Aquilariae Lignum extract attenuates glutamate-induced neuroexcitotoxicity in HT22 hippocampal cells

An imbalance between excitatory and inhibitory neurotransmitters is known to induce neuronal excitotoxicity which is a major cause of neurodegenerative disorders. Excessive glutamate concentration leads to the neuronal death by increasing oxidative stress and affecting the apoptotic signaling pathway. We investigated the anti-excitotoxic effects and associated working mechanisms of 30% ethanol extract of Aquilariae Lignum (ALE) against hippocampal neuronal death by glutamate. HT22 cells were treated with glutamate (20 mM) for 24 h following pretreatment with ALE (5, 10, 25 μg/mL). Cell viability, biochemical analysis, flow chemistry, and Western blotting assays were performed. Glutamate treatment substantially increased the intracellular level of reactive oxygen species (ROS) and Ca²⁺ influx into the cell, which were followed by apoptosis. ALE pretreatment, however, significantly attenuated these excitotoxicity-related features according to the results of Annexin V analysis and the lactate dehydrogenase assay, in which the calpain pathway (in a caspase 3-independent manner) may be involved. ALE pretreatment also significantly attenuated the glutamate-induced activation of both inflammation-associated molecules (extracellular signal-regulated kinase, c-Jun N-terminal kinases and p38) and death-related molecules (p53, apoptosis-inducing factor). The inactivation of brain-derived neurotrophic factor (BDNF) was restored by ALE pretreatment. Our results verified that A. Lignum has potential neuroprotective effects on glutamate-induced excitotoxicity in hippocampal neuron cells, and its underlying mechanism may involve the regulation of ROS-mediated cell death pathways.