Cationic lipids are essential for gene delivery mediated by intravenous administration of lipoplexes

Abstract

It was recently suggested that intravenously administered plasma as determined by an in vitro transfection assay. In lipoplexes serve as a depot for the extracellular release of spite of this high level of transcriptionally active DNA, there naked DNA and it is the naked DNA that mediates gene was no significant gene expression in the lung or any other delivery in the lung. If this is the mechanism responsible organ tested. In addition, when lipoplex containing a for gene expression, we reasoned that continuous infusion reporter gene was injected, followed by an infusion of nonof plasmid DNA should also result in significant lung coding plasmid DNA as a potential competing molecule for expression in the absence of lipoplexes. Moreover, the DNA released from the lipoplex there was no effect on infusion of non-coding plasmid DNA should inhibit gene gene expression. These experiments indicate that the catdelivery by lipoplexes. Infusion of plasmid DNA at a rate ionic lipid component of the lipoplex functions in an active of 80 g/min into the tail vein of a mouse resulted in a DNA capacity beyond that of a simple passive release matrix for serum concentration of 800 g/ml. This was equivalent to plasmid DNA. a transcriptionally active DNA concentration of 120 g/ml Keywords: DNA; infusion; mechanism; nonviral Lipoplex-mediated gene delivery 1,2 in vivo was demonstrated by the pioneering work of Brigham and colleagues. 3 Since then, many cationic lipid-based gene delivery protocols have entered clinical trials. [4][5][6][7][8][9] Despite this progress, the mechanism(s) by which lipoplexes deliver genes in vivo has not been elucidated.Recently, Song et al 10 injected cationic liposomes intravenously (i.v.) 5 min before an i.v. injection of a reporter gene. Surprisingly, the level of transgene expression in the lung was the same as that obtained following injection of the preformed lipoplex. Based on these data, Song et al suggested that extracellular DNA released from the lipoplex is the transfectionally active agent, and that the cationic lipid component serves only to increase pulmonary retention of DNA following systemic administration. 10 Given that naked plasmid DNA is capable of transfecting striated muscle 11,12 , the thyroid gland 13 , the liver 14 , the lung 15 , solid tumors 16 and synovial tissue 17 , we found Song's observations intriguing and believed the hypothesis to be an important conjecture. If the proposal is correct, then any sustained release system for DNA should mediate transfection in the lung. Potentially, one could obtain gene expression without the adverse effects associated with the cationic lipid.We repeated Liu's experiments and confirmed the observations. The pre-injection of cationic liposomes, followed 5 min later by a luciferase reporter gene, yielded We hypothesized that if free DNA is the active transfection agent in pulmonary gene delivery following i.v. lipoplex injection, then establishing a relatively high steady-state plasma concentration of transcriptionally active DNA would yie...

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