Enhanced brain targeting of ApoE-functionalized lipid nanoparticles

The blood-brain barrier (BBB) plays an important role in maintaining the homeostasis of the central nervous system and in protecting the brain from potentially harmful endogenous and exogenous compounds. Nevertheless, it represents also the major obstacle for the diagnosis and therapy of brain diseases. One of the most promising strategies to overcome the limited BBB penetration of drugs and contrast agents is based on nanoparticles (NP). Lipid based NP, mainly liposomes (LIP) and solid lipid nanoparticles (SLN), have several advantages in terms of biocompatibility, non-immunogenicity, non-toxicity; they can be used as carrier systems and they have a prolonged circulation time in blood. Moreover, their surface can be easily modified with ligands which mediate a site-specific targeting. The aim of the present investigation is related to the evaluation of the ability of NP functionalized with Apolipoprotein-E (ApoE) or a peptide derived from ApoE (mApoE) to cross the BBB and reaching the brain parenchyma. The thesis is structured in three main chapters. In the first one, the intratracheal instillation (IT) has been investigated as an alternative, non-invasive delivery route to reach the brain. It has already been proven that LIP functionalized with phosphatidic acid (PA) and mApoE (mApoE-PA-LIP) and administered by intraperitoneal (IP) or intravenous (IV) injection, are able to cross the BBB in vivo. The results here obtained showed that mApoE-PA-LIP were able to cross the pulmonary epithelium ([14C]-PA permeability=6.5±2.0×10-6 cm/min) in vitro and to reach the brain (0.6 ug PA/g brain) in vivo. In the second chapter, the interaction of SLN covalently coupled with mApoE (SLN-mApoE) and brain capillary endothelial cells (hCMEC/D3) has been evaluated. SLN without surface-located peptide displayed less membrane accumulation and cellular uptake compared to SLN-mApoE. Moreover the presence of mApoE significantly enhanced SLN permeability across the BBB in vitro model ([14C]-DPPA permeability=5.7±0.3×10-5 cm/min, [3H]-CE permeability=6.9±0.4×10-5 cm/min). The in vivo biodistribution of SLN has been evaluated by means of fluorescent microscopy tomography system, and the here obtained results demonstrated that IT administration of SLN-mApoE significantly increased SLN-related fluorescence in the brain compared to IV and IP administrations. Finally, the third chapter focuses on an alternative strategy to functionalize the surface of SLN with ApoE by mimicking an artificial apolipoprotein-E mediated protein corona. Two isoforms of apolipoprotein-E were utilized to produce non-covalent functionalized SLN and their in vivo biodistribution after IV injection was assessed. Thirty minutes after injection, SLN+ApoE4 reached the brain thus distributing in the brain microvessels as well as in the brain parenchyma. These results suggest that the functionalization of both LIP and SLN with ApoE-derived peptide increases NP brain targeting and that IT instillation could be exploited as an alternative route for the administration of NP specifically designed for brain targeting. Moreover, the ApoE-mediated artificial protein corona effect could be an elegant alternative to increase SLN-BBB crossing.