alendronate, Fosamax
Alendronate prevents cyclosporin A-induced osteopenia in the rat.

Sass DA, Bowman AR, Yuan Z, Ma Y, Jee WS, Epstein S.

Department of Medicine, Albert Einstein Medical Center, Philadelphia, PA 19141, USA.

Post-transplantation bone disease is an increasingly recognized clinical entity whose etiology is multifactorial. The immunosuppressant agent cyclosporine-A (CsA) has repeatedly been shown experimentally to induce a high-turnover osteopenic state. Alendronate (Alen.) is a new generation bisphosphonate having far greater antiresorptive potency than previous bisphosphonates. It inhibits osteoclast resorption in vitro and in vivo without adversely affecting bone mineralization. This study was designed to investigate whether alendronate could prevent CsA-induced osteopenia in the rat. Forty-eight 8-month-old male Sprague Dawley rats were randomized into four groups to receive the following for 28 days: (1) CsA vehicle (veh.) p.o. daily and alendronate vehicle subcutaneously (s.c.) twice/week, (2) CsA 15 mg/kg p.o. daily and Alen. veh. s.c. twice/week, (3) Alen. 70 micrograms/kg s.c. twice/ week and CsA veh. p.o. daily, and (4) CsA 15 mg/kg p.o. daily and Alen. 70 micrograms/kg s.c. twice/week. Rats were weighed and bled and serum was assayed serially for calcium, PTH, 1,25(OH)2vit.D, and osteocalcin. Tibiae were removed following sacrifice on day 28, after double demeclocycline and calcein labeling, for histomorphometric analysis. Treated groups were compared to the vehicle-treated control. We confirmed previous findings that CsA produces elevated 1,25(OH)2 vitamin D and serum osteocalcin levels. Alendronate treatment by itself decreased osteocalcin by day 28 and resulted in a marginal decrease in serum total calcium on day 14. The histomorphometry findings reconfirmed that the administration of CsA induces a state of high-turnover osteopenia. Alendronate prevented CsA's adverse effects, particularly in maintaining trabecular bone volume, presumably by decreasing bone remodeling. Alendronate would seem to hold therapeutic promise in post-transplantation bone disease.

Online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=9213009&dopt=Abstract alendronate Fosamax



alendronate, Fosamax
Effects of alendronate on the removal torque of implants in rats with induced osteoporosis.

Narai S, Nagahata S.

Department of Oral Surgery, Kagawa Medical University, Kagawa, Japan. satoru kms.ac.jp

PURPOSE: In this study, the removal torques of commercially pure titanium Implants that had been implanted simultaneously with the start of treatment for osteoporosis were compared to those of a group without treatment and a healthy group. MATERIALS AND METHODS: Rats treated by ovariectomy or sham surgery at the age of 12 weeks were used. Twenty-eight days after surgery, the rats treated by ovariectomy were divided into an alendronate-treated group and an untreated (ovariectomy-control) group. At the start of administration of alendronate, a titanium implant was placed in the distal metaphysis of the femur. After 1 month of administration of alendronate and a vehicle, removal torque, the percentage of bone-implant contact (BIC), and parameters of treatment using alendronate were measured. RESULTS: The removal torque values were 10.1 +/- 1.6 Ncm for the group of osteoporotic rats that had been administered alendronate and 6.4 +/- 1.0 Ncm for the group of osteoporotic rats that did not receive alendronate, indicating that the removal torque was significantly higher in the former group than in the latter group. However, there was no significant difference between the alendronate-treated group and the healthy control group (ie, sham surgery) (9.3 +/- 1.3 Ncm). DISCUSSION and CONCLUSION: These results suggested that implant placement together with treatment of osteoporosis is possible in the ovariectomized rat model.

Online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=12705299&dopt=Abstract alendronate Fosamax



alendronate, Fosamax
How does alendronate inhibit protein-tyrosine phosphatases?

Skorey K, Ly HD, Kelly J, Hammond M, Ramachandran C, Huang Z, Gresser MJ, Wang Q.

Department of Biochemistry and Molecular Biology, Merck-Frosst Center for Therapeutic Research, Pointe-Claire-Dorval, Quebec H9R 4P8, Canada.

Alendronate (4-amino-1-hydroxybutylidene 1,1-bisphosphonate) is a drug used in the treatment of osteoporosis and other bone diseases. The inhibition of protein-tyrosine phosphatases (PTPs) by alendronate suggests that PTPs may be molecular targets. As a clear understanding of the inhibition mechanism is lacking, our aim was to analyze the mechanism to provide further insight into its therapeutic effect. We show here that the inhibition of PTPs by alendronate in the presence of calcium followed first-order kinetic behavior, and kinetic parameters for the process were determined. Evidence is presented that the inhibition by alendronate/calcium is active site-directed. However, this process was very sensitive to assay constituents such as EDTA and dithiothreitol. Furthermore, the inhibition of PTPs by alendronate/calcium was eliminated by the addition of catalase. These observations suggest that a combination of alendronate, metal ions, and hydrogen peroxide is responsible for the inhibition of PTPs. The individual effects of alendronate, calcium, or hydrogen peroxide on the inactivation of CD45 were determined. Electrospray ionization mass spectrometry demonstrated that the mass of PTP1B increased by 34 +/- 2 units after the enzyme was inactivated with alendronate/calcium, due to the oxidization of the catalytic cysteine to sulfinic acid (Cys-SO2H). The inhibited PTP1B could be partially reactivated by treatment with reducing agents such as hydroxylamine (NH2OH) and N,N'-dimethyl-N, N'-bis(mercaptoacetyl)hydrazine, indicating the presence of other oxidized forms such as sulfenic acid (Cys-SOH). This further confirms that the inhibition is the result of oxidation of the catalytic cysteine. The relevance of this oxidative inhibition mechanism in a biological system is discussed.

Online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=9278398&dopt=Abstract alendronate Fosamax



alendronate, Fosamax
Clodronate and liposome-encapsulated clodronate are metabolized to a toxic ATP analog, adenosine 5'-(beta, gamma-dichloromethylene) triphosphate, by mammalian cells in vitro.

Frith JC, Monkkonen J, Blackburn GM, Russell RG, Rogers MJ.

Department of Human Metabolism and Clinical Biochemistry, University of Sheffield Medical School, United Kingdom.

Clodronate, alendronate, and other bisphosphonates are widely used in the treatment of bone diseases characterized by excessive osteoclastic bone resorption. The exact mechanisms of action of bisphosphonates have not been identified but may involve a toxic effect on mature osteoclasts due to the induction of apoptosis. Clodronate encapsulated in liposomes is also toxic to macrophages in vivo and may therefore be of use in the treatment of inflammatory diseases. It is generally believed that bisphosphonates are not metabolized. However, we have found that mammalian cells in vitro (murine J774 macrophage-like cells and human MG63 osteosarcoma cells) can metabolize clodronate (dichloromethylenebisphosphonate) to a nonhydrolyzable adenosine triphosphate (ATP) analog, adenosine 5'-(beta, gamma-dichloromethylene) triphosphate, which could be detected in cell extracts by using fast protein liquid chromatography. J774 cells could also metabolize liposome-encapsulated clodronate to the same ATP analog. Liposome-encapsulated adenosine 5'-(beta, gamma-dichloromethylene) triphosphate was more potent than liposome-encapsulated clodronate at reducing the viability of cultures of J774 cells and caused both necrotic and apoptotic cell death. Neither alendronate nor liposome-encapsulated alendronate were metabolized. These results demonstrate that the toxic effect of clodronate on J774 macrophages, and probably on osteoclasts, is due to the metabolism of clodronate to a nonhydrolyzable ATP analog. Alendronate appears to act by a different mechanism.

Online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=9286751&dopt=Abstract alendronate Fosamax



alendronate, Fosamax
Alendronate inhibition of protein-tyrosine-phosphatase-meg1.

Opas EE, Rutledge SJ, Golub E, Stern A, Zimolo Z, Rodan GA, Schmidt A.

Department of Bone Biology and Osteoporosis Research, Merck Research Laboratories, West Point, PA 19486, U.S.A. opas merck.com

Alendronate (4-amino-1-hydroxybutylidene-1,1-bisphosphonate) is a potent bisphosphonate that inhibits osteoclastic bone resorption and has proven effective for the treatment of osteoporosis. Its molecular mechanism of action, however, has not been defined precisely. Here we report that alendronate is a potent inhibitor of the protein-tyrosine-phosphatase-meg1 (PTPmeg1). Two substrates were employed in this study: fluorescein diphosphate and the phosphotyrosyl peptide src-pY527. With either substrate, alendronate was a slow binding inhibitor of PTPmeg1. Among the other bisphosphonates studied, alendronate was more potent and selective for PTPmeg1. The hydrolysis of fluorescein diphosphate by PTP epsilon and PTPmeg1 was sensitive to alendronate, with IC50 values of less than 1 microM; PTPsigma, however, under the same conditions, was inhibited by only 50% with 141 microM alendronate. Similarly, with the src-pY527 substrate, alendronate inhibition was also PTP dependent. Alendronate inhibited PTPmeg1 with an IC50 value of 23 microM, PTPsigma with an IC50 value of 2 microM, and did not inhibit PTP epsilon at concentrations up to 1 mM. The alendronate inhibition of these three PTPs and two substrates is consistent with the formation of a ternary complex comprised of enzyme, substrate, and inhibitor. PTP inhibition by hisphosphonates or vanadate was diminished by the metal chelating agent EDTA, or by the reducing agent dithiothreitol, suggesting that a metal ion and the oxidation of a cysteine residue are required for full inhibition. These observations show substrate- and enzyme-specific PTP inhibition by alendronate and support the possibility that a certain PTP(s) may be the molecular target for alendronate action.

Online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=9310349&dopt=Abstract alendronate Fosamax



alendronate, Fosamax
[Use of alendronate in osteoporosis--is it cost-effective?]

[Article in Norwegian]

Kristiansen IS, Falch JA, Andersen L, Aursnes I.

Statens institutt for folkehelse, Oslo.

The objective of the analysis was to establish the cost-effectiveness of five years intervention with alendronate in women aged 65 years with a bone mineral density (BMD) of the femoral neck 2.5 SD below peak bone mass. A cost-utility analysis based on a simulation model was used. The risk of future fractures was estimated on the basis of clinical and epidemiologic data. The costs of intervention and of fracture treatment were based on market prices (measurement of BMD), the Norwegian DRG price list (in-patient hospital care), the pay scale of the Norwegian Medical Association (out-patient care, doctor's visits, laboratory tests, radiographs), public accounts (nursing home care, rehabilitation) and customary charges (transport, physiotherapy etc.). The discounted cost per Quality Adjusted Life Year (QALY) was NOK 528,000, NOK 291,000 and NOK 147,000 when BMD was respectively 1.5, 2.5 and 3.5 SD below peak bone masa at onset of intervention. Sensitivity analyses indicate that the cost per QALY is relatively sensitive to future risk of fracture, cost of intervention, discount rate, and magnitude and duration of the effects of the intervention. The results indicate that the use of alendronate competes favourably with other commonly used preventive programmes when administered to women with high risk of fragility fractures.

Online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=9324817&dopt=Abstract alendronate Fosamax