EP1177280A1

EP1177280A1 - Method for treatment of an aqueous flux by electropulsation of a field parallel to the flow, pulsation chamber and uses thereof

Info

Publication number: EP1177280A1
Application number: EP00920808A
Authority: EP
Inventors: Marie-Christine Vernhes; Pierre-André René CABANES; Justin Teissie
Original assignee: Electricite de France SA; Centre National de la Recherche Scientifique CNRS
Current assignee: Electricite de France SA; Centre National de la Recherche Scientifique CNRS
Priority date: 1999-04-15
Filing date: 2000-04-14
Publication date: 2002-02-06
Also published as: FR2792207A1; FR2792207B1; US20020155611A1; WO2000063355A1; JP2002541838A; CA2388545A1; US6623964B2

Abstract

The invention relates to a method for treating an aqueous flux which is colonized by cells by means of a pulsed electric field which is applied to the flux, characterized in that the applied field is substantially parallel to the flow of the flux . The invention also relates to the use thereof in the transfer of nucleic acids (RNA,DNA, oligonucleotides) in cells, the transfer of proteins in cells, the extraction of molecules and cytoplasmic macromolecules contained in the cells, cell fusion and the production of hybrids and/or the insertion of membrane proteins. The invention further relates to an electropulsation chamber, a method for cellular destruction and a method for membrane permeabilization.

Description

PROCESS FOR TREATING AN AQUEOUS FLOW BY ELECTROPULSATION WITH A FLOW PARALLEL FIELD, PULSATION CHAMBER AND APPLICATIONS.

The present invention relates to a method of treating an aqueous flow colonized by cells by the application of an electric field parallel to the flow of the flow, a flow and electropulsing chamber as well as their application to cell processing. , in particular the destruction, the transmembrane transfer of molecules, the membrane fusion and the insertion of membrane proteins.

It is known to apply an electric field to cells: when a cell is placed in an electric field, the field lines are deflected by it, which causes an accumulation of charges on the surface of the cell. Thus, this results in an induced transmembrane potential difference ΔV which is superimposed on the native difference ΔΨ Bernardt J. and Pauly H. (1973) :( 1)].

The most complete formula retained in the case of a kinetic field in a square wave and a spherical cell in suspension is the following [Kinosita and Tsong (1979) (2)]:

ΔV (t) = fg (λ) r E (t) cos θ (l-e ^) éq 1

The expression of this potential difference induced at a point M at time t is a function of: E: the intensity of the applied electric field, f: the form factor of the cell (1, 5 in the case of a sphere) , g (λ): is a factor (of the membrane permeability λ) linked to the conductivities of the external and internal media and to that of the membrane, r: the radius of the cell, θ: the angle between the macroscopic electric field vector and the normal to the plane of the membrane at the point considered M, τ _p : is the charging time of the membrane capacity (of the order of a microsecond). t: application time of the field.

When the duration of the pulses is much greater than the charge time of the membrane (t »τ _p ), the term (1-e ^{_t τp} ) becomes very close to 1, we then find, in the stationary state the classical formulation:

ΔV (t) = fg (λ) r E (t) cos θ éq 2

The term in cos θ indicates that for a given field value, the amplitude of this potential difference is not identical at any point in the cell. It is maximum at the points facing the electrodes (poles) and decreases along the cell surface to cancel out at the equator.

This potential difference generated by the field is added to the rest potential difference ΔΨ ₀ . This results in a resulting potential difference ΔVr.

ΔVr = ΔΨ _n + ΔV éq 3

At the level of the cellular hemisphere situated opposite the anode, the numerical values of ΔΨ ₀ and of ΔV are added up to take account of the vectoriality of the field effect, which leads to hyperpolarization of the membrane. On the other hand, at the level of the hemisphere located opposite the cathode, the numerical values of ΔΨ ₀ and of ΔV are entrenched, and the membrane undergoes depolarization. When this resulting difference in membrane potential becomes greater than a threshold value estimated at 200-250 mV [Teissié and Tsong (1981) :( 3)], there is induction of a permeabilization phenomenon [Ho and Mittal (1996): (4)]. The membrane structure responsible for this membrane permeability is unknown to date, and the term transient permeabilization structure (STP) is preferably used, which is usually expressed by the term "pores".

If the conditions of electro-waterproofing are controlled, this permeabilization phenomenon is transient and reversible, and has little or no effect on cell viability. This field-induced property allows direct access to the cytoplasmic content [Mir et al. (1988) :( 5); Tsong (1991) :( 6); Hapala, (1997) :( 7)]. This allows foreign and naturally non-permeable molecules to enter the cell and thus modify its content either temporarily or permanently (electrocharging, electrotransformation, electroinsertion).

On the other hand, under drastic particular electropulsation conditions, electro-waterproofing is an irreversible phenomenon which leads to cell death or electromortality [Hamilton and Sale (1967) :( 8); Sale and Hamilton (1967) :( 9), (1968) :( 10), Hulsheger et al., (1981) :( 11), (1983) :( 12); Mizuno and Hori (1988) :( 13); Kekez et al. (1996) :( 14), Grahl and Markl (1996) :( 15)]. This property has been used either to lyse cells in order to recover a metabolite of interest, not naturally excreted by the cell, or to eradicate cells in the environment (disinfection) or in food fluids (non-thermal sterilization) [Jayaram et al . (1992) :( 16), Knorr et al. (1994) :( 17); Qin et al. (1996) :( 18); Qin et al. (1998) :( 19)].

In the prior art, there are two means of applying a pulsed electric field to a liquid medium, and the choice depends in particular on the volume of liquid medium to be treated. So bed pulsation systems fixed, also called batch have been described. However, these installations (chambers) and methods only allow small volumes of the order of a fraction of ml to be treated. The technical limit is associated with the power available on the electric pulse generators at a reasonable cost. In addition to research work, this approach enables the production of genetically modified organisms (GMOs) in an industrial environment.

Furthermore, the application of an electric field drawn from a flow has been described, which makes it possible to process a flowing cell suspension. For the flow or flow process, two strategies have been described: continuous flow and sequential flow.

In the second so-called sequential flow model, the pulsation chamber is filled, the flow is stopped, the field is then applied then the chamber is emptied, then it is filled again. The cells are stationary during the application of the field. There are therefore no hydrodynamic constraints. The working conditions are therefore identical to those described for fixed bed experiments. The flow rate is limited by the necessity of the downtime present during the application of the pulses. It is however possible to work on large volumes but for long periods. The advantage of the flow system is that it can process large volumes. The flow consists of an uninterrupted flow in the chamber and a synchronization of the pulse trains with the flow rate. It is then possible to apply a well-defined number of pulses to the cells during their residence time in the pulsation chamber. The cells are then in displacement and subjected to hydrodynamic constraints of deformation and orientation. The flow rate can be very high, being limited only by the frequency of the pulses. This approach therefore makes it possible to work on large volumes in short time. Thus, to carry out certain sequential and / or continuous flow treatments and in particular to treat certain colonized flows, it is known to use flow systems by applying a field perpendicular to the flow [Teissié and Conte (1988) :( 20 ); Teissié and Rois, (1988) :( 21); Sixou and Teissié, (1990) :( 22); Teissié et al. (1992) :( 23), Rois et al. (1992) :( 24); Bruggeman et al. (1995) :( 25); Qin et al. (1996) :( 18)].

We have also proposed systems where the flux and the electrodes are coaxial, systems with which a non-uniform field is applied but always perpendicular to the flow [Qin et al. (1996) :( 18); Qin et al. (1998) :( 19)]. In all the previous descriptions, the field is applied perpendicular to the flow.

According to Bruggeman et al. (1995) :( 25), for a given electric field value, the flow technique however results in lower efficiency than that obtained in batch, as has been observed for the electrocharging of inositol hexaphosphate on red blood cells . Thus, according to this method, an increase in the intensity of the electric field by 10% is necessary to obtain with a continuous flow results similar to those obtained in batch. There is then a need to work at a more intense field strength, therefore with higher operating costs. In terms of loading efficiency, the flow approach makes it possible to treat a much larger volume.

It has now been demonstrated that the application of an electric field substantially parallel to the flow can make it possible to obtain better efficiency of the continuous flow treatment methods.

With certain species, in the case of electromortality, the method of the invention allows a total eradication of the population, while the latter, whether in flow at perpendicular field or in fixed bed, is not possible with known methods and installations. In addition, total permeabilization of the population of deformable spherical cells is possible, while a partial effect is obtained with known methods and installations.

In addition, according to the invention, it is possible to work with weaker fields, therefore under economic conditions of more profitable operating cost, by comparison with the batch technique (fixed bed).

Finally, this configuration can also be advantageous for non-spherical cellular systems, for example rod cell systems which undergo the forced orientation linked to the flow constraint.

Thus, according to a first subject of the invention, the latter relates to a process for treating an aqueous flow colonized by cells by a pulsed electric field applied to the flow characterized in that the electric field is applied substantially parallel to the flow.

Another object of the invention relates to a flow and pulsation chamber. Devices for treating aqueous flows by a field are known. According to the invention, the chamber comprises at least two electrodes capable of creating a uniform field substantially parallel to the flow flowing between them.

One way of creating such a configuration of the field is to provide as electrodes capable of creating a uniform field parallel to the flow flowing between them, for example electrodes through which the flow flows. Such electrodes can be perforated plates, grids, fabrics or bars for example.

The cross section of the pulsation chamber can have the shape in particular of a circle or a polygon or an elliptical shape. When they are of the grid or bar type, the electrodes are parallel. However, other configurations are possible which make it possible to create a uniform field parallel to the flux. Furthermore, the longitudinal section is not necessarily with parallel edges. Thus, the colonized flow can be subjected to hydrodynamic stress before, after or during its passage through the chamber. It is possible to envisage more complex geometries in particular of the venturi where a hydrodynamic stress will be applied during the passage through the chamber. Such constraints can be applied in a known manner by the choice of the configuration of the supply and outlet pipes from the flow of the chamber, as well as from the flow to the chamber, and the configuration of the chamber itself. Among the applications of the method and chambers according to the invention, mention may be made of the cellular destruction of undesirable cells present in a colonized aqueous medium and the extraction of cytoplasmic metabolics by permeabilization of the membranes, as well as the modification of the cytoplasmic content by transfer of small molecules or macromolecules (peptides, proteins, nucleic acids oligonucleotides, RNA, DNA), cell fusion and insertion of transmembrane proteins.

In addition, the invention relates to a cell destruction process in which an colonized aqueous flow is subjected to an electric field substantially parallel to its flow. It also relates to a membrane permeabilization process of cells of a colonized aqueous flow, by application of an electric field substantially parallel to the flow.

Finally, the present invention relates to the application of the treatment method to the transfer of nucleic acids (RNA, DNA, oligonucleotides) in cells, to the transfer of proteins into cells, to the extraction of molecules and cytoplasmic macromolecules contained in cells, cell fusion and hybrid production and / or insertion of membrane proteins.

By colonized flow is meant any flow of domestic, natural, food or utility aqueous medium comprising undesirable cells. These cells or microorganisms can generally be any single-celled organism developing or living in the aqueous stream. In certain cases, it is necessary to eradicate them for reasons of health or public hygiene, ecology or maintenance of industrial equipment. Thus, certain cells proliferate in certain environments and their presence or multiplication in the water and liquids to be treated is harmful to the operation of the facilities or to health or well-being. The colonized flow can be an aqueous medium containing cells or microorganisms producing molecules of interest, the content of which it is desired to recover or to introduce effector molecules or macromolecules on its activity (genetic modification for example).

They may be deformable spherical cells but also any cellular system sensitive to the electric field, with a view to electromortality, and other applications of the methods of the invention, and in particular cellular systems having other configurations, such as sticks, bacteria or yeast can be treated.

The present invention will be better understood from the detailed description and the accompanying drawings.

FIG. 1 illustrates, for amoebas, the results in terms of percentage of viability of the cells, by the application of pulsed electric field where the field is applied respectively in parallel to a flow (1-black), in a manner perpendicular to a flow (2-gray) and discontinuously (batch - white).

FIGS. 2A and 2B illustrate, in terms of percentage of permeabilization of the amoeba cell membrane, the effectiveness of a field applied at intensity E (kV / cm) perpendicular to the flow (flux - • - 2A ) and that of a field applied parallel to the flow (flow - • - 2B), compared to that of a field applied discontinuously (batch: -o- 2A and 2B). FIG. 3 represents a schematic view of a cell usable according to the invention.

According to the invention, preferably, the flow is continuous. However, the method of the invention can also be implemented with a sequential flow.

The values defining the applied electric field depend on the installation and the application planned for the process. Thus the difference in electrical potential applied between the two electrodes is a function of the intended use. It is often under the control of the distance between the two electrodes. It must cover ranges of electric fields between a few V / cm and tens of kV / cm. The intensity of the applied electric field can be chosen between 0.1 and 100 kV / cm. The pulse profile is optimized for the type of application. It can be of square wave, trapezoid, sinusoid, triangle or exponential decline. The pulses can be unipolar or bipolar.

The pulse frequency is optimized for the type of application but preferably remains below 1 MHz.

The pulsation system developed in the laboratory to implement the method of the invention comprises the following different elements: a cell reservoir provided in particular with an agitator, a peristaltic pump, a pulsation chamber and a discharge of the treated flow allowing the cells to be recovered, and means for conveying the flow from the reservoir to the chamber and from the chamber to the discharge. An example embodiment of the chamber will be described later in detail.

The peristaltic pump (pump, minipuls 3, Gilson) ensures an overpressure in the cell reservoir, which makes it possible to entrain the cell suspension towards the electropulsing chamber, without passage between the rollers of the pump. This is equipped with a flow meter system which allows the flow to be adjusted precisely. The flow Q used is based on the concept of residence time so that each cell which enters the pulsation chamber undergoes the same electrical conditions. It is defined by the frequency (F), the number (N) of the pulses and by the volume (V) of the pulse chamber by the following relation:

frequency (Hz) x 60 x Chamber volume (ml) Q (ml / minute) = number of pulses applied

According to the invention, the throughput can be optimized for the type of application. The flow rate is of the order of 0.5 ml / min at several m ³ / s.

The electrodes in both systems are connected to a high-voltage pulse generator (1.5 kV / cm, 8 Amp, programmable pulse duration from 5 μs to 24 ms, frequency from 0.1 to 10 and up to 2000 Hz in external control) connected to an oscilloscope (Enertec) thus making it possible to display the electrical parameters delivered. The kinetic profile of the pulses delivered by the generator is said to be in square waves, the intensity of the field remaining constant throughout the duration of the pulses (T). The flexibility of the electropulser allows you to modulate the voltage, duration, number and frequency of the pulses.

Example

Measurement method The experiments were carried out on amoebas, in vegetative form (Naegleria lovaniensis Ar9M1). The cell size is 18.2 μm (8.5 μm - 31.5 μm) x 10.9 μm (4 μm - 21 μm). They are cultivated in axenic condition on plastic boxes at 37 ° C. and using the Chang culture medium. The pulsation medium used is filtered river water and having a conductance of the order of 200 μS / cm. The viability is evaluated 24 hours after the electrical treatment by the crystal violet staining technique.

The permeabilization of cells is quantified by flow cytometry by the use of a naturally non-permeable fluorescent marker, propidium iodide.

1) Description of the fixed bed pulsation system

The pulsation chamber consists of two electrodes with flat stainless steel blades held parallel by insulating shims. The inter-electrode distance is 0.4 cm.

2) Description of the electrodes in flow for a field perpendicular to the flow (comparative).

The stainless steel electrodes consist of two parallel blades separated by an inter-electrode distance of 0.4 cm. The volume of the parallelepipedal pulsation chamber is 0.2 ml.

3) Description of the flow electrodes for a parallel field

The electrodes used in steel are grids made up of a mesh (80 μm x 100 μm) through which the cells pass. The inter-electrode distance is 0.93 cm and the volume of the pulsation chamber is 0.117 ml.

In both cases, the colonized aqueous medium is pumped from a stirred tank. The aqueous flow created is thus entrained in a pipe. The pulsation chamber delimited by the two electrodes whatever the orientation of the field is constituted by a portion of the pipe delimited by two electrodes. The electrodes are in the form of a grid and allow the flux to pass in the case of the parallel field. The electrodes are connected to an electropulsator. The two flow pulsation chambers have different volumes, which explains why the flow rates used to have the same electropulsing conditions are different. The flow rate in the case where the field is perpendicular to the flow is 1.2 ml / min and that of the configuration of the field parallel to the flow is 0.71 ml / min.

The liquid supplied by a connector connected to a feed pump passes through the first electrode, crosses the chamber, then the second electrode before being recovered.

1 - The body: A cylindrical hole (diameter of the order of millimeters) is drilled in a plexiglass plate (thickness from 1 to 10 mm).

Material: plexiglass, which is an electrical insulator, any other insulating material can be envisaged, in particular those which are suitable for being molded. The cross section was chosen for convenience of construction (a drill).

The longitudinal section has parallel edges, which ensures a criterion of good homogeneity of the field, therefore of cell processing.

2 - The electrodes:

Steel wire mesh (grid) or stainless steel needles (bar) were used. For the canvas, the mesh was chosen with a fine pitch to ensure good compliance of the field. This allows cells to be treated more evenly. Any electrically conductive material can constitute the electrodes.

The electrodes are connected to the electric pulse generator. The electrodes are placed against the body of the chamber. The seal is obtained by O-rings and a deposit of silicone. 3 - Fluid supply connectors:

They are inserted into Plexiglas plates kept in intimate contact with the electrodes. O-rings and a silicone deposit ensure sealing.

In Figure 3 appears the flow supply pipe connected by a connector 6 to a connector holder 5. Between an external O-ring 4 and an internal O-ring 3 is held the electrode 2. The internal O-ring 3 provides sealing with the body 1. Another internal O-ring 3 'ensures the sealing with the body 1 and maintains the second electrode 2'. On the path of the flow, elements 4 ′, 5 ′, 6 ′, 7 ′ homologous to the elements 4, 5, 6, 7 above direct the flow towards the output of the device.

The electrodes 2, 2 'are connected to the electric pulse generator (not shown). Results

For the three electropulsation techniques (batch, field parallel to the flow, field perpendicular to the flow), the efficiency for the destruction of amoebae was measured. The cells were electropulsed, in all cases, by ten pulses of 10 ms delivered with a frequency of 1 Hz. The results concerning the evolution of the viability with the intensity of the electric field are presented in FIG. 1.

In the flow configuration with the field parallel to the flow, a drop profile of the viability is obtained, where the viability is all the more affected as the intensity of the electric field increases.

The use in flow of a field parallel to the flow gives the lowest viability rates for each intensity of the electric field studied, and therefore proves to be a very effective technique for eradicating amoebas. For a field value of 1.5 kV / cm, a total elimination of the amoebae is observed. Furthermore, the results obtained with a field perpendicular to the flow show that in this type of configuration, for high field values (= 1 kV / cm), the increase in the intensity of the electric field does not translate by an increase in the mortality rate. 25% of the population is not affected by the lytic effect of the field.

FIGS. 2A and 2B compare the profiles of permeabilization obtained as a function of the intensity of the electric field for the two techniques in flux with respect to the profile of permeabilization obtained in batch. The cells, in the three cases, are electropulsed by ten pulses of 10 ms delivered with a frequency of 1 Hz.

In the configuration where the field is perpendicular to the flow (2A), over a range of electric field intensity from 0 to 0.75 kV / cm, the increase in the intensity of the electric field results in a increased permeability rate. The increase in the intensity of the field does not lead to an increase in the number of permeabilized cells. A plateau of only 40% is obtained.

In the case where the field is parallel to the flow (2B), on all the field values used, the increase in the intensity of the electric field is correlated with an increase in the rate of permeabilization. In terms of flow permeabilization efficiency, the use of a field parallel to the flow gives the best results. The increase in the intensity of the field allows permeabilization of more than 90% of the population.

In addition, permeabilization in flow, with a field parallel to the flow, is triggered for values below the critical value in batch (0.25 kV / cm). REFERENCES

I. Bemhardt J. et al., Biophysik. 10: 89-98 (1973)

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Claims

1. A process of membrane permeabilization of cells in which an aqueous flow colonized by the cells is subjected to a pulsed electric field applied to the flow in a manner substantially parallel to the flow of the flow.

2. Method according to one of claims 1, characterized in that the flow is sequential.

3. Method according to one of claims 1, characterized in that the flow is continuous.

4. Method according to claim 1, 2 or 3, characterized in that the electric field applied is of the order of 0.1 to 100 kV / cm.

5. Method according to one of claims 1 to 4, characterized in that the pulses have a profile in square wave, in triangular wave, in sinusoidal wave, in trapezoidal wave.

6. Method according to one of claims 1 to 5, characterized in that the pulses are delivered by a frequency less than MHz.

7. Method according to one of claims 1 to 6, characterized in that the flow is subjected to a hydrodynamic stress.

8. Flow and pulsation chamber comprising at least two electrodes capable of creating a uniform field parallel to the flow flowing between them, the electrodes being grids or bars arranged substantially parallel to each other, in a plane substantially perpendicular to the flux passing through the electrodes.

9. Application of the methods according to claims 1 to 6, to the transfer of nucleic acids (RNA, DNA, oligonucleotides) into cells, to the transfer of proteins into cells, to the extraction of molecules and cytoplasmic macromolecules contained in them. cells, cell fusion and hybrid production and / or insertion of membrane proteins.