cytochrome-c-t and pinocembrin

Topics: Cell Line, Tumor; Cell Survival; Cytochromes c; Down-Regulation; Flavanones; Humans; MAP Kinase Signaling System; Membrane Potential, Mitochondrial; Mitochondria; Neuroblastoma; Neurons; Neuroprotective Agents; NF-E2-Related Factor 2; Paraquat

Amyloid beta peptide (Aβ) can cause neurotoxicity in Alzheimer's disease (AD). It evokes a cascade of oxidative damage to neurons. Pinocembrin (PCB), the most abundant flavonoid in propolis, has been proven to have neuroprotective effects in vivo and in vitro. In the present study, we investigated the neuroprotective effects of PCB on Aβ25-35-induced neurotoxicity. Exposure of SH-SY5Y cells to 25μM Aβ25-35 for 24h caused viability loss, apoptotic increase and reactive oxygen species (ROS) increase, pre-treatment with PCB for 4h significantly reduced the viability loss, apoptotic rate and attenuated Aβ-mediated ROS production. PCB strikingly inhibited Aβ25-35-induced mitochondrial dysfunctions, including lowered membrane potential, decreased Bcl-2/Bax ratio. In addition, PCB suppressed the release of cytochrome c and the cleavage of caspase-3. PCB treatment also resulted in an increase in Nrf2 protein levels and subsequent induction of heme oxygenase-1(HO-1) expression in SH-SY5Y cells. RNA interference-mediated knockdown of Nrf2 expression suppressed the PCB-induced HO-1 expression. Notably, we found that the HO-1 inhibitor zinc protoporphyrin IX (ZnPP) markedly diminished the neuroprotective effect of PCB against Aβ-mediated neurotoxicity. Taken together, these results indicated that PCB protects SH-SY5Y cells from Aβ25-35-induced neurotoxicity through activation of Nrf2/HO-1 pathways. Thus, activation of Nrf2/HO-1 pathways and inhibition of mitochondria-dependent apoptosis together may protect cells from Aβ25-35-induceded neurotoxicity.

Topics: Amyloid beta-Peptides; Apoptosis; Cell Line, Tumor; Cytochromes c; Dose-Response Relationship, Drug; Flavanones; Gene Expression Regulation, Neoplastic; Heme Oxygenase-1; Humans; Membrane Potential, Mitochondrial; Neuroblastoma; Neuroprotective Agents; NF-E2-Related Factor 2; Peptide Fragments; Reactive Oxygen Species; RNA, Small Interfering; Signal Transduction; Time Factors; Transfection

Bioflavanoids are the major pigments in plants with multitude of biological activities including inhibition of proliferation or induction of apoptosis in tumor cells. Even though the safety records of most flavanoids are exceptional, its therapeutic use is still in its infancy. We have isolated pinocembrin (5,7-dihydroxyflavanone) from Alpinia galanga that showed cytotoxicity against a variety of cancer cells including normal lung fibroblasts with relative nontoxicity to human umbilical cord endothelial cells. The compound induced loss of mitochondrial membrane potential with subsequent release of cytochrome c and processing of caspase-9 and -3 in colon cancer cell line HCT 116. Processing of caspase-8 was minimal. The initial trigger for mitochondrial apoptosis appears to be by the translocation of cytosolic Bax protein to mitochondria. Overexpression of proapoptotic Bax protein sensitized the colon cancer cells to pinocembrin-induced apoptosis and Bax knockout cells were resistant to pinocembrin-induced apoptosis. Antiapoptotic protein Bcl-X(L) only partially prevented apoptosis induced by this compound. The Bax-dependent cell death involving classical cytochrome c release and processing of caspase-9 and -3 suggests that pinocembrin is a classical mitochondrial apoptosis inducer. But the failure of Bcl-X(L) overexpression to completely prevent apoptosis induced by this compound suggests that pinocembrin is capable of triggering mitochondrial-independent cell death that needs to be clarified. The existence of cell death upon Bcl-X(L) overexpression is a promising feature of this compound that can be exploited against drug resistant forms of cancer cells either alone or in combination with other drugs.

Topics: Alpinia; Apoptosis; bcl-2-Associated X Protein; bcl-X Protein; Blotting, Western; Breast Neoplasms; Caspase Inhibitors; Caspases; Chromatin; Colonic Neoplasms; Cytochromes c; Endothelial Cells; Fibroblasts; Flavanones; Fluorescent Antibody Technique; HCT116 Cells; Humans; Lung; Membrane Potential, Mitochondrial; Mitochondria; Proto-Oncogene Proteins c-bcl-2; Transfection; Umbilical Cord