Inhibition of 1 alpha-hydroxy-vitamin D3 stimulated bone resorption in tissue culture by the calcium antagonist verapamil

Treatment with beta-blockers, ACE inhibitors, and calcium-channel blockers is associated with a reduced fracture risk: a nationwide case–control study

BACKGROUND

Cardiovascular diseases are associated with disturbances in calcium metabolism, including increased urinary calcium, vitamin D insufficiency, and decreased bone mineral density. Antihypertensive drugs may increase the risk of falling. However, risk of fracture in patients treated with non-diuretic cardiovascular drugs is largely unknown.

AIM

We investigated associations between fracture risk and treatment with commonly used cardiovascular drugs: beta-blockers, angiotensin-converting enzyme (ACE) inhibitors, and calcium-channel blockers.

DESIGN

A population-based pharmaco-epidemiological case-control study with fracture in year 2000 as outcome and drug use during the previous 5 years as exposure. We used nationwide computerized registers to assess individual use of drugs and related these data to individual fracture records and information on socio-economic and health-related confounders.

RESULTS

We included 124,655 cases that sustained a fracture and 373,962 age and gender-matched controls. After adjustment for potential confounders, risk of any fracture was reduced by 9% [odds ratio (OR) 0.91; 95% confidence interval (CI), 0.88-0.93] in users of beta-blockers, by 6% (OR, 0.94; 95%CI, 0.91-0.96) in users of calcium-channel blockers, and by 7% (OR, 0.93; 95%CI, 0.90-0.96) in users of ACE inhibitors. Moreover, risk of hip fractures was reduced significantly by 7-14% in users of the three groups of drugs. No major differences were found between men and women or in subjects younger or older than 70 years of age. Sub-analyses indicated differences between groups of calcium-channel blockers, as use of non-dihydropyridine drugs was associated with a larger risk reduction than use of dihydropyridine drugs.

CONCLUSION

Treatment with beta-blockers, ACE inhibitors, and calcium-channel blockers is associated with a small but significantly reduced risk of fracture.

No effect of verapamil on the local bone response to in vivo mechanical loading

Verapamil, a calcium channel blocker, alters the intracellular calcium concentration in bone cells in vitro, while mechanical loading stimulates calcium channels. The purpose of this study was to examine the effect of systemic verapamil treatment on the bone response to in vivo external mechanical loading. Female rats (age 5-6 months) were divided into six groups. Half were verapamil treated (0.75 mg/ml drinking water) for 12 weeks. After 8 weeks of treatment, the right tibia was loaded by a four-point bending device. In one set of verapamil and control groups, the right tibia was loaded at 31.8 +/- 0.2 N (36 cycles, 2 Hz, 3 d/wk) for four weeks. A second set was loaded at 40.1 +/- 0.3 N and the third set remained nonloaded. Tibial cortical bone formation and femur bone mineral density (BMD) were evaluated. With loading, bone formation was similarly elevated in loaded tibia of verapamil and control rats (P < 0.003). However, periosteal bone formation (P < 0.001) in the nonloaded tibia, and femoral diaphysis BMD (P < 0.04) were greater in verapamil rats than in controls. We conclude that verapamil, in the dose given, does not interfere with mechanical loading (30, 40 N) at the loaded site and that the voltage-dependent calcium channels, blocked by verapamil, are not significantly involved in the local bone response to increased strain in female rats. However, verapamil increased bone formation and BMD at nonloaded sites of loaded rats. Previously unknown systemic or regional factors associated with loading may explain the potential mechanisms for this interaction and need further investigation.

Comparative study on the effect of calcium channel blockers on basal and parathyroid hormone-induced bone resorption in vitro

A number of clinical and experimental studies suggest that the effects of calcium channel blockers are not limited to the cardiovascular system but might also involve skeletal calcium metabolism due to the presence of L-type calcium channels in osteoblastic cells. We therefore investigated the influence of calcium channel blockers of the dihydropyridine type (nifedipine, amlodipine) as well as of the phenylalkylamine type (verapamil, gallopamil) on basal and parathyroid hormone-induced bone resorption utilizing organ-cultured neonatal mouse calvaria. Only at 10(-4) M, amlodipine, verapamil and gallopamil reduced basal and parathyroid hormone-induced resorption In contrast, nifedipine, between 10(-5)-10(-4) M, exhibited a dose-dependent inhibitory effect on parathyroid hormone-related bone resorption by up to 50%. When calvariae were cultured for 48 hr in the presence of inhibitory concentrations of the calcium channel blockers and then stimulated with parathyroid hormone, only parietal bones pretreated with nifedipine remained completely responsive to the bone resorbing action of the hormone.

Humoral factors of ascites sarcoma 180 stimulate osteoblastic UMR 106-01 cell proliferation and bone resorption via signal transduction pathways, which are clearly different from those of parathyroid hormone

Ascites sarcoma 180 (S180A) is a transplantable tumor that induces hypercalcemia in tumor-bearing mice and stimulates bone resorption in cultured neonatal mouse calvaria without parathyroid hormone (PTH)-like activity. The serum-free conditioned media of S180A cell cultures (S180A-CM) stimulated [3H]thymidine incorporation (178.3% of the control) and inhibited alkaline phosphatase activity (39.0% of the control) in the osteoblastic osteosarcoma cell line UMR 106-01, contrary to PTH. To investigate signal transduction by S180A-CM, we determined the levels of intracellular free calcium ([Ca2+]i), inositol 1,4,5-triphosphate (IP3), 1,2-diacylglycerol (DAG), phosphatidylcholine (PC) and protein kinase (PK) C activity in UMR 106-01 cells. PTH and PTH-related protein (PTHrP), both potent bone-resorbing factors (BRFs), caused an increase in [Ca2+]i and stimulated IP3 production, whereas S180A-CM had little or no effect on these parameters. On the other hand, S180A-CM stimulated DAG production, accompanied by PC breakdown, and the translocation of PKC activity from the cytosol to the membrane fraction. Sphingosine, a specific PKC inhibitor, inhibited bone-resorbing activity (BRA) in S180A-CM more effectively than PTH or PTHrP-stimulated resorption. H-7, an inhibitor of both cAMP-dependent PKA and PKC, completely inhibited BRA in S180A-CM. These results suggest that BRFs of S180A-CM stimulate osteoblastic cell proliferation and bone resorption via two signal transduction pathways, which are different from those of PTH: 1) activation of PKC by DAG resulting from PC hydrolysis and 2) activation of PKA subsequent to prostaglandin E2 production by bone.

Differential depolarization-activated calcium responses in fetal and neonatal rat osteoblast-like cells

The present study evaluates differential occurrence of voltage-dependent calcium channels (VDCC) in the membranes of fetal (FROB) and neonatal (NROB) calvarian rat osteoblastic cells in primary culture. The intracellular calcium concentration ([Ca2+]i) was monitored upon depolarization of the cell membrane with the use of high K+ containing extracellular solutions. [Ca2+]i was measured in populations of cells as well as in individual cells using Fura-2, whereas the membrane potential (Em) was recorded in parallel experiments using patch-clamp techniques. Increasing the extracellular K+ concentration resulted in an instantaneous depolarization of Em of both FROB and NROB. This depolarization of Em did not significantly affect [Ca2+]i of populations of FROB and neonatal osteoblast precursors (NpROB). In contrast to FROB and NpROB, NROB populations responded to depolarization with significant transient [Ca2+]i increases that could be blocked by the calcium antagonist verapamil and were absent if extracellular Na+ was replaced for choline instead of K+. In individual cell measurements, response frequencies as well as the magnitude of [Ca2+]i responses upon depolarization of NROB were much higher than those of FROB, suggesting that more NROB than FROB possess VDCC. This phenomenon might point to a development-related expression of VDCC in the membranes of osteoblast-like cells.

Effects of the calcium channel blocker nifedipine on epiphyseal growth plate and bone turnover: a study in rabbit

The potential effects of a calcium channel blocker (nifedipine) on epiphyseal growth plate and bone remodeling have been investigated in growing rabbits. The treated group received 6 mg/kg/day nifedipine twice daily by gavage for 10 weeks. An untreated group was used as control; with this dose, neither toxic effects nor decrease in the body weight have been observed. No modifications of blood phosphocalcic parameters have been found. In the treated group there is a significant lower cancellous bone volume, lower osteogenesis, shorter labeled perimeters, and lower mineral apposition rate than in the control group. Epiphyseal growth plate thickness is lower than in the untreated animals and considerable morphological changes are observed in the growth zone compared with the control group. A decrease in the growth of humerus length was found. In conclusion, nifedipine affects bone physiology, especially with consequences on bone growth. These effects appear to be quantitatively important, and there is the possibility of bone side effects on therapeutic use in humans, especially in young subjects.

Physiological and pharmacological regulation of biological calcification

Biological calcification is a highly regulated process which occurs in diverse species of microorganisms, plants, and animals. Calcification provides tissues with structural rigidity to function in support and protection, supplies the organism with a reservoir for physiologically important ions, and also serves in a variety of specialized functions. In the vertebrate skeleton, hydroxyapatite crystals are laid down on a backbone of type I collagen, with the process being controlled by a wide range of noncollagenous proteins present in the local surroundings. In bone, cells of the osteoblast lineage are responsible for the synthesis of the bone matrix and many of these regulatory proteins. Osteoclasts, on the other hand, are continually resorbing bone to both produce changes in bone shape and maintain skeletal integrity, and to establish the ionic environment needed by the organism. The proliferation, differentiation, and activity of these cells is regulated by a number of growth factors and hormones. While much has already been discovered over the past few years about the involvement of various regulators in the process of mineralization, the identification and functional characterization of these factors remains an area of intense investigation. As with any complex, biological system that is in a finely tuned equilibrium under normal conditions, problems can occur. An imbalance in the processes of formation and resorption can lead to calcification disorders, and the resultant diseases of the skeletal system have a major impact on human health. A number of pharmacological agents have been, and are being, investigated for their therapeutic potential to correct these defects.(ABSTRACT TRUNCATED AT 250 WORDS)

[Effect of a calcium inhibitor, verapamil, on the development of heterotopic ossifications. An experimental study in rats]

After division of the tendo achilles in rats heterotopic bone forms in the muscle and in the tendon stumps. Tenotomy was performed in 26 male rats. Thirteen received Verapamil (36 mm/Kg) for six days per week for five months, and the remainder were not given this drug. The onset of heterotopic ossification was monitored by monthly x-rays. After five months the animals were killed and the sectioned tendons examined microscopically. The radiographs had shown that the amount of ossification was less in rats treated with Verapamil. This was confirmed at microscopy, but examination of the sections under polarised light showed that the ratio of lamellar to woven bone was the same in the two groups. Verapamil appeared to reduce the amount of heterotopic bone formation but did not influence the substitution of woven by lamellar bone.

Calcium/phosphatidylserine-stimulated protein phosphorylation in bone: effect of parathyroid hormone

The calcium/phosphatidylserine (PS)-stimulated phosphorylation of endogenous proteins in the 100,000 x g particulate fraction from neonatal mouse calvaria was investigated. EGTA selectively inhibited the phosphorylation of a 20K protein. The phosphorylation of this 20K protein was stimulated by calcium and by PS. The combination of calcium plus PS increased the phosphorylation of the 20K protein more markedly than either calcium or PS alone. Parathyroid hormone (PTH) (100 nM) treatment of calvaria rapidly altered the phosphorylation of the 20K protein in a time-dependent manner. The PTH treatment time course demonstrated that after 5 minutes the in vitro phosphorylation of the 20K protein was markedly enhanced, after 15 minutes the 20K protein was not as heavily phosphorylated, and after 30 minutes the in vitro phosphorylation of the 20K was less than control. Our results demonstrate the presence of calcium/PS-stimulated phosphorylation in bone tissue and a rapid effect of PTH on this phosphorylation.

Diphenylhydantoin inhibits parathyroid hormone and prostaglandin E2-stimulated bone resorption in mouse calvaria without affecting cyclic AMP formation

The effect of diphenylhydantoin (DPH) on mouse calvarial bone metabolism was studied in vitro. DPH caused a dose-dependent, reversible inhibition of PTH and PGE2-stimulated bone resorption at concentrations above 20-30 micrograms/ml without affecting cyclic AMP formation. The inhibition was observed already after 60 min and was accompanied by a reduced release of the lysosomal enzymes beta-glucuronidase and beta-N-acetylglucosaminidase. The calcium antagonist Verapamil had similar effects on bone resorption and lysosomal enzyme release and it is suggested that DPH influences bone resorption by interfering with calcium fluxes across osteoclastic cell membranes resulting in low intracellular calcium levels and reduced exocytotic processes.

Effect of 1,25-dihydroxyvitamin D3 and nifedipine on prolactin release in normal man

In normal man 1,25 (OH)2-vitamin D3 [1,25 (OH)2D] increases both basal and TRH-stimulated prolactinemia; this effect is completely reversible by the calcium antagonist nifedipine. Similarly the 1,25 (OH)2D-induced hypercalcemia is totally inhibited by nifedipine. These findings suggest that both biological effects of 1,25 (OH)2D are mediated by calcium-dependent mechanisms.

Effect of levamisole on bone resorption in cultured mouse calvaria

The effects of levamisole (LT), dexamisole (DT), levo-p-bromotetramisole (LBT) and dextro-p-bromotetramisole (DBT) on bone were examined in an organ culture system using calvarial bones from newborn mice. LBT and DBT at concentrations 30 microM and greater and LT and DT at concentrations 100 microM and greater caused a dose-dependent, reversible inhibitory effect on mineral mobilization and matrix degradation. LBT, DBT (100 and 300 microM) as well as LT and DT (greater than or equal to 100 microM) reduced the spontaneous release of beta-glucuronidase without having any marked effect on the release of lactate dehydrogenase (LDH). LT and DT did not influence protein synthesis but LBT and LBT were inhibitory in concentrations at and above 100 microM. Mitotic activity, as assessed by incorporation of [3H]thymidine, was inhibited by LBT and DBT (0.1, 1 mM). LT and LBT caused a stereospecific inhibition of GPase, PPiase and ATPase. It is concluded that tetramisoles are potent, non-stereospecific inhibitors of bone resorption in vitro.

Thrombin, a stimulator of bone resorption

It is shown that thrombin (0.1-7 units/ml) stimulates calcium mobilization and bone matrix degradation, as indicated by release of [3H]proline, from cultured calvarial bones. The second finding in this paper, that indomethacin blocks the stimulating effect of thrombin on bone resorption, is consistent with the concept that prostaglandin synthesis may be involved in this process. It is suggested that thrombin is a potential mediator of bone resorption associated with inflammatory and malignant processes.