My husband, Corin, and I contracted covid. We’re both vaccinated (him Pfizer, me J&J). Neither of us had the vaccine booster when we got sick. Here’s our story.
10/31: Corin felt like he had a cold. He did an at home rapid test. The result was negative.
11/2: Corin thought he might have pneumonia. His lungs were hurting. His second rapid test was negative.
11/3: We went to the doctor’s office to check for pneumonia. His lungs were clear. We ask the doctor to do another covid test. That afternoon we get the call, it’s covid. We immediately shut everything down and got the kids from school. We called everyone we’d been in contact with. Corin was now sleeping 18+ hours a day and feeling terrible. I took myself and our sons for PCR tests. **Corin was so disoriented that he hit a curb and damaged his car coming home from the doctor (first sign of brain fog issues).
11/4: Corin went down hard and was getting sicker by the day. He was waking up for food and home IVs but appeared disoriented and unable to perform small tasks (dropping things and losing his balance). He was becoming dehydrated with a worsening cough. I was checking his pulse ox while he slept – it was holding steady. My results came in- I was positive too.
11/5-7: I presented with a head cold and a minor sore throat – no other symptoms. My husband was much worse and I was very concerned about his “brain fog” symptoms. His pulse ox was in the 90s indicating the brain fog was likely coming from inflammation in his brain. He was getting worse and our doctor was concerned so he was admitted into the ER for a CT scan to rule out a stroke. While he was in the ER they gave him antibodies. The CT showed that he did not have signs of a stroke but he was still experiencing concerning symptoms.
The following weeks were a blur. Our nine year old eventually tested positive but he was asymptomatic. Quarantine felt like forever and I was secretly terrified for my Corin’s health but I was determined to do everything I could to keep him healthy.
“My husband regained all cognitive functioning before we were out of quarantine…”
You might be asking why this story is appearing in a Renew newsletter… I want to talk about NAD+. As you know, I’m a big fan of NAD+ and I get IVs and shots often. NAD+ reduces systemic inflammation and covid can cause inflammatory issues that lead to cytokine storms, loss of taste and smell, brain fog and much more. I went into my covid journey with plenty of NAD+ in my system. My husband didn’t.
I maintained my NAD+ regimen throughout having covid. When Corin was diagnosed he started NAD+ IVs and shots at home. He got an IV every other day with NAD+ and a Myers Cocktail. Corin regained all cognitive functioning before he was out of quarantine.
Covid is complicated and every person’s system is different. I believe that IV hydration with immune boosting vitamins and inflammation fighting NAD+ played a role in minimizing my symptoms and my husband’s quick recovery from brain fog issues. I’m beyond grateful we had access to hydration, nutrients and NAD+ through our covid journey.
Wishing you the best of health.
Please note that we don’t offer medical advice at Renew and the above is my personal experience, not a medical claim.
Concierge IVs coming soon!
Our journey would have been much different without access to IVs. We have decided to offer concierge home services for IVs. We will be introducing the details in early January.
Nicotinamide adenine dinucleotide (NAD+) is an essential cofactor in all living cells that is involved in fundamental biological processes. NAD+ depletion has been associated with hallmarks of aging and may underlie a wide-range of age-related diseases, such as metabolic disorders, cancer and neurodegenerative diseases. Emerging evidence implicates that elevation of NAD+ levels may slow or even reverse the aspects of aging and also delay the progression of age-related diseases. Here we discuss the roles of NAD+-synthesizing and -consuming enzymes in relationships to aging and major age-related diseases. Specifically, we highlight the contribution of NAD+ depletion to aging and evaluate how boosting NAD+ levels may emerge as a promising therapeutic strategy to counter aging-associated pathologies and/or accelerated aging.
Nicotinamide adenine dinucleotide (NAD+) is an important cofactor in all living cells that is involved in fundamental biological processes, namely metabolism, cell signalling, gene expression, DNA repair, among others , , , . Originally, Harden and Young described NAD+ in 1906 as a molecular fraction (“cozymase”) that accelerated fermentation in yeast extracts. Over subsequent years, NAD+ was identified as a nucleosidesugar phosphate, which plays a role in redox reactions. However, evidence stemming from recent studies have unveiled numerous roles of NAD+ metabolism on aging and longevity. In particular, an age-dependent decline in NAD+ levels have consistently been reported, possibly due to an imbalance in the synthesis and consumption of NAD+. Decreased levels of NAD+ are associated with the hallmarks of aging as well as several age-related diseases, including metabolic disorders, cancer and neurodegenerative diseases. Replenishment of NAD+ levels via administration of its precursors have been demonstrated to display beneficial effects against aging and age-related diseases. Importantly, boosting NAD+ levels have been shown to extend lifespan of various laboratory animal models including worms, flies, and rodents , , , , .
As a cofactor, NAD+ is found in abundance in the mitochondria, cytoplasm, and nucleus. It is essential for many cellular metabolism pathways that include: glycolysis, fatty acid β-oxidation, and the tricarboxylic acid cycle. Whilst the reduced form of NAD+ (NADH) is a primary hydride donor in the production of ATP via anaerobic glycolysis and mitochondrial oxidative phosphorylation (OXPHOS) , . On the other hand, NAD+ is consumed by the NAD+-dependent sirtuins and the DNA damage sensors poly (ADP-ribose) polymerases (PARPs) in the processes of protein deacetylation and poly-ADP-ribosylation (PARylation), respectively. In addition, NAD+ glycohydrolases (i.e. CD38 and CD157) also consume NAD+ via conversion of NAD+ into ADP-ribose (ADPR) or cyclic-ADPR , , . Thus, the importance of NAD+ has expanded from a key element in intermediate metabolism to a critical regulator of multiple cell signalling pathways; and is now a major player contributing to aging and age-related diseases .
In mammals, NAD+ is synthetized from a variety of dietary sources, including NAD+ itself (it is metabolized in the gut, then synthesized again in cells) as well as from one or more of its major precursors that include: tryptophan (Trp), nicotinic acid (NA), nicotinamide riboside (NR), nicotinamide mononucleotide (NMN), and nicotinamide (NAM). Based upon the bioavailability of its precursors, there are three pathways for the synthesis of NAD+ in cells: (i) from Trp by the de novobiosynthesis pathway or kynurenine pathway; (ii) from NA in the Preiss–Handler pathway; and (iii) from NAM, NR, and NMN in the salvage pathway , .
Accumulating evidence demonstrates an age-dependent decline in NAD+ levels and associate its depletion to several hallmarks of aging and age-related diseases (Fig. 1) . Here, we summarize the roles of NAD+-synthesizing and -consuming enzymes in aging and age-related diseases. Specifically, we highlight the contribution of NAD+ depletion to mammalian aging and evaluate how boosting endogenous NAD+ levels might emerge as a promising therapeutic strategy to counter aging-associated pathologies and/or accelerated aging.
Fig. 1. NAD+decline at the core of hallmarks of aging. A schematic representation of age-dependent decline in NAD+ levels which contribute to ten hallmarks of aging, namely DNA damage, epigenetic alteration, deregulated nutrient-sensing, loss of proteostasis, altered cellular communication, cellular senescence, stem cell exhaustion, mitochondrial dysfunction, compromised autophagy, and possibly telomere attrition. Figure modified from Fang et al. 2017 .
2. Recent progress on the roles of NAD+ in aging
Mounting evidence has indicated that NAD+ levels decline with age in multiple types of tissues, which include the liver, skeletal muscle, adipose tissue, heart, brain, kidney, pancreas, lungs, spleen, skin, as well as extracellular fluids, . In addition, an age-dependent decline in NAD+ levels in Caenorhabditiselegans (C. elegans), mice, and human post-mortem tissues are reported. Thus, highlighting a universal age-dependent decrease of NAD+ across species. However, it remains elusive whether this is due to increased NAD+ consumption and/or decreased synthesis . In this section, we provide an overview of methods that could potentially boost endogenous levels of NAD+.
2.1. NMN and aging
NMN is a physically stable natural compound that serves as an efficient NAD+ precursor. In mammals, NMN is synthesized from nicotinamide, a form of water-soluble vitamin B3 and 5′-phosphoribosyl-1-pyrophosphate (PRPP), by the rate-limiting enzyme, nicotinamide phosphoribosyl transferase (NAMPT). In addition, it can also be synthesized from NR via NR kinases (NRKs)-mediated phosphorylation reactions. NMN is subsequently converted into NAD+ by NMN adenylyl transferases (NMNATs) . Over the years, it has become increasingly evident that systemic administration of NMN in rodents enhances the biosynthesis of NAD+ in various peripheral tissues including liver, pancreas, adipose tissue, heart, skeletal muscle, kidney, eyes, and blood vessels , , , , , , , , , , . Furthermore, NMN has also been shown to elevate levels of NAD+ in hypothalamus and hippocampus following an intraperitoneal injection, thereby indicating its ability to penetrate the blood-brain barrier (BBB) , . More importantly, long-term (1-year) oral administration of NMN (up to 300 mg/kg) has recently been shown to be well tolerated without any obvious deleterious or toxic effects in normal wild type C57BL/6 mice .
NMN has been shown to have remarkable beneficial effects that counter normal aging. In models of aging, long-term administration of NMN protects against age-associated functional decline as demonstrated by increases in energy metabolism, insulin sensitivity, lipid metabolism, mitochondrial oxidative metabolism, eye function, bone density and immune function , . On the other hand, it suppressed age-related changes in gene expression and adipose tissue inflammation . Moreover, it has been shown to maintain neural stem/progenitor cell population and restore skeletal muscle mitochondrial function as well as arterial function in aged mice , , . In addition, loss of enzymes involved in NAD+ synthesis, namely NAMPT during the process of aging, led to decrease in NAD+ content and reduced SIRT1 activity; consequently, promoted cellular senescence in retinal pigment epithelium, which performs numerous functions critical to retinal health and visual function .
NMN administration may counteract age-predisposed metabolic diseases and neurodegeneration. In age-related pathophysiological conditions, NMN ameliorated impairments in glucose tolerance and promoted insulin secretion/sensitivity in age- or diet-induced diabetic mice, Nampt+/− mice, as well in aged wild-type and β cell-specific Sirt1-overexpressing (BESTO) mice , , , , , . Likewise, promotion and overexpression of the mitochondrial Nmnat3 in mice, also involved in NAD+ biosynthesis, resulted in improved glucose tolerance during the process of aging as well as in models of high-fat induced obesity . The beneficial effect was suggested to be a result of improved mitochondrial function and by an independent mechanism of NAD+–SIRT1–PGC1α axis, which despite previously being reported to contribute to improved mitochondrial function, was not activated in these transgenic mice despite elevated levels of NAD+. Furthermore, NMN protects the heart and brain from ischaemia-induced damage , . In rodent models of Alzheimer’s disease (AD), administration of NMN decreased AD-associated β-amyloid (Aβ) pathology and improved cognitive function. In addition, it restored mitochondrial function and ameliorated inflammation, synaptic loss as well as protected against neuronal cell death , , . The beneficial effect of NMN was also evident in premature aging conditions as demonstrated by extended lifespan and improved healthspan in the C. elegans model of xeroderma pigmentosum group A (XPA, a nucleotideexcision DNA repair (NER) disorder with severe neurodegeneration) , and Ataxia telangiectasia (A-T, due to mutation of ATM which encodes a master regulator of DNA damage response) , . Moreover, in mice with hypomorphic BubR1 (a mitotic check-point kinase) exhibited characteristics of premature aging as evidenced by shorter lifespan, which was restored by NMN supplementation . Altogether, these findings highlight NMN induced restoration of NAD+ levels serve as beneficial therapeutic strategy in countering aging as well as age-related pathological conditions in animal models.
2.2. NR and aging
NR is a natural NAD+ precursor. It can directly be converted into NMN via the activity of NRKs, thereby bypassing the requirement of the NAMPT in the salvage pathway, and therefore offers to provide an additional pathway for elevation of NAD+ levels. Similar to NMN, NR also exhibited beneficial effects in protection against aging and age-related diseases. It has been shown to promote longevity as well improve healthspan in multiple laboratory animal models , , , , , . In age-related disease, in particular obesity, diabetes and cardiovascular conditions NR was able to decrease weight gain, improve glucose tolerance and increase survival rates, respectively in rodents , , . In addition, in models of diabetes and high-fat diet, NR was able to improve metabolic function and reduce lipid accumulation as well as increasing lifespan , , , . Furthermore, supplementation of NR reversed the progressive wasting syndrome and restored endurance in Nampt skeletal muscle knockout mice, mdx model of Duchenne’s muscular dystrophy, .
NR ameliorates neurodegeneration in animal models. In animal models of age-related neurodegenerative diseases such as AD and Parkinson’s disease (PD), NR has been shown to improve memory, learning, motor function and mitochondrial function as well as protected against neuronal cell death , , , . In particular, chronic NR administration in the amyloidogenic models of AD delayed the development and progression of Aβ pathology in AD mice, SH-SY5Y cells, and AD C. elegans, . In addition, it was able to promote longevity and inhibit/delay cognitive decline in AD C. elegans and mice, with the enhanced process of mitochondrial proteostasis and modulation of β-secretase 1 (BACE-1) activity via peroxisome proliferator-activated receptor-gamma coactivator 1 (PGC)-1alpha highlighted as possible underlying mechanisms , . Further evidence reinforcing the beneficial effects of NR as a therapeutic strategy in AD was provided by a recent study using triple transgenic model of AD (3 × Tg), which exhibited not only reduced phosphorylated tau pathology and inhibited cognitive decline; but also, normalised AD-associated neuroinflammation and synaptic dysfunction. Moreover, DNA damage was reduced, in addition, following chronic administration of NR in a DNA repair-deficient 3 × Tg/Polβ+/− mouse model , . The underlying mechanism proposed was the reduction in DNA damage results in reduced activity of NAD+ consuming enzyme PARPs that is involved in DNA repair; thereby increase in the levels of NAD+, which in turn contributes to neurogenesis and inhibits AD-associated pathology, neuroinflammation and mitochondrial dysfunction . Likewise, NR treated induced pluripotent stem cells (iPSCs) derived from PD patients harbouring mutations in the lysosomal enzyme β-Glucocerebrosidase (GBA) gene (GBA-PD), the most common genetic risk for PD, resulted in elevated levels of NAD+ and NAM which coincided with improved mitochondrial morphology and function , . Mitophagy was suggested to be a possible mechanism promoted by NR, which may underlie improved mitochondrial quality control . In addition, flies model of GBA-PD expressing human N370S GBA raised on food containing NR displayed improved motor function and significantly decline in loss of dopamine-containing neuronal population . Additionally, NR has shown significant neuroprotection in a series of DNA repair-deficient premature aging diseases, including XPA, A-T, and Cockayne syndrome (CS, due to impairment of NER) , , .
2.3. NAM and aging
NAM is also a precursor for NAD+ and a key molecule involved in energy metabolism. Low doses of NAM have been shown to increase lifespan in yeast and C. elegans, however, higher doses have been associated with reduced lifespan via inhibition of Sir2 activity , , , , . In models of aging and high fat diet-induced obesity, NAM improved healthspan although it failed to extend lifespan as illustrated by comparable mean and maximum lifespan . In the model of obesity, it has able to restore glucagon storage to similar levels as age-matched standard-diet mice as well as ameliorate diet-induced hepatosteatosis, oxidative stress and inflammation . It was suggested that the beneficial impact of NAM may be attributes to improved mitochondrial function and countering age and high fat diet induced DNA damage . Further evidence reinforcing the beneficial impact of NAM stemmed from a mouse model of glaucoma, which inhibited the development glaucoma in the eyes . Moreover, these findings were replicated by Nmnat1 gene therapy whereby an intravitreal administration of adeno-associated virus AAV2.2 carrying a plasmid to overexpress murine Nmnat1 under a CMV promoter was performed in D2 eyes . The improvement of mitochondrial health and metabolism was suggested to be the underlying mechanism for countering glaucoma mediated by NAM supplementation and Nmnat1 gene therapy .
3. Other approaches to regulate NAD+
3.1. PARP inhibition
The NAD+ consuming enzymes, PARPs, cleave NAD+ into NAM and ADP-ribose (ADPR), as a result generating a chain of ADPR. PARP1 is the most abundant PARPs, which is ubiquitously expressed and is a major consumer of NAD+ in response to DNA damage whereby it contributes to facilitation of the DNA repair process . Both PARPs and sirtuins share NAD+ as a common substrate thus compete for its consumption. It has been reported that PARP1 activity increased with the inevitable process of aging possibly due accumulation of DNA damage . Consequently, the NAD+ pool is depleted which results in reduced activity of sirtuins . Evidence stemming from genetic deletion of PARP1 in mice as well as pharmacological inhibition of PARPs revealed increase in NAD+ content and enhanced activities of sirtuins, in particular SIRT1 and SIRT6, , . Elevated SIRT1 activity was associated with increased mitochondrial content and oxidative metabolism as well as protection against metabolic dysfunction, DNA damage, and neurodegeneration, , .
In addition, increased PARP1 activity has been reported in animal models of age-related neurodegenerative diseases, namely AD and PD , , . Deletion of PARP1 in AD mice protected against cognitive decline as well as attenuated neuroinflammation and Aβ-induced neurotoxicity. In PD rodents, PARP1 pharmacological inhibitors or deletion resulted in resistance to the toxic effects and loss of dopamine-containing neurons in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and 6-hydroxydopamine (6-OHDA), respectively , , . Thus, implicating the contribution of PARP1 hyperactivity in processes leading to neurodegeneration. Moreover, hyperactivity of PARP1 is reported in models of premature aging that resulted decrease in SIRT1 activity, a feature that was reversed by replenishment of NAD+ using its precursors , . Therefore, a potential therapeutic counter for depleted NAD+ pool in aging and age-related diseases could be inhibition of its consumer, PARPs, which will enable activity of sirtuins that plays a pivotal role in regulating cellular processes.
3.2. CD38 inhibition
CD38 is one of the primary NADases in mammals. It can modulate the levels of NAD+ via hydrolysis of NAD+ itself as well degradation of its precursors, NMN and NR. Primarily, CD38 hydrolyses NAD+ to produce of ADPR and NAM , , . It is a key player in several physiological processes, including nuclear Ca2+homoeostasis, immunity, inflammation, glucose and lipid homoeostasis, transferring of mitochondria from astrocytes to neurons, as well as social behaviour , , , , , . An age-dependent increase in levels of CD38 protein has been reported in multiple tissues and organs, which as a result contributes to NAD+ decline . Therefore, CD38-dependent modulation of NAD+ can alter the activity of NAD+-consuming enzymes and affect cellular signalling and metabolism , . Inhibition of CD38 can also promote NAD+ levels and improve glucose and lipid metabolism, which protects against age- and diet-induced diabetes and obesity , . In APP/PS1 model of AD, CD38 depletion resulted in elevation of NAD+ levels that were associated with decrease in Aβ pathology and associated neuroinflammation accompanied by improvement spatial learning behaviour . However, due to the reported important neuroprotective activities of CD38, further stringent and comprehensive evaluation of the procedures of CD38 inhibition as a safe anti-aging strategy , .
3.3. NNMT knockdown
Nicotinamide N-methyltransferase (NNMT) catalyses the methylation of NAM N1-methyl-2- pyridone-5-carboxamide (2py) and N1-methyl-4-pyridone-3-carboxamide (4py) using the universal methyl donor S-adenosyl methionine (Met) (SAM). Both products of NAM methylation are eventually excreted in the urine; thus, NNMT removes NAM from the NAD+biosynthesis pathway and thereby contributes to decrease in levels of NAD+. It is predominantly expressed in the liver and adipose tissue but is also found in other tissues including kidney, lung, muscle, heart, brain, and tumour cells. NNMT has been shown to be involved in various disease conditions such as metabolic disorders, neurodegenerative diseases and cancer . In conditions such as obesity and diabetes, NNMT levels have been reported to be upregulated significantly, which in turn are associated with the disease phenotype , . In fact, genetic knockdown as well as pharmacological inhibition of NNMT was shown to be beneficial in protection against obesity in rodent models of obesity , .
3.4. Genetic promotion of NAD+ biosynthesis
In addition to abovementioned techniques that have shown to enhance NAD+ biosynthesis, genetic tools in the form of Lactobacillus brevis (LbNOX), a water-forming NADH oxidase, has been demonstrated to also induce an increase in compartment-specific levels of NAD+/NADH ratio in HeLa cells . It catalyses a four-electron reduction of oxygen to water (2 NADH + 2H+ + O2 → 2 NAD+ + 2 H2O) , . The NAD+/NADH ratio plays a role in cellular metabolism by affecting the activity of NAD+-dependent enzymes such as sirtuins. LbNOX was shown to ameliorate proliferative and metabolic defects induced by a dysfunctional electron transport chain (ETC) by recycling the pool of NAD+. This, therefore offers to be a novel approach whereby NAD+ levels could potentially be boosted via genetic manipulation in order to understand the fundamental molecular mechanisms in models of aging and age-related diseases.
4. Methods to detect subcellular NAD+
In view of the importance of NAD+ in life, aging, and diseases, it is necessary to accurately detect subcellular NAD+ levels to further unveil its intracellular functions as well as to develop sub-cellular organelle-targeted therapeutic approaches. Traditionally, several assays, such as high-performance liquid chromatography (HPLC)-based methods (e.g., HPLC/MALDI/MS) and fluorometric-based commercial kits have been utilised to detect whole NAD+,  at both cellular levels and/or sub-cellular levels (by isolating sub-cellular fractions ahead). There have some challenges of using these methods to accurately detect sub-cellular NAD+ levels because of the highly instability of NAD+ as well as impossibility of NAD+ detection in live cells/tissues. The recent development of genetically encoded fluorescent biosensors such as SoNar and a biosensor with a bipartite NAD+-binding domain have enabled imaging of relative levels of free NAD+ in the subcellular compartments , . Quantification of NAD+ using fluorescent biosensor targeted to different compartments of mammalian cells showed that mitochondria contain more than twice as much free NAD+ as other compartments . Specifically, the concentration of NAD+ was reported to be approximately 110 μM in the cytoplasm and the nucleus relative to 230 μM in the mitochondrion . These levels are consistent with other reports demonstrating that, in highly metabolically active, post mitotic cells, such as neurons, mitochondria have higher NAD+ levels compared with other sub-cellular compartments . It was further demonstrated genetic and pharmacologic inhibition of NAMPT result in a reduction in NAD+ concentration in all compartments, but depletion of mitochondrial NAD+ occurred at a slower rate. Furthermore, the nuclear and cytoplasmic pools were shown to be readily exchangeable, whilst the mitochondrial pool may maintain mitochondrial NAD+ levels via NAD+ biogenesis by mitochondrial isoform NMNAT3 and import from the cytoplasm . Another recent development has been offered in the form of NAD+ flux quantification that is isotope-tagged and used for analysis of NAD+ metabolism. It demonstrated that approximately 50% decrease in NAD+ consumption following treatment with SIRT1/2 and PARP1/2 inhibitors; thereby implicating both are major consumers of NAD+. The use of such approaches in models of aging and age-related diseases in combination with NAD+ promoting methods would allow the identification of subcellular localisation as well as consumption, which in turn would allow to identify the underlying molecular mechanisms and pathways attributed to NAD+ benefits.
5. Clinical translation
Encouraged by significant and replicable benefits of NAD+ precursors, NR and NMN, in aging and disease animal models, a series of clinical trials of NR and NMN in normal aged population and individuals with diseases have been performed . NAD+ precursors, in particular NR has been demonstrated to elevate blood concentration of NAD+ in healthy individuals in a dose-dependent manner and without any toxic effects . In particular, single oral self-administration of NR (1000 mg) over a period of seven days in a 52 years old male increased blood concentration of NAD+ by 2.7-folds and 45.5-fold increase in nicotinic acidadeninedinucleotide (NAAD), an NAD+biosynthesis intermediate . In addition, a randomized double-blind pharmacokinetic study of single oral administration NR (doses: 100 mg, 300 mg, and 1000 mg) with seven-days gap conducted in 12 healthy patients (aged 30–55 years old) revealed a dose-dependent increase in NAD+ and NAAD levels, with no reported adverse effects . The encouraging results in animal models of aging and age-related diseases of chronic administration of NAD+ precursors have led to studies in humans , . An eight-week randomized, double-blinded, placebo-controlled study in 120 healthy adults (60–80 years old) demonstrated NR (250 mg and 500 mg) induced dose-dependent increase of blood NAD+ level that becomes apparent after 4-weeks and is sustained till the end of the study . Importantly, no serious adverse effects were reported, thereby implicating the chronic administration of NR is a safe and effective way to increase NAD+ levels . These findings are reinforced by a 2 × 6-week randomized, double-blind, placebo-controlled crossover clinical trial conducted in 55–79 years old individuals that showed NR (oral 500 mg, twice a day) to be well tolerated and able to effectively elevates NAD+ levels in healthy adults . Moreover, it was able to reduce systolic blood pressure and aortic stiffness, which are considered measures of cardiovascular disease . Thus, not only the NAD+ precursors are safely administrated but they may also recapitulate the beneficial effects that were evident in animal models, which is an exciting prospect for future clinical trials. However, in conditions such as pancreatic cancer, cell growth has been shown to be dependent of the NAD+ salvage pathway . Hence, inhibition of NAD+ synthesis (via Nampt inhibition) and/or promotion of its consumption (via CD38 NADase) prevented cancer cell growth , . Therefore, implicating that there should be a thorough evaluation for the use of approaches that promote NAD+ biosynthesis as it may be contributor rather than a counter-mechanism in certain conditions. Clinical trials of NAD+ precursors on age-related diseases, such as diabetes, premature aging diseases, and neurodegenerative diseases are in progress .
6. Outstanding questions and future perspectives
Age is the primary cause of the majorly of human diseases and interventional strategies/therapeutics targeting on human aging is arguably the most efficient approach to achieve healthy aging and the improvement of the quality of life worldwide. Although, maintaining a healthy diet, fasting, and exercise may improve the quality of life, it may not be feasible option for all individuals. Therefore, the beneficial effects of NAD+ discussed in the present review, highlight possible ways for improving the quality of life via hindering numerous pathological hallmarks of aging and thereby improving the quality of life and delay age-related diseases (summarized in Fig. 2). Preclinical evidence of NAD+ replenishment that could potentially delay and/or prevent metabolic conditions, hearing loss, muscle atrophy, and cognitive decline are really encouraging for future perspectives. Moreover, NAD+ precursors, in particular NR has been shown to be safely administrated and also able to demonstrate improvement of cardiovascular functions in human. Thus, implicating a possible translational aspect of preclinical benefits of NAD+ supplementation, which is an exciting prospect and opens avenues for future studies to test the impact of elevated NAD+biosynthesis in aging and age-associated diseases in human.
Fig. 2. Physiological and pharmacological strategies for boosting NAD+levels. Inhibiting the age-related decline in NAD+ levels is critical for preventing age- or disease-related frailties. Physiological strategies that could potentially boost NAD+ levels include exercise, fasting, and maintaining a healthy diet. Pharmacologically, boosting NAD+ can be achieved via either supplementation of its precursors, NR and NMN, or inhibition of its consumers by use of CD38 and PARPs inhibitors. Figure modified from Fang et al. 2017 and Fivenson et al. 2017 , .
Despite extensive research on NAD+ biosynthesis and its implications in health and disease, there are major questions that are yet to be explored. Firstly, what levels of NAD+ are to be associated with healthy aging and age-related diseases? In particular, it is of great relevance to elucidate organ and sub-cellular localisation as well levels of NAD+ in health and disease. Such observations would allow to map health- and disease-specific alterations of NAD+, which could be utilised to develop therapeutic interventions that promote NAD+ in a region-specific manner as a counter-mechanism. Decline in NAD+ has been implicated during the process of aging and age-associated diseases, thereby may be affect various processes that are likely to key contributors and drivers of associated dysfunction. Thus, preclinical studies driven towards unveiling the pathways and mechanisms underlying the beneficial effects of NAD+ replenishment in healthy aging and models of disease are required in order to understand how NAD+ contributes to delay and/or prevent hallmarks associated with aging. In particular, it is important to elucidate whether individual or multiple hallmark(s) mechanisms associated with aging are countered by NAD+ replenishment. This would allow understanding of the mode of NAD+ action and the interconnection and contribution of the various hallmarks of aging. NAD+ precursors have thus far shown to be safely and effectively administrated in healthy old humans, elevating NAD+ levels in blood, but its safety and tolerance is yet to be determined in individuals with age-related diseases. Therefore, future clinical trials are required to assess the safety of NAD+ precursors in patients with age-associated diseases such as diabetes and AD. Though, as abovementioned, careful evaluation of the role of NAD+, whether friend or foe in disease, must be taken into account for each disease-condition. Altogether, NAD+ replenishment may serve as a potential therapeutic strategy for aging and multiple conditions to improve the quality of life of the increasing aged population.
Conflicts of interest
The authors declare there is no conflict of interest.
This research was supported by the HELSE SøR-ØST (E.F.F., #2017056), The Research Council of Norway (E.F.F., #262175 and #277813), and two NIA Intra-laboratory grants (2016, 2017 to E.F.F. and V.A.B.). The E.F.F. laboratory has CRADA arrangements with ChromaDex. We thank Øystein Horgmo (Senior Photographer, Medical Photography and Illustration Service, UiO) for making some elements in Fig. 1, Fig. 2.
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COVID-19: NAD+ deficiency may predispose the aged, obese and type2 diabetics to mortality through its effect on SIRT1 activity
The SARS-CoV-2 hyperinflammatory response is associated with high mortality. This hypothesis suggests that a deficiency of nicotinamide adenine dinucleotide (NAD+) may be the primary factor related to the SARS-Cov-2 disease spectrum and the risk for mortality, as subclinical nutritional deficiencies may be unmasked by any significant increase in oxidative stress.
NAD+ levels decline with age and are also reduced in conditions associated with oxidative stress as occurs with hypertension, diabetes and obesity. These groups have also been observed to have high mortality following infection with COVID-19. Further consumption of NAD+ in a pre-existent depleted state is more likely to cause progression to the hyperinflammatory stage of the disease through its limiting effects on the production of SIRT1.
This provides a unifying hypothesis as to why these groups are at high risk of mortality and suggests that nutritional support with NAD+ and SIRT1 activators, could minimise disease severity if administered prophylactically and or therapeutically. The significance of this, if proven, has far-reaching consequences in the management of COVID-19 especially in third world countries, where resources and finances are limited.
COVID-19 may be asymptomatic or manifest in 3 clinical phases, an initial upper respiratory tract infection, with a few patients thereafter progressing to a pneumonic phase, and an even smaller number to the hyperinflammatory phase which may be lethal . The aim of any therapy would be to intervene at an early stage, either prophylactically or therapeutically, to prevent progression of the disease to a point where mechanical ventilation (MV) is required, or significant organ dysfunction occurs .
Risk factors for a poor outcome include older age, comorbidity (in particular diabetes, hypertension and cardiac disease), non-asthmatic respiratory disease, obesity, immunosuppression and male sex , . The independent associations of advancing age, male sex, chronic respiratory conditions (though not well controlled asthma), chronic cardiac and chronic neurological disease with in-hospital mortality, are in line with other international reports . It is difficult however to determine why these conditions specifically are linked to mortality.
Docherty et al. report that severe SARS-CoV-2 infections are rare in those under 18 years of age, comprising only 1.4% of those admitted to hospital. Only 0.8% of those in this study were under 5 years of age, and this “J” shaped age distribution was starkly different from the “U” shaped distribution seen in seasonal influenza . It has not been clear from observational studies however, why SARS-CoV-2 mostly spared children, but it has been speculated that it is due to differential expression of the ACE2 receptor in the developing lung . Similarly, pregnancy has not been reported to be associated with mortality, in contrast to the situation with influenza , .
While the general concept of an excessive or uncontrolled release of pro-inflammatory cytokines is well known, an actual definition of what a hyperinflammatory response or “Cytokine Storm” is, is lacking. Furthermore, there is a poor understanding of the molecular events that precipitate this response and the contribution it makes to pathogenesis. It is also not known what therapeutic strategies might be used to prevent this catastrophic progression of the disease or lessen its severity once initiated .
In this phase, there is an unbalanced and exacerbated inflammatory response with the release of inter alia, tumor necrosis factor (TNF-α), interleukin 1β (IL-1β), interleukin 6 (IL-6), as pro-inflammatory mediators together with interleukin 10 (IL-10) and interferon β as anti-inflammatory mediators. The complex interactions between TNF-α, the interleukins, chemokines and interferons in SARS-CoV-2 are currently poorly understood; however, they are associated with and related to a significant viraemia , .
The fact that most international studies have indicated that certain risk factors were common suggested that a similar systemic abnormality might be present in those at high risk, predisposing to severe illness or mortality.
In this context, the nicotinamide adenine dinucleotide (NAD+)- and zinc-dependent molecule, the Silent Information Regulator 1 (SIRT1) represents a potential common thread in the aetiology of the hyperinflammatory response and increased mortality.
SARS-CoV-2 targets and binds to the angiotensin-converting enzyme 2 receptor (ACE2R), a membrane-associated aminopeptidase also expressed in the vascular endothelium, renal and cardiovascular tissue, and small intestine, testis, and respiratory epithelia . The ACE2R acts as the host cell receptor for the virus which binds via the spike protein on the viral capsid . This stimulates clathrin-dependent endocytosis of both the ACE2R and virus, events that are essential for infectivity. This process induces ADAM 17 activity which reduces expression of ACE2 on the cell surface .
Nicotinamide adenine dinucleotide (NAD+)
NAD+ is a cofactor found in every cell of the body, and it is involved in multiple metabolic pathways. It is a fundamental housekeeping molecule that catalyses electron transfer in metabolic reduction–oxidation reactions, functioning as an electron shuttle in the production of adenosine triphosphate (ATP).
Increased age is a strong predictor of SARS-CoV-2-associated in-hospital mortality after adjusting for comorbidity . Older patients have also been identified as having the lowest levels of NAD+, while, conversely, those with the lowest risk, infants and children have the highest levels.
The decline in NAD+ levels with ageing is mainly dependent on CD38, a 45 kDa transmembrane molecule, encoded on chromosome 4. In leukocytes, it acts as a receptor in adhesion and signalling pathways . CD38 expression is increased with insulin resistance, and may exacerbate the age-dependent decline of NAD+. NAD+ and NADP profoundly affect age-influencing factors such as oxidative stress and mitochondrial activity, and NAD+-dependent sirtuins also mediate the ageing process . As humans age, antioxidant defence mechanisms such as glutathione production are also depleted and the associated increase in reactive oxidative species (ROS) causes all cells  to enter a state of pseudohypoxia in which the ratio of NAD+/NADP declines , , .
Oxidative stress also activates the NAD+-dependent enzyme, poly ADP ribose polymerase 1 (PARP1) . Hyperactivity of PARP1 results in depletion of cellular NAD+ pools, leading to ATP deficiency, energy loss, and subsequent cell death. These processes have the potential to enhance the pro-inflammatory cascade.
NAD+ deficiency impairs SIRT1 function  and its successful activation. Whereas extreme niacin deficiency is associated with the development of pellagra, more subtle decreases occur in diabetes, ageing and hypertension with resultant attenuation of responsiveness to inflammatory stimuli .
Silent Information Regulator 1 (SIRT1)
Sirtuins are an ancient family of seven NAD+-dependent deacylase and mono-ADP-ribosyl transferase signalling proteins that are intrinsically involved in metabolic regulation and cellular homeostasis. Of particular interest is SIRT1, which downregulates ADAM 17 (A Disintegrin and Metalloproteinase Domain 17), also called TNF-α converting enzyme (TACE), by increasing expression of TIMP3 the gene that encodes for tissue metalloproteinase inhibitor 3 . In so doing it decreases levels of TNF-α, IL-1b and IL-6. An increase in TNF-α causes SIRT1 to down-regulate ADAM 17, thereby controlling TNF-α formation in a negative feedback loop that secondarily influences IL-1b and IL-6 production, which are dependent on TNF-α .
SIRT1 is known to play a crucial role in obesity-associated metabolic diseases, cancer, ageing, cellular senescence, cardiac ageing and stress, prion-mediated neurodegeneration, inflammatory signalling in response to environmental stress, embryonal development of the heart, brain, spinal cord and dorsal root ganglia, and placental cell survival . In its inactive or open state, it contains a Zn++ module and an NAD+ -binding site .
Whereas certain conditions such as ulcerative colitis, Crohn’s disease, short bowel syndrome, renal failure, alcoholism, and inadequate meat intake are specifically associated with zinc deficiency there is evidence that zinc intake among older adults might be marginal. An analysis of the Third National Health and Nutrition Examination Survey (NHANES III), 1988–1994 data found that 35–45% of adults aged 60 years or older had a zinc intake below estimated average requirements .
When NAD+ binds to the SIRT1 molecule in the presence of the Zn++ -binding module, it undergoes a structural change, enveloping the NAD+ molecule and causing it to be “closed” or activated . The presence of both the Zn++ and the NAD+ moieties are imperative for its function.
SIRT1 downregulates ADAM17 and cytokine production
ADAM17 is a proteinase encoding gene. TNF-α and the cytokine receptor for IL-6 must be proteolytically cleaved in order to be systemically active, and ADAM17 provides this function. If ADAM17 expression is not downregulated by SIRT1, TNF-α and IL-6 are released, resulting in an uncontrolled hyperinflammatory response as may occur with COVID-19 , , , , . SIRT 1, by inhibition of ADAM17 and thereby TNF-α and IL-6, performs an anti-inflammatory function , , , , , , , .
If oxidative stress is severe, increased ADAM17 attempts to ameliorate tissue injury by converting active iron (Fe2+) to its inert form (Fe3+) which is stored in hepatocytes and macrophages and as ferritin by means of the Fenton reaction (Fe2+ + H2O2 → Fe3+ + HO• + OH−), (Fe3+ + H2O2 → Fe2+ + HO2• + H+). This also potentially transforms haemoglobin to methaemoglobin, reducing its capacity to bind to oxygen .Go to:
COVID-19 replication and SIRT1
SIRT1 not only controls and modifies the inflammatory response, but along with the Sirtuin family (SIRT1–7) is also a primary defence against DNA and RNA viral pathogens . In some respiratory infections and cardiovascular conditions, SIRT1 promotes autophagy (the destruction of damaged or redundant cellular components occurring in vacuoles within the cell), and in so doing inhibits apoptosis and provides protection against hypoxic stress , , , .
Upregulation of SIRT1 directly decreases viral replication and inhibits the activation of ADAM17, thereby decreasing TNF-α, IL-1b and IL-6. Conversely depletion of SIRT1 allows for increased viral replication with little or no inhibition of ADAM17 activity, causing uncontrolled increases in TNF-α, IL-6 and IL-1b. Whereas an increase in TNF-α would usually increase SIRT1 activity to downregulate ADAM17, in the presence of a deficiency of NAD+ or Zn++, this would not occur due to insufficient activation of SIRT1, causing an unchecked increase in TNF-α.
In both obesity and type 2 diabetes mellitus, intracellular NAD+ levels are decreased in multiple tissues, including adipose tissue, skeletal muscle, liver and the hypothalamus.  Furthermore, both conditions are characterised by low-grade inflammation associated with activation of both IL6 and TNF-α , . Obesity or type 2 diabetes mellitus would increase the risk for cytokine storm due to an inability to activate SIRT1.
SIRT1 maintains vascular endothelial function, preventing or reducing the potential for the metabolic syndrome, ischaemia–reperfusion injury and inflammation in obesity. With increasing age however, NAD+ levels and sirtuin activity decline and this is exacerbated by obesity and sedentary lifestyles . SIRT1 is an effective inhibitor of oxidative stress in vascular endothelial cells (EC)  via various signalling pathways .
The endothelial glycocalyx (EG) is a web of membrane-bound glycoproteins on the luminal side of endothelial cells, associated with various glycosaminoglycans that cover the vascular endothelium . The EG separates cellular blood components from the endothelium and maintains osmotic tension of the intravascular compartment , .
Conditions causing damage to, and shedding or fragmentation of the EG, (as seen in SARSCoV-2 under severe oxidative stress induced by the hyperinflammatory response), exposes the endothelium, allowing adhesion, clumping and activation of platelets with degranulation and release of vasoactive substances. The EG has anticoagulant properties as it is a binding site for mediators such as heparin cofactor II, antithrombin, thrombomodulin and tissue factor pathway inhibitor (TFPI). Heparin cofactor II and dermatan sulphate inhibit thrombin, and antithrombin activity is enhanced when bound to heparan sulphate. Conversely, exposure of the endothelial cell surface protein, thrombomodulin, which contains a cofactor for thrombin, chondroitin sulphate, promotes coagulation via activation of tissue factor  as seen in SAR-CoV-2.
The EG is already compromised in systemic inflammatory states, such as diabetes, hyperglycaemia, surgery, trauma and sepsis . Under conditions of more severe oxidative stress, as in the hyperinflammatory response, widespread damage may lead to its destruction, with the occurrence of capillary leak and oedema formation, accelerated inflammation, platelet aggregation, hypercoaguability and a loss of vascular responsiveness . Inflammatory mediators that are implicated in this process are TNF-α, bradykinin, C-reactive protein and mast cell tryptase.
Given the above, it is possible that activation of SIRT1 may be a crucial factor in the prevention of the hyperinflammatory response and may be necessary for a successful defence against viral attack. Vulnerable patient groups would potentially be less likely or unable to ensure sufficient activation of SIRT1 due to low NAD+ levels or associated nutritional deficiencies including Zn++, and as such contribute to an inability to control viral replication and reduce the uncontrolled expression of pro-inflammatory cytokines.Go to:
The SARS-CoV-2 hyperinflammatory response is associated with high mortality. A deficiency of NAD+, in the context of an elevated CD38, may be the primary factor related to the SARS-Cov-2 disease spectrum and the risk of mortality, as subclinical nutritional deficiencies may be unmasked by any significant increase in oxidative stress.
NAD+ levels decline with age and are also reduced in conditions associated with oxidative stress as occurs with hypertension, diabetes and obesity. These same groups have also been observed to have high mortality following infection with COVID-19. Further consumption of NAD+ in a pre-existent depleted state is more likely to cause progression to the hyperinflammatory stage of the disease through its limiting effects on the production of SIRT1.
Given that activation of SIRT1 is dependent on the availability of NAD+ and zinc and that high levels of oxidative stress deplete NAD+, thereby decreasing SIRT1 activity, nutritional support with NAD+ precursors and SIRT1 activators, could minimise disease severity if administered prophylactically and or therapeutically. The significance of this hypothesis, if proven, has far-reaching consequences in the management of COVID-19 especially in third world countries, where resources and finances are limited.Go to:
We hypothesize that reduced Nicotinamide Adenine Dinucleotide (NAD+) levels with consequent deficient activity of the NAD+ dependent molecule SIRT1, which modulates cytokine production, may be the factor that predisposes the aged, obese, type 2 diabetics and other vulnerable groups to an increased mortality.Go to:
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.Go to:
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We are as old as our arteries, the adage goes, so could reversing the aging of blood vessels hold the key to restoring youthful vitality?
The answer appears to be yes, at least in mice, according to a new study led by investigators at Harvard Medical School.
The research, published March 22 in Cell, identifies the key cellular mechanisms behind vascular aging and its effects on muscle health and has successfully reversed the process in animals.
The findings pinpoint a glitch in the normal crosstalk that occurs between muscles and blood vessels and keeps both tissues healthy.
Using the synthetic precursors of two molecules naturally present in the body, the scientists also managed to reverse blood vessel demise and muscle atrophy in aging mice, boosting their exercise endurance in the process.
The achievement, the team said, paves the way to identifying related therapies for humans.
“We’ve discovered a way to reverse vascular aging by boosting the presence of naturally occurring molecules in the body that augment the physiological response to exercise,” said study senior investigator David Sinclair, professor in the Department of Genetics at Harvard Medical School and co-director of the Paul F. Glenn Center for the Biology of Aging at Harvard Medical School.
“The approach stimulates blood vessel growth and boosts stamina and endurance in mice and sets the stage for therapies in humans to address the spectrum of diseases that arise from vascular aging,” added Sinclair, who is also a professor at the University of New South Wales School of Medical Sciences in Sydney, Australia.
The researchers caution that many promising treatments in mice don’t have the same effect in humans due to critical differences in biology. However, the results of the experiments were dramatic enough to prompt the research team to pursue experiments in humans. Clinical trials for safety are already under way, Sinclair said.
As old as our blood vessels
Sinclair and team set out to unravel the mechanisms behind one of biology’s inevitabilities: aging.
As we grow old, we become weak and frail. A constellation of physiological changes—some subtle, some dramatic—precipitate this inevitable decline. What exactly happens inside our cells to cause the biological shifts that lead to aging? It’s a question that has vexed Sinclair and team for years.
As we age, our tiniest blood vessels wither and die, causing reduced blood flow and compromised oxygenation of organs and tissues. Vascular aging is responsible for a constellation of disorders, such as cardiac and neurologic conditions, muscle loss, impaired wound healing and overall frailty, among others. Scientists have known that loss of blood flow to organs and tissues leads to the build-up of toxins and low oxygen levels. The so-called endothelial cells, which line blood vessels, are essential for the health and growth of blood vessels that supply oxygen-rich and nutrient-loaded blood to organs and tissues. But as these endothelial cells age, blood vessels atrophy, new blood vessels fail to form and blood flow to most parts of the body gradually diminishes. This dynamic is particularly striking in muscles, which are heavily vascularized and rely on robust blood supply to function.
Muscles begin to shrivel and grow weaker with age, a condition known as sarcopenia. The process can be slowed down with regular exercise, but gradually even exercise becomes less effective at holding off this weakening.
Sinclair and team wondered: What precisely curtails the blood flow and precipitates this unavoidable decline? Why does even exercise lose its protective power to sustain muscle vitality? Is this process reversible?
In a series of experiments, the team found that reduced blood flow develops as endothelial cells start to lose a critical protein known as sirtuin1, or SIRT1. Previous studies have shown that SIRT1 delays aging and extends life in yeast and mice.
SIRT1 loss is, in turn, precipitated by the loss of NAD+, a key regulator of protein interactions and DNA repair that was identified more than a century ago. Previous research by Sinclair and others has shown that NAD+, which also declines with age, boosts the activity of SIRT1.
A stimulating conversation
The study reveals that NAD+ and SIRT1 provide a critical interface that enables the conversation between endothelial cells in the walls of blood vessels and muscle cells.
Specifically, the experiments reveal that in young mouse muscle, SIRT1 signaling is activated and generates new capillaries, the tiniest blood vessels in the body that supply oxygen and nutrients to tissues and organs. However, as NAD+/SIRT1 activity diminishes over time, the study found, so does the blood flow, leaving muscle tissue nutrient-deprived and oxygen-starved.
Indeed, when researchers deleted SIRT1 in the endothelial cells of young mice, they observed markedly diminished capillary density and decreased number of capillaries, compared with mice that had intact SIRT1. Mice whose endothelial cells lacked SIRT1 had poor exercise tolerance, managing to run only half the distance covered by their SIRT1-intact peers.
To determine SIRT1’s role in exercise-induced blood vessel growth, the researchers observed how SIRT1-deficient mice responded to exercise. After a month-long training regimen, the hind-leg muscles of SIRT1-deficient mice showed markedly diminished ability to form new blood vessels in response to exercise compared with same-age mice that had intact SIRT1 in their endothelial cells.
Exercise-induced blood vessel formation is known to occur in response to growth-stimulating proteins released by muscles under strain. SIRT1, however, appears to be the key messenger relaying growth-factor signaling from muscles to blood vessels, the study found.
Experiments showed that endothelial cells lacking SIRT1 were desensitized to the growth-stimulating proteins released by exercised muscles.
“It’s as if these cells had grown deaf to the signals that muscles sent their way,” Sinclair said.
The observation, he added, explains why age-related loss of SIRT1 leads to muscle atrophy and blood vessel demise.
Since the experiments revealed the critical role of SIRT1 in exercise-induced blood vessel formation, the researchers wondered whether boosting SIRT1 levels would stimulate blood vessel growth and stave off muscle wasting.
Exercise in a pill?
The scientists set their sights on NAD+, a molecule conserved across many life forms, known to decline with age and previously shown to stimulate SIRT1 activity.
“We reasoned that declining NAD+ levels reduce SIRT1 activity and thus interfere with aging mice’s ability to grow new blood vessels,” said study first author Abhirup Das, who conducted the work as a post-doctoral fellow in Sinclair’s lab, currently a visiting scholar in genetics at Harvard Medical School and a post-doctoral research fellow at the University of South New Wales School of Medical Sciences.
To test this premise, scientists used a chemical compound called NMN, a NAD+ precursor, previously shown to play a role in repairing cellular DNA and maintaining cell vitality.
In lab dish experiments, endothelial cells from humans and mice treated with NMN showed enhanced growth capacity and reduced cell death.
Next, the team gave NMN over two months to a group of mice that were 20 months old—the rough equivalent of 70 in human years. NMN treatment restored the number of blood capillaries and capillary density to those seen in younger mice. Blood flow to the muscles also increased and was significantly higher than blood supply to the muscles seen in same-age mice that didn’t receive NMN.
The most striking effect, however, emerged in the aging mice’s ability to exercise. These animals showed between 56 and 80 percent greater exercise capacity, compared with untreated mice the study showed. The NMN-treated animals managed to run 430 meters, or about 1,400 feet, on average, compared with 240 meters, or 780 feet, on average, for their untreated peers.
To see whether the effects of NMN could be further augmented, the researchers added a second compound to the treatment regimen. The compound, sodium hydrosulfide (NaHS), is a precursor to hydrogen sulfide, which also boosts the activity of SIRT1.
A group of 32-month-old mice—the rough equivalent to 90 in human years—receiving the combo treatment for four weeks were able to run, on average, twice as long as untreated mice. In comparison, mice treated with NMN alone ran 1.6 times farther, on average, than untreated animals.
“These are really old mice so our finding that the combo treatment doubles their running capacity is nothing short of intriguing,” said study co-author James Mitchell, associate professor of genetics and complex diseases at the Harvard T. H. Chan School of Public Health. Research led by Mitchell and published in the same issue of Cell also found sodium hydrosulfide to augment blood vessel formation in the muscles of mice.
Interestingly, the NMN treatment did not improve blood vessel density and exercise capacity in young sedentary mice. However, it did boost blood vessel formation and exercise capacity in young mice that had been exercising regularly for a month.
“This observation underscores the notion that age plays a critical role in the crosstalk between blood vessels and muscles and points to a loss of NAD+ and SIRT1 as the reason behind loss of exercise effectiveness after middle age,” Das said.
The researchers say their findings may pave the way to therapeutic advances that hold promise for the millions of older people for whom regular physical activity is not an option.
“Even if you’re an athlete, you eventually decline,” Sinclair said. “But there is another category of people—what about those who are in a wheelchair or those with otherwise reduced mobility?”
The team’s ultimate goal is to replicate the findings and, eventually, move toward developing small-molecule, NMN-based drugs that mimic the effects of exercise—enhanced blood flow and oxygenation of muscles and other tissues. Such therapies may even help with new vessel growth of organs that suffer tissue-damaging loss of blood supply and oxygen, a common scenario in heart attacks and ischemic strokes, the team said.
Neo-vascularization—the formation of new blood vessels—should be treated with caution, the researchers say, because increased blood supply could inadvertently fuel tumor growth.
“The last thing you want to do is provide extra blood and nourishment to a tumor if you already have one,” said study co-author Lindsay Wu, at the University of New South Wales School of Medical Sciences.
Sinclair and Wu point out that experiments done as part of the current study provide no evidence that treatment with NMN stimulated tumor development in animals treated with the compound.
Co-investigators included George Huang, Michael Bonkowski, Alban Longchamp, Catherine Li, Michael Schultz, Lynn-Jee Kim, Brenna Osborne, Sanket Joshi, Yuancheng Lu, Jose Humberto, Trevine-Villareal, Myung-Jin Kang, Tzong-tyng Hung, Brendan Lee, Eric Williams, Masaki Igarashi, James Mitchell, Nigel Turner, Zolt Arany and Leonard Guarente.
The work was supported by the Glenn Foundation for Medical Research (grants RO1 AG028730 and RO1 DK100263), and by the National Institutes of Health/National Heart, Lung and Blood Institute (grant RO1 HL094499).
Nicotinamide adenine dinucleotide (NAD+) and related metabolites are central mediators of fuel oxidation and bioenergetics within cardiomyocytes. Additionally, NAD+ is required for the activity of multifunctional enzymes, including sirtuins and poly(ADP-ribose) polymerases that regulate posttranslational modifications, DNA damage responses, and Ca2+ signaling. Recent research has indicated that NAD+ participates in a multitude of processes dysregulated in cardiovascular diseases. Therefore, supplementation of NAD+ precursors, including nicotinamide riboside that boosts or repletes the NAD+ metabolome, may be cardioprotective. This review examines the molecular physiology and preclinical data with respect to NAD+ precursors in heart failure-related cardiac remodeling, ischemic-reperfusion injury, and arrhythmias. In addition, alternative NAD+-boosting strategies and potential systemic effects of NAD+ supplementation with implications on cardiovascular health and disease are surveyed.
In addition to its central role in mediating oxidation reduction in fuel metabolism and bioenergetics, nicotinamide adenine dinucleotide (NAD+) has emerged as a vital co-substrate for a number of proteins involved in diverse cellular processes, including sirtuins, poly(ADP-ribose) polymerases and cyclic ADP-ribose synthetases. The connection with aging and age-associated diseases has led to a new wave of research in the cardiovascular field. Here, we review the basics of NAD+ homeostasis, the molecular physiology and new advances in ischemic-reperfusion injury, heart failure, and arrhythmias, all of which are associated with increased risks for sudden cardiac death. Finally, we summarize the progress of NAD+-boosting therapy in human cardiovascular diseases and the challenges for future studies.
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