Resin-based biomaterials used in dentistry consist of methacrylate monomers that are polymerized in situ. The conversion to polymer is never complete and cause patient exposure to electrophilic monomers such as 2-hydroxyethyl methacrylate (HEMA). In addition, dental personnel are exposed through handling of uncured materials. In vitro, methacrylates are reported to be cytotoxic in a dose-dependent manner. The mechanisms involved are not fully elucidated, but increased oxidative stress is a suggested key event. Based on this presumption, activation of nuclear factor erythroid 2-related factor 2 (Nrf2) is assumed to play a central role in defending exposed cells against oxidant and electrophilic stresses1. In this study, we aim to elucidate the ability of Nrf2 regulated genes to counteract HEMA toxicity.
The effects of 24 hours HEMA exposure (0-8 mM) on the human bronchial epithelial cell line BEAS-2B and the human alveolar epithelial cancer cell line A549 were compared. The first cell line holds a normal regulation of Nrf2 activity, whereas the latter contain a mutation that results in continuously Nrf2-activity. Western blotting was used to explore altered levels of Nrf2-associated gene products known to be affected by HEMA exposure. Furthermore, viability after 24 hours HEMA exposure (0-8 mM) was measured using MTT assay. Additionally, viability in BEAS 2B cells after 24 hours preincubation with 1 mM HEMA followed by 24 hours of HEMA exposure (0-8 mM) was measured. At least three independent experiments were performed. Statistical analysis was calculated using one-way ANOVA with Dunnett multiple comparisons test by GraphPad prism.
RESULTS AND DISCUSSION
Protein measurements using western blotting revealed that BEAS-2B cells exposed to HEMA significantly increased the investigated Nrf2-associated proteins, while no change was observed in A549 cells. The basal levels of these proteins in A549 cells, however, were comparable to HEMA-exposed BEAS-2B cells. Both BEAS-2B and A549 cells exposed to HEMA resulted in a similar dose-dependent decrease in viability. Although preincubation of BEAS-2B cells with 1 mM HEMA increased Nrf2-activity, the viability loss caused by HEMA was not affected.
These results indicate that HEMA induce the Nrf2 activity in BEAS-2B, while the Nrf2 pathway is constantly activated and not further inducible by HEMA in A549 cells. Furthermore, the results argue that increased Nrf2 activation protects against HEMA induced toxicity.
- Orimoto A, Suzuki T, Ueno A, Kawai T, Nakamura H, Kanamori T. PLOS ONE.2013;8(3):e58907.
Bergitte Olderbø1, Else Morisbak1, Solveig Uvsløkk1, Jan T Samuelsen1
1Nordic Institute of Dental Materials, Norway
2Norwegian Institute of Public Health, Norway
The authors would like to thank Aurora Thori Lima, Ingelin Andrea Neeraas, Renate Gjertsen Ravndal and Siv Skundberg Jensen for excellent technical assistance.