Central nervous system (CNS) infections are formidable diseases with high rates of morbidity and mortality. Since the majority of antimicrobial agents discovered so far do not cross the blood-brain barrier (BBB), the treatment of CNS infections is a major challenge issue. Delivering therapeutic agents in a targeted manner is highly desirable, but tough to achieve. The advent of dendritic polymers offers a new length scale (~3-10 nm) in drug delivery, with significant versatility to incorporate multiple active molecules such as targeting moieties and imaging agents.

In this study, we examine the feasibility of achieving brain-targeted drug delivery by dendrimer (G4 hydroxyl terminated), which were labeled with fluoroisothiocyanate (FITC) through subdural microinjection, intravenous, or intranasal infusions in a well-established rabbit model of cerebral palsy..

Methods:

Pregnant New Zealand White rabbits underwent laparotomy and were injected with 20 Escherichia coli lipopolysaccharide along the length of the uterus on day 28 of gestation. The pups were born spontaneously at term (31 days). The Biodistrbution of dendrimer-FITC or free-FITC in pups brain was compared with that endotoxic group(LPS 20ug/kg) or control group(PBS). 5ug Dendrimer G4-OH-FITC in 10 microl of PBS were infused into CSF through subdural microinjection (10ul/min). Intravenous injection and intranasal infusions were performed using 500ug Dendrimer G4-OH-FITC in 100ul PBS. The same amount Free-FITC in Dendrimer G4-OH-FITC was performed by subdural microinjection, intravenous and intranasal infusions, as a control. At 6h or 24h, two pups from each group were sacrificed and brain was fixed, frozen section, and the brain section of pups were immunostained with tomato-lectin and GFAP, and observed by fluorescent microscope and confocal microscope.

Results:

Upon subdural microinjection in the endotoxin group, the dendrimer-FITC was found to be localized in actived microglial & astrocytes cells, around the lateral ventricle, corpus callosum, hippocampus and internal capsule. In the control group, which normally don't have activated microglia or astrocytes in these regions, did not show appreciable uptake. For comparable doses, the dendrimer-FITC intensity in the endotoxin group was significantly higher than those in the control group. Upon intravenous injection, the dendrimer-FITC were found to be localized in internal ventricle, hippocampus and commissura fornicis region. Dendrimer-FITC is taken up specifically by microglial cells on intravenous injection only in endotoxin group. As a control free-FITC uptake was studied. Free-FITC uptake appears to be non-specific, showing measurable fluorescence only on subdural microinjection. No Free-FITC uptake followed by intravenous injection in both endotoxic group and control group. For intranasal infusions, no Dendrimer-FITC and Free-FITC uptake was seen in both endotoxin group and control group.

Conclusion:

Our findings indicate that dendrimer nanodevices can be used to specifically target activated microglial cells and astrocytes in neuroinflammatory disorders. It suggests that brain-targeted drug delivery can be achieved by infusion of dendrimer nanodevices through subdural microinjection and intravenous infusion.