The ultrasound contrast imaging properties of lipid microbubbles loaded with urokinase in dog livers and their thrombolytic effects when combined with low-frequency ultrasound in vitro.

A new microbubble loaded with urokinase (uPA-MB) was explored in a previous study. However, its zeta potential and ultrasound contrast imaging properties and its thrombolytic effects when combined with low-frequency ultrasound (LFUS) were unclear. The zeta potential and ultrasound contrast imaging property of 5 uPA-MBs loading with 50,000 IU uPA was respectively detected using a Malvern laser particle analyzer and a Logiq 9 digital premium ultrasound system. Its ultrasound contrast imaging property was performed on the livers of two healthy dogs to compare with SonoVue. And the clot mass loss rate, D-dimer concentration and surface morphology of the clot residues were measured to evaluate the thrombolytic effect after treatment with three doses of 5 uPA-MBs combined with LFUS in vitro. The zeta potential of 5 uPA-MBs (-27.0 ± 2.40 mV) was higher than that of normal microbubbles (-36.95 ± 1.77 mV). Contrast-enhanced imaging of the hepatic vessels using 5 uPA-MBs was similar to SonoVue, while the imaging duration of 5 uPA-MBs (10 min) was longer than SonoVue (6 min). The thrombolytic effect of three doses of uPA-MBs combined with LFUS was significantly better than that of the control group and showed dose dependence. The 5 uPA-MBs have a negative charge on their surface and good echogenicity as ultrasound contrast agents. The 5 uPA-MBs combined with LFUS can promote thrombolysis in a dose-dependent manner.