stock solutions of minocycline , dedimethylaminotetracycline ( cmt ) and tetracycline were prepared as aqueous solutions . these solutions were to be used to determine the antibacterial activity of each of these tetracyclines . the minocycline was obtained from sigma chemical company , st . louis , mo ., lot # 60f - 0048 . the tetracycline was also obtained from sigma chemical company , st . louis , mo ., lot # 103f0350 and the dedimethylaminotetracycline was synthetically prepared in accordance withm the method of j . h . boothe et al , j . am . chem . soc ., vol . 80 page 1654 ( 1958 ) and j . r . d . mccormick et al , j . am . chem . soc ., vol . 79 , page 2849 ( 1957 ). the stock solutions were prepared as aqueous solutions containing 100 micrograms per milliliter of each of the compounds . to 10 . 00 mg . of either minocycline , tetracycline or dedimethylaminotetracycline , 10 ml of distilled water was added and the suspension was swirled in a 100 . 0 ml volumetric flask . to each 10 ml suspension of the compound 1 . 0 ml of 1 . 0 sodium hydroxide was added to produce a clear solution of each compound . approximately 70 ml of distilled water was added to each solution and the ph was adjusted to a ph of 8 . 0 to 8 . 3 by the addition of the appropriate amount of 1 . 0n hydrochloric acid . each solution was then made up to 100 . 00 ml in the volumetric flask by the addition of distilled water . the final concentration of each of these compounds was 100 micrograms per ml . the stock solutions were stored in the refrigerator until they were used . stock solutions were made fresh daily . in order to demonstrate that the dedimethylaminotetracycline ( cmt ) had reduced antimicrobial activity a comparison was made of the minimum inhibitory concentration ( mic ) of each of the compounds . a comparison of the mic of minocycline , tetracycline and dedimethylaminotetracycline were carried out in the following manner . to a series of tubes containing 3 . 0 ml of sterile brain heart infusion ( bhi ) broth ( difco ) appropriate amounts of the stock solutions of minocycline , dedimethylaminotetracycline and tetracycline were added to produce concentrations as shown in table 1 . each tube was then adjusted with sterile bhi broth to a final volume of 4 . 0 ml . each tube in the series was then inoculated with 0 . 1 ml of a 24 hour broth culture of bacillus cereus which had been incubated at 37 ° c . the tubes were then vortexed and incubated at 37 ° c . for 24 hours . the tubes were then read for the presence or absence of growth which was determined by turbidity . the results of these comparative evaluations for antimicrobial activity are recorded in table 1 . it was evident that the dedimethyl - aminotetracycline has no detectable antibacterial activity against bacillus cereus . it was more than 100 fold less active than tetracycline and more than 1 , 000 fold less active than minocycline . bacillus cereus was used as the test organism because it is routinely used for tetracycline assays due to its extreme sensitivity to these antibiotics . the organism was obtained from the american type culture collection ( atcc # 11778 ). table i______________________________________summary of the results of the in vitro evaluation of theantibacterial activity of minocycline , tetracycline anddedimethylaminotetracyclineantibiotic conc . antibiotic dedimethylamino -( μg / ml ) minocycline tetracycline tetracycline______________________________________2 . 5 - - + 2 . 0 - - + 1 . 5 - - + 1 . 0 - - + 0 . 5 - - + 0 . 1 - - + 0 . 025 - - + 0 . 010 - + + 0 . 005 - + + 0 . 0025 - + + 0 . 001 + + + ______________________________________ 1 bacillus cereus was selected for this evaluation due to its sensitivit to tetracycline and its use for tetracycline antibiotic assays . 2 + = growth - = no growth conventional animals and animals rendered diabetic were either not treated or treated with metronidazol or dedimethylaminotetracycline in a comparative study to determine the in vivo activity of dedimethylaminotetracycline . in this study four different groups of rats were utilized . group i was an untreated control group of conventional rats harboring a normal oral flora ; group ii was an untreated control group of diabetic rats rendered diabetic by administration of streptozocin ; group iii was a diabetic group treated orally with metronidazol and group iv was a diabetic group of animals treated orally with dedimethylaminotetracycline . at the conclusion of the experiment the rats were sacrificed and samples were removed with sterile currettes from the gingival margin of the molar teeth of rats from each of these groups of animals and transferred to broth and incubated for 72 hours at 37 ° c . the organisms isolated were compared to determine if there was any major change in the composition of the flora following the administration of either metronidazol or dedimethylaminotetracycline . the results of the isolation and identification of the organisms obtained from gingival samples indicated that : ( 1 ) the untreated conventional control animals had slightly more organisms present than the animals in any of the other groups and were easily identified by the amount of growth and by the bacterial compositions , ( 2 ) the diabetic animals receiving metronidazol produced less growth from the gingival samples than any other group and had predominantly gram positive cocci ; ( 3 ) the untreated diabetic control animals and the diabetic animals receiving dedimethylaminotetracycline were essentially indistinguishable in the amount of growth obtained from the gingival samples and in the bacterial composition of each sample . these results are summarized in table 2 . these in vivo studies clearly demonstrated that metronidazol preferentially suppressed the gram negative anaerobic organisms in the crevicular microflora , as expected , whereas the dedimethylaminotetracycline or cmt did not have any detectable effect on the crevicular microflora in contrast to the effect of antibiotic tetracyclines . golub et al , j . periodontal res . 18 : 516 , 1983 demonstrated that an antibiotic tetracycline suppressed the gram - neg anaerobic organisms in the crevicular flora of the diabetic rat , similar to the effect described above for metronidazole . table 2__________________________________________________________________________summary of the results of the organisms isolated from untreated animals ( conventional / diabetic ) and animals treated with either metronidazol orminocycline ( diabetic ) conventional diabeticorganisms untreated untreated metronidazol cmt * __________________________________________________________________________e . coli + + + + bacteroides + - - - fusobacterium + + - + proteus + - - - vellonella + + - + leptotrichia + - - - stretpococcusalpha hemolytic - - + - beta hemolytic - - + - gamma hemolytic + + + + actinomyces + + + + lactobacillus + - - + staphylacoccus - + + + bifidobacterium + - - - candida + (±) - - __________________________________________________________________________ * chemically modified tetracycline + = present - = not present bacterial collagenase ( from c . histolyticum ), which like mammalian collagenase is a calcium dependent metallo - protease , was incubated for 18 hrs . at 27 ° c . with [ 3 h - methyl ] collagen in the presence of 0 , 20 or 60 ug / ml of cmt and the results are shown in fig1 . in the absence of cmt , increasing the bacterial collagenase levels in the incubation mixture from 10 - 100 ng increased the degradation of the radiolabeled collagen substrate ( from 40 - 90 %), as expected . a similar pattern was seen when 20 ug / ml cmt was added , however , at all levels of bacterial collagenase ( 10 - 100 ng ) the breakdown of collagen was lower than that seen in the absence of cmt . increasing the concentration of cmt to 60 ug / ml essentially completely inhibited collagenase activity at all of the enzyme levels tested . another experiment was carried out . in this experiment , a single level of bacterial collagenase was incubated ( a ) with a wide range of concentrations of cmt ( 0 , 2 , 10 , 20 and 60 ug / ml ) and ( b ) with the known inhibitors of metallo - proteases , edta and phenanthroline . as in the first experiment , 10 ng of collagenase degraded about half of the available radiolabeled collagen substrate after an 18 hr . incubation at 27 ° c . in the absence of cmt , fig2 . the very low concentration of 2 ug / ml cmt inhibited collagenase activity by about 20 % while the concentrations of 10 - 60 ug / ml cmt reduced activity about 90 %. these higher concentrations of cmt inhibited collagenase activity by the same extent as the chelating agents , edta and phenanthroline , consistent with the hypothesis that the metal binding characteristics of the tetracyclines ( including cmt ) are responsible , at least in part , for their anti - collagenolytic enzyme properties . a third experiment was carried out and the results are presented in fig3 . in this experiment radiolabeled collagen molecules were incubated ( 18 hrs ., 27 ° c .) with an extract of rat leukocytes known to contain collagenolytic enzyme activity . this mammalian collagenase preparation was incubated with 0 - 60 ug / ml cmt or with the collagenase -- inhibitors , edta or phenanthroline . the collagenase by itself degraded about 55 % of the available collagen substrate . in this experiment , 2 - 10 ug / ml cmt reduced the collagenase activity by about 20 % while 20 and 60 ug / ml reduced the activity about 85 %. edta and phenanthroline , two metal chelating agents , completely inhibited the activity of this mammalian collagenase , as expected , since leukocyte collagenase is known to depend on the presence of the metal ions , calcium and zinc , for normal activity . it is believed that the reason why this mammalian collagenase preparation required a higher concentration of cmt , than the bacterial collagenase preparation , to achieve the same degree of inhibition was two - fold : firstly , the mammalian collagenase was a relatively impure enzyme compared to the highly purified bacterial enzyme . thus , the cmt could have reacted with other metallo - proteases ( e . g . gelatinase ) in the leukocyte preparation , in addition to reacting with collagenase , thus effectively reducing the inhibitor cmt / collagenase ratio . secondly , leukocytes contain a high level of calcium ions and earlier experiments demonstrated that adding calcium to a collagenase / tetracycline mixture could overcome the inhibition of the enzyme activity . four separate groups of rats were set up , one group ( controls ) was left untreated throughout the entire protocol , the second ( the diabetic or d group ) was made diabetic by i . v . injection of streptozotocin as described previously , the third group was made diabetic and then administered by the oral route 75 mg per day of the antibiotic , metronidazole ( d + metronid . group ), and the fourth group was made diabetic and orally administered on a daily basis 20 mg per day &# 34 ; cmt &# 34 ; ( d + &# 34 ; cmt &# 34 ; group ). these doses are 1 / 10 of the daily doses of each of the these drugs when administered for therapeutic reasons to humans . the 1 / 10 value is the same dose that was administered to diabetic rats in previous studies using minocycline and which was found to produce beneficial changes in rats &# 39 ; connective tissues . at several time periods during the experimental protocol , the rats were weighed . on the final day of the experiment ( day 37 ), a blood sample was taken from each rat for glucose analysis , the animals were weighed and then killed . the entire skin from each rat ( except for that over the head , paws , genitals ) and the buccal gingiva were dissected , weighed , minced , extracted ( all procedures at 4 ° c .) and the extracts partially purified by ammonium sulfate precipitation . the collagenase activity in the skin and gingival extracts was measured after incubation with radiolabeled collagen as the substrate . ( skin extract was incubated at 35 ° c ., 48 hrs ., with 14 c glycine labeled collagen fibrils , while gingival extract was incubated at 27 ° c ., 18 hrs ., with [ 3 h - methyl ] collagen molecules ). just prior to killing the rats , a subgingival plaque sample was taken from each animal from the maxillary areas . the samples were immediately placed into prereduced broth ( to protect the anaerobic microorganisms ), incubated under anaerobic conditions , and the relative numbers of the gram - positive , gram - negative and motile microorganisms were assessed . as shown in fig4 the control rats , over the 37 day protocol , gained weight while the untreated diabetics ( d group ) progressively lost weight . daily metronidazole therapy therapy had no effect in retarding the weight loss in the d rats , whereas daily treatment of the d rats with cmt completely inhibited body weight loss . in addition , towards the end of the experiment after [ day 30 ] the &# 34 ; d &# 34 ; rats treated with cmt began to gain weight in a manner paralleling the non - diabetic controls while the untreated &# 34 ; d &# 34 ; rats during the same time period continued to lose weight . the data in fig5 shows a similar pattern of change . the d and d + metronid groups lost more than 50 % of the skin mass by the end of the 37 - day protocol , whereas treating the d rats with cmt on a daily basis inhibited the loss of skin mass ( skin loss is a complication of the diabetic condition ). the data in table 3 shows that all of the diabetic groups ( d group ; d + metronid groups ; d + cmt group ) were severely hyperglycemic ( 638 - 850 mg % blood glucose levels ) compared to the normoglycermic ( 104 mg %) control rats . treating the diabetic rats with metronidazole had absolutely no effect on the pathologically excessive collagenase activity in the diabetics &# 39 ; skins , table 3 , or in the diabetics gingiva , fig6 even though the blood glucose in the metronidazole ( antimicrobial )- treated rats was slightly reduced table 3 . in marked contrast , even though the cmt treatment appeared to have a lesser effect than metronidazole on blood glucose concentration , this modified tetracycline dramatically inhibited skin and gingival collagenase activity by about 50 %, table 3 and fig6 . these data demonstrate that cmt inhibits mammalian collagenase activity ( and collagen resorption ) in vivo , like standard antibiotic tetracyclines , but can accomplish this therapeutic effect without significantly affecting the crevicular microflora . table 3__________________________________________________________________________diabetes stimulates the collagenase activity in rat skin : effect oforally administered metronidazole and &# 34 ; cmi &# 34 ; collagenase activity in skin extracts : blood glucose % reduction inexperimental no . of rats concentration % . sup . 14 c - collagen d group due togroup of rats per group ( mg %)* degraded * drug therapy__________________________________________________________________________controls 4 103 ± 8 5 . 2 ± 0 . 9 -- diabetics ( d ) 3 850 ± 35 47 . 3 ± 0 . 3 -- d + metronid . 5 638 ± 22 46 . 0 ± 3 . 0 2 . 7d + &# 34 ; cmi &# 34 ; 4 713 ± 31 20 . 9 ± 3 . 2 55 . 8__________________________________________________________________________ * each value representrs the mean ± s . e . m . although emphasis in this disclosure and the practices of this invention has been placed on the dedimethylaminotetracycline as the non - antimicrobial or non - antibacterial tetracycline , other substantially non - antimicrobial or non - antibacterial tetracyclines are also useful , such as 6α - benzylthiomethylene tetracycline having the structural formula : ## str1 ## also useful is the nitrile analog of tetracycline having the structural formula : ## str2 ## also useful is the mono n - alkylated amide of tetracycline having the structural formula : ## str3 ## also useful is the 6 fluoro demethyltetracycline having the structural formula : ## str4 ## and also 11α - chlorotetracycline having the structural formula : ## str5 ## the special non - antimicrobial or non - antibacterial tetracyclines of this invention are suitably employed per se or in the form of their salts , such as the hydrochloride salts . other water - soluble salts , such as the sodium or potassium salts , might also be employed . the tetracyclines of this invention might also be encapsulated for oral administration since , as indicated hereinabove , the tetracyclines of this invention appear to be systemically effective as anti - collagenolytic agents . the tetracyclines of this invention can also be formulated in the form of tablets , capsules , elixirs and the like . the tetracyclines of this invention may be formulated into solutions or suspensions for intramuscular or peritoneal administration . additionally , the tetracyclines might also be incorporated or formulated into a polymer carrier or delivery system for use topically or locally , such as in the case of the tretment of periodontal diseases , such as for delivery directly into the periodontal pocket . suitable polymeric materials useful for incorporating therein the tetracyclines of this invention include ethylene vinyl acetate , polycaprolactone , polyurethane , ethylene cellulose which , after having the tetracyclines incorporated or dispersed therein , are suitable shaped or formed into fibers , sheets , film or particles or granular material capable of being shaped or formed into a suitable form for treatment of periodontal diseases and the like or for direct application to a lesion evidencing pathological collagen destruction or resorption . as will be apparent to those skilled in the art in the light of the foregoing disclosures many modifications , alterations and substitutions are possible in the practice of this invention without departing from the spirit or scope thereof .
tetracyclines having substantially no effective antibiotic or antibacterial activity and possessing anti - collagen - destructive enzyme activity or anti - collagenase activity and compositions containing the same have been found useful as anti - collagenolytic agents . such tetracyclines and compositions containing the same are useful in the treatment of periodontal diseases , corneal ulcers , bone deficiency disorders , rheumatoid arthritis diseases characterized by excessive collagen destruction . a special aspect of this invention involves the incorporation of such tetracyclines in animal feed compositions for improved animal nutrition , such as may be evidenced by increased weight gain .