Monomers from composite fillings may impair the immune response of macrophages

Photo: Gunnar Svendsen, DDS

Dental biofilms may contain gram-negative bacteria that release the endotoxin lipopolysaccharide (LPS). This virulence factor plays an essential role in triggering periodontal inflammation. Macrophages are immune cells that remove pathogens and foreign substances. When exposed to LPS they may release pro-inflammatory cytokines such as tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β) as a part of the innate immune response.

In this study we report that relatively low concentrations of the methacrylate monomers TEGDMA (triethylene glycol dimethacrylate) and HEMA (2-hydroxyethyl methacrylate) reduced the LPS-induced cytokine release from the macrophage cell line RAW264.7. In the literature insufficient release of inflammatory mediators has been reported to cause impaired bacterial clearance, which could have implications for the innate immune response. Our experiments suggested that co-exposure to dental monomers caused an additive effect, which means that the response to combined exposure was similar to the sum of the responses induced by the individual monomers. Also, the reduced cytokine release persisted for 24 hours after termination of the monomer exposure, suggesting that the monomers could affect the macrophage function up to 24 hours after exposure. Studies of the mechanisms involved in the observed effects indicated disturbed regulation of synthesis and release of the cytokines, but further studies are necessary to clarify this.

The concentrations of TEGDMA and HEMA used in this study were based on laboratory studies of leakage from dental filling investigating the 24 hour cumulative release of monomers (from a meta-analysis by Van Landuyt et al. (2011)). These concentrations can therefore be considered to be relevant for oral exposure after placement of a composite filling. The applied concentrations were lower than those used previously in similar studies.

In conclusion, the observed reduction in the LPS-induced cytokine release after monomer exposure could have implications for the macrophage immune response. However, further studies are necessary to confirm these findings in other model systems.

From: Dental monomers inhibit LPS-induced cytokine release from the macrophage cell line RAW264.7. Bølling AK, Samuelsen JT, Morisbak E, Ansteinsson V, Becker R, Dahl JE, Mathisen GH. Toxicology Letters 216, 2013, p 130-138.