Effect of levamisole on bone resorption in cultured mouse calvaria

Inhibition of bone resorption by selective inactivators of cysteine proteinases

Inactivators of cysteine proteinases (CPs) were tested as inhibitors of bone resorption in vitro and in vivo. The following four CP inactivators were tested: Ep475, a compound with low membrane permeability which inhibits cathepsins B, L, S, H, and calpain; Ep453, the membrane-permeant prodrug of Ep475; CA074, a compound with low membrane permeability which selectively inactivates cathepsin B; and CA074Me, the membrane-permeant prodrug of CA074. The test systems consisted of 1) monitoring the release of radioisotope from prelabelled mouse calvarial explants and 2) assessing the extent of bone resorption in an isolated osteoclast assay using confocal laser microscopy. Ep453, Ep475, and CA074Me inhibited both stimulated and basal bone resorption in vitro while CA074 was without effect; the inhibition was reversible and dose dependent. None of the inhibitors affected protein synthesis, DNA synthesis, the PTH-enhanced secretion of beta-glucuronidase, and N-acetyl-beta-glucosaminidase, or the spontaneous release of lactate dehydrogenase. Ep453, Ep475, and CA074Me dose-dependently inhibited the resorptive activity of isolated rat osteoclasts cultured on bone slices with a maximal effect at 50 microM. The number of resorption pits and their mean volume was reduced, whilst the mean surface area remained unaffected. Again, CA074 was without effect. Ep453, Ep475, and CA074Me, but not CA074, when administered subcutaneously at a dose of 60 micrograms/g body weight inhibited bone resorption in vivo as measured by an in vivo/in vitro assay, by about 20%. This study demonstrates that cathepsins B, L, and/or S are involved in bone resorption in vitro and in vivo. Whilst cathepsin L and/or S act extracellularly, and possibly intracellularly, cathepsin B mediates its effects intracellularly perhaps through the activation of other proteinases involved in subosteoclastic collagen degradation.

Effect of bromolevamisole and other imidazo [2,1-b] thiazole derivatives on adenylate cyclase activity

We studied the effect of bromolevamisole (BL) and other imidazo [2,1-b] thiazole derivatives--bromodexamisole (BD) and levamisole (LV)--on adenylate cyclase (AC) activity. BL and BD both inhibited forskolin-activated human thyroid AC, while LV had no effect. This inhibition was non-stereospecific and the IC50 values, as measured with 1 mM ATP and 40 microM forskolin, were 0.95 and 0.80 mM for BL and BD, respectively. In contrast, human thyroid alkaline phosphatase (ALP) inhibition was stereospecific, with IC50 values of 0.0012 mM for BL and 0.9 mM for BD. LV was a 10-fold weaker inhibitor of ALP than BL. These results show that ALP inhibition is not correlated with forskolin-activated AC inhibition. Furthermore, in the presence of a competitive inhibitor of GTP (0.1 mM guanosine 5'-O-(2-thiodiphosphate), BL retained its antagonizing effect on forskolin-activated AC which suggests a direct action on the catalytic subunit. The inhibition was of the mixed type, indicating a complex interaction between BL and AC. Glucagon-activated AC activity in rat liver membranes was also inhibited by BL, although to a slightly lesser degree than thyroid stimulating hormone (TSH)-activated AC from human thyroid for a given BL concentration. In cultured human thyroid cells, BL (0.25 mM) induced a potent decrease in cAMP accumulation after 2 hr of stimulation by TSH. Taken together, these results show that BL inhibits AC and that this inhibition is not organ-specific.

Human cystatin C, a cysteine proteinase inhibitor, inhibits bone resorption in vitro stimulated by parathyroid hormone and parathyroid hormone-related peptide of malignancy

The effect of human recombinant cystatin C, a cysteine proteinase inhibitor, on bone resorption in vitro was evaluated. Bone resorption was assessed by analyzing the release of 45Ca and 3H from mouse calvarial bones prelabeled in vivo by injections with 45Ca or [3H]proline, respectively. In 24 h cultures, cystatin C (50 micrograms/ml) significantly inhibited the release of 45Ca and 3H stimulated by parathyroid hormone (PTH, 15 nmol/liter) or parathyroid hormone-related peptide of malignancy (PTHrP, 15 nmol/liter). The degree of inhibition caused by cystatin C in these 24 h cultures was similar to that caused by calcitonin (30 ng/ml). The inhibitory effect of cystatin C on 45Ca release induced by PTH was sustained in 96 h cultures, whereas the initial inhibition caused by calcitonin was transient. Cystatin C, 10-100 micrograms/ml, caused a dose-dependent inhibition of PTH (15 nmol/liter), and PTHrP (15 nmol/liter) stimulated 45Ca release. Addition of 50 micrograms/ml of cystatin C to mouse bone cultures inhibited the release of 45Ca induced by PTH and PTHrP at a wide range of submaximal and maximal concentrations of hormones (0.01-10 nmol/liter). No effect of cystatin C on 45Ca release in dead bones could be observed, nor did the inhibitor decrease the release of calcium in control bones. The inhibition by cystatin C on PTH-induced mineral mobilization was reversible. Cystatin C (1-100 micrograms/ml) did not affect protein synthesis or mitotic activities in mouse calvarial bones as assessed by the incorporation of [3H]proline and [3H]thymidine, respectively. These data show that cystatin C is a potent inhibitor of mineral mobilization and matrix degradation in cultured bones stimulated to resorb by PTH and PTHrP and that this effect is not due to general cytotoxicity.

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)

Enantiomers in arthritic disorders

Drugs which have a center of asymmetry are often administered as an equal mixture of the two possible enantiomeric forms i.e. a racemate. However, there are frequently large pharmacodynamic and pharmacokinetic differences between enantiomers. Consequently, it is possible that while one enantiomer mediates the antiinflammatory or antirheumatic action, the other enantiomer, although adding little to the efficacy of the drug, may contribute to its adverse effects. Asymmetric drugs may also serve as sensitive pharmacological probes of the mechanisms underlying the action of drugs and the inflammatory processes which they modulate. These concepts are the focus for this review.

Different inhibitory actions of immunomodulating agents and immunosuppressive agents on bone resorption of mouse calvaria

In this study, we have investigated the in vitro effects of the immunomodulators lobenzarit and traxanox and a newly synthesized immunosuppressant, mizoribine, as well as cyclosporin A, on bone resorption using neonatal mouse calvariae labelled with 45Ca. As stimulators of bone resorption, bovine parathyroid hormone (PTH), lipopolysaccharide (LPS), interleukin 1 beta (IL-1 beta) and tumor necrosis factor-alpha (TNF-alpha) were used. Lobenzarit, traxanox, mizoribine and cyclosporin A inhibited or tended to inhibit bone resorption stimulated by PTH, LPS, IL-1 beta or TNF-alpha in a dose-dependent manner. Basal bone resorption was inhibited by immunosuppressant cyclosporin A or mizoribine, while immunomodulators lobenzarit and traxanox failed to inhibit basal bone resorption. Removal of lobenzarit from the culture medium resulted in the recovery of bone resorptive activity. These results suggest that the inhibitory effect of immunomodulators on bone resorption is reversible and nonselective. Also, it raises the possibility that immunomodulators and immunosuppressants may affect bone resorption by different mechanisms.

Effects of four bisphosphonates on bone resorption, lysosomal enzyme release, protein synthesis and mitotic activities in mouse calvarial bones in vitro

The effects of 3-amino-1-hydroxy-propylidene-1,1-bisphosphonate (AHPrBP), 1-hydroxyethylidene-1,1-bisphosphonate (HEBP), dichloromethylenebisphosphonate (Cl2MBP) and azacycloheptylidene-2,2-bisphosphonate (AHBP) on bone were examined in organ culture using newborn mice calvaria. AHPrBP, HEBP and Cl2MBP caused a dose-dependent inhibition of PTH-stimulated (10 nmol/l) release of 45Ca from the calvaria, at and above a concentration of 3 mumol/l, whereas AHBP only caused a slight inhibition, at and above 100 mumol/l. AHPrBP inhibited PTH-stimulated release of 3H from bones prelabelled with [3H]-proline. AHPrBP (30 mumol/l) diminished the stimulatory effect of 1 alpha(OH)vitamin D3 (10 nmol/l), prostaglandin E2 (0.1 mumol/l) and renal tumor conditioned media on 45Ca release. AHPrBP and Cl2MBP, at and above 3 mumol/l, decreased PTH-stimulated mobilization of Ca2+ and Pi and in parallel the release of beta-glucuronidase without affecting the release of lactate dehydrogenase. The inhibitory effect of AHPrBP (30 mumol/l) on PTH-induced 45Ca release was irreversible. The inhibition by AHPrBP (30 mumol/l) on spontaneous and PTH-stimulated release of 45Ca can be seen first after 24 h of culture. Similarly the inhibitory effect by HEBP (30 mumol/l) and Cl2MBP (30 mumol/l) was delayed and could be observed after 36 and 24 h of culture, respectively. PTH-stimulated release of Ca2+, Pi, beta-glucuronidase and beta-N-acetylglucosaminidase was reduced by AHPrBP first after 24 h of culture. AHPrBP, HEBP and Cl2MBP, at concentrations which are inhibitory on bone resorption, do not affect protein synthesis and mitotic activities in mouse calvaria. These data show that AHPrBP, HEBP and Cl2MBP inhibit bone resorption in vitro and in parallel decrease lysosomal enzyme release by a mechanism, which is not related to cytotoxicity. In addition, the delayed inhibitory effect on bone resorption and lysosomal enzyme release by all the compounds suggest that bisphosphonates inhibit bone resorption indirectly and not by a direct effect on existing osteoclasts. The delayed inhibition by bisphosphonates on bone resorption may be due to decreased recruitment of new osteoclasts as a consequence of an inhibitory action on mononuclear osteoclast precursor cells.

Alkaline phosphatase inhibition by levamisole prevents 1,25-dihydroxyvitamin D3-stimulated bone mineralization in the mouse

To determine the relationship between alkaline phosphatase (AP), 1,25(OD)2D3 and bone formation in vivo, we have examined the effects of levamisole, a stereospecific inhibitor of AP on bone formation and on 1,25(OH)2D3-stimulated bone mineralization in the mouse. Normal mice were injected daily with levamisole at doses of 40 and 80 mg/kg/b.w. The compound was given alone or in combination with 1,25(OH)2D3 infusion (0.05 micrograms/kg/d) for 7 days. Treatment with levamisole alone inhibited the serum AP activity (mainly of skeletal origin in mice) by 18.4 and 61.3% for the low and high dose respectively. No deleterious effect on body growth, tibia length, and bone cells population was detected. The moderate inhibition of AP activity produced by the lower dose of levamisole alone (18.4%) or in combination with 1,25(OH)2D3 (37.9%) was associated with a reduced endosteal matrix apposition rate (MaAR) determined by double 3H-proline labeling method. This effect was related to a levamisole-induced fall in serum phosphate. Despite the moderate inhibition of AP activity, the mineral apposition rate (MiAR) determined by the double tetracycline labeling method remained normal. Moreover, 1,25(OH)2D3 infusion still resulted in increased MiAR which was stimulated to the same extent as in the absence of levamisole. By contrast, the more severe inhibition of AP activity induced by 80 mg/kg of levamisole alone (61.3%) or in combination with 1,25(OH)2D3 (45.8%) inhibited both the MaAR and the MiAR and prevented the stimulatory effect of 1,25(OH)2D3 on bone mineralization. The data show that AP activity affects the bone matrix and mineral apposition rates in vivo and that severe inhibition of AP activity inhibits the 1,25(OH)2D3-induced stimulation of bone mineralization in the mouse.