Curcumin attenuates peroxynitrite-induced neurotoxicity in spiral ganglion neurons

The present study was designed to investigate the effect of curcumin on peroxynitrite (ONOO−)-induced damage in rat spiral ganglion neurons (SGNs). The primary cultured rat SGNs were exposed to ONOO− with or without curcumin pretreatment. Cell viability was measured by MTT assay. Apoptosis was determined by Ho.33342 and propidium iodide (PI) double staining and flow cytometry. The cellular glutathione (GSH) content, superoxide dismutase (SOD) activity and malonaldehyde (MDA) levels were evaluated by spectrophotometer. The mRNA expressions of Apaf-1, Caspase-9, Caspase-3, Bcl-2, and Bax were examined by RT-PCR, while, the protein expressions of mitochondrial and cytosolic cytochrome c, Caspase-9, Caspase-3, Bcl-2 and Bax proteins were determined by Western blot respectively. The cell viability was markedly reduced, while, the apoptotic rate increased significantly after exposure of ONOO− (100 μM) to SGNs. The activity of SOD and level of GSH were notably reduced, whereas, the MDA level was significantly increased. Pretreatment with curcumin protected SGNs against ONOO−-induced cell damage, declined the apoptotic rate, and improved the levels of SOD and GSH, decreased the elevation of MDA. ONOO− induced cytochrome c release from the mitochondria of SGNs and subsequently activated Caspase-9, Caspase-3 and cell apoptosis. Meanwhile, pretreatment with curcumin abrogated cytochrome c release, blocked activation of Caspase-3, and altered the expression of Bcl-2 family triggered by ONOO−. Our data indicate that curcumin can attenuate ONOO−-induced damage in SGNs by the anti-oxidative activity as well as protect mitochondria from oxidative stress.