Acute phorbol ester treatment inhibits thapsigargin-induced cell death in porcine aortic smooth muscle cells

Baicalein Decreases Hydrogen Peroxide-Induced Damage to NG108-15 Cells via Upregulation of Nrf2

Baicalein is a flavonoid inhibitor of 12-lipoxygenase. Here, we investigated its effect on hydrogen peroxide-induced damage to NG108-15 cells. Hydrogen peroxide activated the mitochondrial apoptotic pathway, decreased Nrf2 expression, increased reactive oxygen species (ROS) levels, reduced viability, and increased cell death after 2-24 h treatment of NG108-15 cells. Co-treatment with hydrogen peroxide and baicalein completely suppressed the activation of mitochondrial apoptotic pathway by upregulating Nrf2 expression and reducing ROS stress and partially inhibited the effects on cell viability and cell death. Silencing of 12-lipoxygenase had a similar protective effect to baicalein on hydrogen peroxide-induced damage by blocking the hydrogen peroxide-induced decrease in Nrf2 expression and increase in ROS levels. Neither protective effect was altered by addition of 12-hydroxyeicosatetraenoic acid, the product of 12-lipoxygenase, suggesting that hydrogen peroxide induced damage via 12-lipoxygenase by another, as yet unknown, mechanism, rather than activating it. Co-treatment of cells with hydrogen peroxide and N-acetylcysteine or the Nrf2 inducer sulforaphane reduced hydrogen peroxide-induced damage in a similar fashion to baicalein, while the Nrf2 inhibitor retinoic acid blocked the protective effect of baicalein. Silencing Nrf2 also inhibited the protective effects of baicalein, sulforaphane, and N-acetylcysteine and resulted in high ROS levels, suggesting ROS elimination was mediated by Nrf2. Taken together our results suggest that baicalein protects cells from hydrogen peroxide-induced activation of the mitochondrial apoptotic pathway by upregulating Nrf2 and inhibiting 12-lipoxygenase to block the increase in ROS levels. Hydrogen peroxide also activates a second mitochondrial dysfunction independent death pathway which is resistant to baicalein.

Dual effect of capsaicin on cell death in human osteosarcoma G292 cells

Thirty percent of osteosarcoma patients die within 5 years. New agents that induce apoptosis of osteosarcoma cells might be therapeutically useful. Here, we characterized the apoptotic mechanism induced by capsaicin in G292 osteosarcoma cells. Our results show that capsaicin induces an increase in the cytosolic Ca(2+) concentration which is independent of the extracellular Ca(2+) concentration and depletes intracellular Ca(2+) stores, suggesting the presence of endoplasmic reticulum transient receptor potential vanilloid receptor type 1. Capsaicin also activates the mitochondrial caspase 3-dependent death cascade. Rapamycin, an inhibitor of mammalian target of rapamycin, evokes autophagy, as do capsaicin or thapsigargin, a sarco(endo)plasmic reticulum Ca(2+) ATPase inhibitor that causes Ca(2+) store depletion. Capsaicin-induced cell death is completely inhibited by co-treatment with the pan-caspase inhibitor Z-VAD-fmk and increased by the autophagy inhibitor 3-methyladenine, suggesting the existence of an autophagy-dependent anti-apoptotic mechanism. Capsaicin also induces ERK phosphorylation, which acts as a downstream effector of autophagy. 3-Methyladenine or PD98059, an ERK kinase inhibitor, restores capsaicin-induced cell death in the presence of Z-VAD-fmk, suggesting that inhibition of autophagy activates a second cell death pathway that is caspase-independent. Taken together, our data show that capsaicin causes Ca(2+) depletion of intracellular Ca(2+) stores and simultaneously activates the mitochondrial caspase-dependent death cascade and autophagy-dependent ERK activation and that the latter counteracts a second death signaling pathway that is caspase-independent.