Aging is the single most significant risk factor for Alzheimer?s disease and related dementia (ADRD), leading to consideration of new therapeutic approaches from the field of Geroscience, such as nicotinamide adenine dinucleotide (NAD+) enhancing dietary supplements that exhibit anti-aging properties and improve lifespan and healthspan in rodents. Maintaining levels of NAD, a central metabolic cofactor in eukaryotic cells that plays a critical role in electron transfer, cellular metabolism, and energy homeostasis, relies in mammals on the salvage of nicotinamide (NAM) by the enzyme nicotinamide phosphoribosyltransferase (NAMPT). NAD is catabolized to NAM by PARPs, sirtuins, and CD38; systems that are upregulated to counteract DNA damage and cellular stress with aging. A decline in the NAD pool plays a crucial role in the aging brain, by increasing mitochondrial dysfunction and various age-related pathologies including enhanced oxidative stress, inflammation and impaired insulin sensitivity. We have discovered a unique NAMPT allosteric site, supported by co-crystal structures of NAMPT positive allosteric modulators (N-PAMs), and plan to optimize these as chemical probes. We hypothesize a N-PAM that selectively activates NAMPT in the brain, increasing NAM turnover and attenuating ATP consumption, will ameliorate the age-related loss of NAD that combines with AD pathology in the pathogenesis ADRD.
In Aim 1 we will optimize N-PAM using our HTS coupled-enzyme assay and supporting biochemical assays, with a focus on properties driving brain bioavailability. Three hit series have been identified with nanomolar potency and affinity and 1.3-1.5A co-crystal structures obtained.
In Aim 2 we will use cell-based phenotypic and target engagement assays to test NMN and NAD levels, mitochondrial rescue, and neuroprotection. NAD dietary supplementation (NMN, NR, NAD) has been studied in models of familial AD (FAD)-Tg and Type 2 diabetes (T2D), including the T2D model of mice on high fat diet (HFD). This HFD/T2D model is the simplest route to determine PK/PD relationships for N-PAMs. Therefore, in Aim 3 we will measure NAD metabolome, insulin sensitivity, and glucose metabolism in HFD mice to derive an efficacious oral dose from PK/PD for an optimized brain bioavailable N-PAM. The effect on behavior, AD pathology, and biomarkers will be studied in male vs. female FAD-Tg mice carrying human APOE3/APOE4. The N-PAM chemical probe will be suitable for future studies to determine: effects in aged animals (alone and in combination with e.g. NAM and NMNAT upregulation); and detailed effects on cellular processes such mitophagy and misfolded protein clearance. N-PAM probes are leads for therapeutic agent development for ADRD and T2D. The team includes experts in drug discovery, ADRD, and T2D.
