Fibrin targeting of tissue plasminogen activator-loaded echogenic liposomes.

We recently reported entrapment of tissue-plasminogen activator (tPA) into echogenic liposomes (ELIP) with retention of echogenicity and thrombolytic effect. Integral to the potential of this agent for ultrasound-detectable local drug delivery is the specific binding of tPA-ELIP to clots. tPA contains fibrin-binding sites; we hypothesized that tPA when associated with ELIP, will maintain fibrin binding properties, rendering further manipulation for targeting of the tPA-ELIP unnecessary. We demonstrated strong fibrin binding of the ELIP-associated tPA. Fibrin binding for ELIP-associated tPA was twice that of free tPA. This strong affinity for fibrin was confirmed using echogenicity analysis of porcine clots in vitro. Both objective (mean gray scale analysis) and subjective (visual estimation by two experienced echocardiographers) evaluation of the clots showed enhanced highlighting of clots treated with tPA-ELIP when compared to control. The findings in this study represent new approaches for fibrin-targeted, ultrasound-directed and enhanced local delivery of a thrombolytic agent.

Ultrasound-facilitated thrombolysis using tissue-plasminogen activator-loaded echogenic liposomes.

INTRODUCTION: Targeted delivery of thrombolytics to the site of occlusion is an attractive concept, with implications for the treatment of many thrombo-occlusive diseases. Ultrasound enhances thrombolysis, which can be augmented by the addition of a contrast agent. We have previously reported development of echogenic liposomes (ELIP) for targeted highlighting of structures with potential for drug and gene delivery. This study evaluated the potential of ELIP for thrombolytic loading, and the effect of ultrasound exposure of thrombolytic-loaded ELIP on thrombolytic efficacy. MATERIALS AND METHODS: Tissue-plasminogen activator (tPA) was loaded into ELIP. Echogenicity was assessed and reported as mean grayscale values. Whole porcine clots were treated with plasma, free tPA, tPA+Optison (echocontrast agent), or tPA-loaded ELIP, with and without ultrasound (1 MHz, continuous wave, 2 W/cm(2), for 2 min). Clots were weighed before and after a 30-min treatment period, and results reported as percent clot mass loss. RESULTS: tPA entrapment into ELIP was feasible with 50% entrapment, and retention of echogenicity. Treatment with tPA-loaded ELIP resulted in effective clot lysis with an effect similar to treatment with free tPA. Ultrasound exposure of tPA-loaded ELIP resulted in enhanced thrombolysis (49.5% relative improvement vs. no ultrasound). Much of the ultrasound effect appeared to be related to drug release from the tPA-ELIP complex. CONCLUSIONS: We have demonstrated entrapment of tPA into ELIP with effective clot lysis and drug release using ultrasound. Our tPA-loaded ELIP has potential for specific highlighting of clots to confirm agent delivery and help focus ultrasound therapy for targeted ultrasound-facilitated thrombolysis.

Cardiac hemodynamic and coronary angiographic characteristics of patients being evaluated for liver transplantation.

With improved survival after liver transplantation (LT), the referral of older candidates has increased. The increasing demand for, and the decreased supply of, liver donors makes careful preoperative cardiac risk assessment imperative. There is a paucity of information regarding the cardiac characteristics of patients being referred for LT in the current era. This study aimed to describe the cardiac hemodynamic and coronary angiographic characteristics of a cohort of patients with end-stage liver disease without known coronary artery disease (CAD) being evaluated for LT. One hundred sixty-one consecutive patients aged>or=45 years with end-stage liver disease who were referred for right- and left-sided cardiac catheterization as part of a liver transplant evaluation were identified. There was a high prevalence of atherosclerotic risk factors; half had hypertension or diabetes, and more than half had >or=2 coronary risk factors other than age. There was a high prevalence of CAD, with 26% having unknown moderate to severe coronary narrowing. Patients with moderate to severe CAD were older, were more likely to be men, and were more likely to have hypertension or diabetes mellitus. Right- and left-sided filling pressures were elevated, suggesting abnormalities in left ventricular diastolic compliance. In conclusion, this study showed a high prevalence of coronary risk factors and unknown moderate to severe CAD in patients with end-stage liver disease being referred for LT.