Effect of dichloromethylene diphosphonate on morphology, enzyme activity, and ash content of bones of thyroparathyroidectomized rats

Effects of bisphosphonates on alkaline phosphatase activity, mineralization, and prostaglandin E2 synthesis in the clonal osteoblast-like cell line MC3T3-E1

The effects of 3 bisphosphonates, AHBuBP, AHPrBP, and Cl2MBP on cell growth, alkaline phosphatase (ALP) activity, mineralization, and prostaglandin E2 (PGE2) synthesis in the clonal osteoblast-like cell line MC3T3-E1 were studied. These bisphosphonates had essentially similar effects on growth and the osteoblastic functions of the cells, i.e., they had no inhibitory effects on cell growth except at higher concentrations, they increased ALP activity, and inhibited PGE2 production. In the presence of AHBuBP, ALP activity was higher than that in the control after day 6 of culture. Lower concentrations of AHBuBP slightly facilitated mineralization by the cells. It is probable that bisphosphonates enhance the functions of osteoblasts in certain concentration and that the inhibition of endogenous PGE2 production may be involved in the mechanism of action of bisphosphonates.

The influence of dichloromethylene bisphosphonate on the healing of a long bone fracture, composition of bone mineral and histology of bone in the rat

The effects of dichloromethylene bisphosphonate (clodronate) on the composition of bone mineral, morphology and histology of a long bone with an artificial femoral fracture were studied in a 22 week experiment. Two hundred twenty-four female rats were allocated to dose groups of 0, 3, 10, and 30 mg/kg clodronate daily subcutaneously. Bone calcium, phosphorus and magnesium concentrations remained stable and fluoride concentration rose with time. There were no statistical differences between different groups. Clodronate did not alter the histology of the callus nor delayed the healing of the fracture. It caused mild to moderate prominence of the metaphyseal area in the fractured bone in a dose- and time-dependent manner. Serum osteocalcin levels were lowered in the treated animals dose-dependently. Other serological as well as haematological values were within normal range. Clodronate seems in this experimental arrangement to be a safe agent to administer in different pathological conditions of bone even when they are complicated by fractures of long bones.

Dichloromethylenebisphosphonate (Cl2MBP) inhibits bone resorption through injury to osteoclasts that resorb Cl2MBP-coated bone

Dichloromethylenebisphosphonate (Cl2MBP, formerly Cl2MDP) inhibits bone resorption in vivo and in vitro. The mechanism by which it inhibits osteoclastic bone resorption has not been established. To investigate this, osteoclasts were isolated from rat long bone and incubated with Cl2MBP (10(-9)-10(-5) M) on bone slices. Bone resorption was assessed as plan area resorbed after 6 and 24 h by scanning electron microscopy. Although Cl2MBP inhibited bone resorption in the first 6 h of culture, inhibition was more marked in the incubation period between 6 and 24 h. This pattern of accelerating inhibition is unlike the pattern we have observed using other resorption-inhibitors, and suggested resorption-mediated osteoclast injury. In keeping with this, we found reduced numbers of osteoclasts, and morphological features of cell injury and degeneration of osteoclasts, after incubation with Cl2MBP on bone slices. Bone seemed to be an essential component in Cl2MBP-mediated injury, since osteoclast numbers and morphology on plastic coverslips were unaffected by the bisphosphonate. Moreover, bone slices preincubated with Cl2MBP showed similar effects on resorption and morphology to cultures in in which osteoclasts on bone were continuously immersed in Cl2MBP. Neither non-resorptive cells (macrophages, UMR 106 cells), nor osteoclasts prevented from resorption by calcitonin, showed evidence of cytotoxicity after incubation on bone slices with Cl2MBP. These results suggest that even relatively high concentrations of Cl2MBP in the fluid phase do not affect osteoclasts, nor does contact with Cl2MBP-coated bone surfaces, but that injury to osteoclasts, and a consequent reduction in bone resorption, occurs when osteoclasts excavate bone surfaces upon which Cl2MBP is adsorbed.

Effects of disodium ethane-1-hydroxy-1, 1-diphosphonate (EHDP) in adult normal and selectively parathyroidectomized rats. I. Effects on plasma calcium, bone tissue, and adrenal glands at low or normal calcium intake

One-year-old intact and selectively parathyroidectomized rats were given a normal or low calcium diet for 8 months and, during the last 3 weeks, diphosphonates (EHDP) at a low dose level of 1.0 mg EHDP/kg body weight/day intraperitoneally. The administration of EHDP impaired the animals' ability to maintain the blood calcium level during a low calcium intake. Calcium-deficient intact animals had significantly reduced plasma calcium during EHDP treatment, while calcium-deficient parathyroidectomized animals showed no further reduction. Calcium deficiency alone resulted in osteoporosis which was prevented by parathyroidectomy. The short period of EHDP treatment had no significant effect on the bone mass in control, osteoporotic, and parathyroidectomized animals. The calcium accretion rate by bone became significantly increased upon a low calcium intake in intact rats but not in parathyroidectomized ones. This increase was counteracted by EHDP which gave rise to reduced accretion in both parathyroidectomized and osteoporotic animals. In addition EHDP caused hypertrophy of the adrenal cortex in all treated groups.

Diphosphonates: history and mechanisms of action

The history of diphosphonates began with studies of inorganic pyrophosphate. This compound was found to occur in many biological fluids and inhibited the precipitation of calcium phosphates. It also slowed the transformation of amorphous calcium phosphate to its crystalline form, and inhibited crystal aggregation and dissolution. These observations suggested that it might be a compound of physiological or pathophysiological significance, perhaps in hypophosphatasia and in renal lithiasis. Diphosphonates are compounds where the P-O-P bond of pyrophosphate is replaced by a P-C-P bond. Many diphosphonates have been synthesized and tested and some relationship of their structure to the spectrum of biological effects has been observed. These analogues have similar properties to pyrophosphate, but unlike pyrophosphate they are resistant to enzymic degradation. Their experimental properties have led to their clinical development as bone scanning agents and in the treatment of disorders of ectopic mineralization and increased bone resorption.

Influence of a diphosphonate on the cellular aspect of young bone tissue

Stimulated by the rather sparse information in the literature on cellular changes induced by EHDP, we carried out electron microscopic investigations on young bone tissue and on de novo bone formation. Cellular changes could be observed during continuous administration of EHDP. The osteoblasts demonstrated temporary storing of crystalloid structures in the mitochondria, and atypical osteocytes showed persistent changes indicative of hyperactivity. The osteoclasts exhibited varying ultrastructural features with respect to the number and appearance of nuclei, Golgi, RER, and lysosomes. These changes under the influence of EHDP could be an indication of altered activity of the osteoclast. The possible interference of EHDP with bone cell metabolism is discussed.