We propose a novel target and new drug to treat Alzheimer?s disease (AD) via the Nrf2 transcriptional pathway. Our drug candidates for this target are currently at the stage of active hit-to-lead optimization, as described below. As background, AD is a condition with loss of synapses and neurons in the brain, characterized by the presence of amyloid beta (A?) plaques and tau tangles, which cause damage to synapses and neurons at least partially via oxidative stress. Our prior studies have indicated that carnosic acid (CA), a component compound in the herb Rosemary, can protect neurons and synapses from damage caused by oxidative stress by activating the Nrf2 transcriptional pathway. Our Preliminary Data show that CA treatment ameliorates various behavioral and histological deficits in AD transgenic mutant mice, while showing no significant side effects. Activation of the Keap1/Nrf2 (kelch-like ECH-associated protein 1/nuclear factor erythroid 2-related factor 2) pathway upregulates transcription of phase II antioxidant and anti-inflammatory proteins. We and others have shown that this can be a valuable therapeutic strategy in several neurodegenerative diseases. Here, we further test this approach in mouse models of AD using carnosic acid (CA), which we have shown in our publications to activate the Keap1/Nrf2 pathway. CA is known to be clinically tolerated because of its presence in herbs like Rosemary. Conversely, in humans with AD, a decreased expression pattern of Nrf2 in hippocampal neurons and astrocytes, as well as a significant decrease in nuclear Nrf2 levels in frontal cortex, have been reported. The Keap1/Nrf2 pathway can be activated by an electrophilic compound when it reacts with a specific thiol on Keap1, releasing Nrf2 in the cytoplasm to enter the nucleus where it binds to the antioxidant responsive element (ARE) on the promoters of phase II genes. An important issue clinically with regard to electrophilic drugs (such as dimethyl fumarate, curcumin, and Bardoloxone) is that they not only react with Keap1 to activate Nrf2, but they also non-specifically react with other thiol groups, which may explain both their actions and side effects. Our alternative, innovative strategy to avoid such side effects is to use pro-electrophilic compounds that are activated by the very oxidation in redox-stressed cells that is injurious. The compound CA represents a starting point for such a pro-electrophilic drug (PED). Accordingly, our Specific Aims/Goals are ? Aim/Goal 1. To screen for and characterize the neuroprotective effects of PEDs that activate the Nrf2/ARE transcriptional pathway in an in vitro model of oligomeric A-induced oxidative damage and neuroinflammation using hiPSC-derived cortical neurons and cerebral organoids.
Aim /Goal 2. To determine the lead PED by assessing neuroprotective effects by neurobehavior and histology in vivo in AD transgenic mouse models (hAPP-J20 and 3x Tg mice) and optimize formulation of the lead. Toxicity testing will also be performed.
For over two millennia, Rosemary has been touted as an ?herb of remembrance,? meaning it was good for memory; however, the underlying cellular mechanism and proof for this effect are not clear. Our preliminary results show that the compound Carnosic Acid (CA) in Rosemary is primarily responsible for its beneficial effects in the nervous system, and support the hypothesis that the predominant mechanism of action of CA is activation of the transcription factor Nrf2, which stimulates production of phase II antioxidant and anti- inflammatory enzymes in the brain. Using human iPSC-derived neurons so that we can study the action of CA in a human context, in conjunction in vivo rodent studies, we will determine if improved, more ?druggable? derivatives of CA can prevent neuronal and synaptic damage in Alzheimer?s disease models.
