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The National Institute on Aging Interventions Testing Program (ITP) has so far identified 12 compounds that extend the lifespan of genetically heterogeneous mice using the log-rank test. However, the log-rank test is relatively insensitive to any compound that does not uniformly reduce mortality across the lifespan. This test may thus miss compounds that only reduce mortality before midlife, for example, a plausible outcome if a compound only mitigates risk factors before midlife or if its efficacy is reduced at later ages. We therefore reanalyzed all data collected by the ITP from 2004-2022 using the Gehan test, which is more sensitive to mortality differences earlier in the life course and does not assume a uniformly reduced mortality hazard across the lifespan. The Gehan test identified 5 additional compounds, metformin, enalapril, 17-dimethylaminoethylamino-17-demethoxygeldanamycin hydrochloride (17-DMAG), caffeic acid phenethyl ester (CAPE), and green tea extract (GTE), which significantly increased survival but were previously missed by the log-rank test. Three (metformin, enalapril, and 17-DMAG) were only effective in males and two (CAPE and GTE) were only effective in females. In addition, 1,3-butanediol, which by log-rank analysis increased survival in females but not males, increased survival in males by the Gehan test. These results suggest that statistical tests sensitive to non-uniformity of drug efficacy across the lifespan should be included in the standard statistical testing protocol to minimize overlooking geroprotective interventions., (© 2024. The Author(s).)

Genetically heterogeneous UM-HET3 mice born in 2020 were used to test possible lifespan effects of alpha-ketoglutarate (AKG), 2,4-dinitrophenol (DNP), hydralazine (HYD), nebivolol (NEBI), 16α-hydroxyestriol (OH_Est), and sodium thiosulfate (THIO), and to evaluate the effects of canagliflozin (Cana) when started at 16 months of age. OH_Est produced a 15% increase (p = 0.0001) in median lifespan in males but led to a significant (7%) decline in female lifespan. Cana, started at 16 months, also led to a significant increase (14%, p = 0.004) in males and a significant decline (6%, p = 0.03) in females. Cana given to mice at 6 months led, as in our previous study, to an increase in male lifespan without any change in female lifespan, suggesting that this agent may lead to female-specific late-life harm. We found that blood levels of Cana were approximately 20-fold higher in aged females than in young males, suggesting a possible mechanism for the sex-specific disparities in its effects. NEBI was also found to produce a female-specific decline (4%, p = 0.03) in lifespan. None of the other tested drugs provided a lifespan benefit in either sex. These data bring to 7 the list of ITP-tested drugs that induce at least a 10% lifespan increase in one or both sexes, add a fourth drug with demonstrated mid-life benefits on lifespan, and provide a testable hypothesis that might explain the sexual dimorphism in lifespan effects of the SGLT2 inhibitor Cana., (© 2024. The Author(s), under exclusive licence to American Aging Association.)

In genetically heterogeneous (UM-HET3) mice produced by the CByB6F1 × C3D2F1 cross, the Nrf2 activator astaxanthin (Asta) extended the median male lifespan by 12% (p = 0.003, log-rank test), while meclizine (Mec), an mTORC1 inhibitor, extended the male lifespan by 8% (p = 0.03). Asta was fed at 1840 ± 520 (9) ppm and Mec at 544 ± 48 (9) ppm, stated as mean ± SE (n) of independent diet preparations. Both were started at 12 months of age. The 90th percentile lifespan for both treatments was extended in absolute value by 6% in males, but neither was significant by the Wang-Allison test. Five other new agents were also tested as follows: fisetin, SG1002 (hydrogen sulfide donor), dimethyl fumarate, mycophenolic acid, and 4-phenylbutyrate. None of these increased lifespan significantly at the dose and method of administration tested in either sex. Amounts of dimethyl fumarate in the diet averaged 35% of the target dose, which may explain the absence of lifespan effects. Body weight was not significantly affected in males by any of the test agents. Late life weights were lower in females fed Asta and Mec, but lifespan was not significantly affected in these females. The male-specific lifespan benefits from Asta and Mec may provide insights into sex-specific aspects of aging., (© 2023. The Author(s).)

Sex differences in aging and longevity have been widely observed, with females consistently outliving males across human populations. However, the mechanisms driving these disparities remain poorly understood. In this study, we explored the influence of post-pubertal testicular effects on sex differences in aging by prepubertally castrating genetically heterogeneous (UM-HET3) mice, a unique mouse model that emulates human sex differences in age-related mortality. Prepubertal castration eliminated the longevity disparity between sexes by reducing the elevated early- to mid-life mortality rate observed in males and extending their median lifespan to match that of females. Additionally, castration extended the duration of body weight growth and attenuated the inverse correlation between early-age body weight and lifespan in males, aligning their growth trajectories with those of females. Our findings suggest that post-pubertal testicular actions in genetically diverse mice are primarily responsible for sex differences in longevity as well as growth trajectories. These findings offer a foundation for further investigation into the fundamental mechanisms driving sex-specific aging patterns and the development of potential pro-longevity interventions., (© 2023 The Authors. Aging Cell published by Anatomical Society and John Wiley & Sons Ltd.)

DNA variants that modulate life span provide insight into determinants of health, disease, and aging. Through analyses in the UM-HET3 mice of the Interventions Testing Program (ITP), we detected a sex-independent quantitative trait locus (QTL) on chromosome 12 and identified sex-specific QTLs, some of which we detected only in older mice. Similar relations between life history and longevity were uncovered in mice and humans, underscoring the importance of early access to nutrients and early growth. We identified common age- and sex-specific genetic effects on gene expression that we integrated with model organism and human data to create a hypothesis-building interactive resource of prioritized longevity and body weight genes. Finally, we validated Hipk1 , Ddost , Hspg2 , Fgd6 , and Pdk1 as conserved longevity genes using Caenorhabditis elegans life-span experiments.

In genetically heterogeneous mice produced by the CByB6F1 x C3D2F1 cross, the "non-feminizing" estrogen, 17-α-estradiol (17aE2), extended median male lifespan by 19% (p < 0.0001, log-rank test) and 11% (p = 0.007) when fed at 14.4 ppm starting at 16 and 20 months, respectively. 90th percentile lifespans were extended 7% (p = 0.004, Wang-Allison test) and 5% (p = 0.17). Body weights were reduced about 20% after starting the 17aE2 diets. Four other interventions were tested in males and females: nicotinamide riboside, candesartan cilexetil, geranylgeranylacetone, and MIF098. Despite some data suggesting that nicotinamide riboside would be effective, neither it nor the other three increased lifespans significantly at the doses tested. The 17aE2 results confirm and extend our original reports, with very similar results when started at 16 months compared with mice started at 10 months of age in a prior study. The consistently large lifespan benefit in males, even when treatment is started late in life, may provide information on sex-specific aspects of aging., (© 2021 The Authors. Aging Cell published by the Anatomical Society and John Wiley & Sons Ltd.)

Canagliflozin (Cana) is an FDA-approved diabetes drug that protects against cardiovascular and kidney diseases. It also inhibits the sodium glucose transporter 2 by blocking renal reuptake and intestinal absorption of glucose. In the context of the mouse Interventions Testing Program, genetically heterogeneous mice were given chow containing Cana at 180 ppm at 7 months of age until their death. Cana extended median survival of male mice by 14%. Cana also increased by 9% the age for 90th percentile survival, with parallel effects seen at each of 3 test sites. Neither the distribution of inferred cause of death nor incidental pathology findings at end-of-life necropsies were altered by Cana. Moreover, although no life span benefits were seen in female mice, Cana led to lower fasting glucose and improved glucose tolerance in both sexes, diminishing fat mass in females only. Therefore, the life span benefit of Cana is likely to reflect blunting of peak glucose levels, because similar longevity effects are seen in male mice given acarbose, a diabetes drug that blocks glucose surges through a distinct mechanism, i.e., slowing breakdown of carbohydrate in the intestine. Interventions that control daily peak glucose levels deserve attention as possible preventive medicines to protect from a wide range of late-life neoplastic and degenerative diseases.

To see if variations in timing of rapamycin (Rapa), administered to middle aged mice starting at 20 months, would lead to different survival outcomes, we compared three dosing regimens. Initiation of Rapa at 42 ppm increased survival significantly in both male and female mice. Exposure to Rapa for a 3-month period led to significant longevity benefit in males only. Protocols in which each month of Rapa treatment was followed by a month without Rapa exposure were also effective in both sexes, though this approach was less effective than continuous exposure in female mice. Interpretation of these results is made more complicated by unanticipated variation in patterns of weight gain, prior to the initiation of the Rapa treatment, presumably due to the use of drug-free food from two different suppliers. The experimental design included tests of four other drugs, minocycline, β-guanidinopropionic acid, MitoQ, and 17-dimethylaminoethylamino-17-demethoxygeldanamycin (17-DMAG), but none of these led to a change in survival in either sex., (© 2020 The Authors. Aging Cell published by the Anatomical Society and John Wiley & Sons Ltd.)

Mammalian aging is associated with reduced tissue regeneration and loss of physiological integrity. With age, stem cells diminish in their ability to regenerate adult tissues, likely contributing to age-related morbidity. Thus, we replaced aged hematopoietic stem cells (HSCs) with young-donor HSCs using a novel mobilization-enabled hematopoietic stem cell transplantation (HSCT) technology as an alternative to the highly toxic conditioning regimens used in conventional HSCT. Using this approach, we are the first to report an increase in median lifespan (12%) and a decrease in overall mortality hazard (HR: 0.42, CI: 0.273-0.638) in aged mice following transplantation of young-donor HSCs. The increase in longevity was accompanied by reductions of frailty measures and increases in food intake and body weight of aged recipients. Young-donor HSCs not only preserved youthful function within the aged bone marrow stroma, but also at least partially ameliorated dysfunctional hematopoietic phenotypes of aged recipients. This compelling evidence that mammalian health and lifespan can be extended through stem cell therapy adds a new category to the very limited list of successful anti-aging/life-extending interventions. Our findings have implications for further development of stem cell therapies for increasing health and lifespan., (© 2020 The Authors. Aging Cell published by the Anatomical Society and John Wiley & Sons Ltd.)

Diets low in methionine extend lifespan of rodents, though through unknown mechanisms. Glycine can mitigate methionine toxicity, and a small prior study has suggested that supplemental glycine could extend lifespan of Fischer 344 rats. We therefore evaluated the effects of an 8% glycine diet on lifespan and pathology of genetically heterogeneous mice in the context of the Interventions Testing Program. Elevated glycine led to a small (4%-6%) but statistically significant lifespan increase, as well as an increase in maximum lifespan, in both males (p = 0.002) and females (p < 0.001). Pooling across sex, glycine increased lifespan at each of the three independent sites, with significance at p = 0.01, 0.053, and 0.03, respectively. Glycine-supplemented females were lighter than controls, but there was no effect on weight in males. End-of-life necropsies suggested that glycine-treated mice were less likely than controls to die of pulmonary adenocarcinoma (p = 0.03). Of the 40 varieties of incidental pathology evaluated in these mice, none were increased to a significant degree by the glycine-supplemented diet. In parallel analyses of the same cohort, we found no benefits from TM5441 (an inhibitor of PAI-1, the primary inhibitor of tissue and urokinase plasminogen activators), inulin (a source of soluble fiber), or aspirin at either of two doses. Our glycine results strengthen the idea that modulation of dietary amino acid levels can increase healthy lifespan in mice, and provide a foundation for further investigation of dietary effects on aging and late-life diseases., (© 2019 The Authors. Aging Cell published by the Anatomical Society and John Wiley & Sons Ltd.)

The female survival advantage is a robust characteristic of human longevity. However, underlying mechanisms are not understood, and rodent models exhibiting a female advantage are lacking. Here, we report that the genetically heterogeneous (UM-HET3) mice used by the National Institute on Aging Interventions Testing Program (ITP) are such a model. Analysis of age-specific survival of 3,690 control ITP mice revealed a female survival advantage paralleling that of humans. As in humans, the female advantage in mice was greatest in early adulthood, peaking around 350 days of age and diminishing progressively thereafter. This persistent finding was observed at three geographically distinct sites and in six separate cohorts over a 10-year period. Because males weigh more than females and bodyweight is often inversely related to lifespan, we examined sex differences in the relationship between bodyweight and survival. Although present in both sexes, the inverse relationship between bodyweight and longevity was much stronger in males, indicating that male mortality is more influenced by bodyweight than is female mortality. In addition, male survival varied more across site and cohort than female survival, suggesting greater resistance of females to environmental modulators of survival. Notably, at 24 months the relationship between bodyweight and longevity shifted from negative to positive in both sexes, similar to the human condition in advanced age. These results indicate that the UM-HET3 mouse models the human female survival advantage and provide evidence for greater resilience of females to modulators of survival., (© 2019 The Authors. Aging Cell published by the Anatomical Society and John Wiley & Sons Ltd.)

To follow-up on our previous report that acarbose (ACA), a drug that blocks postprandial glucose spikes, increases mouse lifespan, we studied ACA at three doses: 400, 1,000 (the original dose), and 2,500 ppm, using genetically heterogeneous mice at three sites. Each dose led to a significant change (by log-rank test) in both sexes, with larger effects in males, consistent with the original report. There were no significant differences among the three doses. The two higher doses produced 16% or 17% increases in median longevity of males, but only 4% or 5% increases in females. Age at the 90th percentile was increased significantly (8%-11%) in males at each dose, but was significantly increased (3%) in females only at 1,000 ppm. The sex effect on longevity is not explained simply by weight or fat mass, which were reduced by ACA more in females than in males. ACA at 1,000 ppm reduced lung tumors in males, diminished liver degeneration in both sexes and glomerulosclerosis in females, reduced blood glucose responses to refeeding in males, and improved rotarod performance in aging females, but not males. Three other interventions were also tested: ursolic acid, 2-(2-hydroxyphenyl) benzothiazole (HBX), and INT-767; none of these affected lifespan at the doses tested. The acarbose results confirm and extend our original report, prompt further attention to the effects of transient periods of high blood glucose on aging and the diseases of aging, including cancer, and should motivate studies of acarbose and other glucose-control drugs in humans., (© 2019 The Authors. Aging Cell published by the Anatomical Society and John Wiley & Sons Ltd.)

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., (Copyright © 2018 Elsevier B.V. All rights reserved.)

The National Institute on Aging Interventions Testing Program (ITP) evaluates agents hypothesized to increase healthy lifespan in genetically heterogeneous mice. Each compound is tested in parallel at three sites, and all results are published. We report the effects of lifelong treatment of mice with four agents not previously tested: Protandim, fish oil, ursodeoxycholic acid (UDCA) and metformin - the latter with and without rapamycin, and two drugs previously examined: 17-α-estradiol and nordihydroguaiaretic acid (NDGA), at doses greater and less than used previously. 17-α-estradiol at a threefold higher dose robustly extended both median and maximal lifespan, but still only in males. The male-specific extension of median lifespan by NDGA was replicated at the original dose, and using doses threefold lower and higher. The effects of NDGA were dose dependent and male specific but without an effect on maximal lifespan. Protandim, a mixture of botanical extracts that activate Nrf2, extended median lifespan in males only. Metformin alone, at a dose of 0.1% in the diet, did not significantly extend lifespan. Metformin (0.1%) combined with rapamycin (14 ppm) robustly extended lifespan, suggestive of an added benefit, based on historical comparison with earlier studies of rapamycin given alone. The α-glucosidase inhibitor, acarbose, at a concentration previously tested (1000 ppm), significantly increased median longevity in males and 90th percentile lifespan in both sexes, even when treatment was started at 16 months. Neither fish oil nor UDCA extended lifespan. These results underscore the reproducibility of ITP longevity studies and illustrate the importance of identifying optimal doses in lifespan studies., (© 2016 The Authors. Aging Cell published by the Anatomical Society and John Wiley & Sons Ltd.)

Rapamycin, an inhibitor of mTOR kinase, increased median lifespan of genetically heterogeneous mice by 23% (males) to 26% (females) when tested at a dose threefold higher than that used in our previous studies; maximal longevity was also increased in both sexes. Rapamycin increased lifespan more in females than in males at each dose evaluated, perhaps reflecting sexual dimorphism in blood levels of this drug. Some of the endocrine and metabolic changes seen in diet-restricted mice are not seen in mice exposed to rapamycin, and the pattern of expression of hepatic genes involved in xenobiotic metabolism is also quite distinct in rapamycin-treated and diet-restricted mice, suggesting that these two interventions for extending mouse lifespan differ in many respects., (© 2014 The Authors. Aging Cell published by the Anatomical Society and John Wiley & Sons Ltd.)

Four agents--acarbose (ACA), 17-α-estradiol (EST), nordihydroguaiaretic acid (NDGA), and methylene blue (MB)--were evaluated for lifespan effects in genetically heterogeneous mice tested at three sites. Acarbose increased male median lifespan by 22% (P < 0.0001), but increased female median lifespan by only 5% (P = 0.01). This sexual dimorphism in ACA lifespan effect could not be explained by differences in effects on weight. Maximum lifespan (90th percentile) increased 11% (P < 0.001) in males and 9% (P = 0.001) in females. EST increased male median lifespan by 12% (P = 0.002), but did not lead to a significant effect on maximum lifespan. The benefits of EST were much stronger at one test site than at the other two and were not explained by effects on body weight. EST did not alter female lifespan. NDGA increased male median lifespan by 8-10% at three different doses, with P-values ranging from 0.04 to 0.005. Females did not show a lifespan benefit from NDGA, even at a dose that produced blood levels similar to those in males, which did show a strong lifespan benefit. MB did not alter median lifespan of males or females, but did produce a small, statistically significant (6%, P = 0.004) increase in female maximum lifespan. These results provide new pharmacological models for exploring processes that regulate the timing of aging and late-life diseases, and in particular for testing hypotheses about sexual dimorphism in aging and health., (© 2013 The Authors. Aging Cell published by the Anatomical Society and John Wiley & Sons Ltd.)

Dietary restriction (DR) extends lifespan in a wide range of animal models. A major obstacle to understanding how DR modulates lifespan and aging-related dysfunction is the multiplicity of physiological and molecular changes associated with DR. Unraveling their importance to the longevity effect of DR remains a major challenge. In this perspective, we review the marked genetic variation in the response to DR of multiple recombinant inbred (RI) mouse strains. We illustrate how this genetic variation can be exploited to probe the mechanisms mediating lifespan extension by DR, as well as uncover its limits as an intervention. RI strains exhibit marked variation in their lifespan as well as physiological responses to DR. Quantitative genetic and statistical tools can use this phenotypic variation to probe the importance of physiological and molecular changes that have been hypothesized to play roles in DR-mediated lifespan extension., (Copyright © 2013 Elsevier Inc. All rights reserved.)

The National Institute on Aging Interventions Testing Program (ITP) was established to evaluate agents that are hypothesized to increase life span and/or health span in genetically heterogeneous mice. Each compound is tested in parallel at three test sites. It is the goal of the ITP to publish all results, negative or positive. We report here on the results of lifelong treatment of mice, beginning at 4 months of age, with each of five agents, that is, green tea extract (GTE), curcumin, oxaloacetic acid, medium-chain triglyceride oil, and resveratrol, on the life span of genetically heterogeneous mice. Each agent was administered beginning at 4 months of age. None of these five agents had a statistically significant effect on life span of male or female mice, by log-rank test, at the concentrations tested, although a secondary analysis suggested that GTE might diminish the risk of midlife deaths in females only.

Interference in insulin and/or insulin-like growth factor 1 (IGF-1) signaling can extend invertebrate life span, and interference in IGF-1 signaling can extend murine life span. Whether interference with murine insulin signaling, which can be diabetogenic and pathological, is also life-extending is controversial. We therefore measured life span in 3 murine strains genetically modified to reduce or increase insulin sensitivity. Mice with reduced insulin sensitivity were hemizygous for a null mutation in the insulin receptor (insulin receptor knockout mice; IRKO(+/-)). Mice with increased insulin sensitivity either had a null mutation of protein tyrosine phosphatase 1B (PTP-1B(-/-)) or overexpressed Peroxisome proliferator-activated receptor-α coactivator (PGC)-1α (PGC-1α(TG)). Life span of insulin insensitive IRKO(+/) mice was increased (males) or unaffected (females). Life spans of mice with increased insulin sensitivity were shortened overall (PTP-1B(-/-) mice) or partially (PGC-1α(TG): survival at the 25th percentile was reduced). These results show that insulin sensitivity in some murine genotypes is inversely related to longevity and provide further evidence for evolutionary conservation of this pathway as a modulator of longevity.

Dietary restriction (DR), one of the most robust life-extending manipulations, is usually associated with reduced adiposity. This reduction is hypothesized to be important in the life-extending effect of DR, because excess adiposity is associated with metabolic and age-related disease. Previously, we described remarkable variation in the lifespan response of 41 recombinant inbred strains of mice to DR, ranging from life extension to life shortening. Here, we used this variation to determine the relationship of lifespan modulation under DR to fat loss. Across strains, DR life extension correlated inversely with fat reduction, measured at midlife (males, r= -0.41, P<0.05, n=38 strains; females, r= -0.63, P<0.001, n=33 strains) and later ages. Thus, strains with the least reduction in fat were more likely to show life extension, and those with the greatest reduction were more likely to have shortened lifespan. We identified two significant quantitative trait loci (QTLs) affecting fat mass under DR in males but none for lifespan, precluding the confirmation of these loci as coordinate modulators of adiposity and longevity. Our data also provide evidence for a QTL previously shown to affect fuel efficiency under DR. In summary, the data do not support an important role for fat reduction in life extension by DR. They suggest instead that factors associated with maintaining adiposity are important for survival and life extension under DR., (© 2011 The Authors. Aging Cell © 2011 Blackwell Publishing Ltd/Anatomical Society of Great Britain and Ireland.)

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.

Dietary restriction (DR) has been used for decades to retard aging in rodents, but its mechanism of action remains an enigma. A principal roadblock has been that DR affects many different processes, making it difficult to distinguish cause and effect. To address this problem, we applied a quantitative genetics approach utilizing the ILSXISS series of mouse recombinant inbred strains. Across 42 strains, mean female lifespan ranged from 380 to 1070days on DR (fed 60% of ad libitum [AL]) and from 490 to 1020days on an AL diet. Longevity under DR and AL is under genetic control, showing 34% and 36% heritability, respectively. There was no correlation between lifespans on DR and AL; thus different genes modulate longevity under the two regimens. DR lifespans are significantly correlated with female fertility after return to an AL diet after various periods of DR (R=0.44, P=0.006). We assessed fuel efficiency (FE, ability to maintain growth and body weight independent of absolute food intake) using a multivariate approach and found it to be correlated with longevity and female fertility, suggesting possible causality. We found several quantitative trait loci responsible for these traits, mapping to chromosomes 7, 9, and 15. We present a metabolic model in which the anti-aging effects of DR are consistent with the ability to efficiently utilize dietary resources., (Copyright 2010 Elsevier Inc. All rights reserved.)

Chronic dietary restriction (DR) is considered among the most robust life-extending interventions, but several reports indicate that DR does not always extend and may even shorten lifespan in some genotypes. An unbiased genetic screen of the lifespan response to DR has been lacking. Here, we measured the effect of one commonly used level of DR (40% reduction in food intake) on mean lifespan of virgin males and females in 41 recombinant inbred strains of mice. Mean strain-specific lifespan varied two to threefold under ad libitum (AL) feeding and 6- to 10-fold under DR, in males and females respectively. Notably, DR shortened lifespan in more strains than those in which it lengthened life. Food intake and female fertility varied markedly among strains under AL feeding, but neither predicted DR survival: therefore, strains in which DR shortened lifespan did not have low food intake or poor reproductive potential. Finally, strain-specific lifespans under DR and AL feeding were not correlated, indicating that the genetic determinants of lifespan under these two conditions differ. These results demonstrate that the lifespan response to a single level of DR exhibits wide variation amenable to genetic analysis. They also show that DR can shorten lifespan in inbred mice. Although strains with shortened lifespan under 40% DR may not respond negatively under less stringent DR, the results raise the possibility that life extension by DR may not be universal.

Inhibition of the TOR signalling pathway by genetic or pharmacological intervention extends lifespan in invertebrates, including yeast, nematodes and fruitflies; however, whether inhibition of mTOR signalling can extend lifespan in a mammalian species was unknown. Here we report that rapamycin, an inhibitor of the mTOR pathway, extends median and maximal lifespan of both male and female mice when fed beginning at 600 days of age. On the basis of age at 90% mortality, rapamycin led to an increase of 14% for females and 9% for males. The effect was seen at three independent test sites in genetically heterogeneous mice, chosen to avoid genotype-specific effects on disease susceptibility. Disease patterns of rapamycin-treated mice did not differ from those of control mice. In a separate study, rapamycin fed to mice beginning at 270 days of age also increased survival in both males and females, based on an interim analysis conducted near the median survival point. Rapamycin may extend lifespan by postponing death from cancer, by retarding mechanisms of ageing, or both. To our knowledge, these are the first results to demonstrate a role for mTOR signalling in the regulation of mammalian lifespan, as well as pharmacological extension of lifespan in both genders. These findings have implications for further development of interventions targeting mTOR for the treatment and prevention of age-related diseases.

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.

This study examined the effect of housing density on the longevity-extending and disease-delaying actions of calorie restriction (CR). Singly or multiply housed (four per cage) mice were either fed ad libitum (AL) or were on CR beginning at 2 months. All CR mice were fed 40% less food than were multiply housed AL mice. CR increased median longevity by 19%, and housing density had no effect on this increase. CR also reduced neoplastic lesions in both housing groups, but lymphoma, the most common neoplasm, was reduced more in singly than in multiply housed mice. Singly housed AL mice ate 40% more food than did multiply housed AL mice, but weighed the same and lived as long as multiply housed AL mice. These results indicate that CR can extend life span as effectively in multiply as in singly housed mice, even though housing density can differentially affect the cancer-reducing effect of CR.

Since 1996, seven genetic mouse models have been reported to show increased lifespan: Ames and Snell dwarf mice, the 'little mouse' (Ghrhr(lit/lit)), mice null for either growth hormone receptor/binding protein (GHR/BP(-/-)) or p66(shc) (p66(shc-/-)), mice heterozygous for the IGF-I receptor (Igf1r(+/-)), and fat-specific insulin receptor knockout mice. In this article, we describe and evaluate these mouse models with respect to their relevance for aging studies. While these seven genetic models all show a significant increase in lifespan, issues of sample size and animal husbandry procedures require further evaluation before firm conclusions can be drawn on the reproducibility of life extension in most of these mouse models. Because data on the age-related pathology and physiological functions are lacking for all of the models, except the dwarf mice, it is too early to conclude that aging is retarded in these mouse models. However, these mouse models are already providing new information about the mechanism underlying mammalian aging.

This article discusses the importance of understanding sex differences in aging and how it can contribute to developing policies that promote healthier and more meaningful lives for older individuals. The article highlights the need for research on sex differences in aging, both in biological mechanisms and environmental and cultural factors. It introduces a genetically diverse mouse model that exhibits sex differences in longevity and resilience, which can be used to study the underlying biological mechanisms. The article also discusses the sex differences in the response to geroprotective therapies and emphasizes the need for considering sex as a critical variable in research and policy development. [Extracted from the article]

Chronic dietary restriction (DR) is considered among the most robust life-extending interventions, but several reports indicate that DR does not always extend and may even shorten lifespan in some genotypes. An unbiased genetic screen of the lifespan response to DR has been lacking. Here, we measured the effect of one commonly used level of DR (40% reduction in food intake) on mean lifespan of virgin males and females in 41 recombinant inbred strains of mice. Mean strain-specific lifespan varied two to threefold under ad libitum (AL) feeding and 6- to 10-fold under DR, in males and females respectively. Notably, DR shortened lifespan in more strains than those in which it lengthened life. Food intake and female fertility varied markedly among strains under AL feeding, but neither predicted DR survival: therefore, strains in which DR shortened lifespan did not have low food intake or poor reproductive potential. Finally, strain-specific lifespans under DR and AL feeding were not correlated, indicating that the genetic determinants of lifespan under these two conditions differ. These results demonstrate that the lifespan response to a single level of DR exhibits wide variation amenable to genetic analysis. They also show that DR can shorten lifespan in inbred mice. Although strains with shortened lifespan under 40% DR may not respond negatively under less stringent DR, the results raise the possibility that life extension by DR may not be universal. [ABSTRACT FROM AUTHOR]

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-α-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. [ABSTRACT FROM AUTHOR]