Aim:Activation of cyclooxygenase-2 (COX-2) expression by nicotine suggests a potential role for nicotine in the pathogenesis of smoking-associated periodontal disease.The aim of this study was to investigate whether chemical interactions can modulate nicotine-induced COX-2 expression in human gingival fibroblasts (HGF).Methods:Cytotoxicity was investigated by using lactate dehydrogenase leakage assays and Weste blotting was used to assess COX-2 expression. Furthermore,buthionine sulfoximine (BSO;an intracellular glutathione synthesis inhibitor) ,2-oxothiazolidine-4-carboxylic acid (OTZ;the precursor of cysteine) , and PD98059 fextracellular signal-regulated protein kinase inhibitor) were added to search for the possible regulation mechanisms of nicotine-induced COX-2 expression.Results:Nicotine was found to elevate lactate dehydrogenase leakage in a dose-dependent manner (P＜0.05).Treatment of HGF with nicotine was shown to mediate COX-2 protein expression.Pretreatment with OTZ decreased nicotine-induced COX-2 protein level by approximately 60% (P＜0.05).However, BSO enhanced nicotine-induced COX-2 protein level up to approximately 3-fold (P＜0.05).Treatment ofHGF with PD98059 decreased nicotine.induced COX-2 protein expression.In addition,nicotine induced extracellular signal-regulated protein kinase phosphorylation in a time-dependent manner (P＜0.05).Conclusion:Nicotine may play a significant role in the pathogenesis of cigarette smoking associated.periodontitis via the activation of COX-2 which is augmented by oxidative stress and mediated by extracellular signal-regulated protein kinase signaling.