Abstract Utilization of neuropharmaceuticals for central nervous system(CNS) disease is highly limited due to the blood-brain barrier(BBB) which restricts molecules larger than 500Da from reaching the CNS. The development of a reliable method to bypass the BBB would represent an enormous advance in neuropharmacology enabling the use of many potential disease modifying therapies. Previous attempts such as transcranial catheter implantation have proven to be temporary and associated with multiple complications. Here we describe a novel method of creating a semipermeable window in the BBB using purely autologous tissues to allow for high molecular weight(HMW) drug delivery to the CNS. This approach is inspired by recent advances in human endoscopic transnasal skull base surgical techniques and involves engrafting semipermeable nasal mucosa within a surgical defect in the BBB. The mucosal graft thereby creates a permanent transmucosal conduit for drugs to access the CNS. The main objective of this study was to develop a murine model of this technique and use it to evaluate transmucosal permeability for the purpose of direct drug delivery to the brain. Using this model we demonstrate that mucosal grafts allow for the transport of molecules up to 500 kDa directly to the brain in both a time and molecular weight dependent fashion. Markers up to 40 kDa were found within the striatum suggesting a potential role for this technique in the treatment of Parkinson's disease. This proof of principle study demonstrates that mucosal engrafting represents the first permanent and stable method of bypassing the BBB thereby providing a pathway for HMW therapeutics directly into the CNS.

Citation: Bleier BS, Kohman RE, Feldman RE, Ramanlal S, Han X (2013) Permeabilization of the Blood-Brain Barrier via Mucosal Engrafting: Implications for Drug Delivery to the Brain. PLoS ONE 8(4): e61694. https://doi.org/10.1371/journal.pone.0061694 Editor: Richard Jay Smeyne, St. Jude Children's Research Hospital, United States of America Received: December 24, 2012; Accepted: March 13, 2013; Published: April 24, 2013 Copyright: © 2013 Bleier et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: This study was funded by the Michael J. Fox Foundation for Parkinson's Research 2011 Rapid Response Innovations Awards Program. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing interests: Benjamin Saul Skorr Bleier is an inventor of the described technique which is protected under a non-provisional US patent(METHODS OF TREATING PAIN AND NEUROLOGICAL DISORDERS, AND DELIVERING PHARMACEUTICAL AGENTS US20130030056 A1). There are no further patents, products in development or marketed products to declare. This does not alter the authors' adherence to all the PLOS ONE policies on sharing data and materials.

Introduction Neurologic disorders affect more than 20 million patients in the US alone and account for over $400 billion in annual expenditure for both their treatment and chronic care [1], [2]. The paucity of effective neurodegenerative therapies is directly attributable to the presence of the blood-brain barrier(BBB) and blood-cerebrospinal fluid barrier(BCSFB). These barriers are composed of densely packed cells with copious intercellular tight junctions(TJ), active efflux pumps, and a trilamellar basement membrane which prevent the absorption of polar or high molecular weight(HMW) molecules larger than 500Da [3]. This results in restriction of up to 98% of all potential neuropharmaceutical agents from reaching the central nervous system(CNS) [3]. Consequently, known charged or macromolecular therapies which may be capable of preventing or even reversing certain neurologic diseases are rendered clinically ineffective due to their inability to cross the BBB. The limitations of the BBB have catalyzed a considerable research effort into ways to circumvent this barrier. Currently described experimental methods such as transcranial catheter placement [4] and the use of protein conjugates [1] may be invasive or require extensive drug manipulation to optimize trans-BBB transport rendering them impractical, morbid, and expensive to scale up for widespread clinical use. Furthermore even if the BBB could be successfully overcome, the majority of these strategies rely on a peripheral delivery route leading to potential systemic toxicity and pulsatile CNS delivery [2]. The evident value of a direct pathway capable of continuous delivery of polar and macromolecular therapies has led to a large body of work seeking to exploit the olfactory mucosa for this purpose. Trans-olfactory CNS uptake of nerve