Synergistic Effect of Hemoglobin and Lipopolysaccharide on Macrophage Inflammatory Response

Periodontitis is a chronic inflammatory disease affecting the tooth-supporting tissue. The continuous and high cytokine production by host cells, including macrophages, triggered by periodontopathogens and more specifically by lipopolysaccharides (LPS) is thought to be responsible of periodontal tissue destruction. Vascular disruption and bleeding occuring during periodontitis is likely to increase the levels of hemoglobin in gingival crevicular fluid. Objective: The aim of this study was to investigate the effect of hemoglobin on the inflammatory response of macrophages stimulated with LPS isolated from periodontopathogens. Methods: The production of interleukin-1 beta (IL-1b), interleukin-6 (IL-6), interleukin-8 (IL-8), tumor necrosis factor alpha (TNF-a), and Regulated on Activation Normal T cell Expressed and Secreted (RANTES) by macrophage-like cells (phorbol myristic acid-differentiated U937 monocytic cell line) following challenges with LPS from Porphyromonas gingivalis and Actinobacillus actinomycetemcomitans in the presence and absence of human hemoglobin was analyzed by ELISA. Results: Hemoglobin and LPS from periodontopathogens acted in synergy to stimulate higher production of IL-1b, IL-6, and IL-8 by macrophages. For instance, when LPS were used at 0.1 mg/ml, synergistic effects were observed in the presence of hemoglobin at 50 mg/ml. Conclusion: This study suggests that hemoglobin contributes to enhance the levels of pro-inflammatory mediators in periodontal sites by acting in synergy with LPS of periodontopathogens. Such a phenomenon may favor the progression of periodontitis. This study was supported by the Canadian Institutes of Health Research.