Resin-based dental materials are a common first choice when restoring dental function. These materials never cure completely and both dental personnel and patients are exposed to methacrylate monomers, one main component in these materials. A concern regarding possible side effects these materials may induce has been the motivation of several in vitro studies. A cytotoxic potential have been described in vitro, but detailed knowledge regarding the underlying molecular interactions of monomers remain scarce. A suggested mechanism, however, involves thiol-reactivity and increased levels of oxidative stress. 2-Hydroxyethylmethacrylate (HEMA) is known to spontaneous form adduct with cysteine in glutathione (GSH), and it is suggested if similar reactions towards nucleophilic amino acids in proteins occurs. The aim of this study was to investigate if the commonly used methacrylate HEMA affects protein cysteines.
For this in vitro study, a bronchial epithelial cell line (BEAS-2B) was used as a model. Cells were grown in Lechner and La Veck (LHC-9) medium and exposed to HEMA. GSH-levels in HEMA-exposed cells were measured by flow cytometry after staining with monobromobimane (mBrB). Specific antibodies were used to detect β-actin and changes in protein S-glutathionylation in cells after HEMA-exposure. Data was quantified using western blot and Odyssey CLx Infrared System. LC-MS was used to detect bindings between HEMA and synthetic peptides containing lysine and/or cysteine. Four different peptides with similar amino acid chain sequence were ordered from GenScript and analysed on UHPLC-MS.
Results showed that exposure to HEMA reduced the levels of GSH and S-glutathionylation of at least one protein (MW approx. 42 kDa) in cells exposed to HEMA. The results further imply that the observed protein is β-actin. LC-MS analysis implies binding between synthetic peptides and HEMA where there was cysteine present in the amino acid chain.
This study has shown that HEMA lowers the level of S–glutathionylation in BEAS-2B cells, and it is suggested that the main protein affected is β-actin. Both altered GSH-levels and competitive binding of HEMA to the S-glutathionylation site of β-actin may explain this effect.