Effect of Tacrine-3-caffeic Acid, A Novel Multifunctional Anti-Alzheimer's Dimer, Against Oxidative-Stress-Induced Cell Death in HT22 Hippocampal Neurons: Involvement of Nrf2/HO-1 Pathway

Aims: Oxidative stress (OS) plays an important role in the pathogenesis of neurodegenerative diseases, including Alzheimer's disease (AD). This study was designed to uncover the cellular and biochemical mechanisms underlying the neuroprotective effects of tacrine3-caffeic acid (T3CA), a novel promising multifunctional anti-Alzheimer's dimer, against OS-induced neuronal death. Methods and Results: T3CA protected HT22 cells against high-concentration-glutamate-induced cell death in time-and concentration-dependent manners and potently attenuated glutamate-induced intracellular reactive oxygen species (ROS) production as well as mitochondrial membrane-potential (Delta Psi) disruption. Besides, T3CA significantly induced nuclear factor erythroid 2-related factor 2 (Nrf2) nuclear translocation and increased its transcriptional activity, which were demonstrated by Western blotting, immunofluorescence, and antioxidant response element (ARE)-luciferase reporter gene assay. Further studies showed that T3CA potently up-regulated heme oxygenase-1 (HO-1), an endogenous antioxidative enzyme and a downstream effector of Nrf2, at both mRNA and protein levels. The neuroprotective effects of T3CA were partially reversed by brusatol, which reduced protein level of Nrf2, or by inhibiting HO-1 with siRNA or ZnPP-IX, a specific inhibitor of HO-1. Conclusions: Taken together, these results clearly demonstrate that T3CA protects neurons against OS-induced cell death partially through Nrf2/ARE/HO-1 signaling pathway, which further supports that T3CA might be a promising novel therapeutic agent for OS-associated diseases.