The research was conducted to study the characteristics of the noninvasive, reversible, targeted opening of the blood-brain barrier (BBB) by use of low-frequency ultrasound (LFU) irradiation and the selective opening of the blood-tumor barrier (BTB) by intracarotid infusion of bradykinin (BK) in small-dose, with the objective of exploring maximum opening of the BTB by combining LFU irradiation with BK infusion. Thus, it provides new therapeutic strategies for targeted transport of macromolecular or granular drugs to the brain. By using the rat C6 glioma model it was shown that extravasation of Evans blue (EB) through the BTB was significantly increased by combining LFU irradiation (frequency = 1.0 MHz, power = 12 mW, duration = 20 s) with intracarotid small-dose BK infusion, compared with utilizing the two methods separately. By transmission electron microscopy (TEM) we observed that this combination significantly increased the number of pinocytotic vesicles of brain microvascular endothelial cells (BMECs) in the BTB. An even more significant increase was observed by using RT-PCR, western blot, immunohistochemistry, and immunofluorescence to detect mRNA and changes of expression of the caveolae structure proteins caveolin-1 and caveolin-2 of BMECs. In summary, this research concludes that LFU irradiation and small-dose BK together selectively enhance the permeability of the BTB and increase the number of pinocytic vesicles of BMECs to a maximum. Significant up-regulation of the level of expression of caveolae structure proteins caveolin-1 and caveolin-2 might be the molecular mechanism of the co-enhanced endocytotic transport by BMECs. Thus, this research provides new therapeutic strategies for targeted transport of macromolecular drugs and the design of drugs.

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.

This study was performed to determine whether low frequency ultrasound (LFU) irradiation, Papaverine (PA) infusion and combination LFU irradiation with PA infusion opened the blood-tumor barrier (BTB) by affecting tight junctions (TJ)-associated proteins zonula occluden-1 (ZO-1), occludin and caludin-5. In a rat brain glioma model, we found that the mRNA and protein expression levels of ZO-1, occludin and claudin-5 were decreased by LFU irradiation and PA infusion. LFU-induced and PA-induced decrease of ZO-1, occludin and claudin-5 was further decreased after combining LFU irradiation with PA infusion. Immunohistochemistry assay showed that the decreased expression of ZO-1, occludin and claudin-5 was the most obvious in the tumor capillaries. Meanwhile, Evans blue assay showed that the permeability of BTB was increased, and transmission electron microscopy (TEM) indicated that TJ was opened. This led to the conclusion that LFU irradiation and PA infusion together can open the BTB by paracellular pathway. Significantly down-regulated expression levels of ZO-1, occludin and claudin-5 might be one of the molecular mechanisms of combining LFU and PA enhancing the permeability of BTB.

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.