Effect of Fibrinogen on Secretion of Pro-inflammatory Cytokines by PMNs

Objectives: Increasing evidences confirm the relation between periodontal disease and cardiovascular disease, although the biological basis is unclear. Previous studies have shown that pro-inflammatory cytokines are key mediators of the inflammatory process in periodontal disease. We investigate the effect of human fibrinogen, an independent risk factor for cardiovascular disease, on the release of pro-inflammatory cytokines of polymorphonuclear leukocytes (PMNs) and sought to explore the mechanisms responsible for the correlation between periodontal disease and cardiovascular disease. Methods: Peripheral PMNs of advanced periodontitis patients and periodontal healthy controls were isolated by discontinuous density gradient centrifugation. The freshly isolated PMNs were cultured in vitro with immobilized human fibrinogen precoated onto the cell culture plates at different concentration (0mg/ml, 2mg/ml and 10mg/ml) and incubated for different time periods (2h, 8h and 24h).The levels of interleukin-1b (IL-1b) and IL-8 in the supernatants produced by cultured cells upon adhesion to immobilized fibrinogen were measured by ELISA technique. N-Formyl-Met-Leu-Phe (fMLP) was used as positive control. Results: After adhesion to immobilized human fibrinogen, the PMNs of periodontal healthy subjects and advanced periodontitis patients secreted significantly higher levels of IL-1b（P＜0.001） and IL-8（P≤0.016）than negative control and fMLP groups. Fibrinogen induced secretion of these pro-inflammatory cytokines by PMNs in a dose- and time-dependent manner. The higher fibrinogen concentration or the longer treatment time, the higher levels of IL-1b and IL-8 were found in the cell supernatants. Fibrinogen tends to stimulate more secretion of these pro-inflammatory cytokines in advanced periodontitis patients than in periodontal healthy controls. Conclusions: Fibrinogen induced the secretion of pro-inflammatory cytokines IL-1b and IL-8 by PMNs and may be involved in magnification of the inflammatory response of periodontium and bone resorption. The present findings indicate that fibrinogen may represent a possible candidate factor that links periodontal disease with cardiovascular disease.