A Histomorphometric Comparison of the Effects of Heparin and Low-Molecular-Weight Heparin on Cancellous Bone in Rats

Examining the controversies in venous thromboembolism prophylaxis for vascular surgery patients: A critical review

BACKGROUND

Venous thromboembolism (VTE) is a significant concern in vascular surgery due to its potentially severe consequences. Effective prophylactic measures are essential to minimize the risks associated with VTE. However, considerable controversy remains regarding the optimal strategies for VTE prevention in patients undergoing vascular procedures.

METHODS

This review critically analyzes key clinical research, guidelines, and expert opinions to explore the advantages and limitations of various VTE prophylaxis approaches. The pharmacological and mechanical methods are explored, with a focus on balancing the risk of VTE against the potential for bleeding complications, particularly in high-risk patients.

RESULTS

The review addresses controversial issues such as the choice of anticoagulants, dosage, timing, and duration of prophylaxis. The lack of consensus in existing guidelines and the variability in clinical practice regarding VTE prevention in vascular surgery patients is highlighted. The role of patient-specific risk factors, including the use of intraoperative anticoagulation and bleeding risks, is also examined.

CONCLUSION

This review provides a comprehensive evaluation of VTE prophylaxis strategies in vascular surgery, emphasizing the need for individualized, evidence-based approaches. Clarifying these controversies is crucial for optimizing patient outcomes and minimizing both thrombotic and hemorrhagic complications.

Enoxaparin and Early Postoperative Tibial Nailing: Increased Nonunion Revision Rates

OBJECTIVES

To determine the association between postoperative enoxaparin use and the risk of requiring surgery for nonunion in patients treated with intramedullary nailing for midshaft fractures of the tibia.

METHODS

DESIGN

Retrospective cohort analysis.

SETTING

Data were sourced from the PearlDiver national database.

PATIENT SELECTION CRITERIA

Patients were identified through the PearlDiver database by using Current Procedural Terminology and International Classification of Diseases (ICD-10) codes. Included patients had undergone intramedullary nailing for midshaft fractures of the tibia between 2015 and 2020 and subsequently underwent revision surgery due to nonunion.

OUTCOME MEASURES AND COMPARISONS

The primary outcome measured in this study was the rate of nonunion following intramedullary nailing for the different types of tibial shaft fractures (closed, Type I/II open, Type III open). For each fracture subtype, the study compared nonunion rates between those who received enoxaparin in the postoperative period and those who did not receive enoxaparin at any time during the first 6 weeks postoperatively. Factors such as the timing and duration of enoxaparin therapy and demographic variables were also considered.

RESULTS

The study included 16,986 patients, average age was 49.2 years (SD 17.3); 43.1% were female. Five hundred four patients required revision surgery for nonunion (3.4%). Among patients who did not receive enoxaparin, the nonunion rates were 1.6%, 3.9%, and 6.9% for closed, Type I/II open, and Type III open fractures, respectively. For patients who received enoxaparin within the first 2 weeks, the nonunion rates were 2.6%, 4.7%, and 7.9% for closed (RR = 1.67, P < 0.0001), Type I/II open (RR = 1.21, P < 0.0001), and Type III open (RR = 1.17, P = 0.355) fractures, respectively. Logistic regression confirmed enoxaparin was independently associated with nonunion (odds ratios [OR] = 1.75, P = 0.0013 for closed fractures; OR = 1.51, P = 0.034 for Type I/II open fractures). Tobacco use was also a contributing factor (OR = 2.43, P < 0.0001 for closed fractures; OR = 2.00, P < 0.0001 for Type I/II open fractures; OR = 2.04, P = 0.0008 for Type III open fractures).

CONCLUSIONS

The postoperative use of enoxaparin was associated with an elevated risk of nonunion in patients treated with intramedullary nailing for fractures of the tibial shaft.

LEVEL OF EVIDENCE

Prognostic Level III. See Instructions for Authors for a complete description of levels of evidence.

Control of tissue homeostasis by the extracellular matrix: Synthetic heparan sulfate as a promising therapeutic for periodontal health and bone regeneration

Proteoglycans are core proteins associated with carbohydrate/sugar moieties that are highly variable in disaccharide composition, which dictates their function. These carbohydrates are named glycosaminoglycans, and they can be attached to proteoglycans or found free in tissues or on cell surfaces. Glycosaminoglycans such as hyaluronan, chondroitin sulfate, dermatan sulfate, keratan sulfate, and heparin/heparan sulfate have multiple functions including involvement in inflammation, immunity and connective tissue structure, and integrity. Heparan sulfate is a highly sulfated polysaccharide that is abundant in the periodontium including alveolar bone. Recent evidence supports the contention that heparan sulfate is an important player in modulating interactions between damage associated molecular patterns and inflammatory receptors expressed by various cell types. The structure of heparan sulfate is reported to dictate its function, thus, the utilization of a homogenous and structurally defined heparan sulfate polysaccharide for modulation of cell function offers therapeutic potential. Recently, a chemoenzymatic approach was developed to allow production of many structurally defined heparan sulfate carbohydrates. These oligosaccharides have been studied in various pathological inflammatory conditions to better understand their function and their potential application in promoting tissue homeostasis. We have observed that specific size and sulfation patterns can modulate inflammation and promote tissue maintenance including an anabolic effect in alveolar bone. Thus, new evidence provides a strong impetus to explore heparan sulfate as a potential novel therapeutic agent to treat periodontitis, support alveolar bone maintenance, and promote bone formation.

Clinical Features, Incidence and Treatment Outcome in Pregnancy-Associated Osteoporosis: A Single-Centre Experience over Two Decades

Pregnancy-associated osteoporosis (PAO) is a rare syndrome which typically presents with vertebral fractures during pregnancy or lactation. The medical records of sixteen patients with PAO who presented to a specialist clinic at the Western General Hospital in Edinburgh over a 20-year period were reviewed to evaluate the mode of presentation, potential risk factors and response to treatment. The most common presentation was back pain occurring in 13/16 (81.2%) individuals due to multiple vertebral fractures. The diagnosis was usually made postpartum and in 12/16 individuals (75.0%), PAO presented during the woman's first pregnancy. Medicines which could have contributed to the development of PAO included thromboprophylaxis therapies in 8 subjects (50.0%), inhaled or injected corticosteroids in 5 (31.3%), anticonvulsants in 2 (12.5%) and a LHRH agonist in 1 (6.3%). Five individuals reported a family history of osteoporosis, and two pregnancies were complicated by hyperemesis gravidarum. Treatments administered included calcium and vitamin D supplements, bisphosphonates and teriparatide. Bone mineral density increased following the diagnosis in all cases, regardless of treatment given. One patient had further fracture during follow-up, but four patients had subsequent pregnancies without fractures. We estimated that in this locality, the incidence of PAO was 6.8/100,000 pregnancies with a point prevalence of 4.1 per 100,000 women. This case series indicates the importance of family history of osteoporosis and thromboprophylaxis drugs as risk factors for PAO while also demonstrating that the reductions in bone density tend to reverse with time, irrespective of the treatment given.

Lipid and Bone Effects of Heparin Use During Hemodialysis

Unfractionated heparin (UFH) and low-molecular-weight heparins (LMWHs) are commonly prescribed anticoagulants for chronic hemodialysis (HD). The dialysis population comprises a unique group that receives heparin three times per week for a long period, with potential long-term cumulative metabolic effects such as osteoporosis and worsening lipid profile. HD patients have approximately half the number of lipases as healthy individuals, and their lipid metabolism is limited because of this decrease as well as partially inhibited function. Administration of UFH or LMWHs for anticoagulation can lead to metabolic starvation despite high triglyceride levels at the end of HD. In vitro studies indicate that UFH and LMWHs inhibit osteoblasts and promote osteoclasts. In patients on HD, long-term use of UFH or LMWHs did not worsen chronic kidney disease-mineral bone disease. Further investigation is needed to elucidate the underlining mechanisms of UFH and LMWHs and their possible influences on maintenance HD patients.

The Auxiliary Role of Heparin in Bone Regeneration and its Application in Bone Substitute Materials

Bone regeneration in large segmental defects depends on the action of osteoblasts and the ingrowth of new blood vessels. Therefore, it is important to promote the release of osteogenic/angiogenic growth factors. Since the discovery of heparin, its anticoagulant, anti-inflammatory, and anticancer functions have been extensively studied for over a century. Although the application of heparin is widely used in the orthopedic field, its auxiliary effect on bone regeneration is yet to be unveiled. Specifically, approximately one-third of the transforming growth factor (TGF) superfamily is bound to heparin and heparan sulfate, among which TGF-β1, TGF-β2, and bone morphogenetic protein (BMP) are the most common growth factors used. In addition, heparin can also improve the delivery and retention of BMP-2 in vivo promoting the healing of large bone defects at hyper physiological doses. In blood vessel formation, heparin still plays an integral part of fracture healing by cooperating with the platelet-derived growth factor (PDGF). Importantly, since heparin binds to growth factors and release components in nanomaterials, it can significantly facilitate the controlled release and retention of growth factors [such as fibroblast growth factor (FGF), BMP, and PDGF] in vivo. Consequently, the knowledge of scaffolds or delivery systems composed of heparin and different biomaterials (including organic, inorganic, metal, and natural polymers) is vital for material-guided bone regeneration research. This study systematically reviews the structural properties and auxiliary functions of heparin, with an emphasis on bone regeneration and its application in biomaterials under physiological conditions.

Impaired bone healing by enoxaparin via inhibiting the differentiation of bone marrow mesenchymal stem cells towards osteoblasts

INTRODUCTION

Enoxaparin is widely used to prevent venous thromboembolism after orthopedic surgery and has some adverse effects, such as osteoporosis and delay in fracture healing. However, the exact mechanism delaying bone healing by enoxaparin is still unclear.

MATERIALS AND METHODS

X-ray and Micro-CT scanning were performed to detect the effects of enoxaparin on bone healing at rat model of bone defeat. CCK-8 assay and flow cytometry were conducted to measure the effects of enoxaparin on bone marrow mesenchymal stem cells (BMSCs). The mRNA/protein levels of osteocalcin (OCN), runt-related transcription factor 2 (Runx2) and bone morphogenetic protein 2 (BMP2) were analyzed by real-time PCR and western blotting, respectively. Alizarin red staining was used to observe the mineralized nodules.

RESULTS

Enoxaparin (2000 AXaIU/kg) not only profoundly increased the trabecular separation, but also notably decreased the trabecular bone volume/tissue volume, trabecular thickness, trabecular number and OCN level, in vivo. Additionally, significantly inhibiting proliferation of BMSCs by enoxaparin (1.0 and 10 AXaIU/ml) was detected. The apoptosis and the ratio of G phase cells in enoxaparin (0.1, 1.0 and 10 AXaIU/ml) group were obviously higher than that in control group. While the ratio of S phase cells was downregulated markedly by enoxaparin (0.1,1.0 and 10 AXaIU/ml) compared with the control group. Most importantly, inducing significant decreases of OCN/Runx2 mRNA/protein expression and formation of mineralized nodules by enoxaparin (0.1, 1.0 and 10 AXaIU/ml) were observed compared with the control group. While the notable decreases of BMP2 mRNA/protein level were only detected in enoxaparin (10 AXaIU/ml) group.

CONCLUSION

It was suggested that enoxaparin impaired bone healing through suppressing the differentiation of BMSCs towards osteoblasts.

Osteogenic and Angiogenic Properties of Heparin as a System for Delivery of Biomolecules for Bone Bioengineering: a Brief Critical Review

The review considers complex, controversial, and individual effects of heparin and its derivatives on the bone and circulatory systems in dependence of the dose, the state of the cells and tissues of the recipient. General data on the anticoagulant activity of heparin and its derivatives are presented; special attention is paid to the effect of heparin on mesenchymal cells and tissues and its role in angiogenesis. We also discuss the ability of heparin to bind osteogenic and angiogenic biomolecules in the context of the development of systems for their delivery and sustained controlled release and propose a schematic representation of the positive and side effects of heparin as a delivery system for biomolecules in tissue engineering.

[Osteogenic and angiogenic properties of heparin as a system of biomolecule delivery for bone bioengineering: a brief critical review]

The review discusses the complex, ambiguous and individual effects of heparin and its derivatives on the bone and circulatory systems, in dependence of the dosage, the state of the cells and tissues of recipients. General data on the anticoagulant activity of heparin and its derivatives are presented; aspects of the effect of heparin on mesenchymal cells and tissues and its role in angiogenesis are considered in details. Particular attention is paid to the ability of heparin to bind osteogenic and angiogenic biomolecules: thus us especially important for the development of systems for their delivery and sustained controlled release. A schematic representation of the positive and side effects of heparin as a delivery system for biomolecules in tissue engineering is proposed.

Osteoporotic fracture rates in chronic hemodialysis and effect of heparin exposure: a retrospective cohort study

Background

Patients receiving chronic hemodialysis treatments are at a higher risk of fracture compared to the general population. While the use of heparin during dialysis is crucial to avoid thrombosis of the extracorporeal circuit, the association of unfractionated heparin (UFH) and the risk of osteoporotic fracture has been shown for many years. However, this association was not as clear for low-molecular-weight heparin (LMWH) and the few collected data originated from studies among pregnant women. Our aim was to measure osteoporotic fracture rate among hemodialysis patients and to evaluate the association of LMWH compared to UFH in hemodialysis.

Methods

A retrospective cohort study was conducted on data extracted from the RAMQ and Med-Echo databases from January 2007 to March 2013 with patients chronically hemodialyzed in 21 participating centers. Incidence rates for each fracture sites were measured per 1000 patient-year (p-y) and their 95% confidence intervals (CI). Osteoporotic fracture risk for a first event with LMWH compared to UFH was estimated using a cox proportional hazard model using demographics, comorbidities and drug use as covariates.

Results

4796 patients undergoing chronic hemodialysis were identified. The incidence rate for all fracture sites was 22.7 /1000 p-y (95% CI: 19.6–26.1) and 12.8 /1000 p-y (95% CI: 10.5–15.4) for hip and femur fractures. We found a similar risk of osteoporotic fracture for LMWH compared to UFH (adjusted HR = 1.01; 95%CI: 0.72–1.42). Age and malignancy increased the risk of fracture while cerebrovascular disease decreased the risk of fracture.

Conclusions

Compared to UFH, LMWH did not change the risk of osteoporotic fracture when used for the extracorporeal circuit anticoagulation in chronic hemodialysis.

Bone Microthrombus Promotes Bone Loss in Iron Accumulation Rats

In the present study, we investigated the changes of the coagulation state, bone microthrombus, microvascular bed and bone density levels in iron accumulation rats. Meanwhile,the effect of anticoagulation therapy on bone mineral density was further investigated. We established two groups: a control (Ctrl) group and an iron intervention (FAC) group. Changes in coagulation function, peripheral blood cell counts, bone microthrombus, bone vessels and bone mineral density were compared between the two groups. We designed the non-treatment group and treatment group to study the changes of bone mineral density by preventing microthrombus formation with the anticoagulant fondaparinux. We found that the fibrinogen and D-dimer contents were significantly higher, whereas the thrombin time (TT) and prothrombin time (PT) were significantly shorter in the FAC group. After ink staining, the microvascular bed in the FAC group was significantly reduced compared with that in the Ctrl group. HE and Martius Scarlet Blue (MSB) staining showed microthrombus in the bone marrow of the iron accumulation rats. Following anticoagulation therapy, the bone microcirculation vascular bed areas in the treatment group rats were significantly increased. Furthermore, the bone mineral density was increased in the treatment group compared with that in the non-treatment group. Through experiments, we found that the blood in iron accumulation rat was relatively hypercoagulable; moreover, there was microthrombus in the bone marrow, and the bone vascular bed was reduced. Additionally, anticoagulation was helpful for improving bone microcirculation, reducing microthrombus and decreasing bone loss.

Effect of long-term use of unfractionated or low-molecular-weight heparin on bone mineral density in maintenance hemodialysis patients

Introduction

Long‐term use of unfractionated heparin (UFH) or low‐molecular‐weight heparin (LMWH) causes bone loss and osteoporosis in patients not receiving hemodialysis. This study aimed to investigate the effect of UFH and LMWH on bone mineral density (BMD) in patients undergoing maintenance hemodialysis (MHD).

Methods

Patients undergoing MHD using UFH or LMWH as anticoagulants were enrolled. BMD (in g/cm²), T‐score and Z‐score (BMDs) were measured at the lumbar spine and femur neck using dual‐energy X‐ray absorptiometry (DXA) at baseline and 2 years later. Patient demographics and clinical indices were collected. Correlation analysis was used to identify significant predictors of bone loss. Multiple linear regression was used to explore the relationship between heparin type and bone loss progression.

Findings

A total of 104 patients were enrolled and completed the baseline BMD test; 72 completed the test again 2 years later. Six patients were excluded because they used both UFH and LMWH. Although BMD decreased in some patients in the UFH group, a slight increase in the BMD was observed on an average in the LMWH group after 2 years. The mean change in BMD (in g/cm²) [0(−0.03,0.04) vs. 0.04(0,0.06), P = 0.023], T‐score [0(−0.40,0.30) vs. 0.35(−0.03,0.53), P = 0.038], and Z‐score [0.10(−0.30,0.40) vs. 0.45(0.08,0.63), P = 0.031] in the lumbar spine in the UFH group was lower than those in the LMWH group. Femur neck BMD did not change significantly. In a linear regression model, after adjusting for diabetes mellitus, parathyroid hormone, and serum phosphate, we did not find an association between heparin substances and BMD.

Discussion

UFH might be associated with loss of lumbar spine BMD in patients undergoing MHD.

Assessment of the effect of pulsed electromagnetic field application on the healing of bone defects in rats with heparin-induced osteoporosis

Osteoporosis is a systemic skeletal disease characterized by an increase in bone fragility and fracture risk due to low bone mass and deterioration of bone tissue. Application of pulsed electromagnetic fields (PEMF), a non-invasive method with a low complication risk, is known to stimulate bone formation. The present study examines the histomorphometric and biochemical effects of PEMF application on the healing of bone defects in rats with heparin-induced secondary osteoporosis. Briefly, 12-month-old male Sprague-Dawley rats were examined in a prospective, randomized, single-blind study. Osteoporosis was induced by administering a daily dose of 2 IU/g heparin for 33 days. Bone defects were created on the right femur on Day 35. PEMF of an average intensity of 0.8 ± 0.2 mT and a frequency of 7.3 Hz, was applied for 1 h/day, for 28 days following surgery. Bone healing was evaluated by histomorphometric and biochemical analyses. The heparin + PEMF group displayed the largest amount of new bone area (P = .002) and the lowest mean CTx on Day 63 (P = .05). This study demonstrates that heparin administration leads to bone loss and osteoporosis, whereas the application of PEMF decreases this effect.

Drug treatment strategies for osteoporosis in stroke patients

INTRODUCTION

Osteoporosis and subsequent fractures are well-recognized complications of stroke. However, drug treatment strategies for osteoporosis after stroke have been rarely discussed in the current guidelines for the management of stroke or osteoporosis.

AREAS COVERED

The authors review the epidemiology, characteristics, pathophysiology, and risk prediction of post-stroke osteoporosis and fractures. Then they provide an overview of existing evidence regarding drug treatment strategies for osteoporosis in stroke patients. They also review the effects on bone mineral density (BMD) and fractures for those drugs commonly used in stroke patients.

EXPERT OPINION

Currently, there is scarce evidence. A small randomized control trial suggested that a single use of 4 mg of intravenous zoledronate within 5 weeks of stroke onset was beneficial for preserving BMD, while simultaneous use of calcium and vitamin D supplements may be effective in preventing hypocalcemia. Further studies are needed to address several important issues of post-stroke osteoporosis, including who (the eligibility for treatment), when (the best timing of treatment), what (which drug), and how long (the best duration of treatment). On the other hand, physicians should bear in mind that drugs commonly used for stroke, such as statins or warfarin, may have beneficial or adverse effects on BMD and fracture risks.

Inhibitory effects of dabigatran etexilate, a direct thrombin inhibitor, on osteoclasts and osteoblasts

INTRODUCTION

Anticoagulants are widely used in orthopedic surgery to decrease the risk of deep vein thrombosis. While significant bone impairment is induced by long-term heparin therapy, little is known about the effects of direct oral anticoagulants (DOACs). Herein, we investigated the effects of dabigatran etexilate (Pradaxa®), a DOAC inhibitor of thrombin, on bone cells using in vitro and ex vivo cell culture models.

MATERIALS AND METHODS

Osteoblasts and osteoclasts exposed to different concentrations of dabigatran etexilate and untreated cells were assayed for cell differentiation and activity. Favorable osteogenic conditions for osteoblasts were tested using titanium with nanotopography (Ti-Nano). In addition, mice treated with a dabigatran etexilate solution had bone marrow cells analyzed for the ability to generate osteoclasts.

RESULTS

Dabigatran etexilate at concentrations of 1 μg/mL and 2 μg/mL did not impact osteoclast or osteoblast viability. The drug inhibited osteoclast differentiation and activity as observed by the reduction of TRAP+ cells, resorption pits and gene and protein expression of cathepsin K. Consistently, osteoclasts from mice treated with dabigatran showed decreased area, resorptive activity, as well as gene and protein expression of cathepsin K. In osteoblast cultures, grown both on polystyrene and Ti-Nano, dabigatran etexilate reduced alkaline phosphatase (ALP) activity, matrix mineralization, gene expression of ALP and osteocalcin.

CONCLUSIONS

Dabigatran etexilate inhibited osteoclast differentiation in ex vivo and in vitro models in a dose-dependent manner. Moreover, the drug reduced osteoblast activity even under optimal osteogenic conditions. This study provides new evidence regarding the negative overall impact of DOACs on bone cells.

Anticoagulants and Osteoporosis

Anticoagulant agents are widely used in the treatment of thromboembolic events and in stroke prevention. Data about their effects on bone tissue are in some cases limited or inconsistent (oral anti-vitamin K agents), and in others are sufficiently strong (heparins) to suggest caution in their use in subjects at risk of osteoporosis. This review analyses the effects of this group of drugs on bone metabolism, on bone mineral density, and on fragility fractures. A literature search strategy was developed by an experienced team of specialists by consulting the MEDLINE platform, including published papers and reviews updated to March 2019. Literature supports a detrimental effect of heparin on bone, with an increase in fracture rate. Low molecular weight heparins (LMWHs) seem to be safer than heparin. Although anti-vitamin K agents (VKAs) have a significant impact on bone metabolism, and in particular, on osteocalcin, data on bone mineral density (BMD) and fractures are contrasting. To date, the new direct oral anticoagulants (DOACs) are found to safe for bone health.

Different type and dosage of heparin were not associated with the progression of coronary artery calcification in haemodialysis patients

AIM

Several studies have verified that unfractionated heparin (UFH) and low molecular heparin (LWMH) can induce bone loss, and bone mineral density has been inversely associated with vascular calcification in some clinical researches. But few have focused on the relationship between types and dosages of heparin and the progression of vascular calcification. We observed the progression of coronary artery calcification (CAC) in maintenance haemodialysis (MHD) patients who were treated with UFH and LMWH.

METHODS

This was a prospective prevalent cohort study of MHD patients. Computed tomography was performed at enrolment and 2 years after enrolment, and CAC score was obtained. Demographic and clinical data, baseline and time-average laboratory indices were collected. Multiple linear regression and logistic regression were used to estimate the influencing factors of progression of CAC.

RESULTS

In this study, (i) we initially enrolled 69 HD patients, and then 56 patients finished the follow-up. (ii) Among the total 56 patients, 27 patients (48.2%) were treated with UFH, 14 (25.0%) with LMWH and 15 (26.8%) with both. The median baseline CAC scores of three groups (UFH, LMWH and both users) were 91.0 (1.0, 1052.0), 134.0 (0, 1292.0) and 250.5 (27.0, 1139.0), respectively, with no significant difference (P = 0.663); the median CAC progression scores were 42.0 (0, 364.0), 172.0 (7.0, 653.0) and 118.5 (0, 434.0), respectively, with no significant difference (P = 0.660). (iii) Pearson and spearman correlation analysis shown that the progression of CAC was not associated with cumulative dosage of heparin used. (iv) After adjusted for diabetes mellitus, time-averaged intact parathyroid hormone, phosphate and alkaline phosphatase, logistic regression analysis showed using different types of heparin was not an independent risk factor for CAC progression; and multiple linear regression analysis showed that the type of heparin used was not associated with CAC progression.

CONCLUSION

There were no significant differences in the effects of the types and dosages of heparin on CAC progression in patients on haemodialysis.

Rivaroxaban significantly inhibits the stimulatory effects of bone-modulating hormones: In vitro study of primary female osteoblasts

BACKGROUND

Anticoagulant therapy is a mainstay of treatment subsequent to major orthopedic surgeries. Evidence linking anticoagulant therapy, osteoporosis, and delayed fracture healing is not conclusive. We have previously reported that rivaroxaban significantly inhibited cell growth and energy metabolism in a human osteoblastic cell line. This study analyzed the response of primary female osteoblast cells to rivaroxaban in combination with various bone-modulating hormones.

METHODS

Bone samples were taken from both premenopausal (pre-Ob) and postmenopausal (post-Ob) women. Cells were isolated from each sample and cultured to sub-confluence. Each sample was then treated with Rivaroxaban (10 µg/ml) in combination with the following hormones or with the hormones alone for 24 hours: 30nM estradiol-17β (E2), 390nM estrogen receptor α (ERα) agonist PPT, 420nM estrogen receptor β (ERβ) agonist DPN, 50nM parathyroid hormone (PTH), and 1nM of vitamin D analog JKF.

RESULTS

No effects were observed after exposure to rivaroxaban alone. When pre-Ob and post-Ob cells were exposed to the bone-modulating hormones as a control experiment, DNA synthesis and creatine kinase (CK)-specific activity was significantly stimulated with a greater response in the pre-Ob cells. When the cells were exposed to rivaroxaban in combination with bone-modulating hormones, the increased DNA synthesis and CK-specific activity previously observed were completely attenuated.

CONCLUSIONS

Rivaroxaban significantly inhibited the stimulatory effects of bone-modulating hormones in both pre-Ob and post-Ob primary human cell lines. This finding may have clinical relevance for patients at high risk of osteoporosis managed with rivaroxaban or other factor Xa inhibitors.

Pharmacology of Heparin and Related Drugs

Heparin has been recognized as a valuable anticoagulant and antithrombotic for several decades and is still widely used in clinical practice for a variety of indications. The anticoagulant activity of heparin is mainly attributable to the action of a specific pentasaccharide sequence that acts in concert with antithrombin, a plasma coagulation factor inhibitor. This observation has led to the development of synthetic heparin mimetics for clinical use. However, it is increasingly recognized that heparin has many other pharmacological properties, including but not limited to antiviral, anti-inflammatory, and antimetastatic actions. Many of these activities are independent of its anticoagulant activity, although the mechanisms of these other activities are currently less well defined. Nonetheless, heparin is being exploited for clinical uses beyond anticoagulation and developed for a wide range of clinical disorders. This article provides a "state of the art" review of our current understanding of the pharmacology of heparin and related drugs and an overview of the status of development of such drugs.

Effects of Long-Term Low-Molecular-Weight Heparin on Fractures and Bone Density in Non-Pregnant Adults: A Systematic Review With Meta-Analysis

BACKGROUND

Adults who require long-term anticoagulation with low-molecular-weight heparin (LMWH) such as cancer patients or the elderly may be at increased risk of fractures.

OBJECTIVE

To determine the effects of LMWH therapy of at least 3 months' duration on fractures and bone mineral density (BMD) in non-pregnant adult populations.

METHODS

We systematically reviewed electronic databases (e.g., MEDLINE, EMBASE), conferences and bibliographies until June 2015 and included comparative studies in non-pregnant adult populations that examined the effects of LMWH (≥3 months) on fractures and BMD. We synthesized evidence qualitatively and used random-effects meta-analysis to quantify the effect of LMWH on fractures.

RESULTS

Sixteen articles reporting 14 studies were included: 10 clinical trials (n = 4865 participants) and four observational cohort studies (3 prospective, n = 221; 1 retrospective, n = 30). BMD and fractures were secondary outcomes in the majority of trials, while they were primary outcomes in the majority of observational studies. In participants with venous thromboembolism and underlying cardiovascular disease or cancer (5 RCTs, n = 2280), LMWH for 3-6 months did not increase the relative risk of all fractures at 6-12 months compared to unfractionated heparin, oral vitamin K antagonists or placebo [pooled risk ratio (RR) = 0.58, 95 % CI: 0.23-1.43; I(2) = 12.5 %]. No statistically significant increase in the risk of fractures at 6-12 months was found for cancer patients (RR = 1.08, 95 % CI: 0.31-3.75; I(2) = 4.4 %). Based on the data from two prospective cohort studies (n = 166), LMWH for 3-24 months decreased mean BMD by 2.8-4.8 % (depending on the BMD site) compared to mean BMD decreases of 1.2-2.5 % with oral vitamin K antagonists.

CONCLUSIONS

LMWH for 3-6 months may not increase the risk of fractures, but longer exposure for up to 24 months may adversely affect BMD. Clinicians should consider monitoring BMD in adults on long-term LMWH who are at increased risk of bone loss or fracture.

Does Anticoagulant Medication Alter Fracture-Healing? A Morphological and Biomechanical Evaluation of the Possible Effects of Rivaroxaban and Enoxaparin Using a Rat Closed Fracture Model

Low molecular weight heparin (LMWH) is routinely used to prevent thromboembolism in orthopaedic surgery, especially in the treatment of fractures or after joint-replacement. Impairment of fracture-healing due to increased bone-desorption, delayed remodelling and lower calcification caused by direct osteoclast stimulation is a well-known side effect of unfractioned heparin. However, the effect of LMWH is unclear and controversial. Recent studies strongly suggest impairment of bone-healing in-vitro and in animal models, characterized by a significant decrease in volume and quality of new-formed callus. Since October 2008, Rivaroxaban (Xarelto) is available for prophylactic use in elective knee- and hip-arthroplasty. Recently, some evidence has been found indicating an in vitro dose independent reduction of osteoblast function after Rivaroxaban treatment. In this study, the possible influence of Rivaroxaban and Enoxaparin on bone-healing in vivo was studied using a standardized, closed rodent fracture-model. 70 male Wistar-rats were randomized to Rivaroxaban, Enoxaparin or control groups. After pinning the right femur, a closed, transverse fracture was produced. 21 days later, the animals were sacrificed and both femora harvested. Analysis was done by biomechanical testing (three-point bending) and micro CT. Both investigated substances showed histomorphometric alterations of the newly formed callus assessed by micro CT analysis. In detail the bone (callus) volume was enhanced (sign. for Rivaroxaban) and the density reduced. The bone mineral content was enhanced accordingly (sign. for Rivaroxaban). Trabecular thickness was reduced (sign. for Rivaroxaban). Furthermore, both drugs showed significant enlarged bone (callus) surface and degree of anisotropy. In contrast, the biomechanical properties of the treated bones were equal to controls. To summarize, the morphological alterations of the fracture-callus did not result in functionally relevant deficits.

Low-Molecular-Weight Heparin for the Treatment of Venous Thromboembolism in the Elderly

Venous thromboembolism (deep vein thrombosis and/or pulmonary embolism) is a common problem in the elderly population. Indeed, increasing age is a significant risk factor for venous thromboembolism. The treatment of venous thromboembolism in the elderly population presents certain unique problems related to aging, such as decreasing body weight, increasing renal insufficiency and numerous comorbid conditions, which complicate therapy. Treatment of venous thromboembolism in the elderly has been complicated by an increased incidence of bleeding, particularly with the use of warfarin. The risk of bleeding may be substantially reduced by carefully adjusting the warfarin dose to maintain a therapeutic INR and for this purpose anticoagulant management clinics have been shown to be useful. The low-molecular-weight heparins have been shown to be efficacious and safe for the treatment of venous thromboembolism in several clinical trials, including many patients in the older age brackets. Furthermore, these agents can safely be used in the out-of-hospital setting. Long-term use of low-molecular-weight heparin is an alternative to the use of oral anticoagulant therapy, particularly in patients with cancer or recurrent venous thromboembolism.

Heparin affects human bone marrow stromal cell fate: Promoting osteogenic and reducing adipogenic differentiation and conversion

Heparins are broadly used for the prevention and treatment of thrombosis and embolism. Yet, osteoporosis is considered to be a severe side effect in up to one third of all patients on long-term treatment. However, the mechanisms underlying this clinical problem are only partially understood. To investigate if heparin affects differentiation of skeletal precursors, we examined the effects of heparin on the osteogenic and adipogenic lineage commitment and differentiation of primary human bone marrow stromal cells (hBMSCs). Due to the known inverse relationship between adipogenesis and osteogenesis and the capacity of pre-differentiated cells to convert into the respective other lineage, we also determined heparin effects on osteogenic conversion and adipogenic differentiation/conversion. Interestingly, heparin did not only significantly increase mRNA expression and enzyme activity of the osteogenic marker alkaline phosphatase (ALP), but it also promoted mineralization during osteogenic differentiation and conversion. Furthermore, the mRNA expression of the osteogenic marker bone morphogenic protein 4 (BMP4) was enhanced. In addition, heparin administration partly prevented adipogenic differentiation and conversion demonstrated by reduced lipid droplet formation along with a decreased expression of adipogenic markers. Moreover, luciferase reporter assays, inhibitor experiments and gene expression analyses revealed that heparin had putative permissive effects on osteogenic signaling via the BMP pathway and reduced the mRNA expression of the Wnt pathway inhibitors dickkopf 1 (DKK1) and sclerostin (SOST). Taken together, our data show a rather supportive than inhibitory effect of heparin on osteogenic hBMSC differentiation and conversion in vitro. Further studies will have to investigate the net effects of heparin administration on bone formation versus bone resorption in vivo to unravel the molecular mechanisms of heparin-associated osteoporosis and reconcile conflicting experimental data with clinical observations.

The Effect of Low Molecular Weight Heparins on Fracture Healing

Venous Thromboembolism is a serious complication in the trauma patient. The most commonly studied and used anticoagulant treatment in prophylaxis of thrombosis is heparin. The prolonged use of unfractionated heparin has been connected with increased incidence of osteoporotic fractures. Low molecular-weight-heparins (LMWHs) have been the golden rule in antithrombotic therapy during the previous two decades as a way to overcome the major drawbacks of unfractioned heparin. However there are few studies reporting the effects of LMWHs on bone repair after fractures. This review presents the studies about the effects of LMWHs on bone biology (bone cells and bone metabolism) and underlying the mechanisms by which LMWHs may impair fracture healing process. The authors' research based on literature concluded that there are no facts and statistics for the role of LMWHs on fracture healing process in humans and the main body of evidence of their role comes from in vitro and animal studies. Further large clinical studies designed to compare different types of LMWHs, in different dosages and in different patient or animal models are needed for exploring the effects of LMWHs on fracture healing process.

Secondary osteoporosis: pathophysiology & diagnosis

Osteoporosis is a skeletal disease characterized by decreased bone mass and microarchitectural changes in bone tissue that increase the susceptibility to fracture. Secondary osteoporosis is loosely defined as low bone mineral density or increased risk of fragility fracture caused by any factor other than aging or postmenopausal status. The purpose of this review is to discuss the current understanding of the pathophysiology and contribution to fracture risk of many of the more common causes of secondary osteoporosis, as well as diagnostic considerations, outlined by organ system. While not comprehensive, included are a wide array of diseases, conditions, and medications that have been associated with bone loss and susceptibility to fractures. The hope is to highlight the importance to the general clinician of screening for and treating the osteoporosis in these patients, so to limit the resultant increased morbidity associated with fractures.

Bone mineral density loss after combat-related lower extremity amputation

OBJECTIVES

Determine the incidence, severity, and associated risk factors for the development of low bone mineral density (BMD) after combat-related lower extremity amputation.

DESIGN

Retrospective case-control comparison.

SETTING

Tertiary care military treatment facility.

PATIENTS/PARTICIPANTS

One hundred fifty-six lower extremity amputees, representing 182 amputations (121 unilateral, 35 bilateral).

INTERVENTION

All patients underwent dual energy x-ray absorptiometry scanning during the treatment period.

MAIN OUTCOME MEASUREMENTS

The Z score was the main outcome measure. We identified all patients with low BMD (Z < -1.0) and conducted multivariate analysis to identify significant risk factors for low BMD development.

RESULTS

The observed rate of low BMD was 42%. The average Z score was -0.6 ± 1.1 among unilateral amputations and -1.2 ± 1.0 among bilateral amputations (P = 0.005). Risk factors for the development of low BMD were prolonged time to first ambulation [odds ratio (OR) = 1.39; 95% confidence interval (CI): 1.003-1.93; P = 0.048], prolonged time to dual energy x-ray absorptiometry (OR = 1.10; 95% CI: 1.02-1.18; P = 0.009), and more proximal amputation level (OR = 7.27; 95% CI: 3.21-16.49; P < 0.001). Among unilateral amputees, we detected a significant difference in the BMD of the intact and amputated limbs (-1.0; 95% CI: -1.1 to -0.8; P < 0.001).

CONCLUSIONS

Proximal amputation level and delayed ambulation demonstrated a significant relationship with low BMD after traumatic and trauma-related amputation. We conclude that transfemoral amputees are at greater risk of BMD loss and that disuse atrophy is a primary factor in the development of low BMD. Prevention should focus on early and aggressive weight bearing rehabilitation and assessing levels and appropriately supplementing calcium and vitamin D.

Heparin concentration is critical for cell culture with human platelet lysate

BACKGROUND AIMS

Culture media for mesenchymal stromal cells (MSCs) are generally supplemented with fetal bovine serum. Human platelet lysate (hPL) has been proven to be a very effective alternative without the risk of xenogeneic infections or immune reactions. In contrast to fetal bovine serum, hPL comprises plasma, and anticoagulants-usually unfractionated heparin (UFH)-need to be added to prevent gel formation.

METHODS

Cultures of MSCs in hPL media with various concentrations of UFH and enoxaparin, a low-molecular-weight heparin (LMWH), were systematically compared with regard to proliferation, fibroblastoid colony-forming unit frequency, immunophenotype and in vitro differentiation.

RESULTS

At least 0.61 IU/mL UFH or 0.024 mg/mL LMWH was necessary for reliable prevention of coagulation of hPL pools used in this study. Higher concentrations impaired cellular proliferation in a dose-dependent manner even without benzyl alcohol, which is commonly added to heparins as a bacteriostatic agent. Colony-forming unit frequency was also reduced at higher heparin concentrations, particularly with LMWH, whereas no significant effect was observed on cellular morphology or immunophenotype. High concentrations of heparins reduced the in vitro differentiation toward adipogenic and osteogenic lineages.

CONCLUSIONS

Heparin concentration is critical for culture of MSCs in hPL media; this is of particular relevance for cellular therapy where cell culture procedures need to be optimized and standardized.

Rivaroxaban, a direct inhibitor of the coagulation factor Xa interferes with hormonal-induced physiological modulations in human female osteoblastic cell line SaSO2

The use of anticoagulants has been associated with systemic osteoporosis and increased risk for poor fracture healing but is inevitable following major orthopedic surgery of lower limbs. Rivaroxaban A (R) is an anticoagulant recently introduced in the clinical setting, which is a specific factor Xa inhibitor. We reported previously that R significantly inhibited cell growth, energy metabolism and alkaline phosphatase activity in human osteoblastic cell line SaOS2, with no effect on mineralization, indicating transient inhibition of bone formation. We now investigated the effects of R on SaOS2 response to osteoblast-modulating hormones. At sub-confluence cells were treated with: estradiol-17β (E2), the phytoestrogens daidzein (D) and biochainin A (BA), the carboxy-pytoestrogenic derivative carboxy-D (cD), the estrogen receptor α (ERα) agonist PPT, the estrogen receptor β (ERβ) agonist DPN, parathyroid hormone (PTH) and several vitamin D metabolites and analogs with/without R for 24h. All hormones tested stimulated significantly DNA synthesis (DNA), creatine kinase (CK) and alkaline phosphatase (ALP) specific activities, but all these stimulations were totally inhibited when given together with R. R had no effect on mRNA expression of ERα, ERβ and 25 Hydroxy-vitamin D3-1α hydroxylase (1OHase), but inhibited hormonal modulations of mRNA expressions. In conclusion R inhibited significantly hormonal stimulation of different parameters indicating inhibition of not only the early stages of bone formation, but also the stimulatory effects of bone modulating hormones with a yet unclear mechanism. The relevance of these findings to human bone physiology is yet to be investigated.

[Long-term low-molecular-weight heparin therapy during pregnancy: is there a bone risk?]

Unfractionated heparin (UFH) and low-molecular-weight heparins (LMWH) are broadly used for the thromboprophylaxis during pregnancy. Long-term heparin therapy has raised concern about the risk of bone loss and osteoporotic fractures while pregnancy by itself favors osteoporosis. Experimental studies show a comparable effect of UFH and LMWH on bone formation while UFH has a more marked effect on bone resorption. Available clinical studies do not provide evidence of a difference between UFH and LMWH or among different LMWH on the bone risk. However, clinical studies show that bone loss observed with LMWH is not different from the physiological loss related to pregnancy, and osteoporotic fractures are associated with comorbidities or osteoporosis risk factors. LMWH represent the preferred alternative for thromboprophylaxis during pregnancy.

In vivo transplantation of autogenous marrow-derived cells following rapid intraoperative magnetic separation based on hyaluronan to augment bone regeneration

INTRODUCTION

This project was designed to test the hypothesis that rapid intraoperative processing of bone marrow based on hyaluronan (HA) could be used to improve the outcome of local bone regeneration if the concentration and prevalence of marrow-derived connective tissue progenitors (CTPs) could be increased and nonprogenitors depleted before implantation.

METHODS

HA was used as a marker for positive selection of marrow-derived CTPs using magnetic separation (MS) to obtain a population of HA-positive cells with an increased CTP prevalence. Mineralized cancellous allograft (MCA) was used as an osteoconductive carrier scaffold for loading of HA-positive cells. The canine femoral multidefect model was used and four cylindrical defects measuring 10 mm in diameter and 15 mm in length were grafted with MCA combined with unprocessed marrow or with MS processed marrow that was enriched in HA(+) CTPs and depleted in red blood cells and nonprogenitors. Outcome was assessed at 4 weeks using quantitative 3D microcomputed tomography (micro-CT) analysis of bone formation and histomorphological assessment.

RESULTS

Histomorphological assessment showed a significant increase in new bone formation and in the vascular sinus area in the MS-processed defects. Robust bone formation was found throughout the defect area in both groups (defects grafted with unprocessed marrow or with MS processed marrow.) Percent bone volume in the defects, as assessed by micro-CT, was greater in defects engrafted with MS processed cells, but the difference was not statistically significant.

CONCLUSION

Rapid intraoperative MS processing to enrich CTPs based on HA as a surface marker can be used to increase the concentration and prevalence of CTPs. MCA grafts supplemented with heparinized bone marrow or MS processed cells resulted in a robust and advanced stage of bone regeneration at 4 weeks. A greater new bone formation and vascular sinus area was found in defects grafted with MS processed cells. These data suggest that MS processing may be used to enhance the performance of marrow-derived CTPs in clinical bone regeneration procedures. Further assessment in a more stringent bone defect model is proposed.

The effects of direct factor Xa inhibitor (Rivaroxaban) on the human osteoblastic cell line SaOS2

Thromboprophylaxis reduces the risk of surgery-related deep vein thrombosis, but anticoagulants were associated with systemic osteoporosis, a known risk factor for poor fracture healing. Rivaroxaban (XARELTO(®)) is a novel anticoagulant with specific ability to inhibit factor Xa, a serine endopeptidase, which plays a key role in coagulation. This study investigated the direct effects of rivaroxaban on bone biology using an in vitro cell culture model from the human female osteoblastic cell line SaOS2. Cells at subconfluence were treated for 24 hr with different concentrations of rivaroxaban and analyzed for DNA synthesis and creatine kinase- and alkaline phosphatase-specific activities, and were treated 21 days for analyzing mineralization. Rivaroxaban (0.01-50 μg/ml) dose-dependently inhibited up to 60% DNA synthesis of the cells. Creatine kinase-specific activity was also inhibited dose-dependently to a similar extent by the same concentrations. Alkaline phosphatase-specific activity was dose-dependently inhibited but only up to 30%. Cell mineralization was unaffected by 10 μg/ml rivaroxaban. This model demonstrated a significant rivaroxaban-induced reduction in osteoblastic cell growth and energy metabolism, and slight inhibition of the osteoblastic marker, alkaline phosphatase, while osteoblastic mineralization was unaffected. These findings might indicate that rivaroxaban inhibits the first stage of bone formation but does not affect later stages (i.e., bone mineralization).

Cardiac risks and management of complications in pregnant women with congenital heart disease

There are a growing number of women with congenital heart disease reaching adulthood and contemplating and/or undergoing pregnancy. However, pregnancy imposes hemodynamic stress on the heart and this can result in maternal, fetal and neonatal complications. Most women with congenital heart disease do well during pregnancy, but some women with high-risk cardiac lesions will not tolerate the hemodynamic changes of pregnancy. Physicians must be aware of the potential risks for the mother both during and after pregnancy, the risks to the fetus and neonate, and the risks and benefits of medications and procedures used during pregnancy. For women with complex cardiac conditions, management during pregnancy benefits from multidisciplinary care involving cardiologists with expertise in pregnancy, obstetricians with expertise in maternal fetal medicine, neonatologists and obstetric anesthetists, among others. This review will focus on the cardiac risks faced by women with congenital heart disease; particularly those at high risk, and on management strategies to mitigate risk and address cardiac complications.

Parenteral anticoagulants: Antithrombotic Therapy and Prevention of Thrombosis, 9th ed: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines

This article describes the pharmacology of approved parenteral anticoagulants. These include the indirect anticoagulants, unfractionated heparin (UFH), low-molecular-weight heparins (LMWHs), fondaparinux, and danaparoid, as well as the direct thrombin inhibitors hirudin, bivalirudin, and argatroban. UFH is a heterogeneous mixture of glycosaminoglycans that bind to antithrombin via a unique pentasaccharide sequence and catalyze the inactivation of thrombin, factor Xa, and other clotting enzymes. Heparin also binds to cells and plasma proteins other than antithrombin causing unpredictable pharmacokinetic and pharmacodynamic properties and triggering nonhemorrhagic side effects, such as heparin-induced thrombocytopenia (HIT) and osteoporosis. LMWHs have greater inhibitory activity against factor Xa than thrombin and exhibit less binding to cells and plasma proteins than heparin. Consequently, LMWH preparations have more predictable pharmacokinetic and pharmacodynamic properties, have a longer half-life than heparin, and are associated with a lower risk of nonhemorrhagic side effects. LMWHs can be administered once daily or bid by subcutaneous injection, without coagulation monitoring. Based on their greater convenience, LMWHs have replaced UFH for many clinical indications. Fondaparinux, a synthetic pentasaccharide, catalyzes the inhibition of factor Xa, but not thrombin, in an antithrombin-dependent fashion. Fondaparinux binds only to antithrombin. Therefore, fondaparinux-associated HIT or osteoporosis is unlikely to occur. Fondaparinux exhibits complete bioavailability when administered subcutaneously, has a longer half-life than LMWHs, and is given once daily by subcutaneous injection in fixed doses, without coagulation monitoring. Three additional parenteral direct thrombin inhibitors and danaparoid are approved as alternatives to heparin in patients with HIT.

VTE, thrombophilia, antithrombotic therapy, and pregnancy: Antithrombotic Therapy and Prevention of Thrombosis, 9th ed: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines

BACKGROUND

The use of anticoagulant therapy during pregnancy is challenging because of the potential for both fetal and maternal complications. This guideline focuses on the management of VTE and thrombophilia as well as the use of antithrombotic agents during pregnancy.

METHODS

The methods of this guideline follow the Methodology for the Development of Antithrombotic Therapy and Prevention of Thrombosis Guidelines: Antithrombotic Therapy and Prevention of Thrombosis, 9th ed: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines in this supplement.

RESULTS

We recommend low-molecular-weight heparin for the prevention and treatment of VTE in pregnant women instead of unfractionated heparin (Grade 1B). For pregnant women with acute VTE, we suggest that anticoagulants be continued for at least 6 weeks postpartum (for a minimum duration of therapy of 3 months) compared with shorter durations of treatment (Grade 2C). For women who fulfill the laboratory criteria for antiphospholipid antibody (APLA) syndrome and meet the clinical APLA criteria based on a history of three or more pregnancy losses, we recommend antepartum administration of prophylactic or intermediate-dose unfractionated heparin or prophylactic low-molecular-weight heparin combined with low-dose aspirin (75-100 mg/d) over no treatment (Grade 1B). For women with inherited thrombophilia and a history of pregnancy complications, we suggest not to use antithrombotic prophylaxis (Grade 2C). For women with two or more miscarriages but without APLA or thrombophilia, we recommend against antithrombotic prophylaxis (Grade 1B).

CONCLUSIONS

Most recommendations in this guideline are based on observational studies and extrapolation from other populations. There is an urgent need for appropriately designed studies in this population.

Proteoglycans and osteolysis

Osteolysis is a complex mechanism resulting from an exacerbated activity of osteoclasts associated or not with a dysregulation of osteoblast metabolism leading to bone loss. This bone defect is not compensated by bone apposition or by apposition of bone matrix with poor mechanical quality. Osteolytic process is regulated by mechanical constraints, by polypeptides including cytokines and hormones, and by extracellular matrix components such as proteoglycans (PGs) and glycosaminoglycans (GAGs). Several studies revealed that GAGs may influence osteoclastogenesis, but data are very controversial: some studies showed a repressive effect of GAGs on osteoclastic differentiation, whereas others described a stimulatory effect. The controversy also affects osteoblasts which appear sometimes inhibited by polysaccharides and sometimes stimulated by these compounds. Furthermore, long-term treatment with heparin leads to the development of osteoporosis fueling the controversy. After a brief description of the principal osteoclastogenesis assays, the present chapter summarizes the main data published on the effect of PGs/GAGs on bone cells and their functional incidence on osteolysis.

Adverse effects of heparin

All the adverse effects of heparins are related to their wide variety of biological activities, with bleeding being the most important safety issue, resulting directly from the potency of heparin as an anticoagulant. However, it is hard to define the bleeding risk, since it depends on numerous parameters including the indication, dosage, method, and duration of heparin application, the clinical study design and definition of bleeding as well as patient characteristics and determinants of bleeding such as type of surgery and co-medication. Nonbleeding complications of heparins are caused by binding of heparin molecules to proteins other than antithrombin and to cells, which is generally more pronounced with unfractionated heparin than with low-molecular-weight heparins. Accordingly, heparin-induced thrombocytopenia, the most severe nonbleeding adverse reaction, occurs about 10 times less with low-molecular-weight heparins than with unfractionated heparin. Frequent and therefore important adverse reactions of heparins are skin lesions resulting from delayed-type hypersensitivity reactions. All the other undesirable effects are discussed as well, but they are mostly clinically irrelevant.

Binding of heparin to metals

Heparin is a major prophylactic and treatment agent for thrombosis. Structurally, this anticoagulant is a polydisperse, highly negatively charged polysaccharide mixture that contains a variable density of sulfate group substituents per molecule. Previous study has shown that heparin molecules have a high affinity for a wide range of metal ions with varying oxidation states. However, reports in literature on binding of heparin to metals have investigated only a small sampling of heparin-metal ion interactions. Since interaction of heparin with fluid phase and cell surface macromolecules in vivo is dependent on the heparin structure when bound in a metal ion complex, a survey of the physical parameters for heparin binding to metals is imperative. Atomic absorption and spectrophotometry experiments were performed for metal quantification, and in this study, the relative values for affinity constants and number of binding sites for heparin binding to several alkaline, alkaline earth, main group, and transition metals in their most common oxidation states are reported. We found an overall trend for heparin-metal affinity to be Mn(2+) > Cu(2+) > Ca(2+) > Zn(2+) > Co(2+) > Na(+) > Mg(2+) > Fe(3+) > Ni(2+) > Al(3+)> Sr(2+), with the trend in N (b) being opposite compared with the K (a).

Effects of antithrombotic drugs fondaparinux and tinzaparin on in vitro proliferation and osteogenic and chondrogenic differentiation of bone-derived mesenchymal stem cells

An unexpected side effect of some classes of anticoagulants has been osteoporosis which may be, at least in part, related to deranged mesenchymal stem cell (MSC) function. The aim of the present study was to compare the effect of fondaparinux (FDP), a novel antithrombotic with a traditional widely used low molecular weight heparin, tinzaparin (TZP) on MSC proliferation and differentiation. MSCs were isolated from trabecular bone of 14 trauma patients by a collagenase-based digestion procedure and expanded in standard conditions until passage 3. Proliferation and differentiation of MSCs to chondrocytes and osteoblasts was assessed with or without the addition of FDP and TZP using standard in vitro assays and a broad range of drug concentrations. Flow cytometry was used for MSC phenotyping. In the age studied group (17-74 years old) the MSC frequency in collagenase-released fractions was 641/10(6) cells (range 110-2,158) and their growth characteristics were ∼4 days/population doubling. Cultures had a standard MSC phenotype (CD73+, CD105+, CD146+, CD106+, and CD166+). Cell proliferation was assessed by both colony-forming unit-fibroblast (CFU-F) and colorimetric tetrazolium salt XTT assays. In both assays, MSC proliferation was inhibited by the addition of TZP, particularly at high concentrations. In contrast, FDP had no effect on MSC proliferation. Osteogenic differentiation and chondrogenic differentiation were not affected by the addition of either TZP or FDP. Whilst MSC proliferation, but not differentiation, is negatively affected by TZP, there was no evidence for adverse effects of FDP in this in vitro model system which argues well for its use in the orthopedic setting.

Effect of a direct thrombin inhibitor compared with dalteparin and unfractionated heparin on human osteoblasts

Purpose:

Osteoporosis is a relevant problem after long term administration of unfractionated heparin (UFH) and low molecular weight heparin. Melagatran is a representative of a new group of direct thrombin inhibitors with comparable data in the prevention of thromboembolic events after orthopaedic surgery. The aim of our in vitro study was to investigate the effect of a direct thrombin inhibitor compared with dalteparin and UFH on human osteoblasts.

Materials and Methods:

Melagatran, dalteparin and UFH were added to primary osteoblast cultures in their therapeutic range and two decimal powers below and above. Cell number, protein synthesis, mitochondrial and alkaline phosphatase activity and collagen type I synthesis were evaluated.

Results:

Melagatran showed the least influence on protein synthesis and cell proliferation with a reduction of cell number to 83.5 ± 9% (p = 0.027) of the control group only in the highest investigated concentration after 15 days of incubation.

Mitochondrial and alkaline phosphatase activity and collagen type I synthesis in osteoblasts incubated with melagatran and dalteparin showed similar patterns. UFH showed the most pronounced influence on cellular metabolism.

Conclusions:

Melagatran showed less inhibitory in vitro effects on human osteoblasts than dalteparin or UFH. The presented study gives first hints that direct thrombin inhibitors may help prevent heparin-induced negative effects on bone metabolism.

Effects of a sulfated exopolysaccharide produced by Altermonas infernus on bone biology

The growth and differentiation of bone cells is controlled by various factors, which can be modulated by heparan sulfates. Here, we investigated the effects of an oversulfated exopolysaccharide (OS-EPS) on the bone. We compared the effect of this compound with that of a native EPS. Long-term administration of OS-EPS causes cancellous bone loss in mice due, in part, to an increase in the number of osteoclasts lining the trabecular bone surface. No significant difference in cancellous bone volume was found between EPS-treated mice and age-matched control mice, underlying the importance of sulfation in trabecular bone loss. However, the mechanism sustaining this osteoporosis was unclear. To clarify OS-EPS activities, we investigated the effect of OS-EPS on osteogenesis. Our results demonstrated that OS-EPS inhibited osteoclastogenesis in two cell models. Using the surface plasmon resonance technique, we revealed that OS-EPS can form a hetero-molecular complex OS-EPS/receptor activator of NF-κB ligand (RANKL)/RANK and that RANK had a higher affinity for RANKL pre-incubated with OS-EPS than for RANKL alone, which would be in favor of an increase in bone resorption. However, in vitro, OS-EPS inhibited the early steps of osteoclast precursor adhesion and therefore inhibited the cell fusion step. In addition, we showed that OS-EPS reduced proliferation and accelerated osteoblastic differentiation, leading to strong inhibition of mineralized nodule formation, which would be in favor of an increase in bone resorption. Taken together, these data show different levels of bone resorption regulation by EPSs, most of them leading to proresorptive effects.

Effect of strontium ranelate on fracture healing in the osteoporotic rats

The aim of this study was to evaluate the effect of strontium ranelate (SrR) on fracture healing in the osteoporotic rat model. Forty female Sprague-Dawley rats aged 3 months were enrolled in the study. Osteoporosis was induced by bilateral ovariectomy and subsequent daily heparin injection started 1 week after surgery and lasted for 4 weeks. Osteoporosis was confirmed by a reduction of bone mineral density (BMD). Twenty of the osteoporotic rats were assigned to the SrR group and the remaining 20 to the control group. An open right tibial midshaft transverse fracture was created and then an intramedullary fixation was performed. SrR group was treated by 450 mg/kg/day SrR per oral. Six weeks after surgical induction of fracture, all animals were sacrificed. One animal from each group died after ovariectomy. Two tibiae from the control group failed to unite. SrR-treated group showed higher mechanical strength and fracture stiffness when compared to the control group (p = 0.006, p = 0.001, respectively). SrR-treated group had mature woven bone or predominantly woven bone compared with osteoporotic control group (p = 0.038). SrR-treated group's callus maturity was significantly higher than control group (p = 0.001). SrR is associated with better fracture healing in the osteoporotic rat model.

Functionalization of chitosan/poly(lactic acid-glycolic acid) sintered microsphere scaffolds via surface heparinization for bone tissue engineering

Scaffolds exhibiting biological recognition and specificity play an important role in tissue engineering and regenerative medicine. The bioactivity of scaffolds in turn influences, directs, or manipulates cellular responses. In this study, chitosan/poly(lactic acid-co-glycolic acid) (chitosan/PLAGA) sintered microsphere scaffolds were functionalized via heparin immobilization. Heparin was successfully immobilized on chitosan/PLAGA scaffolds with controllable loading efficiency. Mechanical testing showed that heparinization of chitosan/PLAGA scaffolds did not significantly alter the mechanical properties and porous structures. In addition, the heparinized chitosan/PLAGA scaffolds possessed a compressive modulus of 403.98 +/- 19.53 MPa and a compressive strength of 9.83 +/- 0.94 MPa, which are in the range of human trabecular bone. Furthermore, the heparinized chitosan/PLAGA scaffolds had an interconnected porous structure with a total pore volume of 30.93 +/- 0.90% and a median pore size of 172.33 +/- 5.89 mum. The effect of immobilized heparin on osteoblast-like MC3T3-E1 cell growth was investigated. MC3T3-E1 cells proliferated three dimensionally throughout the porous structure of the scaffolds. Heparinized chitosan/PLAGA scaffolds with low heparin loading (1.7 microg/scaffold) were shown to be capable of stimulating MC3T3-E1 cell proliferation by MTS assay and cell differentiation as evidenced by elevated osteocalcin expression when compared with nonheparinized chitosan/PLAGA scaffold and chitosan/PLAGA scaffold with high heparin loading (14.1 microg/scaffold). This study demonstrated the potential of functionalizing chitosan/PLAGA scaffolds via heparinization with improved cell functions for bone tissue engineering applications.

A longitudinal study of the effect of heparin thromboprophylaxis during pregnancy on maternal bone metabolism

The aim of this study was to determine the effect of heparin thromboprophylaxis during pregnancy on maternal biochemical markers of bone metabolism. This was a prospective longitudinal study of carboxy terminal pro-peptide of type I collagen (PICP) and cross-linked carboxyterminal telopeptide of type I collagen (ICTP) levels in 15 women, who had heparin thromboprophylaxis during pregnancy compared with those of 18 normal pregnant controls. During pregnancy, the rate of change of PICP and ICTP in women who had heparin thromboprophylaxis was similar to those of women who did not (P = 0.184 for PICP, and P = 0.129 for ICTP), and PICP and ICTP levels at individual time points were similar in both groups. Therefore, heparin thromboprophylaxis during pregnancy does not affect maternal biochemical markers of bone metabolism.

Review: Low-molecular-weight heparin-induced osteoporosis and osteoporotic fractures: a myth or an existing entity?

Long-term use of unfractioned heparin data has been associated with a 2.2-5% incidence of heparin-induced osteoporotic fracture, but for low-molecular-weight heparin (LMWH) data is scarce and there is lack of clarity of the risks of osteoporosis and osteoporotic fractures. In this paper we review the differential diagnosis of osteoporosis and osteoporotic fractures, and we conduct a systematic review of all related cases from case reports and trials. Two new cases of possible LMWH-induced osteoporosis are also presented and the difficulties in making the diagnosis are highlighted. The authors conclude that, until large clinical trials are designed to investigate pre- and post-treatment bone density and to compare different dosages of LMWH effect on the bone density in different patient groups, no safe conclusions can be made.

How I treat the antiphospholipid syndrome

This article discusses how we approach medical decision making in the treatment of the various facets of the antiphospholipid syndrome (APS), including secondary prophylaxis in the setting of venous and arterial thrombosis, as well as treatment for the prevention of recurrent miscarriages and fetal death. The role of primary thromboprophylaxis is also discussed in depth. Great emphasis is given to incorporating the most up-to-date and relevant evidence base both from the APS literature, and from large, recent, randomized controlled trials (RCTs) of primary and secondary thrombotic prophylaxis in the general population setting (ie, the population that has not been specifically investigated for APS).