Plasminogen-enriched pulse-spray thrombolysis with tPA: further developments

Combination treatment with rt-PA is more effective than rt-PA alone in an in vitro human clot model

Incidence of intra-cranial hemorrhage linked to treatment of ischemic stroke with recombinant tissue plasminogen activator (rt-PA) has led to interest in adjuvant therapies such as ultrasound (US) or plasminogen, to enhance rt-PA efficacy and improve patient safety. High-frequency US (∼MHz) such as 2-MHz transcranial Doppler (TCD) has demonstrated increased recanalization in situ. Low-frequency US (∼kHz) enhanced thrombolysis (UET) has demonstrated higher lytic capabilities but has been associated with incidence of intracerebral hemorrhage in some clinical trials. In vitro studies using plasminogen have shown enhancement of lysis. This study compared rt-PA-induced lysis using adjuvant therapies, with 120-kHz or 2-MHz pulsed US, or plasminogen, in an in vitro human whole blood clot model. Blood was drawn from 30 subjects after local institutional approval. Clots were exposed to rt-PA at concentrations of 0 to 3.15 μg/ml. Clots were exposed to rt-PA alone (rt-PA) or in combination with plasminogen (Plg), 120-kHz US (120-kHz), or 2-MHz US (2-MHz). Thrombolytic efficacy was determined by assessing the percent fractional clot loss (FCL) at 30 minutes using microscopic imaging. There was no enhancement of lysis for combination therapy with [rt-PA]=0 μg/ml. Adding rt- PA increased lysis for all groups. As [rt-PA] increased, lysis tended to increase for 120-kHz and Plg (FCL: from 50% to 70%, 120-kHz; 65% to 83%, Plg) but not for 2-MHz (58% to 52%). Lytic efficacy in combination therapy depends on rt- PA concentration and the adjuvant therapy type. For non-zero rt-PA concentrations, all combination therapies produced more lysis than rt-PA alone.

Percutaneous treatment of pediatric thrombosis

While rare, thrombosis in the pediatric population can result serious sequelae including death. The best treatment options have not yet been firmly established for this age group. During childhood, there are age-related changes in components of the coagulation system that can affect treatment choices. This review article gives an overview of pediatric coagulation and describes the current state of percutaneous treatment options including local thrombolysis and thrombectomy.

Alteplase: stability and bioactivity after dilution in normal saline solution

PURPOSE

To characterize the biochemical stability and bioactivity of reconstituted alteplase when diluted to a concentration of 0.01 mg/mL in normal saline solution and stored at ambient temperature for as long as 24 hours in commercial saline solution bags.

MATERIALS AND METHODS

Two commercially available formulations of lyophilized alteplase (2-mg and 50-mg vials, respectively) were reconstituted with sterile water to a final concentration of 1 mg/mL. For each vial configuration, 5 mg of alteplase (5 mL) was added to a commercial 500-mL bag of normal saline solution to achieve a 0.01-mg/mL targeted concentration. Solutions were assayed for optical clarity, pH, protein concentration, and in-vitro clot lysis activity. Assays of the solutions were performed at time points of 0 (control), 4, 8, and 24 hours at ambient room temperature and compared to controls.

RESULTS

On visual inspection, aliquots of the diluted protein solutions in clear glass vials remained clear/colorless after 24 hours. Bioactivity (clot lysis assay) over the course of 24 hours at ambient temperature remained essentially unchanged relative to control (2-mg vial: mean of 98.3%, range of 93.7%-103.3%; 50-mg vial: mean of 103.1%, range of 100.6%-108.3%). The mean protein recovery rates (relative to targeted concentration) over a 24-hour period were 43% (range, 39%-46%) and 42% (range, 40%-45%) for the 2-mg and 50-mg vial configurations, respectively.

CONCLUSIONS

Alteplase diluted in normal saline solution at a concentration of 0.01 mg/mL is biochemically stable and active at ambient temperature for as long as 24 hours as assessed by in vitro clot lysis assays. Alteplase appears to have a bimodal solubility profile in normal saline solution and further studies are required to determine the activity and solubility of alteplase concentrations lower than 0.01 mg/mL.

Pulse-spray thrombolysis with reteplase: optimization and comparison with tPA in a rabbit model

PURPOSE

To critically evaluate and optimize methodology for pulse-spray thrombolysis with reteplase in a rabbit inferior vena cava (IVC) thrombosis model and to compare results with optimized parameters for the use of tissue plasminogen activator (tPA).

MATERIALS AND METHODS

Occlusive IVC thrombus was produced in 102 rabbits and treated 2 days later for 1 hour with pulse-spray thrombolysis using reteplase. Methodologic variables included pulse frequency, concentration and amount of reteplase, infusion versus pulse therapy, and admixture of heparin. After the rabbits were killed, residual thrombus was weighed and percent lysis was estimated on the basis of previous control values. Results were compared with those achieved with tPA in 18 additional rabbits and also with previous tPA results.

RESULTS

As in earlier tPA studies, pulse-spray methods were far more effective than constant infusion. Pulses at 30-second intervals produced better results than pulses at 2-minute intervals. At the optimal concentration of 0.02 U/mL (molarity 90 x 10(-8) ), reteplase produced 79% lysis. At two-fold higher or lower concentrations, lysis was reduced by approximately 25%, and at eight-fold higher or six-fold lower concentrations, lysis was reduced by approximately 50%. Optimal concentration of tPA was 0.02 mg/mL, yielding 78% lysis. Admixture of reteplase with heparin suggested improvement, but differences were statistically insignificant.

CONCLUSION

When used with pulse-spray methodology, reteplase demonstrated a steep bell-shaped response-concentration curve similar in pitch and amplitude to that of tPA. The optimal molar concentration of reteplase was approximately three times that of tPA. However, at their respective optimal concentrations, reteplase and tPA were equally effective.

Basic principles in thrombolysis: regulatory role of plasminogen

During thrombolytic therapy, patients are treated with a plasminogen activator in order to stimulate the fibrinolytic system by converting the precursor plasminogen into the active enzyme plasmin. The fibrinolytic process can be divided into two phases. In the first phase, plasminogen binds to intact fibrin and initial fibrinolysis takes place. As a result, carboxyterminal lysine residues are generated, which represent new binding sites for plasminogen. In the second phase, plasminogen binds to these sites and fibrinolysis is accelerated because the local plasminogen concentration is strongly enhanced and because this plasminogen has a higher reactivity. For instance, both single-chain urokinase-type plasminogen activator (scu-PA) and staphylokinase have a high preference for this type of plasminogen, which explains their fibrin-selective action. A recently discovered thrombin-activatable fibrinolysis inhibitor (TAFI) eliminates carboxyterminal lysine residues from partially degraded fibrin and, thus, inhibits the second phase of fibrinolysis. These mechanisms show that plasminogen plays an important regulatory role in fibrinolysis and thrombolysis.