Gene therapy for streptozotocin-induced diabetic mice by electroporational transfer of naked human insulin precursor DNA into skeletal muscle in vivo

A Critical Review of Electroporation as A Plasmid Delivery System in Mouse Skeletal Muscle

The gene delivery to skeletal muscles is a promising strategy for the treatment of both muscular disorders (by silencing or overexpression of specific gene) and systemic secretion of therapeutic proteins. The use of a physical method like electroporation with plate or needle electrodes facilitates long-lasting gene silencing in situ. It has been reported that electroporation enhances the expression of the naked DNA gene in the skeletal muscle up to 100 times and decreases the changeability of the intramuscular expression. Coelectransfer of reporter genes such as green fluorescent protein (GFP), luciferase or beta-galactosidase allows the observation of correctly performed silencing in the muscles. Appropriate selection of plasmid injection volume and concentration, as well as electrotransfer parameters, such as the voltage, the length and the number of electrical pulses do not cause long-term damage to myocytes. In this review, we summarized the electroporation methodology as well as the procedure of electrotransfer to the gastrocnemius, tibialis, soleus and foot muscles and compare their advantages and disadvantages.

Lineage Reprogramming: A Promising Road for Pancreatic β Cell Regeneration

Cell replacement therapy is a promising method to restore pancreatic β cell function and cure diabetes. Distantly related cells (fibroblasts, keratinocytes, and muscle cells) and developmentally related cells (hepatocytes, gastrointestinal, and pancreatic exocrine cells) have been successfully reprogrammed into β cells in vitro and in vivo. However, while some reprogrammed β cells bear similarities to bona fide β cells, others do not develop into fully functional β cells. Here we review various strategies currently used for β cell reprogramming, including ectopic expression of specific transcription factors associated with islet development, repression of maintenance factors of host cells, regulation of epigenetic modifications, and microenvironmental changes. Development of simple and efficient reprogramming methods is a key priority for developing fully functional β cells suitable for cell replacement therapy.

Follistatin: a novel therapeutic for the improvement of muscle regeneration

Follistatin (FST) is a member of the tissue growth factor β family and is a secreted glycoprotein that antagonizes many members of the family, including activin A, growth differentiation factor 11, and myostatin. The objective of this study was to explore the use of an engineered follistatin therapeutic created by fusing FST315 lacking heparin binding activity to the N terminus of a murine IgG1 Fc (FST315-ΔHBS-Fc) as a systemic therapeutic agent in models of muscle injury. Systemic administration of this molecule was found to increase body weight and lean muscle mass after weekly administration in normal mice. Subsequently, we tested this agent in several models of muscle injury, which were chosen based on their severity of damage and their ability to reflect clinical settings. FST315-ΔHBS-Fc treatment proved to be a potent inducer of muscle remodeling and regeneration. FST315-ΔHBS-Fc induced improvements in muscle repair after injury/atrophy by modulating the early inflammatory phase allowing for increased macrophage density, and Pax7-positive cells leading to an accelerated restoration of myofibers and muscle function. Collectively, these data demonstrate the benefits of a therapeutically viable form of FST that can be leveraged as an alternate means of ameliorating muscle regeneration.

Evaluation of insulin expression and secretion in genetically engineered gut K and L-cells

Background

Gene therapy could provide an effective treatment of diabetes. Previous studies have investigated the potential for several cell and tissue types to produce mature and active insulin. Gut K and L-cells could be potential candidate hosts for gene therapy because of their special features.

Results

In this study, we isolated gut K and L-cells to compare the potential of both cell types to produce insulin when exposed to similar conditions. The isolated pure K and L-cells were transfected with recombinant plasmids encoding insulin and with specific promoters for K or L-cells. Insulin expression was studied in response to glucose or meat hydrolysate. We found that glucose and meat hydrolysate efficiently induced insulin secretion from K and L-cells. However, the effects of meat hydrolysate on insulin secretion were more potent in both cells compared with glucose. Results of enzyme-linked immunosorbent assays showed that L-cells secreted more insulin compared with K-cells regardless of the stimulator, although this difference was not statistically significant.

Conclusion

The responses of K and L-cells to stimulation with glucose or meat hydrolysate were generally comparable. Therefore, both K and L-cells show similar potential to be used as surrogate cells for insulin gene expression in vitro. The potential use of these cells for diabetic gene therapy warrants further investigation.

Protein overexpression in skeletal muscle using plasmid-based gene transfer to elucidate mechanisms controlling fiber size

Plasmid DNA electrotransfer is a direct method of gene delivery to skeletal muscle commonly used to identify endogenous signaling pathways that mediate muscle remodeling or pathological states in adult rodents. When plasmids encoding a protein to be overexpressed are fused to a fluorescent protein or an epitope-tag, plasmid electrotransfer permits visualization of the expressed protein in muscle fibers. Here, we demonstrate the use of electrotransfer of plasmids encoding mutant or wild type proteins to identify the role of the endogenous protein in regulating muscle fiber atrophy. The plasmids used encode a dominant negative form of the inhibitor of kappaB kinase beta (IKKβ) fused to green fluorescent protein (GFP), a constitutively active form of IKKα fused to GFP, and a wild type IKKβ fused to an HA tag. We show the effects of overexpression of these proteins on rat or mouse fiber size either with disuse atrophy or in normal weight bearing muscle. The effects of overexpressed proteins on myofiber size are assessed by comparing cross-sectional area of the transfected, fluorescent myofibers to the nontransfected, nonfluorescent myofibers. Using optimized intramuscular plasmid DNA injection and electroporation, we illustrate high transfection efficiency with no overt muscle damage using medium sized fusion proteins (105 kDa).

Engineering an L-cell line that expresses insulin under the control of the glucagon-like peptide-1 promoter for diabetes treatment

Background

Diabetes mellitus is a complicated disease with a pathophysiology that includes hyperinsulinemia, hyperglycemia and other metabolic impairments leading to many clinical complications. It is necessary to develop appropriate treatments to manage the disease and reduce possible acute and chronic side effects. The advent of gene therapy has generated excitement in the medical world for the possible application of gene therapy in the treatment of diabetes. The glucagon-like peptide-1 (GLP-1) promoter, which is recognised by gut L-cells, is an appealing candidate for gene therapy purposes. The specific properties of L-cells suggest that L-cells and the GLP-1 promoter would be useful for diabetes therapy approaches.

Results

In this study, L-cells were isolated from a primary intestinal cell line to create suitable target cells for insulin expression studies. The isolated cells displayed L-cell properties and were therefore used as an L-cell surrogate. Next, the isolated L-cells were transfected with the recombinant plasmid consisting of an insulin gene located downstream of the GLP-1 promoter. The secretion tests revealed that an increase in glucose concentration from 5 mM to 25 mM induced insulin gene expression in the L-cells by 2.7-fold. Furthermore, L-cells quickly responded to the glucose stimulation; the amount of insulin protein increased 2-fold in the first 30 minutes and then reached a plateau after 90 minutes.

Conclusion

Our data showed that L-cells efficiently produced the mature insulin protein. In addition, the insulin protein secretion was positively regulated with glucose induction. In conclusion, GLP-1 promoter and L-cell could be potential candidates for diabetes gene therapy agents.

Intramuscular delivery of a naked DNA plasmid encoding proinsulin and pancreatic regenerating III protein ameliorates type 1 diabetes mellitus

Type 1 diabetes mellitus (T1DM) is an autoimmune disease characterized by inflammation of pancreatic islets and destruction of β cells. Up to now, there is still no cure for this devastating disease and alternative approach should be developed. To explore a novel gene therapy strategy combining immunotherapy and β cell regeneration, we constructed a non-viral plasmid encoding proinsulin (PI) and pancreatic regenerating (Reg) III protein (pReg/PI). Therapeutic potentials of this plasmid for T1DM were investigated. Intramuscular delivery of pReg/PI resulted in a significant reduction in hyperglycemia and diabetes incidence, with an increased insulin contents in the serum of T1DM mice model induced by STZ. Treatment with pReg/PI also restored the balance of Th1/Th2 cytokines and expanded CD4(+)CD25(+)Foxp3(+) T regulatory cells, which may attribute to the establishment of self-immune tolerance. Additionally, in comparison to the mice treated with empty vector pBudCE4.1 (pBud), attenuated insulitis and apoptosis achieved by inhibiting activation of NF-κB in the pancreas of pReg/PI treated mice were observed. In summary, these results indicate that intramuscular delivery of pReg/PI distinctly ameliorated STZ-induced T1DM by reconstructing the immunological self-tolerance and promoting the regeneration of β cells, which might be served as a promising candidate for the gene therapy of T1DM.

Use of molecular beacons to image effects of titanium surface microstructure on beta1 integrin expression in live osteoblast-like cells

This study used molecular beacon technology to examine substrate-dependent changes in integrin subunit expression in living cells. Molecular beacons are oligonucleotide probes that can be delivered into live cells to allow for real-time imaging of mRNA. They have a stem-loop hairpin structure with a fluorophore-quencher pair, which opens when bound to the target mRNA sequence, resulting in a fluorescent signal upon excitation. A novel molecular beacon that is specific to the beta1 integrin subunit mRNA was developed and used to image osteoblast-like MG63 cells in vitro on both glass and titanium surfaces of varying roughness. Specificity was verified by comparing the molecular beacon signal intensities to real-time PCR results in both wild-type cells and cells with shRNA knockdown of beta1 integrin mRNA. The molecular beacon was able to detect changes due to both surface microtopography and silencing of the mRNA target. The results showed that effects of the substrate on beta1 mRNA noted previously in confluent cultures were evident in pre-confluent cells as well, supporting the hypothesis that beta1 integrin pairs are important in proliferation as well as differentiation of osteoblasts. This technique overcomes the limitations of traditional gene assays (PCR, immunofluorescence) by allowing for the real-time measurement and tracking of specific mRNAs in individual live cells prior to confluence.

Insulin-secreting L-cells for the treatment of insulin-dependent diabetes

Cell-based treatments for insulin-dependent diabetes (IDD) may provide more physiologic regulation of blood glucose levels than daily insulin injections, thereby reducing the occurrence of secondary complications associated with diabetes. An autologous cell source is especially attractive for regulatory and ethical reasons in addition to eliminating the need for immunosuppression. This study uses non-beta-cells, genetically modified for physiologic insulin secretion. Enteroendocrine L-cells, exhibit regulated secretion in response to physiologic stimuli and their endogenous products are fully compatible with prandial metabolism. Murine GLUTag L-cells were transfected with a plasmid co-expressing human insulin and neomycin resistance and the stable cell line, GLUTag-INS, was established. Secretion properties of GLUTag-INS cells were investigated in vitro through induced secretion tests using meat hydrolysate or 3-isobutyl-1-methylxanthine and forskolin as secretagogues. GLUTag-INS cells rapidly co-secreted recombinant insulin and endogenous glucagon-like peptide in response to metabolic cues from the surrounding medium and demonstrated efficient processing of proinsulin to insulin.

Synthesis of the human insulin gene: protein expression, scaling up and bioactivity

Optimized Synthetic human insulin gene was preferred to easy of cloning, plasmid stability, and protein expression away from the native sequence and its rare codons. Two steps to obtain the insulin, so we assembled the gene of 293 bp using a battery of overlapped synthetic oligos, then cloned into pET101directional TOPO expression vector downstream to the T7 promoter. The proinsulin products were produced as inclusion bodies in E. coli at a level of 10%. The batch cultivation of the strain yielded 6 g/L, while the high cell density of fed-batch cultivation yielded 46 g/L. The proinsulin purification yielded 110 mg/gram cell weight, and 1.3 mg/gram of a bioactive insulin. The native insulin was generated by enzymatic conversion of chemically processed proinsulin. The produced insulin was matched with that of a commercial aqueous version at a level of enzyme immunoassys, SDS-PAGE, RP-HPLC, and bioactivity. The present results showed that the produced insulin has a comparable biochemical and potency similar to that of commercial one.

Serum, liver, and kidney proteomic analysis for the alloxan-induced type I diabetic mice after insulin gene transfer of naked plasmid through electroporation

Gene therapy has been reported to be effective in treating diabetes mellitus (DM), while little has been found out about the functional protein changes since. The liver and kidney play important roles in glucose absorption, metabolism, and excretion. Changes in the two organs may reflect pathologic alterations during DM, while the serum has a direct connection with most organs and pathological changes. We used alloxan to induce diabetic mice, electrotranferred the insulin gene into their sural muscles, and discovered that their blood glucose decreased to normal level. Consequently, proteomic approaches were applied to evaluate protein changes in the liver, kidney, and serum of normal, diabetic, and gene transferred mice. Forty-three proteins were found either up-regulated or down-reglulated in the liver, kidney, and serum of the alloxan-induced type I diabetic mice. Only five proteins in the liver, five proteins in the kidney, and seven proteins in the serum of diabetic mice were found to be back-regulated to normal levels after gene transfer. These back-regulated proteins are involved in lipid and glucose metabolism, associated with phosphorylation, signal transduction, oxidation, and immune inflammation. Our findings might promote a better understanding for the mechanism of DM, and provide novel targets for estimating the effects of gene therapy.

Identifying putative contraceptive targets by dissecting signal transduction networks in the epididymis using an in vivo electroporation (electrotransfer) approach

Our studies have focused on understanding how the initial segment is regulated, in particular, by testicular luminal fluid factor(s). Our working hypothesis is that testicular luminal fluid growth factors, e.g. FGFs, regulate initial segment function via activation of signal transduction pathways and PEA3 family transcription factors. These, in turn, regulate downstream genes that are important for providing an appropriate fluid milieu for the protection and survival of sperm and the initial segment. To test this hypothesis and to look for potential contraceptive targets, we used an in vivo electroporation technique to introduce dominant-negative plasmids of FGF Receptor 1 and ERM into the initial segment of the rat epididymis. The levels of several putative downstream genes were estimated using quantitative-PCR (q-PCR). Data suggests that initial segment genes are regulated by 5alpha-reductase-dependent and -independent pathways and that multiple growth factor pathways are activated to coordinate the expression of these genes.

In vivo gene therapy of type I diabetic mellitus using a cationic emulsion containing an Epstein Barr Virus (EBV) based plasmid vector

A cationic emulsion containing an insulin expression plasmid was prepared for the treatment of type 1 diabetic mellitus (DM) in vivo. A rat proinsulin-1 gene was inserted to EBV-based plasmid vectors containing CAG promoter. Cationic emulsion composed of DOTAP and squalene was complexed with the plasmid DNA. An intravenous injection of cationic emulsion containing proinsulin gene decreased blood glucose levels for 7 days within normal range. The cationic emulsion exerted more profound effect on blood glucose levels compared to naked DNA. RT-PCR results confirmed that the proinsulin was expressed in several organs containing liver, lung, spleen, and kidney. The refractory response was invoked by multiple injections of naked DNA or cationic emulsion/DNA complex, which was later proven to be an immune response against expressed proinsulin. Therefore, the cationic emulsion showed a promising result as a novel insulin gene therapy vehicle by decreasing blood glucose level for a month.

Gene therapy for diabetes mellitus in rats by intramuscular injection of lentivirus containing insulin gene

We assessed therapeutic potential of intramuscular insulin gene delivery in a diabetic murine model. The human proinsulin gene cDNA engineered with concensus furin cleavage sequences was inserted into an advanced lentiviral vector that contained CMV early promoter. After injection of concentrated lentiviral vector (3.5 microg p24 Gag antigen) carrying the insulin gene into the thigh muscle, treated rats demonstrated an increase in body weight, increased survivability, attenuated the hyperglycemic response as well as prevented the formation of ketoacidosis. For these reasons, the intraparenchymal injection of lentiviral vectors into the skeletal muscle to ectopically produce insulin may be an easy and therapeutic treatment modality for type 1 diabetes mellitus.

Electric pulse-mediated gene delivery to various animal tissues

Electroporation designates the use of electric pulses to transiently permeabilize the cell membrane. It has been shown that DNA can be transferred to cells through a combined effect of electric pulses causing (1) permeabilization of the cell membrane and (2) an electrophoretic effect on DNA, leading the polyanionic molecule to move toward or across the destabilized membrane. This process is now referred to as DNA electrotransfer or electro gene transfer (EGT). Several studies have shown that EGT can be highly efficient, with low variability both in vitro and in vivo. Furthermore, the area transfected is restricted by the placement of the electrodes, and is thus highly controllable. This has led to an increasing use of the technology to transfer reporter or therapeutic genes to various tissues, as evidenced from the large amount of data accumulated on this new approach for non-viral gene therapy, termed electrogenetherapy (EGT as well). By transfecting cells with a long lifetime, such as muscle fibers, a very long-term expression of genes can be obtained. A great variety of tissues have been transfected successfully, from muscle as the most extensively used, to both soft (e.g., spleen) and hard tissue (e.g., cartilage). It has been shown that therapeutic levels of systemically circulating proteins can be obtained, opening possibilities for using EGT therapeutically. This chapter describes the various aspects of in vivo gene delivery by means of electric pulses, from important issues in methodology to updated results concerning the electrotransfer of reporter and therapeutic genes to different tissues.

Safety and efficacy of adeno-associated viral vector-mediated insulin gene transfer via portal vein to the livers of streptozotocin-induced diabetic Sprague-Dawley rats

BACKGROUND

Previous studies demonstrating the efficacy of insulin gene therapy have mostly involved use of adenoviral vectors or naked DNA to deliver the insulin gene. However, this procedure may not guarantee long-term insulin production. To improve the performance, we prepared recombinant adeno-associated viral vectors (rAAV) harboring the gene encoding a furin-modified human insulin under the cytomegalovirus (CMV) promoter [rAAV-hPPI(F12)].

METHODS

Streptozotocin (STZ)-induced diabetic Sprague-Dawley rats were used as a diabetic animal model. The levels of blood glucose, insulin, and HbA1c were measured to test the effect. An intraperitoneal glucose tolerance test was performed to test the capability of blood glucose disposal. Immunohistochemical staining and Northern blot analyses were performed to survey the expression pattern of the therapeutic insulin gene.

RESULTS

STZ-induced diabetic Sprague-Dawley rats infused via the portal vein with rAAV-hPPI(F12) produced human insulin and after a 6-h fast were normoglycemic for over 90 days post-treatment, whereas diabetic rats treated with recombinant adenoviral vector harboring the hPPI(F12) gene [rAV-hPPI(F12)] were normoglycemic only for days 3 to 13 post-treatment. Insulin mRNA was detected mainly in the liver of the rAAV-hPPI(F12)-treated diabetic rats. The glucose tolerance capability of the rAAV-hPPI(F12)-treated diabetic rats was comparable to that of non-diabetic rats, even without injection of recombinant insulin. Furthermore, blood HbA1c concentrations in rAAV-hPPI(F12)-treated diabetic rats were reduced to almost the normal level. Importantly, studies of rAV or rAAV vector-dependent side effects on the targeted liver strongly suggested that only rAAV treatment caused no side effects.

CONCLUSIONS

These results demonstrate that our rAAV-mediated in vivo insulin gene therapy provides safer maintenance of the insulin gene expression required for long-term and thus more effective blood glycemic control.

A comprehensive study of optimal conditions for naked plasmid DNA transfer into skeletal muscle by electroporation

Efficient gene transfer is a key factor in gene therapy. Reducing the damage caused by gene transfer to muscle by electroporation is very important for its clinical application. Extensive investigation of optimal conditions for gene transfer by electroporation is required. The parameters used for electroporation, including plasmid concentration; injection volume; the plasmid dose of the injection; the concentration of saline media; the size of plasmid DNA; the age of the mice; the lag time between plasmid injection and electroporation; and the effect of repeated gene transfer by electroporation, were systematically investigated in the present study. The efficiencies of gene transfer by electroporation in normal and rodent models of diabetes were also evaluated. We found that electroporation used for non-viral gene transfer could be repeated in the same place in the muscle, but the expression efficiency was closely related to the muscle damage. Increasing pulse times could enhance the efficiency of gene transfer with a lower strength of electric field. It was better to use a higher plasmid concentration than to use a larger dose of plasmid and repeated injection to achieve a high level of transgene expression. Optimal conditions varied in different animal models, being milder for diabetic mice than for normal mice, and it was also shown that the conditions that worked well on these small rodents were not necessarily suitable for larger animals. Our results provide a comprehensive view of the factors that affect the efficiency of gene transfer into skeletal muscle by electroporation.

DNA electrotransfer: its principles and an updated review of its therapeutic applications

The use of electric pulses to transfect all types of cells is well known and regularly used in vitro for bacteria and eukaryotic cells transformation. Electric pulses can also be delivered in vivo either transcutaneously or with electrodes in direct contact with the tissues. After injection of naked DNA in a tissue, appropriate local electric pulses can result in a very high expression of the transferred genes. This manuscript describes the evolution in the concepts and the various optimization steps that have led to the use of combinations of pulses that fit with the known roles of the electric pulses in DNA electrotransfer, namely cell electropermeabilization and DNA electrophoresis. A summary of the main applications published until now is also reported, restricted to the in vivo preclinical trials using therapeutic genes.

Electroporation for gene transfer to skeletal muscles: current status

Naked plasmid DNA can be used to introduce genetic material into a variety of cell types in vivo. However, such gene transfer and expression is generally very low compared with that achieved with viral vectors and so is unsuitable for clinical therapeutic application in most cases. This difference in efficiency has been substantially reduced by the introduction of in vivo electroporation to enhance plasmid delivery to a wide range of tissues including muscle, skin, liver, lung, artery, kidney, retina, cornea, spinal cord, brain, synovium, and tumors. The precise mechanism of in vivo electroporation is uncertain, but appears to involve both electropore formation and an electrophoretic movement of the plasmid DNA. Skeletal muscle is a favored target tissue for three reasons: there is a pressing need to develop effective therapies for muscular dystrophies; skeletal muscle can act as an effective platform for the long-term secretion of therapeutic proteins for systemic distribution; and introduction of DNA vaccines into skeletal muscle promotes strong humoral and cellular immune responses. All of these applications are significantly improved by the application of in vivo electroporation. Importantly, the increased efficiency of plasmid delivery following electroporation is seen in larger species as well as rodents, in contrast to the decreasing efficiencies with increasing body size for simple intramuscular injection of naked plasmid DNA. As this electroporation-enhanced non-viral gene delivery system works well in larger species and avoids the vector-specific immune responses associated with recombinant viruses, the prospects for clinical application are promising.

Mice body weight gain is prevented after naked human leptin cDNA transfer into skeletal muscle by electroporation

BACKGROUND

In this investigation, the feasibility of gene therapy for obesity by electroporational transfer of naked plasmid with leptin cDNA into skeletal muscle was tested. Both young and adult mice were studied.

METHODS

Human leptin cDNA was attached to the human insulin precursor secretion signal peptide gene. The fused gene was then inserted into the mammalian expression vector pcDNA3.1(-) and transferred into skeletal muscle of normal female mice using electroporation.

RESULTS

During the time of exogenic gene expression, daily food intake of leptin cDNA-treated mice was observed to be lower than the control. The body weight gain was prevented efficaciously regardless of if they were young or adult. At the 7th week after gene transfer, the body weight of both young and adult leptin cDNA-treated mice was about 20% lighter than the control. Although the body weight of pair fed controlled adult mice was close to the leptin cDNA-treated mice at the 8th week, they were always heavier than the leptin cDNA-treated mice before this time. The levels of retroperitoneal fats and serum TG of leptin cDNA-treated mice were markedly lower than that of the control. The relative serum hyperleptinemic level could last for about 2 months. The expression of leptin cDNA in muscle cells was also detected by RT-PCR. The levels of serum insulin and glucose of leptin cDNA-treated mice decreased slightly. Our data also showed that the hyperleptinmia resulted in uterus expansion in young mice, but not in the adults.

CONCLUSION

The present study provides evidence of successful electroporation of naked plasmid DNA transfer for prevention or treatment of mice obesity.

Peptide-linked molecular beacons for efficient delivery and rapid mRNA detection in living cells

Real-time visualization of specific endogenous mRNA expression in vivo has the potential to revolutionize medical diagnosis, drug discovery, developmental and molecular biology. However, conventional liposome- or dendrimer-based cellular delivery of molecular probes is inefficient, slow, and often detrimental to the probes. Here we demonstrate the rapid and sensitive detection of RNA in living cells using peptide-linked molecular beacons that possess self-delivery, targeting and reporting functions. We conjugated the TAT peptide to molecular beacons using three different linkages and demonstrated that, at relatively low concentrations, these molecular beacon constructs were internalized into living cells within 30 min with nearly 100% efficiency. Further, peptide-based delivery did not interfere with either specific targeting by or hybridization-induced fluorescence of the probes. We could therefore detect human GAPDH and survivin mRNAs in living cells fluorescently, revealing intriguing intracellular localization patterns of mRNA. We clearly demonstrated that cellular delivery of molecular beacons using the peptide-based approach has far better performance compared with conventional transfection methods. The peptide-linked molecular beacons approach promises to open new and exciting opportunities in sensitive gene detection and quantification in vivo.

Insulin expression in livers of diabetic mice mediated by hydrodynamics-based administration

AIM: Transfer and expression of insulin gene in vivo are an alternative strategy to improve glycemic control in type 1 diabetes. Hydrodynamics-based procedure has been proved to be very efficient to transfer naked DNA to mouse livers. The basal hepatic insulin production mediated by this rapid tail vein injection was studied to determine its effect on the resumption of glycemic control in type 1 diabetic mice.

METHODS: Engineered insulin cDNA was inserted into plasmid vectors under a CMV promoter, and transferred into STZ induced diabetic mice by hydrodynamic procedure. Glucose levels, body weight of treated mice, insulin levels, immunohistology of the liver, and quantity of insulin mRNA in the liver were assayed to identify the improvement of hyperglycemic complication after plasmid administration. Sleeping Beauty, a transposon system, was also used to prolong the insulin expression in the liver.

RESULTS: After plasmid administration, Plasma insulin was significantly increased in the diabetic mice and the livers were insulin-positive by immunostaining. At the same time the hyperglycemic complication was improved. The blood glucose levels of mice were reduced to normal. Glucose tolerance of the treated diabetic mice was improved. Body weight loss was also ameliorated. The rapid tail vein injection did not cause any fatal result.

CONCLUSION: Our results suggested that insulin gene could be efficiently transferred into the livers of diabetic mice via rapid tail vein injection and it resulted in high level of insulin expression. The basal hepatic insulin production mediated by hydrodynamics-based administration improved the glycemic control in type 1 diabetes dramatically and ameliorated diabetic syndromes. Hydrodynamics-based administration offers a simple and efficient way in the study of gene therapy for type 1 diabetes.

Intravascular insulin gene delivery as potential therapeutic intervention in diabetes mellitus

We assessed therapeutic potential of intravascular insulin gene delivery in a diabetic murine model. The rat proinsulin-1 gene cDNA engineered to harbor furin consensus cleavage sequences was inserted into EBV-based plasmid vectors that contained CAG promoter or multimerized rat insulin promoter (RIP). Normal or streptozotocin (STZ)-induced diabetic mice were given an injection of the plasmids via the tail vein under high pressure. Transfection of the CAG-proinsulin construct markedly improved hyperglycemia of diabetic mice, accompanied by a considerable increase in serum insulin concentrations. Although the RIP-plasmid failed to reduce fasting blood glucose, the glucose tolerance test and RT-PCR analysis revealed that insulin production was regulated in the liver in a blood glucose level-dependent manner. The present results suggest a potential therapeutic means of controlling DM.

Gene therapy of streptozotocin-induced diabetes by intramuscular delivery of modified preproinsulin genes

BACKGROUND

Despite improvements in insulin preparation and delivery, physiological normoglycemia is not easily achieved in diabetics. Therefore, there has been considerable interest in developing gene therapy approaches to supply insulin. We studied a nonviral muscle-based method of gene therapy and demonstrated that it could prevent hyperglycemia in murine streptozotocin (STZ)-induced diabetes.

METHODS

A plasmid encoding mouse furin-cleavable preproinsulin II cDNA (FI), or its B10-analogue (B10FI), and a plasmid encoding furin were coinjected into muscle of CD-1 mice, who were treated a day later with STZ to induce diabetes. Electroporation was applied to increase gene transfer. Blood glucose was measured in fed and fasting mice, and fasting plasma insulin was measured by radioimmunoassay. The form of insulin produced and the presence of C-peptide were analyzed by gel filtration chromatography.

RESULTS

A B10FI plasmid codelivered with a furin plasmid reduced fed and fasting blood glucose levels in STZ-treated diabetic mice. The (pro)insulin levels in plasma were increased by up to 70-fold versus blank plasmid-treated diabetic mice. The administration of FI with furin was less effective. (Pro)insulin levels were greatly increased by using two plasmids carrying different promoter elements (CMV and SV40). Insulin was identified in muscle cells by immunohistochemistry. In plasma, 40-70% of the (pro)insulin was processed to the mature form and free C-peptide was identified. Insulin gene-treated mice had improved growth rates and appeared healthier. A single injection of B10FI with SV40Furin DNA increased plasma (pro)insulin for at least 8 weeks and reduced fed blood glucose levels for 5 weeks and fasting levels for 8 weeks.

CONCLUSIONS

This is the first report that electroporation-enhanced intramuscular gene therapy with B10FI can prevent hyperglycemia in murine STZ-induced diabetes. Gene therapy using various routes and methods of furin-cleavable insulin gene delivery has been previously explored but, in muscle, results comparable to ours have not been reported.

Efficacy of interleukin-10 gene electrotransfer into skeletal muscle in mice with collagen-induced arthritis

BACKGROUND

Gene therapy is very promising in the treatment of rheumatoid arthritis (RA). Electrotransfer is a recent method reported to enhance in vivo intramuscular DNA transfection. Interleukin-10 (IL-10) has antiinflammatory effects in RA and in collagen-induced arthritis (CIA), a murine model of RA. In order to improve our strategy of gene therapy, we used electrotransfer to enhance penetration into skeletal muscle with CIA of plasmids encoding IL-10.

METHODS

CIA was induced in DBA/1 mice by immunization with bovine type II collagen. Injection into the tibial cranial muscle of low-dose (200 ng) pCOR plasmid encoding murine IL-10 (pCOR-CMV-mIL-10) was immediately followed by application of square-wave electric pulses (8 pulses of 200V/cm, 20 ms duration at 2 Hz). Control groups received empty plasmid or saline before electrotransfer.

RESULTS

When electrotransfer was performed twice on days 10 and 25 postimmunization, CIA was significantly delayed (P < 0.05) and attenuated (P < 0.001) in groups treated by electrotransfer or pCOR-CMV-mIL-10 plasmid vs. control groups. When electrotransfer of pCOR-CMV-mIL-10 plasmid was performed on days 25 and 40 postimmunization, at disease onset, the clinical severity of CIA was reduced (P < 0.05). All groups which had been electrotransferred early or late by pCOR-CMV-mIL-10 plasmid showed suppression of histological signs of arthritis.

CONCLUSIONS

Taken together, these data indicate that administration of an antiinflammatory plasmid-born gene by electrotransfer of naked DNA is effective in vivo in an arthritis model.

Non-viral gene delivery in skeletal muscle: a protein factory

Ever since the publication of the first reports in 1990 using skeletal muscle as a direct target for expressing foreign transgenes, an avalanche of papers has identified a variety of proteins that can be synthesized and correctly processed by skeletal muscle. The impetus to the development of such applications is not only amelioration of muscle diseases, but also a range of therapeutic applications, from immunization to delivery of therapeutic proteins, such as clotting factors and hormones. Although the most efficient way of introducing transgenes into muscle fibres has been by a variety of recombinant viral vectors, there are potential benefits in the use of non-viral vectors. In this review we assess the recent advances in construction and delivery of naked plasmid DNA to skeletal muscle and highlight the options available for further improvements to raise efficiency to therapeutic levels.

In vivo DNA electrotransfer

The use of electrotransfer for DNA delivery to prokaryotic cells, and eukaryotic cells in vitro, has been well known and widely used for many years. However, it is only recently that electric fields have been used to enhance DNA transfer to animal cells in vivo, and this is known as DNA electrotransfer or in vivo DNA electroporation. Some of the advantages of this method of somatic cell gene transfer are that it is a simple method that can be used to transfer almost any DNA construct to animal cells and tissues in vivo; multiple constructs can be co-transfected; it is equally applicable to dividing and nondividing cells; the DNA of interest does not need to be subcloned into a specific viral transfer vector and there is no need for the production of high titre viral stocks; and, as no viral genes are expressed there is less chance of an adverse immunologic reaction to vector sequences. The ease with which efficient in vivo gene transfer can be achieved with in vivo DNA electrotransfer is now allowing genetic analysis to be applied to a number of classic animal model systems where transgenic and embryonic stem cell techniques are not well developed, but for which a wealth of detailed descriptive embryological information is available, or surgical manipulation is much more feasible. As well as exciting applications in developmental biology, in vivo DNA electrotransfer is also being used to transfer genes to skeletal muscle and drive expression of therapeutically active proteins, and to examine exogenous gene and protein function in normal adult cells situated within the complex environment of a tissue and organ system in vivo. Thus, in effect providing the in vivo equivalent of the in vitro transient transfection assay. As the widespread use of in vivo electroporation has really only just begun, it is likely that the future will hold many more applications for this technology in basic research, biotechnology and clinical research areas.

Human insulin production and amelioration of diabetes in mice by electrotransfer-enhanced plasmid DNA gene transfer to the skeletal muscle

A first-line gene therapy for type 1 diabetes should be based on a safe procedure to engineer an accessible tissue for insulin release. We evaluated the ability of the skeletal muscle to release human insulin after electrotransfer (ET)-enhanced plasmid DNA injection in mice. A furin-cleavable proinsulin cDNA under the CMV or the MFG promoter was electrotransferred to immune-incompetent mice with STZ-induced severe diabetes. At 1 week, mature human insulin was detected in the serum of 17/20 mice. After an initial peak of 68.5 +/- 34.9 microU/ml, insulin was consistently detected at significant levels up to 6 weeks after gene transfer. Importantly, untreated diabetic animals died within 3 weeks after STZ, whereas treated mice survived up to 10 weeks. Fed blood glucose (BG) was reduced in correspondence with the insulin peak. Fasting BG was near-normalized when insulin levels were 12.9 +/- 5.3 (CMV group, 2 weeks) and 7.7 +/- 2.6 microU/ml (MFG group, 4 weeks), without frank hypoglycemia. These data indicate that ET-enhanced DNA injection in muscle leads to the release of biologically active insulin, with restoration of basal insulin levels, and lowering of fasting BG with increased survival in severe diabetes. Therefore the skeletal muscle can be considered as a platform for basal insulin secretion.