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. Hydroxyl dendrimers target reactive microglia in multiple neuroinflammatory models including cerebral palsy (CP). Insights on the differential uptake of dendrimers between subpopulations of microglia will enable better design of precise nanomedicines for the treatment of neuroinflammation. We have previously demonstrated that microglia of CP rabbits undergo change to a pro-inflammatory phenotype that selectively take up dendrimer nanoparticles that is proportional to the severity of the injury. However, the functional changes in microglia associated with this activated phenotype and related mechanisms of dendrimer uptake are not well understood. Here, we established a method for isolating microglia from CP 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 be used to isolate microglia from rabbit brain tissue. A significantly higher proportion of microglia isolated from CP 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 uptake in subpopulations of microglia and was significantly higher in microglia from CP rabbits when compared to healthy controls. This study demonstrates that PAMAM hydroxyl dendrimers are preferentially taken up by microglia especially in CP rabbits, and that subpopulations of microglia demonstrate differential dendrimer uptake. Future work will continue to further evaluate these subpopulations of microglia to facilitate the design of precise nanotherapeutics for targeting specific profiles of microglial activation.