LXR/CD38 activation drives cholesterol-induced macrophage senescence and neurodegeneration via NAD+ depletion

Although dysregulated cholesterol metabolism predisposes aging tissues to inflammation and a plethora of diseases, the underlying molecular mechanism remains poorly defined. Here, we show that metabolic and genotoxic stresses, convergently acting through liver X nuclear receptor, upregulate CD38 to promote lysosomal cholesterol efflux, leading to nicotinamide adenine dinucleotide (NAD+) depletion in macrophages. Cholesterol-mediated NAD+ depletion induces macrophage senescence, promoting key features of age-related macular degeneration (AMD), including subretinal lipid deposition and neurodegeneration. NAD+ augmentation reverses cellular senescence and macrophage dysfunction, preventing the development of AMD phenotype. Genetic and pharmacological senolysis protect against the development of AMD and neurodegeneration. Subretinal administration of healthy macrophages promotes the clearance of senescent macrophages, reversing the AMD disease burden. Thus, NAD+ deficit induced by excess intracellular cholesterol is the converging mechanism of macrophage senescence and a causal process underlying age-related neurodegeneration.

Nicotinamide mononucleotide induces autophagy and ferroptosis via AMPK/mTOR pathway in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is a common malignancy worldwide. Herein, we investigated the role of nicotinamide mononucleotide (NMN) in HCC progression. HCC cells were treated with NMN (125, 250, and 500 μM), and then nicotinamide adenine dinucleotide (NAD+ ) and NADH levels in HCC cells were measured to calculate NAD+ /NADH ratio. Cell proliferation, apoptosis, autophagy and ferroptosis were determined. AMPK was knocked down to confirm the involvement of AMPK/mTOR signaling. Furthermore, tumor-inhibitory effect of NMN was investigated in xenograft models. Exposure to NMN dose-dependently increased NAD+ level and NAD+ /NADH ratio in HCC cells. After NMN treatment, cell proliferation was inhibited, whereas apoptosis was enhanced in both cell lines. Additionally, NMN dose-dependently enhanced autophagy/ferroptosis and activated AMPK/mTOR pathway in HCC cells. AMPK knockdown partially rescued the effects of NMN in vitro. Furthermore, NMN treatment restrained tumor growth in nude mice, activated autophagy/ferroptosis, and promoted apoptosis and necrosis in tumor tissues. The results indicate that NMN inhibits HCC progression by inducing autophagy and ferroptosis via AMPK/mTOR signaling. NMN may serve as a promising agent for HCC treatment.

Role and Potential Mechanisms of Nicotinamide Mononucleotide in Aging

Nicotinamide adenine dinucleotide (NAD+) has recently attracted much attention due to its role in aging and lifespan extension. NAD+ directly and indirectly affects many cellular processes, including metabolic pathways, DNA repair, and immune cell activities. These mechanisms are critical for maintaining cellular homeostasis. However, the decline in NAD+ levels with aging impairs tissue function, which has been associated with several age-related diseases. In fact, the aging population has been steadily increasing worldwide, and it is important to restore NAD+ levels and reverse or delay these age-related disorders. Therefore, there is an increasing demand for healthy products that can mitigate aging, extend lifespan, and halt age-related consequences. In this case, several studies in humans and animals have targeted NAD+ metabolism with NAD+ intermediates. Among them, nicotinamide mononucleotide (NMN), a precursor in the biosynthesis of NAD+, has recently received much attention from the scientific community for its anti-aging properties. In model organisms, ingestion of NMN has been shown to improve age-related diseases and probably delay death. Here, we review aspects of NMN biosynthesis and the mechanism of its absorption, as well as potential anti-aging mechanisms of NMN, including recent preclinical and clinical tests, adverse effects, limitations, and perceived challenges.

NAD+ supplementation prevents STING-induced senescence in CD8+ T cells by improving mitochondrial homeostasis

Understanding the connection between senescence phenotypes and mitochondrial dysfunction is crucial in aging and premature aging diseases. Loss of mitochondrial function leads to a decline in T cell function, which plays a significant role in this process. However, more research is required to determine if improving mitochondrial homeostasis alleviates senescence phenotypes. Our research has shown an association between NAD+ and senescent T cells through the cGAS-STING pathway, which can lead to an inflammatory phenotype. Further research is needed to fully understand the role of NAD+ in T-cell aging and how it can be utilized to improve mitochondrial homeostasis and alleviate senescence phenotypes. We demonstrate here that mitochondrial dysfunction and cellular senescence with a senescence-associated secretory phenotype (SASP) occur in senescent T cells and tumor-bearing mice. Senescence is mediated by a stimulator of interferon genes (STING) and involves ectopic cytoplasmic DNA. We further show that boosting intracellular NAD+ levels with nicotinamide mononucleotide (NMN) prevents senescence and SASP by promoting mitophagy. NMN treatment also suppresses senescence and neuroinflammation and improves the survival cycle of mice. Encouraging mitophagy may be a useful strategy to prevent CD8+ T cells from senescence due to mitochondrial dysfunction. Additionally, supplementing with NMN to increase NAD+ levels could enhance survival rates in mice while also reducing senescence and inflammation, and enhancing mitophagy as a potential therapeutic intervention.

The Role of NAD+ and NAD+-Boosting Therapies in Inflammatory Response by IL-13

The essential role of nicotinamide adenine dinucleotide+ (NAD+) in redox reactions during oxidative respiration is well known, yet the coenzyme and regulator functions of NAD+ in diverse and important processes are still being discovered. Maintaining NAD+ levels through diet is essential for health. In fact, the United States requires supplementation of the NAD+ precursor niacin into the food chain for these reasons. A large body of research also indicates that elevating NAD+ levels is beneficial for numerous conditions, including cancer, cardiovascular health, inflammatory response, and longevity. Consequently, strategies have been created to elevate NAD+ levels through dietary supplementation with NAD+ precursor compounds. This paper explores current research regarding these therapeutic compounds. It then focuses on the NAD+ regulation of IL-13 signaling, which is a research area garnering little attention. IL-13 is a critical regulator of allergic response and is associated with Parkinson's disease and cancer. Evidence supporting the notion that increasing NAD+ levels might reduce IL-13 signal-induced inflammatory response is presented. The assessment is concluded with an examination of reports involving popular precursor compounds that boost NAD+ and their associations with IL-13 signaling in the context of offering a means for safely and effectively reducing inflammatory response by IL-13.

Complementary yet divergent effects of exercise and an exercise mimetic on microbiome in high-fat diet-induced obesity

Exercise is beneficial for obesity, partially through increased mitochondrial activity and raised nicotinamide adenine dinucleotide (NAD), a coenzyme critical for mitochondrial function and metabolism. Recent work has shown that increasing the availability of NAD through pharmacological means improves metabolic health in rodent models of diet-induced obesity and that the effect of these supplements when administered orally may be modulated by the gut microbiome. The gut microbiome is altered by both diet and exercise and is thought to contribute to some aspects of high-fat diet-induced metabolic dysfunction. We examined the independent and combined effects of treadmill exercise and nicotinamide mononucleotide (NMN) supplementation on the gut microbiome of female C57Bl6/J mice chronically fed a high-fat diet. We showed that 8 wk of treadmill exercise, oral-administered NMN, or combined therapy exert unique effects on gut microbiome composition without changing bacterial species richness. Exercise and NMN exerted additive effects on microbiota composition, and NMN partially or fully restored predicted microbial functions, specifically carbohydrate and lipid metabolism, to control levels. Further research is warranted to better understand the mechanisms underpinning the interactions between exercise and oral NAD+ precursor supplementation on gut microbiome.NEW & NOTEWORTHY Exercise and NAD+ precursor supplementation exerted additive and independent effects on gut microbiota composition and inferred function in female mice with diet-induced obesity. Notably, combining exercise and oral nicotinamide mononucleotide supplementation restored inferred microbial functions to control levels, indicating that this combination may improve high-fat diet-induced alterations to microbial metabolism.

The Role of Nicotinamide Mononucleotide Supplementation in Psoriasis Treatment

Psoriasis is one of several chronic inflammatory skin diseases with a high rate of recurrence, and its pathogenesis remains unclear. Nicotinamide mononucleotide (NMN), as an important precursor of nicotinamide adenine dinucleotide (NAD+), has been reported to be a promising agent in treating various diseases, its positive effects including those induced via its anti-inflammatory and antioxidant properties. For this reason, we have aimed to explore the possible role of NMN in the treatment of psoriasis. Psoriasis models were constructed with imiquimod (IMQ) stimulation for 5 days in vivo and with M5 treatment in keratinocyte cell lines in vitro. NMN treatment during the IMQ application period markedly attenuated excess epidermal proliferation, splenomegaly, and inflammatory responses. According to GEO databases, Sirtuin1 (SIRT1) levels significantly decreased in psoriasis patients' lesion tissues; this was also the case in the IMQ-treated mice, while NMN treatment reversed the SIRT1 decline in the mouse model. Moreover, NMN supplementation also improved the prognoses of the mice after IMQ stimulation, compared to the untreated group with elevated SIRT1 levels. In HEKa and HaCaT cells, the co-culturing of NMN and M5 significantly decreased the expression levels of proinflammation factors, the phosphorylation of NF-κB, stimulator of interferon genes (STING) levels, and reactive oxygen species levels. NMN treatment also recovered the decrease in mitochondrial membrane potential and respiration ability and reduced mtDNA in the cytoplasm, leading to the inhibition of autoimmune inflammation. The knockdown of SIRT1 in vitro eliminated the protective and therapeutic effects of NMN against M5. To conclude, our results indicate that NMN protects against IMQ-induced psoriatic inflammation, oxidative stress, and mitochondrial dysfunction by activating the SIRT1 pathway.

Nicotinamide mononucleotide alleviates seizures via modulating SIRT1-PGC-1α mediated mitochondrial fusion and fission

Both human and animal experiments have demonstrated that energy metabolism dysfunction in neurons after seizures is associated with an imbalance in mitochondrial fusion/fission dynamics. Effective neuronal mitochondrial dynamics regulation strategies remain elusive. Nicotinamide mononucleotide (NMN) can ameliorate mitochondrial functional and oxidative stress in age-related diseases. But whether NMN improves mitochondrial energy metabolism to exert anti-epileptic effects is unclear. This study aims to clarify if NMN can protect neurons from pentylenetetrazole (PTZ) or Mg2+ -free-induced mitochondrial disorder and apoptosis via animal and cell models. We established a continuous 30-day PTZ (37 mg/kg) intraperitoneal injection-induced epileptic mouse model and a cell model induced by Mg2+ -free solution incubation to explore the neuroprotective effects of NMN. We found that NMN treatment significantly reduced the seizure intensity of PTZ-induced epileptic mice, improved their learning and memory ability, and enhanced their motor activity and exploration desire. At the same time, in vitro and in vivo experiments showed that NMN can inhibit neuronal apoptosis and improve the mitochondrial energy metabolism function of neurons. In addition, NMN down-regulated the expression of mitochondrial fission proteins (Drp1 and Fis1) and promoted the expression of mitochondrial fusion proteins (Mfn1 and Mfn2) by activating the SIRT1-PGC-1α pathway, thereby inhibiting PTZ or Mg2+ -free extracellular solution-induced mitochondrial dysfunction, cell apoptosis, and oxidative stress. However, combined intervention of SIRT1 inhibitor, Selisistat, and PGC-1α inhibitor, SR-18292, eliminated the regulatory effect of NMN pre-treatment on mitochondrial fusion and fission proteins and apoptosis-related proteins. Therefore, NMN intervention may be a new potential treatment for cognitive impairment and behavioral disorders induced by epilepsy, and targeting the SIRT1-PGC-1α pathway may be a promising therapeutic strategy for seizures.

Effect of Nicotinamide Mononucleotide Concentration in Human Milk on Neurodevelopmental Outcome: The Tohoku Medical Megabank Project Birth and Three-Generation Cohort Study

(1) Background: Breast milk is the only source of nutrition for breastfed infants, but few studies have examined the relationship between breast milk micronutrients and infant neurodevelopmental outcome in exclusively breastfed infants. The aim of this study was to characterize the association between nicotinamide adenine dinucleotide (NAD)-related compounds in the breast milk of Japanese subjects and infant neurodevelopmental outcome. (2) Methods: A total of 150 mother-child pairs were randomly selected from the three-generation cohort of the Tohoku Medical Megabank in Japan. Infants were exclusively breastfed for up to 6 months. Breast milk was collected at 1 month postpartum, and the quantity of NAD-related substances in the breast milk was quantified. The mothers also completed developmental questionnaires at 6, 12, and 24 months. The relationship between the concentration of NAD-related substances in breast milk and developmental indicators was evaluated via ordinal logistic regression analysis. (3) Results: Nicotinamide mononucleotide (NMN) was quantified as the major NAD precursor in breast milk. The median amount of NMN in the breast milk was 9.2 μM. The NMN concentration in breast milk was the only NAD-related substance in breast milk that showed a significant positive correlation with neurodevelopmental outcome in infants at 24 months. (4) Conclusions: The results suggest that NMN in human milk may be an important nutrient for early childhood development.

The identification of new roles for nicotinamide mononucleotide after spinal cord injury in mice: an RNA-seq and global gene expression study

Background

Nicotinamide mononucleotide (NMN), an important transforming precursor of nicotinamide adenine dinucleotide (NAD+). Numerous studies have confirmed the neuroprotective effects of NMN in nervous system diseases. However, its role in spinal cord injury (SCI) and the molecular mechanisms involved have yet to be fully elucidated.

Methods

We established a moderate-to-severe model of SCI by contusion (70 kdyn) using a spinal cord impactor. The drug was administered immediately after surgery, and mice were intraperitoneally injected with either NMN (500 mg NMN/kg body weight per day) or an equivalent volume of saline for seven days. The central area of the spinal cord was harvested seven days after injury for the systematic analysis of global gene expression by RNA Sequencing (RNA-seq) and finally validated using qRT-PCR.

Results

NMN supplementation restored NAD+ levels after SCI, promoted motor function recovery, and alleviated pain. This could potentially be associated with alterations in NAD+ dependent enzyme levels. RNA sequencing (RNA-seq) revealed that NMN can inhibit inflammation and potentially regulate signaling pathways, including interleukin-17 (IL-17), tumor necrosis factor (TNF), toll-like receptor, nod-like receptor, and chemokine signaling pathways. In addition, the construction of a protein-protein interaction (PPI) network and the screening of core genes showed that interleukin 1β (IL-1β), interferon regulatory factor 7 (IRF 7), C-X-C motif chemokine ligand 10 (Cxcl10), and other inflammationrelated factors, changed significantly after NMN treatment. qRT-PCR confirmed the inhibitory effect of NMN on inflammatory factors (IL-1β, TNF-α, IL-17A, IRF7) and chemokines (chemokine ligand 3, Cxcl10) in mice following SCI.

Conclusion

The reduction of NAD+ levels after SCI can be compensated by NMN supplementation, which can significantly restore motor function and relieve pain in a mouse model. RNA-seq and qRT-PCR systematically revealed that NMN affected inflammation-related signaling pathways, including the IL-17, TNF, Toll-like receptor, NOD-like receptor and chemokine signaling pathways, by down-regulating the expression of inflammatory factors and chemokines.

NAD+ Precursors in Human Health and Disease: Current Status and Future Prospects

Significance: Nicotinamide adenine dinucleotide (NAD+) acts as a cofactor in many important biological processes. The administration of NAD+ precursors increases the intracellular NAD+ pool and has beneficial effects on physiological changes and diseases associated with aging in various organisms, including rodents and humans. Recent Advances: Evidence from preclinical studies demonstrating the beneficial effects of NAD+ precursors has rapidly increased in the last decade. The results of these studies have prompted the development of clinical trials using NAD+ precursors, particularly nicotinamide riboside (NR) and nicotinamide mononucleotide (NMN). In addition, in vivo studies of NAD+ metabolism have rapidly progressed. Critical Issues: Several studies have demonstrated that the oral administration of NAD+ precursors, such as NR and NMN, is safe and significantly increases NAD+ levels in humans. However, the efficacy of these NAD+ precursors is lower than expected from the results of preclinical studies. In addition, the identification of the contribution of the host-gut microbiota interactions to NR and NMN metabolism has added to the complexity of NAD+ metabolism. Future Directions: Further studies are required to determine the efficacy of NAD+ precursors in humans. Further in vivo studies of NAD+ metabolism are required to optimize the effects of NAD+ supplementation. There is also a need for methods of delivering NAD+ precursors to target organs or tissues to increase the outcomes of clinical trials. Antioxid. Redox Signal. 39, 1133-1149.

Semirational engineering of Cytophaga hutchinsonii polyphosphate kinase for developing a cost-effective, robust, and efficient adenosine 5'-triphosphate regeneration system

IMPORTANCE

The adenosine 5'-triphosphate (ATP) regeneration system can significantly reduce the cost of many biocatalytic processes. Numerous studies have endeavored to utilize the ATP regeneration system based on Cytophaga hutchinsonii PPK (ChPPK). However, the wild-type ChPPK enzyme possesses limitations such as low enzymatic activity, poor stability, and limited substrate tolerance, impeding its application in catalytic reactions. To enhance the performance of ChPPK, we employed a semi-rational design approach to obtain the variant ChPPK/A79G/S106C/I108F/L285P. The enzymatic kinetic parameters and the catalytic performance in the synthesis of nicotinamide mononucleotide demonstrated that the variant ChPPK/A79G/S106C/I108F/L285P exhibited superior enzymatic properties than the wild-type enzyme. All data indicated that our engineered ATP regeneration system holds inherent potential for implementation in biocatalytic processes.

The Safety and Antiaging Effects of Nicotinamide Mononucleotide in Human Clinical Trials: an Update

The importance of nicotinamide adenine dinucleotide (NAD+) in human physiology is well recognized. As the NAD+ concentration in human skin, blood, liver, muscle, and brain are thought to decrease with age, finding ways to increase NAD+ status could possibly influence the aging process and associated metabolic sequelae. Nicotinamide mononucleotide (NMN) is a precursor for NAD+ biosynthesis, and in vitro/in vivo studies have demonstrated that NMN supplementation increases NAD+ concentration and could mitigate aging-related disorders such as oxidative stress, DNA damage, neurodegeneration, and inflammatory responses. The promotion of NMN as an antiaging health supplement has gained popularity due to such findings; however, since most studies evaluating the effects of NMN have been conducted in cell or animal models, a concern remains regarding the safety and physiological effects of NMN supplementation in the human population. Nonetheless, a dozen human clinical trials with NMN supplementation are currently underway. This review summarizes the current progress of these trials and NMN/NAD+ biology to clarify the potential effects of NMN supplementation and to shed light on future study directions.

Exercise training upregulates intracellular nicotinamide phosphoribosyltransferase expression in humans: a systematic review with meta-analysis

Objective

Aging is associated with decreased nicotinamide adenine dinucleotide (NAD) levels, which in turn cause dysfunctional mitochondria and indirectly affect a myriad of diseases. Intracellular nicotinamide phosphoribosyltransferase (iNAMPT) serves as a central rate-limiting enzyme in NAD synthesis, making it an indispensable health mediator. This meta-analysis examined the effect of exercise training on the expression of iNAMPT in humans.

Methods

We searched PubMed, Scopus, ClinicalTrials.gov, and the International Clinical Trials Registry Platform for studies published between the inception of the database and July 5, 2023. Using the common-effect model, evidence for the change in iNAMPT following exercise training was synthesized as Cohen's d.

Results

The search yielded five eligible studies. The overall effect size is 0.81, with a 95% confidence interval of 0.55 to 1.07. Therefore, a random adult will have a 71.7% probability that iNAMPT will be up-regulated following exercise training. In general, exercise training resulted in a 1.46-fold increase in iNAMPT. Our probability statistics indicate that subgroups of interest may differ practically. Specifically, there is a 79.3% probability of increased iNAMPT in men, compared to a 69.0% probability in the overall population; young adults have a 75.6% probability of having an increased iNAMPT, whereas aged adults have a 68.7% probability; and, iNAMPT has a 75.1% probability increase after aerobic exercise and a 66.4% probability increase after resistance exercise.

Conclusion

Exercise training is effective for increasing iNAMPT levels in skeletal muscles. This essential enzyme regulates not only cellular energetics but also healthspan. Therefore, exercise should be promoted as a natural slow-aging lifestyle.

The Role of NAD+ in Metabolic Regulation of Adipose Tissue: Implications for Obesity-Induced Insulin Resistance

Obesity-induced insulin resistance is among the key factors in the development of type 2 diabetes, atherogenic dyslipidemia and cardiovascular disease. Adipose tissue plays a key role in the regulation of whole-body metabolism and insulin sensitivity. In obesity, adipose tissue becomes inflamed and dysfunctional, exhibiting a modified biochemical signature and adipokine secretion pattern that promotes insulin resistance in peripheral tissues. An important hallmark of dysfunctional obese adipose tissue is impaired NAD+/sirtuin signaling. In this chapter, we summarize the evidence for impairment of the NAD+/sirtuin pathway in obesity, not only in white adipose tissue but also in brown adipose tissue and during the process of beiging, together with correlative evidence from human studies. We also describe the role of PARPs and CD38 as important NAD+ consumers and discuss findings from experimental studies that investigated potential NAD+ boosting strategies and their efficacy in restoring impaired NAD+ metabolism in dysfunctional obese adipose tissue. In sum, these studies suggest a critical role of NAD+ metabolism in adipose biology and provide a basis for the potential development of strategies to restore metabolic health in obesity.

Host-microbiome interactions in nicotinamide mononucleotide (NMN) deamidation

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.

NAD depletion mediates cytotoxicity in human neurons with autophagy deficiency

Autophagy is a homeostatic process critical for cellular survival, and its malfunction is implicated in human diseases including neurodegeneration. Loss of autophagy contributes to cytotoxicity and tissue degeneration, but the mechanistic understanding of this phenomenon remains elusive. Here, we generated autophagy-deficient (ATG5-/-) human embryonic stem cells (hESCs), from which we established a human neuronal platform to investigate how loss of autophagy affects neuronal survival. ATG5-/- neurons exhibit basal cytotoxicity accompanied by metabolic defects. Depletion of nicotinamide adenine dinucleotide (NAD) due to hyperactivation of NAD-consuming enzymes is found to trigger cell death via mitochondrial depolarization in ATG5-/- neurons. Boosting intracellular NAD levels improves cell viability by restoring mitochondrial bioenergetics and proteostasis in ATG5-/- neurons. Our findings elucidate a mechanistic link between autophagy deficiency and neuronal cell death that can be targeted for therapeutic interventions in neurodegenerative and lysosomal storage diseases associated with autophagic defect.

Identification of new resonances in downfield 1 H MRS of human calf muscle in vivo: Potentially metabolite precursors for skeletal muscle NAD. Magn Reson Med 2023. [PMID: 37125620 DOI: 10.1002/mrm.29687] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

PURPOSE

The purpose of this study was to identify and characterize newly discovered resonances appearing in the downfield proton MR spectrum (DF ¹ H MRS) of the human calf muscle in vivo at 7T.

METHODS

Downfield ¹ H MRS was performed on the calf muscle of five healthy volunteers at 7T. A spectrally selective 90° E-BURP RF pulse with an excitation center frequency at 10.3 ppm and an excitation bandwidth of 2 ppm was used for DF ¹ H MRS acquisition.

RESULTS

In all participants, we observed new resonances at 9.7, 10.1, 10.3, and 10.9 ppm in the DF ¹ H MRS. Phantom experiments at 37°C strongly suggest the new resonance at 9.7 ppm could be from H2-proton of the nicotinamide rings in nicotinamide riboside (NR) and nicotinamide mononucleotide (NMN) while the resonance at 10.1 ppm could be attributed to the indole -NH proton of L-tryptophan. We observed that the resonances at 10.1 and 10.9 ppm are significantly suppressed when the water resonance is saturated, indicating that these peaks have either ¹ H chemical exchange or cross-relaxation with water. Conversely, the resonances at 9.7 and 10.3 ppm exhibit moderate signal reduction in the presence of water saturation.

CONCLUSION

We have identified new proton resonances in vivo in human calf muscle occurring at chemical shifts of 9.7, 10.1, 10.3, and 10.9 ppm. These preliminary results are promising for investigating the role of NR/NMN and L-tryptophan metabolism in understanding the de novo and salvage pathways of NAD⁺ synthesis in skeletal muscle.

Ex Vivo Transdermal Delivery of Nicotinamide Mononucleotide Using Polyvinyl Alcohol Microneedles

Nicotinamide mononucleotide (NMN), which has recently been spotlighted as an anti-aging agent, is a precursor of the coenzyme nicotinamide adenine dinucleotide that plays an important role in intracellular redox reactions. NMN capsules for oral administration currently on the market have a problem in that they are almost fully metabolized in the stomach and liver and excreted as nicotinamide. Therefore, there is a need to develop a patient-friendly delivery method that can improve the bioavailability of NMN. For this purpose, various polyvinyl alcohol (PVA)-based microneedle patches were fabricated to develop a transdermal delivery system for NMN. First, the molecular weight effect of PVA on the shape and microstructure of microneedles was studied. After selecting the optimal molecular weight PVA, the swelling of the microneedles and the ex vivo release of NMN were studied. The effect of carboxymethyl cellulose (CMC) and dimethyl sulfoxide on NMN release was also investigated. The highest NMN release of 91.94% in 18 h was obtained using a 9.5 kDa molecular weight PVA microneedle containing NMN and CMC.

Gut microbiota-derived nicotinamide mononucleotide alleviates acute pancreatitis by activating pancreatic SIRT3 signalling

BACKGROUND AND PURPOSE

Gut microbiota dysbiosis induced by acute pancreatitis (AP) exacerbates pancreatic injury and systemic inflammatory responses. The alleviation of gut microbiota dysbiosis through faecal microbiota transplantation (FMT) is considered a potential strategy to reduce tissue damage and inflammation in many clinical disorders. Here, we aim to investigate the effect of gut microbiota and microbiota-derived metabolites on AP and further clarify the mechanisms associated with pancreatic damage and inflammation.

EXPERIMENTAL APPROACH

AP rat and mouse models were established by administration of caerulein or sodium taurocholate in vivo. Pancreatic acinar cells were exposed to caerulein and lipopolysaccharide in vitro to simulate AP.

KEY RESULTS

Normobiotic FMT alleviated AP-induced gut microbiota dysbiosis and ameliorated the severity of AP, including mitochondrial dysfunction, oxidative damage and inflammation. Normobiotic FMT induced higher levels of NAD⁺ (nicotinamide adenine dinucleotide)-associated metabolites, particularly nicotinamide mononucleotide (NMN). NMN administration mitigated AP-mediated mitochondrial dysfunction, oxidative damage and inflammation by increasing pancreatic NAD⁺ levels. Similarly, overexpression of the NAD⁺ -dependent mitochondrial deacetylase sirtuin 3 (SIRT3) alleviated the severity of AP. Furthermore, SIRT3 deacetylated peroxiredoxin 5 (PRDX5) and enhanced PRDX5 protein expression, thereby promoting its antioxidant and anti-inflammatory activities in AP. Importantly, normobiotic FMT-mediated NMN metabolism induced SIRT3-PRDX5 pathway activation during AP.

CONCLUSION AND IMPLICATIONS

Gut microbiota-derived NMN alleviates the severity of AP by activating the SIRT3-PRDX5 pathway. Normobiotic FMT could be served as a potential strategy for AP treatment.

Nicotinamide mononucleotide alters body composition and ameliorates metabolic disorders induced by a high-fat diet

Obesity is caused by an imbalance between calorie intake and energy expenditure, leading to excessive adipose tissue accumulation. Nicotinamide adenine dinucleotide (NAD⁺ ) is an important molecule in energy and signal transduction, and NAD⁺ supplementation therapy is a new treatment for obesity in recent years. Liver kinase B1 (LKB1) is an energy metabolism regulator. The relationship between NAD⁺ and LKB1 has only been studied in the heart and has not yet been reported in obesity. Nicotinamide mononucleotide (NMN), as a direct precursor of NAD⁺ , can effectively enhance the level of NAD⁺ . In the current study, we showed that NMN intervention altered body composition in obese mice, characterized by a reduction in fat mass and an increase in lean mass. NMN reversed high-fat diet-induced blood lipid levels then contributed to reducing hepatic steatosis. NMN also improved glucose tolerance and alleviated adipose tissue inflammation. Moreover, our data suggested that NMN supplementation may be depends on the NAD⁺ /SIRT6/LKB1 pathway to regulate brown adipose metabolism. These results provided new evidence for NMN in obesity treatment.

Enhancing the biosynthesis of nicotinamide mononucleotide in Lactococcus lactis by heterologous expression of FtnadE

BACKGROUND

Nicotinamide mononucleotide (NMN), a key intermediate of nicotinamide adenine dinucleotide, plays an important in anti-aging and disease. Lactococcus lactis, an important probiotic lactic acid bacteria (LAB), has shown great potential for the biosynthesis of NMN, which will significantly affect the probiotic effects of the dairy products.

RESULTS

We used the CRISPR/nCas9 technique to knockout nadR gene of L. lactis NZ9000 to enhance the accumulation of NMN by 61%. The nadE* gene from Francisella tularensis with codon optimization was heterologous in L. lactis NZ9000ΔnadR and has a positive effect on NMN production. Combined with optimization of the concentration of substrate nicotinamide, a final intracellular NMN titer was 2289 μmol L^-1  mg^-1 with 10 g L^-1 nicotinamide supplement, which was 5.7-fold higher than that of the control. The transcription levels of key genes (pncA, nadD and prs1) involved in NMN biosynthesis were up-regulated by more than two-fold, indicating that the increase of NMN titer was attributed to FtnadE* heterologous expression.

CONCLUSION

Our study provides a better understanding of the NMN biosynthesis pathway in L. lactis, and can facilitate NMN production in LAB via synthetic biology approaches. © 2022 Society of Chemical Industry.

Nicotinamide mononucleotide attenuates HIF-1α activation and fibrosis in hypoxic adipose tissue via NAD+/SIRT1 axis

BACKGROUND

Fibrosis is increasingly considered as a major contributor in adipose tissue dysfunction. Hypoxic activation of hypoxia-inducible factor 1α (HIF-1α) induces a profibrotic transcription, leading to adipose fibrosis. Nicotinamide mononucleotide (NMN), a member of the vitamin B₃ family, has been shown to relieve hepatic and cardiac fibrosis, but its effects on hypoxic adipose fibrosis and the underlying mechanism remain unclear. We aimed to elucidate the roles of NMN in regulating HIF-1α and fibrosis in hypoxic adipose tissue.

METHODS

Mice were placed in a hypobaric chamber for four weeks to induce adipose fibrosis. NMN (500 mg/kg, every three days) was administered by intraperitoneal injection. In vitro, Stromal vascular fractions (SVF) cells were treated by hypoxia with or without NMN (200μM), sirtinol (25μM, a SIRT1 inhibitor) and CoCl₂ (100μM, a HIF1α enhancer). The effects of NMN on hypoxia-associated adipose fibrosis, inflammation, NAD⁺/SIRT1 axis alteration, and HIF-1α activation were evaluated by real-time polymerase chain reaction (PCR), western blots, immunohistochemistry staining, immunoprecipitation, and assay kits.

RESULTS

Mice placed in a hypoxic chamber for four weeks showed obvious adipose fibrosis and inflammation, which were attenuated by NMN. NMN also restore the compromised NAD⁺/SIRT1 axis and inhibited the activation of HIF-1α induced by hypoxia. In hypoxia-induced SVFs, the SIRT1 inhibitor sirtinol blocked the anti-fibrotic and anti-inflammatory effects of NMN, upregulated the HIF-1α and its acetylation level. The HIF1α stabilizer CoCl₂ showed similar effects as sirtinol.

CONCLUSION

NMN effectively attenuated HIF-1α activation-induced adipose fibrosis and inflammation by restoring the compromised NAD⁺/SIRT1 axis.

Nicotinamide Mononucleotide Ameliorates Silica-Induced Lung Injury through the Nrf2-Regulated Glutathione Metabolism Pathway in Mice

Nicotinamide mononucleotide (NMN) is a natural antioxidant approved as a nutritional supplement and food ingredient, but its protective role in silicosis characterized by oxidative damage remains unknown. In this study, we generated a silicosis model by intratracheal instillation of silica, and then performed histopathological, biochemical, and transcriptomic analysis to evaluate the role of NMN in silicosis. We found that NMN mitigated lung damage at 7 and 28 days, manifested as a decreasing coefficient of lung weight and histological changes, and alleviated oxidative damage by reducing levels of reactive oxygen species and increasing glutathione. Meanwhile, NMN treatment also reduced the recruitment of inflammatory cells and inflammatory infiltration in lung tissue. Transcriptomic analysis showed that NMN treatment mainly regulated immune response and glutathione metabolism pathways. Additionally, NMN upregulated the expression of antioxidant genes Gstm1, Gstm2, and Mgst1 by promoting the expression and nuclear translocation of nuclear factor-erythroid 2 related factor 2 (Nrf2). Gene interaction analysis showed that Nrf2 interacted with Gstm1 and Mgst1 through Gtsm2. Promisingly, oxidative damage mediated by these genes occurred mainly in fibroblasts. In summary, NMN alleviates silica-induced oxidative stress and lung injury by regulating the endogenous glutathione metabolism pathways. This study reveals that NMN supplementation might be a promising strategy for mitigating oxidative stress and inflammation in silicosis.

Nicotinamide Mononucleotide Administration Prevents Doxorubicin-Induced Cardiotoxicity and Loss in Physical Activity in Mice

Doxorubicin (Doxo) is a widely used antineoplastic drug with limited clinical application due to its deleterious dose-related side effects. We investigated whether nicotinamide mononucleotide (NMN) could protect against Doxo-induced cardiotoxicity and physical dysfunction in vivo. To assess the short- and long-term toxicity, two Doxo regimens were tested, acute and chronic. In the acute study, C57BL6/J (B6) mice were injected intraperitoneally (i.p.) once with Doxo (20 mg/kg) and NMN (180 mg/kg/day, i.p.) was administered daily for five days before and after the Doxo injection. In the chronic study, B6 mice received a cumulative dose of 20 mg/kg Doxo administered in fractionated doses for five days. NMN (500 mg/kg/day) was supplied in the mice's drinking water beginning five days before the first injection of Doxo and continuing for 60 days after. We found that NMN significantly increased tissue levels of NAD+ and its metabolites and improved survival and bodyweight loss in both experimental models. In addition, NMN protected against Doxo-induced cardiotoxicity and loss of physical function in acute and chronic studies, respectively. In the heart, NMN prevented Doxo-induced transcriptomic changes related to mitochondrial function, apoptosis, oxidative stress, inflammation and p53, and promyelocytic leukemia nuclear body pathways. Overall, our results suggest that NMN could prevent Doxo-induced toxicity in heart and skeletal muscle.

Nicotinamide Mononucleotide Prevents Cisplatin-Induced Mitochondrial Defects in Cortical Neurons Derived from Human Induced Pluripotent Stem Cells

Background

Chemotherapy-induced cognitive impairment (CICI) is a neurotoxic side effect of chemotherapy that has yet to have an effective treatment.

Objective

Using cisplatin, a platinum-based chemotherapy together with excitatory cortical neurons derived from human induced pluripotent cells (iPSCs) to model of CICI, our recent study demonstrated that dysregulation of brain NAD+ metabolism contributes to cisplatin-induced impairments in neurogenesis and cognitive function, which was prevented by administration of the NAD+ precursor, nicotinamide mononucleotide (NMN). However, it remains unclear how cisplatin causes neurogenic dysfunction and the mechanism by which NMN prevents cisplatin-induced cognitive impairment. Given that mitochondrial dysfunction is thought to play a prominent role in age-related neurodegenerative disease and chemotherapy-induced neurotoxicity, we sought to explore if NMN prevents chemotherapy-related neurotoxicity by attenuating cisplatin-induced mitochondrial damage.

Results

We demonstrate that cisplatin induces neuronal DNA damage, increases generation of mitochondrial reactive oxygen species (ROS) and decreases ATP production, all of which are indicative of oxidative DNA damage and mitochondrial functional defects. Ultrastructural analysis revealed that cisplatin caused loss of cristae membrane integrity and matrix swelling in human cortical neurons. Notably, pretreatment with NMN prevents cisplatin-induced defects in mitochondria of human cortical neurons.

Conclusion

Our results suggest that increased mitochondrial oxidative stress and functional defects play key roles in cisplatin-induced neurotoxicity. Thus, NMN may be an effective therapeutic strategy to prevent cisplatin-induced deleterious effects on mitochondria, making this organelle a key factor in amelioration of cisplatin-induced cognitive impairments.

Nicotinamide Mononucleotide Protects against Retinal Dysfunction in a Murine Model of Carotid Artery Occlusion

Cardiovascular abnormality-mediated retinal ischemia causes severe visual impairment. Retinal ischemia is involved in enormous pathological processes including oxidative stress, reactive gliosis, and retinal functional deficits. Thus, maintaining retinal function by modulating those pathological processes may prevent or protect against vision loss. Over the decades, nicotinamide mononucleotide (NMN), a crucial nicotinamide adenine dinucleotide (NAD⁺) intermediate, has been nominated as a promising therapeutic target in retinal diseases. Nonetheless, a protective effect of NMN has not been examined in cardiovascular diseases-induced retinal ischemia. In our study, we aimed to investigate its promising effect of NMN in the ischemic retina of a murine model of carotid artery occlusion. After surgical unilateral common carotid artery occlusion (UCCAO) in adult male C57BL/6 mice, NMN (500 mg/kg/day) was intraperitoneally injected to mice every day until the end of experiments. Electroretinography and biomolecular assays were utilized to measure ocular functional and further molecular alterations in the retina. We found that UCCAO-induced retinal dysfunction was suppressed, pathological gliosis was reduced, retinal NAD⁺ levels were preserved, and the expression of an antioxidant molecule (nuclear factor erythroid-2-related factor 2; Nrf2) was upregulated by consecutive administration of NMN. Our present outcomes first suggest a promising NMN therapy for the suppression of cardiovascular diseases-mediated retinal ischemic dysfunction.

Nicotinamide mononucleotide improves spermatogenic function in streptozotocin-induced diabetic mice via modulating the glycolysis pathway

Spermatogenic dysfunction is one of the major secondary complications of diabetes; however, the underlying mechanisms remain ill-defined, and there is no available drug or strategy for the radical treatment of diabetic spermatogenic dysfunction. Therefore, the objective of this study is to investigate the protective effects of nicotinamide mononucleotide (NMN) on testicular spermatogenic function in streptozotocin (STZ)-induced diabetic mice. The results show that oral administration of NMN significantly increases the body and testis weight and the number of sperms. Moreover, the abnormal sperm count and the rate of sperm malformation are significantly decreased compared with the saline-treated diabetic mice. Histological analysis reveals that NMN treatment significantly increases the area and diameter of seminiferous tubules, accompanied by an increased number of spermatogenic cells and sperms. Immunohistochemistry and qRT-PCR results show that NMN increases Bcl-2 expression and decreases Bax expression in the testis. NMN also increases the protein expression of Vimentin and the mRNA expressions of WT1 and GATA4. In addition, qRT-PCR, western blot analysis and immunohistochemistry results also show that NMN increases the expressions of glycolysis-related rate-limiting enzymes including HK2, PKM2, and LDHA. In summary, this study demonstrates the protective effects of NMN on the testis in an STZ-induced diabetic mice model. NMN exerts its protective effects via reducing spermatogenic cell apoptosis by regulating glycolysis of Sertoli cells in diabetic mice. This study provides an experimental basis for the future clinical application of NMN in diabetes-induced spermatogenic dysfunction.

Engineering Embden-Meyerhof-Parnas Glycolysis to Generate Noncanonical Reducing Power

Noncanonical cofactors such as nicotinamide mononucleotide (NMN+) supplant the electron-transfer functionality of the natural cofactors, NAD(P)+, at a lower cost in cell-free biomanufacturing and enable orthogonal electron delivery in whole-cell metabolic engineering. Here, we redesign the high-flux Embden-Meyerhof-Parnas (EMP) glycolytic pathway to generate NMN+-based reducing power, by engineering Streptococcus mutans glyceraldehyde-3-phosphate dehydrogenase (Sm GapN) to utilize NMN+. Through iterative rounds of rational design, we discover the variant GapN Penta (P179K-F153S-S330R-I234E-G210Q) with high NMN+-dependent activity and GapN Ortho (P179K-F153S-S330R-I234E-G214E) with ~3.4 × 106-fold switch in cofactor specificity from its native cofactor NADP+ to NMN+. GapN Ortho is further demonstrated to function in Escherichia coli only in the presence of NMN+, enabling orthogonal control of glucose utilization. Molecular dynamics simulation and residue network connectivity analysis indicate that mutations altering cofactor specificity must be coordinated to maintain the appropriate degree of backbone flexibility to position the catalytic cysteine. These results provide a strategy to guide future designs of NMN+-dependent enzymes and establish the initial steps toward an orthogonal EMP pathway with biomanufacturing potential.

Nicotinamide Mononucleotide Administration Amends Protein Acetylome of Aged Mouse Liver

It is known that the activities of nicotine adenine dinucleotide (NAD⁺)-dependent deacetylase decline in the aging mouse liver, and nicotinamide mononucleotide (NMN)-mediated activation of deacetylase has been shown to increase healthspans. However, age-induced changes of the acetylomic landscape and effects of NMN treatment on protein acetylation have not been reported. Here, we performed immunoprecipitation coupled with label-free quantitative LC-MS/MS (IPMS) to identify the acetylome and investigate the effects of aging and NMN on liver protein acetylation. In total, 7773 acetylated peptides assigned to 1997 proteins were commonly identified from young and aged livers treated with vehicle or NMN. The major biological processes associated with proteins exhibiting increased acetylation from aged livers were oxidation-reduction and metabolic processes. Proteins with decreased acetylation from aged livers mostly participated in transport and translation processes. Furthermore, NMN treatment inhibited the aging-related increase of acetylation on proteins regulating fatty acid β oxidation, the tricarboxylic acid (TCA) cycle and valine degradation. In particular, NAD (P) transhydrogenase (NNT) was markedly hyperacetylated at K70 in aged livers, and NMN treatment decreased acetylation intensity without altering protein levels. Acetylation at cytochrome 3a25 (Cyp3a25) at K141 was also greatly increased in aged livers, and NMN treatment totally arrested this increase. Our extensive identification and analysis provide novel insight and potential targets to combat aging and aging-related functional decline.

Synthesis of nicotinamide mononucleotide from xylose via coupling engineered Escherichia coli and a biocatalytic cascade

β-Nicotinamide mononucleotide (NMN) has recently gained attention for nutritional supplement because it is an intermediate in the biosynthesis of nicotinamide adenine dinucleotide (NAD + ). In this study, we develop NMN synthesis by coupling two modules. The first module is to culture E. coli MG1655 ∆ tktA ∆ tktB ∆ ptsG to metabolize xylose to generate D -ribose in the medium. The supernatant containing D -ribose was applied in the second module which is composed of Ec RbsK- Ec PRPS- Cp NAMPT reaction to synthesize NMN, that requires additional enzymes of CHU0107 and Ec PPase to remove feedback inhibitors, ADP and pyrophosphate. The second module can be rapidly optimized by comparing NMN production determined by the cyanide assay. Finally, 10 mL optimal biocascade reaction generated NMN with good yield of 84% from 1 mM D -ribose supplied from the supernatant of E. coli MG1655 ∆ tktA ∆ tktB ∆ ptsG . Our results can further guide researchers to metabolically engineer E. coli for NMN synthesis.

Nicotinamide Mononucleotide Alleviates Cardiomyopathy Phenotypes Caused by Short-Chain Enoyl-Coa Hydratase 1 Deficiency

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ECHS1 hydrates medium- and short-chain enoyl CoAs and catalyzes the oxidation of fatty acids and branched-chain amino acids.

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The mechanism driving ECHS1 deficiency–associated cardiomyopathy was investigated using conventional biochemistry and molecular biology methods, including immunoprecipitation and polymerase chain reaction.

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Echs1 heterogeneous knockout mice displayed cardiac dysfunction as evaluated by echocardiography.

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ECHS1 deficiency causes cardiomyopathy by enhancing p300-mediated H3K9ac.

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ECHS1 deficiency–induced cardiomyopathy can be prevented using an intervention approach targeting H3K9ac.

Short-chain enoyl-CoA hydratase 1 (ECHS1) deficiency plays a role in cardiomyopathy. Whether ECHS1 deficiency causes or is only associated with cardiomyopathy remains unclear. By using Echs1 heterogeneous knockout (Echs1^+/-) mice, we found that ECHS1 deficiency caused cardiac dysfunction, as evidenced by diffuse myocardial fibrosis and upregulated fibrosis-related genes. Mechanistically, ECHS1 interacts with the p300 nuclear localization sequence, preventing its nuclear translocation in fibroblasts. ECHS1 deficiency promotes p300 nuclear translocation, leading to increased H3K9 acetylation, a known risk factor for cardiomyopathy. Nicotinamide mononucleotide–mediated acetylation targeting suppressed ECHS1 deficiency–induced cardiomyopathy phenotypes in Echs1^+/- mice. Thus, enhancing p300-mediated H3K9ac is a potential interventional approach for preventing ECHS1 deficiency–induced cardiomyopathy.

Safety Evaluation for Restorin® NMN, a NAD+ Precursor

NAD+ is an abundant molecule in the body and vital to all living cells. NAD+ levels decline with age, and this decline correlates with age-related diseases. Therefore, sustaining NAD+ levels offers potential benefits to healthspan and longevity. Here we conducted toxicity studies to evaluate the safety of Restorin® NMN, a high purity form of the direct NAD+ precursor, β-nicotinamide mononucleotide (NMN). Based on the preliminary toxicity study and a 14-days repeated dose toxicity study at a higher dose level exposure, Restorin® NMN was administered orally to Sprague-Dawley rats for 91 days followed by a 14-days recovery period. The oral doses of 500, 1,000, and 2000 mg/kg/day were compared. There were no test item-related findings that could be considered adverse events in animals dosed at 500 mg/kg/day. The findings in the Restorin® NMN high dose group (2000 mg/kg/day) were similar to the reference item (Nicotinamide Riboside Chloride) dosed at 1740 mg/kg/day: reduced body weight, reductions in body weight gains, and diminished food consumption. In conclusion, the No-Observed-Adverse-Effect-Level (NOAEL) for Restorin® NMN is 1,000 mg/kg/day in female rats and 500 mg/kg/day in male rats, and the Low-Observed-Adverse-Effect-Level (LOAEL) for Resotrin® NMN is 2000 mg/kg/day.

NAD+ Metabolism in Cardiac Health, Aging, and Disease

Nicotinamide adenine dinucleotide (NAD⁺) is a central metabolite involved in energy and redox homeostasis as well as in DNA repair and protein deacetylation reactions. Pharmacological or genetic inhibition of NAD⁺-degrading enzymes, external supplementation of NAD⁺ precursors, and transgenic overexpression of NAD⁺-generating enzymes have wide positive effects on metabolic health and age-associated diseases. NAD⁺ pools tend to decline with normal aging, obesity, and hypertension, which are all major risk factors for cardiovascular disease, and NAD⁺ replenishment extends healthspan, avoids metabolic syndrome, and reduces blood pressure in preclinical models. In addition, experimental elevation of NAD⁺ improves atherosclerosis, ischemic, diabetic, arrhythmogenic, hypertrophic, or dilated cardiomyopathies, as well as different modalities of heart failure. Here, we critically discuss cardiomyocyte-specific circuitries of NAD⁺ metabolism, comparatively evaluate distinct NAD⁺ precursors for their preclinical efficacy, and raise outstanding questions on the optimal design of clinical trials in which NAD⁺ replenishment or supraphysiological NAD⁺ elevations are assessed for the prevention or treatment of major cardiac diseases. We surmise that patients with hitherto intractable cardiac diseases such as heart failure with preserved ejection fraction may profit from the administration of NAD⁺ precursors. The development of such NAD⁺-centered treatments will rely on technological and conceptual progress on the fine regulation of NAD⁺ metabolism.

Biosynthesis of a Therapeutically Important Nicotinamide Mononucleotide through a Phosphoribosyl Pyrophosphate Synthetase 1 and 2 Engineered Strain of Escherichia coli

Nicotinamide mononucleotide (NMN), a precursor of NAD⁺, can be synthesized by the conversion of nicotinamide with the help of nicotinamide phosphoribosyl transferase (NAMPT) via the salvage pathway. NMN has recently gained great attention as an excellent therapeutic option due to its long-term effective pharmacological activities. In this study, we constructed a recombinant strain of Escherichia coli by inserting NAMPT and phosphoribosyl pyrophosphate synthetase 1 (PRPS1) and PRPS2 (from Homo sapiens) genes to investigate the effect of PRPS1 and PRPS2 on NMN synthesis. The metabolically engineered strain of E. coli BL21 (DE3) exhibited 1.57 mM NMN production in the presence of Mg²⁺ and phosphates in batch fermentation studies. For further improvement in NMN production levels, effects of different variables were studied using a response surface methodology approach. A significant increment was achieved with a maximum of 2.31 mM NMN production when supplemented with 1% ribose, 1 mM Mg²⁺ and phosphate, and 0.5% nicotinamide in the presence of a lactose (1%) inducer. Additionally, insertion of the PRPS1 and PRPS2 genes in the phosphoribosyl pyrophosphate synthesis pathway and individual gene expression studies facilitated a higher NMN production at the intracellular level than the reported studies. The strain exhibited intracellular production of NMN from cheap substrates such as glucose, lactose, and nicotinamide. Hence, the overall optimized process can be further scaled up for the economical production of NMN using a recombinant strain of E. coli BL21 (DE3), which is the future perspective of the current study.

Nicotinamide mononucleotide ameliorates senescence in alveolar epithelial cells

Alveolar epithelial cells (ACEs) gradually senescent as aging, which is one of the main causes of respiratory defense and function decline. Investigating the mechanisms of ACE senescence is important for understanding how the human respiratory system works. NAD⁺ is reported to reduce during the aging process. Supplementing NAD⁺ intermediates can activate sirtuin deacylases (SIRT1–SIRT7), which regulates the benefits of exercise and dietary restriction, reduce the level of intracellular oxidative stress, and improve mitochondrial function, thereby reversing cell senescence. We showed that nicotinamide mononucleotide (NMN) could effectively mitigate age‐associated physiological decline in the lung of 8–10 months old C57BL/6 mice and bleomycin‐induced pulmonary fibrosis in young mice of 6–8 weeks. Besides, the treatment of primary ACEs with NMN can markedly ameliorate cell senescence phenotype in vitro. These findings to improve the respiratory system function and reduce the incidence and mortality from respiratory diseases in the elderly are of great significance.

β-Nicotinamide Mononucleotide (NMN) Administrated by Intraperitoneal Injection Mediates Protection Against UVB-Induced Skin Damage in Mice

Objective

Ultraviolet light is an important environmental factor that induces skin oxidation, inflammation, and other diseases. Nicotinamide mononucleotide (NMN) has the effect of anti-oxidation and improving various physiological processes. This study explores the protective effect of NMN monomers given via intraperitoneal injection on UVB-induced photodamage.

Methods

We used a murine model of UVB-induced photodamage to evaluate the effect of an NMN monomer on photoaging skin by assessing skin and liver tissue sections, serum and skin oxidative stress levels, inflammatory markers, mRNA expression, and protein expression of skin- and liver-related genes.

Results

The results showed that NMN treatment blocked UVB-induced photodamage in mice, maintaining normal structure and amount of collagen fibers, normal thickness of epidermis and dermis, reducing the production of mast cells, and maintaining complete organized skin structure. NMN intraperitoneal injection also maintained the normal morphology of the mouse liver after UVB exposure. Meanwhile, NMN intraperitoneal injection was found to increase antioxidant ability and regulate the proinflammatory response of the skin and liver to UVB irradiation by enhancing the activity of antioxidant enzymes, release of anti-inflammatory cytokines, reduction of hydrogen peroxide production (H₂O₂), and decreased inflammatory cytokines. Furthermore, RT-qPCR results indicated that NMN reduced oxidative stress of skin and liver by promoting the activation of the AMP-activated protein kinase (AMPK) signaling pathway and further increasing the expression of downstream antioxidant genes of AMPK. RT-qPCR results also revealed that NMN treatment could downregulate the mRNA expression of interleukin (IL)-6, interleukin (IL)-1β, and tumor necrosis factor (TNF)-α, and upregulate NF-kappa-B inhibitor-α (IκB-α) and interleukin (IL)-10 by inhibiting the activation of nuclear factor-κBp65 (NFκB-p65). Finally, NMN upregulated AMPK, IκB-α, SOD1, and CAT in the skin and downregulated NF-κBp65 protein expression, which is in line with the RT-qPCR results.

Conclusion

Based on the above results, NMN monomer treatment with intraperitoneal injection also block the photodamage caused by UVB irradiation in mice by regulating the oxidative stress response and inflammatory response.

Crystal structure determination of the armadillo repeat domain of Drosophila SARM1 using MIRAS phasing

The crystal structure determination of the armadillo repeat motif (ARM) domain of Drosophila SARM1 (dSARM1^ARM) is described, which required the combination of a number of sources of phase information in order to obtain interpretable electron-density maps. SARM1 is a central executioner of programmed axon degeneration, a common feature of the early phase of many neurodegenerative diseases. SARM1 is held in the inactive state in healthy axons by its N-terminal auto-inhibitory ARM domain, and is activated to cleave NAD upon injury, triggering subsequent axon degeneration. To characterize the molecular mechanism of SARM1 activation, it was sought to determine the crystal structure of the SARM1 ARM domain. Here, the recombinant production and crystallization of dSARM1^ARM is described, as well as the unconventional process used for structure determination. Crystals were obtained in the presence of NMN, a precursor of NAD and a potential activator of SARM1, only after in situ proteolysis of the N-terminal 63 residues. After molecular-replacement attempts failed, the crystal structure of dSARM1^ARM was determined at 1.65 Å resolution using the MIRAS phasing technique with autoSHARP, combining data from native, selenomethionine-labelled and bromide-soaked crystals. The structure will further the understanding of SARM1 regulation.

Precursor comparisons for the upregulation of nicotinamide adenine dinucleotide. Novel approaches for better aging

Nicotinamide adenine dinucleotide (NAD) is a coenzyme found in every human cell and regulates a number of systems across multiple cellular compartments and tissue types via an endogenous and exogenous influence. NAD levels are demonstrated to decline with age and therefore measures to counteract the waning of NAD have been devised. A number of NAD precursor candidates such as nicotinamide riboside (NR), nicotinamide mononucleotide (NMN), the reduced form of nicotinamide mononucleotide (NMNH), nicotinic acid (NA) nicotinamide (NAM), and dihydronicotinamide riboside (DNR) increase NAD levels in vitro and in vivo. This discussion will focus on the precursors NR, NMN, NMNH, and DNR in the upregulation of NAD. There are many publications on NAD precursors as it has become popular for human consumption in recent years due to its vital importance to the general consumer. However, there is no consensus between researchers and this was the aim of this review, to determine and discuss their areas of agreement versus disagreement, to highlight the gaps in research, and to give recommendations for future work. Bioavailability and potency of NR, NMNH, NMN, and DNR is also examined on the light of the most recent literature.

Reduced nicotinamide mononucleotide is a new and potent NAD+ precursor in mammalian cells and mice

Nicotinamide adenine dinucleotide (NAD⁺ ) homeostasis is constantly compromised due to degradation by NAD⁺ -dependent enzymes. NAD⁺ replenishment by supplementation with the NAD⁺ precursors nicotinamide mononucleotide (NMN) and nicotinamide riboside (NR) can alleviate this imbalance. However, NMN and NR are limited by their mild effect on the cellular NAD⁺ pool and the need of high doses. Here, we report a synthesis method of a reduced form of NMN (NMNH), and identify this molecule as a new NAD⁺ precursor for the first time. We show that NMNH increases NAD⁺ levels to a much higher extent and faster than NMN or NR, and that it is metabolized through a different, NRK and NAMPT-independent, pathway. We also demonstrate that NMNH reduces damage and accelerates repair in renal tubular epithelial cells upon hypoxia/reoxygenation injury. Finally, we find that NMNH administration in mice causes a rapid and sustained NAD⁺ surge in whole blood, which is accompanied by increased NAD⁺ levels in liver, kidney, muscle, brain, brown adipose tissue, and heart, but not in white adipose tissue. Together, our data highlight NMNH as a new NAD⁺ precursor with therapeutic potential for acute kidney injury, confirm the existence of a novel pathway for the recycling of reduced NAD⁺ precursors and establish NMNH as a member of the new family of reduced NAD⁺ precursors.

Nicotinamide Mononucleotide Alleviates LPS-Induced Inflammation and Oxidative Stress via Decreasing COX-2 Expression in Macrophages

Macrophage activation is an important process in controlling infection, but persistent macrophage activation leads to chronic inflammation and diseases, such as tumor progression, insulin resistance and atherosclerosis. Characterizing metabolic signatures of macrophage activation is important for developing new approaches for macrophage inactivation. Herein, we performed metabolomic analysis on lipopolysaccharide (LPS)-activated macrophages and identified the associated changes in metabolites. Notably, the cellular Nicotinamide adenine dinucleotide⁺ levels were decreased while NADPH was increased, proposing that NAD⁺ restoration can inhibit macrophage activation. Indeed, supplementation of nicotinamide mononucleotide (NMN) increased cellular NAD⁺ levels and decreased cytokine productions in LPS-activated cells. Quantitative proteomics identified that nicotinamide mononucleotide downregulated the expressions of LPS-responsive proteins, in which cyclooxygenase-2 (COX-2) expression was significantly decreased in NMN-treated cells. Consequently, the cellular levels of prostaglandin E₂ (PGE₂) was also decreased, indicating that NMN inactivated macrophages via COX-2-PGE₂ pathway, which was validated in activated THP-1 cells and mouse peritoneal macrophages. In conclusion, the present study identified the metabolic characteristics of activated macrophages and revealed that NMN replenishment is an efficient approach for controlling macrophage activation.

Acidic pH irreversibly activates the signaling enzyme SARM1

SARM1, an executioner in axon degeneration, is an autoinhibitory NAD-consuming enzyme, composed of multiple domains. NMN and its analogs, CZ-48 and VMN, are the only known activators, which can release the inhibitory ARM domain from the enzymatic TIR domain. Here, we document that acid can also activate SARM1, even more efficiently than NMN, possibly via the protonation of the negative residues. Systematic mutagenesis revealed that a single mutation, E689Q in TIR, led to the constitutive activation of SARM1. It forms a salt bridge with R216 in the neighboring ARM, maintaining the autoinhibitory structure. Using this 'acid activation' protocol, mutation K597E was found to inhibit activation, while H685A eliminated SARM1 catalytic activity, revealing two distinct inhibitory mechanisms. The protocol has also been applied to differentiate two classes of chemical inhibitors. NAD, dHNN, disulfiram, CHAPS, and TRX-100 mainly inhibited the activation process, while nicotinamide and Tweens mainly inhibited SARM1 catalysis. Taken together, we demonstrate a new mechanism for SARM1 activation and decipher two distinct inhibitory mechanisms of SARM1.

Exercise-induced benefits on glucose handling in a model of diet-induced obesity are reduced by concurrent nicotinamide mononucleotide

Almost 40% of adults worldwide are classified as overweight or obese. Exercise is a beneficial intervention in obesity, partly due to increases in mitochondrial activity and subsequent increases in nicotinamide adenine dinucleotide (NAD⁺), an important metabolic cofactor. Recent studies have shown that increasing NAD⁺ levels through pharmacological supplementation with precursors such as nicotinamide mononucleotide (NMN) improved metabolic health in high-fat-diet (HFD)-fed mice. However, the effects of combined exercise and NMN supplementation are unknown. Thus, here we examined the combined effects of NMN and treadmill exercise in female mice with established obesity after 10 wk of diet. Five-week-old female C57BL/6J mice were exposed to a control diet (n = 16) or HFD. Mice fed a HFD were either untreated (HFD; n = 16), received NMN in drinking water (400 mg/kg; HNMN; n = 16), were exposed to treadmill exercise 6 days/wk (HEx; n = 16), or were exposed to exercise combined with NMN (HNEx; n = 16). Although some metabolic benefits of NMN have been described, at this dose, NMN administration impaired several aspects of exercise-induced benefits in obese mice, including glucose tolerance, glucose-stimulated insulin secretion from islets, and hepatic triglyceride accumulation. HNEx mice also exhibited increased antioxidant and reduced prooxidant gene expression in both islets and muscle, suggesting that altered redox status is associated with the loss of exercise-induced health benefits with NMN cotreatment. Our data show that NMN treatment impedes the beneficial metabolic effects of exercise in a mouse model of diet-induced obesity in association with disturbances in redox metabolism.NEW & NOTEWORTHY NMN dampened exercise-induced benefits on glucose handling in diet-induced obesity. NMN administration alongside treadmill exercise enhanced the ratio of antioxidants to prooxidants. We suggest that NMN administration may not be beneficial when NAD⁺ levels are replete.

Characterization of Two NMN Deamidase Mutants as Possible Probes for an NMN Biosensor

Nicotinamide mononucleotide (NMN) is a key intermediate in the nicotinamide adenine dinucleotide (NAD+) biosynthesis. Its supplementation has demonstrated beneficial effects on several diseases. The aim of this study was to characterize NMN deamidase (PncC) inactive mutants to use as possible molecular recognition elements (MREs) for an NMN-specific biosensor. Thermal stability assays and steady-state fluorescence spectroscopy measurements were used to study the binding of NMN and related metabolites (NaMN, Na, Nam, NR, NAD, NADP, and NaAD) to the PncC mutated variants. In particular, the S29A PncC and K61Q PncC variant forms were selected since they still preserve the ability to bind NMN in the micromolar range, but they are not able to catalyze the enzymatic reaction. While S29A PncC shows a similar affinity also for NaMN (the product of the PncC catalyzed reaction), K61Q PncC does not interact significantly with it. Thus, PncC K61Q mutant seems to be a promising candidate to use as specific probe for an NMN biosensor.

Nicotinamide Mononucleotide Combined With Lactobacillus fermentum TKSN041 Reduces the Photoaging Damage in Murine Skin by Activating AMPK Signaling Pathway

Long-term exposure to UVB (280-320 nm) can cause oxidative skin damage, inflammatory injury, and skin cancer. Research on nicotinamide mononucleotide (NMN) and lactic acid bacteria (LAB) with regard to antioxidation, anti-inflammation, and prevention of other age-related diseases has received increasing attention. In the present study, the in vitro antioxidant analysis showed that NMN combined with Lactobacillus fermentum TKSN041 (L. fermentum TKSN041) has a high scavenging ability on hydroxyl (OH), 2, 2'-azino-bis (3-ethylbenzthiazoline-6-sulphonic acid) diammonium salt (ABTS) and 1, 1-diphenyl-2-picrylhydrazyl (DPPH), and it also possess a good total antioxidant capacity. The animal experimental results show that NMN combined with LAB maintained normal liver morphology of mice and reduced pathological damage to murine skin. NMN combined with LAB significantly increased the serum levels of total superoxide dismutase (T-SOD), catalase (CAT), and interleukin (IL)-10, but reduced the levels of malondialdehyde, advanced glycation end products, tumor necrosis factor (TNF)-α, and IL-6. NMN combined with LAB increased T-SOD, CAT, IL-10, Na⁺-K⁺-ATPase, and NAD⁺ levels in the skin, but reduced TNF-α level in the skin. NMN combined with LAB increased the mRNA expression levels of SOD1, CAT, glutathione (GSH), inhibitor of NF-κB (IκB-α), IL-10, AMP-activated protein kinase (AMPK), adaptor protein, phosphotyros ineinteraction, PH domain and leucine zipper containing 1 (APPL1), peroxisome proliferator-activated receptor γ co-activator-1α (PGC-1α), and forkhead transcription factor O (FOXO) in the skin and liver, but decreased the mRNA expression levels of nuclear factor (NF)-κBp65, TNF-α, IL-6, and rapamycin target protein (mTOR). NMN combined with LAB increased the protein expression levels of AMPK, IκB-α, SOD1, and CAT in the skin tissues and reduced protein expression of NF-κBp65. NMN combined with L. fermentum TKSN041 improved murine skin damage caused by UVB irradiation, and the protective mechanism may be related to activation of the AMPK signaling pathway. The results of this study are expected to provide a reference for preventing and the treating skin photoaging.

Nicotinamide Mononucleotide Potentiates Resistance to Biotrophic Invasion of Fungal Pathogens in Barley

Nicotinamide mononucleotide (NMN), a precursor of nicotinamide adenine dinucleotide (NAD), induces disease resistance to the Fusarium head blight fungus Fusarium graminearum in Arabidopsis and barley, but it is unknown at which stage of the infection it acts. Since the rate of haustorial formation of an obligate biotrophic barley powdery mildew fungus Blumeria graminis f. sp. hordei (Bgh) was significantly reduced in NMN-treated coleoptile epidermal cells, the possibility that NMN induces resistance to the biotrophic stage of F. graminearum was investigated. The results show that NMN treatment caused the wandering of hyphal growth and suppressed the formation of appressoria-like structures. Furthermore, we developed an experimental system to monitor the early stage of infection in real-time and analyzed the infection behavior. We observed that the hyphae elongated windingly by NMN treatment. These results suggest that NMN potentiates resistance to the biotrophic invasion of F. graminearum as well as Bgh.

Nicotinamide Mononucleotide Alleviates Hyperosmolarity-Induced IL-17a Secretion and Macrophage Activation in Corneal Epithelial Cells/Macrophage Co-Culture System

Background

Hyperosmosis stress (HS) was a key pathological factor in the development of dry eye disease (DED). Nicotinamide mononucleotide (NMN) demonstrated protective effects in the corneal damage, however, its role in the HS-induced DED remained unclear.

Methods

A NaCl based HS in-vitro model (500 mOsm) was generated and used in a co-culture system including corneal epithelial cells (CEC) and macrophage cell line RAW264.7. The effect of NMN on NAD+ metabolism and the expression of HS biomarker, tonicity-responsive element binding protein (TonEBP), was studied in the CEC. The cellular activity, including cell viability, apoptosis status and lactate dehydrogenase (LDH) release through trypan blue staining, flow cytometry and LDH assay, respectively. The mitochondrial membrane potential (MMP) assay would be conducted using the JC1 kit. The expression of IL-17a were detected using RT-PCR, ELISA and Western blot. After co-culture with the CEC in different group for 24 h, the phagocytosis ability and macrophage polarization were assessed in RAW264.7 cells co-cultured with CEC with or without HS or NMN treatment. Besides, the involvement of Notch pathway in the RAW264.7 would be analyzed. The potential involvement of Sirtuin 1 (SIRT1) and IL-17a in the crosstalk between CEC and macrophage was studied with SIRT1 inhibitor EX 527 and anti-IL-17a monoclonal antibody, respectively.

Results

NMN treatment increased NAD+ concentration and thus improved cell viability, reduced apoptotic rate and decreased the LDH release in HS-treated CEC. Besides, NMN alleviated HS-induced MMP, intracellular ROS and LDH release. Besides, it was confirmed NMN improve SIRT1 function and decreased the HS related IL-17a expression in CEC and then alleviated macrophage phagocytosis ability and M1 polarization based on a CEC-macrophage co-culture system. Moreover, NMN treatment of CEC in the CEC could moderate the subsequent macrophage activation through Notch pathway. SIRT1 activation and IL-17a inhibition was regarded as key progress in the function of NMN based on the application of EX 527 and anti-IL-17a antibody in the CEC-macrophage co-culture system.

Conclusion

The findings demonstrated that NMN could alleviated HS-induced DED status through regulating the CEC/macrophage interaction. Our data pointed to the role of SIRT1, IL-17a and Notch pathway in the function of NMN and then provided updated knowledge of potential NMN application in the management of DED.

Nicotinamide mononucleotide (NMN) protects bEnd.3 cells against H2 O2 -induced damage via NAMPT and the NF-κB p65 signalling pathway

An increasing number of studies have shown that nicotinamide mononucleotide (NMN) can inhibit not only ageing but also oxidative stress and inflammatory reactions by improving energy metabolism. However, the role of NMN in regulating the anti‐apoptotic, antioxidative stress and inflammatory responses of brain microvascular endothelial cells is still unknown. Therefore, here we studied the effects of NMN on H₂O₂‐induced oxidative damage of bEnd.3 cells. In this study, we found that NMN could inhibit the NF‐κBp65 inflammatory signalling pathway and increase the expression of the enzymes NAMPT, VEGF and eNOS, alleviating H₂O₂‐induced apoptosis in bEnd.3 cells. Taken together, these results suggest that NMN reduces H₂O₂‐induced oxidative stress and apoptosis and improves cell functions by inhibiting the NF‐κBp65 inflammatory pathway and increasing NAMPT expression.

Subacute Toxicity Study of Nicotinamide Mononucleotide via Oral Administration

Nicotinamide mononucleotide (NMN), a key precursory metabolite of NAD⁺, has been shown to elevate the cellular level of NAD⁺ and ameliorate various age-related diseases. Despite these progresses, systemic evaluation pertaining to the subacute toxicity of NMN remains to be determined. Here, we examine the subacute toxicity of NMN in mice and beagle dogs. Mice were gavaged with a saturated concentration of NMN solution at the maximum intragastric dose once or twice per day for 7 days. Dogs were gavaged twice per day for 14 days. In mice, NMN administrated once per day for 7 days is well tolerated with minimal deleterious effects. Upon higher dosage, we observe slightly increased level of alamine aminotransferase, while other biomarkers remain unchanged. Consistently, administration of NMN in beagle dogs only results in mild increases in creatinine and uric acid. Together, our study highlights the safety of NMN, providing a possible safe dose range for oral administration of NMN.