Thrombosis In Man Research Articles

Multi-sequence non-contrast MRI characterization of deep vein thrombosis in man

Background Deep vein thrombosis (DVT) remains an important medical condition. The biophysical characteristics of thrombus may determine the response to endovascular interventions. We demonstrated that multi-sequence thrombus imaging (MSTI) using magnetization transfer rate (MTR), apparent diffusion coefficient (ADC) and T1 mapping can characterize thrombus organization and identify thrombi amenable to thrombolysis in a murine model. Here, we investigate whether MSTI can be translated to man and how these measurements associate with the outcome of intervention. Methods MSTI was performed in patients with ilio-femoral DVT undergoing lysis at 3T using a 32-channel coil. T2-prepared, bSSFP MR venography (MRV) was acquired with: TR/TE=4.2/2.1ms, flip angle=700, FOV=220x299x200mm, matrix=112x148, slice thickness=2mm, resolution= 2x2mm, averages=1, T2-prep-echo-time=30ms. 3D T1-weighted spoiled-GRE images were acquired with and without an on-resonance MT pre-pulse with: TR/TE=69/ 2.2ms, flip angle=180, FOV=220x299x198mm, matrix= 112x148, slice thickness=6mm, resolution=2x2mm, averages=1. The binomial-block MT pre-pulse had a

Plasma Inhibitors of The Hageman Factor Dependent Pathways

The Hageman factor dependent pathways are influenced by several control proteins which modulate the extent of activation and biologic activity of these enzyme substrates (Fig. 1). C1 INH plays a prominent role by acting at the common initiating step for all three Hageman factor dependent systems and its deficiency produces disease in man. Alpha-2 macroglobulin appears to play an important role in the fibrinolytic sequence, having potent activity towards both plasminogen activator and plasmin. Antithrombin most prominently influences the state of activation of the coagulation sequence by regulating the enzymatic activities of activated Factors XI, IX and X and, most importantly, that of thrombin. Significantly, deficiency of antithrombin results in increased thrombosis in man.

Cavo-portal transposition in rat: a new simple model

BackgroundLiver transplantation in presence of diffuse portal vein thrombosis is possible by using caval blood as portal inflow, through cavo-portal transposition. However, clinical results are heterogeneous and experimental studies are needed, but similar hemodynamic conditions are difficult to obtain, especially in small animals. Herein we describe a new simple model of cavo-portal transposition in rat.MethodsSpontaneous porto-systemic shunts are induced by subcutaneous transposition of the spleen. The presence of porto-caval shunts through the spleen permits the interruption of the main portal vein without splanchnic hemodynamic consequences. Cavo-portal transposition is achieved by anastomosing the inferior vena cava and the main portal vein after division of the pancreatic-duodenal vein.ResultsSelective angiography revealed total splanchnic blood diversion to the systemic venous circulation through the neoformed collaterals; macroscopical examination showed the absence of any signs of acute portal hypertension with normal liver and gut appearance.ConclusionThis model of cavoportal transposition is simple, effective and it simulates the clinical hemodynamic condition since the porto-systemic shunts induced by splenic subcutaneous transposition correspond to the physiological inframesocolic collaterals during chronic portal thrombosis in man.

The fate of 5-hydroxytryptamine in the lungs.

Abstract Isolated guinea-pig lungs perfused with Krebs solution were found to remove 5-hydroxytryptamine (5HT) from the fluid perfusing them. Two processes were involved: (1) the active uptake of 5HT by cells in the lungs, and (2) the metabolism of 5HT to 5-hydroxyindole-acetic acid (5HIAA). The experiments emphasize that the lungs have a metabolic capacity in addition to their passive function of gas diffusion. Derangement of the metabolic functions of the lungs may prove to be as serious clinically as derangement of their respiratory functions. Failure to clear the venous plasma of free 5HT would affect the aggregation of platelets and might thus have a bearing on the problem of deep venous thrombosis in man.

The discovery of the antiplatelet effect of aspirin: a personal reminiscence

The discovery of the antiplatelet effect of aspirin: a personal reminiscence

Fibrinogen as a Factor of Thrombosis: Experimental Study

Epidemiological, clinical, and experimental studies have clearly demonstrated the strong association between baseline fibrinogen level and risk of thromboembolic complications. The pathogenesis of post-operative or post-traumatic thrombosis in man is associated with fibrinogen level in plasma. The purpose of this study was to evaluate the effects of fibrinogen administration on thrombus formation at different dosages. To investigate these effects, we used an experimental model of induced thrombosis in rat microcirculation. This model allows single endothelial cell destruction by laser injuries, thus leading to thrombus formation. Fibrinogen was injected intravenously via penis vein and tested at various dosages (50, 100, and 200 mg/kg), 60 minutes after injection on arterial thrombosis induction and 120 minutes after injection on venous thrombosis induction. Results showed that the administration of fibrinogen increases the number of emboli, the duration of embolization, the amplitude, and the velocity of the ex-vivo platelet aggregation induced by ADP ( p<0.05). A positive correlation between the percent of fibrinogen increase in plasma and the enhancement of thromboembolic risk in the experimented animals was observed.

Cardiovascular chemotherapy: anticoagulants

Anticoagulant therapy has changed dramatically during the past two years. Low molecular weight heparin has substantially replaced unfractionated heparin as the parenteral anticoagulant of choice. The use of warfarin has substantially increased, especially for prevention of stroke in the setting of atrial fibrillation. It has become clear that warfarin cannot be administered effectively in an unmonitored fixed-dose fashion. The parenteral direct thrombin inhibitor desirudin was shown to be efficacious in the prevention of deep vein thrombosis in man. Small thrombin and factor Xa inhibitors with in vivo oral anticoagulant activity have been identified.

Reduction of plasma clot stability by a novel factor XIIIa inhibitor from the Giant Amazon Leech, Haementeria ghilianii.

The blood-sucking leech, Haementeria ghilianii, has evolved a number of agents that attenuate haemostasis. Recently we have isolated a potent inhibitor of factor XIIIa, tridegin, in the salivary glands which is almost certainly involved in feeding. Addition of purified natural tridegin to plasma, prior to clotting with thrombin, results in clots that deform more readily as adjudged by the greatly reduced development of the storage modulus on application of a shear force. The increase in the storage modulus in developing plasma clots is a slow process and continues for many hours. The effect of tridegin is particularly great when the clots are permitted to age in this way, demonstrating the role of factor XIIIa in the process. The IC50 for this inhibition is 138 ng/ml. Clots formed in the presence of tridegin are also lysed more rapidly in vitro by the leech's own fibrinolytic enzyme, hementin (time for 50% lysis, 16.0 +/- 0.8 h versus 22.3 +/- 2.0 h, P < 0.05). The synergy with which these agents act together may provide lessons for therapy of thrombosis in man.

Efficacy of dipyridamole as prophylaxis for stroke and the added value of dipyridamole in combination with aspirin

Although dipyridamole was identified as a potential antithrombotic agent many years ago,(1) its effectiveness as a single agent in secondary prevention of arterial thrombosis in man has never been proven in properly conducted clinical trials with sufficient power. In many clinical trials it has been tested in combination with aspirin, and until recently meta-analyses have failed to show any significant benefit of the combination of aspirin and dipyridamole beyond that shown with aspirin alone.(2,3).

Detection of deep venous thrombosis with indium 111-labelled monoclonal antibody against tissue plasminogen activator

The administration of a radiolabelled monoclonal antibody against tissue plasminogen activator allows detection of areas with increased fibrinolytic activity, i.e. those with an active thrombotic lesion. Eight patients with phlebographically verified deep venous thrombosis were examined. At the time of immunoscintigraphy study they were examined receiving anticoagulant therapy. Some 75-85 MBq indium 111-labelled antibody were injected, and scintigrams were obtained after 30 min and after 24 h. The precise site of the thrombus could not be visualized after 30 min due to high background activity, whereas after 24 h it was detectable in all patients. The thrombus/background ratios achieved are twice as high as those observed in a human antifibrin antibody study. These preliminary data suggest a high sensitivity of our t-PA-specific antibody for the detection of active deep venous thrombosis in man, and our antibody seems to offer theoretical advantages over both platelet and fibrin-specific antibodies.

The thienopyridine ticlopidine selectively prevents the inhibitory effects of ADP but not of adrenaline on cAMP levels raised by stimulation of the adenylate cyclase of human platelets by PGE 1

After oral administration, ticlopidine specifically inhibits ADP-induced platelet aggregation, prolongs the bleeding time and prevents thrombosis in man. Its mechanism of action is not well known. Ticlopidine inhibits ADP-induced binding of fibrinogen to platelet glycoprotein GP IIb-IIIa but not shape change and increases deaggregation. Ticlopidine has no direct effect on the GP IIb-IIIa complex. We studied the effects of ticlopidine (500 mg/day for 8 days) in four healthy male volunteers on washed platelet aggregation induced by 5 μM ADP or thrombin (0.1 units/mL) and potentiated by 1 μM adrenaline (Adr), on basal and 1 μM PGE 1-stimulated cAMP levels and on elevation of cytosolic free Ca 2+ concentration ([Ca 2+] i). We found that: (i) ticlopidine inhibits aggregation by ADP but not the potentiation by Adr of ADP-induced aggregation; (ii) ADP, Adr or thrombin decreases cAMP levels raised by PGE 1, an effect inhibited by ticlopidine only for ADP and not for Adr or thrombin; and (iii) Ca 2+ influx and Ca 2+ mobilization from internal stores were not affected. These results suggested that ticlopidine or a metabolite impairs the coupling mechanism of the ADP aggregation pathway at an unknown level.

Effects of Streptokinase and Recombinant Tissue Plasminogen Activator on Platelet Aggregation in Whole Blood

Streptokinase (SK) frequently induced platelet aggregation when added to citrated whole blood in vitro, but aggregation did not occur in corresponding samples of platelet-rich plasma (PRP). The aggregation occurred at concentrations of SK that are achieved after systemic infusion and was significantly more extensive in blood from men than women. SK-induced aggregation was accompanied by TXB(2) formation and release of (14)C-5HT and was inhibited by aspirin, by sulotroban, a TXA(2) antagonist, and by apyrase, an enzyme which removed ADP from plasma. Aggregation was also inhibited by each of three agents that interrupt the fibrinolytic pathway: epsilon-aminocaproic acid (ACA), aprotinin and alpha-2-antiplasmin. It is suggested that the aggregation is consequent to platelet activation by plasmin formed on the platelet surface, with ADP from red cells playing a part. In contrast to results obtained in vitro, prior administration of SK to man resulted in inhibition of the aggregation that occurs when this agent is added to whole blood. This effect was reproduced in vitro by pre-incubating blood with SK prior to carrying out aggregation studies. Similar inhibition was obtained when plasmin was added to blood and it is suggested that this effect of SK may be mediated by plasmin formed in plasma. In contrast to the pro-aggregatory effects of SK in vitro, recombinant tissue plasminogen activator (rt-PA) only inhibited platelet aggregation in whole blood. rt-PA inhibited the aggregation induced by a wide range of agents suggesting a central mechanism of action. Inhibition of aggregation was prevented by ACA, suggesting that this is also mediated by plasmin formed in plasma. The relevance of these observations is discussed in relation to the increasing use of fibrinolytic therapy in acute thrombosis in man. It is suggested that slow infusion of SK should always be performed so as to maximise the inhibitory rather than potentiatory effect of this agent on platelet aggregation, and that SK should only be used after prior administration of an anti-platelet agent.

A DOSE‐RANGING STUDY OF THE ANTIPLATELET EFFECT OF ENTERIC COATED ASPIRIN IN MAN

Enteric coated aspirin was given to eight human volunteers in escalating doses (20, 40, 60, 80, 100 mg daily), each dose being given over two weeks. In addition, to measure the maximum effect of aspirin, each volunteer was given two single doses of 600 mg of soluble aspirin. At the end of each dosing interval we measured platelet aggregation and thromboxane formation in response to four aggregating agents and to whole blood coagulation. The doses of aspirin required to inhibit platelet aggregation in response to various stimuli were: for collagen 60-80 mg, for adenosine diphosphate and adrenaline 60 mg, and for arachidonate 40 mg. For maximum inhibition of thromboxane formation the doses were: for collagen greater than 100 mg, for adenosine diphosphate and adrenaline 60 mg, for arachidonate 80 mg, and for whole blood coagulation 100 mg. Different aspirin doses are required to inhibit the responses to different stimuli. Furthermore, for some stimuli, inhibition of thromboxane generation may require more aspirin than is required for inhibition of aggregation. The clinical implications of these findings are uncertain since we do not know which stimuli are important in arterial thrombosis in man.

Heparin: Do We Understand Its Antithrombotic Actions?

Heparin: Do We Understand Its Antithrombotic Actions?

Dose Antiplatelet Agents; The Relationship Among Side Effects, and Antithrombotic Effectiveness

Although the platelet active agents that show promise as clinically effective antithrombotic drugs have effects on platelet function that are dose related, there is little information available from controlled clinical trials of the effect of different drug doses on thrombosis in man. Even among the agents whose therapeutic efficacy has been established by prospective controlled clinical trials, there are few data regarding the effect of different doses on thrombosis, and most of our present working knowledge is derived from studies of parallel phenomena, such as platelet survival, platelet aggregation, and similar processes whose relation to thrombosis is not always clear.

Asynchronous left ventricular wall motion early after coronary thrombosis.

To study regional wall motion early in the development of acute myocardial infarction, left ventriculograms performed in 24 patients before thrombolysis and within 3.5(1.2) (mean (SD] hours of the onset of pain were digitised frame by frame. Isometric and contour plots of regional wall motion were constructed. In 19 patients (seven with anterior descending, eight with right, and four with circumflex disease) thrombosis was demonstrated on an underlying stenosis. In 10 patients the two remaining coronary arteries were normal, and in nine, one or both showed important disease. Mean values of global indices of left ventricular function, including end diastolic volume, ejection fraction, peak ejection and filling rates, and cavity shape changes were all within normal limits, though end systolic volume was significantly raised. Total systolic amplitude of wall motion was normal in the affected area in all but seven patients (four with anterior descending, two with right, and one with circumflex thrombosis). Dyskinesis of more than 2 mm was seen in only three patients, all with thrombosis of the anterior anterior descending coronary artery, and hyperkinesis was present in four. The commonest abnormality of wall motion was hypokinesis during ejection followed by prolonged inward motion during isovolumic relaxation, which was seen in four patients with anterior descending, seven with right, and three with circumflex artery thrombosis. This was preceded by outward motion during isovolumic contraction and delayed inward motion during ejection in eight with right or circumflex thrombosis. Five of six patients without thrombosis had simple hypokinesis or dyskinesis without asynchrony. Disease of other coronary arteries did not affect the pattern of wall motion seen after right or circumflex coronary artery occlusion but it reduced the incidence of delayed inward motion along the free wall after thrombosis of anterior descending artery. Thus early after acute coronary thrombosis asynchronous wall motion is commoner than simple hypokinesis or dyskinesis. Its persistence suggests that in the setting of coronary artery thrombosis in man, residual contractile activity may persist for up to six hours after the onset of symptoms.

Fibrinolysis with acyl-enzymes: a new approach to thrombolytic therapy

Deep vein thrombosis in man presents a considerable clinical challenge. Despite the availability of prophylactic measures, therapeutic thrombolysis is often necessary, but is difficult and hazardous. Treatments have included the administration of plasmin, other less specific proteolytic enzymes, the indirect plasminogen activator, streptokinase, and the direct activators, urokinase and streptokinase-human plasmin complex. All these treatments have been associated with some haemostatic breakdown, which has discouraged their widespread application. The enzyme components of the coagulation and fibrinolytic pathways can, in general, be classed as serine proteases, with a catalytic mechanism which operates via acyl-enzyme intermediates. Chase and Shaw showed that p-nitrophenyl-p'-guanidinobenzoate could specifically acylate the active centre of trypsin-like enzymes, giving rise to a stable p-guanidinobenzoyl enzyme and other stable acyl-enzymes have since been described. We report here the fibrinolytic use of acylated derivatives of plasmin (E.C.3.4.21.7) and streptokinase-plasmin(ogen) complexes.

Comparison of bovine lung and porcine intestinal heparin for arterial thrombosis in man

The clinical effectiveness of bovine lung heparin and porcine intestinal heparin for reducing arterial thrombosis was compared in a study of 64 surgical patients (mean age, 63.8 years). Immediately prior to operation, the radial artery was cannulated. The catheters were flushed continuously at a flow rate of 3 ml/hr with 0.9% sodium chloride solution without heparin or with two units per milliliter of either beef lung or pork intestinal mucosa heparin. After 24 hours, arteriography was performed, and vessel diameter and the amount of thrombus present were recorded. The addition of heparin to the flush solution significantly reduced the accumulation of thrombotic material on the surface of intra-arterial cannulae, thus lowering the incidence of clinically detectable arterial occlusion. No significant difference was found in the anticoagulant effectiveness of beef lung-derived heparin as compared with heparin obtained from pork intestinal mucosa.

Production of thromboplastin (tissue factor) and thrombi by polymor phonuclear neutrophilic leukocytes adhering to vein walls

Separation of dog femoral and jugular veins from surrounding structures and transient stasis of blood flow for 30 seconds resulted in a lesion characterized by adhesion of neutrophils to the venous endothelium. Neutrophils harvested from this lesion 5 hours later had developed thromboplastic (tissue factor) activity. In immediately removed veins and veins from neutropenic dogs, this lesion did not occur and scrapings of the vein wall did not have thromboplastic activity. In some veins, gross or microscopic thrombosis was seen. It has been reported that neutrophil adhesion to veins also occurs during human surgery. We suggest, therefore, that neutrophils adhering to veins and producing thromboplastin may be a pathogenetic mechanism of deep vein thrombosis in man.

Dihomo-γ-linolenate suppresses platelet aggregation when administered in vitro or in vivo

Dihomo-γ-linolenate effectively prevented the irreversible aggregation of human platelets induced by collagen or epinephrine. Also, platelets from rats which received daily oral doses of dihomo-γ-linolenate showed significant reductions in platelet aggregatory responses to collagen and ADP which were attributable to increases in plasma and platelet ratios of dihomo-γ-linolenate to arachidonate. Similar results were obtained in rabbits. This data, together with that of enzymatic studies supports a hypothesis that oral ingestion of dihomo-γ-linolenate may effectively prevent arterial thrombosis in man by causing a redirection of platelet prostaglandin biosynthesis. Thus PGE 1 and its non-aggregatory endoperoxide intermediate (PGR 1) are formed at the expense of PGE 2 and LASS endoperoxide which together may induce platelet thrombus formation.