Biodistribution and Gene Expression of Lipid/Plasmid Complexes after Systemic Administration

Abstract

The objectives of this study were to investigate the influence of physicochemical properties of lipid/plasmid complexes on in vivo gene transfer and biodistribution characteristics. Formulations based on 1,2-di-O-octadecenyl-3-trimethylammonium propane (DOTMA) and novel biodegradable cationic lipids, such as ethyl dioleoyl phosphatidylcholine (EDOPC), ethyl palmitoyl myristyl phosphatidylcholine (EPMPC), myristyl myristoyl carnitine ester (MMCE), and oleyl oleoyl l-carnitine ester (DOLCE), were assessed for gene expression after tail vein injection of lipid/plasmid complexes in mice. Gene expression was influenced by cationic lipid structure, cationic lipid-to-colipid molar ratios, plasmid-to-lipid charge ratios, and precondensation liposome size. Detectable levels of human growth hormone (hGH) in serum, human factor IX (hFIX) in plasma, and chloramphenicol acetyltransferase (CAT) in the lung and liver were observed with positively charged lipid/plasmid complexes prepared from 400-nm extruded liposomes with a cationic lipid-to-colipid ratio of 4:1 (mol/mol). Intravenous administration of lipid/CAT plasmid complexes resulted in distribution of plasmid DNA mainly to the lung at 15 min after injection. Plasmid DNA accumulation in the liver increased with time up to 24 hr postinjection. There was a 10-fold decrease in the amount of plasmid DNA in the lung at 15 min after injection, when the lipid/plasmid complex charge ratio was decreased from 3:1 to 0.5:1 (+/–). Bright fluorescent aggregates were evident in in vivo-transfected lung with the positively charged pCMV-CAT/DOLCE:dioleyl phosphatidylethanolamine (DOPE) (1:1, mol/mol) complexes, while more discrete punctate fluorescence was observed with a 4:1 molar ratio of cationic lipid:colipid formulations. Preinjection of polyanions such as plasmid, dextran sulfate, polycytidic acid, and polyinosinic acid decreased hGH expression, whereas the preinjection of both positively charged and neutral liposomes had no effect on hGH serum levels. Of the cationic lipids tested, DOLCE was found to be the most effective potentially biodegradable cationic lipid. A correlation between gene expression and cationic lipid:colipid ratios and lipid-to-plasmid charge ratio was also observed for DOTMA- and DOLCE-based formulations.

Overview summary

Our intent in this study was to characterize lipid/plasmid complexes in terms of their physicochemical properties, in vivo gene transfer efficiency, and organ distribution. In an attempt to improve on the performance of cationic lipid-based systems for systemic gene delivery and expression, various combinations of cationic lipid to colipid, lipid/plasmid ratios, as well as methods of preparation, were tested. Variation of these factors that led, for instance, to alterations in particle size and charge density was found to influence transfection efficiency after systemic administration of pCMV-hGH and pCMV-CAT complexed with cationic lipids (DOTMA, DOLCE, MMCE, EDOPC, and EPMPC). The deposition of DOLCE:DOPE/pCMV-CAT complexes in the lung and liver was mainly influenced by their lipid/DNA charge ratio, but was relatively insensitive to the amount of colipid contained in the formulation, although a significant effect of the cationic lipid-to-colipid molar ratios on gene expression was observed. Significant levels of hGH in serum, hFIX in plasma, and CAT in the lung and liver were observed with several formulations. In general, optimal gene expression was obtained with low amounts of colipid (cholesterol or DOPE), positively charged lipid/plasmid complexes, and liposomes with a diameter ≥200 nm.