NACvsNMN (Nicotinamide Mononucleotide)

NAC is deacetylated to cysteine, the rate-limiting substrate for glutathione synthesis via gamma-glutamylcysteine synthetase and glutathione synthetase. Glutathione (GSH) is the primary intracellular antioxidant in neurons, neutralizing reactive oxygen species and maintaining redox balance. NAC also activates the cystine-glutamate antiporter (System Xc-, composed of SLC7A11 and SLC3A2 subunits), which exchanges extracellular cystine for intracellular glutamate in a 1:1 ratio. This non-vesicular mechanism modulates extrasynaptic glutamate levels, reducing NMDA receptor overactivation and excitotoxicity. The glutamate-modulating effect explains NAC's promise in OCD (reducing corticostriatal glutamate hyperactivity), addiction (normalizing nucleus accumbens glutamate after drug exposure), and neurodegenerative conditions involving glutamate dysregulation.

NMN is transported into cells via the Slc12a8 transporter (highly expressed in the small intestine and brain) and converted to NAD+ by nicotinamide mononucleotide adenylyltransferases (NMNAT1 in the nucleus, NMNAT2 in axons/Golgi, NMNAT3 in mitochondria). Elevated NAD+ activates the sirtuin family of NAD+-dependent protein deacetylases: SIRT1 deacetylates PGC-1alpha to promote mitochondrial biogenesis, SIRT3 activates superoxide dismutase 2 (SOD2) and isocitrate dehydrogenase 2 (IDH2) for mitochondrial antioxidant defense, and SIRT6 promotes base excision repair of oxidative DNA damage. NAD+ is also consumed by poly(ADP-ribose) polymerases (PARP1/2) during DNA repair — age-related NAD+ depletion impairs PARP function, allowing DNA damage accumulation. In neurons, NAD+ is required for glycolysis (GAPDH cofactor), the TCA cycle, and Complex I of the electron transport chain, directly fueling the enormous ATP demands of synaptic transmission. NAD+ decline with aging (approximately 50% reduction between ages 40-60) reduces all of these processes simultaneously, creating a cascade of mitochondrial dysfunction, impaired DNA repair, and neuroinflammation that NMN supplementation aims to reverse.