Disposition and nephrotoxicity of 3-amino-1-hydroxypropylidene-1,1-bisphosphonate (APD), in rats and mice

Adverse events associated with bone-directed therapies in patients with cancer

Bone metastatic disease may lead to serious adverse events in patients with cancer. Bone-directed therapies, including bisphosphonates such as pamidronate and zoledronic acid and the human monoclonal antibody denosumab, are currently approved for the prevention of bone-related adverse events. However, despite the benefits of these drugs, they may cause side effects that are mostly associated with dosages and treatment durations. These side effects range from more frequent, mostly mild, and generally self-limited side effects-such as fever, myalgias, arthralgias, and electrolyte imbalances-to less frequent and more severe side effects such as medication-related osteonecrosis of the jaw and atypical femoral fractures. The purpose of this review is to familiarize clinicians with the literature regarding adverse events associated with bone-directed therapies in patients with cancer. It is important to be aware of these possible adverse events and to educate patients about the predisposing factors associated with side effects from bone-directed therapies and the preventive measures necessary to decrease the risk of occurrence.

Bisphosphonates to reduce bone fractures in stage 3B+ chronic kidney disease: a propensity score-matched cohort study

BACKGROUND

Bisphosphonates are contraindicated in patients with stage 4+ chronic kidney disease. However, they are widely used to prevent fragility fractures in stage 3 chronic kidney disease, despite a lack of good-quality data on their effects.

OBJECTIVES

The aims of each work package were as follows. Work package 1: to study the relationship between bisphosphonate use and chronic kidney disease progression. Work package 2: to study the association between using bisphosphonates and fracture risk. Work package 3: to determine the risks of hypocalcaemia, hypophosphataemia, acute kidney injury and upper gastrointestinal events associated with using bisphosphonates. Work package 4: to investigate the association between using bisphosphonates and changes in bone mineral density over time.

DESIGN

This was a new-user cohort study design with propensity score matching.

SETTING AND DATA SOURCES

Data were obtained from UK NHS primary care (Clinical Practice Research Datalink GOLD database) and linked hospital inpatient records (Hospital Episode Statistics) for work packages 1-3 and from the Danish Odense University Hospital Databases for work package 4.

PARTICIPANTS

Patients registered in the data sources who had at least one measurement of estimated glomerular filtration rate of < 45 ml/minute/1.73 m2 were eligible. A second estimated glomerular filtration rate value of < 45 ml/minute/1.73 m2 within 1 year after the first was requested for work packages 1 and 3. Patients with no Hospital Episode Statistics linkage were excluded from work packages 1-3. Patients with < 1 year of run-in data before index estimated glomerular filtration rate and previous users of anti-osteoporosis medications were excluded from work packages 1-4.

INTERVENTIONS/EXPOSURE

Bisphosphonate use, identified from primary care prescriptions (for work packages 1-3) or pharmacy dispensations (for work package 4), was the main exposure.

MAIN OUTCOME MEASURES

Work package 1: chronic kidney disease progression, defined as stage worsening or starting renal replacement. Work package 2: hip fracture. Work package 3: acute kidney injury, hypocalcaemia and hypophosphataemia identified from Hospital Episode Statistics, and gastrointestinal events identified from Clinical Practice Research Datalink or Hospital Episode Statistics. Work package 4: annualised femoral neck bone mineral density percentage change.

RESULTS

Bisphosphonate use was associated with an excess risk of chronic kidney disease progression (subdistribution hazard ratio 1.12, 95% confidence interval 1.02 to 1.24) in work package 1, but did not increase the probability of other safety outcomes in work package 3. The results from work package 2 suggested that bisphosphonate use increased fracture risk (hazard ratio 1.25, 95% confidence interval 1.13 to 1.39) for hip fractures, but sensitivity analyses suggested that this was related to unresolved confounding. Conversely, work package 4 suggested that bisphosphonates improved bone mineral density, with an average 2.65% (95% confidence interval 1.32% to 3.99%) greater gain in femoral neck bone mineral density per year in bisphosphonate users than in matched non-users.

LIMITATIONS

Confounding by indication was a concern for the clinical effectiveness (i.e. work package 2) data. Bias analyses suggested that these findings were due to inappropriate adjustment for pre-treatment risk. work packages 3 and 4 were based on small numbers of events and participants, respectively.

CONCLUSIONS

Bisphosphonates were associated with a 12% excess risk of chronic kidney disease progression in participants with stage 3B+ chronic kidney disease. No other safety concerns were identified. Bisphosphonate therapy increased bone mineral density, but the research team failed to demonstrate antifracture effectiveness.

FUTURE WORK

Randomised controlled trial data are needed to demonstrate antifracture efficacy in patients with stage 3B+ chronic kidney disease. More safety analyses are needed to characterise the renal toxicity of bisphosphonates in stage 3A chronic kidney disease, possibly using observational data.

STUDY REGISTRATION

This study is registered as EUPAS10029.

FUNDING

This project was funded by the National Institute for Health Research (NIHR) Health Technology Assessment programme and will be published in full in Health Technology Assessment; Vol. 25, No. 17. See the NIHR Journals Library website for further project information. The project was also supported by the National Institute for Health Research Biomedical Research Centre, Oxford.

The role of vitamin E in the prevention of zoledronic acid-induced nephrotoxicity in rats: a light and electron microscopy study

INTRODUCTION

Bisphosphonates are widely used in metastatic cancer such as prostate and breast cancer, and their nephrotoxic effects have been established previously. In this study we aimed to evaluate both the nephrotoxic effects of zoledronic acid (ZA) and the protective effects of vitamin E (Vit-E) on this process under light and electron microscopy.

MATERIAL AND METHODS

A total of 30 male Sprague-Dawley rats were divided into 3 groups. The first group constituted the control group. The second group was given i.v. ZA of 3 mg/kg once every 3 weeks for 12 weeks from the tail vein. The third group received the same dosage of ZA with an additional i.m. injection of 15 mg Vit-E every week for 12 weeks. Tissues were taken 4 days after the last dose of ZA for histopathological and ultrastructural evaluation. Paller score, tubular epithelial thickness and basal membrane thickness were calculated for each group.

RESULTS

For group 2, the p-values are all < 0.001 for Paller score, epitelial thickness, and basal membrane thickness. For group 3 (ZA + Vit. E), the p-values are < 0.001 for Paller score, 0.996 for epitelial thickness, and < 0.001 basal membrane thickness. Significant differences were also observed in ultrastructural changes for group 2. However, adding Vit-E to ZA administration reversed all the histopathological changes to some degree, with statistical significance.

CONCLUSIONS

Administration of ZA had nephrotoxic effects on rat kidney observed under both light and electron microscopy. Concomitant administration of Vit-E significantly reduces toxic histopathological effects of ZA.

Acute kidney injury and bisphosphonate use in cancer: a report from the research on adverse drug events and reports (RADAR) project

PURPOSE

To determine whether acute kidney injury (AKI) is identified within the US Food and Drug Administration's Adverse Events and Reporting System (FDA AERS) as an adverse event resulting from bisphosphonate (BP) use in cancer therapy.

METHODS

A search of the FDA AERS records from January 1998 through June 2009 was performed; search terms were "renal problems" and all drug names for BPs. The search resulted in 2,091 reports. We analyzed for signals of disproportional association by calculating the proportional reporting ratio for zoledronic acid (ZOL) and pamidronate. Literature review of BP-associated renal injury within the cancer setting was conducted.

RESULTS

Four hundred eighty cases of BP-associated acute kidney injury (AKI) were identified in patients with cancer. Two hundred ninety-eight patients (56%) were female; mean age was 66 ± 10 years. Multiple myeloma (n = 220, 46%), breast cancer (n = 98, 20%), and prostate cancer (n = 24, 5%) were identified. Agents included ZOL (n = 411, 87.5%), pamidronate (n = 8, 17%), and alendronate (n = 36, 2%). Outcomes included hospitalization (n = 304, 63.3%) and death (n = 68, 14%). The proportional reporting ratio for ZOL was 1.22 (95% CI, 1.13 to 1.32) and for pamidronate was 1.55 (95% CI, 1.25 to 1.65), reflecting a nonsignificant safety signal for both drugs.

CONCLUSION

AKI was identified in BP cancer clinical trials, although a safety signal for BPs and AKI within the FDA AERS was not detected. Our findings may be attributed, in part, to clinicians who believe that AKI occurs infrequently; ascribe the AKI to underlying premorbid disease, therapy, or cancer progression; or consider that AKI is a known adverse drug reaction of BPs and thus under-report AKI to the AERS.

The risk of cumulative renal effects of intravenous bisphosphonates

Some level of renal dysfunction is common in patients with cancer. This could be a result of an age-related kidney function decrease, the underlying disease (eg, multiple myeloma), or the effects of nephrotoxic medications. Some intravenous (I.V.) bisphosphonates have been associated with occasional renal toxicity in the clinical setting. Therefore, the choice of an I.V. bisphosphonate should take into account the risk of renal deterioration. Preclinical studies also suggest that there might be considerable differences between the renal safety profiles of commonly used I.V. bisphosphonates. Variations in the risk of histopathologic damage and the ability to cause cumulative toxicity have been observed in comparative preclinical studies of I.V. bisphosphonates. The reasons for these apparent differences are not fully understood. Research shows that renal safety profiles might be influenced by pharmacokinetic properties, such as renal tissue half-life, protein binding, and intracellular potency. Preclinical analyses are warranted in order to confirm and evaluate these differences between bisphosphonates.

Is there a role for ibandronate in the treatment of prostate cancer patients with bony metastases?

PURPOSE

Zoledronic acid is widely accepted as the treatment of choice for a number of cancers which metastasise to bone and is the only bisphosphonate licensed for the treatment of prostate cancer. However, drug related nephrotoxicity, although rare, does pose a significant complication when using zoledronic acid. Prostate cancer patients are generally older than 65 years of age and already exhibit some form of impaired renal function. Thus, for prostate cancer patients who are unable to tolerate zoledronic acid there is a need for an alternative bisphosphonate. One possibility could be ibandronate which is also a potent third generation, nitrogen-containing bisphosphonate and is an attractive choice for some patients due to the fact it is available in both intravenous and oral preparations.

METHODS

This article reviews the current published literature regarding the use of ibandronate in the treatment of metastatic prostate cancer.

RESULTS

Preliminary data emerging from small Phase II studies suggests ibandronate may provide a therapeutic alternative for the treatment of metastatic prostate cancer when zoledronic acid is deemed unsuitable.

CONCLUSION

Further in vivo research with ibandronate in prostate cancer is urgently needed in order to elucidate whether this bisphosphonate may play a role in the treatment and palliative management of metastatic prostate cancer.

Bisphosphonate nephrotoxicity

Bisphosphonates are valuable agents for the treatment of post-menopausal osteoporosis (PMO), hypercalcemia of malignancy, and osteolytic bone metastases. Oral bisphosphonates are used mainly to treat PMO and are not associated with significant nephrotoxicity. In contrast, nephrotoxicity is a significant potential limiting factor to the use of intravenous (IV) bisphosphonates, and the nephrotoxicity is both dose-dependent and infusion time-dependent. The two main IV bisphosphonates available to treat hypercalcemia of malignancy and osteolytic bone disease in the United States are zoledronate and pamidronate. Patterns of nephrotoxicity described with these agents include toxic acute tubular necrosis and collapsing focal segmental glomerulosclerosis, respectively. With both of these agents, severe nephrotoxicity can be largely avoided by stringent adherence to guidelines for monitoring serum creatinine prior to each treatment, temporarily withholding therapy in the setting of renal insufficiency, and adjusting doses in patients with pre-existing chronic kidney disease. In patients with PMO, zoledronate and pamidronate are associated with significantly less nephrotoxicity, which undoubtedly relates to the lower doses and longer dosing intervals employed for this indication. Ibandronate is approved in the US for treatment of PMO and in Europe for treatment of PMO and malignancy-associated bone disease. Available data suggest that ibandronate has a safe renal profile without evidence of nephrotoxicity, even in patients with abnormal baseline kidney function.

Differences in Nephrotoxicity of Intravenous Bisphosphonates for the Treatment of Malignancy- Related Bone Disease

Renal dysfunction is a particularly problematic adverse event that requires additional management and can prohibit the use of certain medications. Due to their renal uptake and elimination, some bisphosphonates can cause nephrotoxicity when used for the treatment of skeletal-related events in patients with bone metastases. However, clinical studies and post-marketing experience indicate that renal effects do not appear to be the same for all bisphosphonates. Zoledronic acid and pamidronate appear to be associated with a greater risk of renal toxicity, especially when given in high doses or over short infusion times. In contrast, high loading doses of intravenous ibandronate (3 x 6 mg given on days 1-3) have shown no additional renal safety concerns, and intravenous ibandronate 6 mg appears to have a renal safety profile comparable to placebo. This paper reviews the renal safety of intravenously administered bisphosphonates and makes some suggestions, based on preclinical and clinical data, as to why renal safety profiles may differ.

Acute Renal Effects of Intravenous Bisphosphonates in the Rat

Bisphosphonates are potent osteoclast inhibitors that have been associated with renal toxicity following rapid intravenous administration of high doses, which was hypothesised to be due to precipitation of bisphosphonate aggregates or complexes in the kidney. Five studies were conducted in rats investigating the characteristics of bisphosphonate-related acute renal effects. These studies included single intravenous injections of the nitrogen-containing bisphosphonates (1) ibandronate (1-20 mg/kg), or (2) zoledronate (1-10 mg/kg); (3) a single nephrotoxic dose of the non-nitrogen-containing bisphosphonate, clodronate (2 x 200 mg/kg intraperitoneal injection); (4) a single low dose of ibandronate (1 mg/kg); (5) a single high dose of zoledronate (10 mg/kg). Clinical biochemistry and kidney histopathology were performed 1 and/or 4 days after bisphosphonate dosing. The proximal convoluted tubules were the primary target for renal injury. Tubular degeneration and single cell necrosis of the these tubules were observed with all three bisphosphonates on the fourth, but not the first day after dosing. Differences between the bisphosphonates in the type and/or localisation of the lesions were apparent. Granular deposits in the lumen of distal tubules were apparent with the highest dose of zoledronate (10 mg/kg). However, intraluminal debris was proteinaceous with no evidence of any precipitation of bisphosphonate, or formation of aggregates or complexes in the kidney. Generally, biochemical parameters of renal safety and urinary enzymes did not differ significantly from controls. In summary, bisphosphonate-related renal changes did not appear to be due to the precipitation, aggregation or complexation of bisphosphonate, and biochemical parameters of renal safety did not reliably detect this renal injury.

Preclinical Perspectives on Bisphosphonate Renal Safety

Renal insufficiency is not rare in cancer patients who may receive nephrotoxic medications as antineo-plastic agents or for comorbid conditions. Thus, the choice of a particular bisphosphonate for patients with metastatic bone disease should be based not only on efficacy but also on the risk for renal deterioration. Some i.v. bisphosphonates have been associated with occasional renal toxicity in the clinical setting. Preclinical studies have also shown that there may be considerable differences among bisphosphonate renal safety profiles. Comparative studies show variations in the risk for histopathologic damage and the ability to cause cumulative toxicity during intermittent dosing. Reasons for the differences among bisphosphonates are not fully understood; however, research shows that they may be influenced by pharmacokinetic properties such as renal tissue half-life or protein binding and intracellular potency. Further preclinical analyses are needed to confirm and evaluate differences among bisphosphonates.

The inhibition of RANKL causes greater suppression of bone resorption and hypercalcemia compared with bisphosphonates in two models of humoral hypercalcemia of malignancy

Humoral hypercalcemia of malignancy (HHM) is mediated primarily by skeletal and renal responses to tumor-derived PTHrP. PTHrP mobilizes calcium from bone by inducing the expression of receptor activator for nuclear factor-kappaB ligand (RANKL), a protein that is essential for osteoclast formation, activation, and survival. RANKL does not influence renal calcium reabsorption, so RANKL inhibition is a rational approach to selectively block, and thereby reveal, the relative contribution of bone calcium to HHM. We used the RANKL inhibitor osteoprotegerin (OPG) to evaluate the role of osteoclast-mediated hypercalcemia in two murine models of HHM. Hypercalcemia was induced either by sc inoculation of syngeneic colon (C-26) adenocarcinoma cells or by sc injection of high-dose recombinant PTHrP (0.5 mg/kg, s.c., twice per day). In both models, OPG (0.2-5 mg/kg) caused rapid reversal of established hypercalcemia, and the speed and duration of hypercalcemia suppression were significantly greater with OPG (5 mg/kg) than with high-dose bisphosphonates (pamidronate or zoledronic acid, 5 mg/kg). OPG also caused greater reductions in osteoclast surface and biochemical markers of bone resorption compared with either bisphosphonate. In both models, hypercalcemia gradually returned despite clear evidence of ongoing suppression of bone resorption by OPG. These data demonstrate that osteoclasts and RANKL are important mediators of HHM, particularly in the early stages of the condition. Aggressive antiresorptive therapy with a RANKL inhibitor therefore might be a rational approach to controlling HHM.

Podocyte injury associated glomerulopathies induced by pamidronate

BACKGROUND

Pamidronate has been demonstrated to decrease bone-related complications in multiple myeloma and delay progression of the disease. This has led to its use in supportive and maintenance therapy of myeloma in conjunction with steroids and chemotherapy. It has also been selectively used in patients with breast cancer and other neoplasms.

METHODS

We report on five patients who developed glomerular disease induced by pamidronate. Pamidronate was the only drug common to all patients. Tests for hepatitis B and C and human immunodeficiency virus (HIV) were negative for all patients. The first two patients received a high dose of pamidronate for 8 weeks, whereas the other three patients were on monthly therapy for a prolonged period of time. Sources of data included chart review and pathologic analysis of kidney biopsy.

RESULTS

Three patients were female and two were males and all were Caucasian, ranging in age from 58 to 71 years. Renal biopsy findings included minimal change disease in two, focal segmental glomerulosclerosis in two, and collapsing focal segmental glomerulosclerosis in one. Immunofluorescence was essentially negative in all cases. Electron microscopy showed variable podocyte injury and extensive foot process effacement. There was no evidence of multiple myeloma-related renal disease. After the biopsy, pamidronate was discontinued and renal function stabilized in all patients except the one with the collapsing variant of focal segmental glomerulosclerosis who required hemodialysis. Three patients had resolution of proteinuria, one patient continued to have proteinuria without deterioration in renal function.

CONCLUSION

Pamidronate has been mainly associated with collapsing focal segmental glomerulosclerosis. This report expands that relationship and adds other glomerular diseases linked with podocyte injury. Additional studies are needed to define the cause of the variability of renal histology with this agent.

The renal effects of minimally nephrotoxic doses of ibandronate and zoledronate following single and intermittent intravenous administration in rats

Rapid, intravenous (i.v.) administration of high doses of bisphosphonates has been associated with acute renal toxicity. This controlled, preclinical study over 25 weeks investigated the potential for subclinical renal damage to accumulate to clinically relevant levels when minimally nephrotoxic doses of ibandronate (1 mg/kg) or zoledronate (1 or 3 mg/kg) were given intermittently, with a between-dose interval of 3 weeks, or as a single dose by i.v. injection. In rats, a single dose and intermittent dosing of ibandronate resulted in a similar incidence (one of six and two of six rats, respectively) and severity score (1.0 for both) of proximal tubular degeneration and single cell necrosis. No accumulation of histopathological renal damage occurred. However, intermittent dosing of zoledronate induced a higher incidence (six of six rats) and severity score (3.0) of renal damage compared with single dosing (four of six rats and 1.3, respectively). Accumulation of renal damage was also observed for a lower intermittent dose of zoledronate (1 mg/kg) that had not exhibited histopathological renal damage when given as a single 1 mg/kg dose. Biochemical parameters confirmed these histopathological findings. In summary, the results from this study indicate that administering ibandronate intermittently provides sufficient time for regeneration of potential subclinical renal damage.

Nephrotic proteinuria associated with high-dose pamidronate in multiple myeloma

Five patients receiving increased dose or frequency of pamidronate beyond the recommended dose (90 mg/monthly) exhibited nephrotic proteinuria (range 3.96-24 g/24 h). On dose reduction or discontinuation, three of these patients showed decreased proteinuria to normal levels (< 1 g/24 h), and proteinuria decreased to 4.5 g/24 h from a peak of 24 g/24 h in one patient. One patient on haemodialysis (hence not evaluable) had proteinuria of 2 g/24 h and elevated creatinine levels. One other patient continued to show elevated creatinine levels (272.8 micro mol/l). Renal biopsies obtained in two patients revealed focal segmental glomerulosclerosis.

A Phase I, open label, dose ranging trial of intravenous bolus zoledronic acid, a novel bisphosphonate, in cancer patients with metastatic bone disease

BACKGROUND

Bone metastases typically are associated with osteolytic bone destruction, resulting in bone pain, pathologic fractures, spinal cord compression, and hypercalcemia. Bisphosphonates are potent inhibitors of normal and pathologic bone resorption and represent a significant therapeutic improvement in the management of patients with lytic bone metastases. Zoledronic acid is a new-generation, highly potent, nitrogen-containing bisphosphonate that to the authors knowledge is the most potent inhibitor of bone resorption currently in clinical trials. The objectives of the current study were to assess the safety and tolerability of increasing doses of zoledronic acid and to determine its activity with respect to reducing biochemical markers of bone resorption in cancer patients with bone metastases.

METHODS

Forty-four cancer patients with bone metastases or primary bone lesions were enrolled sequentially into 1 of 5 fixed ascending-dose treatment groups. Each patient received a single intravenous bolus injection of 1, 2, 4, 8, or 16 mg of zoledronic acid over 30-60 seconds. Patients were monitored for 8 weeks for the evaluation of clinical findings, adverse events, vital signs, electrocardiograms, markers of bone resorption, and urinary N-acetyl-beta-D-glucosaminidase.

RESULTS

Zoledronic acid was safe and well tolerated at all dose levels tested. Commonly reported adverse events included bone pain, fever, anorexia, constipation, and nausea, which were experienced by a similar proportion of patients in each treatment group. Seven patients reported serious adverse events, none of which appeared to be related to the study drug. Zoledronic acid effectively suppressed biochemical markers of bone resorption, including the highly specific markers N-telopeptide and deoxypyridinoline, for up to 8 weeks in the 2-16-mg dose groups and for a shorter duration in the 1-mg group.

CONCLUSIONS

In the current study, zoledronic acid was safe and well tolerated and demonstrated potent inhibition of bone resorption. The authors believe it may improve the treatment of metastatic bone disease.

Anticalcification and antiresorption effects of bisacylphosphonates

Some geminal bisphosphonates are used clinically in a number of important bone and calcium-related diseases. This work reports the anticalcification and antiresorption effects of a series of bisacylphosphonates, nongeminal compounds with varying chain lengths having oxo groups in alpha positions relative to the phosphonic functions. We compared the activity of the novel compounds to clinically used geminal bisphosphonates, and to a bisphosphonate devoid of the oxo groups. The interaction of the compounds with calcium was studied by various in vitro and in vivo models. We found that keto groups in alpha positions to the phosphonic functions render activity. The bisacylphosphonates with a shorter chain [(CH2)n, = 4, 6] were found significantly to inhibit hydroxyapatite formation and dissolution in vitro, the calcification of bioprosthetic tissue implanted subdermally in rats, and bone resorption in the intact young animal model. The various in vitro results were found to be in good correlation with the in vivo results. Structure-activity relationship studies indicate that both bisacylphosphonates and geminal bisphosphonates are active only when at least three ionizable groups are present in the molecule. The role of the keto groups is related to their contribution to chelating calcium and/or to their electron-withdrawing influence on acidity.

Parenteral pamidronate prevents thyroid hormone-induced bone loss in rats

Pamidronate (APD) is a bisphosphonate that prevents bone loss from a variety of causes. We studied the role of APD in preventing thyroid hormone-induced bone loss. A total of 32 rats were assigned to one of four treatment groups: (1) -APD/triiodothyronine (-T3), (2) -APD/+T3, (3) +APD/-T3, or (4) +APD/+T3. In the first of two studies, the rats received APD for the first week and T3 for the second week, and then their blood was analyzed for alkaline phosphatase and osteocalcin. Alkaline phosphatase and osteocalcin were significantly higher (p < 0.05) in hyperthyroid rats (-APD/+T3, 3.9 +/- 0.25 mukat/liter and 23 +/- 1.6 nM, respectively) than in control animals (2.53 +/- 0.28 mukat/liter and 18.3 +/- 1.4 nM, respectively). Hyperthyroid rats pretreated with APD (+APD/+T3) had levels of alkaline phosphatase and osteocalcin no different from controls. In a second study, rats were divided into the same four groups, except they received APD/placebo and T3/placebo concomitantly for 3 weeks. At the end of the study, bone mineral density (BMD) of the femur, spine, and whole body was measured by dual-energy x-ray absorptiometry, and the calcium content of the femora was measured directly. In hyperthyroid rats (-APD/+T3) BMD was significantly lower than in controls in the spine (0.201 +/- 0.004 versus 0.214 +/- 0.002 g/cm2, p < 0.05) and femur (0.204 +/- 0.003 versus 0.218 +/- 0.002, p < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of metallic ions and diphosphonates on inhibition of pericardial bioprosthetic tissue calcification and associated alkaline phosphatase activity

This study focused on the association of extrinsic alkaline phosphatase (AP) activity with both early and advanced calcification of glutaraldehyde-pretreated bovine pericardial bioprosthetic (GPBP) tissue, and the inhibition of both calcification and AP activity by pre-incubation in diphosphonates (sodium-ethanehydroxydiphosphonate [NaEHDP], aminopropanehydroxydiphosphonate [APD]) and metallic salts (FeCl3, Ga(NO3)3, AICI3). GPBP specimens were implanted subcutaneously in 3 wk old male rats after pre-incubation. Following explantation of the tissue at 72 h and 21 d, calcification was assessed morphologically by light microscopy and chemically by atomic adsorption spectroscopy for calcium content and by molybdate complexation for phosphorus. AP activity was characterized by enzymatic hydrolysis of paranitrophenyl phosphate and by histochemical studies. In both control and pretreated groups, AP levels were greater in 72 h explants than 21 d retrievals, which demonstrated extensive calcification in control explants. All pre-incubations that resulted in inhibition of calcification after 21 d, except for APD, were associated with 72 h AP content which was lower than control specimens. The typical time of initiation of calcification was 72 h, as determined by previous studies with this model system. Covalently bound APD inhibited calcification. Increased AP activity in the APD group may be due to the toxicity of this agent with resultant acute inflammation, or other incompletely understood effects of diphosphonates on calcification and AP. Furthermore, EHDP and Ga3+ incubations were also associated with decreased GPBP AP at 72 h compared to control, but were not effective for inhibiting calcification after 21 d. We concluded that inhibition of peak GPBP AP activity is not necessarily associated with the prevention of GPBP mineralization.

Pamidronate

OBJECTIVE

The primary objective of this article is to introduce readers to the use of a new agent, pamidronate. The article discusses its use in hypercalcemia of malignancy (HCM), osteolytic lesions, and Paget's disease. Pharmacokinetic data and clinical trials are reviewed, as well as adverse effects and dosage guidelines.

DATA SOURCES

A MEDLINE search was used to identify English-language studies involving pamidronate for the period from 1970 to 1992.

STUDY SELECTION

As comparative trials were few in number, trials using pamidronate as a single agent were also reviewed.

DATA EXTRACTION

Sparse pharmacokinetic data were obtained from clinical trials. All clinical trials available at the time of publication that met the following criteria were reviewed: (1) allowed for adequate rehydration prior to drug therapy; (2) reported standardized and corrected serum calcium concentrations; (3) separated data obtained from patients who received pamidronate alone from those who received pamidronate and concurrent chemotherapy.

RESULTS

Pamidronate has a pharmacologic profile similar to that of etidronate, but pamidronate is more potent and has a longer duration of effect. It has been investigated primarily in the treatment of HCM as well as in the treatment of osteolytic bone metastases and Paget's disease. In hypercalcemia of malignancy it appears to be as effective as established agents with the advantage that a single dose of pamidronate 90 mg iv provides a durable response. In Paget's disease chronic oral administration has also been shown to be effective in relieving bone pain. Adverse reactions with intravenous administration are transient and self-limiting and usually occur with the first dose. The most common adverse effect is a transient and self-limiting fever. Chronic oral administration of doses greater than 600 mg/d is associated with gastrointestinal toxicities.

CONCLUSIONS

Although more well-designed clinical trials comparing pamidronate with standard therapies and other available agents are necessary, initial results indicate that pamidronate is an effective and promising alternative for use in the treatment of HCM.

Measurement of serum [3H]tetracycline kinetics and indices of kidney function facilitate study of the activity and toxic effects of bisphosphonates in bone resorption

The [3H]tetracycline ([3H]TC) model is based on the observation that TC is released from the bones of rats prelabeled with [3H]TC via first-order kinetics, a factor directly reflecting the kinetics of bone resorption. In the present paper we applied the [3H]TC elimination model to rats treated with antiresorptive drugs. The validity of this model was evaluated by examining the effect of the bisphosphonate, 3-amino-1-hydroxypropylidene-1,1-bisphosphonate (ABP), and a novel bisphosphonate, dihydrogen disodium adipoylbisphosphonate (AdBP), on serum TC levels and the elimination rate constant. ABP and AdBP significantly inhibited the TC elimination rate. However, ABP treatment caused impairment of bone mineralization, renal dysfunction, and inhibition of somatic growth. It is concluded that antiresorptive effects of bisphosphonates could be evaluated by the [3H]TC model, but this model is limited to animals with normal kidney function. The experimental conditions provide a technically simple method which is sensitive enough to examine antiresorptive properties in a healthy animal and to detect adverse effects on the kidney. The activity of the novel bisacylphosphonate, AdBP, and lack of its adverse effects indicate the potential of this drug for clinical applications.

Plasma protein binding of APD: role of calcium and transferrin

The bisphosphonate drug APD (pamidronate, 3-amino-1-hydroxypropylidene-1,1-bisphosphonate) has been shown to bind to human plasma proteins. This was an unexpected observation since this hydrophilic, anionic drug is not typical of molecules that exhibit this characteristic. At a concentration of 5 micrograms/ml the extent of binding of APD to fresh human plasma in vitro was variable between subjects 30.2% +/- 8.5% (mean +/- S.D., n = 10). Binding was not influenced by the time or concentration of APD over the range 0.05-10.0 micrograms/ml. At 20 and 50 micrograms/ml some precipitation of APD occurred. Both calcium and iron play a role in the binding of APD to plasma proteins, addition of calcium to plasma increased the degree of binding of APD, whereas the calcium chelators EDTA and EGTA reduced the binding of APD. Similarly, addition of iron to plasma increased the binding and the inclusion of the iron chelator desferrioxamine diminished the binding of the drug. The effects of iron and desferrioxamine were less pronounced than those of calcium and EDTA, indicating that the majority of the binding involves calcium ions and a smaller contribution is made by ferric ions. The equilibrium dissociation constants (Kd) for APD binding to calcium and iron binding sites on plasma proteins were estimated to be 852 microM and 29 microM, respectively. Calcium binding sites were of high capacity but low affinity and the iron binding sites were of lower capacity and higher affinity. Electrophoresis of plasma proteins following incubation with [14C]APD revealed binding to the transferrin and globulin fractions. However, there was some dissociation of protein bound APD during the electrophoresis. The consequences of hypercalcaemia on the pharmacokinetics of APD are discussed.

The pharmacokinetics and distribution of pamidronate for a range of doses in the mouse

The pharmacokinetics of the bisphosphonate drug pamidronate (APD, 3-amino-1-hydroxypropylidene-1,1-bisphosphonate) have been investigated in the mouse by using 14C-APD and following the tissue concentrations for up to 90 days postdose. The accumulation of APD in bone was the highest of all tissues and was linear with increasing dose up to the maximum dose employed (30 mg/kg), which is indicative of the uptake process being a simple chemical phenomenon. Despite the known effects of APD on bone turnover rates and osteoclast activity, the dose appeared to have no significant influence on the biological half-life of APD in bone which was found to be 90-140 days. A high dose of APD (5 mg/kg) appeared to prolong its uptake phase by bone, however, a net movement of APD from the soft tissues is the likely explanation for this finding. The concentrations of APD in the soft tissues investigated (liver, spleen, kidney, lung, and muscle) declined in a biphasic manner, initially in parallel with the fall in the plasma concentration and followed by a gradual fall in APD's concentration in the soft tissues due to renal elimination and a redistribution favoring the calcified tissues. The liver and spleen contained higher concentrations of APD relative to the other soft tissues. The 0-24 hour renal excretion of APD was found to fall with increasing dose above 2.5 mg/kg; this may be due to either nephrotoxicity or increased uptake by soft tissues. For doses over 20 mg/kg, there was some evidence of nephrotoxicity. The data from these studies have been used to formulate a simple physiological model for APD disposition.

Inhibition of gamma-glutamyl transpeptidase potentiates the nephrotoxicity of glutathione-conjugated chlorohydroquinones

Administration of either 2,5-dichloro-3-(glutathion-S-yl)-1, 4-benzoquinone (DC-[GSyl]BQ) or 2,5,6-trichloro-3-(glutathion-S-yl)-1,4-benzoquinone (TC-[GSyl]BQ) to male Sprague-Dawley rats caused dose-dependent (50-200 mumol/kg; iv) renal proximal tubular necrosis, as evidenced by elevations in blood urea nitrogen (BUN), and in the urinary excretion of lactate dehydrogenase (LDH), gamma-glutamyl transpeptidase (gamma-GT) and glucose. Renal proximal tubular necrosis was also confirmed by histological examination of kidney slices prepared from DC-(GSyl)BQ- and TC-(GSyl)BQ-treated animals. Administration of the corresponding hydroquinone conjugates (DC-[GSyl]HQ and TC-[GSyl]HQ), prepared by reducing the quinones with a threefold molar excess of ascorbic acid, resulted in a substantial increase in nephrotoxicity. Moreover, in contrast to other glutathione (GSH)-conjugated hydroquinones, the nephrotoxicity of both DC-(GSyl)HQ and TC-(GSyl)HQ was potentiated when rats were pretreated with AT-125, an irreversible inhibitor of gamma-GT. Neither the quinone-GSH nor the hydroquinone-GSH conjugates caused any effect on liver histology or serum glutamate-pyruvate transaminase levels. The results suggest that coadministration of ascorbic acid with DC-(GSyl)BQ or TC-(GSyl)BQ decreases their interactions with extrarenal nucleophiles, including plasma proteins, and thus increases the concentration of the conjugates delivered to the kidney, and hence toxicity. Furthermore the ability of AT-125 to potentiate the nephrotoxicity of DC-(GSyl)HQ and TC-(GSyl)HQ suggests that metabolism of these conjugates by gamma-GT constitutes a detoxication reaction.