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Purpose: In this study, we evaluated Sideritis stricta (S. stricta), as potential-oxidative agents against parental and epirubicin-HCl resistant H1299 cells. Material and Methods: Oxidative stress biomarkers such as malondialdehyde level determined in cell lysates. Assessment of cell viability was made by CellTiter-Blue® Cell Viability Assay and 3-(4,5-dimethyl-2-thiazolyl)-2,5- diphenyl-2H-tetrazoliumbromide (MTT) assay after 20-600 µg/mL essential oil concentrations treated to parental and epirubicin-HCl (drug) resistant H1299 cells for 24, 48 and 72 h. Malondialdehyde levels were assayed for determining the membrane damaging effects. Results: Parental H1299 cells were found to be more sensitive to cytotoxic effect of the essential oil. Essential oil showed cytotoxic and more selective effects depend on time and concentration. Essential oil caused increasing malondialdehyde level on both parental and drug resistant H1299 cells. The highest concentration of the essential oil (IC70) treatment caused the highest membrane damage on both parental and drug resistant H1299 cells. Conclusions: Parental and epirubicin-HCl resistant H1299 cells showed different cellular response against potential antitumour and pro-oxidative effects of essential oil. [ABSTRACT FROM AUTHOR]

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 (