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.

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.

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.

Chemically modified non-antimicrobial tetracyclines inhibit activity of phospholipases A2

OBJECTIVE

Tetracyclines have been recognized as useful agents for therapy of inflammatory arthritides. However, prolonged use of tetracyclines is limited by their detrimental antimicrobial properties. Recently, a group of chemically modified tetracyclines (CMT) devoid of antimicrobial properties has been synthesized. Some CMT were found to inhibit various matrix metalloproteinases (MMP). We reported previously that antimicrobial tetracyclines inhibit the activity of proinflammatory secretory group II phospholipase A2 (sPLA2). The objective of this study was to detect whether non-antimicrobial CMT also inhibit sPLA2 and other phospholipases A2.

METHODS

Ten synthetic CMT were tested for inhibition of sPLA2 human and porcine PLA2, and Naja naja PLA2. PLA2 activity was assessed by radiolabeled Escherichia coli assay using standard and high calcium concentrations.

RESULTS

Six of 10 CMT inhibited sPLA2 activity at concentrations close to or lower than 50 microg/ml. All 6 CMT had identical C1-3 and C10-12a positions in the 4-ringed nucleus of the tetracycline molecule. Calcium concentrations up to 20 mM did not eliminate the inhibitory activity of CMT. Inhibition of other PLA2 was induced by some CMT, all but one (CMT-9) belonging to the group of strong inhibitors of sPLA2. Thus, inhibition of PLA2 different from sPLA2 does not necessarily require identical C1-3/C10-12a residues.

CONCLUSION

Since CMT, which inhibit proinflammatory sPLA2, are also inhibitors of some MMP, they may be useful for therapy of inflammatory diseases in which both MMP and sPLA2 are overexpressed.

Chemically modified tetracyclines inhibit human melanoma cell invasion and metastasis

Recent work has shown that chemically modified tetracyclines (CMTs) are potent inhibitors of matrix metalloproteinase (MMP) activity, both in vitro and in vivo, which is distinct from their antimicrobial activities (Golub et al. Crit Rev Oral Biol Med, 2, 297-321, 1991; Ryan et al. Curr Opin Rheumatol, 8, 23847, 1996). The process of tumor cell invasion requires MMP-mediated degradation of extracellular matrix barriers as a key step in the metastasic cascade. In this study, we examined the effect(s) of doxycycline and CMTs on extracellular levels of gelatinase A and B activity from a highly invasive and metastatic human melanoma cell line C8161, and correlated these observations with changes in the cells' biological behavior in an in vitro invasion assay and in an in vivo SCID mouse model. The results indicate that coincident with the ability of these compounds to differentially suppress extracellular levels of gelatinase activity, C8161 cells treated with doxycycline, CMT-1, CMT-3, or CMT-6 were less invasive in vitro in a dose-dependent manner (3-50 microg/ml). Furthermore, data derived from the in vivo model indicate that SCID mice dosed orally with CMT-1 or CMT-3 contained a reduced number of lung metastases following i.v. injection of C8161 cells via tail vein inoculation. These observations suggest that careful screening of different CMTs could lead to the identification of compounds which suppress the formation and magnitude of metastases associated with certain cancers, and if used as an adjunct to other treatment regimes, lead to greater efficacy in the treatment of metastatic cancers.

Local and systemic factors in periodontal disease increase matrix-degrading enzyme activities in rat gingiva: effect of micocycline therapy

We previously reported that both local and systemic factors relevant to the pathogenesis of periodontal disease can increase gingival collagenase activity in rats. Since the degradation of extracellular matrix is an essential feature of periodontal disease and this tissue breakdown requires multiple enzyme interactions, the current study was carried out to determine the effects of bacterial endotoxin (LPS) (a local factor) and diabetes (a systemic factor) on a panel of matrix-degrading enzymes (collagenase, gelatinase, elastase, and beta-glucuronidase) in the gingiva of rats. In addition, the effects of therapy with a semisynthetic tetracycline (minocycline) were investigated. Ten male, Sprague-Dawley rats were made diabetic by IV injection of streptozotocin. Four of the ten rats then received minocycline (10 mg/day) by oral gavage on a daily basis for 3 weeks. Nineteen nondiabetic rats served as controls and 9 of them received 10 microliters of E. coli LPS (10 mg/ml) by injection into the labial gingiva every other day during the last week of the study. The other 10 nondiabetic rats were sham injected with saline into the gingiva. At the end of the 3 week experimental period, gingival tissue and skin were dissected from each rat and extracted for enzyme analysis. Our results showed that diabetes markedly increased the four matrix-degrading enzyme activities in both gingiva and skin. In contrast, local LPS injection increased these enzyme activities in the gingiva alone. Systemic therapy with minocycline completely ameliorated these elevated enzyme levels in diabetic rats in both gingiva and skin. Minocycline added in vitro to the enzyme assay systems containing skin extract from diabetic rats also inhibited collagenase and gelatinase activities, but no inhibition was observed for elastase and beta-glucuronidase activities, indicating that the MMPs and other enzymes were inhibited by minocycline, during diabetes, by indirect and indirect mechanisms, respectively.

Tetracyclines inhibit Porphyromonas gingivalis-induced alveolar bone loss in rats by a non-antimicrobial mechanism

Tetracyclines have been widely used as adjuncts in periodontal therapy due to the antimicrobial efficacy of these drugs. Recently, their ability to inhibit host-derived matrix metalloproteinases (collagenase and gelatinase) and bone resorption in organ culture has also been invoked as a therapeutic rationale. The current study was undertaken to determine whether tetracyclines can inhibit alveolar bone loss in vivo due to a non-antimicrobial action of these drugs. Experimental periodontitis was induced by inoculating adult, male Sprague-Dawley rats with P. gingivalis (strain 381) following kanamycin/ampicillin pretreatment. Doxycycline, non-antimicrobial chemically-modified tetracycline (CMT-1) and vehicle alone were administered daily to 3 infected groups of rats (n = 6 rats per group; each group housed in a sterilized inflatable isolator) beginning 10 days after P. gingivalis inoculation. The control group (n = 6; non-infected rats) received only vehicle. After 5 weeks of daily drug administration by gastric intubation, the experiment was terminated and blood samples were taken from each animal to determine antibody levels against P. gingivalis. Plaque samples were collected from each group of animals before and after P. gingivalis inoculation and at the end of the experiment for microbiological examination. The jaws were removed from each rat, defleshed and then analyzed morphometrically and radiographically to assess bone loss. Serum antibody levels against P. gingivalis were significantly elevated in the 3 infected groups compared to the non-infected controls. This, together with the microbiologic findings, indicated that these groups of rats were infected with P. gingivalis.(ABSTRACT TRUNCATED AT 250 WORDS)

Chemically-modified tetracycline normalizes collagen metabolism in diabetic rats: a dose-response study

An earlier study indicated that a chemically-modified non-antimicrobial tetracycline (4-de-dimethylaminotetracycline; CMT-1) can inhibit excess collagenase activity in the connective tissues of diabetic rats, however, the optimum oral dose and resulting serum concentration were not determined. In the current study, adult male Sprague-Dawley rats (body weight approx. 350 g) were made diabetic by streptozotocin injection and administered by oral gavage either 0, 1, 2, 5, or 10 mg CMT-1 per day. After 3 weeks of drug therapy, the rats were killed and gingiva, skin, and serum collected. The tissues were 1) extracted, partially purified and analyzed for collagenase activity using [3H-methyl] collagen as substrate and SDS-PAGE/fluorography; 2) extracted in neutral salt and dilute acid solutions (4 degrees C) to assess collagen solubility; and 3) analyzed for hydroxyproline to determine tissue (skin) collagen mass. Serum was analyzed for glucose and CMT-1 concentration, the latter by HPLC. Inducing diabetes dramatically increased both gingival and skin collagenase activity and reduced skin collagen mass by 69.8%. Increasing the oral dose of CMT-1 progressively increased the serum concentration of the drug from 0.6-6.5 micrograms/ml and progressively decreased the excessive collagenase activity in gingiva and skin (p < 0.01 vs untreated diabetics). Although skin collagen mass tended to be increased at all oral doses of CMT-1, only the 5 mg dose effect was statistically significant (p < 0.01). The diabetes-induced reduction in collagen solubility, a classic abnormality (reflecting excessive collagen crosslinking) of this disease, was also normalized by CMT-1 therapy.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of doxycycline hyclate on corneal epithelial wound healing in the rabbit alkali-burn model. Preliminary observations

We examined the effects of doxycycline hyclate on epithelial healing in vivo in the rabbit alkali-burn model. Twelve 2-3-kg Dutch belted rabbits were divided into three groups and received standard bilateral alkali burns (1 N sodium hydroxide for 30 s in an 11-mm circular plastic well). In group 1, two rabbits (four eyes) served as untreated controls. In group 2, five rabbits (10 eyes) received doxycycline hyclate (1.5 mg/kg) orally daily for 14 days. In group 3, five rabbits (10 eyes) received doxycycline hyclate (5 mg/kg) orally daily for 14 days. The epithelial defects were drawn and photographed on alternate days, after fluorescein staining. At conclusion, extracts of the corneas were evaluated for collagenase activity. At 14 days, the mean percentage of epithelial defects results in groups 1-3 were 50.0, 50.7, and 7.1%, respectively. Using the Wilcoxon rank sum test (two tailed), the differences were found to be statistically significant (p = 0.0015). Preliminary data indicated that oral doxycycline administration also decreased the collagenase activity in corneas obtained from these animals. Our preliminary findings indicated that systematically administered doxycycline hyclate, 5 mg/kg/day, promotes corneal reepithelialization in the rabbit alkali-burn model, a result, perhaps, of the drug's ability to inhibit excessive collagenase activity.

HPLC determination of a chemically modified nonantimicrobial tetracycline: biological implications

Chemically modified tetracycline (4-de-dimethylamino tetracycline), like commercially available tetracyclines, is known to inhibit experimentally induced pathologic collagen breakdown. A method for measurement of chemically modified tetracycline in small volumes (50 microliters) of rat serum was developed using reversed-phase HPLC; this was necessary because this tetracycline analog lacks antimicrobial activity and, therefore, cannot be measured with standard bioassays. This method uses the same solution for extraction and elution thus providing a simple and rapid assay for both drugs. Using this technique, the concentration of chemically modified tetracycline and tetracycline were determined in rat serum at different times after oral administration. The serum concentration of chemically modified tetracycline was much higher than that for tetracycline, and its serum half-life was greater. The IC50 of chemically modified tetracycline and tetracycline, as inhibitors of collagenase from rat polymorphonuclear leukocytes, was determined and found to be 4.1 x 10(-8) M (0.02 micrograms/ml) and 2.4 x 10(-4) M (120 micrograms/ml), respectively. Based on the serum levels of these drugs after oral administration, and their IC50 values, chemically modified tetracycline is potentially a far more potent inhibitor of excess collagenase activity than tetracycline, during pathologic conditions, and may have the added advantage of not producing some of the typical complications of long-term antibiotic therapy.

Tetracyclines inhibit connective tissue breakdown: new therapeutic implications for an old family of drugs

Tetracyclines have long been considered useful adjuncts in peridontal therapy based on their antimicrobial efficacy against putative periodontopathogens. However, recently these drugs were found to inhibit mammalian collagenases and several other matrix metalloproteinases (MMPs) by a mechanism independent of their antimicrobial activity. Evidence is presented that this property may be therapeutically useful in retarding pathologic connective tissue breakdown, including bone resorption. The experiments leading to this discovery are described and possible mechanisms are addressed, including the specificity of tetracyclines' anti-collagenase activity, the role of the drugs' metal ion (Zn2+, Ca2+)-binding capacity, and the site on the tetracycline molecule responsible for this nonantimicrobial property. Of extreme interest, the tetracycline molecule has been chemically modified in multiple ways, generating a new family of compounds called CMTs (chemically modified tetracyclines) that lack antimicrobial but still retain anti-collagenase activity. The first of these CMTs, 4-de-di-methylaminotetracycline, was found not to produce a major side-effect of antimicrobial tetracycline therapy--its administration to experimental animals did not result in the emergence of tetracycline-resistant microorganisms in the oral flora and gut. Numerous examples of the clinical potential of this non-antimicrobial property of tetracyclines in the treatment of periodontal and several medical diseases (e.g., sterile corneal ulcers, rheumatoid arthritis, skin bullous lesions, tumor-induced angiogenesis and metastasis) are discussed.

Topical application of doxycycline on periodontally involved root surfaces in vitro: comparative analysis of substantivity on cementum and dentin

In this study, substantivity of topically applied doxycycline hydrochloride on root surfaces obtained from patients with periodontal disease was studied in vitro. Cementum and dentin specimens were impregnated with aqueous solutions of doxycycline for 3 minutes, and incubated in serum for 10 minutes, 7 days, and 14 days. Substantivity was determined by agar diffusion inhibition assay. Comparative analyses of cementum versus dentin groups were conducted with 2-way analysis of variance. Results indicated that there was no statistically significant differences between the binding potential of doxycycline to cementum and dentin specimens. Antibacterial effect of specimens treated with the concentration of 100 mg/ml persisted for 14 days, indicating the presence of doxycycline in biologically active form. Our findings demonstrate the long lasting substantivity of doxycycline hydrochloride on periodontally diseased root surfaces and supports the concept of using root surfaces as a substrate for the deposition and slow release for local tetracycline delivery.

Low-dose doxycycline therapy: effect on gingival and crevicular fluid collagenase activity in humans

Tetracyclines are now recognized to have non-antimicrobial properties with therapeutic potential--for example, these agents can inhibit pathologic collagenolysis by blocking mammalian collagenases and other matrix-degrading metalloproteinases. In the current study, adult human subjects with moderate chronic periodontitis were administered specially formulated capsules of doxycycline, containing lower-than-usual amounts of this semi-synthetic tetracycline, on a daily basis for 2 weeks prior to a full-thickness flap procedure; control subjects were administered placebo capsules. The gingiva excised during this surgical procedure were extracted, the extracts partially purified and analyzed for collagenase activity using [3H-methyl] collagen as substrate and the techniques of SDS-PAGE/fluorography or liquid scintillation spectrometry. In the absence of any drug pre-treatment, or after a 2-wk regimen of placebo capsules, the gingival extracts exhibited pathologically-excessive mammalian collagenase activity. The 2-wk regimen of low-dose doxycycline capsules reduced this activity by approximately 60-80% (p less than 0.05 and less than 0.01, respectively); in vitro exposure of the gingival extract to doxycycline also inhibited its collagenase activity. Collagenase activity in the crevicular fluid of periodontal pockets of an additional group of subjects was also significantly reduced, as was the severity of inflammation at the same gingival sites. The results suggest that a regimen of low-dose doxycycline capsules may provide a safe (other studies indicate that this regimen may not induce tetracycline resistance in the subgingival plaque) and effective adjunct to instrumentation therapy in the management of pathologic collagenolysis in the periodontal patient. However, further studies are necessary to confirm this hypothesis.

Tetracycline administration prevents diabetes-induced osteopenia in the rat: initial observations

A tetracycline (doxycycline) was administered daily by oral intubation to adult diabetic rats to assess the effect on skeletal tissue; the rationale--osteopenia is a complication of diabetes and tetracyclines (TCs) were recently found to inhibit pathologic collagen loss (e.g. in diabetic rat skin) by a mechanism independent of their antimicrobial efficacy. Osteopenia was induced by streptozotocin-diabetes as indicated by physical (e.g. specific gravity), chemical (e.g. calcium (Ca) content) and ultrastructural characteristics of the femurs, and TC administration (including treatment with a chemically-modified non-antimicrobial analog) appeared to prevent the development of the bone deficiency disease without affecting the severity of hyperglycemia.

A non-antibacterial chemically-modified tetracycline inhibits mammalian collagenase activity

Tetracyclines (including the semi-synthetic analogues, minocycline and doxycycline) are considered useful adjuncts in periodontal therapy because they suppress Gram-negative periodontopathogens. Recently, these antibiotics were found to inhibit mammalian collagenase activity, a property which may also be of therapeutic value. It has been suggested that the anti-collagenase properties of the tetracyclines are independent of their antibiotic efficacy. To advance this hypothesis further, we chemically converted tetracycline hydrochloride to its non-antimicrobial analogue, de-dimethylaminotetracycline. This chemically-modified tetracycline (CMT), although no longer an effective antibiotic, was found to inhibit the in vitro activity of collagenase from partially purified extracts of human rheumatoid synovial tissue and rachitic rat epiphysis. In a preliminary in vivo study, pathologically-excessive collagenase in skin and gingiva was induced by rendering adult male rats diabetic, and the oral administration of CMT to these rats significantly reduced the excessive collagenase activity in both tissues. Moreover, CMT administration did not affect the severe hyperglycemia in these rats but did prevent, at least in part, the diabetes-induced loss of body weight, skin weight, and skin collagen mass; these effects suggest a lack of toxicity in this animal model. A proposed clinical advantage of CMT over conventional tetracyclines, in the treatment of diseases characterized by excessive collagenolytic activity, is the lack of development of antibiotic-resistant micro-organisms during prolonged use. However, the consideration of clinical trials to support this hypothesis must await further laboratory and extensive toxicity tests.

Tetracyclines inhibit human synovial collagenase in vivo and in vitro

To determine if tetracyclines can inhibit human synovial collagenase from rheumatoid tissue, paired synovial tissue (or synovial fluid) was collected from 7 patients before and after oral administration of minocycline (100 mg BID) for 10 days. With each patient serving as his own control, the postminocycline collagenase activities fell an average of 67% from pretreatment values. Qualitative SDS-PAGE revealed decreased loss of alpha collagen components and reduced formation of alpha A digestion fragments. Addition of minocycline or a chemically modified tetracycline to synovial culture media in vitro profoundly inhibited collagenase activity. Further study of this action of tetracyclines could serve as a probe of the role of collagenase in rheumatoid arthritis and lead to development of agents capable of modifying the tissue destructive actions of collagenase.

Systemic tetracycline treatment of alkali-induced corneal ulceration in rabbits

Recent evidence has demonstrated a marked anticollagenolytic effect for the tetracycline antibiotics. We have examined the efficacy of systemic tetracycline hydrochloride in a rabbit model of corneal ulceration. A standard alkali burn (1N sodium hydroxide for 40 s) was delivered to 62 eyes (31 rabbits). Animals were then divided into three groups: group 1 (controls) (ten rabbits [20 eyes]) received no treatment; group 2 (ten rabbits [20 eyes]) received 10 mg/kg/d of tetracycline hydrochloride, given intramuscularly; and group 3 (11 rabbits [22 eyes]) received 50 mg/kg/d. Ulceration occurred in 85% (17/20) of control eyes. The higher dosage of tetracycline was more effective in preventing ulceration than the lower dosage (9.1% vs 55%). Eyes with higher levels of tetracycline in ocular tissues were less likely to ulcerate.

Tetracyclines inhibit tissue collagenases. Effects of ingested low-dose and local delivery systems

In a series of experiments, Golub et al. demonstrated that tetracyclines, but not other antibiotics, can inhibit mammalian collagenases and proposed that this property could be useful in treating diseases, such as periodontal disease (but also included certain medical conditions, e.g., corneal ulcers) characterized by excessive collagen degradation (J Periodont Res 1983, 1984 and 1985; Experientia 1984; Cornea 1984). One effect was the dramatic reduction of tissue collagenase activity within the gingival crevicular fluid (GCF) of periodontal pockets after administering a standard regimen of a tetracycline (e.g., 200 mg minocycline or 1000 mg tetracycline/day). The preliminary studies described below determined the effect of (1) low-dose (LD; 40-80 mg/day) orally administered minocycline on GCF collagenase activity and on the subgingival microflora (Exp. I), and (2) tetracycline-loaded monolithic fibers (TF) on collagenase activity in vitro (Exp. II). In Exp. I, GCF collagenase activity was reduced by 45 to 80% 2 weeks after initiating LD minocycline therapy, an effect that lasted for at least several weeks after stopping drug treatment. No consistent change in the relative proportions of G(+), G(-) and motile subgingival microorganisms was detected as a result of LD treatment suggesting that the reduction in GCF collagenase activity was a direct inhibition of the enzyme by the drug. In Exp. II, 3- and 6-mm lengths of TF in vitro established tetracycline concentrations in 250 microliters of 132 micrograms/ml, from 3-mm lengths, and 265 micrograms/ml, from 6-mm lengths, after an 18-hour incubation.(ABSTRACT TRUNCATED AT 250 WORDS)

In vitro and in vivo studies of cellular lysis of oral bacteria by a lysozyme-protease-inorganic monovalent anion antibacterial system

Compared with anion-activated cell lysis of oral bacteria damaged with either lysozyme or trypsin, cells which were treated with both of these enzymes showed a far greater degree of lysis. This was true regardless of whether turbidimetric, DNA release, or electron microscopic assays were used to monitor the lytic process. At an acidic pH of 5.2 and an NaHCO3 concentration of 100 mM, the kinetics of lysis for two different serotype c strains of Streptococcus mutans were similar. At 0 to 100 mM bicarbonate, however, differences in the lytic susceptibilities of the two strains were evident. At pH 5.2, NaHCO3, but not NaSCN, NaCl, or NaF, was effective in promoting cell lysis of the oral bacteria. At apparent sublytic concentrations of NaHCO3, lysis was achieved by adding appropriate concentrations of NaSCN, NaCl, or NaF to the lysozyme-protease-damaged cells. In in vivo studies, hamsters given a combination of NaHCO3, NaCl, and NaSCN were found to have significantly reduced levels of S. mutans on their molar teeth compared with that found in controls or animals exposed to any one of the salts alone or to a combination of chloride and thiocyanate only. The results suggest that bicarbonate is an essential anion which, together with the other major salivary inorganic monovalent anions, plays an active role in the lysis and ultimate elimination of cariogenic bacteria.

The development of an altered gingival crevicular microflora in the alloxan-diabetic rat

The microflora of the rat gingival crevice were examined at various time intervals after inducing experimental diabetes. A variety of Gram-positive and Gram-negative cocci and short rods were isolated from the normal rat crevice. Within a week after alloxan administration, Leptotrichia buccalis was detected for the first time. Other features in the diabetic animals included an increased frequency of isolation of Proteus spp., Lactobacillus spp. and decrease of Escherichia coli. Occasionally, a decrease was also observed in Bacteroides spp. and Streptococcus spp. No difference was observed between diabetic and non-diabetic animals in the isolation of Selonomonas, Campylobacter, Bifidobacterium and Actinomyces. Plaque accumulation was markedly increased in the diabetic rats. It was concluded that the change in gingival microflora resulted from diabetes-induced alterations in the sulcular environment (such as increased substrate levels, e.g. glucose and urea, and decreased oxygen) and that the microbiological changes preceded the depending of the periodontal pocket.

The role of C. albicans in denture stomatitis

Denture stomatitis is an erythematous disorder of the denture-bearing tissues, especially the maxillary hard palate. Frequently it mimics many oral lesions. Early diagnosis of the lesion is essential to assure rational therapy. A diagnostic procedure based upon the enumeration of Candida albicans appeared to be feasible. A control group of twenty fully dentate subjects with no clinical evidence of stomatitis was sampled to establish normal concentrations of C. albicans in the oral flora. Samples were taken from a triangular area of the hard palate, serially diluted in broth, and all dilutions were incubated aerobically. In the control population, C. albicans never exceeded 100 organisms per square centimeter per subject sample. A population of edentulous patients with denture stomatitis, prior to any therapy, was similarly sampled. In many of these patients the concentration of C. albicans always exceeded 10,000 organisms per square centimeter per patient. The patients received denture replacements and antimycotic antibiotic therapy. Follow-up cultures were taken 4 to 6 weeks after completion of therapy. All patients were found to be free of denture stomatitis.

Cariostatic activity of calcium glycerophosphate in hamsters: topical vs dietary administration

Two experiments were conducted to determine if calcium glycerophosphate administered continuously in a diet or intermittently as a single daily topical application to teeth had an anticaries potential in young hamsters that were fed a cariogenic diet. The hamsters were inoculated with a caries-conductive streptococcal strain. Within the 60-day experimental period, results of these evaluations indicated calcium glycerophosphate significantly reduces caries when fed in the diet at levels of 1% and higher, and significantly reduces caries when applied topically at levels of 2% and higher. There were no observable differences in plaque formation among treatments.