Method: OKF6/TERT2 cells were treated for 24 h with various concentrations of CQ ± blue-light irradiation for 20 s using a dental curing lamp. Cytotoxicity of 0.125-2.5 mM CQ was assessed by fluorescence spectroscopy using the H33342 assay. Cell viability and apoptosis rate influenced by 0.5-2.5 mM CQ (± blue-light irradiation) were evaluated by flow cytometry (Annexin V-FITC/PI assay) and DNA-fragmentation. Bonferroni´s ANOVA (p < 0.05) was used for statistical analysis. All experiments were run three times.
Result: Non-irradiated CQ induced concentration-dependent decrease of total cell number (EC50 = 0.9 ± 0.1 mM). The Annexin V-FITC/PI assay revealed that cells exposed to concentrations of 0.5 mM (1.0 ± 0.4%) and 1.0 mM CQ (2.8 ± 1.4%) showed no increase of apoptotic cells compared to controls (c: 1.1 ± 0.1%), while 2.5 mM CQ caused a slight but significant increase of apoptotic cells (15.5 ± 3.9%). This effect was associated with a very pronounced decrease in cell viability (2.5 mM CQ: 34.8 ± 13.5%; c: 92.3 ± 4.8%). Irradiation of 2.5 mM CQ at the beginning of the treatment did not enhance these effects (apoptosis: 12.9 ± 3.6%; viability: 35.7 ± 17.1%). DNA laddering in agarose gel electrophoresis confirmed that cell death was caused by apoptosis.
Conclusion: Non-irradiated CQ causes significant cytotoxic and apoptotic effects in human oral keratinocytes. Activation of CQ by blue light exposure does not influence these effects, despite the fact that blue-light irradiation triggers the CQ-induced intracellular ROS generation.