Nicotine, LPS, TNF?, and EGCG Differentially Affect Interleukin Secretion

Al Mouabbi, Assia, Michael Byars, and Michelle Wheater

Objectives: In smokers, oral epithelial cells exposed to nicotine can be further stressed by bacterial infection or inflammation. The objective of this study was to determine if epigallocatechin gallate (EGCG), a major catechin component of green tea, can influence cytokine expression in a human oral epithelial cell culture model of nicotine use. Methods: Commercially available human oral epithelial cells (ScienCell, Carlsbad, CA) were treated for 24 hours with 0.1 mM nicotine with or without 10 mg/ml LPS (to model bacterial infection) or 10 mg/ml TNFa (to model inflammation), in the presence or absence of 10 mg/ml EGCG. Culture medium samples were assayed for levels of secreted IL-1a, IL-1b, IL-4, IL-6, IL-8, or IL-10 using ELISA (RnD Systems Quantikine ELISA kits). Results were standardized to total cell number using crystal violet blue staining. Statistical analysis was completed for individual interleukins using ANOVA with probability set at p < 0.05. Results: The levels of IL-4 for all treatments were below the detection limit of the ELISA. For the remaining interleukins, EGCG suppressed (significantly in most treatment comparisons, p< 0.01) the secretion of IL-1b, IL-6, and IL-8. A decrease in interleukin secretion was especially noted in cells treated with TNFa. In contrast, the presence of EGCG resulted in an increase in the secretion of IL-10 (significantly in most treatment comparisons, p< 0.01). Images of treated cells did not reveal any significant differences in morphology. Conclusions: In tobacco users, a combination of nicotine and bacterial infection (LPS) or inflammatory reactions (TNF-a) results in increased cytokine production. This in turn may contribute to increased breakdown of periodontal tissues. This study suggests that tea catechins such as EGCG may function to suppress pro-inflammatory cytokines such as IL-6 and IL-8, and to increase the secretion of the anti-inflammatory cytokine IL-10.