NMRK2 Gene Is Upregulated in Dilated Cardiomyopathy and Required for Cardiac Function and NAD Levels during Aging.

Dilated cardiomyopathy (DCM) is a disease of multifactorial etiologies, the risk of which is increased by male sex and age. There are few therapeutic options for patients with DCM who would benefit from identification of common targetable pathways. We used bioinformatics to identify the Nmrk2 gene involved in nicotinamide adenine dinucleotde (NAD) coenzyme biosynthesis as activated in different mouse models and in hearts of human patients with DCM while the Nampt gene controlling a parallel pathway is repressed. A short NMRK2 protein isoform is also known as muscle integrin binding protein (MIBP) binding the α7ß1 integrin complex. We investigated the cardiac phenotype of Nmrk2-KO mice to establish its role in cardiac remodeling and function. Young Nmrk2-KO mice developed an eccentric type of cardiac hypertrophy in response to pressure overload rather than the concentric hypertrophy observed in controls. Nmrk2-KO mice developed a progressive DCM-like phenotype with aging, associating eccentric remodeling of the left ventricle and a decline in ejection fraction and showed a reduction in myocardial NAD levels at 24 months. In agreement with involvement of NMRK2 in integrin signaling, we observed a defect in laminin deposition in the basal lamina of cardiomyocytes leading to increased fibrosis at middle age. The α7 integrin was repressed at both transcript and protein level at 24 months. Nmrk2 gene is required to preserve cardiac structure and function, and becomes an important component of the NAD biosynthetic pathways during aging. Molecular characterization of compounds modulating this pathway may have therapeutic potential.

Nicotinamide: Oversight of Metabolic Dysfunction Through SIRT1, mTOR, and Clock Genes.

Metabolic disorders that include diabetes mellitus present significant challenges for maintaining the welfare of the global population. Metabolic diseases impact all systems of the body and despite current therapies that offer some protection through tight serum glucose control, ultimately such treatments cannot block the progression of disability and death realized with metabolic disorders. As a result, novel therapeutic avenues are critical for further development to address these concerns. An innovative strategy involves the vitamin nicotinamide and the pathways associated with the silent mating type information regulation 2 homolog 1 (Saccharomyces cerevisiae) (SIRT1), the mechanistic target of rapamycin (mTOR), mTOR Complex 1 (mTORC1), mTOR Complex 2 (mTORC2), AMP activated protein kinase (AMPK), and clock genes. Nicotinamide maintains an intimate relationship with these pathways to oversee metabolic disease and improve glucose utilization, limit mitochondrial dysfunction, block oxidative stress, potentially function as antiviral therapy, and foster cellular survival through mechanisms involving autophagy. However, the pathways of nicotinamide, SIRT1, mTOR, AMPK, and clock genes are complex and involve feedback pathways as well as trophic factors such as erythropoietin that require a careful balance to ensure metabolic homeostasis. Future work is warranted to gain additional insight into these vital pathways that can oversee both normal metabolic physiology and metabolic disease.

Direct in vivo comparison of [18F]PSMA-1007 with [68Ga]Ga-PSMA-11 and [18F]AlF-PSMA-11 in mice bearing PSMA-expressing xenografts.

The aim of this preclinical study was to directly compare [18F]PSMA-1007 with both [68Ga]Ga-PSMA-11 and [18F]AlF-PSMA-11 in mice bearing PSMA-positive tumor xenografts. Uptake was assessed by PET/CT at 1, 2 and 4 h post-injection, and by ex vivo measurement after 4 h. [18F]PSMA-1007 demonstrated the highest tumor uptake of the three tracers. The high uptake in bone for mice injected with [18F]AlF-PSMA-11 suggested rapid in vivo decomposition. This was confirmed by an in vitro plasma stability study.

Epigenomic and Transcriptomic Changes During Human RPE EMT in a Stem Cell Model of Epiretinal Membrane Pathogenesis and Prevention by Nicotinamide.

Epithelial to mesenchymal transition (EMT) is a biological process involved in tissue morphogenesis and disease that causes dramatic changes in cell morphology, migration, proliferation, and gene expression. The retinal pigment epithelium (RPE), which supports the neural retina, can undergo EMT, producing fibrous epiretinal membranes (ERMs) associated with vision-impairing clinical conditions, such as macular pucker and proliferative vitreoretinopathy (PVR). We found that co-treatment with TGF-ß and TNF-α (TNT) accelerates EMT in adult human RPE stem cell-derived RPE cell cultures. We captured the global epigenomic and transcriptional changes elicited by TNT treatment of RPE and identified putative active enhancers associated with actively transcribed genes, including a set of upregulated transcription factors that are candidate regulators. We found that the vitamin B derivative nicotinamide downregulates these key transcriptional changes, and inhibits and partially reverses RPE EMT, revealing potential therapeutic routes to benefit patients with ERM, macular pucker and PVR.

Endogenous nicotinamide riboside metabolism protects against diet-induced liver damage.

Supplementation with the NAD+ precursor nicotinamide riboside (NR) ameliorates and prevents a broad array of metabolic and aging disorders in mice. However, little is known about the physiological role of endogenous NR metabolism. We have previously shown that NR kinase 1 (NRK1) is rate-limiting and essential for NR-induced NAD+ synthesis in hepatic cells. To understand the relevance of hepatic NR metabolism, we generated whole body and liver-specific NRK1 knockout mice. Here, we show that NRK1 deficiency leads to decreased gluconeogenic potential and impaired mitochondrial function. Upon high-fat feeding, NRK1 deficient mice develop glucose intolerance, insulin resistance and hepatosteatosis. Furthermore, they are more susceptible to diet-induced liver DNA damage, due to compromised PARP1 activity. Our results demonstrate that endogenous NR metabolism is critical to sustain hepatic NAD+ levels and hinder diet-induced metabolic damage, highlighting the relevance of NRK1 as a therapeutic target for metabolic disorders.

Vitamin B3 in Health and Disease: Toward the Second Century of Discovery.

This introductory chapter briefly reviews the history, chemistry, and biochemistry of NAD (the term NAD as it is used here refers to both oxidized and reduced forms of the molecule) consuming ADP-ribose transfer enzymes as components of the involvement of vitamin B3 in health and disease.

Rescue of biosynthesis of nicotinamide adenine dinucleotide protects the heart in cardiomyopathy caused by lamin A/C gene mutation.

Cardiomyopathy caused by lamin A/C gene (LMNA) mutations (hereafter referred as LMNA cardiomyopathy) is an anatomic and pathologic condition associated with muscle and electrical dysfunction of the heart, often leading to heart failure-related disability. There is currently no specific therapy available for patients that target the molecular pathophysiology of LMNA cardiomyopathy. Recent studies suggested that nicotinamide adenine dinucleotide (NAD+) cellular content could be a critical determinant for heart function. Biosynthesis of NAD+ from vitamin B3 (known as salvage pathways) is the primary source of NAD+. We showed here that NAD+ salvage pathway was altered in the heart of mouse and human carrying LMNA mutation, leading to an alteration of one of NAD+ co-substrate enzymes, PARP-1. Oral administration of nicotinamide riboside, a natural NAD+ precursor and a pyridine-nucleoside form of vitamin B3, leads to a marked improvement of the NAD+ cellular content, an increase of PARylation of cardiac proteins and an improvement of left ventricular structure and function in a model of LMNA cardiomyopathy. Collectively, our results provide mechanistic and therapeutic insights into dilated cardiomyopathy caused by LMNA mutations.

N1-methylnicotinamide (MNAM) as a guardian of cardiovascular system.

Atherosclerosis is identified as the formation of atherosclerotic plaques, which could initiate the formation of a blood clot in which its growth to coronary artery can lead to a heart attack. N-methyltransferase (NNMT) is an enzyme that converts the NAM (nicotinamide) to its methylated form, N1-methylnicotinamide (MNAM). Higher levels of MNAM have been reported in cases with coronary artery disease (CAD). Further, MNAM increases endothelial prostacyclin (PGI2) and nitric oxide (NO) and thereby causes vasorelaxation. The vasoprotective, anti-inflammatory and anti-thrombotic roles of MNAM have been well documented; however, the exact underlying mechanisms remain to be clarified. Due to potential role of MNAM in the formation of lipid droplets (LDs), it might exert its function in coordination with lipids, and their targets. In this study, we summarized the roles of MNAM in cardiovascular system and highlighted its possible mode of actions.

Nicotinamide N-Methyltransferase: More Than a Vitamin B3 Clearance Enzyme.

Nicotinamide (NAM) N-methyltransferase (NNMT) was originally identified as the enzyme responsible for the methylation of NAM, one of the forms of vitamin B3. Methylated NAM is eventually excreted from the body. Recent evidence has expanded the role of NNMT beyond clearance of excess vitamin B3. NNMT has been implicated in the regulation of multiple metabolic pathways in tissues such as adipose and liver as well as cancer cells through the consumption of methyl donors and generation of active metabolites. This review examines recent findings regarding the function of NNMT in physiology and disease and highlights potential new avenues for therapeutic intervention. Finally, key gaps in our knowledge about this enzymatic system and future areas of investigation are discussed.

Vascular CXCR4 Expression Promotes Vessel Sprouting and Sensitivity to Sorafenib Treatment in Hepatocellular Carcinoma.

Purpose: C-X-C chemokine receptor type 4 (CXCR4) is known to be involved in both developmental and adult angiogenesis; however, its role in tumor angiogenesis remains largely unknown. Here, the role of vascular CXCR4 in regulating vascular structure in hepatocellular carcinoma (HCC) was assessd, and the clinical value of CXCR4 was explored.Experimental Design: The expression of CXCR4 in HCC was determined by IHC and immunofluorescence. Characteristics of CXCR4+ cells were determined by in vitro and mice experiments. Kaplan-Meier survival analysis was used to determine the correlation of CXCR4 expression with prognosis.Results: We found that CXCR4 is selectively expressed on a fraction of tumor endothelial cells (TECs) in HCC tissues, but not on the hepatic endothelium in peritumoral area. High levels of CXCR4 on TECs tended to develop a sinusoidal vasculature in tumors and predicted poor prognosis for patients with HCC. CXCR4+ endothelial cells (EC) displayed the functional features of tip cells, with increased expression of tip cell-related markers. Functional studies revealed that CXCR4 could directly promote vessel sprouting in vitro and in vivo Interestingly, sorafenib treatment reduced the frequency of CXCR4+ ECs in culture and inhibited the formation of sinusoidal vasculature and growth of CXCR4High xenograft tumors. Moreover, high CXCR4 vascular density in resected tumor tissues before sorafenib treatment was associated with prolonged survival in patients with advanced HCC treated with sorafenib.Conclusions: These data revealed that CXCR4 is a novel HCC vascular marker for vessel sprouting and could serve as a potential therapeutic target and a predictive factor for sorafenib treatment in patients with HCC. Clin Cancer Res; 23(15); 4482-92. ©2017 AACR.

Molecular Mechanism and Prediction of Sorafenib Chemoresistance in Human Hepatocellular Carcinoma.

Hepatocellular carcinoma (HCC) is the second leading cause of cancer death worldwide, and prognosis remains unsatisfactory when the disease is diagnosed at an advanced stage. Many molecular targeted agents are being developed for the treatment of advanced HCC; however, the only promising drug to have been developed is sorafenib, which acts as a multi-kinase inhibitor. Unfortunately, a subgroup of HCC is resistant to sorafenib, and the majority of these HCC patients show disease progression even after an initial satisfactory response. To date, a number of studies have examined the underlying mechanisms involved in the response to sorafenib, and trials have been performed to overcome the acquisition of drug resistance. The anti-tumor activity of sorafenib is largely attributed to the blockade of the signals from growth factors, such as vascular endothelial growth factor receptor and platelet-derived growth factor receptor, and the downstream RAF/mitogen-activated protein/extracellular signal-regulated kinase (ERK) kinase (MEK)/ERK cascade. The activation of an escape pathway from RAF/MEK/ERK possibly results in chemoresistance. In addition, there are several features of HCCs indicating sorafenib resistance, such as epithelial-mesenchymal transition and positive stem cell markers. Here, we review the recent reports and focus on the mechanism and prediction of chemoresistance to sorafenib in HCC.

Differentiated thyroid cancer: focus on emerging treatments for radioactive iodine-refractory patients.

BACKGROUND: The treatment of differentiated thyroid cancer refractory to radioactive iodine (RAI) had been hampered by few effective therapies. Recently, tyrosine kinase inhibitors (TKIs) have shown activity in this disease. Clinical guidance on the use of these agents in RAI-refractory thyroid cancer is warranted. MATERIALS AND METHODS: Molecular mutations found in RAI-refractory thyroid cancer are summarized. Recent phase II and III clinical trial data for TKIs axitinib, lenvatinib, motesanib, pazopanib, sorafenib, sunitinib, and vandetinib are reviewed including efficacy and side effect profiles. Molecular targets and potencies of these agents are compared. Inhibitors of BRAF, mammalian target of rapamycin, and MEK are considered. RESULTS: Routine testing for molecular alterations prior to therapy is not yet recommended. TKIs produce progression-free survival of approximately 1 year (range: 7.7-19.6 months) and partial response rates of up to 50% by Response Evaluation Criteria in Solid Tumors. Pazopanib and lenvatinib are the most active agents. The majority of patients experienced tumor shrinkage with TKIs. Common adverse toxicities affect dermatologic, gastrointestinal, and cardiovascular systems. CONCLUSION: Multiple TKIs have activity in RAI-refractory differentiated thyroid cancer. Selection of a targeted agent should depend on disease trajectory, side effect profile, and goals of therapy.

A pre-steady state and steady state kinetic analysis of the N-ribosyl hydrolase activity of hCD157.

hCD157 catalyzes the hydrolysis of nicotinamide riboside (NR) and nicotinic acid riboside (NAR). The release of nicotinamide or nicotinic acid from NR or NAR was confirmed by spectrophotometric, HPLC and NMR analyses. hCD157 is inactivated by a mechanism-based inhibitor, 2'-deoxy-2'-fluoro-nicotinamide arabinoside (fNR). Modification of the enzyme during the catalytic cycle by NR, NAR, or fNR increased the intrinsic protein fluorescence by approximately 50%. Pre-steady state and steady state data were used to derive a minimal kinetic scheme for the hydrolysis of NR. After initial complex formation a reversible step (360 and 30s(-1)) is followed by a slow irreversible step (0.1s(-1)) that defined the rate limiting step, or kcat. The calculated KMapp value for NR in the hydrolytic reaction is 6nM. The values of the kinetic constants suggest that one biological function of cell-surface hCD157 is to bind and slowly hydrolyze NR, possibly converting it to a ligand-activated receptor. Differences in substrate preference between hCD157 and hCD38 were rationalized through a comparison of the crystal structures of the two proteins. This comparison identified several residues in hCD157 (F108 and F173) that can potentially hinder the binding of dinucleotide substrates (NAD+).

Nicotinamide overcomes pluripotency deficits and reprogramming barriers.

Crosstalk between intracellular signaling pathways has been extensively studied to understand the pluripotency of human pluripotent stem cells (hPSCs), including human embryonic stem cells and human induced pluripotent stem cells (hiPSCs); however, the contribution of NAD(+) -dependent pathways remains largely unknown. Here, we show that NAD(+) depletion by FK866 (a potent inhibitor of NAD(+) biosynthesis) was fatal in hPSCs, particularly when deriving pluripotent cells from somatic cells and maintaining pluripotency. NAD and its precursors (nicotinamide [NAM] and nicotinic acid) fully replenished the NAD(+) depletion by FK866 in hPSCs. However, only NAM effectively enhanced the reprogramming efficiency and kinetics of hiPSC generation and was also significantly advantageous for the maintenance of undifferentiated hPSCs. Our molecular and functional studies reveal that NAM lowers the barriers to reprogramming by accelerating cell proliferation and protecting cells from apoptosis and senescence by alleviating oxidative stress, reactive oxygen species accumulation, and subsequent mitochondrial membrane potential collapse. We provide evidence that the positive effects of NAM (occurring at concentrations well above the physiological range) on pluripotency control are molecularly associated with the repression of p53, p21, and p16. Our findings establish that adequate intracellular NAD(+) content is crucial for pluripotency; the distinct effects of NAM on pluripotency may be dependent not only on its metabolic advantage as a NAD(+) precursor but also on the ability of NAM to enhance resistance to cellular stress.

Catalytic contribution of threonine 244 in human ALDH2.

Amongst the numerous conserved residues in the aldehyde dehydrogenase superfamily, the precise role of Thr-244 remains enigmatic. Crystal structures show that this residue lies at the interface between the coenzyme-binding and substrate-binding sites with the side chain methyl substituent oriented toward the B-face of the nicotinamide ring of the NAD(P)(+) coenzyme, when in position for hydride transfer. Site-directed mutagenesis in ALDH1A1 and GAPN has suggested a role for Thr-244 in stabilizing the nicotinamide ring for efficient hydride transfer. Additionally, these studies also revealed a negative effect on cofactor binding which is not fully explained by the interaction with the nicotinamide ring. However, it is suggestive that Thr-244 immediately precedes helix αG, which forms one-half of the primary binding interface for the coenzyme. Hence, in order to more fully investigate the role of this highly conserved residue, we generated valine, alanine, glycine and serine substitutions for Thr-244 in human ALDH2. All four substituted enzymes exhibited reduced catalytic efficiency toward substrate and coenzyme. We also determined the crystal structure of the T244A enzyme in the absence and presence of coenzyme. In the apo-enzyme, the alpha G helix, which is key to NAD binding, exhibits increased temperature factors accompanied by a small displacement toward the active site cysteine. This structural perturbation was reversed in the coenzyme-bound complex. Our studies confirm a role for the Thr-244 beta methyl in the accurate positioning of the nicotinamide ring for efficient catalysis. We also identify a new role for Thr-244 in the stabilization of the N-terminal end of helix αG. This suggests that Thr-244, although less critical than Glu-487, is also an important contributor toward coenzyme binding.

A flavoprotein monooxygenase that catalyses a Baeyer-Villiger reaction and thioether oxidation using NADH as the nicotinamide cofactor.

A gene from the marine bacterium Stenotrophomonas maltophilia encodes a 38.6 kDa FAD-containing flavoprotein (Uniprot B2FLR2) named S. maltophilia flavin-containing monooxygenase (SMFMO), which catalyses the oxidation of thioethers and also the regioselective Baeyer-Villiger oxidation of the model substrate bicyclo[3.2.0]hept-2-en-6-one. The enzyme was unusual in its ability to employ either NADH or NADPH as nicotinamide cofactor. The K(M) and k(cat) values for NADH were 23.7±9.1 µM and 0.029 s(-1) and 27.3±5.3 µM and 0.022 s(-1) for NADPH. However, k(cat) /K(M) value for the ketone substrate in the presence of 100 µM cofactor was 17 times greater for NADH than for NADPH. SMFMO catalysed the quantitative conversion of 5 mM ketone in the presence of substoichiometric concentrations of NADH with the formate dehydrogenase cofactor recycling system, to give the 2-oxa and 3-oxa lactone products of Baeyer-Villiger reaction in a ratio of 5:1, albeit with poor enantioselectivity. The conversion with NADPH was 15 %. SMFMO also catalysed the NADH-dependent transformation of prochiral aromatic thioethers, giving in the best case, 80 % ee for the transformation of p-chlorophenyl methyl sulfide to its R enantiomer. The structure of SMFMO reveals that the relaxation in cofactor specificity appears to be accomplished by the substitution of an arginine residue, responsible for recognition of the 2'-phosphate on the NADPH ribose in related NADPH-dependent FMOs, with a glutamine residue in SMFMO. SMFMO is thus representative of a separate class of single-component, flavoprotein monooxygenases that catalyse NADH-dependent oxidations from which possible sequences and strategies for developing NADH-dependent biocatalysts for asymmetric oxygenation reactions might be identified.

Characterization of Streptococcus pyogenes beta-NAD+ glycohydrolase: re-evaluation of enzymatic properties associated with pathogenesis.

The gram-positive pathogen Streptococcus pyogenes injects a beta-NAD(+) glycohydrolase (SPN) into the cytosol of an infected host cell using the cytolysin-mediated translocation pathway. In this compartment, SPN accelerates the death of the host cell by an unknown mechanism that may involve its beta-NAD(+)-dependent enzyme activities. SPN has been reported to possess the unique characteristic of not only catalyzing hydrolysis of beta-NAD(+), but also carrying out ADP-ribosyl cyclase and ADP-ribosyltransferase activities, making SPN the only beta-NAD(+) glycohydrolase that can catalyze all of these reactions. With the long term goal of understanding how these activities may contribute to pathogenesis, we have further characterized the enzymatic activity of SPN using highly purified recombinant protein. Kinetic studies of the multiple activities of SPN revealed that SPN possessed only beta-NAD(+) hydrolytic activity and lacked detectable ADP-ribosyl cyclase and ADP-ribosyltransferase activities. Similarly, SPN was unable to catalyze cyclic ADPR hydrolysis, and could not catalyze methanolysis or transglycosidation. Kinetic analysis of product inhibition by recombinant SPN demonstrated an ordered uni-bi mechanism, with ADP-ribose being released as a second product. SPN was unaffected by product inhibition using nicotinamide, suggesting that this moiety contributes little to the binding energy of the substrate. Upon transformation, SPN was toxic to Saccharomyces cerevisiae, whereas a glycohydrolase-inactive SPN allowed for viability. Taken together, these data suggest that SPN functions exclusively as a strict beta-NAD(+) glycohydrolase during pathogenesis.

Nicotinamide rescues human embryonic stem cell-derived neuroectoderm from parthanatic cell death.

Abundant cell death is observed when human embryonic stem cells (hESCs) undergo neuralization, a critical first step for future cell-based therapies addressing neurodegeneration. Using hESC neuralization as an in vitro model of human development, we demonstrated that the developing neuroepithelium acquires increased susceptibility to spontaneous cell death. We found that poly(ADP-ribose) polymerase-1 (PARP1)/apoptosis-inducing factor (AIF)-mediated cell death (parthanatos) is a dominant mechanism responsible for cell loss during hESC neuralization. The demise of neural progenitor cells, at least in part, is due to decreased endogenous antioxidant defenses and enhanced reactive oxygen species leakage from mitochondria fuelled by nonphysiological culture conditions. Under such conditions, PARP1 overactivation triggered cell death through the mitochondrial-nuclear translocation of AIF. Blocking PARP1 activity with small hairpin RNA interference or nicotinamide dramatically enhanced hESC neuralization, providing optimal survival of the developing neuroepithelium. Because nicotinamide is a physiological metabolite, our results raise the possibility that neural stem/progenitor cell survival in vivo requires a metabolic niche. We argue that small natural metabolites provide a powerful physiological tool to optimize hESC differentiation compatible with the requirements of regenerative medicine.

Nicotinamide riboside and nicotinic acid riboside salvage in fungi and mammals. Quantitative basis for Urh1 and purine nucleoside phosphorylase function in NAD+ metabolism.

NAD+ is a co-enzyme for hydride transfer enzymes and an essential substrate of ADP-ribose transfer enzymes and sirtuins, the type III protein lysine deacetylases related to yeast Sir2. Supplementation of yeast cells with nicotinamide riboside extends replicative lifespan and increases Sir2-dependent gene silencing by virtue of increasing net NAD+ synthesis. Nicotinamide riboside elevates NAD+ levels via the nicotinamide riboside kinase pathway and by a pathway initiated by splitting the nucleoside into a nicotinamide base followed by nicotinamide salvage. Genetic evidence has established that uridine hydrolase, purine nucleoside phosphorylase, and methylthioadenosine phosphorylase are required for Nrk-independent utilization of nicotinamide riboside in yeast. Here we show that mammalian purine nucleoside phosphorylase but not methylthioadenosine phosphorylase is responsible for mammalian nicotinamide riboside kinase-independent nicotinamide riboside utilization. We demonstrate that so-called uridine hydrolase is 100-fold more active as a nicotinamide riboside hydrolase than as a uridine hydrolase and that uridine hydrolase and mammalian purine nucleoside phosphorylase cleave nicotinic acid riboside, whereas the yeast phosphorylase has little activity on nicotinic acid riboside. Finally, we show that yeast nicotinic acid riboside utilization largely depends on uridine hydrolase and nicotinamide riboside kinase and that nicotinic acid riboside bioavailability is increased by ester modification.

NAD+ and vitamin B3: from metabolism to therapies.

The role of NAD(+) metabolism in health and disease is of increased interest as the use of niacin (nicotinic acid) has emerged as a major therapy for treatment of hyperlipidemias and with the recognition that nicotinamide can protect tissues and NAD(+) metabolism in a variety of disease states, including ischemia/reperfusion. In addition, a growing body of evidence supports the view that NAD(+) metabolism regulates important biological effects, including lifespan. NAD(+) exerts potent effects through the poly(ADP-ribose) polymerases, mono-ADP-ribosyltransferases, and the recently characterized sirtuin enzymes. These enzymes catalyze protein modifications, such as ADP-ribosylation and deacetylation, leading to changes in protein function. These enzymes regulate apoptosis, DNA repair, stress resistance, metabolism, and endocrine signaling, suggesting that these enzymes and/or NAD(+) metabolism could be targeted for therapeutic benefit. This review considers current knowledge of NAD(+) metabolism in humans and microbes, including new insights into mechanisms that regulate NAD(+) biosynthetic pathways, current use of nicotinamide and nicotinic acid as pharmacological agents, and opportunities for drug design that are directed at modulation of NAD(+) biosynthesis for treatment of human disorders and infections.