NAD⁺ Homeostasis and Mitochondrial Modifiability: Resilience in Alzheimer's Disease

Alzheimer's disease (AD) is increasingly associated with mitochondrial dysfunction and disrupted metabolism. Thus, the maintenance of nicotinamide adenine dinucleotide (NAD⁺) homeostasis is proposed as a potential therapeutic strategy. Toward this end, we suggest that AD-related mitochondrial dysfunction might be viewed as a regulatable, redox-dependent vulnerability rather than an inherently degenerative and irreversible process. This perspective advances an evolutionary model in which NAD⁺-mediated redox systems represent a conserved regulatory axis, and that destabilization of this axis during aging may increase susceptibility to degeneration. Here, we assess the potential of a therapeutic approach that combines this understanding of mitochondrial energy metabolism with results from preclinical studies demonstrating the impact of pharmacologic correction of NAD⁺ homeostasis (e.g., P7C3-A20) as contextual motivation. We explicitly elevate redox balance, rather than absolute NAD⁺ abundance, as the mechanistically dominant variable that shapes mitochondrial resilience, inflammatory tone, and neurovascular stability. Accordingly, the key unresolved issue is whether specific physiologic benefits might accrue from increased NAD⁺ availability per se or rather, the restoration of the NAD⁺/NADH redox ratio, with important implications for the interpretation of the results of directed metabolic interventions. Within this framework, metabolic failure in AD can be understood as an upstream permissive condition that explains, rather than replaces, canonical amyloid-β and tau-associated pathologies. While extended human lifespan may expose late-life vulnerabilities in otherwise conserved metabolic systems, claims of causal primacy, disease reversibility, and cross-neurodegenerative generalization remain premature, underscoring the need for redox-resolved, genetic, and clinical validation.