Nicotinamide Adenine Dinucleotide
Nicotinamide adenine dinucleotide (NAD) is a coenzyme found in all living cells. It is a dinucleotide, which means that it consists of two nucleotides joined through their phosphate groups. One nucleotide contains an adenine base, and the other contains nicotinamide.
In metabolism, NAD facilitates redox reactions, carrying electrons from one reaction to another. This means that NAD is found in two forms in the cell; NAD+ is an oxidizing agent that takes electrons from other molecules in order to become its reduced form, NADH. NADH can then become a reducing agent that donates the electrons it carries. The transfer of electrons is one of the main functions of NAD, though it also performs other cellular processes, including acting as a substrate for enzymes that add or remove chemical groups from proteins in post-translational modifications.
NAD+ is created from simple building blocks, such as the amino acid tryptophan, and it is created in a more complex way via the intake of food that contains nicotinic acid (niacin) or other NAD+ precursors. These different pathways ultimately feed into a salvage pathway, which recycles them back into the active NAD+ form.
Nicotinamide adenine dinucleotide (NAD+) biology has seen a great deal of interest in the last few years, partially due to the discovery of two precursors of NAD+ biosynthesis, nicotinamide riboside (NR) and nicotinamide mononucleotide (NMN), which both increase NAD+ in multiple tissues.
Accumulating evidence suggests that NAD+ systemically declines with age in a variety of organisms, including rodents and humans, which contributes to the development of many age-related diseases. For this reason, there is a great deal of interest in creating potential interventions that increase NAD+ levels via precursors, thus delaying or even preventing certain aspects of age-related functional decline and diseases.
You can read more about the fascinating world of NAD+ biology and its role in aging here.