Human stem cells loaded with visible and near-infrared fluorescent core-shell polymeric nanoparticles and revealing tropism toward inflammatory stimuli: in vitro evaluation.

Theranostic approach based on fluorescent nanoparticles (NPs) internalized by stem cells (SCs) injected in the bloodstream allows for reaching cancer or inflammatory foci with tracking and treating purposes. At the same time, the influence of internalized NPs on SCs properties, namely, their homing, migration ability, and functioning, remains scarcely investigated. Here, H1 human embryonic stem cells (hESCs) labeled with visible (Vis) and near-infrared (NIR) fluorescent NPs are studied in vitro, focusing on the NPs internalization and release efficiency, cytocompatibility, intracellular distribution, as well as the migration ability of hESCs carrying NPs. Polymeric NPs with a polystyrene (PolySt) core and a shell of co-polymer of N-isopropylacrylamide (NIPAM) and acrylamide (AA), [Poly(NIPAM-co-AA)] and with an average hydrodynamic diameter of 155 nm are loaded with pyrromethene dye with visible fluorescence peaked at ~ 560 nm (Vis-NPs) or with a NIR dye emitting at ~ 900-1150 nm (NIR-NPs) and comparatively studied. PolySt-Poly(NIPAM-co-AA) core-shell NPs were found to reveal a 57 and 37% increase in size after NIR dye and Vis dye loading, respectively. The study of the dependence of NPs size distribution on temperature demonstrates that NPs exhibit excellent colloidal stability through the explored temperature range (i.e., 25-60 °C), including physiological temperatures. The dye-loaded NPs are efficiently internalized by the targeted cells, mainly localizing within lysosomal compartments, and exhibit negligible toxicity. A sequential fluorescence-based study of extracellular dye release kinetics shows that free dye molecules are released from hESCs much faster than the dye initially loaded to NPs. Finally, hESCs internalized with dye-loaded NPs retain good migration ability and demonstrate tropism toward inflammatory stimuli in an in vitro transwell migration assay (Boyden chamber), revealing a good potential towards targeting neuroinflammation in vivo.