Effect of low molecular weight heparin (dalteparin) and fondaparinux (Arixtra) on human osteoblasts in vitro

Low molecular weight heparin impairs tendon repair

Thrombin has many biological properties similar to those of growth factors. In a previous study, we showed that thrombin improves healing of the rat tendo Achillis. Low molecular weight heparin (LMWH) inhibits the activity and the generation of thrombin. We therefore considered that LMWH at a thromboprophylactic dose might inhibit tendon repair.

Transection of the tendo Achillis was carried out in 86 rats and the healing tested mechanically. Low molecular weight heparin (dalateparin) was either injected a few minutes before the operation and then given continuously with an osmotic mini pump for seven days, or given as one injection before the operation. In another experiment ,we gave LMWH or a placebo by injection twice daily. The anti-factor Xa activity was analysed.

Continuous treatment with LMWH impaired tendon healing. After seven days, this treatment caused a 33% reduction in force at failure, a 20% reduction in stiffness and a 67% reduction in energy uptake. However, if injected twice daily, LMWH had no effect on tendon healing. Anti-factor Xa activity was increased by LMWH treatment, but was normal between intermittent injections.

Low molecular weight heparin delays tendon repair if given continuously, but not if injected intermittently, probably because the anti-factor Xa activity between injections returns to normal, allowing sufficient thrombin stimulation for repair. These findings indicate the need for caution in the assessment of long-acting thrombin and factor Xa inhibitors.

The effects of heparin and low molecular weight heparins on bone

Recent clinical trials have shown that the risk of developing osteoporosis is substantially lower when low molecular weight heparins (LMWHs) are used in place of unfractionated heparin. While the reason(s) for this difference has not been fully elucidated, studies with animals have suggested that heparin causes bone loss by both decreasing bone formation and increasing bone resorption. In contrast, LMWHs appear to cause less bone loss because they only decrease bone formation. Whether all LMWHs decrease bone formation and therefore cause bone loss is unknown. For example, preliminary in vitro studies with the synthetic pentasaccaride, Fondaparinux, have suggested that it may not decrease bone formation and thus, may have no deleterious effects on bone. Further studies are required in order to determine if all LMWHs cause bone loss equally.

How we diagnose and treat thrombotic manifestations of the antiphospholipid syndrome: a case-based review

Antiphospholipid antibodies including anticardiolipin antibodies, lupus anticoagulants, and anti–β2 glycoprotein-1–specific antibodies may identify patients at elevated risk of first or recurrent venous or arterial thromboembolism. Traditionally, published case series supplemented by anecdotal experience have formed the basis of management of patients with these autoantibodies. Over the past several years, studies have described the management of patients with key clinical manifestations of antiphospholipid antibodies, including patients with antiphospholipid antibody syndrome. As a result, evidence-based treatment recommendations are possible for selected patients with, or at risk of, thrombosis in the setting of antiphospholipid antibodies. Unfortunately, most patients encountered in clinical practice do not correspond directly with those enrolled in clinical trials. For such patients, treatment recommendations are based on experience, extrapolation, and less rigorous evidence. This article proposes 5 cases typical of those found in clinical practice and provides recommendations for therapy focused on a series of clinical questions. Whenever possible, the recommendations are based on evidence; however, in many cases, insufficient evidence exists, so the recommendation is experiential.

Bone health in patients with brain tumors

BACKGROUND

Several factors, including the use of antiepileptic drugs, glucocorticoids, anticoagulants, chemotherapy, radiation therapy, and hemiplegia-associated osteopenia, render patients with brain tumor susceptible to bone disease.

METHODS

The authors review the pathophysiology of these factors and their impact upon bone integrity.

RESULTS

Steps that can be taken to minimize or eliminate bone morbidity including measurement of bone mineral density at treatment onset, adequate calcium intake, vitamins D and K supplementation, adequate sunlight exposure, weight-bearing exercises, fall prevention, avoidance of antiepileptic drugs linked to osteopenia, and judicious use and choice of glucocorticoids and anticoagulants are suggested.

CONCLUSIONS

Medical management of osteoporosis related to brain tumor treatment with bisphosphonates, teriparitide, and calcitonin is beneficial, as is kyphoplasty for symptomatic vertebral compression fractures.

New anticoagulants for venous thromboembolic disease

PURPOSE OF REVIEW

In this paper, recent advances in new anticoagulants with the potential to be used for prevention or treatment of venous thrombosis are reviewed.

RECENT FINDINGS

Numerous novel anticoagulants targeting specific stages of the coagulant pathway are in various stages of development. Fondaparinux, an indirect activated factor VII inhibitor, has been shown to be effective for initial treatment and prevention of venous thromboembolism, but still requires parenteral administration. Ximelagatran, an oral direct thrombin inhibitor, has also been shown to effective for treatment and prevention of venous thrombosis. Both agents are associated with bleeding, however, and ximelagatran is associated with hepatic toxicity with long-term use. Direct activated factor X inhibitors, orally available forms of heparin, and other direct thrombin inhibitors remain in early stages of development. Further data on the clinical utility of these agents are likely to emerge in the next few years, and uptake of their use will be affected by the cost considerations.

SUMMARY

Numerous alternative anticoagulants are in varying stages of development. Clinical data have yet to show that these agents have a clearly superior risk-benefit ratio compared with currently used antithrombotics. Many drugs remain in initial stages of development. The ideal anticoagulant agent is being sought but has yet to be discovered.

Alterations of metabolic activity in human osteoarthritic osteoblasts by lipid peroxidation end product 4-hydroxynonenal

4-Hydroxynonenal (HNE), a lipid peroxidation end product, is produced abundantly in osteoarthritic (OA) articular tissues, but its role in bone metabolism is ill-defined. In this study, we tested the hypothesis that alterations in OA osteoblast metabolism are attributed, in part, to increased levels of HNE. Our data showed that HNE/protein adduct levels were higher in OA osteoblasts compared to normal and when OA osteoblasts were treated with H₂O₂. Investigating osteoblast markers, we found that HNE increased osteocalcin and type I collagen synthesis but inhibited alkaline phosphatase activity. We next examined the effects of HNE on the signaling pathways controlling cyclooxygenase-2 (COX-2) and interleukin-6 (IL-6) expression in view of their putative role in OA pathophysiology. HNE dose-dependently decreased basal and tumour necrosis factor-α (TNF-α)-induced IL-6 expression while inducing COX-2 expression and prostaglandin E₂ (PGE₂) release. In a similar pattern, HNE induces changes in osteoblast markers as well as PGE₂ and IL-6 release in normal osteoblasts. Upon examination of signaling pathways involved in PGE₂ and IL-6 production, we found that HNE-induced PGE₂ release was abrogated by SB202190, a p38 mitogen-activated protein kinase (MAPK) inhibitor. Overexpression of p38 MAPK enhanced HNE-induced PGE₂ release. In this connection, HNE markedly increased the phosphorylation of p38 MAPK, JNK2, and transcription factors (CREB-1, ATF-2) with a concomitant increase in the DNA-binding activity of CRE/ATF. Transfection experiments with a human COX-2 promoter construct revealed that the CRE element (-58/-53 bp) was essential for HNE-induced COX-2 promoter activity. However, HNE inhibited the phosphorylation of IκBα and subsequently the DNA-binding activity of nuclear factor-κB. Overexpression of IKKα increased TNF-α-induced IL-6 production. This induction was inhibited when TNF-α was combined with HNE. These findings suggest that HNE may exert multiple effects on human OA osteoblasts by selective activation of signal transduction pathways and alteration of osteoblastic phenotype expression and pro-inflammatory mediator production.

Monitoring the effects and managing the side effects of anticoagulation during pregnancy

LMWHs are the major anticoagulant/antithrombotic treatment given to pregnant women to prevent and treat venous thromboembolism despite the absence of specific clinical trials. An emerging indication, the prevention of adverse pregnancy outcomes, is under investigation. During pregnancy, LMWHs seem to be safe and efficient. Some uncertainties remain about the management of rare potential side effects, particularly in the event of heparin intolerance and with cross-reactivity to danaparoid sodium.

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.

A comparative analysis of phenotype expression in human osteoblasts from heterotopic ossification and normal bone

BACKGROUND AND AIMS

Heterotopic ossification (HO) is a pathological bone formation process in which ectopic bone is formed in soft tissue. The formation of bone depends on the expression of the osteoblast phenotype. Earlier studies have shown conflicting results on the expression of phenotype markers of cells originating from HO and normal bone. The hypothesis of the present study is that cells from HO show an altered expression of osteoblast-specific phenotype markers compared to normal osteoblasts. The aims of the study were to further characterize the expression of osteoblast phenotypemarkers and to provide a comparison with other study results.

PATIENTS AND METHODS

Using an in vitro technique, reverse transcription polymerase chain reaction (RT-PCR), real-time PCR and immunohistochemistry, we compared the phenotype gene expression (type I collagen, alkaline phosphatase, Cbfa-1, osteocalcin) of osteoblasts from resected HO and normal bone (iliac crest).

RESULTS

Cells from HO expressed the osteoblast phenotype (type I collagen, alkaline phosphatase) but were characterized by a depleted osteocalcin expression. The expression of Cbfa-1 (osteocalcin transcription gene) showed a large variety in our study. Preoperative radiotherapy had no effect on phenotype expression in cells from HO.

CONCLUSION

Our results provide a characterization of cells originating from HO and support the thesis of an impaired osteoblast differentiation underlying the formation of HO. The transcription axis from Cbfa-1 to osteocalcin could be involved in the pathogenesis of HO.

Clinical efficacy and safety of fondaparinux in the prevention and treatment of venous and arterial thrombosis

Fondaparinux (Arixtra®) is a synthetic, selective Factor Xa inhibitor. Its pharmacokinetic profile allows once-daily subcutaneous administration of the drug without any laboratory monitoring. The benefit-to-risk ratio of fondaparinux in the prevention of venous thromboembolism has been extensively studied in both surgical and acutely ill medical patients at risk of thrombosis. Its efficacy and safety have also been investigated in the initial treatment of symptomatic deep-vein thrombosis and pulmonary embolism. Finally, a number of Phase II trials investigated the safety and efficacy of fondaparinux in patients with acute coronary syndromes, and a large Phase III program is ongoing in this setting. This review focuses on the use of fondaparinux in the prevention and treatment of thromboembolic disorders.

Minimising the risk of heparin-induced osteoporosis during pregnancy

Unfractionated heparin (UFH) may lead to symptomatic vertebral fractures in up to 3 out of every 100 people on long-term therapy. Ten-times that many people will experience a significant reduction in bone density leading to osteopoenia or osteoporosis. Low molecular weight heparins (LMWH) have been shown to be as effective as UFH in the prevention and treatment of venous thromboembolism. Several well-established advantages of LMWH over UFH include increased bioavailability, more predictable dose response, less intensive coagulation monitoring, and a lower probability of causing immune-mediated thrombocytopenia. There is also some evidence that long-term LMWH therapy is less likely to cause osteoporotic fractures and significant reductions in bone mass than UFH. Both UFH and LMWH undergo pharmacokinetic changes during pregnancy, which sometimes necessitates dosage adjustments. Fondaparinux is a synthetic antithrombotic agent, which specifically binds to antithrombin. It has been shown to be comparable to, or even more effective than, LMWH in the management of both arterial and venous thrombosis. Fondaparinux does not appear to have a negative effect on bone metabolism. Therefore, fondaparinux may be a safe and effective alternative to UFH and LMWH in women who require anticoagulation during pregnancy.