Thyme essential oil inhibits proliferation of DLD-1 colorectal cancer cells through antioxidant effect

Aim. It is a very hot topic to investigate the effects and the mechanisms of action of biological active extracts such as thyme essential oil on various cancer cells. This paper examines the ability of thyme essential oil to inhibit the growth of DLD-1 colorectal cancer cells and if it is the case, determine the contribution of antioxidant effect to this ability. Methods. To do this, we treated human DLD-1 colorectal cancer cells with thyme essential oil and assessed its effects on cell proliferation by using real time cell analyzing system (Xcelligence System). Furthermore, we applied the same concentrations to the L929 fibroblast cells in order to determine if thyme essential oil has cytotoxicity on normal cells in the same concentrations it showed anticancer effects. Then, antioxidant ability of thyme essential oil was evaluated by using DPPH assay. Results. Thyme essential oil treated DLD-1 cells exhibited decreasing cell index values in a concentration-dependent manner. An inhibitor concentration 50 (IC50) value of 0.347 mg/mL was achieved. On the other hand, when thyme essential oil was tested on L929 fibroblast cells, it was observed that thyme essential oil did not show cytotoxic effect on L929 fibroblast cells. IC50 value was 22 mg/mL for this experiment. Besides, thyme essential oil showed a strong antioxidant effect on DPPH assay. Conclusion. When the antiproliferative and the antioxidant effects of thyme essential oil are considered, it can be concluded that thyme essential oil may be an alternative option in the treatment of colorectal cancer.