NAD+

NAD+ (nicotinamide adenine dinucleotide) is an essential coenzyme present in all living cells, functioning as a critical electron carrier in metabolic redox reactions and as a substrate for NAD+-consuming enzymes. NAD+ participates in over 500 enzymatic reactions, shuttling electrons in glycolysis, the TCA cycle, and oxidative phosphorylation as the NAD+/NADH redox pair. Beyond its role as a coenzyme, NAD+ serves as a substrate for sirtuins (SIRT1-7), PARPs (poly-ADP-ribose polymerases), and CD38/CD157 ectoenzymes, all of which consume NAD+ in their catalytic cycles. Intracellular NAD+ levels decline with age, and this decline has been associated with mitochondrial dysfunction, DNA damage accumulation, and altered gene expression in aging research models. NAD+ is synthesized through de novo, Preiss-Handler, and salvage pathways, with the salvage pathway (via NAMPT and NMNAT enzymes) being the primary source in most mammalian tissues.

NAD+ has been investigated for its dual roles as a redox cofactor and signaling substrate. As an electron carrier, NAD+ accepts hydride ions (H⁻) from metabolic substrates to form NADH, which donates electrons to Complex I of the mitochondrial electron transport chain for ATP production. As a sirtuin substrate, NAD+ is cleaved during deacetylation reactions catalyzed by SIRT1-7, producing nicotinamide and O-acetyl-ADP-ribose. Researchers observed that sirtuin activity is directly dependent on NAD+ availability, linking cellular NAD+ levels to epigenetic regulation, mitochondrial biogenesis (SIRT1/PGC-1α), and DNA repair (SIRT6). PARP enzymes consume large quantities of NAD+ during DNA damage repair, potentially competing with sirtuins for the cellular NAD+ pool. Studies suggest that age-related NAD+ decline is driven by increased CD38 expression and reduced NAMPT activity. In preclinical models, researchers observed that NAD+ repletion through supplementation or precursor administration was associated with improved mitochondrial function and metabolic parameters.

NAD+ and Aging

Verdin E (2015) reviewed the role of NAD+ in aging biology, describing how declining NAD+ levels contribute to mitochondrial dysfunction and altered sirtuin signaling in aging tissues [1].

Sirtuin Biology

Imai and Guarente (2014) characterized the NAD+-sirtuin axis in metabolic regulation, demonstrating that NAD+ availability directly controls sirtuin activity and downstream metabolic programs [2].

NAD+ Repletion

Yoshino et al. (2018) reviewed strategies for NAD+ repletion including direct supplementation and precursor approaches (NMN, NR), describing the metabolic effects observed in preclinical aging models [3].