A Highly Potent Apomorphine Derivative Enhancing Neurite Outgrowth via Nrf2 Activation

Apomorphine (APO), a dopamine agonist, activates nuclear factor erythroid 2-related factor 2 (Nrf2) and exerts antioxidant effects, making it a promising candidate for neuroprotection against oxidative stress. This study evaluated neuroplasticity-enhancing properties of newly synthesized APO derivatives, focusing on their ability to promote neurite outgrowth in PC12 cells under nerve growth factor (NGF) stimulation. D55, an APO derivative, retains the hydroxyl group at APO's 11th position while substituting the 10th with an ethoxy group. D55 exhibited the highest potency (EC₅₀ = 0.5661 nM), significantly enhancing neurite outgrowth. APO demonstrated the highest efficacy (Emax ~10-fold increase), while edaravone (Eda) required higher concentrations (EC₅₀ = 22.5 nM) for moderate effects (Emax ~4-fold increase). D30, in which the 11th hydroxyl was replaced with a methoxy group, had no effect. Neurite outgrowth-promoting effects of APO, D55, and Eda were significantly attenuated by Nrf2 siRNA knockdown, confirming that their neuroplasticity effects are Nrf2-mediated. These findings confirm that D55 is a highly potent Nrf2-activating compound with strong neuroprotective potential, providing new insights into its therapeutic applications for neurodegenerative diseases associated with oxidative stress.