THE EXPRESSION OF COLLAGEN-I AND COLLAGEN-XII MESSENGER-RNA IN PORPHYROMONAS-GINGIVALIS-INDUCED PERIODONTITIS IN RATS - THE EFFECT OF DOXYCYCLINE AND CHEMICALLY-MODIFIED TETRACYCLINE

TISSUE REMODELING IS A DYNAMIC State in which a balance is achieved be tween the proteolytic breakdown and synthesis of the extracellular mat rix. Type I collagen is a major component of the gingival connective t issue (GCT) and the periodontal ligament (PDL) throughout development, while type XII collagen has been found in the mature forms of these t issues. The purpose of this study was to investigate the effects of pe riodontitis on the expression of type I and XII collagen and subsequen tly to investigate the effects of doxycycline (DOXY) and chemically mo dified nonantimicrobial tetracycline (CMT-1) on the expression of thes e molecules in this model. Adult barrier-raised male Sprague-Dawley ra ts were inoculated with Porphyromonas gingivalis obtained from humans to create the experimental periodontitis. The animals with the P. ging ivalis-induced periodontitis were then split into the following groups : Group A served as infected untreated controls (PGI group); group B w as treated with doxycycline (DOXY group); and group C was treated with chemically modified tetracycline-l (CMT-1 group). Group D contained u ninfected animals that served as uninfected controls (NIC group). The expression of type I and XII collagen mRNAs was examined by in situ hy bridization in each group, with the co-expression of these molecules r epresenting mature and functional gingival connective tissue. In the N IC group, cells hybridized with digoxygenine-labeled cDNA probes encod ing rat alpha 2(I) or alpha 1(XII) collagens were found distributed un iformly throughout the periodontal connective tissue. The PGI group sh owed little hybridization in the areas of infection, while both the DO XY and CMT-1 groups showed co-expression of the alpha 2(I) and al(XII) probes in the GCT and coronal part of the PDL. This study demonstrate s that doxycycline and CMT-1 moderate or reduce the inhibitory effects of periodontal infection on the expression of type I and type XII col lagen mRNAs. These results suggest that doxycycline and a form of non- antimicrobial tetracycline, chemically modified tetracycline-l, can re duce periodontal destruction by reversing the inhibitory effect of per iodontal infection on collagen synthesis.