Toxic mechanisms of BisGMA on human dental pulp cells

Objectives: After operative restoration, some monomers released from composite resin may induce tissue inflammation and affect the vitality of dental pulp. Whether BisGMA, a major monomer of composite resin, may induce prostaglandin release and cytotoxicity to pulp cells and their mechanisms awaits investigation. Methods: Primary human dental pulp cells were exposed to various concentrations of BisGMA (0.01-0.25 mM) for some periods. Viable cell numbers were evaluated by MTT assay. Culture medium was collected for evaluation of prostaglandin E2 production by enzyme linked immunosorbant assay (ELISA). Changes in cyclooxygenase-2 (COX-2) mRNA expression and protein level were studied by reverse-transcriptase polymerase chain reaction and western blotting. Reactive oxygen species (ROS) production in pulp cells were determined by single cell DCF fluorescence flow cytometry. Results: BisGMA showed marked cytotoxicity to dental pulp cells at concentrations higher than 0.1 mM. BisGMA (0.05-0.1 mM) also stimulated PGE2 production, COX-2 mRNA and protein expression as well as ROS production (as indicated by an increase in cellular DCF fluorescence) in dental pulp cells. N-acetyl-L-cysteine (NAC), catalase (1000 and 2000 U/ml), aspirin (100 and 200 uM) and U0126 (1 and 10 uM, a MEK inhibitor) effectively prevented the BisGMA-induced PGE2 production and COX-2 expression. Moreover, NAC and catalase can protect the pulp cells from BisGMA cytotoxicity, whereas aspirin and U0126 lacked of this protective activity. Conclusion: These results suggest that BisGMA released from composite resin may potentially affect the vitality of dental pulp and induce pulpal inflammation via stimulation of ROS production, MEK/ERK1/2 activation and thereby the COX-2 gene expression and prostaglandin production. Cytotoxicity of BisGMA to dental pulp cells is related to ROS production, but not directly mediated by MEK/ERK activation and PGE2 production. (This study is supported by a grant from National Science Council, Taiwan)