What is NAD+?
Nicotinamide Adenine Dinucleotide (NAD+) is a coenzyme present in all living cells. It consists of two nucleotides — one containing adenine, the other nicotinamide — joined by a phosphate bond. NAD+ exists in two interconvertible forms: its oxidized form (NAD+) and its reduced form (NADH), and the ratio between them is a critical indicator of cellular metabolic state.
First described by Arthur Harden and William John Young in 1906, NAD+ has become one of the most studied molecules in biochemistry, with its importance expanding from basic metabolic function to a central role in aging research, epigenetics, and DNA repair biology.
Cellular Energy Production
NAD+’s most fundamental role in cellular biology is as an electron carrier in oxidation-reduction (redox) reactions central to energy metabolism. During glycolysis and the citric acid cycle (Krebs cycle), NAD+ accepts electrons from metabolic intermediates, becoming NADH. This NADH then donates its electrons to Complex I of the mitochondrial electron transport chain (ETC), generating a proton gradient that drives ATP synthase — the molecular machine that produces ATP, the cell’s primary energy currency.
The importance of this cycle cannot be overstated: without sufficient NAD+ to accept electrons, glycolysis and the citric acid cycle stall, severely impairing cellular energy production. This is why NAD+ availability is closely linked to mitochondrial function and overall metabolic health in model organisms.
Beyond Metabolism: The Sirtuin Connection
One of the most significant discoveries in NAD+ biology was the identification of sirtuins — a family of seven NAD+-dependent deacetylase enzymes (SIRT1–SIRT7) — as key regulators of cellular health and longevity pathways.
Sirtuins consume NAD+ as they remove acetyl groups from target proteins, thereby regulating their function. Their targets include histones (regulating gene expression), p53 (regulating cell death), PGC-1α (regulating mitochondrial biogenesis), and FOXO transcription factors (regulating stress resistance). Through these actions, sirtuins have been linked in model organisms to:
- Extended lifespan in yeast, worms, and flies under caloric restriction conditions
- Improved mitochondrial biogenesis and function
- Enhanced DNA damage repair
- Regulation of inflammatory pathways
- Metabolic effects including improved insulin sensitivity in rodent models
Because sirtuins require NAD+ to function, any decline in cellular NAD+ levels directly impairs sirtuin activity — a key hypothesis linking NAD+ decline to aging phenotypes.
PARP Enzymes and DNA Repair
NAD+ is also the substrate for PARP enzymes (Poly ADP-ribose polymerases), which are critical responders to DNA damage. When DNA strand breaks occur — whether from oxidative stress, radiation, or replication errors — PARPs are rapidly activated and consume large amounts of NAD+ as they signal the repair machinery and modify target proteins.
Under conditions of severe DNA damage, PARP hyperactivation can dramatically deplete cellular NAD+ stores, creating a feedback loop: more damage → more PARP activation → less NAD+ → impaired sirtuin activity and energy metabolism. This PARP–sirtuin competition for NAD+ has become an important concept in understanding how oxidative stress and genomic instability may contribute to aging.
NAD+ Decline with Age
Research in multiple model organisms, and more recently in human tissue studies, has documented a significant decline in NAD+ levels with age. Studies have measured NAD+ concentrations in rodent tissues and found reductions of 40–60% in aged animals compared to young adults.
This age-associated NAD+ decline has been proposed to contribute to hallmarks of aging including:
- Reduced mitochondrial number and function
- Impaired DNA damage repair capacity
- Chronic low-grade inflammation (“inflammaging”)
- Declined sirtuin-mediated epigenetic maintenance
These observations have generated substantial scientific interest in NAD+ precursors — particularly nicotinamide mononucleotide (NMN) and nicotinamide riboside (NR) — as tools for maintaining or restoring NAD+ levels in aging tissues. Multiple clinical trials with these precursors are currently registered or underway.
Research Applications of NAD+
Research-grade NAD+ supplied by Euno Labs is used in laboratory settings for a variety of applications including in vitro enzyme activity assays, cell culture supplementation studies, metabolic flux analysis, and as a biochemical reference standard. All Euno Labs NAD+ is supplied for research use only.
Selected References
Yoshino J, et al. (2018). NAD+ Intermediates: The Biology and Therapeutic Potential of NMN and NR. Cell Metabolism, 27(3), 513–528.
Verdin E. (2015). NAD+ in aging, metabolism, and neurodegeneration. Science, 350(6265), 1208–1213.
Guarente L. (2013). Calorie restriction and sirtuins revisited. Genes and Development, 27(19), 2072–2085.