In Vivo Assessment of Thermosensitive Liposomes for the Treatment of Port Wine Stains by Antifibrinolytic Site-Specific Pharmaco-Laser Therapy

Abstract

Antifibrinolytic site-specific pharmaco-laser therapy (SSPLT) is an experimental treatment modality for refractory port wine stains (PWS). Conceptually, antifibrinolytic drugs encapsulated in thermosensitive liposomes are delivered to thrombi that form in semi-photocoagulated PWS blood vessels after conventional laser treatment. Local release of antifibrinolytics is induced by mild hyperthermia, resulting in hyperthrombosis and complete occlusion of the target blood vessel (clinical endpoint). In this study, 20 thermosensitive liposomal formulations containing tranexamic acid (TA) were assayed for physicochemical properties, TA:lipid ratio, encapsulation efficiency, and endovesicular TA concentration. Two candidate formulations (DPPC:DSPE-PEG, DPPC:MPPC:DSPE-PEG) were selected based on optimal properties and analyzed for heat-induced TA release at body temperature (T), phase transition temperature (Tm), and at T > Tm. The effect of plasma on liposomal stability at 37 °C was determined, and the association of liposomes with platelets was examined by flow cytometry. The accumulation of PEGylated phosphocholine liposomes in laser-induced thrombi was investigated in a hamster dorsal skinfold model and intravital fluorescence microscopy. Both formulations did not release TA at 37 °C. Near-complete TA release was achieved at Tm within 2.0–2.5 min of heating, which was accelerated at T > Tm. Plasma exerted a stabilizing effect on both formulations. Liposomes showed mild association with platelets. Despite positive in vitro results, fluorescently labeled liposomes did not sufficiently accumulate in laser-induced thrombi in hamsters to warrant their use in antifibrinolytic SSPLT, which can be solved by coupling thrombus-targeting ligands to the liposomes.

Stimuli-responsive vesicles as distributed artificial organelles for bacterial activation

“…4C, cyan rhombus). The encapsulation efficiency was determined to be ∼1.6% in accordance with previous reports (48). Furthermore, this rhamnose assay can be employed to determine the efficacy of SEC purification by measuring the free rhamnose present in eluted vesicles that have been kept at 23 °C, when no release has occurred.…”

“…The ability to quickly release the encapsulated content-without compromising the integrity during activation experiments-is fundamental when designing thermoresponsive artificial cells. Accordingly, the final composition was 90:10:4 DPPC:lysoPC: DSPE-PEG 2000, which has been shown to work in vitro (47) and in vivo (48), exhibiting quick release and good stability for drug delivery applications.…”