Inflammatory Pulpal Responses to LPS Repeated Inductions in Rat Molar

Objectives: Repeated lipopolysaccharide (LPS) stimulation is a well-established model of chronic inflammation in conditions such as sepsis, lung disease, and arthritis, where it activates the nuclear factor-κB (NF-κB) pathway. Because deep caries similarly expose dental pulp to bacterial toxins, applying this approach to rat molars could clarify how recurrent LPS challenges drive pulp inflammation. This study evaluated whether one to three inductions of LPS or phosphate-buffered saline (PBS, positive control) induce progressive molecular and histological changes in rat pulp. Methods: Exposed upper first molars received 1-3 inductions of LPS or PBS. Pulp tissue was collected 6, 24, and 48 hours after the final induction for histology and quantitative polymerase chain reaction (qPCR). Results: Gene expression analysis showed significant modulation of inflammatory and remodelling markers (IL6, MMP3, MMP9, CCR7, CXCL1, HO1, and DSPP) with repeated stimulations. Histological alterations were more pronounced after multiple exposures, although no significant differences emerged between LPS- and PBS-treated teeth. The progressive rise in the MMP9/DSPP ratio suggests its potential as an indicator of pulpal tissue degradation. Conclusion: This model offers preliminary knowledge about the sequential molecular and histological responses of rat pulp to repeated bacterial challenges. Although further work is needed to isolate LPS-specific effects and confirm chronic features, these findings help delineate the early dynamics of pulp inflammation.