Nicotinamide riboside has minimal impact on energy metabolism in mouse models of mild obesity.

Supplementation with precursors of NAD has been shown to prevent and reverse insulin resistance, mitochondrial dysfunction, and liver damage in mouse models of diet-induced obesity. We asked whether the beneficial effects of supplementation with the NAD precursor nicotinamide riboside (NR) are dependent on mouse strain. We compared the effects of NR supplementation on whole-body energy metabolism and mitochondrial function in mildly obese C57BL/6N and C57BL/6J mice, two commonly used strains to investigate metabolism. Male C57BL/6N and C57BL/6J mice were fed a high-fat diet (HFD) or standard chow with or without NR supplementation for 8 weeks. Body and organ weights, glucose tolerance, and metabolic parameters as well as mitochondrial O2 flux in liver and muscle fibers were assessed. We found that NR supplementation had no influence on body or organ weight, glucose metabolism or hepatic lipid accumulation, energy expenditure, or metabolic flexibility but increased mitochondrial respiration in soleus muscle in both mouse strains. Strain-dependent differences were detected for body and fat depot weight, fasting blood glucose, hepatic lipid accumulation, and energy expenditure. We conclude that, in mild obesity, NR supplementation does not alter metabolic phenotype in two commonly used laboratory mouse strains.

Induction of the nicotinamide riboside kinase NAD+ salvage pathway in a model of sarcoplasmic reticulum dysfunction.

BACKGROUND: Hexose-6-Phosphate Dehydrogenase (H6PD) is a generator of NADPH in the Endoplasmic/Sarcoplasmic Reticulum (ER/SR). Interaction of H6PD with 11ß-hydroxysteroid dehydrogenase type 1 provides NADPH to support oxo-reduction of inactive to active glucocorticoids, but the wider understanding of H6PD in ER/SR NAD(P)(H) homeostasis is incomplete. Lack of H6PD results in a deteriorating skeletal myopathy, altered glucose homeostasis, ER stress and activation of the unfolded protein response. Here we further assess muscle responses to H6PD deficiency to delineate pathways that may underpin myopathy and link SR redox status to muscle wide metabolic adaptation. METHODS: We analysed skeletal muscle from H6PD knockout (H6PDKO), H6PD and NRK2 double knockout (DKO) and wild-type (WT) mice. H6PDKO mice were supplemented with the NAD+ precursor nicotinamide riboside. Skeletal muscle samples were subjected to biochemical analysis including NAD(H) measurement, LC-MS based metabolomics, Western blotting, and high resolution mitochondrial respirometry. Genetic and supplement models were assessed for degree of myopathy compared to H6PDKO. RESULTS: H6PDKO skeletal muscle showed adaptations in the routes regulating nicotinamide and NAD+ biosynthesis, with significant activation of the Nicotinamide Riboside Kinase 2 (NRK2) pathway. Associated with changes in NAD+ biosynthesis, H6PDKO muscle had impaired mitochondrial respiratory capacity with altered mitochondrial acylcarnitine and acetyl-CoA metabolism. Boosting NAD+ levels through the NRK2 pathway using the precursor nicotinamide riboside elevated NAD+/NADH but had no effect to mitigate ER stress and dysfunctional mitochondrial respiratory capacity or acetyl-CoA metabolism. Similarly, H6PDKO/NRK2 double KO mice did not display an exaggerated timing or severity of myopathy or overt change in mitochondrial metabolism despite depression of NAD+ availability. CONCLUSIONS: These findings suggest a complex metabolic response to changes in muscle SR NADP(H) redox status that result in impaired mitochondrial energy metabolism and activation of cellular NAD+ salvage pathways. It is possible that SR can sense and signal perturbation in NAD(P)(H) that cannot be rectified in the absence of H6PD. Whether NRK2 pathway activation is a direct response to changes in SR NAD(P)(H) availability or adaptation to deficits in metabolic energy availability remains to be resolved.

Nicotinamide Riboside Augments the Aged Human Skeletal Muscle NAD+ Metabolome and Induces Transcriptomic and Anti-inflammatory Signatures.

Nicotinamide adenine dinucleotide (NAD+) is modulated by conditions of metabolic stress and has been reported to decline with aging in preclinical models, but human data are sparse. Nicotinamide riboside (NR) supplementation ameliorates metabolic dysfunction in rodents. We aimed to establish whether oral NR supplementation in aged participants can increase the skeletal muscle NAD+ metabolome and if it can alter muscle mitochondrial bioenergetics. We supplemented 12 aged men with 1 g NR per day for 21 days in a placebo-controlled, randomized, double-blind, crossover trial. Targeted metabolomics showed that NR elevated the muscle NAD+ metabolome, evident by increased nicotinic acid adenine dinucleotide and nicotinamide clearance products. Muscle RNA sequencing revealed NR-mediated downregulation of energy metabolism and mitochondria pathways, without altering mitochondrial bioenergetics. NR also depressed levels of circulating inflammatory cytokines. Our data establish that oral NR is available to aged human muscle and identify anti-inflammatory effects of NR.

Hepatic NAD+ levels and NAMPT abundance are unaffected during prolonged high-fat diet consumption in C57BL/6JBomTac mice.

Dietary supplementation of nicotinamide adenine dinucleotide (NAD+) precursors has been suggested as a treatment for non-alcoholic fatty liver disease and obesity. In the liver, NAD+ is primarily generated by nicotinamide phosphoribosyltransferase (NAMPT), and hepatic levels of NAMPT and NAD+ have been reported to be dependent on age and body composition. The aim of the present study was to identify time course-dependent changes in hepatic NAD content and NAD+ salvage capacity in mice challenged with a high-fat diet (HFD). We fed 7-week-old C57BL/6JBomTac male mice either regular chow or a 60% HFD for 6, 12, 24, and 48 weeks, and we evaluated time course-dependent changes in whole body metabolism, liver steatosis, and abundance of hepatic NAD-associated metabolites and enzymes. Mice fed a 60% HFD rapidly accumulated fat and hepatic triglycerides with associated changes in respiratory exchange ratio (RER) and a disruption of the circadian feeding pattern. The HFD did not alter hepatic NAD+ levels, but caused a decrease in NADP+ and NADPH levels. Decreased NADP+ content was not accompanied by alterations in NAD kinase (NADK) abundance in HFD-fed mice, but NADK levels increased with age regardless of diet. NAMPT protein abundance did not change with age or diet. HFD consumption caused a severe decrease in protein lysine malonylation after six weeks, which persisted throughout the experiment. This decrease was not associated with changes in SIRT5 abundance. In conclusion, hepatic NAD+ salvage capacity is resistant to long-term HFD feeding, and hepatic lipid accumulation does not compromise the hepatic NAD+ pool in HFD-challenged C57BL/6JBomTac male mice.

Nicotinamide riboside kinases display redundancy in mediating nicotinamide mononucleotide and nicotinamide riboside metabolism in skeletal muscle cells.

OBJECTIVE: Augmenting nicotinamide adenine dinucleotide (NAD+) availability may protect skeletal muscle from age-related metabolic decline. Dietary supplementation of NAD+ precursors nicotinamide mononucleotide (NMN) and nicotinamide riboside (NR) appear efficacious in elevating muscle NAD+. Here we sought to identify the pathways skeletal muscle cells utilize to synthesize NAD+ from NMN and NR and provide insight into mechanisms of muscle metabolic homeostasis. METHODS: We exploited expression profiling of muscle NAD+ biosynthetic pathways, single and double nicotinamide riboside kinase 1/2 (NRK1/2) loss-of-function mice, and pharmacological inhibition of muscle NAD+ recycling to evaluate NMN and NR utilization. RESULTS: Skeletal muscle cells primarily rely on nicotinamide phosphoribosyltransferase (NAMPT), NRK1, and NRK2 for salvage biosynthesis of NAD+. NAMPT inhibition depletes muscle NAD+ availability and can be rescued by NR and NMN as the preferred precursors for elevating muscle cell NAD+ in a pathway that depends on NRK1 and NRK2. Nrk2 knockout mice develop normally and show subtle alterations to their NAD+ metabolome and expression of related genes. NRK1, NRK2, and double KO myotubes revealed redundancy in the NRK dependent metabolism of NR to NAD+. Significantly, these models revealed that NMN supplementation is also dependent upon NRK activity to enhance NAD+ availability. CONCLUSIONS: These results identify skeletal muscle cells as requiring NAMPT to maintain NAD+ availability and reveal that NRK1 and 2 display overlapping function in salvage of exogenous NR and NMN to augment intracellular NAD+ availability.