Bisphosphonates inhibit 1,25-dihydroxyvitamin D3-induced increase of osteocalcin in plasma of rats in vivo and in culture medium of rat calvaria in vitro

Relative binding affinities of bisphosphonates for human bone and relationship to antiresorptive efficacy

Potent bisphosphonates (BPs) preferentially bind bone at sites of active osteoclastic bone resorption, where they are taken up by the osteoclast and inhibit resorption. We tested the hypothesis that BP affinity to human bone affects antiresorptive potency. [(1)(4)C]-Alendronate binding to human bone was saturable and reversible with an apparent Kd of 72 microM by Scatchard analysis. In competition binding assays, unlabeled alendronate (Ki: 61 microM) was slightly more potent than pyrophosphate (Ki = 156 microM) in blocking [(1)(4)C]-alendronate binding. Likewise, most tested BPs, including etidronate (Ki: 91 microM), ibandronate (116 microM), pamidronate (83 microM), risedronate (85 microM) and zoledronate (81 microM), showed comparable affinities. Interestingly, tiludronate (173 microM; P < 0.05 vs. all other BPs) and especially clodronate (806 microM; P > 0.0001 vs. all other BPs) displayed significantly weaker affinity for bone. The weak affinity of clodronate translated into a requirement for 10-fold higher dosing in in vitro bone resorption assays when bone was pretreated with BP and subsequently washed prior to adding osteoclasts. In stark contrast, neither alendronate nor risedronate lost any efficacy after washing the bone surface. These findings suggest that most clinically tested BPs may have similar affinities for human bone. For those with reduced affinity, this may translate into lower potency that necessitates higher dosing.

Neridronate and human osteoblasts in normal, osteoporotic and osteoarthritic subjects

The objective of this study was to evaluate the metabolic in vitro effect of the bisphosphonate neridronate on normal and pathological human osteoblasts. Primary human osteoblast cultures were obtained from cancellous bone of osteoarthritic (OA) and osteoporotic (OP) patients and a corresponding healthy control group. Osteocalcin production was evaluated by cultured cells in neridronate 10(-4) M and 10(-6) M, both under basal conditions and after vitamin D3 stimulation. In the absence of neridronate, vitamin D3 increased osteocalcin production in all cell cultures; under the same conditions, and in the absence of vitamin D3, OA osteoblasts showed a significantly higher osteocalcin production whereas OP osteoblasts showed a significantly lower osteocalcin production compared to the normal osteoblasts, respectively. In all cellular populations neridronate at a higher concentration (10(-4) M) induced a reduction in osteocalcin synthesis, but in normal and osteoarthritic osteoblasts did not reduce the stimulatory effect of vitamin D3, whereas it inhibited the vitamin D3-induced increase of osteocalcin synthesis in the osteoporotic cells. In normal and osteoporotic osteoblasts stimulation with the lower neridronate concentration (10(-6) M) significantly increased osteocalcin production, which was further enhanced by vitamin D3 as an additional effect of the combined treatment. In OA osteoblasts, neridronate 10(-6) M did not induce an increase in osteocalcin synthesis and the additional effect of combined treatment with vitamin D3 was not observed. Neridronate can modify the metabolic activity of human osteoblasts by enhancing or decreasing their biosynthetic activity, both in normal and in pathological conditions, depending on compound concentration and on different cell types. These results confirm the validity of using neridronate at doses usually administered in treating osteoporosis, and they suggest using it to treat other diseases which show an altered osteoblast metabolism, such as osteoarthritis.

Bisphosphonates: preclinical review

Bisphosphonates effectively inhibit osteoclast-mediated bone resorption and are integral in the treatment of benign and malignant bone diseases. The evolution of bisphosphonates over the past 30 years has led to the development of nitrogen-containing bisphosphonates (N-BPs), which have a mechanism of action different from that of the nonnitrogen-containing bisphosphonates. Studies conducted over the past decade have elucidated the mechanism of action and pharmacologic properties of the N-BPs. N-BPs exert their effects on osteoclasts and tumor cells by inhibiting a key enzyme in the mevalonate pathway, farnesyl diphosphate synthase, thus preventing protein prenylation and activation of intracellular signaling proteins such as Ras. Recent evidence suggests that N-BPs also induce production of a unique adenosine triphosphate analogue (Apppi) that can directly induce apoptosis. Our increased understanding of the pharmacologic effects of bisphosphonates is shedding light on the mechanisms by which they exert antitumor effects. As a result of their biochemical effects on protein prenylation, N-BPs induce caspase-dependent apoptosis, inhibit matrix metalloproteinase activity, and downregulate alpha(v)beta(3) and alpha(v)beta(5) integrins. In addition, zoledronic acid (Zometa; Novartis Pharmaceuticals Corp.; East Hanover, NJ and Basel, Switzerland) exerts synergistic antitumor activity when combined with other anticancer agents. Zoledronic acid also inhibits tumor cell adhesion to the extracellular matrix and invasion through Matrigel trade mark and has antiangiogenic activity. A growing body of evidence from animal models demonstrates that zoledronic acid and other bisphosphonates can reduce skeletal tumor burden and prevent metastasis to bone. Further studies are needed to fully elucidate these biochemical mechanisms and to determine if the antitumor potential of bisphosphonates translates to the clinical setting.

Mechanisms of bisphosphonate effects on osteoclasts, tumor cell growth, and metastasis

Bisphosphonates are potent inhibitors of osteoclast-mediated bone resorption that also exhibit antitumor activity. There is now extensive in vitro evidence that bisphosphonates inhibit proliferation and induce apoptosis of tumor cell lines. In addition, they appear to inhibit tumor cell adhesion and invasion of the extracellular matrix. These data are supported by a growing body of evidence from animal models demonstrating that bisphosphonates can reduce skeletal tumor burden. This may reflect direct antitumor effects or indirect effects via osteoclast inhibition and alteration of the bone microenvironment. Research has begun to shed light on the complex mechanisms by which bisphosphonates inhibit bone resorption and interfere with the formation and growth of bone lesions. Nitrogen-containing bisphosphonates inhibit protein prenylation and thereby short-circuit intracellular signaling via small guanine triphosphatases, such as Ras, which require membrane localization. As a result of these biochemical effects on the mevalonate pathway, bisphosphonates appear to modulate the expression of bcl-2 leading to caspase-dependent apoptosis, inhibit matrix metalloproteinases, downregulate alphavbeta3 and alphavbeta5 integrins, and increase expression of osteoprotegerin, thereby antagonizing osteoclastogenesis. Further preclinical studies are ongoing to fully elucidate these biochemical mechanisms, and well-designed clinical trials are necessary to investigate whether the antitumor potential of bisphosphonates can be realized in the clinical setting.

Mediators of periodontal osseous destruction and remodeling: principles and implications for diagnosis and therapy

Osteoclastic bone resorption is a prominent feature of periodontal disease. Bone resorption via osteoclasts and bone formation via osteoblasts are coupled, and their dysregulation is associated with numerous diseases of the skeletal system. Recent developments in the area of mediators of osteoclastic differentiation have expanded our knowledge of the process of resorption and set the stage for new diagnostic and therapeutic modalities to treat situations of localized bone loss as in periodontal disease. This review describes the current state of knowledge of osteoclast differentiation and activity, mediators, and biochemical markers of bone resorption and their use and potential use in clinical periodontics. Finally, therapeutic strategies based on knowledge gained in the treatment of metabolic bone diseases and in periodontal clinical trials are discussed, and the potential for future strategies is proposed relative to their biologic basis. The intent is to update the field of periodontics on the current state of pathophysiology of the osteoclastic lesion and outline diagnostic and therapeutic strategies with a rational basis in the underlying biology.

Effects of bisphosphonate on matrix metalloproteinase enzymes in human periodontal ligament cells

BACKGROUND

The host response is a critical component in the pathogenesis of periodontitis. In fact, the clinical benefits associated with regulating the host response have been demonstrated in studies using several different classes of drugs. Biophosphates are one host-modulating class of drugs that has demonstrated this ability. These drugs are clinically effective at reducing bone resorption and have shown the ability to inhibit host degradative enzymes, specifically the matrix metalloproteinases (MMPs). Therefore, the purpose of this study was to investigate the regulatory effects of a bisphosphonate, tiludronate, on MMP levels and activity in human periodontal cells.

METHODS

MMP-1 and MMP-3 were assessed in cultured human periodontal ligament cells treated with a bisphosphonate, tiludronate. Reverse transcription-polymerase chain reaction was used to identify mRNA levels for both enzymes, and also for tissue inhibitors (TIMP-1). Enzyme immunoassay (EIA) and immunocytochemistry were used to assess MMP proteins in these cell cultures. Enzyme activity was assessed using FITC-conjugated substrates and quantitated using spectrophotofluorometry.

RESULTS

Tiludronate significantly inhibited both MMP-1 and MMP-3 activity in a concentration-dependent manner. A maximal reduction in activity of 35% was achieved for each of the enzymes at a 10(-4) M concentration. Tiludronate did not have a significant effect on the mRNA levels for MMP-1, MMP-3, or TIMP-1. Similarly, there were no effects noted for either MMP-1 or MMP-3 on the protein level.

CONCLUSIONS

This study demonstrates an inhibitory effect of tiludronate on the activity of both MMP-1 and MMP-3. These effects appear to occur without altering either mRNA or protein levels for these enzymes, supporting a possible mechanism of action that involves the ability of bisphosphonates to chelate cations from the MMPs. Furthermore, these results support the continued investigation of these drugs as potential therapeutic agents in periodontal disease.

Thiazide diuretics affect osteocalcin production in human osteoblasts at the transcription level without affecting vitamin D3 receptors

Besides their natriuretic and calciuretic effect, thiazide diuretics have been shown to decrease bone loss rate and improve bone mineral density. Clinical evidence suggests a specific role of thiazides on osteoblasts, because it reduces serum osteocalcin (OC), an osteoblast-specific protein, yet the mechanisms implicated are unknown. We therefore investigated the role of hydrochlorothiazide (HCTZ) on OC production by the human osteoblast-like cell line MG-63. HCTZ dose-dependently (1-100 microM) inhibited 1,25-dihydroxyvitamin D3 [1,25(OH)2D3]-induced OC release by these cells (maximal effect, -40-50% and p < 0.005 by analysis of variance [ANOVA]) as measured by ELISA. This effect of HCTZ on OC release was caused by a direct effect on OC gene expression because Northern blot analysis revealed that OC messenger RNA (mRNA) levels were reduced in the presence of increasing doses of the diuretic (-47.2+/-4.0%; p < 0.0001 by paired ANOVA with 100 microM 13.6+/-0.49 pmol/mg protein/15 minutes; p < 0.05) in MG-63 cells. Reducing extracellular Ca2+ concentration with 0.5 mM EDTA or 0.5 mM ethylene glycol-bis(beta-amino ethyl ether)-N,N,N',N'-tetraacetic acid (EGTA) only partly prevented the inhibitory effect of the diuretic on OC secretion (maximal effect, -22.5+/-6.9%), suggesting that thiazide-dependent Ca2+ influx is not sufficient to elicit the inhibition of OC secretion. Because OC production is strictly dependent on the presence of 1,25(OH)2D3 in human osteoblasts, we next evaluated the possible role of HCTZ on vitamin D3 receptors (VDR) at the mRNA and protein levels. Both Northern and Western blot analyses showed no effect of HCTZ (1-100 microM) on VDR levels. The presence of EGTA in the culture media reduced slightly the VDR mRNA levels under basal condition but this was not modified in the presence of increasing levels of HCTZ. The OC gene promoter also is under the control of transcription factors such as Yin Yang 1 (YY1) and cFOS. Western blot analysis revealed no changes in YY1 levels in response to HCTZ either in the presence or in the absence of 0.5 mM EGTA in the culture media. In contrast, HCTZ induced a dose-dependent increase in cFOS levels (p < 0.002 by ANOVA), a situation prevented by incubation with EGTA. These studies indicate that HCTZ inhibits OC mRNA expression independently of an effect on VDR, YY1, or extracellular Ca2+ levels but involves changes in cFOS levels. As OC retards bone formation/mineralization, the inhibition of OC production by HCTZ could explain its preventive role in bone loss rate.

Pamidronate administration improves the secondary hyperparathyroidism due to "Bone Hunger Syndrome" in a patient with osteoblastic metastases from prostate cancer

BACKGROUND

The so-called Bone Hunger Syndrome is a metabolic derangement that sometimes complicates the natural history of prostate cancer patients with osteoblastic bone metastases. An excessive bone formation leads to calcium entrapment in bone and the subsequent increase of parathyroid hormone (PTH) levels, in response to calcium demand. PTH elevation stimulates the osteoclasts in sites distant from those involving the tumor, leading to osteomalacia.

METHODS

PTH and markers of bone turnover were monitored every 3 weeks, from the start of pamidronate treatment in a prostate cancer patient with progressive disease, to luteinizing hormone releasing hormone analog (LHRH-A) administration, developing hyperparathyroidism, hypophosphatemia, and albumin corrected serum calcium close to the lower limit of normality. Serum bone alkaline phosphatase (BALP), assessed by two different methods: electrophoretic and immunoradiometric, and urinary levels of markers of bone collagen breakdown were also remarkably elevated.

RESULTS

As a consequence of pamidronate infusion (60 mg e.v. every 3 weeks for a total of four times), BALP and PTH decreased consistently, serum calcium and phosphorus returned within the normal range, while markers of collagen resorption showed a significant decrease at the 9th week, preceded by a transient rise.

CONCLUSIONS

This case report indicates that bisphosphonates could inhibit both osteoclast activity. The anti-osteoblastic effect is mainly responsible for the improvement of the pretreatment calcium imbalance of our patient towards hypocalcemia and the consequent hyperparathyroidism.

Skeletal response to clodronate in prostate cancer with bone metastases

Bone metastases, together with generalized bone resorption, represent the main complication in patients with advanced prostate cancer, and palliative treatments are required to delay the progression of the metastases and improve the quality of life of these patients. For this reason, the bisphosphonate clodronate was administered to 18 patients (clodronate group) from a total of 30, all of whom were receiving complete androgenic blockade; the remaining 12 formed the control group. Transiliac bone biopsies were taken at the beginning of the study and 6 months later to determine the effect of the bisphosphonate on the skeleton. The results were assessed by bone histomorphometry and showed, although without statistical significance between the groups, an antiresorptive effect of the clodronate expressed as the eroded surface/bone surface and as the osteoclast number/bone surface. However, the bone volume also decreased after 6 months of treatment. Similarly, osteoid formation decreased as indicated by the osteoid surface and by the osteoid volume, probably due to the effect of the drug on the osteoblasts. The mineralization rate was apparently slightly retarded in the clodronate group, although to a lesser degree than in the control group. The results confirm the antiresorptive effect of clodronate and its detrimental effect on osteoblast activity.

Selective effect of thiazides on the human osteoblast-like cell line MG-63

Thiazide diuretics have been shown to decrease bone-loss rate and to improve bone mineral density in patients using this medication. However, the exact role of thiazides on bone cells is still debated. In the present work, we studied whether thiazides could affect the normal features of osteoblasts using the human model cell line MG-63. Hydrochlorothiazide (HCTZ) did not affect cell growth nor DNA synthesis in these cells, yet slightly increased alkaline phosphatase activity in these cells at pharmacologically relevant concentrations. Under similar conditions, HCTZ dose-dependently inhibited 1,25(OH)2D3-induced osteocalcin secretion by these cells (maximal effect, -40 to 50%, P < 0.005). However, HCTZ did not inhibit the basal production of osteocalcin in MG-63 cells (without 1,25(OH)2D3 induction), which was very low to undectable. Two different thiazide derivatives, chlorothiazide and cyclothiazide, and two structurally related sulfonamides with selective inhibition of carbonic anhydrase (Acetazolamide) or hyperglycemic effects (Diazoxide) were also tested. Chlorothiazide (1000 microM) inhibited osteocalcin secretion (-42 +/- 12.7%) at doses 10-fold higher than HCTZ (100 microM) while cyclothiazide was effective at doses of 1 microM (-27 +/- 3.6%), and hence 100-fold lower than HCTZ, compatible with the relative natriuretic effect in vivo of these compounds. Acetazolamide (10 microM) poorly affected osteocalcin secretion at doses 100-fold higher than those needed in vivo to inhibit carbonic anhydrase. Likewise, Diazoxide (100 microM) poorly affected osteocalcin secretion at doses known to promote its biological effect. Higher doses of acetazolamide and diazoxide induced cell death. Neither Acetazolamide nor Diazoxide affected alkaline phosphatase, whereas chlorothiazide had a weak positive effect on this enzymatic activity. The production of macrophage colony-stimulating factor (M-CSF) was stimulated in the presence of 1,25(OH)2D3 (50 nM), TNF-alpha (2 ng/ml) or both in MG-63 cells. HCTZ (25 microM, 24 hr of preincubation) did not modify basal M-CSF production and did not reduce the response to 1,25(OH)2D3 alone. In contrast, HCTZ inhibited the response to TNF-alpha alone (P < 0.05), and also reduced the response to a combination of 1,25(OH)2D3 and TNF-alpha (P < 0.01). In conclusion, these results indicate that thiazide diuretics show a selective inhibition of osteocalcin secretion and M-CSF production by MG-63 cells unlike structurally related drugs. Therefore, these features may explain, in part, the positive effect of thiazides on bone mineral density.

Bisphosphonates act on osteoblastic cells and inhibit osteoclast formation in mouse marrow cultures

We examined the mode of action of bisphosphonates on osteoclastic cell recruitment using mouse marrow cultures with or without osteoblastic cells. Tartrate-resistant acid phosphatase-positive multinucleated cells [TRAP(+)MNC] formed in cultures were determined to be osteoclastic cells. In marrow cultures, TRAP(+) MNC formation in the presence of 10(-8) mol/L 1,25(OH)2D3 was not affected by the addition of 10(-6) mol/L dihydrogen (cycloheptylamino)-methylenebisphosphonate monohydrate (YM175). However, it was inhibited in cocultures of marrow cells with osteoblastic cells. The inhibitory effect was evident throughout the entire culture period. YM175 dose dependently inhibited TRAP(+) MNC formation, and other bisphosphonates--pamidronate and alendronate--also inhibited TRAP(+) MNC formation in the coculture. Similar observations were also made in the coculture of spleen cells with osteoblastic cells. The conditioned media of osteoblastic cells treated with 10(-6) mol/L YM175 inhibited TRAP(+) MNC formation in marrow cultures. The presence of YM175 in methylcellulose cultures affected neither the colony formation of monocyte-macrophage lineage, nor TRAP(+) MNC formation in the succeeding cocultures of recovered cells with osteoblastic cells. These results indicate that YM175 and probably other bisphosphonates as well preferentially inhibit the later stage of osteoclastogenesis through its action on osteoblastic cells. Our findings suggest that part of the inhibitory action by osteoblastic cells in the presence of bisphosphonates is mediated through soluble factor(s).

Management of postmenopausal osteoporosis

More than 25% of postmenopausal women are at risk of osteoporosis. In order to avoid its consequences, it is necessary to find an appropriate prevention and/or treatment. We studied: (1) 15 postmenopausal women treated with percutaneous estradiol (50 micrograms/24 h) plus MPA (10 mg/10 days/month); (2) 15 postmenopausal women treated with synthetic calcitonin nasal spray at the daily dose of 100 IU; (3) 10 postmenopausal women treated with nandrolone decanoate (50 mg every 3 weeks); (4) 10 postmenopausal women treated with ipriflavone (600 mg/day); and (5) 10 postmenopausal women treated with sodium fluoride (20 mg) plus calcium (600 mg). Clinical examination, bone mass measurement (total BMD), hematochemical and urinary parameters of bone metabolism (calcium, urinary hydroxyproline, PTH) and growth factors (as IGF-I and TNF-beta) were evaluated. After 6 months of therapy, a complete prevention of bone resorption was achieved. In agreement with current literature, we observed that the various therapeutic approaches have all some positive effect on BMD, with different results on pain, blood biochemical parameters and growth factors' concentrations.

Biologic, histologic and densitometric effects of oral risedronate on bone in patients with multiple myeloma

Recent studies have shown that treatment with bisphosphonates could be effective against the myelomatous skeletal deterioration. However, the mechanisms of action of these drugs in multiple myeloma (MM) have been poorly studied. In the present study, 11 patients with MM and bone lesions were treated orally with 30 mg/day of risedronate for 6 months, and monitored for 6 additional months. Mean serum calcium decreased from day 4, with a concomitant increase in circulating levels of PTH (1-84) and 1,25-(OH)2D. These parameters reached their nadir on day 7 and returned to baseline value during the treatment period. Markers of bone resorption, pyridinoline and deoxypyridinoline decreased from day 7; they were at 50% and 78% of their basal value at the end of treatment and follow-up periods, respectively. A significant reduction of estimates of bone formation (serum alkaline phosphatase and osteoclacin) appeared at month 3 and persisted for the remainder of the 9-month period. Histomorphometric analysis showed a significant reduction of activation frequency, number of osteoclasts and erosion depth. Bone turnover was high at baseline, and normal after treatment, without mineralisation defects. Mean wall thickness was not different before and after treatment. Spinal bone mineral density measured by dual energy X-ray absorptiometry increased (5.3%) at the end of treatment. We conclude that oral risedronate in multiple myeloma induces a noticeable and rapid inhibition of bone resorption.

The effects of orchidectomy on skeletal metabolism in metastatic prostate cancer

The skeletal metabolic effects of androgen withdrawal have been studied in men with metastatic prostate cancer by using a combination of sequential biochemical measurement, quantitative and subjective bone histology and selective osteoclast inhibition with the bisphosphonate Pamidronate. Results showed dissociation in the levels of biochemical markers of bone formation (alkaline phosphatase and osteocalcin) following castration, whilst markers of bone breakdown (urinary hydroxyproline creatinine (OHP) and calcium excretion (CaE)) increased in the majority of patients. The osteolytic response was inhibited by the bisphosphonate Pamidronate (Aminohydroxypropylidene Bisphosphonate (APD)), thus confirming its osteoclastic origin. Histomorphometry of tumour free bone showed an acute drop in bone volume following surgery (p < 0.05). This effect was blocked by Pamidronate suggesting that osteoclastic activity surges immediately following castration, contributing to the acute bone loss. Histology of metastatic areas showed a marked diminution in bone volume due to decreased osteoblast activity and markedly increased osteoclast mediated osteolysis. In 56% of biopsies there were residual foci of active tumour within metastatic areas after orchidectomy. These disturbed metabolic bone activity in a typically localised manner.

Bisphosphonates act on rat bone resorption through the mediation of osteoblasts

Bisphosphonates are generally considered to act on bone resorption by binding to bone mineral and subsequently inhibiting the activity of the osteoclasts which ingest them. This has been supported by the fact that bisphosphonates adsorbed on mineralized tissue inhibit the resorbing activity of isolated osteoclasts in vitro. However, the effectiveness of different bisphosphonates determined in this system does not reflect their relative potencies in vivo. Employing the well-described isolated osteoclast resorption pit assay, with ivory as the resorption substrate, we show here that this lack of correlation prevails only when the bisphosphonates are added to the mineral before addition of osteoclasts, but not when the cells are treated for a short time (5 min) before allowing them to adhere onto ivory. By using this approach with five different bisphosphonates, a stringent correlation of relative potencies was obtained with those found, both in the rat and in the human, in vivo. Furthermore, by using an osteoblastic cell line (CRP 10/30) which is a powerful promoter of osteoclastic resorption in vitro, we obtained evidence that the inhibitory effect of bisphosphonates was the result of an action on osteoblasts rather than on osteoclasts. Thus, in experiments in which the osteoblastic cells were pretreated for 5 min with bisphosphonates and then cocultured with osteoclasts, inhibition of osteoclastic resorbing activity was obtained. Moreover, it was found that this treatment resulted in a decrease of the stimulatory effect found in CRP 10/30-conditioned medium. In conclusion the present study shows that part of the osteoclast inhibiting action of the bisphosphonates is mediated through an action on osteoblasts.

Expression of collagen, osteocalcin, and bone alkaline phosphatase in a mineralizing rat osteoblastic cell culture

Rat calvaria bone cells isolated by collagenase digestion form a bone-like matrix which mineralizes in vitro in the presence of beta-glycerophosphate, in less than 2 weeks. The purpose of this work was to investigate, in this mineralizing rat osteoblastic cell culture, the synthesis of collagen, osteocalcin, and bone alkaline phosphatase (ALP). The results obtained indicate (1) After 15 days in culture, the extracellular-matrix contains collagen type I, V, and to some extent type III. Metabolic labeling at day 14, during the phase of nodules mineralization as well as new nodules formation, shows that collagen types I and type V are synthesized; (2) During the phase of cell growth, no osteocalcin could be detected in the medium, however, at the point of nodule formation, the osteocalcin level reached values of 3.55 +/- 1.39 ng/ml, followed by a 30-fold increase after nodules became mineralized. At day 14, after metabolic labeling, de novo synthesized osteocalcin was chromatographed on an immunoadsorbing column. With urea-SDS PAGE the apparent molecular weight was determined to be 9,000 daltons. (3) Specific activity of ALP was found to be 10 nmol/min/mg of proteins at cell confluence. At day 15, when nodules are mineralized, this activity was increased by 40-fold. The Michaelis constant was 1.58 10(-3) M/L. ALP was inhibited by L-homoarginine and levamisole but not by L-phenylalanine. ALP was shown to be heat sensitive at 56 degrees C with two slopes of inhibition.(ABSTRACT TRUNCATED AT 250 WORDS)

Disodium pamidronate identifies differential osteoclastic bone resorption in metastatic prostate cancer

In a controlled trial the effects of the osteoclast inhibitor disodium pamidronate were studied over a 6-month period in men with metastatic bone disease from prostate cancer. Using serial biochemical measurement of metabolic bone activity, and complementary subjective and quantitative bone histology, the effects of pamidronate were evaluated in tumour-free and metastatic regions of the skeleton, enabling analysis of the differential mechanisms of bone destruction in this disease. Following treatment, abnormally high markers of bone breakdown fell significantly (fasting urine hydroxyproline/creatinine (OHP): P less than 0.05; fasting urine calcium excretion (CaE): P less than 0.0001), confirming that activated osteoclasts play an integral role in the osteolytic process. Serial histomorphometry of bone from tumour-free areas showed that pamidronate restored abnormal levels of bone erosion to normal in 93% of cases. Suppression of bone destruction was also evident within metastases, although this was incomplete. The results confirm that osteoclast overactivity is responsible for a significant proportion of the accelerated osteolysis seen in both tumour-free and infiltrated bone in patients with prostate cancer. The differential effects in tumour-free and infiltrated bone suggest that the mechanisms of osteoclast activation may differ in metastatic and non-metastatic regions of the skeleton.

Effects of estrogen and tamoxifen on serum osteocalcin levels in ovariectomized rats

Serum osteocalcin levels were measured in ovariectomized rats treated for 35 days with either estrogens (ethynylestradiol administered orally or 17 beta-estradiol administered by subcutaneous injection) or the antiestrogenic compound tamoxifen (administered both orally and subcutaneously). Tamoxifen is a non-steroidal compound that has mixed agonist/antagonist actions in several biological models, but is commonly referred to as an 'antiestrogen'. Administration of tamoxifen, like estrogen, caused a reduction in the increases in animal body weight and femur length during the test period, and greater bone density in the distal femur metaphysis compared to ovariectomized control animals. Both the estrogens and tamoxifen caused a dose-dependent decrease in serum osteocalcin as compared to the levels in the serum of ovariectomized control rats; however, tamoxifen displayed both reduced potency and efficacy compared to estrogens. Serum osteocalcin levels declined in a linear fashion throughout the estrogen dose range, and at the highest doses tested (400 micrograms/kg/d ethynylestradiol; 100 micrograms/kg/d 17 beta-estradiol), osteocalcin levels were reduced by 45-50% compared to those found in ovariectomized control animals. The reduction in serum osteocalcin concentrations in tamoxifen-treated animals, on the other hand, was reduced maximally by about 30% compared to those found in the ovariectomized controls at a dose of 100 micrograms/kg/d. Further reduction in serum osteocalcin beyond this level was not observed with increasing doses of tamoxifen. We conclude that tamoxifen acts as an estrogen agonist with respect to effects on serum osteocalcin levels, but fails to reduce serum levels of osteocalcin to the extent observed with steroidal estrogens.

Direct modulatory effect of hexasodium N,N,N',N'-ethylenediamine-tetramethylene-phosphonate on bone cell function in vitro

The phosphonate hexasodium N,N,N',N'-ethylenediamine-tetramethylenephosphonate (EDITEMP.Na6) reduced alkaline phosphatase (Alp) activity and cAMP response to parathyroid hormone (PTH) in primary cultures of foetal rat calvaria cells in a dose-dependent manner, while not affecting culture DNA content. EDITEMP.Na6 also inhibited the mineralization of three-dimensional bone nodules formed in vitro, but not the number of nodules formed. Bone cell culture DNA content was also reduced by EDITEMP.Na6 but at concentrations in excess of those needed to modulate osteoblastic cell function. Withdrawal of EDITEMP.Na6 led to slow but complete recovery of Alp activity. At EDITEMP.Na6 concentrations of 25 microM and higher, recovery of Alp activity appeared to be independent of protein and/or DNA synthesis. Cell culture acid phosphatase (Acp) activity was not affected by EDITEMP.Na6. The results indicate that EDITEMP.Na6 has a direct inhibitory effect on (mature) osteoblastic cell function. In the presence of bone tissue this inhibition also occurred, although not at a relatively low dose level.

Short-term effects on bone and mineral metabolism of 4-amino-1-hydroxybutylidene-1,1-diphosphonate (ABDP) in Paget's disease of bone

To study the short-term effects on mineral and bone metabolism of a recently introduced amino-diphosphonate (4-amino-1-hydroxybutylidene-1,1-diphosphonate or ABDP), 10 patients suffering from active Paget's disease were examined. Each subject received intravenously 5 mg/day of ABDP for 4 days and the effects of treatment were monitored for 12 days. ABDP administration was followed by an early and significant decrease of the urinary hydroxyproline and calcium excretion, of the theoretical renal threshold for phosphate of the serum calcium. Serum phosphate also decreased, while its urinary excretion increased. Intact parathyroid hormone levels at the end of treatment were four times higher than basal levels. Total and bone alkaline phosphatase tended to decrease only slightly at the end of the observation, whereas serum osteocalcin, tended to increase. These findings indicate that the earlier effect of ABDP is a profound inhibition of bone resorption, which brings about a compensatory parathyroid hormone response. The decrease of urinary hydroxyproline follows an exponential curve, with a calculated half-life of 2.2 days, suggesting an approximate equivalency of 5 mg/day ABDP to slightly more than 30 mg/day 3-amino-1-hydroxypropylidene-1,1-diphosphonate. Bone formation seems scarcely influenced in the short-term, but osteoblastic indices show a contrasting behaviour, which may reflect a different biological origin and/or significance.