NAD+ metabolism: from coenzyme research to clinical questions

From coenzyme to regulatory molecule

The review discussed here traces the development of NAD+ research from its discovery in fermentation to its roles in metabolism, mitochondrial function and cellular regulation.

NAD+ is a coenzyme in redox reactions and a substrate for several classes of enzymes. NMN is one intermediate used to make NAD+. These roles explain the interest in the pathway, but they do not establish a treatment effect from a supplement.

A short history of NAD+

In 1906, Arthur Harden and William Young observed that adding boiled yeast extract to unboiled extract could increase fermentation. They described a heat-stable factor, later associated with the coenzyme historically called cozymase.

Subsequent work by Hans von Euler-Chelpin helped clarify its chemical composition. Otto Warburg's research established its role in transferring reducing equivalents, with the nicotinamide portion participating in the redox reaction.

NAD+ and NADH in energy metabolism

NAD+ and its reduced form, NADH, participate in pathways including glycolysis, interconversion of pyruvate and lactate, the conversion of pyruvate to acetyl-CoA, fatty-acid oxidation, the tricarboxylic-acid cycle and oxidative phosphorylation.

These linked reactions transfer electrons and help coordinate the use of nutrients. A measurement of one metabolite alone does not describe the performance of the entire system.

NADP+ and NADPH

NAD kinases add a phosphate group to generate NADP+. Its reduced form, NADPH, supplies reducing power for processes such as fatty-acid and cholesterol synthesis and antioxidant-related systems.

NAD+/NADH and NADP+/NADPH are related but distinct couples. They should not be treated as alternative spellings for the same molecule or as having identical functions.

Enzymes that consume NAD+

Sirtuins use NAD+ in reactions that regulate protein activity. Other NAD+-consuming enzymes discussed in the archive include poly(ADP-ribose) polymerases and the CD38/CD157 family.

This helps explain renewed interest in how NAD+ is synthesized, consumed and distributed among tissues. The review considers potential links with mitochondrial homeostasis, metabolic disorders and aging-related research.

Conclusion

The paper describes a biological research field and possible routes from laboratory findings to clinical investigation. It does not demonstrate that increasing NAD+ indefinitely is beneficial or that a finished NMN product improves every metabolic outcome.

Cited review: Modulating NAD+ metabolism, from bench to bedside.