Mechanisms of cytotoxicity of nicotine in human periodontal ligament fibroblast cultures in vitro

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Abstract
The use of tobacco products significantly contributes to the progression of periodontal disease and poor response to healing following periodontal therapy. The purpose of this study was to determine the effects of nicotine, a major component of cigarette smoking, on human periodontal ligament fibroblast (PDLF) growth, proliferation, and protein synthesis to elucidate its role in periodontal destruction associated with its use. Human PDLFs were derived from three healthy individuals undergoing extraction for orthodontic reasons. At a concentration higher than 2.5 mM, nicotine was found to be cytotoxic to human PDLFs (P < 0.05). Nicotine also significantly inhibited cell proliferation and decreased protein synthesis in a dose‐dependent manner. At concentrations of 50 and 200 µM, nicotine suppressed the growth of PDLFs by 48% and 86% (P < 0.05), respectively. A 10‐mM concentration level of nicotine significantly inhibited the protein synthesis to only 44% of these in the untreated control (P < 0.05). Furthermore, the effects of antioxidants (superoxide dismutase (SOD); catalase and 2‐oxothiazolidine‐4‐carboxylic acid (OTZ) and buthionine sulfoximine (BSO) were added to search for the possible mechanism of action, as well as a method for the prevention, of cigarette smoking‐associated periodontal diseases. The addition of OTZ, a precursor of cysteine that metabolically promotes GSH synthesis, acted as a protective effect on the nicotine‐induced cytotoxicity. However, SOD and catalase did not decrease the nicotine‐induced cytotoxicity. In contrast, the addition of BSO, a cellular GSH synthesis inhibitor, enhanced the nicotine‐induced cytotoxicity. These results indicate that thiol depletion could be the mechanism for nicotine cytotoxicity. The levels of nicotine tested inhibited cell growth, proliferation, and protein synthesis on human PDLFs. This suggests that nicotine itself might augment the destruction of periodontium associated with cigarette smoking. In addition, these inhibitory effects were associated with intracellular thiol levels. Factors that induce glutathione synthesis of human PDLF may be used for further chemoprevention of cigarette smoking‐related periodontal diseases.