Sirtuin-NAD Activator in Alzheimer's Disease

The sirtuin family of nicotinamide adenine dinucleotide (NAD)-dependent deacetylase enzymes are important regulators of the aging process and mediate many of the beneficial effects of caloric restriction. The upregulation of the sirtuin-NAD pathway by increasing intracellular NAD through administration of NAD precursors, such as niacinamide β nicotinamide mononucleotide (βNMN) and nicotinamide riboside, has been shown to engage fundamental mechanisms of aging and prevent or attenuate Alzheimer's disease (AD) pathology in preclinical models. In contrast to many AD drugs in development that target one mechanism, NAD precursors may prevent AD pathology by multiple mechanisms: by improving mitochondrial energetics; inducing a switch to non-amyloidogenic processing of amyloid precursor protein (APP) due to increased α-secretase activity; reducing the synthesis of oligomerized Aβ peptides; preventing microglia-dependent Aβ toxicity; attenuating neuroinflammation; promoting neuronal regeneration; and improving insulin action.

In spite of the promising preclinical data, the human studies of the clinical pharmacology, physiologic effects, efficacy, and safety of NAD precursors have been few and constrained by several methodological barriers. First, βNMN and nicotinamide riboside (NR) are sold as dietary supplements and these over-the-counter products have suffered from variable manufacturing quality. Second, there is only limited information available on the pharmacokinetics (PK) and pharmacodynamics (PD) of βNMN and NR in humans, and the doses used in some initial studies were low. Third, NAD and many other metabolites of βNMN and NR are labile and susceptible to rapid degradation ex vivo. Furthermore, the assays for the measurement of intracellular NAD, βNMN, and its metabolites have been challenging. Although NR and βNMN have been shown to cross the blood-brain barrier, attenuate AD pathology, and improve cognitive function in preclinical models, no clinical trials have been conducted to determine whether βNMN crosses the blood-brain barrier or engages the target mechanisms in humans.

To overcome these methodological barriers, we have characterized the pharmacokinetics of MIB-626 in phase 1 studies, validated the methods for measuring intracellular NAD, and established the procedures for blood collection to ensure pre-analytical stability. These phase 1 studies have shown that a regimen of 1 g MIB-626 twice daily is safe and effective in substantially raising circulating NAD levels in healthy adults (preliminary data). These foundational methods and single and multiple-dose pharmacokinetic studies have paved the way for the proposed 90-day randomized trial in 24 mild AD dementia participants to determine whether MIB-626 crosses the blood-brain barrier, engages the hypothesized target mechanism, and whether it improves the biomarkers of aging. We hypothesize that MIB-626 administration at the proposed dose will cross the blood-brain barrier and be associated with an increase in brain NAD. Because of the important role of the sirtuin-NAD pathway in regulation of the mechanisms of aging, we will also assess whether MIB-626 is more efficacious than placebo in improving biomarkers of aging in participants with mild AD dementia.