Analysis of pharmacokinetics and PK/PD indices of doxycycline in plasma, gingival crevicular fluid and saliva and evaluation of its effect on the osteoclastogenesis RANKL-mediated.

Author(s)

Gilson Cesar Nobre Franco

• Document type: Doctoral Thesis
• Press: Piracicaba, SP.
• Institution: Universidade Estadual de Campinas (UNICAMP). Faculdade de Odontologia de Piracicaba
• Defense date: 2007-01-30

Examining board members

Pedro Luiz Rosalen; Marcia Pinto Alves Mayer; Rogério Heládio Lopes Motta; Sheila Cavalca Cortelli; Antonio Paulino Ribeiro Sobrinho

• Advisor: Toshihisa Kawai; Francisco Carlos Groppo; Pedro Luiz Rosalen

Abstract

Doxycycline (Dox), a member of the tetracycline family, is an antimicrobial agent with a broad-spectrum of activity against Gram-positive and Gram-negative bacteria. In addition to its antimicrobial properties, Dox is used in the treatment of periodontal diseases as a host response modulator by inhibiting the activity of an important enzyme, matrix metalloproteinase (MMP), which is related to the process of tissue destruction. In this context, this study had the following aims: 1-to determine the pharmacokinetic parameters of Dox and to integrate the PK/PD indices for plasma, gingival crevicular fluid (GCF) and saliva; 2-to analyze the effects in vitro and in vivo of Dox on the osteoclastogenesis and on the osteoclast activation in order to elucidate additional biological properties of Dox on the host response modulation (HRM). Twelve volunteers received single oral administration of Dox (100 mg). Blood, GCF and saliva were collected and the concentrations were measured by bioassay technique. The PK/PD analyses were carried out using the MIC for P. gingivalis. For the second objective, the effect of Dox on the osteoclast differentiation and activation processes was determined, respectively, by the counting of TRAP+ multinuclear cells derived from osteoclast precursory cells sRANKL-stimulated in the presence or absence of Dox and by the analysis of the resorption areas formed by these cells when cultured on dentin discs. In vivo, Dox¿s effect on the osteoclastogenesis was verified using the model of osteoclastogenesis induction in mouse calvaria. sRANKL/LPS was injected in the supra-calvaria area and the animals received Dox or placebo daily by gavage. After the experimental period of 10 days, the calvariae were removed for histochemistry analyses. In addition, the effect of Dox on the expression of genes related to the osteoclast differentiation and activation processes was carried out using RT-PCR technique. MMP production and activity were ensured during in vitro and in vivo experiments by Western-blot and Zymography, respectively. The results demonstrated that Dox achieved the highest concentration in the plasma, following by GCF and saliva. PK/PD analyses showed that the dose of 100 mg was insufficient to get the antimicrobial levels indicated in the literature for AUC/MIC and Cmax/MIC indices. In vitro and in vivo studies of Dox¿s effects on the HRM demonstrated that this drug could inhibit the osteoclast differentiation and activation process. Dox also showed an important property of down-regulation in the expression of proteins directly related to osteoclastogenesis, including TRAP, Cathepsin K and c-Myc. Finally, although Dox did not affect the expression of MMP protein, MMP activity was remarkably decreased by Dox. Therefore, the present study suggests that higher doses than 100 mg would be necessary to obtain effective antimicrobial levels and the effect of DOX on the HRM can be due to not only by MMP inhibition but also by the direct effect on RANKL-mediated osteoclast differentiation and activation, including its gene regulation (AU)