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Insight into the mechanisms by which apigenin, curcumin and sulfasalazine induce apoptosis in colon cancer cells Moussavi, Maryam

Abstract

Two dietary components, curcumin and apigenin along with an anti-inflammatory drug sulfasalazine (SSZ) effect apoptosis in colon cancer cells. However the exact signalling mechanisms involved in this response remain unknown. We investigated their influence, on the ceramide pathway and their effects upon reactive oxygen species (ROS) generation in colorectal cancer (CRC) cell lines. Initial observations confirmed that each agent dose dependently caused an increase in cell death as indicated by release of cytochrome C, cleavage of pro-caspase 3, PI staining and nuclear condensation, indicative of programmed cell death or apoptosis. Since ceramide generation has been linked with apoptosis and cell death, we investigated its role in CRC cells. Here for the first time we have shown that all three agents were able to increase ceramide levels in a dose and time dependent manner. Interestingly, SSZ accomplished this increase through the de novo pathway, while the other two dietary agents (curcumin and apigenin) elevated ceramide generation independently of the de novo pathway. This data is supported by inhibition of ceramide generation by both Myriocin and Fumonisin B-1 (FB-1), inhibitors of de novo synthesis. However this was not mechanistically linked to cell death. Apigenin, curcumin and sulfasalazine also caused an increase in ROS generation in HCT116 cells. Using a series of ROS inhibitors, the route of ROS generation was established. We postulated that apigenin interacted directly with the mitochondrial electron transport chain in order to generate ROS while the other two agents interacted in a more generalized manner in order to generate ROS. Inhibition of ROS in CRC cells treated with each agent lead to increase in cell survival. This study demonstrates that all three compounds are capable of generating both ROS and ceramide through different mechanisms. Additionally, ROS generation due to treatment with each agent is prominent in mediating apoptosis.

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