Aging Projects

Alzheimer’s disease and related dementia (ADRD) constitutes a present and growing health crisis in the aging population. Equally, chronic metabolic diseases such as type 2 diabetes (T2D) are increasing, because of the prevalence of obesity and other risk factors. T2D is itself a significant risk factor and comorbidity with ADRD. Specifically, impaired insulin signaling and glucose metabolism, inflammation, dyslipidemia, and impaired cholesterol mobilization are common underlying pathogenic promoters of dementia in T2D and ADRD. ADRD is characterized by hallmark AD pathology (tau and Aβ), with additional neuropathology, and an underlying dependence on neural resilience. The APOE4 allele is the greatest genetic risk factor for AD. Illustrating the important, functional role of APOE, a rare mutation in APOE3 (the Christchurch mutation) was observed remarkably to protect against cognitive deficits in early-onset, familial AD (FAD) in families in which cognitive loss is normally inevitable. ApoE4 is poorly lipidated and lipidation of the apoE protein, required for stability and positive function, is controlled by the ATP-binding cassette transporter ABCA1. Deletion of ABCA1 in FAD mouse models exacerbates pathology and behavioral deficits; and rare human loss-of-function mutations in ABCA1 increase ADRD risk.

APOE and ABCA1 are gene products of the liver-X-receptor (LXR), prompting a strong research effort from Big Pharma to generate LXR agonists that were validated in FAD mouse and primate AD models. However, LXRα activation causes unwanted side effects in the liver, inducing the lipogenic genes SREBP1c, FAS, and SCD1 leading to elevated triglycerides and steatohepatitis in animal. Unfortunately, even highly selective LXRβ agonists that boost APOE and ABCA1 were perceived to have risk, stalling development. We have validated an alternative phenotypic approach to develop nonlipogenic ABCA1 inducers (NLAIs), by screening for compounds that increase ABCA1 in CCF astrocytoma cells with neutral effects on SREBP1c in HepG2 hepatocarcinoma cells. Two hits, shown to have LXRβ agonist activity, were active delivered orally in multiple mouse models, including mice on high-fat diet (HFD), an obesogenic model of T2D, in which LXR agonists exacerbate lipogenesis: treatment boosted ABCA1/APOE and attenuated inflammation without lipogenesis, prompting optimization of one hit using our primary assays and robust orthogonal/secondary assays to give early lead, CL2-57. In a more detailed HFD mouse study, CL2-57 restored insulin signaling and corrected perturbations across the metabolome. Target deconvolution, showed CL2-57 to be a nonlipogenic full agonist at LXRβ and a weak antagonist at other nuclear receptors, notably blocking upregulation of FAS, and SCD1 and lowering triglycerides. We believe these exciting preliminary data validate our phenotypic drug discovery platform for ADRD and T2D; with our focus on hit-to-lead optimization to enhance CNS bioavailability for treatment of ADRD.

The NIH/NIA Interventions Testing Program reported that mean or maximum lifespan in mice is significantly increased by interventions, including NAD-enhancing drugs. Demonstrated protective actions that combat the aging phenotype include reductions in inflammation, oxidative stress, and metabolic dysfunction, and improving mitochondrial function and autophagy. We hypothesize that the cellular imbalance in NAD+ supply and demand underlies the loss of cognitive resilience that leads to ADRD. Nicotinamide adenine dinucleotide (NAD+) levels and NAD+/NADH ratio decline in the aging brain. Dietary supplementation with NAD+-enhancing drugs (vitamin B3 complex, NMN, NR, NAM, NAD+) has been proposed to enhance lifespan and/or healthspan and reduce diabetes, obesity, and dyslipidemia: all risk factors for cognitive dysfunction and dementia. Miraculous effects were reported with supplementation of NMN. Production of NMN from NAM is catalyzed by the actions of the enzyme nicotinamide phosphoribosyltransferase (NAMPT). NMN is subsequently converted to NAD. Generally, clinical trials on NAD dietary supplements are inconclusive, and ingredients are not standardized. We are designing and developing NAD-enhancing drugs that activate NAMPT, the rate-limiting enzyme in biosynthesis of NAD+, using a unique strategy targeting an allosteric site on NAMPT. These NAMPT positive allosteric modulators (N-PAMs) have the potential to improve cognitive resilience and increase healthspan; and therefore will be of use beyond ADRD, including in age-related metabolic disorders, such as T2D.

The roundworm, C. elegans, is a useful organism for modeling the human nervous system, having a short lifespan. The worms’ transparency allowing visualization of cellular processes. Approximately 85% of the worm proteome has human homologous genes. Genetic manipulation of orthologues in the worm of human genes provides a highly tractable approach to target identification, validation and an invaluable tool in drug discovery. The NAMPT pathway itself, is not present in C. elegans; however, other pathways of NAD synthesis are present providing a parallel approach to NAD regulation using small molecules. This collaboration with the research group of George Sutphin is in its early stages; however, we have much experience with other worms.

NO, just a simple nitrogen connected to oxygen. In 1997, Thatcher founded a start-up with pharmacologists at Queen’s University in Canada, initially focused on small molecules that utilized the benefits of NO initially in neuroprotective therapeutics for ischemic stroke. This company succeeded in completing Phase 1A clinical trials in Alzheimer’s disease (AD) for a small molecule “nomethiazole” (NMZ). This project derived from a long-standing interest in understanding the biological chemistry of nitric oxide as a basis for delivering NO in various disease states. The aim of restoring NO/cGMP/CREB signaling in the AD brain, a concept originally conceived by us, using organic nitrates, is now widely accepted.

We have published extensively in NO chemical biology and drug discovery. This is an area of research with high complexity in chemical reactions and poor precision in accurate measurement of the chemical species produced in these reactions. The bias for ignoring chemistry in biomedical research, combined with the lack of reproducible, precision methods for measurement of chemical species in biological samples has significantly hindered progress in realizing the beneficial effects of NO in multiple disease states. We have recently observed that control of NO/cGMP signaling may be crucial to the chronification of pain (hyperalgesia and allodynia) in migraine and also to the related hyperalgesia that is a key component of withdrawal from opioid addiction, which severely limits the effectiveness of rehabilitation from drug addiction.

We are currently targeting an epitope of tau protein that is linked to pathogenesis of AD and other tauopathies, such as frontotemporal lobe dementia. Tau forms neurofibrial tangles that are one of the two hallmark pathologies of AD. However, this approach to tau is not directed at the conventional strategy to clear tau aggregates, or even to induce tau protein degradation. A function of tau in normal physiology is regulation of axonal transport, a process by which “cargo” is transported along axons and neurites: this cargo includes proteins and even mitochondria, lipids, and synaptic vesicles and is essential for neuronal plasticity and function. The tau epitope is the phosphatase activating domain (PAD), which we are targeting in collaboration with Scott Brady at UIC.

In general, our AD research is not focused on conventional AD pathology, since postmortem brains show individuals with severe pathology that do not have cognitive deficits at time of death. The concept of weakened neural reserve or cognitive resilience being necessary for an individual to decline to dementia, independent of pathology, has been proposed by collaborators10. Elevated basal oxidative stress with aging is widely believed to contribute to loss of resilience and there exist multiple stress-response pathways that may not respond normally with aging, including the master regulator Nrf2 “antioxidant response”. Nrf2 activation is a widely explored strategy for chemoprevention of carcinogenesis, wound-healing, and even neuroprotection.