Gene expression profiles in skeletal muscle after gene electrotransfer

Pulsed Electric Fields Induce STING Palmitoylation and Polymerization Independently of Plasmid DNA Electrotransfer

Gene therapy approaches may target skeletal muscle due to its high protein-expressing nature and vascularization. Intramuscular plasmid DNA (pDNA) delivery via pulsed electric fields (PEFs) can be termed electroporation or electrotransfer. Nonviral delivery of plasmids to cells and tissues activates DNA-sensing pathways. The central signaling complex in cytosolic DNA sensing is the cyclic GMP-AMP synthase-stimulator of interferon genes (cGAS-STING). The effects of pDNA electrotransfer on the signaling of STING, a key adapter protein, remain incompletely characterized. STING undergoes several post-translational modifications which modulate its function, including palmitoylation. This study demonstrated that in mouse skeletal muscle, STING was constitutively palmitoylated at two sites, while an additional site was modified following electroporation independent of the presence of pDNA. This third palmitoylation site correlated with STING polymerization but not with STING activation. Expression of several palmitoyl acyltransferases, including zinc finger and DHHC motif containing 1 (zDHHC1), coincided with STING activation. Expression of several depalmitoylases, including palmitoyl protein thioesterase 2 (PPT2), was diminished in all PEF application groups. Therefore, STING may not be regulated by active modification by palmitate after electroporation but inversely by the downregulation of palmitate removal. These findings unveil intricate molecular changes induced by PEF application.

Immunogenicity of COVID-eVax Delivered by Electroporation Is Moderately Impacted by Temperature and Molecular Isoforms

DNA integrity is a key issue in gene therapy and genetic vaccine approaches based on plasmid DNA. In contrast to messenger RNA that requires a controlled cold chain for efficacy, DNA molecules are considered to be more stable. In this study, we challenged this concept by characterizing the immunological response induced by a plasmid DNA vaccine delivered using electroporation. As a model, we used COVID-eVax, a plasmid DNA-based vaccine that targets the receptor binding domain (RBD) of the SARS-CoV-2 spike protein. Increased nicked DNA was produced by using either an accelerated stability protocol or a lyophilization protocol. Surprisingly, the immune response induced in vivo was only minimally affected by the percentage of open circular DNA. This result suggests that plasmid DNA vaccines, such as COVID-eVax that have recently completed a phase I clinical trial, retain their efficacy upon storage at higher temperatures, and this feature may facilitate their use in low-/middle-income countries.

Transcriptomic Analysis of the Acute Skeletal Muscle Effects after Intramuscular DNA Electroporation Reveals Inflammatory Signaling

Skeletal muscle is a promising tissue for therapeutic gene delivery because it is highly vascularized, accessible, and capable of synthesizing protein for therapies or vaccines. The application of electric pulses (electroporation) enhances plasmid DNA delivery and expression by increasing membrane permeability. Four hours after plasmid electroporation, we evaluated acute gene and protein expression changes in mouse skeletal muscle to identify regulated genes and genetic pathways. RNA sequencing followed by functional annotation was used to evaluate differentially expressed mRNAs. Our data highlighted immune signaling pathways that may influence the effectiveness of DNA electroporation. Cytokine and chemokine protein levels in muscle lysates revealed the upregulation of a subset of inflammatory proteins and confirmed the RNA sequencing analysis. Several regulated DNA-specific pattern recognition receptor mRNAs were also detected. Identifying unique molecular changes in the muscle will facilitate a better understanding of the underlying molecular mechanisms and the development of safety biomarkers and novel strategies to improve skeletal muscle targeted gene therapy.

Regulation of glucose uptake and inflammation markers by FOXO1 and FOXO3 in skeletal muscle

Objective

Forkhead box class O (FOXO) transcription factors regulate whole body energy metabolism, skeletal muscle mass, and substrate switching. FOXO1 and FOXO3 are highly abundant transcription factors, but their precise role in skeletal muscle metabolism has not been fully elucidated.

Methods

To elucidate the role of FOXO in skeletal muscle, dominant negative (dn) constructs for FOXO1 (FOXO1dn) or FOXO3 (FOXO3dn) were transfected by electroporation into mouse tibialis anterior muscle and glucose uptake, signal transduction, and gene expression profiles were assessed after an oral glucose tolerance test. Results were compared against contralateral control transfected muscle.

Results

FOXO1dn and FOXO3dn attenuated glucose uptake (35%, p < 0.01 and 20%, p < 0.05), GLUT4 protein (40%, p < 0.05 and 10%, p < 0.05), and subunits of the oxidative phosphorylation cascade. Intramuscular glycogen content was decreased (20%, p < 0.05) by FOXO3dn, but not FOXO1dn. Transcriptomic analysis revealed major pathways affected by FOXO1dn or FOXO3dn revolve around metabolism and inflammation. FOXO1dn increased Akt protein (140%, p < 0.001), p-Akt^Ser473 (720%, p < 0.05) and p-Akt^Thr308 (570%, p < 0.01), whereas FOXO3dn was without effect. FOXO1dn and FOXO3dn increased mTOR protein content (170% and 190%, p < 0.05), and p-p70S6K^Thr389 (420%, p < 0.01 and 300%, p < 0.01), while p-mTOR^Ser2448 (500%, p < 0.01), was only increased by FOXO1dn. Chemokines and immune cell markers were robustly upregulated in skeletal muscle following the FOXOdn transfections, but not after control transfection.

Conclusions

FOXO1 and FOXO3 regulate glucose metabolism and markers of inflammation in skeletal muscle, implicating transcriptional control governing “immunometabolic” dynamics.

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FOXO1 and FOXO3 transcriptional activity regulates glucose uptake and inflammation.

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Inhibiting FOXO1 transcriptional activity affects more genes compared to FOXO3.

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Inhibiting FOXO1 and FOXO3 leads to similar pathway enrichment.

Perturbations of NAD+ salvage systems impact mitochondrial function and energy homeostasis in mouse myoblasts and intact skeletal muscle

Nicotinamide adenine dinucleotide (NAD⁺) can be synthesized by nicotinamide phosphoribosyltransferase (NAMPT). We aimed to determine the role of NAMPT in maintaining NAD⁺ levels, mitochondrial function, and metabolic homeostasis in skeletal muscle cells. We generated stable Nampt knockdown (sh Nampt KD) C2C12 cells using a shRNA lentiviral approach. Moreover, we applied gene electrotransfer to express Cre recombinase in tibialis anterior muscle of floxed Nampt mice. In sh Nampt KD C2C12 myoblasts, Nampt and NAD⁺ levels were reduced by 70% and 50%, respectively, and maximal respiratory capacity was reduced by 25%. Moreover, anaerobic glycolytic flux increased by 55%, and 2-deoxyglucose uptake increased by 25% in sh Nampt KD cells. Treatment with the NAD⁺ precursor nicotinamide riboside restored NAD⁺ levels in sh Nampt cells and increased maximal respiratory capacity by 18% and 32% in control and sh Nampt KD cells, respectively. Expression of Cre recombinase in muscle of floxed Nampt mice reduced NAMPT and NAD⁺ levels by 38% and 43%, respectively. Glucose uptake increased by 40%, and mitochondrial complex IV respiration was compromised by 20%. Hypoxia-inducible factor (HIF)-1α-regulated genes and histone H3 lysine 9 (H3K9) acetylation, a known sirtuin 6 (SIRT6) target, were increased in shNampt KD cells. Thus, we propose that the shift toward glycolytic metabolism observed, at least in part, is mediated by the SIRT6/HIF1α axis. Our findings suggest that NAMPT plays a key role for maintaining NAD⁺ levels in skeletal muscle and that NAMPT deficiency compromises oxidative phosphorylation capacity and alters energy homeostasis in this tissue.

Noninvasive optical diagnostics of enhanced green fluorescent protein expression in skeletal muscle for comparison of electroporation and sonoporation efficiencies

We highlight the options available for noninvasive optical diagnostics of reporter gene expression in mouse tibialis cranialis muscle. An in vivo multispectral imaging technique combined with fluorescence spectroscopy point measurements has been used for the transcutaneous detection of enhanced green fluorescent protein (EGFP) expression, providing information on location and duration of EGFP expression and allowing quantification of EGFP expression levels. For EGFP coding plasmid (pEGFP-Nuc Vector, 10  μg/50  ml 10  μg/50  ml ) transfection, we used electroporation or ultrasound enhanced microbubble cavitation [sonoporation (SP)]. The transcutaneous EGFP fluorescence in live mice was monitored over a period of one year using the described parameters: area of EGFP positive fibers, integral intensity, and mean intensity of EGFP fluorescence. The most efficient transfection of EGFP coding plasmid was achieved, when one high voltage and four low voltage electric pulses were applied. This protocol resulted in the highest short-term and long-term EGFP expression. Other electric pulse protocols as well as SP resulted in lower fluorescence intensities of EGFP in the transfected area. We conclude that noninvasive multispectral imaging technique combined with fluorescence spectroscopy point measurements is a suitable method to estimate the dynamics and efficiency of reporter gene transfection in vivo.

Optimizing hyaluronidase dose and plasmid DNA delivery greatly improves gene electrotransfer efficiency in rat skeletal muscle

Transfection of rat skeletal muscle in vivo is a widely used research model. However, gene electrotransfer protocols have been developed for mice and yield variable results in rats. We investigated whether changes in hyaluronidase pre-treatment and plasmid DNA delivery can improve transfection efficiency in rat skeletal muscle. We found that pre-treating the muscle with a hyaluronidase dose suitable for rats (0.56 U/g b.w.) prior to plasmid DNA injection increased transfection efficiency by >200% whereas timing of the pre-treatment did not affect efficiency. Uniformly distributing plasmid DNA delivery across the muscle by increasing the number of plasmid DNA injections further enhanced transfection efficiency whereas increasing plasmid dose from 0.2 to 1.6 µg/g b.w. or vehicle volume had no effect. The optimized protocol resulted in ~80% (CI95%: 79–84%) transfected muscle fibers with a homogenous distribution. We also show that transfection was stable over five weeks of regular exercise or inactivity. Our findings show that species-specific plasmid DNA delivery and hyaluronidase pre-treatment greatly improves transfection efficiency in rat skeletal muscle.

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Parameters for effective in vivo skeletal muscle transfection are species specific.

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Pre-treatment with a rat-specific hyaluronidase dose greatly improves transfection efficiency.

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Delivering plasmid DNA more uniformly enhances transfection efficiency in rat skeletal muscle.

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Transfection efficiency is not improved by increasing plasmid DNA dose.

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Exercise training does not affect transfection stability.

Electrotransfection and lipofection show comparable efficiency for in vitro gene delivery of primary human myoblasts

Transfection of primary human myoblasts offers the possibility to study mechanisms that are important for muscle regeneration and gene therapy of muscle disease. Cultured human myoblasts were selected here because muscle cells still proliferate at this developmental stage, which might have several advantages in gene therapy. Gene therapy is one of the most sought-after tools in modern medicine. Its progress is, however, limited due to the lack of suitable gene transfer techniques. To obtain better insight into the transfection potential of the presently used techniques, two non-viral transfection methods--lipofection and electroporation--were compared. The parameters that can influence transfection efficiency and cell viability were systematically approached and compared. Cultured myoblasts were transfected with the pEGFP-N1 plasmid either using Lipofectamine 2000 or with electroporation. Various combinations for the preparation of the lipoplexes and the electroporation media, and for the pulsing protocols, were tested and compared. Transfection efficiency and cell viability were inversely proportional for both approaches. The appropriate ratio of Lipofectamine and plasmid DNA provides optimal conditions for lipofection, while for electroporation, RPMI medium and a pulsing protocol using eight pulses of 2 ms at E = 0.8 kV/cm proved to be the optimal combination. The transfection efficiencies for the optimal lipofection and optimal electrotransfection protocols were similar (32 vs. 32.5%, respectively). Both of these methods are effective for transfection of primary human myoblasts; however, electroporation might be advantageous for in vivo application to skeletal muscle.

Comparison of flow cytometry, fluorescence microscopy and spectrofluorometry for analysis of gene electrotransfer efficiency

In this study, we compared three different methods used for quantification of gene electrotransfer efficiency: fluorescence microscopy, flow cytometry and spectrofluorometry. We used CHO and B16 cells in a suspension and plasmid coding for GFP. The aim of this study was to compare and analyse the results obtained by fluorescence microscopy, flow cytometry and spectrofluorometry and in addition to analyse the applicability of spectrofluorometry for quantifying gene electrotransfer on cells in a suspension. Our results show that all the three methods detected similar critical electric field strength, around 0.55 kV/cm for both cell lines. Moreover, results obtained on CHO cells showed that the total fluorescence intensity and percentage of transfection exhibit similar increase in response to increase electric field strength for all the three methods. For B16 cells, there was a good correlation at low electric field strengths, but at high field strengths, flow cytometer results deviated from results obtained by fluorescence microscope and spectrofluorometer. Our study showed that all the three methods detected similar critical electric field strengths and high correlations of results were obtained except for B16 cells at high electric field strengths. The results also demonstrated that flow cytometry measures higher values of percentage transfection compared to microscopy. Furthermore, we have demonstrated that spectrofluorometry can be used as a simple and consistent method to determine gene electrotransfer efficiency on cells in a suspension.

PhiC31 integrase-mediated genomic integration and stable gene expression in the mouse mammary gland after gene electrotransfer

BACKGROUND

PhiC31 integrase is capable of conferring long-term transgene expression in various transfected tissues in vivo. In the present study, we investigated the activity of phiC31 integrase in mouse mammary glands.

METHODS

The normal mouse mammary epithelial cell line HC11 was transfected with FuGENE® HD Transfection Reagent (Roche Diagnostics, Shanghai, China). Transfection of the mouse mammary gland in vivo was performed by electrotransfer. Transgene expression was detected by western blotting and an enzyme-linked immunosorbent assay. Genomic integration and integration at mpsL1 was confirmed by a nested polymerase chain reaction.

RESULTS

An optimal electrotransfer protocol for the lactating mouse mammary gland was attained through investigation of different voltages and pulse durations. PhiC31 integrase mediated site-specific transgene integration in HC11 cells and the mouse mammary gland. In addition, the site-specific integration occurred efficiently at the ‘hot spot’ mpsL1. Co-delivery of PhiC31 integrase enhanced and prolonged transgene expression in the mouse mammary gland.

CONCLUSIONS

The results obtained in the present study show that the use of phiC31 integrase is a feasible and efficient method for high and stable transgene expression in the mouse mammary gland.

Muscle-derived expression of the chemokine CXCL1 attenuates diet-induced obesity and improves fatty acid oxidation in the muscle

Serum levels and muscle expression of the chemokine CXCL1 increase markedly in response to exercise in mice. Because several studies have established muscle-derived factors as important contributors of metabolic effects of exercise, this study aimed at investigating the effect of increased expression of muscle-derived CXCL1 on systemic and intramuscular metabolic parameters, with focus on fatty acid oxidation and oxidative metabolism in skeletal muscle. By overexpression of CXCL1 in the tibialis cranialis muscle in mice, significant elevations in muscle and serum CXCL1 within a physiological range were obtained. At 3 mo of high-fat feeding, visceral and subcutaneous fat mass were 32.4 (P < 0.01) and 22.4% (P < 0.05) lower, respectively, in CXCL1-overexpressing mice compared with control mice. Also, chow-fed CXCL-transfected mice had 35.4% (P < 0.05) lower visceral fat mass and 33.4% (P < 0.05) lower subcutaneous fat mass compared with chow-fed control mice. These reductions in accumulation of adipose tissue were accompanied by improved glucose tolerance and insulin sensitivity. Furthermore, in CXCL1-transfected muscles, muscular ex vivo fatty acid oxidation was significantly enhanced compared with control muscles (chow fed: 2.2-fold, P < 0.05; high-fat fed: 2-fold, P < 0.05) and also showed increased expression levels of major fatty acid oxidation genes (CD36, CPT I, and HADH). Finally, CXCL1 expression was associated with increased muscle mRNA expression of VEGF and CD31, suggesting a role for CXCL1 in muscle angiogenesis. In conclusion, our data show that overexpression of CXCL1 within a physiological range attenuates diet-induced obesity, likely mediated through a CXCL1-induced improvement of fatty acid oxidation and oxidative capacity in skeletal muscle tissue.

Drug delivery by electropulsation: Recent developments in oncology

Electro-permeabilisation allows the free access of polar compounds to the cytoplasm by a reversible alteration of the cell membrane. It is now used in clinics for the eradication of cutaneous solid tumors. New developments predict its future applications for other anti-cancer treatments.

Muscle gene electrotransfer is increased by the antioxidant tempol in mice

Electropermeabilization (EP) is an effective method of gene transfer into different tissues. During EP, reactive oxygen species (ROS) are formed, which could affect transfection efficiency. The role of generated ROS and the role of antioxidants in electrotransfer in myoblasts in vitro and in Musculus tibialis cranialis in mice were, therefore, investigated. We demonstrate in the study that during EP of C2C12 myoblasts, ROS are generated on the surface of the cells, which do not induce long-term genomic DNA damage. Plasmid DNA for transfection (pEGFP-N1), which is present outside the cells during EP, neutralizes the generated ROS. The ROS generation is proportional to the amplitude of the electric pulses and can be scavenged by antioxidants, such as vitamin C or tempol. When antioxidants were used during gene electrotransfer, the transfection efficiency of C2C12 myoblasts was statistically significantly increased 1.6-fold with tempol. Also in vivo, the transfection efficiency of M. tibialis cranialis in mice was statistically significantly increased 1.4-fold by tempol. The study indicates that ROS are generated on cells during EP and can be scavenged by antioxidants. Specifically, tempol can be used to improve gene electrotransfer into the muscle and possibly also to other tissues.

Calcium electrotransfer for termination of transgene expression in muscle

Gene electrotransfer is expanding in clinical use, thus we have searched for an emergency procedure to stop transgene expression in case of serious adverse events. Calcium is cytotoxic at high intracellular levels, so we tested effects of calcium electrotransfer on transgene expression in muscle. A clinical grade calcium solution (20 μl, 168 mM) was injected into transfected mouse or rat tibialis cranialis muscle. Ca(2+) uptake was quantified using calcium 45 ((45)Ca), and voltage and time between injection and pulsation were varied. Extinction of transgene expression was investigated by using both in vivo imaging of infrared fluorescent "Katushka" and erythropoietin evaluated by ELISA and hemoglobin. Histology was performed. Electrotransfer of Katushka and erythropoietin yielded significant expression. Maximal calcium uptake occurred after injection of Ca(2+) before electropulsing using eight high voltage pulses of 1000 V/cm. Using these parameters, in vivo imaging showed that transgene expression significantly decreased 4 hr after Ca(2+) electrotransfer and was eliminated within 24 hr. Similarly, serum erythropoietin was reduced by 46% at 4 hr and to control levels at 2 days. Histological analyses showed muscle damage and subsequent regeneration. Electrotransfer of isotonic CaCl(2) terminates transgenic protein expression in muscles and may be used for contingency elimination of transgene expression.

Synergistic effects of local temperature enhancements on cellular responses in the context of high-intensity, ultrashort electric pulses

Results of self-consistent analyses of cells show the possibility of temperature increases at membranes in response to a single nanosecond, high-voltage pulse, at least over small sections of the membrane. Molecular Dynamics simulations indicate that such a temperature increase could facilitate poration, which is one example of a bio-process at the plasma membrane. Our study thus suggests that the use of repetitive high-intensity voltage pulses could open up possibilities for a host of synergistic bio-responses involving both thermal and electrically driven phenomena.

Halting angiogenesis by non-viral somatic gene therapy alleviates psoriasis and murine psoriasiform skin lesions

Dysregulated angiogenesis is a hallmark of chronic inflammatory diseases, including psoriasis, a common skin disorder that affects approximately 2% of the population. Studying both human psoriasis in 2 complementary xenotransplantation models and psoriasis-like skin lesions in transgenic mice with epidermal expression of human TGF-β1, we have demonstrated that antiangiogenic non-viral somatic gene therapy reduces the cutaneous microvasculature and alleviates chronic inflammatory skin disorders. Transient muscular expression of the recombinant disintegrin domain (RDD) of metargidin (also known as ADAM-15) by in vivo electroporation reduced cutaneous angiogenesis and vascularization in all 3 models. As demonstrated using red fluorescent protein-coupled RDD, the treatment resulted in muscular expression of the gene product and its deposition within the cutaneous hyperangiogenic connective tissue. High-resolution ultrasound revealed reduced cutaneous blood flow in vivo after electroporation with RDD but not with control plasmids. In addition, angiogenesis- and inflammation-related molecular markers, keratinocyte proliferation, epidermal thickness, and clinical disease scores were downregulated in all models. Thus, non-viral antiangiogenic gene therapy can alleviate psoriasis and may do so in other angiogenesis-related inflammatory skin disorders.

Numerical optimization of gene electrotransfer into muscle tissue

BACKGROUND

Electroporation-based gene therapy and DNA vaccination are promising medical applications that depend on transfer of pDNA into target tissues with use of electric pulses. Gene electrotransfer efficiency depends on electrode configuration and electric pulse parameters, which determine the electric field distribution. Numerical modeling represents a fast and convenient method for optimization of gene electrotransfer parameters. We used numerical modeling, parameterization and numerical optimization to determine the optimum parameters for gene electrotransfer in muscle tissue.

METHODS

We built a 3D geometry of muscle tissue with two or six needle electrodes (two rows of three needle electrodes) inserted. We performed a parametric study and optimization based on a genetic algorithm to analyze the effects of distances between the electrodes, depth of insertion, orientation of electrodes with respect to muscle fibers and applied voltage on the electric field distribution. The quality of solutions were evaluated in terms of volumes of reversibly (desired) and irreversibly (undesired) electroporated muscle tissue and total electric current through the tissue.

RESULTS

Large volumes of reversibly electroporated muscle with relatively little damage can be achieved by using large distances between electrodes and large electrode insertion depths. Orienting the electrodes perpendicular to muscle fibers is significantly better than the parallel orientation for six needle electrodes, while for two electrodes the effect of orientation is not so pronounced. For each set of geometrical parameters, the window of optimal voltages is quite narrow, with lower voltages resulting in low volumes of reversibly electroporated tissue and higher voltages in high volumes of irreversibly electroporated tissue. Furthermore, we determined which applied voltages are needed to achieve the optimal field distribution for different distances between electrodes.

CONCLUSION

The presented numerical study of gene electrotransfer is the first that demonstrates optimization of parameters for gene electrotransfer on tissue level. Our method of modeling and optimization is generic and can be applied to different electrode configurations, pulsing protocols and different tissues. Such numerical models, together with knowledge of tissue properties can provide useful guidelines for researchers and physicians in selecting optimal parameters for in vivo gene electrotransfer, thus reducing the number of animals used in studies of gene therapy and DNA vaccination.

Bioelectric applications for treatment of melanoma

Two new cancer therapies apply bioelectric principles. These methods target tumor structures locally and function by applying millisecond electric fields to deliver plasmid DNA encoding cytokines using electrogene transfer (EGT) or by applying rapid rise-time nanosecond pulsed electric fields (nsPEFs). EGT has been used to locally deliver cytokines such as IL-12 to activate an immune response, resulting in bystander effects. NsPEFs locally induce apoptosis-like effects and affect vascular networks, both promoting tumor demise and restoration of normal vascular homeostasis. EGT with IL-12 is in melanoma clinical trials and nsPEFs are used in models with B16F10 melanoma in vitro and in mice. Applications of bioelectrics, using conventional electroporation and extensions of it, provide effective alternative therapies for melanoma.

Plasmid injection and application of electric pulses alter endogenous mRNA and protein expression in B16.F10 mouse melanomas

The application of electric pulses to tissues causes cell membrane destabilization, allowing exogenous molecules to enter the cells. This delivery technique can be used for plasmid gene therapy. Reporter gene expression after plasmid delivery with eight representative published protocols was compared in B16.F10 mouse melanoma tumors. This expression varied significantly based on the pulse parameters utilized for delivery. To observe the possible influence of plasmid injection and/or pulse application on endogenous gene expression, levels of stress related mRNAs four and 24 hours after delivery were determined by PCR array. Increases in mRNA levels for several inflammatory chemokines and cytokines were observed in response to plasmid injection, electric pulses alone, or the combination. This upregulation was confirmed by individual real-time reverse transcription TaqMan PCR assays. Proteins were extracted at the same time points from identically treated tumors and inflammatory protein levels were assayed by ELISA and by a custom multiplex bead array. Increases in inflammatory protein levels generally paralleled mRNA levels. Some differences were observed, which may have been due to differing expression kinetics. The observed upregulated expression of these cytokines and chemokines may aid or inhibit the therapeutic effectiveness of immune-based cancer gene therapies.

The influence of skeletal muscle anisotropy on electroporation: in vivo study and numerical modeling

The aim of this study was to theoretically and experimentally investigate electroporation of mouse tibialis cranialis and to determine the reversible electroporation threshold values needed for parallel and perpendicular orientation of the applied electric field with respect to the muscle fibers. Our study was based on local electric field calculated with three-dimensional realistic numerical models, that we built, and in vivo visualization of electroporated muscle tissue. We established that electroporation of muscle cells in tissue depends on the orientation of the applied electric field; the local electric field threshold values were determined (pulse parameters: 8 × 100 μs, 1 Hz) to be 80 V/cm and 200 V/cm for parallel and perpendicular orientation, respectively. Our results could be useful electric field parameters in the control of skeletal muscle electroporation, which can be used in treatment planning of electroporation based therapies such as gene therapy, genetic vaccination, and electrochemotherapy.

Physiological effects of high- and low-voltage pulse combinations for gene electrotransfer in muscle

Gene transfer by electroporation is gaining momentum now that high-level, long-term expression of transgenes is being obtained. Several different pulse regimens are efficient, yet little information is available about the physiological muscular response to gene electrotransfer. This paper provides a comprehensive evaluation of the physiological and molecular effects on host tissue after DNA electrotransfer. We have tested several pulse regimens with special emphasis on the pulse combination of a short (100 microsec) high-voltage (HV) pulse followed by a long low-voltage (LV) pulse used for DNA electrotransfer, comparing it with 8 HV pulses designed to ensure extensive permeabilization of the muscle membrane. Using both mouse and rat skeletal muscle tissue, we investigated cell permeabilization by the 51Cr-labeled EDTA assay, lactate dehydrogenase release, Na+ and Ca2+ influx, K+ efflux, ATP release, and water content, as well as muscle function both in vivo and ex vivo, Hsp70 induction, and histology. In all these assays, the HVLV pulse combination gave rise to minimal disturbance of cell function, in all cases significantly different from results when using 8 HV pulses. The evaluated parameters were normalized after 1 week. The addition of DNA caused significantly more transmembrane exchange, and this may be due to entrance of the DNA through the membrane. In conclusion, this study comprehensively documents the immediate effects of DNA electrotransfer and shows that only slight cell disturbances occur with the HVLV pulses used for gene transfer. This is highly important, as minimal perturbation of cell physiology is essential for efficient transgene expression.

Electric pulses used in electrochemotherapy and electrogene therapy do not significantly change the expression profile of genes involved in the development of cancer in malignant melanoma cells

Background

Electroporation is a versatile method for in vitro or in vivo delivery of different molecules into cells. However, no study so far has analysed the effects of electric pulses used in electrochemotherapy (ECT pulses) or electric pulses used in electrogene therapy (EGT pulses) on malignant cells. We studied the effect of ECT and EGT pulses on human malignant melanoma cells in vitro in order to understand and predict the possible effect of electric pulses on gene expression and their possible effect on cell behaviour.

Methods

We used microarrays with 2698 different oligonucleotides to obtain the expression profile of genes involved in apoptosis and cancer development in a malignant melanoma cell line (SK-MEL28) exposed to ECT pulses and EGT pulses.

Results

Cells exposed to ECT pulses showed a 68.8% average survival rate, while cells exposed to EGT pulses showed a 31.4% average survival rate. Only seven common genes were found differentially expressed in cells 16 h after exposure to ECT and EGT pulses. We found that ECT and EGT pulses induce an HSP70 stress response mechanism, repress histone protein H4, a major protein involved in chromatin assembly, and down-regulate components involved in protein synthesis.

Conclusion

Our results show that electroporation does not significantly change the expression profile of major tumour suppressor genes or oncogenes of the cell cycle. Moreover, electroporation also does not changes the expression of genes involved in the stability of DNA, supporting current evidence that electroporation is a safe method that does not promote tumorigenesis. However, in spite of being considered an isothermal method, it does to some extent induce stress, which resulted in the expression of the environmental stress response mechanism, HSP70.

Erythropoietin over-expression protects against diet-induced obesity in mice through increased fat oxidation in muscles

Erythropoietin can be over-expressed in skeletal muscles by gene electrotransfer, resulting in 100-fold increase in serum EPO and significant increases in haemoglobin levels. Earlier studies have suggested that EPO improves several metabolic parameters when administered to chronically ill kidney patients. Thus we applied the EPO over-expression model to investigate the metabolic effect of EPO in vivo.

At 12 weeks, EPO expression resulted in a 23% weight reduction (P<0.01) in EPO transfected obese mice; thus the mice weighed 21.9±0.8 g (control, normal diet,) 21.9±1.4 g (EPO, normal diet), 35.3±3.3 g (control, high-fat diet) and 28.8±2.6 g (EPO, high-fat diet). Correspondingly, DXA scanning revealed that this was due to a 28% reduction in adipose tissue mass.

The decrease in adipose tissue mass was accompanied by a complete normalisation of fasting insulin levels and glucose tolerance in the high-fat fed mice. EPO expression also induced a 14% increase in muscle volume and a 25% increase in vascularisation of the EPO transfected muscle. Muscle force and stamina were not affected by EPO expression. PCR array analysis revealed that genes involved in lipid metabolism, thermogenesis and inflammation were increased in muscles in response to EPO expression, while genes involved in glucose metabolism were down-regulated. In addition, muscular fat oxidation was increased 1.8-fold in both the EPO transfected and contralateral muscles.

In conclusion, we have shown that EPO when expressed in supra-physiological levels has substantial metabolic effects including protection against diet-induced obesity and normalisation of glucose sensitivity associated with a shift to increased fat metabolism in the muscles.

In Vivo Imaging of Far-red Fluorescent Proteins after DNA Electrotransfer to Muscle Tissue

DNA electrotransfer to muscle tissue yields long-term, high levels of gene expression; showing great promise for future gene therapy. We want to characterize the novel far-red fluorescent protein Katushka as a marker for gene expression using time domain fluorescence in vivo imaging. Highly efficient transgenic expression was observed after DNA electrotransfer with 100-fold increase in fluorescent intensity. The fluorescent signal peaked 1 week after transfection and returned to background level within 4 weeks. Katushka expression was not as stable as GFP expression, which was detectable for 8 weeks. Depth and 3D analysis proved that the expression was located in the target muscle. In vivo bio-imaging using the novel Katushka fluorescent protein enables excellent evaluation of the transfection efficacy, and spatial distribution, but lacks long-term stability.

Gene electrotransfer into murine skeletal muscle: a systematic analysis of parameters for long-term gene expression

Skeletal muscle is an attractive target tissue for delivery of therapeutic genes, since it is well vascularized, easily accessible, and has a high capacity for protein synthesis. For efficient transfection in skeletal muscle, several protocols have been described, including delivery of low voltage electric pulses and a combination of high and low voltage electric pulses. The aim of this study was to determine the influence of different parameters of electrotransfection on short-term and long-term transfection efficiency in murine skeletal muscle, and to evaluate histological changes in the treated tissue. Different parameters of electric pulses, different time lags between plasmid DNA injection and application of electric pulses, and different doses of plasmid DNA were tested for electrotransfection of tibialis cranialis muscle of C57Bl/6 mice using DNA plasmid encoding green fluorescent protein (GFP). Transfection efficiency was assessed on frozen tissue sections one week after electrotransfection using a fluorescence microscope and also noninvasively, followed by an in vivo imaging system using a fluorescence stereo microscope over a period of several months. Histological changes in muscle were evaluated immediately or several months after electrotransfection by determining infiltration of inflammatory mononuclear cells and presence of necrotic muscle fibers. The most efficient electrotransfection into skeletal muscle of C57Bl/6 mice in our experiments was achieved when one high voltage (HV) and four low voltage (LV) electric pulses were applied 5 seconds after the injection of 30 microg of plasmid DNA. This protocol resulted in the highest short-term as well as long-term transfection. The fluorescence intensity of the transfected area declined after 2-3 weeks, but GFP fluorescence was still detectable 18 months after electrotransfection. Extensive inflammatory mononuclear cell infiltration was observed immediately after the electrotransfection procedure using the described parameters, but no necrosis or late tissue damage was observed. This study showed that electric pulse parameters, time lag between the injection of DNA and application of electric pulses, and dose of plasmid DNA affected the duration of transgene expression in murine skeletal muscle. Therefore, transgene expression in muscle can be controlled by appropriate selection of electrotransfection protocol.