Effects of Danazol on Mineral Homeostasis in Normal Postmenopausal Women: Preliminary Communication

The effects of danazol on calcium homeostasis in normal postmenopausal women was examined in a 14-day study utilizing a dosage of 800 mg per day. Danazol caused significant falls in plasma ionized calcium and in the fasting urinary calcium/creatinine ratio, indicating inhibition of bone resorption. Retention of phosphate was also observed as expected with this anabolic agent. The plasma total alkaline phosphatase was also depressed by the drug, which had no effect on hepatocellular function as measured by plasma AST. Certain effects induced by treatment with danazol were still apparent two weeks after cessation of treatment. The drug was well tolerated and androgenic side effects were not seen. It is suggested that the minimal dose regimen of danazol which exerts a calcium-sharing effect should be identified, and that this regimen should be considered for use in a prospective study of the effects of danazol on bone mineral content in the postmenopause.

Effect of 1,25-Dihydroxyvitamin D3 on Biochemical Indices of Bone Turnover in Postmenopausal Women

Bone metabolism was estimated by serum alkaline phosphatase (index of bone formation) and fasting urinary excretions of calcium and hydroxyproline (indices of bone resorption) in a group of early postmenopausal women and a group of 70-year-old women, during 12 months' treatment with 1,25-dihydroxycholecalciferol (1,25(OH)2D3), and compared to oestrogen/gestagen treatment or placebo treatment. The groups treated with 1,25(OH)2D3 did not show any change in bone metabolism, neither in bone resorption nor in bone formation, during the treatment period when compared to the placebo group, whereas treatment with female hormones decreased both bone resorption and bone formation.

Effect of long-term vitamin D2 treatment on bone morphometry and biochemical values in anticonvulsant osteomalacia

Quantitative morphometric analyses of iliac crest biopsies from 20 epileptic patients receiving chronic anticonvulsant therapy have been performed before and after 4-8 months of vitamin D2 treatment with 9 000 U per day. Biochemical quantities, including serum 25-hydroxycholecalciferol (25-HCC) and serum parathyroid hormone (iPTH), were measured. The anticonvulsant osteomalacia found in the initial bone biopsies was characterized by an increased amount of ummineralized bone, an increased bone resorption and, contrary to vitamin D deficiency, an increased bone mineralization and bone formation. Bone resorption and bone formation were probably equally increased since the amount of cancellous bone was normal. Except for a slight increase in osteoidcovered surfaces and osteoclastic resorption surfaces, the bone changes were normalized after vitamin D2 treatment, leading to a mean serum level of 25-HCC 2.4 times above normal. Serum iPTH was normal before and unchanged during D2 therapy. The urinary calcium excretion remained decreased. The investigation characterizes anticonvulsant osteomalacia as a specific bone disease different from that of vitamin D deects of vitamin D metabolites on receptor cells.

A pilot, double-blind, controlled 1-year trial of prednisolone treatment in primary biliary cirrhosis: hepatic improvement but greater bone loss

A randomized, double-blind, 1-year pilot study of prednisolone treatment for primary biliary cirrhosis was undertaken. Nineteen patients received 30 mg prednisolone per day initially, with a maintenance dose of 10 mg per day. Seventeen patients received placebo. The groups were matched for age, menopausal status, hepatic histological stage and bilirubin. Treatment was well tolerated without dropouts. Two patients receiving prednisolone developed diabetes, one a duodenal ulcer and one depression. One patient receiving placebo died for liver failure after 3 months. Cholestatic symptoms (itch and fatigue) improved on prednisolone. There was significant (prednisolone vs. placebo) improvement in transaminase (p = 0.0214), alkaline phosphatase (p = 0.0032), procollagen III peptide (p = 0.0103), immunoglobulin G (p = 0.0012) and liver histology (p = 0.016); these changes were greatest among noncirrhotic patients. No patient developed skeletal symptoms. Fifty-seven per cent had abnormal triolein breath tests prior to treatment, and 65% had abnormally low calcium absorption tests. Calcium absorption increased significantly in the treated group vs. placebo at 2 weeks (p less than 0.02), but not at 1 year. Femoral photon absorptiometry fell in the prednisolone group after 1 year (-3.5% vs. placebo +0.5%, p less than 0.05), as did trabecular bone volume (-6% vs. -2.8%, p less than 0.005) and resorption surface (-11% vs. +2%, p less than 0.02) on serial bone biopsy. Prednisolone seems to exert a favorable hepatic effect in primary biliary cirrhosis but at the expense of increased bone loss to approximately twice the expected rate. Prednisolone treatment merits further assessment in primary biliary cirrhosis over a longer period, with attention to selection of patients most likely to benefit and continuing observation of bone mass to better establish the "cost/benefit" ratio.

Inhibition by 17 beta-estradiol of PTH stimulated resorption and prostaglandin production in cultured neonatal mouse calvariae

Previous attempts to show a direct effect of physiological concentrations of 17 beta-estradiol (beta E2) on bone in vitro have been unsuccessful. We describe a culture system using neonatal mouse calvariae in which beta E2 in the range 1 pM to 1 nM inhibited parathyroid hormone (PTH) stimulated prostaglandin E2 (PGE2) release by 50 to 70% in the presence and absence of cortisol. In addition, beta E2 reduced medium calcium concentration and release of previously incorporated 45Ca by 10 and 20%, respectively, in PTH stimulated cultures. Indomethacin did not block beta E2 effects on resorption. 17 alpha-Estradiol (alpha E2) reduced PTH stimulated 45Ca release but not PGE2 release. Thus, beta E2 has direct effects on bone consistent with its known effects to decrease bone resorption in vivo.

Membrane IL-1 induces bone resorption in organ culture

We have studied the role of the membrane-associated form of IL-1 on bone resorption in vitro. Murine macrophages of the P388D1 cell line stimulated with LPS, subsequently fixed with paraformaldehyde, induced the proliferation of C3H/HeJ mouse thymocytes in the presence of a submitogenic concentration of Con A. Membrane IL-1 on P388D1 cells stimulated with LPS induced bone resorption in organ cultures of neonatal BALB/c mouse calvaria. Polyclonal antibodies directed against membrane IL-1 and soluble IL-1 from P388D1, and monospecific rabbit anti-murine rIL-1 alpha serum neutralized the membrane IL-1 activity, as measured by the thymocyte proliferation. In addition, these antibodies suppressed the bone resorption induced by membrane IL-1. The bone resorption induced by membrane IL-1 required direct contact between mouse calvaria and membrane IL-1. Salmon calcitonin strongly suppressed the calcium release from mouse calvaria in the presence of membrane IL-1. Indomethacin partially inhibited the bone resorption induced by membrane IL-1 on P388D1 cells. Moreover, membrane IL-1 on LPS-stimulated BALB/c mouse peritoneal macrophages or LPS-stimulated osteoblastic cells from BALB/c mouse calvaria induced bone resorption in vitro. These results suggest that membrane IL-1 on macrophages and osteoblastic cells may have a significant role in inflammatory bone resorption in vivo.

Glucocorticoids impair bone resorptive activity and viability of osteoclasts disaggregated from neonatal rat long bones

It is generally believed that glucocorticoids cause osteoporosis through a combination of decreased bone formation and increased bone resorption. However, the direct effect of glucocorticoids on osteoclasts has not been determined. We therefore tested the effects of hydrocortisone and dexamethasone on bone resorption by osteoclasts disaggregated from neonatal rat long bones. Hydrocortisone and dexamethasone caused a dose-dependent inhibition of osteoclastic bone resorption in the range 10(-7) to 10(-5) M, and 10(-9) to 10(-6) M, respectively, at concentrations likely to occur during therapy and disease. Inhibition of bone resorption was found to be associated with impaired osteoclast survival: osteoclast numbers were reduced to approximately 25% of control values by 10(-6) M hydrocortisone and 10(-7) M dexamethasone. Osteoclast cytotoxicity by glucocorticoids was completely antagonized by progesterone, which itself had no effect on osteoclast survival. Analysis of the time course of these inhibitory effects showed a nonsignificant reduction in survival by 6 h and marked inhibition of survival by 12 h. We could detect no specific changes in osteoclast morphology in association with this impaired viability. The relative potencies of the glucocorticoids for impairment of osteoclast viability was similar to their relative affinities for binding the glucocorticoid receptor, and this, together with inhibition by progesterone, suggests a receptor-mediated mechanism. Such a receptor-mediated cytotoxic action of glucocorticoids has only previously been reported with lymphoid cells. The sensitivity of osteoclasts to the lethal effects of glucocorticoids suggests that glucocorticoids may have a role in physiology as inhibitors of osteoclastic bone resorption.

Effects of interleukin-1 on bone turnover in normal mice

Interleukin-1 (IL-1) is a potent stimulator of osteoclastic bone resorption in vitro and causes hypercalcemia and increased osteoclastic resorption when infused into normal mice for 72 h. However, its longer term or local effects on bone turnover in vivo are unknown. To study these, we injected IL-1 alpha once daily for 3 days into the sc tissue over the calvariae of normal mice and examined its effects on calvarial bone morphology during the subsequent 4 weeks using quantitative histomorphometry. Increased bone resorption inside the calvariae and elevated plasma calcium concentrations were present 24 h after the last IL-1 injection. These early systemic effects were not prevented by indomethacin. During the following 3-4 weeks most of the bone on the injected side of the calvariae was resorbed by osteoclasts and was subsequently replaced by increased amounts of new bone. These longer term local effects on bone turnover were prevented by indomethacin. However, indomethacin did not prevent the formation of new bone inside the calvariae at sites of resorption induced by IL-1 independent of prostaglandin production. These findings indicate that IL-1 stimulates bone turnover systemically, independent of prostaglandin production, and that it has profound long term local effects on bone turnover that are mediated through prostaglandins.

Effects of a bisphosphonate (1-hydroxy ethylidene-1,1 bisphosphonic acid) on osteoclast number during prolonged bed rest in healthy humans

Acute osteoporosis is known to occur after immobilization in spinal cord injured patients and is related to an early increase in osteoclastic bone resorption. Whether osteoporosis develops in healthy immobilized human patients is still a matter of controversy. Furthermore, acute osteoporosis was thought to be a good model to study the effects of weightlessness on the human skeleton and to adapt preventive procedures. A bed rest experiment was developed in the USSR on 15 healthy human volunteers to determine the precise effects on bone structure and cell activities. A preventive protocol, including an anti-osteoclastic drug (1-hydroxyethylidene-1,1 bisphosphonic acid; K salt) was investigated. Two transiliac bone biopsies were performed on the 15 individuals before and at the end of the 120-day bed rest period. Undecalcified bone biopsies were studied with automatic and semi-automatic image analyzers specially devoted to bone histomorphometry. Trabecular bone volume, osteoid amount, and eroded surfaces were measured. Osteoclast number was measured after histochemical identification of tartrate-resistant acid phosphatase. After the bed rest period, an insignificant bone loss was observed in healthy humans while osteoclast number was highly increased. In bisphosphonate-treated subjects, osteoclast number was markedly reduced and so was osteoid amount. Bisphosphonates were shown to present a highly cytotoxic activity on osteoclasts, a finding that has never been demonstrated in normal subjects.

Parathyroid hormone (PTH) and PTH-like protein (PLP) stimulate interleukin-6 production by osteogenic cells: a possible role of interleukin-6 in osteoclastogenesis

Osteogenic cells mediate PTH-stimulated osteoclastic bone resorption by a yet unidentified mechanism. We show that primairy rat osteoblast-like cells and the clonal osteogenic sarcoma cell line UMR-106 produce interleukin-6 (IL-6) and that bPTH(1-84) and synthetic hPLP(1-34) stimulate this production dose-dependently. With both peptides a close relation between IL-6 and cyclic-AMP production was found, though for PTH concentrations higher than 2.10(-8) M a clear dissociation was observed. Significant IL-6 activity was also detected in media of cultures of 17-day-old fetal mouse radii and metacarpals which was clearly stimulated by PTH. The source of IL-6 in these bone explants seems to be the osteogenic (cartilage) cells. Treatment of bone explants with IL-6 induced osteoclastic resorption which, however, depended on the bone resorption system used. This bone resorbing action of IL-6 is exerted probably through an effect on the formation of osteoclasts (osteoclastogenesis) rather than on the activation of already existing mature osteoclasts. We suggest that IL-6 produced by osteogenic cells may be a mediator in PTH-stimulated osteoclastic bone resorption.

Production of interleukin 1 beta, a potent bone resorbing cytokine, by cultured human myeloma cells

Supernatants of freshly isolated human myeloma cell cultures were examined both for bone-resorbing activity (BRA) in vitro using newborn mouse calvaria, and for identification of the causal substances of the BRA. Eight of 14 culture supernatants of myeloma cells had BRA. All of these BRA-positive supernatants were from patients with marked destructive bone lesions of multiple myeloma. The presence of interleukin 1 (IL-1), especially IL-1 beta, was demonstrated in seven of these BRA-positive supernatants but not in BRA-negative supernatants. The concentrations of IL-1 beta were high enough to induce bone resorption in the newborn mouse calvaria assay and the BRA was totally abolished by pretreatment of the supernatants with anti-IL-1 beta antibody but not with either anti-IL-1 alpha antibody or normal serum. Other bone resorbing cytokines such as tumor necrosis factor or lymphotoxin were not present in high enough concentrations to stimulate bone resorption and their levels did not correlate with the BRA. IL-1 beta mRNA was also identified in BRA-positive myeloma cells. These results demonstrate that IL-1 beta is the principal agent of BRA present in supernatants of myeloma cell cultures, and also identify a possible role of IL-1 beta in destructive bone lesions in patients with multiple myeloma.

Two squamous cell carcinomas not associated with humoral hypercalcemia produce a potent bone resorption-stimulating factor which is interleukin-1 alpha

Conditioned medium (CM) from two squamous cell carcinoma cell lines, SCC-9 and SCC-13, stimulated bone resorption in neonatal mouse calvariae in organ culture. Enhanced bone resorption induced by CM was associated with an increased production of prostaglandin-E2 (PGE2) by the calvariae. Complete inhibition of stimulated PGE2 synthesis by indomethacin only partially inhibited bone resorption-stimulating activity (BRSA) in the CM. Neither SCC-9 nor SCC-13 CM stimulated cAMP production in rat osteosarcoma cells (ROS 17/2.8). The BRSA in CM was completely inhibited by an antibody to interleukin-1 alpha (IL-1 alpha). Fractionation of SCC-9 CM by gel filtration and HPLC ion exchange chromatography revealed a single peak of BRSA and PGE2 synthesis-stimulating activity at 17-20K (termed SCMII). In mouse calvariae, SCMII increased medium Ca2+ and PGE2 in a dose-dependent manner at concentrations from 20 ng protein/ml to a maximum of 500 ng protein/ml. Preincubation of SCMII with antibody to IL-1 alpha completely inhibited SCMII-induced bone resorption. SCMII also enhanced thymocyte proliferation with activity that was equivalent to 353 U/ml IL-1. Antibodies to IL-1 beta and tumor necrosis factor had no effect on SCMII-induced bone resorption. Using specific enzyme-linked immunosorbent assays for IL-1 alpha and IL-1 beta, IL-1 alpha was measured in high concentrations in both crude and partially purified fractions of SCC-9 and SCC-13 CM. In contrast, IL-1 beta was either undetectable or present in amounts below those that stimulate bone resorption. In addition, SCMII did not enhance cAMP production in bone cells. We conclude that the BRSA produced by the two squamous cell carcinoma cell lines SCC-9 and SCC-13 is IL-1 alpha.

Effects of two inhibitors of anion transport on bone resorption in organ culture

The present investigation was undertaken to examine the effects of 4-acetamido-4'-isothiocyanostilbene-2,2-disulfonic acid (SITS) and 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS), known amino-reactive and selective inhibitors of anion exchange across the plasma membrane, on bone resorption in organ cultures of fetal rat long bones. Cultures were treated with SITS and DIDS under control unstimulated conditions or with PTH. Both SITS and DIDS were found to be potent inhibitors of 45Ca release from previously labeled fetal rat long bones. Both control resorption and the response to PTH were inhibited in a dose-related fashion. SITS and DIDS also inhibited the incorporation of [3H]thymidine in bone. The effects on resorption and [3H]thymidine incorporation were reversible when the drugs were withdrawn. These findings indicate that SITS and DIDS are potent inhibitors of bone resorption which may act by blocking the anion exchange, Cl-/HCO3-.

In vivo and in vitro effects of amylin and amylin-amide on calcium metabolism in the rat and rabbit

Amylin is a new member of the calcitonin/CGRP family: it is a 37 amino acid polypeptide which was recently isolated from amyloid deposits in pancreatic islets obtained from type II diabetics. In the present study we investigated the effect of amylin and amylin-amide on calcium metabolism in the rat and rabbit. Two main methods were used: in vivo hypocalcaemic activity was assessed by measuring plasma calcium levels after injection of the peptide in 50 g rats; and in vitro resorption of cortical bone by disaggregated rat osteoclasts was quantified by scanning electron microscopy together with image analysis. We demonstrate that amylin and amylin-amide have calcitonin-like effects: both are powerful inhibitors of osteoclastic resorption and as a consequence lower plasma calcium in both rats and rabbits. We speculate that the peptide may exert systemic or local regulatory effects on bone cells.

Secretion of parathyroid hormone-like activity from human T-cell lymphotropic virus type I-infected lymphocytes

Because many patients with adult T-cell leukemia/lymphoma (ATLL) develop hypercalcemia with similar characteristics to those of humoral hypercalcemia of malignancy (HHM) (Arch. Intern. Med., 148: 921-925, 1988), we investigated if ATLL cells produce parathyroid hormone (PTH)-like activity. Conditioned media from cultures of human T-cell lymphotropic virus type I-infected cell line (MT-2) as well as peripheral lymphocytes from a hypercalcemic ATLL patient stimulated cyclic AMP production in osteoblast-like rat osteogenic sarcoma cells (UMR 106) and bone resportion in organ cultures of fetal mouse calvaria. Furthermore, the stimulation of cyclic AMP production by conditioned medium of MT-2 cells was inhibited by human PTH(3-34), indicating that MT-2 cells secrete PTH-like activity. The PTH-like activity from MT-2 cells was chromatographically indistinguishable from the one extracted from a solid tumor causing HHM. The present results along with our previous observation that MT-2 cells constitutively express mRNA for PTH-related protein (Biochem. Biophys. Res. Commun., 154: 1182-1188, 1988) demonstrate that a PTH-like activity is synthesized and secreted by these cells, and are consistent with the hypothesis that elaboration of PTH-like activity by ATLL cells may be the mechanism by which hypercalcemia develops in ATLL patients as well as in solid cancer patients with HHM. However, these results do not rule out the possibility that other factors such as interleukin 1 are also involved and may act in concert with PTH-like activity in the development of hypercalcemia in ATLL.

Cyclosporin A induces in vivo inhibition of resorption and stimulation of formation in rat bone

We investigated a possible "in vivo" effect of cyclosporin A, an immunosuppressive agent, on normal rat bone remodeling. At an oral daily dose of 7 mg/kg for 14 days, the blood level of cyclosporin A was in the usual effective range and no change in renal function or magnesium metabolism was observed. Treated rats had decreased bone resorption: urinary hydroxyproline, plasma acid phosphatase, and the number of osteoclasts in caudal vertebrae were significantly reduced. By contrast, bone formation assessed by dynamic histomorphometry after double tetracycline labeling was increased. No modification of calciotropic hormones (vitamin D metabolites and parathyroid hormone as assessed by urinary cyclic AMP) was observed at the end of the treatment. These results suggest that in vivo cyclosporin A treatment induces bone remodeling modifications related to either a direct or a lymphokine-mediated effect on bone cells.

Effect of auranofin on resorption, prostaglandin synthesis and ultrastructure of bone cells in cultured mouse calvaria

Auranofin (AF) in concentrations between 3 x 10(-7) and 3 x 10(-6) mol/l stimulated bone resorption in cultured neonatal mouse calvariae significantly with 1 x 10(-6) mol/l being most potent. Complete inhibition by 5 x 10(-7) mol/l indomethacin and increased medium concentrations of prostaglandin (PG) E2 and 6-keto-PGF1 alpha after 72 h indicate a PG mediated mechanism. Morphology revealed active osteoclasts. Cytotoxic effects were observed with 3 x 10(-6) and 1 x 10(-5) mol/l AF with osteocytes and osteoblasts being considerably more sensitive than osteoclasts. The latter concentrations inhibited bone resorption stimulated by parathyroid hormone (PTH) 1,25-dihydroxyvitamin D3, PGE2, thrombin and interleukin 1. The stimulatory effect of AF on PG production and subsequent bone resorption could limit its therapeutic usefulness.

Periodontal and femoral bone status in periodontitis-affected hamsters receiving a high dose indomethacin treatment

The aim of this study was to test the effect of a high dose (6 mg/kg/d) of indomethacin, a PG-synthesis inhibitor, on hamster periodontitis and to verify a possible systemic skeletal action. Thirty animals were separated into three groups: control, untreated periodontitis-affected, and indomethacin treated groups. Compared to affected untreated animals, indomethacin reduced the number of osteoclasts (p less than 0.001) to the control level, and accordingly the extent of resorption (p less than 0.01). A partial decrease in reversal (p less than 0.05) was also obtained; the persistence of aborted reversal lacunae was the scar of the pretreatment period. The extent of formation was markedly increased by indomethacin (p less than 0.01). Bacterial plaque accumulation was not modified but PMNLs investing plaque were dramatically decreased (p less than 0.02). Indomethacin had no influence on the femoral periosteal remodeling, nor on metaphyseal and epiphyseal trabecular density, nor on growth plate thickness. These results confirm the positive effect of indomethacin on hamster periodontitis and emphasize the role of PGs on periodontitic bone disturbances, particularly on the uncoupling of the remodeling sequence. The reduction in PMNL migration is an important feature, which possibly participates in the improvement of the bone status. The lack of femoral changes indicates that a mid-term treatment with indomethacin has no detrimental action on ordered skeletal growth and bone mass.

[Cytokines and osteoclastic action]

In spite of the major advances in our knowledge of the cell biology of the osteoclast, many questions still remain to be answered: where does the osteoclast comes from, what is his fate and how it is activated. Bone resorption is considered in a global perspective as the resultant of two successive steps which are the formation of osteoclast progenitors in hematopoietic tissues, the generation of osteoclasts in bone and the activation of osteoclasts at the contact of mineralized bone. Activated osteoclasts resorb both the mineral and the organic of mineralized bone. All these steps are regulated by hormones and growth factors. Hormones have been studied extensively, but recent work has reveal that growth factors also have significant effects on bone function. The purpose of this article is to review current knowledge in the area of the biology of the osteoclast and to index all the growth factors that are known to act mainly on the formation and/or the activation of the osteoclasts.

Resorption is not essential for the stimulation of bone growth by hPTH-(1-34) in rats in vivo

Chronic low doses of hPTH-(1-34) stimulate bone growth in rats in vivo. The objective of these studies was to determine if the anabolic effect of hPTH-(1-34) on rat bone in vivo is dependent on an initial stimulation of resorption by blocking resorption with either salmon calcitonin (CT) or dichloromethylene diphosphonate (Cl2MDP). Male Sprague-Dawley rats, 70-100 g, were treated with daily subcutaneous (SC) injections of vehicle (V) or hPTH-(1-34), 8 micrograms per 100 g (PTH), for 12 days. In experiment 1, rats were given CT for 3 (CT3) or 12 (CT12) days, either alone or in combination with hPTH-(1-34) (CT3-PTH and CT12-PTH) or vehicle for 12 days. In experiment 2, rats were pretreated for 4 days with Cl2MDP or its vehicle before starting the daily PTH or vehicle injections. Rats were then killed. Sera, femora, tibiae, and kidneys were removed for chemical and histomorphometric analyses. PTH, PTH-CT3, and PTH-CT12 rats showed significant increases in total bone calcium (18-23%), dry weight (DW, 13-25%), and bone-forming surfaces compared with their respective controls. Eroded (resorption) surfaces were comparable between the groups. Although weight gain and serum calcium were normal in rats treated for 3 days with CT, rats treated for 12 days with CT gained 14% less weight than controls and were hypophosphatemic, with reduced serum calcium and urea nitrogen. Total bone mass increased both in Cl2MDP rats (Ca 21%, DW 2%), where resorption was presumably blocked, and in PTH rats (Ca 31%, DW 19%). The increase in bone mass was greater in PTH-Cl2MDP rats (Ca 48%, DW 29%) than in rats treated with Cl2MDP alone, suggesting that although Cl2MDP blocked resorption, the anabolic response to PTH was not altered. As neither short-term treatment with CT nor Cl2MDP blocked the anabolic response of bone to hPTH-(1-34), this response does not appear to depend on the early stimulation of resorption.

Bone-resorbing activity of thyroid hormones is related to prostaglandin production in cultured neonatal mouse calvaria

The bone-resorbing activity of thyroid hormones was evaluated in neonatal mouse calvaria maintained in organ culture for 96 h. Thyroxine (T4) between 10(-8) and 10(-5) mol/liter and triiodothyronine (T3) between 10(-8) and 10(-7) mol/liter caused a dose-dependent release of calcium from cultured bone. The thyroid hormone effect was delayed in onset for at least 24 h, and after 96 h of culture amounted to 50-90% of the bone-resorbing activity of 10(-8) mol/liter parathyroid hormone (PTH). The bone-resorbing action of T4 as well as of T3 was completely blocked by 100 U/ml interferon-gamma (IF-gamma) or 20 mU/ml salmon calcitonin (CT). "Escape" from CT inhibition, which is a well-known phenomenon in the action of PTH, was not observed with thyroid hormone-mediated bone resorption. Thyroid hormone treatment of cultured calvaria resulted in a gradual increase between 48 and 96 h of medium concentrations of prostaglandin (PG) E2 and particularly of 6-keto-PGF1 alpha, the inactive metabolite of prostacyclin (PGI2). The release of PGF2 alpha in general was not significantly affected. Although the effect of thyroid hormones on PG release from cultured calvaria was completely abolished by 5 x 10(-7) mol/liter indomethacin, in some experiments indomethacin reduced thyroid hormone-mediated bone resorption by only 50%. This indicates that thyroid hormone action on bone is also mediated by a PG-independent mechanism.

Cyclosporin A in the oophorectomized rat: unexpected severe bone resorption

Local factors, such as interleukin-1, may mediate the accelerated bone remodeling in the acute estrogen-deficient rat. Cyclosporin A (CsA), which in vitro inhibits some of these local factors, was administered to oophorectomized (OX) rats in an attempt to modify this high turnover state. Three groups of 15 rats were studied. Group A was sham operated, group B was OX, and group C was OX and received CsA (15 mg/kg per day) by gavage commencing 4 days postoophorectomy for 28 days. Estradiol levels were determined to confirm oophorectomy. Blood was sampled on days -7, 0, 7, 14, 21, and 28 for ionized calcium (Ca2+), 1,25-(OH)2-vitamin D, PTH, and bone gla protein (BGP). Rats received tetracycline hydrochloride for bone histomorphometric labeling. All results were compared to group A. Body weight was increased in group B (p less than 0.003) but not in group C. There was no difference in Ca2+ or PTH between the groups. BGP levels were higher in group B by day 28 (p less than 0.005); BGP levels were increased in group C from days 7-28 (p less than 0.002). 1,25-(OH)2-vitamin D was significantly increased in group C (p less than 0.0001) but not in group B. Tibial bone histomorphometry revealed increased measurements of bone formation and osteoclast number without a loss of bone volume (BV/TV) in group B. Group C showed a dramatic increase in bone turnover with significant loss of BV/TV (p less than 0.001). In conclusion, CsA in the OX rat resulted in unexpected enhanced bone remodeling with high BGP levels and severe bone resorption.(ABSTRACT TRUNCATED AT 250 WORDS)

Rainbow trout hypocalcin stimulates bone resorption in embryonic mouse calvaria in vitro in a PTH-like fashion

Hypocalcin, the major hormone with hypocalcaemic action in fish, was isolated from trout corpuscles of Stannius (SCs). The bioactivity of hypocalcin was assessed in a parathyroid hormone (PTH) bioassay involving bone resorption in embryonic mouse calvaria. Calcium and phosphate release and lactate production were stimulated in a dose-dependent manner by hypocalcin. On a molar basis about equal amounts of hypocalcin and PTH were required to obtain similar effects in this assay. Hypocalcin did not stimulate cyclic AMP production either in mouse calvaria or in cultured osteoblasts. In this respect hypocalcin resembles shortened or N-terminus-modified PTH molecules that induce bone resorption without increasing cyclic AMP levels. Since hypocalcin and PTH have comparable bioactivity in this mammalian bioassay (as well as in fish bioassays), we tentatively suggest that both hormones are structurally similar and that both hormones may act via the same receptors. The two hormones show no resemblance to one another in primary structure, so we suggest that they have similarities in tertiary structure.

Effects of pertussis toxin on resorption of 19-day-old fetal rat long bones

We tested the effects that pertussis toxin had on bone resorption mediated by cAMP-dependent and cAMP-independent stimuli in 19-day-old fetal rat long bones. Agents that stimulate cAMP were PTH, prostaglandin E2, and calcitonin. Agents that act independent of cAMP were: phorbol 13-myristate 12-acetate (PMA), 1,25-dihydroxyvitamin D3, murine interleukin-1 alpha, osteoclast-activating factor, and human tumor necrosis factor-alpha. Pertussis (1-10 ng/ml) produced a dose-related inhibition of resorption in unstimulated control cultures. The inhibitory effect was not associated with changes in either [3H]thymidine or [3H]proline incorporation into bones. beta-Glucuronidase activity in the medium was decreased. PMA was the only agonist whose resorptive effect was completely blocked by pertussis. The resorptive response to other stimulators was reduced, but treated/control ratios usually remained the same or increased because of the greater effect of pertussis on control resorption. There was a partial inhibition of the resorptive effect of low doses of prostaglandin E2 (10 nM), but increasing the concentration of agonist overcame the inhibition. Pertussis did not enhance the sensitivity of bones to calcitonin. Pertussis enhanced the cAMP response to PTH, but had no effect on basal cAMP production. Since PMA was inhibited by pertussis while agents that may act through cAMP-mediated or phosphatidylinositol pathways were not affected, we hypothesize that a protein kinase-C dependent pathway can modulate bone resorption.

Parathyroid hormone-related protein and interleukin-1 alpha synergistically stimulate bone resorption in vitro and increase the serum calcium concentration in mice in vivo

To elucidate the mechanism of humoral hypercalcemia elicited by human esophageal carcinoma cells (EC-GI), which constitutively produced interleukin-1 alpha (IL-1 alpha) and PTH-like factor, the effects of IL-1 alpha and PTH-related protein (PTH-rP) on bone resorption in vitro and on serum calcium concentrations in vivo were investigated. Nude mice transplanted with EC-GI cells invariably developed hypercalcemia, although their urinary cAMP excretion remained within the normal range. IL-1 alpha or PTH-rP-(1-34) stimulated 45Ca release from prelabeled fetal mouse forearm bones in a concentration-dependent manner, and when combined, IL-1 alpha and PTH-rP-(1-34) synergistically stimulated bone resorption in vitro. Injection of PTH-rP-(1-34) into mice three times a day for 2 days increased the serum calcium concentration in a dose-dependent manner. Continuous infusion of IL-1 alpha occasionally increased the serum calcium concentration. Simultaneous administration of IL-1 alpha at rates of 1-2.7 micrograms/day and PTH-rP-(1-34) at doses of 15-30 micrograms/day synergistically increased the serum calcium concentration in vivo. These findings suggest that PTH-rP and IL-1 alpha produced by the tumor cells were synergistically responsible for the humoral hypercalcemia observed in both the original patient and the tumor-bearing nude mice, and that at least two bone-resorbing factors [PTH-rP and another nonadenylate cyclase-stimulating bone-resorbing factor(s)] are active in patients with malignancy-associated hypercalcemia, in whom nephrogenous cAMP excretion is neither increased nor decreased.

Bone-resorbing cytokines enhance release of macrophage colony-stimulating activity by the osteoblastic cell MC3T3-E1

It has been observed that bone resorption in response to interleukin 1 (IL 1) or tumor necrosis factor (TNF) is accompanied by an increase in osteoclast number. Because the osteoclast is of hemopoietic lineage, recruitment could be regulated by colony-stimulating factors, one of which may be macrophage colony-stimulating factor (M-CSF). In this study, we show that the constitutive release of M-CSF activity by the osteoblastic cell MC3T3-E1 is enhanced by the presence of recombinant IL 1 alpha, recombinant TNF alpha, or by the concurrent presence of purified transforming growth factor beta (TGF beta) and epidermal growth factor (EGF). Increased release of CSF by the osteoblast in response to these agents may provide a signal for the growth and maturation of osteoclast precursors leading to subsequent bone resorption.

Effects of prostaglandin E3 and eicosapentaenoic acid on rat bone in organ culture

To assess the possibility that diets rich in eicosapentaenoic acid (EPA) could have adverse effects on the skeleton, we examined the resorptive response to its major project, PGE3, and the effects and metabolism of EPA itself in cultured fetal rat long bones and neonatal rat calvaria. PGE3 stimulated bone resorption with a potency similar to that of PGE2. However, EPA was a much less effective precursor for PGE3 than was arachidonic acid (AA) for PGE2. In bones cultured with complement sufficient rabbit serum, which stimulates endogenous PGE release, addition of EPA had little effect on bone resorption while AA produced a substantial increase. Bones labeled with [3H]-AA and incubated with transforming growth factor-alpha (TGF-alpha), which stimulates endogenous PGE production, produced substantial amounts of PGE2, while bones labeled with [3H]-EPA and treated similarly produced less than 1/10th as much labeled PGE3. Thus, EPA appears to be a less effective precursor for the production of bone resorbing prostanoids than AA in cultured rat bone. However, since PGE3 is a potent stimulator of bone resorption, the possibility that dietary EPA can effect the production of bone resorbing prostanoids in man requires further study.

A new way to induce oestrogen-deficiency osteopaenia in the rat: comparison of the effects of surgical ovariectomy and administration of the LHRH agonist buserelin on bone resorption and composition

Prolonged administration of LHRH agonist suppresses pituitary gonadotrophin secretion, thereby lowering blood oestrogen. This study was undertaken to compare the osteopaenic effects of bilateral ovariectomy and chronic administration of the LHRH agonist, buserelin, in the rat. Four groups of animals which had their skeletons labelled with 45Ca were studied for 4 weeks. Group 1 underwent a sham-ovariectomy, group 2 were surgically ovariectomized, group 3 were given buserelin by daily s.c. injection and group 4 were given a continuous infusion of buserelin by osmotic minipump. Plasma concentrations of oestradiol were measured weekly. Bone resorption was assessed by measuring the urinary excretion of 45Ca and hydroxyproline and determining bone 45Ca content. Ovariectomy and buserelin treatments lowered blood oestradiol, increased biochemical indices of bone resorption and decreased femur and total body calcium and 45Ca values. The degree of oesteopaenia elicited by ovariectomy and buserelin treatment was similar. Bone responses to s.c. buserelin and to continuous buserelin infusion were alike. We attribute evidence of increases in bone resorption and induction of osteopaenia with buserelin treatment to hypo-oestrogenism. We have shown for the first time by bone analysis that buserelin induces osteopaenia as effectively as bilateral ovariectomy. This appears to be the first demonstration in the rat that long-term administration of LHRH agonist influences bone. Administration of buserelin provides a new way of inducing oestrogen-deficiency osteopaenia in the rat without removing the ovaries.

[Hypercalcemia in malignant diseases. Physiopathology and treatment]

About 10% of cancer patients develop hypercalcemia. The mechanisms behind the development of hypercalcemia are complex, but the most important facts seems to be increased osteoclastic bone resorption. Several cellular mediators play a part in creating and sustaining hypercalcemia. The article discusses these mechanisms, and reviews the principles of treatment. Emphasis is placed on rehydration and on inhibition of bone resorption. The use of diphosphonates (bisphosphonates), a group of potent osteoclast inhibitors, is discussed in some detail.

Understanding and preventing osteoporosis

Although age-related bone loss due to remodeling is basically a normal, predictable phenomenon, it is one that may be accelerated, at times quite dramatically, by dietary factors, hormonal insufficiency, or lack of exercise. Recent data regarding the long-term prophylactic efficacy of calcium supplementation, estrogen replacement therapy, and exercise are evaluated.

Interaction of cyclosporine A and calcitonin on bone resorption in vitro

Cyclosporine A (CsA), which is a potent immunosuppressive agent, inhibits bone resorption in vitro. The inhibition of bone resorption by CsA is sustained, unlike the transient inhibition of bone resorption produced by calcitonin (CT). These different patterns of inhibition were studied by examining the interaction between CsA and CT on stimulated bone resorption in the neonatal mouse calvarial resorptive system. "Escape" from the CT inhibition of PTH stimulated bone resorption occurred after 24 hr of organ culture. Coincubation with CsA (1 micrograms/ml) delayed the "escape" response of CT + PTH treated bones, so that the full "escape" response did not occur until after 48 hr of organ culture. Likewise, a pretreatment of 24 hr with CsA (1 micrograms/ml) was sufficient to delay "escape" from CT inhibition of PTH stimulated bone resorption until after 48 hr of organ culture. A higher concentration of CsA (10 micrograms/ml) completely prevented the "escape" response. Our data could indicate an interaction between the CsA and CT inhibitory effects on resorption.

Dichloromethylenebisphosphonate (Cl2MBP) inhibits bone resorption through injury to osteoclasts that resorb Cl2MBP-coated bone

Dichloromethylenebisphosphonate (Cl2MBP, formerly Cl2MDP) inhibits bone resorption in vivo and in vitro. The mechanism by which it inhibits osteoclastic bone resorption has not been established. To investigate this, osteoclasts were isolated from rat long bone and incubated with Cl2MBP (10(-9)-10(-5) M) on bone slices. Bone resorption was assessed as plan area resorbed after 6 and 24 h by scanning electron microscopy. Although Cl2MBP inhibited bone resorption in the first 6 h of culture, inhibition was more marked in the incubation period between 6 and 24 h. This pattern of accelerating inhibition is unlike the pattern we have observed using other resorption-inhibitors, and suggested resorption-mediated osteoclast injury. In keeping with this, we found reduced numbers of osteoclasts, and morphological features of cell injury and degeneration of osteoclasts, after incubation with Cl2MBP on bone slices. Bone seemed to be an essential component in Cl2MBP-mediated injury, since osteoclast numbers and morphology on plastic coverslips were unaffected by the bisphosphonate. Moreover, bone slices preincubated with Cl2MBP showed similar effects on resorption and morphology to cultures in in which osteoclasts on bone were continuously immersed in Cl2MBP. Neither non-resorptive cells (macrophages, UMR 106 cells), nor osteoclasts prevented from resorption by calcitonin, showed evidence of cytotoxicity after incubation on bone slices with Cl2MBP. These results suggest that even relatively high concentrations of Cl2MBP in the fluid phase do not affect osteoclasts, nor does contact with Cl2MBP-coated bone surfaces, but that injury to osteoclasts, and a consequent reduction in bone resorption, occurs when osteoclasts excavate bone surfaces upon which Cl2MBP is adsorbed.

Bone resorption by isolated human osteoclasts in vitro: effects of calcitonin

Human osteoclasts were isolated from 12- to 17-week-old fetal tissue and from transiliac crest bone biopsies for an in vitro study of their biology. A hypodermic needle was used to flush either the fetal long bones or the trabeculae of the iliac crest bone biopsy with tissue culture medium and the resulting cell suspension sedimented briefly either onto the surface of plastic tissue culture dishes, for time-lapse microcinematography, or onto slices of devitalized bovine cortical bone for quantitative assay of bone resorption. The osteoclasts were motile, tartrate-resistant acid phosphatase positive and capable of excavating pits in slices of devitalized bovine cortical bone. Human calcitonin, at doses of 1 ng/ml and 1 microgram/ml, caused a 70% inhibition of bone resorption by human fetal osteoclasts over a 24 h period but had no apparent effect on the morphology or motility of either fetal or adult osteoclasts.

Bone remodeling signaled by a dihydropyridine- and phenylalkylamine-sensitive calcium channel

An osteoblast calcium channel demonstrated by single channel recordings is associated with calcium antagonist receptor binding sites in osteoblast-like osteosarcoma cells. By using whole cell current recordings we now show that this channel is stimulated by the dihydropyridine calcium agonist drug BAY K 8644. A physiological relevance of these channels is apparent from the stereoselective, potent inhibition of parathyroid hormone-stimulated calcium uptake into osteoblast-like cells in culture by desmethoxyverapamil, a phenylalkylamine calcium antagonist. Secretion by these cells of the bone matrix protein osteocalcin is stimulated by BAY K 8644 and blocked by desmethoxyverapamil and nitrendipine. Evidence for a role of this channel in bone remodeling in intact animals comes from enhanced bone resorption in fetal rat bones observed with BAY K 8644 and stereoselective, potent blockade of resorption by desmethoxyverapamil.

Cyclic therapy of osteoporosis with neutral phosphate and brief, high-dose pulses of etidronate

We have designed a cyclic regimen for the treatment of osteoporosis based on the activate, depress, free, and repeat (ADFR) concept. Osteoclastic bone resorption is activated by 7 days of oral neutral phosphate and inhibited with a brief pulse (5 days) of etidronate disodium at a high dose (20 mg/kg body weight). Patients next take calcium supplements for 48 days before resuming phosphate to enter the next cycle. Osteoporotic women increased the bone mineral density of the lumbar spine at 6 months by 7.2 +/- 5.2% (mean +/- SD, N = 14) and at 12 months by 8.2 +/- 4.0% (N = 8). Control observations in regularly exercising postmenopausal women (N = 30) showed no significant change in spine mineral density after 20 months (0.5 +/- 3.2%), confirming the stability of the measurement technique. The two patients who responded poorly to the cyclic regimen each showed a blunted rise in serum PTH during oral phosphate administration, suggesting that the rise in PTH induced by oral phosphate may be an important component of this cyclic regimen. This preliminary study does not identify which component or components of the regimen are responsible for the increase in bone mass but provides positive encouragement for randomized studies designed to determine the optimum dosage, duration, and timing of each component of the regimen.

Bone demineralization, biochemical indices of bone remodeling, and estrogen replacement therapy in adults with Turner's syndrome

The study centered on a controversy about whether long-term estrogen replacement therapy may ameliorate the osteoporosis seen in patients with Turner's syndrome. This study comprised 26 adult patients with Turner's syndrome (9 treated and 17 untreated or insufficiently treated) and 12 adult women with pure gonadal dysgenesis (8 untreated and 4 treated). A low bone density below -2 standard deviations from the age- and sex-matched predicted normal mean was documented by dual-photon absorptiometry of the lumbar spine in all the untreated and insufficiently treated patients, but only in 6 treated patients. The biochemical indices of bone resorption (urinary hydroxyproline excretion and plasma tartrate-resistant acid phosphatase activity), as well as osteoblastic function (serum osteocalcin and bone alkaline phosphatase isoenzyme), were significantly increased in untreated and insufficiently treated patients compared with treated patients. A significant negative correlation was found between biochemically documented osteoresorption and spinal bone mineral density corrected for age of the patients. Significant positive correlations were found between serum osteocalcin and bone alkaline phosphatase isoenzyme and between biochemical indices of bone resorption and formation. Although in the patients there was an evidence of a high bone remodeling rate, the rate of bone mass loss seemed to be low, comparable with that seen in oophorectomized women who had already passed their accelerated phase of bone loss. The results indicate that long-term hormonal replacement therapy is justified in gonadal dysgenesis, regardless of the karyotype of the patient, to prevent further bone mass loss.

Regulation of new osteoclast formation by a bone cell-derived macromolecular factor

Medium conditioned by incubation with embryonic chick calvarial bones, which contain osteoblasts but not osteoclasts, stimulated new osteoclast formation in foetal long bone cultures and in adult bone marrow cultures formation of tartrate-resistant acid phosphatase (TRAP) positive cells was greatly stimulated. We have termed the factor responsible for this activity osteoclast growth/inducing factor (OGF). OGF was soluble, heat-stable and of size greater than 10kda. OGF activity was present also in mouse bone conditioned medium and in extracts of demineralized cortical diaphyseal bone of five-week-old chickens. OGF appeared to differ from the osteoblast-derived bone-resorbing factors previously observed as well as from macrophage colony stimulating factor (CSF-1). It is therefore probable that different locally secreted factors independently regulate the formation of osteoclasts and their activity.

Prostaglandins in inflammatory bone pathology: mechanism and therapeutic benefit of etodolac

To investigate the role of PGE2 in the development of bone and joint pathology in rat adjuvant arthritis, hindlimb paws were evaluated by calcified tissue histologic techniques focusing on histochemical visualization of cartilage and bone lesions. Case studies of hindlimbs from normal, adjuvant arthritic, and etodolac-treated arthritic rats demonstrated the association of disease severity with inflammation, chondromalacia, replacement of adipose bone marrow with a fibroid marrow, osteoclastic bone resorption, synovial cysts, and pannus formation within the joints. Extensive periosteal intramembranous bone formation was temporally associated with joint destruction and medullary tissue pathology. In vivo data were correlated with in vitro effects of inflammatory mediators (IL-1, PGE2) on bone resorption. Etodolac blocked bone explant PGE2 accumulation at concentrations of 10(-7) M and higher, and inhibited bone resorption at concentrations of 10(-5) M and higher. The data indicate that in vitro and in vivo models of bone metabolism are well correlated regarding prostaglandin synthesis; that the inflammatory mediator PGE2 is largely responsible for the involvement of skeletal tissue in the adjuvant arthritis model; and that the effects of etodolac are specifically mediated by its ability to inhibit PGE2 accumulation in vivo.

Parathyroid hormone stimulates prostanoid formation in mouse calvarial bones

Bovine parathyroid hormone (bPTH 1-34) caused a time- and dose-dependent enhanced formation of the two prostanoids PGE2 and 6-keto-PGF1 alpha in cultured neonatal mouse calvarial bones, with threshold for action at 0.1 nmol/l. The PGE2 response to PTH was completely blocked by indomethacin, but insensitive to calcitonin. By contrast, indomethacin was without effect on 45Ca release induced by PTH. The PTH analogues (Nle 8, 18, Tyr 34)-bPTH (3-34) amide and (Tyr 34)-bPTH (7-34) amide, which are putative PTH antagonists, did not affect basal production of PGE2, nor did the analogues affect bPTH 1-34 induced PGE2 formation. The data show that PTH stimulates prostanoid formation in mouse bone cells and that this response is not directly linked to PTH-induced bone resorption.

Inhibition of osteoclastic acid phosphatase abolishes bone resorption

Osteoclastic acid phosphatase is a member of a widely-distributed class of iron-containing proteins with acid phosphatase activity. Antibodies raised against one member of this class cross-react with other members from the same or different species, but not with acid phosphatase isoenzymes of different types. When antibodies to one such protein, porcine uteroferrin, are added to medium in which rat osteoclasts are incubated on devitalised cortical bone, both bone resorption and acid phosphatase activity are markedly inhibited. Furthermore, addition of molybdate (an inhibitor of this class of acid phosphatases) also inhibits both bone resorption and enzyme activity. These observations strongly suggest a functional role for osteoclastic acid phosphatase in bone resorption.

Partial purification and characterization of a factor produced by mitogen-stimulated sheep mononuclear cells with thymocyte-activating and cartilage-degrading properties

Ovine peripheral blood mononuclear cells stimulated with concanavalin A released a soluble factor capable of inducing cartilage resorption and thymocyte activation in vitro, but not lysis of the murine L929 cell line. The active moiety has a molecular mass of around 15-20 kDa on gel filtration columns, and can be separated into two molecular species with isoelectric points of 6.3 and 4.6 respectively. These two species were partially purified by gel filtration, chromatofocusing, high performance liquid chromatography on hydroxylapatite and anion exchange columns, and SDS-polyacrylamide gel electrophoresis. Both partially purified species showed a major band on gels at 16 kDa. When the band from the acidic factor was excised and eluted from gels it was found to retain some cartilage-degrading and thymocyte-activating properties. The biochemical and biological characteristics of the two factors is consistent with their being members of the interleukin-1 family of cytokines.

Interleukin-1 and tumor necrosis factor stimulate the formation of human osteoclastlike cells in vitro

Interleukin-1 (IL-1) alpha and beta and tumor necrosis factor (TNF) alpha and beta are potent stimulators of bone resorption in vitro and in vivo. However, the mechanisms underlying this increased bone resorption have not been clearly defined. Increased bone resorption can result from increased activity of individual osteoclasts, increased numbers of osteoclasts, or both. Therefore, we have used a long-term human marrow culture system that forms multinucleated cells (MNC) with the characteristics of osteoclasts to examine the effects of IL-1 and TNF on osteoclast formation. Human recombinant IL-1 alpha and IL-1 beta, and human recombinant TNF-alpha and TNF-beta stimulated MNC formation from 4- to 60-fold. IL-1 alpha, IL-1 beta, TNF-alpha, and TNF-beta significantly increased MNC formation at very low concentrations: 2.5 x 10(-13) M for IL-1 alpha and IL-1 beta, 10(-11) M for TNF-alpha, and 10(-10) M for TNF-beta In addition, these cytokines enhanced MNC formation in the presence of 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3], a potent osteotropic factor that stimulates MNC formation by stimulating fusion of mononuclear precursor cells. Simultaneous addition of IL-1 and TNF to the cultures resulted in a synergistic stimulation of MNC formation. These results suggest that: (1) IL-1 and TNF stimulate bone resorption in part by increasing osteoclast formation and (2) an extremely low concentration of these factors can synergistically increase osteoclast formation in the absence of other factors, such as 1,25-(OH)2D3. These data suggest that synergistic interactions among cytokines play an important role in maintaining bone cell activity in normal and pathologic states.

Synthetic parathyroid hormone-like protein-(1-74): biochemical and physiological characterization

PTH-like protein-(1-74) [PTHLP-(1-74)] was synthesized and purified. On the basis of chromatographic criteria and amino acid composition of the full-length peptide, direct amino acid sequencing of the N-terminus, and amino acid composition and internal sequence of proteolytic fragments of PTHLP-(1-74), the synthetic peptide appears to be of high quality and purity. Physiological comparison of PTHLP-(1-74) to [Tyr36]-PTHLP-(1-36) amide and bovine (b) PTH-(1-34) indicates that all three peptides are of equivalent potency in the fetal rat long bone and rat osteosarcoma 17/2.8 adenylate cyclase assays. However, as in earlier studies with native and N-terminal PTHLPs, PTHLP-(1-74) is considerably less potent (2%) in stimulating the canine renal cortical adenylate cyclase assay than is bPTH-(1-34). Further, PTHLP-(1-74) displayed only 12% of the activity of bPTH-(1-34) in inducing hypercalcemia when infused into rats in vivo. These studies support the possibility that subclasses of PTH receptors or varying PTH- and PTHLP-signalling transduction mechanisms may exist. In addition, they emphasize the need to precisely define the naturally occurring secretory and circulating species of this novel class of peptide hormones.

Effect of alterations in the cyclopentane ring on bone resorptive activity of prostaglandin

Previous studies have shown that the natural prostanoids, PGE2, PGE1 and PGF2 alpha are potent stimulators of bone resorption. In this study, we have examined the effects of alterations in the cyclopentane ring of these prostanoids for their effect on the resorptive response of cultured long bones from 19-day fetal rats as measured by the release of previously incorporated 45Ca. Indomethacin (10(-6)M) was added to minimize endogenous prostaglandin production. In this system PGE2 and PGE1, the 9 keto, 11 alpha hydroxy compounds, were approximately equally effective at concentrations of 10(-8) to 10(-6) M. The 9 alpha hydroxy, 11 alpha hydroxy compound, PGF2 alpha, was active at 10(-7) to 10(-5) M. In contrast, the 9 alpha hydroxy, 11-keto compound, PGD2, showed only a minimal stimulation of bone resorption at 10(-5) M. While these data suggested that the 11 alpha hydroxy group was important for bone resorbing activity, 11 beta PGE2 and 11-deoxy PGE1 were only slightly less potent than their physiologic counterparts. Both 9 beta, 11 alpha PGF2 and 9 alpha, 11 beta PGF2 were less potent than PGF2 alpha but did cause substantial stimulation of bone resorption and were equally effective at 10(-6) to 10(-5) M. 9 alpha, 11 beta PGF2 alpha is of particular interest since it is major metabolite of PGD2. These results suggest that the binding of prostanoids to the receptor which mediates bone resorption is affected by changes at the 9 and 11 positions of the pentane ring but do not support the hypothesis that the 11 alpha OH function is essential for this biological activity.

The tumor cells (FA-6) established from a pancreatic cancer associated with humoral hypercalcemia of malignancy: a simultaneous production of parathyroid hormone-like activity and transforming growth factor activity

Human pancreatic cancer cells (FA-6) producing bone resorbing factor were established in culture. A biopsied lymphnode from a patient with pancreatic cancer associated with humoral hypercalcemia of malignancy (HHM) was transplanted to nude mice, and the cells producing high parathyroid hormone (PTH)-like activity were selected by a limited dilution from outgrowth of the xenografts of the tumor grown in nude mice. The conditioned media contained an activity to stimulate the resorption of mouse calvaria in vitro which was indomethacin-insensitive. The conditioned media had both alpha-type and beta-type transforming growth factor (TGF) activity but no interleukin-1 activity. TGF-alpha activity was co-eluted with PTH-like activity from gel-chromatography at around 15 kDa. The FA-6 cells now established are the first cells of pancreatic cancer associated with HHM producing both PTH-like and TGF-alpha activities along with bone resorbing activity.

Cadmium stimulates prostaglandin E2 production and bone resorption in cultured fetal mouse calvaria

The effect of cadmium on bone resorption was studied using isolated fetal mouse calvaria. Cadmium stimulated bone resorption and PGE2 production in a dose-dependent manner. The minimal concentration of cadmium which stimulated bone resorption was the same as that stimulated prostaglandin E2 production. The stimulatory effects of cadmium (0.5 microM) on bone resorption and prostaglandin E2 production were completely inhibited by indomethacin. Exogenously added PGE2 (100ng/ml) abolished the inhibitory effect of indomethacin on bone resorption stimulated by cadmium. These results strongly indicate that cadmium stimulates bone resorption via prostaglandin E2 mediated mechanism.