Integrity of polymeric micelles regulates bioavailability of cyclosporine A: A FRET-based analysis during oral delivery.

This study comprehensively investigated the effect of structural integrity on the oral delivery efficacy of mPEG-b-PCL polymeric micelles (PMs) using fluorescence resonance energy transfer (FRET) technology. During mucus penetration, the integrity loss of PMs resulted from the "hydration effect" of mucins and the "solubilization effect" of bile salts. Increasing surface PEG density or decreasing particle size <50 nm resisted the "hydration effect", while shortening PCL chain or increasing aggregation number alleviated the "solubilization effect". Fluorescence colocalization studies demonstrated that low surface PEG density and small particle size enhanced the cellular uptake of PMs, but high surface PEG density preserved the intracellular integrity of PMs. Approximately 30 %-60 % of endocytosed PMs were expelled within 4 h, correlating with their cellular uptake efficiency. Transcellular transport results indicated that 5 %-25 % of PMs underwent transcytosis within 4 h, 0.5 %-10 % of initial PMs remained intact. In situ intestine perfusion data confirmed the consistency between the in vitro findings and the actual performance of PMs in vivo. Two types of PMs were selected to encapsulate cyclosporine A (CyA) based on their enhanced integrity and transcytosis efficiency. The PM with a short amphiphilic block and loose structure exhibited comparable in vitro release and in vivo performance to Neoral®, with a Cmax of 1356.28 ± 170.01 ng/mL, a Tmax of 2 h, and an AUC0-t of 16,408.92 ± 1166.78 ng/mL*h. However, the PM with a long amphiphilic block and ordered core PCL arrangement exhibited sustained release of CyA both in vitro and in vivo, decreasing CyA accumulation in major organs and improving the oral bioavailability of CyA, with a Cmax of 757.07 ± 66.19 ng/mL, a Tmax of 9.33 ± 2.31 h, and an AUC0-t of 21,938.44 ± 2183.59 ng/mL*h.