Nicotinamide Riboside Enhances In Vitro Beta-adrenergic Brown Adipose Tissue Activity in Humans

Regulation of and challenges in targeting NAD+ metabolism

Nicotinamide adenine dinucleotide, in its oxidized (NAD+) and reduced (NADH) forms, is a reduction-oxidation (redox) co-factor and substrate for signalling enzymes that have essential roles in metabolism. The recognition that NAD+ levels fall in response to stress and can be readily replenished through supplementation has fostered great interest in the potential benefits of increasing or restoring NAD+ levels in humans to prevent or delay diseases and degenerative processes. However, much about the biology of NAD+ and related molecules remains poorly understood. In this Review, we discuss the current knowledge of NAD+ metabolism, including limitations of, assumptions about and unappreciated factors that might influence the success or contribute to risks of NAD+ supplementation. We highlight several ongoing controversies in the field, and discuss the role of the microbiome in modulating the availability of NAD+ precursors such as nicotinamide riboside (NR) and nicotinamide mononucleotide (NMN), the presence of multiple cellular compartments that have distinct pools of NAD+ and NADH, and non-canonical NAD+ and NADH degradation pathways. We conclude that a substantial investment in understanding the fundamental biology of NAD+, its detection and its metabolites in specific cells and cellular compartments is needed to support current translational efforts to safely boost NAD+ levels in humans.

Dietary Supplementation With NAD+-Boosting Compounds in Humans: Current Knowledge and Future Directions

Advancing age and many disease states are associated with declines in nicotinamide adenine dinucleotide (NAD+) levels. Preclinical studies suggest that boosting NAD+ abundance with precursor compounds, such as nicotinamide riboside or nicotinamide mononucleotide, has profound effects on physiological function in models of aging and disease. Translation of these compounds for oral supplementation in humans has been increasingly studied within the last 10 years; however, the clinical evidence that raising NAD+ concentrations can improve physiological function is unclear. The goal of this review was to synthesize the published literature on the effects of chronic oral supplementation with NAD+ precursors on healthy aging and age-related chronic diseases. We identified nicotinamide riboside, nicotinamide riboside co-administered with pterostilbene, and nicotinamide mononucleotide as the most common candidates in investigations of NAD+-boosting compounds for improving physiological function in humans. Studies have been performed in generally healthy midlife and older adults, adults with cardiometabolic disease risk factors such as overweight and obesity, and numerous patient populations. Supplementation with these compounds is safe, tolerable, and can increase the abundance of NAD+ and related metabolites in multiple tissues. Dosing regimens and study durations vary greatly across interventions, and small sample sizes limit data interpretation of physiological outcomes. Limitations are identified and future research directions are suggested to further our understanding of the potential efficacy of NAD+-boosting compounds for improving physiological function and extending human health span.

NAD+ Precursors in Human Health and Disease: Current Status and Future Prospects

Significance: Nicotinamide adenine dinucleotide (NAD+) acts as a cofactor in many important biological processes. The administration of NAD+ precursors increases the intracellular NAD+ pool and has beneficial effects on physiological changes and diseases associated with aging in various organisms, including rodents and humans. Recent Advances: Evidence from preclinical studies demonstrating the beneficial effects of NAD+ precursors has rapidly increased in the last decade. The results of these studies have prompted the development of clinical trials using NAD+ precursors, particularly nicotinamide riboside (NR) and nicotinamide mononucleotide (NMN). In addition, in vivo studies of NAD+ metabolism have rapidly progressed. Critical Issues: Several studies have demonstrated that the oral administration of NAD+ precursors, such as NR and NMN, is safe and significantly increases NAD+ levels in humans. However, the efficacy of these NAD+ precursors is lower than expected from the results of preclinical studies. In addition, the identification of the contribution of the host-gut microbiota interactions to NR and NMN metabolism has added to the complexity of NAD+ metabolism. Future Directions: Further studies are required to determine the efficacy of NAD+ precursors in humans. Further in vivo studies of NAD+ metabolism are required to optimize the effects of NAD+ supplementation. There is also a need for methods of delivering NAD+ precursors to target organs or tissues to increase the outcomes of clinical trials. Antioxid. Redox Signal. 39, 1133-1149.

NR-SAFE: a randomized, double-blind safety trial of high dose nicotinamide riboside in Parkinson's disease

Nicotinamide adenine dinucleotide (NAD) replenishment therapy using nicotinamide riboside (NR) shows promise for Parkinson's disease (PD) and other neurodegenerative disorders. However, the optimal dose of NR remains unknown, and doses exceeding 2000 mg daily have not been tested in humans. To evaluate the safety of high-dose NR therapy, we conducted a single-center, randomized, placebo-controlled, double-blind, phase I trial on 20 individuals with PD, randomized 1:1 on NR 1500 mg twice daily (n = 10) or placebo (n = 10) for four weeks. The trial was conducted at the Department of Neurology, Haukeland University Hospital, Bergen, Norway. The primary outcome was safety, defined as the frequency of moderate and severe adverse events. Secondary outcomes were tolerability defined as frequency of mild adverse events, change in the whole blood and urine NAD metabolome, and change in the clinical severity of PD, measured by MDS-UPDRS. All 20 participants completed the trial. The trial met all prespecified outcomes. NR therapy was well tolerated with no moderate or severe adverse events, and no significant difference in mild adverse events. NR therapy was associated with clinical improvement of total MDS-UPDRS scores. However, this change was also associated with a shorter interval since the last levodopa dose. NR greatly augmented the blood NAD metabolome with up to 5-fold increase in blood NAD+ levels. While NR-recipients exhibited a slight initial rise in serum homocysteine levels, the integrity of the methyl donor pool remained intact. Our results support extending the dose range of NR in phase II clinical trials to 3000 mg per day, with appropriate safety monitoring. Clinicaltrials.gov identifier: NCT05344404.

Nicotinamide Adenine Dinucleotide in Aging Biology: Potential Applications and Many Unknowns

Recent research has unveiled an expansive role of NAD+ in cellular energy generation, redox reactions, and as a substrate or cosubstrate in signaling pathways that regulate health span and aging. This review provides a critical appraisal of the clinical pharmacology and the preclinical and clinical evidence for therapeutic effects of NAD+ precursors for age-related conditions, with a particular focus on cardiometabolic disorders, and discusses gaps in current knowledge. NAD+ levels decrease throughout life; age-related decline in NAD+ bioavailability has been postulated to be a contributor to many age-related diseases. Raising NAD+ levels in model organisms by administration of NAD+ precursors improves glucose and lipid metabolism; attenuates diet-induced weight gain, diabetes, diabetic kidney disease, and hepatic steatosis; reduces endothelial dysfunction; protects heart from ischemic injury; improves left ventricular function in models of heart failure; attenuates cerebrovascular and neurodegenerative disorders; and increases health span. Early human studies show that NAD+ levels can be raised safely in blood and some tissues by oral NAD+ precursors and suggest benefit in preventing nonmelanotic skin cancer, modestly reducing blood pressure and improving lipid profile in older adults with obesity or overweight; preventing kidney injury in at-risk patients; and suppressing inflammation in Parkinson disease and SARS-CoV-2 infection. Clinical pharmacology, metabolism, and therapeutic mechanisms of NAD+ precursors remain incompletely understood. We suggest that these early findings provide the rationale for adequately powered randomized trials to evaluate the efficacy of NAD+ augmentation as a therapeutic strategy to prevent and treat metabolic disorders and age-related conditions.

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

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

The Role of NAD+ in Metabolic Regulation of Adipose Tissue: Implications for Obesity-Induced Insulin Resistance

Obesity-induced insulin resistance is among the key factors in the development of type 2 diabetes, atherogenic dyslipidemia and cardiovascular disease. Adipose tissue plays a key role in the regulation of whole-body metabolism and insulin sensitivity. In obesity, adipose tissue becomes inflamed and dysfunctional, exhibiting a modified biochemical signature and adipokine secretion pattern that promotes insulin resistance in peripheral tissues. An important hallmark of dysfunctional obese adipose tissue is impaired NAD+/sirtuin signaling. In this chapter, we summarize the evidence for impairment of the NAD+/sirtuin pathway in obesity, not only in white adipose tissue but also in brown adipose tissue and during the process of beiging, together with correlative evidence from human studies. We also describe the role of PARPs and CD38 as important NAD+ consumers and discuss findings from experimental studies that investigated potential NAD+ boosting strategies and their efficacy in restoring impaired NAD+ metabolism in dysfunctional obese adipose tissue. In sum, these studies suggest a critical role of NAD+ metabolism in adipose biology and provide a basis for the potential development of strategies to restore metabolic health in obesity.

Nicotinamide Riboside, a Promising Vitamin B3 Derivative for Healthy Aging and Longevity: Current Research and Perspectives

Many studies have suggested that the oxidized form of nicotinamide adenine dinucleotide (NAD+) is involved in an extensive spectrum of human pathologies, including neurodegenerative disorders, cardiomyopathy, obesity, and diabetes. Further, healthy aging and longevity appear to be closely related to NAD+ and its related metabolites, including nicotinamide riboside (NR) and nicotinamide mononucleotide (NMN). As a dietary supplement, NR appears to be well tolerated, having better pharmacodynamics and greater potency. Unfortunately, NR is a reactive molecule, often unstable during its manufacturing, transport, and storage. Recently, work related to prebiotic chemistry discovered that NR borate is considerably more stable than NR itself. However, immediately upon consumption, the borate dissociates from the NR borate and is lost in the body through dilution and binding to other species, notably carbohydrates such as fructose and glucose. The NR left behind is expected to behave pharmacologically in ways identical to NR itself. This review provides a comprehensive summary (through Q1 of 2023) of the literature that makes the case for the consumption of NR as a dietary supplement. It then summarizes the challenges of delivering quality NR to consumers using standard synthesis, manufacture, shipping, and storage approaches. It concludes by outlining the advantages of NR borate in these processes.

What is really known about the effects of nicotinamide riboside supplementation in humans

Nicotinamide riboside is a precursor to the important cofactor nicotinamide adenine dinucleotide and has elicited metabolic benefits in multiple preclinical studies. In 2016, the first clinical trial of nicotinamide riboside was conducted to test the safety and efficacy of human supplementation. Many trials have since been conducted aiming to delineate benefits to metabolic health and severe diseases in humans. This review endeavors to summarize and critically assess the 25 currently published research articles on human nicotinamide riboside supplementation to identify any poorly founded claims and assist the field in elucidating the actual future potential for nicotinamide riboside. Collectively, oral nicotinamide riboside supplementation has displayed few clinically relevant effects, and there is an unfortunate tendency in the literature to exaggerate the importance and robustness of reported effects. Even so, nicotinamide riboside may play a role in the reduction of inflammatory states and has shown some potential in the treatment of diverse severe diseases.

The NAD salvage pathway in mesenchymal cells is indispensable for skeletal development in mice

NAD is an essential co-factor for cellular energy metabolism and multiple other processes. Systemic NAD+ deficiency has been implicated in skeletal deformities during development in both humans and mice. NAD levels are maintained by multiple synthetic pathways but which ones are important in bone forming cells is unknown. Here, we generate mice with deletion of Nicotinamide Phosphoribosyltransferase (Nampt), a critical enzyme in the NAD salvage pathway, in all mesenchymal lineage cells of the limbs. At birth, NamptΔPrx1 exhibit dramatic limb shortening due to death of growth plate chondrocytes. Administration of the NAD precursor nicotinamide riboside during pregnancy prevents the majority of in utero defects. Depletion of NAD post-birth also promotes chondrocyte death, preventing further endochondral ossification and joint development. In contrast, osteoblast formation still occurs in knockout mice, in line with distinctly different microenvironments and reliance on redox reactions between chondrocytes and osteoblasts. These findings define a critical role for cell-autonomous NAD homeostasis during endochondral bone formation.

Nicotinamide mononucleotide alters body composition and ameliorates metabolic disorders induced by a high-fat diet

Obesity is caused by an imbalance between calorie intake and energy expenditure, leading to excessive adipose tissue accumulation. Nicotinamide adenine dinucleotide (NAD⁺ ) is an important molecule in energy and signal transduction, and NAD⁺ supplementation therapy is a new treatment for obesity in recent years. Liver kinase B1 (LKB1) is an energy metabolism regulator. The relationship between NAD⁺ and LKB1 has only been studied in the heart and has not yet been reported in obesity. Nicotinamide mononucleotide (NMN), as a direct precursor of NAD⁺ , can effectively enhance the level of NAD⁺ . In the current study, we showed that NMN intervention altered body composition in obese mice, characterized by a reduction in fat mass and an increase in lean mass. NMN reversed high-fat diet-induced blood lipid levels then contributed to reducing hepatic steatosis. NMN also improved glucose tolerance and alleviated adipose tissue inflammation. Moreover, our data suggested that NMN supplementation may be depends on the NAD⁺ /SIRT6/LKB1 pathway to regulate brown adipose metabolism. These results provided new evidence for NMN in obesity treatment.

Nicotinamide-riboside shifts the differentiation of human primary white adipocytes to beige adipocytes impacting substrate preference and uncoupling respiration through SIRT1 activation and mitochondria-derived reactive species production

Beige adipocytes play key roles in organismal energy and metabolic balance. In this study, we assessed whether the supplementation of human white adipocytes, differentiated from human adipose tissue-derived stem cells, with nicotinamide riboside (NR), a potent NAD + precursor, can shift differentiation to beige adipocytes (beiging). NR induced mitochondrial biogenesis and the expression of beige markers (TBX1 and UCP1) in white adipocytes demonstrating that NR can declutch beiging. NR did not induce PARP activity but supported SIRT1 induction, which plays a key role in beiging. NR induced etomoxir-resistant respiration, suggesting increases in the oxidation of carbohydrates, carbohydrate breakdown products, or amino acids. Furthermore, NR boosted oligomycin-resistant respiration corresponding to uncoupled respiration. Enhanced etomoxir and oligomycin-resistant respiration were dependent on mitochondrial reactive-species production. Taken together, NR supplementation can induce beiging and uncoupled respiration, which are beneficial for combatting metabolic diseases.

Oral Administration of Nicotinamide Mononucleotide Is Safe and Efficiently Increases Blood Nicotinamide Adenine Dinucleotide Levels in Healthy Subjects

Nicotinamide mononucleotide (NNM) is an orally bioavailable NAD+ precursor that has demonstrated beneficial effects against aging and aging-associated diseases in animal models. NMN is ultimately converted to NAD+, a redox cofactor that mediates many metabolic enzymes. NAD+ also serves as the substrate for poly(ADP-ribose) polymerase (PARP) and sirtuins, and regulates various biological processes, such as metabolism, DNA repair, gene expression, and stress responses. Previous mouse models showed that NMN administration can increase NAD+ in various organs and ameliorate aging-related diseases, such as obesity, diabetes, heart failure, stroke, kidney failure, and Alzheimer's disease through NAD+-mediated pathways. However, evidence of its effect on humans is still scarce. In this study, we conducted a placebo-controlled, randomized, double blind, parallel-group trial to investigate the safety of orally administered NMN and its efficacy to increase NAD+ levels in thirty healthy subjects. Healthy volunteers received 250 mg/day of NMN (n = 15) or placebo (n = 15) for 12 weeks, and physiological and laboratory tests were performed during this period. In addition, NAD+ and its related metabolites in whole blood were examined. Oral supplementation of NMN for 12 weeks caused no abnormalities in physiological and laboratory tests, and no obvious adverse effects were observed. NAD+ levels in whole blood were significantly increased after NMN administration. We also observed the significant rise in nicotinic acid mononucleotide (NAMN) levels, but not in NMN. We also found that the increased amount of NAD+ was strongly correlated with pulse rate before the administration of NMN. These results suggest that oral administration of NMN is a safe and practical strategy to boost NAD+ levels in humans. Clinical Trial Registration: JRCT [https://jrct.niph.go.jp/], identifier: [jRCTs041200034].

Metabolic Disease, NAD Metabolism, Nicotinamide Riboside, and the Gut Microbiome: Connecting the Dots from the Gut to Physiology

The effort to use nutrients as interventions to treat human disease has been important to medicine. A current example in this vein pertains to NAD⁺ boosters, such as nicotinamide riboside (NR) and nicotinamide mononucleotide (NMN), which are in many clinical trials in a variety of disease conditions. Independent laboratories have shown that ingested NR (or NMN) has mitigating effects on metabolic syndrome in mice. V. V. Lozada-Fernández, O. deLeon, S. L. Kellogg, F. L. Saravia, et al. (mSystems 7:e00230-21, 2022, https://doi.org/10.1128/mSystems.00230-21) show that NR shifts gut microbiome contents and that the transplantation of an NR-conditioned microbiome by fecal transfer reproduces some effects of NR in mice on a high-fat diet. The involvement of the gut microbiome as a factor in NR effects is linked to changes to the gut microbiome and its activity to transform NR and downstream catabolites. This commentary draws attention to these findings and focuses on some puzzling aspects of NAD⁺ boosters, exploring the still murky interactions between NAD⁺ metabolism, energy homeostasis, and the gut microbiome.

Nicotinamide riboside supplementation confers marginal metabolic benefits in obese mice without remodeling the muscle acetyl-proteome

Nicotinamide riboside supplements (NRS) have been touted as a nutraceutical that promotes cardiometabolic and musculoskeletal health by enhancing nicotinamide adenine dinucleotide (NAD+) biosynthesis, mitochondrial function, and/or the activities of NAD-dependent sirtuin deacetylase enzymes. This investigation examined the impact of NRS on whole body energy homeostasis, skeletal muscle mitochondrial function, and corresponding shifts in the acetyl-lysine proteome, in the context of diet-induced obesity using C57BL/6NJ mice. The study also included a genetically modified mouse model that imposes greater demand on sirtuin flux and associated NAD+ consumption, specifically within muscle tissues. In general, whole body glucose control was marginally improved by NRS when administered at the midpoint of a chronic high-fat diet, but not when given as a preventative therapy upon initiation of the diet. Contrary to anticipated outcomes, the study produced little evidence that NRS increases tissue NAD+ levels, augments mitochondrial function, and/or mitigates diet-induced hyperacetylation of the skeletal muscle proteome.