The in vivo fractional rate of gingival collagen production in non-diabetic and diabetic rats. Application of a novel approach for quantification-pool expansion

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.

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.

Age-related changes in collagen synthesis and degradation in rat tissues. Importance of degradation of newly synthesized collagen in regulating collagen production

During developmental growth, collagens are believed to be continuously deposited into an extracellular matrix which is increasingly stabilized by the formation of covalent cross-links throughout life. However, the age-related changes in rates of synthetic and degradative processes are less well understood. In the present study we measured rates of collagen synthesis in vivo using a flooding dose of unlabelled proline given with [14C]proline and determining production of hydroxy[14C]proline. Degradation of newly synthesized collagen was estimated from the amount of free hydroxy [14C]proline in tissues 30 min after injection. Collagen fractional synthesis rates ranged from about 5%/day in skeletal muscle to 20%/day in hearts of rats aged 1 month. At 15 months of age, collagen fractional synthesis rates had decreased markedly in lung and skin, but in skeletal muscle and heart, rates were unchanged. At 24 months of age, synthesis rates had decreased by at least 10-fold in all tissues, compared with rates at 1 month. The proportion of newly synthesized collagen degraded ranged from 6.4 +/- 0.4% in skin to 61.6 +/- 5.0% in heart at 1 month of age. During aging the proportion degraded increased in all tissues to maximal values at 15 months, ranging from 56 +/- 7% in skin to 96 +/- 1% in heart. These data suggest that there are marked age-related changes in rates of collagen metabolism. They also indicate that synthesis is active even in old animals, where the bulk of collagens produced are destined to be degraded.

[Periodontal reactions to orthodontic forces in the diabetic metabolic state]

The reaction of the periodontium to orthodontic tooth movement was studied in rats with streptozotocin diabetes. Forces employed to initiate mesial movement of first molar were 10 N 20 N 30 N and the duration of application was three, six, ten and 14 days. The 14-day rats were treated with fluorochrome sequential labelling according to Rahn. Diabetes mellitus in rats is accompanied by characteristic changes: The most important findings were: 1. a slow osseous regeneration, as could be shown by fluorescence microscopy, 2. the new bone ist unable to pick up the labellings in a sequential manner, 3. a weakening of the periodontal ligamentum, 4. microangiopathies in the gingiva area. the specific diabetic changes are more pronounced following orthodontic tooth movement.

Streptozotocin-induced diabetes and the rat periodontium: decreased relative collagen production

This is the first study concerning the extent to which relative collagen production (RCP) in rat periodontal tissues is affected by diabetes. Determination of RCP, rather than individual production rates for collagen or for non-collagen protein, was deemed necessary because saturation of all proline pools in tissues of diabetics (and non-diabetic controls) was not achieved. Such non-saturation occurred despite the injection of a pool-expanding dose of proline (400-1150 mg/rat), non-saturation indicated by the lesser specific radioactivity (S.R.) of free-[3H]proline in tissues than that of the injected solution. RCP was decreased in five periodontal tissues (incisor and molar gingiva, incisor and molar periodontal ligament, antemolar palatal mucosa) and in skin. Diabetes-decreased RCP seems to result from decreased collagen synthesis and increased intracellular degradation, although some evidence is presented for increased extracellular degradation of recently secreted collagen.

Collagen synthesis and degradation in vivo. Evidence for rapid rates of collagen turnover with extensive degradation of newly synthesized collagen in tissues of the adult rat

Collagen turnover is now known to occur more rapidly in body tissues than traditionally believed, but the kinetics and mechanisms for degradation are still poorly understood. Here we measure collagen synthesis rates and the proportion of newly synthesized collagen (probably procollagen) which is rapidly degraded, in tissues of the adult rat after injection of [14C]-proline with a large "flooding" dose of unlabelled proline. Incorporation of [14C]-proline into lung, heart, skeletal muscle and skin collagen and its appearance as hydroxy [14C]-proline, free or in small molecular weight moieties, at various times up to one hour, suggested extremely rapid synthesis and degradation for some tissues of the adult rat. Values in heart, lung, skeletal muscle and skin (with the proportion of degradation of newly synthesized collagen shown in parentheses) were 5.2 +/- 0.7%/day (53 +/- 5%), 9.0 +/- 0.7%/day (37 +/- 2%), 2.2 +/- 0.3%/day (38 +/- 7%) and 4.4 +/- 1.3%/day (8.8 +/- 0.5%). These data provide in vivo evidence, which are consistent with the observation in isolated cells, that a proportion of newly synthesized collagen is degraded rapidly, and probably intracellularly, after its synthesis. They also indicate that collagen may be synthesized and degraded rapidly in normal rat tissues, but the mean turnover rates and the proportions of collagen degraded intracellularly vary widely between tissues.