Inhibitors of bacterial protease enzymes for periodontal therapy.

Locally applied therapeutic agents have become established in the treatment of periodontal disease. Inhibition of human metalloproteases by metal-chelating antibiotics contributes to the utility of local therapy. Adding inhibitors of bacterial proteases might extend and improve local therapy. The periodontal pathogen (Pg) produces two extracellular cysteine proteases (gingipains Rgp and Kgp) that are virulence factors and contribute to destruction of oral tissues. Our aims were to compare efficacy of protease inhibitors against gingipains and evaluate bactericidal activity of the inhibitors. Protease activity was measured in fluorescent assays with specific Rgp and Kgp substrates. Bacterial viability was measured with Light™ (Invitrogen, Inc., Carlsbad, CA) reagents. Pairs of inhibitors of Rgp and Kgp, respectively, were leupeptin and cathepsin B inhibitor II, KYT-1 and KYT-36, and PPACK and Z-FK-ck. The cysteine-protease inhibitor E64 was also tested. Rgp activity was higher than Kgp activity, and activity was higher in Pg 33277 and 49417 cell suspensions than in media. Concentrations required for 50% inhibition of Rgp in cell suspensions were 2 × 10, 2 × 10, 2 × 10, and 5 × 10 M for KYT-1, PPACK, leupeptin, and E64, respectively. Concentrations required for 50% Kgp inhibition were 5 × 10, 1 × 10, and 5 × 10 M for Z-FK-ck, KYT-36, and cathepsin B inhibitor II. E64 did not inhibit Kgp. Inhibition of Rgp could be accounted for by competition for binding between the arginine residue of the substrate and the guanidinobutane portion of E64. PPACK was the least selective, with a 10-fold difference in concentrations that inhibited Rgp and Kgp. KYT-1 and Z-FK-ck inhibited both Rgp and Kgp, but inhibitory concentrations differed by 10,000-fold. At up to 1 × 10 M, only Z-FK-ck was bactericidal. KYT-1 and KYT-36 were remarkably effective even when used in cell suspensions in which bacterial proteins could bind inhibitors or compete for binding to gingipains. These inhibitors might prove useful as an addition to locally applied therapeutic agents.