Background: Cigarette smoking is a major risk factor in the development and further progression of periodontal diseases. COX-2 is an inducible enzyme believed to be responsible for prostaglandin synthesis at site of inflammation. Currently, there is limited information on the regulation of COX-2 expression in smoking-associated periodontal disease. Objectives: The aim of the present study was to investigate the effects of nicotine on the expression of cyclooxygenase-2 (COX-2) mRNA gene and protein in cultured human gingival fibroblasts (HGFs). Furthermore, to elucidate whether induction of COX-2 may be associated with nicotine- induced cytotoxicity, NS-398 (a selective COX-2 inhibitor), was added to test its protective effect. Methods: The quantitative reverse-transcriptase polymerase chain reaction and Western blot assays were used to investigate the effects of human HGFs exposed to nicotine. In addition, NS-398 was added to test how it modulated the effects of nicotine. Results: The exposure of quiescent human HGFs to nicotine resulted in the induction of COX-2 mRNA expression. The levels of the COX-2 mRNAs increased about 1.5 and 2.5 fold after exposure to 2.5 and 15 mM nicotine for 2 h (P < 0.05), respectively. Moreover, the peak of COX-2 mRNA levels induced by nicotine was 10 mM at 2 h incubation period. Investigations of the time dependence of COX-2 mRNA expression in nicotine-treated HGFs revealed a rapid accumulation of the transcript, a signal first detectable at 30 min and diminished to control level after 8 h. In addition, 10 mM nicotine also induced COX-2 protein expression in HGFs. The kinetics of this response showed that COX-2 was detectable at 4 h and diminished nearly to control level after 24 h. NS-398 at non-cytotoxic dose is not able to prevent nicotine-induced cytotoxicity. Conclusions: Taken together, the activation of COX-2 expression by nicotine suggests a potential role for nicotine in the pathogenesis of smoking-associated periodontal disease. In addition, nicotine-induced cytotoxicity is not directly via the induction of COX-2 expression.
