Resin-based biomaterials are widely used in dentistry, and consist of methacrylate monomers that are polymerized in situ. The conversion to polymer is never complete and cause leakage and patient exposure to electrophile monomers such as 2-hydroxyethyl methacrylate (HEMA). In addition, dental personnel that handle these materials are daily exposed. Methacrylates are shown to be cytotoxic in a dose-dependent manner and increased oxidative stress is a suggested key event in the onset of the toxic response. The mechanisms involved in the cytotoxic effects of HEMA have not been fully elucidated; however activation of nuclear factor erythroid 2-related factor 2 (Nrf2) appears to play a central role. Nrf2 is a master regulator of cellular resistance to oxidants. In this study we aim to determine if the in vitro
toxicity to HEMA depend on Nrf2 activity.
The effects of 24 hours of HEMA exposure (0-8 mM) on two human epithelial airway cell lines were compared; the human bronchial epithelial cell line BEAS-2B and the human alveolar epithelial cancer cell line A549. The first cell line holds a normal regulation of Nrf2 activity, whereas the latter contain a mutation in the Keap1 gene, an important regulator of Nrf2 level and activity. The viability was measured using MTT assay and western blot was used to explore altered levels of Nrf2-regulated gene products known to be affected by HEMA exposure.
Both BEAS-2B and A549 cells exposed to 0-8 mM HEMA for 24 hours resulted in dosedependent decrease in viability; however the two different cell lines exhibited different protein expression profiles of the investigated gene products. BEAS-2B cells exposed to HEMA significantly increased Nrf2-regulated proteins, while no change was observed in A549 cells. Interestingly, the basal levels of these proteins in A549 cells were relatively high and comparable to HEMA exposed BEAS-2B cells.
These results indicate that HEMA induce the Nrf2 activity in BEAS-2B, while the Nrf2 pathway is constantly activated in A549 cells as if the cells are under stressed conditions. Furthermore, the viability decreased in both cell lines after HEMA exposure. Consequently it appears that increased Nrf2 activation does not protect against HEMA induced toxicity.