Chronic exposure to lipopolysaccharides as an in vitro model to simulate the impaired odontogenic potential of dental pulp cells under pulpitis conditions

Background: Simulating a bacterial-induced pulpitis environment in vitro may contribute to exploring mechanisms and bioactive molecules to counteract these adverse effects. Aim: To investigate the chronic exposure of human dental pulp cells (HDPCs) to lipopolysaccharides (LPS) aiming to establish a cell culture protocol to simulate the impaired odontogenic potential under pulpitis conditions. Methodology: HDPCs were isolated from four healthy molars of different donors and seeded in culture plates in a growth medium. After 24 h, the medium was changed to an odontogenic differentiation medium (DM) supplemented or not with E. coli LPS (0 - control, 0.1, 1, or 10 µg/mL) (n=8). The medium was renewed every two days for up to seven days, then replaced with LPS-free DM for up to 21 days. The activation of NF-κB and F-actin expression were assessed (immunofluorescence) after one and seven days. On day 7, cells were evaluated for the gene expression (RT-qPCR) of odontogenic markers (COL1A1, ALPL, DSPP, and DMP1) and cytokines (TNF, IL1B, IL8, and IL6) and the production of reactive nitrogen (Griess) and oxygen species (Carboxy-H2DCFDA). Cell viability (alamarBlue) was evaluated weekly, and mineralization (Alizarin Red) at 14 and 21 days. Data were analyzed with ANOVA and post-hocs (α=5%). Results: After one and seven days of exposure to LPS, NF-κB was activated in a dose-dependent fashion. One and 10 µg/mL LPS down-regulated the gene expression of odontogenic markers and up-regulated cytokines. Ten µg/mL LPS increased both the production of reactive nitrogen and oxygen species. LPS decreased cell viability seven days after the end of exposure. One and 10 µg/mL LPS decreased hDPCs mineralization in a dose-dependent fashion. Conclusion: The exposure to 10 µg/mL LPS for seven days creates an inflammatory environment able to impair by more than half the odontogenic potential of HDPCs in vitro, simulating a pulpitis-like condition.