Enzymology of NAD+ synthesis.
Magni G,Amici A,Emanuelli M,Raffaelli N,Ruggieri S
Advances in enzymology and related areas of molecular biology
Beyond its role as an essential coenzyme in numerous oxidoreductase reactions as well as respiration, there is growing recognition that NAD+ fulfills many other vital regulatory functions both as a substrate and as an allosteric effector. This review describes the enzymes involved in pyridine nucleotide metabolism, starting with a detailed consideration of the anaerobic and aerobic pathways leading to quinolinate, a key precursor of NAD+. Conversion of quinolinate and 5'-phosphoribosyl-1'-pyrophosphate to NAD+ and diphosphate by phosphoribosyltransferase is then explored before proceeding to a discussion the molecular and kinetic properties of NMN adenylytransferase. The salient features of NAD+ synthetase as well as NAD+ kinase are likewise presented. The remainder of the review encompasses the metabolic steps devoted to (a) the salvaging of various niacin derivatives, including the roles played by NAD+ and NADH pyrophosphatases, nicotinamide deamidase, and NMN deamidase, and (b) utilization of niacins by nicotinate phosphoribosyltransferase and nicotinamide phosphoribosyltransferase.
Modulation of cytotoxicity of benzamide riboside by expression of NMN adenylyltransferase.
Yalowitz Joel A,Jayaram Hiremagalur N
Current medicinal chemistry
Benzamide riboside (BR) is a nucleoside prodrug that is phosphorylated to its 5'-monophosphate (BRMP) and then converted to its active metabolite, BAD (benzamide adenine dinucleotide), an analogue of NAD by the action of NMN adenylyltransferase (NMNAT). BAD is a potent, reversible, and noncompetitive inhibitor of inosine 5'-monophosphate dehydrogenase (IMPDH) resulting in depletion of guanylates (GTP and dGTP). IMPDH inhibitors such as BR induce differentiation and apoptosis as a consequence of GTP depletion. Tiazofurin (TR) and selenazofurin (SR) require similar metabolism by NMNAT. NMNAT is the rate-limiting step in the synthesis of NAD and NAD analogues. BR- and TR-sensitive leukemic cells contain high NMNAT activity, whereas resistant clones have greatly downregulated NMNAT activity (<0.1% of wild type). Perhaps the applicability of BR and analogues could be enhanced if combined with NMNAT gene expression in BR-resistant leukemic blasts. NAD has important regulatory role in repair of DNA damage and cell growth since it is a substrate for poly(ADP-ribose) polymerase (PARP). PARP appears to direct short-patch base excision repair and induce p53 upregulation leading to apoptosis. BR inhibits PARP at high concentrations when assayed in permeabilized leukemic cells. Several other IMPDH inhibitors (TR, mycophenolic acid, and ribavirin) exhibit similar PARP inhibitory activity. Although this inhibition was reversible, it was not prevented by the addition of guanosine, GTP, or its nonhydrolyzable analog gamma-S-GTP. Therefore, it can be concluded that IMPDH inhibitors directly inhibit PARP. Presumably, the shared IMP-NAD active site of IMPDH has a similar architecture to the NAD-binding pocket of PARP.
Structure and function of nicotinamide mononucleotide adenylyltransferase.
Magni G,Amici A,Emanuelli M,Orsomando G,Raffaelli N,Ruggieri S
Current medicinal chemistry
The enzyme nicotinamide mononucleotide adenylyltransferase (NMNAT), a member of the nucleotidyltransferase alpha/beta phosphodiesterase superfamily, catalyzes the reaction NMN + ATP = NAD + PPi, representing the final step in the biosynthesis of NAD, a molecule playing a fundamental role as a cofactor in cellular redox reactions. NAD also serves as the substrate for reactions involved in important regulatory roles, such as protein covalent modifications, like ADP-ribosylation reactions, as well as Sir2 histone deacetylase, a recently discovered class of enzymes involved in the regulation of gene silencing. This overview describes the most recent findings on NMNATs from bacteria, archaea, yeast, animal and human sources, with detailed consideration of their major kinetic, molecular and structural features. On this regard, the different characteristics exhibited by the enzyme from the various species are highlighted. The possibility that NMNAT may represent an interesting candidate as a target for the rational design of selective chemotherapeutic agents has been suggested.
The NMN/NaMN adenylyltransferase (NMNAT) protein family.
Lau Corinna,Niere Marc,Ziegler Mathias
Frontiers in bioscience (Landmark edition)
NAD biosynthesis has become of considerable interest owing to the important signaling functions of the pyridine nucleotides which have been recognized over the past years. The formation of the dinucleotides from ATP and the mononucleotide of niacin (either nicotinamide or nicotinic acid) constitute the critical step in NAD generation which is catalyzed by NMN/NaMN adenylyltransferases, NMNATs. Recent research has established the molecular, catalytic and structural properties of NMNATs from many organisms. Detailed studies, particularly of the human NMNATs, have revealed distinct isoform-specific characteristics relating to enzyme kinetics and substrate specificity, oligomeric assembly as well as subcellular and tissue distribution. Moreover, direct functional relationships between NMNATs and major NAD-mediated signaling processes have been discovered suggesting that at least some of these proteins might play more than just an enzymatic role. Several investigations have also pointed to a critical role of NMNATs in pathological states such as cancer and neurodegeneration. This article intends to provide a comprehensive overview of the family of NMNATs and highlights some of the recently identified functional roles of these enzymes.
NAD(P) biosynthesis enzymes as potential targets for selective drug design.
Magni G,Di Stefano M,Orsomando G,Raffaelli N,Ruggieri S
Current medicinal chemistry
NAD(P) biosynthetic pathways can be considered a generous source of enzymatic targets for drug development. Key reactions for NAD(P) biosynthesis in all organisms, common to both de novo and salvage routes, are catalyzed by NMN/NaMN adenylyltransferase (NMNAT), NAD synthetase (NADS), and NAD kinase (NADK). These reactions represent a three-step pathway, present in the vast majority of living organisms, which is responsible for the generation of both NAD and NADP cellular pools. The validation of these enzymes as drug targets is based on their essentiality and conservation among a large variety of pathogenic microorganisms, as well as on their differential structural features or their differential metabolic contribution to NAD(P) homeostasis between microbial and human cell types. This review describes the structural and functional properties of eubacterial and human enzymes endowed with NMNAT, NADS, and NADK activities, as well as with nicotinamide phosphoribosyltransferase (NamPRT) and nicotinamide riboside kinase (NRK) activities, highlighting the species-related differences, with emphasis on their relevance for drug design. In addition, since the overall NMNAT activity in humans is accounted by multiple isozymes differentially involved in the metabolic activation of antineoplastic compounds, their individual diagnostic value for early therapy optimization is outlined. The involvement of human NMNAT in neurodegenerative disorders and its role in neuroprotection is also discussed.
Nampt: linking NAD biology, metabolism and cancer.
Garten Antje,Petzold Stefanie,Körner Antje,Imai Shin-Ichiro,Kiess Wieland
Trends in endocrinology and metabolism: TEM
Nicotinamide phosphoribosyltransferase (Nampt) converts nicotinamide to nicotinamide mononucleotide (NMN), a key nicotinamide adenine dinucleotide (NAD) intermediate. Previously identified as a cytokine pre-B-cell colony-enhancing factor and controversially claimed as an insulin-mimetic hormone visfatin, Nampt has recently drawn much attention in several fields, including NAD biology, metabolism and inflammation. As a NAD biosynthetic enzyme, Nampt regulates the activity of NAD-consuming enzymes such as sirtuins and influences a variety of metabolic and stress responses. Nampt also plays an important part in regulating insulin secretion in pancreatic beta-cells. Nampt seems to have another function as an immunomodulatory cytokine and, therefore, has a role in inflammation. This review summarizes these various functional aspects of Nampt and discusses its potential roles in diseases, including type 2 diabetes and cancer.
A possibility of nutriceuticals as an anti-aging intervention: activation of sirtuins by promoting mammalian NAD biosynthesis.
Aging science has recently drawn much attention, and discussions on the possibility of anti-aging medicine have multiplied. One potential target for the development of anti-aging drugs is the SIR2 (silent information regulator 2) family of NAD-dependent deacetylases/ADP-ribosyltransferases, called "sirtuins." Sirtuins regulate many fundamental biological processes in response to a variety of environmental and nutritional stimuli. In mammals, the mammalian SIR2 ortholog SIRT1 has been most studied, and small molecule SIRT1 activators (STACs), including a plant-derived polyphenolic compound resveratrol, have been developed. On the other hand, sirtuin activity is regulated by NAD biosynthetic pathways, and nicotinamide phosphoribosyltransferase (NAMPT) plays a critical role in the regulation of mammalian sirtuin activity. Recent studies have provided a proof of concept for the idea that nicotinamide mononucleotide (NMN), the NAMPT reaction product, can be used as a nutriceutical to activate SIRT1 activity. Based on these recent findings, the possibility of sirtuin-targeted nutriceutical development will be discussed.
NMN/NaMN adenylyltransferase (NMNAT) and NAD kinase (NADK) inhibitors: chemistry and potential therapeutic applications.
Petrelli R,Felczak K,Cappellacci L
Current medicinal chemistry
Nicotinamide adenine dinucleotide (NAD(+)) has a crucial role in many cellular processes, both as a coenzyme for redox reactions and as a substrate to donate ADP-ribose units. Thus, enzymes involved in NAD(+) metabolism are attractive targets for drug discovery against a variety of human diseases. Herein we focus on two of them: NMN/NaMN adenylyltransferase (NMNAT) and NAD kinase (NADK). NMNAT is a key enzyme in all organisms catalyzing coupling of ATP and NMN or NaMN yielding NAD or NaAD, respectively. NADKs are ubiquitous enzymes involved in the last step of the biosynthesis of NADP. They phosphorylate NAD to produce NADP using ATP (or inorganic polyphosphates) in the presence of Mg(2+). No other pathway of NADP biosynthesis has been found in prokaryotic or eukaryotic cells. In this review we provide a comprehensive summary of NMNAT and NADK inhibitors highlighting their chemical modifications by different synthetic approaches, and structure-activity relationships depending on their potential therapeutic applications.
NAMPT in regulated NAD biosynthesis and its pivotal role in human metabolism.
Burgos E S
Current medicinal chemistry
Nicotinamide phosphoribosyltransferase (NAMPT) catalyzes the first reversible step in NAD biosynthesis and nicotinamide (NAM) salvage. The enzyme is designed for efficient capture of nicotinamide by coupling of ATP hydrolysis to assist in extraordinary NAM binding affinity and formation of nicotinamide mononucleotide (NMN). NAMPT provides the mechanism to replenish the NAD pool in human metabolism. In addition to its role in redox biochemistry, NAD fuels the sirtuins (SIRTs) to regulate transcription factors involved in pathways linked to inflammation, diabetes and lifespan. NAMPT-mediated lifespan expansion has caused a focus on the catalytic mechanism, regulation and inhibition of NAMPT. Structural, mechanistic and inhibitor design all contribute to a developing but yet incomplete story of NAMPT function. Although the first generation of NAMPT inhibitors has entered clinical trials, disappointing outcomes suggest more powerful and specific inhibitors will be needed. Understanding the ATP-linked mechanism of NAMPT and the catalytic site machinery may permit the design of improved NAMPT inhibitors as more efficient drugs against cancer.
Rehab of NAD(P)-dependent enzymes with NAD(P)-based inhibitors.
Felczak K,Pankiewicz K W
Current medicinal chemistry
A large number of enzymes that use nicotinamide adenine dinucleotide NAD or its phosphorylated form NADP as a cofactor or substrate were found to play an important role in the growth and reproduction of living organisms. NAD(P)-dependent and NAD(P)-utilizing enzymes [NAD(P)-addicted?] have been extensively investigated and implicated in a wide variety of diseases. NAD, generally considered a key component involved in redox reactions, has been found to participate in a broad spectrum of cellular processes, including signal transduction, DNA repair, and post-translational protein modifications. The reduced form of NADP, i.e. NADPH, guards the cell against oxidative stress and it has been suggested that suppression of NADPH oxidase activity could result in anti-angiogenesis and anticancer effects. Consequently, small molecule NAD(P)-based inhibitors that selectively bind at the NAD(P)-binding domain of the targeted enzyme have been designed for novel treatment of medical disorders. The NAD(P)-binding domain is modular in nature; it can be divided into three sub-sites, the nicotinamide monophosphate (NMN) binding sub-site (N sub-site), the adenosine monophosphate (AMP) binding sub-site (A sub-site), and the pyrophosphate binding sub-site (P sub-site or P-groove). Each sub-site plays an important role in securing proper and tight binding; however, each has its own requirements. In this review we discuss a number of conformational and structural factors that might affect (improve) the affinity of various inhibitors to these sub-sites, as well as to the whole binding domain. We have focused on potential selectivity of NAD(P)-like molecules toward targeted enzymes and their potential application in biology and medicine.
Nampt and its potential role in inflammation and type 2 diabetes.
Garten Antje,Petzold Stefanie,Schuster Susanne,Körner Antje,Kratzsch Jürgen,Kiess Wieland
Handbook of experimental pharmacology
Nicotinamide phosphoribosyltransferase Nicotinamide phosphoribosyltransferase (Nampt Nampt ) is a key nicotinamide adenine dinucleotide (NAD) NAD biosynthetic enzyme in mammals, converting nicotinamide nicotinamide into nicotinamide mononucleotide nicotinamide mononucleotide (NMN NMN ), an NAD intermediate. First identified in humans as a cytokine cytokine pre-B-cell colony enhancing factor pre-B cell colony enhancing factor (PBEF PBEF ) and subsequently described as an insulin-mimetic hormone visfatin visfatin , Nampt has recently excited the scientific interest of researchers from diverse fields, including NAD biology, metabolic regulation, and inflammation. As an NAD biosynthetic enzyme, Nampt regulates the activity of NAD-consuming enzymes such as sirtuins sirtuins and influences a variety of metabolic and stress responses. Nampt plays an important role in the regulation of insulin secretion insulin secretion in pancreatic β-cells. Nampt also functions as an immunomodulatory cytokine cytokine and is involved in the regulation of inflammatory responses. This chapter summarizes the various functional aspects of Nampt and discusses its potential roles in diseases, with special focus on type 2 diabetes mellitus (T2DM).
NMNAT expression and its relation to NAD metabolism.
Jayaram H N,Kusumanchi P,Yalowitz J A
Current medicinal chemistry
Nicotinamide mononucleotide adenylyltransferease (NMNAT), a rate-limiting enzyme present in all organisms, reversibly catalyzes the important step in the biosynthesis of NAD from ATP and NMN. NAD and NADP are used reversibly in anabolic and catabolic reactions. NAD is necessary for cell survival in oxidative stress and DNA damage. Based on their localization, three different NMNAT's have been recognized, NMNAT-1 (homohexamer) in the nucleus (chromosome 1 p32-35), NMNAT-2 (homodimer) in the cytoplasm (chromosome 1q25) and NMNAT-3 (homotetramer) in the mitochondria. NMNAT also catalyzes the metabolic conversion of potent antitumor prodrugs like tiazofurin and benzamide riboside to their active forms which are analogs of NAD. NAD synthase-NMNAT acts as a chaperone to protect against neurodegeneration, injury-induced axonal degeneration and also correlates with DNA synthesis during cell cycle. Since its activity is rather low in tumor cells it can be exploited as a source for therapeutic targeting. Steps involved in NAD synthesis are being utilized as targets for chemoprevention, radiosensitization and therapy of wide range of diseases, such as cancer, multiple sclerosis, neurodegeneration and Huntington's disease.
Comparative genomics of NAD(P) biosynthesis and novel antibiotic drug targets.
Bi Jicai,Wang Honghai,Xie Jianping
Journal of cellular physiology
NAD(P) is an indispensable cofactor for all organisms and its biosynthetic pathways are proposed as promising novel antibiotics targets against pathogens such as Mycobacterium tuberculosis. Six NAD(P) biosynthetic pathways were reconstructed by comparative genomics: de novo pathway (Asp), de novo pathway (Try), NmR pathway I (RNK-dependent), NmR pathway II (RNK-independent), Niacin salvage, and Niacin recycling. Three enzymes pivotal to the key reactions of NAD(P) biosynthesis are shared by almost all organisms, that is, NMN/NaMN adenylyltransferase (NMN/NaMNAT), NAD synthetase (NADS), and NAD kinase (NADK). They might serve as ideal broad spectrum antibiotic targets. Studies in M. tuberculosis have in part tested such hypothesis. Three regulatory factors NadR, NiaR, and NrtR, which regulate NAD biosynthesis, have been identified. M. tuberculosis NAD(P) metabolism and regulation thereof, potential drug targets and drug development are summarized in this paper.
Partial reversal of skeletal muscle aging by restoration of normal NAD⁺ levels.
Mendelsohn Andrew R,Larrick James W
That some aging-associated phenotypes may be reversible is an emerging theme in contemporary aging research. Gomes et al. report that age-associated oxidative phosphorylation (OXPHOS) defects in murine skeletal muscle are biphasic. In the first phase, OXPHOS is decreased because of reduced expression of mitochondrially encoded genes. Treatment of moderately old mice (first-phase OXPHOS defects) with nicotinamide adenine dinucleotide (NAD⁺) precursor nicotinamide mononucleotide (NMN) for 1 week restores oxidative phosphorylation activity and other markers of mitochondrial function in skeletal muscle. However, muscle strength is not restored. In very old animals (second-phase OXPHOS defects), expression of OXPHOS genes from both the nucleus and mitochondria is reduced and mitochondrial DNA integrity is diminished. Gomes et al. propose a model linking decreased NAD⁺ to loss of nuclear SIRT1 activity to stabilization of the hypoxia-associated transcription factor hypoxia-inducible factor 1-alpha (HIF-1a). HIF-1a promotes an hypoxic-like (Warburg effect) state in the cell. The HIF-1a protein interacts with c-Myc, decreasing c-Myc-regulated transcription of the key mitochondrial regulator mitochondrial transcription factor A (TFAM). Low levels of TFAM lead to first-phase OXPHOS dysfunction. The transition to irreversible phase 2 dysfunction remains to be characterized, but may be related to increased reactive oxygen species (ROS) production. This model suggests that intervention in mitochondrial aging may be possible using appropriate NAD⁺ precursors such as nicotinamide riboside. Restoring NAD⁺ levels may be beneficial throughout the organism. For example, aging-associated disturbances in circadian rhythm are linked to diminished SIRT1 activity, and loss of hematopoietic stem cell function to reduced SIRT3. Work to elucidate other biphasic aging mechanisms is strongly encouraged.
Nicotinamide Adenine Dinucleotide Based Therapeutics, Update.
Pankiewicz K W,Petrelli R,Singh R,Felczak K
Current medicinal chemistry
About 500 NAD (P)-dependent enzymes in the cell use NAD (P) as a cofactor or a substrate. This family of broadly diversified enzymes is crucial for maintaining homeostasis of all living organisms. The NAD binding domain of these enzymes is conserved and it was believed that NAD mimics would not be of therapeutic value due to lack of selectivity. Consequently, only mycophenolic acid which selectively binds at the cofactor pocket of NAD-dependent IMP-dehydrogenase (IMPDH) has been approved as an immunosuppressant. Recently, it became clear that the NAD (P)-binding domain was structurally much more diversified than anticipated and numerous highly potent and selective inhibitors of NAD (P) dependent enzymes have been reported. It is likely, that as in the case of protein kinases inhibitors, inhibitors of NAD (P)-dependent enzymes would find soon their way to the clinic. In this review, recent developments of selective inhibitors of NAD-dependent human IMPDH, as well as inhibitors of IMPDHs from parasites, and from bacterial sources are reported. Therapies against Cryptosporidium parvum and the development of new antibiotics that are on the horizon will be discussed. New inhibitors of bacterial NAD-ligases, NAD-kinases, NMN-adenylyl transferases, as well as phosphoribosyl transferases are also described. Although none of these compounds has yet to be approved, the progress in revealing and understanding crucial factors that might allow for designing more potent and efficient drug candidates is enormous and highly encouraging.
NAMPT as a Therapeutic Target against Stroke.
Wang Pei,Miao Chao-Yu
Trends in pharmacological sciences
Nicotinamide phosphoribosyltransferase (NAMPT), also an adipokine known as visfatin, acts via enzymatic activity to synthesize nicotinamide mononucleotide (NMN) and then to maintain homeostasis of nicotinamide adenine dinucleotide (NAD), which plays a dual role in energy metabolism and biological signaling. Of note, the NAMPT metabolic pathway connects NAD-dependent sirtuin (SIRT) signaling, constituting a strong intrinsic defense system against various stresses. Most recently, studies have demonstrated several mechanisms by which NAMPT might serve as a therapeutic target against ischemic stroke, including cerebroprotection in the acute phase as well as vascular repair and neurogenesis in the chronic phase. The molecular mechanisms underlying these benefits have been explored in vivo and in vitro for neural cells, endothelial progenitor cells, and neural stem cells. Therapeutic interventions using NMN, NAMPT activators, and ischemic conditioning are promising for stroke salvage and rehabilitation. This review discusses the current NAMPT data in the context of translational efforts for stroke treatment.
Communication from Tubular Epithelial Cells to Podocytes through Sirt1 and Nicotinic Acid Metabolism.
Hasegawa Kazuhiro,Wakino Shu,Sakamaki Yusuke,Muraoka Hirokazu,Umino Hiroyuki,Minakuchi Hitoshi,Yoshifuji Ayumi,Naitoh Makiko,Shinozuka Keisuke,Futatsugi Koji,Urai Hidenori,Kanda Takeshi,Tokuyama Hirobumi,Hayashi Koichi,Itoh Hiroshi
Current hypertension reviews
We have recently published that tubular epithelial cells affect the podocyte epigenome though nicotinic acid metabolism in diabetic nephropathy (DN), and we have named this relationship "proximal tubule-podocyte communication". In this review, we describe this novel mechanism in the early stage of DN, focusing on the function of renal tubular Sirt1 and Sirt1-related nicotinic acid metabolism. Mainly, we discuss the following three findings. First, we described the details of proximal tubule-podocyte communication. Second, we explained how Sirt1 regulates albuminuria via epigenetic mechanisms. This means that repeated high glucose stress triggers the initial changes in proximal tubules, which lead to the epigenetically irreversible glomerular damages. However, proximal tubular Sirt1 overexpression can rescue these changes. Our previous data indicated that the decrease in Sirt1 expression in proximal tubules caused the reduction in glomerular Sirt1 and the subsequent increase in glomerular Claudin-1. It seemed plausible that some humoral mediator is released from proximal tubules, migrates to podocytes and glomeruli, and affects Sirt1 expression in podocytes. Third, we mentioned a mediator connecting this communication, nicotinamide mononucleotide (NMN). We suggest the potential of Sirt1 or NMN as not only a therapeutic target but also as a prognostic marker of very early stage DN.
Targeting Nicotinamide Phosphoribosyltransferase as a Potential Therapeutic Strategy to Restore Adult Neurogenesis.
Wang Shu-Na,Xu Tian-Ying,Li Wen-Lin,Miao Chao-Yu
CNS neuroscience & therapeutics
Adult neurogenesis is the process of generating new neurons throughout life in the olfactory bulb and hippocampus of most mammalian species, which is closely related to aging and disease. Nicotinamide phosphoribosyltransferase (NAMPT), also an adipokine known as visfatin, is the rate-limiting enzyme for mammalian nicotinamide adenine dinucleotide (NAD) salvage synthesis by generating nicotinamide mononucleotide (NMN) from nicotinamide. Recent findings from our laboratory and other laboratories have provided much evidence that NAMPT might serve as a therapeutic target to restore adult neurogenesis. NAMPT-mediated NAD biosynthesis in neural stem/progenitor cells is important for their proliferation, self-renewal, and formation of oligodendrocytes in vivo and in vitro. Therapeutic interventions by the administration of NMN, NAD, or recombinant NAMPT are effective for restoring adult neurogenesis in several neurological diseases. We summarize adult neurogenesis in aging, ischemic stroke, traumatic brain injury, and neurodegenerative disease and review the advances of targeting NAMPT in restoring neurogenesis. Specifically, we provide emphasis on the P7C3 family, a class of proneurogenic compounds that are potential NAMPT activators, which might shed light on future drug development in neurogenesis restoration.
The pathophysiological importance and therapeutic potential of NAD' biosynthesis and mitochondrial sirtuin SIRT3 in age-associated diseases.
Yamaguchi Shintaro,Yoshino Jun
Nihon rinsho. Japanese journal of clinical medicine
Nicotinamide adenine dinucleotide(NAD') is a classic coenzyme playing a critical role in cellular redox reactions. Emerging evidence demonstrates that NAD' and its key mediators, NAD+-dependent protein deacetylases (sirtuins), together regulate many important meta- bolic pathways including mitochondrial function. Thus, impaired NAD' biosynthesis is critically involved in the pathophysiology of aging and age-associated diseases. Importantly, administration of key NAD+ intermediates, such as nicotinamide mononucleotide(NMN) or nicotinamide riboside (NR), improves mitochondrial function and exerts remarkable therapeutic effects for various age-associated diseases, such as diabetes and cancer, in mice. In this review, we will summarize and discuss pathophysiological relevance and translational potential of NAD' biology and mitochondrial sirtuin(SIRT3) in age-associated diseases.
NAD Intermediates: The Biology and Therapeutic Potential of NMN and NR.
Yoshino Jun,Baur Joseph A,Imai Shin-Ichiro
Research on the biology of NAD has been gaining momentum, providing many critical insights into the pathogenesis of age-associated functional decline and diseases. In particular, two key NAD intermediates, nicotinamide riboside (NR) and nicotinamide mononucleotide (NMN), have been extensively studied over the past several years. Supplementing these NAD intermediates has shown preventive and therapeutic effects, ameliorating age-associated pathophysiologies and disease conditions. Although the pharmacokinetics and metabolic fates of NMN and NR are still under intensive investigation, these NAD intermediates can exhibit distinct behavior, and their fates appear to depend on the tissue distribution and expression levels of NAD biosynthetic enzymes, nucleotidases, and presumptive transporters for each. A comprehensive concept that connects NAD metabolism to the control of aging and longevity in mammals has been proposed, and the stage is now set to test whether these exciting preclinical results can be translated to improve human health.
Regulatory Effects of NAD Metabolic Pathways on Sirtuin Activity.
Zhang Ning,Sauve Anthony A
Progress in molecular biology and translational science
NAD acts as a crucial regulator of cell physiology and as an integral participant in cellular metabolism. By virtue of a variety of signaling activities this central metabolite can exert profound effects on organism health status. Thus, while it serves as a well-known metabolic cofactor functioning as a redox-active substrate, it can also function as a substrate for signaling enzymes, such as sirtuins, poly (ADP-ribosyl) polymerases, mono (ADP-ribosyl) transferases, and CD38. Sirtuins function as NAD-dependent protein deacetylases (deacylases) and catalyze the reaction of NAD with acyllysine groups to remove the acyl modification from substrate proteins. This deacetylation provides a regulatory function and integrates cellular NAD metabolism into a large spectrum of cellular processes and outcomes, such as cell metabolism, cell survival, cell cycle, apoptosis, DNA repair, mitochondrial homeostasis and mitochondrial biogenesis, and even lifespan. Increased attention to how regulated and pharmacologic changes in NAD concentrations can impact sirtuin activities has motivated openings of new areas of research, including investigations of how NAD levels are regulated at the subcellular level, and searches for more potent NAD precursors typified by nicotinamide riboside (NR) and nicotinamide mononucleotide (NMN). This review describes current results and thinking of how NAD metabolic pathways regulate sirtuin activities and how regulated NAD levels can impact cell physiology. In addition, NAD precursors are discussed, with attention to how these might be harnessed to generate novel therapeutic options to treat the diseases of aging.
Mitochondrial regulation of diabetic vascular disease: an emerging opportunity.
Widlansky Michael E,Hill R Blake
Translational research : the journal of laboratory and clinical medicine
Diabetes-related vascular complication rates remain unacceptably high despite guideline-based medical therapies that are significantly more effective in individuals without diabetes. This critical gap represents an opportunity for researchers and clinicians to collaborate on targeting mechanisms and pathways that specifically contribute to vascular pathology in patients with diabetes mellitus. Dysfunctional mitochondria producing excessive mitochondrial reactive oxygen species (mtROS) play a proximal cell-signaling role in the development of vascular endothelial dysfunction in the setting of diabetes. Targeting the mechanisms of production of mtROS or mtROS themselves represents an attractive method to reduce the prevalence and severity of diabetic vascular disease. This review focuses on the role of mitochondria in the development of diabetic vascular disease and current developments in methods to improve mitochondrial health to improve vascular outcomes in patients with DM.
Nicotinamide Mononucleotide: Exploration of Diverse Therapeutic Applications of a Potential Molecule.
Poddar Saikat Kumar,Sifat Ali Ehsan,Haque Sanjana,Nahid Noor Ahmed,Chowdhury Sabiha,Mehedi Imtias
Nicotinamide mononucleotide (NMN) is a nucleotide that is most recognized for its role as an intermediate of nicotinamide adenine dinucleotide (NAD+) biosynthesis. Although the biosynthetic pathway of NMN varies between eukaryote and prokaryote, two pathways are mainly followed in case of eukaryotic human-one is through the salvage pathway using nicotinamide while the other follows phosphorylation of nicotinamide riboside. Due to the unavailability of a suitable transporter, NMN enters inside the mammalian cell in the form of nicotinamide riboside followed by its subsequent conversion to NMN and NAD+. This particular molecule has demonstrated several beneficial pharmacological activities in preclinical studies, which suggest its potential therapeutic use. Mostly mediated by its involvement in NAD+ biosynthesis, the pharmacological activities of NMN include its role in cellular biochemical functions, cardioprotection, diabetes, Alzheimer's disease, and complications associated with obesity. The recent groundbreaking discovery of anti-ageing activities of this chemical moiety has added a valuable essence in the research involving this molecule. This review focuses on the biosynthesis of NMN in mammalian and prokaryotic cells and mechanism of absorption along with the reported pharmacological activities in murine model.
SARM: From immune regulator to cell executioner.
Carty Michael,Bowie Andrew G
SARM is the fifth and most conserved member of the Toll/Il-1 Receptor (TIR) adaptor family. However, unlike the other TIR adaptors, MyD88, Mal, TRIF and TRAM, SARM does not participate in transducing signals downstream of TLRs. By contrast SARM inhibits TLR signalling by interacting with the adaptors TRIF and MyD88. In addition, SARM also has positive roles in innate immunity by activating specific transcriptional programs following immune challenge. SARM has a pivotal role in activating different forms of cell death following cellular stress and viral infection. Many of these functions of mammalian SARM are also reflected in SARM orthologues in lower organisms such as C. elegans and Drosophila. SARM expression is particularly enriched in neurons of the CNS and SARM has a critical role in neuronal death and in axon degeneration. Recent fascinating molecular insights have been revealed as to the molecular mechanism of SARM mediated axon degeneration. SARM has been shown to deplete NAD+ by possessing intrinsic NADase activity in the TIR domain of the protein. This activity can be activated experimentally by forced dimerization of the TIR domain. It is thought that this activity of SARM is normally switched off by the axo-protective activities of NMNAT2 which maintain low levels of the NAD+ precursor NMN. Therefore, there is now great excitement in the field of SARM research as targeting this enzymatic activity of SARM may lead to the development of new therapies for neurodegenerative diseases such as multiple sclerosis and motor neuron disease.
Role of Nicotinamide Adenine Dinucleotide and Related Precursors as Therapeutic Targets for Age-Related Degenerative Diseases: Rationale, Biochemistry, Pharmacokinetics, and Outcomes.
Braidy Nady,Berg Jade,Clement James,Khorshidi Fatemeh,Poljak Anne,Jayasena Tharusha,Grant Ross,Sachdev Perminder
Antioxidants & redox signaling
Nicotinamide adenine dinucleotide (NAD) is an essential pyridine nucleotide that serves as an essential cofactor and substrate for a number of critical cellular processes involved in oxidative phosphorylation and ATP production, DNA repair, epigenetically modulated gene expression, intracellular calcium signaling, and immunological functions. NAD depletion may occur in response to either excessive DNA damage due to free radical or ultraviolet attack, resulting in significant poly(ADP-ribose) polymerase (PARP) activation and a high turnover and subsequent depletion of NAD, and/or chronic immune activation and inflammatory cytokine production resulting in accelerated CD38 activity and decline in NAD levels. Recent studies have shown that enhancing NAD levels can profoundly reduce oxidative cell damage in catabolic tissue, including the brain. Therefore, promotion of intracellular NAD anabolism represents a promising therapeutic strategy for age-associated degenerative diseases in general, and is essential to the effective realization of multiple benefits of healthy sirtuin activity. The kynurenine pathway represents the NAD synthesis pathway in mammalian cells. NAD can also be produced by the NAD salvage pathway. In this review, we describe and discuss recent insights regarding the efficacy and benefits of the NAD precursors, nicotinamide (NAM), nicotinic acid (NA), nicotinamide riboside (NR), and nicotinamide mononucleotide (NMN), in attenuating NAD decline in degenerative disease states and physiological aging. Results obtained in recent years have shown that NAD precursors can play important protective roles in several diseases. However, in some cases, these precursors may vary in their ability to enhance NAD synthesis their location in the NAD anabolic pathway. Increased synthesis of NAD promotes protective cell responses, further demonstrating that NAD is a regulatory molecule associated with several biochemical pathways. In the next few years, the refinement of personalized therapy for the use of NAD precursors and improved detection methodologies allowing the administration of specific NAD precursors in the context of patients' NAD levels will lead to a better understanding of the therapeutic role of NAD precursors in human diseases.
Targeting NAMPT as a therapeutic strategy against stroke.
Wang Shu-Na,Miao Chao-Yu
Stroke and vascular neurology
Stroke is the second and the leading most common cause of death in the world and China, respectively, but with few effective therapies. Nicotinamide phosphoribosyltransferase (NAMPT) is the rate-limiting enzyme for nicotinamide adenine dinucleotide (NAD) salvage synthesis in mammals, thereby influencing NAD-dependent enzymes and constituting a strong endogenous defence system against various stresses. Accumulating in-vitro and in-vivo studies have demonstrated the neuroprotective effect of NAMPT in stroke. Here, we review the direct evidence of NAMPT as a promising target against stroke from five potential therapeutic strategies, including NAMPT overexpression, recombinant NAMPT, NAMPT activators, NAMPT enzymatic product nicotinamide mononucleotide (NMN), and NMN precursors nicotinamide riboside and nicotinamide, and describe the relevant mechanisms and limitations, providing a promising choice for developing novel and effective therapeutic interventions against ischaemic and haemorrhagic stroke.
Implications of altered NAD metabolism in metabolic disorders.
Okabe Keisuke,Yaku Keisuke,Tobe Kazuyuki,Nakagawa Takashi
Journal of biomedical science
Nicotinamide adenine dinucleotide (NAD) is an important coenzyme that participates in various energy metabolism pathways, including glycolysis, β-oxidation, and oxidative phosphorylation. Besides, it is a required cofactor for post-translational modifications such as ADP-ribosylation and deacetylation by poly (ADP-ribose) polymerases (PARPs) and sirtuins, respectively. Thus, NAD regulates energy metabolism, DNA damage repair, gene expression, and stress response through these enzymes. Numerous studies have shown that NAD levels decrease with aging and under disturbed nutrient conditions, such as obesity. Additionally, a decline in NAD levels is closely related to the development of various metabolic disorders, including diabetes and fatty liver disease. In addition, many studies have revealed that administration of NAD precursors, such as nicotinamide mononucleotide (NMN) and nicotinamide riboside (NR), efficiently increase NAD levels in various tissues and prevent such metabolic diseases. These NAD precursors are contained in natural foods, such as cow milk, vegetables, and meats. Therefore, altered NAD metabolism can be a practical target for nutritional intervention. Recently, several human clinical trials using NAD precursors have been conducted to investigate the safety, pharmacokinetics, and efficacy against metabolic disorders such as glucose intolerance. In this review, we summarize current knowledge on the implications of NAD metabolism in metabolic diseases and discuss the outcomes of recent human clinical trials.
Regulation of Glucose Metabolism by NAD and ADP-Ribosylation.
Hopp Ann-Katrin,Grüter Patrick,Hottiger Michael O
Cells constantly adapt their metabolic pathways to meet their energy needs and respond to nutrient availability. During the last two decades, it has become increasingly clear that NAD, a coenzyme in redox reactions, also mediates several ubiquitous cell signaling processes. Protein ADP-ribosylation is a post-translational modification that uses NAD as a substrate and is best known as part of the genotoxic stress response. However, there is increasing evidence that NAD-dependent ADP-ribosylation regulates other cellular processes, including metabolic pathways. In this review, we will describe the compartmentalized regulation of NAD biosynthesis, consumption, and regeneration with a particular focus on the role of ADP-ribosylation in the regulation of glucose metabolism in different cellular compartments.
Multi-targeted Effect of Nicotinamide Mononucleotide on Brain Bioenergetic Metabolism.
Klimova Nina,Kristian Tibor
Dysfunctions in NAD metabolism are associated with neurodegenerative diseases, acute brain injury, diabetes, and aging. Loss of NAD levels results in impairment of mitochondria function, which leads to failure of essential metabolic processes. Strategies to replenish depleted NAD pools can offer significant improvements of pathologic states. NAD levels are maintained by two opposing enzymatic reactions, one is the consumption of NAD while the other is the re-synthesis of NAD. Inhibition of NAD degrading enzymes, poly-ADP-ribose polymerase 1 (PARP1) and ectoenzyme CD38, following brain ischemic insult can provide neuroprotection. Preservation of NAD pools by administration of NAD precursors, such as nicotinamide (Nam) or nicotinamide mononucleotide (NMN), also offers neuroprotection. However, NMN treatment demonstrates to be a promising candidate as a therapeutic approach due to its multi-targeted effect acting as PARP1 and CD38 inhibitor, sirtuins activator, mitochondrial fission inhibitor, and NAD supplement. Many neurodegenerative diseases or acute brain injury activate several cellular death pathways requiring a treatment strategy that will target these mechanisms. Since NMN demonstrated the ability to exert its effect on several cellular metabolic pathways involved in brain pathophysiology it seems to be one of the most promising candidates to be used for successful neuroprotection.
NAD precursor modulates post-ischemic mitochondrial fragmentation and reactive oxygen species generation via SIRT3 dependent mechanisms.
Klimova Nina,Fearnow Adam,Long Aaron,Kristian Tibor
Global cerebral ischemia depletes brain tissue NAD, an essential cofactor for mitochondrial and cellular metabolism, leading to bioenergetics failure and cell death. The post-ischemic NAD levels can be replenished by the administration of nicotinamide mononucleotide (NMN), which serves as a precursor for NAD synthesis. We have shown that NMN administration shows dramatic protection against ischemic brain damage and inhibits post-ischemic hippocampal mitochondrial fragmentation. To understand the mechanism of NMN-induced modulation of mitochondrial dynamics and neuroprotection we used our transgenic mouse models that express mitochondria targeted yellow fluorescent protein in neurons (mito-eYFP) and mice that carry knockout of mitochondrial NAD-dependent deacetylase sirt3 gene (SIRT3KO). Following ischemic insult, the mitochondrial NAD levels were depleted leading to an increase in mitochondrial protein acetylation, high reactive oxygen species (ROS) production, and excessive mitochondrial fragmentation. Administration of a single dose of NMN normalized hippocampal mitochondria NAD pools, protein acetylation, and ROS levels. These changes were dependent on SIRT3 activity, which was confirmed using SIRT3KO mice. Ischemia induced increase in acetylation of the key mitochondrial antioxidant enzyme, superoxide dismutase 2 (SOD2) that resulted in inhibition of its activity. This was reversed after NMN treatment followed by reduction of ROS generation and suppression of mitochondrial fragmentation. Specifically, we found that the interaction of mitochondrial fission protein, pDrp1(S616), with neuronal mitochondria was inhibited in NMN treated ischemic mice. Our data thus provide a novel link between mitochondrial NAD metabolism, ROS production, and mitochondrial fragmentation. Using NMN to target these mechanisms could represent a new therapeutic approach for treatment of acute brain injury and neurodegenerative diseases.
The NMN Module Conducts Nodule Number Orchestra.
Wang Zhijuan,Wang Lixiang,Wang Yongliang,Li Xia
Legumes control nodule number through nodulation and autoregulation of nodulation (AON) pathways. Nodule Inception (NIN) is essential for rhizobial infection and nodule organogenesis in legumes. The GmNINa-miR172c-NNC1 (NMN) module, which consists of two positive regulators, GmNINa and miR172c, and a suppressor, NNC1, integrates both pathways. GmNINa activates miR172c to downregulate NNC1, leading to nodulation, while NNC1 inhibits miR172c expression, forming a negative feedback loop. GmNINa and NNC1 interact with each other and antagonistically fine-tune GmRIC1/RIC2 expression, turning AON on and off. Conversely, activation of AON inhibits GmNINa and miR172c expression, thereby reducing their inhibitory effects on NNC1 to attenuate both nodulation signaling and AON. The NMN module functions not only as an "accelerator" of the nodulation signal to promote nodulation but also as a "brake" on the signal by activating AON to orchestrate nodule number.
Nicotinamide Mononucleotide: A Promising Molecule for Therapy of Diverse Diseases by Targeting NAD+ Metabolism.
Hong Weiqi,Mo Fei,Zhang Ziqi,Huang Mengyuan,Wei Xiawei
Frontiers in cell and developmental biology
NAD+, a co-enzyme involved in a great deal of biochemical reactions, has been found to be a network node of diverse biological processes. In mammalian cells, NAD+ is synthetized, predominantly through NMN, to replenish the consumption by NADase participating in physiologic processes including DNA repair, metabolism, and cell death. Correspondingly, aberrant NAD+ metabolism is observed in many diseases. In this review, we discuss how the homeostasis of NAD+ is maintained in healthy condition and provide several age-related pathological examples related with NAD+ unbalance. The sirtuins family, whose functions are NAD-dependent, is also reviewed. Administration of NMN surprisingly demonstrated amelioration of the pathological conditions in some age-related disease mouse models. Further clinical trials have been launched to investigate the safety and benefits of NMN. The NAD+ production and consumption pathways including NMN are essential for more precise understanding and therapy of age-related pathological processes such as diabetes, ischemia-reperfusion injury, heart failure, Alzheimer's disease, and retinal degeneration.