Role of endothelial cells for nitric oxide production in periapical lesions

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The purpose of this study was to elucidate the role of endothelial cells for nitric oxide production in periapical lesions. Periapical exudates and periapical granulomas were analyzed, and inducible nitric oxide synthase (iNOS) and vascular endothelial (VE-) cadherin were examined in this study. Predominant cells isolated from periapical exudates were polymorphonuclear leukocytes (PMNs), as determined morphologically using hematoxylin-eosin stains. Protein expression and gene expression of iNOS was confirmed by immunocytochemical and RT-PCR analyses, respectively. Two-color immunohistochemistry using cryostat sections of periapical granulomas demonstrated that iNOS-expressing cells were macrophages, lymphocytes, fibroblasts, PMNs and endothelial cells whereas VE-cadherin-expressing cells were only endothelial cells. Thus, endothelial cells co-expressed iNOS and VE-cadherin. Real time PCR demonstrated the gene expression of iNOS and VE-cadherin mRNA in periapical granulomas. The expression levels of iNOS mRNA were higher than those of VE-cadherin. In our in-vitro study, human umbilical vein endothelial cells (HUVEC) were stimulated with interleukin-1 and Escherichia coli derived LPS for 2-24hr. Real time PCR demonstrated that iNOS and VE-cadherin mRNA was expressed in stimulated HUVEC. In addition, the expression levels of VE-cadherin mRNA were higher than that of iNOS. We also examined iNOS inhibitors in in-vitro study using HUVEC. The iNOS inhibitors decreased the expression levels of iNOS mRNA, therefore the possibility of pharmacological application was demonstrated. The data are consistent with a hypothesis suggesting that VE-cadherin expression of endothelial cells in periapical granulomas could be controlled in the association with nitric oxide.