Electroporation of the vasculature and the lung

Abstract

Electroporation has proven to be a highly effective technique for the in vivo delivery of genes to a number of solid tissues. In most of the reported methods, DNA is injected into the target tissue and electrodes are placed directly on or in the tissue for application of the electric field. While this works well for solid tissues, there are many tissues and organs that are not amenable to such an approach. In this review I will focus on the development of electroporation protocols for two such tissues: the vasculature and the lung. Several methods for in vivo electroporation of the vasculature have been developed in recent years that deliver DNA to vessel segments from either the inside or outside of the vessel. The advantages and disadvantages of each are discussed, as are the applications for which they have been used. In more recent work, our laboratory has developed a novel method to deliver genes to the rodent lung that results in high level, uniform, gene expression throughout all cell types of the lung. Most importantly, this technique is safe, and causes no inflammatory response or alterations in normal physiology of the organs. Taken together, these studies demonstrate the utility of electroporation for gene transfer to non injectible tissues.

FIG. 1

Approaches for vascular electroporation. (A) Porous catheter-based electrode (Genetronics) (Dev et al., 1998, 2000). E1 and E2 indicate the electrodes. (B) Double balloon catheter and external electrodes (Matsumoto et al., 2001). (C) Bath electrode (Martin et al., 2000).

FIG. 2

Gene transfer and electroporation of the mesenteric vasculature. (A) The mesenteric vascular tree. (B) DNA solution being pipetted into the electrode. The vessel is draped into the bath electrode, which is surrounded by surgical drapes to maintain a sterile field. At the end of the electroporation of this vessel, the DNA solution can be removed and reused for the next vessel. (C) Placement of electrode during surgery.

FIG. 3

Comparison of gene expression in vivo and ex vivo following gene transfer to the lungs using electroporation. (A) Dose–response curve for ex vivo gene transfer in mice and rats. pCMV-lux-DTS plasmid at the indicated doses was administered to excised mouse (closed circles: female Balb/c, 15–20 g) or rat (open circles: male Sprague–Dawley, 150–400 g) lungs via the bronchi and the individual lobes were electroported by direct placement of electrodes on the lobes using eight square wave pulses of 10 msec duration each at 200 V/cm. Mouse lungs received 200 μl of plasmid and rat lungs received 500 μl. Lungs were placed into medium and luciferase gene expression was measured 24 h later (mean ± SEM, n = 3). (B) Comparison of in vivo and ex vivo gene transfer and expression in the mouse lung. Ex vivo transfer was performed as described in (A). For in vivo electroporation, 20 μg of pCMV-Lux-DTS in 100 μl were injected intratracheally and varying field strengths were applied to the chest of mice (eight pulses of 10-msec duration each). The levels of luciferase gene expression were measured at 2 days posttreatment as previously described (Dean et al., 2003) (mean ± SEM; n = 4 animals/point). Values from (A) are shown for ex vivo expression at the same DNA dose (Dean et al., 2003).