In vivo distribution of liposome-encapsulated hemoglobin determined by positron emission tomography.

Positron emission tomography (PET) is a noninvasive imaging technology that enables the determination of biodistribution of positron emitter-labeled compounds. Lipidic nanoparticles are useful for drug delivery system (DDS), including the artificial oxygen carriers. However, there has been no appropriate method to label preformulated DDS drugs by positron emitters. We have developed a rapid and efficient labeling method for lipid nanoparticles and applied it to determine the movement of liposome-encapsulated hemoglobin (LEH). Distribution of LEH in the rat brain under ischemia was examined by a small animal PET with an enhanced resolution. While the blood flow was almost absent in the ischemic region observed by [(15)O]H(2)O imaging, distribution of (18)F-labeled LEH in the region was gradually increased during 60-min dynamic PET scanning. The results suggest that LEH deliver oxygen even into the ischemic brain from the periphery toward the core of ischemia. The real-time observation of flow pattern, deposition, and excretion of LEH in the ischemic rodent brain was possible by the new methods of positron emitter labeling and PET system with a high resolution.