Regulation of NF-κB Expression by Thymoquinone; A Role in Regulating Pro-Inflammatory Cytokines and Programmed Cell Death in Hepatic Cancer Cells

Background: The miracle herb Nigella sativa (N. sativa) is a member of the Ranunculaceae family that possesses many properties, such as antioxidant, anticancer, analgesic, antibacterial, and anti-inflammatory. Thymoquinone (TQ) is the primary ingredient that makes up N. sativa, which is responsible for its many properties. So, our research focused on the biological role of TQ and its anticancer activities.

Methods: A wide range of TQ concentrations (50µg/µl, 25µg/ µl, and 12.5µg µl) was prepared and evaluated for their potential regulatory role in cell lines of hepatocellular carcinoma (HepG2 cell line) compared with normal hepatocytes cells, untreated and DMSO-treated cells.

Results: The more significant level of LDH obtained after TQ treatment compared to untreated cells provides evidence of the cytotoxic effects of TQ on HepG2 cells. Notably, the normal hepatocyte cells subjected to the same concentrations of TQ showed neglected influence in cell viability rate, indicating the selective regulatory role of TQ in cancer cell proliferation. Interestingly, as a critical mediator of malignancy transformation, the nuclear factor-kappa B expression level (NF-κB) significantly decreased in a time and dose-dependent manner of TQ treatment. Furthermore, we investigated whether TQ regulates the expression of deleted liver cancer 1 (DLC1) and Caspase 3 (Casp3). Notably, the treatment with TQ showed increased expression levels of DLC1 and Casp3 upon treatment. TQ extract sufficiently mediated the secretion of the released pro-inflammatory cytokines from treated cells. This regulation of released cytokines by TQ may affect the activation of NF-κB in treated cells.

Conclusion: These results indicate that TQ mediates the activation of Casp3, DLC1, and NF-κB, providing a new function of TQ in treating hepatocellular carcinoma (HCC).