Biomedical subjects

Brad L Steenwyk

Publications and source records attributed to Brad L Steenwyk.

4 recordsLinked to original sources

PubMed2007

Epsilon-aminocaproic acid inhibition of fibrinolysis in vitro: should the 'therapeutic' concentration be reconsidered?

The therapeutic concentration of epsilon-aminocaproic acid (EACA) has been 130 microg/ml or greater for nearly 50 years. We tested the effects on clot growth/disintegration of EACA with a plasmatic model of hyperfibrinolysis in vitro. Human plasma was exposed to 1000 U/ml tissue-type plasminogen activator containing 0, 13, 65 or 130 microg/ml EACA, with clot growth/disintegration kinetics quantified via thrombelastography. Data were analyzed with one-way analysis of variance or Kruskal-Wallis analysis of variance as appropriate. Exposure of plasma to 1000 U/ml tissue-type plasminogen activator resulted in a brief-lived clot, lasting 2 min. EACA at all concentrations tested significantly increased the rate of clot growth compared with samples with 0 microg/ml EACA. Clot strength was significantly increased by EACA in a concentration-dependent fashion. Similarly, EACA significantly prolonged the time of onset of clot lysis and decreased the rate of lysis. Samples with 130 microg/ml EACA had no sign of lysis present for 30 min. Subtherapeutic to therapeutic concentrations of EACA significantly attenuated or abolished fibrinolysis in the presence of a concentration of tissue-type plasminogen activator more than 2000-fold that encountered systemically during cardiopulmonary bypass. Further clinical investigation is warranted to determine whether smaller concentrations of EACA could provide a reduction in bleeding with a concomitant decrease in thrombotic complications.

Aminocaproic Acid↗

PubMed2007

Qualitative thrombelastographic detection of tissue factor in human plasma.

BACKGROUND: Tissue factor (TF) is the principal in vivo initiator of coagulation, with normal circulating TF concentrations reported to be approximately 23-158 pg/mL. However, patients with atherosclerosis or cancer have been reported to have TF concentrations ranging between 800 and 9000 pg/mL. Of interest, thrombelastographic (TEG)-based measures of clot initiation and propagation have demonstrated hypercoagulability in such patients at risk for thromboembolic events. Thus, our goal in the present investigation was to establish a concentration-response relationship of the effect of TF on TEG variables, and determine specificity of TF-mediated events with a monoclonal TF antibody. METHODS: Thrombelastography was performed on normal human plasma exposed to 0, 500, 1000, or 2000 pg/mL TF. Additional experiments with plasma exposed to 0 or 750 pg/mL TF in the presence or absence of a monoclonal TF antibody (1:360 dilution, 10 min incubation) were also performed. Clot initiation time (R) and the speed of clot propagation (MRTG, maximum rate of thrombus generation) were determined. RESULTS: The addition of TF to normal plasma resulted in a significant, concentration-dependent decrease in R and increase MRTG values. The addition of TF antibody to samples with TF significantly increased R and decreased MRTG values compared to samples with TF addition. CONCLUSIONS: In conclusion, changes in TEG variables in conjunction with use of a TF antibody can detect pathological concentrations of TF in human plasma in vitro. Further investigation is warranted to determine if TEG(R)-based monitoring could assist in the detection and prevention of TF-initiated thromboembolic events.

Blood Coagulation↗

PubMed2006

Argatroban, bivalirudin, and lepirudin do not decrease clot propagation and strength as effectively as heparin-activated antithrombin in vitro.

BACKGROUND: Heparin-induced thrombocytopenia is a potentially limb- and life-threatening response to heparin exposure. Direct thrombin inhibitors (DTIs) have been reported to provide anti-coagulation for cardiopulmonary bypass; however, clot formation within the cardiopulmonary bypass circuit has been reported after the administration of DTIs. We present a case of thrombosis of the cardiopulmonary bypass circuit and, ultimately, death after argatroban administration. An in vitro thrombelastographic assessment of the effects of DTIs on clot kinetics was consequently performed to determine potential causes for this complication. METHODS: Normal human plasma was unmodified or exposed to heparin (1, 2, 3 U/ml), argatroban (5, 10, 50 microg/ml), bivalirudin (12, 20, 120 microg/ml), or lepirudin (3, 6, 10 microg/ml) before activation with tissue factor/kaolin in a thrombelastograph. Clot initiation (R, reaction time), propagation (MTG, maximum thrombus generation), and strength (MG, maximum elastic modulus) were determined. Analysis of variance was performed, with p < 0.05 considered significant. RESULTS: Compared with unmodified plasma, heparin significantly prolonged R and essentially reduced MTG and MG to the limits of detection in an activity-dependent fashion. In general, the DTIs tested prolonged R in a concentration-dependent fashion but did not diminish MTG or MG nearly as well as heparin. The only exception was 10 microg/ml lepirudin, which eliminated coagulation. CONCLUSIONS: DTIs demonstrated a significant prolongation of clot initiation but poor attenuation of propagation and strength. Further in vitro and clinical investigations to design a heparin-equivalent regimen to provide anti-coagulation for patients with heparin-induced thrombocytopenia are indicated.

Anticoagulants↗

PubMed2006

Contact activation prolongs clot lysis time in human plasma: role of thrombin-activatable fibrinolysis inhibitor and Factor XIII.

BACKGROUND: Contact activation system proteins (e.g., Factor XII, kallikrein) have been implicated as direct or indirect activators of plasminogen. However, contact activation and Factor XI have enhanced thrombin-activatable fibrinolysis inhibitor (TAFI) activation and decreased fibrinolysis, and Factor XIII (FXIII) also delays fibrinolysis via alpha(2)-anti-plasmin deposition on fibrin polymers. Thus, the goals of this study were to define how fibrinolysis is modulated in human plasma by contact or tissue factor (TF) activation, and what role TAFI and FXIII plays in this system. METHODS: Normal, TAFI-deficient and TAFI-deficient/FXIII-supplemented plasma was exposed to tissue-type plasminogen activator and activated with either celite or TF. Clot growth/disintegration kinetics were documented with thrombelastography. RESULTS: Normal plasma activated with celite had significantly prolonged onset and duration of clot lysis compared with samples activated with TF. TAFI-deficient plasma activated with celite was noted to have a duration of clot lysis not different from samples activated with TF, but a significant difference in time to onset of lysis persisted. Celite activation of TAFI-deficient/FXIII-supplemented plasma showed significantly prolonged onset and duration of clot lysis compared with samples activated with TF. CONCLUSIONS: Primarily TAFI, and to a lesser extent FXIII, contributed to contact system protein-mediated attenuation of fibrinolysis. Clinical investigation of these phenomena is warranted in clinical settings involving contact activation (e.g., intra-aortic balloon pumps and ventricular assist devices) to determine whether these devices modulate fibrinolysis and perhaps contribute to thromboembolic morbidity.

Carboxypeptidase B2↗