In this study, we developed a procedure to produce gingivitis in rats by in
oculation of Porphyromonas gingivalis and studied the contribution of the b
acterial cysteine proteinases, Arg-gingipain (Rgp) and Lys-gingipain (Kgp),
to the pathology in the gingiva. To adhere the bacterium to periodontal ti
ssues, a cotton thread was inserted between the first and second molar of r
ight maxillary sites of rats. Rats in group A were administered with vehicl
e alone after bacterial (strain W83) inoculation. In group B, the bacteria
were inoculated in combination with leupeptin, a potent inhibitor of Rgp an
d Kgp, and then leupeptin alone was administered the week after. Rats in gr
oup C were administered leupeptin for 6 weeks after bacteria inoculation. A
ll left maxillary gingiva in three groups showed no inflammatory changes. R
ight maxillary gingiva of group A showed most of the clinical landmarks of
gingivitis. Leupeptin exhibited only a little inhibitory effect on this gin
givitis in group B, whereas it had a strong inhibitory effect on the inflam
mation in group C. These results suggest that P. gingivalis-induced gingivi
tis is attributable to Rgp and Kgp and that leupeptin is more effective in
the late phase than the early stage of gingivitis.