Reversible electropermeabilisation of human and rat blood platelets: evaluation of morphological and functional integrity 'in vitro' and 'in vivo'

Advances of blood cell-based drug delivery systems

Blood cells, including erythrocytes, leukocytes and platelets are used as drug carriers in a wide range of applications. They have many unique advantages such as long life-span in circulation (especially erythrocytes), target release capacities (especially platelets), and natural adhesive properties (leukocytes and platelets). These properties make blood cell based delivery systems, as well as their membrane-derived carriers, far superior to other drug delivery systems. Despite the advantages, the further development of blood cell-based delivery systems was hindered by limitations in the source, storage, and mass production. To overcome these problems, synthetic biomaterials that mimic blood cell and nanocrystallization of blood cells have been developed and may represent the future direction for blood cell membrane-based delivery systems. In this paper, we review recent progress of the rising blood cell-based drug delivery systems, and also discuss their challenges and future tendency of development.

Energy-landscape-model analysis for irreversibility and its pulse-width dependence in cells subjected to a high-intensity ultrashort electric pulse

We provide a simple, but physical analysis for cell irreversibility and apoptosis in response to an ultrashort (nanosecond), high-intensity electric pulse. Our approach is based on an energy landscape model for determining the temporal evolution of the configurational probability function p(q). The primary focus is on obtaining qualitative predictions of a pulse width dependence to apoptotic cell irreversibility that has been observed experimentally. The analysis couples a distributed electrical model for current flow with the Smoluchowski equation to provide self-consistent, time-dependent transmembrane voltages. The model captures the essence of the experimentally observed pulse-width dependence, and provides a possible physical picture that depends only on the electrical trigger. A number of interesting features are predicted.

Electrical permeabilization of rat luteal cells: in situ phosphorylation of endogenous protein

Progesterone synthesis in the corpus luteum is regulated primarily by luteinizing hormone which acts via the adenylate cyclase/cyclic AMP/protein kinase A signalling cascade. Protein phosphorylation therefore plays a key role in the regulation of steroidogenesis, but there are relatively few studies of the in situ phosphorylation of luteal cell substrates. This may in part reflect the difficulties inherent in measuring changes in protein phosphorylation in intact cells preloaded with 32P and difficulties in interpreting data obtained using broken cell preparations. We have now applied a method of stable permeabilization of luteal cell plasma membranes by exposure of cell populations to a high intensity electric field. Under optimum conditions (5 kV/cm, six discharges) electrical permeabilization reproducibly produced populations of luteal cells in which 70-80% of the cells were permeabilized, as assessed by Trypan blue exclusion and [14C] sucrose space measurements. Pores were stable for at least 1 h, and there were no ultrastructural changes to the cells that could be detected by transmission electron microscopy. Permeabilized cells showed rapid cyclic AMP-induced changes in phosphorylation of endogenous proteins when provided with [gamma - 32 P] ATP. Our results demonstrate that the electricity permeabilized luteal cell offers a useful model for studying intracellular events in steroidogenic stimulus-response coupling cascades.

Cell membrane resealing by a vesicular mechanism similar to neurotransmitter release

After injury to the cell membrane, rapid resealing of the membrane occurs with little loss of intracellular contents. This process has been studied by measurement of the rate of dye loss after membrane puncture in both the sea urchin embryo and 3T3 fibroblasts. Resealing of disrupted cell membranes requires external calcium that can be antagonized by magnesium. Block of multifunctional calcium/calmodulin kinase, which regulates exocytotic vesicle availability at synapses, and of kinesin, which is required for outward-directed transport of vesicles, inhibited membrane resealing. Resealing was also inhibited by botulinum neurotoxins B and A, suggesting that the two synaptosomal-associated proteins synaptobrevin and SNAP-25 also participate in resealing. This pattern of inhibition indicates that the calcium-dependent mechanisms for cell membrane resealing may involve vesicle delivery, docking, and fusion, similar to the exocytosis of neurotransmitters.

Cell electropermeabilization: a new tool for biochemical and pharmacological studies

Cell electropermeabilization is the transient permeabilization of the plasma membrane by means of short and intense electric pulses. Under optimized conditions, electropermeabilization is compatible with cell survival. It provides a direct access into the cytosol to ions, small molecules, exogenous drugs and macromolecules. As cells remain functional, a large variety of cell biology questions can be addressed. Such 'in situ biochemistry' opens new possibilities beside the more classical studies dealing with unpermeabilized cells or subcellular extracts. Electropermeabilization also allows pharmacological studies with cells, cultured monolayers and in vivo tissues as well as the design of drug controlled-release systems.

Electroporation: a general phenomenon for manipulating cells and tissues

Electroporation is a fascinating cell membrane phenomenon with several existing biological applications and others likely. Although DNA introduction is the most common use, electroporation of isolated cells has also been used for: (1) introduction of enzymes, antibodies, and other biochemical reagents for intracellular assays; (2) selective biochemical loading of one size cell in the presence of many smaller cells; (3) introduction of virus and other particles; (4) cell killing under nontoxic conditions; and (5) insertion of membrane macromolecules into the cell membrane. More recently, tissue electroporation has begun to be explored, with potential applications including: (1) enhanced cancer tumor chemotherapy, (2) gene therapy, (3) transdermal drug delivery, and (4) noninvasive sampling for biochemical measurement. As presently understood, electroporation is an essentially universal membrane phenomenon that occurs in cell and artificial planar bilayer membranes. For short pulses (microsecond to ms), electroporation occurs if the transmembrane voltage, U(t), reaches 0.5-1.5 V. In the case of isolated cells, the pulse magnitude is 10(3)-10(4) V/cm. These pulses cause reversible electrical breakdown (REB), accompanied by a tremendous increase molecular transport across the membrane. REB results in a rapid membrane discharge, with the elevated U(t) returning to low values within a few microseconds of the pulse. However, membrane recovery can be orders of magnitude slower. An associated cell stress commonly occurs, probably because of chemical influxes and effluxes leading to chemical imbalances, which also contribute to eventual survival or death. Basic phenomena, present understanding of mechanism, and the existing and potential applications are briefly reviewed.

Affinity labelling of the Ca(2+)-activated neutral proteinase (calpain) in intact human platelets

Two irreversible calpain inhibitors, benzyloxycarbonyl (Cbz)-Leu-Leu-Tyr-Ch2F and Cbz-Leu-Leu-Tyr-CHN2, were shown earlier [Anagli, Hagmann and Shaw (1991) Biochem. J. 274, 497-502] to penetrate intact platelets and to inactivate calpain. This permitted an evaluation of certain functions attributed to this proteinase. For example, in platelets pretreated with these inhibitors, talin and actin-binding protein were protected from subsequent degradation when the Ca2+ level was raised. On the other hand, additional properties of stimulated platelets attributed to calpain remained unaffected by this treatment, and such hypotheses may be dismissed. Radioiodinated inhibitors permitted confirmation of the labelling of calpain by the procedures used. Although Cbz-Leu-Leu-Tyr-CHN2 is more effective in vitro than the corresponding fluoromethyl ketone, we now show that the latter penetrates more readily. These two inhibitors, and two additional ones, t-butyloxycarbonyl-Val-Lys(Cbz)-Leu-Tyr- CHN2 and Cbz-Leu-Tyr-CH2F, have been radioiodinated to permit a comparison of their intracellular labelling patterns in activated platelets. Calpain is the major target of all four inhibitors. Although they are closely related peptide structures, variations with respect to the labelling of additional proteins were observed. These were minor in the case of the peptidyl diazomethyl ketones, but were major in the case of the fluoromethyl ketones. However, in contrast to calpain, this labelling was neither time-dependent nor Ca(2+)-dependent. Radiolabelling and cellular fractionation studies were used to localize active calpain during platelet activation. Calpain appears to be activated in the cytosol and translocated to the membrane or cytoskeletal sites.

In vivo targeting of inflamed areas by electroloaded neutrophils

Due to their spontaneous accumulation in inflamed or infected areas, blood phagocytes are potent drug vectors with specific targeting. Drug like molecule loading was obtained by use of cell electropermeabilization in which the impermeability of their plasma membrane is transiently impaired. Electrical conditions were used which allow electroloading of a drug like molecule (propidium iodide) in 70% of leukocytes in a whole blood sample while preserving in vitro functional properties. Slow release of entrapped hydrophilic molecules was observed with a half lifetime longer than 4 hours at 4 degrees C and at 37 degrees C. With an in vivo assay, using a rat model of inflammation, we showed that, as for non-pulsed cells, pulsed neutrophils accumulate 10 times more in an inflamed area than they do in control areas. Phagocyte electropermeabilization is therefore a very efficient way of drug targeting. Accumulation of electropulsed neutrophils in an area of inflammation gives targeted release of the electroloaded drug.

Laser balloon angioplasty: potential for reduction of the thrombogenicity of the injured arterial wall and for local application of bioprotective materials

Mitigation of adverse biologic reactivity after balloon angioplasty is necessary before the incidence of restenosis can be appreciably reduced. A brief review of experimental evidence supports the hypothesis that the thrombogenicity of the injured arterial wall can be reduced by a suitable level of thermal denaturation or cross-linking of thrombogenic proteins. In addition, the concept of local pharmacologic therapy, which can be provided with laser balloon angioplasty at the site of arterial injury, is introduced. Preliminary in vitro and in vivo data suggest that guide catheter-injected albumin-heparin conjugates fabricated as water-insoluble microspheres remain adherent to the injured luminal surface and deeper arterial layers after physical trapping by the inflated balloon and subsequent laser/thermal exposure. The combination of initially adequate luminal morphology, reduction of the thrombogenicity of the injured arterial wall and application of local pharmacologic therapy with laser balloon angioplasty may eventually prove helpful in reducing the incidence of restenosis.

Specific electropermeabilization of leucocytes in a blood sample and application to large volumes of cells

Electropermeabilization is obtained when the membrane potential difference reaches a critical threshold. This is performed by submitting cells to an external electric field pulse. The field modulates the endogenous potential difference in a cell-size-dependent way. Computer simulations predict that large cells would be specifically permeabilized in a mixture with smaller cells. This was examined on a mixture of Chinese hamster ovary (CHO) cells and erythrocytes. CHO cells were permeabilized to Trypan blue without any occurrence of haemolysis. A similar 'size' specificity was observed on blood samples. This agreement between prediction and experimental observation indicates that induction of electropermeabilization is mainly under the control of the size of the target cell. Its physiology plays only a minor role, if any. Treating blood with 10 square wave pulses lasting 100 microseconds of an intensity of 1.6 kV/cm induced the permeabilization of 70% of the leucocytes (polymorphs and monocytes) but did not affect erythrocytes. No washing of the sample was needed in a procedure in which cells were pulsed in the plasma. A flow electropulsing process allows the treatment of large blood volumes under conditions where cells are kept viable. These results show that electropermeabilization could be used as an effective way to obtain immunocompatible drug vehicles.

Stable, resealable pores formed in sea urchin eggs by electric discharge (electroporation) permit substrate loading for assay of enzymes in vivo

We describe a simple electroporation procedure for loading suspensions of unfertilized sea urchin eggs with impermeant small molecules under conditions that allow close to 90% successful fertilization and development. Poration is carried out in a low-Ca2+ medium that mimicks the intracellular milieu. The induced pores remain open for several minutes in this medium, allowing loading of the cells; resealing is achieved by adding back millimolar calcium ions to the medium. While the pores are open, an influx of exogenous molecules and efflux of endogenous metabolites takes place, and the eggs can lose up to 40% of their ATP content and still survive. Introduced metabolites are utilized by the cells, e.g., introduced 3H-thymidine is incorporated into DNA. This procedure will be useful for loading impermeant substrates into eggs, permitting in vivo assessment of metabolism, and also for introducing other interesting impermeant molecules, such as inhibitors, fluorescent indicators, etc. Though the details may differ, the principle of electroporation in an intracellular-like medium may prove to be useful for loading other cell types with minimal loss of viability.

High incorporation of [3H]inositol into phosphoinositides of human platelets during reversible electropermeabilisation

A new method for high incorporation of [3H]inositol into human platelets is described. The method involves incorporation of [3H]inositol during reversible electropermeabilisation by high voltage discharge, followed by resealing the cells during incubation at 37 degrees C. Between 10- and 20-fold increase of isotope uptake is achieved compared to control intact cells. Permeabilised resealed platelets maintain good responses to thrombin and collagen. Analysis of the incorporation of the label amongst the phosphoinositides shows 70% to be in PI, 20% in PIP, and 10% in PIP2. Stimulation with thrombin and analysis of the formation of IP1, IP2 and IP3 shows the labelling to occur in a hormone-sensitive pool. These studies indicate that reversible electropermeabilisation can be used to achieve good uptake of non-membrane penetrating substances such as inositol.