Synergistic effect of low‐frequency ultrasound and low‐dose bradykinin on increasing permeability of the blood–tumor barrier by opening tight junction

Abstract

Low-frequency ultrasound (LFU) and bradykinin (BK) have been shown separately to increase the permeability of the blood-tumor barrier (BTB) in the rat model of C6 glioma. This study examined the hypothesis that the combination of LFU and low-dose BK has a synergistic effect on increasing the permeability of BTB and explored the possible underlying mechanism including the involvement of tight junction (TJ). The rats were divided into six groups: control group, LFU group, BK group, 2/3LFU + 1/2BK group, 5/6LFU + 2/3BK group, and LFU + BK group. The BTB permeability was assessed by Evans blue extravasation. The mRNA and protein expressions of TJ-related proteins ZO-1, occludin, and claudin-5 were determined by reverse transcriptase-polymerase chain reaction, immunohistochemistry, immunolocalization, and Western blot test. BTB permeability increased in all the experimental groups, accompanied by opening of local TJ of the BTB, observed by transmission electron microscopy, and decreased mRNA and protein expressions of ZO-1, occludin, and claudin-5. In addition, there was a further increase in BTB permeability and a further reduction in the expressions of TJ-related proteins in 5/6LFU + 2/3BK and LFU + BK groups, compared with LFU or BK group. These results indicate that LFU and low-dose BK applied in combination act in a synergistic manner to increase BTB permeability. The down-regulation of TJ-related proteins ZO-1, occludin, and claudin-5 may be one of the underlying mechanisms of the increase in BTB permeability induced by LFU and BK.

Bradykinin Promotes the Chemotactic Invasion of Primary Brain Tumors

“…Indeed, over-expression of B2R on glioma cells has been shown to enhance BK-mediated tumor blood-brain barrier permeability increase (Uchida et al, 2002). A number of later studies further supported this finding by using small concentrations of BK to insure better and more efficient drug delivery to malignant brain tumors (Xia et al, 2009; Zhang et al, 2009;Wang and Liu, 2009; Sarin et al, 2009; Cote et al, 2010). Of note, B2R was also expressed in normal brain, were it associated with GFAP positive astrocytes, yet highest levels of expression were found in gliomas associated with blood vessels.…”

Mechanism of Low-Frequency Ultrasound in Opening Blood–Tumor Barrier by Tight Junction

“…The ultrasound used in this experiment was at low-pressure amplitude (0.48 MPa) for 20 s, as previously reported by Zhang et al (2009). The microbubbles at the concentration of 50 μl/kg which were developed for ultrasound imaging contain a suspension of albumin-coated perflutren (C3F8) microbubbles and have diameters between approximately 1 and 5 μm which can pass through the capillary network without tissue destruction.…”

Low Intensity Ultrasound Promotes the Sensitivity of Rat Brain Glioma to Doxorubicin by Down-Regulating the Expressions of P-Glucoprotein and Multidrug Resistance Protein 1 In Vitro and In Vivo

“…Ultrasound window was created by craniotomy, with a piece of 3 mm ×3 mm skull removed from 1 mm anterior to sutura coronaria and 3 mm lateral to sagittal suture on the right. The suspension of C6 glioma cell was injected by a Hamilton syringe, under the direction of stereotaxic apparatus [30]. The coordinates were 5 mm lateral to the bregma and 4.5 mm deep to the head of caudate nucleus in the right brain.…”