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

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. Copyright 2009 Wiley-Liss, Inc.