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    Phenols of virgin olive oil protects nuclear DNA against oxidative damage in HeLa cells
    (Pergamon-Elsevier Science Ltd, 2012) Erol, Ozlem; Arda, Nazli; Erdem, Gunnhan
    Oxidative DNA damage is an inescapable consequence for cells constantly exposed to oxidative stress derived from normal metabolic processes and from environmental factors. Phenolic compounds, which have strong antioxidant activity, prevent DNA damage by protecting the cells against harmful effects of oxidative stress. In this study, the effect of virgin olive oil phenolic extract (OOPE) was investigated on H2O2-induced mitochondrial DNA (mtDNA) and nuclear DNA (nDNA) damage in HeLa cells. DNA damage was assessed in mitochondria and two nuclear regions by using quantitative PCR (QPCR) assay. The cells were pre-treated with non-cytotoxic doses of OOPE for 4 h, and DNA damage was determined. OOPE alone does not change the steady-state level of DNA damage. The oxidative stress generated with 750 mu M H2O2 caused two times greater damages in mtDNA compared to nDNA, which included the nonexpressed beta-globin region (1.507 +/- 0.110 lesions/10 kb) and the expressed APEX1 gene (1.623 +/- 0.243 lesions/10 kb) with respect to the control region. When cells were preincubated with OOPE for 4 h, nDNA damage under stress condition was completely inhibited; however, mtDNA damage was not affected by this procedure. These results suggest that OOPE has a protective effect against nDNA damage in HeLa cells. (C) 2012 Elsevier Ltd. All rights reserved.
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    Protective effects of olive oil phenolics and gallic acid on hydrogen peroxide-induced apoptosis
    (Springer Heidelberg, 2012) Erol-Dayi, Ozlem; Arda, Nazli; Erdem, Gunhan
    Olive oil contains several phenolic compounds possessing antioxidant activity. The aim of this study was to investigate the protective effects of olive oil phenolic extract (OOPE) and one of its constituents, gallic acid (GA) against H2O2-induced oxidative stress and apoptotic cell death in HeLa cells, a model for human epithelial cells. The cells were pretreated with nontoxic doses of OOPE or GA for 4, 24 and 48 h, and the intracellular reactive oxygen species (ROS) level was determined, before and after oxidative stress induction with H2O2. As an indicator of apoptosis, caspase 9 activity was measured. All pretreatments reduced ROS generation. Four hour incubation with OOPE or GA completely inhibited ROS generation. Increases in caspase 9 activity by OOPE and GA pretreatment under harsh stress conditions were inhibited 92 and 67.8%, respectively. These results suggest that OOPE and GA act as powerful antioxidants against oxidative stress and exert anti-apoptotic effects.
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    Viscum album L. Extracts Protects HeLa Cells against Nuclear and Mitochondrial DNA Damage
    (Hindawi Ltd, 2012) Onay-Ucar, Evren; Erol, Ozlem; Kandemir, Basak; Mertoglu, Elif; Karagoz, Ali; Arda, Nazli
    Viscum album L. is a semiparasitic plant grown on trees and widely used for the treatment of many diseases in traditional and complementary therapy. It is well known that some activities of Viscum album extracts are varied depending on the host trees, such as antioxidant, apoptosis-inducing, anticancer activities of the plant. The aim of the present study is to examine the comparative effects of methanolic extracts of V. album grown on three different host trees (locust tree, lime tree, and hedge maple tree) on H2O2-induced DNA damage in HeLa cells. Oxidative damage in mitochondrial DNA and two nuclear regions was assessed by QPCR assay. The cells were pretreated with methanolic extracts (10 mu g/mL) for 48 h, followed by the treatment with 750 mu M H2O2 for 1 hour. DNA damage was significantly induced by H2O2 while it was inhibited by V. album extracts. All extracts completely protected against nuclear DNA damage. While the extract from lime tree or white locust tree entirely inhibited mitochondrial DNA damage, that from hedge maple tree inhibited by only 50%. These results suggest that methanolic extracts of V. album can prevent oxidative DNA damage, and the activity is dependent on the host tree.