Glutathione level and genotoxicity in human oral keratinocytes exposed to TEGDMA

Abstract

Triethylene-glycol dimethacrylate (TEGDMA) is an important matrix comonomer used in many resin-modified dental materials. As the monomer-polymer conversion of these biomaterials is up to 80% at best, TEGDMA may leach into the oral cavity and the pulp in millimolar concentrations. Objective of this study was to evaluate whether TEGDMA is genotoxic in immortalized human oral keratinocytes (OKF6/TERT2), for example, due to formation of oxidative DNA-lesions. OKF6-TERT2 cells were exposed to TEGDMA at concentrations ranging from 0.5 mM to 5.0 mM. Cell viability was analyzed by the fluorescent probe propidium iodide (PI), intracellular levels of reactive oxygen species (ROS) were measured by 2',7'-dichlorofluorescein diacetate, whereas glutathione concentrations (GSH) were read using monobromobimane. Genotoxicity was determined quantitatively by the alkaline comet assay. To explore the presence of oxidized bases that could be produced by oxidative events during short-term treatment with TEGDMA, the 8-hydroxyguanine DNA-glycosylase 1 (hOGG1)-modified comet assay was used. TEGDMA induced an early and rapid GSH-depletion in a concentration-dependent manner (p < 0.05). A total of 5 mM TEGDMA reduced GSH to 57.8% ± 8.6% of control values already after 30 min. There was no significant reduction in cell viability during 6 h of incubation, and only moderate ROS-formation was detected after 4 h of treatment with TEGDMA. But after 24 h, TEGDMA-concentrations of ≥2.5 mM induced a significant reduction of total cell numbers and cells' viability. Furthermore, TEGDMA caused a concentration-dependent DNA damage in OKF6/TERT2 cultures, which was not associated with a detectable formation of 8-hydroxy-2'-deoxyguanosine (8-OHdG) in the cellular genome. In conclusion, our results show that TEGDMA influences the intracellular redox metabolism and may exhibit pronounced cyto- and genotoxic effects in human immortalized oral keratinocytes. However, it may be concluded that oxidative stress is not causative for TEGDMA-dependent genotoxicity in these cells.