The Role of Oxidative Stress in Koenimbine-Induced DNA Damage and Heat Shock Protein Modulation in HepG2 Cells

Background. Murraya koenigii (L.) Spreng, is a significant herb of traditional Ayurvedic system of medicine. Koenimbine, a carbazole alkaloid isolated from this plant holds antiproliferative and apoptotic effects. The aim of this study was to assess koenimbine-induced DNA damage and to clarify the role of free radicals in cell death mechanisms, using HepG2 cells. Methods. The level of cytotoxicity was assayed by MTT assay. To elucidate the role of glutathione (GSH), the intracellular GSH level was analyzed. The effect of koenimbine in the cell mitochondria was evaluated using mitochondrial membrane potential (MMP) changes. Single cell gel electrophoresis assay was used to examine the level of DNA damage. Heat shock proteins, Hsp 70 and Hsp 90 expressions were checked at mRNA and protein level. Ascorbic acid and catalase were used as control antioxidants. Results. It was observed that koenimbine considerably increased DNA damage in HepG2 cells at subcytotoxic concentrations. Koenimbine induced the increased levels of reactive oxygen species (ROS) and reduction of GSH level in HepG2 cells, together with time-dependent loss of MMP. In addition, results clearly showed that koenimbine encouraged cells to express Hsp 70 and Hsp 90 in a concentration-dependent manner up to a concentration of 100 µM and a time-dependent manner at 24-hour incubation both at transcriptional and translational levels. The antioxidant capacity of ascorbic acid was found to be not as prominent as to catalase throughout the study. Conclusion. Based on these data it can be concluded that koenimbine causes DNA strand breaks in HepG2 cells, probably through oxidative stress. Moreover, the oxidative stress induced was closely associated with MMP reduction and GSH depletion associated with HSP modulation at subcytotoxic concentration.