Bisphosphonate action. Alendronate localization in rat bone and effects on osteoclast ultrastructure.

Abstract

Studies of the mode of action of the bisphosphonate alendronate showed that 1 d after the injection of 0.4 mg/kg [3Hjalen-dronate to newborn rats, 72% of the osteoclastic surface, 2% of the bone forming, and 13% of all other surfaces were densely labeled. Silver grains were seen above the osteoclasts and no other cells. 6 d later the label was 600-1,000 itm away from the epiphyseal plate and buried inside the bone, indicating normal growth and matrix deposition on top of alendronate-containing bone. Osteoclasts from adult animals, infused with parathyroid hormone-related peptide (1-34) and treated with 0.4 mg/kg alendronate subcutaneously for 2 d, all lacked ruffled border but not clear zone.In vitro alendronate bound to bone particles with a Kd of -1 mM and a capacity of 100 nmol/mg at pH 7. At pH 3.5 binding was reduced by 50%. Alendronate inhibited bone resorption by isolated chicken or rat osteoclasts when the amount on the bone surface was around 1.3 X 10-3 fmol/Mm2, which would produce a concentration of 0.1-1 mM in the resorption space if 50% were released. At these concentrations membrane leakiness to calcium was observed. These findings suggest that alendronate binds to resorption surfaces, is locally released during acidification, the rise in concentration stops resorption and membrane ruffling, without destroying the osteoclasts. (J.

In vitro cytoreductive effects on multiple myeloma cells induced by bisphosphonates

“…Interestingly, the bisphosphonate alendronate induces leakiness for calcium in osteoclasts which results in a rise in free intracellular cytosolic calcium (Ca I ). 19 Such a rise in Ca I has been previously suggested as an inhibitory signal for osteoclasts. 20,21 Furthermore, induced increases in Ca I have also been indicted as second messengers during induction of apoptosis.…”

“…Not only are injected bisphosphonates concentrated in the bony skeleton, they become preferentially bound to skeletal sites of bone resorption. 19 These sites of active bone resorption are most likely adjacent to areas of myeloma growth in patients. 29 Furthermore, during bone resorption, an osteoclast-induced acidification in the immediate milieu would greatly release bound bisphosphonates, 19 resulting in a marked increase in local bisphosphonate concentration, which, for Alendronate, 19 has been estimated to reach as high as 800 M directly at the osteoclast-bone interface.…”

“…19 These sites of active bone resorption are most likely adjacent to areas of myeloma growth in patients. 29 Furthermore, during bone resorption, an osteoclast-induced acidification in the immediate milieu would greatly release bound bisphosphonates, 19 resulting in a marked increase in local bisphosphonate concentration, which, for Alendronate, 19 has been estimated to reach as high as 800 M directly at the osteoclast-bone interface. This would certainly be a toxic concentration for malignant plasma cells but the bisphosphonate concentration away from the immediate vicinity of the resorbing osteoclast is unknown and, furthermore, it is unclear how long high concentrations in the vicinity are maintained.…”

Bisphosphonates antagonise bone growth factors' effects on human breast cancer cells survival

“…In agreement with other authors' data (McCarthy et al, 1989), we observed that IGF-II was about 10-fold less potent than IGF-I to increase breast cancer cell survival under serum-free conditions. Bisphosphonates are synthetic compounds that preferentially accumulate in bone (Sato et al, 1991) by their strong affinity for calcified matrix. They are powerful inhibitors of osteoclastmediated bone resorption (Fleisch, 1991(Fleisch, , 1997aRussell and Rogers, 1999), and they significantly reduce skeletal morbidity in advanced breast cancer patients (Body, 2000).…”

“…Bisphosphonates are very stable compounds that exhibit a high affinity for calcified matrices such as hydroxyapatite in bone (Lin, 1996), and are successfully used as powerful inhibitors of increased bone resorption in several bone diseases (Fleisch, 1997a, b). They act by decreasing the recruitment, proliferation and differentiation of preosteoclasts (Lowik et al, 1988;Hughes et al, 1989;Nishikawa et al, 1996), their adhesion to the mineralised matrix and, most importantly, the resorptive activity of mature osteoclasts (Sato et al, 1991;Selander et al, 1994;Azuma et al, 1995;Murakami et al, 1995). They also shorten osteoclast lifespan by induction of programmed cell death (apoptosis) (Hughes et al, 1995).…”