Regulated expression of mature human insulin in the liver of transgenic mice

Targeted delivery of genes to endothelial cells and cell- and gene-based therapy in pulmonary vascular diseases

Pulmonary arterial hypertension (PAH) is a devastating disease that, despite significant advances in medical therapies over the last several decades, continues to have an extremely poor prognosis. Gene therapy is a method to deliver therapeutic genes to replace defective or mutant genes or supplement existing cellular processes to modify disease. Over the last few decades, several viral and nonviral methods of gene therapy have been developed for preclinical PAH studies with varying degrees of efficacy. However, these gene delivery methods face challenges of immunogenicity, low transduction rates, and nonspecific targeting which have limited their translation to clinical studies. More recently, the emergence of regenerative approaches using stem and progenitor cells such as endothelial progenitor cells (EPCs) and mesenchymal stem cells (MSCs) have offered a new approach to gene therapy. Cell-based gene therapy is an approach that augments the therapeutic potential of EPCs and MSCs and may deliver on the promise of reversal of established PAH. These new regenerative approaches have shown tremendous potential in preclinical studies; however, large, rigorously designed clinical studies will be necessary to evaluate clinical efficacy and safety.

Reversal of diabetes in mice by intrahepatic injection of bone-derived GFP-murine mesenchymal stem cells infected with the recombinant retrovirus-carrying human insulin gene

BACKGROUND

The objective of this study was to assess the effect of intrahepatic injection of bone-derived green fluorescent protein (GFP)-transgenic murine mesenchymal stem cells (GFP-mMSCs) containing the human insulin(ins) gene in streptozotocin-induced diabetic mice.

METHODS

GFP-mMSCs were isolated from the bone marrow of GFP transgenic mice, expanded, and transfected with a recombinant retrovirus MSCV carrying the human insulin gene. C57BL/6J mice were made diabetic by an intraperitoneal administration of 160 mg/kg streptozotocin (STZ), followed by intrahepatic injection of transfected GFP-mMSCs. The variations in body weight and the blood glucose and serum insulin levels were determined after cell transplantation. GFP-mMSCs survival and human insulin expression in liver tissues were examined by fluorescent microscopy and immunohistochemistry.

RESULTS

The body weight in diabetic mice that received GFP-mMSCs harboring the human insulin gene was increased by 6% within 6 weeks after treatment, and the average blood glucose levels in these animals were 10.40 +/- 2.80 mmol/l (day 7) and 6.50 +/- 0.89 mmol/l (day 42), respectively, while the average values of blood glucose in diabetic animals without treatment were 26.80 +/- 2.49 mmol/l (day 7) and 25.40 +/- 4.10 mmol/l (day 42), showing a significant difference (p < 0.05). Moreover, secretion of human insulin of GFP-mMSCs in serum and animal liver was detected by radioimmunoassay (RIA) and immunohistochemistry (IHC).

CONCLUSIONS

Experimental diabetes could be relieved effectively for up to 6 weeks by intrahepatic transplantation of murine mesenchymal stem cells expressing human insulin. This study implies a novel approach of gene therapy for type I diabetes.

Heat-regulated production and secretion of insulin from a human artificial chromosome vector

Human artificial chromosomes (HACs) behave as independent minichromosomes and are potentially useful as a way to achieve safe, long-term expression of a transgene. In this study, we sought to elucidate the potential of HAC vectors carrying the human proinsulin transgene for gene therapy of insulin-dependent diabetes mellitus (IDDM) using non-beta-cells as a host for the vector. To facilitate the production of mature insulin in non-beta-cells and to safely regulate the level of transgene expression, we introduced furin-cleavable sites into the proinsulin coding region and utilized the heat shock protein 70 (Hsp70) promoter. We used Cre-loxP-mediated recombination to introduce the gene cassettes onto 21DeltapqHAC, a HAC vector whose structure is completely defined, present in human fibrosarcoma HT1080 cells. We observed long-term expression and stable retention of the transgene without aberrant translocation of the HAC constructs. As expected, the Hsp70 promoter allowed us to regulate gene expression with temperature, and the production and secretion of intermediates of mature insulin were made possible by the furin-cleavable sites we had introduced into proinsulin. This study can be an initial step on the application of HAC vectors on the gene delivery to non-beta-cells, which might provide a direction for future treatment for diabetes.

Liver-directed gene therapy of diabetic rats using an HVJ-E vector containing EBV plasmids expressing insulin and GLUT 2 transporter

Insulin gene therapy in clinical medicine is currently hampered by the inability to regulate insulin secretion in a physiological manner, the inefficiency with which the gene is delivered, and the short duration of gene expression. To address these issues, we injected the liver of streptozotocin-induced diabetic rats with hemagglutinating virus of Japan-envelope (HVJ-E) vectors containing Epstein-Barr virus (EBV) plasmids encoding the genes for insulin and the GLUT 2 transporter. Efficient delivery of the genes was achieved with the HVJ-E vector, and the use of the EBV replicon vector led to prolonged hepatic gene expression. Blood glucose levels were normalized for at least 3 weeks as a result of the gene therapy. Cotransfection of GLUT 2 with insulin permitted the diabetic rats to regulate their blood glucose levels upon exogenous glucose loading in a physiologically appropriate manner and improved postprandial glucose levels. Moreover, cotransfection with insulin and GLUT 2 genes led to in vitro glucose-stimulated insulin secretion that involved the closure of K(ATP) channels. The present study represents a new way to efficiently deliver insulin gene in vivo that is regulated by ambient glucose level with prolonged gene expression. This may provide a basis to overcome limitations of insulin gene therapy in humans.

Insulin expressing hepatocytes not destroyed in transgenic NOD mice

Background

The liver has been suggested as a suitable target organ for gene therapy of Type 1 diabetes. However, the fundamental issue whether insulin-secreting hepatocytes in vivo will be destroyed by the autoimmune processes that kill pancreatic β cells has not been fully addressed. It is possible that the insulin secreting liver cells will be destroyed by the immune system because hepatocytes express major histocompatibility complex (MHC) class I molecules and exhibit constitutive Fas expression; moreover the liver has antigen presenting activity. Together with previous reports that proinsulin is a possible autoantigen in the development of Type 1 diabetes, the autoimmune destruction of insulin producing liver cells is a distinct possibility.

Methods

To address this question, transgenic Non-Obese Diabetic (NOD) mice which express insulin in the liver were made using the Phosphoenolpyruvate Carboxykinase (PEPCK) promoter to drive the mouse insulin I gene (Ins).

Results

The liver cells were found to possess preproinsulin mRNA, translate (pro)insulin in vivo and release it when exposed to 100 nmol/l glucagon in vitro. The amount of insulin produced was however significantly lower than that produced by the pancreas. The transgenic PEPCK-Ins NOD mice became diabetic at 20–25 weeks of age, with blood glucose levels of 24.1 ± 1.7 mmol/l. Haematoxylin and eosin staining of liver sections from these transgenic NOD PEPCK-Ins mice revealed the absence of an infiltrate of immune cells, a feature that characterised the pancreatic islets of these mice.

Conclusions

These data show that hepatocytes induced to produce (pro)insulin in NOD mice are not destroyed by an ongoing autoimmune response; furthermore the expression of (pro)insulin in hepatocytes is insufficient to prevent development of diabetes in NOD mice. These results support the use of liver cells as a potential therapy for type 1 diabetes. However it is possible that a certain threshold level of (pro)insulin production might have to be reached to trigger the autoimmune response.

Cell therapies for type 1 diabetes mellitus

Type 1 diabetes is caused by autoimmune destruction of pancreatic beta-cells and is characterised by absolute insulin insufficiency. The monocellular nature of this disease and endocrine action of insulin make this disease an excellent candidate for cellular therapy. Furthermore, precedent for cellular therapies has been set by successful cadaveric whole pancreas and islet transplantation. In order to expand the supply of cells to meet current and future needs, several novel cell sources have been proposed, including human beta-cells or islets expanded in culture, islet xenografts and pancreatic ductal progenitor cells. Surrogate beta-cells derived from hepatocytes, intestinal K cells or non-endodermal cell types have also been suggested. Stem cells found in bone marrow and umbilical cord blood have been used extensively to repopulate the haematopoietic system and offer the possibility of autologous transplantation. Recent studies have suggested that these stem cells may also have a broader capacity to differentiate, possibly into beta-cells. Stem cells from embryonic sources, such as human embryonic stem and embryonic germ cells, have the ability to proliferate extensively in culture and have an inherent developmental plasticity that may make them a potentially unlimited source of cells that can sense glucose and produce mature insulin. The wide range of proposed cell sources and our increasingly clear picture of pancreatic development suggest that novel cellular therapies might one day compete with non-cellular glucose sensing and insulin delivery devices.

Metabolic engineering: advances in modeling and intervention in health and disease

The field of metabolic engineering encompasses a powerful set of tools that can be divided into (a) methods to model complex metabolic pathways and (b) techniques to manipulate these pathways for a desired metabolic outcome. These tools have recently seen increased utility in the medical arena, and this paper aims to review significant accomplishments made using these approaches. The modeling of metabolic pathways has been applied to better understand disease-state physiology in a variety of cellar, subcellular, and organ systems, including the liver, heart, mitochondria, and cancerous cells. Metabolic pathway engineering has been used to generate cells with novel biochemical functions for therapeutic use, and specific examples are provided in the areas of glycosylation engineering and dopamine-replacement therapy. In order to document the potential of applying both metabolic modeling and pathway manipulation, we describe pertinent advances in the field of diabetes research. Undoubtedly, as the field of metabolic engineering matures and is applied to a wider array of problems, new advances and therapeutic strategies will follow.

Cell itinerary and metabolic fate of proinsulin in rat liver: in vivo and in vitro studies

Proinsulin, the insulin precursor in pancreatic beta-cells, displays a slower hepatic clearance than insulin and exerts a more prolonged metabolic effect on liver in vivo. To elucidate the mechanisms underlying these differences, the cellular itinerary and processing of proinsulin and insulin in rat liver have been comparatively studied using cell fractionation. As [125I]-insulin, [125I]-proinsulin taken up into liver in vivo was internalized and accumulated in endosomes, in which it underwent dissociation from the insulin receptor and degradation in a pH- and ATP-dependent manner. However, relative to [125I]-insulin, [125I]-proinsulin showed a delayed and prolonged in vivo association with endosomes, a slower in vivo and cell-free endosomal processing, and a higher cell-free endosome-lysosome transfer. Endosomal extracts degraded to a lesser extent proinsulin than insulin at acidic pH; so did, and even proportionally less, at neutral pH, plasma membrane and cytosolic fractions. Proinsulin degradation products generated by soluble endosomal extracts were isolated by HPLC and characterized by mass spectrometry. Under conditions resulting in multiple cleavages in insulin, proinsulin was cleaved at eight bonds in the C peptide but only at the Phe24-Phe25 bond in the insulin moiety. As native insulin, native proinsulin induced a dose- and time-dependent endocytosis and tyrosine phosphorylation of the insulin receptor; but at an inframaximal dose, proinsulin effects on these processes were of longer duration. We conclude that a reduced proteolysis of proinsulin in endosomes, and probably also at the plasma membrane, accounts for its slower hepatic clearance and prolonged effects on insulin receptor endocytosis and tyrosine phosphorylation.

Hepatic insulin gene therapy in insulin-dependent diabetes mellitus

Insulin-dependent diabetes mellitus (IDDM) is an autoimmune disease resulting in destruction of the pancreatic beta-cells in the islets of Langerhans. Commonly employed treatment of IDDM requires periodic insulin therapy, which is not ideal because of its inability to prevent chronic complications such as nephropathy, neuropathy and retinopathy. Although pancreas or islet transplantation are effective treatments that can reverse metabolic abnormalities and prevent or minimize many of the chronic complications of IDDM, their usefulness is limited as a result of shortage of donor pancreas organs. Gene therapy as a novel field of medicine holds tremendous therapeutic potential for a variety of human diseases including IDDM. This review focuses on the liver-based gene therapy for generation of surrogate pancreatic beta-cells for insulin replacement because of the innate ability of hepatocytes to sense and metabolically respond to changes in glucose levels and their high capacity to synthesize and secrete proteins. Recent advances in the use of gene therapy to prevent or regenerate beta-cells from autoimmune destruction are also discussed.

Hepatic expression of the human insulin gene reduces glucose levels in vivo in diabetic mice model

OBJECTIVES

The objective of these studies was to evaluate human insulin gene expression following intraliver plasmid injection in diabetic mice as a potential approach to gene therapy for insulin-dependent diabetes mellitus.

METHODS

The fragment containing human proinsulin gene lacking its own promoter, was cloned into plasmids containing promoter and enhancer of cytomegalovirus or human hepatitis B virus. The resulting gene constructs were first tested in vitro using 3T3 fibroblast cell line and subsequently in vivo applying streptozotocin-induced diabetic mice.

RESULTS

We found significant reduction in glucose levels in both experimental systems, giving evidence that prolonged constitutive systemic secretion of bioactive human (pro)insulin has been attained in non-neuroendocrine cell line in vitro and in mice following intra-liver plasmid injection.

CONCLUSION

Our data demonstrate the reduction of glucose levels in vitro in 3T3 fibroblast cells and in vivo in diabetic mice after treatment with plasmids expressing proinsulin, giving evidence that those constructs may have certain usage also in human gene therapy of diabetes mellitus type 1.

Incorporation of calcium phosphate enhances recombinant adeno-associated virus-mediated gene therapy in diabetic mice

BACKGROUND

Increased efficiency of transgene expression is desired for virus-mediated gene delivery. In the present study, we examined the effect of calcium phosphate (CaPi) on recombinant adeno-associated virus (rAAV)-mediated insulin therapy in diabetic animals.

METHODS

The rAAV vector, rAAV.PEPCK.Ins.EGFP, containing the human insulin gene under control of the phosphoenolpyruvate carboxykinase (PEPCK) promoter and the enhanced green fluorescence protein (EGFP) gene driven by the cytomegalovirus (CMV) IE promoter, was employed in this study. C57BL/6J mice were made diabetic with streptozotocin (STZ), followed by injection into the livers with either rAAV alone, or noncovalent complexes with calcium phosphate. Body weight and blood glucose levels of the animals were routinely monitored after 6 h fasting. Secretion of human insulin in the rAAV-transduced animals was determined by radioimmunoassay (RIA). Expression of human insulin in the livers of the animals was detected by immunohistochemical staining.

RESULTS

Compared with the STZ-treated control mice, administration of rAAV containing the human insulin gene significantly decreased blood glucose levels and maintained body weight of the diabetic animals. Complexation of rAAV with calcium phosphate enhanced the hypoglycemic effect of rAAV-mediated gene transfer. Results obtained from both RIA and immunohistochemical staining demonstrated that incorporation of calcium phosphate enhanced rAAV-mediated gene transfer in vivo, leading to higher expression and secretion of human insulin.

CONCLUSIONS

Administration of rAAV harboring the human insulin gene into livers of the STZ-diabetic mice improved blood glucose levels, maintained body weight of the diabetic animals, and resulted in human insulin secretion. Complexation of rAAV with calcium phosphate significantly potentiated the efficiency of rAAV-mediated diabetic gene therapy.

Gene- and cell-based therapeutics for type I diabetes mellitus

Type 1 diabetes mellitus, an autoimmune disorder is an attractive candidate for gene and cell-based therapy. From the use of gene-engineered immune cells to induce hyporesponsiveness to autoantigens to islet and beta cell surrogate transplants expressing immunoregulatory genes to provide a local pocket of immune privilege, these strategies have demonstrated proof of concept to the point where translational studies can be initiated. Nonetheless, along with the proof of concept, a number of important issues have been raised by the choice of vector and expression system as well as the point of intervention; prophylactic or therapeutic. An assessment of the current state of the science and potential leads to the conclusion that some strategies are ready for safety trials while others require varying degrees of technical and conceptual refinement.

Function of a genetically modified human liver cell line that stores, processes and secretes insulin

An alternative approach to the treatment of type I diabetes is the use of genetically altered neoplastic liver cells to synthesize, store and secrete insulin. To try and achieve this goal we modified a human liver cell line, HUH7, by transfecting it with human insulin cDNA under the control of the cytomegalovirus promoter. The HUH7-ins cells created were able to synthesize insulin in a similar manner to that which occurs in pancreatic beta cells. They secreted insulin in a regulated manner in response to glucose, calcium and theophylline, the dose-response curve for glucose being near-physiological. Perifusion studies showed that secretion was rapid and tightly controlled. Removal of calcium resulted in loss of glucose stimulation while addition of brefeldin A resulted in a 30% diminution of effect, indicating that constitutive release of insulin occurred to a small extent. Insulin was stored in granules within the cytoplasm. When transplanted into diabetic immunoincompetent mice, the cells synthesized, processed, stored and secreted diarginyl insulin in a rapid regulated manner in response to glucose. Constitutive release of insulin also occurred and was greater than regulated secretion. Blood glucose levels of the mice were normalized but ultimately became subnormal due to continued proliferation of cells. Examination of the HUH7-ins cells as well as the parent cell line for beta cell transcription factors showed the presence of NeuroD but not PDX-1. PC1 and PC2 were also present in both cell types. Thus, the parent HUH7 cell line possessed a number of endocrine pancreatic features that reflect the common endodermal ancestry of liver and pancreas, perhaps as a result of ontogenetic regression of the neoplastic liver cell from which the line was derived. Introduction of the insulin gene under the control of the CMV promoter induced changes in these cells to make them function to some extent like pancreatic beta cells. Our results support the view that neoplastic liver cells can be induced to become substitute pancreatic beta cells and become a therapy for the treatment of type I diabetes.

Gene and cell therapies for diabetes mellitus: strategies and clinical potential

The last 5 years have witnessed an explosion in the use of genes and cells as biomedicines. While primarily aimed at cancer, gene engineering and cell therapy strategies have additionally been used for Mendelian, neurodegenerative and metabolic disorders. The main focus of gene and cell therapy strategies in metabolism has been diabetes mellitus. This disease is a disorder of glucose homeostasis, either due to the immune-mediated eradication of pancreatic beta cells in the islets of Langerhans (type 1 diabetes) or resulting from insulin resistance and obesity syndromes where the insulin-producing capability of the beta cell is ultimately exhausted in the face of insensitivity to the effects of insulin in the peripheral glucose-utilising tissues (type 2 diabetes). A significant number of animal studies have demonstrated the potential in restoring normoglycaemia by islet transplantation in the context of immunoregulation achieved by gene transfer of immunoregulatory genes to allo- and xenogeneic islets ex vivo. Additionally, gene and cell therapy has also been used to induce tolerance to auto- and alloantigens and to generate the tolerant state in autoimmune rodent animal models of type 1 diabetes or rodent recipients of allogeneic/xenogeneic islet transplants. The achievements of gene and cell therapy in type 2 diabetes are less evident, but seminal studies promise that this modality can be relevant to treat and perhaps prevent the underlying causes of the disease. Here we present an overview of the current status of gene and cell therapy for type 1 and 2 diabetes and we propose potential therapeutic options that could be clinically useful. For type 1 diabetes, transplantation of islets engineered to evade or suppress the recipient immune response is the most readily-available technology today. A number of gene delivery vectors encoding proteins that impair a variety of immune cells have already been examined and proven versatile. More challenging but, nonetheless, just over the horizon are attempts to promote tolerance to islet allografts. Type 2 diabetes will likely require a better understanding of the processes that determine insulin sensitivity in the periphery. Targeting tissues such as muscle and fat with vectors encoding genes whose products promote insulin sensitivity and glucose uptake is an approach that does not carry with it the side-effects often associated with pharmacologic agents currently in use. In the end, progress in vector design, elucidation of antigen-specific immunity and insulin sensitivity will provide the framework for gene drug use in the treatment of type 1 and type 2 diabetes.

Islet/pancreas transplantation: challenges for pediatrics

Beta cell replacement is a valid alternative to exogenous insulin injections to treat type 1 diabetic patients. The rate of success obtained after whole-pancreas transplantation, performed alone or in combination with kidney, and, as shown recently, by islet transplantation, justifies optimism and sets the stage for a larger clinical application of these approaches. Lifetime immunosuppression, however, required to protect the graft against recurrent autoimmune destruction and allorejection, raises serious doubts about the safety of its employment in children. While it is evident that children may be helped even more than adults by the possibility to correct diabetic metabolic disorders without exogenous insulin, and to lower in a more effective way the chance to develop secondary complications, the drawbacks of the currently used immunosuppressive drugs largely overcome the potential benefits. A great step forward for immediate applicability of transplantation to children involves the optimization of tolerogenic protocols and a better understanding of the concept of immune ignorance. Functional tolerance should be sufficient to entail the absence of immune reactivity against self- and graft antigens, while maintaining immune reactivity against other non-self, non-donor antigens. In addition, novel strategies aimed at utilizing surrogate beta cells obtained from non-islet cells, or by genetic manipulation of beta-cell precursors merit consideration as the use of xenogeneic donors. However, much work is still needed for their safe clinical implementation.

Human liver-derived cells stably modified for regulated proinsulin secretion function as bioimplants in vivo

BACKGROUND

Insulin deficiency is currently treated with pharmacological insulin secretagogues, insulin injections or islet transplants. Secondary failure of pharmacological agents is common; insulin injections often fail to achieve euglycemic control; and islet transplants are rare. Non-beta cells capable of regulated insulin secretion in vivo could be a functional cure for diabetes. Hepatocytes are good candidates, being naturally glucose-responsive, protein-secreting cells, while the liver is positioned to receive direct nutrient signals that regulate insulin production.

METHODS

Human liver-derived Chang cells were modified with a plasmid construct in which a bifunctional promoter comprising carbohydrate response elements and the human metallothionein IIA promoter controlled human proinsulin cDNA expression. Secretory responses of stable cell clones were characterized in vitro and in vivo by proinsulin radioimmunoassay.

RESULTS

Transfected Chang cells secreted 5-8 pmol proinsulin/10(6) cells per 24 h in continuous passage for at least a year in response to 5-25 mM glucose and 10-90 microM zinc in vitro. Glucose and zinc synergistically increased proinsulin production by up to 30-fold. Non-glucose secretagogues were also active. Glucose transporter 2 (GLUT2) and glucokinase cDNA co-transfection enhanced glucose responsiveness. Intraperitoneally implanted Chang cells secreted proinsulin in scid and Balb/c mice. Serum proinsulin levels were further increased 1.3-fold (p<0.05) after glucose and 1.4- to 1.6-fold (p<0.005) after zinc administration in vivo.

CONCLUSIONS

These results are the first to demonstrate stable proinsulin production in a human liver-derived cell line with activity in vitro and in vivo and provide a basis for engineering hepatocytes as in vivo bioimplants for future diabetes treatment.

Gene transfer of human prostacyclin synthase into the liver is effective for the treatment of pulmonary hypertension in rats

BACKGROUND

As one of the future strategies of advanced pulmonary hypertension, intrinsic prostacyclin drug delivery using gene therapy may be useful. We investigated whether transfer of the prostacyclin synthase gene into the liver could ameliorate monocrotaline-induced pulmonary hypertension in rats.

METHODS

The human prostacyclin synthase gene was transfected into the liver of rats with monocrotaline-induced pulmonary hypertension. Hemodynamic indices, blood samples, lung tissues, and survival curves were evaluated between rats receiving the gene and control rats.

RESULTS

High levels of prostacyclin synthase gene expression were found in the hepatocytes of the prostacyclin synthase group. The level of 6-keto-prostaglandin F(1alpha) was significantly higher in the prostacyclin synthase group (prostacyclin synthase, 35.4 +/- 4.4 ng/mL; control, 22.3 +/- 3.3 ng/mL; P =.0436). The right ventricular/femoral artery pressure ratio was significantly lower in the prostacyclin synthase group than in the control group (prostacyclin synthase, 0.60 +/- 0.039; control, 0.88 +/- 0.051; P =.0036). The endothelin-1 levels in the lung tissues were significantly lower in the prostacyclin synthase group than in the control group (prostacyclin synthase, 10.42 +/- 2.01 pg/mg protein; control, 19.94 +/- 2.82 pg/mg protein; P =.0176). The survival ratio was significantly higher in the prostacyclin synthase group than the control group (P =.0375).

CONCLUSION

This drug delivery system using gene transfer can be considered as an alternative for continuous intravenous prostacyclin infusion for pulmonary hypertension.

Counteraction of type 1 diabetic alterations by engineering skeletal muscle to produce insulin: insights from transgenic mice

Insulin replacement therapy in type 1 diabetes is imperfect because proper glycemic control is not always achieved. Most patients develop microvascular, macrovascular, and neurological complications, which increase with the degree of hyperglycemia. Engineered muscle cells continuously secreting basal levels of insulin might be used to improve the efficacy of insulin treatment. Here we examined the control of glucose homeostasis in healthy and diabetic transgenic mice constitutively expressing mature human insulin in skeletal muscle. Fed transgenic mice were normoglycemic and normoinsulinemic and, after an intraperitoneal glucose tolerance test, showed increased glucose disposal. When treated with streptozotocin (STZ), transgenic mice showed increased insulinemia and reduced hyperglycemia when fed and normoglycemia and normoinsulinemia when fasted. Injection of low doses of soluble insulin restored normoglycemia in fed STZ-treated transgenic mice, while STZ-treated controls remained highly hyperglycemic, indicating that diabetic transgenic mice were more sensitive to the hypoglycemic effects of insulin. Furthermore, STZ-treated transgenic mice presented normalization of both skeletal muscle and liver glucose metabolism. These results indicate that skeletal muscle may be a key target tissue for insulin production and suggest that muscle cells secreting basal levels of insulin, in conjunction with insulin therapy, may permit tight regulation of glycemia.

Hepatic insulin production for type 1 diabetes

Type 1 diabetes, along with its long-term complications, imposes a serious impact on public health. In spite of the development and application of various insulin formulations, exogenous insulin neither achieves the same degree of glycemic control as that provided by endogenous insulin, nor prevents the long-term complications associated with type 1 diabetes. As an alternative strategy, insulin gene transfer is being explored to restore endogenous insulin production in type 1 diabetes. Sustained hepatic insulin production has been shown to reverse ketonuria, prevent ketoacidosis, improve body weight gain and significantly ameliorate the adverse effects of insulin deficiency in diabetic animals. However, to achieve adequately regulated insulin production in response to changes in blood glucose concentrations remains a major hurdle. This article will review the most recent advances made to address this crucial limitation. In addition, based on the significance of maintaining basal plasma insulin for management of type 1 diabetes, we discuss the feasibility of developing basal hepatic insulin production as an auxiliary treatment to current insulin therapy for achieving tight glycemic control in type 1 diabetes.

Susceptibility of insulin-secreting hepatocytes to the toxicity of pro-inflammatory cytokines

The liver has been suggested as a suitable target organ for reversing type I diabetes by gene therapy. Whilst gene delivery systems to the hepatocyte have yet to be optimized in vivo, whether insulin-secreting hepatocytes are resistant to the autoimmune process that kills pancreatic beta-cells has never been addressed. One of the mechanisms by which beta-cells are killed in type I diabetes is by the release of the cytokines interleukin-1beta (IL-1beta), tumour necrosis factor-alpha (TNF-alpha) and interferon-gamma (IFN-gamma) by immune cells. To test the effect of the cytokines on insulin-secreting hepatocytes in vitro we exposed the betacyte, also called the HEP G2ins/g cell which possesses cytokine receptors and can synthesize, store and secrete insulin in a regulated fashion to a glucose stimulus, to the above mentioned cytokines for 14 days. Viability of the HEP G2ins/g cells was similar to that of other liver cell lines/primary cells which were more resistant to the cytokines than the beta-cell line NIT-1. The cytokines had no adverse effect for the first six days on insulin secretion, content and mRNA levels of the HEP G2ins/g cells and insulin secretion in response to 1-h exposure to 20 mM glucose was enhanced 14-fold. Our results indicate that genetically engineered hepatocytes and primary liver cells are more resistant than pancreatic beta-cells to the adverse effects of cytokines offering hope that insulin secreting hepatocytes in vivo made by gene therapy are less likely to be destroyed by cytokines released during autoimmune destruction.

Adenoviral vector-mediated insulin gene transfer in the mouse pancreas corrects streptozotocin-induced hyperglycemia

Therapy for type 1 diabetes consists of tight blood glucose (BG) control to minimize complications. Current treatment relies on multiple insulin injections or an insulin pump placement, beta-cell or whole pancreas transplantation. All approaches have significant limitations and have led to the realization that novel treatment strategies are needed. Pancreatic acinar cells have features that make them a good target for insulin gene transfer. They are not subject to autoimmune attack, a problem with pancreas or islets transplantation, they are avidly transduced by recombinant adenoviral vectors, and capable of exporting a variety of peptides into the portal circulation. Recombinant adenoviral vectors were engineered to express either wild-type or furin-modified human insulin cDNA (AdCMVhInsM). Immunodeficient mice were made diabetic with streptozotocin and injected intrapancreatically with the vectors. BG and blood insulin levels have normalized after administration of AdCMVhInsM. Immunohistochemistry and electron microscopy showed the presence of insulin in acinar cells throughout the pancreas and localization of insulin molecules to acinar cell vesicles. The data clearly establish a relationship between intrapancreatic vector administration, decreased BG and elevated blood insulin levels. The findings support the use of pancreatic acinar cells to express and secrete insulin into the blood stream.

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

Transfer of naked plasmid with insulin precursor DNA into skeletal muscle of streptozotocin (STZ)-induced diabetic mice through electroporation and detection of gene expression is described. Four different human insulin precursor DNA fragments were inserted into pcDNA3.1(-), downstream of a CMV promoter. Three of them, with a secretion signal sequence, succeeded in lowering blood glucose at a range of 30-50% in STZ diabetic mice. The other, with a synthetic DNA fragment encoding human proinsulin, failed. The mortality rate of very seriously STZ diabetic mice was reduced significantly by the treatment. The circulating insulin-like protein (mouse insulin, human proinsulin, or intermediates during conversion of proinsulin to insulin) level in the blood of less seriously STZ diabetic mice treated with the human preproinsulin gene with an intron was about 15-23 microU/ml, while that of STZ diabetic mice treated with empty vector was only about 6 microU/ml and that of normal mice was about 18 microU/ml. Transcription of the three human insulin precursor DNAs in mouse skeletal muscle was also detected by RT-PCR. The human preproinsulin gene with the intron showed a slightly higher potency in reducing blood glucose of mildly diabetic mice. These studies indicate that the skeletal muscle transferred with appropriate preproinsulin DNA by electroporation in vivo can secrete insulin-like protein resulting in reduction of blood glucose, and a basal blood insulin level can be achieved for at least 1 month.

Auto-regulated hepatic insulin gene expression in type 1 diabetic rats

Paradigms of insulin gene therapy for type 1 diabetes should incorporate vigorous control for insulin gene expression to be effective in correcting postprandial hyperglycemia and to be safe in preventing fasting hypoglycemia. We hypothesize that hepatic insulin gene expression auto-regulated positively by glucose and negatively by insulin might be both effective and safe in the treatment of type 1 diabetes. Expression of the glucose 6-phosphatase (G6Pase) gene in the liver is both stimulated by glucose and suppressed by insulin. The G6Pase promoter incorporated with intronic enhancers of the aldolase B gene was used to direct insulin gene expression in the liver of streptozotocin-induced diabetic nude rats. In the treated animals, blood insulin levels were elevated after feeding, and nonfasting hyperglycemia was significantly reduced. Glucose tolerance testing also illustrated that the treated animals exhibited accelerated glucose utilization rates. Upon fasting, blood glucose was reduced to normoglycemic range within 4 h and maintained at that level during the prolonged fasting of 16 h. No hypoglycemia was observed in any treated animals at any time throughout the fasting period, as blood insulin gradually declined to the normal range. These results suggest that auto-regulated hepatic insulin expression can potentially be developed as an effective and safe treatment modality for type 1 diabetes.

Glucose-regulated insulin expression in diabetic rats

Retroviral vectors encoding glucose-responsive promoters driving furin expression may provide an amplified, glucose-regulated secretion of insulin. We constructed LhI*TFSN virus to encode a glucose-regulatable transforming growth factor alpha promoter controlling furin expression with a viral LTR promoter driving constitutive expression of furin-cleavable human proinsulin. Autologous BB rat vascular smooth muscle cells transduced with LhI*TFSN virus and cultured in 1.7 and 16.7 mM glucose secreted 50.7 +/- 3.2 and 136.0 +/- 11.0 microU (mean +/- SD) of insulin per 10(6) cells per day, respectively. After the onset of diabetes spontaneously diabetic congenic DR lyp/lyp BB rats received stomach implants containing 2 x 10(6) LhI*TFSN-transduced primary rat vascular smooth muscle cells. In eight treated rats there was a major reduction in insulin requirement to as low as 25% of pretreatment level for up to 3 months and one rat became insulin free without hypoglycemia. Intraperitoneal glucose tolerance tests (IPGTTs) in diabetic rats receiving control implants did not show the characteristic decline in blood glucose of normal rats after glucose administration. In contrast, diabetic rats receiving LhI*TFSN-transduced cells showed significant clearances of blood glucose. These data suggest clinically significant levels of glucose-regulated insulin delivery from implanted vascular smooth muscle cells transduced with LhI*TFSN vector.

Bioartificial pancreas: materials, devices, function, and limitations

The term "bioartificial endocrine pancreas" (BEP) was introduced by Anthony Sun in 1980. It was in 1968, however, that Thomas Chang proposed the use of microencapsulated islets as artificial beta-cells. By applying a semipermeable membrane on the top of microcapsules, a system can be produced that is impermeable to viable islet cells and large effector molecules of the immune system, thus providing a protection for transplanted islets against rejection. Since then, the term BEP has not often appeared in papers. Instead, the term "bioartificial pancreas" (BAP) has gained widespread use. In a broader sense, BAP would include an application of suitable endocrine cells and protective polymeric vehicles, but not necessarily providing a filtration barrier of precisely defined properties (e.g., cells injected into a gel of hyaluronate).

Glucose-stimulated and self-limiting insulin production by glucose 6-phosphatase promoter driven insulin expression in hepatoma cells

The liver is an attractive target organ for insulin gene expression in type 1 diabetes as it contains appropriate cellular mechanisms of regulated gene expression in response to blood glucose and insulin. We hypothesize that insulin production regulated by both glucose and insulin may be achieved using the promoter of the glucose 6-phosphatase gene (G6Pase), the expression of which in the liver is induced by glucose and suppressed by insulin. Recombinant adenoviral vectors expressing the reporter gene CAT or insulin under transcriptional direction of the G6Pase promoter were constructed. Glucose-stimulated as well as self-limiting insulin production was achieved in vector-transduced hepatoma cells in which expression of the insulin gene was controlled by the G6Pase promoter. While insulin strongly inhibited the G6Pase promoter activity under low glucose conditions, its inhibitory capacity was attenuated when glucose levels were elevated. At the physiologic glucose level of 5.5 mM glucose, vector-transduced hepatoma cells produced a self-limited level of insulin at approximately 0.2-0.3 ng/ml, which is within the range of fasting levels of insulin in normal animals. These results indicate that the G6Pase promoter possesses desirable features and may be developed for regulated hepatic insulin gene expression in type 1 diabetes.

Insulin delivery with plasmid DNA

Success in controlling hyperglycemia in type I diabetics will require a restoration of basal insulin. To this end, three plasmid DNAs (pDNA) encoding preproinsulin were compared for constitutive expression and processing to insulin in nonendocrine cells in vitro. The pDNAs were designed to express rat proinsulin I (VR-3501), rat proinsulin I with the B10 aspartic acid point mutation (VR-3502), and a derivative of VR-3502 with a furin cleavage site added at the B-chain and C-peptide junction (VR-3503). Cells transfected with VR-3501 or VR-3502 were able to secrete only proinsulin, whereas transfection with VR-3503 yielded 30-70% mature insulin, which could be increased to >99% by cotransfection with a furin expression plasmid (VR-3505). The insulin produced was biologically active. The bilateral injection of 100 microg of VR-3502 plasmid into the tibialis anterior muscles of mice on two consecutive days yielded, on average, several hundred picograms of heterologous proinsulin per milliliter of serum. In BALB/c mice, serum proinsulin peaked 7-14 days postinjection and declined to preinjection levels by days 21-28. In athymic nude mice, serum proinsulin was sustained for at least 6 weeks. The therapeutic efficacy of delivering insulin via muscle injection of pDNA was evaluated in athymic nude mice made diabetic with the beta cell toxin streptozotocin (STZ). All animals given control DNA died within 1 week of receiving STZ while 40% of the mice coinjected with plasmids VR-3503 and VR-3505 lived through the duration of the 4-week experiment. Muscles of the surviving animals contained 17-100 ng of immune-reactive insulin (IRI), 86-94% of which was mature insulin. The results suggest that heterologous insulin made in muscle increased the survival rate. We propose that insulin plasmid expression in skeletal muscle may be a valid approach to basal insulin delivery. The feasibility of plasmid DNA-based delivery of basal insulin was investigated. An expression system consisting of pDNAs encoding a selectively mutated rat preproinsulin and mouse furin was developed and characterized in vitro and in vivo. When injected with preproinsulin pDNA, the mouse tibialis anterior muscle expressed and released proinsulin into serum at levels comparable to normal basal insulin in rodents. These heterologous proinsulin levels were sustained for several weeks in immune-compromised nondiabetic mice. Mouse muscle coinjected with a pDNA encoding the endopeptidase furin and a pDNA encoding a pre-proinsulin modified to contain two furin cleavage sites produced fully processed insulin. This muscle-made insulin appears to have contributed to the survival of mice treated with a highly diabetogenic dose of streptozotocin, a beta cell toxin. The results demonstrate that skeletal muscle is able to express and deliver therapeutic insulin from plasmid DNA.

Naked plasmid-mediated gene transfer to skeletal muscle ameliorates diabetes mellitus

BACKGROUND

The ability of tissues to take up naked plasmid DNA in vivo suggests an approach for reconstituting systemic metabolic deficiencies without the disadvantages of viral vectors and lipid-DNA complexes. Plasmid-mediated gene transfer into skeletal muscle was investigated as a means of providing a therapeutic source of insulin.

METHODS

Four plasmid constructs, each bearing a mouse furin cDNA transgene and rat proinsulin cDNA (modified for processing by furin) driven by four different promoters were injected into the calf muscles of male Balb/c mice. Insulin and C-peptide concentrations were measured by radio-immunoassays having minimal crossreactivity for proinsulin and partially processed proinsulin.

RESULTS

Intramuscular insulin concentrations increased by up to 3.6-fold over controls seven days after single injections of CMV, beta-actin, hsp70 and myoglobin promoter constructs. The optimal dose for most constructs was 100 micrograms plasmid DNA. Intramuscular plasmid injection into streptozotocin-induced diabetic Balb/c mice raised plasma insulin and C-peptide concentrations, and reduced hyperglycaemia. Two injections (100 micrograms plasmid DNA each) caused higher plasma insulin concentrations and significantly reduced hyperglycemia in diabetic mice than a single injection. Best results were obtained when plasmid injections preceded induction of diabetes by 14 days.

CONCLUSIONS

Skeletal muscle is a potentially useful platform for ectopic secretion of insulin using naked plasmid as a gene transfer vector. Injection at two sites 14 days before the onset of severe hyperglycemia is optimal. This approach could protect Type I diabetics from fatal ketoacidosis and enhance the action of agents that sensitize tissues to insulin in type II diabetes.

Adenovirus-mediated transfer of a modified human proinsulin gene reverses hyperglycemia in diabetic mice

The human proinsulin cDNA was introduced into a replication-defective adenovirus and was found to confer proinsulin expression to a hepatocyte (H4-II-E) cell line upon infection. A second virus was constructed in which the dibasic prohormone convertase recognition sequence was mutated to a tetrabasic furin cleavage site. Cells infected with this virus synthesized both proinsulin and mature insulin. Gel filtration chromatography, competition of insulin binding, and activation of the insulin receptor kinase activity demonstrated that this mature insulin was functionally identical to that of authentic processed insulin. Injection of these viral constructs into the external jugular vein of mice resulted in insulin gene expression in the liver. Expression from the mutated proinsulin virus dramatically improved the glycemic state of diabetic mice. However, the effects of the viral infection were transient, being maximal at approximately 5-7 days and returning to steady-state levels by 14-21 days. These data demonstrate that somatic cell insulin gene delivery by the use of recombinant adenovirus can be used to transiently reverse the diabetic state in mice.