Inhibition of matrix metalloproteinase-mediated periodontal bone loss in rats: a comparison of 6 chemically modified tetracyclines.
BACKGROUND
Chemically modified tetracyclines (CMTs), devoid of antimicrobial activity, inhibit pathologically elevated collagenase activity both in vivo and in vitro. In the current study, doxycycline and 5 different CMTs were tested to prevent matrix metalloproteinase (MMP)-dependent periodontal tissue breakdown in an animal model of periodontitis.


METHODS
Adult male rats received intragingival injections with either 10 microl of physiologic saline or Escherichia coli endotoxin (1 mg/ml) every other day for 6 days and were distributed into 8 treatment groups (12 rats/group): saline (S), endotoxin alone (E), E + CMT-1, E + CMT-3, E + CMT-4, E + CMT-7, E + CMT-8, and doxycycline. All animals were treated daily with 1 ml of 2% carboxymethyl cellulose (CMC) alone or containing one of the above-mentioned CMTs (2 mg/day) orally. The gingival tissues were removed, extracted, and assayed for gelatinase (GLSE). Some rat maxillary jaws from each treatment group were fixed in buffered formalin and processed for histology and immunohistochemistry for the cytokines tumor necrosis factor (TNF), interleukin (IL)-1, and IL-6, and MMP-2 and MMP-9.


RESULTS
Endotoxin injection induced elevated GLSE activity (functional assay and osteoclast-mediated bone resorption), the former identified as predominantly MMP-9 (92 kDa GLSE) by gelatin zymography. All 6 tetracyclines (2 mg/day) inhibited periodontal breakdown in the following order of efficacy: CMT-8 > CMT- 1 > CMT-3 > doxycycline > CMT-4 > CMT-7. Immunohistochemistry was positive for TNF, IL-1, and IL-6 in the inflammatory cells from untreated endotoxin rat tissues, whereas treatment with CMTs decreased the number of immuno-positive stained cells for cytokines and MMPs. The in vivo efficacy of these drugs varied with CMT structure and was significantly correlated with bone resorption: r2 = -0.77, P<0.01; gelatinase inhibitory activity: r2 = -0.84, P <0.01; and serum drug concentrations.


CONCLUSIONS
Since both conventional (antimicrobial) and non-antimicrobial tetracyclines inhibited periodontal bone resorption induced by endotoxin injection, MMP-mediated bone loss in this model can be prevented by inhibition of MMPs.
Ramamurthy
Nungavarum S
NS
State University of New York at Stony Brook, Department of Oral Biology and Pathology, School of Dental Medicine, 11794-8702, USA. nramamur@epo.hsc.sunysb.edu
Rifkin
Barry R
BR
Greenwald
Robert A
RA
Xu
Jing-Wen
JW
Liu
Yu
Y
Turner
Gloria
G
Golub
Lorne M
LM
Vernillo
Anthony T
AT
D016301:Alveolar Bone Loss / Q000139:chemically induced / Q000188:drug therapy* / Q000201:enzymology*; D000704:Analysis of Variance; D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology / Q000627:therapeutic use; D004195:Disease Models, Animal; D004318:Doxycycline / Q000494:pharmacology / Q000627:therapeutic use; D004591:Electrophoresis, Polyacrylamide Gel; D004731:Endotoxins; D018093:Gelatinases / Q000037:antagonists & inhibitors*; D007124:Immunoenzyme Techniques; D007378:Interleukins / Q000032:analysis; D008297:Male; D010518:Periodontitis / Q000139:chemically induced / Q000188:drug therapy* / Q000201:enzymology*; D011480:Protease Inhibitors / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013754:Tetracyclines / Q000494:pharmacology* / Q000627:therapeutic use; D014409:Tumor Necrosis Factor-alpha / Q000032:analysis
D000900:Anti-Bacterial Agents; D004731:Endotoxins; D007378:Interleukins; D011480:Protease Inhibitors; D013754:Tetracyclines; D014409:Tumor Necrosis Factor-alpha; D018093:Gelatinases; D004318:Doxycycline