Inhibition of LPS-Stimulated Cytokine Release by the Resin Monomer TEGDMA

Objectives: Incomplete polymerisation of methacrylate-based resins leads to the release of unreacted resin monomers, such as triethyleneglycol dimethacrylate (TEGDMA), which cause cytotoxic effects in various cell lines. Furthermore, stress-activated protein kinases (MAPK) regulate cell survival, cytokine release or apoptosis, and are activated by resin monomers after long exposure periods. To understand the physiological importance of this effect, the kinetics of cytokine release in macrophages and pulp-derived cells in the presence of TEGDMA was analyzed. Methods: Mouse RAW264.7 macrophages and human pulp-derived cells (tHPC) were exposed to 0.1 µg/ml LPS, 3 mM TEGDMA, or a combination of LPS/TEGDMA for 15min and 30min, 1h, 2h, 6h and 24h. The amounts of the pro-inflammatory cytokines tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) plus the anti-inflammatory interleukin-10 (IL-10) were determined in supernatants of cell cultures using ELISA. Differences between median values (n=4) were statistically analyzed (Mann-Whitney-U-test; p≤0.05). Results: LPS induced a large (up to 40-fold) and time-dependent increase of cytokine release in macrophages. The level of TNF-α in LPS-treated cultures was significantly increased (> 20-fold), and maximum amounts of 5,000-7,500 pg/ml were detected after 2-24 h exposure periods. Similar secretion of IL-6 and IL-10 after LPS exposure occurred, but was delayed for about 1-2 h compared to the release of TNF-α. No induction of cytokine release was observed after the exposure of cells to TEGDMA alone, but TEGDMA instantaneously inhibited the secretion of all tested cytokines in LPS-treated cell cultures. No release of cytokines in human pulp-derived cells (tHPC) was observed after exposure to LPS, LPS/TEGDMA or TEGDMA alone. Conclusion: TEGDMA immediately interferes with fast LPS-stimulated signal transduction pathways leading to cytokine release from cells of the innate immune system. Supported by the Deutsche Forschungsgemeinschaft (Schw 431/11-1) and the German Academic Exchange Service (DAAD).