Enzymatic and Chemical Syntheses of Vacor Analogs of Nicotinamide Riboside, NMN and NAD

Protein Engineering and Dual-Module Optimization for Efficient NMN Production in E. coli

Nicotinamide mononucleotide (NMN) has received widespread attention as a supplement of NAD+ in cells. In this study, a dual-module reaction system was constructed to synthesize NR using uridine and nicotinamide, and further to efficiently synthesize NMN. First, module 1 was constructed, which catalyzed the synthesis of NMN from NR using an efficient NRK and ATP regeneration system. Then module 2 was constructed by introducing pyrimidine nucleoside phosphorylase (PyNP) to synthesize NMN from uridine and NAM under the synergistic catalysis of NRK. Based on the fact that NRK has both phosphorylation and group transfer functions in the dual-module system, the mutant KlmNRKM4 with nearly 4-fold increased stability was obtained through predicted structure and evolutionary conservation analysis. At the same time, the pncC, deoD, ushA, nadR and deoB genes encoding endogenous degradative enzymes in Escherichia coli affect substrate and intermediate conversion were knocked out. Finally, by optimizing the reaction conditions of the dual-module recombination system, a high NMN conversion rate of 81.1% was achieved using 300 mM uridine and nicotinamide as substrates. This study provides a novel and efficient pathway for the biosynthesis of NMN.

Exploring the De Novo NMN Biosynthesis as an Alternative Pathway to Enhance NMN Production

Nicotinamide mononucleotide (NMN) serves as a precursor for NAD+ synthesis and has been shown to have positive effects on the human body. Previous research has predominantly focused on the nicotinamide phosphoribosyltransferase-mediated route (NadV-mediated route) for NMN biosynthesis. In this study, we have explored the de novo NMN biosynthesis route as an alternative pathway to enhance NMN production. Initially, we systematically engineered Escherichia coli to enhance its capacity for NMN synthesis and accumulation, resulting in a remarkable over 100-fold increase in NMN yield. Subsequently, we progressively enhanced the de novo NMN biosynthesis route to further augment NMN production. We screened and identified the crucial role of MazG in catalyzing the enzymatic cleavage of NAD+ to NMN. And the de novo NMN biosynthesis route was optimized and integrated with the NadV-mediated NMN biosynthetic pathways, leading to an intracellular concentration of 844.10 ± 17.40 μM NMN. Furthermore, the introduction of two transporters enhanced the uptake of NAM and the excretion of NMN, resulting in NMN production of 1293.73 ± 61.38 μM. Finally, by engineering an E. coli strain with optimized PRPP synthetase, we achieved the highest NMN production, reaching 3067.98 ± 27.25 μM after 24 h of fermentation at the shake flask level. In addition to constructing an efficient E. coli cell factory for NMN production, our findings provide new insights into understanding the NAD+ salvage pathway and its role in energy metabolism within E. coli.

Adaptation of a Commercial NAD+ Quantification Kit to Assay the Base-Exchange Activity and Substrate Preferences of SARM1

Here, we report an adapted protocol using the Promega NAD/NADH-Glo™ Assay kit. The assay normally allows quantification of trace amounts of both oxidized and reduced forms of nicotinamide adenine dinucleotide (NAD) by enzymatic cycling, but we now show that the NAD analog 3-acetylpyridine adenine dinucleotide (AcPyrAD) also acts as a substrate for this enzyme-cycling assay. In fact, AcPyrAD generates amplification signals of a larger amplitude than those obtained with NAD. We exploited this finding to devise and validate a novel method for assaying the base-exchange activity of SARM1 in reactions containing NAD and an excess of the free base 3-acetylpyridine (AcPyr), where the product is AcPyrAD. We then used this assay to study competition between AcPyr and other free bases to rank the preference of SARM1 for different base-exchange substrates, identifying isoquinoline as a highly effect substrate that completely outcompetes even AcPyr. This has significant advantages over traditional HPLC methods for assaying SARM1 base exchange as it is rapid, sensitive, cost-effective, and easily scalable. This could represent a useful tool given current interest in the role of SARM1 base exchange in programmed axon death and related human disorders. It may also be applicable to other multifunctional NAD glycohydrolases (EC 3.2.2.6) that possess similar base-exchange activity.

Inhibitors of NAD+ Production in Cancer Treatment: State of the Art and Perspectives

The addiction of tumors to elevated nicotinamide adenine dinucleotide (NAD+) levels is a hallmark of cancer metabolism. Obstructing NAD+ biosynthesis in tumors is a new and promising antineoplastic strategy. Inhibitors developed against nicotinamide phosphoribosyltransferase (NAMPT), the main enzyme in NAD+ production from nicotinamide, elicited robust anticancer activity in preclinical models but not in patients, implying that other NAD+-biosynthetic pathways are also active in tumors and provide sufficient NAD+ amounts despite NAMPT obstruction. Recent studies show that NAD+ biosynthesis through the so-called "Preiss-Handler (PH) pathway", which utilizes nicotinate as a precursor, actively operates in many tumors and accounts for tumor resistance to NAMPT inhibitors. The PH pathway consists of three sequential enzymatic steps that are catalyzed by nicotinate phosphoribosyltransferase (NAPRT), nicotinamide mononucleotide adenylyltransferases (NMNATs), and NAD+ synthetase (NADSYN1). Here, we focus on these enzymes as emerging targets in cancer drug discovery, summarizing their reported inhibitors and describing their current or potential exploitation as anticancer agents. Finally, we also focus on additional NAD+-producing enzymes acting in alternative NAD+-producing routes that could also be relevant in tumors and thus become viable targets for drug discovery.

Preparation and evaluation of ovalbumin-fucoidan nanoparticles for nicotinamide mononucleotide encapsulation with enhanced stability and anti-aging activity

Nicotinamide mononucleotide (NMN) has been recognized as a promising bio-active compound in relieving aging-related mitochondrial dysfunction. Self-assembled nanoparticles were prepared based on interaction between ovalbumin (OVA) and fucoidan to improve the stability and bio-accessibility of NMN. The OVA-fucoidan nanoparticles (OFNPs) displayed outstanding thermal stability and entrapment ability of NMN. The reactive oxygen species (ROS) analysis and senescence-associated β-galactosidase (SA-β-gal) staining characterization indicated that NMN encapsulated by OFNPs could effectively alleviate the cellular senescence of d-galactose-induced senescent cells. In vivo Caenorhabitis elegans experiment demonstrated that NMN-loaded OFNPs caused less accumulation of lipofuscin and protected NMN from thermal damage. Compared with free NMN, the NMN-loaded OFNPs prolonged lifespan from 28 to 31 days, increased 26% reproductive ability, and improved 12% body length of Caenorhabitis elegans. The results indicated that the use of nanocarriers could be a good strategy to improve anti-oxidative stress and anti-aging ability of NMN.

Systematic engineering of Escherichia coli for efficient production of nicotinamide riboside from nicotinamide and 3-cyanopyridine

Nicotinamide riboside (NR), a key biosynthetic precursor of NAD⁺, is receiving increasing attention because of its role. In this study, a whole-cell catalysis method to efficiently synthesize NR was established. First, the performance of 5'-nucleotidase (UshA) from Escherichia coli was confirmed to have high catalytic activity to synthesize NR. Then, the endogenous NR degradation pathway was detected, and the genes (rihA, rihB, and rihC) involved in NR degradation were knocked out, which enabled NR biosynthesis. In addition, the important role of the signal peptide of UshA in NR transport had been confirmed. Subsequently, nitrile hydratase was introduced to achieve the conversion of 3-cyanopyridine to NR. Finally, the NR titer reached 25.6 and 29.8 g/L with nicotinamide and 3-cyanopyridine, respectively, as substrates in a 5-L bioreactor, the efficient biosynthesis of NR in E. coli by using nicotinamide and 3-cyanopyridine.

NMNAT2: An important metabolic enzyme affecting the disease progression

Nicotinamide mononucleotide adenylyltransferase 2 (NMNAT2) is an evolutionarily conserved nicotinamide adenine dinucleotide (NAD⁺) synthase located in the cytoplasm and Golgi apparatus. NMNAT2 has an important role in neurodegenerative diseases, malignant tumors, and other diseases that seriously endanger human health. NMNAT2 exerts a neuroprotective function through its NAD synthase activity and chaperone function. Among them, the NMNAT2-NAD⁺-Sterile alpha and Toll/interleukin-1 receptor motif-containing 1 (SARM1) axis is closely related to Wallerian degeneration. Physical injury or pathological stimulation will cause a decrease in NMNAT2, which activates SARM1, leading to axonal degeneration and the occurrence of amyotrophic lateral sclerosis (ALS), Alzheimer's disease, peripheral neuropathy, and other neurodegenerative diseases. In addition, NMNAT2 exerts a cancer-promoting role in solid tumors, including colorectal cancer, lung cancer, ovarian cancer, and glioma, and is closely related to tumor occurrence and development. This paper reviews the chromosomal and subcellular localization of NMNAT2 and its basic biological functions. We also summarize the NMNAT2-related signal transduction pathway and the role of NMNAT2 in diseases. We aimed to provide a new perspective to comprehensively understand the relationship between NMNAT2 and its associated diseases.

Nicotinamide Mononucleotide Supplementation Improves Mitochondrial Dysfunction and Rescues Cellular Senescence by NAD+/Sirt3 Pathway in Mesenchymal Stem Cells

In vitro expansion-mediated replicative senescence has severely limited the clinical applications of mesenchymal stem cells (MSCs). Accumulating studies manifested that nicotinamide adenine dinucleotide (NAD⁺) depletion is closely related to stem cell senescence and mitochondrial metabolism disorder. Promoting NAD⁺ level is considered as an effective way to delay aging. Previously, we have confirmed that nicotinamide mononucleotide (NMN), a precursor of NAD⁺, can alleviate NAD⁺ deficiency-induced MSC senescence. However, whether NMN can attenuate MSC senescence and its underlying mechanisms are still incompletely clear. The present study herein showed that late passage (LP) MSCs displayed lower NAD⁺ content, reduced Sirt3 expression and mitochondrial dysfunction. NMN supplementation leads to significant increase in intracellular NAD⁺ level, NAD⁺/ NADH ratio, Sirt3 expression, as well as ameliorated mitochondrial function and rescued senescent MSCs. Additionally, Sirt3 over-expression relieved mitochondrial dysfunction, and retrieved senescence-associated phenotypic features in LP MSCs. Conversely, inhibition of Sirt3 activity via a selective Sirt3 inhibitor 3-TYP in early passage (EP) MSCs resulted in aggravated cellular senescence and abnormal mitochondrial function. Furthermore, NMN administration also improves 3-TYP-induced disordered mitochondrial function and cellular senescence in EP MSCs. Collectively, NMN replenishment alleviates mitochondrial dysfunction and rescues MSC senescence through mediating NAD⁺/Sirt3 pathway, possibly providing a novel mechanism for MSC senescence and a promising strategy for anti-aging pharmaceuticals.

SARM1 is a multi-functional NAD(P)ase with prominent base exchange activity, all regulated bymultiple physiologically relevant NAD metabolites

SARM1 is an NAD(P) glycohydrolase and TLR adapter with an essential, prodegenerative role in programmed axon death (Wallerian degeneration). Like other NAD(P)ases, it catalyzes multiple reactions that need to be fully investigated. Here, we compare these multiple activities for recombinant human SARM1, human CD38, and Aplysia californica ADP ribosyl cyclase. SARM1 has the highest transglycosidation (base exchange) activity at neutral pH and with some bases this dominates NAD(P) hydrolysis and cyclization. All SARM1 activities, including base exchange at neutral pH, are activated by an increased NMN:NAD ratio, at physiological levels of both metabolites. SARM1 base exchange occurs also in DRG neurons and is thus a very likely physiological source of calcium-mobilizing agent NaADP. Finally, we identify regulation by free pyridines, NADP, and nicotinic acid riboside (NaR) on SARM1, all of therapeutic interest. Understanding which specific SARM1 function(s) is responsible for axon degeneration is essential for its targeting in disease.

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Base exchange is a prominent, and sometimes completely dominant, SARM1 activity

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Physiologically relevant NMN:NAD ratios may regulate all of SARM1's multiple activities

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Physiological NADP may inhibit SARM1 more potently than NAD and via a distinct site

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NaR and VR both selectively inhibit SARM1 and are thus possible effectors or drug leads