desire. In this article I briefly review this history alongside the strategic histories marshalled by the various proponents and opponents to support their claims of legitimacy. The history of anti-ageing medicine is one of an emerging scientific and clinical practice as well as a history of an idea that has very recently made its way out of science fiction and into science future.

Living longer: age retardation and autonomy

Research into human ageing is a growing field of research with two central foci: geriatric medicine works to reduce the incidence and severity of age-related diseases and disabilities by devising adequate therapeutic and preventive strategies. A second focus, this time in the emerging field of biogerontology, is to bring about a general retardation of the ageing process and by this increase the average and maximum human lifespan. This contribution looks into the second focus, i.e. the possibility of age retardation which, for the time being, is merely hypothetical. After outlining research strategies studying age retardation in animal experiments, it will ask how extending human life by technological interventions might play out on the individual, familial and social level. The central concern here will be autonomy-linked issues, seeing that in debates concerning the ethical implications of age-retarding techniques the argument from autonomy is one of the main arguments in favour of the prolongation of human life. In particular, this contribution will assess whether the argument from autonomy does, in fact, unequivocally support the recourse to age-retarding techniques.

Puzzles, promises and a cure for ageing

Recent discoveries in the science of ageing indicate that lifespan in model organisms such as yeast, nematodes, flies and mice is plastic and can be manipulated by genetic, nutritional or pharmacological intervention. A better understanding of the targets of such interventions, as well as the proximate causes of ageing-related degeneration and disease, is essential before we can evaluate if abrogation of human senescence is a realistic prospect.

Making SENSE: strategies for engineering negligible senescence evolutionarily

Thirty years ago, in 1977, few biologists thought that it would be possible to increase the maximum life span characteristic of each species over the variety of environmental conditions in which they live, whether in nature or in the laboratory. But the evolutionary theory of aging suggested otherwise. Accordingly, experiments were performed with fruit flies, Drosophila melanogaster, which showed that manipulation of the forces of natural selection over a number of generations could substantially slow the rate of aging, both demographically and physiologically. After this first transgression of the supposedly absolute limits to life extension, it was suggested that mammals too could be experimentally evolved to have greater life spans and slower aging. And further, it was argued that such postponed-aging mammals could be used to reverse-engineer a slowing of human aging. The subsequent discovery and theoretical explanation of mortality-rate plateaus revealed that aging was not due to the progressive physiological accumulation of damage. Instead, aging is now understood by evolutionary biologists to arise from a transient fall in age-specific adaptation, a fall that does not necessarily proceed toward ineluctable death. This implies that SENS must be based on re-tuning adaptation, not repairing damage. As evolutionary manipulation of model organisms shows us how adaptation can be focused on engineering negligible senescence, there are thus both scientific and practical reasons for making SENS evolutionary; that is making SENSE.

A model of aging as accumulated damage matches observed mortality patterns and predicts the life-extending effects of prospective interventions

The relative insensitivity of lifespan to environmental factors constitutes compelling evidence that the physiological decline associated with aging derives primarily from the accumulation of intrinsic molecular and cellular side-effects of metabolism. Here we model that accumulation starting from a biologically based interpretation of the way in which those side-effects interact. We first validate this model by showing that it very accurately reproduces the distribution of ages at death seen in typical populations that are well protected from age-independent causes of death. We then exploit the mechanistic basis of this model to explore the impact on lifespans of interventions that combat aging, with an emphasis on interventions that repair (rather than merely retard) the direct molecular or cellular consequences of metabolism and thus prevent them from accumulating to pathogenic levels. Our results strengthen the case that an indefinite extension of healthy and total life expectancy can be achieved by a plausible rate of progress in the development of such therapies, once a threshold level of efficacy of those therapies has been reached.

Science and imagery in the ‘war on old age’

Several professional groups present themselves as ‘waging war’ on old age. They construct old age as a naturalised, self-evidently negative, biological phenomenon, which must be attacked and defeated. These groups make different claims to technical expertise and their ability to control natural phenomena, and use different weapons to defeat ageing. There are those who focus on cosmetic interventions, that is, the control of the body and the removal or masking of the signs of ageing. There are those who equate old age with ill-health and identify themselves as warriors in a battle with disease, and others whose objective is to understand the fundamental intra-cellular processes of ageing and what controls the human life span, and then to extend its limits. A fourth group aims to make human immortality possible. Examination of the language and symbolic practices of these groups reveals that they share a dominant cultural view that devalues old age and older people. The use of military metaphors to describe the importance and difficulties of their task is most prolific among the first and fourth of these groups. The second and third groups disguise a contradiction in their aim of understanding the diseases and disorders of old age by advocating the goal of an extended ‘healthy life span’, which avoids having to confront the moral dilemmas of extending the lifespan for its own sake.

Protagonistic pleiotropy: Why cancer may be the only pathogenic effect of accumulating nuclear mutations and epimutations in aging

Since Szilard's seminal 1959 article, the role of accumulating nuclear DNA (nDNA) damage -- whether as mutations, i.e. changes to sequence, or as epimutations, i.e. adventitious but persistent alterations to methylation and other decorations of nDNA and histones -- has been widely touted as likely to contribute substantially to the aging process throughout the animal kingdom. Such damage certainly accumulates with age and is central to one of the most prevalent age-related causes of death in mammals, namely cancer. However, its role in contributing to the rates of other aspects of aging is less clear. Here I argue that, in animals prone to cancer, evolutionary pressure to postpone cancer will drive the fidelity of nDNA maintenance and repair to a level greatly exceeding that needed to prevent nDNA damage from reaching levels during a normal lifetime that are pathogenic other than via cancer or, possibly, apoptosis resistance. I term this the "protagonistic pleiotropy of chromosomal damage" (PPCD) hypothesis, because this interaction of cancer-related and -unrelated damage is the converse of the well-known "antagonistic pleiotropy" phenomenon. I then consider a selection of recent data on the rate of accumulation of nDNA damage in the context of this hypothesis, and conclude that all presently available evidence is consistent with it. If this conclusion is correct, the implications for the feasibility of greatly postponing mammalian (and eventually human) aging and age-related pathology are far-reaching.

The natural biogerontology portfolio: "defeating aging" as a multi-stage ultra-grand challenge

The early days of biogerontology were blessed with an undiluted forthrightness concerning the field's ultimate goals, epitomized by its leaders. Luminaries from Pearl to Comfort to Strehler declared the desirability of eliminating aging with no more diffidence than that with which today's oncologists aver that they seek a cure for cancer. The field's subsequent retreat from this position garnered a modicum of political acceptability and public financial support, but all biogerontologists agree that this fell, and continues to fall, vastly short of the funding that the prospect of even a modest postponement of aging would logically justify. The past 20 years' discoveries of life-extending genetic manipulations in model organisms have weakened the argument that a policy of appeasement of the public's ambivalence about defeating aging is our only option; some of the biogerontologists responsible for these advances have espoused views of which our intellectual forefathers would be proud, without noticeably harming their own careers. With the recent emergence of a detailed, ambitious, but practical roadmap for the comprehensive defeat of aging, this process has moved further: our natural and most persuasive public stance is, more than ever, to reembrace the same unassailable logic that served pioneering biogerontologists perfectly well. In particular, we are in a position to explain that the disparate strands of contemporary biomedical gerontology are not in conflict, but rather that they constitute a portfolio of approaches with a range of potential efficacies and degrees of difficulty of implementation, which can save more lives together than any can save individually, and all of which thus merit intensive pursuit.

Free radicals in aging: causal complexity and its biomedical implications

Superoxide generated adventitiously by the mitochondrial respiratory chain can give rise to much more reactive radicals, resulting in random oxidation of all classes of macromolecules. Harman's 1956 suggestion that this process might drive aging has been a leading strand of biogerontological thinking since the discovery of superoxide dismutase. However, it has become apparent that the many downstream consequences of free radical damage can also be caused by processes not involving oxidation. Moreover, free radicals have been put to use by evolution to such an extent that their wholesale elimination would certainly be fatal. This multiplicity of parallel pathways and side-effects illustrates why attempts to postpone aging by "cleaning up" metabolism will surely fail for the foreseeable future: we simply understand metabolism too poorly. This has led me to pursue the alternative, "repair and maintenance" approach that sidesteps our ignorance of metabolism and may be feasible relatively soon.

Making the case for human life extension: personal arguments

In the close to medium future, the life sciences might permit a vast extension of the human life span. I will argue that this is a very desirable development for the individual person. The question whether death is a harm to the dying is irrelevant here. All it takes is that being alive is good for the living person and not being alive is not good for anyone. Thus, living persons who expect to live on happily are rationally required to want to stay alive. Eventual uncertainty whether it will be possible to be happy in the future provides no objection, but rather an incentive to try. This view, however, may be naive in assuming that persons are unchanging entities that exist separately from their psychological information. Objections have been derived from reductionistic views that value our future experiences in a way that declines with time, so that there will be a future point beyond which only negligible value accrues. If we adopt such a view, then we cannot now be concerned to have experiences beyond that point. I argue that these arguments fail to take into account all the reasons we might have to be concerned for the future and all kinds of such concern that come from them. The adoption of a plausible reductionistic account can arguably weaken our concern for the future and certainly change its quality in important ways. But this provides no objection to the desire to live forever, nor to live at all.

Normal brain ageing: models and mechanisms

Normal ageing is associated with a degree of decline in a number of cognitive functions. Apart from the issues raised by the current attempts to expand the lifespan, understanding the mechanisms and the detailed metabolic interactions involved in the process of normal neuronal ageing continues to be a challenge. One model, supported by a significant amount of experimental evidence, views the cellular ageing as a metabolic state characterized by an altered function of the metabolic triad: mitochondria-reactive oxygen species (ROS)-intracellular Ca2+. The perturbation in the relationship between the members of this metabolic triad generate a state of decreased homeostatic reserve, in which the aged neurons could maintain adequate function during normal activity, as demonstrated by the fact that normal ageing is not associated with widespread neuronal loss, but become increasingly vulnerable to the effects of excessive metabolic loads, usually associated with trauma, ischaemia or neurodegenerative processes. This review will concentrate on some of the evidence showing altered mitochondrial function with ageing and also discuss some of the functional consequences that would result from such events, such as alterations in mitochondrial Ca2+ homeostasis, ATP production and generation of ROS.

Negligible Senescence: How Will We Know It When We See It?

The recent public claim that "SENS is a practical, foreseeable approach to curing aging" has stirred considerable controversy among bio-gerontologists. Testing this hypothesis will not only require precise definitions for the somewhat subjective terms "practical," "foreseeable," and "curing," it will require a precise definition of the term "aging." To facilitate proper experimental design, this definition must focus on the nature of aging itself, not its causes or consequences. Aging in mammals is a process that begins early in adult life and continues steadily thereafter until death. It is manifested by a decline in the functional capacity (or, more precisely, reserve capacity) of a variety of vital physiologic systems leading to increasing risk of morbidity and mortality over time. Aging, however, cannot be measured by simply monitoring morbidity and/or mortality. Aging can only be measured by monitoring the decline of global functional capacity itself. This, in turn, will require an operational definition of aging expressed as a rate function (i.e., it will have units expressing aging as an overall rate of functional change per unit time). Widespread acceptance of such global indexes of aging rate in animal models and humans will greatly facilitate research activity specifically designed to increase the understanding of aging mechanisms and antiaging interventions.

Contentious terminology and complicated cartography of anti-aging medicine

Serving as an introduction to the cultural significance of the contemporary emergence of anti-aging medicine, this article outlines some of the distinctions and controversies regarding the usage of the term "anti-aging medicine." By sketching out the complex field of researchers, practitioners, organizations, companies it is clear that "anti-aging medicine" is a highly contentious term that means different things to different groups. Thus, analysis demands a keen attention to contextualizing its usage. However, despite the critically important distinctions in how "anti-aging medicine" is used and what it connotes both to the user and the audience, the core principle of anti-aging is the notion that aging can be targeted for biomedical intervention. It is the orientation toward this explicit goal that marks anti-aging medicine. While neither advocating for/against anti-aging medicine nor excavating the large body of biological literature, this ethnographically researched article explicates the cultural use of "anti-aging medicine" and maps out its main varieties, controversies, stakes, and challenges.

Extrapolaholics Anonymous: Why Demographers' Rejections of a Huge Rise in Cohort Life Expectancy in This Century are Overconfident

Criticisms of demographers by other demographers have become frequent in scientific literature, generally consisting of accusations that trends observed in the recent past have been extrapolated unjustifiably into the future. Demographers, along with their colleagues in the actuarial profession, are in an invidious position in this regard, knowing full well that extrapolation is almost always only minimally justifiable, but knowing also that their readers, colleagues, and sources of funding tend to be much more interested in the future than in the past. It is unfortunate that, while actuaries typically resolve this dilemma by emphasizing the limitations of their methods and thereby lowering expectations that their predictions will be accurately fulfilled, demographers are more prone to respond combatively, attempting to reinforce the credibility of their extrapolations by recourse to data from areas in which their expertise is less tested, such as biology. This is valuable in that it raises the profile of the debate on the likely rate of scientific progress relevant to mortality rates, but it also runs the risk of lowering the technical quality of that debate, by telling policy makers and the public what they want to hear and thereby entrenching their expectations without recourse to the relevant biological facts. Extrapolations based on plausible sequences of scientific advances and the sociopolitical responses to them, summarized in this article, have led to the prediction of four-digit life expectancies of cohorts born in the 21st century and possibly even in the 20th. This prediction has attracted inevitable ridicule from prominent demographers, but being founded on science and sociology rather than on history it may be much more reliable than the extrapolations that those demographers presently prefer.

You don't need a weatherman: famines, evolution, and intervention into aging

Calorie restriction (CR) is the most robust available intervention into biological aging. Efforts are underway to develop pharmaceuticals that would replicate CR's anti-aging effects in humans ("CR mimetics"), on the assumption that the life- and healthspan-extending effects of CR in lower organisms will be proportionally extrapolable to humans (the "proportionality principle" (PP)). A recent argument from evolutionary theory (the "weather hypothesis" (WH)) suggests that CR (or its mimetics) will only provide 2-3 years of extended healthy lifespan in humans. The extension of healthy human lifespan that would be afforded by intervention into aging makes it crucial that resources for therapeutic development be optimally allocated; CR mimetics being the main direction being pursued for interventive biogerontology, this paper evaluates the challenge to the potential efficacy of CR mimetics posed by the WH, on a theoretical level and by reference to the available interspecies data on CR. Rodent data suggest that the anti-aging effects of CR continue to increase in inverse proportion to the degree of energy restriction imposed, well below the level that would be expected to be survivable under the conditions under which the mechanisms of CR evolved and are maintained in the wild. Moreover, the same increase in anti-aging effects continues well below the point at which it interferes with reproductive function. Both of these facts are in accordance with the predictions of evolutionary theory. Granted these facts, the interspecies data-including data available in humans-are consistent with the predictions of PP rather than those of the WH. This suggests that humans will respond to a high degree of CR (or its pharmaceutical simulation) with a proportional deceleration of aging, so that CR mimetics should be as effective in humans as CR itself is in the rodent model. Despite this fact, CR mimetics should not be the focus of biomedical gerontology, as strategies based on the direct targeting of the molecular lesions of aging are likely to lead to more rapidly developable and far more effective anti-aging biomedicines.