Heparin augments osteoclast resorption-stimulating activity in serum

Fleas and lesions in armadillo osteoderms

Armadillos are bitten by several species of flea. Females of the genus Tunga penetrate the epidermis and when in place are fertilised by males, after which the abdomen swells enormously to form a 'neosome'. Within the penetrans group, T. perforans, makes lesions that perforate the osteoderms within the integument to form ~3 mm diameter cavities occupied by a discoid neosome. We examined these lesions in carapace material from animals which had died in the wild to see whether we could recruit evidence as to how they may be generated, either by the insect or by the host. We studied one species without such lesions, the nine-banded armadillo Dasypus novemcinctus, and two species with, the greater hairy armadillo Chaetophractus villosus and the southern three-banded armadillo Tolypeutes matacus, both showing the characteristic 'flea bite' holes in the external surfaces of the osteoderms. Samples were studied by three-dimensional backscattered electron mode scanning electron microscopy and X-ray microtomography. Both methods showed resorption pit complexes in the external surfaces of the osteoderms characteristic of those made by osteoclasts in active bone resorption. Lesions involved both the syndesmoses (sutures) between adjacent bones and the central regions of the osteoderms. Many lesions showed extensive repair by infilling with new bone. We conclude that the T. perforans neosome creates a local host response which causes bone resorption, creating the space in which it can grow.

New insights into the role of glycosaminoglycans in the endosteal bone microenvironment

The bone microenvironment is a complex tissue in which heterogeneous cell populations of hematopoietic and mesenchymal origin interact with environmental cues to maintain tissue integrity. Both cellular and matrix components are subject to physiologic challenges and can dynamically respond by modifying cell/matrix interactions. When either component is impaired, the physiologic balance is lost. Here, we review the current state of knowledge of how glycosaminoglycans - organic components of the bone extracellular matrix - influence the bone micromilieu. We point out how they interact with mediators of distinct signaling pathways such as the RANKL/OPG axis, BMP and WNT signaling, and affect the activity of bone remodeling cells within the endosteal niche summarizing their potential for therapeutic intervention.

Osteoblastic heparan sulfate regulates osteoprotegerin function and bone mass

Bone remodeling is a highly coordinated process involving bone formation and resorption, and imbalance of this process results in osteoporosis. It has long been recognized that long-term heparin therapy often causes osteoporosis, suggesting that heparan sulfate (HS), the physiological counterpart of heparin, is somehow involved in bone mass regulation. The role of endogenous HS in adult bone, however, remains unclear. To determine the role of HS in bone homeostasis, we conditionally ablated Ext1, which encodes an essential glycosyltransferase for HS biosynthesis, in osteoblasts. Resultant conditional mutant mice developed severe osteopenia. Surprisingly, this phenotype is not due to impairment in bone formation but to enhancement of bone resorption. We show that osteoprotegerin (OPG), which is known as a soluble decoy receptor for RANKL, needs to be associated with the osteoblast surface in order to efficiently inhibit RANKL/RANK signaling and that HS serves as a cell surface binding partner for OPG in this context. We also show that bone mineral density is reduced in patients with multiple hereditary exostoses, a genetic bone disorder caused by heterozygous mutations of Ext1, suggesting that the mechanism revealed in this study may be relevant to low bone mass conditions in humans.

Effects of unfractionated heparin on renal osteodystrophy and vascular calcification in chronic kidney disease rats

Unfractionated heparin (UFH) is the most widely used anticoagulant in hemodialysis for chronic kidney disease (CKD) patients. Many studies have verified that UFH can induce bone loss in subjects with normal bone, but few have focused on its effect on renal osteodystrophy. We therefore investigated this issue in adenine-induced CKD rats. As CKD also impairs mineral metabolism systemically, we also studied the impacts of UFH on serum markers of CKD-mineral and bone disorder (CKD-MBD) and vascular calcification. We administered low and high doses of UFH (1U/g and 2U/g body weight, respectively) to CKD rats and compared them with CKD controls. At sacrifice, the serum markers of CKD-MBD did not significantly differ among the two UFH CKD groups and the CKD control group. The mean bone mineral densities (BMDs) of the total femur and a region of interest (ROI) constituted of trabecular and cortical bone were lower in the high-dose UFH (H-UFH) CKD group than in the CKD control group (P<0.05 and P<0.01, respectively). The BMD of the femoral ROI constituted of cortical bone did not differ between the H-UFH CKD group and the CKD control group. Histomorphometrical changes in the CKD rats indicated secondary hyperparathyroidism, and the femoral trabecular bone volume, but not cortical bone volume, significantly decreased with increasing UFH dose. The same decreasing trend was found in osteoblast parameters, and an increasing trend was found in osteoclast parameters; however, most differences were not significant. Moreover, no distinct statistical differences were found in the comparison of vascular calcium or phosphorus content among the CKD control group and the two UFH CKD groups. Therefore, we concluded that UFH could induce bone loss in CKD rats with secondary hyperparathyroidism, mainly by reducing the trabecular volume and had little effect on cortical bone volume. The underlying mechanism might involve inhibition of osteoblast activity and promotion of osteoclast activity by UFH. We did not find any effect of UFH on vascular calcification in CKD rats with secondary hyperparathyroidism.

Heparin enhances osteoclastic bone resorption by inhibiting osteoprotegerin activity

Heparin is a highly sulfated glycosaminoglycan and has been shown to activate osteoclastic bone resorption though how is not yet clear. Here we investigate the molecule involved in heparin-induced activation of osteoclasts using an in vitro osteoclast culture assay. The formation and activation of osteoclasts are induced by receptor activator of NFkappaB ligand (RANKL) on osteoblasts, and inhibited by osteoprotegerin (OPG), a decoy receptor of RANKL, which is secreted from osteoblasts. In a coculture of mouse bone marrow cells and osteoblasts treated with 1,25-dihydroxyvitamin D(3) and prostaglandin E(2) on dentin slices, the bone marrow cells differentiate into osteoclasts, and resorption pits are formed on the dentin slices. Addition of heparin, various glycosaminoglycans, and chemically modified heparins to the coculture reveals that heparin enhances the pit-forming activity of osteoclasts, and this effect of heparin on the activation of osteoclasts is dependent on its sugar chain structure. By contrast, mRNA expression levels of RANKL, RANK, and OPG in the coculture are not altered by heparin treatment. Furthermore, neither RANK nor RANKL binds to heparin, suggesting that heparin does not directly interact with these proteins. Instead, heparin specifically binds to OPG and prevents OPG-mediated inhibition of osteoclastic bone resorption in the coculture. Heparin treatment does not enhance osteoclastic bone resorption in a monoculture of osteoclasts derived from bone marrow cells, and in the coculture using osteoblasts from OPG-deficient mice. A (125)I-OPG binding assay showed that OPG binds to osteoblasts and that this binding is inhibited by the addition of heparin, suggesting that OPG binds to RANKL on the osteoblast membrane and that heparin blocks this interaction. These results demonstrate that heparin enhances osteoclastic bone resorption by inhibiting OPG activity.

[Non-corticosteroid drug-induced metabolic bone disease]

After osteoporotic fracture or low bone mineral density measurements, it is necessary to look for secondary causes of osteoporosis, such as drugs. Corticosteroids are the most common cause of drug-induced metabolic bone disease. Other drugs responsible for bone disease include: aromatase inhibitors, GnRH agonists, anticonvulsants, heparin, and L thyroxin at TSH-suppressive doses. Confirmation is required of data about neuroleptics and antivitamin K.

Cbfa-1 (Runx-2) and osteocalcin expression by human osteoblasts in heparin osteoporosis in vitro

Heparin may cause adverse effects on bone formation following long-term application. The exact pathomechanism is unclear, but in vitro data suggest an impaired osteoblast function. The transcription axis of Cbfa-1 (Runx-2) and osteocalcin is crucial in maintaining an equilibrium of bone formation and resorption in vivo. We used a human osteoblast cell culture model to further investigate the effect of heparin (low-molecular-weight heparin, dalteparin) on the expression of these two regulators of osteoblast differentiation. At high doses, dalteparin caused a significant inhibition of both osteocalcin and Cbfa-1 expression in vitro. Our data support the hypothesis of a direct inhibition of osteoblast function underlying heparin osteoporosis.

Management of the anticoagulated patient

Excessive bleeding or thrombosis is a preeminent concern for all surgeons. Patients may be at risk because of medical therapy, underlying disease, or complications related to both. An understanding of the coagulation cascade--mechanisms and tests of function--permits a rational, if not always complete, basis for a plan of therapy. Newer anticoagulation medications are changing how thrombotic complications, such a VTE or graft occlusion, are treated or prevented. This entire area is undergoing rapid evolution, and the approaches that have been standard for decades soon will be supplanted. Ultimately, however, the most important assessment is made at the bedside by the clinician.

Vasculature deprivation--induced osteonecrosis of the rat femoral head as a model for therapeutic trials

Experimental Osteonecrosis

The authors' experience with experimentally produced femoral capital osteonecrosis in rats is reviewed: incising the periosteum at the base of the neck of the femur and cutting the ligamentum teres leads to coagulation necrosis of the epiphysis. The necrotic debris is substituted by fibrous tissue concomitantly with resorption of the dead soft and hard tissues by macrophages and osteoclasts, respectively. Progressively, the formerly necrotic epiphysis is repopulated by hematopoietic-fatty tissue, and replaced by architecturally abnormal and biomechanically weak bone. The femoral heads lose their smooth-surfaced hemispherical shape in the wake of the load transfer through the hip joint such that, together with regressive changes of the joint cartilage and inflammatory-hyperplastic changes of the articular membrane, an osteoarthritis-like disorder ensues.

Therapeutic Choices

Diverse therapeutic options are studied to satisfy the different opinions concerning the significance of diverse etiological and pathogenic mechanisms: 1. Exposure to hyperbaric oxygen. 2. Exposure to hyperbaric oxygen and non-weight bearing on the operated hip. 3. Medication with enoxaparin. 4. Reduction of intraosseous hypertension, putting to use a procedure aimed at core decompression, namely drilling a channel through the femoral head. 5. Medication with vascular endothelial growth factor with a view to accelerating revascularization. 6. Medication with zoledronic acid to decrease osteoclastic productivity such that the remodeling of the femoral head is slowed.

Glucocorticoid-related osteonecrosis appears to be apoptosis-related, thus differing from the vessel-deprivation-induced tissue coagulation found in idiopathic osteonecrosis. The quantities of TNF-α, RANK-ligand and osteoprotegerin are raised in glucocorticoid-treated osteoblasts so that the differentiation of osteoclasts is blocked. Moreover, the osteoblasts and osteocytes of the femoral cortex mostly undergo apoptosis after a lengthy period of glucocorticoid medication.

A study of unfractionated and low molecular weight heparins in a model of cholestatic liver injury in the rat

Forty-eight rats with biliary obstruction induced by double ligation and section of the common bile duct were randomly and blindly assigned to receive subcutaneous injection of either conventional heparin sodium (1000IU kg(-1)), three already marketed low molecular weight heparin (LMWH) preparations: nadroparin (1000 anti-Xa IU kg(-1)), tinzaparin (1000 anti-Xa IU kg(-1)), enoxaparin (180 anti-Xa IU kg(-1)) or saline. Drugs were administered once a day, starting 7 days after surgery and continued for 3 weeks. At the end of the treatment period, rats were killed and analyzed for blood biochemistry and liver pathology. Liver fibrosis was assessed by image analysis. Data indicated that treatment with nadroparin decreased plasma total bilirubin, serum alkaline phosphatase (ALP) and gamma glutamyltransferase (GGT) levels by 80.3, 70.7 and 42%, compared with bile duct ligated (BDL) control values. The reduction in plasma total protein observed in BDL controls was prevented by nadroparin. Enoxaparin-treated rats showed significant reduction in plasma total bilirubin and alanine aminotransferase levels by 32.5 and 38.4% versus BDL controls. Liver necrosis evaluated histologically was significantly reduced in the nadroparin- and enoxaparin-treated rats. Morphometric analysis showed significant reduction in fibrosis on nadroparin and enoxaparin treatment: area of fibrosis: 1.66 +/- 0.17% and 14.03 +/- 1.1% versus 18.94 +/- 2.4% (P<0.05); nadroparin and enoxaparin versus BDL control. By contrast, neither conventional heparin nor tinzaparin prevented the bile duct ligation-induced liver damage as indicated by increased plasma aminotransferases, ALP and GGT concentrations and the histological evidence of necrosis. Total serum bilirubin was increased by 27.5% in rats treated with conventional heparin, while ALP and GGT levels were 38.6 and 31.4% higher after tinzaparin treatment versus BDL controls. Significant increase in the area of fibrosis was observed after tinzaparin treatment compared to BDL control group. Results suggest a beneficial effect for nadroparin and enoxaparin in the therapy of patients with obstructive jaundice or cholestatic liver disorders. The present data from bile duct ligated rats suggest an antifibrotic effect for nadroparin and enoxaparin.

Characterization of sugar binding by osteoclast inhibitory lectin

Osteoclast inhibitory lectin (OCIL) is a membrane-bound C-type lectin that blocks osteoclast differentiation and, via binding to its cognate receptor NKRP1D, inhibits natural killer cell-mediated cytotoxicity. OCIL is a member of the natural killer cell receptor C-type lectin group that includes CD69 and NKRP1D. We investigated carbohydrate binding of soluble recombinant human and mouse OCIL in enzyme-linked immunosorbent assay-based assays. OCIL bound immobilized high molecular weight sulfated glycosaminoglycans, including fucoidan, lambda-carrageenan, and dextran sulfate, but not unsulfated dextran or sialated hyaluronic acid. Carbohydrate binding was Ca(2+)-independent. Binding of immobilized low molecular weight glycosaminoglycans, including chondroitin sulfate (A, B, and C forms) and heparin, was not observed. However, the soluble forms of these low molecular weight glycosaminoglycans competed for OCIL binding of immobilized fucoidan (as did soluble fucoidan, dextran sulfate, and lambda-carrageenan), indicating that OCIL does recognize these carbohydrates. Inhibition constants for chondroitin sulfate A and heparin binding were 380 and 5 nm, respectively. Immobilized and soluble monosaccharides did not bind OCIL. The presence of saturating levels of fucoidan, dextran sulfate, and lambda-carrageenan did not affect OCIL inhibition of osteoclast formation. The fucoidan-binding lectins Ulex europaeus agglutinin I and Anguilla anguilla agglutinin did not block osteoclast formation or affect the inhibitory action of OCIL. Although the osteoclast inhibitory action of OCIL is independent of sugar recognition, we have found that OCIL, a lectin widely distributed, but notably localized in bone, skin, and other connective tissues, binds a range of physiologically important glycosaminoglycans, and this property may modulate OCIL actions upon other cells.

A potential role for the mast cell in the pathogenesis of idiopathic osteoporosis in men

Osteoporosis is increasingly being recognized in men. Secondary causes are often implicated, but the mechanism of bone loss remains unclear in about a third of patients. The mast cell is a complex cell that stores a number of factors known to affect bone metabolism. Patients with systemic mastocytosis often demonstrate osteoporosis and bone marrow mast cells may be increased in osteoporotic postmenopausal women. We address the possible role of the mast cell in the pathophysiology of male osteoporosis by studying the relationship between bone marrow infiltration with mast cells and the 24 h urine excretion of N-methylhistamine, and the severity of osteoporosis in 48 consecutive men with idiopathic osteoporosis (bone mineral density Z score of <-1 and/or at least one prevalent vertebral fracture). Secondary causes for osteoporosis were excluded and none of the patients had systemic manifestations of enhanced mast cell activity. A widely variable number of morphologically normal mast cells were counted in toluidine blue-stained sections from 42 of 46 evaluable bone marrow biopsies. In 4 of the 42 biopsies (9%), clusters of abnormal mast cells were identified. These four patients were the only ones who also demonstrated increased 24 h urine excretion of N-methylhistamine. There was a significant positive relationship between mast cell number and the 24 h urine excretion of N-methylhistamine reflecting mast cell activity (p = 0.0001), and this latter measurement correlated negatively with bone mineral density (BMD) at the lumbar spine (p < 0.001). We identified clinically important bone marrow cell infiltration with pathologic mast cells in the absence of systemic manifestations of mast cell hyperactivity as an additional secondary cause for osteoporosis in some 9% of men with idiopathic osteoporosis, and found urinary excretion of N-methylhistamine to be above the upper limit of the normal laboratory reference range diagnostic for this cause of secondary osteoporosis. The more continuous spectrum in the relationship between mast cell activity and BMD supports a potential role for this cell in the pathogenesis of idiopathic male osteoporosis.

The effects of enoxaparin on the reparative processes in experimental osteonecrosis of the femoral head of the rat

The blood supply of one femoral head of 6-month-old rats was severed by incising the periosteum of the neck and cutting the ligamentum teres. The rats were killed on the 30th postoperative day and the femoral bones were obtained for semiquantification of the reparative processes in the necrotic heads. Fourteen rats were treated with enoxaparin and 14 untreated animals served as controls. Statistically, the amounts of necrotic bone in the epiphysis were less, the extent of remodeling of the femoral heads was milder, and the articular cartilage degeneration was slighter in the enoxaparin-treated than untreated rats. There was no significant difference in the quantities of newly formed bone in femoral heads of treated and untreated rats. These findings are in agreement with the known effects of unfractionated and low-molecular-weight heparins which enhance osteoclastic bone resorption and angiogenesis and decrease osteoblastic bone formation. The former activities, operative in minimizing the structural distortion of the femoral head, oppose the crucial event in the pathogenesis of post-osteonecrotic osteoarthritis.

The uptake of lipoprotein-borne phylloquinone (vitamin K1) by osteoblasts and osteoblast-like cells: role of heparan sulfate proteoglycans and apolipoprotein E

Vitamin K is essential for the gamma-carboxylation of Gla-containing bone proteins such as osteocalcin and a suboptimal vitamin K status has been linked to osteoporosis but nothing is known of how the lipoprotein-borne vitamin accesses the bone matrix. We have studied the mechanism of transport of lipoproteins labeled with [3H]-phylloquinone (vitamin K1 [K1]) into osteoblasts using both tumor-derived cell lines and normal osteoblast-rich cell populations. We also investigated the effect of heparin in this model since long-term heparin treatment causes osteopenia and the anticoagulant is known to impair normal lipoprotein metabolism. Heparinase treatment, which removes heparan sulfate proteoglycans (HSPG), reduced uptake of [3H]-K1 from triglyceride-rich lipoproteins (TRL) and low-density lipoproteins (LDL). The effect of heparin in this model was complex depending on cell type, concentration, and time but, overall, the results were consistent with an inhibition of vitamin K uptake by osteoblasts. Anti-apolipoprotein E (apoE) antiserum reduced uptake of TRL-[3H]-K1 by 55 +/- 4% and LDL-[3H]-K1 uptake by 35 +/- 2%. Exogenous apoE4 increased uptake of TRL-[3H]-K1 by 90 +/- 1% compared with 53 +/- 11% for apoE3 and 52 +/- 5% for apoE2. Our findings show that HSPG on the cell surface and apoE in the lipoprotein particles contribute to lipoprotein-K1 uptake by osteoblasts as is known for lipoprotein uptake by hepatocytes. This mechanism is significant in view of the epidemiological association of both undercarboxylation of osteocalcin and the presence of an apo epsilon4 allele with increased fracture risk and reduced bone mineral density (BMD). The inhibition by heparin of lipoprotein-mediated carriage of vitamin K and possibly other lipids to bone may provide a basis for the future understanding of heparin-induced osteoporosis.

Time-course of mast cell accumulation in rat bone marrow after ovariectomy

We previously reported that mast cells accumulate in the tibia bone marrow of ovariectomized (OVX) rats. In this study, the timing of mast cell accumulation and osteoclast generation were compared to determine whether or not mast cell accumulation preceded osteoclast recruitment after ovariectomy. This may be significant because of the number of cytokines released by mast cells that are potentially active on resorption. Sprague-Dawley rats (120) aged 12 weeks were OVX or sham-operated, and killed on days 4, 7, 14, 28, and 56 postsurgery. Ten additional intact rats were used as baseline controls. Ovariectomy was confirmed by a sharp and sustained fall in serum estradiol. The loss in trabecular bone volume (BV/TV) began on day 7, reaching 80% on day 56 (P < 0.001 vs baseline controls). The number of osteoclasts (N.OC/TBPm) increased in the OVX rats between days 4 and 7 (+130%; P < 0.001), and continued rising to day 28. During the next month, it decreased greatly (-63%, P < 0.001 on day 56 vs day 28). In the sham-treated rats, few mast cells were scattered in the bone marrow (1.9 cells/mm2 in the baseline controls). Their number fluctuated during the experimental period, but at each time-point it was lower than in the OVX rats. They were predominantly (90%) of the mucosal subtype. In the OVX rats, their number doubled between days 4 and 14 (P < 0.001), reached 8.6 cells/mm2 on day 28 (a 5.4-fold increase compared with day 4 OVX rats), and plateaued for the next 4 weeks. OVX had no effects on mast cell subtypes. In conclusion, mast cell accumulation and osteoclast differentiation are precocious and concomitant; this does not support a direct role for mast cells in osteoclast recruitment. Rather, the two cell populations may derive from a common precursor or be targeted simultaneously by estrogen depletion through common stimulator(s). Mast cell hyperplasia appears to be a significant, and usually unknown, manifestation of ovariectomy in the bone marrow environment.

Bone density changes in pregnant women treated with heparin: a prospective, longitudinal study

Heparin plus aspirin significantly improves the live birth rate of women with primary antiphospholipid syndrome. Osteopenia is a major concern of long-term heparin therapy. We studied prospectively the bone mineral density (BMD) changes during pregnancy and the puerperium in 123 women with primary antiphospholipid syndrome treated with low-dose aspirin and subcutaneous low-dose heparin (46 women took unfractionated heparin and 77 took low-molecular-weight heparin). Lumbar spine, neck of femur and forearm BMD were measured, using dual energy X-ray absorptiometry, at 12 weeks gestation, immediately postpartum and 12 weeks postpartum. The mean heparin duration was 27 weeks (range 22-29). During pregnancy, BMD decreased by 3.7% (P < 0.001) at the lumbar spine and by 0.9% (P < 0.05) at the neck of femur with no significant change at the forearm. Lactation was associated with a significant decrease in the lumbar spine and neck of femur BMD. There was no significant difference in BMD changes between the two heparin preparations. No woman suffered a symptomatic fracture. Long-term heparin treatment during pregnancy is associated with a small but significant decrease in BMD at the lumbar spine and neck of femur. This decrease is similar to that previously reported to occur in untreated pregnancies.

Syndecan-1 (CD 138) in myeloma and lymphoid malignancies: a multifunctional regulator of cell behavior within the tumor microenvironment

Syndecan-1 is a transmembrane proteoglycan expressed on the surface of tumor cells of various origins including myeloma, Hodgkin's disease, and certain human immunodeficiency virus (HIV) associated lymphomas. Functional studies in myeloma reveal that syndecan-1 may act as a multifunctional regulator of cell behavior in the tumor microenvironment; it mediates cell-cell adhesion, binding of myeloma cells to type I collagen, and inhibits tumor cell invasion into collagen gels. In addition, syndecan-1 is released from the surface of myeloma cells and this shed form of the molecule inhibits growth and induces apoptosis of myeloma cells and may modulate myeloma bone disease by inhibiting osteoclast formation and promoting osteoblast formation. In view of its effects on tumor cell growth, survival, adhesion and invasion and on bone cell differentiation, syndecan-1 may be an important potentially beneficial regulator of myeloma pathobiology. Further studies are needed to define the clinical significance of syndecan-1 in myeloma and to examine its functional significance in other lymphoid malignancies.

Hepatocyte growth factor in serum after injection of unfractionated and low molecular weight heparin in healthy individuals

Soluble heparin displaces the cytokine hepatocyte growth factor (HGF) from heparan sulphate proteoglycans on the cell surface and in the extracellular matrix into the circulation. We examined serum HGF elevation after heparin injections, and whether there is a difference between unfractionated heparin (UH) and low molecular weight heparin (LMWH) in their ability to increase serum HGF. 20 healthy individuals were randomized to a single injection of intravenous or subcutaneous UH or LMWH. There was a significant increase in HGF from pretreatment values. This HGF was bioactive. When these preparations were compared on the basis of their serum concentrations (anti-factor Xa activity or molar concentrations), the increase in HGF was greater in individuals receiving UH than LMWH. When UH or LMWH were administered over a 5 d period, the increase in HGF, as well as the difference between treatments to induce HGF, remained stable throughout the treatment. In five patients treated with continuous intravenous heparin infusion HGF was increased throughout the treatment period of 5-7 d. In summary, the rise in bioactive HGF after heparin treatment was stable during continued treatment. UH was more potent in inducing HGF increase than LMWH, both after a single injection and after several days of treatment.

Conjunctive effects of fibroblast growth factor and glycosaminoglycan on bone metabolism in neonatal bartter syndrome

The calciotropic activity of urine from a subject with neonatal Bartter syndrome (NBS) has been partially purified using ion-exchange and gel chromatographic techniques. A bioassay using bone disks from rat calvaria was used to estimate calciotropic activity, which in the urine of the subject with NBS appears to be due to basic fibroblast growth factor (bFGF) bound to a glycosaminoglycan susceptible to heparitinase digestion. The calciotropic activity is eluted from DEAE-Sephacel and Sepharose CL-6B in a narrow band in association with metachromatic material and is destroyed by heparitinase and blocked by an antibody to bFGF. After treatment of purified preparations with heparitinase, a component that is inactive alone but develops calciotropic activity in association with heparin can be isolated by affinity chromatography on heparin-Sepharose columns. This component is recovered from the column at NaCl concentrations expected to elute bFGF and is inactivated by antibodies to bFGF. No calciotropic activity can be shown in glycosaminoglycan-containing fractions from urine from a normal boy or a normal man, but such fractions exhibit calciotropic activity if bFGF is added to the assay system. When bFGF is added to urine from either normal subject followed by ion-exchange chromatography on DEAE-Sephacel, calciotropic activity is eluted at NaCl concentrations closely similar to those found to elute calciotropic activity from the urine of the NBS subject. It appears that the abnormal findings in NBS urine are due to excess bFGF, although they could be due to some abnormality of the glycosaminoglycan component.

Role of hepatocyte growth factor and its receptor c-met in multiple myeloma

Multiple myeloma is characterised by the clonal expansion of malignant plasma cells. Recently, we reported that a new cytokine, hepatocyte growth factor (HGF), and its receptor c-met are related to this disease. Here we review the observations that associate HGF with myeloma. Malignant plasma cells produce HGF and express the receptor c-met. Many patients have elevated HGF levels, which is unfavourable both in terms of survival and response to treatment. Possible biological roles of HGF in this disease are discussed, with special focus on bone homeostasis and its binding to heparan sulphate proteoglycans.

Secondary osteoporosis

Generalized osteoporosis currently represents a heterogeneous group of conditions with many different causes and pathogenetic mechanisms, that often are variably associated. The term "secondary" is applied to all patients with osteoporosis in whom the identifiable causal factors are other than menopause and aging. In this heterogeneous group of conditions, produced by many different pathogenetic mechanisms, a negative bone balance may be variably associated with low, normal or increased bone remodeling states. A consistent group of secondary osteoporosis is related to endocrinological or iatrogenic causes. Exogenous hypercortisolism may be considered an important risk factor for secondary osteoporosis in the community, and probably glucocorticoid-induced osteoporosis is the most common type of secondary osteoporosis. Supraphysiological doses of corticosteroids cause two abnormalities in bone metabolism: a relative increase in bone resorption, and a relative reduction in bone formation. Bone loss, mostly of trabecular bone, with its resultant fractures is the most incapacitating consequence of osteoporosis. The estimated incidence of fractures in patients prescribed corticosteroid is 30% to 50%. Osteoporosis is considered one of the potentially serious side effects of heparin therapy. The occurrence of heparin-induced osteoporosis appeared to be strictly related to the length of treatment (over 4-5 months), and the dosage (15,000 U or more daily), but the pathogenesis is poorly understood. It has been suggested that heparin could cause an increase in bone resorption by increasing the number of differentiated osteoclasts, and by enhancing the activity of individual osteoclasts. Hyperthyroidism is frequently associated with loss of trabecular and cortical bone; the enhanced bone turnover that develops in thyrotoxicosis is characterized by an increase in the number of osteoclasts and resorption sites, and an increase in the ratio of resorptive to formative bone surfaces, with the net result of bone loss. Despite these findings, the occurrence of pathological fractures in patients with hyperthyroidism is relatively low, and probably due to the fact that deficiencies in bone mass may be reversed by treatment of the thyroid disease. Most, but not all, studies on insulin-dependent diabetes mellitus (IDDM) report an association with osteopenia. In IDDM, the extent of bone loss is usually slight, which helps explain the discrepancy between the frequency of decreased bone mineral density, and the frequency of osteoporotic fractures in long-standing diabetes. Contradictory results have been obtained in non-insulin-dependent diabetes mellitus (NIDDM) patients. Increased rates of bone loss at the radius and lumbar spine were demonstrated either in patients with two-thirds gastric resection and Billroth II reconstruction, or in those with one-third resection and Billroth I anastomosis, and the metabolic bone disease following gastrectomy may consist also of osteomalacia or mixed pattern of osteoporosis-osteomalacia, with secondary hyperparathyroidism. Miscellaneous causes of secondary osteoporosis are also immobilization, pregnancy and lactation, and alcohol abuse.

H1 and H2 histamine receptors modulate osteoclastic resorption by different pathways: evidence obtained by using receptor antagonists in a rat synchronized resorption model

We have previously postulated that mast cells (MC) may act as accessory cells in bone resorption. In this study we obtained evidence that histamine, the most abundant mediator released upon MC degranulation, is one of many factors modulating resorption. As the effect of histamine is mediated through different receptors, we tested the effects of mepyramine (1.5 mg/kg/day) and cimetidine (125 mg/kg/day), that antagonize H1 and H2 receptors, respectively. These effects were assessed morphometrically in a well-defined rat model of synchronized resorption at different stages of the process. On day 4 after induction (i.e., at the peak of resorption in this model), both agents reduced resorption significantly. Mepyramine acted by disturbing osteoclast activation and by reducing osteoclast activity (P < 0.01), while cimetidine principally reduced the size of the osteoclast population (P < 0.01). On day 6 (stage of declining resorption), the same resorption score as on day 4 was maintained in the mepyramine group, mainly through a marked increase in osteoclast activity (P < 0.01). In contrast, cimetidine continued to strongly reduce resorption (P < 0.01) and led to a further drop in the osteoclast population (P < 0.01). One day after induction, nonspecific esterase (NSE)-positive cells (putative osteoclast precursors) were significantly less numerous after treatment with the two agents. Significant changes in the MC population in the vicinity of the zone undergoing resorption occurred on days 4 and 6. The periosteal microvasculature adjacent to the reference bone zone was also markedly modified, especially in the cimetidine group. These results show that histamine intervenes in resorption through both H1 and H2 receptors. However, the mechanisms triggered by these receptors were quite different: H2 receptors appeared to be more strategic, as no replenishment of the osteoclast population occurred after the initial depletion in precursors. Histamine also appears to influence other neighbouring compartments, in which disturbances are probably linked to defective resorption. These findings support our hypothesis by which MC are accessory cells of resorption in this model.

Hazards of heparin: allergy, heparin-induced thrombocytopenia and osteoporosis

Heparin is the commonest mode of thromboprophylaxis used in pregnancy. It does not cross the placenta but has potential adverse effects on the mother, of which the most important is heparin-induced osteoporosis. The hazards of heparin, including bleeding, skin reactions, heparin-induced thrombocytopenia and osteoporosis are discussed and the relevant literature reviewed. Low-molecular-weight heparins have certain advantages over standard unfractionated heparins, especially in obstetrics. Their longer half-life and increased bioavailability enable once-daily injections, making them more convenient and acceptable. They are as effective as standard heparin but have a theoretically more favourable side-effect profile, providing less anticoagulant relative to antithrombotic activity. Current evidence suggests a lower incidence of heparin-induced thrombocytopenia. A reduced risk of osteoporosis is suggested but not yet proven. Although thrombo-embolism is currently the leading cause of maternal mortality in the UK, antenatal heparin prophylaxis is not given to all women with previous thrombo-embolism because of continued fears concerning heparin-induced osteoporosis. A protocol is presented with guidelines for different levels of obstetric prophylaxis depending on the perceived level of risk.

Osteoporosis and vertebral collapse following low-dose, low molecular weight heparin therapy in a young patient

Osteoporosis is a well-recognized complication of long-term heparin (unfractionated) therapy. It has been suggested that the low molecular weight heparins (LMWH) have a lower potential to cause osteopenia than the unfractionated preparations. We report a case of a 29-year-old woman who developed osteoporosis and pathological fracture of lumbar vertebrae following treatment with low dose LMWH (dalteparin) for 3 months. The aim of this report is to alert clinicians to the potential risk of this complication with the prolonged use of LMWH preparations--an increasingly popular choice for long-term anticoagulation.

Effects of short-term, high dose, heparin therapy on biochemical markers of bone metabolism

To evaluate the effects of the short-term, high-dose sodium heparin therapy on biochemical markers of bone metabolism, we studied 20 patients (11 males and 9 females) with pulmonary embolism, treated with sodium heparin (daily dose range: 40,000-45,000 I.U. by continuous i.v. infusion). Heparin therapy lasted 5-7 days, after which patients received warfarin over 12 months. Eleven patients (6 males and 5 females) with ischaemic stroke, treated with i.v. glycerol and pentoxifilline, were used as controls. Before and after therapy serum and urinary markers of bone metabolism were evaluated; in 12 heparin-treated pts., the parameters were also evaluated 4 months after discontinuation of warfarin therapy. After heparin therapy a significant reduction vs. basal value was observed in levels of serum osteocalcin (ng/ml;mean + SEM): 3.32 & 0.19 vs. 2.05 + 0.21; p < 0.001. In the 12 patients evaluated 4 months after discontinuation of warfarin therapy, serum osteocalcin levels returned to basal value: 3.41 + 0.12 ng/ml (p:n.s.). No significant changes of the examined parameters were observed in controls. In conclusion, our data seem to indicate an effect of i.v. short-term heparin therapy on bone metabolism. This effect seems to be characterized by an inhibition of osteoblast function as suggested by the reduction of serum osteocalcin levels.

Effect of tetracyclines which have metalloproteinase inhibitory capacity on basal and heparin-stimulated bone resorption by chick osteoclasts

Several tetracyclines (TETs) are potent inhibitors of collagenase (CGase) and can inhibit connective tissue degradation in a variety of inflammatory and degenerative disorders. The role of CGase in bone resorption by osteoclasts (OC) remains unclear. Disaggregated OCs from chick embryos were cultured for 24 h on devitalized bovine cortical bone +/- heparin in the presence of various TETs. Doxycycline (Dox) inhibited pit formation in a dose-dependent manner. CMT, a TET derivative which inhibits matrix metalloproteinases (MMPs) but is not antimicrobial, also inhibited chick OC bone resorption. Heparin markedly stimulated bone resorption at 5 micrograms/ml, which was reversed by Dox, 5 micrograms/ml. TETs can reversibly inhibit both basal and heparin-stimulated bone resorption by chick OCs. These findings suggest that MMPs may play a role in osteoclastic bone resorption, and that safe and effective inhibitors of MMPs, including certain TETs, might have a potential therapeutic role.

Effects of heparin on osteoclast activity

The effect of heparin on osteoclastic bone resorption was studied in vitro using the disaggregated osteoclast resorption assay. Bone resorption was assessed by counting the resorption lacunae on bone slices by light microscopy. Low concentrations of heparin (5 micrograms/ml) increased bone resorption by isolated chick and rat osteoclasts. Among other glycosaminoglycans tested at 5 micrograms/ml, only dextran sulfate showed a small but significant stimulation of resorption. Chondroitin sulfates A, B, and C were without effect at 25 and 100 micrograms/ml, whereas resorption was increased by 100 micrograms/ml of heparan sulfate. With chick osteoclasts, which could be maintained in serum-free conditions, a stimulatory effect of heparin was found both in the presence of 5% fetal calf serum and in serum-free media containing insulin, transferrin, and selenium. The magnitude of the heparin-induced increase in resorption was similar in the presence or absence of serum. The stimulation of resorption was associated with an increase in the number of osteoclasts on bone slices. Pretreatment of the bone slices with heparin also enhanced resorption. In time course experiments, 5 micrograms/ml of heparin caused a doubling of chick osteoclast activity index (number of resorption pits per number of osteoclasts) at 12 and 24 h. In 24 h cultures, treatment with 10 micrograms/ml of the arginine-rich basic protein, protamine, 1 microgram/ml of the immunosuppressant, cyclosporine A, or 5 micrograms/ml of the cysteine-proteinase inhibitor, leupeptin, negated the heparin effect on bone resorption. Leupeptin also inhibited basal resorption.(ABSTRACT TRUNCATED AT 250 WORDS)