Quantitative analysis of inulin distribution in the brain focused on nose-to-brain route via olfactory epithelium by reverse esophageal cannulation.

This study aimed to determine the effect of intranasal dosing speed and administrating volume of nose-to-brain delivery on candidates for peptide drugs (molecular weight ca. 1-10 kDa). Using inulin as the model molecule of a peptide drug, intranasal administration by cannulation from the airway side through the esophagus was tested in mice. This was done to determine the quantitative distribution levels of the drug in the brain and cerebral spinal fluid (CSF). Distribution levels were increased with slower and constant speed (5 µL/min), with higher dosing volume equivalent to nasal volume per body weight in mice (25 µL), and were recorded 0.27% injected dose per gram of tissue (ID/g) in the brain, and 0.24% injected dose per milliliter (ID/mL) in the CSF at 60 min. Then, brain distribution resulting from reverse cannulation was two times more than that of the typical intranasal administration method using a micropipette. In addition, the percentage of inulin estimated to reach the brain via direct transport (%DTP) during reverse cannulation was estimated to be 93%, suggesting that ~95% of the total dose was transferred directly to the brain via the olfactory mucosa. These results show that distribution of the peptide drug in the brain was increased through constant administration at a slow and constant speed.

Novel Methods for Intranasal Administration Under Inhalation Anesthesia to Evaluate Nose-to-Brain Drug Delivery.

Intranasal administration has been reported to be a potential pathway for nose-to-brain delivery of therapeutic agents that circumvents the blood-brain barrier. However, there have been few reports regarding not only the quantitative analysis but also optimal administration conditions and dosing regimens for investigations of nose-to-brain delivery. The limited progress in research on nose-to-brain pathway mechanisms using rodents represents a significant impediment in terms of designing nose-to-brain delivery systems for candidate drugs. To gain some headway in this regard, we developed and evaluated two novel methods of stable intranasal administration under inhalation anesthesia for experimental animals. We also describe a method for the evaluation of drug distribution levels in the brain via the nose-to-brain pathway using radio-labeled [14C]-inulin (molecular weight: 5,000) as a model substrate of water-soluble macromolecules. Initially, we developed a pipette-based intranasal administration protocol using temporarily openable masks, which enabled us to perform reliable administration to animals under stable anesthesia. Using this system, [14C]-inulin could be delivered to the brain with little experimental error. We subsequently developed an intranasal administration protocol entailing reverse cannulation from the airway side through the esophagus, which was developed to minimize the effects of mucociliary clearance (MC). This technique led to significantly higher levels of [14C]-inulin, which was quantitatively detected in the olfactory bulb, cerebrum, and medulla oblongata, than the pipette method. This appears to be because retention of the drug solution in the nasal cavity was substantially increased by active administration using a syringe pump in a direction opposite to the MC into the nasal cavity. In conclusion, the two methods of intranasal administration developed in this study can be expected to be extremely useful techniques for evaluating pharmacokinetics in rodents. The reverse cannulation method, in particular, could be useful for evaluating the full potential of nose-to-brain delivery of drug candidates.