Optimization of liposomal indocyanine green for imaging of the urinary pathways and a proof of concept in a pig model
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Iatrogenic ureteral injury is an increasing concern in the laparoscopic era, affecting both patient morbidity and costs. Current techniques enabling intraoperative ureteral identification require invasive procedures or radiations. Our aim was to develop a real-time, non-invasive, radiation-free method to visualize ureters, based on near-infrared (NIR) imaging. For this purpose, we interfered with the biliary excretion pathway of the indocyanine green (ICG) fluorophore by loading it into liposomes, enabling renal excretion. In this work, we studied various parameters influencing ureteral imaging.
Fluorescence intensity (FI) of various liposomal ICG sizes and doses were characterized in vitro and subsequently tested in vivo in mice and pigs. Quantification was performed by measuring FI in multiple points and applying the ureteral/retroperitoneum ratio (U/R).
The optimal liposomal ICG loading dose was 20%, for the different liposomes’ sizes tested (30, 60, 100 nm). Higher concentration of ICG decreased FI. In vivo, the optimal liposome size for ureteral imaging was 60 nm, which yielded a U/R of 5.2 ± 1.7 (p < 0.001 vs. free ICG). The optimal ICG dose was 8 mg/kg (U/R = 2.1 ± 0.4, p < 0.05 vs. 4 mg/kg). Only urine after liposomal ICG injection had a measurable FI, and not after free ICG injection. Using a NIR-optimized laparoscopic camera, ureters could be effectively imaged in pigs, from 10 min after injection and persisting for at least 90 min. Ureteral peristaltic waves could be clearly identified only after liposomal ICG injection.
Optimization of liposomal ICG allowed to visualize enhanced ureters in animal models and seems a promising fluorophore engineering, which calls for further developments.
KeywordsIndocyanine green Liposomes Ureteral injury Minimal invasive surgery
The authors are grateful to Guy Temporal and Christopher Burel, professionals in Medical English proofreading, for their valuable help in editing the manuscript.
Compliance with ethical standards
This work was funded by a “Nofar” grant from Israel Ministry of Economy and Industry. Professor Jacques Marescaux is the president of IHU-Strasbourg, which is partly funded by Karl Storz, Siemens Healthcare, and Medtronic. Drs. Sara Eyal, Shlomo Magdassi, and Eran Nizri declare that they have a pending patent application (US Provisional Patent Application No. 62/322,365). Drs. Yael Friedman-Levi, Liraz Larush, Michele Diana, Francesco Marchegiani, Noam Goder, Guy Lahat, and Joseph Klausner have no conflicts of interest or financial ties to disclose.
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