Program for testing biological interventions to promote healthy aging

Pharmacological interventions in human aging

Pharmacological interventions are emerging as potential avenues of alleviating age-related disease. However, the knowledge of ongoing clinical trials as they relate to aging and pharmacological interventions is dispersed across a variety of mediums. In this review we summarize 136 age-related clinical trials that have been completed or are ongoing. Furthermore, we establish a database that describe the trials (AgingDB, www.agingdb.com) keeping track of the previous and ongoing clinical trials, alongside their outcomes. The aim of this review and database is to give people the ability to easily query for their trial of interest and stay up to date on the latest results. In sum, herein we give an overview of the current pharmacological strategies that have been applied to target human aging.

Pleiotropic influence of DNA methylation QTLs on physiological and ageing traits

DNA methylation is influenced by genetic and non-genetic factors. Here, we chart quantitative trait loci (QTLs) that modulate levels of methylation at highly conserved CpGs using liver methylome data from mouse strains belonging to the BXD family. A regulatory hotspot on chromosome 5 had the highest density of trans-acting methylation QTLs (trans-meQTLs) associated with multiple distant CpGs. We refer to this locus as meQTL.5a. Trans-modulated CpGs showed age-dependent changes and were enriched in developmental genes, including several members of the MODY pathway (maturity onset diabetes of the young). The joint modulation by genotype and ageing resulted in a more 'aged methylome' for BXD strains that inherited the DBA/2J parental allele at meQTL.5a. Further, several gene expression traits, body weight, and lipid levels mapped to meQTL.5a, and there was a modest linkage with lifespan. DNA binding motif and protein-protein interaction enrichment analyses identified the hepatic nuclear factor, Hnf1a (MODY3 gene in humans), as a strong candidate. The pleiotropic effects of meQTL.5a could contribute to variations in body size and metabolic traits, and influence CpG methylation and epigenetic ageing that could have an impact on lifespan.

The Role of the National Institute on Aging in the Development of the Field of Geroscience

The conceptualization of the field of geroscience, which began about 10 years ago, marks, together with the publication of "The hallmarks of aging" (see López-Otín C, Blasco MA, Partridge L, Serrano M, Kroemer G. Cell 153: 1194-1217, 2013), a significant watershed in the development of aging research. Based on a very simple and commonly accepted premise, namely, that aging biology is at the core the most significant risk factor for all chronic diseases affecting the elderly, geroscience became possible because of earlier significant developments in the field of aging biology. Here we describe the origins of the concept, as well as its current status in the field. The principles of geroscience provide an important new biomedical perspective and have spawned a significantly increased interest in aging biology within the larger biomedical scientific community.

The Annoying Flaws of Gerontological Research

Gerontological research has accelerated dramatically in the last few decades. However, despite increased public interest, federal funding, an army of researchers, and many notable discoveries and high-impact publications, the goal of achieving even a modest extension of human lifespan seems to be as far away as ever or, at best, remains within the realm of lifestyle and diet optimization efforts. Humanity has already benefited from a lifespan revolution in the first half of 20^th Century, which was brought about by improved sanitation and hygiene, clean water, and our successful war on infectious diseases. Thanks to all these developments, in which gerontologists played no part, our expected lifespan increased by about 40% and our primary causes of death decidedly shifted from extrinsic to intrinsic causality. The next step is not that simple as it implies tackling intrinsic mechanisms of aging, and the lack of working human-specific antiaging solutions likely stems from flawed research strategies.

The protein inputs of an ultra-predictive aging clock represent viable anti-aging drug targets

Machine learning models capable of predicting age given a set of inputs are referred to as aging clocks. We recently developed an aging clock that utilizes 491 plasma protein inputs, has an exceptional accuracy, and is capable of measuring biological age. Here, we demonstrate that this clock is extremely predictive (r = 0.95) when used to measure age in a novel plasma proteomic dataset derived from 370 human subjects aged 18-69 years. Over-representation analyses of the proteins that make up this clock in the Gene Ontology and Reactome databases predominantly implicated innate and adaptive immune system processes. Immunological drugs and various age-related diseases were enriched in the DrugBank and GLAD4U databases. By performing an extensive literature review, we find that at least 269 (54.8 %) of these inputs regulate lifespan and/or induce changes relevant to age-related disease when manipulated in an animal model. We also show that, in a large plasma proteomic dataset, the majority (57.2 %) of measurable clock proteins significantly change their expression level with human age. Different subsets of proteins were overlapped with distinct epigenetic, transcriptomic, and proteomic aging clocks. These findings indicate that the inputs of this age predictor likely represent a rich source of anti-aging drug targets.

The degree of frailty as a translational measure of health in aging

Frailty is a multiply determined, age-related state of increased risk for adverse health outcomes. We review how the degree of frailty conditions the development of late-life diseases and modifies their expression. The risks for frailty range from subcellular damage to social determinants. These risks are often synergistic-circumstances that favor damage also make repair less likely. We explore how age-related damage and decline in repair result in cellular and molecular deficits that scale up to tissue, organ and system levels, where they are jointly expressed as frailty. The degree of frailty can help to explain the distinction between carrying damage and expressing its usual clinical manifestations. Studying people-and animals-who live with frailty, including them in clinical trials and measuring the impact of the degree of frailty are ways to better understand the diseases of old age and to establish best practices for the care of older adults.

Investigational drugs and nutrients for human longevity. Recent clinical trials registered in ClinicalTrials.gov and clinicaltrialsregister.eu

Introduction:Several pharmacological drugs have shown proof of concept for longevity in animal models. I aimed to identify and review those longevity drug candidates that are undergoing clinical trials.Areas covered:Recent (post-2017) longevity clinical trials were found in US and EU clinical trial registries. Longevity drug candidates are the antidiabetic drugs metformin and acarbose, and the immunosuppressant rapamycin. These medicinal drugs are tested on biochemical and clinical markers of aging. In addition, vitamin D supplementation is being investigated in two mega-trials (sample size> 5000) for its efficacy in reducing all-cause mortality.Expert opinion:Anti-aging effects of longevity drug candidates suggest, but do not demonstrate that they prolong life. The two megatrials with vitamin D supplementation make it possible to detect differences in life expectancy between vitamin D and placebo. Therefore, a protocol similar to that for vitamin D could be used to demonstrate pro-longevity effects of metformin, acarbose, and rapamycin.

Turning strains into strengths for understanding psychiatric disorders

There is a paucity in the development of new mechanistic insights and therapeutic approaches for treating psychiatric disease. One of the major challenges is reflected in the growing consensus that risk for these diseases is not determined by a single gene, but rather is polygenic, arising from the action and interaction of multiple genes. Canonically, experimental models in mice have been designed to ascertain the relative contribution of a single gene to a disease by systematic manipulation (e.g., mutation or deletion) of a known candidate gene. Because these studies have been largely carried out using inbred isogenic mouse strains, in which there is no (or very little) genetic diversity among subjects, it is difficult to identify unique allelic variants, gene modifiers, and epigenetic factors that strongly affect the nature and severity of these diseases. Here, we review various methods that take advantage of existing genetic diversity or that increase genetic variance in mouse models to (1) strengthen conclusions of single-gene function; (2) model diversity among human populations; and (3) dissect complex phenotypes that arise from the actions of multiple genes.

Naturally occurring osteoarthritis in male mice with an extended lifespan

Aim: The purpose of this study was to evaluate whether pharmacologic treatments or genotypes shown to prolong murine lifespan ameliorate the severity of age-associated osteoarthritis.Materials and Methods: Male UM-HET3 mice were fed diets containing 17-α-estradiol, acarbose, nordihydroguaiaretic acid, or control diet per the National Institute on Aging Interventions Testing Program (ITP) protocol. Findings were compared to genetically long-lived male Ames dwarf mice. Stifles were analyzed histologically with articular cartilage structure (ACS) and safranin O scoring as well as with quantitative histomorphometry.Results: Depending on the experimental group, ITP mice were between 450 and 1150 days old at the time of necropsy and 12-15 animals were studied per group. Two age groups (450 and 750 days) with 16-20 animals per group were used for Ames dwarf studies. No differences were found in the ACS or safranin O scores between treatment and control groups in the ITP study. There was high variability in most of the histologic outcome measures. For example, the older UM-HET3 controls had ACS scores of 6.1 ± 5.8 (mean±SD) and Saf O scores of 6.8 ± 5.6. Nevertheless, 17-α-estradiol mice had larger areas and widths of subchondral bone compared to controls, and dwarf mice had less subchondral bone area and width and less articular cartilage necrosis than non-dwarf controls.Conclusions: UM-HET3 mice developed age-related OA but with a high degree of variability and without a significant effect of the tested ITP treatments. High variability was also seen in the Ames dwarf mice but differences in several measures suggested some protection from OA.

Genetic cartography of longevity in humans and mice: Current landscape and horizons

Aging is a complex and highly variable process. Heritability of longevity among humans and other species is low, and this finding has given rise to the idea that it may be futile to search for DNA variants that modulate aging. We argue that the problem in mapping longevity genes is mainly one of low power and the genetic and environmental complexity of aging. In this review we highlight progress made in mapping genes and molecular networks associated with longevity, paying special attention to work in mice and humans. We summarize 40 years of linkage studies using murine cohorts and 15 years of studies in human populations that have exploited candidate gene and genome-wide association methods. A small but growing number of gene variants contribute to known longevity mechanisms, but a much larger set have unknown functions. We outline these and other challenges and suggest some possible solutions, including more intense collaboration between research communities that use model organisms and human cohorts. Once hundreds of gene variants have been linked to differences in longevity in mammals, it will become feasible to systematically explore gene-by-environmental interactions, dissect mechanisms with more assurance, and evaluate the roles of epistasis and epigenetics in aging. A deeper understanding of complex networks-genetic, cellular, physiological, and social-should position us well to improve healthspan.

Geroscience and the trans-NIH Geroscience Interest Group, GSIG

Age is by far the major risk factor for most chronic diseases. This has been common knowledge since time immemorial. Aging encompasses the biological changes most often seen as declines of function and increasing burden of disease. The close linkage of these two has led people to believe that aging, like age, is immutable. It is only recently that research into the basic molecular and cellular mechanisms of aging has led to potential interventions that increase lifespan and appear to increase healthspan, as well. Geroscience is an interdisciplinary field that aims to understand the relationship between the biology of aging and the biology of age-related diseases. The "geroscience hypothesis" posits that manipulation of aging will delay (in parallel) the appearance or severity of many chronic diseases because these diseases share the same underlying major risk factor (age). The hope is that this will lead to health improvements in the older population with perhaps greater efficiency than can be achieved through the successful cure and management of diseases of aging as they arise individually or as comorbidities.With those concepts in mind, the Geroscience Interest Group (GSIG) was launched as a trans-institute interest group within the NIH in November 2012. Here, we discuss the genesis of the trans-NIH group and the most salient activities that have occurred in the last 5 years.

Translational Geroscience: From invertebrate models to companion animal and human interventions

Translational geroscience is an interdisciplinary field descended from basic gerontology that seeks to identify, validate, and clinically apply interventions to maximize healthy, disease-free lifespan. In this review, we describe a research pipeline for the identification and validation of lifespan extending interventions. Beginning in invertebrate model systems, interventions are discovered and then characterized using other invertebrate model systems (evolutionary translation), models of genetic diversity, and disease models. Vertebrate model systems, particularly mice, can then be utilized to validate interventions in mammalian systems. Collaborative, multi-site efforts, like the Interventions Testing Program (ITP), provide a key resource to assess intervention robustness in genetically diverse mice. Mouse disease models provide a tool to understand the broader utility of longevity interventions. Beyond mouse models, we advocate for studies in companion pets. The Dog Aging Project is an exciting example of translating research in dogs, both to develop a model system and to extend their healthy lifespan as a goal in itself. Finally, we discuss proposed and ongoing intervention studies in humans, unmet needs for validating interventions in humans, and speculate on how differences in survival among human populations may influence intervention efficacy.

Health relevance of the modification of low grade inflammation in ageing (inflammageing) and the role of nutrition

Ageing of the global population has become a public health concern with an important socio-economic dimension. Ageing is characterized by an increase in the concentration of inflammatory markers in the bloodstream, a phenomenon that has been termed "inflammageing". The inflammatory response is beneficial as an acute, transient reaction to harmful conditions, facilitating the defense, repair, turnover and adaptation of many tissues. However, chronic and low grade inflammation is likely to be detrimental for many tissues and for normal functions. We provide an overview of low grade inflammation (LGI) and determine the potential drivers and the effects of the "inflamed" phenotype observed in the elderly. We discuss the role of gut microbiota and immune system crosstalk and the gut-brain axis. Then, we focus on major health complications associated with LGI in the elderly, including mental health and wellbeing, metabolic abnormalities and infections. Finally, we discuss the possibility of manipulating LGI in the elderly by nutritional interventions. We provide an overview of the evidence that exists in the elderly for omega-3 fatty acid, probiotic, prebiotic, antioxidant and polyphenol interventions as a means to influence LGI. We conclude that slowing, controlling or reversing LGI is likely to be an important way to prevent, or reduce the severity of, age-related functional decline and the onset of conditions affecting health and well-being; that there is evidence to support specific dietary interventions as a strategy to control LGI; and that a continued research focus on this field is warranted.

Drug repurposing for aging research using model organisms

Many increasingly prevalent diseases share a common risk factor: age. However, little is known about pharmaceutical interventions against aging, despite many genes and pathways shown to be important in the aging process and numerous studies demonstrating that genetic interventions can lead to a healthier aging phenotype. An important challenge is to assess the potential to repurpose existing drugs for initial testing on model organisms, where such experiments are possible. To this end, we present a new approach to rank drug-like compounds with known mammalian targets according to their likelihood to modulate aging in the invertebrates Caenorhabditis elegans and Drosophila. Our approach combines information on genetic effects on aging, orthology relationships and sequence conservation, 3D protein structures, drug binding and bioavailability. Overall, we rank 743 different drug-like compounds for their likelihood to modulate aging. We provide various lines of evidence for the successful enrichment of our ranking for compounds modulating aging, despite sparse public data suitable for validation. The top ranked compounds are thus prime candidates for in vivo testing of their effects on lifespan in C. elegans or Drosophila. As such, these compounds are promising as research tools and ultimately a step towards identifying drugs for a healthier human aging.

Nutrition, metabolism, and targeting aging in nonhuman primates

This short review focuses on the importance of nonhuman primate nutrition and aging studies and makes the case that a targeted expansion of the use of this highly translatable model would be advantageous to the biology of aging field. First, we describe the high degree of similarity of the model in terms of aging phenotypes including incidence and prevalence of common human age-related diseases. Second, we discuss the importance of the nonhuman primate nutrition and aging studies and the extent to which the outcomes of two ongoing long-term studies of caloric restriction are congruent with short-term equivalent studies in humans. Third, we showcase a number of pharmacological agents previously employed in nonhuman primate studies that display some potential as caloric restriction mimetics. Finally, we present nonhuman primates as an important model for translation of mechanisms of delayed aging identified in studies of shorter-lived animals. Proof of efficacy and safety of candidate longevity agents in nonhuman primates would be a cost-effective means to bring these exciting new avenues a step closer to clinical application.

Aging and Caloric Restriction Research: A Biological Perspective With Translational Potential

Aging as a research pursuit is fairly new compared with traditional lines of medical research. A growing field of investigators is focused on understanding how changes in tissue biology, physiology, and systemic homeostasis, conspire to create increased vulnerability to disease as a function of age. Aging research as a discipline is necessarily broad; in part because aging itself is multi-faceted and in part because different model systems are employed to define the underlying biology. In this review we outline aspects of aging research that are likely to uncover the pivotal events leading to age-related disease vulnerability. We focus on studies of human aging and discuss the value of research on caloric restriction, an intervention with proven efficacy in delaying aging. We propose that studies such as these will deliver target factors and processes that create vulnerability in human aging, an advance that would potentially be transformative in clinical care.

Impact of genetic background and experimental reproducibility on identifying chemical compounds with robust longevity effects

Limiting the debilitating consequences of ageing is a major medical challenge of our time. Robust pharmacological interventions that promote healthy ageing across diverse genetic backgrounds may engage conserved longevity pathways. Here we report results from the Caenorhabditis Intervention Testing Program in assessing longevity variation across 22 Caenorhabditis strains spanning 3 species, using multiple replicates collected across three independent laboratories. Reproducibility between test sites is high, whereas individual trial reproducibility is relatively low. Of ten pro-longevity chemicals tested, six significantly extend lifespan in at least one strain. Three reported dietary restriction mimetics are mainly effective across C. elegans strains, indicating species and strain-specific responses. In contrast, the amyloid dye ThioflavinT is both potent and robust across the strains. Our results highlight promising pharmacological leads and demonstrate the importance of assessing lifespans of discrete cohorts across repeat studies to capture biological variation in the search for reproducible ageing interventions.

Barriers to the Preclinical Development of Therapeutics that Target Aging Mechanisms

Through the progress of basic science research, fundamental mechanisms that contribute to age-related decline are being described with increasing depth and detail. Although these efforts have identified new drug targets and compounds that extend life span in model organisms, clinical trials of therapeutics that target aging processes remain scarce. Progress in aging research is hindered by barriers associated with the translation of basic science discoveries into the clinic. This report summarizes discussions held at a 2014 Geroscience Network retreat focused on identifying hurdles that currently impede the preclinical development of drugs targeting fundamental aging processes. From these discussions, it was evident that aging researchers have varied perceptions of the ideal preclinical pipeline. To forge a clear and cohesive path forward, several areas of controversy must first be resolved and new tools developed. Here, we focus on five key issues in preclinical drug development (drug discovery, lead compound development, translational preclinical biomarkers, funding, and integration between researchers and clinicians), expanding upon discussions held at the Geroscience Retreat and suggesting areas for further research. By bringing these findings to the attention of the aging research community, we hope to lay the foundation for a concerted preclinical drug development pipeline.

NIA's Intervention Testing Program at 10 years of age

The previous 20 years of basic research on aging has identified a large number of genes and gene products whose expression can be manipulated in a variety of ways to increase the healthy life span of animal models such as yeast, nematodes, fruit flies, and mice. In an overt attempt to capitalize on this information, the National Institute on Aging (NIA) began a program in 2003 to identify nutritional and pharmaceutical interventions that could be safely employed to extend the healthy life span of mice. This program is called the Intervention Testing Program (ITP), and this article briefly describes the development of this initiative and some of the early success achieved during its first 10 years (2004-2014) of operation.

Exploring the role of genetic variability and lifestyle in oxidative stress response for healthy aging and longevity

Oxidative stress is both the cause and consequence of impaired functional homeostasis characterizing human aging. The worsening efficiency of stress response with age represents a health risk and leads to the onset and accrual of major age-related diseases. In contrast, centenarians seem to have evolved conservative stress response mechanisms, probably derived from a combination of a diet rich in natural antioxidants, an active lifestyle and a favorable genetic background, particularly rich in genetic variants able to counteract the stress overload at the level of both nuclear and mitochondrial DNA. The integration of these factors could allow centenarians to maintain moderate levels of free radicals that exert beneficial signaling and modulator effects on cellular metabolism. Considering the hot debate on the efficacy of antioxidant supplementation in promoting healthy aging, in this review we gathered the existing information regarding genetic variability and lifestyle factors which potentially modulate the stress response at old age. Evidence reported here suggests that the integration of lifestyle factors (moderate physical activity and healthy nutrition) and genetic background could shift the balance in favor of the antioxidant cellular machinery by activating appropriate defense mechanisms in response to exceeding external and internal stress levels, and thus possibly achieving the prospect of living a longer life.

Methods of testing pharmacological drugs effects on aging and life span in mice

The methodology of testing antiaging drugs in laboratory mice is presented. It is based on more than 40-year-long authors' experience in the field and includes the selection of mouse strain, sex, age at start of treatment, housing conditions, design of the long-term study, some noninvasive methods of assessment of biomarkers of aging, life-span parameters, pathology examination, and statistical treatment of the results.

Diet and aging

Nutrition has important long-term consequences for health that are not only limited to the individual but can be passed on to the next generation. It can contribute to the development and progression of chronic diseases thus effecting life span. Caloric restriction (CR) can extend the average and maximum life span and delay the onset of age-associated changes in many organisms. CR elicits coordinated and adaptive stress responses at the cellular and whole-organism level by modulating epigenetic mechanisms (e.g., DNA methylation, posttranslational histone modifications), signaling pathways that regulate cell growth and aging (e.g., TOR, AMPK, p53, and FOXO), and cell-to-cell signaling molecules (e.g., adiponectin). The overall effect of these adaptive stress responses is an increased resistance to subsequent stress, thus delaying age-related changes and promoting longevity. In human, CR could delay many diseases associated with aging including cancer, diabetes, atherosclerosis, cardiovascular disease, and neurodegenerative diseases. As an alternative to CR, several CR mimetics have been tested on animals and humans. At present, the most promising alternatives to the use of CR in humans seem to be exercise, alone or in combination with reduced calorie intake, and the use of plant-derived polyphenol resveratrol as a food supplement.

National Institute on Aging at middle age--its past, present, and future

The National Institute on Aging (NIA) at the National Institutes of Health (NIH) leads the federal effort conducting and supporting research on aging. It is also designated as the lead within NIH for research on Alzheimer's disease. Since NIA's establishment in 1974, it has grown to a billion dollar enterprise featuring a balanced program of basic, clinical, and behavioral and social science. Investigator-initiated research and strategic investments have been critical to the NIA's success in bringing new insights and understandings to aging processes and diseases and conditions associated with advancing age. In recent years, constraints in the growth of resources have posed new challenges as the NIA and NIH leadership seek to maintain a robust and productive program. This article will review the history of the NIA, discuss current programs and priorities, and point to new directions in research, looking ahead.

Are sirtuins viable targets for improving healthspan and lifespan?

Although the increased lifespan of our populations illustrates the success of modern medicine, the risk of developing many diseases increases exponentially with old age. Caloric restriction is known to retard ageing and delay functional decline as well as the onset of disease in most organisms. Studies have implicated the sirtuins (SIRT1-SIRT7) as mediators of key effects of caloric restriction during ageing. Two unrelated molecules that have been shown to increase SIRT1 activity in some settings, resveratrol and SRT1720, are excellent protectors against metabolic stress in mammals, making SIRT1 a potentially appealing target for therapeutic interventions. This Review covers the current status and controversies surrounding the potential of sirtuins as novel pharmacological targets, with a focus on SIRT1.

[Biofunctional age diagnosis in humans. Potentials and limits]

The demand and requirements for valid, practicable, and reliable procedures for age diagnosis are increasing worldwide. In contrast, few studies and only a small number of procedures exist. The authors review the theoretical and methodological requirements for the development of models for age diagnostics. They describe the fundamentals for further studies, based on an analysis of current gerontological research in this area. A following publication will report the valid systems measuring vitality and biofunctional age(ing) of human beings.

Rodent models for the preclinical evaluation of drugs suitable for pharmacological intervention in aging

INTRODUCTION

There is a growing scientific and public interest in the development of new antiaging drugs for the purposes of extending mean and/or maximum life span, maintaining normal physiological function, and alleviating the onset and severity of age-associated diseases. This review looks at the current screening approaches used to evaluate the efficacy of such compounds, with a particular focus on those that extend life span.

AREAS COVERED

This article reviews the current preclinical approaches for assessing longevity therapy including the assessment of antiaging drugs (aging reversal) and geroprotectors (drugs that prevent premature aging and/or slowdown or postpone aging). This article also discusses the methods and the importance in evaluating the anticarcinogenic potential and safety of antitumor drugs.

EXPERT OPINION

Based on more than 30 years of experience in the field, the authors believe that the standard testing protocols for antiaging drugs should include the simultaneous evaluation of the drug's safety, as well as its antitumor and anticarcinogenic activity potential. The authors also believe that the principles of international programs for the expert critical evaluation of pharmacological interventions should be created to improve the range of antiaging interventions available for human studies.

Metallothionein and the biology of aging

Metallothionein (MT) is a low molecular weight protein with anti-apoptotic properties that has been demonstrated to scavenge free radicals in vitro. MT has not been extensively investigated within the context of aging biology. The purpose of this review, therefore, is to discuss findings on MT that are relevant to basic aging mechanisms and to draw attention to the possible role of MT in pro-longevity interventions. MT is one of just a handful of proteins that, when overexpressed, has been demonstrated to increase mouse lifespan. MT also protects against development of obesity in mice provided a high fat diet as well as diet-induced oxidative stress damage. Abundance of MT is responsive to caloric restriction (CR) and inhibition of the insulin/insulin-like signaling (IIS) pathway, and elevated MT gene expression has been observed in tissues from fasted and CR-fed mice, long-lived dwarf mice, worms maintained under CR conditions, and long-lived daf-2 mutant worms. The dysregulation of MT in these systems is likely to have tissue-specific effects on aging outcomes. Further investigation will therefore be needed to understand how MT contributes to the response of invertebrates and mice to CR and the endocrine mutations studied by aging researchers.

Rapamycin, but not resveratrol or simvastatin, extends life span of genetically heterogeneous mice

Rapamycin was administered in food to genetically heterogeneous mice from the age of 9 months and produced significant increases in life span, including maximum life span, at each of three test sites. Median survival was extended by an average of 10% in males and 18% in females. Rapamycin attenuated age-associated decline in spontaneous activity in males but not in females. Causes of death were similar in control and rapamycin-treated mice. Resveratrol (at 300 and 1200 ppm food) and simvastatin (12 and 120 ppm) did not have significant effects on survival in male or female mice. Further evaluation of rapamycin's effects on mice is likely to help delineate the role of the mammalian target of rapamycin complexes in the regulation of aging rate and age-dependent diseases and may help to guide a search for drugs that retard some or all of the diseases of aging.

Calorie restriction: what recent results suggest for the future of ageing research

BACKGROUND

Calorie Restriction (CR) research has expanded rapidly over the past few decades and CR remains the most highly reproducible, environmental intervention to improve health and extend lifespan in animal studies. Although many model organisms have consistently demonstrated positive responses to CR, it remains to be shown whether CR will extend lifespan in humans. Additionally, the current environment of excess caloric consumption and high incidence of overweight/obesity illustrate the improbable nature of the long-term adoption of a CR lifestyle by a significant proportion of the human population. Thus, the search for substances that can reproduce the beneficial physiologic responses of CR without a requisite calorie intake reduction, termed CR mimetics (CRMs), has gained momentum.

MATERIAL AND METHODS

Recent articles describing health and lifespan results of CR in nonhuman primates and short-term human studies are discussed. Additional consideration is given to the rapidly expanding search for CRMs.

RESULTS

The first results from a long-term, randomized, controlled CR study in nonhuman primates showing statistically significant benefits on longevity have now been reported. Additionally, positive results from short-term, randomized, controlled CR studies in humans are suggestive of potential health and longevity gains, while test of proposed CRMs (including rapamycin, resveratrol, 2-deoxyglucose and metformin) have shown both positive and mixed results in rodents.

CONCLUSION

Whether current positive results will translate into longevity gains for humans remains an open question. However, the apparent health benefits that have been observed with CR suggest that regardless of longevity gains, the promotion of healthy ageing and disease prevention may be attainable.

Dietary interventions to extend life span and health span based on calorie restriction

The societal impact of obesity, diabetes, and other metabolic disorders continues to rise despite increasing evidence of their negative long-term consequences on health span, longevity, and aging. Unfortunately, dietary management and exercise frequently fail as remedies, underscoring the need for the development of alternative interventions to successfully treat metabolic disorders and enhance life span and health span. Using calorie restriction (CR)-which is well known to improve both health and longevity in controlled studies-as their benchmark, gerontologists are coming closer to identifying dietary and pharmacological therapies that may be applicable to aging humans. This review covers some of the more promising interventions targeted to affect pathways implicated in the aging process as well as variations on classical CR that may be better suited to human adaptation.

Prospects for life span extension

Life expectancy has increased dramatically in the United States and in much of the world in recent years and decades. The factors underlying this increase are incompletely understood and are undoubtedly complex. A question that drives current research is whether life expectancy can be further extended using current knowledge of modifiable risk factors. A still more challenging research focus is on the possibility that life expectancy might be further increased through knowledge gained from studies of the basic biology of aging and its genetic and environmental modifiers.

Design of aging intervention studies: the NIA interventions testing program

The field of biogerontology has made great strides towards understanding the biological processes underlying aging, and the time is ripe to look towards applying this knowledge to the pursuit of aging interventions. Identification of safe, inexpensive, and non-invasive interventions that slow the aging process and promote healthy aging could have a significant impact on quality of life and health care expenditures for the aged. While there is a plethora of supplements and interventions on the market that purport to slow aging, the evidence to validate such claims is generally lacking. Here we describe the development of an aging interventions testing program funded by the National Institute on Aging (NIA) to test candidate interventions in a model system. The development of this program highlights the challenges of long-term intervention studies and provides approaches to cope with the stringent requirements of a multi-site testing program.

Identifying the changes in gene profiles regulating the amelioration of age-related oxidative damages in kidney tissue of rats by the intervention of adult-onset calorie restriction

This study was initiated to investigate gene expression profiles that are involved in the molecular mechanisms regulating the amelioration of age-related oxidative damages in male Fischer-344 rats (12 months) through adult-onset calorie restriction (CR) intervention for 6 months. The adult-onset CR was initiated with 10 and 25% restriction for the first and second weeks, respectively, and then maintained at 40% throughout the experiment. The adult-onset CR significantly (p < 0.05) decreased urinary 8-isoprostane and protein carbonyl in kidney for the markers of lipid peroxidation and protein oxidation, respectively, in rats from the CR group when compared with control group. Based on Yu's and Melk's methods, the age-related renal pathological changes in the kidney of rats from CR group were retarded by adult-onset CR. Such changes could result from the decrease of plasminogen activation inhibition-1 and clusterin and the increase of kallikrein mRNA expressions significantly (p < 0.05) in the kidneys of rats from the CR group. They were further confirmed by quantitative RT-PCR. Moreover, inflammatory response pathway was down-regulated significantly (p < 0.05) in rats from the CR group, while fatty acid synthesis, mitochondrial fatty acid betaoxidation, glycolysis, and gluconeogenesis were considerably up-regulated in kidney tissue of rats. In conclusion, the adult-onset CR could retard the age-related oxidative damages and renal pathological changes due to variations in gene expressions and biological pathways.

Nordihydroguaiaretic acid and aspirin increase lifespan of genetically heterogeneous male mice

The National Institute on Aging's Interventions Testing Program was established to evaluate agents that are purported to increase lifespan and delay the appearance of age-related disease in genetically heterogeneous mice. Up to five compounds are added to the study each year and each compound is tested at three test sites (The Jackson Laboratory, University of Michigan, and University of Texas Health Science Center at San Antonio). Mice in the first cohort were exposed to one of four agents: aspirin, nitroflurbiprofen, 4-OH-alpha-phenyl-N-tert-butyl nitrone, or nordihydroguaiaretic acid (NDGA). Sample size was sufficient to detect a 10% difference in lifespan in either sex,with 80% power, using data from two of the three sites. Pooling data from all three sites, a log-rank test showed that both NDGA (p=0.0006) and aspirin (p=0.01) led to increased lifespan of male mice. Comparison of the proportion of live mice at the age of 90% mortality was used as a surrogate for measurement of maximum lifespan;neither NDGA (p=0.12) nor aspirin (p=0.16) had a significant effect in this test. Measures of blood levels of NDGA or aspirin and its salicylic acid metabolite suggest that the observed lack of effects of NDGA or aspirin on life span in females could be related to gender differences in drug disposition or metabolism. Further studies are warranted to find whether NDGA or aspirin, over a range of doses,might prove to postpone death and various age-related outcomes reproducibly in mice.

An Aging Interventions Testing Program: study design and interim report

The National Institute on Aging's Interventions Testing Program (ITP) has developed a plan to evaluate agents that are considered plausible candidates for delaying rates of aging. Key features include: (i) use of genetically heterogeneous mice (a standardized four-way cross), (ii) replication at three test sites (the Jackson Laboratory, TJL; University of Michigan, UM; and University of Texas, UT), (iii) sufficient statistical power to detect 10% changes in lifespan, (iv) tests for age-dependent changes in T cell subsets and physical activity, and (v) an annual solicitation for collaborators who wish to suggest new interventions for evaluation. Mice in the first cohort were exposed to one of four agents: aspirin, nitroflurbiprofen (NFP), 4-OH-alpha-phenyl-N-tert-butyl nitrone (4-OH-PBN), or nordihydroguiaretic acid (NDGA). An interim analysis was conducted using survival data available on the date at which at least 50% of the male control mice had died at each test site. Survival of control males was significantly higher, at the interim time-point, at UM than at UT or TJL; all three sites had similar survival of control females. Males in the NDGA group had significantly improved survival (P = 0.0004), with significant effects noted at TJL (P < 0.01) and UT (P < 0.04). None of the other agents altered survival, although there was a suggestion (P = 0.07) of a beneficial effect of aspirin in males. More data will be needed to determine if any of these compounds can extend maximal lifespan, but the current data show that NDGA reduces early life mortality risks in genetically heterogeneous mice at multiple test sites.

Methods of evaluating the effect of pharmacological drugs on aging and life span in mice

The methodology of testing anti-aging drugs in laboratory mice is presented. It includes the selection of mouse strain, sex, age at start of treatment, housing conditions, design of the long-term study, some noninvasive methods of assessment, pathology examination, and statistical treatment of the results.

Profiling psychomotor and cognitive aging in four-way cross mice

In part due to their genetic uniformity and stable characteristics, inbred rodents or their F1 progeny are frequently used to study brain aging. However, it is recognized that focus on a single genotype could lead to generalizations about brain aging that might not apply to the species as a whole, or to the human population. As a potential alternative to uniform genotypes, genetically heterogeneous (HET) mice, produced by a four-way cross, were tested in the current study to determine if they exhibit age-related declines in cognitive and psychomotor function similar to other rodent models of brain aging. Young (4 months) and older (23 months) CB6F1 × C3D2F1 mice were administered a variety of tests for cognitive, psychomotor, and sensory/reflexive capacities. Spontaneous locomotion, rearing, and ability to turn in an alley all decreased with age, as did behavioral measures sensitive to muscle strength, balance, and motor coordination. Although no effect of age was found for either startle response amplitude or reaction time to shock stimuli, the old mice reacted with less force to low intensity auditory stimuli. When tested on a spatial swim maze task, the old mice learned less efficiently, exhibited poorer retention after a 66-h delay, and demonstrated greater difficulty learning a new spatial location. In addition, the older mice were less able to learn the platform location when it was identified by a local visual cue. Because there was a significant correlation between spatial and cued discrimination performance in the old mice, it is possible that age-related spatial maze learning deficits could involve visual or motor impairments. Variation among individuals increased with age for most tests of psychomotor function, as well as for spatial swim performance, suggesting that four-way cross mice may be appropriate models of individualized brain aging. However, the analysis of spatial maze learning deficits in older CB6F1 × C3D2F1 mice may have limited applicability in the study of brain aging, because of a confounding with visually cued performance deficits.

The potential for dietary restriction to increase longevity in humans: extrapolation from monkey studies

Based on results emerging from long-term studies of dietary restriction in rhesus monkeys, we offer our views regarding whether dietary restriction can increase longevity in humans. Because lifespan data in monkeys remain inconclusive currently, we respond that "we do not for sure". Based on the vast literature regarding the effects of healthy, low calorie diets on health and longevity in a wide range of species, including humans, and based on data emerging from monkey studies suggesting that dietary restriction improves markers of disease risk and health, we respond that "we think so." Because it is unlikely that an experimental study will ever be designed to address this question in humans, we respond that "we think we will never know for sure." We suggest that debate of this question is clearly an academic exercise; thus, we would suggest that the more compelling discussion should focus on whether basic mechanisms of DR can be discovered and if such discoveries can lead to the development of effective DR mimetics. Even if proof that DR or DR mimetics can increase longevity in humans will likely never emerge, we would suggest that endpoints regarding disease risk and disease incidence as well as maintenance of function can be examined in human clinical trials, and that these will be highly relevant for evaluating the effectiveness of such treatments.

Calorie restriction mimetics: an emerging research field

When considering all possible aging interventions evaluated to date, it is clear that calorie restriction (CR) remains the most robust. Studies in numerous species have demonstrated that reduction of calories 30-50% below ad libitum levels of a nutritious diet can increase lifespan, reduce the incidence and delay the onset of age-related diseases, improve stress resistance, and decelerate functional decline. A current major focus of this research area is whether this nutritional intervention is relevant to human aging. Evidence emerging from studies in rhesus monkeys suggests that their response to CR parallels that observed in rodents. To assess CR effects in humans, clinical trials have been initiated. However, even if results from these studies could eventually substantiate CR as an effective pro-longevity strategy for humans, the utility of this intervention would be hampered because of the degree and length of restriction required. As an alternative strategy, new research has focused on the development of 'CR mimetics'. The objective of this strategy is to identify compounds that mimic CR effects by targeting metabolic and stress response pathways affected by CR, but without actually restricting caloric intake. For example, drugs that inhibit glycolysis (2-deoxyglucose), enhance insulin action (metformin), or affect stress signaling pathways (resveratrol), are being assessed as CR mimetics (CRM). Promising results have emerged from initial studies regarding physiological responses which resemble those observed in CR (e.g. reduced body temperature and plasma insulin) as well as protection against neurotoxicity (e.g. enhanced dopamine action and up-regulated neurotrophic factors). Ultimately, lifespan analyses in addition to expanded toxicity studies must be accomplished to fully assess the potential of any CRM. Nonetheless, this strategy clearly offers a very promising and expanding research endeavor.

Exploiting the rodent model for studies on the pharmacology of lifespan extension

The rodent is a particularly valuable model with which to test therapeutic interventions for aging, as rodent physiology is close enough to human physiology to give the findings relevance for human aging, and it is small enough to allow for use of statistically robust sample sizes. There are many rodent models to choose from, with advantages and disadvantages to each. The choice of model system, as well as other experimental design decisions such as diet and housing, is extremely important for the success of lifespan studies. These issues are discussed in this review of the use of the rodent model. The National Institute on Aging (NIA) Interventions Testing Program, which has grappled with all of these issues, is described.

Twenty years of progress in biogerontology research

The first 10 years of NIA's existence were characterized by funding for descriptive and discovery research, as the field had not yet come of age. As Couzin expressed it in the July 1, 2005 issue of Science, "Just 2 or 3 decades ago, research on aging was a backwater" (Couzin J 2005 How much can human life span be extended. Science 309: 83). With the isolation of long-lived animal mutants and the application of the tools of molecular biology and transgenic technology to biogerontology research, the situation has changed dramatically since then, and aging research has become increasingly mechanistic and respectable. This transition has been aided by some well-thought out research initiatives by the NIA, and the purpose of this article is to provide a brief summary of the progress made in the past 20 years, and describe the part that NIA initiatives and funding have played in this transition.

Developing a Research Agenda in Biogerontology: Basic Mechanisms

The National Institute on Aging (NIA) began operation in 1975, splitting off from the National Institute of Child Health and Human Development. The first 10 years of NIA's existence were characterized by funding descriptive and discovery research, as the field by then had not come of age. With the isolation of long-lived animal mutants and the application of the tools of molecular biology (including whole-genome sequencing) and transgenic technology to biogerontology research, the situation has changed dramatically since then, and aging-related research has become increasingly mechanistic and respectable. This transition has been aided by research initiatives implemented by NIA staff, and the goal of this article is to describe how NIA develops such research initiatives using research progress made in biogerontology over the past 20 years as the basis for the discussion.

Lifelong aspirin supplementation as a means to extending life span

Arising from an initiative by the National Institute of Aging (NIA) requesting novel proposals challenged with increasing lifespan and longevity, our laboratory has generated a hypothesis to test the efficacy of lifelong, low-dosage aspirin administration as a means to achieving this goal. The intervention testing program (currently underway) proposing aspirin as an anti-aging agent evolved from the multitude of properties encompassed in aspirin and the potential of these attributes to prevent the cellular and functional declines, particularly from inflammatory and oxidative sources, evidenced to contribute to aging. Aspirin is a widely administered, cheap, anti-inflammatory, and antioxidant compound that has a variety of positive effects on the immune system and cardiovascular health. Notably, aspirin may affect oxidant production, cytokine responses, and block glycooxidation reactions, thus posing it as a triple threat against the symptoms of aging. Whether aging is molded by interplay between oxidative stress and inflammatory mediators has received little attention; however, we and other laboratories have explored this notion and have observed an elevated inflammatory status with age. Stemming from these observations and in view of the limited success of antioxidant therapies in improving lifespan in long-lived species, in this article we propose a protocol to examine life-long use of a very low dose anti-inflammatory compound such as aspirin to engage the inflammatory and endogenous oxidative insults accompanying aging and, in so doing, attempt to increase maximum and mean life span.

The Future of Aging Therapies

Advances in understanding aging processes and their consequences are leading to the development of therapies to slow or reverse adverse changes formerly considered to be "normal" aging and processes that underlie multiple age-related conditions. Estimating the effectiveness of candidate aging therapies, whose effects on human aging may require many years to determine, is a particular challenge. Strategies for identifying candidate interventions can be developed through multiple approaches, including the screening of molecular targets and pathways in vitro and in animal models, informed as well by evidence from human genetic and epidemiologic data. A number of recently established programs and networks can serve as resources for such research. For all these research approaches, from in vitro molecular studies to clinical trials, contributions of cell and molecular biology are crucial and offer the prospect of therapeutic advances that address fundamental biological processes as well as the clinically important challenges of aging.

Pitfalls of animal model systems in ageing research

Often, reports of anti-ageing research using animal models are overly optimistic and incomplete. Without having the details of the study (issues inherent with the animal models, the condition of the animal colony, the replicability of the findings, for example), even the educated public can find it difficult to interpret the reports accurately. This chapter provides background information about ageing research and animal models in general and arms readers with guidelines they can use to assist them when analyzing reports of ageing research using those models. The article also uses the guidelines to briefly evaluate three anti-ageing treatment candidates: one in the very early stages of testing (resveratrol), one that has been proven unfounded as an anti-ageing intervention by testing [dehydroepiandrosterone (DHEA)] and one that has undergone testing successfully (l-deprenyl).