The applicability of virulence inhibitors as a therapy for Porphyromonas gingivalis infections

Date: 27 January 2015

Venue: CDE, Promotiezaal - Universiteitsplein 1 - 2610 Wilrijk

Time: 4:00 PM - 6:00 PM

PhD candidate: Sofie Clais

Principal investigator: Louis Maes

Co-principal investigator: Paul Cos

Short description: Public Defence Sofie Clais - Departement Pharmaceutical Sciences


The increase in antibiotic resistance urges the need for new therapies. A promising alternative strategy is the inhibition of bacterial virulence factors. Porphyromonas gingivalis, a major causative agent of periodontitis, possesses an arsenal of well characterised virulence factors, including dipeptidyl peptidase IV (DPPIV). The aim of this doctoral thesis was to elucidate the role of DPPIV as a virulence factor and to assess the applicability of DPPIV-inhibitors as an antivirulence therapy for P. gingivalis.

First, an in vitro model for P. gingivalis growth was implemented and three different quantification techniques were compared: viable plate count, turbidity and qPCR. Second, an in vitro biofilm model, with quantification of the total biofilm using crystal violet, was optimised. Finally, to evaluate in vivo pathogenicity, a murine abscess model, where mice were subcutaneously infected with P. gingivalis, was implemented.

Using these laboratory models, the role of DPPIV was assessed. Comparison of different P. gingivalis strains demonstrated high DPPIV activities for bacteria with good biofilm-forming properties. Moreover, the DPPIV activity even increased for sessile bacteria, suggesting a role for DPPIV during biofilm formation. Next, the hypothesis that P. gingivalis DPPIV contributes to tissue destruction by influencing the host inflammatory response was investigated. No effect of P. gingivalis DPPIV on the IL-8 production by human oral keratinocytes could be demonstrated. Nevertheless, when looking at human DPPIV, there is sufficient evidence to believe that P. gingivalis DPPIV influences the inflammatory process. To elucidate the exact role of P. gingivalis DPPIV in host immunity, future experiments are needed. Finally, the effect of DPPIV-inhibitors on P. gingivalis growth, biofilm formation and in vivo pathogenicity was assessed. Three lead compounds were selected from a library of structurally diverse inhibitors of dipeptidyl peptidases. In addition, also the commercial inhibitors vildagliptin and diprotin A were used. Unfortunately, none of the selected compounds demonstrated an effect, pointing to a low applicability of DPPIV-inhibitors as an antivirulence therapy for P. gingivalis. However, additional experiments are recommended before concluding the possible inefficacy of DPPIV-inhibitors. More inhibitors acting selectively on P. gingivalis DPPIV could be evaluated and their effect could be assessed in other laboratory models.