(L-450) Spatial-temporal distribution of different size agents in the brain after intranasal delivery

Blood-brain barrier plays a major obstacle for brain drug delivery in treating Central Nervous System (CNS)  disease. Intranasal administration offers a promising non-invasive brain drug delivery approach, direct delivery the drug from nose to brain, bypassing the BBB and reduce systemic side effects [1, 2]. Despite its potential, clinical application has been limited to small molecular drugs. Therefore, a size-dependent investigation on therapeutic agent is necessary to better understand the transportation routes and dynamics after intranasal (IN) delivery. This study seeks to quantify spatial-temporal distribution of agents in the brain following intranasal (IN) administration and provide detailed visual insights into the size-dependent dynamics of agent distribution in specific cells and brain regions. The research aims to advance targeted and efficient through this noninvasive IN delivery strategy, addressing neurological disorders more effectively and improving treatment for CNS diseases.

Texas-Red labeled Dextran with various size (3Kda, 10Kda and 70Kda) were IN-delivered to the wiletype mice. Mice were sacrifice at 1hr, 4hr, 24hr post IN delivery by transcranial perfusion, with collection brain and blood sample. The Fluorescent imaging were employed to visualize the spatial and temporal distribution of the dextran in brain . The region of dextran delivery was semi-automatically segmented to sagittal atlas to reveal the patterns of dextran distribution in the specific brain region. Cell-specific uptaken of the dextran in different brain regions were also indentified by stainning the neuron, mircoglia and astrocytes. The florecence intensity of the dextran in blood and CSF were quantifiy by plate reader to reveal the potential roles of those two routes in IN delivery.

The 3Kda dextran exhibited superior delivery to both the nasal epithelium and brain compared to the 10Kda and 70Kda dextran. Interestingly, there was no significant difference in fluorescent intensity within the brain between the 10Kda and 70Kda dextran. Additionally, the 3Kda dextran demonstrated higher permeation into the bloodstream compared to the 10Kda and 70Kda dextran. And the microscope image shows that dextran was mainly uptake by neurons in the frontal cortex, midbrain, medulla, and pons instead of other cell types.

The fluorescent intensity of the entire brain was significantly higher at 1 hour and 4 hours following intranasal (IN) delivery compared to 24 hours post-delivery (Figure 1A), suggesting drug clearance after 24 hours. The olfactory bulb and anterior olfactory nucleus exhibited the highest levels of dextran accumulation within the 1 hour, with fluorescence intensity decreasing at 4 hours and 24 hours. After 1 hour, the dextran redistributed to other brain regions, such as the hippocampus, pallidum, and striatum. In contrast, the areas surrounding the trigeminal nerve entry points, including the thalamus, hypothalamus, midbrain, and medulla, showed an increase in fluorescent intensity from 1 hour to 4 hours, reaching the highest levels at 4 hours (Figure 1C). Previous studies have reported that IN-administered drugs reach the brain through the olfactory and trigeminal nerves as entryways. After reaching brain entry points, drugs are distributed throughout the brain via the perivascular spaces (PVS) [3]. The marked fluorescence in the olfactory bulb at 1 hour post-administration suggests fast transportation along the olfactory nerve, while the marked fluorescence in the pons at 4 hours suggests transportation along the trigeminal nerve.

This study demonstrate insights into size effect and spatiotemporal dynamics of dextran distribution in specific brain regions following IN administration. The result emphasize the significance of considering specific brain regions and time points when utilizing IN drug delivery. These findings provides insights for developing targeted IN drug delivery strategies that may enhance treatment outcomes for neurological disorders.