Dysfunctional plasminogen in full-term newborn

O uso da estreptoquinase no tratamento da oclusão arterial aguda pós-cateterização da artéria femoral em crianças com menos de 10 kg

CONTEXTO: O tratamento da oclusão arterial aguda em menores de 5 kg tem constituído tema de discussão. OBJETIVOS: Avaliar o tratamento do quadro da oclusão arterial aguda pós-cateterismo da artéria femoral em crianças com menos de 10 kg com o uso de heparina isolada e também associada com estreptoquinase, e comparar os resultados do exame físico (como diagnóstico), da reversão da oclusão arterial, de complicações e de exames laboratoriais nos dois métodos MÉTODOS: Trinta casos de oclusão da artéria femoral foram identificados em 1.583 cateterismos em crianças no Instituto de Cardiologia de Porto Alegre, entre 1992 e 2000. Os pacientes foram divididos em dois grupos: um usou apenas heparina (14 casos), e o outro usou heparina associada com estreptoquinase (16 casos). Os exames laboratoriais (tempo de protrombina, tempo de tromboplastina parcial ativado e fibrinogênio) coletados antes e durante a infusão intravenosa foram avaliados estatisticamente, assim como o tempo de uso da medicação, as complicações e os resultados. RESULTADOS: O exame físico mostrou-se método fidedigno para avaliar a oclusão; no grupo que utilizou a associação de heparina e estreptoquinase, houve a resolução de 87% dos casos de oclusão arterial, e a principal complicação foi sangramento no sítio de punção em 56,3% dos pacientes. Os resultados apresentaram p < 0,05. Os exames laboratoriais não tiveram significado estatístico. CONCLUSÃO: A estreptoquinase associada com a heparina é mais efetiva do que a heparina isolada no tratamento da oclusão arterial aguda da artéria femoral pós-cateterismo, tanto que sua associação apresenta uma redução do risco relativo de 88% em relação à heparina isolada.

Differences between neonates and adults in carbohydrate sequences and reaction kinetics of plasmin and alpha(2)-antiplasmin

This study investigates reaction kinetics by slow-binding kinetics methods of both adult and fetal plasmin (Types 1 and 2) with adult and fetal alpha(2)-antiplasmin. In addition, carbohydrate sequences of Fetal and Adult Plasminogen Types 1 and 2, as well as fetal and adult alpha(2)-antiplasmin, were determined by mass spectrometric analysis. All curves of plasmin-alpha(2)-antiplasmin interaction followed the same pattern, indicating reversible slow-binding inhibition with an initial loose complex and a following tight complex. Differences between fetal and adult plasmin reactions with alpha(2)-antiplasmin were predominantly due to the initial loose complex. Values for K(i initial) in the reaction with adult alpha(2)-antiplasmin were 1.5 and 1.6 nM for Fetal Plasmin Types 1 and 2, respectively; compared to 0.3 and 0.7 nM for the corresponding adult types. Increasing concentrations of tranexamic acid resulted in a continuous increase of K(i initial) until a plateau was reached which was similar for all plasmin types. Almost identical values could be obtained when fetal alpha(2)-antiplasmin was used instead of adult alpha(2)-antiplasmin. Mass spectrometric analyses of the glycans present on plasminogen revealed a higher level of truncated N-glycans on the fetal material compared to the adult. The O-glycans of fetal and adult plasminogen were closely similar and only minor differences were observed between N-glycans of fetal and adult alpha(2)-antiplasmin. In conclusion, both fetal plasmin isoforms are less inhibited by alpha(2)-antiplasmin compared to the adult plasmin variants. These findings are important for the understanding of the physiology of the fibrinolytic system in neonates and provide further evidence that differences in glycosylation could be associated with marked effects on protein function.

In vitro fibrinolysis after adding low doses of plasminogen activators and plasmin generation with and without oxidative inactivation of plasmin inhibitors in newborns and adults

PURPOSE

The aim of this study was to investigate in vitro fibrinolysis after adding low doses of plasminogen activators and to determine the functional role of plasmin inhibitors in newborns and adults.

PATIENTS AND METHODS

We have studied the kinetics of in vitro fibrinolysis after adding low doses of urokinase (UK) and recombinant tissue plasminogen activator (rt-PA) by use of a microtiter clot lysis assay. Additionally, we have determined plasmin generation with and without oxidative inactivation of plasmin inhibitors in newborns and adults.

RESULTS

The 50% lysis time in the clot lysis assay correlated with the activator dose and was significantly shorter in newborns at rt-PA concentrations of < 0.21 microgram/ml. When UK was used as an activator, the 50% lysis time was slightly but significantly prolonged in newborns at concentrations of 140-200 IU/ml, whereas we could find lower values (non-significant) at 110 and 80 IU/ml. Plasmin generation after oxidative inactivation of plasmin inhibitors was significantly lower in newborns, even when compared with adult plasma, which was diluted 50%. However, in a physiological plasma milieu (containing natural inhibitors), there were no differences in plasmin generation when streptokinase (SK) was used as an activator and only minor differences when UK was used.

CONCLUSIONS

Our data indicate a more rapid clot lysis at low UK and rt-PA concentrations in newborns despite significantly reduced plasminogen levels. The results of the plasmin generation experiments suggest a diminished effect of plasmin inhibitors towards fetal plasmin, which raises an explanation for the concentration-related differences in the clot lysis assay. The experience with thrombolytic agents in newborns is limited. Most dosage regimens for thrombolytic therapy in children or adults consist of an initial bolus infusion, followed by low-dose continuous treatment. Based on the results of our clot lysis experiments, we think that especially the continuous infusion of plasminogen activators after bolus administration should not be enhanced in newborns compared to older children or adults.

Neonatal plasminogen displays altered cell surface binding and activation kinetics. Correlation with increased glycosylation of the protein

Plasminogen isolated from 60 full-term newborns differs from adult plasminogen in carbohydrate composition, kinetic activation constants, and cell binding. Amino acid composition and amino-terminal sequence analysis data indicate that the plasminogens of neonates and adults have the same amino acid sequence. Like the adult, the neonate has two glycoforms, but both have significantly more mannose and sialic acid than the adult forms. The difference in the neonatal glycosylation is probably responsible for the altered migration observed by isoelectric focusing. Moreover, the difference in carbohydrate composition appears to be the basis of the decreased functional activity of the neonatal plasminogen. The kcat/Km ratios indicate that the overall activation rates of the two neonatal plasminogen glycoforms are lower compared with the adult glycoforms. In addition, neonatal plasminogen does not bind as well to cellular receptors compared with adult plasminogen. These studies suggest a basis for the decreased fibrinolytic activity observed in neonates.

Streptokinase treatment for femoral artery thrombosis after arterial cardiac catheterisation in infants and children

Data on 205 children who underwent retrograde arterial catheterisation were studied to assess the frequency of femoral artery thrombosis and the safety and efficacy of systemic streptokinase treatment for this complication. In 29 (14%) a transarterial balloon dilatation was performed. In 15 (7.3%) patients impaired arterial perfusion due to vascular spasm with or without thrombus formation was seen in the cannulated leg after catheterisation. Despite heparinisation, signs of impaired arterial circulation persisted in nine patients (4.4% of the total). In these patients femoral artery thrombosis was strongly suspected. Six (53%) of these had undergone a balloon dilatation. Therefore in this study the risk of femoral artery thrombosis developing was 12 times greater after transarterial balloon dilatation than after arterial catheterisation without dilatation (20.6% v 1.7%). Systemic infusion of streptokinase was started in all patients with femoral artery thrombosis. Arterial perfusion became normal in all patients, though in one this was delayed. Haematological monitoring showed lengthening of the thrombin time and a decrease of the fibrinogen concentration during streptokinase treatment. There were no serious complications. Systemic infusion of streptokinase is a safe and useful treatment in children with persistent femoral artery thrombosis after arterial cardiac catheterisation.

Newborn's fibrinolytic mechanism: components and plasmin generation

Plasminogen activity and antigen, tissue-type plasminogen activator (tPA) activity and antigen, plasminogen activator inhibitor (PAI) activity, and plasmin generation rates were determined in 32 normal newborn plasmas and 25 normal adult plasmas. The newborns showed reduced levels of plasminogen activity and antigen and tPA antigen, and activity, normal levels of PAI activity, and slower plasmin generation rates. The slower generation was shown to be due to the hypoplasminogenemia. The in vitro plasmin generation studies also showed that the newborn needed 11 times the usual concentration of urokinase and 5 times the usual concentration of tPA to achieve the minimal activation rate of the adult.

Multiple idiopathic emboli in a full term neonate

We report a case of multiple idiopathic emboli leading to cerebral infarction and to limb ischaemia in a full term neonate. The increased frequency of diagnosis of cerebral infarction is highlighted. Treatment of cerebral and limb emboli is discussed and the need for further research into the causes and treatment of cerebral infarction is stressed.

Fibrinolytic therapy for femoral arterial thrombosis after cardiac catheterization in infants and children

The charts of 79 patients who required femoral arterial (FA) thrombectomy after cardiac catheterization were reviewed. Fifteen patients (19%) had poor pulses after thrombectomy and 2 had an extremity amputated. One thousand consecutive patients undergoing cardiac catheterization were also studied to prospectively determine the safety and efficacy of systemic fibrinolytic therapy for treatment of FA thrombosis. Among these, 771 patients underwent retrograde arterial catheterization, including 31 patients with left-sided obstructive lesions who had undergone transarterial balloon dilation procedures with large catheters. All patients were given heparin at the time of arterial cannulation. Patients who had a pulseless extremity 4 hours after catheterization continued to receive heparin therapy for 24 to 48 hours. If the extremity continued to have no palpable pulse and the systolic blood pressure was less than 50% of that in the contralateral leg, intravenous streptokinase infusion was begun. The overall incidence of FA thrombosis was 3.6% (28 of 771), including 39% (12 of 31) of all patients undergoing transarterial balloon dilation procedures; 97% (27 of 28) of patients weighed less than 14 kg and the majority weighed less than 10 kg. After an average treatment period of 33 hours, 16 patients continued to have a pulseless extremity and were treated with streptokinase for an average duration of 13 hours. Normal pulses and systolic blood pressure returned in 14 (88%) and were nearly normal in 1 other patient (6%). The incidence of bleeding at the arterial puncture site was 25% and was highest in the patients who had a transarterial balloon dilation procedure. No serious complications occurred.

Fibrinolytic study in a homozygous protein C deficient patient

The fibrinolytic system was evaluated in a patient with homozygous protein C deficiency as well as in several members of his family with a partial deficiency of this protein. Before anticoagulant therapy the patient showed skin lesions which quickly disappeared after administration of fresh plasma. After anticoagulant treatment, the propositus suffered two clinical episodes of "ecchymotic" lesions, which were controlled with fresh plasma. The patient has remained free of new lesions and other clinical episodes up to the present date. The fibrinolytic activity of both the propositus and his family was normal. The patient's father showed adequate release of tissue plasminogen activator after controlled physical exercise. According to clinical and analytical data from our patient and his family, it is suggested that, in spite of the preservation of the fibrinolytic system in this case, a localized deficiency in fibrinolysis could exist in view of the clinical behaviour of the skin lesions described.

Therapeutic catheter procedures in pediatrics

There is a large spectrum of interventional catheter procedures being performed presently in children. The procedures that offer a greater advantage than surgical techniques and that will continue to be established procedures include percutaneous angioplasty of the pulmonary valve, peripheral pulmonary artery and caval stenosis, embolizations of pulmonary collaterals and pulmonary arteriovenous malformations, angioplasty of vascular access shunt, embolization of bronchial arteries for hemoptysis, and percutaneous nephrostomy and abscess drainage procedures. Others that have been successful but not yet routinely established in children include thrombolysis, renal artery angioplasty, embolization of peripheral arteriovenous malformations, dilatation of the urinary and gastrointestinal tract stenosis, and percutaneous biopsy.

Reduced fibrinolytic activity in coronary heart disease in basal conditions and after exercise

Fibrinolysis may be impaired in coronary heart disease patients. 20 coronary heart disease patients and 10 control subjects were examined for tissue-plasminogen activator activity, tissue-plasminogen activator antigen, fast tissue-plasminogen activator inhibitor and other fibrinolytic and haemostatic parameters including antigenic and functional protein C. Both patient and control groups were similar in age and smoking habits. All of these patients had a myocardial infarction between 1-3 months before this study. Assays were evaluated before and after an exercise test. Prothrombin time, activated partial thromboplastin time, protein C, plasminogen, alpha 2-antiplasmin, fibrinogen/fibrin degradation products and contact-activated fibrinolysis were similar before and after exercise in both groups. Fibrinolytic activity assayed by the euglobulin lysis time and fibrin-plate lysis methods was decreased in the patient group as compared with the control group but the difference was not significant. In basal conditions, tissue-plasminogen activator activity was defective in 50% of the coronary heart disease patients (p less than 0.01) and after exercise this percentage rose to 77% (p less than 0.01). However, tissue-plasminogen activator antigen in the coronary heart disease group was similar to that of the control group, both before and after exercise. The activity of the tissue-plasminogen activator inhibitor was persistently increased in coronary heart disease though this increase was not statistically significant. It is concluded that in coronary heart disease patients there is a defective fibrinolytic activity probably due to an increase in tissue-plasminogen activator inhibitor.

Neonatal and maternal fibrinolysis: activation at time of birth

Utilizing chromogenic synthetic substrate-based methods, determination of the plasma concentration of plasminogen, alpha 2-antiplasmin, alpha 2-macroglobulin, and B beta 15-42-related peptides were made at the time of birth in both newborns and mothers. Plasminogen levels were increased in the maternal group (150 +/- 26%), and markedly decreased in the newborn group (67 +/- 14%). The major inhibitors of fibrinolysis, alpha 2-antiplasmin and alpha 2-macroglobulin, were within normal range in both groups. Determination of B beta 15-42-related peptide showed markedly increased levels in the maternal group above control values (115 +/- 102, normal 29 +/- 12); the newborn group showed values only mildly elevated above control values (39 +/- 21). The results demonstrate increased fibrinolytic activity in both groups, though the degree of activation is significantly higher in the maternal group, as reflected by the higher levels of B beta 15-42-related peptides. Fibrinopeptide A levels confirm an activation of coagulation in both maternal and newborn groups (22 +/- 4 ng/ml and 138 +/- 22 ng/ml, respectively) with a significantly increased level in newborns (2-5 ng/ml normal).

Physiological activation of plasminogen in full term newborn infants

Plasminogen in full term newborn infants has been measured by functional and immunological assays. Plasminogen functional activity and antigen concentration in newborn infants were about 44% and 48% of adult values respectively. Physiological activation kinetics of plasminogen in undiluted plasma at pH 7.4 and 37 degrees C using various concentrations of streptokinase and urokinase showed no significant difference in the rate of plasmin generation between plasminogen from newborn infants and adult plasminogen. These findings dispute the suggested existence of functional anomalies in plasminogen from full term newborn infants.

The fibrinolytic system in man

The existence of a system in the human body capable of inducing the dissolution of endogenous pathologically formed thrombi was appreciated in ancient times. Considered in detail in this article are the data that have elucidated the physiologic regulation of which plasmin formation is dependent on, the plasma concentration of plasminogen, availability of activators of plasminogen in the plasma and surrounding tissue environment, the concentration of naturally present inhibitors, and the existence of fibrin in the circulation. Important in this rapidly progressive scientific discipline is consideration of the factors which control the synthesis of the components of this proteolytic enzyme system. Recently abundant information has indicated that this plasminogen-plasmin proteolytic enzyme system can be utilized therapeutically. Knowledge of the mechanisms of this system has permitted identification of agents that can be exogenously administered to releave thrombotic obstruction to blood flow in the venous (pulmonary emboli, deep vein thrombosis) and arterial (peripheral and central vessels) circulatory systems. Particularly important is the demonstration that thrombolytic agents can directly attack and alleviate the immediate cause of acute myocardial infarction. As a result of the innovations in the present decade, it is evident that the plasminogen system can be advantageously employed to reverse the pathologic effects of all thrombotic diseases.

Species specificity of streptokinase

Streptokinase, a bacterial protein, forms a complex with human plasminogen which results in a conformational change in the plasminogen molecule and the exposure of an active center. The plasminogen-streptokinase complex is an activator of plasminogen and is rapidly converted to a plasmin-streptokinase complex which, in the human, is also an activator of plasminogen. Species differences have been found in the reaction of streptokinase with plasminogen varying from no active complex formation at one extreme to the rapid formation of an active activator complex at the other, with resultant differences in rates of complex formation and the yield of plasmin. Explanation of these species differences at a molecular level are discussed as well as the possible application of complex formation in a variety of biological systems as a mechanism to produce variation in enzyme activities in proportion to the concentration of substrate available.