Comparisons of Intranasal Delivery of Fluorescent Probe Cy5.5 and i.v. Injection of Cy5.5

Intranasal drug delivery is a promising approach for delivering drugs across the blood‐brain barriers into the brain. However, there has been insufficient information regarding the pathways of the drugs that are delivered by intranasal drug delivery. In this study we compared the distribution of Cy5.5 that is delivered by intranasal drug delivery and the distribution of Cy5.5 that is delivered by i.v. injection, by using a small animal fluorescence live imaging system. We found that there was a major difference in the distribution of Cy5.5 in internal organs after Cy5.5 was delivered by intranasal drug delivery or by i.v. injection: After i.v. injection of Cy5.5, there were major fluorescent signals in the liver, but not in the stomach; in contrast, after intranasal delivery of Cy5.5, there were major fluorescent signals in the stomach, but not in the liver. We also found that 1–2 hrs after intranasal delivery of Cy5.5, there were significant fluorescent signals in the olfactory bulbs, but not in the other regions of the brain. In contrast, there were fluorescent signals in multiple brain regions 1–2 hrs after intranasal delivery of Cy5.5. In summary, our study has indicated major differences between the pathway of a molecule delivered by intranasal approach and that delivered by i.v. injection. We also provided evidence demonstrating that olfactory bulbs are the major brain tissues that contain high concentrations of drugs after the drugs are delivered by the intranasal approach (Supported by Shanghai Engineering Center Grant of Equipment and Technology of Physical Therapy for Major Diseases #08DZ2211200, and a Key Research Grant of Shanghai Municipal Scientific Committee #08JC1415400).