Antioxidant, antiproliferative, and apoptotic activity of thymoquinone against benzo(a)pyrene-induced experimental lung cancer

Several studies have suggested that increased consumption of phytochemicals is a comparatively easy and practical strategy to significantly decrease the incidence of cancer. In the present study, we have reported the protective effect of a natural compound, thymoquinone (TQ) against benzo(a)pyrene (B(a)P)-induced lung carcinogenesis in Swiss albino mice. B(a)P (50 mg/kg body weight) was administered twice weekly for four successive weeks and left until 20 weeks to induce lung cancer in mice. TQ (20 mg/kg body weight) was given orally as a pretreatment and posttreatment drug to determine its chemopreventive and therapeutic effects. B(a)P-induced lung cancer-bearing animals displayed cachexia-like symptoms along with an abnormal increase in lung weight and the activities of marker enzymes adenosine deaminase, aryl hydrocarbon hydroxylase, gamma-glutamyl transpeptidase, 5 '-nucleotidase and lactate dehydrogenase; tumor marker carcinoembryonic antigen levels. Furthermore, B(a)P-induced animals showed elevated levels of lipid peroxides with subsequent depletion in the antioxidant status and histological aberrations. These anomalies were accompanied by increased expressions of proliferating cell nuclear antigen and cyclin D1 in the lung sections derived from B(a)P-induced animals. On TQ treatment, all the above alterations were returned to near normalcy. Furthermore, TQ administration in B(a)P-induced animals downregulated phosphatidylinositol 3-kinase/protein kinase B signaling pathway and induced apoptosis as evidenced by a decrease in cytochrome c, proapoptotic Bax, caspase-3, and p53 with a parallel increase in antiapoptotic Bcl-2. Our present results demonstrate the potential effectiveness of TQ as an antioxidant, antiproliferative, and apoptotic agent against B(a)P-induced experimental lung tumorigenesis.