Search

Bisphosphonates are now the most widely used drugs for diseases associated with increased bone resorption, such as osteoporosis. Although bisphosphonates act directly on osteoclasts, and interfere with specific biochemical processes such as protein prenylation, their ability to adsorb to bone mineral also contributes to their potency and duration of action. The aim of the present study was to compare the binding affinities for hydroxyapatite (HAP) of 6 bisphosphonates currently used clinically and to determine the effects of these bisphosphonates on other mineral surface properties including zeta potential and interfacial tension. Affinity constants (K(L)) for the adsorption of bisphosphonates were calculated from kinetic studies on HAP crystal growth using a constant composition method at 37 degrees C and at physiological ionic strength (0.15 M). Under conditions likely to simulate bisphosphonate binding onto bone, there were significant differences in K(L) among the bisphosphonates for HAP growth (pH 7.4) with a rank order of zoledronate > alendronate > ibandronate > risedronate > etidronate > clodronate. The measurements of zeta potential show that the crystal surface is modified by the adsorption of bisphosphonates in a manner best explained by molecular charges related to the protonation of their side-chain moieties, with risedronate showing substantial differences from alendronate, ibandronate, and zoledronate. The studies of the solid/liquid interfacial properties show additional differences among the bisphosphonates that may influence their mechanisms for binding and inhibiting crystal growth and dissolution. The observed differences in kinetic binding affinities, HAP zeta potentials, and interfacial tension are likely to contribute to the biological properties of the various bisphosphonates. In particular, these binding properties may contribute to differences in uptake and persistence in bone and the reversibility of effects. These properties, therefore, have potential clinical implications that may be important in understanding differences among potent bisphosphonates, such as the apparently more prolonged duration of action of alendronate and zoledronate compared with the more readily reversible effects of etidronate and risedronate.

Osteogenesis imperfecta (OI) is an inherited disease of bone fragility, usually due to mutation in type 1 collagen. High dose IV bisphosphonates are widely used in children with severe OI. OI type 1 (_mild_ OI) results from decreased synthesis of type 1 collagen; patients also have increased bone turnover. Patients with OI type 1 are often prescribed oral bisphosphonates although to date there is no data regarding the effects in this patient group or the required dose. Patients with OI type 1 were recruited from the metabolic bone and skeletal dysplasia clinics of the Nuffield Orthopaedic Centre, Oxford, UK; from local bone physicians; and from self referral. Entry criteria included age over 18 years, a clinical history of OI type 1, no other conditions contributing to low BMD (assessed by history and biochemical tests), and active contraception in fertile women. Patients were prescribed risedronate (either 5mg daily or 35 mg weekly) for 24 months.BMDwas assessed at lumbar spine (LS) and total hip using Hologic Discovery DXA scanning at time 0 and 24 months. Bone turnover markers (serum P1NP and bonespecific ALP) were assessed at time 0, 6, 12 and 24 months. BMD results were analysed using the paired t test; bone marker results by repeat measurements ANOVA. To date, 18 patients have completed the study (8 men, 10 women, mean age 39 years with range 18 to 76 at entry). At baseline, mean BMDat LS was 0.820 g/cm2 (t score =2.23, z score = 2.02). At 24 months, BMD significantly improved to 0.850 g/cm2, an increase of 3.7% (P = 0.008) (mean t score = 1.94 with mean z score = 1.93). At total hip, mean BMD at baseline was 0.873 g/cm2 (t score = 0.77, z score = 0.56) with no significant change seen at 24 months (P = 0.81). Bone turnover markers showed a significant drop in P1NP (P1NP= 33.6 ng/mL at baseline; P1NP = 18.0 ng/mL at 24 months; P = 0.008; a fall of 47% of baseline value) which was evident by 6 months (P1NP = 23.2 ng/mL; P = 0.002 compared with baseline). There was no significant change in BAP (P = 0.1). This study demonstrates that patients with OI type 1 can respond to oral bisphosphonates at standard doses for idiopathic osteoporosis with significant gain in BMD and decrease in bone turnover, surrogate measures for improved bone strength in these fragile bones. This study was supported by an unrestricted educational grant from Procter and Gamble Ltd.

The present study describes the biological effects of risedronate, a pyridinyl bisphosphonate, on bone and assesses the safety and tolerability of risedronate when given at high doses, with or without calcium, to postmenopausal women with spinal osteoporosis. This single-center descriptive, double-blind, placebo-controlled, randomized, parallel group study included 32 postmenopausal white women with at least one radiographically confirmed vertebral compression fracture. Patients were randomized to one of four different dose regimen groups: (i) R-P, risedronate 20 mg/day for 14 days, followed by placebo for 42 days; (ii) R-CP-P, risedronate 20 mg/day for 14 days, followed by elemental calcium 1000 mg/day and placebo for 14 days, then by placebo for 28 days; (iii) R-CP-R-CP, risedronate 20 mg/day for 7 days, followed by elemental calcium 1000 mg/day and placebo for 21 days, then risedronate 20 mg/day for 7 days, and finally elemental calcium 1000 mg/day and placebo for 21 days; and (iv) P, placebo for 56 days. The biological response was investigated by measuring serum calcium, parathyroid hormone (PTH), and 2 h urinary pyridinoline/creatinine (Pyr/Cr) and deoxypyridinoline/creatinine (DPyr/Cr) ratios at baseline and at days 3, 7, 14, 21, 28, 35, 42, 49, 56, and 84. Overall, there were no consistent trends observed between the active group and placebo for serum calcium. In groups R-P, R-CP-P, and R-CP-R-CP, mean serum PTH levels were elevated above baseline values for the entire 56 day treatment period and remained elevated, although to a lesser extent, at the day 84 follow-up visit. The effect of calcium supplementation on PTH was variable. Urinary Pyr/Cr and DPyr/Cr ratios were decreased from baseline over the entire study period in all groups receiving risedronate. The maximum observed percent decreases from baseline for Pyr/Cr and DPyr/Cr were -46.9% and -58.8%, respectively, at day 49 in the R-CP-R-CP group. In conclusion, risedronate given orally at a dose of 20 mg/day, continuously for 7 or 14 days, resulted in the expected biological response in osteoporotic women. The time course of changes in PTH levels following cessation of dosing was unaffected by calcium supplementation. There was no evidence of a PTH-mediated rebound in bone resorption following cessation of therapy. Furthermore, based on collagen cross-link data, patients did not show an excessive reduction in bone turnover.

BPs can be grouped into two general classes according to their chemical structure and the molecular mechanism by which they inhibit osteoclast-mediated bone resorption. The simple BPs can be metabolically incorporated into non-hydrolysable analogues of ATP that accumulate intracellularly in osteoclasts, causing osteoclast cell death by apoptosis. By contrast, the more potent N-BPs inhibit FPP synthase, an enzyme in the mevalonate pathway. Inhibition of this enzyme in osteoclasts prevents the biosynthesis of isoprenoid lipids that are required for the prenylation of small GTPase signalling proteins necessary for osteoclast function. Inhibition of FPP synthase in cells other than osteoclasts also appears to account for the adverse effects of N-BPs in vivo (including the acute phase reaction) and for the anti-tumour effects of N-BPs in vitro.

The etiology of osteoporosis is multifactorial, but there is evidence from both animal and human studies that the volume of marrow adipose tissue increases when bone volume is reduced in osteoporosis. The cell-related mechanism that may account for this inverse relationship between the volume of marrow adipose tissue and bone remains to be clarified, although it is known that both adipocytes and osteoblasts are derived from stromal cell precursors in bone marrow. We report that retroviral transduction with a temperature-sensitive oncogene (SV40 large T antigen) can generate bipotential cell lines from human marrow stroma that are capable of directed differentiation, in vitro, down either an osteogenic or adipocytic lineage pathway. One such clone, designated hOP 7, expresses type α1(I) procollagen and has low alkaline phosphatase (AP) activity under basal culture conditions that is reminiscent of an osteoprogenitor cell. Exposure of hOP 7 cells to dexamethasone upregulates AP activity and enables the cells to mineralize their extracellular matrix. Also, treatment with calcitriol induces osteocalcin expression and both PTH and PGE 2 induce/augment cAMP formation. Incubation with normal rabbit serum, however, causes the cells to become adipogenic as demonstrated by histological staining with Oil-red-O, expression of mRNA for the early and late adipocyte markers lipoprotein lipase and glycerol 3-phosphate dehydrogenase, respectively, and loss of type α1(I) procollagen mRNA. The generation of homogeneous populations of these cells, as confirmed by Southern blot analysis, demonstrates the capacity of a human clonal cell line to differentiate in either an osteogenic or adipogenic direction.

In this study we tested the hypothesis that exercise induces an adaptive response in the developing skeleton which may be monitored in vivo by measuring biochemical markers of bone metabolism. The effects of exercise on two biochemical markers of bone formation were determined; the carboxyterminal propeptide of type I procollagen (PICP), and the bone-specific isoenzyme of alkaline phosphatase (BAP), and one putative marker of resorption, the pyridinoline crosslinked telopeptide domain of type I collagen (ICTP). All three markers were measured for a year in 2-year-old thoroughbred horses exercised three times a week on a treadmill, and values compared to a control group of age-matched animals. Levels of all three markers fell in both exercised and control groups over the 12-month period reflecting normal age changes. However, there were differences between groups in the pattern of this decrease. When expressed as a percentage of baseline values, BAP was higher (p < 0.05) at 2 months and both BAP and the PICP were higher at 4 months (p < 0.01 and p < 0.05, respectively) in the exercised group, reflecting an increase in bone turnover in this group in the early stages of training. PICP levels were also elevated in the exercised group at 10 months and this result indicates an increase in bone turnover at this time. The changes in ICTP were different; at 2 months, levels were higher in exercised animals than in controls, but there was no significant difference between the two groups at 4 and 6 months. After 8 months, ICTP levels in the exercised group increased returning to near baseline values at 10 months. In summary, the results of these assays for bone ALP and metabolites of type I collagen indicate that the treadmill exercise regimen used for this study resulted in a general increase in bone turnover in 2-year-old thoroughbreds. These findings indicate that biochemical marker determinations may provide a sensitive, noninvasive method of monitoring skeletal turnover during athletic training.

It has been shown in several laboratories that addition of beta-glycerophosphate (beta GP), a substrate for alkaline phosphatase (AP), to cultured osteoblast-like cells induces deposition of orthophosphate (Pi) and Ca within seven days. Even though this effect is regarded as an in vitro model of bone mineralization, it is not known whether it is specific for osteoblasts. We have, therefore, studied the amounts of Pi and Ca deposited after seven days with 10 mM beta GP in culture wells containing confluent cultures of osteoblast-like cells (OB) derived from human trabecular bone explants, human skin fibroblasts (SF), or culture medium alone (MED). Ox liver AP at an activity considerably greater than the endogenous AP activity of the cells, but comparable with that of other osteoblast models, was added to ensure a similar rate of Pi generation from beta GP in all wells. beta GP was converted quantitatively to Pi within seven days, leading to a nonphysiological 10-fold increase in the Pi concentration in the culture medium. After thorough rinsing on day seven, the OB and SF wells contained deposits of Pi and Ca, but the amounts were comparable for the two cell types. Smaller, but significant, amounts of Pi and Ca were also detectable even in rinsed MED wells. This suggests that the detection of such deposits in beta GP experiments cannot necessarily be interpreted as a specific property of osteoblast cultures in vitro, and may simply reflect the presence of AP.(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of the antiviral agent, inosiplex, were assessed in four patients with Paget's disease of bone. Treatment for 6 months did not suppress disease activity as judged by serum alkaline phosphatase and hydroxyprolinuria, and viral inclusions persisted in the one patient from whom a bone biopsy was taken. These results contrasted markedly with the suppressive effects of diphosphonate treatment in these same patients.

Patients with Paget's disease of bone were treated with oral disodium dihydrogen ethylidene-1-hydroxy-1,1-bisphosphonate (EHBP), a drug that is known to stimulate renal tubular reabsorption of orthophosphate (Pi). After 2 weeks of treatment, plasma Pi rose from 1.02 to 1.67 mmol/l. No increase in Pi was observed with the related drug, dichloromethylene bisphosphonate, which also reduces bone turnover in Paget's disease. Intravenous EHBP caused a more rapid increase in plasma Pi, but maximum hyperphosphatemia was not observed until 7-11 days after treatment commenced. It is therefore unlikely that this effect is due to an immediate action of EHBP on the luminal face of the renal brush border Pi transporter. After 2 weeks of oral EHBP, the increase in the Pi concentration in patients' erythrocytes was 31% compared with 64% in plasma. In blood platelets and leukocytes, negligible changes in cellular Pi occurred. The concentrations of 2,3-diphosphoglycerate, adenosine 5'-diphosphate (ADP) and adenosine 5'-triphosphate (ATP) were unaltered, indicating that these organic phosphates were not offsetting a potential change in cellular Pi. The decrease in erythrocyte/plasma distribution ratio for Pi was also observed in patients receiving intravenous EHBP. However, no change occurred in cell/plasma distribution of chloride, suggesting that this apparent regulation of cellular Pi did not arise from changes in erythrocyte membrane potential, pH, or water content. Bone