120 kHz pulsed ultrasound enhanced thrombolysis with tissue plasminogen activator-loaded echogenic liposomes

Meunier, Jason M.; Smith, Denise A. B.; Holland, Christy K.; Huang, Shaoling; McPherson, David D.; Shaw, George J.

doi:10.1121/1.2942880

Cited by 6 publications

(6 citation statements)

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“…It is important to note that plasminogen activator inhibitors found in plasma would be present in vivo . Furthermore, recent studies using a microscopic imaging technique have shown enhanced thrombolysis of in vitro blood clots in plasma exposed to 120 kHz and T-ELIP for 30 minutes (Meunier et al , 2008; Shaw et al , 2009). The co-encapsulation of a drug and gas into liposomes is still in the development stages and the entrapment efficiency will likely increase as manufacturing methods continually improve (Huang, 2008a; Huang et al , 2008b).…”

Section: Discussionmentioning

confidence: 99%

Ultrasound-Triggered Release of Recombinant Tissue-Type Plasminogen Activator from Echogenic Liposomes

Smith

Vaidya

Kopechek

et al. 2010

Ultrasound in Medicine & Biology

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Echogenic liposomes (ELIP) were developed as ultrasound-triggered targeted drug or gene delivery vehicles (Lanza et al., 1997;Huang et al., 2001). Recombinant tissue-type Plasminogen Activator (rt-PA), a thrombolytic, has been loaded into ELIP (Tiukinhoy-Laing et al., 2007). These vesicles have the potential to be used for ultrasound-enhanced thrombolysis in the treatment of acute ischemic stroke, myocardial infarction, deep vein thrombosis, or pulmonary embolus. A clinical diagnostic ultrasound scanner (Philips HDI 5000) equipped with a linear array transducer (L12-5) was employed for in vitro studies using rt-PA-loaded ELIP (T-ELIP). The goal of this study was to quantify ultrasound-triggered drug release from rt-PA-loaded echogenic liposomes. T-ELIP samples were exposed to 6.9-MHz B-mode pulses at a low pressure amplitude (600 kPa) to track the echogenicity over time under four experimental conditions: 1) flow alone to monitor gas diffusion from the T-ELIP, 2) pulsed 6.0-MHz color Doppler exposure above the acoustically driven threshold (0.8 MPa) to force gas out of the liposome gently, 3) pulsed 6.0-MHz color Doppler above the rapid fragmentation threshold (2.6 MPa), or 4) Triton X-100 to rupture the T-ELIP chemically as a positive control. Release of rt-PA for each ultrasound exposure protocol was assayed spectrophotometrically. T-ELIP were echogenic in the flow model (5 ml/min) for thirty minutes. The thrombolytic drug remained associated with the liposome when exposed to lowamplitude B-mode pulses over 60 min and was released when exposed to color Doppler pulses or Triton X-100. The rt-PA released from the liposomes had similar enzymatic activity as the free drug. These T-ELIP are robust and echogenic during continuous fundamental 6.9-MHz B-mode imaging at a low exposure output level (600 kPa). Furthermore, a therapeutic concentration of rt-PA can be released by fragmenting the T-ELIP with pulsed 6.0-MHz color Doppler ultrasound above the rapid fragmentation threshold (1.59 MPa).

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Section: Discussionmentioning

confidence: 99%

Ultrasound-Triggered Release of Recombinant Tissue-Type Plasminogen Activator from Echogenic Liposomes

Smith

Vaidya

Kopechek

et al. 2010

Ultrasound in Medicine & Biology

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“…Removing the syringe exposed the ends of the sample holder to atmospheric pressure, and the clot surface to a static fluid column. Clots were exposed to a specific treatment regimen for 30 minutes; previous studies have shown that the majority of thrombolysis occurs within a 30 minute window [33-35]. …”

Section: Methodsmentioning

confidence: 99%

Making the right choice: Optimizing rt-PA and eptifibatide lysis, an in vitro study

Shaw

Meunier

Lindsell

et al. 2010

Thrombosis Research

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Introduction Recombinant tissue plasminogen activator (rt-PA) is the only FDA approved lytic therapy for acute ischemic stroke. However, there can be complications such as intra-cerebral hemorrhage. This has led to interest in adjuncts such as GP IIb-IIIa inhibitors. However, there is little data on combined therapies. Here, we measure clot lysis for rt-PA and eptifibatide in an in vitro human clot model, and determine the drug concentrations maximizing lysis. A pharmacokinetic model is used to compare drug concentrations expected in clinical trials with those used here. The hypothesis is that there is a range of rt-PA and eptifibatide concentrations that maximize in vitro clot lysis. Materials and Methods Whole blood clots were made from blood obtained from 28 volunteers, after appropriate institutional approval. Sample clots were exposed to rt-PA and eptifibatide in human fresh-frozen plasma; rt-PA concentrations were 0, 0.5, 1, and 3.15 μg/ml, and eptifibatide concentrations were 0, 0.63, 1.05, 1.26 and 2.31 μg/ml. All exposures were for 30 minutes at 37 C. Clot width was measured using a microscopic imaging technique and mean fractional clot loss (FCL) at 30 minutes was used to determine lytic efficacy. On average, 28 clots (range: 6-148) from 6 subjects (3-24) were used in each group. Results and Conclusions FCL for control clots was 14% (95% Confidence Interval: 13-15%). FCL was 58% (55-61%) for clots exposed to both drugs at all concentrations, except those at an rt-PA concentration of 3.15 μg/ml, and eptifibatide concentrations of 1.26 μg/ml (Epf) or 2.31 μg/ml. Here, FCL was 43% (36-51) and 35% (32-38) respectively. FCL is maximized at moderate rt-PA and eptifibatide concentration; these values may approximate the average concentrations used in some rt-PA and eptifibatide treatments.

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“…The 120 kHz ultrasound parameters used were a pressure of 0.35 MPa p-p , a pulse repetition frequency (PRF) of 1667 Hz, and a duty cycle of 50%, and a time-averaged acoustic intensity of 0.5 W/cm 2 . These ultrasound parameters yielded substantial clot lysis in previous work [12,32,39,40]. …”

Section: Methodsmentioning

confidence: 67%

Ultrasound-enhanced thrombolysis with tPA-loaded echogenic liposomes

Shaw

Meunier²,

Huang

et al. 2009

Thrombosis Research

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Background and Purpose Currently, the only FDA-approved therapy for acute ischemic stroke is the administration of recombinant tissue plasminogen activator (tPA). Echogenic liposomes (ELIP), phospholipid vesicles filled with gas and fluid, can be manufactured to incorporate tPA. Also, transcranial ultrasound-enhanced thrombolysis can increase the recanalization rate in stroke patients. However, there is little data on lytic efficacy of combining ultrasound, echogenic liposomes, and tPA treatment. In this study, we measure the effects of pulsed 120-kHz ultrasound on the lytic efficacy of tPA and tPA-incorporating ELIP (t-ELIP) in an in-vitro human clot model. It is hypothesized that t-ELIP exhibits similar lytic efficacy to that of rt-PA. Methods: Blood was drawn from 22 subjects after IRB approval. Clots were made in 20-μL pipettes, and placed in a water tank for microscopic visualization during ultrasound and drug treatment. Clots were exposed to combinations of [tPA] = 3.15 μg/ml, [t-ELIP] = 3.15 μg/ml, and 120-kHz ultrasound for 30 minutes at 37 °C in human plasma. At least 12 clots were used for each treatment. Clot lysis over time was imaged and clot diameter was measured over time, using previously developed imaging analysis algorithms. The fractional clot loss (FCL), which is the decrease in mean clot width at the end of lytic treatment, was used as a measure of lytic efficacy for the various treatment regimens. Results: The fractional clot loss FCL was 31% (95% CI: 26-37%) and 71% (56-86%) for clots exposed to tPA alone or tPA with 120 kHz ultrasound. Similarly, FCL was 48% (31-64%) and 89% (76-100%) for clots exposed to tELIP without or with ultrasound. Conclusions: The lytic efficacy of tPA containing echogenic liposomes is comparable to that of tPA alone. The addition of 120 kHz ultrasound significantly enhanced lytic treatment efficacy for both tPA and t-ELIP. Liposomes loaded with tPA may be a useful adjunct in lytic treatment with tPA.

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120 kHz pulsed ultrasound enhanced thrombolysis with tissue plasminogen activator-loaded echogenic liposomes

Cited by 6 publications

References 0 publications

Ultrasound-Triggered Release of Recombinant Tissue-Type Plasminogen Activator from Echogenic Liposomes

Ultrasound-Triggered Release of Recombinant Tissue-Type Plasminogen Activator from Echogenic Liposomes

Making the right choice: Optimizing rt-PA and eptifibatide lysis, an in vitro study

Ultrasound-enhanced thrombolysis with tPA-loaded echogenic liposomes

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