Thymoquinone suppression of the human hepatocellular carcinoma cell growth involves inhibition of IL-8 expression, elevated levels of TRAIL receptors, oxidative stress and apoptosis
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Hepatocellular carcinoma (HCC) is the fourth most common solid tumor worldwide. The chemokine interleukin-8 (IL-8) is overexpressed in HCC and is a potential target for therapy. Although the transcription factor NF-κB regulates IL-8 expression, and while thymoquinone (TQ; the most bioactive constituent of black seed oil) inhibits NF-κB activity, the precise mechanisms by which TQ regulates IL-8 and cancer cell growth remain to be clarified. Here, we report that TQ inhibited growth of HCC cells in a dose- and time-dependent manner, caused G2M cell cycle arrest, and stimulated apoptosis. Apoptosis was substantiated by activation of caspase-3 and -9, as well as cleavage of poly(ADP-ribose)polymerase. TQ treatments inhibited expression of NF-κB and suppressed IL-8 and its receptors. TQ treatments caused increased levels of reactive oxygen species (ROS) and mRNAs of oxidative stress-related genes, NQO1 and HO-1. Pretreatment of HepG2 cells with N-acetylcysteine, a scavenger of ROS, prevented TQ-induced cell death. TQ treatment stimulated mRNA expression of pro-apoptotic Bcl-xS and TRAIL death receptors, and inhibited expression of the anti-apoptotic gene Bcl-2. TQ enhanced TRAIL-induced death of HepG2 cells, in part by up-regulating TRAIL death receptors, inhibiting NF-κB and IL-8 and stimulating apoptosis. Altogether, these findings provide insights into the pleiotropic molecular mechanisms of TQ-dependent suppression of HCC cell growth and underscore potential of this compound as anti-HCC drug.
KeywordsThymoquinone HCC IL-8 Oxidative stress NF-κB TRAIL Apoptosis
This work was supported by a grant from King Abdulaziz city for science and technology (KACST; Grant No.: ARP-29-265) and the Department of Veterans Affairs Merit Review grant (AKR).
Conflict of interest
We have no personal or financial conflict of interest and have not entered into any agreement that could interfere with our access to the data on the research, or upon our ability to analyze the data independently, to prepare manuscripts, and to publish them.
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