Hinokitiol acts against Porphyromonas gingivalis by inhibiting Autoinducer-2

Hinokitiol is a biocide and a preventive agent against gingival inflammation and periodontal infection. In this study, we evaluated the effects of hinokitiol on Porphyromonas gingivalis quorum sensing. Autoinducer-2 (AI-2) bioassay with Vibrio harveyi revealed that 20-300 μM hinokitiol supplementation inhibited V. harveyi luminescence caused by AI-2. Furthermore, hinokitiol inhibited the AI-2 activity in a culture supernatant of P. gingivalis. We assessed whether hinokitiol reduced biofilm formation and gingipain production at concentrations less than the bactericidal concentrations. A 96-well plate biofilm assay showed that hinokitiol reduced the biofilm biomass. Western blotting revealed that the expressions of membrane-bound Arg-gingipain, secreted Arg-gingipain and Lys-gingipain were suppressed by 30 μM of hinokitiol. These findings suggest that hinokitiol suppresses biofilm formation and gingipain production by inhibiting P. gingivalis quorum sensing by AI-2.