Multifunctional theranostic nanocarrier platform for microglia-selective cytochalasin D delivery to modulate neuroinflammation after acute brain injuries

Targeting microglia to modulate neuroinflammation after acute brain injuries (ABIs) is promising but limited by poor blood-brain barrier (BBB) penetration and systemic toxicity of candidate agents. In addition, multifunctional platforms combining targeted therapy with real-time traceability remain limited. We developed and characterized a multifunctional theranostic, folate-functionalized, polydopamine (PDA)-coated mesoporous silica nanoparticle (FA-NP) system for microglia-selective delivery and intracellular release of cytoskeleton inhibitor Cytochalasin D (CytoD). FA-NPs exhibited ideal physicochemical properties for parenchymal brain accumulation and pH-sensitive PDA shells enabled intracellular retention and gradual degradation. Using radiolabeled and fluorescein-isothiocyanate-functionalized FA-NPs, SPECT/CT imaging, γ-counting, autoradiography, and immunohistochemistry confirmed parenchymal brain accumulation with cellular uptake following systemic administration. Activated microglia upregulated folate receptors (FOLR1/2) and internalized FA-NPs via FOLR-mediated, dynamin-dependent endocytosis. CytoD-loaded FA-NPs (FA-NP[CytoD]) significantly reduced microglial migration, phagocytosis, ROS production, and proinflammatory cytokines, outperforming molecular CytoD while exhibiting notably lower toxicity compared to both CytoD and unfunctionalized particles. In organotypic brain slice models of hypoxia-reoxygenation and traumatic injury, FA-NP[CytoD] reduced inflammation at 24 and 96 h. Systemic administration enabled brain accumulation with clearance over time. Together, this multifunctional theranostic platform integrates selective microglial targeting, controlled drug release, and multimodal imaging, offering translational potential for ABIs.