Novel co-initiators of polymerization: Cytotoxicity profile and modulation of inflammatory mediators in human dental pulp stem cells

Objectives: The aim of this study was to assess the cytotoxicity of novel polymerization co-initiators and their effect on cytokine release from human dental pulp stem cells (hDPSCs), comparing them with commonly used co-initiators. Methods: Cells were isolated from the dental pulp of healthy human third molars. The new co-initiators, namely HDa1, HD4, HD1, and MHPTm, were evaluated and compared with the compounds dimethylaminoethyl amine benzoate (EDAB) and 2-(dimethylamino)ethyl methacrylate (DMAEMA). These compounds were diluted in dimethylsulfoxide (DMSO) at concentrations ranging from 1 to 8 mM. hDPSCs were seeded onto 96-well plates and incubated for 48 h. Subsequently, the cells were exposed to different concentrations of the co-initiators mentioned for 24 h. After this period, the culture medium was removed, and mitochondrial metabolism was evaluated using the MTT assay, while cytokine release (IL-1 beta, IL-6, IL-8, IL-10, TNF-alpha) was analyzed by the MAGPIX assay. Cells without exposure to the tested compounds served as controls. The data were analyzed using one-way ANOVA and Tukey's test. Results: The compounds showed low toxicity, with 8 mM concentration causing the most significant reduction in mitochondrial metabolism. MHPTm was the most toxic co-initiator tested (compound bearing an amine functionality). All compounds up-regulated TNF-alpha, IL-10, IL-6, and IL-8, with HD4 exhibiting the most pronounced increase in IL-6 and IL-8. Significance: The newly proposed co-initiators demonstrated reduced impact on mitochondrial metabolism, comparable to some traditional co-initiators. Despite their lower toxicity, HD4 increased IL-6 and IL-8 release, suggesting its potential involvement in triggering an inflammatory reaction, particularly in the short term.