Ultrasound-assisted membrane permeabilization of endothelial cells under flow conditions

Abstract

Ultrasound-stimulated microbubbles have been shown a feasible approach for localized therapeutic delivery. As applications of this technique span many anatomical sites, so too do the local fluid dynamics experienced by the circulating microbubbles and the adjacent endothelial cells. Our objective was to assess the relative effectiveness of endothelial cell sonoporation as a function of flow conditions. Human umbilical vein (HUVECs) or human brain endothelial cells (HBECs) were cultured as a monolayer in flow chamber slides connected to a fluidic system and placedupon an acoustically-coupled microscope. A suspension of diluted lipid-encapsulated microbubbles and propidium iodide (PI), used as a sonoporation marker, was constantly perfused over the monolayer at either 5 or 30 ml/min. Cells were treated with 1 MHz ultrasound (PRI= 1 ms, 20 cycles, duration = 2 s), and the video-microscopy data were quantified offline to assess the number of PI-positive cells. Our results demonstrate a marked increase in sonoporation efficiency at 30 ml/min as compared to 5 ml/min in both endothelial cell lines under identical acoustic conditions (9.7-fold increase and 2.3-fold increase for HUVECs and HBECs respectively, p < 0.001). Our results suggest the local fluid flow environment plays a role in US-mediated endothelial perforation efficiency and can modulate treatment strategies.