Neuroprotective effects of α-iso-cubebenol on glutamate-induced neurotoxicity.

α-Iso-cubebenol is a natural compound isolated from Schisandra chinensis, and is reported to have beneficial bioactivity including anti-inflammatory and anti-tumor activities. Glutamate-induced oxidative neuronal damage has been implicated in a variety of neurodegenerative disorders. Here we investigated the mechanisms of α-iso-cubebenol protection of mouse hippocampus-derived neuronal cells (HT22 cells) from apoptotic cell death induced by the major excitatory neurotransmitter, glutamate. Pretreatment with α-iso-cubebenol markedly attenuated glutamate-induced loss of cell viability and release of lactate dehydrogenase), in a dose-dependent manner. α-Iso-cubebenol significantly reduced glutamate-induced intracellular reactive oxygen species and calcium accumulation. Strikingly, α-iso-cubebenol inhibited glutamate-induced mitochondrial depolarization, which releases apoptosis-inducing factor from mitochondria. α-Iso-cubebenol also suppressed glutamate-induced phosphorylation of extracellular-signal-regulated kinases. Furthermore, α-iso-cubebenol induced CREB phosphorylation and Nrf-2 nuclear accumulation and increased the promoter activity of ARE and CREB in HT22 cells. α-Iso-cubebenol also upregulated the expression of phase-II detoxifying/antioxidant enzymes such as HO-1 and NQO1. Subsequent studies revealed that the inhibitory effects of α-iso-cubebenol on glutamate-induced apoptosis were abolished by small interfering RNA-mediated knockdown of CREB and Nrf-2. These findings suggest that α-iso-cubebenol prevents excitotoxin-induced oxidative damage to neurons by inhibiting apoptotic cell death, and might be a potential preventive or therapeutic agent for neurodegenerative disorders.