The Hormetic Effect of Arsenic Trioxide on Rat Pulpal Cells: An In Vitro Preliminary Study.

Objectives Despite the agreement that there is no longer any indication for arsenic use in modern endodontics, some concerns are surfacing about the minute amount of arsenic trioxide (As2O3) released from Portland cement-based materials. The present study investigated the effect of different concentrations of As2O3 on rat pulpal cells and the efficacy of N-acetylcysteine (NAC) in preventing As2O3-mediated toxicity. Materials and Methods Cytotoxicities of 50, 10, or 5 µm As2O3 and the effect of cells co-treatment with 50 µm As2O3 and 5,000 µm NAC or 500 µm NAC were tested at 24 hours or 3 days. Cell viability was assessed by means of MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay and cellular morphological changes were observed under phase contrast microscope. Statistical Analysis Two-way analysis of variance with Tukey’s post-hoc test was used to evaluate differences between the groups (α = 0.05). Results At both exposure times, 50 µm As2O3 resulted in lower optical density (OD) values when compared with 10 or 5 µm As2O3. At 24 hours, 10 µm As2O3 resulted in a higher OD value compared with the control; however, at 3 days the difference was statistically insignificant. At each exposure time, the OD value of 5 µm As2O3 group was comparable to the control and 10 µm As2O3 group. There were no significant differences between 50 µm As2O3 group and 500 NAC+50 µm As2O3 group; however, these two groups had lower OD values when compared with 5,000 NAC + 50 µm As2O3 group at 24 hours and 3 days. The latter group showed significantly lower OD value in comparison with the control at 24 hours and 3 days. Control cells were polygonal-shaped while 50 µm As2O3-treated cells exhibited contracted and spherical morphology with increased intercellular spaces. At 24 hours, 10 μm and 5 µm As2O3-treated cells were slightly hypertrophic. Cells co-treated with NAC and As2O3 showed increased intercellular spaces and lower cellular density compared with the control. Conclusions As2O3 displayed a hormetic effect on pulpal cells; however, the proliferative effect induced by low As2O3 concentrations should be interpreted with caution. NAC did not prevent As2O3-mediated toxicity; however, it demonstrated potential for ameliorating this toxicity.