Protective effect of NAC on formaldehyde-containing-ZOE-based root-canal-sealers-induced cyclooxygenase-2 expression and cytotoxicity in human osteoblastic cells

Cyclooxygenase-2 (COX-2) is an inducible enzyme believed to be responsible for prostaglandin synthesis at site of inflammation. Recently, the activation of COX-2 expression may be one of the important pathogenesis of root-canal-sealers-induced periapical inflammation. However, little is known about whether chemical interaction can modulate the COX-2 expression and cytotoxicity induced by formaldehyde-containing-ZOE-based root canal sealers. The aim of this study was to investigate the effects of antioxidants such as catalase, superoxide dismutase (SOD), and N-acetyl-L-cysteine (NAC) on N2- and endomethasone-induced COX-2 mRNA gene and cytotoxicity in human osteoblastic cell line U2OS cells. Our data demonstrated that both formaldehyde-containing- ZOE-based root canal sealers were found to induce COX-2 mRNA gene expression in U2OS cells. The addition of glutathione (GSH) precursor NAC led to decrease the induction of COX-2 mRNA gene expression and cytotoxicity by both N2 and Endomethasone (p < 0.05). However, catalase and SOD lacked the ability to prevent cytotoxicity and COX-2 mRNA gene expression induced by N2 and Endomethasone (p > 0.05). The data presented here demonstrated that the activation of COX-2 mRNA gene expression may be one of the pathogenesis of formaldehyde-containing-ZOE-based root-canal-sealers-induced periapical inflammation. In addition, GSH depletion, but not the attack of oxygen free radicals, could be the mechanism for cytotoxicity and COX-2 mRNA gene expression induced by formaldehyde-containing-ZOE-based root canal sealers. NAC appears as a useful agent in protecting cell damage mediated by formaldehyde-containing- ZOE-based root canal sealers.