Faculty Bibliography

Tetracyclines have nonantimicrobial properties that appear to modulate host response. In that regard, tetracyclines and their nonantimicrobial chemically modified analogues (chemically modified tetracycline molecules [CMTs]) inhibit the extracellular activity of mammalian neutrophil and osteoblast collagenases. The activity of this matrix metalloproteinase appears crucial in the destruction of collagen. Apart from its anticollagenase effect, tetracyclines are also potent inhibitors of osteoclast function. Several recent studies have also addressed the therapeutic potential of tetracyclines and CMTs in periodontal disease. These drugs reduced excessive gingival collagenase activity and severity of periodontal breakdown in rats infected with Porphyromonas gingivalis and in diabetic rats. CMT was not associated with the emergence of resistant microorganisms. In human double-blind clinical trials, low-dose doxycycline therapy substantially reduced collagenase activity in the gingival and crevicular fluid, and prevented the loss of attachment in adult periodontitis without the emergence of doxycycline-resistant microorganisms. Tetracyclines and CMTs have enormous therapeutic potential because these drugs can inhibit the activity of matrix metalloproteinases as well as osteoclast function, and thus prevent the degradation of osseous connective tissues in periodontal as well as arthritic diseases

Recent studies have demonstrated that tetracyclines (TCs) scavenge reactive 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 also activated osteoblast procollagenase and (2) TCs inhibited this enzyme in the presence of HOCl. HOCl (5 microM) activated the proenzyme approximately sixfold (P < 0.01) from the medium of PTH-treated UMR-106-01 osteoblastic osteosarcoma cells as determined by functional collagenase assay (3H-methyl-labeled collagen substrate). Doxycycline (50-400 microM) and chemically modified tetracycline, CMT-1 (100-400 microM), significantly inhibited collagenase activity 50-90% and 40-80%, respectively, in the presence of 5 microM HOCl. Concentrations of 6-25 microM doxycycline and 10-50 microM CMT-1 had no significant effect. Furthermore, an excess concentration of cation (50 mM CaCl2 or 50 microM ZnCl2) added to the incubation mixtures containing either doxycycline or CMT-1 did not restore collagenase activity, as demonstrated by SDS-PAGE-fluorography. These 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 periodontitis and other diseases by several mechanisms that inhibit pathologic collagen breakdown

Tetracyclines (TCs) have wide therapeutic usage as antimicrobial agents; these drugs (e.g., minocycline, doxycycline) remain useful as adjuncts in periodontal therapy. However, TCs also have non-antimicrobial properties which appear to modulate host response. In that regard, TCs and their chemically-modified analogs (CMTs) have been shown to inhibit the activity of the matrix metalloproteinase (MMP), collagenase. The activity of this enzyme appears crucial in the destruction of the major structural protein of connective tissues, collagen. Such pathologic collagenolysis may be a common denominator in tissue destructive diseases such as rheumatoid and Osteoarthritis, diabetes mellitus, bullous dermatologic diseases, corneal ulcers, and periodontitis. The mechanisms by which TCs affect and, possibly, diminish bone resorption (a key event in the pathogenesis of periodontal and other diseases) are not yet understood. However, a number of possibilities remain open for investigation including the following: TCs may 1) directly inhibit the activity of extracellular collagenase and other MMPs such as gelatinase; 2) prevent the activation of its proenzyme by scavenging reactive oxygen species generated by other cell types (e.g. PMNs, osteoclasts); 3) inhibit the secretion of other collagenolytic enzymes (i.e. lysosomal cathepsins); and 4) directly affect other aspects of osteoclast structure and function. Several recent studies have also addressed the therapeutic potential of TCs and CMTs in periodontal disease. These drugs reduced excessive gingival collagenase activity and severity of periodontal breakdown in rats infected with Porphyromonas gingivalis and in diabetic rats. Furthermore, the latter drug (CMT) was not associated with the emergence of TC-resistant microorganisms. In human clinical trials, low-dose doxycycline therapy substantially reduced collagenase activity in the gingiva and GCF, and prevented the loss of attachment in adult periodontitis. Clearly, the non-antimicrobial properties of TCs have enormous medical and dental therapeutic potential since these drugs can inhibit the activity of MMPs and their degradation of non-osseous and osseous connective tissues. J Periodontol 1993; 64:819-827.

The present study was designed to further understand the role of PTH on the secretion of the neutral metalloproteinases, collagenase and gelatinase, from the rat osteosarcoma clonal cell line, ROS 17/2.8. Semiconfluent cells were treated with bovine parathyroid hormone, b-PTH-(1-34) at 100 nM-0.01 nM for 24-96 hours and pooled, concentrated media were analyzed by functional assay for collagenase (3H-methyl collagen) and gelatinase (3H-methyl gelatin). Collagenase activity significantly decreased (P less than 0.01) in the PTH conditioned media in a dose-dependent manner before (98-64%) and after (91-39%) reduction and alkylation. SDS-PAGE and fluorography apparently showed the most degradation to alpha A chains in collagen with controls, whereas this substrate remained intact with PTH (100 nM). PTH (100 nM) media also showed neutral gelatinase activity approximately 2% compared to control before and after reduction and alkylation (P less than 0.01). Significant amounts of an inhibitor to collagenase and gelatinase might have been secreted at 1 nM and 0.01 nM PTH, since collagenase and gelatinase activities were greater after reduction and alkylation. Reduction and alkylation likely destroyed these significant amounts of inhibitor. Polymorphonuclear leukocyte collagenase activity was also inhibited 80% by PTH conditioned media, but not by control. However, upon reduction and alkylation which destroyed inhibitor, the PTH treated media showed only a 14% inhibition against polymorphonuclear leukocyte collagenase (P less than 0.01). PTH appeared to downregulate neutral metalloproteinase activities through its effects on an inhibitor. This downregulation may represent a specific phenotypic response to PTH in ROS 17/2.8 cells