Nicotinamide Adenine Dinucleotide Salvage Research Articles

Suppression of nicotinamide phosphoribosyltransferase expression by miR-154 reduces the viability of breast cancer cells and increases their susceptibility to doxorubicin

BackgroundNicotinamide phosphoribosyltransferase (NAMPT) enzyme acts as the major enzyme in the nicotinamide adenine dinucleotide (NAD) synthesis salvage pathway. Deregulation of NAD could be associated with progression of several cancers such as breast cancer. Here, the consequence of NAMPT inhibition by miR-154 was investigated on breast cancer cells.MethodsMDA-MB-231 and MCF-7 cancer cell lines were transfected with the mimic and inhibitors of miR-154-5p and their corresponding negative controls. Consequently, levels of NAMPT and NAD were assayed employing qRT-PCR, Western blotting and enzymatic method, respectively. Subsequently, flow cytometry and colorimetric methods were performed to evaluate apoptosis and cell viability. Bioinformatics analyses as well as luciferase assay were done to investigate whether the 3′-UTR of NAMPT is directly targeted by miR-154.ResultsAccording to the obtained results, NAMPT was recognized as a target for binding of miR-154 and the levels of this miRNA was inversely associated with both mRNA and protein levels of NAMPT in breast cancer cell lines. Functionally, miR-154 inhibited the NAD salvage pathway leading to a remarkable decrease in cell viability and increased rate of cell death. When breast cancer cells were simultaneously treated with doxorubicin and miR-154 mimic, cell viability was considerably reduced compared to treatment with doxorubicin alone in both cell lines.ConclusionsIt was concluded that the inhibition of NAD production by miR-154 might be introduced as an appropriate therapeutic approach in order to improve breast cancer outcome either alone or in combination with other conventional chemotherapeutic agents.

Switch of NAD Salvage to de novo Biosynthesis Sustains SIRT1-RelB-Dependent Inflammatory Tolerance.

A typical inflammatory response sequentially progresses from pro-inflammatory, immune suppressive to inflammatory repairing phases. Although the physiological inflammatory response resolves in time, severe acute inflammation usually sustains immune tolerance and leads to high mortality, yet the underlying mechanism is not completely understood. Here, using the leukemia-derived THP-1 human monocytes, healthy and septic human peripheral blood mononuclear cells (PBMC), we report that endotoxin dose-dependent switch of nicotinamide adenine dinucleotide (NAD) biosynthesis pathways sustain immune tolerant status. Low dose endotoxin triggered nicotinamide phosphoribosyltransferase (NAMPT)-dependent NAD salvage activity to adapt pro-inflammation. In contrast, high dose endotoxin drove a shift of NAD synthesis pathway from early NAMPT-dependent NAD salvage to late indoleamine 2,3-dioxygenase-1 (IDO1)-dependent NAD de novo biosynthesis, leading to persistent immune suppression. This is resulted from the IDO1-dependent expansion of nuclear NAD pool and nuclear NAD-dependent prolongation of sirtuin1 (SIRT1)-directed epigenetics of immune tolerance. Inhibition of IDO1 activity predominantly decreased nuclear NAD level, which promoted sequential dissociations of immunosuppressive SIRT1 and RelB from the promoter of pro-inflammatory TNF-α gene and broke endotoxin tolerance. Thus, NAMPT-NAD-SIRT1 axis adapts pro-inflammation, but IDO1-NAD-SIRT1-RelB axis sustains endotoxin tolerance during acute inflammatory response. Remarkably, in contrast to the prevention of sepsis death of animal model by IDO1 inhibition before sepsis initiation, we demonstrated that the combination therapy of IDO1 inhibition by 1-methyl-D-tryptophan (1-MT) and tryptophan supplementation rather than 1-MT administration alone after sepsis onset rescued sepsis animals, highlighting the translational significance of tryptophan restoration in IDO1 targeting therapy of severe inflammatory diseases like sepsis.

Sorafenib-Induced Apoptosis in Hepatocellular Carcinoma Is Reversed by SIRT1.

Sorafenib is a multi-kinase inhibitor and one of the few systemic treatment options for patients with advanced hepatocellular carcinomas (HCCs). Resistance to sorafenib develops frequently and could be mediated by the nicotinamide adenine dinucleotide (NAD)-dependent deacetylase sirtuin (SIRT)1. We aimed to test whether sorafenib efficacy is influenced by cellular NAD levels and NAD-dependent SIRT1 function. We analyzed sorafenib effects on apoptosis induction, NAD salvage, mitochondrial function, and related signaling pathways in HCC cell lines (HepG2, Hep3B, und HUH7) overexpressing SIRT1 or supplemented with the NAD metabolite nicotinamide mononucleotide (NMN) compared to controls. Treatment of HCC cell lines with sorafenib dose-dependently induced apoptosis and a significant decrease in cellular NAD concentrations. The SIRT1 protein was downregulated in HUH7 cells but not in Hep3B cells. After sorafenib treatment, mitochondrial respiration in permeabilized cells was lower, citrate synthase activity was attenuated, and cellular adenosine triphosphate (ATP) levels were decreased. Concomitant to increased phosphorylation of adenosine monophosphate (AMP)-activated protein kinase (AMPK), sorafenib treatment led to decreased activity of the mechanistic target of rapamycin (mTOR), indicative of energy deprivation. Transient overexpression of SIRT1, as well as NAD repletion by NMN, decreased sorafenib-induced apoptosis. We can, therefore, conclude that sorafenib influences the NAD/SIRT1/AMPK axis. Overexpression of SIRT1 could be an underlying mechanism of resistance to sorafenib treatment in HCC.

NAMPT and NAPRT, Key Enzymes in NAD Salvage Synthesis Pathway, Are of Negative Prognostic Value in Colorectal Cancer.

Nicotinamide adenine dinucleotide (NAD) is a profoundly important cofactor in redox reactions. Nicotinamide phosphoribosyltransferase (NAMPT) and nicotinate phosphoribosyltransferase (NAPRT) are key enzymes for NAD salvage biosynthesis pathway, which reciprocally synthesize NAD to supply the main source of NAD biosythesis. However, the prognostic value of NAMPT and NAPRT in colorectal cancer (CRC) remains largely unknown. Our present study detected NAMPT and NAPRT protein expression in cancer and adjacent tissues from 261 CRC using immunohistochemical staining. We found that high expression of NAMPT or NAPRT was associated with vascular invasion, invasion depth and advanced TNM stage in CRC. High expression of NAMPT or NAPRT predicts short overall survival and disease-free survival time in CRC patients, which were further confirmed by public datasets. Furthermore, positive correlation between expression of NAMPT and NAPRT was revealed in CRC tissues and cell lines. NAPRThigh/NAMPThigh patients tended to have the shortest survival time. Using the TCGA RNA-sequencing data, we showed that gene amplification, mutation, and methylation of NAPRT are more common than NAMPT. On the other hand, NAMPT gene might be targeted by more miRNAs. Finally, genes that are correlated with NAPRT or NAMPT are enriched in different pathways. In conclusion, we found that high expression of NAMPT or NAPRT predicts poor prognosis of CRC patients, but the regulatory mechanism might be distinct from each other.

Reconstitution of Organismal Liver Clock Function Requires Light

Recently Koronowski et al. (Cell, 2019) showed that reconstitution of the liver circadian clock in otherwise genetically arrhythmic mice revives the daily program of the nicotinamide adenine dinucleotide salvage pathway and glycogenesis in vivo. This liver-autonomous metabolic cycling cannot be sustained under constant darkness, revealing the importance of the daily light cycle to restore liver function.

Nicotinamide Riboside, an NAD + Precursor, Reduces Hepatic Stellate Cell Activation and Attenuates Liver Fibrosis in a Diet-induced Mouse Model of Liver Fibrosis (OR24-06-19)

ObjectivesThere is limited pharmacological treatment for liver fibrosis, which can result from chronic liver injury. In this study, we investigated the effect of nicotinamide riboside (NR), a nicotinamide adenine dinucleotide (NAD) precursor, on the development of liver fibrosis in a diet-induced mouse model of liver fibrosis in vivo and in hepatic stellate cells (HSCs) in vitro. MethodsMale C57BL/6 J mice were randomly assigned to three groups: a low-fat control (LF; 6% fat by wt), a high-fat/high-sucrose/high-cholesterol control (HF; 35%/34%/2.0% by wt, n = 13) or a HF diet supplemented with NR at 400 mg/kg/day (HF-NR, n = 14) for 20 weeks. Features of liver fibrosis were assessed by molecular, histological, and biochemical analyses to determine the effect of NR. Metabolic rates, energy expenditure and physical activity were measured using indirect calorimetry. Primary mouse and human HSCs, the primary extracellular matrix-producing cell-type in the liver, were used to determine the anti-fibrogenic effects of NR in vitro. ResultsHF-NR group had reduced body weight gain, which was attributable to increased energy expenditure. NR supplementation did not affect serum alanine aminotransferase levels and markers of steatosis and inflammation in the liver. However, liver trichrome and picrosirius red staining and total collagen quantification showed significant reductions of collagen by NR. Consistently, hepatic collagen 1a1 mRNA and protein were significantly reduced in the HF-NR group. Liver NAD levels were significantly reduced by HF, but was increased by NR supplementation. RNA-Seq analysis of NAD metabolism genes in quiescent and activated HSCs indicated that NAD levels might be reduced in activated HSCs due to repression of NAD salvage pathway, which regenerates NAD from nicotinamide. Indeed, treatment of primary human and mouse HSCs with NR significantly reduced their activation in vitro. ConclusionsNR supplementation prevented the development of liver fibrosis in a diet-induced mouse model of liver fibrosis independent of hepatic steatosis and inflammation. The data suggest that NR may directly reduce HSC activation to exert its anti-fibrotic effect. NR may be developed as a potential preventative for human liver fibrosis. Funding SourcesThe NIH, USDA Multistate Hatch, and USDA Hatch.

NAD metabolic dependency in cancer is shaped by gene amplification and enhancer remodelling.

Precision oncology hinges on linking tumour genotype with molecularly targeted drugs1; however, targeting the frequently dysregulated metabolic landscape of cancer has proven to be a major challenge2. Here we show that tissue context is the major determinant of dependence on the nicotinamide adenine dinucleotide (NAD) metabolic pathway in cancer. By analysing more than 7,000 tumours and 2,600 matched normal samples of 19 tissue types, coupled with mathematical modelling and extensive in vitro and in vivo analyses, we identify a simple and actionable set of 'rules'. If the rate-limiting enzyme of de novo NAD synthesis, NAPRT, is highly expressed in a normal tissue type, cancers that arise from that tissue will have a high frequency of NAPRT amplification and be completely and irreversibly dependent on NAPRT for survival. By contrast, tumours that arise from normal tissues that do not express NAPRT highly are entirely dependent on the NAD salvage pathway for survival. We identify the previously unknown enhancer that underlies this dependence. Amplification of NAPRT is shown to generate a pharmacologically actionable tumour cell dependence for survival. Dependence on another rate-limiting enzyme of the NAD synthesis pathway, NAMPT, as a result of enhancer remodelling is subject to resistance by NMRK1-dependent synthesis of NAD. These results identify a central role for tissue context in determining the choice of NAD biosynthetic pathway, explain the failure of NAMPT inhibitors, and pave the way for more effective treatments.

NAD metabolism fuels human and mouse intestinal inflammation

ObjectiveNicotinamide phosphoribosyltransferase (NAMPT, also referred to as pre-B cell colony-enhancing factor or visfatin) is critically required for the maintenance of cellular nicotinamide adenine dinucleotide (NAD) supply catalysing the rate-limiting step...

Down-regulation of NAMPT expression by mir-206 reduces cell survival of breast cancer cells

Nicotinamide adenine dinucleotide (NAD) is a critical coenzyme for all living cells. Nicotinamide phosphoribosyltransferase (NAMPT) functions as a key enzyme in the salvage pathway of NAD biosynthesis. Cancer cells have higher rate of NAD consumption and therefore NAMPT is essential for their survival. Thus, we investigated the effect of NAMPT inhibition by miR-206 on breast cancer cell survival. Breast cancer cells were transfected with miR-206 mimic, inhibitor and their negative controls. NAMPT levels were assessed by real-time PCR as well as western blotting. Cell survival assay and quantification of NAD level were performed by using colorimetric methods. Apoptosis assay was performed by labeling cells with Annexin V-FITC and propidium iodide followed by the flow cytometric analysis. Bioinformatics analysis was done to assess whether NAMPT 3′-UTR is a direct target of miR-206 and the results were confirmed by the luciferase reporter assay. NAMPT 3′-UTR was shown to be a direct target of miR-206. miR-206 reduced NAMPT expression at the protein level, leading to a significant decrease in the intracellular NAD level and subsequent decline in cell survival and induction of apoptosis. Targeting of NAMPT-mediated NAD salvage pathway by miR-206 might provide a new insight in the possible molecular mechanism of breast cancer cell growth regulation. This pathway might provide a new approach for breast cancer therapy.

EWS-FLI1 confers exquisite sensitivity to NAMPT inhibition in Ewing sarcoma cells

Ewing sarcoma (EwS) is the second most common bone cancer in children and adolescents with a high metastatic potential. EwS development is driven by a specific chromosomal translocation resulting in the generation of a chimeric EWS-ETS transcription factor, most frequently EWS-FLI1.Nicotinamide adenine dinucleotide (NAD) is a key metabolite of energy metabolism involved in cellular redox reactions, DNA repair, and in the maintenance of genomic stability. This study describes targeting nicotinamide phosphoribosyltransferase (NAMPT), the rate-limiting enzyme of NAD synthesis, by FK866 in EwS cells. Here we report that blocking NAMPT leads to exhaustive NAD depletion in EwS cells, followed by a metabolic collapse and cell death. Using conditional EWS-FLI1 knockdown by doxycycline-inducible shRNA revealed that EWS-FLI1 depletion significantly reduces the sensitivity of EwS cells to NAMPT inhibition. Consistent with this finding, a comparison of 7 EwS cell lines of different genotypes with 5 Non-EwS cell lines and mesenchymal stem cells revealed significantly higher FK866 sensitivity of EWS-ETS positive EwS cells, with IC50 values mostly below 1nM.Taken together, our data reveal evidence of an important role of the NAMPT-mediated NAD salvage pathway in the energy homeostasis of EwS cells and suggest NAMPT inhibition as a potential new treatment approach for Ewing sarcoma.

Small interfering RNA-mediated silencing of nicotinamide phosphoribosyltransferase (NAMPT) and lysosomal trafficking regulator (LYST) induce growth inhibition and apoptosis in human multiple myeloma cells: A preliminary study.

Multiple myeloma (MM) is a malignancy of B lymphocytes or plasma cells. Our array-based comparative genomic hybridization findings revealed chromosomal gains at 7q22.3 and 1q42.3, where nicotinamide (NAM) phosphoribosyltransferase (NAMPT) and lysosomal trafficking regulator (LYST) genes are localized, respectively. This led us to further study the functions of these genes in myeloma cells. NAMPT is a key enzyme involved in nicotinamide adenine dinucleotide salvage pathway, and it is frequently overexpressed in human cancers. In contrast, little is known about the function of LYST in cancer. The expression of LYST is shown to affect lysosomal size, granule size, and autophagy in human cells. In this study, the effects of small interfering RNA (siRNA)-mediated silencing of NAMPT and LYST on cell proliferation and apoptosis were evaluated in RPMI 8226 myeloma cells. Transfection efficiencies were determined by quantitative real time reverse transcriptase PCR. Cell proliferation was determined using MTT assay, while apoptosis was analyzed with flow cytometry using Annexin V-fluorescein isothiocyanate/propidium iodide assay. The NAMPT protein expression in siRNA-treated cells was estimated by enzyme-linked immunosorbent assay. Our results showed that NAMPT and LYST were successfully knockdown by siRNA transfection (p < 0.05). NAMPT or LYST gene silencing significantly inhibited cell proliferation and induced apoptosis in RPMI 8226 cells (p < 0.05). Silencing of NAMPT gene also decreased NAMPT protein levels (p < 0.01). Our study demonstrated that NAMPT and LYST play pivotal roles in the molecular pathogenesis of MM. This is the first report describing the possible functions of LYST in myelomagenesis and its potential role as a therapeutic target in MM.

Nicotinamide Phosphoribosyltransferase Upregulation by Phenylephrine Reduces Radiation Injury in Submandibular Gland

Radiation therapy for head and neck cancer commonly leads to radiation sialadenitis. Emerging evidence has indicated that phenylephrine pretreatment reduces radiosensitivity in the salivary gland; however, the underlying cytoprotective mechanism remains unclear. Nicotinamide phosphoribosyltransferase (NAMPT) is not only a key enzyme for the nicotinamide adenine dinucleotide salvage pathway, but also a cytokine participating in cell survival, metabolism, and longevity, with a broad effect on cellular functions in physiology and pathology. However, the regulatory events of NAMPT in response to the irradiated salivary gland are unknown. The cell viability of primary cultured submandibular gland cells was determined using the PrestoBlue assay. NAMPT expression was measured using reverse transcriptase polymerase chain reaction and Western blotting invitro and invivo. Silent information regulator 1 (SIRT1) and phosphorylated Akt protein levels were examined by Western blotting. The cellular locations of NAMPT and SIRT1 were detected by immunohistochemistry. NAMPT promoter activity was assessed using the luciferase reporter gene assay. NAMPT was mainly distributed in the cytoplasm of granular convoluted tubule cells and ductal cells in normal submandibular glands. mRNA and protein expression of NAMPT was downregulated after radiation but upregulated with phenylephrine pretreatment both invivo and invitro. Moreover, the protein expression of phosphorylated Akt and SIRT1 was decreased in irradiated glands, and phenylephrine pretreatment restored the expression of both. SIRT1 was mainly located in the cell nucleus and cytoplasm in the normal submandibular gland. Phenylephrine dramatically enhanced the expression of SIRT1, which was significantly reduced by radiation. Furthermore, phenylephrine induced a marked increase of NAMPT promoter activity. These findings reveal the regulatory mechanisms of NAMPT expression, which help to understand the mechanism of the cytoprotective role of phenylephrine on irradiated tissues.

Regulation of the Nampt-mediated NAD salvage pathway and its therapeutic implications in pancreatic cancer

Nicotinamide adenine dinucleotide (NAD) is a crucial cofactor for the redox reactions in the metabolic pathways of cancer cells that have elevated aerobic glycolysis (Warburg effect). Cancer cells are reported to rely on NAD recycling and inhibition of the NAD salvage pathway causes metabolic collapse and cell death. However, the underlying regulatory mechanisms and clinical implications for the NAD salvage pathway in pancreatic ductal adenocarcinoma (PDAC) remain unclear. This study showed that the expression of Nampt, the rate-limiting enzyme of the NAD salvage pathway, was significantly increased in PDAC cells and PDAC tissues. Additionally, inhibition of Nampt impaired tumor growth in vitro and tumorigenesis in vivo, which was accompanied by a decreased cellular NAD level and glycolytic activity. Mechanistically, the Nampt expression was independent of Kras and p16 status, but it was directly regulated by miR-206, which was inversely correlated with the expression of Nampt in PDAC tissues. Importantly, pharmacological inhibition of Nampt by its inhibitor, FK866, significantly enhanced the antitumor activity of gemcitabine in PDAC cells and in orthotopic xenograft mouse models. In conclusion, the present study revealed a novel regulatory mechanism for Nampt in PDAC and suggested that Nampt inhibition may override gemcitabine resistance by decreasing the NAD level and suppressing glycolytic activity, warranting further clinical investigation for pancreatic cancer treatment.

Regulation of host immune responses to Schistosoma mansoni by the inhibition of the parasitic NAD salvage pathway.

Abstract T regulatory cells (Tregs) are a subset of FoxP3+ lymphocytes that maintain immune homeostasis through immunosuppressive signaling. In many helminth infections, one mechanism of immune evasion involves the influx and maintenance of Tregs. Multiple mechanisms can control Treg homeostasis including a Nicotinamide adenine dinucleotide (NAD) dependent apoptotic pathway. In most organisms, the two pathways of NAD synthesis include de novo synthesis from amino acid precursors, and the salvage pathway in which nicotinamide-containing precursors are recycled into NAD. A comparative genome analysis of S. mansoni, the parasite that causes Schistosomiasis, enabled the assembly of a putative NAD biosynthetic pathway. Only orthologues of NAD salvage-specific genes were identified and expression was confirmed by PCR. This suggests that S. mansoni decreases host NAD levels in a salvage-specific manner and rescues Tregs from NAD-dependent cell death. As such, we hypothesized that inhibition of NAD biosynthesis through the salvage pathway would result in impaired NAD uptake by S. mansoni and restoration of NAD-mediated cell death of Tregs. Indeed, co-culture with S. mansoni prevented NAD-induced toxicity and death of Tregs. Blockade of the NAD salvage pathway via the inhibition of Schistosoma mansoni NAD catabolizing enzyme (SmNACE) restored NAD-mediated cell death of Tregs. Furthermore, SmNACE inhibition decreased intracellular NAD levels and reduced metabolism and viability of the parasite. Collectively, our data suggest that inhibition of NAD biosynthesis blocks immune evasion and metabolism of S. mansoni, and that targeting the NAD salvage pathway is a promising therapeutic approach for the treatment of Schistosomiasis.

Extensive regulation of nicotinate phosphoribosyltransferase (NAPRT) expression in human tissues and tumors.

Nicotinamide adenine dinucleotide (NAD) is a cofactor in redox reactions and a substrate for NAD-consuming enzymes, such as PARPs and sirtuins. As cancer cells have increased NAD requirements, the main NAD salvage enzymes in humans, nicotinamide phosphoribosyltransferase (NAMPT) and nicotinate phosphoribosyltransferase (NAPRT), are involved in the development of novel anti-cancer therapies. Knowledge of the expression patterns of both genes in tissues and tumors is critical for the use of nicotinic acid (NA) as cytoprotective in therapies using NAMPT inhibitors. Herein, we provide a comprehensive study of NAPRT and NAMPT expression across human tissues and tumor cell lines. We show that both genes are widely expressed under normal conditions and describe the occurrence of novel NAPRT transcripts. Also, we explore some of the NAPRT gene expression mechanisms. Our findings underline that the efficiency of NA in treatments with NAMPT inhibitors is dependent on the knowledge of the expression profiles and regulation of both NAMPT and NAPRT.

Regenerative Neurogenesis After Ischemic Stroke Promoted by Nicotinamide Phosphoribosyltransferase–Nicotinamide Adenine Dinucleotide Cascade

Nicotinamide adenine dinucleotide (NAD) is a ubiquitous fundamental metabolite. Nicotinamide phosphoribosyltransferase (Nampt) is the rate-limiting enzyme for mammalian NAD salvage synthesis and has been shown to protect against acute ischemic stroke. In this study, we investigated the role of Nampt-NAD cascade in brain regeneration after ischemic stroke. Nampt transgenic (Nampt-Tg) mice and H247A mutant enzymatic-dead Nampt transgenic (ΔNampt-Tg) mice were subjected with experimental cerebral ischemia by middle cerebral artery occlusion. Activation of neural stem cells, neurogenesis, and neurological function recovery were measured. Besides, nicotinamide mononucleotide and NAD, two chemical enzymatic product of Nampt, were administrated in vivo and in vitro. Compared with wild-type mice, Nampt-Tg mice showed enhanced number of neural stem cells, improved neural functional recovery, increased survival rate, and accelerated body weight gain after middle cerebral artery occlusion, which were not observed in ΔNampt-Tg mice. A delayed nicotinamide mononucleotide administration for 7 days with the first dose at 12 hours post middle cerebral artery occlusion did not protect acute brain infarction and neuronal deficit; however, it still improved postischemic regenerative neurogenesis. Nicotinamide mononucleotide and NAD(+) promoted proliferation and differentiation of neural stem cells in vitro. Knockdown of NAD-dependent deacetylase sirtuin 1 (SIRT1) and SIRT2 inhibited the progrowth action of Nampt-NAD axis, whereas knockdown of SIRT1, SIRT2, and SIRT6 compromised the prodifferentiation effect of Nampt-NAD axis. Our data demonstrate that the Nampt-NAD cascade may act as a centralizing switch in postischemic regeneration through controlling different sirtuins and therefore represent a promising therapeutic target for long-term recovery of ischemic stroke.

774: Placental visfatin/NAMPT and sirtuin-1 expression in pre-eclampsia

The human placenta expresses Sirtuin-1 (SIRT1) and visfatin/NAMPT (VSF). VSF catalyzes the rate-limiting step in the NAD salvage pathway and regulates the expression of SIRT1. The sirtuin proteins control cell metabolism, proliferation and stress-response. SIRT1 is a nicotinamide adenine dinucleotide (NAD)-dependent deacetylase, associated with inflammation resolution. VSF and SIRT1 are regulators of angiogenesis, especially in ischemic stress. Given that alterations in extravillous trophoblast invasion and endothelial cell changes in maternal spiral arteries contribute to the early pathogenesis of pre-eclampsia (PE), changes in VSF and SIRT1 may have roles in this process.

P7C3 Neuroprotective Chemicals Function by Activating the Rate-Limiting Enzyme in NAD Salvage

The P7C3 class of aminopropyl carbazole chemicals fosters the survival of neurons in a variety of rodent models of neurodegeneration or nerve cell injury. To uncover its mechanism of action, an active derivative of P7C3 was modified to contain both a benzophenone for photocrosslinking and an alkyne for CLICK chemistry. This derivative was found to bind nicotinamide phosphoribosyltransferase (NAMPT), the rate-limiting enzyme involved in the conversion of nicotinamide into nicotinamide adenine dinucleotide (NAD). Administration of active P7C3 chemicals to cells treated with doxorubicin, which induces NAD depletion, led to a rebound in intracellular levels of NAD and concomitant protection from doxorubicin-mediated toxicity. Active P7C3 variants likewise enhanced the activity of the purified NAMPT enzyme, providing further evidence that they act by increasing NAD levels through its NAMPT-mediated salvage.

P7C3 Neuroprotective Chemicals Block Axonal Degeneration and Preserve Function after Traumatic Brain Injury

The P7C3 class of neuroprotective aminopropyl carbazoles has been shown to block neuronal cell death in models of neurodegeneration. We now show that P7C3 molecules additionally preserve axonal integrity after injury, before neuronal cell death occurs, in a rodent model of blast-mediated traumatic brain injury (TBI). This protective quality may be linked to the ability of P7C3 molecules to activate nicotinamide phosphoribosyltransferase, the rate-limiting enzyme in nicotinamide adenine dinucleotide salvage. Initiation of daily treatment with our recently reported lead agent, P7C3-S243, 1 day after blast-mediated TBI blocks axonal degeneration and preserves normal synaptic activity, learning and memory, and motor coordination in mice. We additionally report persistent neurologic deficits and acquisition of an anxiety-like phenotype in untreated animals 8 months after blast exposure. Optimized variants of P7C3 thus offer hope for identifying neuroprotective agents for conditions involving axonal damage, neuronal cell death, or both, such as occurs in TBI.

Dependence of Tumor Cell Lines and Patient-Derived Tumors on the NAD Salvage Pathway Renders Them Sensitive to NAMPT Inhibition with GNE-618

Nicotinamide adenine dinucleotide (NAD) is a critical metabolite that is required for a range of cellular reactions. A key enzyme in the NAD salvage pathway is nicotinamide phosphoribosyl transferase (NAMPT), and here, we describe GNE-618, an NAMPT inhibitor that depletes NAD and induces cell death in vitro and in vivo. While cells proficient for nicotinic acid phosphoribosyl transferase (NAPRT1) can be protected from NAMPT inhibition as they convert nicotinic acid (NA) to NAD independent of the salvage pathway, this protection only occurs if NA is added before NAD depletion. We also demonstrate that tumor cells are unable to generate NAD by de novo synthesis as they lack expression of key enzymes in this pathway, thus providing a mechanistic rationale for the reliance of tumor cells on the NAD salvage pathway. Identifying tumors that are sensitive to NAMPT inhibition is one potential way to enhance the therapeutic effectiveness of an NAMPT inhibitor, and here, we show that NAMPT, but not NAPRT1, mRNA and protein levels inversely correlate with sensitivity to GNE-618 across a panel of 53 non-small cell lung carcinoma cell lines. Finally, we demonstrate that GNE-618 reduced tumor growth in a patient-derived model, which is thought to more closely represent heterogeneous primary patient tumors. Thus, we show that dependence of tumor cells on the NAD salvage pathway renders them sensitive to GNE-618 in vitro and in vivo, and our data support further evaluation of the use of NAMPT mRNA and protein levels as predictors of overall sensitivity.