A comparative evaluation of antioxidant and anticancer activity of essential oil from Origanum onites (Lamiaceae) and its two major phenolic components

The objectives of the present study were to determine the effects of essential oil from Turkish oregano (Origanum onites L.) and its 2 major phenolic components, carvacrol and thymol, on cell viability, and to investigate their cytoprotective (antioxidant) effects against hydrogen peroxide-induced cytotoxicity and membrane damage in hepatoma G2 (Hep G2) cells. Their antioxidant properties were also evaluated with 2 in vitro complementary test systems: DPPH radical scavenging activity and linoleic acid oxidation inhibition. The aerial parts of the essential oil were isolated using a Clevenger-type apparatus (hydrodistillation) and its components were analyzed by gas chromatography/mass spectrometry (GC/MS). The essential oil of O. onites decreased cancer cell viability at higher concentrations. The essential oil was found to be less cytototoxic (IC50: 149.12 μg/mL) than carvacrol and thymol (IC50: 53.09 and 60.01 μg/mL, respectively) for Hep G2 cells. On the other hand, with the O. onites essential oil, carvacrol and thymol protected the cells against H2O2-induced cytotoxicity when the cells were preincubated with the oil and its components at a lower concentration ( IC50) before H2O2 incubation. The malondialdehyde (MDA) level increased in H2O2-exposed cells (IC50 and IC70), but decreased in cells preincubated with the essential oil and its components before H2O2 exposure. The essential oil showed a higher membrane-protective effect than thymol and carvacrol. The 3 major constituents of the essential oil were linalool (50.53%), carvacrol (24.52%), and thymol (15.66%), respectively. The DPPH radical scavenging activity (EC50: 80 μg/mL) of the essential oil was found to be higher than that of carvacrol and thymol. The linoleic acid oxidation inhibition rate of the essential oil (40%) was close to that of its 2 major components. Th ese findings suggest that the essential oil from O. onites and its 2 major components exhibit antioxidant activity and carcinogenesis-reducing potential.