In this review, we focus on the secreted form of nicotinamide phosphoribosyltransferase (NAMPT); extracellular NAMPT (eNAMPT), also known as pre-B cell colony-enhancing factor or visfatin. Although intracellular NAMPT is a key enzyme in controlling NAD metabolism, eNAMPT has been reported to function as a cytokine, with many roles in physiology and pathology. Circulating eNAMPT has been associated with several metabolic and inflammatory disorders, including cancer. Because cytokines produced in the tumour micro-environment play an important role in cancer pathogenesis, in part by reprogramming cellular metabolism, future improvements in cancer immunotherapy will require a better understanding of the crosstalk between cytokine action and tumour biology. In this review, the knowledge of eNAMPT in cancer will be discussed, focusing on its immunometabolic function as a metabokine, its secretion, its mechanism of action and possible roles in the cancer micro-environment.

To investigate the role of NAMPT/visfatin in euthyroid patients with Graves' disease without (GD) and with Graves' ophthalmopathy (GO), we analyzed NAMPT leukocyte expression and its serum concentration. This was a single-center, cross-sectional study with consecutive enrollment. In total, 149 patients diagnosed with Graves' disease were enrolled in the study. We excluded subjects with hyper- or hypothyroidism, diabetes mellitus, other autoimmune disorders, active neoplastic disease, and infection. The control group was recruited among healthy volunteers adjusted for age, sex, and BMI with normal thyroid function and negative thyroid antibodies. Serum levels of visfatin, TSH, FT4, FT3, antibodies against TSH receptor (TRAb), antithyroperoxidase antibodies, antithyroglobulin antibodies, fasting glucose, and insulin were measured. NAMPT mRNA leukocyte expression was assessed using RT-qPCR. NAMPT/visfatin serum concentration was higher in GD (n = 44) and GO (n = 49) patients than in the control group (n = 40) (p = 0.0275). NAMPT leukocyte expression was higher in patients with GO (n = 30) than in GD patients (n = 27) and the control group (n = 29) (p < 0.0001). Simple linear regression analysis revealed that NAMPT/visfatin serum concentration was significantly associated with GD (β = 1.5723; p = 0.021). When NAMPT leukocyte expression was used as a dependent variable, simple regression analysis found association with TRAb, fasting insulin level, HOMA-IR, GD, and GO. In the stepwise multiple regression analysis, we confirmed the association between higher serum NAMPT/visfatin level and GD (coefficient = 1.5723; p = 0.0212), and between NAMPT leukocyte expression and GO (coefficient = 2.4619; p = 0.0001) and TRAb (coefficient = 0.08742; p = 0.006). Increased NAMPT leukocyte expression in patients with GO might suggest a presently undefined role in the pathogenesis of GO.

Nicotinamide (Nam) phosphoribosyltransferase (NAMPT) is the rate-limiting enzyme in mammalian NAD synthesis, catalyzing nicotinamide mononucleotide (NMN) formation from Nam and 5-phosphoribosyl 1-pyrophosphate (PRPP). NAMPT has also been described as an adipocytokine visfatin with a variety of actions, although physiological significance of this protein remains unclear. It has been proposed that possible actions of visfatin are mediated through the extracellular formation of NMN. However, we did not detect NMN in mouse blood plasma, even with a highly specific and sensitive liquid chromatography/tandem mass spectrometry. Furthermore, there is no or little ATP, the activator of NAMPT, in extracellular spaces. We thus questioned whether visfatin catalyzes the in situ formation of NMN under such extracellular milieus. To address this question, we here determined K(m) values for the substrates Nam and PRPP in the NAMPT reaction without or with ATP using a recombinant human enzyme and found that 1 mM ATP dramatically decreases K(m) values for the substrates, in particular PRPP to its intracellular concentration. Consistent with the kinetic data, only when ATP is present at millimolar levels, NAMPT efficiently catalyzed the NMN formation at the intracellular concentrations of the substrates. Much lower concentrations of Nam and almost the absence of PRPP and ATP in the blood plasma suggest that NAMPT should not efficiently catalyze its reaction under the extracellular milieu. Indeed, NAMPT did not form NMN in the blood plasma. From these kinetic analyses of the enzyme and quantitative determination of its substrates, activator, and product, we conclude that visfatin does not participate in NMN formation under the extracellular milieus. Together with the absence of NMN in the blood plasma, our conclusion does not support the concept of "NAMPT-mediated systemic NAD biosynthesis." Our study would advance current understanding of visfatin physiology.

Nicotinamide phosphoribosyltransferase (NAMPT), a rate-limiting enzyme in nicotinamide adenine dinucleotide (NAD) biosynthesis in mammals, converts nicotinamide into nicotinamide mononucleotide (NMN). NMN is subsequently converted to NAD, a component that is critical for cell energy metabolism and survival. Sirtuin 1 (SIRT1), an NAD-dependent histone deacetylase, plays an important role in mediating memory and synaptic plasticity. Here, we found that NAMPT was significantly upregulated in the ventral tegmental area (VTA) of cocaine-conditioned mice. Intraperitoneal or intra-VTA injection of FK866, a specific inhibitor of NAMPT, significantly attenuated cocaine reward. However, such effects were clearly repressed by intra-VTA expression of NAMPT or supplementation with NMN. Using 1H-nuclear magnetic resonance metabolomic analysis, we found that the content of NAD and NMN were increased in the VTA of cocaine-conditioned mice; moreover, the expression of SIRT1 was also upregulated. Interestingly, the inhibitory effect of FK866 on cocaine reward was significantly weakened in Sirt1 midbrain conditional knockout mice. Our results suggest that NAMPT-mediated NAD biosynthesis may modify cocaine behavioral effects through SIRT1. Moreover, our findings reveal that the interplay between NAD biosynthesis and SIRT1 regulation may comprise a novel regulatory pathway that responds to chronic cocaine stimuli.

Nicotinamide phosphoribosyltransferase (NAMPT) upregulation in human pulmonary artery endothelial cells (hPAECs) is associated with pulmonary arterial hypertension (PAH) progression and pulmonary vascular remodeling. The underlying mechanisms regulating NAMPT expression are still not clear. In this study, we aimed to study the regulation of NAMPT expression by microRNA410 (miR410) in hPAECs and explore the role of miR410 in the pathogenesis of experimental pulmonary hypertension. We show that miR410 targets the 3' UTR of NAMPT and that, concomitant with NAMPT upregulation, miR410 is downregulated in lungs of mice exposed to hypoxia-induced pulmonary hypertension (HPH). Our results also demonstrate that miR410 directly inhibits NAMPT expression. Overexpression of miR410 in hPAECs inhibits basal and VEGF-induced proliferation, migration and promotes apoptosis of hPAECs, while miR410 inhibition via antagomirs has the opposite effect. Finally, administration of miR410 mimics in vivo attenuated induction of NAMPT in PAECs and prevented the development of HPH in mice. Our results highlight the role of miR410 in the regulation of NAMPT expression in hPAECs and show that miR410 plays a potential role in PAH pathobiology by targeting a modulator of pulmonary vascular remodeling.

Inhibition of nicotinamide phosphoribosyltransferase (NAMPT) is an attractive therapeutic strategy for targeting cancer metabolism. So far, many potent NAMPT inhibitors have been developed and shown to bind to two unique tunnel-shaped cavities existing adjacent to each active site of a NAMPT homodimer. However, cytotoxicities and resistances to NAMPT inhibitors have become apparent. Therefore, there remains an urgent need to develop effective and safe NAMPT inhibitors. Thus, we designed and synthesized two close structural analogues of NAMPT inhibitors, azaindole-piperidine (3a)- and azaindole-piperazine (3b)-motif compounds, which were modified from the well-known NAMPT inhibitor FK866 (1). Notably, 3a displayed considerably stronger enzyme inhibitory activity and cellular potency than did 3b and 1. The main reason for this phenomenon was revealed to be due to apparent electronic repulsion between the replaced nitrogen atom (N1) of piperazine in 3b and the Nδ atom of His191 in NAMPT by our in silico binding mode analyses. Indeed, 3b had a lower binding affinity score than did 3a and 1, although these inhibitors took similar stable chair conformations in the tunnel region. Taken together, these observations indicate that the electrostatic enthalpy potential rather than entropy effects inside the tunnel cavity has a significant impact on the different binding affinity of 3a from that of 3b in the disparate enzymatic and cellular potencies. Thus, it is better to avoid or minimize interactions with His191 in designing further effective NAMPT inhibitors.

Targeting cancer cells that are highly dependent on the nicotinamide adenine dinucleotide (NAD+) metabolite is a promising therapeutic strategy. Nicotinamide phosphoribosyltransferase (NAMPT) is the rate-limiting enzyme catalyzing NAD+ production. Despite the high efficacy of several developed NAMPT inhibitors (i.e., FK866 (APO866)) in preclinical studies, their clinical activity was proven to be limited. Here, we report the synthesis of new NAMPT Inhibitors, JJ08, FEI191 and FEI199, which exhibit a broad anticancer activity in vitro. Results show that these compounds are potent NAMPT inhibitors that deplete NAD+ and NADP(H) after 24 h of drug treatment, followed by an increase in reactive oxygen species (ROS) accumulation. The latter event leads to ATP loss and mitochondrial depolarization with induction of apoptosis and necrosis. Supplementation with exogenous NAD+ precursors or catalase (ROS scavenger) abrogates the cell death induced by the new compounds. Finally, in vivo administration of the new NAMPT inhibitors in a mouse xenograft model of human Burkitt lymphoma delays tumor growth and significantly prolongs mouse survival. The most promising results are collected with JJ08, which completely eradicates tumor growth. Collectively, our findings demonstrate the efficient anticancer activity of the new NAMPT inhibitor JJ08 and highlight a strong interest for further evaluation of this compound in hematological malignancies.

Nicotinamide phosphoribosyltransferase (NAMPT) is a key enzyme for nicotinamide adenine dinucleotide (NAD) biosynthesis, and can be found either intracellularly (iNAMPT) or extracellularly (eNAMPT). Studies have shown that both iNAMPT and eNAMPT are implicated in aging and age-related diseases/disorders in the peripheral system. However, their functional roles in aged brain remain to be established. Here we showed that upon aging, NAMPT level increased in serum but decreased in brain, decreased in cortex and hippocampus but remained unchanged in cerebellum and striatum in brain, and increased in microglia but likely decreased in neuron. Accordingly, total NAD (tNAD) level significantly decreased in hippocampus, cerebellum and striatum in aged brain. Application of recombinant NAMPT, mimicking the elevated serum NAMPT level, enhanced the susceptibility of cerebral endothelial cells to ischemic injury, while inhibition of iNAMPT by FK866, a specific inhibitor, reduced intracellular NAD level and induced neuronal death. Taken together, we have revealed a region- and cell-specific change of NAMPT level in brain and serum upon aging, deduced its potential consequences, which suggests that NAMPT is a regulatory factor in aging and age-related brain diseases.

Nicotinamide phosphoribosyltransferase (NAMPT) is the key enzyme of the salvage pathway of nicotinamide adenine dinucleotide synthesis. NAMPT can also be secreted and functions as a cytokine. We have previously shown that in the brain, NAMPT expression and secretion can be induced in microglia upon neuroinflammation and injury. Yet the mechanism for NAMPT secretion remains unclear. Here we show that NAMPT can be actively secreted from microglia upon the treatment of ischemia-like injury - oxygen-glucose deprivation and recovery (OGD/R). We confirmed that classical ER-Golgi pathway is not involved in NAMPT secretion. NAMPT secretion was further enhanced by ATP, and the secretion was mediated by P2X7 receptor and by intracellular Ca2+ . Importantly, we found that phospholipase D inhibitor, n-butanol, phospholipase D siRNA, and wortmannin significantly decreased OGD/R-induced and ATP-enhanced release of NAMPT in microglia. After excluding the mechanisms of involving secretory autophagy, endosomes, and secretory lysosome, we have concluded that microglial NAMPT is secreted mainly via exosome. Immune-electron microscopy identifies NAMPT in extracellular vesicles with the size and morphology characteristic of exosome. With the vesicles harvested by ultra-centrifugation, exosomal NAMPT is further confirmed by Western blotting analysis. Intriguingly, the amount of NAMPT relative to exosomal protein markers remains unchanged upon the treatment of OGD/R, suggesting a constant load of exosomal NAMPT in microglia. Taken together, we have identified NAMPT is actively secreted via exosome from microglia during neuroinflammation of ischemic injury.

Our previous study indicated that carborane containing small-molecule 1-(hydroxymethyl)-7-(4'-(trans-3″-(3'″-pyridyl)acrylamido)butyl)-1,7-dicarbadodecaborane (hm-MC4-PPEA), was a potent inhibitor of nicotinamide phosphoribosyltransferase (Nampt). Nampt has been shown to be upregulated in most cancers and is a promising target for the treatment of many different types of cancers, including breast cancers.

Here, we report that Forkhead Box O1 (FOXO1) protein, a tumor suppressor, regulates expression of nicotinamide phosphoribosyltransferase (Nampt) in human breast cancer MCF-7 cells. Nampt plays an important role in the regulation of cell growth, survival, DNA replication and repair, and angiogenesis in tumorigenesis. We revealed that FOXO1 directly inhibits Nampt expression via binding to FOXO1 binding domains in the 5'-flanking region of the nampt gene. Nampt expression was increased by insulin and downstream phosphatidylinositol 3-kinase (PI3K)/Akt signaling, which was inhibited by FOXO1 overexpression. Accordingly, we showed that FOXO1 is also involved in insulin signaling-induced cell survival and proliferation in MCF-7 cells. These results suggest that FOXO1 plays an important role in human breast cancer cells by regulating nampt gene expression.

Nicotinamide phosphoribosyltransferase (NAMPT), alongside being a crucial enzyme in NAD synthesis, has been shown to be a secreted protein (eNAMPT), whose levels are increased in patients affected by immune-mediated disorders. Accordingly, preclinical studies have highlighted that eNAMPT participates in the pathogenesis of several inflammatory diseases. Herein, we analyzed the effects of eNAMPT on macrophage-driven inflammation. RNAseq analysis of peritoneal macrophages (PECs) demonstrates that eNAMPT triggers an M1-skewed transcriptional program, and this effect is not dependent on the enzymatic activity. Noteworthy, both in PECs and in human monocyte-derived macrophages, eNAMPT selectively boosts IFNγ-driven transcriptional activation via STAT1/3 phosphorylation. Importantly, the secretion of eNAMPT promotes the chemotactic recruitment of myeloid cells, therefore providing a potential positive feedback loop to foster inflammation. Last, we report that these events are independent of the activation of TLR4, the only eNAMPT receptor that has hitherto been recognized, prompting the knowledge that other receptors are involved.

Calorie restriction abates aging and cardiometabolic disease by activating metabolic signaling pathways, including nicotinamide adenine dinucleotide (NAD+) biosynthesis and salvage. Nicotinamide phosphoribosyltransferase (NAMPT) is rate-limiting in NAD+ salvage, yet hepatocyte NAMPT actions during fasting and metabolic duress remain unclear. We demonstrate that hepatocyte NAMPT is upregulated in fasting mice, and in isolated hepatocytes subjected to nutrient withdrawal. Mice lacking hepatocyte NAMPT exhibit defective FGF21 activation and thermal regulation during fasting, and are sensitized to diet-induced glucose intolerance. Hepatocyte NAMPT overexpression induced FGF21 and adipose browning, improved glucose homeostasis, and attenuated dyslipidemia in obese mice. Hepatocyte SIRT1 deletion reversed hepatocyte NAMPT effects on dark-cycle thermogenesis, and hepatic FGF21 expression, but SIRT1 was dispensable for NAMPT insulin-sensitizing, anti-dyslipidemic, and light-cycle thermogenic effects. Hepatocyte NAMPT thus conveys key aspects of the fasting response, which selectively dissociate through hepatocyte SIRT1. Modulating hepatocyte NAD+ is thus a potential mechanism through which to attenuate fasting-responsive disease.

Nicotinamide phosphoribosyltransferase (NAMPT) is a pleiotropic protein implicated in the pathogenesis of acute respiratory distress syndrome, aging, cancer, coronary heart diseases, diabetes, nonalcoholic fatty liver disease, obesity, rheumatoid arthritis, and sepsis. However, the underlying molecular mechanisms of NAMPT in these physiological and pathological processes are not fully understood. Here, we provide experimental evidence that a Nampt gene homozygous knockout (Nampt-/-) resulted in lethality at an early stage of mouse embryonic development and death within 5-10 days in adult mice accompanied by a 25.24±2.22% body weight loss, after the tamoxifen induction of NamptF/F × Cre mice. These results substantiate that Nampt is an essential gene for life. In Nampt-/- mice versus Nampt+/+ mice, biochemical assays indicated that liver and intestinal tissue NAD levels were decreased significantly; histological examination showed that mouse intestinal villi were atrophic and disrupted, and visceral fat was depleted; mass spectrometry detected unusual higher serum polyunsaturated fatty acid containing triglycerides. RNA-seq analyses of both mouse and human pediatric liver transcriptomes have convergently revealed that NAMPT is involved in key basic cellular functions such as transcription, translation, cell signaling, and fundamental metabolism. Notably, the expression of all eight enzymes in the tricarboxylic acid cycle were decreased significantly in the Nampt-/- mice. These findings prompt us to posit that adult Nampt-/- mouse lethality is a result of a short supply of ATP from compromised intestinal absorption of nutrients from digested food, which leads to the exhaustion of body fat stores.

Alzheimer's disease (AD) is a neurodegenerative disease of the central nervous system that is characterized by progressive cognitive dysfunction and which ultimately leads to dementia. Studies have shown that energy dysmetabolism contributes significantly to the pathogenesis of a variety of aging‑associated diseases and degenerative diseases of the nervous system, including AD. One focus of research thus has been how to regulate the expression of nicotinamide phosphoribosyltransferase (NAMPT) to prevent against neurodegenerative diseases. Therefore, the present study used 6‑month‑old APPswe/PS1ΔE9 (APP/PS1) transgenic mice as early AD mouse models and sought to evaluate nicotinamide adenine dinucleotide (NAD+) and FK866 (a NAMPT inhibitor) treatment in APP/PS1 mice to study NAMPT dysmetabolism in the process of AD and elucidate the underlying mechanisms. As a result of this treatment, the expression of NAMPT decreased, the synthesis of ATP and NAD+ became insufficient and the NAD+/NADH ratio was reduced. The administration of NAD+ alleviated the spatial learning and memory of APP/PS1 mice and reduced senile plaques. Administration of NAD+ may also increase the expression of the key protein NAMPT and its related protein sirtuin 1 as well as the synthesis of NAD+. Therefore, increasing NAMPT expression levels may promote NAD+ production. Their regulation could form the basis for a new therapeutic strategy.

Bone degenerative disorders like osteoporosis may be initiated by age-related shifts in anabolic and catabolic responses that control bone homeostasis. Although there are studies suggesting that metabolic changes occur with stem cell differentiation, the molecular mechanisms governing energy metabolism and epigenetic modification are not understood fully. Here we reported the key role of nicotinamide phosphoribosyltransferase (Nampt), which is the rate-limiting enzyme in the salvage pathway of NAD biosynthesis from nicotinamide, in the osteogenic differentiation of bone marrow stromal cells.

A series of carborane-containing NAMPT inhibitors were designed and synthesized based on the structure of compounds 1 and the NAMPT inhibitory activity was evaluated using NAMPT Colorimetric Assay. Among the compounds synthesized, compounds 2b and 2c showed significant NAMPT inhibitory activity with IC50 values of 0.098 ± 0.008 and 0.057 ± 0.001 µM, respectively. Docking simulation of compound 2 toward NAMPT using the crystal structure of the FK866-NAMPT complex (PDB code: 2GVJ) with replacing the boron atom type by the C3 atom type of carboranes predicted that the NAMPT inhibitory activity of 2c was improved by the hydrogen bond formation between the carborane amide and H191 of NAMPT. Although dicarborane compounds 38, 50, 51, and 55 were synthesize aiming to two hydrophobic pockets present in the binding pocket of NAMPT, their inhibitory activity was moderate.

The aim of the present study was to investigate the physiological role of nicotinamide phosphoribosyltransferase (NAMPT) associated with odontogenic differentiation during tooth development in mice. Mouse dental papilla cell-23 (MDPC- 23) cells cultured in differentiation media were stimulated with the specific NAMPT inhibitor, FK866, and Visfatin (NAMPT) for up to 10 days. The cells were evaluated after 0, 4, 7, and 10 days. Cell viability was measured using the 3-(4,5-dimethylthiazol- 2-yl)-2,5-diphenyltetrazolium bromide assay. The mineralization assay was performed by staining MDPC-23 cells with Alizarin Red S solution. After cultivation, MDPC-23 cells were harvested for quantitative PCR or Western blotting. Analysis of variance was performed using StatView 5.0 software (SAS Institute Inc., Cary, NC, USA). Statistical significance was set at p < 0.05. The expression of NAMPT increased during the differentiation of murine odontoblast-like MDPC-23 cells. Furthermore, the up-regulation of NAMPT promoted odontogenic differentiation and accelerated mineralization through an increase in representative odontoblastic biomarkers, such as dentin sialophosphoprotein, dentin matrix protein-1, and alkaline phosphatase in MDPC-23 cells. However, treatment of the cells with the NAMPT inhibitor, FK866, attenuated odontogenic differentiation, as evidenced by the suppression of odontoblastic biomarkers. These data indicate that NAMPT regulated odontoblastic differentiation through the regulation of odontoblastic biomarkers. The increase in NAMPT expression in odontoblasts was closely related to the formation of the extracellular matrix and dentin via the Runx signaling pathway. Therefore, these data suggest that NAMPT is a critical regulator of odontoblast differentiation during tooth development.

Aging and obesity are the most prominent risk factors for onset of atrial fibrillation (AF). Nicotinamide phosphoribosyltransferase (Nampt) is the rate-limiting enzyme that catalyzes nicotinamide adenine dinucleotide (NAD) activity. Nampt and NAD are essential for maintenance of cellular redox homeostasis and modulation of cellular metabolism, and their expression levels decrease with aging and obesity. However, a role for Nampt in AF is unknown. The present study aims to test whether there is a role of Nampt/NAD axis in the pathogenesis of obesity-induced AF. Male C57BL/6J (WT) mice and heterozygous Nampt knockout (NKO) mice were fed with a normal chow diet (ND) or a high-fat diet (HFD). Electrophysiological study showed that AF inducibility was significantly increased in WT+HFD, NKO+ND, and NKO+HFD mice compared with WT+ND mice. AF duration was significantly longer in WT+HFD and NKO+ND mice and further prolonged in NKO+HFD mice compared with WT+ND mice and the calcium handling pathway was altered on molecular level. Also, treatment with nicotinamide riboside, a NAD precursor, partially restored the HFD-induced AF perpetuation. Overall, this work demonstrates that partially deletion of Nampt facilitated HFD-induced AF through increased diastolic calcium leaks. The Nampt/NAD axis may be a potent therapeutic target for AF.

Chemotherapy-induced peripheral neuropathy (CIPN) arises from collateral damage to peripheral afferent sensory neurons by anticancer pharmacotherapy, leading to debilitating neuropathic pain. No effective treatment for CIPN exists, short of dose-reduction which worsens cancer prognosis. Here, we report that stimulation of nicotinamide phosphoribosyltransferase (NAMPT) produced robust neuroprotection in an aggressive CIPN model utilizing the frontline anticancer drug, paclitaxel (PTX). Daily treatment of rats with the first-in-class NAMPT stimulator, P7C3-A20, prevented behavioral and histologic indicators of peripheral neuropathy, stimulated tissue NAD recovery, improved general health, and abolished attrition produced by a near maximum-tolerated dose of PTX. Inhibition of NAMPT blocked P7C3-A20-mediated neuroprotection, whereas supplementation with the NAMPT substrate, nicotinamide, potentiated a subthreshold dose of P7C3-A20 to full efficacy. Importantly, P7C3-A20 blocked PTX-induced allodynia in tumored mice without reducing antitumoral efficacy. These findings identify enhancement of NAMPT activity as a promising new therapeutic strategy to protect against anticancer drug-induced peripheral neurotoxicity.