Hepatic delivery of particulates in the submicron range by a hydrodynamics-based procedure: implications for particulate gene delivery systems.
BACKGROUND: A large-volume intravenous (i.v.) injection of DNA, i.e. a hydrodynamics-based transfection procedure, is known to be an efficient and liver-specific method of in vivo gene delivery. However, little is available on an applicable particle size in the procedure. METHODS: We examined the effect of particle size on the hepatic delivery by the hydrodynamics-based procedure, using fluorescein isothiocyanate labeled polystyrene microspheres (MS) of 50, 200 or 500 nm in diameter. MS were injected intravenously to mice by a conventional (normal) or the hydrodynamics-based procedure and their degree of hepatic uptake was determined fluorometrically. RESULTS: For all sizes tested, the two procedures were similar in terms of the apparent degree of hepatic uptake, whereas the intrahepatic localization of MS was apparently different between the procedures as shown by an examination of frozen tissue sections. In mice with gadolinium chloride induced Kupffer cell blockade, the hepatic uptake of MS following the normal procedure was decreased while that of the hydrodynamics-based procedure was less affected. This phenomenon of enhanced hepatic delivery seemed to be more effective for larger particles. Confocal microscopic observation of hepatocyte suspensions indicated that part of the injected MS-50 was delivered intracellularly following the hydrodynamics-based procedure, whereas almost all the observed MS-200 and MS-500 were detected in the extracellular compartment or on the surface of the cells. This was supported by the fact that most of the injected MS existed pericellularly around the transgene-expressing cells. CONCLUSIONS: The hydrodynamics-based procedure facilitated extravasation and hepatic delivery of MS. Larger MS were more efficiently extravasated and trapped by the liver, whereas intracellular delivery hardly occurred with them.