Effect of halogenmethylenebisphosphonates on bone cells in culture and on bone resorption in vivo

Effects of two novel bisphosphonates on bone cells in vitro

Bisphosphonates are now widely used in the treatment of bone diseases, particularly where there is uncontrolled bone resorption, as they are known to be potent inhibitors of osteoclasis. It is still unclear whether the bisphosphonates act by inhibiting osteoclast maturation or by blocking the mechanism of bone resorption, and little is known of their effects on osteoblasts. Recent studies with 3-amino-1, hydroxypropylidene-1,1-bisphosphonic acid (APD) in the treatment of osteolytic metastases in breast cancer have suggested that APD may affect osteoblasts directly. We have now investigated the effects of two novel bisphosphonates, CGP 47072 and CGP 42446A on osteoclastogenesis in fetal rat calvariae cultured on collagen gels and on human osteoblasts (hOB) cultured as explants from bone taken from patients at surgery. We also compared the action of these new bisphosphonates with that of APD, which at concentrations of 2.5 x 10(-6) M to 2.5 x 10(-10) M inhibited osteoclast recruitment, even when this was stimulated by conditioned medium from MCF7 breast cancer cells. This bisphosphonate was particularly potent if cultured with calvaria taken at 19 days gestation, when more immature osteoclast precursors are present. If calvariae from 20 days gestation were used, which contain more mature cells, it produced less inhibition. In contrast, CGP 42446A (2.5 x 10(-6) M to 2.5 x 10(-8) M) was more effective in inhibiting osteoclast maturation in calvariae from 20 days gestation than in those from 19 days. CGP 47072 had a similar pattern of effects but was less potent than either of the other two compounds. APD or CGP 42446A at 10(-5) M significantly inhibited hOB numbers and DNA synthesis, but lower concentrations had little effect. CGP 47072 did not inhibit human osteoblast replication. It is unlikely that these effects are due to calcium chelation, as none of these compounds mimicked results obtained with EDTA, which was effective only at 2.5 x 10(-6) M in reducing osteoclast size and 10(-4) M in human osteoblast cultures. These results demonstrate that all three bisphosphonates are able to inhibit osteoclast formation at low concentrations. APD may be able to influence less mature osteoclast precursors and CGP 42446A and CGP 47072 may exert their effects on the fusion of more mature precursor cells on the bone surface. At these concentrations, however, there is little or no effect on osteoblasts.

Diphosphonates are potent inhibitors of mammalian inorganic pyrophosphatase

Methanediphosphonate and 12 analogs thereof with different substituents at the carbon atom are potent competitive inhibitors of highly purified rat liver and bovine heart inorganic pyrophosphatases. The inhibition constants for the most effective diphosphonates, which contain an NH2 or OH group at the bridge carbon atom, are in the micromolar range. Yeast and Escherichia coli pyrophosphatases are markedly less sensitive to the diphosphonates. Pyrophosphatase inhibition may be related to the numerous biological effects exerted by diphosphonates.

Paget's disease of bone

Paget's disease is a relatively common bone disease. This review aims to present reasonable treatment recommendations with enough background to understand them. To accomplish this end, some aspects of basic bone cell biology, biochemistry, and pathology are presented, as are speculations about possible causes of this disease. Treatment of Paget's disease will be considered in three sections. The first two sections will review treatment with calcitonin and diphosphonates, respectively. These sections briefly will consider the mechanism of action of the drugs, review in detail clinical studies of drug effectiveness, and summarize the advantages and disadvantages of each drug. The third section details specific treatment recommendations for each of the six clinical settings in which treatment of Paget's disease is justified.

Fatty acid oxidation in bone tissue and bone cells in culture. Characterization and hormonal influences

Fatty acid oxidation and its hormonal modulation were investigated in cultured rat calvaria and in cultivated cell populations. The latter were obtained from calvaria of newborn rats by sequential time-dependent digestion with collagenase, yielding eight cell populations: the early ones containing mainly fibroblasts, the middle ones being osteoblast-like, and late ones osteoblast-osteocyte-like. In calvaria, fatty acid oxidation was increased by adding 0.1 mM- and 1.0 mM-palmitate to the medium, containing 10% (v/v) fetal-calf serum. No effect was found after parathyrin addition in vitro or when injected in vivo. All cell populations obtained by sequential digestion were found to oxidize palmitate, whereby the osteoblast-like cells showed a lower oxidation rate than the other populations. Both parathyrin and calcitonin had no effect on fatty acid oxidation. 1,25-Dihydroxycholecalciferol at 1-100 nM and 24,25-dihydroxycholecalciferol at 100 nM increased oxidation primarily in the population enriched with osteoblast-like cells. Insulin at 1.6 microM diminished it in the cell populations enriched with osteoblast-like cells and in the late bone-cell fraction. However, glucagon had no effect. The energy provided by fatty acid oxidation in this system is approx. 40-80% of glucose metabolism, suggesting that this event may be of importance in the energy metabolism of bone.