Research on the biology of NAD+ has been gaining momentum, providing many critical insights into the pathogenesis of age-associated functional decline and diseases. In particular, two key NAD+ ...intermediates, nicotinamide riboside (NR) and nicotinamide mononucleotide (NMN), have been extensively studied over the past several years. Supplementing these NAD+ intermediates has shown preventive and therapeutic effects, ameliorating age-associated pathophysiologies and disease conditions. Although the pharmacokinetics and metabolic fates of NMN and NR are still under intensive investigation, these NAD+ intermediates can exhibit distinct behavior, and their fates appear to depend on the tissue distribution and expression levels of NAD+ biosynthetic enzymes, nucleotidases, and presumptive transporters for each. A comprehensive concept that connects NAD+ metabolism to the control of aging and longevity in mammals has been proposed, and the stage is now set to test whether these exciting preclinical results can be translated to improve human health.
NAD+ is increasingly being recognized to play an important role in the pathogenesis of age-associated functional decline and diseases. Two key NAD+ intermediates, nicotinamide riboside (NR) and nicotinamide mononucleotide (NMN), have been instrumental in driving recent discoveries. We discuss key findings and future therapeutic and translational potential for these molecules.
Resveratrol is a natural compound suggested to have beneficial health effects. However, people are consuming resveratrol for this reason without having the adequate scientific evidence for its ...effects in humans. Therefore, scientific valid recommendations concerning the human intake of resveratrol based on available published scientific data are necessary. Such recommendations were formulated after the Resveratrol 2010 conference, held in September 2010 in Helsingør, Denmark.
Literature search in databases as PUBMED and ISI Web of Science in combination with manual search was used to answer the following five questions: (1)Can resveratrol be recommended in the prevention or treatment of human diseases?; (2)Are there observed "side effects" caused by the intake of resveratrol in humans?; (3)What is the relevant dose of resveratrol?; (4)What valid data are available regarding an effect in various species of experimental animals?; (5)Which relevant (overall) mechanisms of action of resveratrol have been documented?
The overall conclusion is that the published evidence is not sufficiently strong to justify a recommendation for the administration of resveratrol to humans, beyond the dose which can be obtained from dietary sources. On the other hand, animal data are promising in prevention of various cancer types, coronary heart diseases and diabetes which strongly indicate the need for human clinical trials. Finally, we suggest directions for future research in resveratrol regarding its mechanism of action and its safety and toxicology in human subjects.
Resveratrol, a constituent of red wine, has long been suspected to have cardioprotective effects. Interest in this compound has been renewed in recent years, first from its identification as a ...chemopreventive agent for skin cancer, and subsequently from reports that it activates sirtuin deacetylases and extends the lifespans of lower organisms. Despite scepticism concerning its bioavailability, a growing body of in vivo evidence indicates that resveratrol has protective effects in rodent models of stress and disease. Here, we provide a comprehensive and critical review of the in vivo data on resveratrol, and consider its potential as a therapeutic for humans.
Rapamycin, an inhibitor of mechanistic target of rapamycin (mTOR), has the strongest experimental support to date as a potential anti-aging therapeutic in mammals. Unlike many other compounds that ...have been claimed to influence longevity, rapamycin has been repeatedly tested in long-lived, genetically heterogeneous mice, in which it extends both mean and maximum life spans. However, the mechanism that accounts for these effects is far from clear, and a growing list of side effects make it doubtful that rapamycin would ultimately be beneficial in humans. This Review discusses the prospects for developing newer, safer anti-aging therapies based on analogs of rapamycin (termed rapalogs) or other approaches targeting mTOR signaling.
In the past decade, the small polyphenol resveratrol has received widespread attention as either a potential therapy or as a preventive agent for numerous diseases. Studies using purified enzymes, ...cultured cells, and laboratory animals have suggested that resveratrol has anti‐aging, anti‐carcinogenic, anti‐inflammatory, and anti‐oxidant properties that might be relevant to chronic diseases and/or longevity in humans. Although the supporting research in laboratory models is quite substantial, only recently data has emerged to describe the effects of resveratrol supplementation on physiological responses in humans. The limited number of human clinical trials that are available has largely described various aspects of resveratrol's safety and bioavailability, reaching a consensus that it is generally well‐tolerated, but have poor bioavailability. Very few published human studies have explored the ability of resveratrol to achieve the physiological benefits that have been observed in laboratory models, although many clinical trials have recently been initiated. This review aims to examine the current state of knowledge on the effects of resveratrol on humans and to utilize this information to develop further guidelines for the implementation of human clinical trials.
Cellular senescence is a stable growth arrest that is implicated in tissue ageing and cancer. Senescent cells are characterized by an upregulation of proinflammatory cytokines, which is termed the ...senescence-associated secretory phenotype (SASP). NAD
metabolism influences both tissue ageing and cancer. However, the role of NAD
metabolism in regulating the SASP is poorly understood. Here, we show that nicotinamide phosphoribosyltransferase (NAMPT), the rate-limiting enzyme of the NAD
salvage pathway, governs the proinflammatory SASP independent of senescence-associated growth arrest. NAMPT expression is regulated by high mobility group A (HMGA) proteins during senescence. The HMGA-NAMPT-NAD
signalling axis promotes the proinflammatory SASP by enhancing glycolysis and mitochondrial respiration. HMGA proteins and NAMPT promote the proinflammatory SASP through NAD
-mediated suppression of AMPK kinase, which suppresses the p53-mediated inhibition of p38 MAPK to enhance NF-κB activity. We conclude that NAD
metabolism governs the proinflammatory SASP. Given the tumour-promoting effects of the proinflammatory SASP, our results suggest that anti-ageing dietary NAD
augmentation should be administered with precision.
Dietary restriction (DR) delays or prevents age-related diseases and extends lifespan in species ranging from yeast to primates. Although the applicability of this regimen to humans remains ...uncertain, a proportional response would add more healthy years to the average life than even a cure for cancer or heart disease. Because it is unlikely that many would be willing or able to maintain a DR lifestyle, there has been intense interest in mimicking its beneficial effects on health, and potentially longevity, with drugs. To date, such efforts have been hindered primarily by our lack of mechanistic understanding of how DR works. Sirtuins, NAD
+-dependent deacetylases and ADP-ribosyltransferases that influence lifespan in lower organisms, have been proposed to be key mediators of DR, and based on this model, the sirtuin activator resveratrol has been proposed as a candidate DR mimetic. Indeed, resveratrol extends lifespan in yeast, worms, flies, and a short-lived species of fish. In rodents, resveratrol improves health, and prevents the early mortality associated with obesity, but its precise mechanism of action remains a subject of debate, and extension of normal lifespan has not been observed. This review summarizes recent work on resveratrol, sirtuins, and their potential to mimic beneficial effects of DR.
NAD is an obligate co-factor for the catabolism of metabolic fuels in all cell types. However, the availability of NAD in several tissues can become limited during genotoxic stress and the course of ...natural aging. The point at which NAD restriction imposes functional limitations on tissue physiology remains unknown. We examined this question in murine skeletal muscle by specifically depleting Nampt, an essential enzyme in the NAD salvage pathway. Knockout mice exhibited a dramatic 85% decline in intramuscular NAD content, accompanied by fiber degeneration and progressive loss of both muscle strength and treadmill endurance. Administration of the NAD precursor nicotinamide riboside rapidly ameliorated functional deficits and restored muscle mass despite having only a modest effect on the intramuscular NAD pool. Additionally, lifelong overexpression of Nampt preserved muscle NAD levels and exercise capacity in aged mice, supporting a critical role for tissue-autonomous NAD homeostasis in maintaining muscle mass and function.
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•Mice with ∼85% NAD depletion in skeletal muscle are grossly normal as young adults•Reduced NAD content impairs mitochondrial function and fiber integrity over time•Progressive muscle dysfunction can be reversed by the NAD precursor NR•Preventing muscle NAD loss during aging partially preserves exercise performance
NAD levels decline in multiple tissues with age or in disease. Frederick et al. show that impaired intramuscular NAD synthesis compromises skeletal muscle mass and strength over time but can be quickly restored with an oral NAD precursor. Upregulation of the NAD salvage pathway preserves exercise performance in aged mice.
Resveratrol induces mitochondrial biogenesis and protects against metabolic decline, but whether SIRT1 mediates these benefits is the subject of debate. To circumvent the developmental defects of ...germline SIRT1 knockouts, we have developed an inducible system that permits whole-body deletion of SIRT1 in adult mice. Mice treated with a moderate dose of resveratrol showed increased mitochondrial biogenesis and function, AMPK activation, and increased NAD+ levels in skeletal muscle, whereas SIRT1 knockouts displayed none of these benefits. A mouse overexpressing SIRT1 mimicked these effects. A high dose of resveratrol activated AMPK in a SIRT1-independent manner, demonstrating that resveratrol dosage is a critical factor. Importantly, at both doses of resveratrol no improvements in mitochondrial function were observed in animals lacking SIRT1. Together these data indicate that SIRT1 plays an essential role in the ability of moderate doses of resveratrol to stimulate AMPK and improve mitochondrial function both in vitro and in vivo.
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► Resveratrol's ability to improve mitochondrial function requires SIRT1 in vivo ► Moderate doses of resveratrol activate AMPK and raise NAD+ in a SIRT1-dependent manner ► Activation of AMPK in the absence of SIRT1 does not improve mitochondrial function ► Overexpression of SIRT1 mimics resveratrol's effects on AMPK and mitochondria
Age-related NAD+ decline McReynolds, Melanie R.; Chellappa, Karthikeyani; Baur, Joseph A.
Experimental gerontology,
06/2020, Letnik:
134
Journal Article
Recenzirano
Odprti dostop
Nicotinamide adenine dinucleotide (NAD+) is an essential metabolite that is reported to decline in concentration in tissues of aged animals. Strategies to increase NAD+ availability have shown ...promise in treating many conditions in rodents, including age-related degeneration, which has in turn driven intense interest in the effects of supplements on human health. However, many aspects of NAD+ metabolism remain poorly understood, and human data are limited. Here, we discuss the state of the evidence for an age-related decline in NAD+, along with potential mechanistic explanations, including increased consumption or decreased synthesis of NAD+ and changes in the composition of cells or tissues with age. Key challenges for the field involve the development of better tools to resolve information on the NAD+ content of specific cells and subcellular compartments as well as determining the threshold levels at which NAD+ depletion triggers physiological consequences in different tissues. Understanding how NAD+ metabolism changes with age in humans may ultimately allow the design of more targeted strategies to maintain its availability, such as inhibition of key consumers in specific tissues or direct delivery of precursors to sites of deficiency. In the meantime, human clinical trials with oral supplements are poised to provide some of the first direct evidence as to whether increasing NAD+ availability can impact human physiology. Thus, it is an exciting time for NAD+ research, with much remaining to be learned in terms of both basic biology and potential therapeutic applications.
•NAD+ is an essential metabolite that declines with age.•Changes in metabolism and tissue composition may contribute to NAD+ decline.•Lack of cellular/subcellular resolution is a limitation of most studies on NAD+.•Supplementation of NAD+ is beneficial in aged rodents.
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