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Biomedical subjects

Jeffrey I Weitz

Publications and source records attributed to Jeffrey I Weitz.

At least 19 recordsLinked to original sources
PubMed2006

HD1, a thrombin-directed aptamer, binds exosite 1 on prothrombin with high affinity and inhibits its activation by prothrombinase.

Incorporation of prothrombin into the prothrombinase complex is essential for rapid thrombin generation at sites of vascular injury. Prothrombin binds directly to anionic phospholipid membrane surfaces where it interacts with the enzyme, factor Xa, and its cofactor, factor Va. We demonstrate that HD1, a thrombin-directed aptamer, binds prothrombin and thrombin with similar affinities (K(d) values of 86 and 34 nm, respectively) and attenuates prothrombin activation by prothrombinase by over 90% without altering the activation pathway. HD1-mediated inhibition of prothrombin activation by prothrombinase is factor Va-dependent because (a) the inhibitory activity of HD1 is lost if factor Va is omitted from the prothrombinase complex and (b) prothrombin binding to immobilized HD1 is reduced by factor Va. These data suggest that HD1 competes with factor Va for prothrombin binding. Kinetic analyses reveal that HD1 produces a 2-fold reduction in the k(cat) for prothrombin activation by prothrombinase and a 6-fold increase in the K(m), highlighting the contribution of the factor Va-prothrombin interaction to prothrombin activation. As a high affinity, prothrombin exosite 1-directed ligand, HD1 inhibits prothrombin activation more efficiently than Hir(54-65)(SO(3)(-)). These findings suggest that exosite 1 on prothrombin exists as a proexosite only for ligands whose primary target is thrombin rather than prothrombin.

Animals↗
PubMed2006

An evaluation of D-dimer in the diagnosis of pulmonary embolism: a randomized trial.

BACKGROUND: It may be safe to omit additional diagnostic testing in selected patients with suspected pulmonary embolism (PE) who have a negative D-dimer test, but this approach has never been evaluated in a randomized, controlled trial. OBJECTIVE: To determine if additional diagnostic testing can be safely withheld in patients with suspected PE who have negative erythrocyte agglutination D-dimer test results. DESIGN: Randomized comparisons in 2 subgroups of a prospective multicenter study. SETTING: 7 university hospitals. PATIENTS: 1126 outpatients or inpatients with suspected PE; of these, 456 patients with negative erythrocyte agglutination D-dimer test results were randomly assigned to the intervention groups. Patients were classified into 2 clinical probability groups: those with a low clinical probability of PE (low-probability group) and those with a moderate or high clinical probability of PE, a nondiagnostic ventilation-perfusion lung scan, and no evidence of proximal deep venous thrombosis on bilateral ultrasonography (moderate- or high-probability group). INTERVENTIONS: The experimental intervention for both probability groups was no further diagnostic testing for PE. The control intervention for the low-probability group was a ventilation-perfusion lung scan followed by ultrasonography of the proximal deep veins of the legs on the same day. If the lung scan was nondiagnostic, ultrasonography of the legs was repeated 7 and 14 days later. The control intervention for the moderate- or high-probability group was ultrasonography of the proximal deep veins of the legs after 7 and 14 days. In the control and experimental groups, anticoagulation was withheld or withdrawn if PE was not diagnosed. MEASUREMENTS: Symptomatic venous thromboembolism (VTE) during 6 months of follow-up. RESULTS: Prevalence of VTE was 15.2% in the 1126 enrolled patients. In the low-probability group, VTE occurred during follow-up in 0 of 182 patients who had no additional diagnostic testing and in 1 of 185 patients who had additional testing (difference, -0.5 percentage point [95% CI, -3.0 to 1.6 percentage points]). In the moderate- or high-probability group, VTE occurred during follow-up in 1 of 41 patients who had no additional diagnostic testing and in 0 of 41 patients who had additional testing (difference, 2.4 percentage points [CI, -6.4 to 12.6 percentage points]). LIMITATIONS: The authors could not enroll 2000 patients as originally planned; 3 randomly assigned patients did not receive the allocated intervention, and 7 received inadequate follow-up. Personnel who performed follow-up evaluations were not blinded to the results of diagnostic testing at enrollment or to allocation group assignments. CONCLUSION: In patients with a low probability of PE who have negative D-dimer results, additional diagnostic testing can be withheld without increasing the frequency of VTE during follow-up. Low clinical probability and negative D-dimer results occur in 50% of outpatients and in 20% of inpatients with suspected PE.

Fibrin Fibrinogen Degradation Products↗
PubMed2006

Heparin synergistically enhances interleukin-11 signaling through up-regulation of the MAPK pathway.

Using an animal model of heparin-induced osteoporosis we previously demonstrated that heparin causes bone loss, in part, by increasing osteoclast number and activity. Furthermore, we found that, although heparin alone has no effect, it is able to synergistically enhance Interleukin-11 (IL-11)-induced signal transducer and activator of transcription 3 (STAT3) activation and thus increase osteoclast formation in vitro. In the present study, we examine the effect of various serine kinase inhibitors on the ability of heparin to act synergistically with IL-11. Inhibition of the c-Jun N-terminal kinase (JNK), p38 mitogen-activated protein kinase (MAPK), or the phosphatidylinositol 3-kinase pathways had no effect on the ability of heparin to promote either IL-11-induced STAT3.DNA complex formation or osteoclast formation in vitro. In contrast, PD098059, a MAPK kinase inhibitor, completely abolished the synergy between heparin and IL-11. In an attempt to resolve the mechanism by which this was occurring, we examined the effect of heparin on STAT3 Ser-727 phosphorylation and extracellular signal-regulated kinases 1 and 2 (Erk1/2) activation, either in the presence or absence of IL-11. Heparin alone was found to have no effect on Ser-727 phosphorylation, nor did heparin alter the phosphorylation status of Ser-727 in the presence of IL-11. Heparin was, however, found to increase Erk1/2 activation in both a time- and dose-dependent manner. When taken together, these findings suggest that heparin enhances IL-11-induced STAT3 activation and thus osteoclast formation, by a mechanism that is independent of STAT3 Ser-727 phosphorylation but that involves up-regulation of the MAPK pathway.

Animals↗
PubMed2006

Incorporation of fragment X into fibrin clots renders them more susceptible to lysis by plasmin.

Bleeding, the most serious complication of thrombolytic therapy with tissue-type plasminogen activator (t-PA), is thought to result from lysis of fibrin in hemostatic plugs and from the systemic lytic state caused by unopposed plasmin. One mechanism by which systemic plasmin can impair hemostasis is by partially degrading fibrinogen to fragment X, a product that retains clottability but forms clots with reduced tensile strength that stimulate plasminogen activation by t-PA more than fibrin clots. The purpose of this study was to elucidate potential mechanisms by which fragment X accelerates t-PA-mediated fibrinolysis. In the presence of t-PA, clots containing fragment X were degraded faster than fibrin clots and exhibited higher rates of plasminogen activation. Although treatment with carboxypeptidase B, an enzyme that reduces plasminogen binding to fibrin, prolonged the lysis times of fragment X and fibrin clots, clots containing fragment X still were degraded more rapidly. Furthermore, plasmin or trypsin also degraded clots containing fragment X more rapidly than fibrin clots, suggesting that this effect is largely independent of plasminogen activation. Fragment X-derived degradation products were not preferentially released by plasmin from clots composed of equal concentrations of fibrinogen and fragment X, indicating that fragment X does not constitute a preferential site for proteolysis. These data suggest that structural changes resulting from incorporation of fragment X into clots promote their lysis. Thus, attenuation of thrombolytic therapy-induced fragment X formation may reduce the risk of bleeding.

Blood Coagulation↗
PubMed2006

The status of new anticoagulants.

Currently available anticoagulants include heparin, low-molecular weight heparin, fondaparinux and warfarin. Despite advances with low-molecular weight heparin and fondaparinux, the currently available agents have limitations that have provided the impetus for the development of new drugs for prevention and treatment of both venous and arterial thromboembolism. Novel anticoagulants targeting specific steps in coagulation are in various stages of development. This paper reviews the pharmacology of these new agents and describes the results of clinical trials with new anticoagulants in more advanced stages of clinical testing.

Anticoagulants↗
PubMed2006

Emerging anticoagulants for the treatment of venous thromboembolism.

Anticoagulant therapy is the cornerstone of treatment of venous thromboembolism (VTE). Such treatment is divided into two stages. Rapid initial anticoagulation is given to minimize the risk of thrombus extension and fatal pulmonary embolism, whereas extended anticoagulation is aimed at preventing recurrent VTE, thereby reducing the risk of postphlebitic syndrome. With currently available drugs, immediate anticoagulation can only be achieved with parenteral agents, such as heparin, low-molecular-weight heparin, or fondaparinux. Extended treatment usually involves the administration of vitamin K antagonists, such as warfarin. Emerging anticoagulants have the potential to streamline VTE treatment. These agents include idraparinux, a long-acting synthetic pentasaccharide that is given subcutaneously on a once-weekly basis, and new oral anticoagulants that target thrombin or factor Xa. This paper i) reviews the pharmacology of these agents, ii) outlines their potential strengths and weaknesses, iii) describes the results of clinical trials with these new drugs, and iv) identifies the evolving role of new anticoagulants in the management of VTE.

Anticoagulants↗
PubMed2006

Initial treatment of venous thromboembolism.

Immediate anticoagulant treatment is essential to reduce morbidity and mortality in patients with acute venous thromboembolism (VTE). Currently, rapid anticoagulation can only be achieved with parenteral anticoagulants, such as heparin or low-molecular-weight heparin (LMWH). Weight-adjusted LMWH is the treatment of choice, because it produces predictable anticoagulation and does not require coagulation monitoring. If heparin is used, the activated partial thromboplastin time must be monitored and the heparin dose adjusted to ensure a therapeutic level of anticoagulation. Heparin is recommended for patients with renal impairment and for those at high risk of bleeding. The selective factor Xa inhibitor fondaparinux is a recently introduced alternative to heparin or LMWH for initial VTE treatment. Heparin, LMWH, or fondaparinux should be given for at least five to seven days. Vitamin K antagonists should be initiated on the first day, or as soon as possible, in patients who are candidates for an oral anticoagulant. An oral anticoagulant agent to be used without laboratory monitoring for both acute and long-term treatment of VTE remains an unsolved clinical need in the treatment of VTE.

Administration, Oral↗
PubMed2006

A non-anticoagulant synthetic pentasaccharide reduces inflammation in a murine model of kidney ischemia-reperfusion injury.

Fondaparinux is a synthetic pentasaccharide that selectively inhibits factor Xa (FXa) in an antithrombin-dependent fashion. This newly developed anticoagulant is used in the prevention and treatment of venous thromboembolism. Recently, we showed that fondaparinux reduces inflammation and protects the kidney from ischemia-reperfusion (I/R) injury. However, the relative contributions of the anticoagulant and anti-inflammatory activities of fondaparinux to the observed protection is unknown. To address this, we chemically modified fondaparinux to abolish its affinity for antithrombin and analyzed the effect of this non-anticoagulant (NAC)-pentasaccharide on binding of U937 cells to P-selectin in vitro and on inflammation in a murine model of kidney I/R injury. NAC-pentasaccharide was as effective as fondaparinux at inhibiting the binding of U937 cells to P-selectin. In addition, NAC-pentasaccharide significantly reduced IL-6 and MIP-2 expression and injury in the kidney I/R model. These findings indicate that the anti-inflammatory activity of fondaparinux can be dissociated from its anticoagulant activity and that NAC-pentasaccharide is protective in kidney I/R injury.

Animals↗
PubMed2005

Randomized, blinded trial comparing fondaparinux with unfractionated heparin in patients undergoing contemporary percutaneous coronary intervention: Arixtra Study in Percutaneous Coronary Intervention: a Randomized Evaluation (ASPIRE) Pilot Trial.

BACKGROUND: Factor Xa plays a central role in the generation of thrombin, making it a novel target for treatment of arterial thrombosis. Fondaparinux is a synthetic factor Xa inhibitor that has been shown to be superior to standard therapies for the prevention of venous thrombosis. We performed a randomized trial to determine the safety and feasibility of fondaparinux in the percutaneous coronary intervention (PCI) setting. METHODS AND RESULTS: A total of 350 patients undergoing elective or urgent PCI were randomized in a blinded manner to receive unfractionated heparin (UFH), 2.5 mg fondaparinux IV, or 5.0 mg fondaparinux IV. Randomization was stratified for planned or no planned use of glycoprotein (GP) IIb/IIIa antagonists. The primary safety outcome was total bleeding, which was a combination of major and minor bleeding events. The incidence of total bleeding was 7.7% in the UFH group and 6.4% in the combined fondaparinux groups (hazard ratio, 0.81; 95% confidence interval, 0.35 to 1.84; P=0.61). Bleeding was less common in the 2.5-mg fondaparinux group compared with the 5-mg fondaparinux group (3.4% versus 9.6%, P=0.06). The composite efficacy outcome of all-cause mortality, myocardial infarction, urgent revascularization, or need for a bailout GPIIb/IIIa antagonist was 6.0% in the UFH group and 6.0% in the fondaparinux group, with no significant difference in efficacy among the fondaparinux doses compared with UFH. Coagulation marker analysis at 6 and 12 hours after PCI demonstrated that fondaparinux was superior to UFH in inducing a sustained reduction in markers of thrombin generation, as measured by prothrombin fragment F1.2 (P=0.02). CONCLUSIONS: In this pilot study of patients undergoing contemporary PCI, factor Xa inhibition with the synthetic anticoagulant fondaparinux in doses of 2.5 and 5.0 mg was comparable to UFH for clinical safety and efficacy outcomes. These data form the basis for further evaluation of fondaparinux in arterial thrombosis.

Aged↗
PubMed2005

New anticoagulants: beyond heparin, low-molecular-weight heparin and warfarin.

The limitations of traditional anticoagulants, heparin and warfarin, have prompted the development of new anticoagulant drugs for prevention and treatment of both venous and arterial thromboembolism. After a brief review of thrombogenesis and its regulation, this paper focuses on new anticoagulant agents in more advanced stages of clinical testing.

Animals↗
PubMed2005

New anticoagulant therapy.

The development of new anticoagulants is expanding the list of drugs that can be used to prevent and treat venous and arterial thrombosis. New parenteral anticoagulants have been developed to overcome the limitations of heparin and low-molecular-weight heparin, whereas novel orally active anticoagulants have been designed to provide more streamlined therapy than vitamin K antagonists. This review identifies the molecular targets of new anticoagulants, describes the results of clinical trials, and provides clinical perspective on the opportunities for new anticoagulants.

Administration, Oral↗
PubMed2005

Pharmacology and clinical potential of direct thrombin inhibitors.

Direct thrombin inhibitors represent a new class of anticoagulants that bind directly to thrombin and block the enzyme's interactions with its substrates. These agents have been developed, at least in part, to overcome the limitations of heparin and vitamin K antagonists. This paper (a) reviews why thrombin is an ideal target for new anticoagulants, (b) describes the pharmacological profiles of the various direct thrombin inhibitors, (c) outlines the potential mechanistic advantages of parenteral direct thrombin inhibitors over heparin, (d) defines the potential benefits of ximelagatran, the first orally active direct thrombin inhibitor, over vitamin K antagonists, and (e) provides clinical perspective on the strengths and weaknesses of the various parenteral and oral direct thrombin inhibitors.

Animals↗
PubMed2004

Modes and consequences of thrombin's interaction with fibrin.

Thrombin mediates the balance between coagulant and fibrinolytic forces and has numerous cellular effects. This intricate balance is maintained by biochemical mechanisms that regulate thrombin activity. Disruption of this balance could lead to bleeding or thrombosis. Once thrombin is generated, two major mechanisms regulate its activity. By binding fibrin, thrombin's activity is localized to the thrombus, a process that limits its systemic procoagulant effects. Thrombin that escapes into the circulation is efficiently inactivated by plasma inhibitors, such as antithrombin, or is sequestered by thrombomodulin on the endothelium. Although thrombin's interaction with fibrin limits its systemic effects, fibrin-bound thrombin resists inactivation and can produce a local procoagulant stimulus that triggers thrombus growth. Direct thrombin inhibitors were developed, at least in part, to target fibrin-bound thrombin. These agents are finding their niche for the prevention and treatment of venous and arterial thrombosis. The mechanisms by which thrombin binds fibrin are reviewed in this paper. As well, the potential pathological consequences of thrombin's interaction with fibrin are discussed.

Fibrin↗
PubMed2004

Oncogenic events regulate tissue factor expression in colorectal cancer cells: implications for tumor progression and angiogenesis.

Tissue factor (TF) is the primary cellular initiator of blood coagulation and a modulator of angiogenesis and metastasis in cancer. Indeed, systemic hypercoagulability in patients with cancer and TF overexpression by cancer cells are both closely associated with tumor progression, but their causes have been elusive. We now report that in human colorectal cancer cells, TF expression is under control of 2 major transforming events driving disease progression (activation of K-ras oncogene and inactivation of the p53 tumor suppressor), in a manner dependent on MEK/mitogen-activated protein kinase (MAPK) and phosphatidylinositol 3'-kinase (PI3K). Furthermore, the levels of cell-associated as well as circulating (microvesicle-associated) TF activity are linked to the genetic status of cancer cells. Finally, RNA interference experiments suggest that TF expression is an important effector of the K-ras-dependent tumorigenic and angiogenic phenotype in vivo. Thus, this study establishes a causal link between cancer coagulopathy, angiogenesis, and genetic tumor progression.

Alleles↗