Signaling pathways activation by primary endodontic infectious contents and production of inflammatory mediators.

Introduction: This study investigated the bacterial community involved in primary endodontic diseases, evaluated its ability to activate the macrophage Toll-like receptor 4 receptor through p38 mitogen-activated protein kinase (MAPK) and nuclear factor kappa B (NF-κB) signaling pathways, and determined the levels of endotoxins and interleukins (interleukin [IL]-6 and -10) produced by endodontic content-stimulated macrophages.
Methods: Samples were taken from 21 root canals by using sterile/apyrogenic paper points. Raw 264.7 macrophages were stimulated with root canal contents. Checkerboard DNA-DNA hybridization was used for bacterial analysis and the limulus amebocyte lysate assay for endotoxin measurement; p38 MAPK and NF-κB activation was determined by Western blot analysis. IL-6 and IL-10 were measured using the enzyme-linked immunosorbent assay.
Results: Bacteria and endotoxins were detected in 100% of the samples (21/21). The most frequently observed species were Parvimonas micra (16/21, 76%), Fusobacterium nucleatum ssp. nucleatum (15/21, 71%), and Porphyromonas endodontalis (14/21, 66%). Correlations were found between endotoxins and IL-6 and IL-10 (P < .05); p38 phosphorylation had a peak at 60 minutes, and NF-κB was quickly activated after 10 minutes of stimulation.
Conclusions: It was concluded that the complex bacterial community was shown to be a potent activator of TLR-4 determined by the p38 MAPK and NF-κB signaling pathways, culminating in a high antigenicity against macrophages through the levels of IL-6 and IL-10, all significantly affected by endotoxin levels.
(Copyright © 2014 American Association of Endodontists. Published by Elsevier Inc. All rights reserved.)