Effects of oxytetracycline on mineralization of bone in young rats

Age-dependent morphometric change in the lumbar vertebrae of male and female rats: comparison with the femur

The morphological parameters, bone area, marrow area, bone-to-bone+marrow ratio, periosteal-to-total bone surface ratio, and surface-to-volume ratio, were studied in the fourth and fifth lumbar vertebrae of male and female rats (Heiligenberg strain) between birth and the end of lifespan. With increasing age, the bone area and marrow area increased for all ages, whereas the bone-to-bone + marrow ratio, periosteal-to-total bone surface ratio, and surface-to volume ratio decreased during the first 150 days. Afterwards, the bone-to-bone + marrow ratio decreased, whereas the periosteal-to-total bone surface ratio and surface-to-volume ratio were nearly constant. Modelling data were measured by use of the vital labeling technique with calcein. From the stained bone area the bone formation and the bone resorption rates were calculated. The bone formation rate, about 8300%/year, was highest after birth and decreases continuously with increasing age to 14%/year. The bone resorption rate, about 1100%/year, was highest after birth and decreased continuously with increasing age to 9%/year, whereas for all ages the bone formation rate was higher than the bone resorption rate, which led to an increase in bone area. The values obtained for the lumbar vertebra are compared with literature data and with the corresponding data for the distal femur obtained under identical conditions.

Effect of tetracyclines which have metalloproteinase inhibitory capacity on basal and heparin-stimulated bone resorption by chick osteoclasts

Several tetracyclines (TETs) are potent inhibitors of collagenase (CGase) and can inhibit connective tissue degradation in a variety of inflammatory and degenerative disorders. The role of CGase in bone resorption by osteoclasts (OC) remains unclear. Disaggregated OCs from chick embryos were cultured for 24 h on devitalized bovine cortical bone +/- heparin in the presence of various TETs. Doxycycline (Dox) inhibited pit formation in a dose-dependent manner. CMT, a TET derivative which inhibits matrix metalloproteinases (MMPs) but is not antimicrobial, also inhibited chick OC bone resorption. Heparin markedly stimulated bone resorption at 5 micrograms/ml, which was reversed by Dox, 5 micrograms/ml. TETs can reversibly inhibit both basal and heparin-stimulated bone resorption by chick OCs. These findings suggest that MMPs may play a role in osteoclastic bone resorption, and that safe and effective inhibitors of MMPs, including certain TETs, might have a potential therapeutic role.

Age-dependent morphometric alterations in the distal femora of male and female rats

Morphologic parameters, bone area, bone-to-bone + marrow ratio, periosteal-to-periosteal + endocortical surface ratio, mean trabecular thickness, and surface-to-volume ratio were studied in the epiphysis and metaphysis of the distal femora of male and female rats (Heiligenberg strain) between birth and the end of the lifespan. With increasing age, bone area, bone-to-bone + marrow ratio, and mean trabecular thickness increases, whereas periosteal-to-periosteal + endocortical surface ratio and surface-to-volume ratio decreases in both parts of bone during the first 150 days. Afterwards, periosteal-to-periosteal + endocortical surface ratio, mean trabecular thickness, and surface-to-volume ratio remain constant, whereas the bone area and the bone-to-bone + marrow ratio decrease. Modeling data were measured by use of the vital labeling technique with calcein. From the stained bone area, the bone formation, the bone resorption, and the periosteal mineral apposition rates have been calculated. The bone formation rate, about 13,000%/year in the metaphysis and 2,000%/year in the epiphysis, respectively, is greatest after birth and decreases continuously with increasing age to 3.5%/year for both bone regions. During the first 150 days the bone resorption rate is lower than the bone formation rate, leading to an increase in bone area, but afterwards it is higher so that the area decreases. Likewise the periosteal mineral apposition rate is greater in the metaphysis (24 microns/day at day 50) than in the epiphysis (14 microns/day at day 50), but after 700 days it is comparable for both bone regions (0.07 microns/day). The absolute values of body weight, femur length, and bone area of epiphysis and metaphysis are greater in male rats; only the mean trabecular thickness and the periosteal mineral apposition rate are comparable in both sexes. The relative values of bone-to-bone + marrow ratio, periosteal-to-periosteal + endocortical surface ratio, bone formation rate, and bone resorption rate are comparable for both sexes.

Inhibition of epiphyseal cartilage collagenase by tetracyclines in low phosphate rickets in rats

Drugs in the tetracycline family can inhibit mammalian tissue collagenase both in vitro and in vivo by a mechanism that is independent of antibiotic action. The epiphyseal cartilages of rachitic rats contain extremely high levels of collagenase (CGase), and we have used this model to study further the phenomenon of tetracycline inhibition of tissue CGase. Rickets was induced in rats by phosphate/vitamin D deficiency and parameters of gross bone morphology, bone chemistry, and serum chemistry were evaluated in both rachitic and nonrachitic animals with and without treatment with oral tetracyclines (TETs). Minocycline (or doxycycline) partially suppressed the appearance of many of the expected changes in the rachitic animals, including gross bone hardness, growth plate widening, long bone length, suppression of weight gain, and decreased bone ash content. The effects were dose dependent and were associated with marked suppression of the enhanced CGase activity. Examination of collagen breakdown products by SDS-PAGE documented that the rachitic enzyme behaved like other mammalian collagenases including in vitro inhibition with minocycline 10-20 micrograms/ml and with a nonantibiotic tetracycline. No evidence of TET osseous toxicity was noted, and, in fact, administration of TET to nonrachitic animals had a mildly favorable effect on growth and development. TET suppression of CGase can be demonstrated in a well defined model system and this form of pharmacologic enzyme inhibition can be a useful probe for delineating the role of the enzyme in connective tissue pathology.

Effects of salmon calcitonin on synthesis and mineralization of collagen in rats

The effects of salmon calcitonin (CT) on collagen metabolism and mineral deposition in fractures and intact femora, and on collagen metabolism in healing skin wounds and intact skin have been studied in young male rats. Serum calcium and serum phosphorus were reduced 3 h after the daily subcutaneous CT injection (3 MRC-U/kg body weight), whereas a rebound increase in the serum levels of both minerals was observed at 24 hours after the injection. CT had an early transient inhibitory influence on the collagen synthesis, and this resulted in a reduced total content of collagen in bones and skin specimens from treated rats compared to controls. The concentration of collagen in bone and skin was, however, increased in treated animals compared to controls after prolonged CT administration. Following an early transient increase, the incorporation of strontium-85 into the fractured bones was impaired after 30 days of CT treatment. This resulted in a reduced mineral concentration in the fractures of treated rats compared to controls in the last part of the experiment. The recorded effects of CT treatment, which were most pronounced in healing fractures and intact skin specimens, may be interpreted as an inhibitory influence of CT both on synthesis, mineralization and degradation of collagen.

Influence of age on mechanical properties of healing fractures and intact bones in rats

Mechanical properties of fractured and intact femora have been studied in young and adult, male rats. A standardized, closed, mid-diaphyseal fracture was produced in the left femur, the right femur serving as control. The fracture was left to heal without immobilization. At various intervals, both fractured and intact femora were loaded in torsion until failure. The fractured femora regained the mechanical properties of the contralateral, intact bones after about 4 weeks in young and after about 12 weeks in adult rats. For intact bones, both the ultimate torsional moment (strength) and the torsional stiffness increased with age of the animals, whereas the ultimate torsional angle remained unchanged. For bone as a material, however, the ultimate torsional stress (strength) and the modulus of rigidity (stiffness) increased with age only in young rats, being almost constant in the adult animals. The various biomechanical parameters of the healing fractures did not reach those of the contralateral, intact bones simultaneously. The torsional moment required to twist a healing femoral fracture 20 degrees (0.35 radians), a deformation close to what an intact femur can resist, proved to be a functional and simple measure of the degree of fracture repair in rats.

Effects of cloxacillin, doxycycline, fusidic acid and lincomycin on mineralization and solubility of collagen in young rats

The antibiotics doxycycline, fusidic acid and lincoymcin have recently been shown to reduce growth of bones and tensile strength of skin in young rats. Such adverse effects were not found in rats receiving cloxacillin. The present investigation deals with the influences of these four antibiotics on the mineralization of bones and on the solubility of collagen in skin. In rats receiving doxycycline the content of calcium and phosphorus in bones and the concentration of albumin in serum were reduced. None of the antibiotics had a detectable effect on the solubility of collagen.