Regulation of HO-1 expression by nicotine in human gingival fibroblasts

Objectives: Cigarette smoking is a major risk factor in the development and further progression of periodontal diseases. Heme oxygenase-1 (HO-1) is known as a stress-inducible protein and functions as an antioxidant enzyme. There is limited information on the expression of HO-1 in smoking-associated periodontal disease. The aim of the present study was to investigate the effects of nicotine on the expression of HO-1 protein in cultured human gingival fibroblasts (HGFs) in vitro and further to compare HO-1 expression in gingival tissues obtained from cigarette smokers and non-smokers in vivo. Methods: Western blot assay was used to investigate the effects of HGFs exposed to nicotine. In addition, antioxidants catalase, superoxide dismutase (SOD), and N-acetyl-L-cysteine (NAC) were added to test how they modulated the effects of nicotine-induced HO-1 expression. Gingival biopsies taken from the flap surgery of twenty male patients with periodontal disease (ten cigarette smokers and ten non-smokers) were examined by immunohistochemistry. Results: The exposure of quiescent human HGFs to 10 mM nicotine resulted in the induction of HO-1 protein expression in a time-dependent manner (p<0.05). The addition of glutathione (GSH) precursor NAC inhibited the nicotine-induced HO-1 protein expression (p<0.05). However, SOD and catalase did not decrease the nicotine-induced HO-1 protein expression (p>0.05). The results form immunohistochemistry demonstrated that HO-1 expression was significantly higher in cigarette smokers (p<0.05). HO-1 was noted in the basal layers of epithelium, inflammatory cells, and fibroblasts in cigarette smoking specimens. Conclusions: Taken together, these results suggest that HO-1 expression is significantly upregulated in gingival tissues from cigarette smokers and nicotine may among other constituents be responsible for the enhanced HO-1 expression in vivo. The regulation of HO-1 expression induced by nicotine is critically dependent on the intracellular GSH concentration. This study was supported by NSC93-2314-B-040-019.