Characterization of microglial phagocytosis and dendrimer nanoparticle uptake in a neonatal rabbit model of cerebral palsy

Hydroxyl dendrimers target reactive microglia in multiple neuroinflammatory models, including cerebral palsy. Insights on the differential uptake of dendrimers between subpopulations of micro-glia will enable the better design of precise nanomedicines to treat neuroinflammation. We have pre-viously demonstrated that microglia of rabbits with cerebral palsy undergo change to a pro-inflammatory phenotype that selectively takes up dendrimer nanoparticles proportional to the sever-ity of the injury. However, the functional changes in microglia associated with this activated pheno-type and related mechanisms of dendrimer uptake are not well understood. Here, we established a method for isolating microglia from cerebral palsy and healthy neonatal rabbit brains and assessed microglial (1) phagocytic activity ex vivo using fluorescent E. coli bioparticles and (2) dendrimer uptake in vivo after intravenous administration of dendrimer conjugated with a fluorescent dye (D-Cy5). Flow cytometry studies showed that the surface marker CD11b is reliably expressed and could isolate microglia from rabbit brain tissue. Furthermore, a significantly higher proportion of microglia isolated from cerebral palsy rabbits demonstrated increased phagocytosis when compared to controls. To assess differences in dendrimer uptake, microglia were isolated from the brain 24 hours after D-Cy5 administration. D-Cy5 localized only in CD11b+ microglia with differential up-take in subpopulations of microglia and was significantly higher in microglia from cerebral palsy rabbits when compared to healthy controls. This study demonstrates that PAMAM hydroxyl den-drimers are preferentially taken up by microglia, especially in cerebral palsy rabbits, and that sub-populations of microglia demonstrate differential dendrimer uptake. Future work will continue to evaluate these subpopulations of microglia further to facilitate the design of precise nanotherapeu-tics for targeting specific profiles of microglial activation.