REACTIVE OXYGEN SPECIES ACTIVATE AND TETRACYCLINES INHIBIT RAT OSTEOBLAST COLLAGENASE

Recent studies have demonstrated that tetracyclines (TCs) scavenge rea ctive oxygen species (ROS). Hypochlorous acid (HOCl), an ROS produced by neutrophils, has been shown to activate neutrophil procollagenase. The objective of the present study was to determine whether (1) HOCl a lso activated osteoblast procollagenase and (2) TCs inhibited this enz yme in the presence of HOCl. HOCl (5 muM) activated the proenzyme appr oximately sixfold (P < 0.01) from the medium of PTH-treated UMR-106-01 osteoblastic osteosarcoma cells as determined by functional collagena se assay (H-3-methyl-labeled collagen substrate). Doxycycline (50-400 muM) and chemically modified tetracycline, CMT-1 (100-400 muM), signif icantly inhibited collagenase activity 50-90% and 40-80%, respectively , in the presence of 5 muM HOCl. Concentrations of 6-25 muM doxycyclin e and 10-50 muM CMT-1 had no significant effect. Furthermore, an exces s concentration of cation (50 mM CaCl2 or 50 muM ZnCl2) added to the i ncubation mixtures containing either doxycycline or CMT-1 did not rest ore collagenase activity, as demonstrated by SDS-PAGE-fluorography. Th ese data suggested that TCs reduced available HOCl and thus prevented the hypochlorous acid conversion of the osteoblast proenzyme to active collagenase. TCs may have therapeutic potential in the treatment of p eriodontitis and other diseases by several mechanisms that inhibit pat hologic collagen breakdown.