Triggering of apoptosis and cell cycle arrest by fennel and clove oils in Caco-2 cells: the role of combination

Background: Fennel (Foeniculum vulgare) and clove (Syzygium aromaticum) oils are known for their various biological effects, including anticancer properties. Objective: To investigate the anticancer effect of combined fennel and clove oil treatment on Caco-2 cells and normal human lymphocytes (NHL). Methods: GC-MS, in vitro cytotoxicity, morphological, apoptosis-related marker, and flow cytometric cell cycle distribution analyses were conducted. Results: Seventeen volatile compounds were identified in fennel oil, including trans-anethole (68.3%) and (+)-fenchone (8.1%). In clove oil, 22 compounds, including eugenol (71.4%) and caryophyllene (8.7%), were identified. IC50 of the fennel, clove, and oil mixture were 300 +/- 5.0, 150 +/- 4.0, and 73 +/- 2.5 mu g/mL, respectively with combination index (CI) < 1.0. Mechanistic anticancer properties were investigated using 30, 45, and 60 mu g/mL oil mixture. Analysis of apoptotic morphology, flow cytometric cell cycle distribution, and apoptosis-related markers, such as Bcl-2 and Ki-67, confirmed cell cycle arrest and apoptosis induction in Caco-2 cells by the fennel and clove oil combination. Moreover, the oil mixture did not exert significant (p < 0.01) toxicity on NHL in vitro. Conclusion: The oil mixture exerted selective cytotoxicity towards Caco-2 cells through cell cycle arrest and apoptosis, which may occur through synergistic effects between fennel and clove oil active ingredients.