The bisphosphonates HEBP and AHPrBP but not AHBP inhibit mineral mobilization and lysosomal enzyme release from mouse calvarial bones in tissue culture

Cellular biology of bone resorption

Past knowledge and the recent developments on the formation, activation and mode of action of osteoclasts, with particular reference to the regulation of each individual step, have been reviewed. The following conclusions of consensus have emerged. 1. The resorption of bone is the result of successive steps that can be regulated individually. 2. Osteoclast progenitors are formed in bone marrow. This is followed by their vascular dissemination and the generation of resting preosteoclasts and osteoclasts in bone. 3. The exact pathways of differentiation of the osteoclast progenators to mature osteoclasts are debatable, but there is clear evidence that stromal cells support osteoclast generation. 4. Osteoclasts are activated following contact with mineralized bone. This appears to be controlled by osteoblasts that expose mineral to osteoclasts and/or release a factor that activates these cells. 5. Activated osteoclasts dissolve the bone mineral and digest the organic matter of bone by the action of agents secreted in the segregated microcompartments underlying their ruffled borders. The mineral is solubilized by protons generated from CO2 by carbonic anhydrase and secreted by an ATP-driven vacuolar H(+)-K(+)-ATPase located at the ruffled border. The organic matrix of the bone is removed by acid proteinases, particularly cysteine-proteinases that are secreted together with other lysosomal enzymes in the acid environment of the resorption zone. 6. Osteoclastic bone resorption is directly regulated by a polypeptide hormone, calcitonin (CT), and locally, by ionized calcium (Ca2+) generated as a result of osteoclastic bone resorption. 7. There is new evidence that osteoclast activity may also be influenced by the endothelial cells via generation of products including PG, NO and endothelin.

Effects of four bisphosphonates on bone resorption, lysosomal enzyme release, protein synthesis and mitotic activities in mouse calvarial bones in vitro

The effects of 3-amino-1-hydroxy-propylidene-1,1-bisphosphonate (AHPrBP), 1-hydroxyethylidene-1,1-bisphosphonate (HEBP), dichloromethylenebisphosphonate (Cl2MBP) and azacycloheptylidene-2,2-bisphosphonate (AHBP) on bone were examined in organ culture using newborn mice calvaria. AHPrBP, HEBP and Cl2MBP caused a dose-dependent inhibition of PTH-stimulated (10 nmol/l) release of 45Ca from the calvaria, at and above a concentration of 3 mumol/l, whereas AHBP only caused a slight inhibition, at and above 100 mumol/l. AHPrBP inhibited PTH-stimulated release of 3H from bones prelabelled with [3H]-proline. AHPrBP (30 mumol/l) diminished the stimulatory effect of 1 alpha(OH)vitamin D3 (10 nmol/l), prostaglandin E2 (0.1 mumol/l) and renal tumor conditioned media on 45Ca release. AHPrBP and Cl2MBP, at and above 3 mumol/l, decreased PTH-stimulated mobilization of Ca2+ and Pi and in parallel the release of beta-glucuronidase without affecting the release of lactate dehydrogenase. The inhibitory effect of AHPrBP (30 mumol/l) on PTH-induced 45Ca release was irreversible. The inhibition by AHPrBP (30 mumol/l) on spontaneous and PTH-stimulated release of 45Ca can be seen first after 24 h of culture. Similarly the inhibitory effect by HEBP (30 mumol/l) and Cl2MBP (30 mumol/l) was delayed and could be observed after 36 and 24 h of culture, respectively. PTH-stimulated release of Ca2+, Pi, beta-glucuronidase and beta-N-acetylglucosaminidase was reduced by AHPrBP first after 24 h of culture. AHPrBP, HEBP and Cl2MBP, at concentrations which are inhibitory on bone resorption, do not affect protein synthesis and mitotic activities in mouse calvaria. These data show that AHPrBP, HEBP and Cl2MBP inhibit bone resorption in vitro and in parallel decrease lysosomal enzyme release by a mechanism, which is not related to cytotoxicity. In addition, the delayed inhibitory effect on bone resorption and lysosomal enzyme release by all the compounds suggest that bisphosphonates inhibit bone resorption indirectly and not by a direct effect on existing osteoclasts. The delayed inhibition by bisphosphonates on bone resorption may be due to decreased recruitment of new osteoclasts as a consequence of an inhibitory action on mononuclear osteoclast precursor cells.

Effects of disodium ethane-1-hydroxy-1,1-diphosphonate (EHDP) on interleukin 1 production by macrophages

The effects of disodium ethane-1-hydroxy-1,1-diphosphonate (EHDP) on the in vitro functions of guinea pig macrophages were studied. A high dose (1 mg/ml) of EHDP inhibited interleukin 1 (IL 1) production by oil-induced peritoneal macrophages stimulated with muramyl dipeptide (MDP), lipopolysaccharide (LPS), phorbol myristic acetate (PMA), heat-aggregated IgG2 or calcium ionophore A23187. On the other hand, low doses (less than 0.125 mg/ml) of EHDP augmented the MDP induced IL 1 production by macrophages. This biphasic effect was also observed when macrophages were exposed to EHDP at 37 C for 24 hr and then stimulated with IL 1 inducers. Superoxide anion generation induced by formyl peptide or PMA was not affected by preincubation of the macrophages with doses of EHDP up to 1 mg/ml. Adherence and spreading of macrophages was inhibited by EHDP in a dose dependent manner without affecting cell viability. These results demonstrated that EHDP acted on macrophages directly and modulated IL 1 production in vitro.

Bisphosphonates and bone resorption: effects on collagenase and lysosomal enzyme excretion

When added to cultures of parathyroid hormone (PTH)-stimulated bones, dichloromethylenebisphosphonate (C12MBP) and 3-amino-1-hydroxypropydilene-1,1-bisphosphonate (AHPrBP) inhibit completely and in a parallel manner the development of resorption lacunae, the loss of calcium by the explants and their PTH-induced excretion of lysosomal hydrolases (beta-glucuronidase and N-acetyl-beta-glucosaminidase). The loss of collagen (hydroxyproline) by the bones is usually less inhibited than their loss of calcium and their heparin-induced excretion of collagenase is unaffected. To interpret these data, it is proposed that these bisphosphonates act more on the activity of osteoclasts, suppressing simultaneously their excretion of lysosomal enzymes and their erosion of mineralized bone matrix, than on that of other cell types (osteoblasts ?) responsible for collagenase production and the removal of uncalcified collagen.