A micropuncture study of growth cartilage in phosphonate (EHDP) induced rickets

Production of collagenase and tissue inhibitor of metalloproteinases (TIMP) by rat growth plates in culture

Growth plate cartilage from normal and vitamin D-phosphate deficient (-VDP) rats was cultured to study the production of collagenase and tissue inhibitor of metalloproteinases (TIMP) in vitro. All tissues secreted latent collagenase into the medium at a constant rate during the 5 days in culture. Microdissected-VDP growth plates, containing predominatly hypertrophic cells, released up to 8-fold more collagenase into the medium than either intact-VDP or normal growth plates. TIMP was also secreted during the culture, but its rate of production was not as dependent on tissue type as collagenase. The tissue level of collagenase and TIMP before culture was compared with that found in conditioned medium and remnant tissue after culture. During the 5 day culture period microdissected-VDP growth plates, containing predominatly hypertrophic cells, produced 3-times more collagenase/microgram DNA over the starting level than either intact-VDP or normal growth plates. TIMP was never found in tissues after they had been cultured, but was present in all tissues before culture except those containing predominatly hypertrophic cells. The amount of TIMP required to block collagenase was calculated. Growth plates in culture produced enough TIMP to block all collagenase found in the medium and remnant tissue, while extracts of uncultured intact -VDP growth plates, and those divided to contain hypertrophic cells, had an excess of collagenase over TIMP. The results suggest that hypertrophic cells produce far more collagenase than other cells in the growth plate, but all cell types have about the same capacity to synthesize TIMP. As a result, increased collagenase synthesis by hypertrophic cells may surpass increases in TIMP synthesis and lead to collagen removal. This would allow for thinning of the longitudinal septa and expansion of the hypertrophic cells.

Association of collagenase and tissue inhibitor of metalloproteinases (TIMP) with hypertrophic cell enlargement in the growth plate

In the transition from proliferating to hypertrophic cell zones in the growth plate, there is an increased in chondrocyte cell volume and a corresponding decrease in collagen content to allow for cell enlargement. To substantiate our hypothesis that collagenase is responsible for these changes, growth plates from rats treated with bisphosphonate (HEBP) were compared histologically and biochemically with growth plates from normal and vitamin D and phosphate deficient (-VDP) rats. HEBP-treated rats developed an expanded hypertrophic cell zone (HCZ) characterized by the presence of two distinct populations of hypertrophic cells. The proximal hypertrophic cells were only 2-fold enlarged compared to the proliferating cells, whereas 1/6 of the distal hypertrophic cells were enlarged almost 5-fold and appeared morphologically identical with hypertrophic cells from normal and -VDP rats. The HEBP growth plates were divided into cross-sectional thirds and analyzed for active and latent collagenase. The juxta-metaphyseal (lower 1/3) cartilage contained 100% of the fully enlarged hypertrophic cells and appeared identical to those found in normal and -VDP growth plates, along with 81% of the active and 77% of the total collagenase. Collagenase and tissue inhibitor of metalloproteinases (TIMP) were measured in extracts of similarly divided tissues. The presence of true collagenas was confirmed by using [3H]-telopeptide-free collagen. TIMP levels were inversely related to the presence of active collagenase and cellular hypertrophy. Substantial levels of latent collagenase were found in the extracellular fluid at sites of active collagenolysis, but not in the fluid phase surrounding the 2-fold enlarged hypertrophic cells. It is postulated that increased amounts of active collagenase and insufficient levels of TIMP may account for the reduced collagen content seen in the lower HCZ of both -VDP and HEBP rickets. Unlike active collagenase, which remains localized by binding to collagen, latent enzyme is probably restricted in its mobility throughout the extracellular space by diffusion, itself, or the interstices of the extracellular matrix.

1-Hydroxyethylidene-1,1-bisphosphonate (HEBP) simultaneously induces two distinct types of hypomineralization in the rat incisor dentine

Effects of 1-hydroxyethylidene-1,1-bisphosphonate (HEBP) on the dentinogenesis of the rat maxillary incisor were microradiographically examined 96 hours after a single subcutaneous injection. HEBP produced hypomineralized incremental bands in the enamel (HPOe) and in the dentine (outer HPO1 and inner HPO2) in a dose-dependent manner. In the labial dentine, both HPO1 and HPO2 did not extend apically beyond the apical limit of the HPOe and were thus located in the circumpulpal dentine. The two lesions in the labial dentine fully developed with a dosage of 10 mg/ P/kg or larger, and with 15 mg P/kg or larger, gross hypoplastic lesions developed. Therefore, histological analysis at shorter postinjection intervals was carried out on the labial dentine with 10 mg P/kg of HEBP. The HPO1 appeared along the dentine-predentine junction by 24 hours and was characterized by reduced numbers of inorganic crystals and 10 nm particles which invested the collagen fibrils. Therefore, the HPO1 was judged to be produced by the disturbance of transformation of the predentine to dentine. The precursor lesion of HPO2 appeared in the proximal predentine by 4 hours, and was characterized by reduced number of collagen fibrils and unusually coarse interfibrillar stippled material. This lesion migrated to the dentine by 96 hours and became the HPO2, which was characterized by reduced number of collagen fibrils. Individual collagen fibrils in the HPO2 were invested by as many inorganic crystals and 10 nm particles as in the normal dentine. The HPO2 is considered to be produced by the disturbance of organic matrix formation.

EHDP-induced rachitic syndrome in rats is not reversed by vitamin D metabolites

To examine whether either of the two known active vitamin D metabolites 1,25(OH)2D3 or 24,25(OH)2D3 could reverse the mineralization defect induced by 1-hydroxyethylidene-1,1-bis phosphonate (EHDP), a model of EHDP-induced rickets was used. Rats at the age of 31 days were injected for 10 consecutive days with EHDP (10 mg/kg). Other littermates were treated with a combination of EHDP and either 1,25(OH)2D3 or 24,25(OH)2D3 or were treated following 10 days of EHDP, with either of the vitamin D metabolites for an additional 72 hr. Samples of cartilage fluid (Cfl) and of blood were removed prior to sacrifice for biochemical studies of some parameters of calcification. These parameters were correlated with the results of light and electron microscope studies of growth plate cartilage and bone. EHDP-treated rats revealed signs of typical rickets, manifested by widened growth plates and impaired bone mineralization. Transmission electron microscope (TEM) examination revealed matrix vesicles distributed throughout the growth plate; however, there appeared to be an arrest of the spread of the crystals at the provisional zone of calcification. Treatment with either 1,25(OH)2D3 or 24,25(OH)2D3 failed to reverse the rachitic condition of the animals. Serum calcium blood levels were elevated in the 1,25(OH)2D3 and EHDP-treated group. 1,25(OH)2D3 and 24,25(OH)2/D3 further increased the already elevated serum alkaline phosphatase levels observed in EHDP rats, although the increase observed with 1,25(OH)2D3 was not statistically significant.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of N,N,N',N'-ethylenediaminetetramethylene phosphonic acid and 1-hydroxyethylidene-1,1-bisphosphonic acid on calcium absorption, plasma calcium, longitudinal bone growth, and bone histology in the growing rat

Phosphonate compounds are of considerable interest because of their effects on biological mineralization and mineral metabolism. The effects of graded doses given parenterally or orally of N,N,N',N'-ethylenediamine tetramethylene phosphonic acid (EDITEMPA) on calcium absorption, plasma calcium, endochondral bone elongation, and osseous tissue histology of rats were determined. In some experiments 1-hydroxyethylidene-1,1-bisphosphonic acid (HEBP) was included for comparison. Given sc for 7 days, EDITEMPA caused dose-related decreases in net weight gain, intestinal calcium absorption, and longitudinal bone growth. There were also increases in total plasma calcium concentrations and excess osteoid accumulation in bone. When EDITEMPA was given po for 7, 28, or 90 days, few changes in osseous tissues were observed and then only at the highest dose (333 mg/kg/day). An equivalent dose of HEBP caused substantial changes in osseous tissues and calcium parameters.

Structure-activity relationships of various bisphosphonates

A variety of bisphosphonates with aliphatic side chains of increasing length, as well as 3-amino-1-hydroxypropylidene-1,1-bisphosphonate (AHPrBP, formerly APD), dichloromethylene-bisphosphonate (Cl2MBP, formerly Cl2MDP), and dibromomethylene bisphosphonate (Br2MBP, formerly Br2MDP), were compared in vitro and in vivo to find (a) a possible relationship between structure and activity in order to give some indication about their mechanism(s) of action on bone and (b) the most efficient and safe compound having an effect on bone resorption. Some relationship was found between inhibition of calcium phosphate precipitation in vitro and of mineralization in vivo. No correlation existed, however, between any parameter measured and bone resorption. The number of calvaria cells in culture was decreased by compounds with a chain length greater than 5-C, by AHPrBP, Cl2MBP, and Br2MBP. Lactate production by these cells in vitro was increased by the long chain bisphosphonates and AHPrBP, and was decreased by Cl2MBP. No good correlation existed between the inhibition of bone resorption measured in vitro on calvaria and that seen in vivo on rat tibiae metaphyses. The latter was inhibited the most efficiently by the bisphosphonates longer than 5-C and by AHPrBP; these were 10 times more effective than Cl2MBP. Taking into account all factors, 1-hydroxypentylidene-1,1-bisphosphonate and AHPrBP seem to be the most active compounds to inhibit bone resorption.