Role of functionalized liposomes in drug delivery through the blood-brain barrier

The central nervous system (CNS), one of the most delicate microenvironments of the body, is protected by the blood-brain barrier (BBB). The protective properties of the BBB are conferred by the intricate architecture of its endothelium coupled with multiple specific transport systems expressed on the surface of endothelial cells in the brain vasculature. Although the BBB has a key role in regulation of neural biochemical environment, essential for maintaining neuronal integrity, it limits drug delivery to the CNS. In fact, less than 2% of all US Food and Drug Agency (FDA)-approved small-molecule drugs cross the intact BBB to varying degrees. Due to their flexible physicochemical and biophysical properties, the liposomes represent an attractive tool to deliver therapeutic molecules across the BBB. Moreover, their surface can be easily modified with ligands to improve their target and delivery. The peptide gH625, identified as a membrane-perturbing domain in glycoprotein H (gH) of Herpes Simplex virus 1, has been used extensively for vector-mediated strategies that enable passage of a large variety of small molecules as well as proteins across cell membranes in vitro. The goal of this Ph.D. project was to develop a new carrier system to deliver therapeutic molecules through the BBB with high efficacy and minimal toxicity. The project was divided in two parts. In the first part, in vitro and in vivo experiments were performed to investigate the capacity of gH625 peptide to enter and accumulate in neuron and astrocyte cell lines, and its ability to cross the blood-brain barrier in rats. In the second part of the project, the efficiency of liposomes functionalized with gH625 was evaluated on both in vitro model of rat BBB by using a neuroprotective peptide like PACAP (pituitary adenylate cyclase-activating polypeptide) and on in vivo mouse brain by using a hypothermic neuropeptide. The results show that gH625 peptide has a significant ability to penetrate brain cells. In fact, gH625 can be efficiently incorporated by human neuroblastoma (SH-SY5Y) and glioblastoma-astrocytoma cell lines (U-87 MG) without alteration of their cell viability. Furthermore, the in vivo experiments demonstrate that, despite the blood filtration action of the liver, carried out through the gH625 uptake of Kupffer cells, gH625 substantially reaches the brain BBB vessels. In particular, gH625 can be highly accumulated in endothelial cells of the BBB and taken up in some neurons. The results of second part of project show that the functionalization of liposomes with gH625 improves their passage through the endothelium of in vitro BBB model, thus resulting in an increased transport of PACAP and its less accumulation in the endothelial cells. Moreover, the toxicity studies reveal that the gH625-liposomes are nontoxic and do not affect tight junction organization in the BBB endothelium. Finally, further in vivo results demonstrated that the gH625 peptide may improve the efficiency of liposomes in mice. The results of this study suggest that gH625 peptide is a valuable tool to develop functionalized nanosystems for drug delivery to the brain. In particular, gH625-mediated liposomes represent a promising strategy to deliver therapeutic agents to CNS. Taken together, these data may have importance for the treatment of brain diseases and tracking of nanosystems in vivo