Complete Guide to NAD+: Longevity, Sirtuines, and DNA Repair

Le NAD+ (Nicotinamide Adenine Dinucleotide) is a coenzyme present in all living cellsIt is essential for cellular energy production, the activation of sirtuins—the proteins that regulate longevity—and DNA repair. Without NAD+, the cell cannot respire, repair itself, or age healthily. Research conducted over the past two decades has made it one of the most studied molecules in the field of cellular aging and longevity biology.

This guide summarizes the molecular mechanisms of NAD+, its decline with age, and current research directions on its potential applications in neuroprotection, energy metabolism and longevity.

NAD+ acts as a cofactor in over 500 enzymatic reactions. Its main molecular roles are:

• Sirtuines (SIRT1-7): These NAD+-dependent deacetylases regulate gene expression, DNA repair, mitochondrial metabolism, and the stress response. SIRT1 and SIRT6 are particularly studied in the context of aging. Each sirtuin activation cycle consumes one molecule of NAD+.
• PARP (Poly ADP-Ribose Polymerase): These DNA repair enzymes are activated during double-strand breaks. They consume large amounts of NAD+ to synthesize poly-ADP-ribose chains used to recruit repair complexes. In cases of significant damage, PARPs can deplete cellular NAD+ stores.
• CD38: CD38, a pro-inflammatory membrane glycohydrolase, degrades NAD+ in a non-recyclable manner. Its activity increases significantly with age and chronic inflammation, contributing to the decline in NAD+ levels.
• Mitochondria: NAD+ is the main electron acceptor of the mitochondrial respiratory chain (complex I). By being reduced to NADH, it transfers energy from the catabolism of carbohydrates and lipids to the synthesis of ATP.

Studies on human tissues and animal models show a decrease of approximately 50% of intracellular NAD+ levels between 20 and 50 years of ageThis phenomenon is multifactorial:

• Increased consumption: The accumulation of DNA damage with age leads to chronic PARP activation. Low-grade inflammation (inflammaging) stimulates CD38, whose activity can be 2 to 3 times higher in aged tissues.
• Reduction of biosynthesis: The expression of NAMPT (nicotinamide phosphoribosyltransferase), the rate-limiting enzyme of the NAD+ recycling pathway, decreases in many tissues with age.
• Functional consequences: The decline in NAD+ affects sirtuin activity, mitochondrial biogenesis, DNA repair, and circadian rhythm regulation — all processes directly involved in accelerated cellular aging.

This biological cascade makes the maintenance of NAD+ levels a major research target in the biology of longevity (Verdin, 2015; Yoshino et al., 2018).

Longevity and cellular aging

Studies in C. elegans, Drosophila, and mouse models show that increasing NAD+ levels via precursors (NMN, NR) or CD38 inhibition is associated with prolonged lifespan and improved markers of metabolic health. In aged mice, restoring NAD+ improves muscle function, mitochondrial density, and the oxidative stress response.

Neuroprotection

The brain is particularly sensitive to fluctuations in NAD+. Preclinical research is exploring the role of NAD+ in protection against neurodegenerative models (Alzheimer's, Parkinson's). Brain sirtuins—notably SIRT3 at the mitochondrial level and SIRT1 at the nuclear level—are involved in the neuroprotective response.

Energy metabolism

Phase I/II clinical trials are exploring NAD+ precursors (NMN, NR) in the contexts of metabolic syndrome, type 2 diabetes, and chronic fatigue. This work remains exploratory and does not constitute therapeutic validation.

• → NAD+: sirtuins, DNA repair and strategies
• → MOTS-c: mitochondrial peptide
• → Epithalon: longevity and telomerase

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