Stimulating the sir2-pgc-1α axis rescues exercise capacity and mitochondrial respiration in Drosophila tafazzin mutants.

Cardiolipin (CL) is a phospholipid required for proper mitochondrial function. Tafazzin remodels CL to create highly unsaturated fatty acid chains. However, when tafazzin is mutated, CL remodeling is impeded, leading to mitochondrial dysfunction and the disease Barth syndrome. Patients with Barth syndrome often have severe exercise intolerance, which negatively impacts their overall quality of life. Boosting NAD+ levels can improve symptoms of other mitochondrial diseases, but its effect in the context of Barth syndrome has not been examined. We demonstrate for the first time that nicotinamide riboside (NR) can rescue exercise tolerance and mitochondrial respiration in a Drosophila tafazzin mutant and that the beneficial effects are dependent on sir2 and pgc-1α . Overexpressing pgc-1α increased the total abundance of cardiolipin in mutants. In addition, muscles and neurons were identified as key targets for future therapies because sir2 or pgc-1α overexpression in either of these tissues is sufficient to restore the exercise capacity of Drosophila tafazzin mutants.

Metabolic rescue ameliorates mitochondrial encephalo-cardiomyopathy in murine and human iPSC models of Leigh syndrome

Mice with deletion of complex I subunit Ndufs4 develop mitochondrial encephalomyopathy resembling Leigh syndrome (LS). We report that LS mice also develop severe cardiac bradyarrhythmia and diastolic dysfunction. Human induced pluripotent stem cell-derived cardiomyocytes (iPS-CMs) with Ndufs4 deletion recapitulate LS cardiomyopathy. Mechanistically, we demonstrate a direct link between complex I deficiency, decreased intracellular NAD+/ NADH and bradyarrhythmia, mediated by hyperacetylation of the cardiac sodium channel NaV1.5, particularly at K1479 site. Neuronal apoptosis in the cerebellar and midbrain regions in LS mice was associated with hyperacetylation of p53 and activation of microglia. Targeted metabolomics revealed increases in several amino acids and citric acid cycle intermediates, likely due to impairment of NAD+-dependent dehydrogenases, and a substantial decrease in reduced Glutathione (GSH). Metabolic rescue by nicotinamide riboside (NR) supplementation increased intracellular NAD+/ NADH, restored metabolic derangement, reversed protein hyperacetylation through NAD+-dependent Sirtuin deacetylase, and ameliorated cardiomyopathic phenotypes, concomitant with improvement of NaV1.5 current and SERCA2a function measured by Ca2+-transients. NR also attenuated neuronal apoptosis and microglial activation in the LS brain and human iPS-derived neurons with Ndufs4 deletion. Our study reveals direct mechanistic explanations of the observed cardiac bradyarrhythmia, diastolic dysfunction and neuronal apoptosis in mouse and human iPSC models of LS.

Nicotinamide Riboside Promotes Mfn2-mediated Mitochondrial Fusion in Diabetic Hearts through the SIRT1-PGC1α-PPARα Pathway

Background: Myocardial dysfunction is associated with an imbalance in mitochondrial fusion/fission dynamics in patients with diabetes. However, effective strategies to regulate mitochondrial dynamics in the diabetic heart are still lacking. This study investigated whether Nicotinamide riboside (NR) supplementation protects against diabetes-induced cardiac dysfunction by regulating mitochondrial fusion/fission and further explored the underlying mechanisms.Methods: Obese diabetic (db/db) and lean control (db/+) mice were each given NR oral supplementation in this study. NAD+ Content was determined in mice hearts and primary neonatal cardiomyocytes. Cardiac function was detected by echocardiography. Mitochondrial dynamics were analyzed by transmission electron microscopy in vivo and by confocal microscopy in vitro. Results: Here, we show an evident decrease in NAD+ level and mitochondrial fragmentation in the hearts of leptin receptor-deficient diabetic (db/db) mouse model. NR supplementation significantly increased NAD+ content in the diabetic heart tissues. Furthermore, NR treatment increased Mfn2 expression, promoted mitochondrial fusion, suppressed oxidative stress, reduced cardiomyocyte apoptosis and consequently improved cardiac function in db/db mice. In neonatal primary cardiomyocytes cultured in a high-glucose/high-fat medium, NR treatment also promoted mitochondrial fusion, suppressed mitochondria-derived ROS production and reduced cardiomyocyte apoptosis, which were all reversed when Mfn2 was knocked down. Mechanistically, chromatin immunoprecipitation (ChIP) and luciferase report assay analysis revealed that PGC1α and PPARα interdependently regulated Mfn2 transcription by binding to its promoter region. NR treatment elevated NAD+ levels and activated SIRT1, resulting in the deacetylation of PGC1α and promoting the transcription of Mfn2. Furthermore, the inhibition of SIRT1, PGC1α or PPARα blunted the positive effects of NR supplementation on Mfn2 expression and mitochondrial fusion. Conclusion: NR attenuates the development of diabetes-induced cardiac dysfunction by promoting mitochondrial fusion through the SIRT1-PGC1α-PPARα pathway, with PGC1α and PPARα being the interdependent co-regulatory factors for Mfn2. The promotion of mitochondrial fusion via oral supplementation of NR may be a potential strategy for delaying cardiac complications in patients with diabetes.

Synthesis, Stability, and Bioavailability of Nicotinamide Riboside Trioleate Chloride

Nicotinamide riboside chloride (NRCl) is an effective form of vitamin B3. However, it cannot be used in ready-to-drink (RTD) beverages or high-water activity foods because of its intrinsic instability in water. To address this issue, we synthesized nicotinamide riboside trioleate chloride (NRTOCl) as a new hydrophobic nicotinamide riboside (NR) derivative. Contrary to NRCl, NRTOCl is soluble in an oil phase. The results of stability studies showed that NRTOCl was much more stable than NRCl both in water and in oil-in-water emulsions at 25 °C and 35 °C. Finally, we evaluated the bioavailability of NRTOCl by studying its digestibility in simulated intestinal fluid. The results demonstrated that NRTOCl was partially digestible and released NR in the presence of porcine pancreatin in a simulated intestinal fluid. This study showed that NRTOCl has the potential to be used as an NR derivative in ready-to-drink (RTD) beverages and other foods and supplement applications.

Human embryos arrest in a quiescent-like state characterized by metabolic and zygotic genome activation problems

Around 60% of in vitro fertilized (IVF) human embryos irreversibly arrest before compaction between the 3-8-cell stage, posing a significant clinical problem. The mechanisms behind this arrest are unclear. Here, we show that the arrested embryos enter a quiescent-like state, marked by cell cycle arrest, the downregulation of ribosomes and histones and downregulation of MYC and p53 activity. Mechanistically, the arrested embryos can be divided into three types. Type I embryos fail to complete the maternal-zygotic transition, and type II/III embryos have erroneously low levels of glycolysis and variable levels of oxidative phosphorylation. Treatment with resveratrol or nicotinamide riboside (NR) can partially rescue the arrested phenotype. The mechanism of reactivation involves the upregulation of SIRT1, and activation of glycolysis and fatty acid oxidation which forces the embryos out of a quiescent state. Overall, our data reveal how human embryo arrest can be overcome by modulating metabolic pathways.

NAD metabolism modulates mitochondrial function and inflammation and prevents progression of diabetic kidney disease

ABSTRACTBackgroundDiabetes mellitus is the leading cause of cardiovascular and renal disease in the United States. In spite of all of the beneficial interventions implemented in patients with diabetes, there remains a need for additional therapeutic targets in diabetic kidney disease (DKD). Mitochondrial dysfunction and inflammation are increasingly recognized as important causes of the development and progression of DKD. However, the molecular connection between mitochondrial function, inflammation, and fibrosis remains to be elucidated.MethodsIn the present studies we tested the hypothesis that enhancing NAD metabolism could increase mitochondrial sirtuin 3 (SIRT3) activity, improve mitochondrial function, decrease mitochondrial DNA damage, and prevent inflammation and progression of DKD.ResultsWe found that treatment of db-db mice with type 2 diabetes with nicotinamide riboside (NR) prevented albuminuria, increased urinary KIM1 excretion, and several parameters of DKD. These effects were associated with increased SIRT3 activity, improved mitochondrial function, and decreased inflammation at least in part via inhibiting the activation of the cyclic GMP-AMP synthase-stimulator of interferon genes (cGAS-STING) signaling pathway.ConclusionsNR supplementation boosted the NAD metabolism to modulate mitochondrial function and inflammation and prevent progression of diabetic kidney disease.

NAD precursors cycle between host tissues and the gut microbiome

Nicotinamide adenine dinucleotide (NAD) is an essential redox cofactor in both mammals and microbes. Here we use isotope tracing to investigate the precursors supporting NAD synthesis in the gut microbiome. We find that preferred dietary NAD precursors are absorbed in the proximal part of the gastrointestinal tract and not available to microbes in the distal gut. Instead, circulating host nicotinamide enters the gut lumen and supports gut microbiome NAD synthesis. In addition, the microbiome converts nicotinamide, originating from the host circulation, into nicotinic acid. Host tissues uptake and utilize this microbiome-derived nicotinic acid for NAD synthesis, maintaining circulating nicotinic acid levels even in the absence of dietary consumption. Moreover, the main route from oral nicotinamide riboside, a widely used nutraceutical, to host NAD is via conversion into nicotinic acid by the gut microbiome. Thus, NAD precursors cycle between the host and gut microbiome to maintain NAD homeostasis.

BST1 regulates nicotinamide riboside metabolism via its glycohydrolase and base-exchange activities

Nicotinamide riboside (NR) is one of the orally bioavailable NAD+ precursors and has been demonstrated to exhibit beneficial effects against aging and aging-associated diseases. However, the metabolic pathway of NR in vivo is not yet fully understood. Here, we demonstrate that orally administered NR increases NAD+ level via two different pathways. In the early phase, NR was directly absorbed and contributed to NAD+ generation through the NR salvage pathway, while in the late phase, NR was hydrolyzed to nicotinamide (NAM) by bone marrow stromal cell antigen 1 (BST1), and was further metabolized by the gut microbiota to nicotinic acid, contributing to generate NAD+ through the Preiss–Handler pathway. Furthermore, we report BST1 has a base-exchange activity against both NR and nicotinic acid riboside (NAR) to generate NAR and NR, respectively, connecting amidated and deamidated pathways. Thus, we conclude that BST1 plays a dual role as glycohydrolase and base-exchange enzyme during oral NR supplementation.