Plasminogen activation without changes in tPA and PAI-1 in response to subcutaneous administration of ancrod

Isolation of the Anticoagulant and Procoagulant Fractions of the Venom of Iranian Endemic Echis carinatus

Background

The venom of Echis carinatus contains both procoagulant and anticoagulant components that can either promote or block the blood coagulation cascade, and some of these components affect platelet function in different ways.

Objectives

The present study focuses on setting up a procedure for the purification of crude venom and designing appropriate clotting tests in order to characterize the procoagulant and anticoagulant fractions of E. carinatus venom.

Methods

Chromatographic methods, including gel filtration, ion-exchange chromatography, and reverse-phase high-performance liquid chromatography (HPLC), were applied for purifying these fractions. Coagulant activity testing, prothrombin time (PT), and activated partial thromboplastin time (APTT) were used to determine procoagulant and anticoagulant properties. For measuring molecular weight, 15% SDS-PAGE electrophoresis with a molecular weight standard ranging from 6.5 to 200 kDa was used.

Results

We obtained five fractions named F₁, F₂, F₃, F₄, and F₅. The F₁ and F₂ fractions showed procoagulant activity, and the F₅ fraction had anticoagulant activity. The molecular weight of F_2.4.2 from fraction F₂ and F_5.1 from fraction F₅ were analyzed by SDS-PAGE electrophoresis under the reducing condition. These factors were identified as a single protein band at the end of purification. The molecular weights of these purified fractions were estimated to be 7.5 kDa and 38 kDa for F_5.1(b) and F_2.4.2(b), respectively.

Conclusions

Our findings suggest an efficient and suitable procedure for the identification and purification of the procoagulant and anticoagulant factors of the venom of Iranian E. carinatus using the PT and APTT assays.

Ancrod revisited: viscoelastic analyses of the effects of Calloselasma rhodostoma venom on plasma coagulation and fibrinolysis

Fibrinogen depletion via catalysis by snake venom enzymes as a therapeutic strategy to prevent or treat thrombotic disorders was utilized for over four decades, with ancrod being the quintessential agent. However, ancrod eventually was found to not be of clinical utility in large scale stroke trial, resulting in the eventual discontinuation of the administration of the drug for any indication. It was hypothesized that ancrod, possessing thrombin-like activity, may have unappreciated robust coagulation kinetics. Using thrombelastographic methods, a comparison of equivalent tissue factor initiated thrombin generation and Calloselasma rhodostoma venom (rich in ancrod activity) on plasmatic coagulation kinetics was performed. The venom resulted in thrombi that formed nearly twice as fast compared to thrombin formed clots, and there was no difference in fibrinolytic kinetics initiated by tissue-type plasminogen activator. In plasma containing iron and carbon monoxide modified fibrinogen, which may be found in patients at risk of stroke, the coagulation kinetic differences observed with venom was still more vigorous than that seen with thrombin. These phenomena may provide insight into the clinical failure of ancrod, and may serve as an impetus to revisit the concept of fibrinogen depletion via fibrinogenolytic enzymes, not those with thrombin-like activity.

Factor V Leiden mutation enhances fibrin formation and dissolution in vivo in a human endotoxemia model

Disseminated intravascular coagulation in sepsis is associated with microvascular thrombosis and organ dysfunction. It was expected that prothrombotic disposition such as factor V Leiden (FVL) mutation would worsen clinical outcome. Astonishingly, clinical trial and animal experimental data indicate that FVL can be associated with improved survival. This study investigated the effect of FVL on the response to endotoxin of the coagulation and fibrinolytic system in humans. Fourteen healthy male subjects without FVL and 15 healthy males with heterozygous FVL received an intravenous bolus dose of endotoxin, 2 ng/kg of body weight. Blood samples were drawn before and 1, 2, 4, 6, and 24 hours after administration of the endotoxin. Injection of endotoxin led to a more pronounced increase in soluble fibrin in patients with FVL than in controls. Patients with FVL displayed a more sustained increase in plasmin-plasmin inhibitor complex after 4, 6, and 24 hours. Patients with FVL mutation also displayed higher levels of D-dimer and fibrinogen-fibrin degradation products in plasma after 24 hours. Patients with FVL generate higher levels of soluble fibrin, which may serve as cofactor in tissue plasminogen activator-induced plasminogen activation, leading to a more sustained activation of fibrinolysis with production of more fibrinogen- and fibrin-degradation products.

Venom therapy in multiple sclerosis

To date many people with multiple sclerosis (MS) seek complementary and alternative medicines (CAM) to treat their symptoms as an adjunct to conventionally used therapies. Among the common CAM therapies, there is a renewed interest in the therapeutic potential of venoms in MS. The efficacy of this therapeutic method remains unclear. However, venom-based therapy using bee, snakes and scorpions venom and/or sea anemones toxin has been recently developed because current investigations have identified the various components and molecular mechanism of the effects of venoms under in vitro and in vivo conditions. The aim of this review is to describe the recent findings regarding the role of venoms and their components in treatment of MS disease and that whether venom therapy could be recommended as a complementary treatment or not.

NK-cell-dependent acute xenograft rejection in the mouse heart-to-rat model

BACKGROUND

Acute humoral xenograft rejection is characterized by widespread intravascular thrombosis with a significant NK-cell and macrophage infiltrate. Although in vitro and ex vivo data have shown that NK cells are capable of killing xenogeneic tissue, the precise role they play in vivo is still not certain. Consequently, there are few tested strategies for dealing with NK-cell-mediated rejection, should this prove to be a problem. One reason for this has been the lack of a relevant rodent model in which rejection by these cells can be easily studied.

METHODS

Prior to transplantation of mouse hearts, we depleted rat recipients of fibrinogen using a snake venom, ANCROD, from the Malayan pit viper. Graft survival was examined by manual palpation and the rejected hearts were examined by histology. Levels of circulating interferon gamma (IFN-gamma), used as a surrogate marker for NK-cell activation, were determined by an enzyme-linked immunosorbent assay.

RESULTS

Depletion of fibrinogen to approximately 5% of normal allowed surgery without a significant increase in the technical failure rates and prolonged graft survival compared with that seen in unmanipulated rats. Rejected hearts showed no evidence of intravascular thrombosis but did show significant antibody and complement deposition. There was little T-cell infiltration and cyclosporin had no influence on survival. Instead, hearts were infiltrated with NK cells and macrophages and rejection was associated with significant IFN-gamma production. Depletion of NK cells with anti-asialo-GM-1 from ANCROD-treated recipients led to a further significant prolongation of graft survival.

CONCLUSIONS

Inhibition of intravascular thrombosis by fibrinogen depletion, in the absence of any other manipulation, unmasks NK-cell-dependent acute xenograft rejection in the mouse-to-rat heart transplantation model. This relatively simple model is expected to be useful to investigate the mechanisms of NK-cell-mediated rejection and to provide insight into the types of graft manipulation that could modify this process.

Plasmin generation and D-dimer formation during cardiopulmonary bypass

The purpose of this study was to estimate the in vivo rates of plasmin and D-dimer generation for comparison with the rate of fibrin formation during cardiopulmonary bypass (CPB), a procedure known to induce a hyperfibrinolytic state. Plasmin and D-dimer generation rates were based on measured levels of antiplasmin, plasmin-antiplasmin complex and D-dimer obtained before, during and after CPB from nine males, combined with a computer model of each patient's vascular system that continuously accounted for secretion, clearance, hemodilution, blood loss and transfusion. At baseline the average plasmin and D-dimer generation rates were 0.27 +/- 0.07 and 0.18 +/- 0.07 pmol/s, respectively. Within 5 min of CPB initiation, plasmin generation increased over 100-fold to 36 +/- 40 pmol/s while D-dimer generation increased 200-fold to 37 +/- 39 pmol/s. For the remainder of the CPB, average plasmin and D-dimer generation remained 20-fold to 30-fold above baseline levels. During CPB, the rate of D-dimer generation was similar to the rate of total fibrin formation, indicating that, in the absence of fibrinolytic inhibitors, CPB induces plasmin-mediated removal of fibrin from the vascular system at a rate similar to the rate of fibrin formation.

The kinetics of plasmin inhibition by aprotinin in vivo

INTRODUCTION

The purpose of this study was to estimate, in patients undergoing cardiopulmonary bypass (CPB), the in vivo rates of tissue plasminogen activator (tPA) and plasminogen activator inhibitor 1 (PAI-1) secretion, plasmin generation, fibrin degradation, and plasmin inhibition by aprotinin versus antiplasmin.

MATERIALS AND METHODS

Estimates of in vivo rates were based on measured levels of tPA, PAI-1, antiplasmin, plasmin-antiplasmin complex (PAP), total aprotinin, plasmin-aprotinin complex and D-dimer, combined with a computer model of each patient's vascular system that continuously accounted for secretion, clearance, hemodilution, blood loss and transfusion. Plasmin regulation was studied in nine control patients undergoing CPB without aprotinin versus six patients treated with aprotinin.

RESULTS

In controls, plasmin-antiplasmin levels rose from a baseline of 3.0+/-0.9 to a peak of 8.1+/-2.7 nmol/L after CPB due to an average 44-fold rise in the plasmin generation rate. This rise in plasmin generation during CPB lead to increased fibrin degradation causing D-dimer levels to increase from a baseline of 1.2+/-0.6 to a peak of 9.7+/-4.4 nmol/L due to an average 74-fold rise in the D-dimer generation rate. During CPB in the aprotinin group, plasmin-antiplasmin levels dropped, plasmin-aprotinin complex levels rose, while D-dimer levels remained unchanged from baseline. Compared to controls, the aprotinin group showed similar rates of plasmin generation during CPB, but an 11-fold faster plasmin inhibition rate and a 10-fold lower D-dimer generation rate.

CONCLUSIONS

The rise in plasmin generation and fibrin degradation that occurs during standard CPB is suppressed by the addition of aprotinin, which returns the patient to near baseline fibrin degradation rates during CPB.

Clumping factor A-mediated virulence during Staphylococcus aureus infection is retained despite fibrinogen depletion

Clumping factor A (ClfA), a fibrinogen-binding protein expressed on the Staphylococcus aureus cell surface, has previously been shown to act as a virulence factor in experimental septic arthritis. Although the interaction between ClfA and fibrinogen is assumed to be of importance for the virulence of S. aureus, this has not been demonstrated in any in vivo model of infection. Therefore, the objective of this study was to investigate the contribution of this interaction to ClfA-mediated virulence in murine S. aureus-induced arthritis. Ancrod, a serine protease with thrombin-like activity, was used to induce in vivo depletion of fibrinogen in mice. Ancrod treatment significantly aggravated septic arthritis following inoculation with a ClfA-expressing strain (Newman) compared to control treatment. Also, ancrod treatment tended to enhance the arthritis induced by a clfA mutant strain (DU5876), indicating that fibrinogen depletion exacerbates septic arthritis in a ClfA-independent manner. Most importantly, the ClfA-expressing strain was much more arthritogenic than the isogenic clfA mutant, following inoculation of fibrinogen-depleted mice. This finding indicates that the interaction between ClfA and free fibrinogen is not required for ClfA-mediated functions contributing to S. aureus virulence. It is conceivable that ClfA contributes to the virulence of S. aureus through interactions with other host ligands than fibrinogen.

Critical care management of acute ischemic stroke

PURPOSE OF REVIEW

To review and examine the efficacy of recently described medical and surgical interventions after acute ischaemic stroke using data from well conducted, clinical trials and systematic reviews. This review will consider recently published or updated articles.

RECENT FINDINGS

As therapeutic options evolve, including thrombolysis and anti-platelet therapy, prevention of secondary insults, becomes increasingly important during periods of acute cerebral ischaemia in order to prevent worsening of the neurological injury. As in other acute medical conditions, urgent management of patients with acute ischaemic stroke should begin with the assessment and treatment of the airway, breathing, circulation, temperature, and blood glucose control.

SUMMARY

It is estimated that there will be 8.5 million patients with acute ischaemic stroke in the European Union and the USA over the next decade, and of these, about one and a half million will die within six months of stroke onset. Of those who survive, about one third will depend on other people for help with their activities of daily living. Future treatment strategies are likely to involve agents that re-canalise vessels and minimise further neuronal damage.