Short-term administration of Nicotinamide Mononucleotide preserves cardiac mitochondrial homeostasis and prevents heart failure

Advancements in NMN biotherapy and research updates in the field of digestive system diseases

Nicotinamide mononucleotide (NMN), a crucial intermediate in NAD + synthesis, can rapidly transform into NAD + within the body after ingestion. NMN plays a pivotal role in several important biological processes, including energy metabolism, cellular aging, circadian rhythm regulation, DNA repair, chromatin remodeling, immunity, and inflammation. NMN has emerged as a key focus of research in the fields of biomedicine, health care, and food science. Recent years have witnessed extensive preclinical studies on NMN, offering valuable insights into the pathogenesis of age- and aging-related diseases. Given the sustained global research interest in NMN and the substantial market expectations for the future, here, we comprehensively review the milestones in research on NMN biotherapy over the past 10 years. Additionally, we highlight the current research on NMN in the field of digestive system diseases, identifying existing problems and challenges in the field of NMN research. The overarching aim of this review is to provide references and insights for the further exploration of NMN within the spectrum of digestive system diseases.

NAD metabolism and heart failure: Mechanisms and therapeutic potentials

Nicotinamide adenine dinucleotide provides the critical redox pair, NAD+ and NADH, for cellular energy metabolism. In addition, NAD+ is the precursor for de novo NADP+ synthesis as well as the co-substrates for CD38, poly(ADP-ribose) polymerase and sirtuins, thus, playing a central role in the regulation of oxidative stress and cell signaling. Declines of the NAD+ level and altered NAD+/NADH redox states have been observed in cardiometabolic diseases of various etiologies. NAD based therapies have emerged as a promising strategy to treat cardiovascular disease. Strategies that reduce NAD+ consumption or promote NAD+ production have repleted intracellular NAD+ or normalized NAD+/NADH redox in preclinical studies. These interventions have shown cardioprotective effects in multiple models suggesting a great promise of the NAD+ elevating therapy. Mechanisms for the benefit of boosting NAD+ level, however, remain incompletely understood. Moreover, despite the robust pre-clinical studies there are still challenges to translate the therapy to clinic. Here, we review the most up to date literature on mechanisms underlying the NAD+ elevating interventions and discuss the progress of human studies. We also aim to provide a better understanding of how NAD metabolism is changed in failing hearts with a particular emphasis on types of strategies employed and methods to target these pathways. Finally, we conclude with a comprehensive assessment of the challenges in developing NAD-based therapies for heart diseases, and to provide a perspective on the future of the targeting strategies.

NAD+ precursors prolong survival and improve cardiac phenotypes in a mouse model of Friedreich's Ataxia

Friedreich's ataxia (FRDA) is a progressive disorder caused by insufficient expression of frataxin, which plays a critical role in assembly of iron-sulfur centers in mitochondria. Individuals are cognitively normal but display a loss of motor coordination and cardiac abnormalities. Many ultimately develop heart failure. Administration of nicotinamide adenine dinucleotide-positive (NAD+) precursors has shown promise in human mitochondrial myopathy and rodent models of heart failure, including mice lacking frataxin in cardiomyocytes. We studied mice with systemic knockdown of frataxin (shFxn), which display motor deficits and early mortality with cardiac hypertrophy. Hearts in these mice do not "fail" per se but become hyperdynamic with small chamber sizes. Data from an ongoing natural history study indicate that hyperdynamic hearts are observed in young individuals with FRDA, suggesting that the mouse model could reflect early pathology. Administering nicotinamide mononucleotide or riboside to shFxn mice increases survival, modestly improves cardiac hypertrophy, and limits increases in ejection fraction. Mechanistically, most of the transcriptional and metabolic changes induced by frataxin knockdown are insensitive to NAD+ precursor administration, but glutathione levels are increased, suggesting improved antioxidant capacity. Overall, our findings indicate that NAD+ precursors are modestly cardioprotective in this model of FRDA and warrant further investigation.

Insight into the cardioprotective effects of melatonin: shining a spotlight on intercellular Sirt signaling communication

Cardiovascular diseases (CVDs) are the leading causes of death and illness worldwide. While there have been advancements in the treatment of CVDs using medication and medical procedures, these conventional methods have limited effectiveness in halting the progression of heart diseases to complete heart failure. However, in recent years, the hormone melatonin has shown promise as a protective agent for the heart. Melatonin, which is secreted by the pineal gland and regulates our sleep-wake cycle, plays a role in various biological processes including oxidative stress, mitochondrial function, and cell death. The Sirtuin (Sirt) family of proteins has gained attention for their involvement in many cellular functions related to heart health. It has been well established that melatonin activates the Sirt signaling pathways, leading to several beneficial effects on the heart. These include preserving mitochondrial function, reducing oxidative stress, decreasing inflammation, preventing cell death, and regulating autophagy in cardiac cells. Therefore, melatonin could play crucial roles in ameliorating various cardiovascular pathologies, such as sepsis, drug toxicity-induced myocardial injury, myocardial ischemia-reperfusion injury, hypertension, heart failure, and diabetic cardiomyopathy. These effects may be partly attributed to the modulation of different Sirt family members by melatonin. This review summarizes the existing body of literature highlighting the cardioprotective effects of melatonin, specifically the ones including modulation of Sirt signaling pathways. Also, we discuss the potential use of melatonin-Sirt interactions as a forthcoming therapeutic target for managing and preventing CVDs.

The therapeutic perspective of NAD+ precursors in age-related diseases

Nicotinamide adenine dinucleotide (NAD+) is the fundamental molecule that performs numerous biological reactions and is crucial for maintaining cellular homeostasis. Studies have found that NAD+ decreases with age in certain tissues, and age-related NAD+ depletion affects physiological functions and contributes to various aging-related diseases. Supplementation of NAD+ precursor significantly elevates NAD+ levels in murine tissues, effectively mitigates metabolic syndrome, enhances cardiovascular health, protects against neurodegeneration, and boosts muscular strength. Despite the versatile therapeutic functions of NAD+ in animal studies, the efficacy of NAD+ precursors in clinical studies have been limited compared with that in the pre-clinical study. Clinical studies have demonstrated that NAD+ precursor treatment efficiently increases NAD+ levels in various tissues, though their clinical proficiency is insufficient to ameliorate the diseases. However, the latest studies regarding NAD+ precursors and their metabolism highlight the significant role of gut microbiota. The studies found that orally administered NAD+ intermediates interact with the gut microbiome. These findings provide compelling evidence for future trials to further explore the involvement of gut microbiota in NAD+ metabolism. Also, the reduced form of NAD+ precursor shows their potential to raise NAD+, though preclinical studies have yet to discover their efficacy. This review sheds light on NAD+ therapeutic efficiency in preclinical and clinical studies and the effect of the gut microbiota on NAD+ metabolism.

Role and Potential Mechanisms of Nicotinamide Mononucleotide in Aging

Nicotinamide adenine dinucleotide (NAD+) has recently attracted much attention due to its role in aging and lifespan extension. NAD+ directly and indirectly affects many cellular processes, including metabolic pathways, DNA repair, and immune cell activities. These mechanisms are critical for maintaining cellular homeostasis. However, the decline in NAD+ levels with aging impairs tissue function, which has been associated with several age-related diseases. In fact, the aging population has been steadily increasing worldwide, and it is important to restore NAD+ levels and reverse or delay these age-related disorders. Therefore, there is an increasing demand for healthy products that can mitigate aging, extend lifespan, and halt age-related consequences. In this case, several studies in humans and animals have targeted NAD+ metabolism with NAD+ intermediates. Among them, nicotinamide mononucleotide (NMN), a precursor in the biosynthesis of NAD+, has recently received much attention from the scientific community for its anti-aging properties. In model organisms, ingestion of NMN has been shown to improve age-related diseases and probably delay death. Here, we review aspects of NMN biosynthesis and the mechanism of its absorption, as well as potential anti-aging mechanisms of NMN, including recent preclinical and clinical tests, adverse effects, limitations, and perceived challenges.

NAD in pathological cardiac remodeling: Metabolic regulation and beyond

Nicotinamide adenine dinucleotide (NAD) coenzymes are carriers of high energy electrons in metabolism and also play critical roles in numerous signaling pathways. NAD metabolism is decreased in various cardiovascular diseases. Importantly, stimulation of NAD biosynthesis protects against heart disease under different pathological conditions. In this review, we describe pathways for both generation and catabolism of NAD coenzymes and the respective changes of these pathways in the heart under cardiac diseases, including pressure overload, myocardial infarction, cardiometabolic disease, cancer treatment cardiotoxicity, and heart failure. We next provide an update on the strategies and treatments to increase NAD levels, such as supplementation of NAD precursors, in the heart that prevent or reverse cardiomyopathy. We also introduce the approaches to manipulate NAD consumption enzymes to ameliorate cardiac disease. Finally, we discuss the mechanisms associated with improvements in cardiac function by NAD coenzymes, differentiating between mitochondria-dependent effects and those independent of mitochondrial metabolism.

NAD+-A Hub of Energy Metabolism in Heart Failure

Heart failure is a condition where reduced levels of adenosine triphosphate (ATP) affect energy supply in myocardial cells. Nicotinamide adenine dinucleotide (NAD+) plays a crucial role as a coenzyme for electron transfer in energy metabolism. Decreased NAD+ levels in myocardial cells lead to inadequate ATP production and increased susceptibility to heart failure. Researchers are exploring ways to increase NAD+ levels to alleviate heart failure. Targets such as sirtuin2 (sirt2), sirtuin3 (sirt3), Poly (ADP-ribose) polymerase (PARP), and diastolic regulatory proteins are being investigated. NAD+ supplementation has shown promise, even in heart failure with preserved ejection fraction (HFpEF). By focusing on NAD+ as a central component of energy metabolism, it is possible to improve myocardial activity, heart function, and address energy deficiency in heart failure.

Nicotinamide Mononucleotide in the Context of Myocardiocyte Longevity

Cellular and subcellular metabolic activities are crucial processes involved in the regulation of intracellular homeostasis, including cellular and subcellular signaling pathways. Dysregulation of intracellular regulation mechanisms is catastrophic and cumulates into cell death. To overcome the issue of dysregulation of intracellular regulation mechanisms, the preservation of subcellular and extracellular components is essential to maintain healthy cells with increased longevity. Several physiopathological changes occur during cell ageing, one of which is the dysregulation of intracellular physiology of the oxidative phosphorylation process. Nicotinamide mononucleotide (NMN) remains in the debut of anti-aging therapeutic effect. Aged myocardiocyte characterized by disrupted NMN and or its precursors or signaling pathways. Simultaneously, several other pathophysiological occur that collectively impair intracellular homeostasis. The NMN role in the antiaging effect remains unclear and several hypotheses have been introduced into describing the mechanism and the potential outcomes from NMN exogenous supply. Correction of the impaired intracellular homeostasis includes correction to the NMN metabolism. Additionally, autophagy correction, which is the key element in the regulation of intracellular intoxication, including oxidative stress, unfolding protein response, and other degradation of intracellular metabolites. Several signaling pathways are involved in the regulation mechanism of NMN effects on myocardiocyte health and further longevity. NMN protects myocardiocytes from ischemic injury by reducing anabolism and, increasing catabolism and further passing the myocardiocytes into dormant status. NMN applications include ischemic heart, disease, and failed heart, as well as dilated cardiomyopathies. Cytosolic and mitochondrial NADPH are independently functioning and regulating. Each of these plays a role in the determination of the longevity of the myocardiocytes. NMN has a cornerstone in the functionality of Sirtuins, which are an essential anti-senescent intrinsic molecule. The study aims to assess the role of NMN in the longevity and antisenescent of myocardiocytes.

The Safety and Antiaging Effects of Nicotinamide Mononucleotide in Human Clinical Trials: an Update

The importance of nicotinamide adenine dinucleotide (NAD+) in human physiology is well recognized. As the NAD+ concentration in human skin, blood, liver, muscle, and brain are thought to decrease with age, finding ways to increase NAD+ status could possibly influence the aging process and associated metabolic sequelae. Nicotinamide mononucleotide (NMN) is a precursor for NAD+ biosynthesis, and in vitro/in vivo studies have demonstrated that NMN supplementation increases NAD+ concentration and could mitigate aging-related disorders such as oxidative stress, DNA damage, neurodegeneration, and inflammatory responses. The promotion of NMN as an antiaging health supplement has gained popularity due to such findings; however, since most studies evaluating the effects of NMN have been conducted in cell or animal models, a concern remains regarding the safety and physiological effects of NMN supplementation in the human population. Nonetheless, a dozen human clinical trials with NMN supplementation are currently underway. This review summarizes the current progress of these trials and NMN/NAD+ biology to clarify the potential effects of NMN supplementation and to shed light on future study directions.

NAD+ Precursors Nicotinamide Mononucleotide (NMN) and Nicotinamide Riboside (NR): Potential Dietary Contribution to Health

PURPOSE OF REVIEW

NAD+ is a vital molecule that takes part as a redox cofactor in several metabolic reactions besides being used as a substrate in important cellular signaling in regulation pathways for energetic, genotoxic, and infectious stress. In stress conditions, NAD+ biosynthesis and levels decrease as well as the activity of consuming enzymes rises. Dietary precursors can promote NAD+ biosynthesis and increase intracellular levels, being a potential strategy for reversing physiological decline and preventing diseases. In this review, we will show the biochemistry and metabolism of NAD+ precursors NR (nicotinamide riboside) and NMN (nicotinamide mononucleotide), the latest findings on their beneficial physiological effects, their interplay with gut microbiota, and the future perspectives for research in nutrition and food science fields.

RECENT FINDINGS

NMN and NR demonstrated protect against diabetes, Alzheimer disease, endothelial dysfunction, and inflammation. They also reverse gut dysbiosis and promote beneficial effects at intestinal and extraintestinal levels. NR and NMN have been found in vegetables, meat, and milk, and microorganisms in fermented beverages can also produce them. NMN and NR can be obtained through the diet either in their free form or as metabolites derivate from the digestion of NAD+. The prospection of NR and NMN to find potential food sources and their dietary contribution in increasing NAD+ levels are still an unexplored field of research. Moreover, it could enable the development of new functional foods and processing strategies to maintain and enhance their physiological benefits, besides the studies of new raw materials for extraction and biotechnological development.

HSF1 is a novel prognostic biomarker in high-risk prostate cancer that correlates with ferroptosis

BACKGROUND

Prostate cancer (PC) is the most common cancer in older men in Europe and the United States and has the second highest death rate among male cancers. The transcription of heat shock proteins by Heat shock factor 1 (HSF1) is known to regulate cell growth and stress. Nevertheless, the impact of HSF1 on ferroptosis in PC through heat shock protein 10 (HSPE1) remains unexplored.

METHODS

This study employed a range of analytical techniques, including proteomics sequencing, LC-MS/MS, CHIP-qPCR, Western blotting, immunohisto -chemistry, JC-1, CKK-8, MDA, and ROS assays. Bioinformatics analysis was performed using the UALCAN,GEPIA, PCaDB and Metascape platforms.

RESULTS

Compared with levels observed in tumor-adjacent tissue, the levels of proteins associated with fatty acids, amino acids and the oxidative phosphorylation metabolic pathway were significantly upregulated in high-risk PC tissue (Gleason score ≥ 8). HSF1 mRNA and protein levels in high-risk PC tissues were significantly higher than those observed in medium-risk PC (Gleason score = 7) and low-risk PC (Gleason score ≤ 6) tissues. ssGSEA showed that HSF1 was involved in the proliferation and anti-apoptotic processes of PC. Further bioinformatics analysis showed that HSF1 potentially affects the mitochondrial oxidative phosphorylation (OXPHOS) system by targeting HSPE1. In addition, HSF1 alleviates ROS and MDA levels to enhance the resistance of prostate cancer cells to ferroptosis by regulating HSPE1 in vitro, and HSF1 knockout promotes the susceptibility of PC to RSL3 treatment by increasing ferroptosis in vivo.

CONCLUSION

Collectively, our findings suggest that HSF1 exerts a significant influence on PC. HSF1 may represent a promising biomarker for identifying high-risk PC, and the elimination of HSF1 could potentially enhance the therapeutic effectiveness of RSL3.

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.

Nicotinamide Mononucleotide Administration Prevents Doxorubicin-Induced Cardiotoxicity and Loss in Physical Activity in Mice

Doxorubicin (Doxo) is a widely used antineoplastic drug with limited clinical application due to its deleterious dose-related side effects. We investigated whether nicotinamide mononucleotide (NMN) could protect against Doxo-induced cardiotoxicity and physical dysfunction in vivo. To assess the short- and long-term toxicity, two Doxo regimens were tested, acute and chronic. In the acute study, C57BL6/J (B6) mice were injected intraperitoneally (i.p.) once with Doxo (20 mg/kg) and NMN (180 mg/kg/day, i.p.) was administered daily for five days before and after the Doxo injection. In the chronic study, B6 mice received a cumulative dose of 20 mg/kg Doxo administered in fractionated doses for five days. NMN (500 mg/kg/day) was supplied in the mice's drinking water beginning five days before the first injection of Doxo and continuing for 60 days after. We found that NMN significantly increased tissue levels of NAD+ and its metabolites and improved survival and bodyweight loss in both experimental models. In addition, NMN protected against Doxo-induced cardiotoxicity and loss of physical function in acute and chronic studies, respectively. In the heart, NMN prevented Doxo-induced transcriptomic changes related to mitochondrial function, apoptosis, oxidative stress, inflammation and p53, and promyelocytic leukemia nuclear body pathways. Overall, our results suggest that NMN could prevent Doxo-induced toxicity in heart and skeletal muscle.

NAD+ attenuates cardiac injury after myocardial infarction in diabetic mice through regulating alternative splicing of VEGF in macrophages

Diabetic mellitus (DM) complicated with myocardial infarction (MI) is a serious clinical issue that remained poorly comprehended. The aim of the present study was to investigate the role of NAD⁺ in attenuating cardiac damage following MI in diabetic mice. The cardiac dysfunction in DM mice with MI was more severe compared with the non-diabetic mice and NAD⁺ administration could significantly improve the cardiac function in both non-diabetic and diabetic mice after MI for both 7 days and 28 days. Moreover, application of NAD⁺ could markedly reduce the cardiac injury area of DM complicated MI mice. Notably, the level of NAD⁺ was robustly decreased in the cardiac tissue of MI mice, which was further reduced in the DM complicated mice and NAD⁺ administration could significantly restore the NAD⁺ level. Furthermore, NAD⁺ was verified to facilitate the angiogenesis in the MI area of both diabetic mice and non-diabetic mice by microfil perfusion assay and immunofluorescence. Additionally, we demonstrated that NAD⁺ promoted cardiac angiogenesis after myocardial infarction in diabetic mice by promoting the M2 polarization of macrophages. At the molecular level, NAD⁺ promoted the secretion of VEGF in macrophages and therefore facilitating migration and tube formation of endothelial cells. Mechanistically, NAD⁺ was found to promote the generation of pro-angionesis VEGF₁₆₅ and inhibit the generation of anti-angionesis VEGF_165b via regulating the alternative splicing factors of VEGF (SRSF1 and SRSF6) in macrophages. The effects of NAD⁺ were readily reversible on deficiency of it. Collectively, our data showed that NAD⁺ could attenuate myocardial injury via regulating the alternative splicing of VEGF and promoting angiogenesis in diabetic mice after myocardial infarction. NAD⁺ administration may therefore be considered a potential new approach for the treatment of diabetic patients with myocardial infarction.

Role of resveratrol in inhibiting pathological cardiac remodeling

Cardiovascular disease is a group of diseases with high mortality in clinic, including hypertension, coronary heart disease, cardiomyopathy, heart valve disease, heart failure, to name a few. In the development of cardiovascular diseases, pathological cardiac remodeling is the most common cardiac pathological change, which often becomes a domino to accelerate the deterioration of the disease. Therefore, inhibiting pathological cardiac remodeling may delay the occurrence and development of cardiovascular diseases and provide patients with greater long-term benefits. Resveratrol is a non-flavonoid polyphenol compound. It mainly exists in grapes, berries, peanuts and red wine, and has cardiovascular protective effects, such as anti-oxidation, inhibiting inflammatory reaction, antithrombotic, dilating blood vessels, inhibiting apoptosis and delaying atherosclerosis. At present, the research of resveratrol has made rich progress. This review aims to summarize the possible mechanism of resveratrol against pathological cardiac remodeling, in order to provide some help for the in-depth exploration of the mechanism of inhibiting pathological cardiac remodeling and the development and research of drug targets.

LncRNA-ZFAS1 Promotes Myocardial Ischemia-Reperfusion Injury Through DNA Methylation-Mediated Notch1 Down-Regulation in Mice

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The increase of ZFAS1 expression in MIRI is an important cause of cardiomyocyte apoptosis and ROS production.

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ZFAS1 can directly interact with the promoter region of Notch1, recruit DNMT3b to promote DNA methylation in the promoter region of Notch1, and trigger cardiomyocyte apoptosis and ROS production after MIRI.

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Nicotinamide mononucleotide has the potential to attenuate the apoptosis of cardiomyocytes after MIRI by competitively binding to DNMT3b and inhibiting the DNA methylation of Notch1.

The most devastating and catastrophic deterioration of myocardial ischemia-reperfusion injury (MIRI) is cardiomyocyte death. Here we aimed to evaluate the role of lncRNA-ZFAS1 in MIRI and delineate its mechanism of action. The level of lncRNA-ZFAS1 was elevated in MIRI hearts, and artificial knockdown of lncRNA-ZFAS1 in mice improved cardiac function. Notch1 is a potential target of lncRNA-ZFAS1, and lncRNA-ZFAS1 could bind to the promoter region of Notch1 and recruit DNMT3b to induce Notch1 methylation. Nicotinamide mononucleotide could promote the expression of Notch1 by competitively inhibiting the expression of DNMT3b and improving the apoptosis of cardiomyocytes and cardiac function.

Nicotinamide mononucleotide ameliorates acute lung injury by inducing mitonuclear protein imbalance and activating the UPRmt

Mitochondria need to interact with the nucleus under homeostasis and stress to maintain cellular demands and nuclear transcriptional programs. Disrupted mitonuclear interaction is involved in many disease processes. However, the role of mitonuclear signaling regulators in endotoxin-induced acute lung injury (ALI) remains unknown. Nicotinamide adenine dinucleotide (NAD⁺) is closely related to mitonuclear interaction with its central role in mitochondrial metabolism. In the current study, C57BL/6J mice were administrated with lipopolysaccharide 15 mg/kg to induce endotoxin-induced ALI and investigated whether the NAD⁺ precursor nicotinamide mononucleotide (NMN) could preserve mitonuclear interaction and alleviate ALI. After pretreatment with NMN for 7 days, NAD⁺ levels in the mitochondrial, nucleus, and total intracellular were significantly increased in endotoxemia mice. Moreover, supplementation of NMN alleviated lung pathologic injury, reduced ROS levels, increased MnSOD activities, mitigated mitochondrial dysfunction, ameliorated the defects in the nucleus morphology, and these cytoprotective effects were accompanied by preserving mitonuclear interaction (including mitonuclear protein imbalance and the mitochondrial unfolded protein response, UPR^mt). Furthermore, NAD⁺-mediated mitonuclear protein imbalance and UPR^mt are probably regulated by deacetylase Sirtuin1 (SIRT1). Taken together, our results indicated that NMN pretreatment ameliorated ALI by inducing mitonuclear protein imbalance and activating the UPR^mt in an SIRT1-dependent manner.

Harnessing NAD+ Metabolism as Therapy for Cardiometabolic Diseases

PURPOSE OF THE REVIEW

This review summarizes current understanding on the roles of nicotinamide adenine dinucleotide (NAD⁺) metabolism in the pathogeneses and treatment development of metabolic and cardiac diseases.

RECENT FINDINGS

NAD⁺ was identified as a redox cofactor in metabolism and a co-substrate for a wide range of NAD⁺-dependent enzymes. NAD⁺ redox imbalance and depletion are associated with many pathologies where metabolism plays a key role, for example cardiometabolic diseases. This review is to delineate the current knowledge about harnessing NAD⁺ metabolism as potential therapy for cardiometabolic diseases. The review has summarized how NAD⁺ redox imbalance and depletion contribute to the pathogeneses of cardiometabolic diseases. Therapeutic evidence involving activation of NAD⁺ synthesis in pre-clinical and clinical studies was discussed. While activation of NAD⁺ synthesis shows great promise for therapy, the field of NAD⁺ metabolism is rapidly evolving. Therefore, it is expected that new mechanisms will be discovered as therapeutic targets for cardiometabolic diseases.

Cardiac Hypertrophy: From Pathophysiological Mechanisms to Heart Failure Development

Cardiac hypertrophy develops in response to increased workload to reduce ventricular wall stress and maintain function and efficiency. Pathological hypertrophy can be adaptive at the beginning. However, if the stimulus persists, it may progress to ventricular chamber dilatation, contractile dysfunction, and heart failure, resulting in poorer outcome and increased social burden. The main pathophysiological mechanisms of pathological hypertrophy are cell death, fibrosis, mitochondrial dysfunction, dysregulation of Ca 2 + -handling proteins, metabolic changes, fetal gene expression reactivation, impaired protein and mitochondrial quality control, altered sarcomere structure, and inadequate angiogenesis. Diabetic cardiomyopathy is a condition in which cardiac pathological hypertrophy mainly develop due to insulin resistance and subsequent hyperglycaemia, associated with altered fatty acid metabolism, altered calcium homeostasis and inflammation. In this review, we summarize the underlying molecular mechanisms of pathological hypertrophy development and progression, which can be applied in the development of future novel therapeutic strategies in both reversal and prevention.

Targeting NAD+: is it a common strategy to delay heart aging?

Heart aging is the main susceptible factor to coronary heart disease and significantly increases the risk of heart failure, especially when the aging heart is suffering from ischemia-reperfusion injury. Numerous studies with NAD+ supplementations have suggested its use in anti-aging treatment. However, systematic reviews regarding the overall role of NAD+ in cardiac aging are scarce. The relationship between NAD+ signaling and heart aging has yet to be clarified. This review comprehensively summarizes the current studies on the role of NAD+ signaling in delaying heart aging from the following aspects: the influence of NAD+ supplementations on the aging heart; the relationship and cross-talks between NAD+ signaling and other cardiac aging-related signaling pathways; Importantly, the therapeutic potential of targeting NAD+ in delaying heart aging will be discussed. In brief, NAD+ plays a vital role in delaying heart aging. However, the abnormalities such as altered glucose and lipid metabolism, oxidative stress, and calcium overload could also interfere with NAD+ function in the heart. Therefore, the specific physiopathology of the aging heart should be considered before applying NAD+ supplementations. We believe that this article will help augment our understanding of heart aging mechanisms. In the meantime, it provides invaluable insights into possible therapeutic strategies for preventing age-related heart diseases in clinical settings.

The role of nicotinamide mononucleotide (NMN) in anti-aging, longevity, and its potential for treating chronic conditions

Biosynthesis and regulation of nicotinamide adenine dinucleotide (NAD⁺) has recently gained a lot of attention. A systemic decline in NAD⁺ across many tissues is associated with all the hallmarks of aging. NAD⁺ can affect a variety of cellular processes, including metabolic pathways, DNA repair, and immune cell activity, both directly and indirectly. These cellular processes play a vital role in maintaining homeostasis, but as people get older, their tissue and cellular NAD⁺ levels decrease, and this drop in NAD⁺ levels has been connected to a number of age-related disorders. By restoring NAD⁺ levels, several of these age-related disorders can be delayed or even reversed. Some of the new studies conducted in mice and humans have targeted the NAD⁺ metabolism with NAD⁺ intermediates. Of these, nicotinamide mononucleotide (NMN) has been shown to offer great therapeutic potential with promising results in age-related chronic conditions such as diabetes, cardiovascular issues, cognitive impairment, and many others. Further, human interventions are required to study the long-term effects of supplementing NMN with varying doses. The paper focuses on reviewing the importance of NAD⁺ on human aging and survival, biosynthesis of NAD⁺ from its precursors, key clinical trial findings, and the role of NMN on various health conditions.

Antioxidant effect of nicotinamide mononucleotide in tendinopathy

Background

A link between tendinopathy and oxidative stress has been recently reported. Nicotinamide mononucleotide (NMN) is a precursor of nicotinamide adenine dinucleotide, which plays an important role in cell redox homeostasis. The aim of this study was to evaluate the antioxidant effect of NMN on tendinopathy in vitro and in vivo.

Methods

Tenocytes from healthy Sprague-Dawley rats were cultured in regular glucose (RG) and high-glucose (HG) conditions with or without NMN, and were divided into four groups: RG NMN(−), RG NMN(+), HG NMN(−), and HG NMN(+). Cell viability, reactive oxygen species (ROS) accumulation, apoptotic rate, and mRNA expression of nicotinamide adenine dinucleotide phosphate oxidase (NOX)1, NOX4, interleukin (IL)6, sirtuin (SIRT)1, and SIRT6 were investigated. In addition, rats with collagenase-induced tendinopathy were treated with or without NMN. Immunostaining of NOX1 and NOX4; mRNA expression of SIRT1, SIRT6, and IL6; and superoxide dismutase (SOD) activity measurements in the Achilles tendon were performed.

Results

NMN increased the expression of SIRT1 and SIRT6 in rat tenocytes, but decreased the levels of NOX1, NOX4, IL6, ROS, and apoptosis. In Achilles tendons with collagenase-induced tendinopathy, NMN increased the mRNA expression of SIRT1 and SIRT6, as well as SOD activity; while suppressing protein expression of NOX1 and NOX4, and mRNA expression of IL6.

Conclusion

The in vitro and in vivo results of this study show that NMN exerts an antioxidant effect on tendinopathy by promoting the expression of SIRT while inhibiting that of NOX.

Therapeutic Potential of Emerging NAD+-Increasing Strategies for Cardiovascular Diseases

Cardiovascular diseases are the leading cause of death worldwide. Aging and/or metabolic stress directly impact the cardiovascular system. Over the last few years, the contributions of altered nicotinamide adenine dinucleotide (NAD+) metabolism to aging and other pathological conditions closely related to cardiovascular diseases have been intensively investigated. NAD+ bioavailability decreases with age and cardiometabolic conditions in several mammalian tissues. Compelling data suggest that declining tissue NAD+ is commonly related to mitochondrial dysfunction and might be considered as a therapeutic target. Thus, NAD+ replenishment by either genetic or natural dietary NAD+-increasing strategies has been recently demonstrated to be effective for improving the pathophysiology of cardiac and vascular health in different experimental models, as well as human health, to a lesser extent. Here, we review and discuss recent experimental evidence illustrating that increasing NAD+ bioavailability, particularly by the use of natural NAD+ precursors, may offer hope for new therapeutic strategies to prevent and treat cardiovascular diseases.

Nicotinamide mononucleotide attenuates doxorubicin-induced cardiotoxicity by reducing oxidative stress, inflammation and apoptosis in rats

Doxorubicin (DOX) is an effective and widely used antineoplastic drug. However, its clinical application is limited due to its dose-dependent cardiotoxicity. Great efforts have been made to explore the pathological mechanism of DOX-induced cardiotoxicity (DIC), but new drugs and strategies to alleviate cardiac damage are still needed. Here, we aimed to investigate the effect of nicotinamide mononucleotide (NMN) on DIC in rats. The results of the present study showed that DOX treatment significantly induced cardiac dysfunction and cardiac injury, whereas NMN alleviated these changes. In addition, NMN inhibited Dox-induced activation of nucleotide-binding domain-like receptor protein 3 (NLRP3) inflammasome-mediated inflammation, as evidenced by decreased caspase 1 and IL-1β activity. Moreover, NMN treatment increased glutathione (GSH) levels and superoxide dismutase (SOD) activity and decreased the levels of malondialdehyde (MDA) and reactive oxygen species (ROS) in DOX-treated rats. Furthermore, NMN treatment mitigated DOX-induced cardiomyocyte apoptosis and cardiac fibrosis. In conclusion, the results indicated that NMN protects against DIC in rats by inhibiting NLRP3 inflammasome activation, oxidative stress, and apoptosis.

Nicotinamide mononucleotide: An emerging nutraceutical against cardiac aging?

Nicotinamide adenine dinucleotide (NAD) is essential for cellular physiological processes, directly or indirectly affecting metabolism and gene expression. The decline of NAD⁺ levels in the heart is accompanied by aging, causing cardiac pathological remodeling and dysfunction. Niacinamide mononucleotide (NMN) has emerged as a precursor to alleviate age-related cardiac pathophysiological changes by improving cardiac NAD⁺ homeostasis. Preclinical trials on the efficacy and safety of intaking NMN have shown encouraging results, revealing a cardioprotective effect without significant side effects. Strategies for improving the effectiveness of NMN are also evolving. The present review aimed to summarize the potentials of NMN as a nutraceutical against cardiac aging and highlight the relationship between NMN supplementation and cardiac protection.

The Role of Mitochondrial Dysfunction in Atrial Fibrillation: Translation to Druggable Target and Biomarker Discovery

Atrial fibrillation (AF) is the most prevalent and progressive cardiac arrhythmia worldwide and is associated with serious complications such as heart failure and ischemic stroke. Current treatment modalities attenuate AF symptoms and are only moderately effective in halting the arrhythmia. Therefore, there is an urgent need to dissect molecular mechanisms that drive AF. As AF is characterized by a rapid atrial activation rate, which requires a high energy metabolism, a role of mitochondrial dysfunction in AF pathophysiology is plausible. It is well known that mitochondria play a central role in cardiomyocyte function, as they produce energy to support the mechanical and electrical function of the heart. Details on the molecular mechanisms underlying mitochondrial dysfunction are increasingly being uncovered as a contributing factor in the loss of cardiomyocyte function and AF. Considering the high prevalence of AF, investigating the role of mitochondrial impairment in AF may guide the path towards new therapeutic and diagnostic targets. In this review, the latest evidence on the role of mitochondria dysfunction in AF is presented. We highlight the key modulators of mitochondrial dysfunction that drive AF and discuss whether they represent potential targets for therapeutic interventions and diagnostics in clinical AF.

The nuclear sirtuin SIRT6 protects the heart from developing aging-associated myocyte senescence and cardiac hypertrophy

Sirtuins have been shown to regulate the aging process. We have previously demonstrated that Sirt6 blocks the pressure overload-induced cardiac hypertrophy in mice. Here, we show that Sirt6 can also mitigate aging-induced cardiomyocyte senescence and cardiac hypertrophy. We found that aging is associated with altered Sirt6 activity along with development of cardiac hypertrophy and fibrosis. Compared to young mice (4-months), the hearts of aged mice (24-months) showed increased levels of mitochondrial DNA damage, shortened telomere length, and increased accumulation of 8-oxo-dG adducts, which are hallmarks of aging. The aged hearts also showed reduced levels of NAD⁺ and altered levels of mitochondrial fusion-fission proteins. Similar characteristics were observed in the hearts of Sirt6 deficient mice. Additionally, we found that doxorubicin (Dox) induced cardiomyocyte senescence, as measured by expression of p16^INK4a, p53, and β-galactosidase, was associated with loss of Sirt6. However, Sirt6 overexpression protected cardiomyocytes from developing Dox-induced senescence. Further, compared to wild-type mice, the hearts of Sirt6.Tg mice showed reduced expression of aging markers, and the development of aging-associated cardiac hypertrophy and fibrosis. Our data suggest that Sirt6 is a critical anti-aging molecule that regulates various cellular processes associated with aging and protects the heart from developing aging-induced cardiac hypertrophy and fibrosis.

Sirtuins-Mediated System-Level Regulation of Mammalian Tissues at the Interface between Metabolism and Cell Cycle: A Systematic Review

Sirtuins are a family of highly conserved NAD+-dependent proteins and this dependency links Sirtuins directly to metabolism. Sirtuins' activity has been shown to extend the lifespan of several organisms and mainly through the post-translational modification of their many target proteins, with deacetylation being the most common modification. The seven mammalian Sirtuins, SIRT1 through SIRT7, have been implicated in regulating physiological responses to metabolism and stress by acting as nutrient sensors, linking environmental and nutrient signals to mammalian metabolic homeostasis. Furthermore, mammalian Sirtuins have been implicated in playing major roles in mammalian pathophysiological conditions such as inflammation, obesity and cancer. Mammalian Sirtuins are expressed heterogeneously among different organs and tissues, and the same holds true for their substrates. Thus, the function of mammalian Sirtuins together with their substrates is expected to vary among tissues. Any therapy depending on Sirtuins could therefore have different local as well as systemic effects. Here, an introduction to processes relevant for the actions of Sirtuins, such as metabolism and cell cycle, will be followed by reasoning on the system-level function of Sirtuins and their substrates in different mammalian tissues. Their involvement in the healthy metabolism and metabolic disorders will be reviewed and critically discussed.

Comprehensive Metabolic Phenotyping Refines Cardiovascular Risk in Young Adults

BACKGROUND

Whereas cardiovascular disease (CVD) metrics define risk in individuals >40 years of age, the earliest lesions of CVD appear well before this age. Despite the role of metabolism in CVD antecedents, studies in younger, biracial populations to define precise metabolic risk phenotypes are lacking.

METHODS

We studied 2330 White and Black young adults (mean age, 32 years; 45% Black) in the CARDIA study (Coronary Artery Risk Development in Young Adults) to identify metabolite profiles associated with an adverse CVD phenome (myocardial structure/function, fitness, vascular calcification), mechanisms, and outcomes over 2 decades. Statistical learning methods (elastic nets/principal components analysis) and Cox regression generated parsimonious, metabolite-based risk scores validated in >1800 individuals in the Framingham Heart Study.

RESULTS

In the CARDIA study, metabolite profiles quantified in early adulthood were associated with subclinical CVD development over 20 years, specifying known and novel pathways of CVD (eg, transcriptional regulation, brain-derived neurotrophic factor, nitric oxide, renin-angiotensin). We found 2 multiparametric, metabolite-based scores linked independently to vascular and myocardial health, with metabolites included in each score specifying microbial metabolism, hepatic steatosis, oxidative stress, nitric oxide modulation, and collagen metabolism. The metabolite-based vascular scores were lower in men, and myocardial scores were lower in Black participants. Over a nearly 25-year median follow-up in CARDIA, the metabolite-based vascular score (hazard ratio, 0.68 per SD [95% CI, 0.50-0.92]; P=0.01) and myocardial score (hazard ratio, 0.60 per SD [95% CI, 0.45-0.80]; P=0.0005) in the third and fourth decades of life were associated with clinical CVD with a synergistic association with outcome (Pinteraction=0.009). We replicated these findings in 1898 individuals in the Framingham Heart Study over 2 decades, with a similar association with outcome (including interaction), reclassification, and discrimination. In the Framingham Heart Study, the metabolite scores exhibited an age interaction (P=0.0004 for a combined myocardial-vascular score with incident CVD), such that young adults with poorer metabolite-based health scores had highest hazard of future CVD.

CONCLUSIONS

Metabolic signatures of myocardial and vascular health in young adulthood specify known/novel pathways of metabolic dysfunction relevant to CVD, associated with outcome in 2 independent cohorts. Efforts to include precision measures of metabolic health in risk stratification to interrupt CVD at its earliest stage are warranted.

Age-related mitochondrial dysfunction as a key factor in COVID-19 disease

SARS-CoV-2 causes a severe pneumonia (COVID-19) that affects essentially elderly people. In COVID-19, macrophage infiltration into the lung causes a rapid and intense cytokine storm leading finally to a multi-organ failure and death. Comorbidities such as metabolic syndrome, obesity, type 2 diabetes, lung and cardiovascular diseases, all of them age-associated diseases, increase the severity and lethality of COVID-19. Mitochondrial dysfunction is one of the hallmarks of aging and COVID-19 risk factors. Dysfunctional mitochondria is associated with defective immunological response to viral infections and chronic inflammation. This review discuss how mitochondrial dysfunction is associated with defective immune response in aging and different age-related diseases, and with many of the comorbidities associated with poor prognosis in the progression of COVID-19. We suggest here that chronic inflammation caused by mitochondrial dysfunction is responsible of the explosive release of inflammatory cytokines causing severe pneumonia, multi-organ failure and finally death in COVID-19 patients. Preventive treatments based on therapies improving mitochondrial turnover, dynamics and activity would be essential to protect against COVID-19 severity.

Recent Discoveries on the Involvement of Krüppel-Like Factor 4 in the Most Common Cancer Types

Krüppel-like factor 4 (KLF4) is a transcription factor highly conserved in evolution. It is particularly well known for its role in inducing pluripotent stem cells. In addition, KLF4 plays many roles in cancer. The results of most studies suggest that KLF4 is a tumor suppressor. However, the functioning of KLF4 is regulated at many levels. These include regulation of transcription, alternative splicing, miRNA, post-translational modifications, subcellular localization, protein stability and interactions with other molecules. Simple experiments aimed at assaying transcript levels or protein levels fail to address this complexity and thus may deliver misleading results. Tumor subtypes are also important; for example, in prostate cancer KLF4 is highly expressed in indolent tumors where it impedes tumor progression, while it is absent from aggressive prostate tumors. KLF4 is important in regulating response to many known drugs, and it also plays a role in tumor microenvironment. More and more information is available about upstream regulators, downstream targets and signaling pathways associated with the involvement of KLF4 in cancer. Furthermore, KLF4 performs critical function in the overall regulation of tissue homeostasis, cellular integrity, and progression towards malignancy. Here we summarize and analyze the latest findings concerning this fascinating transcription factor.

Emerging Role of Adipocyte Dysfunction in Inducing Heart Failure Among Obese Patients With Prediabetes and Known Diabetes Mellitus

Adipose tissue dysfunction is a predictor for cardiovascular (CV) events and heart failure (HF) in patient population with obesity, metabolic syndrome, and known type 2 diabetes mellitus. Previous preclinical and clinical studies have yielded controversial findings regarding the role of accumulation of adipose tissue various types in CV risk and HF-related clinical outcomes in obese patients. There is evidence for direct impact of infiltration of epicardial adipocytes into the underlying myocardium to induce adverse cardiac remodeling and mediate HF development and atrial fibrillation. Additionally, perivascular adipocytes accumulation is responsible for release of proinflammatory adipocytokines (adiponectin, leptin, resistin), stimulation of oxidative stress, macrophage phenotype switching, and worsening vascular reparation, which all lead to microvascular inflammation, endothelial dysfunction, atherosclerosis acceleration, and finally to increase in CV mortality. However, systemic effects of white and brown adipose tissue can be different, and adipogenesis including browning of adipose tissue and deficiency of anti-inflammatory adipocytokines (visfatin, omentin, zinc-α2-glycoprotein, glypican-4) was frequently associated with adipose triglyceride lipase augmentation, altered glucose homeostasis, resistance to insulin of skeletal muscles, increased cardiomyocyte apoptosis, lowered survival, and weak function of progenitor endothelial cells, which could significantly influence on HF development, as well as end-organ fibrosis and multiple comorbidities. The exact underlying mechanisms for these effects are not fully understood, while they are essential to help develop improved treatment strategies. The aim of the review is to summarize the evidence showing that adipocyte dysfunction may induce the onset of HF and support advance of HF through different biological mechanisms involving inflammation, pericardial, and perivascular adipose tissue accumulation, adverse and electrical cardiac remodeling, and skeletal muscle dysfunction. The unbalancing effects of natriuretic peptides, neprilysin, and components of renin–angiotensin system, as exacerbating cause of altered adipocytokine signaling on myocardium and vasculature, in obesity patients at high risk of HF are disputed. The profile of proinflammatory and anti-inflammatory adipocytokines as promising biomarker for HF risk stratification is discussed in the review.

Caloric restriction mimetics for the treatment of cardiovascular diseases

Caloric restriction mimetics (CRMs) are emerging as potential therapeutic agents for the treatment of cardiovascular diseases. CRMs include natural and synthetic compounds able to inhibit protein acetyltransferases, to interfere with acetyl coenzyme A biosynthesis, or to activate (de)acetyltransferase proteins. These modifications mimic the effects of caloric restriction, which is associated with the activation of autophagy. Previous evidence demonstrated the ability of CRMs to ameliorate cardiac function and reduce cardiac hypertrophy and maladaptive remodelling in animal models of ageing, mechanical overload, chronic myocardial ischaemia, and in genetic and metabolic cardiomyopathies. In addition, CRMs were found to reduce acute ischaemia-reperfusion injury. In many cases, these beneficial effects of CRMs appeared to be mediated by autophagy activation. In the present review, we discuss the relevant literature about the role of different CRMs in animal models of cardiac diseases, emphasizing the molecular mechanisms underlying the beneficial effects of these compounds and their potential future clinical application.

Need for NAD+: Focus on Striated Muscle Laminopathies

Laminopathies are a heterogeneous group of rare diseases caused by genetic mutations in the LMNA gene, encoding A-type lamins. A-type lamins are nuclear envelope proteins which associate with B-type lamins to form the nuclear lamina, a meshwork underlying the inner nuclear envelope of differentiated cells. The laminopathies include lipodystrophies, progeroid phenotypes and striated muscle diseases. Research on striated muscle laminopathies in the recent years has provided novel perspectives on the role of the nuclear lamina and has shed light on the pathological consequences of altered nuclear lamina. The role of altered nicotinamide adenine dinucleotide (NAD⁺) in the physiopathology of striated muscle laminopathies has been recently highlighted. Here, we have summarized these findings and reviewed the current knowledge about NAD⁺ alteration in striated muscle laminopathies, providing potential therapeutic approaches.

Role of NAD+-Modulated Mitochondrial Free Radical Generation in Mechanisms of Acute Brain Injury

It is commonly accepted that mitochondria represent a major source of free radicals following acute brain injury or during the progression of neurodegenerative diseases. The levels of reactive oxygen species (ROS) in cells are determined by two opposing mechanisms—the one that produces free radicals and the cellular antioxidant system that eliminates ROS. Thus, the balance between the rate of ROS production and the efficiency of the cellular detoxification process determines the levels of harmful reactive oxygen species. Consequently, increase in free radical levels can be a result of higher rates of ROS production or due to the inhibition of the enzymes that participate in the antioxidant mechanisms. The enzymes’ activity can be modulated by post-translational modifications that are commonly altered under pathologic conditions. In this review we will discuss the mechanisms of mitochondrial free radical production following ischemic insult, mechanisms that protect mitochondria against free radical damage, and the impact of post-ischemic nicotinamide adenine mononucleotide (NAD⁺) catabolism on mitochondrial protein acetylation that affects ROS generation and mitochondrial dynamics. We propose a mechanism of mitochondrial free radical generation due to a compromised mitochondrial antioxidant system caused by intra-mitochondrial NAD⁺ depletion. Finally, the interplay between different mechanisms of mitochondrial ROS generation and potential therapeutic approaches are reviewed.

Possible Adverse Effects of High-Dose Nicotinamide: Mechanisms and Safety Assessment

Nicotinamide (NAM) at doses far above those recommended for vitamins is suggested to be effective against a wide spectrum of diseases and conditions, including neurological dysfunctions, depression and other psychological disorders, and inflammatory diseases. Recent increases in public awareness on possible pro-longevity effects of nicotinamide adenine dinucleotide (NAD+) precursors have caused further growth of NAM consumption not only for clinical treatments, but also as a dietary supplement, raising concerns on the safety of its long-term use. However, possible adverse effects and their mechanisms are poorly understood. High-level NAM administration can exert negative effects through multiple routes. For example, NAM by itself inhibits poly(ADP-ribose) polymerases (PARPs), which protect genome integrity. Elevation of the NAD+ pool alters cellular energy metabolism. Meanwhile, high-level NAM alters cellular methyl metabolism and affects methylation of DNA and proteins, leading to changes in cellular transcriptome and proteome. Also, methyl metabolites of NAM, namely methylnicotinamide, are predicted to play roles in certain diseases and conditions. In this review, a collective literature search was performed to provide a comprehensive list of possible adverse effects of NAM and to provide understanding of their underlying mechanisms and assessment of the raised safety concerns. Our review assures safety in current usage level of NAM, but also finds potential risks for epigenetic alterations associated with chronic use of NAM at high doses. It also suggests directions of the future studies to ensure safer application of NAM.

Nicotinamide Mononucleotide: A Promising Molecule for Therapy of Diverse Diseases by Targeting NAD+ Metabolism

NAD+, a co-enzyme involved in a great deal of biochemical reactions, has been found to be a network node of diverse biological processes. In mammalian cells, NAD+ is synthetized, predominantly through NMN, to replenish the consumption by NADase participating in physiologic processes including DNA repair, metabolism, and cell death. Correspondingly, aberrant NAD+ metabolism is observed in many diseases. In this review, we discuss how the homeostasis of NAD+ is maintained in healthy condition and provide several age-related pathological examples related with NAD+ unbalance. The sirtuins family, whose functions are NAD-dependent, is also reviewed. Administration of NMN surprisingly demonstrated amelioration of the pathological conditions in some age-related disease mouse models. Further clinical trials have been launched to investigate the safety and benefits of NMN. The NAD+ production and consumption pathways including NMN are essential for more precise understanding and therapy of age-related pathological processes such as diabetes, ischemia–reperfusion injury, heart failure, Alzheimer’s disease, and retinal degeneration.

Overexpression of the histidine triad nucleotide-binding protein 2 protects cardiac function in the adult mice after acute myocardial infarction

AIM

To explore the role of the histidine triad nucleotide-binding 2 (HINT2) protein in heart failure.

METHODS

Neonatal mouse ventricle myocytes (NMVMs) and myocardial infarction-induced heart failure mice were used for in vitro or in vivo experiments. Adenovirus (ADV) and adeno-associated virus serum type 9 (AAV9) vectors were used to regulate HINT2 expression. The expression of HINT2 was determined by quantifying the mRNA and protein levels. Cell survival was analysed using the CCK-8 kit and TUNEL staining. Mitochondrial function was determined by the mitochondrial membrane potential and oxygen consumption rates. AAV9-HINT2 was injected 24 h post-myocardial infarction following which transthoracic echocardiography and histological analyses were performed after 4 weeks. Positron emission tomography tomography-computed tomography (PET/CT) and targeted metabolomics analyses were used to explore the metabolic status in vivo. NAD levels were measured using a colorimetric kit. Computer-simulated rigid body molecular docking was performed using AUTODOCK4. Molecule binding kinetics assays were performed using biolayer interferometry.

RESULTS

HINT2 was down-regulated in NMVMs in hypoxia. ADV-HINT2-induced HINT2 overexpression improved NMVM survival after exposure to hypoxia. Mitochondrial function was preserved in the ADV-HINT2 group under hypoxic conditions. In vivo experiments showed that cardiac function and metabolic status was preserved by HINT2 overexpression. HINT2 overexpression restored mitochondrial NAD levels; this was dependent on nicotinamide mononucleotide (NMN). Using computer-simulated molecular docking analysis and biolayer interferometry, we observed that HINT2 potentially binds and associates with NMN.

CONCLUSION

HINT2 overexpression protects cardiac function in adult mice after myocardial infarction by maintaining mitochondrial NAD homeostasis.

NRH salvage and conversion to NAD+ requires NRH kinase activity by adenosine kinase

Dihydronicotinamide riboside (NRH) has been suggested to act as a precursor for the synthesis of NAD⁺, but the biochemical pathway converting it has been unknown. Here, we show that NRH can be converted into NAD⁺ via a salvage pathway in which adenosine kinase (ADK, also known as AK) acts as an NRH kinase. Using isotope-labelling approaches, we demonstrate that NRH is fully incorporated into NAD⁺, with NMNH acting as an intermediate. We further show that AK is enriched in fractions from cell lysates with NRH kinase activity, and that AK can convert NRH into NAD⁺. In cultured cells and mouse liver, pharmacological or genetic inhibition of AK blocks formation of reduced nicotinamide mononucleotide (NMNH) and inhibits NRH-stimulated NAD⁺ biosynthesis. Finally, we confirm the presence of endogenous NRH in the liver with metabolomics. Our findings establish NRH as a natural precursor of NAD⁺ and reveal a new route for NAD⁺ biosynthesis via an NRH salvage pathway involving AK.

NAD+ therapy in age-related degenerative disorders: A benefit/risk analysis

Nicotinamide adenine dinucleotide (NAD+) is an essential pyridine nucleotide that is present in all living cells. NAD+ acts as an important cofactor and substrate for a multitude of biological processes including energy production, DNA repair, gene expression, calcium-dependent secondary messenger signalling and immunoregulatory roles. The de novo synthesis of NAD+ is primarily dependent on the kynurenine pathway (KP), although NAD+ can also be recycled from nicotinic acid (NA), nicotinamide (NAM) and nicotinamide riboside (NR). NAD+ levels have been reported to decline during ageing and age-related diseases. Recent studies have shown that raising intracellular NAD+ levels represents a promising therapeutic strategy for age-associated degenerative diseases in general and to extend lifespan in small animal models. A systematic review of the literature available on Medline, Embase and Pubmed was undertaken to evaluate the potential health and/or longevity benefits due to increasing NAD+ levels. A total of 1545 articles were identified and 147 articles (113 preclinical and 34 clinical) met criteria for inclusion. Most studies indicated that the NAD+ precursors NAM, NR, nicotinamide mononucleotide (NMN), and to a lesser extent NAD+ and NADH had a favourable outcome on several age-related disorders associated with the accumulation of chronic oxidative stress, inflammation and impaired mitochondrial function. While these compounds presented with a limited acute toxicity profile, evidence is still quite limited and long-term human clinical trials are still nascent in the current literature. Potential risks in raising NAD+ levels in various clinical disorders using NAD+ precursors include the accumulation of putative toxic metabolites, tumorigenesis and promotion of cellular senescence. Therefore, NAD+ metabolism represents a promising target and further studies are needed to recapitulate the preclinical benefits in human clinical trials.

Targeting mitochondria for cardiovascular disorders: therapeutic potential and obstacles

A large body of evidence indicates that mitochondrial dysfunction has a major role in the pathogenesis of multiple cardiovascular disorders. Over the past 2 decades, extraordinary efforts have been focused on the development of agents that specifically target mitochondria for the treatment of cardiovascular disease. Despite such an intensive wave of investigation, no drugs specifically conceived to modulate mitochondrial functions are currently available for the clinical management of cardiovascular disease. In this Review, we discuss the therapeutic potential of targeting mitochondria in patients with cardiovascular disease, examine the obstacles that have restrained the development of mitochondria-targeting agents thus far, and identify strategies that might empower the full clinical potential of this approach.

Both gain and loss of Nampt function promote pressure overload-induced heart failure

The heart requires high-energy production, but metabolic ability declines in the failing heart. Nicotinamide phosphoribosyl-transferase (Nampt) is a rate-limiting enzyme in the salvage pathway of nicotinamide adenine dinucleotide (NAD) synthesis. NAD is directly involved in various metabolic processes and may indirectly regulate metabolic gene expression through sirtuin 1 (Sirt1), an NAD-dependent protein deacetylase. However, how Nampt regulates cardiac function and metabolism in the failing heart is poorly understood. Here we show that pressure-overload (PO)-induced heart failure is exacerbated in both systemic Nampt heterozygous knockout (Nampt+/-) mice and mice with cardiac-specific Nampt overexpression (Tg-Nampt). The NAD level declined in Nampt+/- mice under PO (wild: 377 pmol/mg tissue; Nampt+/-: 119 pmol/mg tissue; P = 0.028). In cultured cardiomyocytes, Nampt knockdown diminished mitochondrial NAD content and ATP production (relative ATP production: wild: 1; Nampt knockdown: 0.56; P = 0.0068), suggesting that downregulation of Nampt induces mitochondrial dysfunction. On the other hand, the NAD level was increased in Tg-Nampt mice at baseline but not during PO, possibly due to increased consumption of NAD by Sirt1. The expression of Sirt1 was increased in Tg-Nampt mice, in association with reduced overall protein acetylation. PO-induced downregulation of metabolic genes was exacerbated in Tg-Nampt mice. In cultured cardiomyocytes, Nampt and Sirt1 cooperatively suppressed mitochondrial proteins and ATP production, thereby promoting mitochondrial dysfunction. In addition, Nampt overexpression upregulated inflammatory cytokines, including TNF-α and monocyte chemoattractant protein-1. Thus endogenous Nampt maintains cardiac function and metabolism in the failing heart, whereas Nampt overexpression is detrimental during PO, possibly due to excessive activation of Sirt1, suppression of mitochondrial function, and upregulation of proinflammatory mechanisms.NEW & NOTEWORTHY Nicotinamide phosphoribosyl-transferase (Nampt) is a rate-limiting enzyme in the salvage pathway of nicotinamide adenine dinucleotide synthesis. We demonstrate that pressure overload-induced heart failure is exacerbated in both systemic Nampt heterozygous knockout mice and mice with cardiac-specific Nampt overexpression. Both loss- and gain-of-function models exhibited reduced protein acetylation, suppression of metabolic genes, and mitochondrial energetic dysfunction. Thus endogenous Nampt maintains cardiac function and metabolism in the failing heart, but cardiac-specific Nampt overexpression is detrimental rather than therapeutic.

Calcium Signaling and Reactive Oxygen Species in Mitochondria

In heart failure, alterations of Na⁺ and Ca²⁺ handling, energetic deficit, and oxidative stress in cardiac myocytes are important pathophysiological hallmarks. Mitochondria are central to these processes because they are the main source for ATP, but also reactive oxygen species (ROS), and their function is critically controlled by Ca²⁺ During physiological variations of workload, mitochondrial Ca²⁺ uptake is required to match energy supply to demand but also to keep the antioxidative capacity in a reduced state to prevent excessive emission of ROS. Mitochondria take up Ca²⁺ via the mitochondrial Ca²⁺ uniporter, which exists in a multiprotein complex whose molecular components were identified only recently. In heart failure, deterioration of cytosolic Ca²⁺ and Na⁺ handling hampers mitochondrial Ca²⁺ uptake and the ensuing Krebs cycle-induced regeneration of the reduced forms of NADH (nicotinamide adenine dinucleotide) and NADPH (nicotinamide adenine dinucleotide phosphate), giving rise to energetic deficit and oxidative stress. ROS emission from mitochondria can trigger further ROS release from neighboring mitochondria termed ROS-induced ROS release, and cross talk between different ROS sources provides a spatially confined cellular network of redox signaling. Although low levels of ROS may serve physiological roles, higher levels interfere with excitation-contraction coupling, induce maladaptive cardiac remodeling through redox-sensitive kinases, and cell death through mitochondrial permeability transition. Targeting the dysregulated interplay between excitation-contraction coupling and mitochondrial energetics may ameliorate the progression of heart failure.

Impaired SIRT3 activity mediates cardiac dysfunction in endotoxemia by calpain-dependent disruption of ATP synthesis

BACKGROUND

Sepsis-induced cardiomyopathy contributes to the high mortality of septic shock in critically ill patients. Since the underlying mechanisms are incompletely understood, we hypothesized that sepsis-induced impairment of sirtuin 3 (SIRT3) activity contributes to the development of septic cardiomyopathy.

METHODS AND RESULTS

Treatment of mice with lipopolysaccharide (LPS) for 6 h resulted in myocardial NAD⁺ depletion and increased mitochondrial protein acetylation, indicating impaired myocardial SIRT3 activity due to NAD⁺ depletion. LPS treatment also resulted in impaired cardiac output in isolated working hearts, indicating endotoxemia-induced cardiomyopathy. Maintaining normal myocardial NAD⁺ levels in LPS-treated mice by Poly(ADP-ribose)polymerase 1 (PARP1) deletion prevented cardiac dysfunction, whereas additional SIRT3 deficiency blunted this beneficial effect, indicating that impaired SIRT3 activity contributes to cardiac dysfunction in endotoxemia. Measurements of mitochondrial ATP synthesis suggest that LPS-induced contractile dysfunction may result from cardiac energy depletion due to impaired SIRT3 activity. Pharmacological inhibition of mitochondrial calpains using MDL28170 normalized LPS-induced cleavage of the ATP5A1 subunit of ATP synthase and normalized contractile dysfunction, suggesting that cardiac energy depletion may result from calpain-mediated cleavage of ATP5A1. These beneficial effects were completely blunted by SIRT3 deficiency. Finally, a gene set enrichment analysis of hearts of patients with septic, ischemic or dilated cardiomyopathy revealed a sepsis-specific suppression of SIRT3 deacetylation targets, including ATP5A1, indicating a functional relevance of SIRT3-dependent pathways in human sepsis.

CONCLUSIONS

Impaired SIRT3 activity may mediate cardiac dysfunction in endotoxemia by facilitating calpain-mediated disruption of ATP synthesis, suggesting SIRT3 activation as a potential therapeutic strategy to treat septic cardiomyopathy.

Emerging potential benefits of modulating NAD+ metabolism in cardiovascular disease

Nicotinamide adenine dinucleotide (NAD⁺) and related metabolites are central mediators of fuel oxidation and bioenergetics within cardiomyocytes. Additionally, NAD⁺ is required for the activity of multifunctional enzymes, including sirtuins and poly(ADP-ribose) polymerases that regulate posttranslational modifications, DNA damage responses, and Ca²⁺ signaling. Recent research has indicated that NAD⁺ participates in a multitude of processes dysregulated in cardiovascular diseases. Therefore, supplementation of NAD⁺ precursors, including nicotinamide riboside that boosts or repletes the NAD⁺ metabolome, may be cardioprotective. This review examines the molecular physiology and preclinical data with respect to NAD⁺ precursors in heart failure-related cardiac remodeling, ischemic-reperfusion injury, and arrhythmias. In addition, alternative NAD⁺-boosting strategies and potential systemic effects of NAD⁺ supplementation with implications on cardiovascular health and disease are surveyed.