A Novel Lipid Microbubble Targeting E-Selectin for Ultrasound Molecular Imaging of Acute Kidney Injury in Rats

Acute kidney injury (AKI) is a common clinical syndrome characterized by abnormal renal function and structure. Microcirculatory perfusion disorders and inflammatory responses are critical pathophysiologies of AKI. Recently, ultrasound molecular imaging has been considered a valuable tool for preclinical and clinical diagnostics that can sensitively target histological structures of interest, particularly in evaluating renal microcirculation. The purpose of this study was to explore a lipid microbubble (MB_E-selectin) that targets E-selectin molecules expressed on the activated endothelium and to perform ultrasound molecular imaging for the kidney in cisplatin-induced AKI in rats. Using freeze-drying methods, three formular nontargeted microbubbles (NMBs-1, NMBs-2, NMBs-3) were prepared, and three corresponding MB_E-selectin suspensions (MB_E-selectin-1, MB_E-selectin-2, MB_E-selectin-3) were constructed via maleimide-thiol conjugation chemistry. The results revealed that the physicochemical characteristics of three NMBs and MB_E-selectin suspensions were usable for intravenous injection as ultrasound contrast agents (UCAs), and the anti-E-selectin antibody successfully conjugated to the lipid shell surface of the bubbles in three MB_E-selectin suspensions, which could bind specifically to E-selectin molecules expressed on human umbilical vein endothelial cells (HUVECs) treated with tumor necrosis factor-alpha (TNF-α). During ultrasound imaging for the kidney in the cisplatin-induced AKI model, the time-to-peak (TTP) and area under the curve (AUC) of the MB_E-selectin-2 suspension significantly increased, but the wash-in rate (WIR) and wash-out rate (WOR) significantly decreased compared with those of the NMBs-2 suspension or the control group. The normalized differential targeted enhancement (NdTE) of the MB_E-selectin-2 suspension was significantly greater than that of the NMBs-2 suspension in the model group, as was the residual-to-saturation ratio (RSR) at 8 min. In conclusion, we successfully prepared a novel MB_E-selectin suspension carrying an anti-E-selectin antibody that can be used for intravenous injection and can enhance ultrasound imaging of the kidney as a UCA, particularly in a cisplatin-induced AKI model. Ultrasound molecular imaging of the MB_E-selectin suspension may be helpful for evaluating renal microcirculation or injury in AKI diseases.