Synthesis and radioiodination of a stannyl oligodeoxyribonucleotide

Synthesis and radioiodination of a stannyl oligodeoxyribonucleotide were undertaken to evaluate a gamma ray emitting ODN ligand for thrombus imaging in vivo . Synthesis of the ODN was based on modified automatedbeta-cyanoethyl phosphoramidite chemistry with an organotin nucleoside (dU*) coupled to a thrombin binding aptamer sequence to give d(U*GGTTGGTGTGGTTGG). The synthesis accommodated dU*, which is destannylated by iodine or acids. Fourteen standard synthesis cycles were followed by one 'stannyl synthesis cycle', distinguished by Fmoc protection, omission of capping, oxidation by an organic peroxide and cleavage by ammonium hydroxide. The organotin nucleoside phosphoramidite {5'-[fluorenylmethoxycarbonyl]-5-(E)-[2-tri-n -butylstannylvinyl]-2'-deoxyuridine-3'-(2-cyanoethyl N,N-diisopropyl phosphoramidite)} was prepared from 5-iodo-2'-deoxyuridine. A customized mild rapid workup included deprotection with methylamine, and reverse phase HPLC with CH3CN/triethylammonium bicarbonate. Pure stannyl ODN was highly retained by reverse phase HPLC. Radioiodination of stannyl ODN (100 microg) provided 123I-labeling yields up to 97%. Five alternative oxidants were effective. High specific activity [123I]- ODN (15 000 Ci/mmol) was recovered, separated from unlabeled isomers. Excellent reverse phase HPLC resolution of ODN isomers (alternatively I, Cl, H or Br in vinyl deoxyuridine) was essential. The affinity of the iodovinyl aptamer analog (Kd = 36 nM) for human alpha-thrombin was similar to the native aptamer (Kd = 45 nM).

The use of D-dimer testing and impedance plethysmographic examination in patients with clinical indications of deep vein thrombosis

OBJECTIVE

To prospectively test the hypothesis that a diagnosis of deep vein thrombosis can be excluded in outpatients who present with clinical indications of deep vein thrombosis and whose results of D-dimer testing and impedance plethysmographic examination on the day of presentation are normal.

DESIGN

Prospective cohort study.

SETTING

Four university-affiliated hospitals.

METHODS

Three hundred ninety-eight consecutive patients with clinical indications of deep vein thrombosis were included in the final analysis. All patients underwent an assessment of pretest probability, bedside D-dimer testing, and impedance plethysmographic examination. In most patients, if the results of D-dimer testing and impedance plethysmographic examination were negative for deep vein thrombosis, anticoagulants were withheld and patients were followed up for 3 months. If the results of one or both tests were abnormal, an examination using venous compression ultrasonography or phlebography was performed.

RESULTS

In the majority of patients (69%), the results of D-dimer testing and impedance plethysmographic examination were normal. This combination had a negative predictive value of 98.5% (95% confidence interval, 96.3-99.6) for deep vein thrombosis.

CONCLUSION

The results of the D-dimer assay and impedance plethysmographic examination on the day of presentation can be used to treat the majority of outpatients who present with clinical indications of deep vein thrombosis without further testing.

A histomorphometric comparison of the effects of heparin and low-molecular-weight heparin on cancellous bone in rats

Long-term heparin treatment causes osteoporosis through, an as yet, undefined mechanism. To investigate this phenomenon and to determine the relative benefits of low-molecular-weight heparin (LMWH) use, we treated rats with once daily subcutaneous injections of either unfractionated heparin (1.0 U/g or 0.5 U/g), the LMWH, Tinzaparin (1.0 U/g or 0.5 U/g), or placebo (saline) for a period of 32 days. The effects on bone were then compared both histomorphometrically and biochemically by measuring urinary type I collagen cross-linked pyridinoline (PYD) and serum alkaline phosphatase, markers of bone resorption and formation, respectively. Histomorphometric analysis of the distal third of the right femur, in the region proximal to the epiphyseal growth plate, demonstrated that both heparin and LMWH decrease cancellous bone volume in a dose-dependent fashion, but that heparin causes significantly more cancellous bone loss than does LMWH. Although both heparin and LMWH decrease osteoblast and osteoid surface to a similar extent, only heparin increases osteoclast surface. In support of these histomorphometric findings, biochemical markers of bone turnover demonstrated that both heparin and LMWH treatment produce a dose-dependent decrease in serum alkaline phosphatase, consistent with reduced bone formation, whereas only heparin causes a transient increase in urinary PYD, consistent with an increase in bone resorption. Based on these observations, we conclude that heparin decreases cancellous bone volume both by decreasing the rate of bone formation and increasing the rate of bone resorption. In contrast, LMWH, causes less osteopenia than heparin because it only decreases the rate of bone formation.

Effect of nonspecific binding to plasma proteins on the antithrombin activities of unfractionated heparin, low-molecular-weight heparin, and dermatan sulfate

BACKGROUND

Nonspecific binding to plasma proteins decreases the anti-factor Xa (anti-Xa) activity of unfractionated heparin (UFH) but not that of low-molecular-weight heparin (LMWH). However, plasma proteins could influence the anti-thrombin (anti-IIa) activity of LMWH. To explore this possibility, we compared the effects of plasma proteins on the anti-IIa activities of UFH and LMWH. We also examined their effects on the anti-IIa activity of dermatan sulfate (DS) because, like UFH, DS binds to plasma proteins.

METHODS AND RESULTS

There was almost complete recovery of anti-IIa activity when UFH, LMWH, or DS was added to plasma from each of 20 healthy volunteers. The addition of a chemically modified heparin with low affinity for antithrombin III to plasma containing UFH increased the anti-IIa activity in a concentration-dependent fashion by displacing UFH from plasma proteins. In contrast, addition of low-affinity heparin had no effect on the anti-IIa activity of LMWH. LMWH does not bind to plasma proteins because the bulk of the LMWH chains are < 6000 D, and only heparin fractions > 6000 D bind nonspecifically to plasma proteins. As further evidence that plasma proteins do not influence the anti-IIa activity of LMWH, the rate of thrombin inhibition in plasma in the presence of LMWH is virtually identical to that in buffer containing physiological amounts of the major antithrombins. In contrast, with UFH or DS, the rate of thrombin inhibition is twofold slower in plasma than in buffer.

CONCLUSIONS

Nonspecific binding of UFH to plasma proteins most likely contributes to the variable anti-IIa response to UFH in patients with thromboembolic disease. Although DS also binds to plasma proteins, the clinical significance of this finding is unclear. In contrast, because LMWH does not bind to plasma proteins, the anti-IIa activity of LMWH should be just as predictable as its anti-Xa activity.

More effective suppression of hemostatic system activation in patients undergoing cardiac surgery by heparin dosing based on heparin blood concentrations rather than ACT

This study was designed to determine whether the maintenance of higher than usual patient-specific heparin concentrations during cardiopulmonary bypass (CPB) was associated with more effective suppression of hemostasis system activation. Thirty-one patients scheduled for repeat cardiac surgery or combined procedures (i.e., coronary revascularization + valve repair/replacement) were consented and enrolled in this study. All patients received porcine heparin and protamine and were randomly assigned to monitoring of anticoagulation by either celite ACT alone (Control, n = 16) or by kaolin ACT combined with on-site measurements of whole blood heparin concentration (Intervention, n = 15). Blood specimens collected before administration of heparin, before weaning from CPB and after administration of protamine were analyzed with a battery of coagulation assays. Patients in the intervention cohort received appreciably greater heparin doses than control patients, resulting in higher anti-Xa heparin levels at the end of CPB. Fibrinopeptide A and D-dimer levels were higher in the control group before discontinuation of CPB. Percent decrease during CPB were greater in the control group for factors V and VIII, fibrinogen and antithrombin III. Percent decrease in complement 3 was greater in the control group after protamine and bleeding times measured in the Intensive Care Unit were significantly more prolonged in this group. Maintenance of higher patient-specific heparin concentrations during CPB more effectively suppresses excessive hemostatic system activation than do standard heparin doses chosen based on measurement of ACT. These findings may explain, at least in part, the significant reduction in perioperative blood loss and blood product use when higher heparin concentrations are maintained.

Histomorphometric analysis of the effects of standard heparin on trabecular bone in vivo

Long-term heparin treatment causes osteoporosis through an as yet undefined mechanism. To investigate this phenomenon, we treated rats with once daily subcutaneous injections of heparin (in doses ranging from 0.25 to 1.0 U/g) or saline for 8 to 32 days and monitored the effects on bone both histomorphometrically and by serial measurements of urinary type 1 collagen cross linked-pyridinoline (PYD) and serum alkaline phosphatase, markers of bone resorption and formation, respectively. Histomorphometric analysis of the distal third of the right femur in the region proximal to the epiphyseal growth plate showed that heparin induces both a time- and dose-dependent decreased in trabecular bone volume, with the majority of trabecular bone loss occurring within the first 8 days of treatment. Thus, heparin doses of 1.0 U/g/d resulted in a 32% loss of trabecular bone. Heparin-treated rats also showed a 37% decrease in osteoblast surface as well as a 75% decrease in osteoid surface. In contrast, heparin treatment had the opposite effect on osteoclast surface, which was 43% higher in heparin-treated rats, as compared with that in control rats. Biochemical markers of bone turnover showed that heparin treatment produced a dose-dependent decrease in serum alkaline phosphatase and a transient increase in urinary PYD, thus confirming the histomorphometric data. Based on these observations, we conclude that heparin decreases trabecular bone volume both by decreasing the rate of bone formation and increasing the rate of bone resorption.

An oral ivermectin regimen that eradicates pinworms (Syphacia spp.) in laboratory rats and mice

Pinworm infection, a common problem in laboratory rodent colonies, is difficult to control because anthelmintics like ivermectin eliminate adult worms but have no effect on ova, which can survive ex vivo for prolonged periods. On the premise that repeated treatments with ivermectin would keep rodents parasite-free until all ova matured into ivermectin-susceptible worms in vivo or died in vivo or ex vivo, 80 rats and 25 mice heavily infected with pinworms (Syphacia obvelata and S. muris) were randomized to receive two to five courses of ivermectin 3 days apart or no treatment. During each treatment, ivermectin was given for 4 days in the drinking water; based on water consumption, the mean ivermectin dose was 2.9 and 4.0 mg/kg of body weight per day in rats and mice respectively. Ova production was monitored by weekly cellophane tape tests; 29 to 32 weeks after treatment ended, all rodents were euthanized, and their evacuated large intestinal contents were examined for adult pinworms and ova. Despite intermittently negative cellophane tape test results in untreated rodents (10 rats and 5 mice), all were infected with parasites at the end of the follow-up period. These findings underscore the limitations of the tape test for diagnosis of pinworm infection. After two courses of ivermectin, 1 of 10 rats and four of five mice were infected, whereas after three courses only 1 of 40 rats and one of five mice had parasites. In contrast, none of the 20 rats or 10 mice given either four or five courses of ivermectin had parasites at 30 to 32 weeks of follow-up evaluation. This simple and well-tolerated ivermectin regimen may help to treat and control pinworm infection in laboratory rodent colonies.

Elevated fibrinopeptide A and B levels during thrombolytic therapy: real or artefactual?

There is good evidence that thrombolytic therapy induces a procoagulant state that retards the lytic process and triggers reocclusion. Thus, both in experimental animal systems and in humans, potent inhibitors of platelets and antithrombin III-independent thrombin inhibitors have been shown to be better than heparin at accelerating thrombolysis and preventing reocclusion. These in vivo observations have lent credence to the concept that elevated FPA levels that are suppressed by heparin reflect systemic activation of coagulation during the thrombolytic process. However, this concept may not be correct. Thus, when heparin is given in conjunction with plasminogen activators only modest increases in FPA levels are found, and our data suggest that this is due, at least in part, to the activity of enzymes other than thrombin. In the absence of concomitant heparin, thrombolytic therapy causes a much greater increase in the FPA values. These high FPA values are rapidly reduced by heparin, even though heparin has limited antithrombotic activity in the setting of pharmacologic thrombolysis. Based on these considerations, we believe that plasma FPA and desarginine FPB levels should not be used as specific markers of thrombin activity during the course of thrombolytic therapy and suppression of elevated FPA values by heparin should not be accepted as evidence that heparin is effective in this clinical setting.

Evaluation of a soluble fibrin assay in patients with suspected pulmonary embolism

In order to determine the clinical utility of an enzyme immunoassay (EIA) for soluble fibrin in patients with suspected pulmonary embolism (PE), 195 unselected patients with suspected PE underwent blood sampling for measurement of plasma levels of soluble fibrin, and objective testing for PE. A soluble fibrin result of < or = 0.75 micrograms/ml showed a sensitivity of 100% for PE and a specificity of 12.8%, whereas a soluble fibrin result of < or = 1.35 micrograms/ml showed a sensitivity of 90.3% and a specificity of 49.4% for PE. The soluble fibrin assay has potential clinical utility in excluding PE.

Lysis of surface-localized fibrin clots by adsorbed plasminogen in the presence of tissue plasminogen activator

The ability of plasminogen adsorbed from buffer onto sulphonated silica glass or lysine-derivatized silica glass to lyse fibrin I clots has been investigated. Clots were formed around the test surface by adding reptilase to fibrinogen solutions in which the surfaces were immersed. Tissue plasminogen activator (t-PA) was then added and the extent of clot lysis was determined by measuring the levels of the specific plasmin cleavage product of fibrinogen, B beta 1-42 peptide. The data indicate that in the presence of t-PA, B beta 1-42 generation per mole of bound plasminogen on the lysinized material is approximately two-fold higher than on the sulphonated material. It is concluded that a preformed clot may be lysed by adsorbed plasminogen in the presence of t-PA, and that clot lysis is significantly enhanced when the plasminogen is adsorbed via its lysine binding sites.

Elevated Fibrinopeptide A and B Levels during Thrombolytic Therapy: Real or Artefactual?

There is good evidence that thrombolytic therapy induces a procoagulant state that retards the lytic process and triggers reocclusion. Thus, both in experimental animal systems and in humans, potent inhibitors of platelets and antithrombin Ill-independent thrombin inhibitors have been shown to be better than heparin at accelerating thrombolysis and preventing reocclusion. These in vivo observations have lent credence to the concept that elevated FPA levels that are suppressed by heparin reflect systemic activation of coagulation during the thrombolytic process. However, this concept may not be correct. Thus, when heparin is given in conjunction with plasminogen activators only modest increases in FPA levels are found, and our data suggest that this is due, at least in part, to the activity of enzymes other than thrombin. In the absence of concomitant heparin, thrombolytic therapy causes a much greater increase in the FPA values. These high FPA values are rapidly reduced by heparin, even though heparin has limited antithrombotic activity in the setting of pharmacologic thrombolysis. Based on these considerations, we believe that plasma FPA and desarginine FPB levels should not be used as specific markers of thrombin activity during the course of thrombolytic therapy and suppression of elevated FPA values by heparin should not be accepted as evidence that heparin is effective in this clinical setting.

Limited fibrin specificity of tissue-type plasminogen activator and its potential link to bleeding

Plasminogen activators initiate the fibrinolytic process by converting plasminogen to plasmin. Though plasminogen activators are effective in the treatment of thrombotic disorders, bleeding complications are associated with their use. The development of plasminogen activators with greater fibrin specificity was expected to reduce the incidence of bleeding complications; however, this has not occurred. In our rabbit model (a) bleeding from standardized ear incisions induced by tissue-type plasminogen activator (t-PA) is attenuated when fibrinogenolysis is reduced by the coadministration of alpha 2-antiplasmin and (b) when used in doses that produce equivalent thrombolysis, vampire bat plasminogen activator (b-PA), an agent that is more fibrin specific than t-PA, causes less bleeding than t-PA. In addition, we have found that the (DD)E complex formed as a result of degradation of crosslinked fibrin is a potent stimulator of t-PA-induced plasminogen activation but has no effect on b-PA. Fragment X, a high-molecular-weight clottable fibrinogen degradation product, accumulates after treatment with t-PA but not with t-PA given with alpha 2-antiplasmin or with b-PA. These findings suggest that there is a link between plasminogen activator-induced fibrinogenolysis and bleeding, and that the composition of fibrin within hemostatic plugs may influence susceptibility to lysis. Whether these results mean that fibrin-specific plasminogen activators like b-PA will have a better risk-to-benefit profile in humans requires rigorous testing in well-designed clinical trials. However, at the very least, our findings suggest that the development of plasminogen activators that are more fibrin specific than t-PA is a worth-while exercise.

Fibrin clot lysis by tissue plasminogen activator (tPA) is impaired in plasma from pediatric patients undergoing orthotopic liver transplantation

Large vessel thrombi can present life-threatening complications following orthotopic liver transplantation (OLT) in pediatric patients. We investigated the thrombolytic response to tissue plasminogen activator (tPA) of stored, pooled plasma (days 4-14 postoperatively) from 41 patients (mean age 4 years, 9 months) who underwent OLT at the Hospital for Sick Children, Toronto between 1986 and 1990. Trace-labeled fibrin clots were prepared by recalcifying 500-microliters aliquots of patient plasma spiked with 125I fibrinogen and then incubated at 37 degrees C in patient plasma in the presence or absence of tPA (0.1 or 0.3 mg/ml). At the end of the incubation period, the extent of clot lysis and concentrations of fibrinogen, plasminogen, and alpha 2 antiplasmin were determined. Pooled adult plasma was used as a control. Fibrin clot lysis in OLT plasma was significantly reduced compared with controls (P < 0.01). Initial concentrations of plasminogen were significantly reduced in OLT plasma. To determine if the low plasminogen levels limited the thrombolytic effect of tPA, we supplemented OLT plasma with purified plasminogen. Fibrin clots placed in OLT plasma containing adult levels of plasminogen showed a similar lytic response as adults. In summary, the reduced fibrinolytic response of OLT fibrin clots to tPA was due to low concentrations of plasminogen and corrected by plasminogen supplementation.

Advances in antithrombotic therapy: novel agents

Most of the clinical evaluation of the direct thrombin inhibitors has been in coronary artery disease. The recent clinical reports suggest that there is a narrower window of safety with recombinant hirudin than initially thought particularly when it is used in conjunction with thrombolytic agents and aspirin in acute myocardial infarction. The efficacy data, however, indicate that the direct thrombin inhibitors have great potential particularly in the initial management of patients with acute unstable angina and non-Q-wave infarction. There is much to learn regarding the mechanism of action, optimal dose, and optimal concomitant therapy in the use of direct thrombin inhibitors in the management of acute coronary ischaemia; and since hirudin and other direct thrombin inhibitors have so much potential in the management of acute coronary ischaemia, it is critical that dose-finding studies be performed to determine safe regimens of these agents to allow their evaluation in large-scale trials with important clinical outcomes. The direct thrombin inhibitors have also shown to have promise in the prevention of deep vein thrombosis in high-risk surgical patients. There is limited clinical data on the other novel anticoagulants which are currently being developed.

A novel and rapid whole-blood assay for D-dimer in patients with clinically suspected deep vein thrombosis

BACKGROUND

The clinical utility of using a novel whole blood assay for D-dimer (SimpliRED), alone or in combination with impedance plethysmography (IPG), was investigated in a two-center, prospective cohort study of 214 consecutive patients with clinically suspected deep vein thrombosis (DVT).

METHODS AND RESULTS

All patients underwent the SimpliRED D-dimer assay, contrast venography, and IPG. According to the results of venography, 43 patients had proximal DVT (popliteal and/or more proximal veins), 10 had isolated calf DVT, and 161 had DVT ruled out. The D-dimer had a sensitivity of 93% for proximal DVT and of 70% for calf DVT, an overall specificity of 77%, and a negative predictive value of 98% for proximal DVT. The sensitivity and specificity of IPG for proximal DVT were 67% and 96%, respectively. When analyzed in combination with the IPG results, it was determined that (1) the combination of a negative D-dimer and a normal IPG had a negative predictive value of 97% for all DVT and of 99% for proximal DVT and occurred in 58% of patients (likelihood ratio, 0.1) and (2) the combination of a positive D-dimer and an abnormal IPG had a positive predictive value of 93% for any DVT and of 90% for proximal DVT and occurred in 14% of patients (likelihood ratio, 42.6). When the D-dimer and IPG results were discordant, it was not possible to exclude or diagnose DVT reliably; discordant results occurred in 28% of patients.

CONCLUSIONS

The SimpliRED D-dimer assay, which can be performed and interpreted at the bedside within 5 minutes, has great potential in patients with clinically suspected DVT, especially for ruling out DVT, and is complementary to IPG. The assay should be evaluated in large clinical management studies.

Activation of blood coagulation by plaque rupture: mechanisms and prevention

Inhibition of thrombosis is proving to be an important treatment goal in many clinical situations, including coronary thrombolysis, angioplasty, and unstable angina. Heparin is a potent inhibitor of thrombin and thrombin generation, but its ability to accelerate thrombolysis, prevent acute reocclusion after vascular injury in angioplasty, and prevent myocardial infarction in unstable angina is relatively limited, possibly because clot-bound thrombin plays an important role in these clinical situations. Thus, when thrombin binds to fibrin, it remains enzymatically active and relatively impervious to inactivation by heparin or other fluid-phase inhibitors. However, direct thrombin inhibitors--such as D-Phe-L-Pro-L-Arg-CH2Cl (PPACK), hirudin, hirugen, and hirulog--inhibit free and clot-bound thrombin with equal efficacy, presumably because their sites of interaction are not masked when thrombin binds to fibrin. Advanced clinical trials suggest that the direct thrombin inhibitors and 7E3, an inhibitor of platelet glycoprotein IIb/IIIa, will soon be incorporated into the armamentarium against arterial thrombosis.

Interactions of plasminogen and fibrinogen with model silica glass surfaces: adsorption from plasma and enzymatic activity studies

The adsorption of fibrinogen and plasminogen from plasma to silica glass, sulfonated silica glass, and lysine-derivatized silica glass has been investigated. The data indicate that the sulfonated material has a high affinity for both fibrinogen and plasminogen, but that the ratio of plasminogen to fibrinogen is greater on the lysine-derivatized surface. The adsorption data also suggest plasminogen as a possible contributor to the fibrinogen Vroman effect, whereby initially absorbed fibrinogen is displaced from the surface. The plasmin activity of plasminogen adsorbed to the lysine-derivatized silica glass and its sulfonated precursor was assessed by both a chromogenic substrate assay and a radioimmunoassay for the plasmin cleavage product of fibrinogen, the B beta 1-42 peptide. The data indicate that 1) the adsorbed plasminogen is not inherently plasmin-like; 2) the enzymatic activity associated with the bound plasminogen is significantly enhanced on both surfaces in the presence of activator; and 3) in the presence of activator, the plasmin activity per mole of bound plasminogen on the lysinized material is approximately a factor of two greater than on the sulfonated material based on the chromogenic substrate assay, and a factor of four greater based on the B beta 1-42 radioimmunoassay. The lysinized material thus exhibits several properties that are different from its sulfonated precursor. It adsorbs more plasminogen relative to fibrinogen after the Vroman peak, and this adsorbed plasminogen appears to be in a conformation that is more readily activated to plasmin. Once activated, the surface bound plasmin shows enhanced ability to cleave either a low molecular weight chromogenic substrate or a macromolecular substrate.(ABSTRACT TRUNCATED AT 250 WORDS)

Alpha 2-antiplasmin supplementation inhibits tissue plasminogen activator-induced fibrinogenolysis and bleeding with little effect on thrombolysis

Tissue plasminogen activator (t-PA) causes fibrinogen proteolysis when alpha 2-antiplasmin levels fall, and this may contribute to t-PA-induced hemorrhage. Because clot-bound plasmin is protected from alpha 2-antiplasmin inhibition, we tested the possibility that alpha 2-antiplasmin supplementation would block t-PA-induced fibrinogenolysis and bleeding without affecting thrombolysis. When added to human or rabbit plasma, alpha 2-antiplasmin inhibits t-PA-induced fibrinogenolysis, but hat little effect on the lysis of 125I-fibrin clots. To examine its effect in vivo, rabbits with preformed 125I-labeled-jugular vein thrombi were randomized to receive t-PA, t-PA and alpha 2-antiplasmin, or saline. alpha 2-Antiplasmin infusion produced a modest decrease in t-PA-induced thrombolysis (from 40.2% to 30.1%, P = 0.12), but reduced fibrinogen consumption from 87% to 27% (P = 0.0001), and decreased blood loss from standardized ear incisions from 5,594 to 656 microliter (P < 0.0001). We hypothesize that alpha 2-antiplasmin limits t-PA-induced hemorrhage by inhibiting fibrinogenolysis and subsequent fragment X formation because (a) SDS-PAGE and immunoblot analysis indicate less fragment X formation in alpha 2-antiplasmin treated animals, and (b) when added to a solution of fibrinogen and plasminogen clotted with thrombin in the presence of t-PA, fragment X shortens the lysis time in a concentration-dependent fashion. These findings suggest that fragment X incorporation into hemostatic plugs contributes to t-PA-induced bleeding. By blocking t-PA-mediated fibrinogenolysis, alpha 2-antiplasmin supplementation may improve the safety of fibrin-specific plasminogen activators.

The effect of antithrombin III-independent thrombin inhibitors and heparin on fibrin accretion onto fibrin-coated polyethylene

Prosthetic vascular grafts become coated with a layer of fibrin that contributes to graft thrombosis and occlusion. We compared the effect of antithrombin III-independent inhibitors of thrombin with heparin for their ability to prevent fibrin accretion onto a model of a vascular graft formed in vitro by coating polyethylene tubing with thrombin bound to a layer of polymerized fibrin. Equivalent antithrombin concentrations of heparin, D-Phe-Pro-Arg CH2Cl (PPACK), recombinant hirudin (r-hirudin), and Hirulog-1 were added to barium chloride-absorbed plasma containing radiolabelled fibrinogen. Whereas, PPACK and r-hirudin persistently inhibited fibrin accretion, the inhibition by heparin was transient. Hirulog-1 had no effect on early fibrin accretion and was actually associated with enhanced accretion at 30 min (control 11.7 +/- 2.0 micrograms fibrin/cm2; Hirulog-1, 18.4 +/- 3.5 micrograms fibrin/cm2, p < 0.001). Both Hirulog-1 and r-hirudin displaced radiolabelled thrombin from the fibrin surface. Whereas hirudin-thrombin complexes are stable, Hirulog-1 produces only transient inhibition of the displaced thrombin thereby accounting for the enhanced fibrin accretion with this anticoagulant. These studies show that the antithrombin III-independent inhibitors, r-hirudin and PPACK, are more effective inhibitors of fibrin accretion onto fibrin-coated polyethylene than heparin or Hirulog-1. In addition, they emphasize the importance of determining the ability of anticoagulants to displace thrombin from fibrin and to form stable thrombin-inhibitor complexes; lack of stability of thrombin-inhibitor complexes must be countered by levels of anticoagulant that are adequate to maintain its effectiveness.

Limitations of impedance plethysmography in the diagnosis of clinically suspected deep-vein thrombosis

OBJECTIVE

To re-evaluate the accuracy of impedance plethysmography (IPG) for the detection of proximal deep-vein thrombosis (DVT).

PATIENTS

A total of 384 of 390 consecutive outpatients referred with their first episode of clinically suspected deep-vein thrombosis.

SETTING

University-based tertiary care medical center associated with a cancer clinic.

DESIGN

A retrospective analysis of a cohort of patients whose data were recorded and stored prospectively on a computerized data base over a 22-month period.

MEASUREMENTS

Patients were evaluated by a physician and underwent IPG testing. Patients with abnormal IPG tests and those with normal IPG results in whom there was a high clinical suspicion of DVT or in whom follow-up IPG testing was not feasible were referred for venography. Venography and IPG results were interpreted by a panel of independent observers. Two models of the IPG instrument were used (Codman 200 and Electrodiagnostic Instruments 800).

RESULTS

Venography (or compression ultrasound) was done in 57 patients with an abnormal IPG test and in 85 patients with normal IPG results. Impedance plethysmography was abnormal in only 37 of 56 patients with confirmed proximal-vein thrombosis (sensitivity, 66%; 95% Cl, 52% to 78%). Of the 57 patients with an abnormal IPG result, 37 had DVT (positive predictive value, 65%). The sensitivity for the detection of proximal DVT did not differ between the IPG 200 and 800 instruments (sensitivity, 63% and 71%, respectively; P > 0.2). Of the 19 proximal-vein thrombi not detected by IPG, 12 (63%) were occlusive and 11 (58%) involved at least the popliteal and superficial femoral veins.

CONCLUSIONS

At our center, IPG has a far lower sensitivity for proximal-vein thrombosis than has been previously reported for symptomatic outpatients. The reason for this low sensitivity is unclear. Our findings indicate that centers using IPG as the initial diagnostic test for suspected DVT should be aware of this potential problem and should consider re-evaluating the sensitivity of their IPG machines by performing venography in a cohort of their patients with normal test results.

The role of protected extracellular compartments in interactions between leukocytes, and platelets, and fibrin/fibrinogen matrices

Polymorphonuclear leukocytes express multiple surface receptors that mediate their adhesion to extracellular matrices and to other cells. These receptors also play roles in cell migration and phagocytosis. We have studied the role of one class of polymorphonuclear leukocytes surface receptors, the beta 2 integrins, in the interactions of these cells with fibrinogen. We have found that the beta 2 integrins, CD11b/CD18 (complement receptor three) and CD11c/CD18 mediate attachment of polymorphonuclear leukocytes to fibrinogen-coated surfaces. Polymorphonuclear leukocytes must be stimulated with chemoattractants, such as fMLP, or with cytokines, such as tumor necrosis factor to bind to fibrinogen via these integrins. Moreover, each of these integrins interacts with a different segment of the fibrinogen molecule. PMN adherence to fibrinogen via CD11b/CD18 depends on the carboxy terminus of fibrinogen, whereas adherence via CD11c/CD18 depends on the amino terminus of fibrinogen's alpha-chain. One of the physiological consequences of these interactions is that polymorphonuclear leukocytes stimulated with either chemoattractants or TNF form protected compartments at their interface with fibrinogen-coated surfaces and that elastase released into these compartments is inaccessible to protease inhibitors present in the plasma. These protected compartments exclude plasma proteins of > 40,000 daltons such as alpha 1 anti-proteinase, thereby allowing polymorphonuclear leukocyte proteases to degrade matrix proteins within this compartment without interference by plasma anti-proteinases.

Sustained antithrombotic activity of hirudin after its plasma clearance: comparison with heparin

Thrombus extension in patients with venous thromboembolism is due to the accretion of fibrin onto existing thrombi. Extension is promoted by both circulating and thrombus-bound thrombin, which convert fibrinogen to fibrin. Heparin is an effective antithrombotic agent, but it requires continuous administration to achieve persistent inhibition of thrombus extension. Heparin is highly effective in inhibiting fluid phase thrombin, but is a relatively ineffective inhibitor of thrombus-bound thrombin. Hirudin, unlike heparin, inactivates both circulating and fibrin-bound thrombin and, therefore, has the potential to prevent thrombus extension even after a short course of treatment. The aim of this study was to evaluate the time course of the accretion of new fibrin onto preexisting rabbit jugular vein thrombi after a 3-hour infusion of saline, heparin, and hirudin. Heparin and recombinant (r)-hirudin (CGP 39399) were infused at doses that doubled the activated partial thromboplastin time (aPTT). At the end of the 3-hour infusions in rabbits treated with saline, heparin (0.75 mg/kg), or r-hirudin (1.25 mg/kg), accretion of 125I-fibrinogen was 59 +/- 5 micrograms, 34 +/- 4 micrograms, and 21 +/- 2 micrograms, respectively (heparin and r-hirudin v saline, P less than .01; r-hirudin v heparin, P less than .01). Three hours after the end of the infusions, the accreted 125I-fibrinogen in the saline-, heparin-, and hirudin-treated animals was 89 +/- 6 micrograms, 51 +/- 7 micrograms, and 23 +/- 3 micrograms, respectively; 9 hours after the end of the infusions, the accreted 125I-fibrinogen was 112 +/- 9 micrograms, 82 +/- 7 micrograms, and 25 +/- 3 micrograms, respectively. aPTT and thrombin clotting time (TCT) returned to the baseline value 90 minutes after the end of heparin or r-hirudin infusion. During in vitro experiments, human fibrin clots previously incubated in human plasma containing r-hirudin did not promote fibrinopeptide A (FPA) generation when washed and then incubated in human plasma in the absence of thrombin inhibitors. This persistent inhibition of FPA production was not observed after incubation in human plasma of human plasma clots preincubated with heparin. We conclude that heparin is effective in inhibiting thrombus extension while it is present in the circulation, but that this effect is rapidly lost after its plasma clearance. In contrast, the antithrombotic activity of r-hirudin is sustained beyond its plasma clearance, presumably because of its ability to inactivate thrombus-bound thrombin. Our findings indicate that r-hirudin might be an effective antithrombotic agent even when used for short periods.

Measurement of markers of activated coagulation in antithrombin III deficient subjects

Functional antithrombin III levels were measured by factor Xa inhibition in 63 members of a large family with type 2 antithrombin III deficiency and individuals were classified as antithrombin III deficient or non-deficient according to the results. F1 + 2 and TAT complexes were measured using an ELISA and FPA levels were measured by radioimmunoassay. Thirty subjects (48%) were classified as antithrombin III deficient and 33 (52%) as antithrombin III non-deficient. The mean level of F1 + 2 was significantly higher in the deficient adults (0.87 +/- 0.26) compared to both the non-deficient adults (0.70 +/- 0.21) (p = 0.03) and the deficient adults receiving warfarin (0.16 +/- 0.01) (p less than 0.001). The differences in the mean values of TAT complexes and FPA between deficient and non-deficient individuals were not statistically significant. These findings suggest that untreated antithrombin III deficient subjects generate more thrombin than their non-deficient family members and that warfarin inhibits this thrombin formation. In this cross-sectional study, it is not possible to correlate the levels of the surrogate makers with future clinical outcome.

Plasma levels of elastase-specific fibrinopeptides correlate with proteinase inhibitor phenotype. Evidence for increased elastase activity in subjects with homozygous and heterozygous deficiency of alpha 1-proteinase inhibitor

There is indirect evidence that unopposed human neutrophil elastase (HNE) is responsible for emphysema in patients with alpha 1-proteinase inhibitor (Pi) deficiency. To directly explore this possibility, we developed an assay for fibrinopeptide A alpha 1-21 and its degradation products and used it to measure HNE activity in 128 subjects of known Pi phenotype. The mean elastase-specific fibrinopeptide (ESF) level in 49 deficient PiZ individuals is significantly higher than that in 56 PiMZ heterozygotes (4.5 and 1.5 nM, respectively; P less than 0.01), while the mean ESF value in heterozygotes is significantly elevated over that in 23 normal PiM subjects (1.5 and 0.6 nM, respectively; P less than 0.01), consistent with increased HNE activity in those deficient in the major regulator of the enzyme. These results are not due to differences in smoking history because after correction for pack-years of smoking, ESF values in PiZ subjects are fourfold higher than those in PiMZ individuals (P = 0.005), while the ESF levels in heterozygotes are threefold higher than those in PiM subjects (P = 0.02). In addition, this analysis suggests that cigarette smoking and alpha 1-proteinase inhibitor deficiency have additive effects on ESF levels thereby explaining why PiZ and some PiMZ individuals are at especially high risk for the development of lung disease if they smoke. Finally, the observation that ESF levels in nonsmoking PiZ subjects are inversely related to the percent of predicted forced expiratory volume in 1 s (FEV 1%) provides direct support for the concept that unregulated HNE activity causes alveolar septal destruction in patients with alpha 1-proteinase inhibitor deficiency.

Antithrombins: their potential as antithrombotic agents

The inhibition of thrombin is the key to the prevention and treatment of thrombotic disorders. Although heparin is an extremely effective anticoagulant, it has certain limitations that are not shared by newer thrombin inhibitors. As a result, these novel inhibitors may have advantages over heparin in certain clinical settings.

Standard and low molecular weight heparin have no effect on tissue plasminogen activator induced plasma clot lysis or fibrinogenolysis

Although heparin is often given as an adjunct to tissue plasminogen activator (t-PA), the effect of heparin on t-PA induced fibrin(ogen)olysis is controversial. To address this controversy, we examined the effects of standard and low molecular weight heparin (enoxaparine) on both t-PA induced clot lysis and t-PA mediated fibrinogenolysis in a human plasma system. Accordingly, 125I-labeled fibrin clots were incubated in t-PA containing citrated plasma in the presence or absence of these glycosaminoglycans, and the extent of thrombolysis was determined by measuring residual radioactivity of the clots, while B beta 1-42 levels were used as a specific index of fibrinogenolysis. Over a wide range of t-PA concentrations (0.1 to 1.6 micrograms/ml), neither heparin nor enoxaparine influences either t-PA induced clot lysis or t-PA mediated B beta 1-42 generation. These findings suggest that either agent could be used as an adjunct to t-PA without compromising either the thrombolytic potential of t-PA or its clot-selectivity.

Soluble fibrin degradation products potentiate tissue plasminogen activator-induced fibrinogen proteolysis

Despite its affinity for fibrin, tissue plasminogen activator (t-PA) administration causes systemic fibrinogenolysis. To investigate the mechanism, t-PA was incubated with plasma in the presence or absence of a fibrin clot, and the extent of fibrinogenolysis was determined by measuring B beta 1-42. In the presence of fibrin, there is a 21-fold increase in B beta 1-42 levels. The potentiation of fibrinogenolysis in the presence of fibrin is mediated by soluble fibrin degradation products because (a) the extent of t-PA induced fibrinogenolysis and clot lysis are directly related, (b) once clot lysis has been initiated, fibrinogenolysis continues even after the clot is removed, and (c) lysates of cross-linked fibrin clots potentiate t-PA-mediated fibrinogenolysis. Fibrin degradation products stimulate fibrinogenolysis by binding t-PA and plasminogen because approximately 70% of the labeled material in the clot lysates binds to both t-PA- and plasminogen-Sepharose, and only the bound fractions have potentiating activity. The binding site for t-PA and plasminogen is on the E domain because characterization of the potentiating fragments using gel filtration followed by PAGE and immunoblotting indicates that the major species is (DD)E complex, whereas minor components include high-molecular weight derivatives containing the (DD)E complex and fragment E. In contrast, D-dimer is the predominant species found in the fractions that do not bind to the adsorbants, and it has no potentiating activity. Thus, soluble products of t-PA-induced lysis of cross-linked fibrin potentiate t-PA-mediated fibrinogenolysis by providing a surface for t-PA and plasminogen binding thereby promoting plasmin generation. The occurrence of this phenomenon after therapeutic thrombolysis may explain the limited clot selectivity of t-PA.

CD11c/CD18 on neutrophils recognizes a domain at the N terminus of the A alpha chain of fibrinogen

Fibrinogen and fibrin serve as adhesive substrates for a variety of cells including platelets, endothelial cells, and leukocytes. Previously, we identified the C terminus of the gamma chain of fibrinogen as the region of the fibrinogen molecule that contains a ligand for CD11b/CD18 (complement receptor 3) on phorbol ester-stimulated polymorphonuclear leukocytes. In contrast, we report here that neutrophils stimulated with tumor necrosis factor adhere to fibrinogen-coated surfaces, but not to human serum albumin-coated surfaces, via the integrin CD11c/CD18 (p150/95). Monoclonal antibodies LeuM5 and 3.9, which are directed against the alpha subunit of CD11c/CD18, but not monoclonal antibodies OKM10 and OKM1, which are directed against the alpha subunit of CD11b/CD18, inhibit the adhesion of tumor necrosis factor-stimulated neutrophils to fibrinogen-coated surfaces. To identify the site on fibrinogen recognized by CD11c/CD18, we have examined the adhesion of tumor necrosis factor-stimulated neutrophils to surfaces coated with various fibrinogen fragments. Stimulated neutrophils adhere to surfaces coated with the N-terminal disulfide knot fragment of fibrinogen or fibrinogen fragment E. Moreover, peptides containing the sequence Gly-Pro-Arg (which corresponds to amino acids 17-19 of the N-terminal region of the A alpha chain of fibrinogen), and monoclonal antibody LeuM5, block tumor necrosis factor-stimulated neutrophil adhesion to fibrinogen and to the N-terminal disulfide knot fragment of fibrinogen. Thus, CD11c/CD18 on tumor necrosis factor-stimulated neutrophils functions as a fibrinogen receptor that recognizes the sequence Gly-Pro-Arg in the N-terminal domain of the A alpha chain of fibrinogen.

Clot-bound thrombin is protected from inhibition by heparin-antithrombin III but is susceptible to inactivation by antithrombin III-independent inhibitors

Propagation of venous thrombi or rethrombosis after coronary thrombolytic therapy can occur despite heparin administration. To explore potential mechanisms, we set out to determine whether clot-bound thrombin is relatively protected from inhibition by heparin-antithrombin III but susceptible to inactivation by antithrombin III-independent inhibitors. Using plasma fibrinopeptide A (FPA) levels as an index of thrombin activity, we compared the ability of thrombin inhibitors to block FPA release mediated by fluid-phase thrombin with their activity against the clot-bound enzyme. Incubation of thrombin with citrated plasma results in concentration-dependent FPA generation, which reaches a plateau within minutes. In contrast, there is progressive FPA generation when fibrin clots are incubated with citrated plasma. Heparin, hirudin, hirudin dodecapeptide (hirugen), and D-phenylalanyl-L-prolyl-L-arginyl chloromethyl ketone (PPACK) produce concentration-dependent inhibition of FPA release mediated by fluid-phase thrombin. However, heparin is much less effective at inhibiting thrombin bound to fibrin because a 20-fold higher concentration is necessary to block 70% of the activity of the clot-bound enzyme than is required for equivalent inhibition of fluid-phase thrombin (2.0 and 0.1 U/ml, respectively). In contrast, hirugen and PPACK are equally effective inhibitors of fluid- and solid-phase thrombin, while hirudin is only 50% as effective against the clot-bound enzyme. None of the inhibitors displace bound 125I-labeled thrombin from the clot. These studies indicate that (a) clot-bound thrombin is relatively protected from inhibition by heparin, possibly because the heparin binding site on thrombin is inaccessible when the enzyme is bound to fibrin, and (b) clot-bound thrombin is susceptible to inactivation by antithrombin III-independent inhibitors because the sites of their interaction are not masked by thrombin binding to fibrin. For these reasons, antithrombin III-independent inhibitors may be more effective than heparin in certain clinical settings.

Urokinase has direct catalytic activity against fibrinogen and renders it less clottable by thrombin

Recently, we demonstrated that tissue plasminogen activator directly releases fibrinopeptides A and B (FPA and FPB) from fibrinogen. The purpose of this study was to determine whether urokinase has similar activity. Incubation of urokinase with fibrinogen or heparinized plasma results in concentration-dependent FPB release unaccompanied by FPA cleavage. For equivalent amidolytic activity, high molecular weight urokinase releases twofold more FPB than the low molecular weight species. In contrast, prourokinase does not release FPB until activated to urokinase. Contaminating thrombin or plasma is not responsible for urokinase-mediated FPB release because this activity is unaccompanied by FPA or B beta 1-42 cleavage, and is unaffected by heparin, hirudin, a monospecific antibody against thrombin, aprotinin, or alpha 2-antiplasmin. FPB release reflects a direct action of urokinase on fibrinogen because release is completely inhibited by a monospecific antibody against the enzyme. Further, urokinase releases FPB from the FPB-containing substrate B beta 1-42, thus confirming its specificity for the B beta 14 (Arg)-B beta 15 (Gly) bond. In addition to FPB release, SDS-PAGE analysis of the time course of urokinase-mediated fibrinogenolysis indicates progressive proteolysis of both the A alpha- and B beta-chains of fibrinogen that occurs after FPB release is completed. As a consequence of urokinase-mediated fibrinogenolysis, there is progressive prolongation of the thrombin clotting time. These studies indicate that urokinase has direct catalytic activity against fibrinogen. By releasing FPB, a potent chemoattractant, and by rendering fibrinogen less clottable by thrombin, urokinase may participate in processes extending beyond fibrinolysis.

Effect of fibrinogen degradation products and lung ground substance on surfactant function

Acute lung injury syndromes have many characteristics including protein-rich alveolar edema, hyaline membranes, and abnormal surface tension at the alveolar air-liquid interface. Increased surface tension can occur because of a relative surfactant deficiency and/or dysfunction. It has been previously demonstrated that surfactant dysfunction occurs when plasma protein inhibitors leak into the alveolar space during the induction of the lung injury and edema formation. The present study investigated whether inhibitors that would be generated during the stage of repair from lung injury could impair surfactant function. We determined whether fibrinogen degradation products (FDP) which would be released during lysis of the fibrin(ogen)-containing alveolar exudate and hyaline membranes, and components of the lungs' ground substance could inhibit the in vitro function of a lipid extract surfactant preparation. FDP were prepared by incubating human fibrinogen with plasmin or neutrophil elastase for 4 min to 60 h and were characterized by SDS-PAGE. Early (fragment X and Y) and late (fragment D and E) plasmin-derived FDP (MW greater than 40,000) inhibited surfactant function as assessed by a bubble surfactometer. The early elastase-derived FDP also inhibited surfactant, but the later and much smaller fragments (MW less than 15,000) did not affect surfactant function. Laminin also inhibited surfactant in a dose-dependent manner. Neither hyaluronic acid nor heparan sulfate affected surfactant performance in vitro. We conclude that plasmin-induced lysis of intraalveolar fibrinogen and hyaline membranes will result in prolonged generation (i.e. days) of surfactant inhibitors.(ABSTRACT TRUNCATED AT 250 WORDS)

Use of a synthetic homologue of human fibrinopeptide A for production of a monoclonal antibody specific for the free peptide

It has been shown that epitopes reactive with one group of rabbit antibodies to human fibrinopeptide A (hFPA, A alpha 1-16) are included in its COOH-terminal region (A alpha 7-16). It was further established that Asp-7, Phe-8, and Arg-16 contribute to immunoreactivity and that intact fibrinogen and hFPA-containing fragments react poorly with such antibodies. The purpose of this investigation was to prepare a synthetic peptide corresponding to A alpha 7-16 and use it for generation of FPA-specific monoclonal antibodies (MoAbs). Such probes would allow for development of assays that could measure hFPA directly in plasma. In our approach, an ovalbumin-conjugate of the hFPA homologue served as immunogen. Mouse spleen cells were fused with the immunoglobulin nonsecretor myeloma (P3X63Ag8.653). A hybridoma (8C2-5) has been isolated that secretes an antibody (MoAb/8C2-5) with the following characteristics: (a) IgG1, kappa isotype; (b) equilibrium dissociation constant of 1.5 +/- 0.2 x 10(7) L/mol with the [125I]-labeled N-tyrosyl derivative of hFPA [( 125I] Tyr-hFPA) as ligand; (c) reacts with hFPA and dog FPA (dFPA) but not with the des Arg (A alpha 1-15) or shorter peptides; (d) does not react with intact fibrinogen or A alpha-chain of human or dog origin; (e) does not react with the elastase-generated hFPA-containing peptide A alpha 1-21. Enzyme-based immunoassays (EIAs) have been developed for measuring plasma hFPA levels in the range 3 x 10(-8) to 5 x 10(-7) mol/L. Since it has already been shown by a number of investigators that hFPA levels in patients with overt defibrination fall into this range, we propose that the MoAb/8C2-5-based assays may serve as useful clinical tools in screening patients at risk of thrombosis. The 8C2-5 antibody may also be helpful in studies dealing with congenital dysfibrinogenemias, particularly in identifying heterozygous propositi with amino acid substitutions at any position within the A alpha 7-16 region. Finally, due to its cross-reactivity with dFPA, assays using this antibody should also be valuable in the canine experimental thrombosis model studies.

Human tissue-type plasminogen activator releases fibrinopeptides A and B from fibrinogen

In five patients with venous thromboembolic disease treated with recombinant tissue-type plasminogen activator (rt-PA), there was a marked increase in the mean concentrations of fibrinopeptide A (from 0.6 to 5.9 nM; P less than 0.0001) and desarginine fibrinopeptide B (from 5.6 nM to 24.1 nM; P less than 0.01) 30 min after a bolus of rt-PA (0.6 mg/kg). Thrombin was unlikely to be responsible because the levels of desarginine fibrinopeptide B exceeded those of fibrinopeptide A and the changes occurred despite concomitant heparin therapy. The purpose of this study therefore, was to determine whether rt-PA directly releases the fibrinopeptides from fibrinogen. Incubation of rt-PA with heparinized plasma or purified fibrinogen resulted in time and dose-dependent release of both fibrinopeptide A and B. Contaminating thrombin was not responsible for this activity by the following criteria: the rate of rt-PA mediated fibrinopeptide B release was considerably faster than that of fibrinopeptide A, and fibrinopeptide release was unaffected by heparin, hirudin, or a monospecific antithrombin IgG. Aprotinin also had no effect on fibrinopeptide release, indicating that this activity was not plasmin mediated. Fibrinopeptide release was shown to be due to rt-PA because this activity was completely blocked by a monoclonal antibody against the enzyme. Further, the specificity of rt-PA for the thrombin cleavage sites on fibrinogen was confirmed by the demonstration that rt-PA released fibrinopeptide A or fibrinopeptide B from fibrinopeptide A or B-containing substrates, respectively. These studies thus demonstrate that (a) rt-PA releases fibrinopeptides A and B from fibrinogen thereby indicating that this enzyme is not specific for plasminogen, and (b) plasma fibrinopeptide A and desarginine fibrinopeptide B levels are not specific markers of thrombin action on fibrinogen in patients receiving rt-PA.

Elastase-mediated fibrinogenolysis by chemoattractant-stimulated neutrophils occurs in the presence of physiologic concentrations of antiproteinases

Plasma levels of the HNE-derived fibrinopeptide A alpha 1-21 reflect in vivo enzyme activity. To provide a possible explanation for the presence of circulating A alpha 1-21 in individuals with normal plasma antiproteinase concentrations we investigated whether PMN-associated HNE is more resistant to inhibition than the free enzyme. PMN were stimulated to migrate across 125I-fibrinogen-coated nitrocellulose filters in response to 10(-7) M FMLP, and the extent of fibrinogenolysis was determined by measuring release of A alpha 1-21 and 125I-labeled fibrinogen degradation products. The fibrinogenolytic activity of migrating PMN was then compared with that of free HNE present in PMN lysates or secreted by PMN stimulated with FMLP. Whereas the fibrinogenolytic activity of soluble HNE was completely inhibited by low concentrations (1%) of plasma or serum and macromolecular antiproteinase (alpha 1 proteinase-inhibitor and soybean trypsin-inhibitor), even in the presence of undiluted plasma or serum the activity of the migrating PMN was incompletely blocked (81-85%). Further, concentrations of alpha 1 proteinase-inhibitor and soybean trypsin-inhibitor that totally inhibited free HNE activity also incompletely blocked (88-89%) the fibrinogenolytic activity of migrating PMN, indicating that FMLP-stimulated PMN demonstrate significant fibrinogenolytic activity in the presence of antiproteinases as small as 20,000 mol wt. A specific low molecular weight HNE inhibitor (MeO-Suc-Ala2-Pro-ValCH2Cl), however, totally blocked PMN-mediated fibrinogenolysis without affecting intracellular HNE activity, HNE secretion from PMN, or PMN migration in response to FMLP. These findings support the hypothesis that PMN migrating on a fibrinogen-coated surface form zones of close contact with fibrinogen, thus preventing access of plasma antiproteinases to HNE released at the cell-substrate interface. The occurrence of this phenomenon in vivo would explain the presence of circulating A alpha 1-21 in individuals with normal antiproteinase concentrations.

Increased neutrophil elastase activity in cigarette smokers

We compared plasma levels of the neutrophil elastase-derived fibrinopeptide A-alpha-1-21 in healthy cigarette smokers with those in nonsmokers. The mean A-alpha-1-21 concentration was fivefold higher (95% confidence interval [CI], 3.0 to 9.6) in ten cigarette smokers than in 20 healthy nonsmokers (2.0 nmol/L compared with 0.4 nmol/L; p less than 0.0001). To evaluate the acute effect of smoking on enzyme activity, a second group of ten smokers was studied. After refraining from smoking for 12 hours, each person smoked three cigarettes. The mean A-alpha-1-21 level in the second group of smokers was not different from that in the first group of smokers (1.8 nmol/L compared with 2.0 nmol/L) but was fivefold higher (95% CI, 2.6 to 8.7) than that in the nonsmokers (1.8 nmol/L compared with 0.4 nmol/L; p less than 0.0001). After smoking three cigarettes, subjects had a twofold elevation (95% CI, 1.6 to 3.5) in the mean A-alpha-1-21 concentration (from 1.8 nmol/L to 4.1 nmol/L; p = 0.002). Our data show that cigarette smoking perturbs the in-vivo elastase-antielastase balance and thus may produce lung disease through this mechanism.

Dysfibrinogenemia in obstructive liver disease

Acquired dysfibrinogenemia was documented in a 4-year-old child with obstructive jaundice of 1-month duration, secondary to a choledochal cyst involving the distal common bile duct. It was characterized by decreased thrombin coagulable protein with elevated immunoassayable fibrinogen resulting in abnormal thrombin and reptilase times. The liver morphology was compatible with extrahepatic obstruction, without evidence of cirrhosis or hepatocyte abnormality. All the coagulation abnormalities promptly resolved after surgical correction of the obstruction. Dysfibrinogenemia has been associated with serious liver disease in adults, including tumors, chronic active hepatitis, and cirrhosis, but never with isolated obstructive jaundice. This report documents a case of acquired dysfibrinogenemia due to extra-hepatic biliary obstruction and also emphasizes the importance of the consideration of this disorder in coagulation abnormalities associated with hepatobiliary disease.

Immunologic identification of the cleavage products from the A alpha- and B beta-chains in the early stages of plasmin digestion of fibrinogen

Fragment X components (Mr 225,000 to 333,000) were distinguished on sodium dodecyl sulfate polyacrylamide gels. Western blotting with monoclonal antibodies to A alpha-chain segments demonstrated that the A alpha-chains of fibrinogen and the largest fragment X components (Mr 285,000-340,000) contained both A alpha 259-276 and A alpha 540-554. Fragment X components of Mr 270,000-285,000 contained A alpha 259-276 but lacked A alpha 540-554, whereas the smallest fragment X components (Mr 225,000-270,000) contained neither A alpha 540-554 nor A alpha 259-276. Studies of the small peptides generated during fragment X formation complemented the studies of the large molecules, by demonstrating peptides containing both A alpha 259-276 and A alpha 540-554 (Mr 41,600-41,800 and Mr 38,700-38,900), peptides containing A alpha 540-554 but not A alpha 259-276 (Mr 20,500-21,000 and Mr 17,300-17,500) and peptides containing only A alpha 259-276 (Mr 23,600-24,000 and Mr 20,500-21,000). Cleavage of B beta 1-42 from the amino terminal ends of the B beta-chains, measured with a specific radioimmunoassay, was linear until 1.6 moles per mole of fibrinogen had been released, and coincided with loss of the central and carboxy terminal A alpha-chain regions, i. e. A alpha 259-276 and A alpha 540-554. Based on present and previously reported data, a model is proposed for the evolution of the heterogeneous group of fragment X derivatives from fibrinogen with the simultaneous release of small peptides.(ABSTRACT TRUNCATED AT 250 WORDS)

Development of an assay for in vivo human neutrophil elastase activity. Increased elastase activity in patients with alpha 1-proteinase inhibitor deficiency

Leukocyte extracts contain enzymes that digest fibrinogen and release a fibrinopeptide A-containing fragment. This study was undertaken to identify the responsible proteinase and to characterize the fibrinopeptide A-containing fragment so that it could be used as an index of enzyme activity. Both the fibrinogenolytic activity and the release of the fibrinopeptide A-containing fragment mediated by the leukocyte extracts were shown to be due to human neutrophil elastase (HNE) by the following criteria: activity was completely blocked by a specific HNE inhibitor or by adsorbing HNE from the extracts with a monospecific antibody and reconstitution with purified HNE restored the ability to release the fibrinopeptide A-containing fragment. This fragment was not released by a variety of other proteinases or by HNE-inhibitor complexes indicating that, at least with respect to the enzymes tested, it is a specific product of HNE and its release requires the free enzyme. By separating the products of HNE digestion of fibrinogen using high performance liquid chromatography, identifying the immunoreactive fractions and subjecting them to amino acid analysis, the fragment was identified as A alpha 1-21, indicating an HNE cleavage site at the Val(A alpha 21)-Glu(A alpha 22) bond. The mean plasma A alpha 1-21 level was markedly higher in patients with alpha 1-proteinase inhibitor deficiency as compared to healthy controls (0.2 nM vs. 7.9 nM; P less than 0.0001), consistent with increased in vivo HNE activity in these individuals.

Development of a radioimmunoassay for the fibrinogen-derived peptide B beta 1-42

The peptide B beta 1-42 is the initial cleavage product of plasmin-mediated proteolysis of the NH2-terminal region of fibrinogen or fibrin I, while beta 15-42 is the major fragment released by plasmin degradation of fibrin II. Numerous studies have described the measurement of plasma B beta 1-42 levels as an index of plasmin activity. Previous assays were indirect and included quantitation of thrombin-increasable fibrinopeptide B immunoreactivity (TIFPB) or measurement of beta 15-42 with an antiserum (132) which cross-reacted with B beta 1-42. We report on a new antiserum (R142) directed against B beta 1-42 which does not cross-react with beta 15-42 or fibrinopeptide B. Employing this antiserum, a specific assay for B beta 1-42 was developed. This assay was used to measure plasmin-mediated B beta 1-42 release from fibrinogen and its subsequent proteolysis by thrombin. The selectivity constant (Kcat/Km) for thrombin cleavage of the B beta 14-15 bond of B beta 1-42 was 10(5)-fold less than that for proteolysis of the same bond in the intact fibrinogen molecule, thus explaining the stability of this peptide in the presence of thrombin activity in the blood. Similarly, the selectivity constant for plasmin cleavage of the B beta 21-22 bond of B beta 1-42 was 140-fold less than that for proteolysis of the B beta 42-43 bond of fibrinogen, indicating that secondary plasmin attack of the B beta 1-42 molecule is not physiologically important. The specific B beta 1-42 assay provided excellent recovery of peptide added to blood or plasma. Comparison of B beta 1-42 levels with TIFPB values in 37 patient samples yielded good correlation over a wide range of levels (r2 = 0.91). The median plasma B beta 1-42 level in 15 normal individuals was 1.2 pmol/mL. This is similar to the previously reported normal range for TIFPB (1 to 4 pmol/mL) but is higher than the normal level of 0.4 pmol/mL reported with the assay employing antiserum 132. This discrepancy reflects rapid removal of Arg (B beta 42) by plasma carboxypeptidase activity resulting in 50% loss of B beta 1-42 immunoreactivity with antiserum 132 but no loss with R142. To circumvent this problem, we have developed a beta 15-42 antiserum (R154) which, like antiserum 132, cross-reacts with B beta 1-42. However, B beta 1-42/beta 15-42 immunoreactivity with R154 is stable in the presence of carboxypeptidase activity.(ABSTRACT TRUNCATED AT 400 WORDS)