Root canal contamination or exposure to lipopolysaccharide differentially modulate prostaglandin E 2 and leukotriene B 4 signaling in apical periodontitis

Abstract Purpose To evaluate the kinetics of apical periodontitis development in vivo , induced either by contamination of the root canals by microorganisms from the oral cavity or by inoculation of bacterial lipopolysaccharide (LPS) and the regulation of major enzymes and receptors involved in the arachidonic acid metabolism. Methodology Apical periodontitis was induced in C57BL6 mice (n=96), by root canal exposure to oral cavity (n=48 teeth) or inoculation of LPS (10 µL of a suspension of 0.1 µg/µL) from E. coli into the root canals (n= 48 teeth). Healthy teeth were used as control (n=48 teeth). After 7, 14, 21 and 28 days the animals were euthanized and tissues removed for histopathological and qRT-PCR analyses. Histological analysis data were analyzed using two-way ANOVA followed by Sidak’s test, and qRT-PCR data using two-way ANOVA followed by Tukey’s test (α=0.05). Results Contamination by microorganisms led to the development of apical periodontitis, characterized by the recruitment of inflammatory cells and bone tissue resorption, whereas inoculation of LPS induced inflammatory cells recruitment without bone resorption. Both stimuli induced mRNA expression for cyclooxygenase-2 and 5-lipoxygenase enzymes. Expression of prostaglandin E 2 and leukotriene B 4 cell surface receptors were more stimulated by LPS. Regarding nuclear peroxisome proliferator-activated receptors (PPAR), oral contamination induced the synthesis of mRNA for PPARδ, differently from inoculation of LPS, that induced PPARα and PPARγ expression. Conclusions Contamination of the root canals by microorganisms from oral cavity induced the development of apical periodontitis differently than by inoculation with LPS, characterized by less bone loss than the first model. Regardless of the model used, it was found a local increase in the synthesis of mRNA for the enzymes 5-lipoxygenase and cyclooxygenase-2 of the arachidonic acid metabolism, as well as in the surface and nuclear receptors for the lipid mediators prostaglandin E2 and leukotriene B4.

摘要
目的：本研究旨在评估两种诱导方式下体内根尖周炎的发生动力学过程：一是通过口腔微生物污染根管，二是接种细菌来源的脂多糖（lipopolysaccharide, LPS），并探究花生四烯酸代谢通路中主要酶类与受体的调控情况。

方法：选取96只C57BL6小鼠，通过两种方式构建根尖周炎模型：将根管暴露于口腔环境（共48颗牙齿），或向根管内接种大肠杆菌来源的脂多糖（10 μL，浓度0.1 μg/μL，共48颗牙齿）；另设健康牙齿作为对照组（共48颗牙齿）。分别于建模后7、14、21、28天处死小鼠，采集组织样本进行组织病理学分析与实时定量聚合酶链反应（qRT-PCR）检测。组织病理学数据采用双因素方差分析（two-way ANOVA）后行Sidak检验，qRT-PCR数据采用双因素方差分析后行Tukey检验（检验水准α=0.05）。

结果：口腔微生物污染可诱导根尖周炎发生，表现为炎性细胞募集与骨组织吸收；而脂多糖接种仅能诱导炎性细胞募集，未引发骨吸收。两种刺激均可上调环氧合酶-2（cyclooxygenase-2）与5-脂氧合酶（5-lipoxygenase）的mRNA表达。前列腺素E2与白三烯B4的细胞表面受体的表达受脂多糖的刺激更为显著。关于核过氧化物酶体增殖物激活受体（peroxisome proliferator-activated receptors, PPAR），口腔微生物污染可诱导PPARδ的mRNA合成，而脂多糖接种则上调PPARα与PPARγ的表达。

结论：口腔微生物污染根管诱导的根尖周炎与脂多糖接种诱导的根尖周炎存在差异，前者骨吸收程度低于后者。无论采用哪种建模方式，花生四烯酸代谢通路中的5-脂氧合酶与环氧合酶-2的mRNA合成均存在局部上调，同时前列腺素E2、白三烯B4的细胞表面受体与核受体的表达亦出现局部升高。