Following intra-cranial administration, levels of H435A in the brain hemispheres did not change over a 24 h period while the levels of N434A significantly decreased over time. Intranasal-to-CNS delivery was used initially because it is a non-invasive technique. For maximal delivery to the brain hemispheres, the test article had to be
applied directly to the olfactory epithelium of the nose (Thorne et al., 2004). Test article then moves in a paracellular fashion, driven by diffusion, past the olfactory epithelium, and into the nasal lamina propria beneath (Dhuria et Dasatinib al., 2010). This space is contiguous with channels through the cribriform plate, which contain the axons of the olfactory neurons. Earlier studies have shown that a certain percentage of cerebrospinal fluid (CSF) exits the
brain through the cribriform plate and enters nasal lymphatics which drain into the cervical lymph nodes (Bradbury et al., 1981, Bradbury and Westrop, 1983 and Cserr et al., 1992). This process could represent a hindrance to molecular flow into the brain. However, subsequent ultra-structural studies have demonstrated the existence of neuronal channels that traverse the subarachnoid space (Field et al., 2003 and Li et al., 2005) thus preventing direct interaction with CSF. These channels are believed to provide direct access into the parenchyma of the brain hemispheres (Dhuria et al., 2010 and Lochhead and Thorne, 2012). Functional studies using both small and large molecules have shown delivery to the hemispheres via this mechanism despite this potential hindrance. Ipilimumab The main driving force for uptake is the concentration gradient
of the test article (Barakat et al., 2006, Evseev et al., 2010, Furrer acetylcholine et al., 2009, Gorbatov et al., 2010, Hoekman and Ho, 2011, Romanova et al., 2010 and Sipos et al., 2010). However, there are two main factors that do impinge on the efficiency of CNS uptake of a molecule using this technique: those related to formulation, and those related to physicochemical characteristics. The formulation considerations include the type, pH, and tonicity of the buffer, and/or the presence of excipients representing transport enhancers, stabilizers, and muco-adhesives (Pujara et al., 1995 and Washington et al., 2000). The important physicochemical characteristics include molecular size, hydrophobicity/hydrophilicity, surface charge, and mucus compatibility (Vyas et al., 2006). The test articles used in these studies are similar in terms of their physicochemical characteristics. Both H435A and N434A have pI values of 7.2, differ by just one amino acid, and have virtually identical secondary and tertiary structures as measured by circular dichroism. Functionally, they only differ in their affinity for the FcRn receptor, have no known targets in the brain and therefore are uniquely suited to use address the role of FcRn in IgG efflux from the brain.