Low-Frequency Ultrasound Irradiation Increases Blood–Tumor Barrier Permeability by Transcellular Pathway in a Rat Glioma Model

Abstract

Low-frequency ultrasound (LFU) irradiation under certain acoustic intensity can increase blood-brain barrier permeability non-invasively and reversibly. The aim of this study was to find out the effect of LFU irradiation on blood-tumor barrier (BTB) permeability in rat C6 glioma model and the possible mechanism. In this research, Evans blue and H&E staining were used to evaluate the optimal parameter of LFU to open the BTB without damaging the normal brain tissue. Transmission electron microscopy was used to observe the changes of the number of pinocytotic vesicles in cerebral or glioma microvascular endothelial cells. The phosphorylation of tyrosine kinase Src, caveolin-1, and caveolin-2 was detected by western blot. The distribution and expressing levels of caveolae proteins, caveolin-1 and caveolin-2, were detected by immunohistochemical and immunofluorescent staining, RT-PCR, and western blot. Our research data showed that, in rat C6 glioma model, LFU irradiation at a frequency of 1 MHz, a power of 12 mW, and exposure time of 20 s induced the increase of BTB permeability temporally, which reached a peak at 1.5 h, then decreased and restored to normal level at 12 h after LFU irradiation. In the glioma microvascular endothelial cells of rat glioma model, LFU irradiation induced a significant increase of the pinocytotic vesicles' density. The phosphorylation of Src, caveolin-1, and caveolin-2 began to increase at 0.5 h and reached a maximum at 1 h. Immunohistochemical and immunofluorescent staining showed that caveolin-1 and caveolin-2 were co-localized in the glioma microvascular endothelial cells and glioma cells. The mRNA and protein expression levels of caveolin-1 and caveolin-2 were up-regulated, reached the peak value at 1.5 h, and re-normalized at 12 h after LFU irradiation. These results demonstrated that LFU irradiation increased BTB permeability by promoting transcellular transport in glioma microvascular endothelial cells. The phosphorylation of tyrosine kinase Src, caveolin-1, caveolin-2 and up-regulation of caveolin-1 and caveolin-2 were involved in LFU-induced caveolae-mediated endocytosis.

Ultrasound-mediated blood–brain barrier disruption for targeted drug delivery in the central nervous system

“…Reorganization of connexin gap junction proteins have also been reported [123]. An increase of endothelial vesicles in normal [124] and tumor microvessels [125] have also been observed on TEM with an up-regulation of caveolin proteins/mRNA, suggesting that caveolae-mediated transcytosis (CMT) as a contributing mechanism for permeability. These researchers also found increased phosphorylation of Src and caveolin-1/2, noting that Src-induced phosphorylation of caveolins is a trigger for CMT [126].…”

Study of the mechanisms underlying the reversal of multidrug resistance of human neuroblastoma multidrug-resistant cell line SK-N-SH/MDR1 by low-intensity pulsed ultrasound

“…LIPUS may damage the structural integrity of the membrane of tumor cells mechanically via sonoporation (16)(17)(18)(19). In our experiment, the effect of proliferation could be excluded by reason of detecting M value immediately after irradiation.…”

Safety Validation of Repeated Blood–Brain Barrier Disruption Using Focused Ultrasound

“…In the ultrasound focal region, an interaction between the micro-bubbles, small gas bubbles usually used as ultrasound contrast agent, and ultrasound waves takes place. Pre-clinical studies have shown that these interactions cause a temporary disassembly of the tight junction proteins and stimulate active transport, making it possible to deliver drugs through the BBB (Fan et al 2011; Hynynen et al 2001; Shang et al 2011; Sheikov et al 2006, 2008; Xia et al 2012). A few hours after the focused ultrasound therapy, the barrier is closed, and the brains appear normal in light microscopy (Baseri et al 2010; Hynynen et al 2005; Hynynen et al 2006; McDannold et al 2005).…”