Cellular and Molecular Pulpal Response to LPS Multi-Injection Induced Inflammation

Objectives: In response to pathogens a dental pulp inflammation called pulpitis occurred, more often clinically diagnosed as reversible or irreversible. But its applicability and the limitation to identify parts of pulp not affected by the inflammation process of this clinical diagnosis is of a great interest in identifying potential biomarkers, as diagnostic tools of pulpal disease. In order to more preserve healthy dental pulp tissue in vital pulp therapy process. In this rat model of LPS multi-injection induced chronic inflammation, we tried to identify a molecular limited point that does not allow the preservation of residual dental pulp vitality.
Methods: In this model, rat molar inflammation is induced by mechanically exposing the pulp and bringing it into contact one, two or 3 times with LPS from Escherichia coli or PBS as a positive control (APAFiS no.19-042)(n=6). Dental pulps were sealed with an obturation cement. 24h after injection, teeth were removed for QPCR, histological and immunohistological analysis.
Results: The histological analysis allowed us to describe tissue changes during chronic inflammation. The inflammation, induced by 3 contacts of LPS, showed a higher expression of MMP9 gene expression compared to the healthy pulp, while DSPP gene expression was downregulated. By immune histochemistry, IL-6 expression was more highly diffused in the residual pulp after 3 contacts of LPS compared with only one. The presence of CD68-positive cells was also higher with 3 LPS contacts.
Conclusions: This model makes it possible to describe dental pulp tissue changes during LPS repeated chronic inflammation. It also allows us to link molecular and cellular events of inflammation to the repair capacities of the pulp dentin complex. Ratio expression of MMP9/DSPP could be a good couple of biomarkers that can be used to identify the possibility to realize or not a vital pulp therapy.