Inhibitory Effect of Flavonoid Luteolin on 6-Hydroxydopamine Cytotoxicity via Suppression of Apoptosis-Related Protein Activation

BACKGROUND: Flavonoid luteolin has been shown to exhibit cell protective effect. However, it is still uncertain whether the effect of luteolin on cellular toxicity of the parkinsonian toxin 6-hydroxydopamine is mediated by apoptosis-related protein activation. METHODS: In differentiated PC12 cells exposed to 6-hydroxydopamine in combination with luteolin, we observed the apoptosis-related protein activation, nuclear damage, formation of reactive oxygen species and cell death. RESULTS: 6-Hydroxydopamine caused apoptosis by inducing a decrease in Bid, Bcl-2, Bcl-xL and survivin levels, increase in Bax levels, cytochrome c release and activation of caspases. Treatment with luteolin reduced changes in the apoptosis-related protein levels, formation of reactive oxygen species, nuclear damage and cell death. CONCLUSIONS: Luteolin may reduce the 6-hydroxydopamine-induced apoptosis in differentiated PC12 cells by suppressing the activation of the caspase-8- and Bid-dependent pathways and the mitochondria-mediated apoptotic pathway, leading to caspase activation. The preventive effect of luteolin may be associated with its inhibitory effect on the production of reactive oxygen species. Luteolin may attenuate the oxidative stress and mitochondrial dysfunction-induced neuronal cell death take place in Parkinson's disease.

Effect of Extracellular Signal-Regulated Kinase Inhibition on Oxysterol 7-Ketocholesterol-Induced Apoptosis

BACKGROUND: Defects in mitochondrial function have been shown to participate in the induction of neuronal cell injury. The extracellular-signal-regulated kinase (ERK) signaling pathway plays a crucial role in almost all cell functions, including proliferation, differentiation, survival, and death. However, the effect of ERK inhibition on oxysterol-induced apoptosis remains uncertain. METHODS: This study assessed the effect of ERK inhibition on the apoptotic effect of 7-ketocholesterol. RESULTS: Treatment with 7-ketocholesterol increased phosphorylated-ERK1/2 levels in differentiated PC12 cells, while the total amount of ERK was not altered. 7-Ketocholesterol decreased Bid and Bcl-2 levels, increased Bax and p53 levels, and promoted cytochrome c release, which elicits the activation of caspases (-8, -9, and -3), nuclear damage, and cell death. ERK and farnesyltransferase inhibitors inhibited the 7-ketocholesterol-induced phosphorylation of ERK1/2, activation of apoptosis-related proteins, and cell death in PC12 cells. CONCLUSIONS: The ERK and farnesyltransferase inhibitors, which did not exhibit toxicity, may inhibit the 7-ketocholesterol toxicity on differentiated PC12 cells by suppressing the activation of the caspase-8-dependent pathway as well as activation of the mitochondria-mediated cell-death pathway, leading to the activation of caspases. The inhibition of ERK may confer a beneficial protective effect against the neuronal cell injury induced by cholesterol oxidation products.