Histology-based profile of inflammatory mediators in experimentally induced pulpitis in a rat model: screening for possible biomarkers.

AIM To profile molecular changes in lipopolysaccharide (LPS)-induced experimental pulpitis in a rat model and explore the feasibility of a molecular-based diagnostic strategy for pulpitis. METHODOLOGY Seventy-three maxillary incisors of Sprague-Dawley rats were used to establish pulpitis models with LPS. Inflammatory grading was performed in four equal sections of the pulp divided from the injured site to the root apex. An antibody array was used to compare the expression of 67 molecules between control pulp and inflamed pulp 12 and 72 h after LPS application. The levels of differentially expressed molecules in the control and inflamed pulp (collected at 3, 6, 9, 12, 24 and 72 h after LPS treatment) were examined via ELISA, and correlations between inflammatory scores and molecule expression were assessed. The molecule distributions in the pulp were investigated by immunofluorescence staining. Data were analysed with paired t-test, one-way anova, Kruskal-Wallis tests, and Spearman's and Pearson's correlations with significance set at P < 0.05. RESULTS Polymorphonuclear neutrophils were observed in the injured site 3 h after LPS stimulation. Inflammatory infiltration peaked at 12 h and was limited to the injured site with osteodentine deposition at 72 h. Thirteen molecules were significantly differentially expressed between the control and LPS-injured pulp. ELISA validated that tissue inhibitor of metalloproteinase-1 (TIMP-1) expression dramatically peaked at 12 h (compared with other time points, P < 0.05) and returned to baseline at 72 h. The TIMP-1 concentration was strongly correlated with inflammation severity in the apical three-quarters of the pulp, and the strongest correlation was found in the lower-middle quarter (r = 0.786, P < 0.001). Immunofluorescence staining revealed that in the apical three-quarters of the pulp, TIMP-1 expression was significantly higher in the 12 h group than in the control and 3, 6, 24 and 72 h groups (P < 0.01). CONCLUSION This study provides a molecular profile of LPS-induced pulpitis in a rat model. TIMP-1 had a strong positive correlation with the severity of dental pulp inflammation, verifying the feasibility of applying biomarkers to identify specific pathological conditions in pulpitis.