Nicotinamide mononucleotide inhibits JNK activation to reverse Alzheimer disease

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.

NMN synbiotics intervention modulates gut microbiota and metabolism in APP/PS1 Alzheimer's disease mouse models

Alzheimer's disease (AD) is a complex neurodegenerative condition with growing evidence implicating the gut microbiota in its pathogenesis. This study aimed to investigate the effects of NMN synbiotics, a combination of β-nicotinamide mononucleotide (NMN), Lactobacillus plantarum, and lactulose, on the gut microbiota composition and metabolic profiles in APP/PS1 transgenic mice. Results demonstrated that NMN synbiotics led to a notable restructuring of the gut microbiota, with a decreased Firmicutes/Bacteroidetes ratio in the AD mice, suggesting a potential amelioration of gut dysbiosis. Alpha diversity indices indicated a reduction in microbial diversity following NMN synbiotics supplementation, while beta diversity analyses revealed a shift towards a more balanced microbial community structure. Functional predictions based on the 16S rRNA data highlighted alterations in metabolic pathways, particularly those related to amino acid and energy metabolism, which are crucial for neuronal health. The metabolomic analysis uncovered a significant impact of NMN synbiotics on the gut metabolome, with normalization of metabolic composition in AD mice. Differential metabolite functions were enriched in pathways associated with neurotransmitter synthesis and energy metabolism, pointing to the potential therapeutic effects of NMN synbiotics in modulating the gut-brain axis and synaptic function in AD. Immunohistochemical staining observed a significant reduction of amyloid plaques formed by Aβ deposition in the brain of AD mice after NMN synbiotics intervention. The findings underscore the potential of using synbiotics to ameliorate the neurodegenerative processes associated with Alzheimer's disease, opening new avenues for therapeutic interventions.

Alleviation of hepatic insulin resistance and steatosis with NMN via improving endoplasmic reticulum-Mitochondria miscommunication in the liver of HFD mice

The interaction between endoplasmic reticulum (ER) and mitochondria has been shown to play a key role in hepatic steatosis during chronic obesity. β-nicotinamide mononucleotide (NMN) has been reported to regulate obesity, however, its molecular mechanism at the subcellular level remains unclear. Here, NMN improved liver steatosis and insulin resistance in chronic high-fat diet (HFD) mice. RNA-seq showed that compared with the liver of HFD mice, NMN intervention enhanced fat digestion and absorption and stimulated the cholesterol metabolism signaling pathways, while impaired insulin resistance and the fatty acid biosynthesis signaling pathways. Mechanistically, NMN ameliorated mitochondrial dysfunction and ER oxidative stress in the liver of HFD mice by increasing hepatic nicotinamide adenine dinucleotide (NAD+) (P < 0.01) levels. This effect increased the contact sites (mitochondria-associated membranes [MAMs]) between ER and mitochondria, thereby promoting intracellular ATP (P < 0.05) production and mitigating lipid metabolic disturbances in the liver of HFD mice. Taken together, this study provided a theoretical basis for restoring metabolic dynamic equilibrium in the liver of HFD mice by increasing MAMs via the nutritional strategy of NMN supplementation.

Excess glucose alone depress young mesenchymal stromal/stem cell osteogenesis and mitochondria activity within hours/days via NAD+/SIRT1 axis

BACKGROUND

The impact of global overconsumption of simple sugars on bone health, which peaks in adolescence/early adulthood and correlates with osteoporosis (OP) and fracture risk decades, is unclear. Mesenchymal stromal/stem cells (MSCs) are the progenitors of osteoblasts/bone-forming cells, and known to decrease their osteogenic differentiation capacity with age. Alarmingly, while there is correlative evidence that adolescents consuming greatest amounts of simple sugars have the lowest bone mass, there is no mechanistic understanding on the causality of this correlation.

METHODS

Bioinformatics analyses for energetics pathways involved during MSC differentiation using human cell information was performed. In vitro dissection of normal versus high glucose (HG) conditions on osteo-/adipo-lineage commitment and mitochondrial function was assessed using multi-sources of non-senescent human and murine MSCs; for in vivo validation, young mice was fed normal or HG-added water with subsequent analyses of bone marrow CD45- MSCs.

RESULTS

Bioinformatics analyses revealed mitochondrial and glucose-related metabolic pathways as integral to MSC osteo-/adipo-lineage commitment. Functionally, in vitro HG alone without differentiation induction decreased both MSC mitochondrial activity and osteogenesis while enhancing adipogenesis by 8 h' time due to depletion of nicotinamide adenine dinucleotide (NAD+), a vital mitochondrial co-enzyme and co-factor to Sirtuin (SIRT) 1, a longevity gene also involved in osteogenesis. In vivo, HG intake in young mice depleted MSC NAD+, with oral NAD+ precursor supplementation rapidly reversing both mitochondrial decline and osteo-/adipo-commitment in a SIRT1-dependent fashion within 1 ~ 5 days.

CONCLUSIONS

We found a surprisingly rapid impact of excessive glucose, a single dietary factor, on MSC SIRT1 function and osteogenesis in youthful settings, and the crucial role of NAD+-a single molecule-on both MSC mitochondrial function and lineage commitment. These findings have strong implications on future global OP and disability risks in light of current worldwide overconsumption of simple sugars.

Brain energy metabolism: A roadmap for future research

Although we have learned much about how the brain fuels its functions over the last decades, there remains much still to discover in an organ that is so complex. This article lays out major gaps in our knowledge of interrelationships between brain metabolism and brain function, including biochemical, cellular, and subcellular aspects of functional metabolism and its imaging in adult brain, as well as during development, aging, and disease. The focus is on unknowns in metabolism of major brain substrates and associated transporters, the roles of insulin and of lipid droplets, the emerging role of metabolism in microglia, mysteries about the major brain cofactor and signaling molecule NAD+, as well as unsolved problems underlying brain metabolism in pathologies such as traumatic brain injury, epilepsy, and metabolic downregulation during hibernation. It describes our current level of understanding of these facets of brain energy metabolism as well as a roadmap for future research.

ABCA7 deficiency causes neuronal dysregulation by altering mitochondrial lipid metabolism

ABCA7 loss-of-function variants are associated with increased risk of Alzheimer's disease (AD). Using ABCA7 knockout human iPSC models generated with CRISPR/Cas9, we investigated the impacts of ABCA7 deficiency on neuronal metabolism and function. Lipidomics revealed that mitochondria-related phospholipids, such as phosphatidylglycerol and cardiolipin were reduced in the ABCA7-deficient iPSC-derived cortical organoids. Consistently, ABCA7 deficiency-induced alterations of mitochondrial morphology accompanied by reduced ATP synthase activity and exacerbated oxidative damage in the organoids. Furthermore, ABCA7-deficient iPSC-derived neurons showed compromised mitochondrial respiration and excess ROS generation, as well as enlarged mitochondrial morphology compared to the isogenic controls. ABCA7 deficiency also decreased spontaneous synaptic firing and network formation in iPSC-derived neurons, in which the effects were rescued by supplementation with phosphatidylglycerol or NAD+ precursor, nicotinamide mononucleotide. Importantly, effects of ABCA7 deficiency on mitochondria morphology and synapses were recapitulated in synaptosomes isolated from the brain of neuron-specific Abca7 knockout mice. Together, our results provide evidence that ABCA7 loss-of-function contributes to AD risk by modulating mitochondria lipid metabolism.

Adipose tissue as a therapeutic target for vascular damage in Alzheimer's disease

Adipose tissue has recently been recognized as an important endocrine organ that plays a crucial role in energy metabolism and in the immune response in many metabolic tissues. With this regard, emerging evidence indicates that an important crosstalk exists between the adipose tissue and the brain. However, the contribution of adipose tissue to the development of age-related diseases, including Alzheimer's disease, remains poorly defined. New studies suggest that the adipose tissue modulates brain function through a range of endogenous biologically active factors known as adipokines, which can cross the blood-brain barrier to reach the target areas in the brain or to regulate the function of the blood-brain barrier. In this review, we discuss the effects of several adipokines on the physiology of the blood-brain barrier, their contribution to the development of Alzheimer's disease and their therapeutic potential. LINKED ARTICLES: This article is part of a themed issue From Alzheimer's Disease to Vascular Dementia: Different Roads Leading to Cognitive Decline. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v181.6/issuetoc.

Biosynthesis of Nicotinamide Mononucleotide: Synthesis Method, Enzyme, and Biocatalytic System

Nicotinamide mononucleotide (NMN) has garnered substantial interest as a functional food product. Industrial NMN production relies on chemical methods, facing challenges in separation, purification, and regulatory complexities, leading to elevated prices. In contrast, NMN biosynthesis through fermentation or enzyme catalysis offers notable benefits like eco-friendliness, recyclability, and efficiency, positioning it as a primary avenue for future NMN synthesis. Enzymatic NMN synthesis encompasses the nicotinamide-initial route and nicotinamide ribose-initial routes. Key among these is nicotinamide riboside kinase (NRK), pivotal in the latter route. The NRK-mediated biosynthesis is emerging as a prominent trend due to its streamlined route, simplicity, and precise specificity. The essential aspect is to obtain an engineered NRK that exhibits elevated activity and robust stability. This review comprehensively assesses diverse NMN synthesis methods, offering valuable insights into efficient, sustainable, and economical production routes. It spotlights the emerging NRK-mediated biosynthesis pathway and its significance. The establishment of an adenosine triphosphate (ATP) regeneration system plays a pivotal role in enhancing NMN synthesis efficiency through NRK-catalyzed routes. The review aims to be a reference for researchers developing green and sustainable NMN synthesis, as well as those optimizing NMN production.

Effect of Nicotinamide Mononucleotide Concentration in Human Milk on Neurodevelopmental Outcome: The Tohoku Medical Megabank Project Birth and Three-Generation Cohort Study

(1) Background: Breast milk is the only source of nutrition for breastfed infants, but few studies have examined the relationship between breast milk micronutrients and infant neurodevelopmental outcome in exclusively breastfed infants. The aim of this study was to characterize the association between nicotinamide adenine dinucleotide (NAD)-related compounds in the breast milk of Japanese subjects and infant neurodevelopmental outcome. (2) Methods: A total of 150 mother-child pairs were randomly selected from the three-generation cohort of the Tohoku Medical Megabank in Japan. Infants were exclusively breastfed for up to 6 months. Breast milk was collected at 1 month postpartum, and the quantity of NAD-related substances in the breast milk was quantified. The mothers also completed developmental questionnaires at 6, 12, and 24 months. The relationship between the concentration of NAD-related substances in breast milk and developmental indicators was evaluated via ordinal logistic regression analysis. (3) Results: Nicotinamide mononucleotide (NMN) was quantified as the major NAD precursor in breast milk. The median amount of NMN in the breast milk was 9.2 μM. The NMN concentration in breast milk was the only NAD-related substance in breast milk that showed a significant positive correlation with neurodevelopmental outcome in infants at 24 months. (4) Conclusions: The results suggest that NMN in human milk may be an important nutrient for early childhood development.

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.

The Combination of Citicoline and Nicotinamide Mononucleotide Induces Neurite Outgrowth and Mitigates Vascular Cognitive Impairment via SIRT1/CREB Pathway

Vascular dementia (VD) is characterized with vascular cognitive impairment (VCI), which currently has few effective therapies in clinic. Neuronal damage and white matter injury are involved in the pathogenesis of VCI. Citicoline has been demonstrated to exhibit neuroprotection and neurorepair to improve cognition in cerebrovascular diseases. Nicotinamide adenine dinucleotide (NAD+)-dependent sirtuin (SIRT) signaling pathway constitutes a strong intrinsic defense system against various stresses including neuroinflammation in VCI. Our hypothesis is that the combined use of citicoline and the precursor of NAD+, nicotinamide mononucleotide (NMN), could enhance action on cognitive function in VCI. We investigated the synergistic effect of these two drugs in the rat model of VCI by bilateral common carotid artery occlusion (BCCAO). Citicoline significantly enhanced neurite outgrowth in Neuro-2a cells, and the combination of citicoline and NMN remarkably induced neurite outgrowth in Neuro-2a cells and primary cortical neuronal cells with an optimal proportion of 4:1. In the rat model of BCCAO, when two drugs in combination of 160 mg/kg citicoline and 40 mg/kg NMN, this combination administrated at 7 days post-BCCAO significantly improved the cognitive impairment in BCCAO rats compared with vehicle group by the analysis of the Morris water maze and the novel object recognition test. This combination also decreased microglial activation and neuroinflammation, and protected white matter integrity indicated by the increased myelin basic protein (MBP) expression through activation of SIRT1/TORC1/CREB signaling pathway. Our results suggest that the combination of citicoline and NMN has a synergistic effect for the treatment of VD associated with VCI.

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.

Gut microbiota-derived short chain fatty acids act as mediators of the gut-brain axis targeting age-related neurodegenerative disorders: a narrative review

Neurodegenerative diseases associated with aging are often accompanied by cognitive decline and gut microbiota disorder. But the impact of gut microbiota on these cognitive disturbances remains incompletely understood. Short chain fatty acids (SCFAs) are major metabolites produced by gut microbiota during the digestion of dietary fiber, serving as an energy source for gut epithelial cells and/or circulating to other organs, such as the liver and brain, through the bloodstream. SCFAs have been shown to cross the blood-brain barrier and played crucial roles in brain metabolism, with potential implications in mediating Alzheimer's disease (AD) and Parkinson's disease (PD). However, the underlying mechanisms that SCFAs might influence psychological functioning, including affective and cognitive processes and their neural basis, have not been fully elucidated. Furthermore, the dietary sources which determine these SCFAs production was not thoroughly evaluated yet. This comprehensive review explores the production of SCFAs by gut microbiota, their transportation through the gut-brain axis, and the potential mechanisms by which they influence age-related neurodegenerative disorders. Also, the review discusses the importance of dietary fiber sources and the challenges associated with harnessing dietary-derived SCFAs as promoters of neurological health in elderly individuals. Overall, this study suggests that gut microbiota-derived SCFAs and/or dietary fibers hold promise as potential targets and strategies for addressing age-related neurodegenerative disorders.

Inhibition of neuronal Kv7 channels ameliorates MK-801-induced cognitive dysfunction in mice via up-regulating NAMPT expression

PURPOSE

Abnormal energy metabolism affects cognitive function in schizophrenia. Nicotinamide phosphoribosyltransferase (NAMPT), as the rate-limiting enzyme of nicotinamide adenine dinucleotide (NAD+), is involved in energy metabolism by regulating the synthesis of NAD+. This study aims to clarify whether inhibition of Kv7 channels improves cognitive impairment by up-regulating NAMPT expression to increase the level of NAD+.

METHODS

The dominant negative pore mutation of KCNQ2 in transgenic mice was achieved by mutating residual 279-Gly to Ser (rQ2-G279S). A cognitive deficit model was established by injecting MK-801 into C57BL/6J mice. Y-maze and prepulse inhibition (PPI) tests were performed to evaluate cognitive ability. Gene and protein expression of NAMPT in the mouse hippocampus, cortex, and PC-12 cells were measured by qRT-PCR and Western blot. The level of NAD+ was measured by a WST-8 assay.

RESULTS

The Y-maze and PPI results showed that genetic or pharmacological inhibition of Kv7 channels by XE991 enhanced cognitive function in mice. Furthermore, inhibition of Kv7 channels increased the gene and protein expression of NAMPT and the level of NAD+ in the hippocampus and cortex of the above animal model. Similarly, XE991 treatment increased NAMPT expression and NAD+ levels in PC-12 cells. NAMPT inhibitor FK866 and Kv7 channel opener retigabine reversed the effects of XE991 in vivo and in vitro. In addition, XE991 increased pAMPK protein expression in PC-12 cells, while AMPK inhibitor Compound C counteracted the effect of XE991 on increasing NAMPT expression and NAD+ levels.

CONCLUSIONS

Suppression of Kv7 channel function improved spatial working memory and PPI impairment. This result may be achieved by activating AMPK to up-regulate NAMPT expression and thus increase NAD+ levels.

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.

Effect of Exercise and Oral Niacinamide Mononucleotide on Improving Mitochondrial Autophagy in Alzheimer's Disease

Oral niacinamide mononucleotide (NMN) and aerobic exercise have been shown to enhance niacinamide adenine dinucleotide (NAD⁺) in the body. NAD⁺ plays a critical role in the body and can directly and indirectly affect many key cellular functions, including metabolic pathways, DNA repair, chromatin remodeling, cell aging, and immune cell function. It is noteworthy that the level of NAD⁺ decreases gradually with increasing age. Decreased levels of NAD⁺ have been causally associated with a number of diseases associated with aging, including cognitive decline, cancer, metabolic diseases, sarcopenia, and frailty. Many diseases related to aging can be slowed down or even reversed by restoring NAD⁺ levels. For example, oral NMN or exercise to increase NAD⁺ levels in APP/PS1 mice have been proven to improve mitochondrial autophagy, but currently, there is no regimen combining oral NMN with exercise. This review summarizes recent studies on the effect of oral NMN on the enhancement of NAD⁺ in vivo and the improvements in mitochondrial autophagy abnormalities in AD through aerobic exercise, focusing on (1) how oral NMN improves the internal NAD⁺ level; (2) how exercise regulates the content of NAD⁺ in the body; (3) the relationship between exercise activation of NAD⁺ and AMPK; (4) how SIRT1 is regulated by NAD⁺ and AMPK and activates PGC-1α to mediate mitochondrial autophagy through changes in mitochondrial dynamics. By summarizing the results of the above four aspects, and combined with the synthesis of NAD⁺ in vivo, we can infer how exercise elevates the level of NAD⁺ in vivo to mediate mitochondrial autophagy, so as to propose a new hypothesis that exercise interferes with Alzheimer's disease (AD).

Technology and functional insights into the nicotinamide mononucleotide for human health

Nicotinamide mononucleotide (NMN), a naturally occurring biologically active nucleotide, mainly functions via mediating the biosynthesis of NAD⁺. In recent years, its excellent pharmacological activities including anti-aging, treating neurodegenerative diseases, and protecting the heart have attracted increasing attention from scholars and entrepreneurs for production of a wide range of formulations, including functional food ingredients, health care products, active pharmaceuticals, and pharmaceutical intermediates. Presently, the synthesis methods of NMN mainly include two categories: chemical synthesis and biosynthesis. With the development of biocatalyst engineering and synthetic biology strategies, bio-preparation has proven to be efficient, economical, and sustainable methods. This review summarizes the chemical synthesis and biosynthetic pathways of NMN and provides an in-depth investigation on the mining and modification of enzyme resources during NMN biosynthesis, as well as the screening of hosts and optimization of chassis cells via metabolic engineering, which provide effective strategies for efficient production of NMN. In addition, an overview of the significant physiological functions and activities of NMN is elaborated. Finally, future research on technical approaches to further enhance NMN synthesis and strengthen clinical studies of NMN are prospected, which would lay the foundation for further promoting the application of NMN in nutrition, healthy food, and medicine in the future. KEY POINTS: • NMN supplementation effectively increases the level of NAD⁺. • The chemical and biological synthesis of NMN are comprehensively reviewed. • The impact of NMN on the treatment of various diseases is summarized.

NMN Alleviates NP-Induced Learning and Memory Impairment Through SIRT1 Pathway in PC-12 Cell

Nonylphenol (NP) is widely used in the chemical industry; it accumulates in organisms through environmental contamination and causes learning memory impairment. Nicotinamide mononucleotide (NMN) has been found to have a positive effect on the treatment of central nervous-related diseases. This study aimed to investigate the protective effect of NMN on NP-induced learning memory-related impairment in vitro and to further identify the underlying mechanisms. The results showed that NP induced oxidative stress and impaired the cholinergic system, 5-HT system in PC-12 cells. NMN alleviated NP-induced learning and memory impairment at the molecular level through alleviating oxidative stress and protective effects on the 5-HT system and cholinergic system. The 50 μM NP group significantly reduced the NAD⁺ content, and the relative expression of SIRT1, PGC-1α, Nrf2, MAOA, BDNF, and p-TrkB were significantly downregulated. Co-treatment of NMN with NP significantly reduced oxidative stress, improved the homeostasis of 5-HT and cholinergic system, enhanced the intracellular NAD⁺ content, and significantly upregulated the expression of SIRT1 pathway proteins. SIRT1 inhibitors reduced the expression of SIRT1 pathway-related proteins, which implied the impairment of learning and memory by NP and the protective effect of NMN might be achieved through the SIRT1-mediated PGC-1α/MAOA/BDNF signaling pathway. Overall, this study not only help us to understand the toxic mechanism of NP on learning memory impairment in vitro, but also have important reference significance to further explore the health care value of NMN and promote the development of related functional foods.

Magnoflorine improves cognitive deficits and pathology of Alzheimer's disease via inhibiting of JNK signaling pathway

BACKGROUND

Cognitive deficit is the main clinical feature of Alzheimer's disease (AD), and the massive death of neuronal cells is the leading cause of cognitive deficits. So, there is an urgent clinical need to discover effective drugs to protect brain neurons from damage in order to treat AD. Naturally-derived compounds have always been an important source of new drug discovery because of their diverse pharmacological activities, reliable efficacy and low toxicity. Magnoflorine is a quaternary aporphine alkaloid, which naturally exist in some commonly used herbal medicines, and has good anti-inflammatory and antioxidant effects. However, magnoflorine has not been reported in AD.

HYPOTHESIS/PURPOSE

To investigate the therapeutic effect and mechanism of magnoflorine on AD.

METHODS

Neuronal damage was detected by flow cytometry, immunofluorescence and western blotting. Oxidative stress was measured by detection of SOD and MDA, as well as JC-1 and reactive oxygen species (ROS) staining. The APP/PS1 mice were given drugs by intraperitoneal injection (I.P.) every day for one month, and then the new object recognition and Morris water maze were used to detect the cognitive ability of the mice.

RESULTS

We demonstrated that magnoflorine reduced Aβ-induced PC12 cell apoptosis and intracellular ROS generation. Further studies found that magnoflorine significantly improved cognitive deficits and AD-type pathology. Most interestingly, the efficacy of magnoflorine was better than that of the clinical control drug donepezil. Mechanistically, based on RNA-sequencing analysis, we found that magnoflorine significantly inhibited phosphorylated c-Jun N-terminal kinase (JNK) in AD models. This result was further validated using a JNK inhibitor.

CONCLUSION

Our results indicate that magnoflorine improves cognitive deficits and pathology of AD through inhibiting of JNK signaling pathway. Thus, magnoflorine may be a potential therapeutic candidate for AD.

Importance of NAD+ Anabolism in Metabolic, Cardiovascular and Neurodegenerative Disorders

The role of nicotinamide adenine dinucleotide (NAD+) in ageing has emerged as a critical factor in understanding links to a wide range of chronic diseases. Depletion of NAD+, a central redox cofactor and substrate of numerous metabolic enzymes, has been detected in many major age-related diseases. However, the mechanisms behind age-associated NAD+ decline remains poorly understood. Despite limited conclusive evidence, supplements aimed at increasing NAD+ levels are becoming increasingly popular. This review provides renewed insights regarding the clinical utility and benefits of NAD+ precursors, namely nicotinamide (NAM), nicotinic acid (NA), nicotinamide riboside (NR) and nicotinamide mononucleotide (NMN), in attenuating NAD+ decline and phenotypic characterization of age-related disorders, including metabolic, cardiovascular and neurodegenerative diseases. While it is anticipated that NAD+ precursors can play beneficial protective roles in several conditions, they vary in their ability to promote NAD+ anabolism with differing adverse effects. Careful evaluation of the role of NAD⁺, whether friend or foe in ageing, should be considered.

Oral nicotinamide riboside raises NAD+ and lowers biomarkers of neurodegenerative pathology in plasma extracellular vesicles enriched for neuronal origin

Declining nicotinamide adenine dinucleotide (NAD+ ) concentration in the brain during aging contributes to metabolic and cellular dysfunction and is implicated in the pathogenesis of aging-associated neurological disorders. Experimental therapies aimed at boosting brain NAD+ levels normalize several neurodegenerative phenotypes in animal models, motivating their clinical translation. Dietary intake of NAD+ precursors, such as nicotinamide riboside (NR), is a safe and effective avenue for augmenting NAD+ levels in peripheral tissues in humans, yet evidence supporting their ability to raise NAD+ levels in the brain or engage neurodegenerative disease pathways is lacking. Here, we studied biomarkers in plasma extracellular vesicles enriched for neuronal origin (NEVs) from 22 healthy older adults who participated in a randomized, placebo-controlled crossover trial (NCT02921659) of oral NR supplementation (500 mg, 2x /day, 6 weeks). We demonstrate that oral NR supplementation increases NAD+ levels in NEVs and decreases NEV levels of Aβ42, pJNK, and pERK1/2 (kinases involved in insulin resistance and neuroinflammatory pathways). In addition, changes in NAD(H) correlated with changes in canonical insulin-Akt signaling proteins and changes in pERK1/2 and pJNK. These findings support the ability of orally administered NR to augment neuronal NAD+ levels and modify biomarkers related to neurodegenerative pathology in humans. Furthermore, NEVs offer a new blood-based window into monitoring the physiologic response of NR in the brain.

A robust LC-MS/MS method to measure 8-oxoGuo, 8-oxodG, and NMN in human serum and urine

OBJECTIVE

To establish and validate a robust LC-MS/MS method for simultaneously measuring 8-oxoGuo, 8-oxodG, and NMN in serum and urine to evaluate the oxidative stress status.

METHODS

A Waters TQ-XS triple quadrupole mass spectrometer system coupled with an Acquity UPLC Primer HSS T3 column was chosen. The clinical performance was verified according to the CLSI C62-A and EP-15 guidelines. Furthermore, matched serum and urine samples from 22 apparently healthy check-ups, 20 patients with atherosclerosis, and 18 individuals with dementia were evaluated.

RESULTS

The recovery for serum 8-oxoGuo, urine 8-oxoGuo, serum 8-oxodG, urine 8-oxodG, serum NMN, and urine NMN was 88.8-112.4%, 102.4-114.1%, 88.5-107.7%, 94.9-102.6%, 98.4-108.9%, and 88.5-108.6%, respectively. Based on the inter-assay results, total coefficient of variation, matrix effect, and carryover, the LC-MS/MS method was deemed robust. The limit of quantification was 0.017, 0.018, and 0.150 nmol/L for 8-oxoGuo, 8-oxodG, and NMN, respectively, which are suitable for accurate measurements in human serum and urine samples. Higher 8-oxoGuo and 8-oxodG levels and lower NMN levels, indicative of significantly higher oxidative stress status, were found in patients with dementia compared to healthy subjects.

CONCLUSION

We established and validated a robust LC-MS/MS method to simultaneously measure 8-oxoGuo, 8-oxodG, and NMN in serum and urine.

Microglia-Mediated Neurovascular Unit Dysfunction in Alzheimer's Disease

The neurovascular unit (NVU) is involved in the pathological changes in Alzheimer's disease (AD). The NVU is a structural and functional complex that maintains microenvironmental homeostasis and metabolic balance in the central nervous system. As one of the most important components of the NVU, microglia not only induce blood-brain barrier breakdown by promoting neuroinflammation, the infiltration of peripheral white blood cells and oxidative stress but also mediate neurovascular uncoupling by inducing mitochondrial dysfunction in neurons, abnormal contraction of cerebral vessels, and pericyte loss in AD. In addition, microglia-mediated dysfunction of cellular components in the NVU, such as astrocytes and pericytes, can destroy the integrity of the NVU and lead to NVU impairment. Therefore, we review the mechanisms of microglia-mediated NVU dysfunction in AD. Furthermore, existing therapeutic advancements aimed at restoring the function of microglia and the NVU in AD are discussed. Finally, we predict the role of pericytes in microglia-mediated NVU dysfunction in AD is the hotspot in the future.

Effects of lifespan-extending interventions on cognitive healthspan

Ageing is known to be the primary risk factor for most neurodegenerative diseases, including Alzheimer's disease, Parkinson's disease and Huntington's disease. They are currently incurable and worsen over time, which has broad implications in the context of lifespan and healthspan extension. Adding years to life and even to physical health is suboptimal or even insufficient, if cognitive ageing is not adequately improved. In this review, we will examine how interventions that have the potential to extend lifespan in animals affect the brain, and if they would be able to thwart or delay the development of cognitive dysfunction and/or neurodegeneration. These interventions range from lifestyle (caloric restriction, physical exercise and environmental enrichment) through pharmacological (nicotinamide adenine dinucleotide precursors, resveratrol, rapamycin, metformin, spermidine and senolytics) to epigenetic reprogramming. We argue that while many of these interventions have clear potential to improve cognitive health and resilience, large-scale and long-term randomised controlled trials are needed, along with studies utilising washout periods to determine the effects of supplementation cessation, particularly in aged individuals.

Cinnamomum verum J. Presl Bark Contains High Contents of Nicotinamide Mononucleotide

The global population is aging, and intervention strategies for anti-aging and the prevention of aging-related diseases have become a topic actively explored today. Nicotinamide adenine dinucleotide (NAD⁺) is an important molecule in the metabolic process, and its content in tissues and cells decreases with age. The supplementation of nicotinamide mononucleotide (NMN), an important intermediate and precursor of NAD⁺, has increased NAD⁺ levels, and its safety has been demonstrated in rodents and human studies. However, the high content of NMN in natural plants has not been fully explored as herbal medicines for drug development. Here, we identified that the leaf of Cinnamomum verum J. Presl (C. verum) was the highest NMN content among the Plant Extract Library (PEL) with food experience, using ultra-performance liquid chromatography–tandem mass spectrometry (UPLC-MS/MS). To validate this result, the extraction and quantitative analysis of bark, leaf, root, and stem of fresh C. verum was conducted. The results revealed that the bark had the highest NMN content in C. verum (0.471 mg/100 g). Our study shed light on the prospects of developing natural plants in the context of NMN as drugs for anti-aging and prevention of aging-related diseases. The future should focus on the development and application of C. verum pharmaceutical formulations.

Optical Redox Imaging of Ex Vivo Hippocampal Tissue Reveals Age-Dependent Alterations in the 5XFAD Mouse Model of Alzheimer’s Disease

A substantial decline in nicotinamide adenine dinucleotide (NAD) has been reported in brain tissue homogenates or neurons isolated from Alzheimer’s disease (AD) models. NAD, together with flavin adenine dinucleotide (FAD), critically supports energy metabolism and maintains mitochondrial redox homeostasis. Optical redox imaging (ORI) of the intrinsic fluorescence of reduced NAD (NADH) and oxidized FAD yields cellular redox and metabolic information and provides biomarkers for a variety of pathological conditions. However, its utility in AD has not been characterized at the tissue level. We performed ex vivo ORI of freshly dissected hippocampi from a well-characterized AD mouse model with five familial Alzheimer’s disease mutations (5XFAD) and wild type (WT) control littermates at various ages. We found (1) a significant increase in the redox ratio with age in the hippocampi of both the WT control and the 5XFAD model, with a more prominent redox shift in the AD hippocampi; (2) a higher NADH in the 5XFAD versus WT hippocampi at the pre-symptomatic age of 2 months; and (3) a negative correlation between NADH and Aβ₄₂ level, a positive correlation between Fp and Aβ₄₂ level, and a positive correlation between redox ratio and Aβ₄₂ level in the AD hippocampi. These findings suggest that the ORI can be further optimized to conveniently study the metabolism of freshly dissected brain tissues in animal models and identify early AD biomarkers.

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.

Bisphenol-A Mediated Impaired DRP1-GFER Axis and Cognition Restored by PGC-1α Upregulation Through Nicotinamide in the Rat Brain Hippocampus

The regulatory network of mitochondrial biogenesis and dynamics is vital for mitochondrial functions and cellular homeostasis. Any impairment in the mitochondrial network leads to neurodegenerative disorders. Our earlier studies suggest that environmental toxicant Bisphenol-A (BPA) exposure reduces neurogenesis by abnormal mitochondrial dynamics and mitochondrial biogenesis through impairment of mitochondrial fission factor dynamin-related protein (DRP1) and mitochondrial import protein GFER, which leads to demyelination, neurodegeneration, and cognitive deficits in the rats. In the present study, we found that chronic BPA exposure reduces PGC-1α levels (master regulator of mitochondrial biogenesis), alters mitochondrial localization of DRP1 and GFER, and reduces the number of PGC-1α/NeuN+ and PGC-1α/β-tubulin+ neurons in the rat hippocampus, suggesting reduced PGC-1α-mediated neurogenesis. Nicotinamide significantly increased PGC-1α protein levels, PGC-1α/NeuN+ co-labeled cells in BPA-treated rat hippocampus and PGC-1α/β-tubulin+ co-labeled cells in neuron culture derived from hippocampal neural stem cells. Interestingly, PGC-1α upregulation by nicotinamide also resulted in increased GFER levels and restored mitochondrial localization of GFER (increased GFER/TOMM20 co-labeled cells) in vitro and in vivo following BPA treatment. Nicotinamide also reduced DRP1 levels and prevented DRP1 mitochondrial localization in BPA-treated neuronal cultures and hippocampus, suggesting reduced mitochondrial fission. This resulted in reduced cytochrome c levels in neuronal culture and reduced hippocampal neurodegeneration (reduced caspase-3/NeuN+ co-labeled neurons) following nicotinamide treatment in BPA-treated group. Consequently, activation of PGC-1α by nicotinamide restored BPA-mediated cognitive deficits in rats. Results suggest that the treatment of nicotinamide has therapeutic potential and rescues BPA-mediated neuronal death and cognitive deficits by upregulating the PGC-1α and GFER-DRP1 link, thus balancing mitochondrial homeostasis.

Metformin, Rapamycin, or Nicotinamide Mononucleotide Pretreatment Attenuate Cognitive Impairment After Cerebral Hypoperfusion by Inhibiting Microglial Phagocytosis

Vascular cognitive impairment (VCI) is the second leading form of dementia after Alzheimer's disease (AD) plaguing the elder population. Despite the enormous prevalence of VCI, the biological basis of this disease has been much less well-studied than that of AD, with no specific therapy currently existing to prevent or treat VCI. As VCI mainly occurs in the elderly, the role of anti-aging drugs including metformin, rapamycin, and nicotinamide mono nucleotide (NMN), and the underlying mechanism remain uncertain. Here, we examined the role of metformin, rapamycin, and NMN in cognitive function, white matter integrity, microglial response, and phagocytosis in a rat model of VCI by bilateral common carotid artery occlusion (BCCAO). BCCAO-induced chronic cerebral hypoperfusion could cause spatial working memory deficits and white matter lesions (WMLs), along with increasing microglial activation and phagocytosis compared to sham-operated rats. We found the cognitive impairment was significantly improved in BCCAO rats pretreated with these three drugs for 14 days before BCCAO compared with the vehicle group by the analysis of the Morris water maze and new object recognition tests. Pretreatment of metformin, rapamycin, or NMN also increased myelin basic protein (MBP, a marker for myelin) expression and reduced SMI32 (a marker for demyelinated axons) intensity and SMI32/MBP ratio compared with the vehicle group, suggesting that these drugs could ameliorate BCCAO-induced WMLs. The findings were confirmed by Luxol fast blue (LFB) stain, which is designed for staining myelin/myelinated axons. We further found that pretreatment of metformin, rapamycin, or NMN reduced microglial activation and the number of M1 microglia, but increased the number of M2 microglia compared to the vehicle group. Importantly, the number of MBP⁺/Iba1⁺/CD68⁺ microglia was significantly reduced in the BCCAO rats pretreated with these three drugs compared with the vehicle group, suggesting that these drugs suppress microglial phagocytosis. No significant difference was found between the groups pretreated with metformin, rapamycin, or NMN. Our data suggest that metformin, rapamycin, or NMN could protect or attenuate cognitive impairment and WMLs by modifying microglial polarization and inhibiting phagocytosis. The findings may open a new avenue for VCI treatment.

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.

Mitophagy and Neurodegeneration: Between the Knowns and the Unknowns

Macroautophagy (henceforth autophagy) an evolutionary conserved intracellular pathway, involves lysosomal degradation of damaged and superfluous cytosolic contents to maintain cellular homeostasis. While autophagy was initially perceived as a bulk degradation process, a surfeit of studies in the last 2 decades has revealed that it can also be selective in choosing intracellular constituents for degradation. In addition to the core autophagy machinery, these selective autophagy pathways comprise of distinct molecular players that are involved in the capture of specific cargoes. The diverse organelles that are degraded by selective autophagy pathways are endoplasmic reticulum (ERphagy), lysosomes (lysophagy), mitochondria (mitophagy), Golgi apparatus (Golgiphagy), peroxisomes (pexophagy) and nucleus (nucleophagy). Among these, the main focus of this review is on the selective autophagic pathway involved in mitochondrial turnover called mitophagy. The mitophagy pathway encompasses diverse mechanisms involving a complex interplay of a multitude of proteins that confers the selective recognition of damaged mitochondria and their targeting to degradation via autophagy. Mitophagy is triggered by cues that signal the mitochondrial damage such as disturbances in mitochondrial fission-fusion dynamics, mitochondrial membrane depolarisation, enhanced ROS production, mtDNA damage as well as developmental cues such as erythrocyte maturation, removal of paternal mitochondria, cardiomyocyte maturation and somatic cell reprogramming. As research on the mechanistic aspects of this complex pathway is progressing, emerging roles of new players such as the NIPSNAP proteins, Miro proteins and ER-Mitochondria contact sites (ERMES) are being explored. Although diverse aspects of this pathway are being investigated in depth, several outstanding questions such as distinct molecular players of basal mitophagy, selective dominance of a particular mitophagy adapter protein over the other in a given physiological condition, molecular mechanism of how specific disease mutations affect this pathway remain to be addressed. In this review, we aim to give an overview with special emphasis on molecular and signalling pathways of mitophagy and its dysregulation in neurodegenerative disorders.

Enzymatic synthesis of high-titer nicotinamide mononucleotide with a new nicotinamide riboside kinase and an efficient ATP regeneration system

BACKGROUND

β-Nicotinamide mononucleotide (NMN) is the direct precursor of nicotinamide coenzymes such as NAD+ and NADP+, which are widely applied in industrial biocatalysis especially involving cofactor-dependent oxidoreductases. Moreover, NMN is a promising candidate for medical uses since it is considered to be beneficial for improving health of aged people who usually suffer from an insufficient level of NAD+. To date, various methods have been developed for the synthesis of NMN. Chemical phosphorylation of nicotinamide riboside (NR) to NMN depends on excessive phosphine oxychloride and delicate temperature control, while fermentation of NMN is limited by low product titers, making it unsuitable for industrial-scale NMN production. As a result, the more efficient synthesis process of NMN is still challenging.

AIM

This work attempted to construct an eco-friendly and cost-effective biocatalytic process for transforming the chemically synthesized NR into the highly value-added NMN.

RESULTS

A new nicotinamide riboside kinase (Klm-NRK) was identified from Kluyveromyces marxianus. The specific activity of purified Klm-NRK was 7.9 U·mg-1 protein, ranking the highest record among the reported NRKs. The optimal pH of Klm-NRK was 7.0 in potassium phosphate buffer. The purified Klm-NRK retained a half activity after 7.29 h at 50 °C. The catalytic efficiencies (kcat/KM) toward ATP and nicotinamide riboside (NR) were 57.4 s-1·mM-1 and 84.4 s-1·mM-1, respectively. In the presence of an external ATP regeneration system (AcK/AcP), as much as 100 g·L-1 of NR could be completely phosphorylated to NMN in 8 h with Klm-NRK, achieving a molar isolation yield of 84.2% and a space-time yield of 281 g·L-1·day-1. These inspiring results indicated that Klm-NRK is a promising biocatalyst which provides an efficient approach for the bio-manufacturing of NMN in a high titer.

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.

Oral Administration of Nicotinamide Mononucleotide Increases Nicotinamide Adenine Dinucleotide Level in an Animal Brain

As a redox-sensitive coenzyme, nicotinamide adenine dinucleotide (NAD⁺) plays a central role in cellular energy metabolism and homeostasis. Low NAD⁺ levels are linked to multiple disease states, including age-related diseases, such as metabolic and neurodegenerative diseases. Consequently, restoring/increasing NAD⁺ levels in vivo has emerged as an important intervention targeting age-related neurodegenerative diseases. One of the widely studied approaches to increase NAD⁺ levels in vivo is accomplished by using NAD⁺ precursors, such as nicotinamide mononucleotide (NMN). Oral administration of NMN has been shown to successfully increase NAD⁺ levels in a variety of tissues; however, it remains unclear whether NMN can cross the blood–brain barrier to increase brain NAD⁺ levels. This study evaluated the effects of oral NMN administration on NAD⁺ levels in C57/B6J mice brain tissues. Our results demonstrate that oral gavage of 400 mg/kg NMN successfully increases brain NAD⁺ levels in mice after 45 min. These findings provide evidence that NMN may be used as an intervention to increase NAD⁺ levels in the brain.

Sirtuins Modulation: A Promising Strategy for HIV-Associated Neurocognitive Impairments

HIV-Associated neurocognitive disorder (HAND) is one of the major concerns since it persists in 40% of this population. Nowadays, HAND neuropathogenesis is considered to be caused by the infected cells that cross the brain-blood barrier and produce viral proteins that can be secreted and internalized into neurons leading to disruption of cellular processes. The evidence points to viral proteins such as Tat as the causal agent for neuronal alteration and thus HAND. The hallmarks in Tat-induced neurodegeneration are endoplasmic reticulum stress and mitochondrial dysfunction. Sirtuins (SIRTs) are NAD+-dependent deacetylases involved in mitochondria biogenesis, unfolded protein response, and intrinsic apoptosis pathway. Tat interaction with these deacetylases causes inhibition of SIRT1 and SIRT3. Studies revealed that SIRTs activation promotes neuroprotection in neurodegenerative diseases such Alzheimer's and Parkinson's disease. Therefore, this review focuses on Tat-induced neurotoxicity mechanisms that involve SIRTs as key regulators and their modulation as a therapeutic strategy for tackling HAND and thereby improving the quality of life of people living with HIV.

Protection against Amyloid-β Oligomer Neurotoxicity by Small Molecules with Antioxidative Properties: Potential for the Prevention of Alzheimer’s Disease Dementia

Soluble oligomeric assemblies of amyloid β-protein (Aβ), called Aβ oligomers (AβOs), have been recognized as primary pathogenetic factors in the molecular pathology of Alzheimer’s disease (AD). AβOs exert neurotoxicity and synaptotoxicity and play a critical role in the pathological progression of AD by aggravating oxidative and synaptic disturbances and tau abnormalities. As such, they are important therapeutic targets. From a therapeutic standpoint, it is not only important to clear AβOs or prevent their formation, it is also beneficial to reduce their neurotoxicity. In this regard, recent studies have reported that small molecules, most with antioxidative properties, show promise as therapeutic agents for reducing the neurotoxicity of AβOs. In this mini-review, we briefly review the significance of AβOs and oxidative stress in AD and summarize studies on small molecules with AβO-neurotoxicity-reducing effects. We also discuss mechanisms underlying the effects of these compounds against AβO neurotoxicity as well as their potential as drug candidates for the prevention and treatment of AD.

Regulation of NAD+ metabolism in aging and disease

More than a century after discovering NAD⁺, information is still evolving on the role of this molecule in health and diseases. The biological functions of NAD⁺ and NAD⁺ precursors encompass pathways in cellular energetics, inflammation, metabolism, and cell survival. Several metabolic and neurological diseases exhibit reduced tissue NAD⁺ levels. Significantly reduced levels of NAD⁺ are also associated with aging, and enhancing NAD⁺ levels improved healthspan and lifespan in animal models. Recent studies suggest a causal link between senescence, age-associated reduction in tissue NAD⁺ and enzymatic degradation of NAD⁺. Furthermore, the discovery of transporters and receptors involved in NAD⁺ precursor (nicotinic acid, or niacin, nicotinamide, and nicotinamide riboside) metabolism allowed for a better understanding of their role in cellular homeostasis including signaling functions that are independent of their functions in redox reactions. We also review studies that demonstrate that the functional effect of niacin is partially due to the activation of its cell surface receptor, GPR109a. Based on the recent progress in understanding the mechanism and function of NAD⁺ and NAD⁺ precursors in cell metabolism, new strategies are evolving to exploit these molecules' pharmacological potential in the maintenance of metabolic balance.

Protective effects of apigenin on methylmercury-induced behavioral/neurochemical abnormalities and neurotoxicity in rats

Methylmercury (MeHg) is a neurotoxin that induces neurotoxicity and cell death in neurons. MeHg increases oligodendrocyte death, glial cell activation, and motor neuron demyelination in the motor cortex and spinal cord. As a result, MeHg plays an important role in developing neurocomplications similar to amyotrophic lateral sclerosis (ALS). Recent research has implicated c-JNK and p38MAPK overactivation in the pathogenesis of ALS. Apigenin (APG) is a flavonoid having anti-inflammatory, antioxidant, and c-JNK/p38MAPK inhibitory activities. The purpose of this study is to determine whether APG possesses neuroprotective effects in MeHg-induced neurotoxicity in adult rats associated with ALS-like neuropathological alterations. In the current study, the neurotoxin MeHg causes an ALS-like phenotype in Wistar rats after 21 days of oral administration at a dose of 5 mg/kg. Prolonged administration of APG (40 and 80 mg/kg) improved neurobehavioral parameters such as learning memory, cognition, motor coordination, and grip strength. This is mainly associated with the downregulation of c-JNK and p38MAPK signaling as well as the restoration of myelin basic protein within the brain. Furthermore, APG inhibited neuronal apoptotic markers (Bax, Bcl-2, and caspase-3), restored neurotransmitter imbalance, decreased inflammatory markers (TNF- and IL-1), and alleviated oxidative damage. As a result, the current study shows that APG has neuroprotective potential as a c-JNK and p38MAPK signaling inhibitor against MeHg-induced neurotoxicity in adult rats. Based on these promising findings, we suggested that APG could be a potential new therapeutic approach over other conventional therapeutic approaches for MeHg-induced neurotoxicity in neurobehavioral, molecular, and neurochemical abnormalities.

CREB1K292 and HINFPK330 as Putative Common Therapeutic Targets in Alzheimer's and Parkinson's Disease

Integration of omics data and deciphering the mechanism of a biological regulatory network could be a promising approach to reveal the molecular mechanism involved in the progression of complex diseases, including Alzheimer's and Parkinson's. Despite having an overlapping mechanism in the etiology of Alzheimer's disease (AD) and Parkinson's disease (PD), the exact mechanism and signaling molecules behind them are still unknown. Further, the acetylation mechanism and histone deacetylase (HDAC) enzymes provide a positive direction toward studying the shared phenomenon between AD and PD pathogenesis. For instance, increased expression of HDACs causes a decrease in protein acetylation status, resulting in decreased cognitive and memory function. Herein, we employed an integrative approach to analyze the transcriptomics data that established a potential relationship between AD and PD. Data preprocessing and analysis of four publicly available microarray datasets revealed 10 HUB proteins, namely, CDC42, CD44, FGFR1, MYO5A, NUMA1, TUBB4B, ARHGEF9, USP5, INPP5D, and NUP93, that may be involved in the shared mechanism of AD and PD pathogenesis. Further, we identified the relationship between the HUB proteins and transcription factors that could be involved in the overlapping mechanism of AD and PD. CREB1 and HINFP were the crucial regulatory transcription factors that were involved in the AD and PD crosstalk. Further, lysine acetylation sites and HDAC enzyme prediction revealed the involvement of 15 and 27 potential lysine residues of CREB1 and HINFP, respectively. Our results highlighted the importance of HDAC1(K292) and HDAC6(K330) association with CREB1 and HINFP, respectively, in the AD and PD crosstalk. However, different datasets with a large number of samples and wet lab experimentation are required to validate and pinpoint the exact role of CREB1 and HINFP in the AD and PD crosstalk. It is also possible that the different datasets may or may not affect the results due to analysis parameters. In conclusion, our study potentially highlighted the crucial proteins, transcription factors, biological pathways, lysine residues, and HDAC enzymes shared between AD and PD at the molecular level. The findings can be used to study molecular studies to identify the possible relationship in the AD-PD crosstalk.

Modulation of NAD+ biosynthesis activates SIRT1 and resists cisplatin-induced ototoxicity

Cisplatin, the most widely used platinum-based anticancer drug, often causes progressive and irreversible sensorineural hearing loss in cancer patients. However, the precise mechanism underlying cisplatin-associated ototoxicity is still unclear. Nicotinamide adenine dinucleotide (NAD+), a co-substrate for the sirtuin family and PARPs, has emerged as a potent therapeutic molecular target in various diseases. In our investigates, we observed that NAD+ level was changed in the cochlear explants of mice treated with cisplatin. Supplementation of a specific inhibitor (TES-1025) of α-amino-β-carboxymuconate-ε-semialdehyde decarboxylase (ACMSD), a rate-limiting enzyme of NAD+de novo synthesis pathway, promoted SIRT1 activity, increased mtDNA contents and enhanced AMPK expression, thus significantly reducing hair cells loss and deformation. The protection was blocked by EX527, a specific SIRT1 inhibitor. Meanwhile, the use of NMN, a precursor of NAD+ salvage synthesis pathway, had shown beneficial effect on hair cell under cisplatin administration, effectively suppressing PARP1. In vivo experiments confirmed the hair cell protection of NAD+ modulators in cisplatin treated mice and zebrafish. In conclusion, we demonstrated that modulation of NAD+ biosynthesis via the de novo synthesis pathway and the salvage synthesis pathway could both prevent ototoxicity of cisplatin. These results suggested that direct modulation of cellular NAD+ levels could be a promising therapeutic approach for protection of hearing from cisplatin-induced ototoxicity.

NAD+ in Alzheimer's Disease: Molecular Mechanisms and Systematic Therapeutic Evidence Obtained in vivo

Mitochondria in neurons generate adenosine triphosphate (ATP) to provide the necessary energy required for constant activity. Nicotinamide adenine dinucleotide (NAD⁺) is a vital intermediate metabolite involved in cellular bioenergetics, ATP production, mitochondrial homeostasis, and adaptive stress responses. Exploration of the biological functions of NAD⁺ has been gaining momentum, providing many crucial insights into the pathophysiology of age-associated functional decline and diseases, such as Alzheimer’s disease (AD). Here, we systematically review the key roles of NAD⁺ precursors and related metabolites in AD models and show how NAD⁺ affects the pathological hallmarks of AD and the potential mechanisms of action. Advances in understanding the molecular roles of NAD⁺-based neuronal resilience will result in novel approaches for the treatment of AD and set the stage for determining whether the results of exciting preclinical trials can be translated into the clinic to improve AD patients’ phenotypes.

Nicotinamide mononucleotide (NMN) as an anti-aging health product – Promises and safety concerns

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Provides an overview of promises and safety concerns of NMN as an anti-aging product.

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Shows that NMN’s beneficial effects supported by in vivo studies.

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Reveals that there is a lack of NMN’s clinical safety and efficacy studies

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Suggests that proper clinical investigations are urgently needed on the effectiveness and safety of NMN supplementation.

Background

Aim of review

Key scientific concepts of review

Risks and rewards of targeting NAD+ homeostasis in the brain

Strategies to correct declining nicotinamide adenine dinucleotide (NAD⁺) levels in neurological disease and biological ageing are promising therapeutic candidates. These strategies include supplementing with NAD⁺ precursors, small molecule activation of NAD⁺ biosynthetic enzymes, and treatment with small molecule inhibitors of NAD⁺ consuming enzymes such as CD38, SARM1 or members of the PARP family. While these strategies have shown efficacy in animal models of neurological disease, each of these has the mechanistic potential for adverse events that could preclude their preclinical use. Here, we discuss the implications of these strategies for treating neurological diseases, including potential off-target effects that may be unique to the brain.

New benzamide derivatives and their nicotinamide/cinnamamide analogs as cholinesterase inhibitors

In this study, a total of 18 new benzamide/ nicotinamide/ cinnamamide derivative compounds were designed and synthesized for the first time (except B1 and B5) by conventional and microwave irradiation methods. The chemical structures of the synthesized compounds were characterized by ¹H NMR, ¹³C NMR, and HRMS spectra. In vitro acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) inhibition effects of the compounds were evaluated to find out new possible drug candidate molecule/s. According to the inhibition results, the IC50 values of the compounds synthesized were in the range of 10.66-83.03 nM towards AChE, while they were in the range of 32.74-66.68 nM towards BuChE. Tacrine was used as the reference drug and its IC50 values were 20.85 nM and 15.66 nM towards AChE and BuChE, respectively. The most active compounds B4 (IC50: 15.42 nM), N4 (IC50: 12.14 nM), and C4 (IC50: 10.67 nM) in each series towards AChE were docked at the binding site of AChE enzyme to explain the inhibitory activities of each series. On the other hand, the compounds B4, N4, and C4 showed satisfactory pharmacokinetic properties via the prediction of ADME profiles.

Epigenetic regulation in Alzheimer's disease: is it a potential therapeutic target?

Introduction: Alzheimer's disease (AD) is the most common neurodegenerative disorder and the primary form of dementia in the elderly. Changes in DNA methylation and post-translational modifications of histone tails are increasingly observed in AD tissues, and likely contribute to disease onset and progression. The reversibility of these epigenetic marks offers the potential for therapeutic interventions.Areas covered: After a concise and updated overview of DNA methylation and post-translational modifications of histone tails in AD tissues, this review provides an overview of the animal and cell culture studies investigating the potential of targeting these modifications to attenuate AD-like features. PubMed was searched for relevant literature between 2003 and 2021.Expert opinion: Methyl donor compounds and drugs acting on histone tail modifications attenuated the AD-like features and improved cognition in several transgenic AD mice; however, there are concerns about safety and tolerability for long-term treatment in humans. The challenges will be to take advantage of recent epigenome-wide investigations to identify the principal targets for future interventions, and to design novel, selective and safer agents. Natural compounds exerting epigenetic properties could represent a promising opportunity to delay disease onset in middle-aged individuals at increased AD risk.

Protective Effects of Nicotinamide Adenine Dinucleotide and Related Precursors in Alzheimer's Disease: A Systematic Review of Preclinical Studies

Data from preclinical studies propose nicotinamide adenine dinucleotide (NAD⁺) as a neuroprotective and bioenergetics stimulant agent to treat Alzheimer's disease (AD); however, there seems to be inconsistency between behavioral and molecular outcomes. We performed this systematic review to provide a better understanding of the effects of NAD⁺ in rodent AD models and to summarize the literature.Studies were identified by searching PubMed, EMBASE, Scopus, Google Scholar, and the reference lists of relevant review articles published through December 2020. The search strategy was restricted to articles about NAD⁺, its derivatives, and their association with cognitive function in AD rodent models. The initial search yielded 320 articles, of which 11 publications were included in our systematic review.Based on the primary outcomes, it was revealed that NAD⁺ improves learning and memory. The secondary endpoints also showed neuroprotective effects of NAD⁺ on different AD models. The proposed neuroprotective mechanisms included, but were not limited to, the attenuation of the oxidative stress, inflammation, and apoptosis, while enhancing the mitochondrial function.The current systematic review summarizes the preclinical studies on NAD⁺ precursors and provides evidence favoring the pro-cognitive effects of such components in rodent models of AD.

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.