Method: OKF6/TERT2 and Caco-2 cells were treated with CQ (0.5-5mM) in the dark with or without visible light (VL) activation (20s). CQ was dissolved in ethanol (0.25%) and added to cells by medium change. CQ-dependent cytotoxicity and ROS-formation were assessed by means of fluorospectrophotometric analyses using propidium iodide and 2´,7´-dichlorodihydrofluorescein diacetate, respectively. Oxidative DNA damage was evaluated by an enzyme-modified comet assay using human 8-hydroxyguanine DNA-glycosylase 1, which converts oxidized 7,8-dihydro-8-oxoguanine (8-oxoguanine) into DNA strand breaks and functions as a marker for oxidative stress. Tail moment (TM) was used for data analysis. All experiments were performed at least three times. Statistical analysis was performed using ANOVA Bonferroni posttest and paired t-test (p < 0.05).
Result: Exposure of OKF6/TERT2 and Caco-2 cells to CQ resulted in a rapid and significant increase in ROS-formation dependent upon concentration (2.5mM CQ OKF6/TERT2: 1928±293%, Caco-2: 1328±323%). Additionally, VL activation enhanced ROS generation in OKF6/TERT2 2.6-fold. DNA damage was found for high CQ-concentrations +VL in OKF6/TERT2 cells (TM, 3.75mM: 0.5±0.08, 4.25mM: 0.60±0.15, 5mM: 1.77±1.13) and for 2.5mM CQ in Caco-2 cells (TM: 3.84±0.53). There was a significant increase in 8-oxoguanine formation resulting in a higher TM for the tested CQ concentrations (OKF6/TERT2 +VL 2.5mM: 2.10±0.83, 3.75mM: 3.36±0.35, 4.25mM: 3.89±1.61, 5mM: 6.30±1.65; Caco-2 2.5mM: 5.54±0.68).
Conclusion: It may be concluded that CQ caused DNA strand breaks and oxidative modifications not only in oral OKF6/TERT2 cells but also in intestinal Caco-2 cells, which are part of these cells´ oxidative stress response.