NAD+ Glossary

Terminology reference for molecules, enzymes, pathways, and concepts used across the knowledge base. Jump by letter.

Bioavailabilityconcept: The fraction of an administered dose that reaches systemic circulation in active form. Oral bioavailability is typically lower than IV due to gut degradation and first-pass liver metabolism.

CD38enzyme: A membrane-bound glycohydrolase that cleaves NAD+. Rising CD38 expression with age and inflammation is the largest contributor to tissue NAD+ decline.
Coenzymeconcept: A small organic molecule required for an enzyme's catalytic activity. NAD+ is the most abundant coenzyme in human metabolism.

DNA Repairpathway: The cellular process of correcting damaged DNA bases and strand breaks. Depends on NAD+-consuming PARP enzymes and sirtuins.

Mitochondriamtconcept: Cellular organelles that generate ATP via oxidative phosphorylation. Hold ~70% of cellular NAD+; depend on the NAD+/NADH redox pair for every electron transport step.

NAD+NAD+molecule: Nicotinamide adenine dinucleotide. A coenzyme essential to redox reactions and a substrate for sirtuins, PARPs, and CD38.
NADHNADHmolecule: The reduced form of NAD+. The NAD+/NADH ratio reports on a cell's metabolic state.
NAMPTNAMPTenzyme: Nicotinamide phosphoribosyltransferase. The rate-limiting enzyme of the NAD+ salvage pathway; converts Nam to NMN.
NicotinamideNammolecule: The amide form of vitamin B3. Enters the NAD+ salvage pathway via NAMPT. Also inhibits sirtuins at high concentrations.
Nicotinamide MononucleotideNMNmolecule: A direct NAD+ precursor one enzymatic step upstream of NAD+. Transported into cells via Slc12a8 in the small intestine.
Nicotinamide RibosideNRmolecule: A pyridine-nucleoside form of vitamin B3. Phosphorylated to NMN by NRK1/2, then adenylated to NAD+.

PARPPARPenzyme: Poly(ADP-ribose) polymerase. Family of enzymes that use NAD+ to tag damaged DNA with poly-ADP-ribose chains, signaling repair machinery.
PharmacokineticsPKconcept: The study of how a drug moves through the body — absorption, distribution, metabolism, and excretion.
Preiss-Handler Pathwaypathway: The three-step enzymatic route that converts niacin (nicotinic acid) into NAD+. Distinct from the salvage pathway.

Salvage Pathwaypathway: The dominant NAD+ regeneration route. NAMPT converts Nam to NMN; NMNAT1-3 adenylates NMN to NAD+.
SirtuinsSIRT1-7enzyme: A family of seven NAD+-dependent deacylases that regulate aging, metabolism, and stress response.
Slc12a8enzyme: A nicotinamide mononucleotide transporter identified in 2019 by Grozio et al. Explains direct NMN uptake in the small intestine.

TMGTMGmolecule: Trimethylglycine (betaine). A methyl donor sometimes co-administered with NAD+ precursors to offset methyl group depletion from Nam methylation.