The Research On Biological Effect And Mechanism Of The Targeted Delivery Of Ultrasound Mediated Cavitation Of Microbubble

With ongoing development of diagnose and manufacture technique of ultrasound contrast agent, ultrasound molecule image and target transmission using ultrasound microbubble as a vehicle is a popular research topic at present. Achievement of targeted delivery not only needs a particular vehicle to carry foreingn matter to targeted cell or tissue safely and effectively, but also need foreign matter can be used in defferent ways to achieve final purpose. Recently, researchs suggests that ultrasound microbubble show an encouraging application perspective in targeted delivery. The basic principle of ultrasound mediated microbubble cavitation target transmission: by applying different sound intensity ultransound to intravascular microbubble contrast agent in the definite position, microbubble is destroyed and then cavitation follow; the pressure and the energy created by cavitation exert a biological effect on the local cell or tissue, resulting in the rupture of endothelium cell and the increased permeability of cell membranes, thus foreign matter can pass endothelium barrier to tissue space. Microbubble cavitation has different biological effect on local tissue or cell decided by different ultrasound microbubble condition. At present the mechanism of ultrasound mediated microbubble cavitation target transmission is not completely illuminated. During the target transmission, we need the endothelium injure which allow the foreign matter enter the cell through membrane, or pass through the endothelium barrier into tissue, but we should make injure as mild as possible in lest that caused serious consequence.Objectives:1,To evaluate influence of microbubble cavitation on the microvessel permeability of rat spinotrapezius and to approach the mechanism of target transmission by ultrasound microbubble cavitation. 2,To investigate influence of microbubble cavitation on the local microcirculation and safty with the application of targeted transmission.Methods:1,The effect of albumin microbubble cavitation on membrane permeability of rat spinotrapeziuAccording to ultrasound power, fifty-six Sprague-Dawley rats were divided randomly into seven groups: 0.25W/cm², 0.75W/cm² and 1.5W/cm² ultrasound microbubble groups and control group and each group were divided into two subset groups: evans blue group and polymer microsphere group. After infusion of contrast agent mixed with evans blue or fluorescent polymer microspheres, ultrasound was applied to the exteriorized spinotrapeziu to destroy contrast agent. The changes of the structure of the spinotrapezius microvessel were observed by microscope under transillumination and counted petechia numbers per 100 times illumination field of view. After destruction of contrast agent by ultrasound, we observed the change of microvessel structure by looking into the petechia with electronic microscope and hematoxylin and eosin stain. The rats infused with mixture ofmicrobubble and evans blue were executed by the way of blood letting 2 hours after microbubble was destroyed, the extracted evans blue contents was measured with method of the standard curve and the absorption spectrometry.2,The influence of microbubble cavitation on microcirculation of rat spinotrapeziuSeventy -two Sprague-Dawley rats were divided randomly into 6 groups of 12 each: normal saline-treated control group, microbubble group, ultrasound group, high-energy ultrasound (1.5 W-cm^-2) microbubble group, medial-energy ultrasound (0.75 W-cm^-2) microbubble group and low-energy ultrasound (0.25 W-cm^-2) microbubble group. The diameter and the flow velocity of microvessel were measured by RBC tracking correlator and IV500 model viedo microscaler respectively in 6 Sprague-Dawley rats of each group. The structure of the injured microvessel was investigated by electron microscopy at different time before and after microbubble destruction in the other rats of each goup.Results:1,No petechiae and fluorescent polymer microspheres extraction were caused by albumin microbubble destructed by low power ultrasound (0.25 W-cm^-2) in rat spinotrapezius but evans blue can be saw to extracted to tissue in rat spinotrapezius. While by high power ultrasound (0.75W/cm² and 1.5W/cm²) petechiae and extraction of fluorescent polymer microspheres and evans blue were caused. (P＜0.05)2,No microvessel or tissue injure or petechiae but widen of endothelium interspace were caused under electronic microscope in low power ultrasound microbuble group. While in the high energy ultrasound groups, The rupture of endothelium cell, the widening of the endothelium interspace and the extraction of red cell to the tissue were revealed by electron microscopy. But endothelium cell rupture was not observed 2 hours after treatment3,Microbubble cavitation had no effect on the mean arterial pressure and the diameter of microvessel, but had a adverse effect on the velocity and blood flow: flow velocity were slowed and blood flow of the microvessle were reduced which reach the bottom at 1 minute after microbubble destruction and then went up slowly. The effect on the microcirculation and the ability of flow velocity and blood flow to recover to normal condition were correlated with ultrasound energy. In the low ultrasound energy group, the flow velocity and blood flow ofveinule were found to recover significantly after about 15 minute, and those of arteriole were found to recover after about one hour. While in the high ultrasound energy groups (0.75W/cm² and 1.5W/cm²), the flow velocity and blood flow ofmicrovessel were not found to recover after two hours completely.Conclusions:1,No petechiae were caused but endothelium interspace was widen by albumin microbubble destructed by low power ultrasound in rat spinotrapezius. The increased permeability, which allow small molecule matter enter to interstitial space, could be the mechanism of low power ultrasound induced microbubble cavitation target transmission.2,the mechanism of the hige power ultrasound induced microbubble cavitation target transmission could be that the microbubble cavitation causes endothelium cell rupture and permeability remarkable increased which permit red cell and 100 nm fluorescent polymer mierospheres extract to the tissue.3,The injure and the influence on the rnicrocirculation caused by microbubble cavitation is affected by ultrasound energy. The rupture is repairable. The repariable effect is correlated with the ultrasound energy.