Nicotine and Smokeless Tobacco effects on gingival and Peripheral Blood Mononuclear Cells

The pathogenesis of tobacco-related periodontal diseases is not well understood. The purpose of this study was therefore to investigate smokeless tobacco extract (ST) and nicotine effects on prostaglandin E₂ (PGE₂) and interleukin-1β (IL-1β) secretion by peripheral blood mononuclear cells (PBMC, consisting of monocytes and lymphocytes) and gingival mononuclear cells (GMC). Both peripheral blood and gingival tissue adjacent to the alveolar crest were taken from non-smoking adult periodontitis patients. Gingival tissue was treated with collagenase and deoxyribonuclease and GMC and PBMC were isolated by Ficoll-Hypaque centrifugation. GMC and PBMC (100,000 cells/200 μl) were cultured for 24 hours in supplemented RPMI 1640 alone (control), or in supplemented RPMI 1640 containing 1% ST, 100 μg/ml nicotine, 1 μg/ml Porphyromonas gingivalis LPS, or 1 μg/ml P. gingivalis LPS and either 100 μg/ml nicotine or 1% ST. Enzyme immunoassays were used to quantify PGE₂ and IL-1β. Treatments were compared by repeated measures ANOVA. 100 μg/ml nicotine (7-fold, p<0.02) and 1% ST (3.5-fold, p<0.004) significantly increased secretion of PGE₂ by PBMC relative to control cultures. 100 μg/ml nicotine and 1% ST, however, had no effect on IL-1β secretion by PBMC. Enhanced PGE₂ secretion also was seen when PBMC were treated with P. gingivalis LPS+100 μg/ml nicotine relative to P. gingivalis LPS alone (p<0.007). In contrast, 100 μg/ml nicotine significantly downregulated IL-1β secretion by GMC relative to medium alone (p<0.008) and had no effect on PGE₂ secretion by GMC. These data indicate that while nicotine and ST can stimulate PBMC to secrete PGE₂, they cannot activate further mononuclear cells extracted from gingiva, possibly due to maximal previous stimulation in the periodontitis lesion.