Electroporation Permeabilization

Recently another electrically assisted drug delivery technology, electroporation, was proposed as an alternative or adjuvant to iontophoresis. Electroporation comprises the use of electric pulses to induce transient changes in the cell membrane architecture that turn it into more permeable barrier. Beside the permeabilization effect on cell membrane, it was postulated that this technique induces electrophoretic effect on charged macromolecules and drives them to move across the destabilized membrane [205]. 

Application of an electric field to lipid bilayers such as those found in cellular membranes causes short-term depolarization of the membrane and formation of pores and other structural changes [17]. These so-called electropores allow the uptake of hydrophilic macromolecules such as plasmid DNA, siRNA, or proteins that are otherwise unable to diffuse passively through this highly regulated barrier. The use of high-voltage electrical pulses to permeabilize cell membranes was first described as a tool to deliver DNA into mammalian cells in 1982 (Wong and Neumann 1982 Neumann et al. 1982). In cuvette-based methods, cells are... 

Extensive research on the attempts to overcome the bilayer membrane barrier has resulted in the emergence of several different methodologies for partial and temporary cell membrane permeabilization. The prominent among them are chemical permea-bilizers, liposomal interactions, ultrasonication, ionizing radiation, and electroporation. 

Electroporation is a process of exposing cells to a controlled electric field for the purpose of cellular membrane permeabilization (61). The intense localized eleetric pulses destabilize the... 

Electroporation is use of electric fields to cause cell membrane permeabilization. 

This is the same as above. Electropermeabilization is technically more correct, as indeed what we know is that permeabilization structures are created, not necessarily that these have a particular shape, as the word pore would imply. However, as the word electroporation has taken precedence and is overwhelmingly used in the literature, this is also the term used in this chapter. 

A large body of literature describes the occurrence of pores, of various sizes and lifetimes, as the result of electroporation. In uiuo these pores may not necessarily be neatly rounded structures, but rather a mixture of shapes of permeabilization structures depending on the effect of transmembrane protein domains, cell shape, and surrounding matrix on the cell membrane response to the field, i.e. these permeabilizahon structures could either be circular in form, or have other forms depending on local factors. 

Figure 8.1 Schematic of cell electroporation. A basic understanding is that when the electric field exceeds the capacitance of the cell membrane, permeabilization structures will occur more prominently at the cell pole facing the positive electrode, due to the...

In tissues, the extracellular volume is small compared to the intracellular volume-completely the opposite of the situation when performing in vitro electroporation where the suspension medium volume by far exceeds the intracellular volume. This means that the threshold for electroporation is lowered [5]. It also means that the cell may tolerate permeabilization better, for example, since loss of ionic homeostasis may be less pronounced [6]. 

Figure 8.2 Cell electroporation a more complex view. The cell membrane as shown in Figure 8.1 is of course a simplistic view of the situation. A more detailed (but far from complete) view would be including the cytoskeleton (dotted lines), which has also been shown to be involved in both formation and resealing of permeabilization structures.

Exploitation of alkaloid release for production purposes requires further studies with respect to timing of the induction of alkaloid biosynthesis, secretion of the edkaloids, and regrowth of the cells. Electroporation has been shown as a possible way to permeabilize T. rugosum cells however, in obtaining complete release of the alkaloids, the cells lost their viability (549). The use of various chemical agents for permeabilization (chloroform, DMSO, Triton X-lOO, hexadecyltrimethylammonium, phen-ethyl alcohol) gave similar results. At concentrations necessary to release berberine from the vacuole, the cells did not grow anymore after the treatment (87). 

There are different techniques to overcome the cell membrane barrier and introduce exogenous impermeable compounds, such as dyes, DNA, proteins, and amino acids into the ceU. Some of the methods include lipofection, fusion of cationic liposome, electroporation, microinjection, optoporation, electroinjection, and biolistics. Electroporation has the advantage of being a noncontact method for transient permeabilization of cells (Olofsson et al., 2003). In contrast to microinjection techniques for single cells and single nuclei (Capecchi, 1980), the electroporation technique can be applied to biological containers of sub-femtoliter volumes, that are less than a few micrometers in diameter. Also, it can be extremely fast and well-timed (Kinosita et al., 1988 Hibino et al., 1991), which is of importance in studying fast-reaction phenomena (Ryttsen et aL, 2000). 

Huang, Y, Rubinsky, B., 1999. Micro-electroporation improving the efficiency and understanding of electrical permeabilization of cells. Biomed. Microdevices 2, 145—150. 

In this article, the underlying concepts and theory of electroporation and also some of the most significant experimental studies on the microfluidic ceU electroporation will be reviewed. It wDl begin by providing the fundamentals and mathematical description of the cell electroporation. Here, the theory of membrane permeabilization and its simplified asymptotic solution will be reviewed. After that, the most... 

Transmembrane potential (TMP) is the difference of the electric potential on two sides of the cell membrane. During the electroporation, the external electric field increases the TMP and consequently rises the energy level of the ceU membrane. While the TMP reaches a critical value (0.5 1 V), the hydrophilic nanopores will be generated on the cell membrane. According to the theory of membrane permeabilization, the hydrophilic nanopores will be created on the cell membrane to minimize the level of absorbed energy be the cell membrane. 

Microfluidic Cell Electroporation, Table 1 Values of the parameters of cell manbrane permeabilization theory... 

Although the theoretical studies on this subject lag the experimental ones, some theoretical studies have been accomplished recently to discover the nature of the membrane permeabilization and cell transfection. It helps the experimentalist to optimize the design and performance of their proposed microfluidic design for electroporation. 

The two most often used methods for DNA delivery into protoplasts are electroporation and treatment with polyethylene glycol (Paszkowski et al., 1984). The observation that short electric pulses of high field strength transiently permeabilize cell membranes led to the development of electroporation-mediated gene transfer techniques for mammalian cells (Neumann et al., 1982) and plant cell protoplasts (Fromm et al., 1985). Electroporation is now the preferred technique for direct DNA transfer to plant protoplasts. 

As discussed above, (a) pulsed electric fields reversibly permeabilize cell lipid membranes, and (b) the multilamellar lipid domains of the stratum comeum act as the rate-limiting moiety for transdermal delivery. Thus, it is reasonable to hypothesize enhanced transport through skin following electroporation. 

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