Toward understanding the prolonged circulation and elimination mechanism of crosslinked polymeric micelles in...

Understanding the behaviors of nanomedicines in vivo is one of the most important prerequisites for the design and optimization of nanomedicines. However, the in vivo tracking of nanomedicines in rodents is severely limited by the restricted imaging possibilities within these animals. To meet these needs, the FRET (fluorescence or Förster resonance energy transfer) imaging combined with visual zebrafish larvae model (7 dpf) was used to study the behaviors of polymeric micelles in vivo at high spatiotemporal resolution. Firstly, the FRET ordinary Pluronic micelles (OPMs) and disulfide bond crosslinked Pluronic micelles (CPMs) were synthesized to quantify their integrity in vitro and in vivo by FRET ratio. The behaviors and integrity of OPMs and CPMs in vivo were visually investigated in zebrafish larvae across the entire living organism and at cellular molecular level after intravenous microinjection. Results showed that OPMs were rapidly disassociated in circulation, then largely sequestrated by the endothelial cells (ECs) of caudal vein (CV) and liver in zebrafish larvae, which resulted in quick elimination from blood circulation. While the CPMs were more stable and escaped the sequestration by ECs of CV and liver, which prolonged their circulation in blood. Moreover, we pioneered to use the zebrafish model to reveal that polymeric micelles were eliminated through hepatobiliary pathway after disassociation. While the intact micelles were relatively difficult to eliminate. We further verified that the scavenger receptors of ECs but not the macrophages mainly mediated the elimination of polymeric micelles in CV and liver of zebrafish larvae. These finding on behaviors and elimination mechanisms of polymeric micelles in zebrafish model could contribute to the rational design and optimization of nanomedicines, further guide their studies in rodents.