Efficient introduction of macromolecules and oligonucleotides into brain capillary endothelial cells using HVJ-liposomes

Brain endothelial cell-cell junctions: how to "open" the blood brain barrier

The blood-brain barrier (BBB) is a highly specialized structural and biochemical barrier that regulates the entry of blood-borne molecules into brain, and preserves ionic homeostasis within the brain microenvironment. BBB properties are primarily determined by junctional complexes between the cerebral endothelial cells. These complexes are comprised of tight and adherens junctions. Such restrictive angioarchitecture at the BBB reduces paracellular diffusion, while minimal vesicle transport activity in brain endothelial cells limits transcellular transport. Under normal conditions, this largely prevents the extravasation of large and small solutes (unless specific transporters are present) and prevents migration of any type of blood-borne cell. However, this is changed in many pathological conditions. There, BBB disruption (“opening”) can lead to increased paracellular permeability, allowing entry of leukocytes into brain tissue, but also contributing to edema formation. In parallel, there are changes in the endothelial pinocytotic vesicular system resulting in the uptake and transfer of fluid and macromolecules into brain parenchyma. This review highlights the route and possible factors involved in BBB disruption in a variety of neuropathological disorders (e.g. CNS inflammation, Alzheimer’s disease, Parkinson’s disease, epilepsy). It also summarizes proposed signal transduction pathways that may be involved in BBB “opening”.

Getting into the brain: approaches to enhance brain drug delivery

Being the most delicate organ of the body, the brain is protected against potentially toxic substances by the blood-brain barrier (BBB), which restricts the entry of most pharmaceuticals into the brain. The developmental process for new drugs for the treatment of CNS disorders has not kept pace with progress in molecular neurosciences because most of the new drugs discovered are unable to cross the BBB. The clinical failure of CNS drug delivery may be attributed largely to a lack of appropriate drug delivery systems. Localized and controlled delivery of drugs at their desired site of action is preferred because it reduces toxicity and increases treatment efficiency. The present review provides an insight into some of the recent advances made in the field of brain drug delivery.The various strategies that have been explored to increase drug delivery into the brain include (i) chemical delivery systems, such as lipid-mediated transport, the prodrug approach and the lock-in system; (ii) biological delivery systems, in which pharmaceuticals are re-engineered to cross the BBB via specific endogenous transporters localized within the brain capillary endothelium; (iii) disruption of the BBB, for example by modification of tight junctions, which causes a controlled and transient increase in the permeability of brain capillaries; (iv) the use of molecular Trojan horses, such as peptidomimetic monoclonal antibodies to transport large molecules (e.g. antibodies, recombinant proteins, nonviral gene medicines or RNA interference drugs) across the BBB; and (v) particulate drug carrier systems. Receptor-mediated transport systems exist for certain endogenous peptides, such as insulin and transferrin, enabling these molecules to cross the BBB in vivo.The use of polymers for local drug delivery has greatly expanded the spectrum of drugs available for the treatment of brain diseases, such as malignant tumours and Alzheimer's disease. In addition, various drug delivery systems (e.g. liposomes, microspheres, nanoparticles, nanogels and bionanocapsules) have been used to enhance drug delivery to the brain. Recently, microchips and biodegradable polymers have become important in brain tumour therapy.The intense search for alternative routes of drug delivery (e.g. intranasal drug delivery, convection-enhanced diffusion and intrathecal/intraventricular drug delivery systems) has been driven by the need to overcome the physiological barriers of the brain and to achieve high drug concentrations within the brain. For more than 30 years, considerable efforts have been made to enhance the delivery of therapeutic molecules across the vascular barriers of the CNS. The current challenge is to develop drug delivery strategies that will allow the passage of drug molecules through the BBB in a safe and effective manner.

Enhanced gene transfer into brain capillary endothelial cells using Antp-modified DNA-loaded nanoparticles

Brain capillary endothelial cells (BCECs) have been considered as one of the primary targets for cerebral gene therapy. However, the cells, well-known for their poor function of endocytosis, are difficult to be transfected by general non-viral vectors. The aim of this study was to enhance the efficiency of transfection and expression in BCECs of DNA/polymer nanoparticles with the modification of membrane-penetrating peptide, Antennapedia peptide (Antp) polyethylenimine (PEI) and polyamidoamine (PAMAM) were chosen to prepare Antp-modified DNA-loaded nanoparticles with a complex coacervation technique. After a 20-min transfection, the efficiency, in terms of transfection and expression, of DNA/PEI NP or DNA/PAMAM NP was enhanced significantly with the modification of Antp. After a 3-h transfection of DNA/Antp/PEI NP, there was no difference in cellular uptake but an enhancement in gene expression, compared to DNA/PEI NP alone. However, both the transfection and expression efficiency of DNA/PAMAM NP were enhanced using Antp. These observations suggest that Antp can increase the membrane-penetrating ability of DNA-loaded nanoparticles, which can be employed as novel non-viral gene vectors.

A Viral Envelope as a Vehicle for Tracer, Drug, and Gene Delivery: Initial Biodistribution Study Using PET Imaging

Viral envelopes can be used as an effective vehicle to deliver imaging tracers as well as therapeutic drugs and genes. However, the current methods for in vivo tracking of viral envelopes are limited. This purpose of this study is to investigate dynamically the in vivo biodistribution of viral envelopes using positron emission tomography (PET) imaging. The hemagglutinating virus of Japan envelope (HVJ-E) was labeled with radioactive fluorine (F-18) for tracking with PET imaging. Due to the low molecular weight of F-18, the encapsulation process by HVJ-E was optimized using the cationic agent poly-L-lysine (PLL, MW 66.7 kDa) and Feridex, a magnetic resonance imaging tracer. After labeling, HVJ-Es were injected intravenously into the normal rat and followed for 2 h using high resolution PET imaging. Region of interest analysis showed a significant increase in average liver accumulation based on radioactivity as compared to all control subjects. Average brain uptake showed a significant increase in radioactivity as compared to control subjects receiving F-18-PLL complexes or F-18 alone. Control subjects showed F-18 uptake primarily in the bones. These results demonstrate a molecular imaging technique that can be used to monitor drug and gene delivery and evaluate potential targeting mechanisms.

Colloidal carriers and blood–brain barrier (BBB) translocation: A way to deliver drugs to the brain?

The major problem in drug delivery to the brain is the presence of the blood-brain barrier (BBB) which limits drug penetration even if in certain pathological situations the BBB is partly disrupted. Therefore, various strategies have been proposed to improve the delivery of drugs to this tissue. This review presents the status of the BBB in healthy patients and in pathologies like neurodegenerative, cerebrovascular and inflammatory diseases. The second part of this article aims to review the invasive and non-invasive strategies developed to circumvent the BBB and deliver drugs into the brain. The use of nanotechnologies (liposomes, nanoparticles) is especially discussed in the ultimate part of the review evidencing their potentiality as non-invasive technique in the brain delivery of drugs with the possibility to target specific brain tissue thanks to ligand linked to carrier surface.

Nanogels for oligonucleotide delivery to the brain

Systemic delivery of oligonucleotides (ODN) to the central nervous system is needed for development of therapeutic and diagnostic modalities for treatment of neurodegenerative disorders. Macromolecules injected in blood are poorly transported across the blood-brain barrier (BBB) and rapidly cleared from circulation. In this work we propose a novel system for ODN delivery to the brain based on nanoscale network of cross-linked poly(ethylene glycol) and polyethylenimine ("nanogel"). The methods of synthesis of nanogel and its modification with specific targeting molecules are described. Nanogels can bind and encapsulate spontaneously negatively charged ODN, resulting in formation of stable aqueous dispersion of polyelectrolyte complex with particle sizes less than 100 nm. Using polarized monolayers of bovine brain microvessel endothelial cells as an in vitro model this study demonstrates that ODN incorporated in nanogel formulations can be effectively transported across the BBB. The transport efficacy is further increased when the surface of the nanogel is modified with transferrin or insulin. Importantly the ODN is transported across the brain microvessel cells through the transcellular pathway; after transport, ODN remains mostly incorporated in the nanogel and ODN displays little degradation compared to the free ODN. Using mouse model for biodistribution studies in vivo, this work demonstrated that as a result of incorporation into nanogel 1 h after intravenous injection the accumulation of a phosphorothioate ODN in the brain increases by over 15 fold while in liver and spleen decreases by 2-fold compared to the free ODN. Overall, this study suggests that nanogel is a promising system for delivery of ODN to the brain.