Nicotinamide adenine dinucleotide emerges as a therapeutic target in aging and ischemic conditions

Personalized Porous Gelatin Methacryloyl Sustained-Release Nicotinamide Protects Against Noise-Induced Hearing Loss

There are no Food and Drug Administration-approved drugs for treating noise-induced hearing loss (NIHL), reflecting the absence of clear specific therapeutic targets and effective delivery strategies. Noise trauma is demonstrated results in nicotinamide adenine dinucleotide (NAD+) downregulation and mitochondrial dysfunction in cochlear hair cells (HCs) and spiral ganglion neurons (SGNs) in mice, and NAD+ boosted by nicotinamide (NAM) supplementation maintains cochlear mitochondrial homeostasis and prevents neuroexcitatory toxic injury in vitro and ex vivo, also significantly ameliorated NIHL in vivo. To tackle the limited drug delivery efficiency due to sophisticated anatomical barriers and unique clearance pathway in ear, personalized NAM-encapsulated porous gelatin methacryloyl (PGMA@NAM) are developed based on anatomy topography of murine temporal bone by micro-computed tomography and reconstruction of round window (RW) niche, realizing hydrogel in situ implantation completely, NAM sustained-release and long-term auditory preservation in mice. This study strongly supports personalized PGMA@NAM as NIHL protection drug with effective inner ear delivery, providing new inspiration for drug-based treatment of NIHL.

The identification of new roles for nicotinamide mononucleotide after spinal cord injury in mice: an RNA-seq and global gene expression study

Background

Nicotinamide mononucleotide (NMN), an important transforming precursor of nicotinamide adenine dinucleotide (NAD+). Numerous studies have confirmed the neuroprotective effects of NMN in nervous system diseases. However, its role in spinal cord injury (SCI) and the molecular mechanisms involved have yet to be fully elucidated.

Methods

We established a moderate-to-severe model of SCI by contusion (70 kdyn) using a spinal cord impactor. The drug was administered immediately after surgery, and mice were intraperitoneally injected with either NMN (500 mg NMN/kg body weight per day) or an equivalent volume of saline for seven days. The central area of the spinal cord was harvested seven days after injury for the systematic analysis of global gene expression by RNA Sequencing (RNA-seq) and finally validated using qRT-PCR.

Results

NMN supplementation restored NAD+ levels after SCI, promoted motor function recovery, and alleviated pain. This could potentially be associated with alterations in NAD+ dependent enzyme levels. RNA sequencing (RNA-seq) revealed that NMN can inhibit inflammation and potentially regulate signaling pathways, including interleukin-17 (IL-17), tumor necrosis factor (TNF), toll-like receptor, nod-like receptor, and chemokine signaling pathways. In addition, the construction of a protein-protein interaction (PPI) network and the screening of core genes showed that interleukin 1β (IL-1β), interferon regulatory factor 7 (IRF 7), C-X-C motif chemokine ligand 10 (Cxcl10), and other inflammationrelated factors, changed significantly after NMN treatment. qRT-PCR confirmed the inhibitory effect of NMN on inflammatory factors (IL-1β, TNF-α, IL-17A, IRF7) and chemokines (chemokine ligand 3, Cxcl10) in mice following SCI.

Conclusion

The reduction of NAD+ levels after SCI can be compensated by NMN supplementation, which can significantly restore motor function and relieve pain in a mouse model. RNA-seq and qRT-PCR systematically revealed that NMN affected inflammation-related signaling pathways, including the IL-17, TNF, Toll-like receptor, NOD-like receptor and chemokine signaling pathways, by down-regulating the expression of inflammatory factors and chemokines.

Bioactive role of vitamins as a key modulator of oxidative stress, cellular damage and comorbidities associated with spinal cord injury (SCI)

Introduction: Spinal cord injury (SCI) cause significant disability and impact the quality of life of those affected by it. The nutritional status and diet are fundamental to diminish the progression of complications; vitamins modulate the inflammatory response and oxidative stress, promote blood-spinal cord barrier preservation and the prompt recovery of homeostasis. A deep knowledge of the benefits achieved from vitamins in patients with SCI are summarized. Information of dosage, time, and effects of vitamins in these patients are also displayed. Vitamins have been extensively investigated; however, more clinical trials are needed to clarify the scope of vitamin supplementation.Objective: The objective of this review was to offer relevant therapeutic information based on vitamins supplementation for SCI patients.Methods: Basic and clinical studies that have implemented the use of vitamins in SCI were considered. They were selected from the year 2000-2022 from three databases: PubMed, Science Direct and Google Scholar.Results: Consistent benefits in clinical trials were shown in those who were supplemented with vitamin D (prevents osteoporosis and improves physical performance variables), B3 (improves lipid profile) and B12 (neurological prophylaxis of chronic SCI damage) mainly. On the other hand, improvement related to neuroprotection, damage modulation (vitamin A) and its prophylaxis were associated to B complex vitamins supplementation; the studies who reported positive results are displayed in this review.Discussion: Physicians should become familiar with relevant information that can support conventional treatment in patients with SCI, such as the use of vitamins, a viable option that can improve outcomes in patients with this condition.

The Role of P53 in Myocardial Ischemia-Reperfusion Injury

PURPOSE

P53 is one of the key tumor suppressors. In normal cells, p53 is maintained at low levels by the ubiquitination of the ubiquitinated ligase MDM2. In contrast, under stress conditions such as DNA damage and ischemia, the interaction between p53 and MDM2 is blocked and activated by phosphorylation and acetylation, thereby mediating the trans-activation of p53 through its target genes to regulate a variety of cellular responses. Previous studies have shown that the expression of p53 is negligible in normal myocardium, tends to increase in myocardial ischemia and is maximally induced in ischemia-reperfused myocardium, demonstrating a possible key role of p53 in the development of MIRI. In this review, we detail and summarize recent studies on the mechanism of action of p53 in MIRI and describe the therapeutic agents targeting the relevant targets to provide new strategies for the prevention and treatment of MIRI.

METHODS

We collected 161 relevant papers mainly from Pubmed and Web of Science (search terms "p53" and "myocardial ischemia-reperfusion injury"). After that, we selected pathway studies related to p53 and classified them according to their contents. We eventually analyzed and summarized them.

RESULTS AND CONCLUSION

In this review, we detail and summarize recent studies on the mechanism of action of p53 in MIRI and validate its status as an important intermediate affecting MIRI. On the one hand, p53 is regulated and modified by multiple factors, especially non-coding RNAs; on the other hand, p53 regulates apoptosis, programmed necrosis, autophagy, iron death and oxidative stress in MIRI through multiple pathways. More importantly, several studies have reported medications targeting p53-related therapeutic targets. These medications are expected to be effective options for the alleviation of MIRI, but further safety and clinical studies are needed to convert them into clinical applications.

Mitochondria-targeted combination treatment strategy counteracts myocardial reperfusion injury of aged rats by modulating autophagy and inflammatory response

BACKGROUND

Aging, as a recognized risk factor for ischemic heart disease, interferes with protective mechanisms and abolishes the optimal effectiveness of cardioprotective interventions, leading to the loss of cardioprotection following myocardial ischemia/reperfusion (I/R) injury. This study was designed to explore the possible interaction of aging with cardioprotection induced by combination therapy with coenzyme Q₁₀ (CoQ₁₀) and mitochondrial transplantation in myocardial I/R injury of aged rats.

METHODS

Male Wistar rats (n = 72, 400-450 g, 22-24 months old) were randomized into groups with/without I/R and/or CoQ₁₀ and mitochondrial transplantation, alone or in a combinational mode. An in vivo model of myocardial I/R injury was established by left anterior descending coronary artery occlusion and re-opening. Mitochondria were isolated from donor rats and injected intramyocardially (150 µl of the mitochondrial suspension containing 2 × 10⁵±0.3 × 10⁵ mitochondria) at the onset of reperfusion in recipient groups. CoQ₁₀ (20 mg/kg/day) was injected intramuscularly for 7 days before I/R operation. Lastly, myocardial function, cTn-I level, expression of autophagy-associated proteins (Beclin1, p62, and LC3-II/LC3-I), and the levels of pro-inflammatory cytokines (TNF-α, IL-1β, and IL-6) were assessed.

RESULTS

Co-application of CoQ₁₀ and mitotherapy concomitantly improved myocardial function and decreased cTn-I level in aged reperfused hearts (P < .001). This combination therapy also modulated autophagic activity and decreased pro-inflammatory cytokines (P < .01 to P < .001). This combinational approach induced noticeable cardioprotection in comparison with monotherapies-received groups.

CONCLUSION

We found that combination of CoQ₁₀ and mitochondrial transplantation attenuated myocardial I/R injury in aged rats, in part by modulating autophagy and inflammatory response, hence, appears to restore aging-related loss of cardioprotection in aged patients.

DNA damage response signaling: A common link between cancer and cardiovascular diseases

DNA damage response (DDR) signaling ensures genomic and proteomic homeostasis to maintain a healthy genome. Dysregulation either in the form of down- or upregulation in the DDR pathways correlates with various pathophysiological states, including cancer and cardiovascular diseases (CVDs). Impaired DDR is studied as a signature mechanism for cancer; however, it also plays a role in ischemia-reperfusion injury (IRI), inflammation, cardiovascular function, and aging, demonstrating a complex and intriguing relationship between cancer and pathophysiology of CVDs. Accordingly, there are increasing number of reports indicating higher incidences of CVDs in cancer patients. In the present review, we thoroughly discuss (1) different DDR pathways, (2) the functional cross talk among different DDR mechanisms, (3) the role of DDR in cancer, (4) the commonalities and differences of DDR between cancer and CVDs, (5) the role of DDR in pathophysiology of CVDs, (6) interventional strategies for targeting genomic instability in CVDs, and (7) future perspective.

Distribution of Nicotinamide Mononucleotide after Intravenous Injection in Normal and Ischemic Stroke Mice

OBJECTIVE

This study determined for the first time the distribution of intravenous nicotinamide mononucleotide (NMN) and its metabolite nicotinamide adenine dinucleotide (NAD) in normal and ischemic stroke mice, examined the therapeutic effect of NMN on ischemic brain infarction, and evaluated acute toxicity of NMN after intravenous injection of NMN.

METHODS

NMN and NAD levels were determined using ultra-high-performance liquid chromatography tandem mass spectrometry in biological samples from mice with or without middle cerebral artery occlusion (MCAO) at different time points post intravenous NMN injection (300 mg/kg). Brain infarction was evaluated 24 h post-MCAO. 2 g/kg NMN was used in the acute toxicity test.

RESULTS

Under either normal or MCAO conditions, serum NMN levels sharply increased after intravenous NMN administration and then decreased rapidly within 15 min, while serum NAD levels remained unchanged during 30 min observation. Both substances displayed tissue accumulation over time and stored faster under MCAO conditions, with kidney having the highest concentrations. Particularly, NMN accumulated earlier than NAD in the brain. Moreover, NMN reduced cerebral infarction at 24 h post-MCAO. No acute toxicity was observed for 14 days. NRK1 and SLC12A8 involved in two pathways of NMN uptake exhibited the highest expressions in kidney and colon, respectively, among 11 different tissues.

CONCLUSION

NMN distributes to various tissues after intravenous injection and has the ability to enter the brain to boost NAD levels, and exhibits safety and therapeutic effect on acute ischemic stroke injury. High renal distribution of NMN indicates its importance in the kidney.

The Aging Heart: A Molecular and Clinical Challenge

Aging is associated with an increasing burden of morbidity, especially for cardiovascular diseases (CVDs). General cardiovascular risk factors, ischemic heart diseases, heart failure, arrhythmias, and cardiomyopathies present a significant prevalence in older people, and are characterized by peculiar clinical manifestations that have distinct features compared with the same conditions in a younger population. Remarkably, the aging heart phenotype in both healthy individuals and patients with CVD reflects modifications at the cellular level. An improvement in the knowledge of the physiological and pathological molecular mechanisms underlying cardiac aging could improve clinical management of older patients and offer new therapeutic targets.

Nicotinamide adenine dinucleotide attenuates acetaminophen-induced acute liver injury via activation of PARP1, Sirt1, and Nrf2 in mice

The aim of this study was to investigate the protective effect of nicotinamide adenine dinucleotide (NAD⁺) against acute liver injury (ALI) induced by acetaminophen (APAP) overdose in mice. First, serum transaminases were used to assess the protective effect of NAD⁺, and the data revealed that NAD⁺ mitigated the APAP-induced ALI in a dose-dependent manner. Then, we performed hematoxylin-eosin staining of liver tissues and found that NAD⁺ alleviated the abnormalities of histopathology. Meanwhile, increase in the malondialdehyde content and decrease in glutathione, superoxide dismutase (SOD), and glutathione peroxidase were identified in the APAP group, which were partially prevented by the NAD⁺ pretreatment. Moreover, compared with the mice treated with APAP only, the expression of poly ADP-ribose polymerase 1 (PARP1), Sirtuin1 (Sirt1), SOD2, nuclear factor erythroid 2-related factor 2 (Nrf2), and hemoxygenase-1 was upregulated, while Kelch-like ECH-associated protein 1 and histone H2AX phosphorylated on Ser-139 were downregulated by NAD⁺ in NAD⁺ + APAP group. Conversely, NAD⁺ could not correct the elevated expression of phospho-Jun N-terminal kinase and phospho-extracellular signal-regulated kinase induced by APAP. Taken together, these findings suggest that NAD⁺ confers an anti-ALI effect to enhance the expression of PARP1 and Sirt1, and to simultaneously stimulate the Nrf2 anti-oxidant signaling pathway.

Acute Treatment with Nicotinamide Riboside Chloride Reduces Hippocampal Damage and Preserves the Cognitive Function of Mice with Ischemic Injury

Nicotinamide adenine dinucleotide (NAD) is a critical cosubstrate for enzymes involved in supplying energy to the brain. Nicotinamide riboside (NR), an NAD⁺ precursor, emerges as a neuroprotective factor after chronic brain insults. However, researchers have not determined whether it improves cognition after acute ischemia. In the present study, mice with middle cerebral artery occlusion were treated with NR chloride (NRC, 300 mg/kg, IP., 20 min after reperfusion). The results of the Morris water maze test revealed better recovery of learning and memory function in the NRC-treated group. Acute NRC treatment decreased hippocampal infarct volume, reduced neuronal loss and apoptosis in the hippocampus. Western blot and high-performance liquid chromatography assays of hippocampal tissues revealed that the activation of Sirtin-1 and adenosine 5' monophosphate-activated protein kinase was increased, the NAD content was elevated, and the production of adenosine triphosphate was strengthened by NRC. Collectively, acute NRC treatment increased the energy supply, reduced the neuronal loss and apoptosis, protected the hippocampus and ultimately promoted the recovery of cognitive function after brain ischemia.

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.

New Crystalline Salts of Nicotinamide Riboside as Food Additives

NR⁺ is a highly effective vitamin B₃ type supplement due to its unique ability to replenish NAD⁺ levels. While NR⁺ chloride is already on the market as a nutritional supplement, its synthesis is challenging, expensive, and low yielding, making it cumbersome for large-scale industrial production. Here we report the novel crystalline NR⁺ salts, d/l/dl-hydrogen tartrate and d/l/dl-hydrogen malate. Their high-yielding, one-pot manufacture does not require specific equipment and is suitable for multi-ton scale production. These new NR⁺ salts seem ideal for nutritional applications due to their bio-equivalence compared to the approved NR⁺ chloride. In addition, the crystal structures of all stereoisomers of NR⁺ hydrogen tartrate and NR⁺ hydrogen malate and a comparison to the known NR⁺ halogenides are presented.

Nicotinamide mononucleotide and melatonin counteract myocardial ischemia-reperfusion injury by activating SIRT3/FOXO1 and reducing apoptosis in aged male rats

It has been documented that aging increases the risk of cardiovascular disease including myocardial ischemia/reperfusion (IR) injury and acute myocardial infarction. In this study, we aimed to investigate the individual or combined effects of nicotinamide mononucleotide (NMN) and melatonin (Mel) treatment on apoptotic markers, expression of SIRT3, and FOXO1, and infarct size of the aged myocardium subjected to IR injury. Sixty aged Wistar rats (22-24 months) were assigned to five groups including sham, IR, NMN+IR, Mel+IR, and NMN+Mel+IR (combination therapy). Isolated hearts were exposed to 30-min regional ischemia followed by 60-min reperfusion. NMN (100 mg/kg/day/i.p.) was injected every second day starting on day 28 before IR injury. Melatonin was added to the perfusion solution five minutes prior to and until 15 min after the start of reperfusion. The infarct size was assessed by computerized planimetry. The mRNA levels of SIRT3, FOXO1, and apoptotic genes Bax, Bcl-2, and Caspase-3 were estimated by real-time PCR. All treatments reduced infarct size as compared with the IR group. Melatonin and NMN upregulated the gene expression of Bcl-2, SIRT3, and FOXO1 and downregulated the gene expression of Bax, and Caspase-3, in comparison to the IR group. Also, the protein levels of SIRT3, quantified by Western blotting, were upregulated by the interventions. The effects of combination therapy were significantly greater than those of melatonin or NMN alone. These findings indicate that the combined administration of NMN and melatonin can protect the aged heart against IR injury by decreasing apoptosis and activating the SIRT3/FOXO1 pathway.

Role of Oxidative DNA Damage and Repair in Atrial Fibrillation and Ischemic Heart Disease

Atrial fibrillation (AF) and ischemic heart disease (IHD) represent the two most common clinical cardiac diseases, characterized by angina, arrhythmia, myocardial damage, and cardiac dysfunction, significantly contributing to cardiovascular morbidity and mortality and posing a heavy socio-economic burden on society worldwide. Current treatments of these two diseases are mainly symptomatic and lack efficacy. There is thus an urgent need to develop novel therapies based on the underlying pathophysiological mechanisms. Emerging evidence indicates that oxidative DNA damage might be a major underlying mechanism that promotes a variety of cardiac diseases, including AF and IHD. Antioxidants, nicotinamide adenine dinucleotide (NAD⁺) boosters, and enzymes involved in oxidative DNA repair processes have been shown to attenuate oxidative damage to DNA, making them potential therapeutic targets for AF and IHD. In this review, we first summarize the main molecular mechanisms responsible for oxidative DNA damage and repair both in nuclei and mitochondria, then describe the effects of oxidative DNA damage on the development of AF and IHD, and finally discuss potential targets for oxidative DNA repair-based therapeutic approaches for these two cardiac diseases.

NAD+ and cardiovascular diseases

Nicotinamide adenine dinucleotide (NAD) plays pivotal roles in controlling many biochemical processes. 'NAD' refers to the chemical backbone irrespective of charge, whereas 'NAD⁺' and 'NADH' refers to oxidized and reduced forms, respectively. NAD⁺/NADH ratio is essential for maintaining cellular reduction-oxidation (redox) homeostasis and for modulating energy metabolism. As a sensing or consuming enzyme of the poly (ADP-ribose) polymerase 1 (PARP1), the cyclic ADP-ribose (cADPR) synthases (CD38 and CD157), and sirtuin protein deacetylases (sirtuins, SIRTs), NAD⁺ participates in several key processes in cardiovascular disease. For example, NAD⁺ protects against metabolic syndrome, heart failure, ischemia-reperfusion (IR) injury, arrhythmia and hypertension. Accordingly, the subsequent loss of NAD⁺ in aging or during stress results in altered metabolic status and potentially increased disease susceptibility. Therefore, it is essential to maintain NAD⁺ or reduce loss in the heart. This review focuses on the involvement of NAD⁺ in the pathogenesis of cardiovascular disease and explores the effects of NAD⁺ boosting strategies in cardiovascular health.

NAD+ metabolism: pathophysiologic mechanisms and therapeutic potential

Nicotinamide adenine dinucleotide (NAD+) and its metabolites function as critical regulators to maintain physiologic processes, enabling the plastic cells to adapt to environmental changes including nutrient perturbation, genotoxic factors, circadian disorder, infection, inflammation and xenobiotics. These effects are mainly achieved by the driving effect of NAD+ on metabolic pathways as enzyme cofactors transferring hydrogen in oxidation-reduction reactions. Besides, multiple NAD+-dependent enzymes are involved in physiology either by post-synthesis chemical modification of DNA, RNA and proteins, or releasing second messenger cyclic ADP-ribose (cADPR) and NAADP+. Prolonged disequilibrium of NAD+ metabolism disturbs the physiological functions, resulting in diseases including metabolic diseases, cancer, aging and neurodegeneration disorder. In this review, we summarize recent advances in our understanding of the molecular mechanisms of NAD+-regulated physiological responses to stresses, the contribution of NAD+ deficiency to various diseases via manipulating cellular communication networks and the potential new avenues for therapeutic intervention.

NAD+ Metabolism as an Emerging Therapeutic Target for Cardiovascular Diseases Associated With Sudden Cardiac Death

In addition to its central role in mediating oxidation reduction in fuel metabolism and bioenergetics, nicotinamide adenine dinucleotide (NAD⁺) has emerged as a vital co-substrate for a number of proteins involved in diverse cellular processes, including sirtuins, poly(ADP-ribose) polymerases and cyclic ADP-ribose synthetases. The connection with aging and age-associated diseases has led to a new wave of research in the cardiovascular field. Here, we review the basics of NAD⁺ homeostasis, the molecular physiology and new advances in ischemic-reperfusion injury, heart failure, and arrhythmias, all of which are associated with increased risks for sudden cardiac death. Finally, we summarize the progress of NAD⁺-boosting therapy in human cardiovascular diseases and the challenges for future studies.

Effect of troxerutin on oxidative stress and expression of genes regulating mitochondrial biogenesis in doxorubicin-induced myocardial injury in rats

Because of limitation of doxorubicin (DOX) clinical application in chemotherapy due to its cardiotoxicity, finding new strategies to reduce DOX challenge and improve patients' outcomes is crucial. Due to positive cardiovascular impacts of troxerutin (TXR), here we have investigated the effect of TXR on DOX-induced cardiotoxicity by evaluating the myocardial oxidative stress and expression of genes regulating mitochondrial biogenesis. Male Wistar rats (250-300 g) were randomly allocated into four groups: control, TXR, DOX, and TXR + DOX. Troxerutin (150 mg/kg) was orally administrated once a day through a gavage tube for 4 weeks before DOX challenge. The TXR-treated and time-matched control rats received intraperitoneal injection of DOX (20 mg/kg). Three days after DOX challenge, the left ventricular samples were obtained to determine the expression of genes regulating mitochondrial biogenesis via real-time PCR. Myocardial creatine kinase (CK-mB), oxidative stress markers, and mitochondrial function (generation of reactive oxygen species or ROS and ATP levels) were also evaluated using commercial kits and spectrophotometric and fluorometric methods. DOX administration significantly increased the levels of CK-mB, malondialdehyde (MDA), and mitochondrial ROS levels, while reduced the cellular ATP production and expression levels of SIRT-1, PGC-1α, and NRF-2 as well as superoxide dismutase, glutathione peroxidase, and catalase activity in comparison to control group (P < 0.05 to P < 0.01). Pretreatment of DOX-received rats with TXR significantly upregulated the expression of all biogenesis genes and antioxidant enzymes with non-significant effect on catalase activity, and significantly reduced CK-mB and MDA levels toward control values (P < 0.05 to P < 0.01). Mitochondrial ROS and ATP levels were also restored significantly by pretreatment with TXR (P < 0.05). The data suggested that preconditioning of rats with TXR had protective effect on DOX-induced cardiotoxicity through inducing antioxidative properties and restoring the mitochondrial function and the expression profiles of myocardial SIRT-1/PGC-1α/NRF-2 network.

N-terminal protein acetylation by NatB modulates the levels of Nmnats, the NAD+ biosynthetic enzymes in Saccharomyces cerevisiae

NAD+ is an essential metabolite participating in cellular biochemical processes and signaling. The regulation and interconnection among multiple NAD+ biosynthesis pathways are incompletely understood. Yeast (Saccharomyces cerevisiae) cells lacking the N-terminal (Nt) protein acetyltransferase complex NatB exhibit an approximate 50% reduction in NAD+ levels and aberrant metabolism of NAD+ precursors, changes that are associated with a decrease in nicotinamide mononucleotide adenylyltransferase (Nmnat) protein levels. Here, we show that this decrease in NAD+ and Nmnat protein levels is specifically due to the absence of Nt-acetylation of Nmnat (Nma1 and Nma2) proteins and not of other NatB substrates. Nt-acetylation critically regulates protein degradation by the N-end rule pathways, suggesting that the absence of Nt-acetylation may alter Nmnat protein stability. Interestingly, the rate of protein turnover (t½) of non-Nt-acetylated Nmnats did not significantly differ from those of Nt-acetylated Nmnats. Accordingly, deletion or depletion of the N-end rule pathway ubiquitin E3 ligases in NatB mutants did not restore NAD+ levels. Next, we examined whether the status of Nt-acetylation would affect the translation of Nmnats, finding that the absence of Nt-acetylation does not significantly alter the polysome formation rate on Nmnat mRNAs. However, we observed that NatB mutants have significantly reduced Nmnat protein maturation. Our findings indicate that the reduced Nmnat levels in NatB mutants are mainly due to inefficient protein maturation. Nmnat activities are essential for all NAD+ biosynthesis routes, and understanding the regulation of Nmnat protein homeostasis may improve our understanding of the molecular basis and regulation of NAD+ metabolism.

Melatonin and Nicotinamide Mononucleotide Attenuate Myocardial Ischemia/Reperfusion Injury via Modulation of Mitochondrial Function and Hemodynamic Parameters in Aged Rats

Ischemic heart diseases are the major reasons for disability and mortality in elderly individuals. In this study, we tried to examine the combined effects of nicotinamide mononucleotide (NMN) preconditioning and melatonin postconditioning on cardioprotection and mitochondrial function in ischemia/reperfusion (I/R) injury of aged male rats. Sixty aged Wistar rats were randomly allocated to 5 groups, including sham, control, NMN-receiving, melatonin-receiving, and combined therapy (NMN+melatonin). Isolated hearts were mounted on Langendorff apparatus and then underwent 30-minue ligation of left anterior descending coronary artery to induce regional ischemic insult, followed by 60 minutes of reperfusion. Nicotinamide mononucleotide (100 mg/kg/d intraperitoneally) was administered for every other day for 28 days before I/R. Melatonin added to perfusion solution, 5 minutes prior to the reperfusion up to 15 minutes early reperfusion. Myocardial hemodynamic and infarct size (IS) were measured, and the left ventricles samples were obtained to evaluate cardiac mitochondrial function and oxidative stress markers. Melatonin postconditioning and NMN had significant cardioprotective effects in aged rats; they could improve hemodynamic parameters and reduce IS and lactate dehydrogenase release compared to those of control group. Moreover, pretreatment with NMN increased the cardioprotection by melatonin. All treatments reduced oxidative stress and mitochondrial reactive oxygen species (ROS) levels and improved mitochondrial membrane potential and restored NAD⁺/NADH ratio. The effects of combined therapy on reduction of mitochondrial ROS and oxidative status and improvement of mitochondrial membrane potential were greater than those of alone treatments. Combination of melatonin and NMN can be a promising strategy to attenuate myocardial I/R damages in aged hearts. Restoration of mitochondrial function may substantially contribute to this cardioprotection.

NAD+ repletion inhibits the endothelial-to-mesenchymal transition induced by TGF-β in endothelial cells through improving mitochondrial unfolded protein response

Endothelial-to-mesenchymal transition (EndMT) plays an important role in the progression of cardiac fibrosis but its mechanism and treatment need to be further understood. Herein, we have found that mitochondrial unfolded protein response (mtUPR) played a critical role in transforming growth factor beta 1 (TGF-β1)-induced EndMT in endothelial cells (ECs). MtUPR was repressed in endothelial cells after exposure to TGF-β1. NAD + precursor nicotinamide riboside (NR) could attenuate TGF-β1-induced EndMT and improve the levels of mtUPR. Significantly, prohibitin proteins (PHB and PHB2) was also regulated by nicotinamide riboside. Moreover, we found that inhibition of prohibitin proteins could prevent the protective effect of nicotinamide riboside on mtUPR and TGF-β1-induced EndMT. Overexpression of prohibitin proteins could alleviate mitochondrial function and TGF-β1-induced EndMT through improving mtUPR. In vivo, The EndMT of ECs induced by Transverse aortic constriction (TAC) in mouse was inhibited by NR. In conclusion, our results indicate that nicotinamide riboside improved the expression of prohibitin proteins to ameliorate EndMT via promotion of mtUPR. Nicotinamide riboside is a potential therapeutic target for cardiac fibrosis.