Uptake of PEGylated Indocyanine Green Loaded Nanocapsules by Cells of Reticuloendothelial System

Optically active nanoparticles are widely pursued as exogenous chromophores in diagnostic imaging and phototherapeutic applications. However, the blood circulation time of nanoparticles remains limited due to the rapid clearance of the nanoparticles by reticuloendothelial system (RES). Coating with Polyethylene glycol (PEG) is a strategy to extend the circulation time of nanoparticles. Here, we report synthesis and cellular studies of polymeric-based nanocapsules loaded with Indocyanine green (ICG), an FDA approved near-infrared dye, and coated with PEG molecules of various molecular weights through reductive amination. We report the effect of PEG's molecular weight on the uptake of these nanocapsules by human spleen macrophages and hepatocytes using flow cytometry. Our results indicate that the phagocytic content of PEGylated nanocapsules in human spleen macrophages was reduced as compared to uncoated nanocapsules. Among PEGylated nanocapsules, low molecular weight (5000 Da) PEG-coated nanocapsules displayed lower intracellular uptake by spleen macrophages than high molecular weight (30,000 Da) PEG-coated nanocapsules for up to 90 minutes. Encapsulation within the polymeric nanocapsules reduced the hepatic content of ICG with normal human hepatocytes for up to two hours, while the molecular weight of PEG did not have a statistically significant effect on the content of the nanocapsules in liver cells. Our results suggest that reduced uptake of nanocapsules by RES cells can result in prolonged blood circulation time of these nanoconstructs.