A supercritical licorice (Glycyrrhiza uralensis) extract inhibits growth of oral pathogens and reduces LPS-induced cytokine secretion by macrophages and whole blood

Periodontal diseases are a group of inflammatory diseases initiated by specific Gram-negative bacteria that lead to the destruction of tooth-supporting tissues. A CO₂-supercritical extract of licorice (G. uralensis) was able to inhibit growth (MIC values of 6.25µg/mL) of the periodontopathogenic bacteria Porphyromonas gingivalis and Prevotella intermedia.

The same extract exhibited potent anti-inflammatory properties, inhibiting the periodontopathogen LPS-induced production of IL-1β, TNF-α, IL-6 and IL-8 by macrophages in a dose-dependent manner (test concentrations of 5, 10 and 25µg/mL). This activity was shown to be in part due to the phosphorylation of important intracellular transcription factors, including NF-kappa-B p65 and Jun encoded AP1. The extract was also a potent inhibitor of the pro-inflammatory cytokine response in the ex-vivo human whole blood model.

Finally, the licorice was evaluated for its ability to inhibit collagenase in vitro. Neutrophil collagenases play a role in the pathological destruction of periodontal connective tissue in periodontitis. The extract showed a dose-dependent inhibition of Clostridium histolyticum collagenase with an IC₅₀ value of 108µg/mL.

The two main components of the extract were isolated and were identified as licoricidin and licorisoflavan A based on spectral data. Quantitative analysis by HPLC-UV showed that the extract contained 15.7% licoricidin and 5.2% licorisoflavan A. This CO₂ extract is a potential candidate for a product to prevent and/or treat periodontis-associated tissue destruction.