Minocycline reduces gingival collagenolytic activity during diabetes. Preliminary observations and a proposed new mechanism of action

Modulation of the host response in periodontal therapy

This paper was prepared by the Research, Science, and Therapy Committee of the American Academy of Periodontology to provide the dental profession an overview of current and potential methods to modulate the host response in the treatment of periodontal diseases. Specifically, it discusses components of periodontal disease pathogenesis (i.e., immune and inflammatory responses, excessive production of matrix metalloproteinases and arachidonic acid metabolites, and regulation of bone metabolism) and their modulation.

Effect of antibiotics on in vitro and in vivo avian cartilage degradation

Antibiotics are used in the livestock industry not only to treat disease but also to promote growth and increase feed efficiency in less than ideal sanitary conditions. However, certain antibiotic families utilized in the poultry industry have recently been found to adversely affect bone formation and cartilage metabolism in dogs, rats, and humans. Therefore, the first objective of this study was to determine if certain antibiotics used in the poultry industry would inhibit in vitro cartilage degradation. The second objective was to determine if the antibiotics found to inhibit in vitro cartilage degradation also induced tibial dyschondroplasia in growing broilers. Ten antibiotics were studied by an avian explant culture system that is designed to completely degrade tibiae over 16 days. Lincomycin, tylosin tartrate, gentamicin, erythromycin, and neomycin sulfate did not inhibit degradation at any concentration tested. Doxycycline (200 microg/ml), oxytetracycline (200 microg/ml), enrofloxacin (200 and 400 microg/ml), ceftiofur (400 microg/ml), and salinomycin (10 microg/ml) prevented complete cartilage degradation for up to 30 days in culture. Thus, some of the antibiotics did inhibit cartilage degradation in developing bone. Day-old chicks were then administered the five antibiotics at 25%, 100%, or 400% above their recommended dose levels and raised until 21 days of age. Thiram, a fungicide known to induce experimental tibial dyschondroplasia (TD), was given at 20 ppm. Birds were then killed by cervical dislocation, and each proximal tibiotarsus was visually examined for TD lesions. The results showed that none of these antibiotics significantly induced TD in growing boilers at any concentration tested, whereas birds given 20 ppm thiram had a 92% incidence rate.

Chemically modified tetracycline (CMT-8) and estrogen promote wound healing in ovariectomized rats: effects on matrix metalloproteinase-2, membrane type 1 matrix metalloproteinase, and laminin-5 gamma2-chain

Estrogen deficiency is associated with impaired cutaneous wound healing. Remodeling of the extracellular matrix in wound healing involves the action of matrix metalloproteinases on basement membrane zone components, especially laminin-5. We studied the effects of estrogen and a potent matrix metalloproteinase inhibitor, chemically modified non-antimicrobial tetracycline, CMT-8, on wound healing in ovariectomized rats. At the tissue level, laminin-5 gamma2-chain expression was decreased and the migration-inductive 80 kDa form of laminin-5 gamma2-chain was absent in ovariectomized rats when compared with sham and CMT-8- or estrogen-treated ovariectomized animals as detected by Western blotting. The highest levels of gelatinolytic activity (matrix metalloproteinase-2 and -9) were found in sham animals. Levels were reduced in ovariectomized rats and were lowest after treating ovariectomized rats with CMT-8 or estrogen as analyzed by functional activity assay and zymography. The total amount of membrane type 1-matrix metalloproteinase was unchanged in all groups. We conclude that CMT-8 and estrogen can promote wound healing in ovariectomized rats, not only by normalizing wound bed total collagen content and structure, but also by recovering the expression and processing of key molecules in wound healing, i.e., laminin-5 gamma2-chain. This study shows, for the first time, the role of estrogen and CMT-8 in laminin-5 gamma2-chain modulation in vivo.

Inhibition of proteolytic, serpinolytic, and progelatinase-b activation activities of periodontopathogens by doxycycline and the non-antimicrobial chemically modified tetracycline derivatives

BACKGROUND

Tetracyclines, particularly doxycycline (Doxy), and their non-antimicrobial chemically-modified derivatives (CMTs) inhibit the activities of human matrix metalloproteinases (MMPs), and reduce the severity and progression of periodontal disease in animal models and humans. In this study, the effects of Doxy and CMT-1, -3, and -5 on proteolytic, serpinolytic, and progelatinase-B activation activities of potent periodontopathogens were studied.

METHODS

The effect of Doxy and CMTs (0.5 to 50 microM) on proteolytic activities were investigated by incubating bacteria with chromogenic substrates or human serum albumin. A collagenolytic fraction of Porphyromonas gingivalis was used to evaluate the effect of these substances on collagenolytic (type I collagen) and serpinolytic (alpha1-proteinase inhibitor) activities. Lastly, the effect of Doxy on progelatinase-B (pro-MMP-9) activation by purified proteinases from P. gingivalis and Treponema denticola was investigated by SDS-PAGE/Western immunoblotting.

RESULTS

Doxy and CMTs, except CMT-5 which lacks the structural elements required for cation chelation, inhibited Arg- and Lys-gingipain activities as well as collagenolytic activity of P. gingivalis. Doxy and CMTs did not markedly affect the chymotrypsin-like activity of T. denticola but inhibited its trypsin-like activity. In addition, degradation of human serum albumin by cells of P. gingivalis and T. denticola was strongly inhibited by Doxy and CMT-1. Doxy and CMT-1 also inhibited the inactivation of alpha1-proteinase inhibitor (serpinolytic activity) by a collagenolytic fraction of P. gingivalis. Lastly, Doxy prevented the latent to active conversion of human neutrophil progelatinase-B (pro-MMP-9) by Arg-gingipains A/B of P. gingivalis but not by the chymotrypsin-like proteinase of T. denticola.

CONCLUSIONS

Data from this study suggest that Doxy and CMTs have the potential to inhibit the periodontopathogenic bacterial proteinases, which contribute to tissue destruction cascades during periodontitis directly and indirectly by triggering the host response.

Inhibition of trypsin-like cysteine proteinases (gingipains) from Porphyromonas gingivalis by tetracycline and its analogues

Extracellular cysteine proteinases, referred to as gingipains, are considered important virulence factors for Porphyromonas gingivalis, a bacterium recognized as a major etiologic agent of chronic periodontitis. We investigated the effect of tetracycline and its analogues, doxycycline and minocycline, on the enzymatic activities of gingipains. Tetracyclines at 100 microM totally inhibited the amidolytic activity of arginine-specific gingipains (HRgpA and RgpB). In contrast, inhibition of Kgp was less efficient and required a somewhat higher concentration of the antibiotic to achieve the same effect. Among tetracycline derivatives, the most potent gingipain inhibitor was doxycycline, followed by tetracycline and minocycline. RgpB was inhibited by doxycycline in an uncompetitive and reversible manner with a 50% inhibitory concentration of 3 microM. Significantly, inhibition was unaffected by calcium, excluding the chelating activity of tetracyclines as the mechanism of gingipain inactivation. In contrast, the inhibitory activities of the tetracyclines were reduced by cysteine, a reducing agent, suggesting an interference of the drug at the oxidative region with the catalytic system of the enzyme. Doxycycline, at 10 microM, significantly inhibited the RgpB-mediated production of vascular permeability-enhancing activity from human plasma, thus proving an effective inhibition of gingipain in vivo. These results indicate a new activity of tetracyclines as cysteine proteinase inhibitors and may explain the therapeutic efficiency of these antibiotics in the treatment of periodontitis.

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.

Old and new drugs used in rheumatoid arthritis: a historical perspective. Part 2: the newer drugs and drug strategies

After a 20-year hiatus, drug development for rheumatoid arthritis resumed in the early 1980s with cyclosporine, continuing in the 1990s with minocycline, leflunomide, and the tumor necrosis factor-alpha antagonists, infliximab and etanercept. Unlike the older disease-modifying antirheumatic drugs (apart from the cytotoxics), the newer drugs were designed with strict reference to proven pathophysiology in rheumatoid arthritis and, apart from minocycline, the intended action of these agents is highly likely the explanation for the observed efficacy. The evidence for the evolution of more rational drug development in rheumatoid arthritis has not altered the fact that efficacy versus toxicity still remains the major determinant in the practical use of these agents, as well as in the use of other, experimental agents briefly discussed. Action, efficacy, and toxicity also determine the rational chronologic use of these drugs alone and, in particular, in combination.

Efficacy of subantimicrobial dosing with doxycycline. Point/counterpoint

BACKGROUND

This article addresses the role of subantimicrobial dosing with doxycycline, or SDD, in the treatment of chronic periodontitis. The authors discuss and debate 10 issues with regard to SDD's utility as an adjunct to scaling and root planing.

TYPES OF STUDIES REVIEWED

The authors reviewed reports of controlled clinical trials that assessed the efficacy of SDD. The main focus of this article is data from the U.S. Food and Drug Administration's phase 3 clinical trial that evaluated the efficacy of SDD in terms of alterations of probing depth, clinical attachment levels and disease progression.

RESULTS

The authors compared data from test groups, which underwent root planing plus SDD, with data from control groups, which underwent root planing alone. The mean data suggest that SDD provides a defined but limited improvement of periodontal status when used in conjunction with scaling and root planing. Furthermore, several in vivo studies indicated that a nine-month course of SDD did not cause development of drug-resistant bacterial strains or alteration of the subgingival microbiota.

CLINICAL IMPLICATIONS

Some patients may benefit from SDD. However, there are several issues that should be clarified before widespread use of SDD is recommended for patients with chronic periodontitis. The evidence indicates that suppression of the bacterial challenge, which reduces the host response, is the most efficient way to control periodontal diseases.

Adjunctive treatment with subantimicrobial doses of doxycycline: effects on gingival fluid collagenase activity and attachment loss in adult periodontitis

OBJECTIVES

The therapeutic effects of doxycycline and other tetracyclines in the treatment of periodontitis involve, at least in part, mechanisms that are unrelated to their antimicrobial activity. Previous clinical studies have shown that doxycycline administered orally, at doses below those needed for antimicrobial efficacy, to human subjects with adult periodontitis resulted in significantly reduced collagenase activity in gingival crevicular fluid (GCF) and in extracts of inflamed gingival tissues. The purpose of the present study was to identify clinically effective dosing regimens using subantimicrobial dose doxycycline (SDD) as an adjunctive therapy in patients with adult periodontitis.

MATERIAL AND METHODS

A total of 75 adult men and women qualified for enrollment into the three-part, placebo-controlled, double-blind, parallel-group study. Patients were stratified based on repeatedly exhibiting pathologic levels of periodontal attachment (ALv) and GCF collagenase activity at several appointments prior to baseline. Patients were administered a scaling and prophylaxis, then 1 of 5 treatment schedules for 12 weeks (part I), followed by a 12-week period of no drug therapy (part II), a second scaling and prophylaxis, and 12 additional weeks of treatment (part III). Primary determinants of efficacy included reductions in GCF collagenase activity and changes in relative ALv.

RESULTS

66 patients completed the 1st 12 weeks (part I) of the 3-part, 36-week study; 51 patients completed the entire 36-week study. From baseline to week 12 (part I), treatment with specially formulated SDD capsules (20 mg) 2x daily (1 x every 12 h) for up to 12 weeks was shown to significantly reduce GCF collagenase activity and to improve ALv, effects not seen in patients treated with placebo. Continuous drug therapy over the 12-week treatment period was needed to maintain and maximize the reduction in GCF collagenase and the improvement in ALv. Improvements in periodontal disease parameters occurred without the emergence of doxycycline-resistant micro-organisms. In patients administered an "on-off-on" regimen of SDD over 36 weeks (parts I-III), essentially no attachment loss occurred in patients receiving the highest of these SDD regimens (20 mg 2x daily during part I and 20 mg 1 x daily in part III), whereas patients administered placebo capsules experienced a mean attachment loss of approximately 0.8 mm at the 24- and 36-week time periods.

CONCLUSIONS

Doxycycline administered at subantimicrobial doses led to improvements in disease parameters, with no apparent side effects, and appears to have significant potential as an oral adjunctive therapy in the long-term management of adult periodontitis.

Phase I clinical trial of oral COL-3, a matrix metalloproteinase inhibitor, in patients with refractory metastatic cancer

PURPOSE

This phase I clinical trial was designed to determine the maximum-tolerated dose and dose-limiting toxicities of the matrix metalloproteinase (MMP) inhibitor COL-3 in patients with refractory solid tumors.

PATIENTS AND METHODS

Thirty-five patients with different cancer types were enrolled. COL-3 doses were escalated from 36 mg/m2/d in successive cohorts of at least three patients. Circulating levels of MMP-2, MMP-9, vascular endothelial growth factor, and basic fibroblast growth factor were assessed during treatment. Pharmacokinetic parameters were assessed for single and multiple doses of drug.

RESULTS

Cutaneous phototoxicity was dose-limiting at 98 mg/m2/d. With the use of prophylactic sunblock, COL-3 was well tolerated at 70 mg/m2/d. The dose of 36 mg/m2/d was well tolerated without the use of sunblock. Other toxicities that did not seem to be related to dose or pharmacokinetics included anemia, anorexia, constipation, dizziness, elevated liver function test results, fever, headache, heartburn, nausea, vomiting, peripheral and central neurotoxicities, fatigue, and three cases of drug-induced lupus. Disease stabilization for periods of 26+ months, 8 months, and 6 months were seen in hemangioendothelioma, Sertoli-Leydig cell tumor, and fibrosarcoma, respectively. There was a potentially statistically significant relationship between changes in plasma MMP-2 levels and cumulative doses of drug when progressive disease patients were compared with those with stable disease or toxicity (P = .042).

CONCLUSION

COL-3 induced disease stabilization in several patients who had a nonepithelial type of malignancy. Phototoxicity was dose-limiting. We recommend the dose of 36 mg/m2/d for phase II trials.

Matrix metalloproteinases: pro- and anti-angiogenic activities

Matrix metalloproteinases (MMP) are a family of structurally related proteinases most widely recognized for their ability to degrade extracellular matrix, although recent investigations have demonstrated other biologic functions for these enzymes. MMP are typically not constitutively expressed, but are regulated by: (1) cytokines, growth factors, and cell-cell and cell-matrix interactions that control gene expression; (2) activation of their proenzyme form; and (3) the presence of MMP inhibitors [tissue inhibitors of metalloproteinases, (TIMP)]. MMP have important roles in normal processes including development, wound healing, mammary gland, and uterine involution, but are also involved in angiogenesis, tumor growth, and metastasis. Angiogenesis, characteristically defined as the establishment of new vessels from pre-existing vasculature, is required for biologic processes such as wound healing and pathologic processes such as arthritis, tumor growth, and metastasis. Blocking of MMP activity has been studied for potential therapeutic efficacy in controlling such pathologic processes. Synthetic MMP inhibitors, most notably the hydroxymates, have been engineered for this purpose and are presently in clinical trial. These inhibitors may have broad versus specific MMP inhibitory activity. As increased non-matrix degrading capabilities of MMP are recognized, however, i.e., cytokine activation, processing of proteins to molecules of distinct biologic function, it becomes less clear whether the nonselective inhibition of MMP activity for all pathologic processes involving MMP is appropriate. This review focuses upon the contribution of MMP to the process of tumor invasion and angiogenesis, and discusses the design and use of MMP inhibitors as therapeutic agents in these processes.

Local anti-angiogenic brain tumor therapies

The critical role of angiogenesis in the growth of solid tumors, including neoplasms of the central nervous system, has provided the impetus for research leading to the discovery of inhibitors of tumor neovascularization. The therapeutic potential of systemically administered antiangiogenic drugs for brain tumors, however, is limited by a variety of anatomic and physiologic barriers to drug delivery. Implantable controlled-release polymers for local drug administration directly into the tumor parenchyma have therefore been developed to achieve therapeutic concentrations of these drugs within the brain while minimizing systemic toxicity. With use of these polymers, successful antiangiogenic therapy for treatment of experimental intracranial malignancies has been achieved. This has been demonstrated with a variety of otherwise unrelated drugs -- including the angiostatic steroids, tetracycline derivatives, and amiloride -- which modulate collagenase activity, and thus, basement membrane and interstitial matrix metabolism. Controlled-release polymers provide a clinically practicable method of achieving sustained antiangiogenic therapy which can be readily used in combination with other treatment modalities such as cytoreductive surgery, radiation, and cytotoxic chemotherapy.

Long-term use of subantimicrobial dose doxycycline does not lead to changes in antimicrobial susceptibility

BACKGROUND

Adjunctive subantimicrobial dose doxycycline (SDD) with scaling and root planing leads to improved clinical parameters of adult periodontitis, but has raised questions about potential changes in antibiotic susceptibility of the host microflora. Our four studies assessed whether long-term SDD changes antibiotic susceptibility of the oral microflora in adults with periodontitis.

METHODS

In studies 1 and 2, adult patients with periodontitis were randomized to receive SDD 10 mg qd, 20 mg qd, 20 mg bid, or placebo. In study 3, patients were randomized to receive SDD 20 mg bid or placebo. No medication was administered in study 4, a follow-up to study 3. Subgingival plaque samples were collected at baseline (all studies) and at 12, 15 to 18, and 24 months (study 1); 12, 18, and 27 months (study 2); 3, 6, and 9 months (study 3); and 3 months post-study 3 (study 4). Antimicrobial susceptibility of isolated bacteria was assessed by: 1) minimum inhibitory concentration (MIC) levels (studies 1 and 2); 2) cross-resistance to non-tetracycline antibiotics (studies 2 and 3); and 3) the proportion of doxycycline-resistant isolates (studies 3 and 4).

RESULTS

Organism MIC levels remained constant among all treatment groups at 18 and 24 months compared with baseline (study 1). Observed changes in susceptibility at 12 and 18 months for the 20 mg groups were attributed to the limited number of isolates tested (study 1). There were no statistically significant differences in the proportion of doxycycline-resistant isolates among treatment groups (studies 3 and 4), and no evidence of multi-antibiotic resistance (studies 3 and 4) or cross-resistance (studies 2 and 3) at any timepoint.

CONCLUSION

Long-term SDD does not contribute to changes in antibiotic susceptibility.

Effects of bisphosphonate on matrix metalloproteinase enzymes in human periodontal ligament cells

BACKGROUND

The host response is a critical component in the pathogenesis of periodontitis. In fact, the clinical benefits associated with regulating the host response have been demonstrated in studies using several different classes of drugs. Biophosphates are one host-modulating class of drugs that has demonstrated this ability. These drugs are clinically effective at reducing bone resorption and have shown the ability to inhibit host degradative enzymes, specifically the matrix metalloproteinases (MMPs). Therefore, the purpose of this study was to investigate the regulatory effects of a bisphosphonate, tiludronate, on MMP levels and activity in human periodontal cells.

METHODS

MMP-1 and MMP-3 were assessed in cultured human periodontal ligament cells treated with a bisphosphonate, tiludronate. Reverse transcription-polymerase chain reaction was used to identify mRNA levels for both enzymes, and also for tissue inhibitors (TIMP-1). Enzyme immunoassay (EIA) and immunocytochemistry were used to assess MMP proteins in these cell cultures. Enzyme activity was assessed using FITC-conjugated substrates and quantitated using spectrophotofluorometry.

RESULTS

Tiludronate significantly inhibited both MMP-1 and MMP-3 activity in a concentration-dependent manner. A maximal reduction in activity of 35% was achieved for each of the enzymes at a 10(-4) M concentration. Tiludronate did not have a significant effect on the mRNA levels for MMP-1, MMP-3, or TIMP-1. Similarly, there were no effects noted for either MMP-1 or MMP-3 on the protein level.

CONCLUSIONS

This study demonstrates an inhibitory effect of tiludronate on the activity of both MMP-1 and MMP-3. These effects appear to occur without altering either mRNA or protein levels for these enzymes, supporting a possible mechanism of action that involves the ability of bisphosphonates to chelate cations from the MMPs. Furthermore, these results support the continued investigation of these drugs as potential therapeutic agents in periodontal disease.

Tetracyclines and the treatment of corneal stromal ulceration: a review

PURPOSE

To demonstrate the potential value of tetracyclines in the treatment of corneal ulceration after moderate to severe ocular chemical injuries.

METHODS

Review of published materials describing landmarks in the development of tetracyclines as matrix metalloproteinase inhibitors in ophthalmology and related disciplines.

RESULTS

Tetracyclines can protect the cornea against proteolytic degradation after moderate to severe ocular chemical injury. They inhibit matrix metalloproteinases by mechanisms independent of their antimicrobial properties, primarily through restriction of the gene expression of neutrophil collagenase and epithelial gelatinase, suppression of alpha1-antitrypsin degradation, and scavenging of reactive oxygen species.

CONCLUSION

Oral tetracyclines can be used along with topical tetracycline preparations and other therapeutic agents to inhibit collagenolytic degradation of the cornea after moderate to severe ocular chemical injuries.

Benefits and risks of minocycline in rheumatoid arthritis

Rheumatoid arthritis is a chronic inflammatory disease affecting about 1% of the adult population. The pathophysiology of rheumatoid arthritis remains incompletely understood. An infectious aetiology of the disease has long been postulated, but not proved. Despite insufficient evidence for the infectious nature of this disorder, several antibacterials, such as sulfa compounds, tetracyclines and rifampicin, have been investigated in the treatment of rheumatoid arthritis. In the last few years, minocycline, a semi-synthetic derivative of tetracycline, has been extensively studied as a therapeutic agent for rheumatoid arthritis. The antirheumatic effect of minocycline can be related to its immunomodulatory and anti-inflammatory, rather than to its antibacterial properties. Its efficacy in rheumatoid arthritis has been reported in 2 open trials and in 3 double-blind controlled studies. The first 2 double-blind studies, 1 in The Netherlands and 1 in the US, were performed in patients with advanced disease. Both studies showed a modest, but statistically significant improvement in the clinical parameters of disease activity and in the erythrocyte sedimentation rate in the minocycline-treated patients. The US study also reported that patients in the minocycline group developed fewer erosions than those in the placebo group. This finding supports the role of minocycline as a disease modifying agent. The common adverse effects of minocycline reported in these 2 studies included gastrointestinal adverse effects, dizziness, rash and headaches. Less common adverse effects were intracranial hypertension, pneumonitis, persistent skin and mucosal hyperpigmentation, lupus-like syndrome and acute hepatic injury. The third double-blind study enrolled only seropositive rheumatoid arthritis patients with early disease (less than 1 year duration), and showed very encouraging results of significant improvement in the disease activity parameters in the minocycline treated group of patients. The same authors later reported that about half of these patients were in or near remission after 3 years of follow up. No adverse effects were reported in this study. Summarising the data of these 3 double-blind studies, we may conclude that minocycline may be beneficial in patients with rheumatoid arthritis, especially when given early in the disease course or in patients with a mild disease.

Blockade of RAGE suppresses periodontitis-associated bone loss in diabetic mice

Diabetes is associated with increased prevalence, severity, and progression of periodontal disease. To test the hypothesis that activation of RAGE (Receptor for Advanced Glycation End products) contributes to the pathogenesis of diabetes-associated periodontitis, we treated diabetic mice, infected with the human periodontal pathogen Porphyromonas gingivalis, with soluble RAGE (sRAGE). sRAGE is the extracellular domain of the receptor, which binds ligand and blocks interaction with, and activation of, cell-surface RAGE. Blockade of RAGE diminished alveolar bone loss in a dose-dependent manner. Moreover, we noted decreased generation of the proinflammatory cytokines TNF-alpha and IL-6 in gingival tissue, as well as decreased levels of matrix metalloproteinases. Gingival AGEs were also reduced in mice treated with sRAGE, paralleling the observed suppression in alveolar bone loss. These findings link RAGE and exaggerated inflammatory responses to the pathogenesis of destructive periodontal disease in diabetes.

Diabetes and periodontal diseases. Committee on Research, Science and Therapy. American Academy of Periodontology

This position paper on diabetes mellitus was prepared by the Research, Science and Therapy Committee of The American Academy of Periodontology. It is intended to: 1) update members of the dental profession on the diagnosis and medical management of patients with diabetes mellitus; 2) summarize current knowledge on the relation between diabetes mellitus and periodontal diseases; 3) provide an overview of factors in diabetic patients relevant to understanding the pathogenesis of periodontal diseases in these subjects; 4) outline special considerations associated with treatment of periodontal diseases in diabetic patients; and 5) discuss possible approaches to the management of diabetic emergencies in the dental office.

Treatment with subantimicrobial dose doxycycline improves the efficacy of scaling and root planing in patients with adult periodontitis

BACKGROUND

In a previous study, subantimicrobial dose doxycycline (SDD) significantly improved clinical parameters associated with periodontal health in patients with adult periodontitis (AP) when used as an adjunct to a maintenance schedule of supragingival scaling and dental prophylaxis. In this double-blind, placebo-controlled, parallel-group, multicenter study, the efficacy and safety of SDD were evaluated in conjunction with scaling and root planing (SRP) in patients with AP.

METHODS

Patients (n = 190) received SRP at the baseline visit and were randomized to receive either SDD 20 mg bid or placebo bid for 9 months. Efficacy parameters included the per-patient mean changes in clinical attachment level (CAL) and probing depth (PD) from baseline, the per-patient percentages of tooth sites with attachment loss (AL) > or = 2 mm and > or = 3 mm from baseline, and the per-patient percentage of tooth sites with bleeding on probing. Prior to analysis, tooth sites were stratified by the degree of disease severity evident at baseline

RESULTS

In tooth sites with mild to moderate disease and severe disease (n = 183, intent-to-treat population), improvements in CAL and PD were significantly greater with adjunctive SDD than with adjunctive placebo at 3, 6, and 9 months (all P <0.05). In tooth sites with severe disease, the per-patient percentage of sites with AL > or = 2 mm from baseline to month 9 was significantly lower with adjunctive SDD than with adjunctive placebo (P<0.05). Improvements in clinical outcomes occurred without detrimental shifts in the normal periodontal flora or the acquisition of doxycycline resistance or multiantibiotic resistance. SDD was well tolerated, with a low incidence of discontinuations due to adverse events.

CONCLUSIONS

The adjunctive use of SDD with SRP is more effective than SRP alone and may represent a new approach in the long-term management of AP.

Iron-chelating activity of tetracyclines and its impact on the susceptibility of Actinobacillus actinomycetemcomitans to these antibiotics

Three tetracyclines (tetracycline, doxycycline, and minocycline) were found to possess iron-chelating activity in a colorimetric siderophore assay. Determination of MICs indicated that the activity of doxycycline against the periodontopathogen Actinobacillus actinomycetemcomitans was only slightly influenced by the presence of an excess of iron that likely saturates the antibiotic. On the other hand, the MICs of doxycycline and minocycline were significantly lower for A. actinomycetemcomitans cultivated under iron-poor conditions than under iron-rich conditions.

Preoperative treatment with doxycycline reduces aortic wall expression and activation of matrix metalloproteinases in patients with abdominal aortic aneurysms

PURPOSE

Matrix metalloproteinases (MMPs) are considered to play a central role in the pathogenesis of abdominal aortic aneurysms (AAAs). Doxycycline (Dox) has direct MMP-inhibiting properties in vitro, and it effectively suppresses the development of elastase-induced AAAs in rodents. The purpose of this study was to determine if treatment with Dox suppresses MMPs within human aneurysm tissue and to elucidate the molecular mechanisms underlying this effect.

METHODS

Aneurysm tissues were obtained from 15 patients with an AAA, eight of whom had been treated with Dox before surgery (100 mg orally twice a day for 7 days). Protein extracts were examined by means of gelatin zymography and immunoblot analysis, and RNA was examined by means of reverse transcription-polymerase chain reaction (RT-PCR). The effects of Dox on MMP production were further examined in human THP-1 mononuclear phagocytes in vitro.

RESULTS

No detectable difference was found between groups by using substrate zymography as a means of assessing total MMP activity, but Dox treatment was associated with a slight (24.4%) reduction in the activated fraction of 72-kDa gelatinase (MMP-2; P <.05). In contrast, a 2.5-fold reduction in the amount of extractable 92-kDa gelatinase (MMP-9) protein in Dox-treated patients was revealed by means of immunoblot analysis (P <.05). Also, a 5.5-fold (81.9%) reduction in MMP-9 messenger RNA (mRNA) in Dox-treated patients was demonstrated by means of quantitative competitive RT-PCR (mean +/- SE, mol MMP-9/mol beta-actin: 1.3 +/- 0.5 vs 7.2 +/- 3.1; P <.04). There was no significant difference between groups in the relative expression of MMP-2 protein or mRNA. In cultured THP-1 monocytes stimulated with phorbol ester, the expression of MMP-9 protein and mRNA were both decreased after exposure to relevant concentrations of Dox in vitro.

CONCLUSION

In addition to its recognized effects as a direct MMP antagonist, Dox may influence connective tissue degradation within human aneurysm tissue by reducing monocyte/macrophage expression of MMP-9 mRNA and by suppressing the post-translational processing (activation) of proMMP-2. Through this complementary combination of mechanisms, treatment with Dox may be a particularly effective strategy for achieving MMP inhibition in patients with an AAA.

Diabetes and periodontal diseases

This position paper on diabetes mellitus was prepared by the Research, Science and Therapy Committee of The American Academy of Periodontology. It is intended to: 1) update members of the dental profession on the diagnosis and medical management of patients with diabetes mellitus; 2) summarize current knowledge on the relation between diabetes mellitus and periodontal diseases; 3) provide an overview of factors in diabetic patients relevant to understanding the pathogenesis of periodontal diseases in these subjects; 4) outline special considerations associated with treatment of periodontal diseases in diabetic patients; and 5) discuss possible approaches to the management of diabetic emergencies in the dental office.

Doxycycline induces Fas/Fas ligand-mediated apoptosis in Jurkat T lymphocytes

Tetracyclines have been used in the treatment of chronic inflammatory diseases associated with local infiltration of inflammatory cells and matrix destruction as observed in rheumatoid arthritis and periodontal disease. Fas/Fas ligand (FasL)-mediated apoptosis plays an important role in maintaining T lymphocyte homeostasis and modulating immune response. The present study demonstrates that doxycycline inhibits Jurkat T lymphocyte proliferation and induces apoptosis. The phytohemagglutinin (PHA)-activated Jurkat cells are more susceptible to doxycycline-induced apoptosis. Furthermore, doxycycline-induced apoptosis is associated with increased Fas/FasL expression in Jurkat cells. The increase of apoptosis in Jurkat cells treated with doxycycline is consistent with the increase of FasL expression. These results suggest that doxycycline may downregulate the inflammatory process in certain diseases by eliminating activated T lymphocytes through Fas/FasL-mediated apoptosis.

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.

MMP-mediated events in diabetes

Both Type I and Type II diabetes mellitus (DM) have been associated with unusually aggressive periodontitis. Accordingly, rat models of both types of DM were used to study (i) mechanisms mediating this systemic/local interaction and (ii) new pharmacologic approaches involving a series of chemically modified tetracyclines (CMTs) that have lost their antimicrobial but retained their host-modulating (e.g., MMP-inhibitory) properties. In vitro experiments on tissues from Type I DM rats demonstrated that several of these CMTs were better matrix metalloproteinase (MMP) inhibitors than was antibacterial doxycycline (doxy), except for CMT-5, which, unlike the other MMP inhibitors, was found not to react with zinc. Data from in vivo studies on the same rat model generally supported the relative efficacy of these compounds: the CMTs and doxy were found to inhibit MMP activity, enzyme expression, and alveolar bone loss. To examine other long-term complications such as nephropathy and retinopathy, a Type II (ZDF) model of DM was studied. Treatment of these DM rats with CMT-8 produced a 37% (p < 0.05), 93% (p < 0.001), and 50% (p < 0.01) reduction in the incidence of cataract development, proteinuria, and tooth loss, respectively; whereas the doxy-treated ZDF rats showed little or no effect on these parameters. CMT treatment decreased mortality of the Type II ZDF diabetic animals, clearly indicating that CMTs, but not commercially available antibiotic tetracyclines (TCs), may have therapeutic applications for the long-term management of diabetes.

MMP inhibition in abdominal aortic aneurysms. Rationale for a prospective randomized clinical trial

Abdominal aortic aneurysms (AAAs) represent a chronic degenerative condition associated with a life-threatening risk of rupture. The evolution of AAAs is thought to involve the progressive degradation of aortic wall elastin and collagen, and increased local production of several matrix metallo-proteinases (MMPs) has been implicated in this process. We have previously shown that tetracycline derivatives and other MMP inhibitors suppress aneurysm development in experimental animal models of AAA. Doxycycline also reduces the expression of MMP-2 and MMP-9 by human vascular wall cell types and by AAA tissue explants in vitro. To determine whether this strategy might have a role in the clinical management of small AAA, we examined the effect of doxycycline on aortic wall MMP expression in vivo. Patients were treated with doxycycline (100 mg p.o. bid) for 7 days prior to elective AAA repair, and aneurysm tissues were obtained at the time of surgery (n = 5). Tissues obtained from an equal number of untreated patients with AAA were used for comparison. By reverse transcription-polymerase chain reaction and Southern blot analysis, MMP-2 and MMP-9 were both found to be abundantly expressed in the aneurysm wall. Preoperative treatment with doxycycline was associated with a 3-fold reduction in aortic wall expression of MMP-2 and a 4-fold reduction in MMP-9 (p < 0.05 compared to untreated AAA). These preliminary results suggest that even short-term treatment with doxycycline can suppress MMP expression within human AAA tissues. Given its pleiotropic effects as an MMP inhibitor, doxycycline may be particularly effective in suppressing aortic wall connective tissue degradation. While it remains to be determined whether MMP inhibition will have a clinically significant impact on aneurysm expansion, it is expected that this question can be resolved by a properly designed prospective randomized clinical trial.

Matrix metalloproteinase inhibition. From the Jurassic to the third millennium

A brief historical introduction to the matrix metalloproteinase (MMP) field, which began in 1962, is followed by an overview of the inhibition of these proteases by natural inhibitors such as alpha 2 macroglobulin and the TIMPs (tissue inhibitors of metalloproteinases) and by synthetic inhibitors, which are largely chelating agents. The latter include thiol, alkylcarbonyl, phosponamidate and hydroxamate compounds, as well as the tetracyclines. A review of the most recent progress concludes with prognostications as to where the field may be going next.

Clinical trials of a matrix metalloproteinase inhibitor in human periodontal disease. SDD Clinical Research Team

After demonstration by Golub et al. of the ability of the tetracyclines to inhibit elevated collagenolytic activity in animal models of periodontal diseases, a clinical development program was initiated to demonstrate the potential of a subantimicrobial dose of doxycycline (SDD) to augment and maintain the improvements in clinical parameters of adult periodontitis (AP) afforded by conventional nonsurgical periodontal therapy. Clinical trials were carried out in which a number of different SDD dosing regimens and placebo were compared in patients administered a variety of adjunctive nonsurgical therapies. Measured parameters included levels of collagenase activity in gingival crevicular fluid (GCF) and gingival specimens, clinical attachment levels (cALv), probing pocket depths (PD), bleeding on probing (BOP), and subtraction radiographic measurements of alveolar bone height. When used as an adjunct to either scaling and root planing or supragingival scaling and dental prophylaxis, SDD was shown to reduce collagenase levels in both GCF and gingival biopsies, to augment and maintain cALv gains and PD reductions, to reduce BOP, and to prevent loss of alveolar bone height. These clinical responses arose in the absence of any significant effects on the subgingival microflora and without evidence of an increase in the incidence or severity of adverse reactions relative to the control groups. It is proposed that one of the mechanisms of action of SDD is as an inhibitor of pathologically elevated MMPs, including neutrophil and bone cell collagenases (MMP-8 and MMP-13), which are associated with the host response in chronic AP, and that SDD provides a novel systemic approach to the management of AP.

MMP inhibition and downregulation by bisphosphonates

Bisphosphonates are a group of drugs capable of inhibiting bone resorption, and are thus used for the treatment of bone diseases, such as Paget's disease, osteoporosis, and for bone metastases of malignant tumors. Their primary cellular target is considered to be the osteoclast. The molecular mechanisms responsible for the downregulation of bone resorption by bisphosphonates have remain unclear. We have discovered that various matrix metalloproteinases (MMPs) are inhibited in vitro by several bisphosphonates. This novel finding may, in part, explain the efficacy of bisphosphonates in their current indications in humans. In enzyme activity tests using purified and recombinant enzymes, we have observed the inhibition of MMP-1, -2, -3, -7, -8, -9, -12, -13, and -14 by clondronate, alendronate, pamidronate, zolendronate, nedrinate, and clodrinate. The IC50s range from 50 to 150 microM. We have also shown that clodronate can downregulate the expression of MT1-MMP protein and mRNA in several cell lines. Additionally, several bisphosphonates decrease the degree of invasion of malignant melanoma (C8161) and fibrosarcoma (HT1080) cells through artificial basement membrane (Matrigel) in cell cultures at IC50s of 50-150 microM and below. Having low toxicity and proven to be well tolerated after several years in human use, bisphosphonates have the potential to become one of the main MMP-inhibitors for MMP-related human soft and hard tissue-destructive diseases in the near future.

Inhibition of the activities of matrix metalloproteinases 2, 8, and 9 by chlorhexidine

Matrix metalloproteinases (MMPs) are a host cell-derived proteolytic enzyme family which plays a major role in tissue-destructive inflammatory diseases such as periodontitis. The aim of the present study was to evaluate the inhibitory effect of chlorhexidine (CHX) on MMP-2 (gelatinase A), MMP-9 (gelatinase B), and MMP-8 (collagenase 2) activity. Heat-denatured type I collagen (gelatin) was incubated with pure human MMP-2 or -9 activated with p-aminophenylmercuric acetate (APMA), and the proteolytic degradation of gelatin was monitored by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and Coomassie blue staining. The effect of CHX on MMP-8 activity was also studied with a cellular model addressing the ability of phorbol myristate acetate (PMA)-triggered human peripheral blood neutrophils (polymorphonuclear leukocytes [PMNs]) to degrade native type I collagen. CHX inhibited the activities of both gelatinases (A and B), but MMP-2 appeared to be more sensitive than MMP-9. Adding calcium chloride to the assay mixtures almost completely prevented the inhibition of MMP-9 activity by CHX, while the inhibition of MMP-2 activity could be reversed only when CHX was used at a low concentration. This observation suggests that CHX may act via a cation-chelating mechanism. CHX dose-dependently inhibited collagenolytic activity of MMP-8 released by PMA-triggered PMNs. MMP-8 without APMA activation was inhibited clearly more efficiently than APMA-activated MMP-8. Our study suggests that the direct inhibition of the MMPs' activities by CHX may represent a new valuable effect of this antimicrobial agent and explains, at least in part, the beneficial effects of CHX in the treatment of periodontitis.

Is there a role for antibiotics in the treatment of patients with rheumatoid arthritis?

Despite many advances in the understanding and treatment of rheumatoid arthritis, its pathophysiology remains incompletely understood. An infectious aetiology of rheumatoid arthritis has long been postulated but, even though many continue to believe that there is a 'triggering agent for rheumatoid arthritis', none has been identified. Currently, both sulfasalazine and minocycline have been shown to be effective treatments for rheumatoid arthritis and are being used increasingly. In the case of minocycline, it appears that its ability to inhibit metalloproteases is an important characteristic that may account for some or part of its action against rheumatoid arthritis. Whether the antibacterial effects of these drugs or others are important in the treatment of rheumatoid arthritis continues to be investigated.

Suppression of experimental abdominal aortic aneurysms by systemic treatment with a hydroxamate-based matrix metalloproteinase inhibitor (RS 132908)

BACKGROUND

Abdominal aortic aneurysms (AAAs) are associated with chronic inflammation, disruption of medial elastin, and increased local production of elastolytic matrix metalloproteinases (MMPs). The purpose of this study was to investigate how treatment with a hydroxamate-based MMP antagonist (RS 132908) might affect the development of experimental AAAs.

METHODS

Male Wistar rats underwent intraluminal perfusion of the abdominal aorta with 50 units of porcine pancreatic elastase followed by treatment for 14 days with RS 132908 (100 mg/kg/day subcutaneously; n = 8) or with vehicle alone (n = 6). The external aortic diameter (AD) was measured in millimeters before elastase perfusion and at death, with AAA defined as an increase in AD (DeltaAD) of at least 100%. Aortic wall elastin and collagen concentrations were measured with assays for desmosine and hydroxyproline, and fixed aortic tissues were examined by light microscopy.

RESULTS

AAAs developed in all vehicle-treated rats, with a mean AD (+/- SE) that increased from 1.60 +/- 0.03 mm before perfusion to 5.98 +/- 1.02 mm on day 14 (DeltaAD = 276.4 +/- 67.7%). AAAs developed in only five of eight animals (62.5%) after MMP inhibition, with a mean AD that increased from 1.56 +/- 0.05 mm to 3.59 +/- 0.34 mm (DeltaAD = 128.1 +/- 18.7%; P <.05, vs vehicle). The overall inhibition of aortic dilatation attributable to RS 132908 was 53.6 +/- 6.8%. Aortic wall desmosine fell by 85.4% in the vehicle-treated rats (1210.6 +/- 87.8 pmol/sample to 176.7 +/- 33.4 pmol/sample; P <.05) but only by 65.6% in the animals treated with RS 312908 (416.2 +/- 120.5 pmol/sample). In contrast, hydroxyproline was not significantly affected by either elastase perfusion or drug treatment. Microscopic examination revealed the preservation of pericellular elastin and a greater degree of fibrocollagenous wall thickening after MMP inhibition, with no detectable difference in the extent of inflammation.

CONCLUSIONS

Systemic MMP inhibition suppresses aneurysmal dilatation in the elastase-induced rodent model of AAA. Consistent with its direct inhibitory effect on various MMPs, RS 132908 promotes the preservation of aortic elastin and appears to enhance a profibrotic response within the aortic wall. Hydroxamate-based MMP antagonists may therefore be useful in the development of pharmacologic approaches to the suppression of AAAs.

Effect of microbial siderophores on matrix metalloproteinase-2 activity

Matrix metalloproteinases (MMPs) are capable of cleaving almost all macromolecules of the extracellular connective tissue matrix and are thought to play a major role in tissue destructive inflammatory diseases such as periodontitis. The aim of this study was to determine the effects of siderophores, which are iron-chelating molecules produced by a variety of microorganisms, on the activity of MMP-2. Heat-denatured type I collagen (gelatin) was incubated with p-aminophenylmercuric acetate-activated MMP-2 and siderophores. Degradation of gelatin was monitored by SDS-PAGE and Coomassie blue staining. Ferrichrome, rhodotorulic acid, desferoxamine mesylate and 2,3-dihydroxybenzoic acid were found to inhibit the MMP-2 activity whereas beta-phenylpyruvic acid had no effect. The inhibition could be reversed by adding an excess calcium chloride or ferric chloride to the assay mixtures. Our study suggests that microbial siderophores may represent new-potential therapeutic molecules for the treatment of destructive inflammatory diseases involving excess MMP-2 activity, such as periodontitis.

Pharmacologic suppression of experimental abdominal aortic aneurysms: acomparison of doxycycline and four chemically modified tetracyclines

BACKGROUND

Matrix metalloproteinases (MMPs) likely contribute to the degradation of medial elastin in abdominal aortic aneurysms (AAAs), and tetracycline antibiotics exhibit MMP-inhibiting properties. The purpose of this study was to compare the effects of doxycycline and several non-antibiotic chemically modified tetracyclines (CMTs) in a rat model of elastase-induced AAA.

METHODS

Fifty-two male Wistar rats underwent intraluminal perfusion of the abdominal aorta with porcine pancreatic elastase. The rats then were treated for 7 days with subcutaneous injections of saline solution, different doses of doxycycline, or 1 of 4 different CMTs. The aortic diameters were measured with microcalipers, and the fixed tissues were examined by means of light microscopy. Gelatin zymography was used to assess the MMP activity in the aortic tissue extracts.

RESULTS

The mean aortic diameter in the control group increased by 126% +/- 14% on day 7 (from 1.57 +/- 0.04 mm to 3.54 +/- 0.27 mm; P <.05), and 5 of 6 animals (83%) had AAAs. Doxycycline appeared to inhibit aortic dilatation in a dose-dependent manner, and AAAs did not develop in any animals. Half-maximal effects were observed at a dose of approximately 6 mg/kg/day, and maximal effects were noted at greater than 30 mg/kg/day. No AAAs were observed in the animals that were treated with CMTs at 15 mg/kg/day. Each of the following CMTs exhibited an efficacy that was similar to that of doxycycline (percent inhibition of aortic dilatation vs control; all P <.05): CMT-3 (47.6%), CMT-4 (38.9%), CMT-7 (47.6%), CMT-8 (54.0%), and doxycycline (51.6%). Tissues from saline solution-treated controls exhibited a transmural inflammatory response and marked destruction of the medial elastic lamellae. Tetracycline derivatives limited the disruption of medial elastin without appearing to alter either the inflammatory response or the rat aortic wall production of metallogelatinases.

CONCLUSION

Tetracycline derivatives suppress the development of AAAs after elastase-induced aortic injury in the rat. The aneurysm-suppressing effects of doxycycline appear to be dose-dependent and distinct from its antibiotic activities, and they coincide with the structural preservation of medial elastin fibers. Further studies are needed to explore the potential of MMP-inhibiting tetracyclines as a novel pharmacologic strategy for the suppression of aortic aneurysms.

Tetracycline-based MMP inhibitors can prevent fibroblast-mediated collagen gel contraction in vitro

Collagen gels in vitro can be contracted by fibroblasts. The role of matrix metalloproteinases (MMPs) in the contraction of collagen lattices by human neonatal foreskin fibroblasts (HuFFs) was investigated in tissue culture media supplemented by various doses of known gelatinase inhibitors. Fluorescent assays with model gelatinase substrates and media conditioned by fibroblasts apparently confirmed the ability of chemically modified tetracyclines (CMTs) to act as inhibitors of MMP2, and zymography demonstrated that this was the major cell-derived MMP activity. There were no observable effects on the rate of contraction of attached FPCLs containing 6 x 10(4) HuFFs (passages 18-25) with either CMT-5 or CMT-2 at all concentrations tested (0-100 micrograms/mL). However, at greater than 20 micrograms/mL doxycycline and greater than 5 micrograms/mL CMT-3, FPCL contraction was completely abolished. Quantitative assessment of cell viability by means of the MTT assay in monolayer and qualitatively within the FPCLs with CalceinAM suggested that differences were not due to cytotoxic effects. Seeding FPCLs with lower-passage fibroblasts produced identical trends. These results may implicate the involvement of MMPs in the process of gel contraction, although tetracyclines have effects additional to their ability to inhibit MMPs directly.

Root-surface caries in rats and humans: inhibition by a non-antimicrobial property of tetracyclines

The incidence of root caries has been found to increase as the population ages and as edentulism becomes less prevalent due to improved dental awareness and care, and as exposure of roots due to gingival recession has also increased in the elderly. The mechanism of root caries is thought to be mediated by both bacterial and mammalian proteases produced by plaque and the periodontal tissues, respectively. In the current study, a rat model of periodontal disease was used in which gnotobiotic rats were infected intra-orally with a periodontal pathogen (P. gingivalis). Infecting the rats with P. gingivalis increased the collagenase activity in the gingival tissue in association with severe alveolar bone loss. Treating P. gingivalis-infected rats with doxycycline or CMT-1 prevented the destruction of the periodontium by MMPs, thus preventing exposure of roots to subgingival bacterial plaque and host tissue collagenases and the subsequent development of root caries. In addition, a low-dose doxycycline (LDD, 20 mg bid, non-antimicrobial dose) for 3 months was used in humans predisposed to increased root caries as the result of heavy use of smokeless (chewing) tobacco, causing gingival recession, subgingival plaque accumulation with Gram-negative bacteria, increased gingival crevicular fluid flow (GCF), and elevated GCF collagenase. Daily administration of LDD in smokeless tobacco patients reduced the GCF collagenase and prevented the further development of root caries.

Safety and efficacy of sub-antimicrobial-dose doxycycline therapy in patients with adult periodontitis

The objectives of the studies presented here were to assess the safety and efficacy of the adjunctive administration of sub-antimicrobial-dose doxycycline (SDD) for the treatment of adult periodontitis and to confirm the optimal dosing regimen. The studies summarized included four double-blind, placebo-controlled, randomized clinical trials, conducted over a period of 9 to 12 months. Analysis of efficacy data demonstrated that adjunctive SDD treatment resulted in: (1) increases in clinical attachment levels; (2) decreases in probing pocket depths; and (3) reductions in bleeding on probing in patients with adult periodontitis. There were no significant adverse events or unwanted long-term antimicrobial effects associated with orally administered SDD. The results of these clinical trials indicate that the adjunctive use of SDD 20 mg BID is an effective and well-tolerated regimen which can significantly improve several indices of periodontal health.

Tetracyclines inhibit connective tissue breakdown by multiple non-antimicrobial mechanisms

A seminal experiment involving a germ-free rat model of connective tissue breakdown (followed soon thereafter by a series of in vitro studies) identified an unexpected non-antimicrobial property of tetracyclines (TCs). This ability of TCs to inhibit matrix metalloproteinases (MMPs) such as collagenase was found to reflect multiple direct and indirect mechanisms of action, and to be therapeutically useful in a variety of dental (e.g., adult periodontitis) and medical (e.g., arthritis, osteoporosis, cancer) diseases. The site on the TC molecule responsible for its MMP-inhibitory activity was identified which led to the development of a series of chemically modified non-antimicrobial analogs, called CMTs, which also have therapeutic potential but do not appear to induce antibiotic side-effects. Longitudinal double-blind studies on humans with adult periodontitis have demonstrated that a sub-antimicrobial dose of doxycycline (previously reported to suppress collagenase activity in the periodontal pocket) is safe and effective and has recently been approved by the FDA as an adjunct to scaling and root planing.

Topically applied CMT-2 enhances wound healing in streptozotocin diabetic rat skin

Delayed wound healing is one of the complications of diabetes mellitus, exhibited by increased wound collagenase and decreased granulation tissues. The current study compared wound healing in normal and diabetic rats, and the effects of topically applied 1% or 3% concentrations of chemically modified tetracycline-2 (CMT-2) on 6-mm circular full-thickness skin wounds healed by secondary intention. On day 7 after wounding, tissues were removed for biochemical analysis and histology. The wound granulation tissue hydroxyproline was less in the untreated diabetic rat with increased collagenase and gelatinase. Treating the diabetic rat wounds with 3% CMT-2 increased the wound hydroxyproline and decreased activities of gelatinase and collagenase. There was a delay in wound filling by granulation tissue in diabetic rats. In CMT-2-treated diabetic rats, the volume of granulation tissue was greater than that in untreated diabetic rats. CMT-2 appears to normalize wound healing in diabetic rats and may be a valuable adjunct in the treatment of chronic wounds.

Tetracyclines inhibit protein glycation in experimental diabetes

Glycation of proteins, which is accelerated in the diabetic state, has been implicated in many of the long-term complications of diabetes. This process can be inhibited by members of the tetracycline family of compounds. This novel finding is supported by studies conducted on drug (streptozotocin)induced Type I and genetic (ZDF/Gmi-fa/fa) Type II diabetic rats. These animals were orally gavaged daily with 5 mg of doxycycline and a variety of non-antimicrobial chemically modified tetracycline derivatives for time periods of 3 weeks to 11 months, while control untreated diabetic and nondiabetic animals were gavaged with vehicle alone (2% CMC). Blood and tissue samples were collected and analyzed for glucose and glycated proteins. None of the treatments had any effect on the severity of hyperglycemia or the intracellular glycation of hemoglobin of either Type I or II diabetic animals. However, the tetracycline analogues did affect the extracellular glycation of several proteins such as those found in the serum as well as skin collagen. In the Type II (ZDF) animals, initial mortality (3-5 months) was seen only in the doxycycline-treated animals, associated with infection by tetracycline-resistant micro-organisms, which was eventually surpassed by mortality rates in the untreated diabetics (6-9 months). CMT treatment not only decreased mortality but also increased longevity in the Type II diabetic animals, most likely by preventing the development of a number of long-term complications of uncontrolled diabetes, including glycation of proteins, that eventually lead to the demise of untreated diabetic animals.

Therapeutic potential of tetracycline derivatives to suppress the growth of abdominal aortic aneurysms

Abdominal aortic aneurysms (AAA) represent a potentially lethal disorder associated with aging and atherosclerosis. Although current management of AAA is predicted on early detection and elective surgical repair, routine screening for AAA is infrequent, because most AAA are too small to warrant repair when first detected and because there are no therapeutic approaches proven to suppress aneurysm expansion. Basic research on this problem suggests that chronic inflammation and increased local production of elastin-degrading proteinases play prominent roles in the process of aneurysmal degeneration. Members of the matrix metalloproteinases (MMP) family appear to be the most prominent elastases produced in human AAA, suggesting that unique therapeutic targets might exist for aneurysm disease. Studies using a representative animal model for AAA support this view, providing a means for further development of pharmacological approaches to suppress aneurysm expansion. Indeed, recent work indicates that tetracycline derivatives have the potential to interrupt the progressive connective tissue destruction that occurs in AAA, by virtue of their non-antimicrobial properties as MMP inhibitors, and they do so at clinically achievable dose schedules. These findings support the view that MMPs are potentially important pharmacotherapeutic targets in AAA and, moreover, that tetracyclines might be useful in suppressing aneurysm expansion in vivo. Because tetracycline derivatives offer a number of distinct advantages as MMP inhibitors for patients with small AAA, prospective clinical trials of this novel therapeutic strategy can be anticipated in the near future.

Long-term sub-antimicrobial doxycycline (Periostat) as adjunctive management in adult periodontitis: effects on subgingival bacterial population dynamics

Previous trials had indicated that various schedules of sub-antimicrobial doxycycline significantly reduced gingival crevicular fluid (GCF) collagenase activity in adult patients with periodontitis with no evidence of emergent tetracycline-resistant (Tcr) marker oral flora. The purpose of this nine-month study was to expand these observations, emphasizing newer microbial diagnostic methods. Subgingival paper point samples were obtained at baseline (BL), 3, 6, and 9 months. Four subject treatment groups in a double-blind design were evaluated by mechanical scaling and root planing (SRP) and/or 20 mg doxycycline BID (Periostat). Thirty-eight patients entered the study at baseline (BL). Dark-field microscopy on 260 samples showed that morphotype distribution was independent of treatment schedule. Culture analysis of the 3 most prevalent isolates recovered showed that Streptococcus and Prevotella species accounted for approximately 85% of the 724 cultures. There did not appear to be any overgrowth or replacement by opportunistic oral flora. Of 658 susceptibility patterns evaluated by Etest, the MIC50/90 and mode MIC showed stable patterns, independent of treatment group. Our findings were different from those of previously published reports, but may be partly explained by the lack of universally standardized methods in oral microbiology and interpretive criteria for susceptibility testing.

Potential application of low-dose doxycycline to treat periodontitis in post-menopausal women

The purpose of this paper is two-fold: (1) to review the evidence that osteoporosis and post-menopausal estrogen deficiency are associated with progressive alveolar bone loss and an elevated risk of tooth loss; and (2) to propose the use of tetracyclines, specifically low-dose doxycycline (LDD) (and, perhaps in the future, the chemically modified tetracyclines), to mitigate alveolar bone loss in post-menopausal osteoporotic/osteopenic women. Design concepts for a randomized clinical trial to study the effects of LDD on progressive alveolar bone loss in this patient population are reviewed. Since osteoporosis affects over 20 million people in the United States, progressive alveolar bone loss in this patient group represents a potentially significant public health problem unique from common adult periodontitis. Stopping progressive alveolar bone loss is essential to prevent both tooth loss and micro-architectural deterioration of alveolar bone.

Tetracycline derivatives induce apoptosis selectively in cultured monocytes and macrophages but not in mesenchymal cells

Evidence for a non-antibiotic activity displayed by certain tetracycline derivatives is presented. This activity is a selective cytotoxicity toward cells of the monocytic lineage (the human histiocytic lymphoma U937 cell line and the mouse macrophage line RAW264) but not toward various cells of a mesenchymal lineage (including primary ovine articular chondrocytes and meniscal cells, murine calvarial osteoblasts and MG-63 osteosarcoma cells, and primary human neonatal foreskin fibroblasts). Cells were incubated with various chemically modified tetracycline derivatives (CMTs) or doxycycline for 24 hrs at a range of concentrations between zero and 50 micrograms/mL in both serum-containing and serum-free culture conditions. Assessment of cell viability by means of the MTT assay demonstrated a potent dose-dependent cytotoxic effect induced by compound CMT-3 and a less potent effect induced by doxycycline, but no apparent cytotoxic effect in the presence of either CMT-2 or CMT-5. Cytospin preparations analyzed by the labeling of DNA fragments indicated the same trends and suggested that cell death was via an apoptotic mechanism. The cytotoxic potency of these tetracyclines toward cells of the monocytic lineage could be diminished but not abolished by either the presence of 10% fetal calf serum within the culture medium, or pre-treatment with phorbol esters to promote a more macrophage-like phenotype. These data provide evidence that, in addition to well-characterized antibiotic and MMP-inhibitory characteristics, tetracyclines may function by a novel mechanism to induce selective apoptosis.

Minocycline for the treatment of rheumatoid arthritis

The scientific basis for the use of antibiotics (with special emphasis on tetracycline and its derivatives) in the treatment of RA is discussed. The data on efficacy and toxicity are presented. The possible place of tetracycline derivatives within the overall strategy of RA treatment is also presented.

Effects of doxycycline on human prostate cancer cells in vitro

Prostate cancer is the most common form of cancer in older men and the major cause of death from prostate cancer is metastatic disease. The matrix metalloproteinases (MMPs) play a significant role in the growth, invasion and metastasis of many tumors, including those of the prostate. We previously demonstrated that doxycycline, a synthetic tetracycline, inhibits MMPs and cell proliferation and induces apoptosis in several cancer cell lines. We also demonstrated that in an in vivo model of metastatic breast cancer in athymic mice doxycycline inhibits tumor size and regrowth after resection. In the present study, gelatinolytic activity in the human prostate cancer cell line, LNCaP, was suppressed and significant inhibition of cell growth occurred after exposure to 5 or 10 microg/ml of doxycycline, while cell growth was normal in untreated cells. Radioisotope incorporation into proteins was reduced by doxycycline. DNA fragmentation, consistent with apoptosis, was demonstrated in cells treated with doxycycline. These data suggest that doxycycline may have potential utility in the management of prostate cancer.

A chemically modified tetracycline inhibits streptozotocin-induced diabetic depression of skin collagen synthesis and steady-state type I procollagen mRNA

Wasting of connective tissues including skin, bone, and cartilage have been closely associated with elevated matrix metalloproteinase (MMP) activity and depressed collagen content in the streptozotocin (STZ)-induced diabetic rat, while tetracyclines have been reported to normalize total body weight, skin hydroxyproline and collagen content in this model, in part through inhibition of MMPs. In the present study, we report the effect of CMT-1, a chemically modified tetracycline that lacks antimicrobial properties but retains divalent cation binding and MMP inhibitory activity, on diabetic skin collagen synthesis and steady-state levels of procollagen alpha 1(I) mRNA. Male, 4-month old Sprague-Dawley rats received a single injection of 75 mg/kg STZ or citrate vehicle alone and diabetic status was confirmed by positive glucosuria. Some diabetic animals received 10 mg/day of CMT-1 by oral gavage and, 28 days after STZ treatment, body weight, blood glucose values and the in vivo rates of skin collagen production were measured using the pool-expansion technique. Steady-state levels of procollagen alpha 1(I) mRNA were analyzed 21 days after STZ treatment by hybridization of total RNA with a 32P labelled cDNA to rat type I procollagen alpha 1(I) mRNA in a dot-blot assay. STZ treatment was found to significantly depress body weight, skin collagen hydroxyproline content, the in vivo rate of collagen production, and hybridizable levels of type I procollagen alpha 1(I) mRNA. CMT-1 administered daily to STZ-treated rats inhibited the diabetic depression of these parameters but had little or no effect on non-diabetic controls or on STZ-induced hyperglycemia. Thus, in addition to the inhibition of MMP mediated extracellular collagen degradation, these results suggest CMT-1 also acts to inhibit diabetic connective tissue breakdown in STZ-induced diabetes by increasing both steady-state levels of type I procollagen mRNA and collagen synthesis through mechanism(s) that are independent of the antibacterial properties of tetracyclines.

Tetracycline inhibits the nitric oxide synthase activity induced by endotoxin in cultured murine macrophages

Here we investigate the effects of tetracycline base and of a semi-synthetic tetracycline derivative, doxycycline, on the induction of inducible nitric oxide synthase and, hence, on the production of nitric oxide (NO) by lipopolysaccharide in J774 macrophage cultured in vitro. The treatment of J774 line with tetracycline base (6.25-250 microM) or doxycycline (5-50 microM) dose-dependently decreased the lipopolysaccharide-stimulated (1 microg/ml) inducible NO synthase activity and, consequently, nitrite formation. For instance, the inhibition was 70% for tetracycline base at 250 microM and 68% for doxycycline at 50 microM. The inhibitory effect of tetracyclines was due neither to a reduction in the viability of the cells, studied as colorimetric 3-[4,5-dimethylthiazol-2yl]-2,5-diphenyltetrazolium bromide (MTT) reduction assay, nor to an indiscriminate inhibition of total protein synthesis, but to a specific decrease in inducible NO synthase protein content in the cells, as attested by the significant reduction of the expression of inducible NO synthase, assayed by sodium-dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) and Western blot. However, no effect of tetracyclines on inducible NO synthase mRNA accumulation could be demonstrated in lipopolysaccharide-stimulated macrophage line, suggesting that the inhibitory effect of tetracyclines on NO synthesis involves post-transcriptional events. The reduction in lipopolysaccharide-stimulated nitrite accumulation produced by tetracyclines was significantly less when they were applied 6 h after lipopolysaccharide and absent 12 h after lipopolysaccharide, indicating that tetracyclines modify an early event in inducible NO synthase activation operating after mRNA transcription. The findings presented in this study indicate that the modulation of NO synthesis is another possible pathway by which tetracyclines may function as anti-inflammatory compounds.