Host modulation with tetracyclines and their chemically modified analogues.

Recent studies have suggested the use of drugs to modulate host response as a new approach in periodontal therapy. In this regard, the tetracycline antibiotics have been found to inhibit host-derived collagenases and other matrix metalloproteinases by a mechanism independent of the antimicrobial activity of these drugs; this effect may suppress connective tissue breakdown during periodontal disease and during a variety of medical disorders including (but not limited to) noninfected corneal ulcers, serious (sometimes life-threatening) skin-blistering diseases, rheumatoid arthritis and osteoarthritis, systemically--as well as locally--induced bone loss, and perhaps even tumor-induced angiogenesis. Two therapeutic strategies based on the host-modulating properties of tetracyclines are currently being developed: 1) the use of low-dose doxycycline (the most potent anticollagenase of commercially available tetracyclines) formulations, which do not appear to result in tetracycline side effects such as the emergence of antibiotic-resistant microorganisms; and 2) the production of a family of chemically modified tetracyclines that have lost their antimicrobial activity, but have retained their anticollagenase activity. A description of several of these compounds and a discussion of their efficacy in inhibiting collagenases in vitro and reducing tissue destruction in several animal models of periodontal and medical diseases is presented.