Apoptosis induced by hydrogen peroxide (H2O2) was investigated in Chinese hamsterovarian (CHO) cells, and compared to apoptosis induced by cisplatin (25 µM), a well-established apoptosis-inducing agent. | Turk J Biol 24 (2000) 685–696 © TÜBİTAK Prevention of Hydrogen Peroxide and Cisplatin Induced Apoptosis by Intracellular Catalase Overexpression H. Barbaros ORAL Department of Microbiology and Infectious Diseases, Immunology Unit, Uludağ University, School of Medicine, Bursa-TURKEY Adrew . GEORGE Department of Immunology, Division of Medicine, Imperial College School of Medicine, Hammersmith Hospital, London-ENGLAND Dorian O. HASKARD Department of Cardiovascular Medicine, National Heart and Lung Institute, Imperial College School of Medicine, Hammersmith Hospital, London-ENGLAND Received: Abstract: Apoptosis induced by hydrogen peroxide (H2O2) was investigated in Chinese hamster ovarian (CHO) cells, and compared to apoptosis induced by cisplatin (25 µM), a well-established apoptosis-inducing agent. In preliminary experiments, CHO cells were treated with low concentrations of H2O2 (250-500 µM) continuously or for 3 hours, followed by washing and further incubation in complete growth medium for 1-10 days. Fluorescence microscopy of acridine orange-stained cells indicated morphological changes of apoptosis. Similar changes were observed in cisplatin-treated cells. DNA-laddering also revealed that DNA fragmentation occurred in both adherent and non-adherent cells by day 2. To prevent H2O2-mediated apoptosis, the catalase gene was isolated, subcloned into a mammalian expression vector (pCDM8) and transfected into CHO cells. Transiently transfected cells contained approximately 8-fold increased catalase levels. Overexpression of intracellular catalase provided protection for the CHO cells from H2O2 as measured by a tetrazolium-formazan reduction assay. Furthermore, cisplatin-mediated apoptosis was prevented by intracellular catalase overexpression, indicating that this cytotoxic drug acts at least in part through an H2O2-dependent pathway. Key Words: Apoptosis, catalase, cisplatin, hydrogen peroxide, transfection. Hücreiçi Katalaz’ın Arttırılması ile .