Evolving concepts in NAD(+) metabolism

Discovery of Dual Function Agents That Exhibit Anticancer Activity via Catastrophic Nicotinamide Adenine Dinucleotide Depletion

Nicotinamide adenine dinucleotide (NAD) is essentially involved in many biological processes of cancer cells, yet chemical intervention of NAD biosynthesis failed to obtain an optimal therapeutic benefit. We herein developed a new strategy to induce catastrophic NAD depletion by concurrently impairing NAD synthesis and promoting NAD consumption. We designed a series of new compounds that conjugate an inhibitor of nicotinamide phosphoribosyltransferase (NAMPT), a rate-limiting enzyme in the NAD salvage pathway, with a DNA-alkylating agent. Among them, compound 11b exhibited potent anticancer efficacy in cancer cell lines and mouse tumor models with intrinsic resistance to the parent compound FK866 or chlorambucil. Compound 11b caused catastrophic NAD depletion via a synergistic effect between the NAD salvage pathway blockade and DNA damage-triggered NAD consumption. Our findings suggest a new intervention strategy for causing catastrophic NAD depletion in cancer cells and provide basis for the development of new inhibitors targeting NAD metabolism.

Resveratrol Improves the Frozen-Thawed Ram Sperm Quality

Cryopreservation generates a substantial quantity of ROS in semen, leading to a decline in sperm quality and fertilization capacity. The objective of this study was to investigate the effects of resveratrol and its optimal concentration on ram sperm quality after cryopreservation. Ram semen was diluted with a freezing medium containing different concentrations of resveratrol (0, 25, 50, 75, and 100 μM). After thawing, various sperm parameters such as total motility, progressive motility, acrosome integrity, plasma membrane integrity, mitochondrial membrane potential, glutathione (GSH) content, glutathione synthase (GPx) activity, superoxide dismutase (SOD) activity, catalase (CAT) activity, lipid peroxidation (LPO) content, malondialdehyde (MDA) content, ROS level, SIRT1 level, DNA oxidative damage, and AMPK phosphorylation level were assessed. In addition, post-thaw sperm apoptosis was evaluated. Comparatively, the addition of resveratrol up to 75 μM significantly improved the sperm motility and sperm parameters of cryopreserved ram sperm. Specifically, 50 μM resveratrol demonstrated a notable enhancement in acrosome and plasma membrane integrity, antioxidant capacity, mitochondrial membrane potential, adenosine triphosphate (ATP) content, SIRT1 level, and AMPK phosphorylation levels compared to the control group (p < 0.05). It also significantly (p < 0.05) reduced the oxidative damage to sperm DNA. However, detrimental effects of resveratrol were observed at a concentration of 100 μM resveratrol. In conclusion, the addition of 50 μM resveratrol to the cryopreservation solution is optimal for enhancing the quality of cryopreserved ram sperm.

Heavy-chain antibody targeting of CD38 NAD+ hydrolase ectoenzyme to prevent fibrosis in multiple organs

The functionally pleiotropic ectoenzyme CD38 is a glycohydrolase widely expressed on immune and non-hematopoietic cells. By converting NAD+ to ADP-ribose and nicotinamide, CD38 governs organismal NAD+ homeostasis and the activity of NAD+-dependent cellular enzymes. CD38 has emerged as a major driver of age-related NAD+ decline underlying adverse metabolic states, frailty and reduced health span. CD38 is upregulated in systemic sclerosis (SSc), a chronic disease characterized by fibrosis in multiple organs. We sought to test the hypothesis that inhibition of the CD38 ecto-enzymatic activity using a heavy-chain monoclonal antibody Ab68 will, via augmenting organismal NAD+, prevent fibrosis in a mouse model of SSc characterized by NAD+ depletion. Here we show that treatment of mice with a non-cytotoxic heavy-chain antibody that selectively inhibits CD38 ectoenzyme resulted in NAD+ boosting that was associated with significant protection from fibrosis in multiple organs. These findings suggest that targeted inhibition of CD38 ecto-enzymatic activity could be a potential pharmacological approach for SSc fibrosis treatment.

Impact of NAD+ metabolism on ovarian aging

Nicotinamide adenine dinucleotide (NAD+), a crucial coenzyme in cellular redox reactions, is closely associated with age-related functional degeneration and metabolic diseases. NAD exerts direct and indirect influences on many crucial cellular functions, including metabolic pathways, DNA repair, chromatin remodeling, cellular senescence, and immune cell functionality. These cellular processes and functions are essential for maintaining tissue and metabolic homeostasis, as well as healthy aging. Causality has been elucidated between a decline in NAD levels and multiple age-related diseases, which has been confirmed by various strategies aimed at increasing NAD levels in the preclinical setting. Ovarian aging is recognized as a natural process characterized by a decline in follicle number and function, resulting in decreased estrogen production and menopause. In this regard, it is necessary to address the many factors involved in this complicated procedure, which could improve fertility in women of advanced maternal age. Concerning the decrease in NAD+ levels as ovarian aging progresses, promising and exciting results are presented for strategies using NAD+ precursors to promote NAD+ biosynthesis, which could substantially improve oocyte quality and alleviate ovarian aging. Hence, to acquire further insights into NAD+ metabolism and biology, this review aims to probe the factors affecting ovarian aging, the characteristics of NAD+ precursors, and the current research status of NAD+ supplementation in ovarian aging. Specifically, by gaining a comprehensive understanding of these aspects, we are optimistic about the prominent progress that will be made in both research and therapy related to ovarian aging.

The NADase CD38 may not dictate NAD levels in brain mitochondria of aged mice but regulates hydrogen peroxide generation

Aging is a time-related functional decline that affects many species. One of the hallmarks of aging is mitochondrial dysfunction, which leads to metabolic decline. The NAD decline during aging, in several tissues, correlates with increase in NADase activity of CD38. Knock out or pharmacological inhibition of CD38 activity can rescue mitochondrial function in several tissues, however, the role of CD38 in controlling NAD levels and metabolic function in the aging brain is unknown. In this work, we investigated CD38 NADase activity controlling NAD levels and mitochondrial function in mice brain with aging. We demonstrate that NADase activity of CD38 does not dictate NAD total levels in brain of aging mice and does not control mitochondrial oxygen consumption nor other oxygen parameters markers of mitochondrial dysfunction. However, for the first time we show that CD38 regulates hydrogen peroxide (H2O2) generation, one of the reactive oxygen species (ROS) in aging brain, through regulation of pyruvate dehydrogenase and alfa-ketoglutarate dehydrogenase, as mitochondria H2O2 leakage sites. The effect may be related to mitochondrial calcium handling differences in CD38 absence. Our study highlights a novel role of CD38 in brain energy metabolism and aging.

Fingerstick blood assay maps real-world NAD+ disparity across gender and age

Nicotinamide adenine dinucleotide (NAD+ ) level has been associated with various age-related diseases and its pharmacological modulation emerges as a potential approach for aging intervention. But human NAD+ landscape exhibits large heterogeneity. The lack of rapid, low-cost assays limits the establishment of whole-blood NAD+ baseline and the development of personalized therapies, especially for those with poor responses towards conventional NAD+ supplementations. Here, we developed an automated NAD+ analyzer for the rapid measurement of NAD+ with 5 μL of capillary blood using recombinant bioluminescent sensor protein and automated optical reader. The minimal invasiveness of the assay allowed a frequent and decentralized mapping of real-world NAD+ dynamics. We showed that aerobic sport and NMN supplementation increased whole-blood NAD+ and that male on average has higher NAD+ than female before the age of 50. We further revealed the long-term stability of human NAD+ baseline over 100 days and identified major real-world NAD+ -modulating behaviors.

NAD+ salvage governs the immunosuppressive capacity of mesenchymal stem cells

Mesenchymal stem/stromal cells (MSCs) possess robust immunoregulatory functions and are promising therapeutics for inflammatory disorders. This capacity is not innate but is activated or 'licensed' by inflammatory cytokines. The licensing mechanism remains unclear. Here, we examined whether inflammatory cytokines metabolically reprogrammed MSCs to confer this immunoregulatory capacity. In response to stimulation by inflammatory cytokines, MSCs exhibited a dramatic increase in the consumption of glucose, which was accompanied by an enhanced use of nicotinamide adenine dinucleotide (NAD+) and increased expression of nicotinamide phosphoribosyltransferase (NAMPT), a central enzyme in the salvage pathway for NAD+ production. When NAD+ synthesis was blocked by inhibiting or depleting NAMPT, the immunosuppressive function of MSCs induced by inflammatory cytokines was greatly attenuated. Consequently, when NAD+ metabolism in MSCs was perturbed, their therapeutic benefit was decreased in mice suffering from inflammatory bowel disease and acute liver injury. Further analysis revealed that NAMPT-driven production of NAD+ was critical for the inflammatory cytokine-induced increase in glycolysis in MSCs. Furthermore, the increase in glycolysis led to succinate accumulation in the tricarboxylic acid cycle, which led to hypoxia-inducible factor 1α (HIF-1α) stabilization and subsequently increased the transcription of key glycolytic genes, thereby persistently maintaining glycolytic flux. This study demonstrated that unlike its proinflammatory role in immune cells, NAD+ metabolism governs the anti-inflammatory function of MSCs during inflammation.

Cold-stimulated brown adipose tissue activation is related to changes in serum metabolites relevant to NAD+ metabolism in humans

Cold-induced brown adipose tissue (BAT) activation is considered to improve metabolic health. In murine BAT, cold increases the fundamental molecule for mitochondrial function, nicotinamide adenine dinucleotide (NAD+), but limited knowledge of NAD+ metabolism during cold in human BAT metabolism exists. We show that cold increases the serum metabolites of the NAD+ salvage pathway (nicotinamide and 1-methylnicotinamide) in humans. Additionally, individuals with cold-stimulated BAT activation have decreased levels of metabolites from the de novo NAD+ biosynthesis pathway (tryptophan, kynurenine). Serum nicotinamide correlates positively with cold-stimulated BAT activation, whereas tryptophan and kynurenine correlate negatively. Furthermore, the expression of genes involved in NAD+ biosynthesis in BAT is related to markers of metabolic health. Our data indicate that cold increases serum tryptophan conversion to nicotinamide to be further utilized by BAT. We conclude that NAD+ metabolism is activated upon cold in humans and is probably regulated in a coordinated fashion by several tissues.

Boosting NAD preferentially blunts Th17 inflammation via arginine biosynthesis and redox control in healthy and psoriasis subjects

To evaluate whether nicotinamide adenine dinucleotide-positive (NAD+) boosting modulates adaptive immunity, primary CD4+ T cells from healthy control and psoriasis subjects were exposed to vehicle or nicotinamide riboside (NR) supplementation. NR blunts interferon γ (IFNγ) and interleukin (IL)-17 secretion with greater effects on T helper (Th) 17 polarization. RNA sequencing (RNA-seq) analysis implicates NR blunting of sequestosome 1 (sqstm1/p62)-coupled oxidative stress. NR administration increases sqstm1 and reduces reactive oxygen species (ROS) levels. Furthermore, NR activates nuclear factor erythroid 2-related factor 2 (Nrf2), and genetic knockdown of nrf2 and the Nrf2-dependent gene, sqstm1, diminishes NR amelioratory effects. Metabolomics analysis identifies that NAD+ boosting increases arginine and fumarate biosynthesis, and genetic knockdown of argininosuccinate lyase ameliorates NR effects on IL-17 production. Hence NR via amino acid metabolites orchestrates Nrf2 activation, augments CD4+ T cell antioxidant defenses, and attenuates Th17 responsiveness. Oral NR supplementation in healthy volunteers similarly increases serum arginine, sqstm1, and antioxidant enzyme gene expression and blunts Th17 immune responsiveness, supporting evaluation of NAD+ boosting in CD4+ T cell-linked inflammation.

B-cell targeting with anti-CD38 daratumumab: implications for differentiation and memory responses

B cell-targeted therapies, such as CD20-targeting mAbs, deplete B cells but do not target the autoantibody-producing plasma cells (PCs). PC-targeting therapies such as daratumumab (anti-CD38) form an attractive approach to treat PC-mediated diseases. CD38 possesses enzymatic and receptor capabilities, which may impact a range of cellular processes including proliferation and differentiation. However, very little is known whether and how CD38 targeting affects B-cell differentiation, in particular for humans beyond cancer settings. Using in-depth in vitro B-cell differentiation assays and signaling pathway analysis, we show that CD38 targeting with daratumumab demonstrated a significant decrease in proliferation, differentiation, and IgG production upon T cell-dependent B-cell stimulation. We found no effect on T-cell activation or proliferation. Furthermore, we demonstrate that daratumumab attenuated the activation of NF-κB in B cells and the transcription of NF-κB-targeted genes. When culturing sorted B-cell subsets with daratumumab, the switched memory B-cell subset was primarily affected. Overall, these in vitro data elucidate novel non-depleting mechanisms by which daratumumab can disturb humoral immune responses. Affecting memory B cells, daratumumab may be used as a therapeutic approach in B cell-mediated diseases other than the currently targeted malignancies.

The acute effect of different NAD+ precursors included in the combined metabolic activators

NAD+ and glutathione precursors are currently used as metabolic modulators for improving the metabolic conditions associated with various human diseases, including non-alcoholic fatty liver disease, neurodegenerative diseases, mitochondrial myopathy, and age-induced diabetes. Here, we performed a one-day double blinded, placebo-controlled human clinical study to assess the safety and acute effects of six different Combined Metabolic Activators (CMAs) with 1 g of different NAD+ precursors based on global metabolomics analysis. Our integrative analysis showed that the NAD+ salvage pathway is the main source for boosting the NAD+ levels with the administration of CMAs without NAD+ precursors. We observed that incorporation of nicotinamide (Nam) in the CMAs can boost the NAD+ products, followed by niacin (NA), nicotinamide riboside (NR) and nicotinamide mononucleotide (NMN), but not flush free niacin (FFN). In addition, the NA administration led to a flushing reaction, accompanied by decreased phospholipids and increased bilirubin and bilirubin derivatives, which could be potentially risky. In conclusion, this study provided a plasma metabolomic landscape of different CMA formulations, and proposed that CMAs with Nam, NMN as well as NR can be administered for boosting NAD+ levels to improve altered metabolic conditions.

Emerging therapies in cancer metabolism

Metabolic reprogramming in cancer is not only a biological hallmark but also reveals treatment vulnerabilities. Numerous metabolic molecules have shown promise as treatment targets to impede tumor progression in preclinical studies, with some advancing to clinical trials. However, the intricacy and adaptability of metabolic networks hinder the effectiveness of metabolic therapies. This review summarizes the metabolic targets for cancer treatment and provides an overview of the current status of clinical trials targeting cancer metabolism. Additionally, we decipher crucial factors that limit the efficacy of metabolism-based therapies and propose future directions. With advances in integrating multi-omics, single-cell, and spatial technologies, as well as the ability to track metabolic adaptation more precisely and dynamically, clinicians can personalize metabolic therapies for improved cancer treatment.

The emerging era of lactate: A rising star in cellular signaling and its regulatory mechanisms

Cellular metabolites are ancient molecules with pleiotropic implications in health and disease. Beyond their cognate roles, they have signaling functions as the ligands for specific receptors and the precursors for epigenetic or posttranslational modifications. Lactate has long been recognized as a metabolic waste and fatigue product mainly produced from glycolytic metabolism. Recent evidence however suggests lactate is an unique molecule with diverse signaling attributes in orchestration of numerous biological processes, including tumor immunity and neuronal survival. The copious metabolic and non-metabolic functions of lactate mediated by its bidirectional shuttle between cells or intracellular organelles lead to a phenotype called "lactormone." Importantly, the mechanisms of lactate signaling, via acting as a molecular sensor and a regulator of NAD+ metabolism and AMP-activated protein kinase signaling, and via the newly identified lactate-driven lactylation, have been discovered. Further, we include a brief discussion about the autocrine regulation of efferocytosis by lactate in Sertoli cells which favoraerobic glycolysis. By emphasizing a repertoire of the most recent discovered mechanisms of lactate signaling, this review will open tantalizing avenues for future investigations cracking the regulatory topology of lactate signaling covered in the veil of mystery.

NAD + salvage governs mitochondrial metabolism, invigorating natural killer cell antitumor immunity

BACKGROUND AND AIMS

Natural killer (NK) cells are key players in tumor immunosurveillance, and metabolic adaptation manipulates their fate and functional state. The nicotinamide adenine dinucleotide (NAD + ) has emerged as a vital factor to link cellular metabolism and signaling transduction. Here, we identified NAD + metabolism as a central hub to determine the homeostasis and function of NK cells.

APPROACH AND RESULTS

NAD + level was elevated in activated NK cells. NAD + supplementation not only enhanced cytokine production and cytotoxicity but also improved the proliferation and viability of NK cells. Intriguingly, the salvage pathway was involved in maintaining NAD + homeostasis in activated NK cells. Genetic ablation or pharmacological blockade of nicotinamide phosphoribosyltransferase (NAMPT), the rate-limiting enzyme in the NAD + salvage pathway, markedly destroyed the viability and function of NK cells. Mechanistically, NAD + salvage dictated the mitochondrial homeostasis and oxidative phosphorylation activity to support the optimal function of NK cells. However, in human HCC tissues, NAMPT expression and NAD + level were significantly down-regulated in tumor-infiltrating NK cells, which negatively correlated with patient survival. And lactate accumulation in the tumor microenvironment was at least partially responsible for the transcriptional repression of NAMPT in NK cells. Further, deficiency of Nampt in NK cells accelerated the growth of HCC and melanoma. Supplementation of the NAD + precursor nicotinamide mononucleotide (NMN) significantly improved NK antitumor response in both mouse and human cell-derived xenografts.

CONCLUSIONS

These findings reveal NAD + salvage as an essential factor for NK-cell homeostasis and function, suggesting a potential strategy for invigorating NK cell-based immunotherapy.

Defining NAD(P)(H) Catabolism

Dietary vitamin B3 components, such as nicotinamide and nicotinic acid, are precursors to the ubiquitous redox cofactor nicotinamide adenine dinucleotide (NAD⁺). NAD⁺ levels are thought to decline with age and disease. While the drivers of this decline remain under intense investigation, strategies have emerged seeking to functionally maintain NAD⁺ levels through supplementation with NAD⁺ biosynthetic intermediates. These include marketed products, such as nicotinamide riboside (NR) and its phosphorylated form (NMN). More recent developments have shown that NRH (the reduced form of NR) and its phosphorylated form NMNH also increases NAD⁺ levels upon administration, although they initially generate NADH (the reduced form of NAD⁺). Other means to increase the combined levels of NAD⁺ and NADH, NAD(H), include the inhibition of NAD⁺-consuming enzymes or activation of biosynthetic pathways. Multiple studies have shown that supplementation with an NAD(H) precursor changes the profile of NAD(H) catabolism. Yet, the pharmacological significance of NAD(H) catabolites is rarely considered although the distribution and abundance of these catabolites differ depending on the NAD(H) precursor used, the species in which the study is conducted, and the tissues used for the quantification. Significantly, some of these metabolites have emerged as biomarkers in physiological disorders and might not be innocuous. Herein, we review the known and emerging catabolites of the NAD(H) metabolome and highlight their biochemical and physiological function as well as key chemical and biochemical reactions leading to their formation. Furthermore, we emphasize the need for analytical methods that inform on the full NAD(H) metabolome since the relative abundance of NAD(H) catabolites informs how NAD(H) precursors are used, recycled, and eliminated.

The Promise of Niacin in Neurology

Niacin (vitamin B3) is an essential nutrient that treats pellagra, and prior to the advent of statins, niacin was commonly used to counter dyslipidemia. Recent evidence has posited niacin as a promising therapeutic for several neurological disorders. In this review, we discuss the biochemistry of niacin, including its homeostatic roles in NAD+ supplementation and metabolism. Niacin also has roles outside of metabolism, largely through engaging hydroxycarboxylic acid receptor 2 (Hcar2). These receptor-mediated activities of niacin include regulation of immune responses, phagocytosis of myelin debris after demyelination or of amyloid beta in models of Alzheimer's disease, and cholesterol efflux from cells. We describe the neurological disorders in which niacin has been investigated or has been proposed as a candidate medication. These are multiple sclerosis, Alzheimer's disease, Parkinson's disease, glioblastoma and amyotrophic lateral sclerosis. Finally, we explore the proposed mechanisms through which niacin may ameliorate neuropathology. While several questions remain, the prospect of niacin as a therapeutic to alleviate neurological impairment is promising.

Therapeutic application of natural products: NAD+ metabolism as potential target

BACKGROUND

Nicotinamide adenine dinucleotide (NAD⁺) metabolism is involved in the entire physiopathological process and is critical to human health. Long-term imbalance in NAD⁺ homeostasis is associated with various diseases, including non-alcoholic fatty liver disease, diabetes mellitus, cardiovascular diseases, neurodegenerative disorders, aging, and cancer, making it a potential target for effective therapeutic strategies. Currently, several natural products that target NAD⁺ metabolism have been widely reported to have significant therapeutic effects, but systematic summaries are lacking.

PURPOSE

To summarize the latest findings on the prevention and treatment of various diseases through the regulation of NAD⁺ metabolism by various natural products in vivo and in vitro models, and evaluate the toxicities of the natural products.

METHODS

PubMed, Web of Science, and ScienceDirect were searched using the keywords "natural products sources," "toxicology," "NAD⁺ clinical trials," and "NAD⁺," and/or paired with "natural products" and "diseases" for studies published within the last decade until January 2023.

RESULTS

We found that the natural products mainly include phenols (curcumin, cyclocurcumin, 4-hydroxybenzyl alcohol, salvianolic acid B, pterostilbene, EGCG), flavonoids (pinostrobin, apigenin, acacetin, tilianin, kaempferol, quercetin, isoliquiritigenin, luteolin, silybin, hydroxysafflor yellow A, scutellarin), glycosides (salidroside), quinones (emodin, embelin, β-LAPachone, shikonin), terpenoids (notoginsenoside R1, ginsenoside F2, ginsenoside Rd, ginsenoside Rb1, ginsenoside Rg3, thymoquinone, genipin), pyrazines (tetramethylpyrazine), alkaloids (evodiamine, berberine), and phenylpropanoids (ferulic acid). These natural products have antioxidant, energy-producing, anti-inflammatory, anti-apoptotic and anti-aging effects, which mainly influence the NAMPT/NAD⁺/SIRT, AMPK/SIRT1/PGC-1α, Nrf2/HO-1, PKCs/PARPs/NF-κB, and AMPK/Nrf2/mTOR signaling pathways, thereby regulating NAD⁺ metabolism to prevent and treat various diseases. These natural products have been shown to be safe, tolerable and have fewer adverse effects in various in vivo and in vitro studies and clinical trials.

CONCLUSION

We evaluated the toxic effects of natural products and summarized the available clinical trials on NAD⁺ metabolism, as well as the recent advances in the therapeutic application of natural products targeting NAD⁺ metabolism, with the aim to provide new insights into the treatment of multiple disorders.

Longitudinal metabolomics analysis reveals the acute effect of cysteine and NAC included in the combined metabolic activators

Growing evidence suggests that the depletion of plasma NAD⁺ and glutathione (GSH) may play an important role in the development of metabolic disorders. The administration of Combined Metabolic Activators (CMA), consisting of GSH and NAD⁺ precursors, has been explored as a promising therapeutic strategy to target multiple altered pathways associated with the pathogenesis of the diseases. Although studies have examined the therapeutic effect of CMA that contains N-acetyl-l-cysteine (NAC) as a metabolic activator, a system-wide comparison of the metabolic response to the administration of CMA with NAC and cysteine remains lacking. In this placebo-controlled study, we studied the acute effect of the CMA administration with different metabolic activators, including NAC or cysteine with/without nicotinamide or flush free niacin, and performed longitudinal untargeted-metabolomics profiling of plasma obtained from 70 well-characterized healthy volunteers. The time-series metabolomics data revealed the metabolic pathways affected after the administration of CMAs showed high similarity between CMA containing nicotinamide and NAC or cysteine as metabolic activators. Our analysis also showed that CMA with cysteine is well-tolerated and safe in healthy individuals throughout the study. Last, our study systematically provided insights into a complex and dynamics landscape involved in amino acid, lipid and nicotinamide metabolism, reflecting the metabolic responses to CMA administration containing different metabolic activators.

Regulation of cleavage embryo genes upon DRP1 inhibition in mouse embryonic stem cells

Dynamic-related protein 1 (DRP1) is a key protein of mitochondrial fission. In this study, we found that inhibition of activity of DRP1 led to increased levels of cleavage embryo genes in mouse embryonic stem cells (mESCs), which might reflect a transient totipotency status derived from pluripotency. This result indicates that DRP1 inhibition in mESCs leads to a tendency to obtain a new expression profile similar to that of the 2C-like state. Meanwhile, we also noticed that the glycolysis/gluconeogenesis pathway and its related enzymes were significantly downregulated, and the key glycolytic enzymes were also downregulated in various 2C-like cells. Moreover, when DRP1 activity was inhibited from the late zygote when cleavage embryo genes started to express, development of early embryos was inhibited, and these cleavage embryo genes failed to be efficiently silenced at the late 2-cell (2C) stage. Taken together, our result shows that DRP1 plays an important role in silencing cleavage embryo genes for totipotency-to-pluripotency transition.

NAD+ metabolism-based immunoregulation and therapeutic potential

Nicotinamide adenine dinucleotide (NAD⁺) is a critical metabolite that acts as a cofactor in energy metabolism, and serves as a cosubstrate for non-redox NAD⁺-dependent enzymes, including sirtuins, CD38 and poly(ADP-ribose) polymerases. NAD⁺ metabolism can regulate functionality attributes of innate and adaptive immune cells and contribute to inflammatory responses. Thus, the manipulation of NAD⁺ bioavailability can reshape the courses of immunological diseases. Here, we review the basics of NAD⁺ biochemistry and its roles in the immune response, and discuss current challenges and the future translational potential of NAD⁺ research in the development of therapeutics for inflammatory diseases, such as COVID-19.

Biomarkers of aging

Aging biomarkers are a combination of biological parameters to (i) assess age-related changes, (ii) track the physiological aging process, and (iii) predict the transition into a pathological status. Although a broad spectrum of aging biomarkers has been developed, their potential uses and limitations remain poorly characterized. An immediate goal of biomarkers is to help us answer the following three fundamental questions in aging research: How old are we? Why do we get old? And how can we age slower? This review aims to address this need. Here, we summarize our current knowledge of biomarkers developed for cellular, organ, and organismal levels of aging, comprising six pillars: physiological characteristics, medical imaging, histological features, cellular alterations, molecular changes, and secretory factors. To fulfill all these requisites, we propose that aging biomarkers should qualify for being specific, systemic, and clinically relevant.

Reverse Electron Transport at Mitochondrial Complex I in Ischemic Stroke, Aging, and Age-Related Diseases

Stroke is one of the leading causes of morbidity and mortality worldwide. A main cause of brain damage by stroke is ischemia-reperfusion (IR) injury due to the increased production of reactive oxygen species (ROS) and energy failure caused by changes in mitochondrial metabolism. Ischemia causes a build-up of succinate in tissues and changes in the mitochondrial NADH: ubiquinone oxidoreductase (complex I) activity that promote reverse electron transfer (RET), in which a portion of the electrons derived from succinate are redirected from ubiquinol along complex I to reach the NADH dehydrogenase module of complex I, where matrix NAD+ is converted to NADH and excessive ROS is produced. RET has been shown to play a role in macrophage activation in response to bacterial infection, electron transport chain reorganization in response to changes in the energy supply, and carotid body adaptation to changes in the oxygen levels. In addition to stroke, deregulated RET and RET-generated ROS (RET-ROS) have been implicated in tissue damage during organ transplantation, whereas an RET-induced NAD+/NADH ratio decrease has been implicated in aging, age-related neurodegeneration, and cancer. In this review, we provide a historical account of the roles of ROS and oxidative damage in the pathogenesis of ischemic stroke, summarize the latest developments in our understanding of RET biology and RET-associated pathological conditions, and discuss new ways to target ischemic stroke, cancer, aging, and age-related neurodegenerative diseases by modulating RET.

Reverse electron transfer is activated during aging and contributes to aging and age-related disease

Mechanisms underlying the depletion of NAD+ and accumulation of reactive oxygen species (ROS) in aging and age-related disorders remain poorly defined. We show that reverse electron transfer (RET) at mitochondrial complex I, which causes increased ROS production and NAD+ to NADH conversion and thus lowered NAD+ /NADH ratio, is active during aging. Genetic or pharmacological inhibition of RET decreases ROS production and increases NAD+ /NADH ratio, extending the lifespan of normal flies. The lifespan-extending effect of RET inhibition is dependent on NAD+ -dependent Sirtuin, highlighting the importance of NAD+ /NADH rebalance, and on longevity-associated Foxo and autophagy pathways. RET and RET-induced ROS and NAD+ /NADH ratio changes are prominent in human induced pluripotent stem cell (iPSC) model and fly models of Alzheimer's disease (AD). Genetic or pharmacological inhibition of RET prevents the accumulation of faulty translation products resulting from inadequate ribosome-mediated quality control, rescues relevant disease phenotypes, and extends the lifespan of Drosophila and mouse AD models. Deregulated RET is therefore a conserved feature of aging, and inhibition of RET may open new therapeutic opportunities in the context of aging and age-related diseases including AD.

Targeting CD38 to Suppress Osteoarthritis Development and Associated Pain After Joint Injury in Mice

OBJECTIVE

This study was undertaken to determine the role of CD38, which can function as an enzyme to degrade NAD⁺ , in osteoarthritis (OA) development.

METHODS

Human knee cartilage from normal donors and OA donors were examined for CD38 expression. "Gain-of-function," through overexpression of CD38 via transient transfection, and "loss-of-function," through pharmacologic inhibition of CD38, approaches were used to assess the effects of CD38 on intracellular NAD⁺ :NADH ratio and catabolic activity in chondrocytes. We also initiated joint injury-induced OA by surgical destabilization of the medial meniscus (DMM) in CD38 knockout mice and wild-type (WT; C57BL/6) mice and in WT male mice in the presence or absence of apigenin treatment. Cartilage degradation, synovial inflammation, subchondral bone changes, and pain behavior were evaluated after DMM surgery. We also examined expression of CD38 and the neuropeptide calcitonin gene-related peptide (CGRP) in knee sections from these mice.

RESULTS

CD38 expression was up-regulated in human knee OA cartilage and in chondrocytes stimulated with the proinflammatory cytokine interleukin-1β (IL-1β). Overexpression of CD38 in chondrocytes resulted in reduced cellular NAD⁺ :NADH ratio and augmented catabolic responses to IL-1β. These effects were reversed by pharmacologic inhibition of CD38. Cartilage degradation and synovial inflammation, associated with increased CD38 expression in cartilage and synovium, osteophyte formation and subchondral bone sclerosis, and pain-like behavior linked to increased CGRP expression in the synovium were observed in WT mice after joint injury. Such effects were significantly reduced in mice deficient in CD38 through either genetic knockout or pharmacologic inhibition.

CONCLUSION

CD38 deficiency exerts OA disease-modifying effects. Inhibition of CD38 has the potential to be a novel therapeutic approach for OA treatment.

Early loss of endogenous NAD+ following rotenone treatment leads to mitochondrial dysfunction and Sarm1 induction that is ameliorated by PARP inhibition

Sarm1 is an evolutionary conserved innate immune adaptor protein that has emerged as a primary regulator of programmed axonal degeneration over the past decade. In vitro structural insights have revealed that although Sarm1 induces energy depletion by breaking down nicotinamide adenine dinucleotide⁺ (NAD⁺ ), it is also allosterically inhibited by NAD⁺ . However, how NAD⁺ levels modulate the activation of intracellular Sarm1 has not been elucidated so far. This study focuses on understanding the events leading to Sarm1 activation in both neuronal and non-neuronal cells using the mitochondrial complex I inhibitor rotenone. Here, we report the regulation of rotenone-induced cell death by loss of NAD⁺ that may act as a 'biological trigger' of Sarm1 activation. Our study revealed that early loss of endogenous NAD⁺ levels arising due to PARP1 hyperactivation preceded Sarm1 induction following rotenone treatment. Interestingly, replenishing NAD⁺ levels by the PARP inhibitor, PJ34 restored mitochondrial complex I activity and also prevented subsequent Sarm1 activation in rotenone-treated cells. These cellular data were further validated in Drosophila melanogaster where a significant reduction in rotenone-mediated loss of locomotor abilities, and reduced dSarm expression was observed in the flies following PARP inhibition. Taken together, these observations not only uncover a novel regulation of Sarm1 induction by endogenous NAD⁺ levels but also point towards an important understanding on how PARP inhibitors could be repurposed in the treatment of mitochondrial complex I deficiency disorders.

An Electrochemical Nanosensor for Monitoring the Dynamics of Intracellular H2 O2 Upon NADH Treatment

Reactive oxygen species (ROS)-based therapeutic strategies play an important role in cancer treatment. However, in situ, real-time and quantitative analysis of intracellular ROS in cancer treatment for drug screening is still a challenge. Herein we report one selective hydrogen peroxide (H₂ O₂ ) electrochemical nanosensor, which is prepared by electrodeposition of Prussian blue (PB) and polyethylenedioxythiophene (PEDOT) onto carbon fiber nanoelectrode. With the nanosensor, we find that the level of intracellular H₂ O₂ increases with NADH treatment and that increase is dose-dependent to the concentration of NADH. High-dose of NADH (above 10 mM) can induce cell death and intratumoral injection of NADH is validated for inhibiting tumor growth in mice. This study highlights the potential of electrochemical nanosensor for tracking and understanding the role of H₂ O₂ in screening new anticancer drug.

Nanosystems for oxidative stress regulation in the anti-inflammatory therapy of acute kidney injury

Acute kidney injury (AKI) is a clinical syndrome that results from a rapid decline in renal structure or renal functional impairment with the main pathological feature of sublethal and lethal damage to renal tubular cells. However, many potential therapeutic agents cannot achieve the desired therapeutic effect because of their poor pharmacokinetics and short retention time in the kidneys. With the recent emergence and progress of nanotechnology, nanodrugs with unique physicochemical properties could prolong circulation time, enhance efficient targeted delivery, and elevate the accumulation of therapeutics that can cross the glomerular filtration barrier and indicate comprehensive application prospects in the prevention and treatment of AKI. In this review, various types of nanosystems (such as liposomes, polymeric nanosystems, inorganic nanoparticles and cell-derived extracellular vesicles) are designed and applied to improve the pharmacokinetics of drug formation, which could further relieve the burden on the kidneys caused by the final cumulative dose of drugs in conventional treatments. Moreover, the passive or active targeting effect of nanosystems can also reduce the total therapeutic dose and off-target adverse effects on other organs. Nanodelivery systems for treating AKI that alleviate oxidative stress-induced renal cell damage and regulate the inflammatory kidney microenvironment are summarized.

Beyond Pellagra-Research Models and Strategies Addressing the Enduring Clinical Relevance of NAD Deficiency in Aging and Disease

Research into the functions of nicotinamide adenine dinucleotide (NAD) has intensified in recent years due to the insight that abnormally low levels of NAD are involved in many human pathologies including metabolic disorders, neurodegeneration, reproductive dysfunction, cancer, and aging. Consequently, the development and validation of novel NAD-boosting strategies has been of central interest, along with the development of models that accurately represent the complexity of human NAD dynamics and deficiency levels. In this review, we discuss pioneering research and show how modern researchers have long since moved past believing that pellagra is the overt and most dramatic clinical presentation of NAD deficiency. The current research is centered on common human health conditions associated with moderate, but clinically relevant, NAD deficiency. In vitro and in vivo research models that have been developed specifically to study NAD deficiency are reviewed here, along with emerging strategies to increase the intracellular NAD concentrations.

Evolving roles of CD38 metabolism in solid tumour microenvironment

Given that plenty of clinical findings and reviews have already explained in detail on the progression of CD38 in multiple myeloma and haematological system tumours, here we no longer give unnecessary discussion on the above progression. Though therapeutic antibodies have been regarded as a greatest breakthrough in multiple myeloma immunotherapies due to the durable anti-tumour responses in the clinic, but the role of CD38 in the immunologic regulation and evasion of non-hematopoietic solid tumours are just initiated and controversial. Therefore, we will focus on the bio-function of CD38 enzymatic substrates or metabolites in the variety of non-hematopoietic malignancies and the potential therapeutic value of targeting the CD38-NAD+ or CD38-cADPR/ADPR signal axis. Though limited, we review some ongoing researches and clinical trials on therapeutic approaches in solid tumour as well.

NMNAT2: An important metabolic enzyme affecting the disease progression

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

Development of prognostic indicator based on NAD+ metabolism related genes in glioma

Background

Studies have shown that Nicotinamide adenine dinucleotide (NAD+) metabolism can promote the occurrence and development of glioma. However, the specific effects and mechanisms of NAD+ metabolism in glioma are unclear and there were no systematic researches about NAD+ metabolism related genes to predict the survival of patients with glioma.

Methods

The research was performed based on expression data of glioma cases in the Cancer Genome Atlas (TCGA) and Chinese Glioma Genome Atlas (CGGA) databases. Firstly, TCGA-glioma cases were classified into different subtypes based on 49 NAD+ metabolism-related genes (NMRGs) by consensus clustering. NAD+ metabolism-related differentially expressed genes (NMR-DEGs) were gotten by intersecting the 49 NMRGs and differentially expressed genes (DEGs) between normal and glioma samples. Then a risk model was built by Cox analysis and the least shrinkage and selection operator (LASSO) regression analysis. The validity of the model was verified by survival curves and receiver operating characteristic (ROC) curves. In addition, independent prognostic analysis of the risk model was performed by Cox analysis. Then, we also identified different immune cells, HLA family genes and immune checkpoints between high and low risk groups. Finally, the functions of model genes at single-cell level were also explored.

Results

Consensus clustering classified glioma patients into two subtypes, and the overall survival (OS) of the two subtypes differed. A total of 11 NAD+ metabolism-related differentially expressed genes (NMR-DEGs) were screened by overlapping 5,995 differentially expressed genes (DEGs) and 49 NAD+ metabolism-related genes (NMRGs). Next, four model genes, PARP9, BST1, NMNAT2, and CD38, were obtained by Cox regression and least absolute shrinkage and selection operator (Lasso) regression analyses and to construct a risk model. The OS of high-risk group was lower. And the area under curves (AUCs) of Receiver operating characteristic (ROC) curves were >0.7 at 1, 3, and 5 years. Cox analysis showed that age, grade G3, grade G4, IDH status, ATRX status, BCR status, and risk Scores were reliable independent prognostic factors. In addition, three different immune cells, Mast cells activated, NK cells activated and B cells naive, 24 different HLA family genes, such as HLA-DPA1 and HLA-H, and 8 different immune checkpoints, such as ICOS, LAG3, and CD274, were found between the high and low risk groups. The model genes were significantly relevant with proliferation, cell differentiation, and apoptosis.

Conclusion

The four genes, PARP9, BST1, NMNAT2, and CD38, might be important molecular biomarkers and therapeutic targets for glioma patients.

Quantification of localized NAD+ changes reveals unique specificity of NAD+ regulation in the hypothalamus

Recently, it has become a consensus that systemic decreases in NAD+ are a critical trigger for age-associated functional decline in multiple tissues and organs. The hypothalamus, which contains several functionally distinct subregions called nuclei, functions as a high-order control center of aging in mammals. However, due to a technical difficulty, how NAD+ levels change locally in each hypothalamic nucleus during aging remains uninvestigated. We were able to establish a new combinatorial methodology, using laser-captured microdissection (LCM) and high-performance liquid chromatography (HPLC), to accurately measure NAD+ levels in small tissue samples. We applied this methodology to examine local NAD+ changes in hypothalamic nuclei and found that NAD+ levels were decreased significantly in the arcuate nucleus (ARC), ventromedial hypothalamus (VMH), and lateral hypothalamus (LH), but not in the dorsomedial hypothalamus (DMH) of 22-month-old mice, compared to those of 3-month-old mice. The administration of nicotinamide mononucleotide (NMN) significantly increased NAD+ levels in all these hypothalamic nuclei. Interestingly, the administration of extracellular nicotinamide phosphoribosyltransferase-containing extracellular vesicles (eNampt-EVs) purified from young mice increased NAD+ levels in the ARC and DMH. These results reveal the unique specificity of NAD+ regulation in the hypothalamus during aging.

Integration of parallel metabolomics and transcriptomics reveals metabolic patterns in porcine oocytes during maturation

Well-controlled metabolism is the prerequisite for optimal oocyte development. To date, numerous studies have focused mainly on the utilization of exogenous substrates by oocytes, whereas the underlying mechanism of intrinsic regulation during meiotic maturation is less characterized. Herein, we performed an integrated analysis of parallel metabolomics and transcriptomics by isolating porcine oocytes at three time points, cooperatively depicting the global picture of the metabolic patterns during maturation. In particular, we identified the novel metabolic features during porcine oocyte meiosis, such as the fall in bile acids, the active one-carbon metabolism and a progressive decline in nucleotide metabolism. Collectively, the current study not only provides a comprehensive multiple omics data resource, but also may facilitate the discovery of molecular biomarkers that could be used to predict and improve oocyte quality.

Nicotinamide prevention in diabetes-induced alterations in the rat liver

Objective. The study was performed to elucidate whether nicotinamide (NAm) can attenuate the diabetes-induced liver damage by correction of ammonia detoxifying function and disbalance of NAD-dependent processes in diabetic rats. Methods. After four weeks of streptozotocin-induced diabetes, Wistar male rats were treated for two weeks with or without NAm. Urea concentration, arginase, and glutamine synthetase activities, NAD+ levels, and NAD+/NADH ratio were measured in cytosolic liver extracts. Expression of parp-1 gene in the liver was estimated by quantitative polymerase chain reaction and PARP-1 cleavage evaluated by Western blotting. Results. Despite the blood plasma lipid peroxidation products in diabetic rats were increased by 60%, the activity of superoxide dismutase (SOD) was reduced. NAm attenuated the oxidative stress, but did not affect the enzyme activity in diabetic rats. In liver of the diabetic rats, urea concentration and arginase activity were significantly higher than in the controls. The glutamine synthetase activity was decreased. Decline in NAD+ level and cytosolic NAD+/NADH ratio in the liver of diabetic rats was observed. Western blot analysis demonstrated a significant up-regulation of PARP-1 expression accompanied by the enzyme cleavage in the diabetic rat liver. However, no correlation was seen between mRNA expression of parp-1 gene and PARP-1 protein in the liver of diabetic rats. NAm markedly attenuated PARP-1 cleavage induced by diabetes, but did not affect the parp-1 gene expression. Conclusions. NAm counteracts diabetes-induced impairments in the rat liver through improvement of its detoxifying function, partial restoration of oxidative stress, NAD+ level, normalization of redox state of free cytosolic NAD+/NADH-couples, and prevention of PARP-1 cleavage.

Modulation of redox homeostasis: A strategy to overcome cancer drug resistance

Cancer treatment is hampered by resistance to conventional therapeutic strategies, including chemotherapy, immunotherapy, and targeted therapy. Redox homeostasis manipulation is one of the most effective innovative treatment techniques for overcoming drug resistance. Reactive oxygen species (ROS), previously considered intracellular byproducts of aerobic metabolism, are now known to regulate multiple signaling pathways as second messengers. Cancer cells cope with elevated amounts of ROS during therapy by upregulating the antioxidant system, enabling tumor therapeutic resistance via a variety of mechanisms. In this review, we aim to shed light on redox modification and signaling pathways that may contribute to therapeutic resistance. We summarized the molecular mechanisms by which redox signaling-regulated drug resistance, including altered drug efflux, action targets and metabolism, enhanced DNA damage repair, maintained stemness, and reshaped tumor microenvironment. A comprehensive understanding of these interrelationships should improve treatment efficacy from a fundamental and clinical research point of view.

Monitoring NAD(H) and NADP(H) dynamics during organismal development with genetically encoded fluorescent biosensors

Cell metabolism plays vital roles in organismal development, but it has been much less studied than transcriptional and epigenetic control of developmental programs. The difficulty might be largely attributed to the lack of in situ metabolite assays. Genetically encoded fluorescent sensors are powerful tools for noninvasive metabolic monitoring in living cells and in vivo by highly spatiotemporal visualization. Among all living organisms, the NAD(H) and NADP(H) pools are essential for maintaining redox homeostasis and for modulating cellular metabolism. Here, we introduce NAD(H) and NADP(H) biosensors, present example assays in developing organisms, and describe promising prospects for how sensors contribute to developmental biology research.

Prognostic value of nicotinamide adenine dinucleotide (NAD+) metabolic genes in patients with stomach adenocarcinoma based on bioinformatics analysis

Background

Because stomach adenocarcinoma (STAD) has a poor prognosis, it is necessary to explore new prognostic genes to stratify patients to guide existing individualized treatments.

Methods

Survival and clinical information, RNA-seq data and mutation data of STAD were acquired from The Cancer Genome Atlas (TCGA) database. Fifty-one nicotinamide adenine dinucleotide (NAD⁺) metabolism-related genes (NMRGs) were obtained from the Kyoto Encyclopedia of Genes and Genomes (KEGG) and Reactome databases. Differentially expressed NMRGs (DE-NMRGs) between STAD and normal samples were screened, and consistent clustering analysis of STAD patients was performed based on the DE-NMRGs. Survival analysis, Gene Set Enrichment Analysis (GSEA), mutation frequency analysis, immune microenvironment analysis and drug prediction were performed among different clusters. Additionally, the differentially expressed genes (DEGs) among different clusters were selected, and the intersections of DEGs and DE-NMRGs were selected as the prognostic genes. Finally, quantitative real-time polymerase chain reaction (qRT-PCR) was performed on a human gastric mucosa epithelial cell line and cancer cell line to verify the expression of the prognostic genes.

Results

A total of 27 DE-NMRGs and two clusters were selected. There was a difference in survival between clusters 1 and 2. Furthermore, 18 DE-NMRGs were significantly different between clusters 1 and 2. The different Gene Ontology (GO) biological processes and KEGG pathways between clusters 1 and 2 were mainly enriched in cyclic nucleotide mediated signaling, synaptic signaling and hedgehog signaling pathway, etc. The somatic mutation frequencies were different between the two clusters, and TTN was the highest mutated gene in the patients of the clusters 1 and 2. Additionally, eight immune cells, immune score, stromal score, and estimate score were different between clusters 1 and 2. The patients in cluster 2 were sensitive to CTLA4 inhibitor treatment. Furthermore, the top five drugs (AP.24534, BX.795, Midostaurin, WO2009093927 and CCT007093) were significantly higher in cluster 1 than in cluster 2. Finally, three genes (AOX1, NNMT and PTGIS) were acquired as prognostic, and their expressions were consistent with the results of bioinformatics analysis.

Conclusions

Three prognostic genes related to NAD⁺ metabolism in STAD were screened out, which provides a theoretical basis and reference value for future treatment and prognosis of STAD.

Integrating RNA-seq and scRNA-seq to explore the biological significance of NAD + metabolism-related genes in the initial diagnosis and relapse of childhood B-cell acute lymphoblastic leukemia

BACKGROUND

Nicotinamide Adenine Dinucleotide (NAD) depletion is reported to be a potential treatment for B-cell Acute Lymphoblastic Leukemia (B-ALL), but the mechanism of NAD metabolism-related genes (NMRGs) in B-ALL relapse remains unclear.

METHODS

Transcriptome data (GSE3912), and single-cell sequencing data (GSE130116) of B-ALL patients were downloaded from Gene Expression Omnibus (GEO) database. NMRGs were sourced from Kyoto Encyclopedia of Genes and Genomes (KEGG) and Reactome databases. Further, the differentially expressed NMRGs (DE-NMRGs) were selected from the analysis between initial diagnosis and relapse B-ALL samples, which further performed functional enrichment analyses. The biomarkers were obtained through random forest (RF) algorithm and repeated cross validation. Additionally, cell type identification by estimating relative subsets of RNA transcripts (CIBERSORT) algorithm was used to evaluate the immune cell differences between the initial diagnosis and relapse samples, and the correlations between biomarkers and gene markers of differential immune cells were analyzed. Furthermore, single cell RNA sequencing was conducted in the GSE130116 dataset to find key cell clusters. In addition, according to biomarkers expressions, cell clusters were categorized into high and low biomarker expression groups, and Gene Set Enrichment Analysis (GSEA) analysis was performed on them. Finally, the cell clusters with the highest expression of biomarkers were selected to explore the roles of biomarkers in different cell clusters and identify transcription factors (TFs) influencing biological markers.

RESULTS

23 DE-NMRGs were screened out, which were mainly enriched in nucleoside phosphate metabolic process, nucleotide metabolic process, and Nicotinate and nicotinamide metabolism. Moreover, 3 biomarkers (NADSYN1, SIRT3, and PARP6) were identified from the machine learning. CIBERSORT results demonstrated that four types of immune cells (B Cells naive, Monocyte, Neutrophils, and T cells CD4 memory Activated) were significantly different between the initial diagnosis and the relapse B-ALL samples, and there were strong correlations between biomarkers and differential immune cells such as positive correlation between NADSYN1 and B Cells naive. The single cell analyses showed that the biomarkers were highly expressed in common myeloid progenitors (CMP), granulocyte-macrophage progenitor (GMP), and megakaryocyte-erythroid progenitor (MEP) cell clusters. Gene set enrichment analysis (GSEA) results indicated that 55 GO terms and 3 KEGG pathways were enriched by the genes in high and low biomarker expression groups. It was found that TF CREB3L2(+) was significantly reduced in the high expression group, which may be the TF affecting biomarkers in the high expression group.

CONCLUSION

This study identified NADSYN1, SIRT3, and PARP6 as the biomarkers of B-ALL, explored biological significance of NMRGs in the initial diagnosis and relapse of B-ALL, and revealed mechanism of biomarkers at the level of the single cell.

Endogenous metabolism in endothelial and immune cells generates most of the tissue vitamin B3 (nicotinamide)

In mammals, nicotinamide (NAM) is the primary NAD precursor available in circulation, a signaling molecule, and a precursor for methyl-nicotinamide (M-NAM) synthesis. However, our knowledge about how the body regulates tissue NAM levels is still limited. Here we demonstrate that dietary vitamin B₃ partially regulates plasma NAM and NAM-derived metabolites, but not their tissue levels. We found that NAD de novo synthesis from tryptophan contributes to plasma and tissue NAM, likely by providing substrates for NAD-degrading enzymes. We also demonstrate that tissue NAM is mainly generated by endogenous metabolism and that the NADase CD38 is the main enzyme that produces tissue NAM. Tissue-specific CD38-floxed mice revealed that CD38 activity on endothelial and immune cells is the major contributor to tissue steady-state levels of NAM in tissues like spleen and heart. Our findings uncover the presence of different pools of NAM in the body and a central role for CD38 in regulating tissue NAM levels.

Role of NAD+ and FAD in Ischemic Stroke Pathophysiology: An Epigenetic Nexus and Expanding Therapeutic Repertoire

The redox coenzymes viz., oxidized β-nicotinamide adenine dinucleotide (NAD⁺) and flavin adenine dinucleotide (FAD) by way of generation of optimal reducing power and cellular energy currency (ATP), control a staggering array of metabolic reactions. The prominent cellular contenders for NAD⁺ utilization, inter alia, are sirtuins (SIRTs) and poly(ADP-ribose) polymerase (PARP-1), which have been significantly implicated in ischemic stroke (IS) pathogenesis. NAD⁺ and FAD are also two crucial epigenetic enzyme-required metabolites mediating histone deacetylation and poly(ADP-ribosyl)ation through SIRTs and PARP-1 respectively, and demethylation through FAD-mediated lysine specific demethylase activity. These enzymes and post-translational modifications impinge on the components of neurovascular unit, primarily neurons, and elicit diverse functional upshots in an ischemic brain. These could be circumstantially linked with attendant cognitive deficits and behavioral outcomes in post-stroke epoch. Parsing out the contribution of NAD⁺/FAD-synthesizing and utilizing enzymes towards epigenetic remodeling in IS setting, together with their cognitive and behavioral associations, combined with possible therapeutic implications will form the crux of this review.

SIRT6 overexpression retards renal interstitial fibrosis through targeting HIPK2 in chronic kidney disease

Introduction: Renal interstitial fibrosis is a common pathophysiological change in the chronic kidney disease (CKD). Nicotinamide adenine dinucleotide (NAD)-dependent deacetylase sirtuin 6 (SIRT6) is demonstrated to protect against kidney injury. Vitamin B3 is the mostly used form of NAD precursors. However, the role of SIRT6 overexpression in renal interstitial fibrosis of CKD and the association between dietary vitamin B3 intake and renal function remain to be elucidated.

Methods: Wild-type (WT) and SIRT6-transgene (SIRT6-Tg) mice were given with high-adenine diets to establish CKD model. HK2 cells were exposed to transforming growth factor β1 (TGF-β1) in vitro to explore related mechanism. Population data from Multi-Ethnic Study of Atherosclerosis (MESA) was used to examine the association between dietary vitamin B3 intake and renal function decline.

Results: Compared to WT mice, SIRT6-Tg mice exhibited alleviated renal interstitial fibrosis as evidenced by reduced collagen deposit, collagen I and α-smooth muscle actin expression. Renal function was also improved in SIRT6-Tg mice. Homeodomain interacting protein kinase 2 (HIPK2) was induced during the fibrogenesis in CKD, while HIPK2 was downregulated after SIRT6 overexpression. Further assay in vitro confirmed that SIRT6 depletion exacerbated epithelial-to-mesenchymal transition of HK2 cells, which might be linked with HIPK2 upregulation. HIPK2 was inhibited by SIRT6 in the post-transcriptional level. Population study indicated that higher dietary vitamin B3 intake was independently correlated with a lower risk of estimate glomerular filtration rate decline in those ≥65 years old during follow-up.

Conclusion: SIRT6/HIPK2 axis serves as a promising target of renal interstitial fibrosis in CKD. Dietary vitamin B3 intake is beneficial for renal function in the old people.

Pgc-1α controls epidermal stem cell fate and skin repair by sustaining NAD+ homeostasis during aging

OBJECTIVE

The epidermal barrier is renewed by the activation, proliferation, and differentiation of keratinocyte stem cells after injury and aging impedes this repair process through undefined mechanisms. We previously identified a gene signature of metabolic dysfunction in aged murine epidermis, but the precise regulators of epidermal repair and age-related growth defects are not well established. Aged mouse models as well as mice with conditional epidermal loss of the metabolic regulator, peroxisome proliferator-activated receptor gamma coactivator-1 alpha (Pgc-1α) were used to explore the cellular pathways which control skin repair after injury and stress.

METHODS

Aged mice or those with epidermal Pgc-1α deletion (epiPgc-1α KO) and young or Pgc1a^fl/fl controls were subjected to wound injury, UVB exposure or the inflammatory agent TPA. In vivo and ex vivo analyses of wound closure, skin structure, cell growth and stem cell differentiation were used to understand changes in epidermal re-growth and repair resulting from aging or Pgc-1α loss.

RESULTS

Aging impairs epidermal re-growth during wound healing and results in lower expression of Pgc-1α. Mice with conditional deletion of epidermal Pgc-1α exhibit greater inflammation- and UVB-induced cell differentiation, reduced proliferation, and slower wound healing. epiPgc-1α KO mice also displayed reduced keratinocyte NAD⁺ levels, shorter telomeres, and greater poly ADP-ribosylation, resulting in enhanced stress-stimulated p53 and p21 signaling. When NAD⁺ was reduced by Pgc-1α loss or pharmacologic inhibition of NAD⁺ synthesis, there was reduced stress-induced proliferation, increased differentiation, and protection against DNA damage via enhanced epidermal shedding. Similarly, aged mice exhibit disrupted epidermal NAD⁺ homeostasis and enhanced p53 activation, resulting in p21 growth arrest after wounding. NAD⁺ precursor treatment restores epidermal growth from old skin to that of young.

CONCLUSIONS

Our studies identify a novel role for epidermal Pgc-1α in controlling epidermal repair via its regulation of cellular NAD⁺ and downstream effects on p53-driven growth arrest. We also establish that parallel mechanisms are evident in aged epidermis, showing that NAD⁺ signaling is an important controller of physiologic skin repair and that dysfunction of this pathway contributes to age-related wound repair defects.

CD38 Mediates Lung Fibrosis by Promoting Alveolar Epithelial Cell Aging

Rationale: A prevailing paradigm recognizes idiopathic pulmonary fibrosis (IPF) originating from various alveolar epithelial cell (AEC) injuries, and there is a growing appreciation of AEC aging as a key driver of the pathogenesis. Despite this progress, it is incompletely understood what main factor(s) contribute to the worsened alveolar epithelial aging in lung fibrosis. It remains a challenge how to dampen AEC aging and thereby mitigate the disease progression. Objectives: To determine the role of AEC CD38 (cluster of differentiation 38) in promoting cellular aging and lung fibrosis. Methods: We used single-cell RNA sequencing, real-time PCR, flow cytometry, and Western blotting. Measurements and Main Results: We discovered a pivotal role of CD38, a cardinal nicotinamide adenine dinucleotide (NAD) hydrolase, in AEC aging and its promotion of lung fibrosis. We found increased CD38 expression in IPF lungs that inversely correlated with the lung functions of patients. CD38 was primarily located in the AECs of human lung parenchyma and was markedly induced in IPF AECs. Similarly, CD38 expression was elevated in the AECs of fibrotic lungs of young mice and further augmented in those of old mice, which was in accordance with a worsened AEC aging phenotype and an aggravated lung fibrosis in the old animals. Mechanistically, we found that CD38 elevation downregulated intracellular NAD, which likely led to the aging promoting impairment of the NAD-dependent cellular and molecular activities. Furthermore, we demonstrated that genetic and pharmacological inactivation of CD38 improved these NAD dependent events and ameliorated bleomycin-induced lung fibrosis. Conclusions: Our study suggests targeting alveolar CD38 as a novel and effective therapeutic strategy to treat this pathology.

Slc12a8 in the lateral hypothalamus maintains energy metabolism and skeletal muscle functions during aging

Sarcopenia and frailty are urgent socio-economic problems worldwide. Here we demonstrate a functional connection between the lateral hypothalamus (LH) and skeletal muscle through Slc12a8, a recently identified nicotinamide mononucleotide transporter, and its relationship to sarcopenia and frailty. Slc12a8-expressing cells are mainly localized in the LH. LH-specific knockdown of Slc12a8 in young mice decreases activity-dependent energy and carbohydrate expenditure and skeletal muscle functions, including muscle mass, muscle force, intramuscular glycolysis, and protein synthesis. LH-specific Slc12a8 knockdown also decreases sympathetic nerve signals at neuromuscular junctions and β2-adrenergic receptors in skeletal muscle, indicating the importance of the LH-sympathetic nerve-β2-adrenergic receptor axis. LH-specific overexpression of Slc12a8 in aged mice significantly ameliorates age-associated decreases in energy expenditure and skeletal muscle functions. Our results highlight an important role of Slc12a8 in the LH for regulation of whole-body metabolism and skeletal muscle functions and provide insights into the pathogenesis of sarcopenia and frailty during aging.

Human CD38 regulates B cell antigen receptor dynamic organization in normal and malignant B cells

CD38 is a multifunctional protein expressed on the surface of B cells in healthy individuals but also in B cell malignancies. Previous studies have suggested a connection between CD38 and components of the IgM class B cell antigen receptor (IgM-BCR) and its coreceptor complex. Here, we provide evidence that CD38 is closely associated with CD19 in resting B cells and with the IgM-BCR upon engagement. We show that targeting CD38 with an antibody, or removing this molecule with CRISPR/Cas9, inhibits the association of CD19 with the IgM-BCR, impairing BCR signaling in normal and malignant B cells. Together, our data suggest that CD38 is a new member of the BCR coreceptor complex, where it exerts a modulatory effect on B cell activation upon antigen recognition by regulating CD19. Our study also reveals a new mechanism where α-CD38 antibodies could be a valuable option in therapeutic approaches to B cell malignancies driven by aberrant BCR signaling.

CD38: An important regulator of T cell function

Cluster of differentiation 38 (CD38) is a multifunctional extracellular enzyme on the cell surface with NADase and cyclase activities. CD38 is not only expressed in human immune cells, such as lymphocytes and plasma cells, but also is abnormally expressed in a variety of tumor cells, which is closely related to the occurrence and development of tumors. T cells are one of the important immune cells in the body. As NAD consuming enzymes, CD38, ART2, SIRT1 and PARP1 are closely related to the number and function of T cells. CD38 may also influence the activity of ART2, SIRT1 and PARP1 through the CD38-NAD⁺ axis to indirectly affect the number and function of T cells. Thus, CD38-NAD⁺ axis has a profound effect on T cell activity. In this paper, we reviewed the role and mechanism of CD38⁺ CD4⁺ T cells / CD38⁺ CD8⁺ T cells in cellular immunity and the effects of the CD38-NAD⁺ axis on T cell activity. We also summarized the relationship between the CD38 expression level on T cell surface and disease prediction and prognosis, the effects of anti-CD38 monoclonal antibodies on T cell activity and function, and the role of anti-CD38 chimeric antigen receptor (CAR) T cell therapy in tumor immunity. This will provide an important theoretical basis for a comprehensive understanding of the relationship between CD38 and T cells.

Oxytocin Dynamics in the Body and Brain Regulated by the Receptor for Advanced Glycation End-Products, CD38, CD157, and Nicotinamide Riboside

Investigating the neurocircuit and synaptic sites of action of oxytocin (OT) in the brain is critical to the role of OT in social memory and behavior. To the same degree, it is important to understand how OT is transported to the brain from the peripheral circulation. To date, of these, many studies provide evidence that CD38, CD157, and receptor for advanced glycation end-products (RAGE) act as regulators of OT concentrations in the brain and blood. It has been shown that RAGE facilitates the uptake of OT in mother’s milk from the digestive tract to the cell surface of intestinal epithelial cells to the body fluid and subsequently into circulation in male mice. RAGE has been shown to recruit circulatory OT into the brain from blood at the endothelial cell surface of neurovascular units. Therefore, it can be said that extracellular OT concentrations in the brain (hypothalamus) could be determined by the transport of OT by RAGE from the circulation and release of OT from oxytocinergic neurons by CD38 and CD157 in mice. In addition, it has recently been found that gavage application of a precursor of nicotinamide adenine dinucleotide, nicotinamide riboside, for 12 days can increase brain OT in mice. Here, we review the evaluation of the new concept that RAGE is involved in the regulation of OT dynamics at the interface between the brain, blood, and intestine in the living body, mainly by summarizing our recent results due to the limited number of publications on related topics. And we also review other possible routes of OT recruitment to the brain.

NAD kinase promotes Staphylococcus aureus pathogenesis by supporting production of virulence factors and protective enzymes

Nicotinamide adenine dinucleotide phosphate (NADPH) is the primary electron donor for reductive reactions that are essential for the biosynthesis of major cell components in all organisms. Nicotinamide adenine dinucleotide kinase (NADK) is the only enzyme that catalyzes the synthesis of NADP(H) from NAD(H). While the enzymatic properties and physiological functions of NADK have been thoroughly studied, the role of NADK in bacterial pathogenesis remains unknown. Here, we used CRISPR interference to knock down NADK gene expression to address the role of this enzyme in Staphylococcus aureus pathogenic potential. We find that NADK inhibition drastically decreases mortality of zebrafish infected with S. aureus. Furthermore, we show that NADK promotes S. aureus survival in infected macrophages by protecting bacteria from antimicrobial defense mechanisms. Proteome-wide data analysis revealed that production of major virulence-associated factors is sustained by NADK. We demonstrate that NADK is required for expression of the quorum-sensing response regulator AgrA, which controls critical S. aureus virulence determinants. These findings support a key role for NADK in bacteria survival within innate immune cells and the host during infection.

Clinical and biochemical footprints of inherited metabolic diseases. VIII. Neoplasias

Cancer, caused by multiple cumulative pathogenic variants in tumor suppressor genes and proto-oncogenes, is a leading cause of mortality worldwide. The uncontrolled and rapid cell growth of the tumors requires a reprogramming of the complex cellular metabolic network to favor anabolism. Adequate management and treatment of certain inherited metabolic diseases might prevent the development of certain neoplasias, such as hepatocellular carcinoma in tyrosinemia type 1 or hepatocellular adenomas in glycogen storage disorder type 1a. We reviewed and updated the list of known metabolic etiologies associated with various types of benign and malignant neoplasias, finding 64 relevant inborn errors of metabolism. This is the eighth article of the series attempting to create a comprehensive list of clinical and metabolic differential diagnosis by system involvement.