A Licorice Extract Reduces Lipopolysaccharide-Induced Proinflammatory Cytokine Secretion by Macrophages and Whole Blood Charles Bodet,* Vu Dang La,* Stefan Gafner, † Chantal Bergeron, † and Daniel Grenier* Background: Periodontal diseases are a group of inflammatory dis- orders initiated by specific Gram-negative periodontopathogenic bacteria that lead to the destruction of tooth-supporting tissues. In this study, we tested whether a carbon dioxide–supercritical extract of Glycyrrhiza uralensis (licorice) can reduce the periodontopathogen- induced inflammatory response. Methods: Monocyte-derived macrophages were treated with various concentrations of the licorice extract prior to being stimulated with Aggre- gatibacter actinomycetemcomitans (previously Actinobacillus actino- mycetemcomitans) and Porphyromonas gingivalis lipopolysaccharide (LPS). The capacity of the licorice extract to mediate the inflammatory response was also tested in an ex vivo whole blood model stimulated with P. gingivalis LPS. The secretion of interleukin (IL)-1b, -6, and -8 and tumor necrosis factor-alpha (TNF-a) in both models was assessed by enzyme-linked immunosorbent assays. Changes in the phosphoryla- tion state of macrophage intracellular kinases induced by A. actinomyce- temcomitans LPS and the licorice extract in the macrophage model were characterized by immunoblotting. Results: The licorice extract exhibited potent anti-inflammatory prop- erties, inhibiting the periodontopathogen LPS-induced IL-1b, -6, and -8 and TNF-a responses of macrophages. The licorice extract inhibited the phosphorylation of important macrophage intracellular signaling proteins, including nuclear factor-kappa B p65 nuclear transcription fac- tor and Jun proto-oncogene-encoded activator protein (AP) 1 transcrip- tion factor, which are involved in inflammatory signaling pathways. The licorice extract was also a potent inhibitor of the proinflammatory cyto- kine response in the ex vivo human whole blood model. Conclusion: This CO 2 -supercritical licorice extract is a potential can- didate for the development of a new therapy to prevent and/or treat periodontitis-associated tissue destruction. J Periodontol 2008;79:1752- 1761. KEY WORDS Aggregatibacter actinomycetemcomitans; anti-inflammatory; cytokine; licorice; periodontitis; Porphyromonas gingivalis. P eriodontal diseases are complex, multifactorial, polymicrobial infections characterized by the destruction of tooth-supporting tissues. These in- flammatory diseases are initiated by an overgrowth of specific peri- odontopathogenic Gram-negative anaerobic bacteria that leads to gingival connective tissue destruc- tion and irreversible alveolar bone resorption. One of these bacterial species, Porphyromonas gin- givalis, is considered the major etiologic agent of chronic peri- odontitis, 1,2 whereas Aggregati- bacter actinomycetemcomitans (previously Actinobacillus actino- mycetemcomitans) has been im- plicated as an important etiologic agent of localized aggressive peri- odontitis. 3,4 The host response to these bacteria and their products, such as lipopolysaccharide (LPS), is a critical determinant for the initiation and progression of peri- odontitis. More specifically, the continuous, high secretion of var- ious cytokines, including interleu- kin (IL)-1b, -6, and -8 and tumor necrosis factor-alpha (TNF-a), by host cells following stimulation by periodontopathogens is be- lieved to modulate periodontal tissue destruction. 5,6 Monocytes * Research Group in Oral Ecology, Faculty of Dentistry, Laval University, Quebec City, QC. † Tom’s of Maine, Kennebunk, ME. doi: 10.1902/jop.2008.080052 Volume 79 • Number 9 1752