Ultrasound fibrin clot destruction in vitro in the presence of fibrinolytic agent

Kinetics of fibrin clots destruction under ultrasonic cavitation

We studied the kinetic features of fibrin clot destruction in vitro under the action of ultrasonic cavitation generated by low-frequency (36 kHz) ultrasound (US) with the intensity I0  of 4.4–51.2 W/cm2, using a flexible waveguide concentrator. It was established that the rate of US destruction of clots immersed in saline at the initial stage of the process is proportional to I0 in the range of 12–51 W/cm2, corresponds to first-order kinetics, and is determined by the erosive processes without the formation of D-dimers and other fibrinolysis products at a minimum contribution of sonochemical reactions. The clot destruction rate is maximum at the initial time moment and decreases with increasing the US exposure duration (by 35 % in 1 min and by 72 % by the end of the second minute at I0 = 51.2 W/cm2). It was shown that in order to increase the completeness of clot destruction at a minimum administered US dose, it is advisable to minimize the US exposure time when using the highest values of the US intensity limited by the level of safe cavitation exposure to the vascular wall, hemostasis, and blood cells.

Effects of low frequency ultrasound on some properties of fibrinogen and its plasminolysis

Background

Pharmacological thrombolysis with streptokinase, urokinase or tissue activator of plasminogen (t-PA), and mechanical interventions are frequently used in the treatment of both arterial and venous thrombotic diseases. It has been previously reported that application of ultrasound as an adjunct to thrombolytic therapy offers unique potential to improve effectiveness. However, little is known about effects of the ultrasound on proteins of blood coagulation and fibrinolysis. Here, we investigated the effects of the ultrasound on fibrinogen on processes of coagulation and fibrinogenolysis in an in vitro system.

Results

Our study demonstrated that low frequency high intensity pulse ultrasound (25.1 kHz, 48.4 W/cm2, duty 50%) induced denaturation of plasminogen and t-PA and fibrinogen aggregates formation in vitro. The aggregates were characterized by the loss of clotting ability and a greater rate of plasminolysis than native fibrinogen. We investigated the effect of the ultrasound on individual proteins. In case of plasminogen and t-PA, ultrasound led to a decrease of the fibrinogenolysis rate, while it increased the fibrinogenolysis rate in case of fibrinogen. It has been shown that upon ultrasound treatment of mixture fibrinogen or fibrin with plasminogen, t-PA, or both, the rate of proteolytic digestion of fibrin(ogen) increases too. It has been shown that summary effect on the fibrin(ogen) proteolytic degradation under the conditions for combined ultrasound treatment is determined exclusively by effect on fibrin(ogen).

Conclusions

The data presented here suggest that among proteins of fibrinolytic systems, the fibrinogen is one of the most sensitive proteins to the action of ultrasound. It has been shown in vitro that ultrasound induced fibrinogen aggregates formation, characterized by the loss of clotting ability and a greater rate of plasminolysis than native fibrinogen in different model systems and under different mode of ultrasound treatment. Under ultrasound treatment of plasminogen and/or t-PA in the presence of fibrin(ogen) the stabilizing effect fibrin(ogen) on given proteins was shown. On the other hand, an increase in the rate of fibrin(ogen) lysis was observed due to both the change in the substrate structure and promoting of the protein-protein complexes formation.

Combined low-frequency ultrasound and streptokinase intravascular destruction of arterial thrombi in vivo

To prevent a distal embolization in the course of ultrasound (US) angioplasty, we combined US thrombus disruption in peripheral artery in vivo with simultaneous administration of streptokinase (SK). Acute thrombosis was induced in the femoral arteries of 23 dogs. Two hours after thrombus formation, thrombus destruction was performed using US (36 kHz) and by a combined US+SK (75,000 U/kg) administration. The results showed that thrombi were disrupted completely by 1.5 ± 0.5 min US. A combined US+SK action resulted in activation of fibrinolysis, as indicated by the increase in the content of fibrinogen and fibrin degradation products and D-dimers by a factor of 1.5-2.0 after 120 min from start of treatment compared with the SK lysis. The duration of clot destruction did not change; the distal embolization was not indicated; platelet aggregation activity dropped after thrombus destruction. In summary, intravascular thrombus destruction by a combined US and SK action in vivo is accompanied by enhancing the enzymatic fibrinolysis and lowering the platelet aggregation activity that assists in preventing the distal embolization of the resulting clot debris.

Direct action on the molecule is one of several mechanisms by which ultrasound enhances the fibrinolytic effects of reteplase

Enhanced fibrinolytic reperfusion therapy may improve the outcome in embolic stroke, where ultrasound exposure has been shown to be one option. We recently verified that the fibrinolytic properties of streptokinase were modulated following ultrasound exposure of the molecule. We have now explored this possibility following ultrasound exposure of the reteplase molecule. The effects on clot lysis of reteplase and ultrasound both separately and in combination were studied by evaluating cumulated release of haemoglobin from whole blood clots following 1 h of exposure. Specifically, we investigated how clot lysis was modulated following pulsed 1 MHz ultrasound pre-exposure of the reteplase solution at intensities ranging between 0.125 and 4 W/cm2 spatial-average temporal-average intensity (SATA) and the effects of reteplase following 1 h of pre-exposure of clots to ultrasound at high intensity (4 W/cm2SATA). Significant enhancement of clot lysis during concomitant reteplase and pulsed ultrasound exposure were observed in two intensity ranges: 0.125-0.25 and 2-4 W/cm2SATA. Pre-exposing reteplase solution to ultrasound significantly increased clot lysis only in the lower intensity range. At high ranges, pre-exposure of clots to ultrasound was followed by an increased fibrinolytic action of reteplase. Pre-exposing reteplase solution to low-intensity ultrasound induced changes in the reteplase molecule that enhanced its fibrinolytic effects. Although this effect disappeared at moderately higher ultrasound intensity, the pre-exposure of clots to ultrasound of higher intensity induced increased fibrinolytic effects of reteplase solution.

Low-energy ultrasound exposure of the streptokinase molecule may enhance but also attenuate its fibrinolytic properties

INTRODUCTION

This study explores the mechanisms of ultrasound-enhanced fibrinolysis by investigating the effects of pre-exposure to pulsed high-frequency, low-energy ultrasound on the fibrinolytic properties of streptokinase.

MATERIALS AND METHODS

Fibrinolytic activity was measured as haemoglobin release from blood clots. The fibrinolytic effects of streptokinase and ultrasound separately and in combination were studied by evaluating cumulative percentages of haemoglobin release following 1 h of exposure using two clots, one for intervention and the other concomitantly as control. In particular, the effects of exposure to ultrasound on clot-free streptokinase solution were compared to those of concomitant exposures of streptokinase solution with clot. The exposures were made at a frequency of 1 MHz (10% duty cycle) and at three intensity levels (0.5, 1.0 and 4.0 W/cm2 intensity I(SATA)).

RESULTS

Increased fibrinolysis (31.2%, P=0.028) was observed after concomitant ultrasound exposure of clot and streptokinase solution at 0.5 W/cm2 intensity. Compared to unexposed streptokinase solution, the lytic effect following exposure of streptokinase solution to ultrasound was significantly increased (32.7%, P=0.002). This enhancement effect disappeared at intensity 1 W/cm2, whilst further increase to 4.0 W/cm2 inhibited the lytic effect of streptokinase, both during concomitant exposure (-25.2%, P=0.028) and after pre-exposure of streptokinase solution to ultrasound (-25.4%, P=0.002).

CONCLUSION

The fibrinolytic property of streptokinase is modulated by exposure to pulsed ultrasound of frequency 1 MHz, being enhanced at low intensity and inhibited at high intensity.

Effect of ultrasound on activation of serine proteases precursors

The effect of ultrasound (US) (26.4 kHz, 26 W/cm2) on the activation process of a mixture of chymotrypsinogen and trypsinogen was studied. US led to a significant decrease in proteolytic activity, as well as inhibition of the activation process in general. It was shown that inhibition of proteinase activity under US influence was a consequence of inhibition of chymotrypsinogen-chymotrypsin transformation and the complete proteolytic trypsin degradation in the proenzymes mixture.