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

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.

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.

Two-way analysis of variance with Tukey's post-hoc test was used to evaluate differences between the groups (α = 0.05).

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 μm NAC+50 μm As₂O₃ group; however, these two groups had lower OD values when compared with 5,000 μm 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.

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.