Cytostatic effects of plant essential oils on human skin and lung cells

Essential oils are volatile compounds extracted from various plants by distillation, hydrodiffusion or compression. In recent years, the use of essential oils has gained popularity. Many pharmaceutical, cosmetic, sanitary, food industry and agriculture studies have revealed that essential oils exert antibacterial, antiviral, antifungal, antiparasitic, insecticidal, anticancer, neuroprotective, psychophysiological and anti-aging effects. Despite their reported uses, recent studies of eukaryotic cells have demonstrated that essential oils exert prooxidant and cytotoxic effects. Therefore, for the effective clinical use of essential oils, an evaluation of their cytotoxicity and the identification of the mechanisms affecting cell viability are required. To evaluate cytotoxicity, the present study determined the IC50 values of 15 essential oils provided by the Korea Forest Research Institute (Pinus densiflora for. multicaulis Uyeki, Trifolium repens, Ligularia fischeri, Abies nephrolepis, Illicium anisatum, Zanthoxylum coreanum, Abies koreana, Lindera obtusiloba, Chamaecyparis obtuse, Pinus densiflora, Magnolia kobus, Picea koraiensis, Picea abies, Abies holophylla and Platycladus orientalis). Their effect was then assessed in human lung cells (A549) and human skin cells (Detroit 551) by performing cell counting kit-8 assays. To identify the mechanism associated with each oil's cytotoxicity, expressions of cytotoxicity-associated marker genes (cyclin A, cyclin B, cyclin D and cyclin E) involved in the cell cycle and caspase-3 (involved in cell death) were examined by performing reverse transcription-quantitative PCR and western blotting. In conclusion, plant essential oils can be used as a good source of medicine. However, without examining the safety of essential oils, they cannot be used in clinics. The results included estimates of the degree of cytotoxicity and the mechanism of cell death for each oil. It is expected that the data obtained from the current study will form guidelines for the clinically appropriate and safe use of these tested essential oils.