Nicotinamide adenine dinucleotide (NAD+) is an essential pyridine nucleotide coenzyme present in every living cell. It functions as the central hydride-ion carrier in cellular metabolism β accepting electrons from glycolysis, the TCA cycle, and beta-oxidation as NADH, then transferring them to the mitochondrial electron transport chain (ETC) for ATP synthesis. Beyond its role as a redox cofactor, NAD+ is a consumed substrate for three major enzyme families: sirtuins (SIRT1β7), which deacylate histones and non-histone proteins to regulate gene expression and metabolism; PARPs (poly-ADP-ribose polymerases), which consume NAD+ during DNA damage repair; and CD38/CD157, cyclic ADP-ribose synthases involved in calcium signalling.
NAD+ levels decline with age, metabolic stress, and DNA damage β a finding that has been replicated across tissues in multiple species including humans. This decline is mechanistically linked to reduced sirtuin activity, impaired mitochondrial function, and accumulated senescent cells. The hypothesis that restoring NAD+ can reverse or attenuate these age-associated deficits has generated extensive preclinical and clinical research over the past decade, with David Sinclair’s laboratory at Harvard and Johan Auwerx’s group at EPFL among the most prominent contributors.
QSC supplies NAD+ in two research-relevant formats: lyophilised injectable vials (100 mg, 500 mg, 1000 mg) for systemic and tissue-targeted administration models, and oral tablets (1200 mg) for bioavailability, pharmacokinetic, and chronic dosing studies. Both formats allow researchers to study the full NAD+ biology β from acute IV replenishment models to long-term oral supplementation protocols.
NAD+ Biosynthesis Pathways β Research Context
Understanding which biosynthetic pathway is active in your model is essential for interpreting NAD+ supplementation results:
Preiss-Handler Pathway
NA β NAMN β NAAD β NAD+. The classical de novo/salvage route from nicotinic acid (niacin). NAPRT is the rate-limiting enzyme. Active in liver and kidney.
Salvage Pathway (Nam β NMN β NAD+)
The dominant NAD+ synthesis route in mammals. NAMPT is the rate-limiting enzyme converting Nam β NMN. NMNAT1-3 then converts NMN β NAD+. Most relevant to NMN/NR supplementation research.
De Novo (Trp) Pathway
Tryptophan β kynurenine β quinolinate β NAMN β NAD+. Contributes ~30% of hepatic NAD+ synthesis. KMO and QPRT are key enzymes. Relevant to neuroinflammation and IDO/TDO research.
NR/NMN Pathway (Riboside Route)
NR β NMN (via NRK1/2) β NAD+. Alternative entry point bypassing NAMPT. NMN β NAD+ via NMNAT. Direct NAD+ administration bypasses all precursor pathways entirely.
Research note: Direct NAD+ administration (injectable) raises intracellular NAD+ independently of NAMPT, NRK, or NMNAT activity β useful when studying NAD+-dependent enzyme activity (sirtuin, PARP) without the confound of NMN/NR conversion efficiency varying across tissues or genotypes.
Research Applications
Sirtuin Activation Research
Sirtuins (SIRT1β7) are NAD+-dependent deacylases that require NAD+ as a co-substrate (not a cofactor) β each catalytic cycle consumes one NAD+ molecule. Elevating NAD+ levels increases sirtuin activity across tissues. SIRT1 targets include PGC-1Ξ± (mitochondrial biogenesis), p53 (apoptosis), and FOXO (stress resistance). SIRT3 regulates mitochondrial acetylation. SIRT6 maintains genomic stability. Injectable NAD+ in rodent models is used to acutely saturate sirtuin substrate availability and study downstream acetylome changes by mass spectrometry.
PARP/DNA Damage Repair Models
PARP1/2 consume NAD+ at high rates during genotoxic stress β DNA strand breaks trigger massive PARP activation that can deplete cellular NAD+ by >80% within minutes. Research uses NAD+ supplementation to maintain PARP substrate availability during DNA damage assays, study the competition between PARP and sirtuins for NAD+, or examine how NAD+ depletion affects cell survival vs apoptosis decisions following genotoxic insults.
Mitochondrial Function & Biogenesis
NADH/NAD+ ratio is a primary regulator of mitochondrial function β high NADH/NAD+ (low NAD+) inhibits the TCA cycle and ETC. Elevating NAD+ through supplementation promotes SIRT1/3 deacetylation of PGC-1Ξ± and TFAM, increasing mitochondrial biogenesis. In aged tissue models where NAD+ is chronically low, NAD+ replenishment restores mitochondrial membrane potential and oxidative capacity β studied by seahorse respirometry, Complex I activity assays, and mtDNA copy number.
Ageing & Senescence Research
NAD+ decline with age has been documented in multiple tissues (liver, muscle, brain, kidney) across rodent and human studies. Replenishment studies in aged mice using NMN, NR, or direct NAD+ have demonstrated improvements in muscle function, cognition, and metabolic parameters. Injectable NAD+ models allow dose-precise replenishment independent of oral bioavailability, tissue-specific conversion efficiency, or NAMPT activity β providing a clean baseline for mechanistic studies.
CD38 / Calcium Signalling
CD38 is an ecto-enzyme that converts NAD+ to cyclic ADP-ribose (cADPR) and ADPR, second messengers for intracellular calcium mobilisation. CD38 expression increases with age and inflammation β and is considered a major driver of age-related NAD+ decline alongside PARP hyperactivation. Research uses NAD+ supplementation combined with CD38 inhibitors (e.g., apigenin, 78c) to study the relative contributions of CD38 vs PARP to NAD+ depletion in aged and inflamed tissue models.
Key Research Studies
Study
Journal
Finding
Gomes et al., 2013
Cell
NMN restores mitochondrial homeostasis in aged mice via SIRT1-dependent pathway; established NAD+-sirtuin-mitochondria axis in ageing
Yoshino et al., 2011
Cell Metab
NMN reverses age-associated decline in energy metabolism in mice; foundational for NAD+ precursor supplementation research
Camacho-Pereira et al., 2016
Cell Metab
CD38 identified as primary driver of age-related NAD+ decline; CD38 KO mice maintain youthful NAD+ levels
Rajman et al., 2018
Cell Metab
Review: Therapeutic potential of NAD+-boosting molecules; comprehensive framework for sirtuin/PARP/CD38 biology
Elhassan et al., 2019
Cell Rep
Human trial: NR supplementation increases NAD+ metabolome in skeletal muscle and blood; first muscle-specific human data
Martens et al., 2023
Nature Aging
Human trial: NMN supplementation increases walking speed and muscle strength in older adults; dose-response data
Injectable vs Oral NAD+ β Choosing the Right Format
QSC supplies NAD+ in both injectable vials and oral tablets β each optimised for different research designs:
Direct NAD+, NMN, and NR are three distinct research tools, not interchangeable:
Direct NAD+ (injectable)
Bypasses all biosynthetic enzymes. Best for: mechanistic studies where NAMPT, NRK, or NMNAT activity should not be a variable. Acute replenishment experiments. Tissue-specific delivery via local injection.
NMN (precursor)
Enters cells via Slc12a8 transporter (in some tissues) or is converted to NR extracellularly. NMNAT1-3 converts NMN β NAD+. Better oral bioavailability vs direct NAD+. Studies NAMPT-independent route. QSC does not currently supply NMN.
NR (nicotinamide riboside)
Enters cells via NRK1/2 β NMN β NAD+. Also converted to Nam in blood. Good oral bioavailability; approved human supplement. Studies NRK-dependent route. Elevates both NAD+ and NAAD. QSC does not currently supply NR.
QSC supplies: Direct NAD+ only (injectable vials + oral tablets). For NMN or NR research, researchers should confirm their institution’s supply chain. For NAMPT-dependent pathway studies, the combination of direct NAD+ (QSC) vs NMN/NR from other suppliers as parallel arms isolates pathway-specific effects.
Peptide Research Tools β Use our free research calculator for reconstitution, dosing, and mixing charts.
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Frequently Asked Questions
What is NAD+ and why do NAD+ levels decline with age?
NAD+ (nicotinamide adenine dinucleotide) is an essential coenzyme and enzyme substrate present in every cell. With age, NAD+ levels decline across multiple tissues due to increased consumption by PARP enzymes (activated by age-related DNA damage accumulation), upregulation of CD38 (an NAD+-consuming ecto-enzyme whose expression increases with inflammation and age), and reduced NAMPT activity (the rate-limiting enzyme in the salvage biosynthesis pathway). The resulting NAD+ deficit impairs sirtuin activity, mitochondrial function, and DNA repair capacity.
What is the difference between injectable NAD+ and oral NAD+ tablets in research?
Injectable NAD+ delivers the molecule systemically with high dose precision, bypassing all biosynthetic enzymes (NAMPT, NRK, NMNAT). This makes it ideal for mechanistic studies where the research question requires controlling NAD+ levels independently of precursor conversion efficiency. Oral NAD+ tablets are better suited for chronic dosing, bioavailability, and pharmacokinetic studies β including comparison with NMN/NR oral supplementation protocols.
How does NAD+ activate sirtuins?
Sirtuins are NAD+-dependent deacylases that require NAD+ as a co-substrate, not a cofactor β each catalytic cycle consumes one NAD+ and produces nicotinamide (Nam), 2-O-acetyl-ADP-ribose, and the deacylated substrate. Elevating cellular NAD+ increases sirtuin activity by increasing substrate availability. SIRT1 deacetylates PGC-1Ξ± (mitochondrial biogenesis), p53 (apoptosis), and FOXO factors. SIRT3 regulates mitochondrial protein acetylation. SIRT6 maintains telomere length and genomic stability.
What QSC NAD+ formats are available?
QSC supplies NAD+ as lyophilised injectable powder (100 mg, 500 mg, and 1000 mg vials, available as 10-vial or 20-vial kits) and as 1200 mg oral tablets (500-count or 1000-count). All formats are HPLC-verified for purity. The injectable vials ship from QSC domestic warehouses in the USA, EU, UK, Canada, and Australia.
Is NAD+ the same as NMN or NR?
No. NAD+, NMN (nicotinamide mononucleotide), and NR (nicotinamide riboside) are related but distinct molecules at different points in the NAD+ biosynthesis pathway. NMN and NR are precursors that must be converted to NAD+ via enzymatic steps (NRK1/2 and NMNAT). Direct NAD+ bypasses these conversion steps entirely. The choice between them is a research design decision based on which pathway you want to engage or avoid.
