ArticlePDF Available

Abstract and Figures

Strategies to restore levels of the enzyme cofactor nicotinamide adenine dinclueotide (NAD) late in life to maintain health by treatment with NAD precursors, such as nicotinamide mononucleotide (NMN), represent an exciting area of research in aging and age-related diseases. A study in Nature Metabolism provides an answer to the hotly debated yet fundamental question: how NMN actually gets into cells.
Content may be subject to copyright.
news & views
The elusive NMN transporter is found
Strategies to restore levels of the enzyme cofactor nicotinamide adenine dinclueotide (NAD) late in life to maintain
health by treatment with NAD precursors, such as nicotinamide mononucleotide (NMN), represent an exciting
area of research in aging and age-related diseases. A study in Nature Metabolism provides an answer to the hotly
debated yet fundamental question: how NMN actually gets into cells.
LindsayE.Wu and DavidA.Sinclair
The enzyme cofactor NAD is essential
for life. Originally discovered in 1906
as an accelerator of yeast fermentation,
NAD is once again at the forefront of
biology, thanks largely to research, again in
yeast, that has identified the oxidized form
of NAD (NAD+) as a signalling molecule
that dictates the health and lifespan of
eukaryotes13. In yeast, increasing NAD
levels through treatment with metabolic
precursors extends lifespan, and in aged
mice, this extends lifespan and improves
motor coordination, eye function, bone
density, insulin sensitivity, liver and kidney
function, physical endurance, muscle
strength, and the function of stem cells and
These findings have raised an important
question: how do cells take up these
precursors to make NAD?4,5 In this issue of
Nature Metabolism, Grozio et al.6 identify
the transporter for NMN, the immediate
precursor to NAD, helping to explain how
mammals absorb and manufacture NAD.
There are three main approaches to
raising NAD+ levels in mammals: inhibiting
NAD destruction by CD38 (ref. 7) or
SARM1 (ref. 8); inhibiting the enzyme
ACMSD, which siphons off NAD precursors
in the de novo NAD synthesis pathway9;
and providing NAD+ precursors such as
nicotinamide riboside (NR)10 and NMN3.
Once taken up by cells via equilibrative
nucleoside transporters, NR is
phosphorylated by nicotinamide riboside
kinase (NMRK1 and NMRK2 (NRK1/2)) to
generate NMN, which is then immediately
converted to NAD+ by nicotinamide
mononucleotide adenylyltransferases
(NMNATs; Fig. 1)11. NR and NMN have
been used in preclinical animal studies5, and
NR raises NAD+ levels in blood lymphocytes
of human subjects10.
A question that has been debated for
years is whether NMN is simply a pro-
drug of NR. For NMN to enter cells, it was
thought to require a dephosphorylation
step on the extracellular surface of cells to
convert it to NR before being taken up by
the equilibrative nucleotide transporters
(ENTs) and then re-phosphorylated by NRK
back into NMN11. This view is consistent
with the metabolism of nucleoside-based
drugs, such as HIV inhibitors, which
are usually first dephosphorylated in the
gut. It remains unclear whether the rapid
kinetics of NMN uptake exhibited by certain
cell types can be explained by a similar
This new study from Grozio et al.6
identifies a previously characterized amino
acid and polyamine transporter called
Slc12a8 (ref. 12) as an NMN transporter.
Slc12a8 has a number of surprising
attributes. It requires sodium and not
chloride for NMN co-transport and is highly
selective for NMN, excluding even nicotinic
acid mononucleotide (NaMN), which differs
from NMN by only one atom.
It is important to note that the discovery
of an NMN transporter by no means
diminishes the importance of uptake via
dephosphorylation11. It does, however,
enrich our knowledge by providing a new
mechanism through which the absorption
and distribution of NAD precursors might
Food or microbiome
Fig. 1 | The NAD precursor NMN enters cells through the co-transporter Slc12a8. Pharmacological
treatment with the metabolic precursor NMN can be used to relieve the age-associated decline in NAD.
The transport of NMN into the cell was thought to require a dephosphorylation step to produce NR
before it could be taken up by ENTs. The discovery of an NMN transporter raises new questions about
the uptake, distribution, and utilization of NMN from the diet and in circulation. NAMPT, nicotinamide
phosphoribosyltransferase; NMNAT1/2/3, NMNAT1–NMNAT3; PARPs, poly (ADP-ribose) polymerases;
Pi, inorganic phosphate.
news & views
be differentially regulated. For example,
the authors find that Slc12a8 is highly
enriched in the small intestine of mice, with
expression that is at least 100-fold higher
in this tissue than in fat or brain tissue.
Interestingly, the expression of Slc12a8
increases in the intestines of old mice as
NAD levels decline4,13, suggesting that
upregulation during aging is a compensatory
The authors speculate that Slc12a8 in the
gut endothelium serves to take up NMN
from naturally occurring dietary sources,
such as fruits, vegetables, and milk, or from
the breakdown of NAD+. But the amount
of NMN needed to raise NAD in a mouse
or human is far beyond what is available
naturally. Both NMN and NR are present
in food3,14 but at concentrations of less than
1 mg per kg of food, whereas hundreds of
milligrams per dose are needed to raise
NAD+ in humans3. And given that cells
make their own NAD from tryptophan, it
is unclear whether dietary uptake of NMN
can meaningfully influence NAD+ levels
or whether Slc12a8 affects NAD synthesis
beyond the liver, where NMN is primarily
metabolised15. One intriguing possibility
is that NMN could be produced by the
microbiome. If so, NMN transport may
prove more important than the low NMN
levels in food imply.
There is no doubt that this new work
will spark a debate about the relative
contributions of NMN transport and
the previously described mechanism11,
which could be addressed by head-to-
head comparisons of NAD precursors
and by following the in vivo metabolism
of isotopically labelled NAD precursors
in knockout animals. Given that NAD
precursors are sold as supplements and are
under development as pharmaceuticals, this
new understanding of NAD physiology is
an important addition to the field, but also
raises new questions about where NAD
precursors are taken up and processed, and
where they naturally come from.
LindsayE.Wu1 and DavidA.Sinclair1,2*
1School of Medical Sciences, UNSW Sydney, Sydney,
New South Wales, Australia. 2Paul F. Glenn Center
for the Biology of Aging, Harvard Medical School,
Boston, MA, USA.
Published online: 7 January 2019
1. Anderson, R. M., Bitterman, K. J., Wood, J. G., Medvedik, O. &
Sinclair, D. A. Nature 423, 181–185 (2003).
2. Zhang, H. et al. Science 352, 1436–1443 (2016).
3. Mills, K. F. et al. Cell Metab. 24, 795–806 (2016).
4. Massudi, H. et al. PLoS One 7, e42357 (2012).
5. Rajman, L., Chwalek, K. & Sinclair, D. A. C ell Metab. 27,
529–547 (2018).
6. Grozio, A. et al. Nat. Metab.
0009-4 (2018).
7. Haner, C. D. et a l. J. Med. Chem. 58, 3548–3571 (2015).
8. Gerdts, J., Brace, E. J., Sasaki, Y., DiAntonio, A. & Milbrandt, J.
Science 348, 453–457 (2015).
9. Katsyuba, E. et al. Nature 563, 354–359 (2018).
10. Trammell, S. A. et al. Nat. Commun. 7, 12948 (2016).
11. Ratajczak, J. et al. Nat. Commun. 7, 13103 (2016).
12. Daigle, N. D. et al. J. Cell. Physiol. 220, 680–689 (2009).
13. Gomes, A. P. et al. Cell 155, 1624–1638 (2013).
14. Trammell, S. A., Yu, L., Redpath, P., Migaud, M. E. & Brenner, C.
J. N utr. 146, 957–963 (2016).
15. Liu, L. et al. Cell Metab. 27, 1067–1080.e5 (2018).
Competing interests
L.W. is a is a founder, equity owner, advisor to, and/or
director of Intravital, EdenRoc Sciences (Metro Biotech/
Bauhaus, Liberty Biosecurity), Jumpstart Fertility, and
Life Biosciences and its daughter companies (Continuum
Biosciences, Jumpstart Fertility, Senolytic Therapeutics,
Animal Biosciences, Selphagy, Spotlight Therapeutics).
D.S. is a founder, equity owner, advisor to, director of,
consultant to, and/or inventor of patents licensed to
Jupiter Orphan Therapeutics, Cohbar, Galilei Biosciences,
EdenRoc Sciences (Arc-Bio, Dovetail Genomics, Claret,
Revere Biosciences, UpRNA, MetroBiotech/Bauhaus,
Liberty Biosecurity), Life Biosciences (Selphagy,
InsideTracker, Senolytic Therapeutics, Spotlight
Therapeutics, Immetas, Animal Biosciences, Iduna,
Continuum Biosciences, and Jumpstart Fertility),
Wellomics, and Vium. MetroBiotech, Liberty Biosecurity,
and Jumpstart are developing NAD boosting molecules/
precursors for the treatment of diseases. D.S. is an inventor
on an invention filed by Mayo Clinic and Harvard Medical
School that has been licensed to Elysium Health. For more
information see
... Thus, NMN must first be dephosphorylated to NR by the enzyme CD73, and then NR enters the cell through nucleoside transporters (ENTs) to equilibrate the pools [3]. However, Grozio et al. recently identified an NMN transporter in the cell membrane called Slc12a8 [44,45]. However, the expression of Slc12a8 is limited to the intestine and others have questioned its ability to transport NMN [46]. ...
Full-text available
NAD+ is an important metabolite in cell homeostasis that acts as an essential cofactor in oxidation–reduction (redox) reactions in various energy production processes, such as the Krebs cycle, fatty acid oxidation, glycolysis and serine biosynthesis. Furthermore, high NAD+ levels are required since they also participate in many other nonredox molecular processes, such as DNA repair, posttranslational modifications, cell signalling, senescence, inflammatory responses and apoptosis. In these nonredox reactions, NAD+ is an ADP-ribose donor for enzymes such as sirtuins (SIRTs), poly-(ADP-ribose) polymerases (PARPs) and cyclic ADP-ribose (cADPRs). Therefore, to meet both redox and nonredox NAD+ demands, tumour cells must maintain high NAD+ levels, enhancing their synthesis mainly through the salvage pathway. NAMPT, the rate-limiting enzyme of this pathway, has been identified as an oncogene in some cancer types. Thus, NAMPT has been proposed as a suitable target for cancer therapy. NAMPT inhibition causes the depletion of NAD+ content in the cell, leading to the inhibition of ATP synthesis. This effect can cause a decrease in tumour cell proliferation and cell death, mainly by apoptosis. Therefore, in recent years, many specific inhibitors of NAMPT have been developed, and some of them are currently in clinical trials. Here we review the NAD metabolism as a cancer therapy target.
... Data mining revealed a strainspecific protein, nicotinamide mononucleotide transporter, which promoted antioxidant activity in L. fermentum XJC60 ( Figure 3A). Nicotinamide mononucleotide transporter can directly transport extracellular NMN into the cell and increase the level of NAM, thereby regulating NAD + metabolism (Wu and Sinclair, 2019;Lloyd-Price et al., 2019;Yachida et al., 2019). We further quantified the LAB metabolites by HPLC and found high levels of NAM (18.50 mg/L) in culture broth from the MNTD of L. fermentum XJC60 ( Figure 3B), validating the pangenomics results. ...
Full-text available
Although lactic acid bacteria (LAB) were shown to be effective for preventing photoaging, the underlying molecular mechanisms have not been fully elucidated. Accordingly, we examined the anti-photoaging potential of 206 LAB isolates and discovered 32 strains with protective activities against UV-induced injury. All of these 32 LABs exhibited high levels of 2,2-diphenyl-picrylhydrazyl, as well as hydroxyl free radical scavenging ability (46.89–85.13% and 44.29–95.97%, respectively). Genome mining and metabonomic verification of the most effective strain, Limosilactobacillus fermentum XJC60, revealed that the anti-photoaging metabolite of LAB was nicotinamide (NAM; 18.50 mg/L in the cell-free serum of XJC60). Further analysis revealed that LAB-derived NAM could reduce reactive oxygen species levels by 70%, stabilize the mitochondrial membrane potential, and increase the NAD+/NADH ratio in UV-injured skin cells. Furthermore, LAB-derived NAM downregulated the transcript levels of matrix metalloproteinase (MMP)-1, MMP-3, interleukin (IL)-1β, IL-6, and IL-8 in skin cells. In vivo, XJC60 relieved imflammation and protected skin collagen fiber integrity in UV-injured Guinea pigs. Overall, our findings elucidate that LAB-derived NAM might protect skin from photoaging by stabilizing mitochondrial function, establishing a therotical foundation for the use of probiotics in the maintenance of skin health.
... Another important aspect of nicotinamide nucleotide biology being intensively investigated relates to the machinery used by cells and organelles to transport NAD pathway metabolites and precursors (Figure 3). This aspect of NAD biology is a source of heated debates (Grozio et al., 2019a(Grozio et al., , 2019bSchmidt and Brenner, 2019;Wu and Sinclair, 2019). Key questions in this field are how NAD(P) precursors are transported from the extracellular to the intracellular space and whether NAD is transported into the mitochondria. ...
NAD(H) and NADP(H) have traditionally been viewed as co-factors (or co-enzymes) involved in a myriad of oxidation-reduction reactions including the electron transport in the mitochondria. However, NAD pathway metabolites have many other important functions, including roles in signaling pathways, post-translational modifications, epigenetic changes, and regulation of RNA stability and function via NAD-capping of RNA. Non-oxidative reactions ultimately lead to the net catabolism of these nucleotides, indicating that NAD metabolism is an extremely dynamic process. In fact, recent studies have clearly demonstrated that NAD has a half-life in the order of minutes in some tissues. Several evolving concepts on the metabolism, transport, and roles of these NAD pathway metabolites in disease states such as cancer, neurodegeneration, and aging have emerged in just the last few years. In this perspective, we discuss key recent discoveries and changing concepts in NAD metabolism and biology that are reshaping the field. In addition, we will pose some open questions in NAD biology, including why NAD metabolism is so fast and dynamic in some tissues, how NAD and its precursors are transported to cells and organelles, and how NAD metabolism is integrated with inflammation and senescence. Resolving these questions will lead to significant advancements in the field.
The nicotinamide adenine dinucleotide (NAD+ ) precursor nicotinamide mononucleotide (NMN) is a proposed therapy for age-related disease, whereby it is assumed that NMN is incorporated into NAD+ through the canonical recycling pathway. During oral delivery, NMN is exposed to the gut microbiome, which could modify the NAD+ metabolome through enzyme activities not present in the mammalian host. We show that orally delivered NMN can undergo deamidation and incorporation in mammalian tissue via the de novo pathway, which is reduced in animals treated with antibiotics to ablate the gut microbiome. Antibiotics increased the availability of NAD+ metabolites, suggesting the microbiome could be in competition with the host for dietary NAD+ precursors. These findings highlight new interactions between NMN and the gut microbiome.
Significance: NAD is an important molecule synthesised from tryptophan or vitamin B3 and involved in numerous cellular reactions. NAD deficiency during pregnancy causes Congenital NAD Deficiency Disorder (CNDD) characterised by multiple congenital malformations and/or miscarriage. Studies in genetically engineered mice replicating mutations found in human patient cases show that CNDD can be prevented by dietary supplements. Recent advances: A growing number of patient reports show that biallelic loss-of-function of genes involved in NAD de novo synthesis (KYNU, HAAO, NADSYN1) cause CNDD. Other factors that limit the availability of NAD precursors, e.g. limited dietary precursor supply or absorption, can cause or contribute to NAD deficiency and result in CNDD in mice. Molecular flux experiments allow quantitative understanding of NAD precursor concentrations in the circulation and their usage by different cells. Studies of NAD-consuming enzymes and contributors to NAD homeostasis help better understand how perturbed NAD levels are implicated in various diseases and adverse pregnancy outcomes. Critical issues: NAD deficiency is one of the many known causes of adverse pregnancy outcomes, but its prevalence in the human population and among pregnant women is unknown. Since NAD is involved in hundreds of diverse cellular reactions, determining how NAD deficiency disrupts embryogenesis is an important challenge. Future directions: Furthering our understanding of the molecular fluxes between the maternal and embryonic circulation during pregnancy, the NAD-dependent pathways active in the developing embryo, and the molecular mechanisms by which NAD deficiency causes adverse pregnancy outcomes will provide direction for future prevention strategies.
Numerous studies demonstrate a global decrease in nicotinamide adenine dinucleotide (NAD+) with aging. This decline is associated with the development of several of the hallmarks of aging such as reduced mitophagy and neuroinflammation, processes thought to play a significant role in the progression of Alzheimer's disease (AD). Augmentation of NAD+ by oral administration of a precursor, nicotinamide riboside (NR), reduces senescence of affected cells, attenuates DNA damage and neuroinflammation in the transgenic APP/PS1 murine model of AD. Inflammation mediated by microglial cells plays an important role in progression of AD and other neurodegenerative diseases. The cytoplasmic DNA sensor, cyclic GMP-AMP synthase (cGAS) and downstream stimulator of interferon genes (STING), generates an interferon signature characteristic of senescence and inflammaging in the brain of AD mice. Elevated cGAS-STING observed in the AD mouse brains and human AD fibroblasts was normalized by NR. This intervention also increased mitophagy with improved cognition and behavior in the APP/PS1 mice. These studies suggest that modulation of the cGAS-STING pathway may benefit AD patients and possibly other disorders characterized by compromised mitophagy and excessive neuroinflammation.
Strategies to correct declining nicotinamide adenine dinucleotide (NAD⁺) levels in neurological disease and biological ageing are promising therapeutic candidates. These strategies include supplementing with NAD⁺ precursors, small molecule activation of NAD⁺ biosynthetic enzymes, and treatment with small molecule inhibitors of NAD⁺ consuming enzymes such as CD38, SARM1 or members of the PARP family. While these strategies have shown efficacy in animal models of neurological disease, each of these has the mechanistic potential for adverse events that could preclude their preclinical use. Here, we discuss the implications of these strategies for treating neurological diseases, including potential off-target effects that may be unique to the brain.
Full-text available
Treatment with nicotinamide mononucleotide (NMN) is a prominent strategy to address the age-related decline in nicotinamide adenine dinucleotide (NAD+) levels for maintaining aspects of late-life health. It is assumed that exogenous NMN is directly incorporated into the NAD+ metabolome in mammals via the canonical recycling pathway. Here, we show that NMN can undergo direct deamidation and incorporation via the de novo pathway, which is in part mediated by the gut microbiome. Surprisingly, isotope labelling studies revealed that exogenous NMN treatment potently increased the endogenous production of unlabelled NAD metabolites, suggesting that exogenous NMN impacts the NAD metabolome through indirect means, rather than through its direct incorporation. This included a striking increase in endogenous production of the metabolites nicotinic acid riboside (NaR) and nicotinamide riboside (NR) which was amplified in antibiotics treated animals, suggesting the production of endogenous NaR/NR through altered metabolic flux, enzyme kinetics and/or an as-yet unidentified pathway that interacts with the gut microbiome.
Full-text available
Nicotinamide mononucleotide (NMN) is a biosynthetic precursor of NAD+ known to promote cellular NAD+ production and counteract age-associated pathologies associated with a decline in tissue NAD+ levels. How NMN is taken up into cells has not been entirely clear. Here we show that the Slc12a8 gene encodes a specific NMN transporter. We find that Slc12a8 is highly expressed and regulated by NAD+ in the murine small intestine. Slc12a8 knockdown abrogates the uptake of NMN in vitro and in vivo. We further show that Slc12a8 specifically transports NMN, but not nicotinamide riboside, and that NMN transport depends on the presence of sodium ion. Slc12a8 deficiency significantly decreases NAD+ levels in the jejunum and ileum, which is associated with reduced NMN uptake as traced by doubly labeled isotopic NMN. Finally, we observe that Slc12a8 expression is upregulated in the aged murine ileum, which contributes to the maintenance of ileal NAD+ levels. Our work identifies the first NMN transporter and demonstrates that Slc12a8 has a critical role in regulating intestinal NAD+ metabolism.
Full-text available
Nicotinamide adenine dinucleotide (NAD⁺) is a co-substrate for several enzymes, including the sirtuin family of NAD⁺-dependent protein deacylases. Beneficial effects of increased NAD⁺ levels and sirtuin activation on mitochondrial homeostasis, organismal metabolism and lifespan have been established across species. Here we show that α-amino-β-carboxymuconate-ε-semialdehyde decarboxylase (ACMSD), the enzyme that limits spontaneous cyclization of α-amino-β-carboxymuconate-ε-semialdehyde in the de novo NAD⁺ synthesis pathway, controls cellular NAD⁺ levels via an evolutionarily conserved mechanism in Caenorhabditis elegans and mouse. Genetic and pharmacological inhibition of ACMSD boosts de novo NAD⁺ synthesis and sirtuin 1 activity, ultimately enhancing mitochondrial function. We also characterize two potent and selective inhibitors of ACMSD. Because expression of ACMSD is largely restricted to kidney and liver, these inhibitors may have therapeutic potential for protection of these tissues from injury. In summary, we identify ACMSD as a key modulator of cellular NAD⁺ levels, sirtuin activity and mitochondrial homeostasis in kidney and liver.
Full-text available
NAD⁺ is a vital redox cofactor and a substrate required for activity of various enzyme families, including sirtuins and poly(ADP-ribose) polymerases. Supplementation with NAD⁺ precursors, such as nicotinamide mononucleotide (NMN) or nicotinamide riboside (NR), protects against metabolic disease, neurodegenerative disorders and age-related physiological decline in mammals. Here we show that nicotinamide riboside kinase 1 (NRK1) is necessary and rate-limiting for the use of exogenous NR and NMN for NAD⁺ synthesis. Using genetic gain- and loss-of-function models, we further demonstrate that the role of NRK1 in driving NAD⁺ synthesis from other NAD⁺ precursors, such as nicotinamide or nicotinic acid, is dispensable. Using stable isotope-labelled compounds, we confirm NMN is metabolized extracellularly to NR that is then taken up by the cell and converted into NAD⁺. Our results indicate that mammalian cells require conversion of extracellular NMN to NR for cellular uptake and NAD⁺ synthesis, explaining the overlapping metabolic effects observed with the two compounds.
Full-text available
Nicotinamide riboside (NR) is in wide use as an NAD⁺ precursor vitamin. Here we determine the time and dose-dependent effects of NR on blood NAD⁺ metabolism in humans. We report that human blood NAD⁺ can rise as much as 2.7-fold with a single oral dose of NR in a pilot study of one individual, and that oral NR elevates mouse hepatic NAD⁺ with distinct and superior pharmacokinetics to those of nicotinic acid and nicotinamide. We further show that single doses of 100, 300 and 1,000 mg of NR produce dose-dependent increases in the blood NAD⁺ metabolome in the first clinical trial of NR pharmacokinetics in humans. We also report that nicotinic acid adenine dinucleotide (NAAD), which was not thought to be en route for the conversion of NR to NAD⁺, is formed from NR and discover that the rise in NAAD is a highly sensitive biomarker of effective NAD⁺ repletion.
Full-text available
Axon degeneration is an intrinsic self-destruction program that underlies axon loss during injury and disease. Sterile alpha and TIR motif-containing 1 (SARM1) protein is an essential mediator of axon degeneration. We report that SARM1 initiates a local destruction program involving rapid breakdown of nicotinamide adenine dinucleotide (NAD(+)) after injury. We used an engineered protease-sensitized SARM1 to demonstrate that SARM1 activity is required after axon injury to induce axon degeneration. Dimerization of the Toll-interleukin receptor (TIR) domain of SARM1 alone was sufficient to induce locally mediated axon degeneration. Formation of the SARM1 TIR dimer triggered rapid breakdown of NAD(+), whereas SARM1-induced axon destruction could be counteracted by increased NAD(+) synthesis. SARM1-induced depletion of NAD(+) may explain the potent axon protection in Wallerian degeneration slow (Wld(s)) mutant mice. Copyright © 2015, American Association for the Advancement of Science.
The redox cofactor nicotinamide adenine dinucleotide (NAD) plays a central role in metabolism and is a substrate for signaling enzymes including poly-ADP-ribose-polymerases (PARPs) and sirtuins. NAD concentration falls during aging, which has triggered intense interest in strategies to boost NAD levels. A limitation in understanding NAD metabolism has been reliance on concentration measurements. Here, we present isotope-tracer methods for NAD flux quantitation. In cell lines, NAD was made from nicotinamide and consumed largely by PARPs and sirtuins. In vivo, NAD was made from tryptophan selectively in the liver, which then excreted nicotinamide. NAD fluxes varied widely across tissues, with high flux in the small intestine and spleen and low flux in the skeletal muscle. Intravenous administration of nicotinamide riboside or mononucleotide delivered intact molecules to multiple tissues, but the same agents given orally were metabolized to nicotinamide in the liver. Thus, flux analysis can reveal tissue-specific NAD metabolism.
Nicotinamide adenine dinucleotide (NAD), the cell's hydrogen carrier for redox enzymes, is well known for its role in redox reactions. More recently, it has emerged as a signaling molecule. By modulating NAD+-sensing enzymes, NAD+controls hundreds of key processes from energy metabolism to cell survival, rising and falling depending on food intake, exercise, and the time of day. NAD+levels steadily decline with age, resulting in altered metabolism and increased disease susceptibility. Restoration of NAD+levels in old or diseased animals can promote health and extend lifespan, prompting a search for safe and efficacious NAD-boosting molecules that hold the promise of increasing the body's resilience, not just to one disease, but to many, thereby extending healthy human lifespan.
NAD⁺ availability decreases with age and in certain disease conditions. Nicotinamide mononucleotide (NMN), a key NAD⁺ intermediate, has been shown to enhance NAD⁺ biosynthesis and ameliorate various pathologies in mouse disease models. In this study, we conducted a 12-month-long NMN administration to regular chow-fed wild-type C57BL/6N mice during their normal aging. Orally administered NMN was quickly utilized to synthesize NAD⁺ in tissues. Remarkably, NMN effectively mitigates age-associated physiological decline in mice. Without any obvious toxicity or deleterious effects, NMN suppressed age-associated body weight gain, enhanced energy metabolism, promoted physical activity, improved insulin sensitivity and plasma lipid profile, and ameliorated eye function and other pathophysiologies. Consistent with these phenotypes, NMN prevented age-associated gene expression changes in key metabolic organs and enhanced mitochondrial oxidative metabolism and mitonuclear protein imbalance in skeletal muscle. These effects of NMN highlight the preventive and therapeutic potential of NAD⁺ intermediates as effective anti-aging interventions in humans.
A dietary supplement protects aging muscle The oxidized form of cellular nicotinamide adenine dinucleotide (NAD ⁺ ) is critical for mitochondrial function, and its supplementation can lead to increased longevity. Zhang et al. found that feeding the NAD ⁺ precursor nicotinamide riboside (NR) to aging mice protected them from muscle degeneration (see the Perspective by Guarente). NR treatment enhanced muscle function and also protected mice from the loss of muscle stem cells. The treatment was similarly protective of neural and melanocyte stem cells, which may have contributed to the extended life span of the NR-treated animals. Science , this issue p. 1436 ; see also p. 1396
Background: Nicotinamide riboside (NR) is a recently discovered NAD(+)precursor vitamin with a unique biosynthetic pathway. Although the presence of NR in cow milk has been known for more than a decade, the concentration of NR with respect to the other NAD(+)precursors was unknown. Objective: We aimed to determine NAD(+)precursor vitamin concentration in raw samples of milk from individual cows and from commercially available cow milk. Methods: LC tandem mass spectrometry and isotope dilution technologies were used to quantify NAD(+)precursor vitamin concentration and to measure NR stability in raw and commercial milk. Nuclear magnetic resonance (NMR) spectroscopy was used to test for NR binding to substances in milk. Results: Cow milk typically contained ∼12 μmol NAD(+)precursor vitamins/L, of which 60% was present as nicotinamide and 40% was present as NR. Nicotinic acid and other NAD(+)metabolites were below the limits of detection. Milk from samples testing positive forStaphylococcus aureuscontained lower concentrations of NR (Spearman ρ = -0.58,P= 0.014), and NR was degraded byS. aureus Conventional milk contained more NR than milk sold as organic. Nonetheless, NR was stable in organic milk and exhibited an NMR spectrum consistent with association with a protein fraction in skim milk. Conclusions: NR is a major NAD(+)precursor vitamin in cow milk. Control ofS. aureusmay be important to preserve the NAD(+)precursor vitamin concentration of milk.