Mechanism of plasmid delivery by hydrodynamic tail vein injection. II. Morphological studies

Preferential delivery of the Sleeping Beauty transposon system to livers of mice by hydrodynamic injection

Nonviral, DNA-mediated gene transfer is an alternative to viral delivery systems for expressing new genes in cells and tissues. The Sleeping Beauty (SB) transposon system combines the advantages of viruses and naked DNA molecules for gene therapy purposes; however, efficacious delivery of DNA molecules to animal tissues can still be problematic. Here we describe the hydrodynamic delivery procedure for the SB transposon system that allows efficient delivery to the liver in the mouse. The procedure involves rapid, high-pressure injection of a DNA solution into the tail vein. The overall procedure takes <1 h although the delivery into one mouse requires only a few seconds. Successful injections result in expression of the transgene in 5-40% of hepatocytes 1 d after injection. Several weeks after injection, transgene expression stabilizes at approximately 1% of the level at 24 h, presumably owing to integration of the transposons into chromosomes.

Gene therapy progress and prospects: hydrodynamic gene delivery

Over the last few years, hydrodynamic tail vein delivery has established itself as a simple, yet very effective method for gene transfer into small rodents. Hydrodynamic delivery of plasmid DNA expression vectors or small interfering RNA allows for a broad range of in vivo experiments, including the testing of regulatory elements, antibody generation, evaluation of gene therapy approaches, basic biology and disease model creation (non-heritable transgenics). The recent development of the hydrodynamic limb vein procedure provides a safe nucleic acid delivery technique with equally high efficiency in small and large research animals and, importantly, the prospects for clinical translation.

Mechanism of plasmid delivery by hydrodynamic tail vein injection. I. Hepatocyte uptake of various molecules

BACKGROUND

The hydrodynamic tail vein (HTV) injection of naked plasmid DNA is a simple yet effective in vivo gene delivery method into hepatocytes. It is increasingly being used as a research tool to elucidate mechanisms of gene expression and the role of genes and their cognate proteins in the pathogenesis of disease in animal models. A greater understanding of its mechanism will aid these efforts and has relevance to macromolecular and nucleic acid delivery in general.

METHODS

In an attempt to explore how naked DNA enters hepatocytes the fate of a variety of molecules and particles was followed over a 24-h time frame using fluorescence microscopy. The uptake of some of these compounds was correlated with marker gene expression from a co-injected plasmid DNA. In addition, the uptake of the injected compounds was correlated with the histologic appearance of hepatocytes.

RESULTS

Out of the large number of nucleic acids, peptides, proteins, inert polymers and small molecules that we tested, most were efficiently delivered into hepatocytes independently of their size and charge. Even T7 phage and highly charged DNA/protein complexes of 60-100 nm in size were able to enter the cytoplasm. In animals co-injected with an enhanced yellow fluorescent protein (EYFP) expression vector and fluorescently labeled immunoglobulin (IgG), hepatocytes flooded with large amounts of IgG appeared permanently damaged and did not express EYFP-Nuc. Hepatocytes expressing EYFP had only slight IgG uptake. In contrast, when an EYFP expression vector was co-injected with a fluorescently labeled 200-bp linear DNA fragment, both were mostly (in 91% of the observed cells) co-localized to the same hepatocytes 24 h later.

CONCLUSIONS

The appearance of permanently damaged cells with increased uptake of some molecules such as endogenous IgG raised the possibility that a molecule could be present in a hepatocyte but its transport would not be indicative of the transport process that can lead to foreign gene expression. The HTV procedure enables the uptake of a variety of molecules (as previous studies also found), but the uptake process for some of these molecules may be associated with a more disruptive process to the hepatocytes that is not compatible with successful gene delivery.