NFE2L2/NRF2, OGG1, and cytokine responses of human gingival keratinocytes against oxidative insults of various origin

Abstract

<div><h3>Objective</h3><p>Bacterial or tobacco-related insults induce oxidative stress in gingival keratinocytes. The aim of this study was to investigate anti-oxidative and cytokine responses of human gingival keratinocytes (HMK cells) against <em>Porphyromonas gingivalis</em> lipopolysaccharide (<em>Pg</em> LPS), nicotine, and 4-nitroquinoline <em>N</em>-oxide (4-NQO).</p></div><div><h3>Materials and methods</h3><p>HMK cells were incubated with <em>Pg</em> LPS (1 µl/ml), nicotine (1.54 mM), and 4-NQO (1 µM) for 24 h. Intracellular and extracellular levels of interleukin (IL)-1β, IL-1 receptor antagonist (IL-1Ra), IL-8, monocyte chemoattractant protein (MCP)-1, and vascular endothelial growth factor (VEGF) were measured with the Luminex® xMAP™ technique, and nuclear factor, erythroid 2 like 2 (NFE2L2/NRF2) and 8-oxoguanine DNA glycosylase (OGG1) with Western blots. Data were statistically analyzed by two-way ANOVA with Bonferroni correction.</p></div><div><h3>Results</h3><p>All tested oxidative stress inducers increased intracellular OGG1 levels, whereas only nicotine and 4-NQO induced NFE2L2/NRF2 levels. Nicotine, 4-NQO, and their combinational applications with <em>Pg</em> LPS induced the secretions of IL-1β and IL-1Ra, while that of IL-8 was inhibited by the presence of <em>Pg</em> LPS. MCP-1 secretion was suppressed by nicotine, alone and together with <em>Pg</em> LPS, while 4-NQO activated its secretion. Treatment of HMK cells with <em>Pg</em>LPS, nicotine, 4-NQO, or their combinations did not affect VEGF levels.</p></div><div><h3>Conclusion</h3><p><em>Pg</em> LPS, nicotine, and 4-NQO induce oxidative stress and regulate anti-oxidative response and cytokine expressions in human gingival keratinocytes differently. These results may indicate that bacterial and tobacco-related insults regulate distinct pathways.</p></div>