N-acetyl cysteine prevents perforation of fibroblastic monolayer by polymetylmethacrylate extracts

Objective: Polymethylmethacrylate (PMMA) resin, a requisite material for prosthodontic treatment, potentially causes serious disorder, especially skin/mucosal irritation and allergy, which possibly involves cell injury, tissue infiltration and oxidative stress by resin component in the onset. N-acetyl cysteine (NAC), anti-oxidant amino acid derivative, can detoxify the resin material. The objective of this study was to investigate whether application of NAC prevented cell injury, tissue infiltration and oxidative stress by PMMA resin extracts using gingival fibroblastic monolayer culture model. Methods: Rat gingival fibroblastic confluent monolayer culture on polystyrene was incubated in D-MEM with or without the extracts from commercial auto-curing PMMA-based dental resin with or without pre-incorporation of NAC. After day 1 of incubation, the cultures underwent methylene blue staining for adherent cells, LDH-based cell injury assay and fluorescent-based quantification of cellular reactive oxygen species (ROS) level. Data was treated with Mann-Whitney test with Bonferroni correction after Kruskal-Wallis test (α=0.05). Results: There were significant differences among the culture conditions at each analysis (p<0.05). The percentage of methylene blue-positive area on the monolayer culture incubated with the PMMA extracts was 55% in contrast with 94% on the untreated culture without the extracts. Meanwhile, the percentage on the culture incubated with the extracts from the NAC pre-incorporated PMMA was 94%. Amount of released LDH from the culture with the extracts was 60% greater than that from the untreated culture, which was markedly reduced by NAC pre-incorporation. Cellular ROS in the culture with the extracts was 30% greater than that in the untreated culture, which was below the level in the untreated culture by NAC pre-incorporation. Conclusion: PMMA resin extracts injured and perforated the cultured fibroblastic monolayer with oxidative stress, implying infiltration into deeper tissue and subsequent initiation of　tissue irritation and allergic reaction. That was prevented by pre-incorporation of NAC into the resin.