Leakage of unpolymerized methacrylate monomers after placement of methacrylate-containing polymeric dental materials leads to human exposure. Based on studies using murine macrophages and LPS from Escherichia coli (E. coli), dental monomers like 2-hydroxyethyl methacrylate (HEMA) are known to inhibit lipopolysaccharide (LPS) induced cytokine release. The aim of this study was to establish a model system with relevance for human oral monomer exposure using exposure to live gram-positive bacteria, and to confirm the HEMA-induced effects on cytokine release in this model.


The human THP-1 monocyte cell line was differentiated to macrophages using phorbol 12-myristate 13-acetate (PMA), before exposure to 0.5–2 mM HEMA and live Staphylococcus aureus (S. aureus) in various multiplicity of infections (MOI). Cytokine release and cytotoxicity were determined after (i) 2–24 h pre-exposure to HEMA followed by 2–4 h S. aureus exposure and (ii) 2–4 h simultaneous exposure. The 24 h pre-exposure regime was also tested in primary human airway macrophages and for phagocytosis of S. aureus in THP-1 macrophages.


HEMA attenuated the cytokine release more strongly in the pre-exposure than combined exposure regime, with a maximal reduction of 95% in the S. aureus-induced cytokine release. A MOI of 0.1 (corresponding to a bacteria-macrophage ratio of 1:10) was determined to be optimal in the THP-1 macrophages as it induced sufficient cytokine release and negligible cytotoxicity. Attenuated release of S. aureus-induced interleukin (IL)-1β after HEMA exposure was confirmed in primary airway macrophages, while HEMA increased the phagocytosis of S. aureus in THP-1 cells.


The model was successfully established and attenuated bacteria-induced cytokine release after HEMA exposure confirmed.

Establishing a macrophage model with relevance for oral methacrylate monomer exposures: Attenuated Staphylococcus aureus-induced cytokine release from human macrophages
Bølling AK, Olderbø BP, Samuelsen JT, Rukke HV.
Dental Materials, 2019