A combination of subtherapeutic doses of chemically modified doxycycline (CMT-8) and a bisphosphonate (clodronate) inhibits bone loss in the ovariectomized rat: a dynamic histomorphometric and gene expression study.

Recent studies have demonstrated that tetracyclines can reduce bone loss in the ovariectomized (OVX) rat model of osteoporosis. In the current study, a non-antimicrobial, chemically modified doxycycline (CMT-8), alone or in combination with a bisphosphonate (Clodronate), was evaluated in this model. Forty-two, 6month old, female rats were randomly assigned to the following groups, (6/ group): a) sham/vehicle, b) OVX/vehicle; c) OVX/1 mg/day CMT-8; d) OVX/2 mg/day CMT-8, e) OVX/1 mg/week Clodronate; and f) OVX/1 mg/day CMT-8 + 1 mg/week Clodronate, CMT-8 was administered by oral gavage, Clodronate injected S/C. Following sham surgery or OVX, the rats were treated for 90 days with CMT-8 or vehicle alone, injected at three different times with fluorochrome labels, the rats were sacrificed, and the tibiae excised for analysis by dynamic bone histomorphometry. Femurs were aseptically removed and analyzed for collagen, collagenase and osteopontin mRNAs by Northern and dot blot analysis. As expected, OVX decreased trabecular bone volume (BV/TV by 73.8% vs. sham p<.01), and also reduced trabecular thickness, numbers, and increased spacing. Bone loss in the OVX animals was partially prevented with either 2 mg/day CMT-8 or 1 mg/wk Clodronate (p<.01), while the 1 mg/day CMT-8 had no effect. Interestingly, the efficacy of the combination therapy of CMT-8 and Clodronate was significantly better than either treatment by itself, maintaining bone mass and structural indices at levels identical to sham values. OVX rats mRNA for collagen, collagenase and osteopontin were elevated indicating high-turnover bone loss. Only COMBO therapy significantly reduced the collagenase and osteopontin mRNA. In summary, CMT-8 mono-therapy (2 mg) alone partially inhibited bone loss in this animal model of osteoporosis. However, 1 mg/day (CMT-8) monotherapy had no effect on bone loss or bone mRNA levels and when combined with Clodronate, interacted to increase efficacy. Thus, a combination of a suboptimal dose of CMT-8 and a bisphosphonate appears to increase the amount of bone by suppressing resorption in a model of osteoporosis.

A chemically modified nonantimicrobial tetracycline (CMT-8) inhibits gingival matrix metalloproteinases, periodontal breakdown, and extra-oral bone loss in ovariectomized rats.

Estrogen deficiency in the postmenopausal (PM) female is the major cause of osteoporosis and may contribute to increased periodontal disease, including alveolar bone loss, seen in these women. In the current study, an animal model of PM osteoporosis, the OVX adult female rat, was studied to determine: (i) the relationship between periodontal breakdown and skeletal bone loss, and (ii) the effect of CMT-8 on gingival collagenase and bone loss. OVX rats were daily gavaged with CMT-8 (1, 2, or 5 mg/rat) for 28 or 90 days; non-OVX rats and those gavaged with vehicle alone served as controls. Elevated collagenase activity, assessed using [3H-methyl] collagen as substrate in the presence or absence of APMA, was seen in the gingiva of the OVX rats, and CMT-8 therapy suppressed this effect. Western blot revealed a similar pattern for MMP-8 and MMP-13 concentrations. The changes in the gingival collagenase activity paralleled changes in periodontal bone loss, which, in turn, reflected trabecular bone density changes. Preliminary studies on PM humans administered sub-antimicrobial tetracycline as a matrix metalloproteinase inhibitor are under way.

A combination of a chemically modified doxycycline and a bisphosphonate synergistically inhibits endotoxin-induced periodontal breakdown in rats.

BACKGROUND: Chemically modified non-antimicrobial tetracyclines (CMTs) have been shown to inhibit pathologically elevated collagenase (and other matrix metalloproteinase, MMP) activity and bone resorption in vivo and in vitro. METHODS: In the current study, suboptimal doses of CMT-8 (a non-antimicrobial chemically modified doxycycline) and a bisphosphonate (clodronate, an anti-bone resorption compound) were administered daily, either as a single agent or as a combination therapy, to rats with experimental periodontitis induced by repeated injection of bacterial endotoxin (LPS) into the gingiva. At the end of the 1-week protocol, the gingival tissues were dissected, extracted, and the extracts analyzed for MMPs (collagenases and gelatinases) and for elastase, and the defleshed jaws were morphometrically analyzed for alveolar bone loss. RESULTS: LPS injection significantly (P<0.001) increased alveolar bone loss and increased collagenase (MMP-8), gelatinase (MMP-9), and elastase activities. Treatment of the LPS-injected rats with suboptimal CMT-8 alone or suboptimal clodronate alone produced slight reductions in the tissue-destructive proteinases and no significant reductions in alveolar bone loss. However, a combination of suboptimal CMT-8 and clodronate "normalized" the pathologically elevated levels of MMPs, elastase, and alveolar bone loss, indicating synergistic inhibition of tissue breakdown in this animal model of periodontitis. CONCLUSIONS: Combination of a CMT and a bisphosphonate may be a useful treatment to optimally suppress periodontal destruction and tooth loss and in other tissue-destructive inflammatory diseases such as arthritis.